Gear Motor Rotor Position Detection Using Output Shaft Encoder
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Solution Overview
Problem
Existing gear motors for motor vehicle wiper systems face challenges in cost-effective control, particularly with brushless direct current electric motors, as they require accurate angular position detection for optimal operation, which is complex and costly with traditional Hall effect sensor solutions, and not applicable for high-load startups.
Innovation Solution
A gear motor design that uses an output angular position sensor to determine the rotor's position, combined with back-electromotive force measurements for high-speed operation, and optionally incorporates one or two Hall effect sensors to correct and calibrate the angular measurement, reducing the need for additional sensors and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If three Hall effect sensors are used to accurately detect rotor angular position, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the angular position detection function from the rotor side (where Hall sensors would be needed) and relocates it to the output shaft side using an optical encoder. This allows rotor position to be inferred through the known gear ratio relationship, eliminating the need for three Hall sensors on the rotor while maintaining measurement precision.
Solution Approach 2:
The patent introduces an intermediary element - the optical encoder on the output shaft - that indirectly provides rotor position information. By measuring the output shaft position and applying the gear ratio, the system obtains rotor angular position without direct sensing on the rotor, thus reducing sensor count while preserving accuracy.
2Device complexity
If back-electromotive force measurement is used for rotor position detection, then device complexity is reduced, but reliability deteriorates during high-load startups
Solution Approach 1:
The patent applies preliminary action by using the optical encoder to establish accurate rotor position information during startup before back-EMF measurement becomes reliable. The encoder provides dependable position data from standstill, enabling the controller to initiate motor operation even under high load conditions where back-EMF would be insufficient for accurate detection.
Solution Approach 2:
The patent replaces the electrical measurement method (back-EMF) with a mechanical/optical measurement method (optical encoder) for position detection. This substitution ensures reliable position information during all operating conditions including high-load startups, where electrical measurement fails, while the mechanical encoder provides continuous accurate feedback.
3Reliability
If an optical encoder is used on the output shaft, then angular position measurement reliability is improved, but device complexity increases
Solution Approach 1:
The patent makes the optical encoder serve multiple functions: it directly measures output shaft position for speed control, indirectly provides rotor position information through gear ratio calculation, and enables reliable operation under all load conditions including startup. This multi-functionality justifies the added device complexity by eliminating the need for separate rotor position sensors.
Solution Approach 2:
The patent merges the output shaft position measurement function with the rotor position detection function. A single optical encoder on the output shaft performs both tasks by direct measurement and mathematical transformation, consolidating what would traditionally require separate sensing systems and reducing overall system complexity despite the encoder addition.
4Device complexity
If gear ratio information is utilized to infer rotor position from output shaft position, then the number of sensors is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent transforms the physical sensing problem into a mathematical calculation problem. Instead of directly sensing rotor position, the system measures output shaft position and transforms this parameter through the gear ratio relationship to derive rotor position. This parameter transformation approach reduces sensor requirements while the precision is maintained through accurate mathematical computation rather than mechanical tolerance.
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 solution enables effective control of brushless direct current electric motors during high-load startups, reducing costs by minimizing the number of sensors required and enhancing accuracy without additional sensor installations.
Implementation Method 1
a first Hall effect sensor arranged on the stator and configured to detect a position of the rotor
Implementation Method 2
a brushless direct current electric motor comprising a rotor, a stator having electromagnetic excitation coils for the rotor
Implementation Method 3
combined with back-electromotive force measurements for high-speed operation
Data Source
AI summary
The present invention relates to a gear motor (101), in particular for a wiper system, comprising: -a brushless DC electric motor (103) including: -a rotor; -a stator having coils for electromagnetically exciting the rotor; -a device for determining the angular position of the rotor; -a control unit configured to generate control signals for supplying power to the electromagnetic excitation coils of the stator; -a reduction mechanism (104) that is linked on one side to the rotor of the electric motor (103) and on the other side to an output shaft (109), the reduction mechanism (104) having a predefined reduction ratio and; -an output angular position sensor (110) that is configured to measure the angular position of the output shaft (109), wherein the output angular position sensor (110) that is configured to transmit a signal corresponding to the measured angular position of the output shaft (109) to the device for determining the angular position of the rotor and said device is configured to determine the position of the rotor on the basis of the transmitted signal by taking into account the predefined reduction ratio of the reduction mechanism (104). The invention also relates to a wiper system and to a method for controlling the electric motor (103).