JPH088789B2 - Vibration type linear motor - Google Patents

Description

The present invention relates to a vibration type linear motor applied to a free piston type machine such as a vibration type compressor, and is particularly suitable for controlling a stroke and a vibration center position. The present invention relates to a sensing method and a control method.

[Conventional technology]

As an example of a free piston type machine to which a vibration type linear motor is applied, a publicly known technique regarding a Stirling refrigerator will be described.

This known example uses a moving magnet type linear motor and applies an alternating current to a fixed coil to apply an axial force acting on the coil to a magnetic field formed by a permanent magnet of a movable part on the permanent magnet side. The structure is such that it is extracted as a reaction force and vibrated. As is clear from this example, when the behavior of the vibrating body is used as monitoring or control information, a method of directly converting the vibration displacement into a voltage signal like a differential transformer is adopted. In the case of a structure in which the vibration displacement cannot be directly measured as the axial displacement, the method of extracting the vibration displacement as the change in the clearance between the taper body formed in the axial direction and the non-contact displacement measuring means such as the gear gussa is also taken. There is.

As another method, there is a method of directly detecting an alternating current to the coil portion and obtaining a vibration behavior in the relation of current → thrust → displacement.

As an example showing the above-mentioned conventional device, the Philipps. technical. Revue. There is Vol.42, No.1 in April 1985.

[Problems to be solved by the invention]

However, the prior art has not considered the following points. That is, when a differential transformer or a gear sensor is provided in the vicinity of the linear motor, the output of the measuring instrument is affected by the magnetic field formed in the motor section, and high-precision measurement cannot be expected. Further, when the output of the measuring device is directly used as the control information, the influence of the above-mentioned magnetic field may cause an erroneous control such that the output is disturbed. Furthermore, in the method of replacing the radial displacement by the gear sensor with the axial displacement, the movement of the bearing portion in the radial direction is spread, and thus the reliability of the measured value is extremely low.

On the other hand, in order to avoid the influence of the magnetic field, increasing the distance between the motor and the sensor part increases the size of the mechanism, and it is difficult to apply it especially where miniaturization is required.

Although the method of measuring the alternating current supplied to the coil and determining the vibration behavior is indirect, high accuracy can be expected. However, information on the magnetic flux density is necessary in the process of converting current to force, and it is possible to obtain the magnetic flux density from the current information in the case of excitation by a DC coil, but it is necessary to directly measure the magnetic flux density in the case of permanent magnet excitation. is there.

An object of the present invention is to positively utilize the influence of a magnetic field, which is a problem when measuring the vibration displacement of a linear motor, so that highly accurate measurement can be performed without enlarging the mechanism.
Another object of the present invention is to propose an oscillating linear motor that can control the amplitude and oscillating center position, which are parameters related to oscillating the motor, by using the improved measurement signal.

[Means for Solving the Problems] In order to achieve the above object, the present invention is configured such that a movable coil is placed in a static magnetic field given by a permanent magnet, and an alternating current flows through the movable coil. In a vibrating linear motor, magnetic flux density measuring means for measuring the magnetic flux density under the influence of the static magnetic field, and computing means for computing the amplitude and vibration center position of the linear motor based on the output of the magnetic flux density measuring means. And amplitude control means for adjusting the AC component of the alternating current supplied to the movable coil according to the deviation between the calculated amplitude and the target value, and the deviation between the calculated vibration center position and the target value. And a vibration center position control means for adjusting the DC component of the alternating current supplied to the movable coil.

In another aspect, in a vibrating linear motor in which a movable coil is placed in a static magnetic field given by a direct current coil, and an alternating current flows through the movable coil, it is under the influence of the static magnetic field. The magnetic flux density measuring means for measuring the magnetic flux density, the calculating means for calculating the amplitude and vibration center position of the linear motor based on the output of the magnetic flux density measuring means, and the deviation between the calculated amplitude and the target value Amplitude control means for adjusting the alternating current supplied to the movable coil according to the above, and vibration center position control for adjusting the direct current supplied to the DC coil according to the deviation between the calculated vibration center position and the target value. And means.

[Action]

As described above, the present invention positively uses the magnetic flux density of the linear motor section to grasp the vibration characteristics of the motor and control the amplitude and the vibration center position. When an electric current flows through a coil placed in a field in the presence of a magnetic field, a force acts on the coil. With respect to this force, if the vibrometer is analyzed in advance, the behavior of vibration, that is, the amplitude and the vibration center position can be obtained. If the information about the force can be obtained from the magnetic flux density, the vibration characteristics can be grasped without considering the large factors that affect the measurement accuracy, while the obtained measured value can be used directly as the control information. it can.

Next, a vibration type linear motor using a permanent magnet will be described as an example. A magnetic field is formed by a permanent magnet in the space of the vibration linear motor. The magnetic flux density at this time is Bg, but if the demagnetization of the permanent magnet is taken into consideration, Bg tends to be small, though not remarkable over time. If a coil having a circumferential length of 1 and a number of turns of N is placed in this air gap magnetic field and a current I is passed, the force F acting on the coil is given by equation (1).

F = NlI (Bg + Bg ^* ) (1) Here, Bg ^* is the magnetic flux density excited by the current I flowing in the coil, and in the case of direct current, it takes either a positive or negative sign depending on the flowing direction. Bg ^{* at} this time is represented by the equation (2).

Here, μg: Permeability of voids On the other hand, when alternating current flows, Bg ^* is expressed by equation (3).

Where: Frequency S: Area of magnetic flux part Er: Reactance voltage Reactance voltage is the supply voltage and effective current value E ₀ , I ₀
Using the coil DC resistance R and Equation (4) gives Equation (4)
Equation (3) can be rewritten using Equation (5).

We are now considering the case where an alternating current is passed and the linear motor is excited. The equation of motion is expressed by equation (6), where x is the displacement during vibration.

m + c + kx = F (t) (6) where, m is the mass of the vibration system, c is the viscosity coefficient, k is the spring constant of the support system, that is, the exciting force F (t) is given by the formula (1). ) To find x max, the amplitude can be found. On the other hand, if the magnetic flux density Bg + Bg ^* is directly measured, not only the information on the magnetic flux density but also the one-sided amplitude of the measured value becomes Bg ^* from its AC component, and the supply current has characteristics such as sine wave and triangular wave. If it is known, not only the effective value I ₀ but also the actual current change I can be known from the equation (5) and F (t) can be obtained.

Further, F (t) is F (t), as is clear from the equation (1).
For (t) = 0, | Imax | × (Bg + Bg ^* ) and | Imax |
The alternating characteristic has the center position shifted by the amount affected by the difference of × (Bg-Bg ^* ). Therefore, the center position initially set is displaced by Δx and vibrates. Now let's analyze how to calculate Δx. If there is no change in the magnetic flux density, the force F ₀ (t) is given by equation (7).

F ₀ (t) = NlIBg (7) On the other hand, even if the magnetic flux density changes, the average value is {(Bg + Bg ^* max) + (Bg−Bg ^* max) when the DC component of the supply current is 0. } / 2 = Bg, so that the amplitude of the force F (t) becomes equal to the expression (7).

The vibration displacement x ₀ when there is no change in the magnetic flux density is given by equation (7)
By rewriting the equation (6) using, the equation (8) is obtained.

m ₀ + c ₀ + kx ₀ = F ₀ (t) (8) From the displacement obtained by equation (6), the center of vibration is (x max + x
min) / 2, the displacement when there is no change in the magnetic flux density is calculated using equation (8) and the center of vibration is calculated as (x ₀ max + x ₀ mi
Since n) / 2, Δx is expressed by equation (9).

_{Δx = (x max + x min} ) / 2 - (x 0max + x 0min) / 2 ...... (9) ie by measuring the magnetic flux density directly, not the vibration amplitude but also to grasp the change in the vibration center position with respect to the initial setting be able to.

As described above, the current value can be controlled by the information on the magnetic flux density, and the amplitude of the vibration linear motor can be controlled. On the other hand, in the equation (5), if the supply current I is an alternating current having a DC component, the peak value of the excited magnetic flux density Bg ^* will be different on the positive and negative sides when I is positive and when it is negative. That is, in the formula for calculating the force shown in formula (1), | I
If the DC component is determined so that max · Bg + Bg ^* ) max | and | Imin · Bg + Bg ^* ) min | are equal, it becomes possible to drive the motor while maintaining the center of vibration at the initial setting. In other words, it is possible to control the direct current component of the supply current based on the information of the hourly velocity density and control the vibration center position of the vibration type linear motor. Further, since the magnetic flux density changes depending on the supply current, that is, the vibration frequency, the vibration frequency of the motor can be grasped from the fluctuation frequency of the magnetic flux density.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a flow chart showing the basic contents of the present invention, which is a compilation of the above-mentioned calculation formulas. First, the magnetic flux density in the air gap around the coil in the vibration type linear motor is measured. An element to which the Hall effect is applied is usually used as the magnetic flux density measuring means. The static magnetic flux density Bg, which is a DC component, and the dynamic magnetic flux density Bg ^* , which is an AC component, are obtained from the signal from the measuring means. If the change or amplitude of Bg ^* is known, the current and voltage supplied to the AC coil can be calculated. Next, the motor thrust F (t) can be calculated from the information on the magnetic flux density and the calculated current value, and the calculated value is used to find the motor amplitude x and the vibration center position x _c from the equation of motion of the vibration system. In parallel with this, the equation of motion is applied to the one obtained by removing the DC component from the change in thrust, and the center position x _0c at the time of setting is obtained.
That is, this value is the center position of the vibration when there is no fluctuation in the temporal flux density, and is the initial setting value.

Next, Δx = x _c −x _0c is _calculated, which is the deviation of the vibration center position from the initial setting. The calculated x and Δx are compared with set target values x ^* and εΔ ^* , but in the case of amplitude, the allowable value εx ^* is also set in advance. First, regarding the deviation of the center position, control is not necessary if it is within the allowable value, but if it deviates from the allowable value, the DC component of the voltage or current supplied to the motor is changed. As is clear from the above equations (1) and (5), the method of change is
If it deviates from the set value to the positive side defined by the mathematical formula, the DC component may be corrected to the negative side, and if it deviates to the negative side, the DC component may be corrected to the positive side. The correction amount per step is 1 / the equivalent current or voltage amount calculated back from the deviation εΔ ^*.
It is considered sufficient to set it to about 10, but this value should be empirically determined by the linear motor to be controlled.

Similarly, regarding the amplitude, as is clear from the equations (1) and (5), the supply current or the AC component of the voltage may be increased or decreased. That is, if the amplitude is larger than the set specification value, the AC component of the current or voltage may be reduced, and conversely, if it is smaller than the target value, the AC component of the voltage or current may be increased.

FIG. 2 shows an example in which a magnetic flux density measuring means is provided in a coil movable vibrating linear motor. The magnetic field is provided by the permanent magnet 2 and the magnetic flux forms a loop through the air gap in which the yoke 3 and the coil are placed. In this example, since there is no leakage flux and the magnetic flux density is constant in the air gap along the permanent magnet 2, only one magnetic flux density measuring means is provided. However, when the magnetic flux density changes in the air gap in which the coil 1 is movable, it is necessary to measure the magnetic flux density at several points and take a weighted average of the obtained magnetic flux density information.

FIG. 3 shows the Hall element 5 as an example of means for detecting the magnetic flux density. When the control current I _c is applied to the element, the magnetic flux density B acting on the element 5 in the arrow direction is obtained as the terminal voltage V _H of the element 5. The relationship between B and V _H at this time is expressed by equation (10).

Where R _H : Hall coefficient Fig. 4 shows the output and calculation when a Hall element is used,
It shows the output waveform required when performing control. The output V _H from the device is converted to Bg in equation (10). Bg ^* is obtained from the AC component at this time. F (t) can be calculated from the information on Bg and Bg ^*, and the displacement waveform can be obtained by solving the equation of motion based on F (t). F (t) and x have the same period as V _H ,
The phases are not always the same due to viscous resistance of the vibration system.
However, the measurement system or control system shown in the present invention can be achieved only by the amplitude and period information.

FIG. 5 is an example of control relating to a moving coil type vibration linear motor in which a magnetic field is formed by the DC coil 7. The signal from the magnetic flux density measuring means 4 is guided to the calculating part 8 to obtain the thrust and the displacement. Information from the calculation unit is the comparison unit 9
Where the comparison with the measured values is made. That is, regarding the vibration center position and the amplitude, information about whether the deviation is within the allowable deviation or outside the deviation is sent to the next control unit 10.

In the control unit 10, the AC power supply 11
Of the voltage or current, control of the AC component, and control of the voltage or current value of the DC power supply 12. This allows the amplitude and vibration center position of the vibration linear motor to be adjusted to the set values. Further, the calculation unit 8 can obtain the period Δt of the waveform from the measurement signal of the magnetic flux density and obtain the frequency from 1 / Δt.

〔The invention's effect〕

As described above, according to the present invention, in a vibration type linear motor that vibrates by passing a current through a coil placed in a magnetic field, the magnetic flux density of a void portion in which the coil is placed is measured, and from this measurement result, Since the vibration characteristics such as the amplitude and the vibration frequency are grasped, it is possible to grasp the vibration characteristics not influenced by the magnetic flux. Further, by using the measured magnetic flux density as the control information, the amplitude and the vibration center position can be controlled without having a displacement measuring means which is a problem when downsizing the equipment and improving the accuracy and reliability of the detected value. It will be possible.

[Brief description of drawings]

FIG. 1 shows a control flow chart of an embodiment of the present invention, and FIG. 2 shows an example of a vibration type linear motor as an object of the present invention. FIG. 3 shows the wiring structure of the Hall element as an example of the magnetic flux density measuring means. FIG. 4 is an example of waveform information and output waveform at the time of measurement and control, and FIG. 5 is a control block diagram relating to a moving coil type vibration motor when a magnetic field is formed by a DC coil. 1 ... Moving coil, 2 ... Permanent magnet, 3 ... Yoke, 4
...... Magnetic flux density measuring means, 5 …… Hall element, 8 …… Calculator, 9 …… Comparison, 10 …… Control.

Claims (2)

[Claims] 1. A vibrating linear motor in which a moving coil is placed in a static magnetic field given by a permanent magnet, and an alternating current flows through the moving coil, the magnetic flux being influenced by the static magnetic field. Depending on the magnetic flux density measuring means for measuring the density, the calculating means for calculating the amplitude and the vibration center position of the linear motor based on the output of the magnetic flux density measuring means, and the deviation between the calculated amplitude and the target value. Amplitude control means for adjusting the AC component of the alternating current supplied to the movable coil, and adjusting the DC component of the alternating current supplied to the movable coil according to the deviation between the calculated vibration center position and this target value. A vibration type linear motor having a vibration center position control means. 2. A vibrating linear motor in which a movable coil is placed in a static magnetic field given by a DC coil, and an alternating current flows through the movable coil, the magnetic flux being influenced by the static magnetic field. Depending on the magnetic flux density measuring means for measuring the density, the calculating means for calculating the amplitude and the vibration center position of the linear motor based on the output of the magnetic flux density measuring means, and the deviation between the calculated amplitude and the target value. Amplitude control means for adjusting the alternating current supplied to the movable coil by means of a vibration center position control means for adjusting the direct current supplied to the direct current coil in accordance with the deviation between the calculated vibration center position and the target value. Vibration type linear motor with and.