GB2528159A

GB2528159A - Sensor

Info

Publication number: GB2528159A
Application number: GB1507875.1A
Authority: GB
Inventors: Stephen Edward Lummes; David Collingwood
Original assignee: Renishaw PLC
Current assignee: Renishaw PLC
Priority date: 2014-06-30
Filing date: 2015-05-08
Publication date: 2016-01-13
Anticipated expiration: 2035-05-08
Also published as: GB2528159B; GB201507875D0; GB201411575D0

Abstract

A method of manufacturing a bearing arrangement for first and second parts 22, 24 of a sensor device 20 is provided. The first and second parts 22, 24 are moveable relative to each other along a linear axis A. The method comprises taking the first and/or second part 22, 24 of the sensor device 20, on which a bearing arrangement 36 with at least one bearing protrusion 38 is provided; and using a tool 14 to finish the crest 40 of the at least one bearing protrusion 38 on the part such that the crest 40 defines a plain bearing region for the other part.

Description

SENSOR

This invention relates to a sensor device, such as a tool setter (e.g. for a coordinate positioning machine, such as a coordinate measuring machine (CMIM) or a machine tool), in particular a linear axis sensor, for example a contact, single linear axis, tool setter.

As will be understood tool sefters are used to determine geometric information about a tool. For example, tool setters are used to determine the position, length, 1 0 radius and/or diameter of a tool. For example tool setters are often used to determine geometric information of tools such as a cutting, grinding, or polishing tool in a machine tool, in particular a (computer) numerically controlled ((C)NC) machine tool, It can be particularly useful to know/determine at least the relative geometry of a range of tools to be used in a machining operation to ensure correct formation of features in'on the workpiece.

In general, sensors (including tool setters) can be classified as "contact sensors" (such as contact tool setters) in which contact with the sensor is needed to measure or "non-contact sensors" (e,g. non-contact tool setters) which utilise non-contact means (e.g, break laser beam systems) to measure, The present invention concerns contact sensors (e,g, contact tool setters), One type of sensor is a single linear axis sensor (e,g, a single linear axis tool setter, also known as a plunger tool setter), Figure 9a is provided to schematically 2 5 illustrate the bearing arrangement for such a known single linear axis sensor, in this case a single linear axis tool setter 600. As shown a bearing body 604 can sit within a housing 602, and a plunger 606 is provided that is moveable relative to the bearing body along a single linear axis A. The plunger 606 has a contact pad/plate 608, the contact pad/plate being connected to the top of a shaft 610 which extends into the main body, The bearing arrangement (which facilitates movement of the plunger relative to the bearing body along the axis A and controls the lateral position of the plunger) comprises a plurality of balls 614 that sit between the bearing body and shaft and which can roll so as to allow smooth movement between the bearing body and shaft. The plunger 606 is biased in a rest position by biasing means (not shown). Furthermore means (not shown) is provided for detecting movement of the plunger away from its rest position and issuing a trigger signal in response to detecting such movement. h use, a tool 612 is brought into contact with the plunger's contact pad 608 vertically along the axis A which causes the plunger to be pushed into the main body along the axis A until the means for detecting movement of the plunger detects that the plunger has been pushed away from its rest position and issues a trigger signal.

Figure 9b is provided to illustrate another known bearing arrangement for a single linear axis tool setter which instead of a plurality of rolling balls simply comprises a plain bearing arrangement, which comprises a smooth cylindrical hole 616 which provides a plain bearing surface for the cylindrical shaft 610.

It can be important to ensure that the bearing arrangement is accurately formed so as to avoid undue lateral motion of the plunger relative to the bearing body. In particular, it can be important to avoid undue rotation of the plunger about an axis perpendicular to the axis along which it is configured to move (in other words "tilting"). Such tilting can adversely affect the performance of the sensor. For example, tiling can permit undetected displacement of the moveable parts of the sensor. For instance, in the case of the tool setter, if the tool contacts the pad/plate 608 off-centre, downward movement of the tool will cause the plunger 608 to initially rotate/tilt rather than travel along the axis A and so the tool will have to 2 5 travel frirther before the trigger signal occurs, resulting in an erroneous measurement.

The present invention provides an improved single linear axis sensor. In particular, the present invention provides an improved "plunger type" contact tool setter.

According to a first aspect of the invention there is provided a method of manufacturing a bearing arrangement for first and second parts of a sensor device that are moveable relative to each other along a linear axis, the method comprising: taking the first arid/or second part on which at least one bearing protrusion is provided, and using a tool to finish the crest of the at least one bearing protrusion on the part such that the crest defines a plain bearing surface for the other part.

The method of the invention provides a simpler and cheaper way to make a tightly toleranced bearing for a sensor compared to the above described prior art 1 0 embodiments which utilise ball bearings or regular cylindrical plain bearings. The particular two-stage technique of initially providing at least one protrusion with a crest which is subsequently processed means that there can be more tolerance in the initial shape of the at least one bearing formation, making the process cheaper and quicker. Furthermore, since the at least one bearing formation has the form of 1 5 a protrusion, a shaping tool can easily and accurately form the plain bearing region(s) as it is much easier to "work" the crest(s) of a protrusion(s) than a flat or regular (e.g. regular cylindrical) surface, owing to the space on the sides of the protrusion.

When assembled, the plain bearing region/surface of the at least one bearing protrusion on the first or second part can cooperate with a bearing surface on the other part so as to facilitate and define relative movement between the first and second parts along a linear axis, whilst controlling their relative lateral position.

The method can additionally comprise the step of assembling the first and second parts. Accordingly, once assembled, the plain bearing region/surface of the at least one bearing protrusion on the first or second part cooperates with a bearing surface on the other part so as to facilitate and define relative movement between the first and second parts along a linear axis, whilst controlling their relative lateral position.

The (or all) bearing protrusion(s) could be provided on just one of the first and second parts. Optionally, at least one bearing protrusion could be provided on the first part and at least one bearing protrusion could be provided on the second part.

In this case, both the first and second parts have bearing protrusions and corresponding bearing surfaces.

The at least one bearing protrusion, before said finishing, could be described as an unfinished bearing protrusion, or a preliminary bearing protrusion.

As will be understood, the at least one bearing protrusion can be a formation provided on the surface of the first or second part. The method of the invention can comprise the step of forming the at least one bearing protrusion (which could also be referred to as a bearing protrusion formation). For example, the method could comprise processing the part (the first and/or second part) to provide the at least one bearing protrusion, Processing could comprise removing and/or displacing material of the part to form the at least one bearing protrusion. For instance, processing could comprise cutting material from the part. In the case of a helical protrusion (see below), processing could comprise tapping/threading the part using a tap or die tool. Accordingly, the method could comprise machining the first and/or second part so as to provide the at east one bearing protrusion.

The method can comprise a machine tool forming the at least one bearing protrusion (eg. the machine tool machining the first and/or second part so as to provide the at least one bearing protrusion), and then the same machine tool using a tool to finish the crest of the at least one bearing protrusion such that the crest defines a plain bearing surface for the other part. This can help to ensure the accuracy of the bearing. Optionally, the step of forming/machining the bearing protrusion and the step of finishing the crest of the bearing protrusion are performed on different machines.

As will be understood, the step of forming the at least one bearing protrusion could be performed prior to the method of the invention (e.g. by a third party). In this case, the method can comprise receiving the first and/or second part of the sensor, on which at least one bearing protrusion is provided, and using a tool to finish the crest of the at least one bearing protrusion on the part such that the crest defines a plain bearing surface for the other part. This could comprise loading the part(s) with the at least one bearing protrusion on a machine tool which then uses the tool finish the crests of the at least one bearing protrusion.

The at least one bearing protrusion could be a point protrusion. In this case, it could be referred to as a nub or lump, for example. Furthermore in this case there will likely be a plurality of bearing protrusions provided on the first and/or second parts so as to adequately control the relative position and motion of the first and 1 0 second parts along the axis.

The at least one bearing protrusion could be elongate. In this case, it could be referred to as a ridge. There could be provided a combination of point and elongate bearing protrusions.

A bearing protrusion, for example an elongate bearing protrusion, could have a regular or irregular shape.

h the case of an elongate bearing protrusion, there could be provided just a single bearing protrusion, For example, a single helically extending bearing protrusion could be provided which wraps around and along the axis. Nevertheless, this need not necessarily be the case and a plurality of elongate bearing protrusions could be provided, e.g. a plurality of helically extending bearing protrusions.

Optionally, the at least one elongate bearing protrusion could be annular, e.g. ring or 0-shaped. The annular bearing protrusion could be contained within a plane, for example a plane perpendicular to the axis. A plurality of annular bearing protrusions could be provided along the axis. A first annular bearing protrusion could be provided toward a first end and a second annular bearing protrusion could be provided toward a second end.

As an additional example, at least one &ongate bearing protrusion could be substantially straight, e.g. could extend parallel to the axis.

As will be understood, a plurality of different types of elongate bearing protrusions could be provided on the first and/or second parts. For example, there could be provided at least one helical bearing protrusion, md at least one annular bearing protrusion.

Said finishing of the crest of the at least one bearing protrusion could comprise removing material from said bearing protrusion, Accordingly, said finishing could comprise cutting the crest of the at least one bearing protrusion.

Accordingly, said tool can comprise a cutting tool, Accordingly, the method can comprise pushing a cutting tool into and past the at least one bearing protrusion so as to cut the at least one protrusion. For example, said finishing can comprise reaming. Accordingly, said tool can comprise a reamer. The method can 1 5 comprise removing any remnants, e.g. burrs, from the at least one protrusion that have been left over from the cutting process. The method can comprise removing any remnants, e.g. buns, from the crest of said at least one protrusion, The method can comprise removing said remnants, e,g, buns, using a bearing protrusion forming tool identical to the bearing protrusion forming tool used to form said at least one bearing protrusion, The method can comprise using the same bearing protrusion forming tool (e.g. on the same machine) to remove said remnants. For example, the method can comprise using the same tap or die cutting tool to remove said buns. In other words, the method can comprise re- 2 5 tapping said at least one helical protrusion to remove said remnants, e.g. buns.

Furthermore, the method can comprise subsequently re-finishing said crests using said tool. Such subsequent re-finishing, e.g. re-reaming, can remove any remaining remnants, e.g. burrs, missed by the previous step (e.g. missed by said re-tapping), Optionally, the predominant effect of said finishing does not involve cutting/removing material. For example, said finishing can comprise displacing, e.g. deforming, the material of the bearing protrusion's crest. Accordingly, said using the tool to finish the crest of the at least one bearing protrusion can comprise using the tool to plastically deform the crest of the at least one protrusion. In other words, the method can comprise using the tool to push the material of the crest out of the way. Such deforming/displacing/pushing results in substantially little or predominantly no removal of material. The material that has been deformed/displaced/pushed remains as part of the bearing protrusion and can contribute to the plain bearing region/surface. The step of defomiing/displacing/pushing the crest of the at least one bearing protrusion can 1 0 result in the deformed material forming a bulge, or overhang, on at least one side, and for example on at least both (or all) sides of the protrusion. Such bulge or overhang could form part of the plain bearing region. Accordingly. the tool can have a smooth surface (unlike a cutting or grinding tool which has teeth or an abrasive rough surface configured to remove material).

Using the tool can comprise pushing a rotating shaping tool into and past the at least one bearing protrusion so as to remove (e.g. cut) and/or plastically deform the at least one protrusion. By rotating the tool, interference and jamming of the tool with the at least one bearing protrusion can be avoided and therefore allows a greater tolerance on the initial forming of the at least one bearing protrusion.

Accordingly, as will be understood, the tool used to finish the crest of the at least one bearing protrusion can comprise any suitable tool for cutting and/or deforming said at least one protrusion. Accordingly, the tool is suitable for mounting on a machine tool, e.g. onto a machine tool's spindle. Accordingly, the tool is separate/different to (i.e. is not) the first or second part. Accordingly, the method can comprise assembling the first and second parts subsequent to using said tool to finish the crest.

The method can comprise providing liquid at the point of interaction between the tool and bearing protrusion during said finishing. This can be particularly advantageous when using a rotating shaping tool. As described in more detail below, entrainment of the liquid can positively affect the deformation of the crests. The liquid can be water based. Optionally, the liquid is coolant, e.g. machine tool coolant.

The first part can comprise a hole, The at least one bearing protrusion can be provided on the hole's (inner) surface. The hole can be substantially circular in cross-section, The hole could be substantially cylindrical. As will be understood, when the hole has the at least one bearing protrusion, the hole's shape (and diameter) is defined by the crest of the at least one bearing protrusion. The at 1 0 least one bearing protrusion can comprise at least one helically extending protrusion/formation provided on the hole's (inner) surface. The second part can comprise a shaft (eg, a substantially cylindrical shaft, e,g, a plain/regular/smooth cylindrical shaft) forbearing against said crest of said at least one helically extending protrusion.

The first part could comprise a female part for receiving the second part, and/or vice versa. The (or all) at least one bearing protrusion(s) could be provided on the female part and/or on the male part.

The first or second part could comprise a bearing body. The other of the first and second part could comprise a plunger, The first and/or second part (eg. the bearing body and/or the plunger) could be part of (e.g. at least partially contained within) another body, e.g. a housing. For example, the sensor device could comprise a first body/housing comprising the first part. The sensor device could 2 5 further comprise a second body/housing comprising the second part.

The first and/or second part can comprise a metal or metal alloy material. The at least one bearing protmsion can comprise a metal or metal alloy material.

Optionally, at least the bearing surfaces of the first and second parts comprise a metal or metal alloy material. Accordingly, optionally no overlay/member layer (comprising for example a non-metallic/non-alloy material, such as a synthetic resin layer) is provided over the bearing surfaces of the first and/or second parts.

In other words, optionally, the bearing arrangement comprises a metal/metal alloy-on-metal/metal alloy interface, e.g. a metal-on-metal, or alloy-on-alloy (or any combination thereof) interface.

For example, steel and brass are appropriate metal alloys. For example, at least the bearing surface of the first part is provided by steel and at least the bearing surface of the second part is provided by the brass, or vice versa.

The first and/or second part (or its housing) could comprise a mount device, e.g. for mounting the sensor device onto a machine, e.g. a machine tool. Any housing provided for the first and/or second part could be configured to protect the first and/or second part, and in particular for example the bearing arrangement, from dirt such as swarf and liquid.

The sensor device could be configured to output a signal indicative of relative motion of the first and second parts. The output could vary depending of the extent of relative motion (and hence indicate the extent of such motion).

Optionally, the output could be a signal which indicates when the extent of relative motion has met a threshold level, e.g. it could be a trigger signal.

The sensor device could be a tool setter. The first part can be bearing body for the second part. The second part can be a plunger. The plunger can comprise a contact face (in other words a contact pad or contact plate) for a tool.

According to another aspect of the invention there is provided a sensor made by the above described process. For example, according to another aspect of the invention there is provided a tool setter made by the above described process.

According to a further aspect of the invention there is provided a single axis sensor device, comprising a first part and a second part moveable relative to the first part along an axis and a detector for detennining movement between the first and second parts, in which the bearing arrangement between the first and second parts comprises at least one bearing protrusion the crest of which provides a plain bearing region to facilitate said relative motion whilst controlling the relative lateral position of the first and second part.

The protrusion's crest can comprise a cut surface. The protrusion's crest can comprise a burr-free plain bearing region. The protrusion's crest can be free-from my overhanging material.

The protrusion's crest can comprise a plastically deformed region. The protrusion can bulge outwardly (in other words laterally) at its crest. Accordingly, the protrusion's crest can comprise an overhang. The protrusion can comprise an overhang on all/both sides. The overhang(s) can provide part of the plain bearing region.

The at least one protrusion can be provided by the first part. The first part can comprise a hole within which at least a part of the second part is received and can move.

The second part can comprise a shaft which can be received within the hole. The second part can comprise a contact pad at the end of the shaft.

Optionally, the difference between the diameter of the hole (e.g. provided by the first or second part) and the diameter of the shaft (provided by the other of the first and second part) is not more than 10Mm (micron), for example not more than 7Mm (micron). Optionally the difference between the diameter of the hole and the diameter of the shaft is not less than 1Mm (micron), for example not less than 2Mm (micron), for instance not less than 3m (micron), such as not less than 4m (micron). Accordingly, for example, the difference between the diameter of the hole and the diameter of the shaft could be in the range of 2m (micron) to iüm (micron), for example 3m (micron) to 8m (micron), for instance 4m (micron) to 7m (micron). As will be understood, for the part comprising the at least one *l1 protrusion, the diameter is measured from crest to crest. As will also be understood, due to thermal expansion, the size of parts can change with temperature and so the above measurements can be the measurements obtained at 20°C (degrees Celsius), for example. As will also be understood, the diameter of the shaft will be smaller than the diameter of the hole.

The at least one bearing protrusion can be elongate, e.g. it could be a ridge. The at least one bearing protrusion can extend at least partially around the at least one axis. The at least one bearing protrusion can extend annularly around the at least one axis, e.g. it could be ring shaped. The bearing protrusion can extend along the axis, The at least one bearing protrusion could extend parallel to the axis, e.g. it could be straight. Preferably, the at least one bearing protrusion extends along and around the axis. For example, the at least one bearing protrusion can comprise a helical formation.

As will be understood, the method of the invention can also be used to make non-sensor devices having a single linear axis, Accordingly, the method of the invention can be useful for making a linear axis bearing per se. Accordingly, the invention could comprise a method of making a bearing arangement for first and second parts of a device that are moveable relative to each other along a linear axis, the method comprising: taking the first and/or second part of the device, on which at least one bearing protrusion is provided, and using a tool to finish the crest of the at least one bearing protrusion (eg, by defonning or cutting the crest) on the part such that the crest defines a plain bearing surface for the other part.

Accordingly, according to another aspect of the invention there can be provided a single axis device, comprising a first part and a second part moveable relative to the first part along an axis, in which the bearing arrangement between the first and second parts comprises at least one bearing protrusion the crest of which provides a plain bearing region to facilitate said relative motion whilst controlling the relative lateral position of the first and second part, e.g. the protrusion's crest comprising a plastically deformed region, Embodiments of the invention will now be described, by way of example only, with reference to the following drawings, in which: Figure 1 illustrates a machine tool with a tool setter; Figure 2 illustrates a tool setter according to the present invention; Figure 3 illustrates a schematic cross-sectional view a tool the setter according to a first embodiment of the invention; Figure 4 illustrates an example process of manufacturing a tool setter according to the invention; Figures 5a and Sb illustrate part of the process of Figure 4; Figure 6 illustrates a schematic cross-sectional view a tool the setter according to a second embodiment of the invention; Figure 7 illustrates another example process of manufacturing a tool setter according to the invention; Figures 8a to 8c illustrate part of the process of Figure 7; and Figures 9a and 9b illustrate example prior art single linear axis tool setters.

Referring to Figure 1, there is shown a machine tool apparatus 2 comprising a machine tool 4, a controller 6, a PC 8 and a transmitter/receiver interface 10. The machine tool 4 comprises motors (not shown) for moving a spindle 12 which can hold a variety of tools. For example, as shown, the spindle 12 can hold a machine tool bit 14 (e.g. a drill bit). Other example tools include measurement tools such as a measurement probe. The motors can be used to move the spindle 12 relative to a worlcpiece 16 located on a table 18. The location of the spindle 12 (and hence the tool bit 14) is accurately measured in a known manner using encoders (not shown) or the like. Such measurements provide spindle position data defined in the machine co-ordinate system (x, y, z). A numerical controller (NC) 18 (which is part of the controller 6) controls x, y, z movement of the spindle 12 within the work area of the machine tool aiid also receives data relating to the spindle position.

As will be understood, in alternative embodiments relative movement in any or all of the x,y and z dimensions could be provided by movement of the table 18 relative to the spindle 12. Furthermore, relative rotational movement of the tool bit 14 and workpiece 16 could be provided by a part of the spindle t2 (e.g. a rotating/articulated head mounted on the spindle 12) and/or a part of table 18 (e.g. a rotary table). Furthermore, movement might be restricted to fewer dimensions, e.g. only x, and/or y. Further still, the embodiment described comprises a 1 5 Cartesian machine tool, whereas it will be understood this need not necessarily be the case and could be for instance a non-Cartesian machine tool. Further still, many other different types of machine tools, including lathes, and parallel-kinematic machines, and robot arms are known and on which the tool setter of the invention could be used.

Referring to Figures 1 and 2 a tool setter 20 according to the invention is provided. In this case, the tool setter 20 is mounted on the machine tool's work table 18. However, as ll be understood, this need not necessarily be the case and could be mounted on other parts of the machine tool, e.g. any part of the machine which the spindle can access.

In general, the tool setter 20 comprises a housing 22 and a plunger 24 which can be pushed into the housing 22 along a single linear axis A (see Figure 3). A swan shield 21 is provided to prevent swaff entering the housing 22, and is attached to and moves with the plunger 24, In use, the machine tool brings the tool bit t4 into contact with the plunger 24 and drives it down into the housing 22 along the axis A until the tool setter issues a trigger signal. The trigger signal is picked up via the receiver interface 10 which in turn causes the machine tool to stop and retract the tool bit 14. From knowledge of the location of the spindle 12 at the time the trigger signal was issued, the machine tool apparatus (e.g. the controller 6) can determine the length of the tool bit 14 (relative to other tools that go through the same process). As schematically illustrated in Figure 1, a signal line is shown between the tool setter 20 and the receiver interface 10. As will be understood, this could be a physical or wireless signal line (e.g. radio or optical transmission).

In this embodiment, the signal line is a physical line which passes through a cable conduit 28.

As shown in Figure 2, the tool setter can comprise an air flow spout 26 which is connected via an air supply line (not shown) to a pump (also not shown) for supplying a flow of air across the top of the plunger 24 so as to blow away debris, swarf and the like.

Referring to Figure 3 there is shown a schematic cross-sectional view of the tool setter 20. The plunger 24 comprises a flat, disc-shaped contact pad/plate 30 which sits above the housing 22. The contact pad 30 is secured to a shaft 32 which extends into the housing 22. In particular, the shaft 32 extends into a bearing body 34 contained within the housing 22. The bearing body 34 has a generally cylindrical hole into and through which the shaft 32 extends, The wall of the hole provided by the bearing body 34 is provided with a bearing arrangement 36 which facilitates and controls movement of the plunger along an axis A. In this embodiment, the bearing arrangement 36 comprises a helical protrusion 38 which 2 5 extends substantiafly along the entire length of the hole. The crest 40 of the helical protrusion 38 (in other words the ridge of the helical protrusion 38) provides a bearing surface for the plunger's shaft 32. The crest 40 is accurately formed as described in more detail below so as to ensure a very high/tight tolerance on the clearance between the crest 40 and the shaft 32, For example, in this case, the required tolerance is between 2 to 5pm (microns), This ensures that the plunger 24 is free to slide smoothly along the axis A, without undue lateral play between the shaft 32 and bearing body 34 (and without undue rotation about an axis perpendicular to the longitudinal axis A). In another particular example, it can be preferred that the difference in the diameter of the hole (measured from crest-to-crest) and the diameter of the shaft 32 of the plunger 24 is at least 3m (microns) and not more than 7Rm (microns), for example nominally 6Mm (microns), at 20°C (degrees Celsius).

The plunger 24 is biased outwardly (of the housing 22) along the axis A by a spring 42. A flange 44 on the bottom of the shaft 32 engages the bottom of the bearing body 34 so as to control the rest position of the plunger 24 along the axis A. A flexible bellows seal 43 can be provided which surrounds the spring 42 and extends between the underside of the contact pad 30 and top of the bearing body 34, to seal the bearing arrangement from contaminants, e.g. liquid, coolant, swarf, dirt, particles, etc. A trigger system 46 is provided for determining movement of the plunger 24 away from its rest position. Tn this embodiment, the trigger system comprises a light emitter 48 and receiver 50 and a light manipulating member 52 attached to the bottom of the plunger 24 (e.g. a light blocking or deflecting member). During use, light is emitted by the emitter 48. When the plunger 24 is in its rest position, light from the emitter 48 is detected by the receiver 50, When a tool bit 14 pushes the plunger 24 down along the axis A, the light manipulating member 52 enters the light path between the emitter 48 and receiver 50 and reduces the amount of light (or can even prevent light) from the emitter 48 reaching the receiver 50. The light manipulating member 52 can achieve this in any suitable way, e.g. by at least one of absorbing, reflecting and scattering the light. The receiver 50 detects such a reduction in light and emits a trigger signal as briefly discussed above. The distance along which the plunger 24 must travel along the A axis before the receiver is triggered can vary from system to system. By way of illustration only, typical trigger distances for a tool setter could be for example as little as 2 jim (microns) and as much as 1mm or more, and in the particular embodiment is 0.8mm.

As will be understood, other types of trigger mechanism could be used. For example, instead of the break-beam technique of the above, a physical electrical connection could be provided which is broken and triggers a signal when the plunger 24 moves relative to the housing 22/ bearing body 34.

Furthermore, especially in the case of sensors other than tool setters, rather than merely outputting a trigger signal, the sensor could provide an output which is representative of the extent of the movement between the two relatively moveable parts of the sensor (e.g. the extent by which the plunger 24 is displaced (with respect to the housing)).

As mentioned above, it is important that the bearing arrangement 36 is accurately formed because it is important to the proper and accurate functioning of the tool setter 20. Figure 4 is a flow chart of an example process 400 for the manufacture of a tool setter 20 of Figure 3. At step 402 a block of material that is to form the bulk of the bearing body is taken and loaded into a machine tool 4. This can be a solid piece of material, e.g. a metal or alloy. It might be that the bearing block has been pre-shaped or alternatively this step involves using the machine tool 4 to shape the bearing block. At step 404 a hole is formed (e.g. drilled) in the bearing block. Of course, the bearing block may have been supplied with a pre-formed hole in which case step 404 can be omitted. At step 406 a continuous helical protrusion 38 is formed that extends along the length of the wall of the hole. In particular, a screw-thread 38 is formed using a tap tool to cut the screw-thread into the wall of the hole. The screw-thread 38 is formed in such a way that after this 2 5 step the internal diameter of the hole is still slightly too small to accommodate the shaft. By way of illustration only, the internal diameter of the hole could for example be configured to be too small by anywhere between 1 I.tm (micron) to 1mm. In the particular example, it is configured to be too small by nominally 50 pm. Of course, the bearing block may have been supplied with a pre-formed helical projection 38 in which case step 406 can be omitted, A schematic illustration of the cross-sectional form of the hole in the bearing body 34 is illustrated in Figure Sa. At step 408 the crestlridge of the helical protrusion 38 is deformed to provide the final bearing surface for the shaft 34. This involves pushing a rotating, smooth cylindrical tool 54 (which as illustrated in Figure Sa has a diameter which is slightly larger than internal diameter of the hole) along the length of the hole. In this embodiment, the tool 54 does not cut the crest/ridge 40, rather it pushes the material of the ridge/crest 40 of the helical protrusion 38 out of the way, thereby causing it to plastically deform. This results in the crest/ridge 40 bulging 41 outwardly/laterally due to the displaced material, Such bulging is facilitated by the presence of a gap 39 next to the crest/ridge 40 into which the material can be displaced.

It has been found that such a displacementldeforming technique can provide a highly accurately formed plain bearing surface for the plunger's shaft 32, Furthermore, such a process results in plain bearing surface with an increased surface area because the bulge itself contributes to the bearing surface.

It has also been found that the tool setter can be made with sufficient accuracy by a process whereby the crests of the bearing protrusions are finished by way of removing the peaks of the protmsions crests (e.g. cutting the material from the protrusion), As illustrated in Figure 6, this results in the helical bearing protrusion having a crest with no-overhang, A suitable example cutting process 700 is illustrated by the flow-chart of Figure 7, This process is similar to the process of Figure 5, and the first three steps can be same. However, rather than deforming the crests, step 708 comprises finishing the crests by removing material from the protrusion via a reaming process, e.g. by pushing a using a rotating reamer 154 along the length of the hole (Figure 8a). As schematically illustrated in Figure 8b, such a cutting/reaming process can leave unwanted remnants (e.g. buns) on the finished crests. If desired, then these can be removed for example, by at step 710 passing the same tool that was used at step 706 to tap the helical protrusion, along the hole so as to cut the undesirable remnants, eg. buns, off the crests. Optionally, at step 712 the reaming process carl be repeated to refinish the crest, removing any remaining buns, such that the crest provides a plain bearing region having no overhang (Figure Sc).

Not only does the presence of space on either side of the bearing protrusion aid the formation of a precision plain bearing region, but it also provides for a gap into which contamination, such as dirt and swarf can reside without adversely affecting the perfommnce of the sensor, For example, if swarf were to enter the tool setter of the prior art embodiment of Figures 9a, then the balls will tend to roll over swarf, causing an uneven bearing motion. Also, if swarf were to enter the tool setter of the prior art embodiment of Figures 9b, then the swarf can easily get jammed between the bearing surfaces of the bearing part and plunger, causing the bearing arrangement to jam. In contrast, it has been found that with the tool setter of the present invention, the provision of a bearing protrusion having a plain bearing region means that any contamination such as swarf that makes its way into the tool setter will tend to be pushed into the space between adjacent crests, thereby maintaining the operating performance and lifetime of the sensor.

It has also been found that the process can be improved by performing the step of cutting/deforming the crest/ridge 40 (step 408) in the presence of fluid. This is because due to surface friction the rotating action of the tool 54 pulls the fluid such that it gets entrained within micro pockets between the rotating tool 54 md the material of the crest/ridge 40. As the tool rotates and squeezes the fluid trapped in such micro pockets against the surface of the crest/ridge 40, the pressure of the fluid is increased to such an extent that the fluid itself acts to modiñ' the deformed surface, resulting in an extremely smooth and accurately formed bearing surface. This effect has been realised with a variety of different fluids, including oil based and water based fluids. However, as will be understood, the process parameters can depend on what type of fluid is being used. For example, oil based fluids can be more easily entrained and so slower rotational speeds can be used, whereas water based fluids (eg. such as machine tool coolant) can require higher rotational speeds to become entrained.

As will be understood, the dimensions of the bearing arangement 36, in particular the height (h) and pitch (p) of the helical protrusion 38, the extent of the deformed, bulged region 41, as shown in the drawings is schematic to aid understanding of the invention. For the sake of completeness, particular dimensions of a product according to the invention could, for example be that the helical protrusion has a finished height of 0.575mm, a pitch of 1mm, providing a hole diameter (d) of 4.997mm for a shaft of diameter 4,995mm hence providing a 2pm (micron) tolerance (a 1pm (micron) to 10pm (micron), in particular 2pm (micron) to 5pm (micron) can be desirable). Before deforming/cutting the crests of the helical projection they could have had an approximate height of 0.599mm, the diameter of the hole (crest to crest) being approximately 4,950mm, 1 0 Accordingly, in this case the process of deforming/cutting the crests could comprise deforming/cutting the protrusion by as little as 0,024mm. As will be understood, these dimensions are specific to a particular example and are provided merely to illustrate one way of implementing the invention. For example, the crests of the bearing protmsion could be deformed/cut by more or by less than that illustrated in the above example.

In another specific example, before the finishing step (e.g. the reaming/deforming step), the diameter of the hole (crest to crest) can be approximately 4.8mm, and the diameter of the hole (crest to crest) after the finishing (e,g. cutting process) is 5mm, (As will be understood, the pre-finished size is only approximate and this is acceptable because it is the finishing step(s) that provides the accurately dimensioned hole). Accordingly, in this case, the heights of the crests can be reduced by as little as 0,1mm. In this particular example, the pitch (p) of the helical form can be substantially 0.9mm, the finished height (h) of the helical protmsion can be approximately 0.25mm, with a protrusion angle (0) of 60° and providing a bearing seat (s) of approximately 0,36mm wide, As will be understood, the most important dimension is the hole diameter and so the actual dimensions of protrusion itselfl such as the pitch (p), height (h), protrusion angle (0) and bearing seat width (s) can be more approximate since the finishing step(s) provides the precise hole diameter that is required, In the above embodiment there is provided a single protrusion that extends helically along the length of the hole. However, this need not necessarily be the case. For instance, a plurality of protrusions can be provided. For instance, a plurality of helical protrusions (either in parallel (e.g. a multi-start thread) or series) can be provided. The protrusions can take the fonn of a series of annular rings, spaced apart along the length of the hole. For example, a first annular ring could be provided toward the top of the hole and a second annular ring toward the bottom of the hole. The protrusions could also comprise straight elongate protrusions extending at least partially along the length of the hole (e.g. the hole could be splined). Other example forms of protrusions comprise an arrangement of point protrusions (as opposed to the elongate helical, or ring-shaped protrusions). In all such cases, the fact that the bearing arrangement comprises at least one protrusion (as opposed to merely a flat surface) the crest of the protrusion(s) can be deformed (into the space surrounding the protrusion).

Furthermore, in the above embodiment the protrusion is provided in the hole, however this need not necessarily be the case. For example, the helical protrusion could be provided on the shaft 32 of the plunger 24. Alternatively, at least one protrusion might be provided on the hole and another on the shaft, Other arrangements are also possible. For example, the plunger's shaft 32 could have an elongate hole which fits over and slides up and down a pole/shaft provided by the bearing body 34.

2 5 The above described embodiment relates to what is commonly known as a tool setter, However, as will be understood, the invention is equally applicable and advantageous to other types of single-axis linear sensors, such as ball-bars and single axis measurement probes (e.g. contact stylus probes for mounting on the quill of a coordinate measuring machine).

Claims

CLAIMS: I. A method of manufacturing a bearing arrangement for first arid second parts of a sensor device that are moveable relative to each other along a linear axis, the method comprising: taking the first and/or second part of the sensor device, on which at least one bearing protrusion is provided, and using a tool to finish the crest of the at least one bearing protrusion on the part such that the crest defines a plain bearing region for the other part.
2. A method as claimed in claim 1, in which said using said tool to finish the crest of the at least one bearing protrusion comprises using the finishing tool to remove material from the at least one protrusion.
3. A method as claimed in claim 2, in which using said tool comprises pushing a cutting tool into and past the at least one bearing protrusion so as to cut the at least one protrusion.
4. A method as claimed in any preceding claim, comprising removing any burs from the crest of said at least one protrusion.
5. A method as claimed in claim 4, comprising using a bearing protrusion forming tool identical to that used to form the at least one bearing protrusion to remove said burrs.
6. A method as claimed in claim 5, comprising using the same bearing protrusion forming tool that was used to form the at least one bearing protrusion to remove said burrs.
7. A method as claimed in any preceding claim, in which said at least one bearing protrusion comprises a helical protrusion, and in which said bearing protrusion forming tool comprises a tap or die cutting tool.
8. A method as claimed in any of claims 5 or 6 and 7, comprising using the same tap or due cuffing tool to remove said burrs.
9. A method as claimed in any of claims 4 to 8, comprising subsequently re-finishing the crest of said at least one bearing protrusion using said tool to finish the crests subsequent to said burr removal.
10. A method as claimed in claim 1, in which said using the tool to finish the crest of the at least one bearing protrusion comprises using the tool to plastically deform the crest of the at least one protrusion.
II. A method as claimed in any preceding claim, in which using the tool to finish the crest comprises pushing a rotating shaping tool into and past the at least one bearing protrusion so as to finish the crest of the at least one protmsion.
12. A method as claimed in any preceding claim, comprising providing liquid at the point of interaction between the tool and bearing protrusion during said finishing.
13. A method as claimed in any preceding claim, in which the method comprises machining the first and/or second part so as to provide the at least one bearing protrusion,
14. A method as claimed in claim 13, in which machining comprises forming at least one helical protrusion using a tap or die cutting tool.IS. A method as claimed in claim 13 or 14 in which said machining and finishing of said crest is performed on the same machine tool.16. A method as claimed in any preceding claim, in which said first part comprises a hole comprising at least one helically extending protrusion and the second part comprises a cylindrical shaft forbearing against said crest of said at least one helically extending protrusion.17. A method as claimed in any preceding claim, in which the sensor device is a tool setter, the first part being a bearing body for the second part, the second part being a plunger.18. A sensor device made by the process of any of the preceding claims.19. A tool setter made by the process of any of the preceding claims.20. A single axis sensor device, comprising a first part and a second part moveable relative to the first part along an axis and a detector for determining movement between the first and second parts, in which the bearing arrangement 1 5 between the first and second parts comprises at least one protrusion the crest of which provides a plain bearing region to facilitate said relative motion whilst controlling the relative lateral position of the first and second part, 21. A sensor device as claimed in claim 20, in which the at least one 2 0 protrusion is provided by the first part.22. A sensor device as claimed in claim 20 or 21, in which the first part comprises a female part for receiving the second part.23. A sensor device as claimed in any of claims 20 to 22, in which the first part comprises a hole, and the second part comprises a shaft.24. A sensor device as claimed in claim 23, in which the at least one bearing protrusion is formed on the hole.25. A sensor device as claimed in claim 23 or 24, in which the difference between the diameter of the hole and the diameter of the shaft is not more than Mm.26. A sensor device as claimed in claim 23 or 24, in which the difference between the diameter of the hole and the diameter of the shaft is not less than 2im.27. A sensor device as claimed in claim 23 or 24, in which the difference between the diameter of the hole and the diameter of the shaft is not more than 7rim and not less than 4gm.28. A sensor device as claimed in any of claims 20 to 27, in which the first part comprises a bearing body, and the second part comprises a plunger.29. A sensor device as claimed in claim 28, in which the plunger comprises a contact face for a tool.30. A sensor device as claimed in any of claims 20 to 29, comprising a mount device for mounting the sensor device onto a machine.31. A sensor device as claimed in any of claims 20 to 30, comprising a housing configured to protect the first and/or second part from dirt.32. A sensor device as claimed in any of claims 20 to 31 configured to output a signai indicative of relative motion of the first and second parts.33. A sensor device as claimed in any of claims 20 to 32, in which the protmsion's crest comprises a plastically deformed region.34. A sensor device as claimed in claim 33, in which the protrusion bulges outwardly at its crest.35. A sensor device as claimed in any of claims 20 to 34, in which the at least one protrusion extends at least partially around the at least one axis.36. A sensor device as claimed in any of claims 20 to 35, in which the at least one protrusion comprises one or more helical formations extending along the length of the axis.37. A sensor device as claimed in any of claims 36, in which the one or more helical formations are provided by the first part, and the second part comprises a substantially cylindrical shaft for bearing against the crest of said at least one 1 0 helically extending protrusion.38. A sensor device as claimed in any of claims 20 to 37, in which the at least one bearing protrusion comprises a metal or metal alloy material, 39. A sensor device as claimed in any of claims 20 to 38, in which the bearing surfaces of the first and second parts comprise a metal or metal alloy material.40. A sensor device substantially as described with reference to Figures 3 to 5, or substantially as described with reference to Figures 6 to 8.41. A sensor device as shown in Figure 3 or as shown in Figure 6, 42. A tool setter for a machine tool comprising a sensor device as claimed in any of daims 20 to 41.43. A coordinate positioning machine comprising a sensor device as claimed in any of claims 20 to 41.44. A machine tool comprising a sensor device as claimed in any of claims 20 to4i,