Harmonic Drive Shaft Disconnect for Free Control Surface Motion
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Solution Overview
Problem
Conventional harmonic drives with fixed couplings between motors and control surfaces in aircraft are inefficient and can cause undesirable constraints on motion, especially when gears jam or motors freeze, limiting the control surface's movement.
Innovation Solution
A balanced harmonic drive with a solenoid coil and spring mechanism that allows the input shaft to move between coupled and decoupled positions, enabling rotational disconnection 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 directly drive the control surface, but the control surface cannot move freely when the gear is jammed or motor is frozen
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 input shaft can dynamically transition between two positions: a first position where it is rotationally coupled to the output shaft for normal operation, and a second position where it is rotationally disconnected to allow free movement of the control surface. This dynamic reconfigurability resolves the contradiction by enabling the system to adapt its coupling state based on operational needs.
Solution Approach 2:
The patent employs parameter changes by altering the axial position of the input shaft between two distinct states. The input shaft moves axially between a first position that engages the wave generator profile for power transmission and a second position that disengages it, allowing the control surface to rotate freely. This parameter change (axial position) enables the system to switch between coupled and decoupled states, resolving the contradiction between fixed coupling reliability and operational mobility.
2Ease of operation
If a solenoid coil and spring mechanism is added to enable shaft disconnection, then the control surface can move freely when needed, but the device complexity increases
Solution Approach 1:
The patent applies the self-service principle through the spring mechanism that automatically biases the input shaft toward the first (coupled) position. The spring provides continuous restoring force, eliminating the need for additional actuators or control systems to maintain the normal coupled state. Only when active intervention is needed (to disconnect) does the solenoid coil engage, after which the spring automatically returns the system to its default state. This self-service approach minimizes complexity by using passive elastic elements for the majority of operational states.
Solution Approach 2:
The patent extracts the disconnection function into a separate, dedicated solenoid coil mechanism rather than integrating it into the main drive train. The solenoid coil is positioned to actuate the input shaft independently, allowing the primary harmonic drive components (wave generator, flex spline, circular spline) to remain unchanged. This extraction approach adds minimal complexity only where needed for the disconnection function while preserving the simplicity of the core harmonic drive mechanism.
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 design enhances operational efficiency by allowing free rotation of the control surface, reducing air resistance and minimizing constraints on motion, even in case of motor failure, by decoupling the input and output shafts when necessary.
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
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Figure 2
AI summary
A harmonic drive, having: a housing (50); an output shaft (90) within the housing (50); an input shaft (60) within the housing (50), the input shaft (60) is configured for being in a first position in which rotation of the input shaft (60) rotates the output shaft (90), and a second position that is axially offset from the first position, in which rotation of the input shaft (60) does not rotate the output shaft (90); a solenoid coil (100) within the housing (50) that, when energized, moves the input shaft (60) to the second position; and a spring (210) within the housing (50) that, when the solenoid coil (100) is not energized, moves the input shaft (60) to the first position.