Pair Of Actuators Research Articles

Sensor enabled closed-loop bending control of soft beams

Control of soft-bodied systems is challenging, as the absence of rigidity typically implies distributed deformations and infinite degrees-of-freedom. In this paper, we demonstrate closed-loop control of three elastomer beams that vary in bending stiffness. The most stiff beam is comprised of a single prismatic structure made from a single elastomer. In the next beam, increased flexibility is introduced via an indentation in the elastomer, forming a joint. The most flexible beam uses a softer elastomer in the joint section, along with an indentation. An antagonistic pair of actuators bend the joint while a pair of liquid–metal-embedded strain sensors provide angle feedback to a control loop. We were able to achieve control of the system with a proportional–integral–derivative control algorithm. The procedure we demonstrate in this work is not dependent on actuator and sensor choice and could be applied to to other hardware systems, as well as more complex multi-joint robotic structures in the future.

Active vibration control of plates using positive postion feedback control with PZT actuators

In this study, the active vibration control of clamped plates using a positive position feedback (PPF) controller with a sensor/moment pair actuator (non-collocation configuration) is considered. To identify the characteristics of the PPF control system, a numerical parametric studies is conducted. The design parameters (gain and damping ratio) of the PPF controller are shown to have a significant effect on the stability and performance of the control system. Using these results, a multi-mode (first and second mode) single-input single-output (SISO) PPF controller is implemented. Two PPF controllers are connected in parallel with the SISO configuration. The final designed multi-mode PPF controller showed good conditional stability and high performance. The vibration levels at the tuned modes are reduced by about 5 dB. Finally, the performance of the PPF controller is experimentally verified. The disturbance levels at the target modes can be reduced by about 5 dB, nearly the same as the theoretical result.

Damage detection sensitivity characterization of acousto-ultrasound-based structural health monitoring techniques

Reliability quantification is a critical and necessary process for the evaluation and assessment of any inspection technology that may be classified either as a nondestructive evaluation or structural health monitoring technique. Based on the sensitivity characterization of nondestructive evaluation techniques, appropriate processes have been developed and established for the reliability quantification of their performance with respect to damage/flaw detection in materials or structures. However, in the case of structural health monitoring methods, no such well-defined and general applicable approaches have been established for neither active nor passive sensing techniques that allow for their accurate reliability quantification. The objective of this study is to characterize the sensitivity of active-sensing acousto-ultrasound-based structural health monitoring techniques with respect to damage detection, as well as to identify the parameters that influence their sensitivity. With such an understanding, it is believed that adequate quantitative methods could then be established to enable the practical use of acousto-ultrasound structural health monitoring methods in the aerospace and mechanical engineering communities. In order to evaluate the sensitivity of a pre-selected active-sensing acousto-ultrasound structural health monitoring system, both numerical simulations and experiments were performed on 30 aluminum coupons each outfitted with a pair of lead zirconate titanate piezoelectric sensors/actuators. A damage index versus damage size relationship was investigated numerically and experimentally to assess the applicability of the traditional nondestructive evaluation linear regression framework for probability of detection for an active-sensing structural health monitoring system. The results of the study show that the position of each sensor–actuator pair with respect to a known damage location and the damage growth pattern are the two most critical parameters influencing the reliability of the same structural health monitoring system applied to identical structural components under the same environmental conditions.

Low-voltage, High-tuning Range MEMS Variable Capacitor Using Closed-loop Control

A low-voltage, high-tuning range variable MEMS capacitor using parallel-plates electrostatic microactuators operated in close-loop is introduced in this paper. The structures were fabricated using an in-house 2-masks process on SOI wafers and the use of a closed-loop controller increases the stable displacements of the structure beyond the pull-in limitation along the full available gap (the limitation are the mechanical stoppers). Additionally, the structure has two pairs of actuators, in opposing directions, enabling bi-directional displacement leading to extended tuning range. The fabricated capacitors have a designed tuning range close to 17. A lower actuation voltage is also a main benefit for future integration on low-power devices (measured pull-in voltage of approximately 3.25V). The devices were characterized and a capacitance variation of 2.3pF was experimentally verified.

Active vibration control of CNT reinforced functionally graded plates based on a higher-order shear deformation theory

This paper presents the active vibration control of carbon nanotube (CNT) reinforced functionally graded plates using piezoelectric actuator and sensor pairs bonded on the top and bottom surfaces of the host plate. Three types of CNT distributions are considered. In this study, Reddy׳s higher-order shear deformation theory (HSDT) is applied to evaluate the displacement fields of the host plate. The equation of motion of the whole structural system is formulated by Hamilton׳s principle. To derive a set of discrete ordinary differential equation, the assumed mode method is used. For the active vibration control, velocity feedback control method is used to design the controller. Responses of the plate subjects to free and forced vibration are determined. The differences of vibrations between the three types of CNT reinforced functionally graded plates are compared. Influence of volume fraction of the CNTs on the vibration amplitude is investigated. The active vibration control effects of the velocity feedback controller are presented and the trend of change in the control effect with placements of piezoelectric patches is also examined.

Aircraft panel with sensorless active sound power reduction capabilities through virtual mechanical impedances

This paper deals with an active structural acoustic control approach to reduce the transmission of tonal noise in aircraft cabins. The focus is on the practical implementation of the virtual mechanical impedances method by using sensoriactuators instead of conventional control units composed of separate sensors and actuators. The experimental setup includes two sensoriactuators developed from the electrodynamic inertial exciter and distributed over an aircraft trim panel which is subject to a time-harmonic diffuse sound field. The target mechanical impedances are first defined by solving a linear optimization problem from sound power measurements before being applied to the test panel using a complex envelope controller. Measured data are compared to results obtained with sensor–actuator pairs consisting of an accelerometer and an inertial exciter, particularly as regards sound power reduction. It is shown that the two types of control unit provide similar performance, and that here virtual impedance control stands apart from conventional active damping. In particular, it is clear from this study that extra vibrational energy must be provided by the actuators for optimal sound power reduction, mainly due to the high structural damping in the aircraft trim panel. Concluding remarks on the benefits of using these electrodynamic sensoriactuators to control tonal disturbances are also provided.

Application of the Udwadia–Kalaba methodology to the active control of shaft vibration

Rotating shafts are prone to vibration and it is necessary to mitigate these vibrations to ensure proper operation of the machine. Such mitigation can be performed by active control. Among the available control strategies, one can apply the methodology proposed by Udwadia and Kalaba for trajectory control of nonlinear systems. In this work, such methodology is analyzed for controlling the lateral vibrations of a rotating shaft. First, this control technique is evaluated by placing the sensor–actuator pair in the point of interest for control (disc position of the shaft). Results show that the kinematic constraints applied by the control strategy are exactly tracked and lateral vibration of the shaft is significantly reduced. Second, the control technique is evaluated by placing the sensor–actuator pair at the bearing position of the shaft, thus far from the point of interest for control (disc position). In this case, vibration is reduced at the point of actuation, but not at the point of interest for control. However, the application of the methodology in an on/off strategy resulted in a successful reduction of the lateral vibrations of the shaft at the point of interest for control when crossing the first critical speeds.

Piezoelectric energy harvesting in internal fluid flow.

We consider piezoelectric flow energy harvesting in an internal flow environment with the ultimate goal powering systems such as sensors in deep oil well applications. Fluid motion is coupled to structural vibration via a cantilever beam placed in a converging-diverging flow channel. Two designs were considered for the electromechanical coupling: first; the cantilever itself is a piezoelectric bimorph; second; the cantilever is mounted on a pair of flextensional actuators. We experimentally investigated varying the geometry of the flow passage and the flow rate. Experimental results revealed that the power generated from both designs was similar; producing as much as 20 mW at a flow rate of 20 L/min. The bimorph designs were prone to failure at the extremes of flow rates tested. Finite element analysis (FEA) showed fatigue failure was imminent due to stress concentrations near the bimorph’s clamped region; and that robustness could be improved with a stepped-joint mounting design. A similar FEA model showed the flextensional-based harvester had a resonant frequency of around 375 Hz and an electromechanical coupling of 0.23 between the cantilever and flextensional actuators in a vacuum. These values; along with the power levels demonstrated; are significant steps toward building a system design that can eventually deliver power in the Watts range to devices down within a well.

An optimal approach to active damping of nonlinear vibrations in composite plates using piezoelectric patches

In this paper a nonlinear approach to studying the vibration characteristic of laminated composite plate with surface-bonded piezoelectric layer/patch is formulated, based on the Green Lagrange type of strain–displacements relations, by incorporating higher-order terms arising from nonlinear relations of kinematics into mathematical formulations. The equations of motion are obtained through the energy method, based on Lagrange equations and by using higher-order shear deformation theories with von Karman–type nonlinearities, so that transverse shear strains vanish at the top and bottom surfaces of the plate. An isoparametric finite element model is provided to model the nonlinear dynamics of the smart plate with piezoelectric layer/ patch. Different boundary conditions are investigated. Optimal locations of piezoelectric patches are found using a genetic algorithm to maximize spatial controllability/observability and considering the effect of residual modes to reduce spillover effect. Active attenuation of vibration of laminated composite plate is achieved through an optimal control law with inequality constraint, which is related to the maximum and minimum values of allowable voltage in the piezoelectric elements. To keep the voltages of actuator pairs in an allowable limit, the Pontryagin’s minimum principle is implemented in a system with multi-inequality constraint of control inputs. The results are compared with similar ones, proving the accuracy of the model especially for the structures undergoing large deformations. The convergence is studied and nonlinear frequencies are obtained for different thickness ratios. The structural coupling between plate and piezoelectric actuators is analyzed. Some examples with new features are presented, indicating that the piezo-patches significantly improve the damping characteristics of the plate for suppressing the geometrically nonlinear transient vibrations.

Collective synchronization and phase locking of fs fiber amplifiers: Requirements and potential solutions

Active coherent beam combination (CBC) of femtosecond pulses requires knowledge of the absolute phase between all the optical pulses: pulse synchronization and phase locking are both mandatory and must be measured and controlled. To assess controller requirements, we study fiber amplifier phase noise for various packaging and power levels. The main contributors are thermal noise (with large amplitude phase noise and frequencies below 5 Hz) and vibrations (with low amplitude phase noise and frequencies from 5 Hz to 2 kHz), leading to a woofer/tweeter pair of actuator. The amplifier packaging is of major importance: a simple PID model shows that in order to achieve a residual phase error of λ/100, the required controller bandwidth ranges from 0.5 Hz to 1 kHz, mostly depending on amplifier packaging. We also shortly review common phase locking techniques either based on pupil-plane sensor or focal-plane sensor. Common focal-plane techniques as SPGD or LOCSET are not directly compatible with pulsed femtosecond operation. Pupil-plane fringe-sensor techniques are more promising and route towards collective synchronization for femtosecond regime are proposed. Following the example of telescope interferometry, the final system might include both a pupil-plane, fringe-sensor and a focal-plane phase-diversity sensor, with pupil-plane sensor for synchronization and phase lock, and focal-plane sensor to control and maintain required focalized beam quality.

Using functional gains for effective sensor location in flow control: a reduced-order modelling approach

The problem of active feedback control of fluid flows falls into a class of problems in the area of distributed parameter control. Distributed parameter systems are typically defined by partial differential equations that model the time and spatial evolution of the process. We consider the problem of locating sensors for effective feedback control of a fluid flow problem described by the Navier–Stokes equations. In this setting, the state of the system is the velocity field$\boldsymbol{v}(t,x)$, and hence all feedback laws are a function of this velocity field or, in most practical settings, a function of sensor outputs. In many designs, the feedback control law can be represented as a linear function of the state defined by an integral operator with a kernel function called the functional gain. In this paper we show that these functional gains can be used to determine effective sensor placement in complex flow control applications. The approach is to choose measurements of the state that would provide good quadrature points for the integral operator. We provide a computational validation of this approach by controlling the vortex shedding in a two-dimensional cylinder flow using a pair of fluid actuators on the cylinder surface. This model is linearized about the mean flow and a feedback control is designed by pole placement. Distributed parameter control theory yields the existence and form of the functional gains which are used to locate sensors. In particular, we use the location of the supports of the functional gains to determine two sets of four sensor locations in the wake. One of these measurement sets coincides with large magnitudes of the gain and the other set coincides with small magnitudes. Numerical experiments with a reduced-order model confirm superior performance of the closed-loop (CL) system using the former sensor set. We also show that choosing sensor locations associated with small magnitudes of the functional gains actually destabilizes the CL system.

3D printing antagonistic systems of artificial muscle using projection stereolithography

The detailed mechanical design of a digital mask projection stereolithgraphy system is described for the 3D printing of soft actuators. A commercially available, photopolymerizable elastomeric material is identified and characterized in its liquid and solid form using rheological and tensile testing. Its capabilities for use in directly printing high degree of freedom (DOF), soft actuators is assessed. An outcome is the ∼40% strain to failure of the printed elastomer structures. Using the resulting material properties, numerical simulations of pleated actuator architectures are analyzed to reduce stress concentration and increase actuation amplitudes. Antagonistic pairs of pleated actuators are then fabricated and tested for four-DOF, tentacle-like motion. These antagonistic pairs are shown to sweep through their full range of motion (∼180°) with a period of less than 70 ms.

Independent Control of Force & Displacement Using Shape Memory Alloy Tactile Display

This paper proposes one of the possible techniques for interacting for shape memory alloy (SMA) actuator based tactile display, which can act as demonstrator devices. This work is focused on developing a model of a pair of antagonistic high strain SMA tension actuators with independent control of force and displacement. The technology employed utilizes two Flexinol 100 micron heat actuated wires of Titanium-Nickel (NiTi) shape-memory alloy which contract when heated under pre-stress and produces up to 5% strain recovery. This phenomenon, which provides a unique mechanism for actuation, is associated with the unique interaction between the martensite and austenite crystal structures of the SMA. Physical measurements of the behaviour of the actuator elements were performed using a laser displacement sensor to verify the fidelity of response to software commands, and to measure step response to pulse-width modulated (PWM) current control at different frequencies and duty cycles. Results yielded high accuracy across a wide range of frequencies and duty cycles, proving the SMA actuation technique has potential to present and convey useful tactile information of surface deformation for virtual environment applications.

Study on the characteristics of a homemade differential-velocity–type compliant joint for robotic manipulators

Design of a new differential-velocity–type compliant joint with two motors is proposed for robotic manipulators. The speed/output torque of the differential-velocity–type joint is synthesized by controlling the differential speeds of a pair of actuators. Descriptions of the design concept, theoretical analysis, and the experiments are presented in this article. The experimental results showed that (1) the stiffness of the differential-velocity–type joint can be regulated by changing the speeds of both motors, (2) the differential-velocity–type joint actually reduced 7.9%−15.7% time compared with the single-drive joint when performing five cycles of reciprocation, and (3) a new design of delta-type robot with differential-velocity–type driving modules was developed for verification. The experimental results showed that the differential-velocity–type delta robot can perform flexible assembly operations within a 0.028-mm tolerance.

Adaptive-passive control of structure-borne noise of rotating machinery using a pair of shunted inertial actuators

In this article, two piezo-based rotating inertial actuators are considered for the suppression of the structure-borne noise radiated from rotating machinery. Each inertial actuator comprises a piezoelectric stack element shunted with the Antoniou’s gyrator circuit. This type of electrical circuit can be used to emulate a variable inductance. By varying the shunt inductance it is possible to realise two tuneable vibration neutralisers to suppress tonal frequency vibrations of a slowly rotating machine. Also, reductions in the noise radiated from the machine housing can be achieved. First, a theoretical study is performed using a simplified lumped parameter model of the system at hand. The simplified model consists of a rotating shaft and two perpendicularly mounted shunted piezo-based rotating inertial actuators. Second, the shunted piezo-based rotating inertial actuators are tested on an experimental test bed comprising a rotating shaft mounted in a frame. The noise is radiated by a plate that is attached to the frame. The experimental results show that a reduction of 11 dB on the disturbance force transmitted from the rotating shaft through the bearing to the housing can be achieved. This also generates a reduction of 9 dB for the plate vibration and the radiated noise.

Simultaneous Optimization of Damping and Tracking Controller Parameters Via Selective Pole Placement for Enhanced Positioning Bandwidth of Nanopositioners

Positive velocity and position feedback (PVPF) is a widely used control scheme in lightly damped resonant systems with collocated sensor actuator pairs. The popularity of PVPF is due to the ability to achieve a chosen damping ratio by repositioning the poles of the system. The addition of a tracking controller, to reduce the effects of inherent nonlinearities, causes the poles to deviate from the intended location and can be a detriment to the damping achieved. By designing the PVPF and tracking controllers simultaneously, the optimal damping and tracking can be achieved. Simulations show full damping of the first resonance mode and significantly higher bandwidth than that achieved using the traditional PVPF design method, allowing for high-speed scanning with accurate tracking. Experimental results are also provided to verify performance in implementation.

Placement optimization of actuators and sensors for gyroelastic body

Gyroelastic body refers to a flexible structure with a distribution of stored angular momentum provided by fly wheels or control moment gyroscopes. The angular momentum devices can exert active torques to the structure for vibration suppression or shape control. This article mainly focuses on the placement optimization issue of the actuators and sensors on the gyroelastic body. The control moment gyroscopes and angular rate sensors are adopted as actuators and sensors, respectively. The equations of motion of the gyroelastic body incorporating the detailed actuator dynamics are linearized to a loosely coupled state-space model. Two optimization approaches are developed for both constrained and unconstrained gyroelastic bodies. The first is based on the controllability and observability matrices of the system. It is only applicable to the collocated actuator and sensor pairs. The second criterion is formulated from the concept of controllable and observable subspaces. It is capable of handling the cases of both collocated and noncollocated actuator and sensor pairs. The illustrative examples of a cantilevered beam and an unconstrained plate demonstrate the clear physical meaning and rationality of the two proposed methods.

Active Control of a Planar Offset Attaching Jet Using Synthetic Jets

A planar jet issued from a contoured nozzle was forced using a pair of synthetic jet actuators located along the upper and the lower edges of the jet exit. The forcing frequency varied from f Hj/Uo of 0.08 to 0.45 for a fixed forcing amplitude u′/U of 0.3. It was found that the time-averaged re-attachment length was reduced by forcing, the decreases were particularly large when the lower actuator was used. The flow field was modified significantly by the forcing when f Hj/Uo was 0.08, strong vortical structures were observed in the flow which increased the turbulent fluctuations along both shear layers.

Design of electrostatic actuators for suppressing vertical disturbances of CMOS-MEMS capacitive force sensors in bio applications

The objective of this work is to design electrostatic actuators for a CMOS-MEMS nano-newton capacitive force sensor to suppress vertical vibrations disturbances. Electrostatic actuators are selected because the movable part of this force sensor is anchored to the fixed parts. In the first step, we propose a framework for simulation of the force sensor based on finite element method. The proposed model is modified utilizing comparison between the simulation and experimental models to improve the performance of the model. Then, 14 pairs of electrostatic actuators are designed for applying the control algorithm and their pull-in voltage is calculated. In next step, Modal Analysis is applied to find dominant natural frequencies and mode shape vectors. In addition, an observer is proposed to estimate the velocity of the modal coordinate. Finally, an optimal controller is designed employing state-space approach to suppress vertical vibration due to undesired out-of-plane excitations generated by environment during manipulation. Simulation results illustrate that employing optimum LQR control approach, the maximum out-of-plane disturbance input is suppressed less than 0.4 s with acceptable range of voltage less than pull-in voltage.

Model based vibration control of smart flexible structure using piezoelectric transducers

This paper focuses on development and implementation of optimal control algorithms for vibration control of flexible beam structures with embedded piezoelectric actuators. Piezoelectric transducers have become the leading active elements in smart structures based on their characteristics and reliability. Piezo laminated beam with collocated pairs of piezoelectric sensors and actuators is modelled using the methodology of system identification. The obtained model has been implemented in the model based optimal control algorithms. Linear quadratic regulator and model predictive control are developed and tested using LabVIEW and NI cRIO platform. The MPC algorithm shows better performance due to the constraint handling and requires more powerfull real-time and FPGA controller target.