JPS589599A - Stepping motor for electronic watch - Google Patents

Abstract

PURPOSE:To enhance the efficiency of a stepping motor, when it is driven by short pulses, by preventing the flow of a negative current after the driving pulses are stopped by opening both ends of a coil. CONSTITUTION:A control circuit is provided so that the pulse width of the driving pulse of the stepping motor is stepwise contracted or expanded and the driving pulses having the minimum pulse width corresponding to a load are sent to the stepping motor. A driving circuit is provided so that both ends of the coil is opened or connected by a high resistance element for a specified time period after the driving pulses are finished within one step of a rotor and thereafter both ends of the coil are shorted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low power consumption drive method for a step motor of an electronic watch with an analog display. As a method of electrification, in addition to improving the electric-mechanical conversion efficiency of the step motor itself, it is possible to drive the step motor with less power by dynamically controlling the drive power of the step motor according to the load of the step motor and the driving environment. There is. Specific methods for controlling drive power include controlling drive pulse width and duty ratio of drive pulses.

A so-called correction drive method is generally used for dynamic control of drive power. In this method, the rotor is normally driven with low power, and only if the rotor does not rotate normally for some reason, the rotor is driven again with high power.

In this type of system, the electric power during normal driving is set at the very limit no matter what type of system it is, and the so-called reserve torque is extremely small. For this reason,
It is extremely important to increase the electromechanical conversion efficiency during low power drive.

The present invention aims to improve the electro-mechanical conversion efficiency during low power driving.

Taking power control using the drive pulse width as an example below, (fH1
The operation of the step motor during g motion will be explained. For convenience of explanation, a case will be exemplified below in which a two-pole motor is used, that is, one step rotation angle of the rotor by one drive pulse is 180 degrees. However, it goes without saying that the present invention can also be applied to a multipolar rotor.

FIG. 1 is an example of a driving voltage waveform of general fixed pulse driving. After the drive pulse ends, both ends of the coil are almost short-circuited in order to electrically brake the rotor's motion.

Therefore, current flows through the coil even after the drive pulse is cut off. An example of this is shown in FIG. 2 (α). Figure 3 shows the current waveform when the pulse IJ is narrowed as a power control method (α
). FIG. 2(h) and FIG. 3 (Ch) both show how the rotor rotates. In the case of FIG. 2, where the pulse width is long, the drive pulse is cut off after the rotor passes 90°, and the angular velocity when passing through 90° is also quite large. On the other hand, the third pulse width is shorter.
In the case shown in the figure, the drive pulse ends before the rotor turns 90 degrees, and after that, the rotor continues rotating toward 180 degrees due to its inertia. For this reason, the angular velocity when the rotor passes through 90° is relatively small, and it finally reaches 90°, which is the neutral point of rotation.
It will pass nearby. After the drive pulse is cut off,
A current flows through the coil, determined by the influence of the L component of the coil and the induced voltage generated by the rotation of the rotor, and this current exerts a force on the rotor. The current value between 1 and 2 in FIG. 3 (α) is negative, and the force due to this current acts in the direction of stopping the rotation of the rotor, thereby suppressing the movement of the rotor. That is, in the case where the drive pulse is short as shown in FIG. 3, the negative current flow from 1 to 2 acts to lower the efficiency of the step motor.

The purpose of the present invention is to eliminate the influence of this negative current and improve efficiency during low power driving.

In other words, after the end of a short drive pulse, by opening both ends of the coil or connecting them with high resistance for a certain period of time, the 90
It eliminates the influence of the electric brake that acts on the rotor near °, and allows the rotor to rotate smoothly. rotor is 9
1 after passing 0° (midpoint of one rotor step)
According to the present invention, both ends of the coil are short-circuited so that the rotor motion is braked and the motion quickly converges from the time when the rotor moves toward 80° (the end point of one step of the rotor). In this case, the output torque becomes larger, and if the pulse width is set to the limit that allows rotation, it is possible to narrow the pulse width, and as a result, the current consumption can be reduced.

Although the present invention has been explained above in connection with controlling the drive pulse width as a means of controlling the drive power, the basic motion state of the rotor during low power driving is not much different even with other drive power control methods, and the present invention can be applied as is. .

Next, the present invention will be specifically explained with reference to Examples.

FIG. 4 shows the current waveform of the step motor used in the example with the minimum drive pulse width that allows rotation without load using a conventional method, and the state of motion of the rotor at that time. (α) is a current waveform, and after the drive pulse is cut off, both ends of the coil are short-circuited. (b) shows the rotation angle of the rotor, (C) shows the angular velocity, and (d) shows the torque acting on the rotor.

The period from t to t is a portion where the current becomes negative at (α).

Figures 5 (α) to (d) show the current waveforms and rotor motion states when the same step motor as in Figures 4 (α) to (d) is driven by the present invention i. . Note that the pulse width is the same as that in FIG. 4. The time for opening both ends of the coil is from t to t3, so in the current waveform in Figure 5 (cL), it is from tl to t3.
Until then, the current value is 0. For this reason, the torque acting on the rotor becomes weaker as shown in ``4Cd'' compared to tl to t2 in Figure 4(d), and the angular velocity of the rotor decreases. Fifth
As shown in Figure (C), compared to Figure 4 (C), tl
It is a large value from t2 to t2. for that,
The motion of the rotor shown in No. 51M(b) becomes faster from before 90° to 180°, and is rotating smoothly.

That is, when comparing the conventional driving method and the driving method according to the present invention with the same pulse width, the output torque increases. When the pulse width is 2.9m5ec, the conventional method results in an output torque of 0.89orm when measured using the minute hand, and the drive method according to the present invention results in an output torque of 0.9orm. −
cm output torque, resulting in an efficiency increase of approximately 12.5%.

When comparing the conventional method and the method according to the present invention by setting the pulse width to the lowest value for normal rotation, the method according to the present invention allows the pulse width to be set narrower, resulting in lower current consumption. Decrease. In this example,
Current consumption decreased by approximately 10%.

Note that the timing to start opening both ends of the coil is preferably 0.3 to O-7fi Sec after the drive pulse ends. This is because it takes a certain amount of time for the current to become zero after the drive pulse is cut off due to the influence of the L component of the coil. This is because while the current is a positive value, it has a better effect on the rotation of the rotor than when the current is zero.

The timing to short-circuit both ends of the open coil again is:
It is effective if the setting is made between when the rotor passes through 90° and when the rotor passes through 180°.

As explained above, when driving with short pulses, the efficiency of the step motor can be increased by opening both ends of the coil to prevent the negative current from flowing after the driving pulse has ended. Yes, the effect is great.

[Brief explanation of drawings]

FIG. 1 shows an example of the driving voltage waveform of general fixed pulse driving, FIG. 2 (α) shows the current waveform when driving with a long pulse width, and (h) shows the rotation of the rotor at that time. Figure 3 (α) shows the current waveform when driving with a short pulse width.
(b) shows how the rotor rotates at that time. Figure 4 (α) shows the current value when the step motor used in the example is driven by the conventional method, (h) is the rotation angle of the rotor, (C) is the angular velocity, and (d) is the current value acting on the rotor. The torque is FIG. 5(cL) shows a current waveform driven by the present invention, where (/l) is the rotation angle of the rotor, (C) is the angular velocity, and (d) is the torque acting on the rotor. Applicant Suwa Seikosha Co., Ltd. Agent Patent Attorney Muminari Mogami Figure 1

Claims (1)

[Claims] A control circuit is provided that reduces or expands the pulse width of the drive pulse of the step motor in stages and sends the drive pulse of the minimum pulse width according to the load to the step motor, and after the drive pulse ends within one step of the rotor. A step motor for electronic watches that has a drive circuit that opens or connects both ends of the coil for a certain period of time, and then shorts both ends of the coil.