Support

Abstract

A positioning device (100) including a support (108) extending in a first direction and a beam (110) extending in a second direction. The beam (110) is movably attached to the support (108) such that it is movable in the first direction and exerts a load on the support. The support includes a contour (302) such that, upon exertion of the load by the beam (110), the contour of the support (108) is deformed such that the beam (110) is maintained in a substantially constant orientation for all locations of the beam (110) along the support (108).

Description

[Technical field]

[0001] The present invention relates to a support for a positioning device, in particular a support for a coordinate measurement machine (CMM). [Background technology]

[0002] A positioning apparatus, such as a CMM, can include one or more members that are movable relative to one another to position a tool, such as an inspection device, relative to a workpiece / artifact. For example, a CMM conventionally includes multiple moveable members, e.g., linearly moveable members arranged in series. Typically, the positioning apparatus is configured to facilitate relative movement of a tool and / or object in at least two or three mutually orthogonal axes, e.g., X, Y and Z. Such positioning apparatus are commonly known as "Cartesian" positioning apparatus (or Cartesian CMMs).

[0003] Usually, the relative movement between the tool and the object can be achieved by mounting the object to a platform and moving the tool relative to the object. Movement of the tool in three orthogonal directions can be achieved by providing a fixed beam attached to two (or more) supports, often called a Y-beam. Another beam can be attached perpendicular to the Y-beam in such a way as to allow movement along the Y-beam, the beam just mentioned often being called an X-beam. A further beam can be attached to the X-beam orthogonal to both the X-beam and the Y-beam in such a way as to allow movement along the X-beam and to allow movement of the further beam (or part of the further beam) in the elongated direction of the further beam (often called the Z-direction). The further beam is often called a quill. Examples of such arrangements are disclosed by US5505004 and EP2594893.

[0004] EP 2 594 893 discloses a device having longitudinal members attached to posts which are connected by cross members forming a frame such that deformations of the frame itself are not coupled to deformations of the posts.

[0005] US5505004 discloses a device in which a beam is connected to a first leg by a pivot joint that allows the leg to rotate in a vertical plane, and the beam is connected to a second leg by a linkage that allows the beam to rotate in a vertical plane and move in the direction of a longitudinal axis relative to the second leg. Summary of the Invention

[0006] According to a first aspect of the invention, there is provided a positioning device including a support extending in a first direction and a beam extending in a second direction, the beam being movably attached to the support such that it is movable in the first direction and exerting a load on the support, the support including a profile such that upon exertion of the load by the beam a profile of the support is deformed such that the beam is maintained in a substantially constant orientation for all locations of the beam along the support. Optionally, the first direction and the second direction are perpendicular. Optionally, the first direction is in a horizontal plane. Optionally, the second direction is in a horizontal plane. Optionally, the load exerted by the beam on the support includes a vertical component.

[0007] The support may be attached to two or more posts. Optionally, the support may be at least 2 metres in length, optionally at least 2.5 metres in length, optionally at least 3 metres in length, optionally at least 3.5 metres in length, optionally at least 4 metres in length, optionally at least 5 metres in length.

[0008] By maintaining a constant orientation of the beam for all locations along the support, improved weather performance may be possible and / or longer beams may be used. This may allow larger objects to be measured with a CMM. Additionally, the present invention may allow the use of lighter beams compared to the prior art while providing the same measurement space. This may reduce moving mass and provide dynamic advantages.

[0009] Optionally, deformation of the support due to loads applied by the beam causes the beam to be maintained at a substantially constant height for all locations of the beam along the support. The beam may be maintained at a substantially constant angle with respect to a horizontal plane.

[0010] Optionally, the support is configured to compensate for deformation in YRX. Optionally, the support is configured to compensate for deformation in YRZ. Optionally, the support is configured to compensate for deformation in both YRX and YRZ. Optionally, the support is configured to compensate for deformation in XRY. Optionally, the support is configured to compensate for XRZ. Optionally, the support is configured to compensate for both XRY and XRZ.

[0011] The beam may extend between the support and a substantially inflexible support. Optionally, the substantially inflexible support comprises granite. Optionally, the beam is movably mounted such that it is movable in a first direction. Optionally, the support comprises a (further) beam. Optionally, the support comprises a pair of substantially parallel, spaced apart supports.

[0012] Optionally, the beam extends between a pair of spaced apart supports (which may include beams) and is movably mounted such that it is movable in a first direction.

[0013] A first support of the pair of parallel spaced apart supports may be optimized to maintain the beam at a constant angle and a second support of the pair of parallel spaced apart supports may be optimized to maintain the beam at a constant height. Alternatively, both parallel spaced apart supports may be optimized to maintain the beam at a constant angle. Optionally, both parallel spaced apart supports may be optimized to maintain the beam at a constant height. Optionally, both parallel spaced apart supports may have the exact same profile.

[0014] Optionally, the positioning device comprises a coordinate measuring machine.

[0015] According to a second aspect of the present invention there is provided a support for a positioning device including a profile as defined in any of the preceding claims.

[0016] According to a third aspect of the invention there is provided a method of manufacturing a positioning device of the first aspect. The method of manufacturing the positioning device of the first aspect may comprise machining a support to have a profile such that when the beam exerts a load the profile of the support is deformed such that the beam is maintained in a substantially constant orientation for all locations of the beam along the support. Optionally, the profile is a non-linear profile. Optionally, at least part of the profile is curved. Optionally, an error map is created relating to deviations in height and / or angle of the beam relative to locations of the beam along the support.

[0017] According to a fourth aspect of the present invention, there is provided a method of measuring an object using a positioning device of the first aspect. The method of measuring an object using a positioning device of the first aspect may include deforming the support with a load applied by the beam as the beam moves in a first direction along the support such that the beam is maintained in a substantially constant orientation for all locations of the beam along the support. Optionally, the load applied by the fist beam to the second beam is due to a weight of the second beam.

[0018] Aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0019] [Figure 1] 1 shows a prior art CMM. [Diagram 2] This shows a partial semantic representation of the CMM. [Diagram 3] A part of the CMM is shown. [Figure 4] The calculation results for a Y beam with 3.5 meters of Y travel are shown below. [Diagram 5] The nonlinear profile of the Y beam is shown. [Figure 6] FIG. 6(a) diagrammatically shows deformation of a portion of the CMM, and FIG. 6(b) diagrammatically shows the Y-beam of the CMM. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] FIG. 1 shows a prior art coordinate measuring machine (CMM) including a base 2 to which a first support 4 and a second support 6 are attached. A Y beam is fixedly attached to the ends of the first support 4 and the second support 6 distal to the base 2. An X beam 10 is movably attached at one end to the Y beam and movably attached at a second end of the X beam 10 to an additional support (not shown) that is parallel to and spaced apart from the Y beam 8 such that the X beam 10 extends in a direction perpendicular to the elongation of the Y beam 8. Without the X beam, the Y beam would be linear and would have a profile that extends parallel to the y-axis. The X beam 10 is capable of moving along the length of the Y beam 8. A quill 12 is movably attached to the X beam 10. The quill 12 is capable of moving along the X beam 10 between the Y beam and the additional support. A tool 14, such as a probe head and a measurement probe, is attached to the end of the quill 12 proximate the base 2. The quill 12 is mounted so as to be movable perpendicularly to the X beam 10 in order to move the tool 14 closer to or farther from the base 2. The arrangement just described allows the tool 14 to be movable in three dimensions with respect to the object 16 to be measured. Movement of the X beam 10 along the Y beam 8 moves the tool 14 in the Y direction, movement of the quill 12 along the X beam 10 moves the tool 14 in the x direction (the x direction being in and out of the plane of the page in FIG. 1 ), and movement of the quill 12 perpendicular to the X beam 10 moves the tool 14 in the z direction.

[0021] As can be seen in FIG. 1, the quill 12 and X beam 10 are at an angle 18 with respect to the y-axis. What has just been said is due to the load applied by the X beam and the quill to the Y beam, in the just-mentioned case, the weight of the X beam and the quill causes the Y beam to sag. The sagging of the Y beam due to the weight of the X beam and the quill causes a change in the orientation of the X beam and the quill, i.e., a change in height and / or angle with respect to the vertical z-axis. The change in angle of the X beam and the quill with respect to the vertical z-axis is called roll or YRX (i.e., a movement along the y-axis leading to a roll about the x-axis). The deformation (sag) of the Y beam due to the load applied by the X beam will vary for different locations of the X beam along the Y beam, and the YRX and height of the X beam and the quill will also vary for different locations of the X beam along the Y beam.

[0022] 2 shows a semantic representation of a portion of a CMM. A base 102 and supports are shown. In the embodiment just described, the supports include a Y-beam 108. The Y-beam 108 is attached to and extends between a first support 104 and a second support 106. In the embodiment just described, the Y-beam 108 extends a distance beyond the first support 104. Y 1, extends a distance Y2 beyond the second strut 106, - Y 1 is Y 2より FIG. 3 shows an embodiment of an X beam 110 attached to a Y beam 108 via an array 120 to facilitate movement of the X beam 110 along the Y beam 108. The X beam 110 is attached to the Y beam via a first mount 121 and a second mount 122, each of which is attached to the Y beam 108 via a support portion. The front and rear support portions are spaced apart along the elongation of the Y beam 108. FIG. 3 also shows a quill 112 that is vertically movable via a quill mount 111. The quill mount 111 is configured to be movable along the elongation of the X beam 110.

[0023] Using beam theory, YRX can be calculated for every position of the X beam 110 along the Y beam 108. Additionally, YRX can be calculated experimentally for every position of the X beam 110 along the Y beam 108. Additionally, YRX can be calculated using numerical methods for every position of the X beam 110 along the Y beam 108.

[0024] FIG. 4 shows the calculation results for bearing deflection and YRX for a beam with 3.5 meters Y travel (i.e. a Y beam that takes into account 3.5 meters of travel of the X beam along with the Y beam for measurement purposes; the additional travel may allow for easier tool change).

[0025] 4 shows a first set of calculation results for a Y beam that has a straight profile when there is no load from the X beam, i.e. the Y beam is linear. The first dashed line 202 represents the deflection of the Y beam (due to the weight of the X beam) relative to the location of the front support of the X beam along the Y beam calculated using beam theory. The second dashed line 204 represents the deflection of the Y beam (due to the weight of the X beam) relative to the location of the rear support of the X beam along the Y beam calculated using beam theory.

[0026] From the calculation results 202, 204, a YRX value 206 can be calculated. This can be accomplished by subtracting the deflection of the rear support portion from the deflection of the front support portion for a particular location of the X beam along the Y beam to find the difference in deflection for that particular location. The difference is then divided by the pitch of the support portions (in the illustrated embodiment, the pitch is 850 mm). This gives the value of YRX for that particular location of the X beam along the Y beam. Performing the calculation just described for all locations of the X beam along the Y beam and subtracting the Y=0 value of YRX from each subsequent position gives the third dotted line 206 shown in FIG. 4.

[0027] To improve the measurement accuracy and simplify the measurement operation as well, it is desirable to reduce or eliminate YRX. This can be achieved by modifying the profile of the Y beam.

[0028] One can calculate the profile of the Y beam required to reduce YRX to substantially zero for all positions of the X beam along the Y beam. With reference to FIG. 2, it will be appreciated that the amount of strain on the Y beam 108 is minimal when the X beam is located directly on top of either of the posts 104, 106. It will further be appreciated that the amount of displacement of the Y beam 108 is greatest when the X beam is located midway between the posts 104, 106 (distance Y1, shown in FIG. 2). Y It is noted that since Y1 and Y2 are not equal, the maximum displacement may not be when the X beam is exactly centered between the posts 104, 106. Still further, if the X beam is outside the middle of the two posts 104, 106 (i.e., Y1 or Y 2), it will be appreciated that there will be deformation of the Y beam 108 due to the load applied by the X beam.

[0029] It will be appreciated that to prevent deformation of the Y beam 108 due to the load applied by the X beam at all locations along the Y beam 108, the beam can be contoured such that the profile of the Y beam increases in height (z direction) based on the amount of deflection caused by the load applied by the X beam to a Y beam having a linear profile. In the present embodiment of a Y beam supported by two posts 104, 106, what has just been said would mean a contoured (i.e. non-linear) Y beam having a profile corresponding to a fourth order polynomial of the form. z=A+By+Cy 2 +Dy 3 +Ey 4 For every given value of coefficients A, B, C, D, E, it is possible to use beam theory to calculate the deflection of the Y beam (due to its weight) for the location of its front support along the Y beam and the deflection of the Y beam (due to its weight) for the location of its rear support along the Y beam, i.e. values ​​similar to lines 202, 204 in Figure 4 for every profile of the Y beam. From these values ​​the YRX of the X beam can be calculated, i.e. a value similar to line 206 shown in Figure 4.

[0030] Using a numerical method, such as the GRG nonlinear model in Microsoft XL (RTM), values ​​for the coefficients A, B, C, D, and E can be iteratively determined such that the X beam is maintained at a substantially constant orientation for all locations along the Y beam.

[0031] Figure 5 shows the desired non-linear profile 302 required for the Y beam such that the X beam is maintained at a substantially constant orientation for all locations along the Y beam. For the profile 302 shown in Figure 5, the deflection of the Y beam (due to the weight of the X beam) for the location of the front support of the X beam along Y beam 208 (similar to line 202) and the deflection of the Y beam (due to the weight of the X beam) for the location of the rear support of the X beam along Y beam 210 (similar to line 204) have been calculated and are shown in Figure 4. Also shown in Figure 4 is a line 212 (similar to line 206) showing the YRX values ​​for all locations of the X beam along the Y beam having the profile 302 shown in Figure 5.

[0032] Alternatively, the coefficients A, B, C, and D can be determined by further calculations.

[0033] In another embodiment, the desired profile for the Y beam can be determined experimentally.

[0034] In one embodiment, a beam having a desired profile can be manufactured by placing a linear beam having a desired length on two supports corresponding to the supports of the CMM and then machined to give the desired profile. Depending on the technique used for machining, it may be necessary to apply a cutter radius offset, such as that represented by line 304 in FIG.

[0035] In another embodiment, a beam with a desired profile is produced by warping the beam and machining the beam flat. What has just been described can be accomplished by placing the beam on two posts (or otherwise suspending the beam and applying a load to the beam). For example, the beam (which may or may not be a linear beam) can be loaded with at least one weight, e.g., warping the beam with a weight suspended from one or more locations along the beam between two posts. The top surface of the beam can then be machined flat. After the beam is machined flat, the weight can be removed and the unloaded beam assumes the desired shape. The location and mass of the weight depends on the shape desired for the beam after machining, and further depends on factors including the length of the beam, the cross section of the beam, the stiffness of the beam, and the load applied by (for example) an X-beam during use. Calculations to determine the mass and location of the required weight can include beam theory or can be determined experimentally.

[0036] Although embodiments have been described that relate to reducing YRX, it will be appreciated that in other embodiments, similar methodologies can be applied to X beams and quills as described above with respect to Y and X beams, for example to reduce XRY (i.e., the roll of the quill at a position along the X beam). In a still further embodiment, the Y beam is contoured such that the change in height (i.e., z position) of the X beam is reduced for all locations of the X beam along the Y beam. In the case just described, beam theory, or experiment, or numerical methods may be used to determine the height of the X beam at a position along the Y beam, and numerical methods, or calculations, or experiments may be used to calculate the desired profile of the Y beam. Other embodiments can include a contoured X beam that reduces the change in quill height at a position along the X beam.

[0037] FIG. 6(a) diagrammatically shows in plan view another example of deformation of the support 108 that can occur due to a load applied by the X beam 110, in which the deformation of the Y beam 108 is exaggerated for illustrative purposes. In the example shown in FIG. 6(a), the Y beam 108 includes a profile that is linear in the horizontal plane (i.e., parallel to the y-axis) when there is no load applied by the X beam 110. When the X beam 110 exerts a load on the Y beam 108, the Y beam 108 deforms toward the measurement area, i.e., the area below the X beam. As can be seen from FIG. 6(a), due to the deformation of the Y beam 108, the X beam 110 no longer extends parallel to the x-axis, but rotates about an axis in the z-direction (YRZ).

[0038] FIG. 6(b) diagrammatically illustrates a Y beam 108 configured to compensate for the deformation of the Y beam shown in FIG. 6(a) and reduce or eliminate the rotation of the X beam (YRZ). The profile of the Y beam 108 shown in FIG. 6(b) is before the X beam is attached. The profile of the Y beam 108 in FIG. 6(b) can be calculated by determining the deformation of a straight Y beam (i.e., the Y beam in FIG. 6(a)) when the load from the X beam is applied to all locations along the Y beam, using beam theory or experimentation in a similar manner as described for the previous embodiment. Once the deformation of the Y beam is known, the above techniques can be used to determine the profile of the Y beam 108 and reduce or substantially eliminate the YRZ.

[0039] In some aspects, the Y beams can be manufactured with a contour configured to compensate for the deformations of YRX and YRZ.

[0040] While in some of the above embodiments a coordinate measuring machine has been described that includes two spaced apart Y beams, in further embodiments two spaced apart supports may be provided, a first of the spaced apart supports including a Y beam as described above (including a beam supported on two (or more) struts) and a second support including a substantially inflexible support, i.e. a support that does not change profile due to the weight of the X beam on the support. The support could include a solid granite support, for example a piece of granite having a length in the Y direction required to allow the desired amount of X beam travel, suitably shaped for mounting the X beam, and having a height (relative to the Z axis) such that the support extends from a base to the desired height of the support.

Claims

1. 1. A positioning device comprising: a support extending in a first direction; and a beam extending in a second direction, the beam being movably attached to the support so as to be movable in the first direction and exerting a load on the support, the support including a contour that is deformed when the beam exerts the load such that the beam is maintained in a substantially constant orientation for all locations of the beam along the support.

2. 2. The positioning device of claim 1, wherein the deformation of the support due to the load applied by the beam is such that the beam is maintained at a substantially constant height for all locations of the beam along the support.

3. 2. The positioning device of claim 1, wherein the beam is maintained at a substantially constant angle relative to a horizontal plane.

4. 4. The positioning device of claim 3, wherein the beam extends between the support and a substantially inflexible support.

5. 2. The positioning device of claim 1, wherein the supports include pairs of substantially parallel, spaced apart supports.

6. 6. The positioning device of claim 5, wherein said beam extends between said pair of spaced apart supports and is movably mounted for movement in said first direction.

7. 7. The positioning apparatus of claim 5 or 6, wherein a first support of the pair of parallel spaced apart supports is optimized to maintain the beam at a constant angle and a second support of the pair of parallel spaced apart supports is optimized to maintain the beam at a constant height.

8. The positioning apparatus of claim 1 , wherein the positioning apparatus comprises a coordinate measuring machine.

9. A support for a positioning device, characterized in that it comprises the contour defined in claim 1.

10. 10. A method of manufacturing a positioning device as defined in claim 1, comprising machining the support having a contour such that when the beam exerts the load, the contour of the support is deformed such that the beam maintains a substantially constant orientation for all locations of the beam along the support.

11. The method of claim 10, wherein the contour is a non-linear contour.

12. 12. The method of claim 11, wherein at least a portion of the contour is curved.

13. 13. A method according to any one of claims 10 to 12, wherein an error map is created relating the deviation of the height and / or angle of the beam relative to its location along the support.

14. 10. A method of measuring an object using the positioning device of claim 1, comprising deforming the support with a load exerted by the beam as the beam moves along the support in the first direction such that the beam maintains a substantially constant orientation for all locations of the beam along the support.

15. 15. The method of claim 14, wherein the load exerted by the beam on the support is due to the weight of the beam.

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