Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
1998-06-23
2002-07-16
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06418797
ABSTRACT:
BACKGROUND OF THE INVENTION
Power measurement devices for bicycles typically fall into one of two basic categories: devices that measure torque and angular velocity in driving components of a bicycle, such as pedals and crank arms, and devices that measure torque and angular velocity in driven components such as the chain rings, chain and rear wheel. Power P is the product of torque T and angular velocity &ohgr;, that is, P=T×&ohgr;. Similarly, power P can be defined as the product of force F and velocity v, i.e., P=F×v.
Certain prior devices that measure torque in driving components have inherent inaccuracies with regard to measuring either the true power exerted by a bicyclist or the true power transmitted to the driven wheel of a bicycle. The total force exerted by a bicyclist will include forces that are applied tangentially to a driving component, e.g., crank arm, and forces that are applied either in another direction in the plane of rotation or in a plane that is perpendicular to the plane of rotation. The portion of force that is tangential to the direction of rotation, when multiplied by the distance from the center of rotation to yield torque and then multiplied by angular velocity, represents a measure of power transmitted to a driven wheel. However, the forces that are in another direction in the plane of rotation and the forces that are perpendicular to the plane of rotation cannot be added to the forces causing rotation, multiplied by angular velocity, and represented as a true measure of power transmitted to the driven wheel. Nor can the total force be multiplied by the angular velocity of a driven component to represent the power exerted by the bicyclist.
U.S. Pat. No. 4,141,248 to Bargenda discloses a torque measurement means which includes a wire strain gauge operatively connected to each of the foot pedal armatures of a bicycle and connected in series in a strain gauge bridge. This means of measuring torque has limited accuracy since it is known that the force exerted into the foot pedals and resolved by the instrumented aramtures is not limited purely to the measurement of force that will be transmitted to the driven wheel. The instrumented armatures will also be affected by significant forces that are perpendicular to the desired torque measurement thereby diluting the significance of the measured power that is assumed to be transmitted back to the driven wheel. Although this means provides a measurement of the exerted forces produced by a cyclist, it is not an accurate measurement of force and power that is usefully produced and efficiently transmitted to the driven wheel.
U.S. Pat. No. 4,423,630 to Morrison discloses a means of measuring power by measuring the force in a driving foot pedal of a bicycle. This method of force measurement also exhibits inaccuracies in that a significant proportion of force registered by the pedals is not transmitted via the bicycle chain.
In general, devices that measure torque in driven components have the potential of registering a more accurate measure of torque and power usefully transmitted by the cyclist to the bicycle wheel. It should be noted that this is not the same as the power exerted by the cyclist. Some of these prior devices include methods of detecting torque in the hub of the driven wheel. The torque in the hub is usually detected by some indirect means such as by optically detecting relative deflection between components in the wheel and converting the detected deflection to a torque measurement.
U. S. Pat. No. 4,811,612 to Mercat discloses a method and device for detecting torque in the rear wheel of a bicycle. Under applied torque to the wheel, special radial spokes deform such that the rim of the wheel angularly deflects relative to the hub of the wheel. Using pairs of infrared-radiation-emitting diodes and photo diodes mounted adjacent to the wheel hub and rim, the device optically detects the angular position of the rim compared to that of the hub by measuring delay in the signals generated by the photo diodes.
U.S. Pat. No. 4,966,380 to Mercat discloses a device used to detect torque in the hub of the rear wheel of a bicycle. The device includes a pair of mating rotatable members which rotate about the axle of the bicycle. The mating members include spiral ramps in contact with each other such that as torque is applied to the hub, one of the mating members is displaced axially along the rotational axis of the hub against a stationary flexible disk. A strain gauge on the stationary flexible disk detects the deflection of the disk. A processor converts the stationary disk deflection measurement into a torque measurement. The device of the '380 patent addresses a problem seen by Mercat as being associated with applying a sensor to the rotating portion of the hub. Mercat therefore uses a stationary detection member, not in the rotational portion or torque-carrying path of the hub, to detect torque in the hub.
U. S. Pat. No. 5,065,633 to Mercat discloses another device used to detect torque in a bicycle hub. The device includes an outer hub and an inner driving axle which are rotatably mounted over the stationary axle of the bicycle and are fixedly attached to each other at a fixed end of the hub and are allowed to rotate relative to each other under applied torque at the opposite free end of the hub. Torque applied to the driving axle is coupled to the outer hub at the fixed end of the hub to rotate the bicycle wheel.
In the '633 patent, the torque measuring device is coupled off of the torque path to the torque-carrying members, i.e., the driving axle and outer hub, to detect relative deflection between the outer hub and the stationary axle at the free end of the hub. A multiplying arm is pivotally attached at one end to the outer hub and rests against a rotatable carrier element at its other end. Magnets are attached to the carrier element at the free end of the hub and the fixed end of the hub and are located in registration with mating magnetic reed contacts mounted on the stationary axle. When torque is applied to the driving axle, the hub rotates slightly with respect to the driving axle. The multiplying arm pivots to move the carrier element and the magnets on the carrier element at the free end of the hub relative to the magnets at the fixed end of the hub. Signals generated by the stationary reed contacts are analyzed to relate the amount of deflection in the outer hub to applied torque.
U. S. Pat. No. 5,031,455 discloses another device used to detect torque in a bicycle hub. The device includes an inner hub and an outer hub connected by torsion bars. The inner hub is driven into rotation and carries the outer hub and the bicycle wheel into rotation via the torsion bars. A pair of discs mounted to the inner hub and outer hub are used to detect relative rotation between the inner and outer hubs. The discs include a plurality of circumferential openings which are aligned under zero torque but are displaced relative to each other under applied torque. The device uses optical or magnetic sensing to detect the amount of relative displacement, which is in turn related to the applied torque.
All of these devices use indirect means to measure torque. Each detection approach carries out torque detection in elements which are outside the path along which torque is coupled through the bicycle driving system. As a result, certain inaccuracies are inherent to such systems, such as those introduced by losses in coupling the special torque detecting components to the actual wheel driving components. Also, the indirect detection approaches used, i.e., optical, magnetic, can also introduce inaccuracies. These approaches rely heavily on the accuracy of the associated components, e.g., the discs and the openings formed therein. Any inaccuracies in fabrication or assembly of any of these associated components can adversely affect the accuracy of the torque measurement.
Also, these approaches generally require large angular deflections to achieve an accurate measurement of torque
Ambrosina Jesse
Pawelka Gerhard
Boyle Fredrickson Newholm Stein & Gratz S.C.
Graber Products, Inc.
Noori Max
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