IMPROVEMENTS RELATING TO SAFETY MECHANISMS FOR INDUSTRIAL MACHINERY

Abstract: A method and apparatus for detecting opaque members when within detection space. The method includes the steps of sequentially effecting a radiant energy transmission across a detection space (3) from a plurality of spaced apart sources (1) and causing a detection signal when such transmission is not sufficiently detected at each of a plurality of receivers (2) at sequentially correspondingly selected locations. The apparatus includes a plurality of radiant energy transmitting devices (1), a corresponding plurality of radiant energy receivers (2) and associated electronic control means, the transmitting means being activated in a predetermined sequence during finite time periods. There are also means provided to detect, between the finite time periods, any stray sources of radiant energy. The apparatus can be interfaced with power machinery to provide a safety mechanism therefor, or be used in an intrusion alarm system.

Description: "IMPROVEMENTS RELATING TO SAFETY MECHANISMS FOR INDUSTRIAL MACHINERY This invention relates to safety apparatus intended for use in conjunction with industrial machinery especially of a type such as presses and guillotines . 5. While reference is made to the use of this invention in connection with industrial machinery, it is to be clear that the concept is not necessarily limited to simply being applied in respect of industrial machinery and at least the broader concepts 10. are intended to be universally applicable. Application such as intrusion alarm systems are also possible with this invention. It is known to use beams of focussed light in spatial detection apparatus, the light being produced 15. by means of incandescent bulbs arranged in a row on one side of the space to be monitored, said bulbs being arranged to project light onto a corresponding row of photo-electric detection devices located at the opposite side of the space to be monitored. 20. Such arrangements suffer because it is difficult to confine the light from the incandescent bulbs so that this will only fall on the corresponding one detector and even slight dislodgement of lenses or other devices needed to assist in this isolation can 25. lead to the guard being ineffective. _O PI /. IPO -Λ, Likewise the cost in providing the lenses and having these constantly monitored to ensure that they are safe is a disadvantage. The object of this invention is to generally 5. mitigate some of the problems expressed above. Other aspects of the invention relate to providing for a very safe combination of detection devices suitable for guarding machinery especially of a type such as press brakes, guillotines or presses. 10. According to one form of this invention then this can be said to reside in the method of detection of opaque members within a detection space which is characterised according to this invention in that it includes the steps of sequentially effecting a radiant 15. energy transmission across a detection space from a plurality of spaced apart sources and causing a detection observed signal when such transmission is not sufficiently detected at each of a plurality of correspondingly located and sequentially 20. correspondingly selected locations. In a further form, it can be said to reside in a method of detecting opaque objects when such an objection is in a detection space between selected transmission and detection members, the members 25. comprising a plurality of radiant energy transmitters and receivers aligned as pairs across the detection OMPI space, the method according to this invention being characterised by including the steps of activating all transmitters during a selected period of time but only one or some but not all during a smaller period of 5. time within the selected overall period of time and interrogating corresponding receivers at least within the period of activation of each oppositely located transmitter and effecting a detection observed signal if the transmitted beam is not adequately received by 10. the corresponding receiver during the mutually effective period. This in one form then conceives sequentially activating both a transmitter and a receiver pair and this therefore enables a designer to place adjacent 15. transmitters and receivers in very close vicinity and the transmitter effect on any other receiver than that activated will be of no consequence. There is therefore immediately a much greater flexibility in the design and much less if any need to 20. incorporate condensers to align any radiation from the transmitters. One difficulty with the arrangement described is the fact that if there is an alternate radiant energy source, the detector could be inadvertently activated 25. during its activation period even though an obstacle is across the transmitter beam. It is therefore a preferred feature and it is regarded as an important feature that each of the receivers is interrogated at least during some period other than the mutually activated period between the 5. transmitter and receiver, and arranging that a stray source detected signal is effected if a selected level of radiant energy is "seen" during this other period. In practice then this stray source detected signal can be used to de-activate the system until any 10. interfering outside energy source is removed. Such an arrangement is conventionally used to detect an intrusion into a dangerous zone of industrial machinery such as a press or guillotine. It is advantageous that such detecting apparatus 15. or method not be operative during some cycle portion of some of these machines. As an illustration, on the downstroke of a press, it is dangerous to have any intrusion into the operating area but this is not the case upon the 20. upstroke. Detectors are therefore proposed which detect the status in the cycle of the particular machine. The problem however is that if any of the detectors fail then the guard effect becomes useless as the machine may well cycle through the operative and non-operative strokes without limit. 5. It is conventional then to provide normally a detection device detecting a commencement of a power stroke or a down stroke and also a device to detect the lowermost position but the problem is to provide that in the event of failure of either of these 10. devices this is very quickly detected and the machine rendered safe. Accordingly, there is a first detector detecting a commencement of a downstroke, a second detector detecting completion of a downstroke and according to 15. a preferred feature, a third detector at least, which detects the position of the operating member of the machine at least during the so called downstroke. It is to be understood that the use of the word "downstroke" is merely illustrative and intended to 20. indicate the cycle of a machine which is considered dangerous . As such, it perhaps might be better to refer to this period of a cycle as the operating period but such definition is not intended to be limiting in any 25. sense to the overall inventive concept in relation to this feature. Consequentially then, if any of the machine cycle status detectors should fail , a dangerous situation could eventuate and it is therefore a further feature of this invention that in combination with apparatus 5. to detect opaque objects when in a detection space between respective members of detecting means there shall be included such machine cycle status detection means related to the detection of the location of the operating member of the industrial machine there being 10. at least three such detecting members two of which are to detect commencement and a finalization of an operative stroke and at least one other detection means responsive to the position of the operating member at least during the operating stroke, the 15. invention characterised in that there are means arranged such that upon the change in state of a selected one of the detection means , this will activate a comparison of at least any two of the said detection means and if a state other than that 20. expected is detected, then the means are arranged to effect a fault detected signal. The problem with using any detection means as a safety device is that if any one of these devices should fail either by component failure or by 25. mechanical failure in the event that the detection means is a switch, a very dangerous situation could exist especially where an operator becomes dependent upon relying on the intrusion detector means. Ϊ WIF Because the various switches or detection means where these are not simply switches are themselves constantly in operation and changing state, it is generally a very difficult procedure to provide such 5. significant safety. The concept then is to provide a means whereby each of the two detection means are checked through each cycle of operation of the industrial machine by using what might be termed a further detection means 10. or in a preferred instance a switch and have this effect what might be termed an interrogation of the state of the othertwo switches. Fairly obviously, once the concept of an interro¬ gation by a third switch is conceived, the various 15. methods by which such interrogation can be effected will be apparent to those familiar with this art. Accordingly in the preferred illustration which will subsequently be described, one particular inter¬ rogation system together with hardware will be 20. described but it is to be clear that the invention is not to be taken as necessarily limited to such a precise description. A further feature according to this invention in which may be considered at least in a preferable 25. arrangement to be in combination with the previous features, involves the problem that in relation to industrial machinery of the type described it is sometimes necessary to provide a high voltage alternating current which couples with a low voltage 30. direct current signal. Q. PI_ VIPO In a preferred arrangement, it is noted that a main relay control output is used to control signi¬ ficant AC voltage currents by reason of slave switching. 5. To detect the status of the AC controlling relay, the voltage appearing across the relay contacts can be examined but this of course will be high voltage and alternating. To interface this critical portion ^ of the circuit 10. with the control circuit which has low voltage power supplies and which is sensitive to voltage differentials and voltage spikes has hitherto been a problem. Accordingly, to avoid susceptibility of devices 15. such as light emitting diodes, it has been discovered that all of these problems are overcome by connecting a gaseous discharge lamp such as a neon lamp across the contacts and then detecting the light output of this device by conventional solid state low voltage 20. members. Such devices are generally known and are usually called opto-couplers but in relation to conventional devices these comprise a light emitting diode with a photo-transistor in combination. 25. Such an arrangement however suffers from the disadvantage that transient voltages can connect through a voltage dropping capacitor coupled to the LED which can be sufficient to destroy the LED within the opto-coupler. OMP We have discovered that this problem can be over¬ come by providing a gaseous type lamp such as a neon lamp as the higher voltage sensitive light transmitter. To assist in a better understanding of this 5. invention this will now be described with the assistance of drawings in which: FIG 1 is a perspective view showing a press brake and including means blocking access to this press brake including transmitter and receiver arrays, 10. FIG 2 illustrates in a very schematic manner the way in which a transmitter array and a receiver array can be aligned and how a first of the transmitter units can transmit a radiant energy pattern which will significantly extend across adjacent receivers without 15. of course having this interfere with the effective operation of the apparatus , FIG 3 is a block diagram of the electronic control members controlling the detection apparatus, FIG is a timing diagram for the system this 20. being also according to the preferred embodiment, FIG 5 is the timing circuit, FIG 6 illustrates the method by which infra-red emitting diodes are controlled by a multiplexer, FIG 7 illustrates in block diagram the position 25. sensing apparatus logic arrangement and FIG 8 illustrates the opto-coupler arrangement according to the preferred embodiment. Referring to FIG 1 this is shown part of trans¬ mitting and detection arrays 1 and 2 a detection space 3 between these arrays being continually scanned by a single time multiplexed energy beam shown typically at 5. 4. In this preferred example, there are indeed 3 separate arrays so as to provide good cover these being shown at 5, 6 and 7. The vertical array 5 is pivotally supported at 10. pivot support 8. To illustrate how adaptable the apparatus is the vertical array 5 can be used with one side horizontal while the other array is vertical and at least with some distances this will still operate very 15. effectively. In this way, the press brake 9 can be operated with significant safety. Referring now to FIG 2, this is schematically arranged so as to show perhaps more visually the 20. effect of the overlap from the transmitters 1 to the receivers 2 and once again shows the detection space 3. The detection space 3 between transmitting and receiving units is continually scanned by a single time multiplexed energy beam 4, the beam being produced by sequentially energising each of the trans- 5. mitters 1 by means of a short duration current pulse. The energy pulse generated by each of the transmitters in this way is projected onto the corresponding detector 2 at the receiving end, as shown in FIG 2 (where the first transmitter has been energised). If 10. wide angle radiation emitters are employed, alignment between transmitting and receiving units is not critical . Associated with each radiation detector is an interface circuit which performs the functions of 15. detector signal amplification, and conversion of the amplified signal to an "0" or "1" logic level signal, depending on whether or not radiation is impinging upon the detector. When a particular transmitter is energised, radiation from that transmitter is 20. projected onto one or more of the detectors at the receiving end, the number of detectors illuminated by the energy beam depending on the directional charac¬ teristic of the transmitters. In practice the trans¬ mitting and receiving units are aligned with respect 25. to each other in such a way as to cause the centre of the radiation beam produced by each transmitter to coincide as closely as possible with the location of the corresponding detector at the receiving end. By sampling only the signal produced by the radiation 30. detector corresponding to an energised transmitter, it can be determined whether or not an obstruction exists along the line joining that transmitter/detector pair. This process is repeated indefinitely and at high speed (200 Hz being typical) for all trans¬ mitter/receiver pairs in the system, thereby causing the zone between transmitting and receiving units to 5. be continually scanned by means of a rapidly moving energy beam. The radiation detectors are sampled sequentially by means of an electrical circuit which time multiplexes each detector output onto a single channel. Provided no obstructions exist between trans- 10. mitter and receiver units, a pulse train occurs on this single channel. However, should one or more of the receiver units fail to detect the energy pulse generated by the corresponding transmitter (either as a result of obstruction between transmitter and 15- receiver units, or as a result of transmitter or detector failure) , the one or more of the pulses normally observed will be missing. By means of a missing pulse detector circuit, an output signal is generated in the event of path obstruction or 20. transmitter/detector failure. As an additional safeguard against circuit failure, an additional cycle is associated with each radiation transmit/receive cycle. Just prior to energising each transmitter the signal output of the 25. corresponding receiver is sampled. If the signal level is not zero, either a circuit failure has occurred, or sufficient extraneous radiation is present, and has been sensed by that detector. Under these circumstances, a stray source signal is 30. generated, which can be used to prevent further operation of a machine when the spatial detection apparatus is used as an industrial safety guard. . OMPI ' In order to facilitate serviceability of the system in the event of circuit failure, a faulty-channel diagnosis circuit has been incorporated into the system. Should any one of the system 5. channels become defective in any way, the binary representation of the faulty channel is immediately stored in digital storage elements, such as D-type flip-flops, the states of which are displayed by means of any convenient visual readout device, such as a row 10. of light emitting diodes. By converting the binary number represented by the LEDs into decimal form, the faulty channel is immediately known, thus allowing rapid repair by field service personnel. A block diagram of the spatial detection 15. apparatus is shown in FIG 3. A clock pulse generator 10 supplies a pulse train of fixed frequency to the binary counter 11. The outputs of the counter control electronic switching units 12 and 13, there being "n" • binary inputs required in a system having 2 20. channels. The apparatus depicted in FIG 3 comprises 15 transmitter/receiver channels, and so 4 binary control lines are required to control the switching of 12 and 13, these being designated Q_ , Q , Q. and Q_. in FIG 2. Thus the channel selected at any instant of 25. time is represented by the binary number Q Q Q Q , where Q are binary digits (i.e. "0" or "1"). OMPI ~ IPO ~ The least significant bit of the binary counter 11 (i.e. Q ) is used to further subdivide the time interval allocated to each of the 15 channels. The time sub-interval corresponding to G = 0 provides a 5. check on the correct functioning of the system, by means of logic inverter gate II, logic AND gate A2, and logic OR gate 01. For all channels in the system, the signal output from each radiation receiver should be zero during each time interval corresponding to Q 10. = 0, since all transmitters are deactivated during that time interval. Thus the signal at point "A" in FIG 3 should always be. at logic 0 level whenever Q = 0. If this is not the case, then either a source of extraneous radiation has been detected, a transmitter 15. has remained on, a receiver interface circuit output has become stuck at logic 1 level or a failure of 13 has occurred. Logic gate A2 is enabled via II whenever Q = 0 , thereby enabling logic signals arising as a result of any of the abovementioned error 20. conditions to occur at point "B" in FIG 3. These signals pass through to point "E" via OR gate 01. The second time sub-interval associated with each of the 16 channels occurs when Q = 1. Monostable 14 is triggered on the logic 0 to 1 transition of Q 25. producing a short duration voltage pulse at its Q output. This voltage pulse is then applied __O V 7 " WI via 12 to one of the radiation transmitters, the transmitter energised being selected according to the state of binary counter outputs Q ... After pro- pagation delays, a signal pulse will occur at all 5. detector outputs corresponding to those detectors illuminated by the energy beam produced by the energised transmitter. The detector output corresponding to the activated transmitter is selected by means of 13, thereby giving rise to a voltage pulse 10. at point "A", provided the path between the selected transmitter/receiver pair is not obstructed. This pulse passes through to point "C" via AND gate Al , which is enabled whenever Q = 1. Thus, a continuous pulse train exists at point 15. "C" , provided no obstructions to the radiated energy exist between any of the transmitter/detector pairs. The pulse repetition frequency at point "C" is identical to the signal frequency observed at the Q output of 11. This frequency, divided by the 20. number of channels in the system, equals the number of times per second that the space between transmitter and receiver units is scanned. The pulse train occurring at point "C" (FIG 3) is fed to a missing pulse detector circuit, designated 15 25. in FIG 3. The output of 15 (point "D" ) undergoes a transition from logical 0 to 1 if one or more of the pulses normally occurring at point "C" are missing. 15 . Thus it is seen that the signal at point "E" is logical 1 whenever a path obstruction exists, when a circuit failure has occurred, or when extraneous radiation has been detected. When the spatial 5. detection apparatus is used as an industrial safety guard in conjunction with potentially hazardous machinery, signals occurring at point "E" are interfaced to the emergency-stop control circuitry of the machine. 10. A timing diagram for the system is shown in FIG 4. The output waveform of the clock pulse generator CPG is illustrated in FIG 4(a). The frequency of the signal generated by 10 is selected according to the number of channels employed in the spatial detection 15. apparatus, as well as in accordance with the desired rate of scan of the area being monitored. For example, if a scan rate of 200 times per second is required in a system comprising 16 channels, the required frequency of CPG is given by 2 x 16 x 200 = 6400 Hz. 20. The circuit of a suitable clock pulse generator is shown in FIG 5. The output of 10 is fed into the clock input of a binary counter, the signal outputs of which are shown in FIGS 4 (b) - (f). The waveforms indicated in FIG 4 25. correspond to a counter in which clocking occurs 'on negative edges. With reference to FIG 3 the Q output serves the dual purpose of triggering Ml (thus energising the selected radiation transmitter), and subdivision of the time interval associated with each 30. channel into two smaller time intervals, as previously described. FIG 4(g) illustrates the short duration pulses produced by Ml . O ' The remaining outputs of the counter CTR are used to select one of the 16 transmitter/receiver pairs, via switching units 12 and 13. For a 16 channel system, 4 control signals must be generated by the 5. binary counter, these being designated Q„ , Q,, Q and Q 5 , in FIGS 3 and 4. The switching action of the switching unit 12 (which functions as a demultiplexer) is illustrated in FIG 4 (h) , in which sequential energisation of the 10. radiation transmitters is depicted. FIG 6 indicates the method by which infra-red emitting diodes are controlled by a demultiplexer. The demultiplexer used may be either a digital or an analogue type. 15. FIG 4 (i) illustrates the time intervals associated with each channel during which the corresponding detector circuit output is sampled. It can be seen that these sampling intervals commence at the same time as energisation of the transmitter for 20. any particular channel. Output signals produced by the detectors during the time intervals shown in FIG 4 (i) are multiplexed onto a single channel (point "C" in FIG 3) by means of 13. Switching units 12 and 13 are switching in 25. synchronism with each other by means of an inter¬ connecting cable between transmitting and receiving units, as indicated in FIG 3. Thus in the event of no obstructions and correct circuit functioning a pulse train as shown in FIG 3 (k) occurs at point "C" in FIG 2. This pulse train is fed to a retriggerable monostable multivibrator whose "on" period is slightly longer than the normal pulse 5. repetition period of the signal depicted in FIG 4 (k). Hence if one or more of the pulses are missing (either as a result of an obstruction between transmitting and receiving units or as a result of a circuit failure), the output of the monostable returns 10. to the logical 0 level at some time after the missing pulse was expected. FIG 4 (k) illustrates the case where the 6th transmitter/receiver pair has been obstructed, and FIG 4 (1) shows the resultant output of the retriggerable monostable. This signal is shown 15. inverted in FIG 4 (m) . The signal of FIG 4 (m) appears at point "D" in FIG 3 under conditions of path obstruction or circuit malfunction. The time intervals during which the circuit self-check cycle occurs are shown in FIG 4 (j). These 20. intervals correspond to Q = logical 0. Any signals detected during any of these time intervals cause a logical 1 signal at point "B" in FIG 3. The channel-fault diagnostic circuit comprises a number "n' of simultaneously clocked D-type flip-flop elements or the like, where the number of channels in the system equals 2 . The D-inputs of the flip-flops 5. are connected to the binary counter outputs in accord¬ ance with FIG 3, while the Q-outputs are used to drive an array of display devices, such as light emitting diodes. By deriving a "latch" or clock signal from point "E" in FIG 3, the D-type flip-flops 16 will 10. display at 17 the state of the counter 11 when the circuit malfunction was detected. Note that for errors detected during the time interval corresponding to Q = 0, the binary number displayed corresponds to the actual state of the counter that prevailed when 15. the error occurred, whereas for faults giving rise to one or more missing pulses (such as transmitter or detector failure), the binary counter has been incremented to the next channel before the error has been detected. Thus by allowing for this factor 20 • faulty channels can immediately be located. Also note that the D-type flip-flops 16 are latched whenever an obstruction (i.e. not a circuit fault) occurs, although this is of no consequence in practice. Any number of channels can be incorporated into 25. the spatial detection apparatus as hereinbefore described, although for a given clock pulse generator frequency, the response time of the apparatus (i.e. the time taken to sense and signal the presence of an obstructing object between transmitting and receiving 30. units) will increase as the number of system channels is increased. The maximum clock frequency is also limited by such factors as the response time of the radiation detectors, and by the maximum frequency square wave that can be conveniently transmitted, via 35. the cable interconnecting the transmitter and receiver units . By using infra-red emitting diodes as the trans¬ mitters, instead of a bank of incandescent lamps such as has been used in the past, glare which might distract an operator is avoided. The use of infra-red 5. radiation also avoids interference from ambient light which might occur for example in a brightly illuminated workshop or factory area. The spatial detection system described herein can be used in a variety of applications, including 10. security guarding systems. The position sensing apparatus will be described with reference to FIG 7. The preferred embodiment of the invention shown in FIG 7 provides a fail safe system for generating a guard inhibit/enable signal 15. when the machinery to which the position sensing apparatus is fitted incorporates a safety guard detector. The functioning of the apparatus will now be described. The three sensing switches employed in the 20. apparatus are shown 'in FIG 7 where they are designated Top Dead Centre 18, Bottom Dead Centre 19and Mid Position 20. The 18 and 19 switches are mounted on the machinery 9 in such a way as to provide a closure when the machine is at a start of an operative stroke 25. (Top Dead Centre) or at the end of an operative stroke (Bottom Dead Centre) respectively. The times at which these two switches open again is irrelevant. The Mid position switch 20, however, must be arranged so that it remains open when the press brake for example is 30. between switch 18 and the halfway-down point, and closed when the brake is between the halfway-down point and switch 19. Thus, the signal at point B in FIG 7 is at the logic 1 level whenever the press blade is in the bottom OM V/IP half of its movement, while the signal at D is logical 1 only when the blade is in the top half of its movement. The signals derived from switches 18 and 19 are passed through differentiator networks 21 and 22, 5. and so positive going pulses occur at A and C when the press reaches 18 and 19 positions respectively. The pulse occurring at point A is fed to the S input of the S-R flip-flop 23, while the pulses occurring at point "C" are fed to the R input. Thus the Q output 10. of 23 is at logical 1 level whenever the information derived from switches 18 and 19 indicates that the press is moving downwards. The Q output is used as an enable signal for the safety guard detector. The arrangement described so far provides a satis- 15. factory means for generating the required guard enable signal, provided that switches 18 and 19 do not fail. If 18 fails, the press will never be guarded, giving rise to a dangerous condition while if 19 fails, the press will always be guarded, giving rise to an 20. inconvenience rather than a hazardous condition. However, the apparatus depicted in FIG 7 monitors the functioning of both the 18 and the 19 switches, in addition to the switch 20. If any of the switches in the system should fail, an error signal is generated, 25. which is interfaced to the emergency stop system within the machinery. The apparatus of FIG 7 carries out four individual checks on the switches during each machine cycle. The first check occurs at the instant when 30. switch 20 closes, which gives rise to a logical 1 signal at B, and a momentary logic 1 pulse at E, by means of D3. The signal at E is ANDed with the Q output of 23 by means of A2. Thus the signal at H is a momentary pulse if the guard is not enabled in the 35. downwards direction, either as a result of failure of switch 18 or 23. This pulse appears at the output 01. The second check occurs when the press reaches the 19 position. When this occurs, a pulse is generated at C, via Dl . If switch 20 is faulty and has not closed, point D will be at the logic 1 level. 5. Thus the pulse at C will also occur at J via A . Thus this check tests for a permanently open mid position switch, and for an open circuit in the interconnecting cable. The pulse at J occurs at the output of 01. The third check occurs when switch 20 opens 10. again, which is halfway between 19 and 18 positions. When this occurs, a logic 1 pulse is produced at F. If the BDC switch 19 has failed to reset 23, the Q of 23 will be at logic 1 level, and so the pulse at F also occurs at I, and thence at the output of 01. 15. The fourth and final check occurs when the 18 switch closes. This produces a logic 1 pulse at point A. However, if switch MP 20 has remained closed, the signal at point B will be at the logic 1 level. Therefore, the pulse at point A also occurs at point 20. G, via Al. As before, this pulse is passed through to the output of 01. Thus, the system provides continual self-checking, producing a momentary output pulse at the output of 01 in the event of failure of any one of 25. switches TDC 18, MP 20 or BDC 19 during one machine cycle. This output pulse can be used to latch a further flip-flop, and the output of this flip-flop can be interfaced to the machine stop circuit. f O FIG 8 illustrates the electrical interfacing circuitry associated with the invention. With this particular embodiment, the main relay control output from the diagnostic board is used to 5. control switching of a solid state relay. The difficulty is to interconnect the AC high voltage signal with the low voltage logic and detection circuitry and to do this in such a way that it is very reliable and promote the general safety of the 10. apparatus. Accordingly the gas discharge lamp 24, which is a neon lamp is connected via a suitable current limiting resistor 25 to the high voltage point within the machinery from which a control signal is to be 15. derived, as shown in FIG 8. The neon lamp 24 illuminates the phototransistor 26 causing the voltage at point A to rise in response to the light pulses produced by the neon lamp when the high voltage supply is an AC source. The capacitor 28 serves to remove 20. the ripple occurring across the load resistor 27, and the time constant RC should be chosen in excess of 10 milliseconds. The signal across the load resistor 27 can then be fed through inverting amplifiers 29 and 30 into a device such as a Schmitt trigger, the output of 25. which will indicate the state of the high voltage signal derived from the machinery. For example, if an inverting Schmitt trigger is employed, the output of this Schmitt trigger will be at the logical o level whenever the neon is illumin¬ ated. If the opposite state signal output is 5. required, an inverter element can be interposed between the Schmitt trigger output and the low voltage interface point, as shown in FIG 8. Under these circumstances, a logic 1 output signal will be produced when the gas lamp is illuminated. For 10. maximum- versatility, complementary logic signal outputs are generally provided, thus allowing selection of either a logic 0 or logic 1 signal in response to the high voltage signal applied to the gas lamp. 15. The invention hereinbefore described provides high reliability interfacing betwen high and low voltage signals due to the rugged nature of gas discharge lamps in general. The invention lends itself to application in a variety of areas requiring 20. interfacing from high voltage equipment to low voltage equipment such as safety guards for use with dangerous machinery. OMPI VvIPO

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS 1. A method of detection of opaque members when within a detection space the method being charac¬ terised according to this invention in that it includes the steps of sequentially effecting a radiant 5. energy transmission across a detection space from a plurality of spaced apart sources and causing a detection observed signal when such transmission is not sufficiently detected at each of a plurality of correspondingly located and sequentially corres- 10. pondingly selected locations. 2. A method of detection of opaque members as in claim 1 wherein the method is further characterised by including the step of interrogating the detection means at times other than when there is a selected 5. transmission of radiant energy from the transmission sources and a stray source signal is raised if suf¬ ficient radiant energy is then detected. 3. A method of detection of opaque members when within a detection space between selected transmission and detection members, the members comprising a plurality of radiant energy transmitters and receivers 5. aligned as pairs across the detection space, the method according to this invention being characterised by including the steps of activating all transmitters during a selected period of time but only one or some but not all during a smaller period of time within the 10. said selected overall period of time and in interrogating corresponding receivers at least within the period of each oppositely located transmitter and effecting a detection observed signal if the trans¬ mitted beam is not adequately received by the corres- 15- ponding receiver during the mutually effective period. 4. A method of detecting opaque members when within a detection space according to any one of the preceding claims where such method of detection is operated with industrial machines having a cyclic 5. operation with an operative stroke and including the further steps of detecting a commencement of the operative stroke by switch means, detecting an end of the operative stroke by switch means , detecting the passage through its operative stroke and interrogating 10. the status of the previously mentioned switches at this time and effecting an error signal if the status of the said two switches is not in accord with a selected status. 5. Apparatus for detection of an opaque member when within a detection space which includes a plurality of transmitters and a plurality of receivers defining therebetween a detection space, means to sequentially 5. effect a radiant energy transmission from each of the transmitters across the detection space, means to sequentially and in correspondence to the transmitters interrogate each of the detectors , and means to raise a detection observed signal when an expected trans- 10. mission is not sufficiently detected by any one of the said detectors. 6. Apparatus for the detection of opaque members as in the last preceding claim further characterised in that there is included means to interrogate each of the detection means at times other than when there is 5. a selected transmission of radiant energy and means to raise a "stray source" signal if a sufficient radiant energy is then detected. 7. Apparatus according to either one of the last two preceding claims further characterised by including means coupled to an industrial machine including a power stroke wherein the machine includes a switch 5. responsive to the commencement of the operative power stroke of the machine, a switch operative upon the machine reaching an end of a power stroke, and a switch operative when the machine is operating the power stroke said lastmentioned switch being coupled 10. to means effective to raise a fault signal when either one or both of the other switches are not in a selected status. 8. Apparatus according to any one of the last preceding claims further characterised in that alter¬ nating current higher voltage outputs controlled by the detection equipment have located thereacross 5. gaseous discharge lights such as a neon light and there are further means adapted to detect the existence of lighting of the said light and arranged to effect a logic signal output upon the result of such output not being in accord with an expected 10. status. 9. A method of detection according to any one of the preceding method claims wherein the radiant energy transmitted by the transmission means is in the infra-red range. 10. A method of detection according to any one of the preceding claims in which each of the transmitters is on one side of the detection space and each of the receivers is on the other side of the detection space. 11. A method of detection of opaque members when within a detection space substantially as described in the specification with reference to it and as illustrated by the accompanying drawings. 12. Apparatus for the detection of opaque members when within a detection space substantially as described in the specification with reference to and as illustrated by the accompanying drawings.

Inventors: DENTON A
Applicants: AMBLER K, DENTON A, RAEDER W
Application year: 1980
Main classification: F16P3
IPC codes: F16P3