GB2115618A

GB2115618A - Stepper motor having linear response member and integral bearing supports

Info

Publication number: GB2115618A
Application number: GB08303846A
Authority: GB
Inventors: Harry Geyer Manson
Original assignee: IMC Magnetics Corp
Current assignee: IMC Magnetics Corp
Priority date: 1982-02-24
Filing date: 1983-02-11
Publication date: 1983-09-07
Also published as: FR2522212A1; GB8303846D0; JPS58157365A; IT8367202A0; DE3306323A1; IT1158802B

Abstract

A stepper motor having a stator (10, 11, 12, 13), a rotor (40), and a member (48) movable linearly in response to rotary movement of the rotor. A pair of bearings (46, 47), spaced apart along the axis of rotation of the rotor, support the rotor at its ends. An attachment plate (28, 33) is fixed to each end face of the stator. Each attachment plate is formed with an integral cylindrical wall (50, 52), the axes of the cylindrical walls being colinear with the axis of rotation of the rotor. One of the bearings is supported by each of the cylindrical walls. The cylindrical wall may support a sleeve bearing (147) or may be part of a cup- like formation within which a ball bearing (46, 47) is seated. One of the attachment plates (33) may be used to mount the stepper motor to a support. <IMAGE>

Description

SPECIFICATION Stepper motor having linear response member and integral bearing supports This invention relates to stepper motors, and more particularly to a stepper motor used as a linear actuator, i.e., wherein the rotary movement of the stepper motor is converted to linear motion of another member.

The invention will be described with reference to stepper motors of the general type illustrated and described in U.S. Patents Nos. Re. 28,705 (particularly Figs. 6 and 8) and 3,633,055.

However, it is to be undetstood that the invention has applicability to other types of stepper motors as well.

Stepper motor linear actuators are used in situations requiring accurate linear movement rather than rotary movement. Such actuators may be used, for example, to control the positioning of the damper of an air conditioning system, to regulate the amount of air flow. They are also useful in piston type pumps and material handling equipment.

It is an object of the present invention to provide a stepper motor/linear actuator having an extremely low cost support arrangement for the rotor bearings.

It is another object of the invention to provide such a stepper motor/linear actuator wherein attachment plates fixed to the stator are integrally formed with cylindrical seats for accommodating the rotor bearings.

It is a further object of the invention to provide such a stepper motor/linear actuator wherein one of the attachment plates also serves for mounting the motor/actuator on a support.

Additional objects and features of the invention will be apparent from the following description, in which reference is made to the accompanying drawings: In the drawings: Fig. 1 is an axial cross-sectional view of a stepper motor, according to the invention, useful as a linear actuator; Fig. 2 is a fragmentary axial cross-sectional view of another embodiment of a stepper motor/linear actuator according to the invention; and Fig. 3 is a side elevational view, partially in cross-section, of still another embodiment of a stepper motor/linear actuator according to the invention.

The stepper motor chosen to illustrate the present invention is of the type shown and described in more detail in co-pending Application Serial No. 285,657, filed July 21, 1 981. The stepper motor shown in Fig. 1 includes two stator plates 10 and 11, and two stator cups 12 and 13. Stator plates 10 and 11 are virtually identical, each being of annular shape. A plurality of tapered poles 1 5 surround the central opening of stator plate 10, the poles being circumferentially spaced apart. All the poles 1 5 project perpendicularly in the same direction from the plane of plate 10. The peripheral margin 1 6 of the plate is deformed out of the plane of the plate in the direction in which poles 1 5 project from the plate.

Stator plate 11 is substantially identical to plate 10, and the parts of plate 11 corresponding to those of plate 10 bear the same reference numerals employed above, following by a prime.

In order to form the inner stator member of the stepper motor, stator plate 10 and 11 are placed back-to-back and permanetly fixed together, such as by welding or by a suitable adhesive.

Stator cup 12 is of annular shape, having a central opening in its back wall 24. A plurality of tapered poles 25 surround the central opening, the poles being circumferentially spaced apart. All the poles 25 project perpendicularly in the same direction from the plane of back wall 24 of the cup. A peripheral side wall 26 projects from back wall 24 in the direction in which poles 25 project from the back wall. The free edge 27 of side wall 26 is enlarged in diameter so that the internal diameter of free edge 27 is about equal to the external diameter of stator plate 10, whereby the peripheral edge 1 6 of plate 10 fits snugly within edge 27 of cup 12.

Stator cup 13 is substantially identical to cup 12, and the parts of cup 13 corresponding to those of cup 1 2 bear the same reference numerals employed above, followed by a prime. A bearing attachment plate 28, having a central opening 29, is fixed to the outer face of back wall 24 of stator cup 12, such as by welding or a suitable adhesive, and a bearing attachment plate 33, having a central opening 35, is similarly fixed to the outer face of back wall 24' of stator cup 13.

Plate 33 is larger than plate 28, and has mounting holes 34 near its extremities, so that it can serve as a mounting plate for the stepper motor.

A coil of eiectrical wire 31 wound on a spool 32 surrounds poles 1 5 and 25 of plate 10 and cup 12, respectively, and a similar coil 31' wound on a spool 32' surrounds poles 15' and 25' of plate 11 and cup 13, respectively. The free edges 27 and 27' of stator cups 12 and 13 are bent into the gap 1 9 between the peripheral edges 27 and 27' of stator plates 10 and 11 at a number of circumferentially spaced-apart locations along the free edges, as indicated at 39. In this way, the edges 27 and 27' are staked into the gap 19 to thereby permanently mechanically join each stator cup 1 2 and 1 3 to its respective stator plate 10and 11.

The rotor, which cooperates with the stator described above, includes a nut 40, having an internally threaded axial bore 41, and a tubular permanent magnet 43 surrounding and fixed to the nut. Beyond the ends of magnet 43, nut 40 is formed with reduced diameter ends 44 and 45 rotatably supported within ball bearings 46 and 47, respectively. An externally threaded, rod-like member 48 is located within bore 41 of nut 40, the threads of member 48 and bore 41 being in cooperative engagement.

Member 48 is free to move longitudinally, but cannot rotate. Consequently, as rotor 40, 43 rotates in stepwise fashion, member 48 moves longitudinally, along a path coincident with the axis of rotation of the rotor.

Attachment plate 28 is formed, such as by a drawing operation, with a cup-like formation in the region immediately surrounding opening 29.

The formation includes a cylindrical side wall 50 and an end wall 51 containing opening 29. The outer race of bearing 46 seats in the corner defined by the intersection of walls 50 and 51, and is fixed to the inner surface of wall 50.

Similarly, attachment plate 33 is formed with a cup-like formation in the region immediately surrounding opening 35. The formation includes a cylindrical side wall 52 and an end wall 53 containing opening 29. The outer race of bearing 47 seats in the corner defined by the intersection of walls 52 and 53, and is fixed to the inner surface of wall 52.

Since cup-like formations 50, 51 and 52, 53 are formed out of the same piece of material as their respective attachment plates 28 and 33, they are much less costly to produce than comparable machine screw parts which must be separately manufactured and then assembled with the attachment plates. Nevertheless, these integral cup-like formations maintain precise alignment of the bearings 46 and 47.

In the embodiment of Fig. 2, those parts which are identical to parts in Fig. 1 bear the same reference numerals as in the previous figure. Parts which are of similar function bear the same reference numerals as in Fig. 1, preceded by "1".

In this embodiment, linearly movable member 148 is moved in one direction by the rotation of rotor 140, 43, and is returned in the opposite direction by a spring 56.

In this type of device, bearing 46 carries a heavier thrust load, and hence a ball bearing seated in cup-like formation 50, 51 is used. The other bearing for the rotor carries very little side loading, and hence a less expensive sleeve bearing 147 can be used.

Bearing 1 47 may be a sintered bronze bearing containing a lubricant.

Attachment plate 133 is formed, such as by a drawing operation, with an inwardly directed cylindrical wall 1 52, the wall being of the same piece of material as plate 133. Bearing 147 is fixed within cylindrical wall 152, such as by a press fit or a suitable adhesive. A snap ring 58, accommodated within an annular channel in nut portion 145, prevents axial movement of the rotor.

As with the Fig. 1 embodiment, the integrally formed bearing supports 50, 51 and 1 52 are inexpensive to produce, and admirably serve to retain the bearings in precise alignment.

In the embodiment of Fig. 3, those parts which are identical to parts of Figs. 1 and 2 bear the same reference numerals as in the previous figures. In this embodiment, attachment plate 128 is elongated, as compared to plate 28 of Fig.

1, and its ends are bent away from the stepper motor to form two arms 60 and 61. These arms extend parallel to the axis of rotation of the stepper motor rotor. The ends of arms 60 and 61 are adapted to be pivotally supported by pins 62 for pivotal movement about an axis perpendicular to the rotor axis of rotation. Thus, in use, the stepper motor is free to pivot about this axis as member 48 moves linearly upon energization of the motor.

Here again, as in Figs. 1 and 2, the integrally formed bearing supports 50,51 and 152 are inexpensive to produce, and yet admirably serve to retain the bearings 46 and 147 in precise alignment.

The invention has been shown and described in preferred form only, and by way of example, and many variations may be made in the invention which will still be comprised within its spirit. It is understood, therefore, that the invention is not limited to any specific form or embodiment except insofar as such limitations are included in the appended claims.

Claims

1. A stepper motor comprising: a stator, and a rotor rotatable with respect to the stator about an axis of rotation, a member movable linearly in response to rotary movement of the rotor, a pair of bearings rotatably supporting the rotor at its ends, the bearings being spaced apart along the axis of rotation, and a pair of attachment plates fixed to the opposite end faces of the stator, each plate being formed with a cylindrical wall such that the wall and plate are a single piece of material, the axes of the cylindrical walls being colinear with the axis of rotation of the rotor, and one of the bearings being coaxial with and fixed to each of the cylindrical walls.

2. A stepper motor as defined in Claim 1 wherein the rotor has a screw thread, and the linearly movable member has a screw thread cooperatively engaging the rotor screw thread.

3. A stepper motor as defined in Claim 1 wherein at least one of the cylindrical walls is part of a cup-like formation, and its respective bearing is a ball bearing seated within the cup-like formation.

4. A stepper motor as defined in Claim 3 wherein each of the cylindrical walls is part of a cup-like formation, and each of the bearings is a ball bearing seated within its respective cup-like formation.

5. A stepper motor as defined in Claim 1 wherein one of the bearings is a sleeve bearing fixed within its respective cylindrical wall.

6. A stepper motor as defined in Claim 1 wherein one of the attachment plates extends radially beyond the contour of the stepper motor stator so as to serve as a mounting plate for mounting it on a support surface.

7. A stepper motor as defined in Claim 1 wherein one of the attachment plates is formed with two arms extending parallel to the axis of rotation of the rotor, and including means for mounting the arms for pivotal movement about an axis perpendicular to the axis of rotation of the rotor.

8. A stepper motor substantially as hereinbefore described with reference to and as illustrated in any one of the accompanying drawings.