Redundant Robot Arm Control via Singularity Avoidance
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Solution Overview
Problem
The use of six-axis robots in industrial applications, such as line tracking and painting, is limited by insufficient degrees of freedom, leading to collision risks, complexity in programming, and instability due to singularity issues, particularly when a seventh axis is introduced without a linear rail, which increases space and cost requirements.
Innovation Solution
A method for controlling a redundant seven-axis robot arm that involves selecting an application, generating an instruction set, modifying the path to avoid singularity positions, and using algorithms to maintain constraints and avoid collisions within a defined robot envelope, thereby stabilizing the robot's motion and reducing the risk of collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a seventh axis is added to the robot without a linear rail, then the robot provides flexible dexterity for collision avoidance and task accomplishment, but the compact space occupied by the redundant robot increases the probability of collision with obstacles and the workpiece
Solution Approach 1:
The control system dynamically adjusts the robot's configuration by modifying the path of the elbow point in real-time to avoid singularities and collisions. The system continuously monitors the robot's position and adjusts joint angles adaptively, transforming a static collision risk into a dynamically managed situation where the robot can avoid obstacles while maintaining task performance.
Solution Approach 2:
The elbow point serves as an intermediary element that mediates between the robot's base and end effector. By controlling the elbow point's path independently, the system can adjust the robot's configuration to avoid collisions without affecting the end effector's task performance, thus resolving the contradiction between compact space and collision avoidance.
2Device complexity
If a seventh axis is added to the robot without a linear rail, then the robot eliminates the need for expensive linear rails and reduces space requirements, but it creates singularity when the redundant axis is aligned in a straight line with a major axis which can create unpredictable robot motion and velocities
Solution Approach 1:
The control system applies preliminary anti-action by detecting potential singularity conditions in advance and modifying the elbow point path to avoid these configurations. The system proactively prevents singularity occurrence by adjusting the robot's configuration before reaching problematic states, thus maintaining motion stability while utilizing the redundant axis for enhanced dexterity.
Solution Approach 2:
The system dynamically adjusts the robot's configuration by modifying the elbow point path in real-time to avoid singularities. This dynamic approach allows the robot to exploit the redundant degree of freedom for collision avoidance and task optimization while maintaining stable and predictable motion by avoiding singular configurations.
3Adaptability or versatility
If a seven axis redundant robot is used, then the robot provides extra degree of freedom for flexible dexterity, but the programming of a seven axis redundant robot is very complex and difficult
Solution Approach 1:
The invention extracts the complexity of redundant axis control by separating it into an independent elbow point path planning subsystem. Instead of programming all seven axes simultaneously, the system independently controls the elbow point's path while the remaining six axes handle the primary task, thus reducing programming complexity while maintaining the benefits of the seventh redundant axis.
Solution Approach 2:
The control system segments the seven-axis robot control into two independent parts: elbow point path control and end effector task control. This segmentation allows programmers to work with simplified six-axis programming for the primary task while the elbow point automatically manages the redundant degree of freedom, significantly reducing programming complexity.
4Reliability
If a six axis robot with a linear rail is used, then the linear rail compensates for the movement of line conveyor and ensures repeatable joint angles, but the linear rail takes up space and adds cost to the painting operation
Solution Approach 1:
The invention replaces the mechanical linear rail system with a computational control system that uses the seventh redundant axis to achieve the same compensation function. Instead of physically moving the robot on a rail, the control system dynamically adjusts the elbow point path and joint angles to compensate for conveyor movement, eliminating the need for space-consuming linear rails while maintaining joint angle repeatability.
Solution Approach 2:
The seventh axis serves multiple functions: it compensates for conveyor movement (replacing the linear rail's function), provides collision avoidance capability, and enables enhanced dexterity for task accomplishment. This multi-functionality eliminates the need for separate linear rail infrastructure, reducing space requirements while maintaining or improving upon the reliability of joint angle repeatability.
Data Source
AI summary
A method for controlling a redundant robot arm includes the steps of selecting an application for performing a robotic process on a workpiece with the arm and defining at least one constraint on motion of the arm. Then an instruction set is generated based upon the selected application representing a path for a robot tool attached to the arm by operating the arm in one of a teaching mode and a programmed mode to perform the robotic process on the workpiece and movement of the arm is controlled during the robotic process. A constraint algorithm is generated to maintain a predetermined point on the arm to at least one of be on, be near and avoid a specified constraint in a robot envelope during movement of the arm, and a singularity algorithm is generated to avoid a singularity encountered during the movement of the arm.