Direct-Drive Ball Screw Linear Actuator Without Planetary Gears
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Solution Overview
Problem
Current linear actuators in humanoid robots suffer from poor real-time control performance, reliability issues, and unbalanced driving force due to the use of brushed motors and multi-stage planetary gear structures, leading to inefficiencies and reliability problems.
Innovation Solution
A linear drive mechanism utilizing a stator and rotor coupled with a ball screw, featuring a hollow screw nut and center screw with ball grooves to form a rolling connection, along with a toothless groove iron core and magnetic ring structure to enhance control and efficiency, and eliminate brush friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If brushed motors and multi-stage planetary gear structures are used in linear actuators, then the actuators can achieve force transmission and motion conversion, but the real-time control performance deteriorates due to significant hysteresis after multiple stages of reduction
Solution Approach 1:
The patent removes the planetary gear reduction stage from the transmission system, directly coupling the motor output to the ball screw mechanism. This extraction of the problematic multi-stage gear structure eliminates the hysteresis and backlash issues while maintaining the necessary force transmission and motion conversion functions through the direct-drive ball screw configuration
Solution Approach 2:
The patent replaces the mechanical planetary gear reduction system with a direct motor-to-ball-screw coupling. This substitution eliminates the mechanical hysteresis inherent in gear teeth meshing and reduces the number of moving parts, thereby improving real-time control performance while maintaining adequate torque transmission through the ball screw's mechanical advantage
2Force
If multi-stage planetary gear structures are used for force transmission, then the actuators can achieve torque multiplication, but the efficiency deteriorates rapidly with an increase in the number of stages
Solution Approach 1:
The patent extracts the intermediate planetary gear stages that cause energy loss, retaining only the essential ball screw mechanism for torque multiplication. This reduces the number of meshing interfaces and friction points, thereby maintaining adequate torque multiplication while significantly improving transmission efficiency
Solution Approach 2:
The patent substitutes the multi-stage planetary gear system with a direct-drive ball screw mechanism. The ball screw provides mechanical advantage through its threaded geometry, achieving torque multiplication with fewer moving parts and lower friction losses, thus improving overall transmission efficiency while maintaining force transmission capability
3Power
If brushed motors are used in linear actuators, then the actuators can achieve rotational motion and torque output, but the reliability deteriorates due to contact problems with brushes causing unbalanced three-phase resistance and torque
Solution Approach 1:
The patent replaces the brushed motor's contact-based commutation system with a brushless motor design using electronic commutation and magnetic field interaction. This substitution eliminates wear, sparking, and contact resistance variations, thereby maintaining full rotational motion and torque output capability while significantly improving reliability and eliminating unbalanced three-phase resistance issues
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 real-time control with high reliability, balanced driving force, and efficient operation, while minimizing size and ensuring stable thrust with minimal fluctuation, suitable for applications in humanoid robot fingers.
Implementation Method 1
the coil winding is configured to drive the rotor to rotate after being energized
Implementation Method 2
a permanent magnet mounted on the magnet-conducting hollow shaft structure is of a radial four-pole magnetic ring structure or a radial six-pole magnetic ring structure
Implementation Method 3
the plurality of balls are sandwiched between the first ball grooves and the second ball grooves in order to form a rolling connection between the screw nut and the center screw
Data Source
AI summary
The present application provides a linear drive mechanism, including a casing, a front cover and a rear cover fixed at opposite ends of the casing, a stator arranged in the casing, a hollow rotor rotatably connected to the stator, and a ball screw including a screw nut and a center screw arranged in the screw nut. The screw nut is provided with first ball grooves recessed inwardly and threadedly spiraled at intervals, and the center screw is provided with a second ball grooves that are spiraled. The ball screw further includes a plurality of balls sandwiched between the first ball grooves and the second ball grooves to form a rolling connection between the screw nut and the screw body. The linear drive mechanism can realize real-time control and has good reliability, high efficiency, more balanced driving force, low overall height, small length, friendly mounting size and simple structure.