Actuators

17 pages, 2258 KiB

Open AccessArticle

Nonlinearity Harmonic Error Compensation Method Based on Intelligent Identification for Rate Integrating Resonator Gyroscope

by Xiaodi Yi, Gongliu Yang, Qingzhong Cai and Yongqiang Tu

Actuators 2025, 14(2), 68; https://doi.org/10.3390/act14020068 (registering DOI) - 3 Feb 2025

Abstract

This paper presents an improved intelligent optimizing algorithm based on parameter identification and drift compensation for the rate-integrating resonator gyroscope (RIRG). Besides damping and frequency imperfections, the RIRG measurement accuracy still suffers from limitations due to nonlinear error. Therefore, the dynamic nonlinear error [...] Read more.

This paper presents an improved intelligent optimizing algorithm based on parameter identification and drift compensation for the rate-integrating resonator gyroscope (RIRG). Besides damping and frequency imperfections, the RIRG measurement accuracy still suffers from limitations due to nonlinear error. Therefore, the dynamic nonlinear error model for RIRG has been established to reveal the relationship between the pattern angle and harmonic drifts. Based on this, a dynamic analysis of the gyroscope operating state is carried out using nonlinear motion equations. The optimal harmonic error parameters are then identified by a particle swarm optimization (PSO) algorithm for the drift error compensation. To further improve the measurement accuracy, chaotic technology is integrated with PSO, leading to more precise identification. Subsequently, the harmonic parameters of the bias drifts are efficiently compensated. Experimental results demonstrate that the bias drift is reduced by over 90% after harmonic error compensation, demonstrating the validity of the proposed method in enhancing the measurement accuracy of RIRGs. Full article

(This article belongs to the Section Precision Actuators)

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12 pages, 1639 KiB

Open AccessArticle

Effectiveness of Powered Hand Exoskeleton on Upper Extremity Function in People with Chronic Stroke

by Shan-Ju Yeh, Yi-Chuan Wang, Wei-Chien Fang, Shyh-Chour Huang and Yu-Sheng Yang

Actuators 2025, 14(2), 67; https://doi.org/10.3390/act14020067 (registering DOI) - 2 Feb 2025

Abstract

Impairment of upper limb function is common after a stroke and is closely linked to decreased functional independence in activities of daily living. Robot-assisted training has been used in clinical settings to improve hand function in stroke patients; however, many existing devices are [...] Read more.

Impairment of upper limb function is common after a stroke and is closely linked to decreased functional independence in activities of daily living. Robot-assisted training has been used in clinical settings to improve hand function in stroke patients; however, many existing devices are costly and require specialized training to operate. This study aimed to propose a novel powered hand exoskeleton (EO) and verify its effectiveness on upper extremity function in people with chronic stroke. Thirty participants were randomly assigned to either the experimental group or the control group. Each participant underwent 30 min interventions twice a week for 8 weeks. The experimental group received 15 min of conventional therapy followed by 15 min of training with the powered hand EO, while the control group received 30 min of conventional therapy. The primary outcome measures included the Fugl-Meyer Assessment for upper extremity function (FMA-UE), the Box and Block Test (BBT), and handgrip dynamometer. Assessments were conducted at baseline and then at 4-week intervals throughout the 8-week period. Results showed that, after the 8-week intervention, the average changes in FMA-UE scores for the experimental group were significantly greater than those for the control group (p < 0.01). A clear upward trend in both FMA-UE and BBT scores was observed in the EO group. Statistical analysis revealed significant improvements in the overall, proximal, and distal components of the FMA-UE scores (all p < 0.01) and in BBT scores (both p < 0.05) in the EO group compared to the control group at 4 and 8 weeks, respectively. However, no significant differences in grip strength were observed between the groups at either time point. Our findings suggest that the proposed powered hand EO is both feasible and safe for training the impaired hand in stroke survivors. Given the characteristics of the device, it has potential for use in hand rehabilitation aimed at regaining upper extremity function. Full article

(This article belongs to the Special Issue Biomechanics, Actuation, and Control Strategies of Prosthetics, Orthotics, and Exoskeletons)

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26 pages, 1836 KiB

Open AccessArticle

Encouraging Guidance: Floating Target Tracking Technology for Airborne Robotic Arm Based on Reinforcement Learning

by Jiying Wu, Zhong Yang, Haoze Zhuo, Changliang Xu, Luwei Liao, Danguo Cheng and Zhiyong Wang

Actuators 2025, 14(2), 66; https://doi.org/10.3390/act14020066 - 31 Jan 2025

Abstract

Aerial robots equipped with operational robotic arms are a powerful means of achieving aerial contact operations, and their core competitiveness lies in target tracking control at the end of the airborne robotic arm (ARA). In order to improve the learning efficiency and flexibility [...] Read more.

Aerial robots equipped with operational robotic arms are a powerful means of achieving aerial contact operations, and their core competitiveness lies in target tracking control at the end of the airborne robotic arm (ARA). In order to improve the learning efficiency and flexibility of the ARA control algorithm, this paper proposes the encouraging guidance of an actor–critic (Eg-ac) algorithm based on the actor–critic (AC) algorithm and applies it to the floating target tracking control of ARA. It can quickly lock in the exploration direction and achieve stable tracking without increasing the learning cost. Firstly, this paper establishes approximate functions, policy functions, and encouragement functions for the state value of ARA. Secondly, an adoption rate controller (ARC) module was designed based on the concept of heavy rewards and light punishments (HRLP). Then, the kinematic and dynamic models of ARA were established. Finally, simulation was conducted using stable baselines3 (SB3). The experimental results show that, under the same computational cost, the convergence speed of the Eg-ac is improved by 21.4% compared to deep deterministic policy gradient (DDPG). Compared with soft actor–critic (SAC) and DDPG, Eg-ac has improved learning efficiency by at least 20% and has a more agile and stable floating target tracking effect. Full article

(This article belongs to the Section Actuators for Robotics)

20 pages, 13831 KiB

Open AccessArticle

Prescribed Performance Global Non-Singular Fast Terminal Sliding Mode Control of PMSM Based on Linear Extended State Observer

by Yifei Yao, Yaoming Zhuang, Yizhi Xie, Peng Xu and Chengdong Wu

Actuators 2025, 14(2), 65; https://doi.org/10.3390/act14020065 - 30 Jan 2025

Abstract

In manufacturing, the position tracking accuracy and stability of Permanent Magnet Synchronous Motors are often challenged by uncertainties, especially in complex environments. Existing control methods struggle to balance fast response with high-precision tracking. To address this, we propose a Prescribed Performance Global Non-Singular [...] Read more.

In manufacturing, the position tracking accuracy and stability of Permanent Magnet Synchronous Motors are often challenged by uncertainties, especially in complex environments. Existing control methods struggle to balance fast response with high-precision tracking. To address this, we propose a Prescribed Performance Global Non-Singular Fast Terminal Sliding Mode Control (PPGNFTSMC) method using a linear extended state observer (LESO). A smooth and bounded prescribed performance function is designed to ensure finite-time convergence while satisfying performance requirements such as overshoot and settling time. Based on this function, the system error is reconstructed to align the system response with predefined specifications. The reconstructed error is then used to design a global non-singular fast terminal sliding mode surface. A LESO is employed for real-time disturbance estimation, and the disturbance estimates, along with the sliding mode surface, are used to derive the control law for the position–speed integrated controller. Experimental results show that the proposed method outperforms the comparison methods in transient response, tracking accuracy, and robustness across various signal types. Full article

(This article belongs to the Special Issue New Control Schemes for Actuators—2nd Edition)

30 pages, 2771 KiB

Open AccessArticle

A Symmetrical RRPRR Robust Coupling for Crossed Axes Transmission

by Toma-Marian Ciocirlan, Stelian Alaci, Florina-Carmen Ciornei, Ionut-Cristian Romanu and Ioan Doroftei

Actuators 2025, 14(2), 64; https://doi.org/10.3390/act14020064 - 29 Jan 2025

Abstract

A new coupling solution for transmitting the rotation motion between two shafts with crossed axes is proposed. Based on structural considerations, a planar (P) pair is introduced into the structure of the mechanism, presenting the advantage of reduced costs due to the constructive [...] Read more.

A new coupling solution for transmitting the rotation motion between two shafts with crossed axes is proposed. Based on structural considerations, a planar (P) pair is introduced into the structure of the mechanism, presenting the advantage of reduced costs due to the constructive and manufacturing simplicity and to high reliability. The proposed mechanism is of the RRPRR type, and the structural symmetry simplifies substantially the construction of the mechanism. The constructive parameters of the mechanism are the angle and distance between the driving and driven shaft and also the length of the common normal between the axes of driving and driven revolute (R) pairs, and the axes of the revolute pairs of the coupling chain, respectively. Due to the presence of the planar pair, the Hartenberg–Denavit method of homogenous operators is not applicable. The kinematic analysis for a specified motion of the driving element requires two stages: finding the relative motions from the revolute pairs and the motions from the planar pair. The RRPRR transmission is analysed for geometrical asymmetrical and symmetrical cases; the latter is more convenient and the design principles are presented. Concerning the dimensional optimization, it is found to be a methodology for ensuring that the transmission ratio of the mechanism can be maintained within a stipulated range. Based on the kinematical calculus and geometrical optimization, the mechanism was designed and manufactured. Full article

(This article belongs to the Section High Torque/Power Density Actuators)

28 pages, 3329 KiB

Open AccessArticle

Development of a Basilar Membrane-Inspired Mechanical Spectrum Analyzer Using Metastructures for Enhanced Frequency Selectivity

by Shantanu H. Chavan and Vijaya V. N. Sriram Malladi

Actuators 2025, 14(2), 63; https://doi.org/10.3390/act14020063 - 29 Jan 2025

Abstract

This study introduces a mechanical spectrum analyzer (MSA) inspired by the tonotopic organization of the basilar membrane (BM), designed to achieve two critical features. First, it replicates the traveling-wave behavior of the BM, characterized by energy dissipation without reflections at the boundaries. Second, [...] Read more.

This study introduces a mechanical spectrum analyzer (MSA) inspired by the tonotopic organization of the basilar membrane (BM), designed to achieve two critical features. First, it replicates the traveling-wave behavior of the BM, characterized by energy dissipation without reflections at the boundaries. Second, it enables the physical encoding of the wave energy into distinct spectral components. Moving beyond the conventional focus on metamaterial design, this research investigates wave propagation behavior and energy dissipation within metastructures, with particular attention to how individual unit cells absorb energy. To achieve these objectives, a metastructural design methodology is employed. Experimental characterization of metastructure samples with varying numbers of unit cells is performed, with reflection and absorption coefficients used to quantify energy absorption and assess bandgap quality. Simulations of a basilar membrane-inspired structure incorporating multiple sets of dynamic vibration resonators (DVRs) demonstrate frequency selectivity akin to the natural BM. The design features four types of DVRs, resulting in stepped bandgaps and enabling the MSA to function as a frequency filter. The findings reveal that the proposed MSA effectively achieves frequency-selective wave propagation and broad bandgap performance. The quantitative analysis of energy dissipation, complemented by qualitative demonstrations of wave behavior, highlights the potential of this metastructural approach to enhance frequency selectivity and improve sound processing. These results lay the groundwork for future exploration of 2D metastructures and applications such as energy harvesting and advanced wave filtering. Full article

(This article belongs to the Special Issue Actuator Technology for Active Noise and Vibration Control)

16 pages, 6815 KiB

Open AccessArticle

Investigating the Power Extraction of Applying Hybrid Pitching Motion on a Wing with Leading and Trailing Flaps

by Suleiman Saleh and Chang-Hyun Sohn

Actuators 2025, 14(2), 62; https://doi.org/10.3390/act14020062 - 27 Jan 2025

Abstract

This research utilized a hybrid trajectory on a wing incorporating a dual flap with the goal of enhancing performance. The hybrid profiles initiate with a non-sinusoidal pattern during the interval 0.0 ≤ t/T ≤ 0.25, evolving toward a sinusoidal pattern within the range [...] Read more.

This research utilized a hybrid trajectory on a wing incorporating a dual flap with the goal of enhancing performance. The hybrid profiles initiate with a non-sinusoidal pattern during the interval 0.0 ≤ t/T ≤ 0.25, evolving toward a sinusoidal pattern within the range 0.25 < t/T ≤ 0.5. Similarly, the hybrid motion follows a non-sinusoidal pattern in the range 0.5 < t/T ≤ 0.75, before shifting back to a sinusoidal pattern within the range 0.75 < t/T ≤ 1.0. The effectiveness of using a hybrid trajectory on a wing with leading and trailing flaps in enhancing the energy harvesting performance is examined through numerical simulations. The results demonstrate that hybrid trajectories applied to a two-flap wing configuration outperform a single flat plate and a wing with leading and trailing flaps both operating under a sinusoidal trajectory. The wing length spans from 45% to 55%, with the leading flap length ranging from 25% to 35%. The trailing flap lengths adjust accordingly to ensure the combined total matches the flat plate’s full length, which is 100%. The wing pitch angle was fixed at 85° while the leading flap’s pitch angle varied between 40° and 55° and the pitch angle of the trailing flap ranged from 0° to 20°. The findings reveal that utilizing hybrid motion on a wing fitted with leading and trailing flaps notably improves power output in comparison to configurations with either one plate or three plates. The power output is achieved at particular dimensions: a leading flap length of 30%, a wing length of 55%, and a trailing flap length of 15%. The corresponding pitch angles are 50° for the leading flap, 85° for the wing, and 10° for the trailing flap. The aforementioned configuration results in a 34.06% increase in output power in comparison to one plate. The maximum efficiency for this setup reaches 44.21%. This underscores the superior performance of hybrid trajectories over sinusoidal trajectories in enhancing energy extraction performance. Full article

(This article belongs to the Special Issue Flow Control and Beyond Enhancing Performance and Energy Efficiency in Complex Fluid System)

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20 pages, 18170 KiB

Open AccessArticle

Accurate Suspension Force Modeling and Its Control System Design Based on the Consideration of Degree-of-Freedom Interaction

by Weiyu Zhang and Aojie Xu

Actuators 2025, 14(2), 61; https://doi.org/10.3390/act14020061 - 26 Jan 2025

Abstract

In this study, an accurate suspension force modeling method for the magnetic bearings of flywheel batteries considering degree-of-freedom (DOF) interactions and their control system is proposed to solve the problem that the traditional flywheel battery suspension force model does not consider DOF interactions, [...] Read more.

In this study, an accurate suspension force modeling method for the magnetic bearings of flywheel batteries considering degree-of-freedom (DOF) interactions and their control system is proposed to solve the problem that the traditional flywheel battery suspension force model does not consider DOF interactions, which makes the control system control effect poor. Firstly, according to the structural characteristics of the flywheel battery used, a suspension force model is established for the radial and axial magnetic bearings, which are most seriously interfered with by the torsional degrees of freedom of the flywheel battery. Next, by proposing DOF interaction factors, the complex changes due to DOF interactions are cleverly summarized into several interaction factors applied to the fundamental model to achieve accurate suspension force modeling considering DOF interactions. To better adapt the established accurate model and ensure precise control of the flywheel battery system under various working conditions, the firefly algorithm is employed to optimize the BP neural network (FA-BPNN). This optimization regulates the control system’s parameters, enabling the achievement of optimal control parameters in different scenarios and enhancing control efficiency. Compared to the flywheel battery controlled using the fundamental model, the radial and axial displacements are reduced by more than 30 percent and 20 percent, respectively, in the uphill condition using the accurate model with FA-BPNN. Full article

(This article belongs to the Special Issue Actuators in Magnetic Levitation Technology and Vibration Control)

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15 pages, 2824 KiB

Open AccessArticle

The Technical Development of a Prototype Lower-Limb Therapy Device for Bed-Resting Users

by Juan Fang, Adrien Cerrito, Simón Gamero Schertenleib, Patrick von Raumer and Kai-Uwe Schmitt

Actuators 2025, 14(2), 60; https://doi.org/10.3390/act14020060 - 26 Jan 2025

Abstract

It is generally recommended that bed-resting patients be mobilised early to promote recovery. The aim of this work was to develop and evaluate the usability of a prototype in-bed lower-limb therapy device that offers various training patterns for the feet and legs, featuring [...] Read more.

It is generally recommended that bed-resting patients be mobilised early to promote recovery. The aim of this work was to develop and evaluate the usability of a prototype in-bed lower-limb therapy device that offers various training patterns for the feet and legs, featuring an intuitive user interface and interactive exergames. Based on clinical interviews, the user requirements for the device were determined. The therapy device consisted of two compact foot platforms with integrated electric motors and force sensors. Movement control strategies and a user interface with computer games were developed. Through a touch screen, the target force and position trajectories were defined. Using automatic position and force control algorithms, the device produced leg flexion/extension with synchronised ankle plantarflexion/dorsiflexion as well as leg pressing with adjustable resistive loading. An evaluation test on 12 able-bodied participants showed that the device produced passive (mean position control errors: 8.91 mm linearly and 1.62° in the ankle joints) and active leg training (force control error: 2.52 N). The computer games were proven to be interesting, engaging, and responsive to the training movement. It was demonstrated that the device was technically usable in terms of mechatronics, movement control, user interface, and computer games. The advancements in well-controlled movement, multi-modal training patterns, convenient operation, and intuitive feedback enable the compact therapy device to be a potential system for bed-resting users to improve physical activity and cognitive functionality. Full article

(This article belongs to the Special Issue Intelligent Systems, Robots and Devices for Healthcare and Rehabilitation)

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23 pages, 5393 KiB

Open AccessArticle

A SAC-Bi-RRT Two-Layer Real-Time Motion Planning Approach for Robot Assembly Tasks in Unstructured Environments

by Qinglei Zhang, Siyao Hu, Jianguo Duan, Jiyun Qin and Ying Zhou

Actuators 2025, 14(2), 59; https://doi.org/10.3390/act14020059 - 26 Jan 2025

Abstract

Due to the uncertainty and complexity of the assembly process, the trajectory planning of a robot needs to consider the real-time obstacle avoidance problem when it completes the assembly in the unstructured workspace. To realize the safe assembly of assembly robots in dynamic [...] Read more.

Due to the uncertainty and complexity of the assembly process, the trajectory planning of a robot needs to consider the real-time obstacle avoidance problem when it completes the assembly in the unstructured workspace. To realize the safe assembly of assembly robots in dynamic and complex environments, a dynamic obstacle avoidance trajectory planning method for robots combining traditional planning algorithms and deep reinforcement learning algorithms is proposed to improve the robot’s agent and obstacle avoidance ability in dynamic and complex environments. The Bidirectional Rapidly-exploring Random Tree (Bi-RRT) method is utilized as a global planner to plan the global optimal path quickly; considering the real-time nature of the assembly process, the Soft Actor-Critic (SAC) is used as a local obstacle avoider to avoid obstacles more accurately and to find the nearest node generated by the Bi-RRT during the planning process, which is regarded as the goal during the local obstacle avoidance to reduce the model’s complexity. By training and testing in the simulation engine and comparing with SAC, DDPG and DQN algorithms, the method can avoid obstacles in dynamic and complex environments more efficiently, which verifies that the proposed hybrid method can accomplish the high-precision planning task with a high success rate. Full article

(This article belongs to the Section Actuators for Robotics)

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32 pages, 20828 KiB

Open AccessArticle

Time-Variation Damping Dynamic Modeling and Updating for Cantilever Beams with Double Clearance Based on Experimental Identification

by Yunhe Zhang, Fanjun Meng, Xueguang Li, Wei Song, Dashun Zhang and Faping Zhang

Actuators 2025, 14(2), 58; https://doi.org/10.3390/act14020058 - 26 Jan 2025

Abstract

The accuracy of a space manipulator’s end trajectory and stability is significantly affected by joint clearance. Aiming to improve the prediction accuracy of vibration caused by clearance, a dynamic clearance modeling method is developed based on parameter identification in this study. First, a [...] Read more.

The accuracy of a space manipulator’s end trajectory and stability is significantly affected by joint clearance. Aiming to improve the prediction accuracy of vibration caused by clearance, a dynamic clearance modeling method is developed based on parameter identification in this study. First, a dynamic model framework for manipulator arms is established based on the Hamilton principle and hypothetical mode method with time-variation damping. Then, a multi-resolution identification is performed for identifying the instantaneous frequency and damping ratio to estimate stiffness and damping by the sensors. The quantum genetic algorithm (QGA) is used to optimize the scale factor, which determines the identification accuracy and calculation efficiency. Finally, a case study is conducted to verify the presented model. In comparison with the initial dynamic model based on constant damping, the modal assurance criterion (MAC) of the proposed improved model based on time-variation damping is improved by 43.97%, the mean relative error (MRE) of the frequency response function (FRF) is reduced by 32.6%, and the root mean square error (RMSE) is reduced by 18.19%. The comparison results indicate the advantages of the proposed model. This modeling method could be used for vibration prediction in control systems for space manipulators to improve control accuracy. Full article

(This article belongs to the Special Issue Power Electronics and Actuators—Second Edition)

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19 pages, 478 KiB

Open AccessArticle

A Robust Cooperative Control Protocol Based on Global Sliding Mode Manifold for Heterogeneous Nonlinear Multi-Agent Systems Under the Switching Topology

by Xiaoyu Zhang, Yining Li, Shuiping Xiong, Xiangbin Liu and Rong Guo

Actuators 2025, 14(2), 57; https://doi.org/10.3390/act14020057 - 25 Jan 2025

Abstract

This study addresses the completely distributed consensus control problem for the heterogeneous nonlinear multi-agent system (MAS) with disturbances under switching topology. First, a global sliding mode manifold (GSMM) is designed for the overall MAS dynamic, which maintains stability without oscillations during topology switching [...] Read more.

This study addresses the completely distributed consensus control problem for the heterogeneous nonlinear multi-agent system (MAS) with disturbances under switching topology. First, a global sliding mode manifold (GSMM) is designed for the overall MAS dynamic, which maintains stability without oscillations during topology switching after achieving the sliding mode. Subsequently, a consensus sliding mode control protocol (SMCP) is proposed, adopting the common sliding mode control (SMC) format and ensuring the finite-time reachability of the GSMM under topology switching. Finally, the proposed GSMM and SMCP are applied to the formation control of multiple-wheeled mobile robots (WMRs), and simulation results confirm their feasibility and effectiveness. The proposed SMCP design demonstrates key advantages, including a simple control structure, complete robustness to matched disturbance, and reduced-order dynamics under the sliding mode. Full article

(This article belongs to the Section Control Systems)

21 pages, 861 KiB

Open AccessArticle

Almost Disturbance Decoupling Control Strategy for a Class of Underactuated Nonlinear Systems with Disturbances

by Renhan Wu, Xiaoping Liu, Tianfei Chen, Lijun Sun and Na Wang

Actuators 2025, 14(2), 56; https://doi.org/10.3390/act14020056 - 25 Jan 2025

Abstract

This paper introduces an almost disturbance decoupling approach to address the disturbance problem for a class of underactuated nonlinear systems. First, a residual system is constructed using a virtual controller and partial differential equations. Next, the unknown disturbances are addressed using an almost [...] Read more.

This paper introduces an almost disturbance decoupling approach to address the disturbance problem for a class of underactuated nonlinear systems. First, a residual system is constructed using a virtual controller and partial differential equations. Next, the unknown disturbances are addressed using an almost disturbance decoupling approach, where Young’s inequality is applied to handle the disturbance terms in the residual system. An almost disturbance decoupling controller is designed for the residual system. The locally asymptotic stability of the closed-loop system is rigorously proven using Lyapunov’s theorem. Finally, simulation results on an IWP system with unknown disturbances and experimental results on an overhead crane are presented to validate the effectiveness of the proposed almost disturbance decoupling control method. Full article

(This article belongs to the Section Control Systems)

16 pages, 3334 KiB

Open AccessArticle

Lead-Free Ceramics in Prestressed Ultrasonic Transducers

by Claus Scheidemann, Peter Bornmann, Walter Littmann and Tobias Hemsel

Actuators 2025, 14(2), 55; https://doi.org/10.3390/act14020055 - 25 Jan 2025

Abstract

Today’s ultrasonic transducers find broad application in diverse technology branches and most often cannot be replaced by other actuators. They are typically based on lead-containing piezoelectric ceramics. These should be replaced for environmental and health issues by lead-free alternatives. Multiple material alternatives are [...] Read more.

Today’s ultrasonic transducers find broad application in diverse technology branches and most often cannot be replaced by other actuators. They are typically based on lead-containing piezoelectric ceramics. These should be replaced for environmental and health issues by lead-free alternatives. Multiple material alternatives are already known, but there is a lack of information about their technological readiness level. To fill this gap, a small series of prestressed longitudinally vibrating transducers was set up with a standard PZT material and two lead-free variants within this study. The entire process for building the transducers is documented: characteristics of individual ring ceramics, burn-in results, and free vibration and characteristics under load are shown. The main result is that the investigated lead-free materials are ready to use within ultrasonic bolted Langevin transducers (BLTs) for medium-power applications, when the geometrical setup of the transducer is adopted. Since lead-free ceramics need higher voltages to achieve the same power level, the driving electronics or the mechanical setup must be altered specifically for each material. Lower self-heating of the lead-free materials might be attractive for heat-sensitive processes. Full article

(This article belongs to the Special Issue Piezoelectric Ultrasonic Actuators and Motors)

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24 pages, 4240 KiB

Open AccessArticle

Digital Hydraulic Transformer Concepts for Energy-Efficient Motion Control

by Helmut Kogler

Actuators 2025, 14(2), 54; https://doi.org/10.3390/act14020054 - 25 Jan 2025

Abstract

Hydraulic linear drive systems with conventional proportional valves result in poor energy efficiency due to resistance control. In systems with multiple actuators connected to one common pressure supply, a load-sensing strategy is often used to reduce these throttling losses. However, like conventional cylinder [...] Read more.

Hydraulic linear drive systems with conventional proportional valves result in poor energy efficiency due to resistance control. In systems with multiple actuators connected to one common pressure supply, a load-sensing strategy is often used to reduce these throttling losses. However, like conventional cylinder actuators, common load-sensing systems are also not able to recuperate the energy, which is actually released when a dead load is lowered. In order to overcome these drawbacks, in this paper, new concepts of a digital hydraulic smart actuator and a load-sensitive pressure supply unit are presented, which are qualified to reduce throttling losses and, furthermore, to harvest energy from the load. According to previous research, the basic concepts used in this contribution promise energy savings in the range of 30% for certain applications, which is one of the main motivations for this study. The operating principles are based on a parallel arrangement of multiple hydraulic switching converters, representing so-called digital hydraulic transformers. Furthermore, the storage module of the presented load-sensitive pressure supply unit is able to boost the hydraulic power in the common pressure rail beyond the maximum power of the primary motor. For exemplary operating cycles of the smart actuator and the pressure supply unit, a significant reduction in the energy consumption could be shown by simulation experiments, which offers a new perspective for energy-efficient motion control. Full article

(This article belongs to the Special Issue Actuation and Control in Digital Fluid Power)

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16 pages, 5309 KiB

Open AccessArticle

Optimizing High-Power Performance of [001]-Oriented Pb(Mg_1/3Nb_2/3)-PbTiO₃ Through Combined DC and AC Polarization Above Curie Temperature

by Yuliang Zhu, Xiaobo Wang, Wenchao Xue, Xinran Wen and Chengtao Luo

Actuators 2025, 14(2), 53; https://doi.org/10.3390/act14020053 - 24 Jan 2025

Abstract

Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ single crystals (PMN-PT SCs) are widely utilized in high-performance piezoelectric devices due to their exceptional piezoelectric properties. Among the various post-processing techniques for domain engineering in PMN-PT SCs, alternating current polarization (ACP) has become a [...] Read more.

Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ single crystals (PMN-PT SCs) are widely utilized in high-performance piezoelectric devices due to their exceptional piezoelectric properties. Among the various post-processing techniques for domain engineering in PMN-PT SCs, alternating current polarization (ACP) has become a widely adopted method for enhancing piezoelectric performance. This study proposes a new ultrahigh-temperature field-cooling polarization (UFCP) technique, combining direct current polarization (DCP) and ACP with field cooling above the Curie temperature. Dielectric spectra indicate that the UFCP method promotes electric field-induced phase transitions above the Curie point, forming a stable multiphase configuration. The transverse piezoelectric coefficient

d_{31}

of UFCP SCs is

1126 p C / N

, and the electromechanical coupling factor

k_{31}

is 0.559. Compared with traditional DCP, UFCP increases

d_{31}

by 68.6%, the mechanical quality factor

Q_{m}

by 16.7%, and the piezoelectric figure of merit (FOM) by 98.3%. Furthermore, under high-power excitation with a root-mean-square voltage of

15 V

, UFCP achieves a 343% increase in power and a 130.5% improvement in the FOM compared with DCP, demonstrating its potential for enhancing high-power performance in practical applications. Full article

(This article belongs to the Special Issue Ultrasonic Transducers for Biomedical Applications)

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16 pages, 4542 KiB

Open AccessArticle

Energy-Based Adaptive Control for Variable-Rope-Length Double-Pendulum Ship-Borne Cranes: A Disturbance Rejection Stabilization Controller Without Overshoot

by Ken Zhong, Yuzhe Qian, He Chen and Shujie Wu

Actuators 2025, 14(2), 52; https://doi.org/10.3390/act14020052 - 24 Jan 2025

Abstract

The operation process of double-pendulum ship-borne cranes with variable rope lengths is frequently complex, with numerous unpredictable circumstances, such as the swing of the load and external environmental interferences, which undoubtedly make the analysis of the swing characteristics of the system and the [...] Read more.

The operation process of double-pendulum ship-borne cranes with variable rope lengths is frequently complex, with numerous unpredictable circumstances, such as the swing of the load and external environmental interferences, which undoubtedly make the analysis of the swing characteristics of the system and the controller design more difficult. On this basis, an active disturbance rejection controller based on an energy coupling method is proposed to inhibit the double-pendulum swing angle. The controller can suppress the swing of the hook and load within 0.5 degrees under the conditions of continuous sea wave disturbances and external disturbances. Firstly, the energy function of the system is constructed by analyzing the dynamic model of the system. Then, an adaptive control method is designed by analyzing the energy function of the system. In addition, an overshoot limit term and an anti-swing term are added to limit the overshoot and swing of underactuated parts of the system. Then, the stability of the closed-loop system is strictly proven by using Lyapunov analysis. Finally, the simulation and experimental results indicate that the proposed controller ensures the accurate positioning of the jib and rope length without overshoot. Additionally, it effectively reduces the double-pendulum swing angle when there is an external interference such as waves, demonstrating strong robustness. Full article

(This article belongs to the Special Issue Modeling and Nonlinear Control for Complex MIMO Mechatronic Systems)

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21 pages, 2616 KiB

Open AccessArticle

Autonomous Tracked Vehicle Trajectory Tracking Control Based on Disturbance Observation and Sliding Mode Control

by Xihao Yan, Shuo Wang, Yuxin He, Aixiang Ma and Sihai Zhao

Actuators 2025, 14(2), 51; https://doi.org/10.3390/act14020051 - 24 Jan 2025

Abstract

This paper examines the path-tracking control issue for tracked mobile robots (TMRs) operating in complex terrains, focusing on improving their autonomous operation capabilities. Considering the system’s complex dynamic model, environmental uncertainties, and non-linear characteristics, especially the phenomenon of track slippage, a dynamic model [...] Read more.

This paper examines the path-tracking control issue for tracked mobile robots (TMRs) operating in complex terrains, focusing on improving their autonomous operation capabilities. Considering the system’s complex dynamic model, environmental uncertainties, and non-linear characteristics, especially the phenomenon of track slippage, a dynamic model that incorporates track slippage is proposed. A sliding factor observer is then designed to estimate slippage parameters, ensuring the control system remains stable and accurate despite uncertainties. A hierarchical control architecture is introduced, with the upper-level controller using a kinematic model to generate desired rotational speed commands for the left and right drive wheels. The lower-level controller, operating on a dynamic model, adjusts motor torque to achieve these desired speeds. Utilizing sliding mode control strategies, combined with adaptive laws and nonlinear control methods, the controller effectively addresses the issue of high-frequency chattering arising from the use of signum functions, thereby enhancing the lifespan of actuators and overall system control performance. A comprehensive simulation and experimental setup for real TMR systems is established to validate the proposed control strategy. Results demonstrate that the control scheme effectively achieves trajectory tracking across various unstructured terrains, exhibiting strong robustness and stability. Full article

(This article belongs to the Special Issue Advanced Actuation and Control Technologies for Vehicle Driving Systems—2nd Edition)

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23 pages, 9002 KiB

Open AccessArticle

A Light-Weight Grasping Pose Estimation Method for Mobile Robotic Arms Based on Depthwise Separable Convolution

by Jianguo Duan, Chuyan Ye, Qin Wang and Qinglei Zhang

Actuators 2025, 14(2), 50; https://doi.org/10.3390/act14020050 - 24 Jan 2025

Abstract

The robotic arm frequently performs grasping tasks in unstructured environments. However, due to the complex network architecture and constantly changing operational environments, balancing between grasping accuracy and speed poses significant challenges. Unlike fixed robotic arms, mobile robotic arms offer flexibility but suffer from [...] Read more.

The robotic arm frequently performs grasping tasks in unstructured environments. However, due to the complex network architecture and constantly changing operational environments, balancing between grasping accuracy and speed poses significant challenges. Unlike fixed robotic arms, mobile robotic arms offer flexibility but suffer from relatively unstable bases, necessitating improvements in disturbance resistance for grasping tasks. To address these issues, this paper proposes a light-weight grasping pose estimation method called Grasp-DSC, specifically tailored for mobile robotic arms. This method integrates the deep residual shrinkage network and depthwise separable convolution. Attention mechanisms and soft thresholding are employed to improve the arm’s ability to filter out interference, while parallel convolutions enhance computational efficiency. These innovations collectively enhance the grasping decision accuracy and efficiency of mobile robotic arms in complex environments. Grasp-DSC is evaluated using the Cornell Grasp Dataset and Jacquard Grasp Dataset, achieving 96.6% accuracy and a speed of 14.4 ms on the former one. Finally, grasping experiments conducted on the MR2000-UR5 validate the practical applicability of Grasp-DSC in practical scenarios, achieving an average grasping success rate of 96%. Full article

(This article belongs to the Section Actuators for Robotics)

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