Inductive displacement sensor system detecting displacements in two directions using a multi-bridge circuit

• US 5,760,578 A
• Filed: 08/16/1996
• Issued: 06/02/1998
• Est. Priority Date: 08/22/1995
• Status: Expired due to Fees

• Current Assignee: Ebara Corporation
• Original Assignee: Ebara Corporation
• Inventors: Watanabe, Katsuhide, Moriyama, Shinichi, Hiraki, Naoji
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US08/697,007
• Time in Patent Office: 655 Days
• Field of Search: 324/207.15-207.26, 324/234, 340/870.32, 340/870.35, 340/870.36
• US Class Current: 324/207.19
• CPC Class Codes: G01B 7/14 for measuring distance or clearance between spaced objects or spaced apertures G01B7/30 takes precedence
• CPC Class Codes: G01B 7/312 for measuring eccentricity, i.e. lateral shift between two parallel axes
• CPC Class Codes: G01D 5/2013 by a movable ferromagnetic element, e.g. a core G01D5/2033 takes precedence

Abstract

A displacement sensor system is provided which is capable of simultaneously and independently detecting displacements in two directions orthogonal to an axis of an object to be detected, using a less number of displacement sensors than before. The displacement sensor system, for enabling the simultaneous detection of displacements in two directions orthogonal to an axial direction of a pillar-shaped member, has a plurality of displacement sensors positioned around the pillar-shaped member, and a detector circuit for receiving outputs of the plurality of displacement sensors to output signals indicative of displacements in the two directions orthogonal to the axial direction of the pillar-shaped member. The detector circuit includes a multi-bridge circuit for parallelly connecting a circuit having the plurality of displacement sensors connected in series to a plurality of resistor circuits. In one embodiment of the present invention, the pillar-shaped member has a square prism portion, and the plurality of displacement sensors include four displacement sensors, where the displacement sensors are positioned in a plane parallel to a set of opposite surfaces of the square prism portion and in the vicinity of four corners of the square prism portion, respectively. The four displacement sensors are connected in series to form an inductance circuit which constitutes a part of the multi-bridge circuit.

Claims

1. A displacement sensor system capable of simultaneously detecting displacements of a pillar-shaped member in two directions orthogonal to an axial direction of said pillar-shaped member, comprising:

a plurality of displacement sensors positioned around said pillar-shaped member, said pillar-shaped member having a rectangular prism portion, and said plurality of displacement sensors including four sensors, said displacement sensors positioned in a plane parallel to a set of opposite surfaces of said rectangular prism portion and in the vicinity of four corners of said rectangular prism portion;

said four displacement sensors being connected in series to form an inductance circuit; and

a detector circuit for receiving outputs of said plurality of displacement sensors and producing output signals indicative of displacements in the two directions orthogonal to the axial direction of said pillar-shaped member, said detector circuit including a multi-bridge circuit, said multi-bridge circuit including;

a first bridge circuit including a first resistor circuit formed of a first resistor and a second resistor having a resistance value three times the resistance value of said first resistor connected in series and said inductance circuit and having an output;

a second bridge circuit including a second resistor circuit formed of third and fourth resistors each having a resistance value twice the resistance value of said first resistor connected in series and said inductance circuit and having an output; and

a third bridge circuit including a third resistor circuit formed of a fifth resistor having a resistance value three times the resistance value of said first resistor and a sixth resistor having the same resistance value as the first resistor connected in series and said inductance circuit and having an output.

2. A displacement sensor system according to claim 1, wherein:

said detector circuit comprises;

a differential amplifier unit including a first differential amplifier for receiving an output from said first bridge circuit, a second differential amplifier for receiving an output from said second bridge circuit, and a third differential amplifier for receiving an output from said third bridge circuit;

an envelope detector unit including envelope detectors for detecting envelopes of outputs of said first-third differential amplifiers, respectively; and

a processing unit for receiving outputs of said respective envelope detectors to output signals indicative of displacements of said rectangular prism portion in two directions orthogonal to an axis of said rectangular prism portion.