Optical position measuring device and method for operating the optical position measuring device

Abstract

To provide an optical position measuring device and a method for operating the optical position measuring device so as to identify a scanning distance as precisely as possible without necessary additional components.SOLUTION: A scale 10 connected to a first object 01 includes a reflective measuring scale 11 extending along a measuring direction with different reflectivities. A scanning unit 20 is connected to a second object 02 and is arranged at a scanning distance ZA relative to the scale 10, and a light source 21 and a detector array 22 are provided. A signal processing unit 24 is configured to generate position signals relating to a position of the first object 01 relative to the second object 02 from photocurrents of the detector array 22, obtain a total photocurrent in a peripheral region of a detector in a central region of the detector, and identify the scanning distance ZA from a photocurrent ratio formed by the total photocurrent in the peripheral region of the detector in the central region of the detector.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an optical position measuring device and a method for operating the optical position measuring device to determine the position of a first object relative to a second object. The position measuring device comprises a reflective measuring scale connected to the first object and a scanning unit connected to the second object. The scanning distance between the measuring scale and the scanning unit can be determined by a signal processing unit. [Background technology]

[0002] In particular, for optical position measuring devices that operate under reflective illumination and are equipped with a scale with a reflective measuring scale, it is important to detect the scanning distance between the measuring scale and the scanning unit, in addition to the actual position information. In the case of modularly assembled position measuring devices, this information can be used, for example, to correctly set the scanning distance when integrating them into various applications. During measurement operation, for example, when this type of position measuring device rotates considerably, it is possible to infer the displacement of the rotation axis or even thermal effects from the continuous monitoring of the scanning distance.

[0003] Many solutions are already known for determining the scanning distance in such position measuring devices.

[0004] For example, Patent Document 1 proposes deflecting light emitted from an additional light source to measure the scanning distance to a reflection track positioned between two measurement scale tracks on a scale. The light reflected from there strikes a detector within the scanning unit, but the beam diameter of the beam incident on the detector changes according to the scanning distance. The scanning distance can be estimated by intensity measurement. Therefore, in this solution, in addition to the components for position measurement, a further light source, a separate reflection track, and an additional detector are required to obtain information regarding the scanning distance.

[0005] The solutions provided in Patent Document 2 or Patent Document 3 address this issue without such additional components. In this case, the grid structure of the measuring scale for position measurement is illuminated, and the grid self-image formed periodically along the scanning distance direction by the Talbot effect is evaluated. Here, the amplitude of the grid self-image becomes a measure of the scanning distance to be determined. The drawback of these embodiments is that a periodic grid structure on the measuring scale is always required; that is, if a non-periodic code structure is involved, these solutions cannot determine the scanning distance. Moreover, such measurement methods require a light source that satisfies certain coherence requirements.

[0006] Furthermore, another solution is known from Patent Document 4, which also proposes using a detector for both position measurement and the identification of changes in scanning distance in a reflective position measuring device. Here, the measure of the change in scanning distance is evaluated as either the change in intensity detected by the detector or the position of the light reflected back from the measuring scale. According to this document, this allows for the identification of changes in scanning distance with a resolution of approximately 0.1 mm. However, this level of resolution is too coarse when identifying the scanning distance, especially when monitoring the corresponding position measuring device during measurement. Moreover, the evaluation of luminosity for identifying distance cannot be well combined with conventional methods for stabilizing the illumination of the measuring scale, which is advantageous for operating the position measuring device. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2001-174287 [Patent Document 2] Japanese Patent Publication No. 2013-113634 [Patent Document 3] Japanese Patent Publication No. 2016-050886 [Patent Document 4] German Patent Application Publication No. 102018104280 Specification [Patent Document 5] European Patent Application Publication No. 3511680 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to provide an optical position measuring device and a method for operating the optical position measuring device, enabling the scanning distance to be determined as accurately as possible without the need for additional components. [Means for solving the problem]

[0009] The problem described above is solved by the present invention, specifically by an optical position measuring device having the features of claim 1.

[0010] An advantageous embodiment of the optical position measuring device according to the present invention is obtained from the solution described in the dependent claim.

[0011] The second problem is solved by the present invention through a method for operating an optical position measuring device having the features of claim 11.

[0012] An advantageous embodiment of the method according to the present invention for operating an optical position measuring device is obtained from the solution described in the claim dependent on claim xx.

[0013] The optical position measuring device according to the present invention is used to determine the position of a first object that is movable along the measurement direction relative to a second object. The first object is connected to a scale having a reflective measuring scale that extends along the measurement direction and has scale regions with different reflectivity. A scanning unit is connected to the second object and positioned at a certain scanning distance relative to the scale. The scanning unit has at least one light source and a detector array having a number of photoelectric detector elements arranged periodically along the measurement direction. Furthermore, a signal processing unit is provided with respect to the scanning unit, and the signal processing unit is configured to generate a position signal relating to the position of the first object relative to the second object from the photocurrent generated by the detector elements, determine the total photocurrent in the central region of the detector and the total photocurrent in at least one peripheral region of the detector, and determine the scanning distance from the photocurrent ratio formed by the total photocurrent in the central region of the detector and the total photocurrent in the peripheral region of the detector.

[0014] Advantageously, the signal processing unit is configured to use a copy of the photocurrent used to generate the position signal in order to form the photocurrent ratio.

[0015] Furthermore, the signal processing unit may be configured to determine multiple photocurrent ratios during the measurement operation, calculate an average value for them, and determine the scanning distance from the averaged photocurrent ratio.

[0016] The signal processing unit determines the scanning distance. - Can it be determined from analytical relationships, or - Calculated from a table stored in the signal processing unit that describes the relationship between the identified photocurrent ratio and scanning distance. It is possible for it to be formed and configured in such a way.

[0017] The measurement scale consists of measurement scale base cells, and in these measurement scale base cells, the area ratio of the total area of ​​the scale range to the total area of ​​the base cells is constant and with respect to the area ratio 0 <V F =FTB1 / F GES <1 Here, V F :=area ratio F TB1 := Total area of ​​the scaled region F GES :=Total area of ​​the base cells. It is preferable that the following relationship holds true.

[0018] In this case, the measuring scale may be formed as an incremental scale having rectangular or annular sector-shaped scale regions with different reflectivity, arranged alternately in one dimension along the measurement direction.

[0019] Alternatively, the measuring scale may have scale regions with different reflectivity, arranged in two dimensions along and perpendicular to the measurement direction.

[0020] Furthermore, the measurement scale may be formed as a pseudo-random code and may have rectangular or annular sector-shaped scale regions with different reflectivity, arranged non-periodically and one-dimensionally along the measurement direction.

[0021] Furthermore, the detector array, -It has a one-dimensional array of rectangular or annular fan-shaped detector elements arranged adjacent to each other along the measurement direction, and the vertical axis of the detector elements is oriented perpendicular to the measurement direction, Or, - It has a two-dimensional array of detector elements that are arranged adjacent to each other, either along the measurement direction or perpendicular to the measurement direction. It may be considered as such.

[0022] Preferably, the light source and detector array are arranged in a plane parallel to the measurement scale.

[0023] A method according to the present invention for operating an optical position measuring device used to determine the position of a first object relative to a second object movable along a measurement direction comprises a scale attached to the first object, having a reflective measuring scale extending along the measurement direction with scale regions of different reflectivity. Furthermore, a scanning unit attached to the second object is provided, positioned at a certain scanning distance from the scale, the scanning unit having at least one light source and a detector array comprising a number of photoelectric detector elements periodically arranged along the measurement direction. A signal processing unit provided with the scanning unit generates a position signal relating to the position of the first object relative to the second object from the photocurrent generated by the detector elements. Furthermore, the total photocurrent in the central region of the detector and the total photocurrent in at least one peripheral region of the detector are determined, and the scanning distance is determined from the photocurrent ratio formed by the total photocurrent in the central region of the detector and the total photocurrent in the peripheral region of the detector.

[0024] Here, the signal processing unit can use a copy of the photocurrent used to generate the position signal in order to form the photocurrent ratio.

[0025] The signal processing unit can determine multiple photocurrent ratios during the measurement operation, calculate the average value from them, and determine the scanning distance from the average photocurrent ratio.

[0026] Furthermore, the signal processing unit adjusts the scanning distance. -Can it be determined from analytical relationships? Or - This can be determined from a table stored in the signal processing unit that describes the relationship between the specified photocurrent ratio and the scanning distance.

[0027] Preferably, the signal processing unit uses twice as many detector elements in the central region of the detector as in the two peripheral regions of the detector that are symmetrically located with respect to the detector center, in order to form the photocurrent ratio.

[0028] An advantage of the solution according to the present invention is that no additional components are required to determine the scanning distance of interest. Elements already used for position measurement, such as a light source, measuring scale, and detector array, can be used for this purpose. Furthermore, the apparatus or method according to the present invention also ensures that the scanning distance can be determined with sufficient accuracy during the measurement operation.

[0029] In addition, the position measuring device according to the present invention may also be formed as a length measuring device, or as a rotation measuring device in the form of, for example, a rotary encoder. The scale used in this case does not necessarily have to be periodically formed.

[0030] Further details and advantages of the present invention will be described below based on the following descriptions of embodiments of the apparatus and methods according to the present invention, as related to the drawings. [Brief explanation of the drawing]

[0031] [Figure 1] This is a schematic diagram illustrating the principle for determining the scanning distance. [Figure 2] This figure shows the relationship between the formed photocurrent ratio and the scanning distance. [Figure 3] This figure schematically shows a cross-sectional view of an embodiment of the optical position measuring device according to the present invention. [Figure 4a] This figure shows a portion of the measurement scale suitable for the optical position measuring device according to the present invention, which is formed as a length measuring instrument. [Figure 4b] This figure shows a portion of the measurement scale suitable for the optical position measuring device according to the present invention, which is formed as a length measuring instrument. [Figure 4c] This figure shows a portion of the measurement scale suitable for the optical position measuring device according to the present invention, which is formed as a length measuring instrument. [Figure 5a] This figure shows a portion of the measurement scale suitable for the optical position measuring device according to the present invention, which is formed as a rotation measuring instrument in the form of a rotary encoder. [Figure 5b]This figure shows a portion of the measurement scale suitable for the optical position measuring device according to the present invention, which is formed as a rotation measuring instrument in the form of a rotary encoder. [Figure 5c] This figure shows a portion of the measurement scale suitable for the optical position measuring device according to the present invention, which is formed as a rotation measuring instrument in the form of a rotary encoder. [Figure 6a] This figure shows a portion of a detector array suitable for the optical position measuring device according to the present invention, which is formed as a length measuring instrument. [Figure 6b] This figure shows a portion of the detector array for the optical position measuring device according to the present invention, which is formed as a length measuring instrument. [Figure 7a] This figure shows a portion of a detector array for an optical position measuring device according to the present invention, formed as a rotation measuring instrument in the form of a rotary encoder. [Figure 7b] This figure shows a portion of a detector array for an optical position measuring device according to the present invention, formed as a rotation measuring instrument in the form of a rotary encoder. [Figure 8] This is a diagram illustrating the method according to the present invention. [Modes for carrying out the invention]

[0032] Next, before describing in detail some embodiments of the optical position measuring device according to the present invention, we will first explain the basic principle that forms the basis for determining the scanning distance in each of these devices, based on Figures 1 and 2. Essentially, this principle involves converting the distance-dependent change in the non-uniform illumination of the photoelectric detector DET by a diverging light source LQ into a distance Z to be determined. Illumination of a small partial detector area dA(x,y) depends, on the one hand, on the solid angle viewed from the light source LQ to the partial detector area dA(x,y), and on the other hand, on the other hand, on the radiant characteristics of the light source LQ. In the example shown in Figure 1, where the light source LQ is formed as an LED and has the radiant characteristics of a Lambert illuminator and is positioned at x=0,y=0,z=0, the illumination intensity dI can be obtained, for example, by the following relationship:

number

[0033] The actual photoelectric detector DET here specifically generates a photocurrent proportional to the integral of dI over the illuminated detector area. From the above relational expressions, when the detector areas are the same, the photocurrent generated with respect to the detector area in the central region of the detector or at the center of the detector, that is, where the values of the x, y coordinates are small, is larger than that with respect to the area where the values of the x, y coordinates are large in the peripheral region of the detector. Therefore, in the center of the detector DET, the luminous intensity is larger than that in the peripheral region.

[0034] When a certain detector area is selected for the central region and the peripheral region of the detector for photocurrent measurement, the ratio V of the photocurrents of these detector areas I depends only on the distance Z between the light source LQ and the detector DET. For example, influencing factors such as the absolute brightness of the light source LQ are filtered out through the formation of the ratio.

[0035] The relationship between the photocurrent ratio of the photocurrent in the central region of the detector and the photocurrent in the peripheral region of the detector, and the distance Z between the light source and the detector, is shown in FIG. 2 for an exemplary arrangement of the light source and the detector. The ratio V of the photocurrent in the central region of the detector to the photocurrent in the peripheral region of the detector I is plotted along the vertical axis, and the distance Z between the detector and the light source along the z direction is shown in mm along the horizontal axis. As is clear from this figure, when the photocurrent ratio V I has a relatively large value, that is, when the difference in intensity between the central region and the peripheral region of the detector is relatively large, the distance Z has a relatively small value, and when the difference in intensity between the central region and the peripheral region of the detector is small, that is, V IWhen the value of is relatively small, conversely, the distance Z becomes relatively large. Conversely, the smaller the distance Z, the greater the difference in intensity between the central region of the detector and the peripheral region of the detector. In this way, the distance Z of interest between the light source and the detector can be determined by the difference in intensity between the central region of the detector and the peripheral region of the detector.

[0036] If the detector area is set to a constant value beforehand and the radiation characteristics of the light source are known (such as the Lambert radiation characteristics assumed earlier), the photocurrent ratio V I The analytical relationship between these two factors can be derived as a function of the distance Z, and this can be solved for Z using analytical or numerical methods.

[0037] Thus, in the example shown in Figure 1, the coordinates of the center are x i ,y i Detection area A i Inside, the intensity I detected in detector DET i This can be approximately described as follows:

number

[0038] Assuming that the two detection areas at the detector center and the detector periphery are of the same size, the photocurrent ratio obtained by measuring the detected intensities I1 and I2 is

number

number

[0039] Instead of these procedures, the distance Z and the photocurrent ratio V, which are determined by calibration, can be used. I It is also possible to store a table describing the functional relationship between and . Such calibration is performed before the actual measurement operation of the position measuring device. During the measurement operation, the measured photocurrent ratio V I The distance Z to can be found in the stored table. In this case, for example, the ratio V can be found using the nearest neighbor approach. I The distance Z corresponding to the closest entered value may be read, or interpolation may be performed between the closest entered values.

[0040] Thus, the distance Z is obtained by the photocurrent ratio V. I This can be determined by any of the following procedures based on the measurement. This is used to determine the scanning distance in the optical position measuring device according to the present invention.

[0041] Figure 3 shows a fairly schematic cross-sectional view of one embodiment of the optical position measuring device according to the present invention. The corresponding position measuring device is formed here as a length measuring device and is used to determine the position O1 of a first object relative to a second object O2 (the first and second objects O1 and O2 are arranged so that they can move relative to each other along a linear measurement direction x). Objects O1 and O2 are, for example, mechanical components that can move relative to each other along the measurement direction x, and the position signal S generated by the position measuring device P These may be mechanical components that are uniquely positioned by a mechanical control unit (not shown) using [a specific method / tool].

[0042] A scale 10 of a position measuring device is connected to the first object O1. The scale 10 has a reflective measuring scale 11 that extends along the measuring direction x, consisting of scale regions 11.1 and 11.2 with different reflectivity arranged alternately along the measuring direction x. Regarding the measuring scale 11, there are various embodiments regarding both the structure and configuration of the measuring scale. For example, the measuring scale 11 may be formed as an incremental scale, or as an absolute measuring scale in the form of a pseudo-random code. Regarding the configuration of the measuring scale, the measuring scale 11 can be configured as either an amplitude grid or a phase grid. In the case of an amplitude grid, the scale regions 11.1 and 11.2 can be formed, for example, as highly reflective and low reflective (or non-reflective). When the measurement scale 11 is configured as a phase grating, different phase shifts are applied to the reflected light beam in the scale regions 11.1 and 11.2; that is, different scale regions have different phase shifts Δ1 and Δ2. For further details on the measurement scale 11 used, please refer to the description below.

[0043] A scanning unit 20 is connected to the second object O2, and further components of the position measuring device according to the present invention are provided with respect to this scanning unit 20. These components include at least one light source 21 and a detector array 22, which, in the illustrated example, are arranged on a common support 23 within the scanning unit 20. As is clear from Figure 3, the light source 21 and the detector array 22 are here arranged within the scanning unit 20 in a common plane E parallel to the measurement scale 11, which strictly means that the detection surface of the detector array 22 and the radiating surface of the light source 21 are arranged in the same plane E as shown in the figure. Thus, the light source 21 and the detector array are at the same distance from the measurement scale 11, and this distance between plane E and the measurement scale is the scanning distance Z A It shall be stipulated as follows.

[0044] In this embodiment, an LED (light-emitting diode) emitting illumination light with a wavelength of approximately 850 nm is provided as a light source 21 within the scanning unit 20. No collimation optical system is provided in front of the light source 21. In other words, the measurement scale 11 is illuminated in a divergent state by the light source 21.

[0045] The detector array 22 has a number of photoelectric detector elements, such as photodiodes, arranged at least periodically along the measurement direction x. When the scale 10 and the scanning unit 20 move relative to each other, the pattern formed by the imaging of the measurement scale 11 within the detection surface is scanned, thereby detecting the modulated photocurrent I i A photocurrent is generated by the detector element, and then this photocurrent is used to generate a position signal S, in particular, regarding the position O1 of the first object relative to the second object O2. P It is used to generate [something].

[0046] Furthermore, a signal processing unit 24 is provided with respect to the scanning unit 20, and this signal processing unit is responsible for a series of functions that will be described in more detail below, among which is the photocurrent I of the detector element. i From position signal S P It is also possible to generate the scan distance Z of interest. A This also includes identifying the signal processing unit 24. In the illustrated example, the signal processing unit 24 is located within the scanning unit 20, but this is not essential to the present invention; that is, the signal processing unit 24 may be incorporated, for example, into a mechanical control unit located downstream of the position measuring device.

[0047] The optical position measuring device according to the present invention is formed as a reflective illumination system. In this case, the luminous beam emitted from the light source 21 in a divergent state strikes the reflective measuring scale 11, and from there is reflected back to the detector array 22 as shown in Figure 3. Therefore, in contrast to the arrangement of the light source LQ and detector DET shown in Figure 1, the detector array 22 is not directly illuminated, but rather the light is reflected back onto the detector array 22 after passing through the structure of the measuring scale 11. When scanning in this manner, by illuminating the measuring scale 11 in a divergent state, and due to the resulting projection effect, an enlarged image of the structure of the measuring scale 11 is generated on the detector array 22. In the position measuring device according to the present invention, the light source 21 and the detector 22 are both arranged in a plane E parallel to the measuring scale 11 within the scanning unit 20, so the same scanning distance Z to the measuring scale 11 is used. A It has such a feature, and as a result any scanning distance Z A In any case, the scale structure will be imaged on the detection surface at a magnification of 2. Furthermore, based on the reflection of light onto the detector array 22 after passing through the measurement scale 11, the identified photocurrent ratio between the central region of the detector and at least one peripheral region of the detector shows that, unlike in Figures 1 and 2, the initial scanning distance Z A Please note that twice that amount will be identified.

[0048] In the optical position measuring device according to the present invention, the photocurrent ratio V between the detector center and at least one detector peripheral region is I Scanning distance Z A To implement the basic principles described with reference to Figures 1 and 2 for identifying the relevant parameters, it is advantageous that certain preconditions are met or certain measures are taken on the side of the measurement scale 11 and / or detector array 22 used. This will be described in detail below with reference to Figures 4a to 7b.

[0049] In this regard, we will first describe the measuring scales used in the optical position measuring device according to the present invention. Figures 4a to 4c show partial diagrams of possible embodiments of measuring scales 111, 211, and 311 for a position measuring device formed as a length measuring instrument, and Figures 5a to 5c show partial diagrams of measuring scales 411, 511, and 611 that can be used in a rotary position measuring device according to the present invention, such as a rotary encoder.

[0050] Here, various measurement scales are formed as amplitude gratings, with scale regions of high reflectivity consistently displayed as dark, and conversely, scale regions of low reflectivity displayed as bright. As already mentioned above, it would be possible in principle to implement the measurement scales as phase gratings. In that case, the bright and dark scale regions would represent scale regions with different phase shift effects.

[0051] Figures 4a and 5a show measuring scales 111 and 411, respectively, which are formed as incremental scales and have rectangular or annular fan-shaped scale regions 111.1, 111.2 or scale regions 411.1, 411.2 with different reflectivity, arranged alternately in one dimension along the measuring direction x. In the case of measuring scale 111 for a length measuring instrument shown in Figure 4a, the measuring direction x extends linearly along the direction in which the measuring scale 111 and the scanning unit can move toward each other. In the measuring scale 411 for a rotary encoder shown in Figure 5a, the measuring direction x extends annularly around a rotation axis (not shown) around which the measuring scale 411 and the scanning unit can rotate toward each other, as can be seen in the figure.

[0052] Figures 4b and 5b show further measuring scales 211 or 511 suitable for length measuring instruments and rotary encoders. Here, scale regions 211.1, 211.2 or scale regions 511.1, 511.2 with different reflectivity are provided, arranged two-dimensionally along and perpendicular to the measuring direction x. These measuring scale regions 211.1, 211.2 or scale regions 511.1, 511.2 of the measuring scales 211, 511 are generally formed in a rhomboid shape. In practice, the proper contours of the scale regions 211.1, 211.2 are not precisely straight lines, but rather curved in a cosine shape, thereby reducing undesirable harmonics in the generated position signal. For further information on such measuring scales 211, 511 and their scanning, please refer to Patent Document 5 of the prior art.

[0053] Finally, Figures 4c and 5c show measuring scales 311 or 611 for length measuring instruments and rotary encoders. These measuring scales are formed as pseudo-random codes and have rectangular or annular sector-shaped scale regions 311.1, 311.2 or 611.1, 611.2, respectively, which are arranged non-periodically in one dimension along the measurement direction x and have different reflectivity.

[0054] Basically, the structure included in the scanned measuring scale necessary for position determination follows the scanning distance Z according to the principle explained earlier. A This is a particular interference. The reason is that when the measuring scale and the scanning unit move relative to each other, the photocurrent ratio V that is formed I This is also affected, that is, the photocurrent ratio V I Scanning distance Z A This is because it does not depend solely on that. However, by properly shaping the measurement scale, the influence that interferes with determining the scanning distance can be reduced. That is, in the case of a measurement scale formed as an amplitude grid in multiple measurement scale base cells (each measurement scale can be combined from these measurement scale base cells without any gaps), the total area of ​​the base cells F GES Total area F of the highly reflective scale region TB1Area ratio V F It is set up so that it remains constant. In Figures 4a to 4c and 5a to 5c, representative basic measurement scale cells 112, 212, 312, 412, 512, and 612 for each measurement scale 111, 211, 311, 411, 511, and 611 that satisfy this condition are drawn with dashed lines.

[0055] Similarly, in the case of a measurement scale formed as a phase grid, for example, the total area F of the basic cells GES The total area F of the scale region with a phase shift Δ1 relative to the given values. TB1 The area ratio will be selected to be constant.

[0056] Thus, the area ratio V F V F :=area ratio,F TB1 := Total area of ​​the scale region and F GES := As the total area of ​​the basic cells, 0 <V F =F TB1 / F GES It is preferable to select to follow <1. In a preferred embodiment, V F It's set to approximately 0.5.

[0057] Each of the measurement scale base cells 112, 212, 312, 412, 512, and 612 has an extent of only a small solid angle relative to the light source. Under the approximation that the radiation characteristics of the light source are constant over this solid angle (which is sufficiently satisfied under these conditions for a light source formed as an LED), the total amount of reflected light is equivalent to the amount of light that the same unstructured measurement scale base cells 112, 212, 312, 412, 512, and 612 would reflect, regardless of how the structured measurement scale base cells 112, 212, 312, 412, 512, and 612 are based on. Assuming that the detector array detects all the light from the measurement scale base cells 112, 212, 312, 412, 512, and 612, the inhibiting effect due to the internal structure formation of the measurement scale base cells 112, 212, 312, 412, 512, and 612 is temporarily smoothed out and removed, and each measurement scale 111, 211, 311, 411, 511, and 611 acts like a mirror with weakened but constant reflectivity. Thus, despite the structure contained within the measurement scales 111, 211, 311, 411, 511, and 611, the photocurrent ratio V between the central region of the detector and at least one peripheral region of the detector can be determined using the basic principle described above. I Scanning distance Z A It is possible to identify this.

[0058] Below, scanning distance Z A To implement the above-described principle for identifying the advantages of the optical position measuring device according to the present invention, any configuration on the side of the detector array 22 is described. Figures 6a and 6b show partial diagrams of possible embodiments of detector arrays 122 and 222 for a position measuring device formed as a length measuring instrument, and Figures 7a and 7b show partial diagrams of detector arrays 322 and 422 that can be used in a rotational position measuring device according to the present invention, such as a rotary encoder.

[0059] Figures 6a and 7a show partial views of detector arrays 122 and 322, which are suitable for scanning incremental scales according to Figures 4a and 5a, and for scanning measuring scales with pseudo-random codes according to Figures 4c and 5c. Detector array 122 according to Figure 6a can be used, for example, in a length measuring instrument where the measuring direction x is linear to scan a measuring scale according to Figure 4a or Figure 4c. Detector array 322 according to Figure 7a can be used in a rotary encoder where the measuring direction x extends annularly around a rotation axis (not shown), i.e., detector array 322 can be used, for example, for scanning a measuring scale according to Figure 5a.

[0060] The detector array 122 shown in Figure 6a, suitable for a length measuring instrument, has a one-dimensional array of multiple identically formed rectangular detector elements 122.i arranged periodically adjacent to each other along a linear measurement direction x. As is clear from the figure, the vertical axis of each detector element 122.i is oriented perpendicular to the measurement direction x.

[0061] The detector array 322 shown in Figure 7a, suitable for a rotary encoder, comprises a one-dimensional array of multiple annular fan-shaped detector elements 322.i arranged periodically adjacent to each other along the measurement direction x that extends in an annular shape. As is clear from the figure, the vertical axis of each detector element 322.i is oriented perpendicular to the measurement direction x.

[0062] To scan the measurement scales 211 and 511 shown in Figures 4b and 5b, the detector arrays 222 and 422 shown in Figures 6b and 7b can be used.

[0063] In the case of the detector array 222 shown in Figure 6b, which is suitable for a length measuring instrument, this detector array consists of a two-dimensional array of multiple detector elements 222.i arranged adjacent to each other along the linear measurement direction x and also adjacent to each other perpendicular to the measurement direction x. This detector array 222 can scan the measurement scale shown in Figure 4b.

[0064] The detector array 422 shown in Figure 7b is suitable for use in a rotary encoder. This detector array consists of a two-dimensional array of multiple detector elements 422.i arranged adjacent to each other along the annular measurement direction x and also adjacent to each other perpendicular to the measurement direction x. Using this detector array 422, for example, the measurement scale 511 shown in Figure 5b can be scanned.

[0065] Figures 6a, 6b, 7a, and 7b show the scanning distance Z described above for each detector array 122, 222, 32, and 422. A The total photocurrent I in the central region MB of the detector and the two peripheral regions RB of the detector in this example, which is necessary for identification. ges,MB ,I ges,RB The diagrams show which detector element 122.i is used to determine the desired result. Each detector element 122.i used for this purpose is distinguished in these diagrams by a different hatching pattern than the other detector elements 122.i. The detector array 122 shown in Figure 6a, suitable for a length measuring instrument, is described in detail below as an example.

[0066] Here, the total photocurrent I ges,RB It should be noted that it is not absolutely necessary to determine this using two detector peripheral regions RB as in this example; basically, it is possible to use only one detector peripheral region for this purpose.

[0067] In the example shown in Figure 6a, the detector array 122 is scanned by the signal processing unit, and the scanning distance Z A To identify the total photocurrent I in the central region MB of the detector, eight adjacent detector elements 122.i are used, which are arranged in mirror symmetry with respect to the symmetry axis S of the detector array 122. ges,MB To form the photocurrent I of these eight detector elements 122.i i,MB These are added together. At the left and right periphery of the detector array 122, in both corresponding peripheral regions RB, four detector elements 122.i are used in the signal processing unit, and their photocurrents I i,RBHowever, one total photocurrent I in the detector peripheral region ges,RB It is added together. As is clear from the figure, the four outermost detector elements 122.i in the left and right peripheral regions RB are selected, respectively. The total photocurrent I in the detector central region MB obtained in this way ges,MB and the total photocurrent I in the detector peripheral region RB ges,RB Next, the signal processing unit determines the photocurrent ratio V I =I ges,MB / I ges,RB A scan distance Z of interest is formed based on this, and the scan distance Z of interest is determined based on this. A It is identified.

[0068] As already mentioned above, this is, for example, the photocurrent ratio V shown in Figure 2. I and scanning distance Z A The relationship between them may also be established by storing it in a table within the signal processing unit.

[0069] The total photocurrent I in the detector central region MB and the detector peripheral region RB of the detector array 122 ges,MB ,I ges,RB The number of detector elements 122.i used to identify the position is preferably selected depending on the imaging or projection of the scale structure onto the detection surface. Therefore, the number of detector elements 122.i in the detector central region MB and the detector peripheral region RB is selected such that integer multiples (n=1,2,3,…) of the measurement scale base cells projected onto the detection surface are detected. Assuming a single-field scan (Einfeld-Abtastung) is performed for each measurement scale base cell, the four detector elements 122.i produce position signals S in the form of four incremental signals shifted by 90° in phase. P Since it is provided to generate the total photocurrent I, in both detector peripheral regions RB, there are (n=1) × 4 = 4 detector elements 122.i in each region. ges,RB Used to form, in the central region MB of the detector, the total photocurrent I ges,MBTo form, as is apparent from FIG. 6a, (n = 2) × 4 = 8 detector elements 122.i are used. As a result, overall, the same number of detector elements 122.i from both detector peripheral regions RB and from the detector central region MB are used to form the photocurrent ratio V I =I ges,MB / I ges,RB and are also used to specify the scanning distance Z A In other words, in the detector central region MB and both detector peripheral regions RB, in this embodiment, the photocurrent from the same number of measured scale basic cells to be scanned is used to specify V I respectively. Here, it should be pointed out that it is not necessarily required in the scope of the present invention that the same number of measured scale basic cells are used in the detector central region and the detector peripheral region.

[0070] Therefore, as is apparent from the previous description, the photocurrent ratio V I is specified by the signal processing unit, and a copy of the photocurrent I P from the selected detector element 122.i is also prepared to generate the shift-dependent position signal S i,MB ,I i,RB The generation of the appropriate copy can also be performed, for example, by a similar method using a so-called current mirror (Stromspiegel) or by a second voltage tap downstream of the current-voltage converter. Alternatively, the photocurrent I i,MB ,I i,RB can first be digitized and the corresponding values can be used multiple times.

[0071] In this example, the position signal S Pis generated by a known method. Therefore, each measurement scale basic cell projected onto the detector array 122 is scanned by the detector element 122.i, and when the scale and the scanning unit are in relative motion, four incremental signals with a 90° phase shift from each other are obtained therefrom. The photocurrents of the detector elements 122.i that generate the in-phase incremental signals are added together and further processed by the signal processing unit by a known method, and then two incremental signals with a 90° phase shift on the output side are used as the position signal S P to be provided for subsequent processing.

[0072] When the photocurrent ratio V I is specified multiple times via the signal processing unit, a further improvement in accuracy can be achieved when determining the scanning distance Z A , for example, during the measurement operation. By specifying the photocurrent ratio V I multiple times, an average value is then calculated, and the scanning distance Z I is specified from this average photocurrent ratio φV A . In this way, inaccuracies during scanning-type distance determination that may be caused by, for example, local contamination of the measurement scale can be avoided. Such averaging can be performed, for example, by periodically calculating the photocurrent ratio V I over a certain period of time and collecting the required predetermined number of photocurrent ratios V I . For example, it is also possible to take an average over a predetermined position range by collecting and averaging the photocurrent ratios V I obtained within the predetermined position range of the position measuring device and outputting the average value for the corresponding position range.

[0073] In the case of the detector array 322 of FIG. 7a suitable for scanning the measurement scale 411 shown in FIG. 5a in a rotary encoder, exactly the same procedure is followed to form the photocurrent ratio V I .

[0074] Similarly, in the case of the detector arrays 222,422 in Figures 6b and 7b, used to scan the measurement scales in Figures 4b and 5b, the selection of detector elements 122.i in the central detector region MB and the peripheral detector regions RB is performed. For example, as explained with reference to Figure 4b, in this example the measurement scale base cell 212 is approximately square. To scan such a rhombus-shaped measurement scale base cell projected onto the detection surface, the detector array 222 in Figure 6b requires groups of 3 × 4 detector elements 222.i, of which 4 detector elements 222.i are arranged adjacent to each other along the measurement direction x, and 3 detector elements 222.i are arranged adjacent to each other perpendicular to the measurement direction x. Therefore, 12 detector elements 222.i are required per group to scan the measurement scale base cell. In this example, in the central detector region MB, 6 such groups of detector elements 222.i of the detector array 222 are used for the photocurrent ratio V I These are used to form the region, and in both peripheral regions RB, three such groups are used by the detector element 222.i.

[0075] A similar procedure is followed in the case of the detector array 422 shown in Figure 7b, which can be used to scan the measurement scale shown in Figure 5b in a rotary encoder.

[0076] Finally, scanning distance Z A The procedure for identifying the present invention will be described again below with reference to Figure 8. Here, the figure essentially shows a fairly schematic representation of the signal processing unit 24 of the optical position measuring device according to the present invention, in terms of its key functional blocks.

[0077] Functional block S100 uses the detector array of the position measuring device according to the present invention to determine the photocurrent I from the light pattern projected onto the detection surface from the measurement scale. i This is generated and transferred to the signal processing unit 24.

[0078] Photocurrent I iThe signal processing unit 24 then, on the one hand, receives a position signal S related to the movement of the scale and scanning unit from there. P Used to generate the position signal S (function block S110). P This could be, for example, an incremental signal of two sinusoidal waveforms whose phases are shifted by 90° from each other, but instead, it could be a position signal S in the form of absolute position data. P A corresponding position signal S may also be generated. P This data will be transferred via a suitable interface 30 to a subsequent electronic device (not shown) for further processing.

[0079] Photocurrent I provided by the detector array i A portion of it is copied, and the total photocurrent I from the central region and peripheral region of the detector is calculated by summing the photocurrents of the selected detector elements. ges,MB ,I ges,RB This is used to find (function block S120).

[0080] Total photocurrent I ges,MB ,I ges,RB Next, V I =I ges,MB / I ges,RB The photocurrent ratio V I A functional block S130 is formed.

[0081] Next, the photocurrent ratio V I Scanning distance Z A This is identified as described above (functional block S140). For this reason, V I and Z A An analytical relationship can be used to describe the relationship, or alternatively, multiple photocurrent ratios V stored within the signal processing unit 24 can be used. I The corresponding scanning distance Z A Scanning distance Z according to the table listed A Identification will also be carried out.

[0082] The scanning distance Z was thus determined. ANext, the signal is output via interface 30, also for subsequent electronic devices to perform further processing.

[0083] In addition to the embodiments described, of course, there are still other possible embodiments within the scope of the present invention.

[0084] Therefore, alternatively or additionally, the determined scanning distance Z A This can be visualized via a display unit, thereby providing support for correct assembly, for example, when assembling a position measuring device.

[0085] Furthermore, the identified scanning distance Z A The results of such evaluations may be evaluated using an appropriate method, and the results of such evaluations may be visualized, for example, in the form of evaluation parameters, and output and / or displayed to subsequent electronic devices via a display unit. Although this application relates to the invention described in the claims, it may also encompass the following configurations as other embodiments. 1. An optical position measuring device that determines the position of a first object (O1) that is movable along the measurement direction (x) relative to a second object (O2), A scale (10) connected to the first object (O1) has a reflective measuring scale (11;111;211;311;411;511;611) that extends along the measuring direction (x) and has scale regions with different reflectivity (11.1,11.2;111.1,111.2;211.1,211.2;311.1,311.2;411.1,411.2;511.1,511.2;611.1,611.2), It is connected to the second object (O2) and scans a certain distance (Z) relative to the scale (10). A A scanning unit (20) located in ) It has a signal processing unit (24) provided for the scanning unit (20), The scanning unit includes at least one light source (21), It has a detector array (22;122;222;322;422) having a large number of photoelectric detector elements (122.i;222.i;322.i;422.i) arranged periodically along the measurement direction (x), The signal processing unit is The photocurrent (I) generated by the detector elements (122.i; 222.i; 322.i; 422.i) i ) from the position signal (S) relating to the position (O1) of the first object relative to the second object (O2). P ) generates, The total photocurrent (I) in the central region (MB) of the detector and in at least one peripheral region (RB) of the detector. ges,MB ,I ges,RB ) is determined, and the total photocurrent (I) in the central region (MB) and the peripheral region (RB) of the detector is calculated. ges,MB ,I ges,RB The photocurrent ratio (V) formed by ) I ) from scanning distance (Z A The optical position measuring device is configured to identify ). 2. The signal processing unit (24) calculates the photocurrent ratio (VI To form a position signal (S P The photocurrent (I) used to generate ) i The optical position measuring device described in 1 above, which is configured to use a copy of the above. 3. The signal processing unit (24) calculates multiple photocurrent ratios (V) during the measurement operation. I ) is calculated, their average value is calculated, and the average photocurrent ratio (φV) is calculated. I ) from scanning distance (Z A An optical position measuring device according to 1 or 2 above, configured to identify ). 4. The signal processing unit (24) is Scanning distance (Z A )of Can it be derived from analytical relationships, or The identified photocurrent ratio (V) is stored in the signal processing unit (24). I ) and scanning distance (Z A It can be obtained from a table describing the relationship with ). An optical position measuring device according to any one of the above 1 to 3, which is formed and configured in such a manner. 5. The measurement scale (11;111;211;311;411;511;611) consists of measurement scale base cells (112;212;312;412;512;612), and in the said measurement scale base cells, the total area of ​​the base cells (F GES The total area of ​​the scale region for ) (F TB1 Area ratio (V F ) is constant and the area ratio (V F ) 0<V F =F HR / F TB1 <1 Here, V F :=area ratio F TB1 := Total area of ​​the scaled region F GES :=Total area of ​​base cells An optical position measuring device as described in any of the above 1 to 4, wherein the relationship holds true. 6. The optical position measuring device according to 5 above, wherein the measuring scale (11;111;411) is formed as an incremental scale having rectangular or annular fan-shaped scale regions (11.1,11.2;111.1,111.2;411.1,411.2) with different reflectivity arranged alternately in one dimension along the measuring direction (x). 7. The optical position measuring device according to item 5 above, having measuring scales (211;511) arranged in two dimensions along and perpendicular to the measuring direction (x), with scale regions (211.1,211.2;511.1,511.2) having different reflectances. 8. The optical position measuring device according to 5 above, wherein the measuring scale (311;611) is formed as a pseudo-random code and has rectangular or annular sector-shaped scale regions (311.1,311.2;611.1,611.2) with different reflectivity arranged non-periodicly in one dimension along the measuring direction (x). 9. The detector array (22;122;222;322;422) is It has a one-dimensional array of rectangular or annular fan-shaped detector elements (122.i;322.i) arranged adjacent to each other along the measurement direction (x), and the vertical axis of the detector elements (122.i;322.i) is oriented perpendicular to the measurement direction (x), Or, It has a two-dimensional array of detector elements (222.i; 422.i) that are arranged adjacent to each other both along the measurement direction (x) and perpendicular to the measurement direction (x). An optical position measuring device as described in any of items 1 to 8 above. 10. The light source (21) and detector arrays (22;122;222;322;422) are arranged in a plane parallel to the measurement scale (11;111;211;311;411;511;611). An optical position measuring device as described in any of items 1 to 9 above. 11. A method for operating an optical position measuring device used to determine the position (O1) of a first object relative to a second object (O2) that is movable along a measurement direction (x), A scale (10) is provided attached to the first object (O1), which has a reflective measuring scale (11;111;211;311;411;511;611) that extends along the measurement direction (x) and has scale regions with different reflectivity. A certain scanning distance (Z) relative to the scale (10) connected to the second object (O2) A A scanning unit (20) is prepared, located in ) The scanning unit (20) is At least one light source (21), A detector array (22;122;222;322;422) comprising numerous photoelectric detector elements (122.i;222.i;322.i;422.i) arranged periodically along the measurement direction (x), A signal processing unit (24) is provided with respect to the scanning unit (20), and the signal processing unit (24) performs the following: Position signal (S) relating to the position (O1) of the first object relative to the second object (O2) P ) generates a photocurrent (I) from the detector elements (122.i;222.i;322.i;422.i). i ) is generated from, The total photocurrent (I) in the central region (MB) of the detector and in at least one peripheral region (RB) of the detector. ges,MB ,I ges,RB ) is determined, and the total photocurrent (I) in the central region (MB) and the peripheral region (RB) of the detector is calculated. ges,MB ,I ges,RB The photocurrent ratio (V) formed by ) I ) from scanning distance (Z A The method for identifying ) 12. The signal processing unit (24) calculates the photocurrent ratio (V I To form a position signal (S P Photocurrent (I) used to generate ) i The method described in 11 above, using a copy of ). 13. The signal processing unit (24) calculates multiple photocurrent ratios (V) during the measurement operation. I ) is calculated, their average value is calculated, and the average photocurrent ratio (φV) is calculated.I ) from scanning distance (Z A The method described in 11 or 12 above to identify ) 14. The signal processing unit (24) controls the scanning distance (Z A )of -Can it be determined from analytical relationships? Or - The specified photocurrent ratio (V) stored in the signal processing unit (24) I ) and scanning distance (Z A This can be obtained from a table showing the relationship between ( ) and The method described in any of items 11-13 above. 15. The signal processing unit (24) calculates the photocurrent ratio (V I The method according to any one of the above 11 to 14, which uses twice as many detector elements (122.i; 222.i; 322.i; 422.i) in the central region (MB) of the detector as in the two peripheral regions (RB) of the detector that are symmetrically located with respect to the detector center, in order to form a detector.

Claims

1. An optical position measuring device that determines the position of a first object (O1) that is movable along the measurement direction (x) relative to a second object (O2), A scale (10) connected to a first object (O1) has a reflective measuring scale (11;111;211;311;411;511;611) that extends along the measuring direction (x) and has scale regions with different reflectivity (11.1, 11.2; 111.1, 111.2; 211.1, 211.2; 311.1, 311.2; 411.1, 411.2; 511.1, 511.2; 611.1, 611.2), A second object (O2) is connected to the scale (10) and scans at a certain distance (Z Ａ A scanning unit (20) located in ) and It has a signal processing unit (24) provided for the scanning unit (20), The scanning unit includes at least one light source (21), It has a detector array (22;122;222;322;422) having a large number of photoelectric detector elements (122.i;222.i;322.i;422.i) arranged periodically along the measurement direction (x), The signal processing unit is, The photocurrent (I) generated by the detector elements (122.i; 222.i; 322.i; 422.i) ｉ ) from the position signal (S) relating to the position (O1) of the first object relative to the second object (O2). Ｐ ) generates, The total photocurrent (I ｇｅｓ，ＭＢ , I ｇｅｓ，ＲＢ ) in the detector central region (MB) and in at least one detector peripheral region (RB) is obtained, and the photocurrent ratio (V ｇｅｓ，ＭＢ , I ｇｅｓ，ＲＢ ) formed by the total photocurrent (I Ｉ ) in the detector central region (MB) and in the detector peripheral region (RB) is used to identify the scanning distance (Z Ａ ). The optical position measuring device is formed and configured as such.

2. The signal processing unit (24) calculates the photocurrent ratio (V Ｉ To form the position signal (S Ｐ The photocurrent (I) used to generate ) ｉ The optical position measuring device according to claim 1, which is configured to use a copy of ).

3. The signal processing unit (24) calculates multiple photocurrent ratios (V) during the measurement operation. Ｉ ) is calculated, their average value is calculated, and the average photocurrent ratio (φV) is calculated. Ｉ ) from scanning distance (Z Ａ The optical position measuring device according to claim 1 or 2, which is configured to identify ).

4. The signal processing unit (24) Scanning distance (Z Ａ )of Can it be derived from analytical relationships, or The identified photocurrent ratio (V) is stored in the signal processing unit (24). Ｉ ) and scanning distance (Z Ａ It can be obtained from a table describing the relationship with ). The optical position measuring device according to claim 1, configured to be formed in such a manner.

5. The measurement scale (11; 111; 211; 311; 411; 511; 611) consists of measurement scale base cells (112; 212; 312; 412; 512; 612), and in the said measurement scale base cells, the total area of ​​the base cells (F ＧＥＳ The total area of ​​the scale region relative to (F ＴＢ１ Area ratio (V) Ｆ ) is constant and the area ratio (V Ｆ ) 0<V Ｆ =FTB1 / FGES<1 Here, V Ｆ := Area ratio F ＴＢ１ := Total area of ​​the scaled region F ＧＥＳ := Total area of ​​base cells The optical position measuring device according to claim 1, wherein the following relationship holds true.

6. The optical position measuring device according to claim 5, wherein the measuring scale (11; 111; 411) is formed as an incremental scale having rectangular or annular sector-shaped scale regions (11.1, 11.2; 111.1, 111.2; 411.1, 411.2) with different reflectivity arranged alternately in one dimension along the measuring direction (x).

7. The optical position measuring device according to claim 5, wherein the measuring scale (211; 511) has scale regions (211.1, 211.2; 511.1, 511.2) with different reflectivity arranged in two dimensions along and perpendicular to the measuring direction (x).

8. The optical position measuring device according to claim 5, wherein the measuring scale (311; 611) is formed as a pseudo-random code and has rectangular or annular sector-shaped scale regions (311.1, 311.2; 611.1, 611.2) with different reflectivity arranged non-periodicly in one dimension along the measuring direction (x).

9. The detector arrays (22; 122; 222; 322; 422) are, It has a one-dimensional array of rectangular or annular fan-shaped detector elements (122.i; 322.i) arranged adjacent to each other along the measurement direction (x), and the vertical axis of the detector elements (122.i; 322.i) is oriented perpendicular to the measurement direction (x), Or, It has a two-dimensional array of detector elements (222.i; 422.i) that are arranged adjacent to each other both along the measurement direction (x) and perpendicular to the measurement direction (x). The optical position measuring device according to claim 1.

10. The optical position measuring device according to 1, wherein the light source (21) and the detector array (22; 122; 222; 322; 422) are arranged in a plane parallel to the measurement scale (11; 111; 211; 311; 411; 511; 611).

11. A method for operating an optical position measuring device used to determine the position (O1) of a first object relative to a second object (O2) that is movable along a measurement direction (x), A scale (10) is provided connected to the first object (O1), and has a reflective measuring scale (11; 111; 211; 311; 411; 511; 611) that extends along the measurement direction (x) and has scale regions with different reflectivity. A certain scanning distance (Z) relative to the scale (10) connected to the second object (O2) Ａ A scanning unit (20) is provided, located in the ) The scanning unit (20) is At least one light source (21), A detector array (22;122;222;322;422) comprising numerous photoelectric detector elements (122.i;222.i;322.i;422.i) arranged periodically along the measurement direction (x), A signal processing unit (24) is provided with respect to the scanning unit (20), and the signal processing unit (24) performs the following: Position signal (S) relating to the position (O1) of the first object relative to the second object (O2) Ｐ ) is a photocurrent (I) generated by the detector elements (122.i; 222.i; 322.i; 422.i). ｉ ) is generated from, The total photocurrent (I) in the central region (MB) of the detector and in at least one peripheral region (RB) of the detector. ｇｅｓ，ＭＢ , I ｇｅｓ，ＲＢ ) is determined, and the total photocurrent (I) in the central region (MB) and the peripheral region (RB) of the detector is calculated. ｇｅｓ，ＭＢ , I ｇｅｓ，ＲＢ The photocurrent ratio (V) formed by ) Ｉ ) from scanning distance (Z Ａ The method for identifying )

12. The signal processing unit (24) calculates the photocurrent ratio (V Ｉ To form the position signal (S Ｐ The photocurrent (I) used to generate ) ｉ The method according to claim 11, which uses a copy of ).

13. The signal processing unit (24) calculates multiple photocurrent ratios (V) during the measurement operation. Ｉ ) is determined, their average value is calculated, and the average photocurrent ratio (φV) is calculated. Ｉ ) from scanning distance (Z Ａ The method according to claim 11 or 12, which specifies ).

14. The signal processing unit (24) controls the scanning distance (Z Ａ )of - Can it be derived from analytical relationships? Or - The specified photocurrent ratio (V) stored in the signal processing unit (24) Ｉ ) and scanning distance (Z Ａ The method according to claim 11, obtained from a table showing the relationship with ).

15. The signal processing unit (24) calculates the photocurrent ratio (V Ｉ The method according to claim 11, wherein in order to form the central region (MB) of the detector, twice as many detector elements (122.i; 222.i; 322.i; 422.i) are used in the two peripheral regions (RB) of the detector that are symmetrically located with respect to the detector center.

Images