Patent Publication Number: US-7585258-B2

Title: Power sensing eddy current resistance unit for an exercise device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 11/387,416 filed Mar. 23, 2006, which claims the benefit of provisional patent application Ser. No. 60/751,776 filed Dec. 20, 2005, and provisional patent application Ser. No. 60/664,343 filed Mar. 23, 2005, the disclosures of which are hereby incorporated by reference. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to an exercise device or system that incorporates a rotating member for resisting input forces applied by a user, and more particularly to a resistance control arrangement for use in such an exercise device or system. 
     Many exercise devices utilize a rotating member that rotates in response to the application of input power by a user. In an exercise device of this type, it is common to provide resistance to rotation of the rotating member in order to provide resistance to the user. One example of an exercise device that incorporates a rotating member is a bicycle trainer, which includes a frame that supports the bicycle and a roller that engages the driven wheel of the bicycle. The rotating member may be in the form of a flywheel that is interconnected with the roller, and that rotates in response to rotation of the roller caused by rotation of the bicycle wheel. Another example of an exercise device that incorporates a rotating member is a stationary exercise cycle, which includes a frame having a seat and handlebars that support a user, in combination with a flywheel that is driven into rotation by operation of a pedal and chain assembly. 
     In a typical rotating member-type exercise device or system, a brake arrangement is used to resist rotation of the rotating member such that the rotating member presents a load in watts. The brake arrangement can be any type of brake, such as a magnetic or mechanical brake. In an electronic exerciser that incorporates a resistive load system, the resistors are modulated between ON and OFF states to brake the rotating member. The degree of resistance to rotation of the rotating member is typically controlled by the user, either manually or automatically. In a manual control system, the user selects a resistance setting and the brake arrangement is responsive to the user-selected setting to establish the resistance level. Changes in the level of resistance are accomplished during an exercise session by manually selecting desired settings at different times in the session. In an automatic system, the user selects a program and the resistance level is automatically varied during an exercise session to adjust resistance according to the program. 
     In the past, e.g. in a magnetic eddy current resistance unit, the position of one or more movable magnets relative to the rotating member is detected, and a lookup table is used to calculate resistance. In such a system, the various parameters are inputted into a controller, to calculate resistance based on magnet position. Systems of this type are functional but are highly inaccurate due to numerous variables that are involved in manufacture, assembly, engagement with the bicycle wheel (in the case of a bicycle trainer), and in operation of the power input system and the resistance unit. This type of system is “open”, in that the system is first calibrated to correlate the magnet position to power, and the controller then alters the positions of the magnet(s) to provide a desired braking force according to the lookup table to create the desired load. The numerous variables significantly limit the accuracy of a system of this type. 
     In the case of an electronic resistance unit, the controller functions to control the duty cycle of the resistors, which controls the load experienced by the user. The duty cycle, in turn, is calibrated such that a certain duty cycle is determined to correspond to a certain load. Again, this is an open system, in that there is no actual measurement of power. The measurement is done in a laboratory to create the lookup table, and when a product is sold the same lookup table is used on all products. Due to the numerous process variations and other variables as noted above, it has been found that systems of this type have accuracy limitations on the order of 15-20%. 
     It is an object of the present invention to provide a rotating member resistance unit that includes the ability to control a user&#39;s power level in response to the degree of resistance applied to the rotating member. It is another object of the present invention to enable a user to monitor his or her own power output, and to control the applied resistance to provide a desired power output. Yet another object of the present invention is to provide control of the braking force that resists rotation of a rotating member in an exercise device resistance unit, regardless of the form of the braking mechanism. A further object of the invention is to measure and control the resistance applied to a rotating member in a resistance unit, which is used in combination with a desired power curve that may either be pre-programmed or inputted by the user, to enable a user to accurately achieve a desired power output. 
     In accordance with one aspect, the present invention contemplates an exercise system including a user input arrangement, a rotatable member that rotates in response to an input force applied by a user on the user input arrangement, and a power sensing arrangement configured to sense power applied to the rotatable member due to the input force applied by the user. The exercise system further includes a variable resistance arrangement interconnected with the power sensing arrangement and with the user input arrangement. The resistance arrangement is operable to apply resistance to rotation of the rotatable input member, and is variable in response to the power sensing arrangement to vary the resistance applied to the rotatable input member. The variable resistance arrangement may be in the form of a brake arrangement that interacts with the rotatable member to resist rotation of the rotatable member, and to thereby resist the input force applied by the user. The variable resistance arrangement includes a controller for controlling the brake arrangement in response to the power sensing arrangement. The power sensing arrangement is in the form of a resistance measuring arrangement for measuring the degree of resistance to rotation of the rotating member applied by the brake arrangement, to determine the power applied by the user to rotate the rotatable member. 
     The power sensing arrangement may also be in the form of a rotatable power sensing member interposed between the user input arrangement and the rotatable member. The rotatable power sensing member is preferably rotatable about an axis of rotation that is concentric with an axis of rotation about which the rotatable member is rotatable. Representatively, the power sensing member may be in the form of a power sensing hub member to which the rotatable member is mounted. 
     The rotatable member may be the wheel of a bicycle, and the resistance arrangement may be associated with a bicycle trainer that supports the bicycle. In this embodiment, the bicycle wheel is engaged with a roller that is interconnected with the resistance arrangement. The power sensing arrangement is carried by the bicycle, and senses power applied by the user on the user input arrangement for imparting rotation to the bicycle wheel. The power sensing arrangement is in the form of a power sensing hub to which the bicycle wheel is mounted. In another embodiment, the power sensing arrangement is associated with the bicycle trainer and senses power applied by the bicycle wheel for imparting rotation to the roller. 
     The rotatable member may also be in the form of a flywheel associated with an exercise cycle, in which the resistance arrangement acts on the exercise cycle flywheel to resist rotation of the exercise cycle flywheel. The power sensing arrangement may be in the form of a power sensing hub to which the flywheel is mounted. The power sensing arrangement may also be in the form of a resistance measuring arrangement for measuring the degree of resistance to rotation of the flywheel applied by the brake arrangement, to determine the power applied by the user to rotate the flywheel. 
     The invention also contemplates a method of controlling operation of a resistance arrangement incorporated in an exercise device or system, in which the exercise device or system includes a rotatable member that rotates in response to a user-applied input force, substantially in accordance with the foregoing summary. The invention further contemplates a resistance arrangement, also in accordance with the foregoing summary. 
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the best mode presently contemplated of carrying out the invention. 
       In the drawings: 
         FIG. 1  is an isometric view of an exercise system, in the form of a bicycle secured to a bicycle trainer, incorporating en electronic resistance unit used in the closed loop resistance control of the present invention; 
         FIG. 2  is an isometric view of a first embodiment of a magnetic resistance unit for use in an exercise system, such as a bicycle trainer, for use in the closed loop resistance control of the present invention; 
         FIG. 3  is an enlarged partial isometric view of the components of the resistance unit of  FIG. 3 ; 
         FIG. 4  is an isometric view of a second embodiment of a magnetic resistance unit for use in an exercise system, such as a bicycle trainer, for use in the closed loop resistance control of the present invention; 
         FIG. 5  is a partial longitudinal section view of the resistance unit of  FIG. 5 ; 
         FIG. 6  is an elevation view of an exercise device, in the form of an exercise cycle, incorporating the closed loop resistance control of the present invention; 
         FIG. 7  is an isometric view of a flywheel incorporated in the exercise cycle of  FIG. 6 ; 
         FIG. 8  is a partial isometric view of the flywheel of  FIG. 7  and its interconnection with the frame of the exercise cycle of  FIG. 6 , showing a resistance application arrangement for use in one embodiment of a closed loop resistance control of the present invention used in a stand-alone exercise device; 
         FIG. 9  is an enlarged partial isometric view of the resistance application arrangement of  FIG. 8 ; 
         FIG. 10  is a schematic representation of the resistance application arrangement of  FIG. 9 ; 
         FIG. 11  is a partial section view through the hub of the flywheel as in  FIG. 7 , showing another embodiment of a closed loop resistance control of the present invention used in a stand-alone exercise device; 
         FIG. 12  is a schematic flow diagram illustrating operation of the closed loop resistance control of the present invention; and 
         FIG. 13  is a flow chart schematic diagram illustrating the electronic components of a closed loop resistance control in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention contemplates several embodiments of an exercise system or device. Each embodiment generally includes a rotating member, a resistance arrangement that either directly or indirectly resists rotation of the rotating member, a power input arrangement for causing rotation of the rotating member, a power sensing arrangement, and a resistance control that interacts with the resistance arrangement to set a resistance level based on the input power sensed by the power sensing arrangement. 
     In a first embodiment, an exercise system  100  includes a resistance unit  102  interconnected with a bicycle computer  104 , which is mounted to a bicycle  114 . Resistance unit  102  is held in position by a frame or support stand  110 , which removably mounts a rear wheel  112  of bicycle  114 , in a manner as is known. Bicycle trainers of this general type are available from Saris Cycling Group, Inc. of Madison, Wis. under its designation CycleOps. 
     Bicycle computer  104  and resistance unit  102  may be connected by a cable  118 , although it is understood that a wireless communication system may also be employed. A rear wheel speed sensor  106   a  and a cadence sensor  106   b  may be interconnected with bicycle computer  104  via a cable, for inputting bicycle operating characteristics to bicycle computer  104 , as is known. Rear wheel sensor  106   a  is located adjacent (or is coupled to) rear wheel  112  of bicycle  114 , for measuring the speed of revolution of rear wheel  112 . Cadence sensor  106   b  is located adjacent the bicycle pedal cranks, to measure the cadence of the user&#39;s pedal stroke. The front wheel  120  of bicycle  114  can be held in position by a riser block  122 . 
     Resistance unit  102  includes a roller  123  that engages rear wheel  112 . Resistance unit  102  provides variable resistance to rotation of rear wheel  112 , according to a desired level of effort for the user. The resistance may be varied according to a predetermined program, such as is shown and described in Henderson et al U.S. Pat. No. 6,450,922, the disclosure of which is hereby incorporated by reference. Alternatively, the resistance applied by resistance unit  102  may be manually controlled by a user through bicycle computer  104 , or the resistance applied by resistance unit  102  may be controlled through a resistance control separate from bicycle computer  104 . Representatively, resistance unit  102  may be an electronic, magnetic or fluid resistance unit, as is known in the art. 
     Rear wheel  112  incorporates a power sensing arrangement in its hub, shown at  122 . The power sensing hub  122  may be such as is shown and described in Ambrosina et al U.S. Pat. No. 6,418,797, incorporated herein by reference. Alternatively, power sensing hub  122  may be such as is shown and described in copending application Ser. No. 10/852,887 filed May 25, 2004, also incorporated herein by reference. Such power sensing hubs are available from Saris Cycling Group, Inc. of Madison, Wis. under the designation PowerTap. 
     In accordance with the invention, power sensing hub  122  is interconnected with resistance unit  102 , as representatively illustrated by dashed line  124 , which represents either a cable-type connection or a wireless connection. In either form, the connection  124  between power sensing hub  122  and resistance unit  102  communicates input torque or power signals from power sensing hub  122  to resistance unit  102 , to control the resistance applied to rear wheel  112 . The input power sensed by power sensing hub  122  is calculated by sensing the torque applied to hub  122  through the bicycle power input arrangement, i.e. the bicycle pedals, combined with information pertaining to the speed of rotation of the bicycle wheel  112 , as detected by wheel speed sensor  106   a . The sensed input torque or power information is communicated to resistance unit  102 . 
     The input torque or power information from power sensing hub  122  is received by the controller of resistance unit  102 , which employs the input torque or power information to improve the overall accuracy of the resistance applied to rear wheel  112  by resistance unit  102 . The “closed” system established by communication between power sensing hub  122  and resistance unit  102  accounts for losses in the coupling between resistance unit  102  and rear wheel  112 , to provide accurate control of resistance unit  102 . That is, in a system such as this, the resistance unit is pushed up against the tire of the bicycle by the user, using a tensioning mechanism to which the resistance unit is mounted. This introduces a significant variable, in that the pressure between the tire and the roller of the resistance unit can significantly affect resistance to rotation of the tire. By using a power sensing hub to obtain power information, the inaccuracies introduced by variables of this type are eliminated. 
       FIGS. 2 and 3  illustrate another application of the closed loop resistance control system of the present invention. In this embodiment, a magnetic resistance unit  200  is adapted for use in providing resistance to rotation of a bicycle wheel, such as  112  ( FIG. 1 ). In a manner similar to resistance unit  102 , resistance unit  200  is adapted for mounting to a trainer frame such as  110  via a yoke  202 , and includes a roller  204  for engagement with the bicycle driven wheel, such as  112 . Resistance unit  200  includes a flywheel  206 , which is adapted to be driven into rotation in response to rotation of roller  204  caused by rotation of bicycle wheel  112 . Representatively, roller  204  and flywheel  206  are mounted to a common shaft (the end of which is shown at  207 ), which is rotatably supported by bearings mounted to yoke  202 . Flywheel  206  includes an inner annular conductive member  208  formed of an electrically conductive material, which is secured to a side wall of flywheel  206  located inwardly of an outer peripheral ring  210 . 
     Magnetic resistance unit  200  includes a magnet assembly  212 , which cooperates with conductive member  208  to establish eddy currents that resist rotation of flywheel  206  when flywheel  206  is rotated. Magnet assembly  212  is mounted to yoke  202 , and includes a magnet carrier  214  to which one or more magnets are mounted so as to overlie conductive member  208 . Magnet carrier  214  is secured to the outer end of a beam  216 , the inner end of which is secured to a bracket  218 . One or more strain gauges  220  are mounted to beam  216 , and are adapted to sense strain experienced by beam  216  when flywheel  206  is rotated to establish eddy current resistance by the interaction between the magnets of magnet carrier  214  and conductive member  208 . Beam  216  may be formed with openings such as  222  and an area  224  of reduced thickness, to increase the tendency of the outer area of beam  216  to bend upon application of eddy current resistance caused by rotation of flywheel  206 , to thereby magnify the strain in the outer area of beam  216  and the accuracy of the readings of strain gauges  220 . 
     Beam mounting bracket  218  is slidably mounted for inward and outward movement to a stationary guide post  226 . A linear actuator, which may be in the form of a linear motor  228  having an output member  230 , is operable to move bracket  218 , and thereby beam  216  and magnet carrier  214 , inwardly and outwardly relative to conductive member  208 . Bracket  218  includes a tab or ear  232 , to which the end area of motor output member  230  is secured. Motor  228  is operated by electronic components carried by a circuit board  234 , to selectively move magnet carrier  214  relative to conductive member  208 . As is known, the proximity of the magnets of magnet carrier  214  relative to conductive member  208  determines the strength of the eddy current resistance when flywheel  206  is rotated. When the magnets of magnet carrier  214  are closer to conductive member  208 , the eddy current resistance is greater than when the magnets of magnet carrier  214  are positioned a greater distance from conductive member  208 . 
     In operation, the embodiment of the present invention illustrated in  FIGS. 2 and 3  functions as follows. When flywheel  206  is rotated by rotation of roller  204  caused by rotation of bicycle wheel  112 , the eddy currents established by the interaction between conductive member  208  and the magnets of magnet carrier  214  resist rotation of flywheel  206 . The forces experienced by magnet carrier  214  cause flexure strain in beam  216 , which is measured by strain gauges  222 . The strain experienced by beam  216  is proportional to the degree of eddy current resistance to rotation of flywheel  206 , which thus provides a measurement of the force required to rotate flywheel  206  since the degree of resistance to rotation of flywheel  206  is equal and opposite to the force required to rotate flywheel  206 . A conventional speed sensor (such as a reed switch and magnet sensor) may be used to determine the speed of rotation of flywheel  206 , which enables calculation of the power required to rotate flywheel  206  on a real time basis. With this information, the position of magnet carrier  214  can be controlled to provide a desired power value. In this system, an adjustment in the resistance is accomplished simply by adjusting the position of magnet carrier  214  relative to conductive member  208 . 
     While the drawings illustrate use of a linear motor to adjust the position of magnet carrier  214 , it is understood that other motive devices may be used to move magnet carrier  214 , including but not limited to piezo actuators, muscle wires (shape memory alloys that change in length when a voltage is applied), or nano-muscles. 
     In another embodiment of the present invention as illustrated in  FIGS. 4 and 5 , a magnetic resistance unit  300  is adapted for use in providing resistance to rotation of a bicycle wheel, such as  112  ( FIG. 1 ). In a manner similar to resistance unit  102 , resistance unit  300  is adapted for mounting to a trainer frame such as  110  via a yoke  302 , and includes a roller  304  for engagement with the bicycle driven wheel, such as  112 . Resistance unit  300  includes a flywheel  306 , which is adapted to be driven into rotation in response to rotation of roller  304  caused by rotation of bicycle wheel  112 . Representatively, roller  304  and flywheel  306  are mounted to a common shaft (the end of which is shown at  307 ), which is rotatably supported by bearings mounted to yoke  302 . Flywheel  306  includes an inner annular conductive member  308  formed of an electrically conductive material, which is secured to a side wall of flywheel  306  located inwardly of an outer peripheral ring  310 . 
     Magnetic resistance unit  300  includes a magnet assembly  312 , which cooperates with conductive member  308  to establish eddy currents that resist rotation of flywheel  306  when flywheel  306  is rotated. Magnet assembly  312  is mounted to yoke  302 , and includes a magnet carrier  314  to which one or more magnets are mounted so as to overlie conductive member  308 . Magnet carrier  314  is secured to the outer end of a beam  316 , the inner end of which is secured to a bracket, which is slidably mounted for inward and outward movement in a manner similar to that describe with respect to  FIGS. 2 and 3 . A linear actuator or the like is operable to move the bracket, and thereby beam  316  and magnet carrier  314 , inwardly and outwardly relative to conductive member  308 . As is known, the proximity of the magnets of magnet carrier  314  relative to conductive member  308  determines the strength of the eddy current resistance when flywheel  306  is rotated. When the magnets of magnet carrier  314  are closer to conductive member  308 , the eddy current resistance is greater than when the magnets of magnet carrier  314  are positioned a greater distance from conductive member  308 . 
     In this embodiment, a rotational torque sensor is used to determine the degree of resistance to rotation of flywheel  306  by magnet assembly  312 . As shown in  FIG. 5 , the rotational torque sensor may be in the form of a series of strain gauges  320  secured to shaft  307  at a reduced diameter area  322  of shaft  307 . Strain gauges  320  are connected to conventional power and communication electronic components (not shown), which are mounted to shaft  307  and rotate with shaft  307 . Stationary power and communication electronic components (not shown) are mounted to yoke  302 , and are inductively coupled to the rotating power and communication electronic components to provide power to strain gauges  320  and to communicate the strain signals from strain gauges  320 . 
     Shaft  307  is secured to roller  304  such that rotation of roller  304  causes rotation of shaft  307 , which in turn transfers such rotation to flywheel  306 . In the illustrated embodiment, a set screw  324  extends into a threaded passage  326  formed in roller  304 , and bears against a flat area  328  formed on shaft  307  so as to non-rotatably secure roller  304  and shaft  307  together. It is understood, however, that shaft  307  and roller  304  may be non-rotatably secured together in any other satisfactory manner. A pair of bearing assemblies  330  are secured to the end of yoke  302 , and are operable to rotatably mount shaft  307 , and thereby roller  304 , to the end of yoke  302 . 
     In operation, the embodiment of the present invention illustrated in  FIGS. 4 and 5  functions as follows. When flywheel  306  is rotated by rotation of roller  304  caused by rotation of bicycle wheel  112 , the eddy currents established by the interaction between conductive member  308  and the magnets of magnet carrier  314  resist rotation of flywheel  306 . The resistive forces experienced by the outer area of flywheel  306  cause torsional strain in shaft  307 , since shaft  307  is between roller  304  (which is the location at which the input power is applied) and flywheel  306  (which is the location at which the resistive load is applied). The reduced diameter area  322  of shaft  307 , at which torsion strain gauges  320  are mounted, provides a localized area at which torsional strain experienced by shaft  207  is magnified, to facilitate strain readings that are obtained by strain gauges  320 . The torsional strain in shaft  307  is measured by torsion strain gauges  320 , and is proportional to the degree of eddy current resistance to rotation of flywheel  306 , which thus provides a measurement of the force required to rotate flywheel  306  since the degree of resistance to rotation of flywheel  306  is equal and opposite to the force required to rotate flywheel  306 . A conventional speed sensor (such as a reed switch and magnet sensor) may be used to determine the speed of rotation of flywheel  306 , which enables calculation of the power required to rotate flywheel  306  on a real time basis. With this information, the position of magnet carrier  314  can be controlled to provide a desired power value. In this system, an adjustment in the resistance is accomplished simply by adjusting the position of magnet carrier  314  relative to conductive member  308 . 
     Another embodiment of the present invention is illustrated in  FIGS. 6-10 . In this embodiment, a cycling exerciser, shown generally at  420 , includes an actuator assembly  422  for braking and for resistance adjustment. In the illustrated embodiment, the actuator assembly  422  is a cable-type actuator assembly that allows for a single caliper actuation cable  424  to be actuated by either a brake cable  426  or a resistance adjustment cable  428  of the cycling exerciser  420 . In a manner as set forth in copending application Ser. No. 11/192,506 filed Jul. 29, 2005 and PCT application serial number PCT/US2005/027134 filed Jul. 29, 2005, the disclosures of which are hereby incorporated by reference, cable-type actuator assembly  22  can be used to actuate a resistance mechanism  430 , such as a caliper-type mechanism including brake pads  431 , or other resistance means on cycling exerciser  420 . 
     Cycling exerciser  420  includes a self-supporting frame  432 . Attached to frame  432  are an adjustable seat  434 , a flywheel or wheel  436  and handlebars  438 . Frame  432  can take a variety of configurations, and is shown in the illustrated embodiment as a rear wheel spin bike incorporating a “forkless frame.” Frame  432  is generally diamond-shaped and includes a neck  433 , an upper frame member  435 , a lower frame member  437 , an upright seat support  440  and a rear fork  442 . A front support member  444  and a rear support member  446  are connected to frame  432  and elevate frame  432  off the ground or other support surface, such that wheel  436  spins freely in the air. Support members  444 ,  446  may also include feet  448  to raise the frame  432  off the ground. A transport wheel  450  may also be included to assist a user in moving the cycling exerciser  420 . 
     Handlebars  438  are adjustably attached to the front of the frame  432  above neck  433 . Handlebars  438  include at least one right handle  454  and one left handle (not shown). Handlebars  438  may additionally include an alternative upright right handle  452  and upright left handle (not shown), which can be utilized when a rider desires a more upright riding position when exercising. 
     Cycling exerciser  420  includes a user power input, in the form of a conventional crank-type pedal assembly  451  rotatably mounted to frame  432  below seat  434 . Pedal assembly  451  includes a chain ring or sprocket  453 , which in turn drives a chain in a manner as is known. In a manner to be explained, the chain is engaged with a rear hub to which flywheel  436  is mounted, so as to impart rotation to flywheel  436  in response to the application of user input power to pedal assembly  451 . 
     At least one brake lever or hand brake  456  is connected to either the left handle or the right handle  454 . Hand brake  456  may be of the conventional type and is operably connected to brake cable  426  in a manner known in the art. Brake cable  426  is a sheath-type tension actuating cable having a conventional construction and operation. Sheath  458  and brake cable  426  extend downwardly from handlebars  438  in a direction towards the upper frame member  435  of the cycle frame  432 . 
     A resistance adjustment mechanism  470  is attached to the handlebars  438 . Resistance adjustment mechanism  470  can take a variety of configurations. In the illustrated embodiment, resistance adjustment mechanism  470  is in the form of an adjustment knob connected to a resistance adjustment controller  472 , which in turn is connected to the end of resistance adjustment cable  428 . Resistance controller  472  is selectively operable to selectively tension and release adjustment cable  428 , to control the resistance to rotation of flywheel  436  applied by resistance mechanism  430 . With this construction, the user is able to select certain resistance settings using resistance adjustment mechanism  470 , and resistance adjustment controller  472  is operable to tension or release cable  428  to adjust the resistance to rotation of flywheel  436  applied by resistance mechanism  428 . Alternatively, resistance adjustment mechanism  470  may be in the form of a computer-based selection mechanism, such as a computer touch screen or up/down button arrangement, with which the user interfaces to select a resistance level. In this embodiment, the resistance controller  472  is responsive to the resistance selection to selectively tension or release cable  428 . 
       FIG. 7  illustrates flywheel  436 , which incorporates a hub  480  that is rotatably supported by frame  432 . Hub  480  includes a sprocket  482  at one side, which is engaged with the chain so as to rotate hub  480 , and thereby flywheel  436 , in response to user operation of pedal assembly  451 . 
       FIGS. 8 and 9  illustrate an alternative resistance mechanism, shown generally at  530 , which may be used in place of the caliper-type resistance mechanism  430  as illustrated in  FIG. 6 . Resistance mechanism  530  includes a brake member  532 , which has a generally V-shaped or U-shaped cross section and is configured to bear on the outer edge of flywheel  436 , to provide resistance to rotation of flywheel  436 . Brake member  532  defines an inner surface to which a brake pad  534  is mounted, to provide a cushion between brake member  532  and flywheel  436 . Brake member  532  further includes a pair of mounting ears  536 , between which an actuating arm  538  is located. Arm  538  is pivotably mounted between ears  536  via a pivot connection  540 . The inner end of arm  538  is pivotably mounted to a mounting member  542  via a pivot connection  544 . Mounting member  542  includes a slot  546  within which the inner end of actuating arm  538  is located. Slot  546  is in communication with the interior of lower frame member  437 . With this construction, an inner arm  548  ( FIG. 10 ) secured to the inner end of actuating arm  538  is connected to the end of actuating cable  424 , to selectively apply or release pressure on the edge of flywheel  436  via brake member  532 . 
     One or more strain gauges  550  are mounted to actuating arm  538  in order to measure the strain in actuating arm  538 , which is a reaction to the pressure applied to flywheel  436  by brake member  532 . That is, there is a direct correspondence between the strain in actuating arm  538  and the resistive force applied by brake member  532  on flywheel  436 . 
     In operation, the embodiment of the present invention as illustrated in  FIGS. 6-10  functions as follows. When flywheel  436  is rotated by operation of pedal assembly  451 , the force applied to the edge of flywheel  436  by brake member  532  resists rotation of flywheel  436 . The reactive force in actuating arm  538  is measured by the strain gauges  550 , and is proportional to the degree of resistance to rotation of flywheel  436 , which thus provides a measurement of the force required to rotate flywheel  436  since the degree of resistance to rotation of flywheel  436  is equal and opposite to the force required to rotate flywheel  436 . A conventional speed sensor (such as a reed switch and magnet sensor) may be used to determine the speed of rotation of flywheel  436 , which enables calculation of the power required to rotate flywheel  436  on a real time basis. With this information, the tension on actuating cable  424  can be controlled to provide a desired power value. In this system, an adjustment in the resistance is accomplished simply by adjusting the tension of actuating cable  424 , which controls the pressure applied by brake member  532  on the edge of flywheel  436 . 
     Another embodiment of the present invention is illustrated in  FIG. 11 . In this embodiment, the power measuring or sensing arrangement is in the form of a power sensing hub  630  that functions to rotatably mount flywheel  436  of cycling exerciser  420  to frame  432 . Power sensing hub  630  includes a sprocket  632  at one side, which is engaged with the chain so as to rotate hub  630 , and thereby flywheel  436 , in response to user operation of pedal assembly  51 . 
     In the illustrated embodiment, power sensing hub  630  includes an inner torque tube  634  that is secured at one end to sprocket  632 . Flywheel  436  includes an inner hub area  636 , which defines a transverse passage through which inner torque tube  634  extends. Sprocket  632  is mounted to an adapter  638 . An axle or spindle  640  extends transversely through adapter  638  and inner torque tube  634 , and functions to mount flywheel  436  to frame  432 , in a manner as is known. A pair of bearings  642  rotatably support inner torque tube  634  on axle or spindle  640 . Inner torque tube  636  defines an annular outer flange  644  at the end opposite sprocket  632 , which is mounted via screws  646  to inner hub area  636  of flywheel  436 . A bearing  648  is located between inner torque tube  634  and the opposite end of inner hub area  636 , to accommodate relative rotational movement between inner torque tube  634  and inner hub area  636 . 
     A series of strain gauges  650  are mounted to inner torque tube  634 , and sense the strain in inner torque tube  634  during the transfer of rotary power from sprocket  632  to flywheel  436 . In a manner as is known, the strain experienced by torque tube  634  corresponds to torque applied to torque tube  634  by the user through pedal assembly  451  and the chain, which is used in combination with the speed of rotation of flywheel  436  to calculate input power. 
     Power sensing hub  630  may have a construction as shown and described in U.S. Pat. No. 6,418,797 entitled Apparatus and Method for Sensing Power in a Bicycle, the disclosure of which is hereby incorporated by reference. Bicycle power sensing hubs of this type are available from Saris Cycling Group, Inc. of Madison, Wis. under the designation PowerTap. 
     In operation, the embodiment of the present invention as illustrated in  FIG. 11  functions as follows. When flywheel  436  is rotated by operation of pedal assembly  451 , the force applied to the edge of flywheel  436  by brake member  532  resists rotation of flywheel  436 . The reactive force experienced by flywheel  436  is measured by the strain gauges  650 , and is proportional to the degree of resistance to rotation of flywheel  436 , which thus provides a measurement of the force required to rotate flywheel  436  since the degree of resistance to rotation of flywheel  436  is equal and opposite to the force required to rotate flywheel  436 . The strain signals are communicated wirelessly to a CPU or other controller. A conventional speed sensor (such as a reed switch and magnet sensor) may be used to determine the speed of rotation of flywheel  436 , which enables calculation of the power required to rotate flywheel  436  on a real time basis. With this information, the tension on actuating cable  424  can be controlled to provide a desired power value. In this system, an adjustment in the resistance is accomplished simply by adjusting the tension of actuating cable  424 , which controls the pressure applied by brake member  532  on the edge of flywheel  436 . 
     While the power sensing feature of the present invention has been shown and described in connection with sensing power applied to rotating flywheel in a cycling exerciser or bicycle trainer, it is understood that the power sensing feature of the invention may be used in connection with a rotating member in any type of exercise device. For example, and without limitation, the power sensing function may be incorporated in an intermediate rotating member between the user power input and the resistance-providing member, e.g. the flywheel or other rotating member which supplies resistance or to which resistance is applied. In addition, while the invention has been shown and described in connection with resistance being applied to a flywheel or rotating bicycle wheel, it is understood that resistance to the user power input may be provided in any part of the drive system that is driven in response to the input of power by the user. Resistance may be applied by any resistive arrangement that acts on and/or resists rotation of a rotating member, or may be applied by a fluid, magnetic, wind or other known type of resistance-providing arrangement that is capable of providing a braking forced on a rotating member. The power sensing function may be provided in any type of exercise device that has a rotating member that is rotated in response to the application of input power by a user, e.g. a rowing exerciser, a swim stroke exerciser, a stair climbing exerciser, an elliptical trainer, etc. The input power may be rotary input power, as in the pedal-type input as shown and described, or a linear power input, or any other type of user-operated input by which a user applies input power to an exercise device. The power sensing function may be accomplished any satisfactory type of power sensing arrangement. The power sensing function may be accomplished at a rotating member that is driven by the user power input, e.g. in the bottom bracket of a pedal-type input wherein the user imparts rotation to a rotary power sensing device that is rotatably supported on the exerciser frame (a “bottom bracket” power sensing application). This is in contrast to prior art power sensing devices that sense input power using the pedal crank arms of a pedal-type input. 
     In an application of the closed loop system of the present invention, the resistive force on the rotating member can then be adjusted so that, if the console or controller is set for a predetermined power value, e.g. 300 watts, the controller is operated to operate the resistance mechanism to apply roughly 300 watts, e.g. according to a lookup table. The force on the resistance mechanism is then continuously measured, and the resistance mechanism is continuously adjusted to attain the exact desired wattage. 
     With the present invention, the actual applied resistance is measured and the measurement is incorporated into the control loop. Typically, the resistance measurement may be used in combination with a lookup table that provides a rough approximation of the desired resistance, and power is then measured as described above. The power measurement is then used to provide an error signal to determine the difference between the desired setting and the actual setting, and the controller then adjusts resistance accordingly. 
     In practice, the system of the invention provides a closed loop, real time system that continually senses and adjusts resistance to provide the desired power output. In this system, the accuracy is limited only by the accuracy of the measurement device. The user is able to adjust a power setting, and the resistance control, in whatever form, adjusts resistance continuously during operation to accommodate changing parameters, e.g. temperature or other variables. For example, if the user establishes a power setting of 300 watts on the console of the exercise device, the resistance mechanism will adjust to provide the desired constant 300 watt setting (to the capability of the measurement device). In the event conditions change, e.g. speed of rotation of the wheel, temperature, cadence, etc., the resistance mechanism continuously compensates and controls the unit to 300 watts. The same holds true for a variable power setting, in that the control continuously adjusts resistance to provide the desired variable power setting. 
     In a basic embodiment of the present invention, the resistance unit is pre-programmed to provide a desired power curve during operation. The resistance is measured as above, and the resistive force is controlled to provide the desired power curve during operation of the resistance unit. This option gives the end user the ability to later upgrade to a system that includes a user input or feedback arrangement. Also, a system such as this enables a user to program a desired power curve into the resistance unit, and then transport the device with the resistance unit to another location (e.g. to a race) for use in pre-race warm up, leaving the console at home. The user can change the power curve to any provide any desired power curve. 
     Another version may include a display with feedback. Various pre-programmed courses and fitness settings are programmed into the controller. Power (in watts) is displayed via a calibrated watts table or measured as described above. 
     Yet another version may include a WIFI antenna that interacts live with the user&#39;s computer network. The wireless option can be used in a home setting, or in a club setting to allow several users to interact with each other. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.