Rotary Actuator Preload and Radial Load Path
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Solution Overview
Problem
Existing rotary actuators face challenges in compact design and durability, particularly in harsh environments with varying temperatures and accelerations, as they struggle to manage thermal expansion and external loads effectively.
Innovation Solution
The electromechanical rotary actuator features a brushless motor with a harmonic drive gear box, preload mechanism, and radial load path configuration, which includes a bearing assembly and spacer to distribute loads radially and accommodate thermal expansion, allowing for compactness and operation in diverse conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional rotary actuator design is used, then the structure is simple, but the actuator cannot effectively manage thermal expansion and external loads in harsh environments
Solution Approach 1:
The actuator is divided into distinct functional modules: a motor assembly, a harmonic drive gear box, a bearing assembly, and a preload mechanism. Each module handles specific aspects of load management and thermal expansion, allowing the complex functionality to be organized into manageable, specialized components that work together to solve the reliability problem.
Solution Approach 2:
The preload mechanism dynamically adjusts the preload force applied to the harmonic drive gear box based on operating conditions. This parameter change allows the system to compensate for thermal expansion and varying external loads, maintaining reliability across different environmental conditions without requiring a completely redesigned structure.
2Reliability
If the actuator is designed to accommodate thermal expansion and external loads, then reliability in harsh environments improves, but the form factor increases
Solution Approach 1:
The bearing assembly integrates multiple functions: supporting radial loads, accommodating axial displacement from thermal expansion, and maintaining preload on the harmonic drive gear box. By combining these functions into a single integrated assembly, the design achieves reliable operation in harsh environments without proportionally increasing the overall form factor.
Solution Approach 2:
The harmonic drive gear box is nested within the motor assembly, and the bearing assembly is positioned to work in conjunction with both. This nested arrangement allows compact packaging of the components needed to handle thermal expansion and external loads, minimizing the overall volume while maintaining reliability.
3Volume of moving object
If a compact form factor is achieved, then space constraints are satisfied, but the actuator may struggle to withstand environmental changes
Solution Approach 1:
The preload mechanism applies a pre-load force to the harmonic drive gear box before operational loads are applied. This preliminary action prepares the system to better withstand subsequent thermal expansion and external loads, ensuring reliability in compact dimensions by pre-configuring the mechanical system for environmental variability.
Solution Approach 2:
The bearing assembly acts as an intermediary between the motor assembly and the external environment. It mediates the effects of thermal expansion and external loads, protecting the compact internal components from direct exposure to environmental changes while maintaining the compact form factor.
4Strength
If the radial load path configuration is implemented, then load distribution improves, but the device complexity increases
Solution Approach 1:
The radial load path configuration uses an asymmetric arrangement of bearing elements and load paths optimized for radial load distribution. This asymmetric design efficiently directs loads through the bearing assembly while maintaining a relatively simple overall structure, achieving improved load distribution without proportionally increasing device complexity.
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 the actuator to maintain internal components within a compact form factor while withstanding environmental changes, ensuring reliable operation across varying temperatures and accelerations, and allowing for use in space-constrained applications.
Implementation Method 1
brushless motor
Implementation Method 2
harmonic drive gear box
Implementation Method 3
accommodate thermal expansion
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An electromechanical rotary actuator (47) includes a housing (100) including first end (104) that extends to a second end (105) through an intermediate portion (107) that defines a longitudinal axis, and an internal cavity (108). An electric motor (114) is arranged within the internal cavity (108). The electric motor (114) includes a shaft (120) having first shaft end (122) and a second shaft end (123). A drive member (154) is arranged within the housing (100) along the longitudinal axis. The drive member (154) includes an input shaft (152) operatively coupled to the first shaft end (122) and an output shaft (155). An output shaft member (170) is coupled to the output shaft (155) of the drive member (154). At least one bearing assembly (138,184) supports one of the output shaft member (170) and the first shaft end (122), and a preload member (196) is arranged within the housing (100) and configured to apply a compressive axial force to the at least one bearing (138,184), the drive member (154) and the electric motor (114).