Note: Descriptions are shown in the official language in which they were submitted.
s~
This invention relates to the control over the
operation of a stitching machine, and particularly to a method
and apparatus ~or controlling a stitching machine in a manner
to conserve thread.
In recent years due to inflation and consequential
cost awareness, the stitching departments of textile companies
have become greatly concerned with the amount and cost of
thread wasted by stitching machine operators. Since most
operators are on a piece rate, they tend to start their
machines long be~ore the work piece is in position for sewing
and they tend to run the piece a long distance past the
needle following completion of the stitching operation so
that it becomes easier to clip the thread. The end result is
a tremendous amount of thread waste and unnecessary expense.
1~ Other factors contributing to the amount of thread
waste are the reaction times of the operators and the speed
of the machines. Some modern machines stitch as fast as 8 to
10 inches per second using multiple needles for chain stitching
, serging and other complex stitching and have as many as 6
spools of thread feeding them. If the operator hesitates for
even half a second in stopping the machine after the stitching
operation is completed, she may run out as much as four or
five inches of dual chain stitching which, when unraveled,
could be over a foot long with each chain made up of three or
~our separate threads. Also, when the machine is operated
without material under the presser foot a severe stress i5
placed upon the moving parts due to metal to metal contact.
When all of the above factors are comblned, the net result
is a tremendous cost in thread waste and machine wear.
Attempts have been made to design a control system
to monitor and reduce thread waste but the general opinion of
the industry is that none of the systems have worked satis-
--1--
factorily and that they have required a great amount o~
maintenance. Most of the design attempts to date are totally
air operated and use pneumatic sensing devices to detect when
the work piece is in position. This type system automatically
operates the machine's treadle and when the sensor detects a
work piece in position, the machine is turned on at maximum
speed. Lint generated when the fabric material passes under
the presser foot, regularly clogs the pneumatic sensor, which
causes the machine to "sense" a work piece to be in position,
l~) causing the machine to go out of control and run continuously.
The air devices are slow in reacting and timing is accomplished
using devices that are sensitive to common air line contaminants
and other factors which afect their repeat timing accuracy.
The operator has no control of speed nor the ability to stop
the machine once it has started. An inexperienced operator
is not able to keep up with the machine while learning to
operate it and as a result many work pieces are ruined in the
training process.
A major problem with many known types of prior
~ systems that were intended to reduce thread waste has been
that the operator can defeat the system by any one of a number
of methods. One such method is turning off the air supply to
the control circuit. Other gimmicks used by operators include
plugging an air jet with chewing gum or taping over the detector
means. This latter gimmick is often employed with photo-
electric detection systems.
In one prior art system for conserving thread in a
stitching operation there is provided a photoelectric cell-type
detector system at the rear of the presser foot of a stitching
machine to detect the completion of the stitching operation.
The signal developed by the photoelectric cell in this prior
art system is employed to activate an electromagnetic device
5~
that incapacitates the common treadle of a s-titching machine
so that the operator cannot continue the stitching opera-
tion past the time when the trailing edge of the work pro-
duct has passed under the presser foot and between the
5 photoelectric cell and its detector component. This type
system is one of the easiest for the operator -to defeat
by merely blocking off the photoelectric cell. Further,
in this prior art system, the operator can start the machine
long before the work piece is ready to be placed under
the presser foot, thereby wasting thread at the beginning
o a stitching operation. Such a system is shown in Patent
No. 3,1~7,702.
It is therefore an object of the present invention
to provide an improved method and apparatus for the control-
1~ ling of a stitching machine wherein there is a maximumconservation of thread. It is another object to provide
a method and apparatus for controlling a stitching machine
wherein the control is not readily defeatable by an opera-
tor. It is another object to provide a method and apparatus
for controlling a stitching machine which will substantially
troubleshoot itself. It is another object of the invention
to provide a method and apparatus for controlling a stitch-
ing machine wherein the cycle and sequence times employed
therein are adjustable. In accordance with the present
invention, a control system is provided for a stitching
machine having a mechanism associated therewith for activat-
ing and deactivating the stitching mechanism. A piston
and cylinder is operatively associated with the mechanism
for activating and deactivating the stitching mechanism.
30 A source of pressurized fluid is provided with a conduit
- 3 -
connecting the source of pressurized fluid to the piston--
cylinder. An electrically operated valve is interposed
in the conduit at a location between the source of pres-
surized fluid and the piston-cylinder, and electrical cir-
cuitry is provided to produce an electrical signal thatis transmitted to the valve to selectively control the
flow of pressurized fluid to the piston-cylinder. The
circuitry includes a detector disposed in the path of a
work piece entering the stitching mechanism and provides
an electrical signal that is representative of the presence
of a workpiece in position for stitching. A total timer
is responsive to the electrical signal of the detector
for timing out after a preselected time period that is
representative of the anticipated time required to complete
a stitching operation and defines a preselected time
envelope. An overrun timer is responsive to the electrical
signal of the detector for timing out after a preselected
time period and is operable within -the time envelope of
the total timer. A gating device is provided for the selec-
tive activation of -the total timer, the valve, and the
overrun timer in response -to the signal developed by the
de-tector.
The present invention may best be understood
by reference to the following description of the invention
2~ when considered in conjunction with the Drawings in which:
FIGURE 1 is a representation of a stitchirg
machine having incorporated therein a control system embody-
ing various features of the invention;
FIGURE 2 is a fragmentary representation of the
needle station of the stitching machine depicted in FIGURE
1 and depicting the location of the photodetector element of
- 3a -
;
:,
~`~s~
the present invention;
FIGURE 3 is a fragmentary representation of a portion
of the drive motor control element of the present invention
FIGURES 4a and ~b comprise an electrical schematic
diagram depicting various features of the present control
system;
FIGURE 5 is an electrical schematic diagram depicting
a power source for use in the control system of the present
invention;
FIGURE 6 is a schematic diagram of a pneumatic
control system embodying various features of the present
invention.
In accordance with the present invention, there is
provided a control system for a stitching machine which in a
preferred embodiment comprises a combination of electronics
and pneumatics that in the automatic mode function selectively
and serially, independent of an operator following initiation,
to provide for operation of a stitching machine uninterruptible
by the operator for a preselected period of time to complete
a given stitching operation. Following initiation of a
stitching operation through actuation of the present control
system, by affirmative operator action, the system internally
o~ itself develops a plurality of interlocks that require the
existence of selected conditions for continuation of "normal"
~5 machine operation and which respond to "abnormal" conditions
by precluding machine operation past preselected termination
points. In its semiautomatic mode, the present control
system permits certain control by the operator, such as start,
stop or speed of the stitching machine, but precludes operation
under conditions that waste thread.
In a specific embodiment, the present s~stem controls
a stitching machine that is driven by means of the well-known
--4--
57
motor-clutch-brake system in which the stitching mechanism is
engaged with the drive motor through a clutch-brake mechanism
that is biased toward a position of clutch disengagement and
brake application. In this system the clutch and brake commonly
are operated by means of a lever arm that is pivotably mounted
to the motor housing. In the prior art, such lever arm is
connected to a foot treadle that is operated by an operator
to selectively activitate or deactivitate the stitchiny mechanism.
In the present control system, when in the automatic mode,
such foot treadle is disabled. In its place, the cylinder
member of a pneumatic piston-cylinder device is connected
rigidly to the lever arm that operates the clutch-brake
mechanism. The piston member of the piston-cylinder device
is disposed in juxtaposition to a solid, i.eO, unyielding,
surface such as the motor housing so that when the piston is
extended it contacts the unyielding surface and urges the
cylinder member toward a position wherein the lever arm
causes the clutch to be engaged and the stitching machine to
operate. As will be seen hereinafter, so long as air pressure
is supplied to the piston-cylinder mechanism to extend the
piston, the stitching machine remains operable. In the
absence of such air pressure, the piston floats and the
stitching machine is inoperative. Notably, the foot treadle
has no effect on starting and stopping of the stitching
'~5
machine when in the automatic mode. As will appear here-
inafter, startup of the stitching machine occurs where a work
piece is in position for stitching and once started, -the
stitching machine continues to operate until certain circumstances
obtain.
Start-up of the stitching machine occurs when light
to a photodetector is blocked by a work piece in position in
-5-
507
front of the needle and presser foot of the stitching machine.
In the present control system, there is developed a reference
electrical signal which has a normally assigned value just
below the usual value of the electrical signal developed by
the photodetector under conditions of ambient light with no
blocking of the photodetector. The signal from the photodetector
is compared to such reference signal and if higher (in the
preferred embodiment), the system provides no air to the
piston-cylinder device and the stitching machine remains
idle. If the photodetector signal is lower than the reference
signal, there is developed an electrical signal which is
fed to a plurality of parallelly connected elements of the
system, namely, a first-timing circuit, and 1st, 2nd, 3rd,
and 4th NOR gates. The first timing circuit is connected in
its monostable mode and when triggered by the signal from the
photodetector develops a short duration pulse that is fed to
a second timing circuit which serves as a total timer, that
is, it is set to time out after a preselected total time of
operation of the stitching machine following initial start-up.
Once triggered, the total timer develops a high signal that
is fed to a 5th NOR gate, said signal being inverted by the
5th gate and fed to the aforesaid 4th gate. This signal,
plus the photodetector signal "open" the 4th gate to feed its
high output signal to a 6th NOR gate. The output of this 6th
gate is connected to a 7th NOR gate where such signal is
paired with a further reference input signal to the 7th
gate, and if a proper preselected result obtains, the output
signal of the 7th gate, in turn, is fed eventually to a
solenoid value that controls the flow of pressurized air to
the piston-cylinder device. However, the 6th gate does not
pass a proper signal to the 7th gate to develop a proper
output signal therefrom until certain conditions obtain
Specifically, the second signal required ~o "open" the 6th
gate is obtained from a proper combination of the output
signals from the 3rd gate, an 8th NOR gate, and a 9th NOR
gate, all of which feed their respective output signals,
directly or indirectly, to an overrun timing circuit. This
overrun timer is set to trigger when the trailing edge of
the work piece passes the photodetector and the total timer
has not timed out. This overrun timer is adjustable and is
preset to provide an output signal therefrom to the 6th gate
which results in opening of the same (and keeping the stitching
machine operational) for a period of time following the
completion of the stitching operation sufficient to run the
stitching out a distance past the trailing edge of the work
piece sufficient to permit cutting of the thread chain. This
distance commonly is very short, i.e., less than one inch.
Notably, the overrun timer will not be triggered unless the
total timer has been triggered but has not timed out, so that
the overrun timer, i~self, cannot bring about actuation of
the stitching machine. That is, the time cycle of the overrun
~ timer operates within the envelope time of the total timer
to prevent false triggering of the stitching operation.
In the event the photodetector output signal to the total
timer goes low (no work piece is blocking the light to the
photodetector) between the time of triggering of the total
timer and before it has timed out, such low signal is gated
to trigger the overrun timer which provides a short time
delay then turns off, hence dropping out the solenoid and
closing off the pressurized air from the piston-cylinder
device and stopping the stitching operation. This action also
serves to reset all functions of the control system for
commencement of a subsequent stitching operation.
In the semiautomatic mode of operation, all elements
3~
of the control system function as in the automatic mcde, except
the piston-cylinder device is positioned differently. For semi-
automatic operation, the cylinder member is secured to the lever
arm that operates the clutch-brake mechanism and the piston rod
is connected to one end of a rigid rod whose opposite end is
secured to the foot treadle (or directly to the treadle as desired).
The source of pressurized air for the piston-cylinder device is
connected to the cvlinder in a manner such that when air is made
available, the piston is urged toward its retracted position and
becomes rigid with respect to the cylinder so that movement of the
foot treadle results in movement of the "rigid" piston-cylinder
device, hence movement o the lever arm. Thus, the operator is
given control over when to start a stitching operation and in
many instances control over the speed of stitching. However,
despite her movement of the foot treadle, the present control system
will not permit commencement of the stitching operation until a work
piece is in position over the photodetector and ready for being
stitched. Moreover, even though the operator holds the fcot treadle
down (machine run position), once the total timer has timed out, the
~ solenoid drops out, air to the piston-cylinder device is closed
oEE, and the piston "floats" in the cylinder to permit the lever
arm to shut down the stitching machine.
With reference to the Figures, in FIGURE 1 there is
depicted an installation oE one embcdiment of the present control
~5 system on a Rimaldi chain stitch stitching machine 10. m is
stitching machine is mounted on the upper surface 12 of a
stand 14 and includes a stitching head 16, a presser foot 18
and a needle 20. An electric motor 22 mounted under the
stand serves to drive the stitching mechanism via a belt 24.
3~ The motor 22 is provided with a conventional brake-clutch
mechanism 26 that is operable through the means of a lever
arm 28 that is pivotally mounted on the motor housing. The
--8--
l13~
outboard end 30 of the lever arm, in the embodiment depicted
in FIGURE 1 is arranged for the semiautomatic mode of operation,
and has secured thereto, by means of a bracket 32, the cylinder
member 34 of a pneuamtic piston-cylinder device 36. The
piston member 38 of the piston-cylinder device 36 is operably
connected to a rigid rod 40 ~hich, in turn is connected to a
foot treadle 42. A source of pressurized air 44 is connected
through a pneumatic control circuit 46 and conduits 48 and 49
to the piston-cylinder device in a manner such that when
pressuri2ed air is available to the device, the piston member
38 is retracted and is rigid with respect to the cylinder
member 34. Under such conditions, movement of the foot treadle
produces movement of the lever arm 28 and resultant operation
of the stitching mechanism. When no air is provided to the
piston-cylinder device, the piston member "floats" so that the
foot treadle is disabled.
As shown in FIGURES 1 and 6, the flow o~ pressurized
air to the piston-cylinder device 36 is regulated by the
pneumatic circult 46 which is connected by a conduit 48 to the
~0
source of pressurized air 44. Comprising the circuit 46 is a
pressure regulator 50, a solenoid valve 52 and a flow control
valve 5~ which is connected to the piston-cylinder device as
re~erred to above. The solenoid valve 52 is operably connected
by an electrical lead 56 to the electrical portion of the
~5
present control system as will be described further hereinafter.
This solenoid valve is also provided with a manual override
53 in a preferred embodiment. In addition, the depicted
circuit 46 includes a vacuum control subassembly comprising
a pneumatically actuated, pilot actuated valve 60, and a
vacuum cutoff delay 62 so connected in the circuit 46 that
when the solenoid valve 52 is open, air is made available
through the vacuum cutoff delay to the valve 60 to
_g_
5~
open the same and permit the flow of air to a conventional
vacuum generator flow control to provide vacuum for pulling
cut thread to a waste collector as is well known in the art.
Following shut down of the stitching machine, the vacuum
cutofE delay 62 delays the closing of the valve 60 for a short
period of time which is sufficient to ensure that any thread
cut off at the end of the stitching operation is pulled into
the waste collector.
In the electrical portion of the present control
system there is provided a photodetector cell 70 (FIGURE 2)
embedded in the top 12 of the stand 14 at a location immediately
in front of the needle and presser foot of the stitching
machine. This cell 70 is exposed to ambient light and lies in
the path to be followed by a work piece being fed into the
stitching machine~ Accordingly, the cell detects less light
when a work piece is in position and develops a lesser output
electrical signal than when there is no such work piece present
covering the cell.
With reference to FI~7URES 4a and 4b in particular,
~ in a preferred embodiment the cell 70 comprises the collector-
base junction of semiconductor PCI and is coupled to a high
gain DC amplifier UIA which amplifies the output signal from
the photodetector and feeds the same from its output through
resistor R2 and capacitor Cl to the input side of a voltage
~$ comparator UIB having approximately 0.5 volts hysterises for
good noise margin. The resistor R2 and capacitor C1 function
as a ripple filter to remove any 60 hz. signal picked up rom
ambient room lighting. There is also fed into the input side
of the voltage comparator UIB a reference electrical signal
which is developed by resistors Pl and R3, such signal being
adjustable in value and preset at a value that is just below
the output of the cell 70 under ambient lighting conditions.
--10--
'7
The two input signals to UIB are compared and the resultant
signal is converted to a digital signal which is fed from the
output of UIs through a resistor R5 to the input side of a
further comparator UIC which is used as an invertor. UIC
changes states as the signal from UIB passes through Vcc/2 in
either direction. The reference signal input to UIC is estab-
lished by the resistors R6 and R7 at Vcc/2 for noise immunity.
The output signal from UIC is fed simultaneously to
a first timing circuit U5 and 1st, 2nd, 3rd and 4th NOR gates
U2A, U2B, U3A and U2D, respectively. The first timing circuit
U5 is set up in the monostable mode as a one shot buffer which
produces a clean, symmetrical square wave pulse that serves to
reset and trigger a second timing circuit U6. On the positive
transition of the output signal from timing circuit U5, such
signal is fed to the base of a semiconductor Q2 to turn on the
same and ensure that the timing capacitor C3 is fully discharged.
The negative transition of the output signal from U5 is AC
coupled to the trigger and reset pins of the timing circuit U6
to trigger the same.
~0
The second timing circuit U6 serves as a total time
timer with its timing range adjustable by resistor P2. Once
set, this timer establishes the maximum total time over which
the stitching mechanism will continue to operate after being
initially triggered. Once U6 times out, the stitching mechanism
is disabled until U6 has been reset and retriggered.
The output signal from the second timing circuit U6
is fed simultaneously to 2nd gate U2B and a 5th NOR gate U2C.
The signals from inverter UlC when the cell 70 is obstructed
and the total timer U6 before it times out, keeps the 2nd
gate U2B closed. If the cell remains obstructed after U6
times out, the output of the 2nd gate U2B goes high to
provide a triggering signal to a third timing circuit U7.
This third timing circuit is set up in the astable mode as a
pulse generator and when triggered generates a 2hz pulse train
which is fed through the 1st gate U2A to pulse a semiconductor
Ql and a light emitting diode LED 1 (if cell 70 remains
obstructed) to cause flashing of LED 1. Only after the
cell 70 has been cleared and the circuitry reset will LED 1
stop flashing.
The output signal from the total timer U6 is fed
also to the 5th gate U2C where it is inverted and fed to the
4th gate U2D. This input signal to U2D and the signal from
the inverter UlC open the 4th gate to develop a signal that is
fed to a 6th NOR gate U3D.
Simultaneously, the inverted output signal from the
5th gate U2C iS fed to an 8th ~OR gate U3B. This signal plus
the output signal from the 3rd gate U3A (which latter signal
is an inversion of the output signal from the inverter UlC)
function to develop an output signal which is fed to a 4th
timing circuit U8. Notably this 4th timiny circuit can be
triggered only while the total timer U6 remains active, i.e.,
has not timed out and if the cell 70 is unobstructed~ Its
timing cycle is adjustable by resistor P3 and it serves to
establish a time period during which the stitching operation
will continue following the passage of the trailing edge of a
wor~ piece past the cell 70 as the stitching operation is
~5 nearing completion. This time period is chosen to be suffi-
cient in duration as ensures completion of the stitching
operation (e.g., X additional stitches) plus sufficient length
of ~hread chain to permit cutting of the chain.
As seen in FIGURE 4b, specifically, the output
signal from the 3rd gate U3A is fed also through a resistor
R24 to the base of a semiconductor Q3 to turn on the same
and ensure the full discharge of the timing capacitor C10.
-12-
.
S7
\
While the cell 70 is obstructed by a work piece, its output
remains low, gate U3~ inverts the same and supplies a high
output to keep Q3 on and capacitor C10 fully discharged. When
the trailing edge of the work piece passes the cell 70, light
strikes the cell, driving its output high, gate U3A inverts to
a low signal which is fed to 8th gate U3B. Since the total
timer U6 has not timed out, its output signal is high, but is
inverted to a low signal by the 5th gate U2C and fed to the
8th gate U3B. These two low signals open gate U3B to develop
a high output signal therefrom which is fed to a 9th NOR gate
U3C, inverted to a low signal and further fed to the ~rigger
pin of the overrun timer U8. The output signal from the 8th
gate U3B is fed to the reset pin of the overrun timer U8 and
turns this pin off when the signal from gate U3B iS high.
During this transition, when the output signal from gate U3A
goes low, Q3 iS turned off.
The output signal from the overrun timer U8 is high
and is fed simultaneously to LED 2 to illuminate the same, and
to the 6th gate U3D. Since the signal from the cell 70 is
~ high at this point in time, the output signal Erom gate U2D
being fed to gate U3D is low, however, pin 3 of the overrun
timer holds the other input of U3B high so that the output
signal from gate U3D remains low.
The output signal from the 6th gate U3D is fed to a
~5 7th gate U4A. This gate is further selectively supplied by
means of a manually operable switch SW2, with a second signal.
When SW2 is closed, two low signals are fed to gate U4A causing
its output signal to go high. This output signal is fed
through a current buffer (gain) comprising a semiconductor Q4,
to the base of a semiconductor Q5 (a power transistor) to turn
on the same and activate an LED 3 and a solenoid SOL 1. In
the present embodiment, activation of the solenoid SOL 1 opens
-13-
the valve associated therewith to admit pressurized air to the
piston-cylinder device 36.
A preferred power source for the depicted electrical
portion of the present control system is shown in FIGURE 5.
The depicted power supply is a conventional 7812 Regulator
which utilizes a source of 110 volt AC current to provide a
highly regulated 12 volt DC output. As depicted in FIGURE 5,
the 110 volt AC current is fed through a transformer Tl and a
bridge rectifier BRl to a voltage regulator VRl, thence through
a series of capacitors C1217 to provide the desired 12 volt DC
output. It will be recognized, of course, that other AC
inputs may be used.
In a typical operation of a stitching machine in the
semiautomatic mode, employing the present control system, a
work piece is positioned by the operator with its leading edge
adjacent the presser foot and needle of the stitching machine
with the material obstructing the cell 70. Thereupon, the
electrical output of the cell is compared to the reference
signal developed by the variable resistor Pl at the voltage
comparator UlB. The output of this voltage comparator is in
the form of a digital signal which is inverted and fed to the
1st NOR gate U2A, the 2nd NOR gate U2B, and the 4th NOR gate
U2D and the 3rd NOR gate U3A and to the timing circuit U5.
At this point in time, the two signals received at
the input of the 1st gate U2A are both low so that its output
is high and LED 1 is on. The cell output signal which is
simultaneously fed to the timing circuit U5 triggers the same
to generate the symmetrical square wave input signal that is
fed to the total timer U6 to trigger the same and produce an
output signal therefrom which is high. This signal is fed
simultaneously to the 2nd NOR gate U2B, thereby providing to
this gate a high signal and a low signal so that its output
remains low and the timing circuit U7 is not triggered. The
output signal from the total timer is simultaneously fed to
inputs of the 5th NOR gate U2C so that this high signal is
inverted and the output from gate U2C becomes low. This low
signal is fed as one input to the 4th gate U2D. Recalling
that the 2nd input signal to the 4th NOR gate U2D comes from
the cell 70 and is low at this point in time, these two low
input signals open the 4th gate and provide a high output
signal therefrom which is fed as one input into the 6th NOR
gate U3D. The low output signal from the 5th NOR gate U2C is
simultaneously fed to the 8th NOR gate U3B as one of the
inputs thereto. The second input signal to the 8th gate U3B
is high at this point in time, being derived from an inversion
of the cell output by the third gate U3A. Accordingly, the
output from U3B is low at this time and no resultant activity
is generated in the overrun timer U8 by the 8th gate U3B. In
like manner, the high output signal from gate U3A is fed to
the base of semiconductor U3B to turn the same on and ensure
the complete discharge of the overrun timer U8. Inasmuch as
the triggering signal to the overrun timer U8 is low at this
point in time, its output remains low so that the 6th gate U3D
output also is low. This low output from the 6th gate is fed
as one of the input signals into the 7th NOR gate U4~. The
second input to the 7th gate is derived through the resistor
~5 R20 and switch SW2. The state of the signal developed when
switch SW2 is closed is low so that both inputs to the 7th
gate are low and its output is high which is then fed to the
base of semiconductor 4 to turn on the same and provide an
electrical signal of sufficient current value to turn on the
semiconductor Q5 to activate LED 3 and the solenoid SOL 1. In
this respect, it will be noted that when the switch SW2 is
open, one o~ the input signals to the 7th gate goes high so
-15-
that its output goes low and the solenoid is deactivated.
Thus, the positioning of the switch SW2 at this location in
the circuitry permits the entire circuitry ahead of the 7th
gate to remain activated ~or maintenance, adjustment and
analysis purposes without activation of the solenoid.
Should the work piece be removed from its blocking
position over the cell 70, the electrical output signal of the
cell 70 goes high to generally reverse each of the functions
referred to above with the result that the first input to the
7th gate U4A from the 6th gate U3D goes high and the output
of the 7th gate goes low as the overrun timer times out to
turn off the solenoid SOL 1 thereby cutting off the source of
pressurized air from the piston-c~linder device and causing
the piston thereof to float thereby disengaging the stitching
machine.
On the other hand, so long as the work piece stays
in its blocking relationship to the cell 70, the machine will
continue to operate until the total timer has timed out where-
upon its output signal goes low with the result that the 1st
input signal to the 7th gate goes high and its output goes low
to deactivate the solenoid SOL 1 and stop the operation of the
machine. Still further, should the work piece pass over the
cell 70 prior to the timing out of the total timer U6, the
cell output signal is reversed so that the input signals to
the 8th gate U3B both are low and its output signal goes high
to trigger the overrun timer U8. Thereupon the output signal
from the overrun timer U8 goes high and is -fed to the 6th gate
U3D as one of the inputs thereof. Under these circumstances,
both inputs into the 6th gate are high so that its output
remains low and the machine continues in the operation until
the overrun timer has timed out whereupon its output signal
reverses and the solenoid SOL 1 is deactivated.
-16-
When the total timer U6 has timed out and its output
signal goes low, and if the cell 70 remains obstructed, this
results in two low inputs into the 2nd gate U2B so that its
output goes high, thereby triggering the timing circuit U7 to
provide a two hertz output pulse theref.om which is fed to the
1st gate U2A to turn off the LED 1 during each pulse~ This
resultan~ flashing of LED 1 tells the operator that the cell
70 is obstructed even though the machine is not operating as
would be expected, and that a problem exists. By reason of
the design of the present control circuit, retriggering of the
several timing circuits occurs only after the cell 70 has been
cleared and the overrun timer has timed out, which will be
recalled to occur within the ~ime cycle of the total timer U6.
Therefore, the operator, if she is fast enough, can run successive
work pieces through the stitching operation in a manner such
that the total timer is activated at all times when in the
fully automatic mode. However, once the work piece has passed
over the cell 70 as when the trailing edge of the work piece
passes over the cell as the completion of the stitching cycle
~ end approaches, the overrun timer prevents the operator from
running the machine continually without inserting a subsequent
work piece into the machine.
As will be recognized from the foregoing description,
when a work piece is in place over the cell 70 and the machine
~5 is operating, LED 1 will be lighted continuously. Likewise,
when the machine is operating, that is when solenoid SOh 1 is
activated, LED 3 will be lighted. Under these same conditions,
LED 2, which is indicative of the activation of the overrun
timer U8 will not be lighted. Therefore, the operator has a
visual indication at all times of the status of the operability
of the various elements of the control system. Moreover, as
noted above, when the switch SW2 is open, the solenoid is
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~; .
deactivated to deactivate the stitching machine, but the
electrical portion of the circuitry remains activated so that
through the use of the LEDS, among other things, the operability
of the various elements of the electrical portion of the
control system may be checked. Further, when the electrical
control system remains activated, appropriate adjustments, as
necessary, may be made in the various adjustable elements of the
circuit. Such adjustments are desirable especially when
training new operators so that the total timer can be adjusted,
1~ for example, to provide longer times for the operator to com-
plete a stitching operation~ As the operator becomes more
experienced, the total time of a stitching operation is reduced
to that time which the operator has demonstrated to be the
approximate maximum time for her to complete a stitching
operation.
By reason of the capability of the present system to
operate either in the automatic or semiautomatic mode by
changing the position of the piston-cylinder device only, the
single system can be used, by an inexperienced operator or in
~ training a new operator who requires more control over the
operation of the stitching machine during the learning process.
Once the operator has become experienced, a relatively simple
rearrangement of the piston-cylinder device as described above
places the machine in the automatic mode of operation so that
a more experienced operator can attain maximum production from
the stitching machine.
` Whereas a specific embodiment of the present control
system has been described herein, it will be recognized that
the present invention is to be limited only in accordance with
the claims appended hereto. Specifically, whereas the present
control system has been termed "electro-pneumatic", it will
be recognized that the piston-cylinder device 36 can be
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operated by means of a pressurized fluid, such as a hydraulic
fluid, so that the term "pneumatic" is intended to include
nhydraulic. n
1~
~0 ;1
~g
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