Modeling, Control, and Numerical Simulations of a Novel Binary-Controlled Variable Stiffness Actuator (BcVSA)

Abstract

This research work aims at realizing a new compliant robotic actuator for safe human-robotic interaction. In this paper, we present the modeling, control, and numerical simulations of a novel Binary-Controlled Variable Stiffness Actuator (BcVSA) aiming to be used for the development of a novel compliant robotic manipulator. BcVSA is the proof of concept of the active revolute joint with the variable recruitment of series-parallel elastic elements. We briefly recall the basic design principle which is based on a stiffness varying mechanism consisting of a motor, three inline clutches, and three torsional springs with stiffness values (K 0 , 2K 0 , 4K 0 ) connected to the load shaft and the motor shaft through two planetary sun gear trains with ratios (4:1, 4:1 respectively). We present the design concept, stiffness and dynamic modeling, and control of our BcVSA. We implemented three kinds of Multiple Model Predictive Control (MPC) to control our actuator. The main motivation of choosing this controller lies in the fact that working principle of multiple MPC and multiple states space representation (stiffness level) of our actuator share similar interests. In particular, we implemented Multiple MPC, Multiple Explicit MPC, and Approximated Multiple Explicit MPC. Numerical simulations are performed in order to evaluate their effectiveness for the future experiments on the prototype of our actuator. The simulation results showed that the Multiple MPC, and the Multiple Explicit MPC have similar results from the robustness point of view. On the other hand, the robustness performance of Approximated Multiple Explicit MPC is not good as compared to other controllers but it works in the offline framework while having the capability to compute the sub-optimal results. We also performed the comparison of MPC based controllers with the Computed Torque Control (CTC), and Linear Quadratic Regulator (LQR). In future, we are planning to test the presented approach on the hardware prototype of our actuator.

A Systematic Design Selection Methodology for System-Optimal Compliant Actuation

“…In the meantime, three review papers are included in references on the subjects to refer the readers who may be interested in compliance modeling and multi-objective optimization. [21][22][23] 1.2. Structure The paper is organized as follows: Section 2 presents the preconditions for an unbiased comparison of designs, introduces the system-optimal co-design method used throughout the selection problem, and provides a formal definition for the proposed systematic design selection methodology.…”

Design Optimization of a Variable Stiffness Actuator for Knee Exoskeleton Application

“…Generally, the developments in VSAs are driven by the need for humans to work in proximity to robots, either via physical interaction (collaboration or cooperation) or via wearable robotic devices [7], [9], [10], [11]. VSAs are capable to tune their stiffness value in order to enhance their performance in terms of safety, accuracy, and energy efficiency [12], [13].…”

Design, Dynamics Analysis, and Real-Time Stiffness Control of a Variable Stiffness Joint

“…Mechanical controlled variable stiffness joints to changes joint stiffness by changing the connection between elastic elements and rigid structures, for example, VS-Joint [13], FSJ [14] and others adjust joint stiffness by change the preload of elastic elements; pVSJ (passive variable stiffness joint) [15], AwAS (actuator with adjustable stiffness) [16][17][18] and others [19][20][21][22] adjust joint stiffness by changing the effective length according to the lever principle. In addition, according to whether the stiffness of variable stiffness joint is continuous, it can be divided into continuous variable stiffness joint and discrete variable stiffness joint, such as BcVSA (Binary-Controlled Variable Stiffness Actuator) [23], pDVSJ (Passive Diskrete Variable Stiffness Joint) [24].…”