2-phase stepping motor

Abstract

The present invention relates to a two-phase stepping motor (100) having a central shaft (1), two electromagnetic coil (3), two ferromagnetic stators (2A, 2B) each accommodating one electromagnetic coil (3), a rotor (4) positioned between the two stators (2A, 2B) and rotationally fixed to the central shaft (1), the rotor (4) having two faces, each face being magnetized, and a spacer (5) arranged between the stators (2A, 2B) to maintain a fixed minimum distance from each other. The central shaft (1) passes through each of the two coils (3) so as to enable rotation of the central shaft (1) within the stators (2A, 2B). Each of the two stators (2A, 2B) has an annular portion disposed around one of the coils and at least two teeth (250) extending from the annular portion, each tooth including a radially extending radial portion (251) between one of the coils (3) and the rotor (4) in the direction of the central shaft (1). All the teeth of the temporarily polarized stator have the same polarity.

Description

Technical Field

[0001] The present invention relates to a stepping motor, and more particularly to a two-phase stepping motor.

Background Art

[0002] Stepping motors, and more particularly small stepping motors, find their use in equipment where high precision is required. The rotation angle of these motors is controlled by a pulse signal, adapting the motors to a wide variety of electrical equipment. Stepping motors are commonly found, for example, in medical devices such as dosing devices, as well as in optical equipment such as microscopes and cameras.

[0003] Various types of stepping motors are known to those skilled in the art, each having a different balance of speed and torque.

[0004] The variable reluctance (VR) type stepping motor includes, for example, a stator and a rotor having a plurality of phases, each providing teeth where magnetic forces concentrate. The rotation angle of the rotor is driven by the teeth of the rotor being attracted to the magnetized opposing poles on the teeth of the stator. VR type motors generally do not include permanent magnets and relatively good speed can be obtained. However, one of their disadvantages is suboptimal torque control.

[0005] The permanent magnet (PM) type stepping motor is relatively slower compared to the VR type stepping motor, but better torque can be obtained.

[0006] A PM stepping motor with a disk-shaped rotor in which the surfaces of the rotor are magnetized alternately has been described so far.

[0007] For example, U.S. Patent No. 5,982,058 describes a two-phase stepping motor having a shaft on which two rotors are rotationally fixed, each rotor comprising first and second permanent magnets each having a plurality of N-pole magnet regions and S-pole magnet regions. The stator is loosely fitted around the shaft and positioned between opposing magnets. The stator has a disk-shaped yoke and structural poles extending from the yoke parallel to the shaft toward the rotor. Electromagnetic wire coils are wound around these structural poles to enable the formation of a plurality of electromagnets.

[0008] Another embodiment of a PM stepping motor with a cylindrical rotor is also known to those skilled in the art. The cylindrical rotor is magnetized in the axial direction, with N and S poles alternating around the cylindrical side surface of the rotor. A part of the stator and / or the electromagnetic coil is generally arranged around the side surface of the cylindrical rotor and interacts with the alternately polarized side surface.

[0009] For example, European Patent Application Publication No. 1,482,626 describes a PM stepping motor comprising a cylindrical rotor assembly with a multi-pole magnetized outer periphery. The stator assembly has a first stator unit and a second stator unit, each having a yoke with a plurality of teeth formed along one side and curving towards the other yoke in the assembled motor. The teeth of the two yokes are connected to each other with a spacer interposed therebetween. The teeth are aligned with the magnetized outer periphery of the cylindrical rotor assembly.

[0010] U.S. Patent No. 4,207,483 describes a cylindrical stepping motor having a stator member aligned on a common axis with a rotor member, one of said members having two sets of comb-shaped pole teeth. Each set of pole teeth comprises inner pole teeth and outer pole teeth, and the coil associated with one set of comb-shaped pole teeth magnetizes the inner and outer pole teeth of that set with opposite polarities. One set of comb-shaped teeth extends perpendicular to the rotor axis from an arrangement, for example, two flat annuli on the same plane.

[0011] The present invention aims to find a small PM stepping motor, preferably cylindrical in shape, which can provide high torque and a large number of angular positions.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0013] [Brief Disclosure of the Invention] One object of the present invention is to provide a small permanent stepping motor that enables fine angular positioning without compromising on small size and is powerful.

[0014] Another object of the present invention is to improve the torque of a small permanent stepping motor.

[0015] Preferably, the stepping motor should be capable of providing higher torque than a conventional PM stepping motor of the same or similar size having the same or similar step angles.

[0016] Another object of the present invention is to provide another arrangement for a small-sized and powerful stepping motor.

Means for Solving the Problems

[0017] According to the present invention, one or more of these objects are achieved by the subject matter of the appended claims, in particular by the independent claims. Further optional embodiments are provided in the dependent claims.

[0018] Specifically, one or more of these objectives are achieved by a stepping motor having a central shaft, two electromagnetic coils, and two ferromagnetic stators each housing one electromagnetic coil. The central shaft of the motor passes through each of the two coils so as to enable rotation of the shaft within the stator.

[0019] The electromagnetic coil is preferably a copper coil of insulated copper wire.

[0020] The stepping motor further includes a rotor fitted onto the central shaft, and the rotor is rotationally fixed to the shaft. The rotor is positioned between the two stators. The rotational movement of the central axis is driven by the angular displacement of the rotor.

[0021] Each of the two stators includes an annular portion disposed around one of the coils and at least two teeth extending from the annular portion. Each tooth has a radial portion extending radially in the direction of the central shaft. The radial portions of the teeth of the stator are layered between the electromagnetic coil housed within the stator and one surface of the rotor.

[0022] To drive the rotor, the stator is temporarily polarized. The teeth of the temporarily polarized stator all have the same polarity.

[0023] The teeth of one of the temporarily polarized stators can have one polarity, and the teeth of the other polarized stator can have the opposite polarity.

[0024] The electromagnetic coil housed by the stator can substantially completely fill the cylindrical internal volume surrounded by the stator, maximizing the coil volume inside the stator.

[0025] Since the teeth of the stator do not project into the cylindrical inner volume defined by the stator, the coil can be wound in the form of a cylinder with a diameter that matches the inner diameter of the cylindrical stator.

[0026] The coil can extend from its core to the inner surface of the cylindrical stator wall.

[0027] The arrangement of the stator, the teeth of the stator, and the magnetic rotor of the present invention enables maximum utilization of the available space for the wound electromagnetic wire on both sides of the magnetic rotor.

[0028] Therefore, this arrangement makes it possible to increase the volume of the electromagnetic wire, for example copper wire, contained in the coil in relation to the volume of the magnet. This increase in the ratio contributes to an improvement in the torque of the motor. Furthermore, the amount of electromagnetic wire in relation to the volume of the ferromagnetic material also increases, making it even more advantageous for high torque.

[0029] In addition, the arrangement of the present invention makes it possible to increase the number of turns of the electromagnetic wire in the coil.

[0030] Unlike a conventional stepping motor in which a plurality of coils are wound around a plurality of teeth, protrusions, magnetic poles, or other structural elements of the stator to provide alternate magnetic poles, the number of turns of the coil in the present invention does not depend at all on the number of teeth or the number of structures providing alternate magnetic poles.

[0031] Preferably, in the space defined by the stator wall, there are no teeth, i.e., no radial protrusions extending. The stator can thus increase the weight of the packaging of the electromagnetic coil windings in the motor.

[0032] The magnitude of the magnetic field strength is directly proportional to the number of turns of the electromagnetic coil. When the packaging of the coils in the stepping motor becomes more efficient, the torque increases. When torque is added, a more powerful stepping motor is provided without the need to increase the current or the size of the motor.

[0033] The teeth of the stator can further have a longitudinal portion that extends as a continuation of the annular portion of the stator parallel to the central shaft towards the rotor. In this embodiment, the radial portion of the teeth is substantially perpendicular to the longitudinal portion.

[0034] Preferably, the inner diameter of the cylindrical volume enclosed by the annular portion of the stator is the same as the inner diameter defined by the longitudinal portion of the teeth of the stator.

[0035] The inner diameter of the stator is preferably constant over the length of the stator. Further, the inner diameter of the stator is preferably also constant in the radial direction of the side surface. This means that no other structural features of the stator protrude into the cylindrical inner volume of the stator.

[0036] The two stators are preferably substantially identical. The teeth of one stator are preferably angularly offset in relation to the teeth of the other stator.

[0037] The motor further comprises a spacer disposed between the stators to maintain the two stators at a fixed minimum distance from each other. The spacer needs to be dimensioned so that the stators do not contact the surface of the rotor. The spacer is preferably at least partially made of an insulating material such as plastic or composite insulator.

[0038] The spacer preferably comprises an annular portion. The annular portion is disposed around the rotor.

[0039] The spacer is preferably arranged to maintain the angular displacement of the teeth of the two stators, and the angular positions of the stators in relation to each other are fixed. The spacer can, for example, have protrusions for engaging between each pair of longitudinal portions of the teeth of adjacent stators. These protrusions preferably protrude from both sides of an annular portion parallel to the central axis, and at least one protrusion on each side is adapted to engage with a corresponding recess between two adjacent teeth of one of the stators.

[0040] The stator includes a stator yoke having a cylindrical portion. The stator can further comprise a flange having a hollow cylindrical member with a smaller diameter than the stator yoke. The cylindrical flange member is axially inserted into the stator yoke for fitting the coil. In this embodiment, the central shaft passes axially through the cylindrical flange member. The cylindrical flange member may be inserted through the center of the coil. The coil may also be wound around the outer surface of the cylindrical flange member.

[0041] The stator may further include a cover member sized to cover the surface of the stator opposite the teeth of the stator. This surface, which is the second surface of the stator, faces away from the rotor in the assembled stepping motor. The cover member may be connected to the cylindrical flange member. However, the cover member may also be included in embodiments of the stator that do not have a cylindrically shaped flange member arranged axially.

[0042] The cover member provides a surface that can connect the motor to an external structure or element. The cover member can, for example, be arranged to fix the motor to a support means. The cover member can also be arranged to attach a gearbox and / or an adapter to the motor.

[0043] The rotor has two faces, each of which is magnetized. The radial portions of the teeth of the stator are arranged between the coil and the rotor to interact with the magnetized faces of the rotor.

[0044] The stator and rotor including teeth are arranged sequentially in the axial direction of the rotor, so that the volume of the magnetic rotor with a defined thickness can be maximized to fit exactly the cylindrical shape of the motor. This arrangement provides distinct advantages compared to PM stepping motors known in the art, where stator components, such as coils, are arranged around the side surface of the rotor, thus increasing the outer diameter of the motor.

[0045] The tooth arrangement in relation to the rotor in the present invention thus enables maximizing the diameter of the magnetic rotor for a given diameter of the stepping motor.

[0046] Furthermore, since the teeth of the ferromagnetic stator interact with two faces of the rotor, no longitudinal magnetization along the side surface of the rotor is required to drive the angular displacement of the rotor. As a result, the rotor can be in a disk shape. The disk-shaped rotor is further advantageous for shortening the overall length of the motor.

[0047] In a preferred embodiment, the rotor has two magnetic rotor disks, and each disk has an even number of disk sectors. The disks are magnetized such that each S pole and N pole alternate across all the disk sectors on each face of the rotor disk. Each disk sector is magnetized axially over the depth of the rotor disk, for example, one pole, which is an S pole, is located on one surface of a disk sector, and the other pole, which is an N pole, is located on the opposite surface of that disk sector.

[0048] The two magnetic rotor disks are positioned with a fixed angular shift in relation to each other. Preferably, each disk sector of one rotor disk is completely superimposed on one disk sector of the other rotor disk. The surfaces of the aligned disk sectors may have the same magnetic poles or opposite magnetic poles. This means that a sector of one rotor disk with an N-S polarization on the axis may be aligned with a sector of the other rotor disk having either an N-S polarization on the axis or an S-N polarization on the axis.

[0049] The disk sectors of the magnetic rotor disks may be equal to twice the number of the radial parts of the teeth of the stator. All the radial parts of the ferromagnetic teeth of the stator should be positioned to interact with the disk sectors of the rotor disk, each providing the same magnetic pole, i.e., either the S pole or the N pole.

[0050] In a preferred embodiment, the central rotor disk forms a layer between the two magnetic rotor disks. The central disk is arranged to fix the magnetic rotor disks in their angular positions. Preferably, the central disk is made of a ferromagnetic material such as steel or iron. The ferromagnetic central disk is involved in the magnetic field of the magnetic rotor disks. Specifically, the ferromagnetic central disk helps direct the magnetic flux of the magnet radially towards the central shaft of the rotor.

[0051] Each of the electromagnet stator coils provides a magnetic phase when an electric current flows through it. The rotational movement of a two-phase stepping motor is driven by alternately switching the phases of the stator. When an electric current flows, the coil temporarily polarizes the teeth of the stator into the S pole or the N pole. The magnetic force concentrates on the teeth of the stator, and the teeth attract the disk sectors of the rotor disk surface having opposite polarizations. By alternately polarizing the two stators, a stepwise angular displacement of the rotor disk and thus the central shaft to which the rotor is attached can be driven.

[0052] The rotation of the rotor can be driven in one predefined direction. It is also possible for the stepping motor to be driven bidirectionally.

[0053] The teeth of the stator may have irregular spacing. In this embodiment, all the radial portions of the teeth of the stator will still be positioned to interact with the disk sectors of the rotor disk, each having the same magnetic pole. However, at least one of the teeth may slightly overlap with the adjacent disk sectors of the opposite poles. The irregular spacing between the teeth generates torque even when no current is temporarily supplied to the coil. The torque so generated smooths the rapid step-like movement of the rotor due to the supply of alternating current. As a result, the rotational speed of the rotor becomes more stable. The stepping motor operates more smoothly without stalling.

[0054] The irregular spacing of the teeth further provides the advantage that the rotor can be easily rotated or its position adjusted when no current is supplied to the stepping motor. In embodiments where the regularly spaced teeth are perfectly aligned with the polarized rotor disk sectors, it is necessary to overcome resistance to move the rotor sections from their aligned positions. This is not the case when the alignment is imperfect, i.e., when at least some of the teeth overlap with unequal-sized portions of two adjacent disk sectors, such as in the case of teeth arranged with irregular spacing. The imperfect alignment results in an unstable angular position of the rotor, which can be smoothly changed when no current is flowing, for example, by manually rotating the central shaft.

[0055] In a preferred embodiment, the electrical tracks for transmitting input signals to and optionally output signals from the stepping motor are arranged on one or more flexible printed circuit boards (PCBs). The tracks can be arranged, for example, in a front flexible PCB and a rear flexible PCB.

[0056] One or both end portions of the flexible PCB can have a ring shape that preferably matches the surface of the cylindrical coil in which they are disposed. In this embodiment, the central shaft passes through the annular end portion of the flexible PCB.

[0057] One or both end portions of the flexible PCB can also have a curved shape that preferably matches the curvature of the surface of the cylindrical coil in which they are disposed.

[0058] The flexible PCB can have different types of end portions, such as an annular end portion and another curved end portion.

[0059] A part of the flexible PCB can be received in a recess on the cylindrical surface of the stator along the length of the stator.

[0060] The tracks of the flexible PCB can be electrically connected to each other and / or to the electromagnetic coil.

[0061] The electrical connection can be provided, for example, by soldering.

[0062] The front flexible PCB can include a first end portion electrically connected to the first surface of the front coil and a second end portion disposed on the second surface of the rear stator.

[0063] As used herein, the first surface of the coil is the surface facing the rotor disk. As used herein, the second surface of the coil is the surface facing away from the rotor disk.

[0064] The second end portion of the front flexible PCB is preferably attached to the second surface of the rear stator, for example, using a suitable adhesive.

[0065] The rear flexible PCB can be configured to supply current to the coil. For this purpose, the rear flexible PCB must be electrically connected to the rear coil, the front flexible PCB, and an external power source.

[0066] The rear flexible PCB may have a first end portion for electrically connecting the PCB to a first surface of the rear coil, which is one coil housed within the rear stator.

[0067] The second end portion of the rear flex is preferably configured to input and optionally output an electrical signal.

[0068] In one embodiment, the rear flexible PCB further has an intermediate annular portion suitable for electrically connecting to the front flexible PCB. The intermediate portion is disposed on the second surface of the rear stator and can preferably be fixed, and the central shaft passes through the annular portion.

[0069] The intermediate portion can be disposed, for example, on the stator yoke or on a suitable cover member covering the second surface of the stator, such as a flange disk.

[0070] The intermediate portion should be disposed or attached to the second surface of the rear stator or its suitable cover without establishing an electrical connection to the stator.

[0071] The second end portion of the front flexible PCB is preferably electrically connected, for example soldered, to the intermediate portion of the rear flexible PCT.

[0072] In this embodiment, the rear flexible PCB preferably has a first longitudinal portion disposed parallel to the central shaft, extending from the first end portion to the intermediate portion of the rear flexible PCB along the outer surface of the rear stator.

[0073] The rear flexible PCB of this embodiment may further have a second longitudinal portion that is folded back toward the front stator over the edge of the second face of the rear stator. The second longitudinal portion can extend longitudinally beyond the front stator along the assembled motor, such that the free end of the rear flexible PCB is accessible for external electrical connection.

[0074] The assembled stepping motor can be encapsulated by an outer sheath. The sheath is preferably of a hollow cylindrical shape for surrounding the stator, rotor, spacer, and optionally at least partially the electrical wires or flexible PCB. Preferably, the two stators, rotor, and spacer are completely covered by the outer sheath. To keep the size of the stepping motor small, the outer sheath should preferably be made of a protective and durable material such as stainless steel, and the outer sheath should have a thickness of 0.05 - 0.5 mm, or 0.1 - 0.3 mm. Preferably, the outer sheath should be waterproof or water-resistant.

[0075] The stepping motor of the present invention can further have an angle encoder. The angle encoder can be, for example, fitted into the flexible PCB. The encoder can be used to measure the angular velocity, angular acceleration, and / or angular position of the central shaft or the rotor.

[0076] The stepping motor of the present invention can further have a magnetic field sensor. The magnetic field sensor can be fitted into the flexible PCB. The sensor provides the advantage of being able to monitor the magnetic field strength. In this way, the current flowing through the coil can be adjusted to achieve a desired magnetic field strength. Monitoring the magnetic field strength provides the additional advantage that defects in the coil can be easily detected. Thus, the coil can be repaired or replaced to ensure the continuous performance of the motor.

[0077] The stepping motor of the present invention is a small stepping motor. Preferably, the stepping motor has a maximum outer diameter of 3 to 70 mm, preferably 4.5 to 22 mm.

[0078] The present invention also relates to a method for assembling the stepping motor described herein.

[0079] [Brief Description of the Drawings] Exemplary embodiments of the present invention are disclosed herein and are illustrated by the following drawings. [Brief Description of the Drawings]

[0080]

Figure 1

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 4C

Figure 5A

Figure 5B

Embodiments for Carrying Out the Invention

[0081] [Embodiment Examples of the Present Invention] An arbitrary embodiment of a stepping motor 100 according to the present invention is shown in FIG. 1. This figure is a schematic exploded assembly view of the motor. This embodiment has a rotor 4 having a plurality of disk sectors, 10 disk sectors in the example shown. These regions are magnetized alternately with N poles and S poles which are opposite poles. The rotor is rotationally fixed to a central shaft 1. The central shaft 1 passes along the entire length of the stepping motor 100.

[0082] The central shaft 1 axially passes through a front stator 2A and a rear stator 2B, and the stators each have stator yokes 20A, 20B. The two stators each accommodate one coil, that is, a front coil or a rear coil. The central shaft 1 passes through the core of each coil so as to be axially rotatable inside the coil.

[0083] The stepping motor shown in this specification has a front flexible PCB 6 and a rear flexible PCB 7. The stepping motor further has a stator support member 91, for example, a bearing.

[0084] The outer surface of the rear stator yoke 20B and / or the front stator yoke 20A is preferably covered by a cover member 24. The cover member can serve as a surface for connecting the motor to an external structure. The cover member 24 may also function as a connection portion with a gear box, an adapter, or other units.

[0085] The cover member is preferably disk-shaped. The cover member may be a support flange member as shown in FIGS. 1 and 4A.

[0086] The distance between the two stators and their angular alignment with respect to each other are ensured by the spacer 5. The spacer shown in this specification has a central annular portion and protrusions 51, and the protrusions respectively correspond to the areas between two adjacent teeth of the stator. The shape of the protrusion 51 is complementary to the shape of the recess between the teeth 250 of the stator, and the spacer 5 is made to conform to the shape of both stators. As a result, it fixes the stator in the angular position of the stator.

[0087] However, the spacer 5 is not limited to the specific shape shown in this figure. The number of protrusions of the spacer may be, for example, less than the number of recesses between the teeth of the stator. Also, it is possible to foresee other protrusions and recesses on the spacer and the stator in order to fix the angular position of the stators in relation to each other.

[0088] The spacer 5 needs to be dimensioned to create a distance between the stators 2A, 2B that is large enough to allow the rotor 4 to be stacked in layers between the stators. The spacer 5 must be dimensioned and arranged so that neither surface of the rotor contacts the stators 2A, 2B. The gap between the rotor 4 and the stator phases 2A, 2B is important so that the polarized teeth of the stator do not stick to the magnetic rotor and thus prevent the rotation of the motor.

[0089] The rotor is shown in more detail in FIGS. 2A and 2B. FIG. 2A is an exploded view of the rotor, and in this embodiment it includes three disks. The two outer disks 41 each have magnetized disk sectors 45 with alternating polarities. The central disk 42 separates the magnetic disks 41 and is preferably made of a magnetic material such as a ferromagnetic material like steel or iron.

[0090] FIG. 2B shows the assembled rotor 4 fixed to the central shaft 1. The disk sectors 45 providing one magnetic pole, for example the N pole, are shown in white, and the disk sectors 45 providing the other magnetic pole, for example the S pole, are shown as striped regions.

[0091] In the assembled motor, the rotor disk can be fixed to the central shaft by a rotor support member 47.

[0092] Any embodiments of the front and rear stators are shown in more detail in the subsequent figures.

[0093] In these embodiments, the stator coils 3 are electrically connected via flexible PCBs 6, 7, which are a preferred option for supplying current to the coils. The flexible PCBs are used to supply input signals and current to the coils, but can also be used to receive signals from electrical components or sensors positioned within the motor and output signals via external connections.

[0094] The flexible PCB may have, for example, an angle encoder or be connected to an angle encoder. The flexible PCB may also have or be connected to sensors such as, for example, a magnetic field sensor or a temperature sensor.

[0095] FIGS. 3A and 3B show a perspective view of an embodiment of the front stator 2A having a front flexible PCB 6.

[0096] FIGS. 4A, 4B, and 4C show an embodiment of the rear stator.

[0097] The front stator 2A and the rear stator 2B each have stator yokes 20A, 20B. The front stator 2A and the rear stator 2B of the illustrated embodiment further have stator flanges provided with axially cylindrical flange members 23 around which the electromagnetic coils 3 are disposed. In the illustrated embodiment, the stator flanges each also have disc-shaped support members 24 for supporting the inserted coils. The support member 24 serves as a cover member for the stator.

[0098] In another embodiment, the cylindrical flange member 23 and the cover member are provided as separate elements and they can optionally be reversibly connected to each other.

[0099] The stator yokes 20A, 20B are substantially cylindrical in shape and have recesses 22 along their outer surfaces for guiding a part of the flexible PCB in the assembled motor.

[0100] The stator yokes 20A, 20B each have an annular portion 200 that is directed away from the rotor in the assembled motor and a plurality of teeth 250, which are five teeth in the example shown, for each of the stator yokes 20A, 20B.

[0101] The teeth of this embodiment have longitudinal portions 252 that extend from the cylindrical side surface of the annular portion towards the rotor in the assembled motor. The stator teeth 250 further each comprise a radial portion 251 that extends perpendicularly from the longitudinal portion 252 towards the geometric central axis of the stator or towards the central shaft 1 in the assembled motor.

[0102] Any one embodiment for the front flexible PCB 6 is also shown in FIGS. 3A and 3B. The front flexible PCB 6 has a first annular-shaped end portion 61 and a second curved end portion 62. The two end portions are connected by a longitudinal intermediate portion.

[0103] The first end portion 61 is electrically connected to the first face of the electromagnet coil, and this face is the face facing the rotor 4 in the assembled motor.

[0104] Generally, the electrical connection can be established by soldering flexible PCBs to each other or to the coil. For this purpose, the end portion can have soldering points 99.

[0105] Figure 3B shows the assembled front stator in which the first end portion of the front flexible PCB is soldered onto the first face of the coil. The middle portion of the front flexible PCB 6 is folded upwards. This middle portion is arranged in the longitudinal direction of the stepping motor, in the direction of the rear stator, in the assembled motor. The middle portion should be dimensioned such that the second end portion 62 of the front flexible PCB can be arranged on the second face of the rear stator, which is the face facing away from the rotor in the assembled motor.

[0106] The rear stator yoke 20B shown in these Figures 4A, 4B and 4C is identical to the front stator yoke 20A. Both stators 2A, 2B have axially cylindrical flange members 23, but the outer surface of the disc-shaped flange member 24 of the rear stator is preferably flat. The flat outer surface is more suitable for the arrangement of the fixing parts of the front and rear flexible PCBs, as is the case in the embodiment shown in the Figures, in particular Figure 1. The support member 24 of the rear stator yoke also has lateral recesses which can be aligned with the guiding recesses 22 of the stator in order to guide the longitudinal portions of the flexible PCB.

[0107] Any embodiment of the rear flexible PCB 7 shown in Figures 4A to 4C has a first annular end portion 71, an annular middle portion 70, and a second end portion 72 for external electrical connection.

[0108] The first longitudinal portion 76 extends between the first end portion 71 and the intermediate portion 70. The second longitudinal portion 77 extends between the intermediate portion 70 and the second end portion 72.

[0109] As shown in FIG. 4A, the first end portion 71 is disposed on and electrically connected to the first surface of the electromagnet coil 3 housed within the rear stator 2B.

[0110] The first longitudinal portion 76 is folded over the edge of the first surface of the coil 3 and is guided by the guide recess 22 along the surface of the rear stator yoke 20B away from the rotor in the assembled motor towards its second surface.

[0111] The intermediate portion 70 can then be folded over onto the second surface of the rear stator over the edge of the cylindrical side surface.

[0112] The assembled rear stator 2B with the rear flexible PCB 7 is shown in FIG. 4C. The intermediate portion 70 is disposed on and preferably adhered to the lower surface of the stator shown herein, which is the second surface of the stator 2B. The second longitudinal portion 77 and the second end portion 72 can be freely further arranged and connected.

[0113] The second longitudinal portion 77 can provide an extension necessary to connect the PCB to an external power source. Optionally, the second longitudinal portion 77 can be folded over the edge of the second surface of the rear stator and longitudinally arranged along the cylindrical surface of the assembled motor in the direction of the front stator 2A and beyond. The second longitudinal portion 77 arranged in this way can be guided by the guide recesses 22 provided on the outer surfaces of the stator yokes 20A, 20B.

[0114] The motor may be covered on its surface by an outer sheath 8. The sheath serves to protect the motor from the environment. The sheath may be waterproof or water-resistant in order to protect the electromagnetic component from moisture. The outer sheath 8 is preferably cylindrical in shape and conforms to the shape of the rotor housed therein. Optionally, the sheath 8 has covers 95 at both ends of its cylindrical shape to enclose the stepping motor within the sheath and allow only the necessary wires, cables, or flexible PCBs to extend outside.

[0115] The embodiments shown in FIGS. 5A and 5B show a stepping motor housed within a sheath 8 with covers 95. The rear flexible PCB protrudes outside through the sheath to enable electrical connection of the motor.

[0116] The two-phase stepping motor of the present invention, particularly the embodiment shown in the figures, can be assembled according to the steps described below.

[0117] To assemble the front stator 2A, the front flexible PCB 6, preferably its first end portion 61, is electrically connected, preferably soldered, onto the first surface of the coil 3. The coil 3 is then inserted into the front stator 2A such that the first surface of the coil 3 is adjacent to the radial portion 251 of the stator teeth.

[0118] Optionally, the coil may be fitted around the hollow cylindrical flange member 23 of the stator yokes 20A, 20B into which the central shaft 1 is inserted.

[0119] To assemble the front stator 2B, the rear flexible PCB 7, preferably its first end portion 71, is electrically connected, preferably soldered, onto the first surface of the second coil 3. The second coil is then inserted into the rear stator such that the first surface of the coil is adjacent to the radial portion of the stator teeth.

[0120] The central shaft 1 is then axially inserted into the stator through the core of the coil housed in the front stator.

[0121] In the next step, the rotor 4 is fitted onto the central shaft 1, the rotor is rotationally fixed to the shaft, the radial portion 251 of the teeth of the front stator faces the rotor, and the rotor 4 is arranged not to contact the radial portion.

[0122] Optionally, a spacer member may be temporarily inserted to ensure that the minimum distance between the rotor 4 and the front stator is maintained during their assembly.

[0123] The spacer 5 can then be arranged on the front stator 2A and around the rotor 4. The spacer 5 should be arranged such that the front flexible PCB 6, particularly its longitudinal portion, protrudes outwardly between the front stator 2A and the spacer 5.

[0124] The rear stator 2B houses the other coil 3 on the shaft, the radial portion of the teeth of the rear stator faces the rotor, the rotor does not contact the radial portion, and the rear flexible PCB protrudes outwardly between the rear stator and the spacer.

[0125] Optionally, the coil may be fitted around the hollow cylindrical flange member 23 of the stators 2A, 2B, and the central shaft 1 may be inserted therein. The flange member 23 must have a central opening through which the central shaft 1 can pass. Preferably, the flange member 23 of the rear stator has a support member 24 with a flat disc-shaped outer surface suitable for covering the open cylindrical-shaped second face of the rear stator. The flat disc-shaped outer surface must be suitable for attaching the flexible PCB.

[0126] Once the two stators 2A and 2B are fitted onto the central shaft 1, the front flexible PCB 6 and the rear flexible PCB 7 are folded towards the second face of the rear stator 2B, which is the face facing away from the rotor 4. The second end portion 62 of the front flexible PCB and the intermediate portion 70 of the rear flexible PCB are arranged on the said second face of the rear stator. The second face of the rear stator may be the outer surface of the support member 24. Preferably, the intermediate portion 70 of the rear flexible PCB is fixed on the second face of the rear stator, for example, by an adhesive.

[0127] The front flexible PCB 6, preferably the second end portion 62 of the front flexible PCB, is then electrically connected, preferably soldered, to the rear flexible PCB 7, preferably the intermediate portion 70 of the rear flexible PCB.

[0128] A part of the rear flexible PCB extends from the second face of the rear stator 2B to enable electrical connection to an external device.

[0129] Optionally, the rear flexible PCB 7 is folded over the edge of the second face of the rear stator 2B, and the rear flexible PCB 7, preferably the second longitudinal portion 77 of the rear flexible PCB, is adapted to extend longitudinally along the assembled motor over the front stator 2A. The rear flexible PCB 7 can be guided along the side surface of the substantially cylindrical assembled motor by the guide recess 22.

[0130] The motor assembled in this way can optionally be inserted into the outer sheath 8. A part of the rear flexible PCB 7, which is folded back rearward over the edge of the rear stator and extends along the length of the assembled stepping motor, is also preferably housed within the outer sheath 8.

Explanation of Reference Signs

[0131] [Reference Numbers Used in the Drawings] 1 Central Shaft 2 Stator 2A Front Stator 2B Rear Stator 3 Coil 3A Front Coil 3B Rear Coil 4 Rotor 5 Spacer 51 Protrusion of Spacer 20A Front Stator Yoke 20B Rear Stator Yoke 22 Guide Recess 23 Cylindrical Flange Member 24 Support Flange Member 200 Annular Portion of Stator Yoke 250 Teeth of Stator 251 Longitudinal Portion of Teeth of Stator 252 Radial Portion of Teeth of Stator 41 Magnetic Rotor Disk 42 Central Rotor Disk 45 Disk Sector of Magnetic Rotor Disk 47 Support for Rotor Disk 6 Front Flexible PCB 61 First End Portion of Front Flexible PCB 62 Second End Portion of Front Flexible PCB 7 Rear Flexible PCB 70 Middle Portion of Rear Flexible PCB 71 First End Portion of Rear Flexible PCB 72 Second End Portion of Rear Flexible PCB 76 First Longitudinal Portion of Rear Flexible PCB 77 Second Longitudinal Portion of Rear Flexible PCB 8 Outer Sheath 91 Bearing 93 Rear Flange Disk 95 Motor Cover Disk 99 Soldering Point 100 Stepping Motor

Claims

1. A two-phase stepping motor (100), comprising: - A central shaft (1); - Two coils (3); - Two ferromagnetic stators (2A, 2B), each accommodating one of the coils (3); The central shaft (1) passes through each of the two coils (3) so as to enable rotation of the central shaft (1) within the stators (2A, 2B); - A rotor (4) positioned between the two stators (2A, 2B) and rotationally fixed to the central shaft (1), the rotor (4) having two faces, each face being magnetized, and - A spacer (5) disposed between the stators (2A, 2B) to maintain a fixed minimum distance between the two stators. It has: Each of the two stators (2A, 2B) includes an annular portion disposed around one of the coils and at least two teeth (250) extending from the annular portion. Each tooth has a radial portion (251) extending radially between one of the coils (3) and the rotor (4) in the direction of the central shaft (1), and A stepping motor in which all the teeth of the temporarily polarized stator have the same polarity.

2. The stepping motor according to claim 1, wherein each tooth (250) has a longitudinal portion (252) extending as a continuation of the annular portion of the stator (2A, 2B) parallel to the central shaft (1) toward the rotor (4), and the radial portion (251) is perpendicular to the longitudinal portion (252).

3. The stepping motor according to claim 1 or 2, wherein the two stators (2A, 2B) are identical, and the teeth of one stator are angularly offset in relation to the teeth of the other stator.

4. The stepping motor according to any one of claims 1 to 3, wherein the spacer (5) has an annular portion made of an insulating material.

5. The stepping motor according to any one of claims 1 to 4, wherein the spacer (5) is arranged to maintain the angular offset of the teeth (250) of the two stators (2A, 2B), such that the angular positions of the stators in relation to each other are fixed.

6. The stepping motor according to any one of claims 1 to 5, wherein the spacer (5) has a protrusion (51) engaging between at least one set of longitudinal portions (252) of adjacent teeth of each stator.

7. The stepping motor according to any one of claims 1 to 6, wherein the rotor (4) has two magnetic disks (41) each having disk sectors (45), each disk sector (45) is polarized to a first magnetic pole, for example, an N pole, and an adjacent magnetic region thereof is polarized to an opposite magnetic pole, for example, an S pole, so that the S and N magnetic poles are alternately arranged in the disk sectors (45) of the magnetic rotor disk (41).

8. The stepping motor according to claim 7, wherein the rotor disks (41) magnetized in the radial direction are angularly shifted in relation to each other.

9. The stepping motor according to any one of claims 1 to 8, wherein the teeth (250) of the stator (2A, 2B) are spaced at irregular intervals.

10. The stepping motor according to any one of claims 1 to 9, wherein two coils (3) are each connected to electric wires arranged on a single or a plurality of flexible printed circuit boards (PCBs) (6, 7).

11. A front flexible PCB (6) having a first end portion (61) that is electrically connected, for example, soldered to a first surface of a coil housed in one of the stators that is the front stator (2A), and the first surface of the coil or the stator faces the rotor disk, and a second end portion (62) that is disposed and preferably fixed on a second surface of the other stator that is the rear stator (2B), and the second surface of the coil or the stator faces away from the rotor disk (41). The stepping motor according to claim 9.

12. The stepping motor according to claim 10 or 11, further comprising a rear flexible PCB (7) configured to supply current to the coil (3), the rear flexible PCB (7) being electrically connected to the front flexible PCB (6), a first end portion (71) of the rear flexible PCB being electrically connected to a first surface of a coil housed in the rear stator (2B), and a second end portion (72) of the rear flexible PCB being configured to input or optionally output an electrical signal.

13. The rear flexible PCB (7) further includes an annular intermediate portion (70), and the annular intermediate portion is electrically connected to the front flexible PCB (6) and is preferably disposed and fixed on the second surface of the rear stator (2B), and the central shaft (1) passes through the intermediate portion (70). The stepping motor according to claim 12.

14. The rear flexible PCB (7) further has a first longitudinal portion (76) disposed in parallel with the central shaft (1) and extending from the first end portion (71) to the intermediate portion (70) of the rear flexible PCB along the outer surface of the rear stator (2B), and a second longitudinal portion (77) extending on the edge of the second surface of the rear stator (2B) such that the free end (72) of the rear flexible PCB can access an external electrical connection. The stepping motor according to claim 13.

15. (i) electrically connecting, preferably soldering, the front flexible PCB (6) to the first surface of the coil which is the front coil; (ii) inserting the front coil into one stator, the front stator (2A), such that the first surface of the front coil is adjacent to the radial portion (251) of the teeth of the stator, wherein the radial portion is directed radially inward from the outer periphery of the front stator (2A); (iii) electrically connecting, preferably soldering, the rear flexible PCB (7) to the first surface of the other coil which is the rear coil; (iv) inserting the rear coil into the second stator which is the rear stator (2B) such that the first surface of the rear coil is adjacent to the radial portion (251) of the teeth of the stator, wherein the radial portion is directed radially inward from the outer periphery of the rear stator (2B); Steps (i) and (ii) may be performed after steps (iii) and (iv). (v) fitting the front stator (2A) provided with the front coil around the central shaft (1); (vi) rotationally fixing the rotor (4) to the central shaft (1) such that the radial portion (251) of the teeth of the front stator (2A) faces the rotor (4) and the rotor does not contact the radial portion (251). Step (vii) of disposing the spacer (5) on the front stator (2A) and around the rotor (4) such that the front flexible PCB (6) protrudes outwardly between the front stator (2A) and the spacer (5); Step (viii) of fitting a rear stator (2B) having a rear coil around the central shaft (1) such that the radial portion (251) of the teeth of the rear stator faces the rotor (4), the rotor (4) does not contact the radial portion (251), and the rear flexible PCB (7) protrudes outwardly between the rear stator (2B) and the spacer (5); Step (ix) of folding the front flexible PCB (6) and the rear flexible PCB (7) towards the second face of the rear stator (2B), the second face facing away from the rotor (4); Step (x) of disposing the free end portion (62) of the front flexible PCB (6) and the intermediate portion (70) of the rear flexible PCB (7) on the second face of the rear stator (2B); Step (xi) of electrically connecting the free end portion (62) of the front flexible PCB, disposed as such, to the intermediate portion (70) of the rear flexible PCB, disposed as such; A method for assembling a stepping motor (100) according to any one of claims 1 to 14, having the above steps.

Images