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The structural composition of two elastic elements, shape memory alloy wire (active actuating element) and spring (the passive bias), offers variable stiffness actuation. Based on this principle, a variable stiffness linear actuator is conceptually designed and developed. It is electromechanical by nature, that is, it is electrically activated and creates translational/linear motion. The variable stiffness linear actuator engages shape memory alloy wire(s) along with a passive compression spring to work synergistically. The biasing element offers recovery force to the shape memory alloy wire as well as compliance to the whole structure. The synergistic configuration exhibits an aiding force, thereby allowing an actuation with large displacement and a wide range of stiffness. The actuator mechanism is implemented through parallel action and further proposes two different modes of operation: pull mode (i.e. the disc moving along a fixed shaft) and push mode (i.e. linear reciprocating motion of the pushrod). The shape memory alloy configured actuator mechanism is analysed theoretically; the working model of the variable stiffness linear actuator is developed and investigated experimentally. The results apprise that the variable stiffness linear actuator is capable of offering large displacement and in reproducing the stiffness profile for active compliance control applications.

In this study the output voltage is controlled by the Cuk converter using Sliding Mode Control. Here to highlight the advantages of SMC, the PI controller is used in Cuk converter to control the output voltage and it is compared with the SMC. The PI and SMC is implemented in the DC-DC converter and the study is carried in MATLAB SIMULINK. The effect of SMC on the DC-DC converter response in steady state, under line variations, load variations and different component variations will be compared with that of PI controller and results are presented.

Variable stiffness actuator is the essential element for force control and motion generation of most mechanical systems that are used for soft robotic, biomimetic and biomedical applications. Mechanical systems when integrated with smart materials enable controlled variation of stiffness in addition to control of force and displacement, thus exhibiting superior characteristics. Active compliant/variable stiffness actuator using shape memory alloy allows simple and compact design, exhibits comparable actuator efficiency and offers directional controllable actuation, self-sensing and a wide range of variable stiffness. The functional characteristics of a synergistically operated translational/linear compliant variable stiffness actuator, configured synergistically with shape memory alloy wire(s) and passive compression spring, are determined experimentally under no load without control to offer translational actuation. Repetitive actuation is made possible through electrical activation (direct Joule heating) of shape memory alloy wire(s) and the aiding force (the restoring (bias) force) of the passive spring. Actuation with variable stiffness is obtained from the inherent stiffness variation of shape memory alloy during its phase transformation, along with the fixed stiffness of the passive compliant element. The scope of improving the range of stiffness through varied forms and connections of the elements is recognized, while retaining the basic structure without compromising its simplicity.

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