Haptic Interface with 7 DOF Using 8 Strings : SPIDAR - G

of the continuous development of computers it ssible to construct various environments. As a an interfaces that allow users to manipulate cts in an intuitive manner, as in the real world, demanded. In this paper, we present a 7 DOF ed haptic interface that allows users to not only bject but also to sense its width. We have a system to utilize the physical action of gripping grasp manipulation in virtual environments. We t a method to calculate the position and display iated with this gripping mechanism. In addition, e possibility of its application to virtual reality. refer to the characteristic of this device and its ough examples. s ension based haptic interface, SPIDAR-G. uction elopment of computer technology is enabling teract with various virtual environments. When to interact with virtual objects in a manner those in the real world, an intuitive haptic ith multiple degrees of freedom (DOF) becomes . In general, the physical act of gripping (or allows human beings to perform several unctions including using instruments to puncture, , and hit objects. Before doing the abovetasks, we select the necessary instruments by Depending on the size and shape of the object, erally grasp an object using our thumb and our rs. So far haptic interfaces have presented users with simple ways of representing thi such as pushing a button in a mou believe that an effective haptic interf provide feedback on the differential sen “intuitive” haptic interface has not bee purpose of this paper is to realize su DOF haptic interface that can allow u an object, but to also sense the width o life object manipulation. 2. Related work We can divide the haptic interfa developed so far into two categories and body-based type. LRP data Cybergrasp force feedback glove by V Inc[2], and Rutgers Masters (RM-II) Rutgers University are well-known exa haptic interfaces. Body-based haptic advantage of allowing the user to gras present the disadvantage of not being weight of an object. Recently, deve overcome this demerit in Vti by fixing feedback glove to a serial link manipul has the disadvantage of not being ef rotational force. Furthermore, the complex in that is cumbersome to put o is difficult to maintain. Ground-based haptic interfaces classified as link type, magnetic levitat based type. Link type haptic in disadvantage of exhibiting backlash, b inertia, and limited work space. Th example of a successful link type hapti s grasping function, se or keyboard. We ace should not only se of width. Such an n developed yet. The ch a tension-based 7 sers to not only pick f an object as in real ces that have been : ground-based type glove by LRP[1], irtual Technologies [3],[4] developed at mples of body-based interfaces have the p an object, but also able to represent the lopers have tried to the Cybergrasp force ator. Still, this device ficient in displaying overall structure is n the users hand and can generally be ion type, and tension terfaces have the ackdrive friction and e PHANToM is an c interface. However, since it has 6 DOF, it is impossible to grasp virtual objects using a single PHANToM. When 2 PHANToMs are used to grasp virtual objects, only 2 fingers are displayed in the virtual environment (thumb and index finger). This setup also suffers from limited workspace, due to inertial effects. Recently, a haptic group at MIT succeeded in integrating the Immersion Impulse Engine, a recent invention by Immersion Corporation[5], and 3 DOF PHANToM[6] (made by Sensable Technologies)[7] for laparoscopic surgery simulation[8]. The system utilized a 5 DOF simulation software with the PHANToM as the laparoscopic tool [9]. Therefore it did not provide feedback of rotation force to its users. The Haptic Master [10] is another well-known parallel-link type haptic interface. Because this device uses a gear, it has backlash and backdrive friction while displaying only 6 DOF. CMU’s magnetic levitation type haptic interface [11], [12] has the advantages of non-contact actuation and sensing, high control bandwidths, high position resolution and sensitivity, but has disadvantages of small workspace (motion range:15-20 degrees rotation, 25mm translation) and only 6 DOF display. Tension based haptic interfaces [13], [14], [17], [18] have the advantages of fast reaction speed, simple structure, smooth manipulation, and scalable work space (since tension based types do not affect backlash, backdrive friction and inertia). The SPIDAR-G has 7 DOF, users can manipulate virtual objects with 6 DOF and can grasp them simultaneously. SPIDAR-G stands for SPace Interface Device for Artificial Reality with Grip. 3. Force displaying using tension One characteristic of using strings to display forces is that they can only be used to represent tension. In other words, the strings can be used to pull and not push. We can determine the number of strings needed by applying vector closure to the indispensable condition of displaying n-DOF reflective forces using strings. When generating a ndimensional force vector n R q ∈ , using m-strings, the force vector q added to the target object from m-strings can be shown like this. [ ]τ m w w w q , , , L 2 1 = (1) ( )T m τ τ τ τ , , , L 2 1 = Where i w represents a force vector, when unit tension is added to the i -th string and τ is tension vector. The following theories (1 and 2) outline the Conditions for a positive τ that can realize any q in equation (1) [15], [16]. Figure 1. Basic structure of SPIDAR-G [ Theory 1 ] If [ ] m w w w A , , , 2 1 L = , the indispensable condition to have positive solution in equation (1) is as follows: m>n [ Theory 2 ] If [ ] 1 2 1 , , , + = n w w w A L , the indispensable condition to have positive solution in equation (1) is as follows: 1. n A rank = ) ( 2. Using remain row vector, any ) 1 , , 1 ( + = n i wi L have to represent as