Development of String-based Force Display: SPIDAR - CiteSeerX

Development of String-based Force Display: SPIDAR Makoto Sato Precision and Intelligence Laboratory, Tokyo Institute of Technology 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan Tel: +81-54-924-5050 Fax: +81-45-924-5016 Email: [email protected] URL: http://sklab-www.pi.titech.ac.jp/ Abstract. This paper presents the development of string-based force display system SPIDAR and its different versions. Ranging from a simple “pick and place” task to more complicated physical based interactions, SPIDAR has emerged as a distinguished haptic interface that have the following advantages: 1) scalability: with simple modification on its structure layout, SPIDAR can be fit to different working space such as desktop, workbench, and human-scale 2) String based: the string-based technology gives the developer the ability to display position, orientation and force feedback at once. Making it an effective mean for pointing and control for 3D environment. 3) Transparency: based on its string-based technology, SPIDAR keeps the working space transparent and do not obscure the visual display. SPIDAR’s quality of haptic feedback continued to improve through time to reach a high level of accuracy and update rate putting it in line with other major haptic systems.

1. Introduction By the end of the eighties, realistic simulation of life-like objects and environments were possible by the mean of new rendering techniques and the considerable advance in hardware equipments. It became possible to provide users and engineers with the ability to design, visualize, and manipulate 3D graphic objects that have a realistic look. However, it was clear later that traditional control devices like keyboard, mouse, and joystick do not fit for 3D manipulation interaction, therefore a new kind of pointing mechanism capable of delivering at least an input of 3DOF was necessary. The introduction of SpaceMouse™ [8], SpaceBall™ [9], and other pointing devices solved the issue and brought the level of interaction in 3D environment to a higher level of realism. Nonetheless, realistic interaction was still missing the ability to physically sense 3D graphics, hence the idea of adding the sense of touch to feel graphical objects emerged by the end of nineties, and since then various haptic devices have been introduced. In the following sections, I will present our contribution to the development of haptic interfaces based on the original SPIDAR system and its different versions and applications. 2. General Concept of SPIDAR In 1989, we have presented our first proposal of a new string-based haptic display named SPIDAR [1], in which the word “SPIDAR” stands for “SPace Interface Device for Artificial Reality”. The physical structure of the interface is composed of a cubic frame that encloses a working space. The main components of the system are four sets of a DC motor, a pulley, an encoder, and a string. Each set is mounted at the corner of the cubic frame. 2 sets are located at the topside of the frame and the 2 others at its bottom side. The sets are positioned in such

way the next corner to each set must be empty, that means an empty corner must be left between each two motors, see fig 1. For each set the encoder and pulley are attached to the motor from different ends, see fig 2.

Fig 1. SPIDAR

Fig 2. Actuator

The encoder is used to count and track motor’s rotation, whereas the pulley is used to wound the string around its surface. The string is wounded around the pulley at one end and to user’s fingertip at the other end. To keep the string straight and follow user’s fingertip, each motor is supplied with a minimum amount of current. Motors and encoders are connected to a remote computer via DA and counter boards. Any hand movement will generate a change in string’s length, which can be estimated based on pulley’s size and its related encoder. Hence, user’s fingertip position in the space can be estimated by solving an equation system resulting from the four sets. Once the spatial position of the user fingertip is established the system will continuously check if the position comes into contact with virtual objects. As soon as the system detect such collision between a virtual object and a user fingertip, appropriate current value will be supplied to each motor to stiffen the pulley’s rotation creating a sense of force feedback as result of collision. By controlling the tension of each string the system is capable of generating a 3DOF force feedback anywhere inside the cubic frame. 3. SPIDAR II The first version of SPIDAR allowed user to touch object via a single contact point. However, in daily life we usually need at least 2 fingers to hold, grasp, and move objects to interact comfortably with the surrounding environment. Such handling ability give lets users estimate some features of the object such as its weight or size, which are important elements in accomplishing certain dexterous tasks. To impart users with such ability, we planted four other sets on the frame in the same way as the previous setting but at the remaining corners. The system provides two end points attached to the thumb and index fingers. The new system is named SPIDAR-II [2], and capable of letting user grasp virtual objects and feel their weights. Actuator

Force feedback applied to 2 fingers

Fig 3. SPIDAR-II

4. Both-Hand SPIDAR Both-hand manipulations are so useful and frequent in our daily life. Without such coordination between both hands a lot of required needs could not be achieved. Providing such interactive ability in virtual environment is for great interest to many applications demanding the use of both hands, such as industrial assembly, surgery etc…. to satisfy such need we integrated two SPIDAR II systems into one frame, providing force feedback sensation to both hands. The new system was named Both-Hands-SPIDAR [3].

Fig 4. Set-up of Both-Hand SPIDAR

Fig 5. Both-Hands SPIDAR in use

5. Networked SPIDAR As networks become widely used, providing users with the ability to physically touch remote objects or remote user will certainly help in improving the collaborative work. For this aim we designed and implemented a networked version of SPIDAR II. Two systems of SPIDARII were installed in two different locations. Local and remote users could perform successfully Hand-Over tasks. Network delay time was optimized in such way objects can’t fell apart from the two users. The developed system is named Networked-SPIDAR [4].

Fig 6. Networked-SPIDAR 6. Big SPIDAR During the past decade many virtual environments with large display system have been developed. Cave system is well known for its large screen and working space that provide user to stand within the simulated environment as if they were present in it. Though their increasing usage and popularity, most of the human-scale VE, if not all, are still missing haptic feedback interface. The challenging problem was always how to display force feedback without obscuring the graphic display while giving users the freedom to move their hands without restriction. So far, and at our knowledge, the Big-SPIDAR [5] haptic interface is the unique interface capable of imparting users with force feedback sensation within

human-scale VE. The system was demonstrated during the Electric Garden, SIGGRAPH’97 in Los Angles, U.S.A. Users were virtually able to make some basketball shots toward a hoop. The used frame was large enough to fit cave-like system within which users can stand at its center. Users could hold a virtual basketball or other objects with both hands, feel their weight, shape, and form.

Fig 7. Big-SPIDAR 7. SPIDAR-G Works to improve the SPIDAR system have been continuously carried on. Recently, a new version SPIDAR-G [6] is proposed as a haptic interface device with 6 degrees of freedom (DOF); 3 DOF for translation and 3 DOF for rotation. This system shows satisfactory performance as a three-dimensional interface device for 3D virtual environment interaction. Combined with a specially designed grip, SPIDAR-G added one more DOF when the grip is closed and released to become a new 7-DOFs string-based haptic interface device. The user can manipulate the virtual objects by translating and rotating in any direction. In addition, the weight of virtual objects can be simulated according to the physical gravity during the manipulation of the virtual objects. Some companies and institutions already expressed their interest in using the SPIDAR-G system, which is undergoing now father quality improvements. The system will be presented during the IEEE VR 2002 conference.

Fig 8. SPIDAR-G

Fig 9. Weighting virtual objects

8. SPIDAR-8 The last version of SPIDAR system is two-handed with multi-fingers type of SPIDAR named SPIDAR-8 [7]. This new system allows a user to use thumb, index, middle, and ring finger on both left and right hands to manipulate virtual objects in the simulated virtual world. The user

can perform the cooperative work using both hands and perceive force feedback at eight fingertips while manipulating the virtual objects. As application, the simulation of the Virtual Rubik’s Cube game was implemented and obviously showed the abilities of the system. Again, SPIDAR-8 was selected to be one of the contributors of Emerging Technologies of SIGGRAPH 2000 demonstrated in New Orleans, USA. Aluminum frame

Rotary encoder DC motor

String Fingertip cap

String’s fulcrum

Fig 10. SPIDAR-8

Pulley

Fig 11. Virtual Rubik’s cube

We would like also to mention about the tentative plan of our works. Closely related with virtual reality (VR), mixed reality (MR) is become more and more attractive and challenging topic. Haptic display system, provided its user with realistic sense of touch, is believed to give enhanced performance by providing also the sense of immerse of the user into the virtual environment. Using SPIDAR-8, image sequences of user’s real hands are to be used instead of computer graphic virtual hands manipulating the virtual objects in the virtual world. Such Visuo-Haptic system is now under implementation. It is believe to be a contribution of great deal in the both VR and MR system.

Fig 12. Virtual reality environment

Fig 13. Mixed reality environment

9. Conclusion The distinguishing features of scalability, string based, and transparency made from SPIDAR system a flexible interface that can accommodate various type of virtual reality systems ranging from desktop, workbench, human-scale and networked environment. Tensioned string technique is proved to be very practical to provide different aspect of force feedback sensations associated with weight, contact, friction and inertia. In the recent years SPIDAR improved its measurement accuracy and force feedback quality to much the required standard and inline with the performances of other major haptic interfaces. The latest version of SPIDAR is a USB 2.0 compatible system capable of delivering a 1 Khz update rate. The new version is equipped with a set of library and software tools that allow developers to adapt the haptic device to any desired interface structure, including new design.

References [1] Y. Hirata and M. Sato, “3-Dimensional Interface Device for Virtual Work Space”, Proceedings of the 1992 IEEE/RSJ International Conference on IROS, 2, pp. 889-896, 1992. [2] M. Ishii and M. Sato, “3D Spatial Interface Device Using Tensed Strings”, PRESENCE-Teleoperators and Virtual Environments, Vol. 3 No. 1, MIT Press, Cambridge, MA, pp. 81-86, 1994. [3] M. Ishii, P. Sukanya and M. Sato, “A Virtual Work Space for Both Hands Manipulation with Coherency Between Kinesthetic and Visual Sensation”, Proceedings of the Forth International Symposium on Measurement and Control in Robotics, pp. 84-90, December 1994. [4] M. Ishii, Masanori Nakata, and M. Sato, “Networked SPIDAR: A Networked Virtual Environment with Visual, Auditory, and Haptic Interactions”, PRESENCE-Teleoperators and Virtual Environments, Vol. 3 No. 4, MIT Press, Cambridge, MA, pp. 351-359, 1994. [5] Laroussi B., Ishii M. and Makoto S. “Multi-Modal Haptic Device For Large-Scale Virtual Environment” ACM Multimedia Nov. 2000 – Los Angeles 2000. pp: 277-283 [6] S. Kim, M. Ishii, Y. Koike, and M. Sato, “Design of a Tension Based Haptic Interface: SPIDAR-G”, Proceedings of World Multiconference on Systemics, Cybernetics, and Informatics: SCI 2000, pp. 422-427, July 2000. [7] S. Walairacht and M. Sato, “4+4 Fingers Haptic Interface Device for Virtual Environment”, Proceedings of World Multiconference on Systemics, Cybernetics, and Informatics: SCI 2000, pp. 427-433, July 2000. [8] http://www.spacemouse.com/products/Classic.htm Profile Makoto SATO graduated in 1973 from Department of Physical Electronics, Faculty of Engineering, Tokyo Institute of Technology, where he obtained the Doctor of Engineering in 1978. He became an assistant in the same faculty, and now a Professor at Precision and Intelligence Laboratory, Tokyo Institute of Technology. He is engaged in researches on string-based interfaces, HCI, virtual reality, pattern recognition, and image processing.