Stepping motor

A stepping motor comprises a stator core, a drive coil which is attached to the stator core and a terminal block having a plurality of terminal pins to be wound with the terminals of the drive coil windings. The stator core and terminal block have respective fitting parts. The fitting part of the terminal block is fitted to the fitting part of the stator core. A gap is provided between the terminal block and the drive coil.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Japanese Application No. 2005-071212, filed Mar. 14, 2005, the complete disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

a) Field of the Invention

This invention relates to a stepping motor. More specifically, this invention relates to a structure of the terminals of the stepping motor.

b) Description of the Related Art

Generally, a stepping motor comprises a rotor part having a magnet fixed onto a rotor shaft, a stator part facing the rotor part, a circular coil bobbin, and a coil wound around the body of the coil bobbin.

In order to attain miniaturization of such a stepping motor, in the case of a motor size of less than 10 mm in diameter for example, the bobbin size has been reduced by integrating the coil bobbin into the inner stator core constituting the stator part by means of insert molding.

Furthermore, when the motor size is less than 5 mm in diameter in which a coil bobbin is molded with the inner stator core as an integrated body, the coil bobbin occupies a large proportion of the motor. As a result, the required winding space cannot be secured and the needed motor torque cannot be obtained.

To overcome this problem, an insulating film is formed on the surface of the stator core, and the coil bobbin is omitted to eliminate the proportion occupied by the coil bobbin. A stepping motor having an elongated space for coil winding has been thus developed (see Unexamined Japanese Patent Application Publication No. 2004-112985, for example). In a stepping motor of this type, terminals are provided at the side planes of the coil windings. As illustrated inFIG. 11, terminal100is made up of a pin which is formed integrally with bobbin101and terminal block102by insert molding. And terminal part103of the coil windings is wound around terminal100.

PROBLEMS TO BE SOLVED BY THE INVENTION/DISCOVERY OF THE INVENTORS

However, since terminal100mentioned above is integrated with bobbin101, in the stepping motor with two coils in which four terminals100are arranged about linearly, it is difficult to reduce the length of the motor of terminal block102along the circumference of the motor. For this reason, even if the size of the motor case is reduced, terminal block102occupies the width, preventing the motor from being miniaturized.

Moreover, the part between the coil body of edge103of the coil windings and terminal100is slanted with respect to terminal100in many cases. For this reason, when an FPC or the like is attached to terminal100later, there is a possibility that the coil windings touch the edge of the through hole through which terminal100of FPC is inserted resulting in their breakage.

OBJECT AND SUMMARY OF THE INVENTION

Therefore, the primary object of the present invention is to provide a stepping motor which can miniaturize a terminal block and prevent the coil windings from their breakage.

In order to achieve this object, the present invention is directed to a stepping motor which comprises a stator core, a drive coil to be attached to the stator core, and a plurality of terminal pins to be wound with the terminals of the drive coils, wherein the fitting part of a terminal block is fitted to the fitting part of the stator core, and a gap is provided between the terminal block and the drive coil. Since the terminal block and the stator core are separate components, the terminals can be arranged with a higher degree of freedom.

Further in accordance with the invention, the periphery of the fitting part of the terminal block on the side to be fitted to the fitting part of a stator core, a plurality of projections are formed to prevent the windings from breaking and the terminal block from falling. In this way, the winding does not touch the edge of the case; this prevents the windings from breaking and the terminal block from falling.

Still further, in accordance with the invention, for the stepping motor comprising a stator core, a drive coil to be attached to said stator core, and a plurality of terminal pins to be wound with the terminals of windings of said drive coil, wherein the fitting part of the terminal block is fitted to the fitting part of the stator core and a step is formed around the terminal pins of the terminal block to prevent the windings from breaking at the time of connection to the outside, and, furthermore, the windings are wound around the terminal pins after being laid along the step. This causes the windings to be wound at a right angle with respect to the terminal pins. As a result, when an FPC or the like is attached from the outside of the motor, the edge of the FPC does not touch the windings, thus preventing the windings from breakage.

Moreover, in accordance with the invention, for the stepping motor as described above, the drive coil is an air core coil. Therefore, a small stepping motor without a coil bobbin can be used.

In accordance with the stepping motor of the present invention, since the terminal block and the stator core are separate components, terminals can be arranged with a higher degree of freedom. As a result, miniaturization of a terminal block can be made possible without the conventional linear arrangement along the circumference; this consequently makes miniaturization of a motor possible. Moreover, since a terminal block can be formed separately from a stator core by insert molding, press fitting, or the like, components can be made at low cost.

Still further in accordance with the stepping motor of the present invention, the windings do not touch the edge of the case; this prevents the windings from breaking and the terminal block from falling. Hence, reliability of the motor can be enhanced.

In addition, according to the stepping motor of the present invention, since the windings are wound at a right angle with respect to the terminal pins, when attaching an FPC or the like from the outside of the motor, the edge of the FPC does not touch the windings; this prevents the windings from breaking. As a result, the motor can be installed with a good yield.

Furthermore, according to the stepping motor in accordance with the present invention, a small stepping motor without a coil bobbin can be used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a cross section of the principal part of the PM (permanent magnet) type stepping motor to which the present invention is applied.

FIG. 2is a diagram showing the structure of stator part3of stepping motor1shown inFIG. 1.

Stepping motor1associated with this embodiment as illustrated inFIG. 1comprises rotor part2having rotor shaft21and rotor magnet22, (permanent magnet) and a stator part3arranged opposite to rotor magnet22via a gap; rotor shaft21is rotatably supported by bearing4, and what is more, it is energized in the axial direction with spring member5contacting one end of rotor shaft21. In addition, the other end side of rotor shaft21is rotatably supported by a bearing (not illustrated) which is different from bearing4. This different bearing is provided, for example, at the opening at the exit end of first stator core31, near the opening inside the mounting plate, or the tip of rotor shaft21via a casing (not illustrated).

To rotor shaft21constituting rotor part2fixed is rotor magnet22with an adhesive, wherein rotor magnet22is constructed with a permanent magnet in about a cylindrical shape.

Furthermore, circular concavities are formed on both ends of rotor magnet22in its axial direction. The formation of these concavities enables rotor magnet22reduces the weight further. Thus, the moment of inertia of the rotor magnet22is reduced by means of the weight reduction.

The other end of rotor shaft21serves as an output axis extended to output the rotation of stepping motor1.

Stator part3is made in a two-phase structure comprising first stator core31and second stator core32fixed onto first stator core31in back to back.

First and second stator cores31and32are constructed in such a manner that a plurality of pole teeth are alternately combined. The outer circumferences of these pole teeth and the inner clip washers between pole teeth are chamfered. As a result, the possibility of deterioration of insulation caused by burrs on pole teeth of air core coil33and34can be reduced. Therefore, it is preferable to chamfer the burrs to keep their sizes within 0.03 mm.

Circular air core coil33is arranged on the outer circumference of each of the pole teeth of first stator core31, and similarly, circular air core coil34is arranged on the outer circumference of each of the pole teeth of second stator core32.

Insulating films50for insulation enhancement are formed on the entire surfaces of these circular air core coils33and34.

Furthermore, insulation sheet40is sandwiched between first stator core31and air core coil33and is firmly bonded to first stator core31and air core coil33with an adhesive in this embodiment. Similarly, insulation sheet40is bonded firmly bonded between second stator core32and air core coil34with an adhesive.

This stepping motor1comprises stator cores31and32, air core coils (drive coils)33and34attached to the stator cores31and32, and terminal block35having a plurality of terminal pins36to be wound around terminals33aand34aof air core coils (drive coils)33and34. As illustrated inFIGS. 3 and 4, fitting part35aof terminal block35is fitted to fitting parts31b,32bof stator cores31and32, and at the same time, gap41is provided between terminal block35and drive coils33and34.

Fitting part35aof terminal block35is in the form of a through hole. Moreover, fitting parts31band32bof stator cores31and32are made up of projections to be pressed into fitting part35a. This enables easy assembly of the part, and what is more, it can prevent terminal block35from collapsing. As shown inFIG. 5, terminal pin36is a metallic L-shaped pin. And terminal pin36is formed as terminal block35by insert molding with an insulation material made of a liquid crystal polymer. The use of liquid polymer provides a high heat-resistance property.

Terminal pin36is arranged in a square configuration. This allows the length of a motor for terminal block35to be shorter in the circumferential direction than the case of the conventional linear arrangement. Motor1can thus be miniaturized.

Each terminal pin36is formed in parallel with the radial direction of motor1. Base36aof each terminal pin36points toward the axial direction of motor1, and it slightly projects from terminal block35. Since this makes wiring to base36apossible, even if wiring cannot be provided to terminal pin36due to lack of installation space or the like, it can be provided to base36a. Moreover, even after motor1is installed in equipment, electrical characteristics of motor1can be checked by utilizing base36a. Furthermore, the L-shape of terminal pin36provides a significantly strong resistance to falling.

Moreover, a plurality of projections42are formed on the periphery of fitting part35aof terminal block35on the side to be fitted to parts31b,32bof stator cores31and32. This prevents terminals33aand34aof windings from touching the edge of the through hole through which the coil of motor case37is taken out as shown inFIG. 5(a); this prevents the wire from breakage caused by the edges. Moreover, capture of projection42with the edge of motor case37prevents terminal block35from falling.

Furthermore, step43is formed around the terminal pin36of terminal block35, and what is more, terminals33aand34aof windings are wound around the terminal pin36after being laid along step43. As a result, as shown inFIGS. 6 and 4, since terminal33aof winding reaches terminal pin36within step43, even if a FPC44or the like is attached later, part33b, which is a portion right before reaching terminal pin36of the winding, does not interfere. This eliminates the possibility for FPC44to break said part33band enables the yield in installation of motor1to be increased.

Furthermore, first stator core31is stored in the other first stator core37, and similarly, second stator core32is stored in the other second stator core38.

Furthermore, in this embodiment, the other first stator core37also functions as a motor case, and it is referred to as first motor case37hereinafter.

Similarly, the other second stator core38is referred to as second motor case38. As shown inFIG. 1, first and second stator cores31and32, first motor case37, and second motor case38are arranged on the same concentricity of the axis of rotor shaft21, and they are firmly bonded by welding.

Here, as shown inFIGS. 7 and 8, motor1comprises motor case37provided with opening46and mounting plate45for mounting said motor case37, and the plane wherein the cross section of opening46of motor case37comes in contact with mounting plate45is fixed with the plane of mounting plate45by welding.

first motor case37is formed in a cylindrical shape with a bottom by reducing work, and the two planes facing each other on the circumferential side plane are cut in the axial direction so as to provide bottom surface37awith an oval shape. Moreover, mounting plate45for installation of the motor case37is sufficiently larger than bottom surface37aof motor case37. And as shown inFIG. 8, laser welding is provided along the axial direction to the step between bottom surface37aof motor case37and mounting plate45(Reference Numeral47in the figure is the point to be welded). Positions and the number of welded location47can be set arbitrarily.

In this embodiment, as illustrated inFIGS. 1 and 2, the relationship among length X along the axial direction formed by first stator core31and first motor case37, length Y along the axial direction of air core coil33, and thickness Z of insulation sheet40is described as X>Y+Z.

In order to secure insulation between the edge along the axial direction of first motor case37and the edge of air core coil33facing the edge of first motor case37, gap S is formed. Similarly, gap S is formed along the axial direction of second motor case38and air core coil34.

Bearing4is made of a resin which has lubricity and rotatably supports one end of rotor shaft21in the radial direction.

Formed on bearing4which supports (stepping motor1) in the radial direction are a bearing part to which rotor shaft21is supported by insertion to the bearing, a press fitting part which is secured onto the inner diameter of second stator core32by press fitting, and a flange part in which a part of the outer circumference of the flange part projects in the radial direction.

The above-mentioned bearing part of bearing4is arranged so that it enters the concavity formed on rotor magnet22, thereby reducing the size of the overall stepping motor1in the axial direction.

Furthermore, as compared to the outer diameter of rotor shaft21, the inner diameter of the above-mentioned bearing part is larger to the degree that it can have a clearance.

Moreover, the above-mentioned flange of bearing4is mounted on second stator core32and aligned in the axial direction.

Spring member5is made up of a sheet of metal plate, and comprises a piece of spring contacting one end of rotor shaft21and a center hole.

Moreover, spring member5is welded and fixed to second motor case38.

The above-mentioned spring of spring member5contacts one end of rotor shaft21and energizes rotor shaft21in the axial direction.

Next, the air core coil constructing a stator part and the insulation sheet are explained with reference toFIG. 2.

In addition, in this embodiment, while stator part3comprises two sets, since they have the same structure, first stator part3is described here, and the description of second stator core32is omitted.

Air core coil33which is fitted to first stator core31is made by coating insulating film50onto the entire surface of a coil with a plurality of windings.

The surface of the above coil windings is provided with a thin self-fusing layer such that the self-fusing layer melts by heating and causes adjacent coil windings to be firmly bonded.

Moreover, insulating film50formed on the entire surface of a coil with a plurality of windings is a paint containing a polyimide resin as its major component in this embodiment.

This air core coil33is manufactured as follows.

First, the above-mentioned coil is wound around a bar which serves as the core coil as many turns as it is required to obtain a given motor torque in such a manner that starting end33aand finishing end33aof the coil are exposed to the surface of the layer of windings.

In addition, the outer diameter of the bar which serves as the coil core is allowed to be about the same as the outer circumference made of a plurality of pole teeth formed on first stator core31.

Hot air blown on the coil from the outside during winding to cause self-fusing simultaneously with winding and to bond coil windings wound around the coil core. After fusing, the bar, which is the coil core, is pulled out. Thus, the coil windings form air core coil33.

Furthermore, self-fusing of the coil may be provided, after winding a coil, by applying a given voltage between starting end33aand finishing end33a, feeding a current through the coil windings to generate heat, and fusing and solidifying the self-fusing layer on the surface of the coil windings, thereby bonding coil windings wound around the coil core.

Next, insulating film50is formed on the surface of air core coil33by dip coating.

In short, dip coating comprises dipping of air core coil33into a tank containing a paint having a polyimide resin as its main component, pulling out the air core coil, and air-blowing to blow away the paint and drying the air core coil. The above-mentioned process is repeated until a given film thickness, for example, about a 30-micrometer in this embodiment is obtained. It is preferable that the thickness of an insulating film be larger than the size of a burr or dimple of a stator core to which the air core coil is fitted or firmly bonded. On the other hand, if an insulating film is too thick, the size of a coil increases. Therefore, it is preferable that the thickness of the insulating film be kept at 100 micrometers or less.

Between edge33halong the axial direction of air core coil33and edge31aof first stator core31, insulation sheet40is sandwiched.

Insulation sheet40has a ring shape, and in this embodiment, its material is polyethylene terephthalate. Although its thickness is 16 micrometers in this embodiment, the withstand voltage is over 100V, which can secure good insulation characteristics.

As compared to insulating film50, insulation sheet40has more tenacity.

Furthermore, in this embodiment, while the inner diameter of insulation sheet40is almost the same as the outer circumferences of a plurality of pole teeth of the first stator core31, and what is more, its outer diameter is smaller than the outer diameter of first stator core31.

The use of a smaller diameter than the outer diameter of first stator core31enables first stator core31and second stator core32to be welded without interference.

Furthermore, air core coil33, insulation sheet40, and first stator core31are fixed with an adhesive. The fixation prevents air core coil33from shifting in the axial direction and contacting the edge of first motor case37facing in the axial direction.

Moreover, in dip coating, in comparison with outer circumference33band inner circumference33cof air core coil33, it is difficult to coat a paint on angled parts33dto33g; an air blow tends to blow away the paint.

As a result, these angled parts33d-33gmay obtain a film thickness thinner than that of outer circumference33bor inner circumference33c.

In other words, in the case that burrs and the like are left on edge31aof first stator core31, and while the root part of a plurality of pole teeth of first stator core31has an R shape, when air core coil33is fitted, these burrs or the R-shaped part pushes it, causing insulating film50to peel off; this may cause a short circuit of the coil windings with first stator core31or break the coil winding.

By sandwiching insulation sheet40, since insulation sheet40is more tenacious than insulating film50, even if it contacts with the burrs generated on first stator core31, the burrs can be covered with no possibility of breakage.

For this reason, insulation sheet40supplements the thickness of insulating film50on edge33h(including the angled part) of air core coil33. In this way, the insulation of first stator core31can be secured.

When assembling the stepping motor1mentioned above, insulation sheet40is bonded firmly with an adhesive to first stator core31(or second stator core32) from which first motor case37(or second motor case38) is removed as shown inFIG. 2.

After bonding, air core coil33(or air core coil34) is fitted to the outer circumferences of pole teeth of first stator core31(or the second stator core32), thereby adhesively fixing air core coil33. And terminal block35is press fitted to fitting parts31b,32bof each of the stator cores31and32to temporarily interlock the terminal block. Moreover, terminals33aand34aof each of the coils33and34are wound around terminal pin36.

Next, first motor case37(or second motor case38) is attached to build stator part3. This stator part3is arranged opposite to rotor magnet22via a gap as shown inFIG. 1. At this point, terminal block35is bonded to motor cases37and38to be secured finally.

In addition, since the assembly of stepping motor1is the same as that of a conventional stepping motor or the like of public domain, its detailed description is omitted here.

Furthermore, although the embodiment described above is an example of preferable modes of the present invention, the present invention is not limited to this. A variety of modifications can be made within the scope of the present invention.

For example, although base36aof terminal pin36is formed in the axial direction of motor1in the mode of this embodiment, the present invention is not limited to this, and it may be formed along the circumference thereof. Moreover, although the edges of base36aproject from the terminal block35, it is not necessary to so project. Furthermore, although projection42and step43are formed on terminal part35in the mode of this embodiment, they do not need to be present; they can be formed when they are required.

Moreover, terminal pin36is formed with an insulation material made of a liquid crystal polymer by insert molding in the mode of this embodiment. However, the mode of this embodiment is not limited to this. It may be insert molded with an insulation material made of a different type of material. Alternatively, terminal pin36may be provided to terminal block35by press fitting and the like.

Furthermore, stepping motor1with two stator cores31and32is used in the mode of this embodiment. However, the present invention is not limited to this. It may have only one stator core. Moreover, although the stepping motor which utilizes an air core coil as a drive coil without a bobbin is adopted. However, the mode of this embodiment is not limited to this. The stepping motor with a bobbin wound with a coil may also be adopted.

Moreover, although first motor case37is formed by cutting, in the axial direction, two planes facing each other on the circumferential side plane of a cylindrical shape with a bottom, the mode of embodiment is not limited to this. As shown inFIG. 10, first motor case37may have an oval shape by reducing work in which a cylindrical shape has a bottom, and the flat side wall parts may be provided with openings by punching. In this case, a small portion of the edge on the bottom37aside of opening46remains and functions as rib37b. In this way, deformation of first motor case37can be suppressed.

Moreover, although laser welding is performed along the axial direction in the mode of this embodiment, it may be performed in the slanted direction. Moreover, although mounting plate45is made sufficiently larger than the bottom37aof motor case37, the mode of this embodiment is not limited to this. Mounting plate45may have the same width as that of bottom37aof motor case37as shown inFIG. 9. In this case, it is preferable that the laser be irradiated in the direction perpendicular to the axis, that is, in parallel with mounting plate45.

In this embodiment, the material of the insulation sheet40is polyethylene terephthalate. However, the material is not limited to this. It may be polyester, polyimide resin, and the like.

In addition, by making insulation sheet40using the same polyimide resin as insulating film50, a stepping motor with excellent insulation and heat-resistance characteristics can be produced.

Moreover, in this embodiment, insulation sheet40is fixed with an adhesive. However, the embodiment is not limited to this, and the insulation sheet40may be fixed by press fitting without an adhesive.

Furthermore, in this embodiment, insulation sheet40has a ring shape. However, the mode of this embodiment is not limited to this, and the insulation sheet may have another shape in which it is provided partially.

By feeding a given current through air core coils33and34of stator part3in stepping motor1configured in the above described manner, the rotor magnet is rotatory energized by the magnetic interaction between stator part3and rotor magnet22, causing rotor shaft21integrated into the rotor magnet to rotate as well.

In addition, since the operation of stepping motor1is the same as that of a conventional stepping motor or the like of public domain, the detailed description of stepping motor1is omitted herein.

The stepping motor comprises a stator core, a drive coil to be attached to the stator core, and a terminal block provided with a plurality of terminal pins to be wound with the terminals of the drive coil windings, wherein the fitting part of the terminal block is fitted to the fitting part of the stator core and a gap is provided between the terminal block and the drive coil. Since a terminal block and the stator core are separate components, the terminals can be arranged with a higher degree of freedom.

According to the stepping motor mentioned above, since a terminal block and the stator core are separate components, terminals can be arranged at a higher degree of freedom. As a result, miniaturization of a terminal block can be achieved without the conventional linear arrangement along the circumference; this consequently makes miniaturization of a motor possible. Moreover, since a terminal block can be formed separately from a stator core by insert molding, press fitting, or the like; components can be made at low cost.

Moreover, in the stepping motor, a plurality of projections are formed on the periphery of the fitting part of the terminal block on the side to be fitted with the fitting part of the stator core to prevent the windings from breaking and the terminal block from falling. In this way, the windings do not touch the edge of the motor case and prevents the windings from breaking and the terminal block from falling.

Furthermore, the stepping motor comprises a stator core, a drive coil to be attached to the stator core, and a terminal block provided with a plurality of terminal pins to be wound with the terminals of the drive coil windings, wherein the fitting part of the terminal block is fitted to the fitting part of the stator core and, at the same time, a step is formed around the terminal pins of the terminal block to prevent the windings from breaking at the time of connection with the outside, and what is more, the windings are wound around the terminal pins after being laid along the step. since the windings are wound at a right angle with respect to the terminal pins, when attaching an FPC or the like from the outside of the motor, the edge of the FPC does not touch the windings; this prevents the windings from breaking.

Furthermore, in the stepping motor, the drive coil is an air core coil. As a result a small stepping motor without a coil bobbin can be used.