U.S. patent number 3,704,396 [Application Number 05/142,620] was granted by the patent office on 1972-11-28 for safety device for machines.
This patent grant is currently assigned to Cincinnati Incorporated. Invention is credited to John L. Macdonald.
United States Patent |
3,704,396 |
Macdonald |
November 28, 1972 |
SAFETY DEVICE FOR MACHINES
Abstract
Photo-electric guard for machines, having a plurality of light
sources and a corresponding plurality of photo-responsive devices.
Each light source is powered by a modulated electric supply and is
aimed at the corresponding one of the photo-responsive devices. The
output of each photo-responsive device is reshaped and compared
with the input to the light source, and any mismatch is effective
to stop further machine operation.
Inventors: |
Macdonald; John L. (Aurora,
IN) |
Assignee: |
Cincinnati Incorporated
(Cincinnati, OH)
|
Family
ID: |
22500598 |
Appl.
No.: |
05/142,620 |
Filed: |
May 12, 1971 |
Current U.S.
Class: |
361/175; 361/186;
250/221; 361/203 |
Current CPC
Class: |
F16P
3/144 (20130101) |
Current International
Class: |
F16P
3/14 (20060101); F16P 3/00 (20060101); G02f
001/28 () |
Field of
Search: |
;317/124,127
;250/220,221 ;340/258R,258B |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shoop, Jr.; William M.
Assistant Examiner: Moose, Jr.; Harry E.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A photo-electronic guard system for a machine comprising:
a. at least one light source;
b. means for supplying a modulated current to said light source to
produce a modulated light signal;
c. a photo-responsive device arranged to receive said modulated
light signal;
d. circuit means associated with said photo-responsive device for
producing an output in response to said modulated light signal,
said circuit means including a time delay feedback circuit whereby
to maintain substantially constant potential across said
photo-responsive device and prevent an output of photo-responsive
device to ambient light changes;
e. comparator circuit means for comparing said output in response
to said modulated light signal with said modulated current supply;
and
f. means for stopping said machine at any time said output in
response to said modulated light signal fails to match said
modulated current supply.
2. The guard system claimed in claim 1 wherein said means for
supplying a modulated current to said light source comprises a
square wave generator.
3. The system claimed in claim 2 wherein the frequency of
modulation of said current is on the order of 500 cycles per
second.
4. The guard system claimed in claim 1 including means for
amplifying said output in response to said modulated light
signal.
5. The guard system claimed in claim 1 including means for
reshaping said response output in to said modulated light signal to
eliminate variations introduced by said light source and to conform
said response to said modulated current.
6. The guard system claimed in claim 1 wherein said comparator
circuit means comprises means for receiving said response output in
to said modulated light signal; means for receiving said modulated
current; and means for producing an output pulse for each cycle in
which said response and said modulated current match.
7. The guard system claimed in claim 6 wherein said means for
stopping said machine comprises means for receiving said output
pulses from said comparator circuit means; and means responsive to
a change in frequency or duration of said pulses to stop said
machine.
8. The guard system claimed in claim 7 wherein said means
responsive to a change in frequency or duration of said pulses
includes a timing circuit adapted to receive and measure the
spacing between said pulses; a second timing circuit adapted to
receive and measure the duration of each said pulse; each said
timing circuit being adapted to produce a changed output in
response to a predetermined change in input, said changed output
being effective to stop said machine.
9. The guard system claimed in claim 1 including means for muting
said guard system during a portion of the cycle of said
machine.
10. The guard system claimed in claim 9 including means for
indicating to an operator the period in which said system is
muted.
11. The guard system claimed in claim 1 including means for
automatically stopping said machine at a specified point in each
cycle.
12. The guard system claimed in claim 1 wherein said means for
stopping said machine at a specified point in each cycle comprises
a circuit for interrupting the supply of current to at least one
light source.
13. The apparatus claimed in claim 1 including logic circuit means
for verifying the condition of machine controls prior to
continuation of machine operation, and preventing continuation of
operation in the event any such control does not function properly.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a safety device for a variety
of machine tools, and particularly to a photoelectric safety device
adapted for use with presses and the like having a reciprocating
ram.
Ram type machines of the type here under consideration have always
presented a potential safety problem by virtue of the severity of
the injury to personnel during the downward stroke of the machine
cycle. This long extant safety problem is compounded by the rapid
advance of machine tool technology and particularly advanced
control technology.
Mechanical guarding mechanisms are very difficult to apply, in
large part because of the material handling problems and the
ability of such machines to utilize different dies and the like
and/or sizes of material. It is generally recognized by the skilled
worker in the art that a guarding system which has to be removed or
changed with every new set-up will often be omitted or improperly
installed and adjusted.
Other safety assists such as palm buttons or pull out devices for
the operator are widely used, but these devices may not always be
used during die changes or parts tryouts. In addition, they do not
protect a third person such as a material handler or a supervisor
who may also be in a hazardous area.
The art has also attempted to utilize photo-electronic safety
devices. Generally speaking, all such photo-electronic safety
systems utilize a light source which is focused on a
photo-electronic cell or receiver. Often, a plurality of light
sources and photo-electronic receivers are arranged in parallel
rows to define a "curtain" adjacent the hazardous area. If the
transmitted light is blocked or is not received by the
photo-electronic receiver, a signal is produced which will
instantly stop the machine.
Photo-electronic guard systems of the type now known suffer from
several serious disadvantages. In the first place, all known
systems are particularly susceptible to changes in ambient
lighting. The ambient lighting problem is particularly acute in the
case of machine tools which are operated 24 hours a day.
Specifically, if the ambient light increases in a particular
situation (such as daybreak), a condition can arise in which the
operator could break the transmitted light curtain without
affecting the output of the photo-electronic receiver. The
potential danger of such a condition should be obvious.
The problem of changes in ambient lighting may in part be
alleviated by the provision of manual sensitivity adjustments.
Experience with such systems has shown that the machine tool
operator must spend valuable time adjusting the sensitivity of the
device rather than working at the machine.
A related problem with currently available photo-electronic
guarding systems is the problem of alignment. For example, if a
light source is not properly aligned or is accidentally jarred or
bumped into an improperly aligned position, a light source can be
projected on two receivers at once. If this should occur, there is
a potentially dangerous area in the light curtain through which the
operator could put his hand or arm without interrupting the light
on the corresponding photo-electronic receiver.
Bearing the foregoing comments in mind, it is an object of this
invention to provide a photo-electronic safety device which will
fully protect the operator and other personnel without decreasing
working efficiency.
A more specific object of the invention is to provide a
photo-electronic guarding system which does not require sensitivity
adjustments for changes in ambient lighting conditions.
It is another object of the invention to provide a photo-electronic
guarding system which includes a logic control circuit for
monitoring machine control functions as well as the output of the
photo-electronic receivers.
Still a further object of the invention is to provide a
photo-electronic guarding system of "fail no-fault" design; that
is, a system in which any malfunction in the system or associated
circuitry will immediately shut down the machine.
SUMMARY OF THE INVENTION
In its broadest terms, this invention contemplates a plurality of
light sources and a corresponding number of photo-electronic
responsive devices arranged to guard the danger zone of a machine
tool. Each light source is powered by a modulated electric supply,
effective to modulate the intensity of the light emitted by the
light sources. The resulting output of the photo-electronic
receivers is reshaped to compensate for variations introduced by
the incandescent light sources, and the output is compared with the
modulated supply. In the event there is any mismatch or lack of
identity between the two signals, the machine tool will be stopped
immediately.
The logic control circuitry associated with the guarding system, in
addition to monitoring the comparisons briefly noted above, will
also monitor a variety of specific machine functions.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic, block diagram of the photo-electronic
guarding system of this invention.
FIG. 2 is an electrical schematic diagram showing the automatic
ambient light adjust, amplifier and wave reshaper associated with
each photo-electronic receiving device.
FIG. 3 is an electrical schematic view showing the matrixing and
comparing circuitry.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, the general arrangement of components
and method of operation will be described. A square wave generator
is indicated generally at 10. For present purposes, the square wave
generator 10 puts out two square wave outputs 180.degree. out of
phase. These outputs are indicated in the drawing as "Phase A" and
"Phase B."
The transmitter stand indicated generally at 12 includes a
plurality of incandescent light sources 14a through 14g. It will of
course be understood that any desired number of light sources may
be utilized, and that the light sources may be arranged in any
desired pattern. For example, the light sources may be arranged to
define a "curtain" which may be either horizontally or vertically
arranged, depending on a variety of conditions.
The Phase A and Phase B outputs of the square wave generator 10 are
connected to alternate lamps in parallel. Specifically, Phase A
output is connected to the lamps 14b, 14d, and 14f, while the Phase
B output is connected to the lamps 14a, 14c, 14 e, and 14 g.
The transmitter stand 12 also includes a lens 16 for each of the
light sources 14a through 14g, by means of which the illumination
of the respective lamps may be focused on a corresponding
photo-sensitive receiver.
The receiver stand indicated generally at 18 includes a
photo-electronic receiver 20a through 20g corresponding in position
and arrangement to the light sources 14a through 14g. Each of the
photo-electronic receivers 20a through 20g is provided with a lens
22 for focusing the respective light beam.
The receiver stand also includes an amplifier and wave shaper 24
for each of the photo-responsive devices 20a through 20g. The
circuitry for the amplifier and wave shaper is shown in FIG. 2 and
will be described in more detail hereinafter. For present purposes,
it will be understood that since the light sources 14a through 14g
are incandescent, the intensity of the emitted light will not be a
perfect square wave; it will however, vary at the same rate as the
input square wave. The amplifier and wave shaper 24 is designed to
reshape the modulated output of the photo-electronic receivers 20a
through 20g into a square wave.
The matrixing and comparing circuit indicated generally in FIG 1 at
26 is shown in more detail in FIG. 3. It will be seen that the
matrixing and comparing circuit 26 receives the outputs from all of
the amplifier and wave shapers 24; the circuitry combines all like
phase outputs and compares them with the output of the same phase
from the generator 10. When they compare correctly, there will be
an output pulse for each cycle of each phase from the circuit
26.
The digital outputs for each phase from the matrixing and comparing
circuit 26 is fed to the three timing circuits indicated in FIG. 1
at 28, 30 and 32. The circuits 28 and 30 are identical, and are
arranged to measure the spacing of the digital pulses from the
matrixing and comparing circuit 26. The timing circuit 32 measures
the duration of each pulse from both digital phase outputs. A
change in the output of any one of the timing circuits 28, 30 and
32 could be used with a nand gate to actuate the machine cycle
relay 34, thereby stopping the machine instantly.
It will be recognized by the skilled worker in the art that the
photo-electronic guarding system, as thus far described, will be
effective during the entire machine cycle. In many applications,
this is not desirable. In the first place, it is only the down
stroke of the ram which presents a substantial safety problem;
there is relatively little danger to the operator or other
personnel during the up stroke. In this connection, it is common
practice for an operator to enter the danger zone during the ram
return stroke, as, for example, to remove a finished piece, to
adjust the workpiece for a subsequent stroke, and the like. It is
desirable that the machine operation not be stopped by these
actions of the operator. Secondly, in the specific case of a press
brake, the bending or forming portion of the cycle at the bottom of
the downward stroke will generally lift the edge of the workpiece
upwardly into a position where it may block the transmitted light
signal. It will be obvious that this action of the workpiece should
not stop further machine operation.
Thus, it is possible to add to the circuitry described above
provision for muting or rendering inoperative the photo-electronic
guarding system during specified portions of the machine cycle.
To this end, a matrixing and muting circuit 36 is interposed
between the outputs of the timing circuits 28, 30 and 32, and the
machine cycle relay 34.
Muting of the photo-electronic guarding system is controlled, in
the embodiment shown, by either the manual key select switch 38 or
the mute cam switch 40. These switches, along with the others to be
described hereinafter, are connected to an AC input to digital
converter 42. The AC input to digital converter will change the
input signal to digital pulses. It may consist of a transformer,
full wave rectification, a resistor divider network, filter
network, and a group of nand gates used in a Schmidt trigger
circuit.
Digital signals representing the position of the key select switch
38 and the mute cam switch 40 will be transmitted from the AC input
to digital converter 42 to the mute control circuit 44; the output
of the mute control circuit 44 may go to both the matrixing and
muting circuit 36, as well as to a visual guard "off" sign 46.
The input to the matrixing and muting circuit 36 will mute or
prevent actuation of the machine cycle relay, even though the other
input to the matrixing and muting circuit 36 would indicate an
interruption in the transmitted light.
The guard "off" sign 46 is a visual indication to the operator that
the photo-electronic guard system is not in operation. The sign may
include a translucent face plate having appropriate lettering on
the back side, so that the lettering is not visible unless the
internal lights are on. Thus, an operator will instantly know
whether or not the photo-electronic system is in operation.
Operation of the guard-off sign 46 is monitored. Failure of
guard-off sign 46 to indicate an unguarded condition will result in
actuation of machine power relay 58, shutting down the machine
until repairs are made.
It will be recalled that early in this specification, reference was
made to the utilization of the logic control circuits of this
invention for monitoring a variety of machine control functions.
The embodiment illustrated in FIG. 1 shows schematically the top
dead center cam switch 48 and the overrun cam switch 50. In
ordinary operation, the top dead center cam switch is utilized to
stop the machine tool after each complete cycle. In other words,
this switch should be effective to stop the ram at its top dead
center position following each "up" stroke. The overrun cam switch
50 is, in effect, a check on the adjustment of the press. In other
words, upon actuation of the top dead center cam switch 48, the ram
should stop at its top dead center position. Through wear and/or
lack of proper adjustment, the ram may overrun its top dead center
position. The overrun cam switch 50 is arranged to detect a
condition wherein the overrun is outside of normal tolerance
limits.
As seen in FIG. 1, both the top dead center cam switch 48 and the
overrun cam switch 50 are connected to the AC input to digital
converter circuit 42. Actuation of the top dead center cam switch
48 is effective to trigger a one shot 52. The pulse from the one
shot 52 triggers a second one shot identified in FIG. 1 as the
overrun check 54. The pulse from the one shot 52 also actuates the
alternate phase non-repeat circuit 56. It will be seen that the
Phase A and Phase B output of the square wave generator 10 are
connected to the lamps 14f and 14g across the alternate phase
non-repeat circuit 56. The alternate phase non-repeat circuit 56
includes flip-flops and gating circuitry effective so that the
pulse from the one shot 52 will alternately interrupt the Phase A
or Phase B input to the lamps 14f and 14g respectively for the
period of that pulse.
It will be apparent to the skilled worker in the art that an
interruption in the supply to one of the lamps 14f or 14g will mean
that the corresponding photo-responsive device 20f or 20g receives
no modulated light signal. This in turn will mean that the output
of one of the amplifier and wave shapers 24 will not match the
input in the matrixing and comparing circuit 26, so that its output
will cause a change in output of one of the timing circuits 28, 30,
and 32, acting through the matrixing and muting circuit 36 to
actuate the machine cycle relay, stopping the machine.
It will also be noted that the output pulse from the one shot 52 is
delivered to the mute control circuit 44 which will trigger a
flip-flop to reset the circuit to the non-muting position.
The overrun check 54, as already indicated, is a second one shot
which produces a pulse of a specified time duration. This pulse is
used to measure the stopping time of the ram at top dead center. If
the overrun cam 50 is depressed before the period of the overrun
check 54 elapses, a signal will be transmitted to the machine power
relay 58 preventing further operation of the machine until the
necessary period has elapsed.
It will also be observed in FIG. 1 that the top dead center cam
switch 48 and the overrun cam switch 50 are used to check each
other. That is, an output from the AC input to digital converter
indicating the position of each of the switches is transmitted to
the switch occurrence check 60. If either cam switch fails, the
output of the switch occurrence check 60 to the machine power relay
58 will stop the machine.
Preferably, each of the two switches 48 and 50 are checked twice
during an individual machine cycle.
Referring now to FIG. 2, an electrical schematic diagram is given
which shows in more detail the amplifier and wave shaper 24
generally described above. It is this circuitry which, in addition
to amplifying and reshaping the received light signal,
automatically adjusts for changing ambient light conditions.
A photocell is indicated at 70, and is connected on one side to a
suitable source of direct current. It will be recognized that the
signal lead 72 of the photocell will have a varying DC voltage,
depending upon the light intensity received by the photocell 70. As
indicated earlier, there will be the rapid variations in intensity
caused by the modulated light source, as well as more gradual
changes in ambient lighting conditions. Ambient light causing
gradual changes of voltage at signal lead 72 of the photocell 70 is
monitored by the ambient light correction circuit, including
resistors 74, 76 and 78, capacitors 80 and 82, and transistor 84,
which is a time delayed negative feedback path which maintains an
average voltage at photocell signal lead 72. This time delay
circuit responds only to gradual changes in ambient light and not
to the rapidly changing modulated light. Both the corrected ambient
light signal voltage and the rapidly modulating light signal
voltages appearing at signal lead 72, are applied to resistors 86
and 94, which are input paths to the operational amplifier 92.
Input path of resistors 86 and 88 and capacitor 90 comprises a time
delay circuit which blocks rapidly changing modulated light
voltages and responds only to the gradual change of ambient light.
Input path through resistor 94 responds to both ambient light and
modulated light. The operational amplifier inputs have a signal
difference of only the rapidly modulating light.
The output of the operational amplifier 92 is connected across the
resistor 96 to the base of the power transistor 98. The combined
effect of the operational amplifier 92 and power transistor 98 is
to reshape the output of the photocell 70 into a square wave. In
other words, an incandescent light source is incapable of
generating a true square wave output; hence, the signal received by
the photocell 70 might be described as a "rounded" square wave. The
combined high gain of the operational amplifier and the transistor
98 serves to reshape the wave and give a square wave output at the
terminal 100.
FIG. 3 is an electrical schematic diagram showing the matrixing and
comparing circuit indicated in FIG. 1 at 26. As already indicated,
this circuit is designed to combine and compare all light phase
outputs from the amplifier and wave shaper circuits 24 with the
corresponding phase output from the square wave generator 10. When
they compare correctly, there will be an output pulse for each
cycle of each phase from this circuit.
FIG. 3 shows a matrixing and comparing circuit which will
accommodate outputs from 16 amplifiers nand wave shapers as
described above. The circuit includes two seventeen input
NAND-gates, 102 and 104. The NAND-gate 102 is hard wired by the
line 106 to the Phase A output of the square wave generator 10, The
contacts 108 will be connected to the amplifier and wave shapers 24
associated with a light source energized by the Phase A supply.
Similarly, the NAND-gate 104 is hard wired as at 110 to the Phase B
output of the square wave generator 10, while the contacts 112
receive the output from the amplifier and wave shapers associated
with the light sources energized by the Phase B supply. All inputs
from the wave shapers of both phases are inverted by the inverters
114 and fed to the opposite NAND gate.
It will be recognized by the skilled worker in the art that the
foregoing systems compares only "lows." Each time there is a full
and complete comparison, there will be an output pulse from the
NAND gate. If any wave shaper 24 output stops in either the "high"
or "low" state, one of the two NAND gates will not give an
output.
No specific circuitry has been shown for the remaining components
identified in FIG. 1. It is believed that in the light of the
objectives to be accomplished as set forth earlier, development of
the digital circuitry for obtaining the result is well within the
purview of the skilled worker in the art.
While the described embodiment of the invention relates to a guard
system for a machine tool having a reciprocating ram, it will of
course be understood that it is equally applicable to any machine
tool for other operation wherein an operating cycle, for safety
reasons, should be interrupted upon the presence of personnel in a
predetermined danger zone.
No limitations are to be inferred or implied from the foregoing
exemplary embodiment, except insofar as specifically set forth in
the claims which follow
* * * * *