Presence sensing and self-checking control system

• US 3,886,413 A
• Filed: 01/29/1973
• Issued: 05/27/1975
• Est. Priority Date: 01/29/1973
• Status: Expired due to Term

• Current Assignee: Dudley B. Hartung, Frederick J.T. Dow
• Original Assignee: Dudley B. Hartung, Frederick J.T. Dow
• Inventors: Hartung, Dudley B., Dow, Frederick J. T.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Moose, Jr., Harry E.
• Application Number:
  US05/327,384
• Time in Patent Office: 848 Days
• Field of Search: 317/DIG.1,DIG.2,146 340/258B,258C,411,248R 307/117
• US Class Current: 361/181
• CPC Class Codes: F16P 3/148 using capacitive technology
• CPC Class Codes: G01V 3/088 operating with electric fields G01V3/082 takes precedence

Abstract

A presence sensing system provided with self-checking operation is disclosed. The system is especially adapted for use in a control system for machines to ensure safe operation thereof. The system comprises a presence sensing section capable of producing output signals indicative of normal, intrusion, and withdrawal conditions in the guarded zone of the machine. A control system comprising a control channel and a self-checking channel responds to the output signals of the sensing section and control the condition of a controller, which in turn is adapted to interrupt machine operation. The control channel and the self-checking channel are both implemented in binary logic. The system is operated under the control of timing means which causes cyclic operation with each cycle divided into separate time slots, one for a testing mode of operation and one for a condition sensing mode of operation. The testing mode time slot is subdivided into plural time slots, each corresponding to a particular test of the system.

Claims

1. A presence detection system of the type comprising sensing means including a sensing element adapted to be disposed adjacent a zone to be monitored and including electrical signal producing means connected with said element, said sensing means having an output adapted to produce a reference signal when said zone is in a normal condition and an intrusion signal when an object intrudes into said zone, and control means having an input connected with the output of said sensing means, said control means including a control circuit and a controller connected thereto, said control circuit being responsive to an intrusion signal to cause actuation of said controller and responsive to a reference signal to cause deactuation thereof, the improvement comprising;

self-checking means including timing means, command signal means cyclically operated by the timing means and connected with an input of said control circuit for periodically applying a simulated intrusion signal thereto, said self-checking means also includIng a logic means having an input connected with a selected point of the control circuit to determine whether a simulated intrusion signal applied to the control circuit is operative to produce a predetermined signal at the selected point in the control circuit during the occurrence of a simulated intrusion signal, said logic means including a self-check bistable element which assumes one state in response to said simulated intrusion signal, gate means having one input connected with the output of the self-check bistable element and having another input connected with a point in said self-checking means having a logic level voltage state indicative of what said one state should be in the absence of a malfunction, said gate means being connected with said controller and being adapted to cause actuation thereof when the bistable element assumes another state in response to said simulated intrusion signal.

2. The invention as defined in claim 1 wherein said control circuit includes first and second control channels, the first channel being connected between the sensing means and a first relay means, the second control channel being connected between the sensing means and a second relay means, said controller comprising said first and second relay means, said first and second channels being redundantly related to each other for causing said first and second relay means to be actuated and deactuated together in response to a signal from the sensing means, monitor means connected with said first and second relay means and having an output producing a logic level voltage state indicative of malfunction in one of said channels, said gate means having said another input connected with the output of said monitor means.

3. The invention defined in claim 1 including monitor means connected with said controller and having an output which produces, in the absence of a malfunction of said controller, a first logic level voltage state indicative of the state that said self-check bistable element should assume in the absence of a malfunction of said control circuit and which produces, in case of a malfunction of said controller, a second logic level voltage whereby said controller is actuated in response to a malfunction in either said control circuit or said controller.

4. The invention defined in claim 1 including monitor means connected with said timing means and having an output which produces, in the absence of a malfunction of said timing means, a first logic level voltage state indicative of the state that said self-check bistable element should assume in the absence of a malfunction of said control circuit and which produces, in case of a malfunction of said timing means, a second logic level voltage whereby said controller is actuated in response to a malfunction in either said control circuit or said timing means.

5. A presence detection system of the type comprising sensing means including a sensing element adapted to be disposed adjacent a zone to be monitored and including electrical signal producing means connected with said element, said sensing means having an output adapted to produce a reference signal when said zone is in a normal condition and an intrusion signal when an object intrudes into said zone, and control means having an input connected with the output of said sensing means, said control means including a control circuit and a controller connected thereto, said control circuit being responsive to an intrusion signal to cause actuation of said controller and responsive to a reference signal to cause deactuation thereof, the improvement comprising;

self-checking means including timing means, command signal means cyclically operated by the timing means and connected with an input of said control circuit for periodically applying a simulated intrusion signal thereto, said self-checking means also including a logic means having an input connected with a selected point of the control circuit to determine whether a simulated intrusion signal applied to the cOntrol circuit is operative to produce a predetermined signal at the selected point in the control circuit during the occurrence of a simulated intrusion signal, first disabling means connected with said control circuit and second disabling means connected with said logic means, said timing means being connected with said first and second disabling means for alternately disabling the control circuit and the logic means whereby self-checking and presence detection are interlaced in time at a frequency established by said timing means, said logic means having an output connected with said controller for causing actuation thereof when said logic means determines that said predetermined signal is not produced by said simulated intrusion signal.

6. The invention as defined in claim 5 wherein said controller includes at least one normally energized relay means, said control circuit being adapted to connect the relay means to a power supply to deactuate the controller whereby the controller is actuated in the event of failure of the power supply.

7. The invention as defined in claim 5 including lock-up means connected with said logic means and being operative to hold said controller in actuated condition when said logic means determines that said predetermined signal is not produced by said simulated intrusion signal.

8. The invention as defined in claim 5 wherein said logic means includes at least one self-check bistable element which assumes one state in response to said simulated intrusion signal in the absence of a malfunction, said bistable element having an output connected with said controller and being ineffective to cause actuation thereof in said one state and effective to cause actuation in the other state, and lock-up means connected with said self-check bistable element and being operative in response to the other state for holding it in said other state thereby holding said controller in the actuated condition.

9. The invention as defined in claim 8 including a manually operated reset circuit connected with the self-check bistable element for resetting the same to its other state.

10. The invention as defined in claim 5 wherein said timing means causes switching of the first and second disabling means at a rate such that the control circuit is disabled for less time during each cycle of operation than that required for the occurrence of a predetermined degree of intrusion.

11. The invention as defined in claim 5 wherein said timing means causes switching of the first and second disabling means such that the control circuit and the logic means are alternately disabled for substantially equal time intervals, the frequency of alternation being at least several times per second.

12. A safety system for controlling a machine, the system being of the type comprising sensing means including a sensing element adapted to be disposed adjacent a zone to be monitored and including electrical signal producing means connected with said element, said sensing means being adapted to produce a reference signal when said zone is in a normal condition, an intrusion signal when an object intrudes into said zone and a withdrawal signal when an object is withdrawn from said zone, and control means connected with said sensing means, said control means including a control circuit and a controller connected thereto, said control circuit being responsive to either an intrusion signal or a withdrawal signal to cause actuation of said controller and responsive to a reference signal to cause deactuation of said controller, the improvement comprising;

self-checking means including timing means, command signal means adapted to produce a simulated intrusion signal and a simulated withdrawal signal and being connected with an input of said control circuit, said self-checking means also including logic means having an input connected with a selected point of the control circuit, said logic means having an output connected with said controller for causing actuation thereof, fIrst disabling means connected with said control circuit, said timing means being connected with said first disabling means for disabling a portion of the control circuit during a test interval preceding an operate interval and for enabling it to cause actuation of said controller during an operate interval, second disabling means connected with said self-check means, said timing means being connected with said second disabling means for disabling the logic means during said operate interval and for enabling the logic means during said test interval to cause actuation of said controller, said timing means also being connected with said command signal means for producing said simulated intrusion and withdrawal signals in succession during said test interval, said logic means being operative to produce an actuating signal when the control circuit is ineffective to produce predetermined signals at the selected point in response to the simulated intrusion and withdrawal signals, said controller being actuated in response to said actuating signal, and said timing means being cyclical in operation whereby said operate interval and test interval are successively repetitive.

13. The invention as defined in claim 12 wherein said logic means includes an intrusion signal test channel and a withdrawl signal test channel, said timing means being connected with said intrusion signal test channel for enabling operation thereof during the simulated intrusion signal, said timing means also being connected with said withdrawal signal test channel for enabling operation thereof during the simulated withdrawal signal.

14. The invention as defined in claim 13 wherein said logic means includes first and second self-checking bistable elements, the first bistable element being adapted to assume one state in response to a simulated intrusion signal in the absence of a malfunction, the first bistable element having its input operatively connected with the output of both of said test channels and having its output connected with said controller, said first bistable elements being ineffective to cause actuation of said controller in said one state and effective to cause actuation in the other state, the second bistable element being adapted to assume one state in response to a simulated withdrawal signal in the absence of a malfunction, the second bistable element having its input operatively connected with the output of both of said test channels and having its output connected with said controller, said second bistable element being ineffective to cause actuation of said controller in said one state and effective to cause actuation in the other state.