C. Stephanidis (Ed.): Universal Access in HCI, Part I, HCII 2007, LNCS 4554, pp. 1040–1049, 2007. © Springer-Verlag Berlin Heidelberg 2007 Usability Design of a Scanning Interface for a Robot Used by Disabled Users Anthony S. White 1 and Stephen Prior 2 1 School of Computing Science, Middlesex University The Burroughs, Hendon, London, NW4 4BT 2 Product Design and Engineering, Middlesex University, Bramley Rd, Trent Park, Enfield, London, N14 4YZ Abstract. The results of examining a scanning user interface implementation with command inputs in the form of head gestures for a rehabilitation robot using Fitts’ law variations and comparing these with a servo eye tracking model are made. Calculations show that the movement time prediction is more accurate in this case using the servo eye model. The response from the linearised eye model predicts that there is a minimum scanning distance that can be used and minimum spacing between commands display. Keywords: scanning user interface, Servo-eye-model, Fitts’ law, rehabilitation, robotics, gestures. 1 Introduction This work results from the charity Aspire supported research programme [1] to develop a cheap robot arm to attach to a wheelchair for assistive technology for paraplegic users. Other workers have examined the use of computer interfaces for disabled users [2], [3]. Keates et al. [2] found quite significant differences in response times for impaired users as well as noisy responses while Lesher et al. [3] found it was possible to allow for anticipation. Two methods for presenting robot language commands to the disabled user were employed by us. The first presented commands in the form of a flat scanning menu system, and was used during initial development and evaluation of the Middlesex Manipulator. The second presentation form employed a Microsoft Windows dialog based graphical user interface. This allowed all control options to be presented simultaneously, allowing for faster task completion. However, the interface required the user to be fairly competent when using a mouse or trackball. This requirement led to the development of a 'Head Mouse' and voice control. These proved to be better suited to use with the flat menu system. A moving bar scanned the menu from left to right and the user responded when the bar was in line with the chosen command. These commands were translated to motor commands using a special robot language JUVO. Fig. 1. Simple scanning system