Robot Rotary Shaft Control for Friction-Free Load Torque Estimation
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Solution Overview
Problem
Current methods for calculating the gravitational torque of a load applied to a motor-driven robot are burdensome for operators, prone to errors, and struggle when dynamical and viscous frictions have different effects depending on the rotation direction, complicating accurate estimation.
Innovation Solution
A method involving a robot with first and second rotary shafts, where the second shaft is rotated at least 90 degrees at a constant angular velocity while the first shaft is vibrated relative to the load, allowing for the calculation of gravitational torque without being affected by dynamical and viscous frictions, by equating the operating angles and using the calculated torques at specific positions to determine the load's mass and center of gravity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the load mass is calculated from the difference in torque between when the robot arm is at a standstill and when the load is applied and slightly lifted, then the robot becomes aware of the load mass, but the operator burden increases due to requiring torque measurements in multiple states and fine-tuning while considering friction direction
Solution Approach 1:
The invention applies mechanical vibration to the first rotary shaft to enable rotation relative to the load without requiring full rotation or lifting. By vibrating the shaft at a specific frequency, the system can measure gravitational torque through the vibration response, eliminating the need for manual torque measurements in multiple states and fine-tuning procedures. This reduces operator burden while maintaining measurement precision.
Solution Approach 2:
The invention replaces the manual mechanical measurement process (requiring operator intervention for torque measurement and fine-tuning) with an automated vibration-based measurement system. The control unit automatically analyzes the vibration characteristics to calculate gravitational torque, substituting the manual mechanical measurement process with an automated dynamic analysis approach.
2Measurement precision
If the mass and position of center of gravity of the load is calculated from gravitational torques while compensating for dynamical and viscous frictions by rotating two orthogonal shafts, then the load estimation can be performed, but the estimation becomes difficult when frictions have different effects depending on rotation direction
Solution Approach 1:
By using mechanical vibration of the first rotary shaft, the system can measure gravitational torque without requiring compensation for dynamical and viscous frictions. The vibration-based measurement captures the gravitational effect directly through the shaft's response characteristics, eliminating the complex friction compensation calculations required in traditional rotation-based methods.
Solution Approach 2:
The invention extracts the gravitational torque measurement from the complex system of friction-compensated rotation measurements. By isolating the gravitational effect through vibration analysis of a single shaft, the method removes the need to account for friction effects in multiple rotating shafts, simplifying the measurement process while maintaining accuracy.
3Reliability
If manual entry of load mass and center of gravity position is required, then the robot controller has accurate load information, but the operator may forget to enter data or make typing errors increasing burden
Solution Approach 1:
The system performs self-service by automatically measuring the load mass and center of gravity position through vibration-based gravitational torque measurement. The control unit calculates these parameters directly from the vibration response without requiring operator input, eliminating typing errors and ensuring data accuracy while reducing operator burden to minimal actions.
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 accurate calculation of gravitational torque even when frictions differ by direction, reducing operator burden and improving precision in load estimation and collision detection, enhancing robotic performance in tasks like welding.
Implementation Method 1
vibrating the first rotary shaft so as to rotate the first rotary shaft relative to the load
Implementation Method 2
rotating the second rotary shaft at a constant angular velocity
Data Source
AI summary
In a robot having a first rotary shaft and a second rotary shaft driven by respective motors and extending in the same direction, the second rotary shaft is rotated while vibrating the first rotary shaft that is holding a load directly or indirectly, thereby rotating the first rotary shaft relative to a load. This enables calculating the gravitational torque of the load applied to the first rotary shaft.