Session: 16-01-01: Poster Session: NSF-Funded Research (Grad & Undergrad)

Paper Number: 100102

100102 - A Novel Discrete Variable Stiffness Actuator Based on a Reconfigurable Parallel-Beam Flexure Mechanism 

Variable stiffness actuators (VSAs) are one of the effective solutions in developing collaborative robots with intrinsic safety for physical human-robot interaction. So far, the majority of VSAs that have been published change the stiffness continuously, however, it is not always necessary to have the continuous stiffness adjustment. This paper presents a novel compact variable stiffness actuator based on a reconfigurable parallel-beam flexure mechanism, named discrete VSA (DVSA). The DVSA is composed of two mechanisms: stiffness adjustment mechanism and stiffness transmission mechanism. The main structure of the stiffness adjustment mechanism is an integrated centrosymmetric four compliant branch mechanism with each branch a parallel-beam flexure mechanism. The primary principle of stiffness change is to change the cross-sectional properties of the parallel beam segment in a discrete manner. This is realized by a block inserting method through a bistable mechanism equipped with a push-pull electromagnet module. The key structures of the stiffness transmission mechanism are four lever pin-slot connections that transmit torque to drive the flexure frame to rotate. Using the superposition method, a generalized analytical model is proposed to model the stiffness modes. Compared to building a pseudo-rigid body model of the parallel beam, this analytical model is suitable for most situations, and it is not limited to fixed beam parameters whose change will cause the coefficients of the pseudo-rigid body to be redetermined That is, our model can immediately calculate deflection and stiffness when changing beam dimensions. For the control of DVSA, our dynamic model is that the motor drives the load to rotate through the VSA. We use the PID method to control the motor and use different PID values for the four different stiffnesses. The stiffness change relationship with various design parameters is investigated using the developed models and validated by finite element analysis (FEA). Based on these results, the optimal parameters and configurations of the DVSA are determined to realize a large span of stiffness adjustment, so that its stiffness change rate can achieve 86.  Compared with the existing VSAs, the DVSA possess the following advantages: First, the structure is relatively simple and compact, and no motors are needed besides the driving motor, which reduces the complexity of the controller. Second, low energy consumption is needed for the stiffness change. The push-pull electromagnet module needs low power to energized when performing variable stiffness tasks. Last but not least is its fast response on stiffness change. The electromagnet module can complete the variable stiffness rapidly after being activated.

 

Presenting Author: Jiaming Fu Purdue University

Presenting Author Biography: Jiaming Fu is a second year Ph.D. student in the School of Engineering Technology at Purdue University, West Lafayette, IN. His major advisor is Dr. Dongming Gan. He got Master’s degree in Mechanical Engineering from Columbia University in 2019 and foucus on soft robot research there. He got Bachelor’s degree in Mechanical Engineering from Florida Institute of Technology in 2017. He has published 8 international journal and conference papers so far. For now, his research interest is on discrete variable stiffness mechinnisms, including discrete variable stiffness units, actuatosr, link, and gripper.

Authors:

Jiaming Fu Purdue University
Ziqing Yu Purdue University
Richard Voyles Purdue University
George Chiu Purdue University
Bin Yao Purdue University
Dongming Gan Purdue University