Robot Torque Compensation for Low-Speed Backdrivability
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Solution Overview
Problem
Existing robot control systems struggle to achieve sufficient backdrivability, which is essential for flexible robot arms that need to coexist with humans and operate using machine learning.
Innovation Solution
A robot control device that includes a speed calculation unit and a compensation value calculation unit. The compensation value unit calculates a viscous resistance compensation value to adjust the torque command, reducing the viscous resistance closer to zero, especially at lower speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control using a disturbance observer is used to compensate for external force, then control accuracy is improved, but backdrivability deteriorates
Solution Approach 1:
The patent segments the control signal into multiple components: a feedforward torque command for basic motion control, and a separate viscous resistance compensation command. This segmentation allows the viscous resistance compensation to be handled independently without interfering with the feedback control loop, thereby improving backdrivability while maintaining control accuracy.
Solution Approach 2:
The patent applies preliminary action by calculating and adding the viscous resistance compensation value to the torque command in advance, before the actual control execution. The compensation is computed based on the current speed and viscosity characteristics, and this pre-computed compensation is integrated into the control signal, allowing the system to counteract viscous resistance proactively rather than reactively.
2Speed
If viscous resistance compensation is applied at high speeds, then motion control is improved, but backdrivability at low speeds deteriorates
Solution Approach 1:
The patent implements dynamic adjustment of viscous resistance compensation based on the actual speed of the output shaft. The control system continuously monitors speed and adjusts the compensation magnitude accordingly: applying larger compensation at high speeds to maintain motion control, and reducing compensation at low speeds to preserve backdrivability. This dynamic adaptation resolves the contradiction between high-speed control performance and low-speed backdrivability.
Solution Approach 2:
The patent changes the compensation parameter (viscous resistance compensation value) based on operating conditions, specifically speed. By making the compensation parameter variable rather than fixed, the system can optimize performance across different speed ranges, improving backdrivability at low speeds while maintaining adequate motion control at high speeds.
Data Source
AI summary
A robot control device includes: a speed calculation unit configured to calculate a speed of an output shaft of a drive unit configured to drive a robot; and a compensation value calculation unit configured to calculate a viscous resistance compensation value, the viscous resistance compensation value being a value for generating a second torque command to be output to the drive unit by compensating for a supplied first torque command in such a manner that a second viscous resistance is closer to zero than a first viscous resistance, the first viscous resistance being a viscous resistance at a first speed detected by the speed calculation unit, and the second viscous resistance being a viscous resistance at a second speed lower than the first speed.