Robot Motor Torque Control via Dual Feedforward Calculators
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Solution Overview
Problem
Existing motor control systems for torque servos in robots fail to accurately control output torque, especially when robots interact with environments, due to lack of consideration for reaction forces and inadequate two-degree-of-freedom control.
Innovation Solution
A control apparatus for motors that combines feedback and feedforward control, using first and second feedforward calculators to calculate motor output torque values based on motor, decelerator, and link models, as well as detected torque values, to accurately generate and adjust torque commands, including a comparator to combine these values and a feedback calculator for disturbance suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a two-degree-of-freedom control is applied to improve target value following property, then the torque command response is improved, but the output torque control accuracy deteriorates when the robot contacts the environment
Solution Approach 1:
The feedforward control is segmented into two independent calculators: a first feedforward calculator that computes torque based on motor models and rotation numbers, and a second feedforward calculator that computes torque based on dynamic models without depending on rotation numbers. This segmentation allows each calculator to specialize in different aspects of torque control, resolving the contradiction between response speed and accuracy.
Solution Approach 2:
A comparator is introduced as an intermediary component that combines the output torque values from both feedforward calculators and adds feedback torque based on detected values. This mediator integrates the fast response from the first calculator with the accurate environment interaction handling from the second calculator, achieving both rapid response and accurate torque control during robot-environment contact.
2Device complexity
If the feedforward control does not consider reaction force when the robot contacts environment, then the control calculation is simplified, but the output torque control becomes inaccurate
Solution Approach 1:
The control system segments the feedforward calculation into two parts: one that handles basic motor dynamics with simple models, and another that specifically addresses reaction force compensation during environment contact. This allows the system to maintain simplicity where possible while adding complexity only where necessary for accurate reaction force handling.
Solution Approach 2:
The comparator incorporates feedback by adding the third motor output torque value calculated based on the torque value detected by the sensor. This feedback mechanism allows the system to automatically compensate for reaction forces during robot-environment contact without requiring complex predictive models, maintaining calculation simplicity while improving accuracy.
Data Source
AI summary
A control apparatus of the motor according to one aspect includes: a first feedforward calculator configured to calculate a first motor output torque value so that a torque value indicated by a torque command signal can be generated in a joint part of a robot based on a model of a motor, a decelerator, or a link and the number of rotations of the motor, a second feedforward calculator configured to calculate a second motor output torque value based on the torque value indicated by the torque command signal without depending on the number of rotations of the motor; and a comparator configured to add the first motor output torque value, the second motor output torque value, and a third motor output torque value calculated based on the torque value detected by a sensor and the torque value indicated by the torque command signal.