Self-Locking Screw Drive for Power-Free Nut Position Holding
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Solution Overview
Problem
Screw drive type linear actuators face challenges in mechanically fixing the axial position of the nut to prevent uncommanded motion, especially under external loads, without requiring electrical power for the lock mechanism.
Innovation Solution
A mechanical nut locking system that automatically engages when the nut is retracted and disengages when the actuator extends, utilizing a torque transmitting screw drive member that translates axially to unlock the nut, allowing it to extend without rotating the screw, and relocks when the nut is retracted, ensuring the nut remains stationary during locking and unlocking operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical locking mechanism is added to fix the axial position of the nut, then the reliability of preventing uncommanded motion is improved, but the device complexity increases
Solution Approach 1:
The locking mechanism is merged with the existing screw drive components. The locking member is integrated into the screw assembly, and the locking engagement occurs automatically through the interaction between existing components (screw, nut, and locking member) without adding a separate independent locking system. This reduces overall device complexity while achieving the reliability goal.
Solution Approach 2:
The locking mechanism operates automatically based on the position of the screw and nut. When the nut retracts to a predetermined position, the locking member automatically engages with the nut to prevent uncommanded motion. The system self-regulates without requiring external control systems or additional actuators, thereby improving reliability while minimizing added complexity.
2Ease of operation
If an electrical power system is used for the locking mechanism, then the ease of operation is improved, but the use of energy increases
Solution Approach 1:
The patent replaces an electrical power-based locking system with a purely mechanical locking mechanism. The locking member engages and disengages through mechanical interaction with the screw and nut positions. This substitution eliminates the need for electrical power consumption while maintaining ease of operation through automatic mechanical engagement based on screw rotation and nut position.
Solution Approach 2:
The locking mechanism is self-actuating based on the mechanical state of the system. When the nut reaches the predetermined retracted position, the locking member automatically engages without requiring electrical power or external control. The system uses its own mechanical motion to trigger and maintain the locking state, achieving ease of operation with zero energy consumption.
3Reliability
If the locking mechanism remains engaged continuously, then the reliability of fixing axial position is improved, but the ease of operation decreases
Solution Approach 1:
The locking mechanism transitions dynamically between engaged and disengaged states based on the operational requirements. The locking member is positioned to engage automatically when the nut retracts to the predetermined position, and it disengages automatically when the screw rotates to extend the nut. This dynamic behavior provides reliability when needed (during retraction) while maintaining ease of operation during extension cycles.
Solution Approach 2:
The locking mechanism operates periodically rather than continuously. It engages during retraction phases and disengages during extension phases, creating a periodic pattern of locking and unlocking. This periodic action ensures reliability during critical retraction positions while allowing free operation during extension, balancing both reliability and ease of operation.
Data Source
AI summary
A screw type linear actuator that includes a system for automatically fixing the nut in an axial position when it is retracted. When the system is commanded to operate the screw, the nut can automatically unlock. When the system screw is retracted fully, it automatically engages a mechanical lock. The lock does not require electrical power to remain engaged.