Torque Detection for Robotic Arm Gravity Compensation
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Solution Overview
Problem
Existing methods for gravity compensation in servo control systems require accurate determination of the arm's mass and center of gravity, making the process cumbersome and prone to errors due to mechanical deviations.
Innovation Solution
A torque detecting method that calculates the actual output torque by detecting gravitational torque and operating torque, using a gravity coefficient based on the arm's position and a correction value to account for mechanical deviations, allowing for accurate gravity compensation without needing to know the arm's mass or center of gravity, and smoothly adjusting torque during rotational direction changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gravity compensation is performed using the method in JP 62-60010 A (calculating gravity coefficient based on arm mass and center of gravity), then gravity compensation can be achieved, but the process becomes cumbersome and requires accurate determination of arm mass and center of gravity position
Solution Approach 1:
The system performs self-calibration by automatically detecting gravitational torque at multiple arm positions and computing the gravity coefficient through mathematical processing, eliminating the need for manual measurement of arm mass and center of gravity. The control unit serves both as the system being controlled and as the calibration instrument.
Solution Approach 2:
The patent replaces mechanical measurement methods (physical measurement of mass and center of gravity) with an electrical/torque-based detection system. The torque sensor and control unit compute gravitational characteristics through electrical signals and mathematical calculations instead of mechanical measurement tools.
2Measurement precision
If torque sensor is mounted on the rotary shaft, then gravitational torque can be detected, but mechanical deviation upon mounting causes torque detection errors
Solution Approach 1:
The system performs preliminary calibration measurements at multiple predetermined arm positions before normal operation. During this calibration phase, the torque sensor detects gravitational torque at known positions, and the control unit computes correction values that compensate for mounting deviations. This preliminary calibration data is stored and applied during subsequent torque detection.
Solution Approach 2:
The patent changes the detection parameters by measuring torque at multiple different arm positions (angles) rather than at a single position. By varying the arm position parameter and analyzing how gravitational torque changes with position, the system can mathematically separate and compensate for mounting deviation effects from actual gravitational torque.
3Measurement precision
If frictional force is considered in torque detection, then more accurate actual output torque can be obtained, but the detection process becomes more complex
Solution Approach 1:
The system performs self-calibration to automatically determine frictional characteristics during the calibration phase. By comparing torque measurements taken during forward and reverse movements at the same positions, the control unit computes frictional force components and incorporates them into the final torque calculation, eliminating the need for separate friction measurement equipment or complex manual procedures.
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
Enables precise gravity compensation and accurate calculation of actual output torque, reducing errors associated with mechanical deviations and simplifying the process by eliminating the need to determine the arm's mass and center of gravity, while ensuring smooth torque transitions during rotational direction changes.
Implementation Method 1
detecting gravitational torque applied to the rotary shaft in a condition in which the position control of the arm is stopped, when the arm is located at a first position
Implementation Method 2
detecting operating torque applied to the rotary shaft during the position control of the arm
Data Source
AI summary
According to a torque detecting method, gravitational torque applied to a rotary shaft of an arm is detected in a condition where position control of the arm is stopped, when the arm is located at a first position at which the arm is oriented in a direction different from a direction of gravitational force. Then, a gravity coefficient used for calculating gravitational torque corresponding to a position of the arm is calculated, based on the gravitational torque and the first position. Then, gravitational torque during position control is calculated, based on the position of the arm detected during the position control, and the gravity coefficient. Further, an actual output torque during the position control is calculated, based on operating torque applied to the rotary shaft and detected during the position control, and the gravitational torque calculated during the position control.