Bicycle Sensor System for Accurate Speed Measurement
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Solution Overview
Problem
Existing bicycle speed sensors, such as Reed sensors and magnetic field sensors, are prone to interference from artificial magnetic fields and struggle to accurately determine speed, especially at low speeds and in environments with motorized support, where precise speed measurement is crucial for legal compliance and reliability.
Innovation Solution
A sensor system combining a rotating magnetic field sensor and a rotating acceleration sensor unit, with an evaluation unit using a Kalman filter to fuse signals and provide accurate rotational speed and orientation measurements, while also detecting potential interference and failures, thereby enhancing measurement accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If only a magnetic field sensor is used to determine wheel speed, then the measurement can be disturbed by artificial magnetic fields generated by coils or permanent magnets, but adding an acceleration sensor unit increases device complexity
Solution Approach 1:
The patent combines a magnetic field sensor and an acceleration sensor unit into a single integrated sensor system. The magnetic field sensor detects the earth's magnetic field during wheel rotation, while the acceleration sensor unit measures centrifugal acceleration. Both sensors are fixed relative to each other at predefined distances from the rotation axis, allowing their signals to be fused by the evaluation unit for redundant and complementary speed measurement, thereby preventing disturbance from artificial magnetic fields.
Solution Approach 2:
The evaluation unit acts as an intermediary that processes and fuses signals from both the magnetic field sensor and the acceleration sensor unit. It acquires signals from both sensors, evaluates them using algorithms (such as a Kalman filter), and determines the wheel's rotational speed and orientation by combining the complementary information from both measurement principles, thereby resolving the reliability issue.
2Productivity
If a magnetic field sensor is used alone, then speed can only be determined once per complete wheel revolution, but using an acceleration sensor unit increases energy consumption
Solution Approach 1:
The acceleration sensor unit continuously measures centrifugal acceleration during wheel rotation, providing continuous speed information rather than discrete measurements once per revolution. This continuous measurement capability allows the system to determine speed at multiple points within each wheel revolution, significantly increasing measurement frequency and productivity while the sensors remain passive and energy-efficient.
3Measurement precision
If the magnetic field sensor and acceleration sensor unit are positioned closer to the rotation axis, then the measured signals become weaker, but positioning them farther away increases device complexity
Solution Approach 1:
The patent specifies optimal parameter values for the distances of the magnetic field sensor and acceleration sensor unit from the rotation axis. These distances are carefully selected to ensure that the sensors measure sufficiently strong signals from the earth's magnetic field and centrifugal acceleration, respectively, while maintaining a compact and simple overall device structure. The predefined distances optimize the balance between signal strength and device compactness.
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
The combined sensor system provides more frequent and accurate speed measurements, reduces interference from artificial magnetic fields, and ensures reliable speed determination across various speeds, including low speeds, and detects potential manipulations or failures, ensuring compliance with legal speed limits for e-bikes.
Implementation Method 1
When the bicycle is moved, the magnetic field sensor rotates in the earth's magnetic field
Implementation Method 2
a centrifugal acceleration also acts on the acceleration sensor unit
Implementation Method 3
the acceleration sensor unit rotates relative to the Earth's gravitational force
Data Source
AI summary
A sensor system for a bicycle. The system system includes a magnetic field sensor and an acceleration sensor unit having at least one acceleration sensor, and an evaluation unit that is designed to acquire signals from the magnetic field sensor and the acceleration sensor unit. The magnetic field sensor and the acceleration sensor unit are designed for attachment to a wheel of the bicycle. The magnetic field sensor and the acceleration sensor unit are fixed relative to each other and are situated at a predefined distance with respect to an axis of rotation. The evaluation unit is designed to evaluate the signals of the magnetic field sensor and the acceleration sensor unit to ascertain a rotational speed and/or orientation of the magnetic field sensor and/or acceleration sensor unit with respect to the axis of rotation.