Working machinery device

Abstract

A touch-trigger probe interface (118; 218; 318; 418) for a machine tool (1) is described, the touch-trigger probe interface (118; 218; 318; 418) including a probe communication portion for receiving probe event information from a touch-trigger probe (104; 204; 304; 404). The machine tool communication portion is also provided for outputting the probe event information to a numerical controller (120; 220; 320; 420) of the machine tool. The machine tool communication portion outputs the probe event information as digital data packets (Tp; Tw), for example, via a digital data bus (222). The digital data packets (Tp; Tw) may include a timestamp and / or the touch-trigger probe interface (118; 218; 318; 418) may receive timing information from the machine tool (1). Also described is a touch trigger probing system and a machine tool system including a probe interface (118; 218; 318; 418).

Description

[Technical field]

[0001] The present invention relates to an apparatus for a machine tool, and in particular to an improved touch-trigger probe interface for a machine tool. The present invention also relates to a probing system and a machine tool incorporating such a touch-trigger probe interface. [Background technology]

[0002] Computer Numerical Control (CNC) machine tools are widely used in the manufacturing industry to cut parts. Such machine tools may also include measurement devices that allow parts or tools to be measured for set-up or inspection purposes. A touch-trigger probe (which is sometimes also called a digital probe) is one known type of measurement device. It is known to mount a touch-trigger probe having a stylus that protrudes into the spindle of a machine tool, among other things, to allow a workpiece to be measured. In such an example, the touch-trigger probe simply acts as a switch, and deflection of the stylus (e.g., when the stylus tip is moved into contact with the surface of an object) causes a trigger signal to be emitted. The machine tool measures the position of the touch-trigger probe in the machine coordinate system (x, y, z) at the moment the trigger signal is emitted, thereby allowing (with appropriate calibration) the position of a point on the surface of the object to be measured. Thus, the touch trigger probe can be repeatedly driven into and out of contact with the surface of a workpiece to make point-by-point position measurements of that workpiece.

[0003] An example of a touch-trigger probe system is described in US Pat. No. 5,399,633. The system includes a touch-trigger probe that may be carried in the spindle of a machine tool, and an associated probe interface that may be mounted on a stationary part of the machine tool. When the touch-trigger probe is "triggered" (e.g. when the stylus touches an object), a trigger signal is passed to the probe interface via a wireless (radio) link. The probe interface also has an output line that is hardwired to a SKIP input of the machine tool controller. Upon receiving a trigger signal from the touch-trigger probe, the probe interface issues a SKIP signal to the controller by changing the state of its output line that is connected to the SKIP input (e.g. by raising it from a low voltage to a high voltage, or vice versa). Upon receiving this SKIP signal, the controller latches or records the current position of the touch-trigger probe in the machine coordinate system (e.g. in x, y, z coordinates).

[0004] In the systems described above, for various reasons there will be a time delay between the actual trigger event (e.g. the physical deflection of the stylus due to touching a point on the surface of an object) and the emission of a SKIP signal by the probe interface. A significant proportion of this time delay may result from a time filtering scheme used in the touch-trigger probe to reduce false triggers; or because the wireless communication protocol used to transmit the trigger information from the touch-trigger probe to the probe interface requires a delay (e.g. for robustness reasons). Software in the machine tool controller which processes the SKIP signal will generate a position offset to take such time delays into account, as part of a calibration procedure. This position offset allows the actual position in machine coordinates at which the probe was triggered to be established. It should be noted that this correction process requires the time delay to be constant, since any variability in the time delay will introduce measurement errors. Thus, up until now, touch-trigger probe systems have been designed to create as constant a time delay as possible (i.e. to ensure that the SKIP signal is emitted at a fixed time interval after the trigger event has occurred).

[0005] However, the inventors have found that the position compensation used to take into account the time delays described above is not always accurate enough. In particular, the position compensation calculation assumes a constant machine speed during the probing move in order to convert the time delay into a position offset. However, it has been found that in certain circumstances the speed of the touch trigger probe is not constant and therefore the position compensation is inaccurate, thereby introducing a source of measurement error. This has been found to be true even for highly accurate machines that are otherwise capable of sub-micron positioning. It is believed that this occurs because the machine tool controller is typically programmed to follow the correct tool path as accurately as possible (i.e. so that it will cut the object into the desired shape), rather than ensuring that the machine tool spindle is always in the commanded place at the commanded time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2004 / 057552 Brochure [Patent Document 2] International Publication No. 2005 / 065884 Brochure [Patent Document 3] European Patent No. 1880163 Summary of the Invention [Means for solving the problem]

[0007] According to a first aspect of the present invention there is provided a touch-trigger probe interface for a machine tool comprising a probe communications portion for receiving probe event information from the touch-trigger probe and a machine tool communications portion for outputting the probe event information to a numerical controller of the machine tool, characterized in that the machine tool communications portion outputs the probe event information as digital data packets.

[0008] The present invention therefore provides a touch-trigger probe interface for use in combination with a machine tool. The probe interface has a probe communications portion enabling it to receive probe event information from an associated touch-trigger probe, for example via a wireless communications link. The communications link between the probe and the probe interface may include a digital wireless transmission system, such as a spread spectrum communications system as described in US Pat. No. 5,399,433. The probe interface also has a machine tool communications portion for outputting the probe event information to a numerical controller of the associated machine tool. The probe event information relayed by the touch-trigger probe interface from the touch-trigger probe to the numerical controller may be, for example, information indicating that a trigger event has occurred due to the touch-trigger probe being moved into a particular positional relationship with a surface of an object.

[0009] It is important to note here that a touch-trigger probe can indicate that a probe event (e.g., a trigger event) has occurred at any time. The time at which the probe event has occurred (and not simply the fact that it has occurred) is important for metrology purposes. In one exemplary embodiment of a touch-trigger probe, a deflectable stylus is connected to an electric switch, and a probe (trigger) event occurs when the switch is opened due to deflection of the stylus (thereby opening an electric circuit). The time at which the probe event has occurred is therefore crucial information, which allows the probe event to be analysed and the position of the point on the surface of the object to be established. Thus, a touch-trigger probe is not a sensor device that can be polled periodically for measurements, but a device that is arranged to report a (asynchronous) probe event that can occur at any time. This is why, prior to the present invention, it was always considered necessary to provide a probe interface that generates a SKIP signal at a specific and invariant time after a probe event has been detected. This allowed the machine tool controller to record machine position data (i.e. describing the location of the touch-trigger probe in the machine tool) upon receiving the SKIP signal. This also relies on establishing a position compensation to take into account the (fixed) delay between the probe event and the SKIP signal being processed by the numerical controller and latching the machine position data, but this has always been thought to be sufficiently accurate. It is only the inventors who realised that such a technique (which relies on the machine tool moving at a constant velocity in the interval between the probe event and the receipt of the SKIP signal by the numerical controller) can introduce measurement inaccuracies.

[0010] As described above, the communication link between the touch trigger probe and the probe interface can include a digital wireless transmission system (e.g. a spread spectrum radio link). However, unlike prior art systems, the machine tool communication portion of the probe interface of the present invention outputs the probe event information as a digital data packet. Thus, the probe event information (e.g. trigger event information) is output digitally to the machine tool's numerical controller, for example via a digital data bus, such as an industrial Ethernet or fieldbus connection. As described below, this enables the probe event information to be sent as a time-stamped digital data packet, in which the timestamp for the probe event relates to a time known by the numerical controller. Alternatively, it enables the probe event information to be provided to the numerical controller in the form of a digital data packet describing machine position data associated with the moment the probe event occurred. Thus, the present invention overcomes measurement accuracy problems associated with prior art touch trigger probe interfaces which route probe event information as a SKIP signal to a dedicated SKIP input of the numerical controller. The probe interface of the present invention may also be easier to install than prior art interfaces and potentially allows more information to be transmitted to and / or from the numerical controller.

[0011] For completeness, it should be noted that so-called scanning probes (also called analogue probes) are also known for use on machine tools. Unlike touch-trigger probes, analogue probes typically provide continuous measurement (e.g. of stylus deflection), thereby allowing a series of measurements to be output at predefined intervals. US Pat. No. 5,399,433 describes a technique that allows an external computer to receive separate streams of scanning probe data and machine position data that are synchronised to a common clock. These data streams can then be combined, although this is not performed in real time. However, the arrangement of US Pat. No. 5,399,433 is not suitable for touch-trigger probes, where probe events can occur at any time.

[0012] It is also important to note that the term "machine tool" refers to machines, such as lathes and machining centers, that are primarily used to cut material, but may also be equipped with measurement probe systems to measure workpieces for inspection or set-up purposes. Such machine tools operate under the control of a numerical controller that runs various cutting and inspection programs. The touch-trigger probe interface of the present invention is therefore an additional component that can be interfaced to the machine tool's numerical controller to add measurement functionality. Machine tools are therefore quite different from dedicated measurement machines, such as inspection robots or coordinate measuring machines (CMMs), that are built to provide only measurement functions.

[0013] Advantageously, the machine tool communication part is configured to communicate with the numerical controller via a digital data bus. In other words, the machine tool communication part includes a digital bus interface. Digital data packets (i.e. containing the probe event information) are thereby passed to the numerical controller via the digital data bus. The digital data bus can be an industrial Ethernet connection. The digital data bus can be a so-called real-time or fast Ethernet connection. The digital data bus can be a so-called field bus. It should be noted that the digital data bus can comply with a particular internationally defined standard (such as, for example, Ethernet), but it can also be a bespoke (manufacturer-specific) data bus.

[0014] Preferably, each digital data packet containing probe event information includes a timestamp indicating the time at which the probe event occurred. In other words, a digital message or data packet emitted by the probe interface to the numerical controller preferably not only indicates that a probe event has occurred, but also includes timing information about when the probe event occurred. Thus, the timestamp indicates when the probe event (e.g. a trigger event) occurred with respect to the position of the machine axes. The digital data packets may include additional information, for example allowing different types of probe events or different probe events to be distinguished from one another.

[0015] The probe interface advantageously has access to timing information from the numerical controller. Thus, the timestamps can relate to clock times known to the numerical controller. Preferably, the machine tool communication part is arranged to receive timing data from the numerical controller of the machine tool (e.g. via a digital data bus). The machine tool communication part can receive such data in various ways. For example, the received timing data can be in the form of a series of digital data packets sent by the numerical controller at known intervals (e.g. at regularly defined intervals). Alternatively, the timing data can comprise a clock message (e.g. a series of clock messages) received from the numerical controller (e.g. via a digital data bus). For example, the probe interface can receive master clock or world time information from the numerical controller of the machine tool. Also, timing signals can be passed to the numerical controller from a master clock external to the machine tool (e.g. provided in the probe interface).

[0016] Conveniently, the machine tool communication portion is configured to receive machine position information in the form of digital data packets. In other words, the numerical controller of the machine tool is capable of sending digital data packets to the machine tool communication portion of the probe interface. These data packets may describe machine position data at a particular instant in time. The digital data packets describing the machine position data may be sent by the numerical controller at defined (e.g. regular) intervals. In other words, the received machine position information conveniently comprises a series of machine position data values ​​output by the numerical controller of the machine tool. The probe interface may include a buffer (e.g. a rolling buffer) for storing the received machine position information. For example, the buffer may store a plurality of machine position data values ​​received by the machine tool communication portion.

[0017] Advantageously, the probe communications portion is configured to receive machine position data directly from a position measuring device (e.g. a position encoder) of the machine tool. While such direct access to measurements acquired by the position measuring device is advantageous, such an arrangement requires that the machine tool is suitably configured to allow such access. However, not all machine tools will provide such access.

[0018] If the probe interface receives machine position information it is able to define a probe event in terms of the machine position at which the event occurred. In other words, time critical information is provided to the numerical controller in the form of a position which defines the probe event, rather than the time at which the event occurred. Thus, the digital data packets output by the machine communications part to report the probe event information are conveniently able to describe the machine position at which the probe event occurred. Thus, a buffer for recording previously measured machine position data may be provided in the probe interface and / or in the numerical controller of the machine tool (as described below).

[0019] The machine tool communications portion outputs probe event information to the numerical controller (e.g. via a digital data bus), but it can also send additional (e.g. non-time critical) data to the numerical controller, for example temperature or probe status data can be passed to the numerical controller.

[0020] A touch trigger probe may monitor for the occurrence of a single probe event, such as, for example, a trigger event that a particular relationship with a surface has been reached. Thus, the probe event information may include a trigger event that indicates that the touch trigger probe has reached a predefined relationship with an object. Alternatively, the touch trigger probe may establish when any one of a number of different probe events occurs. For example, different probe events may occur when different relationships with the object are obtained. For example, a trigger and confirmation measurement process may be implemented as described in more detail below.

[0021] The probe communication part of the probe interface may be of any known type. It may provide a wired connection to a touch trigger probe. Advantageously, the probe communication part includes a wireless communication part for wireless communication with an associated touch trigger probe. The wireless link may be an optical link. The wireless link may be a radio link.

[0022] According to a second aspect of the invention there is provided a touch trigger probing system comprising a touch trigger probe interface according to the first aspect of the invention and a touch trigger probe. The touch trigger probe preferably has a transmitting part for transmitting probe event information to a probe communications part of the touch trigger probe interface. Thus the touch trigger probe and the probe communications part of the probe interface may be of known type.

[0023] The touch-trigger probe can be of any type. The touch-trigger probe can be a non-contact touch-trigger probe. For example, the touch-trigger probe can be a non-contact tool setter. The touch-trigger probe can be a contact touch-trigger probe. For example, the touch-trigger probe can include a deflectable stylus. The touch-trigger probe can be used for workpiece measurement or cutting tool measurement. The touch-trigger probe can be mountable in the spindle of a machine tool. In other words, the touch-trigger probe can be a spindle-mountable touch-trigger probe. The touch-trigger probe can be mountable on the bed of a machine tool. The touch-trigger probe can be mountable on a lathe.

[0024] According to a third aspect of the invention, there is provided a machine tool system including a machine tool having a numerical controller. There may also be provided a touch-trigger probe interface according to the first aspect of the invention. The machine tool may also include a touch-trigger probing system according to the second aspect of the invention. A rolling buffer may be provided for storing a plurality of machine position data values. Advantageously, the numerical controller of the machine tool includes a rolling buffer for storing a plurality of machine position data values. As explained in more detail below, this allows the machine position to be found at a time defined in a timestamped probe event message received from the probe interface.

[0025] Also described in this specification is a touch-trigger probe interface for a machine tool, the touch-trigger probe interface including a probe communications portion for receiving probe event information from a touch-trigger probe and a machine tool communications portion for outputting the probe event information to a numerical controller of the machine tool, the output portion outputting the probe event information in the form of time-stamped digital data.

[0026] Also described herein is a touch-trigger probe interface for a machine tool. The probe interface may include a probe communications portion for receiving probe event information from a touch-trigger probe. The probe interface may include a machine tool communications portion for outputting the probe event information to a numerical controller of the machine tool. The machine tool communications portion may output the probe event information as digital data packets. The machine tool communications portion may output the probe event information via a digital data bus. The probe interface may include any one or more of the individual features described herein, alone or in combination.

[0027] Also described herein is a method for communicating probe event information from a touch-trigger probe interface to a numerical controller of a machine tool. The method includes the step of the probe interface passing the probe event information to the numerical controller in the form of one or more digital data packets. The method may include any of the apparatus or use of the apparatus described herein. [Brief description of the drawings]

[0028] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 illustrates a prior art machine tool and measurement probe apparatus; [Diagram 2] FIG. 2 shows in more detail the connection between the probe interface and the machine tool NC in the prior art system of FIG. 1; [Diagram 3] FIG. 1 illustrates a first embodiment of the invention in which time-stamped probe event information is output via a fieldbus to the NC of a machine tool. [Figure 4] FIG. 4 illustrates how the time-stamped information of FIG. 3 can be produced. [Diagram 5] FIG. 13 illustrates a second embodiment in which the probe interface is configured to receive a clock signal from the NC via an industrial Ethernet link. [Figure 6] FIG. 13 illustrates a third embodiment in which the probe interface receives location information over an industrial Ethernet link. [Figure 7] FIG. 4 shows a fourth embodiment in which the probe interface is connected directly to the drive control bus of the machine tool. [Figure 8] FIG. 8 is a diagram showing the bus configuration of FIG. 7 in more detail. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Referring to FIG. 1, a machine tool 1 is shown diagrammatically having a spindle 2 which carries a touch-trigger probe 4 .

[0030] The machine tool 1 includes various motors 8 for moving the spindle 2 relative to a workpiece 6 positioned on a workpiece holder 7 in the work area of ​​the machine tool. The location of the spindle in the work area of ​​the machine is precisely measured in a known manner using encoders 9. Such encoder measurements provide "machine position data" in a machine coordinate system (x, y, z). A numerical controller (NC) 20 of the machine tool controls the movement of the spindle 2 in the work area of ​​the machine tool and also receives information describing the current spindle position (i.e., machine position data) from the various encoders. It should also be understood that the term numerical controller as used herein means any part of the numerical control system of the machine tool. For example, it can include a programmable logic controller (PLC) and a drive controller, etc. It should be noted that the terms numerical controller (NC), machine tool controller, and controller are used interchangeably herein unless otherwise stated.

[0031] The touch trigger probe 4 comprises a probe body 10 which is attached to the spindle 2 of the machine tool using a standard releasable shank connector. The probe 4 also comprises a workpiece contacting stylus 12 which protrudes from the housing. A stylus ball 14 is provided at the distal end of the stylus 12 for contacting an associated workpiece 6. The touch trigger probe 4 generates a so-called trigger signal when the deflection of the stylus exceeds a predefined threshold. The probe 4 comprises a wireless transmitter / receiver portion 16 for passing the trigger signal to a corresponding wireless receiver / transmitter portion of the probe interface 18. The wireless link can be, for example, RF or optical. In this embodiment, a spread spectrum radio link is provided as described in US Pat. No. 5,399,992. The NC 20 receives machine position data (x, y, z) from the encoder 9 and also has a SKIP input line for receiving a trigger signal (also called a SKIP signal) from the probe interface 18 as will be explained in more detail below. This SKIP input enables machine position data (x, y, z) describing the position of the spindle in the machine coordinate system to be recorded at the moment the probe interface emits a trigger signal to the SKIP input. After appropriate calibration, this enables the position of individual points on the surface of an object, such as the workpiece 6, to be measured. For completeness, it should also be noted that the SKIP input may be given different names on different brands of numerical controllers.

[0032] Referring to FIG. 2, a prior art technique for passing a trigger signal from a probe interface to the controller 20 described with reference to FIG. 1 is illustrated in more detail.

[0033] As explained above, the output from the probe interface 18 is connected to the SKIP input 30 of the controller. The probe interface 18 therefore outputs a SKIP or trigger signal 32 to the SKIP input 30 of the controller when it receives a trigger signal from the touch trigger probe 4. In particular, the probe interface 18 raises the voltage level applied to the SKIP input 30 of the controller 20 to indicate that a trigger event has occurred. The controller 20 therefore monitors its SKIP input 30, and in response to the SKIP signal 32 (i.e. in response to a rising edge associated with a change in voltage on the signal line), it records the current machine position data (x, y, z) and stops further movement of the touch trigger probe.

[0034] As stated above, the probing system (i.e. the measurement probe and the probe interface) does not generate the SKIP signal instantaneously. There will always be some delay between the trigger event (e.g. the stylus contacting the object) and the emission of the SKIP signal. As long as the delay is constant, it is possible to calculate a position correction to take the delay into account. However, as explained above, this position correction is calculated based on the assumption that the touch-trigger probe moves with a constant velocity in the period of time between the trigger event and the emission of the SKIP signal. In practice, it has been found that this assumption is not always correct. In particular, changes in velocity can occur in the period between the trigger event and the emission of the SKIP signal. It has been found that this results in that measurement errors are introduced due to the need to assume a constant velocity in order to calculate the position correction.

[0035] The present invention alleviates the above-mentioned problems by implementing a solution in which trigger signals are communicated to the machine tool controller without using a SKIP input. As will be explained below, each trigger signal is instead passed from the probe interface to the controller in the form of a digital data packet. In particular, trigger event information is passed as digital data to the machine tool controller via an industrial Ethernet connection (e.g. fieldbus). As will also be explained below, the trigger event information contained in the digital packet can be time-stamped with respect to timing signals received from the controller. These time-stamps can be derived in particular from periodic timing messages sent to the probe interface, or by giving the probe interface access to the controller clock via a bus. Alternatively, the probe interface can receive position information collected at known times relative to the controller clock, and can use such position information to establish the actual machine position at the moment the trigger event occurs. These techniques avoid the need to determine position corrections to take into account delays present in prior art systems, and allow the actual position at which the trigger event occurred to be established. This eliminates errors that may occur in prior art techniques due to speed variations. Moreover, connecting the probe interface to the controller via a bus allows other (eg, non-time-critical) information to be passed between the probe interface and the controller.

[0036] Referring to Figure 3, a first embodiment of the present invention is illustrated. In particular, the arrangement shown in Figure 3 replaces the prior art arrangement of probe interface and controller illustrated in Figures 1 and 2.

[0037] There is a numerical controller 120 connected to the probe interface 118 via a fieldbus 122. The touch-trigger probe 104 communicates with the probe interface 118 via a wireless radio link such as that described in US Pat. No. 5,399,633. The numerical controller 120 includes suitable fieldbus hardware including a network port 126 to which the probe interface is connected. The NC 120 is the bus master and the probe interface 118 is the slave device. The numerical controller 120 also includes a memory store or buffer 124 that stores a rolling series of machine position data (i.e. data indicative of the position of the touch-trigger probe in machine coordinates).

[0038] In use, the NC 120 continuously sends a series of digital messages (T1, T2, ... Tn) via the Fieldbus to the probe interface 118. These messages are sent at regular time intervals (T2-T1) and provide a synchronization (timing) reference for both ends of the data link. In other words, the probe interface 118 is provided with timing information that enables it to establish when an event occurred relative to timing events generated by the NC 120. When a trigger event occurs, the probe interface 118 calculates a timestamp (relative to the synchronization reference timing). The fact that a trigger event occurred and a timestamp describing when the trigger event occurred are sent by the probe interface 118 via the Fieldbus to the NC 120 as a digital data packet (Tp).

[0039] With additional reference to FIG. 3, the time stamping technique is illustrated in more detail. In particular, timed messages T1 and T2 are shown being transmitted by NC 120 and received by probe interface 118. Receipt of these messages by probe interface 118 allows probe interface 118 to establish the time when a trigger event (Tp) occurred for timed message T2. Probe interface 118 can then generate and send to NC 120 a time-stamped message describing when the trigger event (Tp) occurred for timed message T2. Because NC 120 transmitted timed message T2 at a known time relative to its local clock, it can then establish when the trigger event (Tp) occurred in its local controller clock time.

[0040] The NC 120 receives the data and, thanks to the timestamp, knows in its local (controller) time when the trigger event occurred. The buffer 124 can then be interrogated to obtain the machine position at the moment the trigger event occurred. In particular, the machine position data points stored in the buffer 124 collected around the relevant time period can be used to line fit and interpolate the machine position associated with the timestamp value. This allows the position of the point on the surface of the object that was contacted by the stylus of the touch trigger probe to be established.

[0041] The probe interface 118 can send only a time-stamped trigger event message to the NC 120, indicating, for example, when the probe changes between a triggered and an untriggered state. However, it is also possible for the probe interface 118 to send additional information to the NC 120 via the fieldbus. The other information can be non-time-critical data, such as probe battery status, measured temperature, probe filter settings, confidence values, etc. This additional metadata can be tagged to the time-stamped digital data packets reporting the trigger event. The probe interface 118 can also receive information from the NC via the fieldbus.

[0042] Additionally, the probe interface 118 may be arranged to send different types of time-critical probe event data to the NC 120. For example, the probe interface 118 may be configured to receive a number of different types of probe event messages from an associated touch-trigger probe.

[0043] For example, if the touch trigger probe 104 is a strain gauge touch trigger probe (e.g., as described in U.S. Patent No. 5,399,933), it may be configured to send two or more types of probe event information to the probe interface 118. For example, a high sensitivity trigger threshold may be set that generates a first type of trigger event (which is more likely to result in the emission of a false trigger), and a lower sensitivity threshold may be set that generates a second type of trigger event (which is less favorable in terms of metrology accuracy, but less likely to result in a false trigger). The probe interface 118 may then send a digital data package to the NC 120, which identifies the type of trigger event that occurred (e.g., a first or second type of trigger event) along with a timestamp that defines when the event occurred. This allows the NC 120 to distinguish between different trigger events and act accordingly. A number of different types of probe event information, such as the different trigger events described above, may be sent to the NC 120 in this manner.

[0044] Following from the above, it would also be possible to implement a confirmation-based measurement process. Consider for example a very sensitive touch-trigger probe and machine tool combination that requires a filter to be implemented before a reliable trigger signal can be generated. Typically such a filter would be time-based (e.g. set to 8ms or 16ms) and would require the touch-trigger probe to remain triggered for this filter duration before a trigger signal is emitted. Instead of waiting the filter duration before emitting a trigger signal, the touch probe could inform the probe interface 118 when a possible trigger is first detected without applying a filter. This could be called a first probe event, and a first time-stamped message could be sent to the NC 120 to report that this first probe event has occurred.

[0045] The touch probe can then also inform the probe interface 118 when a trigger is confirmed as being a reliable trigger, because the trigger event is also produced after application of the filter. This can be called a second probe event, and a second time-stamped message can be sent to the NC 120 to report that this second probe event has occurred. It would also be possible for a confirmation message to be sent to the NC without a time-stamp; that is, only the first probe event describing when the first trigger event is detected can be time-stamped. Thus, the NC 120 can establish machine position data associated with the first probe event, but only use this data to report to the measurement point whether a second (confirming) probe event has subsequently been received. The probe interface 118 can also optionally include a connection to a SKIP input of the NC 120 for safety (but not measurement) or backward compatibility purposes. For example, the probe interface could also send a SKIP signal to the controller's SKIP input when the trigger is confirmed purely to ensure that machine tool motion is stopped at this point. This could be provided as a safety feature in addition to the NC 120 being programmed to stop machine motion in response to a probe event being reported by the probe interface 118 over the fieldbus.

[0046] It should also be noted that the timestamp applied to messages sent by the probe interface 118 to the NC 120 can account for any variation in the delay associated with passing probe event information from the touch probe 104 to the probe interface. As explained in more detail in U.S. Pat. No. 6,399,433, a radio protocol has previously been used in which the output of a trigger signal to the SKIP input of the controller is delayed a fixed time (e.g., 10 ms from the touch event) to ensure radio signal integrity while ensuring a repeatable, low jitter response from the probing system. Among other things, U.S. Pat. No. 6,399,433 describes a radio protocol in which a fixed 10 ms delay allows for retransmission of radio messages from the probe to the probe interface. For example, if the first radio transmission is not received, a second retransmission occurs (e.g., 2 ms later), and if the second retransmission fails, a third retransmission occurs (e.g., 2 ms later). In the majority of cases where the radio signal is good, the signal is correctly received by the probe interface at the first time, and thus this scheme imposes an unnecessary 10 ms delay. This radio protocol may therefore be adapted for use with the present invention by configuring the probe interface 118 to take into account any delays due to retransmissions when calculating the time of a probe event, thus avoiding the need for the interface to impose a fixed 10 ms delay before a probe event is communicated to the NC 120.

[0047] It should also be noted that non-time-critical information may be sent from the probe interface 118 to the NC. For example, temperature information or probe status information (e.g., battery, filter, performance) data. The occurrence of such a non-time-critical event may be communicated via a wireless link to the probe interface 118 and then passed as a digital data packet via the fieldbus to the NC 120. The NC 120 can then alert an operator (e.g., replace the battery) and / or perform a recalibration routine.

[0048] With reference to Figure 5, a variation of the technique described above with reference to Figures 3 and 4 will now be described. There is a numerical controller 220 connected to a probe interface 218 via an industrial Ethernet bus 222. The touch-trigger probe 204 communicates with the probe interface 218 via a wireless radio link such as that described in US Patent No. 5,999,333. The numerical controller 220 includes suitable industrial Ethernet hardware including a network port 226 to which the probe interface 218 is connected. The NC 220 is the bus master and the probe interface 218 is the slave device. The numerical controller 220 also includes a memory store or buffer 224 that stores a rolling sequence of machine position data (i.e. data indicative of the position of the touch-trigger probe in machine coordinates) at known times relative to the master clock.

[0049] The NC 220 includes a communication bus that provides master clock information (which may also be referred to as world time (Wt)) to all devices on the bus. Thus, the probe interface 218 receives this master clock timing data from the NC 220. Thus, the probe interface 218 can timestamp the event with an absolute time value when the trigger event occurs (i.e., the timestamp may be defined in world time). The probe interface can then send the time-stamped trigger event information (Tw) to the NC 220 via industrial Ethernet. The machine position data points stored in the buffer 224 immediately around the timestamp value can then be used to interpolate (or calculate using another suitable technique) the absolute position where the trigger event occurred.

[0050] Referring to Figure 6, a further embodiment of the present invention is illustrated. There is a numerical controller 320 connected to a probe interface 318 via a fieldbus 322. The touch trigger probe 304 communicates with the probe interface 318 via a wireless radio link such as that described in US Patent No. 5,399,633. The numerical controller 320 includes suitable fieldbus hardware including a network port 326 to which the probe interface 318 is connected. The NC 320 is the bus master and the probe interface 318 is the slave device. The probe interface 318 also includes a memory store or rolling buffer 330 for storing a rolling series of machine position data received from the NC 320 via the fieldbus 322.

[0051] In use, the NC 320 is programmed (e.g., through the use of G-code or similar instructions) to send a regular stream of machine position data (P1, P2, P3) to the probe interface 318 via the fieldbus 322. The probe interface 318 stores this machine position data in a rolling buffer 330. The probe interface 318 also timestamps or otherwise relates each received set of machine position data to its local clock. When the probe interface 318 receives a trigger event from the touch-trigger probe 304, this trigger event is also timestamped to the local clock. Thus, the machine position data in the rolling buffer 330 and the trigger event are synchronized to a common (local) clock, which enables the probe interface to calculate the machine position data (Pt) at the time the trigger event occurred. This machine position data (Pt), describing the position of the probe (trigger) event, is then sent by the probe interface 318 to the NC 320 via the fieldbus 322.

[0052] It should also be noted that the NC may be programmed to perform the tasks described above in a variety of ways. The NC may be instructed to output a stream of data to the probe interface using instructions that are built into the NC by the machine tool manufacturer or by user embedded code. For example, the user may embed the appropriate code using a compile cycle or a synchronization action. The exact manner in which this is done will therefore depend on the particular type or configuration of the machine tool being used.

[0053] With reference to Figures 7 and 8 it will be explained how the present invention can be implemented on a machine tool where the probe interfaces share a bus which is also used to control the various drives of the machine tool.

[0054] FIG. 7 shows a machine tool 400 having a numerical controller 420. The NC 420 is connected to a probe interface 418 via an industrial Ethernet bus 422. The touch-trigger probe 404 communicates with the probe interface 418 via a wireless radio link, such as the radio link described in US Pat. No. 5,399,363. It should be noted that the touch-trigger probe 404 will be mounted on the machine tool in use, and FIG. 7 shows it separately, merely to enable its configuration to be described. The numerical controller 420 includes suitable bus hardware, including a network port 426, to which the probe interface 418 is connected. The NC 420 is the bus master, and the probe interface 418 is a slave device. The probe interface 418 also includes a memory store or rolling buffer 430. In this embodiment, the industrial Ethernet system 422 is connected not only to the probe interface 418 and possibly other external devices, but also to the machine tool's own motorized drives 432 and position encoders 434.

[0055] The probe interface 418 is configured to monitor the bus 422 for all communications (not just those related to the probe interface). Thus, the probe interface logs data associated with the drive 432 and the encoder 434. When a probe event occurs (e.g., seated-to-triggered or triggered-to-seated), a timestamp is generated for the clock points T1, T2, or "ticks" used by the bus. Using the drive data points received around the probe event, the probe interface 418 calculates (e.g., by interpolation) a raw machine position (Pr) associated with that probe event. This raw machine position (Pr) is then passed to the NC 420 via the bus 422.

[0056] It should be noted that the machine position data collected over the bus in this way (e.g. collected directly from the encoder 434) is referred to as raw data. This is because the NC 420 typically stores various corrections (e.g. generated during machine tool calibration) that are applied to the raw data to increase the position accuracy of that data. In this embodiment, the probe interface 418 does not have access to such calibration data and can therefore only report the raw machine position (Pr) associated with that probe event to the NC 420. However, the NC 420 can then apply appropriate corrections to the raw machine position (Pr) to generate a corrected machine position value. Alternatively, the calibration data can be passed by the NC 420 to the probe interface 418, or the probe interface 418 can be programmed with calibration data that is calculated separately. For example, the raw machine position data can be manipulated using machine mapping data (e.g. obtained using a Renishaw XM60) to produce an absolute position and this "real" position is sent to the NC 420 over the bus 422.

[0057] It should be noted that the above description merely provides some examples of how the present invention can be implemented. Notably, any type of bus or digital interface can be used to enable a communication link between the machine tool controller and the probe interface. Although a spindle-mounted touch-trigger probe is shown, the present invention will work with any touch-trigger probe. For example, a tool setting or table-mounted touch-trigger probe can also be used. The touch-trigger probe can also be a so-called non-contact probe. For example, it can include a non-contact tool setter, in which a beam of light is broken or not broken by the tool to generate a trigger signal.

Claims

1. 1. A touch-trigger probe interface for interfacing a touch-trigger probe to a machine tool, the touch-trigger probe interface comprising a probe communications portion for receiving asynchronous probe event information from a touch-trigger probe, and a machine tool communications portion for outputting the probe event information to a numerical controller of the machine tool, characterized in that the machine tool communications portion outputs the probe event information as digital data packets including timing information about when a probe event occurred, the probe event information including a trigger event indicating that the touch-trigger probe has reached a predefined positional relationship with an object, the timing information including a timestamp indicating a time (Tp) that the probe event occurred relative to timing data (T2) emitted by the numerical controller.

2. 2. The interface of claim 1, wherein the machine tool communication portion is configured to communicate with a numerical controller via a digital data bus, and the digital data packets are passed to the numerical controller via the digital data bus.

3. The interface of claim 2 , wherein the digital data bus is an industrial Ethernet connection.

4. 4. An interface as claimed in any preceding claim, wherein the received timing data is in the form of a series of digital data packets sent by the numerical controller at regularly defined intervals.

5. 4. An interface as claimed in any preceding claim, wherein the timing data comprises clock messages received from the numerical controller.

6. An interface according to any preceding claim, wherein the machine tool communication portion is arranged to receive machine position information in the form of digital data packets.

7. 7. The interface of claim 6, including a buffer for storing received machine position information.

8. An interface as claimed in claim 6 or 7, wherein the received machine position information comprises a series of machine position data values ​​output by the numerical controller of the machine tool.

9. 8. An interface according to claim 6 or 7, wherein the probe communications portion is arranged to receive machine position data directly from a position measuring device of the machine tool.

10. An interface as claimed in any one of claims 6 to 9, wherein the digital data packets output by the machine tool communications portion for reporting probe event information describe the machine location at which the probe event occurred.

11. An interface according to any one of claims 1 to 10, wherein the machine tool communication portion outputs additional data to the numerical controller.

12. An interface according to any preceding claim, wherein the probe communications portion includes a wireless communications portion for wireless communication with an associated touch-trigger probe.

13. 13. A touch trigger probing system comprising a touch trigger probe interface according to any one of claims 1 to 12 and a touch trigger probe, the touch trigger probe having a transmitting portion for transmitting probe event information to the probe communications portion of the touch trigger probe interface.

14. The system of claim 13 , wherein the touch-trigger probe includes a deflectable stylus.

15. 15. A system according to claim 13 or 14, wherein the touch trigger probe is a spindle mountable touch trigger probe.

16. The system of claim 13 , wherein the touch trigger probe comprises a non-contact tool setter.

17. A machine tool system comprising a machine tool having a numerical controller and a touch-trigger probe interface according to any one of claims 1 to 12 or a touch-trigger probing system according to any one of claims 13 to 16.

18. 20. The machine tool system of claim 17, wherein the numerical controller includes a rolling buffer for storing a plurality of machine position data values.

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