Jenny Mccarthy

Copyright © 2015 by ASME.This paper replaces the hinged pivots of an eight-bar linkage with flexure joints in order to achieve a flexure-connected linkage system that guides rectilinear movement of its end-effector. The goal is a linkage design that can be reduced in size to provide a suspension for the proof masses of a MEMS gyroscope. The symmetric design of the linkage and its long travel relative to other MEMS suspensions has the potential to provide a number of advantages, such as the reduction of quadrature error. The design presented yields 0.1% deviation over its range of movement. An example also presents the driving linkage of the MEMS gyroscope, which is also designed as flexure connected linkage.

Copyright © 2015 by ASME.This paper explores an automated methodology to design eight-bar linkages for five positions, by constraining the user defined 4R open chain and 6R closed chain using RR dyads. The application in focus is that of rectilinear motion. The paper lays down the rules for systematic selection of link pairs for the application of RR constraints, that help automate the synthesis of eight-bar linkages. The methodology performs a random search within the user specified tolerance zones around the task specifications to increase the number of candidate linkage solutions. These linkages are then subjected to forward kinematic analysis using the Dixon determinant elimination procedure to find all possible linkage configurations over the range of motion of the input link. Linkages that have all the task configurations on one branch ensure their smooth movement through them. The result is an array of defect-free eight-bars that can perform approximate rectilinear motion. This method provides increased flexibility and control over the synthesized linkage compared to other known rectilinear motion linkages, owing to the ability to specify the backbone chain. A couple of examples are presented to illustrate the results.

Copyright © 2015 by ASME.The standard recovery treatment for ankle and lower leg injuries consists of using underarm crutches. Hands-free crutches have recently emerged as a more comfortable, natural and energy efficient alternative. However in the currently available devices such as the iWalk-Free the lack of a knee joint results in abnormal motion pattern at the hip and pelvic joints to ensure foot clearance during the swing phase of the gait. To address this shortcoming, the paper describes the kinematic synthesis of a planar passive four-bar linkage that can be used as a mechanical knee in lower limb exoskeletons and other wearable devices. The knee design is based on anthropomorphic foot walking trajectory obtained from optical motion capture system. The task geometry at the foot, related to the contact and curvature constraints between the foot and the ground at two critical positions 'heel strike' and 'toe off' is scaled to the knee level. Velocity and acceleration specifications compatible with the contact and curvature constraints assist in defining the synthesis equations for the knee design. A working prototype of a passive wearable crutch substitute that incorporates the mechanical knee shows the applicability of the proposed technique.