In this study, design and control of a novel parallel elastically actuated (PEA) legged robot are presented. The motion is limited to vertical apex to apex hopping. Design of the robot comprises a symmetric four link mechanism as the leg, a brushless direct-drive DC motor and a wrapping cam with extension spring. Controller is based on templates (the simplest model) and anchors (more realistic model) scheme, where the template is the Spring Loaded Inverted Pendulum (SLIP) including a viscous damper which is virtually tunable. For a given desired apex, the required damping constant is calculated to provide necessary energy to SLIP. This behavior is realized in the anchor model by equating its dynamics to the template dynamics through torque control and the wrapping cam. During the motion, a string is wrapped around the cam by the relative motion between two links of the four link mechanism. The string pulls the spring and desired potential energy function is obtained. Static force experiments are performed to show that cam works as desired. Overall simulations and details of mechanical design are presented. This novel PEA robot architecture provides an accurate and energy efficient solution with a simple mechanical design.


Design of a Parallel Elastic Hopper With a Wrapping Cam Mechanism and Template Based Virtually Tunable Damping Control

Division / Sponsors: 
Dynamic Systems & Control (DSCD)

Paper Proceedings: https://asmedigitalcollection.asme.org/DSCC/DSCC2020/volume/84270

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