Aircraft Wiper Motor Motion Stops for Over-Rotation Protection
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Solution Overview
Problem
Aircraft windshield wiper systems face challenges in preventing over-rotation of the wiper arm, which can lead to damage to the wiper components and the aircraft's windshield, especially when using reversible brushless direct-current motors that lack effective motion control mechanisms.
Innovation Solution
The implementation of a reversible brushless direct-current motor with a ball nut and guide pins that translate along a threaded aft shaft segment, utilizing motion stops to prevent over-rotation by sensing increased current draw when the ball nut contacts predefined stops, thereby limiting the wiper arm's sweep angle and preventing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a reversible brushless direct-current motor is used to achieve oscillatory motion directly, then the device complexity is reduced compared to crank rocker mechanisms, but the risk of over-rotation and damage to components increases due to lack of mechanical constraints
Solution Approach 1:
The patent incorporates motion stops positioned at the forward and aft limits of the oscillatory sweep angle before over-rotation can occur. These stops are pre-configured mechanical features that physically prevent the shaft from rotating beyond the intended angular range, eliminating the need for complex electronic sensors or control systems while ensuring component protection
Solution Approach 2:
The patent introduces a magnetic coupling mechanism as an intermediary between the motor shaft and the output mechanism. This magnetic coupling transmits torque while allowing the motion stops to independently constrain the angular range, providing both the simplicity of direct motor drive and the reliability of mechanical over-rotation protection
2Reliability
If motion stops are added to prevent over-rotation, then the reliability and component protection are improved, but the device complexity increases
Solution Approach 1:
The patent integrates the motion stops directly into the motor housing structure, merging the protective function with the existing mechanical components. The forward motion stop is formed as part of the motor housing, and the aft motion stop is integrated with the end cap assembly, eliminating the need for separate protective devices and minimizing additional complexity
Solution Approach 2:
The motion stops are designed as passive mechanical features that automatically engage when the shaft reaches the limit positions. The system self-regulates the oscillatory motion range through these fixed mechanical constraints without requiring external control systems, sensors, or active components, thereby maintaining simplicity while ensuring reliability
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 configuration effectively prevents over-rotation of the wiper arm, reducing wear on the motor and protecting aircraft components by utilizing a ball screw mechanism with motion stops that activate an over-current trip logic to halt the motor, ensuring reliable operation and minimizing damage from excessive sweep.
Implementation Method 1
a ball nut and guide pins that translate along a threaded aft shaft segment, utilizing motion stops to prevent over-rotation
Implementation Method 2
sensing increased current draw when the ball nut contacts predefined stops, thereby limiting the wiper arm's sweep angle
Data Source
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AI summary
Disclosed is an aircraft windshield wiper system, having: a wiper arm (110); a reversible motor (130) that drives the wiper arm, the motor including: a stator (155a); a rotor (155b) configured to rotate relative to the stator; a forward shaft segment (140b) that is driven by the rotor and being rotationally connected to the wiper arm; an aft shaft segment that is driven by the rotor, the aft shaft segment including a forward end and an aft end; a ball nut that translates along the aft shaft segment from rotation of the aft shaft segment (140c); a forward stop at a forward end of the aft shaft segment, configured to stop forward translational motion of the ball nut along the aft shaft segment; and an aft stop at an aft end of the aft shaft segment, configured to stop aft translational motion of the ball nut along the aft shaft segment.