Axial Actuator Research Articles

Determination of the nonlinear thermal expansion coefficient of an epoxy used as an expander and its effects over a Fabry-Perot cavity filled with a polymer

In this work, the nonlinear thermal expansion coefficient (TEC) of epoxy clay is determined by means of monitoring the changes induced in the optical thickness of a Fabry-Perot cavity filled with polymer. Here, the epoxy is used to form a long sleeve that holds all elements that form a multilayer interferometric fiber tip filter. Additionally, it is shown that this sleeve acts as an axial strain actuator to change the thickness of a polymer cavity in the order of a few microns. This allows the filter’s spectral fringe pattern to be tuned by several orders of interference, inducing considerable changes in its free spectral range (FSR). Furthermore, it is shown that this filter design has an additional advantage that makes it possible to determine either the TEC or the thermo-optic coefficient (TOC) of another layer material of the filter by using the same measured spectra. Here, as a proof of principle, experimental results of the TEC of silicon were estimated, showing that they are quite close to what was reported in the literature and, therefore, that these can be used for reference purposes. Finally, it is demonstrated that by considering the determined TEC of the epoxy, the overall filter spectrum can be very well modeled, and its main features can be explained for a wide range of temperatures.

Experimental evaluation of accuracy and efficiency of two control strategies for a novel foot commanded robotic laparoscope holders with surgeons

The implementation of a laparoscope-holding robot in minimally invasive surgery enhances the efficiency and safety of the operation. However, the extra robot control task can increase the cognitive load on surgeons. A suitable interface may simplify the control task and reduce the surgeon load. Foot interfaces are commonly used for commanding laparoscope-holding robots, with two control strategies available: decoupled control permits only one Cartesian axis actuation, known as decoupled commands; hybrid control allows for both decoupled commands and multiple axes actuation, known as coupled commands. This paper aims to determine the optimal control strategy for foot interfaces by investigating two common assumptions in the literature: (1) Decoupled control is believed to result in better predictability of the final laparoscopic view orientation, and (2) Hybrid control has the efficiency advantage in laparoscope control. Our user study with 11 experienced and trainee surgeons shows that decoupled control has better predictability than hybrid control, while both approaches are equally efficient. In addition, using two surgery-like tasks in a simulator, users’ choice of decoupled and coupled commands is analysed based on their level of surgical experience and the nature of the movement. Results show that trainee surgeons tend to issue more commands than the more experienced participants. Single decoupled commands were frequently used in small view adjustments, while a mixture of coupled and decoupled commands was preferred in larger view adjustments. A guideline for foot interface control strategy selection is provided.

X-crossing pneumatic artificial muscles.

Artificial muscles are promising in soft exoskeletons, locomotion robots, and operation machines. However, their performance in contraction ratio, output force, and dynamic response is often imbalanced and limited by materials, structures, or actuation principles. We present lightweight, high-contraction ratio, high-output force, and positive pressure-driven X-crossing pneumatic artificial muscles (X-PAMs). Unlike PAMs, our X-PAMs harness the X-crossing mechanism to directly convert linear motion along the actuator axis, achieving an unprecedented 92.9% contraction ratio and an output force of 207.9 Newtons per kilogram per kilopascal with excellent dynamic properties, such as strain rate (1603.0% per second), specific power (5.7 kilowatts per kilogram), and work density (842.9 kilojoules per meter cubed). These properties can overcome the slow actuation of conventional PAMs, providing robotic elbow, jumping robot, and lightweight gripper with fast, powerful performance. The robust design of X-PAMs withstands extreme environments, including high-temperature, underwater, and long-duration actuation, while being scalable to parallel, asymmetric, and ring-shaped configurations for potential applications.

Разработка контроллера электромеханического датчика положения

Electromechanical position sensors, including sine-cosine rotary transformers, compared to sensors based on other physical principles, have greater reliability, a simple design and resistance to difficult operating conditions. This makes them attractive for use in various motion control systems that require measurement of the position of the actuator axis. However, the use of such sensors requires special hardware and software devices – controllers that ensure their operation. This article is devoted to the development of such a controller, which generates, captures, and processes signals of the sine-cosine rotary transformer. When developing the controller of the sine-cosine rotary transformer, methods of system analysis of electrical, electromagnetic and information processes and means of their implementation, methods of software development, as well as methods of experimental research were applied. A description of the controller of a sine-cosine rotary transformer in phase mode is given, taking into account the hardware and computing resources of the microcontroller which implements it. At the same time, physical processes are correlated with information processes associated with the generation, capture and procession of signals. The reasons for the decrease in the position measurement accuracy are revealed. Various technical solutions have been applied to take into account and eliminate them. Among them are the coordination of physical and information processes, taking into account the execution time of calculations by the microcontroller, analysis of the correctness of the position measurement results and their smoothing according to moving average method. The controller software has been developed, which can serve as a typical element for microprocessor-based control systems. Experimental results are obtained, illustrating the achievement of the development result. Application of various technical solutions has made it possible to ensure the accuracy of position measurement up to a tenth of a degree with a high intensity of information updating. As a result of the study, a detailed and comprehensive solution of the developing a controller for a sine-cosine rotating transformer problem is given, which is the scientific and practical value of the materials presented in the article. The results obtained can be applied in various motion control systems and serve as the basis for the development of controllers for various electromechanical position sensors.

Development of the CYCLOPS CubeSat payload

The number of CubeSat satellites launched has been increasing over the past decades. These satellites have a number of advantages: short development time, low cost, possibility of modifications for certain scientific tasks and testing of technical solutions and new developments. This article describes payloads of a small spacecraft: CubeSat 3U CYCLOPS designed by D.F.Ustinov Baltic State Technical University "Voenmeh within grant under Space-Pi program. The purpose of the study: is to create, test and study the performance of payload modules of the vehicle, built using commercially available components, under space flight conditions. The text describes the structure of interaction between the payload and the OrbCraft-Pro 3U platform from Sputnix LLC. The process of development of payload control board is considered. The control system software for mechatronic and multi axis actuator modules with logging and error correction is described. Ln addition to the above-mentioned modules, the payload control system was also developed to carry out a series of experiments in die presence of a small spacecraft in orbit. The paper explains how the spacecraft communicates with the ground via special software Houston control application and Houston Telnet. The results describe tests performed on the mechanical components of the spacecraft. Examples of telemetry packets received from on-board the spacecraft are given. The article also reflects further plans for the project and the prospects of using the developed hardware for implementation in large-scale space systems and complexes. Also as part of the project students were able to gain engineering experience in the development of devices designed to work in space conditions.

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.

Development of an Earthworm-Based Intestinal Soft Robot Equipped with a Gripper

An endoscopy is a tool that is used to examine the interior of a hollow organ or cavity of the body by inserting directly into the organ. However, intestinal endoscopy is not friendly to patients due to discomfort, and it can easily cause intestinal damage or even perforation due to the use of the rigid materials of the endoscopy. Here, we provide an earthworm-based intestinal soft robot equipped with a gripper for application on intestinal exams or surgery. The intestinal soft robot is composed of a frontal radial actuator, a central axial actuator, a rear radial actuator and a gripper. The first three actuators drive the robot to move freely in some specific pipes by altering its own deformation, and the gripper, fixed at the end of the frontal radial actuator, is used to pick up “foreign bodies” into and out of the pipes for the purpose of intestinal applications. The different experiments validated that the intestinal soft robot could move forward and backward autonomously in a rigid pipe, a flexible pipe, and a mucus-containing pipe and could extract objects from these pipes. The ultimate weight that the intestinal soft robot extracts is up to 220 g, and the maximum moving speed is 12.0 cm/min in the rigid pipe. This intestinal soft robot is non-destructive to the operating environment, providing a friendly and novel method for the application of intestinal diseases.

Design of in-plane torsion experiment to characterize anisotropic plasticity and fracture under simple shear

A novel experimental set-up is proposed to perform in-plane torsion experiments on grooved disk specimens. As compared to previously proposed systems, an enhanced clamping system is introduced to enable the torsion testing of high strength materials such as dual phase steels. The clamping is achieved without applying the clamping pressure through an axial actuator. Instead a custom-made washer-nut system is used which allows for the monitoring of the entire specimen front surface with cameras. Experiments are performed on three different steels (DC01, DP980, AISI301) to demonstrate the validity of the technique for measuring the stress–strain curve for strains of up to 2, for strain rate jump testing, for cyclic loading and for fracture testing. In particular, the demonstration experiments elucidate the importance of full field strain measurements during in-plane torsion. The strain fields vary along the gage section circumference in a periodic manner that is related to the anisotropy of the tested material. This important observation is confirmed through a finite element study covering a wide range of anisotropic Hill’48 materials with non-associated plastic flow.

Offset-Free Model Predictive Control for a cone-shaped active magnetic bearing system

Active Magnetic Bearings (AMB) are mechatronic systems that support a rotating shaft using magnetic levitation. The standard AMB architecture includes two radial actuators and one for the axial direction. An alternative geometry with cone-shaped magnetic cores allows for a more compact layout without a dedicated axial actuator. However, this configuration reduces the axial force generation capability and requires a more complex control architecture due to the inherent coupling of the axial and radial control actions. When using decentralized control, effective handling of the coil current limitations together with the axial disturbance rejection is difficult to achieve. In this context, the present paper demonstrates the benefits of applying Offset-Free Model Predictive Control (OF-MPC) for a cone-shaped AMB system. A procedure for the overall design is presented and supported by the experimental work conducted in a scaled machine that reproduces an on-board turbo-compressor unit for an aircraft. The modeling of the system is described together with the design of the OF-MPC in all its parts: general control architecture, disturbance model and observer design, target calculation and control problem formulation. An OF-MPC variant with reduced control horizon is proposed and implemented in real time. Experimental results demonstrate that the prototype is compliant with application-specific stability requirements from the ISO 14839-3:2006 standard. In addition, experiments show that OF-MPC outperforms decentralized PID controllers in terms of axial disturbance rejection. OF-MPC yields a favorable constrained optimal control technique for cone-shaped AMBs because intrinsic coupling and current saturation are optimally handled by the controller.

Control of an over-actuated spacecraft using a combination of a fluid actuator and reaction wheels

In 2017, Technische Universität Berlin (TU Berlin) has launched the first space-rated fluid-dynamic actuator (FDA) on the TechnoSat mission. This type of actuator is unique with respect to its dynamic properties, as it offers a very high torque but limited angular momentum storage capabilities in comparison to reaction wheels (RWs). In combination with the tetrahedron RW assembly featured on the spacecraft, a unique combination of attitude control actuators has been formed. The spacecraft axis parallel to the FDA is over-actuated, featuring control actuators of contrasting nature which offers novel options in terms of spacecraft operations. However, with the camera axis on TechnoSat being aligned parallel to the actuator’s axis of rotation, there is limited operational use to this setup.In July 2019, TU Berlin launched Berlin Experimental and Educational Satellite 9 (BEESAT-9) – the first CubeSat featuring a set of three orthogonal RWs and a single picosatellite fluid-dynamic actuator (pFDA) for attitude control. The camera axis of BEESAT-9 is perpendicular to the actuator axis, and therefore allows the demonstration of the proposed novel modes of operation. Among the proposed modes is an artificial increase of the swath and the acquisition of stereo images of multiple, successive targets on the ground. Crucial to these operation scenarios is the control allocation between the RW assembly and the single pFDA.This paper first introduces the spacecraft and describes the proposed novel modes of operation that are enabled by the actuator combination realized on BEESAT-9, followed by a review of the state of the art of control allocation for over-actuated spacecraft. The main part of the paper comprises a description of the implementation of the dynamics models of the attitude control actuators and spacecraft, followed by a description of the implemented high-level control laws and control allocation methods. Finally, simulation results for the artificial swath increase and the single spacecraft stereo imaging mode are appended and discussed.

Capsule robot for gut microbiota sampling using shape memory alloy spring.

Human gut microbiota can provide lifelong health information and even influence mood and behaviour. We currently lack the tools to obtain a microbial sample, directly from the small intestine, without contamination. Shape memory alloy springs are used in concentric configuration to develop an axial actuator. A novel design of sampling mechanism is fabricated for collecting the sample from the gut. Storage chamber (500 µl) is used to protect the sample from downstream contamination. The developed actuator occupies a small space (5 × Ø5.75 mm) and produces sufficient output force (1.75 N) to operate the sampling mechanism. A non-invasive capsule robot was tested ex vivo on the animal intestine, and it captured an average of 134 µl content which was sufficient for microbiome assessment. Laboratory testing revealed that the collected sample had an amino acid signature indicative of microbiota, mucus and digesta, which provided a proof of concept for the proposed design.

Force Analysis of Single Axis Actuator Used in Active Magnetic Bearing (AMB)

This paper presented the force analysis of single coil actuator for Active Magnetic Bearing (AMB) system. Actuator is the most important segment of AMB system. In the bearing system rotor should be levitate before rotation. For the levitation required force is generated by actuator. For the specific structure attractive force is different. These force analysis is done in this manuscript. Depending upon the force appropriate structure can be used for design a perfect AMB system. Here force analysis is performed in ANSYS Maxwell software and characteristics graphs are presented in 2D and three dimensional plots are constructed using MATLAB for the better observation.

Modeling and simulation of trajectory smoothing and feedrate scheduling for vibration-damping CNC machining

The mathematical models of tool path smoothing and feedrate scheduling in Computer Numerical Control (CNC) system are critical for high-precision manufacture. Inthe existing studies, G2/G3 (curvature-continuous/-smooth) trajectory smoothing, and jerk-limited/-continuous feedrate scheduling schemes have been developed. Nonetheless, there are exist some requirements that cannot be satisfied simultaneously, including confined chord error, G01 points interpolated, analytical curvature extremum, real-time performance, kinematic time-optimality, and the smoothness of tool-path and feedrate profile. Recently the scholars found the potentials of the tool path with high-order geometric continuity and the feedrate with high-order kinematic constraints, respectively in increasing the smoothness of tool path and reducing the impact caused by axis actuators during the process. Aiming to reduce the vibration and guarantee high machining efficiency, this work proposes G4 (curvature-variation-smooth) interpolative trajectory model with confined chord error and analytical curvature extrema for trajectory smoothing, and employs jerk-smooth (jerk-differentiable) feedrate mode to perform time-optimal feedrate scheduling. Finally, a real-time tool path processing strategy under various geometric and kinematic constraints is developed. The simulation shows approximation error, curvature extrema, and feedrate fluctuation are reduced compared with G2 transition and G3 interpolation schemes. The experimental results demonstrate advantages of the proposed method in vibration damping, surface quality, compared with the previous works.

A strategy for designing of customized electromechanical actuators of blood pumps.

Congestive heart failure is a pathology of global incidence that affects millions of people worldwide. When the heart weakens and failsto pump blood at physiological rates commensurate with the requirements of tissues, two main alternatives are cardiac transplant and ventricular assist devices (VADs). This article presents the design strategy for development of a customized VAD electromagnetic actuator. Electromagnetic actuator is a brushless direct current motor customized to drive thepump impeller by permanent magnets located in rotor-stator coupling. In this case, ceramic pivot bearings support theVAD impeller. Electronic circuitry controls rotation switching current in stator coils. The proposed methodology consisted of analytical numerical design, tridimensional computational modeling, numerical simulations using Maxwell software, actuator prototyping, and validation inthedynamometer. The axial flow actuator was chosen by its size and high power density compared to theradial flow type. First step consisted of estimating the required torque to drive thepump. Torque was estimated at 2100rpm and mean current of 0.5A. Numerical analysis using finite element method mapped vectors and fields to build stator coils and actuator assemblage. After tests in the dynamometer, experimental results werecompared with numerical simulation and validated the proposed model. In conclusion, the proposed methodology for designing of VAD electromechanical actuator was considered satisfactory in terms of data consistency, feasibility, and reliability.

Novel Design and Validation of a Micro Instrument in an Ear Grommet Insertion Device

An automated surgical device, the ventilator tube applicator (VTA), enables a grommet insertion surgery for patients with otitis media with effusion (OME) to be completed in a short time automatically and precisely, eliminating the use of general anesthesia (GA) typically required in such procedure. However, its current design limits the usefulness of the device as it is restricted by the properties of the tympanic membrane (TM), such as angle, thickness, and strength. Therefore, a novel design was conceptualized and the insertion control algorithm was improved to overcome the current challenges of the VTA. This innovative cover-cutter instrument design allows three-dimensional (3D) motion on an oblique surface using a single axis actuator. Experimental results on mock membranes showed great improvements in terms of robustness and success rate. The new design allowed the procedure to be performed on wider range of TM angles and hence increased the effectiveness of VTA. Grommet insertion force was reduced by an average of 66%, and the overall peak force reduced by an average of 14%. Finite element (FE) analysis on a cadaveric TM model further validated the usefulness of the cover-cutter instrument, and showed some interesting insights in the grommet insertion process.

Morphological change in peristaltic crawling motion of a narrow pipe inspection robot inspired by earthworm’s locomotion

Infrastructure pipes require inspection in order to prevent accidents. However, it is difficult to inspect a 1-in-diameter gas pipe because it is long, narrow and complicated. Therefore, an earthworm-type robot was developed to inspect this 1-in pipe. The robot moved by peristaltic crawling with pneumatic artificial muscles and displayed its suitability as a 1-in pipe inspection robot in experiments. However, its speed was extremely slow to be practically utilized. A major cause for this is the small distance covered in a single motion of the robot. Therefore, in this study, we developed an axial extension actuator to increase the moving distance of the robot in a single motion. Furthermore, we installed this new actuator on our robot and made it possible for the robot to change the morphological motion in peristaltic crawling. The experiments with straight and elbow pipes ascertained the importance of morphological change in peristaltic crawling for increasing the speed of the robot. Moreover, in a continuous elbow pipe, the velocity of the proposed robot was 5.5 mm/s, which is 1.3 times faster than that of the conventional robot. Consequently, we confirmed that the speed of the proposed robot was sufficiently fast for inspecting a 1-in pipe.

Elastic linear analysis of CNC micro blanking machine using finite element method

This study has developed Micro Punch CNC Machine design by optimizing the function of the actuator axis implemented to make an implant plate. This research aimed to plan the simulation of CNC machine construction strength using the blanking operation application. Finite element method (FEM) was used to analyze the material strength. The research results showed that the maximum stress occurring at the punch tools was 428.17 MPa with the thickness of 0.6 mm and the maximum thickness of workpiece allowed in making the implant plate was 1.4 mm with the maximum stress of 999.09 MPa. The obtained data indicate that the most effective material to be used as the material construction in CNC micro blanking machine is St42. This case is proven by the result of the power to resist the stress and the value of maximum deformation from the comparison of both materials.

Investigating the Influence of Geological Heterogeneity on Capillary Trapping of Buoyant CO2 Using Transmitted-light Flow Visualization Experiments

Small scale heterogeneity characteristic of clastic formations has been well known to affect CO2 migration pathways during geologic carbon sequestration. Especially far field from the injection sites, when buoyancy and capillary forces take over from the injection pressure gradients, the effects of such geological features on the CO2 plume movement become compounded. Numerical simulations have established that accumulation and trapping of the buoyant plume is primarily due to the contrast in capillary entry pressures of different rock layers. Capillary trapping can help maximize the storage capacity of reservoirs and hence it is essential to understand the dynamics of CO2 movement and trapping under the influence of small scale heterogeneity and quantify its effects. In this work we propose buoyancy driven migration experiments and simulations conducted at the meter scale using glass beads packed in a quasi 2D glass cell. Using a combination of two linear axis actuators, we demonstrate an automated glass bead filler system that can generate 2D heterogeneous structures in a reproducible manner. A fluid pair that mimics the phase densities and viscosities of CO2-Brine at reservoir pressures and temperatures is employed. Light transmission technique is used for visualization, and to calibrate and quantify saturation of the trapped non-wetting fluid during the experiments. Invasion Percolation is used to simulate the buoyancy driven flow. With the ability to generate different types of heterogeneous structures in a reproducible manner, and by comparing experiments and simulations, a systematic investigation of the effect of heterogeneity on capillary trapping becomes possible.

The axoneme, a biological template to design a swell energy recovery system

The axonemal micro-machinery, the axial skeleton and actuator of cilia and flagella of eukaryotic cells, is able to bend and twist and generates wave trains. We already demonstrated that it can be the template to construct an active trunk robot (Cibert 2013 Bioinspir. Biomim. 8 026006). The work presented in this paper describes how the axonemal model can also be useful to design worm shaped devices to convert swell energy into usable energy such as electricity. Using dynamic simulation we have designed three models either very close to the biological machinery or being a reasonable interpretation of its functioning principles. Their main advantage as compared with another existing device, Pelamis, is the additional twist degree-of-freedom that gives interesting properties to the system.

Characterisation of plasma synthetic jet actuators in quiescent flow

An experimental characterisation study of a large-volume three-electrode plasma synthetic jet actuator (PSJA) is presented. A sequential discharge power supply system is used to activate the PSJA. Phase-locked planar particle image velocimetry (PIV) and time-resolved Schlieren imaging are used to characterise the evolution of the induced flow field in quiescent flow conditions. The effect of orifice diameter is investigated. Results indicate three distinct features of the actuator-induced flow field. These are the initial shock waves, the high speed jet and vortex rings. Two types of shock waves with varied intensities, namely a strong shock wave and a weak shock wave, are issued from the orifice shortly after the ignition of the discharge. Subsequently, the emission of a high speed jet is observed, reaching velocities up to 130 m s−1. Pronounced oscillation of the exit velocity is caused by the periodical behaviour of capacitive discharge, which also led to the formation of vortex ring trains. Orifice diameter has no influence on the jet acceleration stage and the peak exit velocity. However, a large orifice diameter results in a rapid decline of the exit velocity and thus a short jet duration time. Vortex ring propagation velocities are measured at peak values ranging from 55 m s−1–70 m s−1. In the case of 3 mm orifice diameter, trajectory of the vortex ring severely deviates from the actuator axis of symmetry. The development of this asymmetry in the flow field is attributed to asymmetry in the electrode configuration.