Automated Control and Monitoring of Knitting...
Transcript of Automated Control and Monitoring of Knitting...
International Journal of Engineering & Technology Sciences
Volume 03, Issue 01, Pages 22-31, 2015 ISSN: 2289-4152
Automated Control and Monitoring of Knitting Machine
Payam Fathollahi Rad a,*, Bashir Fotouhi b
a Department of Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran. b Department of Engineering, Sanandaj Branch, Islamic Azad University, Sanandaj, Iran.
* Corresponding author. Tel.: +98-21-66916840;
E-mail address: [email protected]
A b s t r a c t
Keywords:
Knitting,
Dobby,
Automation,
AVRxmega,
Servo,
Pattern designing.
In the current article, a new practical method was implemented for control and
monitoring of purely-mechanical dobby knitting machines. A conventional machine
cannot change the fabrication procedure for a pattern change. This machine has a main
motor and four servo motors and its process contains three steps: programming, controlling
and monitoring. The new customized programming language carried out in LabVIEW; a
powerful low-noise microprocessor was used to control the loop and LabVIEW was used
for the monitoring process. The optimized interface protocol exchanges data between
LabVIEW and the control board was a novel high-speed and low-noise protocol with
check sum. Programming, color design, shape design, monitoring and fabrication speed
were performed easier, faster and safer.
Accepted: 26 January2015 © Academic Research Online Publisher. All rights reserved.
1. Introduction
The focus of this paper was on the control of four-
axis dobby knitting machines. These machines are
considered as an important part of the industrial
systems which must texture clothing for people. A
knitting machine may be flat, circular, jacquard and
dobby loom [1-4]. The main concentration of this
paper was studying dobby type knitting machines.
Dobby loom first appeared around 1840, which was
almost 40 years after the invention of Jacquard
device by Joseph Marie invented; this device could
be mounted atop a floor loom to lift individual
heddles and warp threads [1, 2]. Both jacquard and
dobby looms are floor looms in which a device
called heddle is used to attach every warp thread on
the loom to a single shaft. Each shaft controls a set
of threads and the loom including several shafts
gives a huge variety of sheds through which a shuttle
containing weft thread can be thrown. A manual
dobby has a chain of bars or lags with inserted pegs
for selecting the movement of the shaft. In
conventional all mechanical dobby machines, all
shafts are controlled by a treadle. The ability for
handling much longer sequences in the pattern is
considered an important advantage for dobby
machine. A weaver which is working on a loom
must remember the entire sequence of treadling
which makes up the pattern and must always keep
track of their places in the sequence. Getting lost or
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making a mistake can ruin the cloth that is being
woven. Dobby looms are capable of expanding
weaver’s capabilities and removing some of the
tedious works involved in designing and production.
Many newer cloth design techniques, such as
network drafting, only can reach their full potential
on a dobby loom.
Knitting machines could be traced back to 1589
when Rev.Lee invented his knitting frame; this
frame was programmed using paper type. During
recent 40 years, there have been rapid developments
with regard to the introduction of electronic, image
processing, fuzzy, adaptive and neural control of
knitting machines [5-10]. “Knitting machines get
8085 controls” is the title of a well-known industrial
system which was developed by Stonefield
Electronics [11]. Some of these control systems are
based on yarn input tension (YIT) which is an
approach for detecting faults and monitoring the
knitting process [12, 13]. Due to its nature, the yarn
input tension constitutes a valuable way for
diagnosing machine functioning [13]. However,
there was a need for both exact fault detection and
real-time process and monitoring knitting procedure
which made the desirable systems more complicated
[14-16]. Making up garments using earlier
computer-controlled machineries using sensors and
intelligent controls was developed by Department of
Mechanical Engineering, Loughborough University
of Technology [10]. Moreover, modelling and
visualization of 2D and 3D shapes of knitwear
through scanning process led to virtual design and
fast prototyping [17, 18]. Big changes occurred in
the control systems since 2000 when AC servo
brushless motors were introduced in the application
of knitting machines. Due to high speed and
accuracy, servo motors as powerful devices have
been used to precisely place needles in knitting
machines and circular warp knitting machines use
servo motors to place needle in the desired places for
weaving the pattern. This machine uses two servo
motors [19], which require a frequency invertor to
be applied for industrial systems. While using full
potentials of a servo system, all calculations,
communications and control loops need to be
entrusted to a powerful device such as DSP [20, 21].
Linux architecture control system and GUI have
been applied to computerize flat knitting machines.
This system uses a powerful ARM microprocessor
(AT91SAM9261) for controlling the loop [22].
Some others similarly control a jacquard knitting
machine while using the specifications of [22] to the
system [23]. CAD/CAM system recommends image
processing techniques to create of specified knitting
structures and products [23, 24]. Transformation of
grey level images to binary images and path tracing
are the methods used for cotton knitting industry
automation [23]. Wireless monitoring system and
sketch pad for circular knitting machine and
conceptual design of 2D garment patterns are the
boundaries of knitting monitoring technology [25].
Combination of all servo mechanism and signal
processing systems with a powerful monitoring
system has not been introduced yet. Making the
desirable pattern and monitoring the system’s faults,
simple GUI, simple patterning and some other issues
are still open problems in the area of knitting
machines. Therewith, these studies do not include
issues on dobby loom machines.
Accordingly, the first aim of this paper was to
present a set of control and monitoring system based
on the conventional (purely mechanical) four-axis
dobby knitting machine. Moreover, a new simple
programming rules for pattern fabrication and real-
time monitoring were two aspects of open problems
in this kind of machines. The proposed automated
machine used both software and hardware
techniques to overcome basic problems of
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automation. Real-time monitoring of fabrication
process was able to find program faults, errors and
wrong woven areas. The operator did not require
calling the company for the change of desired
pattern. Consequently, simplicity of pattern
programming would make the machine more user-
friendly. Pattern change could be rapidly performed.
Also, the operator could save different patterns in
memory and call them back to the weaving process.
The machine was cost-effective, even though many
servo systems, drives, computer, software and
control board were used. Section two describes
mechanical/electrical parts in the dobby loom. In
Section three, control system including software,
control board, communication protocol and pattern
programming are described.
2. Knitting Machine
The proposed machine was of dobby type and
included four axis. In this machine, two moving
combs, as shown in Figure 1 performed task of
weaving procedure. Different color yarns crossed
into the orifices of horizontal comb “A” and then
needles of hooks of vertical comb “B”. This
operation caused the pattern fabricated, which was
the manner to change position of combs for making
the pattern. Each cycle of comb “B” was equal to a
row of the fabricated pattern. The changing position
of the comb hook “A” shifted the input color to the
equivalent hook in comb “B” and results in different
patterns and colors. Each pair of the combs “A” and
“B” is called an axis. The increasing in the number
of axis enhanced the ability for weaving more
complex patterns. Therefore, the displacement step
of each axis, synchronization of combs and roll
speed of yarn input, language of programming and
control system design of closed loop were all
important. Each step of the comb “A” would result
in a shift in color series and any reciprocating motion
of comb “B” would complete one row fabrication of
the pattern. Again, comb “A” would change the
place in the length of one or more steps and the
subsequent motion of comb “B” would occur again.
These procedures were repeated until the pattern
completion. Figure 2 demonstrates a simple
schematic of comb “A” and its actuator for changing
place in predefined steps. Servo motor rotated CW
and CCW in predefined angular steps; this rotation
displaced the comb “A” again by the predefined
steps related to servo motor step and length of
camshaft, which transformed rotation displacement
to a horizontal type. It should be noted that the total
rotation of servo motor must be less than or equal to
70˚ due to mechanical limitations, both software and
hardware appliances have been implemented.
Assuming that L is the length of camshaft, α is angle
of camshaft to the vertical line and D is distance of
comb “A” to the vertical line of servo motor, thus:
raddkN
radd
dLCosdDL
DSin
61086.022173.1
)()(
(1)
Nk
NkCos
NLkdD
,...,2,1,0
)61086.022173.1
(22173.1
)(
(2)
where k is current step, N number of total steps and
dα rotation angle due to each step. Assuming equal
rotation angle for all the steps, results in the point
that displacement of each hook in comb “A” is a
simple function of the number of current step k. In
the proposed machine, N=15 and each step yielded
the change in servo position of about 4.63˚.
Precision of rotation angle was restricted by the
precision of closed loop servo system, which is
about 0.036˚ and more precise than what we need.
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Fig.1 Horizontal displacement (Comb A) Vertical
displacement (Comb B)
Fig.2 Actuator system of comb “A”
Table. 1: Description of electrical instruments used in the
system
Device Quantity Description
Servo Motor 4 1KW-ASD-
A21021-B
Servo Drive 4 1 KW- ECMA-
F11010AS
AC Motor 1 1.5 KW
Frequency
Inverter
1 1.5 KW-LS-ic5-
SV
Proxy Switch 1 Hall effect
Computer 1 Industrial -
2.4GHz
Software - Labview 2009
Table. 2: Used components of Micro Processor
AVRxmega Description
Clock 32 MHz, Internal
Timer/Counter 7× 16 Bit
USART 5× 115200
DAC 12 Bit, 1 Msps
Used I/O 50
Low Voltage 1.6 V – 3.3 V
EEPROM 128 Kbyte
After all, comb “A” did the job, then comb “B”
should be raised to the top point. All yarns were fed
to hooks of comb “B” and were pulled down while
none of “A” combs change place at this time. Figure
1 is assumed, comb “B” would go up to a place
amidst hooks of comb “A”. If comb “A” changes
place even by one step, hooks of both combs would
knap. It is important to ensure that comb “A” does
not displace while comb “B” moves at the top; both
hardware and software appliances are implemented.
From electrical point of view, this automated
machine must perform the following tasks: an
operator writes the program for a desired pattern, the
operator chooses his/her favorite colors, the system
should compile input pattern and be replayed to the
user if any error exists. The system loads the pattern
to the control board and knitting machine runs to the
end of pattern. Designing a system at a high level of
accuracy which has a user-friendly programming
language is very important. A complete but
simplified schematic of the control system including
four AC servo motors with their own drives, one AC
asynchronized motor with its own frequency
inverter, control board, proxy switch and a PC is
given in Figure 3. To simplify the schematic, yarn
input DC motors were omitted from Figure 3. The
proposed system must be able to properly satisfy
some important features, as listed here: run
continuously and automatically, preserve
mechanical combs from any damage, preserve servo
motors in order not to rotate out of range, simple and
user friendly programming, variable speed control,
position control and monitoring of the servo motors,
monitor speed of the fabrication procedure, monitor
and report the faults, error, status of the machine,
define access level for the users, compile the pattern
and simple language for the pattern to be entered.
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3. Control System
It may be more understandable to do programming,
controlling and monitoring by explaining each part
individually in detail. Each pattern fabrication
procedure must pass through the following chart in
Figure 4. First step is given in parts 3.1 and 3.4 since
conversion of a desired pattern to a specific code is
done by the software. Indeed, pre-defined rules and
programming language are required also. The
second step would be done by the software too, by
compiling the code wrote by the operator. While
loading the program to the control board, the
hardware gets involved with the process for the first
time. This is step explained in parts 3.1, 3.2 and 3.3
because software, hardware and communication
protocol are all involved. Finally, real-time control
and monitoring of the fabrication procedure shall be
explained for each section in all parts. Control loop
only involves control board, servo drives, frequency
inverter and proxy switch and there is no need for
the software. However, monitoring consists of
software, communication protocol, frequency
inverter, proxy switch and control board.
3.1 Software
As the first part of the above-mentioned system, here
the software is briefly explained. The proposed
software which supposed to be the user and machine
interface is LabVIEW-based, because of
compatibility with industrial and personal
computers, high-speed processing and
communication and having a simple and user-
friendly graphical environment.
3.2 Control Circuit
Since the proposed control system must be
compatible with the industrial environment, it is
necessary to use high-speed and low-noise micro
controllers. Since 2008, as a new processor
specialized for industrial environment is available
Fig. 3: A schematic of the control system
Fig. 4: Control and monitoring general step
Some important features of this processor are used
(as listed in Table 2), but the processor is compatible
with higher frequency, higher sampling rate and
other specifications. As shown in Figure 6, all the
tasks of position control of servo motors, set speed
and feedback speed of main motor, comb
commands, setting and reading servo drive
parameters, executing pattern programmed by the
operator and sending monitoring parameters to the
computer are controlled by the board. The control
board decodes the pattern and calculates all servo
positions for each step. Then, servo drive parameters
are set through serial ports of all the drives and four
serial ports on the board; the protocol is MODBUS
and baud rate is 115200 bps.
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Any changes in digital inputs or serial port
commands results in one interrupt; i.e. every servo
drive position command, enabling/disabling the
signals, computer or operator command and proxy
switch signal, which cause specific interruption in
system control. It is important to assign one interrupt
loop and subroutine to each action or reaction of the
system. The ability of making hardware-interrupt for
all digital I/O and software-interrupt for all analogue
I/O keeps precise attention on real-time control and
monitoring. All subroutines and control flowchart
are shown in Figure 5. Every specific time steps, the
control system saves all the essential data such as the
number of steps, remaining steps, and current
positions in order to continue the fabrication process
after the fault or disconnection of power supply. It is
worth mentioning that MODBUS communication
only sets initial conditions in servo drives and
reports their faults/alarms. After the drives are
initialized and parameters are set, the position of
servo motors is controlled through seven digital
inputs of the recommended drive. As a result, servo
motor settling time of the position becomes faster
and safer. To obtain lower power consumption, less
speed of the main motor and high weaving speed
also the need for more cams on the shaft of the motor
is indispensable. Accordingly, four cams are placed
with the same intermediate angles on the shaft.
Intermediate angle is 90˚, H is width of cams and D
is width of proxy switch. Here, H is assumed to be
smaller than and closed to D. While each one of the
cams is placed in front of the proxy switch, comb
“A” moves toward the next step. One rotation of
motor shaft leads to four steps of comb “A”. Thus,
fabrication speed increases by a factor of four. The
applied frequency to the main motor may changes
from 20 to 40 Hz and its nominal speed is 1500
RPM. With some calculations time the circuit needs
to set the position of servo motors in the equation 3.
mSecSecDeffTcross
H
HD
DDeff
41.0
360
16
100
90
(3)
where Deff is effective width of proxy switch which
can sense the cams and Tcross is the time control
board which must set all four servo motor positions.
MODBUS protocol in these servo drives need ten
Bytes to be sent through the serial port with 115200
baud rate and also ten receiving Bytes are required
from each servo drive, which shows the correct
command and setting of position; also, the following
simple calculations can be assumed,
mSecBaudrate
NDNBTm
ND
NB
Baudrate
5.5*8**2
4
10
115200
(4)
where NB is number of Bytes per communication,
ND number of servo drives and Tm is the time all the
commands are sent for all servo drives through the
communication port. After all, at the maximum
speed of communication and minimum speed of the
motor, equations (3) and (4) demonstrate that servo
positions may not settle position at the proper time.
All corner cases calculated as following equation,
mSecTcrossmSecTm
SlowSpeedSlowBaudrate
mSecTcrossmSecTm
SlowSpeedSlowBaudrate
mSecTcrossmSecTm
SlowSpeedSlowBaudrate
mSecTcrossmSecTm
SlowSpeedSlowBaudrate
2,5.5
:1200,:115200
4,5.5
:600,:115200
2,139
:1200,:4800
4,139
:600,:4800
(5)
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As shown by these calculations, there is no way for
MODBUS to set servo positions at the proper time.
Therefore, the control board must send the position
commands through digital inputs of drives. As a
result, when the system is initialized, 15 positions
are defined and saved at the servo drive parameters.
Now, control board can call these positions to be set
by seven digital inputs of each drive. The maximum
number of positions which may be set through these
digital inputs is 64. So, the total angle cycle of 70˚
can be divided to steps of 1.09˚; however, it is not
necessary because mechanical resolution of the
comb “A” just needs a 4.66˚ angle for each step. But,
the control board is extendable to higher resolution
for future works.
3.3 Pattern Programming
All industrial operators respect user-friendly
systems. This feature has the software to accept the
desired pattern by simple rules defined in this paper.
First, the operator defines the pattern on his/her
mind and some rules are followed convert them to
some sequence of steps which should be done by
servo motors. However, the operator must know
how to represent the pattern in servo steps. For
example, s/he calculates the number of steps 1080
for each servo motor and follows the sequence in
Figure 10 which shows one cycle of steps for each
of them separately. Four different programs must be
written by the operator for servo motors which are
equivalent to the special sequence of that servo
motor. First, the basic rules of pattern sequence
programming should be defined in the propose
software: the program must start with the command
START, program must end with the command END.
The Sn command is used to show step number n, Rm
command is used at the end of line and that line is
repeated by m, RAx command is lonely in a line;
then, the program repeats all the steps from START
command to this line. Assume that, for making a
desired pattern, the total step sequence of each servo
motor must contain 240 steps. To understand the
above programming rules, Table.3 is noted by the
equivalent program for step sequence of the servo
motor.
3.4 Communication Protocol
It is essential to avoid any faults in the wrong port
connection and high-speed low-time cost and low-
noise communication protocol. The proposed
system does not use any pre-known protocols;
instead, it uses new special high-speed one shielded
to reduce external noise effects. Supposing that all
four programs of part C are compiled with no errors
and would be downloaded to the control board; if,
the simple serial protocol is used by the system, then
it must send one byte for each step of the sequence.
Finally, the software must send 960 (240×4×1 bytes)
bytes so as to communicate all servo procedure
command to the control board. As explained in
details, the new protocol only requires bytes for
sending all these commands to the control board.
The proposed novel protocol can be explained by
following equations and Figure 11. Each of the four
sub-parts of the final code (C in Figure 11) introduce
a compiled program code in the new protocol. The
first byte of CS1, as shown in Figure 11, is 251,
indicating that servo motor No.1 starts step sequence
code; this is similar for all CSi. CSi is the compiled
program code for the ith servo motor. All bytes of
CS1, between 251 and 250, include the step
sequence of servo No.1, and this is the same for all
CSi. The next part of the compiled code starts with
250, if following byte comes with zero; then, all the
bytes of CS1which are between 250 and 249 include
a repetition number for the first part. It should be
noted that the decreasing amount of start byte of
each part for the ith servo motor is i. Since
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Fig. 6: Top view of the control board and terminals
Fig. 7: Four cams on the shaft and proxy switch design
Fig. 8: The control circuit
Fig. 9: The woven materials and machine view
Fig. 5: Simple control chart and interrupt list
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communicating information between PC and control
board has two different parts of control and
monitoring data frames, two different frames of data
are required to be defined. Control frame includes
any data for the control board to control the system.
As an example, the step sequence of all servo motors
must be sent through control frame; the control
board saves data in E2PROM and calls them back to
be execute. For any 100ms, the control board sends
one monitoring frame to the computer; therefore,
Labview monitoring tab is updated 10 times per
second. Speed, status of all LEDs and all servo
motors, servo motor positions, fault codes and
remaining steps are the most important parts of the
monitoring frame. To avoid any kind of overlapping
in the control and monitoring frames, first, Labview
sends a simple frame in order to activate exchange
of the monitoring frame. Activating frame is 0XF1
0X01 and deactivating frame is 0XF1 0X00; 0X
means Hexadecimal view of the byte.
Table 3. Examples of servo motor step sequence program
Servo No.1 Servo No.2
START START
S8S15S1S4S11->R12 S5S7S11S1->R15
RA3 RA4
END END
Fig. 10: An example for servo step sequences
𝐶𝑆1 251 𝐵11 . . . 250 0 𝑁11 . . . 249 . . . . . . . . .𝐶𝑆2 252 𝐵21 . . . 250 0 𝑁21 . . . 248 . . . . . . . . .𝐶𝑆3 253 𝐵31 . . . 250 0 𝑁31 . . . 247 . . . . . . . . .𝐶𝑆4 254 𝐵41 . . . 250 0 𝑁41 . . . 246 . . . . . . . . .
𝐶 = [𝐶𝑆1 𝐶𝑆2 𝐶𝑆3 𝐶𝑆4]
Fig. 11: The program coded in the new protocol
Fig. 12: Control data frame (a). High part (b). Low
part
Fig. 13: Monitoring data frame (a). High part (b). Low
part
4. Conclusion
In this paper, a conventional purely mechanical
dobby knitting machine was automated. The early
methods of controlling the mechanical process did
not have any chance of changing the pattern; also,
they were not flexible for pattern programming by
the operator and user friendly. New simplified
programming language, new communication
protocol and simple change of the pattern were the
most important areas of novelty in this paper. The
new protocol was able to code pattern program and
transmit them much faster and safer while it uses
almost one percent of the transmitting codes of the
other protocols, such as MODBUS. The proposed
method for the automation of purely-mechanical
dobby machine reduced 50% of operator mistakes
and 20% of the maintenance costs.
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