Actuators — Open Access Journal

Single-port laparoscopic surgery (SLS), which utilises one major incision, has become increasingly popular in the healthcare sector in recent years. However, this technique suffers from several problems particularly the inability of current SLS instruments to provide the optimum angulation that is required during SLS operations. In this paper, the development of a novel latching-type electromagnetic actuator is reported, which is aimed to enhance the function of SLS instruments. This new actuator is designed to be embedded at selected joints along SLS instruments to enable the surgeon to transform them from their straight and slender shape to an articulated posture. The developed electromagnetic actuator is comprised of electromagnetic coil elements, a solid magnetic shell, and a permanent magnet used to enhance the magnetic field interaction along the force generation path and also to provide the latching effect. In this investigation, electromagnetic finite element analyses were conducted to design and optimise the actuator’s electromagnetic circuit. In addition, the performance of the new actuator was numerically and experimentally determined when output magnetic forces and torques in excess of 9 N and 45 mNm, respectively together with an angulation of 30° were achieved under a short pulse of current supply to the magnetic circuit of the actuator. Full article

Smart and soft electroactive polymer actuators as building blocks for soft robotics have many beneficial properties that could make them useful in future biomimetic and biomedical applications. Gelatin—a material exploited for medical applications—can be used to make a fully biologically benign soft electroactive polymer actuator that provides high performance and has been shown to be harmless. In our study, these polypyrrole-gelatin trilayer actuators with choline acetate and choline isobutyrate showed the highest strain difference and highest efficiency in strain difference to charge density ratios compared to a reference system containing imidazolium-based ionic liquid and a traditional polyvinylidene fluoride (PVdF) membrane material. As neither the relative ion sizes nor the measured parameters of the ionic liquids could explain their behavior in the actuators, molecular dynamics simulations and density functional theory calculations were conducted. Strong cation-cation clustering was found and the radial distribution functions provided further insight into the topic, showing that the cation-cation correlation peak height is a good predictor of strain difference of the actuators. Full article

With the rising demand for energy efficiency, displacement-controlled or so-called pump-controlled systems have become an attractive research topic for applications in construction machinery and other off-road vehicles. Pump-controlled systems can be implemented with electro-hydrostatic actuators as electro-hydraulic zones, which are located next to the end actuator as a replacement for the traditional valve-controlled hydraulic actuation systems. In this paper a 9-tonne class excavator is utilized as a study case. A mathematical model of the conventional machine, validated with tests carried out on both the excavator and the single hydraulic components, was previously developed within the Simcenter AMESim^© environment. This mathematical model was modified with electric components for simulating a zonal hydraulics excavator and compared with a conventional load sensing (LS) machine. The energy efficiencies of both the LS circuit and the new solution were evaluated for typical duty cycles, pointing out the obtainable energy efficiency improvements, which were mainly due to the absence of the directional valves and pressure compensators. The results also point out the effect of the pipe losses when the circuit layout requires the pipe for connecting the pump with the actuator; moreover, the effect of a diesel engine downsizing on the energy saving was evaluated. Full article

Improved management and impermeability of refrigerants is a leading solution to reverse global warming. Therefore, crank-driven reciprocating refrigerator compressors are gradually replaced by more efficient, oil-free and hermetic linear compressors. However, the design and operation of an electromagnetic actuator, fitted on the compression requirements of a reciprocating linear compressor, received limited attention. Current research mainly focuses on the optimisation of short stroke linear compressors, while long stroke compressors benefit from higher isentropic and volumetric efficiencies. Moreover, designing such a system focuses mainly on the trade-off between number of copper windings and the current required, due to the large computational cost of performing a full geometric design optimisation based on a Finite Element Method. Therefore, in this paper, a computationally-efficient, multi-objective design optimisation for six geometric design parameters has been applied on a solenoid driven linear compressor with a stroke of 44.2 mm. The proposed multi-fidelity optimisation approach takes advantage of established models for actuator optimisation in mechatronic applications, combined with analytical equations established for a solenoid actuator to increase the overall computational efficiency. This paper consists of the multi-fidelity optimisation algorithm, the analytic model and Finite Element Method of a solenoid and the optimised designs obtained for optimised power and copper volume, which dominates the actuator cost. The optimisation results illustrate a trade-off between minimising the peak power and minimising the volume of copper windings. Considering this trade-off, an intermediate design is highlighted, which requires 33.3% less power, at the expense of an increased copper volume by 5.3% as opposed to the design achieving the minimum copper volume. Despite that the effect of the number of windings on the input current remains a dominant design characteristic, adapting the geometric parameters reduces the actuator power requirements significantly as well. Finally, the multi-fidelity optimisation algorithm achieves a 74% reduction in computational cost as opposed to an entire Finite Element Method optimisation. Future work focuses on a similar optimisation approach for a permanent magnet linear actuator. Full article

Giant magnetostrictive materials (GMMs) have broad application prospects in the field of servo valves, but the giant magnetostrictive actuator (GMA) has problems such as large loss and severe heat generation, which affect the output effect and accuracy. To solve these problems, this paper designs a stacked giant magnetostrictive actuator (SGMA) and analyzes the magnetic circuit and magnetic field distribution of the SGMA. Based on the magnetic field analysis and the Jiles–Atherton model, we analyze the SGMA magnetization model, simplify the traditional model, and give a solution for the simplified model using the Runge–Kutta method. We analyze the eddy current loss of the SGMA, and according to Bessel’s equation and the Kelvin function, we calculate the relationship among eddy current loss, GMM rod radius, and magnetic field frequency. By analyzing the inherent hysteresis of GMMs, a hysteresis loss model of the SGMA is established in this paper. We also calculate the coil impedance and obtain the coil loss model. Based on the loss model, the SGMA cooling system is designed. Based on the above analysis, we design a SGMA prototype, set-up the corresponding experimental platform, and conduct the necessary experiments. The experimental results show that the SGMA responds well to different signals, but as frequency increases, attenuation, deformation, and hysteresis become more pronounced, which verifies the amplitude and phase changes caused by various losses in the theoretical analysis. The experiment also observes the temperature rise of the oil-cooled SGMA at different frequencies, indicating that the cooling system can effectively control the temperature change of the SGMA, which validates the foregoing analysis. Full article

This paper proposes an improved version of the play model for capturing the frequency-dependent hysteresis of a bimorph piezoelectric actuator that includes odd harmonic oscillation and interleaved hysteresis. The proposed model used a single mathematical structure to capture the changes in the actuator response observed with the increase in the input signal frequency. The refinements on the structure of the original play model for capturing the peculiar behavior of the bimorph piezoelectric actuator have been addressed in detail. The parameter identification has been conducted extensively for a range of 1 Hz to 110 Hz, which exceeds the resonance frequency specified by the manufacturer of the actuator. Improved modeling accuracy was confirmed as compared with our previous enhanced Bouc–Wen model based on the calculation of the fitness index. We also attempted to synthesize a hysteresis compensator based on direct inverse multiplication; the results of the experimental validation of the proposed control system are disclosed. Full article

The development and validation of prognostic algorithms and digital twins for Electromechanical Actuators (EMAs) requires datasets of operating parameters that are not commonly available. In this context, we are assembling a test bench able to simulate different operating scenarios and environmental conditions for an EMA in order to collect the operating parameters of the actuator both in nominal conditions and under the effect of incipient progressive faults. This paper presents the design and manufacturing of a planetary gearbox for the EMA test bench. Mechanical components were conceived making extensive use of Fused Deposition Modelling (FDM) additive manufacturing and off-the-shelf hardware in order to limit the costs and time involved in prototyping. Given the poor mechanical properties of the materials commonly employed for FDM, the gears were not sized for the maximum torque of the electric motor, and a secondary torque path was placed in parallel of the planetary gearbox to load the motor through a disc brake. The architecture of the gearbox allowed a high gear ratio within a small form factor, and a bearingless construction with a very low number of moving parts. Full article

In new-generation soft robots, the actuation performance can be increased by using multiple materials in the actuator designs. However, the lifetime of these actuators is often limited due to failure that occurs at the weak multi-material interfaces that rely almost entirely on physical interactions and where stress concentration appears during actuation. This paper proposes to develop soft pneumatic actuators out of multiple Diels–Alder polymers that can generate strong covalent bonds at the multi-material interface by means of a heat–cool cycle. Through tensile testing it is proven that high interfacial strength can be obtained between two merged Diels–Alder polymers. This merging principle is exploited in the manufacturing of multi-material bending soft pneumatic actuators in which interfaces are no longer the weakest links. The applicability of the actuators is illustrated by their operation in a soft hand and a soft gripper demonstrator. In addition, the use of Diels–Alder polymers incorporates healability in bending actuators. It is experimentally illustrated that full recovery of severe damage can be obtained by subjecting the multi-material actuators to a healing cycle. Full article

This article presents the development of a self-bending contraction actuator (SBCA) through the analysis of its structure, kinematics, and torque formulas, and then explores its applications. The proposed actuator has been fabricated by two methods to prove the efficiency of the human body inspiration, which represents the covering of human bones by soft tissues to protect the bone and give the soft texture. The SBCA provides bending behaviour along with a high force-to-weight ratio. As with the simple pneumatic muscle actuator (PMA), the SBCA is soft and easy to implement. Both the kinematics and the torque formula presented for the SBCA are scalable and can be used with different actuator sizes. The bending actuator has been tested under an air pressure of up to 500 kPa, and the behaviour of its bending angle, parameters, dimensions, and the bending torques have been illustrated. On the other hand, the experiments showed the efficient performances of the actuator and validate the proposed kinematics. Therefore, the actuator can be used in many different applications, such as soft grippers and continuum arms. Full article

Chopsticks are a popular tool used every day by 1.5 billion people to pick up pieces of food of different sizes and shapes. Given that the use of chopsticks requires sophisticated muscle control, they are difficult to use for unskilled people. In this study, a chopstick robot that uses a new soft actuator was developed. Firstly, we developed an X-shaped soft actuator and tested its performance. When a voltage was applied to the actuator, the gap in the X shape was reduced by the resulting electrostatic force. Conversely, when the power was turned off, the actuator recovered its original shape owing to the elasticity of its material. We attached the X-shaped soft actuator between the chopsticks. The chopstick robot, controlled by the input voltage, can pick up various objects in the switched-on state and is able to release them when switched off. We tested the performance of the chopstick robot and analyzed the forces acting on the chopsticks. The robot can be used for picking up various objects. Moreover, the X-shaped actuator can be adapted for use in various studies, through different shapes and configurations. Full article

Uncertainty caused by a parameter measurement error or a model error causes difficulties for the implementation of the control method. Experts can divide the uncertain system into a definite part and an uncertain part and solve each part using various methods. Two uncertainty problems of the control system arise: problem A for the definite part—how does one find out the optimal number and position of actuators when the actuating force of an actuator is smaller than the control force? Problem B for the uncertain part—how does one evaluate the effect of uncertainty on the eigenvalues of a closed-loop control system? This paper utilizes an interval to express the uncertain parameters and converts the control system into a definite part and an uncertain part using interval theory. The interval state matrix is constructed by physical parameters of the system for the definite part of the control system. For Problem A, the paper finds out the singular value element sensitivity of the modal control matrix and reorders the optimal location of the actuators. Then, the paper calculates the state feedback gain matrix for a single actuator using the receptance method of pole assignment and optimizes the number and position of the actuators using the recursive design method. For Problem B, which concerns the robustness of closed-loop systems, the paper obtains the effects of uncertain parameters on the real and imaginary parts of the eigenvalues of a closed-loop system using the matrix perturbation theory and interval expansion theory. Finally, a numerical example illustrates the recursive design method to optimize the number and location of actuators and it also shows that the change rate of eigenvalues increases with the increase in uncertainty. Full article

In mobile devices, the screen size limits conveyance of immersive experiences; haptic feedback coupled with visual feedback is expected to have a better effect to maximize the level of immersion. Therefore, this paper presents a miniature tunable haptic stylus based on magnetorheological (MR) fluids to provide kinesthetic information to users. The designed stylus has a force generation, force transmission, and housing part; moreover, in the stylus, all three operating modes of MR fluids contribute to the haptic actuation to produce a wide range of resistive force generated by MR fluids in a limited size, thereby providing a variety of pressing sensations to users. A universal testing machine was constructed to evaluate haptic performance of the proposed haptic stylus, whose resistive force was measured with the constructed setup as a function of pressed depth and input current, and by varying the pressed depth and pressing speed. Under maximum input voltage, the stylus generates a wide range of resistive force from 2.33 N to 27.47 N, whereas under maximum pressed depth it varied from 1.08 N to 27.47 N with a corresponding change in voltage input from 0 V to 3.3 V. Therefore, the proposed haptic stylus can create varied haptic sensations. Full article

In this article, an efficient and fast two-stage approach for controlling DC-DC boost converter using non linear sliding mode controller for a PV power plant is proposed. The control approach is based on two online methods instead of using the conventional combination of online and offline methods to harvest maximum energy and deliver an output PV voltage with reduced ripples. The proposed two-stage maximum power point tracking (MPPT) control can be integrated into many applications such as hybrid electric vehicles. Simulation results compared with the standard approaches P&O prove the tracking efficiency of the proposed method under fast changing atmospheric conditions of an average 99.87% and a reduced average ripple of 0.06. The two-stage MPPT control was implemented involving the embedded dSPACE DSP in comparison to the classical P&O to prove the efficiency and the validity of the control scheme. The experimental set-up system was carried out on boost converter and programmable DC electronic resistive load to highlights the robustness of the proposed controller against atmospheric changes and parametric variation. Full article

In this paper, a voice coil motor (VCM) actuated fast tool servo (FTS) system is developed for diamond turning. To guide motions of the VCM actuator, a crossed double parallelogram flexure mechanism is selected featuring totally symmetric structure with high lateral stiffness. To facilitate the determination of the multi-physical parameters, analytical models of both electromagnetic and mechanical systems are developed. The designed FTS with balanced stroke and natural frequency is then verified through the finite element analysis. Finally, the prototype of the VCM actuated FTS is fabricated and experimentally demonstrated to achieve a stroke of ±59.02 μm and a first natural frequency of 253 Hz. By constructing a closed-loop control using proportional–integral–derivative (PID) controller with the internal-model based resonant controller, the error for tracking a harmonic trajectory with ±10 μm amplitude and 120 Hz frequency is obtained to be ±0.2 μm, demonstrating the capability of the FTS for high accuracy trajectory tracking. Full article

This paper presents a novel method for point-to-point path control for a hydraulic knuckle boom crane. The developed path control algorithm differs from previous solutions by operating in the actuator space instead of the joint space or Cartesian space of the crane. By operating in actuator space, almost all the parameters and constraints of the system become either linear or constant, which greatly reduces the complexity of both the control algorithm and path generator. For a given starting point and endpoint, the motion for each actuator is minimized compared to other methods. This ensures that any change in direction of motion is avoided, thereby greatly minimizing fatigue, jerky motion, and energy consumption. However, where other methods may move the tool-point in a straight line from start to end, the method in actuator space will not. In addition, when working in actuator space in combination with pressure-compensated control valves, there is no need for linearization of the system or feedback linearization due to the linear relationship between the control signal and the actuator velocities. The proposed solution has been tested on a physical system and shows good setpoint tracking and minimal oscillations. Full article

Origami structures are highly demanded for engineering applications. Using origami folding to design and actuate mechanisms and machines offers attractive opportunities. In this paper, we design a crawling robot driven by pneumatic foldable actuators (PFAs) based on Miura-ori, according to the parallel foldable structure and different control patterns, which can perform different movements. The PFA inspired from Miura-ori is composed of a folding part, transition part, and sealing part, made by flexible materials and a paper skeleton. This actuator can obtain a large deformation by folding under negative pressure due to its own characteristics, and the relationship between deformation and pressure is analyzed. According to the different folding and unfolding times of left and right actuators, the crawling robot can perform both linear and turning movements. The speed of the robot is about 5 mm/s and it can turn at a speed of about 15°/s. The crawling robot uses the ability of the foldable structure to cope with the challenges of different environments and tasks. Full article

Twisted and coiled polymer (TCP) can generate large stroke and output high power density, making it a promising artificial muscle. Thermally induced muscles fabricated from nylon or other polymer fibers can be used in robotic, biomedical devices, and energy-harvesting equipment. While fibers with different shapes and materials have different optimal process parameters. Understanding mechanisms of TCP forming and the impact of process parameters is critical to explore stronger, more powerful artificial muscles. In this paper, an elastic-rod-theory-based model was established for capturing the quantitative relationship between tensile actuation and fabrication load. Further experimental results agree with model calculation and TCP muscles used in our research reaches maximum stroke of 52.6%, strain up to 9.8 MPa, and power density of 211.89 J/kg. Full article

This research explores a new ATE (Automatic Testing Equipment) method for Micro Electro Mechanical Systems (MEMS) devices. In this method, microscale aerodynamic drag force is generated on a movable part of a MEMS sensor from a micronozzle hole located a specific distance above the chip that will result in a measurable change in output. This approach has the potential to be generalized for the characterization of every MEMS device in mass production lines to test the functionality of devices rapidly and characterize important mechanical properties. The most important testing properties include the simultaneous application of controllable and non-invasive manipulative force, a single handler for multi-sensor, and non-contact characterization, which are relatively difficult to find with other contemporary approaches. Here we propose a custom-made sensing platform consisting of a microcantilever array interconnected to a data acquisition device to read the capacitive effects of each cantilever’s deflection caused by air drag force. This platform allows us to empirically prove the functionality and applicability of the proposed characterization method using airflow force stimuli. The results, stimulatingly, exhibited that air force from a hole of 5 µm radii located 25 µm above a 200 × 200 µm² surface could be focused on a circular spot with radii of approximately 5 µm with surface sweep accuracy of <8 µm. This micro-size airflow jet can be specifically designed to apply airflow force on the MEMS movable component surface. Furthermore, it was shown that the generated air force range could be controlled from 20 nN to 60 nN, approximately, with a linear dependency on airflow ranging from 5 m/s to 20 m/s, which is from a 5 µm radius microhole air jet placed 400 µm above the chip. In this case-study chip, for a microcantilever with a length of 400 µm, the capacitance curve increased linearly from 28.2 pF to 30.5 pF with airflow variation from 5 m/s to 21 m/s from a hole. The resultant curve is representative of a standard curve for testing of the further similar die. Based on these results, this paper paves the way towards the development of a new non-contact, non-invasive, easy-to-operate, reliable, and relatively cheap air-based method for characterizing and testing MEMS sensors. Full article

Linear motors have been playing a crucial role in mechanical motion systems due to its ability to provide a straight motion directly without mediate mechanical actuators. This paper investigates tracking control problems of Polysolenoid Linear Motor, which is a particular type of permanent magnet linear motor in a tubular structure. In order to deal with unmeasurable velocity, our method proposes a novel observer guaranteed asymptotic convergence of the observer errors. Then, based on observed velocity, our method proposes controllers for position-velocity and current tracking control concerning an unknown disturbance load problem by using Lyapunov direct method. The proposed controllers ensure that the position-velocity tracking error converges to arbitrarily small values by adjusting control parameters. Finally, the validity and effectiveness of our approach are shown in illustrative examples. Full article