347 research outputs found
Adaptive Control of Robotic arm with Hysteretic Joint
This article addresses the problem of control of robotic arm
with a hysteretic joint behavior. The mechanical design of
the one-degree of freedom robotic arm is presented where the
joint is actuated by a Shape Memory Alloy (SMA) wire. The
SMA wire based actuation of the joint makes the robotic arm
lightweight but at the same time introduces hysteresis type
nonlinearities. The nonlinear dynamic model of the robotic
arm is introduced and an Adaptive control solution is presented
to perform the joint reference tracking in the presence
of unknown hysteresis behavior. The Lyapunov stability
analysis of the closed loop system is presented and finally
proposed adaptive control solution is validated through simulation
study on the proposed nonlinear hysteretic robotic
arm
Adaptive Control of Hysteretic Robotic arm in Operational Space
The focus of the current article is on Operational Space Control
of a single degree of freedom robotic arm with hysteretic
joint behaviour due to actuation by a single Shape Memory
Alloy (SMA) wire. A Closed Loop Inverse Kinematics Algorithm
is used in the outer loop with Adaptive joint control
in the inner loop. A composite stability analysis is used to
analyse the stability of the closed loop system and finally
successfully validated through simulation study
Operational space control of a lightweight robotic arm actuated by shape memory alloy wires: a comparative study.
This article presents the design and control of a two-link lightweight robotic arm using shape memory alloy wires as actuators. Both a single-wire actuated system and an antagonistic configuration system are tested in open and closed loops. The mathematical model of the shape memory alloy wire, as well as the kinematics and dynamics of the robotic arm, are presented. The operational space control of the robotic arm is performed using a joint space control in the inner loop and closed-loop inverse kinematics in the outer loop. In order to choose the best joint space control approach, a comparative study of four different control approaches (proportional derivative, sliding mode, adaptive, and adaptive sliding mode control) is carried out for the proposed model. From this comparative analysis, the adaptive controller was chosen to perform operational space control. This control helps us to perform accurate positioning of the end-effector of shape memory alloy wire–based robotic arm. The complete operational space control was successfully tested through simulation studies performing position reference tracking in the end-effector space. Through simulation studies, the proposed control solution is successfully verified to control the hysteretic robotic arm
Magneto-Rheological Actuators for Human-Safe Robots: Modeling, Control, and Implementation
In recent years, research on physical human-robot interaction has received considerable attention. Research on this subject has led to the study of new control and actuation mechanisms for robots in order to achieve intrinsic safety. Naturally, intrinsic safety is only achievable in kinematic structures that exhibit low output impedance. Existing solutions for reducing impedance are commonly obtained at the expense of reduced performance, or significant increase in mechanical complexity. Achieving high performance while guaranteeing safety seems to be a challenging goal that necessitates new actuation technologies in future generations of human-safe robots.
In this study, a novel two degrees-of-freedom safe manipulator is presented. The manipulator uses magneto-rheological fluid-based actuators. Magneto-rheological actuators offer low inertia-to-torque and mass-to-torque ratios which support their applications in human-friendly actuation. As a key element in the design of the manipulator, bi-directional actuation is attained by antagonistically coupling MR actuators at the joints. Antagonistically coupled MR actuators at the joints allow using a single motor to drive multiple joints. The motor is located at the base of the manipulator in order to further reduce the overall weight of the robot. Due to the unique characteristic of MR actuators, intrinsically safe actuation is achieved without compromising high quality actuation. Despite these advantages, modeling and control of MR actuators present some challenges. The antagonistic configuration of MR actuators may result in limit cycles in some cases when the actuator operates in the position control loop. To study the possibility of limit cycles, describing function method is employed to obtain the conditions under which limit cycles may occur in the operation of the system. Moreover, a connection between the amplitude and the frequency of the potential limit cycles and the system parameters is established to provide an insight into the design of the actuator as well as the controller. MR actuators require magnetic fields to control their output torques. The application of magnetic field however introduces hysteresis in the behaviors of MR actuators. To this effect, an adaptive model is developed to estimate the hysteretic behavior of the actuator. The effectiveness of the model is evaluated by comparing its results with those obtained using the Preisach model. These results are then extended to an adaptive control scheme in order to compensate for the effect of hysteresis. In both modeling and control, stability of proposed schemes are evaluated using Lyapunov method, and the effectiveness of the proposed methods are validated with experimental results
Adaptive control for a lightweight robotic arm actuated by a Shape Memory Allow wire
This paper presents the design, model and closed-loop control of a single degree-of-freedom (DOF) lightweight robotic arm actuated by a biased Shape Memory Alloy (SMA) wire. The highly non-linear dynamics of SMAs represent a challenge for control tasks, due to phenomena as hysteresis or parameters uncertainty. With this in mind, we propose a control capable to adapt itself to the hysteretic behavior and update its behavior to deal with the changing parameters of the material over time. An adaptive control for position regulation is presented. This control includes a set of techniques, providing a systematic way to adjust the control parameters in real time, so maintaining the stability of the system and a desired performance, while dealing with parameter and model uncertainties. The closed-loop approach is tested in experimentally showing its effectiveness to deal with the highly non-linear dynamics of the SMA wire
Overtwisting and Coiling Highly Enhances Strain Generation of Twisted String Actuators
Twisted string actuators (TSAs) have exhibited great promise in robotic
applications by generating high translational force with low input torque. To
further facilitate their robotic applications, it is strongly desirable but
challenging to enhance their consistent strain generation while maintaining
compliance. Existing studies predominantly considered overtwisting and coiling
after the regular twisting stage to be undesirable non-uniform and
unpredictable knots, entanglements, and coils formed to create an unstable and
failure-prone structure. Overtwisting would work well for TSAs when uniform
coils can be consistently formed. In this study, we realize uniform and
consistent coil formation in overtwisted TSAs, which greatly increases their
strain. Furthermore, we investigate methods for enabling uniform coil formation
upon overtwisting the strings in a TSA and present a procedure to
systematically "train" the strings. To the authors' best knowledge, this is the
first study to experimentally investigate overtwisting for TSAs with different
stiffnesses and realize consistent uniform coil formation. Ultra-high
molecular-weight polyethylene (UHMWPE) strings form the stiff TSAs whereas
compliant TSAs are realized with stretchable and conductive supercoiled polymer
(SCP) strings. The strain, force, velocity, and torque of each overtwisted TSA
was studied. Overtwisting and coiling resulted in approximately 70% strain in
stiff TSAs and approximately 60% strain in compliant TSAs. This is more than
twice the strain achieved through regular twisting. Lastly, the overtwisted TSA
was successfully demonstrated in a robotic bicep
Experimental validation of adaptive control for a Shape Memory Alloy actuated lightweight robotic arm
This article presents the experimental validation of a Direct Adaptive Control for angular position regulation of a lightweight robotic arm. The robotic arm is single degree-of-freedom (DOF) system, actuated by two Shape Memory Alloy (SMA) wires. The proposed adaptive control is capable of adapting itself to the hysteretic behavior of SMA wires and update its behavior to deal
with the changing parameters of the material over time. The closed-loop approach is tested experimentally showing its effectiveness to deal with the highly nonlinear dynamics of the SMA
wires. These results are discussed and compared with a classical control approach. The updated design and hardware development and modeling of the robotic arm are shown
Adaptive Compliance Shaping with Human Impedance Estimation
Human impedance parameters play an integral role in the dynamics of strength
amplification exoskeletons. Many methods are used to estimate the stiffness of
human muscles, but few are used to improve the performance of strength
amplification controllers for these devices. We propose a compliance shaping
amplification controller incorporating an accurate online human stiffness
estimation from surface electromyography (sEMG) sensors and stretch sensors
connected to the forearm and upper arm of the human. These sensor values along
with exoskeleton position and velocity are used to train a random forest
regression model that accurately predicts a person's stiffness despite varying
movement, relaxation, and muscle co-contraction. Our model's accuracy is
verified using experimental test data and the model is implemented into the
compliance shaping controller. Ultimately we show that the online estimation of
stiffness can improve the bandwidth and amplification of the controller while
remaining robustly stable.Comment: 8 pages, 9 figures, Accepted for publication at the 2020 American
Control Conference. Copyright IEEE 202
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