Analog position encoder

• US 7,091,884 B2
• Filed: 09/23/2004
• Issued: 08/15/2006
• Est. Priority Date: 09/26/2003
• Status: Expired due to Fees

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Rio Doval, Jose M.
• Primary Examiner(s): WAMSLEY, PATRICK G
• Application Number:
  US10/947,146
• Publication Number:
  US 20050092904A1
• Time in Patent Office: 691 Days
• Field of Search: 341/113, 341/2, 341/13, 250/231.13, 250/208.2, 250/208.3, 250/231.15, 250/231.18, 318/594, 324/202, 324/207.17, 340/870.29, 358/1.5, 702/158, 356/485
• US Class Current: 341/13
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence
• CPC Class Codes: G01D 5/2448 Correction of gain, threshold, offset or phase control
• CPC Class Codes: H03M 1/207 using a digital interpolation circuit
• CPC Class Codes: H03M 1/303 Circuits or methods for processing the quadrature signals

Abstract

A position-measuring circuit is described for use with an analog position encoder of the kind comprising a code member and at least two sensors for sensing successive marks on the code member during relative movement between the code member and sensors, the sensors providing two oscillating quadrature signals. The circuit comprising means for obtaining a relatively coarse measure of position by detecting successive instants t0–t3 at which the amplitudes of the sensor signals are equal or at which the amplitude of one signal is equal to the inverse of the amplitude of the other signal. The amplitude of one of the signals or its inverse is stored at each detection instant to alternately establish relatively high and low threshold levels. A fine measure of position at an arbitrary instant T is obtained as a function of the instantaneous amplitude P of one of the signals and the difference between neighbouring high and low thresholds levels.

Claims

1. A position-measuring circuit for use with an analog position encoder comprising a code member and at least one sensor for sensing successive marks on the code member during relative movement between the code member and sensor and providing an oscillating signal in response thereto, the position-measuring circuit comprising means for obtaining a relatively coarse measure of position by detecting successive distinguishable instants in the signal, means for establishing relatively high and low threshold levels based upon the amplitudes of the signal at least at selected detection instants, wherein a value of the high and low threshold levels vary with the sensor position and/or over time, and are set to change dynamically with an amplitude of the signal during operation of the analog position encoder, and means for obtaining a fine measure of position by measuring an instantaneous amplitude of the signal and calculating the fine measure as a function of the instantaneous amplitude of the signal and the difference between neighboring high and low threshold levels.

2. A circuit as claimed in claim 1, wherein the analog position encoder has at least two sensors providing two oscillating quadrature signals, wherein the distinguishable instants are the instants at which the amplitudes of the sensor signals are equal and at which the amplitude of one sensor signal is equal to the amplitude of the inverse of the other sensor signal, and wherein the means for obtaining a fine measure of position obtains said measure as a function of the instantaneous amplitude of a selected one of the signals and the difference between neighbouring high and low threshold levels, the selected signal being that signal which changes monotonically between said neighboring high and low threshold levels.

3. A circuit as claimed in claim 2, wherein the means for establishing the dynamic threshold levels comprises means for storing the amplitude of one of the signals or its inverse at each, or each selected, detection instant to alternately establish relatively high and low threshold levels.

4. A circuit as claimed in claim 3, wherein the means for establishing the dynamic threshold levels includes two sample and hold circuits for alternately storing the amplitude of one of the signals or its inverse at each, or each selected, detection instant such that the two sample and hold circuits contain the most recent high and low threshold levels respectively.

5. A circuit as claimed in claim 1, wherein the sensor signals are triangular signals with rounded maxima and minima, and the means for obtaining a fine measure of position calculates the instantaneous amplitude of one of the signals as a proportion of the difference between neighbouring high and low thresholds levels.

6. A circuit as claimed in claim 5, wherein the means for obtaining a fine measure of position comprises an analog to digital converter whose range is defined by the established high and low threshold levels and which has the instantaneous signal amplitude as input.

7. A circuit as claimed in claim 1, wherein the neighboring high and low threshold levels are the most recently established high and low threshold levels.

8. A circuit as claimed in claim 1, wherein the neighboring high and low threshold levels are the most recent high or low threshold level and the next low or high threshold level respectively.

9. A printer including one or more analog position encoders according to claim 1, each arranged to sense one of paper position and carriage position.

10. A position-measuring circuit for use with an analog position encoder comprising a code member and at least two sensors for sensing successive marks on the code member during relative movement between the code member and sensors, the sensors providing two oscillating quadrature signals, the position-measuring circuit comprising means for obtaining a relatively coarse measure of position by detecting successive instants at which the amplitudes of the sensor signals are equal and at which the amplitude of one sensor signal is equal to the amplitude of the inverse of the other sensor signal, means for establishing relatively high and low threshold levels based upon the amplitudes of the signals at least at selected detection instants, wherein a value of the high and low threshold levels vary with the sensor position and/or over time, and are therefore set to change dynamically with the amplitude of the signal during operation of the analog position encoder, and means for obtaining a fine measure of position by measuring an instantaneous amplitude of the signal and calculating the fine measure as a function of the instantaneous amplitude of one of the signals and the difference between neighboring high and low threshold levels.

11. A method of determining position using an analog position encoder comprising a code member and at least one sensor for sensing successive marks on the code member during relative movement between the code member and sensor and providing an oscillating signal in response thereto, the method comprising the steps of obtaining a relatively coarse measure of position by detecting successive distinguishable instants in the signal, establishing relatively high and low threshold levels based upon the amplitudes of the signal at least at selected detection instants, wherein a value of the high and low threshold levels vary with the sensor position and/or over time, and are set to change dynamically with an amplitude of the signal during operation of the analog position encoder, and obtaining a fine measure of position by measuring an instantaneous amplitude of the signal and calculating the fine measure as a function of the instantaneous amplitude of the signal and the difference between neighboring high and low threshold levels.