The method may be implemented using a tool measurement apparatus mounted to a machine tool. The machine tool may have a spindle that holds the non-toothed tool. The machine tool may be configured to provide the rotation and motion of the non-toothed tool of step (i). Step (ii) may comprise the tool measurement apparatus issuing a trigger signal to the machine tool when the received intensity signal has crossed the threshold for the defined duration. The machine tool may provide a measure of the position of the non-toothed tool on receipt of the trigger signal from which the at least one dimension of the non-toothed tool is derived.

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

Alternatively, the apparatus used in the method may be formed as a plurality of units. For example, a measurement unit may be provided that includes at least the receiver. The measurement unit may also comprise the transmitter. The measurement unit may be mounted within a machine tool enclosure (e.g. it may include protection against the ingress of coolant and other machining contaminants). A separate processing unit (e.g. an interface) may include the processor or the processor may be distributed over several processing unit. The processing unit may form part of the associated machine tool. In the above described arrangement, the received intensity signal may be passed from the measurement unit to the processing unit. This passage may be over a communications link. The communications link may be wired or wireless. A dedicated or shared communications link could be used for this purpose. The received intensity signal may be passed as an analogue signal (e.g. the signal may be a voltage that varies in proportion to received light intensity). Preferably, the receiver of the apparatus includes an analogue-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 it could just output a raw intensity signal or signals.

The transmitter of the apparatus used in the method may comprise a laser, for example a laser diode. The transmitted light beam may have any wavelength (e.g. a red, green, blue etc laser beam may be generated). The light beam may be collimated. The light beam may be a focused beam. The receiver could comprise a single detector element (e.g. a photodiode) for detecting received light intensity. Alternatively, the receiver could include a plurality of detector elements. In such an example, the received light intensity signal may be generated by combining the light intensity measured by a plurality of detector elements. The receiver may include (analogue and/or digital) electronics for pre-processing of the light intensity signal. Additional processing of the received intensity signal may also be performed by a processor before its comparison to the threshold.

The apparatus on which the method is implemented may include a processor that is arranged to issue a trigger signal when the received intensity signal has crossed the threshold for the defined duration. In other words, the issuance of a trigger signal may be used to indicate that the criterion being monitored by the processor (i.e. that the received intensity signal has crossed the threshold for the defined duration) has been met. Issuance of the trigger signal may comprise 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 repeating series of pulses. The trigger signal may be output as an analogue signal or it may be communicated via a digital interface (e.g. as a time-stamped event). An associated machine tool controller may receive and act upon a received trigger signal. In particular, the receipt of the trigger signal may cause the position of the tool within the machine tool to be recorded (i.e. to allow the position of tool when the trigger signal was issued to be established). In this manner, the required measurement of a tool dimension is provided. The receipt of a trigger signal may also stop the movement of the tool relative to (i.e. into or out of) the light beam. If the processor is provided as part of the machine tool controller, there may be no need for such a trigger signal to be generated.

The method may, when the non-toothed tool is a grinding tool, comprise an additional step of grinding a workpiece. In other words, the grinding tool may be used to process (remove material from) a workpiece. As mentioned above, such a grinding tool may be any type of grinding tool (e.g. a diamond coated burr tool). The workpiece that is processed may, for example, be a glass ceramic component (e.g. for use in a consumer electronics device).

Also described herein is a method for measuring a dimension of a tool, such as a grinding tool. The method may comprise a step of directing a beam of light towards a receiver. The receiver may produce a received intensity signal related to the intensity of received light. The method may comprise moving a rotating tool relative to the light beam. Variations in the received intensity signal may be analysed to measure the tool. The method may include a 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 taken for one complete rotation of the tool. Any tool may be measured using the method. Advantageously, the tool is a grinding tool. The tool may be a burr tool. The method may include any other step or steps described elsewhere herein.

Also described herein is a tool measurement apparatus that may be used for measuring a dimension of a tool. The tool measurement apparatus may be configured to implement, or may include any of the features described in the context of, the method described herein. The apparatus may comprise a transmitter. The transmitter may produce a beam of light. The beam of light may be directed towards a receiver. The receiver may produce a received intensity signal. The received intensity signal may be related (e.g. be proportional) to the intensity of received light. A processor may be provided for analysing variations in the received intensity signal. The processor may perform the analysis when a rotating tool is moved through the light beam. The processor may perform the analysis when a rotating tool is moved into the light beam. The processor may perform the analysis when a rotating tool is moved out of the light beam. The analysis may enable a dimension of the tool to be measured. The processor may be configured to determine when the received intensity signal has crossed a threshold for at least a defined duration. The defined duration may be less than the time taken for one complete rotation of the tool. The processor may be configured to determine when the received intensity signal exceeds a threshold for a duration less than the time taken for one complete rotation of the tool. The processor may be configured to determine when the received intensity signal drops below and remains below a threshold for a predetermined duration.

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

FIG. 1 shows a non-contact tool setting device,

FIGS. 2a and 2b illustrate a calibration tool with a contaminant attached thereto,

FIG. 3 shows the effect of the contaminant of FIGS. 2a and 2b on the light intensity profile during a light-to-dark measurement,

FIG. 4 illustrates how the technique of the present invention can exclude the effect of the contaminant,

FIG. 5 is a scanning electron microscope (SEM) image of unwanted clumps of material as formed during the manufacture of a grinding tool,

FIG. 6 schematically illustrates the effect of the clump on the received light intensity during a dark-to-light measurement, and

FIG. 7 is collected data that shows the effect of multiple abrasive elements when measuring a grinding tool.

Referring to FIG. 1, a schematic illustration of a tool measurement apparatus is provided. The apparatus comprises a transmitter 10 for generating a beam of light 12. The transmitter 10 generates the light beam 12 using a laser diode and suitable optics (not shown). A receiver 14 is also illustrated for receiving the beam of light 12. The receiver comprises a photodiode (not shown) for detecting the beam of light 12.

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

The apparatus also comprises an interface 15 connected to the transmitter 10 and receiver 14 via electrical cables 17. The interface 15 provides electrical power to the transmitter 10 and receiver 14 and also receives a beam intensity signal (also termed a received intensity signal) from the photodiode detector of the receiver 14. The interface 15 also comprises a processor 24 that analyses the beam intensity signal and generates a trigger signal. This trigger signal is passed to the SKIP input of a controller 30 of an associated machine tool via a cable 28. The position of the tool, as measured by the machine tool, is captured on receipt of the trigger signal from the interface 15 thereby allowing a tool size (e.g. tool length or diameter) measurement to be made. The trigger signal may be output in a plurality of different ways, depending on the configuration of the controller 30. For example, the trigger signal may be communicated by latching the voltage of 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 may alternatively be passed to the controller 30 over a digital data bus (e.g. as described in WO2018/134585).

FIGS. 2a and 2b show a calibration tool 40 (i.e. an example of a non-toothed tool), which may also be termed a calibration pin, in side-on and cross-sectional views respectively. The calibration tool 40 is an elongate cylinder having a known (e.g. calibrated) radius. Also shown is the presence of a contaminant 42 (the relative size of which is exaggerated for illustration purposes) on the calibration tool 40. The contaminant 42 may, for example, be dirt or debris that attaches itself to the calibration tool 40 and can't be easily removed by high speed rotation or using an air blast or similar tool cleaning technique. FIG. 2b illustrates the calibration tool 40 being rotated at a high speed about its elongate axis whilst also being translated into the light beam 12 that passes between the transmitter 10 and receiver 14 of the above described tool measurement apparatus.

FIG. 3 plots the received intensity signal for one complete tool rotation when the calibration tool 40 shown in FIGS. 2a and 2b is at four different locations relative to the light beam 12. The graph shows the received intensity signal (in percent) plotted against time, where the time taken for a single rotation of the calibration tool 40 is Tr. Also shown is the fifty percent level 48 that is used as a threshold level. It should be noted that the use of fifty percent is arbitrary and the threshold could be set at a different value.

Before the tool 40 enters the light beam 12, the beam is unbroken and hence 100% of the light beam passes to the receiver; this is shown as the plotted line 50. The line 52 shows the received intensity when the tool 40 is moved so that the contaminant 42 just enters the extreme edge of the light beam 12 once per rotation, but before the tool 40 is advanced sufficiency to allow any of the cylindrical core of the tool 40 to enter the beam. The small dip visible in the light intensity plot 52 thus corresponds to the contaminant partially obscuring the beam, once per rotation.

In the prior art NC4 apparatus mentioned above, the received intensity signal is compared to the fifty-percent trigger threshold as the rotating tool is advanced into the light beam 12. The apparatus issues a trigger signal when the received intensity signal drops below the threshold 48; this is the scenario illustrated by the plotted line 54 in FIG. 3. In the prior art tool measurement apparatus, the issued trigger signal would thus cause the associated machine tool to measure the position of the tool 40 when 50% of the beam is blocked at some point during the tool rotation. In this example, the occlusion of the beam by the contaminant would mean the measured position (and hence the measured tool radius) would not be an accurate measure of the diameter of the cylindrical tool body. Instead, the apparatus would measure the radius of the outer flight circle of the contaminant. The measured radius of the calibration tool would thus be greater, by an amount equal to the distance by which the contaminant 42 protrudes from the cylindrical tool body, than the actual radius of the tool.

At this point it should be noted that, for many types of tool, the maximum radius (as defined by the outer “flight circle” of the tool) does provide a suitable measure of the effective cutting radius. In particular, a toothed cutting tool (e.g. for milling, drilling etc) may have multiple teeth but the depth of cut it makes in a workpiece will be determined by the outer flight circle of those teeth. The present inventors have, however, realised that this is not always the case for non-toothed tools. In the example shown in FIGS. 2 and 3, a more reliable measurement of calibration tool radius could be attained by ignoring any small dips in the received intensity signal that arise from contaminants and instead ascertaining the tool position when the bulk of the received intensity signal drops below the threshold