Robot Arm Joint Deflection Compensation for Machining Accuracy
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Solution Overview
Problem
Conventional robot control methods fail to accurately position the tip of a robot arm due to deflection of joints not rotating in the gravity direction, leading to reduced machining accuracy.
Innovation Solution
The method calculates deflection angles for joints with rotary shafts that tilt or pivot, using moment rigidity and spring constants, and applies compensation based on these angles to pivotable joints to correct positional displacement, considering gravitational torque and distance from a virtual straight line passing through the axes of pivotal joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If only joints rotating in the gravity direction are compensated for deflection, then the control complexity is reduced, but the positioning accuracy of the robot arm tip deteriorates due to uncorrected deflection in other joints
Solution Approach 1:
The patent segments the deflection compensation into two distinct parts: (1) deflection in the rotary shaft tilting direction for joints 1 and 4 calculated using moment rigidity, and (2) deflection in the pivoting direction for joints 2 and 3 calculated using spring constants. This segmentation allows comprehensive compensation without overwhelming complexity.
Solution Approach 2:
The patent adds a new dimension to deflection compensation by considering not only the pivoting direction (as in conventional methods) but also the rotary shaft tilting direction. This dimensional expansion enables accurate compensation for all deflection sources while maintaining systematic control.
2Manufacturing precision
If deflection compensation is applied to all joints including those not rotating in gravity direction, then the positioning accuracy is improved, but the calculation complexity and control processing load increase
Solution Approach 1:
The patent applies different compensation methods to different joints based on their local characteristics: joints 1 and 4 use moment rigidity-based compensation for rotary shaft tilting, while joints 2 and 3 use spring constant-based compensation for pivoting. This localized approach optimizes accuracy without uniform complexity.
Solution Approach 2:
The patent performs preliminary calculation of deflection angles for all four joints based on gravitational torque and respective rigidity characteristics, then integrates these into the control commands before execution. This preliminary compensation reduces real-time processing load during operation.
3Manufacturing precision
If deflection angles are calculated using moment rigidity and spring constants for multiple joints, then the machining accuracy is improved, but the computational requirements and control algorithm complexity increase
Solution Approach 1:
The patent changes the computational parameters by using pre-determined moment rigidity values for joints 1 and 4, and spring constant values for joints 2 and 3. These parameters are incorporated into the deflection angle calculations, enabling accurate compensation through standardized computational approaches.
Solution Approach 2:
The patent implements a feedback mechanism where deflection angles are continuously calculated based on gravitational torque and rigidity parameters, then used to adjust joint commands. This closed-loop approach ensures machining accuracy while maintaining manageable computational complexity through systematic feedback processing.
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
This approach effectively suppresses positional displacement of the robot arm tip by compensating for deflection angles across multiple joints, improving machining accuracy and stability by continuously correcting operation.
Implementation Method 1
the arm may be flexurally deformed by its own weight or a load applied to the tip of the arm. This deformation of the arm occurs particularly prominently at a joint with a rotary shaft.
Implementation Method 2
calculating a deflection angle of the first joint based on moment rigidity of the first joint and gravitational torque applied in a tilting direction of the rotary shaft of the first joint
Data Source
AI summary
A determination value calculated based on a distance from a work point of a tip of robot arm (10) to virtual straight line (30) passing through an axis of second joint (J2) and an axis of third joint (J3) is compared with a predetermined threshold. A method of calculating deflection compensation amounts for second joint (J2) and third joint (J3) is changed depending on whether the determination value is larger or smaller than the threshold. Second joint (J2) and third joint (J3) are caused to pivot based on the calculated deflection compensation amounts.