Robot Arm Thermal Displacement Estimation for Sensorless Position Correction
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Solution Overview
Problem
Conventional methods for estimating thermal displacement in robot devices are costly, require sensor installation with potential alignment errors, and necessitate specialist intervention for calibration, leading to inaccuracies and operational interruptions.
Innovation Solution
A robot device with an arm mechanism and motor system that estimates thermal displacement using stored temporal variations in thermal displacement amounts during operation and stopped periods, allowing for accurate positional correction without sensors, enabling immediate on-site correction of positional deviations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensors are installed to measure temperature and displacement for thermal displacement estimation, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The robot arm itself is used to perform the measurement function. By controlling the arm to move between a reference position and a target position, and measuring the actual displacement without external sensors, the system makes the measurement object (arm mechanism) serve the measurement function, thereby eliminating the need for additional sensors and reducing system complexity
Solution Approach 2:
The patent replaces the sensor-based measurement system with a control-based mechanical measurement system. Instead of using sensors to directly measure thermal displacement, the system uses controlled mechanical movement and position feedback to indirectly determine thermal displacement, substituting a mechanical control approach for a sensor-based approach
2Measurement precision
If sensors are installed for thermal displacement measurement, then measurement precision is improved, but installation time and cost increase
Solution Approach 1:
The robot arm's own movement capability is utilized to perform position measurements without requiring external measurement devices. This self-service approach eliminates the time-consuming sensor installation process while maintaining measurement accuracy through controlled mechanical positioning
Solution Approach 2:
The system performs preliminary position measurements during the normal operation cycles of the robot arm. By utilizing the arm's regular movement between reference and target positions, the system continuously gathers measurement data without requiring separate installation or setup time for measurement devices
3Measurement precision
If sensors are used for thermal displacement correction, then measurement precision is improved, but reliability decreases due to sensor misalignment and malfunction
Solution Approach 1:
The robot arm's inherent control system is used to perform measurements, eliminating the reliability issues associated with external sensors. Since the arm's own position control system is used for measurement, there is no risk of sensor misalignment, malfunction, or drift, thereby improving measurement reliability
Solution Approach 2:
The position control system serves dual functions: both controlling the arm's movement and measuring its position. This multi-functionality eliminates the need for separate measurement sensors and their associated reliability problems, as the same control system performs both tasks
4Measurement precision
If sensors are installed for thermal displacement measurement, then measurement precision is improved, but ease of operation worsens due to calibration requirements
Solution Approach 1:
The robot arm's control system automatically performs position measurements during normal operation without requiring manual calibration or intervention. The system uses its own control mechanisms to gather measurement data, making the operation simple and intuitive while maintaining high measurement precision
Solution Approach 2:
The system implements automatic feedback-based measurement where the arm's position is continuously monitored and measured during normal operation. This feedback mechanism eliminates the need for manual calibration procedures, as the system automatically adjusts and records position data based on its own operational states
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
Achieves high-accuracy thermal displacement correction without sensors, allowing for immediate on-site handling of malfunctions and positional errors without relying on specialist technicians, thus reducing costs and operational disruptions.
Implementation Method 1
the temperature of an arm mechanism increases due to heat generation by a motor that is a source of power for joints and frictional heat generated by the inner structure of the joints and the like, and thermal deformation occurs at the arm mechanism due to thermal expansion
Data Source
AI summary
A robot device includes an arm mechanism that includes links and joints. A hand is mounted to a tip of the arm. A motor driver drives motors of the joints. A processor outputs, to the motor driver, a command value for moving a reference point of the hand to a target position. A storage device stores a first thermal displacement amount temporal variation representing a variation with respect to a continuous operation time period in a thermal displacement amount by which the hand reference point is displaced from a cool position to a heat balance position due to heat generation accompanying operation of the arm mechanism, and a second thermal displacement amount temporal variation representing a variation with respect to a continuous stopped time period in a thermal displacement amount by which the hand reference point returns from the heat balance position to the cool position accompanying stopping of operation of the arm mechanism. The processor refers to the first and second thermal displacement amount temporal variations to estimate a thermal displacement amount of the hand reference point based on the continuous operation time period and continuous stopped time period of the arm mechanism, and corrects the target position based on the estimated thermal displacement amount.