Spherical Actuator Research Articles

Nano-Motion X-Y Stage by Pneumatic Servo Spherical Bearing Actuators

With the development of IC technology, ultraprecise positioning actuators with nanometre-order resolution are in demand, especially for semiconductor stepper equipment. A prototype X-Y stage for ultraprecise positioning composed of six pneumatic servo spherical bearing actuators (PSSBAs) was developed and its specifications were evaluated especially focusing on the step response and its minimum resolution. The minimum positioning resolution of the prototype was 3 nm under the best conditions, and the positioning resolution as a practical specification was approximately 10 nm for all conditions, even without feedback controls. With a simple feedback control, the minimum resolution was improved to 1 nm, which is enough to meet the demands of current ultraprecise positioning technology.

Design and control of a three degree-of-freedom permanent magnet spherical actuator

This paper presents a permanent magnet (PM) spherical actuator embedded with a novel three-dimensional (3D) orientation measurement system. The study covers actuator design, torque modeling, and motion control. The spherical actuator consists of a stator with 24 coils and a rotor with 8 PM poles. A high accuracy and resolution, non-blinding 3D measurement mechanism is designed for the rotor orientation detection. The torque output is formulated from finite element (FE) computation and curve fitting method. Due to the nonlinear property of dynamic model, computed torque control law is utilized for the three degree-of-freedom (3-DOF) system motion control. The space geometry method is employed to study the redundancy feature of current inputs, which offers the opportunity for control optimization to improve the power efficiency and the fault tolerance capability of the spherical actuator. Simulations and experiments are then conducted on the developed prototype to validate the design concept, mathematic models and control strategy.

Development of Flexible Spherical Actuator Controlled by Low-Cost Servo Valve and Embedded Controller

A wearable actuator needs to be flexible so as not to injure the human body. The purpose of our study is to develop a flexible and lightweight actuator which can be safe enough to be attached to the human body, and to apply it to a flexible mechanism and rehabilitation device. New types of flexible pneumatic actuator that can be used even if the actuator is deformed by external force have been developed in our previous studies. In this paper, we propose and test a flexible spherical actuator using the novel flexible pneumatic cylinders. The simple spherical actuator consists of two ring-shaped flexible pneumatic cylinders. They are intersected at right angle and are fixed on the base. The low-cost control system using the tested quasi-servo valves and an embedded controller (micro-computer) was also developed. The spherical actuator was also improved so as to suppress the vibration in control and to increase the stiffness of the actuator by changing the structure of the actuator. In addition, by using the quasi-servo valve controlled by the superior embedded controller, the flow rate of supply and exhaust could be controlled independently. As a result, the control performance could be improved using the improved spherical actuator and the quasi-servo valves controlled by the embedded controller with compensational method for exhaust.

REVIEW ON PIEZOELECTRIC, ULTRASONIC, AND MAGNETOELECTRIC ACTUATORS

Piezoelectric actuators operating in piezoelectric-induced strain/stress or electromechanical resonance-induced vibration or wave-motion friction drive mechanism have shown many advantages over traditional electromagnetic motors, especially, when miniaturizing into millimeter-scale size, while magnetoelectric actuators operating in magnetostrictive mechanism are capable of piezoelectric self-sensing and remote operation under an applied magnetic field. This paper summarizes the recent progresses in piezoelectric ceramic and single crystal materials based actuators and micromotors, ferromagnetic/ferroelectric laminated magnetoelectric actuators, including rotary, linear, planner, and spherical motion actuators, and bending motion magnetoelectric actuators. Their driving mechanisms, operation properties, and applications are also explained.

Finite Element Analysis and Structural Optimization of a Permanent Magnet Spherical Actuator

In order to derive the characteristics and adjust the electromagnetic system to the ultimate purpose of achieving better torque output and material usage reduction with constraints, this paper presents the finite element analysis and using improved niche genetic algorithm to the optimal design of a permanent magnet spherical actuator. The magnetic field distribution and torque calculation model based on finite element software are introduced and discussed. The proposed optimization algorithm surmounts effectively the local convergence problem of standard genetic algorithm. The sharing-between-population mechanism is proposed by means of using the better factor of population, saving best result strategy and enhancing global and partial searching ability for earlier achievement of optimal solution. The results show the output torque has been increased and the material has been effectively saved by comparison, which provides the references for related problems. Ill. 5, bibl. 15, tabl. 6 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.114.8.699

Design and Modeling of a Spherical Actuator with Three Dimensional Orientation Measurement System

This paper presents the design and modeling of a permanent magnet spherical actuator which consists of a rotor with eight cylindrical permanent magnet (PM) poles and a stator with twenty-four air-core coils. Torque and dynamic model of this PM spherical actuator are formulated analytically. An optimal design procedure is proposed to achieve a high torque output, and significant design parameters of the actuator are discussed. As there is no effective method for three dimensional orientation measurement of the spherical actuator currently, a novel orientation measurement system is proposed. Finally, experimental works are carried out, and the experiment results demonstrate the effectiveness of the proposed orientation measurement system.

A novel approach for positional sensing of a spherical geometry

Due to the proliferation of new technologies and demands for dexterous robotics manipulators, multi-degree-of-freedom (MDOF) spherical actuators are widely sought after. These actuators are utilized primarily in the assembly sectors, precision machining and active tracking devices. Prior to realizing a feasible MDOF actuator for any practical use, positional closed loop feedback is of paramount importance. To date, commercially available encoders are mainly limited to single-DOF sensing. Furthermore, integration of these sensors inherently introduces mechanical linkages that compromise the overall performance of the system. This paper introduces an alternative approach in orientation sensing leverages on contactless sensing of conventional optical mouse sensors. The theory and design methodology of this sensing method is being discussed and presented. Experimentation was also conducted for conceptual verification. The uniqueness of this technique lies in the exploitation of the imaging capability of the mouse sensor generating incremental counts of the displacement of the spherical rotor surface. The test platform being established is expected to lay the foundation for optimizing key parameters. With the successful implementation and validation of this new sensing system, future development will be improving its performance for real-time feedback control.

A Three Degree-of-Freedom Optical Orientation Measurement Method for Spherical Actuator Applications

The advance of robotics, actuators and manufacturing technology motivates the research on measurement of multiple degree-of-freedom (DOF) rotational motions. A novel laser-based noncontact high-precision spherical displacement measurement methodology has been proposed for spherical actuator applications in this paper. The laser detector is utilized to measure the distance from the target to the detector on several light spots, and thus to calculate the rotation angle of the rigid body in three directions. As there is no physical contact between the laser detector and the moving body, additional mass/moment of inertia and friction on the rotor are avoided, and thus the working efficiency of moving body can be improved. The algorithm of orientation angles has been derived. Experimental apparatuses have been developed to evaluate the working performance of the measurement method. Comparison between experimental and analytical results shows that the proposed method can achieve high-precision measurement for multi-DOF rotational motions. Precision of the laser-based angular displacement measurement method can be improved further by increasing the slot density on the rigid body or using new models of laser detectors.

Neural network identifier-based dynamic decoupling control of a novel permanent magnet spherical actuator

The real-time torque calculation and dynamic modelling have been the difficulties in the motion control of the permanent magnet spherical actuator. Based on the presented new configuration design, a simplified torque calculation model and a non-linear system dynamic model have been proposed. The perturbation of the system parameters, the model error and the external disturbance result in the actual system uncertainties, which have great effects on the control performance and caused the interferences on three degrees-of-freedom. Based on the modelling, this paper also presents the dynamic decoupling control scheme for the permanent magnet spherical actuator with neural network identifier. The feed forward neural network and adaptive learning algorithm are adopted to construct the neural network identifier for online identification of uncertainties and unmodelled dynamic parts in the motion process. The simulation and experiment results show the effectiveness of the proposed method by alleviating the inter-axis cross-coupling influences and offering high robustness to guarantee the static and dynamic performances.

Dynamic Analysis of 3 DOF Actuator Employing 3 D Finite Element Method

This paper describes the dynamic analysis method of a three degree-of-freedom electromagnetic spherical actuator considering the mutual effect among X-, Y- and Z-axis employing the 3-D finite element method, in which the magnetic field equation is fully combined with equations of electric circuit and motion. The validity of the analysis is confirmed by comparing with the measured results on a prototype.

Analysis of Pole Configurations of Permanent-Magnet Spherical Actuators

This paper presents a generic design concept of three degree-of-freedom (3-DOF) permanent-magnet (PM) spherical actuators. A ball-shaped rotor mounted with multiple layers of PM poles is concentrically housed in a spherical-shell-like stator with multiple layers of air-core coils. This design allows more rotor and stator poles to be incorporated to increase torque output and motion range of the actuator. The magnetic field and torque modeling methods are generalized to multiple layers of poles, which provides a convenient way to analyze field distribution and torque performance of spherical actuators with various pole configurations. The simulation results of flux distribution and torque variation of double-layer configuration are compared with those of single-layer one. It shows that the magnetic field distribution and torque variation for both configurations are coincident with PM-pole arrangement on the rotor surface. The tilting torque of double-layer design is larger than that of single layer, and the torque variation is more uniform. The spinning torque of single layer is relatively large. The proposed analyzing methods of field and torque could be employed for preliminary study of other PM spherical actuators.

Hybrid torque modeling of spherical actuators with cylindrical-shaped magnet poles

A ball-joint-like three-degree-of-freedom (3-DOF) spherical actuator which features a ball-shaped rotor with multiple permanent magnet (PM) poles and a spherical-shell-like stator with air-core coils is proposed to achieve omni-directional smooth motion in only one joint. Unlike previous study in which dihedral-shaped PMs are employed as the rotor poles, this paper utilizes cylindrical-shaped PMs to facilitate the fabrication and reduce the system cost significantly. Torque output of the spherical actuator is formulated with a hybrid method, i.e., using both analytical and experimental methodologies. Specifically, the analytical torque model of spherical actuator with dihedral-shaped PM poles is derived. Then a research prototype with cylindrical-shaped PM poles is developed, and a torque measurement testbed is built up to conduct experiment on the prototype. As the torque variation trend of actuators using two different types of PM poles with respect to the rotor orientation is similar, parameters in the analytical model are adjusted to fit with the experimental measurements. The resulting torque model can be employed for real-time motion control of the actuator. The cylindrical-shaped PM poles also reduce the inertial moment of the rotor by 60%, which is favorable for achieving better dynamic performance of the spherical actuator.

Dynamic analysis method of spherical resonant actuator using 3D finite element method

PurposeThe purpose of this paper is to develop a dynamic analysis method of a novel spherical resonant actuator. In this method, the magnetic field equation is coupled with the electric circuit equation and the motion equation with the mesh modification method using the Laplace equation applied to the rotation of the spherical actuator.Design/methodology/approachThe static torque characteristics and dynamic characteristics of the spherical resonant actuator using the proposed method are clarified. The calculated results are compared with the measured ones.FindingsThe calculated static torque agrees well with the measured one. The validity of the computation using the proposed method is quantitatively clarified through the comparison with the measurement.Originality/valueThe paper proposes the dynamic analysis method of the complicated spherical resonant actuator using the mesh modification method by the Laplace equation.

Proposal of electromagnetic spherical actuator with 3‐DOF

PurposeThe purpose of this paper is to propose a new electromagnetic spherical actuator with three‐degree‐of‐freedom. Multi‐degree‐of‐freedom actuators which can be operated in arbitrary axis come to attract attention because of the solution for efficiency, weight, size, and so on. Particularly, spherical actuators are studied as the application to the joints and eyeballs for robots because they can be freely rotated in every axis direction.Design/methodology/approachThe paper proposes a new electromagnetic spherical actuator with three‐degree‐of‐freedom in rotation, and the torque characteristics of the actuator are computed by the 3D finite element method (FEM). The validity of the computation is confirmed through the measurement of a prototype.FindingsIt is found that this actuator realized the high torque of more than 1.0 Nm in every axis circumference.Originality/valueA new spherical three‐degree‐of‐freedom actuator is proposed. The torque characteristics of the improved model are calculated employing the 3D FEM. The validity of the analysis is verified through the comparison with the measured results of the prototype. Furthermore, the improved model is proposed to increase the torque, and the effectiveness of the model is confirmed.

The static response of functionally graded radially polarized piezoelectric spherical shells assensors and actuators

This paper analyzes the static response of a functionally graded spherical shell made ofpiezoelectric materials. A hollow piezoelectric sphere is polarized in the radial direction.Spherically symmetric problems of piezoelectric spherical shells as sensors or actuators areconsidered. For the gradient of power-law behavior, closed-form explicit expressions for theelectroelastic field are derived. These solutions can serve as benchmarks for functionallygraded piezoelectric hollow spheres. For arbitrarily varying gradient, an analyticapproach for reducing the problem to a Fredholm integral equation is suggested toobtain the responses of the electroelastic field. Numerical results for a sphericalpiezoelectric vessel are obtained for special radial nonhomogeneity, and the distributionof the radial and circumferential stresses as well as the response of the electricpotential for sensors and actuators are presented graphically under electrical andmechanical stimuli, respectively. Our results indicate that the gradient indexstrongly affects the stress distribution and electric response. The obtained results arehelpful for optimizing the design of hollow spherical piezoelectric transducers.

三自由度球面アクチュエータの動作特性解析に関する研究

In this paper, coupled method for the dynamic characteristics of a 3-D electromagnetic spherical actuator under the open-loop control is proposed by the 3-D finite element method, in which the magnetic field equation is combined with equations of electric circuit and three-axes motions. The validity of the analysis is confirmed by comparing with the measured results of a prototype.

Electromechanical Modeling of a Permanent-Magnet Spherical Actuator Based on Magnetic-Dipole-Moment Principle

Theoretical modeling in any engineering design is of paramount importance as it establishes the interrelationship between variables being analyzed in a given condition. With regard to the design of a permanent-magnet spherical actuator, electromechanical modeling is crucial as it correlates the input parameters such as current to the output mechanical torque. In this paper, a new approach in electromechanical-torque formulation for this class of spherical actuator employing the magnetic-dipole-moment principle is being discussed. Derivation from first principle and the extension of this novel method in the acquisition of the 3-D resultant torque induced on the rotor are presented. The proposed approach circumvents the need for electromagnetic-energy analysis within the air gap between the rotor and stator poles and, henceforth, providing a direct computation of the resultant torque. The validity of the proposed analytical torque model was verified against numerical and empirical data. Comparisons between the 3-D torque results demonstrate the correctness and soundness of the proposed electromechanical torque model.

Static behaviour of a laminated composite spherical shell cap with piezoelectricactuators

The behaviour of a laminated composite spherical shell cap with piezoelectric layerssubjected to external static load and electrical potential is investigated using the finiteelement method based on first-order shear deformation theory. An eight-node degeneratedisoparametric shell element with five degrees of freedom at each node is considered. Thecontrol of deflection and stresses in a laminated composite spherical shell capwith piezoelectric actuators subjected to external load and electrical potential isinvestigated. Results are presented for the control of deflection and stresses of simplysupported and clamped laminated composite spherical shell caps with piezoelectricactuators subjected to uniform normal pressure by applying an electrical potential.

Design and Analysis of a Permanent Magnet Spherical Actuator

This paper has proposed a 3-DOF spherical actuator consisting of a ball-shaped rotor with a full circle of permanent- magnet (PM) poles and a spherical-shell-like stator with two layers of circumferential air-core coils. One key feature of this design is the parametrization of PM and coil poles. Based on the torque model of the PM spherical actuator, the relationship between poles' parameters and torque output can be demonstrated. As a result, the actuator design aiming at achieving maximum torque output can be carried out from the relationships. Another advantage of this spherical actuator is its singularity-free workspace, which is verified with the actuator torque model and condition numbers.

New Spherical Resonant Actuator

This paper presents a new spherical resonant actuator. And the basic construction and the operating principle of the actuator are described. The dynamic characteristics are computed using the combined method of the 3-D FEM and the Runge-Kutta Method to easily couple with the equations of electric circuit and motion. As a result, computed results agree well with the measurement of the prototype. The effectiveness of the computation method for the spherical actuator is also clarified.