WO1992007374A1 - Circuits de securite - Google Patents

Circuits de securite Download PDF

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Publication number
WO1992007374A1
WO1992007374A1 PCT/GB1991/001786 GB9101786W WO9207374A1 WO 1992007374 A1 WO1992007374 A1 WO 1992007374A1 GB 9101786 W GB9101786 W GB 9101786W WO 9207374 A1 WO9207374 A1 WO 9207374A1
Authority
WO
WIPO (PCT)
Prior art keywords
contacts
contact
relay
circuit
safety circuit
Prior art date
Application number
PCT/GB1991/001786
Other languages
English (en)
Inventor
George Henry Jackson
Original Assignee
Eja Engineering Company Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eja Engineering Company Limited filed Critical Eja Engineering Company Limited
Publication of WO1992007374A1 publication Critical patent/WO1992007374A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
    • H01H47/002—Monitoring or fail-safe circuits
    • H01H47/004—Monitoring or fail-safe circuits using plural redundant serial connected relay operated contacts in controlled circuit
    • H01H47/005—Safety control circuits therefor, e.g. chain of relays mutually monitoring each other

Definitions

  • the present invention relates to safety circuits for preventing unsafe nnfiratinn nf mar.hinerv.
  • Machine tools or material handling plant for example can be a source of great danger to operatives if the equipment can operate when operatives are exposed to moving parts. Accordingly it is conventional practice to protect machines with guards which cooperate with for example closure detecting switches to prevent machine starting until the guards are closed. It is also conventional practice to duplicate essential control components which if they failed could for example prevent a machine being stopped. Accordingly many machines can only be operated if two series connected contactors are both closed. If one of the contactors welds in the closed position the other can still be opened to stop the machine.
  • the known safety circuits greatly reduce the risk of injury to operatives but sometimes fail as a result of component failure. For example, if one of the two main contactors welds in the closed position, this can go undetected. If the other one then welds a dangerous situation results. Equally, safety circuits monitoring the position of guards can fail to an unsafe condition, indicating that a guard is closed when it is not.
  • a safety circuit for controlling the energisation of a machine through two contactors connected in series with a power supply for the machine, the safety circuit being arranged such that when energised it enables closure of both contactors only if predetermined safety conditions have been indicated, comprising two double pole changeover relays which if operating normally are switched simultaneously between a first state when the predetermined safety conditions are indicated and a second state when the predetermined safety conditions are not indicated, each relay having a pair of first contacts and a second contact which switches simultaneously with the first contacts, the second contact being switchable between first and second positions, each relay when operating normally having either the first contacts closed and the associated second contact in the first position, or having the first contacts open and the associated second contact in the second position, each first contact of one relay being connected in series with a respective first contact of the other relay such that when both of a pair of interconnected first contacts are closed energisation of a respective contactor is enabled, and the second contacts being connected in series with each other and with a
  • the invention also provides a safety circuit for controlling the energisation of a machine through two contactors connected in series with a power supply for the machine, the safety circuit being arranged such that when energised it enables closure of both contactors only if predetermined safety conditions having been indicated, comprising a secondary set of contacts which switch in synchronism with main contacts of the contactors, a pair of changeover relays arranged such that each relay is energised in dependence upon the condition of a respective secondary set of contacts, each changeover relay having one normally closed contact and one normally open contact with one side of one contact of each relay being connected to one source of potential and one side of the other contact of each relay being connected to another source of potential, and a gate circuit connected to the said other sides of the contacts of the two relays to compare the potentials appearing at the said other sides, the gate circuit being arranged to disable the safety circuit if the compared potentials indicate that the main contacts of one contactor are open and the main contacts of the other contactor are closed.
  • Each second contact may comprise a pair of contacts one of which is closed only when the second contact is in the first position and the other of which is closed only when the second contact is in the second position, the pair of contacts being interconnected to form two parallel circuits arranged to connect the power supply to the safety circuit if both second contacts are simultaneously in either the first or the second positions.
  • Each relay may be switchable by a respective coil, a safety circuit, according to claim 1 or 2 wherein each relay is switchable by a respective coil, each coil being energisable by a respective circuit responsive to at least two independent safety indicator inputs, and each circuit being arranged to energise the respective coil only if all said indicator inputs indicate the predetermined safety conditions.
  • one indicator input may represent detection of closure of a guard by a first sensing circuit and a second said indicator input represents detection of closure of the said guard by a second sensing circuit.
  • One indicator input may be representative of the condition of one said contactor and the further said indicator input is representative of the condition of the other of said contactors, the circuit being arranged to disable the safety circuit unless both contactor conditions are the same.
  • each contactor may be detected by a coil connected in series with contacts controlled by the respective contactor, energisation of the coil indicating closure of the contacts controlled by the contactor.
  • Each coil may control a respective further changeover relay, each further changeover relay having one normally closed contact and one normally open contact with one side of one contact being connected to one source of potential and one side of the other contact being connected to another source of potential, and a gate circuit being connected to the other sides of the contacts to compare potentials appearing at the said other sides, the gate circuit providing at least one said indicator input representative of the comparison made between the said potentials.
  • Fig. 1 is a schematic illustration of a machine guard closure indicator
  • Fig. 2 is a block schematic diagram of a complete machine control system according to the invention.
  • Fig. 3 to 7 illustrate circuits corresponding to functional blocks shown in Fig. 2.
  • Fig. 1 illustrates the circuit of a sensing head intended to provide an output indicative of whether or not an actuator is in a predetermined position relative to that sensing head.
  • the actuator could be mounted on a moving component of a guard, eg a door which may be opened to gain access to a machine, and the sensing head would be mounted on a fixed assembly, for example a door frame.
  • an actuator is indicated schematically by reference numeral 1, the actuator comprising a pick up coil 2 connected to a tuned circuit 3 and a permanent magnet 4.
  • a broken line 5 indicates the spacing between the actuator and a transformer
  • the sensing head comprises a magnetically operated reed switch
  • the reed switch 7 controls a transistor 8 which provides an output on terminal 9 that is indicative of whether or not the reed switch 7 is closed and thus whether or not the magnet 4 is in a position indicating closure of the guard.
  • the transformer 6 forms part of a tuned oscillator based upon a standard chip integrated circuit 10.
  • the oscillator resonates when the actuator tuned circuit is in the position shown and when resonating the positive voltage appearing across the capacitor 11 is discharged via the parallel resistor. The voltage across capacitor 11 appears at output 12. If the actuator 1 is moved away from the position shown the oscillator ceases resonating and the voltage appearing at output 12 returns to its former DC level.
  • FIG. 2 this illustrates in schematic form the way in which the output signals appearing on outputs 9 and 12 of Fig. 1 are used to control the supply of power to a machine which is guarded by sensing heads of the type illustrated in Fig. 1.
  • the system to be described is set up to operate with up to four independent sensing heads but the same system could also be used to monitor systems incorporating one, two or three sensing heads.
  • a machine 13 is enclosed within a guard 14 provided with doors (not shown).
  • the guard is intended to prevent access to the machine if the machine is being supplied with power.
  • the system must be capable of preventing energisation of the machine if any guards are open and disabling the machine if any guards are opened when the machine is operating.
  • the machine is supplied with AC power from an AC mains supply 15 through a pair of contactors 16 arranged in series. Thus if either one of the two contactors 16 is open the machine cannot operate.
  • outputs from the contactors 16 are provided which indicate in respect of each of the contactors whether or not the contactors are closed, that is in the current delivering condition.
  • AC mains supply 15 When an attempt is made to start the machine, AC mains supply 15 is turned on delivering AC power to the contactors 16, a high risk safety relay assembly 17, and a power supply 18.
  • the safety relay assembly 17 is capable of energising contactor coils 19 the energisation of which controls the state of the contactor 16. With the exception of the safety relay assembly 17, all of the other component parts of the system are energised from the power supply 18. To avoid over-complication of Fig. 2 the necessary connections from the power supply 18 to the various system components are not shown.
  • each door in the guard 14 is provided with an actuator 1 the position of which determines the state of a tuned oscillator 6 and a reed switch 7.
  • each of the door sensing circuit comprises the components illustrated in Fig. 1. Only one such arrangement is shown in Fig. 1 but it will be appreciated that for example up to four such arrangements could be provided.
  • the outputs of the reed switches 7 are passed by input amplifier stage 19 to a reed switching logic circuit 20.
  • the outputs of the tuned oscillator 6 are applied to an oscillator switching logic circuit 21.
  • the outputs of the logic circuits 20 and 21 are applied to a safety guard position indicator circuit 22 which simply indicates to the operator whether or not the guards are in the appropriate closed position.
  • the output of the oscillator switching logic circuit 21 is applied to a summing circuit 23 and the output of the reed switching logic circuit 20 is applied to a summing circuit 24.
  • the summing circuit 23 also receives the output of a further summing circuit 25 controlled by a head sense circuit 26 which in turn is controlled by a deselection link circuit 27.
  • the deselection link circuit 27 enables the system which is designed to cope with up to four sensing head assemblies to operate with only one, two or three assemblies by simply inserting appropriate links in the head sense circuit 26.
  • the output of the summing circuit 25 is in essence an indicator of whether or not any of the oscillator and reed switching logic circuits are deliberately isolated from respective sensing head assemblies.
  • a checking circuit 28 indicates to the operator the status of the guard doors.
  • the same signals that are monitored by the circuit 28 are also applied to a pair of summing circuits 29 and 30 and combined with the outputs respectively of circuits 31 and 32.
  • Circuit 31 provides an output indicative of whether or not the first of the two contactors 16 is switched to an appropriate condition given the status of the other of the two contactors 16. This signal is derived from a contactor weld sense circuit 33 connect to the contactor 16.
  • the circuit 32 performs an equivalent function to circuit 31 but receives an input from a contactor weld sense circuit 34 connected to the other of the two contactors 16.
  • the circuit 29 receives a signal indicative of whether or not all the reed switches 7 of the guards are in a condition indicating guard closure, a signal indicative of whether or not the tuned circuits 6 are in a condition indicative of guard closure, and a signal indicative of whether or not the contactors 16 are in an appropriate state.
  • the summing circuit 30 produces a similar sum and thus parallel decision channels are established through the entire system with the two circuits 29, 30 providing outputs to relay drive circuits 35 and 36. Only if both these drive circuits 35 and 36 receive enabling inputs are the safety relays 17 switched to a condition in which the contactor coils 19 are energised to close both pairs of contactors in the contactor assembly 16.
  • Fig. 3 this illustrates in some detail circuitry corresponding to components 20, 21, 26 and 27 of Fig. 2.
  • the B signals are applied to input amplifiers 37 (component 19 from Fig. 2) the outputs of which are applied to the D inputs of flip-flops 38.
  • the A inputs are applied directly to the dynamic input of the flip-flop 38.
  • the A and B signals are also inverted in inverters 39 and applied to the dynamic and D inputs of the further flip-flop 40.
  • the flip-flops 38 and 40 may be conventional integrated circuits.
  • the Q output of the two flip-flops provide signals AA and BB both of which will be "high” if and only if the two signals received from the respective guard sensing assembly indicate that the guard is safely closed.
  • the arrangement of Fig. 3 produces eight output signals AAO, AA1, AA2, AA3 and BBO, BB1, BB2 and BB3.
  • the components described for converting the A and B signals to the AA and BB signals correspond to the components identified in Fig. 2 by reference numerals 20 and 21.
  • the flip-flops 40 receive a reset signal SWOP generated from the power supply (Fig. 2 component 18) when the system is first energised.
  • the reset signal resets the flip-flops to an initial condition in which the machine is disabled.
  • Fig. 4 this illustrates the component of the system illustrated in Fig. 2 which is identified by numeral 22.
  • the pairs of signals AA0-BB0, AA1-BB1, AA2-BB2, and AA3-BB3 are applied to respective AND gates 44.
  • the outputs of the AND gates 44 control respective transistors 45 controlling the energisation of respective light emitting diodes 46. If and only if both the inputs to one of the AND gates 44 indicates that the respective guard is closed will the respective transistor 45 be turned off.
  • the magnetic or oscillator controlled circuits of the sensing head provide an output indicating that the respective guard is open the respective light emitting diode 46 is illuminated.
  • the operator can immediately see if any one of the four guards has not been closed properly or has been opened.
  • the illustrated components correspond to components 24, 25 and 28 of Fig. 2.
  • the four B outputs of the sensing head assemblies that is signals BBO, 1, 2 and 3 are applied to the inputs of a first AND gate 47.
  • the output of the AND gate 47 (B-sum) distinguishes between the case on the one hand of all ' the magnetically operated reed switches of the four sensing heads being closed to indicate guard closure and on the other hand any one of the reed switches being open to indicate the guard being open.
  • the four AA inputs are applied to an AND gate 48 producing an output A-sum.
  • the three signals LI, L2 and L3 are applied to a still further AND gate 49.
  • the AND gates 47, 48 and 49 correspond to the components 24, 23 and 25 of Fig. 2.
  • the outputs on the AND gates 47, 48 and 49 control respective transistors 50, 51 and 52, and these in turn control the energisation of light emitting diodes 53 and 54.
  • Diode 53 lights up when the last door of the guard is closed to indicate that the machine can now be powered up. The LED is then extinguished.
  • LED 54 lights up when one of the previously closed doors is opened.
  • the indications given by the diodes 53 and 54 enable the operator to monitor the operation of the safety circuits.
  • FIG. 6 the upper portion of this figure illustrates relays which are energised in dependence on the condition of the main contactors through which current is delivered to the protected machine and the lower portion illustrates the arrangement of contacts and logic circuits which derive control outputs from the condition of these relays.
  • the upper portion of Fig. 6 corresponds to components 33 and 34 of Fig. 2 and the lower portion corresponds to components 31 and 32.
  • a first relay coil 55 is connected in series with a pair of terminals 56 and 57. Between the terminals 56 and 57 are connected a pair of contacts (not shown) which switch in unison with one of the two main contactors which are connected in series with the machine.
  • terminals 56 and 57 are connected when the associated main contactor is closed either deliberately or inadvertently due to a failure such as contact welding.
  • the terminals 56 and 57 are isolated from each other if the associated main contactor is open to isolate the machine.
  • a second relay 58 is connected in series with terminals 59 and 60 which are connected to a second set of contactors that move in unison with the other of the two main contactors connected in series with the machine.
  • the relay 55 controls contacts 61 and the relay 58 controls contacts 62.
  • One of the contacts 61 is normally open, the other normally closed. The same is true of the contact set 62.
  • the outputs of the two contacts of each of the contact sets 61 and 62 are combined and applied to respective inputs of a pair of exclusive OR gates 63 and 64. If only one of the relay sets 61 and 62 switches, indicating failure of one of the main contactors, all the inputs to the gates 63 and 64 will be at the same voltage. If they both switch together, one input to each of the gates will be zero volts and the other input to each of the gates will be a positive voltage.
  • both the outputs of the gates 63 and 64 will be logic "one" when the contactor sets 61 and 62 are in a position indicating that the main contactor sets are operating correctly, i.e. either both open or both closed simultaneously. These outputs appear on terminals 65 and 66.
  • AND gates 67 and 68 receive identical combinations of signals, that is the signals appearing on terminals 65 and 66 (see Fig. 6) and the signals A-sum and B-sum (see Fig. 5). Only if all of these signals are logic level "one" will their outputs be at the same logic level. If the outputs are at logic level "one" respective transistors 69 and 70 are turned on to energise main contactor relays 71 and 72.
  • Both of the relays 71 and 72 must be energised to close the pair of series connected contactors through which current must be delivered to the machine if it is to be operated.
  • the relay 71 controls contacts 73 to 78 whereas the relay 72 controls contact 79 to 84.
  • a live input is provided via a fuse 85 and a live output appears as described below at terminal 86. This output is used to energise the safety circuit.
  • the power supply 18 is disabled, thereby preventing further circuit operation.
  • Power for delivery to one of the main machine contactors is applied via a fuse 87 to contact 76 and power for the other main contactor coil is delivered via a fuse 88 to contact 78.
  • the first of the main contactor coils is connected to terminal 89 and the second to terminal 90, those two terminals being connected respectively to contacts 82 and 84.
  • the machine contactors are de-energised. Power is delivered via fuse 85, contact 73 and contact 79 to output 86. The signal appearing at output 86 is applied to the power supply for powering up the rest of the circuitry. If all the contacts shown in Fig. 7 are switched simultaneously, power is distributed to terminal 86 from fuse 85 via contacts 74 and 80, maintaining energisation of the power supply. If only one of the two contactor sets of Fig. 7 is switched, the entire safety circuit is disabled as no power is delivered to the circuitry from terminal 86.

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  • Safety Devices In Control Systems (AREA)

Abstract

Circuit de sécurité permettant de commander l'excitation d'une machine à travers deux contacteurs reliés en série avec une alimentation pour ladite machine. Ledit circuit de sécurité est conçu pour ne permettre, lorsqu'il est excité, la fermeture des contacts principaux commandés par les contacteurs que lorsque des conditions de sécurité prédéterminées ont été réalisées. Le circuit de sécurité comprend deux relais inverseurs bipolaires qui, lorsqu'ils fonctionnent normalement, s'enclenchent simultanément. Chaque relais inverseur a une paire de premiers contacts et un deuxième contact. Les premiers contacts commutent entre une position ouverte et une position fermée, tandis que les deuxièmes contacts commutent entre une première position et une seconde position. Chaque premier contact d'un relais est connecté en série à un premier contact correspondant de l'autre relais, de sorte que lorsque les deux contacts d'une paire interconnectée de premiers contacts sont fermés, un contacteur respectif est excité. Les deuxièmes contacts sont disposés de manière à déconnecter le circuit de sécurité à moins que les deux relais inverseurs ne soient commutés ensemble. Ainsi, si l'un des premiers contacts se ferme, le contact fermé maintient le deuxième contact associé dans sa position commutée. Dès que les relais sont commutés à nouveau, le deuxième contact associé au premier contact fermé ne commute pas, de sorte que l'alimentation du circuit de sécurité est déconnectée. Ainsi, la fermeture d'un contacteur principal est détectée et l'erreur ne peut rester en sommeil. De plus, un circuit peut être utilisé pour détecter la condition des deux contacteurs et déconnecter le circuit de sécurité au cas où les contacts d'un des contacteurs seraient fermés tandis que les contacts de l'autre contacteurs sont ouverts.
PCT/GB1991/001786 1990-10-13 1991-10-14 Circuits de securite WO1992007374A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9022283.7 1990-10-13
GB909022283A GB9022283D0 (en) 1990-10-13 1990-10-13 Safety circuits

Publications (1)

Publication Number Publication Date
WO1992007374A1 true WO1992007374A1 (fr) 1992-04-30

Family

ID=10683687

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1991/001786 WO1992007374A1 (fr) 1990-10-13 1991-10-14 Circuits de securite

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AU (1) AU8661891A (fr)
GB (1) GB9022283D0 (fr)
WO (1) WO1992007374A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2347564A (en) * 1998-12-31 2000-09-06 Honeywell Inc Power switching system monitors for welded relay contacts
EP2653940A1 (fr) * 2012-04-18 2013-10-23 Schneider Electric Industries SAS Système de détection sécurisée

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1958017A1 (de) * 1969-11-13 1971-05-19 Licentia Gmbh Schaltungsanordnung zur gesicherten Steuerung von Schalthandlungen
USRE28822E (en) * 1972-04-03 1976-05-18 Amana Refrigeration, Inc. Safety interlock system for microwave ovens
US4091438A (en) * 1977-01-31 1978-05-23 The Minster Machine Company Press control system
EP0105054A1 (fr) * 1982-10-01 1984-04-11 Square D Starkstrom GmbH Circuit pour le contrôle actif d'interrupteurs de fin de course rangés par paires

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1958017A1 (de) * 1969-11-13 1971-05-19 Licentia Gmbh Schaltungsanordnung zur gesicherten Steuerung von Schalthandlungen
USRE28822E (en) * 1972-04-03 1976-05-18 Amana Refrigeration, Inc. Safety interlock system for microwave ovens
US4091438A (en) * 1977-01-31 1978-05-23 The Minster Machine Company Press control system
EP0105054A1 (fr) * 1982-10-01 1984-04-11 Square D Starkstrom GmbH Circuit pour le contrôle actif d'interrupteurs de fin de course rangés par paires

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2347564A (en) * 1998-12-31 2000-09-06 Honeywell Inc Power switching system monitors for welded relay contacts
GB2347564B (en) * 1998-12-31 2003-04-16 Honeywell Inc Power switching system
EP2653940A1 (fr) * 2012-04-18 2013-10-23 Schneider Electric Industries SAS Système de détection sécurisée
FR2989848A1 (fr) * 2012-04-18 2013-10-25 Schneider Electric Ind Sas Systeme de detection securisee
US9222967B2 (en) 2012-04-18 2015-12-29 Schneider Electric Industries Sas Secured detection system

Also Published As

Publication number Publication date
GB9022283D0 (en) 1990-11-28
AU8661891A (en) 1992-05-20

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