Sensor apparatus and safety apparatus for protecting approach to machines

• US 6,376,939 B1
• Filed: 04/03/2000
• Issued: 04/23/2002
• Est. Priority Date: 04/02/1999
• Status: Expired due to Fees

• Current Assignee: Sumitomo Chemical Company Limited
• Original Assignee: Sumitomo Chemical Company Limited
• Inventors: Suzuki, Takashi, Washizaki, Ichirou, Umezaki, Shigeo
• Primary Examiner(s): Ballato, Josie
• Assistant Examiner(s): Deberadinis, Robert L.
• Application Number:
  US09/541,600
• Time in Patent Office: 750 Days
• Field of Search: 307/109, 307/116, 307/326, 307/320, 361/181, 340/562, 340/870.37, 327/517, 324/687
• US Class Current: 307/326
• CPC Class Codes: F16P 3/148 using capacitive technology
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/96075 involving bridge circuit

Abstract

A sensor apparatus and a safety apparatus which can ensure significantly enhanced safety by monitoring constantly whether the sensor apparatus is operating normally. An auxiliary electrode plate of a small area is disposed in parallel and in opposition to an electrode plate with a short distance therefrom. A switching element is turned on every second for a period of milliseconds repetitively. When the switching element is turned on under the control of a central processing unit, the auxiliary electrode plate is connected to the ground potential, as a result of which a capacitance ΔC effective between the auxiliary electrode plate and the electrode plate is electrically connected in parallel with a capacitor C₀ effective between the electrode plate and a machine component, resulting in that the capacitance C₀ is increased by a proportion corresponding to the capacitance ΔC. Consequently, change of the capacitance C₀ comparable to that brought about upon detection of the human body takes place, whereby a substantially similar detection signal as the human body detection signal is made available. On the basis of this detection signal, it is possible to monitor whether or not the sensor apparatus is operating normally.

Claims

1. A sensor apparatus for a machine grounded electrically, comprising:

at least one electrode plate disposed relative to said machine with a predetermined space from said machine;

an auxiliary electrode disposed in opposition to a portion of said at least one electrode plate;

a capacitance change detecting circuit for detecting whether a predetermined dielectric exists or not within said space on the basis of change of capacitance between said at least one electrode plate and said machine; and

monitor for monitoring normality of dielectric detecting operation of said sensor apparatus by electrically connecting periodically said auxiliary electrode plate to said capacitance change detecting circuit.

2. A sensor apparatus according to claim 1, further comprising:

a guard plate disposed at a rear side of said electrode plate; and

a shielding plate disposed at a rear side of said guard plate, said shielding plate being electrically grounded.

3. A safety apparatus for detecting entrance of at least a part of human body in a predetermined area of a machine grounded electrically, to thereby actuate safety securing means, said safety apparatus, comprising:

at least one electrode plate disposed relative to said machine with said area being interposed between said machine and said electrode plate;

an auxiliary electrode disposed in opposition to a portion of said at least one electrode plate;

a capacitance change detecting circuit for detecting whether a part of the human body exists or not in said area on the basis of change of capacitance between said at least one electrode plate and said machine; and

monitor for monitoring normality of human body detecting operation of said sensor apparatus by electrically connecting periodically said auxiliary electrode to said capacitance change detecting circuit.

4. A sensor apparatus, comprising:

a pair of electrode plates disposed in opposition to each other with a predetermined space being interposed therebetween;

an auxiliary electrode disposed in opposition to a portion of either one of said electrode plates;

a capacitance change detecting circuit for detecting whether a predetermined dielectric exists or not within said space on the basis of change of capacitance between said pair of electrode plates; and

monitor for monitoring normality of dielectric detecting operation of said sensor apparatus by electrically connecting periodically said auxiliary electrode to said capacitance change detecting circuit.

5. A sensor apparatus according to claim 4, further comprising:

a pair of shielding plates grounded electrically and disposed in opposition to said pair of electrode plates at sides opposite to said space, respectively.

6. A safety apparatus for detecting entrance of at least a part of human body in a predetermined area of a machine grounded electrically, to thereby actuate safety securing means, said safety apparatus, comprising:

a pair of electrode plates disposed in opposition to each other with said area being interposed between said pair of electrode plates;

an auxiliary electrode disposed in opposition to a portion of either one of said electrode plates;

a capacitance change detecting circuit for detecting whether at least a part of the human body exists or not in said area on the basis of change of capacitance between said pair of electrode plates; and

monitor for monitoring normality of human body detecting operation of said sensor apparatus by electrically connecting periodically said auxiliary electrode to said capacitance change detecting circuit.