Method for measuring a toothless tool using a non-contact tool setter

Abstract

An improved method for measuring the size (e.g., diameter) of a toothless tool (e.g., a grinding tool such as a diamond-coated burr) is described. The method can be implemented on a machine tool (e.g., a lathe, a machining center, etc.). The method includes passing a light beam from a transmitter (10) to a receiver (14). The receiver (14) produces a received intensity signal related to the intensity of the received light. Changes in the received intensity signal are analyzed as the rotating tool (40; 88) moves relative to the light beam (12) to enable the size of the tool (40; 88) to be measured. In particular, it can be determined when the received intensity signal has crossed a threshold for at least a defined duration (Tq) that is less than the time (Tr) it takes for the tool to rotate a full revolution.

Description

[0001] This invention relates to tool measurement. In particular, this invention relates to an improved method for measuring toothless tools (such as grinding tools, deburring tools, calibration pins, etc.) using a non-contact tool setting system.

[0002] Tool measuring devices for machine tools (e.g., machining centers, lathes, milling machines, etc.) are known. For example, the so-called NC4 non-contact tool setting system is sold by Renishaw plc of Wotton-Under-Edge, England. The NC4 device includes a transmitter comprising a laser source for generating a beam. The beam is guided to a receiver through a free-space area where a rotating tool can be placed. During tool measuring operations, the machine tool with the tool setter is programmed to move the tool into and / or out of the beam. An output signal from the receiver indicates the amount of beam obstruction, and the device compares the received intensity signal to a threshold. The device generates a so-called trigger signal to indicate that the tool has reached a certain position relative to the beam. The trigger signal allows the machine tool to establish the tool's position, thereby allowing measurement of the tool's length or diameter and / or allowing monitoring of any breakage or wear on the tool. WO 01 / 38822 and WO 2007 / 096585 describe aspects of the NC4 system. A similar system for tool measurement is also described in DE 102005043659.

[0003] As will be explained in more detail below, the NC4 system can operate in several different modes to measure the dimensions of a rotating tool. For example, the so-called bright-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 drops below a threshold of fifty percent. The dark-to-bright tool measurement mode involves initially blocking the light beam with the rotating tool and then moving the tool out of the beam. In this mode, a trigger signal is issued when the light intensity exceeds the fifty percent threshold for a period longer than one rotation of the tool.

[0004] The aforementioned NC4 system allows for the measurement of cutting dimensions of various types of cutting tools, but it is primarily designed for measuring toothed cutting tools, which consist of a small number of radially distributed cutting teeth separated by tooth grooves. The inventors have found that such prior art tool measurement techniques are not optimal for certain measurement tasks. In particular, the inventors have found that defects common in unused diamond deburring files, etc., can protrude significantly further from the tool axis than multiple abrasive diamond particles that define the relevant grinding dimensions of the deburring tool in use. The inventors have found that using the aforementioned prior art tool measurement techniques introduces unexpected and significant errors in the measurement of the effective dimensions (e.g., diameter) of such tools. The present invention aims to mitigate at least some of the disadvantages of prior art measurement techniques.

[0005] According to a first aspect, a method is provided for measuring at least one dimension of a toothless cutting tool using a cutting tool measuring device, the cutting tool measuring device including a transmitter and a receiver, the transmitter generating a light beam directed towards the receiver, the receiver generating a received intensity signal related to the intensity of the received light, the method including the following steps;

[0006] (i) Rotating the toothless tool about its longitudinal axis while simultaneously moving the toothless tool relative to the beam, and

[0007] (ii) Determine at least one dimension of the toothless tool by analyzing the changes in the received intensity signal that occur during step (i).

[0008] The feature is that the signal analysis performed in step (ii) includes determining when the received intensity signal has exceeded a threshold for at least a limited duration, which is less than the time taken for the toothless tool to complete one full rotation.

[0009] Therefore, the present invention relates to a method for measuring at least one dimension (e.g., tool diameter, tool length, etc.) of a toothless cutting tool using a tool measuring device. In one particular embodiment, the method can be used to measure a rotating (toothless) grinding tool on a machine tool before first using such a tool to grind or polish a workpiece. The tool measuring device for implementing the method includes a transmitter and a receiver. In use, a light beam is transmitted from the transmitter to the receiver. The amount of light reaching the receiver is measured and a received intensity signal is generated, which has a value that varies in relation to (e.g., proportionally) the amount of light received. The tool can be moved into and out of the area between the transmitter and the receiver, thereby (completely or partially) blocking the light beam. Such a tool measuring device is also commonly referred to as an optical “beam-break” tool measuring device or a non-contact tool setter.

[0010] This method includes steps (i) of rotating a toothless tool and simultaneously moving the toothless tool relative to a light beam, and (ii) of analyzing the received intensity signal during the movement in step (i). As explained below, step (i) may include moving the toothless tool into the light beam (so-called bright-to-dark measurement) and / or moving the toothless tool out of the light beam (so-called dark-to-bright measurement). During the measurement, in addition to this movement of the tool relative to (i.e., into or out of) the light beam, the tool also rotates about its longitudinal axis (e.g., via the spindle of an associated machine tool in which the tool may be held). This tool rotation will also cause any protrusions from the toothless tool to periodically enter and exit the light beam during each rotation, depending on the tool's position relative to the light beam. The analysis of the received intensity signal is then used in step (ii) to determine the tool(s) dimensions. In other words, the size of the tool (e.g., radius, length, etc.) or a certain feature of the tool is determined. This analysis of the changes in the received intensity signal may be performed by a processor, which in one embodiment may be configured as part of a tool measuring device.

[0011] The invention is characterized by a step of determining when a received intensity signal has crossed a threshold for at least a defined duration. This threshold can be set at a level relative to the (maximum) received light level (e.g., the intensity signal received when the beam is completely unobstructed). For example, a threshold level of fifty percent of the maximum light level can be used. The defined duration is set to be less than the time taken for the tool to complete one full rotation (i.e., the tool rotates or returns 360°). Instead of using a single threshold crossing event for tool measurement purposes, the invention alternatively determines when the threshold has been crossed and has remained crossed for a (predefined) time period. The time period for which the threshold needs to remain crossed (i.e., the defined duration) is set to be less than the time taken for the tool to complete one full rotation. As explained below, different defined durations can be used for different types of measurement applications. It is also important to note that the defined duration is set relative to the speed of tool rotation (i.e., the time taken for the tool to complete one full rotation), and therefore can be adjusted by changing the speed of tool rotation and / or by changing the absolute time period used to analyze the received intensity signal. In a preferred embodiment, once the received intensity signal exceeds a threshold for a defined duration, the processor issues a trigger signal (e.g., this trigger signal can be transmitted to the associated machine tool). The position of the tool upon receiving such a trigger signal can then be measured (e.g., via the associated machine tool) to provide tool size measurements.

[0012] The advantage of the method of the present invention is that it can eliminate certain protrusions from the tool (e.g., contaminants on calibration tools or unwanted material clumps on diamond-coated deburring tools) from tool measurements. For example, the aforementioned known NC4 devices implement both dark-to-light and light-to-dark measurement modes. In the prior art light-to-dark mode, the rotating tool is moved toward the beam, and a trigger signal is issued when the received intensity signal first drops below a 50% threshold. In the prior art dark-to-light mode, the tool starts from a position within the beam and is moved out of the beam. In this mode, the received intensity signal increases as the tool is moved out of the beam, and a trigger signal is issued after the received intensity signal exceeds a 50% threshold for the entire tool rotation (i.e., indicating that the entire tool has sufficiently avoided the beam). Therefore, all prior art NC4 measurement modes measure the maximum radius (or outermost flight circle) of the tool, even if this maximum radius is caused by protrusions on the tool (e.g., contaminants or non-abrasive defects) rather than the size of the tool it is intended to measure (e.g., the effective tool radius).

[0013] Compared to the prior art methods implemented by NC4 equipment, the present invention allows the exclusion of such defects or contaminants from tool measurements by determining when a threshold is first crossed for a defined duration. In other words, instead of simply using a single threshold crossing event for tool measurement, this method alternatively evaluates when the threshold has been crossed for a certain period of time (i.e., the defined duration) during one revolution of the tool. The threshold can be crossed consecutively for the defined duration. Alternatively, the threshold can be crossed discontinuously for the defined duration (i.e., multiple periods during one revolution of the tool may exist where the threshold is crossed, and these periods total equal to or exceed the defined duration). Setting such a defined duration, which is less than the time taken for a complete revolution of the tool, allows any threshold crossings caused by convex defects (e.g., contaminants, non-abrasive defects, oversized grit particles, etc.) that are to be excluded from tool measurements to be ignored. Therefore, a more robust, reliable, and adaptable tool measurement method is provided that is highly suitable for measuring grinding tools.

[0014] The same method can be used to detect concave defects. In particular, setting the defined duration to only a small percentage (e.g., less than 20% or less than 10%) of the time taken for the tool to complete one revolution can be used to measure such concave defects. Examples of concave defects can include surface cavities in toothless cutting tools. Bare spots or defective patches on grinding tools (e.g., missing diamond in a specific section of a diamond-coated tool) can also cause such concave defects. While such concave defects (cavities or dents) within a tool may not affect overall tool geometry measurements, they can still lead to poor surface quality on the workpiece and / or reduced tool life.

[0015] This method can be used to measure one or more dimensions (e.g., tool radius, tool length, etc.) of any toothless cutting tool. Toothless cutting tools can include calibration tools (sometimes also called calibration pins and used for calibration purposes, not for workpiece machining) or grinding tools for workpiece machining (i.e., tools that remove material from a workpiece through a grinding or polishing process). In this context, a toothed tool refers to a cutting tool that includes one or more discrete cutting teeth that can be separated by tooth grooves (i.e., recesses or channels for removing cutting chips, coolant, etc.). Therefore, a toothless cutting tool is a tool that does not include such cutting teeth. Toothless cutting tools may have a nominally circular profile (although with multiple small protrusions or particles for grinding surfaces). Toothless cutting tools may be nominally rotationally symmetric.

[0016] In a preferred embodiment, the toothless tool includes a (toothless) grinding tool. As used herein, the term "grinding tool" should be understood to include any type of grinding tool used to grind, remove, or file material from a workpiece by a grinding (i.e., lapping rather than cutting) process. In other words, the term grinding encompasses techniques such as polishing, grinding lubrication, grinding, honing, super-polishing, and buffing. Grinding tools can be deburring (also spelled "bur") tools, grinding wheels, core drills, etc. Grinding tools may have a nominally circular cross-sectional profile. Grinding tools may be nominally rotationally symmetric. Grinding tools may have a nominally continuous outer surface, or they may include one or more longitudinal slots to aid in the removal of coolant or cutting chips.

[0017] Grinding tools can be any type of abrasive material from the object being machined. Grinding tools can include a shaft with a roughened surface, or they can include a roughened surface coating applied to a central shaft. Grinding tools can include multiple abrasive particles or pebbles embedded within or coated onto a substrate (e.g., in the form of a rod or shaft). This substrate can be vitreous, glass, resin, metal, or any suitable combination of materials. The pebbles can include abrasive or superhard abrasive particles. The pebbles can include particles of diamond, cubic boron nitride (CBN), alumina, iron oxide, etc. Any such pebbles can retain material within the particle matrix by means of (e.g., softer or less abrasive) materials. As explained below, this method is particularly suitable for measuring grinding tools formed through an electroplating process (i.e., electroplated grinding tools), because blistering often occurs during the manufacturing process of such tools. In the example outlined below, this method is implemented to measure grinding tools in the form of pebbly-based grinding deburring files, particularly diamond-coated deburring files (DCB).

[0018] Toothless cutting tools may alternatively include calibration tools or pins. Such calibration tools can be precision-manufactured bars with a nominally circular cross-section and a smooth outer surface, used for calibration purposes. Calibration tools may also include reference spheres or hemispheres. Calibration tools may also include measuring probes with styluses. These styluses may include shafts with ends in the form of ruby ​​or diamond spheres.

[0019] A technician will select a defined duration suitable for the specific tool measurement being performed in the method. As described above, a preferred application of the method of the present invention is to measure grinding tools, such as deburring tools having multiple (e.g., grit-like) abrasive elements. In this embodiment, a defined duration used by the processor can be selected to allow measurement of the dimensions (e.g., effective radius) of the deburring tool unaffected by any (non-abrasive) material clumps present on the tool (e.g., caused by manufacturing defects). In other words, the defined duration is selected to allow the influence of any protruding clumps formed on the surface of the diamond-coated deburring tool to be substantially excluded from at least one dimension determined in step (ii). As explained below, the defined duration used in the method of the present invention can also be selected for contaminant or dirt suppression purposes (e.g., to exclude the influence of dirt that may adhere to the tool on tool size measurements).

[0020] The defined duration can be adjustable (e.g., user- or manufacturer-adjustable). For example, the device can be programmed (e.g., by the user / manufacturer) to have a defined duration to be used in the analysis. In particular, the device may include a processor for analysis and appropriate commands for setting the defined duration can be sent to the processor. As mentioned above, the defined duration depends on the tool rotation speed used during tool measurement. Therefore, the defined duration can be set by adjusting the clock or timing signal used to analyze the received intensity signal (e.g., within the processor) and / or by changing the tool rotation speed. Thus, the step of adjusting the defined duration may include the step of adjusting the tool rotation speed. The tool may rotate at high speeds during measurement. For example, the tool may rotate at speeds exceeding 200 revolutions per minute (rpm), exceeding 1000 rpm, exceeding 5000 rpm, exceeding 10,000 rpm, exceeding 20,000 rpm, exceeding 40,000 rpm, exceeding 60,000 rpm, or exceeding 100,000 rpm. The defined duration may be expressed as a time value (e.g., in microseconds or milliseconds) or as a proportion (e.g., a percentage) of the time taken for the tool to rotate one revolution. The command line invocation used to run the method of the present invention may include a variable that defines the defined duration as a proportion (e.g., a percentage) of the time taken for the tool to rotate one revolution. The defined duration is conveniently set based on the specific tool or tool type to be measured. The method can be repeated multiple times on the same tool using different defined durations (e.g., to exclude or include surface features of different sizes).

[0021] Advantageously, the defined duration is greater than 1% of the time taken for the tool to rotate one revolution. 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 the tool to rotate one revolution. Advantageously, the defined duration is less than 99% of the time taken for the tool to rotate one revolution. 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 the tool to rotate one revolution. The defined duration may be less than 25%, less than 10%, or less than 5% of the time taken for the tool to rotate one revolution; for example, to allow for the measurement of concave defects, etc.

[0022] The analysis in step (ii) can establish whether, for each tool rotation cycle, the threshold is continuously or discontinuously crossed for a defined duration. For example, step (ii) may include determining whether the received intensity signal has continuously crossed the threshold for at least the defined duration. Alternatively, step (ii) may include establishing the total (resulted) duration for which the threshold is crossed in each revolution (i.e., even if this includes multiple discrete time intervals for the threshold to be crossed). This can be done by identifying each instance of the received intensity signal crossing (e.g., exceeding or falling below the threshold, depending on the situation) the threshold and determining when the total duration exceeds the defined duration. Any other suitable analysis techniques can be implemented. The time the threshold is crossed during each rotation can also be recorded and used to identify or map the location of any defects on the toothless tool.

[0023] As described above, the method may include so-called bright-to-dark tool measurement. In other words, step (i) may include moving a rotating toothless tool from a position away from the beam into the beam. Therefore, as the rotating tool moves into the beam from a position away from the beam (i.e., outside the beam), the changes in the received intensity signal can be analyzed. In this arrangement, the beam is initially unobstructed, so the received intensity signal will take its maximum (e.g., 100%) value. As the rotating tool begins to enter the beam, any protrusions from the tool will begin to periodically enter the beam as the tool rotates. As the tool continues to move into the beam, the received intensity signal will decrease, and may even momentarily drop below a threshold (which may be set at 50% of the maximum intensity).

[0024] In the aforementioned prior art light-to-dark mode measurement, the received intensity signal is monitored to determine when the received intensity signal first drops below a threshold. Alternatively, the method of the present invention determines when the received intensity signal has dropped below a threshold and remains below that threshold for at least a defined duration. The received intensity signal may be continuously maintained below the threshold for the defined duration. Alternatively, the received intensity signal may drop below the threshold and rise above the threshold multiple times during one revolution of the tool, wherein the total time the received intensity signal remains below the threshold is at least equal to the defined duration. When this criterion has been met, the tool position is measured, thereby providing a measurement of the desired tool size.

[0025] Therefore, the method of the present invention effectively ignores any instantaneous dips in the received intensity signal shorter than a defined duration when performing bright-to-dark tool measurements. Instead, it is established when the beam is sufficiently blocked so that the received intensity signal drops below a threshold for a duration equal to or exceeding the defined duration. In one embodiment, a trigger signal is issued by the processor of the tool measuring device when the received intensity signal drops below the threshold for a defined duration. The associated machine tool carrying the tool can use the trigger signal to provide a measurement of the tool position, from which the tool size can be established.

[0026] It should be noted that when performing light-to-dark tool measurements, a so-called drip suppression filter can be implemented. In the prior art arrangement, the filter only issues a trigger signal when a second such event occurs after a threshold event, the time interval between the second event and the first event being equal to one full rotation of the tool. This ensures that any coolant drips that may momentarily pass through the beam and do not normally occur at regular intervals are not misinterpreted as the presence of a tool in the beam. A similar drip suppression filter can be used in this invention. In other words, a trigger signal is only issued when a second similar event occurs after a first event in which the received intensity signal drops below a threshold for a defined duration, the time interval being equal to one full rotation of the tool.

[0027] This method may include a so-called dark-to-light tool measurement. In other words, step (i) may include removing a rotating toothless tool from the beam. This measurement may be performed in place of a light-to-dark measurement or in conjunction with a light-to-dark measurement. For such a measurement, the changes in the received intensity signal are analyzed as the rotating tool, located in the beam, is removed from the beam. In this arrangement, the beam is initially blocked (e.g., completely blocked to prevent all light from the transmitter from reaching the receiver) and the received intensity signal will therefore initially be at its minimum or zero. As the rotating tool begins to leave the beam, any protrusions from the tool (e.g., bubbles, dirt, etc.) will periodically leave and then re-enter the beam as the tool rotates. As the tool continues to leave the beam, the received intensity signal will generally increase (note that there may be slight flickering in the signal from the grinding tool due to multiple abrasive particles on the tool surface), but there will be periodic drops or dips in the signal as the protrusions re-enter the beam. Thus, during each tool rotation, sometimes the received light intensity will exceed a threshold (which can be set again at fifty percent of the maximum intensity), while at other times the received light intensity will drop back below the threshold. In the prior art dark-to-light mode measurement described above, the received intensity signal is monitored, and it is determined when the received light intensity exceeds a threshold for at least the entire rotation of the tool (i.e., the beam is unobstructed for at least one rotation of the tool). Alternatively, the processor of the present invention determines when the received intensity signal has exceeded the threshold for a defined duration (this defined duration is less than the time taken for the tool to complete one rotation). The received intensity signal may continuously exceed the threshold for the defined duration. Alternatively, the received intensity signal may exceed the threshold and fall below the threshold multiple times during one rotation of the tool, wherein the total time the signal exceeds the threshold is at least equal to the defined duration. When this criterion has been met, the position of the tool is measured, thereby providing a measurement of the desired tool size.

[0028] Therefore, when used for measuring tools from dark to light, the present invention determines when the received intensity signal exceeds a threshold for a defined duration (i.e., the defined duration is less than the time taken for the tool to complete one full rotation). In one embodiment, a trigger signal is issued by the tool measuring device when the received intensity signal exceeds the threshold for the defined duration. The associated machine tool carrying the tool can use this trigger signal to provide a measurement of the tool position, from which the tool size can be established. Thus, the method of the present invention does not wait for the threshold to be exceeded for the entire rotation of the tool, as in the prior art, but instead determines when the threshold has been exceeded for a certain proportion or portion of one rotation. This allows the influence of protrusions on the tool (e.g., contaminants or material clumps in the case of deburring tools) to be excluded or ignored.

[0029] This method can be implemented using a tool measuring device mounted to a machine tool. The machine tool may have a spindle that holds the toothless tool. The machine tool may be configured to provide rotation and movement of the toothless tool in step (i). Step (ii) may include the tool measuring device sending a trigger signal to the machine tool when a received intensity signal has exceeded a threshold for a defined duration. Upon receiving the trigger signal, the machine tool may provide a measurement of the position of the toothless tool, from which at least one dimension of the toothless tool is derived.

[0030] The various components of the device used in the method of this invention can be distributed as needed. For example, a single housing unit (e.g., which may be mounted within a machine tool housing) can house each of the transmitter, receiver, and processor. A trigger signal can be generated by the processor and transmitted from the housing unit to the associated machine tool controller. The trigger signal can be transmitted via a wired or wireless link. A wired link can provide power to the components of the housing unit, or the housing unit may include a battery power source.

[0031] Alternatively, the device used in this method can be configured as multiple units. For example, a measuring unit including at least a receiver can be provided. The measuring unit may also include a transmitter. The measuring unit may be mounted within a machine tool housing (e.g., the machine tool housing may include protection against the ingress of coolant and other machining contaminants). A separate processing unit (e.g., an interface) may include a processor, or processors may be distributed across several processing units. The processing units may form part of an associated machine tool. In the above arrangement, the received intensity signal can be transmitted from the measuring unit to the processing unit. This transmission can be via a communication link. The communication link can be wired or wireless. Dedicated or shared communication links can be used for this purpose. The received intensity signal can be transmitted as an analog signal (e.g., the signal may be 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 can then be transmitted as a digital signal to the processor. The receiver may include signal processing electronics, or the receiver may simply output one or more raw intensity signals.

[0032] The transmitter of the device used in this method may include a laser, such as a laser diode. The transmitted light beam can have any wavelength (e.g., red, green, blue, etc. laser beams can be generated). The beam can be collimated. The beam can 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 this example, the received light intensity signal can be generated by combining the light intensities measured by multiple detector elements. The receiver may include (analog and / or digital) electronics for preprocessing the light intensity signal. Additional processing of the received intensity signal may also be performed by a processor before it is compared with a threshold.

[0033] The device implementing this method may include a processor arranged to issue a trigger signal when a received intensity signal has exceeded a threshold for a defined duration. In other words, the issuance of the trigger signal can be used to indicate that a criterion being monitored by the processor (i.e., the received intensity signal has exceeded a threshold for a defined duration) has been met. Issuing the trigger signal may include latching a signal line (e.g., raising the level of a signal line 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 it may be transmitted via a digital interface (e.g., as a timestamped event). The associated machine tool controller may receive the received trigger signal and act on it. In particular, receiving the trigger signal may cause the tool's position within the machine tool to be recorded (i.e., to allow the tool's position at the time the trigger signal was issued). In this way, the required measurement of the tool's dimensions is provided. Receiving the trigger signal may also stop the tool's movement relative to the beam (i.e., moving it into or out of the beam). If the processor is provided as part of the machine tool controller, it may not be necessary to generate such a trigger signal.

[0034] When the toothless tool is a grinding tool, the method may include the additional step of grinding the workpiece. In other words, the grinding tool can be used to machine the workpiece (remove material from the workpiece). As mentioned above, such a grinding tool can be any type of grinding tool (e.g., a diamond-coated deburring tool). The workpiece being machined can be, for example, a glass-ceramic component (e.g., for consumer electronics devices).

[0035] This document also describes a method for measuring the dimensions of a cutting tool (such as a grinding tool). The method may include the step of directing a light beam towards a receiver. The receiver may generate a received intensity signal relating to the intensity of the received light. The method may include moving a rotating cutting tool relative to the light beam. Changes in the received intensity signal may be analyzed to measure the cutting tool. The method may include the step of determining, during the movement step, when the received intensity signal crosses a threshold for at least a defined duration. The defined duration may be less than the time it takes for the cutting tool to complete one full rotation. This method can be used to measure any cutting tool. Advantageously, the cutting tool is a grinding tool. The cutting tool may be a deburring tool. The method may include any other one or more steps described elsewhere herein.

[0036] This document also describes a tool measuring device that can be used to measure the dimensions of a tool. The tool measuring device can be configured to implement the methods described herein or can include any features described in the context of the methods described herein. The device can include a transmitter. The transmitter can generate a light beam. The light beam can be directed at a receiver. The receiver can generate a received intensity signal. The received intensity signal can be related to (e.g., proportional to) the intensity of the received light. A processor can be provided for analyzing changes in the received intensity signal. The processor can perform the analysis as a rotating tool moves through the light beam. The processor can perform the analysis as the rotating tool moves into the light beam. The processor can perform the analysis as the rotating tool moves out of the light beam. This analysis enables the dimensions of the tool to be measured. The processor can be configured to determine when the received intensity signal has exceeded a threshold for at least a defined duration. The defined duration can be less than the time taken for the tool to complete one revolution. The processor can be configured to determine when the received intensity signal exceeds the threshold for a duration less than the time taken for the tool to complete one revolution. The processor can be configured to determine when the received intensity signal drops below the threshold and remains below the threshold for a predetermined duration.

[0037] The invention will now be described by way of example only, with reference to the accompanying drawings, in which;

[0038] Figure 1 A non-contact tool setting device is shown.

[0039] Figure 2a and Figure 2b The calibration tool with contaminants attached was displayed.

[0040] Figure 3 The measurement period from bright to dark is shown. Figure 2a and Figure 2b The effect of pollutants on the light intensity curve,

[0041] Figure 4This demonstrates how the technology of the present invention can eliminate the effects of pollutants.

[0042] Figure 5 These are scanning electron microscope (SEM) images of unwanted material clumps that form during the manufacturing of grinding tools.

[0043] Figure 6 The effect of clumps on the intensity of received light during the dark-to-bright measurement period is schematically illustrated.

[0044] Figure 7 It is a collection of data showing the effects of multiple abrasive elements when measuring grinding tools.

[0045] refer to Figure 1 A schematic illustration of a tool measuring device is provided. The device includes a transmitter 10 for generating a light beam 12. The transmitter 10 uses a laser diode and suitable optics (not shown) to generate the light beam 12. A receiver 14 is also shown for receiving the light beam 12. The receiver includes a photodiode (not shown) for detecting the light beam 12.

[0046] Both transmitter 10 and receiver 14 are attached to a common base 20 via supports 18. This arrangement ensures that transmitter 10 and receiver 14 maintain a fixed spacing and orientation relative to each other. The base 20 can then be directly mounted to the machine tool bed or even any suitable part. It should also be noted that a variety of different alternative structures can be used for mounting the transmitter and receiver. For example, a common housing for the transmitter and receiver can be provided, or separate transmitter and receiver units can be mounted separately to the machine tool.

[0047] The device also includes an interface 15, which is connected to the transmitter 10 and receiver 14 via cable 17. Interface 15 provides power to the transmitter 10 and receiver 14 and also receives a beam intensity signal (also referred to as the received intensity signal) from a photodiode detector of receiver 14. Interface 15 also includes a processor 24 that analyzes the beam intensity signal and generates a trigger signal. This trigger signal is transmitted via cable 28 to the SKIP input of the controller 30 of the associated machine tool. Upon receiving the trigger signal from interface 15, the tool position (e.g., as measured by the machine tool) is captured, allowing for tool size (e.g., tool length or diameter) measurement. Depending on the configuration of controller 30, the trigger signal can be output in several different ways. For example, the trigger signal can be transmitted by latching the voltage of the line connected to the SKIP input or by generating a pulse or a series of pulses transmitted to the SKIP input. Alternatively, the trigger signal can be transmitted to controller 30 via a digital data bus (e.g., as described in WO 2018 / 134585).

[0048] Figure 2a and Figure 2b The calibration tool 40 (i.e., an example of a toothless tool), which may also be referred to as a calibration pin, is shown in side and cross-sectional views. The calibration tool 40 is an elongated cylinder with a known (e.g., calibrated) radius. A contaminant 42 is also shown on the calibration tool 40 (the relative size of the contaminant is exaggerated for illustrative purposes). The contaminant 42 may be, for example, dirt or debris that adheres to the calibration tool 40 itself and cannot be easily removed by high-speed rotation or by using air jets or similar tool cleaning techniques. Figure 2b The calibration tool 40 is shown to rotate at high speed around its elongated axis and is simultaneously translated into a beam 12 passing between the transmitter 10 and the receiver 14 of the aforementioned tool measuring device.

[0049] Figure 3 The plot shows the effect of the tool rotating a full circle. Figure 2a and Figure 2b The graph shows the received intensity signals when the calibration tool 40 is in four different positions relative to the beam 12. The graph illustrates the received intensity signals as a percentage of time, where the time taken for a single rotation of the calibration tool 40 is T. r The 50 percent level 48 is also shown as a threshold level. It should be noted that the use of 50 percent is arbitrary and the threshold can be set at different values.

[0050] Before the cutter 40 enters the beam 12, the beam is uninterrupted, so 100% of the beam is transmitted to the receiver; this is shown as plotted as line 50. Line 52 shows the received intensity when the cutter 40 is moved such that the contaminant 42 just enters the extreme edge of the beam 12 with each revolution, but before the cutter 40 has advanced sufficiently to allow any cylindrical core of the cutter 40 to enter the beam. Therefore, the small dip visible in the light intensity plot 52 corresponds to the contaminant partially obscuring the beam with each revolution.

[0051] In the aforementioned prior art NC4 device, when the rotating tool advances into the beam 12, the received intensity signal is compared with a 50% trigger threshold. When the received intensity signal drops below the threshold 48%, the device issues a trigger signal; this is Figure 3The situation is illustrated by line 54 in the diagram. In prior art tool measuring devices, when 50% of the light beam is blocked at a certain point during tool rotation, the emitted trigger signal will therefore cause the associated machine tool to measure the position of the tool 40. In this example, the light beam being blocked by the contaminant means that the measured position (and therefore the measured tool radius) will not be an accurate measure of the diameter of the cylindrical tool body. Instead, the device will measure the radius of the outer flight circle of the contaminant. Therefore, the measured radius of the calibrated tool will be larger than the actual radius of the tool by an amount equal to the distance by which the contaminant 42 protrudes from the cylindrical tool body.

[0052] It should be noted that for many types of cutting tools, the maximum radius (as defined by the tool's outer "flying circle") does indeed provide a suitable measure of the effective cutting radius. In particular, toothed cutting tools (e.g., for milling, drilling, etc.) can have multiple teeth, but their depth of cut in the workpiece will be determined by the outer flying circles of these teeth. However, the inventors have realized that this is not always the case for toothless cutting tools. (See Figure 2 and...) Figure 3 In the example shown, a more reliable measurement of the calibrated tool radius can be obtained by ignoring any small dips in the received intensity signal caused by contaminants and instead determining the tool position when most of the received intensity signal drops below a threshold of 48. This is in Figure 3 As shown in Figure 56.

[0053] Next reference Figure 4 This will describe how the device can measure better. Figure 2a and Figure 2b The radius of the (toothless) calibration tool 40 shown.

[0054] As the tool moves into the beam, the received intensity signal is continuously compared to a threshold 48. However, a trigger signal is only issued when the received intensity signal drops below the threshold and then remains below that threshold for a duration Tq. This contrasts with prior art light-to-dark measurements, where trigger signal generation is based on the first threshold crossing (regardless of whether the received intensity signal then increases and crosses back above the threshold). Therefore, this method effectively creates the requirement for a trigger signal to be issued only after the received intensity signal drops below the threshold 48 and remains below that threshold for a time window Tq. Figure 4 In this configuration, the duration Tq is set to be equal to half the time it takes for the tool to rotate one revolution (i.e., Tq = Tr / 2). This means that momentary dips in the received intensity signal are effectively ignored (i.e., they do not cause the generation of a trigger signal) and a trigger signal is only issued when the received intensity signal drops below the threshold 48 for a duration Tq.

[0055] Next reference Figures 5 to 7 Further applications of the present invention for measuring deburring tools (i.e., further examples of toothless tools) will be described.

[0056] Grinding tools (such as grinding deburring files) are commonly used to modify the contours of glass-ceramic parts. In recent years, the use of such deburring files has increased in the manufacture of smartphones, tablets, and other products. Many different manufacturing processes are used to create diamond-coated deburring files, such as sintering and / or electroplating. In sintered tools, diamond is bonded to the substrate at very high temperatures, resulting in a tool with several layers of diamond. Dressing or cleaning such tools with alumina stones helps improve grinding quality, thus maintaining the life of the deburring file or wheel by exposing a new layer of diamond each time. Electroplated tools involve a single layer of coated diamond bonded to the tool using materials such as nickel or stainless steel. While electroplated tools have a shorter lifespan than sintered tools, they are a less expensive alternative. Of course, tools containing abrasive particles other than diamond (such as CBN, alumina, etc.) can also be used.

[0057] A potential problem is that deburring tools may encounter quality issues. In particular, "clumps" (often called blistering or nodules) of bonded (i.e., non-abrasive) material may be present on the surface. Oversized particles or contaminants (dirt) may also form protrusions with a similar effect. Figure 5 SEM images of these lumps (i.e., protrusions measuring 191 μm x 516 μm) on deburring tools are shown. These lumps are defects from the manufacturing process (e.g., electroplating). If the tool is optically measured before use, the measured tool geometry may be affected by these lumps, although they are likely to be knocked off when the tool is first used to modify the surface of the part. Attempts to clean such tools with an air jet before measurement have been found insufficient to remove these defects.

[0058] Figure 6 It schematically demonstrates the use of Figure 1 The effect of contaminants (material clumps) on deburring tools when the tool measuring equipment performs dark-to-light measurements. Figure 6 Two superimposed plots show the change in received light intensity over time for two positions of the tool relative to the beam. In this dark-to-bright measurement, the tool is initially positioned to completely block the beam. The tool, rotated about its elongated axis, is then moved (translated) out of the beam while the received intensity signal is monitored.

[0059] In existing dark-to-light measurements, the device determines when the cutter avoids the light beam (i.e., when the received intensity signal continuously exceeds a threshold of 50%). Specifically, existing devices issue a trigger signal after the received intensity signal exceeds the 50% threshold and remains above that threshold for more than one complete rotation of the cutter. This only occurs when a clump of material on the cutter no longer blocks more than half of the light beam as it passes through it. Figure 6 The dashed line 60 indicates the last rotation of the tool when 50 percent of the threshold 48 has been crossed. A trigger signal is issued after the tool completes another rotation, which is the first point in time at which the signal can be confirmed not to drop back below 50 percent of the threshold 48. For completeness, it should be noted that the effect of this constant delay (i.e., a delay equal to the duration of one rotation of the tool) can be accounted for through appropriate calibration without affecting the accuracy of the position measurement.

[0060] The aforementioned prior art dark-to-light measurement thus measures the outermost flight circle of the tool. For deburring tools, this means that the radius measured using the prior art dark-to-light method is equal to the radius of the tool near the material lump. As explained above, during the grinding process, the material lump is likely to break, meaning the measured radius is larger than the effective radius of the tool (potentially hundreds of micrometers larger). For high-tolerance manufacturing processes, this level of error can cause problems and may lead to parts having to be scrapped.

[0061] In the method of this invention, the device issues a trigger signal after the received intensity signal exceeds a threshold of fifty percent and remains above that threshold for a defined time period Tq. The time period Tq is less than the time taken for the tool to complete one revolution (i.e., Tr), and in this example, it is equal to half the time taken for the tool to complete one revolution. Figure 6 Solid line 62 illustrates the first rotation that satisfies the criterion and triggers the signal after a time period Tq. It should be noted that the intensity distribution of solid line 62 precedes the intensity distribution shown by dashed line 60 (i.e., the tool is withdrawn a small distance from the beam using the method of the present invention, after which the trigger signal is emitted). The tool's position upon receiving the trigger signal provides a measure of the tool's radius, but excludes the influence of material clumps. This provides a more practical measurement of the tool radius.

[0062] The example above illustrates how to determine when a received intensity signal continuously exceeds 50% of a threshold for a defined duration (Tq). However, it should be noted that it is not necessary to continuously exceed the threshold for the defined duration (Tq). If the intensity signal received during each tool rotation crosses the threshold multiple times, it is alternatively possible to measure the total amount of time the threshold is exceeded during each tool rotation and determine whether that total time is at least equal to the defined duration. In other words, the durations of multiple time intervals (e.g., T1, T2, T3, etc.) during a single tool rotation can be summed to determine whether the threshold has been exceeded for at least the defined duration.

[0063] The example above relates to protrusions on a deburring tool. However, such a deburring tool may also include cavities (i.e., indentations or valleys) in other circular surfaces. In this example, Figure 6 The received intensity signal shown exhibits a spike rather than a dip. Geometry information about this cavity can be measured by setting the defined duration (Tq) short enough (e.g., 5% to 10% of the rotation duration) to trigger when the spike in the received intensity signal crosses a threshold. This will allow the device to measure the cavity's dimensions.

[0064] It should be noted that the various intensity diagrams described above have been simplified for ease of interpretation. The following will refer to... Figure 7 Practical examples describing embodiments of the present invention are provided.

[0065] exist Figure 7 The figure shows the received intensity signal collected for a newly manufactured (i.e., unused) deburring tool as part of a dark-to-light measurement. The figure illustrates a repeating pattern of light detected as the tool rotates at high speed and is also translated to remove it from the beam. Specifically, twenty-nine rotations of the tool are shown as it withdraws from the beam. The individual dips in the signal are caused by the various abrasive particles from the deburring tool entering and obscuring the beam with each rotation of the tool.

[0066] The first set of sinkholes 70 in the signal is caused by the longest particle protruding from the tool, which is a defect (or clump) of the type described above. The second set of sinkholes 72 in the signal relates to the second longest particle, which protrudes slightly more than the third, fourth, and fifth longest particles that produce the series of three sinkholes marked 74. Many other particles protrude by a similar amount to the third, fourth, and fifth longest particles, and these sinkholes in the signal are marked 76.

[0067] from Figure 7 It can be seen that, except for the first group of subsidences of 70, the intensity associated with most of the minimum subsidences follows a similar pattern of intensity increasing over time. However, in Figure 7 Throughout the entire duration of the collected dataset shown, the longest (defective) particle still completely obscures the beam with each rotation.

[0068] If the existing dark-to-light measurement method is used, the tool will continue to move out of the beam until the longest (defective) particle obscures no more than half of the beam during tool rotation. This will give incorrect results because such a particle will simply detach from the tool upon contact with the object to be cut. Instead, this method effectively excludes the first set of sinking 70 in the signal from the evaluation process when the 50% "trigger" threshold has been exceeded. This is done by ensuring that the received intensity signal exceeds the 50% threshold ( Figure 7 This is accomplished by immediately issuing a trigger signal when the voltage (2.4V) is maintained above this threshold for a duration less than the time required for one complete rotation of the tool. Specifically, in... Figure 7 In the example, a complete tool rotation occurs every 30 ms. The trigger signal is emitted after the beam first returns to open (i.e., exceeds the 2.4V threshold) and remains open for at least 20 ms. Therefore, at timestamp 320.54 ms (i.e., as shown in the example), the trigger signal is emitted after the beam first returns to open (i.e., exceeds the 2.4V threshold) and remains open for at least 20 ms. Figure 7 The trigger signal is emitted as indicated by the dashed line marked 78 in the middle.

[0069] It should be noted that the duration for which the beam needs to remain unobstructed before issuing the trigger signal (i.e., so that the signal exceeds 50 percent of the threshold) can be reduced to also exclude the influence of the second set of sinking 72 related to the second longest particle in the signal. The radius of the third longest particle is then measured. Thus, it can be seen that an appropriate setting of the duration for which the beam needs to remain unobstructed can be used to exclude certain protrusions from tool position measurements. In other words, the width of the time window for the intensity signal to cross the threshold can be increased and decreased as needed to selectively exclude the desired number of longest protruding particles present on the tool from tool measurements.

[0070] In the example above, a trigger signal is issued when the intensity signal exceeds the threshold for 20 ms during the 30 ms it takes for the tool to complete one revolution. Therefore, the defined duration is 20 ms or two-thirds (66%) of the time it takes for the tool to complete one revolution. Other defined durations can be used for different measurement tasks, as summarized in a non-exhaustive list of examples below:

[0071] • Effective grinding diameter to eliminate bubbling: Measure the outer edge of the deburring file while the tool is rotating, preferably for a duration of at least 75% of the time it takes for the tool to rotate one revolution.

[0072] • Exclude the length measurement of blistering: When measuring the end of a deburring file, since the entire cross-section is within the beam, the defect will pass through the beam twice per revolution. Therefore, the defined duration should be less than 50% (e.g., 40%) of the revolution duration.

[0073] • Cavities (manufacturing defects in the roundness of the deburring file). This is to detect imperfections that occur during the manufacturing process of the deburring file, which look like dents or valleys in the other rounded surfaces of the deburring file. Valley defects in the deburring file can be detected with a very low percentage of the rotation time period. A limited duration of 10% or less of the rotation time would be most suitable (i.e., it would allow for the measurement of geometric information about such valleys).

[0074] In the example mentioned above, the device is arranged such that it can ignore unexpected contaminants or particles on the toothless cutting tool. The size and location of such contaminants on each tool are unknown and will vary from tool to tool.

[0075] In all the embodiments described above, the device includes an interface for analyzing the received intensity signals. It is important to note that this is not mandatory, and the method of the invention can be implemented in many different configurations of the device. For example, a tool measuring device (e.g., having a transmitter / receiver) can be configured as a unit mounted within a machine tool housing. The received intensity signals can be output from the tool measuring device (e.g., in digital or analog form) to an interface, computer, controller, etc., having a processor for analyzing the received intensity signals. The processor can even be split across multiple units and / or can perform other control or analysis functions.

Claims

1. A method for measuring at least one dimension of a toothless cutting tool using a cutting tool measuring device, the cutting 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 relating to the intensity of the received light, the method comprising the following steps; (i) Rotating the toothless cutter about its longitudinal axis while simultaneously moving the toothless cutter relative to the light beam, and (ii) By analyzing the changes in the received intensity signal that occur during step (i), at least one dimension of the toothless cutting tool is determined. Its features are, The signal analysis performed in step (ii) includes determining when the received intensity signal has exceeded a threshold for at least a defined duration, the defined duration being less than the time taken for the toothless cutter to complete one full rotation.

2. The method according to claim 1, wherein, The toothless cutting tool includes a grinding tool.

3. The method according to claim 2, wherein, The grinding tool is a diamond-coated deburring tool.

4. The method according to any one of claims 1 to 3, wherein, The defined duration is selected to detect concave defects in the toothless tool.

5. The method according to any one of claims 1 to 3, wherein, The specified duration is greater than 5% of the time it takes for the tool to rotate one revolution.

6. The method according to any one of claims 1 to 3, wherein, The specified duration is less than 95% of the time it takes for the tool to rotate one revolution.

7. The method according to any one of claims 1 to 3, wherein, The at least one dimension determined in step (ii) includes the tool radius and / or tool length.

8. The method according to any one of claims 1 to 3, wherein, Step (ii) includes establishing the total duration during which the threshold is held to be crossed in each revolution by identifying each time the received intensity signal crosses the threshold, and thereby determining when the total duration exceeds the defined duration.

9. The method according to any one of claims 1 to 3, wherein, Step (ii) includes determining whether the received intensity signal has continuously crossed the threshold for at least the defined duration.

10. The method according to any one of claims 1 to 3, wherein, Step (i) involves moving a rotating toothless cutter from a position away from the beam into the beam.

11. The method according to any one of claims 1 to 3, wherein, Step (i) involves removing the rotating toothless cutter from the beam.

12. The method according to any one of claims 1 to 3, wherein, The tool measuring device is mounted to a machine tool having a spindle that holds the toothless tool, and the machine tool is configured to provide rotation and movement of the toothless tool in step (i).

13. The method according to claim 12, wherein, Step (ii) includes the tool measuring device sending a trigger signal to the machine tool when the received intensity signal has exceeded the threshold for the defined duration, the machine tool providing a measurement of the position of the toothless tool upon receiving the trigger signal, and deriving the at least one dimension of the toothless tool from the measurement.

14. The method according to any one of claims 1 to 3, wherein, The toothless tool is a grinding tool, and the method includes the additional step of grinding the workpiece using the grinding tool.

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