WO1992019877A1

WO1992019877A1 - Process for starting a machine fitted with a rotor on magnetic bearings and circuit for implementing the process

Info

Publication number: WO1992019877A1
Application number: PCT/EP1992/000298
Authority: WO
Inventors: Randolf Paul Rolff
Original assignee: Leybold Aktiengesellschaft
Priority date: 1991-05-04
Filing date: 1992-02-12
Publication date: 1992-11-12
Also published as: DE4114566A1; DE4114566C2; CN1066493A; TW287250B

Abstract

The invention relates to a process for starting a machine fitted with a rotor on magnetic bearings and a circuit for implementing said process; in order to automate this process, the procedure is such that the fact that an axial stop bears on the rotor at rest and the correct position of the rotor when running -- its unstable equilibrium -- is about half a possible total travel of the rotor away from the momentary rotor stop position is used as information in order to apply electric power to the deflection coil in such a way that the rotor assumes its correct position virtually independently of the offset and that initially one of the two possible rotor stop positions is assumed to be given and an attempt is made to stabilise the rotor at about half of the possible total travel of the rotor from the assumed rotor stop position.

Description

Process for commissioning a machine equipped with a magnetically mounted rotor and circuit for carrying out this process.

The. The invention relates to a method for starting up a machine equipped with a magnetically mounted rotor according to the preamble of claim 1. Furthermore, the invention relates to a circuit suitable for carrying out this start-up method.

DE-PS 34 09 047 discloses a magnetic bearing cell with permanent magnets, which support the rotor stably in the radial direction and unstably in the axial direction. In addition, an axial sensor, a controller and two deflection coils are provided which keep the rotor in its equilibrium position which is unstable in the axial direction during operation of the machine. For this purpose, the deflection coils are supplied with currents, the strength of which depends on the deviation of the rotor from its unstable equilibrium position.

Magnetic bearings of this type have been used in practice for mounting the rotor of turbomolecular vacuum pumps. They are also equipped with a control device which causes an automatic compensation of the currents flowing in the deflection coils in such a way that the current has the value zero in the unstable equilibrium position of the rotor ("current-to-zero" regulator). In addition, a potentiometer is provided with which the target position of the rotor is specified in order to be able to compensate for tolerances of the pump and its converter (control, power supply, etc.) within the magnetic bearing control.

The tolerances of the pump include, above all, the relatively large offset error of the axial sensor and the target positions of the rotor, which are dependent on the installation position of the pump. Since the range that the "current to zero" controller can regulate is limited, the balancing potentiometer must be reset after each new installation of the system. Even after changing the connecting cable between the pump and the converter, a new adjustment often has to be carried out manually, since the offset error of the axial sensor also depends on the length of the connecting cable. Usually, the pump tolerances must first be manually adjusted in the manufacturer's test field. After installation of the pump at the customer, a new adjustment is already necessary. later in the event of changes to the installation and irregularities within the storage. Since the customer cannot usually carry out the manual adjustment of the magnetic bearings himself, the maintenance effort associated with the installation and operation of the pumps is very high.

The object of the present invention is to create a method of the type mentioned at the outset and a circuit suitable for carrying out this method, in which a manual adjustment procedure can be omitted.

According to the invention, this object is achieved by the characterizing measures of the claims.

In the adjustment according to the invention, which proceeds in a particularly advantageous manner without manual intervention, the fact that the stationary rotor rests on an axial stop becomes the first Information used. The target position of the rotor in operation - its unstable equilibrium position - is about half the possible total stroke of the rotor from the current rotor stop position. However, since two axial stops exist and it is not known which stop positions the stationary rotor has assumed, one of the two rotor stop positions is initially assumed to be the case. For commissioning, the signal of the axial sensor, which has an offset error, is initially compensated by an equally large signal with inverse polarity. The voltage transmitter then supplies a voltage value corresponding to half the stroke with a specific polarity. If the voltage value has the wrong polarity, the current supplied to the deflection coils will rise, for example, because the rotor cannot assume its equilibrium position. If this current exceeds a maximum limit, this attempt is stopped. Thereafter, a half ^'Rotorhub voltage value corresponding to the reversed polarity is supplied from the voltage generator. This voltage value causes the rotor to lift from its stop position so that the machine equipped with the rotor can be started up.

Further advantages and details of the invention will be explained with reference to FIGS. 1 and 2. Show it

- Fig. 1 is a highly simplified block diagram and

- Fig. 2 is a block diagram with a circuit example for the

Control device.

In the block diagram shown in the figure for a circuit with which the method according to the invention can be carried out, the axial sensor is designated by 1. Its signals are fed via an amplifier 2 to a control device, which is generally designated 3. The output current signals of the control device 3 are amplified (amplifier 4) and fed to the deflection coil 5. Only one deflection coil 5 is shown. In practice, two or more deflection coils are usually present. In practice, two or more deflection coils are usually present.

In this axial active controlled system, which is known per se, control takes place in such a way that the axial sensor 1 generates signals the size of which corresponds to the deviation of the rotor from its desired position. The currents flowing from the amplifier 4 into the deflection coil 5 cause the rotor to return to its desired position. As will be explained further below, when the rotor has reached its unstable equilibrium position, the current flowing through the deflection coil 5 should be zero. For this purpose, a "current to zero" controller is present, which is part of the control device 3. In addition, the control device 3 is designed so that the steps according to the invention are carried out.

FIG. 2 shows a circuit diagram with an example of the design of the control device 3. With this circuit, the signal emitted by the amplifier 2 is also fed to a so-called sample & hold element (block-dotted block 6, input 21) which is provided by the resistors 7, 8, the capacitor 9, the operational amplifier 10 and the field effect transistor 11 is formed. A sample and hold element has the property that its output accepts and holds the voltage value of an input signal, here with inverse polarity. The output 12 of the sample and hold element 6 is connected to an adder 13. In addition, the adder 13 is connected to the amplifier 2 and a voltage transmitter 14. The sum signal is fed to a controller 15.

Logic 16 is also provided to control the sequence of the commissioning method according to the invention. The logic 16 is supplied with signals via the line 17 which correspond to the currents flowing from the amplifier 4 to the deflection coil 5. The logic 16 is also connected via the control lines 18, IS and 20 to the field effect transistor 11, the voltage generator 14 and the amplifier 4, so that an automatic control of these components is possible. Finally, the line 22 is provided with the resistor 23, which the The commissioning of a magnetically levitated machine equipped with this circuit takes place as follows: after switching on, the transistor 11 is initially conductive. The transistor 11 then forms, together with the amplifier 10, the resistors 7, 8 and the capacitor 9, the sample & hold element 6. Since the input 21 of this element 6 is connected to the output of the amplifier 2, its supply is provided Output 12 a voltage value of the same size with inverse polarity. The signal from sensor 1, which has a more or less large error and is amplified in amplifier 2, is thus initially canceled by the sample and hold element signal supplied to adder 3.

The transistor 11 is then blocked, so that changes in the signal from the sensor 1 amplified in the amplifier 2 are no longer canceled, and at the same time the amplifier 4 is released via the line 20 and the adder 13 (and thus the controller 15) from the voltage generator 14 a voltage value supplied with a certain polarity, which corresponds to half a stroke of the rotor. Since it is not known at which of its two axial stops the stationary rotor rests, this voltage value can be correct or incorrect. This question is checked on the basis of voltage or current changes in the area of the axial active controlled system.

In the exemplary embodiment shown, the logic 16 is connected to the output of the amplifier 4 via the line 17. After the feeding of the half stroke of the rotor corresponding Span¬ voltage value to the controller 15, the rotor either in Rich¬ tung its desired position move ^is' may or may not. If he cannot assume the desired target position, after the amplifier 4 is released by the logic 16, the current flowing to the deflection coil 5 will increase due to the axial active control without the rotor moving. If the logic 16 registers via line 17 that a set limit value has been exceeded, the experiment is stopped because it is now clear that the voltage supplied by the voltage generator 14 had the wrong polarity. The logic 16 will then reverse the voltage transmitter 14 such that it inverts its output. Because of this right tension now when the amplifier 4 is released again, the rotor will catch and assume approximately its desired position. Since the transistor 11 is blocked at the same time as the amplifier 4 is released, the amplifier 10, together with the capacitor 9 and the resistor 23, takes on the function of an integrator, ie the function of a “current-to-zero” control . The current flowing to the deflection coil 5 is therefore regulated to zero in the long term. This regulation is able to compensate for any remaining deviations of the rotor from its target position, which for example does not correspond exactly to half the stroke when the rotor shaft is not horizontal.

In the dargeεtellen and described embodiment, the accuracy of the voltage supplied by the voltage generator 14 ^■ value is detected from the current flowing from the amplifier 4 to the deflection coil. 5 Another possibility is, for example, to observe the signal supplied by the axial sensor - before or after amplification. A line 24 connecting the output of the sensor 1 to the logic 16 is shown in dashed lines. If the voltage value supplied by the voltage transmitter is incorrect, the sensor signal will not change significantly since the rotor cannot move. If the voltage value supplied by the voltage sensor is correct, the rotor will catch. This will also change the signal of the axial sensor, so that the correctness of the voltage supplied by the voltage sensor can be seen from this change.

The entire control device 3, including the automatic offset adjustment, can also be implemented with a digital regulating and control unit. The control of the capture attempts is then generally realized with the help of a program.

Claims

PATENT CLAIMS

1. Method for starting up a machine equipped with a magnet-bearing rotor, the magnetic bearing of which has the following features:

Permanent magnets, which bring about a stable mounting in the radial direction and unstable in the axial direction of the rotor;

an axial sensor (1), a controller (3, 15) and at least one deflection coil (5), which hold the rotor approximately in its axially unstable equilibrium position during operation of the machine by supplying the deflection coil (5) with currents, which depend on the deviation of the rotor from its unstable equilibrium position (active axial control system);

a control device (9, 10, 11) which automatically compensates the currents flowing in the deflection coil (5) such that the current in the unstable equilibrium position of the rotor has the value zero ("current-to-zero" - Regulation) ,

- Means for an adjustment of offset errors of the magnetic bearing system, in particular of the axial sensor, necessary for the start-up of the machine characterized in that the adjustment of offset errors is automated, - by the fact that the stationary rotor rests on an axial stop and the target position of the rotor in operation - its unstable equilibrium position - thus by about half the possible total stroke of the rotor of the current rotor stop position is distant, as information is used to supply the deflection coil in such a way that the rotor assumes its nominal position almost independently of the offset, and that one of the two possible rotor stop positions is assumed and attempted as given Stabilize the rotor by about half the possible total stroke of the rotor away from the assumed rotor stop position.

2. The method according to claim 1, characterized in that in the event that the rotor stop position not applicable had been assumed as given, then the other rotor stop position is assumed as given and attempts to the rotor by about half the possible total stroke of the rotor stabilize away from the now adopted rotor stop position.

3. The method according to claim 1 or 2, characterized in that the current flowing into the deflection coil (5) is registered to check the correctness of the rotor stop positions assumed as given.

4. The method according to claim 1 or 2, characterized in that the signal emitted by the axial sensor (1) is used to check the correctness of the rotor stop positions assumed to be given.

5. The method according to any one of claims 1 to 4, characterized gekenn¬ characterized in that the control device (3) including the Steuer¬ unit for the automatic adjustment of offset errors is realized with the aid of a digital control and regulation unit.

6. The method according to any one of claims 1 to 4, characterized gekenn¬ characterized in that the following measures are initiated by means of a controller (16):

When the rotor is at rest and is in contact with one of its two possible axial stops, the controller (15) is supplied with the signal from the axial sensor (1), which is subject to offset errors, and an equally large, inverse signal;

Thereafter, the controller (15) is supplied with a voltage signal from a voltage generator (14), the size and direction of which is selected on the assumption that the rotor abuts a specific (first) stop such that the rotor is moved by approximately half the distance Distance between its stops from the first stop,

Using a voltage or current profile on a component of the axial active controlled system, it is checked whether the assumed rotor stop position was correct or incorrect,

if the stop position is incorrectly assumed, the regulator (15) is supplied with an inverse signal by the voltage transmitter (14) and then the "current-to-zero" control is started,

If the stop position is correctly assumed, the rotor will assume its approximate target position and the "current-to-zero" control (9, 10, 11) will start.

7. The method according to claim 6, characterized in that the current flowing into the deflection coil (5) is registered to check the correctness of the voltage value given by the voltage transmitter (14).

8. The method according to claim 6, characterized in that for checking the accuracy of the voltage generator (14) emitted voltage value, the signal emitted by the axial sensor (1) is used.

9. Circuit for performing the method according to one of claims 1 to 4, 6, 7 or 8 with an axial Aktivrege¬ treatment (1, 2, 3) and a "current-to-zero" control (9, 10, 23rd ), characterized in that it is equipped with a circuit (6) for generating a signal inverted to the signal of the axial sensor (1).

10. A circuit according to claim 9, characterized in that the circuit (6) is a sample _ • hold element.

11. The circuit according to claim 10, characterized in that the operational amplifier (10) of the sample and hold element (6) after the blocking of the transistor (11) is part of the "current-to-zero" control.