Linear Electromechanical Actuator Ball Screw Design
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Solution Overview
Problem
Existing linear electromechanical actuators face challenges in providing high axial thrust with minimal bulk and complexity, particularly in space-constrained applications like motorcycle brake calipers, due to the use of epicycloid gear sets which increase size and cost while reducing performance.
Innovation Solution
The actuator employs a brushless electric motor with a gear mechanism comprising toothed members and ball screw threads to achieve a non-unitary transmission ratio, allowing for high thrust forces with reduced travel and eliminating the need for epicycloid gear sets, resulting in a compact and economical design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If epicycloid gear sets are used to achieve high reduction ratio, then the axial thrust is improved, but the bulk of the actuator increases
Solution Approach 1:
The patent merges the reduction function and thrust transmission function into a single integrated ball screw mechanism. The ball screw directly converts rotational motion to linear motion while providing the necessary mechanical advantage, eliminating the need for separate epicycloid gear sets. This integration achieves high axial thrust with significantly reduced bulk by combining multiple functions into one compact component.
Solution Approach 2:
The patent replaces the complex epicycloid gear mechanical system with a ball screw mechanism. The ball screw uses a different mechanical principle (screw thread mechanics with ball recirculation) to achieve the same thrust multiplication effect, but with a much more compact structure. This substitution maintains the high reduction ratio capability while dramatically reducing the actuator's overall volume.
2Force
If epicycloid gear sets are used to achieve high reduction ratio, then the axial thrust is improved, but the complexity of the actuator increases
Solution Approach 1:
The patent combines the reduction stage and thrust generation stage into a single ball screw assembly. This merging eliminates the need for multiple separate epicycloid gear mechanisms working in sequence, thereby reducing the number of components, simplifying the overall structure, and lowering manufacturing complexity while maintaining the high thrust capability.
Solution Approach 2:
The patent substitutes the complex multi-stage epicycloid gear system with a single ball screw mechanism. This replacement simplifies the mechanical system by using a well-established, straightforward screw thread principle with ball recirculation for efficiency, eliminating the need for complex gear train assemblies and reducing overall device complexity.
3Force
If the velocity of rotation of the motor is reduced, then the thrust is improved, but the travel of the thruster becomes excessive
Solution Approach 1:
The patent changes the pitch parameter of the ball screw to optimize the relationship between rotation and linear travel. By selecting an appropriate pitch value, the system achieves high thrust through the mechanical advantage of the screw mechanism while controlling the linear travel distance to remain within acceptable limits. The parameter optimization ensures that torque multiplication does not come at the cost of excessive thruster displacement.
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 enables high axial thrust with reduced size and complexity, allowing for efficient operation in limited spaces while maintaining performance, and simplifying the construction and cost of the actuator.
Implementation Method 1
a screw-nut screw transmission, to a thruster able to translate along its own axis
Implementation Method 2
the screw-nut screw coupling is of the ball screw type
Implementation Method 3
a gear mechanism comprising toothed members and ball screw threads to achieve a non-unitary transmission ratio
Data Source
Figure 1a~5
Figure 2a~2b
Figure 3a~4b
AI summary
A linear electromechanical actuator comprises a coating structure (2), a first lead nut (6) rotatable around a main axis of rotation (X) and connected to the rotor (5) of an electric motor entirely contained in the coating structure (2) to receive a driving torque from the electric motor. The actuator (1) comprises a screw (8) defining a thruster of the actuator (1), rotatably coupled to the first lead nut (6) by screwing around the main axis of rotation (X) to receive an motion of advance along said main axis of rotation (X) as a result of a rotation of the first lead nut (6). The screw (8) is rotatable relative to the coating structure (2) around the main axis of rotation (X) and it is connected to actuating means (10) able to determine a velocity of rotation of the screw (8) around the main axis of rotation (X) such as to determine the velocity of advance of the screw (8) along the main axis of rotation (X).