Measuring device and method

Abstract

A protective member (126) for an optical measuring device, such as a broken beam tool setting device (2) for a machine tool, is described. The protective member (126) comprises a duct (140) through which light and air can pass. The duct (140) is configured such that, in use, a light beam passes through the duct along an optical axis (O) and an air flow is directed out of the duct along an airflow axis (A). The optical axis (O) is not parallel to the airflow axis (A), and the duct (140) has a varying cross-sectional profile along the airflow axis (A). Improved measurement repeatability is provided.

Description

[0001] The present invention relates to optical (non-contact) measuring devices, and in particular to devices in which a flow of expelled air is used to protect various optical components from contaminants of a common type found in a machine tool environment.

[0002] It is known to protect non-contact measuring devices, such as non-contact tool measuring devices, from contaminants (e.g. coolant, cutting debris, etc.) generated by machining operations performed by a machine tool. One example of such a non-contact tool measuring device is a laser tool setter which is used to detect when a tool held by a machine tool interrupts a narrow laser beam, thereby allowing tool measurements such as tool length and diameter to be obtained.

[0003] EP 1050368 and EP 1502699 describe examples of such laser tool setters in which a laser beam is passed from an emitter portion to a receiver portion via a free space region. The laser beam is passed into and out of the device via a narrow channel or duct in each of the emitter portion and the receiver portion. In such devices, each channel is formed (e.g. by a bore) at an oblique angle to the optical axis along which the laser beam passes between the emitter and the receiver. As a result, expelled air is directed (angularly) away from the free space optical path through which the laser beam passes. For example, these angled air channels are illustrated in Figure 4 c and EP 1502699. Figure 4 The NC4 non-contact tool setter system sold by Renishaw plc of Wotton-Under-Edge, UK is an example of a device which includes such angled apertures. An example of a break-beam tool setter device which expels air along its optical axis is described in US2018 / 111240. US 2010 / 0206384 describes an alternative apparatus in which a tubular air shield is provided by an array of air nozzles surrounding a central aperture through which the laser beam passes.

[0004] Although the known devices of the above type reduce air turbulence in the free space optical path through which the laser beam passes, the present inventors have found that some air turbulence effects can still be present, thereby degrading the repeatability of the measurements.

[0005] There is provided according to the present invention a protection member for an optical measuring device, the protection member comprising a duct through which light and air can pass, the duct being configured such that, in use, a light beam passes through the duct along an optical axis and a flow of air is directed out of the duct along an air flow axis, the optical axis being non-parallel to the air flow axis, characterised in that the duct has a varying cross-sectional profile along the air flow axis.

[0006] Accordingly, the present invention relates to a protective member for an optical measuring device, such as a non-contact tool measuring device. The protective member comprises a duct or passage through which both a light beam and an air flow (air stream) pass in use. In use, light passes along an optical axis through the duct, which can be normal to an outer surface of the protective member. Air that is directed through the duct is discharged from the duct along an air flow axis that is inclined or angled relative to the optical axis. The discharged air is thus directed away from the light beam in an attempt to prevent turbulent air flowing along the free space path of the light beam.

[0007] The invention features that the duct has a varying (i.e. changing) cross-sectional profile along the length of the air flow axis. In particular, the cross-sectional area and / or the cross-sectional shape of the duct varies along its length in order to reduce turbulence of the air that is discharged therefrom. This is in contrast to the ducts of EP 1050368 and EP 1502699, which are formed by, for example, drilling a hole in a blank protective member (thus resulting in a duct having a constant cross-sectional profile along the length of the air flow axis). It has been found that the varying shape of the duct reduces the overall air flow turbulence of the discharged air, thereby reducing the amount of turbulence that is present in the free space beam path. The varying shape can also serve to reduce the amount of air that needs to be discharged to provide a degree of protection from external contaminants. It has been found that both of these improvements provide an improvement in measurement repeatability.

[0008] It should again be noted that the duct is also configured to allow the light beam to pass along the optical axis (i.e. an axis that is angled relative to the air flow axis). The light beam that passes through the duct can be constrained (e.g. attenuated or shaped) by the duct or the light beam can pass through the duct unhindered. Thus, the above-mentioned improvements to the air flow characteristics can be achieved without affecting the optical performance of the protective member.

[0009] Advantageously, the duct has an inlet opening for receiving air and an outlet opening for discharging air. The inlet opening conveniently has a different cross-sectional area to the outlet opening. Preferably, the cross-sectional area of the inlet opening is greater than the cross-sectional area of the outlet opening. In other words, the inlet of the duct can be wider than the outlet. This variation (e.g. reduction) in cross-sectional area along the duct reduces the turbulence of the air within the duct before it is discharged, thereby reducing the turbulence of the discharged air. The inlet opening can also have an at least partially slot-shaped profile. For example, any “sharp” edges can be smoothed to provide a smoother, less turbulent air flow. In a preferred embodiment, the duct can be drilled and then widened and suitably shaped using a laser cutting process. This two-stage process minimises burrs that can otherwise introduce some air turbulence.

[0010] Advantageously, at least a portion of the duct has an asymmetric cross-sectional profile. For example, the circular or elliptical cross-section of prior art ducts can be replaced by an asymmetric cross-section. Thus, the duct can be non-cylindrical. Conveniently, the duct has an outlet opening which is substantially D-shaped when viewed along the optical axis.

[0011] Advantageously, the duct presents a substantially circular cross-section for light passing therethrough along the optical axis. In other words, the duct is shaped so that a substantially circular beam of light can pass therethrough along the optical axis. The duct can confine or shape the beam of light. Alternatively, substantially all of the incident beam of light can pass directly through the duct along the optical axis.

[0012] The protective member can comprise other components which serve to help direct the airflow through the duct and / or to interact with the beam of light. For example, the protective member can comprise an optical aperture (i.e. an aperture separate from the duct) which serves to confine the beam of light passing along the optical axis. The optical aperture can shape and / or attenuate the beam of light. The cross-section of the duct for light when viewed along the optical axis can be slightly larger than the associated optical aperture. For example, the effective radius of the duct along the optical axis can be 0.1 mm greater than the radius of such an optical aperture. All of the air expelled via the protective member can also pass through the optical aperture. Alternatively, there can be other apertures or channels through which some air can pass (i.e. not through the optical aperture).

[0013] All of the air exiting the duct can be directed in substantially the same direction (i.e. along an airflow axis). For example, all of the airflow expelled from the duct can be directed upwards, downwards or to one side of the optical axis. The airflow axis is not parallel (e.g. inclined or skewed) with respect to the optical axis, so the possible influence of the airflow on the light passing along the optical axis is minimal. In particular, the protective airflow preferably traverses the optical path in a very localised region and in only one direction. This provides a stable airflow arrangement which improves measurement reproducibility. Advantageously, a substantial portion of the airflow expelled from the duct does not move in a direction along or parallel to the optical axis. In other words, the air is preferably ejected in an off-axis direction.

[0014] Conveniently, the airflow axis can be at an angle of greater than 5° with respect to the optical axis. The airflow axis can be at an angle of greater than 10° with respect to the optical axis. The airflow axis can be at an angle of greater than 15° with respect to the optical axis. The airflow axis can be at an angle of greater than 20° with respect to the optical axis. The airflow axis can be at an angle of less than 45° with respect to the optical axis. Preferably, the airflow axis is at an angle of approximately 30° with respect to the optical axis. Although a greater angle directs the air further away from the path of the free-space beam, this does require a larger duct (i.e. to ensure that the beam can still pass along the optical axis) and so reduces the entry protection and / or more air must be expelled.

[0015] The protection member preferably consists of only a single duct. This single duct can have only a single outlet aperture from which air is expelled. The physical shape of this single duct can define the direction of the air flow. Preferably, all air expelled through the protection member passes through the single duct. Thus, the complex arrangement of multiple air jets of the type described in US 2010 / 0206384 can be avoided. The amount of air consumption required to provide a degree of protection against the ingress of contaminants is also reduced.

[0016] The protection member can be formed integrally with the optical measurement device. For example, the protection member can form part of the housing or casing of such a device. Conveniently, the protection member can comprise one or more features for releasably attaching to the emitter or receiver of the optical measurement device. For example, the protection member can be formed as a cap which can be attached to and detached from the optical measurement device. Variants of such a cap can then be provided for different configurations of the optical measurement device. Such caps can be configured to fit existing technology measurement devices (i.e. they can be retrofittable). The optical components (e.g. lenses / detectors) of the optical measurement device are preferably recessed within the device (i.e. behind the duct of the protection member).

[0017] The present invention also extends to an optical measurement device comprising at least one protection member as described above. The optical measurement device can comprise an emitter having a protection member and / or a receiver having a protection member. In such examples, the protection members can be nominally identical or can be different. For example, the emitter and receiver can be provided with protection members having ducts of different sizes and / or optical apertures of different sizes. The air turbulence generated at the emitter can be less than the air turbulence generated at the receiver. A kit of multiple protection members having ducts and / or optical apertures of different sizes can also be provided to allow the measurement device to be configured as required.

[0018] The optical measurement device can comprise other optical components (lenses, light sources, receivers etc.). The optical measurement device can comprise other air flow control devices (e.g. control valves, flow restrictors, one-way valves etc.). Advantageously, the optical measurement device can comprise an internal air chamber adjacent to the duct of each protection member. Such an internal air chamber can help to reduce the air turbulence entering the duct of the protection member, thereby reducing the turbulence of the expelled air. The air flow through the internal air chamber can also be arranged to avoid the optical path through the air chamber. Furthermore, the air flow through the chamber can be converging at the duct. This can reduce the effect of turbulence on the light beam as it passes through the air chamber.

[0019] The dimensions of the duct can be selected to achieve an optimum balance between repeatability and air consumption versus accuracy. For example, the dimensions of the optical aperture can be maintained and repeatability improved. Alternatively, the dimensions of the optical aperture can be increased to improve metrology while maintaining repeatability. Thus, a suitably dimensioned guard member can be used for each required application.

[0020] In preferred embodiments, the optical measurement device is a tool measurement device, such as an interrupter beam tool measurement device. The tool measurement device can be mounted to the bed of a machine tool. Air or other gas (e.g. from a shop compressed air supply) can be fed into the device. The supply of air can be a substantially constant flow rate. Alternatively, the air flow can be variable during use (e.g. based on the degree of protection required). For example, a low flow rate and a high flow rate can be used. The air supply can be stopped completely, for example when no air protection is required. The guard member can also form part of the shutter assembly described in our patent application PCT / GB2020 / 050581.

[0021] A guard member for an optical measurement device is also described herein. The guard member can comprise a duct through which light and gas (e.g. air) can pass. The duct can be configured such that, in use, a light beam passes through the duct along an optical axis. The duct can be configured such that, in use, an air (or other gas) flow is directed out of the duct along an air flow axis. The optical axis can not be parallel to the air flow axis. The duct can have a varying cross-sectional profile along the air flow axis. The duct can be a substantially smooth aerodynamic duct. The substantially smooth aerodynamic duct can be venturi-like. The duct can be substantially smooth (e.g. by chamfering or blending radii during manufacture). The member can comprise any other feature described herein, individually or in combination.

[0022] The application will now be described, by way of example only, with reference to the accompanying drawings in which;

[0023] Figure 1 A non-contact tool setting device is shown,

[0024] Figure 2 shows a prior art cap for a non-contact tool setting device,

[0025] Figure 3 A cutaway view of a cap for use with a non-contact tool setting device according to the present application is shown,

[0026] Figure 4 A front view of the cap of Figure 3 is shown,

[0027] Figure 5 A cutaway view of a cap with additional air flow insert according to the present application is shown,

[0028] Figure 6 is made of a structure according to Figure 3 a photo of a cap made of a structure according to

[0029] Figure 7 shows air turbulence in the x-y plane associated with a cap of the prior art,

[0030] Figure 8 shows air turbulence in the x-y plane associated with a cap of the present invention,

[0031] Figure 9 shows air turbulence in the y-z plane associated with a cap of the prior art, and

[0032] Figure 10 shows air turbulence in the y-z plane associated with a cap of the present invention.

[0033] With reference to Figure 1 , a partly exploded view of a tool setting device 2 of the prior art is shown. The device comprises a transmitter unit 10 comprising a laser diode and appropriate optics (not shown) for generating a light beam 12. A receiver unit 14 comprising a photodiode (not shown) is also provided for detecting the intensity of the received light beam 12. Both the transmitter unit 10 and the receiver unit 14 are attached to a common base 20, maintaining a fixed spacing and orientation relative to each other. The base 20 can then be mounted directly to the bed of the machine tool or even to any appropriate part. It should also be noted that a variety of different alternative structures for mounting the transmitter and receiver can be used. For example, a common housing for the transmitter and receiver can be provided, or the transmitter unit and receiver unit can be mounted to the machine tool separately. An electrical socket 22 is provided on the base 20 for connection by a cable to an associated interface (not shown) which provides power and receives the beam intensity signal from the detector of the receiver unit 14.

[0034] The tool setting device 2 is designed to operate in the harsh environment of a machine tool, where there are often pressurized coolant flows, coolant mist and cutting debris, etc. Long-term and reliable device operation in such harsh conditions is possible by using a so-called air protection system. Thus, the transmitter unit 10 and the receiver unit 14 comprise an air cap 26 comprising a channel or duct 28 through which the light beam 12 passes. In Figure 1In use, compressed air is fed into the body of the device from an air inlet 30. The device is arranged so that at least some of this air is discharged from the device via the light-transmitting cap 26 in the same conduit 40. This continuous air discharge prevents contaminants from entering the device while still allowing light to pass in and out of the device as appropriate so that measurements can be made.

[0035] Reference is now also made to Figure 2 which illustrates the configuration of the prior art air cap 26 in more detail. Each air cap 26 comprises an inclined passageway or conduit 40 through which air is discharged. This conduit 40 is formed by drilling through the blank cap at an oblique angle to the surface normal of the outermost surface of the component. The dimensions and oblique angle of the conduit 40 are chosen so that a light beam passing through the optical aperture 42 in a direction normal to the outermost surface of the component (i.e. along the optical axis of the light beam) can also pass through the conduit. The conduit 40 also discharges air that has been forced under pressure into the chamber 44 through a series of air holes 46, optionally via an air flow restrictor 48. The conduit is formed at an angle at which air is discharged in a direction generally parallel to the angle. In other words, air is discharged along an air flow axis (A) that is at an oblique angle (θ) to the optical axis (O) of the light beam. As explained in EP 1050368 and EP 1502699, this arrangement helps to direct the air flow away from the free space optical path of the beam (i.e. the free space path between the emitter and receiving units through which the light beam passes), thereby reducing the impact that such air flow can have on the measurement accuracy of the device.

[0036] While the prior art arrangement provides reliable protection against contaminants, the present inventors have found that turbulence within the discharged air flow can still disrupt the air flow along the free space optical path of the beam, thereby adversely affecting the measurement performance of the device. As will be described below, it has been found that the present invention improves the measurement accuracy of the device by reducing the turbulence of the air flow associated with the discharged air. In particular, it has been found that varying the cross-sectional profile along the conduit (i.e. in the direction along the air flow axis A) can significantly reduce the turbulence of the air discharged from such a conduit compared to the prior art conduit having a constant cross-section along its length. For example, it has been found that removing any sharp edges in the air flow path through the conduit and / or reducing the cross-sectional area of the conduit along its length (i.e. in the direction of the air flow axis) reduces the turbulent flow of the discharged air.

[0037] Reference Figure 3 and Figure 4 illustrates an air cap 126 in accordance with the present invention. The air cap comprises a conduit 140 having a region 142 of constant cross-section but including a region 144 of increased cross-sectional area. In particular, the sharp edge 90 visible in the air cap 26 of Figure 2 is removed byFigure 3 The flat section 190 shown in the middle is replaced. Thus, this change in the shape of the opening of the duct 140 provides a "D-shaped" duct 140 when viewed from the direction of the surface normal, i.e. along the optical axis, as Figure 4 illustrated. When mounted on a tool setting device (e.g. as Figure 1 shown), air is expelled along an air flow axis A, while the light beam passes along the optical axis O. The air flow axis A is tilted or angled with respect to the optical axis O.

[0038] Figure 5 Reference is made to Figure 3 and Figure 4 described how the air cap 126 can further comprise an optical aperture 150, which for example can limit the light beam passing therethrough. An optional air flow restrictor 152 is also provided; it has been found that providing such an air flow restrictor with a uniform cross-section and a widened aperture serves to further reduce the turbulence of the air flow into the chamber 154. In this example, the diameter of the aperture in the air flow restrictor 152 is about 1.7mm, and the diameter of the optical aperture 150 is about 0.5mm. A flow rate of about thirty litres per minute is passed through the air cap 126. The shape of the air flow restrictor 152 is preferably free of steps or cross-sectional discontinuities; this helps to reduce air turbulence effects.

[0039] Figure 6 are photographs of air caps made according to Figure 3 and Figure 4 illustrated. The D-shaped ducts are formed by drilling a hole through the blank along the direction of its surface normal, and then laser cutting the remaining profile. Of course other manufacturing techniques are possible.

[0040] Reference is next made to Figures 7 to 10 presents air flow modelling results to illustrate that reduced air turbulence results when using an air cap as described with reference to Figures 3 to 6 compared to prior art air caps as shown in Figure 2. In particular, Figure 7 shows air turbulence in the XY plane for a prior art air cap as shown in Figure 2. It can be seen that the air turbulence extends to the optical axis O along which the light beam passes. Figure 8 shows air turbulence in the XY plane for an air cap of the present invention as described with reference to Figures 3 to 6 It can be seen that the modification to the duct shape reduces the overall turbulence associated with the expelled air, and greatly reduces the amount of air turbulence in the vicinity of the optical axis O. This can also be seen from the air turbulence in the YZ plane for a prior art air cap as shown in Figure 9 and for an air cap of the present invention as shown in Figure 10 Of course, the air cap can be placed in any desired orientation with respect to the axes of the associated measuring device or machine tool.

[0041] It should be kept in mind that the above is only one example of the application and that the skilled person will understand possible variations. For example, the air cap can be mounted only to one of the receiver or transmitter unit, or a combined transmitter / receiver unit of the reflection device. The air cap can also be used on other measurement devices than just a gage. Although a removable air cap is described, it is also possible to form the duct etc. as an integral part of the measurement device. For example, the duct can be provided as part of a service panel or a housing part.

Claims

1. An optical measuring device comprising at least one protective member, said at least one protective member including a conduit through which light and air can pass, said optical measuring device being configured such that, in use, a light beam passes through the conduit along an optical axis (O), while an airflow is guided out of the conduit along an airflow axis (A), said optical axis (O) not being parallel to said airflow axis (A), characterized in that, The duct has a varying cross-sectional profile along the airflow axis (A).

2. The optical measuring device according to claim 1, wherein, The pipe has an inlet opening for receiving air and an outlet opening for discharging air, wherein the inlet opening has a different cross-sectional area than the outlet opening.

3. The optical measuring device according to claim 2, wherein, The cross-sectional area of ​​the inlet opening is greater than the cross-sectional area of ​​the outlet opening.

4. The optical measuring device according to claim 3, wherein, The inlet opening has at least a partially groove-shaped profile.

5. The optical measuring device according to claim 1, wherein, At least a portion of the pipe has an asymmetrical cross-sectional profile.

6. The optical measuring device according to claim 1, wherein, The conduit has an outlet opening that is substantially D-shaped when viewed along the optical axis.

7. The optical measuring device according to claim 1, wherein, The conduit presents a substantially circular cross-section for light passing through it along the optical axis (O).

8. The optical measuring device according to claim 1, wherein, The at least one protective member further includes an optical aperture for constraining the light beam transmitted along the optical axis (O).

9. The optical measuring device according to claim 1, wherein, The airflow axis (A) forms an angle greater than 10° with respect to the optical axis (O).

10. The optical measuring device according to claim 1, wherein, The at least one protective member includes one or more features for releasably attaching to the transmitter or receiver of the optical measuring device.

11. The optical measuring device according to claim 1, wherein, The optical axis (O) is perpendicular to the outer surface of the at least one protective member.

12. The optical measuring device of claim 1, further comprising an internal airflow control component for minimizing turbulence in the airflow directed to the duct of the at least one protective component.

13. The optical measuring device of claim 1, comprising an internal air chamber adjacent to the conduit of each of the at least one protective member.

14. The optical measuring apparatus according to any one of claims 1 to 13, wherein, The optical measuring device is an interrupted beam cutting tool measuring device.

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