Search

EP-4735832-A1 - POSITION ENCODER READHEAD, POSITION ENCODER AND METHOD OF MINIMIZING POSITION ERROR

EP4735832A1EP 4735832 A1EP4735832 A1EP 4735832A1EP-4735832-A1

Abstract

The invention relates to a position encoder readhead comprising a sensor with five sensing elements (h1, h2, h3, h4, h5). An adding unit generates from the output responses (H1, H2, H3, H4, H5) - a first common signal SIN = H1/2 - H2 - H3 + H4 + H5/2, and - a second common signal COS = H1/2 + H2 - H3 - H4 + H5/2; where the common signals are used to calculate the position X of the readhead relative to an information carrier embedded in the position encoder and including a repeating pattern with a length of a period P. The distances (r) between two adjacent sensing elements (h1, h2, h3, h4, h5) are substantially the same and a sensor pitch (R) is equal to the sum of the mutual distances (r) between the adjacent sensing elements. The ratio between the length of the period (P) and the sensor pitch (R) is in the range of 0.8 to 1.2, preferably 0.9 to 1.1.

Inventors

  • DOLSAK, GREGOR

Assignees

  • RLS Merilna tehnika d.o.o.

Dates

Publication Date
20260506
Application Date
20240627

Claims (10)

  1. 1 . A position encoder readhead comprising a sensor comprising five sensing elements (hi , h2, h3, h4, h5), each of them generating a respective output response (H1 , H2, H3, H4, H5); an adding unit that generates from the output responses (H1 , H2, H3, H4, H5) - a first common signal SIN = H1/2 - H2 - H3 + H4 + H5/2, and - a second common signal COS = H1/2 + H2 - H3 - H4 + H5/2; the first common signal SIN and the second common signal COS being used to calculate the position X of a readhead relative to an information carrier embedded in the position encoder and including a repeating pattern with a length of a period P; wherein the distances (r) between two adjacent sensing elements (hi , h2, h3, h4, h5) are substantially the same and a sensor pitch (R) is equal to the sum of the mutual distances (r) between the adjacent sensing elements (hi , h2, h3, h4, h5); the ratio between the length of the period (P) and the sensor pitch (R) being in the range of 0.8 to 1 .2, preferably 0.9 to 1 .1 .
  2. 2. Readhead of claim 1 , characterized in that the sensor comprises sensing elements (hi , h2, h3, h4, h5) configured as magnetic sensing elements, and the information carrier embedded in the magnetic position encoder is configured as a magnetic information carrier.
  3. 3. Readhead of claim 2, characterized in that the magnetic sensing elements (hi , h2, h3, h4, h5) are configured as Hall elements.
  4. 4. Readhead of claim 1 , characterized in that the sensor comprises sensing elements (hi , h2, h3, h4, h5) configured as optical sensing elements, and the information carrier embedded in the optical position encoder is configured as an optical information carrier.
  5. 5. Readhead of claims 1 to 4, characterized in that the position X of the readhead relative to the information carrier is calculated from the first common signal SIN and the second common signal COS on the basis of the inverse tangent (ArcTan) function of their ratio.
  6. 6. Readhead of claim 5, characterized in that the position X of the readhead relative to the information carrier is calculated by equation:
  7. 7. A position encoder comprising an information carrier including a repeating pattern with a length of the period (P) and the readhead of claims 1 to 5.
  8. 8. A method for calculating the position X of the readhead relative to the information carrier in the position encoder, characterized by comprising the following steps: a. receiving output responses (H1 , H2, H3, H4, H5) of the sensing elements (hi , h2, h3, h4, h5); b. generating - a first common signal SIN = H1/2 - H2 - H3 + H4 + H5/2, and - a second common signal COS = H1/2 + H2 - H3 - H4 + H5/2; c. calculating the position X on the basis of the first common signal SIN and the second common signal COS.
  9. 9. Method of claim 8, characterized in that the calculation of the position X on the basis of the first common signal SIN and the second common signal COS is performed on the basis of the inverse tangent (ArcTan) function of their ratio.
  10. 10. Method of claim 9, characterized in that the following equation is used to calculate the position X:

Description

Position encoder readhead, position encoder and method of minimizing position error The invention relates to a position encoder readhead comprising a sensor with sensing elements, such as Hall elements, the outputs of which are used to generate two periodic signals as a function of the readhead movement with respect to an information carrier, which are used to determine, by computational methods, a readhead position with respect to the information carrier, above which the readhead is located. Position encoders are used in a variety of applications, for example in machine tools to determine the position of a tool, in robots to measure joint angles, in video surveillance systems and in electric motors to determine the position of a rotor, which allows these devices to be controlled automatically, for example by software. A readhead may be attached to a measured part, while an information carrier is attached to a base, or vice versa. A readhead position may be expressed as a distance or angle from a starting point and, in certain applications, also velocity or angular velocity of a readhead or information carrier can be calculated by taking time into account. The invention further relates to a position encoder and a method of minimizing position error. Prior art position encoders are configured in various ways. For example, magnetic position encoders have a magnetic sensor with sensing elements in the readhead, and the information carrier is configured as a magnetic information carrier in which information is embedded in the form of a magnetic track with a repeating pattern containing segments, the magnetization of which points in pairs in opposite directions, indicated, for instance, as north (N) and south (S). Optical position encoders have an optical sensor with sensing elements in the readhead, and the information carrier is for instance configured as a tape with alternating dark and light segments that are detected by the optical sensor. Although the present invention will be explained in the following in detail on an example of magnetic position encoders, the present invention may also relate to all position encoders having a readhead and an information carrier that includes a repeating pattern of segments with a period P, which are detected by the sensor in the readhead. Known prior art discloses position encoders that are configured as magnetic position encoders that comprise a readhead and an information carrier configured as a magnetic information carrier. The readhead in such encoders comprises a sensor configured as a magnetic sensor and detecting the magnetic field of the magnetic information carrier, and during operation located above the information carrier, more specifically moving above it. In linear position encoders, the information carrier extends along a linear path; in different variants, the information carrier may extend over a curved path, for instance in circular position encoders over a circular path, as for instance disclosed in US8134359B2. While the readhead moves along the path relative to the information carrier, it is desired for the readhead to have a constant distance from the information carrier such that the differences in the distance do not have impact on the detection of the segment pattern on the information carrier, for instance on the response of sensing elements to a magnetic field. An information carrier configured as a magnetic information carrier comprises in longitudinal direction at least two groups of different magnetic segments which form a repeating magnetic pattern with a period P in the longitudinal direction. Typically, two groups of magnetic segments are used on a magnetic information carrier to form a pattern: segments permanently magnetized upwards (north), and segments permanently magnetized downwards (south). One of possible magnetic information carriers in prior art is configured as an elasto-ferrite tape on a rigid metallic base, the segments on the elasto-ferrite tape being alternately magnetized on opposite sides in the longitudinal direction. In such a case, the period P of a repeating magnetic pattern in the longitudinal direction of the magnetic information carrier is formed of two adjacent magnetic segments magnetized in opposite directions. A readhead in magnetic position encoders in known prior art (e.g. W00075673A1) includes a magnetic sensor having four sensing elements (hi , h2, h2 and h4), for instance Hall elements. A response (H1 , H2, H3 and H4) at the output of a respective sensing element (hi , h2, h2 and h4), which is the Hall voltage in case of Hall elements, is proportional to the component of the magnetic field density perpendicular to the surface of a sensing element. The sensing elements are arranged in the sensor at an equal mutual distance r in the longitudinal direction, wherein the sensor pitch R in these examples from known prior art is determined as a product of the mutual distance r and the number of sensing elements.