Principle and Characteristics of Novel 2-degree-of-freedom Electro-mechanical Transformers Used in Valves
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A novel 2-degree-of-freedom electro-mechanical transformer (2-DOF EM) with two moving parts was proposed to meet the high speed response of electro-mechanical transformer required by servo proportional valves. The principle on which it decreased the response time of a servo proportional valve was explained. Three of its several possible structures were introduced. The magnetic circuit of one typical structure, a hybrid two-input 2-DOF EM was analyzed, and its output characteristics in every case were derived with finite element method (FEM). Analysis results indicate that the 2-DOF EM can control the two linear moving parts simultaneously, drive them to move in the same or opposite direction. It can be used in the control of servo proportional valves and other equipments which have two linear moving parts.Keywords:
Electrohydraulic servo valve
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This paper proposes a computational method for predicting the dynamic response characteristics of a long stroke-linear solenoid actuator with complicated shaped armature. In this method, the magnetic field is coupled with the electrical supply and the mechanical movement of the actuator, employing the axisymmetric finite clement method (FEM). The influence of applied voltage on the response characteristics are investigated. As the result of that, computational error of 22.8% arises when applied voltage of 4.8 V is fed, however, the error remains less than 2% when the applied voltage is higher; 5.8 V and 6.8 V. These results verify the utility of this method. In addition, the influence of the control method on transient response during positioning control is also examined, and the validity of PID (proportional, integral and differential) control is confirmed.
Solenoid
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In this paper, the servo thrust and mechanical structure are analyzed in frequency domain using Maxwell Tensor and Dale Bert’s principle, respectively. Three modes of mechatronic coupling are found as follows. 1) The thrust spectrum varies with velocity, which leading to a worse dynamic precision and even instability when the coupling occurs at a certain resonance frequency between the thrust and the mechanical structure; 2) The coupling occurs between mechanical structure and servo system when adjusting the gain in speed control loop or current control loop. 3) The output of linear encoder will fluctuate due to the variation of normal force between the mover and stator, which leading to the variation of the servo thrust spectrum and a re-coupling between servo drive and mechanical structure. In addition, the mechanism and influence factors of the three types of coupling are studied, respectively. The results show that the spectrums of servo drive system and mechanical structure evolve under different control parameters and operational condition, and happen to interaction once at the same natural frequency. Finally, the associated experiments are performed to verify the previous analysis.
Servomechanism
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In keeping with consumers’ preferences for electromagnetic motors of ever smaller power consumption, it is necessary to improve the power efficiency of the electromagnetic motors used in unmanned aerial vehicles and robots without sacrificing their performance. Three-degree-of-freedom (3-DOF) spherical motors have been developed for these applications. Accordingly, this study modifies the 3-DOF spherical motor proposed by Hirata’s group in a previous study (Heya, A.; Hirata, K.; Niguchi, N., Dynamic modeling and control of three-degree-of-freedom electromagnetic actuator for image stabilization, IEEE Transactions on Magnetics 2018, 54, 8207905.) to accomplish a 3-DOF spherical motor for camera module with higher torque output in the large rotation angle. The main contribution of this study is to improve the static torque in the X- and Y-axes with an improved electromagnetic structure and a particular controlling strategy. In the structural design, eight symmetrical coils with specific coil combination are used instead of conventional four symmetrical coils. In this study, the development of the proposed 3-DOF spherical motor was constructed and verified by using a 3D finite-element method (3D FEM). The simulation results show that the proposed 3-DOF spherical motor has higher torque output in the large rotation angle when compared to the original 3-DOF spherical motor.
Voice coil
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This paper introduces a self-sensing technique of self-bearing motor by using the differential transformer principle. This self-sensing technique has wide linear range than the other technique due to the use of the carrier frequency component. Therefore it is expected to have robust displacement information for the temperature fluctuation. This technique uses the structure of the motor and levitation coils which are similar to the differential transformer. In this paper, the fundamental principle is introduced how the self-sensing is achieved by the differential transformer principle. Then the differential output characteristics is examined experimentally. Finally levitated rotating test is carried out by self-sensing control.
Magnetic Levitation
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Multi-degrees-of-freedom (DOF) actuators have become more useful in the field of robotics, as a result of the increasing number of DOFs of systems. The general features of ultrasonic motors are suitable for constructing a direct-drive multi-DOF actuator. However, previously developed ultrasonic motors do not have advantages in volume and weight in contrast to multi-DOF motion units composed of plural electromagnetic motors. In the present study, authors developed a novel multi-DOF ultrasonic motor with a compact plate stator and spherical rotor. First, a new driving principle of the motor is proposed. Next, the stator geometry is designed in detail using the finite element method, and a prototype of the multi-DOF ultrasonic motor is produced. Then, vibration characteristics of the stator and driving characteristics of the motor have been measured, respectively. The results confirm that the motor successfully provides the desired multi-DOF motion of the rotor around orthogonal axes driven by a single plate stator. Finally, a novel self-oscillation driving circuit for the motor is proposed and driving tests using the circuit are conducted.
Ultrasonic motor
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The present work deals with a method for the modeling of a three-way servo-proportional valve actuated by a proportional solenoid. The model incorporates the primary nonlinear phenomenon exist in the solenoid, such as the hysteresis, nonlinear inductance and counter-electromotive force. Two ways are employed to simplify the model for the purpose of controller design. Firstly, the relations of current supply vs. flux linkage and flux linkage vs. electromagnetic force under different displacements of armature are captured by curve fitting and interpolation, with the advantage of keeping the nonlinear characteristics. Then the linearization method around the null-position of the spool is implemented, where the solenoid is modeled as a 1-order system, and the body of valve is treated as mass-spring 2-order system. Then the test-bed for the identification of main parameters and verification of the model is designed. The parameters are obtained from the experimental results where the armature and spool are locked at different positions. Finally, the model is verified as the dynamic responses of current supply and displacement of spool obtained from the simulation model agree well with the experimental results when the armature and spool are unlocked.
Flux linkage
Solenoid
Solenoid valve
Counter-electromotive force
Linearization
Servomechanism
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Synchronous planar actuators with moving magnets, stationary coils and a 6-DOF magnetic suspension are complicated to control. It is not possible to decouple forces and torques by applying a sinusoidal commutation scheme as is common in regular synchronous AC motors. Several commutation methods are developed based on the coupling matrix, that links the current in each coil to the force and torque vector on the actuator. Accurately calculating this position varying coupling matrix in real-time while the actuator is moving, is critical in controlling the planar actuator. In this paper, a look-up table based method is proposed that uses several small look-up tables and symmetries in the design that allows accurate real-time calculation of the coupling matrix.
Commutation
Matrix (chemical analysis)
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Proportional electromagnetic valve is an important element in hydraulic pressure systems.The operation behavior of a hydraulic system mainly depends on the characteristic of the electromagnetic actuator used.Therefore,how to improve property of the actuator(driver)proportional valve,when designed well,Permanent magnetic moving winding liner motor can offer it can be controlled easily and can be used in many situations.Akind of permanent magnetic moving winding liner motor is designed in this thesis.
Linear actuator
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To control differential cylinders with an AC servo motor driven constant pump is a new method and recently becomes the research focus for energy saving in electro-hydraulic control systems.Since the pilot check valve for flow distribution was incompetent,three flow distribution windows were used to compensate the different volumetric flow caused by differential cylinder area ratio.This method can reduce the flow exchange of the pilot check valve,and improve the system's energy efficiency.Due to the existed problems,such as serious non-linearity,bump leakage and other uncertain factors in the system,higher noise and stronger vibration were generated when the cylinder was retracted.To overcome these disadvantages,a compound control algorithm that combined velocity and acceleration feed-forward compensation with anti-saturation integral separation PID controller was adopted.The controller's parameters were determined by simulation.The experimental results demonstrate that the proposed method has effectively improved the system's dynamic properties and robust stability,reduced noise and vibration,and thus achieve the symmetry of moving speed in both directions.
Electrohydraulic servo valve
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Background: Linear motion devices for industrial machines and robots are expected to realize their high efficiency drive and simple structure. Usually, a feed screw mechanism composed of a rotary motor and a ball-screw or slide-screw is employed. However, it has some problems such as the decrease of the drive efficiency, flexibility against external forces, noise, etc. Various linear actuators and motors have been developed utilizing the feature of a direct drive.
Aim: In this paper, we propose a novel linear actuator which 2 movers can be independently controlled using 3-phase and 6-phase superimposed currents for decreasing the size and weight of the system. The proposed linear actuator is driven by the operating principle of a vernier motor which is expected to achieve a high thrust force density per permanent magnet volume.
Methods: The operating principle and the static thrust force characteristics of the proposed linear actuator are verified by an electromagnetic field analysis using 3-D finite element method, and the back electromotive force characteristics are also analyzed. In addition, the dynamic characteristics under position feedback control are analyzed. The control system uses a vector control using PID controller, and the control input is given by the 3-phase and 6-phase superimposed currents.
Results: The static force characteristics were investigated. From the analyzed results, the force interference between the two movers was small. Moreover, the interference of the back electromotive force of the 3-phase and 6-phase movers were not observed. The movers could be independently driven under position feedback control using 3-phase and 6-phase superimposed currents. The dynamic characteristics analyses showed that the mover well followed a target position. From a step response, the time constant and the response of the position feedback system were investigated.
Conclusion: This paper presents a linear vernier actuator with two movers. The basic structure and operating principle of the actuator were described. Moreover, the static characteristics and the dynamic characteristics under position feedback control were analyzed. It was found that the movers can be independently driven.
Linear actuator
Counter-electromotive force
Ball screw
Linear motion
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