VariLeg - A Lower Limb Exoskeleton with Variable Impedance Actuation for Paraplegics

We believe that ideal assistive devices for lower limbs, like exoskeletons, should be capable of varying their impedance to achieve performance comparable to human legs. The VariLeg exoskeleton was designed to restore natural gait for paraplegic users with complete loss of motor functions in their legs. The novelty of this device is that the knee joint is driven by a external page variable stiffness actuator (VSA). The VSA will be used in an impedance controller modulating stiffness according to data found in human gait, which is thought to improve stability and efficiency of ambulation.

Before using the full capabilities of the VSA, it was important to develop a device that allowed pilots to walk safely. Therefore, two users with paraplegia were first trained in the VariLeg using the VSA like a classical series elastic actuator at a chosen static stiffness. After one year of training and the successful participation in the Cybathlon 2016, the acquired feedback from the test users was integrated in the design iterations.

Especially, the user attachment system was improved to allow better adaptations to each pilot. This is an important step, as every actuation and control approach cannot optimally be leveraged if the pilot is not properly connected to the device. Now that both pilots are familiar with walking in the VariLeg, we strive to explore the capabilities of the VSA and compare it to a VariLeg with stiff joints as well as a VariLeg with series elastic actuation.