Method of pairing a tool with a coordinate positioning machine

Abstract

Disclosed is a method of confirming the existence of a physical coupling between a moveable support of a coordinate positioning machine and a tool that is intended to be coupled to the support, comprising controlling the machine to move the support in a particular way and detecting whether the tool makes a corresponding movement. The movement imparted to the support may comprise at least one rotational movement of the support and / or at least one translational movement of the support, for example a series of such rotational and / or translational movements.

Description

[0001] Method of Pairing a Tool with a Coordinate Positioning Machine

[0002] The present invention relates to a method of pairing a tool with a coordinate positioning machine, and more generally to a method of confirming the existence of a physical coupling between a moveable support of a coordinate positioning machine and a tool that is intended to be coupled to the support, for example after a pairing process has been performed between the tool and the coordinate positioning machine. The present invention relates particularly, but not exclusively, to a method of pairing a wireless measurement probe or tool setter with a machine tool.

[0003] Computer Numerically Controlled (CNC) machine tools are widely used in manufacturing industry for machining or cutting parts. With such machine tools, it is known to exchange a cutting tool for a measurement probe to enable parts or tools to be measured for set-up or inspection purposes. Such a measurement probe may be a contact probe having a workpiece-contacting stylus for measuring the position of points on the surface of a workpiece, such as described in US4145816 and US4153998. Rather than having a workpiece-contacting stylus, any of these types of probe may instead sense the workpiece using optical, capacitive, inductive (e.g. using eddy currents) or other non-contact techniques.

[0004] Since a measurement probe for use in machine tools is exchangeable with cutting tools, it can be difficult to provide wires or cables to connect the probe’s output signal to the controller of the machine. Consequently, various wireless signal transmission techniques are typically used, including inductive transmission, optical transmission and radio transmission. An example of an optical transmission systems between the probe and the controller of the machine tool is shown in US5150529, while WO 2004 / 057552 provides an example of a wireless measurement probe that communicates with a remote probe interface over a spread spectrum radio link. In order for such a wireless link to be established, to enable real time data transfer between the probe and interface, the probe and interface are typically paired together exclusively. This pairing can be achieved by assigning each measurement probe a unique identity code during probe manufacture. This unique identity code is included with each packet of digital data that is transmitted by the probe. An initial “pairing” procedure is performed by the user, in which an interface associated with a particular machine tool learns the unique identity code of the probe that is to be used therewith. Once paired, that interface will only process data or communications that contain the unique identity code of the paired probe.

[0005] This pairing process prevents an interface from receiving and processing data or communications that originate from any other probes (i.e. probes having different identity codes) that may be in the vicinity, for example in nearby machine tools, and allows multiple interface / probe pairs to be operated in close proximity. The pairing process is intended to ensure the measurement probe communicates only with the probe interface of the machine tool on which it is mounted (i.e. communication with adjacent probe interfaces is prevented).

[0006] In use, a set-up routine would typically be performed in which a measurement probe (e.g. a spindle mountable probe) and the interface are placed in “pairing” mode. The probe and the interface would typically have hard coded pairing communication parameters that are used when either are in the pairing mode. Once initiated, the interface would communicate with any probe that is also in the pairing mode and then a positive action from the user on the probe would initiate the data transaction with the interface. This would then allow the devices to synchronise and communicate using unique parameters. Alternatively, as described in EP2019284A2, the pairing procedure could involve the measurement probe repeatedly transmitting its identity code. In such a case, the interface would search for any identity codes transmitted by an unpaired probe and, when the relevant measurement probe identity code is received, it would be stored by the interface. After pairing, the interface would ignore any data it receives that does not contain the stored identity code.

[0007] The present applicant has appreciated that, in some instances, such a pairing operation may not be performed properly or even at all. In the absence of a failsafe mechanism which would prevent the machine tool operating at all in these circumstances, this could result in serious damage to the machine tool as no control signal is provided to stop motion of the measurement probe when it is driven into contact with the surface of an object. Such machine tool crashes can result in expensive repairs and lengthy down times.

[0008] It can happen that a wireless pairing procedure inadvertently pairs a machine tool with a probe which is resident in another nearby machine tool, or which is waiting to be loaded into the intended machine tool. If that probe remains in range during a probing operation on the intended machine tool, a machine crash could result unless careful probe toolpath programming practices are employed.

[0009] An equivalent scenario exists for a probe which is manually paired and then accidentally left next to the intended machine tool, or placed into the wrong machine tool, although this may be less likely due to the machine operator’s involvement in the process. However, with a predicted growth in automated pairing activities, the opportunity for error is thereby likely to increase. A further equivalent scenario exists for probes which have been correctly paired and are in the intended machine tool, but resident in the incorrect pocket of the tool changer, and so do not actually end up in the machine tool spindle when they are expected to be.

[0010] If the pairing procedure is not performed correctly, it is possible for the measurement probe to continue to communicate with a probe interface of a different machine tool than the one it is mounted on, meaning that the machine tool movement will continue even if the stylus has been deflected, thereby resulting in a machine tool crash that can seriously damage the machine tool. The possibility of a measurement probe mistakenly being paired with the probe interface of the wrong machine tool raises the risk of serious damage or injury due to a machine crash.

[0011] It is desirable to address the above-mentioned issues associated with the pairing of a measurement probe (or indeed any other type of tool) to a machine tool (or indeed any other type of coordinate positioning machine).

[0012] According to a first aspect of the present invention, there is provided a method of confirming the existence of a physical coupling between a moveable support of a coordinate positioning machine and a tool that is intended to be coupled to the support, comprising controlling the machine to move the support in a particular way and detecting whether the tool makes a corresponding movement.

[0013] Such a method provides a quick and convenient way to confirm that the tool (for example measurement probe) is coupled to the support (for example spindle) of the correct coordinate positioning machine (for example machine tool), for example after performing a pairing procedure to pair the tool with the coordinate positioning machine.

[0014] The movement imparted to the support may comprise at least one characteristic movement of the support.

[0015] The movement imparted to the support may comprise at least one rotational movement of the support and / or at least one translational movement of the support, for example a series of such rotational and / or translational movements.

[0016] The movement imparted to the support may be determined so as to be unique, or may at least be determined so as to minimize (or at least reduce) the risk of clashing with a corresponding movement being made by another coordinate positioning machine, for example when also performing a method according to the present invention. The movement imparted to the support may comprise a random or pseudo random movement or sequence of movements.

[0017] The movement imparted to the support may comprise one or more movements selected from a lookup table comprising a plurality of different characteristic movements.

[0018] The method may comprise determining whether the tool has made a corresponding movement using motion signals or derived motion data from at least one motion sensor on the tool.

[0019] The method may comprise determining whether the tool has made a corresponding movement by comparing movement represented by the motion signals or derived motion data with the movement imparted to the support, for example by comparing the motion signals or derived motion data with motion signals or derived motion data expected to result from the movement imparted to the support.

[0020] The method may comprise sending the motion signals or derived motion data from the tool to the machine controller, and using the motion signals or derived motion data at the machine controller to determine whether the tool has made a corresponding movement.

[0021] The method may comprise using the motion signals or derived motion data at the tool to determine whether the tool has made a corresponding movement, and sending a message from the tool to the machine controller based on the determination.

[0022] The tool may be adapted or programmed to recognise a predetermined movement as a trigger, and to send the message in response to the trigger.

[0023] The method may comprise switching the tool into a monitoring mode in which it is expecting to receive and act on movement from the machine via the support.

[0024] The at least one motion sensor may comprise at least one accelerometer, for example at least one linear accelerometer.

[0025] The at least one motion sensor may comprise at least two or at least three accelerometers arranged substantially orthogonal to one another.

[0026] The tool may comprise at least one of: an axial accelerometer for measuring acceleration along an axis of the tool; and first and second radial accelerometers for measuring acceleration respectively in first and second substantially orthogonal radial directions towards the tool axis.

[0027] The machine may be operable to rotate the tool around a rotational axis of the machine.

[0028] The movement may comprise at least one rotational movement about the rotational axis of the machine.

[0029] The tool may be coupled to the support with the axis of the tool substantially aligned with the rotational axis of the machine.

[0030] The support may be provided by an articulating probe head. The rotational axis of the machine may be selected from one or more rotational axes of the probe head.

[0031] The coordinate positioning machine may be a coordinate measuring machine, a measuring robot, or the like.

[0032] The coordinate positioning machine may be a machine tool.

[0033] The support may be a spindle of the coordinate positioning machine. The support may be a moveable table of the coordinate positioning machine.

[0034] The rotational axis of the machine may be a rotational axis of the spindle.

[0035] The tool may be a measurement device such as a measurement probe (e.g. a touch trigger probe, scanning probe or analogue probe) or a tool setter.

[0036] The tool may be a wireless tool (i.e. communicating over wireless communications channel).

[0037] The tool setter may be an optical tool setter (for example, a non-contact laser tool setter).

[0038] The measurement device (e.g. tool setter) may be mounted to a moveable table of the coordinate positioning machine.

[0039] The measurement device (e.g. measurement probe) may be mounted to a spindle of the coordinate positioning machine.

[0040] The measurement device may be a wireless measurement device.

[0041] The method may comprise determining that the tool is physically coupled to the support if it is determined that the tool has made a corresponding movement.

[0042] The method may comprise performing an operation, or preventing the performance of an operation, based on the determination as to whether the tool is physically coupled to the support.

[0043] The movement imparted to the support may be one that is not a normal movement or sequence of movements that the tool would make during normal operation (for example when measuring a workpiece, in the case where the tool is a measurement probe, or when being moved around the working volume, or when being moved to or from a tool changer rack). For example, a rotation around a longitudinal axis of a measurement probe would not typically be a movement which is made during normal operational use of the probe.

[0044] The or each of the movements may be characterised by (and / or distinguishable from each other of the movements) by one or more of: (a) a property of the movement, such as its speed and / or duration; (b) a type of the movement, such as whether it is a clockwise or anticlockwise rotation; (c) a magnitude of acceleration; (d) a direction of acceleration; (e) a speed or velocity of the movement; (f) a direction of the movement; (g) a duration of the movement; (h) a timing of movement; (i) the order of the movement within a sequence of movements; and (j) a temporal relationship between the movement and one or more other movements within a sequence of movements. Whether or not one movement or type of movement is distinguishable from another movement or type of movement is particularly relevant from the perspective of the probe, which is where the detection, identification and analysis of movements takes place. It is also noted that a movement can be characterised by a range of property values (such as a rotation speed between 100 and 200 rpm or a rotation speed greater than 300 rpm or a duration between 3 and 7 seconds) rather than by a specific value of a property (e.g. a rotation speed of exactly 100 rpm) though in practice even a specific property value would typically amount to a small range of values due to measurement and motion control tolerances.

[0045] Movement may comprise rotational and / or translational movement.

[0046] The method may comprise mounting the tool on the machine before controlling the machine to impart the one or more movements to the support.

[0047] The measurement probe may be adapted for measuring the position of points on the surface of an object. The measurement probe may be a contact probe having a deflectable stylus. The measurement probe may be a non-contact probe (e.g. an optical, inductive or capacitive probe). The measurement probe may be a touch trigger probe. The measurement probe may be a scanning or analogue probe. The measurement probe may be configured for measuring a workpiece. For example, the measurement probe may comprise a shank that allows it to be mounted in the spindle of a machine tool; i.e. it may comprise a spindle-mountable measurement probe. The measurement probe may be mountable elsewhere on the machine tool.

[0048] A measurement probe may also be referred to as a dimensional measurement probe, or a probe for sensing the position of (one or more points on) an object.

[0049] The measurement device may be battery operated (e.g. it may include one or more internal batteries for powering the control circuitry, primary wireless communications module etc).

[0050] According to a second aspect of the present invention, there is provided a method of pairing a tool with a coordinate positioning machine, comprising performing a pairing procedure to pair the tool with the machine, followed by a method according to the first aspect of the present invention to confirm that the tool is physically coupled to the support of the machine.

[0051] The pairing procedure may be a wireless pairing procedure.

[0052] The pairing procedure may establish a wireless communications channel between the machine and the tool.

[0053] According to a third aspect of the present invention, there is provided a tool for use in a method according to the first aspect of the present invention, the tool being couplable to the support of the machine and comprising: at least one motion sensor for sensing movement imparted to the tool via the support; and a controller adapted either: (a) to send sensor motion signals or data derived therefrom to the machine controller for use at the machine controller to determine whether the tool has made a corresponding movement; or (b) to use the sensor motion signals or data derived therefrom at the tool to determine whether the tool has made a corresponding movement and to send a message from the tool to the machine controller based on the determination.

[0054] The at least one motion sensor may comprise a transducer that is used for the core function of the tool itself. For example, in the case where the tool is a scanning probe, the transducer may comprise a strain gauge sensor that is used by the scanning probe to measure deflection of the stylus. Or, in the case where the tool is a touch trigger probe, the transducer may comprise a plurality of electrical contacts at least one of which is broken when the stylus is deflected.

[0055] The at least one motion sensor may comprise at least one dedicated motion sensor, i.e. at least one motion sensor that is not used for the core function of the tool itself.

[0056] According to a fourth aspect of the present invention, there is provided a tool or controller or coordinate positioning machine configured to perform or use a method according to the first aspect of the present invention.

[0057] According to a fifth aspect of the present invention, there is provided a computer program which, when run by a computer or a controller, causes the computer or controller to perform or use a method according to the first aspect of the present invention.

[0058] According to a sixth aspect of the present invention, there is provided a computer- readable medium having stored therein computer program instructions for controlling a computer or a controller to perform or use a method according to the first aspect of the present invention.

[0059] Reference will now be made, by way of example, to the accompanying drawings, in which:

[0060] Figure l is a schematic illustration of a machine tool in which an embodiment of the present invention is implemented, showing a drill bit being used to perform machining operations on a workpiece;

[0061] Figure 2 shows the machine tool of Figure 1 having swapped a drill bit for a measurement probe for performing measurement operations on the workpiece;

[0062] Figure 3 provides a more detailed illustration of the measurement probe of Figures 1 and 2;

[0063] Figure 4 provides a more detailed illustration of the drill bit of Figures 1 and 2;

[0064] Figure 5 is a schematic illustration of a method embodying the present invention for confirming the existence of a physical coupling between a machine tool spindle and a measurement probe;

[0065] Figure 6 is a variant of Figure 5 to illustrate what happens in a situation where the measurement probe has been mounted to the wrong machine tool;

[0066] Figure 7 is a variant of Figure 5 in which the processing of motion data is performed at the measurement probe rather than at the machine tool itself;

[0067] Figures 8, 9, 10, 11, 12 and 13 illustrate various different possibilities for the characteristic movements imparted to the spindle for confirming the existence of a physical coupling between the machine tool spindle and the measurement probe;

[0068] Figures 14A, 14B and 14C illustrate how a movement can be characterised by accumulated acceleration; and

[0069] Figures 15A and 15B show a probe mounted in a vertical and horizontal machine tool spindle respectively.

[0070] Figure l is a schematic illustration of a machine tool 1 which would typically be installed in a factory or machine shop environment. The machine tool 1 is primarily intended to perform machining operations on a workpiece 6, which is illustrated in Figure 1 as being loaded onto a base or bed 7 of the machine tool 1. The machine tool 1 comprises a spindle 3, into which a drill bit 2 for performing machining operations on the workpiece 6 is mounted. The spindle 3 is in turn supported by a support member 4 which is itself moved by a movement system 5, thereby enabling the drill bit 2 to be moved into position for working on the workpiece 2. The movement system 5 would typically provide for movement of the drill bit 2 in three degrees of freedom (along three axes) X, Y, Z, and the spindle 3 is controllable to rotate rapidly around its longitudinal axis R in order to cause the drill bit 2 to machine a feature in workpiece 2.

[0071] The movement system 5 is controlled by a machine controller 10, and these elements are connected via communications link 11, which is typically a wired connection. Separately, the machine tool 1 also comprises a probe interface 12, which will be discussed below, and a user interface 14 which is used by the operator to set up and program the machine tool 1 (for example the machine controller 10). To the left side of the window of the machine tool 1 shown in Figure l is a tool holder or rack 8, which is shown holding a measurement probe 20. After the machine tool 1 has finished working on the workpiece 6, or has finished working on a particular feature of the workpiece 6, the machine controller 10 can be used to perform a series of movements which results in the drill bit 2 of Figure 1 being interchanged with the measurement probe 20.

[0072] After such a tool change operation to swap the drill bit 2 for the measurement probe 20, as shown in Figure 2, the machine tool 1 can then be controlled to perform a measurement operation on the workpiece 6 to inspect it and to check that any machined features are within tolerance. During the measurement operation, the spindle 3 and the attached measurement probe 20 would not typically be rotated around its longitudinal axis, because such a movement is not typically required or desirable. During the measurement operation the measurement probe 20 communicates with the probe interface 12 over a separate communications link 13 (for example a radio or optical communications channel), for example to send commands to the probe 20 and / or to receive measurement data from the measurement probe 20. This communications link 13 can be considered to be a primary communications channel for the measurement probe 20, and is the one referred to above in the introductory part of the present application when describing the concept of pairing the measurement probe 20 and probe interface 12.

[0073] Following the measurement operation, if there is further work to be performed on the workpiece 6 then the measurement probe 20 can be swapped for the drill bit 2 (or some other tool held in the tool rack 8) for further machining or processing operations.

[0074] Figure 3 provides a more detailed illustration of the measurement probe 20 of Figures 1 and 2, showing in particular a shank 29 that is adapted to couple with the spindle 3 of the machine tool 1 using a standard releasable shank connector. Although, as mentioned above, the probe 20 is not typically rotated during normal use (e.g. during a measurement operation), the longitudinal rotation axis R is also shown in Figure 4 because this is relevant further below when describing a method embodying the present invention. Figure 4 provides a more detailed illustration of the drill bit 2 of Figures 1 and 2, also having a shank 9 that is adapted similarly to couple with the spindle 3 of the machine tool 1 using the standard releasable shank connector; the longitudinal rotation axis R is also shown in Figure 4.

[0075] Since the measurement probe 20 illustrated in Figure 3 is battery powered, it also comprises a battery compartment 24 into which a battery can be inserted. The measurement probe 20 in this example is a touch trigger type probe and accordingly comprises a workpiece-contacting stylus 22. The measurement probe 20 also has an annular window 26 through which optical signals can be transmitted to and received from the probe interface 12 over the wireless communications link 13 illustrated in Figure 2. The elements illustrated schematically within the window 26 are the optical transmitters and receivers, and associated exposed electronic components.

[0076] Also illustrated schematically in the probe 20 of Figure 3 are one or more movement sensors 21 for use in an embodiment of the present invention to sense movement imparted to the measurement probe 20 via the spindle 3 by the machine controller 10, and a controller 25 for controlling operation of the measurement probe 20, for example to process and / or send signals from the movement sensors 21 back to the probe interface 12 over the communications link 13. As will be explained below, these movement sensors 21 can be used in an embodiment of the present invention as a way of confirming the existence of a physical coupling between the spindle 3 and the measurement probe 20.

[0077] Figure 5 is a schematic illustration of a method embodying the present invention for pairing the measurement probe 20 with the machine tool 1 and for checking that the measurement probe 20 has actually been mounted on the spindle 3 of the machine tool 1.

[0078] In step SI, the machine tool 1 pairs with the probe 20 using a radio pairing routine as described above, thereby establishing a primary (wireless) communications channel. As part of this procedure, the probe 20 would typically first be put into radio pairing mode and the radio interface 12 would be put into an acquisition state (or radio pairing mode). At this stage, although the pairing procedure has been successful, it is not yet known whether the probe 20 is mounted to the spindle 3 of the machine tool 1.

[0079] In this case, when step SI is performed the probe 20 is not yet mounted to the spindle 3, because this happens afterwards in step S2. However, the order of steps SI and S2 could of course be reversed. However, even after step S2 has been performed, it is still not yet known whether the probe 20 has actually been mounted to the spindle 3 of the correct machine tool 1 (which in this case it has). After step S2, a process is commenced to check whether the probe 20 has been mounted to the spindle 3 of the correct machine tool 1. As will become apparent, this is achieved by controlling the machine tool 1 to move the spindle 3 in a particular way and detecting whether the probe 20 makes a corresponding movement. If so, it will have been determined that there is indeed a physical coupling between the probe 20 and the spindle 3 of the intended machine tool 1, i.e. that the probe 20 has been mounted to the spindle 3 of the correct machine tool 1.

[0080] Accordingly, in step S3 it is determined what type of movement is to be imparted to the spindle 3 as part of this process. Any type of movement would be suitable, so long as it is a known type of movement that can be compared later with a sensed movement. For example, there may be a lookup table comprising a plurality of different characteristic movements, and step S3 would comprise selecting one or more of those characteristic movements. In this way, the selected characteristic movements can be considered to represent a pattern or signature, which is later checked against a pattern or signature derived or decoded from movements sensed at the probe 20, as will become more apparent below with reference to steps S9 and S10.

[0081] The movement that is determined in step S3 is preferably unique to the machine tool 1, or is at least determined so as to reduce the risk if it being the same as (or clashing with) that which might be determined by another machine tool 1 which happens to be performing the same routine at the same time (which may happen for example when multiple similar machine tools 1 are switched on at the same time). For example, the movement pattern could be derived or selected based on a unique identity code that is associated specifically with the machine tool 1. The movement(s) determined in step S3 could even be a random or pseudo random movement or sequence of movements, so long as information which characterises the movement(s) is recorded so that it can subsequently be determined (in steps S9 and S10) whether the probe 20 has been made a corresponding movement or sequence of movements based on motion data returned from the probe 20. One benefit of using a random or pseudo random sequence of movements is that there is a low risk of it clashing with that used by another machine tool 1 in the same working environment; it is effectively unique if generated based on a sufficiently large number of possible combinations.

[0082] In step S4 the probe 20 is put into a movement monitoring mode, in which the movement sensors 21 described above are activated and ready to sense movements of the probe 20. This is preferable because motion detection is typically quite power intensive (using up limited battery resources) and therefore it is better to enter this monitoring mode only as and when required. Then, in step S5 the machine tool 1 is controlled to impart the movement(s) determined in step S3 to the spindle 3 (and the probe 20 in this case, because the probe 20 is mounted correctly to the intended spindle 3), for example by using the movement system 5 and / or by rotating the spindle 3 around the rotational axis R, as described above with reference to Figures 1 to 4.

[0083] In step S6, because in this case the probe 20 is mounted to the intended spindle 3, these movement(s) are sensed at the probe 20 by the movement sensors 21, and in step S7 motion data from the sensors 21 are communicated to the probe interface 12 of the machine tool 1 over the primary communications channel 13 established previously in step SI. This motion data is received at the probe interface 12 in step S8.

[0084] In step S9, the received motion data is passed from the probe interface 12 to the machine controller 10, and is processed at the machine controller 10 to determine what movement is represented by the motion data, i.e. what type of movement the probe 20 was making when the motion data was captured. In step S10, the movement(s) represented by the motion data are compared with the movements(s) actually imparted to the spindle 3 in step S5, and if these are determined to match then in step Si l a physical coupling between the spindle 3 and the probe 20 is confirmed, i.e. that the probe 20 has been coupled to the correct machine tool 1. Some action may be performed based on this positive determination, for example to provide an appropriate confirmation on the user interface 14.

[0085] If the result of the comparison in step S10 is negative, then the opposite is confirmed, i.e. that there is no physical coupling between the spindle 3 and the probe 20 and that the probe 20 has likely been coupled to the wrong machine tool 1 (or not coupled to any machine tool 1 at all). This alternative scenario is illustrated explicitly in the flow diagram shown in Figure 6. The steps of Figure 6 are the same as for Figure 5, except that in Figure 6 there are two different machine tools A and B and in step S2 of Figure 6 the probe 20 is mounted on machine tool B whereas the intention was that it would be mounted on machine tool A. Accordingly, while steps S3 to S6 proceed as described above with reference to Figure 5, in step S6 of Figure 6 the movements are not those imparted to the probe 20 by machine tool A as a result of performing step S5 but instead are arbitrary or unrelated movements imparted to the probe 20 by machine tool B (or even no movement). Steps S7 to S10 proceed as described above with reference to Figure 5, but in step SI 1 of Figure 6 the movement(s) represented by the motion data are found not to match the movements(s) actually imparted to the spindle 3 in step S5. Therefore, in step SI 1 of Figure 6 it is concluded that there is no physical coupling between the spindle 3 of machine tool A and the probe 20, and therefore that the probe 20 has likely been coupled to the wrong machine tool 1 (or not coupled to any machine tool 1 at all).

[0086] The flow diagram of Figure 7 illustrates a variation to the procedure described above with reference to Figure 5, though operating according to the same basic principle, which is to control the machine tool 1 to move the spindle 3 in a particular way and detecting whether the probe 20 makes a corresponding movement (and if so, concluding that that there is a physical coupling between the probe 20 and the spindle 3 of the intended machine tool 1). Steps SI to S6 of Figure 7 are performed as described above with reference to Figure 5. However, rather than sending the sensed motion data back to the probe interface 12 in steps S7 and S8 for processing at the machine tool 1 in steps S9 to SI 1 of Figure 5, in the procedure of Figure 7 these steps S9 to SI 1 are carried out instead at the probe 20, for example by the probe controller 25, though also based on the movement(s) sensed in step S6 in an equivalent way. For the comparison carried out in step S10 of Figure 7, the probe 20 would need to know what movements(s) were actually imparted to the spindle 3 in step S5, i.e. what pattern or signature to recognise. This could either be pre-programmed into the probe 20 or it could be sent over the primary (wireless) communications channel 13 for example as part of step SI. In step S12 a confirmation or acknowledgment message is sent over the primary (wireless) communications channel 13 and received at the probe interface 12 in step S13.

[0087] An advantage of the scheme of Figure 5 (compared to that of Figure 7) is that in Figure 5 the probe 20 does not need to know in advance the movement pattern which will be used, and this allows better security of pairing. However, the data transmission is likely to be more complex because the probe is continuously sending quantised data about the motion stimulus to the probe interface 12. The scheme of Figure 7 has an advantage (compared to that of Figure 5) in that data transmission is somewhat simpler, because it is not necessary to transmit a stream of motion data from the probe 20 to the probe interface 12.

[0088] Various possibilities for the characteristic movements of the probe 20, referred to above in relation to step S3, will now be described with reference to Figures 8 to 13. Each of the plurality of possible characteristic movements is distinguishable from each of the other characteristic movements. For example, Figure 8 shows a sequence of rotational movements imparted to the spindle 3 in step S5, each of which is in a clockwise direction for the same duration, but at different respective rotational speeds. As such, each of these movements can be described as a characteristic movement because each movement is distinguishable from each other movement by virtue of the rotational speed, which is detectable either at the probe controller 25 or at the machine controller 10 using motion data from the movement sensors 21. A characteristic movement in this context can also be considered to be an individual one of the rotational movements of Figure 8, or a combination of movements (for example a signature sequence consisting of all five rotations shown in Figure 8, in that order and with those rotational speeds).

[0089] Figure 9 shows a different sequence of rotational movements imparted to the spindle 3 in step S5, each of which is in a clockwise direction, but for different respective durations and at different respective rotational speeds. As such, each of these movements (or a combination of such movements) can be described as a characteristic movement because each movement is distinguishable from each other movement by virtue of both the duration and the rotational speed, both of which are measurable at the probe 20.

[0090] Figure 10 shows another sequence of rotational movements imparted to the spindle 3 in step S5, each of which at the same rotational speed, but in different respective directions (some clockwise, some anticlockwise) and for different respective durations. As such, each of these movements (or a combination of such movements) can be described as a characteristic movement because each movement is distinguishable from each other movement by virtue of both the duration and the rotational direction, both of which are measurable at the probe 20.

[0091] Figure 11 shows another sequence of rotational movements imparted to the spindle 3 in step S5, at different respective rotational speeds, rotational directions and durations. As such, each of these movements (or a combination of such movements) can be described as a characteristic movement because each movement is distinguishable from each other movement by virtue of the rotational speed, rotational direction and duration, all of which are measurable at the probe 20.

[0092] A characteristic movement can also be a rotational movement combined with a translational movement of the probe 20, as illustrated in Figures 12 and 13. In Figure 12, an anticlockwise rotation combined with a movement (acceleration) in the Z direction (in either direction) is used to encode an information bit ‘O’, while in Figure 13 a clockwise rotation combination with a movement in the Z direction (in either direction) is used to encode an information bit ‘ 1 ’ . In this way, a sequence of such characteristic movements can be used to form a signature movement to impart to the spindle 3 in step S5. The bit periods could be of a fixed duration or could be separated by null periods of zero movement.

[0093] A movement of the spindle 3 can also be characterised at least in part by its linear and / or rotational acceleration (in contrast to its linear and / or rotational speed). For example, when considering the Z movement of Figures 12 and 13, this movement in Z could be characterised by its linear acceleration rather than its linear speed. Movement of the machine in the Z direction (which is imparted to the probe 20) would in practice consist of an acceleration phase followed by a deceleration phase as shown in Figure 14A. It is not practical for the machine tool 1 to provide extended periods of high acceleration, since the velocity of the accelerated machine components (including the probe 20) would end up becoming too great. One possible implementation would be to take the absolute output of the linear accelerometer for the Z axis, which is shown in Figure 14B, and for each of the bit periods to derive a cumulative or accumulated acceleration, as shown in Figure 14C. When the accumulated acceleration of Figure 14C reaches a predetermined threshold (as marked in Figure 14C), then the movement is determined to be a characteristic Z movement in the context of Figures 12 and 13. In this way, high accelerations of machine components can be avoided.

[0094] In each of the examples shown in Figures 8 to 13, modulation of angular velocity (rotation) is used to characterise the different movements of the spindle 3. For the examples shown in Figures 12 and 13, modulation of angular velocity (rotation) is combined with modulation of linear acceleration modulation (in the Z direction).

[0095] In summary, the or each of the movement(s) imparted to the spindle 3 (and to the probe 20 if it is properly mounted to the correct spindle 3) may be distinguishable from each other of the movement(s) by one or more of: (a) magnitude of acceleration; (b) direction of acceleration; (c) speed of movement; (d) direction of movement; (e) duration of movement; (f) timing of movement; and (g) order of movement within a sequence of movements. Movement may comprise rotational and / or translational movement.

[0096] A characteristic movement should also preferably be readily distinguishable from other movements that might be made by the probe 20 during normal operation, such as translational movements around the working volume of the machine tool 1. For this reason, it is preferable to use rotation around the longitudinal axis R of the probe 20 to form at least part of a characteristic movement, since this is not a type of movement that would normally be imparted to the probe 20 during normal operational use (except in specific circumstances such as for a measurement cycle in which the probe 20 might e.g. be rotated to deal with stylus runout). However, this is not essential so long as the movements can be distinguished from normal operational movements in some way. A movement (or acceleration) in the Z direction is chosen for the characteristic movements shown in Figures 12 and 13 because some machine tools move the machine table 7 (and workpiece 6) in X and Y rather than the support 4, with the movement system 5 only moving the support 4 (and spindle 3) in a Z direction, and since the idea would ideally work consistently on multiple machine tools 1 with differing acceleration profiles, complex signatures would not be possible. However, it is also possible where appropriate to use translational movements or accelerations in X and Y to characterise (at least partly) a characteristic movement of the spindle 3.

[0097] It will be appreciated that the movement imparted to the spindle 3 in step S5 need not be a series of discrete movements, but could be a continuously-varying movement, so long as the imparted movement can be characterized in some way so as to enable a comparison with the sensed movement in step S10. Furthermore, the movements need not be ones that are performed specifically for the purposes of detecting the existence of a physical coupling. Instead, it would be possible to use the movements that would be performed anyway as a basis for detecting the existence of a physical coupling. For example, a tool change routine would typically have a recognisable pattern or signature of movements associated with it, and this could be used in steps S10 and SI 1 to confirm the presence (or otherwise) of a physical coupling to the correct machine tool 1.

[0098] In the embodiments described above the probe 20 is stated as being mounted to (and moved by) the spindle 3 of the machine tool 1. However, it is also possible that probe 20 is mounted to (and moved by) some other support of the machine tool 1, such as a tool change carousel, or some other part of the machine tool 1. It would not be possible to validate that the probe 20 is actually in the spindle 3 itself, but it would still provide useful validation that the probe 20 is in the machine tool 1. Another example of this would be a tool setter mounted on a moveable machine table (noting that, for such table-mounted devices, accelerations can also be multi-directional).

[0099] Previous implementations of machine tool probes, such as described in WO 2004 / 090467, typically utilise centripetal acceleration experienced by an accelerometer mounted in the probe as a means of detecting axial rotational velocity when the probe is mounted in a machine tool spindle. The detected centripetal acceleration is independent of the direction of rotation and hence the probe is only able to detect the rotation, but not the direction. With an embodiment of the present invention, detection of the direction of rotation (or other characteristic movements) can be used to facilitate more complex functionality. In addition to this, modulation of the angular velocity can also be used as a distinguishing factor. The advent of low power MEMS (microelectromechanical systems) gyroscopes in conjunction with a three-axis accelerometer (so called Inertial Measurement Units) facilitates the determination of rotation direction as well as magnitude, in three rotational degrees of freedom (three rotational axes). When used in conjunction with acceleration information in three linear axes can provide measurement with six degrees of freedom. The implementation of movement sensors 21 would ideally be able to account for the fact that the probe 20 could be mounted in either a vertical machine tool spindle 3, as shown in Figure 15 A, or a horizontal machine tool spindle 3, as shown in Figure 15B. Although motion of the measurement probe 20 can be sensed using dedicated motion sensors 21 as described above, it is also possible to use a measurement transducer that is used for the core function of the measurement probe 20 itself, for example a strain gauge sensor that is used by a scanning probe to measure deflection of the stylus 22, or even a touch trigger type of probe 20 which triggers when electrical contacts in the stylus support are broken when the stylus 22 is deflected. The stylus 22 in such a scheme could effectively be used as a rotational accelerometer, with the stylus 22 being pushed off-centre by centripetal forces as the probe 20 is rotated about the longitudinal rotation axis R shown in Figure 3. For a strain gauge type of probe 20, an output from the strain gauge sensor could be recorded as the motion data referred to above, or a touch trigger type of probe 20 will eventually trigger as the rotational speed is increased and these triggers would form part of the motion data. The deflection of the stylus 20 would be more pronounced the longer the stylus 20 or the more off-centred it is. The weighting of the stylus 20 could even be altered to make it more effective when used in such a scheme by adding small mass that is offset from the rotation axis R, or a pre-existing stylus 20 could be selected that intrinsically has an off-centre mass distribution anyway. It may be that the rotational speed required to gather suitable motion data would be outside the range which is recommended for normal operation of the probe 20, but still within a range in which internal damage will not be caused. Relating this to the flow diagrams shown in Figures 5 to 7, such a scheme might proceed as follows. In step S3, a sequence of movements would be determined consisting of a period of rotational movement sufficient to deflect the stylus 22, followed by a period without any rotation (or rotation at a lower rotational speed which does not deflect the stylus 22 sufficiently), followed by a further period of rotational movement, then a period without rotation, and so on, for example in a random code pattern. This sequence of movements would be imparted to the spindle 3 in step S5, and in step S 10 the sensed movements (determined from the motion data in steps S8 and S9) would be compared against the movement pattern determined previously in step S3. Based on the comparison made in step S10, in step SI 1 it would then be confirmed whether the probe 20 is correctly mounted in the spindle 3 that was subject to these movements in step S5.

[0100] It is noted that an embodiment of the present invention is not limited to use in connection with a measurement probe 20 such as that shown in Figure 3 but is applicable to any suitable tool, such as the drill bit 2 illustrated in Figure 4, so long as the tool is provided with appropriate movement sensors 21 and a controller 25, as well as other appropriate communications components, as illustrated in Figure 4. Such a tool, having active sensors and control circuitry, can be referred to as a smart tool.

[0101] Although an embodiment of the present invention is described above in the context of a machine tool, the same technique can be used with such a probe mounted on other types of coordinate positioning machine. For example, when used with a robot arm, rotation around one or more of the rotary joints of the robot arm can be used to perform the procedure described above in an entirely equivalent manner (to replace rotation of the spindle 3 around axis R as described above). An articulated robot arm would often have a final rotary joint having a rotational axis that is arranged axially in relation to the arm, so this final joint (with attached probe) could be used in a very similar manner to rotation of the spindle 3 in the machine tool embodiment above.

[0102] Furthermore, it will be appreciated that the present invention is not limited to use in the context of a wireless pairing procedure, nor indeed limited to use in the context of a pairing procedure at all. An embodiment of the present invention will find application in other scenarios as a quick and convenient way to confirm that a tool (which could be a measurement probe) is coupled to a moveable support (which could be a spindle) of the correct coordinate positioning machine (which could be a machine tool). One specific application of this concept, as a check that is performed after a pairing procedure to pair a tool with a coordinate positioning machine, is set out in the above embodiments. However, such a check need not be associated specifically with a pairing procedure. For example, such a check could be made at any time to ensure for example that a tool is in the correct tool change pocket, by moving the pocket in a particular way and detecting whether the tool makes a corresponding movement. It will also be appreciated that the tool need not be a wireless tool that requires a pairing procedure to establish wireless communication with the correct interface but could be wired directly to a specific interface. Even in this scenario the present invention would find use for checking that the tool is mounted to the correct part of the machine before an operation is performed, by moving that part in a particular way and detecting whether the tool makes a corresponding movement.

[0103] It will also be appreciated that, when an embodiment of the present invention is used in association with a pairing procedure as described above (for example as a check to ensure that the paired components are the ones that are physically coupled to one another, such as in the case of the probe 20 coupled to the spindle 3), the communications channel that is established by the pairing procedure need not specifically be a radio communications channel but could be any type of communications channel, for example an optical or even wired communications channel. Accordingly, in step SI referred to above, the machine tool 1 could be paired with the probe 20 using an optical pairing routine (which relies on proximity and / or line of sight for security and / or exclusivity of pairing) or just by way of a physical cable (which relies on the physical connection for security and / or exclusivity of pairing). The specific details of the pairing routine are not particularly relevant to the present invention and therefore there is no need for a detailed description herein.

[0104] The machine controller 10 and probe controller 25 may be a dedicated electronic control system and / or may comprise a computer operating under control of a computer program. For example, the machine controller 10 may comprise a realtime controller to provide low-level instructions to the motion system 5, and a PC to operate the real-time controller. It will be appreciated that operation of the coordinate positioning machine 1 can be controlled by a program operating on the machine 1, and in particular by a program operating on a machine controller 10 such as that illustrated schematically in Figure 1. It will also be appreciated that operation of the probe 20 can be controlled by a program operating on the probe 20, and in particular by a program operating on a probe controller 25 such as that illustrated schematically in Figure 4. Such a program can be stored on a computer-readable medium, or could, for example, be embodied in a signal such as a downloadable data signal provided from an Internet website. The appended claims are to be interpreted as covering a program by itself, or as a record on a carrier, or as a signal, or in any other form.

Claims

CLAIMS1. A method of confirming the existence of a physical coupling between a moveable support of a coordinate positioning machine and a tool that is intended to be coupled to the support, comprising controlling the machine to move the support in a particular way and detecting whether the tool makes a corresponding movement.

2. A method as claimed in claim 1, wherein the movement imparted to the support comprises at least one rotational movement of the support and / or at least one translational movement of the support, for example a series of such rotational and / or translational movements.

3. A method as claimed in claim 1 or 2, comprising determining whether the tool has made a corresponding movement using motion signals or derived motion data from at least one motion sensor on the tool.

4. A method as claimed in claim 3, comprising determining whether the tool has made a corresponding movement by comparing movement represented by the motion signals or derived motion data with the movement imparted to the support, for example by comparing the motion signals or derived motion data with motion signals or derived motion data expected to result from the movement imparted to the support.

5. A method as claimed in claim 3 or 4, comprising sending the motion signals or derived motion data from the tool to the machine controller, and using the motion signals or derived motion data at the machine controller to determine whether the tool has made a corresponding movement.

6. A method as claimed in claim 3 or 4, comprising using the motion signals or derived motion data at the tool to determine whether the tool has made a corresponding movement, and sending a message from the tool to the machine controller based on the determination.

7. A method as claimed in claim 6, wherein the tool is adapted or programmed to recognise a predetermined movement as a trigger, and to send the message in response to the trigger.

8. A method as claimed in any one of claims 3 to 7, comprising switching the tool into a monitoring mode in which it is expecting to receive and act on movement from the machine via the support.

9. A method as claimed in any one of claims 3 to 8, wherein the at least one motion sensor comprises at least one accelerometer, for example at least one linear accelerometer.

10. A method as claimed in claim 9, wherein the at least one motion sensor comprises at least two or at least three accelerometers arranged substantially orthogonal to one another.

11. A method as claimed in any preceding claim, wherein the tool comprises at least one of: an axial accelerometer for measuring acceleration along an axis of the tool; and first and second radial accelerometers for measuring acceleration respectively in first and second substantially orthogonal radial directions towards the tool axis.

12. A method as claimed in any preceding claim, wherein the machine is operable to rotate the tool around a rotational axis of the machine.

13. A method as claimed in claim 12, wherein the movement comprises at least one rotational movement about the rotational axis of the machine.

14. A method as claimed in claim 12 or 13, when dependent on claim 11, wherein the tool is coupled to the support with the axis of the tool substantially aligned with the rotational axis of the machine.

15. A method as claimed in claim 12, 13 or 14, wherein the support is provided by an articulating probe head, and wherein the rotational axis of themachine is selected from one or more rotational axes of the probe head.

16. A method as claimed in any one of claims 1 to 14, wherein the support is provided by a spindle of the coordinate positioning machine.

17. A method as claimed in claim 16, when dependent on claim 12, wherein the rotational axis of the machine is a rotational axis of the spindle.

18. A method as claimed in any one of claims 1 to 14, wherein the support is provided by a moveable table of the coordinate positioning machine.

19. A method as claimed in any preceding claim, wherein the coordinate positioning machine is a machine tool.

20. A method as claimed in any preceding claim, where the tool is a measurement device.

21. A method as claimed in claim 20, wherein the measurement device is a wireless measurement device.

22. A method as claimed in claim 20 or 21, wherein the measurement device is a measurement probe or a tool setter.

23. A method as claimed in any preceding claim, wherein the movement imparted to the support is determined so as to be unique, or is at least determined so as to minimize or at least reduce the risk of clashing with a corresponding movement being made by another coordinate positioning machine.

24. A method as claimed in any preceding claim, wherein the movement imparted to the support comprises a random or pseudo random movement or sequence of movements.

25. A method as claimed in any preceding claim, comprising determining that the tool is physically coupled to the support if it is determined that the tool has made a corresponding movement.

26. A method as claimed in any preceding claim, comprising performing an operation, or preventing the performance of an operation, based on the determination as to whether the tool is physically coupled to the support.

27. A method of pairing a tool with a coordinate positioning machine, comprising performing a pairing procedure to pair the tool with the machine, followed by a method as claimed in any preceding claim to confirm that the tool is physically coupled to the support of the machine.

28. A method as claimed in claim 27, wherein the pairing procedure is a wireless pairing procedure.

29. A method as claimed in claim 27 or 28, wherein the pairing procedure establishes a wireless communications channel between the machine and the tool.

30. A tool for use in a method as claimed in any preceding claim, the tool being couplable to the support of the machine and comprising: at least one motion sensor for sensing movement imparted to the tool via the support; and a controller adapted either: (a) to send sensor motion signals or data derived therefrom to the machine controller for use at the machine controller to determine whether the tool has made a corresponding movement; or (b) to use the sensor motion signals or data derived therefrom at the tool to determine whether the tool has made a corresponding movement and to send a message from the tool to the machine controller based on the determination.

31. A tool as claimed in claim 30, wherein the at least one motion sensor comprises a transducer that is used for the core function of the tool itself.

32. A tool or controller or coordinate positioning machine configured to use a method as claimed in any one of claims 1 to 29.

33. A computer program which, when run by a computer or a controller, causes the computer or controller to perform or use a method as claimed in anyone of claims 1 to 29.

34. A computer-readable medium having stored therein computer program instructions for controlling a computer or a controller to perform or use a method as claimed in any one of claims 1 to 29.

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