Absolute position encoder scale having layers in a stacked configuration

• US 9,435,663 B2
• Filed: 08/22/2014
• Issued: 09/06/2016
• Est. Priority Date: 08/22/2014
• Status: Active Grant

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Cook, Ted Staton
• Primary Examiner(s): Tang, Minh N
• Assistant Examiner(s): FREDERIKSEN, DAVID B
• Application Number:
  US14/466,865
• Publication Number:
  US 20160054154A1
• Time in Patent Office: 746 Days
• US Class Current: 1/1
• CPC Class Codes: G01B 3/205 provided with a counter for digital indication of the measured dimension
• CPC Class Codes: G01D 5/2046 by a movable ferromagnetic element, e.g. a core
• CPC Class Codes: G01D 5/2066 by movement of a single coil with respect to a single other coil
• CPC Class Codes: G01D 5/2455 with incremental and absolute tracks on the same encoder
• CPC Class Codes: G01D 5/249 using pulse code
• CPC Class Codes: G01D 5/34776 Absolute encoders with analogue or digital scales

Abstract

An absolute position encoder scale includes first and second layers in a stacked configuration. A read head moves relative to spatial modulation patterns of first (top) and second (lower) signal layers along a measuring axis, and a sensing portion produces one or more scale sensing fields to sense the signal layers. A higher frequency scale sensing field may provide a first limited sensing depth to sense position relative to the top signal layer pattern, and a lower frequency field may provide a second deeper sensing depth to sense position relative to the lower signal layer pattern. In some embodiments, an isolation layer between the first and second layers may include a spatial modulation pattern that complements the first layer pattern, to nullify its signal effects when sensing position relative to the second layer pattern using the second sensing depth.

Claims

1. A position sensing device usable to measure a position of a first member with respect to a second member along a measuring axis, the position sensing device comprising:

a scale comprising first and second layers that extend along the measuring axis and that are stacked on one another along a depth direction that is approximately normal to the scale layers, the first layer comprising material forming a first spatial modulation pattern along the measuring axis, and the second layer comprising material forming a second spatial modulation pattern along the measuring axis that is different than the first spatial modulation pattern over an absolute range along the measuring axis; and

a read head for being moved relative to the scale along a direction of the measuring axis, the read head comprising a sensing portion arranged along the depth direction relative to the scale and configured to produce at least one scale sensing field that may be modulated by the first and second spatial modulation patterns of the first and second layers and provide first and second position signal components based on using first and second circuit configurations to provide a first smaller signal-sensing depth and a second smaller signal-sensing depth for the at least one scale sensing field;

and configured wherein;

the first layer is closer to the read head along the depth direction than the second layer, and the first spatial modulation pattern of the first layer provides a dominant first position signal component sensed using the first circuit configuration;

the second spatial modulation pattern of the second layer provides a significant second position signal component sensed using the second circuit configuration and a less significant second position signal component when using the first circuit configuration; and

the first and second spatial modulation patterns are configured such that the second position signal component includes a signal characteristic that provides a plurality of unique values relative to the first position signal component at corresponding positions along the absolute range.

2. The position sensing device of claim 1, configured wherein the second spatial modulation pattern of the second layer provides an insignificant second position signal component when using the first circuit configuration.

3. The position sensing device of claim 1, wherein the at least one scale sensing field is a changing field and the first circuit configuration corresponds to a higher temporal frequency or frequency range of the scale sensing field, and the second circuit configuration corresponds to a lower temporal frequency or frequency range of the scale sensing field.

4. The position sensing device of claim 3, wherein the first and second circuit configurations are operate according to at least one of one of a) or b), comprising:

a) the first circuit configuration provides a first scale sensing field at the higher temporal frequency or frequency range at a first time, the second circuit configuration provides a second scale sensing field at the lower temporal frequency or frequency range at a second time, and the read head senses the first position signal component at the first time and the second position signal component at the second time, or

b) the first circuit configuration senses the modulation of the at least one scale sensing field using a higher limited or filtered frequency range which corresponds to the higher temporal frequency or frequency range, and the second circuit configuration senses the modulation of the at least one scale sensing field using a lower limited or filtered frequency range which corresponds to the lower temporal frequency or frequency range.

5. The position sensing device of claim 4, wherein the first and second circuit configurations operate according to b), and the read head is configured to generate a changing scale sensing field that simultaneously includes both the higher and lower temporal frequencies or frequency ranges.

6. The position sensing device of claim 3, wherein the first and second circuit configurations are responsive to respective eddy currents that arise in a material of the first and second spatial modulation patterns and modulate the at least one scale sensing field in order to provide the first and second position signal components.

7. The position sensing device of claim 3, wherein the first layer has a thickness along the depth direction that is at least one times a first skin depth, wherein that first skin depth is determined based on a material forming the first spatial modulation pattern and the higher temporal frequency or frequency range corresponding to the first circuit configuration.

8. The position sensing device of claim 3, wherein the first layer has a thickness along the depth direction that is at most 0.5 times a second skin depth, wherein that second skin depth is determined based on a material forming the first spatial modulation pattern and the lower temporal frequency or frequency range corresponding to the second circuit configuration.

9. The position sensing device of claim 3, wherein a thickness along the depth direction of the material forming the second spatial modulation pattern of the second layer is at least two times a thickness along the depth direction of the material forming the first spatial modulation pattern of the first layer.

10. The position sensing device of claim 1, wherein the scale further comprises an isolating layer comprising one of a) a material forming a uniform layer, or b) a material forming a third spatial modulation pattern, that extends along the measuring axis and is located between the first and second layers.

11. The position sensing device of claim 10, wherein the isolating layer is a material forming a uniform layer, and a thickness of the first layer added to a thickness of the isolating layer along the depth direction is at least one times a first skin depth, wherein that first skin depth is determined based on the material forming the uniform layer and the higher temporal frequency or frequency range corresponding to the first circuit configuration.

12. The position sensing device of claim 10, wherein:

the isolating layer is a material forming a third spatial modulation pattern; and

the third spatial modulation pattern of the isolating layer is configured in relation to the first spatial modulation pattern of the first layer to at least partially nullify the modulation effect of the first spatial modulation pattern when using the second circuit configuration and thereby at least partially nullify the first position signal component when using the second circuit configuration.

13. The position sensing device of claim 12, wherein:

the material forming the first and third spatial modulation patterns is the same material; and

the first and third spatial modulation patterns are complements such that a combined thickness along the depth direction of the material forming the first and third spatial modulation patterns is nominally constant between the read head and the second layer.

14. The position sensing device of claim 13, wherein the first spatial modulation pattern is periodic and has a wavelength P, the third spatial modulation is periodic and has the wavelength P, and the first and third spatial modulation patterns are shifted along the measuring axis by approximately 180 degrees of spatial phase shift relative to one another.

15. The position sensing device of claim 13, wherein each of the first and third spatial modulation patterns comprise one of a) material thickness modulations along the depth direction, or b) material width modulations along a direction transverse to the depth direction and the measuring axis.

16. The position sensing device of claim 10, wherein:

the isolating layer is a material forming a third spatial modulation pattern; and

the third spatial modulation pattern of the isolating layer is configured work in combination with the second spatial modulation pattern of the second layer to provide a combined modulation effect of the second and third spatial modulation patterns in the second position signal component sensed using the second circuit configuration.

17. The position sensing device of claim 1, wherein the first spatial modulation pattern is periodic and has a first wavelength P, and the second spatial modulation pattern comprises at least one of a) a periodic pattern that has a second wavelength P′

different than the wavelength P to provide a spatially periodic second position signal component that provides a plurality of unique phase relationship values relative to a spatially periodic first position signal component at corresponding positions along the absolute range, or b) a pattern that varies linearly or nonlinearly to provide a second position signal component that provides a plurality of unique signal amplitude values relative to the first position signal component at corresponding positions along the absolute range.

18. The position sensing device of claim 1, wherein each of the first or second spatial modulation patterns comprise one of a) material thickness modulations along the depth direction, or b) material width modulations along a direction transverse to the depth direction and the measuring axis.

19. The position sensing device of claim 18, wherein the material thickness or width modulations of the first or second spatial modulation patterns are fabricated by machining or forming a homogeneous material, or in printed circuit board materials using printed circuit board fabrication techniques.

20. The position sensing device of claim 1, wherein the first and second layers comprise fabricated portions of a monolithic piece of scale material, or comprise layers in multilayer printed circuit board.