JPH0458278B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a positioning device using an electric motor that can be used in semiconductor manufacturing, precision dimension measurement, precision machine tools, etc. where precise positioning is required. .

Conventional configuration and its problems First, the characteristics of a DC brushless motor and a synchronous motor, both of which have a synchronous machine as their basic structure, will be explained. Figure 1 shows the principle of a Type 2 three-phase DC brushless motor.

In FIG. 1, numeral 1 indicates a rotor composed of two-pole permanent magnets. 2, 3, and 4 are armature windings (hereinafter abbreviated as windings) wound around the armature 5, which is a stator. Reference numeral 6 denotes a known rotor position detector (hereinafter abbreviated as RPS) for detecting the position of the rotor 1. 7 is a known power amplifier that selectively excites the windings 2, 3, and 4 with a current of a required magnitude according to the commands from the electronic rectifier circuit 8. 8 is a well-known electronic rectifier circuit, and according to the signal from RPS6,
For example, in order to rotate the rotor 1 in the counterclockwise direction as shown by arrow A, the windings 2, 3, and 4 are selectively energized to produce magnetic poles (hereinafter abbreviated as winding magnetic poles) 9, The power amplifier 7 is controlled to rotate the magnetic poles 9 and 10 counterclockwise so that the magnetic poles 9 and 10 follow the rotation of the rotor 1 and are always at a position deviated from the magnetic pole of the rotor 1 by π/2 in terms of magnetic spatial angle. There is a need to. This electronic rectifier circuit, together with the RPS6,
It has the role of brushes and commutator of traditional DC motor.

The electronic rectifier circuit 8 also has the function of controlling the currents in the windings 2, 3, and 4 so that the rotational speed matches the speed command.

If the magnetic spatial angle θ formed between the winding magnetic poles 9 and 10 and the different magnetic poles of the rotor 1 is hereinafter referred to as the torque angle θ, the largest torque will be generated when θ=π/2. , is normally set to θ=π/2 in the conventional DC motor with brushes and commutator and the DC brushless motor shown in FIG. 1, and remains constant regardless of the size of the load. Speed control in this type of electric motor depends on the strength of the winding magnetic poles 9, 10, that is, the magnitude of the current that excites the windings 2, 3, 4, or in other words, the magnetic poles of the rotor 1 and the winding magnetic poles 9, 10. This is control of the magnitude of the torque that acts on the rotor 1 and is produced by the action of the rotor 1. A motor having the above characteristics is called an asynchronous motor.

Another method for operating a brushless motor with asynchronous motor characteristics will be described next.

The torque angle is controlled by the signal from the RPS 6 which detects the position of the rotor 1 in the same way as described above while keeping the strength of the winding magnetic poles 9 and 10 constant, that is, keeping the winding current constant. Since it is possible to obtain torque according to the torque angle, asynchronous characteristic operation is possible.

This method not only allows speed control by simply changing the torque angle, but also reverse rotation by making the torque angle negative, and even if the torque angle is always set to π/2, the magnitude of the winding current The configuration can be simpler than the method of controlling the speed by changing the winding current and reversing the direction of the winding current to reverse rotation.

In either method, in order to improve the responsiveness of speed control in an asynchronous motor, it is generally necessary to apply a speed minor loop using a speed detector (not shown).

Next, a two-pole three-phase synchronous motor will be explained. As shown in FIG. 2, in the synchronous motor as well, the rotor 21 is a permanent magnet as in FIG. 1, and 22, 23, and 24 are windings wound around an armature 25.

26 is a variable frequency oscillator 27 (hereinafter abbreviated as VFO) which causes three-phase alternating current to flow through the windings 22, 23, and 24 with a phase difference of 2π/3 in time, in accordance with a command from the variable frequency oscillator 27 (hereinafter abbreviated as VFO). , 24 (hereinafter abbreviated as wire-wound magnetic poles) are rotated counterclockwise when the rotor 21 is rotated counterclockwise as shown by arrow B.

VFO27 is an oscillator whose oscillation frequency can be varied to achieve a rotational speed that matches the speed command. When the rotational speed (rps) is n, the oscillation frequency (Hz) is f, and the number of poles of the rotor is P, n = 2f. /P so that f
is determined and the power amplifier 26 is commanded.

Therefore, in this electric motor, the rotor 21 rotates in synchronization with the rotation of the winding magnetic poles 28 and 29, and when there is no load, the torque angle θ is 0 as shown in FIG. 2, but when a load is applied, the torque angle θ is 0. As shown in Fig. 3, θ is the torque that tries to make θ=0 due to the attraction and repulsion between the magnetic poles 28, 29 and the magnetic poles of the rotor 21 due to θ deviation (hereinafter, this torque is referred to as synchronous torque)
and the load torque change until they reach balanced values.

In other words, the torque angle θ changes depending on the size of the load, and as the load torque increases, θ also increases. If the rotor is a permanent magnet, the synchronous torque is maximum when θ = π/2, and when θ exceeds π/2. If a load torque exceeding this limit is applied, a so-called step-out phenomenon will occur, and the rotor 21 will stop. Such characteristics will be referred to as synchronous motor characteristics. Since an electric motor having this characteristic must be used with a torque angle margin, its efficiency is inferior to that of an electric motor such as the asynchronous motor that can always be operated at maximum torque at a torque angle of π/2.

However, the rotational speed of a synchronous motor is the same as the frequency of the three-phase AC, that is, the rotational speed of the magnetic field, regardless of the load size, as long as it does not step out, so there is no need for a speed minor loop for speed control like in an asynchronous motor. It has the characteristic of being

In a synchronous motor, the followability to a rotating magnetic field is better as △T/△θ is larger, where △T is the load torque fluctuation and △θ is the torque angular movement at that time. The synchronous motor that most closely meets the above requirements is a pulse motor. As shown in Figure 2, a pulse motor with a permanent magnet as a rotor is a permanent magnet type (PM
However, a pulse motor with a rotor 32 made of soft magnetic material and having convex poles 30 and 31 as shown in Fig. 4 is called a variable reluctance type (VR type). .

The operating principle of the VR type motor is the winding magnetic poles 33, 3.
4, due to the reaction, rotor 3
Different types of magnetic poles are induced in the two convex poles 30 and 31 to treat the rotor 32 as if it were made of permanent magnets, and it has the same synchronous motor characteristics as the PM type. A pulse motor that combines the PM type and VR type is called a hybrid type (HB type) and has similar synchronous motor characteristics.

In a pulse motor, a current that changes in a stepwise manner is passed through the windings to rotate the rotating magnetic field in a stepwise manner, and the rotor is also rotated in a stepwise manner. If it flows, the rotating magnetic field will rotate continuously, and the rotor will also rotate continuously.

Note that the current flowing through the winding does not necessarily need to change continuously, but may be a current that changes stepwise, which is called vernier drive.

If the driving distance corresponding to the amount of current change in one step when changing the current stepwise is made sufficiently smaller than the required positioning resolution, there will be no problem in positioning even if the current is changed stepwise.
That is, it is sufficient to generate a rotating magnetic field that rotates substantially continuously by passing a current that changes substantially continuously.

Since the pulse motor can be positioned in an open loop, the fact that it rotates continuously means that it is theoretically possible to position with infinitesimal resolution.

The above-mentioned characteristics are not limited to pulse motors, but are characteristics possessed by electric motors having synchronous motor characteristics.

Next, we will explain the difference in characteristics between a DC brushless motor and a synchronous motor when viewed as drive sources used for positioning control.

Positioning means that when the position deviation becomes 0, the speed becomes 0.
Therefore, the index of positioning responsiveness is given by the position loop gain Kp shown in the first equation.

Kp=V/ε( ^-S ) ......(1) However, V is the speed and ε is the position deviation. The larger Kp is, the better the response is, but depending on the mechanical rigidity of the power transmission system, the performance of the electric motor and drive amplifier, etc.
The optimal value of Kp is determined.

On the other hand, in order to position with high precision, it is necessary to be able to drive with high resolution. Increasing resolution is No. 1.
This means that ε in the formula becomes smaller. No. (1)
Since Kp in the equation is constant, as ε becomes smaller, V also becomes smaller in proportion.

In an asynchronous motor, when the required speed becomes small, it enters the dead zone of the speed detector necessary to form a speed minor loop, making low speed control difficult, and the limit of positioning accuracy determined by the limit of low speed control is about ±0.04 μm. It is.

On the other hand, in synchronous motors, as mentioned earlier, speed control is possible without the need for a speed minor loop, so even if the resolution increases and the required speed becomes smaller, a speed detector is not required, so it is possible to control the speed in the low speed range. Since the dead zone can be made extremely small, stable low-speed control is possible and positioning accuracy is improved. Especially among synchronous motors, the above-mentioned △T/△
In a pulse motor with a large θ and excellent responsiveness, by continuously rotating a rotating magnetic field, the resolution is theoretically infinitesimal, as mentioned earlier, and experimentally 1 × 10 ^-6 rotations and angles. positioning with a resolution of about 1 second. This resolution is equivalent to ±0.004 μm when using a screw with a lead of 4 mm, and much higher positioning accuracy can be expected than when using an asynchronous motor.

Further, in high-precision positioning, it is common to use a digital position detector such as a laser interferometer. A digital position detector has a 1-bit dead zone, so if an asynchronous motor is used and the target position is within the dead zone, the motor torque will be 0 and the positioning rigidity will be 0. On the other hand, in a synchronous motor, even if the target position is in the dead zone, the above-mentioned △
Since it has a rigidity represented by T/Δθ, it also has excellent stopping stability.

From the above, among synchronous motors, pulse motors have better characteristics than asynchronous motors in high-resolution driving, but as mentioned earlier, like asynchronous motors that operate with synchronous motor characteristics, pulse motors have better characteristics at the maximum torque point. Since it cannot be operated, the high acceleration/deceleration motion characteristics necessary for high-speed positioning will be inferior.

Therefore, it can be seen that both asynchronous motors and synchronous motors have their own advantages and disadvantages.

OBJECTS OF THE INVENTION The present invention provides a motor positioning device that achieves high-speed, high-resolution positioning using a single synchronous machine structure motor.

Composition of the Invention The present invention operates an electric motor with a synchronous machine structure near a target position using asynchronous electric motor characteristics using torque angle control that has large torque and excellent high acceleration/deceleration and high-speed characteristics.
This is a positioning device using an electric motor that then operates up to the target position using synchronous motor characteristics with excellent high resolution characteristics.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. Regarding positioning using a linear scale, a configuration using a two-pole three-phase synchronous motor structure will be described as an example.

In FIG. 5, reference numeral 40 denotes an electric motor having the same synchronous machine structure as in FIGS.
It is a winding wire wound around 5. 46 and 47 are RPS and power amplifiers similar to 6 and 7 in FIG. 1, respectively.

48 is the winding 42,
This is a torque angle control circuit that selectively excites 43 and 44 to control the torque angle so that the speed of the rotor 41 becomes a value corresponding to the speed command. 49 is a VFO similar to 27 in FIG. Both 50 and 51 are changeover switches. Reference numeral 52 drives a table 53 by a feed screw connected to the rotor 41. 54 is a linear scale fixed to the table 53 to detect the position of the table 53. 55 is a counter of the linear scale 54, which together with the linear scale 54 forms a known position feedback loop. 56 outputs a position command, and
This is a command circuit that controls the changeover switches 50 and 51. 57 is the position command and the counter 55
This is a known deviation counter that outputs the deviation from the position feedback signal from the position as the position deviation.

58 is a known D/A converter that converts the digital position error signal into an analog speed command voltage. Further, the position deviation signal is input to the command circuit 56.

When the motor 40 is operated as an asynchronous motor using the torque angle control circuit 48 in the above system, a known speed minor loop for improving the responsiveness of speed control, that is, for providing damping in the position control system, is shown in FIG. It is omitted here.

Next, the positioning operation will be explained. Electric motor 4
0 with asynchronous characteristics, the command circuit 56 controls the changeover switches 50 and 51 from the torque angle control circuit 48.
After switching to enter the loop, a position command to the target position is output to the deviation counter 57. The deviation counter 57 calculates the deviation between the position command and the position feedback signal, and outputs the calculated position deviation to the D/A converter 58. The D/A converter 58 converts the positional deviation into a speed command using the position loop gain shown in equation (1) above, and outputs it to the torque angle control circuit 48 via the changeover switch 51. The torque angle control circuit 48 is as described above.
In cooperation with the RPS 46, the means 40 is decelerated and driven at high speed with a non-movement characteristic, and the feed screw 52 is rotated to drive the table 53 toward the target position. Along with the movement of the table 53, the linear scale 54
A position feedback signal commensurate with the amount of movement is input to the deviation counter 57 via the counter 55. At the beginning of driving, the position deviation is large, so the speed command is also large, but as time passes, the position deviation becomes smaller and the speed command also becomes smaller.The position deviation is determined by a preset value, that is, the size of the position deviation. When the value of the speed command reaches the dead band level of the speed control of the asynchronous operation system, the command circuit 56 determines this from the position deviation feedback signal 59 from the deviation counter 57, and
In order to run the motor with a synchronous characteristic by passing a substantially continuously changing current through its motor windings, the changeover switches 50 and 51 are switched so that the VFO 49 enters the loop. Then, the rotor 41 rotates at a speed equal to the speed command in synchronization with the rotating magnetic field that rotates substantially continuously as described above, and the table 53 further approaches the target position. The closer the position is to the target position, the lower the speed becomes. When the target position is reached, the positional deviation becomes 0, the speed also becomes 0, and positioning is completed.
As mentioned before, the speed decreases and VFO49
Since the speed can be controlled simply by changing the oscillation frequency according to the speed command, even very low speeds just before stopping can be easily controlled, making stable positioning possible. Further, by driving most of the driving distance with asynchronous characteristics using torque angle control with excellent acceleration/deceleration characteristics, positioning can be performed in an extremely short time.

Note that even if the motor is not a rotary type as in the example, it is a linear type, it is not limited to a two-pole three-phase type, it is a multi-polar type, and even if it is a pulse motor, it can be a motor with a synchronous machine structure. That's fine. The position detector is not limited to a linear scale, but the effects of the present invention can be more effectively achieved if it is a length measuring device with high resolution such as a laser interferometric length measuring device. In addition, when driving at high speed with high resolution, for example, the maximum speed is 100 with a resolution of 0.01 μm.
If mm/S, the operating frequency of the deviation counter is 10M.
Hz, and the number of bits required for the D/A converter also increases. In this case, not only is the nozzle resistance disadvantageous, but the circuit configuration for high-speed signal processing becomes extremely expensive. The above problem can be solved by doing the following.

When the resolution is 0.01μm and the maximum speed is 100μm/S,
If the asynchronous characteristic is used to drive up to 1 μm before the target position, the resolution of the asynchronous characteristic drive may be 1 μm. Therefore, the signal from the position detector is also 0.01μm.
If the frequency is divided and processed at 1 μm, the operating frequency of the deviation counter can be 100KHz, which makes signal processing considerably easier. Optimal position loop gain 100
( ^-S ), the gain of the D/A converter during asynchronous characteristic driving should be 100 μm/S per 1 μm of positional deviation (1 pulse). If synchronous characteristic drive is entered, the maximum position deviation is at most 2 μm and the maximum speed is 200 μm/S, so even if the resolution is returned to 0.01 μm, the resolution is 20 KHz, so there is no problem at all. Also, at this time, the gain of the D/A converter is due to the position error.
The rate may be 1 μm/S per 0.01 μm (1 pulse).
By performing the above operations, the operating frequency can be reduced by 1/
100, and the capacity of the D/A converter is also 1/100.
It can be done.

Effects of the Invention The present invention provides a first driving means that controls a means for driving an electric motor having a synchronous machine structure so that the torque angle becomes a value corresponding to the required speed, and drives the electric motor with asynchronous motor characteristics, and and a second drive means driven by a synchronous motor characteristic that rotates in synchronization with the rotating magnetic field, and the first drive means drives the moving body to the vicinity of the target position, and the movable body is driven from the vicinity of the target position to the target position. By driving up to the target position by the second driving means, it is possible to drive to the vicinity of the target position at high speed in a short time and then drive to the target position with high resolution. This makes it possible to achieve highly accurate positioning.

Furthermore, by performing asynchronous operation using torque angle control rather than current control, speed and rotation direction can be controlled simply by changing the torque angle, making it possible to simplify the configuration of the asynchronous operation system compared to the former method. . Furthermore, when switching from asynchronous operation to synchronous operation, the current control method requires an operation to switch the torque angle from π/2 to 0, but with torque angle control, the torque angle approaches 0 in the low speed range during asynchronous operation. Since there is no need for the former operation, it is possible to shift to synchronous operation with a torque angle of 0 very easily.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing the operating principle of a 2-pole 3-phase DC brushless motor, Fig. 2 is a principle diagram showing the operating principle of a 2-pole 3-phase synchronous motor, and Fig. 3 is a principle diagram showing the operating principle of a 2-pole 3-phase DC brushless motor. FIG. 4 is a principle diagram for explaining the operation of a synchronous motor having another structure, and FIG. 5 is a block diagram showing the configuration of a positioning device using an electric motor in an embodiment. 1, 21, 32, 41...rotor, 2, 3, 4,
22, 23, 24, 42, 43, 44... Armature winding, 9, 10, 28, 29, 33, 34... Magnetic pole produced by armature winding, 6, 46... Rotor position detector (RPS), 8...Electronic rectifier circuit, 48...Torque angle control circuit, 27, 49...Variable frequency oscillator (VFO), 50, 51...Selector switch, 52...Feed screw, 53...Table, 54...Linear scale, 55...Counter, 56 ...Command circuit, 57...Deviation counter, 58...D/A converter.

Claims (1)

[Scope of Claims] 1. An electric motor having a synchronous machine structure, a first driving means for driving the electric motor with asynchronous motor characteristics so that the torque angle becomes a value corresponding to the required speed, and a second driving means for driving a moving body with synchronous motor characteristics by passing a current that changes substantially continuously through the windings to generate a rotating magnetic field that rotates substantially continuously; driving and moving the electric motor by the driving means of 1;
A positioning device using an electric motor, comprising: control means for controlling the motor to be driven by the second means to move the movable body from the vicinity of the target position to the target position. 2. The first driving means is configured to include a movable element position detecting means for detecting the position of the movable element of the electric motor, and a torque angle that is controlled by the movable element position detecting means to generate a torque corresponding to the required speed of the movable element. a first excitation means for selectively exciting the windings of the electric motor; 2. A positioning device using an electric motor according to claim 1, comprising a second excitation means for driving the movable element at a required speed in synchronization with the speed.