Actuators

In this paper, the experimental validation of an innovative clutch based on magnetorheological fluids (MRFs) excited by permanent magnets is described. The device, used in automotive applications to engage and disengage the vacuum pump, is tested using a standardized Worldwide harmonized Light-duty Test Cycle (WLTC). A test bench is built, and the system is observed in its operation for one hour, considering two consecutive WLTCs. The temperature increase slightly impacts the clutch’s behavior; in particular, the on-state performance of the device, mainly determined by the magnetic field-induced torque, remains largely unaffected by the temperature increase. The results showed that the performance of the proposed MRF-based device is only marginally affected by the phenomena that take place during the actual operation (e.g., temperature increase, shaft slip), confirming the effectiveness of the design. Full article

We propose to study the nonlinear stroke and lower-order modal interactions of a clamped–clamped shallow-arch flexible micro-electrode. The flexible electrode is electrically actuated through an in-plane parallel-plates field superimposed over out-of-plane electrostatic fringing fields. The in-plane electrostatic fields result from a difference of potential between the initially curved flexible electrode and a lower stationary parallel-grounded electrode. Moreover, the out-of-plane fringing fields are mainly due to the out-of-plane asymmetry of the flexible shallow arch and two respective surrounding stationary side electrodes (left and right). A nonlinear beam model is first introduced, consisting of a nonlinear partial differential equation governing the flexible shallow-arch in-plane deflection. Then, a resultant reduced-order model (ROM) is derived assuming a Galerkin modal decomposition with mode-shapes of a clamped–clamped beam as basis functions. The ROM coupled modal equations are numerically solved to obtain the static deflection. The results indicate the possibility of mono-stable and bi-stable structural behaviors for this particular device, depending on the flexible electrode’s initial rise and the size of its stationary side electrodes. The eigenvalue problem is also derived and examined to estimate the variation of the first three lower natural frequencies of the device when the microbeam is electrostatically actuated. The proposed micro-device is tunable with the possibility of pull-in-free states in addition to modal interactions through linear coupled mode veering and crossover processes. Remarkably, the veering zone between the first and third modes can be electrostatically adjusted and reach $22.6$kHz for a particular set of design parameters. Full article

Underwater manipulation is one of the most significant functions of the deep-sea crawling and swimming robot (DCSR), which relies on the high-accuracy control of the body posture. As the actuator of body posture control, the position control performance of the underwater mechanical leg (UWML) thus determines the performance of the underwater manipulation. An adaptive super-twisting sliding mode control method based on the extended state observer (ASTSMC-ESO) is proposed to enhance the position control performance of the UWML by taking into account the system’s inherent nonlinear dynamics, uncertainties, and the external disturbances from hydrodynamics, dynamic seal resistance, and compensation oil viscous resistance. This newly designed controller incorporates sliding mode (SMC) feedback control with feedforward compensation of the system uncertainties estimated by the ESO, and the external disturbances of the hydrodynamics by fitting the parameters, the dynamic seal resistance, and the compensation oil viscous resistance to the tested results. Additionally, an adaptive super-twisting algorithm (AST) with integral action is introduced to eliminate the SMC’s chattering phenomenon and reduce the system’s steady-state error. The stability of the proposed controller is proved via the Lyapunov method, and the effectiveness is verified via simulation and comparative experimental studies with SMC and the adaptive fuzzy sliding mode control method (AFSMC). Full article

Fast and precise pressure control for an electropneumatic brake system is essential for ensuring the safe operation of trains. However, the nonlinearity and uncertainties of the system make controller design challenging. This paper proposes a prescribed performance control method integrating an extended state observer to address this issue. A thermodynamical model of the brake cylinder is first built based on the pneumatic characteristics of the braking system, considering multiple modes, coupling effects, and input saturation. Then, an extended state observer is designed to estimate model uncertainty due to temperature variation and disturbances and to achieve online compensation of the model. A feedback control law with a specified prescribed performance function is developed based on the updated thermodynamic model to guarantee the transient and steady-state performance of the pressure control. A parameter adaptive method is also utilized to handle input saturation. The observer’s bounded convergence and stability analysis of the closed-loop control system is given using the Lyapunov theory. Compared experimental results are provided to verify the effectiveness of the proposed method. Full article

Most existing ESC (electronic stability control) and ADS (auto drive system) stability controls rely on the measurement of yaw rate and sideslip angle. However, the existing sensors are too expensive, which is one of the factors that makes it difficult to measure the side slip angle of vehicles directly. Therefore, the estimation of sideslip angle has been extensively discussed in the relevant literature. Accurate modeling is complicated by the fact that vehicles are highly nonlinear. This article combines a radial basis function neural network with an unscented Kalman filter to propose a new sideslip angle estimation method for controlling the dynamic behavior of vehicles. Considering the influence of input data type and sensor ease of measurement factors on the results, a two-degrees-of-freedom vehicle nonlinear dynamic model was established, and a radial basis function neural network estimation algorithm was designed. In order to reduce the impact of noise and improve the reliability of the algorithm, the neural network algorithm was combined with the Kalman filter. The information collected from low-cost sensors for actual vehicle operation (longitudinal vehicle speed, steering wheel angle, yaw rate, lateral acceleration) was trained using a radial basis function neural network to obtain a “pseudo slip angle”. The “pseudo slip angle”, yaw rate, and lateral acceleration are input as observations of the Kalman filter. The sideslip angle obtained from different observation methods was compared with the values provided by the Carsim 2020. The experiment shows that the sideslip angle estimator based on the radial basis function neural network and unscented Kalman filter achieves the optimal effect. Full article

Hydraulic cylinders are well known as cheap and robust actuators for moving heavy loads, especially in harsh environments. For this reason, they are often used in construction machines such as excavators. Basically, the hydraulic cylinders are controlled by four-way proportional spool valves, resulting in poor energy efficiency due to resistance control. Furthermore, because all valve edges are located at the same spool, common proportional valves suffer from limited flexibility with regard to different loads. Independent metering (IM) is a well-known strategy for making proportional hydraulic drives more efficient and more flexible because each port of the actuator can be connected individually to pressure or tank by independent two-way proportional valves. In this paper, the IM concept is realized as an open-loop control for a hydraulic cylinder drive, which, in combination with a human operator, constitutes a so-called cybernetic proportional system (CPS). The piston velocity commanded by the operator is controlled by the compensation of the static characteristics of the proportional seat-type valves. Basic simulations show the benefits and also the problems of open-loop independent metering. Furthermore, measurements on one actuator of a real excavator regarding controllability and energy consumption are presented. Full article

In this study, the mechanical models of a multilayer combined extrusion cylinder and a steel-wire-winding extrusion cylinder were established and compared using a finite element simulation and existing experimental cases. This work provides theoretical support for the selection of an ultrahigh-pressure extrusion cylinder. Comparative analysis of an ultrahigh-pressure extrusion structure was carried out. The mathematical optimization model is established based on the mechanical model, and the ultimate bearing capacities of the schemes are compared. Additionally, the winding mode and the number of core layers of the extrusion cylinder are compared and analyzed, which provides a theoretical basis for the parameter design of the steel-wire-winding ultrahigh-pressure extrusion cylinder. This work holds good theoretical significance and practical value for the promotion and application of ultrahigh-pressure hydrostatic extrusion technology. Full article

This study proposes a method for designing a class of rotationally symmetric Stewart platforms (RSSPs) with an insensitive condition number (ICN), which is used to minimize the condition number to achieve a high accuracy for a multi-degree-of-freedom (multi-DOF) shaker. Considering the rotational symmetry of RSSPs, an analytical relationship between the architecture parameters and transfer coefficients is first established. Then, the decoupling conditions of the RSSPs are derived, and the transfer coefficient formulas are simplified by the given decoupling conditions and iso-length assumption. Following further analyses and discussions, the ICN condition and analytical form of the condition number are provided. The area of the ICN (AICN) is, subsequently, derived to evaluate the insensitivity of the condition number. To validate the effectiveness of the method, a design example (ICN-RSSP), along with a numerical analysis, is implemented, and, finally, a multi-DOF shaker is developed. The results of the numerical analysis show a smaller condition number and a larger AICN than those of the RSSP, for comparison. And the experiment results of the multi-DOF shaker show a high accuracy of vibration waveform reproduction. The method can reduce the condition number of RSSPs, improve the insensitivity, and further improve the accuracy of the multi-DOF shaker. Full article

There is a complex coupling relationship between the structural parameters and various performance indicators of a permanent magnet eddy current coupler. In order to obtain the optimal combination of structural parameters that can improve the overall performance of the coupler, it is necessary to reasonably balance the contradiction and competition among performance indicators of the permanent magnet eddy current coupler. A multi-objective optimization method for permanent magnet eddy current couplers based on scaled conjugate gradient back propagation neural network modeling, improved opposition-based learning, and normal distribution crossover operator non-dominated sorting genetic algorithm-II is proposed. The optimization results are compared with those of the traditional non-dominated sorting genetic algorithm-II and the Pareto envelope-based selection algorithm-II, and it is verified that the proposed multi-objective optimization algorithm is accurate, reliable, and has better convergence and versatility. Compared with the original model, the output torque of the optimized coupler increased by 8.54%, and the eddy current loss and cost decreased by 3.71% and 8.74%, respectively. Finally, the correctness of the theoretical analysis was verified through 3D finite element simulation and an experimental simulation platform. Full article

The technique of morphing in aerospace engineering is a relatively new discipline targeting the improvement of aircraft performance, even through dramatic changes to some critical geometrical and mechanical features, to adapt aircrafts’ configurations to evolving operation conditions. The development path of morphing systems is complex and shall pass through articulated gates to prove its readiness level due to the concurrence of different disciplines and approaches. The characterization and demonstration of the concepts in a representative environment, such as wind tunnel test facilities, are some of the most relevant steps needed for the maturation of the engineering technique. The practical size limitations of test facilities usually impose the use of scaled models. In the case of morphing systems, whose architecture is strictly dependent on the available room, and whose performance is tightly correlated with the general structural stiffness, changes in dimensions may affect the overall behaviour significantly. Therefore, the adaptive design may change a lot until it arrives to the formation of completely different products. Transportability issues of certain architectural forms, as well as the different classes of vehicles, are also related to that aspect. The scope of this paper is to investigate the impact of some effects of scaling processes on certain features of a morphing system, particularly focusing on the stiffness parameters, for their impact on several features such as the load bearing capability and structural stability in both steady and dynamic conditions. As a case study, a rotorcraft blade segment integrated with torsional shape memory alloy (SMA) actuators was considered. Relevant numerical models were exploited to highlight the different evolution laws of the characteristic structural parameters vs. the referred scale factors. In this investigation, the axial, flap, lag bending, and torsion stiffnesses, as well as normal modes and stress levels, are considered. The achieved results confirm the complexity of attaining an effective reproduction of the targeted morphing architecture, as scaled configurations are considered. In spite of the unavoidable specificity of the analysis herein reported, it is believed that such attainments can have a general validity at least to some extent, and the outcomes may be exported to other morphing systems, at least as guidelines. This study took place within the European project SABRE (Shape Adaptive Blades for Rotorcraft Efficiency, H2020). Full article

Series iron core reactors are one of the most commonly used electrical equipments in power systems, which can limit short-circuit currents and suppress harmonic waves from capacitor banks. However, the vibration of the reactor will not only generate noise pollution but also diminish the service life of the reactor and jeopardize power system safety. In order to reduce the vibration noise in the core disc region of the reactor, the vibration characteristics of a core reactor are calculated by modifying the anisotropy parameters of the Young’s modulus of the core disc lamellar structure and introducing the core magnetostriction effect based on the simulation analysis method of electromagnetic and mechanical coupling. A detachable single-phase series core reactor model is established, and the validity of the simulation calculation is measured and verified. At the same time, from the perspective of improving the air gap size of the series core reactor and the arrangement of electrical steel sheets, the corresponding iron core vibration reduction scheme is given. The average vibration reduction in the reactor is about 11.6% after comprehensive improvement according to the vibration reduction scheme, which provides an effective method for realizing the vibration and noise reduction in the reactor. Full article

This work focuses on the consensus problem for multi-agent systems (MASs) with actuator failures and time-varying state constraints, and presents a fixed-time self-triggered consensus control protocol. The use of time-varying asymmetrical barrier Lyapunov functions (BLF) avoids the violation of time-varying state constraints in MASs, ensuring stability and safety. Meanwhile, the system’s performance is further enhanced by leveraging the proposed adaptive neural networks (NNs) control method to mitigate the effects of actuator failures and nonlinear disturbances. Moreover, a self-triggered mechanism based on a fixed-time strategy is proposed to reach rapid convergence and conserve bandwidth resources in MASs. The mechanism achieves consensus within a predefined fixed time, irrespective of the system’s initial states, while conserving communication resources. Finally, the proposed method’s effectiveness is confirmed through two simulation examples, encompassing diverse actuator failure scenarios. Full article

In the present article, the solution for choosing the optimal structural variant of an industrial robot for extracting castings from die casting machines is considered. For this purpose, the process of extracting the castings from the mold is analyzed. On this basis, functions are defined, and a functional structure of the robot is built. Alternative variants of devices for each function are developed. The set of possible structural variants are constructed, considering the compatibility between devices and the possibility of performing more than one function with one device. The problem of choosing an optimal structural variant is formulated, and its characteristic features are determined. The main stages of a methodology and application software for the problem’s solution are presented. After an analysis of requirements for the extractor, the set of criteria for evaluating the structural variants are determined. The set includes criteria that minimize the production costs, production floor space, as well as the energy costs in the operation process, which is of particular importance in the conditions of global energy crisis. A mathematical model of the problem is built. The formulated multi-criteria optimization problem is solved, both with equal objective functions and with different priority. Full article

The current reliance on manual rescue is inefficient, and lightweight, highly flexible, and intelligent robots need to be investigated. Global seismic disasters occur often, and rescue jobs are defined by tight timetables and high functional and intellectual requirements. This study develops a hydraulically powered redundant robotic arm with seven degrees of freedom. To determine the force situation of the robotic arm in various positions, the common digging and handling conditions of the robotic arm are dynamically simulated in ADAMS. A finite element analysis is then performed for the dangerous force situation to confirm the structural strength of the robotic arm. The hydraulic manipulator prototype is manufactured, and stress–strain experiments are conducted on the robotic arm to verify the finite element simulation’s reliability. Full article

Modular self-configurable robot (MSR) systems have been investigated for decades, and their applications have been widely explored to meet emerging automation needs in various applications, such as space exploration, manufacturing, defense, medical industry, entertainment, and services. This paper aims to gain a deep understanding of up-to-date research and development on MSR through a thorough survey of market demands and published works on design methodologies, system integration, advanced controls, and new applications. In particular, the limitations of existing mobile MSR are discussed from the reconfigurability perspective of mechanical structures. Full article

Aiming at the requirements of distributed braking and advanced automatic driving, a brake-by-wire unit based on a direct drive pump–valve cooperative is proposed. To realize the wheel cylinder pressure regulation, the hydraulic pump is directly driven by the electromagnetic linear actuator coordinates with the active valve. It has the advantages of rapid response and no deterioration of wheel side space and unsprung mass. Firstly, by analyzing the working characteristics and braking performance requirements of the braking unit, the key parameters of the system are matched. Then, in order to ensure the accuracy of the simulation model, the co-simulation model of the brake unit is established based on the Simulink-AMESim co-simulation platform. Then, the influence law of key parameters on the control performance is analyzed. Finally, the experimental platform of the brake unit is established. The accuracy of the co-simulation model and the feasibility of the brake-by-wire unit based on direct drive pump–valve cooperative are verified through the pressure control experiment and ABS simulation, which shows that the braking unit has good dynamic response and steady-state tracking effect. Full article

This study developed a three-axis vibrational haptic wearable device (RCWS) utilizing Linear Resonant Actuators (LRAs) to simulate grinding vibrations. The implementation of RCWS is described in detail. By recording the normal force during manual grinding with a load cell and converting it into a series of PWM commands, the LRA on the RCWS was controlled in open-loop mode using these PWM commands. Three methods were tested for force-to-PWM conversion, two of which showed a linear correlation (>0.7) with raw data. In the correlation between PWM commands and generated acceleration, all three methods exhibited a high linearity of at least 0.85. This wearable RCWS offers a promising approach for users to experience the machining force from the versatile and critical remote machining process with a finger vibratory sensation. Full article

The maglev planar motor is one of the most promising industrial applications. The planar motor can increase flexibility in modern manufacturing with the multidirectional motion of the mover. In levitation control, the decoupling matrix is used to decouple the strong cross-coupling effect. The Lorentz force-based wrench matrices can be precomputed and stored in the lookup table. However, the motion range is restricted by the data range. This paper presents a wrench–current decoupling strategy to extend the use of small lookup data for long-range planar motion. The horizontal data range is 40 mm by 40 mm, which is determined from the minimally repetitive area of the planar coil array. The quadrant symmetry transformation is used to estimate the data for other areas. The experiment results demonstrated the accomplishment of the developed technique for long-range motion with a maximum motion stroke of 380 mm. The disc-magnet movers can levitate with a large air gap of 30 mm and have a total roll and pitch rotation range of 20 degrees. Full article

High-precision industrial manipulators are essential components in advanced manufacturing. Model-based feedforward is the key to realizing the high-precision control of industrial robot manipulators. However, traditional feedforward control approaches are based on rigid models or flexible joint models which neglect the elasticities out of the rotational directions and degrade the setpoint precision significantly. To eliminate the effects of elasticities in all directions, a high-precision setpoint feedforward control method is proposed based on the output redefinition of the extended flexible joint model (EFJM). First, the flexible industrial robots are modeled by the EFJM to describe the elasticities in joint rotational directions and out of the rotational directions. Second, the nonminimum-phase EFJM is transformed into a minimum-phase system by using output redefinition. Third, the setpoint control task is transformed from Cartesian space into joint space by trajectory planning based on the EFJM. Third, a universal recursive algorithm is designed to compute the feedforward torque based on the EFJM. Moreover, the computational performance is improved. By compensating the pose errors caused by elasticities in all directions, the proposed method can effectively improve the setpoint control precision. The effectiveness of the proposed method is illustrated by simulation and experimental studies. The experimental results show that the proposed method reduces position errors by more than 65% and the orientation errors by more than 62%. Full article