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Fuzzy Logic Based Force and Position Control of an Ankle Rehabilitation Robot

Abstract Medical rehabilitation treatments are carried out to reinstate physical disorders caused from an injury or stroke. Robots can significantly assist the therapist to carry out an effortless and yet controlled rehabilitation program simultaneously on a number of patients to save on time and efforts of both the therapist and the patient. Ankle joint injuries, due to their complexities and growing number worldwide and in New Zealand have attracted researchers and a few ankle rehabilitation robot designs have been proposed. Following a careful study it was revealed that there are opportunities of improvement in the existing robots designs. Almost all of these robots are redundantly actuated and require patient’s foot to be placed on top of a moving platform which is manoeuvred by the actuators placed below. This configuration of actuators is contrary to the natural placement of muscles in the human leg. Owing to this conflicting placement of actuators, the position of ankle joint and the shinbone keeps changing during motion (Fig. 1), causing control errors and discomfort to the patient. Moreover all the previous designs are quite heavy and hence are stationary devices which can only be used in a clinic or at a fixed location. Patients have to travel in their disable state to attend the clinical sessions which is undesirable especially when they have lower limb injuries such as ankle joint disorder. In the light of above, we have proposed a novel wearable parallel robot (Fig. 3) which allows three rotational degrees of freedom to the ankle joint without causing any displacement of the shinbone and the ankle joint. The moving platform of the proposed robot is attached to the patient’s foot and the actuators are placed parallel to the shinbone (Fig. 2) emulating the natural arrangement of muscles. Various ankle joint rotations are achieved by controlling the lengths of the actuators. The robot is light weight (less than 3kg) and portable, allowing the patient to wear it comfortably while doing his routine work at home or at workplace.