Displacement sensor and displacement detection method

Patent metadata

Field	Value
Publication number	US-9772198-B2
Application number	US-201314759710-A
Country	US
Kind code	B2
Filing date	Dec 18, 2013
Priority date	Jan 10, 2013
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

In a linear displacement sensor, two magnets with different polarities define one pitch of a magnetic scale. kn (k is a natural number greater than or equal to 2, n is a natural number greater than or equal to 1) sensor units configured to output a plurality of signals whose period is one pitch and whose phases with respect to the pitch are different are arranged along the magnetic scale in a one-pitch segment. Periodic errors with n periods per pitch of the sensor units are canceled out by averaging the phases from the kn sensor units.

First claim

What is claimed is:

1. A displacement sensor for detecting a position based on a magnetic scale by magnetic elements, the displacement sensor comprising:
a magnetic scale including a plurality of pitches arranged linearly in a single line and including two magnets with different polarities or a pair of a magnetic element and a non-magnetic element;
4n sensor units aligned in series in one pitch in a single line along the magnetic scale such that 4n signals with phases θ with respect to the pitch, each shifted by (90/n) degrees, are output, where n is 2 or 4;
an averaging unit configured to output an average of the 4n signals; and
a drive circuit configured to apply an AC signal with a sin ωt waveform to the 4n sensor units; wherein
each of the 4n sensor units includes a bridge including four magnetic elements and a phase detection unit configured to retrieve signals corresponding to sin θ sin ωt and cos θ sin ωt from the bridge and output a signal indicating the phase θ with respect to the pitch according to an addition theorem, and signals of phase detection units of the 4n sensor units indicating the phase θ are 4n signals having periodic errors in which one pitch of the magnetic scale corresponds to n periods.

2. The displacement sensor according to claim 1 , wherein
the sensor units are configured to output offset signals of the pitches during detection; and
the averaging unit is configured to obtain an average of the signals indicating the phases and the offset signals.

3. The displacement sensor according to claim 2 , wherein the magnetic scale is a magnet array for a linear motor.

4. A linear displacement sensor for detecting a linear position based on a magnetic scale by magnetic elements, the linear displacement sensor comprising:
a magnetic scale including a plurality of pitches arranged linearly in a single line and including a pair of two neighboring magnets with different polarities in a magnet array for a linear motor;
4n sensor units aligned in series in a single line along a length of one pitch such that when the length of the one pitch is p, positions along the magnetic scale differ by p/(4n), where n is 2 or 4;
an averaging unit configured to output an average of outputs from the 4n sensor units; and
a drive circuit configured to apply an AC signal with a sin ωt waveform to the 4n sensor units; wherein
each of the 4n sensor units includes a bridge including four magnetic elements and a phase detection unit configured to retrieve signals corresponding to sin θ sin ωt and cos θ sin ωt from the bridge and output a signal indicating the phase θ with respect to the pitch according to an addition theorem, and signals of phase detection units of the 4n sensor units indicating the phase θ have periodic errors with n periods per pitch.

5. The linear displacement sensor according to claim 4 , wherein the averaging unit is configured to add an average value of pitch origin coordinates bi detected by the 4n sensor units to an average value of intra-pitch coordinates ai from the 4n sensor units, where i is a natural number from 1 to 4n, and the 4n sensor units are configured to detect two adjacent pitches.

6. A method for detecting a displacement by detecting a position based on a magnetic scale by magnetic elements, the method comprising:
providing a magnetic scale including a plurality of pitches arranged linearly in a single line and including a pair of two neighboring magnets with different polarities in a magnet array for a linear motor;
providing 4n sensor units aligned in series in one pitch in a single line along the magnetic scale such that 4n signals with phases θ with respect to the pitch, each shifted by (90/n) degrees, are output, where n is 2 or 4;
providing a drive circuit configured to apply an AC signal with a sin ωt waveform to the 4n sensor units, each of the 4n sensor units including a bridge including four magnetic elements and a phase detection unit configured to retrieve signals corresponding to sin θ sin ωt and cos θ sin ωt from the bridge and output a signal indicating the phase θ with respect to the pitch according to an addition theorem, and signals of phase detection units of the 4n sensor units indicating the phase θ are 4n signals having periodic errors in which one pitch of the magnetic scale corresponds to n periods; and
averaging the 4n signals using an averaging unit to cancel out the periodic errors.

7. The displacement detection method according to claim 6 , wherein the magnetic scale is a magnet array for a linear motor.

8. The displacement sensor according to claim 1 , wherein each of the 4n sensor units outputs a pair of signals of cos θ•cos ωt and sin θ•sin ωt.

9. The displacement sensor according to claim 8 , wherein the phase detection unit converts the pair of signals output by each of the 4n sensor units to the signal cos(θ+ωt)=cos θ•cos ωt−sin θ•cos ωt.

Assignees

• Murata Machinery Ltd

Inventors

• Shimizu Tetsuya
• Kubo Hideki
• Hanaka Satoshi
• Ota Tatsuo
• Terada Shogo

Classifications

• G01D5/14 Primary

  influencing the magnitude of a current or voltage · CPC title

• G01D5/24476 Primary

  Signal processing (G01D5/2448 - G01D5/24495 take precedence) · CPC title

• G01R25/005

  Circuits for comparing several input signals and for indicating the result of this comparison, e.g. equal, different, greater, smaller, or for passing one of the input signals as output signal · CPC title

• G01R17/00

  Measuring arrangements involving comparison with a reference value, e.g. bridge · CPC title