Abstract:
An electronic hand tool type caliper includes a scale track located along a scale member reference edge that forms a sliding bearing with a mating surface of the caliper slide, thereby maintaining proper alignment of the slide jaw. Placing the scale track along the reference edge is advantageous in that the reference edge surface is inherently precisely machined and particles are excluded by the inherently close fit and the wiping action of the sliding bearing. A readhead sensor is mounted within the slide surface that mates to the reference edge to provide the sliding bearing. Thus, a very small readhead sensor may be reliably positioned at an extremely small gap relative to the scale in a protected operating environment, without detrimentally affecting cost, slider friction, or signal strength. High resolution digital signals may be provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to metrology systems, and more particularly to electronically sensing movement or position between two members such as the moving parts of a caliper. 
       BACKGROUND OF THE INVENTION 
       [0002]    Various electronic calipers are known that use electronic position encoders. These encoders are generally based on low-power inductive, capacitive, or magnetic position sensing technology. In general, an encoder may comprise a readhead and a scale. The readhead may generally comprise a readhead sensor and readhead electronics. The readhead outputs signals that vary as a function of the position of the readhead sensor relative to the scale, along a measuring axis. In an electronic caliper the scale is generally affixed to an elongated scale member that includes a first measuring jaw and the readhead is affixed to a slide which is movable along the scale member and which includes a second measuring jaw. Thus, measurements of the distance between the two measuring jaws may be determined based on the signals from the readhead. 
         [0003]    Compact electronic hand tool type calipers, (e.g., those having a measurement range on the order of 100-250 mm) have evolved to have a relatively standardized configuration including a refined set of dimensions and ergonomics, as well as extremely low power consumption. Hand tool type calipers that are even slightly larger or heavier than the standardized configuration are generally rejected in the marketplace. In conventional calipers, the elongated scale member typically has a relatively wide top surface and relatively narrow edges. The encoder scale is affixed to the top surface and the readhead is affixed to a surface of the movable slide such that it moves along the top surface over the scale. An appropriate operating gap is provided between the readhead sensor and the scale. Among other advantages, this configuration allows the readhead to be collocated with the display and the other electronic components of the caliper, which is economical. This configuration also allows the use of a relatively large sensing region between the readhead sensor and scale. This is beneficial because the S/N ratio of the types of position encoders used in electronic calipers and typically benefits from increasing the sensing region dimensions for a given operating gap. Thus, this has been the conventional configuration. For example, U.S. Pat. Nos. 6,229,301; 6,724,186; 6,332,278; RE37,490; 5,973,494; and 5,574,381, each of which is hereby incorporated by reference in its entirety, show calipers conforming to this configuration. 
         [0004]    U.S. Pat. No. 5,029,402, discloses a slightly different configuration used in an unconventional large caliper-type sliding gauge, which is described as being usable for measuring large objects such as tree trunks, etc. The sliding gauge includes a rod and a slide. The rod is disclosed as having eight sides. The rod includes markings that may be sensed by a length sensor on the slide. FIG. 6 of the &#39;402 patent shows various surfaces where markings and length sensors may be applied, separated by an appropriate operating gap. In some embodiments, the widest surfaces of the rod are not used. However, the disclosure of &#39;402 patent discloses a “caliper” that is not compact, and furthermore offers no clear advantages over the conventional caliper configuration outlined above, for conventional hand tool type caliper applications. 
         [0005]    It would be desirable to advance the state of the art of compact hand tool type electronic calipers, and certain related compact “jawless” calipers that comprise similar or identical components used as low cost linear scales. For example, it would be desirable to further lower the cost of electronic calipers, and/or make them more reliable. 
       SUMMARY OF THE INVENTION 
       [0006]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
         [0007]    The present invention is directed to an improved caliper configuration that provides certain cost and/or reliability advantages, and that enables the use of readhead and scale elements that have not been practical to use in known hand tool type caliper configurations. A caliper utilizing a high resolution magnetic scale track positioned along a reference edge of a scale member is provided. 
         [0008]    In accordance with one aspect of the invention, the scale track may be located along an edge surface of the scale member that forms a sliding bearing with a mating surface of the caliper slide, thereby maintaining proper alignment of the slide jaw. Such an edge surface is therefore denoted a reference edge (also called a reference edge surface). In contrast, in known caliper configurations the scale track has been placed on the broad top surface of the scale member. Placing the scale track along the reference edge is advantageous in that the reference edge surface is inherently precisely machined. This is because the reference edge must guide the slide such that the measuring jaws of the caliper remain precisely parallel, to prevent measurement errors. Thus, the reference edge surface and the mating surface of the slide are inherently straight, smooth and flat. In addition, when the two surfaces slide against each other particles are excluded by the inherently close fit and the wiping action. 
         [0009]    In accordance with another aspect of the invention, the readhead sensor may be mounted within the slide surface that mates to the reference edge. Thus, the readhead sensor may be reliably positioned at an extremely small gap relative to the scale, in a manner that is unprecedented in a hand tool type caliper configuration. Such a small gap allows an extremely small sensor to provide good signal strength and a high signal-to-noise ratio. 
         [0010]    In a caliper, a loading edge (also called a loading edge surface) is located on the opposite side of the scale member from the reference edge surface. Typically, adjustment screws press a loading member against the loading edge to adjust the slide pressure and friction on the edge surfaces of the scale member. In accordance with another aspect of the invention, in some embodiments, the scale track may be located along the loading edge. In some embodiments, scale tracks may be located on both the loading edge and the reference edge. In general, for any readhead and scale configuration that is indicated as being positioned along the reference edge herein, in an alternative embodiment an analogous readhead and scale configuration may be positioned along the loading edge. 
         [0011]    In accordance with another aspect of the invention, the extremely small gap between the readhead sensor and the scale track allow the use of previously-impractical miniature sensor technologies, such as miniature magnetic field sensors that require a close proximity between a magnetic scale and the sensor due to spacing loss. 
         [0012]    In accordance with another aspect of the invention, in one embodiment the edge surface of the scale member may be used for a high resolution scale track, and the broad top surface of the scale member is used for a coarser resolution absolute position indicating scale track that is read by a known type of absolute position readhead. 
         [0013]    In accordance with another aspect of the invention, in one embodiment the magnetic scale track information along the reference edge (may be included in a ferromagnetically soft material that is coated, painted, sputtered, embedded, or inlaid, wherein the presence, absence, or concentration of the material spatially delineates the scale information. In some embodiments, magnetically inert material can fill voids between magnetic materials along the edge. In some embodiments, the entire edge can be coated by a protective overcoat. The scale may be formed and detected as a change in the magnetic permeability along the length of the reference (or loading) edge in such embodiments. 
         [0014]    In accordance with another aspect of the invention, in another embodiment, a magnetic coating can be uniformly painted, coated, inlaid, or sputtered along the reference edge, using a hard magnetic substance that is magnetizable. In one implementation, information may be written into such a material, where the magnetization direction and/or magnitude varies spatially and is detected by a readhead sensor which detects the field. Alternatively, in another embodiment, the scale member reference edge itself may be fabricated completely out of such a magnetizable material, for example a special hard ferromagnetic alloy, or a hard ferromagnetic ferrite ceramic or glass. In some embodiments, the reference edge may be protected by a protective coating, regardless of its composition. 
         [0015]    According to this invention, a very small readhead sensor may be reliably positioned at an extremely small gap relative to the scale track in a protected operating environment, without detrimentally affecting cost, slider friction, or signal strength. High resolution digital signals may be provided from the readhead sensor, eliminating the need for analog signal interpolation in order to provide typical caliper measurement resolution. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0017]      FIG. 1  is a diagram of a first exemplary embodiment of a hand tool type caliper including a magnetic sensor assembly and scale track along the reference edge surface of the scale member in accordance with the present invention; 
           [0018]      FIG. 2  is a diagram of a first exemplary embodiment of a magnetic sensor assembly usable in the caliper of  FIG. 1 ; 
           [0019]      FIG. 3  is a diagram of a first exemplary embodiment of the sensing element head of the magnetic sensor assembly of  FIG. 2 ; 
           [0020]      FIG. 4  is a diagram of a first exemplary embodiment of the magnetic field sensing elements of the sensing element head of  FIG. 3 ; 
           [0021]      FIG. 5  is a diagram of a first exemplary embodiment of the slider assembly of  FIG. 1  including the magnetic sensor assembly of  FIGS. 2-4 ; 
           [0022]      FIG. 6  is a diagram of a portion of the scale member of  FIG. 1  including a scale track with scale elements arranged in a first exemplary pattern according to a scale pitch, for use with the magnetic sensor assembly of  FIGS. 2-5 ; 
           [0023]      FIG. 7  is a diagram of a second exemplary embodiment of a magnetic sensor assembly usable in the caliper of  FIG. 1 ; 
           [0024]      FIG. 8  is a diagram of a second exemplary embodiment of the slider assembly of  FIG. 1  including the magnetic sensor assembly of  FIG. 7 ; 
           [0025]      FIG. 9  is a diagram of a portion of the scale member of  FIG. 1  including a scale track with scale elements arranged in a second exemplary pattern according to a scale pitch, for use with the magnetic sensor assembly of  FIGS. 7 and 8 ; 
           [0026]      FIG. 10  is a diagram of a third exemplary embodiment of a magnetic sensor assembly usable in the caliper of  FIG. 1 ; 
           [0027]      FIG. 11  a diagram of a third exemplary embodiment of the slider assembly of  FIG. 1  including the magnetic sensor assembly of  FIG. 10 ; and 
           [0028]      FIG. 12  is a diagram of a portion of the scale member of  FIG. 1  including a scale track with scale elements arranged in a third exemplary pattern having a scale pitch, for use with the magnetic sensor assembly of  FIGS. 10 and 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]      FIG. 1  is an exploded view diagram of a first exemplary embodiment of a hand tool type caliper  100  including a magnetic sensor assembly  158  and scale track  143  positioned along the reference edge surface  142  of an elongated scale member  102  in accordance with the present invention. The magnetic sensor assembly  158  is positioned in a slider  138  to form a slider assembly  120 , to which an electronic assembly  152  is attached. A portion of the slider  138  is shown in wireform outline, to better illustrate the magnetic sensor assembly  158 . The general mechanical structure and physical operation of the caliper  100  is similar to that of certain prior electronic calipers, such as that of U.S. Pat. No. 5,901,458, which is hereby incorporated by reference in its entirety. The scale member  102  is a rigid or semi-rigid bar having a generally rectangular cross section. In some embodiments, a groove  106  may be formed in its wide upper surface to accept an elongated thin substrate (not shown). The elongated thin substrate may be rigidly bonded in the groove  106 , and may include visual length indications and/or absolute position scale elements that cooperate with corresponding absolute readhead elements (not shown) included in electronic assembly  152 , in a manner similar to that used in known electronic calipers and as described in previously incorporated RE37,490 and U.S. Pat. No. 6,400,138, which is incorporated herein by reference in its entirety. The thin substrate may fill the groove  106 , with its top surface coplanar with the top edges of scale member  102 . 
         [0030]    A pair of jaws  108  and  110  are integrally formed near a first end  112  of the scale member  102 . A corresponding pair of jaws  116  and  118  are formed on a slider  138 . The outside dimensions of a workpiece are measured by placing the workpiece between a pair of engagement surfaces  114  of the jaws  108  and  116 . Similarly, the inside dimensions of a workpiece are measured by placing a pair of engagement surfaces  122  of the jaws  110  and  118  against opposing internal surfaces of the workpiece. In a position sometimes referenced as the zero position, the engagement surfaces  114  abut one another, the engagement surfaces  122  are aligned, and both the outside and inside dimensions measured by the caliper  100  may be indicated as zero. 
         [0031]    The measured dimension may be displayed on a digital display  134 , which is mounted within a cover  136  of an electronic assembly  152  of the caliper  100 . The electronic assembly  152  may also include a set of push button switches  130 ,  131  and  132  (e.g., an on/off switch, mode switch, and zero set switch), and a signal processing and display circuit board  154  comprising a readhead signal processing circuit  160 . 
         [0032]    As shown in  FIG. 1 , the slider assembly  120  includes a slider  138  and provides a reference edge interface configuration and a loading edge interface configuration. In various embodiments, the reference edge interface configuration includes an internal reference surface  140  of the slider  138 , and the loading edge interface configuration includes an internal loading surface  144  of the slider  138  (also shown in  FIG. 5 ). In the embodiment shown in  FIG. 1 , the reference edge interface configuration also includes the magnetic sensor assembly  158 , and the loading edge interface configuration also includes the loading member  148 , and adjustment screws  149 B. 
         [0033]    In operation, the slider  138  straddles the scale member  102 , the internal reference surface  140  mates against the reference edge surface  142 , and the internal loading surface  144  opposes the loading edge surface  146  with the loading member  148  (e.g., a resilient pressure bar) compressed in between by the adjustment screws  149 B, as described in greater detail below with reference to  FIG. 5 . As will be described in greater detail below, in various embodiments according to this invention, at least one of the reference edge  142  and the loading edge  146  include a scale track  143  that includes periodically arranged magnetic scale elements. In the embodiment shown in  FIG. 1 , the reference edge  142  includes the scale track  143 . 
         [0034]    As previously indicated, the electronic assembly  152  is attached to the slider assembly  120 , such that they move as a unit. In one embodiment, the bottom surface of the signal processing and display circuit board  154  is mounted to abut the top surfaces of the slider  138  on either side of the scale member  102 . The magnetic sensor assembly  158  is connected to the readhead signal processing circuit  160  by connecting an array of connection pads on the connector end  232  to the connector pad array  162  on the signal processing and display circuit board  154 . In some embodiments, the connector end  232  may be routed through a resilient seal (not shown) that is compressed between the cover  136  and the signal processing and display circuit board  154 , such that the electronic assembly  152  is completely sealed against contamination. In the slider assembly  120 , the magnetic sensor assembly  158  is mounted in the slider  138  to sense the scale track  143  along the reference edge surface  142  of the scale member  102 , as described in greater detail below with reference to  FIG. 5 . 
         [0035]    It will be appreciated that locating the scale track  143  along the inherently precisely machined reference edge  142  provides unexpected advantages. The reference edge  142  is inherently precisely machined and designed to retain its integrity (clean, flat, smooth, “ding-free”) in all calipers, because the reference edge  142  must guide the internal reference surface  140  of the slide  138  such that the engagement surfaces  114  of the caliper remain precisely parallel, to prevent measurement errors. Since the internal reference surface  140  must slide against the reference edge  142 , this inherently provides a wiping action and “zero gap” between them, which inherently excludes contaminating particles. Thus, in the novel configuration of the caliper  100 , the magnetic sensor assembly  158  is positioned in the slider  138  with miniature magnetic sensors located proximate to the scale track  143 , to use this protected interface in a novel manner—to provide the extremely small, reliable, particulate-free gap relative to the scale track that is required for such a miniature magnetic sensors. It should be appreciated that while providing such a small, reliable gap ordinarily requires costly fabrication of close-tolerance features, in the configuration of the caliper  100  such a gap is provided “for free.” Conversely, the novel use of this protected interface, to provide an extremely small, reliable, particulate-free gap at little or no additional cost, enables the use of previously-impractical miniature magnetic field sensor technologies that require a close proximity between a magnetic scale and the magnetic field sensor in order to avoid spacing loss. In the current context, spacing loss refers to the degradation of the signal from a magnetic sensor as its gap increases relative to a magnetic information track with a magnetic flux transition pitch of X along the magnetic track. It is known that the signal strength decreases approximately 55 dB*(λ/d) as the gap d increases. 
         [0036]    It should be appreciated that prior art electronic calipers have generally located larger magnetic, capacitive, or inductive sensors proximate to a larger scale track along the wide top surface (e.g., in a groove similar to the groove  106 ), in order to use a large gap that was obtained with low fabrication cost, and overcome the associated “large gap” spacing loss by using a larger sensor. An unexpected drawback that occurs if it is attempted to use an additional sliding interface to facilitate a small gap along the wide top (or bottom) surface of a caliper member, is that the friction between the slider  138  and the scale member  102  increases (e.g., the friction force may approximately double). It turns out that the associated force on the slider to overcome this addition friction is generally ergonomically unacceptable. Conversely, an unexpected advantage of the configuration of the caliper  100  according to this invention, is that an extremely small and reliable sensing gap is provided proximate to a sliding interface that is inherently necessary to maintain the alignment of the engagement surfaces  114 , which means no features are introduced which might increase the minimum required amount of friction force between of the scale member  102  and the slider assembly  120 . 
         [0037]      FIG. 2  is a diagram of a first exemplary embodiment of the magnetic sensor assembly  158  of  FIG. 1 . As shown in  FIG. 2 , the magnetic sensor assembly  158  includes a sensing element head  210 , a flexible connector  220 , a bottom assembly block  240 , a top assembly block  250 , a mounting member  260 , and a wire spring  280 . The sensing element head  210  includes a sensing element array  214  and a connector pad array  216  which are disposed on a substrate  212 . As will be described in more detail below with respect to  FIG. 3 , the sensing element array  214  may be coupled to the connector pad array  216  by a series of wires (e.g., circuit traces.) 
         [0038]    As shown in  FIG. 2 , the flexible connector  220  has a first end  222  which includes a connector pad array  226 , which couples to the connector pad array  216  on the readhead sensing element head  210 . The flexible connector  220  also has a second end  232  which includes an array of connector pads  236  which couple to a connector pad array  162  on the signal processing and display circuit board  154  of  FIG. 1 . During operation, the sensing element array  214  is responsive to magnetic field modulating elements of the scale track  143  and transmits measurement signals through the flexible connector  220  to the readhead signal processing circuit  160  on the signal processing and display circuit board  154 . 
         [0039]    The magnetic sensor assembly  158  may be assembled by compressing the sensing element head  210  and first end  222  of the flexible connector  220  between the bottom assembly block  240  and the top assembly block  250 . More specifically, the bottom assembly block  240  includes mounting holes  242  and  244 , while the top assembly block  250  includes mounting holes  252  and  254 , which receive assembly screws  272  and  274  for compressing the blocks  240  and  250  together. The mounting member  260  is also attached to the top of the assembly block  250 , and includes a mounting hole  264  which receives the assembly screw  274 , and a clearance hole  262  which provides clearance around the assembly screw  272 . As will be described in more detail below with respect to  FIG. 5 , the mounting member  260  fixes the magnetic sensor assembly  158  relative to the slider  138  of the slider assembly  120 . 
         [0040]    The wire spring  280  includes ends  286  and  288  which are received by holes  246  and  248  in the bottom assembly block  240 . The wire spring  280  is shaped with a slight bend so as to push the magnetic sensor assembly  158  away from the slider  138  and against the reference edge  142  and/or the scale track  143  with a desired force, to insure that the sensing element array  214  is located with the desired gap (e.g., a small gap, or no gap) relative to the scale track  143 . 
         [0041]      FIG. 3  is a diagram of the sensing element head  210  of the magnetic sensor assembly  158  of  FIG. 2 . As shown in  FIG. 3 , the sensing element head  210  includes the sensing element array  214  and a connector pad array  216  which are disposed on a substrate  212 . The sensing element array  214  includes individual sensing elements  320  while the connector pad array  216  includes individual connector pads  330 . The individual sensing elements  320  are connected to the individual connector pads  330  by a series of wires (e.g., circuit traces.) More specifically, a first individual sensing element  320  is shown to be coupled to two individual connector pads  330  by wires  322  and  324 , respectively. The individual sensing elements  320  may be arranged in sensing pattern cells that each consist of one or more sensing elements  320 , and the pattern cells may be periodically spaced along the measuring axis direction (the x axis) at a sensing pattern pitch Pp, which may depend on a spatial wavelength or pitch P T  of the scale track  143 . In some embodiments, Pp=N*P T , where N is a small integer (e.g., 1, 2, 3, etc.). In the embodiment shown in  FIG. 3 , a sensing pattern cell consists of two sensing elements  320  arranged at an intra-cell pitch of Pc. The individual sensing elements  320  are responsive to magnetic field modulating elements arranged along the scale track  143 , as described in more detail below with respect to  FIG. 6 . 
         [0042]    It should be appreciated that although the sensing element head  210  is illustrated in a single-sided embodiment, more generally a sensing element head may have sensing elements and/or connector elements fabricated on both sides of a substrate, or two single-sided substrates may be laminated together, in order to provide additional sensing elements within a given set of substrate dimensions, or to provide additional space between connector pads on each side of a two-sided sensing element head, or both. In general, any of the magnetic sensor assembly embodiments disclosed herein may be adapted to use such double-sided sensing element heads, with suitable connector modifications. 
         [0043]      FIG. 4  is a diagram of an exemplary embodiment of magneto-resistive magnetic field sensing elements  320 ′ which may be used to provide a first embodiment of the sensing elements  320  of  FIG. 3 . This first embodiment is most appropriate when magnetized hard ferromagnetic material forms the magnetic field modulating elements along scale track  143 . As shown in  FIG. 4 , two of the sensing elements  320 ′, labeled A and B, may be disposed on a non-magnetic substrate  212 ′ (e.g., glass or ceramic) at an intra-cell pitch of Pc′. Each of the sensing elements  320 ′ includes a patterned thin magneto-resistive film  420 , separated by an insulating film (not show) from an adjacent high permeability magnetic film  430 , which acts as a magnetic flux concentrator. The patterned magneto-resistive film  420  is shown to have two terminal ends  422  and  424 , which are coupled to circuit traces (not shown), such as the circuit traces  322  and  324  of  FIG. 3 . 
         [0044]    Due to the magneto-resistive effect, the resistance between the ends  422  and  424  of the patterned magneto-resistive film  420  depends of the flux density provided in the adjacent high permeability magnetic film  430 . Thus, when a sensing element  320 ′ is moved along the magnetic scale track  143 , the resistance between the terminal ends  422  and  424  of the patterned magneto-resistive film  420  is modulated depending on the relation of the sensing element  320 ′ to the field modulating elements of the scale track  143  (e.g., magnetized elements or track portions). The readhead signal processing circuit  160  may provide measurement signals based on that resistance, according to known techniques. 
         [0045]    The high-permeability magnetic film  430  guides the magnetic field of the field modulating elements to the magneto-resistive film  420 , to enhance the associated resistance modulation effect. The end portion of the high-permeability magnetic film  430  extends to the edge of the substrate  212 ′, to couple as strongly as possible to the spatially modulated magnetic field of the scale track  143 . A dimension W C  of the end portion along the measuring axis direction may be chosen in cooperation with a parallel dimension of the field modulating elements of the scale track  143  to provide a desired signal modulation profile as the end portion is moved past the scale elements along the measuring axis. A dimension W R  of the sensing element  320 ′ may be wider than the dimension W C , to provide a desired size and flux sensitivity for the sensing element  320 ′. In the embodiment shown in  FIG. 4 , when the field modulating elements of the scale track  143  are arranged according to a scale wavelength or pitch P T , the intra-cell pitch of Pc′ of the A and B sensing elements  320 ‘may be Pc’=(N*P T )+P T /4, which provides A and B quadrature signals from the A and B sensing elements  320 ′. The utility of quadrature signals is known to one skilled in the art. Various other sensing pattern cell arrangements are possible using 3 or 4 sensing elements, or more, in order to provide additional measurement signals having additional spatial phase relationships, if desired. 
         [0046]    The sensing element  320 ′ may be further understood and/or modified by reference to similar elements disclosed in U.S. Pat. No. 5,889,403, which is hereby incorporated by reference in its entirety. Other sensing pattern cell arrangements and related signal processing may be understood with reference to U.S. Pat. Nos. 5,949,051; 5,386,642; 5,036,276; 6,229,301; and 7,173,414, each of which is hereby incorporated by reference in its entirety. Thus, it will be appreciated that  FIG. 4  indicates one of many possible configurations for magneto-resistive sensors that may be used according to this invention, and is exemplary only, not limiting. 
         [0047]    More generally, when the scale track  143  provides modulations of magnetic field strength or direction (e.g., by spatially modulated magnetization of a hard ferromagnetic material) the magnetic sensing elements  320  may utilize effects other than the magneto-resistive effect. For example, in one embodiment, the sensing elements  320  may include special inductor elements comprising a non-linear core material, where the inductance depends on the local magnetic field surrounding the inductor elements. Field modulations along the scale track  143 , may be directed to the inductor elements via a magnetic circuit formed by the pattern of an adjacent highly permeable ferromagnetic film. The varying inductance of the sensing elements may be detected as the change in impedance across their terminal ends, according to known techniques. Various configurations that can be adapted for such sensing elements are disclosed in U.S. Pat. Nos. 7,180,146; 7,038,448; and 6404192, each of which is hereby incorporated by reference in its entirety. 
         [0048]    In some embodiments, the scale track  143  may include modulations in the permeability of a magnetically soft ferromagnetic material. In some such embodiments, the magnetic sensing elements  320  may comprise of inductors whose impedance is altered depending on their proximity to the permeability modulations along the reference scale  143 . In some such embodiments, the magnetic sensing elements  320  may comprise a small magnetic circuit that is perturbed by the permeability modulations along the scale track  143 . For example, in one embodiment, the magnetic sensing elements  320  may include elements that are driven to generate a local magnetic field which is coupled to and modulated by the permeability modulations along the scale track  143 . Such magnetic sensing elements  320  may further comprise special inductor elements similar to those outlined above, which are responsive to the modulations of the generated local magnetic field. In one configuration corresponding to such sensing elements, a sensing element comprises first and second miniature planar windings located adjacent to one another (e.g., along the edge of the substrate  212 , within a sensor dimension W R ) such that they are electrically isolated and inductively coupled. The first winding is a generator winding that is driven to generate a changing magnetic field that extends to the second winding, which is a sensing winding. The resulting signal induced in the second winding depends on the changing magnetic flux density in the coupled magnetic field, which is modulated by the permeability modulations along the scale track  143 . It will be appreciated that all of the foregoing sensing element configurations benefit from the small sensing gap that is provided according to this invention. 
         [0049]      FIG. 5  is a diagram of the slider assembly  120  of  FIG. 1 , including the slider  138  and the magnetic sensor assembly  158  of  FIGS. 2-4 .  FIG. 5  shows one exemplary reference edge interface configuration and one exemplary loading edge interface configuration in greater detail. As shown, in the reference edge interface configuration the magnetic sensor assembly  158  is mounted in a recess along the internal reference surface  140  of the slider  138 , such that the sensing element array  214  is exposed toward the magnetic scale track  143 . In various embodiments, the magnetic sensor assembly  158  is mounted such that the surfaces of the assembly blocks  240  and  250  slide along the reference edge surface  142  and the sensing element array  214  is aligned along the scale track  143 . The sensing element array  214  may be assembled flush with, or at a small gap, relative to the adjacent sliding surfaces of the assembly blocks  240  and  250 , to provide the desired operating gap for the sensing element array  214  relative to the scale track  143 . As previously outlined with reference to  FIG. 2 , a wire spring  180  (hidden in  FIG. 5 ) may push the magnetic sensor assembly  158  away from the slider  138  with a desired force, to insure that the sliding surfaces of the assembly blocks  240  and  250  slide against the reference edge  142  and/or the scale track  143 . A mounting screw  578  attaches the compliant mounting member  260  to the slider  138 . The mounting member  260  is stiff along the direction of the measuring axis and compliant along directions normal to the measuring axis direction. As shown in  FIG. 5 , the internal reference surface  140  may be configured to have a slight clearance surrounding two sliding surface portions  140 A and  140 B that straddle the magnetic sensor assembly  158  and slide against the reference edge  142  during operation. The portions  138 A and  138 B of the slider  138  are shown in wireframe, to more clearly illustrate the sliding surface portions  140 A and  140 B, which may be precision ground surface portions and/or portions coated with an anti-wear and/or anti-friction coating. Threaded holes  150  may receive screws that mount the electronic assembly  152  to the slider assembly  120 . 
         [0050]    Opposite the internal reference surface  140 , in the loading edge interface configuration, the loading member  148  (e.g., a resilient pressure bar) is positioned between the internal loading surface  144  of the slider  138  and the loading edge  146  of the scale member  102 . The loading member  148  includes two holes  149  that receive the tips of adjustment screws  149 B that are threaded through the holes  149 A. The adjustment screws  149 B are adjusted such that a sliding surface portion of the loading member  148  is forced against the loading edge  146  with a desired force, which causes the internal reference surface  140  (e.g., the sliding surface portions  140 A and  140 B) to be forced against the reference edge  142  with approximately the same force. 
         [0051]    As previously indicated, in some embodiments, a magnetic scale track  143  may be provided along the loading edge  146 . In one such embodiment, the loading edge interface configuration may include a loading member that is “split” to provide separate sliding surface portions analogous to the sliding surface portions  140 A and  140 B. In another such embodiment, the loading member  148  may be omitted and the gap between the loading edge  146  and the internal loading surface  144  may be set to a practical minimum (e.g., approximately 50 microns). The tips of adjustment screws  149 B that are threaded through the holes  149 A may be flat and/or may include anti-ware and/or anti-friction materials and may be adjusted to slide against the loading edge  146 , to provide separate sliding surface portions analogous to the sliding surface portions  140 A and  140 B. In either of these embodiments, the magnetic sensor assembly  158  may be mounted in a recess in the internal loading surface  144  of the slider  138 , in a configuration that is approximately a “mirror image” of the configuration shown in  FIG. 5 , such that the sensing element array  214  is positioned at a small operating gap along the magnetic scale track  143  provided on the loading edge  146 , straddled by sliding surface portions that govern and protect the operating gap according to design principles outlined above. 
         [0052]      FIG. 6  is a diagram of a portion of the scale member  102  of  FIG. 1 , including scale elements  612  arranged along the scale track  143  according to a first exemplary scale pattern  643 . The scale pattern  643  is usable with the magnetic sensor assembly  158  of  FIGS. 2-5 . As shown in  FIG. 6 , the scale elements  612  are arranged according to a scale pitch P T , and are coextensive with the scale track width H T  orthogonal to the measuring axis direction, which may be less than the dimension H RE  of the narrow reference edge  142 . Each scale element  612  may have a dimension of approximately P T /2 along the measuring axis direction. 
         [0053]    In some embodiments, the scale track pattern  643  is formed as magnetized pattern in a hard ferromagnetic material formed along the reference edge  142 . In such embodiments, the magneto-resistive sensing elements  320 ′ or the alternative outlined above with reference to  FIG. 4  may be used in the magnetic sensor assembly  158 . In such embodiments, it is desirable that the material be hard magnetically with a large remanence. In one implementation, the material can be formed from a coating of a variety of potential materials (e.g., resin and ferrites, resin and metal powder, electroplated alloys, sputtered alloys similar to those used in the magnetic hard disk industry, sputtered materials such as used for magneto-optic data recording, etc.) Alternatively, the material may be inlaid or formed in a shallow scale track groove along the reference edge surface  142 . Alternatively, in some embodiments, the reference member  102  may be formed of a suitable magnetizable material. In any case, the scale track material is chosen with careful consideration of tradeoffs between the design of the sensing elements  320 , achievable signal strength and scale pitch P T , and other considerations are similar to those related to magnetic data storage technology. In one embodiment, the magnetic scale track pattern  643  may be written into the scale track material using an appropriate inductive write head. In another embodiment, the scale track  143  may initially be uniformly magnetized in one direction and subsequently the magnetic scale track pattern  643  may be written by locally heating the scale track material (e.g., with a laser) to a temperature just above its Curie temperature, whereupon it is cooled in a field of opposite polarity to the initial uniform magnetization direction. More generally, any suitable known magnetic information writing technique may be used. In some embodiments, it is desirable that the scale track material and pattern writing technique are able to provide a scale track pitch P T  on the order of at most 20 microns, or 10 microns, or less. In such embodiments, it may be possible to provide a desired measurement resolution that is suitable for hand tool type calipers with little or no signal interpolation. Of course, in other embodiments, coarser measurement resolution may be accepted, or some level of signal interpolation may be used, and the corresponding scale track pitch P T  may be larger (e.g., on the order of approximately 100 microns). 
         [0054]    In another embodiment, the scale track pattern  643  may be formed from magnetized, physically discrete, features along the scale track  143 . An example would be laser drilled or cut holes in the form of the scale track pattern  643 , which are filled with materials and magnetized approximately as outlined above with reference to a uniformly coated scale track. Alternatively, a uniformly coated scale track may be processed by known techniques to remove portions of the scale track material, leaving a desired pattern of physically discrete features that are magnetized or magnetizable. 
         [0055]    In some embodiments, the scale elements  612  are not magnetized scale elements. In such embodiments, the scale elements do not directly provide a spatially modulated magnetic field that is sensed by the sensor elements of the magnetic sensor assembly  158 . Rather, the sensor elements  320  of the of the magnetic sensor assembly  158  may be one of the “active” types outlined above as alternatives to the sensing elements  320 ′, and the scale track pattern  643  may comprise scale elements that provide a material variation (e.g., physically discrete regions of a particular material) that affects their operation. For example, the scale elements may comprise discrete portions of a magnetically soft ferromagnetic material that modulates the magnetic permeability along the scale track  143 . In some such embodiments, the magnetic sensing elements  320  may comprise miniature field generating elements including a small magnetic circuit that is perturbed by the permeability modulations along the scale track  143 . For example, such magnetic sensing elements  320  may include elements that are driven to generate a local magnetic field which is coupled to and modulated by the permeability modulations along the scale track  143 . Such magnetic sensing elements  320  may further comprise special inductor elements, which are responsive to the modulations of the generated local magnetic field. In such embodiments, although the scale elements do not directly provide a spatially modulated magnetic field, they modulate the magnetic field generated within an active magnetic sensing element  320 , as it passes by. In general, known suitable materials and fabrications techniques may be used. For reasons outlined previously, in some embodiments, it is desirable that the scale track material and fabrication techniques are able to provide a scale track pitch P T  on the order of at most 20 microns, or 10 microns, or less, whereas in other embodiments a larger scale track pitch P T  may be used (e.g., on the order of approximately 100 microns). 
         [0056]    It should be appreciated that although the scale track pattern  643  shows only the scale elements  612 , more generally, in some embodiments the spaces between the scale elements  612  may be comprise a plurality of “opposite polarity” or “neutral” scale elements. For example, in one some embodiments, if the scale elements  612  each comprise a region magnetized with a first magnetization polarity, then each of the spaces between them may comprise regions that have an opposite magnetization polarity that may be introduced either inherently, or intentionally, during the pattern writing process. In other embodiments, if the scale elements  612  each comprise a strongly magnetized region, then each of the spaces between them may comprise regions that are nominally “unmagnetized.” In such embodiments, certain types of sensor elements and/or their associated signal processing may be designed to provide enhanced measurement signals based on differences between the scale elements  612  relative to the regions between them. That is, the sensor elements may have a distinctive response to the regions between the scale elements  612 , as well as to the scale elements  612  themselves. 
         [0057]    In any case, the caliper configuration corresponding to the  FIGS. 5 and 6  can provide signals that may be combined to provide a robust high-resolution displacement signal (e.g., quadrature signals with a measuring resolution of at least P T /4). 
         [0058]    With regard to specific example dimensions for the scale track pattern  643  and sensing element head  210 , in one specific embodiment the reference edge may have a dimension H RE  that is at most 4000 microns (e.g., H RE =3500 microns), the scale track  143  may have a width dimension H T =1500 microns, and a scale pitch P T =20 microns, or 10 microns. In one specific embodiment, the sensing element head  210  may have 16 sensing pattern cells arranged with a sensing pattern pitch Pp=80 microns. Each sensing element may have a dimension W C =P T /2, and a dimension W R =P T . In one embodiment, at least some of the sensing pattern cells may include at least two sensing elements arranged in quadrature, with an intra-cell pitch Pc=(P T +P T /4). The connector pad array  216  may have a center-to-center spacing of approximately 200 microns. The overall width of the substrate  212  along the x axis direction may be approximately 13 millimeters. It should be appreciated that this specific embodiment is exemplary only, and is not limiting. 
         [0059]      FIGS. 7-12  illustrate alternative embodiments for the magnetic sensor assembly  158 , the slider assembly  120 , and the scale track pattern  643  on the reference edge surface  142 . As will be described in more detail below, in the embodiments of  FIGS. 7-12 , the scale elements of the scale track form are arranged in multiple sub-tracks, and the sensing element head (e.g., the sensing element head  210 ) is oriented at an angle relative to the measuring axis direction. 
         [0060]      FIGS. 7 and 8  are diagrams including a second exemplary embodiment of a magnetic sensor assembly  158 ′ usable in place of the magnetic sensor assembly  158  shown in  FIGS. 1 ,  2  and  5 . Briefly stated, the magnetic sensor assembly  158 ′ shown in  FIG. 7  is similar in construction, assembly, and operation to the magnetic sensor assembly  158  of  FIG. 2 , except as otherwise described below. Similarly numbered elements may be similar or identical between the magnetic sensor assemblies  158 ′ and  158 . As shown in  FIG. 7 , the magnetic sensor assembly  158 ′ includes a bottom assembly block  740  and a top assembly block  750 . In contrast to the assembly blocks  240  and  250  of  FIG. 2 , the assembly blocks  740  and  750  of  FIG. 7  position the sensing element head  210  such that it is tilted in the magnetic sensor assembly  158 ′, to distribute the sensing elements  320  over a dimension approximately equal to the width dimension H T  of the scale track  143 , for reasons described further below. 
         [0061]      FIG. 8  is a diagram second exemplary embodiment of a slider assembly  120 ′ including the magnetic sensor assembly  158 ′ of  FIG. 7 . The slider assembly  120 ′ is usable in place of the slider assembly  120  shown in  FIGS. 1 and 5 . Briefly stated, the slider assembly  120 ′ shown in  FIG. 7  is similar in construction, assembly, and operation to the slider assembly  120  of  FIG. 2 , except as otherwise described below. Similarly numbered elements may be similar or identical between the slider assemblies  120 ′ and  120 . As shown in  FIG. 7 , the sensing element array  214  is tilted such that its individual sensing elements  320  are distributed across the scale track  143  along the direction of the z axis, as well as along the x axis. Thus, the sensing elements  320  are individually aligned with respective scale elements that are arranged to form codes in a plurality of respective sub-tracks along the scale track  143 , as described in more detail below with reference to  FIG. 9 . 
         [0062]      FIG. 9  is a diagram of a portion of the scale member  102  of  FIG. 1 , including scale elements  912  that are arranged along the scale track  143  according to a second exemplary scale pattern  943 . The scale pattern  943  is usable with the magnetic sensor assembly  158 ′ of  FIGS. 7 and 8 . Briefly stated, the scale elements  912  in the scale pattern  943  (and the associated sensing elements  320 ) may be similar in fabrication and operation to scale elements  612  in the scale pattern  643  of  FIG. 6 , except as otherwise described below. The scale pattern  943  includes a plurality of parallel subtracks  945  within the scale track  143 , with each of the subtracks  945  including scale element zones  944  arranged along the scale pattern  943  according to a scale pitch P T . The intersection of each subtrack  945  with each scale element zone defines a code zone. The scale elements  912  are configured to locate their portions in some code zones, but not in others, such that the magnetic sensor assembly  158 ′ outputs coded sets of signals, as it is moved or positioned along the measuring axis relative to the scale pattern  943 . Thus, an embodiment of the caliper  100  corresponding to the  FIGS. 7-9  can provide signals that may be combined to provide a robust high-resolution displacement signal (e.g., quadrature signals with a measuring resolution of at least P T /4), as well to a provide a unique absolute position code associated with each measurement signal period (each spatial period) of the high-resolution displacement signal. It should be appreciated that the particular arrangement of the scale elements  912  in the scale pattern  943  is just a schematic illustration representative of many alternative arrangements, and is not limiting. 
         [0063]    It should be noted that in discussion related to  FIGS. 3 and 4 , it was suggested that a sensing pattern pitch Pp of the sensing element head  210  may be selected such that Pp=N*P T . However, when the sensing element head  210  is tilted at an tilt angle TA relative to the measuring axis as described for the configuration of  FIGS. 7-9 , then the relationship between the sensing pattern pitch Pp and scale pitch P T  is more appropriately Pp*cos(TA)=N*P T . Similarly, the relationship between the intra-cell pitch of Pc′ of the A and B sensing elements  320 ′ shown in  FIG. 4  is more appropriately Pc′*cos(TA)=(N*P T )+P T /4, in order to provide A and B quadrature signals from the A and B sensing elements  320 ′. 
         [0064]    With regard to specific example dimensions for the scale track pattern  943  and sensing element head  210 , in one specific embodiment using 16 sensor elements  320  and 16 subtracks  945 , the reference edge may have a dimension H RE  that is at most 4000 microns (e.g., H RE =3500 microns), the scale track  143  may have a width dimension H T =2400 microns, with subtrack widths of 150 microns, and a scale pitch P T =20 microns, or 10 microns. In one specific embodiment, the sensing element head  210  may be tilted at an angle of approximately TA=30 degrees from x axis, and may have 16 sensing pattern cells arranged with a sensing pattern pitch Pp=300 microns. Each sensing element may have a dimension W C =P T /2, and a dimension W R =P T . In one embodiment, at least some of the sensing pattern cells may include at least two sensing elements arranged in quadrature, with an intra-cell pitch P C =(P T +P T /4). The connector pad array  216  may have a center-to-center spacing of approximately 200 microns. The overall width of the substrate  212  along the x axis direction may be approximately 13 millimeters. It should be appreciated that this specific embodiment is exemplary only, and is not limiting. 
         [0065]      FIG. 10  is a diagram of a third exemplary embodiment of a magnetic sensor assembly  158 ″ usable in place of the magnetic sensor assembly  158  shown in  FIGS. 1 ,  2  and  5 . In the magnetic sensor assembly  158 ″ a sensing element head  1010  is oriented orthogonal to the measuring axis direction. This configuration allows the magnetic sensor assembly  158 ″ to read information from a scale track  143  that includes multiple parallel sub-tracks, as described below with reference to  FIG. 12 . The magnetic sensor assembly  158 ″ includes the sensing element head  1010 , a flexible connector  1020 , an assembly block  1040 , a mounting member  1060  and a wire spring  1080 . The sensing element head  1010  includes a plurality of the previously described sensing elements  320 , which form a sensing element array  1014  that is connected to a connector pad array  1016  by a series of wires, all disposed on a substrate  1012 . In the sensing element array  1014 , the sensing elements  320  are generally evenly spaced such that each one will coincide with one of the subtracks  1245  shown in  FIG. 12 . The arrays  1014  and  1016  are shown schematically in  FIG. 10 , for clarity. In various embodiments the arrays  1014  and  1016  may include more elements than illustrated in  FIG. 10 . 
         [0066]    The flexible connector  1020  has a first end  1022  which includes a connector pad array  1026 , which is connected to the connector pad array  1016  on the readhead sensing element head  1010 . The flexible connector  1020  also has a second end  1032 , which includes a connector pad array  1036 , which is connected to a connector pad array on the signal processing and display circuit board  154  of  FIG. 1 . 
         [0067]    The magnetic sensor assembly  158 ″ may be assembled by bonding the sensing element head  1010  into the slot  1041  in the assembly block  1040 , with the sensing element array  1014  located proximate to the surface of the assembly block  1040  that will slide on the reference edge  142 . The mounting member  1060  is attached to the top of the assembly block  1040 , which includes a mounting hole  1064  that receives the assembly screw  1074 . As shown in  FIG. 11 , the mounting member  1060  is used to fix the magnetic sensor assembly  158 ″ relative to the slider  138 ′ of the slider assembly  120 ″. The wire spring  1080  includes ends  1086  and  1088  which are received by holes  1046  and  1048  in the assembly block  1040 . The wire spring  1080  is shaped with a slight bend so as to push the magnetic sensor assembly  158 ″ away from the slider  138 ′ and against the reference edge  142  and/or the scale track  143  with a desired force, to insure that the sensing element array  1014  is located with the desired gap (e.g., a small gap, or no gap) relative to the scale track  143 . 
         [0068]      FIG. 11  is a diagram of a third exemplary embodiment of a slider assembly  120 ″ including the magnetic sensor assembly  158 ″ of  FIG. 10 . The slider assembly  120 ″ is usable in place of the slider assembly  120  shown in  FIGS. 1 and 5 . Briefly stated, the slider assembly  120 ″ shown in  FIG. 7  is similar in construction, assembly, and operation to the slider assembly  120  of  FIG. 2 , except as otherwise described below. Similarly numbered elements may be similar or identical between the slider assemblies  120 ″ and  120 . As shown in  FIG. 11 , the sensing element array  1014  is orthogonal to the measuring axis direction such that its individual sensing elements  320  are distributed across the scale track  143  along the direction of the z axis. Thus, the sensing elements  320  are individually aligned with respective scale elements that are arranged to form codes in a plurality of respective sub-tracks along the scale track  143 , as described in more detail below with reference to  FIG. 12 . 
         [0069]      FIG. 12  is a diagram of a portion of the scale member  102  of  FIG. 1 , including scale elements  1212  that are arranged along the scale track  143  according to a third exemplary scale pattern  1243 . The scale pattern  1243  is usable with the magnetic sensor assembly  158 ″ of  FIGS. 10 and 11 . Briefly stated, the scale elements  1212  in the scale pattern  1243  (and the associated sensing elements  320 ) may be similar in fabrication and operation to scale elements  612  in the scale pattern  643  of  FIG. 6 , except as otherwise described below. The scale pattern  1243  includes a plurality of parallel subtracks  1245  within the scale track  143 , with each of the subtracks  1245  including scale element zones  1244  arranged along the scale pattern  1243  according to a scale pitch P T . The intersection of each subtrack  1245  with each scale element zone defines a code zone. The scale elements  1212  located in some code zones, but not in others, such that the magnetic sensor assembly  158 ″ outputs coded sets of signals, as it is moved or positioned along the measuring axis relative to the scale pattern  1243 . Thus, an embodiment of the caliper  100  corresponding to the  FIGS. 10-12  can provide signals that may be combined to a provide a unique absolute position code associated with each spatial period, or each scale element zone, at the scale pitch P T . In the embodiment shown in  FIG. 12 , subtracks  1245 QA and  1245 QB are configured to provide quadrature signals with a period of 2*P T , with the scale element zones  1244 Q of the subtrack  1245 QB offset by P T /4 along the measuring axis, relative to the scale element zones  1244 . The quadrature signals of the subtracks  1245 QA and  1245 QB may provide a measurement resolution of P T /2. It should be appreciated that the particular arrangement of the scale elements  1212  in the scale pattern  1243  is just a schematic illustration representative of many alternative arrangements, and is not limiting. 
         [0070]    With regard to specific example dimensions for the scale track pattern  1243  and sensing element head  1010 , in one specific embodiment using 16 sensor elements  320  and 16 subtracks  1245 , the reference edge may have a dimension H RE =3500 microns, the scale track  143  may have a width dimension H T =2400 microns, with subtrack widths of 150 microns, and a scale pitch P T =10 microns, or 5 microns. The sensing element head  1010  may have a center-to-center spacing of 150 microns between 16 sensor elements  320  in the sensing element array  1014 , and the connector pad array  1016  may comprise 2 rows of pads with a center-to-center spacing of approximately 200 microns between the pads in each row. The overall width of the substrate  1012  along the z axis direction may be approximately 3.4 millimeters. It should be appreciated that this specific embodiment is exemplary only, and is not limiting. 
         [0071]    As outlined previously, certain compact “jawless” calipers are used as low cost linear scales. Such compact jawless calipers generally comprise similar or identical components to related compact hand tool type calipers the include jaws. Such jawless calipers are characterized by similar sliding surfaces at the reference and loading edges, similar reference and loading edge dimensions, and similar measurement resolutions. Thus, although the various embodiments illustrated herein include jaws, it will be understood that such embodiments are representative of addition embodiments in which the jaws (e.g., the jaws  116 ,  114 ,  118  and  110 ) may be omitted. 
         [0072]    While the preferred embodiment of the invention has been illustrated and described, numerous variations in the illustrated and described arrangements of features and sequences of operations will be apparent to one skilled in the art based on this disclosure. Thus, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.