Compact Robot Joint with Nested Harmonic Drive
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Solution Overview
Problem
Existing robot joints are not compact enough to meet the requirements of robots with a compact form factor, as they occupy excessive axial space due to the size of the motor and speed reducer components.
Innovation Solution
A robot joint design that incorporates a harmonic drive mechanism, where the harmonic drive is almost completely received within the casing, along with a motor assembly and encoder configuration, allowing for reduced axial dimensions by utilizing a circular spline and flex spline arrangement, and strategically placing components to minimize space usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a conventional motor and speed reducer configuration is used, then the joint can provide sufficient torque and speed reduction, but the axial dimension becomes excessively large
Solution Approach 1:
The harmonic drive mechanism is nested within the motor assembly, with the circular spline and flex spline arranged concentrically around the motor shaft. The wave generator is received within the flex spline, creating a compact nested structure that reduces axial dimension while maintaining torque output capability.
Solution Approach 2:
The patent transitions from a conventional axial arrangement of motor and speed reducer to a radial arrangement where the harmonic drive components are positioned radially around the motor shaft. This dimensional reorganization allows the speed reduction function to be achieved without increasing the axial dimension.
2Length of moving object
If the harmonic drive is completely received within the rotor, then the axial dimension is reduced, but the encoder and output shaft arrangement becomes more complex
Solution Approach 1:
The joint is divided into distinct functional segments: the motor assembly with integrated harmonic drive, a separate encoder assembly, and an output shaft assembly. The encoder is positioned at the end of the motor shaft where it can detect rotational position without interfering with the harmonic drive mechanism, while the output shaft is coaxially arranged to receive power from the flex spline.
Solution Approach 2:
The motor shaft serves multiple functions: it acts as the rotor of the motor, serves as the input shaft for the harmonic drive, and provides a mounting position for the encoder. The encoder detects the rotational position of the motor shaft, which corresponds to the input position of the harmonic drive, enabling precise control without additional complex mechanisms.
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
The design achieves a compact robot joint with reduced axial dimensions, enabling efficient relative rotary motion between adjacent links while maintaining accurate angular position detection and heat dissipation, thus addressing the space constraints of compact robot designs.
Implementation Method 1
When the stator is energized, a rotating magnetic field is generated and drives the rotor to rotate, which enables mechanical power to be transmitted through the motor shaft.
Implementation Method 2
The wave generator is received in the flex spline and configured to drive the flex spline to rotate with respect to the circular spline.
Data Source
AI summary
A robot joint includes a casing, a motor assembly including a stator and a rotor that are arranged within the casing, and a harmonic drive received, at least in part, in the rotor. The harmonic drive includes a circular spline, a wave generator fixed to the rotor, and a flex spline. The circular spline is arranged around and engaged with the flex spline. The wave generator is received in the flex spline and configured to drive the flex spline to rotate with respect to the circular spline. The robot joint further includes an output shaft fixed to the flex spline.