Robot Motion Control for Small Shape Generation
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Solution Overview
Problem
Existing methods for controlling industrial robot motion for small shape cutting are limited by friction, backlash, and lost motion, particularly on major axes, leading to path deviation and inaccuracy, especially when cutting thick materials or requiring full robot reach.
Innovation Solution
A system and method that fixes at least one major axis during motion, allowing the robot to move about minor axes to maintain cutting approach orientation and path accuracy, using a controller to determine interpolated positions and align the approach vector with the cutting axis, enabling the formation of cuts with squared sides and maintaining hole accuracy regardless of part Z coordinate placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the robot moves all axes to achieve full range of motion and positioning, then the robot can reach any position and orientation, but friction, backlash, and lost motion increase leading to path deviation and reduced accuracy
Solution Approach 1:
The robot's six axes are segmented into two groups: major axes (1-3) that remain fixed to eliminate friction and backlash, and minor axes (4-6) that move to achieve the required tool position and orientation. This segmentation allows the system to maintain full adaptability through the minor axes while eliminating the harmful effects of moving all axes simultaneously.
Solution Approach 2:
Instead of the conventional approach where major axes move to position the tool and minor axes orient it, this invention inverts the approach by keeping major axes fixed and using only minor axes for both positioning and orientation. This inversion eliminates the source of friction and backlash from the positioning function while maintaining full robotic capability through coordinated minor axis movement.
2Manufacturing precision
If the robot fixes major axes to reduce friction and backlash, then path accuracy improves, but the robot loses ability to maintain general path and orientation
Solution Approach 1:
The invention compensates for the reduced degrees of freedom from fixing major axes by utilizing the full range of motion of the three minor axes in a coordinated manner. The controller calculates specific motion trajectories for the minor axes that achieve both positioning and orientation functions, effectively using dimensional coordination to compensate for the fixed major axes.
3Manufacturing precision
If only wrist axes are moved to eliminate major axis errors, then short move precision improves, but robot path cannot be maintained and orientation is sacrificed
Solution Approach 1:
The minor axes are designed to perform multiple functions simultaneously: they position the tool center point, orient the tool approach vector, and maintain the robot path. By making the minor axes universal in their capability, the system achieves short move precision without sacrificing orientation or path maintenance capability.
Data Source
AI summary
A method of controlling robot motion for small shape generation is provided. The method includes the steps of: a) providing a robot having a plurality of interconnected distal links with a respective plurality major axes and a respective plurality of minor axes, the robot having a controller for moving the robot to a starting position and along a path including a series of interpolated positions to be followed relative a workpiece; b) moving the robot to the starting position; c) determining a next interpolated position on the path, wherein the robot remains fixed in position about at least one of the major axes and a location and an approach vector of the next interpolated position can be achieved; and d) moving the robot to the next interpolated position. A method where the robot remains fixed in position about all major axes is also provided.