Connecting device

Abstract

A coupling device (30) is provided for connecting a measuring device (14) to a coordinate positioning machine (1), and the coupling device (30) is adapted to provide over-travel protection for the measuring device (14) when the measuring device (14) is moved toward the interface (37) between them with respect to the coupling device (30). The coupling device (30) is adapted to provide over-travel protection by, advantageously, causing the measuring device (14) to be at least partially disconnected from the machine (1). The coupling device (30) is adapted so that the measuring device (14) remains partially connected to the machine (1) when in an over-travel condition.

Description

Technical Field

[0001] The present invention relates to a connecting device for connecting a measuring device to a machine. The present invention particularly relates to, but is not limited to, a connecting device for connecting a measuring probe, such as a contact trigger measuring probe, to a coordinate positioning machine, such as an articulated robot.

Background Art

[0002] Articulated robots are commonly used in a variety of manufacturing applications, such as assembly, welding, bonding, painting, pick-and-place (such as printed circuit boards), packing and labeling, palletizing, and product inspection. They have a large reach and high movement flexibility, are versatile and robust, which gives them advantages and makes them ideal for use in a production environment.

[0003] In FIG. 1 of the accompanying drawings, an articulated robot (or, for short, simply "robot") is schematically shown. The articulated robot comprises an articulated robot arm 1 extending from a fixed base 2 to a movable flange 3, with the flange 3 supporting a tool (or end effector) 4. Usually, the flange 3 is provided with a joint that allows the tool 4 to be conveniently replaced, so that various tools, devices, or end effectors can be used according to the relevant application. Examples include grippers, vacuum cups, cutting tools (including both mechanical and laser cutting tools), drilling tools, milling tools, deburring tools, welding tools, and other special tools or devices.

[0004] Arm 1 comprises multiple segments 5 connected by a combination of lateral rotation axes 6 and inline (or longitudinal) rotation axes 7, forming a mechanical link from one end to the other. In the example shown in Figure 1, there are three lateral rotation axes 6 and three inline rotation axes 7, forming a total of six rotation axes, alternating between the lateral rotation axes 6 and the inline rotation axes 7. An additional inline rotation axis 7 (not shown in Figure 1) may be provided between the last lateral rotation axis 6 and the flange 3, providing convenient rotation of the tool 4 around its longitudinal axis, forming a total of seven rotation axes.

[0005] The arm 1 in Figure 2 shows another common device, which includes the aforementioned additional inline rotation axis 7 between the last lateral rotation axis 6 and the flange 3, and the device also omits the second inline rotation axis 7 from Figure 1 (in order from the base end to the head end), thereby forming a total of six rotation axes. The tool 4 in Figure 2 is a gripper. The arm 1 in Figure 1 is a schematic diagram of the well-known IRB140-6 axis industrial robot from ABBRobotics. The last three axes 6, 7 form the “wrist” of the robot arm 1, and the center of the wrist is at the center of the last lateral rotation axis 6. The center of the wrist is invariant with respect to the rotation of the three rotation axes 6, 7 of the wrist, and the operation of the three rotation axes 6, 7 changes the orientation of what is attached to the wrist (in this case, the gripper 4) without changing the position of the center of the wrist, and the first three rotation axes 6, 7 of the robot arm 1 determine the position of the center of the wrist. The wrist may be easily detachable from the rest of the arm 1.

[0006] The articulated robotic arm 1 in Figures 1 and 2 is an example of a non-orthogonal coordinate positioning machine, as its axes are not arranged orthogonally according to an orthogonal coordinate system, in contrast to orthogonal machines such as conventional 3-axis (X, Y, Z) coordinate measuring machines (see, for example, Figure 1 of Patent Document 1). The arm 1 in Figures 1 and 2 is also an example of a "series kinematic" coordinate positioning machine, as its axes of motion are arranged in series. In this sense, such a machine is similar to a conventional 3-axis orthogonal coordinate measuring machine, which is also an example of a "series kinematic" coordinate measuring machine, and should be contrasted with "parallel kinematic" coordinate positioning machines such as hexapods, whose axes of motion are instead arranged in parallel.

[0007] Each joint or axis in a coordinate positioning machine contributes to positional errors or uncertainties. In series kinematic machines, such as those shown in Figures 1 and 2, these errors accumulate due to the series nature of the links. While this accumulation of positional errors does not occur in the same sense in parallel kinematic machines, regardless of the type of machine, it is important to calibrate the machine to adjust for these errors and uncertainties. When properly calibrated, given that various geometric parameters of the machine (such as the length of each segment 5 and the rotational angle offset of each rotation axis or joint 6, 7) are known, it is possible to more reliably predict where the tool 4 will actually be when various axes or joints 6, 7 are commanded by the robot controller 8 to move to different positions. In other words, the machine parameters resulting from such calibration provide a more accurate characterization of the machine's geometry.

[0008] Calibrating any type of non-orthogonal coordinate system machine is a major challenge, especially for articulated arms such as those shown in Figures 1 and 2, which have multiple axes of rotation that are (a) arranged in series, (b) not fixed to each other, and (c) can be combined in complex ways to position a tool within a work area. Calibrating orthogonal coordinate system machines is usually simpler because such machines have three clearly defined axes fixed in an orthogonal arrangement to each other, and each axis is largely independent of the others. In the case of articulated robots, the position and orientation of each axis depend on the position and orientation of each other axis, and consequently, the calibration will differ for each different orientation of the machine. These concepts relating to the calibration of coordinate positioning machines in general, and especially robot arms, are explored in more detail in Patent Documents 2, 3, and 4. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2021 / 074625 [Patent Document 2] International Publication No. 2019 / 162697 [Patent Document 3] International Publication No. 2021 / 116685 [Patent Document 4] International Publication No. 2023 / 170166 [Non-patent literature]

[0010] [Non-Patent Document 1] HJJ Braddick, "Mechanical Design of Laboratory Apparatus," Chapman & Hall, London, 1960, pp. 11-30. [Non-Patent Document 2] “Exact Constraint” by James G. Skakoon, Mechanical Engineering, September 2009 issue [Overview of the project] [Problems that the invention aims to solve]

[0011] However, even after using known calibration methods, errors will usually remain due to the challenges associated with calibrating non-orthogonal coordinate system machines, such as those shown in Figures 1 and 2. As a result, the accuracy of such machines is usually not as high as that of conventional three-axis orthogonal coordinate systems. For example, it would likely find use in assembly (such as pick-and-place) operations in manufacturing environments, like the setup shown in Figure 2, where speed, reach, and flexibility are usually more important than absolute positioning accuracy, and would generally not be considered suitable for measurement operations.

[0012] Furthermore, due to all errors that remain even after calibration, and all errors that occur after calibration (e.g., when components wear out or shift from their intended position), the resulting positioning errors can be large enough to cause problems, especially due to the cumulative errors associated with serial kinematic non-orthogonal machines such as robot arms, where delicate tools or instruments at the end of a kinematic chain may not be in their expected location (based on the calibrated machine parameters) and could be damaged when the machine inadvertently moves them to stationary objects in the workspace.

[0013] This problem can also occur, regardless of calibration, and often with the most serious consequences, when the machine is under manual (human) control or when the motion control system used to control the machine is not properly programmed, which is common with articulated robots during setup. The short travel range typically associated with contact probes would usually rule out their use in machines with relatively inaccurate motion control, long stopping distances, and high speeds, as is the case with robot arms. [Means for solving the problem]

[0014] According to a first aspect of the present invention, a coupling device is provided for coupling a measuring device to a coordinate positioning machine, the coupling device being adapted to provide (additional and / or independent) over-stroke protection to the measuring device when the measuring device is coupled to the machine via the coupling device and moved relative to the coupling device in a predetermined direction toward (and / or across) the interface between the measuring device and the coupling device.

[0015] The coupling device embodying the present invention is advantageous because it can be used as part of a modular and adaptive system in which the robotic arm can be used for conventional tasks such as assembly, using tools that are intentionally designed to be robust for use with the robotic arm in harsh working environments, and then for measurement tasks using existing measuring probes that are more delicate and not specifically designed with robustness in mind. Easily available measuring probes can be used advantageously without modification and coupled to the robotic arm via the coupling device embodying the present invention, which adds a level of over-stroke protection to the measuring probe, enabling it to cope with potentially harsher handling (compared to the more controlled environment of conventional coordinate measuring machines). In other words, there is no need to provide specific and redesigned versions of the measuring probe for these environments. However, embodiments of the present invention are not limited to use with robotic arms and will find use in any coordinate positioning machine where over-stroke protection is required for any reason.

[0016] A coupling device can be adapted to provide over-stretch protection by causing a device (coupled to a machine via the coupling device) to be at least partially disconnected (or at least prone to being disconnected) from the machine. This can occur when a device is moved relative to the coupling device toward the interface between them (e.g., directly toward the interface) by at least a predetermined distance and / or by a predetermined force. Without the disconnection action provided by such a coupling device, this type of movement would otherwise result in the measuring device being pushed in and compressed into an inflexible coupling, thereby resulting in an undesirable (potentially damaging) compressive force being exerted on the measuring device. When a device is thus at least partially disconnected from the machine, this can be referred to as an over-stretch condition or situation, or a condition or situation in which it is at least partially disconnected.

[0017] By being at least partially decoupled when such movement occurs, an additional range of relative movement between the device and the machine in that direction is provided without damaging the measuring device (which would otherwise not be available). The movement may be along a predetermined axis of the measuring device. The predetermined axis may be the Z-axis of the measuring device. The predetermined axis may be the generally longitudinal axis of the measuring device. The predetermined axis may be the axis of the measuring device that has the smallest available movement (of all available measuring axes associated with the measuring device). For a typical measuring probe, the smallest available movement is usually along the Z-axis (or generally the longitudinal axis of the probe), and a larger range of movement will usually be available in the X and Y directions (corresponding to lateral runout across the Z-axis, or usually the longitudinal axis of the probe).

[0018] The first aspect of the invention described above may instead be described as providing a coupling device adapted to provide (additional and / or independent) over-travel protection to the measuring device when the measuring device is coupled to the machine via the coupling device and is moved relative to the coupling device along a predetermined axis of the measuring device (e.g., towards the interface between the measuring device and the coupling device).

[0019] The coupling device may be adapted to keep the device partially coupled to the machine when in an over-travel state (while allowing additional relative movement between the device and the machine). This not only ensures that the device does not fall completely off the machine, but it also facilitates re-coupling of the device to the machine via the coupling device.

[0020] The coupling device may be adapted to constrain the device with six degrees of freedom relative to the machine when in a coupled state. The coupling device may be adapted to remain coupled to the machine with at least one degree of freedom when in an over-travel state (or at least tend to do so). In other words, the coupling device may be adapted to keep the device constrained relative to the machine with at least one degree of freedom (or by at least one restraint against relative movement). By doing so, the device remains at least partially coupled to the machine when in an over-travel state.

[0021] When in an over-travel state (or at least tending to be so), the connecting device can be adapted such that the device is decoupled from the machine in a single degree of freedom and remains connected to the machine in the other five degrees of freedom (out of the six available degrees of freedom). In other words, the connecting device can be adapted such that the device remains constrained to the machine in five degrees of freedom (or by five constraints on relative movement), and relative movement is possible in only the single remaining degree of freedom. This is beneficial because if there is a general return movement towards the original connection state (i.e., not moving away from it), there is only one degree of freedom available for relative movement and no possibility of deviating from the original starting point, so the device will necessarily return to the same connection state again. The remaining five constraints on relative movement can define an axis of rotation about which the device rotates or pivots relative to the machine.

[0022] The single degree of freedom (i.e., the degree of freedom that remains available for relative movement after a single constraint has been substantially removed) can be a degree of freedom of rotation. The single constraint can be a constraint on relative rotational movement between the device and the machine.

[0023] The connecting device can be adapted to reconnect the device to the machine in the same relative position and orientation as before it was at least partially decoupled (when no longer in an over-travel state). In other words, the relative position and orientation defined by the connecting device can preferably be reproducible. The measurement device returning to reseat in the same (reproducible) position and orientation is particularly beneficial in the context of measurement because if the measurement device returns to reseat in a different position and / or orientation after an over-travel event, then the measurement data before and after the event will not be consistent.

[0024] The connecting device can be adapted to provide a kinematic or pseudo-kinematic connection between the device and the machine (when in a connected state).

[0025] A coupling device can be adapted to constrain a device to a machine with six degrees of freedom (when coupled). The coupling device defines six contact points, which are arranged relative to each other to constrain the device to the machine with the corresponding six degrees of freedom (when coupled), thereby providing a precise or kinematic constraint of six degrees of freedom. When at least partially disconnected, one or more of these contact points are lost, thereby losing the constraint of one or more corresponding degrees of freedom. These contact points do not have to be mathematical points in a purely mathematical sense (and would likely not be in practice). Rather, each of them can actually be a small area close to a point, and thus can be called a pseudo-contact point.

[0026] The six points (or pseudopoints) can be arranged in a "1-2-3" configuration, with three points in total. In other words, the six points (or pseudopoints) can be arranged as follows: one point in the first position (providing a single constraint on relative movement between the device and the machine), two points in the second position (providing two constraints on relative movement), and three points in the third position (providing three constraints on relative movement).

[0027] The coupling device can be adapted to disconnect at a single point (or constraint) (in the case of an over-stretch condition) while remaining coupled at the other five points (or constraints). This leaves the device constrained to the machine with five degrees of freedom, leaving only one degree of freedom for relative movement. The single point may provide constraint on the relative movement between the device and the machine in the rotational degree of freedom. The coupling device can be adapted to disconnect consistently at the same single point (or constraint).

[0028] The six contact points can be arranged in a "2-2-2" configuration, with three positions.

[0029] The plane defined by the contact point may be positioned at an angle to a given axis of the measuring device. The angle may be acute. The angle may be between 20 and 70 degrees. The angle may be between 35 and 55 degrees. The angle may be approximately 45 degrees.

[0030] The contact point may be offset from a predetermined axis of the measuring device.

[0031] The coupling device may include a retaining mechanism adapted to prevent the device from falling completely from and / or detaching from the machine, even after the device has been disconnected from the machine, in all six degrees of freedom (or at all six constraints or contact points) described above.

[0032] The holding mechanism can be adapted so that it is only effective when the coupling device is in an over-stroke state.

[0033] The holding mechanism may be adapted to prevent the device from being detached from the machine in at least one of the aforementioned degrees of freedom (i.e., the coupling device may be adapted to ensure that the device remains coupled to the machine in at least one degree of freedom when in an over-stroke state).

[0034] In this context, at least one degree of freedom could be one of the five degrees of freedom described above (i.e., if it is explained that the coupling device can be adapted such that the device remains constrained by five degrees of freedom with respect to the machine, or by five constraints with respect to relative motion).

[0035] As previously stated, if the five constraints define an axis of rotation or pivot, the holding mechanism will prevent the device from coming off this axis, and as a result, the device will still have the opportunity to rotate or pivot around this axis to return to its original connected state.

[0036] These five constraints may be provided by the "2-3" portion of the aforementioned "1-2-3" arrangement, in other words, the retaining mechanism may be adapted to prevent the device from being detached from the machine at those positions, providing two and three contact points (or constraints).

[0037] The holding mechanism can be adapted to prevent relative movement in any remaining degree of freedom beyond a predetermined limit, for example, in the case of a single remaining rotational degree of freedom, to prevent rotation or pivoting around an axis.

[0038] The retaining mechanism may be adapted to allow the device to be removed from the machine only when it is in a predetermined relative orientation (for example, when it cannot be rotated or turned relative to each other around an axis in the case of a single remaining rotational degree of freedom).

[0039] The coupling device may be adapted to at least partially detach the device from the machine when the device is moved relative to the coupling device in a direction that intersects the interface between the device and the coupling device (or along a line or along an axis).

[0040] A coupling device can be adapted to disconnect (or disengage, separate, or change from a coupled to a disconnected state) when the coupled parts are moved generally toward each other (not generally toward each other, or in the same way as moving toward each other). In other words, a coupling device can be a reverse coupling device and can have a reverse coupling configuration. A reverse coupling device can be a reverse kinematic (or at least pseudo-kinematic) coupling device.

[0041] The over-travel protection provided by the coupling device may be independent of, and / or separate from, and / or added to, any over-travel protection that could be said to be provided within the measuring device itself. For example, a contact trigger probe typically allows a small amount of movement after contact is made in the Z direction (i.e., along the stylus). However, this is because, in such a probe, the transducer used to convert a physical stimulus (i.e., contact) into a signal relies on some additional movement to enable the contact to be detected from the signal (the signal then shows a clear transition from a non-contact state to a contact state, distinguishing the noise). Therefore, a small range of movement in the Z direction is usually required to accommodate the normal operation of the transducer. Also, in practice, it is not possible to stop the machine precisely when contact occurs (and there may be a short time delay between when contact occurs and before the machine can be stopped), and the normal range of movement is adaptable to this. However, in the context of this application, this is considered to be equal to the normal range of movement rather than over-travel in itself.

[0042] The measuring device may comprise a sensor or transducer adapted to convert physical stimuli (such as contact between the workpiece contact portion of the measuring device and the workpiece being measured by the measuring device) into an electrical signal. The measuring device may be considered a fully functional or standalone measuring device, and not, for example, a stylus for a contact trigger probe.

[0043] The measuring device may be a contact-type measuring device or a non-contact-type measuring device. A contact-type measuring device can be considered a type of measuring device in which the measurement is initiated by contact with the object being measured (such as a workpiece).

[0044] The measuring device may be a measuring probe.

[0045] The measuring device may be a contact-triggered measuring probe. The measuring probe may comprise a stylus that contacts the workpiece. The direction of stroke overprotection (or a predetermined direction) may be along the approximately longitudinal axis of the stylus. The predetermined direction (or the approximately longitudinal axis of the stylus) may be referred to as the Z-axis of the measuring probe, or may coincide with it.

[0046] In the context of this application, such a stylus does not constitute a measuring device, but may form part of a measuring device.

[0047] The coupling device may be considered to be separate from the measuring device and / or not to form part of the measuring device.

[0048] The measuring device may include a form of coupling that allows the measuring device to be firmly connected to the machine, whether or not via a coupling device.

[0049] The measuring device may be equipped with a quick-release coupling (a type of coupling that allows for quick and easy connection and disconnection without the need for tools or additional equipment, such as a magnetic coupling) that enables the measuring device to be removably connected to a machine, whether or not via a coupling device.

[0050] The measuring device could be a fully functional measuring device (perhaps one that does not involve power or signal processing, or signal analysis).

[0051] The coupling device can be adapted to accept the measuring device without any modification or alteration to the measuring device, and the measuring device can otherwise be coupled to the machine without an intermediate coupling device.

[0052] An over-travel condition can occur when a measuring device is moved by the machine toward an object (or workpiece) within the machine's working volume, causing the measuring device to come into contact with the object, and even after contact has been made, when the machine continues to move the measuring device in that direction beyond its normal range of motion.

[0053] The coupling device can be adapted such that when a force greater than a predetermined force (or a predetermined threshold) is applied to the device side of the coupling device in a predetermined direction toward (and / or across) the interface, the measuring device is at least partially disconnected from the machine (or, at that time, changes from a coupled state to a at least partially disconnected state).

[0054] The coupling device can be adapted such that, when a compressive force exerted in a predetermined direction in the measuring device is greater than a predetermined force (or a predetermined threshold), the measuring device is at least partially disconnected from the machine (or, at that time, changes from a coupled state to a state of at least partially disconnection).

[0055] The aforementioned force (or compressive force) may be brought about by the measuring device being moved by the machine in the direction of the aforementioned object and coming into contact with the aforementioned object (and, even after contact has been made, by the machine continuing to move the measuring device in that direction).

[0056] Providing over-stroke protection to a measuring device can provide an additional relative movement range between the measuring device and the machine (e.g., beyond the normal range of relative movement) without damaging the measuring device (i.e., in the absence of over-stroke protection, additional relative movement would otherwise damage the measuring device).

[0057] The coupling device may be adapted to cause the measuring device to be at least partially disconnected from the machine when the measuring device is moved relative to the coupling device by a predetermined distance and / or by a predetermined force (or a force greater than a predetermined threshold) toward the interface. The predetermined distance / force may be the maximum distance / force expected during the normal operation of the measuring device. The predetermined distance / force may be a distance / force beyond which damage to the measuring device (or at least a part of the measuring device) may occur.

[0058] The coupling device may be adapted to provide over-travel protection along a predetermined axis of the measuring device, in which case the predetermined axis is one or more of the Z-axis of the measuring device, the substantially longitudinal axis of the measuring device, and the axis of the measuring device having the smallest available travel.

[0059] In the case of contact-type measuring devices, measurement is initiated by contact between the measuring device (e.g., its stylus) and the object being measured, and a predetermined force (or threshold) may be greater than the minimum contact force (along the same direction or in a predetermined direction) required to initiate measurement. For example, in the case of a contact-triggered measuring probe, one embodiment of the present invention effectively combines a low-force, low-travel coupling (i.e., a coupling provided internally in the probe as part of a contact detection mechanism) with a high-force, high-travel coupling (i.e., a coupling provided by a coupling device embodying the invention), resulting in a breakout (i.e., at least partial disconnection) of the coupling device occurring after the contact-trigger mechanism is activated, i.e., after the measurement is taken or recorded (but before any damage is caused to or within the probe).

[0060] In this regard, the sequence of events is likely to be: (a) relative movement between the measuring device and the object results in contact between the measuring device and the object, but the force is still below the minimum contact force to initiate measurement; (b) further relative movement causes the force to exceed the minimum contact force, thereby initiating measurement; (c) further relative movement causes the force to increase further, but still below a predetermined force (or threshold) required to initiate over-stroke protection; and (d) further relative movement causes the force to increase further, exceeding the predetermined force (or threshold), thereby activating over-stroke protection.

[0061] The measuring device provides a first joint having a first coupling force (or strength) and / or a first range of motion, and the coupling device may provide a second joint having a second coupling force (or strength) greater than the first coupling force (or strength) and / or a second range of motion greater than the first range of motion. The first joint may be an internal joint of the measuring device relating to the measuring function of the measuring device. At least a portion of the first range of motion may correspond to a measuring range for the measuring device. The first joint may be associated with a sensor or transducer of the measuring device, which is, for example, one of those described above.

[0062] Thus, during normal operation, the force generated by the contact between the measuring device and (for example) the workpiece is sufficient to cause relative movement between the two parts of the first joint, thereby enabling the measuring function to be performed, but not sufficient to cause relative movement between the two parts of the second joint, thereby maintaining the stability and integrity of the measurement. However, further increasing the force will eventually be sufficient to overcome the second joint, thereby providing the desired over-stretch protection to the measuring device and preventing damage to the measuring device.

[0063] In this context, the second joint may provide over-travel protection to the measuring device. The coupling force (or strength) and range of motion in this context may be within a given direction or along that direction (e.g., from the measuring device towards the interface or vice versa) and / or along a given axis of the measuring device (e.g., along the Z-axis of the measuring device). The coupling force (or strength) in this context may be considered as the force required to separate, disengage, or disconnect the joint. The range of motion of the joint in this context may also be referred to as the normal range of motion, expected range of motion, or maximum range of motion of the joint. In the case of a contact trigger probe or other such contact measuring device, the first joint may be a joint (such as a kinematic joint) that connects the stylus of the measuring device to the stylus support of the measuring device.

[0064] The first joint is considered to provide a high-precision joint, and the second joint is considered to provide a low-precision joint (or a joint having at least lower precision than the first joint), where precision in this context relates, for example, to the positional precision or repeatability provided by the joint.

[0065] If the sensor or transducer of the measuring device cannot be said to provide a joint by itself, the above description relating to the first joint will be equally applicable to a support device of the measuring device that provides relative movement between two parts of the measuring device (e.g., a stylus and a stylus support), and that relative movement is sensed and / or measured in such a way that a measuring function can be performed.

[0066] Therefore, the measuring device may comprise a sensor or transducer adapted to sense or measure (or convert) relative movement between two parts of the measuring device (e.g., the stylus and the stylus support) in order to perform the measuring function of the measuring device (e.g., when contact is made between the stylus and the workpiece), the sensor or transducer being operable within a predetermined (or normal, or operational, or work) range of force (or intensity) and / or within a predetermined (or normal, or operational, or work) range of movement, and the coupling device having a coupling force (or intensity) greater than the predetermined (or normal, or operational, or work) range of force (or intensity) of the sensor or transducer, and / or a range of movement greater than the predetermined (or normal, or operational, or movement) range of movement of the sensor or transducer. The range of force (or intensity) may be in the direction toward the interface and / or along a predetermined axis of the measuring device. The connecting force (or strength) may be in the direction toward the interface and / or along a predetermined axis of the measuring device. The range of motion may be in the direction toward the interface and / or along a predetermined axis of the measuring device.

[0067] The coupling device may include a kinematic or pseudo-kinematic coupling for connecting the coupling device to a coordinate positioning machine. This could make the coupling device suitable for use, for example, in an automated exchange system.

[0068] Stroke overprotection may be at least 10% of the typical dimensions or length of the device in the direction of the overstroke (or a predetermined direction), preferably at least 15%, more preferably at least 25%, and more preferably at least 50%.

[0069] The stroke overload protection may be at least 10 mm, preferably at least 20 mm, more preferably at least 30 mm, and more preferably at least 50 mm in the direction of stroke overload (or a predetermined direction).

[0070] The measuring device may have a normal mounting direction, and the coupling device may be adapted to mount the measuring device in the opposite direction to the normal direction. The normal mounting direction may be from the working part of the measuring device, such as the stylus tip of a measuring probe, to the mounting part, for example, along the generally longitudinal axis of the measuring device.

[0071] Thus, the coupling device can be considered an adapter, and the combination of the measuring device and the adapter connects to and disconnects from the machine in a generally reversed manner compared to normal.

[0072] A coupling device can be thought of as an adapter for altering the properties of a coupling that would otherwise exist (to provide over-process protection for the device).

[0073] The interface between the device and the coupling device may be the location where the device is attached to or coupled to the coupling device.

[0074] The machine is either a non-orthogonal machine or may be a non-orthogonal machine.

[0075] The machine is either a parallel kinematic machine or may be equipped with a parallel kinematic machine.

[0076] The machine is either a series kinematic machine or may be equipped with a series kinematic machine.

[0077] The machine is a series kinematic machine having multiple segments connected in series via a rotary joint, or it may comprise a series kinematic machine.

[0078] The machine is a robotic arm, or may be equipped with a robotic arm.

[0079] The measuring device may be any type of tool or instrument other than a measuring device.

[0080] A coordinate positioning machine can be any other type of machine besides a coordinate positioning machine.

[0081] According to a second aspect of the present invention, a kit is provided comprising a measuring device and a coupling device according to a first aspect of the present invention.

[0082] According to a third aspect of the present invention, a coordinate positioning machine is provided comprising a measuring device coupled to a machine via (and / or using) a coupling device according to a first aspect of the present invention. The coupling device may be provided between the machine and the measuring device.

[0083] The coordinate positioning machine may include a movable support member, and the measuring device may be connected to the movable support member via a coupling device. The coupling device may be connected to the movable support member via a kinematic joint or a pseudo-kinematic joint (for example, as part of an automatic exchange system).

[0084] The coordinate positioning machine may be a robotic arm. The movable support member may be the end effector of the robotic arm.

[0085] The coordinate positioning machine may be a hexapod machine. The movable support member may be a movable platform for the hexapod machine.

[0086] A fourth aspect of the present invention provides a method for connecting a measuring device to a coordinate positioning machine, the method comprising connecting the device to a movable support member of the machine via a connecting device according to a first aspect of the present invention. The connecting device may be provided between the machine and the measuring device.

[0087] Here, a reference to the attached drawing will be made as an example. [Brief explanation of the drawing]

[0088] [Figure 1]This is a schematic diagram of the coordinate positioning arm of the articulated robot discussed above. [Figure 2] This is a schematic diagram of a multi-joint robot having a different arrangement of rotation axes than that of Figure 1, as discussed above. [Figure 3] Figure 1 is a schematic diagram of a measurement probe connected to a multi-joint robot of the type shown. [Figure 4] This figure is used to illustrate a problem related to the configuration of the joint used in Figure 3 to connect a measuring probe to an articulated robot. [Figure 5] This is a schematic diagram of a coupling device embodying the present invention, used to connect a measuring probe to an articulated robot. [Figure 6] Figure 5 shows how the coupling device provides over-stroke protection for the measuring probe in a situation equivalent to that in Figure 4. [Figure 7] Figure 5 is a plan view showing how the two halves of the coupling device of the type shown interact with and connect to each other. [Figure 8] Figure 5 shows a schematic diagram of an alternative configuration for the coupling device, where the coupled measuring probe is more aligned with the flange rather than being offset. [Figure 9] Figure 8 shows a slight deformation of the coupling device. [Figure 10] This is a schematic diagram of an alternative configuration of the coupling device embodying the present invention, in which the measuring probe is connected upward to the flange, but is offset from there. [Figure 11] This is a schematic diagram showing a coupling device similar to the one shown in Figure 5, but in which the articulated robot is attached to the coupling device from the side. [Figure 12] Figure 11 is a plan view showing how the two halves of the coupling device of the type shown interact with and connect to each other, and is similar to the diagram shown in Figure 7. [Figure 13] This is a side view of the coupling device shown in Figure 12, in its connected state. [Figure 14]Figure 12 is a side view of the coupling device, which is in a partially disconnected or partially coupled state, thereby providing over-travel protection for the measuring probe. [Figure 15] This is a side view of the coupling device, based on the coupling device in Figure 13, but modified to include a holding mechanism. [Figure 16] Figure 15 is a side view of the coupling device, similar to the coupling device shown in Figure 14, but it illustrates the operation of the holding mechanism in a partially disconnected or partially connected state. [Figure 17] This diagram shows the operation of the holding mechanism of the coupling device in Figure 15, where the measuring probe is upside down and the coupling device is partially disconnected or partially connected. [Figure 18] This is a side view of a coupling device based on the coupling device in Figure 16, but with a different configuration of the holding mechanism. [Figure 19] Figure 18 shows a side view of the coupling device, illustrating the operation of the holding mechanism in a partially disconnected or partially connected state. [Figure 20] This figure shows a coupling device embodying the present invention, based on a "2-2-2" configuration instead of a "1-2-3" configuration. [Figure 21] Figure 20 is a schematic diagram showing one method of connecting the measuring probe to the robot arm using the coupling device. [Figure 22] Figure 20 is a schematic diagram illustrating another method of connecting the measuring probe to the robot arm using the coupling device. [Figure 23] Figure 20 is a schematic diagram illustrating yet another method of connecting the measuring probe to the robot arm using the coupling device. [Figure 24] Figure 20 is a schematic diagram of the holding mechanism of the coupling device, showing the coupling device in the seated position. [Figure 25] Figure 24 schematically illustrates how the holding mechanism works to prevent the complete separation of the two halves of the coupling device. [Figure 26]Figure 8 is a schematic diagram showing a modified configuration of the arrangement, in which an additional kinematic device is provided between the coupling device and the robot arm. [Modes for carrying out the invention]

[0089] Figure 3 is a schematic diagram of a measuring probe 14 connected to the articulated robot 1 of the type described above, with reference to Figure 1. In this example, the measuring probe 14 is a contact-triggered measuring probe having a workpiece contact stylus 15 terminated at a stylus tip 16. Such measuring probes are well known and do not require detailed explanation, but for the reasons mentioned above, measuring probes are not typically used in combination with articulated robots for measuring tasks. In this example, the measuring probe 14 is connected to the flange 3 of the robot arm 1 via a kinematic (or at least pseudo-kinematic) coupling device 9, which is securely attached to the flange 3.

[0090] The applicant recognizes that when the robot arm 1 is controlled to perform various measurement tasks using the measuring probe 14, there is a risk that the measuring probe 14 may be unintentionally driven beyond its normal range of motion. An example of this is shown in Figure 4, in which the measuring probe 14 is driven too far in the Z direction toward the fixed base 2, resulting not only in the stylus 15 breaking, but also in the stylus 15 transmitting excessive force to the body of the measuring probe 14, causing internal damage. This overshoot may result from errors in the current mechanical parameters (resulting in the end of the robot arm 1, and therefore the stylus tip 16 of the measuring probe 14, not being in the position where it is expected to be), errors in programming the robot controller 8 for the measurement routine, or human errors when manually controlling the robot arm 1 using a joystick controller or the like (whether or not it is part of the measurement routine), or a combination of these.

[0091] As will be explained in detail below, attempting to force the measuring probe 14 to move beyond its normal range of motion, which is usually very small and does not take into account the errors described above, can lead to damage to the measuring probe 14 (not only to the stylus 15 but also to the delicate internal mechanisms of the measuring probe 14), potentially requiring expensive replacement and / or repair of the measuring probe 14. Perhaps more importantly, this can also cause disruption and delays to measurement and manufacturing procedures in facilities where the measuring probe 14 is used. Therefore, the applicant recognized the desirability of producing a system that is more resistant to the adverse events described above, which actually inevitably occur and can cause damage to the measuring probe 14, especially when mounted on the robot arm 1.

[0092] In light of the above context, Figure 5 shows the same robot arm 1 as described above with reference to Figure 3, the robot arm 1 having multiple segments 5 connected by a combination of a lateral rotation axis 6 and an inline rotation axis 7. However, in Figure 5, the measuring probe 14 is connected to the flange 3 of the robot arm 1 via a coupling device 30 that embodies the present invention. The coupling device 30 is provided between the measuring probe 14 and the flange 3 of the robot arm 1, instead of the coupling device 9 in Figures 3 and 4. The coupling device 30 is securely attached to the flange 3, and in this example, the measuring probe 14 is securely attached to a portion 10 of the coupling device, for example, via a screw connection.

[0093] The coupling device 30 is specifically adapted to provide over-travel protection for the measuring probe 14. In particular, in this example, the coupling device 30 is adapted to at least partially detach the measuring probe 14 from the flange 3 of the robot arm 1 when the measuring probe 14 is moved (more than desired) in a predetermined direction relative to the coupling device 30 toward the interface 37 between them, thereby providing over-travel protection for the measuring probe 14 by allowing additional relative movement in that direction without damaging the measuring probe 14.

[0094] This is schematically shown in Figure 6, in which the measuring probe 14 is driven more in the Z direction and perpendicular to the fixed bed 2 than intended. As shown in Figure 4 and as will be explained in more detail below, the two parts 10 and 20 of the coupling device 30 are seated (at least partially) apart from each other, without causing damage, thereby allowing an additional range of movement in this direction without causing any damage to the measuring probe 14 itself.

[0095] The measuring probe 14 will typically allow a very small amount of movement in this direction after contact with the bed 2, but only enough to record the contact and describe the normal, expected stopping distance for the machine it is connected to. In this regard, the measuring probe 14 will preferably include a sensor or transducer adapted to convert a physical stimulus (in this example, contact between the tip of the stylus 16 and the bed 2) into an electrical signal (in this example, a contact trigger signal) in all directions, including the Z direction (where the Z direction is along the roughly longitudinal axis of the measuring probe 14, i.e., within the reference frame of the probe rather than the reference frame of the machine). This conversion can be performed, for example, by disconnecting internal electrical contacts or by bending an internal structure with mounted strain gauges, both of which depend on at least a small amount of relative movement. In other words, the measuring probe 14 is not merely a part of a measuring device, but a fully functional measuring device in itself. The measuring probe 14 may itself be modular, as in Renishaw's TP20 and TP200 probing systems, in which a common probe body (mounted on the machine) can be connected to any of several different probe modules (also referred to as stylus modules) having different characteristics or responses, which in turn can hold any of several different styluses having different lengths or structures. Each probe module in the TP20 / TP200 probing system incorporates a kinematic switching contact sensor mechanism and is equipped with a stylus assembly for connection to a stylus. In this context, the measuring device is considered to be a combination of the probe body, probe module, and stylus, or at least a combination of the probe module and stylus, or at a minimum, the probe module. In particular, a stylus cannot be adapted to measure anything (by itself), and therefore, in this context, it is not considered a measuring device. For example, a stylus would not have a sensor or transducer adapted to convert a physical stimulus (e.g., deflection caused by contact) into an electrical signal.Conversely, the coupling device embodying the present invention does not provide (and / or is not intended to provide) any measurement-related functions to the measuring device coupled to the coordinate positioning device, but can be said to provide only a coupling function (with over-cycle protection).

[0096] Furthermore, the coupling device 30 can be advantageously adapted to accept the measuring probe 14 without requiring any modifications to the measuring probe 14 itself. For example, the measuring probe 14 can be coupled to the flange 3 of the robot arm 1 with or without the coupling device 30 provided in the middle. The measuring probe 14 will typically have a quick-release coupling, that is, a coupling that allows for quick and easy coupling and uncoupling without the need for any special tools or equipment. For example, the measuring probe 14 may have a magnetic quick-release coupling (e.g., the magnetic kinematic mount between the probe body and probe module of the TP20 / TP200 probe system described above) or it may have a threaded quick-release coupling (e.g., the Renishaw OMP40 and OMP60 modular systems, and the Renishaw LP2 modular probe system which can also be integrated with them, or the TP20 / TP200 probe system described above if the probe body has a threaded connection to the machine). Therefore, the same measuring probe 14 can be used in a three-axis coordinate measuring machine with a conventional coupling device, or in a robot arm shown in Figure 5 via the coupling device 30 embodying the present invention, or the measuring probe 14 can be directly attached to the robot arm 1 without over-stroke protection, as shown in Figure 3. This flexibility and ease of use is a major advantage of the coupling device 30 embodying the present invention, as it can be used in combination with existing probe systems as needed and when required.

[0097] Simply put, the coupling device 30 comprises two parts 10 and 20 connected together via a kinematic (or at least pseudo-kinematic) joint, in an arrangement opposite to that of the coupling device 9 shown in Figure 3, and can therefore be referred to as a reverse kinematic device. The kinematic joint is highly repeatable by its nature, which is advantageous because the two parts 10 and 20 of the coupling device 30 can be uncoupled (to protect the measuring probe 14 from damage) and then recoupled in exactly the same relative orientation, i.e., as if nothing had happened.

[0098] The coupling device 30 in Figure 5 can be said to be in the reverse orientation compared to the coupling device in Figure 3, because it connects downward to the flange 3, even though the measuring probe 14 in Figure 5 is positioned below the flange 3. This is achieved by positioning part 10 to seat on part 20 when coupled. Comparing this to the coupling device 9 in Figure 3, in Figure 3, the measuring probe 14 connects upward to the flange 3. Because the coupling device 30 in Figure 5 is in the reverse orientation compared to the coupling device 9 in Figure 3, the coupling device 30 in Figure 5 would result in the measuring probe 14 being detached if it is pushed with excessive force toward the flange 3, whereas this would not happen with the coupling device 9 in Figure 3, and instead the measuring probe 14 would be subjected to excessive (and potentially damaging) compressive force. In other words, the coupling device 30 in Figure 5 would tend to disengage when the two parts 10 and 20 are pressed together, rather than when they are pulled apart from each other (as would be the case with the coupling device 9 in Figure 3).

[0099] A more detailed example of how these two parts 10 and 20 interact and connect to each other is shown in Figure 7. The measuring probe 14 is attached to part 10, and the other part 20 is attached to the robot arm 1 via the flange 3. The kinematic features 11, 12, and 13 are located on the underside of part 10 (according to the directions shown in Figures 5 and 6). The first (flat) feature 11 at the first position 31 provides a single contact point with the corresponding ball 21 on the other part 20 of the coupling device 30; the second (V-groove) feature 12 at the second position 32 provides two contact points with the corresponding ball 22 on the other part 20 of the coupling device 30; and the third (tetrahedron) feature 13 at the third position 33 provides three contact points with the corresponding ball 23 on the other part 20 of the coupling device 30.

[0100] As a result, the coupling device 30 is adapted to provide a kinematic or pseudo-kinematic coupling between the measuring probe 14 and the robot arm 1, defining six contact points in a "1-2-3" arrangement across three positions 31, 32, and 33 (with one contact point at the first position 31, two contact points at the second position 32, and three contact points at the third position 33, hence referred to as the "1-2-3" arrangement, the three elements of the "1-2-3" arrangement are shown in Figure 7 by the circled numbers 1, 2, and 3, respectively). The six contact points constrain the measuring probe 14 and the robot arm 1 with six degrees of freedom (although in reality these are not points in a mathematical sense, but rather small regions close to points).

[0101] In the context of positioning one object relative to another, kinematic design considerations are met by using a minimum number of constraints to restrict the degrees of freedom of motion of the objects, and in particular by avoiding excessive constraints. Excessive constraints result in multiple points of contact between the two objects, allowing one object to rest at two or more positions relative to the other. Thus, the object's position cannot be reproduced because it is unknown at which of several positions the object will rest. In particular, when there are excessive constraints, inconsistencies arise between the constraints that are set, and it is not possible to reliably determine which combination of constraints determines the actual position of the object. These concepts are explained in Non-Patent Literature 1 and Non-Patent Literature 2.

[0102] The two parts 10 and 20 of the coupling device 30 are magnetically held by magnets 24 and 25 on part 20, and part 10 is made of a magnetic material (or at least the part closest to the magnets 24 and 25) and is therefore magnetically attracted by the magnets 24 and 25. However, when the measuring probe 14 is pushed with enough force to overcome the magnetic bias force from the magnets 25 positioned on either side of the first position 31, the magnetic coupling between parts 10 and 20 is broken at the first position 31 (i.e., the position that provides one of the six constraints on the relative movement between the two parts 10 and 20), but not at the second position 32 and the third position 33 (i.e., the positions that provide the other five constraints on the relative movement), so the coupling is only partially broken.

[0103] In this example, by losing a single constraint that is a constraint on relative rotational motion, this provides a single degree of freedom for relative motion between the two parts 10 and 20, which in this example is a rotational degree of freedom around axis 34. In other words, the two parts 10 and 20 are separated by one degree of freedom but remain connected by five degrees of freedom. Advantageously, the magnet 24 is cylindrical, and the axis of the cylinder is positioned to coincide with the axis 34 between the two balls 22 and 23 (positions 32 and 33), which allows part 10 to rotate around axis 34 relative to part 20 when rotation occurs, while maintaining a nearly constant magnetic attraction between parts 10 and 20. This rotational motion will also become apparent from the following description with reference to the embodiments shown in Figures 12-14. Furthermore, it should be noted that the cylindrical magnet 24 could instead be a cylindrical target made of a magnetic material, and the magnet itself is on part 10, i.e., the magnetic coupling is reversed, and similarly, the magnetic coupling formed by magnet 25 could also be reversed.

[0104] Since the separation is only partial, the two parts 10 and 20 remain attached to some extent, and therefore the measuring probe 14 also remains attached and does not detach and fall (thus causing damage). Additional retaining configurations may be provided to make it more difficult for the two parts 10 and 20 to separate completely, for example, by requiring them to be realigned parallel to each other before separation. This possibility will be described in more detail below with reference to Figures 15-19.

[0105] It should be noted, generally speaking, that the kinematic couplings used in coupling devices embodying the present invention are not limited to the "1-2-3" arrangement described above. For example, the kinematic coupling may also be formed by three rotationally symmetric V-grooves in a "2-2-2" arrangement, which share the common feature of providing exactly six contact points to provide precise constraints for all six degrees of freedom. However, in the embodiment shown in Figure 7, the "1-2-3" arrangement is preferred because it allows for the generation of a pivot axis with the loss of only one constraint, as described above. This is advantageous for embodiments in which partial disconnection occurs, or perhaps more important for embodiments in which it leads to proper reconnection following partial disconnection or over-stroke events.

[0106] In this regard, if the connection is broken at one of the three positions in the "2-2-2" configuration, there will be a loss of two constraints (corresponding to the generation of two degrees of freedom), since each position provides two constraints on the relative movement between the two parts 10, 20. This means that the two parts 10, 20 will remain constrained with only four degrees of freedom (not five), and will be able to rotate not only around an axis defined between the two remaining positions (an axis like the axis 34 described above), but also around a second axis perpendicular to the plane containing the three positions. The drawback of this is that when the two parts 10, 20 become one again, the kinematic features in the first position can no longer be aligned due to the additional rotation around the second axis, so the two parts 10, 20 will not return to the same relative position and orientation.

[0107] On the other hand, in the "1-2-3" configuration, with only a single axis of rotation generated by the loss of a single constraint, the only possibility is that the two parts 10 and 20 reintegrate with their kinematic features still aligned at the first position 31, thereby reconnecting in a kinematic and repeatable manner without changing the relative position and orientation of parts 10 and 20. This is because movement is only possible along (or around) a single axis, and there can be no deviation from that axis, and as a result, the movement always returns to the same place along (or around) that axis, which is essentially like movement along a single "track". An alternative coupling device may be devised in which a single linear constraint, rather than a single rotational constraint, is severed, and as a result, it will be understood that one part 10 will translate rather than rotate or turn relative to the other part 20.

[0108] Instead of the offset coupling device 30 shown in Figures 5-7, a more inline coupling device may be provided, for example, as shown in Figures 8 and 9. Furthermore, a reverse kinematic type arrangement is not required to achieve the intended effect; instead, this can be achieved when the measuring probe 14 is offset from the flange 3, as shown in Figure 10, and as a result, the measuring probe 14 will tend to rotate (disengage) when it is moved toward the interface between the measuring probe 14 and the coupling device 30, even though it is not strictly a reverse arrangement (i.e., the measuring probe 14 connects to the flange 3 upward via the coupling device 30, just as it connects in Figure 3).

[0109] Figure 11 schematically shows a side-mounted structure, where the normal of the flange 3 of the robot arm 1 is perpendicular to the longitudinal axis of the measuring probe 14, unlike the structure in Figure 5 where the normal of the flange 3 of the robot arm 1 is parallel to the longitudinal axis of the measuring probe 14. Embodiments of this type of structure will be described in more detail next with reference to Figures 12-14.

[0110] The coupling device 30 shown in the plan view of Figure 12 is substantially the same as that shown in Figure 7, and therefore no detailed explanation is necessary, except for some slight changes in the relative positions of the kinematic features 11, 12, and 13 of part 10 and the corresponding kinematic features 21, 22, and 23 of part 20. This allows for a more compact overall structure, and the measuring probe 14 is mounted lateral to the first (flat) kinematic feature 11 at position 31, with a notch 27 provided in part 20 to accommodate it. A mounting plate 26 is provided in combination with part 20, and the mounting plate 26 is adapted to be mounted on the flange 3 of the robot arm 1. Also, a recess 17 is provided in part 10 corresponding to the position of the cylindrical magnet 24, and the cylindrical magnet 24 partially protrudes into the recess 17, thereby allowing part 10 and part 20 to sit closer together with a higher magnetic bias force.

[0111] Figure 13 shows a side view of the coupling device 30 of Figure 12 in a fully coupled state, and also shows the interface 37 between the measuring probe 14 and the coupling device 30 (specifically, in this example, part 10 of the coupling device 30). In this respect, the movement of the measuring probe 14 relative to the robot arm 1 toward the interface 37 results in the measuring probe 14 being partially detached from the robot arm 1. Conversely, the movement of the robot arm 1 relative to the measuring probe 14 (specifically, in this example, the flange 3 of the robot arm 1) toward the measuring probe 14 in the opposite direction results in partial detachment.

[0112] When the tip 16 of the stylus contacts the fixed bed 2 (or other object such as a workpiece) in the vertical or Z direction, the measuring probe 14 initially begins measuring through movement within its normal range of motion provided in this direction. However, if the flange 3 of the robot arm 1 is inadvertently driven further in this direction, a compressive force is generated in the measuring probe 14, which will eventually be sufficient to break the magnetic connection provided by the magnet 25 located near the first position 31. The strength of this magnet 25 is selected to ensure that the connection is broken at the first position 31 before a compressive force sufficient to cause damage is generated in the measuring probe 14. Conversely, the strength of the magnet 25 is also selected so that the connection is not broken at the first position 31 before the measuring probe 14 begins measuring; in other words, the biasing force provided in the Z direction by the magnet 25 is set to be greater than the minimum contact force required to initiate the Z direction measurement by the measuring probe 14. This allows the measuring probe 14 to function normally, and measurements to start as usual in all directions (X, Y, and Z), while also protecting the measuring probe 14 from overshooting in the Z direction.

[0113] As shown in Figure 14, the two parts 10 and 20 of the coupling device 30 are separated at a first position 31 (defined by features 11, 21), but remain connected at a second position 32 and a third position 33 (defined by features 12, 22 and 13, 23, respectively), as described above with reference to the embodiment in Figure 7, and rotate around them. Part 10 rotates or turns around an axis 34 generated between the second and third positions, and the magnetic coupling strength remains substantially constant during rotation because the cylindrical magnet 24 is positioned along the axis 34. Figure 14 shows the coupling device 30 in a partially separated (or over-stretched) state compared to the connected state shown in Figure 13. Thereafter, the coupling device 30 provides over-stretch protection for the measuring probe 14, allowing for additional relative movement in the Z direction (or along the substantially longitudinal axis of the measuring probe 14) without causing any damage.

[0114] Next, when the robot arm 1 is controlled to move the measuring probe 14 away from the fixed bed 2 again, the over-stroke condition is released, and the two parts 10, 20 of the coupling device 30 will rotate toward each other to their original positions, re-coupling and magnetically holding each other. Since the coupling is broken at position 31, and thereby substantially loses only one constraint on relative motion, and so there is only relative motion along (or around) a single axis, as described above with reference to Figure 7, it is ensured that parts 10, 20 will re-couple with aligned kinematic features at all positions 31, 32, 33. Furthermore, due to the beneficial properties and characteristics of the kinematic coupling, the two parts 10, 20 (and therefore also the measuring probe 14 and flange 3) will re-couple in exactly the same relative orientation as before they were separated. In other words, the relative positions between these parts are repeatable, and the measuring probe 14 can be detached from and reattached to the robot arm 1 multiple times, and it will always reattach to the robot arm 1 in the same (replicable) relative position.

[0115] On the other hand, further movement in the same direction from the partially connected state shown in Figure 14 may result in the connection being severed, even at the second position 32 and the third position 33, in which case the coupling device 30 will then be completely detached. Thus, the measuring probe 14 will be completely removed from the robot arm 1 and, therefore, may be damaged if it subsequently falls from the robot arm 1 to the floor. Next, a holding (or capture, holding, detent) mechanism to address this situation will be described with reference to Figures 15 and 16.

[0116] The coupling device 30 shown in Figure 15 is substantially identical to the one shown in Figure 13, and therefore requires no further explanation. The only difference is that the coupling device 30 in Figure 15 is provided with a retaining mechanism 35, which comprises a post 28 firmly fixed to the part 20 and a molded recess 18 formed within the part 10. Figures 15 and 16 show the coupling device 30 in the same coupling state as in Figures 13 and 14, respectively; that is, Figure 15 shows the fully coupled state, and Figure 16 shows the partially disconnected (or partially coupled) state.

[0117] The recess 18 is configured to receive the post 28 when parts 10 and 20 of the coupling device 30 are substantially parallel to each other, as shown in Figure 15, which thus allows the coupling device 30 to be coupled and uncoupled. The recess 18 and the post 28 are also configured toward each other so that when part 10 is rotated away from part 20, as shown in Figure 16, the enlarged portion of the post 28 is received on the side of the recess 18, above the protruding portion of the recess 18. In order to be completely uncoupled, part 10 needs to be uncoupled from part 20 at positions 32 and 33 (it is already uncoupled at position 31). However, in the state shown in Figure 16, this is no longer possible because the retaining mechanism 35 functions to prevent part 10 from being lifted away from part 20 and breaking the coupling at these positions, and also, in this embodiment, functions as a stopper to prevent part 10 from being rotated further away from part 20.

[0118] This prevents part 10 from completely separating from part 20, thereby preventing the measuring probe 14 from potentially causing damage if it were to detach from the robot arm 1 and fall to the floor. Furthermore, it means that the only way part 10 can move is to rotate back toward part 20 around the axis 34, which is the only degree of freedom available to part 10, and as a result, part 10 will be correctly reattached, as shown in Figure 15. Moreover, due to the reproducible nature of the kinematic linkage described above, the measuring probe 14 will reattach to the robot arm 1 in the exact same relative position and orientation as it was before it was at least partially detached (i.e., the relative position and orientation are reproducible). The measuring probe 14 can be separated and reattached many times without falling off and without any recalibration required to redetermine where the stylus tip 16 of the measuring probe 14 is positioned relative to the flange 13 of the robot arm 1.

[0119] As shown in Figure 16, if the part is partially detached (or over-stride), when the over-stride condition is released, i.e., when the tip of the stylus 16 is moved away from the bed 2 (or other object such as a workpiece), the part 10 and the attached measuring probe 14 will fall naturally due to gravity and therefore will not fall completely naturally, but will instead be fully reconnected as shown in Figure 15. The use of the holding mechanism 35 is particularly advantageous in situations where, for example, to measure the underside of a workpiece or the inside of a hole accessible only from below, the robot arm 1 rotates the coupling device 30 (and measuring probe 14) so ​​that the coupling device 30 (and measuring probe 14) is upside down in the working area, and then the operation of the coupling device 30 partially detaches the part for over-stride protection, thereby preventing the measuring probe 14 from falling completely off. In this case, part 10 and the attached measuring probe 14 would fall naturally due to gravity, but would be prevented from completely detaching by the holding mechanism 35, and in the worst case, would end up hanging from part 20 attached to the robot arm 1 in the state shown in Figure 17 (which can be considered as remaining attached via the holding mechanism 35 but completely detached). To reattach the measuring probe 14 to the robot arm 1, the operator can manually push up part 10 until it re-engages with part 20, or the robot arm 1 can be controlled to rotate the coupling device 30 (and measuring probe 14) back, and the constraints provided by the holding mechanism 35 (and gravity) first result in parts 10 and 20 re-engaging at positions 32 and 33, as shown in Figure 16, thereby re-forming the axis of rotation 34, and then gravity results in parts 10 and 20 rotating back to the fully coupled state shown in Figure 15.

[0120] It should be noted that, at least in the fully connected state shown in Figure 15, a gap exists between the post 28 and the wall of the recess 18, resulting in no contact between these two parts. If contact were to occur, this would create additional constraint between parts 10 and 20, which, in turn, would generate undesirable excessive constraint between these parts for the reasons stated above. It is desirable to maintain a pure kinematic connection with exactly six contact points and six corresponding constraints (one for each of the six degrees of freedom). Therefore, the presence of the retaining mechanism 35 does not hinder the kinematic nature of the joint in the fully connected state. Furthermore, it is preferable that the gap be maintained even in the partially connected state when rotating around the shaft 34, in order to preserve the purity of the shaft 34, rather than creating an extra constraint in the retaining mechanism 35 that would tend to oppose the five remaining constraints generated at positions 32 and 33, which would generate uncertainty (and extra friction) in the position and orientation of the shaft 34.

[0121] It is understood that other forms of retaining mechanisms may be used, and another example is shown in Figures 18 and 19. The retaining mechanism 35 in this example comprises a curved bar 19 securely attached to the outer surface of part 10, the curved bar 19 being movable along a corresponding curved groove or track 29 machined into the outer surface of part 20, both of which are partially circular and have a curve concentric with a pivot axis 35 defined between kinematic positions 32 and 33. As seen in Figure 19, when part 10 rotates away from part 20 around the axis 35, the curved bar 19 will move within and around the curved groove 29. This will act as a "hook" to prevent part 10 from separating from part 20, keeping part 10 pivotally or rotatably connected to part 20 via the axis 35. The only way the curved bar 19 can be removed from the curved groove 29 is by rotating the part 10 in the opposite direction toward the part 20 around the axis 35, since the part 10 cannot be moved linearly away from the part 20 due to the action of the mutually cooperating (curved) parts of the retaining mechanism 35. Ideally, there should be a gap between the bar 19 and the groove 29, at least when the fully connected state shown in Figure 18, but preferably, there should also be a gap in the partially separated (or over-stretched) state shown in Figure 19.

[0122] It should be noted that, in addition to the examples shown in Figures 15-19, several other forms of retaining mechanisms may be used. While the examples provided herein are relatively easy to implement and still effective, more sophisticated forms of retaining mechanisms may be used instead. For example, an active retaining mechanism may be employed instead of a passive one.

[0123] One embodiment of the present invention may be based on a kinematic coupling having a "2-2-2" arrangement instead of a "1-2-3" arrangement, such an embodiment is shown in Figure 20. The coupling device 30 shown in Figure 20 is substantially the same as that shown in Figure 7 and does not require further explanation. The main difference is that each of the kinematic features 11, 12, and 13 is a V-groove (hence referred to as the "2-2-2" arrangement) that provides two of the six contact points, thereby providing precise constraints in all six degrees of freedom.

[0124] Figures 21 and 22 show two different ways (two of many ways) in which the coupling device 30 of Figure 20 (or, in fact, any coupling device embodying the present invention) may be positioned to provide over-stroke protection for a measuring probe 14 (or other type of measuring device) supported on a robot arm 1 (or other type of coordinate positioning machine). The position shown in Figure 21 is substantially the same as the position shown in Figure 11, but compared to Figure 11, the coupling device is mounted perpendicular to the flange. The angled position shown in Figure 22 may be useful in some situations because it may provide improved protection against impacts from the side, or, when tilted at an angle, equivalent protection against movement in the Z direction on a surface that is subjected to excessive force in both the Z and X or Y (i.e., lateral) directions, because a rotational motion will be generated which will result in the two halves of the coupling being separated from each other. In this respect, the position in Figure 22 will provide some degree of over-stroke protection against impacts in either direction indicated by the arrows.

[0125] The measuring probe (or other type of measuring device) may also be mounted to a "2-2-2" kinematic joint, as shown in Figure 23, so that the Z-axis of the measuring probe 14 is substantially in the plane of the three positions 31, 32, and 33 of the coupling device 30. This may be referred to as a side-mounting configuration (the probe 14 is mounted to the side of the part 10) in contrast to the bottom-mounting configuration in Figure 20 (the probe 14 is mounted to the bottom of the part 10). In such a mounting configuration, overshoot in the Z direction also causes the coupling device 30 to deseed, with its portion moving away from its seated position (outside the page of the drawing) and rotating, for example, around a centrally located retaining pin (into the page of the drawing) that provides constrained rotation (but with sufficient clearance so that it does not provide any additional contact points when the joint is properly mounted). A biasing member (e.g., a spring) may be provided to return the joint to the seated position.

[0126] The "2-2-2" coupling device 30 in Figure 20 would not provide a kinematically defined axis of rotation during the separation process, as would be the case in the aforementioned embodiment based on the "1-2-3" arrangement. However, the "2-2-2" arrangement has the advantage of having 3x rotational symmetry (if at least three positions 31, 32, and 33 are arranged as an equilateral triangle), thereby allowing for more uniform separation (e.g., shaking) from any direction of impact than would be the case in the "1-2-3" kinematic arrangement, which has only 1x rotational symmetry. With appropriate design, it can still be ensured that the two halves separate regularly from each other, while also ensuring that after the separation event they are guided back to their seated "2-2-2" kinematic position.

[0127] As described in relation to the embodiments described above, a suitable trapping mechanism may also be provided to ensure that the two halves do not completely separate from each other. A simple schematic diagram of one possibility is shown in Figure 24, in which a post 41 firmly fixed to part 10 protrudes through a hole 42 formed through part 20, and as a result when the joint is disseaten as part of an over-stretch event, part 10 rotates at its rear corner or end relative to part 20, but only to a stopping position generated by contact with the post 41 on the other side of part 20, as shown in Figure 25. This prevents part 10 from completely disengaging from part 20, and as a result, part 10 may be able to reseat (a suitable guiding means may be provided to assist in reseat, although not shown). When in the seated position shown in Figure 24, the two parts 10 and 20 can be separated from each other by lifting part 10 directly from part 20 without relative rotation, and the post 41 is sized to fit into the hole 42. Furthermore, in the seated position, a gap exists between the post 41 and the side of the hole 42 so as not to generate any additional contact points that would otherwise lead to inaccurate (or non-kinematic) constraints.

[0128] In any of the embodiments described above, it would be possible to mount the coupling device 30 to the robot 1 via an additional kinematic coupling so that the coupling device 30 can be used in an automated, interchangeable manner with other tools and attachments (such as Renishaw's "Automatic Exchange System") (which would be beneficial in many situations). For example, Figure 26 is a schematic diagram of a modification of the embodiment of Figure 8, in which an additional kinematic coupling 36 is provided between part 20 (of the coupling device 30) and the flange 3 of the robot arm 1. This would allow the coupling device 30 (with or without the probe 14 attached) to be easily and readily interchangeable (as a unit) with other tools (including other types of measuring probes) from, for example, an automatic exchange rack. This concept can be extended to any other embodiment. It should be noted that in the arrangement shown in Figure 26, for a particular type of probe 14, there are effectively three kinematic couplings arranged in a row: the first is provided internally in the probe 14 as part of the probe 14's measuring function (as described above), the second is provided as part of the coupling device 30, and the third will be provided by an additional kinematic coupling 36.

[0129] As already mentioned above, in some designs of contact trigger probes, a reverse kinematic coupling is used internally, but it is used as an inherent part of the contact detection design rather than as a form of over-travel protection itself. The kinematic coupling in the contact trigger probe needs to be highly sensitive to contact, sufficiently repeatable and accurate, and therefore low-force kinematic, meaning it is not subjected to heavy loads. It also needs to be sealed to the environment to prevent dust and other debris from entering between the two halves of the kinematic. This also means that the probe housing needs to be very compact in order to maintain lightness, which is a desirable feature of the probe in any case. Therefore, the range of motion is very narrow and does not provide any effective protection against over-travel in the Z direction (i.e., the direction along the stylus). Where "over-travel" is referred to (in the literature for these devices), this is often a reference to a travel amount greater than the theoretical minimum travel amount of zero, and hereof it is considered equal to the normal range of motion of the probe, rather than over-travel itself.

[0130] One embodiment of the present invention is intended to be used in combination with such a contact trigger probe and to provide, in addition to and independently of, any "over-stroke" that the measuring probe inherently has as part of its design, protection against over-stroke of the measuring probe. Furthermore, since the coupling device embodying the present invention is not intended for measurement purposes, it can therefore be more robust and capable of higher loads. Due to the larger load compared to the load on the kinematics inside the contact probe, debris entering the coupling is not as much of a problem, and therefore the coupling device embodying the present invention does not need to be sealed.

[0131] By mere rough comparison and without any intention to limit, the aforementioned LP2 probe typically has approximately 6.5 mm of usable travel in the Z direction (as part of its contact trigger function in this direction), while the coupling device embodying the present invention typically provides at least 30 mm of over-travel protection for such probes, i.e., over-travel protection in addition to any usable travel provided by the design of the probe itself. A typical stylus for an LP2 probe has a length of 50 mm–100 mm, but rotates within the probe body (in the X, Y directions) for approximately 20 mm beyond the upper end of the stylus, resulting in an effective or typical length between 70 mm and 120 mm. Thus, the travel allowed in the Z direction by such a probe design is approximately 5%–9% of the typical length, while the coupling device would allow for approximately 25%–45% over-travel of the typical length (although this may be greater in different designs). This comparison is for illustrative purposes only, and the exact values ​​will depend entirely on the relevant application and the probe system used.

[0132] It will be understood that the present invention is applicable to types of devices other than measuring devices, for example, devices other than the measuring probe 14 described above, and more broadly, to any device that can be coupled to a coordinate positioning machine and would benefit from over-stroke protection. This applies to contact-type devices that are designed to come into contact with objects in order to perform their intended function and are therefore most likely to require over-stroke protection, but also to non-contact-type devices, because even if contact is not required for normal operation, this does not mean that operating errors in the machine may nevertheless cause false contact between the device and a stationary object. It will also be understood that the present invention is applicable to types of coordinate positioning machines other than robot arms, for example, three-axis Cartesian coordinate measuring machines, non-orthogonal hexagonal coordinate positioning machines, delta robots, selective compliance assembly robot arms (SCARA), etc.

Claims

1. A coupling device for connecting measuring devices to a coordinate positioning machine, wherein the coupling device is adapted to provide over-travel protection to the devices when the devices are moved toward the interface between them with respect to the coupling device.

2. A coupling device according to claim 1, wherein the coupling device is adapted to provide over-cycle protection by causing the device to be at least partially detached from the machine.

3. A coupling device according to claim 2, wherein the coupling device is adapted such that the device remains partially coupled to the machine when the device is in an over-stroke state.

4. A coupling device according to claim 2 or 3, wherein the coupling device is adapted such that the device remains coupled to the machine with at least one degree of freedom when it is in an over-stroke state.

5. A coupling device according to claim 2, 3, or 4, wherein the coupling device is adapted such that when the device is in an over-stroke state, the device is detached from the machine with one degree of freedom and remains coupled to the machine with the other five degrees of freedom.

6. A coupling device according to claim 5, characterized in that the single degree of freedom is a rotational degree of freedom.

7. A coupling device according to any one of claims 2 to 6, wherein the coupling device is adapted to reconnect the device to the machine in the same relative position and orientation as before it was at least partially disconnected when the device is no longer in an over-stroke state.

8. A coupling device according to any one of claims 1 to 7, wherein the coupling device is adapted to provide over-travel protection along a predetermined axis of the measuring device, the predetermined axis being one or more of the Z-axis of the measuring device, the substantially longitudinal axis of the measuring device, and the axis of the measuring device having the minimum available travel.

9. A coupling device according to any one of claims 1 to 8, wherein the coupling device is adapted to provide a kinematic or pseudo-kinematic coupling between the device and the machine.

10. A coupling device according to any one of claims 1 to 9, wherein the coupling device defines six contact points, and these contact points are arranged relative to each other so as to restrain the device with respect to the machine with respect to six corresponding degrees of freedom.

11. A coupling device according to claim 10, characterized in that the six contact points are arranged in a "1-2-3" configuration at three positions.

12. A coupling device according to claim 10 or 11, characterized in that the coupling device is adapted to be disconnected at a single contact point and remain connected at other contact points when in an over-stroke state.

13. A coupling device according to claim 10, characterized in that the six contact points are arranged in a "2-2-2" configuration at three positions.

14. A coupling device according to any one of claims 10 to 13, wherein, if dependent on claim 8, the plane defined by the contact point is positioned at an angle with respect to the predetermined axis of the measuring device, and the angle is acute, for example between 20 and 70 degrees, for example between 35 and 55 degrees, for example about 45 degrees.

15. A coupling device according to any one of claims 10 to 14, wherein, when dependent on claim 8, the contact point is offset from the predetermined axis of the measuring device.

16. A coupling device according to any one of claims 1 to 15, characterized in that it comprises a retaining mechanism adapted to prevent the device from falling completely from the machine and / or detaching.

17. A coupling device according to claim 16, wherein, if dependent on claim 4, the holding mechanism is adapted to prevent the device from being detached from the machine in at least one degree of freedom.

18. A coupling device according to claim 16 or 17, wherein the holding mechanism is adapted to allow the device to be removed from the machine only when it is in a predetermined relative orientation.

19. A coupling device according to any one of claims 1 to 18, wherein the coupling device is adapted to separate when the coupled portions are moved toward each other.

20. A coupling device according to any one of claims 1 to 19, wherein the measuring device is a contact measuring device.

21. A coupling device according to any one of claims 1 to 20, wherein the measuring device is a measuring probe.

22. A coupling device according to claim 21, wherein, if dependent on claim 20, the measuring device is a contact trigger measuring probe.

23. A coupling device according to any one of claims 1 to 22, wherein the coupling device is adapted to provide over-stroke protection by causing the measuring device to be at least partially disconnected from the machine when a force greater than a predetermined force is applied to the device side of the coupling device in the direction toward the interface, wherein the force is a compressive force generated in the measuring device after contact with an object.

24. A coupling device according to any one of claims 1 to 23, wherein the coupling device is adapted to provide over-travel protection by causing the measuring device to be at least partially disconnected from the machine when the measuring device is moved toward the interface with respect to the coupling device by a predetermined distance and / or a predetermined force.

25. A coupling device according to claim 23 or 24, wherein, when dependent on claim 20 or 22, the predetermined force is greater than the minimum contact force required to initiate measurement by the contact measuring device.

26. A coupling device according to any one of claims 1 to 25, wherein the coupling device is adapted such that the measuring device is at least partially disconnected from the machine only after the measuring device has started measuring.

27. A coupling device according to any one of claims 1 to 26, wherein the measuring device comprises a sensor or transducer adapted to sense or measure relative movement between two parts of the measuring device in order to perform a measuring function, the sensor or transducer being operable within a predetermined force range and / or a predetermined range of movement, and the coupling device having a coupling force greater than the predetermined force range and / or a range of movement greater than the predetermined range of movement.

28. A coupling device according to any one of claims 1 to 27, wherein the measuring device provides a first coupling having a first coupling force and / or a first range of motion, and the coupling device provides a second coupling having a second coupling force greater than the first coupling force and / or a second range of motion greater than the first range of motion.

29. A coupling device according to claim 28, wherein, if dependent on claim 20 or 22, the measuring device comprises a stylus and a stylus support, and the first coupling is a coupling such as a kinematic coupling that internally connects the stylus to the stylus support.

30. A coupling device according to any one of claims 1 to 29, characterized in that it comprises a kinematic or pseudo-kinematic coupling for connecting the coupling device to the machine.

31. A coupling device according to any one of claims 1 to 30, wherein the machine is a robot arm or comprises a robot arm.

32. A kit comprising a measuring device and a coupling device according to any one of claims 1 to 31.

33. A coordinate positioning machine comprising a measuring device connected to the machine via a coupling device according to any one of claims 1 to 31.

34. A machine according to claim 33, wherein the coordinate positioning machine comprises a movable support member, and the measuring device is connected to the movable support member via the coupling device.

35. A machine according to claim 34, wherein the coupling device is connected to the movable support member via a kinematic or pseudo-kinematic joint.

36. A machine according to claim 33, 34, or 35, wherein the coordinate positioning machine is a robotic arm.

37. A method for connecting a measuring device to a coordinate positioning machine, the method comprising connecting the device to a movable support member of the machine via a connecting device described in any one of claims 1 to 31.

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