Does DOF Separation on Elastic Devices Improve User 3D Steering Task Performance? G´ ery Casiez, Patricia Pl´ enacoste, and Christophe Chaillou LIFL (UMR CNRS 8022) & INRIA Futurs Universit´ e des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France {gery.casiez, patricia.plenacoste, christophe.chaillou}@lifl.fr Abstract. We investigated the use of a new haptic device called the DigiHaptic in a 3D steering task. Unlike other devices intended to interact in 3D with one end-effector, the DigiHaptic has three levers that the user may handle simultaneously or not in elastic mode to rate control objects. We compared it to the SpaceMouse - another elastic device - to evaluate the influence that degrees of freedom (DOF) separation have in terms of accuracy (coordination and errors) and speed (time). The task consisted of steering paths that required the use of two or three DOF simultaneously. We found that users performed faster on the SpaceMouse but were less coordinated and accurate than on the DigiHaptic for the most complicated paths. 1 Introduction The majority of existing devices for three dimensional interaction have one end-effector that the user manipu- lates with his hand. They can be isotonic or isometric/elastic depending on their mechanical architecture. The latter are better for rate control rather than position control where the former are better, according to the experiments of Zhai [1]. For example, the PHANToM is an isotonic device that provides an intuitive interaction similar to everyday gestures through the manipulation of a stylus or thimble, and the SpaceMouse [2] is an elastic device to rate control objects in 3D. Devices for 3D interaction with one end-effector are integral as it is possible to move diagonally across dimensions as defined by Jacob et al. [3]. Nevertheless the user has no individual control on each DOF. If the user moves the device in one particular direction, the pointer will not go exactly in that direction due to human limb limitations. Rice et al [4] observed that controlling six DOF with one hand is difficult. Some teleoperation systems, such as the Shuttle Remote Manipulator require two-handed operation: one hand for rotation control and the other for translation control. In the same way, can we improve 3 DOF devices by subdividing them in multiple lower DOF near fingers? To evaluate DOF separation in 3D interaction, we have designed a new haptic device called the DigiHaptic proposing a novel interaction concept that consists of the separation and association of the degrees of freedom in an intuitive way to three fingers [5]. The device comprises three levers associated with the thumb, forefinger and ring finger as illustrated in figure 1. Each lever is connected to a DC-motor through a thread to provide force feedback or simulate behaviors such as springs on levers [6]. Depending on the motor command, the DigiHaptic can be used in isotonic and elastic mode with force feedback, and in isometric mode. In elastic mode, springs are simulated so as to always return the lever to a neutral position set at equal distances of the lever boundaries. Considering that the user handles each lever over a 60 ◦ range, this give 4cm of movement amplitude. Moreover it is possible to adjust spring stiffness from low to high depending on the user preferences. Although it is a separable device [3], the three DOF can be handled simultaneously. In each mode there is an isomorphism between fingers and object movements. Objects are translated according to the width of the screen (x axis) with thumb, the height of the screen (y axis) with the ring finger and the depth of the screen (z axis) with the forefinger 1 . As there is a direct relationship between the fingers and the object’s movements, we hope to make the use of the device intuitive. Objects can also be rotated around the corresponding axis in rotation mode after pressing a switch on the device with the middle finger. In this paper, we only use the translation mode. In the same way the keyboard is a device with multiple separated end-effectors and the way a person playing a shooting game like Quake uses it shows that separated DOF can be used if arranged in an intuitive 1 In this paper, we use the following convention (OpenGL convention): x axis is from the viewer’s left side to the right side, y axis is the bottom up direction, and z axis is the direction the viewer facing