A new servo controller
for a Materials Testing
Machine - MTM
Final Presentation B
Students : Uri Goldfeld & David Schwartz
Supervisor : Daniel Alkalay & Amir Reoven
General System Description
The MTM system we work on is a
mechanical system that allows us to
test the physical properties of materials
and structures.
Testing is done by applying static or
dynamic loads, using an hydraulic
actuator in closed-loop servo control.
Feedback for closed loop control uses
displacement OR Strain sensors.
The MTM system enables us to
determine tensile/compressive
strength, fatigue resistance, crack
growth resistance ect.
The Original System
Main Project Goals
The global purpose is to develop a modern computer based
mechanical testing system, using current hardware and
software tools.
Part A:
Servo
+
hydraulics
Part B:
Old
Software
control
controller
system
FPGA
LabView
Goals achieved Part A
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•
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Learning LabVIEW
Learning the required control tools
Performing system identification
Implementation of a simulation environment
Simulate the whole system using our
controller
• Keeping the environment General
Hardware: - E series 6036 DAQ card
- M series 6122 DAQ card
- hp33120 waveform generator
via RS232
Software:
- NI LabVIEW 7.1
- DaqMx toolbox
- PID toolbox
Project Goals of Part B:
•
•
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Learn LabVIEW FPGA module
Learn LabVIEW RT module
Build the control system in FPGA
Generate all required experiment waveforms
Build a general system which can be easily
adjusted when hardware is changed
Allow control on most functions and
parameters
Build an “easy to use” GUI
Hardware:
- PXI 8187 chassis
- NI FPGA PXI-7811R
- Valve driver (amplifier)
- LVDT signal conditioner
- Load Cell signal conditioner
- Power supply
Software:
- LabVIEW 7.1
- LabVIEW FPGA module
LabVIEW FPGA module
The LabVIEW FPGA program consists of two parts:
1. host VI
2. FPGA VI
The Host VI executes on windows and the FPGA VI
must be compiled and downloaded to FPGA.
New system overview
PXI 8187
LabVIEW windows
FPGA 7831R
PID , Limit check
Interlock check
Signal generation
Gui, configurations
valve
driver
Lvdt
conditioner
Load Cell
conditioner
Lvdt
Load Cell
Valve
Power
supply
Inputs
Outputs to FPGA
User configurations
[physical]
PV from FPGA
PID Parameters
LabVIEW
windows
Limits [V]
Limits status
Stimulus signal [V]
Set Point (encoder)
configurations
User configurations
• Choose control sensor and limit sensor
• Configure Limits for load (Kg) and displacement
(cm)
User configurations (cont.)
• Waveform type, amplitude, frequency
• PID parameters (optional)
• Sensor Calibration parameters (optional)
return
Signal Generation
• User specification are in
•
physical units i.e
Kg, cm, mm/min Kg/min
Signals supported – sine,
ramp, square,
idle, set point, triangle,
haversine,
havertriangle,
haversquare.
Initialization data
Unit
converts
Idle
Signal type
mux
User
configurations
Master int.
Signal
Generation
V2B
Amplitude &
Freq. calc
FPGA
VI hierarchy
return
Inputs
Outputs
Configurations from
windows
External: Stimulus
signal to “Valve
driver”
LVDT conditioner
Load Cell conditioner
“Hard” interlocks
Optional feature:
internal “signal
conditioner” to
LVDT (get
response “sine”)
FPGA
7831R
Internal: Response
signals to windows
Limits check result
to windows
Details
send stimulus “sine”
and calculat the
valve’s location
FPGA 8187 details
• Hardware: NI PXI-7811R:
•
- 1M gate FPGA, 160 DIO for PXI
- 16 bit A/D,D/A
- ± 10V@20mA excitation
Phases:
1. Filter input signal (sample every
20 uSEC)
2. Check limits on input signal
if o.k. pass to phase 3
3. Every 1mSEC send input signal to
PID for control
4. Send control signal to “valve driver”
windows
Setup of limits
Master interlocks
Limit
check
Filtering
SP
A/D
PV
LVDT
PID
Load
Rate Limiter
Cell
return
D/A
Valve
Driver
Internal signal conditioner (LVDT)
System Description:
LVDT input: requires an excitation
sine of 5KHz, 10V.
LVDT output: amplitude modulated
sine and sign (ΔΦ = 0 or 180 )
To find the position of the servo
valve, the LVDT output is divided
be the excitation, then filtered to
get the correct DC value
return
Valve driver
• Servo drive requirements : ±10V @ 70mA
• PXI D/A spec: ±10V @ 20 mA.
• The servo valve input requires a Bipolar excitation
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•
•
(0 and π)
The PXI 7831R synthesizes one vector, internal 16bit
D/A drives the external power amplifier.
The power amplifier generates the Bipolar signals
Valve driver – power amp Specs:
–
–
–
–
2 x opa541 power operational amplifiers
+-15V supply, max current output 500mA
Output over load & temp protection
DC offset 5mV
return
conditioners
LVDT: singer EL-15 series
zero & gain trimmers
±12V power supply
10V, 5.7Khz sine excitation voltage
Load Cell:
10V DC excitation voltage
12V power supply
Features summary
• Generic servo valve control system: suitable to
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general servo valves and conditioners
configurations
Auto tune system: auto adjustments of control
system parameters
Supports all required experiment waveforms
Supports load and displacement control
Friendly GUI
Can be extended for additional waveforms,
sensors, actuators and different GUI.
Forward
Calibration and Manual tune
Tuning and calibration is required After changing a
part of the system (valve, sensors , ect..)
return
Auto Tuning
• Different program was made for auto tuning.
It finds the PID gains automatically for the servo valve,
according to user requirements.
return
System Limitation (Bottlenecks)
• FPGA :
1.Only 1M gates. (we use ~75% of it)
2.Long compile times for every change.
3.FPGA Emulator can’t simulate RT loops.
• LabVIEW Windows :
1. maximum time resolution of 1 ms.
2. Other programs running in the background
may cause control gaps.
possible solutions :
1.additional memory
2.LabVIEW RT
Future work
• Connect hydraulic and Hard interlocks to the
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•
FPGA.
integrate all Electronics and mechanical controls
on to a suitable Enclosure.
Add data logging capabilities .
Provide a client server function (web control).
Optional : Change execution environment from
LabVIEW windows to LabVIEW’s RT module.
Demonstrations
1. Sine experiment LabVIEW
2. Sine experiment Caliber
3. Ramp experiment LabVIEW
4. Ramp experiment Caliber
THE END