Electric Actuator Rotor-Nut Layout for Shorter Axial Length
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Solution Overview
Problem
Existing electric actuators with a planetary gear speed reducer configuration are limited in size due to the axial arrangement of motor, planetary gear speed reducer, and nut member, restricting their application to devices with sufficient axial space.
Innovation Solution
The electric actuator design overlaps the rotor of the motor and nut member in the radial direction, reducing the axial size by using a cylindrical portion to transmit torque between the rotor and nut member, and incorporates a thrust bearing to support reaction forces, enhancing assembly ease and operational accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the motor, planetary gear speed reducer, and nut member are arranged in series in the axial direction, then the torque transmission and motion conversion are achieved, but the axial dimension of the housing and electric actuator increase
Solution Approach 1:
The patent transitions from a one-dimensional axial arrangement to a two-dimensional radial arrangement. The nut member is positioned on the inner periphery of the rotor, allowing torque transmission through a radial gap via a cylindrical portion. This dimensional change enables the actuator to fit into applications with limited axial space while maintaining full torque transmission capability.
2Length of moving object
If the nut member is arranged on the inner periphery of the rotor with a radial gap, then the axial size is reduced, but the torque transmission between rotor and nut member becomes complex
Solution Approach 1:
A cylindrical portion is introduced as an intermediary element between the rotor and nut member. This cylindrical portion bridges the radial gap and transmits torque from the rotor to the nut member. The intermediary structure simplifies the overall design by providing a dedicated torque transmission path rather than requiring direct contact or complex mechanical linkages.
Solution Approach 2:
The torque transmission function is segmented into distinct components: the rotor generates torque, the cylindrical portion transmits torque across the radial gap, and the nut member receives and utilizes the torque. This segmentation allows each component to be optimized independently and simplifies the overall assembly and maintenance.
3Length of moving object
If the hollow rotary shaft is used with inner raceway surface for rolling bearings, then the axial size is further reduced, but the manufacturing complexity increases
Solution Approach 1:
The hollow rotary shaft integrates multiple functions into a single component: it serves as the rotor core, provides the inner raceway surface for rolling bearings, and supports the nut member on its inner periphery. This merging of functions reduces the total number of parts and axial dimension, while the manufacturing complexity is managed through precision machining of the integrated structure.
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 reduces the axial size of the electric actuator, improves mountability, and enhances operational accuracy and durability by effectively suppressing moment loads, allowing for more versatile and compact device integration.
Implementation Method 1
The hollow rotary shaft is rotatably supported by rolling bearings arranged at two positions apart from each other in the axial direction
Implementation Method 2
when the inner peripheral surface of the cylindrical portion is fixed to the outer peripheral surface of the nut member through press-fitting, ease of assembly of the electric actuator can be improved
Implementation Method 3
a thrust bearing may be arranged adjacent to the nut member on the another side in the axial direction. With this configuration, a reaction force (thrust load) acting on the nut member along with the linear motion (advance) of the screw shaft toward the one side in the axial direction can be directly supported by the thrust bearing
Data Source
Figure 1
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Figure 3
AI summary
Provided is an electric actuator (1), including: a motor part (A); and a motion conversion mechanism part (B). The motion conversion mechanism part (B) includes: a screw shaft (33) arranged coaxially with a rotation center of a rotor (24) of the motor part (A); a nut member (32) rotatably fitted to an outer periphery of the screw shaft; and a planetary gear speed reducer (10) configured to reduce a speed of rotation of the rotor (24) and output the rotation. The screw shaft (33) is configured to advance toward one side in an axial direction or retreat toward another side in the axial direction in accordance with a rotation direction of the nut member (32), and the nut member (32) is arranged on an inner periphery of the rotor (24), and is coupled to a planetary gear carrier (43), which is an output member of the planetary gear speed reducer (10), so as to be capable of transmitting torque.