GB2245768A

GB2245768A - Stepping motor stator phase adjustment

Info

Publication number: GB2245768A
Application number: GB9111644A
Authority: GB
Inventors: Shigeru Furuki
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1990-06-27
Filing date: 1991-05-30
Publication date: 1992-01-08
Anticipated expiration: 2011-05-30
Also published as: DE4120985C2; GB9111644D0; DE4120985A1; GB2245768B

Abstract

In a stepping motor having a rotor integrally formed of a cylindrical magnet and ring-formed first and second stators (4, 5), which have the rotor inserted in the central cavity portion thereof and are fixedly joined together at the bottom face of one stator and the top face of the other stator, the pole teeth 7a, 9a of the stator cores of the stators are joined together at the bottom face of one and the top face of the other thereof and are disposed so as to have a phase difference (Q) between 30 and 80 degrees or between 100 and 150 degrees in electrical angle. This provides high starting torque with low torque at the time of settling if the number of steps for each motion is even. <IMAGE>

Description

STEPPING MOTOR This invention relates to a stepping motor driven through

two-phase magnetization. Such stepping motors are used in disk drive devices for example.

An object of the present invention is to provide a stepping motor which. can achieve start up with a highload and have a short settling time.

According to the present invention, there is provided a stepping motor in which a second stator is fixedly attached at its top face to the bottom face of a first stator wherein the pole teeth of the stator cores are arranged so as to have a phase difference between 30 and 80 degrees or between 100 and 150 degrees in electrical angle therebetween and, hence the magnitude of the combined torque of the torques generated by the pole teeth of both of the stators becomes larger when the number of steps is odd and becomes smaller when the number of steps is even. Therefore, in the case where the number of steps used for setting up each motion is an even number at all times, the torque at the time of startup can be increased and the torque at the time of settling can be decreased.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a development of pole teeth of a twophrase steeping motor; Figure 2 is a characteristic curve showing a combined torque A + B of the torques of phase A and phase B; Figure 3 is a characteristic curve showing a combined torque A - B of the torques of phase A and phase B; Figure 4 is a characteristic curve showing a generated torque at the time of stepping; 0 2 - K1579 Figure 5 is a sectional view showing a basic structure of a two-phase stepping motor; Figure 6 to Figure 9 are drawings pertaining-to a previously proposed stepping motor of which; Figure 6 is a development of pole teeth of a previously proposed two- phase stepping motor; Figure 7 is a characteristic curve showing a combined torque A + B'of torques of phase A and phase B; Figure 8 is a characteristic curve showing a combined torque A - B of the torques of phase A and phase B; and Figure 9 is a characteristic curve showing a generated torque at the time of stepping.

Figure 5 shows the basic structure of a two-phase stepping motor.

Referring to the figure, a rotor 1 comprises a cylindrical magnet 2, magnetized such that poles N and poles S are alternately formed in its circumferential direction, and a shaft 3 arranged along the central axis of the magnet 2. Both end portions of the shaft 3 are supported for rotation by bearings, not shown. A first stator 4 and a second stator 5 are provided, both being ring-formed and having the rotor 1 inserted in the central cavity portion therein with a gap therebetween. The bottom face of the first stator 4 and the top face of the second stator 5 are fixedly joined together. The first stator 4 is formed of a combination of an upper core 6 and a lower core 7 with a high permeability characteristic and an annular exciting coil 8 arranged between both the cores 6 and 7. on the inner circumferential portion of the upper core 6, there are provided pole teeth 6a protruding downward in the form of a comb, and on the inner circumferential portion of the lower core 7, there are provided pole teeth (not shown) protruding upward in the form of a comb, these plural t j K1579 pole teeth being interleaved with each other and confronting the outer circumferential face (magnetized face) of the magnet 2. Similarly, the second stator-5 is formed of a combination of an upper core 9, with pole teeth (not shown) protruding downward in the form of a comb on its inner circumferential portion, and a lower core 10 with pole teeth 10a protruding upward in the form of a comb on its inner circumferential portion, and an annular exciting coil 11 arranged between both the cores 9 and 10. As described further below, the pole teeth of the first stator 4 are offset in the circumferential direction from the pole teeth of the second stator 5, whereby there is usually provided a phase difference of degrees in electrical angle between both of the stators 4 and 5.

The stepping motor arranged as described above is adapted such that the rotor 1 is rotated by an angle corresponding to the number of steps when the exciting coils 8 and 11 are supplied with pulse currents and, thereby, the pole teeth of the cores 6, 71 9 and 10 of the first and second stators 4 and 5 are energized.

Figures 6 is a development of pole teeth of a conventional stepping motor of the above described type, in which the pole teeth 6a and 7a of the upper and lower cores 6 and 7 of the first stator 4 are interleaved with a pitch a, evenly dividing the total circumference.

Also, the pole teeth 9a and 10a of the upper and lower cores 9 and 10 of the second stator 5 are interleaved with the pitch a, but the pole teeth of the first stator 4 (the phase thereof will be called phase A) and the pole teeth of the second stator 5 (the phase thereof will be called phase B) are arranged to be offset from each other by e = a/2 in the circumferential direction. Here, since the angle a corresponds to an electrical angle of 180 degrees, the phase difference e between the phase A and 1 K1579 the phase B corresponds to 90 degrees in electrical angle.

The pattern of excitation of the above described two-phase stepping motor is as shown in Table 1 below. The combined torques A + B and A - B respectively vary with the angle of rotation as shown in Figure 7 and Figure 8.

Table 1

Step Energization Energization Logic of of Phase A of Phase B Combined Torque 0 + + A + B 1 + A - B 2 (A + B) 3 + (A - B) 1 1 4 + 1 + 1 A + B Accordingly, in the above described stepping motor, the combined torques A + B and A - B become of equal magnitude (refer to Figure 7 and Figure 8) and the torque generated at the time of stepping becomes as shown in Figure 9.

In a two-phase-excited operation of such a stepping motor as described above, when the number of steps used for setting up each notion is an even number at all times, starting up with a large load can be achieved by increasing the torque at the time of the startup (odd-numbered step) and decreased in overshoot and shortening of settling time can be achieved by reducing the torque at the time of settling (evennumbered step). However, the torques at the time of startup and settling in the above described conventional motor are of the same magnitude, ie, the generated torque is not changed with the number of steps. Therefore, 1 K1579 there has been a difficulty that if it is attempted to increase the torque at the tite of starting up, the torque at the time of settling is also increased, ana conversely, if it is attempted to decrease the latter, the formed is also decreased.

An embodiment'of the present invention will now be described with reference to Figure 1 to Figure 4 Figure 1 is a'development of pole teeth of a twophase stepping motor according to the present embodiment, in which parts corresponding to those in Figure 5 and Figure 6 are denoted by like reference numerals.

As shown in Figure 1, the pole teeth 6a of the upper core 6 and the pole teeth 7a of the lower core 7 of the first stator 4 are juxtaposed in the form of combs whose teeth are interleaved with each other with a pitch of a, and similarly, the pole teeth 9a of the upper core 9 and the pole teeth 10a of the lower core 10 of the second stator 5 are juxtaposed in the form of combs whose teeth are interleaved with each other with a pith of a.

However, the pole teeth of the first stator 4 (whose phase will be called phase A) are offset from the pole teeth of the second stator 5 (whose phase will be called phase B) by an electrical angle 135 degrees in the circumferential direction. More specifically, the phase difference 8 between the phase A and the phase B is set to 135 degrees in the present embodiment, compared to 90 degrees in the conventional types.

The pattern of excitation in such a two-phase stepping motor is as shown in the above Table 1 and the combined torques A + B and A - B vary with the angle of rotation as shown in Figure 2 and Figure 3. As shown in these figures, the combined torque A - B is larger than the combined torque A + B. Consequently, as shown in Figure 4, the generated torque at the time of stepping becomes larger when the step number is an odd number and 1 K1579 becomes smaller when it is an even number.

Therefore, when the number of steps used for setting up each motion is an even number at all times, the torque at the time of startup (at an oddnumbered step) becomes larger and the torque at the time of settling (at an even- numbered step) becomes smaller, and thus, starting up with a high load can be achieved and overshoot can be reduized and settling time can be shortened.

Although the phase difference 8 between the phase A and phase B is set to an electrical angle of 135 degrees in the above described embodiment, any phase difference satisfying the relationship "combined torque at the time of settling < combined torque at the time of startup" may be set up. Virtually the same effects as described above can be obtained if, for example, the phase difference is set within the range from 100 to 150 degrees or within the range from 30 to 80 degrees in electrical angle.

According to the present invention as described in the foregoing, since the phase difference between the pole teeth of the first stator and the pole teeth of the second stator is set to be between 30 and 80 degrees or between 100 and 150 degrees in electrical angle, the generated torque at the time of stepping is increased when the step number is odd and decreased when the step number is even. Therefore, when the number of steps used for setting up each motion is an even number at all times, such good effects can be obtained that the torque at the time of startup is increased and, hence, starting up with a high load is achieved and the torque at the time of settling can be decreased and, hence, the settling time is shortened.

W 1 4 K1579

Claims

1. A stepping motor comprising a rotor having a cylindrical magnet magnetized such that multiple poles are arranged in its circumferential direction and supported for rotation, an annular first stator having said rotor inserted inthe central cavity portion therein with a gap therebetween, having numbers of juxtaposed pole teeth in the form of combs whose teeth are interleaved with each other disposed at a position confronting the outer circumferential face of said magnet, and having an exciting coil disposed on the side of the outer circumference of said pole teeth, and an annular second stator having said rotor similarly inserted in the central cavity portion therein with a gap therebetween, constructed similarly to said first stator, and being fixedly attached to the first stator, said pole teeth of both of said stators, which are offset from each other in the circumferential direction so that a predetermined phase difference is provided therebetween, being energized to rotate said rotor, said stepping motor being adapted such that the phase difference between said pole teeth of said first and second stators are set to be between 30 and 80 degrees or between 100 and 150 degrees in electrical angle.

2. A stepping motor as claimed in Claim I wherein the phase difference is 135 degrees.

3. A stepping motor as claimed in Claim 1 and substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.

Published 1991 at The Patent Office, Concept House. Cardiff Road. New?orE. Gwent NP9 111H. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys. New-port. NP1 7HZ. Printed by Multiplex techniques ltd. st Mary Cray. Kent.