Patent Publication Number: US-10758765-B2

Title: Stationary exercise machine with a power measurement apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/633,689, filed Jun. 26, 2017, entitled “STATIONARY EXERCISE MACHINE WITH A POWER MEASUREMENT APPARATUS,” now issued as U.S. Pat. No. 10,226,657, which claims benefit under 35 U.S.C. § 119 of the earlier filing date of U.S. Provisional Application No. 62/440,873, filed Dec. 30, 2016, entitled “STATIONARY EXERCISE MACHINE WITH A POWER MEASUREMENT APPARATUS,” which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Certain stationary exercise machines with reciprocating leg and/or arm portions have been developed. Such stationary exercise machines include stair climbers and elliptical trainers, each of which typically offers a different type of workout. For example, a stair climber may provide a lower frequency vertical climbing simulation while an elliptical trainer may provide a higher frequency horizontal running simulation. Additionally, these machines may include handles that provide support for the user&#39;s arms during exercise. However, the connections between the handles and leg portions of traditional stationary exercise machines may not enable sufficient exercise of the user&#39;s upper body. Generally, existing stationary exercise machines typically have minimal adjustability mainly limited to adjusting the amount of resistance applied to the reciprocating leg portions. Also, existing stationary machines with both upper and lower inputs (e.g., responsive to leg and arm movements) may not be equipped with means for determining the amount of power generated by one of the upper or lower inputs versus the other. It may therefore be desirable to provide an improved stationary exercise machine which addresses one or more of the problems in the field and which generally improves the user experience. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description will be more fully understood with reference to the following figures in which components may not be drawn to scale, which are presented as various embodiments of the exercise machine described herein and should not be construed as a complete depiction of the scope of the exercise machine. 
         FIG. 1  is a right side view of an exemplary exercise machine. 
         FIG. 2  is a left side view of the machine of  FIG. 1 . 
         FIG. 3  is a partial view of the machine of  FIG. 2 . 
         FIG. 4  is a perspective view of a magnetic brake of the machine of  FIG. 1 . 
         FIG. 5  is a perspective view of an embodiment of the machine of  FIG. 1  with an outer housing included. 
         FIG. 6  is a right side view of the machine of  FIG. 5 . 
         FIG. 7  is a front view of the machine of  FIG. 1 . 
         FIG. 8  is a block diagram of an energy tracking system for an exercise machine such as the machine of  FIG. 1 . 
         FIG. 9  is a view of a measurement apparatus for an exercise machine such as the machine in  FIG. 1   
         FIG. 10  is a partial perspective view of components of the measurement apparatus of  FIG. 9 . 
         FIG. 11  is an exploded view of the measurement apparatus of  FIG. 9 . 
         FIG. 12  is a perspective view of the code wheels of the measurement apparatus of  FIG. 9 . 
         FIG. 13  is an exploded view of resiliently coupled rotating components of the exercise machine of  FIG. 1  associated with operation of the measurement apparatus of  FIG. 9 . 
         FIG. 14A-14C  are waveforms illustrative of signal pulses produced by the measurement apparatus of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     Described herein are embodiments of stationary exercise machines having reciprocating foot and/or hand members, such as foot pedals that move in a closed loop path. The disclosed machines can provide variable resistance against the reciprocal motion of a user, such as to provide for variable-intensity interval training. Some embodiments can comprise reciprocating foot pedals that cause a user&#39;s feet to move along a closed loop path that is substantially inclined, such that the foot motion simulates a climbing motion more than a flat walking or running motion. Some embodiments can further comprise reciprocating hand members that are configured to move in coordination with the foot pedals and allow the user to exercise the upper body muscles. Variable resistance can be provided via a rotating air-resistance based fan-like mechanism, via a magnetism based eddy current mechanism, via friction based brakes, and/or via other mechanisms, one or more of which can be rapidly adjustable while the user is using the machine to provide variable intensity interval training. 
       FIGS. 1-7  show an embodiment of an exercise machine  100 . The machine  100  includes a frame  112 , which includes a base  114  for contact with a support surface, a vertical brace  116  extending from the base  114  to an upper support structure  120 , and first and second inclined members  122  that extend between the base  114  and the vertical brace  116 . The various components shown in  FIGS. 1-7  are merely illustrative, and other variations, including eliminating components, combining components, rearranging components, and substituting components are all contemplated. 
     The machine  100  may include an upper moment-producing mechanism and a lower moment producing mechanism. The upper moment-producing mechanism and the lower moment producing mechanism may each provide an input into a crankshaft  125  (see e.g.,  FIGS. 2 and 7 ) inducing a tendency for the crankshaft  125  to rotate about axis A. Each of the upper and lower moment-producing mechanisms may include one or more links operatively connected into a linkage that produces the moment on the crankshaft  125 . For example, the upper moment-producing mechanism may include one or more upper links extending from the handles  134  to the crankshaft  125 . The lower moment-producing mechanism may include one or more lower links extending from the pedal  132  to crankshaft  125 . In one example, the machine may include left and right upper linkages  90 , each including a plurality of links configured to connect an input end (e.g., a handle end) of the upper linkage to the crankshaft  125 . Likewise, the machine may include left and right lower linkages  92 , each including a plurality of links configured to connect an input end (e.g., a pedal end) of the lower linkage to the crankshaft  125 . The crankshaft  125  may have a first side and a second side and may be rotatable about the crankshaft axis A. The first side of the crankshaft  125  may be connected e.g., to the left upper and lower linkages, and the second side of the crankshaft  125  may be connected e.g., to the right upper and lower linkages. 
     In various embodiments, the lower moment-producing mechanism may include a first lower linkage  92  and a second lower linkage  92  corresponding to a left and right side of machine  100 . Each of the first and second lower linkages may include one or more links operatively arranged to transform a force input from the user (e.g., from the lower body of the user) into a moment about the crankshaft  125 . For example, the first and second lower linkages may include one or more of first and second pedals  132 , first and second rollers  130 , first and second lower reciprocating members  126  (also referred to as foot members  126 ), and/or first and second crank arms  128 , respectively. The first and second lower linkages may operably transmit a force input from the user into a moment about the crankshaft  125 . 
     The first and second crank arms  128  are fixed relative to the respective side of the crankshaft  125 . The machine  100  may optionally include first and/or second crank wheels  124  which may be rotatably supported on opposite sides of the upper support structure  120  about a horizontal rotation axis A. The crank arms  128  may be positioned on outer sides of the crank wheels  124  and may be fixed relative to the respective first and second crank wheels  124 . The crank arms  128  may be rotatable about the rotation axis A, such that rotation of the crank arms  128  causes the crankshaft  125  and/or crank wheels  124  to rotate. The first and second crank arms  128  extend from the crankshaft  125  (e.g., from the axis A) in opposite radial directions to their respective radial ends. For example, the first side and the second side of the crank shaft  125  may be fixedly connected to the output ends of the first and second crank arms  128  and the input ends of each crank arm may extend radially from the connection between the crank arm and the crank shaft. First and second lower reciprocating members  126  may have forward ends (i.e., output ends) that are pivotably coupled to the radial ends (i.e., input ends) of the first and second crank arms  128 , respectively. The terms pivotably and pivotally are used interchangeably herein. The rearward ends (i.e., input ends) of the first and second lower reciprocating members  126  may be coupled to first and second foot pedals  132 , respectively. The rearward ends (i.e., input ends) of the first and second lower reciprocating members  126  may thus be interchangeably referred to as pedal ends. 
     First and second rollers  130  may be coupled to the first and second lower reciprocating members  126 , respectively, for example to or proximate the pedal ends or to an intermediate location. In various examples, the first and second rollers  130  may be connected to the pedals, e.g., the first and second pedals  132  may each have first ends with first and second rollers  130 , respectively, extending therefrom. Each of the first and second pedals  132  may have second ends with first and second platforms  126   b  (or similarly pads), respectively. First and second brackets  126   a  may form the portion of the first and second pedals  132  which connects the first and second platforms  132   b  and the first and second brackets  132   a . The first and second lower reciprocating members  126  may be fixedly connected to the first and second brackets  126   a  between the first and second rollers  130 , respectively, and the first and second platforms  132   b , respectively. The connection may be closer to a front of the first and second platform than the first and second rollers  130 . The first and second platforms  132   b  may be operable for a user to stand on and provide an input force. The first and second rollers  130  rotate about individual roller axes T. The first and second rollers may rotate on and travel along first and second inclined members  122 , respectively. The first and second inclined members  122  may form a travel path along the length and height of the first and second incline members. The rollers  130  can rollingly translate along the inclined members  122  of the frame  112 . In alternative embodiments, other bearing mechanisms can be used to provide translational motion of the lower reciprocating members  126  along the inclined members  122  instead of or in addition to the rollers  130 , such as sliding friction-type bearings. 
     When the foot pedals  132  are driven by a user, the pedal ends of the reciprocating members  126  (also referred to as foot members  126 ) translate in a substantially linear path via the rollers  130  along the inclined members  122 . In alternative embodiments, the inclined members can comprise a non-linear portion, such as a curved or bowed portion, such that pedal ends of the foot members  126  translate in non-linear path via the rollers  130  along the non-linear portion of the inclined members. The non-linear portion of the inclined members can have any curvature, such as a curvature of a constant or non-constant radius, and can present convex, concave, and/or partially linear surfaces for the rollers to travel along. In some embodiments, the non-linear portion of the inclined members  122  can have an average angle of inclination of at least 45°, and/or can have a minimum angle of inclination of at least 45°, relative to a horizontal ground plane. 
     The output ends of the foot members  126  move in circular paths about the rotation axis A, which drives the crank arms  128  and/or the crank wheels  124  in a rotational motion about axis A. The circular movement of the output ends of the foot members  126  causes the pedal ends to pivot at the roller axis D as the rollers (and thereby roller axis D) translates along the inclined members  122 . The combination of the circular motion of the output ends, the linear motion of the pedal ends, and pivotal action about the axis D, causes the pedals  132  to move in non-circular closed loop paths, such as substantially ovular and/or substantially elliptical closed loop paths. The closed loop paths traversed by different points on the foot pedals  132  can have different shapes and sizes, such as with the more rearward portions of the pedals  132  traversing longer distances. A closed loop path traversed by the foot pedals  132  can have a major axis defined by the two points of the path that are furthest apart. The major axis of one or more of the closed loop paths traversed by the pedals  132  can have an angle of inclination closer to vertical than to horizontal, such as at least 45°, at least 50°, at least 55°, at least 60°, at least 65°, at least 70°, at least 75°, at least 80°, and/or at least 85°, relative to a horizontal plane defined by the base  114 . To cause such inclination of the closed loop paths of the pedals  132 , the inclined members  122  can comprise a substantially linear portion over which the rollers  130  traverse. The inclined members  122  form a large angle of inclination a relative to the horizontal base  114 , such as at least 45°, at least 50°, at least 55°, at least 60°, at least 65°, at least 70°, at least 75°, at least 80°, and/or at least 85°. This large angle of inclination which sets the path for the foot pedal motion can provide the user with a lower body exercise more akin to climbing than to walking or running on a level surface. Such a lower body exercise can be similar to that provided by a traditional stair climbing machine. 
     In various embodiments, the upper moment-producing mechanism may include a first upper linkage  90  and a second upper linkage  90  corresponding to a left and right side of machine  100 . Each of the first and second upper linkages may include one or more links operatively arranged to transform a force input from the user (e.g., from the upper body of the user) into a moment about the crankshaft  125 . For example the first and second upper linkages may include one or more of first and second handles  134 , first and second links  138 , first and second upper reciprocating members  140  (also referred to herein as hand member  140 ), and/or first and second virtual crank arms  142   a , respectively. The first and second upper linkages may operably transmit a force input from the user, at the handles  134 , into a moment about the crankshaft  125 . The first and second handles  134  may be pivotally coupled to the upper support structure  120  at a horizontal axis D. 
     The handles  134  may be rigidly connected to the input end of respective first and second links  138  such that reciprocating pivotal movement of the handles  134  about the horizontal axis D causes corresponding reciprocating pivotal movement of the first and second links  138  about the horizontal axis D. 
     For example, the first and second links  138  may be cantilevered off of handles  134  at the pivot aligned with the D axis. Each of the first and second links  138  may have angle ω with the respective handles  134 . The angle ω may be measured from a plane passing through the axis D and the curve in the handle proximate the connection to the link  138 . The angle ω may be any angle such as angles between 0 and 180 degrees. The angle ω may be optimized to one that is most comfortable to a single user or an average user. The links  138  are pivotably coupled at their radial ends (i.e., output ends) to first and second reciprocating hand members  140 . The lower ends of the hand members  140  may include respective circular disks  142  (see e.g.,  FIG. 3 ) which are rotatable relative to the rest of the hand member  140  about respective disk axes B. The disk axes B, which are located at the center of each disk  142 , are parallel to the rotation axis A. The disk axes B of the disks  142  positioned on opposite sides of the crank shaft  125  are offset radially in opposite directions from the axis A. Virtual crank arms  142   a  may thus be defined between the centers of the circular disks  142  (i.e., between axes B) and the rotation axis A. 
     The lower ends of the upper reciprocating members  140  may be pivotably connected to the first and second virtual crank arms  142   a  (see  FIG. 3 ), respectively. The first and second virtual crank arms  142   a  may be rotatable relative to the rest of the upper reciprocating members  140  about respective axes B (which may be referred to as virtual crank arm axes). Axes B may be parallel to the crank axis A. Each axis B may be located proximal to an end of each of the upper reciprocating members  140 . Each axis B may also be located proximal to one end of the virtual crank arm  142   a . Each axis B may be offset radially in opposite directions from the axis A. Each respective virtual crank arm  142   a  may be perpendicular to axis A and each of the axes B, respectively. The distance between axis A and each axis B may define approximately the length of the virtual crank arm. This distance between axis A and each axis B is also the length of the moment arm of each virtual crank arm  142   a  which exerts a moment on the crankshaft. As used herein, the virtual crank arm  142   a  may be any device which exerts a moment on the crankshaft  125 . For example, as used above, the virtual crank arm  142   a  may be the disk  142  (e.g., the distance between the center of the disk  142  and the radial location on disk  142  through which axis A passes. In another example, the virtual crank arm  142   a  may be a crank arm similar to crank arm  128 . Each of the virtual crank arms may be a single length of semi-rigid to rigid material having pivots proximal to each end with one of the reciprocating members pivotably connected along axis B proximal to one end and the crankshaft fixedly connected along axis A proximally connected to the other end. The virtual crank arm may include more than two pivots and have any shape. As discussed hereafter, the virtual crank arm is described as being disk  142  but this is merely as an example, as the virtual crank arm may take any form operable to apply a moment to crankshaft  125 . As such, each embodiment including the disk may also include the virtual crank arm or any other embodiment disk herein or would be understood by one of ordinary skill in the art as applicable. 
     The links  138  are pivotably coupled at their radial ends (i.e., output ends) to first and second upper reciprocating members  140 . The links  138  and upper reciprocating members  140  are pivotally coupled at respective pivots coaxial with axes C. The lower ends of the upper reciprocating members  140  include respective annular collars  141  and respective circular discs  142 , each rotatable within the respective collar. As such, the respective circular disks  142  are rotatable relative to the rest of the upper reciprocating member  140  about respective disk axes B. The disk axes B are parallel to the rotation axis A and offset radially in opposite directions from the axis A. 
     As the handles  134  articulate back and forth (i.e., reciprocate pivotally about axis D), the links  138  move in corresponding arcs, which in turn articulates the upper reciprocating members  140 . Via the fixed connection between the upper reciprocating member  140  and annular collar  141 , the articulation of handle  134  also moves annular collar  141 . As rotatable disk  142  is fixedly connected to and rotatable around the crankshaft which pivots about axis A, rotatable disk  142  also rotates about axis A. As the upper reciprocating member  140  articulates back and forth it forces the annular collar  141  toward and away from the axis A along a circular path with the result of causing axis B and/or the center of disk  142  to circularly orbit around axis A. As the crank arms  128  and/or crank wheels  124  rotate about the axis A, the disk axes B orbit about the axis A. The disks  142  are also pivotably coupled to the crank axis A, such that the disks  142  rotate within the respective lower ends of the upper reciprocating members  140  as the disks  142  pivot about the crank axis A on opposite sides of the upper support member  120 . The disks  142  can be fixed relative to the respective crank arms  128 , such that they rotate in unison around the crank axis A when the pedals  132  and/or the handles  134  are driven by a user. 
     The upper linkage assemblies may be configured in accordance with the examples herein to cause the handles  134  to reciprocate in opposition to the pedals  132  such as to mimic the kinematics of natural human motion. For example, as the left pedal  132  is moving upward and forward, the left handle  134  pivots rearward, and vice versa. As shown in  FIG. 10 , the machine  100  can further comprise a user interface  102  mounted near the top of the upper support member  120 . The user interface  102  can comprise a display to provide information to the user, and can comprise user inputs to allow the user to enter information and to adjust settings of the machine, such as to adjust the resistance. The machine  100  can further comprise stationary handles  104  mounted near the top of the upper support member  120 . 
     The exercise machine  100  may include a resistance mechanism operatively arranged to resist the rotation of the crankshaft. In some embodiments, the exercise machine may include one or more resistance mechanism such as an air-resistance based resistance mechanism, a magnetism based resistance mechanism, a friction based resistance mechanism, and/or other resistance mechanisms. 
     For example, resistance may be applied via an air brake, a friction brake, a magnetic brake or the like. The machine  100  may include an air-resistance based resistance mechanism, or air brake  150 , that is rotationally mounted to the frame  112  on a horizontal shaft  166 . The machine  100  may additionally or alternatively include a magnetic-resistance based resistance mechanism, or magnetic brake  160  (see e.g.,  FIGS. 1 and 4 ), which includes a rotor  161  rotationally mounted to the frame  112  and a brake caliper  162  also mounted to the frame  112 . The rotor  161  and the air brake  150  may be coupled to the same horizontal shaft (e.g., shaft  166 ). The air brake  150  and rotor  161  are driven by the rotation of the crankshaft  125  and are each operable to resist the rotation of the crankshaft  125 . In the illustrated embodiment, the shaft  166  is driven by a belt or chain  148  that is coupled to a pulley  146 . Pulley  146  is coupled to another pulley  125  mounted coaxially with the axis A by another belt or chain  144 . The pulleys  125  and  146  can be used as a gearing mechanism to set the ratio of the angular velocity of the air brake  150  and the rotor  161  relative to the reciprocation frequency of the pedals  132 . 
     One or more of the resistance mechanisms can be adjustable to provide different levels of resistance at a given reciprocation frequency. Further, one or more of the resistance mechanisms can provide a variable resistance that corresponds to the reciprocation frequency of the exercise machine, such that resistance increases as reciprocation frequency increases. For example, one reciprocation of the pedals  132  can cause several rotations of the air brake  150  and rotor  161  to increase the resistance provided by the air brake  150  and/or the magnetic brake  160 . The air brake  150  can be adjustable to control the volume of air flow that is induced to flow through the air brake at a given angular velocity in order to vary the resistance provided by the air brake. 
     The magnetic brake  160  provides resistance by magnetically inducing eddy currents in the rotor  161  as the rotor rotates. As shown in  FIG. 4 , the brake caliper  162  includes high power magnets  164  positioned on opposite sides of the rotor  161 . As the rotor  161  rotates between the magnets  164 , the magnetic fields created by the magnets induce eddy currents in the rotor, producing resistance to the rotation of the rotor. The magnitude of the resistance to rotation of the rotor can increase as a function of the angular velocity of the rotor, such that higher resistance is provided at high reciprocation frequencies of the pedals  132  and handles  134 . The magnitude of resistance provided by the magnetic brake  160  can also be a function of the radial distance from the magnets  164  to the rotation axis of the shaft  166 . As this radius increases, the linear velocity of the portion of the rotor  161  passing between the magnets  164  increases at any given angular velocity of the rotor, as the linear velocity at a point on the rotor is a product of the angular velocity of the rotor and the radius of that point from the rotation axis. In some embodiments, the brake caliper  162  can be pivotably mounted, or otherwise adjustable mounted, to the frame  116  such that the radial position of the magnets  134  relative to the axis of the shaft  166  can be adjusted. For example, the machine  100  can include a motor coupled to the brake caliper  162  that is configured to move the magnets  164  to different radial positions relative to the rotor  161 . As the magnets  164  are adjusted radially inwardly, the linear velocity of the portion of the rotor  161  passing between the magnets decreases, at a given angular velocity of the rotor, thereby decreasing the resistance provided by the magnetic brake  160  at a given reciprocation frequency of the pedals  132  and handles  134 . Conversely, as the magnets  164  are adjusted radially outwardly, the linear velocity of the portion of the rotor  161  passing between the magnets increases, at a given angular velocity of the rotor, thereby increasing the resistance provided by the magnetic brake  160  at a given reciprocation frequency of the pedals  132  and handles  134 . 
     In some embodiments, the brake caliper  162  can be adjusted rapidly while the machine  10  is being used for exercise to adjust the resistance. For example, the radial position of the magnets  164  of the brake caliper  162  relative to the rotor  161  can be rapidly adjusted by the user while the user is driving the reciprocation of the pedals  132  and/or handles  134 , such as by manipulating a manual lever, a button, or other mechanism positioned within reach of the user&#39;s hands (see e.g.,  FIGS. 2 and 3 ) while the user is driving the pedals  132  with his feet. Such an adjustment mechanism can be mechanically and/or electrically coupled to the magnetic brake  160  to cause an adjustment of eddy currents in the rotor and thus adjust the magnetic resistance level. The user interface  102  can include a display to provide information to the user, and can include user inputs to allow the user to enter to adjust settings of the machine, such as to adjust the resistance. In some embodiments, such a user-caused adjustment can be automated, such as using a button on the user interface  102  that is electrically coupled to a controller and an electrical motor coupled to the brake caliper  162 . In other embodiments, such an adjustment mechanism can be entirely manually operated, or a combination of manual and automated. In some embodiments, a user can cause a desired magnetic resistance adjustment to be fully enacted in a relatively short time frame, such as within a half-second, within one second, within two seconds, within three second, within four seconds, and/or within five seconds from the time of manual input by the user via an electronic input device or manual actuation of a mechanical device. In other embodiments, the magnetic resistance adjustment time periods can be smaller or greater than the exemplary time periods provided above. 
       FIGS. 5 and 6  show an embodiment of the exercise machine  100  with an outer housing  170  mounted around a front portion of the machine. The housing  170  can house and protect portions of the frame  112 , the pulleys  125  and  146 , the belts or chains  144  and  148 , lower portions of the upper reciprocating members  140 , the air brake  150 , the magnetic brake  160 , motors for adjusting the air brake and/or magnetic brake, wiring, and/or other components of the machine  100 . The housing  170  can include an air brake enclosure  172  that includes lateral inlet openings  176  to allow air into the air brake  150  and radial outlet openings  174  to allow air out of the air brake. The housing  170  can further include a magnetic brake enclosure  179  to protect the magnetic brake  160 , where the magnetic brake is included in addition to or instead of the air brake  150 . The crank arms  128  and/or crank wheels  124  can be exposed through the housing such that the lower reciprocating members  126  can drive them in a circular motion about the axis A without obstruction by the housing  170 . 
     A stationary exercise machine in accordance with some examples herein may include a frame, a crankshaft rotatably supported by the frame, an upper moment-producing mechanism and a lower moment-producing mechanism both operatively engaged to the crankshaft to cause the crankshaft to rotate. In some examples, the lower moment producing mechanism includes at least one crank arm coupled to the crankshaft to cause rotation of the crankshaft responsive to rotation of the crank arm. In some examples, the upper moment producing mechanism may include at least one link coupled to the crankshaft to also cause rotation of the crankshaft responsive to movement of the link. In some examples, the link may be a rigid link, such as a straight bar member, or a portion of a rotating disk, or a plurality of links operatively coupled to the crankshaft to cause it to rotate. The link may also be referred to as a virtual crank arm. The lower moment-producing mechanism and the upper moment-producing mechanism may be resiliently coupled to one another, such as via a resilient coupling between the crank arm of the lower moment-producing mechanism and the link or virtual crank arm or the upper moment-producing mechanism. In some examples, herein, the stationary exercise machine may further include a measurement apparatus which may be configured to measure differential forces between the upper and lower mechanisms. The measurement apparatus may employ one or more optical sensing components, strain gauges, load cells, etc. for measuring the applied force via the upper moment-producing mechanism and independently and/or relatively via the lower moment-producing mechanism. In one embodiment, the measurement apparatus may include an optical sensor operatively arranged with a pair of code wheels to detect a relative displacement between the two code wheels. In some examples, the first code wheel may be coupled such that it rotates synchronously with the crank arm of the lower moment-producing mechanism. For example, the first code wheel may be rigidly coupled to the crank shaft and/or the crank arm of the lower moment-producing mechanism. The second code wheel may be coupled such that it rotates synchronously with the virtual crank arm, e.g., by being rigidly or otherwise operatively coupled to the virtual crank arm. The two code wheels may be movable relative to one another to allow a relative displacement between the code wheels responsive to application of force via both of the upper and lower moment-producing mechanisms. In some examples, the code wheels may be coaxially coupled to one another and rotatable about the crank shaft axis. 
     Referring now also to  FIGS. 8-14 , in accordance with some examples herein, the exercise machine  100  may include an energy tracking system  200 , which may be configured to provide information to the user, for example including in whole or in part the energy or power generated by the user during exercise. The energy tracking system  200  may include a processing circuit  210  and a memory  212 . The energy tracking system  200  may be operatively (e.g., communicatively) coupled to the user interface  102  for displaying information to the user (e.g., resistance level, energy or power generated by the user, calories burned, etc.) and/or receiving input from the user (e.g., weight of the user). The energy tracking system  200  may receive as input signals from one or more measurement apparatuses  220 , which may be operatively coupled with moving components of the exercise machine  100 . For example, the energy tracking system  200  may be operatively coupled with one or more load sensors, strain gauges, or the like, to measure the torque applied to the crankshaft  125 . The torque and the angular displacement of the crankshaft  125  can be used to calculate the work and thus the power applied to the crankshaft  125 , which is indicative of the power generated by the user during exercise. The angular displacement can be measured using an angular position sensor such as a rotary encoder (e.g., an optical incremental encoder) or it can be obtained from measurements of the angular velocity (i.e., rotational speed of the crankshaft), which can be measured using for example a tachometer. The processing circuit  210  may receive signals from the one or more measurement apparatuses (e.g., measurement apparatus  230 ) and determine various exercise performance parameters (e.g., energy or power output, resistance level, calories burned, etc.), which may be stored in memory (e.g., memory  210 ) and/or displayed via the user interface  102 . 
     In some embodiments, the upper and lower moment-producing mechanisms  90  and  92  of exercise machine  100  may be resiliently coupled to one another such that force applied to the crank shaft via one of the moment-producing mechanisms versus the other may be determined. A resilient coupling is generally a coupling which may deform (e.g., bend, stretch, deflect, compress) under loads typical for normal use and is able to recoil or spring back substantially into its original shape, configuration, or position after deforming (e.g., bending, stretching, deflecting, or being compressed), for example as is typical for components such as springs or other compliant members (e.g., a compliant material such as rubber). The terms compliant and resilient may be used interchangeably herein. In one example, and as described, the crank arms  128  may be rigidly coupled to the crank shaft  125  to cause the crank shaft  125  to rotate responsive to movement of the pedals  132 . On the other hand, the output member of the upper moment-producing mechanism  90  (e.g., disk  142  of one of the left or right upper linkages  90 ) may be resiliently coupled to the crank shaft  125  thereby enabling some relative movement (e.g., slip) between the disk  142  and the crank shaft  125  when load from the upper moment-producing mechanism  90  is being applied to the crank shaft  125 . The relative movement or slip may be temporary, e.g., while load is being applied to each of the two resiliently coupled components or assemblies, and the relative displacement may be removed (e.g., due to the resilience of the coupling) in the absence of applied loads. 
     In some embodiments, the processing circuit  210  of the energy tracking system  200  may be communicatively coupled to a measurement apparatus  230 , which may be operable to generate signals indicative of relative movement of the upper and lower moment-producing mechanisms  90  and  92 , respectively, as will be further described. The measurement apparatus  230  may be operatively coupled to one or more moving components of the exercise machine  100 . For example, as shown in  FIG. 9 , components of the measurement apparatus  230  may be coupled to the crank shaft  125 , to the eccentrically mounted disk  142 , and the frame (e.g., upright brace  116 ) to generate signals indicative of relative angular displacement between a rotating component (e.g., a link or other rotating member, such as the virtual crank arm defined by the eccentrically mounted disk  142 ) of the upper moment-producing mechanism  90  relative and a rotating component (e.g., crank arm  128 ) of the lower moment-producing mechanism  92 . 
     The measurement apparatus  230  may be implemented using an optical sensing component  260  in conjunction with a pair of concentric code wheels  240  and  250 . For example, as shown in  FIGS. 9 and 10 , the measurement apparatus  230  may include an optical sensing component  260  which includes a light emitter (e.g., an LED) in one of the sensor supports  262 - 1  and a light detector (e.g., a photo sensor) in the other sensor support  262 - 2 . The light emitter and sensor are arranged on the supports facing one another such that light emitted by the light emitter can be detected by the light detector. The two supports  262 - 1  and  262 - 2  and thus the light emitter and light detector are positioned on opposite sides of the pair of concentrically arranged and rotatable coupled code wheels (e.g., first wheel  240  and second wheel  250 ). One of the code wheels (e.g., first code wheel  240 ) may be rigidly coupled to the crank shaft  125  such that it rotates synchronously with the crankshaft. As such, the angular position and velocity of one of the code wheels (e.g., first code wheel  240 ) corresponds to the angular position and velocity of the crank shaft  125 . As described, the crank shaft  125  is rigidly coupled to the crank arm  128 , thus the code wheel  240  rotates also synchronously with rotation of the crank arm  128 , e.g., responsive to force applied via the lower moment-producing mechanism  92 . Thus, the force applied to the crank shaft  125  via the crank arm  128 , and thus via the lower moment-producing mechanism  92 , can be determined by tracking the angular position and/or velocity of the first code wheel. 
     The other code wheel (e.g., second code wheel  250 ) may be rigidly coupled to the virtual crank arm  142   a , in this case rigidly coupled to the disk  142  which defines the virtual crank arm  142   a . The disk  142  rotates eccentrically about the axis A of the crank shaft  125 . The code wheel  250  may be coaxially arranged at the axis A such that the code wheel  250  rotates about axis A synchronously with rotation of the disk  142 , e.g., responsive to force applied via the upper moment-producing mechanism  90 . Thus, the force applied to the crank shaft  125  via the virtual crank arm  142   a , and thus via the upper moment-producing mechanism  90 , can be determined by tracking the angular position and/or velocity of the second code wheel. As described, the upper and lower moment-producing mechanisms  90  and  92  may be resiliently coupled. For example, the upper and lower moment-producing mechanisms  90  and  92  may be resiliently coupled by a resilient coupling between at least one of the left or right crank arms  128  and the respective disk  142 . This may result in a slight relative displacement (e.g., a shift or offset) between the crank arm  128  and the disk  142  and thus between the first and second code wheels  240  and  250 . The slight relative displacement (e.g., a shift or offset) may be indicative of the difference in force/energy applied to either side of the resilient member. The energy tracking system  200  may be configured to detect this slight relative displacement (e.g., shift or offset) and thus determine relative input of force via the upper moment-producing mechanism  90  versus the lower moment producing mechanism  92 . 
     Resilient coupling between the upper and lower moment-producing mechanisms  90  and  92  may be achieved for example in accordance with the embodiment shown in  FIG. 13 . The crank arm  128  may be pivotally coupled to the disk  142  using a pin  129  such that movement of either one of the upper and lower moment-producing mechanisms results in movement of the other one of the upper and lower moment-producing mechanisms. The pin  129  may be rigidly connected to the crank arm  128 . The pin  129  may be rotatably received in an opening  145  in the disk  142 . Movement of the crank arm  128  may be transmitted to the disk  142  and vice versa via the pin  129  bearing on the wall of the opening  145 . The crank arm  128  may be resiliently pivotally coupled to the disk  142  for example, using a compliant member  143  (e.g., a rubber disk) positioned in the opening  145  between bearing surface of the pivotal coupling (e.g., between the pin  129  and walls of the opening  145 ). The compliant member  143  may compress in the direction of rotation when sufficient force is being transmitted from the crank arm  128  to the disk  142  or vice versa which may cause some relative movement (e.g., slip) between the crank arm  128  and the disk  142 , and thus between the first and second code wheel. 
     Each of the code wheels  240  and  250  includes a plurality of slots or windows (e.g., first windows  242 - 1  through  242 - 9  of the first code wheel  240  and second windows  252 - 2  through  252 - 9  of the second code wheel  250 ). In some examples, the code wheels  240  and  250  may each include the same number of windows. In some examples, the first windows  242  of the code wheel  240  may have the same width W 1  and the width W 2  of the second windows  252  of the code wheel  250 . The windows  242 ,  252  of each code wheel may be arranged radially along the peripheral portion of each code wheel at about the same radial distance from the center of each code wheel such that at least a portion of each window of the one of the code wheels overlaps a portion of a respective window of the other code wheel, to define an effective window of the pair of code wheels. That is, as shown e.g., in  FIGS. 10 and 12 , at least a portion of each of the first windows  242 - 1  through  242 - 9  overlaps a portion of a respective one of the second windows  252 - 1  through  252 - 9 . In some example, the first and second windows  242 ,  252 , respectively, may overlap only partially, as in the example in  FIGS. 10 and 12 , while remaining portions of the windows are blocked by the solid portions of the code wheels. For example, solid portions of the wheel  240  adjacent to each window  242  may block a portion of the opening of respective windows  252  and similarly, solid portions of the wheel  250  adjacent to each window  252  may block a portion of the opening of respective windows  242  defining an effective window of the pair of code wheels which has a width W E . The width W E  in this example is less than the widths W 1  and W 2  of the first and second windows. The widths W 1  and W 2  of the windows and the amount of overlap (e.g., the width W E  of the effective window) may be selected based upon the stiffness of the resilient coupling between the upper and lower moment-producing mechanisms. For example, the widths W 1  and W 2  of the windows and the amount of overlap may be selected to allow an increase of the width W E  to about the widths W 1  and W 2  or a decrease of the width W E  to a non-zero minimum width upon the application of maximum expected force via the upper moment-producing mechanism. 
     In  FIG. 12 , the pair of concentrically arranged code wheels  240  and  250  is shown in a neutral alignment (e.g., as indicated by the alignment features  243  and  253  of the respective first and second code wheels  240  and  250 ). In this position, the width W E  of the effective window defined by the pair of code wheels may be referred to as the neutral or starting width of the effective window. The neutral or starting width of the effective window may thus correspond to the width of the effective window in the absence of applied load to either of the two code wheels, or when load is being applied only to one of the code wheels. In the illustrated example in  FIG. 12 , the starting width is less than the widths W 1  and W 2  of the first and second windows, respectively. In other examples, the starting width may be substantially the same as the widths of the first and second windows (e.g., in a case where the windows are not offset but overlap substantially fully). In such examples, the relative displacement of the code wheels (e.g., shift or offset) may be determined by detecting (e.g., using the sensing component) a narrowing of the starting width of the effective window. In such examples, the direction of slip may be determined, for example, using a second radial array of encoding (e.g., slots) which may be slightly offset to allow the phase shift between the two arrays to be monitored in order to track direction of rotation of the wheels and consequently the direction of relative displacement of the wheels. The starting width of the effective window may be stored in memory  320  and retrieved by the processing circuit  210  for use in determining the amount of relative slip between the code wheels. 
     During use, e.g., when the crank shaft  125  is rotated only responsive to force applied by one of the moment-producing mechanism (e.g., the lower moment-producing mechanism  92 ), the sensing component  260  may produce a signal pattern having a generally rectangular waveform  310 - 1  as shown in  FIG. 14A . The positive pulses  312  of the wave form  310 - 1  correspond to the periods of time when light is being detected by the light detector through the effective window defined by the pair of code wheels. The negative pulses  314  correspond to the periods of time when light is not being detected by the light detector (i.e., the periods of time when the light emitter is blocked by the solid portions of the code wheels between adjacent windows. The angular velocity (e.g., revolutions per unit time) may thus be determined from the frequency of the wave form and the total number of windows of the pair of code wheels. For example, if the detected frequency is 900 pulses per minute, the processing circuit  210  may determine that the angular velocity of a pair of code wheels having a total of 9 effective windows is 100 revolutions per minute. 
     The machine  100  may be configured such that, during use of the machine, the pair of code wheels remain in the neutral position (e.g., with the alignment features  243  and  253  substantially aligned) relative to one another if force is being applied via only one of the upper or lower moment-producing mechanisms  90 ,  92 , typically via the lower moment-producing mechanisms  90  which is driven by the legs of the user. This may be achieved for example, by selecting the stiffness of the resilient coupling between the upper or lower moment-producing mechanisms  90 ,  92  such that the resilient coupling does not appreciably deform in the absence of force from both the upper and lower moment-producing mechanisms  90 ,  92 . Thus, in some examples, the resilient coupling may be sufficiently stiff to prevent any appreciable compression, and thus any detectable slip, absent the application of force by both the upper and lower moment-producing mechanisms  90 ,  92 . The energy tracking system  200  may be configured to detect variations from the neutral alignment, e.g., by detecting a change in the width W E  of the effective window. Such variations from the neutral alignment may thus be indicative of slip and thus indicative of the application of force via the upper moment producing mechanism. 
     Returning back to the illustrated examples, the width of a positive pulse  312  may correspond to the width of the effective window. Thus, when force is applied via the upper moment-producing mechanism in a direction causing the wheel to slip in the same direction as the rotation direction (e.g., direction  270 ) of the crank shaft, the width of the effective window may decrease, and correspondingly the period of the positive pulse  312  may decrease as shown in the wave form  310 - 2   FIG. 14B . Conversely, if force is applied via the upper moment-producing mechanism in a direction causing the wheel to slip in the opposite direction as the rotation direction of the crank shaft (e.g., direction  271  in  FIG. 10 ), the width of the effective window may increase, and correspondingly the period of the positive pulse may increase as shown in  FIG. 14C . Thus, the narrowing or widening of the effective window may be indicative of force being applied to the crank shaft via the upper moment-producing mechanism (e.g., positive or negative to the force applied by the lower moment-producing mechanism). Thus, the narrowing or widening of the effective window can be used to determine whether positive or negative work is being done by the upper body of the user. 
     When no appreciable force is being applied by the upper moment-producing mechanism (e.g., responsive to upper body work by the user such as when the user&#39;s arms are free riding on work produced by the user&#39;s lower body), the pair of code wheels may remain in the neutral alignment. The energy tracking system  200  may be configured to display an indication of zero or nominal work being performed by the user&#39;s upper body. The narrowing of the effective window may be indicative of additional force being applied by the upper moment-producing mechanism (e.g., additional to just allowing the arm links to free ride on the force applied by the lower moment-producing mechanism). In such instances, the energy tracking system  200  may be configured to display an indication of positive work being performed by the user&#39;s upper body. Depending on the amount of narrowing of the effective window, the energy tracking system  200  may be configured to determine and display an indication of the relative amount of additional work being performed by the user&#39;s upper body. A widening of the effective window may be indicative of resistive force being applied by the upper moment-producing mechanism (e.g., against the work being done by the lower moment-producing mechanism). In such instances, the energy tracking system  200  may be configured to display an indication of negative work being performed by the user&#39;s upper body and/or the amount of negative work based on the amount of narrowing of the effective window. In some examples, the energy tracking system  200  may be additionally or alternatively configured to display an instruction to modify movement of the upper body (e.g., to increase the speed or effort exerted by the upper body). The instruction may be displayed until the energy tracking system  200  detects zero or nominal work being performed by the user&#39;s upper body, or in some cases until the energy tracking system  200  detects positive work being performed by the user&#39;s upper body. 
     All relative and directional references (including: upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, side, above, below, front, middle, back, vertical, horizontal, and so forth) are given by way of example to aid the reader&#39;s understanding of the particular embodiments described herein. They should not be read to be requirements or limitations, particularly as to the position, orientation, or use unless specifically set forth in the claims. Connection references (e.g., attached, coupled, connected, joined, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other, unless specifically set forth in the claims. 
     Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall there between.