Robot Screw Actuator With Universal Joints for Low Backlash
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Solution Overview
Problem
Existing screw actuators in robots face challenges such as friction, complexity, alignment issues, wear, and increased backlash due to sliding anti-rotation constraints and spherical bearings, which degrade performance and reduce the lifespan of robotic systems.
Innovation Solution
Implementing screw actuators with universal joints and rolling-element bearings to support thrust loads and react torque, minimizing inertia and backlash, while using telescoping pistons and thrust bearings to resist buckling and tilting, and incorporating a rotor coupled to the screw shaft for reduced friction and improved motion range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If sliding anti-rotation constraints (keyed shaft or linear rail) are used to react torques, then torque reaction capability is improved, but friction and device complexity increase
Solution Approach 1:
The patent removes the sliding anti-rotation constraint (keyed shaft or linear rail) from the system entirely. Instead, torque reaction is achieved through the spherical bearing's inherent ability to handle radial and axial loads while allowing rotational movement, eliminating the need for separate anti-rotation mechanisms and reducing overall device complexity
Solution Approach 2:
The spherical bearing is designed to perform multiple functions simultaneously: it supports thrust loads, reacts torque, and provides anti-rotation capability without requiring additional specialized components. This multi-functional approach reduces device complexity while maintaining torque reaction capability
2Adaptability or versatility
If spherical bearings are used to connect screw actuators to robot structures, then misalignment and structural deflection are accommodated, but wear and backlash increase over time
Solution Approach 1:
The patent replaces the traditional spherical bearing mechanism with a universal joint configuration that uses rolling-element bearings. This substitution maintains the ability to accommodate misalignment and structural deflection while eliminating the wear and backlash problems associated with traditional spherical bearings, as rolling-element bearings provide more stable and durable performance
3Force
If screw actuators are designed for high torque amplification, then motor torque is increased, but inertia of the actuator increases
Solution Approach 1:
The patent positions the motor mass proximally within the robot limb using the universal joint configuration, effectively moving mass from the distal end to the proximal end. This dimensional repositioning reduces the moment of inertia about the joint axis while maintaining torque amplification capabilities through the screw transmission mechanism
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 solution provides a low-inertia, low-friction, and low-backlash actuation system with enhanced motion range and durability, supporting high torque and acceleration capabilities suitable for robotic applications.
Implementation Method 1
universal joints with rolling-element bearings can help provide a low-friction, low-backlash interface between the actuator and one or more attached robot structures
Implementation Method 2
The screw actuator includes a screw having a screw shaft and a screw nut. The screw shaft defines a first longitudinal axis along its length. The screw nut at least partially surrounds the screw shaft.
Implementation Method 3
In some embodiments, a thrust bearing supports the axial load on the screw and/or constrains the rotation of the screw and/or rotor.
Data Source
AI summary
The invention includes a screw actuator. The screw actuator includes a screw having a screw shaft and a screw nut. The screw shaft defines a first longitudinal axis along its length. The screw nut at least partially surrounds the screw shaft. The screw actuator includes a motor having a stator and a rotor. The rotor is mechanically coupled to the screw shaft. The stator at least partially surrounds the rotor. The screw actuator includes a first rigid member having a length dimension oriented along the first longitudinal axis. The screw actuator includes a second rigid member mechanically constrained relative to the first rigid member. The second rigid member is configured to move along a direction of the first longitudinal axis.