Abstract:
A method of extracting electrical energy from mechanical motion includes reusing an elastic portion of energy in a transducer by transferring the elastic portion of energy to another transducer. An apparatus for extracting electrical energy from mechanical motion includes at least two transducers coupled such that an elastic portion of energy in one transducer is transferable to the other transducer. The transducers are coupled by a member defining a waved surface, and each transducer defines a coupler in contact with the waved surface for movement following the waved surface. Couplers of two transducers are positioned such that they move out-of-phase relative to each other. The transducers are bound to a plate positioned between members such that the plate is deformed. The plate and members are configured such that relative rotation therebetween produces a wave that travels along the plate.

Description:
This application claims priority from U.S. provisional application No. 60/241,905, filed Oct. 20, 2000, and U.S. provisional application No. 60/251,696 filed Dec. 6, 2000. 
    
    
     BACKGROUND 
     The invention relates to generators for portable devices, and more particularly to piezoelectric generators. 
     Transducers such as piezoelectrics, electrostrictors, and magnetostrictors, can be used to convert one form of energy to another. Energy from a mechanical input, for example, a periodic force applied to a device containing a piezoelectric or electrostrictive material, can be converted to electric energy. Therefore, such materials provide a means for harvesting electric power from a mechanical input. 
     The equations for such a piezoelectric element can be written as: 
     
       
         
           ky−Nv=F  
         
       
     
     
       
         
           Ny+Cv=Q  
         
       
     
     where y is the deformation of the transducer element, F is the force applied, v is the voltage across the electrodes of the transducer, Q is the charge produced, k is the equivalent stiffness of the transducer taking into account any mechanical amplification or geometric factors, N is the piezoelectric constant scaled by appropriate geometric factors, and C is the capacitance of the device. 
     SUMMARY 
     A generator employs piezoelectric elements to convert mechanical power to electrical power. The generator includes one or more piezoelectric transducers that are actuated by a mechanical input. The resulting electrical power is stored or used to run an electronic device. The generator is hand or foot operated. 
     According to one aspect of the invention, a method of extracting electrical energy from mechanical motion includes reusing an elastic portion of energy in a transducer by transferring the elastic portion of energy to another transducer. 
     According to another aspect of the invention, an apparatus for extracting electrical energy from mechanical motion includes at least two transducers coupled such that an elastic portion of energy in one transducer is transferable to the other transducer. 
     Embodiments of this aspect of the invention may include one or more of the following features. 
     The transducers are coupled by a member defining a waved surface, for example, a sinusoidal surface, and each transducer defines a coupler in contact with the waved surface for movement following the waved surface. The coupler contacts the waved surface on a first side of the coupler. The member defines a second waved surface, and the coupler contacts the second waved surface on a second side of the coupler opposite the first side. Couplers of two transducers are positioned such that they move out-of-phase relative to each other. 
     In a particular embodiment, the transducers are bound to a plate. The plate is positioned between members such that the plate is deformed. The plate and members are configured such that relative rotation therebetween produces a wave that travels along the plate. 
    
    
     DESCRIPTION OF DRAWINGS 
     Other objects, features and advantages of the invention will be apparent from the following description, taken together with the drawings, in which: 
     FIG. 1 is a perspective view of a piezoelectric generator according to the invention; 
     FIG. 2 is an exploded view of the generator; 
     FIG. 3 is an exploded view of a crank handle of the generator; 
     FIGS. 4-4B are perspective, side and bottom views, respectively, of a wave plate of the generator; 
     FIG. 5 is a perspective view of a blade assembly of the generator; 
     FIG. 6 is a top view of a mounting plate of the blade assembly of FIG. 5; 
     FIG. 6A is a cross-sectional side view of the mounting plate of FIG. 6, taken along lines  6 A- 6 A; 
     FIG. 6B is a bottom perspective view of the mounting plate of FIG. 6; 
     FIG. 7 shows a blade of the blade assembly of FIG. 5; 
     FIG. 7A is an exploded view of the blade of FIG. 7; 
     FIG. 7B is an exploded view of a piezoelectric layer of the blade of FIG. 7; 
     FIGS. 8 and 8A are top and bottom perspective views, respectively, of a circuit board of the generator; 
     FIGS. 9 and 9A are circuit diagrams of the generator electronics; 
     FIGS. 10-10B are top and two side views, respectively, of the generator; 
     FIG. 11 is a side view of a transducer element coupled to a sinusoidal cam; 
     FIGS. 12 a - 12   l  show waveforms corresponding to the response of the system of FIG. 11; 
     FIG. 13 is a side view of two transducer elements coupled to the sinusoidal cam of FIG. 11; 
     FIGS. 14 a - 14   l  show waveforms corresponding to the response of the system of FIG. 13; 
     FIGS. 15 a - 15   l  show waveforms corresponding to the response of a system with three transducers; 
     FIGS. 16 a - 16   l  show waveforms corresponding to the response of a system with four transducers; 
     FIG. 17 a  is a perspective view of a piezoelectric generator according to the invention; 
     FIG. 17 b  is an exploded view of the generator; 
     FIG. 18 shows a crank handle and insert of the generator with the crank handle in an open position; 
     FIG. 19 is an exploded view of a case of the generator; 
     FIG. 20 a  is a perspective view of a wave plate and a blade assembly of the generator; 
     FIGS. 20 b  is an exploded view of the blade assembly; 
     FIGS. 20 c - 20   f  show various components of the blade assembly; 
     FIG. 21 is a perspective view of a case cover; 
     FIGS. 22 a  and  22   b  are perspective views of an alternative embodiment of a generator mechanism, a top plate of the mechanism shown removed for illustrative purposes in FIG. 22 b;    
     FIGS. 23 a  and  23   b  are perspective views of another alternative embodiment of a generator mechanism, with only one transducer element being shown in FIG. 23 a  for clarity; 
     FIG. 24 is a perspective view of an alternative embodiment of a piezoelectric generator according to the invention; 
     FIG. 25 is an exploded view of the piezoelectric generator of FIG. 24; 
     FIG. 26 is a further exploded view of the piezoelectric generator of FIG. 24; 
     FIG. 27 shows a blade assembly of the piezoelectric generator of FIG. 24; 
     FIG. 28 shows a piezoelectric bimorph of the blade assembly of FIG. 27; and 
     FIG. 29 shows a representation of an active element in sequential stages of longitudinal and rotational deflection. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a handheld piezoelectric generator  10  employing piezoelectric elements for harvesting electric power from a mechanical input includes a housing  12  and a crank handle  14 . Handle  14  is coupled to housing  12  for rotation relative thereto, and includes an arm  16  and a knob  18 . Referring also to FIG. 2, housing  12  includes a case  20  and a case cover  22  attached to case  20  with screws  24 . Located within housing  12  are a wave plate  30 , a piezoelectric blade assembly  32 , and a circuit board  34 . 
     When assembled, circuit board  34  rests on a top surface  36  of case cover  22  and is restrained within a peripheral wall  38  of the case cover. Circuit board  34  and blade assembly  32  are separated by a spacer  54  that is glued onto bottom surface  56  of blade assembly  32 . Handle  14  screws onto a shaft  40  that couples handle  14  and wave plate  30  such that rotating handle  14  causes wave plate  30  to rotate. Shaft  40  includes threaded regions  42 ,  44  and  46 , an enlarged, unthreaded region  58  between threaded regions  44  and  46 , and an unthreaded region  60  between threaded regions  42  and  44 . Threaded region  44  is received within a threaded hole  50  in wave plate  30 , and threaded region  46  passes through an unthreaded hole  53  in case  20  and is received within a threaded hole  52  in handle arm  16 . Region  58  spans across hole  53  in case  20 . 
     Blade assembly  32  includes a post  61  having an inner wall  62  defining a through bore  63 . When assembled, region  60  of shaft  40  is located within through bore  63  with ball bearings  64 ,  65  between shaft  40  and inner wall  62  of post  61 . Ball bearings  64 ,  65  are separated by a spacer  66 . Threaded region  42  of shaft  40  is received within a nut  48 , which holds shaft  40  in place. Between nut  48  and bearing  64  is a shim  67 , and between bearing  65  and a lower surface  67  of wave plate  30  are shims  68 . Case cover  22  defines four through holes  69   a  through which screws  24  pass, and case  20  defines four threaded holes  69   b  which receive screws  24 . 
     Referring to FIG. 3, handle arm  16  includes a mount  70  over which an elbow member  71  is placed. Mount  70  defines a threaded hole  72  which receives a screw  73  for securing elbow member  71  to mount  70  while permitting elbow member  71  to rotate relative to mount  70 . Mount  70  has a bulge  74  and elbow member  71  defines a through hole  75  with a ledge  76  that engages bulge  74  when handle  14  is turned clockwise. If one tries to turn handle  14  counterclockwise, elbow member  71  merely rotates about mount  70 . This limits possible damage to blade assembly  32 , which may occur if wave plate  30  is turned counterclockwise. Elbow member  71  includes a cylindrical extension  77  defining a threaded hole  78 . Knob  18  is received over extension  77  and secured to extension  77  with a screw  80 . 
     Referring to FIGS. 4-4B, wave plate  30  includes a base section  86  and a peripheral wall  88 . Peripheral wall  88  has a face  90  formed with a sinusoidal wave pattern  92 . Wave pattern  92  includes thirty-three waves peak-to-peak. The waves are offset relative to the wave plate diameter, i.e., the wave axis, X, is at an angle, β, of about 40° relative to plate diameter, D, such that the waves mate with blade tips  126 . Wave plate  30  is formed of aluminum with a Teflon impregnated hardcoat finish for low friction, thus increasing efficiency. 
     Referring to FIG. 5, blade assembly  32  includes a mounting plate  100  and twenty-four equally, circumferentially spaced blades  102  attached to plate  100  and bendable relative to plate  100 . Referring to FIGS. 6-6B, mounting plate  100  includes twenty-four angled slots  104 , each for receiving a blade  102 . Lower surface  56  of mounting plate  100  defines circumferential cut-outs  106 ,  108  to reduce the weight of the mounting plate. The cut-outs form circumferential lips  110 ,  112  and  114 . Inner wall  62  of post  61  has a middle region  66   a  of a first diameter for receiving spacer  66 , an outer regions  64   a ,  65   a  of larger diameter for receiving bearings  64 ,  65 , respectively. 
     The thirty-three sine waves in pattern  92  and the twenty-four blades  102  define eight different phases of contact between pattern  92  and blades  102 . At all times, three equally spaced blades  102 , 120° apart, are at the same phase and thus contacting pattern  92  at the same point in an individual sine wave. This stabilizes wave plate  30  and blade assembly  32  by providing three points of even contact between the wave plate and blade assembly, and spaces the timing of maximum deflection of the blades. Having multiple phases has the effect of providing low ripple torque. 
     Referring to FIGS. 7-7B, each blade  102  includes a steel shim  120  sandwiched between two piezoelectric layers  122   a ,  122   b . Each piezoelectric layer  122   a ,  122   b  includes a wafer or active fiber preform  123  between two uniform or interdigitated electrodes  125 . Each electrode  125  includes a circuit connector  127  with electric leads  128  for making connection to a circuit, described below. Shim  120  includes a bent extension member  124  with an outer surface  126  that rides along face  90  of wave plate  30 . Each blade  120  has a thickness of about 0.04 inches. Blades  102  are shaped and orientated on mounting plate  100  to pack tightly, and are triangular in shape to spread the stress evenly over substantially all of the piezoelectric material. The blade thickness and shape are designed to maximize electromechanical coupling between the tip deflection and electric output. Shim  120  includes tabs  140  which aid in positioning shims  120  on mounting plate  100 . 
     Referring to FIGS. 8,  8 A,  9  and  9 A, circuit board  34  has a top surface  150 , a bottom surface  152 , and  24  holes  154  through which circuit connectors  127  extend. On top surface  150  are located a switching regulator  156 , a transformer  158 , and capacitors  160   a ,  160   b . On bottom surface  152  are rectifier bridges  162   a-d  and capacitors and resistors  164 . 
     Electric leads  128  of circuit connectors  127  are connected to rectifier bridges  162   a-d  with each of the three blades  102  undergoing deformation in phase jointly connected to a side of one of the rectifier bridges. Rectifier bridges  162   a-d  are connected to capacitors  160   a ,  160   b . Capacitors and resistors  164  act as filtering components for switching regulator  156 . Switching regulator  156  maintains the voltage across capacitors  160   a ,  160   b  at voltage which maximizes power transfer from piezoelectrics  123 . For example, the peak-to-peak open circuit voltage of piezoelectrics  123  is 800 volts and capacitors  160   a ,  160   b  are maintained at about 200 volts. 
     The voltage level at which capacitors  160   a ,  160   b  are maintained is controlled by zener diode  170  and resistors  172 ,  174 . For example, for a 160 volt zener diode  170 , 1 meg resistor  172 , and 20K resistor  174 , when the voltage across capacitors  160   a ,  160   b  reaches about 200 volts, a transistor  176  is turned on, enabling switching regulator  156 . As switching regulator  156  switches on and off, current flows from capacitors  160   a ,  160   b  through the primary of transformer  158 . The secondary of transformer  158  outputs power at a low voltage (about 5 volts) for powering an external device. The circuit has a power conversion efficiency as high as about 80%. 
     Referring to FIGS. 10-10B, generator  10  is sized to fit in a users palm having an overall length, L 1 , of about 4.5 inches, and overall width, W 1 , of about 3 inches, and an overall height, H 1 , of about 2 inches. Housing  12  has an overall length, L 2 , of about 4.2 inches, and an overall height, H 2 , of about 1 inch. 
     Generator  10  can be an independent device with a power cord that plugs into a device being powered, or generator  10  can be an integral component of the device being powered. 
     Other embodiments are within the scope of the invention. 
     For example, rather than turning handle  14 , generator  10  can be actuated by a squeezing action or by pulling a string. Rather than a wave plate  30 , generator  10  can include a jagged toothed plate which cause free vibration of blades  102 . There can be a gear, cam, chain or belt drive between handle  14  and wave plate  30  such that wave plate  30  rotates, for example, four times for every turn of handle  14 . The piezoelectric element can have any number of geometries, for example, a single wafer, a stack, or a bimorph. The device can incorporate mechanical levering or amplification systems. 
     When energy is supplied to blades  102  by a mechanical input, a fraction of the energy is stored as electric energy, while the remainder is stored as mechanical (i.e. elastic) energy. For example, if the transducer element represented by equation (1) is deformed, while the transducer is open circuit (Q=0), the voltage on the piezoelectric material is: 
     
       
         
           v=−Ny/C  
         
       
     
     Total Work done on the system is:          E   in     =         1   2          ky   2       +       1   2          Cv   2                                
     Total mechanical energy stored in the system is:          E   mech     =       1   2          ky   2                              
     Total electrical energy stored in the system is:          E   elec     =       1   2          Cv   2                              
     The square root of the ratio between the stored electrical energy, and the total work done on the system is known as the coupling coefficient (K) of the transducer element, and is a function of the material properties and geometry of the element:          K   2     =         E   elec       E   in       =       N   2       kC   +     N   2                                  
     E elec  represents the maximum amount of electric energy which can be harvested from the system in each cycle. The remainder of the work that was done on the system (E mech ) cannot be harvested electrically as it is stored in the elastic deformation of the transducer element. As the transducer is returned to its undeformed position, the mechanical energy is returned to the mechanical input. In many cases, however, the mechanical input cannot efficiently absorb the returned energy. Thus this energy is wasted. Based on this analysis, the maximum conversion efficiency of such a device is generally limited by the coupling coefficient squared. Depending on the type of transducer material and the geometry, this efficiency can range between 0.1-0.4. 
     This fundamental limit on conversion efficiency can be circumventing by reusing the mechanical energy (E mech ) that would otherwise be wasted, for example, by transferring the energy to other transducer elements in the device. To explain this, referring to FIG. 11, we first consider a system  300  including one transducer element  301 , conceptually represented as a spring, coupled to a cam  302  having a sinusoidal groove  303 . As cam  302  is pushed in the x direction, transducer element  301  moves up and down in the y direction within groove  303 . A bearing  304  can be used such that the friction between cam  302  and transducer element  301  is negligible. Under these conditions, the system can be described by the transducer equations (1) and the following cam equations:        y   =     A                   sin        (     x   /   l     )                   F   x     =     F             y          x                                
     F is the force on transducer element  301  as calculated from equation (1), while F x  is the force applied to cam  302  by the mechanical input. 
     FIGS. 12 a - 12   l  show waveforms corresponding to the response of such a system. FIGS. 12 a - 12   f  show the response during open circuit operation. FIG. 12 a  shows the deformation of transducer element  301 . FIG. 12 b  shows the voltage generated by transducer element  301 . FIG. 12 c  shows the force applied to transducer element  301  by cam  302 . FIG. 12 d  shows the force that is applied to cam  302  by the mechanical input. FIG. 12 e  shows the power input to the system by the mechanical input (solid line) as well as the electrical power extracted (dashed line). In the open circuit case, no electrical energy is extracted from transducer element  301 . FIG. 12 f  shows the integral of the power in and power extracted. 
     FIGS. 12 g - 12   l  show corresponding waveforms obtained when transducer element  301  is connected to a harvesting circuit such as described in U.S. Ser. No. 09/584,881, entitled Electrical Power Extraction from Mechanical Disturbances, filed Jun. 1, 2000, hereby incorporated by reference herein in its entirety. For example, during each cycle, as the voltage of transducer element  301  reaches a maximum or a minimum, a switch (not shown) is turned on, and the electrical energy is extracted through an inductor (not shown). It can be seen from FIG. 12 k  that a significant fraction of the mechanical power that flows into the device flows back out during each cycle. The power flowing out would generally be wasted and is the main reason for the low conversion efficiency. 
     Referring to FIG. 13, to reuse the energy a second transducer element  305  coupled to cam  302  is used. By positioning the two elements such that they are 90 degrees out of phase with respect to each other, energy being returned by one element is transferred to the other through the cam and vice versa. As shown in FIG. 13, transducer element  301  is in an unstressed condition and transducer element  305  is stressed. As cam  302  moves in the direction of arrow, X, the stress on transducer element  305  decreases, and the stress on transducer element  301  increases. Thus, energy being returned by transducer element  305  is transferred to transducer element  301  through cam  302 . 
     This can be seen in the waveforms shown in FIG.  14 . FIGS. 14 a - 14   f  show the response during open circuit operation. The key feature is that because the two transducer elements  301 ,  305  are 90 degrees out of phase, the net force on the cam is zero. Thus, during open circuit operation (and in the absence of frictional losses), no energy is required to move the cam. As the cam moves, the energy required to move one transducer element is balanced by the mechanical energy being returned by the other transducer element. 
     FIGS. 14 g - 14   l  show the corresponding waveforms when the system is connected to a harvesting circuit. In this case, since electrical energy is being removed from the system, the net force on the cam is not zero (FIG. 14 j ). However, as can be seen from FIG. 14 k , no mechanical power flows out of the device. As seen from FIG. 14 l , the mechanical energy input in the device balances the electrical energy harvested. Thus the coupling coefficient of an energy harvesting system using this configuration can be as high as 1. That is 100% of the mechanical energy supplied to the device can be extracted as electrical energy. In the presence of loss mechanisms such as friction, and cam flexibility, the conversion efficiency will be lower that 100%. However, even in the presence of such losses the efficiency will be higher than the efficiency that would be achieved without reusing the mechanical elastic energy. 
     FIGS. 15 and 16 show similar waveforms for a system using three transducer elements and a system using four transducer elements, respectively. Three transducers at 60 and 120 degrees of phase will produce the desired cancellation. Four transducers at 90 degrees of phase between the transducer elements will produce the desired effect. 
     Referring to FIG. 17 a , a handheld piezoelectric generator  310 , which functions in the above described quasi-static mode in which non-converted mechanical energy is redistributed within the system, includes a housing  312  and a crank handle  314 . Handle  314  is coupled to housing  312  for rotation relative thereto, and includes an arm  316  and a finger grasp  318 . Referring also to FIG. 17 b , housing  312  includes a case  320  and a case cover  322  attached to case  320  with screws, not shown. Located within housing  312  are a wave plate  330 , a blade assembly  332 , and a circuit board  334 . 
     Referring to FIGS. 17 a  and  18 , handle arm  316  is mounted to an insert  370  by a pin  316   a  such that handle arm  316  can be moved from the closed position of FIG. 17 a  to the open, actuation position of FIG.  18 . Finger grasp  318  is coupled to handle arm  316  by a member  371  that is mounted to handle arm  316  by a pin  371   a  such that finger grasp  318  can be moved from the closed position of FIG. 17 a  to the open, actuation position of FIG.  18 . Finger grasp  318  is mounted to member  371  to rotate along arrow  318   a . Insert  370  is received within an opening  370   a  in case  320 . 
     Referring to FIGS. 18 and 19, insert  370  has an inner side  340  defining three cut-out regions  342 . Mounted within each cut-out region  342  is a gear  344 . Below gears  344  is a washer  346  for holding the gears in place. As shown in FIG. 19, case  320  includes a stationary internal gear ring  348  extending from an inner surface  350  of case  320 . Gears  344  extend through opening  370   a  in case  320  and mate with gear ring  348 . In operation, rotation of handle  314 , for example, in the clockwise direction, causes rotation of insert  370  and gears  344  in the clockwise direction. The mating of gears  344  with gear ring  348  causes gears  344  to rotate about their own axes in the counterclockwise direction at four times the speed of the clockwise rotation. Positioned around gear ring  348  and against inner surface  350  is a bearing  372 . 
     Referring to FIG. 20 a , wave plate  330  includes a gear  352  that is received between gears  344 . Clockwise rotation of gears  344  causes counterclockwise rotation of gear  352  and wave plate  330 . The relative number of gear teeth in gear ring  348 , gears  344 , and gear  352  is such that, for example, for each rotation of handle  314 , gear  352  rotates four times. Wave plate  330  includes a base section  386  and gear  352  is mounted to base section  386 . Base section  386  has a ledge  387  against which bearing  372  rests, and extending upward from a bottom surface  385  of wave plate  330  is a peripheral wall  388 . Peripheral wall  388  has an outer face  390  with a cut-out  391  bounded by upper and lower surfaces  391   a ,  391   b  each formed in a matching sinusoidal wave pattern  392 . Wave pattern  392  includes 10 waves peak-to-peak. 
     Referring also to FIG. 20 b - 20   e , blade assembly  332  includes a support  400  (FIG. 20 c ) and eight layers  402  of piezoelectric material mounted to support  400  and bendable relative to support  400  in the directions of arrow  404 . There are three distinct regions  406  per layer  402  (FIG. 20 d ), each with two piezoelectric elements  407 . Layers  402  are separated by shims  408  (FIG. 20 e ), and top layer  402   a  is separated from a bottom surface  385  (FIG. 20 a ) of wave plate  330  by a top shim  408   a . Extending from support  400  are six pins  410  that extend through holes  412  and  414  defined in layers  402  and shims  408 , respectively. A shaft  415  extends through holes  416 ,  417  and  418  defined in support  400 , layers  402 , and shims  408 , respectively, and through a hole  410  defined in wave plate  330 . A bearing (not shown) is located between shaft  415  and wave plate  330 . 
     Blade assembly  332  is coupled to wave plate  330  by six coupling mounts  430  (FIG. 20 f ). Each coupling mount  430  defines eight slots  432 , each slot  432  for receiving one layer  402 . Each coupling mount  430  has a bearing  434  mounted thereto (FIG. 20 a ) that rides within cut-out  391  in wave plate  330 . Bearings  434  provide a low friction coupling between wave plate  330  and blade assembly  332 . 
     Coupling mounts  430  define three pairs of coupling mounts  430   a ,  430   b ,  430   c . The spacing of the six coupling mounts stabilizes wave plate  330  and blade assembly  332 , and spaces the timing of maximum deflection of the blades. The two coupling mounts  430  within each pair are in phase and the different pairs are 120 degrees out of phase. As wave plate  330  rotates, blade assembly  332  remains rotationally stationary while bearings  434  ride up and down following sinusoidal patter  392 . The motion of bearings  434  causes each layer  402  to flex upward and downward, straining the piezoelectric elements. The ten sine waves in pattern  392  and the six contact points between blade assembly  332  and wave plate  330  define three different phases of contact between pattern  292  and blade assembly  332 , each phase corresponding to one of the pairs of coupling mounts  430   a ,  430   b ,  430   c . Bounding bearings  434  between upper and lower sinusoidal surfaces  391   a ,  391   b  provides for maximum deflection of layers  402  in both the upward and downward directions. 
     Referring to FIGS. 17 b  and  21 , circuit board  334  has a support  350  with three arms  352 . Case cover  322  has three sets of rails  354  defining slots  356  for receiving arms  352 . Mounted to circuit board  334  is circuitry  358  such as described above. 
     Generator  310  is sized to fit in a users palm having an overall length of about 4.5 inches, and overall width of about 3 inches, and an overall height of about 1.2 inches. Generator  310  can be an independent device with a power cord that plugs into a device being powered, or generator  310  can be an integral component of the device being powered. 
     Rather than turning the handle, the generator can be actuated by a squeezing action or by pulling a string. 
     Referring to FIG. 24, an alternative embodiment of a piezoelectric generator  501 , which functions in the above described quasi-static mode in which non-converted mechanical energy is redistributed within the system, can be embedded within the heel of a boot. The device  501  includes a top plate  502  and bottom plate  503  that are connected to one another through a pivot  504 . Stepping on the heel of the boot causes top plate  501  to be pressed towards bottom plate  503 . 
     Referring to FIG. 25, top plate  502  is connected to a helical screw  505  and compression springs  514 . Referring also to FIG. 26, as helical screw  505  is pushed down through a matching helical nut  506 , screw  505  forces the helical nut to rotate. The helical nut  506  is mated to a one-way clutch bearing  507 , which is in turn mated to an insert  508 , thus causing the insert to rotate along with the helical nut. Insert  508  has three holes  508   a  that receive pins  509  for holding gears  510 . As shown in FIG. 25, a mounting plate  511  includes a stationary internal gear ring  512  which mates with gears  510 . In operation, downward motion of top plate  502  causes counter-clockwise rotation of helical nut  506 , insert  508  and gears  510 . The mating of gears  510  with the internal gear  512  causes gears  510  to rotate about their own axes in clockwise rotation at, for example, 2.3 times the speed of the counter-clockwise rotation. 
     A wave plate  513  includes a gear  513   a  fixed to the bottom side of the wave plate. Gear  513   a  is received between gears  510  such that counter-clockwise rotation of gears  510  causes clockwise rotation of wave plate  513 . The relative number of gear teeth in internal gear  512 , gears  510 , and wave plate gear  513   a  is such that, for example, for each rotation of helical nut  506 , the wave plate rotates 3.5 times. Wave plate  513  includes a cut-out  514  having a nearly sinusoidal wave pattern. The wave pattern includes eleven waves peak-to-peak. 
     As the heel is lifted off the ground, the compression springs  514  causes the top plate and bottom plate to move apart again. As the helical nut  505  moves up, the one-way clutch bearing  507  allows the helical nut  506  to rotate freely (without causing rotation of the gears and wave plate). 
     Referring also to FIGS. 27 and 28, blade assemblies  515  include a support  516 , and eight layers of piezoelectric bimorphs  517 . The layered construction of each piezoelectric bimorph includes a shim  518  and a piezoelectric element  519  on each side of the shim. The bimorphs are clamped at the base through holes  520 . Each blade assembly  515  is coupled to the wave plate through a bearing  521  located in cut-out  514 . Bearings  521  provide a low friction coupling between wave plate  513  and the blade assembly  515 . 
     As wave plate  513  rotates, the bearings  521  move from side to side in the sinusoidal wave pattern  514 . The motion of the bearings causes each blade assembly to flex side to side. The four bearings  521  and the eleven sine waves in pattern  514  define four phases between pattern  514  and the blade assemblies  515 . The four blade assemblies move with 90 degrees of phase between them, to produce the desired redistribution of mechanical energy in the system. 
     FIGS. 22 a  and  22   b  show an alternative embodiment of the invention. A generator mechanism  450  includes a segmented piezoelectric disk  452  bonded to a circular plate  454 . Plate  454  is sandwiched between upper and lower plates  458   a ,  458   b . Located between plate  454  and upper plate  458   a  are a series of ball bearings or rollers  456   a , and between plate  454  and lower plate  458   b  are an additional series of ball bearings or rollers  456   b . Plate  454  is deformed under pressure from ball bearings  456   a ,  456   b  acting on the top and bottom surfaces  459 ,  460  of plate  454 . Ball bearings  456   a ,  456   b  are spaced to produce a wave along the circumference of the circular plate  454 . 
     In operation, upper and lower plates  458   a ,  458   b  are stationary and plate  454  is rotated. Rotation of plate  454  causes ball bearings  456   a ,  456   b  to rotate at half the speed of plate  454 . As plate  454  is rotated, the wave travels around the circumference of the plate. As a result, each segment of piezoelectric disk  452  experiences cyclic loads, resulting in a voltage generated by the piezoelectric. This signal is rectified to extract electrical energy from the system. Since the plate deformation corresponds to a wave with constant amplitude, the total mechanical energy in the system remains substantially unchanged. Instead, the locations with maximum mechanical energy rotate around the disk. This system is similar to the system of FIG. 17 a ; however, instead of several discrete transducer elements that operate with different phases, a continuous transducer element with segmented electrodes is used. As a result, the mechanical energy is reused. The mechanical energy present in deforming each transducer segment is transferred to the next transducer segment as the wave travels around disk  452 . As a result, all the energy being put into the system to rotate plate  454  is converted to electrically energy (minus the frictional losses or other dissipative effects). As a result, the effective coupling coefficient for the device is very high (close to 1). 
     In another embodiment, the energy stored in the form of mechanical energy in the transducer element is harvested by taking advantage of free vibrations of the element. Referring to FIGS. 23 a  and  23   b , a generator includes cantilevered bimorph transducer elements  472  mounted to a stationary member  473 , and a rotatable disk  474  for inducing a deflection at the tip  476  of each transducer element  472 . Disk  474  includes teeth  478  for deflecting transducer elements  472 . When a transducer element  472  clears the tip  480  of a tooth  478 , transducer element  472  is free to vibrate. As each transducer element  472  goes through multiple cycles during free vibration, an electronic circuit, such as described in U.S. Ser. No. 09/584,881, supra, coupled to the transducer element extracts electric power. 
     During the initial swing, as transducer element  472  reaches the peak of its deformation, a fraction of the energy is stored as electrical energy and the remainder is stored as mechanical energy. The electrical energy is harvested by the electric circuit connected to the transducer element. As transducer element  472  swings back towards it equilibrium position, the mechanical energy is converted to kinetic energy. As transducer element  472  continues to swing to the peak deformation in the opposite side, again a fraction of the energy is stored in electrical energy and the remainder is stored as mechanical energy. 
     Thus, during each cycle of the vibration, a portion of the transducer element&#39;s total energy can be harvested. The remainder of the energy is redistributed to electrical and mechanical energy in the next cycle. Since there are multiple opportunities to extract the energy from the transducer element, a larger portion of the total energy can be extracted, resulting in higher effective coupling coefficient, and higher efficiency than could be achieved by static loading of the transducer elements. 
     Referring to FIG. 29, a controlled interface generator includes a rotary or translating body  610 , which is acted on by an external force or torque, F, and exhibits rotation or translation resulting from this external force or torque. One or more active elements  612  intermittently make contact at single or multiple contact points with body  610 . Alternately, the active element can be acted on directly by the external force or torque and exhibit rotation or translation and the body can be fixed. 
     The active element  612  has two primary functions or behaviors. First, element  612  is configured to make controllable intermittent contact with body  610  at one or more contact points. This controllable motion into or out of contact with body  610  is the contact component of motion (COCM). The contact component of motion (COCM) enables active element  612  to make contact with body  610 , and is typically loosely aligned with normal to body  610  at the contact point(s). The second, called the Carry component of motion (CACM), enables active element  612  to translate with a motion parallel to the motion of body  610  at the contact point(s) due to the motion of body  610 . Thus, active element  612  has two components of motion at the contact point(s). 
     When contact is made between active element  612  and body  610 , there is a frictional or mechanical coupling between the active element and the body such that forces exist between the active element and the body causing the active element to move in the CACM direction, i.e., parallel to the motion of the body at the contact point. 
     The contact component of motion (COCM) of the active element can be controlled by a contact control mechanism, for example, electromagnetics, pneumatics, hydraulics, thermal actuation, or active materials such as magnetostrictive, piezoelectric, electrostrictive, etc. The contact control mechanism allows controllable intermittent contact between active element  612  and body  610 . This can be achieved through quasi-static motion or dynamic motion of the contact point. As an example of a dynamic motion, a piezoelectric element can be coupled to a vibration mode of the active element, which has motion at the contact point(s) in the COCM direction. If the piezoelectric element is excited at a frequency at or near the natural resonance frequency of that mode, the resonance of the active element will cause relatively large amplitude motion in the COCM direction. If the vibrating active element is positioned in proximity to the body  610 , intermittent contact will occur during some portion of the vibration cycle. The vibrating active element can also be pushed against the body by a soft support and intermittent contact will also occur since the soft support cannot maintain contact between the active element and the body at the contact points during all portions of the vibration cycle. As an example of quasi-static contact control means, the contact point on the active element can be moved into contact with the body through control signals, (voltage drive or a piezoelectric stack, or bimorph) at frequencies below the first mode of the active element which has motion components in the COCM direction of the contract points. 
     Electrical energy is generated from mechanical motion and forces in the CACM direction transmitted between active element  612  and body  610  during contact. A piezoelectric or piezomagnetic element (magnetostrictive, electrostrictive magnetic shape memory alloy etc) is coupled to (and configures in) the active element such that CACM direction forces and motion are coupled to the voltage and current or charge (collectively the electrical states of the system) at a set of generating element electrodes or electrical terminals. These electrodes are in turn connected to electronics for extraction of electrical power from the mechanical disturbances represented by the intermittent forcing of the active element by the above mentioned contact forces. The electronics can be a passive diode arrangement (passive energy harvesting) such as a full bridge or more complex electronics involving switches under active control (active energy harvesting), as discussed in U.S. Ser. No. 09/584,881, supra. 
     As a result of the above mentioned electromechanical coupling, the controlled intermittent contact (potentially periodic) to body  610  produces an intermittent (periodic) deformation of active element  612  and resulting oscillation of the voltage or current signal present at the generating element electrodes. This allows for electrical energy extraction from the active or passive extraction circuitry. 
     The CACM direction motion of the active element at the contact point can be dynamic or quasi-static depending on the implementation. As an example of a dynamic implementation, consider a coupling between the generating element and a mode of the active element that has large motion at the contact points in the CACM direction. Then periodic mechanical excitation of this mode by the controlled periodic (intermittent) contact forces in the CACM direction can result in forced excitation of the dynamic (resonant) modal oscillation of the active element and through its coupling, the generating element. Oscillatory forcing of the generating element and connected extraction electronics then enable electrical power extraction. 
     In the case that the CACM (coupled to the generator element) and the COCM (coupled to and controlled by the contact control means) both involve resonant modes of the active element it is 1) desirable to have these modes close to each other such that the contact forcing frequency will excite both the CACM mode and the COCM mode and 2) it is desirable to pick the contact forcing frequency such that the CACM and COCM are near 90 degrees out of phase (i.e., CACM is zero when COCM is max or min, etc). This is achieved by designing the active element such that the two modes are separated in natural frequency but close enough in frequency such that the phase transitions between the driving phase and the response signal phase for the given modes overlap. This allows for a driving frequency picked between the two modes (not coincident with either modal frequency exactly) to excite both modes with a net phase difference near 90 degrees. This will allow for an elliptical trajectory of the active element motion at the contact point derived from the CACM and COCM motion being out of phase. Contact is made over only a portion of the elliptical trajectory (when the COCM is largest and contact is made) and recovery of the active element occurs over the rest (than the COCM moves out of contact with the rotor/slider). 
     As a specific example of a resonant system consider the longitudinal/torsional configuration described in “Piezoelectric Ultrasonic Motor using Longitudinal-Torsional Composite Resonance Vibration” Ohnishi, Myohga, Uchikawa, Tamegai, and Inoue,  IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control , Vol 40, No 6, November 1993, hereby incorporated by reference herein in its entirety. FIG. 1 is a motor but if the Piezoelectric element labeled (L) excited the COCM and the Piezoelectric element labeled (T) acts as the generator element and is electrically connected to extraction electronics, then external forcing of the rotor and high frequency forcing of the COCM by Piezo(L) at the appropriate frequency will result in extracted power. 
     A quasi-static version of the system can use, for example, a burleigh inchworm motor with an expander as the generator element.