Abstract
This paper proposes a new type of noncontact magnetic suspension system using two permanent magnets driven by rotary actuators. The paper aims to explain the proposed concept, configuration of the suspension system, and basic analyses for feasibility by FEM analyses. Two bar-shaped permanent magnets are installed as they are driven by rotary actuators independently. Attractive forces of two magnets act on the iron ball which is located under the magnets. Control of the angles of two magnets can suspend the iron ball stably without mechanical contact and changes the position of the ball. FEM analyses have been carried out for the arrangement of two permanent magnets and forces are simulated for noncontact suspension. Hence, successfully the required enough force against the gravity of the iron ball can be generated and controlled. Control of the horizontal force is also confirmed by the rotation of the permanent magnets.
Keywords
Introduction
In recent years, miniaturization and refinement in machine products has been remarkable, and in the production process, here is a need for a transfer device capable of maintaining the accuracy of precision parts, a functional assembly device in a clean room environment. At present, these operations are mainly performed by robot arms and human hands, but there may be problems such as deformation of parts due to contact and the decrease in accuracy and generation of dust. Therefore, it is thought that if these parts could be supported without contact, these problems could be solved.
The use of air pressure, static electricity and magnetic force, etc. has been proposed for noncontact support [1]. Those using air pressure can obtain relatively high levitation force, and there are few restrictions on the object, but the generation of dust due to air ejection is considered to be unsuitable for a clean room environment. In the case of using static electricity, the levitation force acts if the object is not an insulator, but it is difficult to construct the support mechanism because the levitation force is very small. The object using magnetic force is limited to magnetic material, but no dust is generated and a large levitation force can be obtained. From this, it is clear that utilization of magnetic force is the most effective.
There are many kinds of magnetic suspension systems [2]. The noncontact support mechanism using magnetic force can mainly use permanent magnets and/or electromagnets. The support mechanism using only permanent magnets, which adjusts the magnetic force by controlling the air gap with the floating body by an actuator [3–5]. It has a wide range of operability and does not have the problem of heat generation like an electromagnet. This research proposes and develops a new type of noncontact support mechanism using permanent magnets.
Proposed noncontact suspension mechanism
Figure 1 shows an outline of the proposed noncontact magnetic suspension system. Two permanent magnets are actually driven and rotate around their respective rotation axes. An iron ball is the target object which is supported without mechanical contacts and handled in the horizontal and vertical directions. Rotation control is performed as the gravity and the magnetic force acting on the iron ball are balanced. The motion of the target is controlled in the x-axis (horizontal) and y-axis (vertical) directions by the rotation of two permanent magnets. In the figure 𝛼 and 𝛽 is angle of permanent magnets, and L is the distance between the rotation axes of magnets.
Outline of proposed levitation system.
The principle of force control strategies is shown in Fig. 2. The force in the vertical direction is controlled by the opposite rotations of the two magnets shown in Fig. 2(a). The force in the horizontal direction is controlled by the same rotations of the magnets as shown in Fig. 2(b). For the feasibility study of the proposed system, these principles are confirmed by FEM analyses and using experimental examinations. The independent control of the vertical and horizontal direction forces is also examined.
Principle of vertical and horizontal force generation.
In order to make a prototype system the feasibility study of the proposed system is necessary. First, we determined the specification of an iron ball and permanent magnets as shown in Table 1. Under these conditions, we decided the pole arrangement of two permanent magnets and the distance between two magnets using FEM analyses and the experimental examinations.
Specification of permanent magnet and iron ball
Specification of permanent magnet and iron ball
In order to study the arrangement of poles, we examined which is better with the same poles facing to the target or the different poles facing. For example, Fig. 1 shows a different pole arrangement. The poles towards to the ball is an S and N.
Electromagnetic field analysis software JMAG was used for FEM analysis. We analyzed and compared the magnetic flux lines on the xy plane at L = 45 [mm], when the angles of magnets are 𝛼 = 𝛽 = 45 [°] and 𝛼 = 𝛽 = 55 [°]. Figure 3 shows the magnetic flux lines when the same poles facing each other and Fig. 4 shows the opposite poles facing each other. The results seem a little asymmetric. This is mainly because of 3D analysis. Some asymmetric flux lines which pass through out of the plane of the magnet and the ball caused by small calculation error are displayed.
When we focus on the flux lines passing through the iron ball, it can be seen that the number of magnetic flux lines passing through the inside of the iron ball varies depending on the angle when opposite poles facing each other. Therefore, it is thought that the magnetic force acting on the iron ball changes due to the rotation of the magnet when opposite poles facing each other.
Results of FEM analyses when same poles facing to target.
Results of FEM analyses when different poles facing to target.
Next, we determined the optimal value of the distance L between the centers of two magnets as shown in Fig. 1. It was determined by vertical force control performance by the experimental results. Force was measured using an experimental device as shown in Fig. 5. From Fig. 5, a load cell measures the vertical force acting on the iron ball installed at the end of the load cell. Position and angle of permanent magnets are fixed by screws. The magnetic force measured by changing L, 𝛼, 𝛽 in Fig. 1.
Experimental setup for measuring the force in the vertical direction.
Experiments were conducted with opposite poles facing each other. At L = 40, 42.5, 45, 47.5, 50 [mm], the magnetic force acting on the iron ball was measured when 𝛼 and 𝛽 were 35, 40, 45, 50, 55, 60 [°]. The center of the iron ball is assumed as it is positioned at the center of both magnets. The height of the iron ball was fixed so that the distance between the center of the magnets and the ball is 30 [mm] according to the y axis.
The measurement results are shown in Fig. 6. The dotted line in the graph represents the supporting force at which the iron ball balances with the gravity and the value 0.629 [N]. Focusing on variation of the force of each line near the equilibrium force of 0.6 N, at L = 45 [mm] the line changes linearly for 15 degrees (from 45 degrees to 60 degrees). Hence, the stable magnetic force variation can be obtained by rotation of the magnet.
Next, when L is fixed as 45 [mm] and the magnetic force was measured when the same poles facing each other for comparison. The results are shown in Fig. 7. When the same poles facing each other, the linear variation of the magnetic force according to the rotation of the magnet was not obtained.
Experimental results of force in the vertical direction.
Comparison of forces of N–N and N–S.
In order to support the floating body in the y-axis direction, it is necessary to obtain a larger and smaller magnetic force than the gravitational force of the target by the rotation of the magnets. From Fig. 6 and 7, it is considered that the line around the intersection with the equilibrium force is changing linearly when L = 45 [mm], and it can be considered as the force control is very easy to obtain by the rotation of the magnets. Also, from the Fig. 7 and the analysis results of the magnetic flux lines, it was found that the stable change of the magnetic force due to the rotation can be obtained when the opposite poles facing each other.
When the opposite poles facing each other and L = 45 [mm], the two magnets were rotated in the opposite direction and in the same direction to analyze the magnetic forces acting on the iron ball in the x and y axis directions. The permanent magnet was rotated as shown in Table 2, and the magnetic force was analyzed at every 1 [°] using FEM analyses.
Angle combinations of magnets during FEM analyses examination.
Angle combinations of magnets during FEM analyses examination.
Figure 8 shows the magnetic force acting on the iron ball in the opposite direction rotation of magnets. When magnets rotate in the opposite direction, it was found that the change in magnetic force was obtained in the vertical direction, and control was possible in the vertical direction. Also, we can find the force in the horizontal direction keeps almost zero.
In Fig. 8, crosses represent experimental results at L = 45 [mm] as shown in Fig. 6 and Fig. 7. As compared between FEM analysis and experimental results about the vertical force, the maximum force is a little different, however, both forces around the equilibrium are almost same. We can confirm the result of FEM analysis are valid. The difference around 40 degrees is due to magnetic materials near the permanent magnets and the iron ball in the experimental examination.
Next, FEM analysis in the same direction rotation of the magnets was carried out for confirmation of the horizontal force control. From Fig. 8, when the angles of 𝛼 and 𝛽 are 53 degrees, the vertical magnetic force become equal to the equilibrium (the weight of the iron ball). FEM analysis in the same direction rotation was carried out on the basis of this angle value 53 degrees.
The result is shown in Fig. 9. When rotating in the same direction, it was found that the change in magnetic force was obtained in the horizontal direction, and control was possible in the horizontal direction. Also, at this rotation, the vertical direction force is almost same. These results confirmed that independent force control in horizontal and vertical direction may be achieved.
FEM analysis of magnetic forces when magnets rotate in the opposite direction.
FEM analysis of magnetic forces when magnets rotate in the same direction.
A new type of noncontact handing mechanism using active rotation of permanent magnets has been proposed. The outline of the suspension system was introduced and principle of force control strategies is introduced. A prototype handling system has been designed for the feasibility of the proposed suspension system. The feasibility study is performed by FEM analyses and experimental examinations of magnetic force. Different pole arrangement and a distance of 45 mm between magnets, is suitable for the noncontact handling systems, because the magnetic force can be changed linearly by rotation of magnets and also, we found that the magnetic force can be changed in the horizontal and vertical directions independently by rotation control of permanent magnets.
Fabrication of prototype system and experimental suspension examination are future works.