Non-contact tool setting device and method

Abstract

To provide a method and a device for evaluating a tool profile.SOLUTION: A receiver generates a beam intensity signal that describes an intensity of received light. A non-contact tool setting device is attached to a coordinate positioning device such as a machine tool that enables movement of a tool 80 with respect to the non-contact tool setting device. A method includes using the coordinate positioning device for moving the tool 80 with respect to the non-contact tool setting device along a tool inspection path 88. The tool inspection path is selected so that a light beam advances substantially along a circumference of a peripheral edge of the tool 80 to be inspected. When the tool inspection path 88 is passed, beam intensity data, which describes the beam intensity signal generated by the receiver, is collected, and analysis of the collected beam intensity data is used for evaluating a tool profile.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] This invention relates to non-contact tool setting apparatus for coordinate positioning apparatus, and in particular to an improved method and apparatus for measuring the profile of a tool. [Background technology]

[0002] A beam-blocking tool setting device for use with a machine tool is known, for example, from US Pat. No. 5,399,366. A tool setting device of this type comprises a light source which generates a light beam which is directed to a light detector. During a tool setting operation, the machine tool is operated to move the tool in and out of the light beam. Blockage of the light beam by the tool is detected by analysis of the detector output signal and the device generates a so-called "trigger signal" to indicate to the associated machine tool that the light beam has been blocked. Typically, this trigger signal is issued when the light level reaches 50% of the "beam through" condition (i.e. when 50% of the light beam is blocked from reaching the detector). On receipt of the "trigger signal", the machine tool records the position of the tool relative to the tool setting device, thereby enabling a single position on the tool edge to be determined. This measuring operation may be repeated multiple times in order to measure multiple different positions on the edge of the tool one by one. This arrangement thus enables tool sizes, such as tool length and / or tool diameter, to be measured.

[0003] US Pat. No. 5,399,633 describes an alternative method of generating a "trigger signal" during a measurement move in which a rotating or non-rotating tool is moved in and out of a light beam. In particular, US Pat. No. 5,399,633 describes digitizing the detector output signal and identifying minimum and / or maximum values ​​in the digitized data that correspond to one or more teeth of the cutting tool moving in and out of the beam during the measurement move. A digital processor determines in real time whether the minimum / maximum values ​​fit an expected type of curve and issues a trigger signal only if such a fitted curve exceeds a threshold value. In this way, it is possible to measure the position of single points on the tool during their movement in and out of the light beam. For stationary tools, the measured position is on the edge that blocks the light beam. For rotating tools with multiple cutting teeth that are rotated in and out of the beam, the measured position is on the cutting edge with the largest diameter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 6,496,273 [Patent Document 2] European Patent Application Publication No. 1587648 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-described tool setting apparatus thus enables the position of a point on the edge of the tool to be established relatively quickly, thus providing a measurement of the tool length or tool diameter. It is also possible to measure the profile of the tool by repeating a measurement move to measure multiple different points along the edge of the tool, but such a process can be very time consuming (i.e. the tool must be moved in and out of the beam multiple times) and is usually considered impractical. Further details of such prior art tool measurement processes are described below with reference to FIG. 9a. [Means for solving the problem]

[0006] According to a first aspect of the present invention there is provided a method of assessing a profile of a tool using a non-contact tool setting device comprising a transmitter for emitting a beam of light and a receiver for receiving the beam of light, the receiver generating a beam intensity signal representative of an intensity of the received light, the non-contact tool setting device being mounted to a coordinate positioning apparatus enabling the tool to be moved relative to the non-contact tool setting device, the method comprising: (i) using a coordinate positioning apparatus to move a tool relative to a non-contact tool setting device along a tool inspection path selected such that the light beam travels substantially along a periphery of the tool being inspected; (ii) collecting beam intensity data describing beam intensity signals generated by the receiver as the tool inspection path of step (i) is traversed; and (iii) analyzing the beam intensity data collected in step (ii) to evaluate a tool profile.

[0007] Thus, a first aspect of the invention relates to a method for evaluating a profile of a tool using a non-contact tool setting device. The profile evaluated is the shape, position, or dimension of one or more cutting structures of the tool. The non-contact tool setting device includes a beam-break type tool detection system in which a light beam (e.g., a laser beam) emitted from a transmitter (e.g., by a laser diode of the transmitter) is passed through a region of free space to a receiver. The receiver detects the received light (e.g., using a photodiode) and generates a beam intensity signal representative of the intensity of the received light. The non-contact tool setting device is mounted to a coordinate positioning device, such as a machine tool, which can be programmed to move the tool relative to the non-contact tool setting device. The relative movement can be imparted by moving the tool and / or the non-contact tool setting device.

[0008] The method of the invention comprises step (i) of using a coordinate positioning apparatus to provide a relative motion between the light beam and the tool to define a tool inspection path. In particular, step (i) comprises moving the tool relative to a non-contact tool setting apparatus such that the light beam travels along the periphery of the tool. The coordinate positioning apparatus is therefore arranged to move the light beam along a tool inspection path which results in the light beam being scanned along the periphery of the tool. In other words, the tool inspection path is selected such that the light beam is moved in a direction substantially tangential to the periphery of the tool. This should be contrasted with the prior art described above, in which the tool is moved in and out of the light beam (i.e. in a direction substantially perpendicular to the edge of the tool) to obtain the measurement points.

[0009] In the case of a non-rotating (stationary) tool, the tool periphery is simply the edge of the tool to be inspected. If the tool is rotating, the tool inspection path is set to step the light beam along the outermost extent of the rotating tool's edges. Thus, the movement of stepping the light beam along the tool's periphery is also performed in addition to any rotating tool movement (e.g., rotation of the tool around the tool's longitudinal axis), which causes various parts of the tool's periphery to be rotated in and out of the light beam. The movement of stepping the light beam along the tool's periphery is preferably only linear (translational) and does not include any rotational movement. In other words, the tool inspection path preferably defines only linear movements of the tool relative to the light beam (e.g., movements along mutually orthogonal x, y and / or z axes). Depending on the shape of the tool, the tool inspection path may be linear and / or may include one or more curved portions to trace the periphery of a curved tool. The tool inspection path may pass only a portion of the tool to be measured or may pass around the entire periphery of the tool. Preferably, at least a portion of the light beam impinges on the tool during a passage through the tool inspection path, which may include a single pass around the tool periphery or may include multiple passes around the tool periphery, as described below.

[0010] Step (ii) includes sampling the beam intensity signal generated as the tool inspection path is passed, thereby generating beam intensity data. For example, the beam intensity signal may be digitized by an analog-to-digital converter to generate a set of beam intensity data. In other words, the beam intensity signal, which represents the level of beam obscuration, will typically change as the tool inspection path is passed. Step (ii) includes periodically sampling the beam intensity signal to generate beam intensity data to be analyzed. Any suitable sampling rate may be used. For example, for a rotating tool, a higher sampling rate may be used (e.g., to obtain beam intensity data describing the beam obscuration as the tool is rotated). The sampling rate may be changed as the light beam passes through the tool inspection path, allowing more beam intensity data to be collected at a particular area of ​​the tool. It should also be noted that the light beam may pass through the tool inspection path at a single constant speed, or may be moved at different speeds when passing along different portions of the tool inspection path. There may also be one or more dwell periods defined as part of the tool inspection path during which the light beam is not moved relative to the tool (although during such dwell periods the tool itself may still continue to rotate). Beam intensity data collected during such dwell periods is particularly useful when measuring rotating tools (e.g., to allow the positions of multiple points around the periphery of the tool to be measured, such as the edges of different cutting teeth). During such dwell periods it is also possible to obtain more accurate information from the coordinate positioning device regarding the tool position relative to the non-contact tool setting device.

[0011] As described below, the collected beam intensity data contains information about the profile of the tool. Thus, step (iii) includes analysing the beam intensity data using any one of the techniques described below. The analysis may include analysing all of the collected beam intensity data, or may include selecting a subset of the data (e.g., from a region or regions of interest along the tool inspection path). In this manner, the profile of the tool may be assessed.

[0012] The present invention therefore provides a quick and simple technique for measuring the profile of a tool. Instead of measuring multiple points around the tool individually by repeatedly driving the tool in and out of the light beam, as in the touch-trigger type measurement described above, the periphery of the tool can be measured in detail in a scanning type operation that steps the light beam around the periphery of the tool. This makes the tool profiling process quick and simple.

[0013] Advantageously, the tool inspection path is selected such that the light beam follows a path along a nominal position around the tool. In other words, the tool inspection path may be generated using knowledge of a nominal or expected tool profile. For example, the tool inspection path may be generated from tool design (e.g. CAD) data of the tool. The tool inspection path may be selected such that, for a tool that meets its nominal specifications, the light beam is interrupted at a certain pre-set level (e.g. 50%) when the tool passes through the tool inspection path. Thus, deviations in the beam intensity data from the pre-set level indicate that the tool profile deviates from the nominal value. Thus, step (iii) may comprise evaluating whether the collected beam intensity data corresponds to data that would be expected if the profile of the tool to be inspected fits its nominal profile. Deviations exceeding a certain amount may be used to indicate that a required tool tolerance has not been met. Alternatively, the deviations may be used to adjust the assumed dimensions of the tool.

[0014] As explained above, any deviation in the beam intensity data from a preset level (e.g., from a 50% level) can be used to indicate that the tool profile deviates from the nominal value. Also, a calibration process can be performed before the measurement to ascertain the change in the beam intensity signal that would occur when there is a certain displacement in the position of the tool edge in the light beam. For example, a calibration table or function can be generated that describes the relationship between the tool edge position in the beam and the beam intensity signal. It should be noted that the relationship between the tool edge position and the beam intensity signal can be non-linear, especially for larger changes in position in the beam. Such a calibration process can include, for example, moving the tool edge from a position that results in 50% beam obscuration in small intervals (e.g., 10 μm intervals) and recording the resulting beam intensity signal at each position. This type of calibration allows any change in the beam intensity signal (e.g., a shift from 50% to 60% or 50% to 40%) to be translated into an excursion or shift in the tool edge position. In this way, the notional dimensions of the tool can be adjusted based on the measurements obtained.

[0015] Advantageously, step (iii) comprises comparing the beam intensity data collected in step (ii) with previously acquired beam intensity data. The comparison may be a direct comparison of individual beam intensity data values. Alternatively, an indirect comparison (e.g. of minimum intensity values ​​for a rotary tool as described below) may be performed. Conveniently, the previously acquired beam intensity data comprises data collected from a previous measurement of the same tool. For example, the previously acquired beam intensity data may be collected before the tool is used for cutting purposes. Alternatively, the previously acquired beam intensity data may comprise data collected from a measurement of a reference tool having the same nominal profile as the tool. In other words, a "golden" or reference tool nominally identical to the tool being measured may provide a reference or baseline measurement against which the beam intensity data collected in step (ii) is compared. Step (iii) may therefore conveniently provide an indication of whether the tool profile has changed relative to a previous measurement. This may include indicating whether any significant portion of the tool profile has been altered beyond an amount that may impair cutting performance. The indication may therefore comprise raising an error flag when a particular tool profile change occurs.

[0016] The method may be carried out using a non-rotating tool (i.e. the only movement during the measurement may be that of the tool relative to the light beam along the tool inspection path). Alternatively, the tool may be rotated during the measurement. The tool may thus be held on a rotatable spindle of a coordinate positioning apparatus. The tool may include one or more cutting teeth located around its radius. Conveniently, the tool is rotated around its longitudinal axis whilst being moved along the tool inspection path. In this way, during rotation of the tool different cutting teeth are sequentially moved in and out of the light beam, generating minima and / or maxima in the beam intensity data. Step (iii) may thus conveniently comprise identifying minima and / or maxima in the beam intensity data. Identification of such minima and / or maxima may be carried out by digital signal processing methods of the type described in US Pat. No. 5,399,992.

[0017] Advantageously, the tool includes a plurality of cutting teeth. Conveniently, step (iii) includes identifying minimum and / or maximum values ​​associated with each tooth of the tool. In this way, it is possible to assess the profile of each tooth individually. For example, variations in minimum and / or maximum values ​​associated with a tooth that occur as the tool inspection path is passed can be used to assess the profile of that tooth. This allows individual profiling of different teeth of a rotary tool to be performed in a single pass of the tool inspection path. For example, size deviations of individual teeth can be determined using previously acquired calibration data as described above, or any such deviations can be compared to previous measurements. In addition to identifying minimum and / or maximum values, the shape of the minimum and / or maximum values ​​can be used to infer certain tool profile information. Thus, step (iii) can include analysing the shape of the minimum and / or maximum values ​​in order to assess the profile of the tooth that produces the minimum and / or maximum value.

[0018] Advantageously, step (ii) comprises digitising the beam intensity signal to produce beam intensity data. This is carried out using an analogue to digital converter (ADC) to sample the beam intensity signal. A sampling rate of at least 10 kHz is preferably used (e.g. for a tool rotating at 3000 rpm). Conveniently, a sampling rate of at least 100 kHz is used. Sampling frequencies between 100 kHz and 500 kHz may conveniently be used. Step (iii) advantageously comprises analysing the beam intensity data using a digital signal processor (DSP). This may be carried out after all data has been collected or the analysis may commence whilst data is still being collected. As above, a constant sampling rate may be used. Alternatively, the sampling rate may be varied as the tool inspection path is traversed.

[0019] The tool inspection path may be pre-calculated before the coordinate positioning apparatus moves the tool. In other words, the tool inspection path may comprise a pre-programmed path that the coordinate positioning apparatus is programmed to follow before starting step (i). Alternatively to such known path techniques, the tool inspection path may be generated during step (i) using feedback passed from a non-contact tool setting apparatus to the coordinate positioning apparatus. For example, the tool inspection path may be selected to maintain the beam intensity signal within a particular range.

[0020] Any suitable coordinate positioning apparatus may be used to carry out the method. Advantageously, the coordinate positioning apparatus is a machine tool (e.g. a computer numerically controlled or CNC machine tool). Alternatively, the coordinate positioning apparatus may be a coordinate measuring machine (CMM), a flexible gage (such as the Equator system sold by Renishaw plc of Wotton-Under-Edge, UK) or an off-line tool inspection apparatus.

[0021] The non-contact tool setting device used in the method may include separate transmitter and receiver units, each of which may be mounted on a bracket. Alternatively, a single unit including a transmitter and receiver may be provided. The device may include an interface separate from the transmitter / receiver unit or the interface may be integrally formed with such a unit. A processor may be provided for performing step (iii) of the method. An ADC may be provided for performing step (ii). The processor and / or ADC may be located in a separate processing unit, within the interface, or provided as part of the coordinate positioning device.

[0022] Advantageously, the transmitter includes a laser for generating the light. The transmitter may also include optics for providing a collimated light beam. Alternatively, the transmitter may provide a focused (rather than collimated) laser beam. The light beam may have a substantially elliptical or circular profile (e.g., a Gaussian beam profile). The light beam may have a diameter of less than 0.5 mm, less than 1 mm, less than 2 mm, or less than 3 mm.

[0023] A second aspect of the invention comprises an apparatus for performing non-contact tool profile measurement on a coordinate positioning apparatus, the apparatus comprising a transmitter emitting a light beam, a receiver receiving the light beam and generating a beam intensity signal describing the intensity of the light received at the receiver, an analogue to digital converter generating beam intensity data from the beam intensity signal, and a processor for analysing the beam intensity data, the processor being configured to assess a profile of the tool by analysing the beam intensity data generated as the tool is moved along a tool inspection path, the tool inspection path being selected to step the light beam around a periphery of the tool. The apparatus may include any one or more of the features above in the context of a similar method.

[0024] According to a third aspect of the present invention, there is provided a method of measuring a tool using a non-contact tool setting device including a transmitter emitting a light beam and a receiver receiving the light beam, the receiver generating beam intensity signals describing the intensity of the received light, the non-contact tool setting device being mounted to a coordinate positioning device enabling the tool to be moved relative to the non-contact tool setting device, the method comprising the steps of (i) using the coordinate positioning device to move the tool through the light beam, and (ii) collecting beam intensity data describing the beam intensity signals generated by the receiver in step (i), and (iii) comparing the beam intensity data collected in step (ii) with previously obtained beam intensity data, the comparison providing an indication of whether a profile of the tool has changed. Step (i) may include moving the tool along a tool inspection path, the previously obtained beam intensity data may have been created by moving the tool along the same inspection path.

[0025] The invention will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 illustrates a non-contact tool setting device of the present invention. [Diagram 2] FIG. 2 shows a cutting tool with a light beam moved along its periphery. [Diagram 3] FIG. 3 illustrates beam intensity data collected as the path shown in FIG. 2 is traversed. [Figure 4] FIG. 1 illustrates a multi-tooth cutting tool that is rotated while a light beam is moved along an inspection path along its periphery. [Diagram 5] FIG. 5 illustrates beam intensity data collected as the path shown in FIG. 4 is traversed. [Figure 6] FIG. 6 shows intensity minima associated with different teeth of the tool shown in FIG. 5 plotted as a function of position along the inspection path. [Figure 7] FIG. 13 shows a strength minimum curve plotted against previous measurements of the same tool. [Figure 8] FIG. 2 illustrates how a camera is used to capture any particular tool defect. [Figure 9a] FIG. 1 illustrates a prior art tool inspection process. [Figure 9b] FIG. 13 illustrates a tool periphery scan of the present invention. [Figure 9c] FIG. 13 illustrates a tool periphery scan of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Referring to Figure 1, a tool setting apparatus of the present invention is shown. The apparatus includes a transmitter 10 for generating a substantially collimated light beam 12. The transmitter 10 includes a laser diode and appropriate optics (not shown) for generating the collimated light beam 12. Also shown is a receiver 14 for receiving the light beam 12. The receiver includes a photodiode (not shown) for detecting the light beam 12.

[0028] Both the transmitter 10 and receiver 14 are fixed to a common base 20 by posts 18. This arrangement ensures that the transmitter 10 and receiver 14 maintain a constant spacing and orientation relative to one another. The base 20 may then be mounted directly to the bed of a machine tool, or indeed to any suitable part. It should also be noted that various alternative structures for mounting the transmitter and receiver may be used. For example, a common housing may be provided for the transmitter and receiver, and separate transmitter and receiver units may be separately mounted to the machine tool.

[0029] The apparatus also comprises an interface 15 connected to the transmitter 10 and the receiver 14 via an electrical cable 17. The interface 15 provides power to the transmitter 10 and the receiver 14 and also receives the beam intensity signal from the photodiode detector of the receiver 14. The interface 15 includes an analog-to-digital converter (ADC) 18 that samples the analog beam intensity signal generated by the receiver 14 and generates a stream of digital beam intensity values. This stream of digital beam intensity values, also referred to as beam intensity data, is passed to a digital signal processor (DSP) 20 for analysis. The results of the analysis may be passed to a machine tool 30 via a link 28. In this example, the ADC 18 and the DSP 20 are provided in the interface 15, but may be included in any part of the system (e.g., the receiver, the machine tool controller, etc.). So far, the apparatus is similar to that described in US Pat. No. 5,399,992.

[0030] 2 and 3, the tool profile evaluation technique of the present invention will be described for a non-rotating tool. Figure 2 shows a cutting tool 50 including a cutting edge 52. The cutting tool has a nominal tool profile and is held by a moveable spindle (not shown) of a machine tool. The position of the cutting tool and the position of the tool setter within the machine tool are known, and the machine tool can be programmed to move the cutting tool 50 relative to the tool setter.

[0031] In use, the machine tool is configured to move the tool and the light beam initially strikes a first point 54 on the tool periphery. At this initial position, approximately 50% of the light beam is obscured. The tool is then moved and the light beam follows a tool inspection path (as indicated by a pair of dashed lines 56) around the periphery of the tool until it reaches a second point 58. It can be seen that the movement along the tool inspection path is substantially tangential to the periphery of the tool. During movement of the beam along the tool inspection path 56, beam intensity data is collected and stored, generated by the tool setter's ADC 18 from the beam intensity signal.

[0032] Referring now to FIG. 3, beam intensity data 60 is plotted as a function of position P along the tool inspection path. If the machine tool moves the tool at a constant velocity, the relative position along the tool inspection path can be easily inferred from the acquisition time of the beam intensity data. FIG. 3 also shows nominal or predicted beam intensity data 62 that would be expected if a tool of nominal dimensions were moved along the same tool inspection path. The difference between the collected beam intensity data 60 and the predicted beam intensity data 62 provides a measure of how much the tool 50 deviates from its nominal size and shape.

[0033] Referring now to FIG. 4, a rotatable cutting tool 80 is shown having four cutting teeth. It should be noted that three teeth 82a, 82b and 82c are shown in solid lines, while a fourth tooth 82d, which is located on the rear face of the tool shaft in the orientation shown in FIG. 4, is shown in dashed lines. The tool 80 is measured while being rotated about its longitudinal axis R by the spindle of the machine tool on which it is held. The light beam travels around the periphery of the tool along a tool inspection path. In particular, the tool inspection path extends from a first point 84 to a second point 86 around the periphery of the tool. The spatial extent of the light beam as it passes through the path is shown by dashed lines 88. During movement of the beam along the tool inspection path, beam intensity data generated by the ADC 18 of the tool setter is collected and stored.

[0034] FIG. 5 shows a portion of the beam intensity data collected during inspection of a tool as described with reference to FIG. 4. The beam intensity data is plotted as a function of position P along the tool inspection path. Again, this position can be inferred from the time of data collection if the path is traversed at a constant speed. The tool continues to rotate during the measurement, and therefore the beam intensity data includes minima that occur when each one of the four cutting teeth significantly obscures the beam. A series of minima are generated by each of the four teeth in turn as they rotate into the beam. Thus, the minima labeled a, b, c, and d in FIG. 5 correspond to beam obscurations obtained when each of the four different cutting teeth 82a-d respectively obscures the beam. The minima may be identified by the DSP 20 using any of the techniques described in U.S. Pat. No. 6,399,323. Additionally, the DSP 20 may be configured to separate minima obtained from different teeth of the cutting tool.

[0035] FIG. 6 shows the beam intensity at each identified minimum plotted as a function of position along the tool inspection path. In particular, curves 90a, 90b, 90c, and 90d show the minima resulting from teeth 82a, 82b, 82c, and 82d, respectively. It should be noted that only a small amount of collected beam intensity data (i.e., data collected during three rotations of the tool) is shown in FIG. 5, and the curves of FIG. 6 are generated from a large number of such minima. Thus, curves 90a, 90b, 90c, and 90d show the extent to which each of the four different teeth 82a, 82b, 82c, and 82d of the cutting tool obscures the light beam as the tool inspection path is passed by the rotating tool.

[0036] The data plotted in FIG. 6 allows chips or material buildup on any teeth of the cutting tool to be identified. In particular, peak 92 of curve 90d indicates a chip on tool tooth 82d, which results from an increase in the intensity of the minimum associated with tooth 82d because the tip allows more light to pass to the receiver. Similarly, valley 94 of curve 90c indicates an excess material buildup on tooth 82c, which results from a further decrease in the intensity of the minimum associated with tooth 82c because the excess material blocks more light. Additionally, the location of the defect (e.g., chip or excess material) on each tooth may be determined from the location P of the peak and / or valley along the tool inspection path.

[0037] The minimum values ​​shown in FIG. 6 alone allow the presence and location of defects to be determined. It is also possible to compare a plot of the minimum values ​​measured for a certain tool with previously obtained minimum data for that tool, as shown in FIG. 7. In particular, the process of determining the intensity of a certain identified minimum value as a function of the position along the tool inspection path can be repeated multiple times. For example, such minimum value data can be collected from the tool before using it for cutting purposes. Thus, a reference curve 100 can be obtained that provides information about the profile of an unused tool. After the tool has been used in a cutting operation, the measurement process can be repeated using the same tool inspection path. A minimum value curve 102 can then be generated and compared with the reference curve 100. Any differences in the wear and chipping or material build-up on the cutting surface that the curve indicates can also be identified from the difference between the curve 102 and the reference curve 100. The plot difference (i.e., subtracting the curve 102 from the curve 100 or vice versa) can be used to provide a visual indication of any differences that exist.

[0038] With reference to FIG. 8, the addition of a camera for visually inspecting a tool is described. In particular, FIG. 8 shows a tool setter 150 of the type described above, emitting a light beam 152 and mounted on the bed 160 of a machine tool. The tool setter 150 is arranged to inspect a tool 170 held by a spindle 172 of the machine tool when the tool is located in a region 174 of the light beam 152. As described above, the tool setter 150 allows defects 188 in the tool 170 to be identified, and in particular it allows the location of such defects on the tool to be determined. In addition to the tool setter 150, a front-illuminated camera system 180 may also be provided. The camera system emits a white light beam 182 and may take an image of any object located within its field of view 184. The positions of the fields of view 184 are known relative to the tool setter 150, i.e. they are spaced apart by a position difference V.

[0039] In use, the tool setter 150 is used to identify defects 188 on the tool 170. The position of the tool setter 150, the field of view 184 of the camera, and the tool 170 are all known in the machine tool coordinate system. This means that as the machine tool moves the spindle 172, the defect 188 on the tool 170 identified by the tool setter 150 can be located within the field of view 184 of the camera system 180. This allows an image of the tool defect to be captured, and further allows an operator to assess the nature of the detected defect. The tool setter 150 is preferably of the type described above, but may include any tool setter.

[0040] For completeness, a detailed comparison of conventional tool setting techniques to the techniques of the present invention will be presented with reference to Figures 9a-9c.

[0041] With reference to FIG. 9a, a prior art tool measurement process is shown. As explained in the introduction above, the light beam of a prior art non-contact tool setter is moved from an initial position 204 away from the tool 202 towards the tool 202. In practice, the light beam is usually stationary and the tool is moved into the light beam, but the same relative motion occurs as when the light beam is moved. The light beam therefore moves along a path that is substantially perpendicular to the edge of the tool 202 to be measured. In FIG. 9a, the light beam is initially at the start position 204. At a point 206 where the tool 202 obscures 50% of the light beam, a trigger signal is emitted by the non-contact tool setter. The machine tool receives the trigger signal and records the position where the trigger event occurred. This allows the position of a single point 208 on the surface of the tool 202 to be determined. This process can be repeated to measure multiple points of the tool edge.

[0042] FIG. 9b illustrates a tool measurement process according to the invention. As mentioned above, the light beam is directed to a start position 222 on the edge of the tool. In this example, a tool of nominal dimensions would obscure about 50% of the light beam. The light beam then travels along the periphery of the tool from the start position 222 to the end position 224 (the path followed by the light beam is the so-called tool inspection path). Beam intensity data is collected at a number of points 226 along the tool inspection path. The tool inspection path may travel in a continuous motion (e.g., at a constant speed) or the speed may be varied as the path is traversed. It is also possible to dwell at each of the points 226 (i.e., momentarily stop the movement of the light beam relative to the tool) and, optionally, perform an averaging procedure at each point (e.g., to improve the signal-to-noise ratio of the beam intensity data and / or to obtain a more accurate measurement of the position of the tool relative to the non-contact tool setting device).

[0043] For a perfect tool (i.e., a tool that corresponds exactly to the nominal tool profile), 50% of the light beam will be obscured (in this example) at each point along the tool inspection path. For a real tool (a tool that has worn or experienced material build-up during machining), any local deviations in the tool edge position will cause the amount of obscured light beam to differ from the 50% level expected for a nominal tool. In other words, deviations in the beam intensity data from the expected 50 percent at each point 226 indicate that the tool is larger (obscuring more of the light beam) or smaller (obscuring less of the light beam) than expected. The beam intensity data is combined with information from the machine tool describing the position of the light beam 220 at each point 226 to provide multiple measurements of the tool's surface position. In this way, multiple points 226 can be measured in a rapid scanning type motion without the need to move the tool back and forth in the beam, as in the prior art approach shown in FIG. 9a.

[0044] 9c, it is noted that the tool inspection path may include multiple passes around the circumference of the tool. This may be done, for example, if the uncertainty in the nominal position of the tool edge is significantly greater than the width of the light beam.

[0045] FIG. 9c shows a tool inspection journey in which the light beam is moved linearly downward from an initial position 250 to a first position 252. The light beam is then stepped laterally to a second position 254 before being moved linearly upward to a third position 256. It is then stepped laterally to a fourth position 258 before being moved linearly downward to a final position 260. The linear movement between the second position 254 and the third position 256 is sufficient by itself to measure the edge of the tool 264 in its nominal position, but it would not be able to measure a tool displaced from its nominal position by more than a beam width (e.g., to a tool position shown by the tool 266 in dashed outline). However, providing multiple journeys would allow a larger deviation of any such position (or tool size) to be measured. For example, beam intensity data collected as the light beam moves from the fourth position 258 to the final position 260 would allow the edge of the tool 266 in dashed outline to be measured. Of course, it is also possible to use beam intensity data from different passes of the light beam, for example if the tool is curved and different regions of the tool edge are present in different passes of the light beam. As an alternative to such multi-pass techniques, the width of the light beam can be increased.

[0046] Those skilled in the art will appreciate that variations on the above embodiments are possible, for example the method may be performed using a non-contact tool setting device mounted on any coordinate positioning device (e.g., CMM, robot, offline tool inspection system, etc.) as well as a machine tool.

Claims

1. 1. A method of evaluating a profile of a tool using a non-contact tool setting device mounted on a coordinate positioning device including a transmitter for emitting a beam of light and a receiver for receiving the beam of light, the receiver generating a beam intensity signal describing an intensity of received light, the non-contact tool setting device enabling a tool to be moved relative to the non-contact tool setting device, the method comprising: (i) using the coordinate positioning device to move the tool relative to the non-contact tool setting device along a tool inspection path selected such that the light beam travels substantially along a periphery of the tool being inspected; (ii) collecting beam intensity data describing the beam intensity signals generated by the receiver as the tool inspection path is traversed in step (i); (iii) performing a machining operation using said coordinate positioning apparatus and said tool; (iv) using the coordinate positioning device to move the tool relative to the non-contact tool setting device along the same tool inspection path used in step (i); (v) collecting beam intensity data describing the beam intensity signals generated by the receiver as the tool inspection path is traversed in step (iv); (vi) comparing the beam intensity data collected in step (ii) with the beam intensity data collected in step (v) and determining therefrom any changes in the profile of the tool resulting from the machining of step (iii).

2. 2. A method according to claim 1, characterized in that the tool is held on a rotatable spindle of the coordinate positioning apparatus, and the tool is rotated about its longitudinal axis whilst the tool is moved along the tool inspection path in steps (i) and (iv).

3. 3. A method according to claim 1 or 2, characterized in that the tool inspection path comprises a pre-programmed path which the coordinate positioning apparatus is programmed to follow prior to commencing step (i).

4. A method according to any one of claims 1 to 3, characterized in that the sampling rate used to collect the beam intensity data in step (ii) is the same as the sampling rate used to collect the beam intensity data in step (v).

5. 5. A method according to any one of claims 1 to 4, wherein steps (ii) and (v) include collecting the beam intensity data whilst the tool is moved relative to the non-contact tool setting device.

6. A method according to any one of the preceding claims, characterised in that during movement along the tool inspection path in steps (i) and (iv), there is no feedback from the non-contact tool setting device to the coordinate positioning device.

7. A method according to any one of claims 1 to 6, characterized in that step (vi) comprises using the deviations in the profile of the periphery of the tool to calculate one or more adjusted dimensions of the tool, the method comprising the further step (vii) of using the coordinate positioning apparatus and the tool to perform a further machining operation using the one or more adjusted dimensions.

8. A method according to any one of claims 1 to 7, characterized in that the tool comprises a plurality of cutting teeth and is rotating during steps (i) and (iv).

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