Position transducer

• US 6,630,659 B1
• Filed: 06/28/1999
• Issued: 10/07/2003
• Est. Priority Date: 06/01/1994
• Status: Expired due to Fees

• Current Assignee: Stridsberg Innovation AB
• Original Assignee: Stridsberg Innovation AB
• Inventors: Stridsberg, Lennart
• Primary Examiner(s): SMITH, ZANDRA V
• Application Number:
  US09/340,156
• Time in Patent Office: 1,562 Days
• Field of Search: 250/231.13, 250/231.16, 250/231.14, 250/231.18
• US Class Current: 250/231.13
• CPC Class Codes: G01D 5/3473 Circular or rotary encoders

Abstract

A compact position and velocity transducer having a high speed resolution and a fast speed response and that does not place much demand on the precision of the bearings. The transducer includes an optical encoder that, when assembled in motors, is assembled on a short protruding part of the rotor close to the torque-creating parts. The optical incremental encoder signals are fed both to a moderate frequency digital counter that counts 4 counts per basic encoder period and to an A/D-converter that samples and digitizes the primary encoder analog signals. A processor uses a linearization algorithm on the sampled and digitized signals that yields position information that is locally highly continuous.

Claims

1. A position transducer comprising:

an encoder disc rigidly connected to a rotor of an electric motor rotatable about an axis, the encoder disc having an annular track for directly indicating an angular position of the encoder disc;

detector means comprising at least two detector groups, each of the at least two detector groups arranged to read the annular track at a reading place and to produce position signals directly indicating the position of the encoder disc, the reading places of the at least two detector groups being substantially symmetrically oriented around the axis of the encoder disc;

calculating means connected to each of the at least two detector groups for receiving the position signals and for independently of each other calculating values of the angular position of the encoder disc from the position signals received from each of the at least two detector groups; and

adding or averaging means connected to the calculation means for adding or averaging the values of the angular position to give a corrected value indicating the angular position of the encoder disc whereby, through the adding or averaging operation, position misreadings caused by radial movements of the encoder disc are canceled out of the corrected value.

2. The position transducer of claim 1, wherein the detector means comprise two detector groups, the reading places of the two detector groups being located on substantially opposite sides of the axis of the encoder disc.

3. The position transducer of claim 1, wherein the detector means comprise three detector groups, the reading places of the two detector groups having angular positions in regard of the encoder axis which are substantially 120°

apart from each other.

4. The position transducer of claim 1, wherein each of the at least two detector groups comprises at least two separate detector elements for producing the position signals delivered from each detector group, all of the at least two separate detector elements being located to read the annular track at the reading place of the detector group, with the separate detector elements in each detector group being located at a small distance from each other in a direction of the annular track and adapted to the distance of fields comprised in the annular track.

5. The position transducer of claim 4, wherein the at least two separate detector elements in the at least two detector groups are located at such a distance from each other that a periodic signal detected by one of the at least two separate detector elements has a considerable phase difference in relation to another periodic signal detected by the other of the at least two detector elements of the same detector group.

6. The position transducer of claim 5, wherein the considerable phase difference is between 60°

and 120°

.

7. The position transducer of claim 5, wherein the considerable phase difference is substantially 90°

.

8. A position transducer comprising:

an encoder disc rigidly connected to a rotor of an electric motor rotatable about an axis, the encoder disc having an annular track for directly indicating an angular position of the encoder disc;

detector means comprising at least two detector groups, each of the at least two detector groups arranged to read the annular track at a reading place and to produce position signals directly indicating the position of the encoder disc, the reading places of the at least two detector groups being substantially symmetrically oriented around the axis of the encoder disc;

adding or averaging means connected to the detector means for adding the position signals produced by the at least two detector groups to produce an added or averaged position signal, whereby, through the adding or averaging operation, position misreadings caused by radial movements of the encoder disc are eliminated from the added or averaged position signal; and

calculating means connected to the adding or averaging means for receiving the added or averaged position signal and for calculating values of the angular position of the encoder disc from the added or averaged position signal.

9. The position transducer of claim 8, wherein the detector means comprise two detector groups, the reading places of the two detector groups being located on substantially opposite sides of the axis of the encoder disc.

10. The position transducer of claim 8, wherein the detector means comprise three detector groups, the reading places of the two detector groups having angular positions in regard of the encoder axis which are substantially 120°

apart from each other.

11. The position transducer of claim 8, wherein each of the at least two detector groups comprises at least two separate detector elements for producing the position signals delivered from each detector group, all of the at least two separate detector elements being located to read the annular track at the reading place of the detector group, with the separate detector elements in each detector group being located at a small distance from each other in a direction of the annular track and adapted to the distance of fields comprised in the annular track.

12. The position transducer of claim 8, wherein each detector group comprises a same number of separate detector elements and the adding or averaging means comprising the same number of separate adding or averaging elements, one adding or averaging element being connected to one detector element in each detector group to receive the position signals produced by said detector elements.

13. The position transducer of claim 11, wherein the at least two separate detector elements in the at least two detector groups are located at such a distance from each other that a periodic signal detected by one of the at least two separate detector elements has a considerable phase difference in relation to another periodic signal detected by the other one of the at least two detector elements of the same detector group.

14. The position transducer of claim 13, wherein considerable phase difference is between 60°

and 120°

.

15. The position transducer of claim 13, wherein the considerable phase difference is substantially 90°

.