JP2001231111A - Magnetic levitation apparatus and electromagnet used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic levitation apparatus that can control three degrees of freedom of a discrete levitating body to achieve reduction in size and weight of simplified levitation structure elements. SOLUTION: In a magnetic levitation apparatus comprising a support means 5 consisting of a ferro-magnetic material, a magnetic unit provided to a levitating body and a magnetic support control means for controlling an attracting force of the electromagnet of a magnet unit in order to provide a structure that the levitating body is supported on the non-contact basis with the support means 5, the magnet unit is a 4-pole electromagnet having four poles that are arranged to form the four magnetic circuits and the attitude of three degrees of freedom of the levitating body is controlled by independently controlling a gap 6 between the levitating body and support means at each pole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic levitation device, and more particularly to a magnetic levitation device capable of controlling three degrees of freedom of a levitation body by itself.

[0002]

2. Description of the Related Art The magnetic levitation technique is a technique for supporting an object in a non-contact manner by a magnetic force. The magnetic levitation technology is useful as a means for solving various problems such as friction / wear, vibration / noise, limitation of use environment due to lubricating oil, maintenance, and high speed rotation limit of the mechanical support means. There are several types of magnetic levitation means. Attraction control type (Electromagnetic suspension,
EMS) has various practical advantages such as low leakage flux, small size and strong, no special materials and equipment such as superconductivity, and the possibility of stationary levitation. It is widely used in industry, mainly for systems.

In the EMS system, since the levitation system is inherently unstable, stabilization by feedback control is required. Conventionally, in an EMS system, a so-called U-shaped or E-shaped electromagnet is used as an electromagnet of an attraction force generating source. In such a magnet, one magnet forms one magnetic circuit with the opposing ferromagnetic material. Therefore, although these have two poles, only one degree of freedom can be controlled for one magnet.

However, generally, in order to levitate a rigid body, if the vertical axis is the rotation axis, the vertical direction, pitching,
It is necessary to control at least the three degrees of freedom of yawing. Therefore, a magnetic levitation system cannot be constituted only by a single U-shaped electromagnet or by arranging it on the same straight line. Therefore, in the conventional EMS system, a large number of U-shaped electromagnets (for example, four) are arranged in a plane, and a cooperative control of the whole is performed to form a levitation system.

In such a configuration, the levitation system is inevitably increased in size, weight, and complexity, and this is particularly severe in a system in which levitation components are arranged on the levitation surface.
Also, in a system in which the levitation components are arranged on the levitation surface, since the electromagnet constantly consumes power, a current collecting mechanism from the ground is required, and it is difficult to realize completely non-contact magnetic levitation. there were.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a magnetic levitation apparatus which can control three degrees of freedom of a floating body by itself. Is what you do. Another object of the present invention is to
By employing such a magnetic levitation device, it is possible to reduce the size, weight, and simplification of the levitation components.

[0007]

In order to solve the above-mentioned problems, the technical means adopted by the present invention include a support portion made of a ferromagnetic material, a magnet unit provided on a floating body, and an attraction of an electromagnet of the magnet unit. A magnetic support device for controlling a force, wherein the magnet unit forms four magnetic circuits in a magnetic levitation device configured to support the levitation body in a non-contact manner with respect to the support portion. Is a four-pole electromagnet having four poles arranged as described above, and by independently controlling the gap between the electromagnet and the supporting portion at each pole, the attitude of the floating body with three degrees of freedom is controlled. It is characterized by having comprised so that it may perform. Preferably, the magnetic unit includes a core having a rectangular flat base and four pillars (equivalently arranged in a rectangular shape at a regular interval) standing at corners of the base. It has a yoke and an electromagnet winding wound around the columnar portion.

[0008] The four-pole electromagnet according to the present invention can incorporate four magnetic circuits with respect to the levitating body, and can independently control the attraction force of each pole for each pole. By independently controlling the suction force of each pole, the vertical gap at each pole can be controlled independently, thus controlling the three degrees of freedom when the floating body is regarded as a rigid body by itself. Can be.

In the magnetic levitation device according to the present invention, so-called zero power control is possible by employing a permanent magnet in addition to the electromagnet. The zero power control is a control method in which most of the magnetomotive force required for the electromagnet is applied by a permanent magnet so as to reduce the power consumption of the electromagnet at no load and at the time of additional loading. The zero power control method itself is publicly known, and the zero power control method is described in, for example, Japanese Patent Application Laid-Open No. H6-178409 and Japanese Patent No. 2793227.
No. 2,563,912 and 2,760,491. For the concept and method of the zero power control method, the descriptions in these publications can be referred to.

The state variables at the input of the conventional zero power control system include a gap length (detected by a gap sensor),
There are a gap speed (estimated value) and an exciting current (detected by a current sensor). One of the zero power control methods adopted by the present invention is a voltage calculated from a gap length, a gap speed (estimated value), and an exciting voltage. It is characterized in that a state variable is composed of a deviation integral with a command value and an excitation current (estimated value). By directly controlling the excitation voltage and estimating the current using a state observer, the current detector (current sensor) used in the conventional zero power method is not required. Here, as for the fact that the exciting voltage to the electromagnet winding can be adopted as the input of the zero power feedback loop, see Japanese Patent No. 27.
93240 and JP-A-6-178409. However, all of them have a current detector, and there is no technical idea that the current detector becomes unnecessary by positively adopting the excitation voltage to the winding as an input. In addition, as a reminder,
The control system in the magnetic levitation apparatus according to the present invention does not exclude the input of the exciting current to the winding, and adopts the conventional zero power control method.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view and a side view of a magnet unit. The magnet unit has a square base portion 1 having an opening at the center and a top surface of each of four corner portions of the base portion 1. An iron core yoke composed of four columnar portions 2 at the same height and standing upright, and an electromagnet winding 3 wound around each columnar portion 2. By exciting the winding 3, each column 2 around which the winding 3 is wound constitutes an electromagnet, and the upper end side of each column forms four poles. A permanent magnet 4 is provided on the upper end side of each column 2. By arranging the permanent magnet 4 and the electromagnet winding 3 at each pole, the two magnetic fluxes can be overlapped in the floating gap.
The poles of the columnar part 2 adjacent in the weft direction in plan view have different polarities. In the embodiment, the iron core yoke is formed by combining and integrating four L-shaped ones, so that an opening is formed at the center of the base 1. The base 1 may be a flat plate, but the one having an opening in the base 1 is superior in reducing the weight of the magnet constituting the floating body. Further, such an opening can be used as a space for mounting other components.

FIG. 2 is a schematic overall configuration diagram of an experimental machine constituting the magnetic levitation apparatus. A gap sensor 7 is provided so as to face a floating gap 6 between a track 5 exemplified as a support portion made of a ferromagnetic material and each pole.
Is fed back to supply a predetermined current to the electromagnet winding 3. In the experimental machine, the magnet unit forms a floating body. The theoretical model and simulation described later have been verified by the experimental machine shown in FIG.

In FIGS. 1 and 2, the columnar portion 2 has a prismatic shape, but the shape of the columnar portion 2 is not limited to a prismatic shape, and may be, for example, a cylindrical shape. In addition, the columnar portion 2 is not limited to one having a uniform cross section uniformly in the length direction, and may have a partially different cross section. In addition, the position where the permanent magnets 4 are provided is provided at the upper end of the columnar portion 2 in the drawing, but the portion where the permanent magnets are provided is not limited to this, and is slightly lower than the upper end of each columnar portion 2. A portion may be provided so as to be interposed in an iron core. The portion where the permanent magnet 4 is provided is the columnar portion 2.
However, the present invention is not limited to this, and four permanent magnets 4 may be provided between adjacent columnar portions 2.

The levitation control of the levitation system using the quadrupole electromagnet according to the present invention will be described below. First,
The floating control algorithm will be described. The coordinate axes are set as shown in FIG. The degree of freedom of the levitation body in the magnetic levitation system using the quadrupole electromagnet is three, that is, the vertical gap z, the α-axis attitude angle θ, and the β-axis attitude angle ψ. Feedback control of these three degrees of freedom realizes a stable levitation system. As a specific control direction, from the vertical gaps z ₁ , z ₂ , z ₃ , z ₄ at each pole, (α,
β, ψ) is evaluated, and each pole current i ₁ , i ₂ , i ₃ , i ₄ is controlled. Here, the information used for the feedback assumes the output of the gap sensor and the output of the current sensor in each pole. However, in the output of the gap sensor, the following rigid condition of the floating body is satisfied.

(Equation 1) Here, the current actually passed through the electromagnet coil is each pole current.However, when designing a control system, a motion mode in which the motion with three degrees of freedom is decomposed and the control system is designed independently for each motion mode Apply another control method. Therefore, as shown in FIG. 3, the vertical control current, the α-axis attitude control current, β
The current around the axis attitude control current is virtually set. At this time, the following current conversion formula is established for each actual pole magnet current and virtual winding current.

(Equation 2) Also, the following conversion equation similar to the equation (2) is set for the voltage.

(Equation 3)

A specific flying control algorithm will be described with reference to FIG. The floating body position (z, θ, ψ) is calculated from the output of each pole gap sensor, and the virtual current of each degree of freedom control is calculated from the output of each pole current sensor. (Conversion operation 1)

(Equation 4)

(Equation 5) Actually, as described below, since each pole voltage is determined from three degrees of freedom by the virtual system, it can be said that the one-degree-of-freedom constraint is substantially satisfied for the current actually flowing through each pole. Further, in the levitation control system using only the gap length, the conversion of the equations (8), (9), and (10) becomes unnecessary.

Each degree of freedom independent controller determines a voltage applied to each degree of freedom control virtual winding which is a control input. (Z axis direction controller, α axis controller, β axis controller). For example, when a state feedback control system is configured, it is expressed as follows.

(Equation 6)

The conversion of equation (3) is performed to calculate the actual applied voltage of each pole electromagnet winding. (Conversion operation 2). The proposed method is a method in which the virtual current for each degree of freedom control is superimposed directly on the actual current, and is expected to be strongly affected by the mutual interference between the three degrees of freedom. It is possible to suppress the influence of mutual interference by feedback by linearizing at points and by giving each degree of freedom control system robustness. In a three-degree-of-freedom magnetic levitation system using a quadrupole electromagnet proposed from the above theory,
The following two circuit systems exist. From equations (2) and (3), they can be converted to each other.

(Equation 7)

Next, a plant model of a magnetic levitation system constituted by a quadrupole electromagnet with respect to an iron core orbit will be analytically described. First, we derive an analytically rigorous ideal model that considers the nonlinearity of electromagnetic force and the mutual interference between three degrees of freedom.
An analytical rigorous model is decomposed into three degrees of freedom independently to derive a linear approximation model for control system design that is linearized near the equilibrium point.

The following preconditions are assumed to simplify the analysis. Ignores the magnetic resistance of the iron core. Ignores eddy currents and hysteresis. Ignore leakage flux and fringing.

The rigorous analytical model will be described. FIG.
Fig. 3 shows a magnetic equivalent circuit formed by a four-pole electromagnet with respect to an iron core orbit. The analysis is performed in the following procedure. The magnetic energy W of the system is derived as a six-variable function of the floating body position and each degree of freedom control current. From the principle of the virtual displacement, W is partially differentiated by each variable of the position of the floating body, and the electromagnetic force in each direction of the degree of freedom applied to the floating body is obtained.

The magnetic energy W of the system is the magnetic energy stored in the gaps of the poles and the permanent magnets, ignoring the magnetic resistance of the iron core, and is expressed by the following equation.

(Equation 8)

(Equation 9) From the above equations (15) to (20), the vertical attractive force and the unbalanced torque around the α and β axes acting on the quadrupole electromagnet as the floating body are expressed by the following equations, respectively.

(Equation 10)

FIG. 6 shows a curved surface showing an example of mutual interference between three degrees of freedom.

Next, the analysis of the electric circuit system will be described. As shown in (14), the electric circuit system of the quadrupole electromagnet is divided into a virtual electric circuit system and a real electric circuit system.
The analytical exact expression of the virtual electric circuit system of the quadrupole electromagnet is as follows.

[Equation 11] Here, the first term on the right side is the voltage drop due to the winding resistance, the second term is the winding self, the induced electromotive force due to the mutual inductance,
The three terms respectively represent the speed electromotive force due to the magnetic flux of the permanent magnet. Here, the self, mutual inductance, and the flux linkage due to the permanent magnet in the equation (25) are the values of z, θ, ψ expressed using the magnetic pole permeances calculated respectively.
It is a three-variable function.

On the other hand, the analytical exact formula of the real electric circuit system is expressed by the following formula.

(Equation 12) Here, as in equation (25), the first term on the right side is the voltage drop due to the winding resistance, the second term is the self-induction of each winding, the induced electromotive force due to the mutual inductance, and the third term is the speed electromotive force due to the magnetic flux of the permanent magnet. Respectively. FIG. 7 shows a block diagram of an exact model derived from the above analysis results.

A linear approximation model for control system design will be described. From the derived rigorous analytical model, the motion modes are decomposed independently for each degree of freedom, ignoring the mutual interference between the three degrees of freedom,
Further, a linear approximation model for control system design is derived by linearizing near the equilibrium operating point (z, θ, ψ) = (z ₀ , ₀ , 0).

The vertical levitation system will be described. The equation of motion of the levitation body in the vertical direction is expressed by the following equation.

(Equation 13)

The linearization near the equilibrium point will be described.

[Equation 14]

(Equation 15) FIG. 8 shows a linear model of the vertical levitation system and a linear model of the attitude system around the center of gravity axis. FIG. 8 or equation (3)
Looking at (2) and (33), it can be seen that the types of the transfer function are equal in the vertical direction and around the center of gravity.

A levitation control system is designed from the linear approximation model for control system design, and verification of magnetic levitation with three degrees of freedom is performed by simulation. The levitation system design is performed for each of the gap length control system and the zero power control system. In particular, the design of a state observer using only the gap length as the measurement output, and the time integration of the coil voltage, which is the control input, are added to the state variables to the voltage command 0-type zero power levitation system constituting the expansion system. Here, basically, only the vertical levitation system among the three degrees of freedom will be referred to, but the posture system around the α, β center of gravity axes is similarly designed.

As a method of designing a levitation control system from a linear approximation model, a method of classical control theory by PID control and a method of modern control theory by state feedback are generally used. In this paper, we construct a control system based on the latter state feedback control.

The gap length command floating control system will be described. A gap length command type levitation control system which responds to a position command of a levitation body without a steady-state error is used in a vertical levitation system for a next four-dimensional expansion system (34) in which a gap length deviation integral is added to a state variable. , An optimal regulator theory for finding a state feedback rule (36) that minimizes the evaluation function (35).

(Equation 16) The expansion system (34) is a controllable system, and can arrange poles of a closed loop system arbitrarily by state feedback. A levitation system is designed for given simulation parameters. Each of the weight coefficients Q and R is appropriately set with emphasis on obtaining a relatively fast response. For reference, one example of the control system design is shown in FIG.

The magnetic levitation with three degrees of freedom is verified by simulation. The results of a simulation performed on the control system are shown. An analytically rigorous model is applied to the plant model.

The gap length command type levitation control system will be described. The simulation conditions are as follows.
(Z, θ, ψ) = (0.005, 0, 0) during stable levitation, after 1 [s], unbalanced load Fdz = 5 [N], Tdα =-
It was assumed that 0.02 [N · m] and Tdβ = −0.02 [N · m] were added in steps. The posture command value is always (0.
005,0,0). As shown in FIG. 10, a steady state is reached in about 0.2 [s] after the step-like disturbance is applied, and each degree of freedom control current becomes (iz, iα, iβ) =
At (5, -0.8, -0.4), it can be seen that stable levitation has been achieved according to the attitude command value.

The zero power levitation control system will be described.
The simulation conditions are the same as in the gap length command type. As shown in FIG. 11, (z, θ, ψ) = (0.003) in about 0.5 [s] after the step-like disturbance is applied.
(2, 0.005, 0.0025), which is a steady state. It can be seen that the unbalanced zero power levitation can be realized by actively tilting the levitation posture with respect to the unbalanced load.
From the comparison between FIGS.
It can be seen that the tilt attitude angle for generating an unbalanced suction force equivalent to 8 [A] is only about 0.29 °.

A control system using a state observer will be described. A state feedback control system was constructed, and the validity of the proposed three-degree-of-freedom magnetic levitation control algorithm was verified by simulation. As the state variables here, the gap length, gap speed, and coil current are used.
Assuming that all of these can be measured, we considered ideal state feedback control. However, in general, the amount that can be directly measured is the gap length by the gap sensor and the coil current by the current sensor. Since the gap speed cannot be directly measured, it must be estimated by some method. As a method of estimating the gap velocity, a pseudo differential and a state observer can be considered. Here, a control system that actively uses the state observer is proposed.

The pseudo differential and the state observer will be described.
The most common method for estimating the gap speed is to pseudo-differentiate the gap length signal. The pseudo differential is expressed by the following equation.

[Equation 17] Pseudo differentiation is the easiest method for calculating the gap speed, but it is necessary to set the time constant τ of the LPF slightly larger in order to suppress the influence of high frequency noise. On the other hand, τ
Increasing means that high frequency dynamics are also sacrificed, and trade-offs must be considered to degrade control performance.

A state observer using only the gap length will be described. Using the state observer gives an estimated signal of the gap velocity that is more resistant to high-frequency noise than the pseudo-differential. However, if control using the state observer is further developed, the plant can be observed even if only the gap length is detected. By utilizing this fact, a state observer using only the output of the gap sensor can be constructed. By using only the output of the gap sensor without using the current sensor, the burden on PID control of a normal voltage operation type and the measurement becomes completely equal, and the levitation system can be improved only by software. Further, by not using the current sensor, the influence of noise and drift due to the current sensor can be eliminated.

The voltage command type zero power control system will be described. Using a state observer that uses only the gap length,
The deviation between the coil voltage ez as the control input and its target value 0 is fed back to the control input ez again via the integrator. This is proposed as a voltage command type zero power control system. The proposed control system can be realized by configuring an expanded system (Equation 38) in which the deviation integral of the control input is incorporated in the state variable, and configuring a state feedback controller + state observer.

(Equation 18) The expansion system (38) is a controllable system, and any pole arrangement can be made by a feedback gain matrix. On the other hand (3
In 8), the rank of the observable matrix is 3 for the entire extended system, and the observability is not satisfied. However, the newly added state variable is the deviation integral of the control input and can be calculated directly. Therefore, a control system can be constructed by estimating the three original state variables of the plant with a state observer using only the gap length (FIG. 12).

The voltage command type zero power levitation control system constitutes an expansion system in which the integral of the deviation between the control input voltage and the target value 0 is again incorporated into the state variable. In this system, no current sensor is required, and the coil current is guaranteed to be completely zero regardless of the sensor error. Physically speaking, it can be said that the voltage command type zero power levitation control is a kind of magnetic flux control.

[0039]

The present invention has the following advantageous effects. Four magnetic circuits can be efficiently incorporated in the iron core track under one constraint condition, and the magnetic flux of each pole can be controlled with three degrees of freedom. That is, the minimum required three degrees of freedom for floating a general rigid body can be controlled independently, and floating alone can be theoretically possible. In other words, the quadrupole electromagnet has a minimum necessary structure for forming a magnetic levitation system. Further, the levitation device according to the present invention has good adaptability to two-dimensional driving using a linear motor, and is suitable for a flexible transportation system that actively utilizes branching. The quadrupole electromagnet enables so-called zero power control by arranging a permanent magnet and an electromagnet winding on each pole and superposing the magnetic fluxes of the two in a floating gap. An ideal energy-saving levitation system can be realized by zero power control. The quadrupole electromagnet can also generate an unbalanced attractive force by actively tilting the floating posture. By combining the zero power control with this property, even when an unbalanced load is applied to the levitation body, unbalanced zero power levitation that compensates for the unbalanced load by actively tilting the levitation posture becomes possible.

[Brief description of the drawings]

FIG. 1 is a plan view and a side view of a magnet unit including a four-pole electromagnet.

FIG. 2 is an overall schematic diagram of an experimental machine of a magnetic levitation device.

FIG. 3 is a diagram showing current conversion.

FIG. 4 is a diagram showing a levitation control algorithm.

FIG. 5 is a diagram showing a magnetic equivalent circuit.

FIG. 6 is a curved surface showing an example of mutual interference between three degrees of freedom.

FIG. 7 is an analytical rigorous model that takes into account nonlinearity and mutual interference.

FIG. 8 is a view showing a linear approximation model of a vertical levitation system and a linear approximation model of a posture system around a center of gravity.

FIG. 9 is a diagram illustrating a design example of a zero-power levitation control system with three degrees of freedom.

FIG. 10 is a diagram showing a simulation result of a magnetic levitation control with a three-degree-of-freedom gap length command.

FIG. 11 is a diagram showing a simulation result of a zero-power magnetic levitation control with three degrees of freedom.

FIG. 12 is a diagram showing a voltage command type zero power control system.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Koji Yakushi, Inventor 5-30-8 Sendagi, Bungi-ku, Tokyo 202 Maison Sendagi 202 (72) Inventor Takaaki Koseki 2-20-31, Osawa, Mitaka-shi, Tokyo 1 −403 (72) Inventor Satoru Sone 1-1-40 Shinkino, Abiko-shi, Chiba F-term (reference) 5H113 CC10 DB05 DB13 DB15 DB18 GG04 GG12 GG30 HH02 HH05 HH14

Claims (10)

[Claims] A magnet unit provided on a floating body, and magnetic support control means for controlling an attractive force of an electromagnet of the magnet unit. In a magnetic levitation apparatus configured to support the levitation body in a non-contact manner, the magnet unit has four poles arranged to form four magnetic circuits.
A magnetic levitation device, which is a polar electromagnet, and is configured to control the attitude of the levitation body with three degrees of freedom by independently controlling a gap in each pole. 2. The three degrees of freedom include a vertical direction, pitching,
The magnetic levitation device according to claim 1, wherein the magnetic levitation device is yaw. 3. The magnet unit has a permanent magnet, and the permanent magnet is shared by a magnetic path made by the electromagnet and a magnetic path made by the permanent magnet in a gap between the electromagnet and the support. The magnetic levitation device according to claim 1, wherein the magnetic levitation device is arranged as described above. 4. The apparatus according to claim 1, wherein said magnetic control means is configured to stabilize a magnetic path by controlling an exciting current flowing through said electromagnet such that a steady-state value of the exciting current flowing through said electromagnet becomes zero. The magnetic levitation device according to claim 3, wherein: 5. The magnetic control means is configured to control an excitation voltage applied to the electromagnet so as to make an average value of the excitation voltage applied to the electromagnet zero, thereby stabilizing a magnetic path. The magnetic levitation device according to claim 3, wherein: 6. The magnetic control means detects a gap length between the electromagnet and the support and an excitation voltage applied to the electromagnet as a detection value, and an excitation current applied to the electromagnet uses a state observer. The magnetic levitation device according to claim 1, wherein the estimated value is used. 7. The magnetic unit according to claim 1, wherein the magnetic unit includes a base having a rectangular shape in a plan view, an iron core yoke including four pillars erected at corners of the base, and an electromagnet winding wound on the pillars. 7. The magnetic head according to claim 1, wherein the attraction force of each pole is independently controlled for each pole by incorporating four magnetic circuits. 8. Magnetic levitation device. 8. The magnetic levitation device according to claim 7, wherein a permanent magnet is provided on the columnar portion. 9. The magnetic levitation device according to claim 1, wherein the magnet unit forms at least a part of the levitation body. 10. An iron core yoke integrally formed of a base having a rectangular shape in a plan view and four pillars erected at corners of the base, an electromagnet winding wound on the pillars, And a permanent magnet provided on each of the columnar portions.