Simultaneous Force and Stiffness Control of a Pneumatic Actuator

2007 ◽  
Vol 129 (4) ◽  
pp. 425-434 ◽  
Author(s):  
Xiangrong Shen ◽  
Michael Goldfarb
Keyword(s):  
Dynamic Range ◽  
Variable Stiffness ◽  
Pneumatic Actuator ◽  
Force Output ◽  
New Approach ◽  
Control Approach ◽  
Simultaneous Control ◽  
Output Force ◽  
Maximum Minimum ◽  
Series Elastic

This paper proposes a new approach to the design of a robot actuator with physically variable stiffness. The proposed approach leverages the dynamic characteristics inherent in a pneumatic actuator, which behaves in essence as a series elastic actuator. By replacing the four-way servovalve used to control a typical pneumatic actuator with a pair of three-way valves, the stiffness of the series elastic component can be modulated independently of the actuator output force. Based on this notion, the authors propose a control approach for the simultaneous control of actuator output force and stiffness. Since the achievable output force and stiffness are coupled and configuration-dependent, the authors also present a control law that provides either maximum or minimum actuator output stiffness for a given displacement and desired force output. The general control and maximum/minimum stiffness approaches are experimentally demonstrated and shown to provide high fidelity control of force and stiffness, and additionally shown to provide a factor of 6 dynamic range in stiffness.

scholarly journals Pneumatic Variable Series Elastic Actuator

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Hao Zheng ◽  
Molei Wu ◽  
Xiangrong Shen
Keyword(s):  
Equilibrium Point ◽  
Variable Stiffness ◽  
Pneumatic Actuator ◽  
Control Action ◽  
Working Fluid ◽  
Loop Control ◽  
Air Masses ◽  
Series Elastic Actuator ◽  
Stiffness Control ◽  
Series Elastic

Inspired by human motor control theory, stiffness control is highly effective in manipulation and human-interactive tasks. The implementation of stiffness control in robotic systems, however, has largely been limited to closed-loop control, and suffers from multiple issues such as limited frequency range, potential instability, and lack of contribution to energy efficiency. Variable-stiffness actuator represents a better solution, but the current designs are complex, heavy, and bulky. The approach in this paper seeks to address these issues by using pneumatic actuator as a variable series elastic actuator (VSEA), leveraging the compressibility of the working fluid. In this work, a pneumatic actuator is modeled as an elastic element with controllable stiffness and equilibrium point, both of which are functions of air masses in the two chambers. As such, for the implementation of stiffness control in a robotic system, the desired stiffness/equilibrium point can be converted to the desired chamber air masses, and a predictive pressure control approach is developed to control the timing of valve switching to obtain the desired air mass while minimizing control action. Experimental results showed that the new approach in this paper requires less expensive hardware (on–off valve instead of proportional valve), causes less control action in implementation, and provides good control performance by leveraging the inherent dynamics of the actuator.

A Unified Approach to H∞ Control of Singular Markovian Jump Systems

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Guoliang Wang ◽  
Hongyi Li
Keyword(s):  
Transition Probability ◽  
Markovian Jump Systems ◽  
Linear Matrix ◽  
Markovian Jump ◽  
New Approach ◽  
Control Approach ◽  
Singular Markovian Jump Systems ◽  
Jump Systems ◽  
Bounded Uncertainties ◽  
The Given

This paper considers the H∞ control problem for a class of singular Markovian jump systems (SMJSs), where the jumping signal is not always available. The main contribution of this paper introduces a new approach to a mode-independent (MI) H∞ controller by exploiting the nonfragile method. Based on the given method, a unified control approach establishing a direct connection between mode-dependent (MD) and mode-independent controllers is presented, where both existence conditions are given in terms of linear matrix inequalities. Moreover, another three cases of transition probability rate matrix (TRPM) with elementwise bounded uncertainties, being partially unknown and to be designed are analyzed, respectively. Numerical examples are used to demonstrate the effectiveness of the proposed methods.

scholarly journals Fully-Printable Soft Actuator with Variable Stiffness by Phase Transition and Hydraulic Regulations

Actuators ◽  
2021 ◽  
Vol 10 (10) ◽  
pp. 269
Author(s):  
Tingchen Liao ◽  
Manivannan Sivaperuman Kalairaj ◽  
Catherine Jiayi Cai ◽  
Zion Tsz Ho Tse ◽  
Hongliang Ren
Keyword(s):  
Transition Period ◽  
Shape Memory Polymer ◽  
Variable Stiffness ◽  
Pressure Variation ◽  
Soft Actuator ◽  
Output Force ◽  
Load Carrying ◽  
Force Variation ◽  
Stiffness Variation ◽  
Short Transition

Actuators with variable stiffness have vast potential in the field of compliant robotics. Morphological shape changes in the actuators are possible, while they retain their structural strength. They can shift between a rigid load-carrying state and a soft flexible state in a short transition period. This work presents a hydraulically actuated soft actuator fabricated by a fully 3D printing of shape memory polymer (SMP). The actuator shows a stiffness of 519 mN/mm at 20 ∘C and 45 mN/mm at 50 ∘C at the same pressure (0.2 MPa). This actuator demonstrates a high stiffness variation of 474 mN/mm (10 times the baseline stiffness) for a temperature change of 30 ∘C and a large variation (≈1150%) in average stiffness. A combined variation of both temperature (20–50 ∘C) and pressure (0–0.2 MPa) displays a stiffness variation of 501 mN/mm. The pressure variation (0–0.2 MPa) in the actuator also shows a large variation in the output force (1.46 N) at 50 ∘C compared to the output force variation (0.16 N) at 20 ∘C. The pressure variation is further utilized for bending the actuator. Varying the pressure (0–0.2 MPa) at 20 ∘C displayed no bending in the actuator. In contrast, the same variation of pressure at 50 ∘C displayed a bending angle of 80∘. A combined variation of both temperature (20–50 ∘C) and pressure (0–0.2 MPa) shows the ability to bend 80∘. At the same time, an additional weight (300 g) suspended to the actuator could increase its bending capability to 160∘. We demonstrated a soft robotic gripper varying its stiffness to carry objects (≈100 g) using two individual actuators.

Variable stiffness control of series elastic actuated biped locomotion

2018 ◽  
Vol 11 (3) ◽  
pp. 225-235 ◽  
Author(s):  
Jianwen Luo ◽  
Shuguo Wang ◽  
Ye Zhao ◽  
Yili Fu
Keyword(s):  
Variable Stiffness ◽  
Biped Locomotion ◽  
Stiffness Control ◽  
Series Elastic

A New Approach of Direct Digital Control for Spool Valves

1999 ◽  
Author(s):  
J. Ruan ◽  
R. Burton
Keyword(s):  
Digital Control ◽  
Stepper Motor ◽  
Hydraulic Control ◽  
New Approach ◽  
Control Approach ◽  
Speed Of Response ◽  
Spool Valves ◽  
Spool Valve ◽  
Direct Digital Control ◽  
Hydraulic Control System

Abstract In many applications, digital valves driven from stepping motors are often characterized by quantitative errors and in some cases, slow response. A new means of direct digital control is introduced for a spool valve actuated by a stepper motor. With this control strategy, both excellent speed of response and accuracy are simultaneously sustained for the valve. By way of illustration, the characteristics of a digital spool valve are theoretically and experimentally investigated. This paper also deals with the design of the controller and some concepts concerning the digital control of a valve, such as initialization, false protection, etc. An example is given to demonstrate the effectiveness of this digital control approach for a practical electro-hydraulic control system.

scholarly journals USING DYNAMIC NEURAL NETWORKS TO GENERATE CHAOS: AN INVERSE OPTIMAL CONTROL APPROACH

2001 ◽  
Vol 11 (03) ◽  
pp. 857-863 ◽  
Author(s):  
EDGAR N. SANCHEZ ◽  
JOSE P. PEREZ ◽  
GUANRONG CHEN
Keyword(s):  
Neural Networks ◽  
Optimal Control ◽  
Chaotic Attractors ◽  
Control Law ◽  
Inverse Optimal Control ◽  
Dynamic Neural Network ◽  
Dynamic Neural Networks ◽  
New Approach ◽  
Control Approach ◽  
Optimal Control Approach

This Letter suggests a new approach to generating chaos via dynamic neural networks. This approach is based on a recently introduced methodology of inverse optimal control for nonlinear systems. Both Chen's chaotic system and Chua's circuit are used as examples for demonstration. The control law is derived to force a dynamic neural network to reproduce the intended chaotic attractors. Computer simulations are included for illustration and verification.

Design of a Novel Variable Stiffness Series Elastic Actuator for Extended Linearity

2019 ◽  
Author(s):  
Seung Ho Lee ◽  
Hyeok Jin Lee ◽  
Kyeong Ha Lee ◽  
Ji Min Baek ◽  
Ja Choon Koo
Keyword(s):  
Linear Relationship ◽  
Variable Stiffness ◽  
Linear Series ◽  
Torque Sensor ◽  
Industrial Automation ◽  
Linear Relations ◽  
Series Elastic Actuator ◽  
Robotic Applications ◽  
Adjustable Compliance ◽  
Series Elastic

Abstract Recently, Series Elastic Actuator (SEA) has been popularly used as a torque sensor thanks to its notable ability to calibrate the relation between torque and displacement. It has been applied to many robotic applications and used in a various industrial automation fields. However, most of the current SEAs have nonlinear torque-displacement characteristics which could not be easily alleviated. In order to be utilized as a feasible torque sensor, the wide linearity of a SEA in torque-displacement relationship is not an option. Also, adjustable compliance is needed to implement a mechanism with different stiffness, depending on the various cases where SEA can be applied. In this paper, we designed a Variable Stiffness Linear Series Elastic Actuator (VLSEA) mechanism that can achieve variable stiffness with a linear relationship between torque and displacement. At first, a design with a four-bar link was proposed for linear relations, but it was difficult to implement variable stiffness. We modified the design using the Scotch Yoke mechanisms for the model to have variable stiffness. Simulation of the designed model then verifies that the model can properly implement linearity and variable stiffness.

Optimization-Based Whole-Body Control of a Series Elastic Humanoid Robot

2016 ◽  
Vol 13 (01) ◽  
pp. 1550034 ◽  
Author(s):  
Michael A. Hopkins ◽  
Alexander Leonessa ◽  
Brian Y. Lattimer ◽  
Dennis W. Hong
Keyword(s):  
Inverse Dynamics ◽  
Contact Forces ◽  
Joint Torque ◽  
Whole Body ◽  
Quadratic Program ◽  
Successful Implementation ◽  
Control Approach ◽  
Floating Base ◽  
High Level ◽  
Series Elastic

As whole-body control approaches begin to enter the mainstream of humanoid robotics research, there is a real need to address the challenges and pitfalls encountered in hardware implementations. This paper presents an optimization-based whole-body control framework enabling compliant locomotion on THOR, a 34 degree of freedom humanoid featuring force-controllable series elastic actuators (SEAs). Given desired momentum rates of change, end-effector accelerations, and joint accelerations from a high-level locomotion controller, joint torque setpoints are computed using an efficient quadratic program (QP) formulation designed to solve the floating-base inverse dynamics (ID). Constraints on the centroidal dynamics, frictional contact forces, and joint position/torque limits ensure admissibility of the optimized joint setpoints. The control approach is supported by an electromechanical design that relies on custom linear SEAs and embedded joint controllers to accurately regulate the internal and external forces computed by the whole-body QP. Push recovery and walking tests conducted using the THOR humanoid validate the effectiveness of the proposed approach. In each case, balancing is achieved using a planning and control approach based on the time-varying divergent component of motion (DCM) implemented for the first time on hardware. We discuss practical considerations that led to the successful implementation of low-impedance whole-body control on our hardware system including the design of the robot’s high-level standing and stepping behaviors and low-level joint-space controllers. The paper concludes with an application of the presented approach for a humanoid firefighting demonstration onboard a decommissioned US Navy ship.

Nonlinear Two Stage Control Strategy of a Wind Turbine for Mechanical Load and Extreme Moment Reduction

2011 ◽  
Author(s):  
Jonathan Chauvin ◽  
Yann Creff
Keyword(s):  
Control Strategy ◽  
Nonlinear Dynamic ◽  
Mechanical Load ◽  
Dynamic Feedback ◽  
Rotor Speed ◽  
Model Uncertainties ◽  
New Approach ◽  
Control Approach ◽  
Second Stage ◽  
Speed Regulation

This paper presents a new approach for the control of wind turbines. The proposed strategy can be decomposed in two part. In a first stage control strategy, we provide a nonlinear dynamic feedforward strategy for rotor speed regulation along with a nonlinear dynamic feedback to be robust to model uncertainties. It guarantees convergence of the rotor speed to its desired value. This first part only looks at the rotor dynamics and the aerodynamics. The tower dynamics is not taken into account. In a second stage control strategy, we provide a control action that minimize the tower fatigue. The strategy is largely validated for the onshore case. The proposed control approach can be extended to the offshore case and a first validation is proposed.

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