Today the US Patent & Trademark Office published a patent application from Apple titled "Calculating an Estimate of Wind Resistance Experienced by a Cyclist." Apple's invention is designed to extend Apple Watch activities and monitoring to include cycling. Improved techniques and systems are disclosed for determining the components of resistance experienced by a wearer of an Apple Watch engaged in an activity such as bicycling or running. By monitoring data using the wearable device, improved estimates can be derived for various factors contributing to the resistance experienced by the user in the course of the activity. Using these improved estimates, data sampling rates may be reduced for some or all of the monitored data.
A wearable device can be worn by a person riding a bicycle. A cyclist may wish to receive a measurement or estimate of their power output and/or calories burned while they ride. One way by which power output can be measured is the installation of a power meter onto a bicycle.
However, such meters require installation and may be expensive. Another method for estimating power output is to measure the cyclist's heart rate and generate an estimate of power output based on the heart rate. While inexpensive, heart rate measurements and estimation of cyclist power output based on heart rate can require significant power to operate the sensor. Another approach is to estimate power output based on distance traveled and/or speed at which that distance is traveled.
However, estimation based on these quantities can be inaccurate. For example, calculating an estimate of power output based on distance traveled and/or speed at which that distance is traveled will not account for dynamically experienced resistance such as that provided by wind, or by changes in elevation during the ride.
When riding a bicycle, three main factors contribute to total energy expenditure: rolling resistance, contributed by friction of the bicycle tires against the ground; grade, contributed by the force of gravity pulling against the mass of the cyclist and bicycle; and wind resistance or drag, contributed by the force of air drag against the cyclist and bicycle moving through the atmosphere. When riding a bicycle at a constant speed, the total of these three main factors represents the major power output of the cyclist.
Apple's invention relates generally to determining estimates for the resistances experienced by a cyclist and thus the total power output of the cyclist. In particular, estimates of the wind resistance experienced by a cyclist can be obtained through calibration of the effective resistance a cyclist experiences as a function of heading, and thereby separated from the effective resistance due to rolling resistance and grade. Once such estimates are obtained, the user's total power output can be more accurately tracked throughout an activity.
The invention may include a wearable device such as an Apple Watch and techniques for estimating total power output and/or the contribution of wind resistance to the total power output of a cyclist wearing the wearable device. The watch may include one or more microprocessors, a display, and a variety of sensors, such as a heart rate sensor and one or more motion sensors.
In order to improve estimates of the contribution of each of the three portions of total power output, and thus of total power output, a cyclist may wear a wearable device such as an Apple Watch. The wearable device can include a heart rate sensor to provide a series of measurements of cyclist heart rate.
The wearable device can also include motion sensors to collect data about the wearable device's position and orientation in space and to track changes to the wearable device's position and orientation over time.
Apple's patent FIG. 1 noted below is an Apple Watch: FIG. 5 shows the various relevant forces acting on a cyclist during a ride and the relevant velocities of the cyclist; and FIG. 6 shows a method for determining an estimate of wind resistance.
Apple further notes that accelerometers in the device may track acceleration, including high frequency variation in acceleration, and use this to detect surface type. Because a cyclist can wear the wearable device, the orientation of the device can provide information about the cyclist's body position.
For example, when cycling, the cyclist's arms may be in a variety of positions, depending on the cyclist's style of riding and the type of handlebars on the bicycle. If the cyclist wears the wearable device on the cyclist's wrist, the wearable device may be able to infer the cyclist's hand position, and based on this hand position may be able to infer the cyclist's riding position and thereby provide an estimate of drag contributed by the cyclist's body (e.g., less drag when riding in a tuck or more drag when riding sitting upright.)
Combining these measurements of heart rate, position and orientation, velocity, altitude, and riding position, the cyclist's total power output and the contribution of each component of that power output may be estimated.
By estimating the relative contribution of each component to total power output, a less expensive and more power-efficient technique for providing accurate estimates of cyclist power output can be created.
In some embodiments, the motion sensors may include, for example, an accelerometer, a gyroscope, a barometer or altimeter, a magnetometer or compass, etc. The wearable device may also include a motion coprocessor, which may be optimized for low-power, continuous motion sensing and processing.
Apple's patent FIGS. 8A/B/C illustrates hands in various hand positions when riding a bike termed "Tops, Hoods and Drops." FIG. 9 shows a method for using an accelerometer to improve estimation of C.sub.rr; and FIG. 10 shows a method for calculating power output.
More specifically, FIGS 8A/B/C illustrates various hand positions riders may take. Each of these positions influences the body positioning of the cyclist, as shown in FIGS. 8A-8C, and thus influences the air drag by changing the exposed surface area A.
In some embodiments of the present disclosure, a wearable device worn on the cyclist's wrist or hand may detect the cyclist's hand position. For example, a direction of gravity as experienced by the wearable device, combined with knowledge of the wrist on which the device is worn, may be used to estimate the hand position of the rider. Based on hand position, the body position of the cyclist may be estimated, and this estimate may be used to refine A and C.sub.d and/or to adjust these parameters in real-time as the cyclist's body position changes. By adjusting the air drag parameters with the cyclist's changes in body position, estimates of total power output may be made more accurate.
Apple's patent application 20170074897 was filed back in Q3 2016. Considering that this is a patent application, the timing of such a product to market is unknown at this time.
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