• Sajiv Shah

Application of a Variable Stiffness Actuator: Passively Compliant Robot Leg

In looking for a proper application for a variable stiffness actuator, I drew inspiration from a presentation in a workshop I attended about biology inspired robotics. The presentation talked about active and passive compliance in robot legs, specifically the ones found in robotic dogs rather than humanoids or biped robots. I figured that a robot dog leg would be a great test platform for a variable stiffness actuator because it would not only be fun to make but also be able to demo passive traction applied by the actuator, gravity compensation, and most importantly a jump.

With a variable stiffness actuator, a robot would be able to mimic the human action of a jump, where humans store energy in their stiff leg muscles and launch into the air, then land with compliance in their leg muscles in order to absorb the shock and some of the energy from the landing. Furthermore, when the actuator stiffness changes, it itself causes the potential energy in a spring to snap into kinetic energy, offering a method for jumping.

An example of the CAD for the system is shown to the left. By using a cardan gear , we can convert the rotational motion of one variable stiffness actuator into the linear motion of this entire leg. One actuator controlling both legs allows for simplicity in the direct measurement of the effectiveness of this design. The setup of this leg system allows us to determine the effectiveness of our variable stiffness system. A few things this can demonstrate are the ability to land with passive compliance, and land with no oscillatory motion and energy storage.

A major barrier to building this system is my lack of experience in a very complicated field, electronics. We will need to create a robust electronics setup for this design that is reliable and not faulty in order to accurately measure values.

In the next few posts I'll go over some of the electronics setup, the sensors we are using, and some of the variables we want to compare, as well as what they mean for a VSA.