Selective control of gait subtasks in robotic gait training: foot clearance support in stroke survivors with a powered exoskeleton

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http://www.jneuroengrehab.com/content/10/1/3/abstract

Abstract (provisional)

Background

Robot-aided gait training is an emerging clinical tool for gait rehabilitation of neurological patients. This paper deals with a novel method of offering gait assistance, using an impedance controlled exoskeleton (LOPES). This method is based on a recent finding that, in the control of walking, different modules can be discerned that are associated with different subtasks. In this study, a Virtual Model Controller (VMC) for supporting one of these subtasks, namely the foot clearance, is presented and evaluated.

Methods

The developed VMC provides virtual support at the ankle to increase foot clearance. Therefore, we first developed a new method to derive reference trajectories of the ankle position. These trajectories consisted of splines between key events, which are dependent on walking speed and body height. The VMC was evaluated in twelve healthy subjects and six chronic stroke survivors. The impedance values of the support were altered between trials to investigate whether the controller allowed gradual and selective support. Additionally, an adaptive algorithm was tested, that automatically shaped the amount of support to the subjects' needs. Catch trials were introduced to determine whether the subjects tended to rely on the support. We also assessed the additional value of providing visual feedback.

Results

With the VMC, the step height could be selectively and gradually influenced. The adaptive algorithm clearly shaped the support level to the specific needs of every stroke survivor. The provided support did not result in reliance on the support for both groups. All healthy subjects and most patients were able to utilize the visual feedback to increase their active participation.

Conclusion

The presented approach can provide selective control on one of the essential subtasks of walking. This module is the first in a set of modules to control all subtasks. This will enable the therapist to focus the support on the subtasks that are impaired, and leave the other subtasks up to the patient, encouraging him to actively participate in the training. Additionally, the speed-dependent reference patterns will provide the therapist with the tools to easily adapt the treadmill speed to the capabilities and progress of the patient.

The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production.