JP4251683B2 - Electromagnet drive device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an electromagnet driving device for a device that controls the position of an object with two electromagnets, and is effective when used for magnetic levitation of a magnetic bearing of a high-speed rotating body and various conveying devices.
[0002]
[Prior art]
FIG. 4 shows the structure of an apparatus conventionally used for applications such as magnetic bearings. In the figure, 1 is a first drive coil that constitutes a first electromagnet together with a first iron core 61, 2 is a second drive coil that constitutes a second electromagnet together with a second iron core 62, and 31 and 41 are respectively First and second variable current power sources for driving the first and second drive coils 1 and 2, 7 is a rotating shaft to be controlled, 81 is a first drive coil bias current Ib 1 and a control current i An adder for adding and controlling the output current of the first variable current power supply 31 to (Ib1 + i) by the output, 82 subtracts the control current i from the second drive coil bias current Ib2, and the second by the output This subtractor controls the output current of the variable current power supply 41 to (Ib2-i).
[0003]
When an object is controlled by two electromagnets, it is common to use push-pull driving in which the suction force on one side is increased by + i and the other suction force is reduced by -i. The bias currents Ib1 and Ib2 are necessary to support a load due to the weight of the rotating shaft 7 or the like. 9 is a control amplifier that outputs a control current i and has various configurations. For example, its input 91 receives a gap sensor output for detecting a gap between the rotating shaft 7 and the first iron core 61, and the gap length is A configuration such as PID control (not shown) is performed so as to be constant.
[0004]
FIG. 5 shows a circuit for driving the conventional apparatus coils 1 and 2 of FIG. 4. The variable current power sources 31 and 41 are connected in parallel to the coils 1 and 2, respectively, and the respective output currents are (Ib1 + i), ( Set to Ib2-i).
[0005]
[Problems to be solved by the invention]
As described above, the variable current power sources 31 and 41 are individually used for the two coils 1 and 2. Although the bias currents Ib1 and Ib2 are constant DC values, the control current i includes a considerable high-frequency component because the gap length fluctuates due to disturbance such as vibration of the rotating shaft 7, and the variable current power sources 31 and 41 Requires a fairly fast response. In general, the coils 1 and 2 may be driven at a low pressure, but a large current is required. Therefore, in order to realize high-precision and high-speed characteristic control, the variable current power sources 31 and 41 are required to have large current capacity and quick response. However, there are few such devices on the market, and Even if it is made or manufactured, it becomes very expensive.
[0006]
[Means for Solving the Problems]
In view of such a point, the present invention uses a single variable current power source, reduces the current capacity, and achieves the same effect with an inexpensive apparatus. Specifically, in a control system that controls the position of an object with two electromagnets, the drive coils of the two electromagnets and the variable current power supply are all connected in series to form a closed circuit. A constant current power supply is connected in parallel with the drive coil.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the details of the present invention will be described with reference to the drawings. FIG. 1 shows a drive circuit for a first drive coil 1 and a second drive coil 2 according to the present invention. Reference numeral 3 denotes a constant current power source for driving the first drive coil 1, which outputs a bias current Ib1. A constant current power source 4 drives the second drive coil 2 and outputs a bias current Ib2. Reference numeral 5 denotes a variable current power source that outputs a control current i, which drives the first drive coil 1 in the positive direction and the second drive coil 2 in the negative direction. The output current of the variable current power source 5 is controlled by a device similar to the control amplifier 9 of FIG. It is obvious that the coils 1 and 2 are driven by currents (Ib1 + i) and (Ib2-i) as in the conventional apparatus shown in FIGS.
[0008]
[Action]
When the conventional electromagnet driving device shown in FIG. 5 is compared with the electromagnet driving device according to the present invention shown in FIG. 1, the variable current power source is changed from two units 31 and 41 to one unit, and 5 is a bias current Ib1 or Ib2. Since it is sufficient to output only the control current i without supplying the power, a very small capacity is required, and the apparatus is much cheaper than the conventional apparatus.
[0009]
【Example】
FIG. 2 shows an embodiment of a constant current power source that supplies a bias current Ib1 to the first drive coil 1, and 5 is a variable current power source that supplies a control current i. The same applies to the second drive coil, but is omitted here. 32 is a constant voltage power source, 33, 34 and 35 are resistors, 36 is an operational amplifier, and 37 is a pnp transistor. As is well known, the positive and negative input voltages of the operational amplifier 36 that is active without being saturated are substantially equal. Therefore, when the voltage of the constant voltage power supply 32 is E, the voltage at the positive input terminal of the operational amplifier 36 is E +, the emitter current of the transistor 37 is Ie, and the resistance value of the resistor 35 is R.
E + = E−R × Ie (1)
Is established. Since the collector current Ic of the transistor 37 is substantially equal to the emitter current Ie, the drive coil 1 is driven at a constant current by Ie in the equation (1). The current value can be adjusted by changing the positive side input terminal voltage E + of the operational amplifier 36 by the resistors 33 and 34, and Ie is set to be the bias current Ib1. It is apparent that the control current i is superimposed on the drive coil 1 from the variable current power source 5 in addition to Ib1.
[0010]
FIG. 3 shows an embodiment of a variable current power source for supplying a control current i. Reference numerals 51 to 57 denote resistors, 58 and 59 denote operational amplifiers, 101 denotes an npn transistor, and 102 denotes a pnp transistor. A voltage Ei corresponding to the control current i, which is the output of the control amplifier 9 in FIG. The transistors 101 and 102 are for lowering the output impedance of the operational amplifier 58 and supplying a sufficient current to the drive coils 1 and 2 that are loads, and their collector terminals are connected to a positive power source and a negative power source. Resistors 55 and 56 are for protecting the transistors 101 and 102 from an overcurrent such as an output short circuit. The operational amplifier 59 operates as an output voltage buffer device. Assuming that the resistance value of the resistor 57 is Ro and the current value output through the resistor 57 is Io, Io = Ei / Ro is obtained by almost the same analysis as in FIG. 5, and the output current can be adjusted by Ei. .
[0011]
Assuming that the connection voltage of the resistors 55 and 56 is Eo, the positive side input terminal voltage of the operational amplifier 59 is (Eo−Io × Ro), and the operational amplifier 59 operates as a buffer device. Output voltage. The resistance values of the resistors 51 and 52 are selected to be equal, and the positive input terminal voltage of the operational amplifier 58 is (Ei + Eo−Io × Ro) / 2. Since the resistance values of the resistors 53 and 54 are also selected to be equal, the negative input voltage of the operational amplifier 58 is Eo / 2, which is equal to the positive input voltage, leading to Io = Ei / Ro A current Io proportional to the current i is taken out.
[0012]
2 and 3 are based on technical documents IEB554 and IEA519 concerning operational amplifiers of NEC Corporation.
[0013]
【The invention's effect】
According to the present invention, it is possible to drive two electromagnets used for magnetic bearings and magnetic levitation by an inexpensive current power source, and the industrial effect is great.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit configuration of the present invention.
FIG. 2 is a diagram showing an embodiment of a constant current power source according to the present invention.
FIG. 3 is a diagram showing an embodiment of a variable current power supply according to the present invention.
FIG. 4 is a diagram showing a configuration of a magnetic bearing device to which the present invention is applied.
FIG. 5 is a diagram showing a circuit configuration of a conventional device.
[Explanation of symbols]
1, 2 Driving coil 3, 4 Constant current power source 5 Variable current power source 7 Rotating shaft 9 Control amplifier 31, 41 Variable current power source 32 Constant voltage power source 33, 34, 35, 51-57 Resistor 36, 58, 59 Operational amplifier 37 , 102 pnp transistors 61, 62 Iron core 81 Adder 82 Subtractor 91 Control amplifier input terminal 101 npn transistor

Claims (1)

In a control system that controls the position of an object with two electromagnets, the two electromagnet drive coils and the variable current power supply are all connected in series to form a closed circuit, and in parallel with each electromagnet drive coil. An electromagnet drive device characterized by connecting a constant current power source.

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