Actuator Stroke Research Articles

Multilevel synergically controlling wavefront correction of a high-power slab laser system.

We present a multilevel synergically controlling wavefront correction method that can apply in a slab laser system. To fully utilize the response frequency and the stroke of actuators of the single deformable mirror (DM), we design a set of multilevel wavefront correction devices to reduce the root-mean square of wavefront aberration before the DM. As the wavefront of slab geometry solid-state lasers mainly consists of fourth and longitudinally distributed aberration, such as 5th, 9th, and 14th orders of Legendre polynomials. We design a precompensating level of the aberration with a slow-drift mirror, fast-steer mirror, one-dimensional adjustable slab-aberration compensator, and beam-shaping system to reduce these orders of wavefront aberration with low spatial resolution and large stroke. As the controlling bandwidth of different devices is diverse, the coupling oscillation between the precompensating level and adaptive optics (AO) level occurs, then we develop the multilevel synergically control to address the coupling. With the precompensating level, the experimental result shows the residual wavefront aberration of the slab laser is compensated well by the AO level effectively within the compensating capability. We clean up a 9.8kW slab laser system with the beam quality β of far-field focus spots improved from 17.71 to 2.24 times the diffraction limit.

Kinematic analysis of three redundant parallel mechanisms for fracture reduction surgery

This paper mainly deals with the kinematic analysis and performance comparisons of three redundant parallel mechanisms for fracture reduction surgery. First, two novel kinematically redundant parallel mechanisms for surgical robots are proposed based on the Gough–Stewart parallel platform. The kinematics of the three mechanisms are established, and their workspaces are analyzed. The analysis result shows that the workspace volume of the redundant mechanism can be improved by 71.6%. Second, considering the stroke of redundant actuators, the effects of the slider strokes on the position and orientation workspaces are obtained. The multi-objective optimization method is used to optimize the geometric parameters of the three mechanisms. Third, the singularities of the three redundant parallel mechanisms are compared based on the dimensionally homogeneous Jacobian matrix. Finally, experiments are conducted to verify the effectiveness of the performance comparison methods in this paper.

Design of an SMA-driven compliant constant-force gripper based on a modified chained pseudo-rigid-body model

Compliant grippers are important devices for assembling small parts. Analyzing the mechanism efficiently and accurately and designing grippers carefully have also become crucial. In this paper, a shape memory alloy-driven compliant constant-force gripper is developed to create extensive and safe operations. A modified chained pseudo-rigid-body model with additional prismatic pairs is proposed for optimal performance according to mechanical analysis. In the developed gripper, a two-beam binding constant-force mechanism is proposed to apply a constant gripping force in the gripper’s jaws; a constant-force guide mechanism is utilized to extend the actuation stroke and connect the jaws with the actuator. The simulation results of the functional parts are in good agreement with the theoretical results, demonstrating the high accuracy of the proposed beam model. In addition, experimental studies on the gripping force and grasp-release operations verify the effectiveness of the designed gripper and its components.

Design and optimization of a decoupled serial constant force microgripper for force sensitive objects manipulation

AbstractTo address coupling motion issues and realize large constant force range of microgrippers, we present a serial two-degree-of-freedom compliant constant force microgripper (CCFMG) in this paper. To realize a large output displacement in a compact structure, Scott–Russell displacement amplification mechanisms, bridge-type displacement amplification mechanisms, and lever amplification mechanisms are combined to compensate stroke of piezoelectric actuators. In addition, constant force modules are utilized to achieve a constant force output. We investigated CCFMG’s performances by means of pseudo-rigid body models and finite element analysis. Simulation results show that the proposed CCFMG has a stroke of 781.34 ${\unicode[Times]{x03BC}}\mathrm{m}$ in the X-direction and a stroke of 258.05 ${\unicode[Times]{x03BC}}\mathrm{m}$ in the Y-direction, and the decoupling rates in two directions are 1.1% and 0.9%, respectively. The average output constant force of the clamp is 37.49 N. The amplification ratios of the bridge-type amplifier and the Scott–Russell amplifier are 7.02 and 3, respectively. Through finite element analysis-based optimization, the constant force stroke of CCFMG is increased from the initial 1.6 to 3 mm.

Enabling High‐Performance Artificial Muscles via a High Strength Fiber Reinforcement Strategy

AbstractCoiled‐polymer‐fiber‐based artificial muscles can provide large contractile actuation stroke. However, it is a challenge to achieve high actuation load and high actuation stroke for artificial muscle simultaneously. Herein, a powerful coiled‐polymer‐fiber‐based artificial muscle with a “rigid‐and‐flexible” structure is fabricated by cotwisting rigid heterocyclic aramid (HA) fibers with flexible silver‐plated nylon (SPN) fibers. The artificial muscle based on coiled HA@SPN fibers can lift a load over 108 MPa with a fast response time of 0.6 s, which is 309 times heavier than the load that human muscle can lift, and generate a work density per temperature of 41.3 J (kg °C)−1. The coiled HA@SPN fiber muscle exhibits high actuation stability of over 30 000 cycles. The coiled HA@SPN fiber muscle can provide a contractile actuation stroke of up to 8.2% and generate an average gravimetric mechanical energy density of 702 J kg−1, which is 18.1 times that of human skeletal muscle (≈38.8 J kg−1). An average contractile power density of 1168 W kg−1 is obtained for coiled HA@SPN fiber muscle, which is 23.4 times that of human skeletal muscle (≈50 W kg−1).

Magnetically and Electrically Responsive Soft Actuator Derived from Ferromagnetic Bimetallic Organic Framework.

The advancement in smart devices and soft robotics necessitates the use of multiresponsive soft actuators with high actuation stroke and stable reversibility for their use in real-world applications. Here, this work reports a magnetically and electrically dual responsive soft actuator based on neodymium and iron bimetallic organic frameworks (NdFeMOFs@700). The ferromagnetic NdFeMOFs@700 exhibits a porous carbon structure with excellent magnetization saturation (166.96 emu g-1 ) which allows its application to a dual functional material in both magnetoactive and electro-ionic actuations. The electro-ionic soft actuator, which is fabricated using NdFeMOFs@700 and PEDOT-PSS, demonstrates 4.5 times higher ionic charge storage capacity (68.21 mF cm-2 ) and has excellent cycle stability compared with the PEDOT-PSS based actuator. Under a low sinusoidal input voltage of 1V, the dual-responsive actuator displays bending displacement of 15.46mm and also generates deflection of 10mm at 50 mT. Present results show that the ferromagnetic bimetallic organic frameworks can open a new way to make dual responsive soft actuators due to the hierarchically porous structures with its high redox activity, superior magnetic properties, and larger electrochemical capacitance. With the NdFeMOFs@700 based soft actuators, walking movement of a starfish robot is demonstrated by applying both the magnetic and electric fields.

Cost Analysis Investigation of Toothed Belt Driven Electromechanical and Pneumatic Long Stroke Actuators

Otomasyon çalışmalarında pnömatik sistemler yaygın olarak kullanılmakla birlikte günümüzde elektromekanik tahrikli sistemlerin kullanımının yaygınlaşmaya başladığı gözlemlenmektedir. Elektromekanik sistemlerin pek çok farklı çeşidi bulunmaktadır. Genellikle servo motorun kontrol edilmesi ile hareket aktarımı sağlanmakta, bilyalı vidalı mil, dişli kayış vb. sistem elemanları ile dönme hareketi doğrusal harekete çevrilmektedir. Kontrol edilebilirliklerinin kolay, konumlama hassasiyetlerinin yüksek olması, uzun yıllar boyunca bakım istememesi gibi avantajlarıyla beraber bu tip sistemlerin kullanıcı tarafından tercih edilmesindeki en büyük tereddüt ilk yatırım maliyetlerinin yüksek olması olarak görünmektedir. Ancak ürün seçiminde ilk yatırım maliyeti ön plana çıkarken enerji tüketimi, bakım gibi parametrelerin de değerlendirilmesinin gerekliliği genellikle ikinci planda kalmaktadır. Bu çalışmada uzun stroklu, milsiz silindirli pnömatik bir sistem ile dişli kayış tahrikli elektromekanik bir sistemin ilk yatırım, bakım ve kullanım ömrü boyunca öngörülen enerji tüketim maliyetleri farklı çalışma senaryoları ile incelenmiş ve karşılaştırmalı olarak değerlendirilmiştir. Yatay yönde hareket eden iki sistemde de eşdeğer yük, strok, yıllık çalışma süresi ve kullanım zamanı dikkate alınarak deneysel çalışmalar ve teorik hesaplamalar yapılarak değerlendirilmiştir. Servo motorun ilk yatırım maliyetinin, pnömatik sistemin besleme basıncının, çevrim sayısının, bekleme süresinin sistemlerin maliyetlendirilmesinde önemli ve dikkate alınması gereken kriterler olduğu görülmüştür.

Development and prototyping of SMA-metamaterial biaxial composite actuators

Shape memory alloys (SMA) are excellent candidates for implementation in actuator systems due to their ability to recover their original shape after high-strain loading through a thermally-induced phase transition. In this work, we propose and develop a novel SMA-metamaterial actuator which is capable of exhibiting a reversible, global elongation in multiple directions induced by the unidirectional contraction upon heating of a single SMA component. This actuator consists of (a) an SMA component, (b) a bias component and (c) the metamaterial geometry, with each component having a distinct function: (a) actuation activation, (b) reversibility of actuation upon deactivation and (c) amplifying and re-directing the uni-directional SMA actuation globally throughout the actuator, respectively. A prototype actuator was designed and tested in various configurations over multiple activation/deactivation cycles in order to demonstrate the functionality and reusability of this system. Furthermore, a theoretical model which predicts the actuation stroke of the system on the basis of the material properties of the SMA and bias components as well as the geometry of the metamaterial system was developed and validated. The findings of this work demonstrate the considerable potential of SMA-metamaterial actuators for implementation in systems requiring a multi-axial actuation output.

Design and fabrication of shape memory alloy based 4D-printed actuator for FWMAV: A performance study

Flapping Wing Micro Aerial Vehicles (FWMAVs) use flapping wings to create lift and thrust, akin to bird flight. In this work, we seek to design and fabricate a Shape Memory Alloy (SMA) based 4D-printed actuator that behaves as a wing structure to achieve the desired flapping action in an FWMAV. The integration of SMA in the static matrix facilitates the desired motion by bending SMA as a response to a stimulus. The properties of SMA such as the work density, stroke angle, etc., are greatly enhanced in contrast to more complex, conventional motor-driven mechanisms. The study includes the investigation of the actuator's performance, which is evaluated using image processing based on parameters such as the stroke angle, actuation speed, and recovery force, and helps in utilizing the actuator based on the needs and demands of specific targeted applications by referring to the baseline data recorded by conducting a series of experiments.

Insect-scale jumping robots enabled by a dynamic buckling cascade

Millions of years of evolution have allowed animals to develop unusual locomotion capabilities. A striking example is the legless-jumping of click beetles and trap-jaw ants, which jump more than 10 times their body length. Their delicate musculoskeletal system amplifies their muscles' power. It is challenging to engineer insect-scale jumpers that use onboard actuators for both elastic energy storage and power amplification. Typical jumpers require a combination of at least two actuator mechanisms for elastic energy storage and jump triggering, leading to complex designs having many parts. Here, we report the new concept of dynamic buckling cascading, in which a single unidirectional actuation stroke drives an elastic beam through a sequence of energy-storing buckling modes automatically followed by spontaneous impulsive snapping at a critical triggering threshold. Integrating this cascade in a robot enables jumping with unidirectional muscles and power amplification (JUMPA). These JUMPA systems use a single lightweight mechanism for energy storage and release with a mass of 1.6 g and 2 cm length and jump up to 0.9 m, 40 times their body length. They jump repeatedly by reengaging the latch and using coiled artificial muscles to restore elastic energy. The robots reach their performance limits guided by theoretical analysis of snap-through and momentum exchange during ground collision. These jumpers reach the energy densities typical of the best macroscale jumping robots, while also matching the rapid escape times of jumping insects, thus demonstrating the path toward future applications including proximity sensing, inspection, and search and rescue.

Theoretical study of the electroactive bistable actuator and regulation methods

ABSTRACT Dielectric elastomer actuators have attracted growing interest for soft robot due to their large deformation and fast response. However, continuous high-voltage loading tends to cause the electric breakdown of the actuator due to heat accumulation, and viscoelasticity complicates precise control. The snap-through bistability of the Venus flytrap is one of the essential inspirations for bionic structure, which can be adopted to improve the shortcoming of dielectric elastomer actuators and develop a new actuation structure with low energy consumption, variable configuration, and multi-mode actuation. Hence, in this paper, the structural design principles of electroactive bistable actuators are first presented based on the total potential energy of the structure. Following that, a feasible design parameter region is provided, the influence of crucial parameters on the actuation stroke, trigger voltage, and actuation charge are discussed. Finally, according to the coupling relationship between the bending stiffness and the bistable property of the actuator, the adjusting methods of bistable actuation are explored. A qualitative experiment was performed to verify the feasibility and correctness of the bistable design methodology and the actuation regulation strategy. This study provides significant theoretical guidance and technical support for developing and applying dielectric elastomer actuators with multi-mode, high-performance, and long-life characteristics.

A Brief Analysis of the Working Load and Stroke of the Linear Actuator for the Passenger Aircraft Cargo Door

Towards the cargo door actuator of the passenger aircraft, the load type during service is analyzed, and the load profile is identified and illustrated. For the door actuation system composed of a rear support beam, linear actuator, door, etc., the theoretical working load and stroke of the actuator are calculated, as well as the load and stroke when the components are elastomers. The comparison results show that the reduction of the door stiffness will increase the actuator load, and the reduction of the rear support beam and actuator stiffness will increase the stroke. This study can provide a reference for engineering problems such as door system stiffness allocation, door opening stroke design, and evaluation.

Effects of temperature on the properties of HL32 oil in the conventional hydraulic actuators

Present study pays more attention to optimize the performance of the hydraulic system by selecting the accurate position of the traditional hydraulic actuators. It was used HL32 as working oil, due to its ability to withstand high temperatures (15–200) °C as well as having the best mechanical properties, since the density and viscosity are the most important factors that are extremely affected on the hydraulic system. Hence, this work examined the effect of the variation kinematic, dynamic viscosity, and the density of HL32 oil on the accurate position of conventional hydraulic actuators. The kinematic and dynamic viscosity was obtained theoretically and experimentally over a wide range of temperatures ranged (20–80) °C. It was found that the percentage error between the theoretical and experimental results ranged (21∗10−6–0.023), respectively. Whereas, the deviation of the results in the actuator stroke displacement were observed 4.8%, 6%, 6.5% and 4.8% for pressure supply of 20, 30, 40 and 50 bar separately.

Tunable Actuation of Humidity-Driven Artificial Muscles via Graphene Nanofillers

Humidity-responsive soft actuators can be driven by external stimuli and provide biomimetic environmental adaptations. Here, we report a humidity-responsive axial soft actuator of sulfonated polyether ether ketone which shows greatly tailorable actuation performance upon embedding graphene nanoplatelets (GNPs). Analysis of the experimental data shows that adding only 0.5 wt % GNP increases the actuation by 50% and provides a maximum actuation stroke of 24% and work capacity of 230 J/kg. In addition, 0.5 wt % GNP facilitates faster actuation, with significantly enhanced rates of both contraction and expansion. However, the addition of 1 wt % GNP slightly decreases the actuation magnitude. The nonmonotonic actuation performance was correlated with ion exchange capacity, water uptake, and GNP dispersion. By utilizing actuation magnitude tunability via GNP, the axial actuators were converted into a walking robot stacked of two active layers consisting of fibers of the same material system. The bilayer robot demonstrated self-crawling and locomotion ability in response to humidity changes. This study shows a uniquely tunable humidity actuator that demonstrates linear and bending actuation.

Silicon-based soft parallel robots 4D printing and multiphysics analysis

Four-dimensional printing has set the stage for a new generation of soft robotics. The applications of rigid planar parallel robotic manipulators are also significant because of their various desirable characteristics, such as lower inertia, higher payload, and high accuracy. However, rigid planar parallel robots are heavy and require different actuators and components. This study introduces a novel technique to produce a light three degrees of freedom soft parallel manipulator at a low cost, which can be stimulated easily. This technique allows researchers to customize the actuator’s design based on the requirement. The robot is made by 3D printing based on fused deposition modelling and a direct ink writing process. The design, development, and additive manufacturing of a soft parallel robot electrothermally driven by a linear silicon-based actuator and polylactic acid parts are presented. Silicon-based soft actuators replace the rigid conventional linear actuators in this study to drive the planar parallel manipulator. The actuation of actuators is conducted using simple heating compared to the conventional rigid actuator. Various heating approaches and configurations are compared and analysed to find the most suitable one for the effective linear stroke of the soft actuator. The finite element model is used to analyse the performance of the electrothermally silicon-ethanol soft actuators in ABAQUS. The kinematics of the planar parallel robotic manipulator are simulated in MATLAB to achieve its workspace. The final soft parallel robot mechanism and the active and passive links are fabricated and tested experimentally.

Triple physically cross-linked hydrogel artificial muscles with high-stroke and high-work capacity

Owing to the high-water content and excellent biocompatibility, polymeric hydrogels are good candidates to mimic natural muscles in biomedical and bioengineering fields, but the low stroke and low work capacity limited them to be used as artificial muscles. Herein, inspired by the ordered structure of skeletal muscles, high performance anisotropic hydrogels comprising of triple physically cross-linked networks are developed by the electrostatic interactions between positively charged tunicate cellulose nanocrystals (TCNC) and –COO− of polymers, hydrophobic association of stearyl methacrylate (SMA) moiety in sodium dodecyl sulfate (SDS) micelles, and –COO−/Fe3+ ionic coordination. The elastic potential energy can be stored in polymeric networks by locking the pre-stretched hydrogel via ionic coordination, which can be released by dissociating the ionic coordination under acidic condition. Based on their excellent mechanical property reinforced by TCNCs, the developed hydrogel artificial muscles exhibit high actuation stroke (75 %) and high-work capacity (210 J kg−1), which are higher than those of skeletal muscles. These hydrogel muscles demonstrated potential for wide applications in being designed as biceps to lift skeleton’s arm and as micromotors to drive boat model under acidic condition because of their high-stroke, high-work capacity and comparable output efficiency with natural muscles.

Disturbance Modeling and Prediction of Closed-Loop Micro-Actuator Stroke Usage in Dual-Stage Hard Disk Drives

Abstract This letter presents a method to model the disturbance environment of a dual-stage hard disk drive (HDD), which is then used to predict the actuator stroke usage (i.e., the range of actuator displacement used) of a closed-loop track-following controller. In particular, a data-driven disturbance modeling approach is proposed and the stochastic interpretation of the H2 norm is used to systematically estimate the micro-actuator (PZT) stroke usage of the HDD controller. Upper- and lower-bound models of the frequency response of the external disturbance environment are used to provide a range of possible stroke usage, which involves a data-driven calibration process. The accuracy of the prediction model is validated in experiments with a controller that differs from the controllers in the calibration data set.

What is the speed limit of martensitic transformations?

ABSTRACT Structural martensitic transformations enable various applications, which range from high stroke actuation and sensing to energy efficient magnetocaloric refrigeration and thermomagnetic energy harvesting. All these emerging applications benefit from a fast transformation, but up to now their speed limit has not been explored. Here, we demonstrate that a thermoelastic martensite to austenite transformation can be completed within 10 ns. We heat epitaxial Ni-Mn-Ga films with a nanosecond laser pulse and use synchrotron diffraction to probe the influence of initial temperature and overheating on transformation rate and ratio. We demonstrate that an increase in thermal energy drives this transformation faster. Though the observed speed limit of 2.5 × 1027 (Js)1 per unit cell leaves plenty of room for further acceleration of applications, our analysis reveals that the practical limit will be the energy required for switching. Thus, martensitic transformations obey similar speed limits as in microelectronics, as expressed by the Margolus – Levitin theorem.

Actuation performance of machined helical springs from NiTi shape memory alloy

Machined helical springs were designed and fabricated from NiTi shape memory alloy tube stock by cutting helical slots to make the coils, which provided them with high design flexibility and actuation potential. The springs were then subjected to isothermal tensile testing at temperatures of 20°C and 80°C, the experimental data showed that they could generate more than 50% actuation stroke at the applied force of 300 N. A material model was introduced to describe the thermally-induced actuation behavior of the machined NiTi spring. Finite element simulation of the springs was carried out to investigate the effects of geometries and applied loads on the actuation performance. With increasing applied load, the actuation stroke and transformation temperature increased as well, indicating more actuation potential at high loads. The actuation stroke was positively correlated to the outer diameter and the cross-sectional aspect ratio, negatively correlated to the cross-sectional area, and independent of the coil pitch. A variable-sweep wing actuated by two antagonistic machined springs was designed and numerically analyzed, the actuator could generate a steady cyclic motion up to 40 mm and allowed the swept-back angle of the wings to be continuously varied from zero to 90 degrees.

Case Study of a MEMS Snap-Through Actuator: Modeling and Fabrication Considerations

MEMS actuators rely on the deformation of silicon structures. Using dimensions smaller than dozens of micrometers reveals that the micro-electro-mechanical systems (MEMS) actuators are affected by fabrication inaccuracies, leading to hardly predictable forces and/or actuation results. In this paper, MEMS bistable buckled beam actuators are presented. A series of structures based on pre-shaped buckled beams of lengths ranging from 2 to 4 mm, constant width of 5 μm and actuation stroke ranging from 20 to 100 μm was fabricated. Experimental data show a significant difference with predictions from a conventional analytical model. The model commonly used for buckled beams design assumes a rectangular beam section, but it is not the case of the fabricated beams. Furthermore, only symmetric buckling modes (mode 1, mode 3…) are supposed to exist during snap-through. In this paper, new analytical models have been developed on the basis of the models of the literature to consider the effective beam shape. The first improved analytical model enabled prediction of the MEMS buckled beams mechanical behavior in a 30% margin on the whole range of operation. A second model has been introduced to consider both the effective shape of the beam and centro-symmetric buckling modes. This refined model exhibits the partial suppression of buckling mode 2 by a central shuttle. Therefore, mode 2 and mode 3 coexist at the beginning and the end of snap-through, while mode 3 quickly vanishes due to increasing rotation of the central shuttle to leave exclusive presence of mode 2 near the mid-stroke. With this refined model, the effective force-displacement curve can be predicted in a margin reduced to a few percentages in the center zone of the response curve, allowing the accurate prediction of the position switch force. In addition, the proposed model allows accurate results to be reached with very small calculation time.