Patent Publication Number: US-2015065301-A1

Title: Method of Harvesting Energy from Exercise Equipment

Description:
RELATED APPLICATION 
     This application is a divisional application of co-pending U.S. Patent Application Ser. No. 13/282,046, filed 26 Oct. 2011, and entitled “Energy Harvester For Exercise Equipment,” which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/409,122, filed 2 Nov. 2010, both of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     The present disclosure relates generally to exercise equipment and, more specifically, pertains to strength training equipment that functions using one or more rotating members to independently power an electrical system that is part of the equipment. 
     Modern cardiovascular fitness equipment, such as treadmills and elliptical machines typically include a system of displaying exercise metrics and cardiovascular performance feedback to the user of the equipment. These systems have generally been called fitness feedback systems. This type of feedback is generally accomplished via an LED or LCD screen and provides the user real-time data as well as workout summary information. This type of feedback display system is standard and pervasive and has become a consumer expectation. 
     In a typical fitness gym layout, a section of the facility will be dedicated to cardiovascular equipment which is normally powered by an external source. The cardiovascular machines are generally arranged in parallel rows, facing televisions or may even have an integrated television screen. The equipment will generally plug into 120 VAC or 240 VAC outlets in the United States. In a facility that was purpose-built for fitness, an electrical infrastructure can be designed to make it convenient to plug in the cardiovascular equipment. In many gym facilities, the routing of electricity to the machines must be accomplished retroactively and can lead to costly and unsightly electrical infrastructure. 
     Though less common, some cardiovascular equipment such as certain stationary cycle designs, have successfully harnessed the energy input of the user (human-powered). This allows for a degree of freedom in the layout of the fitness gym because the equipment need not be in close proximity to an electrical outlet. Another advantage is that, especially in gyms with many machines, the human-powered machines can reduce facility electricity costs because the equipment does not draw power from the electric utility. 
     In contrast to the cardiovascular equipment described above, modern strength machines generally lack an analogous strength performance or fitness feedback display system. There is, however, lust as pronounced a consumer need as in the cardiovascular market to have the experience of performance feedback on strength training equipment. Users of strength equipment can utilize a feedback system to further improve their strength conditioning, and more precisely meet their strength training goals when compared with using equipment that does not have a feedback or reporting system. 
     Several factors have limited the adoption of such a fitness feedback display system in strength equipment. A significant factor is related to the practical problem of routing electricity to such a system. The equipment layout requirements in the weight/strength training areas of a fitness gym are substantially different than in the cardiovascular areas. Some key reasons driving these differences are summarized below: 
     1. Strength training areas do not use the same or even similar type of equipment as in the card to areas. There are different types of strength equipment for each muscle group of the human body. In addition, many gyms will provide two different manufacturers of strength equipment to better meet the varied preferences of their members. Each of these machines requires a different footprint of floor area, and has a different entry access requirement, e.g. side, front, rear for the user of the equipment. As a result, it is virtually impossible to design an electrical outlet infrastructure ahead of time to conveniently support the necessary mix of strength machines in the gym. 
     2. As gyms adopt new and improved equipment to satisfy their customers, a previous electrical infrastructure will be very unlikely to conveniently support the new equipment types, and is not a constraint that the gym manager wants to address. 
     3. Strength workout areas require users of the equipment to access the equipment from multiple directions. In addition, exercisers in a strength area often walk between machines to access other areas of the gym. As a result, running electrical cords to outlets on the floor pose a significant tripping hazard to the users and/or require a highly inconvenient equipment layout to avoid such hazards. 
     4. Strength equipment has a tendency to move on the floor over time. This is due to the necessary reaction forces taken through the floor mounts, which arise naturally through the normal use of equipment. These slight, but persistent movements, would be problematic for ensuring that the equipment does not become unplugged, or create an electrical hazard. 
     For these reasons, it is desirable for strength equipment with a performance feedback and display system to avoid the use of the gym facility electrical outlet and outlets. 
     Methods of eliminating the external power requirement for exercise feedback systems, i.e., strength performance feedback system, in strength equipment have not been widely adopted in modern equipment. Batteries have been used to a limited extent as a means of powering a fitness feedback system or a repetition counter. Batteries are problematic because the functionality of the fitness feedback system must be reduced such that the electronics require sufficiently low power to accommodate a reasonable battery life. An additional disadvantage of batteries is the required operating cost due to the need for the batteries to be replaced and/or recharged. 
     SUMMARY OF THE INVENTION 
     An embodiment of a method according to the present invention includes the step of generating a DC link voltage as a result of rotating a shaft of an electricity generator in two directions, wherein the generator shaft is rotated in both of the two directions as a result of a reciprocating motion of a user of exercise equipment. 
     According to one aspect of a method according to the present invention, the DC link voltage fluctuates during the reciprocating motion. 
     An embodiment of a method according to the present invention may include the step of generating a DC link voltage having a varying amplitude, which may be clamped, wherein the generating step is caused by a single repetition of a reciprocating motion of a user of exercise equipment, and wherein the varying amplitude has a plurality of maximum amplitudes. 
     According to yet another aspect of a method according to the present invention, the plurality of maximum amplitudes may be separated by a time period of lower amplitude. 
     According to yet another aspect of a method according to the present invention, the method may further include the step of converting the DC link voltage to a DC output voltage having a generally constant average value. The DC output voltage may be delivered to a feedback system associated with the exercise equipment. 
     An embodiment of a method according to the present invention relates to producing and utilizing electrical power in exercise equipment having a motion control arrangement moveable in repeating cycles of movement along a reciprocating motion path. This embodiment may include the steps of (a) converting kinetic energy created due to the reciprocating movement of the motion control arrangement of the exercise equipment to a variable electrical power output utilizing a generator assembly; and (b) converting the variable electrical power from the generator assembly into a DC link voltage. The variable electrical power output may be dependent upon a velocity of movement of the motion control arrangement along the reciprocating motion path. Additionally, the DC link voltage may be clamped if the velocity of movement of the motion control arrangement exceeds a threshold, and the DC link voltage may be converted into a DC output voltage having a generally constant average value. The DC output voltage may be delivered to a feedback system associated with the exercise equipment, wherein the feedback system may provide information related to use of the exercise equipment. 
     According to an aspect of a method according to the present invention, the generally constant average value of the DC output voltage may be independent from the instantaneous velocity of movement of the motion control arrangement. 
     According to another aspect of a method according to the present invention, the DC link voltage may be controlled such that the DC link voltage varies during each cycle or repetition of movement and has a generally constant average over one or more cycles of movement of the motion control arrangement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a perspective view of exercise equipment having an energy harvester system according to the present disclosure; 
         FIG. 1B  illustrates a rear view of the exercise equipment depicted in  FIG. 1A ; 
         FIG. 2A  illustrates a front view of a pulley generator assembly having an electrical generator, a high speed pulley, a coupling belt, and a low speed pulley that is used in the energy harvester system with the exercise equipment of  1 A; 
         FIG. 2B  illustrates a side view of the pulley generator assembly of  FIG. 2A ; 
         FIG. 2C  illustrates a view of the pulley generator assembly of  FIG. 2A  utilized with a low speed pulley connecting a weight stack cable or belt at a 90 degree angle; 
         FIG. 2D  illustrates a view of the pulley generator assembly of  FIG. 2A  utilized with a low speed pulley connecting a weight stack cable or belt at a 180 degree angle; 
         FIG. 2E  illustrates a view of a gear generator assembly connecting a weight stack cable or belt at a 90 degree angle; 
         FIG. 3A  illustrates a front view of an exemplary console for displaying exercise related information, having an integrated photovoltaic array as part of a system for the energy harvester system; 
         FIG. 3B  illustrates a side view of the console of  FIG. 3A ; 
         FIG. 4A  is a block diagram illustrating the components and interfaces of control electronics for the energy harvester system; 
         FIG. 4B  is a block diagram illustrating an alternative embodiment of  FIG. 4A  showing the photovoltaic energy harvester with an MPPT apparatus; 
         FIG. 4C  is a block diagram similar to  FIG. 4A  showing the control electronics provided with overvoltage protection; 
         FIG. 5A  illustrates corresponding three phase output voltages of the pulley generator assembly depicted in  FIG. 2A , when the pulleys of  FIG. 2A  are in motion at a constant speed; and, 
         FIG. 5B  illustrates the motion and corresponding electrical signals of the control electronics depicted in the block diagram of  FIG. 4A , when a user performs a repetition using the exercise equipment of  FIG. 1A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 
     The present disclosure relates to an energy harvester system for use with an exercise device. In particular, the energy harvester system produces output power which is suitable for an electronics load that can be used in strength training equipment, including, but not limited to, LCD and LED displays, microcontrollers, memory devices, sensors and wireless communication electronics. A typical use of electronics and strength exercise equipment is for a fitness feedback system. The energy harvester system relies on two modes of operation. In the first mode (kinetic harvesting mode), the energy harvester system converts kinetic energy due to the motion of the exercise equipment into electrical energy. In the second mode (the standby harvesting mode), the energy harvester system converts energy from the environment, such as the energy in the ambient-radiated light, into electrical energy. The two nodes may be employed by the energy harvester system at different times, or at the same time, and operate without requiring any battery or source of external power. 
     Referring now to the drawings,  FIGS. 1A and 1B  illustrate exercise equipment  10 , as exemplified by strength training equipment, provided with an independent power generating energy harvester system depicted as reference numeral  12  in  FIG. 4A . 
     The strength training equipment  10  is shown as a weight training machine having a seated portion  14  connected to an upright support portion  16 . The seated portion  14  includes a pair of laterally extending arms  18  equipped with a pair of inner pulleys  20  and a pair of outer pulleys. The upright support portion  16  includes a resistance arrangement embodied in a weight stack  24  formed by a plurality of we plates which are arranged to move up and down in various combination on guides as is well known in the exercise equipment art. A belt or cable  26  is guided around the outer pulleys  22 , along the arms  18 , around the inner pulleys  20  and down along the seated portion  14  into the upright support portion  16 . 
     The belt or cable  26  is then directed around an upper pulley  28  connected to a top end of an upright support portion  16 , a lower pulley  30  secured to the upper end of the weight stack  24 , and a pulley generator assembly  32  also joined to the top end of the upright support portion  16 . The pulley generator assembly  32  forms part of the energy harvester system  12  and takes the lace of a standard pulley which would normally be present in the weight training machine  10 . However, it would also be possible to dedicate a pulley as an “energy harvester pulley,” whereby the standard pulleys would remain, and an energy harvester would be added. The belt or cable  26  has outermost ends attached to a pair of gripping handles  34  so that the selected weight plates in weight stack  24  may be moved up and down to provide variable resistance when a user pulls and releases the handles  34 . The pulleys  20 ,  22 , weight stack  24 , belt or cable  26 , pulleys  28 ,  30 , and handles  34  all cooperate with the pulley generator assembly  32  to form a motion control arrangement configured to move in response to stimulus in out a user seated in the equipment  10 . One skilled in the art should appreciate that the motion control arrangement may otherwise be formed by different linkages, and resistance components used in combination with the pulley generator assembly  32 . 
     The strength training equipment  10  includes a fitness feedback system  36  for processing and providing information related to the user of the equipment  10 . The if feedback system  36  is typically comprised of suitable electronics, such as LCD or LED displays, sensors, data entry keyboard, touch screens, microcontrollers, and wireless communication devices for providing user identification, strength performance and workout summary data. In the example shown in  FIG. 1A , the fitness feedback system  36  includes an electronic display console  38  which is mounted to a front face of the upright portion  16  of the strength training equipment  10  so that it will be clearly visible and accessible to the user positioned on the seated portion  14 . The feedback system  36  could also be designed to provide and process information by means of speech input and output. 
     In one embodiment of the present disclosure, the energy harvester system  12  is incorporated in and responsive to motion of the exercise equipment  10  as a result of a stimulus supplied by the user. The energy harvester system  12  is generally comprised of a kinetic energy harvester for converting kinetic energy provided due to the motion of the equipment  10  into electrical energy, a photovoltaic energy harvester for converting photovoltaic energy provided by ambient light environment associated with the equipment  10  into electrical energy, and control electronics for controlling the kinetic and photovoltaic energy harvesters to provide electrical power to an electronics load of the fitness feedback system  36  exclusive of any battery or external power source. 
     Referring to  FIGS. 2A and 2B , the kinetic energy harvester includes the pulley generator assembly  32  having an electricity generator  40  and a belt and pulley system  42  which are mounted to a frame  44  that is secured to the upright portion  16  of the exercise equipment  10 . 
     The electricity generator  40  is preferably a three phase radial flux permanent magnet-type and consists of a round rotating member or rotor  46  that is rotatably mounted on frame  44 , and a stationary member or stator  48  that is fixed to the frame  44  by a mounting clamp  50 . The rotor  46  consists of a plurality of permanent magnets disposed on the outer circumference of the rotor  46  arranged such that the magnetic polarity of the magnets is alternating. The stator  48  consists of a hollow core of ferromagnetic material, comprising a circular inner diameter that captures the magnetic flux from the rotor magnets, and a plurality of electrically conducting coils  52  disposed in the slots of the core. The inner diameter of the stator  48  is larger than the outer diameter of the rotor  46 . The rotor  46  s supported by a bearing  54  that allows the rotor  46  to rotate freely about an axis of rotation, and limits the motion of the rotor  46  in the axial direction so that the rotor  46  remains substantially centered inside the stator  48  both radially and axially. An electrical connection or wire  56  extends between the stator  48  and the control electronics. 
     It is understood that other types of electricity generators may be used and fall within the scope and spirit of this disclosure. Other permanent magnet generator types include, but are not limited to, interior permanent magnet synchronous generators, rotors that employ flux focusing magnet arrays, and axial flux generators using single or double sided stators. These alternative permanent magnet generator topologies are applied in various industries and would be obvious to those skilled in the art. 
     The belt or pulley system  42  includes a bi-directional low speed belt pulley  58  with a first diameter, a bi-directional high speed belt pulley  60  with a second diameter less than the diameter of the low speed pulley  58 , and a belt  62  that couples the rotation of the pulleys  58 ,  60 . The pulleys  58 ,  60  are rotatably mounted to the frame  44 . The high speed belt pulley  60  is coupled to the rotor  46  of the electricity generator  40 , and generally shares the same high speed bearing  54 . The low speed belt pulley  58  is engaged with belt or cable  26  (as seen in.  FIGS. 2C and 2D ), and is coupled to a pulley such as  28  that rotates due to the motion of the exercise equipment  10  and can generally share the same low speed bearing system. The high speed pulley  60  rotates in proportion to the motion of the low speed pulley  58  in either direction of rotation. The ratio of the rotational speed of the high speed belt pulley  60 , ω ES  and the rotational speed of the low speed belt pulley  58  ω LS  is defined as the motion ratio, MR. The motion control ratio is determined by the diameters of the pulleys  58 ,  60 , D LS  and D HS , respectively, as defined in equation 2: 
         MR=ω   HS /ω L3    (1)
 
         MR=D   LS   /D   HS    (2)
 
     where in deriving equations (1) and (2), it has been assumed that the belt  62  does not slip on the pulleys  58 ,  60 . The selection of the motion ratio is a design parameter that can be optimized to the specific strength training equipment  10 . A primary goal of the motion ratio of the pulley system is to minimize the size and the cost of the electricity generator  40 . For a desired level of power generated, an electricity generator  40  that rotates at a higher speed requires proportionally less torque than would be required if the speed of the electricity generator rotation was equal to that of the low speed pulley  58 . The size of the electricity generator  40  is proportional to the torque (and not the power), thus it is generally advantageous to define the speed of rotation of the high speed pulley  60  to be much greater than the speed of the low speed pulley  58 . 
     There are limitations of the appropriate maximum value of the motion ratio. A significant factor is that the inertia of the energy harvester system  12 , as reflected by the motion of the strength training equipment  10 , increases quadratically as the motion ratio is increased. The inertia reflected by the motion of the strength machine appears as an apparatus mass to the user of the strength training equipment  10 . For motion ratios that are too high, the apparent mass will be perceived by the user and may become objectionable. This effect is one factor that can be used to determine the upper limit of the desired motion ratio. 
     A variety of configurations may be used to create a desired motion ratio without departing from the scope and spirit of this disclosure. Different belt types including, but not limited to, V-belts, knurled belts, and tread belts may be used in accomplishing the function of the belt and pulley system  42 . Furthermore, alternative methods of creating rotational motion ratios are well known and include, but are not limited to, teeth gears, friction gears, helical stages and planetary gears. 
     For example, the pulley generator assembly  32  can be suitably replaced by a gear generator assembly  64  illustrated in  FIG. 2E . Instead of employing pulleys  58 ,  60 , the gear generator assembly  64  utilizes a set of gears, namely a gear wheel  66  having a first diameter in meshing engagement with a pinion or gear wheel  68  having a second diameter less than the diameter of the gear wheel  66 . The gear wheels  66 ,  68  are rotatably mounted to the frame  44 . The pinion  68  is coupled to the rotor  46  of the electricity generator  40 , and the gear wheel  68  is engaged with belt or cable  26 . 
     Referring to  FIG. 4A , the photovoltaic energy harvester includes a photovoltaic array  70  that converts ambient light energy from commercial lighting and/or sunlight in the equipment environment into electrical energy, and a parallel electrical energy storage element.  72 , such as a capacitor  74 , connected at the output of the photovoltaic array  70 . The array  70  generally includes a plurality of photovoltaic cells, connected in series, parallel or a combination thereof, to produce a desired output power characteristic for the electronics load of the feedback system  36  or to the control electronics. The output voltage of the photovoltaic energy harvester operates at a load current that results in a substantially constant voltage when connected to an electronics load or standby electronics load. 
     The parallel electrical energy storage element  72  is able to provide power to the electronics load or standby load when the available output power from the photovoltaic array  70  is less than the power required by the electronics load of the feedback system  36 . When the power from the photovoltaic array  70  exceeds the power required by the electronics load, the parallel electrical energy storage element  72  can be charged resulting in an increase in stored energy. 
     In an alternative embodiment shown in  FIG. 4B , the photovoltaic energy harvester comprises a photovoltaic array  76  that converts ambient light energy into electrical energy, and a maximum power point tracker (MPPT)  78 . The output of the photovoltaic array  70  connects to the input of the maximum power point tracker  73 . The output voltage of the maximum power point tracker  78  connects to the electronics load, or standby electronics load and the parallel electrical energy storage element  72 . In this embodiment, the maximum power point tracker  78  is a DC/DC converter that can be controlled in such a way that the maximum power is harvested from the photovoltaic array  76  at any point in time. The same DC/DC converter can also be used in a mode that is used to control the amount of stored energy in the parallel electrical energy storage element  72 . Those who are skilled in the art will recognize that there are a variety or well known maximum power point control apparatus and techniques that can be applied to maximize energy capture from the photovoltaic array  76 . Those who are skilled in the art will also recognize that there are a variety of well known controlled apparatus and techniques that can be applied to manage the amount of energy stored in the photovoltaic energy storage element  66 , and these techniques fall within a scope and spirit of the present disclosure. 
     As seen in  FIGS. 1A and 1E , the photovoltaic energy harvester is a separate subassembly within the energy harvester system  12 . In this embodiment, the array  70  or  76  of the photovoltaic energy harvester is located on a top end of the support portion  16  of the strength training equipment  10  at a location and in an orientation such that the ambient-radiated light energy is substantially orthogonal to the photovoltaic cells that comprise the photovoltaic array  70  or  76 . The photovoltaic energy harvester has mechanical features to allow the orientation of the photovoltaic array  70  or  76  to be manually adjusted at the installed location in the fitness facility. The mechanical features allow the photovoltaic energy harvester to be rotated, tilted or otherwise positioned at an orientation that can maximize the capture of radiated light energy for a given location of the fitness equipment on which the harvester is installed. Advantages of this configuration include the ability to locate the photovoltaic array  70  or  76  precisely to capture the maximum amount of power from the ambient-radiated light and fitness environment. 
     In an alternative embodiment shown in  FIGS. 3A and 3B , the photovoltaic energy harvester array  70  or  76  is integrated into the fitness feedback display console  38  of the weight machine  10 . Advantages of this location are that the photovoltaic energy harvester may be packaged cost effectively into a singe fitness feedback display assembly. In this embodiment, the array  70  or  76  will be close to the standby electronics load to which it is connected, and also the display console  38  will generally be easily accessible for cleaning and occasional removal of any soil or debris build up on the photovoltaic array  70  or  76 . 
     A variety of photovoltaic array technologies may be used without departing from the scope and spirit of this disclosure. Examples of photovoltaic technologies include, but are not limited to, polycrystalline and monocrystiline silicone and variants thereof, and thin film technology such as amorphous silicone, cadmium telluride, CIGS, etc. 
     With further reference to  FIG. 4A , the control electronics generally includes a three phase power inverter  80 , a DC/DC converter  82 , a combiner circuit  84  and a harvester controller  86  that controls components  80 ,  82  and  84 . The AC terminals of the three phase power inverter  80  are connected to the three phase AC electricity generator  40  and can be considered the input terminals of the inverter  80 . The DC terminals of the three phase power inverter  80  can be considered as the output terminals, and are connected to a DC link, which consists of an electrical energy storage element  88 , such as a capacitor  90 . The purpose of the three phase power inverter  80  is to convert the variable voltage amplitude, variable frequency AC input power to a DC output power that has a non-zero, non-negative average value of voltage. For proper operation of the energy harvester system  12 , the DC output voltage of the inverter  80  can be controlled to be constant, but more generally may be varying as long as the condition of the non-zero, non-negative average voltage are met. 
     Furthermore, the purpose of the three phase power inverter  80  is to control the electricity generator  40  to operate efficiently, and therefore produce desired electrical output power without requiring excessive mechanical power to be derived from the low speed pulley  58 . The three phase inverter  80  consists of efficient power switching devices, such as MOSFETs, that are capable of being controlled by the harvester controller  86 . The three phase inverter  80  may also consist only of diodes to operate a standard rectifier. Those who are skilled in the art will recognize that there are a variety of well known generator and inverter control techniques that can be applied to optimize the efficiency and/or the energy capture from the electrical generator  40  as well as the overall efficiency and/or energy capture of the energy harvester system  12 . 
     The DC/DC converter  82  provides a constant regulated output voltage, i.e. the DC supply voltage, for use by the electronics load of the feedback system  36 . The input of the DC/DC converter  82  is connected to the DC link, the DC link generally operating at a higher voltage than the DC supply voltage and consisting of the capacitor  90  connected in parallel with the input of the DC/DC converter  82  and the output of the three phase inverter  80 . The DC/DC converter  82  is capable of providing constant DC supply voltage even in the presence of varying DC link voltage caused by fluctuations of the power output of the three phase inverter  80  as depicted a  FIG. 5B . The DC/DC converter  82  need only provide unidirectional power flow from the DC link  88  to the electronics load of the feedback system  36 . The DC/DC converter  82  will generally operate as a buck converter, but may also operate as a boost converter if the DC link voltage is operating at a voltage that is less than the DC supply voltage. Those who are skilled in the art will recognize that there are a variety of well known unidirectional DC/DC converter types that can be used to effectively and efficiently convert, a first generally varying DC input voltage to a second constant DC output voltage level. 
     The combiner circuit  84  is used to apply the best available power source to the electronics load of the fitness feedback system  36 . In one embodiment, the combiner circuit  84  consists of two diodes with a first diode anode connected to the output of the kinetic energy harvester and a second diode anode connected to the output of the photovoltaic energy harvester. The cathodes of each diode are connected together at the combiner circuit output voltage node. If power is available from the kinetic energy harvester, the combiner circuit  84  will transfer kinetic power to the electronics load in a kinetic harvesting mode. If power is not available from the kinetic energy harvester, the combiner circuit  84  will apply only the power available from the photovoltaic energy harvester in a photovoltaic or standby harvesting mode. Those who are skilled in the art will recognize that there are a variety of well known techniques for combining the power output of two time varying DC voltages, not limited to the technique described above. 
     In an alternative embodiment, a combiner circuit  84  is not used. Instead, the output of the kinetic energy harvester is directly connected to the electronics comprised off fitness feedback system  36  so that the control electronics  80 ,  82 ,  86 , control only the electrical power from the kinetic energy harvester. The output of the photovoltaic energy harvester is connected to provide power only to the electronics that comprise the user identification portion of the feedback system  36 , and/or other circuitry that may rewire power while energy not available from the kinetic energy harvester. 
     The control electronics regulate the instantaneous power that is developed by the kinetic energy harvester in the kinetic harvesting mode. During the use of strength exercise equipment  10 , the input motion of the user can generally be considered as creating reciprocating motions. Therefore, during a single repetition or a series of repetitions there will be periods of slow motion, periods of fast motion, as well as brief periods of zero motion. When the exercise motion is slow (i.e. low velocity) the control electronics will harvest an amount of power that is less than the average output power from the kinetic energy harvester. When the exercise motion is fast, the control electronics will harvest an amount of power that is greater than the average output power from the kinetic energy harvester. During the brief periods of zero motion that are typical, for example, between the repetitions that comprise a set of exercise, the control electronics will harvest zero power from the exercise equipment  10 . 
     Therefore, it can be observed that the operation of the kinetic energy harvester is such that the instantaneous power that is harvested from the exercises is generally not equal to (either more or less than) the output power supplied by the DC supply voltage of the kinetic energy harvester. 
     To observe the difference in instantaneous power at the output of the electricity generator  40  and the output power of the kinetic energy harvester (i.e. the DC supply voltage), the control electronics also includes the passive, electrical energy storage element  88 , such as the parallel connected capacitor  90 . When a total exercise motion is at or near a point of zero motion, the output power of the kinetic energy harvester will be substantially supplied by the electrical energy storage element  88 , and therefore the electrical energy storage element  88  will be partially discharged. When a total exercise motion is at or near a point of fast motion, the electrical energy storage element  88  will be discharged as required, and the output power of the kinetic energy harvester will be substantially supplied by the electricity generator  40 . 
     It should be reiterated that one intent of the present disclosure is to eliminate the need for any long term energy storage elements, such as rechargeable or non-rechargeable electrochemical batteries, as well as the need for any external power, so that the energy harvester system  12  is completely self-sufficient. 
     A variety of passive energy storage elements may be used without departing from the scope and spirit of this disclosure. For example, different types of capacitors including electrolytic, film, ultra capacitors and super capacitors can be used, as well as methods of inductive energy storage. 
     In one embodiment of the present disclosure, when a condition of very little motion or no motion persists, the control electronics detects this condition, and switches to the photovoltaic energy harvester or the standby harvesting mode where the average power of the electronics load is harvested from the photovoltaic array  70  or  76 . The transition to the standby harvesting mode generally does not occur until the energy stored in the energy storage element  88  has been substantially discharged sum that it can no longer supply power to the electronics load of the fitness feedback system  36 . The photovoltaic energy harvester converts power in the form of radiated light in the ambient environment, for example, the commercial lighting typically used in fitness facilities into DC electrical power. The photovoltaic energy harvester can also convert radiated, naturally appearing sunlight that may be present in the exercise equipment environment into DC electrical power. 
     In one embodiment of the present disclosure, the output power from the photovoltaic array  70 ,  76  can be used directly (i.e. without the need for active electronics to control power from the array) as the output DC supply voltage. The photovoltaic energy harvester may be configured such that the electrical power created by the photovoltaic array  70 ,  76  is available as a separate DC supply voltage, or connected to the same output DC supply voltage terminals used during the kinetic harvesting mode. 
     Thus, it should be appreciated that in the kinetic harvesting mode, the energy harvester system  12  produces a steady output voltage and output power in the presence of reciprocating user input motion that is caused by the use of strength training equipment  10 . Furthermore, when no input motion is present, the energy harvester system  12  is able to provide a reduced amount of power for the purposes of powering standby functions (the standby harvesting mode). An example of a powered standby function is a user identification system, via console  38 , such as passive or active RFID system, capacitive or resistive touch screen systems, and other forms of contact and non-contact user identification systems. In the standby harvesting mode, the average power required by the electronics load is supplied by the photovoltaic array  70  or  76  of the energy harvester system  12 . 
     It should be further understood that the control electronics is able to control the current in the electricity generator  40 . When motion is present, the electricity generator  40  produces an AC output voltage amplitude that is proportional to the velocity of the exercise motion. The control electronics controls the n current in the generator coils  52  so that the mechanical power available during the motion of the strength equipment  10  is converted to electrical power at the electrical terminals of the electrical generator  40 . The control electronics converts the AC output voltage from the generator  40  into an average, positive DC link output voltage. The DC link output voltage may be controlled to be constant or varying, and in the varying case, the voltage will always have a positive value and therefore retain an average DC value. This DC link output voltage is generally not suitable for use by the exercise equipment electronics or a fitness feedback system  36 . However, the DC/DC converter  82  of the control electronics also converts the variable DC link voltage into a constant DC supply voltage, typically 3.3 Vdc, 5 Vdc, or 12 Vdc (or any value that is less than the DC link operating voltage). The constant DC supply voltage is the output DC voltage that is suitable for use by the exercise equipment electronics such as the electronics, for the fitness feedback system  46 . 
     As represented in  FIG. 3A , the electrical power supplied from the kinetic voltage energy harvesters is used to independently, without any battery or external electricity, power the display console  38  of the feedback system  36  to identify, for example, via a display screen resistance being used, the number of sets and repetitions expended, and the amount of rest between the sets of exercise. Other data may be provided to or input for processing by the user. 
     During typical operation of strength training equipment  10 , the weight stack  24  and related pulleys  28 ,  30  are exposed to a typical range of linear and rotational velocities, respectively. For a given machine (e.g. a lateral pull down machine), this range of velocities depends on factors such as the exercise in of the person using the equipment  10 . The kinetic energy harvester is designed to reliably provide power to the fitness feedback system  36  over this typical velocity range, which corresponds to a range of different user styles and user workout intents. Though infrequent, under certain circumstances, the typical range of velocities can be exceeded substantially, which can be considered to be a high velocity condition. A high velocity condition may occur because of misuse, or in the event of an overly aggressive exercise movement, by the user. 
     Without a provision to handle a high velocity condition, damage to the circuits and components (e.g. the AC to DC inverter  80 ) that comprise kinetic energy harvester can occur. In order to prevent damage during these conditions, an overvoltage protection arrangement, as depicted in  FIG. 4C , is included in the kinetic energy harvester. 
     The overvoltage protection arrangement provides a means of reliably limiting voltage (AC voltage or DC link voltage, or both) during a high velocity condition. In one embodiment of the present disclosure, the overvoltage protection arrangement can be accomplished by means of a voltage clamp apparatus  94  disposed across the DC link  88  (i.e. a parallel connection). The clamp network consists of a fast switch with DC blocking capability, a surge-rated power resistor, and a means of controlling the switch to connect the resistor across the DC link  88  in response to a high velocity condition. When switched in, the resistor dissipates energy from the electricity generator  40  that would otherwise act to rapidly charge the DC link  88  capacitor and produce a damaging overvoltage condition. In an alternative embodiment, an AC switch  96  in is disposed between the AC terminals of the electricity generator  40  and the AC terminals of the AC to DC inverter  80  (i.e. connected in series). The switch  96  is opened in response to a high velocity condition in order to prevent excessive voltage build up in the DC link  88 . To those skilled in the art, it should be obvious that there are a variety of overvoltage protection methods, arrangements and topologies that may be applied while still falling within the scope and sod sit of this invention. These arrangement include, but are not limited to series or parallel connections of switches, resistors, and overvoltage protection devices (such as TVS clamp diodes, MOV, or zener diodes) located in the DC link  88  or located between the AC terminals of the electricity generator  40  and the AC terminals of the AC to DC inverter  80 . 
     Although the energy harvester system  12  has been described in use with the strength training equipment  10 , it should be understood that the energy harvester system  12  can also be adapted to other exercise equipment having motion control components. 
     Various alternatives are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention. 
     The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.