Legged Robot Screw Actuator Layout for Low Knee Inertia
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Solution Overview
Problem
Existing actuators in legged robots, particularly electromechanical actuators, suffer from high rotational inertia which limits responsiveness and performance characteristics, especially in smaller robots, due to the influence of gear ratios and motor inertia.
Innovation Solution
Implementing a screw actuator configuration that shifts the motor mass away from the knee joint and uses a planetary roller screw mechanism to reduce rotational inertia, thereby enhancing responsiveness and acceleration capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If traditional electromechanical actuators with gear mechanisms are used, then torque amplification is achieved, but rotational inertia increases and responsiveness decreases
Solution Approach 1:
The patent extracts the motor mass from the distal location near the knee joint and relocates it to the proximal location at the hip joint. This removal of mass from the distal position reduces the rotational inertia at the knee joint, thereby improving responsiveness and acceleration capabilities while maintaining torque requirements through the screw mechanism's mechanical advantage
Solution Approach 2:
The patent replaces the traditional gear mechanism with a planetary roller screw mechanism. This substitution eliminates the need for high gear ratios that increase rotational inertia, while the screw mechanism's inherent mechanical advantage provides the necessary torque amplification with reduced distal mass
2Power
If motor mass is positioned distally near the knee joint, then direct drive capability is improved, but rotational inertia at the knee joint increases
Solution Approach 1:
The motor mass is extracted from the distal position and relocated proximally, removing the source of high rotational inertia from the knee joint while maintaining the actuator's power delivery capability through the screw mechanism
Solution Approach 2:
The patent changes the spatial dimension of motor placement from distal to proximal location, fundamentally altering the mass distribution along the longitudinal axis of the leg, which reduces rotational inertia without sacrificing actuation capability
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 screw actuator design reduces distal mass and rotational inertia at the knee joint, allowing for higher acceleration and improved force control strategies, thus enhancing the performance of legged robots.
Implementation Method 1
uses a planetary roller screw mechanism to reduce rotational inertia
Implementation Method 2
uses a planetary roller screw mechanism to reduce rotational inertia
Data Source
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AI summary
An example robot (300) includes: a leg (304, 306) having an upper leg member (410) and a lower leg member (412) coupled to the upper leg member at a knee joint (404); a screw actuator (400) disposed within the upper leg member, where the screw actuator has a screw shaft (406) and a nut (408) mounted coaxial to the screw shaft such that the screw shaft is rotatable within the nut; a motor (402) mounted at an upper portion of the upper leg member and coupled to the screw shaft; a carrier (414) coupled and mounted coaxial to the nut such that the nut is disposed at a proximal end of the carrier; and a linkage (418, 422) coupled to the carrier, where the linkage is coupled to the lower leg member at the knee joint.