Mechanical design and validation of an auxiliary active device for rehabilitation of the knee and quadriceps

Motion difficulties, specifically the walk and displacement, are very common afflictions, mainly caused by some type of injury. The recurrent kind of rehabilitation treatments involve exercises of active and passive mobility. The success in the treatment and the early return to sports activity depends largely on the rehabilitation process. This should begin immediately after the production of the wound or the surgical process to repair the damage. The objective of this work is to develop a low-cost, easy manufacturing and assembly device, capable of providing exercises of active mobility. We designed an affordable and adaptable six-bar Watt linkage, coupled to a conventional leg extension machine. Structural and dynamic studies determine its safeness and its efficiency. The results of the kinematic and dynamic studies showed that the available range of motion for the different configurations goes from 24° to 109°. Its structural integrity was analyzed, pointing out that the weakest link had a Factor of Safety of 1.3, while the highest presents a value of 14.7, so that, the material overpasses the load needs. Based on the obtained results, a six-bar linkage is a viable option for the development of low-cost, therapeutic active devices.