JPH01286767A - Movable magnet linear dc motor - Google Patents

Abstract

PURPOSE:To reduce a thrust ripple by increasing the number of poles of a magnet for a magnetic sensor more than that of the poles of a field magnet. CONSTITUTION:A movable magnet linear DC motor has field magnets 1-1-4, coils 2-1-5, magnetic sensors 3-1-5, and magnets 4-1-5 for the sensors, which are disposed at predetermined positions and composed. In this case, points of detecting the magnetisms of the magnets 4-1-5 are added at one pole 4-5 in addition to the four poles 4-1-4 of the same pole construction as that of the poles 1-1-4 of the field magnet as five poles. Thus, the sensor 5-1-5 detect the magnetisms of the magnets 4 and supply currents to the corresponding coils 2-1-5, thereby applying a predetermined thrust to a movable element. Thus, since the thrust is not varied according to the position of the movable element, it can be reduced in size and enhanced in its power.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a moving magnet linear DC motor having a field magnet on the movable side and a coil on the stator side and having very small thrust ripple.

[Conventional technology]

FIG. 6 shows field magnets 1-1 to 1-4, coils 2-1 to 2-5, and magnetic sensors 3-1 to 3-5 to explain the operation of a conventional moving magnet linear DC motor of this type. It is a figure which shows an example of a structure with.

As is well known, the example of the linear DC motor shown in FIG. 6 has four pole field magnets 1-1 to 1-4, and the magnet width P of one pole. On the other hand, the coils 2-1 to 2-5 are arranged at a pitch of 4/3PH, and the magnetic sensors 3-1 to 3-5 are connected to the respective coils 2-1 to 2-5 as shown in FIG. On the other hand, it is a moving magnet linear DC motor that is arranged at a position shifted by 1/2 P to the right from the coil center line.

Money Measure 6 Place the field magnet 1-1~ in the position as shown in Figure A.
1-4, coils 2-2 and 2-3 are determined by Fleming's left-hand rule according to the polarity of field magnets 1-2 and 1-3 by magnetic sensors 3-2 and 3-3, respectively. A predetermined thrust can be applied to the movable element by passing current. However, regarding the coil 2-4, since the magnetic sensor 3-4 is only applied to the end of the magnetic pole of the field magnet 1-4, only a very small amount of magnetism can be detected, and furthermore, the current flowing through the coil 2-4 is Naturally, the current direction is opposite between the right and left halves of the moving part, but if the magnetic field applied to the coil is coil 2-4, the same phase field from field magnet 1-4 is applied to both the right and left halves of the coil. Therefore, the thrust generated by Fleming's left-hand rule is canceled by the right and left halves of the effective part of the coil 2-4, and no thrust is applied to the mover. Coil 2-2.2
-3. Two of the three coils in 2-4 provide effective thrust to the mover.

In addition, field magnets 1-1 to 1-4 are located at the positions shown in FIG. 6B.
If there is, in this case, the coil 2-
If we consider 2.2-3.2-4.2-5 in the same way as above, coil 2-3 will give an effective thrust to the mover, but coil 2-2 will give an effective thrust of the coil effective part. Since the field is only applied to the right half, only the thrust equivalent to 172 coils can be given to the mover.On the other hand, regarding coil 2-5, although the field is applied to the left half of the effective coil part, the magnetic field for coil 2-5 is Since the sensor 3-5 does not detect magnetism, current does not flow through the coil 2-5 and thrust cannot be applied to the mover.
In the case of FIG. 6A, it is impossible to apply thrust to the movable element in the same manner as described above. Therefore, in the case of FIG. 6B, 1.5 coils end up providing effective thrust to the movable element.

[Problem to be solved by the invention]

As mentioned above, in the case of an example of a conventional moving magnet linear motor, the number of coils that provide effective thrust to the mover varies between 1.5 and 2 depending on the position of the mover. The ratio or ripple rate is ((2,0-1,5)+2
．． 0I x100-25%, which is extremely large, making it difficult to move the mover at a constant speed, which has a great negative effect on positioning control, and at the same time makes it impossible to draw out the full power of the motor, which is generally required for linear motors. These problems include the inability to fully meet the needs for smaller size, higher power, and higher speed. In order to solve this problem, it has been proposed to increase the number of field magnets.
122355 r 5 In field magnet has been proposed. However, even in this case, the number of coils that provide effective thrust to the mover depends on the position of the mover. , it changes between O and 2.5, and the ripple is 20%, which has only a slight improvement effect, but on the other hand, there are problems such as increased cost due to the increase in the number of magnetic field magnets and difficulty in high-speed operation of the mover due to the increase in the weight of the mover. remains.

Another idea is to use three-phase drive. That is, the i-th coil and the i+3n-th coil (n is!, 2
．． In this method, currents of the same phase are passed through all the coils (positive integers of
Since the current in the same phase as 2 also flows to the coil 2-5, the left half of the effective part of the coil 2-5 can also give an effective thrust to the movable element, so the total movable thrust is equivalent to the effective thrust of 2 coils. You can give it to your child. However, in the case of this method, wasteful current is similarly passed through coils to which no field is applied at all, for example, in the case of Fig. 6A, all the coils to the right of coil 2-5. Particularly for long-stroke linear motors, unnecessary current is passed through many coils that are not subjected to the field of the movable magnet, resulting in problems such as increased power consumption and increased coil heat generation.

Another way of thinking is that installing two or more magnetic sensors per coil at predetermined positions on the left and right of the center line of the coil can be solved by constructing an appropriate logic circuit.
Increasing the number of expensive magnetic sensors leads to an increase in cost, and problems such as complicating wiring and circuits remain.

The conventional moving magnet linear DC motor shown in Fig.
It had the structure shown in Fig. 8 and Fig. 8. The coil 2 is attached to the fixed yoke 7 via the coil substrate 5, and the magnetic sensor 3 is also attached.

A movable yoke 6 is slidably held by a bearing 8 facing the fixed yoke 7, and a field magnet 1 is attached to the movable yoke 6. These field magnets 1 were extended so as to face the coil 2 and to face the magnetic sensor 3. For this reason, many expensive rare earth magnets were used.

It is an object of the present invention to solve the above-mentioned problems and provide a high-performance moving magnet linear DC motor with small thrust ripple.

[Means to solve the problem]

According to this invention, the mover is provided with a field magnet having at least 61 poles and a magnetic sensor magnet separate from the field magnet, and a coil and a magnetic sensor arranged along the running direction of the mover are provided. In a movable magnet linear DC motor in which a stator is provided with a magnetic sensor that detects the magnetism of a sensor magnet, the number of magnetic poles of the magnetic sensor magnet is greater than the number of magnetic poles of a field magnet.

According to such a moving magnet linear DC motor, there is no need to increase the number of magnetic sensors, or require complicated wiring or control, or to pass unnecessary current to the coil in the part where there is no mover. A movable magnet linear DC motor can be obtained that has small thrust ripples only by improving the structure and arrangement of the magnets, and therefore has no speed fluctuations and can draw out sufficient motor power.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a moving magnet linear DC motor according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows field magnets 1-1 to 1-4 for explaining an embodiment of a moving magnet linear DC motor according to the present invention.
, is a diagram showing the arrangement of coils 2-1 to 2-5, magnetic sensors 3-1 to 3-5, and magnetic sensor magnets 4-1 to 4-5. The movable magnet linear DC motor shown in Fig. 1 is almost the same as the conventional known case explained using Fig. 6 in terms of the arrangement and configuration of the field magnet, coil, and magnetic sensor, but In the conventionally known example, the magnetic sensor for detection directly detects the magnetism of a field magnet, whereas in the present invention, as shown in FIG. 1, magnetic sensor magnets 4-1 to 4-5 They differ in that they detect magnetic fields. The magnetic sensor magnet has a field magnet pole configuration (1-
The magnetic sensors 3-1 to 3-5 consist of 4 poles (4-1 to 4-4) with the same pole configuration as 1-1-4) and 5 poles with the addition of another pole 4-5. The magnetism of the magnetic sensor magnet is detected and a current is applied to the corresponding coils 2-1 to 2-5 to apply a predetermined thrust to the movable element according to Fleming's left-hand rule.

The structure of the field magnet 1-1-1-4 must be arranged so that the surface facing the coil alternates with the Nl and S poles, as is conventionally known, but the magnetic sensor magnet 4-1
~4-5 is also arranged with the same width and the same rod configuration as the field magnets 1-1 to 1-4 in each column, with N poles and S poles alternately arranged, and furthermore, in this embodiment, as shown in FIG. The magnetic sensors 3-1 to 3-5 are arranged at positions shifted by 1/2 PN (P, l is the width of one field magnet) to the right from the center line of each of the coils 2-1 to 2-5. In this case, the magnetic sensor magnet also has a configuration in which one pole is added on the right side of the field magnet. In addition, the width of the added l-pole of the magnetite for the magnetic sensor must be greater than the length of the magnetic sensor that is applied to the corresponding coil when the field of the field magnet is applied to the corresponding coil. In the embodiment, the width of one rod of the field magnet is P, l.
The total width of the coil is also P, l, and the pitch between each coil is 4/3.
At P, 1, the magnetic sensor is 1/2 from the center line of each coil.
When placed at a position shifted to the right by Pal, the magnetic sensor magnet has a pole configuration in which one pole of P and width is similarly added to the right with respect to the pole configuration of the field magnet.

Next, in the case of a movable magnet linear DC motor having the structure of an embodiment of the present invention as described above, what kind of thrust acts depending on the position of the mover will be compared with a movable magnet linear DC motor of similar prior art. I will explain.

Field magnets 1-1 to l-4 are placed in the positions shown in Figure A of Kintei 1.
If there is, an effective thrust can be given to the movable element by passing a current according to Fleming's left-hand rule through the two coils 2-2 and 2-3. In this case, there is no meaning in changing the number of magnetic sensor magnets to 5 and adding 4-5, and it is exactly the same as what was explained using FIG. 6A as a conventionally known example.

However, if the field magnet 1 is placed in the position shown in Fig.
-1 to 1-4, the magnetic sensor 3-5 corresponding to the coil 2-5 can cause a current to flow through the coil 2-5 by detecting the magnetism of the magnetic sensor magnet 4-5. In addition, since the field of the field magnet 1-4 is applied to the left half of the effective part of the coil 2-5 (the part indicated by the symbol in the figure), the effective thrust according to Fleming's left-hand rule is can be given to the mover. Therefore, in the case described above using FIG. 6B as a conventionally known example, only 1.5 coils were able to apply effective thrust to the mover because no current was flowing through the coils 2-5. In the case of the example, effective thrust for a total of two coils including the left half of coil 2-5 can be applied to the mover. As can be seen by sequentially moving the position of the field magnet, which is the mover, with respect to the coil array in Figure 1, the thrust force equivalent to two coils is always applied to the mover regardless of the position of the mover. It turns out that it can be done.

Similarly, when the mover is moved, there is a case (case 1) with a four-pole field magnet of the prior art, a case (case 2) with a five-pole field magnet, and an embodiment of the present invention. Comparing the number of coils that provide effective thrust to the mover in each case of a 4-pole field magnet and a 5-pole magnetic sensor magnet (Case 3), it is found that 1 pole of the field magnet The change is as shown in FIG. 2, where one cycle is the convergence P9. In other words, in case 1, it changes between 1.5 coils and 2 coils, and in case 2, it changes between 2 coils and 2.5 coils, but in case 3 of this invention, it is related to the position of the mover. There are always 2 coils. Being able to always apply a constant thrust to the mover in this way is very effective in controlling the positioning of the mover, and in moving magnet linear DC motors with the same number of field magnet poles, compared to conventional technology. As is clear from comparing the case (case 1 described above) and the case according to an embodiment of the present invention (case 3 described above), the motor has the ability to always draw out sufficient power from the motor. Therefore, it is possible to provide a small moving magnet linear DC motor with high power and good control performance.

A side view of the movable magnet linear DC motor according to an embodiment of the present invention described above is shown in FIG. 3, and FIG.
-Y sectional view. In FIGS. 3 and 4, parts corresponding to those in FIGS. 7 and 8 are given the same reference numerals. In this embodiment, a rare earth 11 magnet was used for the field magnet in order to achieve miniaturization and high power, but a light and inexpensive plastic magnet was used for the magnetic sensor magnet. When comparing field magnets, it is clear that the conventional technology requires extending the field magnet to the position of the magnetic sensor 3, uses a large amount of expensive rare earth magnets, and increases the weight of the mover. There are drawbacks. As described above, this embodiment has the effect of keeping the power constant, and also has the effect of reducing costs due to the small size of the field magnet and reducing the weight of the mover.

In the explanation of this embodiment described above, the case where the magnetic sensors are placed at a position shifted to the right by 1/2 P (PM is the width of one pole of the field magnet) from the center line of the corresponding coil. As explained above, if the magnetic sensor corresponding to the position shifted to the left by 1/2 P from the coil center line falls down, the magnetic sensor magnet will also have one pole added to the left side of the field magnet. A five-pole configuration may be used.

Alternatively, as an example of another control method, for example, a magnetic sensor may be placed on the center line of a corresponding coil.

In such a case, as shown in Fig. 5, it is sufficient to add magnetic poles of the necessary width to the left and right sides of the field magnet structure, as shown in Fig. 5. In other words, the field of the field magnet is The pole configuration of the magnetic sensor magnet is such that magnetic poles of a predetermined width are added to the right, left, or left and right sides of the pole configuration of the field magnet so as to apply a predetermined magnetic field to the magnetic sensor corresponding to the coil. By doing so, it becomes possible for a constant number of coils to always provide effective thrust to the mover.

〔Effect of the invention〕

The movable magnet linear motor according to the present invention is configured as described above, and unlike conventional movable magnet linear motors, the thrust does not change depending on the position of the mover. It enables higher power and improved positioning control performance, and is extremely useful in fields that require high-speed linear motion, such as driving printer heads and driving yarn feeders in flat knitting machines.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a coil, a field magnet, and a magnetic sensor magnet of a moving magnet linear DC motor according to the present invention, and FIG. 2 is a diagram showing a moving magnet linear DC motor according to the prior art and a moving magnet linear DC motor according to the present invention. A graph showing changes in the number of coils that provide an effective thrust to the movable element depending on the position of the movable element in the motor. Fig. 3 is a side view showing an embodiment of the movable magnet linear DC motor according to the present invention. Fig. 4 is a sectional view taken along the X-Y line in FIG. 3, FIG. 5 is a diagram showing another embodiment of the moving magnet linear DC motor according to the present invention, and FIG. 6 is a diagram showing the coil and field magnet of a conventional moving magnet linear DC motor. FIG. 7 is a side view of an example of a movable magnet linear DC motor according to the prior art, and FIG. 8 is a sectional view taken along the line X'-Y' in FIG. Patent applicant: Asahi Kasei Industries Co., Ltd. Representative: Takuo Kusano 1
Figure 2 Figure O 3 Figure O 5 Figure O 6 Figure

Claims (1)

[Claims] (1) A movable element is provided with at least one pole field magnet and a magnetic sensor magnet separate from the field magnet, and a coil arranged along the running direction of the movable element and a magnetic sensor magnet separate from the field magnet. A movable magnet linear DC motor, wherein a magnetic sensor for detecting the magnetism of the magnet is provided on the stator, and the number of magnetic poles of the magnet for the magnetic sensor is greater than the number of magnetic poles of the field magnet.