Apparatus for magnetically detecting position or speed or moving body utilizing bridge circuit with series connected MR elements

• US 4,818,939 A
• Filed: 02/26/1987
• Issued: 04/04/1989
• Est. Priority Date: 03/05/1986
• Status: Expired

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Takahashi, Tadashi, Miyashita, Kunio, Kawamata, Syooichi, Yamashita, Seizi
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US07/019,545
• Time in Patent Office: 768 Days
• Field of Search: 324/207, 324/208, 324/251, 324/252, 324/249, 324/173, 324/174, 324/178, 324/179, 324/260, 324/262, 338/32 R, 338/32 H
• US Class Current: 324/207.21
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/24438 Special design of the sensing element or scale
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence
• CPC Class Codes: G01P 3/487 delivered by rotating magnets

Abstract

Magnetic poles are provided continuously with a pitch λ on the peripheral portion of a drum rotated in accordance with a movement of a moving body. A magnetic sensor is provided in opposition to these poles. The sensor is formed of two magnetoresistive element pairs which are spaced from each other at λ/6, and the two elements in each pair are arranged in positions spaced from each other at λ/2. The two elements in each pair are connected in series to form a bridge circuit. The signals obtained from the nodes of the series-connected elements in the two element pairs are differentially amplified so that third harmonic wave components are eliminated, and a signal having no distortion and representative of the position or speed of the moving body can be obtained.

Claims

1. An apparatus for magnetically detecting the relative position or speed between moving and stationary bodies, comprising:

a magnetic medium provided on either one of the moving and stationary bodies, and having a plurality of magnetic poles arranged continuously thereon at a constant pitch λ

;

sensing means including plural MR elements, provided on the other of the moving and stationary bodies in opposition to said magnetic medium, for sensing a magnetic field generated by said magnetic poles to thereby cause variation in the electric resistance thereof, in which said MR elements constitute k sets of element pairs, each set consisting of two MR elements arranged at positions spaced at (m+1/2)λ

from one another, where m is an integer, and said element pairs being spaced by (n+1/3λ

from each other, wherein n is an integer; and

output circuit means, including said MR elements connected in a bridge circuit so that said two MR elements of each element pair are connected in series and said k sets of series connections of said MR elements are connected in parallel with each other with respect to a power source of the bridge circuit, for synthesizing k sets of voltages appearing at nodes of said two MR elements connected in series and which include third harmonic components having a phase difference of 2 π

/k from each other so as to produce an output signal.

2. An apparatus for magnetically detecting the relative position or speed between moving and stationary bodies according to claim 1, wherein said magnetic medium and said MR elements are opposed so closely that saturation in variation of the electric resistance of said MR elements causes distortion in the waveforms of voltages appearing across said MR elements, and said output circuit means enables an increase in the amplitude of the output signal.

3. An apparatus for magnetically detecting the relative position or speed between moving and stationary bodies according to claim 1, wherein said output circuit means provides a sinusoidal output signal.

4. An apparatus for magnetically detecting the position or speed of a moving body according to claim 1, wherein said MR elements constitute two MR element pairs, two MR elements in each pair being arranged in positions spaced at λ

/2, said MR element pairs being spaced from each other at λ

/6.

5. An apparatus for magnetically detecting the position or speed of a moving body according to claim 1, wherein said MR elements constitute two MR element pairs, two MR elements in each pair being arranged in positions spaced at 5λ

/2, said MR element pairs being spaced from each other at λ

/6.

6. An apparatus for magnetically detecting the position or speed of a moving body according to claim 1, wherein said MR elements constitute two MR element pairs, two MR elements in each pair being arranged in positions spaced at λ

/2, said MR element pairs being spaced from each other at 7λ

/6.

7. An apparatus for magnetically detecting the position or speed of a moving body according to claim 1, wherein said MR elements constitute two MR elements pairs, two MR elements in each pair being arranged in positions spaced at λ

/2, said MR element pairs being spaced from each other at 5λ

/6.

8. An apparatus for magnetically detecting the position or speed of a moving body according to claim 1, wherein said MR elements constitute three MR element pairs, two MR elements in each pair being arranged in positions spaced from each other at λ

/2, said MR element pairs being from each other at λ

/9.

9. An apparatus for magnetically detecting the position or speed of a moving body according to claim 1, wherein said MR elements constitute two MR element pairs.

10. An apparatus for magnetically detecting the position or speed of a moving body according to claim 9, wherein a voltage obtained from a node of each of said two pairs of series-connected MR elements is inputted into a differential amplifier, and an output is derived from said differential amplifier as a signal representative of the position or speed of said moving body.

11. An apparatus for magnetically detecting the position or speed of a moving body according to claim 10, wherein said MR elements in said two pairs of series-connected MR elements are connected so that the phases of the third harmonic components contained in the voltages obtained from the nodes thereof becomes opposite to each other, and said voltages are added to each other.

12. An apparatus for magnetically detecting the position or speed of a moving body according to claim 11, wherein said added voltages are inputted into one terminal of said amplifier with an offsetting voltage applied to the other terminal thereof.

13. An apparatus for magnetically detecting the position or speed of a moving body according to claim 1, wherein said MR elements constitute two MR element pairs, said output circuit means has a first connection formed by electrically connecting first elements in first and second MR element pairs together so that the third harmonic components contained in the voltages appearing in the respective elements offset each other and a second connection formed by electrically connecting second elements in said first and second MR element pairs together so that the third harmonic components contained in the voltage appearing in the respective elements offset each other, and said two connections are series-connected together and further to said power source to obtain said signal representative of the position or speed of said moving body from a node of said two series-connected connections.