Background
Industrial robotic manipulators are highly precise and adaptable but have limited reach. For decades, coordinated motion between manipulators and external axes—fixed-location rails or gantries—has been the most common solution to expand reach. While coordinated motion between industrial manipulators and mobile platforms would be more flexible and less expensive, robust integration has not been available. Instead, when systems include both a manipulator and a mobile base, they operate in a stop-and-go fashion, use complex and expensive hardware, or require external monitoring infrastructure. Several recently developed technologies may, together, enable a navigation and manipulator planning framework where true coordinated motion is possible. This project aimed to explore the viability of a coordinated motion platform, free of external infrastructure, and assess its performance against process constraints in applications where continuous processing is necessary, such as sealing or structural welding.
Approach
In this project, we investigated methods for continuous-process tasks where the complete kinematic solution of a coupled mobile base and manipulator is highly valuable. We aimed to achieve high-frequency command and control of both the robot and mobile base. Full coordinated motion requires the mobile base not only to correct errors in its movement but also to consider the manipulator’s workspace and move such that the target will always remain within reach of the end-effector. We implemented the coupled kinematic solution to integrate with SwRI’s Tesseract framework and supplemented it with several techniques to mitigate hypothesized deficiencies. We also integrated motion planning libraries developed in previous internal research and development (IR&D) projects, including a prior targeted IR&D (10-R6208) that investigated real-time optimization-based path planning. We ran the planner in real time to replan motion planning during execution to account for remaining errors in the mobile base. We then measured process accuracy using a high-resolution motion capture system.
Accomplishments
We designed and implemented a coordinated motion planning software library that was responsive to changes in simulation and underwent testing with hardware. We successfully integrated a commercially available industrial manipulator and mobile base so they could be controlled as a single motion planning unit. As a result of this project’s success, we filed a patent application for this software framework and gained substantial knowledge about these systems and the limitations of their open-source drivers. Additionally, we successfully executed planned motions simultaneously on both systems, including feedback and dynamic re-planning. This development initially resulted in considerable instability, but further testing and fine-tuning allowed us to execute stable motions with less than 5 mm of error.