Parallel Elastic Actuator for Hopping Robots
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Solution Overview
Problem
Existing hopping robots require high-speed and high-force actuation for non-trivial ground clearance, which is challenging due to the use of bulky and safety-hazardous hydraulic actuators, and existing prismatic actuators face difficulties in converting rotary motion to linear motion with unacceptable friction and hysteresis.
Innovation Solution
A compact and lightweight prismatic actuator mechanism using a voice coil motor in parallel with compression springs, known as LEAP (Linear Elastic Actuator in Parallel), which provides direct translational motion with negligible friction and hysteresis, allowing for efficient energy injection into springs to achieve hopping motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If hydraulic actuators are used for high-speed and high-force actuation, then the hopping robot can achieve non-trivial ground clearance, but the robot becomes bulky and unsafe due to large compressors and high-pressure systems
Solution Approach 1:
The patent replaces the hydraulic actuation system with an electrical motor system. Specifically, it uses a rotary motor (such as a voice coil motor or other linear motor) coupled with a screw mechanism to convert rotational motion into linear actuation, eliminating the need for hydraulic pumps, compressors, and high-pressure fluid systems while maintaining the required force output for hopping
Solution Approach 2:
The patent changes the actuation parameters by using elastic elements (springs) in parallel with the motor-screw mechanism. This parallel elastic configuration allows the system to store and release energy efficiently, reducing the peak force requirements on the motor while maintaining high force output during the hopping phase, thereby enabling a more compact and lighter design
2Speed
If rotary motors with gearing are used to convert rotary motion to linear motion, then translational motion can be achieved, but friction and hysteresis due to gearing backlash become unacceptable
Solution Approach 1:
The patent eliminates the gear transmission system by using a direct-drive approach where a rotary motor is coupled to a screw mechanism that directly converts rotational motion to linear motion. This removes the intermediate gearing stages that cause friction and backlash, resulting in more reliable and consistent force output while maintaining high actuation speed
Solution Approach 2:
The patent introduces a screw mechanism as an intermediary between the rotary motor and the linear actuation. The screw thread acts as a mechanical transformer that converts rotational motion to linear motion with high precision and minimal backlash, while the parallel elastic elements further smooth out force variations and reduce the impact of any residual friction
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 LEAP mechanism enables a lightweight and compact hopping robot design that achieves significant hopping height with optimal spring stiffness, reducing power consumption and eliminating safety hazards associated with hydraulic actuators, while maintaining high force and speed requirements.
Implementation Method 1
A type of direct-drive linear motor, such as a voice coil motor, voice coil actuator, or, more simply, a voice coil, may offer a useful alternative to the use of hydraulic linear actuators
Implementation Method 2
The actuator may be considered a linear elastic actuator in parallel or 'LEAP' that combines a voice coil motor in parallel with one or more compression springs
Data Source
AI summary
A prismatic actuator for imparting a hopping motion to a supported load such as a leg of robot. The apparatus includes a direct drive motor, such as a voice coil, operable to provide translational motion. The apparatus includes a spring element and a prismatic guide assembly. The guide assembly is configured to support the direct drive motor to constrain the translational motion to be along a drive axis and support the spring element to constrain compression and expansion of the spring element along a longitudinal axis parallel to the drive axis. The apparatus includes a controller that: (1) first controls the direct drive motor to compress the spring element during a first time period beginning when the apparatus initially contacts a surface; and (2) second controls the direct drive motor to expand the spring element when the apparatus has zero velocity while contacting the surface.