JP2642240B2 - Linear motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear motor in which a movable coil moves linearly in a magnetic gap formed between opposed permanent magnets.

[Conventional technology]

Conventionally, as a driving device for positioning an object within a long stroke range of 10 cm to 100 cm, for example, a moving coil type device disclosed in Japanese Patent Publication No. 58-49100 and Japanese Utility Model Application Laid-Open No. 63-93783 is known. Linear motors are frequently used. In this linear motor, a plurality of permanent magnets magnetized in the thickness direction are arranged so as to face each other so that the magnetizing directions are different, and move in a direction perpendicular to the magnetic flux in a gap formed between the facing permanent magnets. It has a structure in which a movable coil assembly is provided.

In such a linear motor, the magnetic circuit does not have a center yoke, and the magnetic flux forms a plurality of closed loops in the air gap so that the magnetic flux does not concentrate on a part of the magnetic path. A uniform magnetic flux density can be generated over the entire area.

FIG. 10 is an explanatory view of a main part showing a conventional linear motor. In FIG. 10, reference numeral 1 denotes a yoke formed of, for example, a flat plate made of a ferromagnetic material such as an iron plate. Reference numeral 2 denotes a permanent magnet, which is magnetized in the thickness direction and is disposed and fixed in the longitudinal direction of the yoke 1 so that NS magnetic poles appear alternately on the surface. The yoke 1 formed as described above is disposed via the gap 3 so that the different poles of the permanent magnet 2 face each other. Reference numeral 4 denotes a support plate which is fixed to both ends in the longitudinal direction of the yoke 1 to secure the gap 3. Note that the support plate 4 is preferably formed of the same ferromagnetic material as the yoke 1. Next, reference numeral 5 denotes a coil, which is formed by a flat multi-phase coil whose winding direction is orthogonal to the magnetic flux in the gap 3. In other words, a plurality of coils can be disposed slightly shifted in the direction in which the permanent magnets 2 are disposed, the direction of the magnetic poles can be detected via means such as a magnetic field detecting element, and the coils through which current flows and the direction can be switched. It is formed as follows. The coil 5 is integrally supported by a holder (not shown) to form a mover.

According to the above configuration, when a current flows through the coil 5, the winding direction of the coil 5 is orthogonal to the magnetic flux generated by the permanent magnet 2, so that the coil 5 is driven in the longitudinal direction of the yoke 1 by Fleming's left-hand rule. As a result, the mover (not shown) integrally supporting the coil 5 moves in the longitudinal direction of the yoke 1. Next, when a current in the opposite direction is applied to the coil 5, a driving force in the opposite direction acts on the coil 5, so that the mover moves in the opposite direction. Therefore coil 5
By selecting the direction of current flow and its current,
The mover can be moved to a predetermined position.

[Problems to be solved by the invention]

In the linear motor configured as described above, the permanent magnet 2 is generally formed in a rectangular parallelepiped shape, and has the same cross-sectional area orthogonal to the moving direction of the coil 5, that is, the same thickness and width. Further, the magnetic flux density between the plurality of permanent magnets 2 is smaller than that at the intermediate portion of the permanent magnet 2 due to a gap, the presence of an adhesive, a short circuit of magnetic flux, and the like. The magnetic flux distribution in the moving direction of the coil 5 as a whole of the permanent magnet 2 is substantially arc-shaped.

In general, in a motor in which the rotor side is a permanent magnet field and the outside is a fixed armature, an appropriate control circuit is required to maintain the vertical relationship between the rotor magnetic flux and the armature magnetomotive force. It is necessary to establish a wave armature current and to form a sinusoidal gap magnetic flux distribution. With this configuration, the torque generated by the motor depends only on the product of the maximum value of the armature current and the maximum value of the magnetic flux density, and a torque is generated irrespective of the displacement angle of the rotor from the reference axis. That is, the occurrence of torque ripple due to the displacement angle can be prevented.

On the other hand, a linear motor is one in which the diameters of the rotor and the armature are formed to be infinite, and the above theory is naturally applied. Therefore, if the magnetic flux density distribution in the moving direction of the coil 5 in the permanent magnet 2 shown in FIG. 10 is formed in a sine wave shape, torque ripple due to the moving position of the coil 5 can be eliminated, and a linear motor with excellent linearity can be obtained. You can do it.

However, in the conventional linear motor, since the permanent magnet 2 is formed as described above, the magnetic flux density distribution in the moving direction of the coil 5 becomes a non-sinusoidal wave, torque ripple occurs, linearity is lost, and positioning accuracy is reduced. Has the problem of adversely affecting

Japanese Utility Model Laid-Open Publication No. 63-93783 discloses a proposal in which a surface of a magnet facing an armature is formed in a gentle concave portion in order to reduce a thrust ripple in a DC linear motor.

However, in the linear motor proposed above, since a position detecting element (magnetoelectric conversion element) is provided for each coil to reverse the direction of the current flowing through each coil, it is necessary to provide a current control means for each coil. . Therefore, when the number of coils is increased for the purpose of obtaining high thrust, there is a disadvantage that the structure becomes complicated. In addition, a gentle concave portion (arc shape) is formed at the boundary between adjacent magnets. However, in such a shape of the magnet, the magnetic flux easily concentrates in the concave portion, and the peak value of the magnetic flux density decreases. At the same time, in the magnetic flux density distribution, the vicinity of the peak value may be tapered. Further, in such a linear motor, it is described that a sinusoidal current is supplied to the coil. However, the output of the position detecting element is affected by the sinusoidal magnetic flux distribution, and is consequently input to the coil. The current becomes a sinusoidal current, and there is no change in being essentially a linear DC control system.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems existing in the prior art and to provide a linear motor with less torque ripple.

[Means for solving the problem]

In order to achieve the above object, in the first invention,
Multiple permanent magnets are used so that the polarities of adjacent magnetic poles are different.
A movable element composed of a multi-phase coil is provided in the gap so as to be movable in the direction in which the permanent magnets are arranged, and a sine wave driving current is supplied to the poly-phase coil. In a linear motor equipped with a drive circuit for supplying the magnetic field, the cross-sectional area of the permanent magnet in a plane perpendicular to the moving direction of the mover is expressed as Ac> Ae (where Ac: the cross-sectional area in the middle, Ae: (Cross-sectional area) and the cross-sectional shape of the permanent magnet in a plane parallel to the moving direction of the mover is substantially trapezoidal.

Next, in the second invention, a plurality of permanent magnets are arranged so that the adjacent magnetic poles have different polarities so that different poles face each other via a gap, and a plurality of permanent magnets are formed in the gap. In a linear motor, wherein a mover is provided so as to be movable in a direction in which the permanent magnet is provided, and a drive circuit for supplying a sine-wave drive current to the multi-phase coil is provided. Ac>
Ae (however, Ac: the cross-sectional area at the middle part, Ae: the cross-sectional area at the end), the thickness dimension is the same, and the profile of both side edges of the permanent magnet along the moving direction of the mover is approximately sinusoidal. The technical means of forming was adopted.

[Action]

With the above configuration, the magnetic flux distribution of the permanent magnet in the coil moving direction becomes sinusoidal, and the torque ripple can be significantly reduced by applying a sinusoidal current to the coil.

〔Example〕

FIG. 1 is a sectional view of an essential part showing an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a base, which is formed in a flat plate shape from a ferromagnetic material such as mild steel. Reference numeral 12 denotes a center yoke, and 13 denotes a side yoke, each of which is formed in a flat plate shape using the same material as the base 11, and is fixed on the base 11 with a space therebetween. Next, reference numeral 14 denotes a permanent magnet formed of, for example, a rare earth magnet to have a shape and a size as described below, and a plurality of permanent magnets are provided on the opposing surfaces of the center yoke 12 and the side yoke 13 so that adjacent magnetic poles have different magnetism. Are arranged such that different poles face each other with the gap 15 therebetween. In FIG. 1, the direction in which the permanent magnets 14 are disposed is a direction orthogonal to the paper surface. Then 16
Denotes a mover, and a coil frame is provided below the carriage 17.
The coil frame 18 is fixed, and the coil frame 18 is provided movably in the space 15 in a direction perpendicular to the plane of the drawing. The coil frame 18 is formed of a non-magnetic material in order to prevent thrust ripple from occurring. That is, for example, a resin (for example, epoxy resin containing glass) substrate is mounted on the surface of an aluminum alloy frame (the surface is anodized to provide insulation), and a coil (described later) is mounted on the substrate.
19 is fixedly formed. If the coil frame 18 is formed of a magnetic material, or if the back yoke exists on the side of the mover 16, imbalance due to the attraction force of the permanent magnet 14 occurs, which is one of the causes of thrust ripple. Reference numeral 19 denotes a coil, which is formed in a flat shape and provided on both sides of the coil frame 18.

FIG. 2 is a perspective view of a main part showing the coil frame 18 in FIG. 1, and the same parts are denoted by the same reference numerals as in FIG. The coil 19 is, for example, a three-phase coil (see Japanese Patent Application Laid-Open No. Sho 62-193543). All the phases are connected in series, and the phases are Y-connected.

The linear motor of the present invention uses a polyphase coil as described above and supplies a sinusoidal drive current to the polyphase coil. However, as the number of phases increases, the power factor decreases. Since it is necessary to increase the current, it is desirable to adopt a two-phase or three-phase conduction method. That is, it is desirable that the linear motor of the present invention has a configuration in which a magnetic circuit having a permanent magnet of a specific shape as described later is combined with a two-phase or three-phase sine wave current output type drive circuit.

FIG. 3 is a side view of a main part showing a positional relationship between the position detecting element and the coil 19 in FIGS. 1 and 2, and the same parts are denoted by the same reference numerals as in FIGS. 1 and 2.
In FIG. 3, the mover 16 is a magnetic pole pitch of the permanent magnet 14.
Three flat coils Lu ₁ , Lw ₁ , and Lv ₁ wound in a plane parallel to the paper and having a width of 1/6 of lm are displaced by the coil width (the center of each flat coil is heavy). Must not) coil 19
a, and coils 19b, 1 configured similarly to this coil 19a
9c. The mover 16 has three position detection elements.
20 is the coil pitch lc (equal to the magnetic pole pitch lm)
It is provided at a distance l _h of 1/6. These position detecting elements 20 are offset from the flat coils Lu ₁ , Lw ₁ , Lv ₁ to the interval l ′, respectively. However, since this offset state can be electrically processed, there is no practical problem at all. . Then, a three-phase current waveform shifted by 120 ° is created by a driving circuit (not shown), and this is combined with the flat coil Lu ₁ ,
By supplying the current to Lw ₁ and Lv ₁ (the arrows in FIG. 3 indicate the direction of the current), the mover 16 moves continuously. In the case of three phases, the interval l _h between the position detecting elements 20 is theoretically
It is set to 1/3 of the coil pitch lc (equal to the magnetic pole pitch lm), but in the example shown in FIG. 3, it is set as described above for mounting reasons. That is, the flat coils Lu ₁ , Lw ₁ , Lv _1, etc. can be arranged at arbitrary positions every 180 ° n (n is a positive integer) times by reversing the energizing direction.

In the present embodiment, the position of the flat coil to be energized and the direction of the current are switched or selected by the position detecting element 20 and a control circuit (not shown).
As 20, a known element such as a Hall element can be used. The control circuit may also use a normal permanent magnet as a field, for example, a configuration similar to that of a synchronous AC servomotor.

Further, in the present invention, even when the three-phase coils (19a to 19b) are of a six-row type, the position can be detected using the three position detecting elements 20. Accordingly, a single-phase or three-phase sine wave current is used as the supplied current, and only the timing of inverting the Hall element from positive (negative) to negative (positive) (zero cross) is used as a synchronization means. . 2
When the phase energization method is adopted, the position detecting elements 20 are provided on the mover 16 at intervals of 1/4 of the magnetic pole pitch lm, and 90
゜ A two-phase current waveform with a shifted position may be created and supplied to the coil.

Next, FIG. 4 is a perspective view showing the shape and dimensions of the permanent magnet 14 in FIG. 1, and a plurality of permanent magnets are arranged in the moving direction (arrow A) of the coil frame 18. Is formed in a substantially trapezoidal shape. For example, a part of the surface contour of the permanent magnet 14 in the moving direction (the direction of the arrow A) of the coil frame 18 is formed in an oblique linear shape. That is, the thickness at the end in the moving direction is set to 6.5 mm, and the thickness at the middle is set to 10 mm. The permanent magnet 14 is magnetized in the thickness direction, that is, in the vertical direction.

With respect to the linear motor of the embodiment formed as described above, the movement direction of the mover 16, that is, the relationship between the stroke and the magnetic flux density was measured. FIG. 5 is a view showing the result, wherein a shown with a mark corresponds to the embodiment.
It is recognized that the curve is very similar to the sine wave b shown by the mark. Note that c indicated by □ is a conventional configuration in which a permanent magnet is formed in a rectangular parallelepiped shape having a width of 50 mm, a length of 30 mm, and a thickness of 10 mm. As is clear from FIG. 5, c indicates a semi-elliptical shape or an arc shape, and the shape is significantly different from the sine wave shown in b. Therefore, the torque ripple is large and the linearity is low. On the other hand, in the case of the present embodiment, it was confirmed that the torque ripple was significantly reduced and excellent linearity was exhibited.

FIG. 6 is a plan view showing the shape and size of a permanent magnet according to another embodiment of the present invention.
It is formed to 50 mm in the middle part, and the outline of both side edges is formed in a sine wave shape. The thickness was set to 10 mm, and a linear motor was constructed by magnetizing in the thickness direction as described above. When the magnetic flux density distribution in the direction of arrow A was measured, it was confirmed that the distribution had a sinusoidal shape similar to a shown in FIG.

7 and 8 are end views showing a permanent magnet in a comparative example, and the same parts are denoted by the same reference numerals as in FIGS. 4 and 6. 7 and 8, the dimensions of the permanent magnet 14 are 50 mm in width, 30 mm in length, and 10 mm in maximum thickness.
mm and correspond to those shown in FIGS. 4 and 6. FIG. 7 shows an example in which the slope of the upper surface of the permanent magnet 14 is formed in a convex arc shape (for example, so that the cross-sectional shape becomes a semicylindrical shape), and that shown in FIG. Is different from the above.

FIG. 9 is a view showing the relationship between the stroke and the magnetic flux density in the linear motor using the permanent magnet 14 shown in FIGS. 4 and 8, and corresponds to FIG. In FIGS. 9A and 9B, curves a and d represent the permanent magnets 1 shown in FIGS. 4 and 8, respectively.
4 is for a linear motor. As is apparent from FIG. 9, the curve d (corresponding to FIG. 8) has a low peak value of the magnetic flux density and a triangular curve with a tapered portion in the vicinity of the peak value. When the radius of the arc of the concave portion of the permanent magnet 14 shown in FIG. 8 is increased, the peak value of the magnetic flux density further decreases. When the permanent magnet 14 shown in FIG. 7 is used, the magnetic flux density distribution has a substantially sinusoidal curve shape, but it is estimated that the vicinity of the peak value becomes slightly wider than the curve a shown in FIG. Is done. Accordingly, when a trapezoidal permanent magnet is used in a cross section in a plane parallel to the moving direction of the mover, as shown in FIG. 4, the permanent magnet 14 in the moving direction (arrow A) of the mover or the coil frame is used. Is preferably an oblique straight line.

〔The invention's effect〕

Since the present invention has the configuration and operation as described above, the torque ripple in the linear motor can be greatly reduced, and the linearity and reliability can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of an essential part showing an embodiment of the present invention, FIG. 2 is a perspective view of an essential part showing a coil frame in FIG. 1, and FIG. 3 is a position detecting element and a coil in FIGS. 4 is a perspective view showing the shape and dimensions of the permanent magnet in FIG. 1, FIG. 5 is a view showing the relationship between stroke and magnetic flux density, and FIG. 6 is a view showing the present invention. FIGS. 7 and 8 are end views showing permanent magnets according to comparative examples, and FIG. 9 is a permanent magnet shown in FIGS. 4 and 8. FIG. FIG. 10 is a diagram showing a relationship between a stroke and a magnetic flux density in a linear motor using the motor, and FIG. 10 is an explanatory view of a main part showing an example of a conventional linear motor. 14: permanent magnet, 16: mover.

Claims (2)

(57) [Claims] A plurality of permanent magnets are disposed so that adjacent magnetic poles have different polarities so that different poles face each other via a gap, and a mover comprising a multi-phase coil is provided in the gap. In a linear motor, which is provided so as to be movable in the direction in which the permanent magnets are provided and includes a drive circuit for supplying a sine-wave drive current to the polyphase coil, When the cross-sectional area is Ac> Ae (where Ac:
(Ae: cross-sectional area at the middle, Ae: cross-sectional area at the end)
A linear motor characterized in that the cross-sectional shape of the permanent magnet in a plane parallel to the moving direction of the mover is substantially trapezoidal. 2. A plurality of permanent magnets are arranged so that adjacent magnetic poles have different polarities such that different poles face each other via a gap, and a mover comprising a multi-phase coil is provided in the gap. In a linear motor, which is provided so as to be movable in the direction in which the permanent magnets are provided and includes a drive circuit for supplying a sine-wave drive current to the polyphase coil, When the cross-sectional area is Ac> Ae (where Ac:
(Ae: cross-sectional area at the middle, Ae: cross-sectional area at the end)
A linear motor having the same thickness dimension and the outline of both side edges of a permanent magnet along a moving direction of a mover formed in a substantially sinusoidal shape.