Radially Stacked Actuator Layout for High Torque in Tight Robot Space
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Solution Overview
Problem
Humanoid robots face a tradeoff between actuator size and performance due to limited space, necessitating actuators that offer a better performance-to-volume ratio while fitting within a human-like form.
Innovation Solution
Radially stacked series elastic actuators are designed, featuring a motor, gearbox, and actuator output with a radial load path, incorporating a spring for deflection measurement and sensors for precise torque and position control, optimized for a cylindrical shape to enhance torque density and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If larger actuators are used to improve performance, then torque density and bandwidth are improved, but the robot cannot fit within the human envelope
Solution Approach 1:
The actuator employs a nested configuration where the gearbox is positioned inside the motor housing, and the spring is contained within the gearbox assembly. This nested doll approach allows multiple functional components to occupy overlapping spatial volumes, achieving high torque density without increasing the external envelope of the actuator.
Solution Approach 2:
The patent transitions from traditional linear/axial actuator layouts to a radial configuration where the load path extends outward from the central motor axis. The radial load path allows the actuator to generate torque in a direction perpendicular to the motor shaft, enabling compact cylindrical packaging that fits within the human envelope while maintaining high power density.
2Volume of moving object
If actuators are made smaller to fit within the human envelope, then volume is reduced, but performance (torque density and bandwidth) deteriorates
Solution Approach 1:
The actuator employs a flexible spring element that serves multiple functions: it stores elastic potential energy, provides mechanical compliance, and transmits torque. This flexible component allows the actuator to maintain compact dimensions while achieving high torque density through elastic energy storage and release, effectively decoupling size from power output.
Solution Approach 2:
The series elastic actuator utilizes elastic deformation of the spring as a form of mechanical energy storage analogous to pneumatic/hydraulic systems. The spring's elastic properties enable the actuator to achieve high bandwidth and torque density in a compact package by rapidly storing and releasing mechanical energy, similar to how pneumatic systems use compressed gas.
3Power
If a radial load path is implemented to improve torque density, then performance-to-volume ratio is improved, but device complexity increases
Solution Approach 1:
The spring element in the actuator serves multiple functions simultaneously: it acts as a torque transmitter, an energy storage device, a mechanical compliance element, and a position sensor reference. This multi-functionality reduces the need for separate components, thereby lowering overall device complexity despite the radial load path configuration.
Solution Approach 2:
The patent merges the gearbox and motor housing into a single integrated assembly, with the spring contained within the gearbox structure. This consolidation of components reduces the number of separate parts and interfaces, simplifying manufacturing and assembly while maintaining the high-performance radial load path architecture.
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
These actuators achieve superior cumulative performance metrics, including torque density, specific torque, and torque resolution, optimizing performance within the limited volume of humanoid robots.
Implementation Method 1
A spring, such as a planar torsion spring, can be coupled between the motor ground and the actuator ground such that the spring deflects as the motor ground rotates relative to the actuator ground.
Implementation Method 2
A spring displacement sensor can be provided to measure the displacement of the motor ground relative to the actuator ground. In an example embodiment, the spring displacement sensor is a capstan-reduction encoder that amplifies torque resolution.
Implementation Method 3
a wave generator bearing into which the wave generator is inserted and that contacts the flex spline based on the position of the wave generator to cause the flex spline to mesh with the circular spine in limited areas.
Data Source
AI summary
A radial stacked actuator includes an actuator ground; a motor including a motor ground constrained to the actuator ground with one or more rotational degrees of freedom; a spring coupled between the motor ground and the actuator ground; a gearbox coupled to the motor at an input of the gearbox; and an actuator output coupled to an output of the gearbox. The spring is configured to deflect as the motor ground rotates relative to the actuator ground.