Patent Publication Number: US-9835473-B2

Title: Absolute electromagnetic position encoder

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation-in-part of U.S. patent application Ser. No. 15/070,881, entitled “ABSOLUTE ELECTROMAGNETIC POSITION ENCODER,” filed Mar. 15, 2016, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates generally to precision metrology and, more particularly, to linear and rotary absolute electromagnetic position encoders. 
     Description of the Related Art 
     Position encoders (more particularly, induced current encoders) typically have a readhead that is movable relative to a scale member, and includes one or more transducers comprising a field generator (e.g., an excitation winding) and a field detector (e.g., receiver winding(s)). Typical absolute position encoders employ multiple parallel scale tracks juxtaposed with parallel sets of field generators and field detectors in the readhead to determine an absolute position. 
     U.S. Pat. No. 6,329,813, which is commonly assigned and hereby incorporated herein by reference in its entirety, discloses an absolute position encoder transducer employing multiple parallel scale tracks for determining an absolute position. While the &#39;813 patent provides a high accuracy configuration, in some applications it is desirable to provide an absolute position encoder transducer which employs a more compact single scale track and a readhead comprising a set composed of a field detector and a field generator to determine an absolute position while further providing stronger position signals, a larger gap between the scale track and readhead, and/or lower power consumption. 
     BRIEF SUMMARY 
     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. 
     An absolute electromagnetic position encoder is provided. The absolute electromagnetic position encoder comprises a readhead and an absolute scale extending along a measuring axis of the position encoder. The readhead comprises a field generation and detection configuration and a readhead processor connected to the field generation and detection configuration, and is configured to operate the field generation and detection configuration as a field generator to provide an energy transfer cycle, and to operate the field generation and detection configuration as a first cycle field detector to provide a first signal generating cycle and to operate the field generation and detection configuration as a second cycle field detector to provide a second signal generating cycle. The readhead is movable relative to the absolute scale along the measuring axis. The absolute scale comprises an active periodic signal pattern comprising a periodic spatially modulated signal generating element that extends along the measuring axis and has a first wavelength and is configured to generate a corresponding periodic spatially modulated field that couples to the readhead to generate spatially periodic signals in the first cycle field detector as a function of readhead position relative to the absolute scale along the measuring axis, and an active absolute signal pattern comprising at least a first spatially modulated signal generating element configured to generate a corresponding spatially modulated field that couples to the readhead to provide at least one corresponding signal in the second cycle field detector that exhibits a unique relationship with the spatially periodic signals for each unique readhead position relative to the absolute scale within a first absolute range that exceeds the first wavelength of the periodic spatially modulated signal generating element. The absolute scale further comprises timing and activation circuitry connected to the active absolute signal pattern and the active periodic signal pattern. The absolute electromagnetic position encoder comprises an energy transfer cycle configuration that is used to provide an energy transfer cycle wherein, during the energy transfer cycle, the readhead processor is configured to energize a winding of the field generation and detection configuration to operate as a field generator and generate an energy transfer cycle field, and at least one of the signal generating elements of the absolute scale couples to the energy transfer cycle field and provides energy to the timing and activation circuitry, and the timing and activation circuitry is configured to receive and store energy during the energy transfer cycle. The absolute electromagnetic position encoder comprises a first signal cycle configuration that is used to provide a first signal generating cycle wherein, during the first signal generating cycle, the timing and activation circuitry is configured to drive the periodic spatially modulated signal generating element to generate a corresponding periodic spatially modulated first cycle field, and the first cycle field detector couples to the periodic spatially modulated first cycle field to generate first cycle spatially periodic signals in the first cycle field detector. The absolute electromagnetic position encoder comprises a second signal cycle configuration that is used to provide a second signal generating cycle wherein, during the second signal generating cycle, the timing and activation circuitry is configured to drive the first spatially modulated signal generating element to generate a corresponding spatially modulated second cycle field, and the second cycle field detector couples to the spatially modulated second cycle field and provides a corresponding second cycle input to the readhead processor, and during the second signal generating cycle the readhead processor is configured to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead that exhibits a unique relationship with the first cycle spatially periodic signals and is indicative of a unique position within the first absolute range. The readhead processor is further configured to determine an absolute position of the readhead relative to the absolute scale based on at least the second cycle signal and the first cycle spatially periodic signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A, 1B, 1C, and 1D  are schematic diagrams of portions or a whole of a first implementation of an absolute electromagnetic position encoder; 
         FIG. 2  is a schematic diagram of a portion of a second implementation of an absolute electromagnetic position encoder; 
         FIG. 3  is a schematic diagram of a third implementation of an absolute electromagnetic position encoder; 
         FIG. 4  is a timing diagram showing operations of the absolute electromagnetic position encoder of  FIGS. 1A, 1B, 1C, and 1D ; 
         FIGS. 5A and 5B  show a flow diagram illustrating one exemplary implementation of a routine for operating an absolute electromagnetic position encoder; 
         FIGS. 6A, 6B and 6C  are schematic diagrams of portions of a fourth implementation of an absolute electromagnetic position encoder; 
         FIGS. 7A, 7B and 7C  are schematic diagrams of portions of an absolute electromagnetic position encoder; and 
         FIGS. 8A and 8B  show a flow diagram illustrating one exemplary implementation of a routine for operating an absolute electromagnetic position encoder. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A, 1B, 1C, and 1D  are schematic diagrams of portions or a whole of a first implementation of an absolute electromagnetic position encoder  100 . The absolute electromagnetic position encoder  100  comprises a readhead  110  (shown in  FIG. 1A ), and an absolute scale  120  (shown in  FIGS. 1B and 1C ) extending along a measuring axis MA of the absolute electromagnetic position encoder  100 . The readhead  110  comprises a spatially modulated signal coupling configuration  111 , which comprises a field generator  112  and a field detector  113 , and a readhead processor  114  configured to provide a first signal generating cycle and a second signal generating cycle. The readhead  110  is movable relative to the absolute scale  120  along the measuring axis MA. The absolute scale  120  comprises a passive signal pattern  130  (shown in  FIG. 1B ) comprising a periodic pattern of signal modulating elements  131  distributed periodically at a first wavelength λ 1  along the measuring axis MA and configured to modulate a field coupling between the field generator  112  and the field detector  113  to generate spatially periodic signals in the field detector  113  as a function of a readhead position X relative to the absolute scale  120  along the measuring axis MA, and an active signal pattern  140  (shown in  FIG. 1C ) comprising a first spatially modulated signal generating element  141  and a second spatially modulated signal generating element  142 . The first spatially modulated signal generating element  141  is configured to generate a corresponding spatially modulated field that couples to the readhead  110  to provide at least one corresponding signal in the readhead  110  that exhibits a unique relationship with the spatially periodic signals for each unique readhead position X relative to the absolute scale  120  within a first absolute range AR 1  that exceeds the first wavelength λ 1  of the periodic pattern of signal modulating elements  131 . The second spatially modulated signal generating element  142  is configured to generate a corresponding spatially modulated field that couples to the readhead  110  to provide a unique corresponding signal in the readhead  110  for each unique readhead position X relative to the absolute scale within an absolute range AR including the first absolute range AR 1 . The absolute scale  120  further comprises a timing and activation circuit  143  connected to the active signal pattern  140 . 
     The passive signal pattern  130  and the active signal pattern  140  may be arranged along a single track in a stacked configuration such that the readhead  110  may receive signals from both. 
     The absolute electromagnetic position encoder  100  comprises a first signal cycle configuration that is used to provide a first signal generating cycle wherein, during the first signal generating cycle the readhead processor  114  is configured to energize the field generator  112  to generate a first cycle field and generate first cycle spatially periodic signals in the field detector  113  based on the passive signal pattern  130  modulating the field coupling between the field generator  112  and the field detector  113 . At least the first signal generating element  141  (and in some implementations, the second spatially modulated signal generating element  142 ) of the active signal pattern  140  couples to the first cycle field and provides energy to the timing and activation circuit  143 . The timing and activation circuit  143  is configured to receive and store energy during the first signal cycle. 
     The absolute electromagnetic position encoder  100  comprises a second signal cycle configuration that is used to provide a second signal generating cycle wherein, during the second signal generating cycle, the timing and activation circuit  143  is configured to drive the first spatially modulated signal generating element  141  to generate a corresponding spatially modulated second cycle field, and at least one of the field generator  112  and the field detector  113  couples to the spatially modulated second cycle field and provides a corresponding second cycle input to the readhead processor  114 , and during the second signal generating cycle the readhead processor  114  is configured to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead  110  that exhibits a unique relationship with the spatially periodic signals and is indicative of a unique position within the first absolute range AR 1 . 
     The absolute electromagnetic position encoder  100  comprises a third signal cycle configuration that is used to provide a third signal generating cycle wherein, during the third signal generating cycle, the timing and activation circuit  143  is configured to drive the second spatially modulated signal generating element  142  to generate a corresponding spatially modulated third cycle field. At least one of the field generator  112  and the field detector  113  couples to the spatially modulated third cycle field and provides a corresponding third cycle input to the readhead processor  114 . During the third signal generating cycle the readhead processor  114  is configured to receive the third cycle input and provide a corresponding third cycle signal indicative of a unique position within the absolute range AR including the first absolute range AR 1 . 
     The readhead processor  114  is further configured to determine an absolute position X of the readhead  110  relative to the absolute scale  120  based on at least the second cycle signal, the third cycle signal and the first cycle spatially periodic signals. 
       FIG. 1D  shows an exploded isometric view diagram of a hand tool type caliper  105  which incorporates the absolute electromagnetic position encoder  100 . In this example, the caliper  105  comprises a slider assembly  170  and a scale substrate  125  including the absolute scale  120  (a cut-away segment including the passive signal pattern  130  is illustrated) positioned in a groove  127  along an elongated scale member  129 . The active signal pattern  140  and the timing and activation circuit  143  are shown. The slider assembly  170  includes an electronic assembly  160  attached to a slider  180 . The readhead  110  is included in the electronic assembly  160 . A measured dimension may be displayed on a digital display  154 , which is mounted within a cover  150  of the electronic assembly  160  of the caliper  105 . The electronic assembly  160  may include a circuit board mounted to abut the top surfaces of the slider  180  on either side of the scale member  129 . It should be appreciated that the caliper  105  is an example of a measurement tool which may utilize the absolute electromagnetic position encoder  100 , but the absolute electromagnetic position encoder  100  may be used in other measurement tools to provide similar measurement operations. 
     The absolute electromagnetic position encoder  100 , or a similar encoder configured according to the principles disclosed herein, may provide the advantage of a more compact single scale track absolute scale configuration, stronger position signals, a larger gap between the absolute scale and readhead, and/or lower power consumption. 
     It should be appreciated that while the active signal pattern  140  comprises the first spatially modulated signal generating element  141  and the second spatially modulated signal generating element  142 , an absolute electromagnetic position encoder may be constructed according to the principles disclosed herein with only one spatially modulated signal generating element (e.g., the first spatially modulated signal generating element  141 ). 
     In some implementations, the readhead processor  114  may be configured to determine a value A for the second cycle signal and a value B for the third cycle signal, and the readhead processor  114  may be configured to determine a processed signal (A−B)/(A+B) which is indicative of a unique position in the first absolute range. 
     In some implementations, generating the second cycle periodic signal may be initiated after generating the first cycle periodic signals, and generating the third cycle periodic signal may be initiated after generating the first cycle periodic signals. 
     In some implementations such as that shown in  FIG. 1B , the first spatially modulated signal generating element  141  and the second spatially modulated signal generating element  142  have substantially the same shape, but the shape of one is flipped relative to the other about the measuring axis MA and an axis perpendicular to the measuring axis MA. 
     In some implementations, during the second signal generating cycle, the field generator  112  may couple to the spatially modulated second cycle field and provide a corresponding second cycle input to the readhead processor  114 . In some implementations, during the third signal generating cycle, the field generator  112  may couple to the spatially modulated third cycle field and provide a corresponding third cycle input to the readhead processor  114 . In alternative implementations, during the second signal generating cycle, the field detector  113  may couple to the spatially modulated second cycle field and provide a corresponding second cycle input to the readhead processor  114 . In some implementations, during the third signal generating cycle, the field detector  113  may couple to the spatially modulated third cycle field and provide a corresponding third cycle input to the readhead processor  114 . 
     In some implementations, the passive signal pattern  130  and the active signal pattern  140  may be constructed on different scale layers and may be superimposed in the same scale track along the measuring axis direction MA. 
     In some implementations, the signal modulating elements of the periodic pattern of signal modulating elements  131  may be conductive loops which modulate the field coupling between the field generator  112  and the field detector  113 . 
     In some implementations, the signal modulating elements of the periodic pattern of signal modulating elements  131  may be plates of material which modulate the field coupling between the field generator  112  and the field detector  113 . 
     In some implementations, the field detector  113  may comprise a plurality of detectors arranged to generate spatially periodic signals in quadrature. For example, in  FIG. 1 , the field detector  113  is shown to comprise a first set of windings  113 A, indicated by solid lines, which is configured to sense spatially periodic signals at spatial phases corresponding to 0 and 180 degrees, and a second set of windings  113 B, indicated by dashed lines, which is configured to sense spatially periodic signals at spatial phases corresponding to 90 and 270 degrees. In other implementations, the field detector  113  may comprise a plurality of detectors arranged to generate three spatially periodic signals corresponding to spatial phase corresponding to 0, 120, and 240 degrees. 
     In some implementations, such as that shown in  FIG. 1B , the effective width of the first spatially modulated signal generating element  141  may vary linearly as a function of position along the measuring axis direction MA. As shown in  FIG. 1B , the effective width of the second spatially modulated signal generating element  142  also varies linearly as a function of position along the measuring axis direction MA. 
       FIG. 2  is a schematic diagram of a portion of a second implementation of an absolute electromagnetic position encoder  200 . As shown in  FIG. 2 , the absolute electromagnetic position encoder  200  comprises an absolute scale  220  which comprises an active signal pattern  240  comprising a spatially modulated signal generating element  241  which may be used in place of the spatially modulated signal generating element  141  in an absolute electromagnetic position encoder which is similar to the absolute electromagnetic position encoder  100 . The active signal pattern  240  also comprises a timing and activation circuit  243 . The spatially modulated signal generating element  241  comprises a first winding portion  241 A having a first winding polarity (indicated by the “+” sign), and a second winding portion  241 B having the opposite winding polarity (indicated by the “−” sign). The first winding portion  241 A and the second winding portion  241 B are connected to one another and are connected to the timing and activation circuit  243  by the same leads. 
     The absolute electromagnetic position encoder  200  comprises a second signal cycle configuration as described above with respect to  FIG. 1 . The active signal pattern  240  is configured such that during a second signal generating cycle, the timing and activation circuit  243  is configured to drive the spatially modulated signal generating element  241  (more specifically both the first winding portion  241 A and the second winding portion  241 B) to generate a corresponding spatially modulated second cycle field, and at least one of a field generator (e.g., the field generator  112 ), a field detector (e.g., the field detector  113 ), or a readhead (e.g., the readhead  110 ) couples to the spatially modulated second cycle field and provides a corresponding second cycle input to a readhead processor (e.g., the readhead processor  114 ), and during the second signal generating cycle the readhead processor is configured to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead that exhibits a unique relationship with the spatially periodic signals and is indicative of a unique position within a first absolute range. For various positions of a readhead along the measuring axis MA, the second cycle signal is a differential signal as a function of the readhead position X. More specifically, a field detector will simultaneously couple to individual field contributions from the first winding portion  241 A and the second winding portion  241 B which have opposite polarities and provide a combined spatially modulated second cycle field which is a difference between the magnitudes of each of the individual field contributions. 
       FIG. 3  is a schematic diagram of a third implementation of an absolute electromagnetic position encoder  300 . As shown in  FIG. 3 , the absolute electromagnetic position encoder  300  comprises an absolute scale  320  which comprises an active signal pattern  340  comprising a spatially modulated signal generating element  341  which may be used in place of the spatially modulated signal generating element  141  in the absolute electromagnetic position encoder  300 , which is otherwise similar or identical to the absolute electromagnetic position encoder  100 . The active signal pattern  340  also comprises a timing and activation circuit  343 . 
     The spatially modulated signal generating element  341  comprises a periodic array of loops, distributed periodically at a second wavelength λ 2  arranged from a single winding coupled to the timing and activation circuit  343 . Like the absolute electromagnetic position encoder  100 , the absolute electromagnetic position encoder  300  comprises a second signal cycle configuration that is used to provide a second signal generating cycle. During the second signal generating cycle, the timing and activation circuit  343  is configured to drive the spatially modulated signal generating element  341  to generate a corresponding spatially modulated second cycle field, at least one of a field generator or a field detector of a readhead (e.g., the readhead  110 ) couples to the spatially modulated second cycle field and provides a corresponding second cycle input to a readhead processor (e.g., the readhead processor  114 ), and, during the second signal generating cycle, the readhead processor is configured to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead that exhibits a unique relationship with the spatially periodic signals and is indicative of a unique position within the first absolute range. In the absolute electromagnetic encoder  100 , the active signal pattern  140  is configured to provide a second cycle signal and a third cycle signal which each vary approximately linearly with a position X along the measuring axis direction. In contrast, the active signal pattern  340  is configured to provide a second cycle signal which varies periodically according to the second wavelength λ 2 . This second cycle signal exhibits a unique relationship with the spatially periodic signals of a passive signal pattern (e.g., the passive signal pattern  130 ). For a passive signal pattern with a wavelength λ 1 , a phase difference between the spatially periodic signals and the second cycle signal may vary according to an envelope with a synthetic wavelength λ syn . The value of the synthetic wavelength λ syn  may be given by the expression: 
     
       
         
           
             
               
                 
                   
                     λ 
                     syn 
                   
                   = 
                   
                     
                       
                         λ 
                         1 
                       
                       ⁢ 
                       
                         λ 
                         2 
                       
                     
                     
                        
                       
                         
                           λ 
                           2 
                         
                         - 
                         
                           λ 
                           1 
                         
                       
                        
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The phase difference between the spatially periodic signals and the second cycle signal may be used in conjunction with the synthetic wavelength λ syn  to determine an absolute position within a first absolute range which is less than or equal to the synthetic wavelength λ syn . 
       FIG. 4  is a timing diagram  400  showing operations of the absolute electromagnetic position encoder  100 . 
     At a time t 0 , a first signal generating cycle begins. The readhead processor  114  energizes the field generator  112  to generate a first cycle field and generate first cycle spatially periodic signals in the field detector  113  based on the periodic pattern of signal modulating elements  131  of the passive signal pattern  130  modulating the field coupling between the field generator  112  and the field detector  113 . The first spatially modulated signal generating element  141  and the second spatially modulated signal generating element  142  are inactive. The first spatially modulated signal generating element  141  (and in some implementations, the second spatially modulated signal generating element  142 ) of the active signal pattern  140  couple to the first cycle field and provide energy to the timing and activation circuit  143  which is configured to receive and store energy during the first signal cycle. In some implementations, the energy provided to the timing and activation circuit  143  near the time t 1  may provide a reference time point to the timing and activation circuit  143  to synchronize operations with the readhead processor  114 . At a time t 2 , the first signal generating cycle ends. 
     At a time t 3 , a second signal generating cycle begins. The timing and activation circuit  143  is configured to drive the first spatially modulated signal generating element  141  to generate a corresponding spatially modulated second cycle field, and the field generator  112  couples to the spatially modulated second cycle field and provides a corresponding second cycle input to the readhead processor  114  which is configured to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead  110  that exhibits a unique relationship with the spatially periodic signals and is indicative of a unique position within the first absolute range AR 1 . At a time t 4 , the second signal generating cycle ends. 
     At a time t 5 , a third signal generating cycle begins. The timing and activation circuit  143  is configured to drive the second spatially modulated signal generating element  142  to generate a corresponding spatially modulated third cycle field, and the field generator  112  couples to the spatially modulated third cycle field and provides a corresponding third cycle input to the readhead processor  114  which is configured to receive the third cycle input and provide at least one corresponding third cycle signal in the readhead  110  that exhibits a unique relationship with the spatially periodic signals and is indicative of a unique position within the first absolute range AR 1 . At a time t 6 , the third signal generating cycle ends. 
     It should be appreciated that in the implementation shown in  FIG. 4 , during the second and third signal generating cycles, the field generator  112  couples to the spatially modulated second cycle field and provides a corresponding second cycle input to the readhead processor  114 . However, in alternative implementations, during the second and third signal generating cycles, the field detector  113  may couple to the spatially modulated second cycle field and provide a corresponding second cycle input to the readhead processor  114 . 
       FIGS. 5A and 5B  show a flow diagram  500  illustrating one exemplary implementation of a routine for operating an absolute electromagnetic position encoder. 
     At block  510 , an absolute electromagnetic position encoder is provided. The absolute electromagnetic position encoder comprises a readhead and an absolute scale extending along a measuring axis of the position encoder. The readhead comprises a spatially modulated signal coupling configuration, which comprises a field generator and a field detector, and a readhead processor configured to provide a first signal generating cycle and a second signal generating cycle. The readhead is movable relative to the absolute scale along the measuring axis. The absolute scale comprises a passive signal pattern comprising a periodic pattern of signal modulating elements distributed periodically at a first wavelength along a measuring axis and configured to modulate a field coupling between the field generator and the field detector to generate spatially periodic signals in the field detector as a function of readhead position relative to the absolute scale along the measuring axis, an active signal pattern comprising at least a first spatially modulated signal generating element configured to generate a corresponding spatially modulated field that couples to the readhead to provide at least one corresponding signal in the readhead for each unique readhead position relative to the absolute scale within a first absolute range that exceeds the first wavelength of the periodic pattern, and a timing and activation circuit connected to the active signal pattern. 
     At block  520 , during a first signal generating cycle, the readhead processor is operated to energize the field generator to generate a first cycle field and generate first cycle spatially periodic signals in the field detector based on the passive signal pattern modulating the field coupling between the field generator and the field detector, such that at least the first signal generating element of the active signal pattern couples to the first cycle field and provides energy to the timing and activation circuit, and the timing and activation circuit receives and stores energy during the first signal cycle. 
     After block  520 , the routine continues to block A which continues in  FIG. 5B . 
     As shown in  FIG. 5B , the routine continues from block A to block  530 . At block  530 , during a second signal cycle, the timing and activation circuit is operated to drive the first spatially modulated signal generating element to generate a corresponding spatially modulated second cycle field, such that at least one of the field generator and the field detector couples to the spatially modulated second cycle field and provides a corresponding second cycle input to the readhead processor, and the readhead processor is operated to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead that exhibits a unique relationship with the spatially periodic signals and is indicative of a unique position within the first absolute range. 
     At block  540 , an absolute position of the readhead  110  is determined relative to the absolute scale  120  based on at least the second cycle signal and the first cycle spatially periodic signals. 
       FIGS. 6A, 6B and 6C  are schematic diagrams of portions of a fourth implementation of an absolute electromagnetic position encoder  600 . The absolute electromagnetic position encoder  600  comprises a readhead  610  (shown in  FIG. 6A ), and an absolute scale  620  (shown in  FIGS. 6B and 6C ) extending along a measuring axis MA of the absolute electromagnetic position encoder  600 . The readhead  610  comprises a spatially modulated signal coupling configuration  611  comprising a field generator  612 , a periodic field detector  613 , an absolute field detector  615 , and a readhead processor  614  configured to provide a first signal generating cycle and a second signal generating cycle. The readhead  610  is movable relative to the absolute scale  620  along the measuring axis MA. The absolute scale  620  comprises an active signal pattern  630  (shown in  FIG. 1B ) comprising a periodic pattern of signal modulating elements  631  distributed periodically at a first wavelength λ 1  along the measuring axis MA and configured to generate a spatially periodic field that couples to the periodic field detector  613  to generate spatially periodic signals in the periodic field detector  613  as a function of readhead position relative to the absolute scale  620  along the measuring axis MA, and a passive signal pattern  640  comprising a spatially modulated signal generating element  641  configured to modulate a field coupling between the field generator  612  and the absolute field detector  615  to provide at least one corresponding signal in the readhead  610  that exhibits a unique relationship with the spatially periodic signals for each unique readhead position relative to the absolute scale  620  within a first absolute range AR 1  that exceeds the first wavelength λ 1  of the periodic pattern of signal modulating elements  631 . The absolute scale  620  further comprises a timing and activation circuit  633  connected to the active signal pattern  630 . 
     The field detector  613  is shown to comprise a first set of windings  613 A and a second set of windings  613 B. 
     It should be appreciated that while the active signal pattern  630  is constructed from just two windings, individual instances of the periodic pattern of signal modulating elements  631  are formed as periodic rectangular portions of each of the two windings. 
     The active signal pattern  630  and the passive signal pattern  640  may be arranged along a single track in a stacked configuration such that the readhead  610  may receive signals from both. 
     The absolute electromagnetic position encoder  600  comprises a first signal cycle configuration that is used to provide a first signal generating cycle wherein, during the first signal generating cycle, the readhead processor  614  is configured to energize the field generator  612  to generate a first cycle field and generate a first cycle signal in the absolute field detector  615  based on the passive signal pattern modulating the field coupling between the field generator  612  and the absolute field detector  615 , and the signal generating elements of the active signal pattern  630  couple to the first cycle field and provide energy to the timing and activation circuit  633 , and the timing and activation circuit  633  is configured to receive and store energy during the first signal cycle. 
     The absolute electromagnetic position encoder  600  comprises a second signal cycle configuration that is used to provide a second signal generating cycle wherein, during the second signal generating cycle, the timing and activation circuit  633  is configured to drive the periodic pattern of signal generating elements  631  to generate a corresponding spatially periodic second cycle field, and the periodic field detector couples to the spatially periodic second cycle field and provides corresponding spatially periodic signals to the readhead processor  614 . 
     The readhead processor  614  is further configured to determine an absolute position of the readhead  610  relative to the absolute scale  620  based on at least the first cycle signal and the spatially periodic signals. 
       FIGS. 7A, 7B and 7C  are schematic diagrams of portions of an absolute electromagnetic position encoder  700 . The absolute electromagnetic position encoder  700  comprises a readhead  710 , and an absolute scale  720  extending along a measuring axis MA of the absolute electromagnetic position encoder  700 . The readhead  710  comprises a field generation and detection configuration  711  and a readhead processor  714  connected to the field generation and detection configuration  711 , and is configured to operate the field generation and detection configuration  711  as a field generator to provide an energy transfer cycle, and to operate the field generation and detection configuration  711  as a first cycle field detector to provide a first signal generating cycle and to operate the field generation and detection configuration  711  as a second cycle field detector to provide a second signal generating cycle. The readhead  710  is movable relative to the absolute scale  720  along the measuring axis MA. The field generation and detection configuration  711  comprises a winding portion  712  and a periodic winding portion  713 . In the implementation shown in  FIG. 7A , the winding portion  712  is a single winding. The periodic winding portion  713  comprises a first set of detector windings  713 A and a second set of detector windings  7136  configured for quadrature detection in a similar manner as the field detector  113  shown in  FIG. 1A . In various implementations, the periodic winding portion  713  may be operated as the first cycle field detector and either the winding portion  712  or the periodic winding portion  713  may be operated as the second cycle field detector. 
     The absolute scale  720  comprises an active periodic signal pattern  730  comprising a periodic spatially modulated signal generating element  731  that extends along the measuring axis and has a first wavelength λ 1  and is configured to generate a corresponding periodic spatially modulated field that couples to the readhead  710  to generate spatially periodic signals in the first cycle field detector as a function of readhead position relative to the absolute scale  720  along the measuring axis MA, and an active absolute signal pattern  740  comprising at least a first spatially modulated signal generating element  741  configured to generate a corresponding spatially modulated field that couples to the readhead  710  to provide at least one corresponding signal in the second cycle field detector that exhibits a unique relationship with the spatially periodic signals for each unique readhead position relative to the absolute scale  720  within a first absolute range AR 1  that exceeds the first wavelength λ 1  of the periodic spatially modulated signal generating element  741 . The absolute scale further comprises timing and activation circuitry  743  connected to the active absolute signal pattern  740  and the active periodic signal pattern  730 . The absolute electromagnetic position encoder  700  comprises an energy transfer cycle configuration that is used to provide an energy transfer cycle wherein, during the energy transfer cycle, the readhead processor  714  is configured to energize a winding of the field generation and detection configuration (more specifically, the winding portion  712 ) to operate as a field generator and generate an energy transfer cycle field, and at least one of the signal generating elements of the absolute scale  720  couples to the energy transfer cycle field and provides energy to the timing and activation circuitry  743 , and the timing and activation circuitry  743  is configured to receive and store energy during the energy transfer cycle. The absolute electromagnetic position encoder  700  comprises a first signal cycle configuration that is used to provide a first signal generating cycle wherein, during the first signal generating cycle, the timing and activation circuitry  743  is configured to drive the periodic spatially modulated signal generating element  731  to generate a corresponding periodic spatially modulated first cycle field, and the first cycle field detector couples to the periodic spatially modulated first cycle field to generate first cycle spatially periodic signals in the first cycle field detector. The absolute electromagnetic position encoder  700  comprises a second signal cycle configuration that is used to provide a second signal generating cycle wherein, during the second signal generating cycle, the timing and activation circuitry  743  is configured to drive the first spatially modulated signal generating element  741  to generate a corresponding spatially modulated second cycle field, and the second cycle field detector couples to the spatially modulated second cycle field and provides a corresponding second cycle input to the readhead processor  714 , and during the second signal generating cycle the readhead processor  714  is configured to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead  710  that exhibits a unique relationship with the first cycle spatially periodic signals and is indicative of a unique position within the first absolute range AR 1 . 
     The readhead processor  714  is configured to operate the field generation and detection configuration as a third cycle field detector to provide a third signal generating cycle. The active absolute signal pattern  740  comprises a second spatially modulated signal generating element  742  configured to generate a corresponding spatially modulated field that couples to the readhead  710  to provide at least one corresponding signal in the third cycle field detector that exhibits a unique relationship with the spatially periodic signals for each unique readhead position relative to the absolute scale  700  within the first absolute range AR 1 . The absolute electromagnetic position encoder  700  comprises a third signal cycle configuration that is used to provide the third signal generating cycle wherein, during the third signal generating cycle, the timing and activation circuitry  743  is configured to drive the second spatially modulated signal generating element  742  to generate a corresponding spatially modulated third cycle field, and the third cycle field detector couples to the spatially modulated third cycle field and provides a corresponding third cycle input to the readhead processor  714 , and during the third signal generating cycle the readhead processor  714  is configured to receive the third cycle input and provide at least one corresponding third cycle signal in the readhead  710  that exhibits a unique relationship with the first cycle spatially periodic signals and is indicative of a unique position within the first absolute range AR 1 . In various implementations, either the winding portion  712  or the periodic winding portion  713  may be operated as the third cycle field detector. In various implementations such as  FIG. 7A , the second cycle field detector and the third cycle field detector may be provided by the same element of the field generation and detection configuration  711 . 
     The readhead processor  714  is further configured to determine an absolute position X of the readhead  710  relative to the absolute scale  720  based on at least the second cycle signal, the third cycle signal and the first cycle spatially periodic signals. 
     It should be appreciated that in some implementations, the timing and activation circuitry  743  may comprise first and second independent circuitry portions connected respectively to the active periodic signal pattern  730  and the active absolute signal pattern  740 . However, in the implementation shown in  FIGS. 7B and 7C , the timing and activation circuitry  743  is a single portion connected to both the active periodic signal pattern  730  and the active absolute signal pattern  740 . 
     In some implementations, the readhead processor  714  may be configured to determine a value A for the second cycle signal and a value B for the third cycle signal and determine a processed signal (A−B)/(A+B) which is indicative of a unique position in the first absolute range AR 1 . 
     In some implementations, generating the second cycle periodic signal may be initiated after generating the first cycle periodic signals. In some implementations, generating the third cycle periodic signal may be initiated after generating the first cycle periodic signals. 
     In some implementations such as that shown in  FIG. 7C , the first spatially modulated signal generating element  741  and the second spatially modulated signal generating element  742  may have substantially the same shape, but the shape of one may be flipped relative to the other about the measuring axis and an axis perpendicular to the measuring axis MA. 
     In some implementations, the active periodic signal pattern  730  and the active absolute signal pattern  740  may be constructed on different scale layers and are superimposed in the same scale track along the measuring axis MA. 
     In some implementations, the first cycle field detector may comprise a plurality of detectors arranged to generate spatially periodic signals in quadrature. For example, in  FIG. 7A , the winding portion  713  is shown to comprise a first set of windings  713 A indicated by solid lines which is configured to sense spatially periodic signals at spatial phases corresponding to 0 and 180 degrees, and a second set of windings  713 B indicated by dashed lines which is configured to sense spatially periodic signals at spatial phases corresponding to 90 and 270 degrees. In other implementations, the first cycle field detector may comprise a plurality of detectors arranged to generate three spatially periodic signals corresponding to spatial phase corresponding to 0, 120, and 240 degrees. 
     In some implementations, such as that shown in  FIG. 7C , the effective width of the first spatially modulated signal generating element  741  may vary linearly as a function of position along the measuring axis direction MA. As shown in  FIG. 7C , the effective width of both the first spatially modulated signal generating element  741  and the second spatially modulated signal generating element  742  vary linearly as a function of position along the measuring axis MA. 
     In some implementations, such as that shown in  FIG. 7B , the periodic spatially modulated signal generating element of the active periodic signal pattern  730  may comprise a periodic array of loops arranged from a single winding coupled to the timing and activation circuitry  743 . 
     It should be appreciated that in some implementations, alternative arrangements of an absolute signal pattern may be incorporated in place of the active absolute signal pattern  740 . For example, the active signal pattern  240  or the active signal pattern  340  may be incorporated in place of the active absolute signal pattern  740 . 
     It should be appreciated that a timing pattern of the energy transfer cycle, the first signal generating cycle, the second signal generating cycle and the third signal generating cycle will be understood by one of ordinary skill in the art, and the timing described with respect to  FIG. 4  may be easily adapted and modified to the foregoing description of  FIGS. 7A, 7B and 7C . 
       FIGS. 8A and 8B  show a flow diagram  800  illustrating one exemplary implementation of a routine for operating an absolute electromagnetic position encoder. 
     At block  810 , an absolute electromagnetic position encoder is provided. The absolute electromagnetic position encoder comprises a readhead and an absolute scale. The readhead comprises a field generation and detection configuration, and a readhead processor connected to the field generation and detection configuration, and is configured to operate the field generation and detection configuration as a field generator to provide an energy transfer cycle, and to operate the field generation and detection configuration as a first cycle field detector to provide a first signal generating cycle and to operate the field generation and detection configuration as a second cycle field detector to provide a second signal generating cycle. The absolute scale extends along a measuring axis of the position encoder. The readhead is movable relative to the absolute scale along the measuring axis. The absolute scale comprises an active periodic signal pattern comprising a periodic spatially modulated signal generating element that extends along the measuring axis and has a first wavelength and is configured to generate a corresponding periodic spatially modulated field that couples to the readhead to generate spatially periodic signals in the first cycle field detector as a function of readhead position relative to the absolute scale along the measuring axis, an active absolute signal pattern comprising at least a first spatially modulated signal generating element configured to generate a corresponding spatially modulated field that couples to the readhead to provide at least one corresponding signal in the second cycle field detector that exhibits a unique relationship with the spatially periodic signals for each unique readhead position relative to the absolute scale within a first absolute range that exceeds the first wavelength of the periodic spatially modulated signal generating element, and timing and activation circuitry connected to the active absolute signal pattern and the active periodic signal pattern. 
     At block  820 , during an energy transfer cycle, the readhead processor is operated to energize a winding of the field generation and detection configuration to operate as a field generator and generate an energy transfer cycle field, and couple at least one of the signal generating elements of the absolute scale to the energy transfer cycle field and providing energy to the timing and activation circuitry, and operate the timing and activation circuitry to receive and store energy during the energy transfer cycle. 
     After block  820 , the routine continues to block A which continues in  FIG. 8B . 
     As shown in  FIG. 8B , the routine continues from block A to block  830 . At block  830 , during a first signal generating cycle, the timing and activation circuitry is operated to drive the periodic spatially modulated signal generating element to generate a corresponding periodic spatially modulated first cycle field, and couple the first cycle field detector to the periodic spatially modulated first cycle field to generate first cycle spatially periodic signals in the first cycle field detector. 
     At block  840 , during a second signal generating cycle, the timing and activation circuitry is operated to drive the first spatially modulated signal generating element to generate a corresponding spatially modulated second cycle field, and couple the second cycle field detector to the spatially modulated second cycle field, and provides a corresponding second cycle input to the readhead processor, and the readhead processor is operated to receive the second cycle input and provide at least one corresponding second cycle signal in the readhead that exhibits a unique relationship with the first cycle spatially periodic signals and is indicative of a unique position within the first absolute range. 
     At block  850 , an absolute position of the readhead is determined relative to the absolute scale based on at least the second cycle signal and the first cycle spatially periodic signals. 
     While preferred implementations of the present disclosure have 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. Various alternative forms may be used to implement the principles disclosed herein. In addition, the various implementations described above can be combined to provide further implementations. All of the U.S. patents and U.S. patent applications referred to in this specification are incorporated herein by reference, in their entirety. Aspects of the implementations can be modified, if necessary to employ concepts of the various patents and applications to provide yet further implementations. 
     These and other changes can be made to the implementations in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific implementations disclosed in the specification and the claims, but should be construed to include all possible implementations along with the full scope of equivalents to which such claims are entitled.