Fault-Tolerant Electromechanical Linear Actuator Design
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Solution Overview
Problem
Electromechanical linear actuators are unreliable for safety-critical applications due to electrical, electronic, and mechanical faults, and existing redundancy solutions increase weight and complexity, while differential gear boxes are not suitable for fast operations.
Innovation Solution
An electromechanical linear actuator with a Fault Tolerant Differential Direct Drive design, featuring independent lead nuts and an intermediate coupling stage, ensuring fault tolerance and reduced weight, complexity, and friction, without using differential systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two identical actuators are used to provide redundancy, then reliability is improved, but weight and complexity increase
Solution Approach 1:
The actuator is divided into two independent drive systems (first and second electric motors with separate lead nuts) that can operate independently. Each drive system can function autonomously to move the control surface, providing redundancy without requiring a complete duplicate actuator system. This segmentation allows fault tolerance while reducing overall system complexity compared to using two full actuators.
2Reliability
If a differential gear box is used to provide redundancy, then reliability is improved, but device complexity and friction increase
Solution Approach 1:
The differential gear box is extracted and replaced with a direct-drive configuration. The two electric motors directly drive the lead nuts without intermediary mechanical transmission components. This eliminates the complex differential mechanism while maintaining the ability of both motors to independently control the control surface, thereby reducing mechanical complexity and friction.
3Reliability
If a differential gear box is used, then redundancy is provided, but speed and dynamic performance deteriorate
Solution Approach 1:
The mechanical differential gear box system is replaced with an electrical control system. Two independent electric motors with separate control electronics directly drive the lead nuts, eliminating the need for mechanical power division and transmission. This substitution removes the speed-limiting friction and clearance inherent in differential gear boxes, enabling faster and more responsive operation while maintaining redundancy.
4Reliability
If motors are sized for full torque in fault conditions, then reliability is improved, but weight and energy consumption increase
Solution Approach 1:
The system uses partial action by allowing one motor to operate independently at reduced capacity when the other fails. Each motor is sized to handle the control surface movement in normal dual-motor operation, but the system is designed so that either motor can function alone if needed. This avoids the need to oversize both motors for worst-case single-motor operation, reducing total weight and energy consumption while maintaining fault 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
The actuator provides reliable, efficient, and fault-tolerant operation for primary control surfaces, minimizing weight and complexity while maintaining high dynamic performance and efficiency, even under failure conditions.
Implementation Method 1
the reduction apparatus comprises a lead nut with a screw sliding thereon (or a screw with a lead nut sliding thereon), which in turn is connected to the pushing member
Data Source
AI summary
An electromechanical linear actuator may include: a containment structure; a pushing member designed to translate relative to the containment structure to at least partially come out of the containment structure during operation of the electromechanical linear actuator; a mechanical reduction apparatus in the containment structure and configured to rotate about an axis of rotation; motor means in the containment structure operably connected with the mechanical reduction apparatus to rotate about the axis of rotation; a shaft inserted in the mechanical reduction apparatus and connected to the pushing member, wherein the shaft is mechanically connected with the mechanical reduction apparatus so that a rotational movement of the mechanical reduction apparatus will cause the shaft to translate along the axis of rotation; and a rotation-preventing mechanism operable on the shaft to prevent the shaft from rotating about the axis of rotation.