Generic force server for haptic devices

This paper presents a novel architecture allowing a generic force-feedback device to be used by different software tools dedicated to teleoperation and mission planning. This architecture relies on a “force-server” program running between the real-time controller of the haptic device and a set of applications using it. Possible applications include mission ground control system interfaces, telemetry systems coming back from real robots, or external simulation programs. The force-server concept is based on a high-level description of the forces to be generated. This description consists of spatial constraints defined by their type (point, line, plane and mesh), position and orientation. A force profile (space and/or time dependent) is assigned to each constraint. This description enables the generation of complex fields of forces by combining basic constraints. The advantage of this method is that an application can send force updates by simply modifying several parameters of the constraint. Between two updates (from the application) the force-server is able to continously compute new forces corresponding to the actual position of the device handle. This approach enables the control loop of the force feedback device to easily run at 500Hz when the application may send updates only at 25Hz. This novel method widens the use of force-feedback devices by providing a common interface to the different applications, and allowing multiple clients to use the same haptic device. A testbed using a 6 DOF haptic device has been developed. The device generates forces coming simultaneously from three different sources: a Java interface to experiment various force profiles, a rover simulator, and a scientific visualization tool used during planetary missions.