Transradial Prosthesis: Artificial Vision for Control of Prehension *Strahinja Došen and *†Dejan B. Popovic ´ *Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark; and †School of Electrical Engineering, University of Belgrade, Belgrade, Serbia Abstract: We present a practical system for controlling the prehension of a transradial prosthesis. The system is mounted on the artificial hand and comprises simple hard- ware and software that are convenient for real-time implementation. The hardware consists of a standard web camera and an ultrasound distance sensor. The control algorithm mimics biological mechanisms for the control of grasping and uses the measured distance to the target object and the method of computer vision to estimate the object’s size and orientation. Based on these estimates, the algorithm outputs the following commands for the control of prehension: (i) the type of grasp and the aperture size appropriate for the target object; and (ii) the angle through which the wrist should be rotated (pronation/supination) in order to properly position the hand for the grasp.We have tested the system’s performance with different targets (planar geometric shapes, real-life objects) under static conditions (i.e., when the system is stationary) and dynamic conditions (i.e., when the system moves toward the target). The size estimation was more accurate in the static experi- ments (error < 36%). Importantly, the system showed to be very robust with respect to the estimation errors, and the correct control commands were generated in most of the tested cases. The presented system is only one component of the hand controller, related strictly to the prehension phase of grasping. The final solution is envisioned as a combination of the presented system, inertial sensors (hand orientation), and a myoelectric control (triggering). Key Words: Transradial prosthesis—Com- puter vision—Prehension—Control. The loss of an arm and hand presents a major disability because it ultimately prevents an individual to reach and grasp, thereby reducing her/his ability to function independently while decreasing the quality of life. The existing assistive systems are not good enough to eliminate this disability. The design of an intelligent, multi-finger artificial hand that includes an active wrist to substitute for pronation/supination and wrist movements is a challenging task that has been addressed recently by several research groups (1). Many recent studies are related to the develop- ment of replicas of the human hand as well as the integration of numerous sensors into the hand to duplicate its sensory systems (2). The basic idea is to feed the sensor information from the hand to the higher centers (i.e., the brain) of the user, thereby substituting for the lost sensation, and to provide sufficient flexibility of the hand such that the motor commands can be sent to the hand and promote a biological-like grasp. There is limited information on the development of an intelligent forearm and wrist, which is instrumental for the efficient use of a multi- functional artificial hand. The interface between the user and the artificial hand is presently envisioned by many as the so-called brain-controlled system. This system in some cases is considered to be a brain–computer interface; however, much more realistically, most systems are indirect brain prostheses that facilitate communica- tion via electrical activities recorded from muscles (EMG). The EMG or myoelectric control (3) relies on the ability of an amputee to generate voluntary contraction of either a muscle that would have nor- mally been used for the same function before the disability or some other synergistic muscle at her/his subconscious level. If several degrees of freedom doi:10.1111/j.1525-1594.2010.01040.x Received November 2009; revised February 2010. Address correspondence and reprint requests to Dr. Strahinja Došen, SMI, Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7D3, Aalborg 9220, Denmark. E-mail: sdosen@hst.aau.dk Artificial Organs ••(••):••–••, Wiley Periodicals, Inc. © 2010, Copyright the Authors Journal compilation © 2010, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc. 1