Using a Robotic Gait Orthosis as Haptic Display - A Perception-Based Optimization Approach

The actuated gait orthosis Lokomat has been developed at University Hospital Balgrist for patients with impairments due to neurological or orthopedic lesions. To enhance rehabilitation with the Lokomat, patient-cooperative techniques have been developed. Patient-cooperative means that the technical system considers the patient intention and efforts rather than imposing any predefined movement or inflexible strategy. It is hypothesized that patient-cooperative techniques have the potential to improve the therapeutic outcome compared to classical rehabilitation strategies. One example for patient-cooperative techniques are immersive, multi-modal scenarios. They can provide task-specific feedback and are expected to increase patient´s motivation to contribute. One interaction possibility is haptic feedback which can be provided by the gait orthosis to simulate interaction with solid objects. The work described here investigated the potential of the Lokomat to provide haptic feedback. Frequency response measurements under closed-loop conditions were conducted to determine the force and position bandwidths. The final goal was to develop an approach for haptic rendering and optimize its parameters with experiments. Optimization criteria were object hardness and stability during object contact. Results of the bandwidth measurements show that the angle bandwidth is 3 Hz (excitation angle amplitude: 3deg) and the force bandwidth 8 Hz (excitation force amplitude: 10 N). The implemented haptic approach combines an impulsive force component, a penalty force component, and a component for lateral friction force. Best results were achieved for a combination of sine shape impulse, spring constant K with 2000 ^N/m, and modified damping coefficient B with 300 ^Ns/m².