Closed Loop Control Of a Torque -Tension
Machine
Sean Declan Tobin
This thesis is submitted to Dublin City University as fulfilment of the
requirement for the award of a Degree of
Bachelor of Engineering
School of Mechanical and Manufacturing Engineering
Dublin City University
May 2000
1
I wish to dedicate this work to my family whose loving support especially
through the last four years is greatly appreciated
Declaration
This is to certify that the material presented in this thesis is entirely my own work, except
where specific references have been made to the works of others, and no part of this work
has been submitted in support of an application for another degree or qualification to this
or any other establishment.
Signed:__________________
Sean Tobin
May 2000
Student Number 96507594
Acknowledgements
I would like to thank Dr. Paul Young for his supervision and guidance during this project
work. I would also like to thank Dermot Brabazon for his help and advice in designing
the Labview program.
I would like to express my thanks to Liam Dominican and Keith Hickey for their
technical assistance at various stages throughout this project.
Introduction
In many industries it is important to know the load carrying capabilities of a structure.
Designers have to consider the elasto-plastic behaviour, which depends on the stresses
and strains of the structure, to establish the load deformation characteristics. In many
structures it is the joints that have to withstand most of the structural load. In joint
technology the most frequently used method of joining is fastening bolts. In industries
where precision is crucial the margin of safety of the structure has to be as small as
possible and therefore it is more important that these joints don’t fail under fatigue or
extra loading. The cost of bolted joints is minuscule in the initial design but if the joint
collapses it can destroy the entire structure and the entire cost of the structure can be
attributed to the bolted joint. Therefore attention must be paid to the characteristics of the
joint and the changes it undergoes with additional external load and over tightening.
It has been found by engineering research that by tightening the bolt to the bolt torquetension yield point it can withstand substantial external loads without deformation and
higher clamping forces can be obtained to strengthen the joint. After yield tightening it
has been found that there is reserve strength in the tensile stress which means that the bolt
can withstand additional tensile load. When external loads are applied to the torquetension yield tightened bolt, the bolt behave elastically.
A thesis for a Ph.D., Plastic Yielding Characteristics of a Rod Under Successively
Applied Torsion and Tension Loadings, was finished in 1995 on a torque-tension
machine. The torque-tension machine can carry a maximum tensile load of 100kN and
maximum torque of 200Nm. The dimensions of the machine are 0.84m in length 1m in
width and 1.96m in height. The machine weighs in total approximately a tonne. There are
two drive systems on the machine, the first for applying tension or axial load and the
second for applying
torque. The first drive system uses a servo motor and gearbox assembly to transmit
power to ball screws to move the cross head (the top half of the shaft that holds the
specimen) up and down to apply axial loads at speeds in the range of 0-100mm/min. The
second drive uses a smaller servo motor and gearbox assembly to rotate the bottom shaft
that holds the specimen to apply torque at speeds of 0-10rpm. When voltages are applied
to these drive systems they create torque and tension to the specimen held in the machine.
The drive systems can operate simultaneously or separately, at different speeds and can
hold one parameter constant while adjusting other parameters.
The four test that the machine was designed to carry out are as follows
Test 1
Keeping axial load constant apply increasing torque
Test 2
Keeping torque constant apply increasing axial load
Test 3
Keeping axial displacement constant apply increasing torque
Test 4
Keeping angle of twist constant apply increasing load
Abstract
The torque tension machine is designed to measure the load and torque carrying
capabilities of steel and aluminium specimens. By testing the material under load and
torque, conclusions can be drawn as to how the material in bolts would withstand torque
or tension in the structure. Each of the tests represents a case where the bolt is either preloaded or pre-stressed and then the bolt is subjected to an additional load or torque. i.e.
for test 1 the constant load represents the pre-load and the application of torque
represents the torque exerted on the bolt from the structure.
The aim of this project is to control the machine and record reading from the transducers
on the machine to create a closed loop control system that can carry out the four tests.
Machine
Control
Panel
PC
Apply tension &
torque to specimen
Labview
Control Board
Motor
Controllers
Amplifiers
Transducers
Motors &
Grippers
The transducers were calibrated and all the equipment was set up so as a Labview
program could be executed to create the closed loop control. The front panel or user
interface of the Labview program can be seen here.
In this instance the torque was increased as the load was kept constant and the load began
to decrease, so the cross-head moved up to keep the load constant. This is test 1.
A lot of noise and overshoot can be observed in this system and suggestions have been
made to reduce both by using a filter and PID controller created using control system
analysis techniques.
List of Figures
Fig 2.1: Block Diagram of Complete System
6
Fig 2.2: Load Motor Characteristic Curve
7
Fig 2.3: Load Motor to Specimen
9
Fig 2.4: Torque Motor Characteristic Curve
10
Fig 2.5: Torque Motor to Specimen
11
Fig 2.6: Control Board Flow Chart
11
Fig 2.7: The Axial Load Cell Position in Cross Head
13
Fig 2.8: Strain Gauges Set Up
13
Fig 2.9: Electrical Circuit of Strain Gauges
13
Fig 2.10: Torque Strain Gauges Set Up
14
Fig 2.11: Electrical Circuit of LVDT
15
Fig 2.12: 4-Bit Electromechanical Encoder
16
Fig 2.13: Position of Transducers on Machine
17
Fig 3.1: AT-AO-6 DAQ Device 1
20
Fig 3.2: AT-MIO-16E DAQ Device 2
21
Fig 3.3: Servo Motor Control Board Diagram
21
Fig 3.4: Assignment of Analogue Input Channels
23
Fig 4.1:Gain and Zero Switches on the Amplifier
25
Fig 4.2:Axial Load Cell Calibration Graph
26
Fig 4.3: Torque Calibration Graph
27
Fig 4.4: LVDT Calibration Graph
28
Fig 4.5: Angular Position Calibration Graph
29
Fig 5.1: Flow Chart for Wire Diagram
36
Fig 6.1: Stable Response to Bounded Input
45
Fig 6.2: The Front Panel showing the Overshoot And Noise in the System
46
Fig 6.3: Transient Response to a Step Input
47
Fig 6.4: Load Motor Block Diagram
48
Fig 6.5: Torque Motor Block Diagram
48
Fig 6.6: Servo Motor
49
Fig 6.7: Gearbox
50
Fig 6.8: Least Squares Code
51
Fig 6.9: Transfer Function from Matlab
52
Fig 6.10: Actual versus Model System Response
53
Fig 6.11: PID Control and Filter in System
54
Fig 7.1: The Graphs for Test 1
57
Fig 7.2: Section of Output File for Test 1
57
Fig 7.3: The Graphs for Test 3
58
Fig 7.4: Section of Output File of Test 3
59
Table of Contents
Declaration
Acknowledgements
Introduction
Abstract
List of Figures
Chapter One
Literature Review
1
1.1 Introduction
2
1.2 Creating the Closed Loop Control
2
1.3 Labview Programming
3
1.4 Investigation into Improving the System Performance
3
Chapter Two
Equipment
5
2.1 Introduction
6
2.2 The Application of Tensile Force to the Specimen
7
2.2.1 The Load Motor
7
2.2.2 The Load Gearbox
7
2.2.3 Timing Pulleys and Timing Belt
8
2.2.4 Ball Screws
8
2.2.5 Guide Rods and Super Ball Bushing
8
2.3 The Application of Torque to the Specimen
10
2.3.1 The Torque Motor
10
2.3.2 The Torque Gearbox
10
2.3.3 Spur Gears
10
2.3.4 Square Drive
11
2.4 Signal to Machine
12
2.4.1 Labview
12
2.4.2 DAQ Devices
12
2.4.3 Servo Motor Controllers
12
2.5 Signals from the Transducers
13
2.5.1 The Axial Load Cell
13
2.5.2 The Torque Load Cell
14
2.5.3 The LVDT
15
2.5.4 The Angular Position Transducer
16
2.5.5 Amplifier
16
Chapter Three
Connections
3.1 Control
18
19
3.1.1 PC to Labview
19
3.1.2 Labview to Control Board
20
3.1.3 Control Board to Motor
20
3.2 Feedback
22
3.2.1 Transducers to Amplifier
22
3.2.2 Amplifier to Labview
22
3.2.3 Labview to PC
23
Chapter Four
Calibration
24
4.1 Introduction
25
4.2 The Calibration of the Axial Load Cell
26
4.3 The Calibration of the Torque Load Cell
27
4.4 The Calibration of the LVDT
28
4.5 The Calibration of the Angular Position Transducer
29
Chapter Five
Labview Programming
5.1 Introduction
5.1.1 Pseudo Code
5.2 Front Panel
31
32
32
33
5.2.1 Set Up Mode
33
5.2.2 Test Mode
34
5.2.3 Test Procedure
34
5.3 Wiring Diagram
36
5.3.1 Outside Case Sequence
38
5.3.2 Case Sequence 0
38
5.3.3 Case Sequence 1
38
5.3.3.1 Set Up Mode
39
5.3.3.2 Test Mode
39
5.3.3.3 Test 1
40
5.3.3.4 Test 3
40
5.3.3.5 Test 2 and 4
41
5.3.4 Case Sequence 2
Chapter Six
Control Systems Analysis
42
43
6.1 Introduction
44
6.2 Stability
44
6.3 Overshoot and Noise
46
6.4 Creating a System Transfer Function
48
6.5 Creating a System Model
51
6.6 Creating a PID Controller and Filter
54
Chapter Seven
Testing and Results
55
7.1 Introduction
56
7.2 Test 1
56
7.3 Test 2
58
7.4 Test 3
58
7.5 Test 4
59
Chapter Eight
Discussion
60
8.1 Problems with Equipment
61
8.2 Problems with Software
62
8.3 Problems with Safety
62
8.4 Improvements
63
Conclusions and Recommendations
64
References
65
Appendix 1
Labview Program
Appendix 2
Presentation
CHAPTER ONE
LITERATURE REVIEW
1.1
Introduction
Page 1_______________________________________Closed Loop Control of a Torque-Tension Machine
Most of the early investigation carried out was to achieve a good understanding of the
machine, its dynamics and capabilities. The addition of transducers and an amplifier to
the system gave the required feedback loop. A good working knowledge of these
components was obtained, so as they can be used effectively and efficiently.
There was a great deal of time spent understanding and gathering knowledge of Labview
programming and the connections to the PC. Once the program was written and
subsequently tested, investigation began to improve the system’s performance. This lead
to extensive research into control system analysis, PID controllers and noise filters.
1.2
Creating the Closed Loop Control
In the initial open loop control there were two controls for each motor, velocity and
torque voltage. It was important to fully understand what these voltages were controlling.
The thesis on the machine[1] gave a good description on the two motor systems and
subsequently what the voltages were controlling. The torque voltage applied the effective
power of the motor and the velocity voltage controlled the speed of the motor. It was
decided that it was enough to just vary the speed of the motor and keep the power to a
maximum at all times. For all AC servo motors the higher the speed the lower the torque
but as the speed reduces the torque increases[2]. As the shaft of the motor turns and
therefore turns the bottom of the specimen it experiences a reaction force from the
resistance from the material. When the shaft of the motor experiences this reaction force
the speed of the motor reduces and then the torque of the motor increases to overcome
this force.
The transducer were already in place in the machine and the thesis[1] gave a description
of how they were position and details on their construction. Further reading [3] gave a
better understanding of how all the transducers gave their milli-Volt output for variations
on the input conditions. The same reference[3] explained some of the errors that can
occur in the transducer outputs, and also gave an overview of the performance of a closed
loop control.
When connecting the transducers to the amplifier, to convert the low level milli-volt
reading to voltage readings, the manuals on the amplifier modules were consulted [4,5,6].
These manuals clearly state how to take the double ended input signal and set appropriate
Page 2_______________________________________Closed Loop Control of a Torque-Tension Machine
gain to give a signal ended output. C.J. Chesmonds book, reference [3] again gave a good
description of how such an amplifier convert the input signal to the desired output signal.
1.3
Labview Programming
Firstly the data acquisition cards or devices were installed in the PC and the channel
name and numbers were assigned. Referring to the data acquisition manuals [7,8] the
connections from the machine were made and the connections to the machine were
verified. The Labview manuals [9,10,11] were firstly used to identify what the software
can achieve. Then it was decided what the program had to entail to develop the closed
loop system, and the pseudo code was written. Intensive programming began with regular
reference to the manuals and the Labview help file[12] on the PC.
1.4
Investigation on Improving the System Performance
After performing a few initial tests it was clear that there was a lot of noise in the system
that was shown on the graphs of the transducers. There was also a big overshoot in the
system, particularly for torque, as the readings shoot up before settling down to the
correct value.
To reduce both noise and overshoot in the system it was decided to introduce a filter and
PID controller into the system. To design these the system needs to be represented in one
transfer function. This transfer function can be calculated, by combining the transfer
function of the various components in the system. The transfer function of the motor and
gearbox were calculated with reference again to reference[2&13]. Before getting the
transfer function for the three phase AC servo motor it was important to know the
workings and construction of the motor. A good description of a two phase servo motor
was found in reference[14]. This described how linear approximation of physical systems
can be calculated and then using Laplace Transforms to create the transfer function.
However the transfer function for the shafts and other dynamic components are difficult
to obtain without analysing the system in great detail to find the inertia or friction in the
components. Therefore a model of the system was created to give an approximate
Page 3_______________________________________Closed Loop Control of a Torque-Tension Machine
transfer function for the whole system[15]. A PID controller and pre-filter can be
designed now using ITAE methods outlined in reference[14].
The thesis was again referenced as to what the results of the tests should be to ensure the
system is operating correctly.
Page 4_______________________________________Closed Loop Control of a Torque-Tension Machine
CHAPTER TWO
EQUIPMENT
Page 5_______________________________________Closed Loop Control of a Torque-Tension Machine
2.1
Introduction
The overall system can be seen below in fig. 2.1. The torque-tension machine apply
torque and tension to a specimen in the grippers using two different motors. Therefore
two separate sub-systems can be considered, one to apply torque the other tension. The
components of the two systems can be seen below in fig 2.3 and 2.5. The machine is
controlled by the PC and Labview to output the motor voltage and direction. Amplified
transducer signals are then sent back to the PC with information from the machine to
complete the feedback loop.
Machine
Control
Panel
PC
Apply tension &
torque to specimen
Labview
Control Board
Motor
Controllers
Amplifiers
Transducers
Motors &
Grippers
Fig. 2.1: Block Diagram of Complete System
2.2
The Application of Tensile Force to the Specimen
Page 6_______________________________________Closed Loop Control of a Torque-Tension Machine
2.2.1
The Load Motor
This is a ‘Moog’ D315-L15 type brushless AC servo motor. It is a three phase permanent
magnet servo motor. It has a continuous stall torque capacity of 8.1Nm and a nominal
speed of 3000rpm. It has a continuous stall current capacity of 12.3 Amps. The
characteristic curve of the motor (torque v speed) is shown in fig. 2.2. This motor has
also the following features:
-High energy magnets of low inertia rotor
-Sinusoidal back emf for improved low speed performance and higher efficiency
-Light weight-aluminum housing for maximum heat transfer
-Pre-loaded sealed bearings pre-lubricated with high temperature grease for
extended life
Fig 2.2: Load Motor Characteristic Curve
2.2.2
The Load Gearbox
This is a ‘Carl Bockwoldt’ three stage CB59-NF80 type helical gearbox. The gear ratio is
295.8:1 and the gearbox has a maximum permissible output torque at rated power of
1200Nm and input speed of 4000rpm. The motor and gearbox are assembled together in
one unit.
2.2.3
Timing Pulleys and Timing Belt
Page 7_______________________________________Closed Loop Control of a Torque-Tension Machine
The timing pulleys are made of stainless steel with steel flanges and each have 40 teeth.
Two pulleys are keyed to the output shaft of the gearbox and one to each of the ball
screws. A polyurethane ‘Bando’ type timing belt is mated around one of the pulleys on
the gearbox output shaft to one of the pulleys on the ball screws. These belts are capable
of transmitting approximately 30 kW with an efficiency of 98%, with no slip or backlash.
Each belt has 121.
2.2.4
Ball Screws
The two induction hardened carbon steel ball screws are on either side of the machine the
width of the crosshead apart. They are used to drive the cross head up and down as they
transform the torque from the timing pulleys to apply axial load to the specimen. This
transformation is attained by a long nut in each ball screw, that is screwed to the cross
head, that creates a linear motion of the cross head as the ball screws rotate.
2.2.5
Guide Rods and Super Ball Bushing
These are two steel shafts that withstand the twisting created by the torque applied to the
specimen from the torque motor. By withstanding this bending moment the guide rods
ensure that the ball screws don’t experience any torque form the torque motor. The super
ball bushings are a pair of linear ball bearings that allow almost friction-less axial
motion.
Page 8_______________________________________Closed Loop Control of a Torque-Tension Machine
Fig 2.3: Load Motor to Specimen
Page 9_______________________________________Closed Loop Control of a Torque-Tension Machine
2.3
The Application of Torque to the Specimen
2.3.1
The Torque Motor
A ‘Moog’ brushless AC servo motor of type D413-L10 is used. The motor’s
characteristic curve (torque verses speed) is shown in fig.2.4. The continuous stall torque
of this motor is 2.7Nm and has a nominal speed of 4000rpm. Its continuous stall current
capacity is 6.7 Amps and has the same features as the load motor.
Fig 2.3: Torque Motor Characteristic Curve
2.3.2
The Torque Gearbox
This is a ‘Carl Bockwoldt’ three stage helical gearbox of type CB29-NF-63. It has a gear
ratio of 150.7:1 and has a maximum permissible output torque at rated power of 300Nm
and input speed of 4000rpm. The motor and gearbox were like the load motor and
gearbox assembled as one unit.
2.3.3
Spur Gears
A pair of case hardened steel spur gears both with 94 teeth were used to transmit the
torque from the gearbox to the torsion shaft. One spur gear was keyed to the output shaft
of the gearbox and the other to the end of the torsion shaft.
2.3.4
Square Drive
Page 10_______________________________________Closed Loop Control of a Torque-Tension
Machine
A steel block of square cross-section connects the top of the torque load cell to the
bottom of the torque-tension shaft as can be seen in fig. 2.5. The drive experiences only
the torque applied to the specimen and does not transmit any axial forces from the drive
system to the mechanism.
Fig. 2.5:Torque Motor to Specimen
Fig 2.6: Control Board Flow Chart
Page 11_______________________________________Closed Loop Control of a Torque-Tension
Machine
2.4
Signal to the Machine
2.4.1
Labview
This is very powerful interfacing tool which acquires input and output data to perform
analysis operations and communicate between the PC and external systems. Programs
can be written to control and analyse these systems by using a ‘front panel’ which is the
user interface and the block diagram which is the source code. The external system is
wired into data acquisition (DAQ) devices which makes a connection from the PC to the
outside world. Internal buses within the PC communicate with the software and sends
and receives signals to and from the DAQ devices. On the front panel of Labview the
required inputs are selected and Labview sends voltages signals to the DAQ devices
connected to the PC in either analogue or digital form.
2.4.2
DAQ Devices
Two data acquisition devices AT-AO-6 and AT-MIO-16E were used to send the voltage
signals to the servo motor controllers from analogue and digital output channels on the
devices.
2.4.3
Servo Motor Controllers
The two identical ‘Moog T161-603’ brushless motor controllers along with two extended
function cards were used to control the load and torque motors. These are high
performance servo controllers have a 16 bit microprocessor providing closed loop control
of the servo motor velocity. The flow chart of the operation principle can be seen in fig.
2.6 on the previous page.
Page 12_______________________________________Closed Loop Control of a Torque-Tension
Machine
2.5
Signals from the Transducers
2.5.1
The Axial Load Cell
The RDP Electronics D/8745-01 axial load cell is a donut shaped 133.5kN capacity
compression type load cell, used to measure the applied axial load. This load cell has
bonded foil type strain gauges and has a maximum excitation voltage of 10 Volts DC.
The output for a full scale deflection for a 10VDC excitation is 28.945 mV. Therefore the
load cell gives a 0.216816mV/kN reading. The donut shaped load cell sits around the
shaft of the top gripper inside the cross head. As the cross head moves up the load cell
compresses and the voltage output is proportional to the tensile force being applied to the
top gripper and therefore to the specimen(fig. 2.7). Fig 2.8 shows the set up of the strain
gauges on the load ring sensor in the load cell. In the electrical circuit in fig 2.9 V is the
10 Volt input and Vo is the output voltage signal from the transducer.
Fig 2.7: The Axial Load Cell Position in Cross Head
Fig 2.8: Strain Gauge Set Up
Fig 2.9: Electrical Circuit of Strain Gauges
Page 13_______________________________________Closed Loop Control of a Torque-Tension
Machine
2.5.2 The Torque Load Cell
The torque load cell is a Norbar 50241 ETS rotary torque transducer of 500Nm capacity
and has been calibrated up to 200Nm, to measure the torque applied. This load cell is a
strain gauge torsion bar made from a heat treated alloy. It has a full bridge arrangement
with a full excitation voltage of 10Volts. The output for a full scale deflection is 8.17mV
giving a 0.04084mV/Nm reading for a 10V excitation. The top of the load cell is
connected to the bottom gripper shaft and the bottom of the load cell is connected to the
torsion shaft. The load cell has a centre shaft which rotates with the torsion shaft and the
outside housing measures the torque of the shaft. Fig 2.10 shows the set up of the strain
gauges on the torque load cell shaft. The same electrical circuit is used as in fig 2.9.
Fig 2.10: Torque Strain Gauge Set Up
Page 14_______________________________________Closed Loop Control of a Torque-Tension
Machine
2.5.3 The LVDT
The SPS Linear Velocity Displacement Transducer has a 26mm stroke length capacity
and is used to measure the total deformation of the specimen along the axial direction.
The LVDT is positioned to measure the movement of the cross head as the load increase
or reduces. Fig 2.11 shows the electrical circuit which shows that when the rod moves up
and down the ferrous core transforms varying voltage to V1 and V2 which in turns varies
the output voltage. The output voltage is the signal sent out form the transducer.
Fig 2.11:Electrical Circuit of the LVDT
Page 15_______________________________________Closed Loop Control of a Torque-Tension
Machine
2.5.4
The Angular Position Transducer
The angular position transducer is a Penny+Giles 30/10/300 and is used to measure the
angle of twist of the specimen. The output reading is 33mV/degree rotation of the shaft
for a 10VDC input. However for a full rotation the linear output is only 300 degrees and
the linear output voltage range is from 50mV to 995mV. The transducer shaft is screwed
into a small hole on the end of the torsion shaft and experiences the same angle of twist
as the torsion shaft. The output is determined by the position of the shaft inside the
transducer. As the shaft turns the position is read in binary and outputted in volts.
Fig. 2.12 4-Bit Electromechanical Encoder
2.5.5
Amplifier
The RDP Module 600 has three modules with two channels of transducer excitation and
signal conditioning for use with both low and high sensitivity AC and DC transducers.
The front panel controls include fine gain, zero and excitation with a push button for
shunt calibration. The amplifier takes in a double ended input signal from the transducers
and amplifies the low level milli-volt reading to give a signal ended 0-10 Volts output
reading.
Page 16_______________________________________Closed Loop Control of a Torque-Tension
Machine
Fig 2.13: Position of Transducers on Machine
Page 17_______________________________________Closed Loop Control of a Torque-Tension
Machine
CHAPTER THREE
CONNECTIONS
Page 18_______________________________________Closed Loop Control of a Torque-Tension
Machine
3.1
Control
3.1.1
PC to Labview
On the Labview front panel the controller sets his/her desired inputs to the system. The
parameters are set on the screen and voltage signals are then sent to the data acquisition
DAQ devices connected to the back of the PC. The parameters can be divided into
analogue and digital signal generation:
Analogue
-the force and torque to be applied to the specimen
-the rotational speed of each motor
0-10V analogue signals are sent to the DAQ devices via analogue output channels
which are assigned within Labview. Each device however has only two analogue
output channels so the analogue signals for the force motor are sent to device 1
and the torque signals to device 2. The force and the torque applied to the
specimen is created by the torque of the motors which is determined by the
voltage applied. The motors first have to move to a point where the torque of the
motor can exert a force on the specimen. For this reason the rotational speed is
specified by applying a voltage which gives the rpm of the motor.
Digital
-the direction of movement of each motor
-whether the motor is in run or hold mode
-if the system needs to be reset
0-5V digital signals are sent to the DAQ device 2 via a digital input/output (I/O)
channel. As there is only one digital channel on the device each of it’s eight lines
are written to separately.
Page 19_______________________________________Closed Loop Control of a Torque-Tension
Machine
3.1.2
Labview to control boards
Each of these output signals were then wired up to the servo motor controller boards
using three separate cables. The first cable links all the force output signals from the
DAQ devices to the XA7 connector on the control board, so this cable is called the XA7
cable. The second cable links the torque output signals to the XB7 connector on the
control board and is known as the XB7 cable. Another cable takes both reset output
signals and some power from the PC to the control board.
3.1.3
Control boards to Motor
The control board were mounted together on the side of the machine are connected to the
motor via heavy insulated wires.
XA7
1
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
VOUT0
EXTREF0
VOUT1
AGND0
VOUT2
EXTREF2
VOUT3
AGND2
VOUT4
EXTREF4
VOUT5
AGND4
VOUT6
EXTREF6
VOUT7
AGND6
VOUT8
EXTREF8
VOUT9
AGND8
ADIO1
ADIO3
BDIO5
BDIO7
DGND
Velocity (F)
Torque (T)
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
IOUT0
RGND0
IOUT1
AGND1
IOUT2
RGND2
IOUT3
AGND3
IOUT4
RGND4
IOUT5
AGND5
IOUT6
RGND6
IOUT7
AGND7
IOUT8
RGND8
IOUT9
ADIO0
ADIO2
BD1O4
BDIO6
EXTUPDT
+5V
Fig 3.1: AT-A0-6 DAQ device 1
Page 20_______________________________________Closed Loop Control of a Torque-Tension
Machine
68
34
67
33
66
32
65
31
64
30
63
29
62
28
61
27
60
26
59
25
58
24
57
23
amp o/p ch 3
amp o/p ch 1
amp o/p ch 4
ACH 0
ACH 8
AIGND
ACH 1
ACH 9
AIGND
ACH 2
ACH 10
AIGND
ACH 3
ACH 11
AIGND
AISENSE
ACH 4
ACH 12
AIGND
ACH 5
ACH 13
AIGND
ACH 6
ACH 14
AIGND
ACH 7
ACH 15
force ch 0
12
46
13
47
14
48
15
49
16
50
17
51
18
52
19
53
20
54
21
55
22
56
angle ch 1
LVDT ch 2
Torque ch 3
XA7 cable
XB7 cable
DIGND
SCNCLK
DIGND
DIO 3
+5V
DIO 7
DIGND
DIO 2
DIO 6
DIGND
DIO 1
DIO 5
DIGND
DIO 0
DIO 4
DIGND
EXTREF
AOGND
DAC 1
AIGND
DAC 0
AIGND
Run/Hold (F)
Direction (F)
Run/Hold (T)
Reset (F)
Direction (T)
Reset (T)
Velocity (T)
Torque (T)
Fig 3.2: AT-MIO-16E DAQ Device 2
XB4
XA4
Voltage
to
Torque
Motor
Voltage
to
Load
Motor
XB5
XB7
1 not connected
2 pos. feedback
3 direction
4 velocity i/p
5 not connected
6 run/hold
7 torque I/p
8 o/p command
9 not connected
Reset
and
Enable
XA5
Power
from
Mains
XA7
1 not connected
2 pos. feedback
3 direction
4 velocity i/p
5 not connected
6 run/hold
7 torque I/p
8 o/p command
9 not connected
Reset
and
Enable
XB6
X5
Reset
and
Enable
XA6
Signals
to
Torque
Motor
Signals
to
Torque
Motor
Fig 3.3: Servo Motor Control Board Diagram
Page 21_______________________________________Closed Loop Control of a Torque-Tension
Machine
3.2
Feedback
3.2.1
Transducers to amplifiers
There are four transducers in place around the machine. These transducers produce milli
volt readings which have to be amplified to achieve readable and accurate results. An
RDP Module 600 amplifier replaced the four amplifiers that were used previous. This
amplifier had multiple channels, a variable gain setting and a zeroing and calibration
function. Each module has two channels A and B and there a module for strain gauges.
At the back of the amplifier there is two inputs and one output for each channel. The
transducers were connected up as follows:
-LVDT was connected to channel 1A
-Axial load cell was connected to channel 3A
-Angular Displacement transducer was connected to channel 3B
-Torque load cell was connected to channel 4A
The transducers can output various voltages ranges and these ranges need to be set up for
each channel by flicking the correct switches on the circuit boards of each channel. The
switches and the input ranges of each transducer can be seen in fig 4.1 in the next chapter
on calibration.
3.2.2
Amplifiers to Labview
The output of each channel on the amplifier is the input to the analogue input channels on
the DAQ device 2. The input to the amplifiers is a differential or double ended signal and
the amplifier produces a single ended output with respect to ground. The output of
module 3 has the single ended output signals of two transducers and a common ground to
give the different input to the analogue channel on the DAQ device.
3.2.3
Labview to PC
Page 22_______________________________________Closed Loop Control of a Torque-Tension
Machine
All of the channels use the differential mode. The channels are paired as shown in fig.3.4
with analogue channels 0 & 8 together, 1 & 9 etc. Each of these pairings give an
analogue input channel which are assigned a name. These are all ±10V input channels
but are converted into their respective units as dealt with in the calibration section. All
the transducer readings are shown on the front panel in graph form and all the data
received is recorded against time in a file.
Pins
68
34
33
66
65
31
30
63
Pin Names Channel Names Channel Number
ACH 0(+)
Force
0
ACH 8(-)
ACH 1(+)
Angle
1
ACH 9(-)
ACH 2(+)
Displacement
2
ACH 10(-)
ACH 3(+)
Torque
3
ACH 11(-)
Fig 3.4: Assignment of Analogue Input Channel
Page 23_______________________________________Closed Loop Control of a Torque-Tension
Machine
CHAPTER FOUR
CALIBRATION
Page 24_______________________________________Closed Loop Control of a Torque-Tension
Machine
4.1
Introduction
The instruments that need to be calibrated are all the transducers on the machine.
The Axial Load Cell using the Instrom machine
The Torque Load Cell using a Crane Electronics Digital Torque Wrench
The LVDT using the Instrom machine
The Angular Transducer using 360 markings around bottom gripper
The position of each of these transducers on the machine can be seen in fig 2.13 in
chapter 2. All the transducers are wired to the amplifier which has the following switches
on its component circuit board.
Gain Switches
Input Signal
Range for +/-10V
Output
Switch
Toggles
ON
5-10V
2.5-5V
1.3-2.5V
0.7-1.3V
0.3-0.7V
0.15-0.3V
80-150V
40-80mV
20-40mV
10-20mV
5-10mV
none
6
1
6+1
2
6+2
3
6+3
4
6+4
5
Zero Switches
Approx.
Toggle
Output
ON
Shift in
Volts
1
3
1+3
5
1+4
7
1+5
9
2
-3
2+3
-5
2+4
-7
2+5
-9
Fig 4.1: The Zero and Gain Switches of the Amplifier
The inverse of the slopes of these calibration graphs give the scaling factor for each of
the readings in the Labview wiring diagram to give the readings in their own respective
units. The factors are stated under each graph:
Page 25_______________________________________Closed Loop Control of a Torque-Tension
Machine
4.2
The Calibration of the Axial Load Cell
1. Removed the axial load cell from the Torque-Tension machine by loosening the
screws on the plates that hold the load cell in place on the cross-head.
2. Place the load cell in the Instrom machine and place heads that will give an applied
load on the diameter of the load cell.
3. The Labview program ‘Calibration’ was set up to read the signals coming into the
Analogue Input channel assigned to Force which is channel 0. On the front panel of
the program the input data was represented on a graph and a digital indicator gave
precise readings.
4. On the RDP Modular 600 amplifier module 3 board was removed from the amplifier
to change the input range to the amplifier. This was accomplished by turning on the
appropriate gain switches as shown in fig.4.1 taken from amplifier operator’s manual.
5. The input signal was zeroed against the zero axis on the graph by adjusting the ‘zero
screw’ on the amplifier on the appropriate channel.
6. Increasing loads of 5kN were applied to the load cell on the Instrom machine. The
precise load applied and the input voltage from the digital indicator on the front panel
was recorded for each load.
7. These values recorded were entered into Microsoft Excel and the data graphed to find
the slope of the best fit line (fig. 4.2). The inverse of this slope gave the scaling factor
for Load = 12.5312 kN/V
Load cell calibration
4.5
y = 0.0798x
4
3.5
3
Volts
2.5
2
1.5
1
0.5
0
0
10
20
30
Force kN
40
50
60
Fig 4.2: Axial Load Cell calibration graph
Page 26_______________________________________Closed Loop Control of a Torque-Tension
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4.3
The Calibration of the Torque Load Cell
1. Removed the bottom gripper from the Torque-Tension machine and replace it with a
plate attachment.
2. Screw the digital torque wrench onto this plate and ensure a tight fit is achieved.
3. The Labview program ‘Calibration’ was set up to read the signals coming into the
Analogue Input channel assigned to Torque which is channel 3. On the front panel of
the program the input data was represented on a graph and a digital indicator gave
precise readings.
4. On the RDP Modular 600 amplifier module 4 board was removed from the amplifier
to change the input range to the amplifier. This was accomplished by turning on the
appropriate gain switches as shown in fig.4.1 taken from amplifier operator’s manual.
5. The input signal was zeroed against the zero axis on the graph by adjusting the ‘zero
screw’ on the amplifier on the appropriate channel.
6. Increasing torque of 10Nm were applied to the torque-tension shaft on the machine
using the toque velocity voltage control. The precise torque applied from the torque
bar and the output voltage from the transducer on the front panel was recorded for
each torque.
7. These values recorded were entered into Microsoft Excel and the data graphed to find
the slope of the best fit line (fig. 4.3). The inverse of this slope gave a scaling factor
for torque = 23.42 Nm/V.
torque cal cw
8
y = 0.0512x
7
6
volts
5
4
3
2
1
0
0
20
40
60
80
torque Nm
100
120
140
Fig 4.3:Torque Load Cell Calibration
Page 27_______________________________________Closed Loop Control of a Torque-Tension
Machine
4.4
The Calibration of the LVDT
1. Place the LVDT in the Instrom machine set up with flat heads.
2. The Labview program ‘Calibration’ was set up to read the signals coming into the
Analogue Input channel assigned to LVDT which is channel 2. On the front panel of
the program the input data was represented on a graph and a digital indicator gave
precise readings.
3. On the RDP Modular 600 amplifier module 1 board was removed from the amplifier
to change the input range to the amplifier. This was accomplished by turning on the
appropriate gain switches as shown in fig.4.1 taken from amplifier operator’s manual.
4. The input signal was zeroed against the zero axis on the graph by adjusting the ‘zero
screw’ on the amplifier on the appropriate channel.
5. Increasing axial displacement of 2 and then 1mm were applied to the LVDT on the
Instrom machine using the plunge depth gauge. The precise axial displacement and
the input voltage from the digital indicator on the front panel was recorded for each
displacement.
6. These values recorded were entered into Microsoft Excel and the data graphed to find
the slope of the best fit line (fig. 4.4). The inverse of this slope gave the scaling facotr
for the LVDT = 1.3mm/V.
LVDT calibration
15
y = 0.7698x - 14.591
volts
10
5
0
0
5
10
15
20
25
30
35
-5
-10
distance mm
Fig 4.4: LVDT Calibration graph
4.5
The Calibration of the Angular Position Transducer
Page 28_______________________________________Closed Loop Control of a Torque-Tension
Machine
1. The motor encoder is already mounted on the end of the torsion shaft.
2. A 360 degree markings were place around the bottom gripper shaft and an indicator
was created using a hole in the shaft.
3. The Labview program ‘Calibration’ was set up to read the signals coming into the
Analogue Input channel assigned to Angle of Twist which is channel 1. On the front
panel of the program the input data was represented on a graph and a digital indicator
gave precise readings.
4. On the RDP Modular 600 amplifier module 3 board was removed from the amplifier
to change the input range to the amplifier. This was accomplished by turning on the
appropriate gain switches as shown in fig.4.1 taken from amplifier operator’s manual.
5. The input signal was zeroed against the zero axis on the graph by adjusting the ‘zero
screw’ on the amplifier on the appropriate channel.
6. Torque velocity voltage was applied from the front panel of the Labview program. To
rotate the bottom gripper clockwise. Using the run/hold switch on the front panel the
angle was recorded against the input voltages read on the graph for each angle.
7. These values recorded were entered into Microsoft Excel and the data graphed to find
the slope of the best fit line (fig. 4.5). The inverse of this slope gave the scaling factor
for the angle of twist = 22.88 /V.
angle cal
10
y = 0.0437x - 3.1421
8
volts
6
4
2
0
-2
0
50
100
150
200
250
300
angle deg
Fig 4.5: Angle of Twist Calibration graph
Page 29_______________________________________Closed Loop Control of a Torque-Tension
Machine
The gain settings can be changed on the front of the amplifier so to ensure setting
remains unchanged the ‘cal’ button when pressed should show the following values:
Load = 50kN
Torque=100Nm
LVDT=26mm
Angle of Twist 300 degrees
Before a test is carried out these settings should be verified using the gain calibration
button.
Page 30_______________________________________Closed Loop Control of a Torque-Tension
Machine
CHAPTER FIVE
LABVIEW PROGRAMMING
5.1
Introduction
Page 31_______________________________________Closed Loop Control of a Torque-Tension
Machine
The requirements of the Labview program are as follows:
-To send voltages to control the servo motors in both directions via the control board
-To read in the amplified transducer values from the machine and graph the results
-The ability to perform the following tests on the specimen:
Keeping the tensile force constant apply torque gradually
Keeping the torque constant apply tension gradually
Keeping the axial displacement constant apply torque gradually
Keeping the angle of twist constant apply tension gradually
-Record all data in an Excel spreadsheet against time
5.1.1 Pseudo Code
-Set up all the analogue and digital input and output channels in Measurement and
Automation
-Design a set up mode to move the grippers to insert and remove the specimen
-Set up a global start time and have clocks in the program so as the total and loop
times can be calculated
-Adjust the transducer readings to convert the values in their respective
-Design test 1 to keep the load constant and vary the torque applied using feedback to
keep the load within a certain limit
-Design test 2 to keep the torque constant and vary the load applied using feedback to
keep the torque within a certain limit
-Design test 3 to keep the axial displacement constant and vary the torque applied
using feedback to keep the axial displacement within a certain limit
-Design test 4 to keep the angle of twist constant and vary the load applied using
feedback to keep the angle of twist within a certain limit
-Set up a logic circuit take can switch between the different modes
-Choose suitable speeds and ranges to bring the various constant parameters back
within the limits set
5.2
Front Panel
Page 32_______________________________________Closed Loop Control of a Torque-Tension
Machine
The start/stop switch button when ON starts the entire program running and initialises the
set up mode if none of the test modes are ON. The time is recorded from the second the
start/stop button is pressed and can be viewed in the ‘Total Time’ indicator. The loop
time for the last loop is also shown on the front panel and all the loop time are recorded.
5.2.1
Set Up Mode
The two controls are for the torque and tension applied to the specimen held in the
grippers of the machine. Each has four variable inputs the speed and direction of the
motors and whether the motor is in run or hold mode or in reset mode or not. The
speed(velocity) control is controlled by a velocity voltage knob that supplies a 0-10V
analogue signal output. The other three control inputs are selected by flicking switches
that give a 1 or 0 to a digital output.
This set up mode is for positioning the grippers to insert or remove the specimen for
testing. This mode may also be used to bring the torque or load levels to a certain point
before entering one of the test modes. As the velocity voltage for either motor is varied
the resultant torque, load, angular and axial displacement experienced in the system are
outputted to the four separate graphs on the right of the set up mode. The angular and
axial displacement readings, which can be viewed in the digital indicator that
accompanies each graph, can be used to align the grippers to insert the test specimen. The
torque velocity voltage can be varied in the clockwise direction to increase the angle of
twist or counter clockwise direction to decrease the angle of twist. The load velocity
voltage can be varied in the up direction to increase the axial displacement or down to
decrease the axial displacement.
5.2.2
Test Modes
There are four tests number 1 to 4 as follows:
Page 33_______________________________________Closed Loop Control of a Torque-Tension
Machine
Test 1 Varying torque for a constant load
Test 2 Varying load for a constant torque
Test 3 Varying torque for a constant axial displacement
Test 4 Varying load for a constant angle of twist
When any of the test modes are switched on the set up mode becomes an obsolete
control. The graphs remain synonymous to whatever mode is on. Test1 and 3 use the
same load run/hold switch and torque control and likewise test 2 and 4 use the same
torque run/hold switch and load control. The front panel is shown in appendix 1.
5.2.2.1 Test Procedure
The procedure for carrying out the tests follows assuming the specimen is in place.
Test 1
Press the ‘Test 1 Off’ button and enter the constant load required.
Enter the tolerance to which the constant load has to remain within. i.e. if 1kN was
chosen, the tolerance is 1kN either side of the constant load.
Flick the load run/hold switch and wait.
The load motor will bring the applied load to within the tolerance specified.
The torque can now be varied by adjusting the torque velocity voltage knob.
Flick the torque run/hold switch to apply the torque.
The torque will ramp up as the load remains within its limits until the specimen
breaks(yields).
Test 2
Press the ‘Test 2 Off’ button and enter the constant torque required.
Page 34_______________________________________Closed Loop Control of a Torque-Tension
Machine
Enter the tolerance to which the constant torque has to remain within. i.e. if 1Nm was
chosen, the tolerance is 1Nm either side of the constant torque.
Flick the torque run/hold switch and wait as the torque motor will bring the applied
torque to within the tolerance specified.
The load can now be varied by adjusting the load velocity voltage knob.
Flick the load run/hold switch to apply the load as the load will ramp up as the torque
remains within its limits until the specimen breaks(yields).
Test 3
Press the ‘Test 3 Off’ button enter the constant axial displacement required.
Enter the tolerance to which the constant axial displacement has to remain within. i.e. if
1mm was chosen, the tolerance is 1mm either side of the constant axial displacement.
Flick the load run/hold switch and wait as the load motor will bring the axial
displacement to within the tolerance specified.
The torque can now be varied by adjusting the torque velocity voltage knob.
Flick the torque run/hold switch to apply the torque as the torque will ramp up as the
axial displacement remains within its limits until the specimen breaks(yields).
Test 4
Press the ‘Test 4 Off’ button and enter the constant angle of twist required.
Enter the tolerance to which the constant angle of twist has to remain within. i.e. if 1deg
was chosen, the tolerance is 1deg either side of the constant torque.
Flick the torque run/hold switch and wait as the torque motor will bring the angle of twist
to within the tolerance specified.
The load can now be varied by adjusting the load velocity voltage knob.
Flick the load run/hold switch to apply the load.
The load will ramp up as the angle of twist remains within its limits until the specimen
breaks(yields).
5.3
Wiring Diagram
Page 35_______________________________________Closed Loop Control of a Torque-Tension
Machine
A flowchart for the wiring diagram is shown in fig. 5.1 to give a an overall view of an
otherwise complicated program. The full wire diagram is attached in appendix 1.
Case 0
Case 1
Test Mode Within Case 1-True
Fig 5.1: Flow Chart for Wire Diagram
Page 36_______________________________________Closed Loop Control of a Torque-Tension
Machine
Test 1 within Test Mode
Case 2
Fig 5.1 (contd.): Flow Chart for Wire Diagram
Page 37_______________________________________Closed Loop Control of a Torque-Tension
Machine
5.3.1
Outside Case Sequences
Outside the main for loop a global variable is defined as time. This is global variable is
taken from the PC clock at the time the program begins running. The torque voltage to
both the load and torque motor is set to 10V to give the motors the maximum power and
the speed of the motors will vary the load and torque applied to the specimen. The AO
multi-point generates a waveform and sends the signal to the analogue output channels
labelled. Both signals are sent to channel 1 but on different devices, load to device 1 and
torque to device 2.
5.3.2
Case Sequence 0
Inside the for loop there is a case sequence with three cases. The for loop continues until
the start/stop button on the front panel is depressed to stop. On the first iteration of the
loop the iteration number is zero and so begins time tick count in the case sequence 0.
5.3.3
Case Sequence 1
In the case sequence 1 there are numerous case structures and is the main section of the
program. A case structure has two separate sections of program with only one active at a
time depending on whether the input to the structure is true or false. A small logic circuit
is set up outside the initial case structure which reads as ‘if any of the tests are on then
input true to the case structure otherwise false’.
5.3.3.1 Set Up Mode
Page 38_______________________________________Closed Loop Control of a Torque-Tension
Machine
In the false case the set up mode is in use. In this case the velocity voltage from both load
and torque are read in from the front panel and are outputted to the analogue output
channels 0 on device 1 for load and device 2 for torque. The digital output from the front
panel switches, run/hold, direction and reset of both motors are sent to separate lines of
the one digital output channel on device 2. Refer to fig. 3.1 and 3.2 for channel
configuration.
The amplified input signals from the transducers are also read in here. All are read from
device 2 from channels 0-3. The readings are adjusted to give the appropriate ranges used
in each of their respective units.
i.e. changing load reading from V to kN. These
adjustments were calculated in the calibration section.
5.3.3.2 Test Mode
In the true case structure (when one of the tests is ON) there are further case structures
for each test. If this case is false it contains another case structure inside with test 1 in the
false case and test 2 in the true case. If this case is true it contains another case inside
with test 3 in the true case and test 4 in the false case. The program for each test is similar
in design, particularly for test 1 and 3 as torque is varied against a constant parameter and
for test 2 and 4 where it is load that is varied against a constant parameter.
The indicators that output the transducers measurements to both the graphs and the excel
spreadsheet are outside all of the case structures. Therefore whichever test is on the
reading will all be outputted to the same graphs.
5.3.3.3 Test 1
Page 39_______________________________________Closed Loop Control of a Torque-Tension
Machine
In test 1 the load is to stay constant. To achieve this the load motor moves the cross head
to reapply the required constant load. The constant load and the tolerance are entered on
the front panel and the range is calculated to give the high and low limit. The amplified
load cell signal is compared with the high and low limits, to determine whether the load
is above, below or inside the tolerance band. If the reading is within the tolerance band
the velocity of the load motor is set to zero to keep the load within the tolerance. Also the
torque motor is read in and the torque is applied once the input is non-zero.
However if the load is above the high limit the load motor moves the cross head down to
decrease the load. Similarly if the load is below the low limit the load motor moves the
cross head up to increase the load. The speed at which the load motor moves the cross
head up and down is determined by a constant input set to 0.7 volts. The torque velocity
voltage is read in whether the load is inside or outside the tolerance band. Therefore the
load motor is keeping the load constant while the torque motor is applying additional
torque to the specimen simultaneously.
5.3.3.4 Test 3
Test 3 is similar to test 1 except that the axial displacement transducer reading is
compared with the axial displacement tolerance band. If the axial displacement is higher
than the high limit the load motor moves the cross head down just like in test 1 to reduce
the axial displacement. Likewise if the axial displacement is below the low limit the load
motor moves the cross head up to increase the axial displacement. If the axial
displacement is within its tolerance the load motor doesn’t move. Therefore the load
motor keeps the axial displacement constant while the torque motor applies additional
torque to the specimen.
5.3.3.5 Test 2 and 4
Page 40_______________________________________Closed Loop Control of a Torque-Tension
Machine
For test 2 and 4 it is the load that is varied and torque that stays constant in case of test 2
and the angle of twist that stays constant in test 4. The same design is used as can be seen
in appendix 1. However it is the torque motor that keeps the torque or angle of twist
constant moving counter clockwise to reduce the torque or angle of twist and moving
clockwise to increase the torque or the angle of twist.
5.3.4
Case Sequence 2
Page 41_______________________________________Closed Loop Control of a Torque-Tension
Machine
In the final case sequence, case 2, the readings from the transducer indicators are inputted
to an array along with the loop time and total time. This array is then sent to a while loop
and into a ‘write to spreadsheet’ function which saves all the data in a file that can be
viewed in Excel. A wait function is placed in the while loop to limit the number of
readings taken to one a second. The time for the loop is calculated by taking the time in
the last case sequence from the time in the first sequence and dividing by 1000 to give
the time in seconds. The total time is the time in the last sequence taken from the global
variable time recorded in the first sequence and again dividing by a 1000 to convert to
seconds.
Page 42_______________________________________Closed Loop Control of a Torque-Tension
Machine
CHAPTER SIX
CONTROL SYSTEM ANALYSIS
Page 43_______________________________________Closed Loop Control of a Torque-Tension
Machine
6.1
Introduction
After performing a few initial tests it was clear that there was a lot of noise in the system
that was shown on the graphs of the transducers. There was also a big overshoot in the
system, particularly for torque, as the readings shoot up before settling down to the
correct value.
To reduce both noise and overshoot in the system it was decided to introduce a filter and
PID controller into the system. To design these the system needs to be represented in one
transfer function. This transfer function can be calculated, by combining the transfer
function of the various components in the system. The transfer function of the motor and
gearbox could be calculated, however the transfer function for the shafts and other
dynamic components are difficult to obtain without analysing the system in great detail to
find the inertia or friction in the components. Therefore a model of the system was
created to give an approximate transfer function for the whole system. From this model a
PID controller and pre-filter could be created.
6.2
Stability
Firstly in the analysis of a control system it is important to investigate the system’s
stability. A stable system can be defined as a system with a bounded (limited) system
response[13]. Therefore the system has to be stable to give a response within certain
limits to a bounded input or disturbance. The stability of the system was investigated by
implementing Test 1 and setting up the tolerance band as the limits for the response to
stay within. Referring to section 5.3.3.3 the velocity voltage set while the reading is
within the tolerance is set to zero. However if the velocity voltage isn’t set to a particular
value and allowed to remain at the same voltage as it was outside the tolerance band the
response can be seen in fig 6.1.
Page 44_______________________________________Closed Loop Control of a Torque-Tension
Machine
Fig 6.1:Stable Response to Bounded Inputs
In the load graph the load has to remain within the tolerance and soon as it goes outside
the tolerance the direction of the changes bringing the load back within the tolerance
again. The result on the graph proves that the response of the system can stay within
limits and therefore the system is stable.
6.3
Overshoot and Noise
Page 45_______________________________________Closed Loop Control of a Torque-Tension
Machine
Fig 6.2: The Front Panel showing the Overshoot and Noise in the System
The figure 6.2 above shows the overshoot and the noise experienced in the system. The
noise in the system is due to the transducers and the high frequency noise from the motor
and gearbox. The noise in the readings is due to the transducers experiencing the noise
from the motor and gearbox when rotating and any hysteresis in the gearbox. Another
reason could be that the shafts are over-designed and the strain values that the strain
gauges of the torque load cell measure are too small to give a good signal to noise
separation.[3]
Page 46_______________________________________Closed Loop Control of a Torque-Tension
Machine
Fig 6.3: Transient Response to Step Input
For second or higher order systems the transient response to a step input is as above. ζ is
the damping ratio which determines the speed of response. If this value is low then the
system responds very fast and the rise time is small, but the overshoot is large. If the
system is damped then the rise time is smaller but a more accurate response is created
and the overshoot is less. By putting a PID controller into the system the overshoot can
be changed, along with the rise time and settling time to get the best response possible.
Page 47_______________________________________Closed Loop Control of a Torque-Tension
Machine
6.4
Creating a System Transfer Function
A control system is an interconnection of components forming a system configuration
that will provide a desired system response[13].
Each component in the system can be considered as a block with an input which has
usually been amplified or changed to a different property to give an output. The block
contains a transfer function which tries to characterise the physical elements of the
mechanical or electrical component. Fig.6.4 and 6.5 show the block diagram for the
torque and load systems from the motors to the application of the torque and tension to
the specimen. These are both open loop control systems and so represent the system in
the set up mode. Some of these variables can’t be obtained from relatively simple studies
of this system. The inertia due to mass and the friction in the dynamic components in the
system are difficult to evaluate. For this reason it will only be demonstrated how the
transfer functions for the motor and gearbox could be calculated.
Fig. 6.4: Load Motor Block Diagram
Fig 6.5: Torque Motor Block Diagram
The transfer function for a three phase AC servo motor is derived as follows:[2]
Page 48_______________________________________Closed Loop Control of a Torque-Tension
Machine
Fig 6.6: Servo Motor
The motor torque can be written as:
T = K mVa − Fmω m
where Km is the motor torque constant in Nm/V
Fm is the motor viscous friction in Nm/rad/sec
However Fm can be gotten from the slope of the torque-speed curves at constant Va and
Km is the change in torque per unit change in control voltage Va at constant speed. The
graphs of both motors are shown in the equipment section.
dω m
T = K mVa − Fmω m = ( J m + J L )
+ FLω m
dt
where JL is the load inertia
Jm is the motor inertia
FL is load viscous friction
dω m
+ ( Fm + FL )ω m
dt
Using the Laplace Transforms the transfer function for the motor is
Km
ω m ( s)
F
=
V a ( s ) 1 + sτ m
where F= FL + Fm
τ m = J/F the mechanical time constant of the system
J = JL + Jm
⇒ K mVa = ( J m + J L )
Transfer function for the gearbox is derived as follows:[2]
Page 49_______________________________________Closed Loop Control of a Torque-Tension
Machine
Fig 6.7: Gearbox (gear train)
Tm = J1θ&& + F1θ& + T1
for shaft 1 and 2
T = J θ&& + F θ& + T
2
2
2
L
If R1 and R2 are radii of the gears then the linear distance travelled by each gear is
R1θ1 = R2θ 2
identical
and
θ1 N1
=
θ 2 N2
as the number of teeth on each gear being proportional to the gear radius.
If there is no power loss on the gear train then
T1θ 1 = T2θ 2
T1 θ 1 N 1
θ&& θ&
N
=
=
differentiating 1 = 1 = 1
&
&
&
T2 θ 2 N 2
θ2 θ2 N2
N2
N
andθ&&2 = 2 θ&&1
N1
N1
From the shaft equations and substituting for T1 and T2
N
TL = 2 (Tm − J 1θ&& − F1θ&1 ) − J 2θ&&2 − F2θ&2
N1
⇒ T2 = T1
⇒ TL =
N2
(Tm − J 1θ&& − F1θ&1 − J 2θ&&1 − F2θ&1 )
N1
The Laplace Transform gives the following transfer function
N2
Tm ( s ) − TL ( s )
N
N1
= 2 {( J 1 + J 2 ) s 2 + ( F1 + F2 ) s}
θ ( s)
N1
6.5
Creating a System Model
Page 50_______________________________________Closed Loop Control of a Torque-Tension
Machine
To model the system an approximate transfer function is created. The procedure for
creating this is dealt with below using Matlab. Matlab is a computer package that can
analysis and simulate systems that are given in the form of transfer function. Matlab can
send an input to a system, which it models using a transfer function, and simulate the
output of the system. However it can also calculate an approximate transfer function of a
system given the inputs and outputs of the actual system. This is what is required for this
system. So for the torque motor system in the machine, the inputs and outputs were
recorded as in fig 6.10. ‘Vin’ is the voltage input and ‘Aout’ is the angle of twist.
Using the code in fig. 6.8 Matlab gave the transfer function below. The line ‘nn = [2 2
1];’ the user decides what values are entered here. The first 2 represents the order of the
denominator and 2 the numerator plus 1 and 1 is the difference between numerator and
denominator. These values were decided from the transfer function of the motor and
gearbox. The real inputs and outputs and the model inputs and outputs are shown here.
These numbers were decided by trial and error and the most accurate result was given by
the number chosen. By looking at the transfer functions of the motor and gearbox
however a good estimate can be made. This code will output a discrete time and
continuous transfer function. However it is the discrete time function that most accurately
represents the system as the system updates more than 10 times a second.
z=[aout,vin];
nn=[2 2 1];
th=arx(z,nn);
[nummod,denmod]=th2tf(th);
sys=tf(nummod,denmod,1.65)
sysc=d2c(sys,'zoh')
Fig 6.8 Least Squares Code
Page 51_______________________________________Closed Loop Control of a Torque-Tension
Machine
The transfer functions obtained were
Transfer function:
6.759 z
---------------------z^2 - 1.137 z + 0.1387
Sampling time: 1.65
Transfer function:
3.245 s + 5.695
----------------------s^2 + 1.197 s + 0.00165
Fig 6.9: Transfer Functions from Matlab
When the discrete transfer function was used to model the system a step input of 1 and 2
volts were inputted to the system and the system’s simulation gave the results in figure
6.10 on the next page
Page 52_______________________________________Closed Loop Control of a Torque-Tension
Machine
vin
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
aout
result1
0
0.44195
6.9293
15.7755
24.9164
32.1412
38.0384
46.8846
54.4041
62.0709
69.7376
77.1089
84.6284
92.2951
99.8146
106.744
114.558
122.078
129.744
136.968
144.931
152.745
159.821
167.783
175.155
181.79
189.309
197.123
204.642
211.719
219.09
226.904
234.424
241.206
248.136
254.918
263.174
271.873
279.687
287.059
294.283
300.033
0
0
6.759
14.444
22.2443
30.0474
37.8376
45.6128
53.3727
61.1173
68.8465
76.5605
84.2593
91.9429
99.6113
107.2646
114.9027
122.5258
130.1338
137.7268
145.3049
152.8679
160.416
167.9492
175.4676
182.9711
190.4598
197.9337
205.3928
212.8372
220.2669
227.682
235.0824
242.4682
249.8394
257.1961
264.5382
271.8658
279.179
286.4778
293.7621
301.032
vin1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
aout1
0.14732
0.44195
17.1023
33.1733
47.9167
63.2503
78.141
93.6219
108.071
123.404
138.296
154.219
169.257
183.411
198.892
212.604
227.642
242.238
256.098
273.2
288.239
300.033
result1.1
0
0
13.518
28.888
44.4887
60.0949
75.6753
91.2256
106.7454
122.2345
137.693
153.1211
168.5186
183.8858
199.2226
214.5291
229.8055
245.0516
260.2677
275.4537
290.6097
305.7358
Fig 6.10: Actual versus Model System Response
Page 53_______________________________________Closed Loop Control of a Torque-Tension
Machine
6.6
Creating a PID Controller and Filter
One of the ways to design this PID controller is to use the ITAE criterion for a step input
[13]. From the ITAE table and the transfer function for the system the PID controller can
be calculated and its performance maximised by choosing appropriate values for the
settling time and damping ratio. A pre-filter can then be designed using the ITAE method
again and placed in the system as in fig. 6.11 below. This should considerably reduce the
overshoot in the actual system and eliminate a lot of the noise in the signals form the
transducers.
input
output
PreFilter
PID
Controller
Approximation
Model
feedback
Fig 6.11: PID Control and Filter in System
Page 54_______________________________________Closed Loop Control of a Torque-Tension
Machine
CHAPTER SEVEN
TESTING & RESULTS
Page 55_______________________________________Closed Loop Control of a Torque-Tension
Machine
7.1
Introduction
For the results section the four tests were carried out on a steel specimen held in the
grippers. For each test a random value was chosen for the constant parameter and the
load or torque was increased for a short period of time until it became clear how the test
was performing.
7.2
Test 1
The load was kept constant at 10kN and a torque voltage of 0.2V was applied. The torque
voltage was applied and then held so as not to break the specimen. The torque reading
shot up and then settled down and then load momentarily came below its low limit and
then moved back up within the tolerance band again. As the torque is applied the load
decreases all the time therefore the load motor is constantly applying more load to keep
the load constant. The load could stay within a tolerance band of 0.5kN, which is 0.25kN
above or below the specified constant load. Any tolerance lower than this and the motor
was doing too much work to keep the load within its limits mainly due to noise and
disturbance that the load cell was experiencing. The graphs for this test are shown in fig.
7.1. The output file for this test is in fig. 7.2. This the section of the output file for the
major increase in the torque that can be viewed on the above torque graph. On the load
graph and from the output file it can be seen that the load remained inside its tolerance as
the torque increased initially. Eventually the load dropped outside the tolerance before
the load motor brought the load back up within the tolerance.
Page 56_______________________________________Closed Loop Control of a Torque-Tension
Machine
Fig. 7.1:The Graphs of Test 1
Load
10.157
10.157
9.668
10.157
10.218
10.035
9.668
9.545
9.607
8.811
10.157
LVDT
8.315
8.315
8.315
8.322
8.322
8.544
8.315
8.315
8.315
8.315
8.303
Torque
9.148
5.489
33.277
51.231
57.292
66.555
67.698
37.051
31.562
29.161
32.934
Angle
105.176
108.252
110.889
113.965
116.602
119.385
121.875
121.289
120.41
120.557
120.703
Total Time
103.58
104.58
105.585
106.58
107.585
108.585
109.585
110.585
111.58
112.59
113.585
Loop time
0.053
0.053
0.058
0.053
0.058
0.058
0.058
0.058
0.052
0.062
0.057
Fig. 7.2: Section of Output for Test 1
Page 57_______________________________________Closed Loop Control of a Torque-Tension
Machine
7.3
Test 2
The torque was kept constant at 35Nm and a load of 0.2kN was applied sparingly so as
not to break the specimen prematurely. This test didn’t work all that well at all. There
was too much noise in the readings to keep the torque within a reasonable tolerance. The
smallest tolerance achievable was 8Nm.
7.4
Test 3
This test was by far the most accurate. The linear displacement was kept constant at 5mm
and a torque of 0.1Nm was applied. As the torque increased and load began decreasing
but the axial displacement remained constant. The linear displacement could be kept to
within a tolerance band of 0.1mm. The graphs of test 3 are shown below in fig. 7.3 and
the relevant section of the output file is shown in fig. 7.4.
Fig 7.3:The Graphs of Test 3
Page 58_______________________________________Closed Loop Control of a Torque-Tension
Machine
Load
21.049
20.131
19.091
17.867
16.827
15.909
15.113
14.196
13.461
12.911
12.238
11.748
11.197
10.708
10.28
10.341
10.586
10.402
10.402
10.463
10.402
10.769
10.463
10.524
10.463
10.463
6.853
6.792
LVDT
5.008
5.015
5.015
5.015
5.027
5.021
5.034
5.027
5.027
5.034
5.034
5.034
5.04
5.04
5.04
5.04
5.046
5.04
5.046
5.046
5.046
5.046
5.046
5.046
5.046
5.053
4.977
4.958
Torque
52.26
55.119
63.81
69.299
73.531
72.501
76.847
76.046
77.076
79.02
77.762
78.562
79.591
79.363
77.419
47.801
41.625
37.852
36.251
34.993
31.905
28.703
27.102
36.937
35.45
35.336
40.482
36.594
Angle Total Time Loop Time
106.055
190.51
0.058
108.398 191.505
0.053
111.182 192.505
0.053
114.404 193.505
0.053
117.627 194.505
0.053
120.41
195.505
0.053
123.34
196.505
0.053
126.123 197.505
0.053
129.492 198.505
0.053
132.422 199.505
0.053
135.205 200.505
0.053
137.549 201.505
0.053
140.479 202.505
0.053
143.408
203.51
0.058
146.777
204.51
0.058
145.459
205.51
0.058
144.873 206.505
0.053
145.02
207.505
0.053
144.434
208.51
0.058
144.434 209.505
0.053
144.434
210.51
0.057
144.287 211.505
0.052
144.434
212.51
0.057
144.434
213.51
0.057
144.434
214.51
0.058
144.434
215.51
0.058
144.58
216.505
0.053
144.434
217.51
0.058
Fig. 7.4: Section of Output File of Test 3
7.5
Test 4
This test did not work well either due to the slow reaction of the torque motor. Also the
frequent inability of the torque motor to turn in the counter clockwise direction even with
a high velocity voltage applied made it very difficult to carry out this test.
Page 59_______________________________________Closed Loop Control of a Torque-Tension
Machine
CHAPTER EIGHT
DISCUSSION
8.1
Problems with Equipment
Page 60_______________________________________Closed Loop Control of a Torque-Tension
Machine
The open loop system that was in place was to be updated or created into a closed loop
system. However there were some serious problems with the equipment in place. There
wasn’t sufficient money or time to rebuild any part of the machine, so the equipment had
to do.
To begin with, the torque motor and gearbox unit makes a lot of noise which effects the
transducer readings. A greater problem was the fact that it takes over 6.5 volts in a
counter clockwise direction. In the counter clockwise direction 0-3 volts turns the motor
clockwise, 3-6.5 volts does nothing and 6.5-10 volts turns it counter clockwise. This
leaves a small scale to work with in this direction.
Other problems with the equipment was that the angular position transducer has only a
300 degree electronic angle, which means there is effectively a blind spot of 60 degrees.
This however does not effect the results, as the blind spot should never be reached in
testing.
The torque load cell is positioned too close to the motor and gearbox units as the
extensive noise of these components greatly disturb the torque readings. All of the
transducers experience noise but the torque load cell is by far the worst affected.
The torque load cell is positioned too far from the specimen to accurately read the torque
felt by the specimen. The torque load cell is situated on the top of the torsion shaft and
below the square drive. The reading is from the torque that the specimen feels, therefore
the assumption is made that the same torque is transferred to the torque-tension shaft
through the square drive and to the torque load cell. This however is not the case. The
torque exerted on the specimen when the motor is on, is different than the torque exerted
when the motor is off.
8.2
Problems with Software
Page 61_______________________________________Closed Loop Control of a Torque-Tension
Machine
The shortest loop time is 60 milli-seconds which may not be fast enough to read in the
values from the transducers as they change to move within a certain tolerance and can
cause an overshoot effect. The PC can be very slow at times and doesn’t respond. This
could happen while testing and could cause equipment damage or destroy a complete
experiment.
8.3
Problems with Safety
As already stated the PC sometimes being slow is a safety issue but a bigger one is the
fact that there is no emergency stop button on the machine. One should be positioned so
as it is accessible particularly to the user sitting at the PC. Another safety issue, more to
do with the conservation of equipment, is that the LVDT has a rather small stroke in
comparison to how far the cross-head can travel. There is already a margin of safety in
the set up of the LVDT of 5mm but this then restricts the range at which it can operate. If
the cross head is lowered any more than the height at which a specimen can enter the
gripper the LVDT can be can experience the full force of the cross head and load motor.
8.4
Improvements
Page 62_______________________________________Closed Loop Control of a Torque-Tension
Machine
In the chapter on testing only the test 1 and 3 could function with a certain degree of
accuracy. These two tests are dependant on the control of the load motor and also the
torque motor but only in one direction. Tests 2 and 4 are dependant on the control of the
torque motor in both directions. Here is where the major problems lie in the system.
Before any further more important testing is carried out on the machine it would be
advised to replace the existing motor and gearbox unit or repair it.
When further testing is carried out and the values of the constant and varying parameters
are decided then the tests can become more accurate. Additional tolerance ranges can
easily be set up if there are large variations on the constant parameters. Different velocity
voltages are set depending on how far the reading is outside it’s limits. Using the test
carried out on test 1 in section 7.2 when the constant load was 10kN as an example. If the
reading is within +/- 4kN the motor moves at a 0.7V velocity input and if the reading is
outside this range the motor moves at a 1V velocity input. This is designed so as the load
moves within the tolerance band faster which becomes important when the torque is
applied.
Conclusions and Recommendations
Page 63_______________________________________Closed Loop Control of a Torque-Tension
Machine
The initial system was controlled by input voltages to both motors set on the front panel.
The system now in place has the capabilities to control four essential parameters in the
investigation of elastic plastic behaviour of rods under torque and tension. The accuracy
of this control can be improved relatively easily once the equipment is performing
efficiently.
This project has shown how well two out of the four tests can be carried out using this
closed loop system. Unfortunately due to problems outlined in Chapter 8 there were some
major problems with the equipment that prevented the complete testing of this system.
However the complete system is in place and I am confident that as soon as these
problems are rectified all four tests will work with sufficient accuracy for testing
specimens.
The accuracy and performance of the complete system can be improved using PID
control and filters but the entire system has to be understood fully and an accurate model
created. I would recommend that a complete control systems analysis should be carried
out on the system to validate the machine and any test results obtained.
I would also recommend that all the parameters that can be entered into the machine
should be accurately controlled. This would allow the user to enter a ramp input torque or
load rather than a motor velocity voltage.
References
Page 64_______________________________________Closed Loop Control of a Torque-Tension
Machine
1. Abu Rayham Mohammed Ali “Plastic Yielding Characteristics of a Rod Under
Successively Applied Torsion and Tension Loading” a DCU PhD. Thesis 1995.
2. Nagrath, I.J. and Gopal, M. “Control Systems Engineering 2nd Edition” 1986
3. Chesmond, C. J. “Control Systems Technology”, Senior Lecturer in Control
Engineering Queensland Institute of Technology 1982.
4. RDP Technical Manual for Modular 600 System
5. RDP Technical Manual for Two Channel DC Amplifier Module Type 611
6. RDP Technical Manual for Dual Transducer Amplifier Module Type 621
7. National Instruments DAQ AT-AO-6/10 User Manual
8. National Instruments DAQ AT-MIO/AI E Series User Manual
9. Labview Quick Start Guide
10. Labview User Manual
11. Labview Function and VI Reference Manual
12. Labview Help File
13. Dorf, Richard C. and Bishop, Robert H. “Modern Control Systems” 1998
14. Sen,P.C. “Principles of Electric Machines and Power Electronics”
Page 65_______________________________________Closed Loop Control of a Torque-Tension
Machine
15. Bruton, Jennifer “Notes on Model Simulation for Mechatronic Degree Course”
Page 66_______________________________________Closed Loop Control of a Torque-Tension
Machine
APPENDIX 1
LABVIEW PROGRAM
Page 67_______________________________________Closed Loop Control of a Torque-Tension
Machine
APPENDIX 2
PRESENTATION
Page 68_______________________________________Closed Loop Control of a Torque-Tension
Machine
Closed Loop Control
of
Torque-Tension
Machine
by
Sean Tobin
Supervised by
Dr. Paul Young
Page 69_______________________________________Closed Loop Control of a Torque-Tension
Machine
Introduction
In industry it is important for designers and structural
engineers to know the capabilities of materials they are
working with to reduce large factors of safety and
maximise load to weight ratios. Particularly important
in the design of aircraft, missiles and space applications.
This machine can apply torque and tension to a
specimen separately and simultaneously.
Designed to carry out experiments to investigate the
elastic-plastic response of pre-stressed rods when
subjected to additional applied parameters (torque or
axial load).
The 4 tests are:
Keeping load constant vary the torque applied
Keeping torque constant vary the axial load applied
Keeping axial displacement constant vary the torque applied
Keeping the angle of twist constant vary the axial load applied
Method Of Approach
Page 70_______________________________________Closed Loop Control of a Torque-Tension
Machine
Understanding of machine
Set Up of Equipment
Calibration of Transducers
& Amplifier
Set Up of Closed Loop
Control
Design Each Test
Show and record all data
from tests
Investigate any
Improvements to the
System
Page 71_______________________________________Closed Loop Control of a Torque-Tension
Machine
Machine
Control
Panel
PC
Apply tension &
torque to specimen
Labview
Control Board
Motor
Controllers
Amplifiers
Transducers
Motors &
Grippers
Page 72_______________________________________Closed Loop Control of a Torque-Tension
Machine
Calibration
Torque cal
Load cell calibration
6
4.5
y = 0.0427x
y = 0.0798x
4
5
3.5
Volts
3
4
Volts
2.5
2
1.5
3
2
1
1
0.5
0
0
0
20
40
60
0
50
Force kN
angle cal
10
100
150
torque Nm
LVDT calibration
y = 0.0437x - 3.1421
15
8
y = 0.7698x - 14.591
10
volts
volts
6
4
2
5
0
0
10
20
30
-5
0
0
50
100
150
-2
200
250
300
-10
angle deg
axial displacement mm
Page 73_______________________________________Closed Loop Control of a Torque-Tension
Machine
40
Page 74_______________________________________Closed Loop Control of a Torque-Tension
Machine
Load
10.157
10.157
9.668
10.157
10.218
10.035
9.668
9.545
9.607
8.811
10.157
10.202
10.141
10.141
10.141
10.141
10.141
10.202
10.186
9.362
9.423
9.362
9.362
10.035
10.218
10.218
10.218
10.218
10.218
LVDT
8.315
8.315
8.315
8.322
8.322
8.544
8.315
8.315
8.315
8.315
8.303
8.296
8.296
8.303
8.303
8.296
8.303
8.29
8.296
8.309
8.315
8.315
8.315
8.303
8.303
8.296
8.303
8.303
8.417
Torque
9.148
5.489
33.277
51.231
57.292
66.555
67.698
37.051
31.562
29.161
32.934
27.903
28.131
29.618
28.36
29.504
29.046
29.389
29.161
32.934
31.219
41.511
41.397
43.112
29.961
29.504
29.389
29.161
28.932
Angle
105.176
108.252
110.889
113.965
116.602
119.385
121.875
121.289
120.41
120.557
120.703
120.41
120.41
120.41
120.703
120.41
120.557
120.41
120.557
120.41
120.557
120.557
120.557
120.557
121.875
120.557
122.314
120.557
120.557
Total Time
103.58
104.58
105.585
106.58
107.585
108.585
109.585
110.585
111.58
112.59
113.585
114.585
115.58
116.585
117.585
118.58
119.585
120.58
121.59
122.587
123.585
124.585
125.585
126.58
127.58
128.58
129.58
130.585
131.585
Loop time
0.053
0.053
0.058
0.053
0.058
0.058
0.058
0.058
0.052
0.062
0.057
0.057
0.052
0.058
0.058
0.053
0.058
0.053
0.063
0.06
0.058
0.058
0.058
0.053
0.053
0.053
0.053
0.058
0.058
Page 75_______________________________________Closed Loop Control of a Torque-Tension
Machine
input
output
PreFilter
PID
Controller
Approximation
Model
feedback
Page 76_______________________________________Closed Loop Control of a Torque-Tension
Machine
What has been achieved?
A Closed Loop Control system has been created
taking readings from the machine to feedback the
application of toque and tension to the specimen.
And
Torque tension, axial displacement and angle of twist
can now be controlled while applying force or torque.
Page 77_______________________________________Closed Loop Control of a Torque-Tension
Machine