Position encoder readhead, position encoder and method of minimizing position error
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- RLS MERILNA TEHNIKA D O O
- Filing Date
- 2024-06-27
- Publication Date
- 2026-05-06
AI Technical Summary
Position encoders, particularly in circular variants, face significant errors in calculating the position of a readhead relative to an information carrier due to discrepancies between the detected period P and the sensor pitch R, which is exacerbated by the curved design and varying distances between the readhead and the information carrier's center.
Incorporating an additional sensing element positioned at a distance r from the existing sensing elements, allowing the generation of new periodic signals that, when combined with existing signals, minimize the error by calculating the readhead's position using the inverse tangent function of the ratio of common signals, thereby aligning the sensor pitch R with the period P.
This configuration significantly reduces the positional error by canceling out amplitude deviations and maintaining a minimal phase shift error, resulting in a more accurate readhead position calculation across varying ratios of period P to sensor pitch R.
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Abstract
Description
[0001] Position encoder readhead, position encoder and method of minimizing position error
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] In different position encoders, for instance in optical position encoders, the sensing elements are configured as optical sensing elements and the information carrier includes repeating patterns of alternating optical segments with a length of the period P detected by the sensing elements, so the explanations regarding the responses (H1 , H2, H3, H4) at the outputs of respective sensing elements (hi , h2, h3, h4) given above and in the continuation apply by analogy also to other position encoders, for instance optical position encoders.
[0008] If the sensor pitch R of the sensing elements is essentially equal to the period P of the repeating magnetic pattern on a magnetic information carrier (or optical pattern on an optical information carrier), two periodic signals can be calculated by adding or subtracting responses at the outputs of respective sensing elements as a function of movement (x) of the readhead, namely
[0009] SIN1 (x) = (H1 - H2 - H3 + H4) / 2 (1)
[0010] COS1 (x) = (H1 + H2 - H3 - H4) / 2 (2)
[0011] A position X of the readhead relative to the information carrier within one period P can be calculated by the known method (e.g. US4949289A) on the basis of the inverse tangent (ArcTan) function of the periodic signal ratio. For instance, the position X of the readhead can be calculated using the following equation:
[0012] By analogy, a position expressed as an angle can also be calculated, for example in the case of a circular encoder with a circular information carrier.
[0013] In this method, a problem is encountered when the sensor pitch R is not equal to the period P, as an error E occurs in calculating the position X in these cases, which is a difference between the calculated position X and the actual position of the readhead as will be explained below. This problem is not so distinct in linear position encoders having a linear information carrier since a sensor design, i.e. a precise distance r between the sensing elements, precisely determines the sensor pitch R with respect to the period P, and the distance between the information carrier and the sensor during operation, more specifically the arrangement of the sensor with respect to the information carrier during operation does not have any impact on said error E.
[0014] However, this problem is more distinct in circular position encoders, in particular in axial variants of circular position encoders, since the length of the period P as detected by the sensor is, due to the curved path and the related design of the information carrier, dependent on the arrangement of the sensor relative to the information carrier, for instance on the distance between the sensor and the centre of the circular curve of the path defined by the information carrier design. Irrespective of how accurately the 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 P as detected by the sensor. This may result in undesired differences between the length of the period P and the sensor pitch R regardless of the manufacturing accuracy of the sensor and readhead.
[0015] The readhead of the present invention substantially solves the problem of error E in measuring the position X, which results from a difference between the period P as detected by the sensor and the sensor pitch R. The readhead of the invention comprises a sensor with existing sensing elements hi , h2, h3 and h4 arranged at a mutual identical distance r, with corresponding responses H1 , H2, H3, H4 at outputs, and with an additional sensing element h5 with a corresponding response H5 at the output, positioned at a distance r from the last or first existing sensing element. The sensor pitch R is defined in the readhead of the present invention as a sum of the mutual distances r between the adjacent sensing elements and is ideally also identical to the length of the period P. In real-life cases, 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.
[0016] Using an additional sensing element h5 in combination with the existing sensing elements hi , h2, h3, h4, two additional periodic signals can be generated as a function of the readhead movement, namely:
[0017] SIN2(x) = (- H2 - H3 + H4 + H5) / 2 (4) COS2(x) = (H2 - H3 - H4 + H5) / 2 (5)
[0018] If signals SIN1 and SIN2 and signals COS1 and COS2 are added together, common signals SIN and COS are obtained, in which the error E of the calculated position X due to a difference between the length of the period P and the sensor pitch R is considerably minimized, which will be explained in more detail in the continuation.
[0019] SIN(x) = (H1 - H2 - H3 + H4) / 2 + (- H2 - H3 + H4 + H5) / 2 = H1 / 2 - H2 - H3 + H4 + H5 / 2 (6)
[0020] COS(x) = (H1 + H2 - H3 - H4) / 2 + (H2 - H3 - H4 + H5) / 2 = H1 / 2 + H2 - H3 - H4 + H5 / 2 (7)
[0021] The position X of the readhead relative to the information carrier within one period P is calculated from a first common signal SIN and a second common signal COS on the basis of the inverse tangent (ArcTan) function of their ratio. For instance, the above equation (3) is used to calculate the position X of the readhead, in which the values of the common signals SIN and COS are inserted instead of the values of the signals SIN1 and COS1 :
[0022] As a result, the position X of the readhead, calculated by equation (8), has a considerably minimized error E due to a difference between the period P and the sensor pitch R.
[0023] Addition or subtraction of the responses H1 , H2, H3, H4, H5 to generate said periodic signals SIN1 , COS1 , SIN2, COS2 and the common signals SIN and COS is performed by an adding unit operably included in the readhead.
[0024] Embodiments of the readhead of the present invention and the operation will be explained in more detail hereinbelow and shown in the figures:
[0025] Figure 1 shows a schematic representation of positions of four sensing elements hi , h2, h3 and h4 in a prior art sensor compared to a period P of a magnetic field of a magnetic information carrier in an ideal case when the period P is identical to the sensor pitch R.
[0026] Figure 2 shows the shape of signals SIN1 and COS1 as a function of readhead movement, which are calculated from the responses H1 , H2, H3 and H4 of the sensing elements hi , h2, h3 and h4 of a prior art sensor in an ideal case when the period P is identical to the sensor pitch R.
[0027] Figure 3 shows the shape of signals SIN1 , COS1 , their amplitudes ASINI and Acosi and the shape of the size of error E of position X normalized by the period P (E / P) as a function of movement of the readhead from prior art in a non-ideal case, when the length of the period P does not match the sensor pitch R, namely P / R = 0.95.
[0028] Figure 4 shows the amplitudes ASINI and Acosi of the signals SIN1 , COS1 and the ratio between the total value Epp of error E and the period P (Epp / P) as a function of the ratio between the length of the period P and the sensor pitch R (P / R).
[0029] Figure 5 shows a schematic representation of positions of four existing sensing elements hi , h2, h3 and h4 and an additional sensing element h5 in an embodiment of the magnetic sensor of the present invention compared to a period P of a magnetic field of a magnetic information carrier in an ideal case when the period P is identical to the sensor pitch R.
[0030] Figure 6 shows the amplitudes ASIN2 and Acos2 of the signals SIN2, COS2 and the ratio between the total value Epp of error E and the period P (Epp / P) as a function of the ratio between the length of the period P and the sensor pitch R (P / R).
[0031] Figure 7 shows the amplitudes ASIN and Acos of the signals SIN, COS and the ratio between the total value Epp of error E and the period P (Epp / P) as a function of the ratio between the length of the period P and the sensor pitch R (P / R).
[0032] Figure 8 shows a phase shift between the signals SIN and COS as a function of the ratio between the length of the period P and the sensor pitch R (P / R).
[0033] Figure 9 shows three different examples of placement of the readhead with a magnetic sensor having four sensing elements (hi , h2, h3, h4; hi h2', h3', h4'; hi ", h2", h3", h4") above the magnetic information carrierwith a circular path in an axial version of a circular position encoder to show various lengths of the period P as detected by the readhead depending on the placement of the readhead.
[0034] Figure 1 shows a schematic representation of positions of four sensing elements hi , h2, h3 and h4 in a prior art sensor with respect to the period P of a magnetic information carrier in an ideal case when the length of the period P is identical to the sensor pitch R (P = R). In a position of the magnetic head, in which the first sensing element hi is located exactly above the beginning of the period P, the second sensing element h2 is located above a point P / 4, the third sensing element h3 is located above a point P / 2 (2P / 4), the fourth sensing element h4 is located above a point 3P / 4, while there is no sensing element above the end of the period P. The abscissa axis of the diagram of the position of the sensing elements (top) shows a share of the sensor pitch R and the abscissa axis of the representation of the magnetic field (bottom) shows a share of the entire period P. In a concrete prior art example, the sensor pitch R and the period R equal 2 mm, so a mutual distance r between the sensing elements in this variant equals to 0.5 mm. The ordinate axis of the representation of the magnetic field (bottom) above the magnetic information carrier shows units mT, so the amplitude of the magnetic field density in this representation is 40 mT, which represents an example of typical values of magnetic field density in such applications.
[0035] Figure 2 shows the shape of signals SIN1 and COS1 from the prior art readhead with sensing elements hi , h2, h3, h4 which are shown in Figure 1 , i.e. in an ideal case when P = R. The signals SIN1 and COS1 depend on readhead movement (x) and are calculated from the responses H1 , H2, H3 and H4 of the sensing elements hi , h2, h3 and h4 of the magnetic sensor by formula (1) and (2). The figures evidently show that the two signals SIN1 and COS1 have completely identical amplitudes and are in a regular phase shift TT / 2, as this is an ideal case. The abscissa axis shows the readhead movement (x) within the period P of the magnetic information carrier. The ordinate axis shows a normalized value of the signals SIN1 and COS1 , such that the amplitude of these ideal signals equals 1 .
[0036] Figure 3 shows the shape of real signals SIN1 , SIN1 and the normalized error E, i.e. a ratio between the error E and the period P (E / P) as a function of movement (x) of the readhead with a sensor having four sensing elements from prior art, in a real case, when the length of the period P does not match the sensor pitch R, it is shown as a concrete real case, when P / R = 0.95. Figure 3 also implies the amplitudes ASINI and Acosi of the signals SIN1 and COS1 . The position X is calculated from the signals SIN1 and COS1 using formula_(3) above. The abscissa axis and the left side of the ordinate axis are defined identically as in Figure 2, while the right side of the ordinate axis shows a normalized error E of the position X, i.e. a ratio between the error E and the period P (E / P). The figure clearly shows that the amplitude SIN1 is in this case larger compared to ideal conditions due to the inequality between P and R, and the amplitude COS1 is smaller. A phase shift between the signals SIN1 and COS1 is the same as in an ideal case, i.e. TT / 2. The error E of the position X in Figure 3 is expressed in a normalized form, it is normalized by the period P (E / P), and the figure clearly shows that the error E is also a periodic function depending on the readhead (x) position with half the length of the period relative to the length of the period P. In this real case, when P / R = 0.95, the amplitude of the periodic function of the error normalized by the period P (E I P) equals 0.0063. Figure 3 also displays the total value Epp of error E normalized by the period P (Epp / P), the total value Epp of the error E being defined as a difference between the highest and the lowest value of the error E (peakto peak) during readhead movement within the period P. Forthis concrete case, when P / R = 0.95, Epp / P amounts to 0.0126 = 0.0063 - (-0.0063).
[0037] Figure 4 shows a graph of three values as a function of the ratio between the length of the period P and the sensor pitch R (P / R) in the range of this ratio of 0.9 to 1 .1 ; namely the amplitude ASINI of the signal SIN1 , the amplitude Acosi of the signal COS1 and the total value Epp of the error E which is normalized by the period P, i.e. (Epp I P). The total value Epp is, as mentioned above, defined as a difference between the highest and the lowest value of the error E (peak to peak) during readhead movement within the period P. For example, the total value Epp of error E normalized by the period P (Epp / P) in the concrete case shown in Figure 3, when the ratio P / R = 0.95, amounts to 0.0126 = 0.0063 - (-0.0063). The position X is calculated from the signals SIN1 and COS1 using formula (3) above. On the left side of the ordinate axis is a scale for the amplitudes ASINI , Acosi, and on the right side of the ordinate axis is a scale for the total value Epp of the error E normalized by the period P (Epp / P). In a real-life situation, the potential difference between the length of the period P and the sensor pitch R will be within the range of said ratio (P I R). The figure shows that the amplitudes ASINI and Acosi are identical and also the total value of the error Epp is zero when said ratio (P I R) equals 1 , when the length of the period P is equal to the sensor pitch R. By decreasing said ratio (P I R) from value 1 , the total value of the error Epp, or more specifically the total value Epp of error E normalized by the period P (Epp / P) as shown in the figure, practically increases linearly due to the increased difference between the amplitudes ASINI and Acosi of the signals SIN1 and COST By decreasing said ratio (P I R) from value 1 , the amplitude Acosi of the signal COS1 decreases, while the amplitude ASINI of the signal SIN1 increases. By increasing said ratio from value 1 , the total value of the error Epp, or more specifically the total value Epp of error E normalized by the period P (Epp / P), increases linearly due to the increased difference between the amplitudes ASINI and Acosi of the signals SIN1 and COS1 , wherein the amplitude ASINI is decreasing and the amplitude Acosi is increasing. In Figure 4, a phase shift between SIN1 and COS1 is not shown, but it is constant and the same as in an ideal case, namely TT / 2, in the whole illustrated range of the ratio P / R, namely from 0.9 to 1.1.
[0038] Figure 5 shows a schematic representation of positions of five sensing elements hi , h2, h3, h4, h5 in the readhead of the present invention with respect to the period P of the magnetic information carrier in an ideal case when the length of the period P is equal to the sensor pitch R (P = R), namely four existing sensing elements hi , h2, h3 and h4 and an additional sensing element h5. In a position of the magnetic head, in which the first sensing element hi is located exactly above the beginning of the period P, assuming ideal conditions are available where P = R, the second sensing element h2 is located above a point P / 4, the third sensing element h3 is located above a point P / 2 (2P / 4), the fourth sensing element h4 is located above a point 3P / 4 and the firth - additional sensing element h5 - is located above the end of the period P or above the beginning of a next period. In other words, the distance between the first hi and the last h5 sensing element is exactly equal to the sensor pitch R which is, in the readhead of the present invention, equal to the sum of all mutual distances r and in the illustrated ideal case where P = R also equal to the length of the period P.
[0039] Figure 6 shows a graph of three values as a function of the ratio between the length of the period P and the sensor pitch R (P / R) in the range of this ratio of 0.9 to 1 .1 ; namely the amplitude ASIN2 of the signal SIN2, the amplitude Acos2 of the signal COS2 and the total value Epp of the error E of the calculated position X normalized by the period P, i.e. (Epp I P); the position X being calculated from said signals SIN2 and COS2 by using the above formula (4) by analogy, only that the signals SIN1 and COS1 from the formula are replaced by SIN2 and COS2. The abscissa axis and the two ordinate axes are defined in the same way as in Figure 4. The comment given in Figure 4 regarding the amplitudes ASINI and Acosi and the linear shape of the total value of the error Epp or the total value Epp of error E normalized by the period P (Epp / P) applies by analogy also to Figure 6, with the essential difference being that in the range where said ratio (P / R) decreases from value 1 , the amplitude Acos2 is increasing, while Acosi is decreasing in the same range (as shown in Figure 4). A similar situation applies to the amplitude ASIN2 which is decreasing in this range, while the amplitude ASINI (as shown in Figure 4) is increasing in this range. A similar situation applies to the range where said ratio (P I R) is increasing from value 1 , namely the amplitude Acos2 is decreasing, the amplitude Acosi (as shown in Figure 4) is increasing, the amplitude ASIN2 is decreasing, and the amplitude ASINI (as shown in 4) is decreasing. In Figure 6, a phase shift between SIN2 and COS2 is not shown, but it is constant and the same as in an ideal case, namely TT / 2, in the whole illustrated range of the ratio P / R, namely from 0.9 to 1 .1 .
[0040] Due to the described symmetry of the deviation of the pairs of amplitudes ASINI , ASIN2 and Acosi, Acos2 from the ideal conditions, within said relevant range when (P I R) is from 0.9 to 1 .1 , the deviations in the amplitudes cancel each other in the summed signals, namely SIN = SIN1 + SIN2 and COS = COS1 + COS2. So, to calculate the position X in the readhead of the present invention equation (8) is used, which is substantially identical to equation (3), only that instead of the signals SIN1 and COS1 in formula (4) the newly summed signals SIN and COS are used.
[0041] Figure 7 shows a graph of three values as a function of the ratio between the length of the period P and the sensor pitch R (P / R) in the range of this ratio of 0.9 to 1.1 ; namely the amplitude ASIN of the signal SIN, the amplitude Acos of the signal COS and the total value Epp of the error E of the calculated position X which is normalized by the period P, i.e. (Epp I P); the position X being calculated from said signals SIN and COS using the above formula (8). The figure shows that the amplitudes ASIN and Acos have considerably less deviations as a function of the ratio P / R, furthermore, the amplitudes ASIN and Acos deviate in the same direction and not in the opposite direction as in SIN1 and COS1 , which is why these tiny deviations additionally cancel each other out in equation (8), because in the inverse tangent (ArcTan) function there is a ratio between the amplitudes ASIN and Acos. As a result, the total value Epp of the error E, in Figure 7, which is normalized by the period P (Epp I P), is by an order of magnitude smaller in the readhead of the present invention compared to the readhead from prior art. However, because of the difference between the length of the period P as detected by the readhead and the sensor pitch R, the total value of the error Epp is not quite zero in the readhead of the invention, since in the summed signals SIN and COS, a considerable error is eliminated due to the undesired changes in the amplitudes ASINI , ACOSI and ASIN2, ACOS2, but a new error is generated due to a deviation in the phase shift between the signals SIN and COS, i.e. when the phase shift between the signals SIN and COS deviates from the ideal phase shift TT / 2 due to a difference between the length of the period P as detected by the readhead and the sensor pitch R. A further advantage of the readhead of the present invention is that the new error E, more specifically the total value of the error Epp due to deviations in the phase shift, does not increase linearly from the ideal situation, when the ratio P / R equals 1 , but on a less sloped curve.
[0042] Figure 8 shows a phase difference between the signals SIN and COS in the readhead of the present invention as a function of the P / R ratio, in degrees on the left side of the ordinate axis. In ideal conditions, when P = R and the ratio P / R = 1 , the phase shift between both signals is exactly TT / 2, SO a phase shift of 90° is shown in the figure. To the left and right of the ideal conditions, the phase shift is increasing but, as said, the deviation in the phase shift contributes significantly less to the error E of the calculated position X than the deviation in the amplitudes ASINI and Acosi in the readhead from prior art shown in Figure 4.
[0043] Figure 9 shows why axial variants of circular position encoders from prior art have a more pronounced problem of the difference between the length of the period P and the sensor pitch R. Figure 9 shows a half of a circular magnetic information carrier in said axial variant, which includes 20 periods on the whole circular curve of the magnetic information carrier, each consisting of two oppositely magnetized segments N (north) and S (south). Above the magnetic information carrier, three various placements of a magnetic sensor having four sensing elements are schematically marked (for instance of such a magnetic sensor, the ideal case of which is shown in Figure 1). The sensing elements in all three positioning arrangements have an identical sensor pitch R, however, they will detect a different length of the period P as a function of the distance between the magnetic sensor and the centre of the path defined by the design of the magnetic information carrier. The magnetic sensor positioned closest to the centre and having the sensing elements hi , h2, h3 and h4, will detect a shorter length of the period P than the sensor pitch R, so P / R is larger than 1. A centrally positioned magnetic sensor having the sensing elements hT, h2', h3' and h4' will detect a length of the period P that is equal to the sensor pitch R, hence P / R = 1 , which is an ideal case. The magnetic sensor most distant from the centre and having the sensing elements hi", h2", h3" and h4" will detect a period P that is longer than the sensor pitch R.
[0044] As mentioned earlier, the graphs in Figures 4, 6 and 7 show the total value Epp of error E, which is normalized by the period P (Epp I P), this is why the normalized total value Epp of the error on the left side is larger than that on the right side, although the total value of the error Epp in the unnormalized form is the same, since the length of the period P on the left side of the graph is shorterthan R and than the ideal length P = R, while on the right side it is shorter than R and than the ideal length P = R.
[0045] The related method of the present invention to calculate the position X of the readhead relative to the information carrier includes 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; and c. calculating the position X on the basis of the first common signal SIN and the second common signal COS. The calculation of the position X of the readhead relative to the information carrier is carried out on the basis of the inverse tangent (ArcTan) function of their ratio.
[0046] In one of possible embodiments, the following equation is used for the calculation:
Claims
CLAIMS: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. 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. Readhead of claim 2, characterized in that the magnetic sensing elements (hi , h2, h3, h4, h5) are configured as Hall elements.
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. 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. Readhead of claim 5, characterized in that the position X of the readhead relative to the information carrier is calculated by equation:
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. 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. 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. Method of claim 9, characterized in that the following equation is used to calculate the position X: