Light curtain system with system and watchdog microcontrollers

• US 5,218,196 A
• Filed: 09/05/1991
• Issued: 06/08/1993
• Est. Priority Date: 09/05/1991
• Status: Expired due to Term

• Current Assignee: Frost Controls Incorporated
• Original Assignee: Frost Controls Incorporated
• Inventors: Sarkar, Sandip, Dogul, James, Thomson, Robert, Thomson, Frederick
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Messinger, Michael
• Application Number:
  US07/755,566
• Time in Patent Office: 642 Days
• Field of Search: 250/221, 250/222.1, 250/222.2, 250/223 R, 395/575, 340/555, 340/556, 340/557
• US Class Current: 250/221
• CPC Class Codes: F16P 3/144 using light grids
• CPC Class Codes: G01V 8/20 using multiple transmitters or receivers
• CPC Class Codes: G06F 11/0757 by exceeding a time limit, i.e. time-out, e.g. watchdogs
• CPC Class Codes: G06F 11/261 by simulating additional hardware, e.g. fault simulation
• CPC Class Codes: G08B 13/183 by interruption of a radiation beam or barrier
• CPC Class Codes: H01H 47/002 Monitoring or fail-safe circuits

Abstract

A photodetection system and related circuitry designed to sense the intrusion of an opaque object in a light plane. Upon sensing the intrusion, the system quickly initiates a machine-stopping sequence prior to the opaque object coming into contact with the machine while that machine is operating. The system comprises a SYSTEM microcontroller and a WATCHDOG microcontroller, both of which operate an output control device of the light curtain switch of the invention, wherein the output control device comprises a plurality of electromechanical relays. Both microcontrollers also perform system hardware and software integrity checks. Furthermore, the WATCHDOG microcontroller evaluates the performance of the SYSTEM microcontroller by transmitting a false intrusion signal to a photosource, determining whether the false signal has been detected, and then verifying that the SYSTEM microcontroller has initiated the machine-stopping sequence. The machine-stopping sequence may be overridden by the WATCHDOG microcontroller, or it may be initiated if the false signal is not detected. The combination of electronic, mechanical, and optical modules of the present invention provides improved reliability and accuracy. In addition, the SYSTEM microcontroller and the WATCHDOG microcontroller are designed so as to reduce the system'"'"'s sensitivity to spurious signals.

Claims

1. A light curtain presence-sensing system comprising a light curtain, a System microcontroller and a Watchdog microcontroller, wherein said System microcontroller is programmed to run all light curtain functions and said Watchdog microcontroller is programmed to monitor and verify said functions initiated by said System microcontroller and to take over said functions and also cause an output control device to open upon finding that any of said functions have not been carried out.

2. A light curtain presence-sensing system as described in claim 1, wherein said Watchdog microcontroller is further programmed to periodically simulate a partial light blockage, to monitor how said System microcontroller responds to said partial light blockage, and, upon finding that said System microcontroller has responded correctly, to override any attempt of said System microcontroller to cause said output control device to open.

3. A light curtain presence-sensing system as described in claim 2, wherein said Watchdog microcontroller and said System microcontroller are further programmed to cooperatively run a series of circuit operation tests at powerup and during operation of said system, wherein said tests comprise

a) an equipment mismatch test involving a photosource array, and a photodetector array;

b) an alignment test to ensure that said photosource array is aligned with said photodetector array;

c) an output control device integrity check;

d) a system integrity test;

e) internal code verification checks

wherein upon failure of one of said operation test during said operation, said Watchdog microcontroller causes said output control device to open, and wherein upon failure of one of said operation tests during said powerup, said Watchdog microcontroller prevents said output device from closing.

4. A light curtain presence-sensing system as described in claim 3, wherein said system additionally comprises a fault rate measuring means wherein said fault rate measuring means ensures that only when one of said circuit operation tests has been failed a specified number of times within a specified period of time before said Watchdog microcontroller causes said output control device to open, wherein said fault rate measuring means comprises a register subcircuit connected to a clock means.

5. In conjunction with a light curtain presence-sensing system as described in claim 1, a dual power supply for converting line power and voltage into two filtered, separately-regulated, low dc voltage power sources for a control circuit and output control device of said system, wherein one of said dc voltage power sources is used to power all of said control circuit except said output control device and is protected against voltage fluctuation arising from current draw on the other of said dc voltage power sources, which is connected to power said output control device.

6. An improved presence-sensing system comprising:

a. a light-source gray comprising a plurality of individual light sources;

b. a light-detector array comprising a plurality of individual light detectors;

c. directing means for concentrating and directing light from each of said individual light sources onto a particular one of said individual light detectors;

d. means of sequentially activating said plurality of individual light sources;

e. means of sequentially activating said plurality of individual light detectors;

f. means of causing said light-source array to produce labelled light;

g. means of discriminating in favor of said labelled light and against all other light when said labelled light and said other light arrives concurrently at said light-detector array;

h. an output control device;

i. a programmable System microcontroller; and

j. a programmable Watchdog microcontroller,

wherein said System microcontroller is electrically connected to said photosource array and to said photodetector array and configured to be said means of sequentially activating said plurality of individual light sources and said means of sequentially activating said plurality of individual light detectors in such a way that each of said plurality of individual light sources is synchronously activated with a matching light detector, wherein said System microcontroller is programmed to operate said light curtain and said Watchdog microcontroller is programmed to verify operations of said System microcontroller and to intervene upon detecting an error in said operations.

7. The device as claimed in claim 6 wherein said Watchdog microcontroller further comprises

a. means for causing a signal simulating light blockage to be sent from said detector array to said System microcontroller,

b. means for overriding a response of said System microcontroller which is appropriate to said signal simulating light blockage,

c. means for providing said response in the even that said System microcontroller fails to do so,

wherein said means for causing a signal simulating light blockage comprises a link to input of said photosource array and means to superimpose a current reducing pulse onto said link.

8. An integrity-ensuring device for circuitry which, when triggered by a particular input signal, is supposed to produce an output control signal, said circuitry comprising circuit input signal terminals and output control signal terminals, said device comprising a system microcontroller for monitoring said circuitry and causing said output control signal upon detecting said particular input signal at said input signal terminals,

a Watchdog microcontroller for monitoring said System microcontroller and for simulating said particular input signal at said input signal terminals,

wherein said System microcontroller and said Watchdog microcontroller are interconnected so as to be able to exchange data and both said System microcontroller and said Watchdog microcontroller are connected to said circuitry,

wherein said Watchdog microcontroller is programmed to periodically simulate said particular input signal,

wherein said Watchdog microcontroller is connected to and able to control means for overriding said output signal,

wherein said Watchdog microcontroller is programmed to override said output control signal through said means for overriding said output signal should said System microcontroller produce said output signal at said output signal terminals following simulation of said particular input signal,

and wherein said Watchdog microcontroller is programmed to cause said output signal itself is and only if said System microcontroller fails to produce said output signal following said simulation, wherein said circuitry is a light-activated presence sensor comprising:

a. a plurality of photosources,

b. a plurality of photodetectors aligned to receive light emitted by said plurality of photosources,

c. signal analysis means, and

d. an output control device,

wherein said System microcontroller is connected to said plurality of photosources through a multiplexer means,

whereins said multiplexer means is designed to generate a sequential source activation wherein said sequential source activation causes each of said plurality of photosources to be activated one at a time by means of a photosource voltage,

wherein said multiplexer means is designed to generate a sequential detector activation wherein said sequential detector activation causes each of said plurality of photodetectors to be activated one at a time synchronously with the activation of said photosources,

wherein each of said plurality of photodetectors generates a detector signal correlated with light received from each of said photosources,

wherein said System microcontroller is connected to said plurality of photodetectors through a demultiplexer means,

wherein said demultiplexer operates to receive said detector signal from each of said plurality of photodetectors and to output a detector pulse train to said System microcontroller,

wherein said signal analysis means within said System microcontroller can analyze said detector pulse train so as to determine whether any single pulse in said detector pulse train falls below a critical threshold,

wherein sid particular input signal comprises any single pulse in said detector pulse train falling below said critical threshold, and

wherein said System microcontroller is programmed to produce said output control signal when said signal analysis means determines that any single pulse in said detector pulse train has fallen below said critical threshold.

9. The device as claimed in claim 8 wherein said means for simulating said particular input signal comprises transmission of a light-decreasing pulse from said Watchdog microcontroller to one of said plurality of photosources.

10. The device as claimed in claim 8 wherein said plurality of photodetectors is aligned so that each of said plurality of photodetectors receives light emitted from one and only one of said plurality of photosources and so that each of said plurality of photosources illuminates one and only one of said plurality of photodetectors.

11. The device as claim in claim 8 wherein said plurality of photosources comprises an array of light-emitting diodes.

12. The device as claimed in claim 8 wherein each of said plurality of photosources and each of said plurality of photodetectors is shielded.

13. A process for ensuring the integrity of circuitry triggered by a particular input signal so as to produce an output control signal, wherein said circuitry is a light-activated presence sensor comprising circuit input signal terminals and output control signal terminals, a plurality of photosources, a plurality of photodetectors receiving light emitted by said plurality of photosources, and an output control device, said process comprising the steps of:

a. connecting a System microcontroller to said plurality of photosources through multiplexer means and to said photodetectors through demultiplexer means;

b. activating each of said plurality of photosources with said multiplexer means, wherein said multiplexer means generates a sequential source activation and wherein said sequential source activation causes each of said plurality of photosources to be activated one at a time by means of a photosource voltage;

c. activating each of said plurality of photodetectors with said demultiplexer means, wherein said demultiplexer means generates a sequential detector activation, wherein said sequential detector activation causes each of said plurality of photodetectors to be activated one at a time synchronously with the activation of said photosources;

d. correlating each of said plurality of photodetectors with light from each of said plurality of photosources;

e. combining within said demultiplexer means a plurality of detector signals transmitted by said plurality of photodetectors;

f. transmitting from said demultiplexer means to said System microcontroller a single pulse detector train, wherein said single pulse detector train is formed within said demultiplexer means by the combination of said plurality of detector signals;

g. analyzing said detector pulse train to determine whether any one of said plurality of detector signals from any one of said plurality of photodetectors has fallen below a critical threshold;

h. transmitting said output control signal from said System microcontroller to said output control device when said detector signal has fallen below said critical threshold;

i. detecting said particular input signal at said circuit input signal terminals with said System microcontroller;

j. producing said output control signal at said output control signal terminals upon the detection of said particular input signal;

k. transmitting a signal from said System microcontroller to a Watchdog microcontroller indicating the detection of said particular input signal;

l. periodically transmitting a simulated particular input signal from said Watchdog microcontroller to said circuit input signal terminals and;

m. overriding said output control signal from said System microcontroller to said output control signal terminals if and only if said particular input signal detected by said System microcontroller is said simulated particular input signal.

14. The process as claimed in claim 13 wherein the step of activating said photosources sequentially further comprises the steps of:

a. inputting a source voltage pulse train from said System microcontroller to said multiplexer;

b. transforming said source voltage pulse train into a source current pulse series; and

c. sequentially directing each member of said source current pulse series to each of said plurality of photosources.

15. The process as claimed in claim 14 wherein the step of periodically transmitting said simulated particular input signal comprises superimposing on any member of said source current pulse series a single error pulse of such sign as to cause an amplitude reduction in the light emitted by a corresponding photosource by such an amount that a corresponding detector signal falls below said critical threshold.

16. An improved presence-sensing system comprising:

a. a photosource array comprising a plurality of individual photosources;

b. a photodetector array comprising a plurality of individual photodetectors;

c. directing means for concentrating and directing light from each of said individual light sources onto a particular one of said individual light detectors;

d. a multiplexer designed to generate a sequential source activation upon receiving a source pulse train, wherein said sequential source activation causes each of said plurality of photosources to be activated one at a time with a photosource voltage;

a means of generating a sequential detector activation, wherein said sequential detector activation causes each of said plurality of photodetectors to be activated one at a time synchronously with the activation of said plurality of photosources;

f. means of causing said light-source array to produce labelled light;

g. means of discriminating in favor of said labelled light and against all other light when said labelled light and said other light arrives concurrently at said light-detector array;

h. a compound, monitorable electromagnetic relay system comprising;

i. a primary relay with primary relay contacts normally open;

ii. a primary solenoid wired to said primary relay so as to close said primary relay contacts when said primary solenoid is energized; and

iii. a primary relay monitor circuit comprising;

(a) a dummy relay with dummy relay contacts normally closed;

(b) a dummy resistor wired in series with said dummy relay;

(c) a ground connector on a proximal end of said monitor circuit and a constant dc-voltage connector on a distal end of said monitor circuit; and

(d) voltage-measuring means connected across said dummy resistor, wherein said dummy relay is mechanically coupled but electrically isolated from said primary relay in such a way that when said primary relay contacts are open, said dummy relay contacts are closed;

iv. a backup relay with backup relay contacts normally open, wherein said backup relay contacts are connected in series with said primary relay contacts; and

v. a backup solenoid coupled to said backup relay so as to close said backup relay contacts when said backup solenoid is energized.

i. a programmable System microcontroller; and

j. a programmable Watchdog microcontroller;

wherein said System microcontroller is electrically connected to said photosource array and to said photodetector array, wherein said System microcontroller controls said multiplexer and said demultiplexer, wherein said System microcontroller and said Watchdog microcontroller are interconnected so as to be able to exchange data, wherein said Watchdog microcontroller is programmed to periodically transmit a simulated particular input signal comprising a light-decreasing pulse to one of said plurality of photosources,

wherein said Watchdog microcontroller is able to override an output signal transmitted by said System microcontroller when said System microcontroller receives said simulated particular input signal from said pulse detector train, and wherein said Watchdog microcontroller is programmed to cause said output signal itself if and only if said System microcontroller fails to produce said output signal following said simulation.