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EP-4735833-A1 - POSITION ENCODER AND READHEAD TO MINIMIZE POSITION ERROR

EP4735833A1EP 4735833 A1EP4735833 A1EP 4735833A1EP-4735833-A1

Abstract

The invention relates to a position encoder and a readhead to minimize position error, the readhead comprising a magnetic sensor with magnetoresistive (MR) elements that are electrically connected to each other to form a circuit that comprises a subcircuit to generate a first periodic signal and a subcircuit to generate a second periodic signal as a function of the readhead movement relative to a magnetic information carrier, which are used to determine a readhead position X and/or speed with respect to the magnetic information carrier. In the readhead of the invention, at least one of the MR elements in one of the subcircuits is replaced by one MR pair of two half MR elements having a resistance constant R 0 /2, while the remaining MR elements outside of MR pairs remain unchanged and have the resistance constant R 0 . The first half MR element of a MR pair remains substantially in the same position within the magnetic sensor as the replaced MR element, while the second half MR element of the MR pair is substantially in a position which is at a distance λ 0 with respect to the first half MR element.

Inventors

  • DOMAJNKO, Dora
  • DOL AK, Gregor

Assignees

  • RLS Merilna tehnika d.o.o.

Dates

Publication Date
20260506
Application Date
20240627

Claims (15)

  1. 1 . A position encoder comprising a magnetic information carrier and a readhead to determine the position X and/or speed of the readhead with respect to the information carrier, the information carrier comprising in the longitudinal direction periodically repeating magnetic segments with a length of the period P; the readhead comprising a magnetic sensor with at least four magnetoresistive (MR) elements (R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 ', R2, R3, R4, R5) to detect magnetic field intensities of the magnetic segments on the information carrier by changing the resistance of the (MR) elements (R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 R2, R3, R4, R5), wherein the resistance of each individual MR element (R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 R2, R3, R4, R5) is changed with the period by the movement x of the readhead in the longitudinal direction with respect to the magnetic information carrier, the MR elements (R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 ', R2, R3, R4, R5) in the readhead magnetic sensor being arranged in spatial positions substantially in the longitudinal direction, the MR elements (R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 ', R2, R3, R4, R5) being electrically connected to a circuit, wherein a first subset of MR elements (R1 ', R3, R5, R7', R9, R10; R1 ', R3, R5) is connected to a first subcircuit A to generate a first periodic signal SIN' and a second subset of MR elements (R2, R4, R6, R8; R2, R4), which does not include the MR elements (R1 ', R3, R5', R7, R9, R10; R1 ', R3, R5) from the first subset is connected to a second subcircuit B to generate a second periodic signal COS'; the subcircuit A and the subcircuit B comprising one branch or two branches, preferably two branches, wherein in each branch at least two MR elements (R1 ', R3, R9; R5', R7, R10; R2, R4; R6, R8; R1 ', R3, R5; R2, R4) are electrically connected in series between a voltage source Vcc and ground GND, wherein between the position in the readhead of the first MR element (R1 ') from the first subcircuit A, viewed from a certain side of the longitudinal direction, and the position of the first MR element (R2) from the second subcircuit B, viewed from the same side, there is a distance r and the distance Ao is defined as four times the distance r (Ao = 4 * r), wherein at least one distance between the positions of two MR elements (R1 ', R3; R7, R10; R2, R4; R6, R8) in each branch is substantially equal to Ao/2 + J * Ao, the number J being zero or a natural number, preferably zero; the position X of the readhead relative to the magnetic information carrier being determined on the basis of the first periodic signal SIN' and the second periodic signal COS'; characterized in that at least one branch in one or both of the subcircuits (A or B) comprises a MR pair of two half MR elements (R1 ', R9; R5', R10; R1 ', R10; R5', R9; R1 ', R5), which means they have half the resistance constant Ro (Ro/2) compared to the remaining MR elements (R2, R3, R4, R6, R7, R8; R2, R3, R4) outside the MR pairs; and the distance in the longitudinal direction between the spatial position of the first half MR element of a MR pair and the position of the second half MR element of this MR pair is substantially equal to the distance Ao.
  2. 2. Position encoder of claim 1 , characterized in that the first MR element (R1 '), with respect to the spatial position of all MR elements (R1 ', R2, R3, R4, R5', R9, R6, R7, R8, R9, R10; R1 R2, R3, R4, R5) in the magnetic sensor, viewed from a certain side of the longitudinal direction, belongs to a MR pair of half MR elements (R1 ', R9; R1 ', R5) of a certain subcircuit (A) and the position of the second MR element (R9; R5) from this MR pair is offset by the distance Ao in the longitudinal direction, viewed from the same side, with respect to the position of the first MR element (R1 ') of this MR pair; wherein the remaining subcircuit (B) does not comprise any MR pairs of half MR elements.
  3. 3. Position encoder of claims 1 to 2, characterized in that the first subcircuit (A) and the second subcircuit (B) have two branches each and that the distance between the position of one of the MR elements (R1 ') in the first branch of a certain subcircuit (A or B) and the position of one of the MR elements (R5’) in the second branch of the same subcircuit (A or B) is equal to the distance S * Ao + £, wherein the number S is zero or a natural number, and £ assumes the values between about - Ao/4 and Ao/4.
  4. 4. Position encoder of claim 3, characterized in that the number S is one and the distance £ is 0.
  5. 5. Position encoder of claim 4, characterized in that one of the half MR elements (R9) of the first MR pair and one of the half MR elements (R5 1 ) of the second MR pair are connected to each other in series to the same branch and are configured as an integral MR element with a resistance constant Ro.
  6. 6. Position encoder of claim 3, characterized in that the number S is zero and the distance £ is Ao/8.
  7. 7. Position encoder of claim 3, characterized in that the number s is zero and the distance £ is zero.
  8. 8. Position encoder of claim 3, characterized in that one subcircuit (A) comprises two MR pairs of half MR elements (R1 ' and R9, R5' and R10) and the remaining subcircuit (B) does not comprise any MR pairs.
  9. 9. Position encoder of claims 2 and 8, characterized in that the position of the second half MR element (R10) of the second MR pair is offset by the distance Ao, viewed from the same side of the longitudinal direction, with respect to the first half MR element (R5 1 ) of the second MR pair.
  10. 10. Position encoder of claims 3 to 9, characterized in that the first periodic signal SIN' is obtained between two intermediate nodes of the two branches of the first subcircuit (A) and the second periodic signal COS' is obtained between two intermediate nodes of the two branches of the second subcircuit (B).
  11. 1 1 . Position encoder of claims 1 to 2, characterized in that the first subcircuit (A) and the second subcircuit (B) comprise one branch each.
  12. 12. Position encoder of claim 11 , characterized in that only one subcircuit (A or B) comprises one MR pair of two half MR elements (R1 ', R5) with a resistance constant Ro/2, while the remaining MR element (R2, R3, R4) have the resistance constant Ro.
  13. 13. Position encoder of claims 11 to 12, characterized in that the first periodic signal SIN' is obtained between the intermediate node of the branch of the first subcircuit (A) and half the voltage of the voltage source Vcc and the second periodic signal COS' is obtained between the intermediate node of the branch of the second subcircuit (B) and half the voltage of the voltage source Vcc.
  14. 14. Position encoder of claims 1 to 13, characterized in that the position X of the readhead relative to the magnetic information carrier is determined on the basis of the inverse tangent (ArcTan) function of the ratio between the first periodic signal SIN' and the second periodic signal COS'.
  15. 15. Position encoder readhead of claims 1 to 14.

Description

Position encoder and readhead to minimize position error Introduction The invention relates to a position encoder and a readhead housed therein and comprising a magnetic sensor with magnetoresistive (MR) elements that are electrically connected to each other to form a circuit, the nodes of which represent scanning points for a first periodic signal and a second periodic signal as a function of the readhead movement relative to a magnetic information carrier, which are used to determine a readhead position and/or speed with respect to the magnetic information carrier, above which the readhead is located. Such 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 the rotor, which allows these devices to be controlled automatically, for example by software. A readhead may be attached to a moving measured part, while a magnetic information carrier is attached to a static base, or vice versa. The moving measured part and the static base form a measured system. 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 can be calculated by taking time into account. Prior art Known prior art discloses position encoders that comprise a readhead and a magnetic information carrier, the readhead including a magnetic sensor with a plurality of magnetoresistive (MR) elements. The magnetic sensor is arranged within the readhead and detects the magnetic field of the magnetic information carrier, while during operation it is located above the magnetic information carrier, more specifically moves above it. In linear position encoders, the magnetic information carrier extends along a linear path; in different versions, the magnetic information carrier may extend over a curved path, for instance in circular position encoders the magnetic information carrier extends over a circular path. While the readhead moves along a path relative to the magnetic information carrier, it is desired for the readhead to have a constant distance from the magnetic information carrier such that the differences in the distance do not have impact on the magnetic field measurement. The magnetic information carrier for such position encoders from prior art comprises at least two groups of different magnetic segments which form a repeating magnetic pattern with a length of a period P in the longitudinal direction. Typically, two groups of magnetic segments are used on a magnetic information carrier, namely 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 length of the period P of the repeating magnetic pattern in the longitudinal direction of the magnetic information carrier is formed of two adjacent magnetic segments magnetized in opposite directions. A magnetic sensor with MR elements for magnetic field detection exploits the property of some materials, the resistance R of which actually changes under the influence of the magnetic field, for instance as a function of an angle between the magnetic field and the direction of current through the resistor. If these changes in resistance are measured, for instance as voltage on the nodes of a circuit, to which the MR elements are connected, magnetic field information is obtained, so they are used as magnetic sensors. In prior art, anisotropic magnetoresistive (AMR) effect sensors and tunnel magnetoresistive (TMR) effect sensors are most often used, which means that AMR sensing elements and TMR sensing elements are known that are generally designated in this application as MR elements, which further include giant magnetoresistive effect (GMR) sensing elements and colossal magnetoresistive effect (CMR) sensing elements. In general, the equation for the actual resistance R of an individual MR element includes a resistance constant Ro which determines the invariable part of the actual resistance R, usually also described as resistance of the MR element in the absence of a magnetic field, and which has a proportional effect on the variable part of resistance of the MR element. In AMR sensing elements, for instance, the variable part of resistance represents only a few per cent of the total resistance or resistance constant Ro, while in TMR sensing elements, the variable part of resistance may represent up to tens of per cent of the total resistance or resistance constant Ro. The resistance constant Ro is defined by the design of a MR element and is normally identical for all MR elements within individual magnetic