High resolution absolute encoder

• US 9,007,057 B2
• Filed: 04/30/2012
• Issued: 04/14/2015
• Est. Priority Date: 12/28/2011
• Status: Active Grant

• Current Assignee: Servosense SMC Ltd.
• Original Assignee: Servosence Limited
• Inventors: Villaret, Yves
• Primary Examiner(s): Phan, Huy Q
• Assistant Examiner(s): SPLIT, JAMES G
• Application Number:
  US14/369,730
• Publication Number:
  US 20150070001A1
• Time in Patent Office: 1,079 Days
• Field of Search: 324200-263, 250/231.13, 250/231.14, 250/231.18, 341/9, 341/10, 341/13, 341/15
• US Class Current: 324/207.25
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence
• CPC Class Codes: G01D 5/2455 with incremental and absolute tracks on the same encoder

Abstract

The device to measure the absolute rotation angle of a rotating shaft includes a rotating disc, fixed to the shaft. A group of permanent magnets of different sizes and polarities is disposed on a circular track. Further, a group of Hall sensors, fixed to a static part of the device, are disposed on a circular path, in proximity of the rotating disc magnets tracks, and generate electric signals proportional to the strength of the magnetic field produced by the magnets in proximity. The signs of these electric signals are used to calculate a code characteristic of a low resolution absolute angular position. Two analog signals are associated to the obtained code, according to a predefined table. The associated analog signal having the closest value to zero is used as an entry to a pre-recorded table containing the correspondent angular position of the shaft.

Claims

1. A high resolution encoder device to measure the angular position of a rotating element, comprising:

a) a rotating disc fixed to the rotating element, said rotating disc including a circular track having sections of a first property and sections of a second property according to a given pattern;

b) a plurality of fixed sensors positioned in proximity to said circular track, each sensor outputting an electrical signal having a maximal value when in proximity to a section of the circular track of said first property and a minimum value when in proximity to a section of the circular track of said second property, and continuously and monotonously changing intermediate values in between said maximal value and said minimum value when said rotating disc rotates from a position for which said sensor is in proximity to a section of said first or said second property to a position for which said sensor is in proximity to a section of the other property;

c) a memory to store pre-recorded encoder characteristics; and

,

d) processing means to process values of said electrical signals of said sensors, and

wherein, in a first processing step, a bit is set for each sensor as a result of a comparison of said electrical signal of a respective sensor to a pre-defined threshold stored in said memory, and all bits of all sensors are combined in a word, the value of this word defining a code, wherein two electrical signals are associated to each code value,

wherein, in a second processing step, said two electrical signals associated to said code are compared, and an electrical signal having the closest value to the threshold is selected, and

wherein, in a third processing step, a high resolution angular position of the rotating disc is deduced from the code and said selected electrical signal.

2. The encoder of claim 1, wherein sections of said first and second property sectors include permanent magnets generating magnetic field in two different directions, and wherein said sensors are sensible to magnetic field direction.

3. The encoder of claim 2, wherein said circular track of the rotating disc includes two concentric rows of permanent magnets, creating inward and outward radial magnetic fields and said sensors being positioned in a median line between said two concentric rows.

4. The encoder of claim 1, wherein said sensors are equally distributed on a circumference of a static part, and said rotating disc is placed so that the sensors can sense the property of the section of track in proximity to them, wherein said sensors provide an analog output and said memory stores characteristics of said encoder device and said processing means processes analog output signals of each sensor.

5. The encoder of claim 4, further comprising an analog to digital converter unit configured to digitize signals of said analog output from said sensors and then to transfer said digitized analog output signals to said processing means.

6. The encoder of claim 5, wherein output signals of said different ones of said sensors comprise similar shapes respectively, shifted by a value representing their relative position on said circular track.

7. The encoder of claim 6, wherein said circular track comprises annular rings of permanent magnets generating a radial magnetic field between them, and wherein said sensors comprise Hall Effect sensors placed on a circular line between said annular rings of permanent magnets.

8. The encoder of claim 5, wherein said circular track comprises annular rings of permanent magnets generating a radial magnetic field between them, and wherein said sensors comprise Hall Effect sensors placed on a circular line between said annular rings of permanent magnets.

9. The encoder of claim 4, wherein said sensors are distributed equally on said circular track.

10. The encoder of claim 9, wherein output signals of said different ones of said sensors comprise similar shapes respectively, shifted by a value representing their relative position on said circular annular track.

11. The encoder of claim 4, wherein said circular track comprises annular rings of permanent magnets generating a radial magnetic field between them, and wherein said sensors comprise Hall Effect sensors placed on a circular line between said annular rings of permanent magnets.