Optical door interlock

• US 4,583,082 A
• Filed: 06/09/1983
• Issued: 04/15/1986
• Est. Priority Date: 06/09/1983
• Status: Expired due to Term

• Current Assignee: IGT (International Game Technology)
• Original Assignee: IGT (International Game Technology)
• Inventors: Naylor, Mark C.
• Primary Examiner(s): Rowland, James L.
• Assistant Examiner(s): TUMM, BRIAN
• Application Number:
  US06/502,872
• Time in Patent Office: 1,041 Days
• Field of Search: 340/545, 340/600, 340/555, 340/556, 340/557
• US Class Current: 340/545.3
• CPC Class Codes: G08B 13/181 using active radiation detection systems
• CPC Class Codes: G08B 13/183 by interruption of a radiation beam or barrier

Abstract

Method and apparatus for monitoring the opening and closing of a door and for detecting unauthorized opening of the door. The apparatus comprises a light emitting diode and a sensor mounted with respect to the door so as to be in optical communication with one another when the door is closed. A microprocessor monitors and controls the operation of the light emitting diode and sensor. When the sensor is receiving light, preliminarily indicating that the door is closed, the microprocessor verifies that the light emitting diode and sensor are still in optical communication with one another. In the preferred embodiment verification is achieved by causing the light emitting diode to emit a predetermined sequence of pulses and monitoring whether the sensor tracks the predetermined sequence of pulses. An alarm signal is provided when the sensor senses light and the microprocessor determines that the light emitting diode and sensor are not in optical communication with one another.

Claims

1. Door interlock apparatus for monitoring the opening and closing of a door comprising:

a radiative emitter and a sensor positioned in operative association with said door so as to communicate with one another across a gap when said door is in closed position;

first means connected to said sensor and having a first state indicating said sensor is receiving radiation and a second state indicating said sensor is not receiving radiation;

second means connected to said emitter and responsive to said first means for interrogating said sensor, said second means causing said emitter to emit a predetermined sequence of a fixed number of pulses only when said first means is in said first state to verify whether said sensor is in communication with said emitter and hence that said door is closed;

third means connected to said sensor and providing a signal whenever said sensor fails to track said predetermined sequences; and

fourth means connected to said third means and providing an indication of unauthorized opening of said door in response to said signal.

2. Door interlock apparatus for monitoring the opening and closing of a door comprising:

a radiative emitter and a sensor positioned in operative association with said door so as to communicate with one another across a gap when said door is in closed position;

first means connect to said sensor and having a first state indicating said sensor is receiving radiation and a second state indicating said sensor is not receiving radiation;

second means connected to said emitter and responsive to said first means for interrogating said sensor, said second means causing said emitter to emit at least one pulse when said first means is in said first state to verify whether said sensor is in communication with said emitter and hence that said door is closed;

third means connected to said sensor and providing a signal whenever said sensor fails to track said at least one pulse;

fourth means connected to said third means and providing an indication of unauthorized opening of said door in response to said signal; and

fifth means providing an indication that said door is open whenever said first means is in said second state for a predetermined period.

3. The door interlock apparatus of claim 2 wherein said radiative emitter and said sensor operate at different current levels thereby to frustrate attempts to simulate communication of said emitter and sensor by shunting said emitter and sensor together.

4. Door interlock apparatus for monitoring the opening and closing of a door comprising:

a radiative emitter and a sensor positioned in operative association with said door so as to communicate with one another across a gap when said door is in closed position, wherein said emitter and said sensor operate at different current levels thereby to frustrate attempts to simulate communication of said emitter and sensor by shunting said emitter and sensor together;

first means connected to said sensor and having a first state indicating said sensor is receiving radiation;

second means connected to said emitter and responsive to said first means for interrogating said sensor, said second means causing said emitter to emit a predetermined sequence of pulses when said first means is in said first state to verify whether said sensor is in communication with said emitter and hence that said door is closed;

third means connected to said sensor and providing a signal whenever said sensor fails to track said predetermined sequence; and

fourth means connected to said third means and providing an indication of unauthorized opening of said door in response to said signal.

5. A method of monitoring the opening of a door, wherein a radiative emitter and a sensor are positioned in operative association with said door to communicate with one another when said door is in closed position, the method comprising the steps of:

monitoring whether radiation to said sensor is continuously interrupted for a predetermined duration;

when radiation to said sensor is continuously interrupted for said duration, providing a first signal for indicating said door is in open position;

when radiation to said sensor is not continuously interrupted for said duration, determining whether said emitter and said sensor are still in communication with one another, and when not still in communication with one another, providing a second signal indicating unauthorized opening of said door; and

when said emitter and said sensor are still in communication with one another, repeating the above-named steps.

6. The method of claim 5, further comprising the step of storing in a memory device in response to said second signal an indication that said door was opened.

7. Door interlock apparatus for monitoring entry to the interior of a secured cabinet by monitoring the opening and closing of an access door to said cabinet, the apparatus comprising:

light emitting means and light sensing means for receiving light from said light emitting means, one of said light emitting means and said light sensing means being mounted on said door and the other of said light emitting means and said light sensing means being mounted within said cabinet in position to communicate with said door-mounted means when said door is in closed position;

a microprocessor for verifying whether said door is open or closed, said microprocessor including;

input means responsive to said light sensing means and storing a sensor-status bit indicating whether said light sensing means is sensing light;

a counter responsive to said input means for counting off a predetermined time interval when said sensor-status bit indicates said light sensing means is not sensing light; and

output means connected to said light emitting means and providing a pulse control signal for pulsing said light emitting means when said sensor-status bit indicates said light sensing means is sensing light;

first indicator means connected to said microprocessor and providing an indication that said door is open whenever said counter counts off said predetermined time interval; and

second indicator means connected to said microprocessor and providing an indication of unauthorized access to said cabinet whenever said sensor-status bit fails to track said pulse control signal for a predetermined sequence of pulses.

8. The door interlock apparatus of claim 7 wherein said light emitting means and said light sensing means operate at different current levels thereby to frustrate attempts to simulate communication of said emitting means and sensing means by shunting said emitting means and said sensing means together.

9. The door interlock apparatus of claim 8, wherein said light emitting means is provided by a light emitting diode.

10. The door interlock means of claim 9, wherein said light sensing means is provided by a phototransistor.

11. A method of monitoring the opening of a door, wherein a radiative emitter and a sensor are positioned in operative association with said door to communicate with one another when said door is in closed position, the method comprising the steps of:

monitoring whether radiation to said sensor is continuously interrupted for a predetermined duration, said monitoring step including the substeps of;

providing an indicative signal whenever said sensor is receiving radiation; and

periodically determining over said predetermined duration whether said indicative signal is being provided, whereby failure to detect said indicative signal for the predetermined duration indicates that radiation to said sensor has been interrupted;

when radiation to said sensor is continuously interrupted for said duration, providing a first signal for indicating said door is in open position;

when radiation to said sensor is not continuously interrupted for said duration, determining whether said emitter and said sensor are still in communication with one another; and

when said emitter and said sensor are still in communication with one another, repeating the above-named steps.

12. A method of monitoring the opening of door, wherein a radiative emitter and a sensor are positioned in operative association with said door to communicate with one another when said door is in closed position, the method comprising the steps of:

providing a first signal when said sensor is receiving radiation;

causing said emitter to emit a sequence of a fixed number of pulses in response to said first signal;

monitoring whether said sequence is received by said sensor; and

providing a second signal to an indicator means when said sensor fails to receive said sequence, thereby indicating that said emitter and said sensor are not in communication with one another, for indicating an attempt to tamper with said door.

13. The method of claim 12, further comprising the step of operating said emitter and said sensor at different current levels, thereby to make said emitter and sensor inoperative when shunted together.

14. The method of claim 12, wherein said emitter is caused to emit said fixed number of pulses in a random sequence.

15. The method of claim 12, wherein said emitter is caused to emit said fixed number of pulses in a predetermined sequence.