Small diameter stepping motor, bobbin used therein and manufacturing method thereof

In a small diameter stepping motor including two stator units each including a bobbin formed of an insulating material, each bobbin includes: a circular hollow cylinder portion having a winding; two flanges disposed respectively at the both ends of the cylinder portion; and a terminal structure disposed at one of the two flanges and including two terminal blocks and a pair of electrical contact members at which the lead-out lines of the winding are terminated, wherein the two terminal blocks are circumferentially shifted in position from each other with respect to the cylinder portion axis extend axially outwardly, and the terminal blocks of one bobbin intermesh with the terminal blocks of the other bobbin such that the terminal blocks of the one bobbin overhang a part of the winding wound on the other bobbin and vice versa when the two stator units are coupled to each other.

The present application is based upon and claims the benefit of priority from Japanese Patent Application No. JP2007-103596 filed on Apr. 11 of 2007, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a small diameter stepping motor including two stator units each including a bobbin, and to a method for manufacturing the stepping motor.

2. Description of the Related Art

Stepping motors are extensively used in various electronic devices. Some stepping motors include two stator units each including a bobbin which is made of an insulating material, and which has a circular hollow cylinder portion, two flanges formed integrally with the cylinder portion so as to be disposed respectively at the both ends of the cylinder portion, and a terminal structure disposed at one flange of the two flanges and adapted to terminate a pair of lead-out lines of a winding disposed around the cylinder portion. The terminal structure generally includes a terminal block made of an insulating material integrally with the one flange, and two electrical contact members (for example, terminal pins) implanted in the terminal block and connected to the pair of lead-out lines of the winding.

A stepping motor for use in small devices, such as a digital camera (refer toFIG. 11showing, as an application example, a mechanism of a typical digital camera, where a stepping motor1having a small diameter is incorporated in a shutter mechanism2disposed behind a lens of a digital camera, such that the stepping motor is disposed at the outer circumference of a circular cylindrical frame3to support the shutter mechanism2, and is adapted to drive the lens for automatic focusing, to conduct an aperture mechanism, and to perform other like functions.) and a mobile telephone, is increasingly required to be downsized without impairing its performance or even with achieving an enhanced performance. Under such circumstances, the configuration of the terminal structure of a bobbin is a critical factor in terms of ensuring the workability of assembling a stepping motor in the effort of downsizing its diameter.

FIGS. 12 to 15each show both or one of a pair of conventional bobbins101and201to be housed in respective stator frames. The bobbins101and201are structured to achieve the downsizing of a stepping motor (refer to Japanese Patent Application Laid-Open No. 2004-7899).

Referring toFIGS. 12 and 13, the bobbins101and201are made of an insulating material, and each of the bobbins101and201includes a circular hollow cylinder portion102(202), and two flanges103and103(203and203) integrally formed with the cylinder portion102(202) and disposed respectively at the both ends of the cylinder portion102(202). The bobbins101and201structured as described above and housed in respective stator frames (not shown) are put together coaxially with respect to an axis O such that their respective one flanges103and203are set adjacent to each other.

The bobbins101and201further include terminal structures111and211, respectively. The terminal structures111and211are disposed respectively at the one flanges (hereinafter referred to as terminal flanges as appropriate)103and203which are set adjacent to with each other. The terminal structure111(211) includes a terminal block121(221), a bridge portion122(222) connecting the terminal block121(221) integrally with the terminal flange103(203), and a pair of terminal pins131(231) and132(232) as electrical contact members which are made of an electrical conductive material, implanted at the terminal block121and to which lead-out lines of a winding wound around the cylinder portion102(202) are connected.

The bridge portion122(222) is formed integrally with the terminal flange103(203) so as to extend axially outwardly from the outer circumference of the terminal flange103(203), that is to say, extend away from the other flange (non-terminal flange)103(203). The terminal block121(221) integrally extends axially from the distal end of the bridge portion122(222) so as to overhang a part of the cylinder portion202(102) of the bobbin201(101) to which the bobbin101(201) is coupled.

Referring additionally toFIGS. 14 and 15, the bridge portion122has a width (circumferential direction dimension) defined by W1, and is positioned circumferentially off a diametrical line L1(FIG. 14) of the bobbin101, which passes substantially the center of the terminal block121. In the same way, though not specifically shown, the bridge portion222has a width (circumferential direction dimension) defined by W1, and is positioned circumferentially off a diametrical line (not shown) of the bobbin201, which passes substantially the circumferential center of the terminal block221.

As seen inFIG. 14and understood from the preceding description, the terminal block121/221is divided into two substantially equal portions with respect to the diametrical line L1of the bobbin101(201), and the terminal pin131(231) disposed at one half portion of the terminal block121(221) is located line-symmetric with the terminal pin132(232) disposed at the other half portion thereof with respect to the diametrical line L1.

The above-described two bobbins101and201having their respective windings thereon are coupled to each other in the following manner. The bobbins101and201are brought together coaxially such that the respective terminal flanges103and203having the terminal structures111and211are set adjacent to each other with their bridge portions122and222circumferentially shifted from each other. Then, the bobbins101and201are rotated relatively with respect to each other in the circumferential direction indicated by an arrow Z (seeFIG. 14) until the respective opposite circumferential ends of the bridge portions122and222come into contact with each other. The bobbins101and201arranged as described above are disposed in the respective stator frames (not shown).

The above-described configuration of the terminal structure111(211) of the bobbin101(201) is advantageous and effective in reducing the diameter of a stepping motor, and the following description explains the background for the advantage and effectiveness by taking as an example a stepping motor having a bobbin diameter of, for example, more than 10 mm, which is generally considered to be a relatively large diameter in the field of the present invention, specifically for use in a digital camera, a mobile telephone, and the like.

Referring toFIGS. 16A and 16Bshowing typical terminal pin layouts of stepping motors with a relatively large diameter as described above, in the both layouts, when two bobbins301and401are coupled to each other, a pair of terminal pins331and332of the bobbin301and a pair of terminal pins431and432of the bobbin401are usually arranged in a substantially straight line located along the interface plane between two stator frames housing the bobbins301and401, respectively. In such a terminal pin arrangement, a distance S1defined between the respective centers of two adjacent terminal pins (for example, terminal pins331and431) is about half of a distance S2defined between the respective centers of the pair of terminal pins331and332(431and432) of the bobbin301(401). Under the circumstance described above, if the stepping motor is to be downsized making the distance S1smaller, it becomes practically difficult to perform a soldering operation for connecting the terminal pins331,332,431and432to a flexible printed circuit (FPC), and the like.

Accordingly, if the minimum distance required between two adjacent terminal pins for allowing a soldering operation to be performed at each terminal pin without impairing the workability is defined “S3(not indicated inFIGS. 16A and 16B; to be further described later with reference to FIG.5C)”, the aforementioned distance S2between the centers of the pair of terminal pins must be set equal to or greater than double the minimum distance S3, thus establishing a formula: S2≧2×S3(or S2/2≧S3). Since the distance S2is proportional to the diameter of a bobbin, the minimum value of the bobbin diameter is subject to restriction, and it is practically not possible to set the diameter of a stepping motor at, for example, 10 mm or less.

On the other hand, in the pin terminal arrangement resulting from the structure of the bobbin101(201) shown inFIGS. 12 to 15, it is not necessary to pay attention to the above-defined distance S1in consideration of the workability in a soldering operation, and the above-defined distance S2can be as small as the above-defined distance S3, thus establishing a formula: S2≧S3. Consequently, the diameter of the bobbin101(201), to which the distance2S is proportional, can be reduced to about half of the diameter of the bobbin301(401) whose terminal pin layouts are shown inFIGS. 16A and 16B.

In the bobbin101(201), however, the bridge portion122(222) formed by injection molding, or a like method integrally with the terminal flange103(203) is likely to be deformed as a whole causing positional change of the terminal block121(221) formed to communicate directly with the bridge portion122(222), which results in materially deteriorating the positional accuracy of the pair of terminal pins131and132(231and232) implanted in the terminal block121(221), thus yielding defective windings and also hindering automation of a soldering process at an FPC.

Also, when the bobbins101and201are coupled to each other, the terminal flanges103and203having their respective terminal structures111and211are coaxially set adjacent to each other by axial direction operation with their respective terminal structures111and211shifted from each other, and then the bridge portions122and222of the terminal portions111and211are brought into contact with each other by circumferential rotation operation, thus requiring two different operation steps, which results in an increased time for production.

Further, the lead-out lines from the windings, if loosely wired to the terminal pins131,132,231and232, are likely to be caught by some portions of the bobbins101and201and broken at the time of the aforementioned rotation operation.

SUMMARY OF THE INVENTION

The present invention has been made in order to overcome the problems described above, and it is an object of the present invention to provide a stepping motor in which the positional accuracy of terminal pins is enhanced for enabling automation of the process of soldering to an external circuit (flexible printed board), bobbins have an identical configuration and are so structured as to allow two stator units to be assembled with a reduced number of process operations, and lead-out lines of a winding are prevented from getting scrubbed or caught to be damaged during the process operations, also to provide a method of manufacturing such the stepping motor, and further to provide a bobbin for use in such the stepping motor.

According to a first aspect of the present invention, there is provided a small diameter stepping motor including two stator units which each have an opening portion and each include a bobbin formed of an insulating material. In the stepping motor, the bobbin includes: a circular hollow cylinder portion having a winding wound therearound; two flanges disposed respectively at the both ends of the cylinder portion; and a terminal structure disposed at one flange of the two flanges, radially projecting out through the opening portion, and including at least two terminal blocks and a pair of electrical contact members at which lead-out lines of the winding are terminated, wherein the at least two terminal blocks are shifted in position from each other in a circumferential direction about an axis of the cylinder portion and extend axially outwardly, and the terminal blocks of one bobbin of the two bobbins intermesh with the terminal blocks of the other bobbin of the two bobbins such that the terminal blocks of the one bobbin overhang a part of the winding wound on the other bobbin and vice versa when the two stator units are coupled to each other.

In the first aspect, a formula: Y≧(√{square root over (3)}/2)X may be established, where X is a circumferential distance between the pair of electrical contact members of each of the two bobbins, and Y is an axial shift distance between the electrical contact member of the one bobbin and the electrical contact member of the other bobbin.

In the first aspect, the two bobbins each may have grooves to guide and house the lead-out lines of the winding.

In the first aspect, the opening portion may have a shape corresponding to a configuration of the terminal structure such that the opening portion is substantially fully occupied by the at least two terminal blocks of the bobbin when the two stator units are coupled to each other.

In the first aspect, the two bobbins may be configured identically with each other.

According to a second aspect of the present invention, there is provided a method of manufacturing a small diameter stepping motor, which includes: a first step, where a bobbin, which is formed of an insulating material, and which includes: a hollow circular cylinder portion; two flanges formed respectively at both ends of the cylinder portion; and a terminal structure which is formed at one flange of the two flanges, includes at least two terminal blocks located circumferentially shifted from each other and extending axially outwardly, and which further includes a pair of electrical contact members to have lead-out lines of the winding terminated thereat, is put into an outer yoke of a stator frame which has a plurality of pole teeth at its inner circumference; a second step, where an inner yoke of the stator frame having a plurality of pole teeth at its inner circumference is attached to the outer yoke having the bobbin housed therein, such that their respective pole teeth intermesh with each other thereby forming a stator unit; and a third step, where two of such stator units are engagingly coupled to each other such that the at least two terminal blocks of the terminal structure of the bobbin of one stator unit intermesh with the at least two terminal blocks of the terminal structure of the bobbin of the other stator unit.

In the second aspect, the two stator units may be engagingly coupled to each other without rotation operation.

According to a third aspect of the present invention, there is provided a bobbin formed of an insulating material, which includes: a hollow circular cylinder portion having a winding wound therearound; two flanges disposed respectively at the both ends of the cylinder portion; and a terminal structure disposed at one flange of the two flanges and including at least two terminal blocks and a pair of electrical contact members at which starting and finishing lead-out lines of the winding are terminated, wherein the at least two terminal blocks are shifted in position from each other in a circumferential direction about an axis of the cylinder portion and extend both axially outwardly and radially outwardly, and wire paths each adapted to guide and house one of the starting and finishing lead-out lines of the winding is provided at any terminal block of the at least two terminal blocks, that is provided with the electrical contact member.

In the third aspect, the wire path for the starting lead-out line of the winding may be disposed at one terminal block provided with the electrical contact member and connect between the one terminal block and the cylinder portion, and the wire path for the finishing lead-out line of the winding may be disposed at a portion of another terminal block provided with the electrical contact element, the portion facing the one terminal block having the wire path for the starting lead-out line.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present invention will be described with the accompanying drawings.

A first embodiment of the present invention will hereinafter be described with reference toFIGS. 1 to 7C.

Referring toFIGS. 1 and 2, a stepping motor11according to the first embodiment is basically composed of a stator assembly and a rotor assembly. The rotor assembly includes a magnet12and a shaft13. The stator assembly is made up of two (first and second) stator units21and31which respectively include: first and second stator frames22+23and32+33having a cylindrical configuration; first and second bobbins41and51housed respectively in the first and second stator frames22+23and32+33; and first and second windings44and54wound respectively around the first and second bobbins41and51.

The first stator frame22+23is structured such that an outer yoke22is engaged with an inner yoke23thereby forming a doughnut-shaped case having therein an empty space24to house the first bobbin41. A front plate26for attachment to, for example, a camera frame is fixedly attached to the outer yoke22, and a bearing27to rotatably support the rotary shaft13is engagingly attached at the center of the front plate26.

The second stator frame32+33is composed of outer and inner yokes32and33and structured in the same way as the first stator frame22+23, thereby forming a doughnut-shaped case having therein an empty space34to house the second bobbin51. A rear plate36is fixedly attached to the outer yoke32, and a bearing37to rotatably support the rotary shaft13is engagingly attached at the center of the rear plate36. The first and second stator frames22+23and32+33having the first and second windings44and45therein are coupled to each other with their respective inner yokes23and33set in contact with each other.

The outer yokes22and32, which constitute the outer circumferences and the outer ends of the first and second stator frames22+23and32+33, respectively, have respective opening portions25and35formed at their outer circumferences, through which a structure for wire termination (to be described later) projects out radially, whereby starting and finishing lead-out lines441and442of the first winding44and starting and finishing lead-out lines541and542of the second winding54are allowed to go out of the first and second stator frames22+23and32+33, respectively. In this connection, the opening portion25/35may alternatively be shaped according to the configuration of the structure for wire termination such that there is no substantial open area left (refer toFIG. 5B) when the two stator units21and31are coupled to each other, whereby foreign substances are prevented from coming into the stator frames22+23and32+33, which results in eliminating a short circuit problem, and the like.

The first and second bobbins41and51have the same configuration (structure). Referring toFIGS. 3 and 4, the first (second) bobbin41(51) is integrally formed of an insulating material (resin material) by injection molding and includes: a circular hollow cylinder portion42(52); two flanges43(53) formed integrally at respective both ends of the cylinder portion42(52); and a first (second) terminal structure (i.e., the aforementioned structure for wire termination)45(55) which is integrally formed at one flange (terminal flange) of the two flanges43(53) and at which the lead-out lines441and442(541and542) of the first (second) winding44(54) wound around the cylinder portion42(52) are terminated.

The terminal structure45(55) includes: a first terminal block451(551) and a second terminal blocks452(552) which are both formed in a substantially rectangular solid, have a circumferential direction dimension substantially equal to each other, are positioned to be circumferentially shifted from each other with a gap therebetween substantially equal to the circumferential direction dimension of each of the first and second terminal blocks451and452(551and552), and which extend radially outwardly in parallel with each other along the diametrical line of the cylinder portion42(52) while extending axially outwardly in parallel with each other from the outer circumferential end of the terminal flange43(53); and a pair of terminal pins461and462(561and562) as electrical contact members implanted respectively in the first and second terminal blocks451and452(551and552). The first and second terminal blocks451and452and (551and552) are made of an insulating material (resin material) to communicate integrally with the terminal flange43(53), and the pair of terminal pins461and462(561and562) are of a wire wrap type made of an electric conductive material, around which the lead-out lines441and442(541and542) of the winding44(54) are wrapped for termination.

When the first and second stator units21and31including the first and second stator frames22+23and32+33, in which the first and second bobbins41and51having the first and second windings44and54wound therearound are housed respectively, are coupled to each other, the terminal blocks451and452of the first terminal structure45of the first bobbin41are adapted to overhang a part of the second bobbin51so as to engage with the terminal blocks551and552of the second terminal structure55of the second bobbin51, which overhang a part of the first bobbin41, as shown inFIG. 1.

In the stepping motor11according to the present embodiment, the terminal pins461462,561and562of the first and second bobbins41and51disposed in the first and second stator frames22+23and32+33are arranged, as shown inFIG. 5A, such that the pair of terminal pins461and462of the first bobbin41and the pair of terminal pins561and562of the second bobbin51are located to be axially shifted in respective opposite directions away from the interface plane between the first and second stator frames22+23and32+33, specifically between the inner yokes23and33thereof, rather than arranged in a substantially straight line located along the interface plane between two stator frames (refer toFIGS. 16A and 16B).

In the stepping motor11according to the present embodiment, the terminal pin layout is determined so that the following formula is established: Y≧(√{square root over (3)}/2)X, where X is a circumferential distance between the respective centers of the pair of terminal pins461and462(561and562) of the bobbin41(51), and Y is an axial shift distance between the terminal pin461/462of the first bobbin41and the terminal pin561/562of the second bobbin51. From the formula set forth above, the circumferential distance X can be set to as small as the earlier mentioned minimum distance3S (for allowing a soldering operation to be performed at each terminal pin without impairing the workability). When the axial shift distance Y is set at the smallest, that is to say Y=(√{square root over (3)}/2)X, an equilateral tangle is defined by three of the four terminal pins461,462,561and562as shown inFIG. 5C, where the circumferential distance X is set to the minimum distance3S.

Referring toFIG. 3, the bobbin41(51) further includes a first wire path71to guide and house the starting lead-out line451(551) of the winding44(54) connected to the terminal pin461(561), and a second wire path81to guide and house the finishing lead-out line452(552) of the winding44(54) connected to the terminal pin462(562).

The first wire path71is constituted by a groove formed at the inner face of the terminal flange43(53) in line with an outer edge line73of an axially proximal end face74of the first terminal block451(551) facing the non-terminal flange43(53). The first wire path71starts at the cylinder portion42(52) and communicates flush with the end face74of the first terminal block451(551), whereby the starting lead-out line451(551) is prohibited from protruding above the plane of the inner face of the terminal flange43(53), which results in preventing the starting lead-out wire451(551) from getting scrubbed or caught and also results in enabling alignment winding.

Referring also toFIG. 4, the second wire path81is composed of an axial passage811formed at the radially inward edge of a circumferentially facing face of the second terminal block452(552) facing the first terminal block451(551), and a radial passage812formed at a portion of the axially distal end face of the second terminal block452(552) located toward the aforementioned circumferentially facing face, wherein the axial passage811communicates with the radial passage812at the corner. Provision of the axial passage811, in combination with the radial passage812, works not only to neatly guide the finishing lead-out line442(542) but also to securely keep the finishing lead-out line442(542) away from an edge E of the opening portion25(35) of the first and second stator frames22+23and32+33.

A corner portion of the axially proximal end face74of the first terminal block451(551), which is located toward the second terminal block452(552), is removed thus forming a chamfered face78as shown inFIG. 3. This chamfered structure of the corner portion of the first terminal block451(551) prevents the finishing lead-out line442(542) from getting scrubbed or caught with any part of the first terminal block451(551) when the finishing lead out line442(542) is wired through the axial passage811.

With the first and second wire paths71and81arranged as described above, the lead-out lines441(541) and442(542) of the winding44(54) can be guided respectively to the pair of terminal pins461(561) and462(562) without crossing each other as shown inFIG. 6A.

Referring toFIG. 6A, in the wire path structure described above, the wire path81to guide the finishing lead-out line442(542) is disposed at a portion of the second terminal block452(552) located closer to the center of the cylinder portion42(52) of the bobbin41(51), whereby the finishing lead-out line442(542) is adapted to take off from the outer circumference of the winding44(54) at a reduced angle thus preventing it from happening that the finishing lead-out line442(542) is very close to or even in contact with the edge E of the stator frame22+23(32+33) as shown inFIG. 6Bwhere the finishing lead-out line442(542) goes directly to the terminal pin462(562).

In this connection, for preventing the finishing lead-out line462(562) from making contact with the edge E of the stator frame22+23(32+33), the starting and finishing lead-out lines441(541) and442(542) may be arranged to cross each other as shown inFIG. 6C, but such a wire arrangement is likely to cause a problem, such as a short circuit, which can be surely prevented by the wire arrangement shown inFIG. 6Awhere the finishing lead-out line442(542) does not cross the starting lead-out line441(541).

Description will now be made on a method of manufacturing the stepping motor11according to the first embodiment.

The method of manufacturing the stepping motor11shown inFIGS. 1 and 2includes the following process of preparing a stator assembly:

a step1, where the first and second bobbins41and51, each of which is formed of an insulating material and basically includes: the hollow circular cylinder portion42(52) having the winding44(54) wound therearound; the two flanges43and43(53and54) formed respectively at the both ends of the cylinder portion42(52); and the terminal structure45(55) formed at the terminal flange43(53) of the two flanges43and43(53and53) and including the first and second terminal blocks451and452(551and552) located circumferentially shifted from each other, extending axially outwardly and provided respectively with the pair of terminal pins461and462(561and562) having the lead-out lines441and442(541and542) of the winding44(54) wrapped therearound, are put respectively into the outer yokes22and32each of which has a plurality of pole teeth at its inner circumference;

a step2, where the inner yokes23and33each of which has a plurality of pole teeth at its inner circumference are attached respectively to the outer yokes22and32having the bobbins41and51housed therein, such that their respective pole teeth intermesh with each other, thereby forming the two stator units21and31; and

a step3, where the two stator units21and31are engagingly coupled to each other such that the first and second terminal blocks451and452of the terminal structure45of the bobbin41intermesh with the first and second terminal blocks551and552of the terminal structure55of the bobbin51.

In the above-described process of producing the stator assembly of the stepping motor11, the two stator units21and31can be firmly coupled together without requirement of circumferential rotation operation.

The stator assembly prepared as described above is put together with the rotor assembly including the magnet12and the shaft13via the bearings27and37, and the stepping motor11shown inFIG. 1is completed.

In the stepping motor11according to the first embodiment as described above, the four terminal pins461,462,561and562are disposed such that the pair of terminal pins461and462of the first bobbin41are located over the outer circumference of the second bobbin51while the pair of terminal pins561and562of the second bobbin51are located over the outer circumference of the first bobbin41, wherein the pair of terminal pins461and462of the first bobbin41stand away from the pair of terminal pins561and562, respectively, by a distance Y in the axial direction as shown inFIG. 5A. In such a terminal pin layout, a distance X defined between the pair of terminal pins461and462(561and562) in the circumferential direction can be set to the earlier described minimum distance S3which allows a soldering operation to be performed at each terminal pin without impairing the workability. That is to say, comparing with the disposition of the four terminal pins, specifically one pair of331and332, and another pair of431and432, which are arranged in a line in the circumferential direction as shown inFIGS. 16A and 16B, the distance between the pair of terminal pins461and462(561and562) in the stepping motor11can be reduced to the half of the distance S2between the pair of terminal pins331and431(331and432), whereby the diameter of the bobbin41(51), consequently the diameter of the stepping motor11, can be comfortably reduced.

The advantages of the stepping motor11according to the first embodiment of the present invention will be described with reference toFIGS. 7A,7B and7C.FIG. 7Ashows a stepping motor91having a large diameter. The stepping motor91includes four terminal pins, specifically a pair of331and332, and pair of431and432, which are arranged in a substantially straight line in the circumferential direction as described earlier (refer toFIGS. 16A and 16B). Referring toFIG. 7B, a stepping motor91A has a smaller diameter than the stepping motor91ofFIG. 7Abut includes the same terminal pin arrangement and dimension the stepping motor91has.

Referring now toFIG. 7Cshowing the first embodiment of the present invention, in the stepping motor11which has the same diameter as the stepping motor91A ofFIG. 7B, the four terminal pins461,462,561and562are arranged such that the pair of461and462and the pair of561and562are arrayed circumferentially in respective two straight lines apart from each other as shown inFIG. 5A, and therefore the distance between the pair of461and462(561and562) can be reduced to about half of the distance between the pair of331and332(431and432), which results in significantly reducing the circumferential dimension (w2inFIG. 7C) of the entire terminal pin layout. Thus, open areas are generated at the sides of the terminal pin layout. Such the open areas are valuable in a small device, such as the earlier mentioned digital camera shown inFIG. 11. For example, some components93and94of the digital camera may be effectively placed in the open areas as shown inFIG. 7C.

Thanks to the terminal pin arrangement of the stepping motor11according to the first embodiment of the present invention, the motor diameter can possibly be reduced to as small as 6 mm or less.

Also, in the stepping motor11, the terminal blocks451and452of the bobbin41having the terminal pins461and462and the terminal blocks551and552of the bobbin51having the terminal pins561and562are shaped basically in a simple rectangular solid body axially outwardly extending directly from the terminal flanges43and53of the bobbins41and51so as to overhang parts of the bobbins51and41, respectively, as shown inFIGS. 3 and 4, and therefore can be formed of an insulating resin material by injection-molding into an integrated structure with reduced possibility of deformation compared with the conventional structure where the terminal block communicates with the flange of the bobbin via a bridge portion. Accordingly, the dimensional and positional accuracy of the terminal blocks451,452,551and552can be enhanced, which consequently enhances the positional accuracy of the terminal pins461,462,561and562implanted therein.

Thanks to the reliability of the positional accuracy of the terminal pins461,462,561and562, the process of soldering the terminal pins to an outside circuit (flexible printed circuit) can be better automated.

The two stator units21and31of the stepping motor11respectively including the bobbins41and51can be engagingly coupled to each other such that the two stator units21and31are axially brought together such that the terminal blocks451and452of the bobbin41intermesh with the terminal blocks551and552of the bobbin51. Thus, the two stator units21and31can be coupled together by an axial direction operation only rather than additionally requiring a circumferential rotation operation, which results in improving the productivity.

Since the circumferential rotation operation is not required for coupling together the two stator units21and31, the lead-out lines441and442of the winding44and the lead-out lines541and542of the winding54, even if loosely wired, are unlikely to get scrubbed or caught during the process of coupling the stator units21and31, thus preventing wire damages at this process.

Also, in the stepping motor11, the terminal pins461,462,561and562are arranged so that the formula Y≧(√{square root over (3)}/2)X is established where X is the circumferential distance between the pair of terminal pins461and462of the bobbin41(or between the pair of terminal pins561and562of the bobbin51), and Y is the axial distance between the terminal pin461/462of the bobbin41and the terminal pin561/562of the bobbin51. Accordingly, the bobbin diameter or motor diameter can be successfully reduced as long as the circumferential distance X is set at or above the minimum required for allowing the soldering work at each terminal pin to be performed without impairing the workability.

Further, in the stepping motor11, the bobbin41(51) is provided with the first and second wire paths71and81adapted to guide and house the lead-out lines441and442(541and542) of the winding44(54), whereby the lead-out lines441and442(541and542) are prevented from sticking out above the inner face of the terminal flange43(53) and sticking out of the terminal blocks451and452(551and552). Consequently, it is prevented from happening that the lead-out lines441and442(541and542) get scrubbed or caught to be damaged at the process of forming the winding44(54) or coupling together the two stator units21and31including the bobbins41and51, thus enhancing the productivity and reliability.

Since the two bobbins41and51in the stepping motor11are structured identically with each other, only one same molding die is required, and also the number of components is reduced, whereby the production cost can be reduced and also the parts control can be eased.

A second embodiment of the present invention will be described with reference toFIGS. 8,9and10. In explaining the example ofFIGS. 8,9and10, any components that correspond to those of the first embodiment and basically have the same structure are denoted by the same reference numerals, and a detailed description thereof will be omitted.

Referring toFIGS. 8 and 9, a stepping motor12according to the second embodiment includes two stator units21A and31A which respectively include first and second bobbins41A and51A having respective windings44and54(seeFIG. 10) therearound and housed respectively in first and second stator frames like the stepping motor11according to the first embodiment. The first/second bobbin41A (51A) includes a first terminal block451(551) and a second terminal block452(552). The first terminal block451(551) is provided with a first wire path71A formed so as to connect between a cylinder portion42(52) and a terminal pin461(561) and adapted to guide and house a starting lead-out line441(541) of the winding44(54) wound around the cylinder portion42(52), and the second terminal block452(552) is provided with a second wire path81A to connect between the outer peripheral rim of a terminal flange43(53) and a terminal pin462(562) and adapted to guide and house a finishing lead-out line442(452) of the winding44(54) wound around the cylinder portion42(52).

The first and second wire paths71A and81A are composed differently from the first and second wire paths71and81of the stepping motor11according to the first embodiment. The first wire path71A is composed of an axial passage711formed at an radially outer face76of the first terminal block451(551) so as to start from the foot area of the terminal pin461(561), to extend along and close to an edge line of the radially outer face76facing the second terminal block462(562) and to arrive at a proximal end face74of the first terminal block451(551) communicating with the inner face of the terminal flange43(53) in a flush manner, and a passage712formed as to continue from the axial passage711through the proximal end face74of the first terminal block451(551) and then through the inner face of the terminal flange43(53) and to arrive at the cylinder portion42(52). The second wire path81A is composed of an axial passage811formed at an edge line of the second terminal block452(552) adjacent to the terminal flange43(53) so as to start from the inner face of the terminal flange43(53) up to the middle of the edge line, and a radial passage814formed at a side face85of the second terminal block452(552) facing the first terminal block462(562) so as to continue from the axial passage811toward the terminal pin462(562).

Referring toFIG. 10, thanks to the provision of the wire path81A, the finishing lead-out line442(542) of the winding44(54) is allowed to take off from the outer circumference of the winding44(54) at a reduced angle, whereby the finishing lead-out line442(542) is less likely to make contact with an edge E of the stator frame of the stator unit21A (31A) thus preventing problems such as wire damage, short circuit, or the like. Also, this eliminates the necessity of crossing the lead-out lines441(541) and442(542) thus preventing a short circuit problem.

While the present invention has been illustrated and explained with respect to specific embodiments thereof, it is to be understood that the present invention is by no means limited thereto but encompasses all changes and modifications that will become possible within the scope of the appended claims.

For example, the present invention is not limited in the number of terminal blocks for each bobbin to “two” as explained in the embodiments described above, and three or more terminal blocks for engagement coupling may be disposed for each bobbin depending on step control accuracy, or other conditions. Also, an electrical contact member does not have to be shaped like “pin” (terminal pin) but may be shaped like “elongate plate”, or the like, according to the structure of the mating member.