Mechatronics最新文献

Health monitoring of robot manipulators is crucial for their long-term reliable operation. Since the feedback data provided by the controller of robot manipulators are most often from the actuator’s side, health monitoring of rotate-vector (RV) reducers housed on the output of actuators is challenging. To avoid the increased cost and complexity of adding sensors to robot manipulators, this paper investigates the long-term health monitoring of RV reducers, using only feedback data from the controller. A generic model for RV reducers is first developed to characterize their nonlinear behaviours and performance degradation. The model is then extended to robot manipulators to analyse their dynamic response under the time-varying excitation generated by healthy and faulty RV reducers. Next, a new motor-torque-based residual together with an adaptive threshold is proposed for the health monitoring of RV reducers, taking payload, measurement noise and friction disturbance into account. The proposed threshold depends only on the variance of measurement noise, and is therefore easy to implement in practice. Extensive simulations and experiments are conducted on two robot manipulators to validate the proposed model, residual and threshold. The results show that the proposed model is able to account for the effects of faults and nonlinear behaviours of RV reducers on the motor performance. The proposed residual with an adaptive threshold is sensitive to faults in RV reducers and robust to friction disturbance and time-varying payload, and it outperforms conventional momentum-based residuals.

Harvesting energy from wind-induced vibration utilizing piezoelectric mechanism has attracted much attention for enabling energy-autonomous wireless sensor systems over the past decade. To offer a promising solution for low reliability, poor environmental adaptability and narrow operating bandwidth of existing piezoelectric wind energy harvesters, a wind-isolated galloping energy harvester with an embedded piezoelectric transducer (EPT-WGEH) is proposed in this paper. Unlike previous most directly-excited piezoelectric wind energy harvesters, the EPT-WGEH was characterized by an indirectly-excited shelter-structure, which isolates the embedded piezoelectric transducer (EPT) from the flow environment. Meanwhile, the horizontal swing of the hollow cylinder and the elastic pendulum beam is transformed into the vertical swing of the EPT mounted in the hollow cylinder under wind excitation. Therefore, this 2-DOF indirectly-excited EPT-WGEH could possess both high reliability and small volume. A CFD simulation model was established to analyze the influence of structural parameters on the vibration characteristics of EPT-WGEH. To verify the feasibility of the principle and design regarding the proposed EPT-WGEH, a prototype of the EPT-WGEH was fabricated and tested in terms of electrical output and operating bandwidth. The results showed that the length of elastic pendulum beam, proof mass, and wind speed brought significant effects on the electrical output, minimum working wind speed and operating bandwidth. The maximal output voltage increased with the decreasing length of elastic pendulum beam or the increasing proof mass. Meanwhile, there existed some optimal combinations of parameters to minimize the minimum working wind speed of EPT-WGEH. Besides, the optimal output power of EPT-WGEH could reach 2.4 mW at load resistance of 600 kΩ. The EPT-WGEH could light up 75 series-connection commercial blue LEDs simultaneously at the wind speed of 15 m/s and demonstrated its practical power supply capability by charging capacitors.

Most hydraulic drive systems for robots are configured with one single pump and multiple cylinders, which suffers from low energy efficiency in the case of driving the variable loads. To solve the problem, this paper presents a multi-chamber hydraulic cylinder based on the bionic muscle drive mechanism. Firstly, the mechanical structure is designed, the mathematical models are derived, the mechanism of high energy efficiency is analyzed. Then, the simulation of load matching control is carried out, which shows the high energy efficiency improvement and the good position tracking. Finally, the multi-chamber hydraulic cylinder prototype is developed for experimental study, and output forces, output displacement, energy consumption, and friction characteristics are researched. The theoretical analysis and experimental research show that the bionic multi-chamber hydraulic cylinder can realize the power matching between the single power source and the variable loads in the hydraulic system, which provide a novel idea for the energy efficient hydraulic equipment.

Sample-tracking vibration isolators position their mover such that the distance to a targeted sample is constant to provide a vibration-free environment, for example, for inline metrology with high resolution. To achieve high vibration isolation and rejection especially at low frequencies, this paper proposes a sample-tracking vibration isolator that integrates a flexure-guided hybrid reluctance actuator (HRA) with a negative stiffness for quasi-zero stiffness (QZS). The negative stiffness cancels the flexure stiffness for QZS, by which vibrations transmitted from the actuator’s stator can be significantly reduced. Unlike conventional QZS systems, the negative stiffness is magnetically realized with rigid components such as a permanent magnet and ferromagnetic cores. Consequently, the proposed vibration isolator has mechanical resonant frequencies of around 2.5 kHz and higher. This hardware design with a feedback controller realizes a motion with nanometer resolution and a high closed-loop control bandwidth of 991 Hz for further vibration isolation and sample tracking. To evaluate the performances of the proposed vibration isolator, the negative stiffness is tuned to cancel a flexure stiffness at experiments. Experimental results show that the fine tuning decreases transmissibility from $-30$  dB to $-62$  dB by a factor of 40 at a low frequency of 10 Hz. Furthermore, the tracking error of the mover position is measured for a demonstration of the vibration rejection performance in the time domain. The results also show that the stiffness cancellation decreases the tracking error with feedback control from 2.7 nm (rms) to 1.3 nm (rms) by 52% at a steady state. The proposed sample-tracking vibration isolator successfully demonstrates high vibration isolation performance by utilizing the rigid negative stiffness of the HRA.

This paper investigates a practical adaptive internal model control (IMC) for an unmanned surface vehicle (USV) with unknown time-varying nonlinear model parameters and environmental disturbances. Firstly, an internal model of the USV is presented using the Bidirectional Long Short-Term Memory (BiLSTM) neural network. Then, an adaptive neural IMC controller is designed for the trajectory tracking of USV by using the IMC method. The internal model and the controller are updated by an error threshold algorithm. The proposed control scheme comprises of a trajectory guidance module via the Line-of-Sight (LOS) guidance method and a tracking control module designed by IMC theory. Under the proposed control scheme, the development processes of the vehicle platform and the control algorithms are described, and accurate tracking control can be achieved. Finally, the results of simulation and field experiments are presented and discussed to validate the effectiveness of the proposed control scheme.

The paper presents a control-oriented modeling method for wet clutch friction, considering thermal dynamics, with a focus on paper-based friction linings. Abrupt engagements of such clutches may lead to discomfort and reduce the overall lifespan. The limitations of feedback control, attributed to restricted sensors and modeling inaccuracies, underscore the effectiveness of model-based control employing precise and invertible models. The study extensively explores the largest model uncertainty in slip control—clutch friction. The proposed model integrates the Coulomb friction coefficient, incorporating variables such as pressing force, friction speed, and the temperature of the friction surface. The proposed torque model enables model inversion, allowing the determination of desired oil pressure from torque requirements. Experimental data, comprising 184 sets, validate the model accuracy, with a focus on temperature effects. The Coulomb friction coefficient model exhibits exponential and linear components, capturing the Stribeck effect and temperature variations. Model verification through experiments demonstrates good agreement, supporting its efficacy for wet clutch control performance. The study contributes insights into wet clutch friction models for model-based control.

As wind turbines become larger and move into deeper sea, their operating environment worsen. The torque fluctuation inside the drive chain is aggravated, which leads to the premature failure of the wind turbines. To improve the transmission stability of wind turbines, the mechanical-hydraulic hybrid transmission system (MHHTS) has been applied. However, existing research has issues with structure and hydraulic control. An MHHTS structure was proposed to meet the requirements of structural simplicity and high efficiency, corresponding to the design principles summarized in the article. Based on this structure, we have selected a hydraulic control mode, the constant displacement pump variable displacement motor (CPVM), that satisfies the reasonable utilization of displacement and the stability of control. This mode was chosen by comparing the displacement and pressure variation rules of three hydraulic control modes that meet the maximum power point tracking (MPPT) control principle of the wind turbine. In this study a co-simulation model of a 10 MW MHHTS wind turbine was built using Simulink and AMEsim. The correctness of the structural and control mode ware verified by co-simulation with a uniformly varying wind. Moreover, a method that can suppress fluctuations in output power by controlling the motor displacement was proposed. Different-step winds response analyses were conducted to explore the relationship between the displacement response speed and the output power fluctuations. The non-linear relationship between the displacement and the wind speed can also have an impact on the previous relationship. Finally, the feasibility of the control method was verified through simulation of an actual turbulent wind. These achievements should guarantee the future application of the novel transmission system in wind turbines.

A modular magnetic levitation system with static square coils and a moving 2D Halbach array is proposed in this paper. The mover achieves six degrees of freedom (DOF) motion with long stroke translational motion and yaw motion. A novel 2D lookup table is used to model the force and torque on the mover, including the edge effect. The 2D lookup table uses force decay ratio (FDR) and effective torque arms (ETA) to reduce the table dimension. At each levitation height, the proposed data-driven model reduces table size from 964,806 points to 791 points. This reduced-dimension table is validated to support the 6 DOF motion, including infinite yaw rotation. Then, a direct wrench and active coil selection method is used to decouple the force and torque and determine the coil currents. With the force and torque model and the active coil selection method, the mover can move across different sets of active coils for long stroke movement. Lastly, experimental validation results are presented. The motion range is $\pm$120 mm in the horizontal direction, with a maximum speed of 500 mm/s. The system is validated to have a full 360° range of yaw motion with a maximum speed of 75 °/s.

In this paper, a new type of robotic finger is introduced that uses a twisted string actuator (TSA) and modular passive return rotational (PPR) joints. The design is intended to be simple, compact, lightweight, and energy-efficient while producing high grasping force with a relatively small motor. The PPR joints are based on the beam-buckling principle and are designed to match the non-linear TSA force profile, resulting in high grasping force throughout the finger’s full flexion motion and passive finger extension. To evaluate the performance of the robotic finger, we fabricated a prototype and conducted experiments to assess its object grasping cycle, passive finger extension, grasping force, stable grasping condition, shape adaptability, and energy consumption. The finger weighs 170 grams and achieved a high force throughout the flexion motion, producing a maximum grasping force of 43.3 N at full flexion using a stall torque of 32 mNm. The modularity of the PPR joint allows for scalability and adaptability to handle different objects. We also demonstrated the finger’s potential as a wearable sixth robotic finger (SRF), evaluating its object grasping competency, shape adaptability, and wearability. The finger was able to grasp various objects with a maximum payload of 1.0 kg and a hanging payload of up to 5 kg. Overall, the proposed robotic finger has the potential to be used as an SRF to compensate for arm disorders’ grasping capability.

Robotic machining systems have been widely implemented in the assembly sites of large components of aircraft, such as wings, aircraft engine rooms, and wing boxes. Milling is the first step in aircraft assembly. It is considered one of the most significant processes because the quality of the subsequent drilling, broaching, and riveting steps depend strongly on the milling accuracy. However, the chatter phenomenon may occur during the milling process because of the low rigidity of the components of the robotic milling system (i.e., robots, shape-preserving holders, and rod parts). This may result in milling failure or even fracture of the robotic milling system. This paper presents a feasible spindle speed interval identification method for large aeronautical component milling systems to eliminate the chatter phenomenon. It is based on the chatter stability model and the analysis results of natural frequency and harmonic response. Firstly, the natural frequencies and harmonics of the main components of the robot milling system are analyzed, and the spindle speed that the milling system needs to avoid is obtained. Then, a flutter stability model considering the instantaneous cutting thickness is established, from which the critical cutting depth corresponding to the spindle speed can be obtained. Finally, the spindle speed interval of the robotic milling system could be optimized based on the results obtained from the chatter stability model and the analysis result of the natural frequency and harmonic response of the milling system. The effectiveness of the proposed spindle speed interval identification method is validated through time-domain simulation and experimental results of the large aeronautical component milling system.