Coordinate positioning machine

Abstract

A non-Cartesian coordinate positioning machine is provided, including a first platform and a second platform, and a plurality of extendable leg assemblies arranged between the first platform and the second platform for positioning the first platform and the second platform relative to each other. Each extendable leg assembly includes: (i) a first member and a second member that move relative to each other when the extendable leg assembly changes length, and (ii) a measuring member fixed to the first member for measuring the length associated with the extendable leg assembly; wherein the first member is at least partially formed of a composite material.

Description

[0001] This application is a divisional application. The original application is PCT application with application number PCT / GB2017 / 050909, application date March 31, 2017, which entered the Chinese national phase on October 8, 2018. The application number is 201780022495.X, and the title is "Coordinate Positioning Machine". Technical Field

[0002] This invention relates to a coordinate positioning machine, and more particularly to a non-Cartesian coordinate positioning machine, such as a hexapod coordinate positioning machine. Coordinate positioning machines include, for example, coordinate measuring machines (CMMs) and machine tools. Background Technology

[0003] As shown in the attached diagram Figure 1 The non-Cartesian coordinate positioning machine 1, schematically shown, generally includes first and second platforms 2, 4, which are supported by a plurality of telescopic or extendable legs 6 disposed therebetween and movable relative to each other. The extendable legs 6 are sometimes also referred to as struts or links, and in cases with six such extendable legs 6 (e.g., ...), Figure 1 As shown in the diagram, the machine is usually referred to as a hexapod.

[0004] Extendable outriggers 6 are typically mounted on platforms 2 and 4 via ball joints 8, wherein each outrigger 6 has its own ball joint 8 at one or both ends (e.g., Figure 1 As shown in the figure), or share a ball joint 8 with the adjacent leg 6 at one or both ends.

[0005] The different relative positions and orientations between the first platform and the second platforms 2 and 4 can be achieved by extending the outriggers 6 by different amounts, such as... Figure 1 As shown by arrow 7. The relative position and orientation at any given time are monitored by multiple length measuring sensors 10, for example, one of which is associated with each extendable leg 6. The length measuring sensors may include encoder scales paired with the read head.

[0006] One of platforms 2 and 4 is typically provided as part of the fixed structure of the positioning machine 1, while the other of platforms 4 and 2 moves 5 and 3 relative to the fixed structure. Components (e.g., probes or tools) can be mounted on the moving platform and the workpiece can be mounted on the fixed structure, or vice versa, to enable operations to be performed on the workpiece (e.g., measurement, probing or scanning in the case of a coordinate measuring machine, or machining in the case of a machine tool).

[0007] For example, such as Figure 1As shown, the lower platform 4 is fixed while the upper platform 2 is movable, wherein the workpiece 12 is mounted on the lower platform 4 and the probe component 14 is mounted on the upper platform 2. A working volume 9 is defined between the upper platform 2 and the lower platform 4, wherein the probe component 14 is positioned within the working volume 9 by the operation of the extendable legs 6. Although the vertical arrow 3 is shown as indicating movement, the platform 2 can of course also be moved horizontally and can also be tilted by properly controlling the respective legs 6.

[0008] Alternatively, the upper platform 2 can be fixed while the lower platform 4 is movable, wherein the probe is mounted to the lower surface of the lower platform 4 and the workpiece is mounted to part of the fixed structure located below the lower platform, such that the working volume (or operating volume) of the machine is below the lower platform 4 rather than between the upper platform 2 and the lower platform 4.

[0009] Various types of non-Cartesian coordinate positioning machines are described in more detail in WO 91 / 03145, WO 95 / 14905, WO 95 / 20747, WO 92 / 17313, WO 03 / 006837, WO2004 / 063579, WO 2007 / 144603, WO 2007 / 144573, WO 2007 / 144585, WO 2007 / 144602 and WO2007 / 144587.

[0010] For example, WO 91 / 03145 describes a hexapod machine tool including a movable upper platform attached to a base via six hydraulically extendable legs, which is similar in principle to the one described above. Figure 1 The platform shown is similar. These extendable legs are attached to the base and the movable platform via ball joints. These extendable legs are hydraulic and include piston rods that can move within a cylinder. The amount of leg extension is measured by mounting a magnetic scale to the cylinder and attaching a suitable reading head to the piston rod. Thus, the extension of the leg causes the scale to move past the reading head, allowing the length of the leg to be measured. A computer controller takes action to set the length of each leg to provide the required platform movement.

[0011] Position accuracy and repeatability are important for any measuring device, and various schemes have been proposed to improve the position accuracy and repeatability of non-Cartesian coordinate positioning machines.

[0012] For example, WO 2007 / 144573 recognizes that load forces occurring in the device during use can introduce distortion into the metering element of the device, thereby causing position inaccuracies. Therefore, WO 2007 / 144573 describes an improvement to WO 91 / 03145, wherein the position measuring device has a metering frame separate from the thrust (or load support) frame. Thus, any load forces that may occur in the load support structure are not transmitted to the metering structure, thereby preventing any substantial distortion of the metering frame and ensuring that measurement accuracy is not reduced. The spacing between the load support structure and the metering structure applies to each of the six extendable legs, wherein each leg has a load support outer structure and a metering inner structure, wherein the metering structure of these legs is mechanically isolated from the load support structure. This is from WO 2007 / 144573. Figure 3 This is especially evident in the middle.

[0013] WO 95 / 14905 describes a variant of the above-mentioned hexapod, wherein the length of each extendable leg is measured by interferometry. Summary of the Invention

[0014] A first aspect of the invention provides a non-Cartesian coordinate positioning machine including an extendable leg assembly for positioning components within the working volume of the machine. The extendable leg assembly includes a first member and a second member that move relative to each other when the extendable leg assembly changes length. The first member includes an axial arrangement of magnets forming part of a linear motor for extending and retracting the extendable leg assembly, and at least one elastic member for absorbing (arranged to absorb) at least a portion of any axial thermal expansion or contraction of these magnets in use.

[0015] The drive motors used in non-Cartesian coordinate positioning machines for extending and retracting extendable legs generate heat during operation. If this heat is not properly managed, there is a risk that it will cause thermal expansion (and subsequent contraction) of the metering structure, which in turn will adversely affect the metering results. This is especially true when the drive motor is close to or even part of the metering structure.

[0016] For example, in embodiments of the invention, the extendable leg assembly forms part of the metering structure, and a magnet arrangement is provided within the extendable leg assembly itself to form part of a linear motor for extending and retracting the extendable leg assembly. A linear motor can be considered as a motor in which the movable portion moves in a substantially linear (i.e., linear) manner. The use of an elastic member associated with or part of the magnet arrangement allows at least a portion of any thermal expansion or contraction of the magnets to be absorbed by the elastic member without affecting the length of the extendable leg assembly. This has a certain effect on improving the metering results of non-Cartesian coordinate positioning machines.

[0017] The magnets and the at least one elastic member can be axially arranged between the first stop and the second stop of the first member. At least one of the first stop and the second stop can be an end of the first member, or can be located at or near an end of the first member, or can form an end of the first member. The magnets can be internally arranged along at least a portion of the length of the first member. The at least one elastic member can be considered to be axially arranged or provided as part of an axial arrangement; the axial arrangement is therefore an axial element arrangement, wherein these elements include the magnets and the at least one elastic member.

[0018] The at least one elastic member may include a spring. The at least one elastic member may include an elastic material. The elastic material may include a silicone material. The elastic material may be non-magnetic. The elastic material may be non-conductive. The elastic material may include a low-viscosity silicone material. The elastic material may be disposed between at least some of the magnets and / or between at least one magnet and the inner wall of the first member.

[0019] The machine may include at least one non-magnetic spacer arranged axially between at least one pair of corresponding magnets of the linear motor, the at least one non-magnetic spacer being effectively part of the magnet arrangement. The at least one non-magnetic spacer may be considered as an axial arrangement or provided as part of an axial arrangement; the axial arrangement is therefore an axial element arrangement, wherein the elements include the magnets and the at least one non-magnetic spacer.

[0020] The first component and / or the second component (e.g., a tube of the first component and / or the second component) may be formed of a composite material. The composite material may include a graphite composite material. The composite material may include a carbon fiber material.

[0021] The first and second components may be elongated. The machine may include multiple such extendable leg assemblies, for example, six.

[0022] The machine can be a coordinate measuring machine. The machine can be a comparator.

[0023] The coordinate positioning machine may include a measuring component (e.g., as part of the extendable leg assembly itself) for measuring the distance between the two ends of the extendable leg assembly, or some other length associated with the extendable leg assembly. An example of such a measuring component is an encoder scale.

[0024] The machine may include a measuring component for measuring the length associated with the extendable leg assembly. The length associated with the extendable leg assembly may be the interval between the two ends of the extendable leg assembly or related to this interval. The measuring component may include an encoder scale. The measuring component may be fixed to the first member. The measuring component may be fixed to the outside of the first member, wherein the axial arrangement of the magnet is arranged within the first member.

[0025] The first component may be provided in the form of a tube.

[0026] The linear motor can be a linear shaft motor. The magnets can be permanent magnets.

[0027] The first and second components can move linearly relative to each other as the length of the extendable leg assembly changes. For example, the first and second components can slide over or across each other (e.g., telescopically). The first and second components can together form an elongated member of the extendable leg assembly.

[0028] The extendable leg assembly can be supported (or held) in the machine by at least one support member, such as at one end (or joint) of the extendable leg assembly. The extendable leg assembly can be positioned between a first platform and a second platform of the machine, wherein the first platform and the second platform are positioned relative to each other by the extendable leg assembly. A component can be attached to one of the first platform and the second platform. One of the first platform and the second platform can be fixed (stationary), wherein the component is attached to the other of the first platform and the second platform. The term "platform" is a broad term used to describe any type of structure and is not intended to imply any limitation regarding shape or form.

[0029] The machine may include a balancing arrangement for supporting at least a portion of the weight that will be additionally supported by the linear motor. This balancing arrangement may support at least a portion of the weight of the first or second platform, such as a non-stationary platform.

[0030] It will be understood that, in the cases described herein where a component is moved to a specific location within the working volume, this can be achieved by a drive mechanism provided by a coordinate positioning machine (e.g., as part of, or at least associated with, the extendable leg assembly itself), or by some external influence (e.g., by the operator manually positioning the component).

[0031] Furthermore, in describing the use of the extendable leg assembly for positioning a component within the working volume, this will be understood to mean setting the position of the component within the working volume (by actively moving the component to that position), or determining the position of the component within the working volume (the component has been moved to that position by any means), or a combination of these. In either case, positioning a component within the working volume is associated with moving the component around within the working volume and is not intended to merely cover determining the position of a static component (e.g., a workpiece) placed within the working volume.

[0032] The component may be directly or indirectly attached to the end of the extendable leg assembly and / or move together with the end of the extendable leg assembly, such that the component can be moved around within the working volume by the operation of the extendable leg assembly. The component may be a measuring probe or a portion thereof (such as a stylus or stylus tip). The component may be a tool or a portion thereof, such as a tool commonly found in machine tools for forming or machining metal or other rigid materials. The component may even be considered part of the extendable leg assembly itself (e.g., a movable end), for example defined by a ball joint at that end.

[0033] Furthermore, the term 'working volume' is intended to refer only to the portion of the working volume to which the invention has an effect. The term 'working volume' will be interpreted accordingly and should not be taken as 'at least a portion of the working volume' where appropriate.

[0034] Components located within the working volume of the machine may include measuring components or measuring instruments, such as measuring probes.

[0035] A second aspect of the invention provides a linear actuator comprising a first member and a second member that move relative to each other when the linear actuator changes length. The first member includes an axial arrangement of magnets forming part of a linear motor for extending and retracting the linear actuator, and at least one elastic member for absorbing (arranged to absorb) at least a portion of any axial thermal expansion or contraction of these magnets during use. This linear actuator can be used as an extendable leg assembly or part thereof for positioning components within the working volume of a non-Cartesian coordinate positioning machine.

[0036] A third aspect of the invention provides a non-Cartesian coordinate positioning machine comprising an extendable leg assembly for positioning components within a working volume of the machine. The extendable leg assembly includes a first member and a second member that move relative to each other when the extendable leg assembly changes length, wherein the first member and / or the second member is formed of a composite material. The composite material may include a graphite composite material. The composite material may include a carbon fiber material. The first member may include an axial arrangement of magnets forming part of a linear motor for extending and retracting the extendable leg assembly. An elastic member may provide at least a portion for absorbing any axial thermal expansion or contraction of these magnets during use.

[0037] A fourth aspect of the invention provides a non-Cartesian coordinate positioning machine including an extendable leg assembly for positioning components within a working volume of the machine. The extendable leg assembly includes: a first member and a second member that move relative to each other when the extendable leg assembly changes length; a linear motor arrangement for extending and retracting the extendable leg assembly; and a balancing arrangement for supporting at least a portion of a weight that will be additionally supported by the linear motor arrangement. The first member may include an axial arrangement of magnets forming part of the linear motor arrangement. An elastic member may provide at least a portion for absorbing any axial thermal expansion or contraction of these magnets during use.

[0038] Another aspect of the invention provides a non-Cartesian coordinate positioning machine, comprising an extendable leg assembly for positioning a component within the working volume of the machine, the extendable leg assembly being supported in the machine by at least one support member; and a retaining element for biasing the extendable leg assembly to engage with the support member. The retaining element may include a spring member.

[0039] Another aspect of the invention provides a non-Cartesian coordinate positioning machine including an extendable leg assembly for positioning components within the working volume of the machine. The extendable leg assembly is supported in the machine by at least one support member, the support member including a retention element cooperating with a retention element on the extendable leg assembly to prevent complete axial disengagement of the extendable leg assembly from the support member, while allowing disengagement of the extendable leg assembly from the support member by a substantially radial (or non-axial, or lateral) movement following a minor axial movement.

[0040] Another aspect of the invention provides a non-Cartesian coordinate positioning machine comprising an extendable leg assembly for positioning components within the machine's working volume. The extendable leg assembly includes a first member and a second member that move relative to each other when the extendable leg assembly changes length. The first member includes a magnet arrangement forming part of a linear motor for extending and retracting the extendable leg assembly; and at least one elastic member for absorbing (arranged to absorb) at least a portion of any thermal expansion or contraction of these magnets in use. The magnets may be arranged axially, and the at least one elastic member may be arranged to absorb at least a portion of any axial thermal expansion or contraction of these magnets in use.

[0041] Another aspect of the invention provides a non-Cartesian coordinate positioning machine, including a first platform and a second platform, and a plurality of extendable leg assemblies arranged between the first platform and the second platform for positioning the first platform and the second platform relative to each other, wherein each extendable leg assembly includes: (i) a first member and a second member that move relative to each other when the extendable leg assembly changes length, and (ii) a measuring component fixed to the first member for measuring the length associated with the extendable leg assembly; wherein the first member is at least partially formed of a composite material. The second member is at least partially formed of a composite material. The composite material includes a graphite composite material. The composite material includes a carbon fiber material. The measuring component includes an encoder scale. Each extendable leg assembly includes a linear motor for extending and retracting the extendable leg assembly. The linear motor includes an axial arrangement of magnets. Each extendable leg assembly includes at least one elastic member, such as an elastic material, for absorbing at least some of the magnets that would otherwise affect the length associated with the extendable leg assembly due to axial thermal expansion or contraction. The machine also includes a balancing arrangement for supporting at least some of the weight that would otherwise be supported by the operation of the linear motors. The machine comprises a metering frame and a separate thrust or load support frame. Each extendable leg assembly includes a metering structure and a thrust or load support structure, wherein the metering structure is separate from and / or mechanically isolated from the thrust or load support structure. The linear motor is located close to the metering structure and / or does not form part of the metering structure. The surface to which the metering component is fixed is at least partially formed of the composite material.

[0042] Another aspect of the invention provides a non-Cartesian coordinate positioning machine, including a first platform and a second platform, and a plurality of extendable leg assemblies arranged between the first platform and the second platform for positioning the first platform and the second platform relative to each other, wherein each extendable leg assembly includes a first member and a second member that move relative to each other when the extendable leg assembly changes length, and a linear motor for extending and retracting the extendable leg assembly, and wherein the machine further includes a balancing arrangement for supporting at least some of the weight that would otherwise be supported by the operation of the linear motor.

[0043] Another aspect of the invention provides a non-Cartesian coordinate positioning machine, including a first platform and a second platform, and a plurality of extendable leg assemblies arranged between the first platform and the second platform for positioning the first platform and the second platform relative to each other, wherein each extendable leg assembly is supported in the machine by at least one support member, and wherein: (a) a retaining element, such as a spring member, is provided for biasing the extendable leg assembly to engage with the support member; and / or (b) the support member includes a retaining element that cooperates with the retaining element on the extendable leg assembly to prevent complete axial disengagement of the extendable leg assembly from the support member when the extendable leg assembly is directly lifted off the support block, while allowing disengagement of the extendable leg assembly from the support member by a substantially radial or non-axial or lateral movement following a minor axial movement. A measuring probe is supported on the first platform or the second platform, and / or wherein the machine is at least one of: (a) a hexapod coordinate positioning machine; (b) a coordinate measuring machine; (c) a comparator; and (d) a machine tool.

[0044] Other aspects of the invention, relating to each of the foregoing aspects, provide an extendable leg assembly for use in a coordinate positioning machine. Attached Figure Description

[0045] The following examples will be used with reference to the accompanying drawings, in which:

[0046] Figure 1 This is a schematic illustration of a hexapod non-Cartesian coordinate positioning machine with six extendable legs;

[0047] Figure 2 This is an overall view of a non-Cartesian coordinate positioning machine according to an embodiment of the present invention, the non-Cartesian coordinate positioning machine including an extendable leg assembly;

[0048] Figure 3 yes Figure 2 A close-up view of a part of the machine, showing in more detail the connection between the extendable leg assembly and the lower platform of the machine;

[0049] Figure 4 yes Figure 2 A close-up view of a portion of the machine, showing the connection between the extendable leg assembly and the upper platform of the machine, specifically showing two associated constraint members in the extendable leg assembly;

[0050] Figures 5A to 5C A schematic illustration of an elongated member of an extendable leg assembly, showing an arrangement of a linear motor (or linear actuator) according to an embodiment of the invention;

[0051] Figure 6 yes Figures 5A to 5C The first component of the extendable leg assembly shown is schematically illustrated only.

[0052] Figure 7 The diagram schematically illustrates a magnet arrangement, excluding elastic members, located inside a component of a linear shaft motor according to an embodiment of the present invention.

[0053] Figures 8A to 8L It shows Figures 5A to 5C and Figure 6 Various alternative embodiments of the first component shown in the figure;

[0054] Figure 9 A view is provided that more clearly illustrates how the magnets are arranged in a practical embodiment of the invention;

[0055] Figure 10 This is an overall view of a non-Cartesian coordinate positioning machine according to another embodiment of the present invention, the non-Cartesian coordinate positioning machine including a linear motor for driving a stylus and a balancing arrangement;

[0056] Figure 11 It shows Figure 10 Another view of a non-Cartesian coordinate positioning machine; and

[0057] Figure 12 It shows Figure 10 Another view of the non-Cartesian coordinate positioning machine. Detailed Implementation

[0058] Figure 2 An overall view of a non-Cartesian coordinate positioning machine 100 implementing the present invention is provided. The non-Cartesian coordinate positioning machine 100 is in principle similar to the above reference. Figure 1 The machine described is a non-Cartesian coordinate positioning machine. Figure 2 The non-Cartesian coordinate positioning machine 100 shown includes six extendable leg assemblies 60 arranged between an upper platform 20 and a lower platform 40, these extendable leg assemblies generally having the same construction. Each of the six extendable leg assemblies 60 includes an upper tube 62 and a lower tube 64, wherein the upper tube 62 slides telescopically within the lower tube 64.

[0059] At once Figure 2 In the specific example shown, the upper platform 20 is fixed, while the lower platform 40 is movable relative to the upper platform by operating six extendable leg assemblies 60, wherein the probe 14 is mounted to the lower surface of the lower platform 40. In this configuration, a workpiece (not shown) is mounted on a portion of the fixed structure of the machine 100, located below the lower platform 40, such that the working volume of the machine 100 is below the lower platform 40 rather than between the upper platform 20 and the lower platform 40.

[0060] and Figure 1 Like the machine, the extendable leg assembly 60 is used to support the components (in) Figure 2 In the example shown, the component is probe 14, or at least a specific portion of probe 14 (such as the tip of probe 14), positioned within the working volume of the machine. Constraint members 50, each associated with the extendable leg assembly 60, prevent (or at least reduce) unwanted rotation of the extendable leg assembly 60 about its corresponding longitudinal axis.

[0061] The upper and lower ends of each extendable outrigger assembly 60 are connected to the upper platform 20 and the lower platform 40 respectively via separate ball joints 80. Figure 2 Only the lower ball joints 80 of the first two extendable leg assemblies in the extendable leg assembly 60 are visible, while Figure 3 The lower ball joint is shown in more detail below. The lower ball joint 80 is supported by the support block 42 of the lower platform 40, while the upper platform 20 is supported on the upper ball joint 80 via the support block 22 of the upper platform 20. Figure 4 The connection between the upper platform 20 and the extendable leg assembly 60 is shown in more detail.

[0062] The upper tube 62 and lower tube 64 of each extendable outrigger assembly 60 enclose the elongated member 66. Figure 2 One of the extendable leg assemblies is shown in dashed outline, where the encoder scale 10 is fixed to an elongated member 66. The elongated member 66 itself is extendable, for example, by means of a telescopic arrangement. Each elongated member 66 extends from its upper connector 80 to its lower connector 80, and it is precisely the corresponding length of the elongated member 66 that determines the precise positioning and orientation of the lower platform 40 (and therefore the probe 14). Therefore, it is precisely the length of the elongated member 66 that must be precisely measured during workpiece measurement or scanning operations to determine the precise position of the stylus tip when it contacts the workpiece surface. See below for reference. Figures 5A to 5C The operation of the extendable slender member 66 is described in more detail.

[0063] Figure 3 This is a close-up view, showing in more detail the connection between the extendable leg assembly 60 and the lower platform 40. (As shown in...) Figure 3The bottom, shown in a zoomed-out view, features three spheres 84 arranged in a triangle at the lower end of the elongated member 66, with the plane of this triangle substantially perpendicular to the longitudinal axis of the elongated member 66. A support block 42 has a larger, fixed sphere 82 that acts to support the three spheres 84 at the end of the elongated member 66, with the larger sphere 82 nested within the smaller spheres 84.

[0064] At the upper end, each extendable leg assembly 60 has a constraint member 50 (or associated therewith) that is attached to an elongated member 66 of the extendable leg assembly 60 and to another member (support block 22) disposed on the upper platform 20. The constraint member 50 effectively 'ties' the elongated member 66 to the upper platform 20 in order to prevent (or at least reduce) undesirable rotation of the elongated member 66 about its longitudinal axis.

[0065] Figure 4 This is a close-up view, showing in more detail the connection between the extendable leg assembly 60 and the upper platform 20 of the machine 100, specifically showing in more detail the connection with... Figure 2 The extendable leg assembly 60 comprises two associated restraint members 50. The restraint member 50 can generally be described as a multi-part or multi-segment hinge. The illustrated example includes four parts or segments 52, 54, 56, and 58, which are connected by rotary joints or joints 53, 55, and 57 having substantially parallel axes of rotation. Joints 53, 55, and 57 may have a standard pin and bearing configuration, and ball bearings may be used to reduce frictional effects. The use, construction, and operation of the restraint member 50 are described in more detail in co-pending UK patent application number 1513850.6.

[0066] Now refer to Figures 5A to 5C , Figure 6 and Figures 8A to 8L The linear motor (or linear actuator) used for extending and retracting the extendable leg assembly 60 is described in more detail.

[0067] Figure 5 A to Figure 5C This is a schematic illustration of an elongated member 66 of one of the extendable leg assemblies 60. The elongated member 66 includes a first elongated member and second elongated members 63 and 65 that move relative to each other when the extendable leg assembly 60 changes length. The first elongated member and the second elongated members 63, 65 are arranged such that their respective longitudinal axes are substantially aligned with each other, and slide over or across each other when the extendable leg assembly 60 extends and retracts. (See Figures 5A to 5B) Figure 5C In the example shown, the first elongated member 63 slides telescopically within the second member 65. For simplicity, the first elongated member 63 and the second elongated member 65 will be referred to as the first member 63 and the second member 65, respectively.

[0068] The first component 63 includes a plurality of magnets 72 arranged internally along at least a portion of its length, these magnets 72 forming part of a linear motor 70 for extending and retracting the extendable leg assembly 60. This type of linear motor is sometimes referred to as a linear shaft motor. In the illustrated example, the N / S orientation of the magnets alternates along a series of magnets 72, with the N or S pole of one magnet 72 facing the N or S pole of an adjacent magnet 72 in the series, although other arrangements are possible.

[0069] The second component 65 is provided with a coil 74 for forming another part of the linear motor. The coil 74 is sometimes referred to as a force applicator and in this example is shown as a three-phase coil with three phases represented by U, V, and W. This type of linear shaft motor is known, therefore a detailed explanation is not required here regarding how the three-phase U, V, and W coils relate to the N and S pole positions of the magnet 72, nor is a detail about how to control these three phases U, V, and W to actuate the motor.

[0070] Figure 5A , Figure 5B and Figure 5C The extendable leg assembly 60 is shown to have three different corresponding extension configurations L1, L2 and L3 for three corresponding positions of the probe component 14 in the working volume.

[0071] exist Figure 5A In this configuration, the extendable outrigger assembly 60 is fully extended, or at least fully extended to the extent permitted by the linear motor 70. Figure 5B In this configuration, the extendable leg assembly 60 is slightly retracted, wherein the coil 74 has been controlled to generate a magnetic field that interacts with the magnet 72 to produce a force that moves the first member 63 relative to the second member 65, causing the first member 63 to retract further into the second member 65, thereby shortening the overall length of the extendable leg assembly 60. Figure 5C In the middle, the extendable outrigger assembly 60 is further retracted.

[0072] Figure 6 A separate, unaffected first member 63 is shown, and thus the magnet arrangement 72 within the first member 63 is shown more clearly. The first member 63 is in the form of a hollow tube 78 having any suitable cross-section (e.g., square or circular). As can be seen, the magnet 72 extends substantially from a first end 77 of the first member 63 to the other (second) end 79, which facilitates maximizing the range of relative displacement between the first member 63 and the second member 65, and thus maximizing the extension and retraction range of the extendable leg assembly 60.

[0073] To provide the key benefits of the invention, in this embodiment, an elastic material 76 is provided around the magnets 72, that is, between the magnets 72 and also between the ends 77, 79 of the stack of magnets 72 and the first member 63.

[0074] Typically, in linear actuators, the presence of this elastic (or flexible or compliant) material 76 is unnecessary or even disregarded by the technician. For example, Figure 7 The diagram schematically illustrates how a component 630 of a linear axis motor (not shown in the first aspect of the invention) is typically constructed, wherein a magnet 720 extends from one end to the other without any gaps or “wasted” space.

[0075] However, when using such in the context of non-Cartesian coordinate positioning machines Figure 7 When examining the linear actuator component 630 shown, the applicant discovered that very small measurement inaccuracies (though small, significant in the context of high-precision metrology) could be attributed to the design of the actuator component, and specifically to the arrangement of the magnets therein. The applicant determined that these metrological errors were caused by the thermal expansion and contraction of the magnets within the actuator component, which in turn led to minute changes in the length of the actuator component, and thus to metrological errors. These effects are typically insignificant in linear motors because the function of the linear motor is not affected, but they are significant in a metrological context. This problem is exacerbated because the heat generated in the linear motor coils is very close to the magnets.

[0076] By using elastic materials (as shown in Figure 5A to...) Figure 5C and Figure 6 (As shown) to absorb at least a portion of any thermal expansion or contraction of the magnet in use, the applicant has overcome this problem, which is very specific to the metrological context. It has been found that this can significantly improve metrological results. Figure 6 In the embodiment shown, the magnet effectively “floats” inside the first member 63, although the elastic material 63 has sufficient mechanical stiffness so that the electromagnetic force acting on the magnet 72 due to the action of the coil 74 is transmitted to the housing of the first member 63 so that the first member (and not just the magnet 72) moves relative to the second member 65.

[0077] It will be understood that the present invention is not limited to Figure 6 The arrangement shown in which the linear motor magnet 72 is effectively embedded or floated within the elastic material 76. Reference will now be made to... Figures 8A to 8L The illustration shown is used to describe the implementation and Figure 6 Various alternative embodiments of the technical benefits shown are similar to those of the technical benefits.

[0078] For ease of comparison, Figure 6 Repeated as Figure 8A .exist Figure 8B In the illustrated embodiment, spacers 71 are axially arranged between magnets 72, with each spacer 71 contacting a magnet 72 on each side. There are no gaps between the spacers 71 and the magnets 72, and therefore no elastic material 76 between the magnets 72. However, when considered as a stack (or group), there are gaps filled with elastic material 76 at each end of the stack (between the magnets 72 and the first and second ends 77, 79 of the member 63). The elastic material 76 at each end is sufficient to absorb the thermal expansion of the magnets 72.

[0079] It doesn't even require the elastic material 76 at each end of the magnet 72 stack. Figure 8C One embodiment is shown in which the elastic material 76 is disposed only at one end, there are spacers between each magnet 72, and there is also a spacer between the first magnet 72 and the first end 77 of the member 63. The elastic material 76 at the second end 79 is sufficient to absorb the thermal expansion of the magnet 72.

[0080] For elastic material 76, the applicant has determined that low-viscosity silicones provide good results. Silicones are polymers comprising any inert, synthetic compound consisting of repeating siloxane units, which are chains of alternating silicon and oxygen atoms, typically bonded to carbon and / or hydrogen. Figure 8B and Figure 8C The spacer 71 is non-magnetic (e.g., formed of aluminum) and has mechanical rigidity. In one embodiment, the spacer 71 is half the length (in the axial direction) of the magnet 72.

[0081] It can be constructed by alternately inserting the magnet 72 and the spacer 71 into the second end 79 of the opening of the first member 63. Figure 8C In the illustrated embodiment, as each new magnet 72 or spacer is inserted into the first end 79, the ever-elongating stack of magnets 72 and spacers 71 is continuously pushed toward the first end 77 into the tube 78. The tube 78 may be initially open at both ends, or closed at one end and open at the other end, to allow insertion of the magnets 72 and spacers 71.

[0082] The magnets and spacers typically have a cross-section similar to, but slightly smaller than, the inner profile of the first member 63 to allow them to move from the second end 79 to the first end 77 without flipping over (especially considering the repulsive magnetic force exerted by the adjacent magnets 72), but have small gaps in the radial direction to allow them to move freely.

[0083] All the magnets and spacers are pushed together in this manner so that they come into contact with each other in the axial direction to form a stack extending most of the length of the tube 78, but leaving a small gap at the second end 79. Silicone is then injected into the tube 78 to fill the aforementioned radial gap between the stack and the inner wall of the tube 78, as well as the axial gap at the second end 79.

[0084] In a metrological context, the presence of a small radial gap and therefore the presence of an elastic material 76 within this gap is not particularly advantageous, since the radial thermal expansion of the magnet 72 (and thus the tube 78) generally does not affect the metrological results. However, the presence of the elastic material 76 within the radial gap at least helps prevent the magnet 72 from wobbling around, and doing so is mechanically advantageous. Not only is this wobbling noise (and disturbing in high-precision instruments), but associated vibrations can also negatively impact metrology. Therefore, preventing such radial movement can also benefit metrological results, but not as obviously or directly as the benefits derived from having an elastic material arranged to absorb thermal expansion and contraction in the radial direction.

[0085] Figure 8D An embodiment is schematically shown in which the elastic member, in the form of a spring member 73, is disposed between the end magnet 72 and the second end 79 of the first member 63. Like... Figures 8A to 8C The elastic material 76 is the same. Figure 8D The spring member 73 actuates to absorb at least a portion of any thermal expansion and contraction of the magnet 72 in the axial direction.

[0086] Figure 8D It is also shown that the elastic material 76 is not necessary to surround the magnet 72 in the radial direction, because Figure 8D The embodiment does not have this feature. The air gap should ideally be small enough to prevent significant radial movement of the magnet 72, but not too small, otherwise the radial thermal expansion of the magnet 72 would cause it to expand into the tube 78. Meanwhile, the radial thermal expansion of the tube 78 will not directly affect the metering because such thermal expansion does not cause a change in the length of the first member 63. If the magnet 72 radially pushes against the inner wall of the tube 78, further thermal expansion of the frictionally engaged magnet 72 could lead to axial expansion of the first member 63 (which could directly affect the metering). However, if the friction between the magnet 72 and the tube 78 is low enough to allow the magnet 72 to expand freely in the axial direction, no radial gap is needed at all; this applies to… Figures 8A to 8L All embodiments shown.

[0087] Figure 8E The illustrated embodiments are similar to Figure 8DThe embodiments are similar, except that the elastic material 76 has been injected downward along the radial gap to prevent radial movement (e.g., wobbling) of the magnet 72.

[0088] Figure 8F The illustrated embodiments are similar to Figure 8D Similar embodiments exist, in which the spring member 73 is replaced by a general-purpose elastic member 75, which can be of any suitable form. For example, the elastic member 75 can take the form of a rubber spacer or a rubber block.

[0089] Figure 8G It is shown that the elastic member 75 does not have to be located at either end of the stack of magnets 72, but can be located anywhere in the middle. Figure 8H The spring member 73 is shown to be compatible with... Figure 8B The inelastic spacer 71 described herein is used in conjunction with it. Figure 8I The diagram shows a combination of an elastic spacer 75 and a non-elastic spacer 71 that can be used. Figure 8J It is shown that the elastic spacer 75 can be disposed at each end of the stack and between each pair of adjacent magnets 72. Figure 8K yes Figure 8J A variant in which elastic material 76 fills the radial gap.

[0090] at last, Figure 8L This demonstrates that the stack does not necessarily extend from one end of tube 78 to the other. The axial arrangement of magnet 72 and spacer 71 is held in place within tube 78 by two stops 69, a position that can be offset any suitable distance from either end of tube 78. Figure 8L In the demonstration, both stops 69 are offset from the corresponding ends 77, 79 of the tube 78, but one or both stops 69 may coincide with ends 77, 79. Stops 69 may form the ends 77, 79 of the tube 78, for example, forming caps. Figures 8A to 8K In the illustrated embodiment, the stop 69 is provided at the corresponding ends 77 and 79 of the tube 78.

[0091] according to Figures 8A to 8LIt is evident that there are various ways in which embodiments of the invention can be implemented. A common feature is that the first member 63 includes an axial arrangement of a magnet 72 forming part of a linear motor 70 for extending and retracting the extendable leg assembly 60, and elastic members 73, 75, 76 arranged to absorb at least a portion of any axial thermal expansion or contraction of the magnet 72 in use. Generally, this can be considered an axial element arrangement, wherein the elements of this axial arrangement include at least the magnet 72 and elastic members 75 (wherein elastic member 75 represents any suitable elastic member, including spring 73 or elastic material 76), and optionally elements such as non-magnetic spacers 71. The presence of the elastic members as part of the axial element arrangement results in at least a portion of any thermal expansion and contraction of the magnet being absorbed in use. The axial element arrangement may be disposed between the two stops described above, which may be respective ends of the member.

[0092] It should be understood that the magnets do not have to be arranged in the order NS-SN-NS-SN-NS as shown, and other arrangements are possible.

[0093] Although Figure 5 A to Figure 5C , Figure 6 and Figures 8A to 8L The first component 63 is shown in a rather illustrative manner, but Figure 9 A more realistic (less illustrative) view is provided to more clearly show how the magnet 72 is arranged in a practical embodiment of the invention. Figure 9 In the middle, the hollow tube 78 of the first component 63 is partially cut off to show the alternating magnets 72 and spacers 71, for example as shown in the image. Figure 8C The hollow tube 78 is schematically depicted. It has a generally square cross-section. Similarly, the magnet 72 has a generally square cross-section to match the cross-section inside the hollow tube 78, however, the former is smaller to allow for the small radial clearance described above. In this example, the magnet 72 is provided with chamfered corners and edges, such that these magnets can pass through the tube 78 at least partially when the first members 63 are placed together. In this example, the spacer 71 has a generally circular cross-section. An encoder scale 10 fixed to the outside of the tube 78 is also shown.

[0094] It should be understood that although the magnets are shown as separate from each other, i.e. formed as individual elements, in the accompanying drawings, a single block of magnetic material can be magnetized in some way to form multiple magnets within the same block of material. Therefore, multiple magnets are not to be construed as being limited to multiple individual and separate magnetic elements.

[0095] Just as the thermal expansion of magnet 72 leads to an increase in the length of the first component 63, the applicant has also recognized that the material of the tube 78 forming the first component 63 may itself be subject to thermal expansion, and is in fact the material of the second component 65. Therefore, the applicant has found it advantageous to form the first component 63 and / or the second component 65 from a composite material (such as carbon fiber) having a very low coefficient of thermal expansion and high specific stiffness (stiffness divided by density) and high specific strength (strength divided by density).

[0096] The applicant has found, as described above, that the use of a linear motor (or linear actuator) 70 is very convenient and effective for extending and retracting the extendable leg assembly 60 of a non-Cartesian coordinate positioning machine. As per... Figure 2 Clearly, the weight of the lower platform 40 and probe 14 is supported by extendable leg assemblies 60, which in turn are formed from the first telescopic member 63 and the second telescopic member 65. As described above, a linear motor 70 is provided for moving members 63 and 65 relative to each other. Furthermore, the linear motor 70 is also needed to prevent the two members 63 and 65 from being pulled apart, for example, under the influence of gravity acting on the lower platform 40 and probe 14. Therefore, in this case, the linear motor 70 also typically acts as a kind of brake, applying a force equal to and opposite to gravity to keep the platform 40 stationary when the system is "stopped".

[0097] The applicant has recognized that this presents a problem related to the aforementioned issue in the context of metrology, namely, heat generation from the linear motor 70. This heat has a negative impact on metrology because it causes thermal expansion and contraction of components in the metering loop, resulting in inaccurate measurement results. Figures 10 to 12 As shown, the applicant has solved this problem by introducing a balancing arrangement 90, which is specific to the combination of a non-Cartesian coordinate positioning machine and the use of a linear motor for outrigger extension.

[0098] The balancing arrangement 90 acts to support at least a portion of the weight of the lower (moving) platform 40 and any components attached to it, thereby reducing the load on the linear motor 70 (relieving stress). Since the weight is no longer supported by the linear motor 70, the current flowing through the coil 74 can be significantly reduced, and consequently, the heat generated by the coil is also reduced. A combination of a non-Cartesian coordinate positioning machine, a linear motor for outrigger extension, and a balancing arrangement for reducing stress on the linear motor has not been previously proposed.

[0099] It should be understood that the balancing arrangement 90 does not need to provide support precisely equal to the weight carried by the linear motor. This is the ideal situation, but in practice, a benefit is achieved by balancing at least a portion of this weight, as the current flowing through coil 74 is reduced. Therefore, the design of the balancing arrangement 90 is not critical, as providing precise balance is not required, which is particularly difficult to achieve across the entire working volume of machine 100. Therefore, based on known balancing arrangements of this type, those skilled in the art will not have difficulty providing a suitable balancing arrangement.

[0100] By way of the example shown, Figures 10 to 12 An example design of the balancing arrangement 90 is shown, but this is in no way intended to limit the scope of the invention. This example of the balancing arrangement 90 includes a first arm 92 and a second arm 94 connected to each other via a joint 93. The first arm 92 is connected to the top of the lower platform 40 via the joint 92, and the second arm 94 is connected to a fixed portion (not shown) of the machine 100 via a joint 95. Figure 11 (Most clearly shown). Figure 12 Details of connector 93 are shown.

[0101] Figure 10 (Most clearly shown in the extended sub-view) Two additional advantageous features of this embodiment are also shown, which can be used independently of the balanced arrangement 90. First, a retaining spring 88 is provided for each ball joint 80, which is connected on one side to the support block 42 of the lower platform 40 and on the other side to the lower end of the extendable leg assembly 60. The retaining spring 88 holds the three balls 84 at the end of the elongated member 66 (see...) Figure 3 The extended subview) is biased to contact the ball 82 on the support block 42 and helps prevent the extendable leg assembly 60 from being lifted off the support block 42 and removed from the support block during use (which can happen accidentally by a large and unintentional movement of the lower platform 40). Therefore, this retaining element acts to bias the extendable leg assembly 60 into engagement with the support of the extendable leg assembly 60.

[0102] Secondly, a retaining cover 86 is provided on the support block 42, which at least partially surrounds (captures) a retaining flange 87 located at the lower end of the extendable leg assembly 60. When attempting to lift the extendable leg assembly 60 directly away from the support block 42, the retaining flange 87 is contained within the cover 86, thus preventing the extendable leg assembly 60 from completely disengaging from the support block 42. This again helps to prevent the extendable leg assembly 60 from being accidentally lifted away from the support block 42 and detached from the support block during operation. However, the retaining cover 86 is open to one side, and there is a small gap above the retaining flange 87 when engaged, thereby allowing the retaining flange 87 (and therefore the extendable leg assembly 60) to disengage by lateral movement following a slight lift. More generally, this retention feature includes a retention feature on the support that cooperates with the retention feature on the extendable leg assembly to prevent complete axial disengagement while allowing disengagement by substantially radial movement following a small axial gap.

[0103] The combination of the two retention features described above is particularly advantageous because the retention cap 86 and the retention flange 87 prevent serious disengagement, while the retention spring 88 helps to prevent the flange 87 from accidentally separating from the retention cap 86 by biasing the balls 82, 84 into engagement (and thus prevents the radial movement required to remove the flange 87 from the cap 86).

[0104] At least in Figure 2 and Figure 10 Another advantageous feature of the machine 100 shown is that the upper platform 20 (also referred to as the "top frame") is removable (detachable) from the machine 100. In known non-Cartesian machines, the top frame typically forms an integral part of the machine and is not removable. In the illustrated embodiment, the upper platform 20 comprises six balls, which are equivalent to... Figure 3 The balls marked 82 are included, and the upper platform 20 is removable, which allows the platform 20 (including the balls) to be measured using a CMM for calibration purposes, and the platform can then be returned to the machine 100, for example, to measure the position and / or spacing of the balls.

[0105] Although the non-Cartesian coordinate positioning machine shown in the accompanying drawings has six extendable leg assemblies, the non-Cartesian coordinate positioning machine implementing the present invention is certainly not limited to having six extendable leg assemblies, wherein the number and configuration of the extendable leg assemblies are determined by the application of interest.

[0106] Although embodiments of the invention have been described primarily in the context of coordinate measuring machines and comparators, the invention is more generally applicable to any type of coordinate positioning machine, such as scanners, machine tools, robots, positioning devices (e.g., for optical components), prototyping machines, and various other uses.

Claims

1. A non-Cartesian coordinate positioning machine comprising a first platform and a second platform, and a plurality of extendable leg assemblies arranged between the first and second platforms for positioning the first and second platforms relative to one another, wherein, Each extendable leg assembly includes: (i) a linear motor for extending and retracting the extendable leg assembly; (ii) a first member and a second member that move relative to each other as the extendable leg assembly changes length, and (iii) an encoder scale (10) fixed to the first member for measuring a length associated with the extendable leg assembly; wherein a surface of the first member to which the encoder scale (10) is fixed is at least partially formed from a composite material.

2. The machine of claim 1, wherein, The second member is at least partially formed from a composite material.

3. The machine of claim 1 or 2, wherein, The composite material comprises a graphite composite material.

4. The machine of claim 1 or 2, wherein, The composite material comprises a carbon fibre material.

5. The machine of claim 1, wherein, The linear motor comprises an axial arrangement of magnets.

6. The machine of claim 5, wherein, Each extendable leg assembly includes at least one resilient member for absorbing at least some axial thermal expansion or contraction of the magnets that would otherwise affect a length associated with the extendable leg assembly.

7. The machine of claim 5 or 6, wherein, The machine further includes a counterbalance arrangement for supporting at least some weight that would otherwise be supported by operation of the linear motor.

8. The machine of claim 1, wherein, The machine has a metrology frame and a separate thrust or load bearing frame.

9. The machine of claim 1, wherein, Each extendable leg assembly includes a metrology structure and a thrust or load bearing structure, wherein the metrology structure is separate and / or mechanically isolated from the thrust or load bearing structure.

10. The machine of claim 9, wherein, The linear motor is proximate to the metrology structure, and / or the linear motor does not form part of the metrology structure.

11. The machine of claim 6, wherein, The at least one resilient member is a resilient material.

12. The machine of claim 1, wherein, A measurement probe is supported on the first or second platform, and / or wherein The machine is at least one of: (a) a hexapod coordinate positioning machine; (b) a coordinate measuring machine; (c) a comparator; and (d) a machine tool.

13. A non-Cartesian coordinate positioning machine comprising a first platform and a second platform, and a plurality of extendable leg assemblies arranged between the first and second platforms for positioning the first and second platforms relative to one another, wherein, Each extendable leg assembly includes a first member and a second member that move relative to each other as the extendable leg assembly changes length, and a linear motor for extending and retracting the extendable leg assembly, wherein the machine further includes a counterbalance arrangement for supporting at least some weight that would otherwise be supported by operation of the linear motor, and wherein the counterbalance arrangement is connected between the first platform and the second platform.

14. The machine of claim 13, wherein, A measurement probe is supported on the first or second platform, and / or wherein The machine is at least one of: (a) a hexapod coordinate positioning machine; (b) a coordinate measuring machine; (c) a comparator; and (d) a machine tool.

15. A non-Cartesian coordinate positioning machine comprising a first platform and a second platform, and a plurality of extendable leg assemblies arranged between the first and second platforms for positioning the first and second platforms relative to one another, wherein, Each extendable leg assembly is supported in the machine by at least one support, and wherein: the support includes a retention element that cooperates with a retention element on the extendable leg assembly to prevent the extendable leg assembly from becoming fully axially disengaged from the support when the extendable leg assembly is lifted directly off the support, while allowing the extendable leg assembly to be disengaged from the support through a combination of non-axial and axial movement.

16. The machine of claim 15, wherein, A measurement probe is supported on the first or second platform, and / or wherein The machine is at least one of: (a) a hexapod coordinate positioning machine; (b) a coordinate measuring machine; (c) a comparator; and (d) a machine tool.

17. The machine of claim 15, wherein, The binding is non-axial movement following a small axial movement.

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