GB1579020A - Machine guards - Google Patents

Description

(54) MACHINE GUARDS (71) I, DONALD VIVIAN PULL, of 2, Elm Close, Campton, Bedfordshire, a British subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to machine guards of the type which use a "curtain" of radiation intended to be positioned at a machine, for example a press or press brake, for the purpose of stopping or preventing operation of the machine should the curtain of radiation be interrupted by an operator, except at those times when the guard is deliberately muted or otherwise rendered inoperative to permit a workpiece or the operator to approach the machine.

It is an object of the present invention to provide an improved machine guard.

The present invention consists in a safety guard for a machine, which includes a transmitter having one or more units arranged to be fired to produce a train of pulses of radiation directed towards a receiver which includes a series of sensors each arranged to be switched on one at a time in turn in readiness to respond to a particular pulse of radiation in the train, an electrical circuit arranged so that only when a sensor has received its pulse of radiation is that sensor switched off and the next succeeding sensor in the series switched on in readiness to receive its particular pulse of radiation in the train, and a monitoring circuit for providing a stop signal when the sequence of switching of the sensors is interrupted.

In the accompanying drawings:- Figure 1 is a schematic diagram showing the operation of one form of machine guard according to the present invention, and Figure 2 illustrates a feature of the guard of Figure 1.

In carrying the invention into effect according to one convenient mode by way of example, figure 1 shows a machine guard which includes a transmitter TX and receiver RX coupled together with control circuitry.

The transmitter TX has a series of sixteen transmitters Tl, T2, , each in the form of a light-emitting diode directed towards the receiver RX, and the receiver RX has a series of sixteen receivers Rl, R2, .........., each in the form of a sensor for infra-red radiation and each associated with its own enable gate EN and inhibit gate INH.

There is thus established between the transmitter TX and the receiver RX a "curtain" of infra-red radiation. This curtain is positioned in the front danger area of a machine to serve as a safety guard arranged to stop the operation of the machine and give a warning should the radiation incident upon the receiver RX be interrupted.

The control circuitry includes a clock 11 providing a constant time base operating at a fixed frequency of 4 Khz. On switching on, the first clock pulse constitutes an initiation signal which resets the entire system by preparing transmitter drive 12 to fire the first transmitter T1 and by preparing only the first receiver R1 of the receiver RX to respond to infra-red radiation by switching off its inhibit gate INH and switching on its enable gate EN via logic circuits 13 and 14.

The second pulse from clock 11 causes, via transmitter drive 12, the first transmitter T1 to be fired emitting a cone of infra-red radiation of 5 micro seconds duration.

When this radiation impinges upon receiver Rl, a pulse A will be fed to monostable circuit 15 for odd pulses which will cause logic circuit 14 to feed a pulse to switch on the inhibit gate INH of receiver Rl and to switch off its enable gate EN.

When this happens, receiver Rl is no longer sensitive to infra-red radiation but a pulse is fed from the enable gate EN of the first receiver R1 to the inhibit gate INH of the second receiver R2, thereby switching off this inhibit gate INH and switching on the enable gate EN of the second receiver R2, thereby rendering this receiver responsive to infra-red radiation.

The third pulse from clock 11 then causes transmitter T2 to be fired and when its radiation impinges upon receiver R2 a pulse B is fed to monostable circuit 17 for even pulses, receiver R2 consequently then being rendered insensitive and receiver R3 responsive in the manner previously described.

This cascade action will continue until receiver R16 (not shown) is first switched on and then off whereupon a pulse is sent via line 16 to cause receiver R1 to be made sensitive again and a further cycle is repeated, the danger area in front of the machine being scanned some 250 times each second.

Any interruption of the curtain is detected in the following manner. A comparator circuit 18 receives trains of pulses from the odd receiver Rl, R3, etc. via monostable 15, from the even receivers R2, R4, etc. via monostable 17 and from the inhibit and enable gates INH and EN over lines 1, 2, 3 2,3,.......

etc. The presence of all pulses in their correct phase relationship is monitored, using missing pulse techniques, and when all is well two output signals OPI and OP2 in anti-phase are produced by logic circuit 14, and these signals are used in conventional manner in an interlock with the machine controls to permit operation of the machine.

If a missing or wrong pulse is detected, two stop signals will be generated at outputs OPI and OP2, thereby preventing further operation of the machine. The system will then also generate continuously initiation signals endeavouring to restart the cascade sequence for transmitter Tl onwards until the interruption is removed. It will be appreciated that stop pulses can be produced not only when the curtain is interrupted, but also when there is a malfunction in a component of the system.

It will also be appreciated that since the transmitters T1, T2 etc. are fired in turn and since the receivers R1, R2 etc. are made sensitive one at a time in turn, it does not matter if each receiver receives radiation from a transmitter other than the one with which it is associated. The alignment of the transmitter and receiver is thus not critical and figure 2 shows, by way of example, that receivers Rl and R2 may lie within the boundary 1 of the radiation from transmitter T1, receivers R1, R2 and R3 may lie within the boundary 2 of the radiation from transmitter T2 and so forth.

Indeed, it is possible that the radiation from all or any transmitter, such as transmitter T4, may, as at 41, encompass all the receivers. In this case, if desired, the transmitters T1, T2 etc. could be arranged in a vertical series with the receivers R1, R2 etc. in a horizontal or inclined series.

Thus the guard described above avoids many of the disadvantages associated with phtoto-electric systems, such as adjustment of sensitivity alignment and focus, and the guard also has the advantage that it can operate equally well in total darkness or full sunlight.

Although it is intended that in normal applications a number of diodes and a number of sensors should be used, it will be understood that for certain applications one diode and two sensors may provide an adequate configuration, the diode being fired twice each cycle, once for each sensor.

It will be appreciated that, if necessary, the transmitter and the receiver may be on the same side of the curtain, a mirror being provided on the other side of the curtain to reflect radiation from the transmitter back to the receiver. Alternatively, one or more intermediate mirrors may be provided to provide a curtain in two or more planes.

Although the invention has been described by way of example with reference to the use of light-emitting diodes as the transmitters it will be appreciated that other forms of electromagnetic or other radiation may be used. For example, the transmitter units may generate ultra-violet or ultrasonic radiation.

WHAT I CLAIM IS: 1. A safety guard for a machine, which includes a transmitter having one or more units arranged to be fired to produce a train of pulses of radiation directed towards a receiver which includes a series of sensors each arranged to be switched on one at a time in turn in readiness to respond to a particular pulse of radiation in the train, an electrical circuit arranged so that only when a sensor has received its pulse of radiation is that sensor switched off and the next succeeding sensor in the series switched on in readiness to receive its particular pulse of radiation in the train, and a monitoring circuit for providing a stop signal when the sequence of switching of the sensors is interrupted.

2. A safety guard as claimed in claim. 1, wherein the electrical circuit includes an inhibit gate and an enable gate associated with each sensor, the arrangement being such that when a sensor receives its pulse of radiation its inhibit gate is switched on and its enable gate switched off, the switching off of the enable gate causing the switching off of the inhibit gate and the switching on of the enable gate associated with the next succeeding sensor in the series.

3. A safety guard as claimed in claim 1 or 2, wherein there are an equal number of transmitter units and sensors, the units being arranged to be fired one at a time in sequence and the sensors being arranged to be switched on in a sequence corresponding to the transmitter unit sequence.

4. A safety guard as claimed in claim 1, 2 or 3, wherein an electrical circuit is provided for generating two trains of pulses corresponding to reception of radiation by alternate sensors, the monitoring circuit being arranged to detect missing or wrong pulses in these two trains.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. pulses, receiver R2 consequently then being rendered insensitive and receiver R3 responsive in the manner previously described. This cascade action will continue until receiver R16 (not shown) is first switched on and then off whereupon a pulse is sent via line 16 to cause receiver R1 to be made sensitive again and a further cycle is repeated, the danger area in front of the machine being scanned some 250 times each second. Any interruption of the curtain is detected in the following manner. A comparator circuit 18 receives trains of pulses from the odd receiver Rl, R3, etc. via monostable 15, from the even receivers R2, R4, etc. via monostable 17 and from the inhibit and enable gates INH and EN over lines 1, 2, 3 2,3,....... etc. The presence of all pulses in their correct phase relationship is monitored, using missing pulse techniques, and when all is well two output signals OPI and OP2 in anti-phase are produced by logic circuit 14, and these signals are used in conventional manner in an interlock with the machine controls to permit operation of the machine. If a missing or wrong pulse is detected, two stop signals will be generated at outputs OPI and OP2, thereby preventing further operation of the machine. The system will then also generate continuously initiation signals endeavouring to restart the cascade sequence for transmitter Tl onwards until the interruption is removed. It will be appreciated that stop pulses can be produced not only when the curtain is interrupted, but also when there is a malfunction in a component of the system. It will also be appreciated that since the transmitters T1, T2 etc. are fired in turn and since the receivers R1, R2 etc. are made sensitive one at a time in turn, it does not matter if each receiver receives radiation from a transmitter other than the one with which it is associated. The alignment of the transmitter and receiver is thus not critical and figure 2 shows, by way of example, that receivers Rl and R2 may lie within the boundary 1 of the radiation from transmitter T1, receivers R1, R2 and R3 may lie within the boundary 2 of the radiation from transmitter T2 and so forth. Indeed, it is possible that the radiation from all or any transmitter, such as transmitter T4, may, as at 41, encompass all the receivers. In this case, if desired, the transmitters T1, T2 etc. could be arranged in a vertical series with the receivers R1, R2 etc. in a horizontal or inclined series. Thus the guard described above avoids many of the disadvantages associated with phtoto-electric systems, such as adjustment of sensitivity alignment and focus, and the guard also has the advantage that it can operate equally well in total darkness or full sunlight. Although it is intended that in normal applications a number of diodes and a number of sensors should be used, it will be understood that for certain applications one diode and two sensors may provide an adequate configuration, the diode being fired twice each cycle, once for each sensor. It will be appreciated that, if necessary, the transmitter and the receiver may be on the same side of the curtain, a mirror being provided on the other side of the curtain to reflect radiation from the transmitter back to the receiver. Alternatively, one or more intermediate mirrors may be provided to provide a curtain in two or more planes. Although the invention has been described by way of example with reference to the use of light-emitting diodes as the transmitters it will be appreciated that other forms of electromagnetic or other radiation may be used. For example, the transmitter units may generate ultra-violet or ultrasonic radiation. WHAT I CLAIM IS:

1. A safety guard for a machine, which includes a transmitter having one or more units arranged to be fired to produce a train of pulses of radiation directed towards a receiver which includes a series of sensors each arranged to be switched on one at a time in turn in readiness to respond to a particular pulse of radiation in the train, an electrical circuit arranged so that only when a sensor has received its pulse of radiation is that sensor switched off and the next succeeding sensor in the series switched on in readiness to receive its particular pulse of radiation in the train, and a monitoring circuit for providing a stop signal when the sequence of switching of the sensors is interrupted.

2. A safety guard as claimed in claim. 1, wherein the electrical circuit includes an inhibit gate and an enable gate associated with each sensor, the arrangement being such that when a sensor receives its pulse of radiation its inhibit gate is switched on and its enable gate switched off, the switching off of the enable gate causing the switching off of the inhibit gate and the switching on of the enable gate associated with the next succeeding sensor in the series.

3. A safety guard as claimed in claim 1 or 2, wherein there are an equal number of transmitter units and sensors, the units being arranged to be fired one at a time in sequence and the sensors being arranged to be switched on in a sequence corresponding to the transmitter unit sequence.

4. A safety guard as claimed in claim 1, 2 or 3, wherein an electrical circuit is provided for generating two trains of pulses corresponding to reception of radiation by alternate sensors, the monitoring circuit being arranged to detect missing or wrong pulses in these two trains.

5. A safety guard as claimed in any one of

claims 1 to 4, wherein further pulses indicative of the switching of the sensors are derived and the monitoring circuit is also arranged to detect missing or wrong pulses in these further pulses.

6. A safety guard as claimed in any one of the preceding claims wherein the monitoring circuit is also arranged to monitor the firing timing of the transmitter units.

7. A safety guard as claimed in any one of claims 1 to 6, wherein each transmitter unit is a light-emitting diode.

8. A safety guard substantially as described with reference to the accompanying drawings.