Abstract:
An exercise bicycle includes a flywheel, a drive train coupled to the flywheel, and pedals coupled to the drive train. A user of the exercise bicycle expends power by exerting force on the pedals to spin the flywheel. The exercise bicycle further includes a power meter. The power meter includes a friction pad comprising a flywheel contact surface in contact with the flywheel and a temperature sensor located within the friction pad. The temperature sensor measures the temperature of the flywheel contact surface. The power meter further includes an output meter coupled to the temperature sensor, the output meter converting a temperature change of the flywheel contact surface as measured by the temperature sensor into a calculated power expended by the user.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to exercise equipment and in particular to a method and apparatus for measuring power generated by a user on a spin type bicycle. 
     BACKGROUND OF THE INVENTION 
     The exercise industry has moved forward from using simple resistance techniques to create a resistive force to push against, to using heart rate monitors to determine actual physical exertion. Most recently, user power output on bicycles has gained acceptance as a more accurate determination of actual physical exertion. Power meters by several companies are available based on several approaches. Strain gauges that measure the forces applied to bicycle cranks attached to the pedals of a bicycle have been shown to be the most accurate, while strain gauges installed in the rear wheel hub measuring the forces applied to the wheel through the chain can also determine the power that a rider is exerting. Other techniques include measuring the chain vibration (although this has been shown to be less accurate). 
     Power measurement can significantly enhance ones ability to exercise in a controlled manner and can be used to determine direct physical improvements in both endurance and muscular power. When coupled with heart rate measurement, power and heart rate can be used to determine overall fitness improvements. 
     Unfortunately, the currently available power measurement techniques are only applicable to the traditional bicycle and have not been applied to the common exercise bicycle due to the significant cost of the power measuring devices which can exceed the cost of the exercise bike. CycleOp™ currently manufactures a commercially available exercise bike, commonly called a spin bike, although the cost of the bike is several thousand dollars due in large part to the power measurement device. 
     If a low cost technique could be found that provides repeatable power measurement, the significant advantages of current bicycle power measurement could be translated to exercise (spin) bikes in health clubs and private homes. This would allow more controlled exercise and would enable the user to determine actual improvements in fitness over time. Furthermore, current exercise bikes (spin bikes) are highly variable based on bike to bike comparisons, so that workouts are difficult to gauge from day to day. The implementation of a power meter would significantly improve the repeatability of the exercise experience on a day to day and even week to week basis. 
     SUMMARY OF THE INVENTION 
     An embodiment provides a power measuring technique that is accurate and inexpensive to implement on exercise (spin) bicycles. 
     In accordance with one embodiment, a power measuring device is provided that includes a friction pad in contact with a flywheel of an exercise bike. A temperature measuring device is imbedded in the friction pad without penetrating the friction pad through to the flywheel. 
     As the user increases the force of the friction pad on the flywheel through a mechanical means, friction between the friction pad and the spinning flywheel increases, resulting in increased temperature of the friction pad which is directly measured by the temperature measuring device. 
     In accordance with one embodiment, temperature measurements are converted to a power measurement providing a direct output to the user of a measurement of the power generated during exercise. 
     In one embodiment, a thermocouple wire is used as the temperature measuring device. 
     In accordance with another embodiment, a multilayer friction pad assembly based on varying materials with specific thermal conductivities is presented. 
     These and other features of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a spin bike with a flywheel and a power sensor that measures power based on a temperature sensor in contact with a friction pad in accordance with one embodiment; 
         FIG. 2  is an enlarged side view of the friction pad in contact with the flywheel of  FIG. 1 ; 
         FIG. 3  is a perspective view of the friction pad of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of the friction pad of  FIG. 3 ; and 
         FIG. 5  is a cross-sectional view of a friction pad in accordance with another embodiment. 
     
    
    
     In the following description, the same or similar elements are labeled with the same or similar reference numbers. 
     DESCRIPTION 
     In accordance with one embodiment, a method and apparatus for measuring power generated by a user on a spin type bike is presented. 
       FIG. 1  is a side view of a spin bike  100  including a flywheel  102  and a friction pad  104 . Friction pad  104  makes contact with flywheel  102 . Flywheel  102  is constructed of a thin cylindrical shaped metal disk with significant weight. 
     Friction pad  104  creates friction and increased work to a user when friction pad  104  is in contact with flywheel  102 . The user sits on a seat  106  that supports the weight of the user. The user also can stabilize the user&#39;s position and move on and off of seat  106  by holding handlebars  108 . Handlebars  108  are typically a bar with two areas at each end to position the user&#39;s hands. 
     Pedals  110  are small platforms connected to a drive train  112  of spin bike  100  that allows the user to push through the soles of the user&#39;s feet and translate the user&#39;s energy into forward rotational motion of flywheel  102 . Drive train  112  can include gears and a chain or pulleys and a belt. Drive train  112  allows the force applied through pedals  110  to be translated to flywheel  102 . 
     Flywheel  102  is typically of significant weight so that once flywheel  102  is in motion from the force of the user through pedals  110  and drive train  112 , little power is required by the user to continue motion of flywheel  102 . To increase the work required by the user and therefore increase the user&#39;s energy output, an adjusting knob  114  is connected to a shaft  115  connected to friction pad  104 . Adjusting knob  114  is turned to either increase the force of friction pad  104  on flywheel  102  or to decrease the force. 
     In one embodiment, friction pad  104  is outfitted with a temperature sensor  116  or similar device that can measure temperature changes in a flywheel contact surface  117  of friction pad  104  contacting flywheel  102 . Since flywheel contact surface  117  of friction pad  104  is in intimate, i.e., direct, contact with flywheel  102 , the friction between flywheel contact surface  117  of friction pad  104  and flywheel  102  will generate heat as flywheel  102  spins. 
     The heat that is generated is directly related to the force that the user applies to pedals  110  that are coupled to flywheel  102  through drive train  112  to maintain any given rotational speed of flywheel  102 . The higher the friction and the faster the rotational speed, the higher the force that is applied by the user to pedals  110 . 
     The higher friction and rotational speed translate into higher temperature of flywheel contact surface  117  of friction pad  104 . 
     One can directly determine the power output, Q, knowing an empirically derived power conversion factor, Pcf, and the temperature change as set forth in the following relationship (1):
 
 Q =( T  exercise− T  ambient)*Pcf
 
     Temperature, i.e., T exercise and T ambient, is measured in Celsius, the power conversion factor, Pcf, is given in Watts/Celsius. Note that the starting ambient temperature, T ambient, is simply the temperature of flywheel contact surface  117  of friction pad  104  prior to beginning exercise. Further, the current temperature, T exercise, is simply the temperature of flywheel contact surface  117  of friction pad  104  during exercise. 
     In one embodiment, the power conversion factor, Pcf, is empirically determined as follows. The starting ambient temperature, T ambient, of flywheel contact surface  117  of friction pad  104  is measured prior to spinning of flywheel  102 . A known power input, i.e., Q, is applied to drive train  112 , e.g., from a motor to spin flywheel  102 . After flywheel  102  reaches a constant temperature, the temperature, T exercise, is measured. The power conversion factor, Pcf, is then calculated from the following relationship (2):
 
Pcf= Q /( T  exercise− T  ambient).
 
     In one embodiment, the power is determined by temperature sensor  116 , for example a wire thermocouple that is directly connected to flywheel contact surface  117  of friction pad  104  in direct contact with flywheel  102  in  FIG. 1 . Flywheel  102  is put into motion through drive train  112  to pedals  110  by the user positioned on seat  106  holding handlebars  108 . 
     Temperature sensor  116  is slightly spaced apart from flywheel contact surface  117 , with a portion of friction pad  104  in between. Accordingly, a small temperature drop will occur between flywheel contact surface  117  and temperature sensor  116 . However, this temperature drop is negligible. Thus, the temperature measured by temperature sensor  116  is referred to herein as the temperature of flywheel contact surface  117 . 
     An output meter  118  is coupled to temperature sensor  116  that is directly coupled to flywheel contact surface  117  of friction pad  104  in contact with flywheel  102 . Prior to any exercise, output meter  118  registers the starting ambient temperature, i.e., T ambient, through temperature sensor  116 . The ambient temperature, sometimes called baseline temperature, is subtracted from all subsequent temperature measurements. 
     Upon initiation of exercise, the user, sometimes called rider, adjusts adjusting knob  114 , sometimes called a tension knob, by turning adjusting knob  114  to increase the force applied by friction pad  104  against flywheel  102 . Higher tensions result in higher forces required on pedals  110  by the user transferred through drive train  112  to flywheel  102 . These higher tensions result in higher friction between flywheel contact surface  117  of friction pad  104  and flywheel  102  leading to a higher temperature of flywheel contact surface  117  of friction pad  104 . 
     The higher temperature is measured by output meter  118  through temperature sensor  116  with the starting ambient temperature subtracted to determine the actual temperature increase, i.e., temperature change, that is the result of the force applied by the user to pedals  110 . The temperature change is then multiplied by the pre-determined power conversion factor, resulting in a value, i.e., calculated power, that is displayed to the user on output meter  118  mounted at handlebars  108 . 
     Decreasing the friction with adjusting knob  114  reduces the contact force between flywheel contact surface  117  of friction pad  104  and flywheel  102 . This, in turn, results in a lower temperature difference between ambient temperature and the measured exercise temperature, which results in a lower calculated power displayed at output meter  118 . 
     Since output meter  118  is a simple device that converts the measured temperature change to a calculated power reading that is displayed to the user, many different types of electronic display devices can be used to calculate the power and display the results. 
     The output meter  118  can also measure the user&#39;s heart rate and other cycling functions that are typically determined by a common bike computer, such as speed, cadence and room temperature. Furthermore, the output meter  118  can display power, heart rate and the other measurements above in numerical, graphical or tabular form. Generally, friction pad  104 , temperature sensor  116 , and output meter  118  form a power meter, sometimes called a power measuring device or power sensor. 
       FIG. 2  is an enlarged side view of friction pad  104  in contact with flywheel  102  of  FIG. 1 . In  FIG. 2 , more detail of friction pad  104  and connection of friction pad  104  to output meter  118 , sometimes called a power meter, via temperature sensor  116  is illustrated. The simple configuration illustrated in  FIG. 2  results in a metering system that can be readily implemented on a wide range of spin type exercise bikes, or other exercise equipment that uses friction based systems to apply resistive forces for the user to oppose. 
     An example of a temperature sensor that can be used as temperature sensor  116  is a type “K” thermocouple which has an error of +/−0.75% of readings above 0° C. which is sufficient for this application in one embodiment. A specific example of a type “K” thermocouple is Cole Parmer catalog #K-08439-62. 
     Since the temperature measurement is referenced to the starting ambient temperature, absolute temperature measurement is not critical. Only the temperature difference between the ambient and exercise temperatures is important. 
     More particularly, temperature sensor  116  is mounted in a position in contact with flywheel contact surface  117  of a friction pad surface material  120  of friction pad  104  that is in actual contact with flywheel  102 . Since friction pad  104  sometimes does not contact flywheel  102  over the entire flywheel contact surface  117 , temperature sensor  116 , for example a thermocouple wire, is placed in a location on flywheel contact surface  117  where flywheel contact surface  117  always contacts flywheel  102 . In one embodiment, temperature sensor  116  is located in the center of friction pad  104  as determined from the distance side to side and should be centered (as much as possible) in the center of flywheel  102  width. 
       FIG. 3  is a perspective view of friction pad  104  of  FIG. 2 . Referring now to  FIGS. 2 and 3  together, friction pad  104  includes two materials in one embodiment. More particularly, friction pad  104  includes friction pad surface material  120  that contacts flywheel  102  and a support material  122 . 
     Support material  122  acts as a structural support of friction pad surface material  120  to insure that the relative shape and position on flywheel  102  of friction pad surface material  120  does not change as a function of the tension that is applied via adjusting knob  114 . Since friction pad surface material  120  is typically a poor thermal conductor, support material  122  has little to no impact on the temperature changes in friction pad surface material  120 . This is also why temperature sensor  116  contacts friction pad surface material  120  in the area directly in contact with flywheel  102  without protruding through friction pad surface material  120  itself. Friction pad surface material  120  includes flywheel contact surface  117  as an outer surface in direct contact with flywheel  102 . 
       FIG. 4  is a cross-sectional view of friction pad  104  of  FIG. 3 . Friction pad  104  includes friction pad surface material  120 , support material  122  and temperature sensor  116 . Temperature sensor  116  extends through support material  122  to friction pad surface material  120 , e.g., through a hole in support material  120  as illustrated. Temperature sensor  116  is constructed in such a way that temperature sensor  116  directly contacts friction pad surface material  120  without protruding through friction pad surface material  120 . To insure that friction pad surface material  120  is not punctured, a countersunk hole  123  is formed in friction pad surface material  120  to insure that temperature sensor  116  is as close as possible to flywheel contact surface  117  of friction pad surface material  120 . 
       FIG. 5  is a cross-sectional view of a friction pad  104 A in accordance with another embodiment. Friction pad  104 A of  FIG. 5  is similar to friction pad  104  of  FIG. 4  and only the significant differences are discussed below. 
     In this embodiment, countersunk hole  123  is filled with a high thermally conductive material  124 . High thermally conductive material  124  allows the thermal energy, i.e., heat, generated between friction pad surface material  120  and flywheel  102  to be “collected” and more readily transmitted to temperature sensor  116 , sometimes called a thermal sensor. More particularly, high thermally conductive material  124  has a thermal conductivity greater than a thermal conductivity of friction pad surface material  120 . 
     Table 1 lists some friction pad surface materials  120  that are suitable for use on spin cycles and other exercise equipment. 
     
       
         
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Common Friction Pad Materials 
               
               
                 Material 
               
               
                   
               
             
             
               
                 Cotton 
               
               
                 Leather 
               
               
                 Cork 
               
               
                 Mineral Insulation 
               
               
                   
               
             
          
         
       
     
     The drawings and the forgoing description gave examples of the present invention. The scope of the present invention, however, is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of the invention is at least as broad as given by the following claims.