2003 Automatic Control Conference
2023
Design and Implementation of a Computerized Flat Knitting
Machine
王明賢 1 ,梁耀星 2 ,廖鴻文 3 ,陳旺承 3 ,葉育杰 2
Ming-Shyan Wang 1 , Yao-Hsing Liang 2 , Houang-Wen Laio 3 , Wang-Cheng Chen 3 , and Yeh-Yu Chieh 2
2
南台科技大學電機工程系
南台科技大學電子工程研究所
Department of Electrical Engineering
Research Institute of Electronic Engineering
Southern Taiwan University of Technology
1, Nan-Tai St. Yung Kang City, Tainan Hsien, Taiwan, 710
Tel: (06) 2533131 ext. 3342
E-mail: mswang@mail.stut.edu.tw
3
Eternity Electronics Industry Co., Ltd.
TEL: (06)2797611
1
Abstract
In the paper, the control system of a computerized
flat knitting machine is designed and implemented. A
permanent magnet synchronous motor is used to
operate the machine. We design the motor drive that
discrete power MOSFETs are adapted in the inverter
to reduce the cost. In order to get zero steady-state
error, the PI control is considered in the velocity
control loop. Microcontroller, 8052, programs the
drives of seven step motors to manipulate the controls
of cam, left stitch, and right stitch of front-end and
back-end, and racking. The color and style of the
accessories of clothing is programmed by using the
keyboard, PC, or the external memory card. There are
three communication protocols, RS232, RS422, and
RS485, used in the system to transfer the instructions
and data.
Keywords: Computerized flat knitting machine;
permanent magnet synchronous motor; PI control;
communication protocol.
National Science Council to look for professors that
are expert in programmable control of a flat knitting
machine. It lets us see that this mechatronic system
will be more interesting in the market.
“Design and implementation of a computerized flat
knitting machine” is the second project that we
co-operate with Eternity Electronics Industry Co., Ltd.
“Original design manufacture an AC servo motor
drive” was the first project [2]. The technique and
experience in the design of AC servo motor drives is
transferred to the design in the computerized flat
knitting machine such that the cost of the
computerized control system has been reduced to be
half of that made in Japan.
The paper divides into four branches with further
discussion as follows: Section 1, the introduction;
section 2, the architecture of a computerized flat
knitting machine; section 3, the driving and control of
step motors and AC servo motors, and; section 4,
conclusions.
2. System architecture
摘要
本文介紹電腦化自動橫編織機電控系統之設
計與製作，系統內我們使用一永磁同步馬達帶動機
頭之移動，馬達驅動器自行設計，並以獨立功率
MOSFET 元件設計換流器以降低成本，並採 PI 控
制速度以達零穩態誤差。使用 8052 規劃七個步進
馬達之驅動，完成前床及後床之三角、左度目及右
度目，與搖床之控制。規劃布片及領子等之花色及
式樣的程式可由鍵盤輸入，PC 下載，或記憶卡讀
取。系統內之通訊協定有 RS232，RS422 及 RS485
等作為指令與資料之傳輸。
關鍵詞： 電腦化自動橫編織機，永磁同步馬達，
PI 控制，通訊協定。
1. Introduction
A mechatronic system designer must assemble
digital and analog circuits, microprocessors and
computers, mechanical devices, sensors and actuators,
and controls so that the final design achieves a desired
goal [1]. In September 2002, there was an email from
The block diagram of the control system of a
micro-computerized flat knitting machine is shown in
Figure 1. Each block is described as follows:
2.1 Human-machine interface, PC, LCD,
keyboard, and memory card :
The generation of the accessories with the desired
color and style of clothing is programmed such that
the operation of a flat knitting machine proceeds in
order. There are three ways for human-machine
interface to obtain the program, using a keyboard to
keyin the program, downloading it from a PC via
RS232C communication, or reading it from an
external memory card. Similarly, after a program has
been modified in the human-machine interface, we are
able to upload it to PC or store it to the external
memory card. The 128x64 LCD is used to display the
keyined program or machine parameters and monitor
the operation of the flat knitting machine. The
human-machine interface transfers the instructions
and data to the main drive block via a RS422
transceiver. Figure 2 depicts the more detailed block
2024
diagram of the human-machine interface. The CPU-1
is microcontroller 8052.
2.2 Main drive, AC servo motor, torque
motor, magnetic valve and its drive circuit,
and I/O unit:
The main drive includes CPU-2, RS422 transceiver,
RS485 transceiver, torque motor control, I/O control,
and AC servo motor drive, shown in Figure 3. The
main drive receives the program from human-machine
interface via RS422 and transmits commands to three
step motor drives by using RS485 protocol. AC servo
motor drive controls the servo motor and transmission
belt to run the machine at programmed speed during
machine operation. The specification of the AC servo
motor 6CC401 that is a permanent magnet
synchronous motor (PMSM) is listed in Table 1.
The block diagram shown in Figure 4 is a
well-known architecture, consisting of position,
velocity, and current control loops, of an AC servo
drive [3-7]. The feedback currents are sensed by the
current transducers (CTs), and the optical encoder
provides the information of velocity and position.
There are one Z pulse and 2000 phase A and B
respective pulses per revolution for this encoder. Of
course, these pulses are output via line transmitters
26LS31 in differential form. The CPU-2 used in the
drive is M16C that is a 16-bit microcontroller [2]. The
family of M16C provides different size but sufficient
ROM for program instructions, multifunctional 16-bit
timers to generate three-phase PWM signals and a
periodic interrupt, 25 internal and 8 external interrupt
sources, serial I/O for RS232C and RS485, 8 10-bit
ADC channels, 2 8-bit DAC channels, one watchdog
timer, and some programmable I/Os, etc. The shortest
instruction execution time is only 50 ns at 20MHz
clock source. Generally, it takes 2 or 3 clock cycles to
complete one instruction since it is not a DSP.
The interface between CPU and encoder has been
designed in a CPLD. In order to reduce the cost,
discrete power MOSFETs are adapted to be switches
of the inverter, instead of intelligent power module
(IPM) that provides protections from over-current,
overheat, load short-circuit, and under-voltage.
There are four yarn feeders with different color
driven by magnetic valves. And, the take-down roller
is driven by the torque motor to work at programmed
level.
I/O unit composes of circuits to detect the abnormal
conditions and emergency, such as yarn breakage,
fabric drop, over-wrap, over-torque, press-off, needle
shocking, and others.
2.3 Step motors and their drives:
There are seven step motors and drives for
front-end cam, left stitch, and right stitch, back-end
cam, left stitch, and right stitch, and racking controls.
Figure 5 shows the block diagram of front-end (or
2003 Automatic Control Conference
back-end) step motor drive. The racking one is similar
to, but simpler than that. CPU-3, 8052, controls three
step motors and accepts the commands from main
drive via RS485. The programmed color and style of
the accessories of clothing is executed by the seven
step motors.
There is one more block not shown in Figure 1,
power modular, to be considered in the system. The
AC 110V is connected to R and S pins in the main
drive, and rectified by full-bridge diodes to generate
310 V DC as DC link of the inverter. There are other
power supplies in the system, such as 5V for digital
circuits, 15V for operational amplifier circuit, step
motor drive, and photo-couplers, 24V for I/O detection
circuits and solenoids.
3. Driving and control
3.1 Step motor:
There are three modes of excitation in use for step
motors, single-phase excitation, two-phase excitation,
and half-step operation [8]. In Figure 5, the step motor
drive comprises two step motor drive ICs, NJM3370A,
that provide the selection of half-step and full-step
operation, selection of 0%, 20%, 60%, and 100% of
rated current output, LS-TTL input stage, high power
H-bridge output stage, and wide voltage range 10-45V.
Figure 6 depicts the timing of the operation of 3370A.
3.2 AC servo motor:
It is well-known that the dq-transformation is often
used in the drive design for a PMSM [3-7]. That is, the
abc-model,
0
0  ia  ea 
va   R  pL
v    0
R  pL
0  ib   eb 
 b 
vc   0
0
R  pL ic  ec 
(1)
where L is the phase inductance, R is stator
resistance, v j , i j , and e j , j  a, b, c , represent
the phase j voltage, current, and back emf, respectively,
and
becomes
dq-model
after
p  d dt ,
transformation as
vd   R  pL   re L  id   0 
v   
    
 q    re L R  pL iq  eq 
(2)
where v e , i e , and e e , e  d , q , represent the direct
and quadrature voltage, current, and back emf,
respectively, and  re is the electric velocity. If the
model (2) is used, we know that the control of (2) is
easier than that of (1). The output torque of the motor
2003 Automatic Control Conference
2025
i g  2 A (generator output current),
is only controlled by i q . And, the motor has higher
TLMT  TR ,
id  0 , and works magnetic
field weakening for negative i d . However, it’s
and k p  0.1875 and k p  0.4375,
efficiency on power for
necessary to compute the dq-transformation and
inverse dq-transformation in the control loop.
Although the calculations of them can be replaced
with a lookup table, it would need a while time for a
general non-DSP type micro-controller, for example,
16-bit M16C/62 group. And, because of the
trapezoidal back emf and the consequent
non-sinusoidal variation of the motor inductances with
rotor angle for the blushless DC motor (BLDCM), the
dq-model is not necessarily the best approach for
modeling and simulation [4]. The single phase model
(1) offers many advantages. Moreover, there are
several similarities in the overall drive scheme of the
PMSM and the BLDCM. The configuration of the
power stage, inverter, is same for both motors. The
main difference is on current control that sinusoidal
stator current are designed to output a steady torque in
the PMSM, whereas rectangular current is generated
to give a steady torque in the BLDCM. So, for the
uniform design algorithm of drives of PMSM and
BLDCM, the single phase model (1) is adopted even
the necessary compensation for e j in the control
loop.
When the current control loop is simplified by
1 (1  Tc s) and 1 Tc is its bandwidth, the speed
control block diagram will become as shown in Figure
7. The PI control is applied to the speed control loop
of the drive to get zero steady-state error,
k
(3)
Gs ( s)  k p  I
s
2J M
kp 
(4)
5 K T Tc
kI 
2J M k p
25 K T Tc
(5)
And, the proportional gain constant k p and integral
gain constant k I are determined on Bode plot, shown
in Figure 8, and adjusted according to the load.
Figure 9 manifests the 3000 rpm step responses for
k p  0.1875 and torque limit TLMT  TR and shows
the corresponding waveforms of current command and
i a . Figure 10 discloses the results for
k p  0.4375 and TLMT  TR . It is easily seen that the
higher
k p the system supplies, the faster response
and less overshooting it possesses. And, with the rated
torque constraint, the current command and phase
current i a are clamped to the rated current of the
motor.
Replacing the dummy load with some other PMSM,
the solutions come in Figure 11 that it was tested by
respectively.
The 3000 rpm of the speed has abruptly dropped as
soon as the load is applied. But, it recovers itself
immediately.
4. Conclusions
The mechatronic control of a computerized flat
knitting machine is considered in the paper. The cost
and performance of a mechatronic system play the
main role on automation market. The drive of a
PMSM is designed by us, instead of buying a
universal one which is more expensive. And, the
excellent speed response and load recovery of the
servo system have been shown. We hope that the
completion of this project is a milestone on research
of mechanic control systems.
References:
[1] M. B. Histand and D. G. Alciatore, Introduction to
Mechatronics
and
Measurement
systems,
McGraw-Hill, New York, 1999.
[2] 王明賢, “全數位 AC 伺服馬達驅動器研製”,第
一屆全國技專校院工程技術類產學合作暨技術
移轉成果發表會,電機 10-1,2001.
[3] P.Pillay and R.Krishnan , “ Modeling, Simulation,,
and analysis of Permanent-Magnet Motor Drives,
Part I : The Permanent-Magnet Synchronous
Motor Drive “ , IEEE Trans. on Ind. Appl., vol. 25,
No. 2, pp.265-273, 1989.
[4] P.Pillay and R.Krishnan, “ Modeling, Simulation,
and analysis of Permanent-Magnet Motor Drives,
Part II: The Permanent-Magnet Synchronous
Motor Drive “, IEEE Trans. on Ind. Appl. , vol. 25 ,
No. 2 , pp.274-279 , 1989.
[5] J.P.Karunadasa and A.C. Renfrew, “ Design and
implementation of microprocessor based on
sliding mode controller for brushless servomotor “,
IEE Proc-B, vol. 138, No. 6, pp.345-363, 1991.
[6] J.-L. Hsien , Y.-Y. Sun, and M.-C. Tsai, “ H∞
control for a sensorless permanent-magnet
synchronous drive “ , IEE Proc-Electr. Power
Appl., vol. 144 , No. 3 , pp.173-181 , 1997.
[7] 劉昌煥主編,電機機械, 東華書局, 1999.
[8] Takashi Kenjo, Steeping Motors and Their
Microprocessor Controls, Oxford University Press,
New York, 1999.
Acknowledgments
The
authors
would
like
to
express
their
appreciation to NSC for supporting under contact
NSC 91-2213-E-218-023.
2026
2003 Automatic Control Conference
Magnetic
Valve
RS232
PC
Front-end
Step Motor
Drive
Magnetic
Valve
Drive
Human Machine
Interface
LCD
Keyboard
RS422
Main Drive
AC
Servo
Motor
Memory
Card
Cam Step
Motor
RS485
Torque
Motor
Left Stitch
Step Motor
Right Stitch
Step Motor
Cam Step
Motor
Back-end
Step Motor
Drive
Left Stitch
Step Motor
Right Stitch
Step Motor
Racking
Step Motor
Racking
Step Motor
Drive
I/O Unit
Figure 1 The block diagram of the control system of a computerized flat knitting machine.
RS232
Transceiver
RS422
Transceiver
RS422
Transceiver
I/O
Unit
External
EEPROM
Torque
Motor
Control
CPU-1
LCD
R
S
KEY
Power
Module
AC Servo Drive
RAM
E
Figure 2 The block diagram of
interface.
Position
command
+
human-machine
Velocity
command
-
Torque
Motor
BUS
CPU-1
EEPROM
RS485
Transceiver
Position
gain +
-
M
Figure 3 The block diagram of main drive.
Current
command
Velocity
gain +
-
Current
gain
PWM
inverter
M E
Current loop
Velocity loop
Position loop
Figure 4 Block diagram of a drive
Velocity sensor +
Position sensor +
2003 Automatic Control Conference
2027
RS485
Transceiver
Step Motor
Drive 1
Step Motor
Drive 2
CPU-3
Step Motor
Drive 3
Power
Module
Figure 5 The block diagram of front-end step motor drive.
Figure 6 The timing of the operation of 3370A.
TL
r*
+
r
Gs (s)
1
1  Tc s
KT
Te +
 40 dB / dec
1
JM s
K sp 
r
 20 dB / dec
0 dB
 pi
K si
s
G c ( s )
c
 sc
 20 dB / dec
KT
JM s
1
Tcs  1

 40 dB / dec
Figure 7 Speed control block diagram.
Figure 8 The Bode plot for PI control.
2028
2003 Automatic Control Conference
(a) Speed command and response.
(a) kp=0.1825,
(b) ia and current command.
Figure 9 The 3000rpm step responses for
kp=0.1875 and TLMT=TR.
(b) kp=0.4375,
Figure 11 The speed loop load shock recovery
tests: speed response and load shock for ig=2A and
TLMT=TR .
Table 1 Parameters of PMSM 6CC401.
(a) Speed command and response.
(b) ia and current command.
Figure 10 The 3000rpm step responses for
kp=0.4375 and TLMT=TR.
Output power
Torque
Stator current
Speed
Torque constant
Back emf
constant
Inertia
Stator resistance
Stator
inductance
PR
TR
IR
NR
KT
400W
1.274 N．m
3.5A
3000 rpm
0.409 Nm/A
KE
42.8 V/Krpm
JM
R
0.29 Kg．cm2
0.937 
L
2.11 mH