Pair Of Actuators Research Articles

Modular reconfigurable rotary style soft pneumatic actuators

Modular soft robots have the advantage in their ability to be reconfigured and change their morphology on-demand according to a specified task. The actuator design and particularly the inter-unit connectivity strength commonly govern the usability and functionality of these modular robots and their applications. In this paper, we present development of reconfigurable modular rotary soft actuators that allow the construction of highly versatile soft robotic actuators and systems. These pneumatically driven modular actuators are composed of an inner balloon and a flexible arched reinforcement structure to produce a rotary motion. They serve as building blocks which may be combined in various configurations to construct linear assemblies capable of extensile or bending motions. The connection scheme allows for the larger actuators to grow or shrink with the addition or removal of modules. Using finite element simulations and physical characterizations, we systematically explore the mechanical response of individual modular actuators and the role of various connection schemes on their motions upon pressurization. A key conceptual contribution of this work lies in the idea that for a modular soft robotic system, offsetting and tuning actuator alignment relative to an axis of symmetry can lead to substantial changes in mechanical performance. Utilizing these modules we demonstrate the reconfigurability of this modular system by both reconfiguring a large actuator into a pair of smaller actuators that can grasp delicate objects, and reconfiguring actuators to develop a linear crawling robot.

Tilt effect on squeeze-film damping in electrostatic micro-actuators

In this study, we theoretically explore the impact of tilt on the switching dynamics of a MEMS device operated by a pair of electrostatic actuators and subject to pronounced squeeze-film damping in the transition and free molecular flow regimes. Our investigation reveals that inducing tilt, achieved through the application of uneven voltages on the electrodes, introduces additional source terms in the modified Reynolds equation governing the pressure distribution in the squeeze-film gap. These added terms result in an accelerated decay of the squeeze film force, facilitating faster device switching between the initial and target configurations.To analyze the device dynamics, we develop a coupled numerical model and employ evolutionary multi-objective optimization to determine an optimal actuation scheme. This optimization is carried out for scenarios where initially different voltages are applied to the electrodes during a certain pre-defined time interval before transitioning to the steady voltage corresponding to the target gap size at equilibrium. Our findings highlight that the suggested actuation strategy leads to substantial improvements in the switching time of the device. Furthermore, we provide insights into the conditions favoring tilt actuation over parallel-motion actuation where the initially applied voltages are equal.

Active vibration control of rotating carbon nanotube reinforced composite cylindrical shells via piezoelectric patches

This paper addresses the active vibration control of rotating carbon nanotube reinforced composite (CNTRC) cylindrical shells via piezoelectric actuator and sensor pairs. Considering circumferential initial stresses and Coriolis forces induced by rotation, an electromechanical coupling model of a simply supported CNTRC cylindrical shell, covered with surface-bonded piezoelectric sensors/actuators is established using the Lagrange equations and the model validation is carried out through a comparative analysis with existing literature. To suppress vibrations of rotating CNTRC cylindrical shells over a range of speeds, an LQR (Linear Quadratic Regulator) closed-loop controller is designed and its effectiveness is analyzed and evaluated through dynamic response analysis. Furthermore, the optimization of piezoelectric patch layout is performed by analyzing the performance of the controller for rotating CNTRC shells with typical piezoelectric sensors/actuators distributions. This paper presents and validates a strategy for vibration control of rotating CNTRC cylindrical shells using piezoelectric patches. The findings derived can offer guidance for vibration suppression of rotating thin-walled structures in practical engineering applications.

Use of machine learning to optimize actuator configuration on an airfoil

Machine learning was used to optimize the geometric arrangement of a pair of unsteady actuators on flow separation over an efficient low Reynolds number airfoil in post-tall conditions. Large eddy simulation was used to validate the results. Two actuators: one with blowing and the other with suction openings were installed on the top surface of an airfoil at low Reynolds number of 60,000. An SD7003 airfoil at a post stall angle of attack of 13° was utilized. The boundary layer flow of the top surface was manipulated by the actuators to control flow separation. The influence of several actuator parameters: frequency, energy input, opening area, location and orientation angle were considered in an optimization of the dual actuator configuration. A genetic algorithm-based optimization was implemented to find the most effective configuration of this coupling. Since the optimization process is time-consuming, machine learning was used to train artificial neural networks to be coupled with genetic algorithm to reduce the computational cost. The artificial neural networks and their training was constantly upgraded during the optimization cycle. Results for the optimal case indicated an increase in lift coefficient and the objective function in comparison to uncontrolled case by factors of 1.88 and 3.33 respectively. We also found a reduction in drag coefficient. It was also found that using a pair of actuators was more efficient than using a single actuator.

Improved Damage Mapping with Hyperbola Approach for Guided Waves Based Structural Health Monitoring Using Fiber Bragg Grating sensors

Ultrasonic guided waves (GW) are commonly used in aerospace, civil, and mechanical industries for inspecting the health of a structure non-destructively. Traditionally the piezoelectric based actuators and sensors have been used for the actuation and sensing of GW. But the use of fiber Bragg grating sensors (FBG) is on the increase due to the unique opportunities offered by these sensors. There are several techniques that are used for damage mapping. The most commonly used in reflection based assessment domain are the ellipse based and hyperbola based approaches. Hyperbola approach is based on the time difference of arrival (TDOA). The time difference in the arrival time for two sensors with a common actuator is used for obtaining the hyperbola. The superposition of these hyperbolas for all possible actuator and sensor pairs may be used for damage localization. In this paper a new improved hyperbola approach for damage mapping is proposed by combining it with the ellipse based approach. In order to limit the number of computations a binary variable is introduced to check if the pixel fulfils the hyperbola and ellipse conditions. So only the regions of the structure which fulfil both conditions are mapped. This limits the number of hyperbolas which are identified as possible damage and improves the damage localization. The methodology is employed on a simple aluminium plate with acoustically FBG sensors. The performance of the new approach is compared with existing methods. The results indicate that indeed the improved hyperbola approach improves the localization. Also the computational load is reduced allowing more real time damage mapping.

Mapping Solar Flux Distribution in Parabolic Trough Collectors to Assess Optical Performance

This paper describes the development and testing of a novel device capable of mapping the flux distribution in parabolic trough solar collectors (PTCs). Accurate knowledge about the flux distribution is essential in any concentrated solar power (CSP) application, in particular PTCs equipped with concentrator photovoltaic (CPV) cells, since their efficiency highly depends on the collector’s light focusing properties. However, the assessment of CSP collectors’ optical performance requires sophisticated measurement technology, as the error budget of any sun-tracking optical device comprises a variety of factors ranging from physical properties such as mirror reflectivity to mechanical aspects like gravity sag and play in gears. The presented approach features a scanner consisting of a CPV cell mounted on a pair of linear actuators. A thorough state of the art analysis was conducted and numerous technological approaches were assessed. Design aspects such as component selection, cooling, and data acquisition are discussed and finally exemplary measurement results are presented.

도로와 험지 주행이 가능한 구동부 설계

The applications of robots are increasing progressively along with their capabilities. A driving unit is an essential element in any robot and the performance of the robot is directly related to its performance. This study aims to design a transmission that adopts multiple caterpillar and wheel driving arrangement with low contact pressure for versatile applications. The limitations of similar previous studies are highlighted and a practical model to address them is presented. FEM analysis and formulae are applied for system optimization. Driving and switching can be done using a pair of motors and actuators connected to the rear wheel. The wheel axis is mechanically connected to the motor and the tension is adjusted by pose change through the actuator of the outer pulley on the parallel axis. This helps to overcome the problem and allows continuous operation by eliminating the delay time when switching a driving pose. The stability of the system is verified through stress analysis of the deceleration system, where the largest torque is applied internally. Finally, the validity of the proposed design is proved through the fabrication of a mock-up model of actual size.

Dynamic Control of Contractile Force in Engineered Heart Tissue

Here, we demonstrate a technique to control afterload while monitoring contractile force exerted by EHTs. We developed an apparatus that can regulate EHT boundary conditions using real-time feedback control. The system is comprised of a pair of piezoelectric actuators that can strain the scaffold and a microscope that can measure EHT force and length. Closed loop control allows dynamic regulation of effective EHT boundary stiffness. When controlled to switch instantaneously from auxotonic to isometric boundary conditions, EHT twitch force immediately doubled. Changes in EHT twitch force as a function of effective boundary stiffness were characterized and compared to twitch force in auxotonic conditions. EHT contractility can be regulated dynamically through feedback control of effective boundary stiffness. The capacity to alter the mechanical boundary conditions of an engineered tissue dynamically offers a new way to probe tissue mechanics. This could be used to mimic afterload changes that occur naturally in disease, or to improve mechanical techniques for EHT maturation.

Analysis of the Antagonistic Arrangement of Pneumatic Muscles Inspired by a Biological Model of the Human Arm

Technical solutions based on biological models are the subject of research by a wide range of experts and mainly concern their mechanical use. When designing a suitable actuator, they use the physical methods of biological representatives, of which a large group consists of actuators generally referred to as artificial muscles, while another group uses compressed air as an energy carrier. In order to perform the measurements described in this article, a test mechanism based on the opposing arrangement of a pair of pneumatic muscles was constructed. Measurements on the test mechanism were made at set constant pressures in the range of 0.4 MPa to 0.6 MPa, while at each pressure, measurements were made for the counterload range from 0 N to 107.87 N. The measured values were recorded using a microcontroller and subsequently processed into graphic outputs. As part of the measurements, a comparative measurement of the same opposite arrangement of a pair of linear double-acting pneumatic actuators with a single-sided piston rod was also performed. The experiment and measurements were carried out in order to determine the suitability of using pneumatic artificial muscles in the selected arrangement for the implementation of a mechanism imitating the human arm. The target parameters of the experiment were the reaction speed of the course of force when filling the muscle under load and the reaction of the mechanism to a change in the set pressure in the pneumatic system. The summary of the comparison of the measured results is the content of the discussion in this article.

Optimal Voltage Distribution on PZT Actuator Pairs for Vibration Damping in Beams with Different Boundary Conditions

In recent decades, many studies have been conducted on the use of smart materials in order to dampen and control vibrations. Lead zirconate titanate piezoceramics (PZT) are very attractive for such applications due to their ability of delivering high energy strain in the structure. A pair of piezoelectric actuators can actively dampen the resonances of the structure, but the damping effectiveness strongly relies on its location. Damping effectiveness can be substantially increased if the structure is fully covered with PZT actuator pairs and the voltage distribution on each pair is optimized. In this way, each actuator pair contributes to the vibration attenuation and only the driving voltage’s sign, distributed on each actuator pair, needs to be identified for each resonance. This approach is here applied to the case of Euler–Bernoulli beams with constant cross-section and the optimal voltage distribution is investigated for several boundary conditions. The theoretical model results were corroborated with finite element simulations, which were carried out considering beams covered by ten PZT actuator pairs. The numerical results agree remarkably well with the theoretical predictions for each examined case (i.e., free-free, pinned-pinned, and fixed-fixed).

Optimised Voltage Distribution on Piezoelectric Actuators for Modal Excitations Damping in Tapered Beams

Vibration mitigation is a prominent matter in several engineering fields. Several adverse phenomena are related to vibrations, such as fatigue, noise, etc. The availability of smart materials increases the solutions for both vibration damping and energy harvesting applications. Piezoelectric materials seem to be the most promising for these applications. However, their positioning significantly affects their efficiency. Several studies were performed on the positioning of piezoelectric actuators to dampen a target resonance in cantilever beams with constant cross-sections. Here, an analytical model for the optimal voltage distribution on an array of piezoceramic (PZT) actuator pairs is proposed in the case of tapered beams. The effect of tapering on the optimal voltage distribution was investigated for several eigenmode excitations and tapering ratios. The model outcomes were corroborated via FEM simulations and a fair agreement was found for each considered case.

A novel approach to reduce fan rotor blades stress in case of resonance due to inlet flow distortion by means of piezoelectric actuators

Resonant vibration condition involves a drop in the life-cycle of the components and is one of the main causes of high cycle fatigue failure (HCF) in turbomachinery blades. As a consequence vibration damping techniques play a key role for turbomachinery designers. Even though resonant vibration conditions can be identified by means of the Singh’s Advanced Frequency Evaluation (SAFE) diagram at the design level, not all resonant conditions can be avoided. Among these methods, systems of piezoelectric (PZT) actuators can be tuned to actively damp the vibrations caused by resonant excitations. In this work, an analytical model was developed to identify the optimal voltage distribution that maximises the reduction in blade stress. The model considers the flexural–torsional–extensional deformations coupling due to the pre-twisting, non-constant cross-section and inertial loads of the rotating blades. A typical case was examined to demonstrate the effectiveness of the proposed method, which involved vibration induced by inlet flow distortion in an axial fan stage coupled with a three-strut front frame. A decoupled approach based on Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulations was used to evaluate the aerodynamic loads and to numerically validate the optimal voltage distribution on the PZT actuator pairs. The results show that the proposed method alleviates the effects of the resonant response to an inlet flow distortion on a fan integrally bladed disc (blisk) and the optimal voltage distribution predicted by the model is the one that achieves the highest blade stress mitigation.

Design, Construction and Control of a Manipulator Driven by Pneumatic Artificial Muscles

This paper describes the design, construction and experimental testing of a single-joint manipulator arm actuated by pneumatic artificial muscles (PAMs) for the tasks of transporting and sorting work pieces. An antagonistic muscle pair is used in a rotational sense to produce a required torque on a pulley. The concept, operating principle and elementary properties of pneumatic muscle actuators are explained. Different conceptions of the system realizations are analyzed using the morphological-matrix conceptual design framework and top-rated solution was practically realized. A simplified, control-oriented mathematical model of the manipulator arm driven by PAMs and controlled with a proportional control valve is derived. The model is then used for a controller design process. Fluidic muscles have great potential for industrial applications and assembly automation to actuate new types of robots and manipulators. Their characteristics, such as compactness, high strength, high power-to-weight ratio, inherent safety and simplicity, are worthy features for advanced manipulation systems. The experiments were carried out on a practically realized manipulator actuated by a pair of muscle actuators set into an antagonistic configuration. The setup also includes an original solution for the subsystem to add work pieces in the working space of the manipulator.

Sensor/actuator colocation feasibility for distributed damping control using active power modulation

Multi-use distributed active power modulation devices, including energy storage, have the potential to transform the dynamic performance and resilience of modern power systems. Rapid response characteristics relative to traditional power delivery equipment paired with traditional uses (arbitrage, reserve, etc.) make storage an obvious choice for multi-use operation, adding value for asset owners while augmenting stability for reliable operation. Limitations to distributed power control are investigated to provide guidance for those interested in separated sensors and actuators. Substantive distance between the sensor/actuator pair results in non-minimum phase (NMP) which complicates the control design, reducing feedback system effectiveness. It is shown that wide-area control (WAC) is limited by the presence of NMP induced by closed right-half plane (CRHP) zeros - a consequence of sensors placed at locations separated from modulation bus(es). Such geographic separation may be driven by economics, asset owner jurisdiction, technology and/or policy, and is therefore unavoidable. This work suggests that system designers must perform a collocation study before control design and testing. A well-known WAC architecture using synchrophasors as sensors and energy storage devices for active power injection is presented as a detailed case study. • Collocated sensor–actuators pose difficulties which may force modest separation. • Closed right-half plane (CRHP) zeros may result due to such separation. • Noncollocated sensor–actuator pairs may reduce performance and threaten stability. • Bandwidth and performance limitations regarding collocation are determined.

Flow induced by a pair of plasma actuators on a circular cylinder in still air under duty-cycle actuation

A pair of surface mounted dielectric-barrier-discharge (DBD) plasma actuators is placed diametrically on a circular cylinder model. The flow field generated by the actuators in steady and duty-cycle actuation modes is measured by particle image velocimetry. Salient features of the flow and vortices are discovered for the duty-cycle actuation modes with frequency ranging from 5 to 1000 Hz and duty-cycle ratio from 0.01 to 0.99. The results are compared with those for continuous steady actuation. For a given duty-cycle ratio, a discrete vortex is generated by each of the DBD actuator in an actuation cycle for low frequencies. Such vortices are created alternately from each side of the cylinder. They interact and move laterally in response to the on-off signals of the actuators. As the frequency increases, the distance between the vortices generated from successive duty-cycles decreases and the lateral motion of the vortices becomes smaller so that the vortices are packed together as a vortex train along a narrow path on each side of the cylinder. As the frequency is further increased, the vortices in the vortex trains lose their individual characteristics and the vortex trains become steady jets. Regardless of the actuation frequency, the direction of the average total momentum of the air is found to be continuously dependent on the duty-cycle ratio. The magnitude of the average total momentum depends on the frequency. An optimum frequency exists for maximum average momentum, which may exceed that in the continuous steady actuation mode.

A Simple Configuration of an Actively Synthesized Gyroscopic-Nonreciprocal Acoustic Metamaterial

Abstract A simple configuration of an active nonreciprocal gyroscopic metamaterial (NGMM) is presented. In the proposed NGMM system, a one-dimensional acoustic cavity is provided with piezoelectric boundaries acting as a collocated pair of sensors and actuators. The active piezo-boundaries are controlled by a simple control algorithm that synthesizes a virtual gyroscopic control action to impart desirable nonreciprocal characteristics which are tunable both in magnitude and phase. The dynamic model of a prototype of the NGMM cell is experimentally identified in an attempt to provide means for predicting the characteristics of the virtual gyroscopic controller for various control gains during forward and backward propagations. The theoretical predictions are validated experimentally without the need for any physical dynamic controller which was provided, in earlier studies, by using a dummy NGMM cell. Such a simplified arrangement enables the fast execution of the controller with enhanced frequency bandwidth capabilities. The experimental and theoretical characteristics of the NGMM cell are monitored and predicted for different control gains in order to evaluate its behavior for both forward and backward propagations. The obtained experimental results are compared with the theoretical predictions and found to be in close agreement. The presented concepts provide the foundation necessary for the implementation of NGMM that can be employed in more complex 2D and 3D critical structures in order to achieve nonreciprocal behavior in a simple and programmable manner.

Drag reduction of a slanted-base cylinder using sweeping jets

In this work, a pair of sweeping jet actuators is installed underneath the endplate of a slanted-base cylinder at ReD = 200 000. The sweeping jets form a 30° inclined angle with the endplate and are placed at different streamwise locations, and their strength is varied with a momentum coefficient, Cμ, ranging from 3.8 × 10−3 to 6.0 × 10−2. For all the cases examined in this paper, it is found that while a higher Cμ produces a higher drag reduction, the flow control energy efficiency decreases rapidly as Cμ increases. A net energy saving is achieved when Cμ is less than 0.01, and the highest energy efficiency obtained in the present study is 2.8% when the actuator pair is placed at the most upstream location tested. The drag reduction is attributed to the reaction force and an increase in the surface pressure force acting on the endplate produced by the jet pair. The contribution from the former constitutes an increasing proportion of the total drag reduction as Cμ increases leading to lower energy efficiency in flow control. Depending on the relative positions between the trajectory of the sweeping jet and afterbody vortex, sweeping jets are not only capable of altering the surface pressure distributions via directly imposing a footprint of high pressure on the surface, but also affecting the roll-up of the afterbody vortex and/or reducing its strength via injecting turbulence into the afterbody vortex.

Muscle-Inspired Linear Actuators by Electrochemical Oxidation of Liquid Metal Bridges.

Progress in artificial muscles relies on new architectures that combine soft matter with transduction mechanisms for converting controlled stimuli into mechanical work. Liquid metal, in particular eutectic gallium–indium (EGaIn), is promising for creating an artificial muscle since it is intrinsically deformable and capable of generating significant force and shape change through low voltage stimulation. In this work, a muscle‐inspired structure for designing liquid metal actuators is presented, where EGaIn droplets are configured with copper pads to linearly contract. By theory and experiments, it is demonstrated that this design enables higher work densities and stress, making it a favorable actuator at smaller length scales. Furthermore, higher frequency (up to 5 Hz) operation is achieved by prestretching an antagonistic pair of actuators, where energy bistability enables fast‐switching actuation. Overall, this muscle‐inspired architecture shows a unique combination of low voltage operation, higher energy density at smaller scales, structural scalability, and higher frequency actuation.

Overconstrained coaxial design of robotic legs with omni-directional locomotion

While being extensively researched in literature, overconstrained linkages’ engineering potential is yet to be explored. This study investigates the design of overconstrained linkages as robotic legs with coaxial actuation starting with the simplest case, Bennett linkage, to establish the theoretical foundations and engineering advantages of a class of overconstrained robots. We proposed a parametric design of the spatial links and joints in alternative forms so that one can fabricate these overconstrained limbs via 3D printing and then attach the linkage coaxially to a pair of servo actuators as a reconfigurable leg module. We adopted multi-objective optimization to refine the design parameters by analyzing its manipulability metric and force transmission, enabling omni-directional ground locomotion projected from a three-dimensional surface workspace. The proposed prototype quadruped was capable of omni-directional locomotion and had a minimal turning radius (0.2 Body Length) using the fewest actuators. We further explored the kinematics and design potentials to generalize the proposed method for all overconstrained 5R and 6R linkages, paving the path for a future direction in overconstrained robotics.

Assisting Forearm Function in Children With Movement Disorders via A Soft Wearable Robot With Equilibrium-Point Control.

Wearable robots are envisioned to amplify the independence of people with movement impairments by providing daily physical assistance. For portable, comfortable, and safe devices, soft pneumatic-based robots are emerging as a potential solution. However, due to the inherent complexities, including compliance and nonlinear mechanical behavior, feedback control for facilitating human–robot interaction remains a challenge. Herein, we present the design, fabrication, and control architecture of a soft wearable robot that assists in supination and pronation of the forearm. The soft wearable robot integrates an antagonistic pair of pneumatic-based helical actuators to provide active pronation and supination torques. Our main contribution is a bio-inspired equilibrium-point control scheme for integrating proprioceptive feedback and exteroceptive input (e.g., the user’s muscle activation signals) directly with the on/off valve behavior of the soft pneumatic actuators. The proposed human–robot controller is directly inspired by the equilibrium-point hypothesis of motor control, which suggests that voluntary movements arise through shifts in the equilibrium state of the antagonistic muscle pair spanning a joint. We hypothesized that the proposed method would reduce the required effort during dynamic manipulation without affecting the error. In order to evaluate our proposed method, we recruited seven pediatric participants with movement disorders to perform two dynamic interaction tasks with a haptic manipulandum. Each task required the participant to track a sinusoidal trajectory while the haptic manipulandum behaved as a Spring-Dominate system or Inertia-Dominate system. Our results reveal that the soft wearable robot, when active, reduced user effort on average by 14%. This work demonstrates the practical implementation of an equilibrium-point volitional controller for wearable robots and provides a foundational path toward versatile, low-cost, and soft wearable robots.