Design and experimental investigation of a variable stiffness device

Abstract

Many mechanisms and applications use mechanical springs for the purpose of reducing shocks, applying a force, storing energy or changing natural frequencies. There are many types of springs such as the leaf springs, compression springs, torsion springs etc. These springs have constant stiffness. In this project, the aim is to design a device with variable stiffness characteristics. Variable stiffness characteristics are important and useful in robots. During the motion of the arm, a low stiffness is favorable for safety reason should a collision occurs. At the end of the motion, high stiffness will be important for positional accuracy. The proposed design of the Variable Stiffness Device (VSD) uses four torsion springs arranged in parallel. The design is compact and will allow the user to control and vary the stiffness accordingly. Tensile tests are carried out to determine the stiffness of the device of up to 100N. The results are tabulated in a graph in which the stiffness of the spring is compared to the design stiffness. It is shown that stiffness of the device can multiply up to three times compared to original stiffness of the spring. In addition, it is also found that with smaller specifications of the springs, better results for the stiffness could be obtained but it also comes with some limitations.