Surface sensing device and position determining device for use in a position determining device

Abstract

A surface sensing device and a position determining device for use in a position determining device are disclosed. The surface sensing device (4) is mounted on an articulated probe head (7) of a coordinate measuring machine. The device (4) comprises an elongated probe holder (8) rotatable about an axis (C). An elongated sensing module (10) comprises a surface finish or surface roughness probe having a stylus tip (5). The elongated sensing module is connected to the probe holder (8) by an adjustable joint (12). To determine the geometry of the surface sensing device (4), which comprises a tip normal (TN) of the stylus tip (5) and a drag vector (DV), the orientation of the probe holder (8) and the sensing module (10) is determined by probing points (44A, 44B, 46A, 46B) spaced along the length of the probe holder and the sensing module using a separate probe (32).

Description

Surface sensing device and location determination device used in a location determination device

[0001] This application is a divisional application. The original application is PCT application No. PCT / GB2018 / 050387, filed on February 13, 2018, which entered the Chinese national phase on August 14, 2019. The original application is application No. 201880011837.2, entitled "Method for calibrating a surface sensing device, corresponding calibration program for controlling a computer, and corresponding calibration kit". Technical Field

[0002] This invention relates to a surface sensing device used in positioning equipment or machines, such as coordinate measuring machines (CMMs), scanners, machine tools, or inspection / measuring robots. More specifically, this invention relates to the calibration of such surface sensing devices. Background Technology

[0003] Such positioning devices or machines can be used to measure workpieces and typically include a component movable in three axial directions (X, Y, Z) relative to a worktable supported on the workpiece. The movement of the component in each of these directions is measured by transducers on the machine. Surface sensing devices or probes mounted on the movable component generate signals indicating their relationship to the surface of the workpiece being measured. The position of the surface can thus be determined. In alternative machines (such as certain types of machine tools), the worktable moves along the X and Y axes, and the movable component moves along the Z axis.

[0004] Certain types of contact probes (e.g., touch-triggered probes and contact scanning probes) perform three-dimensional motion. Typically, they can approach the workpiece surface in any direction within the X, Y, Z coordinate system of a machine's transducer, and they have deflectable styluses with workpiece contact tips. Before measurement with such probes, a calibration called "datuming" is usually performed. This involves contacting the stylus tip with a reference surface (such as a reference sphere) to determine a repeatable position of the stylus tip within the machine's X, Y, Z coordinate measurement system.

[0005] In a flexible measurement system, to reach different workpiece surfaces, probes can be mounted on a CMM via a motorized hinge, through which the probes can rotate about two mutually orthogonal axes. The machine and the motorized hinge can be operated under computer control.

[0006] The probes (or surface sensing devices) can be replaceable. When not in use, they are stored in the corresponding storage ports of the storage rack. When a measurement is needed, the hinge can automatically pick up the probe from the storage port of the storage rack and then return it to the storage port, all under computer control. The applicant, Renishaw plc, sells such systems under the trademark Autochange. To align the hinge with the storage rack, the Autochange storage rack is equipped with fixed touch-triggered probes. When the storage rack is installed, the surface of the hinge contacts the probes of the storage rack. This establishes a spatial relationship between the hinge and the port of the storage rack to ensure their alignment.

[0007] US Patent Nos. 8006399 (Wallace et al.) and 8468672 (Wallace) describe a surface sensing device. To reach different workpiece surfaces, the surface sensing device is mounted on a CMM via a hinge joint, allowing it to rotate about two mutually perpendicular axes of rotation. The surface sensing device may include a surface finish probe for unidirectional sensing of the surface, or it may include another type of unidirectional (single-axis) probe, such as an optical probe (e.g., a laser spot or laser line probe). To enable such a unidirectional probe to reach surfaces with different orientations, the surface sensing device has a third axis of rotation that allows the surface sensing device to be manually rotated. This third axis of rotation may be aligned with the generally longitudinal axis of the surface sensing device, allowing the surface sensing device to sense the surface in directions transverse to or deviating from the third axis. Alternatively, the surface sensing device may be arranged at an angle to the third axis of rotation.

[0008] However, this third axis of rotation only allows the surface to be reached in certain possible orientations. There is also the issue of benchmarking or calibrating the geometry of such a surface sensing device. Summary of the Invention

[0009] The present invention provides a method for calibrating a surface sensing device for a location determination device, the surface sensing device including one or more elongated members mounted on the location determination device and a surface sensing element mounted on the device via the one or more elongated members, the method including probing at least one of the elongated members with a separate probe to determine its orientation.

[0010] One of the one or more elongated members can be connected to a pivotable joint, so that it can be set at a desired angle.

[0011] A single probe can detect one or more side positions of an elongated component or multiple elongated components. The same probe can be used to probe the elongated component multiple times.

[0012] A first elongated member and a second elongated member may exist, and the pivotable joint connects the first elongated member and the second elongated member, so that the second member can be set at a desired angle relative to the first member, the first elongated member is connected to the position determining device, and the surface sensing element is carried by the second elongated member.

[0013] Preferably, the detection step includes detecting at least the second elongated member using the separate probe to determine its orientation. The method may also include detecting the first elongated member using a separate probe to determine its orientation, and then determining the angle of the second elongated member relative to the first elongated member.

[0014] Suitablely, the elongated member, or each elongated member, is detected at at least two locations spaced apart along its length. Preferably, the elongated member, or each elongated member, is detected at at least six locations. This allows for more accurate indication of the orientation and position of the elongated member in space.

[0015] In a preferred embodiment, the surface sensing device is a unidirectional sensing device, such as a surface finish or surface roughness probe. The surface sensing element may be a stylus with a tip, which is mounted to deflect along the normal direction when the stylus tip is dragged across the surface, and connected to a transducer to measure the deflection of the stylus, thereby determining the surface finish or surface roughness.

[0016] The method may include determining the normal direction of the stylus tip and / or the direction in which the tip is dragged along the surface. This can be determined based on the orientation of the one or more elongated elements.

[0017] The method may include determining an offset describing the position of the stylus tip relative to the position determining device. This offset can be calculated based on the orientation and length of the one or more elongated members. Alternatively, the offset can be determined by probing the surface sensing device near the stylus tip with a separate probe.

[0018] The surface sensing device may include a rotary joint configured to rotate an elongated member connected to the position determining device approximately about a longitudinal axis of the elongated member. The method may include determining the orientation of the rotation axis (which may not precisely coincide with the orientation of the elongated member). The rotary joint may have a motor for rotating the elongated member.

[0019] The surface sensing device can be mounted to the position determining device via a hinge joint configured to allow the surface sensing device to rotate about two mutually orthogonal axes. The hinge joint may include a motor for rotating the surface sensing device about the mutually orthogonal axes.

[0020] The present invention also provides a program for a computer controller for a location determination device, the program being configured to perform any of the methods described above.

[0021] Another aspect of the present invention provides a kit for use with a location determination device, the kit comprising: a surface sensing device including one or more elongated members for mounting to the location determination device, a surface sensing element mounted to the device via the one or more elongated members, and a method procedure configured to perform any of the methods described above.

[0022] The programs discussed in this article can be set on any suitable machine-readable medium, including storage disks, memory sticks, memory cards, or local or remote servers from which programs can be downloaded. Attached Figure Description

[0023] Preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

[0024] Figure 1 is an isometric view of the surface sensing device mounted on the hinged probe head;

[0025] Figure 2 shows a cross section passing through axes A and B in Figure 1;

[0026] Figure 3 is a schematic diagram of the geometry of the surface sensing device; and

[0027] Figures 4 through 7 show the surface sensing device and articulated probe head mounted on a coordinate measuring machine (CMM). Detailed Implementation

[0028] Figure 1 shows a hinged probe head 7 that supports a surface sensing device 4 for rotating about two mutually orthogonal axes of rotation A and B. Figure 2 shows a cross-sectional view of the through-hinged probe head 7 and the surface sensing device 4 in the plane defined by axes A and B.

[0029] The articulated probe head 7 includes a first housing member 1 and a second housing member 2. The first housing member 1 is adapted for attachment to a positioning device, such as a movable arm 26 of the CMM as shown in FIG. 4. The CMM moves the arm 26 in three linear dimensions X, Y, and Z. As shown in FIG. 2, housing member 1 houses a motor M1 for angular displacement of a first shaft 20 about a first axis A. The second housing member 2 is attached to the first shaft 20 and houses a motor M2 for angular displacement of a second shaft 22 about a second axis B. A surface sensing device 4 is attached to the second shaft 22 to rotate with it. The CMM is driven in the X, Y, and Z directions under the control of a program in a computer controller 3, which also controls the movement of motors M1 and M2 about axes A and B.

[0030] The surface sensing device 4 includes an elongated probe holder 8 that extends generally along an axis C that is transverse to and intersects axis B. The elongated probe holder is attached to a hinge joint 7 via a housing 9. The housing 9 contains a motor M3, which is also controlled by a program in a computer controller 3 to rotate the probe holder 8 about axis C.

[0031] To enable replacement of different types or configurations of surface sensing devices, housing 9 has a known type of motion coupling 6 through which the retainer 8 of the surface sensing device 4 can be attached to and detached from housing 9. When not in use, the surface sensing device can be stored in port 34 of storage rack 30, as shown at 4A in FIG4. Under the control of a program in computer controller 3, the replacement of the surface sensing device is performed automatically by moving the CMM arm 26 and hinge joint 7. When the surface sensing device 4 is reattached, the motion coupling 6 ensures that it can be repeatedly positioned relative to housing 9, so that the calibration described below does not need to be repeated each time the surface sensing device is replaced. The motion coupling 6 includes a magnet (not shown) that holds the surface sensing device in place during use.

[0032] The surface sensing device 4 includes an elongated sensing module 10 containing a surface finish or surface roughness sensor. The module 10 is pivotally attached to the retainer 8 via a joint 12. This allows the module to be manually oriented relative to the retainer 8 to a desired set angle before a measurement task. The joint 12 then holds the module at that angle by friction, or the joint may have a fastening screw. To access different surfaces of the workpiece, the orientation of the module 10 can be further changed during a measurement task by rotating it about axis C via a motor M3 under program control.

[0033] The surface finish or roughness sensor included in module 10 can be of a known type, for example, as described in the aforementioned U.S. Patent Nos. US 8006399 and US 8468672. Typically, the surface finish or roughness sensor includes a surface sensing element in the form of a needle or stylus 5, having a surface sensing tip that is relatively small compared to the irregularity of the surface being measured. The surface sensing tip can be deflected laterally relative to the slider 14 (FIG. 3) in the elongated sensing module 10. In use, under the control of a program in computer controller 3, the slider and stylus tip are dragged across the surface by the X, Y, Z movements of CMM arm 26 or by the rotation of hinge joint 7. Stylus 5 is connected to a transducer in module 10 to measure the resulting deflection of the stylus orthogonal to the surface, thereby indicating its surface finish or surface roughness. The results are sent back to computer 3 and processed in the computer.

[0034] The holder 8 and sensing module 10 can be configured in a variety of different ways to suit various measurement tasks. For example, they can be configured to different lengths, or the outer end of module 10, as shown by the dashed line 10A in Figure 3, can be angled for better contact with the surface to be measured. Different types of sliders can also be provided to accommodate different types of measurements.

[0035] The sensing module 10 includes a motion coupling 16 that provides "overtravel" in a known manner. This allows the outer end of the module 10 to deflect against the action of a spring (not shown) to protect it from damage should it accidentally move too far toward the workpiece and collide with it. The motion coupling 16 repeatedly positions the outer end of the module so that it returns to the same position after being removed without contacting the workpiece. Since it does not require removability or replaceability, coupling 16 can be simpler than motion coupling 6. The coupling may include a spring flexure that typically holds the outer end of the module against a stop.

[0036] Before use, the geometry of the surface sensing device 4 is calibrated or referenced. Calibration is performed after the elongated sensing module 10 has been manually set to the desired angle at the articulated joint 12, which can be approximately set using a protractor. Calibration is performed under program control from the control computer 3. The calibration determines several aspects of the geometry, as shown in Figure 3:

[0037] • The direction and origin of the rotation axis C relative to the X, Y, Z coordinate system of the CMM. The slope and runout of axis C can also be determined.

[0038] • The axis 40 of the elongated retainer 8. This can be determined, for example, relative to axis C. (It should be understood that due to manufacturing tolerances, axis 40 will not exactly coincide with axis C. This is exaggerated in Figure 3 for illustrative purposes.)

[0039] • The axis 42 of the elongated sensing module 10 provides a more accurate measurement of the intersection point K of axes 40 and 42 at joint 12 and the angle θk between these axes.

[0040] • Vector TN (tip normal), which describes the deflection direction of tip 5 (which should be aligned with the normal of the measured surface during subsequent measurements).

[0041] • The drag vector (DV) describes the direction in which the tip 5 is dragged along the surface being measured. Figure 3 shows this drag vector in the longitudinal direction of the sensing module 10, but if a lateral scan is intended, the drag vector can be calculated laterally relative to the sensing module (as a supplement or alternative to the longitudinal vector).

[0042] • The offset of tip 5 relative to the origin C0 of axis C (tip offset).

[0043] Calibration can determine all the individual geometric aspects listed above, or any one of these geometric aspects individually or in any combination, to suit the measurement task to be performed.

[0044] The calibration will now be described in more detail.

[0045] As shown in Figures 4 through 7, a separate touch-triggered probe 32 is provided, which has a deflectable stylus 36. The probe 32 is fixed relative to the CMM or other positioning device. Suitable, it can be fixed to a storage rack 30. In order to link the measurements of the surface sensing device 4 to the coordinate measurement system of the CMM, the touch-triggered probe 32 should have been desiccated in the CMM coordinate system. This can be accomplished by probing the tip of its stylus with a reference probe held on the movable arm 26, as is known to those skilled in the art.

[0046] During the calibration of the surface sensing device 4, under the control of the calibration program in the control computer 3, the holder 8 and module 10 of the surface sensing device (pre-set at a desired angle on the articulated joint 12) contact the deflectable stylus 36 of the contact trigger probe 32 in various positions and orientations, as shown, for example, in Figures 5, 6, and 7. This contact causes the stylus 36 to deflect, thereby causing the contact trigger probe to send a trigger signal to the computer controller 3.

[0047] Preferably, the contact of these individual contact trigger probes 30 is performed by first rotating the hinge 7 about its axes A and B to orient the surface sensing device 4 in the desired direction. Then, the surface sensing device is moved linearly along the X, Y, Z directions by driving the CMM along its X, Y, Z axes. Upon receiving each trigger signal, the control computer 3 freezes the readings of the X, Y, Z position sensors of the CMM, which indicate the X, Y, Z coordinates of the point on the holder 8 or module 10 that has made contact.

[0048] All the following measurements were taken with axis A and axis B of the hinge joint 7 in a single orientation.

[0049] Referring more specifically to Figure 3, axis C is driven to a selected orientation, for example, such that the elongated retainer 8 and sensing module 10 are approximately located in the YZ plane. The CMM is then driven along its X, Y, Z axes to bring the elongated retainer 8 into contact with the contact trigger probes 32 at points 44A and 44B. These points are suitably located on the sides of the retainer 8. Readings of the X, Y, Z coordinates are obtained for each point. These points are taken at at least two locations 44A and 44B spaced apart along the length of the elongated retainer. The orientation of axis 40 is thus determined. Preferably, at least six points are taken in total, as this allows for precise determination of the cylinder defining the retainer 8, and thus the orientation of its axis 40.

[0050] To determine the direction of the rotation axis C and its origin C0, motor M3 is now operated to rotate the surface sensing device about axis C to two or more other orientations. For example, two other orientations could be 120° to the YZ plane. The process of obtaining readings at points 44A and 44B described above is repeated in each orientation. This gives the direction of axis 40 in each of the three orientations about axis C, which allows the direction and origin of the rotation axis C to be calculated, and the angle of axis 40 of the elongated retainer 8 relative to axis C to be calculated. The slope and runout of axis C can also be calculated.

[0051] If it is certain that axis 40 coincides with the axis of rotation C (within the desired tolerance), it is not necessary to repeat the determination of axis 40 in two or more other orientations.

[0052] Conveniently, the offset of the rotation axis B (the zero position of axis B) can now be mathematically set such that when axis B is at the zero position, the rotation axis C (as determined above) lies in the plane defined by axis A and axis B. This simplifies future measurements.

[0053] Next, with the motor M3 on axis C in one of the aforementioned orientations (e.g., the last one measured), points 46A and 46B are acquired on the elongated sensing module 10 in the same manner as described above (appropriately on the side of the module). These points, similar to points 44A and 44B, should preferably be located at two spaced-apart positions along the length of module 10, and preferably at least six points in total are acquired to accurately determine the cylinder defining module 10. This gives the orientation of axis 42 of sensing module 10. Knowing axes 40 and 42 in the selected orientation, their intersection point K at joint 12 and the accurate value of the angle θk between these axes can be directly calculated.

[0054] However, while a preference is placed on six points 46A and 46B at two spaced-apart locations, fewer points can be used. For example, if the length L1 from the origin C0 relative to axis C to point K is known with sufficient accuracy, axis 42 can be determined, for example, by combining three points 46B at one location along module 10. In this case, the determination is based on the fact that points 46B and point K are spaced apart along the length of module 10.

[0055] Furthermore, based on the nominal design lengths L1 and L2 of the elongated retainer 8 and module 10, as well as point K and joint angle θk, an approximate value for the tip offset TO of tip 5 relative to the origin C0 of axis C can now be directly calculated. Based on the joint angle θk and nominal lengths L1 and L2, the values ​​of the tip normal TN and the drag vector DV can be calculated. If it is desired to laterally scan the sensing module 10 on the surface, an appropriate drag vector (and / or alternative to the longitudinal vector DV) at 90° to the vector DV can be calculated. Of course, if the sensing module has an alternative geometry (e.g., shown by dashed line 10A), the nominal values ​​of the angles and lengths of this alternative geometry should be considered.

[0056] During subsequent measurements, the aforementioned calibration values ​​enable tip 5 to contact and measure at the desired location on the surface of the complex-shaped workpiece, all automatically under program control, without any collision or impact between the retainer 8 or the sensing module 10 and other surfaces of the workpiece. The program can be written based on the workpiece's CAD data without requiring manual positioning of the surface sensing device using a joystick controller. This is useful, for example, in narrow locations such as slots or in situations where the workpiece has internal blind spaces (where it is impossible to see the surface sensing device for manual positioning with a joystick).

[0057] It may be desirable to obtain a more accurate value for the tip offset TO in order to precisely position the tip 5 at a point on the surface to be measured and to more accurately determine the surface topography. In this case, three or more additional points 48 can be obtained on the end (nose) of the sensing module 10 near the tip 5. Two such points 48 are shown in Figure 3, and another point is hidden because it should be on a different surface of the end. These points precisely locate the position and orientation of the end, and the position of the tip 5 can be determined based on knowledge of the nominal design geometry of the tip relative to the end of the sensing module.

[0058] The present invention does not necessarily require all of the aforementioned calibrations. For example, it may be determined that only some calibrations are important, such as the tip normal TN, drag vector DV, and / or tip offset TO, which affect the accuracy of subsequent measurements, not just the ability to position the surface sensing device without collision or impact. In other cases where there is a greater risk of collision or impact, it may be more important to determine the geometry of the surface sensing device by accurately determining the positions K and angles θk of axes 40, 42 and / or articulation joint 12.

[0059] As described above, all the calibration measurements were performed with axes A and B of the hinge 7 held in a single direction. However, it may be desirable to repeat them in other orientations of axes A and B, as shown in Figures 5, 6, and 7. This could be, for example, if the elongated holder 8 and / or the elongated sensing module 10 of the surface sensing device sags due to gravity as it moves from the vertical position of Figure 5 to the horizontal position of Figure 6. Calibration at each position can calibrate the sag.

[0060] It should be understood that the above-mentioned geometric calibration is separate from any calibration of the transducer in the sensing module 10 that can be performed.

[0061] The preferred embodiments of the present invention described above relate to contact-type surface finish or surface roughness probes having a stylus that drags across the surface to be measured. However, the present invention can be used with other contact and non-contact surface sensing devices. For example, the present invention can be used with non-contact optical surface finish and surface roughness probes. The present invention can also be used with touch-triggered probes and contact scanning probes. Other non-contact probes include, for example, optical probes, capacitance probes, and inductive probes. Optical probes include laser spot and laser line probes.

[0062] This invention is particularly applicable to single-axis probes, such as optical probes and surface finish or surface roughness probes. This is because for these types of probes, rotation, especially around a longitudinal axis (axis C in the above embodiment), greatly increases the number of surfaces the probe can reach. Rotation around this axis is also particularly useful for laser line probes, as they can rotate around the axis of the surface sensing device (the third axis as described above).

Claims

1. A surface sensing device (4) for use in a positioning device, the surface sensing device comprising: A first elongated member (8) and a second elongated member (10), wherein the first elongated member and the second elongated member can be installed to the position determining device; A slider, the slider being provided on the second elongated member; The device includes a surface sensing element that can be mounted to the position determining device via a first elongated member and a second elongated member, wherein the first elongated member and the second elongated member are pivotally connected such that the second elongated member can be set at a desired angle relative to the first elongated member, the first elongated member is connected to the position determining device, and the surface sensing element is carried by the second elongated member, wherein the surface sensing device is a unidirectional sensing device, wherein the surface sensing device is a surface finish or surface roughness probe, and wherein the surface sensing element is a stylus (5) with a tip, the stylus (5) being mounted to deflect along the normal direction relative to the slider of the surface sensing device when the tip of the stylus (5) is dragged on the surface, and connected to a transducer to measure the deflection of the stylus (5) relative to the slider, thereby determining the surface finish or surface roughness.

2. The surface sensing device according to claim 1, wherein, The surface sensing device (4) includes a rotary joint configured to rotate the first elongated member and the second elongated member connected to the position determining device approximately about the longitudinal axis (C) of the first elongated member.

3. The surface sensing device according to claim 2, wherein, The rotary joint has a motor (M3) for rotating the elongated member.

4. The surface sensing device according to any one of claims 1 to 3, wherein, The surface sensing device (4) can be automatically attached to and detached from the position determining device via a motion coupling connector (6).

5. The surface sensing device according to any one of claims 1 to 3, wherein, The surface sensing element includes a motion coupling (16) that provides an overtravel mechanism that allows the outer end of the surface sensing element to deflect against the action of a spring to protect the surface sensing element from damage if it accidentally travels too far toward the workpiece and collides with it. The motion coupling (16) is capable of repeatedly positioning the outer end of the surface sensing element such that it returns to the same position after being removed without contacting the workpiece.

6. The surface sensing device according to claim 4, wherein, The surface sensing element includes a motion coupling (16) that provides an overtravel mechanism that allows the outer end of the surface sensing element to deflect against the action of a spring to protect the surface sensing element from damage if it accidentally travels too far toward the workpiece and collides with it. The motion coupling (16) is capable of repeatedly positioning the outer end of the surface sensing element such that it returns to the same position after being removed without contacting the workpiece.

7. A position determination device, the position determination device comprising a surface sensing device (4) according to any of the preceding claims, the surface sensing device being mounted on the position determination device.

8. The location determination device according to claim 7, wherein, The surface sensing device (4) is mounted to the position determining device via a hinge joint (7), the hinge joint being configured to rotate the surface sensing device (4) about two mutually orthogonal axes (A, B), wherein the hinge joint includes motors (M1, M2) for rotating the surface sensing device about the mutually orthogonal axes.

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