阅读说明：本技术 用于控制坐标测量机器的方法以及坐标测量机器 (Method for controlling a coordinate measuring machine and coordinate measuring machine ) 是由 U.斯塔登 W.庞蒂加姆 F.舍尼格 于 2020-04-22 设计创作，主要内容包括：一种用于确定测量物体的尺寸和/或几何特性的坐标测量机器具有测量元件,该测量元件限定了参考点、并且可相对于测量物体接收座沿着多条移动轴线移动。所述多条移动轴线包括多条线性轴线和至少一条旋转轴线。为了相对于测量物体来控制测量元件,提供了该参考点的期望位置以及限定了容许速度和/或加速度的极限值的参数。根据该参考点的期望位置和这些参数来确定针对所述多条移动轴线的相应独立轴向位置的多个独立时间序列。这些独立时间序列在相继的独立轴向位置之间具有相应的独立时间区间。这些独立时间序列与共同的定时周期时钟同步,该定时周期时钟针对每个目标位置分别使用最长的独立时间区间。(A coordinate measuring machine for determining dimensional and/or geometric properties of a measuring object has a measuring element which defines a reference point and is movable relative to a measuring object receptacle along a plurality of movement axes. The plurality of movement axes includes a plurality of linear axes and at least one rotation axis. For controlling the measuring element relative to the measuring obj ect, a desired position of the reference point and parameters defining limit values for permissible speeds and/or accelerations are provided. Determining a plurality of independent time series of respective independent axial positions for the plurality of movement axes from the desired position of the reference point and the parameters. These independent time series have respective independent time intervals between successive independent axial positions. These independent time sequences are synchronized with a common timing cycle clock that uses the longest independent time interval for each target location.)

1. A method for controlling a coordinate measuring machine (10) comprising a measuring object receptacle (12) and a measuring element (26), wherein the measuring element (26) defines a reference point (46) for measuring a measuring object (28) and is movable relative to the measuring object receptacle (12) along a plurality of movement axes within a measurement volume, and wherein the plurality of movement axes comprises a plurality of linear axes (X, Y, Z) and at least one rotation axis (a, B, C), the method comprising the steps of:

-providing desired positions (S1, S2, S3, S4) of the reference point (46) within the measurement volume,

-providing a plurality of parameters (58) defining limit values of allowable speed and/or acceleration along said plurality of movement axes,

-determining (72) a series of successive target positions of the measuring element (26) along said linear axes (X, Y, Z), respectively, as a function of the desired position (S1, S2, S3, S4) of the reference point (46) and the parameters (58),

-determining (74) successive rotation angle values, each rotation angle value representing a suitable rotation angle of the measuring element (26) around the at least one rotation axis (a, B, C) at the successive target positions. And

-moving the measuring element (26) to the successive target positions within a first defined timing cycle clock and rotating the measuring element (26) using said plurality of rotation angle values,

characterized in that independent time sequences of respective independent axial positions for the movement axes are determined from the desired position (S1, S2, S3, S4) of the reference point (46) and the parameters (58), wherein the independent time sequences have respective independent time intervals between successive independent axial positions and are synchronized with a common second timing cycle clock (76) which uses the longest independent time interval for each target position.

2. Method according to claim 1, characterized in that from said plurality of desired positions (S1, S2, S3, S4) a desired measurement path (50) of the reference point (46) within the measurement volume is determined by means of interpolation, wherein the series of successive target positions are determined from the desired measurement path (50).

3. The method according to claim 1 or 2, characterized in that a position-dependent desired radial velocity profile (66) and a position-dependent desired tangential velocity profile (68) of the reference point (46) along the desired positions (S1, S2, S3, S4) are determined from the parameters (58).

4. A method according to claim 3, characterized by determining (70) a desired time velocity profile of the reference point (46) within the measurement volume from the position dependent desired radial velocity profile and from the position dependent desired tangential velocity profile.

5. The method according to any one of claims 1 to 4, characterized in that the measuring element (26) defines a measuring line (44) having a plurality of measuring points, wherein the measuring line extends through the reference point (46).

6. Method according to claim 5, characterized in that the series of successive target positions and the successive rotation angle values of the measuring element (26) are determined from the spatial orientation of the measuring line (44).

7. The method according to claim 6, characterized in that the spatial orientation of the measurement line (44) is selected transversely to the path (50) of the plurality of desired positions (S1, S2, S3, S4) along the reference point.

8. The method according to claim 6 or 7, characterized in that the spatial orientation of the measuring line (44) is selected such that the reference point (46) leads or lags the measuring element (26) along the plurality of desired positions (S1, S2, S3, S4).

9. The method according to any one of claims 1 to 8, characterized in that the sequence of control data for the machine controller (32) of the coordinate measurement machine (10) is determined from a plurality of independent time sequences of respective independent axial positions.

10. A method as claimed in claim 9, characterized in that the control data sequence is determined with a predefined control data timing cycle clock by determining the intermediate position (Z)_i) Derived from the common second timing cycle clock.

11. The method according to any one of claims 1 to 10, wherein the measuring object receptacle (12) comprises a rotary table.

12. A coordinate measuring machine for determining dimensional and/or geometric properties of a measuring object (28) comprises a measuring object receptacle (12) and a measuring element (26), the measuring element defines a reference point (46) for measuring a measuring object (28) and is movable relative to the measuring object receptacle (12) along a plurality of movement axes within a measuring volume, and wherein the plurality of movement axes comprises a plurality of linear axes (X, Y, Z) and at least one rotation axis (A, B, C), the coordinate measurement machine comprises a CMM controller (32) configured to move the measurement element (26) along the plurality of movement axes in accordance with control data to record measurement values at the measurement object (28), and the coordinate measuring machine comprises a manipulation terminal (34) comprising:

an interface (38) receiving desired positions of the reference point (46) at the measurement object (28),

-a memory (42) in which parameters defining limit values of the permissible speed and/or acceleration of the measuring element (26) along said movement axes can be stored, and

a processor (40) configured to determine control data of the CMM controller (32) from the desired position of the reference point (46) and the parameters,

characterized in that the processor (40) is configured for determining independent time series of respective independent axial positions for the movement axes from the desired position (S1, S2, S3, S4) of the reference point (46) and the parameters (58), wherein the independent time series have respective independent time intervals between successive independent axial positions, wherein the processor (40) is further configured for synchronizing the independent time series with a common timing cycle clock using the longest independent time interval for each target position, respectively, and wherein the processor (40) is further configured for determining control data for the CMM controller (32) from the independent time series and the common timing cycle clock.

13. A computer program product comprising program code configured for performing the method according to any one of claims 1 to 11 when the program code is run on a processor (40) of a coordinate measuring machine according to claim 12.

Technical Field

The invention relates to a method for controlling a coordinate measuring machine comprising a measuring object receptacle and a measuring element, wherein the measuring element defines a reference point for measuring a measuring object and is movable relative to the measuring object receptacle along a plurality of movement axes within a measuring volume, and wherein the plurality of movement axes comprises a plurality of linear axes and at least one rotation axis, the method comprising the steps of:

-providing a plurality of desired positions of the reference point within the measurement volume,

-providing a plurality of parameters defining limit values for allowable speed and/or acceleration along the plurality of movement axes,

determining a series of successive target positions of the measuring element along said linear axes respectively as a function of the desired position of the reference point and of the parameters,

-determining a plurality of successive rotation angle values, each rotation angle value representing a suitable rotation angle of the measuring element about the at least one rotation axis at the successive target positions, and

-moving the measuring element to the successive target positions within a first defined timing cycle clock and rotating the measuring element using the plurality of rotation angle values.

The invention also relates to a coordinate measuring machine for determining dimensional and/or geometric properties of a measurement object, comprising a measurement object receptacle and a measurement element defining a reference point for measuring the measurement object and being movable relative to the measurement object receptacle along a plurality of movement axes within a measurement volume, and wherein the plurality of movement axes comprises a plurality of linear axes and at least one rotation axis, the coordinate measuring machine comprising a machine controller configured for moving the measurement element along the plurality of movement axes in accordance with control data for recording measurement values at the measurement object, and the coordinate measuring machine comprising a manipulation terminal comprising:

an interface for receiving a plurality of desired positions of the reference point at the measurement object,

-a memory in which parameters defining limit values for the permissible speed and/or acceleration of the measuring element along said movement axes can be stored, and

-a processor configured for determining control data of the machine controller depending on the desired position of the reference point and the parameters.

Background

Such a method and such a coordinate measuring machine are known from EP 0866390B 1.

DE 19529547 a1 discloses a method for controlling a coordinate measuring machine. In the method, a probe pin (tactile measurement element) is moved according to set value data. In the computer of a coordinate measuring machine, the required control data of the machine controller are determined as a sequence of points from the geometric data of the measuring object, for example CAD data. For this purpose, the computer determines a speed profile intended to ensure a movement process without jolts and a shortest possible measurement time, by suitably selecting the distances between the points in the sequence of points. This known method has proven worthwhile in practice, but is limited to the control of coordinate measuring machines with tactile measuring elements which move only along a linear axis within the measuring volume.

EP 0866390B 1, mentioned at the outset, discloses another general type of method using a tactile measuring element, wherein the measuring element can now be moved relative to the measuring object along a linear axis and along at least one rotational axis. The rotation axis may be realized by means of a rotary table on which the measuring object rests. In other variations, the coordinate measuring machine may include a rotary pivot joint by which the feeler pin can be rotated and pivoted to different orientations. This known method involves calculating the associated desired rotational angle value of the probe pin immediately after determining the target position of the probe head. If the angular velocity and the associated angular acceleration required to obtain the desired rotation angle value exceed a predefined maximum value, the distance between the target positions is corrected until conditions on the maximum angular velocity and the maximum angular acceleration can be met. Subsequently, the feeler pin is moved between the target positions and also rotated by the calculated rotation angle within a defined timing cycle clock. This known method enables almost any profile on the measuring object to be measured in an automated manner.

Automatic measurement of a measurement object with tactile measurement elements that are movable relative to the measurement object along a plurality of linear axes and along one or more axes of rotation has enabled particularly rapid measurement of free-form surfaces. However, the tactile measuring element only gives one coordinate measurement value of the measuring object at each measuring instant. Therefore, a complete 3D measurement of the measurement object ("3D scan") using the tactile measuring element can only be realized with difficulty.

An alternative to a tactile measuring element is a measuring element which can detect a measuring point on a measuring object without contact, in particular optically. For example, WO 2013/144293 a1 discloses a measuring cell with a light source that generates a light plane and an image sensor that captures light reflected from the surface of the measuring object. The light plane generates a line on the surface of the measurement object, which provides a plurality of measurement points adjacent to each other on the surface of the measurement object. The inventors provide a further known measuring element under the name EagleEye II (which determines coordinate measured values by means of laser lines projected onto a measuring object according to the triangulation principle) for achieving quality assurance in the production of motor vehicle bodies.

The optimal alignment of the laser lines on the surface of the measuring object in each case and the image capture rate of such measuring elements impose new requirements on the control of coordinate measuring machines, in particular when large-area automatic measurements are desired.

Disclosure of Invention

On this background, it is an object of the invention to specify a method for controlling a coordinate measuring machine which enables a measuring element to be moved quickly and accurately along a plurality of linear axes and axes of rotation, taking into account a number of different boundary conditions. In particular, it is an object of the invention to specify a method for controlling a coordinate measuring machine which enables effective large-area measurement of a measurement object with a measuring element which can detect a plurality of measurement points on the measurement object simultaneously. In addition, it is an object of the invention to specify a coordinate measuring machine in which the measuring element can be controlled in an efficient manner in order to scan the measuring object in an automated manner.

According to an aspect of the invention, the object is achieved by a method of the type mentioned at the outset, wherein a plurality of independent time sequences for respective independent axial positions of the plurality of movement axes is determined depending on the desired position of the reference point and the parameters, wherein the independent time sequences have respective independent time intervals between successive independent axial positions, and wherein the independent time sequences are synchronized with a common second timing cycle clock, which uses the longest independent time interval for each target position.

According to a further aspect, a coordinate measuring machine of the type mentioned at the beginning is proposed, wherein the processor is configured for determining independent time series of respective independent axial positions for the movement axes depending on the desired position of the reference point and the parameters, wherein the independent time series have respective independent time intervals between successive independent axial positions, wherein the processor is further configured for synchronizing the independent time series with a common timing cycle clock, which clock uses the longest independent time interval for each target position, respectively, and wherein the processor is further configured for determining control data of the CMM controller depending on the independent time series and the common timing cycle clock.

The novel method and the corresponding coordinate measuring machine first determine temporally successive axial positions along the linear axis and the rotational axis in a temporally independent manner from one another in a first method part. Thus, the time series for each axis of movement first has respective independent time intervals between successive axial positions. Independent of the respective independent axial positions, the time series are also independent in that they have independent time intervals between successive axial positions. Thus, as a temporary result, the novel method and corresponding coordinate measuring machine give independent time series of axial positions for independent linear and rotational axes, wherein these axial positions are intended to be obtained each at the same time during a subsequent control procedure. The time series is initially unsynchronized.

Only in the second method part, these independent time sequences are synchronized with each other. In this case, for each time interval between two successive axial positions, the "slowest" movement axis is used as the "leading axis", respectively. The "slow" is here not necessarily related to the absolute value of the movement speed of the axis, but to the duration of time required for the "slowest" movement axis (taking into account the boundary conditions related to this movement axis) to pass from a preceding independent axial position to a following independent axial position. Thus, "slow" may also be due to the fact that the affected movement axis must span a relatively long movement distance.

The leading axis function therefore typically alternates during synchronization. For example, in a first time interval required from all first axial positions along the movement axis to all respective subsequent second axial positions, the linear axis (e.g., the X-axis) of the coordinate measurement machine may, for example, have a leading axis function, while for a later time interval between the second axial position and the respective subsequent third axial position, the rotation axis has a leading axis function. The movement axis may have a leading axis function for time synchronization over a plurality of successive time intervals, but in the case of the novel method and corresponding coordinate measuring machine, the leading axis function typically alternates back and forth a plurality of times between the different movement axes. The longest time interval in each case, i.e. the longest time interval required for the displacement axis to reach the next individual axial position, always determines the duration available for changing all displacement axes from the respective preceding first individual axial position to the following second individual axial position. On the other hand, the longest time interval also limits the duration of the position change along all axes, so that a synchronized position change will occur as fast as possible, taking into account all independent boundary conditions of all axes.

Time synchronization with a plurality of persons may be demonstrated, all following a respective independent route plan with independent target points. Each person changing from his/her current individual target point to his/her next individual target point may have a uniform duration. For each change in position, the uniform duration is determined by the person who needs the longest time to make his/her current change in position. All other persons are then guided thereby. In the event of a premature arrival at their next target point, they may wait until all other persons have arrived at their respective next independent target point, and/or they may reduce their independent movement speed until the next target point is reached, the last being generally preferred.

In a similar manner, after synchronization, all axes of movement may have a time interval of uniform length to reach a subsequent independent axial position from a previous independent axial position. For each time interval, the respective lengths of these time intervals of uniform length are determined by using the longest time interval each as a uniform synchronization interval for all axes of movement. After synchronization is completed in this manner, the independent movement speeds along the independent movement axes can then be determined according to the uniform time intervals.

The novel method and the corresponding coordinate measuring machine therefore first receive a plurality of desired positions at which the reference points of the measuring elements are intended to be positioned within the measurement volume. In principle, the measuring element can be a tactile measuring element. Preferably, however, the measuring element is an optical measuring element which can detect a plurality of measuring points on the measuring object simultaneously. Preferably, the measurement points that are detected simultaneously are along a line, such as in the case of e.g. a laser triangulation sensor and/or within a defined area, such as in the case of e.g. a fringe projection sensor.

Preferably, these desired positions represent a plurality of selected measurement points on the surface of the measurement object. Advantageously, the desired position may be determined from a dataset representing the measurement object, such as a CAD dataset or a measurement dataset acquired on the same type of measurement object. In an exemplary embodiment employing a tactile measuring element, the reference point may be a ball center point of the probe ball. In the case of an optical measuring element, the reference point may be the focal point of the measuring optical unit. In some cases, the reference point is the so-called Tool Center Point (TCP). The desired position of the reference point defines a desired measurement path relative to the surface of the measurement object along which the reference point is intended to move. In a preferred exemplary embodiment, the desired positions are discrete support points of a desired measurement path, the remainder of the measurement path being continuous.

In addition, the novel method and corresponding coordinate measuring machine use a plurality of parameters defining upper and/or lower values of the speed and/or acceleration of the measuring element along said plurality of movement axes. Further parameters may include the size and/or weight of the measuring element, and/or the desired position of the reference point, and/or the orientation of the measuring element relative to the measuring object. These desired positions and parameters form input variables from which the independent control data ultimately used to move the measuring elements are determined.

A plurality of target positions of the measuring element along the linear axis and the rotation axis are determined based on the desired position of the reference point and the parameters. In contrast to the prior art, a plurality of independent time series of respective independent axial positions along the movement axis is determined as if different movement advances along the movement axis can be made in a mutually independent manner. Only in the latter method part, these independent time sequences are synchronized with a common timing cycle clock and thus combined to form a combined movement advance. It can be provided here that the movement of the measuring element along each movement axis and within each time interval can each take place with the maximum possible acceleration and speed along the respective axis, which is possible taking into account the parameters mentioned at the outset. Thus, it is first assumed that the movement along all axes of movement is as fast as possible. The measuring element is therefore also moved as quickly as possible after synchronization.

In addition, the novel method and corresponding coordinate measuring machine enable coordinated overall movement of the measuring element along multiple axes of movement, taking into account a number of different boundary conditions that are only partially applicable to independent axial movements. In particular, the novel method and the corresponding coordinate measuring machine are suitable for automatically moving the optical measuring element, so that a complete 3D scan of the measuring object can be performed in an efficient manner. Thus, the above-mentioned objects are fully achieved.

In a preferred embodiment of the invention, a desired measurement path of the reference point within the measurement volume is determined by means of interpolation from the plurality of desired positions, wherein the series of successive target positions is determined from the desired measurement path.

Preferably, the desired measurement path is determined by means of spline interpolation, in particular using cubic-quadratic Bezier spline. Determining successive target positions from such a desired measurement path enables controlling the measuring element in an efficient manner without jolting and jolting within the measurement volume.

In a further configuration, a plurality of position-dependent desired radial velocity profiles and a position-dependent desired tangential velocity profile of the reference point along the plurality of desired positions are first determined from the parameters. It is particularly advantageous to use the above-mentioned desired measurement path for determining the two mentioned desired speed profiles.

Determining the desired radial velocity profile makes it possible to take into account in a simple manner the centrifugal forces which occur as a result of the bending movement of the measuring element and to ensure that the lateral acceleration of the measuring element remains below a predefined maximum value. This advantageously facilitates improved measurement accuracy and reduced wear. Determining the position-dependent desired tangential velocity profile makes it possible in a simple manner to keep the velocity and the acceleration in the direction of movement within predefined limit values. This also advantageously facilitates improving the measurement accuracy and achieving a high measurement resolution.

By using an optical measuring element with an image or camera sensor, it is also advantageous if the speed of the measuring element along the desired measuring path is adapted to the image capture rate of the image or camera sensor. This is disadvantageous for the measurement resolution if the measuring element is moved too fast along the desired measurement path. In contrast, if the measuring element is moved too slowly, this is detrimental to productivity. The determination of the two desired speed profiles makes it possible in a simple manner to optimize the movement of the measuring element relative to the measuring object with regard to the measuring accuracy, the measuring resolution and the measuring speed.

In a further configuration, a desired time velocity profile of the reference point within the measurement volume is determined from the position-dependent desired radial velocity profile and from the position-dependent desired tangential velocity profile.

In this configuration, the two separate position-dependent desired speed profiles are combined to form a common temporal desired speed profile. This configuration offers the following simple possibilities: the movement of the measuring element along the plurality of movement axes is derived from a common reference variable.

In a further embodiment, the measuring element defines a measuring line with a plurality of measuring points, wherein the measuring line extends through the reference point.

In this configuration, the novel method and the corresponding coordinate measuring machine use, in particular, laser line sensors which operate according to the triangulation principle. A measuring element of this type makes it possible to record a plurality of measuring points along a measuring line simultaneously and is therefore particularly suitable for a complete 3D scan of a measuring object. The advantages of the novel method and of the corresponding coordinate measuring machine emerge in particular in combination with such measuring elements.

In a further embodiment, the series of successive target positions of the measuring element and the successive rotation angle values are determined as a function of the spatial orientation of the measuring line. These target position and rotation angle values are preferably also determined from the respective orientation of the surface of the measurement object, in particular from the respective local normal vector of the surface of the measurement object.

This configuration advantageously facilitates the optimization of the measuring line of the respective local orientation of the measuring element in each case optimally towards the measuring object surface, in particular towards the measuring object surface, at each measuring instant. This configuration thus facilitates achieving a uniformly high measurement accuracy during a 3D scan of the measurement object.

In a particularly preferred exemplary embodiment, in order to obtain each desired position along the desired measurement path, auxiliary points are generated at constant distances and in the direction of the respective surface normal at the desired point of the measurement object surface, and a second interpolation curve parallel to the desired measurement path, in particular in the form of a spline interpolation, is determined. The desired measuring path is thereby supplemented with information about the normal direction at each desired position of the measuring object surface, and the supplemented desired measuring path enables the optimum orientation of the measuring element at the measuring object surface to be determined for each measuring point in a simple manner.

In a further configuration, the spatial orientation of the measurement line is selected transversely to the path of the plurality of desired positions along the reference point, i.e. thus transversely to the desired measurement path mentioned above. In some preferred exemplary embodiments, the orientation of the measuring lines is selected to be perpendicular to the desired measuring path in the respective case. In a further preferred exemplary embodiment, the angle formed between the measuring line and the desired measuring path can be made selectable, so that the operator can input the desired angle between the measuring line and the desired measuring path as a parameter value.

In a further configuration, the spatial orientation of the measuring line is selected such that the reference point leads or lags the measuring element along the plurality of desired positions.

This configuration advantageously reduces measurement errors caused by unwanted reflections at the surface of the specularly reflective measurement object.

In a further configuration, a sequence of control data for a machine controller of the coordinate measurement machine is determined from the plurality of independent time sequences of respective independent axial positions.

Advantageously, the control data sequence is determined using a time sequence that is clock synchronized with the common timing cycle. This configuration has the advantage that the time series of the respective individual axial positions can be converted very simply and quickly into control data for the individual axes of the coordinate measuring machine. Preferably, the control data of the controller of the coordinate measuring machine (CMM controller) comprises a separate control data sequence for each movement axis, which control data sequences are determined directly from the respective associated time sequence and the synchronized axial position.

In a further embodiment, the control data sequence is determined with a predefined control data clock cycle which is derived from the common second clock cycle by determining the intermediate position.

This configuration advantageously facilitates providing the control data with a timing cycle clock that is adapted to the machine controller, wherein the control data timing cycle clock may be different from the common timing cycle clock of the independent axial position sequences. This configuration enables the novel method to be simply adapted for use with different coordinate measuring machines having different control data timing cycle clocks. Determining the intermediate position is a very efficient possibility to adapt the time sequence to a higher control data timing cycle clock.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the specified combination in each case but also in other combinations or alone without departing from the scope of the invention.

Drawings

Exemplary embodiments of the invention are illustrated in the accompanying drawings and described in more detail in the following description. In the drawings:

figure 1 illustrates one exemplary embodiment of a novel coordinate measuring machine,

figure 2 shows a simplified representation of the measuring cell of the coordinate measuring machine of figure 1 during movement along the surface of the measuring object,

FIG. 3 illustrates an exemplary desired measurement path having a plurality of desired positions, an

FIG. 4 shows a flow chart for explaining one exemplary embodiment of the novel method.

Detailed Description

In FIG. 1, one exemplary embodiment of the novel coordinate measuring machine is indicated generally by the reference numeral 10. The coordinate measuring machine 10 has here a base 12 on which a gantry 14 is arranged so as to be movable in the Y direction. The gantry 14 carries a slide 16 which is mounted movable in the X direction. The slide 16 carries a sleeve 18, which is mounted so as to be movable in the Z direction. Reference numeral 20 indicates linear scales arranged along the three movement axes X, Y, Z, so that the respective positions of the mast 14, the slide 16, and the sleeve 18 along the axis X, Y, Z can be determined by means of suitable sensors (not shown here).

Coordinate measuring machine 10 is one exemplary embodiment of a coordinate measuring machine having three linear axes arranged orthogonally to each other. In further exemplary embodiments, the novel coordinate measuring machine may be a horizontal arm coordinate measuring machine, a coordinate measuring machine of cantilever design, a coordinate measuring machine of bridge design with a stationary column and a movable bridge, or a coordinate measuring machine with a stationary gantry, for example, in which the workpiece receptacle is movable along one or two linear axes. In general, exemplary embodiments of the novel coordinate measuring machine may have any kinematic configuration to enable movement of the measuring element relative to the measuring object along a plurality of linear axes. This includes coordinate measuring machines that movably hold a measurement object on a rotary table or within a measurement object receptacle that is movable in some other way.

At the free lower end of the sleeve 18, a replacement interface 22 is arranged, to which a multi-axis rotary joint 24 is fixed. The rotary joint 24 carries a measuring element 26 which is movable relative to the measuring object 28 along a linear axis X, Y, Z and along an axis of rotation (explained below). Fig. 1 shows by way of example how the measuring object 28 is measured in the region of the bore 29 by means of the measuring element 26.

Reference numeral 30 denotes an evaluation and control unit. The evaluation and control unit 30 comprises a CMM controller 32 which actuates the drives (not separately shown here) of the coordinate measuring machine 10 as a function of control data and correspondingly provides for movement of the measuring element 26 relative to the measuring object 28 along the linear and rotational axes.

The evaluation and control unit 30 also comprises an operator terminal 34 with a monitor 36 and a keyboard 38. In a typical exemplary embodiment, the operation terminal 34 is realized by means of a commercially available personal computer, which may be implemented with an operating system, such asLinux or MacOS operates and runs thereon software which firstly enables the generation of control data for the machine controller 32 and secondly serves to evaluate the obtained measurement results. For example, reference may be made to measurement and evaluation softwareWhich is commercially available by the applicant.

The operator terminal 34 has, as is known per se, a processor 40 on which, in an exemplary embodiment of the novel method, the measurement and evaluation software is run. The operator terminal 34 also has a memory 42 in which a plurality of parameters are or can be stored, which define limit values for the permissible speed and/or acceleration of the measuring element 26 along the axis of movement of the coordinate measuring machine 10. In some exemplary embodiments, these parameters may be input, selected and/or edited via the operator terminal 34.

While exemplary embodiments of the novel coordinate measuring machine and novel method may be implemented with tactile measuring elements, in a preferred exemplary embodiment, coordinate measuring machine 10 has measuring elements 26, preferably optical measuring elements, that perform non-contact measurements. In some preferred exemplary embodiments, the measuring element 26 is a laser triangulation sensor, such as is commercially available, for example, by the present applicant under the trade name EagleEye II. Fig. 2 shows a very simplified illustration of such a measuring element.

As shown in fig. 2, in a preferred exemplary embodiment, the measuring element 26 can be rotated or pivoted about one, two, or even three axes of rotation relative to the measuring obj ect 28. For example, three axes of rotation A, B, and C are shown. Advantageously, the B axis extends here orthogonally to the a axis and the C axis. It is particularly advantageous if the a-axis and the C-axis run substantially parallel to one another and are offset laterally relative to one another in the direction of the B-axis. Further, in further exemplary embodiments, the measurement object 28 may be mounted on a rotary table and/or may be rotatable relative to the measurement element 26 about one, two or three axes of rotation (not shown here).

The measuring element 26 here has, as is known per se, a light source (not shown) which projects a light ray 44 onto the surface of the measuring object. In some exemplary embodiments, the light source is a laser diode that projects a laser line 44 onto the surface of the measurement object. The measuring element 26 here also has a camera sensor (not shown) which is arranged in a defined position and orientation relative to the light source. The measuring element 26 captures an image of the object surface and the light rays 44 by means of a camera sensor. The distance between the object surface illuminated by the light 44 and the measuring element 26 can then be calculated from these images based on a triangulation relationship. Unlike the present exemplary embodiment, in other exemplary embodiments, the measurement element 26 may project other light patterns onto the object surface, such as a light pattern having a plurality of parallel stripes.

In all preferred exemplary embodiments, the measuring element 26 defines a reference point 46 for measuring the measuring object. In the exemplary embodiment illustrated herein, the reference point 46 is located at the center of the measurement line 44 and preferably at the focal point of the camera sensor. In other exemplary embodiments, the reference point may be defined elsewhere on the measuring element 26, such as at a ball center point of a probe ball of the tactile measuring element. In some exemplary embodiments, the reference point is a so-called Tool Center Point (TCP) of the measurement element 26.

In order to measure the measurement object using the measuring element 26, the measuring element 26 is moved relative to the measurement object such that the reference point 46 moves along a path 48 which runs here exactly on the surface of the measurement object. In a preferred exemplary embodiment, the camera sensor of the measuring element 26 captures respective images of the measuring object surface and the measuring line 44 during the movement at defined time intervals. In fig. 2, four temporally successive positions of the measuring line 44 along the path 48 are indicated by reference numerals 44 ', 44 "and 44'".

In addition, in fig. 2, reference numeral 46' indicates a variant in which reference point 46 leads measuring element 26 in movement along path 48. This may be achieved by pivoting the measuring element 26 in the direction of the path 48. In other exemplary embodiments, the measuring element 26 may pivot during the measuring movement such that the reference point 46 falls behind the measuring element 26 in the movement. Additionally, in further exemplary embodiments, the measurement lines 44, 44 ', 44 ", 44'" may be oriented obliquely with respect to the path 48. As explained in more detail below, in a preferred exemplary embodiment, the desired orientation of the measurement line 44 relative to the path of travel 48 is taken into account in determining the control data of the machine controller 32.

In fig. 3, the desired measuring path along which the reference point 46 is intended to be moved on the surface of the measuring object is denoted by reference numeral 50. In a preferred exemplary embodiment, the desired measurement path 50 is determined by means of spline interpolation, which uses a plurality of desired positions S1, S2, S3, S4 as support points. In some preferred exemplary embodiments, the desired position S is passed_iSets a cubic-quadratic spline of the betz curve to determine the desired measurement path 50. In this case, these desired positions can be specified as vectors in a coordinate system which is freely definable in principle.

Advantageously, an assistance point H is determined for each desired position in this case_iAuxiliary points H as in FIG. 3₁As indicated. Auxiliary point H_iAt the corresponding surface normal N_i(e.g. surface normal N)₁Indicated) with the desired point S_iA constant distance is maintained. Here, additional cubic-quadratic bezier curves splines are set through these auxiliary points. Thus, the two splines extend in a manner similar to a rail, wherein the respective surface normals at the desired locations form a "railroad tie". In a preferred exemplary embodiment of the novel method, a secondary approach can be advantageously usedPoint of help H_iTo obtain the corresponding optimal orientation of the measuring line 44 on the surface of the object.

An exemplary embodiment of the novel method will now be explained with reference to fig. 4.

The starting points are a plurality of desired positions S selected and/or defined, for example, by an operator of the coordinate measuring machine 10 based on CAD data of the measurement object 28_i. These desired positions are read in via the operating terminal 34, for example by the operator by means of the keyboard 38 and/or using a mouse, a stylus or some other input means, based on the CAD representation of the measurement object, according to step 54. According to step 56, a plurality of parameters 58 are read from memory 42 and/or entered by an operator of operator terminal 34. The parameters 58 include, among others, one or more of the following: velocity v of reference point 46_TCPAcceleration/deceleration a of reference point 46_TCPMeasuring the velocity v of the element 26 along the linear axis_CMMMeasuring the acceleration a of the element along a linear axis_CMMAn angular velocity ω and/or an angular acceleration α of the measuring element about the rotation axis A, B, C, a lead angle or a fall angle of the reference point 46 (see reference numeral 46 of fig. 2) along the movement path 48, and an angle between the measuring line 44 and the movement path 48.

The desired measurement path 50 is determined from the read-in desired position using spline interpolation, according to step 60. According to step 62, an auxiliary spline 64 is determined here at a constant distance d from the desired measurement path 50 (see fig. 3).

Next, according to step 66, a position-dependent desired radial velocity profile (a curvature-dependent desired velocity profile) of the reference point 46 along the desired measurement path 50 is determined. This can be advantageously achieved by using the permissible acceleration limit amax of the reference point 46_TCPTo be implemented. At each desired position S_iAt radial acceleration v_i ²The ratio/r is intended to be less than the acceleration amax_TCP. Therefore, it is necessary to keep the following for the radial velocity at each desired position:

where ρ is_iIs the average curvature of the successive polynomial curvatures at the desired location Si. Further, the radial velocity is intended to be:

that is, the curvature-dependent speed is intended not to exceed the limit value of the maximum allowable speed. Thus, in step 66, a curvature-dependent/radial velocity profile along the desired measurement path 50 is obtained.

Step 68 involves determining a position dependent tangential velocity curvature (acceleration dependent velocity profile) of the reference point 46 moving along the desired measurement path 50. At the beginning and end of the tangential velocity profile, the following holds:

v`<sub>0</sub>＝v`_n-1＝U，

that is, the speed at the start and end of the movement is 0.

For a given a_maxAnd given distances, the following holds recursively for an increase in velocity in a tangential velocity curve with increasing exponent

And i is 1, n-2,

wherein the velocity of the tangential velocity profile must not exceed the velocity of the curvature dependent velocity profile

Next, step 70 involves calculating a position-dependent velocity curve v (S) from the position-dependent velocity curve v ═ v (S)_i) By relationship

Δ t to determine a time-dependent velocity curve v ═ v (t)_i). In this caseThe following equation holds₀＝0

And recursively

Steps 72 and 74 then involve determining the appropriate axial position along the linear axis X, Y, Z and the rotational axis A, B, respectively. By a boundary condition, i.e. a vector T from the measuring element 26 to the surface of the measuring object at each desired position_iAim at the normal vector N_iAnti-parallel, and the measurement line 46 at each desired position is intended to extend perpendicular to the movement path 48, the angle of rotation at the desired position can be calculated. In addition, the axial position of the measuring element 26 along the linear axis can be determined here by using spline interpolation for the desired position of the measuring element 26 within the measurement volume. As a result of steps 72 and 74, a time series of target positions along each linear axis and a time series of rotation angles for each rotation axis are obtained, i.e. thus a time series of independent axial positions.

The obtained time series are then synchronized according to the respective maximum possible velocities and accelerations along the axis according to step 76 to obtain a correlation of these independent movements. Each change from a first axial position i to the next axial position i +1 requires a separate time interval, depending on the maximum allowable speed and acceleration, and the separate time intervals along the separate axes may vary between the desired positions. Then for each desired position, the longest time interval is used as a basis in each case:

ts_i＝ts_i-1+max(ta_i-ta_i-1) Wherein i is 1, 2, 3 … n-1 and ts₀＝0。

The letter a here represents movement along each axis. Accordingly, for each synchronized time interval ts_i-1、ts_iThe temporally longest movement is used as a basis for synchronization and the correspondingly shorter movement duration of the other axes is extended to the temporally longest axial movement. In this way, alongAll time series of axial positions of the linear axis and the rotation axis obtain a common time basis and are correlated in time and space.

The machine controller 32 typically needs to continuously control the control data of the measuring element 26 with a defined control data timing cycle clock that is different from the synchronous timing cycle clock of the axial position of steps 74, 76. Thus, step 78 herein involves determining the intermediate position Z for each axis of movement_iSo that for all deltat_{Control of}The current control data may each be used for independent axial movement.

FIG. 3 illustrates two intermediate positions Z on the desired measurement path 50₁And Z₂. For example, the intermediate position Z can be recursively assigned_iIs inserted on the desired measurement path 50 to determine a modified synchronized time sequence based thereon according to steps 72 to 76. This is indicated by reference numerals in fig. 3.

According to step 80, control data is clocked at control data timing period clock Δ t_{Control of}Internally to the CMM controller 32 and by means of the transmitted control data moves the measuring element 26 in a manner known per se.