Magnetic encoder using a displacement detecting circuit thereof

• US 5,949,051 A
• Filed: 10/27/1997
• Issued: 09/07/1999
• Est. Priority Date: 11/01/1996
• Status: Expired due to Term

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Kiriyama, Tetsuro
• Primary Examiner(s): LEE, MICHAEL GUNYOUNG
• Application Number:
  US08/958,153
• Time in Patent Office: 680 Days
• Field of Search: 235/449, 235/375, 235/439, 235/447, 235/450, 235/493, 235/494, 902/27
• US Class Current: 235/449
• 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 5/2451 Incremental encoders G01D5/2454 takes precedence

Abstract

A magnetic encoder that allows the power consumption to be reduced has a first member 1 magnetized at pitches λ and a second member 2 disposed so as to be relatively movable to the first member 1. The second member 2 has at least four MR devices Ma1, Mb1, Ma2, and Mb2 with phases that differ from by λ/4 each. The MR devices Ma1, Mb1, Ma2, and Mb2 are connected as a bridge circuit. Thus, a displacement detecting circuit 30 that outputs two-phase sine wave signals INA and INB is structured. The detecting circuit 30 is intermittently activated by analog switches Sa1, Sb1, Sa2, and Sb2 driven by a first clock CK1. The output signals INA and INB of the detecting circuit 30 are sampled by sample hold circuits 41a and 41b, respectively. The sampled values are compared by comparators 42a and 42b, whereby binary data is obtained. The comparators 42a and 42b each have a bias circuit 44 that is intermittently driven by a second clock CK2.

Claims

1. A magnetic encoder, comprising:

a first member having N magnetic pole portions and S magnetic pole portions alternately arranged in predetermined pitches;

a second member, disposed opposite to said first member and being relatively movable with respect to said first member, said second member having at least four magnetoresistance devices with phases that differ by 90°

, each corresponding to the pitches of the magnetic pole portions of said first member;

a displacement detecting circuit for obtaining a difference between output signals of the magnetoresistance devices with phases that differ by 180°

to output two-phase sine wave signals, amplitudes of the two-phase sine wave signals being varied corresponding to the relative movement of said first member and said second member, said displacement detecting circuit being driven by a DC power supply;

a signal processing circuit for generating two-phase square wave signals based on the two-phase sine wave signals obtained by said displacement detecting circuit;

a counter for counting the two-phase square wave signals generated by said signal processing circuit to obtain a relative position of said first member and said second member; and

a switch circuit for intermittently turning on/off an output of the DC power supply to said displacement detecting circuit corresponding to a first clock having a predetermined frequency.

2. The magnetic encoder according to claim 1,

wherein said displacement detecting circuit is a bridge circuit in which respective two devices of at least four magnetoresistance devices with phases that differ by 180°

are connected in series.

3. The magnetic encoder according to claim 1,

wherein said displacement detecting circuit has:

a sense circuit in which at least four magnetoresistance devices are connected to the DC power supply through respective current sources, the sense circuit having output terminals that are the connection nodes between the magnetoresistance devices and the current sources; and

two differential circuits for obtaining the difference of output signals obtained at the output terminals of the sense circuit with phases that differ by 180°

.

4. The magnetic encoder according to claim 1,

wherein said signal processing circuit has:

a pair of sample hold circuits for sampling and holding the two-phase sine wave signals obtained from said displacement detecting circuit by the first clock;

a pair of comparators, intermittently activated by a second clock with a phase delayed from the phase of the first clock, for comparing output signals of the sample hold circuits with a constant reference voltage to obtain binary data; and

a pair of flip-flops for receiving the binary data from the comparators to output the two-phase square wave signals.

5. The magnetic encoder according to claim 4,

wherein each of said sample hold circuits has an amplifying circuit disposed at one of an input terminal and an output terminal thereof, the amplifying circuit being activated by the first clock.

6. The magnetic encoder according to claim 1,

wherein said signal processing circuit has:

a pair of sample hold circuits for sampling and holding the two-phase sine wave signals obtained from said displacement detecting circuit by the first clock; and

an interpolation circuit for interpolating output signals of the sample hold circuits to obtain the two-phase square wave signals, the interpolation circuit being intermittently activated by a second clock with a phase delayed from the phase of the first clock.

7. The magnetic encoder according to claim 1,

wherein said signal processing circuit has:

a pair of comparators for comparing the two-phase sine wave signals received from said displacement detecting circuit with a predetermined reference voltage to obtain binary data, the comparators being intermittently activated with the first clock; and

a pair of flip-flops for receiving the binary data from the comparators to output the two-phase square wave signals.

8. The magnetic encoder according to claim 1,

wherein said signal processing circuit, said counter, and said switch circuit are disposed on said second member, and

wherein said second member has a display that displays output data of said counter.

9. A magnetic encoder, comprising:

a first member having N magnetic pole portions and S magnetic pole portions alternately arranged in predetermined pitches;

a second member, disposed opposite to said first member and being relatively movable with respect to said first member, said second member having at least four magnetoresistance devices with phases that differ by 90°

, each corresponding to the pitches of the magnetic pole portions of said first member;

a displacement detecting circuit for obtaining a difference between output signals of the magnetoresistance devices with phases that differ by 180°

to output two-phase sine wave signals, amplitudes of the two-phase sine wave signals being varied corresponding to the relative movement of said first member and said second member, said displacement detecting circuit being driven by a DC power supply;

a signal processing circuit for generating two-phase square wave signals based on the two-phase sine wave signals obtained by said displacement detecting circuit; and

a counter for counting the two-phase square wave signals generated by said signal processing circuit to obtain a relative position of said first member and said second member,

wherein a plurality of sets, each of which is composed of at least four of the magnetoresistance devices whose phases are 90°

shifted from each other, are arranged, and

wherein the magnetoresistance devices with same phase in the sets are connected as magnetic detecting devices in series.

10. The magnetic encoder according to claim 9,

wherein the pitches P of the magnetoresistance devices on said second member are represented by

11. The magnetic encoder according to claim 9,

wherein the four-phase magnetoresistance devices compose bridge circuits of which the magnetoresistance devices with phases that differ by 180°

are connected in series.

12. The magnetic encoder according to claim 9,

wherein said signal processing circuit is disposed in an IC chip disposed on said second member, and

wherein said magnetoresistance devices are composed by patterning a magnetoresistance thin film formed on an insulation film that coats the IC chip.

13. The magnetic encoder according to claim 12,

wherein said second member is an insulation substrate on which wiring lines and lead terminals are formed, the IC chip being disposed in a concave portion on a first surface of the insulation substrate, the first surface being opposite to said first member, the portion of which the IC chip is disposed being sealed with a resin in such a manner that the height of the portion is the same as the height of the peripheral portion of the insulation substrate.

14. The magnetic encoder according to claim 12,

wherein said second member is a substrate having a first surface and a second surface, the first surface being opposite to said first member, the second surface having wiring lines and input/output terminals, the IC chip being disposed on the second surface.