Scanning Probe

Abstract

A scanning probe for a coordinate positioning apparatus, such as a machine tool, is described, the probe comprising a probe body connected to a stylus holder (102) by a strain sensing structure (100). The strain sensing structure has an inner portion (202) connected to an outer portion (200) by a plurality of bendable members (204). A proximal end (220) of each bendable member (204) is attached to the inner portion (202) and a distal end (222) of each bendable member (204) is attached to the outer portion (200). The inner and outer portions (200, 202) are centered on a central axis, and the plurality of bendable members (204) comprise at least one strain sensing element (210). The proximal and distal ends (220, 222) of each bendable member (204) are disposed at different angles about the central axis. Such an arrangement allows for both scanning and touch trigger measurements to be obtained.

Description

[Technical field]

[0001] The present invention relates to a scanning probe for a coordinate positioning apparatus, such as a machine tool, which is provided with one or more strain sensing elements for sensing deflection of an object-contacting stylus. [Background technology]

[0002] A variety of measurement probes are known for use with machine tools or other coordinate positioning apparatus. These include touch-trigger probes, which issue a trigger signal when the stylus is deflected due to contact with an object, and so-called scanning probes, which output a stream of data describing the amount of stylus deflection that occurs as the stylus is scanned along a surface. The output from such measurement probes, in combination with information from the machine tool describing the position of the measurement probe relative to the object, can be used to measure the position of points on the surface of an object. These measurements can be used for part set-up or inspection purposes.

[0003] Touch-trigger probes may contain a simple electrical circuit that breaks when the stylus is deflected, thereby generating a trigger signal which is passed to the machine tool. It is also known to use strain sensors to measure when the stylus is deflected due to contact with an object.

[0004] The '661 patent describes a measurement probe in which a stylus holder is attached to the probe body via an intermediate member. The intermediate member is configured to sense small stylus deflections, while spring means are provided to accommodate larger stylus deflections. Various embodiments in which the deflection of the intermediate member is measured are described in the '661 patent. In one specific embodiment of the '661 patent (shown in Figures 5 and 6 of the '661 patent), an intermediate member 122 includes an inner region 122B and an outer ring 128 connected by three straight limbs 127 extending tangentially about a central axis 121A of the intermediate member. A reduced thickness section is provided at each end of each limb 127 on which a pair of strain gauges 130 are mounted to measure any bending of those elongated limbs.

[0005] Nos. 5,993,333 and 5,993,366 describe a measurement probe for touch-trigger measurements having a strain-sensing structure connecting the stylus holder to the probe body. The strain-sensing structure includes three straight radially extending spokes on which the strain-sensing elements are attached. Signals from the strain-sensing elements are combined and a trigger signal is issued when the combined signal exceeds a certain threshold. This arrangement provides a robust, accurate and reliable touch-trigger probe.

[0006] US Pat. No. 5,399,433 describes a robust scanning probe suitable for use in machine tools. Unlike the configurations described in US Pat. No. 5,399,433, US Pat. No. 5,399,433 and US Pat. No. 5,399,433, which allow touch-trigger measurements, the scanning probe of US Pat. No. 5,399,433 is able to transmit stylus deflections over a much larger range. In particular, the scanning probe of US Pat. No. 5,399,433 includes a capacitive transducer in combination with a spring arrangement that maintains the stylus holder suspended in a rest position in the absence of applied external forces. The capacitive transducer is used to measure (in three dimensions) any deflection of a stylus attached to the stylus holder away from a rest position, and a stream of three-dimensional deflection data is output by the scanning probe while the stylus tip is moved (i.e. scanned) along the surface of the object being measured. Such a scanning probe allows a large number of surface position measurements to be obtained relatively quickly compared to touch-trigger probes. However, the complex and relatively expensive spring and transducer configurations typically limit the use of such scanning probes to higher-end measurement applications. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent Application Publication No. 0068899 [Patent Document 2] International Publication No. 2006 / 100508 Brochure [Patent Document 3] International Publication No. 2006 / 120403 Brochure [Patent Document 4] International Publication No. 2002 / 061378 Brochure Summary of the Invention

[0008] According to the present invention there is provided a scanning probe for a coordinate positioning apparatus comprising a probe body, a stylus holder and a strain sensing structure connecting the stylus holder to the probe body, the strain sensing structure having an inner portion connected to an outer portion by a plurality of bendable members, a proximal end of each bendable member attached to the inner portion and a distal end of each bendable member attached to the outer portion, the inner portion and the outer portion being centred on a central axis, the plurality of bendable members including at least one strain sensing element, the proximal and distal ends of each bendable member being arranged at different angles around the central axis, and each bendable member being curved within the plane of the strain sensing structure.

[0009] The present invention therefore relates to a scanning probe, optionally operable as a touch-trigger probe, configured for use with a coordinate positioning apparatus. In a preferred example, the scanning probe is configured for use with a machine tool. The scanning probe comprises a probe body or housing. The probe body is the part of the scanning probe that is fixed to the coordinate positioning apparatus. For example, the probe body may be bolted to a shank that can be held in a spindle or quill of the machine tool. A stylus holder is also provided that can be deflected relative to the probe body. The stylus holder may incorporate a stylus or may include a connector (e.g. a threaded opening) to which the stylus can be secured. The stylus may comprise an elongated rod with a ball attached to its distal end. The stylus holder may thus define a central axis along which the longitudinal shaft of the attached stylus projects.

[0010] The stylus holder is flexibly connected to the probe body via a strain-sensing structure. The strain-sensing structure comprises an inner portion having the same central axis as the outer portion. In other words, the inner and outer portions are concentric or centered on a common (central) axis. In a preferred embodiment, the inner portion may include a circular hub and the outer portion may include a (circular) ring having a larger diameter than the circular hub. The central axis about which the inner and outer portions are centered may also coincide with the elongated axis defined by the stylus holder. The inner and outer portions are connected by a plurality of bendable members (which may also be referred to as bendable arms, legs, or limbs). In particular, a proximal end of each bendable member is attached to the inner portion and a distal end of each bendable member is attached to the outer portion. As described below, the inner and outer portions may be relatively stiff. The one or more bendable members conveniently provide the only connection between the inner and outer portions. As described below, when the stylus holder moves relative to the probe housing (i.e. when the inner and outer portions move relative to one another), the plurality of bendable members bend. At least one strain sensing element is provided to measure bending of the bendable members. In a preferred embodiment, each bendable member includes at least one strain sensing element to enable bending of each such bendable member to be measured.

[0011] The scanning probe has the proximal and distal ends of each bendable member disposed at different angles around the central axis. In other words, the proximal end of each bendable member is angularly offset from its distal end (i.e., has a different angle around the central axis). Thus, the bendable members do not extend purely radially (i.e., there is no change in angle around the central axis), but rather circumferentially around the central axis of the strain sensing structure (i.e., the angle around the central axis of each bendable member changes along its length). Furthermore, each bendable member is curved in the plane of the strain sensing structure. This means that each bendable member is curved as it extends at an angle from the inner portion to the outer portion. Of course, there can also be a radial offset between the ends of each bendable member (i.e., the bendable members can extend at an angle around the central axis of the strain sensing structure and can extend radially outward from the inner portion to the outer portion).

[0012] The advantages of the present invention over the conventional strain gauge touch trigger probes described in US Pat. No. 5,399,633, US Pat. No. 5,493,366 and US Pat. No. 5,523,313 arise from the configuration (shape) of the bendable members. In particular, the length of each bendable member can be greater than the radial separation between the inner and outer portions. This allows the length of the bendable members to be increased for a given outer dimension or diameter of the strain sensing structure. The provision of longer bendable members allows for greater bending for a given stiffness and elasticity of the material. This in turn increases the measurable working range of deflection of the stylus holder relative to the probe body. Furthermore, providing curved bendable members has been unexpectedly found to minimize or eliminate undesirable twisting of the bendable members when the bendable members are bent out of plane by movement of the inner portion relative to the outer portion (e.g., due to stylus deflection, etc.). In particular, providing bendable members that are curved within the plane of the strain sensing structure has been found to significantly reduce twisting compared to straight (unbent) bendable members of the type used in prior art measurement probes. As explained above, prior art measurement probes include straight (unbent) bendable members because this was previously believed to be the best way to obtain a uniform and predictable response to an applied force. However, this assumption has been found to be incorrect and curved bendable members have been found to improve bending characteristics. Furthermore, the curvature allows strain to be concentrated in a particular section of each bendable member, allowing the strain sensing elements to be placed in an optimal position to measure such bending. As a result, the present invention provides a scanning probe that can in fact only be used as a touch-trigger probe, in contrast to the configurations described in US Pat. No. 5,399,623, US Pat. No. 5,399,623 and US Pat. No. 5,499,623.

[0013] The present invention thus combines the robustness, compactness, and cost advantages of using strain sensing elements (e.g., strain gauges) with the advantages of scanning rather than touch-trigger measurements. It is noted that it is also possible to use the scanning probe of the present invention to make touch-trigger measurements, as described below.

[0014] The plurality of bendable members are curved (i.e., bent) within the plane of the substantially planar strain sensing structure. The strain sensing structure may be a generally flat or planar structure that is substantially circular. For example, the strain sensing structure may include a substantially planar disk (i.e., the strain sensing structure may be substantially disk-shaped). In such an example, the central axis may coincide with the center point of the disk, and this central axis may extend perpendicular to the plane of the disk. Although a disk shape is preferred, other shapes of surface sensing structures can be used. In such an example, the curvature of the bendable members is preferably in the plane of the disk. Thus, this curvature of the bendable members may be in a plane perpendicular to the direction or plane in which the bendable members are configured to bend during use. For example, the bendable members may lie flat in a plane with curved inner / outer edges and be bendable out of that plane (i.e., during measurement).

[0015] The lateral extent or (in-plane) width of each curved bendable member may also be configured to optimize bending. Advantageously, the width of each bendable member varies along its length. For example, the width of each member may increase from its proximal end to its distal end, or vice versa. In this regard, it is noted that the "width" (or lateral width, etc.) of each bendable member is the dimension across its length (the length being defined in the direction from the proximal end to the distal end of each bendable member). In a preferred example, the outermost and / or innermost edges of the bendable members may be curved. Preferably, both the outermost and innermost edges of the bendable members are curved.

[0016] In a preferred embodiment, the outermost and innermost edges of each bendable member are curved, and the curvature of the innermost and outermost edges are respective arcs centered at different points. The arcs may also have different radii. The curvature of the innermost and outermost edges may conveniently be centered about a point that is not coincident with the central axis of the strain sensing structure. This has been found to further reduce undesirable twisting of the bendable members when bent by movement of the inner portion relative to the outer portion (e.g., due to stylus deflection). This also helps to further concentrate the strain on a particular section of each bendable member, allowing the strain sensing element to be placed in an optimal position for measuring bending effects.

[0017] The inner portion preferably comprises a circular central hub, which is preferably rigid and may be formed from a single piece. The central hub may be attached to either the probe body or the stylus holder. The outer portion may conveniently include an outer (circular) ring, which is preferably rigid and formed as a single continuous piece. The outer ring may be attached to the other of the stylus holder or the probe body.

[0018] In a preferred embodiment, the plurality of bendable members comprises three bendable members that are conveniently equally spaced from one another (i.e. about a central axis). By locating a strain sensing element on each of the three bendable members, the direction of deflection of the stylus holder can be measured using the strain sensed at each of the bendable members.

[0019] The strain-sensing structure may be assembled from multiple components. Advantageously, the strain-sensing structure comprises a single (integral) part. In a preferred embodiment, the strain-sensing structure is formed as a single machined part. In other words, a blank substrate (e.g., a stainless steel blank disk) may be machined (e.g., using an EDM process) to form the inner and outer parts with bendable members connecting the parts. Providing such a single strain-sensing structure reduces hysteresis effects that may arise due to slip between components that are attached or clamped to each other. This allows the stylus holder to adopt a highly repeatable rest or neutral position relative to the probe body, as described below.

[0020] Advantageously, the strain sensing structure is formed from an elastic material. Depending on the range of deflection to be measured, a variety of different materials can be used. For example, a low stiffness, and therefore low Young's modulus value material (e.g., aluminum) can be used for high deflection range applications. Alternatively, a high stiffness, and therefore high Young's modulus value material (e.g., ceramic) can be used for high sensitivity (low deflection range) applications.

[0021] The strain sensing structure may be formed from a metal. Conveniently, the strain sensing structure is formed from a martensitic stainless steel (e.g., grades 416, 420, 440, 440C or X15TN stainless steel). Alternatively, a carbon (bearing) steel such as EN31 may be used. Aluminum (e.g., 6000 series aluminum) would be another option. The strain sensing structure may also be formed from a ceramic or from a polymer. The different materials listed above are suitable for different applications with different material property requirements such as endurance limits and Young's modulus. The polymers may be machined or molded. The ceramics may be sintered molded parts.

[0022] The strain sensing element may be bonded to the bendable member (e.g., using an adhesive). A diamond-like coating (DLC) coating (particularly an electrically insulating DLC ​​coating) may be applied to the bendable member (e.g., if the bendable member is made from a conductive material). This provides a layer of electrical insulation to prevent the strain sensing element from being shorted by the conductive substrate. If the strain sensing structure is formed of aluminum, an anodization process may be used as an alternative to a DLC coating. Ceramics and polymers would not require such an isolation layer.

[0023] The thickness of the strain-sensing structure may be configured to provide a desired level of flexibility to different portions of the structure. For example, certain portions of the strain-sensing structure may be thin to enhance flexibility. In a preferred embodiment, the inner and outer portions may be relatively thick and therefore relatively stiff. In contrast, each of the multiple bendable members may be relatively thin (i.e., thinner than the inner / outer portions) to provide increased flexibility. Any movement of the inner portion relative to the outer portion then results in bending of the (untransduced) bendable member with minimal bending of the (transduced) inner and outer portions. In this way, movement between the stylus holder and the probe body causes bending of the bendable member that can be measured by the strain-sensing element. Advantageously, the thickness of each bendable member is substantially invariant along its length. This allows for a consistent and controllable bending member without unwanted twisting.

[0024] As mentioned above, the strain sensing structure may be substantially planar. The strain sensing structure may also be formed from an elastic material. In a preferred embodiment, the plurality of movable members may be bendable (i.e. elastically deformable) in a direction perpendicular to the plane of the strain sensing structure. In other words, when the stylus holder is deflected relative to the probe body, the bendable members may bend out of the plane of the strain sensing structure. Upon removal of the applied external force, the elasticity of the strain sensing structure may mean that it acts like a spring and returns to a resting state. The strain sensing structure may be the only connection between the probe body and the stylus holder. Alternatively, there may be other springs or mechanisms supporting the stylus holder relative to the probe body.

[0025] Advantageously, at least one strain sensing element is arranged on each bendable member. Each bendable member may be provided with only a single strain sensing element. Each bendable member may be provided with more than one strain sensing element. For example, each bendable member may include a pair of strain sensing elements. When using a pair of strain sensing elements, they may be arranged on opposite surfaces (e.g., upper and lower surfaces) of the bendable member, which allows for differential strain measurements that help reduce or eliminate certain temperature effects. The strain sensing elements provided on each bendable member may be similar to each other. Alternatively, the strain sensing elements provided on each bendable member may be different. For example, a bendable member may carry p-type and n-type semiconductor strain sensing elements on its upper and lower surfaces, respectively, to compensate for resistance temperature effects. It is also possible that only some of the multiple bendable members include strain sensing elements.

[0026] An analysis of the strain characteristics of the bendable member may be performed to optimize the placement of the strain sensing elements. For example, a strain map of the bendable member design may be used to optimize the placement of the strain sensing elements. In this way, the location of the strain sensing elements may be optimized to obtain a measurable change in strain over a given stylus deflection range. Advantageously, each strain sensing element may be fixed to a region of the bendable member where the change in strain is proportional (e.g., by a linear relationship) to the bending of the bendable member.

[0027] Advantageously, the strain sensing elements are fixed to areas of each bendable member that exhibit low strain variations when the stylus holder is in a rest (undeflected) position. Each strain sensing element may be located where, for a given stylus deflection, the strain gradient is low along the axis of the element (thereby reducing the effect of small changes in the position of the strain sensing element). The position of each strain sensing element may be at or near the midpoint of the bendable member (e.g. approximately half the width of the bendable member). The strain sensing elements may also be aligned with the local elongated axis of the bendable member. This avoids edge effects and stress concentrations. The strain sensing elements are also preferably located at positions along the bendable member where the innermost and / or outermost edges are curved (i.e. they are not located in any straight part of the bendable member).

[0028] Advantageously, the strain sensing elements are mounted at or near the ends of the bendable members attached to the probe body. The strain sensing elements may be mounted only at or near the ends of the bendable members attached to the probe body. For example, if the inner portion is attached to the probe body, each strain sensing element may be mounted at or near the proximal end of each bendable member. In this way, the change in strain occurring during deflection of the stylus is maximized. The width of each bendable member may conveniently increase towards the end of the bendable member attached to the probe body. Furthermore, the length of the electrical connections to the strain sensing elements may be minimized with such an arrangement, without the need to run electrical (e.g. copper) tracks along the length of each bendable member (which may introduce hysteresis in the bendable members).

[0029] Of course, it is also possible to desensitize the structure by appropriate positioning of the strain sensing elements. For example, the strain sensing elements can be moved away from the ends of the bendable members fixed to the probe body in order to reduce the level of strain they are subjected to. Similarly, the strain sensing elements can be rotated (e.g., away from the elongated axis of the bendable members) to adjust their sensitivity to stylus deflection. This change in position and / or orientation of the strain sensing elements can be used, for example, to enable the same strain sensing disk to be used for measurements over different stylus deflection ranges.

[0030] The scanning probe may include at least one temperature sensor. The at least one temperature sensor may be used to compensate any measurements made using the strain sensing element for changes in temperature. The at least one temperature sensor may be attached to the strain sensing structure. For example, one or more temperature sensors may be attached to the inner and / or outer portions. Advantageously, the temperature sensor may be attached to the strain sensing structure near the strain sensing element. For example, the temperature sensor may be attached to one or more bendable members. It is preferred to attach the temperature sensor to the bendable member near the strain sensing element. The temperature sensor may include a thermocouple or a thermistor. Alternatively, one or more additional strain sensing elements (i.e. not used to measure bending) may be used to measure temperature to enable temperature compensation.

[0031] As mentioned above, the stylus holder may incorporate an integral stylus or the stylus holder may carry a removably attachable stylus. The strain sensing structure may include an opening (through hole) through which the stylus holder or stylus may pass. The opening may be circular. The opening may be located on a central axis. The stylus holder may hold the stylus such that the stylus axis (i.e., the elongated axis of the stylus) is on the central axis. As described below, this configuration is convenient because it allows a protection mechanism to be built into the scanning probe to protect the strain sensing structure from excessive deflection of the stylus.

[0032] As mentioned above, the strain sensing structure connects the stylus holder to the probe body. This means that any deflection of the stylus holder relative to the probe body will impart a bending force to the strain sensing structure. Preferably, any bending will occur primarily in the bendable members of the strain sensing structure. The outer part may be fixed to the probe housing and the stylus holder may be connected to the inner part. In a preferred embodiment, the inner part is fixed to the probe housing and the stylus holder is connected to the outer part. This is advantageous because the stylus holder may then include multiple arms that extend radially from the central axis to where they engage with the outer part. This can magnify the effect of any force applied to the stylus (i.e. by a lever effect). As mentioned above, the strain sensing structure may also act as a spring to return the stylus holder to a rest position in the absence of an applied external force.

[0033] The scanning probe preferably adopts a rest position (which may also be referred to as a neutral or undeflected position) when no external force is applied to the stylus holder. The stylus holder preferably returns to substantially the same rest position after it has been deflected. Thus, the strain-sensing structure may act as a return spring that returns the stylus holder to the rest position. The inventors have found that, in the embodiments described below, the same rest position can be reached to within 1 μm for a 100 mm stylus. This high level of mechanical repeatability allows for accurate touch triggering and scanning measurements. The provision of such a mechanically defined rest position is advantageous as it reduces transducer drift effects that may occur with freely suspended stylus holder structures. For example, auto-zeroing the output of the strain-sensing element when the stylus holder is in a mechanically defined rest position can ensure that all measurements taken are tied to the same (mechanically defined) rest position. Thus, the effects of short or long term transducer drift can be mitigated.

[0034] A breakout mechanism or protection mechanism may be provided to protect the strain sensing structure from damage due to excessive deflection of the stylus (i.e., deflection of the stylus beyond the operable deflection range). In other words, the stylus holder may be connected to the strain sensing structure by a protection mechanism. The protection mechanism may include a spring (e.g., a coil or compression spring) for contacting the stylus holder with the strain sensing structure in the absence of an externally applied force. The stylus holder and the strain sensing structure may include mutually engageable elements that repeatedly position the stylus holder relative to the strain sensing structure. For example, a kinematic arrangement may be provided (e.g., a ball is provided on the strain sensing structure and a groove is provided on the stylus holder). Then, each time the stylus holder engages with the strain sensing structure, the same position of the stylus holder relative to the strain sensing structure (e.g., within 1 μm for a 100 mm stylus) is adopted.

[0035] The protection mechanism also allows the stylus holder to disengage the strain-sensing structure when an external force applied to the stylus holder exceeds a threshold level. In other words, if the force is too great, the stylus holder is lifted off the strain-sensing structure, preventing it from exerting a force on that structure large enough to cause damage. The stylus holder then re-engages the strain-sensing structure, returning to the same rest position the stylus holder was in before, so no recalibration is required. This provides kinematic breakout (crash) protection. The protection mechanism may include a spring for bringing the stylus holder into contact with the strain-sensing structure. In a preferred embodiment, the spring force reacts against the strain-sensing structure. For example, a force applied to the stylus holder may be transmitted to the outer portion, and a spring force may also react against the outer portion. This ensures that a consistent residual force (e.g., kinematic retention force) is applied to the strain-sensing structure. In this way, measurement performance is improved.

[0036] During movement of the scanning probe, there may be a vibration motion between the inner and outer parts. Therefore, the scanning probe may include at least one fluid damper for damping vibrations of the strain sensing structure. The at least one fluid damper may include a magnet and a ferrofluid (i.e., magnetofluid). The magnet may hold the ferrofluid in a desired position. At least one seal and / or gap for trapping the ferrofluid may also be provided to prevent loss of the ferrofluid when the scanning probe is subjected to high speed rotation (e.g., when rotated in a machine tool spindle).

[0037] As mentioned above, the present invention provides a scanning probe. Thus, a scanning unit (e.g. disposed within the probe body) may be provided that is configured to receive signals from at least one strain sensing element and generate scanning data for output to a coordinate positioning machine (e.g. via a remote probe interface). The scanning unit may include a processor. The scanning data may provide a measurement of the magnitude of stylus deflection. The scanning data may provide a measurement of the direction of stylus deflection. A two-dimensional measurement of the stylus deflection direction may be provided. Preferably, a three-dimensional measurement of the stylus deflection direction is provided. The sensitivity and / or deflection range in the x- and y-directions may differ from the sensitivity along the z-direction, the z-direction being the direction coinciding with the elongated shaft of the stylus. Preferably, both the magnitude and direction of stylus deflection are generated and output. For example, the stylus deflection measured in three Cartesian coordinates (x, y, z) may be output. The output may be via a wireless (e.g. RF / optical) link or a wired link. The scanning probe may be battery powered.

[0038] Although a scanning probe is provided according to the present invention, such a scanning probe can also be used as a touch-trigger probe. In other words, the scanning probe may also be operable in a touch-trigger mode where a larger range of stylus deflection measurements is not required. Thus, the probe may also include a touch-trigger unit (e.g., disposed within the probe body) configured to receive a signal from at least one strain sensing element. The touch-trigger unit may include a processor. The touch-trigger unit may compare the received signal with a stylus deflection threshold and generate a trigger signal for output to a remote probe interface when the stylus deflection threshold is exceeded. The scanning trigger unit and the touch-trigger unit may be implemented as a single unit (e.g., operable in touch-trigger and / or scanning modes). In this way, the scanning probe may be backward compatible with touch-trigger probe systems, thereby enabling touch-trigger measurements to be made, but with the addition of additional scanning functionality.

[0039] The scanning probe may be mountable or attached to the spindle of the machine tool (e.g., in place of a tool used to cut the workpiece). The machine tool spindle may be configured to move the scanning probe within the machine tool to measure points on a surface of an object, such as a workpiece. Alternatively, the scanning probe may be mountable to another part of the machine tool. For example, it may be mounted to the machine tool bed, a tool setting arm, or a grinding wheel head. The scanning probe may be used to measure any object. For example, the scanning probe may be positioned to measure a workpiece (including a workpiece blank) that has been or will be processed (e.g., cut) by the machine tool. The scanning probe may also be used to measure a tool used by the machine tool (i.e., it may be used for tool inspection or setting on the machine).

[0040] The scanning probe may be arranged to carry any suitable stylus. For example, the scanning probe may include a standard stylus having an elongated shaft and a ball attached to its distal end. In this manner, form measurements may be collected. The scanning probe may also be arranged to carry a surface finish stylus. A surface finish stylus may be non-slip. In this manner, surface finish (e.g., surface roughness, waviness, etc.) measurements may be collected. Any attached stylus may be cranked or angled to achieve desired access to part features.

[0041] The scanning probe may also be provided with an associated interface for receiving measurement data (e.g. scan and / or touch-trigger data) from the scanning probe. The interface may be part of the machine tool controller or may comprise a separate unit connected to the machine tool controller.

[0042] Also described herein is a strain sensing structure for connecting a stylus holder to a probe body, the strain sensing structure having an inner portion connected to an outer portion by a plurality of bendable members, a proximal end of each bendable member attached to the inner portion and a distal end of each bendable member attached to the outer portion, the inner portion and the outer portion being centered on a central axis, the plurality of bendable members including at least one strain sensing element, and the proximal and distal ends of each bendable member being disposed at different angles about the central axis. Such a strain sensing structure may be incorporated into a measurement probe, such as a scanning probe. Any of the above features of the invention may also be included.

[0043] Also described herein is a strain sensing structure for connecting a stylus holder to a probe body, the strain sensing structure having an inner portion connected to an outer portion by a plurality of bendable members, a proximal end of each bendable member attached to the inner portion and a distal end of each bendable member attached to the outer portion, the inner portion and the outer portion being centered on a central axis, the plurality of bendable members including at least one strain sensing element, and the plurality of bendable members being thinner than the inner portion and the outer portion. The strain sensing structure may be formed from a resilient material such as stainless steel. Such a strain sensing structure may be incorporated into a measurement probe. Any of the above features of the invention may also be included.

[0044] Also described herein is a strain sensing structure (e.g., a strain sensing disk) for connecting a stylus holder to a probe body, the strain sensing structure having an inner portion connected to a concentric outer portion by a plurality of curved bendable members, a proximal end of each bendable member being attached to the inner portion and a distal end of each curved bendable member being attached to the outer portion. Such a strain sensing structure may be incorporated into a measurement probe. Any of the above features of the invention may also be included.

[0045] Accordingly, a measurement probe is described herein. The measurement probe may be for a coordinate positioning apparatus. The measurement probe may be a scanning probe. The scanning probe may also be operable as a touch trigger probe. The measurement probe may include a probe body. The measurement probe may include a stylus holder. A strain sensing structure may be provided. The strain sensing structure may connect the stylus holder to the probe body. The strain sensing structure may have an inner portion. The strain sensing structure may have an outer portion. The inner portion may be connected to the outer portion by a plurality of bendable members. The bendable members may be curved. A proximal (or first) end of each bendable member may be attached to the inner portion. A distal (or second) end of each bendable member may be attached to the outer portion. The inner and outer portions may be centered on a central axis. The plurality of bendable members may include at least one strain sensing element. The proximal and distal ends of each bendable member may be disposed at different angles about the central axis. Any of the above features of the invention may also be included.

[0046] Methods of obtaining scanning measurements using a measurement probe as described above are also envisaged.

[0047] The invention will now be described, by way of example only, with reference to the accompanying drawings in which: [Brief description of the drawings]

[0048] [Figure 1] FIG. 1 shows a prior art strain gauge touch trigger probe as described in US Pat. No. 5,399,633. [Diagram 2] FIG. 2 shows a prior art strain sensing disk having radially extending spokes for use in the touch-trigger probe of FIG. [Diagram 3] FIG. 3 is a perspective view of a strain gauge and stylus holder arrangement of the present invention. [Figure 4] FIG. 4 shows a cross section through a scanning probe of the present invention. [Diagram 5] FIG. 5 shows a cutaway view of the scanning probe shown in FIG. [Figure 6a] FIG. 6a shows a perspective view of the top surface of the strain sensing structure of the present invention. [Figure 6b] FIG. 6b shows a perspective view of the underside of the strain sensing structure of the present invention. [Figure 7a] FIG. 7a shows a plan view of the top surface of the strain sensing structure of the present invention. [Figure 7b] FIG. 7b shows a plan view of the underside of the strain sensing structure of the present invention. [Figure 8a] FIG. 8a shows a strain simulation of the strain sensing structure of the present invention when it is not deflected. [Figure 8b] FIG. 8b shows a strain simulation of the strain sensing structure of the present invention when it is deflected. [Figure 9a] Figure 9a shows the reaction force at the strain gauge location on the strain sensing structure. [Figure 9b] Figure 9b shows the reaction force at the strain gauge location on the strain sensing structure. [Figure 10] FIG. 10 illustrates the measurement range obtained using the scanning probe of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] Referring to Figures 1 and 2, there is shown a (prior art) touch trigger probe 10 as described with reference to Figures 1 and 2 of US Patent No. 5,999,633. For clarity, the view of the probe in Figure 1 is a partial cross-section at the cross section indicated as 1-1 in Figure 2. This plane is not completely flat, but includes two planes at 120° to each other.

[0050] Figure 1 shows a touch-trigger probe 10 attached to a coordinate positioning apparatus 5 via a boss 12. As mentioned above, the coordinate positioning apparatus may include a coordinate measuring machine (CMM), robot, machine tool, etc. capable of moving the probe 10 relative to an object 50. The coordinate positioning apparatus 5 is configured to measure the position of the probe 10 in the illustrated x, y and z directions (i.e. in a Cartesian machine coordinate system).

[0051] The probe 10 has a stylus 14 with a spherical tip 16 at its distal end for contacting an object, such as the object 50 shown. In this example, the stylus 14 also includes an integrated stylus holder, although it should be noted that these may be provided as separable components. The probe 10 also includes a body 18, a circuit board 20, a spring cage 22, a compression spring 24, a top member 26 at the proximal end of the stylus 14, and a strain sensing structure 30. The spring cage 22 and a central portion 37 of the strain sensing structure 30 are both fixed to the body 18 of the probe 10. The top member 26 of the stylus 14 includes three pairs of rollers 27 urged by the compression spring 24 into engagement with three balls 31 on the strain sensing structure 30. The balls 31 and corresponding pairs of rollers 27 provide a kinematic position (i.e., using six contact points) that ensures that the top member 26 adopts a repeatable position relative to the strain sensing structure 30.

[0052] The strain sensing structure 30 is shown in more detail in Figure 2. The outer ring portion containing the ball 31 is attached to a circular central portion 37 via three radially extending arms 32. A semiconductor strain gauge 33 is fixed to each of the arms 32. As mentioned above, the circular central portion 37 is fixed to the probe body 18. Thus, changing the force applied to the ball 31 changes the strain in the radially extending arms 32, which can be measured by the strain gauges 33.

[0053] Thus, in use, a force applied to the stylus tip 16 in either the x, y, or z directions will change the force applied to the strain sensing structure 30 via the ball 31. In other words, a force applied to the stylus causes a deflection of the radially extending arm 32 of the strain sensing structure 30 relative to the body 18. Signals from the strain gauges 33 are passed to the circuit board 20 and processed to ascertain when a force exceeding a certain magnitude has been applied. In particular, signals from the strain gauge sensors can be combined using a sum-of-squares technique as described in US Pat. No. 5,999,333. A trigger signal is then output when it is determined that the stylus has made contact with an object.

[0054] It should be noted that one advantage of the prior art touch-trigger probes discussed above is their robustness. Excessive force on the stylus in the x or y direction, or pulling of the stylus in the z direction away from the probe body, results in closure of the gap 28 between the strain sensing structure 30 and the probe body 18 (i.e. the probe body effectively acts as a mechanical stop to limit bending of the strain sensing structure 30). Excessive force applied to the stylus in the z direction towards the probe body causes compression of the spring 24 which disconnects the upper stylus member 26 and the strain sensing structure 30, i.e. this force overcomes the force applied by the compression spring 24. When such force is removed, the pair of balls 31 and corresponding rollers 27 ensure that the stylus reseats in the same (repeatable) position relative to the strain sensing structure 30. These features give the probe the robustness required to enable operation in machine tool environments and the like.

[0055] The touch trigger measurement probe described above therefore internally analyses the output of the strain gauges 33 of the strain sensing structure 30, which provide a measurement of the amount of stylus deflection. However, these strain sensor signals are not output from the probe. The only measurement signal output from the probe is a trigger signal which is issued when the strain gauge signal exceeds a certain threshold, thus indicating that the stylus has contacted an object.

[0056] The above prior art arrangements are only suitable for touch trigger measurements because the strain sensing structures are highly sensitive but can only sense stylus deflection over a very small deflection range (e.g., stylus deflection of more than about 30 μm for a 100 mm stylus will saturate the strain gauge). This deflection range is insufficient for use in a stream of stylus deflection data captured as the stylus is moved (scanned) along a surface for combination with associated machine data. In other words, in most measurement applications, the expected position change of the surface being measured is likely to far exceed the viable deflection range provided by the above prior art probe structures.

[0057] According to the present invention, a modified strain sensing structure has been devised which has the advantages of robustness and sensitivity of the prior art touch trigger probes described above, but which significantly increases the working range of deflection without increasing the overall size of the measurement probe. This modified strain sensing structure can provide, for example, a measurable deflection range of more than 1.5 mm (for a 100 mm stylus), which is sufficient to enable its use not only as a touch trigger probe, but also as a scanning probe. Furthermore, the robustness advantages of the prior art touch trigger probes can be retained. Thus, the advantages of a strain gauge touch trigger probe can be combined with the advantage of the speed of being able to scan a surface rather than making a series of touch trigger measurements.

[0058] Referring to Figure 3, some of the internal workings of a scanning probe according to the present invention are shown. Other features of the scanning probe not shown in Figure 3 (e.g. probe body, mounting to a coordinate positioning apparatus, etc.) may be conventional or similar to those described above with reference to Figures 1 and 2. In particular, Figure 3 shows a strain sensing structure 100, a three-armed stylus holder plate 102 which engages three balls 104 attached to the strain sensing structure 100, a return force cage 106, and a coil spring 108. As with the prior art devices described above, the coil spring 108 acts to urge the stylus holder plate 102 into engagement with the balls 104 of the strain sensing structure 100.

[0059] The configuration shown in FIG. 3 minimizes any external forces that could potentially affect the repeatability of the mechanical rest position adopted by the stylus holder plate 102. In particular, the kinematic retention force (i.e. the spring force applied to maintain the engagement of the stylus holder plate 102 with the ball 104) is returned to the outer rigid region of the strain sensing structure 100. This has the advantage that the kinematic compression spring 108 remains substantially parallel to the outer region moving portion of the strain sensing structure 100 when providing the required retention force. This mechanism also has built-in protection features to avoid overstressing the structure during overtravel and crash events. This includes having mechanical offloading features on both sides of the strain sensing structure for XY and Z overtravel and crash occurrences.

[0060] FIG. 4 is a cross-sectional view through a measurement probe including the internal mechanism shown in FIG. 3. A stylus holder 110 including a three-armed stylus holder plate 102 is shown pressed into engagement with the strain sensing structure 100 via a ball 104. The stylus holder also includes a threaded recess 112 for receiving the proximal end of the stylus shaft. Also shown is a diaphragm seal 114 that prevents external contaminants from entering the probe mechanism. The diaphragm is configured to have a low geometric stiffness to minimize its effect on the ability of the stylus holder to return to a repeatable rest position. For example, the diaphragm 114 is located as close as possible to the center of rotation of the structure to minimize any moment effects, and an O-ring is mounted axially against the diaphragm to prevent the diaphragm from slipping.

[0061] FIG. 5 is a cross-sectional view of certain components of the scanning probe shown in FIGS. 3 and 4, and the inset in FIG. 5 shows a perspective view (exemplary) of such components. The stylus holder 110 is shown with the stylus 120 attached. The ball 104 attached to the strain sensing structure 100 is shown engaged with the stylus holder plate 102. Also shown is a fixture 132 that attaches the strain sensing structure 100 to the probe body or casing (not shown in FIG. 5). It can also be seen from FIG. 5 how the stylus holder pivots about a pivot point 130 that is in the plane of the disk-shaped strain sensing structure 100. Furthermore, the separation "d" between the damper 116 and the longitudinal axis 136 of the stylus holder 110 provides a mechanical advantage that amplifies the force applied to the strain sensing structure 100 when the stylus tip 138 is displaced (e.g., by contact with an object).

[0062] The damper 116 includes a shaft 142 attached to the strain sensing structure 100 and a cavity containing ferrofluid 146 and a magnet 148. A retainer 150 is also shown with a ferrofluid void 152 for retaining the ferrofluid when the probe is rotated at high speeds. The damper 116 is arranged to damp the movement of the strain sensing structure 100 such that vibrations that would otherwise occur are reduced. In particular, the damping reduces the magnitude of vibrations during probe movements, scanning events, and approaching or leaving a surface. This has the advantages of rapid damping of output settling times after leaving a surface, repeatable stylus return or zero position, and damping fluid retention even during high speed spin events.

[0063] With reference to Figures 6a, 6b, 7a and 7b, the strain sensing structure 100 will be described in more detail. Figures 6a and 7a show, in perspective and plan views, respectively, a first or top surface of the strain sensing structure 100. Figures 6b and 7b show, in perspective and plan views, respectively, a second or bottom surface of the strain sensing structure 100.

[0064] The strain sensing structure 100 is a circular disk having an outer (ring) portion 200 connected to an inner (hub) portion 202 by three bendable members or arms 204. The structure comprises martensitic stainless steel and is formed by an EDM (electrical discharge machining) process, particularly a wire EDM process. As noted above, other materials and manufacturing techniques (e.g., stamping, machining, etc.) could be used. The inner and outer portions include thicker (and therefore harder) regions, while the bendable arms 204 are machined to be significantly thinner.

[0065] As mentioned above, the inner (hub) part 202 of the strain sensing structure 100 is rigidly attached to the probe housing via three mounting holes 206. The inner part 202 is therefore fixed relative to the probe housing. The outer part 200 is also in the form of a rigid ring that is sufficiently stiff not to deform when a force is applied to the ball 104 by the movable stylus holder. The outer part 200 therefore moves with the stylus holder. The underside of the outer part 200 comprises three equally spaced balance stiffeners 201. The geometry of the areas of the stiffeners 201 is also optimized to generate approximately equal and opposite deformations of the centre when a stylus holder force is applied via the ball 104. The outer part also includes an opening 103 in which the return force cage 106 (which engages the coil spring 108) is attached. The inner part 202 is concentric with the outer part 200. The inner portion 202 also includes a centrally located opening 214 through which the stylus holder can pass, thereby allowing the central axes of the inner and outer portions to coincide with the longitudinal axis 136 of the stylus holder and stylus.

[0066] The bendable arms 204 are helical, low stiffness members that connect the fixed inner portion 202 of the structure to the rigid outer portion 200. In particular, the proximal end 220 of each arm is attached to the inner portion 202 adjacent to the mounting hole 206. The distal end 222 of each arm is attached to the outer portion 200 adjacent the location of the ball 104. Attaching the distal end 222 of each arm to the portion of the outer portion 200 adjacent to the ball 104 minimizes the effect of any deformation of the outer portion 200 between the kinematic balls. The geometry of the proximal and distal ends of each bendable arm is also optimized to generate a passive strain response from applied kinematic forces and minimize stress concentrations at the interface with the stiffer inner / outer portions.

[0067] Unlike the configurations described in US Pat. No. 6,399,623 and US Pat. No. 6,399,636, it can be seen that the bendable arms 204 do not extend linearly outward (i.e., purely radially), but instead extend in a generally circumferential direction. In other words, the proximal end 220 of each arm (i.e., the end attached to the inner portion 202) is disposed at a different angle around the central axis of the strain sensing structure 100 than the distal end 222 of each arm (i.e., the end attached to the outer portion 200). This allows the bendable arms 204 to be longer than if they extended only radially, thereby increasing the amount of bending that can occur for a given diameter of the strain sensing structure 100. In other words, the profile of the spiral arms is optimized to maximize the length of the arms in a compact solution.

[0068] The bendable arms 204 are also thinner than the inner / outer portions and are curved in the plane of the strain sensing structure 100. In particular, the radially innermost and outermost edges of the arms 204 are curved around different center points that are also spaced away from the center of the structure. This minimizes space allowing for a compact solution with a stiffer outer region in the same space. The arm profile also minimizes twisting of the beam during use and promotes more bending at the fixed proximal end 220 adjacent to where the strain gauges 210 are located.

[0069] A force applied by the stylus holder (via the ball 104) to the outer portion 200 causes bending of the bendable arms 204. A strain gauge 210 (i.e., an example of a strain sensing element) is attached to each bendable arm 204. The outputs from the three strain gauges are processed (e.g., by a processor mounted in the measurement probe) to measure the deflection of the stylus. The use of three strain gauge outputs allows the magnitude and direction of the deflection of the stylus to be sensed in three dimensions (i.e., in the xy plane, which is parallel to the plane of the disk, and along the z direction, which is perpendicular to the disk). If touch trigger measurements are required, these signals can be combined using a sum-of-squares method of the type described in US Pat. No. 5,999,333. A fourth strain gauge 212 is also attached to the inner portion 202, which is used to allow mitigating the effect of temperature on the strain measured by the strain gauges 210.

[0070] 8a, 8b, 9a and 9b, modelled strains are shown within a portion of the strain sensing structure 100. This analysis allows optimising the position of the strain gauge 210 on the bendable arm 204.

[0071] FIG. 8a shows a strain map of the portion of the strain sensing structure 100 adjacent the proximal end 220 of the bendable arm 204 when no bending force is applied to the stylus of the device (i.e., this shows the residual strain of the strain sensing structure in the absence of an applied external force). It can be seen that the high stiffness of the outer portion 200 minimizes the deformation and strain levels. The fixed inner portion 202 also has a very low strain. As mentioned above, the strain gauges 210 are placed at the proximal end of the bendable arm. The exact location of each strain gauge 210 is selected to coincide with a passive strain region, i.e., a location where there is a low magnitude of strain induced by an applied kinematic (spring) force. In other words, the residual or parasitic strain at the strain gauge location is minimized so that the strain caused by arm bending when a force is applied to the stylus can be measured.

[0072] Figure 8b shows a strain map of a portion of the strain sensing structure 100 adjacent the proximal end 220 of the bendable arm 204 when a deflection force is applied that induces a strain close to the upper strain limit. Note that the scale and dimensions of the image in Figure 8b are different from those in Figure 8a. Figure 8b shows how the strain caused by the deflection of the stylus is concentrated near the proximal end 220 of the bendable arm 204, which is in close proximity to the strain gauge 210. This high concentration of strain allows the strain gauge 210 to be highly responsive to changes in strain that occur as the amount of stylus deflection changes.

[0073] It should be noted that a certain amount of stress, and therefore strain, is necessary to achieve the desired sensitivity per unit deflection. Thus, a balance is struck between achieving sufficient sensitivity, providing adequate range, and achieving an adequate level of robustness. This balance can be alleviated to some extent by reacting the kinetic forces as described above in combination with the selection of hardened and tempered 440C martensitic stainless steel, which provides a high fatigue endurance limit.

[0074] 9a and 9b each show that the reaction from the applied kinematic forces in the structure is perpendicular to the bendable arm 204, and the reaction moment is along the gauge location. This minimizes undesirable twisting of the bend arm 204.

[0075] Therefore, the location of the strain gauges has been selected to be in an area that has a passive response to applied kinematic forces and is susceptible to minimal changes in sensitivity due to position placement errors. Note that in addition to the adhesive bond layer, a diamond-like carbon (DLC) coating is applied to the stainless steel strain sensing structure to provide electrical insulation. This allows a very thin, single layer of adhesive to be used to bond the strain gauges to the structure, maximizing strain transfer and promoting consistency between gauges. Testing of the strain sensing structure over 12 million Z-overtravel movements demonstrated no loss of performance or delamination of the coating.

[0076] The strain gauge undergoes a compressive strain during mounting due to the adhesive cure temperature and the difference in thermal expansion of the gauge and construction materials. During operation, the gauge is exposed to strains of plus or minus several hundred με with respect to the fitted compressive strain. The advantage of the kinematic loading configuration of the present invention is that the gauge remains compressed, avoiding the potential nonlinear region in the transition between compression and tension. An additional advantage to the kinematic configuration is that the strain sensing structure is essentially unloaded in the rest position. The effect of gravity on the mass of the structure and stylus is minimal, so the average stress in the rest position is close to zero. This arrangement approaches an analogy of the ideal "simple rotating bending" used in SN curve fatigue analysis. This approach has the great advantage of increasing the fatigue life and therefore the robustness of the structure during scanning events.

[0077] FIG. 10 shows raw experimental results collected using a series of measurement probe designs as described above. The figure shows scans of increasing deflection using a ring gauge. The lower (less than 1 mm) deflection scans (not shown) show a constant deflection with no lobes present. The 1.25 mm deflection scan has a single lobe feature on the positive horizontal axis, while the remainder of the scan is circular. The 1.35 mm scan clearly shows a three lobe region. Thus, it is possible to scan with a deflection of up to about 1.25 mm. Note that the scans shown in FIG. 10 are electronically limited. However, it is predicted that a usable deflection range of up to 1.8 mm (for a 100 mm stylus) can be provided by the strain sensing structure shown. This is well beyond the 1 mm deflection range typically required for scanning measurements.

[0078] Thus, the measurement probe configuration described herein has been shown to make it possible to obtain a translation range of about 1.25 mm. This is large enough to obtain scanning measurements using the measurement probe. The measurement probe may therefore be operated as a scanning probe. For example, an output module may be provided that takes the raw strain gauge signals and outputs them (e.g., as a series of stylus deflection measurements) to an external interface or computer. This data transmission may be via a wired or wireless (e.g., optical or RF) link. Some processing of the signals may be performed within the measurement probe (e.g., using a processor provided with the probe) and / or within the associated probe interface (e.g., including a processor). The measurement probe may also be operated as a touch-trigger probe. For example, the strain gauge outputs may be combined (e.g., using the techniques described in US Pat. No. 5,399,363) and compared to a trigger threshold. The output module may then output a trigger signal when the trigger threshold is exceeded. The measurement probe may be switchable between touch-trigger and scanning modes, or may output both the scanning data and the touch-trigger signal simultaneously.

[0079] It is also important to remember that the above description is merely illustrative of the invention. Those skilled in the art will appreciate the many alternative variations that may be possible.

Claims

1. 1. A scanning probe for a coordinate positioning apparatus, comprising: A probe body; a stylus holder; a strain sensing structure connecting the stylus holder to the probe body, a strain sensing structure having an inner portion connected to an outer portion by a plurality of bendable members, a proximal end of each bendable member attached to the inner portion and a distal end of each bendable member attached to the outer portion, the inner and outer portions being centered on a central axis, the plurality of bendable members including at least one strain sensing element; Equipped with A scanning probe wherein the proximal and distal ends of each bendable member are disposed at different angles about the central axis, and each bendable member is curved within the plane of the strain sensing structure.

2. 10. The scanning probe of claim 1, wherein the width of each bendable member varies along its length.

3. 2. The scanning probe of claim 1, wherein the outermost and innermost edges of each bendable member are curved, the curvatures of the innermost and outermost edges being arcs of circles centered about different points.

4. 2. The scanning probe of claim 1, wherein the thickness of each bendable member is substantially constant along its length.

5. 2. The scanning probe of claim 1, wherein the inner portion includes a circular central hub, the outer portion includes an outer ring, and the plurality of bendable members comprises three bendable members equally spaced apart from one another.

6. The scanning probe of claim 1 , wherein the strain sensing structure comprises a single machined part.

7. The scanning probe of claim 1 , wherein the thickness of the plurality of bendable members is less than the inner and outer portions.

8. The scanning probe of claim 1 , wherein the strain sensing structure is substantially planar, and the plurality of bendable members are bendable in a direction perpendicular to the plane of the strain sensing structure.

9. The scanning probe of claim 1 , wherein at least one strain sensing element is disposed on each bendable member.

10. A scanning probe according to claim 1 , wherein the stylus holder holds a stylus such that the stylus axis lies on the central axis.

11. A scanning probe according to any preceding claim, wherein the inner part is fixed to a probe housing and the stylus holder is connected to the outer part.

12. 2. The scanning probe of claim 1, wherein the stylus holder is connected to the strain sensing structure by a protection mechanism, the protection mechanism comprising a spring that urges the stylus holder into contact with the strain sensing structure but allows the stylus holder to disengage the strain sensing structure when the external force applied to the stylus holder exceeds a threshold level.

13. The scanning probe of claim 1 , comprising at least one fluid damper for damping vibrations of the strain sensing structure.

14. The scanning probe of claim 1 , comprising a scanning unit configured to receive signals from the at least one strain sensing element and generate scan data for output to a remote probe interface.

15. 10. The scanning probe of claim 1, further comprising a touch trigger unit configured to receive a signal from the at least one strain sensing element, compare the received signal with a stylus deflection threshold, and generate a trigger signal for output to a remote probe interface when the stylus deflection threshold is exceeded.

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