Robot Arm Joint Deflection Compensation for Tip Position 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 and pivot, using moment rigidity and spring constants, and adjusts compensation amounts based on distances and gravitational torque to correct positional displacement, specifically considering the deflection of joints with rotary shafts that do not rotate in the gravity direction.
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 positional 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 rotation direction of joints with rotary shafts, and (2) deflection in the tilting direction of rotary shafts. By separating these two types of deflection and applying different compensation methods for each, the system achieves comprehensive accuracy improvement without overwhelming complexity
Solution Approach 2:
The patent extends the compensation approach from one dimension (rotation direction only) to two dimensions by also compensating for deflection in the tilting direction of rotary shafts. This dimensional expansion ensures that both rotational and tilting deflections are addressed, thereby improving positional accuracy without excessive complexity
2Manufacturing precision
If deflection compensation is applied to all joints including those not rotating in gravity direction, then the positional accuracy of the robot arm tip is improved, but the calculation complexity and control processing time increase
Solution Approach 1:
The patent pre-calculates and stores the relationship between joint angles and deflection amounts in lookup tables before actual operation. During real-time control, the system only needs to perform simple table lookups and additions rather than complex calculations, significantly reducing processing time while maintaining high accuracy
Solution Approach 2:
The patent creates simplified mathematical models that replicate the complex deflection behavior of joints. By using these simplified models with pre-computed parameters, the system can quickly estimate deflection amounts without performing full-scale complex calculations, thus reducing processing time while preserving accuracy
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
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
Implementation Method 2
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
Data Source
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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.