METHOD AND DEVICE FOR MEASURING A MEASURING OBJECT

Description

[0001] The invention relates to a method for measuring a measuring object, namely for measuring the width and / or the flatness of a measuring object, with a measuring system movable along a linear axis, wherein the measuring system has at least one sensor and wherein means are arranged for detecting a position of a reference point of the measuring system.

[0002] Furthermore, the invention relates to a device for measuring a measuring object, namely for measuring the width and / or the flatness of a measuring object, using a method according to one of claims 1 to 7, with a measuring system movable along a linear axis, wherein the measuring system has at least one sensor and wherein means for detecting a position of a reference point of the measuring system are arranged.

[0003] Non-contact distance sensors are known from the prior art. These are mounted on a measuring system with a driven linear axis and measure the distance to a measuring object and the position of the measuring system on the linear axis during a traversing movement. The measured value of the sensor (e.g. distance or edge position) and the sensor position or the position of a reference point of the measuring system arranged at a defined distance from the sensor, which thus moves uniformly on the linear axis, are recorded synchronously. Edge positions and distances to measuring objects can be measured in this way. The edges of the measuring objects or the distances to the measuring objects can be recorded non-contact using optical sensors such as triangulation sensors, confocal sensors or optical micrometers. Depending on the sensor type and measuring task, different system arrangements can be used. For one-sided measurement, one axis above or below the measuring object is sufficient.below the measurement object. If the sensor's transmitter and receiver are arranged opposite each other, either a C-frame with one axis or an O-frame design with two axes is used. With the O-frame concept, it is important to ensure that the sensor's transmitter and receiver (each mounted on opposite axes) are moved synchronously. With the C-frame concept, the entire C-frame is usually moved on a single linear axis.

[0004] EP 0342267 A1 discloses a method for determining the coordinate values of a probe element, in which an inclination of a carrier for the probe element is measured by electronic inclinometers in the carrier and taken into account in the form of correction values.

[0005] The problem with the known systems is that different sources of error exist, which result in the measured values being inaccurate.

[0006] The present invention is therefore based on the object of designing and developing a method and a device for measuring a measuring object of the type mentioned at the outset in such a way that precise measurement is possible in a simple manner.

[0007] According to the invention, the above object is achieved with regard to the method by the features of claim 1. This specifies a method for measuring a measurement object, namely for measuring the width and / or flatness of a measurement object, with a measuring system movable along a linear axis, wherein the measuring system has at least one sensor and wherein means are arranged for detecting a position of a reference point of the measuring system, wherein at least one measured value of the measurement object is detected with the sensor and wherein a measurement error of the measured value caused by an inclination of the linear axis by an inclination angle β is determined and wherein the measured value is corrected by the measurement error, wherein the local inclination angle β of the linear axis is determined via an inclination sensor of the measuring system.

[0008] With regard to the device, the above object is achieved by the features of claim 8.

[0009] In accordance with the invention, it was initially recognized that tilting (rotating) the measuring system on or with a linear axis from its horizontal position distorts the position of an integrated sensor. This unwanted change in the position of the sensor—and thus unwanted shifting of the measuring spot on the measuring object—at different positions on the linear axis leads to measurement errors, for example, in a width measurement (evaluation of the sensor values in the direction of the linear axis) or in a flatness measurement with one-sided distance measurement (evaluation of the sensor values in the vertical direction to the linear axis).

[0010] In a further embodiment of the invention, it has been recognized that a measurement error caused by an inclination of the linear axis can be compensated for if the angle of inclination and the position of a reference point of the measuring system relative to the measurement object are known. The resulting change in position of the measuring spot on the measurement object can be compensated for by a correction unit, for example a computer with appropriate software. For a width measurement of the measurement object, it is sufficient to consider only the horizontal position change in the traversing direction. The inclination can in principle mean an absolute inclination of the entire linear axis, or according to the invention a local inclination, caused e.g. by a deflection or curvature of the linear axis. To simplify the further description of the invention, the absolute inclination of the linear axis is always shown below.

[0011] Specifically, it is conceivable that the measuring system is mounted on at least one driven linear axis. Alternatively or additionally, the measuring system can have a frame on which the at least one sensor is arranged. The frame can be a C-frame with one axis, an O-frame with two axes, or any other frame, depending on the measuring task to be performed. With an O-frame, the sensor transmitter and receiver could each be installed on opposite linear axes and moved synchronously.

[0012] With a C-frame, the entire C-frame could be moved on a single linear axis.

[0013] Furthermore, the means for detecting the position of a reference point can be a position sensor of the linear axis. For example, the position of the reference point can be determined absolutely using an incremental magnetic tape. Any other sensor technology can be used in this case.

[0014] Other measuring tasks are also conceivable for the method and device according to the invention, such as a flatness measurement, preferably with a C-frame. Here, too, the inclination of the linear axis influences the sensor's measured value – but this time the position change in height (vertical measurement value) is important. This height change can also be corrected if the C-frame dimensions and inclination angle(s) of the linear axis are known, for example, using a correction unit with appropriate software. It is also conceivable that vertical measurement errors and horizontal measurement errors are corrected simultaneously.

[0015] The measurement uncertainty caused by the inclination of the linear axis depends essentially on the following factors: from the flatness (=inclination) of the linear axis from the height difference of the linear axis to the measuring object from the horizontal distance of the measuring position to the carriage of the linear axis

[0016] The term "angle of inclination" describes an inclination of the linear axis - which thus leads to an inclination of the measuring system - in the direction of extension or against the direction of extension of the linear axis.

[0017] Advantageously, a horizontal measurement value of the measurement object is recorded, which indicates a position in the extension direction of the linear axis. Alternatively or additionally, a vertical measurement value of the measurement object can be recorded, which indicates a position in a direction perpendicular to the extension direction of the linear axis. In this disclosure, the terms "horizontal" and "vertical" therefore do not describe an absolute orientation relative to the direction of the gravitational force, but rather an orientation relative to the extension direction or direction of movement of the linear axis. The recording of horizontal measurement values can thus be used to determine the width of a measurement object, whereas the recording of vertical measurement values can be used to determine the flatness of a measurement object.

[0018] The at least one sensor can advantageously be a non-contact sensor, in particular an optical sensor, preferably a triangulation sensor, a confocal sensor, or an optical micrometer. The optical micrometer can, for example, determine the dimensions and position of the measurement object in a non-contact manner using the principle of shadowing or light quantity measurement.

[0019] According to an advantageous embodiment, a horizontal measurement error ph of the horizontal measured value can be determined using the following formula: p h = r ⋅ sin β where r is the vertical distance between the linear axis and the measuring object. A corresponding correction can be implemented in a particularly simple manner.

[0020] In a particularly advantageous manner, a horizontal measurement error ph,ges of the horizontal measured value can be determined using the following formulas: p 1 = r ⋅ sin β p 2 = a − a ⋅ cos β p h , ges = p 1 − p 2 where r is the vertical distance between the linear axis and the measurement object, and a is the horizontal distance between an edge of the measurement object and the reference point. This allows for a particularly precise determination of the measurement error and thus the correction of the measured value, enabling precise measurement of the measurement object.

[0021] According to a further advantageous embodiment, a vertical measurement error pv of the vertical measured value can be determined using the following formula: p v = r − r ⋅ cos β where r is the vertical distance between the linear axis and the measuring object. A corresponding correction can be implemented in a particularly simple manner.

[0022] In a particularly advantageous manner, a vertical measurement error pv,ges of the vertical measured value can be determined using the following formula: p 3 = r − r ⋅ cos β p 4 = a ⋅ sin β p v , ges = p 3 + p 4 where r is the vertical distance between the linear axis and the measurement object, and a is the horizontal distance between an edge of the measurement object and the reference point. Calculating the vertical measurement error using the above formulas is extremely accurate, significantly improving the precision of the measurement of the measurement object.

[0023] In a further advantageous manner, the inclination angle of the linear axis can be determined at defined measuring points. In general, a one-time (or occasional) determination of the inclination angle may be sufficient. However, it is conceivable that the inclination profile of the linear axis changes over time due to various factors (screw-on points of the axis, changes in the substructure of the axis, e.g. due to temperature influences, etc.). It can therefore be advantageous to repeatedly determine the inclination angle of the linear axis. According to the invention, an inclination sensor arranged on the measuring system is used for this purpose. Inclination sensors of any design are conceivable, provided they guarantee the necessary resolution and accuracy for the measurement.

[0024] There are several options for measuring the inclination angle of linear axes: If an inclination sensor can detect the change in inclination while the linear axis is moving, the inclination value of the linear axis can be detected synchronously with the position values of the reference point and the sensor's measured values. The measured values can then advantageously be corrected using the formulas above. If non-uniform movements of the measuring system on the linear axis (e.g. vibrations, accelerations, etc.) influence the measurement accuracy of the inclination sensor, detection of the inclination angle while the linear axis is moving can be omitted. If the inclination sensor can only correctly detect the change in inclination when the linear axis is stationary, the inclination angle of the linear axis could be detected at defined measuring points while the system is stationary, preferably in a fixed grid (e.g. every 15 cm).Based on the measuring points, a suitable function could be determined that represents the change in the inclination angle as a function of the position of the measuring system's reference point on the linear axis. This function can then be used during the measurement run to determine the inclination angle as a function of the position of the reference point. The determination of the measuring points can preferably be repeated at regular intervals.

[0025] It should be noted that the method according to the invention also has a device-related embodiment. The device according to the invention can have the corresponding features and advantages described with reference to the method. Likewise, features and advantages of the device according to the invention with a method-related embodiment can be part of the method according to the invention.

[0026] There are now various possibilities for advantageously embodying and developing the teaching of the present invention. For this purpose, reference is made, on the one hand, to the claims subordinate to the claim and, on the other hand, to the following explanation of preferred embodiments of the invention with reference to the drawing. In conjunction with the explanation of the preferred embodiments of the invention with reference to the drawing, generally preferred embodiments and developments of the teaching are also explained. The drawing shows: Fig. 1 is a schematic representation of an embodiment of a device according to the invention for carrying out the method according to the invention, Fig. 2a to 2c are schematic representations of the effect of an inclination of the linear axis on the horizontal measured value, Fig. 3 is a schematic representation of an approximation of the horizontal measurement error when the linear axis is inclined, Fig. 4 is a schematic representation of the real horizontal measurement error when the linear axis is inclined, Fig. 5 is a schematic representation of an illustration of the angle of inclination, Fig. 6 is a change in the angle of inclination of a linear axis measured on several days, and Fig. 7 is a schematic representation of the real vertical measurement error when the linear axis is inclined.

[0027] To improve clarity, not all elements in the figures are always provided with a reference symbol, whereby identical elements in the figures are identified by the same reference symbols.

[0028] With Figure 1 The measurement errors to be compensated by the invention are explained using a width measurement. For a flatness measurement, Figure 1 A sensor system for distance measurement should be outlined. Instead of the horizontal measurement direction, the vertical measurement direction should be considered.

[0029] Figure 1shows an embodiment of a device for measuring the width of a measurement object 1. The device has a measuring system 2 with a C-frame 3 and a sensor 4, which in this embodiment is designed as an optical micrometer. The sensor 4 detects the relative edges 5, 6 of the measurement object 1 to the C-frame 3 in a horizontal measuring direction, i.e. along the extension direction of the linear axis 7. In order to determine the position of the sensor 4, a reference point 8 is provided, the position of which on the linear axis 7 can be determined using suitable means 9 for detecting the position. In this embodiment, the position of the reference point 8 can be determined absolutely using an incremental magnetic tape 9, which thus serves as means 9 for detecting the position. Other embodiments of the means 9 are conceivable, for example a sensor, in particular an optical sensor or a cable pull sensor.If both position values are recorded synchronously during the measurement run, the absolute edge position of the measuring object can be determined by simply adding the two values.

[0030] The difference between the measured values of the sensor 4, ie the measured positions of the two edges 5, 6 of the measuring object 1, corresponds to the width of the measuring object 1, whereby the latter must not be moved during the width measurement.

[0031] Furthermore, in Figure 1A correction unit 10 is shown, which may, for example, be a computer with appropriate software. The correction unit 10 serves to correct measurement errors caused by an inclination of the linear axis 7 by an inclination angle β. To detect the inclination angle β, the measuring system 2 has an inclination sensor 11. To simplify the illustration, the correction unit 10 and the inclination sensor 11 are not shown in the other figures, but may nevertheless be provided therein.

[0032] In the Figures 2a to 2c The horizontal measurement error is illustrated, with three situations on the linear axis 7 being shown: Ideal alignment ( Figure 2a ): the actual position of the edge 6 of the measuring object 1 and the detected position of the edge 6 of the measuring object 1 on the linear axis 7 match. Tilt forward ( Fig. 2b): the detected position of the edge 6 of the measuring object 1 is lagging behind the actual position of the edge 6 of the measuring object 1. Inclination backwards ( Fig. 2c ): the detected position of the edge 6 of the measuring object 1 is leading to the actual position of the edge 6 of the measuring object 1.

[0033] If the inclination angle β and the geometric position of the measuring object 1 are known, the position deviation can be determined in the manner according to the invention.

[0034] Figure 3shows the principal error in a simplified manner. The edge 6 of the measuring object 1 has been chosen as the pivot point 12 for the inclination. The expected horizontal measurement error ph is plotted on the direction of the linear axis 7. The representation is simplified in that the recorded measured value of the edge 6 of the sensor 4 and the recording of the reference point 8 (e.g. sensor of the magnetic tape on the carriage of the linear axis 7) are geometrically superimposed. If this is not the case, a slightly different calculation results, which is shown in the Figure 4 is shown. In Figure 4 only the horizontal position changes are shown.

[0035] According to Figure 3 the corresponding inclination of the measuring system 2 caused by the inclination angle β of the linear axis 7 can be split into two movements: The rotational movement causes a vertical height change (difference between measuring object 1 and linear axis 7), which can be ignored for a width measurement. This change is relevant for the flatness measurement, as the measurement distance is then distorted due to the inclination. The rotational movement causes a horizontal distance change between the measured value of edge 6 detected by sensor 4 and the reference point 8 of linear axis 7.

[0036] If the angle of inclination β and the height difference r between linear axis 7 and measuring object 1 are known, the position changes in the horizontal direction, ie the horizontal measurement error ph , and the position changes in the vertical direction, ie the vertical measurement error pv , can be calculated as follows: p h = r ⋅ sin β p v = r − r ⋅ cos β

[0037] If the distance between the edge 6 of the measuring object 1 and the reference point 8 on the measuring system 2 is also taken into account for the inclination, Figure 4schematically the facts.

[0038] The horizontal measurement error ph,ges can be determined by two movements. As in Figure 3 As shown, the height difference r causes the majority of the position change p 1 . The distance a between the edge 6 of the measuring object 1 and the reference point 8 causes a second horizontal position change p 2 . The difference between the two position changes results in the total horizontal measurement error p ges : p 1 = r ⋅ sin β p 2 = a − a ⋅ cos β p h , ges = p 1 − p 2

[0039] From the formula for p 2 it can be seen that this distance value can be neglected for small inclination angles β.

[0040] Figure 6shows the measured change in inclination of a linear axis 7 with a length of 2.2 m. The inclination of the linear axis 7 was measured over several days. Inclination values are usually given in degrees [°]. Since the expected values of an inclination change on a linear axis 7 are relatively small and in order to get a better idea of the expected error, [µm / m] was chosen as the unit, i.e. the change in inclination is plotted against each other in [µm] per meter of reference distance. If the height difference between the edge 5, 6 of the measuring object 1 and the linear axis is 1 m, the expected inclination error is shown in [µm]. Figure 5 illustrates the relationship. An inclination of 600 µm / m corresponds to an angle of approximately 0.057°.

[0041] Depending on the location of edges 5, 6, the angle of inclination β of linear axis 7 influences the result of a width measurement to a greater or lesser extent. The method and device according to the invention allow the measured values of the positions of edges 5, 6 to be corrected, thus minimizing the expected measurement uncertainty.

[0042] In Figure 3 The vertical measurement error pv , caused by the inclination angle β of a linear axis, is already shown. The largest part of the measurement uncertainty is caused by the horizontal distance a between the measurement position on the measuring object 1 and the reference point 8 on the linear axis. The relationship is shown in Figure 7 shown. Edge 6 on the measuring object 1 was again selected as the virtual pivot point 12.

[0043] In Figure 3 The vertical measurement error pv is shown, which can be determined as follows: p v = r − r ⋅ cos β = p 3

[0044] In addition, the horizontal distance a between the edge 6 of the measuring object 1 and the reference point 8 causes a further vertical position change p 4 . This can be calculated using the following formula: p 4 = a ⋅ sin β

[0045] The total vertical position change pv,ges , caused by the axis inclination, can be determined by adding the two values p 3 and p 4 : p v , ges = p 3 + p 4

[0046] With a known inclination angle β of the linear axis 7 and known geometric dimensions of the measuring system to the measuring position, the resulting vertical measurement error pv,ges can be calculated and corrected.

[0047] With regard to further advantageous embodiments of the device according to the invention and the method according to the invention, reference is made to the general part of the description and to the appended claims in order to avoid repetition.

[0048] Finally, it should be expressly pointed out that the above-described embodiments of the device according to the invention and the method according to the invention serve only to explain the claimed teaching, but do not limit it to the embodiments. List of reference symbols

[0049] 1Measurement object 2Measurement system 3Frame 4Sensor 5Edge (measurement object) 6Edge (measurement object) 7Linear axis 8Reference point 9Position detection device 10Correction unit 11Inclination sensor 12Pivot point βInclination angle rDistance (linear axis - measurement object) aDistance (measurement point - reference point)

Claims

1. Method for measuring a measurement object (1), that is to say, for width measurement and / or flatness measurement of a measurement object (1), having a measurement system (2) which can be moved along a linear axis (7), wherein the measurement system (2) has at least one sensor (4) and wherein means (9) for detecting a position of a reference point (8) of the measurement system (2) are arranged, wherein with the sensor (4) at least one measurement value of the measurement object (1) is detected and wherein a measurement error, which is caused by an inclination of the linear axis (7) about an inclination angle β, of the measurement value is established and wherein the measurement value is corrected by the measurement error, characterised in that via an inclination sensor (11) of the measurement system (2) the local inclination angle β of the linear axis (7) is established.

2. Method according to claim 1, characterised in that a horizontal measurement value of the measurement object (1) which indicates a position in the extent direction of the linear axis (7) is detected and / or in that a vertical measurement value of the measurement object (1) which indicates a position in the direction perpendicular to the extent direction of the linear axis (7) is detected.

3. Method according to claim 2, characterised in that a horizontal measurement error ph of the horizontal measurement value is established with reference to the formula p h = r ⋅ sin β wherein r is the vertical spacing between the linear axis (7) and the measurement object (1).

4. Method according to claim 2 or 3, characterised in that a horizontal measurement error ph.ges of the horizontal measurement value is established with reference to the formulae: p 1 = r ⋅ sin β p 2 = a − a ⋅ cos β p h . ges = p 1 − p 2 wherein r is the vertical spacing between the linear axis (7) and the measurement object (1) and wherein a is the horizontal spacing between an edge (5, 6) of the measurement object (1) and the reference point (8).

5. Method according to any one of claims 2 to 4, characterised in that a vertical measurement error pv of the vertical measurement value is established with reference to the formula p v = r − r ⋅ cos β wherein r is the vertical spacing between the linear axis (7) and the measurement object (1).

6. Method according to any one of claims 2 to 5, characterised in that a vertical measurement error pv.ges of the vertical measurement value is established with reference to the formula p 3 = r − r ⋅ cos β p 4 = a ⋅ sin β p v . ges = p 3 + p 4 wherein r is the vertical spacing between the linear axis (7) and the measurement object (1) and wherein a is the horizontal spacing between an edge (5, 6) of the measurement object (1) and the reference point (8).

7. Method according to any one of claims 1 to 6, characterised in that at defined measurement locations the inclination angle ß of the linear axis (7) is established.

8. Apparatus for measuring a measurement object (1), that is to say, for width measurement and / or flatness measurement of a measurement object (1), using a method according to any one of claims 1 to 7, having a measurement system (2) which can be moved along a linear axis (7) of the apparatus, wherein the measurement system (2) has at least one sensor (4) and an inclination sensor (11) for determining the local inclination angle ß of the linear axis (7), wherein the apparatus has means (9) for detecting a position of a reference point (8) of the measurement system (2) and a correction unit (10), wherein with the sensor (4)at least one measurement value of the measurement object (1) can be measured, wherein a measurement error, which is caused by an inclination of the linear axis (7) about an inclination angle ß, of the measurement value can be established by the correction unit (10), wherein the measurement value can be corrected by the correction unit (10) by the measurement error.