User-Specified Virtual Fixtures for Augmenting Human-Robot Interaction

Abstract

Humans can interact with existing robots/manipulators using either telemanipulation or cooperative manipulation. During telemanipulation the manipulator replicates hand movements of the human controlling a master device. In cooperative manipulation the user manually moves the robot’s end effector using admittance control while the robot holds the tool. In both scenarios there is a need to provide users with assistive manipulation control laws that help improve the safety and precision of task execution. These control laws (known as virtual fixtures or active constraints) may be used to enforce guidance or barrier features in task space in order to assist the human in carrying a specific task (e.g. following a curve or staying on a plane).

While the fundamental work on virtual fixtures has been a subject of intensive research in the past 20 years, we put forth and explore a new concept of user-specified virtual fixtures. The research is motivated by the fact that, in many application domains, the delineation of safety zones within the environment may not always be possible prior to task execution. For example, in surgical domains where surgeons deal with highly flexible anatomy there is a difficulty in maintaining correspondence between pre-planned safety boundaries and the actual surgical scene. To overcome this challenge, we explore a simple concept of visually-guided user-specified safety boundaries. According to this approach, the user specifies the safe resection/manipulation zone by tracing a visible spectrum laser which is used to define the prescribed allowable surgical zone and this data is then fed into a high-level assistive manipulation controller. A high-level assistive control law is then used to construct and enforce a virtual fixture providing assistive behaviors for following a curve, staying on a plane and for staying within a closed contour on a plane.

We demonstrate our research assuming the robot is an admittance slave and the master is an impedance master. We demonstrate the same concepts of virtual fixtures in cooperative manipulation scenarios. All of the demonstrations are carried out using a custom-made real-time controller for a Puma 560 robot.