Strain Feedback Research Articles

Dynamic error prediction and link strain feedback control for a novel heavy load multi-DOF envelope forming machine

Thin walled and high rib components (TWHRC) are widely used for rocket cabins, aircraft wings, panels and frames in aerospace equipment as critical load bearing structures. This paper is aimed to develop a novel multi-DOF envelope forming machine (MEFM) with parallel kinematic mechanism (PKM) to realize efficient manufacturing of TWHRC with high performance. Since the heavy load MEFM with PKM has many total differences with the light load PKM, such as dynamic error and precision control, this paper conducts research on dynamic error prediction modelling and precision control method for this novel heavy load MEFM.Firstly, the configuration of MEFM is developed and the kinematic model of MEFM is established. Then, a RFC (rigid-flexible coupling) and RFE (rigid finite element) coupling dynamic model of MEFM is established considering time-variation of kinematic configuration caused by large deformation of all the kinematic elements. Based on the dynamic model, the dynamic deformation and error of MEFM are predicted and their generation mechanisms are revealed. It is found that the linear compression deformation of two-force links is the largest among all the kinematic elements, and it is the most sensitive to the heavy forming load and the most insensitive to the installation error of strain gauges, thus suiting for the feedback of large deformation of MEFM. Based on the above findings, a novel link strain feedback and dynamic error compensation control method is proposed. Finally, experiments under different control methods are conducted, showing that the motion precision of envelope tool and forming precision of formed components under the proposed control method are remarkably improved compared with that under the traditional control method (The geometric deviation of formed components under the proposed control method is remarkably reduced to −18 ∼ 32um from −64 ∼ 54um under the traditional control method). The experimental results verify that the proposed dynamic error prediction model and link strain feedback control method for heavy load MEFM are reasonable.

A Mode Sensitivity Enhancement Method for Beam Bridge Using High-Density Strain Feedback

Abstract Closed-loop damage diagnosis method has attracted some attention in recent years; however, for lack of sufficient measuring points, it is difficult to achieve robust control of large structures cause the output dimension is not enough to meet the demand of system controllability and observability. On this basis, a mode sensitivity enhancement method for beam bridge using high-density strain feedback is proposed, in which high density dynamic strain measurements of the girder structure can be collected by distributed fiber sensor. Utilizing strain–displacement transformation relationship of the girder structure, the dynamic displacements can be obtained and used as output with high dimension to achieve the feedback control for eigenvalue sensitivity enhancement. To verify the proposed method, a series of numerical case studies of a beam bridge structure are performed, and it is demonstrated that the eigenvalue sensitivity can be enhanced effectively.

Dual hydrodynamic trap based on coupled stagnation point flows

Recent advancements in science and engineering have allowed for trapping and manipulation of individual particles and macromolecules within an aqueous medium using a flow-based confinement method. In this work, we demonstrate the feasibility of trapping and manipulating two particles using coupled planar extensional flows. Using Brownian dynamics simulations and a proportional feedback control algorithm, we show that two micro/nanoscale particles can be simultaneously confined and manipulated at the stagnation points of a pair of interconnected planar extensional flows. We specifically studied the effect of strain rate, particle size, and feedback control parameters on particle confinement. We also demonstrate precise control of the interparticle distance by manipulating the strain rates at both junctions and particle position at one of the junctions. We further discuss the advantages and limitations of the dual hydrodynamic trap in comparison to existing colloidal particle confinement methods and outline some potential applications in polymer science and biology. Our results demonstrate the versatility of flow-based confinement and further our understanding of feedback-controlled particle manipulation.

Adaptive Notch Filter in a Two-Link Flexible Manipulator for the Compensation of Vibration and Gravity-Induced Distortion

This paper presents a 2-link, 2-DOF flexible manipulator control using an inverse feedforward controller and an adaptive notch filter with a direct strain feedback controller. In the flexible manipulator, transient and residue vibrations inhibit the full potential of the manipulator. Vibrations caused by abrupt changes in the direction of the links are referred to as transient vibrations, whereas residual vibrations occur when the arm takes too long to settle after engaging in the intended task. The feedforward adaptive notch filter will reduce transient vibration caused by the manipulator arm beginning and halting suddenly, while the strain feedback will assure the quick decay of leftover vibrations. Maple, Maplesim, and MATLAB tools were used to model the manipulator and create the inverse controller and adaptive notch filter. The experiments took place in the dSPACE control desk environment. The experimental results of the spectral power of strain resulting from the two strategies are compared. From the results, the adaptive notch filter control had over an 80% improvement in the reduction in resonant frequencies that contribute to vibration. The results confirmed the feasibility of the approach, characterized by very minimal transient vibrations and a quick settling of the end effector.

Hybrid vibration control of an industrial CFRP composite robot-manipulator system based on reduced order model

This paper introduces a novel hybrid vibration control of an industrial flexible link manipulator (FLM) with carbon-fiber reinforced polymer (CFRP) composite material. The hybrid controller consists of a closed-loop direct strain feedback controller (DSFC) and a new open-loop input shaper (OLIS), and its performance is examined and compared by numerical simulation and experiment. Vibration attenuation is also verified by a spare sensor, an accelerometer. Thanks to the design of an analog isolator circuit, data acquisition of the real-time experiments are carried out noise-free from the servo driver. Reduced-order-model (ROM) is generated for the composite link with three different loading conditions and model for servo system is derived via system identification. Impulse force test hammer (IFTH) equipment is used to excite the system with force input and the results of the experiments/simulations confirm that the controller is robust against the impulse disturbances. As a result, a decrease of 88 ± 6.9 percent in vibration amplitudes and a decrease of 90 ± 7 percent in vibration duration confirms that the proposed controller is effective for vibration control of the flexible arm even under disturbance. Controller performance also enabled the FLM to work with payloads 16 times of its own weight.

Field Experimental Research on Application of Strain Special Optical Cable and Parallel Optical Cable

With the rapid development of China’s oil and gas pipeline mileage, pipeline construction will be unable to avoid crossing high-risk areas such as disaster risk areas, densely populated areas, environmentally sensitive areas. The traditional extensive pipeline patrol method has been unable to meet the requirements of fine management, which puts forward a new test for the upgrade of safety monitoring technology. In this paper, the distributed optical fiber sensing technology which has been studied intensively in recent years is introduced. Through in-depth analysis of pipeline requirements and characteristics of accompanying optical cable, a single-end BOTDA solution suitable for long-distance oil and gas pipelines is proposed. A 400-meter pipeline trench was excavated along the route of a domestic product oil pipeline. Strain special cables and GYTA53 cables were laid concurrently. Twelve strain monitoring sections were set up using vibrating wire strain sensors. The strain of two kinds of optical cables was monitored under various working conditions, such as partial backfilling, full backfilling, manual compaction and heavy mechanical compaction, as well as the monitoring values of two kinds of optical cable for soil temperature. The test results show that: 1) the strain-sensitive fiber optic cable is sensitive to strain feedback, and can produce rapid feedback to 2m3 pile soil, while the stress feedback of pipeline-accompanying fiber optic cable to soil is very small. 2) The temperature around the pipeline can be accurately reflected by the fiber optic cable, and it can be used for temperature compensation in strain monitoring.

A Systematic Study of Wearable Multi-Modal Capacitive Textile Patches

We present a study on wearable capacitive patches with engineered dielectrics to be used as a strain sensor and a piezoelectric sensor with multi-modal sensing capabilities. The patches consist of a parallel plate capacitive structure with highly (100%) stretchable textile electrodes and silicone or PDMS elastomers. The gauge factor of the capacitive strain sensor is enhanced two-fold with the inclusion of high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> Barium Titanate (BTO) nanoparticles dispersed in the silicone dielectric layer without sacrificing their excellent linearity or superb durability easily exceeding 2000 cycles. In addition to enhanced dielectric response, inclusion of BTO as well as other additives, namely PZT and PVDF-TrFE, in PDMS also induces piezoelectricity in the sensors at different weight ratios systematically studied by bending and vibrational tests. Corona poling of the piezo dielectrics improves their voltage output by at least two folds. Besides the piezoelectricity, tests on unpoled samples also uncovered evidence for triboelectricity in the nanocomposites. The proposed textile patches can simultaneously detect multiple stimuli such as strain, pressure, temperature, bending, vibration, and acoustic feedback. Deployed in appropriate locations and geometries, the patches can capture critical information on the type, strength, and duration between episodic movements and environmental factors, as demonstrated via a shoe-insert, elbow tracker, respiratory and heart-rate monitors. Accordingly, capacitive textile patches offer unique capabilities for multi-modal sensing in biomedical and robotic applications as well as overall system integration that are advantageous for sensor fusion and machine learning.

Towards FBG-Based Shape Sensing for Micro-scale and Meso-Scale Continuum Robots with Large Deflection.

Endovascular and endoscopic surgical procedures require micro-scale and meso-scale continuum robotic tools to navigate complex anatomical structures. In numerous studies, fiber Bragg grating (FBG) based shape sensing has been used for measuring the deflection of continuum robots on larger scales, but has proved to be a challenge for micro-scale and meso-scale robots with large deflections. In this paper, we have developed a sensor by mounting an FBG fiber within a micromachined nitinol tube whose neutral axis is shifted to one side due to the machining. This shifting of the neutral axis allows the FBG core to experience compressive strain when the tube bends. The fabrication method of the sensor has been explicitly detailed and the sensor has been tested with two tendon-driven micro-scale and meso-scale continuum robots with outer diameters of 0.41 mm and 1.93 mm respectively. The compact sensor allows repeatable and reliable estimates of the shape of both scales of robots with minimal hysteresis. We propose an analytical model to derive the curvature of the robot joints from FBG fiber strain and a static model that relates joint curvature to the tendon force. Finally, as proof-of-concept, we demonstrate the feasibility of our sensor assembly by combining tendon force feedback and the FBG strain feedback to generate reliable estimates of joint angles for the meso-scale robot.

Coupling and Hysteresis Characteristics during Multiple Actuation in Shape-deformable Space Reflector

For the observation of microwave in space over 100 GHz by radio astronomical satellites, this study develops shape-deformable antenna reflectors. When a certain portion of the antenna reflector prototype is deformed, the entire reflector is affected by the partial deformation. The purpose of this study is firstly clarifying the effect of coupling in reflector displacement. Secondly, this study tries the performance evaluation of hysteresis elimination by a piezoelectric strain feedback system under the effect of the displacement coupling. To achieve these objectives, this study quantifies the displacement coupling, the relations between piezoelectric strain and reflector displacement, and the residual reflector displacement error under the feedback control when multiple actuators are driven simultaneously. As a result, this study clarifies that there is a non-negligible coupling effect and the stress history dependence in the reflector surface deformation, causing the limit in the accuracy of the feedback system. Based on these experimental observations, this paper presents three design improvement plans that will possibly solve these problems.

Disturbance Rejection for an Unmanned Rotary Aircraft System Using Strain Sensing

This paper presents a bioinspired approach for fast reaction to external disturbances as applied to small unmanned aerial systems platforms. A disturbance rejection method for a quadrotor vehicle is proposed by means of force-adaptive feedback using strain measurements. These strain measurements provide a reactive mechanism to counteract atmospheric disturbances acting on the vehicle. The reactive response from force-sensitive strain measurements is initiated before the disturbance propagates to lower-order pose and velocity states, while simultaneously reducing the latency in the feedback. These measurements are provided by means of strain gauges attached to the quadrotor arms. The location and feedback gain of the strain gauges were determined based on expected forces and moments as well as regions of high strain. The airframe section that hosted the strain sensors was manufactured and designed for a balance between structural stability and force sensitivity. The response of the quadrotor system was characterized using an induced disturbance to simulate a vertical gust. This heave perturbation was mitigated using a strain feedback controller. Improvements in gust response were demonstrated by measuring the effects of the disturbance on vehicle states.

Strain-programmable fiber-based artificial muscle.

Artificial muscles may accelerate the development of robotics, haptics, and prosthetics. Although advances in polymer-based actuators have delivered unprecedented strengths, producing these devices at scale with tunable dimensions remains a challenge. We applied a high-throughput iterative fiber-drawing technique to create strain-programmable artificial muscles with dimensions spanning three orders of magnitude. These fiber-based actuators are thermally and optically controllable, can lift more than 650 times their own weight, and withstand strains of >1000%. Integration of conductive nanowire meshes within these fiber-based muscles offers piezoresistive strain feedback and demonstrates long-term resilience across >105 deformation cycles. The scalable dimensions of these fiber-based actuators and their strength and responsiveness may extend their impact from engineering fields to biomedical applications.

A Guide to Monitoring Respiration

Professionals can monitor respiration using six biofeedback modalities: strain gauges, surface electromyography, capnometers, oximeters, inspirometers, and feedback thermometers. This article emphasizes the importance of the breathing rhythm, describes how to effectively use each modality, and explains how to minimize contamination by artifacts that masquerade as respiratory activity.

Strain- or Stress-Sensing in Mechanochemical Patterning by the Phytohormone Auxin.

Both chemical and mechanical fields are known to play a major role in morphogenesis. In plants, the phytohormone auxin and its directional transport are essential for the formation of robust patterns of organs, such as flowers or leaves, known as phyllotactic patterns. The transport of auxin was recently shown to be affected by mechanical signals, and conversely, auxin accumulation in incipient organs affects the mechanical properties of the cells. The precise interaction between mechanical fields and auxin transport, however, is poorly understood. In particular, it is unknown whether transport is sensitive to the strain or to the stress exerted on a given cell. Here, we investigate the nature of this coupling with the help of theoretical models. Namely, we introduce the effects of either mechanical stress or mechanical strain in a model of auxin transport and compare the patterns predicted with available experimental results, in which the tissue is perturbed by ablations, chemical treatments, or genetic manipulations. We also study the robustness of the patterning mechanism to noise and investigate the effect of a shock that changes abruptly its parameters. Although the model predictions with the two different feedbacks are often indistinguishable, the strain feedback seems to better agree with some of the experiments. The computational modeling approach used here, which enables us to distinguish between several possible mechanical feedbacks, offers promising perspectives to elucidate the role of mechanics in tissue development, and may help providing insight into the underlying molecular mechanisms.

Two-degree-of-freedom control of a multilink flexible manipulator using filtered inverse feedforward controller and strain feedback controller

This research paper presents a hybrid solution to both residue vibration and transient vibration as addressed using filtered inverse feedforward controller and strain feedback controller on a 3D 2 links flexible manipulator. The feedforward filtered inverse will minimize on the transient vibration due to sudden starting followed sudden stopping of the manipulator arm while the strain feedback will ensure rapid decay of the residue vibrations. Transient and residue vibrations stand in the way to reaping all the numerous advantages of the flexible manipulator. Transient vibration refers to vibrations resulting from sudden changes in the direction of the links while residue vibrations means that the arm takes too long to settle to do some useful work. Modelling of the manipulator and development of the inverse controller was carried out in Maple, MapleSim and MATLAB softwares. Experiments carried out in dSPACE control desk environment considering the manipulator without load and a case where a load of 100g was attached at the distal end of link 2.

Enhanced vibration control of a multilink flexible manipulator using filtered inverse controller

Flexible manipulators have numerous advantages such as lightweight, high operation speed, and low power consumption. However, they suffer from link vibrations, especially when operated at high speeds followed by sudden stops. This limitation has been addressed using techniques such as adaptive filters, adaptive strain feedback gain, state feedback control, etc. This article presents a filtered inverse controller for the mitigation of link vibrations in a multi-link flexible manipulator. To this end, the plant model, developed and linearized in Maple/Maplesim was inverted in MATLAB. The internal dynamics of the inverse model were stabilized using the state feedback technique. For safe and high-speed operations, the inverse model was augmented with a low pass filter to form the filtered inverse which was used as feedforward controller. Practical experiments were carried out in the dSPACE environment. Results show that filtered inverse controller yield not only faster response but relatively minimal link vibration when compared with the manipulator without vibration controller.

Temperature and strain feedback control for shape memory alloy actuated composite plate

There are several input variables that can be used to control the deflection of a shape memory alloy (SMA) composite system such as the resistance or temperature of the SMA actuator and position or strain of the composite plate. It is common to control the actuator directly, however SMA is nonlinear and it exhibits hysteresis which may result in inaccurate control of the plate’s deflection. Thus controlling the plate’s deflection may be more effective by using input measurement from the composite plate. The aim of this study is to propose the optimal feedback variable deflection control of a fiberglass composite plate system using SMA actuators. Two types of variables were investigated which were temperature of the SMA actuator and strain of the composite plate. The feedback control system for SMA actuated composite plate was implemented with different types of sensors; thermocouple and strain gauge. When current is supplied to the SMA actuator, it will contract and produce a force that will deflect the composite plate. During this process, the SMA actuator’s temperature changes with the current supplied and the strain of the composite plate changes during deflection due to torsion and bending. Thus, it is proposed to use these variables as the input to the feedback of the smart composite plate system to control the movement of the plate. Using the adopted control technique of the experimental test bench presented here, the strain feedback system was more effective and energy efficient compared to the temperature feedback for the control of morphing composite plate.

Unimorph deformable mirror with an integrated strain feedback layer.

The correction accuracy of a pint-sized unimorph deformable mirror (DM) is significantly influenced by the nonlinear hysteresis error of piezoelectric ceramics, especially in an open-loop state. Moreover, the control bandwidth is also reduced by the nonlinearity. In this paper, we fabricated a three-unit pint-sized unimorph DM with strain gauges integrated on the actuators as a feedback layer for the first time. An experimental platform was built and utilized to test each electrode's strain signal. Testing results show that, under quasi-static condition, the hysteresis curve of the mirror's central displacement is corrected and the hysteresis rate could be reduced from 11% to less than 2% by adopting the strain feedback signal. More specifically, the DM's initial surface, Zernike defocus, together with spherical aberration can also be corrected by this method, and the correction accuracy is improved more than 20% compared to the open-loop state. By introducing a closed-loop control the gaps of the DMs under open loop are supplied. This demonstrates that adding a strain feedback layer is promising to enhance the performance of a unimorph DM.

Strain feedback gain tuning using neural network for the vibration control in a multilink flexible manipulator

Strain feedback gain tuning using neural network for the vibration control in a multilink flexible manipulator

A Strain Feedback Compensation Method during Cell Tensile Experiments

Cell tensile technique is an important and widely used tool in cell mechanical research. However, the strain control condition in traditional tensile experiments is not satisfied and would result in big errors. These strain errors will seriously impact the experimental accuracy and decrease the reliability and comparability of experimental results. In order to achieve the accurate strain control of the membrane during stretching, a strain feedback compensation method based on the digital image correlation is proposed in this paper. To evaluate the effect of the proposed compensation method, a series of stretching experiments in different strains ranging from 5% to 20% were performed. The results showed that our proposed method significantly decreased the errors of strain control. These results indicate that the strain feedback compensation method is very effective in controlling strain and can greatly improve the experimental accuracy.

On the Equivalence of Direct Strain Feedback and Lumped Parameter Wave Echo Control for Oscillation Damping of Elastic-Link Arms

The work discusses two control concepts. Both approach oscillation damping for elastic link robotic arms from fundamentally different theoretical directions. Despite their principal difference, the work consolidates both control schemes by mathematically deriving the equivalence of the resulting control laws. This letter demonstrates the practical application of the oscillation damping on a multi-elastic-link experimental setup. With a special emphasis on the influence of static deflections due to gravity, the letter finally compares the damping action as a modulation to the joint position, joint velocity, and joint motor current reference. The comparison leads to recommendations for strain-based oscillation damping of elastic-link arms under gravitational influence.