As an approach to this problem, a control system is developed here for a force feedback ... time virtual environment system shows several problems which are, in ...
Integration of a Force Feedback Joystick with a Virtual Reality System Alfredo C. Castro+, José F. Postigo+, Jorge Manzano* +
Instituto de Automática. Facultad de Ingeniería.Universidad Nacional de San Juan Av. San martín 1109 (oeste). 5400. San Juan. ARGENTINA. Tel.: +54 264 4213303 – Fax: +54 264 4213672 e-mail:{acastro,jpostigo}@inaut.unsj.edu.ar
Keywords: teleoperation, force feedback, virtual environment, network, man-machine interface. Abstract The integration of force feedback with a complete real-time virtual environment system shows some more difficult problems than those found in building a typical force feedback system. Particularly, bulky computations for graphics or simulation require decoupling the haptic servo-loop from the main application loop if highquality forces (realistic) are to be obtained. As an approach to this problem, a control system is developed here for a force feedback joystick (Impulse 2000 -Immersion Corp.) along with its integration to a virtual environment. Technical issues on the development of stable control architectures for Internet-based exchange of haptic information are discussed. Some experiments were developed to show the performance of both the force feedback joystick and the virtual reality system. This work was carried out in the Laboratories of the Robotics and Informatics Division of ENEA under an ENEA’s project grant. Rome, Italy. 1
Introduction The integration of force feedback to a complete realtime virtual environment system shows several problems which are, in general, more difficult to solve than those found in building a standard force feedback system. In particular, bulky computations for graphics or simulation require a decoupling of the haptic servo-loop from the main application loop if high-quality forces are to be produced (Mark et al., 1996). Likewise, to use haptic devices over the Internet is a much more challenging problem than to transfer audio and video data, because these devices must remain stable in spite of the typical fluctuations of performance of the Internet. Typically, Internet data present random timedelay and packet losses, which would make a control system unstable if it were used to close the control loop over Internet (Fiorini and Oboe, 1997). In this work, we present an approach to solve these problems by especially proposing a controller for the force-feedback joystick “Impulse Engine 2000” by Immersion Corp. Its integration to a virtual environment and the possibility of exchanging haptic information through Internet are also described here. In a Virtual Reality (VR) training environment, although 3D visualization is a useful tool for learning to teleoperate a complex procedure, it does not suffice for developing a physical skill which requires a haptic interaction as a necessary component of the training process (Colgate et al., 1995). This work was performed within the framework of the ENEA projects “TINA” and “RAS”. The former project is financed by the Italian Ministry for Scientific Research and it is aimed at improving ENEA‘s *
telemanipulator MASCOT. The RAS project is within the Italian Scientific Research Program of Antarctica and it is aimed at implementing a remotely operated vehicle equipped with a teleoperated arm (Manzano, 1997; Fichera et al., 1997). 1.1
The Mascot teleoperation system In 1961 the researchers from ENEA developed the first Mascot unit, a telemanipulator for nuclear plant operation. This manipulator was, and still is, one of the best machines available in the world as regards the force feeling it can transmit back to the operator (force feedback signals). The Mascot is a Master/Slave telemanipulator of the force feedback type (see Fig. 1). Each arm has seven servocontrolled joints: six links for six degrees-of-freedom plus a gripper. Each joint is driven by its own actuator through gears or steel cables. The control algorithm is based on comparing the position and velocity of the joints of the Master and Slave arm, sensed at the same instant. These values, the position and velocity errors, are then multiplied by adequate proportional coefficients to determine the torques to be applied to the Slave arm actuators (which is thus forced to follow the Master) and to those of the Master arm, to generate the force feedback to the operator. These torques are applied in order to minimize the position errors. 1.2
Work objectives The RAS and TINA projects impose several new features to the last version of MASCOT. Some of these, addressed here, are: § To increase the field of applications via VR: To use the real master with a Mascot virtual slave for training with virtual reality techniques or to use other device as an alternative master. In this work, virtual environment applications were developed.
Divisione Robotica e Informatica Avanzata. Dipartimento Innovazione. Ente per le Nuove Tecnologie, l’Energia e l’Ambiente (ENEA). Rome, Italy.
§ To lower the costs: Use of less expensive devices as an alternative to the master arm. This device may be a market-available device or another developed at the ENEA. In this work, we use a market-type device.
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Main Features This quality force feedback joystick for research has the following features, as supplied by Immersion Corporation: §
Two degrees of Freedom.
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ISA bus interface (PC).
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Cable-driven capstan transmission.
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6" x 6" (15.2 x 15.2 cm) Workspace Size.
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0.0008" (1100 dpi) Position Resolution.
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2lbs. (8.9N) Max Force Output.
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