Code disk, optical encoder, and motor system

• US 8,525,459 B2
• Filed: 07/15/2010
• Issued: 09/03/2013
• Est. Priority Date: 07/15/2010
• Status: Active Grant

• Current Assignee: HEIDENHAIN Corp. (Dr. Johannes Heidenhain GmbH)
• Original Assignee: HEIDENHAIN Corp. (Dr. Johannes Heidenhain GmbH)
• Inventors: Setbacken, Robert M., Franklin, Ruth E.
• Primary Examiner(s): Ip, Paul
• Application Number:
  US12/837,071
• Publication Number:
  US 20120013279A1
• Time in Patent Office: 1,146 Days
• Field of Search: 318/400.04, 318/400.37, 318/254, 318/567, 318/651, 318/662, 318/266, 318/400.4, 318/640, 250/231.13, 250/231.14, 250/237.G, 250/231.18, 324/207.22
• US Class Current: 318/400.4
• CPC Class Codes: G01D 5/3473 Circular or rotary encoders
• CPC Class Codes: G01D 5/34792 with only digital scales or both digital and incremental scales

Abstract

An optical encoder includes a light source, a light sensor array, and a code disk having a data track and a commutation pattern. The commutation pattern includes first, second, and third commutation tracks, each including a series of apertures configured to allow light to continuously pass from the light source to a respective light sensor of the light sensor array as the series of apertures passes over the first light sensor. The relative positions of the first, second, and third commutation tracks correspond to a commutation sequence of a brushless motor.

Claims

1. An optical encoder, comprising:

a light source;

a light sensor array; and

a code disk including;

a data track having a plurality of slots configured to allow light from the light source to pass to the light sensor array to determine a rotational position and direction of the code disk; and

a commutation pattern having;

a first commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a first light sensor of the light sensor array such that the first light sensor continuously receives light as the series of apertures passes over the first light sensor;

a second commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a second light sensor of the light sensor array such that the second light sensor continuously receives light as the series of apertures passes over the second light sensor; and

a third commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a third light sensor of the light sensor array such that the third light sensor continuously receives light as the series of apertures passes over the third light sensor;

wherein the relative positions of the first, second, and third commutation tracks correspond to a continuous commutation sequence of a first coil, a second coil, and a third coil of a brushless motor.

2. The optical encoder of claim 1, wherein the first commutation track is disposed at a first radial distance from a rotation axis of the code disk, the second track is disposed at a second radial distance from the rotation axis, the second radial distance being less than the first radial distance, and the third commutation track is disposed at a third radial distance from the rotation axis, the third radial distance being less than the second radial distance.

3. The optical encoder of claim 1, wherein the apertures of the first, second, and third tracks are circular.

4. The optical encoder of claim 3, wherein the diameter of the apertures of the first, second, and third tracks is between 0.1 and 0.2 mm.

5. The optical encoder of claim 3, wherein the diameter of the apertures of the first, second, and third tracks is 0.16 mm.

6. The optical encoder of claim 1, wherein:

adjacent apertures of the series of the first track are spaced apart from each other by a first distance;

adjacent apertures of the series of the second track are spaced apart from each other by a second distance, the second distance being less than the first distance; and

adjacent apertures of the series of the third track are spaced apart from each other by a third distance, the third distance being less than the second distance.

7. The optical encoder of claim 1, wherein the data track is disposed at a fourth radial distance from the rotation axis, the fourth radial distance being greater than the first radial distance.

8. The optical encoder of claim 1, wherein the commutation sequence corresponds to a one pole-pair brushless motor.

9. The optical encoder of claim 8, wherein the brushless motor has a stator having exactly three electromagnets.

10. The optical encoder of claim 1, wherein the thickness of the code disk is between 25 microns and 40 microns.

11. The optical encoder of claim 1, wherein:

the series of apertures of the first commutation track extends 180 mechanical degrees around the rotation axis;

the series of apertures of the second commutation track extends 180 mechanical degrees around the rotation axis; and

the series of apertures of the third commutation track extends 180 mechanical degrees around the rotation axis.

12. The optical encoder of claim 11, wherein, moving clockwise around the rotation axis of the code disk, the first aperture in the series of the second commutation track is disposed 120 mechanical degrees from the first aperture of the series of the first commutation track, and the first aperture in the series of the third commutation track is disposed 120 mechanical degrees from the first aperture in the series of the second commutation track.

13. The optical encoder of claim 1, wherein the first commutation track, the second commutation track, and the third commutation track each include two series of apertures, the two series being separated by disk portions that prevent light from passing from the light source to the respective light sensor.

14. The optical encoder of claim 13, wherein each series of apertures of the first commutation track, the second commutation track, and the third commutation track extends 90 mechanical degrees around the rotation axis.

15. The optical encoder of claim 1, wherein the optical encoder is an incremental encoder.

16. The optical encoder of claim 15, wherein the optical encoder is an absolute encoder.

17. A motor system, comprising:

a brushless motor; and

an optical encoder including;

a light source;

a light sensor array; and

a code disk including;

a data track having a plurality of slots configured to allow light from the light source to pass to the light sensor array to determine a rotational position and direction of the code disk; and

a commutation pattern having;

a first commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a first light sensor of the light sensor array such that the first light sensor continuously receives light as the series of apertures passes over the first light sensor;

a second commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a second light sensor of the light sensor array such that the second light sensor continuously receives light as the series of apertures passes over the second light sensor; and

a third commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a third light sensor of the light sensor array such that the third light sensor continuously receives light as the series of apertures passes over the third light sensor;

wherein the relative positions of the first, second, and third commutation tracks correspond to a continuous commutation sequence of a first coil, a second coil, and a third coil of the brushless motor.

18. The motor system of claim 17, further comprising a controller configured to supply current to electromagnetic coils in the motor stator based on the signals received from the first, second, and third light sensors.

19. The motor system of claim 17, wherein the brushless motor is a one pole-pair brushless motor.

20. A code disk for an optical encoder, comprising:

a data track having a plurality of slots configured to allow light from a light source to pass to a light sensor array to determine a rotational position and direction of the code disk; and

a commutation pattern having;

a first commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a first light sensor of the light sensor array such that the first light sensor continuously receives light as the series of apertures pass over the first light sensor;

a second commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a second light sensor of the light sensor array such that the second light sensor continuously receives light as the series of apertures passes over the second light sensor; and

a third commutation track including a series of apertures which are spaced closely enough together to allow light to continuously pass from the light source to a third light sensor of the light sensor array such that the third light sensor continuously receives light as the series of apertures passes over the third light sensor;

wherein the relative positions of the first, second, and third commutation tracks correspond to a continuous commutation sequence of a first coil, a second coil, and a third coil of a brushless motor.