Coordinate positioning machine

Abstract

A coordinate positioning machine comprises: a plurality of drive shafts (61), each of which is a rotary drive shaft or a linear drive shaft, for positioning a platform (12) within a working volume of the machine; and a linear balancing shaft (L), which is separate from any of the drive shafts (61), for balancing the platform (12). With such a balancing arrangement (50), the individual linear balancing shafts (L) can be substantially invariant to changes in orientation of the drive shafts (61), and can therefore be balanced, for example by a simple counterweight (30), to provide an ideal or near ideal balance for the platform (12) throughout the working volume of the machine. A balancing arrangement (50) is also disclosed, in which the balancing shafts (R1, L1, L2) and the force generator (30) are arranged relative to each other so that horizontal movement of the platform (12) does not substantially result in a net movement of the force generator (30) and / or does not substantially result in work being done on the force generator. A balancing arrangement (50) is also disclosed, in which a series of balancing shafts (R1, L1, L2) has at least one rotating balancing shaft (R1), and in which a force generator (30) is arranged behind or at a predetermined horizontal distance from a first rotating balancing shaft (R1) in the series. A balancing arrangement (50) having a series of balancing shafts (R1, L1, L2) with at most one rotating balancing shaft (R1) between the force generator (30) and the ground (14) is also disclosed.

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 coordinate measuring machine 1 of a known type is shown, having three linear axes x, y and z arranged in series orthogonally to each other, wherein the z-axis is aligned with gravity g. A measuring probe 3 is mounted on a vertical column 8 which is slidable in the z-direction within a carriage 2; this relative movement defines the z-axis. The carriage 2 itself is supported on a horizontal beam 7 and is slidable along the beam 7 in the y-direction; this relative movement defines the y-axis. In turn, the beam 7 is slidable in the x-direction on a pair of guide rails 6; this relative movement defines the x-axis. A computer controller 5 operates to drive each component (column 8, carriage 2, beam 7) to the appropriate position along its corresponding respective axis to place the measuring probe 3 in the desired position within the working volume of the machine and to move it so as to be in sensing relationship with a workpiece 9 supported on a fixed platform 4. The measuring probe 3 may be mounted to the vertical column 8 in a fixed manner as shown, or the measuring probe may be moved by a control system such as a control system such as a computer controller 5. Figure 1 An articulated probe head shown in the inset of FIG. 8 is mounted on a vertical column 8 , wherein the articulated probe head provides two rotational axes a, b in addition to the three linear axes x, y, z.

[0003] Each axis x, y, z is driven independently of each other axis by a corresponding respective motor (not shown). Each axis x, y, z is also encoded or sensed independently of each other axis by a corresponding respective sensor, wherein the output from the sensor is used to determine the position of the measurement probe 3 (or any tool attached to the column 8). Each axis is equipped with a length measurement transducer having an encoder scale (in Figure 1 In order to measure relative movement between two parts, an encoder scale is suitably mounted on one part and a readhead is suitably mounted on the other part.

[0004] Figure 1 The coordinate measuring machine 1 of FIG. 1 can be referred to as a Cartesian coordinate measuring machine, because it has three linear axes x, y and z arranged orthogonally to each other. Figure 1The Cartesian or orthogonal axis arrangement shown, in the absence of any drive (or other braking force) from the motors associated with the x, y, z axes respectively, the system will be stable or self-supporting along the x, y axes, since the z axis is aligned with gravity and the x, y axes are orthogonal to gravity, but along the z axis, the vertical column 8 will naturally fall to its lowest possible position due to the force of gravity. In order to stabilize the system in the z direction, it is known to provide a balance specifically for the z axis to offset the weight of the vertical column 8 (and any components attached thereto, such as the measurement probe 3). For example, such z-axis balancing arrangements for Cartesian coordinate measurement or positioning machines are known from US6058618, US5257461, US4964221A and US4229136.

[0005] In the attached figure Figure 2 Another type of coordinate measuring machine 10 is schematically illustrated. The coordinate measuring machine 10 generally includes a movable platform 12 and a fixed platform 14 that are supported and move relative to each other by a plurality of telescopic or extendable legs 16 disposed therebetween. The fixed platform 12 forms part of the fixed structure of the machine 10. The movable platform 12 and the fixed platform 14 may also be referred to as worktables (or structures or parts), and the extendable legs 16 may also be referred to as struts (or actuators). When there are six such extendable legs 16 (e.g., Figure 2 ), the machine 10 is generally referred to as a hexapod machine.

[0006] The extendable legs 16 are typically mounted on the platforms 12, 14 via ball joints 18, wherein each leg 16 has a respective ball joint 18 at one or both ends thereof (e.g., Figure 2 14 (shown), or sharing a ball joint 18 at one or both ends with an adjacent leg 16. Each extendable leg 16 is typically formed as a pair of tubes, wherein one tube is telescopically moved within the other tube by a drive mechanism (e.g., a linear motor) to provide extension and retraction of the extendable leg 16, as indicated by arrows within each extendable leg 16, and as described in more detail in WO 2017 / 174966. As described in WO 2007 / 144573, a degree of separation may also be provided between the drive parts and the metrology parts of each strut. As described in WO 2019 / 073246, a drive arrangement that is not only separate from but also different from the metrology arrangement may also be provided.

[0007] Different relative positions between the movable platform 12 and the fixed platform 14 can be achieved by extending the legs 16 by different amounts. The relative position at any time is monitored by a plurality of length measuring transducers 17, one for each extendable leg 16. Each length measuring transducer 17 may include an encoder scale paired with a readhead, wherein the encoder scale is suitably mounted on one of a pair of telescopic tubes and the readhead is suitably mounted on the other telescopic tube. Extension of the legs 16 thus causes the encoder scale to move past the readhead, thereby allowing the length of the extendable leg 16 to be measured (or derived from the measurement). The computer controller 15 operates to set the length of each extendable leg 16 to provide the desired relative movement between the platforms 12, 14. By having six such length measuring transducers 17, relative position can be measured in six corresponding respective degrees of freedom (three translational degrees of freedom and three rotational degrees of freedom).

[0008] The workpiece 19 is mounted on the lower (fixed) platform 14, and the measuring probe 13 is mounted on the upper (movable) platform 12. A working volume (or operating volume) 11 is defined between the upper (movable) platform 12 and the lower (fixed) platform 14, wherein the measuring probe 13 is positioned (i.e. moved to a desired position) in the working volume 11 by operating the extendable legs 16. Figure 2 The arrangement can be referred to as a "bottom-up" arrangement because the extendable legs 16 extend upward from the fixed platform 14 to the movable platform 12. Figure 3 This arrangement is shown more schematically in .

[0009] Alternatively, as shown in the accompanying drawings Figure 4 In the case of a "top-down" arrangement, as schematically shown in FIG, the extendable legs 16 extend downwardly from the fixed structure 14 to the movable platform 12, wherein the measurement probe 13 is mounted to the lower surface of the movable platform 12, and the workpiece is mounted to another part of the fixed structure 14 below the movable platform. These types of arrangements are discussed in more detail in WO 2019 / 073246, which also describes the use of non-hexapod drive arrangements in combination with hexapod metrology arrangements.

[0010] The measuring probe 13 is only one example of an operating tool that can be mounted on the movable platform 12 to enable operations to be performed on the workpiece 19. Depending on the intended application, the operating tool can be suitable for measuring, probing or scanning in the case of a coordinate measuring machine, or for machining or drilling in the case of a machine tool. It is also possible to mount the workpiece 19 on the movable platform 12 and the measuring probe 13 (or other operating tool) on the fixed platform 14.

[0011] Figure 2The coordinate measuring machine 10 of can be referred to as a non-Cartesian coordinate measuring machine because, unlike, for example Figure 1 In contrast to the presented Cartesian machine, the axes are not arranged orthogonally according to the Cartesian coordinate system. Figure 2 The coordinate measuring machine 10 can be considered to have six axes of movement (or six drive axes), corresponding to (and defined by) the six extendable legs 16. In this sense, the axes of the coordinate positioning machine can be considered to be associated with the degrees of freedom sensed (e.g., by transducers or encoders), noting that axes can be linear or rotational, and that a coordinate positioning machine can have a combination of linear and rotational axes.

[0012] Figure 2 The coordinate measuring machine 10 can also be referred to as a "parallel kinematics" coordinate measuring machine because its movement axes are arranged in parallel. Figure 1 This is in contrast to the coordinate measuring machine 1 of , which can be referred to as a "serial kinematic" coordinate measuring machine, because its axes of movement are instead arranged in series. Another type of serial kinematic machine is an inspection robot or manual articulated arm, which has multiple articulated arm members connected in series by multiple rotary joints.

[0013] Figure 2 The movable platform 12 and measurement probe 13 of the coordinate measuring machine 10 will have an associated weight that needs to be supported by the extendable legs 16. Therefore, the motors for extending and retracting the extendable legs 16 will need to work to even hold the movable platform 12 in a stable vertical position, and this will use energy and generate heat. Energy efficiency is particularly important in metrology applications because the heat generated by the motors can cause thermal expansion of the components, which is uncontrolled and unknown and can affect the metrology results in a way that cannot be calibrated.

[0014] For this reason, a counterbalance may be provided in such a machine to support at least a portion of the weight of the movable platform 12. An exemplary counterbalance arrangement for a hexapod coordinate positioning machine is disclosed in WO 2017 / 174966 and is shown in the accompanying drawings. Figure 5 Shown in. Figure 5 The hexapod coordinate positioning machine has similar Figure 493 and is provided with a balancing arrangement 90 having a first arm 92 and a second arm 94 connected to each other via a hinge 93. The first arm 92 is connected to the movable platform 12 via a ball 91 which is inserted into a retaining element 26 on top of the movable platform 12, forming a universal ball joint, and the second arm 94 is connected to a fixed part of the machine 10 (not shown) via a rotary joint 95 and to the hinge 93 via another rotary joint 97. The hinge 93 generates a balancing force by means of a spring 96 which is just visible through an opening in the sheet forming the housing of the hinge 93; the spring 96 is as shown in FIG. Figure 5 90. These springs 96 generate a force acting between the first arm 92 and the second arm 94, and in particular, this force applies a moment (or torque) to the first arm 92 about the rotary joint 98, which in turn applies a balancing force to the platform 12 via the ball 91 and the retaining element 26. When the platform 12 moves in the horizontal plane, the second arm 94 swings about the rotary joint 95, thereby also moving the hinge 93 in a large arc in the horizontal plane. When the platform 12 moves in the horizontal plane, the hinge 93 and the spring 96 also rotate about the rotary joint 97, so that the spacing between the spring 96 and the rotary joint 95 varies depending on the position of the platform 12 in the working volume.

[0015] The applicant has realized that, for example Figure 5 The presented balancing arrangements for non-Cartesian machines suffer from one or more of the following disadvantages.

[0016] Firstly, such a counterbalancing arrangement has a moving arm which, in certain positions of the movable platform 12, extends outside the normal working volume, which increases the overall size of the machine and can also create a hazard to the operator. Figure 5 For the machine, this occurs when the platform 12 moves laterally toward the rotary joint 95, pushing the upper portion of the L-shaped second arm 94 to swing back and forth outside the normal working volume.

[0017] Secondly, such a balanced arrangement may exhibit non-ideal behavior, particularly in certain parts of its operating range, such that the weight of the movable platform 12 is not evenly supported around the working volume 11. For example, for Figure 5 Because of the different spring tensions involved, the balancing force provided by spring 96 will vary slightly depending on the z position of platform 12.

[0018] Third, in such a balancing arrangement, the arms 92, 94 and springs 96 adopt different positions and orientations relative to the movable platform 12, depending on the position of the movable platform 12 in the working volume 11. It is particularly desirable that the springs 96 be relatively bulky (and therefore relatively heavy) in order to generate sufficient balancing force to balance the heavy movable platform 12 (and any tools or components coupled thereto). Even for horizontal movement of the movable platform 12, these heavy springs 96 move around, and for certain movements of the movable platform 12 at certain positions within the working volume, the springs 96 may be subjected to very high and highly non-uniform accelerations. Accordingly, for these reasons, the dynamic response of the system (e.g., when accelerated) may be very inconsistent. This is Figure 5 This is a consequence of the fact that the balanced arrangement of comprises only rotational axes (no linear axes, i.e. no linear degrees of freedom), wherein at least two rotational axes are between the heavy spring 96 and the fixed structure of the machine, which causes complex movements of the spring 96. Figure 5 In the balancing arrangement of FIG. 1 , there are two rotational balancing axes 95, 97 between the force generator (i.e., the spring 96) and the ground (i.e., the fixed structure of the machine), but in similar balancing arrangements of known type, there can effectively be three rotational balancing axes between the force generator and the ground. This will be explained below with reference to the accompanying drawings. Fig.11 and Fig.44 for a more detailed discussion.

[0019] Finally, the type of z-axis balancing arrangement described above in connection with Cartesian machines is not applicable at all to non-Cartesian machines, since non-Cartesian machines do not have a fixed z-axis that can be balanced directly. Figure 2 The hexapod coordinate positioning machine 10 shown actually has six linear axes (i.e., six drive axes associated with the six extendable legs 16, respectively), but none of these drive axes are always aligned with gravity, and none of these drive axes are independent of the other drive axes. Instead, movement of the platform 12 in the z-direction involves changes in all six drive axes of the hexapod coordinate positioning machine 10 (i.e., changes in the length of all six extendable legs 16), so it is not possible to provide a z-axis balancing arrangement such as used in Cartesian machines.

[0020] It would therefore be desirable to provide an improved balancing arrangement for a coordinate positioning machine, particularly, but not exclusively, for a non-Cartesian coordinate positioning machine.

[0021] A coordinate positioning machine forming the basis of several aspects of the invention comprises a plurality of drive axes for positioning a movable structure within a working volume of the machine, a plurality of balancing axes for balancing the movable structure, and a force generator for generating a balancing force applied to at least one of the balancing axes.

[0022] According to one aspect of the invention, the balancing axis comprises a linear balancing axis, and the balancing force is applied to the linear balancing axis.

[0023] According to another aspect of the invention, the balancing axis and the force generator are arranged relative to each other such that a movement of the movable structure in a direction perpendicular to gravity substantially does not result in a (net) movement of the force generator other than due to a rotation of the force generator about at most one rotational balancing axis.

[0024] According to another aspect of the invention, the balance axis and the force generator are arranged relative to each other so that a movement of the movable structure in a direction perpendicular to gravity substantially results in no (net) work being done on the force generator (as a whole) other than due to a rotation of the force generator about at most one rotational balance axis.

[0025] According to another aspect of the invention, the balancing axes are arranged in series, the balancing axes include at least one rotational balancing axis, and the force generator is arranged behind the first rotational (or only) balancing axis in the series of balancing axes (or of the series of balancing axes) (when viewed in the direction toward the movable structure).

[0026] According to another aspect of the invention, the balancing axes are arranged in series, the balancing axes include at least one rotational balancing axis, and the force generator is arranged (or positioned) at a predetermined horizontal distance (or spacing or offset) from the first rotational (or only) balancing axis among the balancing axes in series (or of the balancing axes in series) (when viewed in the direction toward the movable structure).

[0027] According to another aspect of the invention, the balancing axis is arranged in series with at most one rotational balancing axis (of the balancing axes in series) between a force generator and a fixed structure of the machine.

[0028] According to another aspect of the invention, there is provided a coordinate positioning machine comprising a plurality of drive axes (each of which is either a rotary drive axis or a linear drive axis) for positioning a movable structure within a working volume of the machine, and a linear balancing axis (separate from any of the drive axes) for balancing the movable structure.

[0029] According to another aspect of the invention, there is provided a method of balancing a coordinate positioning machine having a plurality of drive axes, each of which is a rotary drive axis or a linear drive axis, for positioning a movable structure within a working volume of the machine, the method comprising providing a linear balancing axis, separate from any one of the drive axes, and balancing the movable structure via the linear balancing axis.

[0030] It should be understood that the above aspects may be used independently of each other, or in any suitable combination.

[0031] Embodiments of the invention which employ a linear balancing axis are particularly advantageous for non-Cartesian coordinate positioning machines in which none of the machine's drive axes have a fixed orientation and none of the drive axes can therefore be balanced directly. By providing a separate linear balancing axis which can be balanced directly, the machine can be used, for example, as described below with reference to the accompanying drawings Figure 6 The benefits of the simple (but very effective) linear balancing arrangement described are as follows. Such a balancing arrangement is able to provide ideal (or near ideal) balancing behavior regardless of the position (particularly the z position) of the movable structure within the working volume, unlike, for example, the above reference Figure 5 This is possible in embodiments of the present invention because the orientation of the linear balancing axis does not substantially change with changes in the orientation of the drive axis, thereby providing a stable and constant reference for the balancing arrangement.

[0032] For such embodiments of the invention, when the movable structure moves horizontally (except possibly due to rotation of the force generator about at most one rotational equilibrium axis), no force generator is caused to move (or no net work is done on the force generator), thus, for example, referring to Figure 5 The drive arrangement does less work (uses less energy and generates less heat) than the balanced arrangement described above. In this regard, the force generator is typically relatively heavy (e.g., a large counterweight or bulky spring), so the benefit of moving the force generator back and forth as little as possible can be significant. Figure 5 Compared to the type of balanced arrangement shown, even where the force generator moves about at most one axis of rotation, the dynamic response is more controlled and / or less extreme without rapid changes in acceleration of the force generator.

[0033] For embodiments where the force generator is arranged behind the first rotational balance axis in the series of balance axes, the force generator does not rotate for any movement of the movable structure, which again results in less work being done by the drive arrangement. Even if not strictly arranged in series behind the first rotational axis, it is advantageous to place the force generator close to (preferably along) the rotational balance axis to reduce the amount of work done when rotating the force generator.

[0034] Reducing the amount of work done by the drive arrangement is advantageous because this in turn reduces the heat generated by the drive arrangement, thereby reducing the adverse effects of thermal expansion and contraction of machine parts on metrology results. For hexapod coordinate positioning machines, it is beneficial to avoid having the drive arrangement do additional work, especially for horizontal movement of the platform, because the drive struts are generally more powerful in the vertical direction than in the horizontal direction due to their predominantly vertical orientation.

[0035] Unless otherwise stated, the balancing axes may be arranged in series.

[0036] Unless otherwise stated, a coordinate positioning machine may include at most one rotational balance axis (in a series of balance axes) between a force generator and a fixed structure of the machine.

[0037] Unless otherwise stated, the balance axis may comprise at least one linear balance axis.

[0038] The balance axis includes at least two linear balance axes.

[0039] The balance axis includes two linear balance axes.

[0040] The or each linear balance axis may have a substantially constant orientation relative to gravity.

[0041] The coordinate positioning machine may include a linkage for transmitting the counterbalancing force to the movable structure.

[0042] The linkage may be a rigid linkage.

[0043] The linkage may be a mechanical linkage.

[0044] The linkage may include a plurality of rigidly interconnected linkages connected by a plurality of joints.

[0045] The linkage may be adapted to provide movement of the moveable structure in a direction perpendicular to gravity while causing the balancing force to do substantially no work.

[0046] The linkage and force generator may be arranged relative to one another to maintain the balancing force in a substantially constant orientation relative to gravity as the movable structure moves about the working volume.

[0047] The balancing force transmitted to the movable structure by the linkage may be substantially aligned with the force of gravity.

[0048] The linkage may be separate and / or independent from any of the drive axes.

[0049] The force generator and linkage may be arranged substantially in a plane with respect to one another and remain so as the moveable structure moves about the working volume.

[0050] The plane may be substantially aligned with gravity.

[0051] The linkage and force generator may be arranged relative to each other such that the direction of the balancing force does not substantially change as the movable structure moves back and forth in the working volume.

[0052] During the vertical movement of the movable structure, the linkage does not change significantly in form. During the vertical movement of the movable structure, the linkage can move as a whole.

[0053] The balance axis may include first and second linear balance axes arranged substantially perpendicular to each other.

[0054] The second linear balance axis may be provided by a linkage.

[0055] The linkage may be adapted to produce a change in motion from linear to substantially vertical.

[0056] The linkage may be a Scott Russell linkage. The linkage may be a Scott Russell type linkage.

[0057] The balancing force may be applied to a predetermined linear balancing axis among the plurality of balancing axes.

[0058] The orientation of the predetermined linear balance axis may be substantially invariant to any changes in the orientation of the drive axis.

[0059] The orientation of the predetermined linear equilibrium axis may not substantially change with actuation of the drive axis.

[0060] The predetermined linear equilibrium axis may have a substantially constant orientation relative to gravity.

[0061] The predetermined linear equilibrium axis may be substantially aligned with gravity.

[0062] The predetermined linear balance axis may be a first linear balance axis.

[0063] The predetermined linear balancing axis may be behind any rotational balancing axis in the series of balancing axes (as viewed in the direction towards the movable structure).

[0064] The predetermined linear balancing axis may be in front of at least one rotational balancing axis of the balancing axes connected in series (as viewed in a direction towards the movable structure).

[0065] The linkage may be adapted to absorb horizontal movement of the movable structure and convert vertical movement of the movable structure into corresponding vertical movement of the linkage along a predetermined linear equilibrium axis. Such vertical movement of the linkage may be vertical movement of the entire linkage along a predetermined linear equilibrium axis without substantial change in form.

[0066] The linkage may be adapted to maintain the balancing force in a direction substantially parallel to the predetermined balancing axis.

[0067] The movable structure may be balanced along a predetermined linear balance axis via a linkage.

[0068] At least a portion of the weight of the moveable structure may be supported via the linkage by a substantially constant balancing force (or a component thereof) applied to the linkage along a predetermined linear balancing axis.

[0069] The coordinate positioning machine may include at least one support member (e.g., slidably) coupled to a predetermined linear balancing axis. The balancing force may be arranged to act on the at least one support member, and a linkage may be connected (or coupled) between the movable structure and the at least one support member (to transfer the balancing force from the at least one support member to the movable structure).

[0070] At least one support member may be arranged to be slidably movable along a predetermined linear balancing axis, for example along a linear track.

[0071] The or each support member may provide a rotational balancing axis of a plurality of balancing axes.

[0072] Vertical movement of the movable structure caused by the drive arrangement can be converted by the linkage device into a corresponding vertical movement of at least one supporting member, resulting in work done by a balancing force applied to (acting on) the at least one supporting member, and the work done is substantially equal to but opposite in direction to the work done by the force of gravity acting on the movable structure.

[0073] A first value may be considered substantially equal to a second value if the first value is within 20%, or more preferably within 10%, or more preferably within 5%, or more preferably within 1% of the second value.

[0074] Horizontal movement of the moveable structure caused by the drive arrangement may be converted by the linkage into at most vertical movement of the at least one support member, resulting in the force(s) applied to the at least one support member doing substantially no work overall.

[0075] The coordinate positioning machine may comprise a first support member and a second support member, each support member being arranged to slideably move along a track substantially aligned with gravity. Movement of the movable structure in a direction perpendicular to the or each track may be converted by a linkage into movement of the second support member along its track, without the first support member substantially moving along its track. Movement of the movable structure in a direction parallel to the or each track may be converted by a linkage into movement of at least the first support member along its track in the same direction and by the same amount.

[0076] The balancing force may be applied to the first support member instead of the second support member.

[0077] The force generator can apply a force F in a direction substantially opposite to the force of gravity. iapplied to each support member i, where ∑ i F i ~mg, the linkage device translates or converts the changes dx, dy, dz in the movable structure into the changes dx in each supporting member i i ,dy i 、dz i , so that∑ i F i dz i ~mg.dz、dx i ~0 and dy i ~0, where m is the mass of the movable structure, g is the acceleration due to gravity, and i is an integer greater than or equal to 1, and where F i At least one of them can be zero.

[0078] The balancing force generated by the force generator may act between at least one support member of the machine and the fixed structure.

[0079] Unless stated otherwise, the balancing axis may comprise at least one rotational balancing axis.

[0080] The balance axes may include a single rotational axis (eg, excluding any rotational axes that may be provided as part of a universal joint) or four rotational balance axes (eg, three of which may be provided as part of a universal joint).

[0081] Unless otherwise stated, the force generator may be arranged at a predetermined horizontal distance (or spacing or offset) behind or from a first rotational balancing axis in (or of) the balancing axes in the series (when viewed in the direction towards the movable structure).

[0082] The force generator may be arranged close to the first rotational balance axis. In other words, the predetermined horizontal distance may be small. The predetermined horizontal distance may be substantially zero.

[0083] The predetermined horizontal distance may be less than 50% (or more preferably less than 25%, or more preferably less than 10%, or more preferably less than 5%) of a representative horizontal distance (or spacing or offset) between the first rotational balance axis and the movable structure. This may be the case for any (normal or real) position of the movable structure within the working volume.

[0084] The representative horizontal distance (between the first rotational balance axis and the movable structure) may be determined relative to a representative point of the movable structure, such as the geometrical centre of the movable structure or its centre of gravity.

[0085] Alternatively, the representative horizontal distance may be between the first rotational balance axis and the center of the working volume, or may be a representative width of the working volume.

[0086] The predetermined horizontal distance (between the first rotational balance axis and the force generator) may be determined relative to a representative point of the force generator, such as the geometric center of the force generator or its center of gravity.

[0087] The predetermined horizontal distance (between the force generator and the first rotational balance axis) may be substantially constant, and this may be maintained as the movable structure moves about the working volume.

[0088] Unless otherwise stated, the balance axis and the force generator can be arranged relative to each other so that movement of the movable structure in a direction perpendicular to gravity does not substantially result in a net movement of the force generator other than due to rotation of the force generator about at most one rotational balance axis.

[0089] Unless otherwise stated, the balance axis and the force generator can be arranged relative to each other so that a movement of the movable structure in a direction perpendicular to gravity substantially does not result in work being performed on the force generator, other than due to a rotation of the force generator about at most one rotational balance axis.

[0090] At most one rotational balancing axis may be the first (or only) rotational balancing axis of the balancing axes in series (when viewed in a direction towards the movable structure).

[0091] Each drive axis of the plurality of drive axes may be a rotary drive axis or a linear drive axis.

[0092] Each of the plurality of balancing axes may be a rotational balancing axis or a linear balancing axis.

[0093] The balancing axis may be separate from the drive axis.

[0094] Each balancing axis may be separate and / or independent and / or distinct from each of the drive axes.

[0095] The balancing force generated by the force generator may be substantially aligned with the force of gravity.

[0096] The or each balancing axis to which the balancing force is applied may have a substantially constant orientation relative to gravity.

[0097] The or each balancing axis to which the balancing force is applied may be substantially aligned with gravity (eg in the case of a linear balancing axis) or substantially perpendicular to gravity (eg in the case of a rotational balancing axis).

[0098] The balance axis and the force generator may be arranged relative to each other such that movement of the movable structure in a direction parallel to gravity causes work done on the force generator to be substantially equal to the work done by the force of gravity acting on the movable structure.

[0099] As described above, a first value may be considered substantially equal to a second value if the first value is within 20%, or more preferably within 10%, or more preferably within 5%, or more preferably within 1% of the second value.

[0100] The force applied to the balancing axis may be at least a component of the actual balancing force generated by the force generator. For example, the force applied to the balancing axis may be a component of the balancing force about the balancing axis (eg, along a linear balancing axis or about a rotational balancing axis).

[0101] Applying the balancing force to the balancing axis may include applying the balancing force along or about the balancing axis (eg, along a linear balancing axis or about a rotational balancing axis).

[0102] The balancing axis may be passive and / or inactive and / or undriven and / or unpowered.

[0103] Balancing the movable structure may include providing a balancing force to the movable structure. Balancing the movable structure may include supporting at least a portion of the weight of the movable structure.

[0104] The balancing force applied to the balancing axis may be transferred to the movable structure via at least one of the other balancing axes.

[0105] The balancing force can be transmitted via a linkage.

[0106] The balancing force may be a substantially constant balancing force.

[0107] The force generator may be adapted to generate a substantially constant balancing force.

[0108] The balancing force (or at least its magnitude) may be substantially equal to the force (or at least its magnitude) of gravity acting on the movable structure.The force generator may be adapted to generate a balancing force (of a magnitude) substantially equal to the force of gravity acting on the movable structure.

[0109] The force generator may include a counterweight that creates tension in a string or cord or cable or wire or the like coupled thereto.

[0110] The force generator may include a spring that generates a spring force. The spring may be a constant force spring, such as a fusee spring.

[0111] Each balance axis (except those forming part of the universal joint) may have (or maintain) a substantially constant orientation relative to gravity (as the moveable structure moves about the working volume).

[0112] It may be the case that (as the moveable structure moves about the working volume) none of the drive axes has (or maintains) a substantially constant orientation relative to gravity.

[0113] The balancing axis may be arranged between the movable structure and the fixed structure of the machine.

[0114] The drive axis may be arranged between a movable structure and a fixed structure of the machine.

[0115] The machine may include a fixed structure.

[0116] Relative movement about a rotational (drive or balance) axis may be sensed by a corresponding rotational transducer.

[0117] Relative movement along a linear (drive or balance) axis may be sensed by a corresponding linear transducer.

[0118] The drive axis may form part of a drive arrangement for moving the movable structure about the working volume, and the balancing axis forms part of a balancing arrangement for supporting at least part of the weight of the movable structure.

[0119] The machine may comprise a fixed structure, and the drive arrangement and the balancing arrangement may be split and / or connected in parallel between the movable structure and the fixed structure.

[0120] The drive arrangement and the balancing arrangement may be separately connected to the movable structure.

[0121] The balancing arrangement may be arranged such that at least 80% of its total mass (or of the total mass of the force generator) is within 10% of the horizontal spacing between the (linear and / or first rotational) balancing axis (of the balancing axes in series) and the centre of the working volume.

[0122] The drive arrangement may include a plurality of extendable legs connected between a movable structure and a fixed structure of the machine.

[0123] The extendable legs may be oriented (on average) closer to vertical than to horizontal (at least for a central position of the moveable structure within the working volume).

[0124] The coordinate positioning machine may include six such extendable legs.

[0125] A linear (drive or balancing) axis may be an axis that provides (of the drive arrangement or the balancing arrangement, as the case may be) a linear degree of freedom.

[0126] A linear (drive or balancing) axis may be an axis that provides constrained relative linear motion between two machine elements (of the drive arrangement or balancing arrangement as the case may be)).

[0127] The rotational (drive or balancing) axis may be the axis that provides (of the drive arrangement or the balancing arrangement, as the case may be) a rotational degree of freedom.

[0128] A rotational (drive or balancing) axis may be an axis that provides constrained relative rotational motion between two machine elements (of a drive arrangement or a balancing arrangement, as the case may be).

[0129] A balancing force may be generated along an axis that is substantially constantly aligned with or remains substantially constantly aligned relative to gravity as the moveable structure moves about the working volume.

[0130] The coordinate positioning machine may comprise a brake for maintaining the moveable structure in the same position in the working volume when the drive axis is not being controlled to move the moveable structure around the working volume.

[0131] Each of the drive axes may be a linear drive axis.

[0132] Drive axes may be respectively associated with the extendable legs.

[0133] The coordinate positioning machine may comprise a metrology arrangement for measuring the position of the moveable structure within the working volume.

[0134] The metrology arrangement may be adversely affected by the heat generated by the drive arrangement.

[0135] The drive arrangement and the metrology arrangement may be connected between the movable structure and the fixed structure, respectively.

[0136] The metrology arrangement may comprise a plurality of length measuring transducers.

[0137] Each length measurement transducer may comprise an encoder scale mated to a readhead.

[0138] The transducers may be respectively associated with the extendable legs.

[0139] The coordinate positioning machine may be a non-Cartesian coordinate positioning machine. The drive axes of the coordinate positioning machine may not be mutually orthogonal.

[0140] The coordinate positioning machine may be a parallel kinematic coordinate positioning machine. The drive axes of the coordinate positioning machine may be arranged in parallel.

[0141] The coordinate positioning machine may be a hexapod coordinate positioning machine.

[0142] The movable structure may include a movable platform and at least one tool supported on the movable platform.

[0143] The tool may be or may include a measurement probe.

[0144] The coordinate positioning machine may be a coordinate measuring machine.

[0145] According to another aspect of the invention there is provided a coordinate positioning machine comprising: a movable structure; a drive arrangement for moving the movable structure back and forth within a working volume of the machine; and a counterbalancing arrangement for supporting at least a portion of the weight of the movable structure that would otherwise be supported by the drive arrangement.

[0146] The balancing arrangement may be rotatable about a balancing axis, which may be a fixed balancing axis.The balancing arrangement may comprise a force generator for generating a balancing force and a linkage for transmitting the balancing force to the movable structure.

[0147] The balancing arrangement (e.g., the linkage of the balancing arrangement) may be arranged and / or adapted to provide (or accommodate or allow or enable) at least one of the following:

[0148] (a) relative movement between the movable structure and the equilibrium axis in a direction perpendicular to gravity and / or perpendicular to the equilibrium axis without substantially causing (net) work to be done on the force generator (by the drive arrangement) and / or without substantially causing the force generator to move or be moved and / or without substantially causing (net) movement of the force generator; and

[0149] (b) movement of the movable structure (e.g., relative movement between the movable structure and the balance axis, optionally in a direction perpendicular to gravity and / or perpendicular to the balance axis) without substantially changing (or modifying or affecting) the spacing (or offset or distance) and / or the relative orientation of the force generator and / or the balance force (generated by the force generator) and the balance axis (or gravity in the case of relative orientation).

[0150] Moving the movable structure around the balance axis by a predetermined angle may cause the linkage device and / or the force generator and / or the balance force to move around the balance axis by a corresponding angle.

[0151] Moving the movable structure vertically a predetermined amount within the working volume may cause the linkage to move vertically (eg, translate or slide) a corresponding amount.

[0152] The force generator and / or the balancing force may be arranged substantially in, on, or along a plane containing the balancing axis and the connection between the linkage and the moveable structure, and this may remain so as the moveable structure moves about the working volume.

[0153] The force generator and / or the counterbalancing force, the counterbalancing axis and the linkage may be arranged substantially in one plane and may remain so as the movable structure moves about the working volume.

[0154] The equilibrium axis may be arranged outside the working volume, for example laterally of the working volume.

[0155] The linkage may be arranged such that for such movement of the movable structure relative to the equilibrium axis, the force generator (and the equilibrium force generated thereby) performs substantially no work (or work) (net or gross work).

[0156] The linkage may be arranged such that for such movement of the movable structure relative to the axis of equilibrium there is substantially no (net) movement of the force generator in a direction perpendicular to gravity.

[0157] The linkage may be arranged such that for movement of the movable structure in a direction aligned with gravity, the work done by the force generator (the balancing force produced by the force generator) is substantially equal but opposite to the work done by gravity acting on the movable structure.

[0158] The linkage may be adapted to isolate or decouple movement of the moveable structure relative to the axis of equilibrium from the force generator.

[0159] The force generator may be arranged on or close to the equilibrium axis.

[0160] The force generator may be (closely) associated with the equilibrium axis.

[0161] A force generator may be coupled to the balance axis.

[0162] At least a portion of the force generator may be arranged on or along the equilibrium axis.

[0163] The balancing arrangement or force generator may have at least 80% of its total mass within 10% of the horizontal spacing between the balancing axis and the centre of the working volume.

[0164] The (net) distance moved by the force generator (eg under the action of a force derived or induced or generated by the drive arrangement) may be less than 10% of the distance moved by the movable structure during such movement relative to the equilibrium axis.

[0165] The linkage may be adapted to isolate or decouple movement of the moveable structure relative to the equilibrium axis from the at least one support member so that a substantially constant orientation relative to gravity can be maintained.

[0166] The spacing between the force generator and the balance axis can be determined based on a representative point of the force generator, such as the geometric center or center of gravity of the force generator. In this regard, the force generator can include multiple parts that move relative to each other, so that if one part moves, another part can move in the opposite direction so that the center point does not move.

[0167] The linkage arrangement may be arranged and / or adapted to cause (or provide or allow) the movable structure to move relative to the equilibrium axis in a direction perpendicular to gravity without causing (through the drive arrangement) any work (or any work being done) on the force generator (net work or gross work).

[0168] The linkage arrangement may be arranged and / or adapted to cause (or provide or allow) the movable structure to move or be moved relative to the equilibrium axis in a direction perpendicular to gravity without causing (through the drive arrangement) any work to be done (or any work to be done) on the force generator (net work or gross work).

[0169] The linkage arrangement may be arranged and / or adapted to enable movement of the movable structure relative to the equilibrium axis in a direction perpendicular to gravity without substantially doing work on the force generator (or without causing the drive arrangement to do work or work on the force generator) (net work or gross work).

[0170] The linkage arrangement may be arranged and / or adapted such that for movement of the movable structure in a direction perpendicular to gravity, there is substantially no movement (or at least no net movement) of the force generator relative to the balance axis and the force generator (or the balance force) does substantially no work (or causes no work to be done).

[0171] The linkage arrangement may be arranged and / or adapted such that substantially no work is done on the force generator or substantially no work is done by the force generator at least when the movement of the movable structure in a direction perpendicular to gravity is also in a direction towards / away from the equilibrium axis (or along a line intersecting therewith).

[0172] The linkage may be arranged and / or adapted such that for movement of the movable structure in a direction perpendicular to gravity, movement relative to the equilibrium axis does substantially no work on the force generator and the force generator does substantially no work (or does not cause it to do work).

[0173] The linkage may be arranged and / or adapted such that for movement of the movable structure in a direction perpendicular to gravity, there is substantially no net movement of the force generator relative to the equilibrium axis and the force generator does substantially no work (or is not caused to do work).

[0174] The linkage arrangement may be arranged and / or adapted to allow movement of the movable structure in a direction perpendicular to gravity without substantially performing work on (or causing work to be performed on) the force generator or substantially without performing work on (or causing work to be performed on) the force generator.

[0175] The linkage may be arranged and / or adapted to isolate (at least partially isolate) such movement of the moveable structure from the force generator so as not to result in work (or work being done) on the force generator.

[0176] The linkage may be arranged and / or adapted to maintain a balancing force in a direction substantially parallel to or relative to the balancing axis when the moveable structure is moved about the working volume by the drive arrangement.

[0177] A force generator may alternatively also be referred to as a (balancing) force source or (balancing) force origin.

[0178] Movement of a movable structure relative to other objects (e.g., an axis of balance) can be considered to be related to movement of a particular part or point on the movable structure (e.g., a connection between the movable structure and a linkage (a part or point or location at which the linkage is connected or coupled to the movable structure), or the center of gravity of the movable structure, or the center of a platform that forms part of the movable structure).

[0179] Movement relative to the balance axis may be considered as movement (directly) toward or away from the balance axis. Movement relative to the balance axis may be considered as movement in a direction (or along a line) that intersects the balance axis. Movement relative to the balance axis may be considered as movement radially relative to the balance axis. Movement relative to the balance axis may be considered as movement along a radius extending from the balance axis. Movement relative to the balance axis may be considered as movement along a line extending radially from the balance axis.

[0180] Work done on a force generator is not the same as work performed by the force generator. Work done by a force generator is work done by the force generated internally by the force generator itself (note that the work done may be negative); if a force is applied to an object, then the work done by a force generator (or the force generated by the force generator) is equal to the force multiplied by the distance the object moves under the influence of that force. On the other hand, work done on a force generator is work done by a force generated external to the force generator and applied to the force generator, and the work done on the force generator is equal to the force multiplied by the distance the force generator moves under the influence of that force. If the force generator does not move at all for a particular movement of the movable structure, then no work is done on the force generator, because otherwise it would have been caused to move (accelerate). It will become apparent from the detailed description that follows that there may be some relative internal movement of parts of the force generator, as long as there is no net movement overall (and thus no net work done). For the above references Figure 5 The known balancing arrangement described, although the spring (force) does no work on the movement of the horizontal platform because there is no change in the elongation of the spring, there is certainly work done by the drive strut on the spring (ie the force generator) because the spring is moved (accelerated).

[0181] The term "position" as used herein may be considered to refer to a position and / or orientation. The term "vertical" as used herein may be considered to refer to a direction substantially aligned with gravity. The terms "horizontal" or "lateral" as used herein may be considered to refer to a direction substantially perpendicular to gravity.

[0182] To distinguish the situation where the stated characteristics apply only to a small portion of the artificially restricted movements of the movable structure (i.e., not to the full type and range of movements that normally occur in a normal working routine), the stated characteristics of the balanced arrangement can be considered to apply to all possible movements of the movable structure in at least one contiguous portion of the working volume (or at least those movements that comply with any stated restrictions, such as movements perpendicular to gravity) of not less than 25% of the working volume, more preferably not less than 50% of the working volume, more preferably not less than 75% of the working volume, and more preferably the entire working volume.

[0183] In the case where the force generator includes multiple parts that are movable relative to each other (e.g., multiple counterweights), reference to the absence of movement of the force generator can be taken to mean that there is no overall or net movement of the parts forming the force generator. For example, if one part (e.g., a counterweight) moves upward and another part moves downward, it can be considered that there is an overall or net movement. It will also be understood that in this context, the rotation of only one part (e.g., a pulley) does not count as movement of that part because the center of the part does not move.

[0184] Alternatively, the force generator may be considered to have a representative point, and the position (and therefore movement) of the force generator may be determined based on the representative point. For example, the representative center point may be the geometric center or center of gravity of the force generator, or a weighted average position of multiple parts taking into account the corresponding forces acting on the parts (e.g., the force generator may include one counterweight supported by a single pulley arrangement and another counterweight of twice the mass supported by a dual pulley arrangement).

[0185] When reference is made to substantially no movement of a first part caused by a particular movement of a second part (optionally relative to a third part), this may be understood to mean that the movement of the first part is less than 10%, more preferably less than 5%, more preferably less than 1% of the movement of the second part (optionally relative to the third part).

[0186] Similarly, when it is stated that substantially no work is done on a first part as a result of a particular movement of a second part, this is understood to mean that the work done on the first part is less than 10%, more preferably less than 5%, more preferably less than 1% of the work done on the second part by such movement.

[0187] Reference will now be made, by way of example, to the accompanying drawings, in which:

[0188] Discussed above Figure 1 is a schematic diagram of a Cartesian coordinate positioning machine;

[0189] Discussed above Figure 2 is a schematic diagram of a non-Cartesian coordinate positioning machine;

[0190] Discussed above Figure 3 is corresponding to Figure 2 A schematic diagram of a bottom-up arrangement of a non-Cartesian coordinate positioning machine;

[0191] Discussed above Figure 4 is a schematic diagram of a top-down arrangement, which is Figure 3 An alternative to bottom-up deployment;

[0192] Discussed above Figure 5 A known type of balancing for a non-Cartesian coordinate positioning machine is shown;

[0193] Figure 6 and Figure 7 A balancing arrangement for a non-Cartesian machine is schematically illustrated, which is stable in the z-direction but unstable in the x- and y-directions; such an arrangement does not constitute an embodiment of the present invention;

[0194] Figure 8 yes Figure 6 and Figure 7 A more schematic representation of the balanced arrangement of;

[0195] Fig. 9 Provided Figure 8 A broader representation, showing instead Figure 8 Universal force generator of the pulley and counterbalance arrangement depicted;

[0196] Fig.10 is a schematic representation of a coordinate positioning machine according to an embodiment of the present invention, Fig. 9 the development of the presented scheme;

[0197] Fig.11 yes Figure 5 A schematic diagram of a known balanced arrangement of , for ease of comparison, is similar in form to Fig.10 form;

[0198] Fig.12 It is used for Figure 1 A schematic diagram of a known balancing arrangement for the z-axis of a Cartesian coordinate positioning machine is shown, which for ease of comparison is similar in form to Fig.10 form;

[0199] Fig.13 is a schematic diagram of a known balancing arrangement for the z-axis of a Cartesian coordinate positioning machine having Fig.12 Different x, y and z axis arrangements, for ease of comparison, the schematic is similar to Fig.10 form;

[0200] Fig.14 A side view of a non-Cartesian coordinate positioning machine including a balancing arrangement embodying the present invention is provided;

[0201] Fig.15 Provided Fig.14 A partial top view of a non-Cartesian coordinate positioning machine is shown;

[0202] Fig.16 shows a balanced arrangement with Fig.14 and Fig.15 Compared to linear and rotational balancing axes arranged in different ways;

[0203] Fig.17 yes Fig.14 , Fig.15 and Fig.16 A more schematic representation of the machine, and forming the basis for an analysis of the inherent stability of the balanced arrangement;

[0204] Fig.18 Mainly shows Fig.17 linkages and platforms in order to account for the forces acting on these parts;

[0205] Fig.19 It shows how lateral movement of the platform results in no vertical movement of the lower support and only vertical movement of the upper support;

[0206] Fig. 20 based on Fig.10 The schematic representation shown is Fig.10 The supporting structure is Fig. 20 a set of one or more support members;

[0207] Fig.21 and Fig. 22 Corresponding to Fig.18 and Fig.19 , but shows an alternative linkage arrangement that is not suitable for use in embodiments of the present invention;

[0208] Fig.23 and Fig.24 Corresponding to Fig.18 and Fig.19 , showing another alternative linkage arrangement that is not suitable for use in embodiments of the present invention;

[0209] Figure 25 to Figure 27 Respectively similar to Fig.19 , Fig. 22 and Fig.24 , showing how the platform moves when the upper support member moves vertically with the lower support member fixed in place;

[0210] Fig.28 Demonstrates the same operating principle Fig.17 An "upside-down" alternative to the arrangement of

[0211] Fig.29 Demonstrates the same operating principle Fig.28 "Longer reach" alternatives to the arrangement of

[0212] Fig.30 Shows something like Fig.29 , but using a slightly different linkage arrangement;

[0213] Fig.31 Demonstrates the same operating principle Fig.17 A "double pulley" alternative to the arrangement;

[0214] Fig.32 Provides the formation Fig.18 Illustration of how the connecting rods of a linkage arrangement may be shaped in practice;

[0215] Fig.33 Provides the formation Fig.30 Illustration of how the connecting rods of a linkage arrangement may be shaped in practice;

[0216] Fig.34 shows how a platform can be supported by two equilibrium arrangements, in this example, Fig.17 Of the type shown, each balancing arrangement provides only a partial balancing force;

[0217] Fig.35 An alternative balancing arrangement is shown in which forces are applied to both supports and in which, when the platform moves laterally, the two supports move vertically, but in opposite directions;

[0218] Fig.36 Shown Fig.35 Variations of the arrangement;

[0219] Fig.37Demonstrates the same operating principle Fig.35 An alternative balancing arrangement to that shown and also including a double pulley arrangement associated with each support;

[0220] Fig.38 Shown in about Fig.37 How a constant force spring (such as a uniform force conical wheel spring) can be used in any of the previous embodiments in this example of the embodiment;

[0221] Fig.39 Demonstrates constant force springs in Fig.18 Use in the embodiments of the present invention;

[0222] Fig.40 A different form of linkage than that shown in the previous embodiments is shown, having telescoping tubes and also including a double pulley arrangement;

[0223] Fig.41 It is demonstrated that the balancing arrangement implementing the operating principles set out in the preceding embodiments can also be applied to balancing Cartesian coordinate positioning machines;

[0224] Fig.42 Demonstrated a method for balancing a serial kinematic non-Cartesian robot arm Fig.16 Balanced arrangement;

[0225] Fig.43 A Cartesian balancing arrangement embodying the invention is shown for balancing a Cartesian or non-Cartesian coordinate positioning machine; and

[0226] Fig.44 Demonstrated based on Figure 5 However, a modification is made so that the origin of the balancing force returns to an embodiment that is in line with the first rotational balancing axis.

[0227] Figure 6 For example, the above reference Figures 2 to 5 A schematic diagram of a simple type of balancing arrangement for a non-Cartesian coordinate positioning machine is shown. A balancing arrangement embodying the invention may be considered as starting from Figure 6 The balanced arrangement shown is inspired by Figure 6 The balanced arrangement does not in itself constitute an embodiment of the present invention. Figure 6 The examples are limited to platform 12 moving in two dimensions (x and z) within the plane of the page, i.e., the illustrated balancing arrangement is not capable of addressing platform 12 moving within the entire three-dimensional working volume. In fact, as will be discussed in more detail below, Figure 6 The balancing arrangement is not even suitable for balancing movements of the platform 12 in the x-direction; of more interest is the response of the balancing arrangement to movements of the platform 12 in the z-direction.

[0228] Different from the above reference Figure 5The described known balance has non-ideal balance performance for different z positions of the movable platform 12. The applicant has realized that for example Figure 6 The simple balancing arrangement shown is desirable because it provides a constant balancing response regardless of the z position of the movable platform 12. In this respect, the mass m of the counterweight 30 is provided to match exactly (or in practice as closely as possible) the mass of the movable structure (i.e. the movable platform 12 and the measurement probe 13) moved by the drive arrangement. The drive arrangement comprises a plurality of extendable legs 16, each of which has an associated linear drive axis 61.

[0229] Since the working volume in which the platform 12 operates must be substantially free of obstructions, the counterweight 30 is conveniently positioned outside the side of the working volume, with the platform 12 connected to the counterweight 30 via a thin rope 32 extending over two pulleys 46 having a lateral spacing sufficient to provide suitable lateral spacing between the platform 12 and the counterweight 30.

[0230] To obtain a given acceleration a, the force F exerted on the object must be equal to its mass m times the acceleration a. Thus, when an object falls under the influence of gravity, the force F acting on the object is equal to its mass m times the acceleration due to gravity g, so that F = mg, where g is the gravitational constant.

[0231] Thus, assuming no support from the extendable legs 16, a gravitational force mg will act downwardly on both the platform 12 and the counterweight 30, and a corresponding tension will be generated in the string 32 which will provide an upward force also mg, rendering the system perfectly balanced in the z direction.

[0232] Furthermore, regardless of the z position of the platform 12, exactly the same balancing force will be applied, i.e., the system is not affected by Figure 6 The effect of changing dz is shown, which is consistent with Figure 5 The depicted known balancing arrangements are different. When the mass of the movable structure changes (e.g., if tools of different masses are attached to the platform 12), the mass of the counterweight 30 can also be conveniently adjusted by adding or removing mass (e.g., in the manner of balancing weights used with old-fashioned weighing scales).

[0233] However, if Figure 7 As shown, the balancing arrangement is certainly unstable for movement in the x-direction toward and away from the counterweight. As the x-position of the platform 12 changes by dx, because the string 32 has a constant length, the counterweight 30 will have to rise, and doing so involves doing work. The concept of work applied to the balancing system is explored in more detail below when considering the operation of an embodiment of the present invention.

[0234] Accordingly, in Figure 7After such movement (dx) as shown, when the platform 12 is released, the counterweight 30 will naturally tend to fall back to the position shown in FIG. Figure 6 Its previous (lower energy) state as shown, and the platform will swing inwardly (in the x-direction) back to the center (directly below the left pulley 46).

[0235] So, despite some useful features, Figure 6 and Figure 7 The balancing arrangement shown is not particularly suitable for use in stabilising the movable structure of a coordinate positioning machine because, ideally, the movable structure in such a machine is stable in the x, y and z directions in the absence of drive from the drive arrangement, rather than just along a single axis in the z direction.

[0236] Figure 8 Provided Figure 6 and Figure 7 A more schematic representation of a balancing arrangement of a machine is shown, showing a movable platform P and a counterweight C connected via a pulley arrangement, which is itself supported by (connected to) a fixed structure of the machine, conveniently referred to as being connected to the "ground" G. The movable platform P is connected to the ground G via a drive arrangement D and a metrology arrangement M, respectively. The drive arrangement D is responsible for moving or driving the platform P around the working volume, and the metrology arrangement is responsible for measuring the position of the platform P in the working volume. The multiple drive axes of the drive arrangement D are schematically represented as a plurality of lines (corresponding to, for example, Figure 2 The six drive struts or extendable legs of the machine 16 or Figure 1 The x, y, z drive axes of the machine) and similarly correspond to the measuring axes of the measuring arrangement M; these axes may be kinematic axes in parallel or in series, the kinematic axes being Cartesian or non-Cartesian.

[0237] As mentioned above, the metrology arrangement M may be formed integrally with the drive arrangement, e.g. Figure 2 As shown, the measuring arrangement may be separated from the drive arrangement D at least to some extent, for example as described in WO 2007 / 144573 and WO 2019 / 073246. Figure 8 In the representation of , the metrology arrangement M and the drive arrangement D are shown as separate entities, each separately connected to the ground G, but they may in fact be the same entity (i.e. the combined drive and metrology arrangement D / M). It will also be understood that the platform P refers not only to the platform 12, but also to anything supported by the platform 12 (such as a tool, e.g. a measurement probe). In view of this, the term "movable platform" may be considered herein to be equivalent to and interchangeable with "movable structure".

[0238] Fig. 9 Provided Figure 8A more general representation of Figure 8 The pulley and balancing arrangement depicted in is replaced (or represented) by a force generator Q, which produces a balancing force mg acting between the platform P and the ground G. Fig. 9 is exactly equivalent to Figure 8 The balance force mg is Figure 8 The tension created in the string on the left side of the pulley arrangement. Figure 8 The pulley arrangement of can be considered as merely to reverse the direction of the balancing force generated by the counterweight C (which acts downwards, while the balancing force must act upwards on the platform P). It should be noted that the force acting on the ground G will be 2 mg (also taking into account the offset Figure 8 The force required to generate the tension mg in the thin line on the right side of the support counterweight C; although not shown in the figure, the tension in the thin line acts downward on the pulley and upward on the platform P and counterweight C).

[0239] Fig.10 The present invention is schematically shown in the following embodiments. The applicant has designed a new machine architecture, which draws on Fig. 9 The beneficial aspects of the simple equilibrium scheme of , namely, complete (or nearly complete) equilibrium stability in the z (vertical) direction, but modified Fig. 9 A solution is provided to overcome the disadvantages as described above, thereby also providing balanced stability in the x and y (horizontal) directions.

[0240] Simply put, from Fig. 9 The constant equilibrium force mg is maintained, but Fig.10 In the solution of FIG. 1 , this force mg does not act directly between the platform P and the ground G, but rather acts between an intermediate support S and the ground G, the support S being movable (e.g., slidable) along a vertically arranged linear balancing axis L. In turn, the platform P is supported by the support S via a linkage K. With this arrangement, the platform P is still balanced in the vertical direction by the balancing force mg acting along the linear balancing axis L, but via the linkage K instead of directly. Such a machine architecture thus provides a plurality of drive axes for positioning the platform P within the working volume, and also provides a single linear balancing axis L for balancing the platform P.

[0241] The linkage K transfers the balancing force mg generated by the force generator Q to the platform P (or alternatively, this can be viewed as the linkage K transferring the weight mg of the platform P to the support S). As will be described in more detail below, the linkage mechanism K provides or enables horizontal movement of the platform P relative to the support S (and the balancing force mg), and does so in a manner that does not affect the vertical balance provided by the force mg acting between the ground G and the support S. The linkage K can be viewed as isolating the horizontal movement of the platform P from the support S. These characteristics of the linkage K enable the use of Figure 6 A simple (and very effective) vertical balancing solution is provided, even for a platform P that moves horizontally and vertically within the working volume.

[0242] Since a constant balancing force mg matching the weight of the platform P (and any supported components) can be generated (e.g., via a simple balancing arrangement), and this constant balancing force F acts in a constant direction regardless of the position of the platform P in the working volume, the balancing arrangement according to an embodiment of the present invention has the benefit of being fully (or nearly fully) balanced throughout the working volume, which is consistent with Figure 5 This is different from the known balanced arrangements of FIG.

[0243] It should be understood that Fig.10 In the drawings, it is appropriate to refer to the balancing force (generated by force generator Q) as simply F rather than mg, thereby acknowledging that the balancing force F does not strictly need to match the weight mg of the movable platform P exactly, but the balancing force F is sufficient to support at least some of the weight mg that would otherwise have to be supported by the drive arrangement (thereby reducing the amount of heat generated and work done by the drive arrangement).

[0244] In order to enable the platform P to move fully in all three dimensions within the working volume, including into and out of the drawing page, the balancing arrangement may be provided with additional degrees of freedom, Fig.10 The additional degrees of freedom are shown as rotational degrees of freedom about the rotational balancing axis R. The additional degrees of freedom can in turn become translational degrees of freedom. The additional degrees of freedom can be provided in the linkage K itself or as part of it. Fig.10 The rotational balancing axis R is shown, it should be noted that the linear balancing axis L (and the balancing force F) may be offset from (and parallel to) the rotational balancing axis R, wherein the linear balancing axis L and the rotational balancing axis R are effectively arranged in series, which will be referred to below Fig.14 It is apparent from the specific embodiment described. The linear balance axis L can also be coaxial with the rotational balance axis R, Fig.16 This is the case with the embodiment of .

[0245] In a tandem arrangement, the rotational balancing axis R may also be before (behind) or after (in front of) the linear balancing axis L (in the direction from the ground G to the platform P). The linear balancing axis L may be considered as a first linear balancing axis L1, and the linkage K may be considered as providing a second linear balancing axis L2 for the balancing arrangement. The rotational balancing axis R may also be considered as a first rotational balancing axis R1, with three additional rotational balancing axes R2 / 3 / 4 being provided by a coupling between the linkage K and the platform P. Fig.10 Two possible arrangements of these axes are schematically shown in the inset to the right and will be referred to separately below. Fig.14 and Fig.16 This is discussed in more detail. In both arrangements, the balancing force F is applied to (along) the linear balancing axis L1 .

[0246] The linkage K and the force generator Q are advantageously arranged relative to each other to ensure that, for movement of the platform P in a direction perpendicular to the gravity g, substantially no net work is done on the force generator Q (and there is no net movement of the force generator Q), except possibly due to rotation of the force generator about at most one rotational equilibrium axis (which may be arranged to pass through the force generator Q or at least close to the force generator). This is advantageous because in order to generate sufficiently large equilibrium forces to support the heavy platform P, it is necessary for the force generator Q to be relatively large, having a large mass. Moving (accelerating) such a large mass requires the application of a relatively large force (because force is equal to mass times acceleration), which in turn means that the drive arrangement does a relatively large amount of work in doing so (because the work done on an object is equal to the force applied to the object times the distance the object moves).

[0247] In the context of coordinate measuring machines, which require high accuracy and which are adversely affected by unknown and / or uncontrolled and / or non-uniform heat sources (and associated thermal expansion of critical parts of the machine), it is desirable to reduce the amount of work done (heat generated) by the drive arrangement. Figure 2 In a hexapod coordinate positioning machine of the type shown, it is particularly beneficial to avoid having the drive arrangement do additional work for horizontal movement of the platform because the drive struts 16 are more powerful in the vertical direction than in the horizontal direction due to their physical arrangement (so it is easier to accelerate the platform and any auxiliary mass vertically than horizontally).

[0248] for Figure 5In the balanced arrangement, even when the platform 12 is moved horizontally, there is movement of the heavy force generator (i.e., the spring 96 carried by the hinge 93), which requires the drive strut 16 on the hinge 93 to do work (to accelerate it). In addition, the acceleration of the hinge 93 is not uniform for all positions of the platform 12 within the working volume, with some movements of the platform 12 causing very high accelerations of the hinge 93 and other movements causing much lower accelerations; this has an adverse effect on the dynamic response of the coordinate positioning machine. In an embodiment of the present invention, for radial movement of the platform toward and away from the balance axis, substantially no work is done on the force generator, and for circular movement of the platform about the balance axis, the acceleration is uniform, so that the dynamic response is better controlled.

[0249] The linkage K and the force generator Q also advantageously cooperate to maintain the balancing force F in a substantially constant orientation relative to the gravity g (and relative to the balancing axis L or R) when the platform P is moved about the working volume by the drive arrangement D. This greatly simplifies the technical requirements of the force generator Q so that the force generator can generate a constant-force balancing force F. For example, in Figure 5 In the case of a balanced arrangement, for vertical movement of the platform 12, the arms 92, 94 will change angles relative to each other and the direction of the spring force generated by the spring 96 will change. This in turn will cause a varying spring force from the spring 96 and a balancing force for the platform 12 which will not remain constant throughout the working volume unless a complex and bulky (heavy) constant force spring is used.

[0250] Through Fig.10 Compared with the scheme of Fig.11 Provided in Figure 5 Schematic representation of a known non-Cartesian balancing arrangement. Platform P is connected to the ground G via a combined drive and metrology arrangement D / M, and on the other side, a hinge H is provided on a balancing arm A that swings about an indicated axis of rotation R1, hinge H also rotates about axis of rotation R2, and arm B rotates about axis of rotation R3 (plus an additional three axes of rotation R4 to R6 provided by a universal joint connecting arm B to platform P). Force generators Q (e.g. Figure 5 The spring 96) generates a balancing force F. The arrangement of the balancing axis is schematically shown in Fig.11 In the lower box, this also indicates that the balancing force F is applied to (and about) the rotational balancing axis R3. It should be noted that the balancing arm A must swing about the marked rotational axis R1 and the hinge H must swing about the rotational axis R2 even for a movement of the platform P in the plane of the drawing; such a movement would not be possible with a fixed linkage. Fig.10 The embodiments shown are different. Fig.11In the case of the known balancing arrangement represented, the balancing force F does not act in a constant direction and is not directly connected to the ground G. Furthermore, even for a movement of the platform P towards or away from the arm A, the force generator Q moves (accelerates), which means that the drive arrangement D does work on the force generator Q, and as mentioned above, such a movement is not uniform around the working volume. This is due to Fig.11 The balanced arrangement comprises only the axis of rotation, the force generator Q having at least two axes of rotation ( R1 and R2 ) between it and the ground G.

[0251] Fig.12 In a similar form, the Figure 1 A schematic representation of a known balancing arrangement for a Cartesian machine is shown. As mentioned above, because a Cartesian machine has a simple x, y, z arrangement of orthogonal axes, the z axis (i.e. Figure 1 The column 8) can be balanced individually via a balancing force F acting effectively between the z-axis and the adjacent y-axis. For a Cartesian machine with a different series arrangement of axes (such as disclosed in US 4229136), the balancing arrangement looks more like Fig.13 , where the balancing force F acts between the z-axis and the ground. However, as mentioned above, it is not obvious how such a balancing arrangement is applicable to non-Cartesian machines, because Fig.13 In the case of the arrangement, the z drive axis is directly balanced, but non-Cartesian machines do not have a z drive axis to be balanced.

[0252] Now refer to Fig.14 and Fig.15 describe Fig.10 As with the non-Cartesian coordinate positioning machine described above, the movable platform 12 supports the measurement probe 13 and is driven back and forth within the working volume by the extendable legs 16, in particular by a controller, such as Figure 2 The controller 15 shown in FIG. 1 is controlled to move the measurement probe 13 so that it is in sensing relationship with a workpiece 19 supported on a fixed structure 14 of the machine. The fixed structure 14 includes a fixed structure 14 as described above with reference to FIG. Figure 4 The illustrated "top-down" arrangement includes a lower portion on which the workpiece 19 is supported and an upper portion that supports the extendable legs. As described above, each extendable leg 16 extends and retracts in a linear manner such that Fig.14 The drive arrangement of can be considered to include a plurality of linear drive axes 61 respectively associated with the plurality of extendable legs 16. As the platform 12 moves about the working volume, the orientation of each of these linear drive axes 61 changes.

[0253] Fig.14 The machine is provided with a balancing arrangement 50, which is based on the above reference Fig.10 The principle operation described above has a counterweight 30 connected to the lower one of the two support members 24 via a pulley arrangement. The support members 24 (including the upper support member and the lower support member 24) can be collectively referred to as a support. The pulley arrangement has a string (or rope or cable) 32 connected to the counterweight 30 at one end and to the lower support member 24 at the other end, and the string 32 passes through two pulleys 46 which are themselves supported by the housing 40. The counterweight 30 can be considered as a force generator (with an associated mass) for the balancing arrangement 50, generating a balancing force mg in the form of tension in the string 32, which is connected to the lower support member 24 (via the pulley 46 and the string 32) so as to apply tension (balancing force) to the lower support member 24. Since the counterweight 30 generates a balancing force that acts downward (in the direction of gravity), and since the balancing force applied to the lower support member 24 must act upward (in the direction opposite to gravity), the pulley 46 and the string 32 can be considered to provide a function of reversing the direction of the gravity force mg acting downward on the counterweight 30 to provide a balancing force mg acting upward on the lower support member 24. A single pulley 46 may be used instead of two pulleys as long as the pulley 46 has sufficient width to provide the desired lateral spacing between the counterweight 30 and the track 44.

[0254] The support member 24 can slide along a vertically arranged track or guide 44 attached to the housing 40, thereby providing a balanced arrangement 50 (equivalent to Fig.10 The balancing arrangement shown) defines a linear balancing axis L. The linear balancing axis L is in line with the balancing force mg acting upward on the lower support member 24 (but these linear balancing axes can be offset relative to each other and / or the balancing force can be applied to the lower support member 24 at a certain angle to the balancing axis L, wherein the components of the balancing force act along the balancing axis L). The housing 40 is itself rotatably attached to the fixed structure 14 of the machine via a rotary joint 41, allowing the housing 40 (with the counterweight 30) to rotate about a vertical rotation axis R. This rotation axis R defines the balancing arrangement 50 (equivalent to Fig.10 The arrangement shown) has a rotational balance axis R.

[0255] It should be noted (in this embodiment) that the rotational balance axis R is offset from the linear balance axis L (i.e., offset from the line of the balance force mg applied to the lower support member 24), but in other embodiments, the two axes may be coincident or coaxial (see Fig.16). Despite the offset, in this embodiment the counterweight 30 itself is disposed on (or along) the balancing axis R (i.e., the offset from the balancing axis R is zero), which is advantageous because as the balancing arrangement 50 rotates about the rotational balancing axis R, due to the circumferential movement of the platform 12 about the balancing axis R, it is desirable to have as much of the rotating mass as possible as close to the rotational axis R to minimize the work done by such movement (work done by the moving mass).

[0256] Therefore, it is desirable to at least position the counterweight 30 as close to the rotational balance axis R as possible, if not directly on the rotational balance axis R. In this regard, the mass of other parts of the balancing arrangement 50, such as the support member 24, the track 44, the pulley 46, the string 32, and even the housing 40, may be considered insignificant compared to the mass of the counterweight 30 itself. In any case, it is desirable to position as much of the mass of the balancing arrangement 50 as possible as close to the rotational balance axis R as possible.

[0257] Use from Fig.10 Borrowed term, Fig.14 A series arrangement is shown, where the order of the elements when viewed from the ground G to the platform P is as follows: [G → R → L → K → P], which is Fig.14 The rotation axis R can be considered to be after (or before) the linear axis L (when viewed in the order from G to P). Since everything after R in the series arrangement will rotate about R, and since the force generator Q (counterweight 30) is associated (connected) with the linear axis L after the rotation axis R in the series arrangement, the force generator Q (counterweight 30) will also rotate about the rotation axis R. Therefore, when the machine elements are arranged in this order, the rotation axis R is after the linear axis L, and it is advantageous to arrange the force generator Q (counterweight 30) along the rotation axis R or at least close to the rotation axis.

[0258] It should be noted that the linkage K effectively provides a second linear axis (i.e., a second linear degree of freedom) for the balancing arrangement 50, while the universal joint 26 effectively provides three rotational axes (three rotational degrees of freedom), so that the total axes are effectively as follows: [G→R1→L1→L2→R2→R3→R4→P]. This is Fig.14 The balancing arrangement 50 includes, in addition to the rotational balancing axes (R2 to R4) provided by the universal joint 26, a single rotational balancing axis (R1) and two linear balancing axes (L1 and L2).

[0259] The balancing force F generated by the force generator Q is applied to (along) the linear balancing axis L1. The force generator Q itself is housed within a housing 40 that is in front of the rotation axis R1 in a serial arrangement of axes. Since the force generator Q is in series in front of the rotation axis R1, it rotates with R1. However, as indicated in the inset portion (B), although the force generator Q is in series in front of the rotation axis R1, the force generator Q is physically substantially in line with the rotation axis R1 so that the mass of the force generator Q is as close to the rotation axis R1 as possible. Recall that the mass of the force generator Q will be quite large because, in this embodiment, it is substantially matched to the mass of the platform 12 and anything attached thereto, so it is beneficial to place the force generator G as close to the rotation axis R1 as possible. However, it is not necessary to place the force generator G directly on the rotation axis R1, as certain benefits are obtained simply by moving the force generator G from the linear axis L1 to the rotation axis R1.

[0260] As described above, the balancing arrangement 50 effectively has two linear balancing axes (i.e., two linear degrees of freedom) and four rotational balancing axes (i.e., four rotational degrees of freedom), or a total of six balancing axes (i.e., six degrees of freedom). In general, to provide full relative movement between two bodies, six degrees of freedom are required (e.g., three linear degrees of freedom and three rotational degrees of freedom, or six linear degrees of freedom, or some other suitable combination of linear degrees of freedom and rotational degrees of freedom), so Fig.14 The balanced arrangement 50 has a full complement of six degrees of freedom. Fig.14 The two linear axes (L1, L2) of the universal joint are substantially perpendicular to each other, the first linear axis (L1) is substantially aligned with gravity, and the second linear axis (L2) is substantially perpendicular to gravity, while the first rotational axis (R1) is substantially parallel to the first linear axis (L1). The three rotational axes (R2 to R4) of the universal joint can be considered to be arranged in series, even if they act in parallel about the same point, because two different rotational axes cannot act in parallel between two rigid structures, because they would conflict with each other (some bending of the connected structure is required to avoid such conflict, but this is not the case here).

[0261] The platform 12 is connected to the support member 24 via a linkage 22, which effectively provides a second linear axis of balance (L2). The linkage mechanism 22 used in this embodiment is called a Scott Russell linkage, which includes two rigid rods, one rod is twice the length of the other rod, and one end of the shorter rod is pivotally connected to the center of the longer rod. The other end of the shorter rod is pivotally connected to the lower support member 24. One end of the longer rod is pivotally connected to the upper support member 24, and the other end is connected to the platform 12 via a universal joint 26. The linkage 22 is connected to the platform 12 via the universal joint 26, which is shown enlarged in the inset portion (C).

[0262] As will be referenced below Fig.17 In more detail, the linkage 22 and force generator (counterweight 30) are arranged relative to each other to maintain the balancing force mg in a substantially constant orientation relative to the gravity force g as the platform 12 is moved about the working volume by the drive arrangement (extendable legs 16). In this regard, the linkage 22 is adapted to isolate or decouple lateral movement of the platform 12 from the lower support member 24 so that this constant orientation can be maintained, which in this embodiment allows the platform 12 to move freely in the x, y and z axes while the lower support member 24 is constrained to move linearly along the track 44 so that the constant orientation of the balancing force mg can be maintained through such platform movement. This will be described below with reference to Fig.17 becomes more apparent in the description.

[0263] It is apparent that the force generator (counterweight 30) is arranged substantially in a plane defined by the balance axis R and the connection 26 between the linkage 22 and the platform 12, and this remains true even when the platform 12 moves about the working volume. It is also apparent that the force generator (counterweight 30), the balance axis R and the linkage 22 are arranged substantially in a plane, and remain so even when the platform 12 moves about the working volume.

[0264] It will be apparent that the linear balance axis L (also labeled L1) is arranged in series with the rotational balance axis R (also labeled R1). When viewed in the direction from the fixed structure 14 to the movable structure 12, in this embodiment, the rotational axis R precedes the linear axis L, but these axes may be arranged in another order, such as having a pivotable connection between the linkage 22 and the support member 24, which allows rotation about a vertical axis. In such an embodiment, when viewed in the direction from the fixed structure 14 to the movable structure 12, the rotational axis R will be behind the linear axis L. Referring to FIG. Fig.16 Such an embodiment is described.

[0265] Fig.15 Shows Fig.14 The top view more clearly illustrates how the linkage 22 provides radial movement of the platform 12 toward and away from the counterweight 30, while the rotary joint 42 provides angular movement of the platform 12 about the rotation axis R. This allows the platform 12 to move in both the x and y directions, or more specifically by r and The platform 12 can be moved in the z-direction by movement of the support member 24 along the vertical track 44 , with the z-direction movement of the platform 12 being transferred to the support member 24 via the linkage 22 .

[0266] refer to Fig.11 In the known balancing arrangement shown, it has been mentioned above that the balancing arm A must oscillate about the axis of rotation R1 even if the platform P moves in the plane of the drawing (i.e. towards and away from the axis of rotation). Fig.14 The embodiment of the present invention also has a rotation axis R, but Fig.11 (and Figure 5 ), this axis of rotation R is not required for movement of the platform 12 in the plane of the drawing (i.e., for movement towards and away from the axis of rotation R). Inevitably, the balancing arrangement requires additional degrees of freedom to enable movement out of the plane of the drawing, and the axis of rotation R in this embodiment is a consequence of this necessity rather than a consequence of the core balancing design. In other embodiments, the axis of rotation R is not required (the additional degrees of freedom may be provided by linear axes, as with Fig.43 When restricted to two-dimensional movement in the plane of the drawing, Fig.14 In this embodiment, the axis of rotation R is not required. Moreover, in this embodiment, the balancing force applied to the support member 24 is always aligned with the gravity force, regardless of where the platform 12 is located in the working volume, and acts between the fixed structure 14 of the machine and the lower support member 24. In this regard, the balancing force is provided by the tension in the string 32, which in turn is supported by the fixed structure 14 (via the joint 42), as shown in FIG. Fig.10 The same as in the representation of .

[0267] exist Fig.14 and Fig.15 In the illustrated embodiment, the rotational balance axis R is offset from the linear balance axis L and is arranged in series before the linear balance axis L (when viewed in a direction from the fixed platform 14 to the movable platform 12 ). Fig.16 An alternative embodiment is shown in which the rotational balancing axis R coincides with the linear balancing axis L and is connected in series after the linear balancing axis L. Fig.16 In the illustrated embodiment, the housing 40 is fixedly attached to the fixed structure 14 of the machine, rather than being attached via Fig.14Instead, the rotary joint is incorporated into the support member 24, such as Fig.16 Each support member 24 includes an inner portion 24b rotatably supported by an outer portion 24a about a rotation axis R. The rotation axis R is in series with the linear axis L because the outer portion 24a of the support member 24 slides along the linear axis L and the inner portion 24b rotates about the rotation axis R relative to the outer portion 24a.

[0268] borrow Fig.10 The terminology used in Fig.16 A series arrangement is shown, in which the order of elements when viewed from the ground G to the platform P is as follows: [G → L → R → K → P], which is Fig.16 The rotational axis R can be considered to be in front of (or behind) the linear axis L. Anything in series after R will rotate about R, and anything in series before R will not rotate about it. Therefore, since the force generator Q (counterweight 30) is associated with the linear axis L, in this embodiment, the force generator Q (counterweight 30) will advantageously not rotate about the rotational axis R.

[0269] Note that, as described above, linkage K effectively provides a second linear axis (a second linear degree of freedom) for the balancing arrangement 50, while universal joint 26 effectively provides three rotational axes (three rotational degrees of freedom), so that the total axes are effectively as follows: [G→L1→R1→L2→R2→R3→R4→P]. This is in Fig.16 In this arrangement, when viewed along the axis of the series from G to P, the balancing axis (L1) to which the balancing force is applied is located behind any rotating balancing axis (R1 to R4).

[0270] The position of the force generator Q in the equilibrium axis arrangement is also marked in the inset (B). Fig.14 Different, in Fig.16 , force generator Q is located behind the rotation axis R1 in the series arrangement of the balancing axes, the balancing force is still applied to (along) the linear balancing axis L1. The force generator Q in series behind the rotation axis R1 does not rotate with R1, which is beneficial because not only is there no work to move the force generator Q to move the platform 12 horizontally with the plane of the page (toward and away from the balancing axis L1 and / or R1), but also for horizontal movement of the platform 12 away from the plane of the page (circumferentially around the balancing axis R1).

[0271] Fig.17 This is more schematically shown in Fig.14 and Fig.16 The arrangement will be used to illustrate the operating principles of these embodiments, and in particular the characteristics of the Scott Russell linkage mechanism 22, which make it suitable for use as a reference Fig.10 The platform 12 and any tool supported by the platform 12 (such as a measuring probe 13) are Fig.17 It is schematically represented as a single platform P in FIG, and the connection between the platform P and the linkage is simplified in this two-dimensional representation, because in order to allow anything more than small movements in the y direction (into and out of the page), of course suitable joints are required, such as Fig.14 and Fig.15 joint 26 in; this applies to most of the schematic representations described below, which are intended to illustrate the principle of two-dimensional operation, the third dimension (entering and leaving the page) being handled by the rotating balance axis R, for example.

[0272] When a force is applied to an object, the work W done on the object (or the energy imparted to the object) is equal to the force F applied multiplied by the distance the object moves under the influence of force F:

[0273] W=F×distance

[0274] Work is the transfer of energy from one place to another, or from one form to another; for example, a force applied by a spring to an object will transfer energy stored in the spring to the object in the form of kinetic energy and / or gravitational potential energy (e.g., to lift the object in the z-direction). Work may be negative if the object moves against the force; for example, when an object is lifted vertically, the work done by the force of gravity is negative because gravity opposes the direction of displacement (but work done by the lifting force is positive).

[0275] Now consider Fig.17 The arrangement shown, in which the platform P and the counterweight C are considered as moving bodies, and for simplicity the linkage is considered to have negligible mass. The change dE in the gravitational potential energy E of the two-body system is given by the total work done by the force of gravity on the two bodies (F=mg):

[0276] dE=F×distance

[0277] =mg×(dh+dz)

[0278] Where m is the mass of the platform P and the counterweight C, g is the gravitational constant, dh is the change in h, and dz is the change in z. For positive dh and dz, the change dE is positive because a positive value of either of these two values ​​is equivalent to lifting the mass against gravity, thereby transferring gravitational potential energy to the mass.

[0279] from Fig.17 It is obvious that:

[0280] h=av

[0281] =a-(lbc-2q sinθ)

[0282] =a-l+b+c+2q sinθ

[0283] Where l is the fixed length of the string (to the center point of the counterweight). In the above expressions, a, l and c are constants, while b will vary depending on the overall height of the linkage K within the machine. It is also obvious that:

[0284] z=ab-2q sinθ

[0285] Substituting these into the expression for dE above, we obtain the following expression for dE:

[0286] dE=mg(db+2q cosθdθ-db-2q cosθdθ)

[0287] =0

[0288] Therefore, a change dθ in the variable θ does not produce a change dE in the total potential energy E of the system, and thus the system is stable; there is no tendency for θ to increase or decrease because doing so would not induce a lower energy state, and thus the system is stable, and in the absence of any externally applied forces the balancing mass performs its intended function of keeping the system in a stable configuration.

[0289] In particular, the platform P is stable in both the z-direction (aligned with gravity) and in the x and y-directions (perpendicular to gravity), so that if the platform P is moved by the drive arrangement D to a desired position in the working volume of the machine and then the drive arrangement D is deactivated, the platform P will remain in the same position even without any drive. Furthermore, compared to known balancing arrangements, this is a substantially "pure" or "complete" form of stabilization, as the forces involved in different positions of the platform P in the working volume do not vary at all.

[0290] Not considered Fig.17 The work done on the platform P and the counterweight C by the downward arrows from these objects represents the force of gravity. Now consider only Fig.18 The forces shown in a slightly simplified version of . In particular, consider the work done on the support members by the tension in the strings of the pulley system and the work done on the platform by the force of gravity. Since the system is (theoretically) perfectly balanced, the tension in the strings is equal to mg, and this force acts upward on the lower support member. The upper support member is not attached to the strings, and therefore the force acting on it in the vertical direction is zero. The force of gravity acting downward on the platform is of course equal to mg.

[0291] In general, the total work done by the tension(s) on the support(s) is given by:

[0292]

[0293] Among them, F i is the force acting on the support member i, and dz i is the distance that the support member i moves along the z direction. Fig. 20 (Based on Fig.10 This concept is schematically shown in the schematic representation of FIG. 1 . In general, it can be considered that there are N support members i=0...(N-1), where N is an integer greater than or equal to 1, and the support member i has a linear balance axis L i The force F applied between the support member i and the ground G i .

[0294] like Fig.19 As graphically illustrated, a key feature of the Scott Russell linkage is that when the platform P moves horizontally by an amount dx in a direction perpendicular to gravity, this horizontal movement is converted or transformed by the linkage only into a vertical movement dz1 of the upper support member (with no balancing force applied thereto), while the lower support member (with a balancing force applied thereto) has no vertical movement dz0, and each support member has no horizontal movement dx, dy.

[0295] Therefore, the total work done by the tension in the string on the supporting structure is given by:

[0296] W=F0×dz0+F1×dz1

[0297] =F0×0+0×dz1

[0298] =0

[0299] In the above, the lower support member has been assigned index i=0, the upper support member has been assigned index i=1, and the same is true for the case where dz0=0 (the lower support member does not move in the z direction) and F1=0 (the upper support member is not attached to the pulley rope).

[0300] Therefore, for horizontal motion of the platform, the total work done by the balancing forces applied to the support members is zero. In other words, horizontal movement of the platform does not cause a change in the total energy state, so the platform has no motivation or tendency to move sideways or horizontally, and the system is therefore stable in a direction perpendicular to gravity.

[0301] When the platform P moves vertically by an amount dz in a direction aligned with gravity, this vertical movement is converted into a corresponding vertical movement dz of each support member i through the linkage. iTherefore, the force F acting on the supporting member i The total work done is as follows:

[0302]

[0303] for Fig.18 For example, the above expression is equivalent to:

[0304]

[0305]

[0306] Accordingly, the force F i The work done exactly matches the work done by gravity acting on platform P, i.e. both are equal to mg × dz. Accordingly, the total energy state does not change with a change dz in the z position of the platform, so platform P has no motivation or tendency to move vertically, and the system is therefore stable in a direction aligned with gravity.

[0307] Again, due to the nature of the balancing arrangement, these forces do not vary at all for different locations of platform P within the working volume, and the balancing arrangement can be considered to provide perfect or near perfect balance at all times, assuming that the weight of the balancing mass C matches or nearly matches the weight of platform P. Of course, in practice, the balancing mass C may not perfectly match the weight of platform P (or, including, the moveable structure of anything also attached to the platform), but if there is a perfect match, then the balancing mass can be considered to be perfect, or at least nearly perfect.

[0308] It is also apparent from the above analysis that the linkage design is such that for any movement of the platform there is no horizontal movement of either support member, which enables the support members to follow their respective tracks and thus enables the balancing forces to be maintained in a substantially constant orientation relative to gravity as the platform moves about the working volume. Any lateral movement of the lower support member would in particular result in the above referenced Figure 6 and Figure 7 The problem explained above is that the balancing force is not maintained in a substantially constant orientation relative to gravity as the platform moves about the working volume. Being able to maintain the balancing force in a substantially constant orientation relative to gravity while still allowing the platform to move about the working volume provides a very effective balancing arrangement. This is particularly true for non-Cartesian machines, which inherently do not have any drive axes that are maintained in a fixed orientation relative to gravity.

[0309] Fig.21 shows an imperfect version of the equilibrium with a longer arm length of 3q instead of 2q. The expression for h remains the same as above, while the expression for z becomes:

[0310] z=ab-3q sinθ

[0311] therefore:

[0312] dE=mg(db+2q cosθdθ-db-3q cosθdθ)

[0313] =-mgq cosθdθ

[0314] Where θ is in the range of 0° to 90° ( Fig.21 This is the case with the arrangement where cosθ is in the range 1 to 0 (i.e. cosθ is positive), so that for a small positive change dθ in θ, the gravitational potential energy of the system decreases, since dE is negative. Therefore, in the absence of any other forces, the tendency is for θ to decrease, rather than remain stable, so Fig.21 The arrangement will naturally collapse. Therefore, Fig.21 The arrangement is not suitable for use as a balancing weight and does not constitute an embodiment of the present invention. Fig. 22 Corresponds to Fig.19 , and graphically illustrates how horizontal movement of the platform causes z-direction movement of the two support members.

[0315] Fig.23 An imperfect version of the equilibrium is shown, with shorter arm lengths of 1.5q instead of 2q. The expressions for dE and h remain the same, while the expression for z becomes:

[0316] z=ab-1.5q sinθ

[0317] therefore:

[0318] dE=mg(db+2q cosθdθ-db-1.5q cosθdθ)

[0319] =0.5mgq cosθdθ

[0320] In view of the above, it is obvious that Fig.23 The arrangement of is also unstable, where the natural tendency is for θ to increase; similarly, Fig.23 The arrangement is therefore also not suitable for use as a balancing weight and does not constitute an embodiment of the present invention. Fig.24 Corresponds to Fig.19 , and graphically illustrates how horizontal movement of the platform causes z-direction movement of the two support members.

[0321] Figure 25 to Figure 27 Respectively similar to Fig.19 , Fig. 22 and Fig.24, but instead shows how the platform moves when the upper support member moves vertically with the lower support member (i.e. the support member to which the balancing force is applied) in a constant z position. Fig.26 and Fig. 27 ), the z position of the platform changes with this motion, causing an overall change in the energy of the system and therefore introducing inherent instability into these arrangements.

[0322] also, Fig.14 and Fig.16 The linear axis L in Fig.25 It is marked as the first linear axis L1, and it is obvious that Fig.25 The linkage of the Scott Russell linkage effectively provides a second linear axis L2 that is substantially perpendicular to the first linear axis L1. Since the first linear axis L1 is substantially aligned with gravity (substantially vertical), the second linear axis L2 is substantially perpendicular to gravity (substantially horizontal). This is because the nature of the Scott Russell linkage is such that it produces a right-angle change in motion from linear to linear. Therefore, when the linkage is coupled to the first linear axis L1, the linkage effectively produces the second linear axis L2, thereby providing two (substantially orthogonal) linear degrees of freedom for the balanced arrangement. On the other hand, for Fig.26 and Fig. 27 This is not the case for the linkages shown in , where in both cases the linkages produce a distinct non-linear axis NL coupled to the linear (vertical) axis L.

[0323] Fig.28 An alternative balancing arrangement is shown, which is a reference to the above Fig.17 The "inverted" form of the description. Fig.28 In the arrangement of , the upper support member is attached to the pulley string, rather than the lower support member. A similar analysis applies to the above combined Fig.17 The analysis given:

[0324] z=u+2q sinθ

[0325] h=av

[0326] =a-(lcb)

[0327] =a-(lc-(au-2q sinθ))

[0328] =2a-l+cu-2q sinθ

[0329] In the above expressions, a, l and c are constants, while u will vary depending on the overall height of the linkage K within the machine. Therefore:

[0330] dE=mg(du+2q cosθdθ-du-2q cosθdθ)

[0331] =0

[0332] Therefore, a change dθ in the variable θ does not produce a change dE in the total potential energy E of the system, and the system is therefore stable; θ has no tendency to increase or decrease because doing so would not induce a lower energy state, and the system is therefore stable, and in the absence of any externally applied forces, the balancing mass performs its intended function of keeping the system in a stable configuration. Fig.25 As stated, Fig.28 The linkage also effectively creates two orthogonally arranged linear balance axes.

[0333] Further embodiments of the present invention will now be described based on the same principles as those set forth above. Accordingly, the description of these further embodiments is not as detailed as given above.

[0334] Fig.29 Shown Fig.28 A "longer reach" alternative to the arrangement of , with additional links and joints. Fig.29 The linkage device has Fig.28 The same characteristics of the linkage of the upper support member, that is, when the platform moves only horizontally, the upper support member does not move, and does not attempt to move horizontally for any movement of the platform, thereby maintaining the balancing force in a substantially constant orientation relative to gravity. Fig.25 As stated, Fig.29 The linkage also effectively creates two orthogonally arranged linear balance axes.

[0335] Fig.30 Shows something like Fig.29 but using a slightly different linkage arrangement with three links of length 1.5q and one link of length 0.5q. Again, Fig.30 The linkage of has the same characteristics as the other linkages described above, namely, the support member attached to the counterbalancing force does not move when the platform moves only horizontally, and does not attempt to move horizontally for any movement of the platform, thereby maintaining the counterbalancing force in a substantially constant orientation relative to gravity. Fig.25 As stated, Fig.30 The linkage also effectively creates two orthogonally arranged linear balance axes.

[0336] Fig.31 A "double pulley" arrangement is shown in connection with a force generator. Fig.17Using a counterweight twice the weight of the platform, the total potential energy of the system remains stable because the counterweight only moves half the vertical distance of the platform, and the tension in the pulley string supporting the lower support member is half the weight acting on the counterweight, which is equal to the weight acting on the platform. Fig.25 As stated, Fig.31 The linkage also effectively creates two orthogonally arranged linear balance axes.

[0337] Fig.32 Provides the formation Fig.18 1 is an illustration of how the links of the linkage arrangement may in practice be shaped using only sheet or plate-like material (e.g., aluminum or steel material) to provide structural rigidity to the linkage. Similarly, Fig.33 Provides the formation Fig.30 Illustration of how a connecting rod of a linkage arrangement may be shaped and formed in practice.

[0338] Fig.34 shows how a platform can be supported by two balancing arrangements, in this example, Fig.17 Of the type shown, each balancing arrangement provides only half the balancing force to the platform, so that the total balancing force is the same as in the previous embodiment.

[0339] Fig.35 An alternative balancing arrangement is shown in which force is applied to both support members, rather than just one of the support members as in the previous embodiment, and in which the linkage is adapted so that when the platform moves horizontally, the two support members move vertically, but in opposite directions. The force generator (via a corresponding pulley arrangement) applies a force of 1 / 2 mg to each support member in an upward direction, so that when one support member moves upward and the other moves downward, the work done by one balancing force is positive and the work done by the other balancing force is negative, with the total work done being zero, i.e., ∑ i F i dz i = 0, so that there is equilibrium stability in the horizontal direction, and the sum of the forces F i Still matches the weight of the platform, that is, ∑ i F i = mg, so there is also equilibrium stability in the vertical direction. Fig.25 As stated, Fig.35 The linkage also effectively creates two orthogonally arranged linear balance axes.

[0340] Fig.36 Shown Fig.35A variant of the arrangement in which the counterweights are arranged to slide on respective inclined supports, i.e. in a direction not aligned with gravity. However, the forces acting on the support members remain unchanged.

[0341] Fig.37 Shown Fig.35 An alternative balancing arrangement to the arrangement shown, in which force generators are used to apply balancing forces to two support members respectively, wherein the linkage is adapted so that when the platform moves horizontally the two support members move vertically, but in opposite directions, and wherein vertical movement of the platform is converted into corresponding vertical movement of the support members. Fig.37 The balancing weight includes a double pulley arrangement associated with each support member. Fig.25 As stated, Fig.37 The linkage also effectively creates two orthogonally arranged linear balance axes.

[0342] In each of the specific embodiments described above, a counterweight has been used to generate a balancing force (in the form of tension in a string) which is applied to one or more of the supporting members of the balancing arrangement. Using a counterweight that is precisely matched to the weight of the structure (platform plus supported tooling) is a very convenient way to implement the invention and is a straightforward way to provide precise balancing (using a constant balancing force that precisely balances the weight of the movable structure). However, it is not necessary to use a balancing system as a force generator to provide a constant balancing force of the correct magnitude, and pneumatic elements or constant force springs may be used as force generators instead. Constant force springs are a variation of extension springs and are characterized by applying a substantially constant force regardless of the degree of elongation. An example of a constant force spring is the well-known uniform force conical pulley spring arrangement, which utilizes a conical pulley with a spiral groove around which a rope is wound; the rope is attached to a coiled main spring which provides a force that decreases with elongation, but the helical nature of the pulley compensates for the reduced force provided by the main spring when the string is untied, thereby providing a substantially constant force. Like a counterweight, in order to provide sufficient force to act as a counterweight, a spring has a non-negligible mass associated with it, and a significant amount of work needs to be done on it to move it.

[0343] Fig.38 An embodiment based on the use of a constant force spring as a force generator is schematically shown. Fig.37 Similarly, Fig.39 Shown in Fig.18In some embodiments, a constant force spring is used as a force generator. In some applications, the use of such a constant force spring as a force generator may be considered to have advantages over the use of a physical counterweight 30, since with a physical counterweight 30, the counterweight 30 must be accelerated when the platform 12 is moved vertically. However, in practice, the physical counterweight 30 provides a very convenient solution due to its ease of use and the ability to fine-tune the weight of the counterweight 30 simply by adding or removing additional mass elements. In addition, for example, Figure 2 In the depicted non-Cartesian machine, the extendable legs 16 are able to transmit considerable drive forces in the z direction by extension and retraction of the legs 16, so it is not particularly difficult to accelerate the additional weight of the counterweight 30; on the other hand, it would be more difficult for such a machine to have to drive the additional mass horizontally, but this is not the case with embodiments of the present invention because no work is done on the counterweight 30 (or the counterweight does no work) as the platform 12 moves horizontally, and for example in Fig.14 and Fig.16 In the embodiment of FIG. 1 , when the platform 12 moves horizontally, the counterweight 30 does not move at all.

[0344] Fig.40 A linkage arrangement of a different form to that of the previously described embodiments is shown having a horizontally arranged telescopic tube (or relatively slidable rod) 72 rigidly connected by a rigid connector 76 to a vertically slidable carriage 74 to which the balancing force is applied, and also including a double pulley arrangement as part of a force generator. Fig.40 The linkage also effectively produces the same as the previous embodiment and as mentioned above Fig.25 Two orthogonally arranged linear balance axes are illustrated.

[0345] Furthermore, although the balancing arrangement described above provides effective balancing for non-Cartesian machines, it can also provide balancing for Cartesian machines. Fig.41 The balancing arrangement demonstrating the implementation of the operating principles set forth in the foregoing embodiments can also be applied to balancing Cartesian coordinate positioning machines.Such a balancing arrangement can also be used to balance non-Cartesian serial kinematic coordinate positioning machines, such as a robotic arm with multiple rotary drive axes.

[0346] For example, Fig.42 Shown with Fig.16 The same balancing arrangement 50 as shown is used, but in which a robotic arm 60 is used to move the platform 12 instead of a hexapod drive arrangement. The robotic arm 60 includes a plurality of segments 62 connected by a mixture of transverse rotary joints (or "swivel joints") 64 and linear rotary joints (or "torsion joints") 66, thereby forming a mechanical linkage from one end to the other. Accordingly, Fig.16 Compared with the multiple linear drive axes 16, Fig.42 The drive arrangement has multiple rotary drive axes 64, 66. The balanced arrangement is also applicable to coordinate positioning machines having mixed linear drive axes and rotary drive axes.

[0347] Although the above reference Fig.14 and Fig.15 The balancing arrangement 50 is illustrated as rotating about the axis of rotation R so that the platform 12 can be rotated in three dimensions x, y, z (or r, z) on the movement, but this is not necessary. Instead, not based on Fig.14 and Fig.15 The balancing arrangement itself can be based on a Cartesian x, y, z coordinate system with orthogonal axes x, y, z, in the radial coordinate system shown. With such an arrangement, the z axis will be balanced and the x, y axes will provide the x, y axis movement of the platform 12 without interfering with the balancing forces provided by the vertical balancing forces. Independent of the drive arrangement of the machine, the balancing arrangement is provided between the fixed structure 14 of the machine and the movable platform 12. Fig.43 Such an arrangement is shown in , in which a Cartesian balancing arrangement embodying the invention is used to balance a Cartesian coordinate positioning machine or a non-Cartesian coordinate positioning machine.

[0348] Based on the above Fig.17 The arrangement shown gives an analysis in which points S0 and S1 are constrained to move along a vertical track or rail, while point P is free to move within a range of movement defined by the rigid rod. However, other arrangements are possible in which points S0 and S1 are not so constrained, or are constrained in a different manner. It will also be understood that although a linkage (such as a ScottRussell linkage) is described as being linear in nature (thereby providing a linear balance axis), a series of rotational balance axes (such as each rotational balance axis aligned with gravity) may replace this second linear balance axis, like the links of a bicycle chain, so that there is only a single linear balance axis (to which the balancing force is applied).

[0349] As explained above, the balancing arrangement embodying the present invention has proven to be very effective in practice, completely eliminating the need for a braking system because the balancing weights provide essentially complete balance no matter where the platform 12 is in the working volume 11, so that the platform 12 is stable without the need for brakes to prevent the platform from moving away from that position without separate support from the drive arrangement.

[0350] Fig.44 Demonstrates a closer approach based on Figure 5 The arrangement of the balancing axis does not change, so that effectively there is Fig.44 As shown (as shown in the above reference Figure 5 and Fig.11 The six rotational balance axes R1 to R6 discussed above are provided. It should be noted that the rotational balance axis R3 is substantially perpendicular to gravity, so that when a balancing force is applied to (applied about) the rotational axis R3, the resultant force applied to the connecting arm 92 is in a substantially vertical plane, and the rotational balance axes R1 and R2 are substantially aligned with gravity. The rotational axis R3 is substantially perpendicular to the rotational axes R1 and R2. The rotational axes R4 to R6 are provided by the universal joints that couple the arm 92 to the platform 12.

[0351] and Figure 5 The key modification is that Fig.44 In this respect, the mass generating the balancing force is brought back so as to be in line with the first rotational balancing axis R1, rather than being located behind the rotational axis R2. Fig.44 In the embodiment of the present invention, the force generator is a simple counterweight C with a thin rope 99, which transmits the generated balancing force through the arm 94 to the hinge 93, where the balancing force can be Figure 5 The difference is that in this embodiment, the balancing force is provided to the hinge 93 via the tension in the string 99, and the force source (counterweight C) is far away from the hinge 93. Figure 5 In the arrangement, the source of force (spring 96) is located at the hinge 93 itself.

[0352] Fig.44 The layout is better than Figure 5 The benefit of the arrangement is that by positioning the mass of the force generator C along (or beside or at least close to) the first balance axis R1 of the series of balance axes R1 to R6 (when viewed in a direction towards the platform 12), the mass does not move (or at least does not move inconsistently) as the platform 12 moves about the working volume, except for rotation only about the single rotational balance axis R1 (rather than about two or more rotational balance axes as in known balancing arrangements) due to the twisting / rotation of the mass by the string 99. The force generating mass is still connected to the hinge 93 via the string 99 to transfer the balancing force where it is needed (at the rotational balance axis R3), but the force generating mass itself is positioned close to (e.g. along) the first rotational axis R1.

[0353] This can refer to Fig.44 The illustrations (A) to (C) in the illustrations are described in a broad sense and are compared with the Fig.14 and Fig.16 The illustration part (A) is used for Figure 5A known balancing arrangement is shown, showing the arrangement of the balancing axes R1 to R6 and the position of the force generator Q (counterweight C) in the balancing axis arrangement. The force generator Q is located in front of the rotation axes R1 and R2 (in the hinge 93), and the balancing force F is applied to the rotational balancing axis R3 (applied around the rotational balancing axis R3). The force generator Q is connected in series in front of the two rotation axes R1 and R2, and rotates with R1 and R2 in a complex manner as described above.

[0354] The arrangement shown in the inset portion (B) represents a similar type of balancing mass used in the DS10 contact scanner sold by Renishaw plc (also formerly sold under the Incise trade name), which is also a parallel kinematic machine. The balancing force F is again applied to (applied about) the rotational balancing axis R3, and the force generator Q is again located in front of the rotational axes R1 and R2 in the series arrangement. However, the force generator Q (actually a spring) is physically located slightly in front of the rotational axis R3, and is actually connected to a point along the associated arm (between R3 and R4 / 5 / 6) which is some distance away from the axis R3, more like Fig.11 . Accordingly, force generator Q effectively rotates about three rotation axes R1, R2 and R3, but rotation about rotation axis R3 only occurs when the movement of platform 12 has a vertical component, not for purely horizontal movement. However, even for purely horizontal movement of platform 12, the effect of rotation about rotation axis R2 may be more significant because force generator Q is not located close to rotation axis R2.

[0355] In contrast to the arrangement shown in inset portion (C), which shows Fig.44 The balancing force F is still applied to (and about) the rotational balancing axis R3, but the force generator Q is now physically located behind the rotational axes R2 and R3 and is substantially in line with the rotational axis R1. Thus, the force generator Q is effectively shielded or isolated from the rotational motion about the rotational axes R2 and R3 and is only affected by the rotational motion about the rotational axis R1, thereby providing a rotational force generator Q having ... Fig.14 Similar benefits of the embodiments.

[0356] 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.

[0357] It will be appreciated that the operation of the coordinate measuring machine may be controlled by a program running on the machine, and in particular by a program running on a coordinate measuring machine controller, such as the respective Figure 1 and Figure 2 1 and 2. It will be appreciated that control of the extendable legs may be provided by a program running on the controller 5 or 15. 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, for example. 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.

[0358] Although the above embodiments are described primarily in the context of coordinate measuring machines, the concepts are more generally applicable to any type of coordinate positioning machine, such as comparators, scanning machines, machine tools, robots, positioning devices (e.g. for optical components), prototyping machines, and various other uses.

Claims

1. A coordinate positioning machine comprising: a plurality of drive shafts for positioning a movable structure within a working volume of the machine; a plurality of balancing axes for balancing the movable structure, wherein the balancing axes include linear balancing axes, and wherein the orientation of the linear balancing axes does not substantially change with changes in orientation and / or actuation of the drive shaft; and A force generator for generating a balancing force; at least one support member coupled to the linear balancing shaft, wherein the balancing force is arranged to act on the at least one support member; and A linkage is coupled between the at least one support member and the movable structure to transmit the counterbalancing force to the movable structure.

2. A coordinate positioning machine as claimed in claim 1, wherein: The linkage is adapted to provide movement of the moveable structure in a direction perpendicular to gravity while causing the counterbalancing force to perform substantially no work.

3. A coordinate positioning machine as claimed in claim 1 or 2, wherein: The balancing shafts are arranged in series.

4. A coordinate positioning machine as claimed in claim 3 including at most one rotational balance axis between the force generator and a fixed structure of the machine.

5. A coordinate positioning machine as claimed in claim 1, 2 or 4, wherein: The linear balance axis has a substantially constant orientation relative to gravity.

6. A coordinate positioning machine as claimed in claim 1, 2 or 4, wherein: The linear balancing axis is a first linear balancing axis, wherein the balancing axis comprises a second linear balancing axis, and wherein the first linear balancing axis and the second linear balancing axis are arranged substantially perpendicular to each other.

7. A coordinate positioning machine as claimed in claim 6, wherein: The second linear balance axis is provided by the linkage.

8. A coordinate positioning machine as claimed in claim 1, 2, 4 or 7, wherein: The linkage is a Scott Russell linkage and / or wherein the linkage is adapted to produce a substantially vertical change of motion from linear to linear.

9. A coordinate positioning machine as claimed in claim 1, 2, 4 or 7, wherein: The linear balance axis has a substantially constant orientation relative to gravity.

10. A coordinate positioning machine as claimed in claim 9, wherein: The linear balance axis has an orientation substantially aligned with gravity.

11. A coordinate positioning machine as claimed in claim 1, 2, 4, 7 or 10, wherein: The linkage is adapted to absorb horizontal movements of the movable structure and to convert vertical movements of the movable structure into corresponding vertical movements of the linkage along the linear balancing axis.

12. A coordinate positioning machine as claimed in claim 1, 2, 4, 7 or 10, wherein: The movable structure is balanced along the linear balance axis via the linkage.

13. A coordinate positioning machine as claimed in claim 12, wherein: At least a portion of the weight of the moveable structure is supported via the linkage by a substantially constant balancing force applied to the linkage along the linear balancing axis.

14. A coordinate positioning machine as claimed in claim 1, 2, 4, 7, 10 or 13, wherein: The at least one support member is slidably coupled to the linear balancing shaft, or wherein the at least one support member is arranged to be slidably movable along the linear balancing shaft.

15. A coordinate positioning machine as claimed in claim 1, 2, 4, 7, 10 or 13, wherein: Vertical movement of the moveable structure caused by the drive arrangement is converted by the linkage into corresponding vertical movement of the at least one support member, thereby causing the work done by the balancing force applied to the at least one support member to be substantially equal but opposite to the work done by the gravitational force acting on the moveable structure.

16. A coordinate positioning machine as claimed in claim 1, 2, 4, 7, 10 or 13, wherein: Horizontal movement of the moveable structure caused by the drive arrangement is converted by the linkage into at most vertical movement of the at least one support member, resulting in substantially no net work being done on one or more forces applied to the at least one support member.

17. A coordinate positioning machine as claimed in claim 1, 2, 4, 7, 10 or 13, comprising a first support member and a second support member, each support member being arranged to be slidably movable along a track substantially aligned with gravity, wherein Movement of the movable structure in a direction perpendicular to the track or each of the at least two tracks for the first support member and the second support member is converted by the linkage device into movement of the second support member along its track, while the first support member does not substantially move along its track; wherein movement of the movable structure in a direction parallel to the track or each of the at least two tracks for the first support member and the second support member is converted by the linkage device into movement of at least the first support member along its track by the same amount in the same direction.

18. A coordinate positioning machine as claimed in claim 17, wherein: The balancing force is applied to the first supporting member instead of the second supporting member.

19. A coordinate positioning machine as claimed in claim 1, 2, 4, 7, 10, 13 or 18, wherein: The force generator applies a force F in a direction substantially opposite to the force of gravity. i applied to each support member i, where ∑ i F i ~mg, and the linkage converts the changes dx, dy, dz in the movable structure into changes dx in each supporting member i i ,dy i 、dz i , so that∑ i F i dz i ~mg.dz、dx i ~0 and dy i ˜0, where m is the mass of the movable structure, g is the acceleration due to gravity, and i is an integer greater than or equal to 1.

20. A coordinate positioning machine as claimed in claim 19, wherein: At least one of Fi is zero.

21. A coordinate positioning machine as claimed in claim 1, 2, 4, 7, 10, 13, 18 or 20, wherein: The balancing shaft includes at least one rotating balancing shaft.

22. A coordinate positioning machine as claimed in claim 21, wherein: The balancing shafts are arranged in series, and wherein the force generator is arranged behind a first rotating balancing shaft of the balancing shafts in the series or at a predetermined horizontal distance from the first rotating balancing shaft.

23. A coordinate positioning machine as claimed in claim 22, wherein: The predetermined horizontal distance is substantially constant, and / or wherein the force generator is arranged close to the first rotational balancing axis.

24. A coordinate positioning machine as claimed in claim 23, wherein: The predetermined horizontal distance is less than 50% of a horizontal distance between the first rotational balancing shaft and the movable structure.

25. A coordinate positioning machine as claimed in claim 1, 2, 4, 7, 10, 13, 18, 20, 22, 23 or 24, wherein: The balancing shaft and the force generator are arranged relative to each other such that movement of the movable structure in a direction perpendicular to gravity results in substantially no net movement of the force generator other than due to rotation of the force generator about at most one rotational balancing shaft.

26. A coordinate positioning machine as claimed in claim 25, wherein: The balancing shafts are arranged in series, and the at most one rotating balancing shaft is the first rotating balancing shaft or the only rotating balancing shaft of the balancing shafts in the series.

27. The coordinate positioning machine of claim 1, 2, 4, 7, 10, 13, 18, 20, 22, 23, 24 or 26, wherein: The balancing shafts are separate from the drive shafts and / or wherein each balancing shaft is separate from and / or independent and / or distinct from each of the drive shafts.

28. The coordinate positioning machine of claim 1, 2, 4, 7, 10, 13, 18, 20, 22, 23, 24 or 26, wherein: The balancing force is a substantially constant balancing force.

29. The coordinate positioning machine of claim 1, 2, 4, 7, 10, 13, 18, 20, 22, 23, 24 or 26, wherein: The force generator includes a counterweight that generates tension in a string coupled thereto.

30. The coordinate positioning machine of claim 1, 2, 4, 7, 10, 13, 18, 20, 22, 23, 24 or 26, wherein: Each of the drive shafts is a linear drive shaft, and / or wherein, None of the drive shafts has or maintains a substantially constant orientation relative to gravity as the moveable structure moves about the working volume.

31. The coordinate positioning machine of claim 1, 2, 4, 7, 10, 13, 18, 20, 22, 23, 24 or 26, wherein: The machine is a non-Cartesian coordinate positioning machine.

32. A coordinate positioning machine as claimed in claim 31, wherein: The machine is a parallel kinematic coordinate positioning machine.

33. A coordinate positioning machine as claimed in claim 31, wherein: The machine is a hexapod coordinate positioning machine.

34. The coordinate positioning machine of claim 31, wherein: The machine is a coordinate measuring machine.

35. A method of balancing a coordinate positioning machine having a plurality of drive axes, each of which is a rotary drive axis or a linear drive axis, for positioning a movable structure within a working volume of the machine, the method comprising providing a linear balancing axis separate from any of the drive axes, and balancing the movable structure by applying a balancing force to a support member coupled to the linear balancing axis and transmitting the balancing force to the movable structure using a linkage coupled between the support member and the movable structure, wherein The orientation of the linear balance shaft does not substantially change with changes in orientation and / or actuation of the drive shaft.

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