Induced current absolute position transducer method using a code-track-type scale and read head

• US 6,054,851 A
• Filed: 01/20/1998
• Issued: 04/25/2000
• Est. Priority Date: 01/29/1997
• Status: Expired due to Term

• Current Assignee: Mitutoyo Corporation
• Original Assignee: Mitutoyo Corporation
• Inventors: Atherton, Kim W., Masreliez, Karl G., Andermo, Nils Ingvar
• Primary Examiner(s): STRECKER, GERARD R
• Application Number:
  US09/009,130
• Time in Patent Office: 826 Days
• Field of Search: 324/207.15-207.19, 324/207.24, 336/45, 336/130, 336/131, 336/136, 340/870.32, 340/870.33, 340/870.35, 340/870.36, 341/9-11, 341/13, 341/15, 341/16, 318/653
• US Class Current: 324/207.17
• CPC Class Codes: G01D 5/2053 by a movable non-ferromagnetic conductive element

Abstract

A high-accuracy inductive absolute position transducer system has two members movable relative to each other and includes a code track transducer and may include a fine track transducer. The code track transducers includes a code track transmitter winding and at least one set of code track receiver windings. Each set of code track receiver windings includes n balanced pairs. Each balanced pair extends along the measuring axis and includes a positive polarity winding and a negative polarity winding. A code track has a plurality of flux modulator zones distributed along the measuring axis. Flux modulators are formed in at least some of the flux modulator zones. A signal generating and processing circuit is connected to the transmitter winding and each balanced pair. The code track transmitter winding and each balanced pair form an inductive coupling. The flux modulators modulate the inductive coupling between each balanced pair and the code track transmitter winding based on the relative position between the read head member and the scale member. The flux modulators are distributed along the measuring axis such that each pair of adjacent flux modulator zones forms one of a set of output states in an overlying balanced pair. The pairs of adjacent flux modulator zones form a series of code elements extending along the measuring axis such that each set of m adjacent code elements forms a unique codeword. Each unique codeword defines an absolute position of the read head member relative to the scale member to a first resolution.

Claims

1. A method for determining an absolute position of a first member relative to a second member in an inductive position transducer, comprising:

taking a coded first-resolution absolute position measurement between the first and second members at a first resolution, comprising;

inputting a set of n adjacent code element measurements, each code element measurement responsive to at least one of a plurality of flux modulating code elements positioned along the measuring axis of one of the first and second members,

converting each of the n code element measurements into an output value,

combining the n output values into a multi-bit codeword, and

determining the first-resolution absolute position measurement from the multi-bit codeword.

2. The method of claim 1, further comprising:

taking a second-resolution incremental position measurement between the first and second members at a second resolution; and

determining a second-resolution absolute position measurement between the first and second members from the first-resolution absolute position measurement and the second-resolution incremental position measurement;

wherein the first resolution is coarser than the second resolution.

3. The method of claim 2, wherein the second-resolution incremental position measurement taking step comprises:

determining a phase φ

_F of the second resolution incremental position measurement, and

determining the second-resolution incremental position measurement from the phase φ

_F and an incremental scale wavelength λ

_F of the scale electrodes.

4. The method of claim 1, wherein, within any set of n adjacent code element measurements, at least two adjacent flux modulating code elements are identical to each other, such that at least one of the n code elements measurements produces an extreme measurement value independently of the relative positions of the first and second members along the measuring axis.

5. The method of claim 4, wherein the step of converting each of the n code elements includes adjusting at least one conversion limit for converting the n code elements using the extreme measurement value.

6. The method of claim 1, wherein, within any set of n adjacent code element measurements, at least two adjacent flux modulating code elements are identical to each other such that at least one of the n code elements measurements produces a maximum extreme measurement value independently of the relative positions of the first and second members along the measuring axis and at least two adjacent flux modulating code elements are identical to each other such that at least one of the n code elements measurements produces a minimum extreme measurement value independently of the relative positions of the first and second members along the measuring axis.

7. The method of claim 6, wherein the step of converting each of the n code elements includes adjusting conversion limits for converting the n code elements using the minimum and maximum extreme measurement values.

8. The method of claim 1, wherein the step of converting each of the n code elements includes:

identifying code elements measurements having an unambiguous output value,

identifying a position within the set of n code element measurements for each code element measurement having an unambiguous output value, and

determining an output value for each code element measurement that does not have an unambiguous output value based on the output values of the code element measurements having unambiguous output values and the identified positions within the set of n code element measurements for each code element measurement having an unambiguous output value.

9. The method of claim 1, wherein taking the coded first-resolution absolute position measurement further comprises inductively sensing a plurality of code elements positioned along the measuring axis.

10. The method of claim 1, wherein taking the coded first-resolution absolute position measurement further comprises independently sensing a plurality of code elements positioned along the measuring axis.

11. The method of claim 1, wherein taking the coded first-resolution absolute position measurement further comprises:

generating a magnetic field; and

spatially modifying the magnetic field.

12. The method of claim 11, wherein taking the coded first-resolution absolute position measurement further comprises sensing a strength of each of at least one portion of the spatially modified magnetic field.

13. The method of claim 12, wherein taking the coded first-resolution absolute position measurement further comprises:

outputting a first voltage signal if the strength of the spatially modified magnetic field has a first pattern; and

outputting a second voltage signal if the strength of the spatially modified magnetic field has a second pattern.

14. The method of claim 11, wherein taking the coded first-resolution absolute position measurement further comprises independently sensing the strength of at least one portion of the spatially modified magnetic field.

15. The method of claim 14, wherein taking the coded first-resolution absolute position measurement further comprises:

outputting a first voltage signal if the strength of the spatially modified magnetic field has a first pattern; and

outputting a second voltage signal if the strength of the spatially modified magnetic field has a second pattern.