Position encoder and readhead to minimize position error

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 R0 / 2, while the remaining MR elements outside of MR pairs remain unchanged and have the resistance constant R0. 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 λ0 with respect to the first half MR element.

Description

[0001] Position encoder and readhead to minimize position error

[0002] Introduction

[0003] 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.

[0004] 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.

[0005] Prior art

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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 sensors in prior art.

[0011] As the actual resistance R of an individual MR element depends on the magnetic field generated by the magnetic information carrier, above which the MR element is located, the change in resistance can be converted, using an appropriate electrical circuit to which the MR elements are connected to, to a corresponding electrical signal, such as voltage signal. The corresponding signal of an individual MR element, as a function of displacement x of this MR element along the magnetic information carrier, is periodic with the length of the period A, which is a consequence of the magnetic field periodicity above the magnetic information carrier with the length of the period P. It is a known fact that in TMR sensing elements the length of the period A of the corresponding signal is substantially equal to the length of the period P of the magnetic pattern on the magnetic information carrier (A = P). In AMR sensing elements, the length of the period A is substantially equal to half the length of the period P of the magnetic pattern on the magnetic information carrier (A = P / 2). It is known that the circuit to which MR elements are connected contains a first subcircuit A, to which a first subset of MR elements is connected, to generate a first periodic signal SIN with the length of the period A, and a second subcircuit B, to which a second subset of MR elements is connected, which do not belong to the first subset of MR elements, to generate a second periodic signal COS with the length of the period A.

[0012] The position of the readhead X and / or consequently the speed of the readhead relative to the information carrier is determined on the basis of the first periodic signal SIN and the second periodic signal COS, normally based on the inverse tangent (ArcTan) function of the ratio between the periodic signals SIN and COS, as for instance disclosed in US4949289A. In one of the embodiments, the following equation is used to calculate the position X:

[0013] A SINM

[0014] X = — ArcTan( )

[0015] 2TT COS xy

[0016] By analogy, the position expressed as an angle can also be calculated in known ways, for example in the case of a circular position encoder having a circular magnetic information carrier.

[0017] Several versions of circuits to which MR elements are connected exist in prior art. For instance, the subcircuit A and / or the subcircuit B may have only one branch, to which at least two MR elements are connected in series between a DC voltage source Vcc and ground; however, it may also have two bridged branches, wherein in each branch at least two MR elements are connected in series between a voltage source Vcc and ground. When a subcircuit has only one branch, the corresponding periodic signal (SIN or COS) is obtained at the intermediate node of this branch, namely between two MR elements which are connected in series in this branch. When a subcircuit has two branches, the corresponding periodic signal (SIN or COS) is obtained between two intermediate nodes of the two branches of a respective subcircuit.

[0018] The positions of MR elements in the readhead magnetic sensor are spatially arranged substantially in the longitudinal direction. The position of each MR element is fixed with respect to the positions of other MR elements in the magnetic sensor. There is normally a certain distance between the positions of adjacent MR elements, however, two MR elements or rather their centroids may also be located in the same position in the magnetic sensor, which means that they detect substantially the same magnetic field from the magnetic information carrier.

[0019] Between the spatial position of the first MR element from the first subcircuit A, viewed from a certain side of the longitudinal direction, and the spatial position of the first MR element from the second subcircuit B, viewed from the same side of the longitudinal direction, there is a distance r. Four times the distance r represents the distance Ao (Ao = 4 * r) which is, in combination with the length of the period A, used as a criterion of deviation from ideal conditions as will be described in more detail below.

[0020] In each branch of the circuit, at least one distance between the positions of two MR elements which are electrically connected to the respective branch is substantially equal to Ko / 2, or, more generally, equal to Ko / 2 + J * Ao, the number J being zero or a natural number. The number J is preferably zero, because one of the desired properties of the magnetic sensors is the fact of being short, while increasing the number J would increase the length of the magnetic sensor. Most frequently, two MR elements are connected in series in one branch and the distance between them is Ko / 2.

[0021] In cases, in which the subcircuits (A, B) have two branches each, the distance between the position of the first MR element in the first branch, as viewed from a certain side of the longitudinal direction, and the position of the first MR element in the second branch, as viewed from the same direction, is generally expressed as S * Ao + £, wherein S is zero or a natural number, preferably zero or 1 , more preferably zero, and the distance £ in actual applicable examples assumes the values between about - Ao / 4 and Ao / 4.

[0022] Technical problem

[0023] In prior art position encoders, an error E occurs, which is a difference between the actual and the calculated position X of the readhead in cases when the periodic signals SIN and COS are not ideally harmonic in shape, if they have different amplitudes, if their offsets are not zero or if a phase difference F between them differs from A / 4.

[0024] It emanates from the prior art design of a magnetic sensor with MR elements that the amplitudes of the periodic signals SIN and COS are identical, if the values of the resistance constant Ro are identical for all MR elements. The phase difference F between the periodic signals SIN and COS, which may also be expressed as a distance that the readhead has to travel for the value of the first periodic signal SIN to become equal to the value of the second periodic signal COS in the initial position, is equal to Ao / 4.

[0025] When the length of the period A and the distance Aodo not match, an error E occurs when determining the position X of the readhead with respect to the magnetic information carrier because of the deviation of the phase difference F between the periodic signals SIN and COS from the ideal value A / 4 (or in the normalized form TT / 2). The greater the discrepancy between the length of the period A and the distance Ao, the greater the error E. In ideal conditions, the length of the period A and the distance Ao match (A = Ao).

[0026] The reasons for the discrepancy between the length of the period A and the distance Ao in real-life conditions are, for instance, design related inaccuracies or errors in production of the magnetic sensor in the readhead, specifically the distance between the MR elements, or in production of the magnetic information carrier, specifically the length of magnetic segments in the longitudinal direction. A discrepancy between the length of the period A and the distance Ao may also be due to the final design of the position encoder or the attachment of the position encoder to the system to be measured.

[0027] In the continuation, the ratio between the length of the period A and the distance Ao (A / Ao) will denote a degree of deviation from ideal conditions. When A is equal to Ao, said ratio is 1 , these are ideal conditions. When said ratio is less than 1 , A is smaller than Ao; and by analogy, when said ratio is more than 1 , A is larger Ao. In practical cases of position encoders, said ratio (A / Ao) is in the range between 0.8 and 1 .2, even more frequently between 0.9 in 1 .1 .

[0028] The problem of discrepancy between the distance Ao and the length A of the period is particularly pronounced in circular position encoders because, due to the magnetic information carrier being curved, the distance between the readhead and the magnetic information carrier, which is finally determined only upon the installation of the position encoder on the system to be measured, determines how the MR elements will detect the magnetic field with the period P on the magnetic information carrier, i.e. the distance between the readhead and the magnetic information carrier will have impact on the length of the period A.

[0029] In addition, the problem may also occur in axial versions of circular position encoders irrespective of said distance between the readhead and the magnetic information carrier. Due to the curved path and the related design of the magnetic information carrier, the length of the period A which is defined by detection by MR elements, still further depends on the installation of the readhead relative to the information carrier, for instance on the distance between the readhead and the centre of the circular curve of the path defined by the magnetic information carrier design. Irrespective of how accurately the magnetic sensor is manufactured, when mounting the readhead with the sensor, there may be different distances between the readhead and the centre of the circular curve of the path, resulting in different lengths of the period A. This may result in an undesired difference between the length of the period A and the distance Ao irrespective of the manufacturing accuracy of the magnetic sensor and readhead.

[0030] Present invention - introduction

[0031] The position encoder and the associated read head of the present invention are intended to minimize the error E in determining the position X of the readhead relative to the magnetic information carrier, said error occurring due to a discrepancy between the length of the period A and the distance Ao. The main inventive idea lies in the design of an improved readhead having a magnetic sensor, in which 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 Ro / 2, while the remaining MR elements outside of said MR pair remain substantially unchanged, the resistance constant Ro also remains unchanged. 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 Ao with respect to the position of the first half MR element.

[0032] In versions of the readhead of the present invention, in which one of the subcircuits A or B, in which a MR element is replaced by a MR pair, has two branches, a preferred version of the readhead is the one in which in each of these branches one MR element is replaced by a MR pair of two half MR elements, the spatial position of which is described above.

[0033] Said half MR elements may be electrically connected to a circuit in various ways. In the most basic connection, two half MR elements in a MR pair are connected to each other in series and connected to the same branch as the replaced MR element. However, the MR elements and the half MR elements may also be connected to each other in different ways. Different, yet equivalent connections, in terms of efficiency, may be obtained in a way that, in terms of electrical connection, any two half MR elements are replaced within a certain subcircuit (Aor B) with the resistance constant Ro / 2 irrespective of whether they belong to the same branch or not. Further, in terms of electrical connection, two MR elements with a full resistance constant (Ro) may be interchanged within a certain subcircuit (A or B), provided that the distance between their positions is S * Ao + £.

[0034] In the following, the present invention will be described in more detail and illustrated by embodiments and in figures:

[0035] Figure 1 shows a spatial arrangement of MR elements and their connection to a circuit for a prior art position encoder with eight MR elements, which is the basis for the first embodiment of the present invention.

[0036] Figure 2 shows a first subcircuit A consisting of MR elements which form a signal SIN of the position encoder of Figure 1 , and a second subcircuit B consisting of MR elements which form a signal COS of the position encoder of Figure 1 .

[0037] Figure 3 shows the shape of signals SIN, COS, their amplitudes ASIN and Acos, and the shape of the size of error E of the calculated position X normalized by the length of the period A (E / A) as a function of movement x of the readhead of the position encoder shown in Figure 1 in real-time conditions, when the length of the period A does not match the distance Ao, namely A / Ao = 0.95. Figure 4 shows a diagram of a phase difference F, in degrees, between the periodic signals SIN and COS and the total value Epp of error E normalized by the length of the period A (Epp / A) for the prior art position encoder shown in Figure 1 as a function of the ratio between the length of the period A and the distance Ao (A / Ao), which is shown in the diagram between the ratio value of 0.9 to 1.1.

[0038] Figure 5 shows a spatial arrangement of MR elements and their connection to a circuit for a first illustrated embodiment of the position encoder of the present invention, which is an improvement of the prior art position encoder shown in Figure 1.

[0039] Figure 6 shows a first subcircuit A consisting of MR elements which form a signal SIN’ of the position encoder shown in Figure 5.

[0040] Figure 7 shows a diagram of the phase difference F between the signals SIN’ and COS’ and the total value Epp of error E normalized by the length of the period A (Epp / A) for the position encoder of the invention shown in Figure 5 as a function of the ratio between the length of the period A and the distance Ao (A / Ao), which is shown in the diagram between the ratio value of 0.9 to 1 .1 .

[0041] Figure 8 shows a circuit of a first additional example of a first embodiment shown in Figure 5, which has in principle the same spatial arrangement of MR elements, yet a different connection of MR elements to a circuit.

[0042] Figure 9 shows a spatial arrangement of MR elements and their connection to form a circuit for a prior art position encoder with four MR elements, which is the basis for the second embodiment of the present invention.

[0043] Figure 10 shows a first subcircuit A consisting of two MR elements, which forms a signal SIN of the position encoder of Figure 9, and a second subcircuit B consisting of two MR elements, which forms a signal COS of the position encoder of Figure 9.

[0044] Figure 11 shows a spatial arrangement of MR elements and their connection to a circuit for a second illustrated embodiment of the position encoder of the present invention, which is an improvement of the prior art position encoder shown in Figure 9.

[0045] Figure 12 shows a first subcircuit A consisting of MR elements which form a signal SIN’ of the position encoder shown in Figure 11 .

[0046] Figure 13 shows a third embodiment of the position encoder of the invention comprising ten MR elements, wherein the distance between the positions of the MR elements in one branch is Ao / 2 + Ao. First embodiment The first embodiment of the position encoder and the associated readhead of the invention is based on a prior art position encoder shown in Figure 1. This is a position encoder comprising eight MR elements R1 , R2, R3, R4, R5, R6, R7 and R8, the spatial arrangement and electrical connection of which are shown in Figure 1. To provide a clearer illustration, the electrical connection of the first subcircuit A to generate the first periodic signal SIN and the second subcircuit B to generate the second periodic signal COS is shown in Figure 2.

[0047] The first subcircuit A and the second subcircuit B have two branches each, to which respective two MR elements are connected in series between a voltage source Vcc and ground GND. The first subcircuit A includes a first branch with MR elements R1 and R3 connected in series and a second branch with MR elements R5 and R7 connected in series.

[0048] Between two positions of MR elements in the same branch, e.g. between R1 and R3, the distance is Ao / 2 in this embodiment, which applies to all branches in both subcircuits (A and B). The number J from the general formula for the distance between the positions of two MR elements in one branch (Ao / 2 + J * Ao) is zero.

[0049] The subcircuit B includes a first branch with MR elements R2 and R4 connected in series and a second branch with MR elements R6 and R8 connected in series.

[0050] The distance r between the position of the first MR element R1 from the first subcircuit A and the position of the first MR element R2 from the second subcircuit B, both viewed from the left side as shown in Figure 1 , is Ao / 4.

[0051] The first subcircuit A and the second subcircuit B are configured as bridges, each comprising two branches which are connected between the ground GND and the voltage source Vcc.

[0052] The node in the first branch of the subcircuit A between the MR elements R1 and R3 represents a first scanning point (USIN+) for the first periodic signal SIN, and the node in the second branch of the subcircuit A between the elements R7 and R5 represents a second scanning point (USIN') for the first periodic signal SIN.

[0053] The node in the first branch of the subcircuit B between the MR elements R2 and R4 represents a first scanning point (UCOs+) for the second periodic signal COS, and the node in the second branch of the subcircuit B between the elements R8 and R6 represents a second scanning point (UCos') for the second periodic signal COS.

[0054] Figure 1 clearly shows that the distance between the position of the first MR element R1 of the first branch of the subcircuit A and the position of the first element R5 of the second branch of the subcircuit A, viewed from the left side in Figure 1 , is Ao + £, wherein the distance £ in this case is about 20% of the distance Ao. Figure 1 also clearly shows that the distance between the position of the first MR element R2 of the first branch of the subcircuit B and the position of the first MR element R6 of the second branch of the subcircuit B, viewed from the left side in Figure 1 , is also Ao + £, wherein the distance £ is about 20% of the distance Ao.

[0055] The number S from the general formula for the distance between the first MR element in the first branch of one subcircuit and the first MR element in the second branch of the same subcircuit (S * Ao + £) is 1 in this embodiment.

[0056] In a more preferred example, where the number S is 1 , which is not shown in Figures 1 and 2, £ would be zero, however, to provide a clearer explanation of a general example and the distance £, the Figures 1 and 2 show a more general and non-preferred embodiment, when £ is not zero.

[0057] All MR elements in the position encoder in Figures 1 and 2 have substantially the same resistance constant Ro, so they substantially equally contribute to the generation of periodic signals SIN and COS following the equations:

[0058] These equations show, among other things, why a bridge connection of MR elements is used in these position encoders. The variable part of the total resistance which includes the useful signal is relatively small based on the total resistance of the MR element. Since the resistance of MR elements in the equations for the signals SIN and COS are represented in fractions, the invariable parts of the total resistance of individual MR elements are effectively cancelled. As each of the signals SIN and COS in this embodiment of the position encoder is taken from two nodes, i.e. as a difference of two voltages, an additional increase in the voltage amplitudes of the signal SIN and COS is achieved, which is contributed by the variable part of the resistance on individual MR elements.

[0059] The position X of the readhead relative to the information carrier within one period A can be calculated by known methods on the basis of the periodic signals SIN and COS, e.g. the inverse tangent (ArcTan) function of the ratio of the periodic signals SIN and COS.

[0060] In real-life conditions, when the length of the period A is not necessarily equal to the distance Ao, an error E occurs in calculating the position X based on the signals SIN and COS due to the deviation of the phase difference F between the signals SIN and COS from the ideal conditions 90° (TT / 2).

[0061] Figure 3 shows the shape of both signals SIN (solid line) and COS (dashed line) in real-life conditions when K / Ko = 0.95, and the shape of the error E (dotted line) normalized by the length of the period K (E / A); all shapes are shown as a function of the movement x of the position encoder readhead. The abscissa axis shows the readhead movement x and is expressed by the length of the period K. The amplitude ASIN of the first periodic signal SIN and the amplitude Acos of the second periodic signal COS are also shown. Figure 3 shows that also the error E which is shown in the normalized form (E / A) is a periodic function depending on the movement x of the readhead. In the continuation, the total value of the error Epp (peak to peak) will be used to show the size of the error, which is defined as a difference between the maximum value of the error E and the minimum value of the error E and is shown in Figure 3 in the normalized form (Epp / A). The left side of the ordinate axis shows a scale for the amplitudes of the periodic signals SIN and COS in a normalized form, so that the ideal value of the amplitude of an individual signal SIN and COS is 1 . On the right side of the ordinate axis, there is a scale for the error E (E / A) normalized by the length of the period A and a scale for the total value Epp of error E (Epp / A) normalized by the length of the period A. In the concrete example of the position encoder in real-life conditions when A / Ao = 0.95, Epp / A is 0.0125. Figure 3 does not clearly show the deviations of the phase difference F between the periodic signals SIN and COS from the ideal conditions (TT / 2).

[0062] Figure 4 shows a diagram of the phase difference F (solid line) between the periodic signals SIN and COS and the normalized total value Epp of error E (Epp / A - dotted line) for the prior art position encoder shown in Figure 1 and Figure 2 as a function of the ratio between the length of the period A and the distance Ao (A / Ao), which is shown in the diagram on the abscissa axis between the ratio value of 0.9 to 1 .1 . The left side of the ordinate axis shows the scale of the phase difference F between the signals SIN and COS in degrees. The ideal value of the phase difference F is 90° and this value is achieved when the ratio A / Ao is 1 . The right side shows the scale for the normalized total value Epp of error E (Epp / A). It becomes more evident in this figure that due to the discrepancy between the length of the period A and the distance Ao, the phase difference F deviates from the ideal 90° in a substantially proportional dependence on the ratio A / Ao. The normalized value Epp / A also has the value 0 in ideal conditions when the ratio A / Ao is 1 and increases proportionally with the actual conditions further deviating from the ideal conditions, i.e. when said ratio is decreasing from the value 1 or increasing above the value 1 . The reason for the asymmetry of the shown normalized total value Epp / A between the left and right sides of the diagram relative to the ideal ratio which is 1 lies in the fact that the total value Epp is normalized by the length of the period A which is larger on the right side of the diagram than on the left side. If the total value Epp in the figure were not normalized, the diagram would be symmetrical with respect to the vertical line intersecting the ratio A / Ao in the value 1. Figure 5 shows a spatial arrangement of MR elements and their connection to a circuit for a first illustrated embodiment of the position encoder of the present invention, which is an improvement of the prior art position encoder shown in Figures 1 to 4. The first embodiment comprises ten MR elements listed based on the spatial position in the magnetic sensor from the left side to the right side: R1 R2, R3, R4, R9, R5', R6, R7, R8 and R10.

[0063] Compared to prior art, the readhead of the present invention is configured in a way that in the first subcircuit A, shown in Figure 6, the MR element R1 is replaced by a MR pair of two MR elements, R1 ' and R9, which have half the resistance constant Ro (Ro / 2) and are connected to each other in series to substantially the same spot in the subcircuit A, wherein the spatial position in the readhead of the first MR element R1 ' of this MR pair is substantially identical to the position of the replaced MR element R1 , and the position of the second MR element R9 of this MR pair is substantially at the distance Ao with respect to the position of the first MR element R1 ' in this MR pair, viewed from the left side to the right side on Figure 5.

[0064] By analogy, in the first subcircuit A, shown in Figure 6, the MR element R5 is also replaced by an additional MR pair of two MR elements, R5' and R10, which have half the resistance constant Ro (Ro / 2) and are connected to each other in series to substantially the same spot in the subcircuit A, wherein the spatial position in the readhead of the first MR element R5' of this additional MR pair is substantially identical to the position of the replaced MR element R5, and the position of the second MR element R10 of this additional MR pair is substantially at the distance Ao with respect to the position of the first MR element R5' in this additional MR pair, viewed from the left side to the right side on Figure 5.

[0065] As evident from Figures 5 and 6, compared to Figures 1 and 2, the remaining MR elements R3 and R7 keep the same resistance constant Ro, remain in the same spot in the subcircuit A and in the same spatial position.

[0066] The distance r between the position of the first MR element R1 ’ from the first subcircuit A and the position of the first MR element R2 from the second subcircuit B, viewed from the left side towards the right side, as shown in Figure 5, is Ao / 4.

[0067] The node in the first branch of the subcircuit A between the MR elements R1 and R3 represents the first scanning point (USIN+) for the first periodic signal SIN’, and the node in the second branch of the subcircuit A between the elements R7 and R10 represents the second scanning point (USIN') for the first periodic signal SIN’.

[0068] Given the fact that the MR elements R1 ' and R9 in the first MR pair are interchangeable in terms of electrical connection, the node in the first branch of the subcircuit A between the elements R9 and R3 would in a different connection (not shown in Figure 6) represent the first scanning point (USIN+) for the first periodic signal SIN'. The same applies to the MR elements R5' and R10 in the second MR pair, they are namely interchangeable in terms of electrical connection, so the node in the first branch of the subcircuit A between the elements R7 and R5’ would in a different connection (not shown in Figure 6) represent the second scanning point (USIN') for the first periodic signal SIN'.

[0069] In this embodiment, the second subcircuit B remains unchanged compared to the second subcircuit B from the prior art position encoder shown in Figure 2, including all MR elements R2, R4, R6 and R8 having the same resistance constant Ro, this is why it is not shown separately. As a result, the second periodic signal COS' is the same as the second periodic signal COS from the prior art position encoder shown in Figures 1 and 2.

[0070] The equation for calculating the first periodic signal SIN’ of the position encoder of the invention shown in Figures 5 and 6 is as follows:

[0071] The equation for calculating the second periodic signal COS’ is, due to the identical subcircuit B, identical as in the prior art position encoder shown in Figures 1 and 2:

[0072] Compared to the prior art position encoder shown in Figures 1 and 2, the first embodiment of the position encoder of the present invention has considerably better characteristics regarding the deviation of the phase difference F between the signals SIN' and COS' from the ideal value 90° (TT / 2) and consequently better characteristics in relation to error E.

[0073] Figure 7 shows a diagram of the phase difference F (solid line) between the signals SIN’ and COS’ and the total value Epp of error E normalized by the length of the period K (Epp / A - dotted line) for the first embodiment of the position encoder of the present invention shown in Figure 5 as a function of the ratio between the length of the period K and the distance Ao (A / Ao), as shown on the abscissa axis. Degrees for the phase difference F are indicated on the left side of the ordinate axis, while the total value Epp of error E is indicated on the right side, which is normalized by the length of the period A (Epp / A). As evident from Figure 7, the phase difference F in the position encoder of the first embodiment of the present invention has the minimum deviation from the ideal value of 90°, so the deviations are not visible to the naked eye. A comparison between the normalized total value of error Epp / A in Figure 7 for the position encoder of the present invention and the total value of error Epp / A in Figure 4 for the prior art position encoder reveals that the error E in the position encoder of the present invention is smaller by an order of magnitude and on top of that its rising curve - when the ratio A / Ao deviates from the ideal value of 1 - is less steep than in the prior art position encoder.

[0074] First additional example of the first embodiment

[0075] As mentioned above, it is possible to interchange, in terms of electrical connection in the circuit, any two MR elements within a relevant subcircuit, in this case the subcircuit A, provided that they have the same resistance constant (either Ro or Ro / 2) irrespective of whether these two MR elements are located in the same or different branch. Figure 8 shows the first additional example of the first embodiment having the same spatial arrangement of positions of MR elements including the half MR elements, yet a different electrical connection. In Figure 8, the half MR elements R9 and R10 have their positions in the electrical connection interchanged compared to the circuit shown in Figure 5 and Figure 6, while there is no interchange in the second subcircuit B.

[0076] The equation for the first periodic signal SIN’ of the circuit in Figure 9 is different accordingly, but the periodic signal SIN’ is effectively the same in the circuit in Figure 5 and in the circuit in Figure 8. The amended equation for the first periodic signal for the circuit in Figure 8 is:

[0077] Second additional example of the first embodiment

[0078] The second additional example of the first embodiment, which is not shown in Figures, relates to the same circuit as shown in Figure 8, with a single difference being in the spatial arrangement of positions of MR elements, the distance £ is namely equal to zero. This means, among other things, that the half MR elements R9 and R5’ are substantially in the same position within the magnetic sensor. Since they are connected to each other in series, they may be configured as one MR element located in this position and having the resistance constant Ro instead of two separate MR elements with half the resistance constant (Ro / 2). Second embodiment

[0079] The second embodiment of the position encoder and the associated readhead of the invention is based on the prior art position encoder shown in Figure 9. This is a position encoder comprising four MR elements R1 , R2, R3 and R4, the spatial arrangement and electrical connection of which are shown in Figure 9. To provide a clearer illustration, the electrical connection of the first subcircuit A to generate the first periodic signal SIN and the second subcircuit B to generate the second periodic signal COS is shown in Figure 10.

[0080] The first subcircuit A comprises one branch with two MR elements R1 and R3 which are connected to each other in series between the voltage source Vcc and ground GND. The distance between the spatial position of the MR element R1 and the position of the MR element R3 in the readhead is Ko / 2. The number J from the general formula for the distance between two MR elements in one branch (Ko / 2 + J * Ao) is zero.

[0081] The second subcircuit B comprises one branch with two MR elements R2 and R4 which are connected to each other in series between the voltage source Vcc and ground GND. The distance between the spatial position of the MR element R2 and the position of the MR element R4 in the readhead is Ko / 2. The number J from the general formula for the distance between two MR elements in one branch (Ko / 2 + J * Ao) is also zero.

[0082] The distance r between the position of the first MR element R1 from the first subcircuit A and the position of the first MR element R2 from the second subcircuit B, both viewed from the left side as shown in Figure 9, is Ao / 4.

[0083] The node in the branch of the first subcircuit A between the MR elements R1 and R3 represents a scanning point (USIN) for the first periodic signal SIN, wherein, in order to achieve a minimum or zero deviation, one half of the voltage of the voltage source Vcc needs to be subtracted from the zero position of the first periodic signal SIN. This is done by measuring the voltage of the first periodic signal SIN between the first scanning point (USIN) and the half voltage of the voltage source Vcc as shown in Figure 10.

[0084] The node in the branch of the second subcircuit A between the MR elements R2 and R4 represents a scanning point (UCos) for the first periodic signal COS, wherein, in order to achieve a minimum or zero deviation, one half of the voltage of the voltage source Vcc needs to be subtracted from the zero position of the first periodic signal SIN. This is done by measuring the voltage of the first periodic signal SIN between the first scanning point (USIN) and the half voltage of the voltage source Vcc as shown in Figure 10. All MR elements in the position encoder in Figures 9 and 10 have substantially the same resistance constant Ro, so they substantially equally contribute to the generation of periodic signals SIN and COS following the equations:

[0085] The position X of the readhead relative to the information carrier within one period A can be calculated by known methods on the basis of the inverse tangent (ArcTan) function of the ratio of the periodic signals SIN and COS.

[0086] In real-life conditions, as already mentioned, when the length of the period A is not equal to the distance Ao, an error E occurs in calculating the position X based on the signals SIN and COS due to the deviation of the phase difference F between the signals SIN and COS from the ideal conditions 90° (TT / 2).

[0087] Figure 11 shows a spatial arrangement of MR elements and their connection to a circuit for a second illustrated embodiment of the position encoder of the present invention, which is an improvement of the prior art position encoder shown in Figures 9 and 10. This embodiment comprises five MR elements listed based on the position from the left side: R1 ', R2, R3, R4 and R5.

[0088] Compared to prior art, the readhead of the present invention is configured in a way that in the first subcircuit A, shown in Figure 9, the MR element R1 is replaced by a MR pair of two MR elements, R1 ' and R5, which have half the resistance constant Ro (Ro / 2) and are connected to each other in series to substantially the same spot in the subcircuit A, wherein the spatial position in the readhead of the first MR element R1 ' of the MR pair is substantially identical to the position of the replaced MR element R1 , and the position of the second MR element R5 of the MR pair is substantially at the distance Ao with respect to the first MR element R1 ' in the pair, viewed from the left side to the right side on Figure 11 .

[0089] As evident from Figures 11 and 12, compared to Figures 9 and 10, the MR element R3 keeps the same resistance constant Ro, remains in the same spot in the magnetic sensor in the subcircuit A and in the same spatial position.

[0090] The distance r between the position of the first MR element R1 from the first subcircuit A and the position of the first MR element R2 from the second subcircuit B, viewed from the left side as shown in Figure 11 , is Ao / 4.

[0091] The node in the branch of the subcircuit A between the MR elements R5 and R3 represents a scanning point (USIN) for the first periodic signal SIN’, wherein, in order to achieve a minimum or zero deviation, one half of the voltage of the voltage source Vcc needs to be subtracted from the zero position of the first periodic signal SIN. This is done by measuring the voltage of the first periodic signal SIN between the first scanning point (USIN) and the half voltage of the voltage source Vcc as shown in Figure 12.

[0092] Given the fact that the MR elements R1 ' and R5 in the MR pair are interchangeable in terms of electrical connection, the node in the branch of the subcircuit A between the elements RT and R3 would in a different connection (not shown in Figures 11 and 12) represent the first scanning point (USIN+) for the first periodic signal SIN'.

[0093] In the second embodiment, the second subcircuit B remains unchanged compared to the second subcircuit B from the prior art position encoder shown in Figure 9, including the two MR elements R2 and R4 having the same resistance constant Ro, this is why it is not shown separately. As a result, the second periodic signal COS' is the same as the second periodic signal COS from the prior art position encoder shown in Figures 9 and 10.

[0094] The equation for calculating the first periodic signal SIN’ of the position encoder of the invention shown in Figures 11 and 12 is as follows:

[0095] The equation for calculating the second periodic signal COS’ is, due to the identical subcircuit B, identical as in the prior art position encoder shown in Figures 9 and 10:

[0096] Compared to the prior art position encoder shown in Figures 9 and 10, the first embodiment of the position encoder of the present invention has considerably better characteristics regarding the deviation of the phase difference F between the signals SIN' and COS' from the ideal value 90° (TT / 2) and consequently better characteristics in relation to error E.

[0097] Third embodiment Figure 13 shows the third embodiment of the position encoder and readhead of the invention, in which both subcircuits A and B have two branches. This one differs from the other illustrated embodiments in that the number J in the general equation Ao / 2 + J * Ao, which represents the distance between the positions of two MR elements in one branch, is 1. The number J was zero in all previously illustrated embodiments. So, the distance between the MR elements within each branch according to the third embodiment is Ao / 2 + Ao. This is evident from Figure 13 because the distances between the positions of the following MR elements are equal to Ao / 2 + Ao, namely the distances between R1 ' and R3, between R7 and R5', R2 and R4, as well as R6 and R8.

[0098] The distance r between the position of the first MR element R1 from the first subcircuit A and the position of the first MR element R2 from the second subcircuit B, both viewed from the left side as shown in Figure 13, is Ao / 4.

[0099] The number S from the general formula S * Ao + £, which represents the distance between the position of the first MR element in the first branch of the first subcircuit A, viewed from a certain side of the longitudinal direction, and the position of the first MR element in the second branch of the first subcircuit A, viewed from the same side, is 1 , and the distance £ from said formula is about 20% of the distance Ao. In the first subcircuit A of the third embodiment, this is the distance between the position of the MR element R1 ' and the position of the MR element R5’, viewed from the left side in Figure 13, which is Ao + £.

[0100] The same applies by analogy also for the distance between the position of the first MR element R2 in the first branch of the second subcircuit B and the position of the first MR element R6 in the second branch of the second subcircuit, viewed from the left side in Figure 13, which is Ao + £, too.

[0101] The distance between the position of the MR element R6 and the position of the MR element R3 in Figure 13 is equal to Ao / 4 - £.

[0102] The equations for the first periodic signal SIN’ and the second periodic signal COS’ for the position encoder shown in Figure 3 are as follows:

[0103] R2 RS

[0104] COS' = Vcc( - ) R2 + R4- R6 + RS' The third embodiment is not one of the preferred examples because the distances between the positions of two MR elements in a respective branch are larger, because the number J is 1 and not zero as are the distances in other illustrated embodiments when the number J is zero. All this extends the total length of the magnetic sensor and the readhead, which is not desired.

[0105] Present invention - general

[0106] The invention generally refers to a position encoder comprising a magnetic information carrier and a readhead to determine the position 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 read head comprises 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 Rn 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 A 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 are arranged in spatial positions substantially in the longitudinal direction. In some embodiments, two or more MR elements R5’, R9 can be provided in the same spatial position. The spatial position of the MR element R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 ', R2, R3, R4, R5 determines which part of the magnetic field generated by the magnetic information carrier will be detected by an individual MR element R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 ', R2, R3, R4, R5. The MR elements R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1', R2, R3, R4, R5 are electrically connected to a circuit, wherein a first subset of MR elements R1 ', R3, R9, R5', R7, R10; R1 ', R3, R5 is connected to a first subcircuit A to generate a first periodic signal SIN' with the length of the period A, and a second subset of MR elements R2, R4, R6, R8; R2, R4, which does not include the MR elements from the first subset, is connected to a second subcircuit B to generate a second periodic signal COS' with the length of the period A. Each subcircuit A and B comprises one branch or two branches, preferably two branches, wherein in each branch at least two MR elements are electrically connected in series between the voltage source Vcc and ground GND. 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, the distance Ao being defined as four times the distance r (Ao = 4 * r). At least one distance between 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. J is preferably zero, especially in terms of sensor length, because we want the sensor to be as short as possible. The position X of the readhead relative to the magnetic information carrier is determined on the basis of the first periodic signal SIN’ and the second periodic signal COS’, for example based on the inverse tangent (ArcTan) function of the ratio between the first periodic signal SIN’ and the second periodic signal COS’. The first periodic signal SIN’ is obtained on the intermediate node of the branch of the first subcircuit A, when this subcircuit only comprises one branch, or between two intermediate nodes of two branches of the first subcircuit A, when this subcircuit comprises two branches. The second periodic signal COS’ is obtained on the intermediate node of the branch of the second subcircuit B, when this subcircuit only comprises one branch, or between two intermediate nodes of two branches of the second subcircuit B, when this subcircuit comprises two branches.

[0107] At least one branch in at least one, preferably one, 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. 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 from the same MR pair is substantially equal to the distance Ao.

[0108] In cases, in which the first subcircuit A and / or the second subcircuit B comprises two branches, the distance between the position of the first MR element R1 ’ in the first branch of one subcircuit A, as viewed from a certain side of the longitudinal direction, and the position of the first MR element R5’ in the second branch of the same subcircuit A, as viewed from the same side of the longitudinal direction, is equal to S * Ao + £, wherein the number S is zero or a natural number, preferably zero or one, and £ assumes the values between about - Ao / 4 and Ao / 4.

[0109] As mentioned above, the MR elements R1 ', R2, R3, R4, R9, R5', R6, R7, R8, R10; R1 ', R2, R3, R4, R5 with defined positions in the magnetic sensor may be electrically connected to a circuit in various ways. In the most basic connection, two half MR elements R1 ', R9; R5', R10; R1 ', R5 in the same MR pair are connected to each other in series and connected to the same branch as the replaced MR element R1 , R5. Different, yet equivalent connections, in terms of efficiency, may be obtained in a way that, in terms of electrical connection, any two half MR elements are replaced within a certain subcircuit A or B with the resistance constant Ro / 2, irrespective of whether they belong to the same branch or not. Further, in terms of electrical connection, two MR elements with a full resistance constant Ro may be interchanged within a certain subcircuit A or B, provided that the distance between their positions is S * Ao + £.

[0110] Bearing the interchangeability of the MR elements within an individual subcircuit A or B in mind, under the conditions described in the previous paragraph, the distance S * Ao + £ in a more general sense represents the distance between the position of one of the MR elements R1 ' in the first branch of a certain subcircuit A and the position of one of the MR elements R5’ in the second branch of the same subcircuit A, which is particularly evident from Figure 8. By analogy this also applies to the subcircuit B when it comprises two branches. In the embodiments where the number S is zero, the distance £ is preferably zero. In other embodiments where the number S is one, the distance £ is preferably zero or Ao / 8. In the embodiments where the number S is zero and the distance £ is zero, the positions of the MR elements, the distance of which is defined by the equation S * Ao + £ or rather their centroids are located in the same position in the magnetic sensor, which means that they detect substantially the same magnetic field from the magnetic information carrier.

[0111] In preferred embodiments, in which the first MR element, with respect to the spatial position of all MR elements in the magnetic sensor, viewed from a certain side of the longitudinal direction, belongs to a MR pair of half MR elements of a certain subcircuit, the position of the second MR element of this MR pair is offset by the distance Ao in a direction, viewed from the same side, with respect to the position of the first MR element of this MR pair. The remaining subcircuit does not comprise any MR pairs of half MR elements. In such embodiments, in which a certain subcircuit comprises two branches, the second branch preferably also comprises the second MR pair of the half MR elements, the position of the second MR element of the second MR pair being offset by the distance Ao in a direction, viewed from the same side, with respect to the position of the first MR element of the second MR pair.

Claims

CLAIMS1 . 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. Position encoder of claim 1 , characterized in that the first MR element (R1 '), with respect to thespatial 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. 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. Position encoder of claim 3, characterized in that the number S is one and the distance £ is 0.

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 (R51) 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. Position encoder of claim 3, characterized in that the number S is zero and the distance £ is Ao / 8.

7. Position encoder of claim 3, characterized in that the number s is zero and the distance £ is zero.

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. 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 (R51) of the second MR pair.

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).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. 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. 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. 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. Position encoder readhead of claims 1 to 14.

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