Passive Actuators Research Articles

Alt Uzuv Dış İskelet Robot Eklemlerinde Kararlılık İçin Sönümleme Katsayıları ve Momentlerinin Hesaplanması

Exoskeleton robots are wearable electromechanical structures which can work interacting with human limbs. Theserobotsareused as assistivelimbs, rehabilitationandpoweraugmentationpurposesforelderly or paralyzedpersons andhealthypersons respectively.Human body neuro-muscular system varies the stiffness and damping of the human joints regularly and thus provides flexible and stable movement capability with minimum energy consumption. Damping coefficients and torques in the joints needs to be adjusted with the change of stiffness to provide stable behavior during walking cycles. Magneto-rheological brake are the passive actuators that can adjust the damping torques in a very short response time. However, the maximum values of damping coefficients and torques are needed for the design of MR dampers to be used in the joints of exoskeleton robots. Shamaei et. al. (2013) derived a set of statistical equations to predict thejoint stiffnessin a gait cycle for the persons with different height and weights. In this paper, the maximum values of damping coefficients and torques are calculated for the design of MR dampers to provide stability in the joints of exoskeleton robots. The results can be used as initial design criteria of MR dampers which will be added to the biomimetic joints of exoskeleton robots, prostheses, ortheses and humanoid robots

A Single-Step Digital Nucleic Acid Amplification Platform by Digital Plasma Separation on a Chip

Quantitative nucleic acid detection is the future for precision molecular medicine. However, multiple sample preparation steps and thermal heat cycles of PCR are necessary for nucleic acid (NA) analysis. We developed a single-step isothermal digital NA amplification microfluidic platform by a technique termed digital plasma separation. We invented an innovative biophysical microcliff design that allows the removal of blood cells based on inertia; it can skim plasma into 224 wells (100nl/well) in one-step (>99% separation efficiency for 6μm particles). By separating the blood cells that obstruct optical detection, the microcliff design enabled quantitative DNA detection via an isothermal DNA amplification technique called Recombinase Polymerase Amplification (RPA) in 30 minutes directly from human blood samples. We were able to perform endpoint quantitative digital RPA with a dynamic range of 10∼1000 copies/μl via automatic compartmentalization of the samples. The precise control of fluid flow on chip is accomplished by passive degas-driven flow actuation, which does not require external tubing or pumps, thus making the chip portable. A large amount of sample (∼100μl of blood samples) can be processed. We envision this single-step digital blood plasma separation platform will benefit low cost quantitative molecular diagnostics in both developed and developing countries.

Conceptual Design of a Powered Ankle-foot Prosthesis for Walking with Inversion and Eversion

Abstract Human ankle is a series of joints that are highly integrated [1] , [2] , where tolecular joint (permits dorsiflexion-planter flexion) and subtalar joint (permits inversion-eversion) play vital roles.A conceptual design of an ankle joint is presented here to facilitate the terrain adaptability maintaining natural gait patterns and stability for person with single limb transtibial amputation. The design consists of physiological ankle movements during walking on flat surface as well as uneven terrain. The ankle joint (spherical joint) permits planter flexion-dorsiflexion by the control of passive actuators (springs) and active actuator (motor). It further allows movement in the frontal plane inward/outward about an imaginary centre line of body in order to adapt the roughness of surface. The kinematic behavior of the prosthesis is analyzed. Foot portion of the ankle prosthesis are conceptualize as composite structure to minimize ground contact shock. A 3D prototype is created to represent the conceptual design, which successfully demonstrated the ankles rotational motion.

Обоснование и определение основных параметров спирально-пластинчатого рабочего органа

Justification and analytical derivation of the equations to determine the basic parameters (including forms) of rotary (circular, screw, a helical-type and etc.) working parts of tillers were the subject of investigations by several authors. Also from literature sources, we can say that the working parts of passive rotary actuator (jet - the drive from the soil) for the crumbling of the soil and associated operations will require further theoretical and experimental studies. Therefore, we investigated spiral plate-type working part with corrugated (wavy) work surface and a cutting edge with teeth, accomplished at the site of the logarithmic spiral. Thus, the wavy form of the working surface has an influence on the cutting edge. In consequence of that, the teeth of the cutting edge radially disposed on a path, extending along a helical line and rejected in two directions (right and left turn). Based on the foregoing, we justified and prepared relations to define the basic parameters of the working surface of the teeth and the cutting edge of the working part spiral plate-type elements: the diameter (D), the number of teeth (Z3), the depth of cut (C'), the distance between adjacent teeth - tooth pitch (S3 ), length of the front cutting edge of the tooth (ℓ 3), the length of back edge of the tooth (ℓ t), lead of a screw (tmax), the width of the operating element (H), width of a tooth at its apex (B3) and the distance from the apex of the tooth to its leading edge (L3 ). The analytical dependence can justify the choice of the main design parameters of the operating element and design the toothed spiral plate-type working part, which is reduced to the calculation of the basic dimensions and meaningful implementation.

Magnetic Field and Specific Axial Load Capacity of Hybrid Magnetic Bearing

Permanent magnet bias hybrid magnetic bearing (HMB) which combines active and passive actuators in one unit is very suitable for rotational applications in spacecraft. In the past, numerous studies focusing on the active actuator have been widely reported. However, few have addressed on the passive unit which is essential to the suspension system. In this paper, a sufficiently precise and concise analytical method which is based on the conformal transformation is proposed for the analysis and design of the HMB with specific axial load capacity. With this approach, important parameters used for optimal MB designing, such as magnetic leakage coefficient, as well as the flux density of main flux and fringing flux are given as simple formulas, which educe the axial restoring magnetic force and the axial passive stiffness. The coupling effect of these two units of the HMB is analyzed. The torque generated by the control current of the radial bearing is educed. Experimental investigation via an experimental apparatus to measure the axial specific capacity is introduced. Flywheel prototypes suspended by this kind of HMB system are tested, and the consequence is compared with the analytical data and the finite-element method data to get a final conclusion, which demonstrates the specific load capacity and the conciseness and accuracy of the analytical method.

Stabilization of absolute instability in spanwise wavy two-dimensional wakes

AbstractControlling vortex shedding using spanwise-varying passive or active actuation (namely three-dimensional control) has recently been reported as a very efficient method for regulating two-dimensional bluff-body wakes. However, the mechanism of how the designed controller regulates vortex shedding is not clearly understood. To understand this mechanism, we perform a linear stability analysis of two-dimensional wakes, the base flow of which is modified with a given spanwise waviness. Absolute and convective instabilities of the spanwise wavy base flows are investigated using Floquet theory. Two types of base-flow modification are considered: varicose and sinuous. Both of these modifications attenuate absolute instability of two-dimensional wakes. In particular, the varicose modification is found to be much more effective in the attenuation than the sinuous one, and its spanwise lengths resulting in maximum attenuation show good agreement with those in three-dimensional controls. The physical mechanism of the stabilization is found to be associated with the formation of streamwise vortices from tilting of two-dimensional Kármán vortices and the subsequent tilting of these streamwise vortices by the spanwise shear in the base flow. Finally, the sensitivity of absolute instability to spanwise wavy base-flow modification is investigated. It is shown that absolute instability of two-dimensional wakes is much less sensitive to spanwise wavy base-flow modification than to two-dimensional modification. This suggests that the high efficiency observed in several three-dimensional controls is not due to the sensitive response of the wake instability to the spanwise waviness in the base flow.

A nonlinear control of an QZS isolator with flexures based on a lyapunov function

This paper presents an active control method for a quasi-zero stiffness (QZS) isolator using flexures based on a Lyapunov function. First, shown is a dynamic model of an active QZS isolator having indirect horizontal actuation. In the model, the control force is applied along the horizontal direction to compensate for vertical vibrations. Next, a nonlinear control algorithm for the active isolator is developed based on a Lyapunov function. Simulation of the active isolator model which consists of passive QZS isolators, sensors and actuator dynamic models is done to study the effects of control tuning gain on the system performances. In order to verify the active isolation performances, developed is an experimental model including an active QZS isolator, an exciter device and various sensors. Finally, experiments for such as impulse disturbance rejection and transmissibility are performed and the results show that the indirect horizontal actuation by the active QZS isolator using flexure attenuates impulse disturbance as well as isolates the base vibration effectively.

Stress, strain, and resistance behavior of two opposing shape memory alloy actuator wires for resistance-based self-sensing applications

Shape memory alloy actuator wires undergo a significant (∼4%) contraction and a corresponding change in resistance because of a temperature- and load-induced phase transformation. When a restoring force such as a pre-stretched bias spring is placed in series with a shape memory alloy wire, the system becomes an actuator that can generate a repeatable force. Simultaneously, the resistance of the wire can be correlated to strain and enable self-sensing, eliminating the need for external feedback sensors. The self-sensing task, however, is complicated in applications requiring multiple coupled wires, for example, advanced two-dimensional or three-dimensional positioning. The presence of coupled (passive or active) actuator wires with nonlinear, hysteretic force–displacement characteristics has a strong impact on an individual wire’s resistance behavior that has not been systematically studied to date. This article expands upon previous work that studied a single-shape memory alloy–spring system by adding a second opposing shape memory alloy wire and focusing on the resistance to strain mapping that is crucial for self-sensing applications. Systematic stress–strain and resistance–strain experiments are presented alongside physics-based modeling results that help to identify several sources of hysteresis in the resistance–strain behavior and facilitate intelligent calibration schemes for multifunctional self-sensing and actuation applications.

Detailed evaluation of safety injection tank effects on in-vessel severe accident progression in a small break LOCA without safety injection

The effects of coolant injection into a reactor vessel by the passive actuation of SITs (Safety Injection Tanks) on the in-vessel core melt progression under a severe accident have been evaluated in an APR (Advanced Power Reactor) 1400. A best estimate simulation from initiating events of 2-in. and 3-in. break SBLOCAs (Small Break Loss Coolant Accidents) without SI (Safety Injection) to a reactor vessel failure has been carried out using the SCDAP/RELAP5 computer code in conditions with and without the passive actuation of the SITs. The SCDAP/RELAP5 results have shown that the passive coolant injection into the reactor vessel by the actuation of the SITs leads to postpone the reactor vessel failure time by 4–5h in the SBLOCA without SI. At the time of the reactor vessel failure, 44.5% and 42.8% of the fuel rod cladding were oxidized in the 2-in. and 3-in. SBLOCAs with the actuation of the SITs, respectively. However, 37.5% and 34.6% of the fuel rod cladding were oxidized in the 2-in. and the 3-in. SBLOCAs without the actuation of the SITs, respectively. Even though the SITs are designed for a large break LOCA, their actuation is very effective on the delay of a reactor vessel failure in spite of more hydrogen generation in the SBLOCA without SI.

Passive Actuator Fault-Tolerant Control for a Class of Overactuated Nonlinear Systems and Applications to Electric Vehicles

This paper presents a passive actuator fault-tolerant (FT) controller for a class of overactuated nonlinear systems and its experimental investigations on an electric vehicle. As the actuator fault information is unknown before the fault detection and diagnosis procedure finishes, the passive FT control is of great necessity in maintaining system stability and achieving acceptable performance. In this paper, three types of actuator faults are considered, and a passive FT controller that works for all of the studied fault types is designed. By grouping control efforts that have similar effects on the system into the same subsystem, the proposed control method can automatically distribute the higher level control signals to the actuators while minimizing a defined cost function. The FT control method was applied to control of a four-wheel-independently-actuated (FWIA) electric ground vehicle. Experimental results obtained on a FWIA electric vehicle show the effectiveness of the proposed method.

Mechanical Characterisation of the NiTi Shape Memory Alloy for Microfluidic Valve Applications

ABSTRACTPhotonics Integrated Circuits (PICs) are being applied by the telecommunications industry as transceivers for fibre optic networks. The core component of a typical PIC is the laser array and these devices can have relatively low operating temperatures (15°C - 25°C) with a tight operating range (±0.1K). To accommodate such a specification, a thermal control system is required that can change the cooling rate through feedback. The power density of next generation PICs is at such a level to demand novel thermal management architectures including developments such as near source liquid cooling. In order to control the thermal performance of fluidic devices, effective methods for varying the rate of coolant are an essential component. Consequently, micro-valve structures are required, ideally involving passive actuation to meet stringent reliability standards. One solution to this challenge is to exploit the phase-change driven shape memory effect of the NiTi Shape Memory Alloy (SMA). A micro-valve could be developed from the NiTi SMA, thermally coupled to the laser array component in order to work passively to regulate the flow of coolant in a micro-channel. Such a valve would have to be intrinsically reliable, and the goal of this paper is to investigate the conditions that will affect this reliability. The objective of the work is to investigate the mechanical properties relevant to the design of a passive NiTi SMA micro-valve, with a focus on the formation of stress-induced Martensite bands. It is not understood why these bands form on a plane inclined at ∼55° to the axis of loading and in this paper theory is presented that suggests a reasoning for this. A plate sample of NiTi was tested in uni-axial tension and Digital Image Correlation (DIC) used to analyse the strain fields across the surface of the sample. The DIC results revealed areas of high stress concentrations occurring in bands inclined on average 53.86° to the axis of loading. The theory and experimental observations are in agreement with the literature but to validate the theory the crystal texture needs to be analysed in the stress concentration regions. This paper provides valuable insight into the mechanical behaviour of a passive NiTi SMA micro-valve subjected to a sufficient pressure to form stress-induced Martensite.

Hybrid control algorithm to improve both stable impedance range and transparency in haptic devices

An ideal haptic device should transmit a wide range of stable impedances with maximum transparency. When using active actuators, transparency improvement algorithms tend to decrease the range of attainable impedances. Passive actuators can transmit high impedances stably, but are not sufficient alone for transparency. In this study, a hybrid force control algorithm employing active and passive actuators was developed to improve the stable impedance range and transparency in haptic devices. A new transparency-Z-width plot is proposed as a way to evaluate the stable impedance range and transparency together. The hybrid control algorithm uses parameters to share the torque demand between two actuators with smooth transition. These parameters were determined and an artificial neural network (ANN) was used to extend them to the entire achievable impedance range. The algorithm was tested experimentally on a 1-DOF haptic device. The transparency experiments employed an excitation motor located at the user side of the device to evaluate various algorithms in time and frequency domains. Results showed that the proposed hybrid control algorithm enables simulation of higher range of impedances with higher transparency than the conventional algorithms.

Virtual needle insertion with haptic feedback using a hybrid actuator with DC servomotor and MR-brake with Hall-effect sensor

In many haptics applications, fast and stable force response with high strength is highly desired. While the existing active and passive actuators cannot fully satisfy these requirements alone, their cooperation could provide better results. This study aimed at the development of a hybrid actuator by combining a DC servomotor and a magnetorheological (MR) brake. Serpentine flux path architecture was used to design a compact MR-brake. By embedding a Hall-effect sensor in the brake, the hysteresis challenges and residual off-state torque were eliminated. In this approach, the sensor measures the flux across the MR-fluid while a PI controller directly manipulates the magnetic induction level. To the best of our knowledge, this is the first such design incorporated into an MR-brake. The control scheme determines the motor and brake inputs separately based on their capabilities. During operation, the brake is activated to provide an average force profile while the motor superimposes the finer details on this profile. The hybrid actuator can provide a stiff wall collision effect when the needle touches a bone. It can also enable fast tracking during sudden force variations as they happen during virtual needle insertion and removal into virtual tissue layers.

Mechatronic Design of a New Humanoid Robot with Hybrid Parallel Actuation

Humanoid robotics is unquestionably a challenging and long-term field of research. Of the numerous and most urgent challenges to tackle, autonomous and efficient locomotion may possibly be the most underdeveloped at present in the research community. Therefore, to pursue studies in relation to autonomy with efficient locomotion, the authors have been developing a new teen-sized humanoid platform with hybrid characteristics. The hybrid nature is clear in the mixed actuation based on common electrical motors and passive actuators attached in parallel to the motors. This paper presents the mechatronic design of the humanoid platform, focusing mainly on the mechanical structure, the design and simulation of the hybrid joints, and the different subsystems implemented. Trying to keep the appropriate human proportions and main degrees of freedom, the developed platform utilizes a distributed control architecture and a rich set of sensing capabilities, both ripe for future development and research.

Performance evaluating of the AP1000 passive safety systems for mitigation of small break loss of coolant accident using risk assessment tool-II software

The successful performance of defense barriers in the operating nuclear power plants is vital to avoid any release of highly radioactive fission products. Passive safety systems, independent of the electrical power, are implemented in modern NPPs to improve their reliability on demand.In this study, the SB-LOCA CDF is evaluated for the AP1000 to assess the performance of passive safety systems. The core damage states are examined to identify the most considerable risk contributors. Besides, importance measures rank the failures. Risk assessment tool-II has been designed and developed, in the safety research center of Shiraz University, to develop the PSA level 1 models.Using redundant passive and diverse reliable safety systems result in the low CDF of SB-LOCA (i.e. 1.934E−08). Considering the dominant sequences indicates that relying on passive automatic actuation mitigating processes, independent of operator actuations and electrical motive power leads to the considerable decrease in the probability of common cause failures and the CDF. However, importance analysis reveals the high contribution of CCF_BEs in the SB-LOCA CDF.The results identify the weak points of operation and the most important risk contributors, in order to improve the inadequacies in design, test and maintenance and required human actions.

Numerical modeling of flow control on a symmetric aerofoil via a porous, compliant coating

A passive actuation technique, that entails covering the suction side of an aerofoil with a poro-elastic carpet, is presented. Numerical modeling of the coupled fluid-structure interaction problem is performed for a low Reynolds number regime, characteristic of micro aerial vehicles. The immersed boundary technique is employed, which offers the advantage of using Cartesian grids for complex geometries. By suitably selecting the characteristics of the carpet, to synchronise characteristic time scales of the fluid and the structural systems, significant drag reduction and/or lift enhancement can be achieved, associated with modifications of the length scales of the shed vortices and a mild intensification of their intensity. A parametric analysis shows that such a coating is able to affect the topology of the flow in the proximity of the rear of the aerofoil, by adapting spontaneously to the separated flow.

Research on hybrid isolator technique

This paper presents a new hybrid isolator technique that composes of passive vibration device and active actuator. It contains the advantages of both active and passive isolation system. During the optimization design, the passive vibration isolator as cylindrical rubber is designed, then the active actuator is designed as electromagnetic actuator with advantages of compact construction and larger forces. After manufacturing the prototype designed, the vibration active control experiment is carried out, which can verify the hybrid isolator's performance. During the mono-layer active control experiment, vibration of the upper layer mass reduced about 29dB~40dB. In the two-stage experiment, it has gained a good effect in both single and double frequency excitation. It means that the hybrid isolator technique designed has good performance of anti-vibration in practical application.

Design of Active Bias Sma Actuators for Morphing Wing Applications

Shape Memory Alloys (SMAs) can provide compact and effective actuation for a variety of mechanical systems. Generally speaking, SMA-driven actuator systems can be divided into three subsystems: a) SMA active element, b) the transmission and c) a bias element. In respect to the type of bias, two actuator configurations can be distinguished: passive bias actuators where the SMA active element is coupled with an elastic bias element (spring), and active bias actuators in which two SMA active elements are connected together. This work is focused on designing an SMA actuator using active bias elements for morphing wing applications. Keywords: SMA actuator, active bias, antagonist, design, morphing wing

Modeling of Biomimetic Robotic Fish Propelled by Passive Tail with Suitable Rigidity

This paper proposes a physics-based cruising speed model for biomimetic robotic fish propelled by the passive plastic foil actuator. Inspired by biological body and fins, a plastic foil with suitable rigidity and innovative structure are designed to acquire better propelling effect. The model captures the speed based on the analysis of the interaction between the tail and the water which considers the hydrodynamics. Experimental results have shown that the proposed model is able to predict the steady-state cruising speed of the robotic fish under a periodic actuation input. Since most of the model parameters are expressed in terms of fundamental physical properties and geometric dimensions, the model is expected to be beneficial in optimal design of the robotic fish.

Development of a lightweight deployable/stowable radiator for interplanetary exploration

This paper experimentally and analytically evaluates the heat rejection/retention performance of a lightweight 100 W-class re-deployable radiator with environment-adaptive functions. This radiator, reversible thermal panel (RTP), which consists of flexible high thermal conductive graphite sheets and a single crystal shape memory alloy as a passive reversible actuator, changes its function from a radiator to a solar absorber by deploying/stowing the reversible fin upon changes in the heat dissipation and thermal environment. The RTP was considered as a candidate methodology for thermal control of Venus mission, PLANET-C, in order to save survival heater power. An RTP prototype was tested and evaluated. An analytical thermal model of the RTP was also developed, and basic performances of the RTP were evaluated. Thermal performance of the RTP when applied to the longwave infrared camera of the PLANET-C was evaluated with an analytical thermal model as functions of fin deployment directions and rear surface properties of the RTP’s fin. The analytical results showed that the RTP can save survival heater power in comparison to a conventional radiator. ► New thermal control device for spacecraft with high-thermal-conductivity graphite sheets. ► Heat rejection performance can be changed based on its temperature. ► Thermal vacuum test demonstrates autonomous thermal control performance. ► A case study was conducted, and effectiveness was analytically evaluated.