Marine Steering Actuator With Roller Screw for Long Stroke
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Solution Overview
Problem
Current marine vessel steering systems face limitations in efficiency and geometric constraints due to conventional actuator designs, which restrict the stroke length and lead to increased system size and complexity.
Innovation Solution
The proposed steering system incorporates a novel electric actuator with a roller screw assembly, a motor with a stator and rotor, and an adjustable clutch mechanism, featuring annular rollers and a central screw, allowing for axial translation of the output shaft and enabling a longer stroke length within a smaller envelope, along with impact absorbers for compliance and adjustable stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional ball screw actuator is used, then the steering system achieves basic steering function, but the stroke length is limited and system size increases
Solution Approach 1:
The output shaft is nested within the rotor, with the rotor's inner bore receiving the output shaft. This allows the output shaft to reciprocate within the motor assembly envelope, maximizing stroke length without increasing external dimensions. The annular rollers are nested within the rotor bore, further optimizing space utilization.
Solution Approach 2:
The invention transitions from a conventional linear actuator geometry to a rotational-dimension geometry by placing the ball screw mechanism radially within the motor rotor. This dimensional reconfiguration allows the stroke to extend along the rotational axis rather than radially outward, effectively increasing stroke length within the same envelope volume.
2Volume of moving object
If the actuator envelope is reduced, then system size decreases, but bending loads increase on the screw assembly
Solution Approach 1:
End glands are introduced as intermediary components that engage the output shaft and minimize bending load transfer to the screw assembly. These glands act as load-bearing intermediaries that absorb and redistribute bending stresses, protecting the precision screw mechanism from damaging lateral loads while maintaining compact dimensions.
3Reliability
If a clutch mechanism is added, then precise control and back-driving prevention are improved, but device complexity increases
Solution Approach 1:
The clutch mechanism is designed to automatically engage and disengage based on load conditions without requiring external control signals. The friction clutch plate automatically slips when back-driving forces exceed the friction threshold, providing self-regulating protection against motor overload and eliminating the need for complex electronic control circuits.
4Productivity
If annular rollers are used instead of traditional ball screws, then steering efficiency is maximized, but manufacturing precision requirements increase
Solution Approach 1:
The invention changes the fundamental operating parameters of the screw mechanism by using annular rollers that rotate on the screw threads rather than traditional ball recirculation. This parameter change from linear ball movement to rotational roller movement reduces sensitivity to manufacturing tolerances while maintaining high efficiency through continuous rolling contact.
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 steering efficiency by maximizing stroke length, reducing system size, and providing adjustable stiffness, while minimizing bending loads and allowing for precise control through the clutch mechanism, thereby improving the overall performance and adaptability of the marine steering system.
Implementation Method 1
The clutch may include an electromagnet fixed to the housing and a clutch plate translatable axially relative to the housing. The clutch plate may be preloaded to be spaced-apart from the electromagnet and abutting the rotor. The clutch may be disengaged by powering the electromagnet to attract the clutch plate towards the electromagnet, creating an air gap between the clutch plate and the rotor
Implementation Method 2
The clutch may alternatively include a permanent magnet fixed to the housing and a clutch plate translatable axially relative to the housing. The clutch plate may be attracted by the permanent magnet to abut the housing. The clutch may include an electromagnetic coil. The clutch may be disengaged by powering the electromagnetic coil to cancel the force of the permanent magnet
Implementation Method 3
The clutch may include an electromagnetic coil. The clutch may be disengaged by powering the electromagnetic coil to cancel the force of the permanent magnet
Implementation Method 4
Friction between the clutch plate and the rotor may inhibit relative rotation of the rotor
Data Source
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AI summary
An electric actuator comprises a housing and an output shaft reciprocatingly received by the housing. There is a screw assembly disposed within the housing and coupled to the output shaft. The screw assembly includes a plurality of annular rollers and a central screw received by the annular rollers. The annular rollers are rotatable about the central screw. There is a motor which includes a stator and a rotor. The rotor has an inner bore which engages the annular rollers. Rotation of the rotor causes the central screw to translate axially relative to the rotor and the output shaft to reciprocate relative to the housing.