Showing papers on "Actuator published in 2017"

Automatic design of fiber-reinforced soft actuators for trajectory matching.

Abstract: Soft actuators are the components responsible for producing motion in soft robots. Although soft actuators have allowed for a variety of innovative applications, there is a need for design tools that can help to efficiently and systematically design actuators for particular functions. Mathematical modeling of soft actuators is an area that is still in its infancy but has the potential to provide quantitative insights into the response of the actuators. These insights can be used to guide actuator design, thus accelerating the design process. Here, we study fluid-powered fiber-reinforced actuators, because these have previously been shown to be capable of producing a wide range of motions. We present a design strategy that takes a kinematic trajectory as its input and uses analytical modeling based on nonlinear elasticity and optimization to identify the optimal design parameters for an actuator that will follow this trajectory upon pressurization. We experimentally verify our modeling approach, and finally we demonstrate how the strategy works, by designing actuators that replicate the motion of the index finger and thumb.

Adaptive Sliding-Mode Control of Markov Jump Nonlinear Systems With Actuator Faults

Abstract: This technical note is concerned with the design problem of adaptive sliding-mode stabilization for Markov jump nonlinear systems with actuator faults. The specific information including bounds of actuator faults, bounds of the nonlinear term and the external disturbance is not available for the controller design. The main attention focuses on designing the adaptive sliding-mode controller to overcome these problems. Firstly, a sliding-mode surface is constructed such that the reduced-order equivalent sliding motion is stochastically stable. Secondly, the adaptive sliding-mode controller can drive the state trajectories of the system onto the sliding-mode surface in finite time, and can estimate the loss of effectiveness of actuator faults and bounds of the nonlinear term and the external disturbance online. Thirdly, the stochastic stability of the closed-loop system can be guaranteed. Finally, a practical example is provided to demonstrate the effectiveness of the presented results.

New soft robots really suck: Vacuum-powered systems empower diverse capabilities

Abstract: We introduce a vacuum-powered soft pneumatic actuator (V-SPA) that leverages a single, shared vacuum power supply and enables complex soft robotic systems with multiple degrees of freedom (DoFs) and diverse functions. In addition to actuation, other utilities enabled by vacuum pressure include gripping and stiffening through granular media jamming, as well as direct suction adhesion to smooth surfaces, for manipulation or vertical fixation. We investigate the performance of the new actuator through direct characterization of a 3-DoF, plug-and-play V-SPA Module built from multiple V-SPAs and demonstrate the integration of different vacuum-enabled capabilities with a continuum-style robot platform outfitted with modular peripheral mechanisms. We show that these different vacuum-powered modules can be combined to achieve a variety of tasks—including multimodal locomotion, object manipulation, and stiffness tuning—to illustrate the utility and viability of vacuum as a singular alternative power source for soft pneumatic robots and not just a peripheral feature in itself. Our results highlight the effectiveness of V-SPAs in providing core soft robot capabilities and facilitating the consolidation of previously disparate subsystems for actuation and various specialized tasks, conducive to improving the compact design efficiency of larger, more complex multifunctional soft robotic systems.

Shape Memory Alloy-Based Soft Gripper with Variable Stiffness for Compliant and Effective Grasping.

Abstract: Soft pneumatic actuators and motor-based mechanisms being concomitant with the cumbersome appendages have many challenges to making the independent robotic system with compact and lightweight configuration. Meanwhile, shape memory actuators have shown a promising alternative solution in many engineering applications ranging from artificial muscle to aerospace industry. However, one of the main limitations of such systems is their inherent softness resulting in a small actuation force, which prevents them from more effective applications. This issue can be solved by combining shape memory actuators and the mechanism of stiffness modulation. As a first, this study describes a shape memory alloy-based soft gripper composed of three identical fingers with variable stiffness for adaptive grasping in low stiffness state and effective holding in high stiffness state. Each finger with two hinges is fabricated through integrating soft composite actuator with stiffness changeable material where each hinge ...

Actuator and sensor faults estimation based on proportional integral observer for TS fuzzy model

Abstract: This paper presents a novel method to address a Proportional Integral observer design for the actuator and sensor faults estimation based on Takagi–Sugeno fuzzy model with unmeasurable premise variables. The faults are assumed as time-varying signals whose kth time derivatives are bounded. Using Lyapunov stability theory and L2 performance analysis, sufficient design conditions are developed for simultaneous estimation of states and time-varying actuator and sensor faults. The Proportional Integral observer gains are computed by solving the proposed conditions under Linear Matrix Inequalities constraints. A simulation example is provided to illustrate the effectiveness of the proposed approach.

High-Precision Robust Force Control of a Series Elastic Actuator

Abstract: A series elastic actuator (SEA) is a promising actuation method in force control applications that intelligently interacts with environments. The SEA is characterized by a spring placed between a load and an actuator, which is an electric motor in most cases. Since the spring plays the role of a transducer between position (i.e., the spring deflection) and force, it is able to control the output force (torque) precisely by utilizing typical position control methods. However, the force control performance of the SEA is considered to have limitations due to its elasticity, and thus, to be inferior to rigid actuators in terms of bandwidth. This paper proposes that the force control performance of the SEA can be improved by exploiting the dynamic model of the SEA. To this end, the SEA is modeled and analyzed utilizing the two-mass dynamic model, which is a well-known and widely accepted model of the flexible system. The disturbance observer and feedforward controller are introduced as the model-based control algorithms for the SEA to achieve the high-precision force control. In addition to high-bandwidth force control, the proposed controller can address the robust stability and performance against model parameter variance and exogenous disturbances. For the analytic and quantitative assessment of the proposed force control system, the dynamic characteristics of an SEA under various control algorithms are analyzed, and the experimental results are provided for an actual SEA system in this paper.

Sliding Mode Observer-Based FTC for Markovian Jump Systems With Actuator and Sensor Faults

Abstract: This paper addresses the stabilization problem for nonlinear Markovian jump systems (MJS) with output disturbances, actuator and sensor faults simultaneously. This kind of plants are common in practical systems, such as mobile manipulators with switching joints. In this paper, a sliding mode observer design scheme is proposed for a new descriptor augmented plant. By employing the developed observer, the effects of actuator and sensor faults can be eliminated. It is shown that the stabilization of the overall closed-loop plant can be guaranteed by the proposed fault tolerant control (FTC) scheme. Finally, an example concerning mobile manipulators with Markovian switching joints is presented to show the effectiveness and applicability of the theoretical results.

Electrically and Sunlight-Driven Actuator with Versatile Biomimetic Motions Based on Rolled Carbon Nanotube Bilayer Composite

Abstract: Designing multistimuli responsive soft actuators which can mimic advanced and sophisticated biological movements through simple configuration is highly demanded for the biomimetic robotics application. Here, inspired by the human's flick finger behavior which can release large force output, a soft jumping robot mimicking the gymnast's somersault is designed based on the rolled carbon nanotube/polymer bilayer composite actuator. This new type of rolled bilayer actuator with tubular shape is fabricated and shows electrically and sunlight-induced actuation with remarkable performances including ultralarge deformation from tubular to flat (angel change >200° or curvature >2 cm−1), fast response (<5 s), and low actuation voltage (≤10 V). Besides jumping, the uniquely reversible rolling–unrolling actuation can lead to other smart soft robots with versatile complex biomimetic motions, including light-induced tumbler with cyclic wobbling, electrically/light-induced crawling-type walking robots and grippers, electrically induced mouth movement, and ambient-sunlight-induced blooming of a biomimetic flower. These results open the way for using one simple type of actuator structure for the construction of various soft robots and devices toward practical biomimetic applications.

Study on Self-Tuning Tyre Friction Control for Developing Main-Servo Loop Integrated Chassis Control System

Abstract: The inherent flexibility of hierarchical structure scheme with main-servo loop control structure is proposed to the problem of integrated chassis control system for the vehicle. It includes both main loop, which calculates and allocates the aim force using the optimal robust control algorithm and servo loop control systems, which track and achieve the target force using the onboard independent brake actuators. In fact, for the brake actuator, the aim friction is obtained by tracking the corresponding slip ratio of target force. For the coefficient of tire-road friction varying with different road surface, to get the nonlinear time-varying target slip ratio, the most famous quasi-static magic formula is proposed to estimate and predict real-time coefficient of different road surface and the constrained hybrid genetic algorithm (GA) is used to identify the key parameters of the magic formula on-line. Then, a self-tuning longitudinal slip ratio controller (LSC) based on the nonsingular and fast terminal sliding mode (NFTSM) control method is designed to improve the tracking accuracy and response speed of the actuators. At last, the proposed integrated chassis control strategies and the self-tuning control strategies are verified by computer simulations.

A Prestressed Soft Gripper: Design, Modeling, Fabrication, and Tests for Food Handling

Abstract: This study presented a prestressed soft gripper fabricated with 3-D printing technology. The gripper can realize a large contact area while grasping and simultaneously generate large initial opening without deflating the soft actuators. The soft actuator was 3-D printed as two separate parts: the soft chambers with a rigid connector and a cover to seal the chambers. The chamber part was stretched longitudinally and sealed by gluing the cover onto it. The actuator was then released, and an initial curl occurred due to the remaining prestress. Finite element (FE) simulations were performed to validate this concept and the designed structure. Actuator fabrication and experimental tests were presented, and agreements between the FE simulations and test results were achieved. A gripper consisting of four prestressed actuators was constructed and experimentally tested by picking-and-placing food materials in different weights and different sized containers. To adapt to objects of different sizes and shapes, the gripper base was designed to have two configurations and two openings. The results showed that the prestressed gripper could stably handle various types of food and still remain compact with a simple supporting system.

System and method for variable velocity surgical instrument

Abstract: A system and method of variable velocity control of a surgical instrument in a computer-assisted medical device includes a surgical instrument having an end effector located at a distal end of the instrument, an actuator, and one or more drive mechanisms for coupling force or torque from the actuator to the end effector. To perform an operation with the instrument, the computer-assisted medical device is configured to set a velocity set point of the actuator to an initial velocity and monitor force or torque applied by the actuator. When the applied force or torque is above a first force or torque limit it is determined whether a continue condition for the operation is satisfied. When the continue condition is satisfied the operation is paused and when the continue condition is not satisfied it is determined whether forced firing of the actuator should take place.

Amplitude-Saturated Nonlinear Output Feedback Antiswing Control for Underactuated Cranes With Double-Pendulum Cargo Dynamics

Abstract: When modeling cranes, the hook and the suspended cargo are usually regarded roughly as one mass point for simplicity, ie, the cargo swing is modeled as that of a single pendulum However, in practice, when the hook mass is nonnegligible or the cargo has a large size, the crane always exhibits double-pendulum swing dynamics, which is much more complicated and makes most existing control methods unapplicable In addition, all existing closed-loop controllers for (double-pendulum) cranes require full state feedback, while velocities are unavailable in most cases Moreover, they need to linearize the nonlinear crane model and cannot respect the actuator's practical saturation constraint, which may probably lead to actuator saturation and badly degrade the control performance (even unstable) In response to these practical issues, we suggest a novel amplitude-saturated output feedback (OFB) control approach for underactuated crane systems exhibiting double-pendulum effects We provide explicit Lyapunov-based analysis to rigorously prove that the equilibrium point of the closed-loop system is almost globally asymptotically stable, without any approximation to the original nonlinear dynamics As far as we know, this paper presents the first closed-loop control method that can achieve control for an underactuated double-pendulum crane with merely OFB and theoretically-guaranteed saturated control efforts Hardware experimental results demonstrate the superior performance of the proposed approach over existing methods and its strong robustness as well

Integral Sliding Mode Flight Controller Design for a Quadrotor and the Application in a Heterogeneous Multi-Agent System

Abstract: This paper investigates a novel integral sliding mode control (ISMC) strategy for the waypoint tracking control of a quadrotor in the presence of model uncertainties and external disturbances. The proposed controller has the inner–outer loop structure: The outer loop is to generate the reference signals of the roll and pitch angles, while the inner loop is designed by using the ISMC technique for the quadrotor to track the desired $x$ , $y$ positions and roll and pitch angles. The Lyapunov stability analysis is provided to show that the negative effects of the bounded model uncertainties and external disturbances can be significantly decreased. The designed controller is then applied to a heterogeneous multi-agent system (MAS) consisting of quadrotors and two-wheeled mobile robots (2WMRs) to solve the consensus problem. We present the control algorithms for the 2WMRs and quadrotors. Consensus of the heterogeneous MAS can be reached if the switching graphs always have a spanning tree. Finally, the experimental tests are conducted to verify the effectiveness of the proposed control methods.

A Novel Trapezoid-Type Stick–Slip Piezoelectric Linear Actuator Using Right Circular Flexure Hinge Mechanism

Abstract: A trapezoid-type stick–slip piezoelectric linear actuator using a right circular flexure hinge mechanism was proposed, designed, fabricated, and tested with the aim of accomplishing linear driving based on stick–slip motion. The angle adjustment of the trapezoid beam was used for generating lateral motion on the driving foot of the flexure hinge mechanism. A method of tuning the lateral motion of the flexure hinge mechanism was discussed. Based on the finite-element method, a proper angle of the trapezoid beam was obtained. The analysis results proved that asymmetrical flexure hinge mechanism can increase static friction force in slow extension stage and decrease kinetic friction force in quick contraction stage by lateral motion of the driving foot. A prototype was fabricated and its experimental system was established. The mechanical output experiments showed that the prototype achieved maximum output velocity and load of 5.96 mm/s and 3 N at a voltage of 100 V $p-p$ and a frequency of 500 Hz, respectively.

Multi-responsive actuators based on a graphene oxide composite: intelligent robot and bioinspired applications

Abstract: Carbon-based electrothermal or photothermal actuators have attracted intense attention recently. They can directly convert electrical or light energy into thermal energy and exhibit obvious deformations. However, if the actuation mechanism is only limited to thermal expansion, the deformation amplitude is difficult to increase further. Moreover, complex shape-deformation is still challenging. Although a few materials were reported to realize twisting or untwisting actuation by cutting the samples into strips along different orientations, each single strip could perform only one shape-deformation mode. In this work, we propose multi-responsive actuators based on a graphene oxide (GO) and biaxially oriented polypropylene (BOPP) composite, which are designed with different shapes (strip-shape and helical-shape). The strip-shape GO/BOPP actuator shows great bending actuations when driven by humidity (curvature of up to 3.1 cm−1). Due to a developed dual-mode actuation mechanism, the actuator shows a bending curvature of 2.8 cm−1 when driven by near infrared (NIR) light. The great actuation outperforms most other carbon-based actuators. Then, an intelligent robot based on the GO/BOPP composite is fabricated, which can switch between the protection mode and weightlifting mode with different external stimuli. Inspired from plant tendrils, a bioinspired helical GO/BOPP actuator is further realized to show both twisting and untwisting actuations in a single actuator, fully mimicking the deformation of plant tendrils. Finally, a robot arm consisting of strip-shape and helical GO/BOPP actuators can grasp an object that is 2.9 times heavier than itself, demonstrating promising bioinspired applications.

Adaptive Fuzzy Decentralized Control for a Class of Large-Scale Nonlinear Systems With Actuator Faults and Unknown Dead Zones

Abstract: This paper studies the fault-tolerant control problem for a class of uncertain large-scale nonlinear systems with unknown dead zones and actuator failures, including outage, loss of effectiveness, and stuck. It is assumed that the lower and upper bounds of actuator efficiency factor, the unparametrizable time-varying stuck fault, the system coefficient, and the uncertain functions of our considered systems are unknown. By introducing a smooth function, fuzzy logic systems and a bound estimation approach, a decentralized backstepping design method of fault-tolerant tracking controller is developed for the systems under consideration. The proposed controller can compensate the effects of actuator faults and dead zones completely. It is proved that all the signals in the closed-loop systems are ultimately bounded, and the tracking control performance can be achieved by the proposed controller. In comparing with the existing results, the restrictions on the number of failures are removed and the stuck fault is allowed to be time-varying. Finally, simulation results show the efficiency of the proposed control scheme.

Analytical Thermal Model for Fast Stator Winding Temperature Prediction

Abstract: This paper introduces an innovative thermal modeling technique which accurately predicts the winding temperature of electrical machines, both at transient and steady state conditions, for applications where the stator Joule losses are the dominant heat source. The model is an advanced variation of the classical lumped-parameter thermal network approach, with the expected degree of accuracy but at a much lower computational cost. A seven-node thermal network is first implemented and an empirical procedure to fine-tuning the critical parameters is proposed. The derivation of the low computational cost model from the thermal network is thoroughly explained. A simplification of the seven-node thermal network with an equivalent three-node thermal network is then implemented, and the same procedure is applied to the new network for deriving an even faster low computational cost model. The proposed model is then validated against experimental results carried on a permanent magnet synchronous machine which is part of an electro-mechanical actuator designed for an aerospace application. A comparison between the performance of the classical lumped-parameter thermal network and the proposed model is carried out, both in terms of accuracy of the stator temperature prediction and of the computational time required.

Interaction Forces of Soft Fiber Reinforced Bending Actuators

Abstract: Soft-bending actuators are inherently compliant, compact, and lightweight. They are preferable candidates over rigid actuators for robotic applications ranging from physical human interaction to delicate object manipulation. However, characterizing and predicting their behaviors are challenging due to the material nonlinearities and the complex motions they can produce. This paper investigates a soft-bending actuator design that uses a single air chamber and fiber reinforcements. Additionally, the actuator design incorporates a sensing layer to enable real-time bending angle measurement for analysis and control. In order to study the bending and force exertion characteristics when interacting with the environment, a quasi-static analytical model is developed based on the bending moments generated from the applied internal pressure and stretches of the soft materials. Comparatively, a finite-element method model is created for the same actuator design. Both the analytical model and the finite-element model are used in the fiber reinforcement analysis and the validation experiments with fabricated actuators. The experimental results demonstrate that the analytical model captures the relationships of supplied air pressure, actuator bending angle, and interaction force at the actuator tip. Moreover, it is shown that an off-the-shelf bend angle sensor integrated to the actuator in this study could provide real-time force estimation, thus eliminating the need for a force sensor.

Passification of Uncertain Singular Semi-Markovian Jump Systems With Actuator Failures Via Sliding Mode Approach

Abstract: This paper investigates the problem of robust passivity-based sliding mode control (SMC) for uncertain singular systems with semi-Markov switching and actuator failures. The attention is focused on designing a common sliding surface to weaken the jumping effect and developing a sliding mode controller to accommodate to actuator faults for passification of the singular semi-Markovian jump system. Based on linear matrix inequality technique, sufficient conditions are derived to ensure the closed-loop system to be stochastically admissible and robustly passive. Then the finite-time reachability of the sliding surface is guaranteed by the proposed SMC law. Finally, a numerical example is provided to demonstrate the effectiveness of the obtained result.

Dynamic Control of the Bionic Handling Assistant

Abstract: In the previous decade, multiple approaches for kinematic controllers of continuum manipulators were successfully developed. However, for fast and exact motions of continuum robots that are hardly seen so far, dynamic controllers are necessary—especially for spatial manipulators with multiple sections. Therefore, a dynamic controller in actuator space is developed that both exploits input constraints and decouples the actuators in order to provide a good and intuitive dynamic behavior of the manipulator. Having a pneumatically actuated manipulator with multiple actuators, this can be achieved using a cascaded control approach with a centralized actuator length controller and an underlying decoupled pneumatic controller. For both the outer multiple-input multiple-output (MIMO) controller and the inner single-input single-output (SISO) controllers, model-based controllers are developed based on suitable models using feedback linearization and a combination of feedforward control and linear PD-controllers. The resulting actuator controller can be used for tracking optimized trajectories in actuator space and also for possible extensions towards direct tool center point feedback.

Adaptive Neural Network Based Variable Stiffness Control of Uncertain Robotic Systems Using Disturbance Observer

Abstract: The variable stiffness actuator (VSA) has been equipped on many new generations of robots because of its superior performance in terms of safety, robustness, and flexibility However, the control of robots with joints driven by VSAs is challenging due to the inherited highly nonlinear dynamics In this paper, a novel disturbance observer based adaptive neural network control is proposed for robotic systems with variable stiffness joints and subject to model uncertainties By utilizing a high-dimensional integral Lyapunov function, adaptive neural network control is designed to compensate for the model uncertainties, and a disturbance observer is integrated to compensate for the nonlinear VSA dynamics, as well as the neural network approximation errors and external disturbance The semiglobally uniformly ultimately boundness of the closed-loop control system has been theoretically established Simulation and extensive experimental studies have also been presented to verify the effectiveness of the proposed approach

Integrated Design and Simulation of Tunable, Multi-State Structures Fabricated Monolithically with Multi-Material 3D Printing.

Abstract: Multi-material 3D printing has created new opportunities for fabricating deployable structures. We design reversible, deployable structures that are fabricated flat, have defined load bearing capacity, and multiple, predictable activated geometries. These structures are designed with a hierarchical framework where the proposed bistable actuator serves as the base building block. The actuator is designed to maximise its stroke length, with the expansion ratio approaching one when serially connected. The activation force of the actuator is parameterised through its joint material and joint length. Simulation and experimental results show that the bistability triggering force can be tuned between 0.5 and 5.0 N. Incorporating this bistable actuator, the first group of hierarchical designs demonstrate the deployment of space frame structures with a tetrahedron module consisting of three active edges, each containing four serially connected actuators. The second group shows the design of flat structures that assume either positive or negative Gaussian curvature once activated. By flipping the initial configuration of the unit actuators, structures such as a dome and an enclosure are demonstrated. A modified Dynamic Relaxation method is used to simulate all possible geometries of the hierarchical structures. Measured geometries differ by less than 5% compared to simulation results.

Soft Pneumatic Actuator Fascicles for High Force and Reliability

Abstract: Soft pneumatic actuators (SPAs) are found in mobile robots, assistive wearable devices, and rehabilitative technologies. While soft actuators have been one of the most crucial elements of technology leading the development of the soft robotics field, they fall short of force output and bandwidth requirements for many tasks. In addition, other general problems remain open, including robustness, controllability, and repeatability. The SPA-pack architecture presented here aims to satisfy these standards of reliability crucial to the field of soft robotics, while also improving the basic performance capabilities of SPAs by borrowing advantages leveraged ubiquitously in biology; namely, the structured parallel arrangement of lower power actuators to form the basis of a larger and more powerful actuator module. An SPA-pack module consisting of a number of smaller SPAs will be studied using an analytical model and physical prototype. Experimental measurements show an SPA pack to generate over 112 N line...

Resilient Sampled-Data Control for Markovian Jump Systems With an Adaptive Fault-Tolerant Mechanism

Abstract: This brief investigates the problem of passivity-based resilient sampled-data control for Markovian jump systems subject to actuator faults via an adaptive fault-tolerant mechanism. By constructing a proper Lyapunov function, a set of sufficient conditions is obtained in terms of linear matrix inequalities (LMIs), which ensures that the closed-loop system is stochastically passive. In order to reflect the imprecision in controller, the additive gain variations is considered. Then, the resilient sampled-data control parameters can be determined by solving the obtained LMIs. Finally, an illustrative example is presented to show the validity and applicability of the proposed design technique.

Robust Adaptive Fault-Tolerant Control for a Class of Unknown Nonlinear Systems

Abstract: This paper studies the fault-tolerant tracking control problem for a class of strict-feedback nonlinear systems subjected to actuator faults and external disturbances. The prior knowledge for actuator fault, nonlinearity, and external disturbance is totally unknown, besides the control directions. Based on a backstepping approach, an adaptive fault-tolerant control scheme is developed, without utilizing neural networks. In the control design, a group of new feedback mechanisms are proposed to compensate for the unknown system dynamics and actuator faults. Furthermore, to relax a requirement of the initial system states, a modification technique is designed to adjust the reference signal and virtual control laws for a short time. It is shown that the global closed-loop stability is guaranteed and the tracking performance is achieved. The above result is illustrated via simulations on a one-link manipulator and a ship autopilot.