JPH04185271A - Pm type stepping motor - Google Patents

Abstract

PURPOSE:To improve the angular precision of the 1-2 phase excitation of a PM type stepping motor by arranging the constitution such that a slight air gap is provided between an outer yoke and a frame, and that the magnetic pole teeth of the outer yoke are arranged at the position being slid a little from the middle to the pole teeth of the inner yoke. CONSTITUTION:Though two-phase excitation and one-phase excitation changes over alternately, the static position of the rotor 11 of two-phase excitation is in the middle of the standstill position of the one-phase excitation, and the in one-phase excitation, the pole teeth being excited in S poles and the pole teeth being excited in N poles by the coil 10 of only the first phase are balanced with the N poles and the S poles of a rotor 11, whereby holding torque is gotten. Hereupon, in case of one-phase excitation, the region where the standstill position of the rotor 11 becomes unstable exists in the oblique line part. Therefore, the standstill position is not stabled and is slid a little. This slippage can be made small by providing an air gap between the outer yoke 8 and the frame 2 and sliding the pole teeth to the pole teeth of the inner yoke 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a PM type stepping motor used particularly in the OA field and AV field.

Conventional technology The role of stepping motors in recent office automation equipment is as follows:
It has become so important that printers, faxes, and FDDs are indispensable.

An example of a conventional PM stepping motor will be described below with reference to the drawings.

FIG. 4 is a structural diagram of a conventional stepping motor. P
The M-type stepping motor has two sets of stator yokes, each of which has inner yokes 4, 7, . Coil bobbin 5, 9. It consists of an outer yoke 3.8.

1 is the shaft, 2 is the frame, 6, 10 is the coil, 11
is a rotor, and 12 is a bracket.

The relationship between the pole teeth of the inner yoke and the outer yoke is such that one pole tooth is sandwiched between the other pole teeth, and the pole teeth of each stator set are electrically 90" (inner yoke The structure is such that the pole tooth pitch of the rotor is shifted by 1/4).By adjusting this shift and switching the direction of the excitation current of each coil, the N pole and S pole magnetized on the rotor are The rotational force is obtained by the force acting between the S and N poles of the pole teeth.This is in the case of one-phase excitation, and in the case of two-phase excitation, the rotor's rest position is excited by the two N poles. The rotor comes to rest so that the S pole of the rotor is balanced between the pole teeth.

Problems to be Solved by the Invention In the structure of the yoke pole teeth of such a conventional PM stepping motor, in the 1-2 phase excitation drive that switches between 1-phase excitation and 2-phase excitation, when only one phase is excited, The rotor resting position becomes unstable, and the rotor does not come to rest in the middle of the resting position when two-phase excitation is performed, but rather shifts slightly, resulting in poor angular accuracy.

The present invention solves the above problems and aims to improve the angular accuracy of 1-2 phase excitation of a PM stepping motor.

Means for Solving the Problems In order to achieve the above object, the present invention provides a slight air gap between the outer yoke and the frame, and the pole teeth of the outer yoke are slightly smaller than the middle with respect to the pole teeth of the inner yoke. It has a structure in which it is placed in a shifted position.

Effect of the Invention With the above-described configuration, the present invention can reduce the deviation of the static position of the rotor in 1-phase excitation from the middle of the static position of the rotor in 2-phase excitation, thereby improving the angular accuracy of 1-2 phase excitation. be able to.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, the pole teeth of the inner yokes 4.7 and the pole teeth of the outer yokes 3, 8 are in a staggered relationship, that is, the inner yokes 4.
The pole teeth of the outer yokes 3 and 8 are located between the pole teeth of the outer yokes 3 and 8. Furthermore, the pole teeth of the inner yokes 4 and 7 are shifted from each other by 1/4 pitch. This deviation corresponds to 90 degrees in electrical angle, and corresponds to the step angle of rotation by one-phase excitation of the stepping motor in mechanical angle.

In the stepping motor of the present invention, an air gap is provided between the outer yokes 3.8 of each of the two sets of stator yokes and the frame (Fig. 2), and the pole teeth of the outer yokes 3, 8 are connected to the inner yokes 4, 7. The outer yoke 3 has a structure in which all the pole teeth are shifted in the direction a of the inner yoke B that is in contact with the inner yoke A, and the outer yoke 8 has a structure in which all the pole teeth are shifted in the direction a of the inner yoke A (first figure).

To explain the operation in the above configuration, in 1-2 phase excitation, 2-phase excitation and 1-phase excitation are alternately switched, but the resting position of the rotor in 2-phase excitation is between the resting position in 1-phase excitation,
A static torque, that is, a holding torque, is obtained by the attractive force between the pole teeth excited by the first phase coil and the pole teeth excited by the second phase coil. On the other hand, 1
In phase excitation, the pole teeth excited to the S pole and the pole teeth excited to the N pole by the coil of the first phase only (or only the second phase) balance the N and S poles of the rotor to obtain holding torque. ing. Here, in the case of one-phase excitation, as shown in FIG. 1, there is a region in the shaded area where the static position of the rotor becomes unstable. Therefore, the static position of the rotor during one-phase excitation is not stable and shifts slightly. This deviation can be reduced by the method described above, that is, by providing an air gap between the outer yoke and the frame and by shifting the pole teeth of the outer yoke with respect to the pole teeth of the inner yoke.

The reason for this is that when one yoke is excited, the adjacent inner yoke is also slightly excited, but since the inner yokes are shifted by 1/4 pitch, a corresponding force is generated on the rotor, resulting in one-phase excitation. The resting position of the rotor will shift slightly and the angular accuracy will deteriorate. Therefore, by shifting the outer yoke, this force can be canceled, and as a result, the angular accuracy of 1-2 phase excitation can be improved.

In reality, experiments have confirmed that the amount by which the pole teeth of the outer yoke are shifted has a certain regularity. The experimental results are shown in Figure 3. Here, the amount of shift of the pole teeth is expressed as 1 on the horizontal axis.
-Draw a graph with the angular accuracy of two-phase excitation on the vertical axis (and it will be shown in Figure 3.) Also, from the graph, the angular accuracy is better when the pole teeth of the outer yoke are shifted in the direction of a than when they are in the middle of the inner yoke. It can be seen that the accuracy tends to improve.The angular accuracy is the best with a 7.5° step motor at approximately 0.4
It was °. Furthermore, it was confirmed through experiments that shifting the pole teeth improves the rotation direction of the rotor in both cw and ccw directions.

Since both cw and ccw are improved, it can be inferred that the resting position of the rotor under one-phase excitation is intermediate between the resting position of the rotor under two-phase excitation.

Furthermore, by shifting the pole teeth in a direction that improves angular accuracy, detent torque was also reduced. It was also confirmed that angular accuracy deteriorates when the pole teeth are shifted beyond a certain degree. Furthermore, the amount by which this pole tooth is shifted is a step angle of 3.75.
In the case of a motor of 1.5°, the step is approximately 0.2°, which is half of the 7.5° step, and there was almost no change in the motor characteristics other than angular accuracy and detent torque.

Further, this state of deviation of the pole teeth can also be estimated from the phase difference between the induced voltages induced in the first phase and the second phase by rotating the stepping motor from the outside with another motor. According to experiments, when a stepping motor is externally excited at a constant speed from the first phase to the second phase, the induction occurs in the first phase when the motor is rotated in the opposite direction to the direction in which it rotates. As with voltage, when the period (seconds) of the induced voltage generated in the second phase divided by the phase difference (seconds) between the two is around 3.85, the static angle accuracy of 1-2 phase excitation is best. (It was confirmed that this was true. However, the angular accuracy was improved by shifting the pole teeth only when there was an air gap between the outer yoke and the frame.

As described above, according to the stepping motor having the yoke pole tooth structure according to the embodiment of the present invention, the deviation of the rotor from the intermediate position of the rotor in one-phase excitation and the rest position of the rotor in two-phase excitation can be reduced. The angular accuracy of 1-2 phase excitation can be improved.Furthermore, the condition can be confirmed by examining the induced voltage without disassembling the motor.

Effects of the Invention As is clear from the above embodiments, according to the present invention, the resting position of the rotor in one-phase excitation is in the middle of the resting position of the rotor in two-phase excitation, so the angular accuracy of one-two phase excitation can be improved. It can be improved. In addition, if this inspection method is used, 1 of the motor
- The angular accuracy of two-phase excitation can be estimated in a short time.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining how to shift the pole teeth of the stator yoke according to an embodiment of the present invention, Fig. 2 is a structural diagram of the motor of the present invention, and Fig. 3 shows that angular accuracy is improved by shifting the pole teeth. FIG. 4 is a structural diagram of a conventional stepping motor, which shows experimental results showing what can be done. 1...Shaft, 2...Frame, 3
, 8... Outer yoke, 4, 7... Inner yoke, 5, 9... Coil bobbin, 6, 10...
... Coil, 11 ... Rotor, 12 ...
··bracket. Name of agent: Patent attorney Haruaki Ogata (2 persons) Figure 2 Figure 4

Claims (1)

[Claims] A PM stepping motor consisting of a frame with a cup-shaped structure, two sets of stator yokes, two coil bobbins, one multi-pole magnetized rotor magnet, and a bracket, the outer yoke of the stator yoke being A PM stepping motor has an outer shape that creates a slight air gap with the frame, and has a structure in which the pole teeth of the outer yoke are shifted in a certain direction with respect to the pole teeth of the inner yoke.