Magnetic position detecting device

• US 20040075426A1
• Filed: 05/07/2003
• Published: 04/22/2004
• Est. Priority Date: 05/08/2002
• Status: Active Grant

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Kamogi, Yutaka, Wakiyama, Koji
• Granted Patent: US 6,940,274 B2
• Time in Patent Office: Days
• US Class Current: 324/207.12
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06

Abstract

To provide a magnetic position detecting device which is capable of extremely accurately detecting a reference position.

In a magnetic position detecting device for detecting a position of a moving body 2 to a fixed body 1 on the basis of a change of a magnetic flux density that a Hall element 4 senses when the moving body 2 provided with a magnet 6 and the fixed body 1 provided with the Hall element 4 move relatively to each other. An S-pole and an N-pole of the magnet 6 are juxtaposed along a direction in which the magnet 6 and the Hall element 4 move relatively to each other. When the Hall element 4 passes a boundary position between the S-pole and the N-pole of the magnet 6, a magnetic flux density that the Hall element 4 senses is zero. The polarities of the magnetic field are completely inverted. Therefore, a variation of the position where the magnetic flux density sensed by the Hall element 4 is zero is completely eliminated. Only during a fixed period that the magnet 6 and the Hall element 4 mutually approach, a detect signal which depends on a magnetic flux density sensed by the Hall element 4 is compared with a reference signal. By detecting a position where both the signals are equal in level, a reference position is considerably accurately detected.

Claims

1. A magnetic position detecting device in which a magnet is mounted on one of a fixed body and a moving body, and a magnetism-sensitive element is mounted on the other of said fixed body and said moving body and a position of said moving body to said fixed body is detected based on a change of a magnetic flux density that said magnetism-sensitive element senses, the improvement being characterized in that

an S-pole and an N-pole of the magnet are juxtaposed along a direction in which said magnet and said magnetism-sensitive element move relatively to each other, and

said magnetic position detecting device comprises:

a reference signal generating circuit for generating a signal for detecting a position at which a magnetic flux density that said magnetism-sensitive element senses is zero;

a comparing circuit for comparing a detect signal which depends on an output signal of said magnetism-sensitive element, with said reference signal, and for producing a reference position detect signal of a predetermined level when said detect signal and said reference signal are equal in level; and

a comparing signal control circuit for controlling said detect signal or said reference signal to be input to said comparing circuit so that said reference position detect signal of a predetermined level is output only during a fixed period that said magnet and said magnetism-sensitive element mutually approach.

2. A magnetic position detecting device according to claim 1, wherein said reference signal generating circuit produces a signal having a level equal to an average level of an output signal of said magnetism-sensitive element, in the form of said reference signal.