Robot Revolute Joint With Slip Ring for Continuous Rotation
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Solution Overview
Problem
Existing robot joints lack efficient and reliable mechanisms for continuous rotation and position tracking, often relying on dynamic cabling that can fail due to fatigue, and require complex output force sensors, increasing cost and complexity.
Innovation Solution
A revolute joint incorporating a planetary gear set with an electric motor and a coaxial slip ring for continuous rotation, eliminating the need for dynamic cabling and reducing complexity by using a rotary encoder or hall effect sensor for motor control, with additional methods for position tracking such as inertial measurement units and magnetometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If dynamic cabling is used to power the motor during rotation, then the joint can be powered during movement, but the cabling fatigues over time due to flexing, resulting in conductor or sheathing failure
Solution Approach 1:
The patent extracts the power and signal transmission function from dynamic cabling by introducing a slip ring assembly. The slip ring assembly provides continuous rotational electrical connection without the flexing and fatigue problems of dynamic cabling, thereby eliminating the reliability issue while maintaining power supply capability.
Solution Approach 2:
The patent replaces the mechanical dynamic cabling system with an electrical slip ring system. The slip ring assembly uses contactless or minimal-contact electrical sliding contacts to transmit power and signals during rotation, substituting the mechanical flexing cabling with a more reliable electrical transmission mechanism.
2Measurement precision
If an output force sensor is used to measure output force, then accurate force measurement is achieved, but the system complexity and cost increase
Solution Approach 1:
The patent implements feedback by measuring the input force at the motor and using the known transmission ratio of the planetary gear set to calculate the output force. This feedback approach eliminates the need for a separate output force sensor, reducing system complexity while maintaining measurement accuracy through mathematical relationship.
Solution Approach 2:
The system uses its own internal components (motor force sensor and planetary gear set) to provide the measurement function that would otherwise require a separate output force sensor. The transmission mechanism itself serves the dual purpose of force transmission and force measurement through its known mechanical advantage.
3Force
If a planetary gear set with reduction is used, then torque multiplication is achieved, but the input encoder may roll over when powered off and backdriven, causing position error
Solution Approach 1:
The patent implements preliminary action by indexing the input encoder position relative to the joint output every time the robot is powered on. This preliminary calibration step uses measurements from inertial measurement units or magnetometers to determine the correct position relationship, preventing position errors before operation begins.
Solution Approach 2:
The patent introduces intermediary sensors (inertial measurement units, magnetometers, or simple output encoders) that serve as mediators between the input encoder and the actual joint position. These intermediaries provide reference measurements that help track and correct encoder rollover events, maintaining position accuracy despite the reduction 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 reliable and efficient continuous rotation with reduced complexity and cost by eliminating the need for dynamic cabling and output force sensors, ensuring accurate position tracking through software integration.
Implementation Method 1
a planetary gear set, which in some embodiments is nested with an electric motor
Implementation Method 2
In the joint output there is a coaxial slip ring that allows continuous rotation of the joint
Implementation Method 3
An axle of the planetary gear set turns a pulley that engages with a belt, which drives a pulley that turns an output shaft of the joint
Implementation Method 4
the motor is controlled based on a signal from a hall effect sensor that is associated with the rotor of the motor
Data Source
AI summary
A revolute joint incorporates a planetary gear set, which may be nested with an electric motor. An axle of the planetary gear set turns a pulley that engages with a belt, which drives a pulley that turns an output shaft of the joint. In the joint output there is a coaxial slip ring that allows continuous rotation of the joint, meaning that output revolutions are not limited for maximum possible range of motion for the robot arm. The slip ring replaces dynamic cabling (which can fatigue over time), which is good for reliability/cycle life.