Balanced Harmonic Drive Disconnect for Jammed Motor Override
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Solution Overview
Problem
Control surfaces of aircraft are inefficiently maneuvered with traditional harmonic drives, and when a jammed gear or frozen motor occurs, the fixed coupling between the motor and control surface results in undesirable constraints on motion.
Innovation Solution
A harmonic drive with a solenoid coil and spring mechanism that allows the input shaft to move between a coupled and decoupled position, enabling rotational decoupling between the input and output shafts, thereby allowing free movement of the control surface when the solenoid is energized.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed coupling between the motor and control surface is used, then the motor can reliably drive the control surface, but the control surface cannot move freely when the motor is frozen or the gear is jammed
Solution Approach 1:
The patent applies the dynamics principle by making the coupling between the input shaft and output shaft changeable rather than fixed. The wave generator can dynamically shift between engaged and disengaged positions relative to the flexspline, allowing the system to transition from a coupled state (for reliable drive) to a decoupled state (for free movement when motor fails). This is achieved through the axial movement capability of the wave generator along the input shaft.
2Power
If traditional harmonic drives are used, then high ratio gearing is achieved, but the drives are inefficient for maneuvering control surfaces
Solution Approach 1:
The patent improves maneuvering efficiency by enabling the wave generator to dynamically disengage from the flexspline during certain phases of control surface movement. This allows the control surface to move more freely and efficiently, particularly during trimming operations or when aerodynamic forces need to overcome motor resistance. The high ratio gearing is maintained when engaged, but the system gains efficiency through the ability to disengage when full power transmission is not needed.
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
Enables efficient control surface movement and minimizes air resistance by allowing the control surface to freely rotate, even if the motor fails, by decoupling the input and output shafts, thus overcoming the constraints caused by jammed gears or frozen motors.
Implementation Method 1
a solenoid coil within the housing that, when energized, moves the input shaft to the second position
Implementation Method 2
a spring within the housing that, when the solenoid coil is not energized, moves the input shaft to the first position
Data Source
AI summary
A harmonic drive, having: a housing; an output shaft within the housing; an input shaft within the housing, the input shaft is configured for being in a first position in which rotation of the input shaft rotates the output shaft, and a second position that is axially offset from the first position, in which rotation of the input shaft does not rotate the output shaft; a solenoid coil within the housing that, when energized, moves the input shaft to the second position; and a spring within the housing that, when the solenoid coil is not energized, moves the input shaft to the first position.