GB2527525A

GB2527525A - Stepper motor

Info

Publication number: GB2527525A
Application number: GB1411175.1A
Authority: GB
Inventors: Thibaut Marqueyrol
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2014-06-24
Filing date: 2014-06-24
Publication date: 2015-12-30
Also published as: GB201411175D0

Abstract

A stepper motor 10 (fig 1 not shown) has a rotor 20 and a stator 30. The stator 30 has a insulating stator body forming a central rotor chamber 341 and a plurality of stator pole support arms 342 extending radially from the central chamber 341 to outer portions 363 which stator body supports the stator poles. The stator poles comprise pairs of radially engaged stator pole components 36 mounted on a plurality of stator arms 342, the pole surface being formed by inner portions 361. The stator poles outer portions 363 are separated by a plurality of circumferential openings, allowing for winding coils to be wound on the stator poles from outside the stator 30. Subsequently a cylindrical outer ring is mounted about the stator which closes the magnetic circuit and act as a cover protecting the winding coils. Alternatively the pole portions may be axially engaged. The stator body supports terminal post 42 on an end face (fig 1) each phase being wound using a single wire. The rotor employs permanent magnets. Use of a reluctance rotor is also disclosed. An assembly method is described.

Description

TITLE

[0001] Stepper Motor

FIELD OF THE INVENTION

[0002] This invention relates to a stepper motor and to a method of manufacturing a S stepper motor.

BACKGROUND OF THE INVENTION

[00031 Brushless electric motors, which include stepper motors and servo motors, are typically of the radial flux type. comprising a permanent magnet rotor that rotates within a wound stator. In order to manufacture the wound stator, several different methods may be used. For example, coils may be pre-wound and inserted onto stator poles. However, assembling pre-wound coils onto a stator typically requires extra manufacturing processes. increasing the complexity and cost of motor manufacture. lii addition, connecting wires from different pre-wound coils in a muhipolar motor structure can be difficult, and carries a risk of connection failure. Alternatively, the coils maybe stitched into the coil volume, by passing a wire in between one or more pole slots of the motor with the inner circumference of the stator. However, it is often difficult to achieve a high coil fill factor when stitching coils onto stator poles within a closed stator, especially when the motor is small.

[0004] On the other hand, brushed motors typically comprise a wound rotor, with permanent magnets located on the stator. The rotor windings can be applied to a rotor core amination stack from an outer circumference of the rotor, before the rotor is inserted into the stator. Because the windings are applied from the outer circumference of the rotor instead of an inner circumference of the stator as in brushless motors, a higher wire filling factor can be achieved. However, while a high wire filling factor increases motor efficiency, having winding coils on the rotor often results in higher rotor inertia in comparison with rotors that only have permanent magnets. This is disadvantageous for stepper motors that are used for dynamic and low noise positioning devices, due to the need for rapid or dynamic acceleration/deceleration. In addition, higher inertia may result in greater vibration and noise.

SUMMARY OF THE INVENTION

[0005] Hence there is a desire for a stepper motor having windings that are easy to asseniblc.

[00061 Accordingly, in one aspect thereof, the present invention provides a stepper motor, comprising a rotor and a stator disposed around the rotor; wherein the rotor comprises a shaft and a permanent magnet core fixed to the shaft; and wherein the stator comprises a plurality of stator poles arranged cireumferentially around the stator and separated by a plurality of circumferential openings on an outer circumference of the stator; a plurality of winding coils wrapped around the plurality of stator poles; and an outer ring enclosing the plurality of stator poles.

[0007] Preferably. the plurality of stator poks comprises a p'urality of stator pole components mounted on a stator body component, the stator body component comprising: a central chamber accommodating at least a portion of the rotor; and a plurality of stator arms extending in a radial direction from the central chamber, wherein the p'urality of stator arms correspond to the plurality of stator poles.

[00081 Preferably. the stator pole components are made of a magnetic material.

[0009] Preferably. the stator body component is made of an insulating material.

[0010] Preferably. a stator pole component of the plurality of stator pole components comprises a bent or stamped sheet of metal having an inner portion housed within the central chamber, and a central portion and an outer portion accommodated within a stator arm of the plurality of stator arms.

[0011] Preferably. a stator pole of the plurality of stator poles comprises two stator pole components accommodated within a stator arm of the plurality of stator arms, such that a winding coil of the plurality of winding coils is wound around the central portions of the two stator pole components, and the inner portions of the two stator pole components form a pole shoe within the central chamber.

[0012] Preferably. the inner and outer portions of the stator pole component are configured to be longer than the central portion in an axial direction of the motor.

[0013] Preferably. the outer ring is made of a magnetic material.

[0014] Preferably. the plurality of winding coils are associated with a plurality of phases, and wherein winding coils associated with the same phase are wound using a single wire.

[0015] According to a second aspect, the present invention provides a process for assembling a stepper motor, comprising: forming a stator having a plurality of stator poles arranged circumferentially around the stator and separated by a plurality of circumferential openings in an outer circumference of the stator: forming a rotor by fixing S a permanent magnet core to a shaft; inserting the rotor into the stator; winding a plurality of winding coils around the plurality of stator poles through the plurality of circumferential openings; and forming a flux path across the circumferential openings in the outer circumference of the stator by encircling the stator with an outer ring formed of a magnetic material.

[0016] Preferably. forming a stator comprises forming a plurality of stator pole components by stamping or bending a metal sheet.

[0017] Preferably. forming a stator further comprises mounting the plurality of stator pole components to a stator body component, and forming the stator body component with a plurality of guiding surfaces for mounting thc plurality of stator pole components.

[0018] Preferably, the process further comprises forming the stator body component with a central chambcr to accommodate at least a portion of the rotor and with a plurality of stator arms extending in a radial dircction from thc central chamber, wherein the plurality of stator arms colTespond to the plurality of stator poles.

[0019] Preferably, the process further comprises the step of mounting an inner portion of each stator pole component within the central chamber, and accommodating a central portion and an outer portion of each stator pole component within a corresponding stator arm of the plurality of stator arms.

[0020] Preferably. inserting the rotor into the stator comprises placing a first axial end of the rotor core within the central chamber of the stator body component.

[0021] Preferably. the process further comprises enclosing the rotor by placing a second stator body component over the rotor, such that a second axial end of the rotor core is accommodated within a central chamber of the second stator body component.

[0022] Preferably, winding a plurality of winding coils comprises winding a plurality of winding coils associated with a plurality of phases, and electncally connecting in series winding coils of the same phase.

[0023] Preferably. winding coils associated with the same phase are wound using a single wire.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] A preferred embodiment of the invention will now he described, by way of S example only. with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labelled with a same reference numeral in all the figures in which they appear.

Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below.

[0025] Fig. 1 illustrates a stepper motor in accordance with the preferred embodiment of the present invention; [0026] Fig. 2 illustrates a permanent magnet rotor, being a part of the stepper motor of Fig. 1; [0027] Figs. 3A and 3B illustrate stator pole components used in the stepper motor of Fig. 1; [0028] Fig. 4 illustrates a stator body component used in the stepper motor of Fig. 1; [0029] Fig. S illustrates a plurality of stator pole components mounted in the stator body component of Fig. 4; [0030] Figs. 6A and 6B illustrate the rotor and a plurality of stator po'e components mounted in the stator body component; [0031] Fig. 6C illustrates the stator and rotor of the stepper motor in a partially assembled state: [0032] Fig. 7 illustrates a process for assembling a stepper motor in accordance with the preferred embodiment; [0033] Fig. S is a schematic view of a partiafly assemified stepper motor in accordance with an alternative embodiment; and [0034] Fig. 9 illustrates a stator pole component used in the stepper motor of Fig. S.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Fig. 1 illustrates a stepper motor 10 in accordance with the preferred embodiment, comprising a rotor 20 configured to rotate within a stator 30. As illustrated in Fig. 2, rotor 20 has a shaft 22 and a permanent magnet core 24. The core is preferably a ring magnet fixed to the shaft via a base. Alternatively, the ring magnet may be replaced by individual permanent magnets fixed to the base. Alternatively, the core may be formed from a moulded permanent magnet material, which is directly fixed to the shaft. In some embodiments. penmment magnet core 24 may be laterally polarized. In other embodiments, motor 10 may be a reluctance motor, wherein rotor 20 comprises a stack of laminations (not shown) instead of a permanent magnet, wherein the bmination stack has a plurality of teeth and is made of a magnetic material, such as silicon steel.

[0036] As shown in Fig. I, stator 30 is encircled by an outer ring or housing 32, and has a stator body comprising one or more stator body components 34. a plurality of stator poles comprising a plurality of stator pole components 36, and winding coils 40 associated with a plurality of phases and wound around the plurality of stator poles.

Winding coils 40 are terminated on terminals 42 fixed in holes formed in one of the stator body components 34.

[0037] Outer ring 32 is substantially annular or cylindrical, and made of a magnetic material, such as soft magnetic iron. Outer ring 32 is used to enclose the stator body and stator poles. closing the stator magnetic circuit during operation of motor 10. as well as to cover and protect the winding coils.

[0038] Stator pole components 36 are made of a magnetic material, such as soft magnetic iron or silicon steel, and are used to define a plurality of stator poles upon which a plurality of winding coils are to be wound. In the preferred embodiments, stator pole components 36 are formed through bending or stamping a metal sheet.

[0039] Fig. 3A illustrates the prefelTed stator pole component 36. Stator pole component 36 comprises a central portion 362, about which the winding coils are to be wound, positioned between an inner portion 361 and an outer portion 363. In an assembled motor 10, central portion 362 extends in a radial direction relative to the axis of motor 10. innerportion 361 is located nearrotor 20, while outer portion 363 is adjacent outer ring 32.

[00401 Central portion 362 is shorter in the axial direction of motor 10 compared to inner and outer portions 361 and 363, providing a volume for accommodating the winding coils. In addition, central portion 362 being shorter in the axial direction than inner and outer portions 361 and 363 allows for the winding coils wound around central portion 362 to have shorter wire lengths and forms additional space to accommodate the winding head. Furthermore, inner and outer portions 361 and 363 may act as guiding flanges for the winding coils. Inner portion 361 functions as a pole shoe forming a path for the flow of magnetic flux during motor operation.

[0041] lii the preferred embodiments, each stator pole of stator 30 comprises two stator pole components 36. For example, Fig. 3B illustrates two stator pole components 36A and 36B placed together to form a single stator pole. The central portions 362A and 362B are direcfly adjacent to each other, such that a winding coil may he wrapped around both stator pole components 36A and 36B. In addition, inner portions 361A and 361B extend in opposite directions away from central portions 362A and 362B to form the pole shoe.

[0042] Stator body component 34 is used to hold stator pole components 36 in place relative to rotor 20, and is made of an insulating material, such as a plastics material. Fig. 4 illustrates one of two stator body component 34 used in the motor of Fig. 1. while Fig. illustrates a plurality of stator pole components 36 mounted on one of die stator body components 34. Figs. 6A and 6B illustrate a plurality of stator pole components 36 and a rotor 20 mounted on the stator body component 34. As mentioned, motor 10 comprises two stator body components 34, one on each axial end of motor 10, as shown in, for example, in Fig. 6C. In Fig. 6C rotor 20 am! stator pole components 36 are sandwiched between a pair of stator body components 34A and 34B. The coils of the stator winding and the outer ring are not shown. However, holes 44 for fixing the teiminals for the winding coils are visible.

[0043] As shown in Fig. 6A. stator body components 34 comprise a central chamber 341 within which the core 24 of rotor 20 is accommodated, and a plurality of stator arms 342 that extend radially outwards from central chamber 341. Stator pole components 36 are mounted on stator body components 34, such that inner portions 361 of the stator pole components 36 interface with the sidewalls of central chamber 341, and central portions 362 and outer portions 363 of stator pole components 36 are accommodated by stator arms 342.

[00441 The sidewalls of central chamber 341 and the surfaces of stator arms 342 may act as guiding surfaces for holding stator pole components 36 in place. As illustrated in Fig. 6A, a length L of stator arms 342 is matched to a length of central portions 362 of stator pole components 36. such that stator pole components 36 fit with stator body components 34. Deformable ridges are formed on the inner surface of the stator arms to urge the central portions of a pair of stator pole components together.

[0045] The number of stator arms 342 on stator body components 34 colTesponds to the number of stator poles of the motor. For example, in the Ulustrated embodiment.

stator 30 defines four stator poles, and comprises eight stator pole components 36 mounted on four stator arms 342 of the two stator body components 34 (two stator pole components for each stator pole).

[0046] When mounted in stator body component 34. outer portions of adjacent stator poles are separated by circumferential openings or gaps 37, allowing for winding coils to be wound directly around the stator poles. Because the winding coils can be wound from the outer circumference of stator 30 instead of having to be threaded into a closed cylindrical stator. a high fill factor can be achieved. In addition, because gaps 37 allow for winding coils to be wrapped directly on an assembled stator 30, winding coils associated with the same phase may be wound in series using a single wire, eliminating wire connection problems that may be associated with winding the coils separately and then mounting them on the stator.

[0047] In some embodiments, an axial end of stator body component 34 contains one or more through holes 344 or passages which interface with shaft 22 or other features of rotor 20 through one or more bearings providing a mechanical coupling between moving and stationary parts (not shown). The bearings may be of any suitable type including ball hearings, sleeve bushings, self-aligning hearings, specia' surfaces provided on the stator body components. etc. This allows rotor 20 to be accommodated within central chamber 341, and for shaft 22 to extend outside stator 30. In some embodiments, through holes 344 or other structural features on stator body component 34 may function as guides for rotor 20, allowing rotor 20 to be accommodated within stator body component 34 without touching stator pole components 36.

[0048] Fig. 7 illustrates a flowchart of a process for manufacturing a stepper motor in accordance with some embodiments. At step 702, a plurality of stator poles for the motor are formed. In some embodiments, this comprises fomilng a plurality of stator pole components and mounting them onto a stator body component. In some embodiments, the individual stator pole components are formed by bending or stamping a sheet of metal.

[0049] The stator body components and stator pole components are configured such that when assembled, there is a gap between adjacent pairs of stator poles on the outer circumference of the stator. For example, Fig. 5 illustrates eight stator pole components 36 defining four stator poles mounted onto a stator body component 34, wherein adjacent pairs of stator poles are separated by a gap 37 on an outer circumference of the stator.

[0050] At step 704, the rotor is inserted within the stator. For example. the rotor may be placed within a stator body component, such that the shaft of the rolor is coaxial with a through hole on an axial end of the stator holder. For example, Figs. 6A and S illustrate rotor 20 placed within stator body component 34.

[0051] In addition, once the rotor has been placed within the stator, the stator may he closed such that it encloses the core of the rotor. For example, Fig. 6C illustrates a second stator body component 34B placed over rotor 20, such that the rotor core and stator pole components 36 are enclosed on both axial ends by stator body components 34A arid 34B.

Shaft 22 of rotor 20 extends outside the stator 30 through a through hole 344 on an axial surface of one or both of the stator body components 34.

[0052] At step 706, winding coils are wound around the stator poles of the motor.

Due to gaps between adjacent stator poles in the outer circumference of the stator. the winding coils can he wound directly around the stator poles with a high fill factor. In addition, because the gaps allow for winding coils to be wrapped directly on stator, winding coils associated with the same phase may be wound in series using a single wire.

[0053] At step 708, the outer housing or ring 32 is placed around the stator, endosing or encircling the winding coils within (e.g.. see Fig. 1, wherein outer ring 32 is disposed around stator body components 34. encircling the stator.). In some embodiments, one or more axial end caps may also he placed over the axial ends of the motor, in order to prevent outside particles from entering the stator from an axial direction.

[0054] Fig. S is a schematic diagram of a motor 10 according to an alternative embodiment. Windings and stator body components are omitted to show the working

S

principle. Fig. 9 illustrates a pair of stator pole components 36 of the motor of Fig. 8. ffi the illustrated embodiment, the stator poles of motor 10 are formed by stator pole components 36 formed using a bent or stamped sheet of metal. Stator pole components 36 are mounted on one or more stator body components (not shown). Whilst the stator poles of the embodiment illustrated in Fig. 1 are formed using two stator pole components 36 circumferentially adjacent to each other, the stator poles of motor 10 illustrated in Fig. 8 are formed from a pair of stator pole components 36 stacked axially. In addition, central portions 362 of stator pole components may be disposed in a plane substantially perpendicular to the axis of the motor, instead of a plane substantially parallel to the axis of the motor. In some embodiments, outer ring 32 may have an axial length shorter than the axial length of thc core of rotor 20 and stator pole components 36, such that thcy cxtend bcyond outcr ring 32.

[0055] hi the forcgoing specification. various aspects have been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes maybe made thereto without departing from the broader spirit and scope of various embodiments described herein. For example, the above-described systems or modules are described with reference to particular arrangements of components. Nonetheless, the ordering of or spatial relations among many of the described components may he changed without affecting the scope or operation or effectiveness of various embodiments described herein. hi addition, although particular features have been shown and described, it will be understood that they are not intended to limit the scope of the claims or the scope of other embodiments, and it will be clear to those skilled in the art that various changes and modifications may he made without departing from the scope of various embodiments described herein. The specification and drawings are, accordingly, to be regarded in an illustrative or explanatory rather than restrictive sense. The described embodiments are thus intended to cover alternatives.

modifications, and equivalents.

[0056] hi the description and claims of the present application, each of the verbs "comprise", "include", "contain" and "have", and variations thereof, are used in an inclusive sense, to specify the presence of the stated item hut not to exclude the presence of additional items. Also, reference throughout this specification to "some embodiments" or "other embodiments" means that a particular feature, structure, material, process, or characteristic described in connection with the embodiments is included in at least one embodiment. Thus, the appearances of the phrase "in some embodiments", "in one or more embodiments", or "in other embodiments" in various places throughout this specification are not necessarily referring to the same embodiment or embodiments. In addition, an embodiment need not have all the aspects or advantages illustrated.

Claims

CLAIMS: 1. A stepper motor, comprising a rotor and a stator disposed around the rotor; wherein the rotor comprises a shaft and a permanent magnet core fixed to the shalt; and S wherein the stator comprises a plurality of stator poles arranged circumferentially around the stator and separated by a plurality of circumferential openings on an outer circumference of the stator; a p'urality of winding coils wrapped around the plurality of stator poles; and an outer ring enclosing the plurality of stator poles.
2. A stepper motor according to Claim 1, wherein the plurality of stator poles comprises a plurality of stator pole components mounted on a stator body component, the stator body component comprising: a central chamber accommodating at least a portion of the rotor; and a plurality of stator arms extending in a radial direction from the central chamber.wherein the plurality of stator aims colTespond to the plurality of stator poles.
3. A stepper motor according to Claim 2, wherein the stator pole components are made of a magnetic material.
4. A stepper motor according to Claim 2 or 3, wherein the stator body component is made of an insulating material.
5. A stepper motor according to Claim 2, 3 or 4, wherein a stator pole component of the plurality of stator pole components comprises a bent or stamped sheet of metal having an inner portion housed within the central chamber, and a central portion and an outer portion accommodated within a stator arm of the plurality of stator arms.
6. A stepper motor according to Claim 5, wherein a stator pole of the plurality of stator poles comprises two stator pole components accommodated within a stator arm of the plurality of stator arms, such that a winding coil of the plurality of winding coils is wound around the central portions of the two stator pole components, and the inner portions of the two stator pole components form a pole shoe within the central chamber.
7. A stepper motor according to Claim 5 or 6. wherein the inner and outer portions of the stator pole component are configured to be longer than the central portion in an axial direction of the motor.
8. A stepper motor according to any one ol Oaims I to 7, wherein the outer ring is S made of a magnetic material.
9. A stepper motor according to any one o1Caims I to 8. wherein the plurality ol winding coils are associated with a plurality of phases, and wherein winding coils associated with the same phase are wound using a single wire.
10. A process for assembling a stepper motor, comprising: forming a stator having a plurality of stator poles arranged circumferentially around the stator and separated by a plurality of circumferential openings in an outer circumference of the stator; forming a rotor by fixing a permanent magnet core to a shaft; inserting the rotor into the stator; winding a plurality of winding coils around the plurality of stator poles through the plurality of circumferential openings; and forming a flux path across the circumferential opcnings in the outer circumfcrcncc of the stator by encircling the stator with an outer ring formed of a magnetic material.
11. A process according to Claim 10. wherein forming a stator comprises forming a plurality of stator pole components by stamping or bending a metal sheet.
12. A process according to Claim 10 or 11, wherein forming a stator further comprises mounting the plurality of stator pole components to a stator body component. and forming the stator body component with a plurality of guiding surfaces For mounting the plurality oF stator pole components.
13. A process according to Claim 12. further comprising forming the stator body component with a central chambcr to accommodate at least a portion of the rotor and with a plurality of stator arms extending in a radial direction from the central chamber, wherein the plurality of stator arms correspond to the plurality of stator poles.
14. A process according to Claim 13. further comprising the step of mounting an inner portion of each stator pole component within the central chamber, and accommodating a central portion and an outer portion of each stator pole component within a corresponding stator arm of the plurality of stator arms.
15. A process according to Claim 13. wherein inserting the rotor into the stator comprises placing a first axial end of the rotor core within the central chamber of the stator body component.
16. A process according to Claim 15, lurther comprising enclosing the rotor by placing a second stator body component over the rotor, such that a second axial end of the rotor core is accommodated within a central chamber of the second stator body component.
17. A process according to any one of Claims 10 to 16, wherein winding a plurality of winding coils comprises winding a plurality of winding coils associated with a plurality of phascs, and eectricaUy connecting in series winding cofls of the samc phase.
18. A process according to Claim 17. wherein winding coils associated with the same phase are wound using a single wire.
19. A process for manufacturing a stepper motor, substantially as herein before descrihcd with reference to the accompanying drawings.
20. A stepper motor substantially as herein before described with reference to the accompanying drawings.