Electronic personnel safety sensor

• US 3,947,734 A
• Filed: 09/06/1974
• Issued: 03/30/1976
• Est. Priority Date: 09/06/1974
• Status: Expired due to Term

• Current Assignee: Stanley Works Limited (Stanley Black & Decker, Inc.)
• Original Assignee: Stanley Works Limited (Stanley Black & Decker, Inc.)
• Inventors: Fyler, Norman F.
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): Moose, Jr., Harry E.
• Application Number:
  US05/503,970
• Time in Patent Office: 571 Days
• Field of Search: 317/DIG. 2, 317/146, 317/123, 340/258 R, 340/258 B, 340/258 C, 307/116, 192/130, 323/75 M
• US Class Current: 361/181
• CPC Class Codes: F16P 3/148 using capacitive technology

Abstract

An electronic personnel safety sensor is provided capable of causing a machine or operation to be shut off to prevent injury to personnel or damage to equipment protected, by detecting, indicating, and acting upon a predetermined increase or decrease in effective capacitance caused by the introduction, or intrusion, or withdrawal of material to or from a field or protection zone created by a suitably designed and connected electrode structure. The sensor is operable in a fail-safe manner inasmuch as it does not contain any single component, part or electrical connection, the failure or removal of which would cause the sensor to permit the protected machine or operation to operate. The sensor embodies circuitry wherein all activated units thereof are connected in series and are furnished an enabling signal from a common source. The initial signal may be provided from a crystal controlled, amplitude regulated oscillator signal generator source and is AC coupled to a modified null electronic capacity sensing type bridge. The latter bridge has two symmetrically disposed arms, one of which contains a fixed reference capacitor and the other of which contains the combination of an antenna and an adjustable capacitance. The latter is used to bring the two arms of the bridge to the "null" set condition that corresponds with normal operation of the protected machine or implied non-penetration of the protection field. The original signal from the oscillator is modified by the bridge according to the state of balance. The portion of the signal passed on by the bridge is larger at a state of unbalance and a minimum but not zero, at optimum balance. This modulated signal is again AC coupled to the next stage, i.e., an operational amplifier via a suitable transformer but at the input of the operational amplifier the signal is processed to produce rectified AC with a polarized or DC component that in a specific manner in combination with the adjusted characteristics of the operational amplifier causes the latter and the following units including a normally open relay which has been moved to a closed contact position to deenergize, i.e., to completely and precipitously to effectively stop amplifying or passing the original signal if the unbalance of the bridge falls outside of prescribed limits.

Claims

1. An electronic personnel safety sensor operable to cause a machine or operation to be shut off to prevent injury to personnel or damage to equipment being protected comprising:

a. a power source including terminal means connectible to a power supply to provide to the sensor, said power source further including a bridge rectifier and a transformer connected in series circuit relation with said terminal means and AC coupled to said bridge rectifier;

b. electronic circuit means including a signal source and a multiplicity of AC coupled selectively saturable subsequent stages connected in series circuit relation with said signal source, said signal source providing a signal therefrom operable to effect excitation of said multiplicity of AC coupled selectively saturable subsequent stages, said electronic circuit means also including transformers interposed between successive ones of said multiplicity of AC coupled selectively saturable subsequent stages operable to provide the AC coupling therebetween, said transformers being purposefully tuned to provide said transformers with a preselected resonance, said electronic circuit means additionally including a capacitance sensing bridge coupled to said signal source having a predetermined state of balance condition corresponding to the normal operating state of the equipment being protected and operable to modify said signal from said signal source according to the deviation from said predetermined state of balance condition of said capacitance sensing bridge, said capacitance sensing bridge having four legs, two of said four legs of said capacitance sensing bridge comprising inductors operable to inductively couple said capacitance sensing bridge to one of said multiplicity of AC coupled selectively saturable subsequent stages, said one of said multiplicity of AC coupled selectively saturable subsequent stages comprising amplifying means operable for amplifying said modulated signal received thereby from said capacitance sensing bridge, said amplifying means being coupled to another one of said multiplicity of AC coupled selectively saturable subsequent stages, said another one of said multiplicity of AC coupled selectively saturable subsequent stages comprising a relay driver; and

c. relay means connected in circuit relation with said relay driver and excitable by said modulated signal received thereby from said relay driver, said relay means being deactivated when said modulated signal departs from a preestablished level corresponding to said predetermined state of balance condition of said capacitance sensing bridge, said relay means comprising a pair of redundant relays and associated contacts.

2. The electronic personnel safety sensor as set forth in claim 1 wherein said signal source of said electronic circuit means comprises a transistor.

3. The electronic personnel safety sensor as set forth in claim 1 wherein one of the other two legs of said four legs of said capacitance sensing bridge includes a fixed reference capacitor and the other one of the other two legs of said four legs of said capacitance sensing bridge includes an antenna and an adjustable capacitance connected in electrical series circuit relation with said antenna.

4. The electronic personnel safety sensor as set forth in claim 1 wherein said amplifying means of said electronic circuit means consists of a transistor amplifier.

5. An electronic personnel safety sensor operable to cause a machine or operation to be shut off to prevent injury to personnel or damage to equipment being protected comprising:

a. a power source including terminal means connectible to a power supply to provide power to the sensor, said power source further including a pair of integrated circuits, a pair of bridge rectifiers each connected in circuit relation with a corresponding one of said pair of integrated circuits, and a pair of transformers connected in circuit relation with said terminal means and each AC coupled to a corresponding one of said pair of bridge rectifiers;

b. electronic circuit means including a signal source and a multiplicity of AC coupled selectively saturable subsequent stages connected in series circuit relation with said signal source, said signal source providing a signal therefrom operable to effect excitation of said multiplicity of AC coupled selectively saturable subsequent stages, said electronic circuit means also including transformers interposed between successive ones of said multiplicity of AC coupled selectively saturable subsequent stages operable to provide the AC coupling therebetween, said transformers being purposefully tuned to provide said transformers with a preselected resonance, said electronic circuit means additionally including a capacitance sensing bridge coupled to said signal source having a predetermined state of balance condition corresponding to the normal operating state of the equipment being protected and operable to modify said signal from said signal source according to the deviation from said predetermined state of balance condition of said capacitance sensing bridge, said capacitance sensing bridge having four legs, two of said four legs of said capacitance sensing bridge comprising inductors operable to inductively couple said capacitance sensing bridge to one of said multiplicity of AC coupled selectively saturable subsequent stages comprising amplifying means operable for amplifying said modulated signal received thereby from said capacitance sensing bridge, said amplifying means being coupled to another one of said multiplicity of AC coupled selectively saturable subsequent stages, said another one of said multiplicity of AC coupled selectively saturable subsequent stages comprising a relay driver; and

c. relay means connected in circuit relation with said relay driver and excitable by said modulated signal received thereby from said relay driver, said relay means being deactivated when said modulated signal departs from a preestablished level corresponding to said predetermined state of balance condition of said capacitance sensing bridge, said relay means comprising a pair of redundant relays and associated contacts.

6. The electronic personnel safety sensor as set forth in claim 5 wherein one of the other two legs of said four legs of said capacitance sensing bridge includes a fixed reference capacitor and the other one of the other two legs of said four legs of said capacitance sensing bridge includes an antenna and an adjustable capacitance connected in electrical series circuit relation with said antenna.

7. The electronic personnel safety sensor as set forth in claim 5 wherein said signal source comprises a 465 khz crystal control, amplitude regulated oscillator.

8. The electronic personnel safety sensor as set forth in claim 5 wherein said amplifying means of said electronic circuit means comprises an integrated circuit operational amplifier operated in a region of near saturation.

9. The electronic personnel safety sensor as set forth in claim 5 wherein said relay driver consists of four transistors connected in circuit relation so as to be arranged in a complementary array.