Colloquia

Samenvatting

For most of us, walking is so fundamental to our human functioning that envisioning life without it is nearly unimaginable. There are, however, many individuals who do not have the privilege of utilizing this skill. Robotic solutions can help in rehabilitation and reintegration into social life, of which the Wearable Exoskeleton 2 (WE2), a lower limb exoskeleton located at the University of Twente, is a great example. Currently, this exoskeleton is already able to stand autonomously (without external support), withstanding pushes up to 30 Newtons.

This thesis enhances the exoskeleton's capabilities by successfully enabling stepping in simulation. First, it is shown that the exoskeleton can exert the forces on the CoM required to perform a step by considering friction constraints and the mechanical design of the exoskeleton. Afterwards, two distinct trajectory generation methods are used to take a step, both facilitating stepping of the WE2 in a simulation environment without falling. For both methods, optimal parameters have been found for the construction of the trajectory, as well as the settings of the Momentum-Based controller. As a result, a forward step could be taken with an error of less than 1% (for the foot in the anteroposterior direction) when executing a forward step of 0.1 meters and a maximum step length could be achieved of 0.7 meters.

The optimal parameter configuration of one trajectory generation method has been analyzed on its robustness against discrepancies between the controller model and the virtual WE2. When modelling the mass of each component as a normally distributed probability density function around the actual components mass, the results show that the WE2 can take a forward step without falling up to a standard deviation of 15% of its component’s mass, which falls within the bounds of realistic uncertainties during relevant applications.

Lastly, an attempt was made to translate successful stepping to the real WE2. This was not achieved however, as the real WE2 was not able to stand on one leg for longer than 70 milliseconds, before vibrating heavily and reaching an error state. This showed that fundamental work on the controller should first be executed, before successful autonomous stepping in simulation could be translated to successful autonomous stepping in real life.