Coordinate positioning machine

Abstract

A coordinate positioning machine comprises a drive frame (37) and a metrology frame (36). The drive frame (37) comprises a drive arrangement (28) for moving a movable structure (22) around within a working volume (34) of the machine. The metrology frame (36) comprises a metrology arrangement (26) for measuring the position of the structure (22) within the working volume (34). In one aspect, the metrology arrangement (26) is a hexapod metrology arrangement and the drive arrangement (28) is a non-hexapod drive arrangement. The coefficient of thermal expansion of the metrology frame (36) is lower than the coefficient of thermal expansion of the drive frame (37). The drive frame (37) is coupled to the metrology frame (36) via a coupling arrangement (38) that prevents at least a portion of deformation associated with any additional thermal expansion and contraction of the drive frame (37) from being transferred to the metrology frame (36). In another aspect, the drive arrangement (28) moves the structure (22) about within the working volume (34) in less than six degrees of freedom, and the metering arrangement (26) measures the position of the structure (22) within the working volume (34) in more degrees of freedom than the drive arrangement (28).

Description

[0001] The present invention relates to a coordinate positioning machine. Coordinate positioning machines include, for example, coordinate measuring machines (CMMs) and machine tools.

[0002] In the attached figure Figure 1 A non-Cartesian coordinate positioning machine 1 is schematically illustrated in FIG. The coordinate positioning machine 1 generally includes a first structure 2 and a second structure 4 that are supported and move relative to each other by a plurality of retractable or extendable legs 6 disposed therebetween. The first structure 2 and the second structure 4 are sometimes referred to as platforms or tables, and the extendable legs 6 are sometimes referred to as struts or links. In the case where there are six such extendable legs 6 (e.g., Figure 1 ), the machine is often referred to as a hexapod.

[0003] The extendable legs 6 are typically mounted on the structures 2, 4 via ball joints 8, wherein each leg 6 has its own ball joint 8 at either one or both ends (e.g. Figure 1 ), or share a ball joint 8 at one or both ends with an adjacent leg 6. Each extendable leg 6 is typically formed as a pair of tubes, one of which is telescopically movable within the other by a drive mechanism (e.g., a motor) to extend and retract the extendable leg 6.

[0004] Various relative positions between the first structure 2 and the second structure 4 can be achieved by extending the legs 6 by different amounts, such as Figure 1 4. The relative position at any moment is monitored by a plurality of length measuring transducers 10, for example one of which is associated with each extendable leg 6. Each length measuring transducer 10 may comprise an encoder scale paired with a read head, wherein the encoder scale is suitably mounted to one of a pair of telescopic tubes and the read head is suitably mounted to the other tube. Extension of the leg 6 thus causes the encoder scale to move past the read head, thereby allowing the length of the extendable leg 6 to be measured. The computer controller 5 operates to set the length of each extendable leg 6 to provide the required relative movement between the structures 2, 4. By having six such length measuring transducers 10, relative position can be measured in six corresponding respective degrees of freedom (three translational degrees of freedom and three rotational degrees of freedom).

[0005] One of the structures 2, 4 is typically arranged as part of a fixed structure of a coordinate positioning machine 1, wherein the other of the structures 4, 2 moves 12, 11 relative to the fixed structure. A tool (e.g. a measuring probe or a drill bit) may be mounted on the mobile structure and a workpiece mounted on the fixed structure, or vice versa, to enable operations to be performed on the workpiece (e.g. measuring, probing or scanning in the case of a coordinate measuring machine, or machining in the case of a machine tool).

[0006] For example, Figure 1 , the lower structure 4 is fixed and the upper structure 2 is movable, the workpiece 9 is mounted on the lower structure 4 and the probe member 3 is mounted on the upper structure 2. When the upper structure 2 and the lower structure 4 are in their most distant positions, a working volume 14 is defined between the upper structure and the lower structure, and the probe member 3 is positioned in the working volume 14 by operation of the extendable legs 6. Although the arrows 11 are shown as indicating translational movement, the structure 2 can also be tilted by appropriate control of the individual legs 6.

[0007] Alternatively, the upper structure 2 may be fixed and the lower structure 4 movable, with the probe mounted to the lower surface of the lower structure 4 and the workpiece mounted to a portion of the fixed structure located below the lower structure, so that the working volume (or operating volume) of the machine is located below the lower structure 4 rather than above it.

[0008] 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, WO 2004 / 063579, WO 2007 / 144603, WO 2007 / 144573, WO 2007 / 144585, WO 2007 / 144602 and WO 2007 / 144587.

[0009] For example, WO 91 / 03145 describes a hexapod machine tool comprising a movable superstructure attached to a base by six hydraulically extendable legs, similar in principle to the above-mentioned Figure 1 The extendable legs are attached to the base and movable structure via ball joints. The extendable legs are of the hydraulic type and comprise a piston rod movable within a cylinder. The amount of leg extension is measured by mounting a magnetic scale to the cylinder and a suitable read head on the piston rod. Thus, extension of the leg causes the scale to move past the read head, allowing the length of the leg to be measured. A computer controller operates to set the length of each leg to provide the required movement.

[0010] EP 3054265 A1 discloses using a delta robot to move an end effector and using an imaging detector to capture image data of at least a portion of the end effector. Based on the captured image data, in particular based on reference points on the end effector, the position of the end effector can be determined by photogrammetry.

[0011] According to a first aspect of the invention, there is provided a coordinate positioning machine comprising a drive frame and a metrology frame, the drive frame comprising a drive arrangement for moving a movable structure around within a working volume within the machine, and the metrology frame comprising a metrology arrangement for measuring the position of the mechanism within the working volume, wherein the metrology arrangement is a hexapod metrology arrangement and the drive arrangement is a non-hexapod drive arrangement, wherein the coefficient of thermal expansion of the metrology frame is lower than the coefficient of thermal expansion of the drive frame, thereby causing (in use) the drive frame to have additional thermal expansion and contraction compared to the metrology frame, and wherein the drive frame is connected to the metrology frame via a coupling arrangement, the coupling arrangement preventing (being suitable for preventing) at least a portion of thermal expansion or contraction of the drive frame (compared to the metrology frame), or at least a portion of deformation associated with additional thermal expansion or contraction of the drive frame (compared to the metrology frame), from being transmitted to the metrology frame.

[0012] According to a second aspect of the invention, there is provided a coordinate positioning machine comprising a drive frame and a metrology frame, the drive frame comprising a drive arrangement for moving a movable structure around within a working volume of the machine in less than six degrees of freedom, and the metrology frame comprising a metrology arrangement for measuring the position of the structure within the working volume in more degrees of freedom than the drive arrangement, wherein the metrology frame has a coefficient of thermal expansion lower than that of the drive frame, thereby causing (in use) the drive frame to have additional thermal expansion and contraction compared to the metrology frame, and wherein the drive frame is coupled to the metrology frame via a coupling arrangement, the coupling arrangement preventing (being suitable for preventing) at least a portion of thermal expansion or contraction of the drive frame (compared to the metrology frame), or at least a portion of deformation associated with additional thermal expansion or contraction of the drive frame (compared to the metrology frame), from being transmitted to the metrology frame.

[0013] According to a third aspect of the invention, there is provided a coordinate positioning machine comprising a drive frame and a metrology frame, the drive frame comprising a drive arrangement for moving a movable structure around within a working volume within the machine, and the metrology frame comprising a metrology arrangement for measuring the position of the structure within the working volume, wherein the metrology arrangement comprises a plurality of measurement transducers arranged in parallel for providing a corresponding plurality of measurement values ​​from which the position of the movable structure can be determined, wherein the drive arrangement comprises a plurality of mechanical linkages arranged in parallel between the movable structure and a fixed structure of the machine , and wherein each mechanical linkage is actuated by a drive mechanism acting between the fixed structure and the mechanical linkage, wherein the coefficient of thermal expansion of the metrology frame is lower than the coefficient of thermal expansion of the drive frame, thereby causing (in use) the drive frame to have additional thermal expansion and contraction compared to the metrology frame, and wherein the drive frame is connected to the metrology frame via a coupling arrangement, which prevents (is suitable for preventing) at least a portion of thermal expansion or contraction of the drive frame (compared to the metrology frame) or at least a portion of deformation associated with additional thermal expansion or contraction of the drive frame (compared to the metrology frame) from being transmitted to the metrology frame.

[0014] According to a fourth aspect of the invention, there is provided a coordinate positioning machine comprising a drive frame and a metrology frame, the drive frame comprising a drive arrangement for moving a movable structure around within a working volume within the machine, and the metrology frame comprising a metrology arrangement for measuring the position of the mechanism within the working volume, wherein the metrology arrangement comprises a plurality of measuring transducers arranged in parallel for providing a corresponding plurality of measurement values ​​from which the position of the movable structure can be determined; and wherein the drive arrangement comprises a plurality of actuators arranged in parallel of a type different from that of the metrology arrangement, wherein the coefficient of thermal expansion of the metrology frame is lower than the coefficient of thermal expansion of the drive frame, thereby causing (in use) the drive frame to have additional thermal expansion and contraction compared to the metrology frame, and wherein the drive frame is coupled to the metrology frame via a coupling arrangement, the coupling arrangement preventing (being suitable for preventing) at least a portion of thermal expansion or contraction of the drive frame (compared to the metrology frame), or at least a portion of deformation associated with additional thermal expansion or contraction of the drive frame (compared to the metrology frame), from being transmitted to the metrology frame.

[0015] The additional thermal expansion and contraction mentioned above can be considered to be the additional thermal expansion or contraction that occurs in the drive frame compared to the metrology frame for the same (or at least similar or predetermined) temperature change of both the drive frame and the metrology frame. Such temperature changes can be caused, for example, by changes in the ambient temperature in which the machine is operated, where the temperatures of the drive frame and the metrology frame vary closely with the ambient temperature. Unless the environment in which the machine is operated (e.g., a manufacturing facility) is very tightly controlled, the ambient temperature will vary continuously throughout the day and sometimes vary significantly, for example due to heat generated by other machines operating nearby or due to ambient heating and / or cooling systems.

[0016] Embodiments of the present invention ensure that any thermal effects causing additional expansion or contraction of the drive frame do not result in deformation of the metrology frame, or at least ensure that such effects are reduced. Thus, isolating the metrology frame from the drive frame in this manner prevents or at least reduces any significant deformation of the metrology frame due to different thermal expansion / contraction of the drive frame compared to the metrology frame, thereby providing metrology measurements of higher accuracy than previously considered metrology devices, or at least more consistent measurements at different operating temperatures.

[0017] The metering frame advantageously has a low coefficient of thermal expansion (CTE). Advantageously, the coefficient of thermal expansion of the metering frame is less than 15 ppm / °C, more preferably less than 10 ppm / °C, more preferably less than 5 ppm / °C, more preferably less than 3 ppm / °C, more preferably less than 2 ppm / °C, or more preferably less than 1 ppm / °C, wherein for example 1 ppm / °C means 1 x 10-6 / °C.

[0018] The metrology frame may be formed at least in part from a composite material, such as carbon fiber, which typically has a coefficient of thermal expansion of less than 5 ppm / °C, depending on its exact composition. The metrology frame may be formed at least in part from INVAR(TM), which is a nickel-iron alloy having a coefficient of thermal expansion of about 0.5-1.5 ppm / °C, depending on its exact composition. The metrology frame may be formed at least in part from a glass-ceramic material, such as ZERODUR(TM), which has a coefficient of thermal expansion of about 0.02 ppm / °C or less, depending on the exact composition. Such a low coefficient of thermal expansion may be more than an order of magnitude smaller than conventional materials, such as aluminum (24 ppm / °C), brass (19 ppm / °C), or steel (13 ppm / °C), which may be used to form at least a portion of the drive frame.

[0019] The coefficient of thermal expansion of the metrology frame may be less than half of the coefficient of thermal expansion of the drive frame. The coefficient of thermal expansion of the metrology frame may be less than one-third of the coefficient of thermal expansion of the drive frame. The coefficient of thermal expansion of the metrology frame may be less than one-quarter of the coefficient of thermal expansion of the drive frame. The coefficient of thermal expansion of the metrology frame may be less than one-fifth of the coefficient of thermal expansion of the drive frame. The coefficient of thermal expansion of the metrology frame may be less than one-eighth of the coefficient of thermal expansion of the drive frame. The coefficient of thermal expansion of the metrology frame may be less than one-tenth of the coefficient of thermal expansion of the drive frame.

[0020] Providing a metrology frame made of a material with a low coefficient of thermal expansion (e.g., carbon fiber and / or INVAR and / or ZERODUR) prevents or at least reduces the likelihood of introducing significant metrology errors due to temperature changes. However, such materials are generally difficult to machine and are typically significantly more expensive than standard shop materials (such as aluminum). Therefore, embodiments of the present invention combine the metrology benefits of low CTA materials (such as carbon fiber) with the ease of manufacturing associated with materials such as aluminum. For example, a metrology frame consisting primarily of a low CTE material (such as carbon fiber) can be combined with a drive frame consisting primarily of a more traditional material, such as aluminum (where certain components, such as guide rails, that require greater hardness and / or rigidity and / or durability may be formed of other materials such as steel).

[0021] It is not necessary that every part of the metering frame has a lower coefficient of thermal expansion than every part of the drive frame. In fact, for practical and engineering reasons, it is often necessary that some parts of the metering frame be formed from materials that are easier to work with, such as aluminum or steel or plastic, and / or from materials that are more wear-resistant or durable. For example, the support between two parts of a telescopically extendable metering leg may be formed from steel.

[0022] It may be considered important that the representative coefficient of thermal expansion of the metrology frame is lower than the representative coefficient of thermal expansion of the drive frame. The representative coefficient of thermal expansion may be the coefficient of thermal expansion obtained when the associated frame is treated as a unitary structure having a single total (e.g., average) coefficient of thermal expansion. The representative coefficient of thermal expansion may be the coefficient of thermal expansion (or a measure thereof) of one or more portions of the associated frame that contribute the most to the thermal expansion and contraction of the frame (e.g., contributing at least 25%, or at least 50%, or at least 75%). The representative coefficient of thermal expansion may be the coefficient of thermal expansion (or a measure thereof) of the material that forms the largest portion (e.g., by weight, and / or by volume, and / or by length, and / or by width, and / or by depth) of the associated frame. The representative coefficient of thermal expansion may be the coefficient of thermal expansion (or a measure thereof) of one or more portions of the associated frame that has a significant effect on the metrology result of the coordinate positioning machine for a predetermined temperature change. The metrology result may be a position determined or a measurement made by the coordinate positioning machine, such as the distance between two points on a representative workpiece that occupies at least one quarter (or at least half) of the working volume of the machine. A significant effect may be at least 0.01% of the metered result, or at least 0.1% of the metered result, or at least 1% of the metered result, or at least 5% of the metered result.The predetermined temperature change may be 1°C or 5°C or 10°C.

[0023] The metrology arrangement may comprise a plurality of measuring transducers arranged in parallel for providing a corresponding plurality of measurement values ​​from which the position of the movable structure can be determined.

[0024] The measuring transducer may be a length measuring transducer.

[0025] The measurements may relate to different respective spacings between the movable structure and fixed structure of the machine.

[0026] The measuring transducer may be adapted to provide a direct measurement of the spacing.

[0027] The measuring transducer may be adapted to provide direct measurements of changes in the separations as the structure moves about within the working volume, from which changes the separations may be determined.

[0028] Each of these measurement transducers may include an encoder scale and an associated readhead.

[0029] The metrology arrangement may comprise a plurality of extendable legs arranged in parallel, the extendable legs corresponding in number to the number of measuring transducers, and each measuring transducer of the plurality of measuring transducers being associated with a different respective one of the plurality of extendable legs.

[0030] The coordinate positioning machine may comprise six such measurement transducers.

[0031] The plurality of measuring transducers may be a plurality of independent measuring transducers.

[0032] The multiple measurement transducers described herein are to be contrasted with image-based or photogrammetric metrology arrangements, for example, in which each image capture device does not make a direct or independent measurement of any length or spacing of a movable structure or of the position of at least a portion thereof; the position of the movable structure is determined based on a photogrammetric combination of images from all image capture devices. With image-based or photogrammetric metrology arrangements, distances can only be inferred indirectly from the image data.

[0033] The drive arrangement may be a non-telescopic drive arrangement.With a telescopic arrangement, one part of the arrangement moves telescopically within or at least along another part in a linear manner, wherein the parts remain substantially aligned with each other during this movement.

[0034] The metering arrangement may be a top-down metering arrangement. Alternatively, the metering arrangement may be a bottom-up metering arrangement. In the case where the metering arrangement is connected between a movable structure and a fixed structure of the machine, when the metering arrangement is top-down, the movable structure is arranged below the fixed structure, wherein the metering arrangement extends downwardly from the fixed structure to the movable structure. On the other hand, when the metering arrangement is bottom-up, the movable structure is arranged above the fixed structure, wherein the metering arrangement extends upwardly from the fixed structure to the movable structure.

[0035] The drive arrangement may be a top-down drive arrangement. Alternatively, the drive arrangement may be a bottom-up drive arrangement. When the drive arrangement is connected between a movable structure and a fixed structure of the machine, when the drive arrangement is top-down, the movable structure is arranged below the fixed structure, wherein the drive arrangement extends downwardly from the fixed structure to the movable structure. On the other hand, when the drive arrangement is bottom-up, the movable structure is arranged above the fixed structure, wherein the drive arrangement extends upwardly from the fixed structure to the movable structure.

[0036] The drive arrangement may be adapted to maintain the moveable structure in a substantially constant orientation when moving about within the working volume.

[0037] The drive arrangement may include a plurality of mechanical linkages connected in parallel between the movable structure and a fixed structure of the machine.

[0038] Each mechanical linkage may be actuated (or driven) by a drive mechanism acting between the fixed structure and the mechanical linkage. A distinction will be made here between such a drive mechanism and a drive mechanism acting, for example, between two parts (or links) of a mechanical linkage. For example, in the case of a typical hexapod drive arrangement, the motor of each extendable leg will act between the two parts of the extendable leg, pushing the two parts away from each other to extend the leg, and doing the opposite to retract the leg. The motor does not act between the extendable leg (mechanical linkage) and the fixed structure. It can therefore be considered that in embodiments of the present invention, each mechanical linkage may be actuated (or driven) by a drive mechanism acting directly between the fixed structure and the mechanical linkage.

[0039] Movement of the driven portion of a mechanical linkage may be caused by a drive mechanism associated with that mechanical linkage, rather than by one or more other drive mechanisms associated with other mechanical linkages of the drive arrangement.

[0040] The driven part of the mechanical linkage may be a carriage arranged to move linearly along a corresponding track. A plurality of such tracks may be arranged substantially parallel to one another. In the case of a triple slip drive arrangement, three such tracks are provided.

[0041] The drive mechanism may be a rotary drive mechanism such as in a delta robot.

[0042] Such a drive mechanism may be arranged to drive a driven portion of the mechanical linkage in a substantially rotational manner relative to a fixed structure.

[0043] The rotary drive mechanism may be a direct rotary drive mechanism.

[0044] The drive mechanism may be, for example, a three-slide arrangement or a linear drive mechanism in a cable robot.

[0045] Such a drive mechanism may be arranged to drive the driven portion of the mechanical linkage in a substantially linear manner relative to the fixed structure, such as along a substantially linear feature of the fixed structure, such as along a substantially linear track of the fixed structure.

[0046] The linear drive mechanism may be a direct linear drive mechanism.

[0047] The linear drive mechanism may be arranged to translate the end of the mechanical linkage in a substantially linear manner.

[0048] The linear drive mechanism may include a linear motor.

[0049] Each mechanical linkage may include at least two substantially parallel rods to maintain the moveable structure in a substantially constant orientation as it moves about within the working volume.

[0050] The drive arrangement may include three such mechanical linkages.

[0051] The drive arrangement may be a triple slip arrangement.

[0052] The metrology arrangement may comprise a plurality of mechanical linkages arranged in parallel between the fixed structure and the movable structure, with a corresponding plurality of measurement transducers being respectively associated with the plurality of mechanical linkages. There may be six such mechanical linkages of the metrology arrangement and six corresponding respective measurement transducers.

[0053] Each mechanical linkage of the metering arrangement may be connected between points on the fixed structure and the movable structure respectively, and may be adapted to allow the spacing between those points to vary.

[0054] A measurement transducer associated with the mechanical linkage of the metering arrangement may be adapted to provide a spacing dependent output.

[0055] Each mechanical linkage of the metering arrangement may be an extendable or extending leg.

[0056] A mechanical linkage may also be referred to or considered a kinematic chain or a mechanical assembly.

[0057] A drive mechanism may be provided individually for each mechanical linkage of the drive arrangement.

[0058] A drive mechanism associated with the mechanical linkage may be arranged to act between the fixed structure and an end of the mechanical linkage.

[0059] Each mechanical linkage may include at least one rigid rod.

[0060] Each mechanical linkage may include at least two substantially parallel rods to maintain the moveable structure in a substantially constant orientation as it moves about within the working volume.

[0061] Each of the mechanical linkages may have substantially the same arrangement or design.

[0062] A drive arrangement having three mechanical linkages, each with a linear drive mechanism, is referred to as a triple-slip arrangement.

[0063] The drive arrangement may comprise or be in the form of a delta robot arrangement or provide a delta robot arrangement.

[0064] The drive arrangement may comprise or be or provide a linear delta robot arrangement.

[0065] The drive arrangement may be adapted to move the structure about the working volume in less than six degrees of freedom, and the metrology arrangement may be adapted to measure the position of the structure within the working volume in more degrees of freedom than the drive arrangement.

[0066] The metering arrangement may be a hexapod metering arrangement.

[0067] The drive arrangement may be a non-hexapod drive arrangement.

[0068] The drive arrangement may be adapted to move the structure about within the working volume in three degrees of freedom.

[0069] The three degrees of freedom may be three translational degrees of freedom.

[0070] The metrology arrangement may be adapted to measure the position of the structure in six degrees of freedom (three translational degrees of freedom and three rotational degrees of freedom, ie position and orientation).

[0071] The metering arrangement and the drive arrangement may each be arranged between (eg connected to) the movable structure and a fixed structure of the machine.

[0072] The metering arrangement and the drive arrangement may each be connected or coupled to both the movable structure and the fixed structure.

[0073] The metering arrangement may be formed predominantly (eg, more than 50% or 75% by weight) from a composite material, such as carbon fibers, or some other material, such as INVAR or ZERODUR.

[0074] The drive arrangement may comprise a plurality of actuators arranged in parallel. This is in contrast to the serial arrangement of actuators found in conventional three-axis (x, y, z) coordinate measuring machines (CMMs).

[0075] The drive arrangement may comprise a plurality of actuators of a different type than the metering arrangement, arranged in parallel.

[0076] The drive arrangement may be formed predominantly (eg more than 50% or 75% by weight) from an engineering material such as aluminium or steel.

[0077] The drive arrangement may comprise a plurality of measuring transducers separate from the measuring transducers of the metrology arrangement for providing corresponding respective measurements from which the position of the movable structure may be determined independently of the position determined based on the measurements from the metrology arrangement. In other words, the drive arrangement may be encoded independently of the metrology arrangement.

[0078] The drive arrangement may be coupled to the metering arrangement via a coupling arrangement, the coupling arrangement preventing at least a portion of a deformation associated with the drive arrangement from being transferred to the metering arrangement.

[0079] The coupling arrangement may be a kinematic or pseudo-kinematic coupling arrangement. Such a coupling arrangement constrains six degrees of freedom between the coupled parts without providing any redundant constraints. Kinematic coupling arrangements may, for example, include cones, v-shaped grooves, and flat plate arrangements.

[0080] The coupling arrangement may comprise a plurality of balls.

[0081] The coupling arrangement may include a plurality of resilient spacers or pads.

[0082] The movable structure may comprise a drive portion associated with the drive arrangement and a metering portion associated with the metering arrangement, the drive portion of the movable structure being coupled to the metering portion of the movable structure via the coupling arrangement.

[0083] The coefficient of thermal expansion of the metering portion of the movable structure may be less than the coefficient of thermal expansion of the driving portion of the movable structure. Representative values ​​(relative and absolute) suitable for these coefficients of thermal expansion are explained above with respect to the metering frame and the driving frame. The metering portion of the movable structure may be mainly (e.g., more than 50% or 75% by weight) formed of a composite material, such as carbon fiber or some other material, such as INVAR or ZERODUR. The driving portion of the movable structure may be mainly (e.g., more than 50% or 75% by weight) formed of an engineering material, such as aluminum or steel.

[0084] The drive part of the movable structure may be coupled to the drive arrangement.

[0085] The metering portion of the movable structure may be coupled to the metering arrangement.

[0086] The metrology frame may be considered to comprise a metrology portion of the movable structure.

[0087] The drive frame may be considered to comprise the drive portion of the movable structure.

[0088] The coordinate positioning machine may comprise a fixed structure having a drive portion associated with the drive arrangement and a metrology portion associated with the metrology arrangement, the drive portion of the fixed structure being coupled to the metrology portion of the fixed structure via the coupling arrangement.

[0089] The coefficient of thermal expansion of the metering portion of the fixed structure may be less than the coefficient of thermal expansion of the driving portion of the fixed structure. The metering portion of the fixed structure may be formed primarily (e.g., more than 50% or 75% by weight) of a composite material, such as carbon fiber, or some other material, such as INVAR or ZERODUR. The driving portion of the fixed structure may be formed primarily (e.g., more than 50% or 75% by weight) of an engineering material, such as aluminum or steel.

[0090] The drive portion of the fixed structure may be coupled to the drive arrangement.

[0091] The metering portion of the fixed structure may be coupled to the metering arrangement.

[0092] The metrology frame may be considered to include a metrology portion of the fixed structure.

[0093] The drive frame may be considered to comprise the drive portion of the fixed structure.

[0094] The drive frame may be considered to include any portion of the fixed structure that is not part of the metrology frame.

[0095] The drive frame may be considered to include any part of the machine that is not part of the metrology frame.

[0096] The metrology frame can be provided entirely within the drive frame (e.g., within the boundaries of the drive frame). Conversely, the drive frame can be disposed entirely outside the metrology frame (e.g., outside the boundaries of the metrology frame). The metrology frame can be spatially separated from the drive frame within the metrology frame (e.g., the two do not overlap). There may be no portion of the drive frame between the metrology portion of the fixed structure and the metrology portion of the movable structure. The metrology portion of the fixed structure can be disposed between the drive portion of the fixed structure and the movable structure. Such an arrangement provides a simple machine architecture that facilitates assembly and maintenance of the machine and provides an effective thermal barrier between the metrology frame and any heat generating drive devices (e.g., motors) in the drive frame.

[0097] The movable structure may carry an operating tool. In other words, the operating tool may be carried by the movable structure while the metrology arrangement is coupled to the movable structure. A coordinate measuring machine in this configuration is ready for operational use (with a working tool in place) rather than just ready for calibration (without a working tool in place).

[0098] The machine may be a coordinate measuring machine.

[0099] The machine may be a comparator.

[0100] The operating tool may be a surface sensing device or a measuring probe.

[0101] The machine may be a machine tool.

[0102] The operating tool may be a machine tool for shaping or machining a material.

[0103] The metrology arrangement may comprise only measuring transducers arranged in parallel with one another, ie without any measuring transducers arranged in series with one another.

[0104] The metrology arrangement may comprise six measuring transducers arranged in parallel for providing six corresponding respective measurements from which the position of the movable structure can be determined. A metrology arrangement having less than six measuring transducers arranged in parallel is not a hexapod metrology arrangement (e.g. a tripod, not a hexapod).

[0105] The metrology arrangement may be considered as being for measuring different positions of the movable structure within the working volume resulting from different respective states or configurations of the drive arrangement. In other words, the metrology arrangement measures the position of the movable structure in a first configuration of the drive arrangement (the first position), the drive arrangement is then moved into a second configuration different from the first configuration, and the metrology arrangement measures the position of the movable structure in the second configuration of the drive arrangement (the second position). The drive arrangement may be considered as comprising all parts of a machine for moving the movable structure from the first position to the second position.

[0106] The metrology arrangement may comprise six extendable legs arranged in parallel, six measuring transducers being respectively associated with the six extendable legs.

[0107] The measuring transducer may be an interferometric measuring transducer.

[0108] The drive arrangement may comprise fewer than six actuators arranged in parallel.

[0109] The drive arrangement may be a parallel kinematic arrangement.

[0110] The drive arrangement may be a non-Cartesian arrangement.

[0111] The drive arrangement may comprise fewer than six actuators.

[0112] The parallel arrangement of actuators associated with the drive arrangement may be different from the parallel arrangement of measuring transducers associated with the metering arrangement.

[0113] The drive arrangement may comprise a plurality of measuring transducers for providing corresponding respective measurements from which the position of the movable structure may be determined.

[0114] The measuring transducer may be a mechanical measuring transducer instead of an optical measuring transducer or an image-based or photogrammetric measuring transducer.

[0115] The measuring transducer may be a length measuring transducer. Measuring the length of a portion of a machine, such as an extendable leg, may be considered equivalent to measuring the separation between two portions of the machine, such as the end of an extendable leg. The transducer may not measure an absolute length or separation, but may measure a change in length or separation, from which measurement an absolute length or separation may be determined (e.g. based on a geometric model of the machine). Examples of sensors that do not measure length but may be used in conjunction with other sensor data to determine position are accelerometers (accelerometers), tilt sensors, and gyroscopes.

[0116] The measurement transducer may be sampled at a first clock rate which is comparable to (eg at least half the second clock rate, or at least the second clock rate, or substantially the same as) a second clock rate used to control the drive arrangement.

[0117] The measurements received from the measurement transducer may allow the position of the structure to be determined without reference to other sensor or transducer data (such as photogrammetric data from an image sensor) which may be obtained at a third clock rate that is lower than the first clock rate.

[0118] The first clock rate may be higher than 1 kHz, more preferably higher than 10 kHz, more preferably higher than 15 kHz.

[0119] The metering arrangement may be coupled to the movable structure in a contactless manner, such as optically, wherein the metering arrangement is an optical metering arrangement.

[0120] The metering arrangement may be mechanically coupled to the movable structure, such as where the metering arrangement is a hexapod metering arrangement.

[0121] The metrology arrangement may be a mechanical metrology arrangement, for example rather than an optical or image-based or photogrammetric metrology arrangement.

[0122] The metering arrangement may be mechanically coupled to the movable structure.

[0123] The extendable legs may include any mechanical arrangement (eg, a mechanical linkage) that allows the spacing between a point on the fixed structure and a point on the moveable structure to be changed.

[0124] The movable structure may be adapted to support or carry an object to be moved around within the working volume. The object may be an object to be picked up and / or placed within the working volume. The object may be a tool for interacting with or operating on another object such as a workpiece located in the working volume. The tool may be a surface sensing device. The surface sensing device may be a measurement probe. The measurement probe may be a contact probe. The contact probe may include a stylus that, in use, physically contacts the surface of the workpiece to perform a measurement. The measurement probe may be a non-contact probe.

[0125] The non-contact probe may be an optical probe. The tool may include a camera for imaging the surface of the workpiece. The tool may be a machine tool typically found in a machine tool for forming or machining metal or other rigid materials.

[0126] The movable structure may be adapted to carry an operating tool, to which the metrology and drive arrangements are also coupled. The coordinate positioning machine may be provided with the operating tool already coupled to the movable structure and ready to perform its intended operation. In other words, the coordinate positioning machine may be provided for operation, not just for calibration.

[0127] The hexapod metering arrangement may be coupled to the movable structure via an attachment different from the attachment used to attach the working tool to the movable structure.

[0128] The hexapod metering arrangement may be coupled directly to the movable structure.

[0129] A "transducer" may be considered herein as a device that converts a change in a physical quantity into an electrical signal (a "sensor," such as the measuring transducer described herein that measures or senses a change in length), or vice versa, a device that converts an electrical signal into a physical quantity (an "actuator," such as the motor and associated actuator linkage described herein that moves a structure based on an input or drive signal).

[0130] Measuring the "position" of a structure is to be understood as measuring the position and / or orientation of the structure in an appropriate number of degrees of freedom. For example, where the position is measured in six degrees of freedom, both the position and orientation of the structure are determined. However, if the position is measured in only three degrees of freedom, this may or may not include determining the orientation of the structure. The term "measuring the position" should be interpreted accordingly.

[0131] According to a fifth aspect of the invention, there is provided a method for controlling a coordinate positioning machine according to any of the above aspects, the method comprising: connecting a tool to a movable structure, using a drive arrangement to move the tool around within a working volume, wherein a metering arrangement is also connected to the movable structure, and performing an operation using the tool.

[0132] The method may comprise using a metrology arrangement to determine a position of a tool within the working volume for an operation.

[0133] The method may include associating the determined location with the performed operation.

[0134] The operation may be a measuring operation. The operation may be a machining operation.

[0135] The tool may be a measurement probe and the operation may be a measurement operation, such as a touch-trigger measurement of a workpiece located in a working volume.

[0136] The method may be performed based on the structure rather than the location of the tool, or based on a combination thereof.

[0137] According to a sixth aspect of the present invention, there is provided a controller for a coordinate positioning machine, wherein the controller is configured to perform the method according to the fifth aspect of the present invention.

[0138] According to a seventh aspect of the invention, there is provided a computer program which, when run by a coordinate positioning machine controller, causes the controller to perform a method according to the fifth aspect of the invention, or, when loaded into a coordinate positioning machine controller, causes the coordinate positioning machine controller to become a coordinate positioning machine controller according to the sixth aspect of the invention. The program may be carried on a carrier medium. The carrier medium may be a storage medium. The carrier medium may be a transmission medium.

[0139] According to an eighth aspect of the present invention, there is provided a computer readable medium having stored therein computer program instructions for controlling a coordinate positioning machine controller to perform the method according to the fifth aspect of the present invention.

[0140] Reference will now be made by way of example to the accompanying drawings, in which:

[0141] Discussed above Figure 1 is a schematic representation of a hexapod coordinate positioning machine having six extendable legs;

[0142] Figure 2 yes Figure 1 A schematic side view of a hexapod coordinate positioning machine;

[0143] Figure 3 is a schematic side view of a coordinate positioning machine on which an embodiment of the present invention is based, the coordinate positioning machine having a metrology arrangement and a separate drive arrangement;

[0144] Figure 4 is a schematic side elevation view of a coordinate positioning machine embodying the invention in which the metering arrangement is somewhat decoupled from the drive arrangement;

[0145] Figure 5 Shows Figure 4 A first perspective view of a practical embodiment of a coordinate positioning machine;

[0146] Figure 6 Shows Figure 5 A second perspective view of an embodiment of;

[0147] Figure 7 Shows Figure 5 A side view of an embodiment of the present invention;

[0148] Figure 8 Shows Figure 5 A top view of an embodiment of the present invention;

[0149] 9A to 9E is a schematic illustration of the operation of an embodiment of the present invention;

[0150] Fig.10 yes Figure 4 Schematic representation of a top-down variation of a coordinate positioning machine;

[0151] Fig.11 yes Fig.10 Schematic representation of a variation of a top-down coordinate positioning machine;

[0152] Fig.12 Shows Figures 5 to 8 A slight variation of the coordinate positioning machine;

[0153] Fig.13 Shows Fig.12 A top-down variation of a coordinate positioning machine;

[0154] Fig.14 Shows Fig.13 A variation of a top-down coordinate positioning machine;

[0155] Fig.15 Shows Fig.13 Another variation of a top-down coordinate positioning machine;

[0156] Fig.16A and Fig. 16B Schematically illustrated are embodiments with different types of non-hexapod drive arrangements;

[0157] Fig.17 Shown Fig.16A and Fig. 16B A practical embodiment of a coordinate positioning machine;

[0158] Fig.18A and Fig.18B Schematically shows Fig.16A and 16BA variation of an embodiment in which the metering arrangement is decoupled to some extent from the drive arrangement;

[0159] Fig.19 Schematically shows Fig.16A and Fig. 16B A variation of an embodiment having a bottom-up rather than top-down hexapod metering arrangement;

[0160] Fig. 20 Schematically shows Fig.16A and Fig. 16B A variation of an embodiment in which a fixed length metering strut is used in the hexapod metering arrangement;

[0161] Fig.21 Schematically shows Fig. 20 A variation of the embodiment wherein an offset pivot plate is used for the metering strut;

[0162] Fig. 22 Schematically shows an embodiment with a non-hexapod drive arrangement of the delta robot type;

[0163] Fig.23 Schematically shows Fig. 22 A variation of the embodiment of the invention having an increased decoupling between the metering arrangement and the drive arrangement;

[0164] Fig.24 Schematically shows Fig. 22 A variation of an embodiment of the invention having a reduced decoupling between the metering arrangement and the drive arrangement;

[0165] Fig.25 An embodiment of a non-hexapod drive arrangement having a serial kinematics type is schematically shown;

[0166] Fig.26 Another embodiment of a non-hexapod drive arrangement of the serial kinematics type is schematically illustrated;

[0167] Fig. 27 Concepts for providing a drive arrangement with fewer degrees of freedom than a metering arrangement are presented;

[0168] Fig.28 A dual hexapod arrangement was demonstrated, where the hexapod drive arrangement had restricted movement;

[0169] Fig.29 is a flow chart representing a method of controlling a coordinate positioning machine embodying the present invention;

[0170] Fig.30 is a perspective view of a kinematic coupling between a metering arrangement and a drive arrangement suitable for use in an embodiment of the present invention;

[0171] Fig.31 yes Fig.30 A top view of a first portion of the coupling member is shown;

[0172] Fig.32 yes Fig.30 A perspective view of a first portion of a coupling member;

[0173] Fig.33 Shown with Fig.30 how the ball associated with the second portion of the coupling sits in the V-shaped groove of the first portion;

[0174] Fig.34 It shows the six contact points created by the sphere sitting in the V-shaped groove;

[0175] Fig.35 shows how the contact point moves when the first and second parts of the coupling experience different thermal expansions; and

[0176] Fig.36 Another form of kinematic coupling between a metering arrangement and a drive arrangement suitable for use in embodiments of the present invention is shown.

[0177] Figure 2 The above reference is schematically shown in Figure 1 A side view of the coordinate positioning machine 1 in question. The coordinate positioning machine 1 comprises a superstructure 2 movable within a working volume 14 of the machine 1. Six extendable legs 6 form both a hexapod drive arrangement 18 (shown in solid lines) for moving the superstructure 2 around within the working volume 14 and also a hexapod metrology arrangement 16 (shown in dashed lines) for measuring the position of the superstructure 2 within the working volume 14. The coordinate positioning machine 1 thus has a combined drive and metrology support.

[0178] In contrast, Figure 3 Schematically shows a coordinate positioning machine 21 on which an embodiment of the present invention is based. Figure 2 The coordinate positioning machine 21 includes an upper structure 22 movable within a working volume 34 of the machine 21, a drive arrangement 28 (shown in solid lines) for moving the upper structure 22 around within the working volume 34, and a metering arrangement 26 (shown in dotted lines) for measuring the position of the movable upper structure 22 within the working volume 34.

[0179] Although in Figure 2 In the coordinate positioning machine 1 shown in FIG. 1 , the hexapod metering arrangement 16 and the hexapod drive arrangement 18 are combined, but in a coordinate positioning machine 21 (such as FIG. 21 ) embodying the present invention Figure 3), the drive arrangement 28 is distinct from and separate from the metering arrangement 26. Technical advantages are achieved by separating the metering arrangement 26 from the drive arrangement 28 in this way, as it allows the two different arrangements to be designed taking into account very different (sometimes conflicting) technical considerations.

[0180] Separating and distinguishing the metering arrangement 26 from the drive arrangement 28 allows the drive arrangement 28 to be made relatively light and quickly, enabling the structure 22 to be moved quickly around within the working volume 34 with high accelerations and rapid changes of direction. While concerns about factors like weight and speed may sacrifice a certain degree of positional accuracy in the drive arrangement 28, this can be overcome by providing the metering arrangement 26 which is instead designed with positional accuracy in mind.

[0181] Because the metering arrangement 26 is passive and does not require any driven components that add weight and generate heat, metering errors caused by inertia and thermal deformation of various parts (including the measuring scale used to measure the distance) can be controlled and reduced.

[0182] The use of a metrology arrangement 26 which is separate and distinct from the drive arrangement 28 provides a coordinate positioning machine 21 in which a movable structure can be driven rapidly within a working volume while still maintaining the accuracy required for demanding positioning applications.

[0183] With this design, a relatively cheap, off-the-shelf drive mechanism can also be selected for the drive arrangement 28, which drive mechanism is not specifically designed with high precision in mind, knowing that it will be coupled by a dedicated metering arrangement 26 to provide the required precision, and this therefore allows production costs to be reduced.

[0184] Mechanical metering arrangements also benefit from having low friction joints, whereas drive arrangements typically require more robust and strong joints which inevitably have higher degrees of friction (particularly under load), so there is a design conflict that is overcome by separating the metering arrangement 26 from the drive arrangement 28. The joints of the metering arrangement 26 may be of a low friction type and will also not be under the same loads as the drive arrangement 28. Hysteresis effects (which may result in different measurements being recorded depending on the direction of approach of the workpiece) may accordingly be reduced by separating the metering arrangement 26 from the drive arrangement 28.

[0185] exist Figure 3In the coordinate positioning machine 21 of , the metrology arrangement 26 is a hexapod arrangement and the drive arrangement 28 is a non-hexapod arrangement (i.e. an arrangement in addition to or other than a hexapod arrangement). The use of a hexapod-based metrology arrangement 26 is particularly advantageous because the hexapod provides a robust mechanical system with parallel arranged measuring transducers that provide direct measurements of distances from which very accurate and reliable determinations of position in six degrees of freedom can be derived.

[0186] The hexapod-based metrology arrangement 26 has advantages over some image-based metrology arrangements in terms of the rate at which the position of the mobile structure 22 can be determined or sampled. For image-based (photogrammetric) metrology arrangements, the sampling rate is inherently limited by the sampling rate of the image sensor, and further by the time it takes to perform complex calculations based on the large amount of image information in order to deduce the position of the mobile platform. For example, in the image-based system of EP 3054265 A1, it is noted that "the frame rate provided by the imaging detector typically only reaches a few hundred hertz"; this is described as a benefit because it avoids detecting undesirable high-frequency movements, such as vibrations.

[0187] However, the present applicants have realised that a much higher dynamic bandwidth can be achieved by directly sampling data from measurement transducers associated with the extendable legs of a hexapod metrology arrangement. For example, a machine controller typically requests position data from an absolute encoder every 65 μs (15 kHz), but higher sampling rates are possible. Incremental encoder systems produce a continuous sinusoidal output which still allows finer motion control, limited only by the rate at which the continuous output can be sampled. Unlike image-based systems, the calculations required to determine the position of the movable structure from these values ​​are not too time consuming.

[0188] It is also noted that the image-based system of EP 3054265 A1 does not describe the use of parallel arranged measuring transducers which independently provide corresponding sets of measurement values, wherein each measurement value in the set directly represents or relates to a distance or spacing between a different point on the mobile platform and a point on the fixed structure, and from which the position and / or orientation of the mobile platform can be determined. In particular, EP 3054265 A1 does not describe the use of a hexapod metrology arrangement.

[0189] Using Figure 1In a hexapod drive arrangement such as the one shown in , each of the six struts requires a motor which must form part of (i.e. move with) the associated strut. Therefore, when the hexapod is actuated to move the movable structure around within the working volume, the weight of the relatively heavy motor parts is also moved around. Having to move these extra masses around reduces the potential speed (or acceleration) of the drive arrangement and generates additional heat in the machine which has a negative effect when it reaches the metering arrangement. By providing e.g. Figure 3 Non-hexapod drive arrangements, such as the one shown in , can overcome these problems because they allow the motor part to be moved away from the moving part.

[0190] Furthermore, by using a non-hexapod drive arrangement that moves the movable structure 22 in less than six degrees of freedom, fewer actuators are required (i.e., less than the six actuators required in a hexapod arrangement), thereby reducing cost and complexity due to the smaller number of heat-generating motor parts and also reducing the heat generated, and thereby improving metrology results.

[0191] Figure 3 The hexapod metering arrangement 26 is generally similar to Figure 1 and Figure 2 The hexapod arrangement is similar to that of the conventional hexapod arrangement, but without providing any actuation or motor components required for the drive. In this example, the drive arrangement 28 is referred to as a "triple slide" arrangement, for example, as disclosed in US2003 / 0005786, with three carriages 56 moving along three corresponding respective linear rails 51 arranged substantially in parallel. Figures 5 to 8 These arrangements are described in more detail.

[0192] Reference again Figure 3 , the coordinate positioning machine 21 comprises a lower structure 24, which forms part of the fixed structure of the machine 21, and a workpiece 29 is mounted on the lower structure 24. A measurement probe 30 is supported on the upper structure 22 so that it can be moved around within a working volume 34. When the upper structure 22 and the lower structure 24 are in their most distant positions, a working volume 34 is defined between the upper structure and the lower structure, and the probe member 30 is positioned in the working volume 34 by operation of the drive arrangement 28.

[0193] Figure 3 2 , a controller C is schematically shown for controlling the drive arrangement 28 to cause the desired movement of the structure 22; the controller C may be implemented as hardware or software or a combination thereof. Purely for the sake of clarity and brevity, the controller C is omitted in the subsequent figures.

[0194] Figure 4An embodiment of the present invention is shown. To further decouple the drive arrangement 28 from the metering arrangement 26, the drive arrangement 28 is coupled to the metering arrangement 26 via a coupling arrangement 38 that prevents at least a portion of the thermally induced deformation associated with the drive arrangement 28 from being transferred to the metering arrangement 26 (as described in more detail below). In this embodiment, the coupling arrangement 38 includes a first coupling member 38a associated with the movable structure 22 and a second coupling member 38b associated with the fixed structure 24.

[0195] exist Figure 4 In the exemplary embodiment shown in , the movable structure 22 includes a metering portion 22a associated with a metering arrangement 26 and a driving portion 22b associated with a driving arrangement 28, the metering portion 22a of the movable structure 22 being coupled to the driving portion 22b of the movable structure 22 via a first coupling 38a. The metering portion 22a of the movable structure 22 is coupled to the metering arrangement 26. The driving portion 22b of the movable structure 22 is coupled to the driving arrangement 28.

[0196] Similarly, the fixed structure 24 comprises a metering portion 24a associated with the metering arrangement 26 and a driving portion 24b associated with the driving arrangement 28, the metering portion 24a of the fixed structure 24 being coupled to the driving portion 24b of the fixed structure 24 via a second coupling 38b. The metering portion 24a of the fixed structure 24 is coupled to the metering arrangement 26. The driving portion 24b of the fixed structure 24 is coupled to the driving arrangement 28.

[0197] In this example, each coupling 38a, 38b of the coupling arrangement 38 is in the form of a kinematic or pseudo-kinematic coupling. In the scenario where a subject is positioned relative to another subject, kinematic design considerations are met by constraining the subject's degrees of freedom of motion using a minimum number of constraints, and in particular, avoiding overconstraints. Overconstraints can result in multiple contact points between the two subjects, allowing one subject to lean against the other subject at multiple positions. Therefore, the position of the subject is not repeatable because it is not known which of the several positions the subject will lean against. In particular, in the presence of overconstraints, there is a conflict between the constraints in place, making it impossible to determine exactly which combination of constraints will determine the actual position of the subject. These concepts are described in the following document: HJJBraddick, "Mechanical Design of Laboratory Apparatus", Chapman & Hall, London, 1960, pp. 11-30.

[0198] Such a kinematic coupling (having a minimum number of contact points (or point contacts) to provide an ideal constraint) is also very effective in isolating deformations in one half of the coupling from being transmitted to the other half of the coupling. Thus, the first coupling 38a helps prevent deformations of the drive portion 22b of the movable structure 22 (caused by the forces acting on that portion by the drive arrangement 28) from being transmitted to the metering portion 22a (and thereby to the metering arrangement 26), and similarly for the second coupling 38b in terms of the fixed structure 24. This will be discussed below with reference to Figure 30 to Figure 36 Discuss in more detail.

[0199] This provides a clearly delineated metrology frame 36 (i.e., the metrology portion 24a of the fixed structure 24, the metrology portion 22a of the movable structure 22, and the metrology arrangement 26) that is mechanically isolated to a good degree from the drive frame 37 (i.e., the portion outside the metrology frame 36, including the drive portion 22b of the movable structure 22, the drive portion 24b of the fixed structure 24, the drive arrangement 28, the defining track 51, and the bracket 56). The mechanical isolation provided by the first and second couplings 38a, 38b effectively decouples the drive frame 37 from not only drive-related or load-related deformations of the metrology frame 36, but also effectively decouples the effects of thermal expansion and contraction of the drive frame 37 from the metrology frame 36. Furthermore, the metrology frame 36 is formed of a material having a low coefficient of thermal expansion (CTE) to remain substantially unaffected by any changes in the thermal environment. The first and second couplings 38a, 38b between the metering frame 36 and the drive frame 37 also ensure that thermal expansion or contraction of the parts of the device constituting the drive frame 37 does not cause deformation of the metering frame 37, or at least ensures that any such deformation of the metering frame 37 is at least reduced.

[0200] For example, the extendable legs of the metering arrangement 26 (see below) Figures 5 to 8 38a and ZERODUR) can be formed of a composite material such as carbon fiber, while one or both of the metering portion 24a of the fixed structure 24 and the metering portion 22a of the movable structure 22 can be formed of a material such as INVAR (TM) or ZERODUR (TM), or alternatively, a composite material such as carbon fiber. However, such low CTE materials are generally difficult to machine and are typically significantly more expensive than standard shop materials such as aluminum. Although the CTE of aluminum is much higher than materials such as carbon fiber, INVAR and ZERODUR, the mechanical / thermal isolation provided by the first and second connectors 38a and 38b allows key portions of the drive frame 37 to be formed of such conventional materials such as aluminum without introducing deformation to the metering frame 36 due to thermal expansion / contraction differences between the drive frame 37 and the metering frame 36.

[0201] For example, one or both of the metering portion 24a of the fixed structure 24 and the metering portion 22a of the movable structure 22 (as well as the extendable legs of the metering arrangement 26) can be formed of carbon fiber, while one or both of the drive portion 24b of the fixed structure 24 and the drive portion 22b of the movable structure 22 can be formed of aluminum or steel. For example, the drive platform 22b (formed of aluminum or steel) expands and contracts more with temperature changes than the metering platform 22a (formed of carbon fiber) to which it is connected (via the connector 38a), but the nature of the connector 38a allows one half to expand and / or contract relative to the other half without causing different stresses; features on one side of the connector slide easily over features on the other side of the connector without causing or transmitting any stress. The same applies to the metering platform 24a and the connected drive platform 24b at the other end. It has been found that this provides significant metering benefits in environments where the ambient temperature can vary.

[0202] In this embodiment, each coupling 38a, 38b includes a set of three balls to provide three contact points (at Figure 4 Only two are shown in the schematic representation of ). It is also advantageous to use a plurality of elastic spacers or pads instead of rigid balls, for example three such spacers arranged at the corners of a triangle. This provides a certain degree of kinematic coupling, even if the contact points are not point-shaped but rather spread over small areas of the elastic spacers. The use of elastic spacers (for example made of rubber) is advantageous because they act to absorb some of the vibrations and / or thermal expansion / contraction from the drive frame 37 so that the vibrations are not transmitted to the metering frame 36 (and in particular not to the metering arrangement 26). Instead of using rigid spheres in the kinematic couplings 38a, 38b, spheres with a certain degree of flexibility (for example made of rubber) can also be used to allow at least part of the absorption of any different expansion and / or contraction to be achieved in a direction orthogonal to the movable structure 22 and / or the fixed structure 24.

[0203] It should also be understood that such a connection can be provided at both ends (i.e., associated with the movable structure 22 and the fixed structure 24), or at only one end (i.e., associated with only one of the movable structure 22 and the fixed structure 24), or no such connection can be provided at all (i.e., neither at the movable structure 22 nor at the fixed structure 24).

[0204] Now refer to Figures 5 to 8 The embodiment is described in more detail with Figure 3 and Figure 4 A more detailed representation of the machine structure is shown compared to the schematic representation.

[0205] Figures 5 to 8The hexapod metering arrangement 26 shown in FIG. 1 includes six extendable legs 60, which are generally of the same configuration, disposed between the upper structure 22 and the lower structure 24. Figure 4 The upper structure 22 comprises a metering portion 22a associated with a metering arrangement 26 and a driving portion 22b associated with a driving arrangement 28, the metering portion 22a of the movable structure 22 being coupled to the driving portion 22b of the movable structure 22 via a first coupling 38a. The metering portion 22a of the movable structure 22 is coupled to the metering arrangement 26 via a ball joint 68. The driving portion 22b of the movable structure 22 is coupled to the driving arrangement 28 via a ball joint 58.

[0206] Similarly, the fixed structure 24 comprises a metering portion 24a associated with the metering arrangement 26 and a driving portion 24b associated with the driving arrangement 28, the metering portion 24a of the fixed structure 24 being coupled to the driving portion 24b of the fixed structure 24 via a second coupling 38b. The metering portion 24a of the fixed structure 24 is coupled to the metering arrangement 26. The driving portion 24b of the fixed structure 24 is coupled to the driving arrangement 28.

[0207] Each of the six extendable legs 60 includes an upper tube 64 and a lower tube 62 that slides telescopically within the upper tube 64. The extendable legs 60 generally have a similar construction to those described in WO 2017 / 021733 and application number PCT / GB 2017 / 050909, except that in this embodiment, there is no need to drive the extendable legs and therefore no motor-related components are required. However, the overall construction of the extendable legs 60 is generally similar.

[0208] exist Figures 5 to 8 In the example shown in FIG. 1 , the lower structure 24 is fixed, and the upper structure 22 is movable relative to the lower structure 24 by operation of the six extendable legs 60, and the measurement probe 30 is mounted to the lower surface of the upper structure 22. In this configuration, the workpiece ( Figures 5 to 8 The measuring probe 30 (not shown) will be mounted on top of the metering portion 24a of the lower structure 24 so that the working volume of the machine 21 is located between the metering portions 22a, 24a of the upper and lower structures 22, 24, respectively. The measuring probe 30 comprises a stylus with a workpiece contacting end, and the measuring probe 30 is connected to the metering portion 22a of the mobile structure 22 via a sleeve 32.

[0209] The extendable legs 60 are used to locate (i.e. determine the position of) a component supported by the movable structure 22 (in the example shown, the component is the measurement probe 30), or at least a portion of a specific part of the component (such as the end of the measurement probe) is located within the working volume of the machine.

[0210] The upper end and the lower end of each extendable leg 60 are connected to the upper structure 22 (specifically, the metering portion 22a of the upper structure 22) and the lower structure 24 (specifically, the metering portion 24a of the lower structure 24) via independent ball joints 68, respectively. The upper tube 62 and the lower tube 64 of each extendable leg 60 surround the elongated member 66 (at Figure 5 The encoder scale 10 is attached to an elongate member 66 (shown in dashed outline in one of the extendable legs of the upper structure 22). The elongate members 66 are themselves extendable, for example by a telescopic arrangement. Each elongate member 66 extends from its upper joint 68 to its lower joint 68, and it is the respective length of the elongate members 66 that determines the precise positioning and orientation of the metering portion 22a of the upper structure 22 (and therefore of the measurement probe 30). It is therefore the length of the elongate member 66 that must be accurately measured during a measurement or scanning operation on a workpiece in order to determine the precise position of the stylus tip when it comes into contact with the workpiece surface.

[0211] The drive arrangement 28 in this embodiment is known as a "triple slip" arrangement, for example as described in US2003 / 0005786. The triple slip arrangement is provided by three mechanical linkages 50 of substantially identical design connected in parallel between the movable structure 22 and the fixed structure 24. Each mechanical linkage 50 comprises two substantially parallel rigid rods 52, 54 of fixed length which are used to keep the movable structure 22 in a substantially constant orientation as it moves around within the working volume 34. Each mechanical linkage 50 also comprises a bracket 56 to which the rods 52, 54 are pivotally coupled at their lower ends by ball joints 58 and at their upper ends to the drive portion 22b of the movable structure 22.

[0212] The three linear rails 51 are arranged substantially vertically (substantially in parallel) on the drive portion 24b of the fixed structure 24, and the three carriages 56 are arranged to move (up and down) along the three linear rails 51 respectively. The three linear rails 51 effectively form part of the fixed structure of the coordinate positioning machine 21 and can be regarded as an extension of the fixed structure 24 (specifically, the drive portion 24b of the fixed structure 24). Each carriage 56 is driven along its corresponding corresponding rail 51 in a substantially linear manner by a linear drive mechanism, which is located at Figure 3 29. The linear drive mechanism may include a linear motor. The linear drive mechanism may include a stepper motor.

[0213] Thus, each mechanical linkage 50 is actuated by a drive mechanism that acts between a fixed structure (linear track) 51 and the mechanical linkage 50. More specifically, the drive mechanism acts between the fixed structure (linear track) 51 and the end of the mechanical linkage 50 (i.e., the bracket 56). In other words, the drive mechanism effectively couples the mechanical linkage directly to the fixed structure ("coupled to the ground"), providing a force therebetween for pushing or pulling the mechanical linkage (for a linear drive mechanism) or rotating the mechanical linkage (for a rotary drive mechanism). There is no additional movable linkage between the drive mechanism and the fixed structure, wherein such additional linkage can cause movement of the driven portion of the mechanical linkage that is not caused by the drive mechanism itself.

[0214] For example, using Figures 5 to 8 in (and in Figure 3 and Figure 4 ), each carriage 56 is driven linearly up and down along its respective track 51 by the action of a motor (not shown) associated with the carriage 56, rather than by the action of any other motors associated with the other carriages 56. In the case of a typical hexapod drive arrangement (such as Figure 1 ), the motor in a particular extendable leg can only extend or retract the leg linearly along its length, however, in use, each leg will also move laterally; the lateral movement of the leg (and its associated motor) must be caused by the action of other motors in other legs, so that each motor is actually moving the weight of the other legs (along with their corresponding motors).

[0215] Therefore, using Figures 3 to 8 With the drive arrangement shown in FIG. 5 , the moving parts can be kept relatively lightweight (thin and light rods 52, 54 in this example), and it is not a case of each motor moving around the weight of the other motors (as in, for example, Figure 1 This allows a lightweight drive arrangement that can move quickly with high acceleration and rapid changes of direction.

[0216] The telescopic construction of the six extendable legs 60 of the metering arrangement 26 is contrasted with the non-telescopic construction of each mechanical linkage 50 of the drive arrangement 28. With a telescopic arrangement, one part of the arrangement slides or moves in a linear manner within or at least telescopically along another part, thereby maintaining substantial alignment with each other during such movement. However, this is not the case with the drive arrangement 28 of the present embodiment, as each bracket 56 moves linearly along its corresponding respective track 51, and one part of the arrangement (rigid rods 52, 54) does not remain substantially aligned with or even at a constant angle to another part of the arrangement (track 51), and the angle between the two parts changes when the drive arrangement 28 is actuated. Therefore, it can be Figures 3 to 8 The drive arrangement 28 shown is described as a non-telescopic drive arrangement. However, each of the parallel linkages of the drive arrangement 28 may still be considered to be an extendable leg or provide an extendable leg, even though not telescopically extendable (i.e., not a telescopically extendable leg), just as a human leg may be described as extendable even though it is not telescopic. An extendable arrangement may be considered to be any type of arrangement between two points that allows the spacing between those points to vary.

[0217] Returning to a more schematic format, we will now refer to 9A to 9E The operation of the three-slip embodiment is described. 9A to 9E Each of these uses Figure 3 The two carriages are labeled 56a and 56b, respectively, and the two linear rails are labeled 51a and 51b, respectively. For simplicity, see above Figure 4 The described coupling arrangement 38 is 9A to 9E Not shown in , but present in embodiments of the invention (at the mobile structure 22 or the fixed structure 24 or both).

[0218] Due to the above reference Figures 5 to 8 Due to the constraints provided by the parallel rods 52, 54 described above, the movement of the movable structure 22 (through the operation of the three-slide drive arrangement 28) is restricted to three translational degrees of freedom, so that the movable structure 22 maintains a substantially constant orientation as it moves around within the working volume. This constraint on movement in three degrees of freedom is Fig. 9A Indicated by the arrow labeled 3DOF.

[0219] On the other hand, using six extendable legs 60 of the hexapod metrology arrangement 26 (including six corresponding measuring transducers arranged in parallel), six corresponding corresponding measurement values ​​are provided, based on which the position of the movable structure can be determined in all six degrees of freedom, such as Fig. 9A This is indicated by the arrow marked 6DOF.

[0220] like Fig. 9B As shown, by lowering carriage 56a and raising carriage 56b along their respective tracks 51a, 51b, the movable structure 22 (and with it the measurement probe 30) moves leftward and downward within the working volume 34, thereby maintaining substantially the same orientation, since the rods 52, 54 of the mechanical linkage 50 are of fixed length. This causes the extendable legs 60 closest to carriage 56a to shorten, and the extendable legs 60 closest to carriage 56b to lengthen, these changes in length being measured by the measurement transducers (e.g., encoders) 10 in the extendable legs 60. From these transducer measurements, the position of the movable structure 22 within the working volume 34 can be determined, and because the measurement probe 30 is in a known and fixed spatial relationship with the movable structure 22, the position of the measurement probe 30 (and the probe tip) can also be determined. Fig. 9C and Fig. 9B The same, but without the movement indication for clarity, shows the final position of the component after the movement operation.

[0221] Similarly, if Fig.9D As shown, by raising the carriage 56a and lowering the carriage 56b along its respective tracks 51a, 51b, the movable structure 22 (and the measurement probe 30 with it) can be moved to the right within the working volume 34, thereby again maintaining substantially the same orientation. This causes the extendable leg 60 closest to the carriage 56a to lengthen, and the extendable leg 60 closest to the carriage 56b to shorten, these changes in length being measured by the measurement transducers (e.g., encoders) 10 in the extendable legs 60. From these transducer measurements, the position of the movable structure 22 and the measurement probe 30 within the working volume 34 can be determined. Fig.9E and Fig.9D The same, but without the movement indication for clarity, shows the final position of the component after the movement operation.

[0222] For the three-slide embodiment described above, the extendable legs 60 of the hexapod metering arrangement 26 and the rod 50 of the drive arrangement 28 extend upward from the bottom, and therefore this embodiment can be described as a "bottom-up" arrangement. Fig.10An alternative "top-down" arrangement is shown which is generally the same as the "bottom-up" arrangement except that the extendable legs 60 of the hexapod metrology arrangement 26 and the rods 50 of the drive arrangement 28 extend downwardly from the top (hence a "top-down" arrangement). In order to achieve this, a frame 25a is provided to support the hexapod metrology arrangement 26 so that it can effectively "hang down" from the top. The frame 25a effectively forms part of the fixed structure of the coordinate positioning machine 21 as an extension of the fixed structure 24 (in this case the hexapod portion 24a of the fixed structure 24, i.e. also part of the metrology frame 36). As with the previous embodiments, coupling arrangements 38a, 38b are provided to isolate the metrology frame 36 (particularly the metrology arrangement 26) from the drive frame 37 (particularly the drive arrangement 28).

[0223] Fig.11 Another "top-down" arrangement is shown schematically. This is similar to Fig.10 The embodiment of FIG. 2 differs in that the hexapod metrology arrangement 26 is supported by a frame 25 extending around the top and is arranged inside the three-slide drive arrangement 28. The frame 25 effectively forms part of the fixed structure of the coordinate positioning machine 21 as an extension of the fixed structure 24, with the vertical linear track 51 also becoming part of the frame 25. Fig.11 The embodiment of the invention is also provided with a coupling arrangement 38 to isolate the metering arrangement 26 from the drive arrangement 28, but in Fig.11 In the embodiment of the present invention, this is only at the movable structure 22 and not at the fixed structure 24. The measuring probe 30 is mounted to the lower surface of the metering portion 22a of the movable structure 22 and extends through the driving portion 22b of the movable structure 22 without touching it (for example, through a hole formed in the driving portion 22b of the movable structure 22).

[0224] In order to Figures 13 to 15 For comparison, Fig.12 To illustrate a practical three-slip embodiment, which corresponds closely to the above reference Figures 5 to 8 The embodiment described, differs mainly in having a closed drive frame, while providing additional rigidity and stability to the vertical track 51 through the top plate of the drive frame. Like the previous embodiment, Fig.12 The metering frame is decoupled from the drive frame at least to some extent both at the top, ie at the movable structure, and at the bottom, ie at the fixed structure.

[0225] Fig.13 Shows Fig.11 A practical embodiment of a "top-down" arrangement is schematically shown in FIG. Fig.11 The example of is different in that the drive frame and the metrology frame are decoupled to some extent at the movable structure. Fig.14 yes Fig.13 A variation of the present invention disengages the drive frame from the metering frame both at the movable structure and at the fixed structure. Fig.15 is another variation, having a separate metrology frame disposed within the drive frame, the drive frame being decoupled from the metrology frame at both the movable structure and the fixed structure.

[0226] It will be appreciated that the present invention is not limited to embodiments in which the drive arrangement 28 is in the form of three slides. Fig.16A An embodiment of a hexapod metering arrangement 26 coupled to a different type of non-hexapod drive arrangement 28 is schematically shown. Rather than a fixed length rod 52 having one end linearly driven along a track 51 by a bracket 56 as in the three-slide embodiment, Fig.16A In the embodiment of the present invention, the fixed length extension rod is instead driven by a suitable linear drive mechanism disposed in the guide member 76 through the pivoting guide member 76, thereby changing the Fig.16A The interval indicated by the arrow in FIG. 2 and thereby moves the structure 22 .

[0227] exist Fig.16A and Fig. 16B In, similar to Fig.11 The metering and drive arrangements 26, 28 are supported in a top-down manner by a frame 25 which forms part of the fixed structure of the coordinate positioning machine 21. Fig.16A When both rods are driven downwardly through their respective guides 76, the structure 22 can be moved to the position shown. Fig. 16B As previously described, the position of the structure 22 is measured by the hexapod metrology arrangement 26. In a manner similar to the previous embodiments, the metrology frames 22a, 26 are isolated to some extent from the drive frames 22b, 28 by the coupling 38a between the portions 22a and 22b of the movable structure 22, with the fixed frame 25 conceptually being part of both the drive frame and the metrology frame (so that there is a thermal / mechanical decoupling at the movable structure 22, but not at the fixed structure 24). Fig.16A and Fig. 16B The drive arrangement 28 is also a non-telescopic drive arrangement, as each drive strut has a fixed length rod that extends from either side of the (much shorter) guide and moves therethrough; this cannot be considered a telescopic arrangement.

[0228] It should be understood that, as with the three-slip arrangement, Fig.16A Each mechanical linkage of the drive arrangement 28 in the embodiment of FIG. 1 is actuated by a drive mechanism acting between the fixed structure and the mechanical linkage, so this embodiment has the same advantages in terms of speed and acceleration.

[0229] Fig.17 Shown Fig.16A A practical embodiment of the arrangement is schematically shown. Fig.17 The embodiment of is closely based on a non-Cartesian coordinate measuring machine sold by the applicant Renishaw plc under the trade mark EQUATOR. The hexapod metrology arrangement 26 is generally similar to Figure 5 The embodiment includes six extendable legs, each extendable leg having an upper tube 64 and a lower tube 62, the lower tube 62 sliding telescopically within the upper tube 64. In this embodiment, the extendable legs are supported in a top-down arrangement from the frame 25 to the metering platform 22a (part of the movable structure 22). The pivot guide 76 is Fig.17 The structure of the frame 25 is hidden in the middle. Three fixed-length drive rods 72 pass through three pivot drive guides 76 respectively and are connected to the drive plate 22b (a part of the movable structure 22) at their lower ends. In this embodiment, the two parts 22a, 22b of the movable structure 22 are spatially separated by a rigid column 23. Similar to Figure 5 The rods 52, 54 and three sets of parallel rod pairs 72, 74 are arranged to constrain the motion in three degrees of freedom.

[0230] Returning to a more schematic representation, Fig.18A and Fig.18B Shows Fig.16A and Fig. 16B A variation of the machine in which the metering arrangement 26 (part of the metering frame 36) is even further isolated / decoupled from the drive arrangement 28 (part of the drive frame 37). This is similar to the above reference Fig.10 A three-slip embodiment has been described and therefore requires no further description. Fig.19 Shows Fig.16A An alternative to the arrangement of has a bottom-up hexapod metering arrangement 26 rather than a top-down arrangement.

[0231] Fig. 20 Schematically shows Fig.16A and Fig. 16B A variation of the embodiment of the invention in which a fixed length metering strut is used in the hexapod metering arrangement 26, similar to the fixed length strut of the drive arrangement 28 of this embodiment. Fig. 20 The six fixed length extension struts shown are considered to be functionally equivalent to the six extendable struts of the previous embodiment, with the variable length portions of the struts being provided by Fig. 20 The arrow in the figure indicates that this part is equivalent to the extendable support of the previous embodiment. Therefore, the terms "extendable support leg" and "extension support leg" should be understood as equivalent in this article, meaning any type of mechanical arrangement or linkage between two points that allows the spacing between these points to be changed. However, Fig. 20Each fixed length extension strut of the metering arrangement 26 cannot be described as a telescopic arrangement, i.e., each metering strut is a non-telescopic arrangement. The drive arrangement 28 is still a non-hexapod drive arrangement because it has only three extension struts, such as Fig.17 As shown in more detail in FIG. Fig.21 Schematically shows Fig. 20 A variant of the embodiment in which a fixed support (pivot plate) 25a is used to spatially offset the metering strut from a fixed support (pivot plate) 25b for the drive strut, wherein a coupling 38b (e.g., three spheres forming a kinematic coupling according to the previous embodiment) provided between these plates 25a, 25b provides thermal / mechanical decoupling between the drive frame and the metering frame. Of course, modifications may be made Fig.21 Embodiments of the invention to also provide a breakaway at the movable platform 22 (similar to Fig. 20 ).

[0232] Embodiments have been described above in which two different types of non-hexapod drive arrangements have been employed: a three-slip linear drive arrangement (e.g. Figure 5 ) and pivoting linear drive arrangements (e.g. Fig.17 ), both of which are non-telescopic arrangements. There are many other possibilities for the drive arrangement, only a few of which will now be briefly described; other possibilities will be apparent to the skilled person.

[0233] Fig. 22 An embodiment with a non-hexapod (and non-telescopic) drive arrangement of the delta robot type is schematically shown. A delta robot is a parallel robot and an example is described in detail in US 4,976,582. Fig.23 Schematically shows Fig. 22 A variation of the embodiment of has an increased decoupling between the metering frame and the drive frame. Fig.24 Schematically shows Fig. 22 A variation of the embodiment of the invention is provided which decouples the metrology frame from the drive frame at the mobile structure rather than the drive frame. It will be appreciated that, as with the three-slip arrangement, in the case of the delta robot arrangement each mechanical linkage is actuated by a drive mechanism acting between the fixed structure and the mechanical linkage and therefore these delta robot embodiments have the same advantages in terms of speed and acceleration (in the case of the delta robot arrangement the drive mechanism is a rotary drive mechanism, whereas in the case of the three-slip arrangement the drive mechanism is a linear drive mechanism). Furthermore, with appropriate constraints (such as those described in US 4976582), the delta robot drive arrangement 28 may be adapted to provide movement in three degrees of freedom (i.e. fewer degrees of freedom than measured by the hexapod metrology arrangement 26) to the structure 22.

[0234] The position of the rotary drive mechanism is determined by Fig. 22 The reference numeral 27 in FIG. 1 indicates the position of the linear drive mechanism. Figure 3 In each case, the drive mechanism acts directly between the fixed structure and the drive arrangement. Figure 3 In the case of Figure 5 A portion of the mechanical linkage 50 shown in FIG. Fig. 22 In the case of , the drive mechanism acts to drive (rotate) the upper portion of the mechanical linkage attached between the movable structure and the fixed structure.

[0235] Another example of a non-hexapod drive arrangement suitable for use in embodiments of the present application is a cable-driven robot arrangement (or referred to as a cable-suspended robot, or simply a cable robot, or a cable-driven robot). This is a parallel manipulator (parallel kinematic arrangement) in which a plurality of flexible cables are used as actuators. One end of each cable is wound around a rotor rotated by a corresponding respective motor, and the other end is connected to an end effector. An example of a cable robot is disclosed in US 2009 / 0066100 A1. Since cables are typically much lighter than the rigid linkage of a serial or parallel robot, the end effector of a cable robot can achieve high acceleration and high speed. The combination of a hexapod metering arrangement with a cable-driven arrangement is particularly advantageous due to the high measurement rate and dynamic bandwidth, as well as the high precision, that can be achieved using a hexapod metering arrangement.

[0236] Other types of non-hexapod drive arrangements are also contemplated. For example, Fig.25 Schematically illustrated is an embodiment of a non-hexapod (and non-telescopic) drive arrangement of the serial kinematics (rather than parallel kinematics) type, with a plurality of segments or links connected in series by revolute joints, with one end of the drive arrangement attached to the ground and the other end attached to a metering arrangement. Figure 4 As in the example shown in Fig.25 The drive arrangement shown in is attached to the metering arrangement via a coupling, which helps to prevent drive-related deformations from being transferred to the metering arrangement. Fig.26 Another embodiment of a non-hexapod drive arrangement of serial kinematics type is schematically shown, which non-hexapod (and non-telescopic) drive arrangement has a plurality of axes that can be respectively moved along orthogonal axes x, y and z (such as Fig.26 The three parts of the serial connection are marked as (). Therefore, Fig.26 The embodiment has a Cartesian type serial drive arrangement, while Fig.25 The embodiment has a non-Cartesian type serial drive arrangement. These types of drive arrangements are well known and do not need further explanation here.

[0237] As specifically referenced above Fig. 9A As explained, the drive arrangement 28 provides three translational degrees of freedom for the movable structure 22, while the hexapod metrology arrangement 26 is adapted to perform measurements in six degrees of freedom. According to one aspect of the invention, a coordinate positioning machine is provided, the coordinate positioning machine comprising a structure movable within a working volume of the machine, a drive arrangement for moving the structure around within the working volume in less than six degrees of freedom, and a metrology arrangement for measuring the position of the structure within the working volume in more degrees of freedom than the drive arrangement. Fig. 27 One or both of the drive arrangement and the metering arrangement may be a parallel kinematic arrangement such as a hexapod arrangement, a triple-slide arrangement or a delta robot arrangement. In particular, it is noted that in this respect the metering arrangement need not be a hexapod metering arrangement.

[0238] It is not normal to provide measurements, especially direct measurements, in more degrees of freedom than movement. Typically, there are N drives (rotational or linear), each of which is separately encoded to give N corresponding measurements. For example, for a three-axis CMM, there are three driven linear axes, each with a position encoder, and therefore three corresponding measurements (i.e. both driving and measuring in three degrees of freedom). For a hexapod robot, there are six variable length struts, each with a position encoder, and six corresponding measurements (i.e. both driving and measuring in six degrees of freedom).

[0239] However, the applicant has appreciated the attraction and advantage of being able to couple a drive arrangement that is relatively imprecise and constrained to move in a limited number (e.g., three) of degrees of freedom with a separate metrology arrangement that is highly accurate and capable of measuring in all six degrees of freedom and is therefore able to compensate for any inaccuracies in the mechanically constrained drive arrangement. For example, where a mobile platform is constrained to translate within a working volume without rotating, there may be some unintentional rotation of the platform due to deformations or other types of inaccuracies in the structure, at least a portion of which may be caused by dynamic effects associated with high-speed motion. Such rotation may be detected by measuring in more degrees of freedom than the drive. It may even be possible to measure the rotation of the platform in a manner that is consistent with the mechanical constraints of the drive arrangement. Fig. 27 The solution is applied to Fig.28 Schematically illustrated dual hexapod arrangement, where the actuated hexapod is constrained to move in less than six degrees of freedom by appropriate mechanical constraints.

[0240] It will be apparent to the skilled person that there are many other forms of non-hexapod drive arrangements, or drive arrangements that are constrained to less than six degrees of freedom. For example, there are many possible variations of the three-slip arrangement shown. One variation is to provide an arrangement with more than three drive arrangements and associated mechanical linkages. And, instead of Figure 3 Instead of the vertical track 51 shown, the track could be arranged horizontally, for example radially outwardly from a point, so that movement of the structure 22 is also affected by movement of the carriage 56 along the horizontal track. Many other such possibilities exist.

[0241] Although embodiments of the present invention have been described primarily with respect to the use of a contact probe, in which the stylus of the contact probe makes physical contact with the surface of a workpiece for measurement, it should be understood that the present invention is not limited to a contact probe. The same concept also applies to non-contact probes such as optical probes, in which the surface is sensed without physical contact. The present invention is generally applicable to any surface sensing device suitable for sensing a surface, whether or not by contact. The present invention can also be applied to the positioning of components other than surface sensing devices, such as for orienting components of an article during the manufacture of the article. Alternatively, the component can be a tool or part thereof, such as a tool commonly found in a machine tool for forming or machining metal or other rigid materials. The component can be the movable structure itself. The component can include a camera for imaging the surface of the workpiece. The component can include an eddy current probe for detecting and / or measuring eddy currents at or near the surface of the workpiece. Many other possibilities will be apparent to the skilled person.

[0242] It should be noted that in an embodiment of the present invention, the hexapod metering arrangement 26 is not provided purely for calibration purposes, temporarily connected to the movable structure to perform calibration of the combined drive and metering arrangement, and then removed for operational use of the machine. Instead, the hexapod metering arrangement is intended to remain connected to the movable structure to provide position measurements related to the movable structure during operational use. In an embodiment of the present invention, in contrast to a metering arrangement that is only calibrated, the movable structure is suitable for carrying an operating tool, and the metering arrangement and the drive arrangement are also connected to the movable structure. The hexapod metering arrangement can be connected to the movable structure via an attachment different from the attachment used to attach the operating tool to the movable structure. The hexapod metering arrangement can be directly connected to the movable structure (for example, rather than via an attachment that is primarily intended for an operating tool).

[0243] pass Fig.29The flowchart of shows a method for controlling a coordinate positioning machine. In step S1, the metering arrangement 26 is connected to the movable structure (or platform) 22. In step S2, the drive arrangement 28 is connected to the movable structure (or platform) 22. In step S3, a tool (such as a measuring probe 30 or a cutting tool) is connected to the movable structure (or platform) 22. Therefore, at this point, all three components are connected to the movable structure (or platform) 22. In step S4, the drive arrangement 28 is used to move the tool around in the working volume 34 (the metering arrangement 26 is still connected to the movable structure). In step S5, an operation is performed using the tool, such as performing a touch trigger operation on the workpiece surface using the measuring probe 30, or performing a machining operation on the workpiece surface using a cutting or machining tool. In step S6, when the operation occurs (for example, so that the position of the tip of the measuring probe 30 or the cutting tool can be determined), the metering arrangement 26 is used to determine the position of the tool in the working volume 34. In step S7, the determined position is associated with the operation performed (eg so that a touch trigger event can be associated with a position measurement for the event).

[0244] See above Figure 4 It is described that the kinematic coupling is very effective in isolating deformation in one half of the coupling from being transmitted to the other half of the coupling. Thus, the first coupling 38a helps prevent deformation of the drive portion 22b of the movable structure 22 (caused by the forces acting on that portion by the drive arrangement 28) from being transmitted to the metering portion 22a (and thereby to the metering arrangement 26), and similarly for the second coupling 38b with respect to the fixed structure 24. Referring now to Figure 30 to Figure 35 Let us describe such a kinematic connection in more detail.

[0245] Fig.30 is a perspective view of a kinematic coupling 80 having a first portion 81 and a second portion 82. The kinematic coupling 80 may be applied to Figure 4 For example, when applied to the (lower) coupling 38b, Fig.30 The first part 81 and the second part 82 correspond to Figure 4 The first part 81 has three V-shaped grooves 83a, 83b, 83c, which are engaged with three corresponding balls 84a, 84b, 84c of the second part 82 (when the first part 81 and the second part 82 are connected to each other). Fig.30Also shown are biasing features 85 and orientation features 86. In this example, the biasing feature 85 is an aperture through which a biasing member (such as a bolt) can pass to engage with a corresponding threaded aperture (not shown) in the second part 82; the biasing member is arranged not to touch the sides of the aperture so as not to provide any additional constraints, and the biasing member acts only to bias the first part 81 toward the second part 82 to ensure that the two halves remain in kinematic contact with each other and do not separate. However, the biasing can be provided by gravity or magnetic devices instead, for example. In this example, the optional orientation feature 86 is two eccentric apertures through which corresponding protruding pins (not shown) on the second part 82 protrude to ensure that the first part 81 is correctly oriented on the second part 82; for example, in the case where the V-shaped groove is arranged without any rotational symmetry, the orientation feature is not required. In practice, the distance between the features of the kinematic coupling 80 may be farther than suggested by the illustration; the spacing of these features depends on the overall size of the associated platform and takes into account mechanical stability and force transmission requirements.

[0246] Fig.31 and Fig.32 1 and 2 show a top view and a perspective view of the first part 81. In use, the first part 81 is positioned onto the second part 82 so that the three balls 84a, 84b, 84c of the second part 82 each sit in and abut against one of the three V-shaped grooves 83a, 83b, 83c of the first part 81, as shown in FIG. Fig.33 When coupled, each ball 84a, 84b, 84c makes point contact with the opposite side of the V-shaped groove 83a, 83b, 83c on which it rests, thereby forming a total of six point contact portions C1 to C6, as shown in FIG. Fig.34 As shown. According to the principles of kinematic constraints, as further explained above, each point contact provides constraint in one of the six degrees of freedom, and having exactly six point contacts results in perfect (kinematic) constraint without over-constraint. In practice, it will be appreciated that although pure point contacts give theoretical kinematic constraints, in practice the loads will be spread over a small surface area rather than concentrated at a single point; but the basic principles of kinematic constraints still apply. By using six constraints to constrain the six degrees of freedom, one half of the connector is maintained in a fixed spatial relationship with the other half of the connector; see, for example, Figure 4 , the metering portion 22a of the movable structure 22 maintains a fixed spatial relationship with the driving portion 22b of the movable structure 22.

[0247] As mentioned above, when applied to Figure 4 When the lower connecting member 38b is Fig.30 The second part 82 corresponds to Figure 4The drive portion 24b has a higher coefficient of thermal expansion than the metering portion 24a (the CTE of these parts are not matched). Accordingly, when the machine experiences the same ambient temperature in use, any increase in ambient temperature will cause the drive portion 24b (including the second connecting portion 82) to expand more than the metering portion 24a (including the first connecting portion 81). Normally, the different CTEs of the parts on both sides of a rigid connecting member cause strains to occur in the connecting member (or in other words, at the interface between two parts with different CTEs), but in this case, the kinematic design of the connecting member helps to avoid the development of such strains. This is because the triangle formed by the three spheres 84a to 84c (see Fig.30 ) simply expands outward relative to the other side of the coupling, wherein each pair of contact points C1 / C2, C3 / C4, C5 / C6 moves linearly along its corresponding V-shaped groove 83a, 83b, 83c. This does not generate additional strain in the coupling. Fig.30 The connector 80 is used for Figure 4 A similar analysis applies when the upper link 38a of FIG. 1 is moved. In this context, the effectiveness of the kinematic link can be explained by the fact that each of the point constraints C1 to C6 only constrains a single degree of freedom while allowing (if necessary) movement in other degrees of freedom (for example, if one part expands or contracts or deforms differently than another part), thereby preventing undesirable strains in the link.

[0248] It will be appreciated that other forms of kinematic coupling are possible in which the arrangement of the six contact points C1 to C6 is different. Fig.36 A 3-2-1 arrangement of contact points is shown, wherein contact of ball 84a with the conical recess creates a set of three contact points C1, C2, C3, contact of ball 84b with the V-groove recess creates a pair of two contact points C4, C5, and contact of ball 84c with the planar surface creates a single point C6. Such a kinematic coupling also helps prevent the development of strains in the coupling due to differential thermal expansion and contraction of portions 81 and 82, wherein contact points C4, C5 move outwardly along their V-grooves and contact point C6 moves along the planar surface as portion 82 expands relative to portion 81. Although there may be some relative rotation between portions 81 and 82, this effect is controlled and can be compensated for by, for example, the same amount of rotation at the other end of metering arrangement 26 (i.e., such that Figure 4 The rotation at coupling 38a in the embodiment is the same as the rotation at coupling 38b, thereby causing the entire metering arrangement 26 to rotate slightly without any change in the overall configuration).

[0249] Other types of non-kinematic couplings are also suitable for other applications, such as the elastomeric spacers or washers mentioned above, as these also prevent at least a portion of any additional thermal expansion and contraction of the drive frame from being transferred to the metrology frame.

[0250] It will be appreciated that the operation of the coordinate measuring machine 21 may be controlled by a program running on the machine 21, and in particular by, for example Figure 3 The control of the extendable legs may be provided by a program running on a coordinate measuring machine controller such as the controller C schematically shown in FIG. It will be appreciated that control of the extendable legs may be provided by a program operating on the controller C. Such an operating program may be stored on a computer readable medium, or may be embodied in a signal such as a downloadable data signal provided from a website on the Internet. The appended claims should be understood to cover the operating program itself, or as a record on a carrier, or as a signal, or in any other form.

[0251] Although the above embodiments are primarily described in the context of coordinate measuring machines, the concepts are more generally applicable to any type of coordinate positioning machine, such as comparators, scanners, machine tools, positioning devices (e.g., for optical components), prototype manufacturing machines, and various other uses.

Claims

1. A coordinate positioning machine comprising a drive frame and a metrology frame, the drive frame comprising a drive arrangement for moving a movable structure around within a working volume of the machine, and the metrology frame comprising a metrology arrangement for measuring the position of the movable structure within the working volume, in, the metering arrangement and the drive arrangement are coupled to the movable structure and the fixed structure of the machine, respectively, wherein (a) the metrology arrangement is a hexapod metrology arrangement and the drive arrangement is a non-hexapod drive arrangement, the non-hexapod drive arrangement being adapted to move the movable structure relative to the fixed structure within the working volume of the machine, and / or (b) the drive arrangement is constrained to move the movable structure about within the working volume of the machine in less than six degrees of freedom relative to the fixed structure, and the metrology arrangement is adapted to measure the position of the movable structure within the working volume relative to the fixed structure in more degrees of freedom than the drive arrangement, wherein the metrology frame has a lower coefficient of thermal expansion than the drive frame, thereby causing the drive frame to have additional thermal expansion or contraction compared to the metrology frame, and wherein the drive frame is coupled to the metrology frame via a coupling arrangement adapted to prevent at least a portion of the additional thermal expansion or contraction of the drive frame, or at least a portion of the deformation associated with the additional thermal expansion or contraction of the drive frame, from being transferred to the metrology frame, wherein the movable structure is adapted to carry an operable tool, wherein the metering arrangement and the drive arrangement are also coupled to the movable structure; wherein the operable tool is a tool for interacting with or operating on a workpiece located within the working volume during operational use of the machine; and Therein, the metrology arrangement remains coupled to the moveable structure to provide position measurements relative to the moveable structure during operational use of the machine, rather than purely for calibration purposes.

2. A coordinate positioning machine as claimed in claim 1, wherein: The metrology arrangement comprises a plurality of measuring transducers arranged in parallel for providing a corresponding respective plurality of measurement values ​​from which the position of the movable structure can be determined.

3. The coordinate positioning machine of claim 2, wherein the plurality of measurement transducers is a plurality of independent measurement transducers.

4. The coordinate positioning machine of claim 2, wherein: The measuring transducer is a length measuring transducer.

5. A coordinate positioning machine as claimed in any one of claims 2 to 4, wherein: The measurements relate to different respective spacings between the moveable and fixed structures of the machine.

6. A coordinate positioning machine as claimed in claim 5, wherein: The measurement transducer is adapted to provide a direct measurement of the separation, or a direct measurement of a change in the separation as the structure moves about within the working volume, from which change the separation can be determined.

7. A coordinate positioning machine as claimed in any one of claims 2 to 6, wherein: Each of the measuring transducers comprises an encoder scale and an associated readhead.

8. A coordinate positioning machine as claimed in any one of claims 2 to 7, wherein: The metrology arrangement comprises a plurality of extendable legs arranged in parallel, the extendable legs corresponding in number to the number of measuring transducers, and each measuring transducer of the plurality of measuring transducers is associated with a different respective extendable leg of the plurality of extendable legs.

9. A coordinate positioning machine as claimed in any one of claims 2 to 8, comprising six such measurement transducers.

10. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement is a non-telescopic drive arrangement.

11. A coordinate positioning machine as claimed in any preceding claim, wherein: The metering arrangement is a top-down metering arrangement.

12. A coordinate positioning machine as claimed in any one of claims 1 to 10, wherein: The metering arrangement is a bottom-up metering arrangement.

13. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement is a top-down drive arrangement.

14. A coordinate positioning machine as claimed in any one of claims 1 to 12, wherein: The drive arrangement is a bottom-up drive arrangement.

15. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement is adapted to maintain the moveable structure in a substantially constant orientation when moving about within the working volume.

16. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement comprises a plurality of mechanical linkages connected in parallel between the movable structure and a fixed structure of the machine, each mechanical linkage being actuated by a drive mechanism acting between the fixed structure and the mechanical linkage.

17. A coordinate positioning machine as claimed in claim 16, wherein: The drive mechanism is a rotary drive mechanism.

18. The coordinate positioning machine of claim 16, wherein: The drive mechanism is a linear drive mechanism.

19. A coordinate positioning machine as claimed in claim 16, 17 or 18, wherein: Each mechanical linkage includes at least two substantially parallel rods to maintain the moveable structure in a substantially constant orientation as it moves about within the working volume.

20. A coordinate positioning machine as claimed in any one of claims 16 to 19, wherein: The drive arrangement comprises three such mechanical linkages.

21. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement is a three-slip arrangement.

22. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement is adapted to move the structure about within the working volume in three degrees of freedom.

23. A coordinate positioning machine as claimed in claim 22, wherein: The three degrees of freedom are three translational degrees of freedom.

24. A coordinate positioning machine as claimed in any preceding claim, wherein: The metrology arrangement is adapted to measure the position of the structure in six degrees of freedom.

25. A coordinate positioning machine as claimed in any preceding claim, wherein: The metering arrangement and the drive arrangement are each arranged between the movable structure and a fixed structure of the machine.

26. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement comprises a plurality of actuators arranged in parallel.

27. A coordinate positioning machine as claimed in claim 26, wherein: The drive arrangement comprises a plurality of actuators of a different type than the metering arrangement, arranged in parallel.

28. A coordinate positioning machine as claimed in any preceding claim, wherein: The drive arrangement comprises a plurality of measuring transducers, separate from the measuring transducers of the metrology arrangement, for providing corresponding respective measurement values ​​from which the position of the movable structure can be determined independently of a position determined based on the measurement values ​​from the metrology arrangement.

29. A coordinate positioning machine as claimed in any preceding claim, wherein: The joint arrangement is a kinematic or pseudo-kinematic joint arrangement.

30. A coordinate positioning machine as claimed in any preceding claim, wherein: The movable structure comprises a drive portion associated with the drive arrangement and a metering portion associated with the metering arrangement, the drive portion of the movable structure being coupled to the metering portion of the movable structure via the coupling arrangement.

31. A coordinate positioning machine as claimed in any preceding claim, comprising a fixed structure having a drive portion associated with the drive arrangement and a meter portion associated with the meter arrangement, the drive portion of the fixed structure being coupled to the meter portion of the fixed structure via the coupling arrangement.

32. A coordinate positioning machine as claimed in claim 30 or claim 31, wherein: The thermal expansion coefficient of the metering portion is lower than the thermal expansion coefficient of the driving portion.

33. A coordinate positioning machine as claimed in any preceding claim, wherein: The movable structure carries an operating tool.

34. A coordinate positioning machine as claimed in any preceding claim, wherein: The machine is a coordinate measuring machine or a comparator.

35. A coordinate positioning machine as claimed in claim 33, wherein: The machine is a coordinate measuring machine or a comparator and the operating tool is a surface sensing device or a measuring probe.

36. A coordinate positioning machine as claimed in any one of claims 1 to 33, wherein: The machine is a machine tool.

37. A coordinate positioning machine as claimed in claim 33, wherein: The machine is a machine tool and the operating tool is a mechanical tool for shaping or machining a material.

38. A method of controlling a coordinate positioning machine according to any preceding claim, the method comprising: An operating tool is coupled to the movable structure, the operating tool is moved about within the working volume using the drive arrangement, wherein the metering arrangement is also coupled to the movable structure, an operation is performed with the operating tool, and a position of the operating tool within the working volume is determined using the metering arrangement.

39. A method as claimed in claim 38, in the context of controlling a coordinate positioning machine as claimed in claim 34 or 35, wherein: The operation is a measuring operation.

40. A method as claimed in claim 38, in the context of controlling a coordinate positioning machine as claimed in claim 36 or 37, wherein: The operation is a machining operation.

41. A computer program which, when executed by a controller for a coordinate positioning machine, causes the controller to perform the method of claim 38, 39 or 40.

42. A computer readable medium having stored thereon computer program instructions for controlling a coordinate positioning machine controller to perform the method of claim 38, 39 or 40.

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