Inverted Harmonic Gear Actuator Design for Torque Density
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Solution Overview
Problem
Conventional electric motor actuators require external gearing to reduce output speed and increase torque, resulting in increased size, weight, and complexity due to the need for multiple stages in planetary gear drives.
Innovation Solution
Incorporating an inverted harmonic gear actuator within the electric motor, where the wave generator is radially inward of the motor rotor, allowing the actuator output shaft to extend axially with a splined interface and roller bearings, eliminating external gearing and enhancing torque-to-weight ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If external gearing is used to reduce output speed and increase torque, then torque is increased, but size and weight increase
Solution Approach 1:
The patent combines the motor and harmonic gear actuator into a single integrated unit. The wave generator is positioned radially inward of the motor rotor, and the flex spline is radially interposable between the wave generator and output shaft, merging functions that were previously separate into one compact structure that provides both motor function and speed reduction/gear function
Solution Approach 2:
The harmonic gear mechanism is nested within the motor structure. The wave generator is radially inward of the rotor, the flex spline is radially between the wave generator and output shaft, creating a nested arrangement where each component is positioned within the radial space of the previous component, maximizing space utilization and reducing overall size
2Force
If multiple stages of planetary gear drive are used to increase reduction ratio, then torque is increased, but device complexity increases
Solution Approach 1:
The patent uses an inverted harmonic gear configuration where the wave generator is radially inward of the motor rotor rather than outward, and the flex spline is positioned between the wave generator and output shaft. This inverted arrangement achieves high reduction ratios with a single stage, eliminating the need for multiple planetary gear stages and their associated complexity
3Speed
If external gearing is attached to the end of the motor, then speed reduction is achieved, but length increases
Solution Approach 1:
The motor and harmonic gear actuator are merged into a single integrated unit with concentric coaxial arrangement. The wave generator, flex spline, and output shaft are all concentric with the motor rotor, allowing the speed reduction mechanism to be incorporated within the motor's radial space rather than extending the actuator length
4Volume of moving object
If the actuator package is made compact, then size is reduced, but cooling requirements become more difficult
Solution Approach 1:
The patent positions hotter components such as motor windings radially outward of the actuator, utilizing the radial dimension for thermal management. This arrangement allows heat to dissipate outward through the motor housing while maintaining a compact overall volume, effectively using the radial space for both mechanical function and thermal management
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 size and weight of the actuator while providing increased torque and reducing the need for external gearing, allowing for improved cooling and a more compact package.
Implementation Method 1
a plurality of roller bearings radially disposed between the radially inner surface of the wave generator and a radially outer surface of the flex spline
Implementation Method 2
a plurality of windings coupled to the motor stator and a plurality of magnets coupled to the motor rotor
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
An inverted harmonic gear actuator (100) is provided and includes a motor stator (202) and a motor rotor (208) radially disposed within the motor stator (202). The inverted harmonic gear actuator (100) also includes a wave generator (103) radially disposed within the motor rotor (208), where the wave generator (103) has a radially inner surface with a cammed shape. An actuator output shaft (106) is radially disposed within the wave generator (103). A flex spline (102) is radially interposable between the radially inner surface of the wave generator (103) and the actuator output shaft (106). The flex spline (102) is deformable to conform to the radially inner surface of the wave generator (103) and drive rotation of the actuator output shaft (106) slower than rotation of the motor rotor (208).