Friction Compensation Device for Robot Control

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Solution Overview

Problem

Existing friction models for robots and industrial machines fail to accurately estimate friction torque due to variations at constant velocity and temperature, as they only consider motor velocity, neglecting the effects of inertial, centrifugal, and Coriolis forces, and gravity.

Innovation Solution

A friction compensation device that calculates friction torque by incorporating motor position, velocity, and acceleration to estimate friction forces, using a drive torque calculation unit and a friction estimate value calculation unit, which includes a friction correction value calculation to account for inertial, centrifugal, and Coriolis forces, and gravity, improving accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a friction model determined only by motor velocity is used, then the calculation is simple, but the friction torque estimation accuracy is insufficient

Engineering Contradiction:

Improvefriction model complexityVSAvoidfriction torque estimation accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The friction model is enhanced by adding new parameters (motor acceleration and position) to the existing velocity parameter. This transforms the friction torque calculation from a single-parameter model to a multi-parameter model that captures the dynamic variations in friction torque more accurately.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The friction torque is segmented into multiple components: velocity-dependent friction, acceleration-dependent friction, and position-dependent friction. Each component is calculated separately and then summed to obtain the total friction torque, allowing for more precise estimation of each contribution.

Inventive Principle:

Principle #1Segmentation

2Device complexity

If friction torque variation is not considered, then the control system is simpler, but collision detection accuracy deteriorates

Engineering Contradiction:

Improvecontrol system complexityVSAvoidcollision detection accuracy

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The control system uses feedback from multiple sensors (velocity sensors and position sensors) to continuously monitor and adjust the friction torque estimation. This feedback mechanism allows the system to adapt to real-time variations in friction torque, improving collision detection reliability without excessive complexity.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system performs preliminary calculation of friction torque using the enhanced model before collision detection occurs. By pre-calculating the friction torque with higher accuracy, the system prepares more reliable baseline data for subsequent collision detection, reducing the need for complex real-time adjustments.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS11691282B2Friction compensation device, and robot control device

Publication Date: 2023.07.04 MITSUBISHI ELECTRIC CORP

AI summary

A friction compensation device of the present disclosure includes a drive torque calculation unit that calculates output torque of a transmission mechanism from a motor's position, velocity, and acceleration, the transmission mechanism being connected to a motor via a shaft to transmit the driving force of the motor, and a friction estimate value calculation unit that calculates a friction estimate value that is an estimate value of a friction force on the shaft. The friction estimate value calculation unit includes a friction correction value calculation unit that calculates a friction correction value to correct the friction force on the shaft, in accordance with the output of the drive torque calculation unit.