Coordinate positioning arm

Abstract

Disclosed is a coordinate positioning arm (A) comprising a base end (B) and a head end (H), a drive frame (D) for moving the head end (H) relative to the base end (B), and a metrology frame (M) for measuring the position and orientation of the head end (H) relative to the base end (B). The drive frame (D) comprises a plurality of drive axes (D1, D2, D3) arranged in series between the base end (B) and the head end (H). The metrology frame (M) comprises a plurality of measurement axes (R1, R2, R3, R4, R5, R6) arranged in series between the base end (B) and the head end (H). Advantageously, the metrology frame (M) is adapted and arranged to be substantially separate and / or independent from the drive frame (D).

Description

[Technical Field]

[0001] The present invention relates to a coordinate positioning arm, such as an articulating robot or measuring arm. [Background technology]

[0002] Articulated robots are commonly used in a variety of manufacturing applications, including assembly, welding, gluing, painting, picking and placing (e.g., printed circuit boards), packaging and labeling, palletizing, product inspection, etc. Their versatility and robustness, along with their long reach and flexibility of movement, make them ideal for use in production environments.

[0003] An articulated robot (or simply "robot") is shown schematically in Figure 1 of the accompanying drawings and includes an articulated arm 1 extending from a fixed base 2 to a movable flange 3, which supports a tool (or effector end) 4. Typically, the flange 3 is provided with a coupling that allows the tool 4 to be conveniently interchangeable so that a variety of tools or end effectors can be used depending on the application involved. Examples include grippers, vacuum cups, cutting tools (including both mechanical and laser cutting tools), drilling tools, milling tools, deburring tools, welding tools, and other specialised tools.

[0004] Arm 1 includes multiple segments 5 connected by a mixture of transverse rotary joints 6 and inline rotary joints 7, forming a mechanical linkage from one end to the other. In the example shown in FIG. 1, there are three transverse rotary joints 6 and three inline rotary joints 7, alternating between the transverse rotary joints 6 and the inline rotary joints 7, making a total of six rotary joints. In the context of a robotic arm, the transverse rotary joints 6 are sometimes called "rotational joints" and the inline rotary joints 7 are sometimes called "twisting joints," with other types of joints being "linear joints," "orthogonal joints," and "revolving joints."

[0005] Perhaps the most common configuration for industrial robots is to have six revolute joints, but robots may also have one or more linear joints. Having multiple joints allows for flexibility in moving the tool 4 around the work volume and manipulating it into a variety of different poses. The degree of flexibility can be changed by adding or removing joints in the arm.

[0006] The drawback of having additional joints (and therefore additional flexibility) is that each joint contributes to positional errors or uncertainties, and due to the serial nature of the linkage, these errors are cumulative. It is important to tune the robot to map these errors and uncertainties.

[0007] However, calibrating any type of non-Cartesian machine is a significant challenge, especially for articulated arms with multiple rotary joints, such as the one shown in Figure 1, which are not fixed to one another and can combine in complex ways to position the tool in the work volume. Calibrating Cartesian machines is typically simpler because such machines have three well-defined axes that are fixed to one another in an orthogonal arrangement, with each axis being largely independent of the others. For articulated robots, the position and orientation of each axis depends on the positions and orientations of the other axes, resulting in different calibrations for each pose of the machine.

[0008] Many calibration techniques have a common goal of specifying a parametric model of the relevant machine, where multiple parameters are used to characterize the machine's geometry. Uncalibrated values ​​are initially assigned to these parameters as a starting point for the machine's geometry. During calibration, the machine is moved to a variety of different poses (based on current estimates of the machine's parameters). For each pose, a calibrated measurement device is used to measure the actual pose, so that a measure of the error between the expected machine pose and the actual machine pose can be determined.

[0009] The task of calibrating the machine then becomes one of determining the set of values ​​for the machine's various parameters that minimizes the error, using known numerical optimization or error minimization techniques. An example of such a technique is the well-known Levenberg-Marquardt algorithm, which uses a least-squares approach to minimize the error knowing the derivative of the error according to each optimized parameter ("A Method for Solving Certain Nonlinear Problems in the Method of Least Squares," Kenneth Levenberg, 1944, Quarterly of Applied Mathematics, 2:164-168, and "An Algorithm for the Least-Square Estimation of Nonlinear Parameters," Donald Marquardt, 1963, SIAM Journal on Applied Mathematics, 11(2):431-441). Other techniques, such as those based on the maximum likelihood approach, are also possible.

[0010] For a robot such as that shown in FIG. 1, these machine parameters may include various geometric parameters such as the length of each segment 5, the rotational angular offset of each revolute joint 6 (the angle from the encoder plus the actual calibrated offset), and various mechanical parameters such as joint compliance and friction. When all of these machine parameters are known and properly calibrated, it is possible to more reliably predict where the tool 4 will actually be when the various joints 6 are commanded by the robot controller 7 to move to their different respective positions. In other words, the machine parameters obtained from such a calibration provide a more accurate characterization of the machine geometry.

[0011] However, even after calibration of such articulated robots, errors remain, and these errors accumulate due to the serial nature of the mechanical linkages. As a result, the accuracy and repeatability of articulated robots are typically not as good as, for example, traditional 3-axis Cartesian machines. Therefore, although articulated robots have the advantages of long reach, flexibility, and versatility, they are typically not suitable for use in the most demanding applications where high precision and repeatability are required. Summary of the Invention

[0012] Applicant has realised that it would be desirable to address the above-mentioned shortcomings to provide a coordinate positioning arm that can benefit from the reach and flexibility of an articulated robot, but also provide improved accuracy and / or repeatability.

[0013] Applicant has also realised the desirability of providing a coordinate measuring arm that is adapted primarily for measurement applications rather than manufacturing applications where precision is paramount. Such a coordinate measuring arm (or simply a measuring arm) would ideally have sufficient precision to be used in applications where more traditional coordinate measuring machines (e.g., 3-axis Cartesian coordinate measuring machines) must be used, yet benefit from the reach and flexibility of a non-Cartesian articulated flexion-extension arm configuration.

[0014] According to an aspect of the present invention, there is provided a coordinate positioning arm including a base end and a head end, a drive frame for moving the head end relative to the base end, and a metrology frame for measuring the position and orientation of the head end relative to the base end. The drive frame comprises a plurality of drive axes arranged in series between the base end and the head end. The metrology frame comprises a plurality of measurement axes arranged in series between the base end and the head end. Advantageously, the metrology frame is (substantially) separate and / or independent from the drive frame.

[0015] Substantial separation and / or independence between the metrology frame and the drive frame may be achieved by providing the coordinate positioning arm with one or more of the following features:

[0016] The metrology frame may be supported by and / or coupled to the drive frame substantially only at (or via) the base and head ends, which avoids the presence of intermediate supports or constraints between the metrology frame and the drive frame (at locations between the base and head ends), thereby allowing separation between the metrology frame and the drive frame to be maintained.

[0017] For each possible configuration of the drive frame, the metrology axis may provide enough degrees of freedom for the metrology frame so as not to impose additional constraints on the drive frame between the base and head ends (other than those already provided by the drive axis itself, since the drive axis can be thought of as acting as a constraint on the relative motion between the base and head ends.) If the presence of the metrology frame did impose additional constraints, this would compromise the separation between the metrology frame and the drive frame.

[0018] For each possible configuration of the drive frame, the metrology axes may provide enough degrees of freedom for the metrology frame to avoid over-constraining the metrology frame and the drive frame. If there are more constraints than necessary between the metrology and drive frame (i.e., over-constraining), this will compromise the separation between the metrology and drive frame.

[0019] The metrology axes may be arranged to provide the metrology frame with insufficient degrees of freedom to allow multiple configurations for the metrology frame for each configuration of the drive frame. In other words, the metrology axes and the drive axes may be arranged relative to one another to provide only one possible configuration for the metrology frame for each configuration of the drive frame. In other words, for each possible configuration of the drive frame, there is preferably only one possible configuration for the metrology frame. This avoids the need for intermediate supports or constraints between the metrology frame and the drive frame, allowing the metrology frame to be forced or guided into the correct one of several possible configurations, thereby maintaining separation between the metrology frame and the drive frame.

[0020] The metrology frames' measurement axes may be arranged such that, for each possible configuration of the drive frame, there is no measurement axis redundancy (e.g., in terms of enabling and measuring relative movement between the head and base ends in all required degrees of freedom). Said another way, the measurement axes and drive axes may be arranged such that there is no configuration of the drive frame in which two measurement axes of the metrology frame are aligned. This prevents the effective loss of degrees of freedom within the metrology frame, which would create additional constraints between the metrology frame and the drive frame, thereby reducing or eliminating the separation and / or independence between them.

[0021] For each drive axis that has both an associated primary measurement axis (to measure the primary or intended motion associated with the drive axis) and an associated secondary measurement axis (to measure the secondary or unintended motion associated with the drive axis), the secondary measurement axis may be positioned (in serial order from the base end to the head end) before the primary measurement axis. This helps prevent measurement axis redundancy. See above.

[0022] The drive frame may include three or fewer drive axes and the metrology frame may include six or fewer measurement axes. For example, the drive frame may include three drive axes and the metrology frame may include six measurement axes. Having a relatively small number of drive axes and associated measurement axes facilitates separation between the drive frame and the metrology frame, as described in more detail below.

[0023] When it is stated that the metrology frame is substantially separate and / or independent from the drive frame (or that the metrology frame and the drive frame are arranged relative to one another and adapted to be substantially separate and / or independent of one another), this does not mean that the metrology frame is insensitive to changes in the configuration of the drive frame. As described above, the drive frame is adapted and arranged to move the head end relative to the base end, and the metrology frame, in turn, is adapted and arranged to measure the position and orientation of the head end relative to the base end. The base end and head end can be considered to be neither part of the metrology frame nor part of the drive frame. Thus, the metrology frame may be coupled to the drive frame via the base end and the head end (so that when the drive frame moves the head end relative to the base end, this also changes the configuration of the metrology frame, and measurements from the metrology axes are used to determine the position and orientation of the head end relative to the base end). However, the metrology frame itself can still be considered to be substantially separate and / or independent from the drive frame itself.

[0024] Other features that also help maintain separation and / or independence between the metrology frame and the drive frame are described below. Technical advantages over known articulating robotic arms are also described in more detail.

[0025] To address the above-mentioned shortcomings of the articulated robotic arm considered above, and to provide a coordinate positioning arm that can benefit from the reach and flexibility of an articulated robotic arm, but also has improved accuracy and / or repeatability, Applicant recognizes the importance of avoiding motion of the metrology frame (e.g., bending or twisting motion) or motion within the metrology frame that is not enabled by any combination of one or more of the metrology axes. Such motion of the metrology frame would not be measured, since it is the metrology axes themselves that are actually being encoded (measured). If the metrology frame and drive frame can be manufactured and coupled together in perfect alignment and maintained that way during use, it is sufficient to ensure that a metrology axis is provided (and aligned) for each drive axis, and the motion associated with each drive axis can be measured. These measurements effectively provide a set of machine coordinates from which the position and orientation of the head end relative to the base end can be determined.

[0026] However, Applicant understands that in practice there are imperfections in the manufacturing process and that using mechanical parts will tend to drift out of alignment over time. Additionally, each drive joint will necessarily have a natural degree of play associated with it, and thus, along with the primary rotation about the primary drive axis, there will necessarily be some secondary (undesirable) rotation about the orthogonal axes. Furthermore, while each segment of the drive frame and metrology frame has a nominal (ideal) length, in practice the actual length may differ from the ideal length and may change with operating temperature due to thermal expansion and contraction.

[0027] In particular, Applicant has recognized that these non-ideal behaviors tend to create constraints between the metrology frame and the drive frame, where the metrology frame tends to "fight" against the drive frame, and the drive frame attempts to position the metrology frame in a configuration that is incompatible with the metrology frame's available measurement axes, which leads to unmeasured distortions of the metrology frame and adversely affects the measurement results (ultimately, measurements of the position and orientation of the head end relative to the base end).

[0028] Applicant recognizes that it is desirable to avoid unnecessary constraints between the drive frame and the metrology frame, particularly at intermediate positions between the head and base ends of the arm, as in US20050166413A1, where multiple transmission means are provided along the length of the arm to support the internal metrology structure. These transmission means create constraints between the internal metrology structure and the exoskeleton, which embodiments of the present invention seek to avoid by having a metrology frame that is substantially separate and / or independent from the drive frame. This is also true for the arm structure disclosed in US4606696, where the internal metrology beam must be supported at an intermediate position between the base and head ends. Furthermore, in the arm disclosed in US20050166413A1, each drive axis is provided with a single corresponding measurement axis, which (as will be apparent from the accompanying drawings and the following description) is insufficient to prevent excessive constraints between the internal metrology structure and the exoskeleton, particularly at 90-degree joints. This is something that an embodiment of the present invention seeks to avoid.

[0029] By employing one or more of the features described above or below in connection with aspects of the present invention, a coordinate positioning arm can be manufactured that is optimized for accuracy, for example, accurate enough to be used as a coordinate measuring machine in demanding metrology applications, while benefiting from the flexibility and reach of a conventional robotic arm. Ensuring separation between the metrology frame and the drive frame also allows the drive frame to be built at a lower cost than usual, and for example does not need to be as rigid as designed into the various joints, because the separate metrology frame provides direct measurement of the head end relative to the base end and is not subject to any inaccuracies or imperfections in the drive frame.

[0030] And because the measurement axes of the coordinate positioning arm are arranged in series, by ensuring that any secondary measurement axis associated with a drive axis is arranged in front of that drive axis' corresponding primary measurement axis (in series from the base end to the head end), when the head end of the arm rotates about the drive axis, this ensures that the orientation of the secondary measurement axis does not change (as the head end of the metrology frame comes in front of the rotating primary measurement axis). This in turn ensures that a secondary measurement axis does not align with another measurement axis as a result of such a change in the drive frame configuration, thereby effectively resulting in the loss of a measurement axis and the potential for undesirable constraints between the metrology frame and the drive frame (and consequently, unmeasured flexing of the metrology frame). This concept is discussed further below, along with other advantageous features that can be used to further improve the performance and accuracy of coordinate positioning arms.

[0031] The metrology frame may include multiple metrology joints, each of which includes at least one of the metrology frames' metrology axes. At least one lateral metrology joint (corresponding to a lateral drive joint) may include metrology axes providing primary and secondary rotational degrees of freedom (for the metrology joint), the primary rotational degree of freedom being substantially aligned with the corresponding lateral drive axis (i.e., the drive axis of the corresponding drive joint) and disposed serially after the secondary rotational degree of freedom (in order from the base end to the head end).

[0032] Such a metrology joint advantageously provides two rotational degrees of freedom: one for measuring the primary rotation associated with the primary (i.e., intended) rotation of the drive shaft, and another for measuring the secondary (i.e., unintended) rotation associated with the drive shaft. Furthermore, the specific sequential ordering of these two degrees of freedom within the metrology frame ensures that the orientation of the secondary axis (relative to the underlying metrology frame) is maintained even when the above metrology frame rotates about the primary axis. This helps ensure that the metrology axes do not always become aligned during use of the arm. Alignment of the metrology axes results in a redundant metrology axis, leaving the metrology frame with insufficient degrees of freedom (or flexibility) to handle all possible movements of the drive frame (both intended and unintended), exceeding the constraint between the metrology frame and the drive frame. As mentioned above, such constraints can result in changes in the metrology frame configuration that are not registered in the metrology results, leading to inaccurate determination of the position and orientation of the head end of the arm relative to the base end. One embodiment of the present invention seeks to avoid this.

[0033] The drive frame may include (exactly) three rotational drive axes arranged in series between the base end and the head end, two of which are lateral and one of which is in-line. The metrology axes may provide the metrology frame with (exactly) three primary rotational degrees of freedom (each associated with the three drive axes), (exactly) two secondary rotational degrees of freedom (each associated with the two lateral drive axes), and (exactly) one secondary linear degree of freedom (at least not directly associated with any of the drive axes) to the metrology frame.

[0034] For example, compared to a typical articulating robot, having a relatively small number of rotational drive axes greatly simplifies the calibration of a coordinate positioning arm, allowing the arm to be optimized for precision. Fewer drive axes also allows for a similarly small metrology frame. Furthermore, having fewer drive axes allows for a metrology frame that is freestanding, i.e., supported only at the base and head ends without intermediate supports (or negligible intermediate supports). In this regard, if an arm has, for example, seven rotational drive axes (which is common), there must be at least seven metrology axes to measure all seven of the drive axes. However, having seven rotational metrology axes means that the metrology frame must be supported by the drive frame in intermediate positions, as the metrology frame flips between different possible configurations. This not only results in collisions between the metrology frame and the drive frame, but also, without collisions, the applicant has realized that having multiple possible solutions for the metrology frame for the same position of the drive frame is problematic because each of these metrology solutions needs to be calibrated, and it is not possible to predict in advance which of two possible metrology solutions will be employed for any particular position of the drive frame. The applicant has therefore realised that there are many advantages associated with limiting the number of drive axes in a coordinate positioning arm, and where further drive axes are required it is possible to chain several of these "core" units together, with each unit being similar to a composite structure with the advantages of the present invention.

[0035] The metrology axes may preferably be arranged (collectively) to provide the metrology frame with one or more of the following characteristics for each (or any) possible configuration of the drive frame, or at least a subset of the possible configurations of the drive frame, e.g. a subset including drive frame configurations that are used or that could reasonably be used during normal use (including at least some, e.g. all drive frame configurations where the lateral drive axes are at 180 degrees, and at least some, e.g. all drive frame configurations where the lateral drive axes are at 90 degrees): (a) enough degrees of freedom (for that configuration of the driving frame) to not exceed (create) the constraints between the measurement frame and the driving frame; (b) Sufficient degrees of freedom to avoid creating additional constraints on the drive frame between the base end and the head end (other than those already provided by the drive shaft itself for that configuration of the drive frame); and (c) There are insufficient degrees of freedom to provide (or allow or enable) multiple possible configurations for the metrology frame (i.e., there is a unique solution or configuration of the metrology frame for that configuration of the drive frame).

[0036] For each possible configuration of the drive frame, there is preferably substantially no redundancy in the measurement axes of the metrology frame. In other words, each of the measurement axes is not (or is not) aligned with any of the other measurement axes or combinations thereof. Thus, there are no redundant measurement axes or no measurement axis redundancy. The measurement axes and drive axes are preferably arranged such that there is no configuration of the drive frame in which two or more rotational measurement axes of the metrology frame are aligned.

[0037] The metrology frame may be substantially coupled to (or supported or constrained relative to) the drive frame at only the base and head ends. This avoids creating intermediate constraints between the base and head ends, or otherwise creating additional constraints on the drive frame between the base and head ends, thereby avoiding creating excessive constraints between the metrology frame and the drive frame. This also applies to intermediate constraints that may in fact only act substantially while the arm is moving (i.e., dynamic constraints rather than static constraints).

[0038] The metrology frame may include a plurality of metrology joints, each of which includes at least one of the metrology axes of the metrology frame, and each drive axis may be provided with (or associated with) a corresponding one of the metrology joints.

[0039] At least one measurement axis (corresponding to or associated with a drive axis) of each measurement joint may provide a primary degree of freedom (of the measurement joint) that is substantially aligned with the corresponding drive axis (i.e., the drive axis of the corresponding drive joint).

[0040] At least one (and preferably each) lateral measurement joint (i.e., a measurement joint corresponding to or associated with a lateral drive axis) preferably includes a measurement axis providing a primary and secondary rotational degree of freedom (for the lateral measurement joint), the primary rotational degree of freedom being substantially aligned with the corresponding drive axis (i.e., the drive axis of the corresponding drive joint).

[0041] The primary rotational degree of freedom (or primary rotational axis) may be disposed in series (in the direction from the base end to the head end) after the secondary rotational degree of freedom (or secondary rotational axis).

[0042] The orientation of the secondary rotational degree of freedom (or secondary rotational axis) may be substantially invariant to rotation (of the metrology frame) about the primary rotational degree of freedom (or primary rotational axis).

[0043] The orientation of the first rotational degree of freedom (or first rotational axis) can be changed by rotation (of the metrology frame) about the second rotational degree of freedom (or second rotational axis).

[0044] The primary and secondary degrees of rotation may be provided by primary and secondary rotation measurement axes, respectively.

[0045] The primary and secondary rotational measurement axes may be substantially intersecting (or alternatively may be offset from one another).

[0046] The primary and secondary rotational measurement axes may be provided by a universal joint, a Cardan joint, or a Hooke's joint.

[0047] The primary and secondary rotary measurement axes may be encoded by first and second rotary encoders, respectively.

[0048] The secondary rotational degree of freedom (or secondary rotational axis) may be substantially orthogonal to the primary rotational degree of freedom (or primary rotational axis).

[0049] The secondary rotational degree of freedom (or secondary rotational axis) may be substantially perpendicular to the longitudinal axis of the segment of the metrology frame connected to the metrology joint from below (i.e., in the direction from the base end towards the metrology joint).

[0050] The segments may alternatively be referred to as links or struts.

[0051] The first rotational degree of freedom can be (adapted or provided) to measure first order rotations, and the second degree of freedom can be (adapted or provided) to measure second order rotations that are smaller than the first order rotations (e.g., by at least an order of magnitude).

[0052] For at least one lateral measurement joint, one or more measurement axes (within the series of measurement axes) arranged (in series) in front of the measurement joint (in the direction from the base end to the head end) may provide the measurement joint with a third rotational degree of freedom.

[0053] At least one of the one or more measurement axes providing the third rotational degree of freedom may form part of another lateral measurement joint.

[0054] Each transverse measurement joint may also have a third rotational degree of freedom.

[0055] A segment of the metrology frame moving about the first rotational degree of freedom may always be within 45 degrees of either the second or third rotational degree of freedom.

[0056] A segment of the metrology frame that moves about the first rotational degree of freedom may be rotatable about its longitudinal axis for any rotation angle about the first rotational degree of freedom by a second rotational degree of freedom or a third rotational degree of freedom, or a combination of these (depending on the rotation angle).

[0057] The metrology frame may comprise further metrology joints that are not associated with or correspond (at least directly) to any particular drive axis.

[0058] A further measurement joint may be positioned between the two lateral rotation measurement joints.

[0059] The at least one further metrology joint may comprise one or more metrology axes (collectively) providing a linear degree of freedom (for the metrology frame), which may be a secondary degree of freedom.

[0060] The one or more metrology axes of the further metrology joint may include a linear metrology axis.

[0061] One or more measurement axes of the further measurement joint may include a combination of rotational measurement axes arranged to be substantially equivalent to linear measurement axes (at least for small relative movements along the linear degrees of freedom).

[0062] The linear degrees of freedom may be provided by two (or at least two) rotational measurement axes.

[0063] Note that linear degrees of freedom do not mean that relative motion is constrained in a linear manner, but merely that relative motion is allowed in a linear manner (and that with the associated encoders such relative motion will be measured in a linear manner).

[0064] A first degree of freedom (or axis) of the metrology frame can be adapted or provided to measure a first (or intended or ideal) movement of the drive frame, and a second (or third) degree of freedom (or axis) of the metrology frame can be adapted or provided to measure a second (or unintended or non-ideal) movement of the drive frame that is smaller than the first movement.

[0065] The second movement may be at least an order of magnitude smaller than the first movement.

[0066] The second movement may be at least ten orders of magnitude smaller than the first movement.

[0067] The second movement may be at least 100 orders of magnitude smaller than the first movement.

[0068] The coupling between the metrology frame and the drive frame at the base end and head end may be located after the last drive shaft in the series and before the first drive shaft in the series.

[0069] The coupling between the metrology and drive frames at the base and head ends may be a rigid coupling.

[0070] The metrology frame may be coupled to the drive frame substantially only at the base and head ends.

[0071] The head end may be adapted to receive and carry a manipulation tool (e.g., a gripper or welding tool, or a probe head or measurement probe). To this end, the head end may be provided with a coupling or coupling feature adapted to couple with a corresponding coupling or coupling feature provided on the manipulation tool. The manipulation tool may be considered to be intended to be positioned by the coordinate positioning arm. In this regard, the coordinate positioning arm is not typically intended to exist in isolation simply to position the head end relative to the base end without any other purpose, but rather is intended to attach some tool or other thing to the head end (to be positioned by the arm) so that the arm can use the tool to perform a useful task.

[0072] A coordinate positioning arm embodying the present invention can be considered to be a functional (or functional, or usable, or unitary, or independent) entity in itself, and not merely any section or part of a longer coordinate positioning arm (e.g., not any three axes in a seven-axis arm). Any selection of axes from a longer arm is not considered to be functioning as a coordinate positioning arm.

[0073] A coordinate positioning arm according to an embodiment of the invention may be removably connectable to another structure without substantially affecting its function as a coordinate positioning arm. The arm may be considered to be an independent entity in its own right. It is possible that the coordinate positioning arm (metrology and drive frame) does not (or may not) have any other metrology or drive shafts (arranged in series between the base end and the head end) than those mentioned above.

[0074] The head end may be removably connectable (or have a connection for removably connecting) to another structure such as a manipulation tool (e.g., a gripper or welding tool or measurement probe), and the base end may be removably connectable (or have a connection for removably connecting) to another structure such as a fixed base of a machine.

[0075] Two or more such coordinate positioning arms can be joined together (e.g. the base end of one arm joined to the head end of another arm) to form a longer compound coordinate positioning arm, but even in such a case each arm is functionally independent of the others. A coordinate positioning arm in this context can be thought of with all its joints or axes usually calibrated as a group, rather than in isolation from one another.

[0076] The term releasably attachable may be taken to mean readily attachable and detachable / separable in the normal operational use of the arm or as part of the routine operation of the arm other than during assembly, disassembly, or manufacture of the arm, where the arm is not still fully functional during the process of assembly or disassembly.

[0077] Advantageously, the configuration of the metrology frame (for each configuration of the drive frame) is determined (or is determinable) (e.g., substantially only) by the configuration of the drive frame and the coupling between the metrology frame and the drive frame at the base end and head end (preferably without intermediate constraints to force the metrology frame into a particular one of two or more different possible configurations).

[0078] The metrology frame may be coupled to the drive frame at the base end and the head end in a manner that affects measurements of the position and orientation of the head end relative to the base end.

[0079] The base end is not necessarily located at the actual base (or other such end) of the coordinate positioning arm. The base end may be spaced apart from the distal end of the coordinate positioning arm. The base end may be considered to include any part that comes before the first (drive and / or measurement) axes of the plurality. The (drive frame) of the coordinate positioning arm may not have a drive axis arranged in series before the base end. The (measurement frame) of the coordinate positioning arm may not have a measurement axis arranged in series before the base end. The base end may alternatively and / or equivalently be referred to as a base member.

[0080] The head end is not necessarily located at the actual head (or other such limb) of the coordinate positioning arm. The head end may be spaced from the distal end of the coordinate positioning arm. The head end may be considered to include any part that comes after the final (drive and / or measurement) axes. The coordinate positioning arm may not have drive axes and / or measurement axes in series after the head end. The drive frame of the coordinate positioning arm may not have drive axes arranged in series after the head end. The (measurement frame) of the coordinate positioning arm may not have measurement axes arranged in series after the head end. The head end may alternatively and / or equivalently be referred to as a head member.

[0081] The coordinate positioning arm (measurement frame) may not have any measurement axes (arranged in series between the base end and the head end) other than the above-mentioned multiple. In other words, the coordinate positioning arm may not have any measurement axes arranged in series after the multiple measurement axes closest to the head end or before the multiple measurement axes closest to the base end. The coordinate positioning arm (drive frame) may not have any drive axes (arranged in series between the base end and the head end) other than the above-mentioned multiple. In other words, the coordinate positioning arm may not have any drive axes arranged in series after the multiple drive axes closest to the head end or before the multiple drive axes closest to the base end.

[0082] Multiple axes may be considered to include any axes corresponding to joints or portions of the arm that are typically calibrated together when calibrating a coordinate positioning arm.

[0083] The drive frame may include (eg, only) a rotating drive shaft.

[0084] The drive frame may include three or fewer rotational drive shafts.

[0085] The drive frame may include exactly three rotational drive axes.

[0086] The drive frame may include two lateral rotary drive shafts and one in-line rotary drive shaft.

[0087] Consider an exemplary drive frame with three rotational drive axes, two of which are lateral and one of which is in-line. In such a drive frame, the metrology frame may include metrology axes that provide three primary rotational degrees of freedom (each associated with the three drive axes), two secondary rotational degrees of freedom (each associated with the two lateral drive axes), and one secondary linear degree of freedom (at least not directly associated with any of the drive axes).

[0088] The in-line rotary drive shaft may be positioned (in serial order from the base end to the head end) before the lateral rotary drive shaft.

[0089] Each drive shaft may provide (as part of a drive joint) relative rotational movement between two connected segments of the drive frame.

[0090] The degrees of freedom (provided by the measurement axes) may include multiple drive axes that are substantially coincident with (or aligned with) each of the multiple drive axes to measure motion associated with the drive axes.

[0091] The measurement and drive axes may be arranged such that there is no configuration of the drive frame (or at least configurations that could reasonably be adopted in normal use of a coordinate positioning arm) in which the two (rotational) measurement axes of the measurement frame are aligned (or would be aligned). At least in this context, two (rotational) axes may be considered to be aligned when they are arranged substantially along the same line (or substantially coincident or colinear) rather than simply parallel to each other. At least in this context, when a linear measurement axis is provided by a combination of rotational axes, the rotational axis that constitutes the linear measurement axis is not considered to be a rotational measurement axis (rather, it is a rotational axis that constitutes a linear measurement axis).

[0092] The metrology frame may be substantially (or primarily) contained, positioned or attached inside (or substantially or primarily surrounded by) the drive frame.

[0093] The measurement axis may be encoded using an encoder.

[0094] The measurement axis may be encoded using an absolute encoder.

[0095] The metrology frame may be (positioned and / or adapted to) measure the position and orientation of the head end relative to the base end in six degrees of freedom.

[0096] The number of measurement axes may be sufficient to measure the position and orientation of the head end relative to the base end in six degrees of freedom.

[0097] The multiple measurement axes may be arranged and / or adapted to measure the position and orientation of the head end relative to the base end in six degrees of freedom.

[0098] A metrology axis can be considered to be an axis of the metrology frame that contributes (in a meaningful or substantial way) to the measurement of the position and orientation of the head end relative to the base end.

[0099] The metrology frame may include six (or fewer) metrology axes.

[0100] The drive frame may include three (or fewer) drive shafts.

[0101] The metrology frame may include a number of metrology axes equal to (or less than) the number of degrees of freedom along which the metrology frame is adapted to measure the position and orientation of the head end relative to the base end.

[0102] The metrology frame may contact the drive frame substantially only at the head and base ends.

[0103] The configuration of the metrology frame is, or can be, substantially influenced only by the coupling between the drive frame and the metrology frame at the head end and the coupling between the drive frame and the metrology frame at the base end.

[0104] A manipulation tool may be (or be) connectable to the head end.

[0105] The metrology frame may have only one solution (or configuration) for each configuration of the drive frame. The metrology frame may have only one solution for each position of the head end relative to the base end. The drive frame may also have only one solution for each position of the head end relative to the base end. By ensuring there is a single metrology configuration for each drive configuration, no intermediate constraints (between the head end and the base end) are needed to encourage or hold the metrology frame in the proper configuration for any position of the head end relative to the base end. Instead, the metrology configuration naturally follows from (is determined by) the drive configuration as the arm moves in a predictable manner. This allows the metrology frame to be completely or substantially unsupported except at the base and head ends.

[0106] The coordinate positioning arm may be a coordinate measuring arm.

[0107] A surface sensing device (e.g., a measurement probe) may be coupled to the head end. Any type of coordinate measuring apparatus can be coupled to the head end to enable the coordinate positioning arm to function as a coordinate measuring arm. The sensing device may be contact or non-contact. Examples include touch-trigger probes, scanning probes, and optical probes. The surface sensing device may be coupled to the head end via a (pre-calibrated) probe head, whereby the probe head itself is coupled to the head end with the surface sensing device coupled to it. The probe head may be a two-axis or three-axis probe head.

[0108] Preferably, there are no unmeasured drive axes or drive degrees of freedom between the head end and the surface sensing device.

[0109] A lateral revolute joint between two segments can be considered a revolute joint with an axis of rotation lateral (or perpendicular) to the respective longitudinal axes of both connected segments. A lateral revolute joint allows the segments (or their respective longitudinal axes) to change orientation relative to one another, with one assuming an orientation that is lateral to the other. The joint can be considered as having an input (e.g., drive) segment and an output (e.g., drive) segment. In a lateral revolute joint, the input and output segments are relatively rotatable about the lateral (perpendicular) axis of rotation of the joint.

[0110] An in-line revolute joint between two segments can be considered a revolute joint with an axis of rotation that is aligned with (or parallel to, or coaxial with) the respective longitudinal axes of both connected segments. An in-line revolute joint allows the segments to be and remain coaxial with one another. The joint can be considered to have an input (e.g., drive) segment and an output (e.g., drive) segment, and an in-line revolute joint 7 allows the input and output segments to the joint to be axially aligned and relatively rotatable about their common axis. An in-line revolute joint can also be called an axial or coaxial revolute joint.

[0111] The metrology axis may be considered separate and / or independent from the drive axis, and in particular not coupled to the drive axis. The metrology and drive frames may be substantially separate and / or mechanically isolated from the other frames, except for the base and head ends. The metrology frame may be substantially coupled to the drive frame only at the base and head ends. The metrology frame may not be substantially supported by the drive frame, except for the base and head ends.

[0112] In this regard, it is preferred that the majority of the metrology frame's weight be supported at the base and head ends, with the remainder (minority) of the weight being supported at a point midway between the base and head ends. How this support is distributed between the base and head ends will depend on the particular configuration or pose adopted by the coordinate positioning arm, taking into account its orientation relative to gravity. Preferably, at least 80% of the metrology frame's weight is supported at the base and head ends. Preferably, at least 90% of the metrology frame's weight is supported at the base and head ends. Preferably, at least 95% of the metrology frame's weight is supported at the base and head ends. Preferably, at least 99% of the metrology frame's weight is supported at the base and head ends. Preferably, at least 99.9% of the metrology frame's weight is supported at the base and head ends. Preferably, all of the metrology frame's weight is supported at the base and head ends. Because the weight supported by the base and head ends (relative to the weight supported at any midpoint between the base and head ends) typically varies depending on the drive configuration (pose), the above conditions can be considered to apply (a) to each possible drive configuration, (b) to a "worst-case" drive configuration in which most weight is supported at the midpoint and least weight is supported by the base and head ends, or (c) to an average or some other similar measure across a representative number of drive configurations. Whether the relevant conditions are met can be readily determined for any particular arm by measurement.

[0113] It is preferred that the measure of the coupling strength or force (either static or dynamic) between the drive frame and metrology frame at any intermediate position(s) between the base end and the head end is at least one order of magnitude less (more preferably five orders of magnitude, more preferably ten orders of magnitude, more preferably one hundred orders of magnitude) than the coupling strength or force required at the base end and the head end.

[0114] The presence (or alternatively removal) of any intermediate support (between the base end and the head end) preferably has an insubstantial effect on measurements or measurement signals from or associated with any or each of the metrology frame's measurement axes and / or on representative measurements of the position and orientation of the head end or points on the head end (e.g., positions in x, y, and z) relative to the base end. By insubstantial effect, we mean an effect (or change) of preferably 5% or less, more preferably 1% or less, more preferably 0.5% or less, more preferably 0.1% or less, more preferably 0.01% or less, and more preferably 0.001% or less. The effect can be readily determined by comparing the measurement signals from each metrology encoder (associated with each measurement axis) with or without a predetermined position of the intermediate support. Again, the above conditions can be considered to apply (a) to each possible drive configuration, (b) to a "worst-case" drive configuration, or (c) to an average or some other similar measure across representative drive configurations.

[0115] It should be understood that in one embodiment of the present invention, the metrology frame and drive frame are described herein as being compatible with one another and having certain desirable properties that apply to situations in which the coordinate positioning arm is in use, the metrology frame is active, and provides motion measurements. In other words, the described properties apply when the arm is in an active state with the metrology frame providing motion measurements of the head end relative to the base end. When measurements are not being provided or in use, additional constraints are of course possible in place between the metrology frame and the drive frame, since the metrology frame, whether distorted or not, does not provide true or accurate measurements of the position and orientation of the head end relative to the base end. Such a coordinate positioning arm may have additional constraints only when it is not in motion or actively in use, yet still be considered within the scope of the present invention, as recited in the appended claims. Similarly, the properties recited in the appended claims need only apply to typical operating configurations of the drive frame and need not apply to other configurations or poses of the arm, for example, when a manipulation tool (e.g., a measurement probe) directly or indirectly coupled to the head end is within the normal operating volume of the machine and is not actually in use.

[0116] The metrology frame and drive frame can be considered constrained relative to one another, such that for a particular configuration of the drive frame, constraints between the metrology frame and the drive frame (e.g., rigid connections at the base and head ends) attempt to force the metrology frame into a configuration that it cannot reach (due to insufficient degrees of freedom). This results in a situation where the metrology frame is "fighting" against the drive frame because it is trying to place the metrology frame in a configuration different from the configuration that the metrology frame is forcing it to. This leads to the metrology frame experiencing stresses, such as bending or twisting in places where it should not be. This means that the metrology results do not provide a true representation of the position and orientation of the drive frame because the metrology frame undergoes unmeasured motions (e.g., bending) (there are no corresponding measurement axes along which undesired bending occurs).

[0117] Alternatively, excessive constraint can be considered avoided if the presence of the metrology frame provides substantially no additional constraint between the base end and the head end of the drive frame (other than that already provided by the drive frame itself). In this regard, the head end is constrained relative to the base end by the drive frame, and the head end is constrained to move relative to the base end according to the degrees of freedom provided by the drive axes of the drive frame. In one embodiment of the present invention, the metrology frame does not provide any additional constraint between the base end and the head end, allowing the drive frame to move substantially as if the metrology frame were not present at all. This would be the case, for example, if a piece of string were attached between the base and head ends, because the available degrees of freedom would be so great that its presence effectively does not create any additional constraint.

[0118] Thus, when it is stated or explained that a metrology axis provides the metrology frame with sufficient degrees of freedom to avoid (create) beyond constraints between the metrology frame and the drive frame, this can be read as the metrology axis providing the metrology frame with sufficient degrees of freedom to create (or create, or provide substantially no additional constraints) additional constraints for the drive frame between the base end and the head end (other than those already provided by the drive axes of the drive frame).

[0119] The "head end" of a coordinate positioning arm can be considered to be any part beyond the final drive axis in a series of drive axes, i.e., any part that is driven via the final drive axis. Similarly, the "base end" of a coordinate positioning arm can be considered to be any part before the first drive axis in a series of drive axes. In other words, the "end" of a coordinate positioning arm does not necessarily mean the very extreme end of the arm, but nothing beyond it, since at least the head end is likely to have a manipulation tool attached to it, which can also be considered to form part of the arm in use. When two or more such coordinate positioning arms are connected in series to form a composite arm, each component arm of the composite arm will have a base end and a head end, as will the composite arm itself. It should be noted that where it is described that the metrology frame is coupled to the drive frame substantially only at its base and head ends, the coupling may be anywhere after the final drive axis (in the case of the head end) and anywhere before the first drive axis (in the case of the base end), and that a drive axis is only considered a drive axis if it can affect the position and orientation of the head end relative to the base end (i.e., it does not include redundant axes located after the head end or before the base end of the associated arm, although there may be additional arms connected in series as described above). The terms "head end" and "base end" may alternatively be referred to as "first portion" and "second portion," or "head member" and "base member," respectively, so as not to imply that they are located at the exact head or base of the arm.

[0120] The drive frame may alternatively be referred to as the drive configuration, and the metrology frame may alternatively be referred to as the metrology configuration.

[0121] The drive axis can be thought of as acting as a constraint on relative motion between the base end and the head end. When it is stated that a rotational degree of freedom is substantially aligned with another axis, it means that the axis of rotation of the rotational degree of freedom is substantially aligned with the other axis. The lateral rotation measurement joint is the joint corresponding to the lateral rotation drive axis.

[0122] A transverse axis of rotation can be considered to be transverse (usually perpendicular) to the segments connected by the axis of rotation. An in-line axis of rotation can be considered when the axis of rotation is substantially coincident with the segments connected by the axis of rotation.

[0123] A "configuration" of a drive frame can alternatively be referred to as the "pose" or "disposition" or "state" of the drive frame. A configuration is defined or characterized by the state of each of the drive frame's drive axes, i.e., the rotational angle of the drive frame about each of the drive axes, including the in-line drive axis (i.e., the rotational angle of the segment connected by the associated drive axis). Thus, a configuration of a drive frame can be considered to include the set of rotational angles associated with the drive axes of the drive frame. A configuration of a drive frame can be likened to machine coordinates, a common concept in the context of coordinate measuring machines. The same considerations apply equally with respect to the "configuration" of a metrology frame.

[0124] The primary axes (or degrees of freedom) of the metrology frame are intended to measure the principal or intended motions typically expected of the drive frame, i.e., resulting from actuation or drive of the drive axes. Inevitably, the drive frame will also have unintended or undesired motions due, for example, to manufacturing tolerances and inaccuracies in axis alignment, and variations in motion due, for example, to thermal expansion or contraction or mechanical loads. The secondary axes (or degrees of freedom) of the metrology frame (whether rotary, combinatorial, rotary, or linear) are intended to measure these unintended motions of the drive frame. Primary motions are typically at least an order of magnitude larger, or even as much as ten orders of magnitude larger, than the corresponding secondary motions.

[0125] According to another aspect of the present invention, there is provided a coordinate positioning arm including a base end and a head end, a drive frame for moving the head end relative to the base end, and a metrology frame for measuring the position and orientation of the head end relative to the base end, wherein the drive frame includes a plurality of drive axes (which act as constraints for relative motion between the base end and the head end) arranged in series between the base end and the head end, and the metrology frame includes a plurality of (separate or independent) measurement axes arranged in series between the base end and the head end, the metrology frame being coupled to the drive frame at the base end and the head end, and (for each possible configuration of the drive frame) the measurement axes (collectively) being coupled to the metrology frame: provides sufficient (or necessary) degrees of freedom to avoid (or create) beyond the constraints between the metrology frame and the drive frame (or for the drive frame between the base end and the head end, e.g., so as not to create additional constraints beyond those already provided by the drive shaft itself), and (for each possible configuration of the drive frame) the configuration of the metrology frame is determined (or determinable) (substantially only) by the configuration of the drive frame and the coupling between the metrology frame and the drive frames at the base end and the head end (without intermediate constraints to force the metrology frame into a particular one of two or more different possible configurations);

[0126] According to another aspect of the present invention, a coordinate positioning arm is provided, the coordinate positioning arm including a base end and a head end, a drive frame for moving the head end relative to the base end, and a metrology frame for measuring the position and orientation of the head end relative to the base end. The drive frame includes multiple drive axes arranged in series between the base end and the head end, and the metrology frame includes multiple measurement axes arranged in series (separately) between the base end and the head end. The drive axes can be considered to act as (or provide) constraints on the relative motion between the base end and the head end. For each configuration (or pose or arrangement) of the drive frame, the measurement axes provide (or are arranged to provide) sufficient degrees of freedom for the metrology frame to avoid (create) exceeding the constraint between the metrology frame and the drive frame. In other words, for each configuration (or pose or arrangement) of the drive frame, the measurement axes provide (or are arranged to provide) sufficient degrees of freedom for the metrology frame to avoid (create) any additional constraints of the drive frame between the base end and the head end (other than those already provided by the drive axes themselves).

[0127] According to another aspect of the present invention, there is provided a coordinate positioning arm including a first part and a second part, a drive frame for moving the first part relative to the second part, and a metrology frame for measuring the position and orientation of the first part relative to the second part, wherein the drive frame has a plurality of drive axes arranged in series between the first part and the second part, and the metrology frame has a plurality of (separate or independent) measurement axes arranged in series between the first part and the second part, the measurement axes providing the metrology frame with sufficient (or necessary) degrees of freedom to avoid (or create) beyond constraints between the metrology frame and the drive frame, and wherein the configuration of the metrology frame is determined (or determinable) by (substantially only) the configuration of the drive frame and by the coupling between the metrology frame and the drive frame.

[0128] According to another aspect of the present invention, there is provided a coordinate positioning arm comprising: a base end and a head end; a drive frame for moving the head end relative to the base end, the drive frame comprising a plurality of serially arranged drive axes (each drive axis contributing to the position and orientation of the head end relative to the base end); and a metrology frame (6 degrees of freedom) for measuring the position and orientation of the head end relative to the base end, the metrology frame comprising a plurality of serially arranged measurement axes (each measurement axis contributing to the measurement of the position and orientation of the head end relative to the base end), wherein the metrology frame is coupled to the drive frame substantially only at the base end and head end (in a manner that affects the measurement of the position and orientation of the head end relative to the base end), and the measurement axes (collectively) provide the metrology frame with enough degrees of freedom to not exceed (create) constraints between the metrology frame and the drive frame, but insufficient to provide one or more possible configurations or poses or arrangements for the metrology frame.

[0129] According to another aspect of the present invention, there is provided a coordinate positioning arm comprising a drive frame having a plurality of revolute joints, the revolute joints being transverse revolute joints, and a separate measurement frame having a plurality of measurement joints respectively corresponding to the plurality of revolute joints, the measurement joints corresponding to the transverse revolute joints having mutually orthogonal major and minor axes of rotation, the major axis of rotation being substantially aligned with an axis of rotation of the transverse revolute joint and for measuring rotation of the transverse revolute joint, and the minor axis of rotation being for measuring inadvertent rotation of the transverse revolute joint, the orientation of the minor axis being invariant to rotation about the major axis.

[0130] According to another aspect of the present invention, there is provided a coordinate positioning arm comprising a base end and a head end, a drive frame for moving the head end relative to the base end, and a metrology frame for measuring the position and orientation of the head end relative to the base end, wherein the drive frame comprises multiple drive axes arranged in series between the base end and the head end, and the metrology frame comprises multiple measurement axes arranged in series between the base end and the head end. Each drive axis has a corresponding primary measurement axis (for measuring primary or intended motion associated with that drive axis), and at least one (preferably each) rotational drive axis (except for the first serial from the base end) also has at least one corresponding secondary measurement axis (for measuring secondary or unintended motion associated with that drive axis), where the or each secondary measurement axis is sequentially positioned from the base end to the head end before the corresponding primary measurement axis (such that rotation of the head end about a drive axis does not affect the orientation of the or each secondary measurement axis, thereby avoiding measurement axis redundancy for a particular configuration of the drive frame). Either or each primary and secondary measurement axis may be substantially orthogonal to one another. The primary and secondary measurement axes may substantially intersect. At least one of the secondary measurement axes may be formed by a combination of measurement axes. At least one of the secondary measurement axes may be formed by a primary measurement axis associated with another drive axis or by a combination including such a primary measurement axis.

[0131] According to another aspect of the present invention, there is provided a coordinate positioning arm comprising a base end and a head end, a drive frame for moving the head end relative to the base end, and a metrology frame for measuring the position and orientation of the head end relative to the base end, wherein the drive frame includes a plurality of drive axes arranged in series between the base end and the head end, and the metrology frame includes a plurality of measurement axes arranged in series between the base end and the head end, the measurement axes (collectively) providing each (lateral) rotational drive axis (except a first) (or associated drive joint), and three orthogonal rotational degrees of freedom (in the metrology frame) including the first degree of freedom (or each measurement axis corresponding to or aligned with the drive axis) and two further degrees of freedom where the measurement axes are arranged (in serial order from the base end to the head end) before the first degree of freedom (or each axis for the first degree of freedom), and preferably the or each measurement axis is further associated in series with a lower rotational drive axis (if any).

[0132] According to another aspect of the present invention, there is provided a coordinate positioning arm having a base end and a head end, a drive arrangement for moving the head end relative to the base end, and a measurement arrangement (6 degrees of freedom) for measuring the position and orientation of the head end relative to the base end, wherein the drive arrangement has a plurality of drive axes arranged in series (each drive axis contributing to the position and orientation of the head end relative to the base end), and the measurement arrangement has a plurality of measurement axes arranged in series (each measurement axis contributing to the measurement of the position and orientation of the head end relative to the base end), the measurement arrangement is coupled to the drive arrangement substantially only at the base end and the head end (in a manner that affects the measurement of the position and orientation of the head end relative to the base end), and the measurement axes provide sufficient degrees of freedom (number and / or type and / or orientation) to avoid exceeding (creating) constraints between the measurement arrangement and the drive arrangement, but insufficient degrees of freedom to provide one or more possible configurations for the measurement configuration for each configuration of the drive arrangement (without using the constraint between the measurement arrangement and the drive arrangement between the base end and the head end).

[0133] According to another aspect of the present invention, there is provided a coordinate positioning arm including a drive arrangement for moving a head end of an arm relative to a base end of the arm and a measurement arrangement for measuring the position and orientation of the head end relative to the base end, wherein the drive arrangement includes multiple rotational axes arranged in series between the head end and the base end, and the measurement arrangement includes multiple rotational axes arranged in series between the head end and the base end. For each drive axis, each rotational measurement joint includes first and second rotational measurement degrees of freedom, and a third rotational measurement degree of freedom is provided in series (towards the base end) from one or more lower measurement joints, thereby providing three rotational degrees of freedom to the measurement arrangement connected above the joint (towards the head end). The first rotational degree of freedom is a primary rotational degree of freedom for measuring the primary rotational degree of freedom of the corresponding drive joint, and for any position of the first rotational degree of freedom, the first, second, and third rotational degrees of freedom remain transverse to each other.

[0134] According to another aspect of the present invention, there is provided a coordinate positioning arm comprising a drive arrangement including a plurality of rotary drive axes arranged in series between a fixed end and a movable end of the arm, and a measurement arrangement including a plurality of measurement axes for measuring the position and orientation of the movable end of the arm, wherein the measurement arrangement is coupled to the drive arrangement only at the fixed and movable ends (and in particular not at any of the rotary drive axes), and wherein for each configuration of the drive arrangement there is only one possible configuration for the measurement arm, and no excessive constraints exist between the measurement arrangement and the drive arrangement in any configuration.

[0135] According to another aspect of the present invention there is provided a coordinate positioning machine comprising a drive arrangement for positioning a moveable structure within a working volume of the machine and a measurement arrangement for measuring the position (and / or orientation) of the moveable structure within the working volume, the drive arrangement including a plurality of rotary (drive) axes arranged in series; The measurement arrangement includes corresponding multiple rotary (measurement) axes arranged in series to measure the primary (or intended) rotation (of the drive arrangement) about each corresponding rotary drive axis, the drive arrangement and the measurement arrangement are connected in parallel (separately and / or independently) between a fixed structure and a movable structure of the machine, the measurement arrangement is configured so that it does not touch the drive arrangement except via the movable structure at one end (of the series) and the fixed structure at the other end (of the series), and for each configuration of the drive arrangement there is only one possible configuration of the measurement arrangement.

[0136] According to another aspect of the present invention, there is provided a coordinate positioning machine comprising a drive arrangement for positioning a moveable structure within a working volume of the machine, and a separate (or independent) measurement arrangement for measuring the position (and / or orientation) of the moveable structure within the working volume, the drive arrangement comprising a plurality of rotary (drive) joints (arranged in series), each having a rotary drive axis, and the measurement arrangement comprising a corresponding plurality of rotary (measurement) joints (arranged in series), each having a (primary) rotational measurement axis for measuring a primary (or intended) rotation (of the drive arrangement) about (the rotational drive axis) (of the corresponding rotary drive joint), each of at least two of the rotational measurement joints also comprising a secondary rotational measurement axis for measuring a secondary (or unintended) rotation relative to the corresponding rotary drive joint, the secondary rotational measurement axis being arranged in series with (and before) the primary measurement rotation axis (when viewed towards the moveable structure).

[0137] According to another aspect of the present invention, there is provided a coordinate positioning machine comprising a drive arrangement (connected between a fixed structure and a movable structure) including a plurality of rotary (drive) axes (arranged in series), and a separate (or independent) measurement arrangement (arranged in series) including a corresponding plurality of rotary (measurement) axes (arranged in series), each rotational measurement axis being arranged to measure a primary (or intended) rotation (of the drive arrangement) about a corresponding rotational drive axis (primary rotational measurement axis), and each of at least two of the (primary) (lateral) rotational measurement axes being provided (or paired) with a secondary rotational measurement axis for measuring a secondary (or unintended) rotation relative to the corresponding rotational drive axis, the secondary rotational measurement axes being arranged in series with the (primary) rotational measurement axes (when viewed towards the movable structure).

[0138] According to another aspect of the present invention there is provided a compound coordinate positioning arm comprising a plurality of coordinate positioning arms as described herein.

[0139] According to another aspect of the present invention there is provided a manufacturing or assembly method using a coordinate positioning arm as defined in any preceding claim to position one or more manufacturing or assembly tools for manufacturing or assembling an article, and to position a measurement or inspection tool for measuring or inspecting the manufactured or assembled article, wherein the measurement tools may be coordinate measurement tools such as touch trigger probes or scanning probes.

[0140] A machine controller is also usefully provided for controlling the operation of the coordinate positioning arm. The machine controller may be a dedicated electronic control system and / or may include a computer operating under the control of a computer program. For example, the machine controller may comprise a real-time controller for providing low-level instructions to the coordinate positioning machine and a PC for operating the real-time controller.

[0141] It will be appreciated that the operation of a coordinate measuring machine may be controlled by a program running on the machine, such as by a program running on a coordinate measuring machine controller, such as the controller shown schematically in Figure 1. Such a program may be stored on a computer readable medium or may be embodied in a signal, for example a downloadable data signal provided from an internet website. [Brief explanation of the drawings]

[0142] Reference will now be made, by way of example, to the accompanying drawings in which: [Figure 1] FIG. 1 is a schematic diagram of a coordinate positioning arm in the form of an articulating robot, as discussed above; [Figure 2] FIG. 2 shows a coordinate positioning arm similar to that shown in FIG. 1, but with only three axes of rotation. [Figure 3] FIG. 3 shows how the three-axis coordinate positioning arm of FIG. 2 can be given an additional degree of freedom by coupling it to a separate two-axis (or three-axis) probe head. [Figure 4] FIG. 1 illustrates the operational versatility of a 3-axis coordinate positioning arm coupled to a separate 2-axis (or 3-axis) probe head. [Figure 5] FIG. 10 illustrates the concept of providing the drive frame of a 3-axis coordinate positioning arm with a separate internal metrology frame that is coupled to the drive frame only at the base and head ends of the arm. [Figure 6] 6A and 6B are diagrams illustrating the need for additional degrees of freedom in the metrology frame compared to that shown in FIG. [Figure 7] FIG. 6C illustrates the ambiguity that can arise from measurements without the additional rotational degrees of freedom provided in FIG. 6B. [Figure 8] FIG. 10 shows a schematic diagram illustrating the need for at least six rotational degrees of freedom in the metrology frame for a fully three-dimensional example. [Figure 9]FIG. 10 uses a mirrored representation to show that the metrology frame has a generally similar form to the drive frame with metrology joints corresponding to each of the drive joints. [Figure 10] FIG. 10 is a schematic illustration of how the metrology frame actually fits within the drive frame, coupled only to the ends of the coordinate positioning arms and effectively freestanding therebetween; this is a non-mirrored version of FIG. [Figure 11] FIG. 9 shows the coordinate positioning arm of FIG. 8 in a fully extended pose, and is used to explain issues associated with this measurement axis placement. [Figure 12] FIG. 12 is a side view of the full extension coordinate positioning arm of FIG. [Figure 13] FIG. 10 shows a pose for the coordinate positioning arm with only one of the lateral revolute joints fully extended, and is used to explain another issue related to the placement of this measurement axis. [Figure 14] FIG. 14 illustrates a method by which the problem described with reference to FIG. 13 can be overcome. [Figure 15A] FIG. 15 illustrates the problem even with the workaround suggested in FIG. [Figure 15B] FIG. 15 illustrates the problem even with the workaround suggested in FIG. [Figure 16] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 17] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 18] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 19] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 20]1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 21A] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 21B] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 21C] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 22] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 23] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 24] 1 is a series of schematic diagrams that do not represent embodiments of the present invention, but are used to introduce design principles that form the basis of embodiments of the present invention. [Figure 25] FIG. 1 is a schematic diagram illustrating a coordinate positioning arm according to an embodiment of the present invention, where the metrology frame includes two universal joints, a pivot joint and a linear joint, providing the metrology frame with six degrees of freedom. [Figure 26] 26 illustrates in more detail the universal joint used in the metrology frame of FIG. 25 and to explain how the axes that make up the universal joint are ordered in an embodiment of the invention. [Figure 27] FIG. 27 is a view corresponding to FIG. 26, but showing the axes of the universal joints ordered in the opposite direction. [Figure 28] FIG. 1 is a schematic diagram of a coordinate positioning arm with various measurement axes annotated to show their order, in accordance with an embodiment of the present invention; [Figure 29] Figure 13 shows a front view of a coordinate positioning arm according to an embodiment of the invention, in a pose corresponding to that of the positioning arm of Figures 11 and 12 for ease of comparison. [Figure 30] Figure 13 shows a side view of a coordinate positioning arm according to an embodiment of the invention, in a pose corresponding to that of the positioning arm of Figures 11 and 12 for ease of comparison. [Figure 31] FIG. 29 shows a coordinate positioning arm not embodying the present invention, with the arm positioned in a pose corresponding to the embodiment shown in FIG. 28, and with the axes of the universal metrology joints in the wrong order. [Figure 32] Figures 32 and 33 respectively show a coordinate positioning arm that does not implement the present invention and a coordinate positioning arm that implements the present invention in the same pose for ease of comparison, with Figure 32 showing a coordinate positioning arm that does not implement the present invention. [Figure 33] Figures 32 and 33 respectively show a coordinate positioning arm not embodying the invention and a coordinate positioning arm embodying the invention in the same pose for ease of comparison, and Figure 33 shows a coordinate positioning arm embodying the invention. [Figure 34A] FIG. 11 is a schematic diagram corresponding to that shown in FIG. 10 of how a metrology frame is provided within the envelope of a drive frame in an embodiment of the invention. [Figure 34B] FIG. 1 is a diagram to explain some of the terms used in this specification. [Figure 35] FIG. 31 is a side view corresponding to that of FIG. 30 of an alternative embodiment in which the linear degrees of freedom in the metrology frame are provided by rotational axes rather than linear axes. [Figure 36A] FIG. 36 shows in more detail how linear degrees of freedom are provided by rotational axes in the alternative embodiment of FIG. 35. [Figure 36B] FIG. 36 shows in more detail how linear degrees of freedom are provided by rotational axes in the alternative embodiment of FIG. 35. [Figure 37A]FIG. 10 is a diagram intended to be used to illustrate the concept of over-constraint, or rather the lack of over-constraint, in measurement joints used in embodiments of the present invention. [Figure 37B] FIG. 10 is a diagram intended to be used to illustrate the concept of over-constraint, or rather the lack of over-constraint, in measurement joints used in embodiments of the present invention. [Figure 37C] FIG. 10 is a diagram intended to be used to illustrate the concept of over-constraint, or rather the lack of over-constraint, in measurement joints used in embodiments of the present invention. [Figure 37D] FIG. 10 is a diagram intended to be used to illustrate the concept of over-constraint, or rather the lack of over-constraint, in measurement joints used in embodiments of the present invention. [Figure 38A] FIG. 10 is a diagram used to illustrate the concept of over-constraint in a measurement joint used in a positioning arm that does not embody the present invention. [Figure 38B] FIG. 10 is a diagram used to illustrate the concept of over-constraint in a measurement joint used in a positioning arm that does not embody the present invention. [Figure 38C] FIG. 10 is a diagram used to illustrate the concept of over-constraint in a measurement joint used in a positioning arm that does not embody the present invention. [Figure 38D] FIG. 10 is a diagram used to illustrate the concept of over-constraint in a measurement joint used in a positioning arm that does not embody the present invention. [Figure 38E] FIG. 10 is a diagram used to illustrate the concept of over-constraint in a measurement joint used in a positioning arm that does not embody the present invention. [Figure 39A] FIG. 37D shows that when the joint of FIG. 37C is flipped over, there is still no over-constraint. [Figure 39B] FIG. 37D shows that when the joint of FIG. 37C is flipped over, there is still no over-constraint. [Figure 39C] FIG. 37D shows that when the joint of FIG. 37C is flipped over, there is still no over-constraint. [Figure 39D]FIG. 37D shows that when the joint of FIG. 37C is flipped over, there is still no over-constraint. [Figure 40A] FIG. 38D shows that the excess constraint is still present when the joint of FIG. 38C is inverted, but is in fact avoided when considering an in-line rotation axis below the joint. [Figure 40B] FIG. 38D shows that the excess constraint is still present when the joint of FIG. 38C is inverted, but is in fact avoided when considering an in-line rotation axis below the joint. [Figure 40C] FIG. 38D shows that the excess constraint is still present when the joint of FIG. 38C is inverted, but is in fact avoided when considering an in-line rotation axis below the joint. [Figure 40D] FIG. 38D shows that the excess constraint is still present when the joint of FIG. 38C is inverted, but is in fact avoided when considering an in-line rotation axis below the joint. [Figure 40E] FIG. 38D shows that the excess constraint is still present when the joint of FIG. 38C is inverted, but is in fact avoided when considering an in-line rotation axis below the joint. [Figure 41A] 1A and 1B are diagrams used to explain the main properties of the transverse measurement joint used in embodiments of the present invention. [Figure 41B] 1A and 1B are diagrams used to explain the main properties of the transverse measurement joint used in embodiments of the present invention. [Figure 41C] 1A and 1B are diagrams used to explain the main properties of the transverse measurement joint used in embodiments of the present invention. [Figure 42A] Figures 42A-42C are for comparison with Figures 41A-41C, and Figure 42A is used to illustrate the properties of the transverse measurement joint that are unsuitable for use in embodiments of the present invention, and shows that redundant axes in certain poses result in excessive constraints. [Figure 42B]42A-42C are for comparison with FIGS. 41A-41C, and FIG. 42B is used to illustrate the properties of the transverse measurement joint that are unsuitable for use in embodiments of the present invention, and shows that redundant axes in certain poses result in excessive constraints. [Figure 42C] Figures 42A-42C are for comparison with Figures 41A-41C, and Figure 42C is used to illustrate the properties of the transverse measurement joint that are unsuitable for use in embodiments of the present invention, and shows that redundant axes in certain poses result in excessive constraints. [Figure 43A] FIG. 10 illustrates the lack of over-constraint between the metrology frame and the drive frame in the case of misalignment between the in-line rotary drive axis and the metrology axis. [Figure 43B] FIG. 10 illustrates the lack of over-constraint between the metrology frame and the drive frame in the case of misalignment between the in-line rotary drive axis and the metrology axis. [Figure 44A] FIG. 10 illustrates how multiple coordinate positioning arms embodying the invention can be combined in series to create a longer arm with more axes overall. [Figure 44B] FIG. 10 illustrates how multiple coordinate positioning arms embodying the invention can be combined in series to create a longer arm with more axes overall. [Figure 44C] FIG. 10 illustrates how multiple coordinate positioning arms embodying the invention can be combined in series to create a longer arm with more axes overall. [Figure 44D] FIG. 10 illustrates how multiple coordinate positioning arms embodying the invention can be combined in series to create a longer arm with more axes overall. [Figure 45] 1 is a schematic diagram of a two-axis coordinate positioning arm embodying the present invention; [Figure 46] FIG. 1 is a schematic diagram of a single axis coordinate positioning arm embodying the invention, primarily for use as a component of a longer coordinate positioning arm embodying the invention; [Figure 47]FIG. 10 illustrates how a three-axis component arm can be combined in series with another three-axis component arm to create a six-axis coordinate positioning arm embodying the present invention. [Figure 48] FIG. 10 illustrates how a three-axis component arm can be combined in series with a two-axis component arm to create a five-axis coordinate positioning arm embodying the present invention. [Figure 49A] FIG. 1 illustrates a manufacturing system utilizing a coordinate positioning arm embodying the present invention. [Figure 49B] FIG. 1 illustrates a manufacturing system utilizing a coordinate positioning arm embodying the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0143] Figure 2 shows a coordinate positioning arm 10 that forms the basis of an embodiment of the present invention. The coordinate positioning arm 10 is similar to that shown in Figure 1 but stripped down to have only three axes of rotation: two lateral rotation axes 6 and one in-line rotation axis 7. The aim is to provide a coordinate positioning arm 10 with a low axis count and to optimise the coordinate positioning arm 10 for high accuracy. How this is achieved will be explained in more detail below.

[0144] While having just three axes of rotation may be sufficient for some applications, to provide sufficient versatility for other applications, Figure 3 shows how additional degrees of freedom can be provided by coupling the three-axis coordinate positioning arm 10 of Figure 2 with a separate (and already calibrated) two-axis (or three-axis) probe head 12. Examples of such probe heads are those manufactured and sold by Renishaw Plc under the brand names Revo® and PH 20®. The probe head is a separable and separate entity to the coordinate positioning arm itself and is not considered to form an integral part of the coordinate positioning arm itself.

[0145] As shown in Figure 2, the coordinate positioning arm 10 provides axes of rotation R1, R2 and R3, while the probe head 12 provides orthogonal axes of rotation R4 and R5, and optionally a further axis of rotation R6, for a total of up to six axes of rotation. A measurement probe 14 is attached to the probe head 12, which is itself attached to the coordinate positioning arm 10. The measurement probe may be a touch-trigger probe or a scanning probe. To enable this separability and modularity, the coordinate positioning arm 10 is provided with mounting or coupling features that engage with corresponding mounting or coupling features on the probe head 12, allowing the probe head 12 to be removably and easily coupled to the coordinate positioning arm 10.

[0146] Figure 4 illustrates the operational versatility of such a three-axis coordinate positioning arm 10 coupled to a separate two-axis (or three-axis) probe head 12, the combined structure 10, 12 having five rotational axes available for positioning and orienting the measurement probe 14 to a rough feature of the workpiece 16, such as an angled bore 18, and also having a sixth rotational axis available for rotating the probe 14 about its longitudinal axis (this is particularly useful where the probe 14 is a unidirectional probe, such as a surface finishing probe).

[0147] In this way, the precise coordinate positioning arm 10 of Figure 2 can be combined with a separate probe head 12 to provide a flexible and precise measurement system. The coordinate positioning arm 10 and the probe head 12 can be calibrated separately from each other.

[0148] The three-axis coordinate positioning arm 10 itself will now be described, beginning with an analysis of the problems associated with providing a metrology frame for such a positioning arm, and explaining in more detail how the applicant understands the causes of these problems and has the insight to overcome them.

[0149] 5 is a schematic diagram of a three-axis coordinate positioning arm A having an outer drive frame D and a separate internal metrology frame M. The metrology frame M is coupled to and supported by the drive frame D only at the base end B and head end H of the arm A. As will be explained in more detail below, the coordinate positioning arm A can provide increased metrology performance or accuracy by having a separate metrology frame M. This is because the metrology frame M can be isolated from stresses induced by loads on the drive frame D of the arm A, as well as due to certain design considerations that apply to the metrology frame M.

[0150] Figure 6A shows the three rotational measurement axes R1, R2, and R3 of the metrology frame M of arm A of Figure 5, which correspond to the three rotational drive axes of drive frame D. Rotational axis R1 is the in-line rotational axis, and rotational axes R2 and R3 are lateral rotational axes. In Figure 6A, there is a rigid connection between the metrology frame M and drive frame D at both the head end H and the base end B.

[0151] Now consider the case where, due to manufacturing tolerances, the final segment of drive frame D is shorter than expected (shorter than that of FIG. 6A), as shown in FIG. 6B. The length of the final segment is reduced from L1 to L2. To accommodate the different (more compact) configuration required for metrology frame M to fit metrology frame F into the shorter overall length of drive frame D, an additional metrology degree of freedom is required at head end H, and this additional degree of freedom is provided by an additional rotational metrology axis R4.

[0152] Figure 7 illustrates the error or ambiguity that can arise from measurements without the additional rotational degrees of freedom provided in Figure 6B. Figure 7 shows the same measurement configuration as Figure 6B, but (incorrectly) assumes that the length of the drive segments is the same as in Figure 6A with a rigid connection at the head end H. This leads to the (incorrect) conclusion that the final drive segment is positioned at an angle to the vertical, when in fact the final drive segment is vertically aligned as shown in Figure 6B.

[0153] Of course, Figure 6B is a simplified two-dimensional example in which only a single additional measurement axis R4 is provided. Figure 8 is a schematic diagram of the situation in three dimensions, illustrating the need for three additional measurement axes R4, R5, and R6 at head end H, providing a total of six rotational degrees of freedom R1-R6 in measurement frame M for a full three-dimensional example. In the configuration (or pose) shown in Figure 8, linear displacement of head end H into the page can be accommodated by rotation about axis R1 (in combination with changes in the other measurement axes R2-R6).

[0154] As an alternative to the schematic representation of Figure 8, Figure 9 uses a mirrored representation in which metrology frame M is drawn outside of drive frame D and mirrored about the vertical dotted line to show how metrology frame M is in overall similar form to drive frame D, with each metrology joint corresponding to a drive joint. Figure 10 is a non-mirrored version of Figure 9 showing schematically how metrology frame M actually fits within drive frame D, coupled only to, and effectively freestanding between, the head end H and base end B of coordinate positioning arm A.

[0155] Figure 11 shows the coordinate positioning arm of Figure 8 in a fully extended pose (or configuration) and is used to illustrate the problems associated with this arrangement of measurement axes R1-R6. In this pose, linear displacement of the head end H-piece toward the page (caused, for example, by the drive joint corresponding to measurement axis R3 having a small amount of nonideal or undesired rotation about an axis parallel to axis R5) can no longer be accommodated (measured). Figure 12 shows a side view of the coordinate positioning arm of Figure 11, with a double-headed arrow added to indicate the movement that cannot be measured with this combination of measurement axes R1-R6.

[0156] Applicant understands that this problem arises because measurement axes R1 and R6 have become aligned or coincident with one another in this arm pose (i.e., positioned along the same line). This effectively means that there are now only five degrees of freedom instead of six, and therefore insufficient degrees of freedom to measure the commanded movement of the head end in measurement frame M. A seventh degree of freedom would clearly need to be added (at least in the absence of further insight by Applicant) to return to having six "usable" degrees of freedom in this pose, i.e., sufficient degrees of freedom to measure the commanded movement of the head end in this pose.

[0157] The entire metrology frame M can be rotated 90 degrees about axis R1 and the above motion can then be measured, but measurement axes R2 and R3 are then offset by 90 degrees from their corresponding drive axes, which is problematic for other reasons. In any case, even if metrology frame M is flipped 90 degrees in this way, it is no longer possible to measure the displacement of head edge H horizontally in the plane of the page; in other words, it cannot do both simultaneously.

[0158] Figure 13 shows a configuration or pose of the coordinate positioning arm where only one of the lateral rotational joints (associated with measurement axis R3) is fully extended. This also presents a problem because measurement frame M does not have enough degrees of freedom to measure the extension of drive frame D (for example, in the event of thermal expansion of the segments that make up drive frame D). Figure 14 shows that the problem described with reference to Figure 13 can be overcome by "pre-buckling" measurement frame M, slightly lengthening each segment so that there is enough "slack" at the start to be able to measure small amounts of extension using any combination of rotational measurement axes R2-R4.

[0159] However, Figures 15A and 15B illustrate a problem understood by applicants even with the workaround suggested in Figure 14. In particular, for each pose or configuration of drive frame D, there are now two possible configurations for metrology frame M (i.e., "two metrology solutions"), one of which will cause metrology frame M to collide with drive frame D.

[0160] Figures 16-24 are a series of schematic diagrams used to introduce the design principles that form the basis of embodiments of the present invention. Each of these figures uses the three-axis arm of Figure 5 as an example, with separate metrology and drive frames as described above, and each of Figures 16-24 shows this arm in four different configurations or poses. Some of the issues discussed below with reference to Figures 16-24 echo, at least to some extent, the issues also discussed above with reference to Figures 6-15.

[0161] In each of Figures 16-24, the first pose is a vertical pose in which the upper and middle links are positioned vertically and both lateral drive joints are 180 degrees (i.e., straight). In the second pose, the upper drive joint is rotated 90 degrees to the left, causing the upper drive link to be horizontal to the left. In the third pose, the lower drive joint is instead rotated 90 degrees to the left, with the upper drive joint 180 degrees (i.e., straight), causing the upper and middle drive links to be horizontal to the left. Compared to the third pose, in the fourth (and final) pose, the lower drive joint is rotated only 45 degrees left from vertical and the upper drive joint is 180 degrees (i.e., straight).

[0162] Starting with Figure 16, this shows the "ideal geometry" where the metrology and drive frames are precisely and accurately manufactured with ideal link (or segment) lengths and ideal axis alignment, so that there are no problems in any of the four example poses (as indicated by the checks above each of the four poses shown). There are no conflicts between the metrology and drive frames, and the movement of drive frame D can be accurately and precisely measured by metrology frame M.

[0163] Continuing with FIG. 17, this illustrates the case where the central link of the metrology frame (depicted with dashed lines rather than solid lines) is longer than ideal, for example, due to manufacturing or assembly tolerances. For the first pose, because metrology frame M is rigidly coupled to drive frame D at head end H, the longer metrology frame M cannot be accommodated within drive frame D, as indicated by metrology frame M having to extend beyond drive frame D at head end H. In practice, this would result in drive frame D and metrology frame M "fighting," or colliding with each other, because both would like to adopt different configurations. This is, of course, not ideal, as indicated by the crosses above the first pose. Notably, such conflicts result in changes to metrology frame M that do not directly correspond to changes in drive frame D, resulting in measurement errors and an inaccurate representation of the position and orientation of head end H relative to base end B.

[0164] The second pose in Figure 17 is also problematic because the longer middle measurement link means that the measurement and drive axes of the upper joint are not aligned, so the upper link in measurement frame M needs to be at an angle, while the upper link in drive frame D needs to be exactly horizontal. This mismatch again leads to a conflict between measurement frame M and drive frame D, as indicated by the cross. Similarly, the third and fourth poses in Figure 17 have similar problems as the first pose.

[0165] To overcome the problems described with reference to FIG. 17, a "slider" element is added in FIG. 18 to provide an additional degree of freedom to the metrology frame M. The additional degree of freedom is a linear degree of freedom that hopefully can accommodate the increased length of the middle metrology link. As an example, in FIG. 18, a linear slider element is inserted into the top metrology link. However, while this can be seen to improve the situation for the first, third, and fourth poses, the second pose is still problematic because the slider does not help address the angular conflict between the top metrology and drive link. In FIG. 19, the linear slider element is moved to the bottom link. This helps with the first and second poses, but not the third and fourth poses.

[0166] Thus, adding a linear slider, as shown in Figures 18 and 19, was helpful for some poses but not others. Figure 20 shows an alternative solution to the problem caused by the longer central measurement link using an additional measurement axis at the head end H (corresponding to that discussed above with reference to Figure 6B). This is helpful for all four poses shown in Figures 17-19, the first two of which are also shown in Figure 20. However, as shown by the third and fourth poses in Figure 20, the use of an additional measurement axis at the head end H leads to a different problem. The third pose in Figure 20 is reached by starting with the arm in the second pose in Figure 20 and rotating it 180 degrees to the right through the upper joint, as indicated by the curved arrow. Because the upper axis of metrology frame M has been displaced above by a longer intermediate metrology link so that it no longer coincides with the upper axis of the drive frame, when the arm moves from the second pose to the third pose in Figure 20, the upper metrology axis (or joint) is pushed to the right using the rotation of the lower metrology axis, and without constraint from drive frame D, it would end up in the configuration shown in the third pose in Figure 20, i.e., a configuration extending outside of drive frame D. In fact, because the drive frame is like a shell that surrounds metrology frame M, metrology frame M and drive frame D could collide severely before reaching the configuration shown in the third pose, leading to damage to one or the other or both. This problem is marked by a cross above the third pose in Figure 20. On the other hand, if the arm were instead moved directly from the second pose to the fourth pose in Figure 20 by rotating about the lower (in-line or vertical) drive joint, as indicated by the arrow in the fourth pose in Figure 20, the problem shown in the third pose would be avoided, and metrology frame M would remain within the range of drive frame D throughout the movement. However, this complicates the control of the arm and in practice it is difficult to avoid problems in all cases, since it is not always known exactly when a problem will occur.

[0167] The problem shown in Figure 20 is equivalent to the problem discussed above with reference to Figure 15, and although adding an upper metrology axis can be effective in overcoming the different lengths of the metrology links, the problem is that there are now two possible metrology solutions for each pose (one of which is outside the boundaries of the drive frame). This problem of multiple metrology solutions is further illustrated in the example poses shown in Figures 21A, 21B, and 21C, which show that for each configuration of the metrology frame M, there is another alternative configuration that can be found to reflect the metrology frame's links within a "mirror line" 13 (see Figure 21C) drawn between the second and fourth metrology axes.

[0168] This leads to the arrangement shown in Figure 22, where the linear slider element introduced in Figures 18 and 19 is now located in the middle metrology link, rather than in the upper metrology link (Figure 18) or the lower metrology link (Figure 19). In this position, as illustrated in Figure 22, the linear slider element is effective in avoiding four-pose collisions between metrology frame M and drive frame D. Furthermore, this arrangement is also effective when the upper metrology link (rather than the middle metrology link) is made longer, as shown in Figure 23, or when the lower metrology link (rather than the middle metrology link) is made longer, as shown in Figure 24.

[0169] The configurations of metrology frame M shown in Figures 22-24 have been shown to be valid for all exemplary configurations of drive frame D and therefore form the basis for embodiments of the present invention. However, it should be noted that the above examples focus on the "ideal" movement of the joints of drive frame D, where each drive joint has a single axis of rotation. Applicant understands that not only do each drive joint have a "primary" axis of rotation, but in practice, they also introduce inadvertent or undesirable degrees of rotation about "secondary" axes of rotation. To achieve best performance, these secondary (non-ideal) rotations in drive frame D must also be considered and measured by metrology frame M.

[0170] Considering the above, a complete solution for implementing the present invention is shown diagrammatically in FIG. 25. The metrology frame M in FIG. 25 is closely based on that shown in FIGS. 22-24, with three rotational measurement joints corresponding to the three rotary drive joints, as well as a linear measurement joint located between two lateral measurement joints. Two of the rotational measurement joints are lateral rotational measurement joints, while the other rotational measurement joint is an in-line rotational measurement joint, matching its corresponding drive joint. However, in the arrangement shown in FIG. 25, the two lateral rotational measurement joints are "universal joints," "Hooke's joints," or "Cardan joints," each providing two measurement axes, thereby providing metrology frame M with a total of six degrees of freedom. These six measurement axes (degrees of freedom) are marked M1-M6 in FIG. 25.

[0171] Applicant has recognized that because metrology frame M has only six axes or degrees of freedom M1-M6, and ideally the position and orientation of head end H of Arm A relative to base end B of Arm A is measured in six degrees of freedom, it is desirable to avoid "singularities" in metrology frame M, where two axes in metrology frame M coincide, thereby effectively losing degrees of freedom in metrology frame M, thereby leaving fewer degrees of freedom than are necessary to measure the relative motion of head end H and base end B in all six degrees of freedom. These issues were discussed above with reference to FIG. 11.

[0172] To overcome the "singularity" problem mentioned above, the measurement axes in each universal measurement joint in an embodiment of the present invention are arranged in a specific order (i.e., the pair of measurement axes M2, M3 and the pair of measurement axes M5, M6 shown in FIG. 25). This is explained in more detail with reference to FIG. 26, which shows a type of universal joint suitable for use in the measurement frame M of FIG. 25. Such a universal joint provides two intersecting rotation axes P, S oriented at 90 degrees to each other. Although intersecting each other, the two rotation axes P, S are effectively arranged in series, so the ordering can vary, as will now be explained with reference to FIGS. 26 and 27.

[0173] In Figure 26, the two shafts (corresponding to segments of metrology frame M) connected by a universal joint are marked B and H to indicate that they are (but not necessarily) located towards the base end B and head end H of the arm, respectively. The rotation axis P in the solid box outline is shown as the "primary" metrology axis P for the joint, and the rotation axis S in the dotted box outline is shown as the "secondary" metrology axis S for the joint. Because the primary metrology axis P is substantially aligned with the primary drive axis of the joint, when arm A is controlled to rotate about this joint, the primary motion is as shown in the schematic diagram at the bottom of Figure 26.

[0174] A key feature of the arrangement shown in FIG. 26 is that, when viewed in the direction from the base end B to the head end H, the measurement axes P and S of the joint are positioned with the primary measurement axis P after the secondary measurement axis S. This ensures that the orientation of the secondary measurement axis S is maintained even when the metrology frame M is rotated about the primary measurement axis P. In the schematic diagram at the bottom of FIG. 26, the primary axis P is shown as a small open circle (with the primary axis P oriented perpendicular to the plane of the page) and the secondary axis S is shown as a short horizontal line between the forks of the universal joint (with the secondary axis S oriented in the plane of the page). It can be seen that as the head end H rotates to the left, the orientation of the secondary axis S is maintained (unchanging) (in particular, the orientation is maintained with respect to the segment of the metrology frame M that connects to the joint from below, i.e., from the base end B). For this reason, as will become apparent from the following discussion (with particular reference to FIG. 41), the arrangement shown in FIG. 26 is suitable for use in embodiments of the present invention.

[0175] Contrast this with FIG. 27, which closely corresponds to FIG. 26 but shows the measurement axes P, S of the universal joint ordered in the opposite direction: the primary measurement axis P (corresponding to the joint's primary drive axis) comes before the secondary measurement axis S (when viewed from the base end B toward the head end H). As shown in the schematic diagram at the bottom of FIG. 27, with this ordering of the measurement axes P, S, as the head end H rotates to the left, the orientation of the joint's secondary measurement axis S is no longer maintained (in particular, the orientation is not maintained with respect to the segment of the measurement frame M connected to the joint from below, i.e., from the base end B). Rather, the secondary measurement axis S rotates from a horizontal orientation (perpendicular to the measurement segment connected to the joint from below) to a vertical orientation (aligned with the measurement segment connected to the joint from below). For this reason, as will become apparent from the following discussion (with particular reference to FIG. 42), the arrangement shown in FIG. 27 is not suitable for use with embodiments of the present invention.

[0176] Figure 28 is a schematic diagram of a coordinate positioning arm embodying the present invention, with the various measurement axes annotated to show their sequential order from the base end B to the head end H of the arm A. This is the same arrangement of measurement axes as shown in Figure 25. In the direction from the base end B to the head end H, the measurement axes are ordered as follows: R1, R2, R3, L4, R5, R6. The primary measurement axes (shown with solid box outlines) are R1, R3, and R6, and the secondary measurement axes (shown with dotted box outlines) are R2, L4, and R5. Measurement axis R1 (primary) is located at the in-line rotary measurement joint corresponding to in-line rotary drive joint D1. A pair of measurement axes R2, R3 (secondary, primary) is provided at the first lateral rotation measurement joint (corresponding to the first lateral rotation drive joint D2), and a pair of measurement axes R5, R6 (secondary, primary) is provided at the second lateral rotation measurement joint (corresponding to the second lateral rotation drive joint D3). The coupling between the metrology frame M and the drive frame D at the base end B and head end H can be a rigid coupling, or optionally a kinematic coupling that allows the metrology frame M and the drive frame D to be easily coupleable and separable in a repeatable manner.

[0177] Figures 29 and 30 show front and side views, respectively, of a coordinate positioning arm according to an embodiment of the present invention, at a pose corresponding to that of the positioning arm of Figures 11 and 12 for ease of comparison. As shown in Figures 29 and 30, using a coordinate positioning arm according to an embodiment of the present invention, there is no longer a problem measuring the position and orientation of the head end H relative to the base end B in all of the degrees of freedom (as there was with the positioning arm of Figures 11 and 12), because with a positioning arm embodying the present invention there are no redundant measurement axes for this pose (there are no "singular points" in the metrology frame M where two or more measurement axes, or combinations thereof, are aligned).

[0178] A redundant measurement axis in this context can be considered to be one that can be removed from the metrology frame (for relative motion between the head end and the base end) without losing a degree of freedom of the metrology frame, at least for a particular configuration of the drive frame. It can also be considered to be one that does not provide any additional degrees of freedom (for relative motion between the head end and the base end) to the metrology frame, at least for a particular configuration of the drive frame. For example, in metrology frame M of FIG. 11, either measurement axis R1 or R6 can be removed (for at least that pose), but both provide degrees of freedom of movement of the head end H relative to the base end B. Therefore, metrology frame M of FIG. 11 still has five degrees of freedom for that pose, even if one or the other of axes R1 and R6 is removed. Note that this concept of redundancy also applies to combinations of measurement axes. So, for example, if the degree of freedom provided by measurement axis Ra for a particular pose is also provided by a combination of measurement axes Rb, Rc, and Rd, then measurement axis Ra can be considered a redundant measurement axis for that pose (even though none of measurement axes Rb, Rc, and Rd actually align with measurement axis Ra). One can think of the measurement axes of the measurement frame for that configuration of drive frames as being redundant.

[0179] FIG. 31 illustrates a coordinate positioning arm not embodying the present invention, with the axes of the universal measurement joint in the "wrong" order and the arm positioned in a pose corresponding to the embodiment shown in FIG. 28. Referring to FIG. 32, such an arm cannot measure the rotation R of the head end H about the longitudinal axis of the final segment (i.e., head end H) when both the intermediate and final segments are horizontal. In such a pose, as shown in FIG. 32, measurement axis R3 aligns with measurement axis R1, effectively reducing the total "available" degrees of freedom in metrology frame M from six to five, similar to the problem situation shown in FIG. 11. Thus, there is no measurement axis available to measure the rotation R of the head end H about the longitudinal axis of the final segment (although drive frame extension can be measured using measurement axis L4, i.e., the linear slider element described above). In other words, as shown in FIG. 32, for the configuration of drive frame D, there is redundancy in the measurement axes of metrology frame M (there are five degrees of freedom in the metrology M frame regardless of whether one or both of measurement axes R1 and R3 are active).

[0180] In contrast, Figure 33 shows a coordinate positioning arm embodying the present invention in the same pose as the non-embodiment of Figure 32 for ease of comparison. In the arm of Figure 33, the axes of the universal metrology joints are in the "correct" order. Therefore, with this arrangement of metrology axes, there are no singularities in metrology frame M, and as a result, the secondary metrology axis R2 is available to measure the inadvertent (non-ideal) rotation R of the head end H about the longitudinal axis of the last arm segment. In other words, for the configuration of drive frame D as shown in Figure 33, there is no redundancy in the metrology axes of metrology frame M (dropping any one of metrology axes R1-R6 reduces the number of degrees of freedom provided by metrology frame M).

[0181] It will be appreciated that in embodiments of the present invention, drive frame D and metrology frame M are substantially separate and / or independent of one another. To better understand what this means, note that (for example) drive frame D and metrology frame M of FIG. 5 cannot be considered separate and / or independent of one another, even though they are coupled only at the head end H and base end B. This is because the presence of metrology frame M imposes additional constraints on drive frame D due to the presence of three metrology axes (at least six metrology axes are required to accommodate all six degrees of freedom in which head end H can move relative to base end B). In embodiments of the present invention, there is a degree of separation or independence or mechanical isolation between drive frame D and metrology frame M that allows drive frame D to effectively move as if metrology frame M were not present (metrology frame M provides substantially no extra constraints for any possible configuration of drive frame D).

[0182] Figure 34A is a schematic diagram of how metrology frame M is provided within the envelope of drive frame D, which includes two Hooke's joints of metrology frame M, in an embodiment of the invention corresponding to that shown in Figure 10. Figure 34B is intended to explain some of the terms used herein, such as coordinate positioning arm 20, head end 21, base end 22, metrology frame 23, drive frame 24, segments 25, lateral rotational metrology joints 26 (each including two rotational metrology axes), lateral rotational drive joints 27 (each including a single lateral rotational drive axis), in-line rotational metrology joint 28 (including a single in-line rotational metrology axis), in-line rotational drive joint 29 (including a single in-line drive axis), and linear metrology joint 30 (including a single linear metrology axis).

[0183] FIG. 35 is a side view corresponding to that of FIG. 30 of an alternative embodiment in which the linear degree of freedom L4 in the metrology frame M is provided by multiple rotational measurement axes rather than by a linear measurement axis itself. In the alternative embodiment of FIG. 35, instead of the linear measurement axis L4 of FIG. 30, an additional rotational measurement axis R4 is provided, so that the metrology frame M is, in effect, entirely composed of rotational degrees of freedom or axes. However, a combination of rotational degrees of freedom can still be considered to provide a linear degree of freedom corresponding to L4, and therefore the same overall principles as before still apply. In particular, the change in length previously measured by the linear axis L4 is now measured by the combination of rotational axes R2, R4, and R5. This is shown in more detail in FIGS. 36A and 36B, which show only R2, R4, and R5 of FIG. 35 in a simplified format. In FIG. 36A, L4 represents the separation between axes R2 and R5, and FIG. 36B shows in more detail how small changes in separation L4 (not directly measured in this embodiment) cause small changes ΔR2, ΔR4, and ΔR5 associated with rotational axes R2, R4, and R5, respectively. From measurements of ΔR2, ΔR4, and ΔR5, a value for ΔL4 can be derived. It will be understood that because these are secondary measurement axes, they are only intended to measure small (non-ideal) movements so that the combination of rotational axes R2, R4, and R5 can approximate linear axis L4 quite accurately. Therefore, the measurement frame M in FIG. 35 can still be considered to include linear measurement axis L4.

[0184] Coordinate positioning arms are now considered more with respect to the concept of constraints and how the metrology performance of the arm can be improved in embodiments of the invention by avoiding or reducing unnecessary constraints between the drive frame and metrology frame of the arm. For example, consideration is given to how the ordering of the measurement axes within the arm can affect the constraints between the metrology frame and drive frame of the arm, improving metrology performance by considering the principles already outlined with respect to the placement and ordering of measurement axes within the metrology frame.

[0185] FIGS. 37A-37D are intended to illustrate the concept of constraints regarding measurement joints used in embodiments of the present invention. The illustrations are side views of one of the transverse measurement joints of the measurement frame M described above, i.e., corresponding to the view shown in FIG. 30. The primary and secondary measurement axes are marked in FIG. 37A by solid and dotted outlines, respectively, at the R ring. The joint's drive axis X (and corresponding primary measurement axis) is located in the plane of the page. In FIGS. 37A and 37C, the joint is straight (at 180 degrees), while in FIGS. 37B and 37D, the joint's head (top) H is rotated 90 degrees into the page relative to the joint's base (bottom) B. For simplicity, the joint is shown as a complete unit, with the measurement frame M and drive frame D rigidly connected at the base end B and head end H (as noted above, even in embodiments of the present invention, the joint will form part of a larger whole).

[0186] Figures 37A and 37B show the linear and rotated joint configurations, respectively, for the ideal case where the drive axis X and primary measurement axis R are perfectly aligned. This corresponds to an ideal joint (or arm) manufactured with no alignment errors. As shown in Figure 37B, the rotation of the drive frame D is perfectly accommodated by the measurement frame M, so that the primary measurement axis of the measurement joint measures the exact amount of rotation, and the secondary measurement axis is not moved at all (measuring zero rotation).

[0187] However, in practice, some manufacturing error will always occur, within certain manufacturing tolerances, such that the drive axis X is slightly misaligned relative to the machine (arm). This is shown in FIG. 37C for a straight joint configuration. Even in this straight configuration, misalignment of the drive axis X can be accommodated by the metrology joint, and the secondary metrology axis of the metrology joint provides an extra degree of freedom that allows the metrology frame M to follow the misaligned drive frame D. Importantly, this allows the metrology frame M to follow the shape of the drive frame D without introducing additional constraints or tensions between them, so that misalignment of the drive axis X is measured by the secondary metrology axis. Similarly, in the rotated configuration shown in FIG. 37D, even though the head end H of the drive frame D is angled or misaligned, this is accommodated by the two degrees of freedom provided by the metrology joint; i.e., there is some degree of freedom in the metrology joint to address this misalignment.

[0188] In the joint shown in FIG. 37, the primary measurement axes are positioned after the secondary measurement axes in serial order from base end B to head end H, as previously described with respect to embodiments of the present invention. Even with manufacturing or assembly errors, there is no over-constraint between the drive frame D and the measurement frame H. This is in contrast to what would occur if the primary and secondary measurement axes were positioned in the "wrong" direction, with the primary measurement axes positioned serially ahead of the secondary measurement axes from base end B to head end H. This situation is shown in the illustrations of FIGS. 38A-38E, which are used to illustrate the concept of over-constraint in a measurement joint used in a positioning arm that does not embody the present invention.

[0189] Figures 38A and 38B correspond to Figures 37A and 37B, respectively, showing the case where drive axis X is perfectly aligned (and so that drive axis X is perfectly aligned with the primary measurement axis of the joint). There are no problems associated with this joint motion, and the available measurement axes are able to perfectly measure changes in joint configuration because there are no constraints between measurement frame M and drive frame D.

[0190] FIG. 38C corresponds to FIG. 37C , showing misalignment introduced into drive axis X such that it is no longer aligned with the primary measurement axis. For the linear joint configuration shown in FIG. 38C , this misalignment of drive axis X can be measured by the secondary measurement axis, and there is no over-constraint between drive frame D and measurement frame M. However, for the rotated joint configuration of FIG. 38D , the near end (i.e., joint) of the rotated (i.e., upper) segment of drive frame D is not aligned with the far end, but there are no degrees of freedom available in the measurement frame to address this. The bottom half of measurement frame M desires what is shown in FIG. 38D , but the top half of measurement frame M desires what is shown in FIG. 38E . The measurement and drive frames can “fight” with each other, and as shown in FIGS. 38D and 38E , there is an over-constraint between drive frame D and measurement frame M for the configuration of drive frame D. Applicant understands that such a constraint between drive frame D and measurement frame M is undesirable because it results in flexion of measurement frame M that is not measured by any measurement axis. In this regard, it is only rotation about the measurement axes that results in a measurement signal; any bending, flexing, or twisting of the structure between the measurement axes will not result in a change in the measurement signal, despite a topological change in the measurement frame M. This will result in measurement errors and inaccuracies in the calculated position and orientation of the head end H of the arm A relative to the base end B.

[0191] To alleviate this constraint, one could add another in-line (vertical) rotational degree of freedom to the metrology frame M above the joint, but this would lead to a redundant axis and multiple metrology solutions (as described above) since there is in fact already a vertical axis below the joint. One embodiment of the present invention can avoid such a constraint between the metrology frame and the drive frame without requiring an extra degree of freedom in the metrology frame M, even for the rotational configuration of the drive frame D, as shown in Figure 37D.

[0192] From the above, it is clear that when the primary and secondary measurement axes of a measurement joint are in the "wrong" order, over-constraints between the measurement frame and the drive frame occur for certain configurations of the drive frame. On the other hand, when the primary and secondary measurement axes of a measurement joint are in the "correct" order, no such over-constraints occur for those configurations of the drive frame. Of course, whether a joint is over-constrained should not depend on the absolute orientation of the joint in space when considered in isolation. For example, simply inverting the joint in FIG. 37C (so that the joint's measurement axes are clearly in the "wrong" order) should not suddenly introduce over-constraints between the drive and measurement frames when none were present before. This is explained with reference to FIGS. 39 and 40.

[0193] Figure 39A shows the joint from Figure 37C without any changes other than flipping the joint, and Figure 39B shows the joint from Figure 39A with a slight reorientation to make the lower segment vertical for consistency with the representation in Figure 37. In Figure 39C, the only further modification is fitting the upper segment within the lower segment for consistency with the representation in Figure 37. Thus, the measurement axes were in the "correct" order before flipping (Figure 37C), and are now in the "wrong" order after flipping (Figure 39C). However, when the joint is in the rotated configuration shown in Figure 39D, there is still no conflict between the measurement and drive frames because the drive and measurement axes are aligned. In particular, the vertical (secondary) measurement axis of the Hooke joint corresponds to the upper segment being angled to the left (the distal end face of the segment is angled relative to the page). Therefore, as expected, there is still no constraint between the measurement and drive frames. However, this is despite the measurement axes now being in the "wrong" order. However, it should be noted that the simplified representation considers a single joint in isolation, with rigid connections at the base and head ends—effectively a single-axis arm. In reality, this joint is one of multiple joints in the arm, and while that joint configuration in FIG. 39D does not exhibit over-constraint, despite the axes being in the “wrong” order, it is still unsuitable for embodiments of the present invention because the joint's secondary instrumentation axis rotates and, as noted above, risks creating singularities in the instrumentation frame for certain other configurations of the drive frame. Such singularities (leading to insufficient instrumentation axes) create constraint problems even when certain configurations of one joint (as shown in FIG. 39D) are normal. The concept of over-constraint, particularly the desire to avoid constraints between the instrumentation frame and the drive frame, applies collectively to all axes, not just a subset of axes, as will become clear from the discussion related to FIG. 40.

[0194] Figure 40A shows the joint of Figure 38C without any changes other than flipping the joint, and Figure 40B shows the joint of Figure 40A slightly reoriented to make the lower segment vertical for consistency with the representation in Figure 38. In Figure 40C, the only further modification is fitting the upper segment within the lower segment for consistency with the representation in Figure 38. For the rotated joint configuration, as illustrated in Figure 40D, even though the joint's primary and secondary measurement axes are now clearly in the "correct" order (after flipping where they were in the "wrong" order from Figure 38C), this is clearly over-constrained, since the lower half wants its primary axis in the plane of the page, while the upper half (folded) wants it angled toward the distal end (rotated about a vertical axis). Certainly, it would not be possible to create a joint at this point by simply flipping the joint spatially. However, in practice, when provided as part of a complete arm, as illustrated in Figure 40E, this configuration works (i.e., does not result in undue constraints between the measurement frame and the drive frame), especially when considering the rotational measurement axes from further down. As shown in Figure 40E, an extra rotational measurement axis below the joint can accommodate the angle of the upper segment in the rotated drive configuration, thereby avoiding over-constraint between the measurement frame and the drive frame. As noted above, the concept of over-constraint, and particularly the desire to avoid constraints between the measurement frame and the drive frame, applies to all axes of the arm collectively, not just a subset of axes.

[0195] Figures 41A-41C are used to explain the characteristics of the transverse rotational joint used in embodiments of the present invention. The characteristics of a transverse rotational joint are that (a) it has two rotational degrees of freedom (primary R1, secondary R2) from the joint itself, (b) it has another rotational degree of freedom (R3) from other joints located below the joint, and (c) the joint provides an axial rotational degree of freedom to anything above the joint. Note that there does not necessarily need to be a corresponding rotational drive axis below the joint, just another rotational measurement axis (the drive frame may be rigid below the joint). Also, note that due to the relative ordering of the primary and secondary measurement axes R1 and R2, the movement segments (see solid lines in the bottom schematic) are always within 45 degrees of the rotational measurement degrees of freedom (R2, R3) throughout the change in joint configuration from straight (Figure 41A) to angled (Figure 41B) to right angle (Figure 41C). Notably, the secondary measurement axis (R2) does not move, thereby preventing the occurrence of singularities. This allows the metrology frame M to handle (measure) small non-ideal movements of the head end H, such as torsion, regardless of the drive configuration, because there is always a measurement axis or combination of axes that can handle (measure) such movements.

[0196] Figures 42A-42C are for comparison with Figures 41A-41C and are intended to illustrate the characteristics of a transverse metrology joint that is unsuitable for use in embodiments of the present invention: the joint's primary and secondary metrology axes are in the wrong order, and redundant axes in certain poses result in excessive constraints. With particular reference to the joint configuration shown in Figure 42C, it can be seen that redundant axes (R2, R3) are present, which in turn means that (measurable) rotation around the strut axis (i.e., the longitudinal axis of the moving strut) is not possible because there are no metrology axes available. This then results in an over-constraint between the metrology and drive frame, and the redundant axes are over-constrained due to insufficient degrees of freedom available. Thus, the metrology frame "fights" with the drive frame. This can be addressed by adding more degrees of freedom, but then a multiple metrology solution is undesirable because there are too many degrees of freedom available for other drive configurations (or poses).

[0197] 43A and 43B focus more on the in-line rotary drive and measurement axes (rather than the lateral rotary drive and measurement axes) and show that even in the case of misalignment between the in-line rotary drive and measurement axes (e.g., due to manufacturing or assembly errors), there is no undue constraint between the metrology frame and the drive frame. In particular, it can be seen that sufficient degrees of freedom are available in metrology frame M to avoid over-constraining the metrology frame M and drive frame D, and that "slack" is captured (and specifically measured) by the combination of the metrology axes. FIG. 43B shows a view rotated 90 degrees compared to the view of FIG. 43A.

[0198] Figures 44A-44D show how multiple "core units" from Figure 41 are joined together in series to create an arm according to one embodiment of the present invention. In particular, Figure 44A shows two such core units positioned separately, Figure 44B shows them brought together but not fully interlocked, Figure 44C shows them fully interlocked, and Figure 44D shows the introduction of an additional linear measurement axis at the point where the two units are interlocked. The resulting arm A is as described above.

[0199] FIG. 45 is a schematic diagram of a two-axis coordinate positioning arm embodying the present invention, i.e., a coordinate positioning arm with two drive axes D1 and D2. To make this two-axis version work for all poses (drive configurations), as well as an in-line rotary measurement axis (primary) corresponding to the in-line drive axis D1, and a universal measurement joint (with secondary / primary measurement axes R2 / R3) corresponding to the lateral rotary drive joint D2, another linear axis L4 (secondary) and another universal measurement joint (with secondary measurement axes R5 and R6) are introduced. Thus, the measurement axes in this embodiment, in order from the base end B to the head end H, are R1 (primary), R2 (secondary), R3 (primary), L4 (secondary), R5 (secondary), and R6 (secondary). The order of these two axes R5 and R6 is not important because there is no drive axis corresponding to the universal measurement joint containing measurement axes R5 and R6, and therefore both of these are secondary measurement axes.

[0200] Figure 46 is a schematic diagram of a single axis coordinate positioning arm embodying the invention, having a single lateral rotational drive axis D1. This embodiment is the same as that shown in Figure 45, but the primary measurement axis R1 in Figure 45 becomes the secondary measurement axis R1 in Figure 46 because there is no drive axis associated with this measurement joint. Single axis units such as those shown in Figure 46 are primarily used as components of longer coordinate positioning arms embodying the invention.

[0201] Figure 47 illustrates how a three-axis component arm can be combined in series with another three-axis component arm to create a six-axis coordinate positioning arm embodying the present invention. The axial rotation drive axis of the second component arm (i.e., the axis closest to the head end H) can be removed so that the corresponding segment is completely rigid. In that case, the corresponding measurement axis R1 can also be removed or considered to provide a secondary measurement axis (without any corresponding drive axis). The same applies to the axial rotation drive axis of the first component arm (i.e., the axis closest to the base end B), but in practice it is retained to provide the necessary versatility for the arm. Figure 48 illustrates how a three-axis component arm can be combined in series with a two-axis or single-axis component arm to create a five-axis or four-axis coordinate positioning arm embodying the present invention. Other combinations are possible.

[0202] As already mentioned, the head end H of the arm A is advantageously adapted to receive and carry a manipulation tool, such as a measurement probe in metrology applications or a gripper in assembly or manipulation applications. Similar to what was described with reference to FIGS. 3 and 4, the tool is advantageously carried by the arm via a pre-calibrated probe head 12 to provide the arm with two or three extra axes. To this end, the head end H includes mating features adapted to mate with corresponding mating features provided on the manipulation tool (or probe head). These possibilities are shown schematically in FIGS. 49A and 49B, which illustrate a manufacturing system and method using a coordinate positioning arm A embodying the present invention. As previously mentioned, the measurement axes R1-R6 of the metrology frame M of the arm A are also marked in FIG. 49A, as are the drive frame D, base end B, and head end H.

[0203] As shown in FIG. 49A, a tool rack (or tool holder) 50 is provided within the working volume of Arm A. Various tools are held within the rack 50, including grippers 42, milling tools 44, laser cutting tools 46, drilling tools 48, and measurement probes 14. A modular coupling system is used, i.e., each tool can be picked up from the rack 48 and used to perform an operation, removably coupled to the robot 10 as needed, and then returned to the rack 48 to pick up another tool as needed. The detachable coupling allows this to be achieved relatively simply and in an automated manner without manual intervention, thereby enabling use in automated manufacturing processes. Due to the inherent precision of Arm A, the aforementioned features allow Arm A to function as both a positioning machine and a measuring machine.

[0204] For example, Arm A may use gripper 42 to pick up and place workpiece 16 on the machine bed (performed in steps prior to those shown in FIG. 49A), then swap gripper 42 for drilling tool 48 (steps performed in FIG. 49A), and then use drilling tool 48 to drill workpiece 16 (as shown in FIG. 49B). Subsequently, drilling tool 48 may be swapped out for measurement probe 14 from tool rack 50 (in steps performed after those shown in FIG. 49B), and Arm A may return to the machined workpiece 16 to measure and inspect the machined features to ensure that the features are within required tolerances.

Claims

1. 1. A coordinate positioning arm comprising: a base end and a head end; a drive frame for moving the head end relative to the base end; a metrology frame for measuring the position and orientation of the head end relative to the base end; Equipped with the drive frame includes a plurality of drive shafts arranged in series between the base end and the head end; the metrology frame includes a plurality of metrology axes arranged in series between the base end and the head end; the metrology frame is substantially separate and / or independent from the drive frame; (a) the metrology frame provides three first order rotational degrees of freedom, two second order rotational degrees of freedom, and one second order linear degree of freedom; A coordinate positioning arm characterized by:

2. 2. A coordinate positioning arm according to claim 1, wherein the measurement axis provides sufficient degrees of freedom to the metrology frame to avoid creating more than sufficient constraints between the metrology frame and the drive frame, and / or wherein the measurement axis provides sufficient degrees of freedom to the metrology frame so as not to create additional constraints on the drive frame between the base end and the head end other than those already provided by the drive axis itself.

3. 3. A coordinate positioning arm according to claim 1 or claim 2, wherein the measurement axis is arranged to provide the metrology frame with insufficient degrees of freedom to allow multiple configurations for the metrology frame for each configuration of the drive frame, and / or the measurement axis and drive axis are arranged relative to each other to provide only one possible configuration for the metrology frame for each configuration of the drive frame.

4. 4. A coordinate positioning arm according to any one of claims 1 to 3, wherein for each configuration of the drive frame there is no redundancy in the measurement axes of the metrology frame and / or the measurement axes and drive axes are arranged such that there is no configuration of the drive frame in which two measurement axes of the metrology frame are aligned.

5. 5. A coordinate positioning arm according to any one of claims 1 to 4, wherein for each drive axis having an associated primary measurement axis and an associated secondary measurement axis, the secondary measurement axis is positioned before the primary measurement axis in serial order from the base end to the head end.

6. 6. A coordinate positioning arm according to any one of claims 1 to 5, wherein the metrology frame is supported by and / or coupled to the drive frame substantially only at the base end and the head end.

7. 7. A coordinate positioning arm according to claim 6, wherein any intermediate supports between the base end and the head end have a non-substantial effect on measurements or measurement signals from or associated with any or each of the measurement axes of the metrology frame and / or on any or each of the values ​​derived relating to the position and / or orientation of the head end or points on the head end relative to the base end.

8. 8. A coordinate positioning arm according to any preceding claim, wherein the metrology frame is adapted to measure the position and orientation of the head end relative to the base end in six degrees of freedom.

9. 9. A coordinate positioning arm according to any one of claims 1 to 8, wherein the drive frame comprises three drive shafts.

10. 10. A coordinate positioning arm according to claim 9, wherein the three measurement axes are substantially aligned with the three drive axes, respectively.

11. A coordinate positioning arm according to any one of claims 1 to 10, wherein the metrology frame comprises six measurement axes.

12. 12. A coordinate positioning arm according to any one of claims 1 to 11, wherein the metrology frame comprises at least one linear measurement axis having a degree of freedom in a linear direction.

13. 13. A coordinate positioning arm according to any preceding claim, wherein the drive frame includes three rotational drive axes, two of which are lateral and one of which is in-line.

14. 14. A coordinate positioning arm according to claim 13, wherein the three primary rotational degrees of freedom are associated with the three respective rotational drive axes, the two secondary rotational degrees of freedom are associated with the two respective lateral drive axes, and the second linear degree of freedom is at least not directly associated with any drive axis.

15. A coordinate positioning arm according to any preceding claim, wherein the head end is adapted to receive and carry a manipulation tool.

16. 16. A coordinate positioning arm according to claim 15, wherein the head end is adapted to receive and carry a manipulation tool by having a coupling or coupling feature that mates with a corresponding coupling or coupling feature on the manipulation tool.

17. A coordinate positioning arm according to claim 15 or 16, wherein the manipulation tool is a gripper or a welding tool, or a probe head or a measurement probe.

18. 18. A coordinate positioning arm according to any preceding claim, wherein the coordinate positioning arm is a coordinate measuring arm.

19. 19. A coordinate positioning arm according to any preceding claim, wherein a surface sensing device, such as a measurement probe, is coupled to the head end.

20. 20. A coordinate positioning arm according to claim 19, wherein the surface sensing device is coupled to the head end via a probe head, whereby the probe head is itself coupled to the head end with the surface sensing device coupled to the probe head.

21. A coordinate positioning arm according to claim 20, wherein the probe head is a pre-calibrated probe head and / or a two-axis or three-axis probe head.

22. A compound coordinate positioning arm comprising a plurality of coordinate positioning arms according to any one of claims 1 to 21 connected in series.

23. 23. A manufacturing or assembly method using a coordinate positioning arm according to any one of claims 1 to 22 to position one or more manufacturing or assembly tools for manufacturing or assembling an article, and to position a measurement or inspection tool for measuring or inspecting the manufactured or assembled article.

24. 22. A coordinate positioning arm according to any one of claims 1 to 21, wherein an additional degree of freedom is provided by coupling it to a separate two or three axis probe head.

25. A coordinate positioning arm, comprising: a base end and a head end; a drive frame for moving the head end relative to the base end; a metrology frame for measuring the position and orientation of the head end relative to the base end; Equipped with the drive frame includes a plurality of drive shafts arranged in series between the base end and the head end; the metrology frame includes a plurality of metrology axes arranged in series between the base end and the head end; the metrology frame is substantially separate and / or independent from the drive frame; (b) the metrology frame includes a plurality of metrology joints, each of which includes at least one of the metrology axes of the metrology frame, and the at least one lateral metrology joint includes a metrology axis providing a first and a second rotational degree of freedom, the first rotational degree of freedom being substantially aligned with a corresponding drive axis; (i) the orientation of the second rotational degree of freedom is substantially invariant to rotation about the first rotational degree of freedom; or (ii) the first rotational degree of freedom is provided for measuring a first rotation and the second rotational degree of freedom is provided for measuring a second rotation that is smaller than the first rotation; or (iii) for at least one transverse measurement joint, one or more measurement axes arranged in series before the measurement joint provide the measurement joint with a third rotational degree of freedom; A coordinate positioning arm characterized by:

26. A coordinate positioning arm as described in Claim 25, characterized in that the measurement axis provides sufficient degrees of freedom to the measurement frame to avoid creating more than the constraints between the measurement frame and the drive frame, and / or the measurement axis provides sufficient degrees of freedom to the measurement frame to avoid creating additional constraints on the drive frame between the base end and the head end other than those already provided by the drive axis itself.

27. ​​A coordinate positioning arm as described in claim 25 or claim 26, characterized in that the measurement axis is arranged to provide the measurement frame with insufficient degrees of freedom to allow multiple configurations for the measurement frame for each configuration of the drive frame, and / or the measurement axis and the drive axis are arranged relative to each other to provide only one possible configuration for the measurement frame for each configuration of the drive frame.

28. A coordinate positioning arm as described in any one of claims 25 to 27, characterized in that for each configuration of the drive frame, there is no redundancy in the measurement axes of the measurement frame, and / or the measurement axes and drive axes are arranged so that there is no configuration of the drive frame in which the two measurement axes of the measurement frame are aligned.

29. A coordinate positioning arm as described in any one of claims 25 to 28, characterized in that for each drive axis having an associated primary measurement axis and an associated secondary measurement axis, the secondary measurement axis is positioned in front of the primary measurement axis in serial order from the base end to the head end.

30. A coordinate positioning arm as described in any one of claims 25 to 29, characterized in that the measurement frame is supported by and / or connected to the drive frame substantially only at the base end and the head end.

31. A coordinate positioning arm as described in Claim 30, characterized in that any intermediate support between the base end and the head end has a non-substantial effect on measurements or measurement signals from or associated with any or each of the measurement axes of the measurement frame, and / or on any or each of the values ​​derived regarding the position and / or orientation of the head end or points on the head end relative to the base end.

32. A coordinate positioning arm as described in any one of claims 25 to 31, characterized in that the measurement frame is adapted to measure the position and orientation of the head end relative to the base end in six degrees of freedom.

33. A coordinate positioning arm as described in any one of claims 25 to 32, characterized in that the drive frame has three drive axes.

34. A coordinate positioning arm as described in Claim 33, characterized in that each of the three measurement axes is substantially aligned with the three drive axes.

35. A coordinate positioning arm as described in any one of claims 25 to 34, characterized in that the measurement frame has six measurement axes.

36. A coordinate positioning arm as described in any one of claims 25 to 35, characterized in that the measurement frame has at least one linear measurement axis having a degree of freedom in a linear direction.

37. A coordinate positioning arm as described in any one of claims 25 to 36, characterized in that each drive axis is provided with a corresponding measurement joint.

38. A coordinate positioning arm as described in any one of claims 25 to 37, characterized in that at least one measurement axis of each measurement joint provides a first degree of freedom that is substantially aligned with the corresponding drive axis.

39. A coordinate positioning arm as described in any one of claims 25 to 38, characterized in that the first rotational degree of freedom is arranged in series after the second rotational degree of freedom.

40. A coordinate positioning arm as described in any one of claims 25 to 39, characterized in that the orientation of the first rotational degree of freedom is changed by rotation around the second rotational degree of freedom.

41. A coordinate positioning arm described in any one of claims 25 to 40, characterized in that the first rotational degree of freedom and the second rotational degree of freedom are provided by a first rotational measurement axis and a second rotational measurement axis, respectively.

42. A coordinate positioning arm as described in claim 41, characterized in that the primary and secondary rotational measurement axes substantially intersect.

43. A coordinate positioning arm as described in claim 41 or claim 42, characterized in that the primary and secondary rotational measurement axes are provided by universal joints, Cardan joints, or Hooke's joints.

44. A coordinate positioning arm as described in any one of claims 41 to 43, characterized in that the primary and secondary rotational measurement axes are encoded by first and second rotational encoders, respectively.

45. A coordinate positioning arm as described in any one of claims 25 to 44, characterized in that the secondary rotational degree of freedom is substantially perpendicular to the primary rotational degree of freedom.

46. A coordinate positioning arm as described in any one of claims 25 to 45, characterized in that the secondary rotational degree of freedom is substantially perpendicular to the longitudinal axis of the segment of the measurement frame connected to the measurement joint from below. (iii) for at least one lateral measurement joint, one or more measurement axes arranged in series in front of the measurement joint provide a third rotational degree of freedom for the measurement joint; 47. A coordinate positioning arm according to any one of claims 25 to 46, wherein at least one of the one or more measurement axes providing the third rotational degree of freedom forms part of a further lateral measurement joint. (iii) for at least one lateral measurement joint, one or more measurement axes arranged in series in front of the measurement joint provide a third rotational degree of freedom for the measurement joint; 48. A coordinate positioning arm according to any one of claims 25 to 47, wherein each lateral metrology joint also provides a third rotational degree of freedom. (iii) for at least one lateral measurement joint, one or more measurement axes arranged in series in front of the measurement joint provide a third rotational degree of freedom for the measurement joint; 49. A coordinate positioning arm according to any one of claims 25 to 48, wherein the first, second and third rotational degrees of freedom all pass through the measurement joint. (iii) for at least one lateral measurement joint, one or more measurement axes arranged in series in front of the measurement joint provide a third rotational degree of freedom for the measurement joint; 50. A coordinate positioning arm according to any one of claims 25 to 49, wherein the first, second and third rotational degrees of freedom intersect. (iii) for at least one lateral measurement joint, one or more measurement axes arranged in series in front of the measurement joint provide a third rotational degree of freedom for the measurement joint; 51. A coordinate positioning arm according to any one of claims 25 to 50, wherein the segment of the metrology frame that moves about the first rotational degree of freedom is always within 45 degrees of either the second rotational degree of freedom or the third rotational degree of freedom. (iii) for at least one lateral measurement joint, one or more measurement axes arranged in series in front of the measurement joint provide a third rotational degree of freedom for the measurement joint; 52. A coordinate positioning arm according to any one of claims 25 to 51, wherein the segment of the metrology frame that moves about the first rotational degree of freedom is rotatable about its longitudinal axis for any angle of rotation about the first rotational degree of freedom using the second rotational degree of freedom or the third rotational degree of freedom, or a combination thereof, depending on the angle of rotation.

53. A coordinate positioning arm as described in any one of claims 25 to 52, characterized in that the measurement frame has further measurement joints not associated with or corresponding to any particular drive axis.

54. A coordinate positioning arm as described in Claim 53, characterized in that the further measurement joint is positioned between two lateral rotation measurement joints.

55. A coordinate positioning arm as described in claim 53 or claim 54, characterized in that at least one of the further measurement joints has one or more measurement axes providing linear degrees of freedom.

56. A coordinate positioning arm as described in Claim 55, characterized in that the one or more measurement axes of the further measurement joint include a linear measurement axis or a combination of rotational measurement axes arranged to be substantially equivalent to a linear measurement axis.

57. A coordinate positioning arm as described in Claim 56, characterized in that the linear degrees of freedom are provided by two rotational measurement axes.

58. A coordinate positioning arm as described in any one of claims 25 to 57, characterized in that the head end is adapted to receive and transport an operating tool.

59. A coordinate positioning arm as described in Claim 58, characterized in that the head end is adapted to receive and transport an operating tool by having a coupling or coupling feature that couples with a corresponding coupling or coupling feature on the operating tool.

60. A coordinate positioning arm as described in claim 58 or claim 59, characterized in that the manipulation tool is a gripper or a welding tool, or a probe head or a measuring probe.

61. A coordinate positioning arm as described in any one of claims 25 to 60, characterized in that the coordinate positioning arm is a coordinate measuring arm.

62. A coordinate positioning arm as described in any one of claims 25 to 61, characterized in that a surface sensing device such as a measurement probe is coupled to the head end.

63. A coordinate positioning arm as described in Claim 62, characterized in that the surface sensing device is coupled to the head end via a probe head, whereby the probe head itself is coupled to the head end with the surface sensing device coupled to the probe head.

64. A coordinate positioning arm as described in Claim 63, characterized in that the probe head is a pre-calibrated probe head and / or a two-axis or three-axis probe head.

65. A composite coordinate positioning arm comprising a plurality of coordinate positioning arms described in any one of claims 25 to 64 connected in series.

66. A manufacturing or assembly method using a coordinate positioning arm described in any one of claims 25 to 65 to position one or more manufacturing or assembly tools for manufacturing or assembling an article, and position a measuring or inspection tool for measuring or inspecting the manufactured or assembled article.

67. A method in which an additional degree of freedom is provided to a coordinate positioning arm described in any one of claims 25 to 64 by coupling it to a separate two-axis or three-axis probe head.

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