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Closed-loop power dissipation control for cardio-fitness equipment

Closed-loop power dissipation control for cardio-fitness equipment description/claims

This application claims priority to U.S. Provisional Patent Application No. 60/817,657, filed Jun. 28, 2006, and entitled “Closed-Loop Power Dissipation Control For Cardio-Fitness Equipment,” by John Fisher et al., and is hereby incorporated herein by reference.

This application is related to and cross-references U.S. application Ser. No. 11/433,778, filed May 11, 2006, and entitled “Cardio-Fitness Station With Virtual-Reality Capability,” by John Fisher et al., the contents of which application are hereby incorporated by reference.

1. Field of Invention

This invention relates to stationary exercise equipment and power dissipation control used by such equipment. More specifically, the invention relates to closed-loop power dissipation control for cardio-fitness equipment.

A major sports equipment industry has developed over the last decades round providing fitness equipment for home and indoors exercises based on so-called stationary exercise equipments, which can be but are not limited to stationary exercise bicycles, in which the action of pedaling is used to dissipate power by the person (rider) exercising. The resistance to pedal rotation is allowed for power dissipation, which is an integral part of the exercise. State of the art exercise equipments often feature heart-rate monitoring, entertainment, and a varying degree of pedaling resistance, which is used to control the amount of power the rider dissipates while pedaling.

On many stationary exercise equipments, the power necessary to pedal can be set directly to a predetermined level by the rider, yet on some, the power can be set in terms of real-world parameters, such as slope of a hill, to give the rider the impression that he or she is riding a real bicycle up a hill. Cardio-fitness stations, the most advanced exercise tools, offer virtual reality capabilities in which the rider interacts with a virtual environment shown on a video monitor and experiences a virtual bicycle ride through a predetermined landscape with hills, valleys, and road obstacles. Such feature has given rise to competition between riders exercising on two cardio-fitness stations, i.e., the riders can operate separate cardio-fitness stations to ride jointly in a race through the same predetermined virtual landscape. Furthermore, with the advance of exercise equipments, many riders have increased their demands for accurate monitoring of their performance and performance history.

A fact not immediately apparent to an average rider of stationary equipments is that their performance, i.e., the resistance to pedal these cardio-fitness stations under a specified setting or virtual terrain slope, is not always consistent among the stations. This is noticeable when one rider is racing another rider riding another unit and the other rider may have an easier time making it to the finish line. Furthermore, for a given constant cadence and same resistance setting, stationary equipment will deliver pedal resistance that depends on the history of the cadence and torque in a practically unpredictable manner due to the cumulative effect of machine temperature and wear.

All these problems arise from the fact that pedal-rotation-resistance mechanism implemented in present-day exercise equipments is not intended for such precise setting and repeatability of pedal torque, which has been the choice of the manufacturers for cost reasons and the fact that it was not required by the riders. The source of the drift and unit-to-unit variation in the relationship between the setting of pedal resistance and the actual value of resistance experienced by the rider comes from the drift in the performance of mechanical and electrical elements, for non-limiting examples, manufacturing tolerance, mechanical wear, and heating effects on the equipment. Such variation ultimately yields unsatisfactory accuracy of power dissipation and an incorrect assessment of total amount of work that rider has performed during his or her exercise session, which makes it next to impossible to execute a fair race between riders on two separate cardio-fitness stations.

There are several ways known in the industry that enable the stationary exercise equipments to provide and control resistance to pedaling. For a non-limiting example, the rotational pedal motion may be transferred to a rotating flywheel whose rotation is slowed down by mechanical friction. The rotation of the flywheel may be converted to electrical energy using an alternator, and then the generated power is dissipated on an electrical load. Finally, the resistance to the rotation of the flywheel may be provided by a magneto-resistive device in which the eddy currents induced by an electromagnet give rise to magnetic fields that oppose the flywheel rotation, thereby slowing the flywheel down. The type of control of pedaling resistance may include discrete levels of resistance settings available as a switch or a level accessible to the rider, or is controlled by a computer program which is guiding the rider (person exercising) or is being guided by the rider, as in an exercise session on a cardio-fitness station with virtual reality capability.

In order to determine the power output by the rider, one has to determine the product of the torque applied on the pedals and the angular velocity of the pedals, from now on referred to as cadence. Neither the torque exerted on the pedals nor the cadence is uniform in time—both depend on the pedal position (angle) with respect to the rider's legs (or ground) and/or the condition and the performance of the rider. The total energy (kcal) dissipated can be found by integrating (calculating the integral of) the torque and the instantaneous cadence.

There are a number of ways of dissipating the rotational power delivered by the pedals practiced in the industry. Most of the ways offer options for adjusting the amount of resistance to pedal rotation. Three common ways for dissipating pedal power and the associated mechanisms for adjustment of resistance are presented here. The first example is by dissipating the pedal power on a flywheel which is being slowed down by a belt, wherein the resistance to rotation is adjusted by tightening or loosening the belt placed around the flywheel. Although options for adjusting the resistance are provided, there is no precise measurement of the torque induced with the belt, and hence no attempt is made to correct the tightness of the belt to meet the setting. The second and third examples of ways to dissipate pedal power commonly practiced today involve conversion of pedal rotational energy into electricity and then adjusting the dissipation of the electrical power.

The second example is involved in stationary fitness bicycles that use an alternator to convert mechanical energy into electrical energy, and then dissipate this electrical energy on an electrical (resistive) load. The adjustment of dissipated power is achieved via adjustment of the magnitude of the electrical current through the resistive load where the generated electrical power is converted to heat. The third example of a way to dissipate power, recently more commonly used, is to use a metallic flywheel and adjust the strength of a magnetic field through which at least one part of the flywheel is passing as it rotates. The magnetic field established by an electromagnet induces eddy currents in the flywheel and the induced currents dissipate energy on the electrical resistance in the flywheel. The power dissipation heats the flywheel, while the eddy currents establish a magnetic field which opposes the rotation of the flywheel, thereby exerting resistance to rotation experienced (caused) by the rider. The adjustment of the pedal resistance (torque) is performed by adjusting the current flowing into the electromagnets. Fitness equipment that uses this type of power dissipation method is commonly referred to as equipment with a magnetic resistance device (MRD).

The way above approaches are generally implemented is that for a particular design, the pedal resistance is experimentally evaluated in advance for every cadence and resistance setting, and used in the form of a look-up table or a formula based on a fit to the experimental data. This is generally done for every design, namely, an identical formula or look-up table for a specific model, but is not cost effective to evaluate on every unit a company ships. Even if this were done for every unit, the systematic variation and wear on the equipment could not be predicted, and therefore the look-up table would not be solving the entire problem—it would drift out of sync over time.

In the case of an MRD, the variation in the size of the gap between the flywheel and the electromagnet produces most dramatic changes in the relationship between the electromagnet current and the resistive force. This is because the gap, which is air filled, dramatically impacts the magnetic circuit made up from the electromagnet and the flywheel. The gap between the magnet and the flywheel changes due to manufacturing tolerances and the temperature of the flywheel. As the temperature of the flywheel rises, it expands and closes the gap between the flywheel and the magnets, thereby increasing the strength of the resistance to rotation for a given current. The value of the flywheel resistance affects the rate of heating and varies from flywheel to flywheel. Due to the large thermal capacity of the flywheel, the temperature depends on a long history of pedaling at any time. These factors make the relationship between the pedaling resistance and the current energizing the electromagnets very difficult to predict and repeat. Consequently, the tracking between the pedal resistance setting and the actual value of pedal resistance is insufficient to produce consistent exercise results and/or fair competition done on two cardio-fitness stations of the same design.

In all of the above methods for providing pedal resistance, the value of the resistance is set by the rider or a computer program, but it is not measured to check the accurate value of the resistance and no attempt is made to make correction to the quantity that controls the resistance (electrical current of the electromagnets in the MRD, for a non-limiting example). This is a potential disadvantage of all prior art commercially available stationary bicycles.

Today, there are many options for measuring power and torque accurately and researchers have gone through development of experiments and tools to provide such experiments. See, for a non-limiting example, Bicycle Science by David Gordon Wilson (3rd edition, The MIT Press, Cambridge, Mass., 2004). However, these tools are used in research environments for monitoring and have not been manufactured in a form suitable for commercial products. The primary reasons for this are cost and complexity needed to implement a sophisticated power monitoring system. In addition, it has never become apparent that an accurate calibration of exercise equipment would be needed.

One embodiment of the present invention provides an inexpensive apparatus enabling measurement of power dissipated by the rider of a cardiofitness station (or any other stationary exercise equipment) that does not depend on the manufacturer, manufacturing tolerances, or machine condition. In addition, a method of using the data measured by such an apparatus to improve the quality of the exercise experience is provided.

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