High-frequency oscillation type proximity sensor

• US 7,030,626 B2
• Filed: 06/17/2002
• Issued: 04/18/2006
• Est. Priority Date: 06/18/2001
• Status: Active Grant

• Current Assignee: Yamatake Corporation
• Original Assignee: Yamatake Corporation
• Inventors: Hayashi, Takumi, Hatanaka, Hiroshi, Kawai, Shinichi
• Primary Examiner(s): DEB, ANJAN K
• Application Number:
  US10/480,990
• Publication Number:
  US 20040150412A1
• Time in Patent Office: 1,401 Days
• Field of Search: 324/635, 324/655, 324/207.15, 324/236, 331/176
• US Class Current: 324/635
• CPC Class Codes: G01V 3/10 using induction coils

Abstract

A high-frequency oscillation proximity sensor with an improved detection sensitivity uses, as a detection coil 11, a two-thread coil formed of substantively two coil conductors joined together at their first ends to form a joint connection end and twisted together, one of the two coil conductors being used as a resonance circuit coil L1 and the other as a copper resistance compensation coil L2, and comprises a drive circuit 12 for supplying a drive current to the joint connection end of the two-thread coil to thereby drive the detection coil to oscillate, a buffer 13 for taking out an oscillating output voltage generated at the joint connection end of the two-thread coil, and a phase shift circuit 15 for turning the phase of the oscillating output voltage taken out by the buffer by a predetermined angle and feeding it back to the copper resistance compensation coil to thereby negate the copper resistance of the two-thread coil. The drive circuit comprises a nonlinear amplifier 21 for changing the amplitude of the oscillating voltage generated at the two-thread coil in multiple stages to thereby impart a soft oscillation characteristic to a high-frequency oscillation circuit comprising the nonlinear amplifier and the two-thread coil.

Claims

1. A high-frequency oscillation proximity sensor, comprising:

a two-thread coil formed of two coil conductors each having a first end and a second end, joined together at their respective first ends to form a joint connection end and twisted together, one of the two coil conductors being used as a resonance circuit coil and the other as an internal resistance compensation coil,

a drive circuit for supplying a drive current to the joint connection end of the two-thread coil for oscillation,

a compensation means for making a current having the same intensity as a current flowing from the first end to the second end of the resonance circuit coil flow from the second end of the resonance circuit coil to the second end of the internal resistance compensation coil to thereby virtually short-circuit an internal resistance of the resonance circuit coil.

2. The high-frequency oscillation proximity sensor according to claim 1, wherein the internal resistance of the resonance circuit coil is virtually short-circuited by the compensation means in the manner that in an equivalent circuit for the two-thread coil in which an internal resistance of the resonance circuit coil and an internal resistance of the internal resistance compensation coil are each series-connected to a joint connection point of a series circuit comprising a self-inductance of the two-thread coil and an AC resistance thereof connected in series, said joint connection point is virtually grounded.

3. The high-frequency oscillation proximity sensor according to claim 1, wherein the compensation means comprises an inverting amplifier for inverting and amplifying a voltage generated at the second end of the internal resistance compensation coil and negatively feeding it back to the second end of the resonance circuit coil.

4. The high-frequency oscillation proximity sensor according to claim 3, wherein the inverting amplifier is an operational amplifier arranged to have virtually an infinitely large gain.

5. The high-frequency oscillation proximity sensor according to claim 1, wherein the drive circuit for supplying a drive current to the joint connection end of the two-thread coil for oscillation comprises a nonlinear amplifier for changing the oscillation amplitude at the joint connection end depending on change in Q of the two-thread coil.

6. The high-frequency oscillation proximity sensor according to claim 5, wherein the nonlinear amplifier changes the amplitude of the oscillating voltage generated at the two-thread coil in multiple stages to thereby impart a soft oscillation characteristic to a high-frequency oscillator circuit comprising the nonlinear amplifier and the two-thread coil.