Robot Arm Gravity Compensation Control for Safe Stopping
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Solution Overview
Problem
Robot arms with high back-drivability, used for interacting with humans, pose a safety risk when power is cut off due to potential dropping caused by gravity, especially when positioned high, as they lack sufficient joint friction to maintain stability.
Innovation Solution
Implementing a gravity compensation control method that calculates and applies a compensation torque to maintain the robot arm's position, using motor currents and joint angles to determine if the arm is in safety mode and outputting torque to prevent falling, allowing safe stopping and user escape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the robot arm is designed with high back-drivability for human interaction, then the robot arm achieves flexibility and ease of movement, but the robot arm becomes unstable and drops due to gravity when power is cut off
Solution Approach 1:
The patent implements gravity compensation control that calculates and applies a counter-torque equal to the gravitational torque acting on the robot arm. This counter-torque compensates for the weight of the arm segments, effectively creating an anti-gravity effect that prevents the arm from dropping when power is interrupted, while maintaining high back-drivability during normal operation.
2Adaptability or versatility
If the joint friction is reduced to enable high back-drivability, then the robot arm becomes more flexible for human interaction, but the robot arm cannot maintain its position when power is cut off
Solution Approach 1:
The patent replaces reliance on mechanical friction for position maintenance with an active gravity compensation control system. The control unit continuously calculates the gravity torque based on joint angles and applies compensating torque through the motor, substituting the passive mechanical friction mechanism with an active control-based solution that maintains precision while preserving back-drivability.
3Object-affected harmful factors
If the robot arm operates in safety mode to stop operation during emergencies, then user safety is improved, but the robot arm drops due to gravity without position maintenance
Solution Approach 1:
The patent applies preliminary anti-action by implementing gravity compensation control before power is completely cut off during an emergency. The control system detects the emergency condition and maintains compensating torque until the arm reaches a safe position, preventing the harmful effect of uncontrolled dropping while still enabling safe stopping and user escape.
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
Ensures safe stopping and prevents collisions by maintaining the robot arm's position through gravity compensation, enhancing user safety and preventing damage to the robot and its environment.
Implementation Method 1
calculating a compensation torque of gravity applied to the robot arm... performing a gravity compensation control of the robot arm according to the calculated compensation torque of gravity
Data Source
AI summary
Disclosed are a robot arm having high back-drivability to interact with a human being, which is safely stopped, and a method of controlling the robot arm. When the operation of the robot arm having high back-drivability to interact with a human being is converted into a safety mode due to the occurrence of an emergency, in which the operation of the robot arm is stopped, only a torque having a degree to compensate for gravity applied to the robot arm, i.e., only a torque to maintain the kinematical position of the current state of the robot arm without falling of the robot arm due to gravity, is outputted to control the robot arm as if the robot arm is in a weightless state, thus being capable of safely stopping the robot arm.