Dual-Axis Accelerometer Sensor for Bicycle Cadence Measurement
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Solution Overview
Problem
Existing bicycle cadence and speedometers based on accelerometers face accuracy issues at higher cadences and wheel speeds due to angular velocity and acceleration effects, requiring simplifying assumptions, integration/differentiation of signals, and additional sensors for accurate measurements.
Innovation Solution
A dual-axis accelerometer system mounted on a rotating part of a bicycle, processing signals from two dual-axis accelerometers to directly determine angular position, velocity, and acceleration without relying on simplifying assumptions or additional sensors, thereby improving measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single dual-axis accelerometer is used to measure cadence and speed, then the device complexity is reduced, but the measurement precision deteriorates at higher cadences and wheel speeds due to angular velocity and acceleration effects
Solution Approach 1:
The patent divides the measurement task into two separate dual-axis accelerometers: one dedicated to measuring gravity effects for determining angular position, and another dedicated to measuring angular velocity and acceleration effects. This segmentation allows each sensor to specialize in one type of measurement, resolving the contradiction by maintaining low device complexity while improving measurement precision through functional separation.
Solution Approach 2:
The patent assigns different measurement functions to different locations and orientations of the accelerometers. The first accelerometer is positioned and oriented to primarily capture gravity effects, while the second is positioned and oriented to primarily capture rotational dynamics effects. This local quality differentiation enables precise separation of measurement functions, allowing accurate cadence and speed measurement without increasing overall system complexity.
2Device complexity
If simplifying assumptions such as uniform cadence are made, then the device complexity is reduced, but the measurement precision deteriorates because it cannot accurately determine angular position throughout the pedal stroke
Solution Approach 1:
The patent extracts and removes the need for simplifying assumptions by using two dual-axis accelerometers that directly measure both gravity effects and rotational dynamics effects simultaneously. This extraction of the assumption requirement allows the system to handle non-uniform cadence accurately without increasing device complexity, as the additional sensor provides the necessary data to compute angular position without assuming uniform motion.
3Measurement precision
If integration of velocity signal is used to determine angular position, then the measurement precision improves, but loss of information increases due to drift and accumulation errors
Solution Approach 1:
The patent implements a feedback mechanism where the first dual-axis accelerometer continuously measures gravity effects to determine current angular position, which then serves as feedback to correct any drift that may have accumulated from integrating the velocity signal from the second accelerometer. This feedback loop maintains measurement precision while preventing information loss due to drift and accumulation errors.
4Measurement precision
If additional sensors such as magnet and reed switch are added to reinitialize integration process, then the measurement precision improves, but device complexity increases
Solution Approach 1:
The patent makes the first dual-axis accelerometer multi-functional by using it both for determining angular position through gravity effects and for providing feedback to correct integration drift. This universality eliminates the need for additional dedicated sensors like magnets and reed switches, maintaining measurement precision while avoiding increased device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy of cadence and speed measurements by isolating gravity effects from angular velocity and acceleration, eliminating the need for integration and additional sensors, resulting in more precise data transmission without drift or accumulation errors.
Implementation Method 1
The signal from the accelerometer varies with the effect of gravity as the crank arm or wheel rotates
Implementation Method 2
This is due to the effect of the angular velocity and angular acceleration on the accelerometer signal
Implementation Method 3
This is due to the effect of the angular velocity and angular acceleration on the accelerometer signal
Data Source
AI summary
The present disclosure provides a sensor system for measuring a parameter of a body. The sensor system includes a housing mountable to a rotating part of the body. The housing includes a first dual-axis accelerometer having a first measurement axis and a second measurement axis, the first dual-axis accelerometer arranged to measure a first acceleration along the first measurement axis and a second acceleration along the second measurement axis and a second dual-axis accelerometer having a third measurement axis and a fourth measurement axis, the second dual-axis accelerometer arranged to measure a third acceleration along the third measurement axis and a fourth acceleration along the fourth measurement axis. The sensor system also includes a processor configured to receive the first, second, third and fourth measured accelerations and determine from the first, second, third and fourth measured accelerations the parameter.