Measurement method for non-toothed tools using a non-contact tool setter

Abstract

An improved method is described for measuring dimensions (e.g., diameter) of non-toothed tools, such as grinding tools, e.g., diamond-coated burrs. The method may be implemented in a machine tool, such as a lathe or machining center. The method includes passing a beam of light from a transmitter (10) to a receiver (14). The receiver (14) generates a received intensity signal related to the intensity of the received light. Analysis of variations in the received intensity signal is performed as the rotating tool (40; 88) moves relative to the light beam (12) to allow the dimensions of the tool (40; 88) to be measured. In particular, it may be determined when the received intensity signal exceeds a threshold value for at least a defined duration (Tq), the defined duration being less than the time (Tr) taken for one complete rotation of the tool.

Description

[Technical Field]

[0001] The present invention relates to tool measurement, and more particularly to an improved method using a non-contact tool setting system for measuring non-toothed tools such as grinding tools, burr tools, calibration pins, etc. [Background technology]

[0002] Tool measurement devices for use with machine tools (machining centers, lathes, milling machines, etc.) are known. For example, the so-called NC4 non-contact tool setting system is sold by Renishaw plc, Wotton-Under-Edge, UK. The NC4 device includes a transmitter including a laser source for generating a light beam. The light beam is directed toward a receiver through a region of free space in which a rotary tool can be positioned. During a tool measurement operation, the machine tool to which the tool setter is attached is programmed to move the tool into and / or out of the light beam. An output signal from the receiver indicates the amount of obscuration in the light beam, and the device compares this received intensity signal with a threshold. A so-called trigger signal is generated by the device to indicate that the tool has reached a specific position relative to the beam. The trigger signal allows the machine tool to establish the tool's position, thereby allowing the tool's length or diameter to be measured and / or the tool to be monitored for any damage or wear. U.S. Patent No. 5,629,999 and U.S. Patent No. 5,629,999 describe aspects of the NC4 system. A similar system for tool measurement is also described in U.S. Patent No. 5,629,999.

[0003] As described in more detail below, the NC4 system can operate in a variety of different modes for measuring the dimensions of rotating tools. For example, a so-called light-to-dark tool measurement mode involves moving the rotating tool into the light beam and issuing a trigger signal when the received light intensity first falls below a 50% threshold. In a dark-to-light tool measurement mode, the rotating tool first obscures the light beam before moving the rotating tool out of the beam. In this mode, a trigger signal is issued when the light intensity exceeds the 50% threshold for longer than one tool revolution. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 01 / 38822 Brochure [Patent Document 2] International Publication No. 2007 / 096585 Brochure [Patent Document 3] German Patent Application Publication No. 102005043659 [Patent Document 4] International Publication No. 2018 / 134585 Brochure Summary of the Invention

[0005] While the above-described NC4 system is capable of measuring the cutting dimensions of various types of tools, it is primarily designed for use in measuring toothed cutting tools that include a small number of radially dispersed cutting teeth separated by flutes. The inventors have discovered that such prior art tool measurement techniques are not optimal for certain measurement tasks. In particular, the inventors have found that defects commonly found in unused diamond burrs, for example, can protrude significantly farther from the tool shaft than the multiple abrasive diamond particles that define the relevant grinding dimensions of an in-use burr tool. This, the inventors have discovered, can result in unexpected and significant errors in measuring the effective dimensions (e.g., diameter) of such tools using the above-described prior art tool measurement techniques. The present invention aims to alleviate at least some of the shortcomings of prior art measurement techniques.

[0006] According to a first aspect, there is provided a method of measuring at least one dimension of a non-toothed tool using a tool measuring device including a transmitter and a receiver, the transmitter generating a beam of light directed to the receiver, the receiver generating a received intensity signal related to an intensity of the received light, the method comprising: (i) rotating the non-toothed tool about its longitudinal axis while also moving the non-toothed tool relative to the light beam; (ii) determining at least one dimension of the non-toothed tool by analyzing variations in the received intensity signal that occur during step (i); The signal analysis performed in step (ii) includes determining when the received intensity signal exceeds a threshold value for at least a specified duration, the specified duration being characterized as being less than the time it takes for one complete revolution of the non-toothed tool.

[0007] Accordingly, the present invention relates to a method for measuring at least one dimension (e.g., tool diameter, tool length, etc.) of a non-toothed tool using a tool measuring device. In one particular embodiment, the method may be used to measure a rotary (non-toothed) grinding tool on a machine tool prior to the first use of such tool to wear or grind a workpiece. A tool measuring device for implementing the method includes a transmitter and a receiver. In use, a beam of light passes from the transmitter to the receiver. The amount of light reaching the receiver is measured, and a received intensity signal is generated having a value that varies related to (e.g., proportional to) the amount of light received. The tool can be moved in and out of the region between the transmitter and receiver, thereby obscuring (fully or partially) the light beam. Such tool measuring devices are often referred to as optical "break-beam" tool measuring devices or non-contact tool setters.

[0008] The method includes step (i) of rotating a non-toothed tool while moving it relative to the light beam and step (ii) of analyzing the received intensity signal during the movement of step (i). As described below, step (i) may include moving the non-toothed tool into the light beam (so-called light-dark measurement) and / or moving the non-toothed tool out of the light beam (so-called dark-light measurement). In addition to such movement of the tool relative to the light beam (i.e., into or out of the light beam), the tool is also rotated about its longitudinal axis during the measurement (e.g., by the spindle of an associated machine tool on which it may be held). This tool rotation also causes protrusions from the non-toothed tool to periodically move in and out of the light beam during each rotation, depending on the tool's position relative to the beam. Analysis of the received intensity signal is then used in step (ii) to establish the dimension (or dimensions) of the tool. In other words, the size (e.g., radius, length, etc.) of the tool or a specific feature of the tool is established. This analysis of the fluctuations in the received intensity signal may be performed by a processor and, in one embodiment, may be provided as part of a tool measurement device.

[0009] The present invention features a step of determining when the received intensity signal exceeds a threshold for at least a defined duration. The threshold may be set to a specific level relative to a (maximum) received light level, such as the intensity signal received when the light beam is not completely blocked. For example, a threshold level of 50% of the maximum light level may be used. The defined duration is set to be shorter than the time it takes for one complete rotation of the tool (i.e., 360° of tool rotation or revolution). Instead of using a single threshold-crossing event for tool measurement purposes, the present invention instead determines when the threshold is crossed and remains crossed for a specific (predefined) period. The period (i.e., the defined duration) that the threshold must remain crossed is set to be shorter than the time it takes for one complete rotation of the tool. As described below, different defined durations may be used for different types of measurement applications. It should also be noted that the defined duration is set relative to the speed of tool rotation (i.e., the time it takes for one complete tool rotation) and therefore can be adjusted by changing the speed of tool rotation and / or changing the absolute time period used to analyze the received intensity signal. In a preferred embodiment, the processor issues a trigger signal (which can be passed to an associated machine tool, for example) as soon as the received intensity signal exceeds a defined duration threshold. The position of the tool upon receiving such a trigger signal can then be measured (for example, by the associated machine tool) to provide a tool dimension measurement.

[0010] An advantage of the method of the present invention is that certain protrusions from the tool (e.g., contaminants on a calibration tool or chunks of unwanted material on a diamond-coated burr tool) can be excluded from the tool measurement. For example, the known NC4 device described above implements both dark-light and light-dark measurement modes. In the prior art light-dark mode, a rotating tool is moved toward the light beam, and a trigger signal is issued when the received intensity signal first falls below a 50% threshold. In the prior art dark-light mode, the tool starts in a position within the light beam and moves out of the beam. In this mode, the received intensity signal is changed as the tool is moved out of the beam, and a trigger signal is issued after the received intensity signal exceeds a 50 percent threshold throughout the entire tool rotation (i.e., indicating that the entire tool is sufficiently far from the light beam). Thus, both prior art NC4 measurement modes measure the maximum radius (or outermost flying circle) of the tool, rather than the tool dimension (e.g., effective tool radius) that is intended to be measured, even if the protrusions result from tool protrusions (e.g., contaminants or non-grinding defects).

[0011] In contrast to the prior art method implemented by the NC4 machine described above, the present invention allows for the exclusion of such defects or contaminants from tool measurement by determining when the threshold is first crossed for a defined period of time. In other words, the present method does not simply use a single threshold-crossing event for tool measurement; instead, it evaluates when the threshold is crossed for a specific period (i.e., a defined duration) during one tool revolution. The threshold may be crossed continuously for the defined duration. Alternatively, the threshold may be crossed discontinuously for the defined duration (i.e., there may be multiple periods when the threshold is crossed during one tool revolution that equal or exceed the defined duration). By setting the defined duration shorter than the time it takes for one complete tool revolution, threshold crossings resulting from convex defects (e.g., contaminants, non-abrasive defects, oversized abrasive grains, etc.) that are desired to be excluded from tool measurement can be ignored. This provides a more robust, reliable, and adaptable tool measurement method that is well suited for measuring grinding tools.

[0012] The same method can also be used to detect concave defects. In particular, such concave defects can be measured by setting the defined duration to a small percentage (e.g., less than 20% or less than 10%) of the time it takes for one rotation of the tool. Examples of concave defects can include surface cavities on non-toothed tools. Bald spots on grinding tools or defective patches (such as missing diamonds in certain parts of a diamond-coated tool) can cause such concave defects. Such concave defects (cavities or dents) in the tool may not affect the overall geometric measurement of the tool, but they may reduce the surface quality of the workpiece or shorten the tool's lifespan.

[0013] The method can be used to measure one or more dimensions (e.g., tool radius, tool length, etc.) of any non-toothed tool. Non-toothed tools can include calibration tools (also called calibration pins, sometimes used for calibration rather than workpiece machining) or grinding tools for workpiece machining (i.e., tools that remove material from a workpiece by a polishing or grinding process). In this context, a toothed tool refers to a cutting tool that includes one or more distinct cutting teeth, which may be separated by flutes (i.e., recesses or channels for removing cutting debris, coolant, etc.). A non-toothed tool is therefore a tool that does not include such cutting teeth. A non-toothed tool can have a nominally circular profile (but with multiple small protrusions or particles for wearing the surface). A non-toothed tool may also be nominally rotationally symmetric.

[0014] In a preferred embodiment, the non-toothed tool comprises a (non-toothed) grinding tool. As used herein, the term "grinding tool" should be understood to include any type of abrasive tool used to grind, remove, or file material from a workpiece by a grinding (i.e., polishing rather than cutting) process. In other words, the term grinding encompasses techniques such as polishing, lapping, burnishing, honing, superfinishing, and linishing. A grinding tool may be a burr (also spelled "bur") tool, a grinding wheel, a core drill, and the like. A grinding tool may have a nominally circular cross-sectional profile. A grinding tool may also be nominally rotationally symmetric. A grinding tool may have a nominally continuous outer surface or may include one or more longitudinal slots to aid in the evacuation of cooling water or cutting debris.

[0015] The grinding tool may be of any type that abrades material from the object being processed. The grinding tool may include a shaft with a roughened surface or a roughened coating applied to a central shaft. The grinding tool may include a plurality of abrasive particles or grit pieces embedded within or coated on a substrate (e.g., in the form of a rod or shaft). Such substrates may be vitreous, glass, resin, metal, or any suitable combination of materials. The grit may include abrasive or superabrasive particles. The grit may include particles such as diamond, cubic boron nitride (CBN), aluminum oxide, iron oxide, etc. Any such grit particles may be held in the particle matrix by a (e.g., softer or less abrasive) retaining material. As described below, this method is particularly suitable for use in measuring grinding tools formed by electroplating processes (i.e., electroplated grinding tools) because blisters are often produced during such tool manufacturing processes. In the example outlined below, a method is implemented to measure grinding tools in the form of grit-based grinding burrs, specifically diamond coated burrs (DCB).

[0016] The non-toothed tool may alternatively include a calibration tool or pin. Such a calibration tool may be a precision-manufactured rod with a nominally circular cross-section and a smooth outer surface used for calibration purposes. The calibration tool may also include a datum sphere or hemisphere. The calibration tool may also include a measurement probe with a stylus. Such a stylus may include a shaft with a tip in the shape of a ruby ​​or diamond sphere.

[0017] Those skilled in the art will select a defined duration for use in the method appropriate for the particular tool measurement being performed. As noted above, a preferred use of the method of the present invention is to measure abrasive tools, such as burr tools, having multiple (e.g., grit-like) abrasive elements. In such an embodiment, the defined duration used by the processor may be selected to allow a dimension (e.g., effective radius) of the burr tool to be measured that is unaffected by any (non-abrasive) masses of material present on the tool (e.g., resulting from manufacturing defects). In other words, the defined duration may be selected to allow the effect of any protruding masses formed on the surface of the diamond-coated burr tool to be substantially excluded from at least one dimension determined in step (ii). As described below, the defined duration used in the method of the present invention may also be selected for contamination or dirt removal purposes (e.g., to eliminate the effect of dirt that may adhere to the tool on tool dimension measurements).

[0018] The defined duration may be adjustable (e.g., user or manufacturer adjustable). For example, the device may be programmed (e.g., by the user / manufacturer) with the defined duration to be used for the analysis. In particular, the device may include a processor for the analysis, and an appropriate command to set the defined duration may be sent to the processor. As described above, the defined duration depends on the tool rotational speed used during the tool measurement. Therefore, the defined duration may be set by adjusting a clock signal or timing signal (e.g., in the processor) used to analyze the received intensity signal and / or by changing the tool rotational speed. Therefore, adjusting the defined duration may include adjusting the tool rotational speed. The tool may rotate at a high speed during the measurement. For example, the tool may rotate at more than 200 revolutions per minute (rpm), more than 1000 rpm, more than 5000 rpm, more than 10,000 rpm, more than 20,000 rpm, more than 40,000 rpm, more than 60,000 rpm, or more than 100,000 rpm. The defined duration may be expressed, for example, as a time value (e.g., microseconds or milliseconds) or as a fraction (e.g., percentage) of the time taken for one revolution of the tool. The callup command line used to execute the method of the present invention may include a variable that defines the defined duration as a fraction (e.g., percentage) of the time taken for one revolution of the tool. The defined duration is conveniently set based on the particular tool or tool type being measured. The method may be repeated on the same tool multiple times using different defined durations (e.g., to exclude or include surface features of different sizes).

[0019] Advantageously, the defined duration is greater than 1% of the time taken for one rotation of the tool. More preferably, the defined duration is greater than 2%, or greater than 5%, or greater than 10%, or greater than 20%, or greater than 25% of the time taken for one rotation of the tool. Advantageously, the defined duration is less than 99% of the time taken for one rotation of the tool. More preferably, the defined duration is less than 95%, or less than 90%, or less than 80%, or less than 75%, or less than 50% of the time taken for one rotation of the tool. The defined duration may be less than 25%, less than 10%, or less than 5% of the time taken for one rotation of the tool, allowing, for example, recessed defects to be measured.

[0020] The analysis of step (ii) may determine whether the threshold is crossed continuously or non-continuously for a defined duration of each tool rotation period. For example, step (ii) may include determining whether the received intensity signal continuously exceeds the threshold for at least the defined duration. Alternatively, step (ii) may include establishing the total (resulting) duration per rotation that exceeds the threshold (i.e., even if this includes multiple individual periods that exceed the threshold). This may be done by identifying each time the received intensity signal crosses the threshold (e.g., above or below the threshold, as appropriate) and determining when the total duration exceeds the defined duration. Any other suitable analysis technique may be implemented. The time of threshold crossing during each rotation may also be recorded and used to identify or map the location of any defects on the non-toothed tool.

[0021] As described above, the method may include so-called light-dark tool measurement. In other words, step (i) may involve moving a rotating, non-toothed tool from a position away from the light beam into the light beam. Therefore, analysis of fluctuations in the received intensity signal may occur as the rotating tool is moved from a position away from (i.e., outside) the light beam into the light beam. In this configuration, the light beam is initially unobstructed, and the received intensity signal therefore assumes a maximum value (e.g., 100%). Once the rotating tool enters the beam, protrusions from the tool periodically enter the light beam as the tool rotates. As the tool continues to move into the light beam, the received intensity signal decreases and may even temporarily fall below a threshold value (which may be set to 50% of the maximum intensity).

[0022] In the prior art light-dark mode measurement described above, the received intensity signal is monitored to determine when it first falls below a threshold. Instead, the method of the present invention determines whether the received intensity signal falls below a threshold and remains below that threshold for at least a defined duration. The received intensity signal may remain below the threshold for the defined duration. Alternatively, the received intensity signal may fall below the threshold and rise above the threshold multiple times during one rotation of the tool, with the total time the received intensity signal remains below the threshold at least equal to the defined duration. The tool position is measured when this criterion is met, providing the required measurement of the tool dimension.

[0023] Thus, when performing light-dark tool measurement, the method of the present invention effectively ignores any temporary dips in the received intensity signal having a duration shorter than a defined time duration. Instead, a trigger signal is established when the light beam becomes sufficiently obscured such that the received intensity signal falls below the threshold for a time equal to or greater than the defined time duration. In one embodiment, a trigger signal is issued by the processor of the tool measurement device when the received intensity signal falls below the threshold for the defined time duration. The trigger signal can be used by an associated machine tool equipped with the tool to provide a measurement of the tool position from which tool dimensions can be established.

[0024] It should be noted that when performing light-dark tool measurements, it is possible to additionally implement a so-called drip rejection filter. In prior art configurations, this filter issues a trigger signal only if a threshold-crossing event is followed by a second such event that is temporally separated from the first by a time interval equal to one complete tool revolution. This ensures that droplets of coolant or other liquids that may temporarily pass through the light beam, which do not typically occur at regular intervals, are not mistakenly interpreted as the presence of a tool in the light beam. A similar drip rejection filter can be used in the present invention. In other words, a trigger signal can be issued only if a first event in which the received intensity signal is below the threshold for a defined duration is followed by a second such event after a time interval equal to one complete tool revolution.

[0025] This method may include so-called dark-light tool measurement. In other words, step (i) may include moving the rotating non-toothed tool out of the light beam. This measurement may be performed instead of, or as well as, light-dark measurement. For such measurements, the fluctuations in the received intensity signal are analyzed as the rotating tool positioned within the light beam is moved out of the light beam. In such a configuration, the light beam is initially obstructed (e.g., completely blocked to block all light from the transmitter to the receiver), and therefore the received intensity signal initially assumes a minimum or zero value. As the rotating tool begins to exit the beam, protrusions from the tool (blisters, dirt, etc.) periodically leave and re-enter the light beam as the tool rotates. As the tool continues to move out of the light beam, the received intensity signal generally rises (note that there may be slight flicker in the signal from the grinding tool due to multiple abrasive particles on the tool surface), but there are periodic drops or dips in the signal due to protrusions re-entering the beam. Thus, during each tool revolution, there may be times when the intensity of the received light exceeds a threshold (which may also be set to 50% of maximum intensity) and times when it is below the threshold. In the prior art dark-light mode measurement described above, the received intensity signal is monitored to determine when the received light intensity exceeds the threshold for at least a full rotation of the tool (i.e., the beam is clear for at least one rotation of the tool). Alternatively, the processor of the present invention determines whether the received intensity signal exceeds the threshold for a defined duration (shorter than the time it takes for one complete rotation of the tool). The received intensity signal may remain below the threshold for the defined duration. Alternatively, the received intensity signal may fall below the threshold and rise above the threshold multiple times during one rotation of the tool, with the total time the received intensity signal remains below the threshold at least equal to the defined duration. The tool position is measured when this criterion is met, providing the required measurement of the tool dimension.

[0026] Thus, when used for dark-light tool measurement, the present invention determines when the received intensity signal exceeds a threshold for a defined duration (i.e., less than the time it takes for one complete rotation of the tool). In one embodiment, a trigger signal is issued by the processor of the tool measurement device when the received intensity signal falls below the threshold for a defined duration. The trigger signal can be used by an associated machine tool carrying the tool to provide a measurement of tool position from which tool dimensions can be established. Thus, rather than waiting for an entire tool rotation to exceed a threshold as in the prior art, the method of the present invention instead determines when a threshold value exceeds a certain percentage or portion of a rotation. This allows the effects of protrusions on the tool, such as contaminants or chunks of material in the case of a burr tool, to be filtered out or ignored.

[0027] The method can be implemented using a tool measuring device attached to a machine tool. The machine tool can have a spindle that holds a non-toothed tool. The machine tool can be configured to provide rotation and movement of the non-toothed tool in step (i). Step (ii) can include the tool measuring device issuing a trigger signal to the machine tool when the received intensity signal exceeds a threshold for a defined duration. The machine tool can provide a measurement of the position of the non-toothed tool upon receiving the trigger signal, from which at least one dimension of the non-toothed tool is derived.

[0028] The various components making up the apparatus used in the method of the present invention can be distributed as needed. For example, a single housing unit (e.g., mountable within a machine tool enclosure) can contain each of the transmitter, receiver, and processor. A trigger signal can be generated by the processor and passed from the housing unit to an associated machine tool controller. The trigger signal can be communicated via a wired or wireless link. The wired link can provide power to the components of the housing unit, or the housing unit can include a battery power source.

[0029] Alternatively, the device used in this method may be formed as multiple units. For example, a measurement unit including at least a receiver may be provided. The measurement unit may also include a transmitter. The measurement unit may be mounted within the machine tool housing (e.g., may include protection against ingress of cooling water and other machining contaminants). A separate processing unit (e.g., interface) may include the processor, or the processor may be distributed across several processing units. The processing units may form part of the associated machine tool. In the above configuration, the received intensity signal may be passed from the measurement unit to the processing unit. This passing may be via a communication link. The communication link may be wired or wireless. A dedicated or shared communication link may be used for this purpose. The received intensity signal may be passed as an analog signal (e.g., a voltage that varies proportionally to the received light intensity). Preferably, the receiver of the device includes an analog-to-digital converter (ADC). The received intensity signal may then be passed to the processor as a digital signal. The receiver may include signal processing electronics or may simply output the raw intensity signal or signals.

[0030] The transmitter of the device used in this method may include a laser, e.g., a laser diode. The transmitted light beam may have any wavelength (e.g., red, green, blue, etc. laser beams may be generated). The light beam may be collimated. The light beam may be a focused beam. The receiver may include a single detector element (e.g., a photodiode) for detecting the intensity of the received light. Alternatively, the receiver may include multiple detector elements. In such an example, the received light intensity signal may be generated by combining the light intensities measured by the multiple detector elements. The receiver may include electronics (analog and / or digital) for preprocessing the light intensity signal. Additional processing of the received intensity signal may also be performed by a processor before comparing it with a threshold value.

[0031] The apparatus in which the method is implemented may include a processor arranged to issue a trigger signal when the received intensity signal exceeds a threshold for a defined duration. In other words, the issuance of the trigger signal may be used to indicate that a criterion monitored by the processor (i.e., the received intensity signal has exceeded the threshold for a defined duration) has been met. The issuance of the trigger signal may involve latching a signal line (e.g., raising its level from low to high). Alternatively, the trigger signal may be issued as a pulse or a series of repeated pulses. The trigger signal may be output as an analog signal or communicated via a digital interface (e.g., as a time-stamped event). An associated machine tool controller may receive and act on the received trigger signal. In particular, receipt of the trigger signal may record the position of the tool within the machine tool (i.e., allowing the tool's position at the time the trigger signal was issued to be established). In this way, the necessary measurement of tool dimensions is provided. Receipt of the trigger signal may also stop the tool's movement relative to the light beam (i.e., into or out of the light beam). If the processor is provided as part of the machine tool controller, such a trigger signal may not need to be generated.

[0032] The method may include the additional step of grinding the workpiece if the toothless tool is a grinding tool. In other words, the grinding tool may be used to process (remove material from) the workpiece. As noted above, such a grinding tool may be any type of grinding tool (e.g., a diamond-coated burr tool). The workpiece being processed may be, for example, a glass ceramic part (e.g., for use in a consumer electronics device).

[0033] Also described herein is a method for measuring a dimension of a tool, such as a grinding tool. The method may include directing a beam of light to a receiver. The receiver may generate a received intensity signal related to the intensity of the received light. The method may include moving a rotating tool relative to the light beam. Variations in the received intensity signal may be analyzed to measure the tool. The method may include determining, during the moving step, when the received intensity signal exceeds a threshold value for at least a defined duration. The defined duration may be less than the time it takes for one complete rotation of the tool. Any tool can be measured using the method. Advantageously, the tool is a grinding tool. The tool may also be a burr tool. The method may include any other step or steps described elsewhere herein.

[0034] Also described herein is a tool measurement device that can be used to measure a dimension of a tool. The tool measurement device may be configured to implement the methods described herein or may include any of the features described in the context of the methods described herein. The device may include a transmitter. The transmitter may generate a beam of light. The beam of light may be directed to a receiver. The receiver may generate a received intensity signal. The received intensity signal may be related to (e.g., proportional to) the intensity of the received light. A processor may be provided to analyze variations in the received intensity signal. The processor may perform the analysis when the rotating tool is moved through the light beam. The processor may perform the analysis when the rotating tool is moved into the light beam. The processor may perform the analysis when the rotating tool is moved out of the light beam. The analysis may enable measuring a dimension of the tool. The processor may be configured to determine when the received intensity signal exceeds a threshold for at least a defined duration. The defined duration may be less than the time it takes for one complete rotation of the tool. The processor may be configured to determine when the received intensity signal exceeds the threshold for a period of time less than the time taken for one complete rotation of the tool. The processor may be configured to determine when the received intensity signal falls below the threshold and remains below the threshold for a predetermined duration.

[0035] The invention will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 shows a non-contact tool setting device; [Figure 2a] FIG. 2a shows the calibration tool with the contaminant attached. [Figure 2b] FIG. 2b shows the calibration tool with the contaminant attached. [Figure 3] FIG. 3 shows the effect of the contaminants of FIGS. 2a and 2b on the light intensity profile during a light-dark measurement. [Figure 4] FIG. 4 shows how the techniques of the present invention can eliminate the effects of contaminants. [Figure 5] FIG. 5 is a scanning electron microscope (SEM) image of a chunk of unwanted material formed during the manufacture of the milling tool. [Figure 6] Figure 6 shows a schematic representation of the effect of mass on the received light intensity during dark-light measurements. [Figure 7] FIG. 7 shows data collected that shows the effect of multiple abrasive elements when measuring a grinding tool. DETAILED DESCRIPTION OF THE INVENTION

[0037] Referring to Figure 1, a schematic diagram of a tool measurement apparatus is provided. The apparatus includes a transmitter 10 that generates a light beam 12. The transmitter 10 generates the light beam 12 using a laser diode and appropriate optics (not shown). 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.

[0038] Both the transmitter 10 and the 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 a variety of alternative structures for mounting the transmitter and receiver may be used. For example, a common housing may be provided for the transmitter and receiver, or separate transmitter and receiver units may be separately mounted to the machine tool.

[0039] The apparatus also includes an interface 15 connected to the transmitter 10 and receiver 14 via an electrical cable 17. The interface 15 provides power to the transmitter 10 and receiver 14 and receives a beam intensity signal (also referred to as a received intensity signal) from the photodiode detector of the receiver 14. The interface 15 also includes a processor 24 that analyzes the beam intensity signal and generates a trigger signal. This trigger signal is passed via a cable 28 to a skip input of a controller 30 of the associated machine tool. The tool position, as measured by the machine tool, is captured upon receiving the trigger signal from the interface 15, thereby enabling measurement of the tool size (e.g., tool length or diameter). The trigger signal can be output in several different ways, depending on the configuration of the controller 30. For example, the trigger signal can be communicated by latching the voltage on a line connected to the skip input or by generating a pulse or series of pulses that are passed to the skip input. The trigger signal can alternatively be passed to the controller 30 via a digital data bus (e.g., as described in U.S. Patent No. 5,949,299).

[0040] 2a and 2b show, in side and cross-sectional views, respectively, a calibration tool 40 (i.e., an example of a non-toothed tool), which may also be referred to as a calibration pin. The calibration tool 40 is an elongated cylinder with a known (e.g., calibrated) radius. Also shown is the presence of contaminants 42 (the relative sizes of which are exaggerated for illustrative purposes) on the calibration tool 40. The contaminants 42 may be, for example, dirt or debris that adheres to the calibration tool 40 and cannot be easily removed by high-speed rotation or using air blasting or similar tool cleaning techniques. FIG. 2b shows that the calibration tool 40 is rotated at high speed about its elongated axis while being converted into a light beam 12 that passes between the transmitter 10 and receiver 14 of the tool measurement device described above.

[0041] 3 plots the received intensity signal for one complete rotation of the calibration tool 40 shown in FIGS. 2a and 2b when the tool is in four different positions relative to the light beam 12. The graph shows the received intensity signal (in percent) plotted against time, where Tr is the time it takes for a single rotation of the calibration tool 40. Also shown is a 50 percent level 48 used as a threshold level. Note that the use of 50 percent is arbitrary and the threshold can be set to a different value.

[0042] Before tool 40 enters light beam 12, the beam is uninterrupted, and therefore 100% of the light beam passes to the receiver, which is shown as plotted line 50. Line 52 shows the received intensity when tool 40 is moved forward a sufficient amount to allow any of the cylindrical core of tool 40 to enter the beam, such that contaminant 42 enters the extreme edges of light beam 12 only once per revolution. Thus, the small dip visible in light intensity plot 52 corresponds to contaminant partially obscuring the beam once per revolution.

[0043] In the prior art NC4 machine described above, as the rotating tool advances into the light beam 12, the received intensity signal is compared to a 50 percent trigger threshold. The machine issues a trigger signal when the received intensity signal falls below threshold 48; this is the scenario illustrated by plotted line 54 in FIG. 3. In prior art tool measurement machines, the issued trigger signal therefore causes the associated machine tool to measure the position of the tool 40 when 50% of the beam is blocked at some point during tool rotation. In this example, the beam blockage by the contaminant means that the measured position (and therefore the measured tool radius) is not an accurate measurement of the diameter of the cylindrical tool body. Instead, the machine measures the radius of the contaminant's outer flight circle. Thus, the measured radius of the calibration tool is greater than the tool's actual radius by an amount equal to the distance the contaminant 42 protrudes from the cylindrical tool body.

[0044] At this point, it should be noted that for many types of tools, the maximum radius (defined by the tool's outer "flight circle") provides an adequate measurement of the effective cutting radius. In particular, toothed cutting tools (e.g., milling cutters, drilling cutters, etc.) may have multiple teeth, but the depth of cut they make in a workpiece is determined by the outer flight circle of those teeth. However, the inventors recognize that this is not necessarily the case for toothless tools. In the example shown in Figures 2 and 3, a more reliable measurement of the calibrated tool radius can be achieved by ignoring any small drops in the receive intensity signal resulting from contaminants and instead confirming tool position when the majority of the receive intensity signal is below threshold 48. This is shown as plot 56 in Figure 3.

[0045] Referring now to Figure 4, we will now explain how the apparatus can better measure the radius of the (non-toothed) calibration tool 40 shown in Figures 2a and 2b.

[0046] The received intensity signal is again continuously compared to threshold 48 as the tool moves into the beam. However, a trigger signal is issued only when the received intensity signal falls below the threshold and then remains below that trigger threshold for the duration of time Tq. This is in contrast to prior art light-dark measurements, in which trigger signal generation is based on the first threshold crossing (regardless of whether the received intensity signal subsequently increases in intensity and crosses back above the threshold). Thus, the present method effectively requires that the received intensity signal fall below threshold 48 and remain below threshold 48 within a window of time Tq before a trigger signal is issued. In FIG. 4, duration Tq is set to be equal to half the time it takes for one rotation of the tool (i.e., Tq = Tr / 2). This means that transient dips in the received intensity signal are effectively ignored (i.e., they do not result in the generation of a trigger signal), and a trigger signal is issued only when the received intensity signal remains below threshold 48 for duration Tq.

[0047] 5 to 7, a further application of the present invention for measuring burr tools (i.e., a further example of a non-toothed tool) will now be described.

[0048] Grinding tools (e.g., grinding burrs) are often used to modify the profile of glass-ceramic components. In recent years, the use of such burrs has increased in the manufacture of smartphones, tablets, and other devices. Several different manufacturing processes are used to produce diamond-coated burrs, including sintering and / or electroplating. In sintered tools, the diamond is bonded to a matrix at very high temperatures, resulting in several layers of diamond on the tool. Dressing or cleaning such tools with an aluminum oxide stone helps improve grinding quality and thus preserve the life of the burr or wheel by revealing a new layer of diamond each time. Electroplated tools contain a single layer of coated diamond bonded to the tool using nickel, stainless steel, or other materials. While electroplated tools have a shorter lifespan than sintered tools, they are a cheaper alternative. Of course, it is also possible to use tools containing abrasive particles other than diamond (e.g., CBN, aluminum oxide, etc.).

[0049] A potential problem is that the burr tool may have quality issues. In particular, "lumps" (often called blisters or nodules) of joining (i.e., non-abrasive) material may be present on the surface. Also, oversized particles or contaminants (dirt) may form protrusions with a similar effect. Figure 5 shows an SEM image of such a lump (i.e., a protrusion with dimensions of 191 μm × 516 μm) on a burr tool. These alumps are defects from the manufacturing (e.g., electroplating) process. If the tool is optically measured before use, the measured tool shape may be affected by such a lump, even though it is very likely that such a lump will be knocked off when the tool is first used to modify the component surface. Attempts to clean such tools before measurement using air blasting have proven insufficient to remove such defects.

[0050] Figure 6 shows a schematic of the effect of contaminants (such as chunks of material) on a burr tool when performing a dark-light measurement using the tool measurement device of Figure 1. Figure 6 shows two overlaid plots of the received light intensity as a function of time for two positions of the tool relative to the light beam. In such a dark-light measurement, the tool is first positioned so that it completely blocks the light beam. The tool, rotating about its elongated axis, is then moved (translated) out of the beam while the received intensity signal is monitored.

[0051] In prior art dark-light measurements, the device determines when the tool is clear of the light beam (i.e., when the received intensity signal exceeds the 50 percent threshold for consecutive rotations of the tool). Specifically, prior art devices issue a trigger signal after the received intensity signal exceeds the 50 percent threshold and remains above that threshold for two or more complete rotations of the tool. This condition occurs only if a mass of material on the tool does not obscure more than half of the light beam as it passes through it. The dashed line 60 in Figure 6 indicates the last rotation of the tool, where the 50 percent threshold 48 is crossed. The trigger signal is issued after one additional rotation of the tool, which is the first time it can be confirmed that the signal has not dropped below the 50 percent threshold 48. For completeness, it should be noted that the effect of such a constant delay (i.e., a delay equal to the duration of one tool rotation) can be accounted for by appropriate calibration without affecting the accuracy of the position measurement.

[0052] Therefore, the prior art dark-light measurement described above measures the outermost flying circle of the tool. In the case of a burr tool, this means that the radius measured using the prior art dark-light method is equal to the radius of the tool near the mass of material. As explained above, the mass of material can break during the grinding process, meaning that the measured radius is larger than the effective radius of the tool (perhaps by hundreds of microns). In a highly tolerant manufacturing process, this level of error can be problematic and may require the part to be scrapped.

[0053] In the method of the present invention, the device issues a trigger signal after the received intensity signal exceeds a 50 percent threshold and remains above that threshold for a defined period of time Tq. The time period Tq is less than the time it takes for one complete tool rotation (i.e., Tr), and in this example, is equal to half the time it takes for one tool rotation. Solid line 62 in Figure 6 indicates the first rotation where this criterion is met, and the trigger signal is issued after time period Tq. Note that the intensity profile of solid line 62 is generated before the intensity profile shown by dashed line 60 (i.e., using the method of the present invention, the tool is withdrawn from the beam a smaller distance before the trigger signal is issued). The tool position at the time the trigger signal is received provides a measurement of the tool radius, but excludes the effect of the material mass. Thus, a more realistic tool radius measurement is provided.

[0054] The above example illustrates determining when the received intensity signal continuously exceeds a 50 percent threshold for a defined duration (Tq). However, it should be noted that the threshold need not be continuously exceeded for the defined duration (Tq). If the received intensity signal crosses the threshold multiple times per tool revolution, it would instead be possible to measure the total time the threshold is exceeded per tool revolution and determine whether this is at least equal to the defined duration. In other words, the durations of multiple periods (e.g., T1, T2, T3, etc.) when the threshold is exceeded during a single tool revolution could be added together to determine whether the threshold was exceeded for at least the defined period.

[0055] The above example concerns protrusions on a burr tool. However, it is possible that such a burr tool may contain cavities (i.e., depressions or valleys) in an otherwise round surface. In such an example, the received intensity signal shown in Figure 6 would have spikes rather than depressions. Geometric information about such cavities can be measured by setting the defined duration (Tq) to be sufficiently short (e.g., 5% to 10% of the rotation duration) to trigger when the spike in the received intensity signal exceeds a threshold. This allows the device to measure the dimensions of the cavities.

[0056] It should be noted that the various intensity plots above have been simplified to aid in explanation. A practical example of the implementation of the present invention will now be described with reference to FIG.

[0057] In Figure 7, the received intensity signal collected for a newly manufactured (i.e., unused) burr tool as part of a dark-light measurement is shown. The plot shows the repeating pattern of light detected as the tool rotates at high speed and translates to move out of the light beam. In particular, 29 rotations of the tool are shown while the tool is being withdrawn from the light beam. The various drops in signal are caused by various abrasive particles on the burr tool penetrating and blocking the beam on each tool rotation.

[0058] The first set of dips 70 in the signal are caused by the longest particles protruding from the tool, which are the type of defects (or lumps) described above. The second set of dips 72 in the signal are for the second longest particles, which protrude slightly more than the third, fourth, and fifth long particles creating a series of three dips labeled 74. Many further particles protrude by a similar amount as the third, fourth, and fifth longest particles, and these dips in the signal are labeled 76.

[0059] From Figure 7, it can be seen that, with the exception of the first set of dips 70, the intensities associated with most of the dip minima follow a similar pattern of increasing intensity over time. However, the longest (defect) grain completely obscures the beam at each rotation for the entire duration of the collected data set shown in Figure 7.

[0060] If the prior art method of dark-light measurement were used, the tool would continue to move away from the beam until the longest (defective) particle obscured less than half of the light beam during tool rotation. Such particles would simply detach from the tool upon contact with the object being cut, potentially resulting in erroneous results. Instead, the present method effectively excludes the first set of dips 70 in the signal from the evaluation process when a 50 percent "trigger" threshold is exceeded. This is done by issuing a trigger signal as soon as the received intensity signal exceeds the 50 percent threshold (2.4V in Figure 7) in less time than it takes for one tool revolution. Notably, in the example of Figure 7, a complete tool revolution occurs every 30 ms. The trigger signal is issued after the beam is first cleared (i.e., after crossing the 2.4V threshold) and remains cleared for at least 20 ms. Therefore, the trigger signal is issued at timestamp 320.54 ms (i.e., indicated by the dashed line labeled 78 in Figure 7).

[0061] Note that the duration for which the beam must remain clear (i.e., for the signal to cross the 50 percent threshold) before a trigger signal is issued can be decreased to also exclude the effect of the second set of dips 72 in the signal associated with the second-longest particles. Next, the radius of the third-longest particle is measured. Thus, it can be seen that, using appropriate setting of the duration for which the beam must remain clear, certain protrusions can be excluded from the tool position measurement. In other words, the width of the window of time during which the intensity signal crosses the threshold can be increased and decreased as desired to selectively exclude a desired number of the longest protruding particles present on the tool from the tool measurement.

[0062] In the example above, a trigger signal is issued when the intensity signal exceeds a threshold of 20 ms during the 30 ms taken for one tool revolution. The defined duration is therefore 20 ms or two-thirds (66%) of the time taken for one tool revolution. Other defined periods can be used for different measurement tasks, as summarized in the non-exhaustive list of examples below.

[0063] Effective grinding diameter excluding burrs: It is desirable to measure the outer edge of the burr while the tool is rotating for a defined duration of at least 75% of the time taken for one tool revolution.

[0064] Length measurement excluding bulges: When measuring the edge of a burr, the entire cross section is within the beam, so the defect passes through the beam twice per revolution. Therefore, the defined duration must be less than 50% (e.g., 40%) of the revolution duration.

[0065] Cavities (round manufacturing defects in burrs): This is to detect defects that occur during the burr manufacturing process that appear as depressions or valleys in the round surface of the burr. Burr valley defects can be detected at very low rotation period percentages. A defined duration of 10% or less of the rotation period is most suitable (i.e. geometric information about such valleys can be measured).

[0066] In the above example, the equipment is positioned to ignore unexpected contaminants or particles on the toothless tools, which are of unknown size and location on each tool and vary from tool to tool.

[0067] In all of the above embodiments, the apparatus includes an interface for analyzing the received intensity signal. It is important to note that this is not required and the methods of the present invention can be implemented in many different configurations of apparatus. For example, the tool measurement apparatus (e.g., having a transmitter / receiver) may be provided as a unit mounted within the machine tool housing. The received intensity signal may be output from the tool measurement device (e.g., in digital or analog form) to an interface, computer, controller, etc. having a processor for analyzing the received intensity signal. The processor may be divided into multiple units and / or perform other control or analysis functions.

Claims

1. 1. A method of measuring at least one dimension of a non-toothed tool using a tool measuring device comprising a transmitter and a receiver, the transmitter generating a light beam directed to the receiver, the receiver generating a received intensity signal related to an intensity of the received light, the method comprising: (i) rotating the non-toothed tool about its longitudinal axis while moving the non-toothed tool relative to the light beam; (ii) determining at least one dimension of the non-toothed tool by analyzing variations in the received intensity signal that occur during step (i); Equipped with The method, wherein the signal analysis performed in step (ii) includes determining when the received intensity signal crosses a threshold value for at least a defined duration, the defined duration being less than the time it takes for one complete rotation of the non-toothed tool.

2. The method of claim 1 , wherein the non-toothed tool comprises a grinding tool.

3. The method of claim 2 wherein the grinding tool is a diamond coated burr tool.

4. 4. The method of claim 3, wherein the defined duration is selected such that the effect of any protruding masses formed on the surface of the diamond coated burr tool is substantially eliminated from at least one dimension determined in step (ii).

5. The method according to any one of claims 1 to 3, wherein the defined duration is selected to detect concave defects in the non-toothed tool.

6. The method of claim 1 , wherein the defined duration is greater than 5% of the time it takes for one revolution of the tool.

7. 7. The method of claim 1, wherein the defined duration is less than 95% of the time it takes for one revolution of the tool.

8. The method of claim 1 , wherein the at least one dimension determined in step (ii) comprises a tool radius.

9. 9. A method according to any one of claims 1 to 8, wherein step (ii) comprises establishing the total time per revolution that the threshold remains crossed by identifying each time the received intensity signal crosses a threshold and determining from there when the total time exceeds a defined duration.

10. 10. A method according to any one of claims 1 to 9, wherein step (ii) comprises determining whether the received power signal exceeds a threshold value continuously for at least the defined duration.

11. 11. A method according to any one of claims 1 to 10, wherein step (i) comprises moving the rotating non-toothed tool from a position away from the light beam into the light beam.

12. 12. A method according to any one of claims 1 to 11, wherein step (i) comprises moving the rotating non-toothed tool out of the light beam.

13. 13. A method according to any one of claims 1 to 12, wherein the tool measuring device is mounted on a machine tool having a spindle that holds the non-toothed tool, the machine tool being configured to provide rotation and movement of the non-toothed tool in step (i).

14. 14. The method of claim 13, wherein step (ii) comprises the tool measuring device issuing a trigger signal to the machine tool when the received intensity signal crosses a threshold for the defined duration, the machine tool providing a measurement of the position of the non-toothed tool on receipt of the trigger signal, from which at least one dimension of the non-toothed tool is derived.

15. 15. The method of any one of claims 1 to 14, wherein the non-toothed tool is a grinding tool, and the method comprises the additional step of grinding a workpiece using the grinding tool.

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