JPH0775389A - Step motor drive method and image forming device by drive method - Google Patents

Abstract

PURPOSE:To reduce time required for drive by increasing the acceleration even in a range where the drive torque of a stepping motor is not sufficient for achieving a rapid acceleration when driving an object with a large inertia moment using the step motor. CONSTITUTION:An object with a large inertia moment is driven by a step motor. At a low-torque region closer to the natural frequency of a step motor 105, first drive controls 101, 106, 109, and 104 for driving after shifting the natural frequency to a lower frequency are provided. Further, at a high torque region of the step motor, second drive controls 101, 109, and 104 for driving at a frequency with a large acceleration of the step motor and a switching control 107 for switching between the first and second drive controls as required are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to a rotation switching control by a step motor of an image forming apparatus having a rotary developing device including a plurality of developing devices. .

[0002]

2. Description of the Related Art Conventionally, for example, four developing devices of different colors are provided on a rotating body, and by driving the stepping motor with a step motor as a power source, the developing devices are appropriately moved to selectively switch the developing devices. 2. Description of the Related Art An electrophotographic image forming apparatus incorporating a rotary developing device cutting machine is known.

In this type of apparatus, an electrostatic latent image is formed by exposing and scanning a photosensitive member using laser light modulated according to input information, and the electrostatic latent image is developed with a developing material and recorded. It is configured as a so-called laser beam printer that transfers an image onto paper.

Further, recently, in order to realize a color laser printer which prints four colors of Y (yellow), M (magenta), C (cyan) and Bk (black) and develops these colors, A model in which the container is installed on the rotating body has been announced.

In this type of printer device,
Step motors are often used for rotationally driving a rotating body, because the drive control thereof can be relatively easily realized. In the rotation drive control of the step motor, the rotating body is rotated by a predetermined amount in 90 degree units in order to increase the rotation speed of the rotating body, and the developing device of the desired color is swiftly and surely rotated to a predetermined position and stopped. Is important.

[0006]

However, according to the conventional step motor drive control, the speed is controlled to slew up / down at a constant acceleration in order to rapidly drive the rotating body by a predetermined amount. Was there. In this way, if the rotating body is quickly rotated 90 degrees, stopped, and the vibration is suppressed, the drive control is performed so that the developing device of the desired color comes into contact with the vicinity of the photosensitive drum. Vibration will be generated, and it will take a long time before the vibration stops.

As described above, the natural frequency of the step motor which causes unnecessary vibration is, for example, in the vicinity of 100 Hz to 200 Hz, and can be changed by the method of driving the step motor. Therefore, if this natural frequency causes a problem in control, slewing up / down may be performed while avoiding the frequency that causes this natural vibration. However, if this control is performed, the self-starting frequency will become a problem this time. , For example, when starting the slew up from a frequency higher than 200Hz and stopping it,
A driving method is adopted in which the slew down is completed at a higher frequency.

By the way, in the case of controlling the driving of a rotating body having a large moment of inertia, the self-starting frequency becomes low, so that it is difficult to avoid the frequency which becomes a problem in control.

Therefore, conventionally, as shown in the drive waveform diagram of FIG. 9, a method of reducing the current value of the step motor drive has been adopted. When the current value is reduced in this way, the natural frequency moves to a low region, so that the step motor can be driven at a desired drive frequency.

In another step motor driving method, when the rotational speed is the same, the 1-2 phase excitation has a frequency twice that of the two phase excitation. There is a method of driving at a rate of 1-2 phase excitation. Also in the case of this 1-2 phase excitation, the natural frequency is the same as that of the two phase excitation, for example, 100 Hz to 200 Hz, so 1-2
With phase excitation, it becomes possible to set the frequency that is a problem in control in the region of substantially half the rotational speed. As a result, when the slew-up drive is started from the same speed, it becomes possible to drive at a frequency twice as high as that of the two-phase excitation by the one-two phase excitation, so that it is possible to avoid a frequency which causes a problem in control.

However, as described above, when a rotary body having a large moment of inertia is rotationally driven by a step motor, the acceleration cannot be increased in a range where the driving torque is insufficient, and therefore the acceleration must be gradually increased. However, there is a problem that a long driving time is required and the printing speed of the entire apparatus is lowered.

That is, the method of lowering the current value for driving the step motor or the method of replacing the two-phase excitation with the one-two phase excitation is an effective means for avoiding the natural frequency of the step motor from the self-starting frequency. However, since the driving torque is also reduced at the same time, the acceleration for driving the rotating body cannot be made large, resulting in a long driving time, resulting in a decrease in the printing speed of the entire apparatus.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide an insufficient driving torque of the step motor when an object having a large moment of inertia is driven by the step motor. Even in the range, the acceleration can be made large to enable rapid acceleration and shorten the time required for driving.

[0014]

[Means for Solving the Problems] and

In order to solve the above problems and achieve the purpose,
The present invention is a driving method for moving the natural frequency of a step motor which is a problem in control to a substantially low frequency range,
By selectively adopting one of the driving methods capable of increasing the acceleration of the step motor according to the natural frequency of the driving system, it is possible to achieve control with low vibration and the shortest driving time.

That is, in order to avoid the natural frequency in a region lower than about 1.5 times the natural frequency of the preset frequency determined from the natural frequency of the step motor under high torque driving condition, for example, in order to avoid the natural frequency. By lowering the current value, the natural frequency is moved to a lower frequency, and in a region where the natural frequency is higher than, for example, about 1.5 times, the driving method is switched to a driving method in which the current value can be increased to obtain a large acceleration torque. As a result, an object having a large moment of inertia is driven to drive the step motor in a short time.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] A preferred embodiment of the present invention, in which a step motor driving method is applied to a color laser printer, will be described below with reference to the drawings.

FIG. 1 shows an example of the structure of a color laser beam printer. In this figure, a photosensitive drum 1 having a semiconductor layer such as selenium or cadmium sulfide rotatably instructed in a housing H on its surface is shown. , Is rotated in the direction of arrow A in the figure. The laser light L emitted from the semiconductor laser 2 that emits the laser light L is incident on the beam expander 3 and becomes a laser light having a predetermined beam diameter. This laser light is a polyhedral mirror 4 having a plurality of mirror surfaces.
Is incident on. Since the polyhedral mirror 4 is rotated at a predetermined speed by the constant speed motor 5, the laser light L emitted from the beam expander 3 is reflected by the polyhedral mirror 4 rotating by a predetermined amount so that it becomes substantially horizontal. To be scanned.

Following this, the laser beam L passes through the imaging lens 6 having the f-θ characteristic, the return mirror 11, and the spot on the photosensitive drum 1 charged by the charger 13 to a predetermined polarity. It is imaged as light.

The laser light L reflected by the beam detecting reflection mirror 8 is detected by the beam detector 7. On the other hand, the timing of the modulation operation of the semiconductor laser 2 for obtaining the desired optical information on the photosensitive drum 1 is determined based on the detection signal of the beam detector 7.

On the other hand, an electrostatic latent image is formed on the photosensitive drum 1 by the laser light image-formed and scanned according to the input information. These latent images are visualized by the color developing materials in the rotary developing device 9 containing the Y, M, C, and Bk color developing devices, and then the recording paper 15 stored in the lower cassette 10 is used.
Is wound around the outer peripheral surface of the transfer drum 14,
The Y, M, C, and Bk color developing materials are transferred. When the recording paper 15 thus transferred passes through the fixing device 12, the latent image is fixed on the recording paper 15 and is discharged to a discharging device (not shown).

The rotary developing device 9 has a step motor 1
Reference numeral 05 is meshed via a gear train to drive the rotary developing device 9 in a predetermined manner so that the rotary developing device 9 accommodating the Y, M, C and Bk color developing devices is rotationally driven to a predetermined position. Is configured.

Next, a block diagram of FIG. 2 shows an example of the structure of the stepping motor driving device of the rotary developing device 9.

In the figure, the main CPU 101, which controls the entire apparatus, has a motor excitation phase switching time table,
ROM 102 storing control programs and the like, CP
Oscillator 1 that creates clocks and other components required for U101 operation
03 is connected. In addition, the step motor 1 described above
Reference numeral 05 denotes a motor driver 104 for driving this.
Are connected. The motor driver 104 has a PWM (Pulse Width Modulation) 106 for reducing the current value by reducing the excitation duty, and a drive control is switched at a boundary of, for example, about 1.5 times the fundamental frequency of the step motor. The analog switch 107 and the pull-up resistor 108 for setting the logic of one input of the AND circuit 109 to “High” when the analog switch 107 is released are connected between the CPU 101 as shown in the figure. ing.

As described above, each phase drive pattern is ANDed with the PWM signal via the analog switch 106 to output an excitation pattern signal with a reduced excitation duty to the motor driver 104.

FIG. 3 shows a speed profile at the timing of switching the driving method in the structure shown in FIG. In this figure, 0 to T1 which is less than or equal to the speed Vf
Up to (sec) and after T2, the basic vibration is set to the low-frequency moving region of the basic frequency that moves to the low frequency,
A high torque region is set between T1 and T2 (sec), and an individual driving method is used for each region. Here, the speed Vf is a speed corresponding to, for example, about 1.5 times the natural frequency of the high torque driving method.

Further, there is the following relationship between the speed V (rad / sec) and the step motor drive frequency N (pps).

V = 2πN / n (where n is the number of steps per rotation of the step motor) Next, FIG. 4 shows a specific example of driving the step motor. FIG. 4A is an operation explanatory view of the two-phase unipolar step motor. 2 in FIG.
In the excitation pattern of the phase excitation method, for example, when the excitation pattern is changed as shown in the figure, the rotation is performed in the direction of the arrow in FIG. 4A. Further, the excitation pattern in the natural frequency low frequency movement region is shown in FIG.
To obtain a signal modulated in this way, in FIG.
It is possible to obtain a modulated signal by short-circuiting the analog switch 107 according to a command from the CPU 101 and ANDing the modulation signal created by the PWM circuit 106 and the drive pattern signal.

By sending the drive pattern signal thus modulated to the motor driver 104, the drive current can be reduced and at the same time the natural frequency can be reduced. That is, by driving the step motor in this way, the self-starting frequency can be kept away from the natural frequency, and unnecessary vibration can be reduced.

Subsequently, in the high torque region, the modulation pattern signal is released via the analog switch 107, so that the excitation pattern signal from the CPU 101 is directly input to the motor driver 109, so that the current value increases, so that It is possible to drive in the torque range.

Since the torque becomes large in this high torque region, the acceleration can be made large, and in the velocity profile, the inclination of the velocity can be made higher than that in the low frequency moving region of natural frequency, and the step motor 105 is meshed. The driving time of the rotary developing device 9 can be shortened.

4 (a) and 4 (b) are shown as a diagram of the constant velocity region in which the excitation switching time is constant, the switching time gradually decreases in the acceleration region.
Needless to say, it gradually becomes longer in the deceleration region.

[Second Embodiment] FIG. 5 shows a circuit configuration diagram of a second embodiment of the present invention. In this figure, in this embodiment, instead of using the above-mentioned modulation signal, the constant current control means is directly switched.

In FIG. 5, 110 is a motor coil of a stepping motor, 111 is a switching transistor, 112 is a current detection resistor, 113 is a comparator, and 114.
Is an AND circuit, 115 is a diode for current regeneration, 116
Is a transistor for switching comparison current, and 117 is a resistor for generating comparison current. The operation in the circuit diagram of FIG. 5 will be described with the timing chart of FIG.

First, in the high torque region in FIG. 3, the control signal C remains "Low". Coil 110 here
When it is desired to pass the current i through the gate, the gate of the AND circuit 114 is opened by setting “A” to “High”. Initially the motor current i
Is "zero", the voltage effect of the current detection resistor is "zero", the output of the comparator 113 is "High", the switching transistor 111 is "ON", and the current i starts to flow.

As soon as the current i continues to flow, the voltage value of the current detection resistor exceeds the voltage value of the comparison current generating resistor, the output of the comparator 113 is set to "Low", and the switching transistor 111 is "OFF". Then, the current i is cut off.

When a delay circuit time (not shown) elapses,
The comparator 113 re-compares the voltage value for current detection with the voltage value of the resistance for creating the comparison current, and when it knows that the current value i has decreased, it becomes “High” again, and the current starts to flow.

By repeating the above, constant current control is established. In such a circuit, when it is desired to reduce the current value, the control signal “C” is switched from “Low” to “High” to change the resistance value for creating the comparison current from Rc to the parallel resistance of Rb and Rc. Only the set value of the comparison current is decreased, and the constant current operation is established at a low current value.

With the above circuit configuration, the switching operation of the current value i as shown in FIG. 6 is possible, and the stepping motor is operated so that the current value becomes small in the low frequency movement region of the natural frequency, and the high torque is increased. In the region, it becomes possible to operate so as to increase the current value.

[Third Embodiment] Next, a third embodiment of the present invention will be described with reference to FIGS. 7 and 8.

In both figures, in this embodiment, two-phase excitation is switched to 1-2-phase excitation or W1-2-phase excitation. Further, in this embodiment, the natural frequency is not directly moved to the low frequency region, but the speed of vibration in the speed region is moved to the low speed, which is the same as the above-described first and second embodiments. .

First, in FIG. 8, FIG. 8A is a timing diagram of two-phase excitation, FIG. 8B is a timing diagram of 1-2-phase excitation, and FIG. 8C is a W1-2-phase excitation. It is a timing diagram, and the half of the resolution of the 1-2 phase excitation is realized by further adding two kinds of current values to the timing of the 1-2 phase excitation.

That is, as shown in FIG. 7, the natural frequency of the driving method by two-phase excitation which is the first driving method is, for example, 1.
In the region slower than the speed corresponding to 5 times the frequency, FIG.
(B) is 1-2 phase excitation, FIG. 8 (c) is W (double) 1-
Two-phase excitation is used, and two-phase excitation is used in a region faster than a speed corresponding to, for example, 1.5 times the natural frequency of the above-described drive method using two-phase excitation.

As can be seen from FIG. 7, one step is required for two-phase excitation, two states are required for 1-2 phase excitation, and four states are required for W1-2 phase excitation to advance one step. That is, in order to rotate at the same speed, it is 2 in 1-2 phase excitation.
A step motor drive frequency that is twice that of phase excitation and four times that of two-phase excitation is required for W1-2 phase excitation.

Further, since the natural frequency for generating unnecessary vibration is constant, conversely, focusing attention on the rotation speed, 1/2 of 2-phase excitation is used for 1-2 phase excitation, and 1 of 2-phase excitation is used for W1-2 phase excitation.
At a rotation speed of / 4, unnecessary vibration due to the natural frequency is generated.

From this, the two-phase excitation is replaced with the 1-2-phase excitation to double the step switching frequency at the time of start-up and immediately before the stop affected by the natural frequency, or with the W1-2-phase. By replacing with excitation and quadrupling the step switching frequency, the natural frequency can be kept away from the self-starting region.

In this embodiment, the resolution of one step is twice or four times that of two-phase excitation, 1-2-phase excitation, W
Although the 1-2 phase excitation has been described, it goes without saying that generally N times microstep driving may be used.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus. As described in detail above, according to the present invention, a driving method that substantially moves the natural frequency that is a problem in control to a low frequency region and a driving method that can take a large acceleration are By selectively adopting it according to the number, it became possible to realize a stepping motor driving device that has a low vibration and enables the control of the driving time as short as possible. If this step motor driving device is applied to the rotation switching control of the electrophotographic image forming apparatus including the rotary developing device including a plurality of developing devices, it is possible to enhance the printing speed and to increase the printing speed. It is no longer necessary to use an unnecessarily powered up motor to achieve the print speed specification requirement, and it is possible to configure with a smaller and cheaper step motor.

[0048]

As described above, according to the present invention, when an object having a large moment of inertia is driven by the step motor, the acceleration can be made large even in the range where the driving torque of the step motor is insufficient. Therefore, it is possible to accelerate rapidly and reduce the time required for driving.

[Brief description of drawings]

FIG. 1 is an external view of a configuration example of a color laser beam printer.

FIG. 2 is a circuit diagram of the first embodiment.

FIG. 3 is a diagram illustrating a method of accelerating a step motor.

FIG. 4 is a diagram illustrating a driving sequence of a step motor according to the first embodiment.

FIG. 5 is a circuit configuration diagram of a second embodiment.

FIG. 6 is a timing diagram for explaining a second embodiment.

FIG. 7 is a diagram illustrating a method of accelerating a step motor according to a third embodiment.

FIG. 8 is a timing diagram illustrating a third embodiment.

FIG. 9 is an explanatory diagram of conventional stepping motor current control drive.

[Explanation of symbols]

 9 rotary developing device 101 CPU 102 ROM 103 oscillator 104 motor driver 105 step motor 106 PWM circuit 107 analog switch 108 AND logic

Claims (7)

[Claims] 1. A step motor driving method for driving an object having a large moment of inertia by a step motor, wherein the natural frequency is driven to a lower frequency in a low torque region close to the natural frequency of the step motor. In the high torque region of the step motor, the second drive control that drives the step motor at a frequency that allows a large acceleration, the first drive control, and the second drive control. A stepping motor driving method comprising: switching control for switching at any time. 2. The step motor control device according to claim 1, wherein the first drive control uses a modulated drive signal. 3. The step motor drive method according to claim 1, wherein the one drive control is drive for reducing a current value of the constant current control means. 4. The one drive control uses a drive method in which a step motor has a frequency increased with an increased resolution by an integer multiple in a low torque region and a drive method in which a acceleration is increased in a high torque region. The step motor driving method according to claim 1, which is used. 5. The stepping motor driving method according to claim 4, wherein the driving in which the resolution of the one step is increased and the frequency is increased by an integral multiple is 1-2 phase excitation driving. 6. The step motor drive method according to claim 4, wherein the drive in which the resolution of the one step is increased and the frequency is increased by an integral multiple is double 1-2 phase excitation drive. 7. The step motor according to claim 1, wherein the object is applied to a rotating body holding a plurality of developing devices, and the driving method is applied to control rotation of the rotating body. Image forming apparatus using a driving method.