INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING Int. J. Adapt. Control Signal Process. 2005; 19:327–338 Published online 17 December 2004 in Wiley InterScience (www.interscience.wiley.com) DOI:10.1002/acs.852 Gain scheduling control of functional electrical stimulation for assisted standing up and sitting down in paraplegia: a simulation study Fabio Previdi 1,n,y , Maurizio Ferrarin 2,z , Sergio M. Savaresi 3,} and Sergio Bittanti 3,} 1 Dipartimento di Ingegneria Gestionale e dell’Informazione, Universita ´ degli Studi di Bergamo, Via Marconi 5, 24044 Dalmine (BG), Italy 2 Centro di Bioingegneria FDG, Fondazione Don Carlo Gnocchi ONLUS IRCCS, Milano, Italy 3 Dipartimento di Elettronica e Informazione, Politecnico di Milano, Milano, Italy SUMMARY This paper reports on a simulation study that concerns the design of a non-linear controller for the standing up and the sitting down of a paraplegic patient by means of functional electrical stimulation. The simulations refer to a specific experimental device developed at the Fondazione Don Gnocchi (Italy). This is a seesaw, with the patient on one side and a weight on the other side. The patient is seated so that its posture can be fully known in real-time by continuously monitoring the knee joint angle. By delivering a suitable electrical stimulation to the quadriceps muscles groups, the patient can be raised and made to sit via smooth movements. Hitherto, the only feedback control law, which has been implemented in this area, is based on a PID controller and usually provides poor tracking performances. Hence, in this work, a non- linear gain scheduling controller has been designed and tested in a series of simulation experiments. The controller is tuned following a gain scheduling strategy: a set of local linear quadratic controllers is designed using a set of linear tangent models. A global non-linear gain scheduled controller is then obtained via interpolation. The gain- scheduled controller is implemented following an advanced strategy that guarantees that the so-called linearization property holds. Copyright # 2004 John Wiley & Sons, Ltd. KEY WORDS: gain scheduling control; functional electrical stimulation; rehabilitation engineering 1. INTRODUCTION Functional electrical stimulation (FES) is a technique that uses electrical pulses to induce skeletal muscle contraction and limb movements. In a paraplegic patient who suffered a spinal cord injury (SCI) at the thoracic level, partial motion activity of the lower limbs can be induced by means of FES. In fact, an injury causing a complete lesion of the spinal cord results in an Received 13 October 2004 Accepted 13 October 2004 Copyright # 2004 John Wiley & Sons, Ltd. y E-mail: previdi@unibg.it n Correspondence to: F. Previdi, Dipartimento di Ingegneria Gestionale e dell’Informazione, Universita´ degli Studi di Bergamo, Via Marconi 5, 24044 Dalmine (BG), Italy. z E-mail: m.ferrarin@cbi.dongnocchi.it } E-mail: savaresi@elet.polimi.it } E-mail: bittanti@elet.polimi.it