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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to controllers similar to the type known in the
metal stamping industry as malfunction detectors which are used to monitor
and stop various automatic stamping processes upon reception of a
machine-element or work-piece malfunction signal. In particular, this
invention relates to controllers suitable for use in conjunction with
continuous cycle punch presses or the like for monitoring the process to
prevent or decrease machine, tooling, and work-piece damage, and also to
initiate or control various steps or functions of the process.
Continuous process metal stamping machines (e.g., punch presses equipped
with progressive or transfer dies which form and punch out integral parts
from a continuous strip of material) are subject to inordinate shutdown
and expensive repair or replacement of tooling when an anomaly occurs in
the processing cycle such as: mis-feed (mis-registration of the work-piece
or strip), mis-position of machine element (broken spring or actuator),
part not ejected, etc., and the machine is not stopped before the next
strike (die closure). Since these machines are usually run at speeds
ranging from 50 strokes per minute to 150 strokes per minute, a human
operator is not physically able to react to a malfunction and stop the
machine before damage occurs, especially as the most potentially damaging
problems arise from process malfunctions occurring inside the dies and
usually not visible to an operator.
The evolution and use of malfunction detectors as bolt-on equipment
peripheral to punch presses and the like has advanced through
manufacturers' need to reduce occurrence and costs of damaged tooling, and
the reluctance of machine manufacturers to enter the field of process
control due to installation and maintenance demands, and the wide
variations of processes which can be served by such equipment.
Early malfunction detectors were crude and consisted of a pair or more
contacts or switches actuated by the work-piece and a machine-element
connected in a series/parallel arrangement with the punch press RUN relay
control power. This arrangement often exposed the set-up man or machine
operator to electric shock hazard.
Later malfunction detectors provided individual channels, each comprised of
sensor, go/no-go circuit, lamp indication and relay control of run control
power. Timing and acceptance of sensed signals were accomplished by
charge/discharge of resistance-capacitance (RC) networks which are
influenced by component age, temperature, and line voltage variations.
There was no provision for sensing failures occurring in the internal
circuits of the malfunction detector.
More recently, some malfunction detectors were manufactured with
solid-state components and have rudimentary circuit failure sensing means.
In these embodiments, however, it is still possible for the monitored
machine to continue running for one or more strokes after a circuit
failure has occurred, and, in which case, the punch press stop-point is
generally indeterminate due to the continued practice of using RC timing
circuits, allowing tooling damage to occur in some instances.
Present tooling in the metal stamping industry has become more complicated
and thereby more costly, and the need for increased production has raised
punch press speeds with a consequent demand for better protection of
tooling.
A continuous-feed punch press is comprised, basically, of a motor and
controls, a crank shaft with an attached brake and clutch, a moveable ram
connected to the crank shaft, a fixed bed, and a rigid frame to hold these
parts in an aligned, working arrangement. During normal operation, the
main shaft is continuously revolved in one direction and the
crank-connected ram moves up and down repetitively in response. A die-set
containing various punching and forming tools is fixed to ram and bed. A
means of feeding strip material (often steel) into the die-set is
ordinarily a pair of smooth metal rollers which grip the strip and,
powered from the main shaft by a crank and rack and pinion gear, advance
the strip on alternate half-revolutions of the main shaft through a
unidirectional clutch. The feed mechanism is usually adjusted so the feed
occurs half during the up-stroke after the die opens and half during the
down-stroke before the die closes on the strip. A cam operated roller
release mechanism causes the rollers to grip the strip during the feed
operation and to release the strip during the punching part of the machine
cycle.
In operation, after the strip has been advanced, and before the feed
rollers release, pilot members of the die enter pilot holes in the strip
which holes were punched in a previous stroke. The feed rollers then
release and as the die closes, the pilots register the strip in the die
accurately. Punching and forming members do their work as the die
continues to close.
On the up-stroke, the die begins to open, the feed rollers grip the strip
and after the pilots emerge from the strip, the rollers begin to advance
the strip.
In progressive dies, the number of stations (die segments) the strip
progresses or advances through increases in direct proportion to the
complexity of the part being fabricated. In this type of stamping
operation, the feeding of strip material is a very important function and
parameter, and should be monitored because if for some cause, such as
roller slippage, or blocking in the die of the progression of the strip by
a piece of scrap material, etc., the strip fails to advance far enough for
the pilots to enter the pilot holes, the pilots (of blunt, bullet-nosed
shape) will deform the strip and may split the die section under them at
the point of impact as the die closes.
For the above circumstance, feed completion is monitored by a mis-feed
malfunction detector channel and if the strip does not advance the correct
amount, the protective circuits will stop the machine before the pilots
enter the strip.
In punch presses as described above, in which feeding occurs over an arc of
180.degree. of one revolution, it is advantageous to begin the feed as
early on the up-stroke as possible so that feeding is completed as early
on the down-stroke as possible in order to give enough time for the ram to
be stopped by release of the clutch and actuation of the brake before the
pilots enter the strip in the case of a protective stop on mis-feed.
A mis-feed channel could be termed "end of feed detector," because the
signal of importance would occur at or very near the time of the end or
completion of the feed advancement. Such a channel would have a single
sensor which could be an electrically insulated metal probe with an
exposed metal tip positioned in or near the die so as to make contact with
the metal strip only when the strip is advanced the full feed increment.
The probe would be connected by wire to one terminal of a low voltage
relay coil, the other terminal of which connected to one terminal of a low
voltage source. The other terminal of the low voltage source would be
connected to common ground. The frame of the machine is also connected to
common ground. Thus, when the strip contacts the probe, the circuit for
the coil is completed through metal on metal contacts: probe to strip,
strip to die, die to bed, bed to frame. So energized, a set of N.O.
(normally open) contacts on the relay close, which contacts are wired in
parallel with a set of contacts (N.O.) of a cam operated switch which are
being held closed by a cam positioned on or geared to the main shaft of
the machine. The cam is so shaped as to hold the switch contacts closed
until just after the end of the feed occurs, at which time the cam
releases the switch for some period corresponding to a definite shaft
angle. This shaft angle is determined in part by the point in the cycle at
which the projecting strip (now a formed part) is cut off as a finished
piece and thus breaks contact with the probe. The parallel set of contacts
described are wired in series with the power to the "run" control circuit
of the punch press. If both contacts open at the same time, the machine
stops. Therefore, if on every machine cycle, the feed probe makes
continuous contact with the strip while the cam operated switch is open,
the machine will continue to operate. In this case of a mis-feed, when the
cam operated switch opens, the relay not having been energized by probe to
strip contact, has open contacts also and the machine is stopped by loss
of power to the run control circuit. Optimumly, the probe and cam and the
feed cycle have all been adjusted for best performance and the punch press
stops before any damage is done.
In the above example, the machine continues to run until a missing end of
feed signal, hence: a miss.
One draw-back of the above circuitry (equivalent to the early forms of
malfunction detectors) is the false signal. A false signal would be
generated in the above example by a piece of scrap or other metal
continuously maintaining a connection between the probe and common ground
(die, bed, or frame of machine). In such a case, when the cam operated
switch opened to check the end of feed, the scrap metal continuously
provides an "OK to run" (RUN) signal regardless of the feed condition. If
under these circumstances, a mis-feed occurs, the punch press would
continue to run and tooling damage would occur. There is no inherent
protection in the above described circuitry to prevent such an event from
bypassing the purpose of the mis-feed detector channel. An operator, due
to some misunderstanding of the purpose of such a detector, and not having
success in getting the machine to run continuously with it due to a
possible failure in another part of the circuit, e.g., faulty cam switch,
cam loose or misadjusted, loose or broken wire, etc., may choose to
purposely bypass the circuit by simply connecting the probe or its
connecting wire to common ground.
Another draw back of the above circuit is the fault condition. A fault
signal would occur when the cam operated switch failed in the closed
position. In such a case, the switch contacts maintain Run control power
continuously and, although the probe and its associated relay work
consistently, the cam operated switch contacts never open to allow the end
of feed signal presence to be checked. Therefore, on a mis-feed, a fault
signal will allow the punch press to continue to run and again tooling
damage will occur.
SUMMARY OF THE INVENTION
It is, therefore, a primary object of the present invention to provide a
digital type controller for a punch press or the like (hereinafter called
machine) which operates to decrease the occurrence of tooling damage.
Another object of the invention is to provide such a controller which
operates with accuracy and repeatability by using control pulses
corresponding to specific shaft angles of the main shaft of the machine.
Another object of the invention is to provide such a controller which
generates control pulses corresponding to specific main shaft angles.
It is a further object of the invention to provide such a controller which
decreases the reception of false sensor signals by accepting sensor
signals at selectable main shaft angles. Another object of the invention
is to provide such a controller which decreases the reception of false
sensor signals by accepting such signals in a selectable prescribed order.
An additional object of the invention is to provide such a controller
which stores input sensor signals for sampling at a later time (or further
main shaft angle). Another object of the invention is to provide such a
controller which samples the storage means for presence of the previously
accepted input sensor signals at selectable shaft angles.
It is another object of the invention to provide such a controller which
initiates a machine stop in response to a missing signal or malfunction at
selectable main shaft angles. A further object of the invention is to
provide such a controller which will perform reliably by sensing false
signals as equivalent to missing signals or malfunction signals. Another
object of the invention is to provide such a controller which performs
reliably by initiating a machine stop upon detection of a fault signal. An
additional object of the invention is to provide such a controller which
will initiate a machine stop immediately upon reception of certain sensor
signals regardless of the main shaft angle.
It is an additional object of the invention to provide such a controller
which can operate auxilliary electrical loads such as relays or the like
in support of the machine and process or in support of another machine
and/or process at selectable shaft angles of the machine. Another object
of the invention is to provide such a controller which is versatile and
adaptable to many process configurations by means of its programming
capability whereby sensor channels may be preselected to be on or off,
sensors may be set to be N.O. or N.C., sensors may be enabled at
selectable main shaft angles, sensors may be prescribed to sense signals
in a specific order, stored signals may be sampled at selectable main
shaft angles, and electrical loads may be energized and deenergized at
selectable main shaft angles.
Another object of the invention is to provide such a controller which
displays a continuous indication of the condition of the process, the
machine, and the controller on a status indication panel. A further object
of the invention is to provide such a controller, though capable of
controlling large amounts of power, uses very little power for its own
operation or status indication. Another object of the invention is to
provide a versatile all-purpose switching circuit for use in such machine
controllers and the like which accepts input signals such as sensor
signals, control signals and programming signals and provides an output
signal in response to specific combinations of those input signals. An
additional object of the invention is to provide a means of generating
control pulses corresponding to specific machine main shaft angles, to
order the control pulses in a lattice array, and to provide for selection
of one or more individual control pulses corresponding to a specific main
shaft angle for the operation of each of a plurality of control pulse
responsive circuits at the selected main shaft angles.
The invention is directed to a control system for a cyclicly machine and
includes means for generating position pulses corresponding to positions
of the machine in its operating cycle, sensors for generating sensor
signals indicating conditions of the machine, means having the machine
position pulses and the sensor signals as inputs and providing output
signals representative of the machine condition at preselected machine
positions, and means responsive to such output signals for stopping or
otherwise controlling the machine operation for various signal situations.
When a fault condition is sensed by a preselected sensor means at a
preselected machine position, the machine operation is interrupted.
Similarly, when the sensor signals are not generated in a preselected
sequence, indicating a malfunction in the sensors, machine operation is
interrupted. Machine operation may be stopped immediately or may be
stopped after a time delay, depending on the criticality of the condition
and the position in the operating cycle. The invention may be used in a
simple form for handling one machine condition at one machine position and
may be produced in a more complex form for handling a plurality of machine
conditions and a plurality of machine positions. The specific embodiment
illustrated may handle up to ten machine conditions at thirty-six machine
positions in the operating cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of a punch press incorporating the presently
preferred embodiment of the invention;
FIG. 2 is a side view of a die set of the press of FIG. 1;
FIG. 2a is a top view of a strip of metal in the die set of FIG. 2;
FIG. 3 is an exploded side view of a probe used in the die set of FIG. 2;
FIG. 4 is a diagram of the pulse train generated in the shaft encoder of
the press of FIG. 1 plotted against degrees of input shaft rotation;
FIG. 5 is an electrical diagram of the presently preferred embodiment of a
shaft encoder/decoder suitable for use with the press of FIG. 1;
FIG. 6 is a diagram of a pulse receiving circuit;
FIG. 7 is a diagram of a sampling, reset and run circuit;
FIG. 8 is a diagram of a sensor signal circuit;
FIG. 9 is a diagram of a control circuit incorporating the circuits of
FIGS. 6, 7 and 8;
FIG. 10 is a diagram of a control circuit incorporating the circuit of FIG.
5 and a plurality of the circuits of FIG. 9; and
FIG. 11 illustrates and identifies the symbols used in the preceeding
figures.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 is shown a punch press similar to a BLISS 200 Ton punch press
comprised of frame 20, ram 22, bolster 24, bed 26, motor 28, shaft 30,
clutch, brake and flywheel 32, motor controller 34, input power 36,
solenoid control power 38, air supplies 40, solenoids 42, exhaust mufflers
44, top stop control 46, operator's control panel 48, air cylinder and
piston 50, gripper 52, die set 54 and 56, strip 58, main shaft and timing
gear 60, chain 62, shaft encoder shaft 69, shaft coupling 65, shaft
encoder housing 66, degree wheel 68, bracket 67, digital controller 70,
connecting plugs 85 and 87, interconnecting cable 72, power source 74,
power cable 76, solenoid control power cable 78, Run control power cable
80, parts chute 82, parts bin 84, probe wire 86 and probe wire 88.
The condition of a process is characterized in its parameters. The process
parameters which one may want to monitor in a stamping operation are:
Process: End of Feed (if or when full feed occurred) Broken Spring or
Actuator Stock Depleted (strip material used up) Pilot Swtich Actuation
Part Ejected
Machine: Overstress Loss of Motion In Run mode
Controller: All Input Sensor Signals False Input Sensor Signals All
Generated Signals Fault Signals Protective Stop Reset Voltages and
Currents
In FIG. 2 is shown the die set 54 and 56 containing pilot hole punches 96,
pilot pins 98, slot punches 100, scrap relief holes 102, pilot holes 104,
cut off tool 106, hardened insert 108, strip 58, end of feed probe 120,
insulated mounting means 122, probe 116 and insulated connecting wires 86
and 88. The probe 116 is shown in detail in FIG. 3. Probe tip 124 is
springloaded by spring 126 in capsule 128 which seats in receptacle 130
which rests in insulator 132 which fits into the die 56. An insulated
probe wire 88 with metal connector 134 fits into receptacle 130 making
electrical connection. The connecting wire 86 or 88 is connected to the
controller at its other end.
FIG. 2a shows the strip 58. The strip 58 enters the die being moved from
right to left by the feed mechanism (not shown). At the end of feed
progression, the punch section 54 closes on the die section 56 and the
strip 58, punching pilot holes 138 in the strip. The punch section 54
retreats, the strip progresses and the punch section 54 again moves toward
the strip and the first pilots 98 enter the previously punched holes 138,
registering the strip accurately. As the punch section 54 continues to
close on the die section 56, punches 96 form holes 138 and 140. On the
next stroke, punch 100 forms slot 142 as well. The strip continues to
advance through the stations in the die set until part 110 is severed from
strip 58 at line 148 by cut off tool 106. During this initial feeding
operation, the operator controls the machine in INCH or JOG mode during
which the machine runs only as long as the operator manually holds in the
RUN buttons. Once the strip progresses successfully to the point where
finished parts are being cut off, the punch press can be run in SINGLE -
STROKE operation for one or more cycles to permit the operator to assess
the proper operation of the machine and the proper formation of the part.
As the strip advances on each stroke, the part 110 first formed will
contact probe 120, generating a ground signal which will be transmitted to
the controller by wire 86.
Still in SINGLE - STROKE operation, the operator will check for reception
of the end of feed signal by the digital controller. At the shaft angle
that the probe contacts the strip, there will be an indication, say CH 1
(channel one) on the controller's status indicator panel. If the
indication is present at the proper point in the machine cycle, the
operator can shift to AUTOMATIC mode on the punch press control panel,
RESET the controller, and push the RUN buttons to initiate continuous
cycle stamping. Once this is done, the controller will monitor the feed
and will stop the machine when a mis-feed occurs.
In some dies, the finished parts do not project from the end of the die
before they are cut off the strip. In those dies, the parts drop through
the die and another method of progression checking must be used. The probe
116 is insulated from the die by insulator 132 and the probe tip 124 is in
contact with the strip until the strip advances to a position where the
probe tip 124 engages hole 150 in the strip. At that point in the feed
cycle, the probe tip, being of smaller diameter than the hole 150, breaks
contact with the strip and common ground, generating a signal carried by
insulated wire 88 to the controller. The controller channel which monitors
this signal will have been selected to monitor a normally closed
(grounded) circuit for an open circuit indication which occurs when the
probe tip breaks contact with the strip at hole 150. Thus, the machine may
be run on AUTOMATIC with this type of end of feed sensor.
The shaft encoder 66 may be conventional and provides an electrical pulse
output varying as a function of machine shaft rotation. The shaft encoder
functions to close switches 182, 184, 186, 188, 190, 192 and 194 (FIG. 5)
to provide output pulses at 10.degree. intervals as shown in FIG. 4.
Since the pulse output exhibits mirror symmetry across a line 181 through
180.degree., the same pulse train or sequence will be produced for a
complete counter clockwise revolution as well as for a complete clockwise
revolution of the input shaft. One of the advantages of the above
arrangement is that the shaft encoder will serve to generate shaft
position information equally as well for machines having main shafts
normally rotating clockwise and for machines having main shafts normally
rotating counterclockwise.
Input signals to the controller and the sources of the signals may be
categorized as follows:
A. Sensor Signals (generates a signal in direct relationship to the
condition or parameter)
1. Probe (senses contact with conductive material which is at ground
potential)
2. Switch or Relay Contacts (change of condition)
3. Circuit Potential (Hi or Low)
B. Control Signals (gates, times, sets, resets)
1. Shaft Encoder (shaft angles)
2. Cam Switch (shaft angle or ram position)
3. Push-button, Switch or Relay
C. Programming Signals (on, off, enable, disable, degrees, timing)
1. Switch
2. Wire Connection
3. Matrix Board
4. Module (plugged in or out)
5. Availability of Power
D. Power Signals (available or unavailable)
1. Unit Power (115VAC)
2. power Supply (15VDC)
3. output (115VAC Relay Control Power)
The input signals and their sources may be classified as follows:
A. Cyclic Input Signals (patterned)
1. Probe
2. Switch
3. Relay Contacts
4. Pulse from internal circuit
B. Constant Input Signals
1. External Switch or Relay Contacts
2. Circuit Potential
3. Pulse Train (averaged)
THE SHAFT ENCODER/DECODER
In FIG. 5 is shown the schematic of the shaft encoder/decoder. A means of
generating input pulses at discrete input shaft angles such as the pulse
train of FIG. 4) is provided, which, in FIG. 5 is represented by switches
182, 184, 186, 188, 190, 192, and 194. Terminal 196 is connected to
B.sup.+ (15VDC). The switches make or close at the appointed shaft angles,
generating positive pulses across resistors 252, 254, and 256 and through
current limiting resistors 258, 260, and 262 to pairs of inverters 264 and
266, and 270, 272 and 274. The inverter pairs serve to shape the input
pulse form so the pulses appearing at the inputs 276 and 280 to decode
counter/dividers 288 and 290 have steep leading edges. The counters 288
and 290, such as RCA device CD 4017A accept a train of input clock pulses,
advancing the 1 of 10 output high (+) condition to the next output
conductor for each input clock pulse received. For pulses received at
terminal 276, the counter 288 advances its high output successively from
conductor 300 to conductor 302 to 304 to 306 to 308 to 310, successively
pulsing inverters 312, 314, 316, 318, 320, and 322. Five of the six
inverter output conductors 324, 326, 328, 330, 332, and 334 are at a high
or positive voltage after any input pulse and one of the six is at a low
or zero voltage. A method of selecting which output conductors 324 - 334
are connected to which input conductors 412 - 430 of the NOR gates 440 -
458 is, in this case a matrix pin board 47 which is a 6 by 10 array. The
switch 192 makes, generating a pulse which advances counter 290 as in the
previous description, providing five of the six conductors 374 - 384 with
high signals and one with a low signal. Another matrix pin board 472 is
provided for making connection between output conductors 374 - 384 and
input conductors 392 - 410 of NOR gates 440 - 458.
Switches 182 - 190 provide pulses at the 10.degree., 20.degree.,
30.degree., 40.degree., and 50.degree. increment of every 60.degree.
segment about the center of input shaft rotation. Switch 192 provides a
pulse at every 60.degree. of 360.degree. of input shaft rotation, and
switch 194 provides a pulse for every 360.degree. of shaft rotation as is
shown in FIG. 4. The switches provide a series of pulses which occur, in
this embodiment, at 10.degree. intervals, with switch 194 producing a
pulse which coincides with and overlaps the pulse produced by switch 192
at its sixth 60.degree. increment (360.degree.).
In operation, the shaft at 0.degree. makes switches 192 and 194, presenting
input pulses at terminals 278, 280, and 282. The signal present at 278
resets counter 288 to zero, making output conductor 300 high which is
inverted by inverter 312 and makes conductor 324 low. All the other
outputs 302 - 310 are low and the conductors 326 - 334 are high. The high
signal at terminal 282 of counter 290 overrides the signal at terminal 280
due to the counter's internal logic, thereby resetting counter 290 to zero
which produces a high output on conductor 342 and low outputs on
conductors 344 - 352, making, through inverters 362 - 372, conductor 374
low and conductors 376 - 384 high. As the shaft rotates to the 10.degree.
position, switches 192 and 194 break, removing their signals from the
counters, and switch 182 makes with the resultant pulse at terminal 276
advancing counter 288 one step, making conductor 300 low and 302 high. As
a result, conductor 326 is low and conductors 324, 328, 330, 332, and 334
are high. As the shaft rotates to the 20.degree. position, switch 182
breaks and switch 184 makes, advancing counter 288 another step which
makes 302 low and 304 high, making conductor 328 low and 324, 236, 330,
332, and 334 high. In like manner, conductor 330 becomes the low one at
30.degree., 332 the low one at 40.degree. and 334 the low one at
50.degree.. At the 60.degree. position, switch 192 is made, producing a
pulse at terminals 278 and 280. The signal at 278 resets counter 288 to
zero (300 high). The signal at 280 advances counter 290 one step, thereby
making conductor 344 high, making conductor 376 low, and 374, 378, 380,
382, and 384 high. As the shaft rotates to the 110.degree. position,
switches 182, 184, 186, 188, and 190 make and break in succession every
10.degree., advancing counter 288 through its steps as before,
successively making conductors 326 through 334 low. At the 120.degree.
position, counter 290 advances another step making conductor 346 high and
344 low. In like manner, counter 288 advances through its steps and is
reset as the shaft is rotated to 180.degree. and counter 290 is advanced
one step again. As the shaft rotates to 360.degree., counter 288 is
advanced through its steps and is reset three times while counter 290 is
advanced through its remaining two steps (at 240.degree. and 300.degree.)
and reset by switch 194 at 360.degree..
If we take conductors 324 - 334 as corresponding to 10.degree. increments
of input shaft rotation, and conductors 374 - 384 as corresponding to
60.degree. increments of input shaft rotation, we have a mechanism for
pinning out any 10.degree. shaft angle for operation of any of the NOR
gates 440 - 458. For example, a connecting pin in the matrix board 470 at
the juncture of conductors 412 and 324, interconnecting them at that
point, and a connecting pin in the matrix board 472 at the juncture of
conductors 392 and 374 interconnecting them at that point will provide to
NOR gate 440, two low input signals at CRM the 0.degree. position of the
input shaft, producing a high output from gate 440. During all other
10.degree. positions of shaft rotation, the output of gate 440 will be
low. A pin at the juncture of 394 and 374 and another at the juncture of
414 and 326 will produce an output control pulse from NOR gate 442 at the
10.degree. position of input shaft rotation. A pin at the juncture of 396
and 380 and another at the juncture of 416 and 334 will produce an output
control pulse from NOR gate 444 at 230.degree.. In like manner, any of the
NOR gates 440 - 458 may be selected by connecting pins to produce an
output control pulse at any 10.degree. position of the input shaft
rotation. Any input line to NOR gates 440 - 458 not selected will produce
no output control pulse for the corresponding gate regardless of shaft
position.
This combination of switches, counters, inverters, matrix boards and pins
and NOR gates provide for selection of 10.degree. shaft positions from
0.degree. - 360.degree.. Other variations are possible.
In the system of FIG. 5, NOR gates 440 and 442 make one pair of ON - OFF
control circuits whose outputs occur at selectable angles of input shaft
position corresponding to machine main shaft angles. The output of NOR
gate 440 is the selectable ON signal, the output of NOR gate 442 is the
selectable OFF signal. NOR gates 444 and 446 constitute another pair of ON
- OFF control circuits. NOR gates 448 and 450, 452 and 454, and 456 and
453 constitute similar pairs of ON - OFF control circuits with output
signals occurring at selectable shaft angles. The number of control
circuits is not limited to the number shown.
PULSE RECEIVING CIRCUIT
The purpose of the circuit in FIG. 6 is to receive momentary ON and OFF
pulses, translate them into latching SET and RESET outputs and monitor the
alternating sequence of ON, OFF, ON, OFF signals and provide a FAULT
output signal when an improper sequence occurs such as ON, OFF,---, OFF
(ON pulse missing), OFF, ON,---, ON (OFF pulse missing), or when ON and
OFF signals are present at the same time (either one or the other
continuously energized). When this circuit is used to translate and
monitor positive logic signals from two NOR gates such as 440 and 442
(FIG. 5), which are activated alternately, the circuit fault output
(normal = +) will fall to zero upon a wrong sequence such as above, or if
both ON and OFF signals are received at the same time.
Improper sequence or both ON and OFF signals received at the same time is
the result of component failure (i.e., open switch), missing component
(i.e., matrix board pin), or spurious signal received due to circuit or
component failure or loose contacts or wiring or radio frequency
interference. In any of these cases, it is better to stop the machine when
any of these faults occur than to permit the machine to continue running
with faulty or improper control signals.
Referring to FIG. 6, in which there are seven 2-input NOR gates 494, 496,
498, 500, 502, 504, 516, and three 2-input NAND gates 508, 510 and 512,
and an inverter 514, and four buffers 520, 522, 524 and 526; the input
terminal 480 receives positive (+) ON pulses from NOR gate 440 (FIG. 5) at
the shaft position selectable by one connecting pin in each conductor 392
and 412, and the input terminal 482 receives positive (+) OFF pulses from
NOR gate 442 (FIG. 5) at the shaft position selectable by one connecting
pin in each conductor 394 and 414 as previously described. Outputs from
the circuit in FIG. 6 are SET 484, RESET | | |
