JPH04261397A - Driving method of step motor - Google Patents

Abstract

PURPOSE:To suppress noise at the time of starting a device by blocking holding current supply to a step motor at the time of driving thereof even in such a case where a power transmission system is driven through the step motor. CONSTITUTION:A rated voltage supply transistor 6 and a predrive current supply transistor 4 for switching voltages to be applied on the exciting coils 2A, 2B, 2a, 2b of a step motor 1 are provided. At first, the transistor 4 is turned ON for a short time and a predrive voltage lower than a rated voltage is applied on the exciting coils 2A, 2B, 2a, 2b. Consequently, the step motor 1 rotates with low torque and gears in a power transmission system driven through the step motor 1 also rotate. At that time, even if there is a gap between a pair of mating gears, the gears make pressure contact slowly without producing noise. Subsequently, the transistor 6 is turned ON to apply a rated voltage onto the exciting coils 2A, 2B, 2a thus rotating the step motor normally.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a stepping motor whose rotation is controlled stepwise by drive pulses, and more particularly to a method for driving a stepping motor that drives a power transmission system equipped with gears.

0002

2. Description of the Related Art For example, in an image recording device such as an electrophotographic copying machine, recording paper is transported from a paper feed tray to a transfer unit by a paper transport device, and a toner image formed on a photoreceptor is transferred onto the recording paper. be done. After the transfer, the recording paper is discharged to the outside of the machine via a fixing device by another paper conveyance device. In such an image recording apparatus, it is desirable that the time from when an instruction to start recording is given to when the recording paper after recording the image is actually ejected is short. Therefore, it has been proposed to transport the recording paper at high speed from the paper feed tray to the transfer section, and to transport the recording paper in accordance with the rotational speed of the photoreceptor during transfer. However, servo motors commonly used in paper conveyance devices suddenly change the conveyance speed and
Moreover, it is difficult to accurately maintain each conveyance speed.

[0003] Therefore, stepping motors have begun to be used instead of servo motors. The stepping motor rotates stepwise by a predetermined accurate angle by applying a drive pulse, so the rotation speed can be easily changed by changing the period of the drive pulse. Furthermore, since the rotational speed is uniquely determined by the period of the drive pulse, accurate control of the rotational speed is possible.

When driving a stepping motor, the rotor is rotated by sequentially applying driving pulses to excitation coils of a plurality of stators arranged around the rotor. FIG. 5 is a schematic diagram showing the principle of rotation of a stepping motor. In addition, in FIG. 5, the movement in the circumferential direction is converted into the movement in the linear direction. Now, assuming that voltage is applied only to the excitation coil of stator A,
As shown in FIG. 5(a), among the teeth of the rotor C, 5 to 8
The numbered part is pulled by stator A and rotor C
The position of is defined. Next, if the application of voltage to the excitation coil of stator A is stopped and voltage is applied only to the excitation coil of stator B, then among the teeth of rotor C, the portions numbered 1 to 4 is drawn to stator A. Therefore, the rotor C moves to the right by 1/4 pitch of the tooth period, resulting in the state shown in FIG. 5(b). This operation is repeated for each adjacent stator to rotate the rotor.

By the way, when a stepping motor is used in a place where an external force is applied to the rotor, the excitation coil is kept at a certain level even when the stepping motor is not rotating, so that the rotor does not rotate due to the external force. Holding current is flowing. However, constantly supplying current to the excitation coil increases energy consumption. Therefore,
In devices such as paper conveyance devices in which no external force is applied to the stepping motor, energy conservation is achieved by completely cutting off the current when the stepping motor is not being driven.

[0006]

[Problems to be Solved by the Invention] For example, in a paper conveyance device, the rotation of the rotor of a stepping motor is
The power is transmitted to non-driving members, ie, conveyor rolls and conveyor belts, through a power transmission system having gears, but backlash exists in the gears. Furthermore, if the holding current is not applied to the stepping motor, the stationary position of the rotor when not being driven cannot be controlled. Therefore, when the stepping motor is not driven, the resting position of the rotor of the stepping motor varies within the range of backlash even if the non-driving member is stationary.

Now, if the stepping motor is rotationally driven from left to right in FIG. The rotor C rotates while the teeth are in contact with each other, but when the stepping motor becomes completely non-driven, the rotor C returns from the state shown in FIG. 5(b) to the state shown in FIG. 5(a) and stops. There are cases. In this case, a gap, or backlash, occurs between the teeth of a pair of meshing gears in the power transmission system. When a drive pulse is applied again in this state, the stepping motor starts rotating in the forward direction, but at this time, the teeth of the gears that were previously separated collide with each other, producing an impact sound. Therefore, there is a problem in that an abnormal noise is generated every time the paper conveyance device starts operating, which is unpleasant to the ears.

The present invention was devised in order to solve the above-mentioned problems, and when the power transmission system is driven using a stepping motor, a holding current is not passed through the stepping motor when it is not driven. The purpose of the present invention is to prevent abnormal noise from occurring when the device starts operating even if the device is configured to do so.

[0009]

[Means for Solving the Problems] The present invention is a method for driving a stepping motor that drives a power transmission system equipped with gears, in which a voltage lower than the rated voltage is applied to an excitation coil for a short period of time, and then the excitation coil is It is characterized by applying a rated voltage to the coil.

0010

[Operation] In the present invention, first, a voltage lower than the rated voltage is applied to the excitation coil of the stepping motor. This causes the stepper motor to rotate with a small torque,
Gears in the power transmission system driven by the stepping motor also rotate. At this time, even if there is a gap between the teeth of the pair of gears that mesh with each other, no abnormal noise is generated because the teeth are in gentle pressure contact. Thereafter, the rated voltage is applied and normal rotation occurs, but at this point, the teeth are already in pressure contact and the backlash has been eliminated, so no noise is generated.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, features of the present invention will be specifically explained based on embodiments with reference to the drawings.

FIG. 1 is a circuit diagram showing a stepping motor drive circuit to which the stepping motor drive method of the present invention is applied.

In this embodiment, the stepping motor 1 includes four exciting coils 2A, 2B, 2a, and 2b. These exciting coils are arranged in an annular shape around the rotor, and are sequentially excited to rotate the rotor as described later. The rotation of the rotor is transmitted to, for example, a conveyance roll, a conveyance belt, etc. of a paper conveyance device of a copying machine via a power transmission system having gears. One end of each excitation coil 2A, 2B, 2a, 2b is commonly connected and led out as a common terminal TC, and the other terminals TA, TB, Ta, Tb of each excitation coil are connected to an NPN drive transistor 3A, respectively. It is connected to the collectors of 3B, 3a, and 3b. Each drive transistor 3A, 3B, 3a
, 3b are grounded, and each base receives four-phase driving pulses φA, 3b shown in FIGS. 2(a) to 2(d).
φB, φa, and φb are applied.

The common terminal TC of the stepping motor 1 is connected to the collector of an NPN type pre-drive voltage supply transistor 4. The emitter of this transistor 4 has
The pre-drive voltage is lower than the rated voltage for driving the stepping motor 1, but is sufficient to rotate the rotor of the stepping motor 1 to an extent that can absorb the backlash of gears in the power transmission system driven by the stepping motor 1. , for example, +5V is applied to the base, and the pre-drive voltage supply control signal S as shown in FIG. 3(a) is applied to the base.
1 is supplied. Further, the collector of an NPN type rated voltage supply transistor 6 is connected to the common terminal TC via a diode 5 for preventing backflow. A rated voltage, for example +24V, is applied to the emitter of the transistor 6,
A rated voltage supply control signal S2 as shown in FIG. 3(b) is supplied to the base.

Next, the operation of the above-mentioned stepping motor drive circuit will be explained.

First, a pre-drive voltage supply control signal S1 shown in FIG. 3(a) is supplied to the base of the pre-drive voltage supply transistor 4. As a result, the transistor 4 is turned on during the period T1, and the common terminal T of the stepping motor 1
+5V is applied to C as shown in FIG. 4(a). The bases of the drive transistors 3A, 3B, 3a, and 3b are provided with four-phase drive pulses φA and φA shown in FIGS.
Since φa, φB, and φb are applied, each drive transistor 3A, 3B, 3a, and 3b is sequentially turned on, and the excitation coils 2A, 2B, 2a, and 2b are sequentially excited. Therefore, the rotor of the stepping motor 1 starts rotating. At this time, since a voltage lower than the rated voltage is applied to the common terminal TC of the stepping motor 1, the rotational torque is small. Therefore, there is a gap between the teeth of the gears of the power transmission system driven by the stepping motor 1.
In other words, even if there is backlash, no abnormal noise is generated because the teeth are in gentle pressure contact. Note that the rotational torque at this time only needs to be large enough to drive the gear to the extent that the backlash of the gear can be absorbed, and there is no need for a large torque to rotate the final load. Moreover, the period T1 only needs to be the time required to absorb the backlash of the gear. For example, when the time difference t (see FIG. 2) between adjacent drive pulses is 2 ms, the period T1
is about 10ms.

Next, a rated voltage supply control signal S2 shown in FIG. 3(b) is applied to the base of the rated voltage supply transistor 6.
is supplied. As a result, the transistor 6 in period T2
is turned on, and +24V is applied to the common terminal TC of the stepping motor 1 as shown in FIG. 4(b). Since the four-phase drive pulses are also being supplied at this time, each exciting coil 2A, 2B, 2a, 2b is excited at the rated voltage, and the rotor rotates with sufficient torque to drive the load. At this point, the teeth of the gears in the power transmission system are already in pressure contact, so no noise is generated. In addition, period T
2 corresponds to the rotation time of the stepping motor 1, and the length is arbitrary.

[0018]

[Effects of the Invention] As described above, in the present invention, first, a voltage lower than the rated voltage is applied to the excitation coil of the stepping motor to absorb gear backlash, and then the stepping motor is driven at the rated voltage. . This prevents gear teeth from colliding with each other, and even if no holding current is applied when rotation is stopped, no abnormal noise is generated from the gear when rotation starts.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a stepping motor drive circuit to which a stepping motor drive method of the present invention is applied.

FIG. 2 is a waveform diagram showing four-phase drive pulses.

FIG. 3 is a waveform diagram showing a control signal for switching the voltage applied to the excitation coil of the stepping motor.

FIG. 4 is a waveform diagram showing the voltage applied to the excitation coil of the stepping motor.

FIG. 5 is a schematic diagram showing the principle of rotation of a stepping motor.

[Explanation of symbols]

1 Stepping motor 2A, 2B, 2a, 2b Excitation coil 3A, 3B, 3
a, 3b Drive transistor 4 Front drive voltage supply transistor 5 Diode 6 Rated voltage supply transistor

Claims (1)

[Claims] 1. A method for driving a stepping motor that drives a power transmission system equipped with gears, the method comprising applying a voltage lower than a rated voltage to an excitation coil for a short time in advance, and then applying a rated voltage to the excitation coil. A stepping motor driving method characterized by: