Indexed optical encoder, method for indexing an optical encoder, and method for dynamically adjusting gain and offset in an optical encoder

• US 8,513,589 B2
• Filed: 10/19/2012
• Issued: 08/20/2013
• Est. Priority Date: 08/28/2008
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: York, Frederick
• Primary Examiner(s): LEE, JOHN R
• Application Number:
  US13/656,078
• Publication Number:
  US 20130112861A1
• Time in Patent Office: 305 Days
• Field of Search: 25023113-23118, 250/237.G, 341/2, 341/3, 234/161, 234/166, 234/175, 702/145, 702/147, 702/148, 702/150, 702/151, 702/85, 702/94, 702/95, 702/104, 324/161, 324/166, 324/175
• US Class Current: 250/231.14
• CPC Class Codes: G01D 18/00 Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence
• CPC Class Codes: G01D 5/2457 Incremental encoders having reference marks
• CPC Class Codes: G01D 5/34 the beams of light being detected by photocells
• CPC Class Codes: G01D 5/34707 Scales; Discs, e.g. fixation, fabrication, compensation
• CPC Class Codes: G01D 5/3473 Circular or rotary encoders
• CPC Class Codes: G06F 17/18 for evaluating statistical data , e.g. average values, frequency distributions, probability functions, regression analysis forecasting specially adapted for a specific administrative, business or logistic context G06Q10/04

Abstract

An optical encoder may include an encoder disk, an illumination system, and a detector to detect light diffracted from the encoder disk. The encoder disk may include a signal track comprising a diffraction grating, and an index track comprising a reflective index mark, wherein a width of the index mark is larger than a pitch of the diffraction grating. An indexing method may include providing an encoder disk, providing an illumination system to direct light to the encoder disk, providing a detector structured to detect light diffracted from the encoder disk, calculating an estimated count of quadrature states from a rising edge of an index pulse to a middle of the index interval, and calculating the quadrature state at an approximate center of the index pulse. A dynamic parameter correction method may include calculating a target gain and offset and correcting values based on the target gain and offset.

Claims

1. An indexing method for use with an optical encoder, the indexing method comprising:

providing an encoder disk, comprising;

a signal track comprising a diffraction grating formed as a ring on the encoder disk; and

an index track formed as a ring on the encoder disk, the index track comprising an index mark provided at an index angular coordinate;

providing an illumination system structured to direct light to the encoder disk;

providing a detector structured to detect light diffracted from the encoder disk, the detector comprising;

two offset detectors structured to detect light diffracted from the signal track and output a quadrature signal; and

an index detector structured to detect light reflected from the index track and output an index pulse;

calculating an estimated state count k_est of quadrature states from a rising edge of the index pulse to a middle of the index pulse;

calculating Q_kest, wherein Q_kest is the quadrature state at k_est and corresponds to the quadrature state at an approximate center of the index pulse; and

determining an offset correction to be applied to the optical encoder based on a value of Q_kest.

2. The indexing method of claim 1, wherein the calculating an estimated state count k_est comprises calculating a value of K further comprising:

calculating k_est as K/2 in a case that K is even;

or

calculating k_est as ((K+1)/2) in a case that K is odd;

wherein K is equal to a quadrature count from the beginning to the end of the index pulse.

3. The indexing method of claim 2, wherein Q_kest is equal to Q_{(kest mod 4)}, wherein Q_kest is the quadrature state at k_est and Q_{(kest mod 4)} is the quadrature state at (k_est mod 4).