Gait training is a major part of neurological rehabilitation. Robotic gait training systems provide paraplegic patients with consistent, labor-saving, and adjustable physical therapy over traditional manual trainings. However the high cost and social-technical concerns on safe operation currently limit their availability to only a few large rehabilitation institutions. This paper describes the synthesis of a linkage mechanism for gait pattern generation in a sagittal plane. The synthesis of the mechanism starts with the definition of a closed ankle trajectory obtained from normative gait data. The synthesis process we developed includes (1) construction of the desired ankle trajectory, (2) formulation of an objective function to be used for linkage optimization, (3) development of a procedure for transforming an initial guess to a starting set of design variables for optimization, and (4) development of a point-matching process needed for implementation. A set of stature-referenced parameters was successfully produced for a crank-rocker mechanism to generate the desired gait path. A simple linkage mechanism can be used as the pattern generator in a gait training system, and the presented process has been used to synthesize a linkage for a specific gait pattern.
A conceptual gait rehabilitation system was developed to generate the coordinated motion of the hip and knee joints according to normal physiological gait pattern with a pair of linkage mechanisms (one for each leg). This article presents the design of a mechanical timing mechanism for the motion control and coordination of the linkage mechanisms in the system. The desired motion of the input crank of the linkage mechanism is first obtained for the control purpose. To facilitate the implementation of different modes of operation of the gait rehabilitation system, a combination of cam and planetary gears is developed to achieve both timing and coordination through mechanical means. Motion simulation of the new timing mechanisms shows that the proper timing of the gait mechanisms, thus the hip and knee joints, is achieved with a constant speed input.
This paper presents a procedure for minimizing the size of roller-follower disc cam mechanisms under the constraint of maximum pressure angle. The pressure angle constraint is realized through establishing the permissible region for the cam centre. The problem of cam-size minimization is reduced to locate the cam centre at the intersection of boundary curves of the permissible region. Its implementation is illustrated through examples.
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