In this paper, we have developed a low-cost and compact force feedback device as a new user interface to communicate with a computer. We adopted a DC-motor powered joystick to create the force feedback. Without tirodi@ng the source code of video games. we intercept the interrupt r e s e n d for mouse, colorrnap and keyboard input and replace it with a new interrupt service routine in which force eflects are addedfor the new gmres.
IntroductionA key problem in interacting with objects in a virtual environment is the lack of tactile and forcc feedback. In real world, we explore the environmcnt by five kinds of perception. Among tlie scnsory information obtained by these pcrccptions. visual. auditory, and haptic information dominate how \ve experience the environmcnt. The way to display visual and auditory information has been ivell rcscarclicd and the techniques are quite mature now with the haptic display left less researched.Early work on force feedback joysticks at MIT and UNC[3] resulted in a three degree-of-frccdoni device but the cost was high. Our purpose is to reduce thc cost and let the force feedback joystick be enough for commcrcial use.Our work developcd mainly following the work of [3]. We employ a motor-driven 2-dinicnsional joystick as the force feedback device and siinulatcd tlie behajrior of objects such as a spring, a wall, and icy ground. We also combine the force display with a PC-bascd entertainment game DOOMTM to espcriencc how this device benefits the entertainment fields.
Structure of the force fectlh;icl< joystickOur joystick is similar to a traditional joystick, and has a handle pivoting at a ball bearing. We adoptcd tn'o DC motors with induction gears as the actuators OF thc force feedback joystick to create the torque rcquircd. The motors are couplcd in a set of two yokcs. Thc position information are measured by the two potcntiometers attached on the yokcs at thc bottom of thc joystick. The mechanical structure of the joystick is illustrated in Figure l(a). Figure 1@) is thc configuration of the system. The platform we adopt is a n IBM PC 80486. A 12-bit AD/DA card is uscd to colicct the position data and control thc torquc of motors. , Figure l@). Tlie n m h u i i c a l s t r u c t u r e o r l l 1 e j o y s l i c k i J X Z~-'~ Position 1 Jovstick Digital r--t Velocltv ~ .
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