JPH06335110A - Magnetic levitation conveyor - Google Patents

Abstract

PURPOSE:To always stably control a gap between a truck and rails constantly in a magnetic levitation conveyor for moving the truck along rails while holding a gap between the truck and the rails constant by magnetism. CONSTITUTION:Currents Ia-Id to be supplied to coils 16a-16d for controlling magnetic fluxes of composite magnets 17a-17d are detected by current detecting sensors 41a-41d, and supplied to a levitation controller 42. The controller 42 corrects gap values Za-Zd between a truck 14 and levitation rails 11 detected by gap sensors 23a-23d in response to detection signals ia-id of the sensors 41a-41d, a true gap value is obtained, the currents Ia-Id are obtained in response to the true gap value, and supplied to the coils 16a-16d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic levitation transfer device, and more particularly to a magnetic levitation transfer device for moving a dolly along a rail while keeping a constant gap between the rail and the dolly by magnetism.

Since semiconductor devices are extremely reluctant to dust, it is required to reduce the generation of dust in a semiconductor device manufacturing factory for manufacturing semiconductor devices. Therefore, in a semiconductor device manufacturing factory, a magnetic levitation transfer device is used as a transfer device for transferring a wafer. The magnetic levitation transfer device controls the magnetic attraction force with the magnetic rail, levitates while maintaining a constant gap, and transfers wafers, etc.Because there is no contact between the magnetic rail and the dolly, it does not collect dust. It is configured to prevent such problems.

In such a magnetic levitation transport device, it is necessary to always keep the gap constant in order to carry the transport stably.

[0004]

2. Description of the Related Art FIG. 5 is a cross-sectional view of a magnetic levitation transport device. In the figure, 11 is a levitation rail and 12 is a movement rail. The levitation rails 11 and the movement rails 12 are fixed to the ceiling 13 and extend in the movement direction of the carriage 14 (in FIG. 5, the direction perpendicular to the paper surface). The bogie 14 is sucked onto the levitation rail 11 and holds the bogie 14 in a floating state.
The dolly 14 is provided with composite magnets 17a to 17d composed of permanent magnets 15a to 15d and coils 16a to 16d at four corners of the dolly 1 facing the levitation rail 11.
No. 4 is levitated when the composite magnets 17a to 17d are magnetically attracted to the levitating rail 11. At this time, the control unit 24 controls the current supplied to the coil 16 so that the gap detected by the gap sensor 23 that detects the gap between the carriage 14 and the levitation rail 11 becomes a constant value, and the trolley 14 and the levitation rail 11 are controlled. The gap with 11 is kept constant, and is levitated without contact.

The carriage 14 is provided with a guide roller 18, and even if a sudden load change occurs in the carriage 14 in the direction of arrow B, the guide roller 18 abuts on the guide rail 19 and the movement of the carriage 14 is restricted. The carriage 14 is prevented from falling off.

A drive unit 20 is provided on the carriage 14 so as to face the moving rail 12. The drive unit 20 constitutes a linear motor together with the moving rail 12 and moves the carriage 14. A holding portion 22 for holding the transported object 21 is provided below the trolley 14, and the transported object 21 is transported by the trolley 14 moving along the levitation rail 11 and the moving rail 12. Has been done.

FIG. 6 shows a schematic configuration diagram of an example of a conventional levitation control system. The composite magnets 17 are provided at the four corners of the carriage 14 so that the levitation can be balanced when the object 21 is mounted.
a to 17d are provided. Compound magnets 17a-17d
The coils 16a to 16d are connected to the levitation control circuit 24 and are excited in accordance with the drive current from the levitation control circuit 24.

The levitation control circuit 24 is a gap sensor 23a.
The drive current is controlled according to the detection gap signal corresponding to the gap between the levitation rail 11 and the carriage 14 supplied from 23d. The composite magnet 17 controls the magnetic flux generated according to the drive current supplied from the levitation control circuit 24, and controls the gap between the carriage 14 and the levitation rail 11.

FIG. 7 shows a block diagram around the composite magnet 17.

One compound magnet 17a of the magnetic levitation carriage 14
Has a permanent magnet 15a arranged in the center thereof, and a coil 16a (a few hundred turns of an electric wire wound around an iron core) wound around the core 25 on both sides of the permanent magnet 15a. a magnetic force occurring in 15a, a magnetic force is generated in both sides of the coil 16a is superimposed and the magnetic flux [Phi _B is generated, carriage by changing the magnitude of the magnetic flux [Phi _B by a current flowing through the coil 16a Is kept floating.

That is, the composite magnets 17a to 17d arranged at the four corners of the dolly 14 are supplied with respective manipulated variables from the levitation control circuit 24, and the equilibrium points (of the levitation gap set by the dolly 14). That's about 3mm)
When it is deviated in the positive direction from (to the positive direction, it means that it is larger than the equilibrium point), the magnetic flux Φ _B must be increased. Therefore, by passing a current in the positive direction through the coils 16a to 16d, the permanent magnets 15a to 15d When the magnetic force is increased and the magnetic flux is deviated in the negative direction, the magnetic flux Φ _B must be reduced. Therefore, the magnetic force of the permanent magnets 15a to 15d is weakened by causing a negative current to flow through the coils 16a to 16d. Further, when the equilibrium state is maintained, it is not necessary to supply a large amount of current to the coil, and the permanent magnets 15a to 15d are provided.
It is configured to levitate only by the magnetic force of the power consumption to reduce power consumption.

FIG. 8 is a block diagram of the gap sensor 23, and FIGS. 9 and 10 are diagrams for explaining the operation of the gap sensor 23.
11 to 13 show operation waveform diagrams of the gap sensor 23,
FIG. 14 shows an operation characteristic diagram of the gap sensor 23.

The eddy current type gap sensor 23 is an oscillation circuit 2
Sensor head 26 constituting the detection of 7: coil 28
A high-frequency current is passed through (C: a capacitor constitutes a high-frequency oscillation type parallel resonance circuit) to penetrate the high-frequency magnetic field toward the rail 11. Here, as shown in FIG. 9, if the magnetic field has a magnitude and direction of Φ _A at a certain time (in this case, the magnetic field is a magnetic flux), an induced electromotive force is generated in the target and an induced current (rotational Current is called eddy current.), And this eddy current generates a magnetic field Φ _A 'in the direction counter to Φ _A according to the law of electromagnetic induction, so that the coil receives mutual induction action and the inductance decreases, and oscillation occurs. Gap detection is performed by utilizing the fact that the effective impedance of the circuit decreases and the oscillation voltage decreases accordingly.

That is, when a certain alternating magnetic field is emitted from the coil 16, the above-mentioned eddy current becomes large when the rail 11 approaches as shown in FIG. 10, so that Φ _A 'also becomes large and the mutual induction action is strengthened. , the inductance decrease in the coil becomes significantly as a result, occurs attenuation of the effective impedance and the oscillation voltage, and when the rails 11 as shown in FIG. 10 away Conversely, the eddy currents as described above is for [Phi _a 'is small small , The effect of mutual induction weakens and the inductance of the coil increases, and as a result,
An increase in effective impedance and oscillation voltage occurs. The oscillation voltage (see FIG. 1- (d)) obtained as described above is as shown in FIG.
9 is rectified, and the gap value is taken out as a DC voltage as shown in FIG.

Generally, the DC voltage obtained by the rectifying / smoothing circuit 29 is converted into a linear correction circuit 30 and an analog output circuit 31.
Is output via. Further, the oscillation circuit 28, the rectifying / smoothing circuit 29, the linear correction circuit 30, and the analog output circuit 31 are configured so that a stable voltage is supplied from the power supply circuit 32 and accurate detection can be performed.

[0016]

However, since the gap sensor is arranged as shown in FIG. 7 in the conventional magnetic levitation transport device, it is easily affected by the magnetic flux of the composite magnet 17, and the current in the positive direction flows through the coil. And magnetic flux Φ _A '
Is superimposed on Φ _B and becomes larger than the actual value, the oscillation voltage shifts upward as shown in FIG. 12 (A). As a result, as shown in FIG. When the detection gap Z of the sensors 23a to 23d outputs a value smaller than the true gap Z ', and when a current flows in the negative direction in the coil on the contrary, the magnetic flux Φ _A ' is superimposed on the magnetic flux Φ _B, and the Due to the decrease, the oscillation voltage shifts downward as shown in FIG. 13A, and as a result, the gap sensor outputs a gap larger than the true gap as shown in FIG. 13B. Resulting in. Therefore, a graph of the above relationship is shown in FIG.
When a negative current is flowing in the coil as shown in Fig. 4, the gap sensor outputs a value larger than the actual gap (Z '), and when a positive current is flowing in the coil, the gap is as shown by the curve. The sensor is the actual gap (Z ')
Since it has the characteristic of outputting a smaller value, it is not possible to perform accurate levitation control. As a result, the levitation control between the carriage and the rails tends to oscillate, causing vibrations and shocks to the carriage, causing the conveyed object to drop or be damaged.

Further, due to the magnetic flux generated in the composite magnet, an error occurs in the detection signal of the gap sensor, and this error causes an unnecessary control signal to flow into the composite magnet, resulting in an increase in current consumption. It was Further, in order to eliminate the influence of the composite magnet, when a reflection type optical sensor (light emitted from the light emitting portion is received by the light receiving portion and gap detection is performed by the change in the light amount) is used for the gap sensor, Problems such as being easily affected by ambient light such as lighting, changing the characteristics of the surface roughness of the rail, and not being able to detect gaps at the rail joints because the projection spot is small with a diameter of less than 2 mm. was there.

The present invention has been made in view of the above points,
An object of the present invention is to provide a magnetic levitation transfer device that can hold a gap between a dolly and a rail uniformly and stably.

[0019]

FIG. 1 shows the principle of the present invention. The rail 2 extends in the moving direction A of the carriage 1.

The levitation means 3 is mounted on the trolley 1 so as to face the rail 2, and levitation is carried out by magnetism so that the distance from the rail 2 becomes constant. The gap detecting means 4 magnetically detects the gap between the carriage 1 and the rail 2. The drive signal detection means 5 detects a drive signal that causes the levitation means 3 to generate magnetism.

The control means 6 corrects the gap value according to the drive signal and the detected gap value of the gap detection means 4,
The levitation means 3 is controlled according to the corrected gap value.

[0022]

According to the present invention, the control means corrects the detection gap value in accordance with the drive signal and the detection gap value detected by the gap detection means, and controls the drive signal in accordance with the corrected gap value. Even if the detection gap value magnetically detected by the gap detection means is different from the true gap value due to the influence of the magnetism of the means, the drive signal supplied to the levitation means is controlled by the gap value obtained by correcting the detection gap value. be able to.

Therefore, the levitation control can be performed without being affected by the magnetism generated in the levitation means, and the gap between the carriage and the rail can always be kept constant.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a schematic configuration diagram of an embodiment of the present invention. In the figure, the same components as those in FIG.
The description is omitted. Reference numerals 41a to 41d denote current detection sensors which serve as the drive signal detection means 5 in FIG. The current detection sensors 41a to 41d detect the current supplied to the coil 16 that controls the magnetic flux of the composite magnet 17, and supply it to the levitation control circuit 42 that serves as the control unit in FIG.

FIG. 3 shows a block diagram of the levitation control circuit 42. The levitation control circuit 42 includes a timing circuit 43, A /
D converter 44, CPU 45, D / A converter 4
6 and a driver 47.

The timing circuit 43 includes the gap sensor 2
3a to 23d supply the detection gap signals Za to Zd and the current detection sensors 41a to 41d supply the detection current signals ia corresponding to the drive currents Ia to Id supplied to the coils 16a to 16d constituting the composite magnets 17a to 17d. ~
id is supplied. The timing circuit 43 detects the detection gap signals Za to Zd from the gap sensors 23a to 23d and the detection current signal ia from the current detection sensors 21a to 21d.
~ Id and sample hold at the same timing,
It is supplied to the / D converter 24.

The A / D converter 24 is the timing circuit 2
Analog signal detection gap signal Za supplied from
-Zd and detected current signals ia-id are converted into digital data and supplied to the CPU 25. CPU25 is A /
Detection gap signal Za supplied from the D converter 24
~ Zd and the digital data corresponding to the detected current signal are subjected to the processing described later to calculate digital data corresponding to the control signal to be supplied to each of the composite magnets 17a to 17d, and the digital data is supplied to the D / A converter 26. .

The D / A converter 26 converts the digital data supplied from the CPU 25 into an analog signal,
It is supplied to the driver 27. The driver 27 supplies drive currents Ia to Id to the coils 16a to 16d forming the composite magnets 17a to 17d according to the analog signal supplied from the D / A converter 26.

FIG. 4 shows a processing flowchart of the CPU 25. Since the levitation control is separately executed by each of the composite magnets 17a to 17d, and the processing in the CPU 25 is also separately executed, the processing relating to the signal to be supplied to one composite magnet 17a will be described.

First, the CPU 25 inputs the detected current value detected by the current detection sensor and the detected gap value detected by the gap sensor from the A / D converter 24 at a predetermined timing. (Step S1).

Next, the CPU 25 determines whether the detected current value ia is positive or negative (step S2). here,
The fact that the detected current ia is positive means that the composite magnet 17a
Indicates a direction in which the attraction force between the rail 11 and the rail 11 is increased, and "negative" indicates a direction in which the attraction force between the composite magnet 17a and the rail 11 is reduced.

When it is determined in step S2 that the detected current value is positive, the gap error ΔZa (+) that occurs when the detected current value ia is next positive is determined from the detected current value ia and the detected gap value Za ( Step S3). Here, the gap error ΔZ when the detected current value ia is plus
(+) Is calculated by the following equation. Gap error ΔZa (+) = α (Za) · ia ³ + β (Za) ia ² + γ (Za) (1) (α (Za), β (Za), γ (Za) are detected by experiment. (Function for gap value Za) Expression (1) is shown in FIG.
The current value in the experimental characteristic diagram as shown in (B) is obtained from the characteristic in the plus side region. At this time, FIG.
Since the characteristic of the region on the plus side of the current i in (B) is a curve, it can be determined by the cubic equation of the current value ia.
Next, the gap error ΔZa obtained in step S3
The detection gap Za is corrected using (+), and the true gap value Za 'is obtained (step S4).

Here, since ΔZa (+) is an error in the negative direction, the true gap value Za 'is obtained by the following equation.

Za ′ = Za + ΔZa (+) (2) Next, the manipulated variable Ua for controlling the current to be supplied to the composite magnet 17 based on the true gap value Z ′ obtained by the equation (3).
Is calculated (step S5).

Next, the manipulated variable Ua obtained in step S5.
Is supplied to the D / A converter 26 (step S6).
With the above, the processing for one cycle when the current value ia in the CPU 25 is positive is completed.

If it is determined in step S2 that the detected current value ia is negative, the detected current value ia is next calculated.
Then, the gap error ΔZa (−) that occurs when the value is minus is obtained from the detected current value ia and the detected gap value Za (step S7).

At this time, the gap error ΔZa (-) when the detected current value i is minus is obtained by the following equation.

Gap error ΔZa (−) = ρ (Za) · ia (3) (ρ (Za) is a function of the detection gap value Za obtained experimentally) Equation (3) is shown in FIG. 14 (B). It is obtained from the negative characteristics of such experimental characteristics. At this time,
Since the characteristic in the region where the current value i is negative in FIG. 6B is a straight line, it can be determined by a linear equation of the current value i.

Next, the current value i obtained in step S7
Error ΔZ (-) and detection gap value Za
A more true gap value Za 'is obtained (step S8).

Here, since the error ΔZa (-) becomes an error in the plus direction, the true gap value Za 'is obtained by the following equation.

Za ′ = Za−ΔZa (−) (4) Next, the manipulated variable U for controlling the current to be supplied to the composite magnet 17 based on the true gap value Za ′ obtained by the equation (4).
a is calculated (step S5).

Next, the manipulated variable Ua obtained in step S5.
Is supplied to the D / A converter 26 (step S6).
With the above, the processing for one cycle when the current value i in the CPU 25 is negative is completed.

The above steps S1 to S8 are repeated in a predetermined cycle to maintain the gap at a constant value.

The digital data of the manipulated variable Ua output from the CPU 25 is converted into an analog signal by the D / A converter 26 and supplied to the driver 27. Driver 2
7 generates a drive current according to an analog signal corresponding to the operation amount U supplied from the D / A converter 26, and supplies the drive current to the coil 16 of the composite magnet 17.

As described above, the coils 16a to 16d of the composite magnets 17a to 17d are supplied with the drive current i generated according to the true gap value in which the influence of the magnetic flux generated in the composite magnets 17a to 17d is corrected. Therefore, gap control according to the true gap value can be performed.

Therefore, the gap sensors 23a-23d are provided.
Can be provided close to the composite magnets 17a to 17d, and highly accurate gap control can be performed.

In this embodiment, the carriage 14 is the rail 11
Although it is disposed in the lower portion and is of a suspension type, the present invention is not limited to this, and a rail may be disposed in the lower portion of the carriage 14 so that the carriage floats on the rail.

[0048]

As described above, according to the present invention, the detection error generated in the detection signal of the gap detecting means is corrected according to the current supplied to the floating means, and the floating means is controlled by the correction value. It has features such that the trolley can always be stably levitated with a constant gap amount, and the reliability of levitation control of the trolley can be improved.

[Brief description of drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment of the present invention.

FIG. 3 is a block diagram of a levitation control circuit according to an embodiment of the present invention.

FIG. 4 is an operation flowchart of a main part of one embodiment of the present invention.

FIG. 5 is a cross-sectional view of the magnetic levitation transport device.

FIG. 6 is a schematic configuration diagram of an example of a conventional levitation control system.

FIG. 7 is a configuration diagram of a composite magnet.

FIG. 8 is a block diagram of a gap sensor.

FIG. 9 is a diagram illustrating the operation of the gap sensor.

FIG. 10 is an operation explanatory diagram of the gap sensor.

FIG. 11 is an operation waveform diagram of the gap sensor.

FIG. 12 is an operation waveform diagram of the gap sensor.

FIG. 13 is an operation waveform diagram of the gap sensor.

FIG. 14 is an operating characteristic diagram of the gap sensor.

[Explanation of symbols]

 1 dolly 2 rail 3 levitation means 4 gap detection means 5 drive signal detection means 6 control means 41a to 41d current detection sensor 42 levitation control circuit 45 CPU

Claims (2)

[Claims] 1. A magnet provided in opposition to a rail (2) extending in a moving direction (A) of a carriage (1), which generates magnetism according to a drive signal, and the magnetism causes the carriage (1) to move. Levitation means (3) for levitating from the rail (2) and the carriage (1)
And a gap detecting means (4) for magnetically detecting the gap value between the rail (2) and a drive signal for driving the levitation means according to the detected gap value of the gap detecting means (4). A magnetic levitation transport device for controlling the levitation of the carriage (1) from the rail (2) at a constant interval, wherein the detection gap is determined according to the drive signal and a detection gap value of the gap detection means (4). A magnetic levitation transfer apparatus comprising a control means (5) for correcting a value and controlling a drive signal for driving the levitation means (3) according to the corrected cap value. 2. The control means (5) detects the gap value Z of the gap detection means (4) when the drive signal is trying to make the trolley (1) and the rail (2) smaller than the predetermined distance. Gap value Z ′ = Z + ΔZ (+) (ΔZ = α
(Z) · i ³ + β (Z) · i ² + γ (Z); α (Z),
β (Z) and γ (Z) are the drive signals generated based on an experimentally obtained function depending on the detection gap value Z, and the drive signals generate the drive signal between the carriage (1) and the rail (2). When it is attempted to make it larger than the fixed interval, the gap value Z ′ = Z−ΔZ obtained by subtracting the gap error ΔZ (−) from the detected gap value Z of the gap detecting means (4).
2. The drive signal is generated based on (−) (ΔZ = ρ (Z) · i, ρ (Z) is a function obtained experimentally according to the detection gap value Z). Magnetic levitation transport device.