MIT-Skywalker: A Novel Gait Neurorehabilitation Robot for Stroke and Cerebral Palsy

Abstract

The MIT-Skywalker is a novel robotic device developed for the rehabilitation or habilitation of gait and balance after a neurological injury. It represents an embodiment of the concept exhibited by passive walkers for rehabilitation training. Its novelty extends beyond the passive walker quintessence to the unparalleled versatility among lower extremity devices. For example, it affords the potential to implement a novel training approach built upon our working model of movement primitives based on submovements, oscillations, and mechanical impedances. This translates into three distinct training modes: discrete, rhythmic, and balance. The system offers freedom of motion that forces self-directed movement for each of the three modes. This paper will present the technical details of the robotic system as well as a feasibility study done with one adult with stroke and two adults with cerebral palsy. Results of the one-month feasibility study demonstrated that the device is safe and suggested the potential advantages of the three modular training modes that can be added or subtracted to tailor therapy to a particular patient's need. Each participant demonstrated improvement in common clinical and kinematic measurements that must be confirmed in larger randomized control clinical trials.

Fig. 1

A study participant with impairments due to Cerebral Palsy trains on the MIT-Skywalker. Subject is looking at a monitor that displays the training goals in a form of video-games.

Fig. 2

The MIT-Skywalker concept of assistance. Top row shows healthy gait: the leg supports the trunk while it moves backward relative to the trunk during the stance phase; at toe-off the support is shifted, the ankle completes a propulsive plantarflexion movement, and initiates a dorsiflexion movement to clear the ground initiating the swing phase. The walking surface is necessary during the stance phase, but it inhibits the leg during the swing phase and requires clearing the surface and propelling the leg forward. In the MIT-Skywalker, the split treadmill moves the patient's foot to the toe-off position. Once the vision acquisition system recognizes the heel x-position has reached a minimum (patient-initiated swing phase), the track is dropped, allowing the foot to swing forward freely for another step partially assisted by gravity (pendulum) and by patient's effort.

Fig. 3

Sagittal Plane actuator and transmission. A. Brushless servo motor. B. Pinion gear. C. Rack Gear. D. Linear Cam. E. Linear Bearing. F. Treadmill Track. G. Cam follower mount.

Fig. 4

Tri-zone linear cam path. A: Track drop path B: Horizontal resting position C: Track raise path.

Fig. 5

Treadmill motion control loop.

Fig. 6

Schematics for the heel x-position estimation. Left: Analysis for rhythmic and balance programs. Right: Analysis for discrete program.

Fig. 7

View from the MIT-Skywalker. A large screen is used to display games and real-time webcam video of the subject.

Fig. 8

Discrete training mode stepping. A target is shown (white bar). The participant locates the target position with the heel. The success rate can be seen in front of the participant to keep her engaged in the training session.

Fig. 9

The bottom graph shows the speed in mph of each treadmill. Left of the vertical dotted line represents the step lengths recorded over a 30 second diagnostics session prior to training and right of the dotted line represents the post training diagnostic session. The middle section shows block 5/5 of the 11^th training session of 16 (the sixth rhythmic session, R6). The top graph shows the step length of each step before, during and after training. For this day of training, P1's initial gait showed slight asymmetry to start with an average left step length 0.2% longer than the right. After training with a longer left step, the final diagnostic showed the left step length to be 2.8% shorter than the right, statistically significant via the paired t-test (p < 0.05).