JPH11341853A - Circuit and method for driving linear motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the current command value following-up ability of a linear motor by reducing thrust variation by giving a plurality of current command values having driver phase differences to the motor based on relative positional information, and connecting coils and drivers to each other in such a way that their polarities are inverted for each in-phase coil. SOLUTION: A controller G decides the current command values A and P, which are made to flow from current drivers D1 and D2 from the value of an absolute encoder F and outputs the values A and B. A magnet group M is magnetized so that a thrust variation may become the minimum, when current relation between coils in two phases is a sine wave having a phase difference of 90 deg., and makes the output of the absolute encoder E zero when the center of a mover M is positioned at the center of a coil Cn. The controller G selects two coils to be conducted, based on the value of the encoder E and turns on or off the corresponding relays -Rn-2 to Rn+2. The current drivers D1 and D2 generate currents so that the actual currents become equal to the command values A and B. Since the total of thrusts generated by each coil from the current of the driver D2 becomes the same as the thrust when current is made to flow into one coil, no variation in thrust occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear motor and a driving circuit and a driving method thereof.

[0002]

2. Description of the Related Art In a moving magnet type two-phase excitation linear motor, since a mover (mover) is a magnet, electric wires for driving are sufficient on a stator (stator) side, so that stress is not applied to the electric wires and there is a fear of disconnection. It is characterized by the fact that there is no heat generation and the heat is generated on the stator side, so that it can be easily cooled by a refrigerant, etc., and is being used in various fields including semiconductor manufacturing equipment that requires high reliability and accuracy . In particular, in a scan exposure type semiconductor manufacturing apparatus (scanner) using an exposure method that makes full use of the effective angle of view of a projection lens, a linear motor that generates a more stable thrust than a sequential exposure type semiconductor exposure apparatus (stepper) is required. It has been demanded.

When a long stroke is required compared to the size of a mover, a plurality of coil pairs are required. If all coil pairs are connected to the same current driver, it is possible to generate thrust.However, coils that do not reach the mover's magnetic field do not generate thrust, but only loss (heat generation) due to coil electrical resistance, The efficiency of the motor will be extremely low. In order to prevent this, a current driver is connected to each coil pair, and the current command value of the current driver connected to each coil can be individually given, so that no current flows to the coil beyond the magnetic field of the mover A method is conceivable. This method requires as many current drivers and command value generators as the number of coil pairs, and the cost increases in proportion to the stroke. Therefore, this method cannot be used for long strokes.

As another method, it is possible to connect a current driver to each coil via a relay or the like so as to selectively supply current only to coils in the magnetic field range of the mover. 284785, JP-A-8-
No. 111998).

FIG. 3 is a diagram showing a configuration of a conventional linear motor drive circuit using a relay. In this figure, M
Is a magnet group that is a mover (mover) of a linear motor, Cn-2 to Cn + 2 are coil groups that are a stator (stator) of the linear motor, and Rn-2 to Rn + 2 are relays for selectively energizing each coil. , D1 and D2 are current drivers for flowing coil current, E is an absolute encoder for detecting the relative position of the mover and the stator, and G is a current commander for the current drivers D1 and D2 by referring to the value of the absolute encoder E. This is a controller that gives values (A, B). The drawing shows only the vicinity of the coil Cn of interest. Further, as shown in the figure, the interval between the in-phase coils is 1.5 times the period of the magnetic field of the magnet.

FIG. 4 is a graph showing a signal of a drive circuit when the linear motor of FIG. 3 moves. The transition of the switching state of the relay R and the absolute encoder E from the top are shown in FIG.
, And the changes in the currents of the current drivers D1 and D2. In this case, since all the polarities of the coils are connected in the same direction, it is necessary to invert the sign of the current command value when switching the coils as shown in FIG.

FIG. 5 shows the thrust to the mover generated in response to the relay switching state and the transition of the current shown in FIG.
In the figure, FA and FB indicate the thrust to the mover generated by currents A and B, respectively, and FA + FB indicates F
Shows the resultant force of A and FB.

[0008]

As shown in FIG. 5, when the reaction time of the relay element is longer than the move time of one pitch of the mover and the relay OFF time is longer than the ON time, the two coils of the same phase are connected. Since current flows at the same time, the thrusts generated by the two coils are opposite to each other and cancel each other out in the phase. Therefore, the thrust of the phase is not generated during that time, and the thrust recovers instantaneously at the time of ON,
The thrust (FA + FB) of the linear motor is disturbed, making it difficult to perform smooth control.

On the other hand, when the relay OFF time is shorter than the ON time, a period occurs in which current does not flow through both of the two coils of the same phase. During that period, the thrust of the phase is not generated as in the above case, and the thrust is instantaneously recovered when the power is ON, and the thrust of the linear motor is disturbed.

In order to switch the in-phase coil when the current command value given to the current driver is 0, it is necessary to invert the sign of the current command value when the change in the current command value is greatest. At this time, the derivative of the change in the current command value becomes infinite, so that the current driver follows the current command value poorly. In order to improve the followability, a current driver having good responsiveness is required, and there is a disadvantage that the cost is increased.

The present invention has been made in view of the above points, and an object of the present invention is to provide an inexpensive linear motor drive circuit which has a small change in thrust, has good current command value followability, and is inexpensive.

[0012]

In order to achieve the above object, a linear motor drive circuit according to the present invention comprises a coil array having a plurality of in-phase coils and a magnet moving relatively to the coil array. A plurality of drivers for supplying a current to each phase of the common-mode coil; Means for measuring the relative position between the row and the magnet; means for selectively energizing a plurality of in-phase coils based on the measured relative position information; and a plurality of current commands having a phase difference to the driver based on the relative position information. Means for giving a value, wherein the coil and the driver are connected so that the polarity is inverted for each in-phase coil.

[0013] The linear motor drive circuit of the present invention, in particular,
The coil array is a stator and the magnet is a mover. 2
It is suitably used for a phase excitation type linear motor.

Here, the means for selectively energizing is usually means for energizing only the coils within the range of the magnetic field of the magnet, but in the present invention, selectively energizing to reduce the change in thrust. When switching the coil to be energized by the means, it is preferable that the time required for ON is shorter than the time required for OFF. That is, when switching the coils to be energized, both of the switched in-phase coils are temporarily energized.

Further, the linear motor driving method of the present invention comprises:
This is a method for driving a linear motor using the above drive circuit.

A linear motor according to the present invention includes a coil array having a plurality of in-phase coils, a magnet that moves relatively to the coil array, and the above-described drive circuit. (Integer + 0.
5) It is characterized by being twice.

According to the present invention, even if two coils of the same phase are switched, the drive circuit is not affected by variations in the switching time of the relay, has good current command value followability, and minimizes disturbance of thrust. Can be provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a drawing showing a configuration of a linear motor drive circuit according to one embodiment of the present invention. In FIG. 1, components denoted by the same reference numerals as those in FIG. 3 indicate the same components.
Also, in FIG. 1, the coil Cn of interest is similar to FIG.
Only the vicinity is shown.

First, the controller G determines and outputs the current command values A and B supplied by the current drivers D1 and D2 based on the value of the absolute encoder E. The current command value is calculated by the following equation (1).

[0020]

(Equation 1)

Here, it is assumed that the magnet group M is magnetized so that the thrust unevenness is minimized when the relationship between the currents of the two-phase coils is a sine wave having a phase difference of 90 degrees. The output of the absolute encoder E when the center of the mover M is located at the center of the coil Cn is assumed to be zero.

Next, two coils to be energized are selected from the value of the absolute encoder E, and the corresponding relay R
Turn on / off n-2 to Rn + 2. Current driver D1,
D2 generates a current such that the current command values A and B are equal to the actual current. The mover M receives a thrust from the coil Cn so as to move from left to right in FIG.

Here, the process of switching from the coil Cn-1 to Cn + 1 will be described as an example. When the center of the mover M is on the left side of the center of the coil Cn, the relay Rn−
1 and the relay Rn are turned on, and the others are turned off. The moment the center of the mover M moves to the right from the center of the coil Cn, the relay Rn + 1 is turned on. At this time, since the relay Rn-1 is still ON, the coil Cn-1 and the coil Cn + 1 are connected in parallel, and half of the current command value B flows through each coil. Since the sum of the thrusts generated by the respective coils due to the current of the driver D2 is the same as when the current flows through one coil, the thrust does not fluctuate.

Next, the relay Rn-1 is turned off,
All the current from the driver D2 flows through the coil Cn + 1. In this process, the current of the driver D2 only changes smoothly, and no transient fluctuation occurs.

In one phase, the relay Rn remains ON. The current of the coil Cn is given by the driver D1, and the current command value A is in a state where the change is the smallest.

As described above with reference to the example before and after the coil Cn, a drive circuit with small linear motor thrust fluctuation at the time of coil switching is realized at low cost.

(Other Embodiments) In the first embodiment, a two-phase excitation type linear motor is used. However, the same effect can be obtained in the case of three phases. FIG. 6 shows the configuration of the three-phase excitation type linear motor according to the present invention. In FIG. 6, the same reference numerals as in FIG. 1 denote the same members. As shown in the figure, the in-phase coil interval is 0.5 times the period of the magnetic field.

Although the above embodiment has been described assuming that the relay is mechanical, a switch or relay realized by using a semiconductor element may be used. further,
Although the relay is configured on only one side of the coil in order to reduce the cost, the same applies to the configuration on both sides.

Although the current drivers in FIGS. 1 and 6 are described as push-pull circuits, they may have a single-ended configuration.

In the first embodiment, the number of magnets is four. However, the number of magnets is not limited to four, and may be five or six. Further, the magnets need not be a pair, and may be one in which a magnetic path is formed of a magnetic material on one side.

In the first embodiment, an absolute encoder is used as a relative position measuring device. However, a relay switch can be used without a controller by a position detecting means such as a Hall element or a photo switch, which has only a logical output. The same effect can be obtained even when ON / OFF is performed.

[0032]

As described above, according to the present invention,
Thrust fluctuation at the time of coil switching can be minimized, and a long-stroke high-precision linear motor drive circuit can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a linear motor drive circuit of the present invention.

FIG. 2 is a diagram showing signals of the linear motor drive circuit of FIG.

FIG. 3 is a diagram illustrating an example of a conventional linear motor drive circuit.

FIG. 4 is a diagram showing signals of the linear motor drive circuit of FIG. 3;

FIG. 5 is another diagram showing signals of the linear motor drive circuit of FIG. 3;

FIG. 6 is a diagram showing another embodiment of the linear motor drive circuit of the present invention.

[Explanation of symbols]

M: Mover (magnet group), C (Cn-3 to Cn +
7): Coil (stator), R (Rn−3 to Rn +)
7): Relay, E: Absolute encoder, D1
D3: current driver, G: controller, A: current of current driver D1, B: current of current driver D2, FA:
Thrust to the mover generated by the current of the current driver D1 in FIG. 3, FB: Thrust to the mover generated by the current of the current driver D2 in FIG. 3, FA + FB: Thrust to the mover of FIG. 3 (combined force of FA and FB) .

Claims (9)

[Claims] A coil array having a plurality of in-phase coils;
A driving circuit for driving a linear motor having a magnet that moves relatively to the coil array, wherein the interval between each in-phase coil is (integer + 0.5) times the period of the magnetic field of the magnet. A plurality of drivers for flowing a current to each phase of the in-phase coil; a unit for measuring a relative position between the coil array and the magnet; and selectively selecting the plurality of in-phase coils based on the measured relative position information. And a means for providing a plurality of current command values having a phase difference to the driver based on the relative position information, wherein the coils and the driver are configured such that the polarity is inverted for each in-phase coil. A linear motor drive circuit, which is connected. 2. The linear motor drive circuit according to claim 1, wherein the coil array is a stator, and the magnet is a mover. 3. The linear motor drive circuit according to claim 1, wherein the means for selectively energizing energizes only a coil within a range of a magnetic field of the magnet. 4. The method according to claim 1, wherein when the coil to be energized is switched by the means for selectively energizing, a time required for ON is shorter than a time required for OFF.
4. A linear motor drive circuit according to claim 1. 5. The linear motor drive circuit according to claim 1, wherein said linear motor is a two-phase excitation type linear motor. 6. The apparatus according to claim 1, wherein the interval between the in-phase coils is 1.5 times the period of the magnetic field of the magnet.
6. The linear motor drive circuit according to any one of claims 1 to 5. 7. A coil array having a plurality of in-phase coils;
A magnet that moves relative to the coil array;
A driving method for a linear motor, comprising: a plurality of drivers for flowing a current to each phase of the in-phase coil, wherein an interval between the in-phase coils is (integer + 0.5) times a period of a magnetic field of the magnet. Measuring the relative position of the coil and the magnet of the linear motor, providing a plurality of current command values having a phase difference to the driver based on the relative position information, and a plurality of in-phase coils of the linear motor Selectively energizing based on the relative position information, wherein a current having an inverted polarity is supplied to adjacent in-phase coils. 8. The linear motor driving method according to claim 1, wherein when the coils to be energized are switched in the step of selectively energizing, both of the in-phase coils to be switched are temporarily energized. 9. A coil array having a plurality of in-phase coils;
A magnet that moves relative to the coil array;
A linear motor having the drive circuit according to claim 1, wherein an interval between each in-phase coil is (integer + 0.5) times a period of a magnetic field of the magnet.