JP3571786B2 - Laser beam printer - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for detecting the number of revolutions of a rotating polygon mirror driving means (scanner motor) used in a laser beam printer, and to an improvement in a first print time using the method.
[0002]
[Prior art]
FIG. 7 shows a configuration of a laser beam printer to which the present invention is applied. The image forming operation of the laser beam printer will be described with reference to FIG.
[0003]
An image signal (VDO signal) 101 is input to the laser unit 102. Reference numeral 103 denotes a laser beam on / off modulated by the laser unit 102. Reference numeral 104 denotes a scanner motor that rotates a rotating polygon mirror (polygon mirror) 105 in a steady state. An imaging lens 106 focuses a laser beam 107 deflected by a polygon mirror on a photosensitive drum 108 which is a surface to be scanned.
[0004]
Therefore, the laser beam 107 modulated by the image signal 101 is horizontally scanned on the photosensitive drum 108 (scanning in the main scanning direction). A beam detection port 109 receives a laser beam from a slit-shaped entrance port. The laser beam entering from this entrance passes through the optical fiber 110 and is guided to the photoelectric conversion element 111. The laser beam converted into an electric signal by the photoelectric conversion element 111 becomes a horizontal synchronization signal (hereinafter, referred to as a BD signal) after being amplified by an amplifier circuit (not shown). Reference numeral 112 denotes a transfer sheet. The latent image formed on the photosensitive drum 108 becomes a toner image visualized by a developing unit (not shown), and is transferred to the transfer sheet 112 by a transfer unit (not shown).
[0005]
Next, a control signal for forming an image will be described with reference to FIG.
[0006]
Reference numeral 121 denotes a transfer sheet for forming an image. The toner image is formed on the transfer paper 121, and an area (image forming area) where laser exposure can be performed so that the toner image formed by the shift or the like of the transfer paper 121 does not protrude from the transfer paper 121. ) 122 is provided. An image controller (not shown) that outputs the image signal 126 is often provided by a controller separate from a control unit that handles control signals such as BD signals, or an external computer. In such a configuration, the image forming area 122 is also provided so that the photoconductor is not exposed even when the image controller turns on the image signal in the non-image area. Therefore, each of the image forming areas 122 has a different size according to the size of the transfer paper 121.
[0007]
Next, an image forming signal for forming an image corresponding to one main scanning line 123 on the transfer paper 121 will be described. The BD signal 124 is the synchronization signal in the main scanning direction described above, and generates other signals in synchronization with the BD signal.
[0008]
The mask signal 125 is a signal that is turned on and off in accordance with the mask area 122 on the transfer paper 121, thereby prohibiting the image signal 126 having image information and prohibiting the exposure outside the image forming area 122.
[0009]
In this way, an image for one page is formed by repeatedly performing image formation for each main scan.
[0010]
When the image forming operation described above is roughly divided into two, the motor is rotated to control the sub-scanning direction in which the transfer paper is fed, the image is formed and the paper is discharged, and the mask signal is generated and the polygon mirror is rotated by a predetermined rotation. The control is divided into control in the main scanning direction in which rotation is performed by a number.
[0011]
In each control, the sub-scanning is controlled in synchronization with the vertical synchronization signal, and the main scanning is controlled in synchronization with the horizontal synchronization signal (BD signal).
[0012]
Next, the first print time will be described. The first print time is the time from when the image forming unit of the printer receives a print instruction from the image developing unit to form an image and discharge the paper. This time is an important value as one of the basic performances of the printer. The first print time will be described with reference to FIG. FIG. 9 is a diagram for explaining the breakdown of the first print time of the laser beam printer. In FIG. 9, events related to the first print time are described on the vertical axis, and time is plotted on the horizontal axis.
[0013]
Each event can be considered to be a sequential one that proceeds to the next operation after each event.
[0014]
First, upon receiving a print instruction, the image forming unit of the printer starts the paper feed operation and simultaneously starts up the scanner motor (131). Although the paper feeding operation depends on the configuration of the printer, in the case of a small laser beam printer, the paper feeding operation often ends before the scanner motor starts up. Not listed. (That is, a configuration that does not become a factor that restricts the first print time will be described.) The completion of the startup of the scanner motor is determined by the ready signal of the scanner motor. However, as shown in FIG. 10, the scanner motor has a fluctuation for a while after a rotation instruction is given and a steady rotation speed 135 is reached. Therefore, the ready signal of the scanner motor is set to be ready with a certain width with respect to the target rotation speed. For this reason, it is impossible to determine from the output of the ready signal that the scanner motor is rotating at a normal rotation speed (a rotation speed with sufficient accuracy to form an image). Therefore, the image forming apparatus shifts to image formation with a certain waiting time (132). If the image forming operation is started without this fixed waiting time or in a state where the waiting time is not sufficiently secured, a fluctuated image is output at the top of the image because the horizontal ratio of the image is not normal. .
[0015]
Next, in the image forming operation (133), as described above, an image is formed based on the electrostatic photographic process, and thereafter, a sheet discharging operation (operation for transporting the sheet to the sheet discharging tray including fixing) ( 134).
[0016]
[Problems to be solved by the invention]
However, in the above conventional example, it is necessary to set the waiting time with a sufficient margin so that a normal image is output even when the fluctuation of the scanner motor is the largest.
[0017]
Therefore, in most cases, even though the scanner motor is operating at a normal rotation speed (even though an image can be formed), the scanner motor waits without doing anything for this waiting time. State exists. This has been a factor that increases the first print time.
[0018]
[Means for Solving the Problems]
Therefore, the present invention provides a rotating polygon mirror for scanning a laser beam onto a photoreceptor, a beam detecting means for detecting a laser beam scanned by the rotating polygon mirror and generating a beam detection signal, counting means for counting a reference clock in synchronism with the beam detect signal generated from means, an acquiring means for acquiring period information of the beam detection signal by using the counting means, the period information obtained by the obtaining means The rotating polygon mirror is rotated and converged by a difference between a current cycle obtained by the obtaining means and a past cycle stored in the storing means being a predetermined value or less. Determining means for determining a state .
[0019]
【Example】
(Example 1)
A first embodiment will be described with reference to FIG. Reference numeral 16 denotes a CPU that controls the sequence of the laser beam printer, and controls various actuators, monitors operation states using sensors, and the like. However, since these circuits are not directly related to the present invention, they are omitted in FIG. Reference numeral 2 denotes a register for writing a control signal generation timing in the main scanning direction, data indicating the start and end timings of the image mask signal 4, and unblanking for forcibly emitting a laser beam in order to detect a BD. Data indicating the start and end timings of the signal 5 and data indicating the start and end timings of the BD allowance signal 10 for ignoring a BD signal that is out of the specified range due to external noise or the like are stored. A main scanning counter 13 is reset by the BD signal 14 and counts up the reference clock. This count value is compared with the value of the register 2 described above by the comparator 3. If the comparison results match, the result is sent to the control signal generator 17 via the next-stage J / K flip-flops 4, 5, and 10. In 17, a laser forced emission signal 6 and an enable signal 7 for permitting laser emission by an image signal are sent to the laser driver from these signals.
[0020]
The portion enclosed by the broken line 11 is a circuit characteristic of the present invention. When the main scanning counter 13 is cleared by the BD signal 14, the count value is stored in the register 12 at the same time.
[0021]
The CPU 16 can know that the contents of the register 12 have been updated because the BD signal is connected to the interrupt terminal 8 of the CPU 16.
[0022]
Hereinafter, the operation of the CPU 16 when the number of polygon mirrors is six will be described with reference to the flowchart of FIG.
[0023]
FIG. 2 shows an interrupt processing routine (21) executed when an interrupt signal (in this case, a BD signal) is input to the interrupt terminal 8 of the CPU 16.
[0024]
First, when an interrupt occurs, the register R (i) in the CPU 16 is referred to. For the six-surface polygon mirror, six registers R (1) to R (6) are secured in the registers in the CPU so that the BD cycle for each surface can be stored.
[0025]
If i = 1 now, it is determined whether or not the absolute value of the difference between R (1) and R12 is equal to or smaller than a certain value C (22). This C is a value determined in advance, and is a value at which the polygon mirror can be regarded as normal rotation. When the absolute value is smaller than C, it is determined that the scanner motor has the specified number of revolutions (23), and the process proceeds to the next image forming sequence. If the absolute value is equal to or larger than C, it is determined that the scanner is in a state before reaching the steady state, and the process proceeds to 24. At 24, the current value of R12 is secured in a register in the CPU 16. The value of i is incremented by 1 for the next BD (26). If i = 6, i is set to 1 (25, 27). After the above processing, the interrupt processing routine ends.
[0026]
The reason why the comparison is performed for each surface of the polygon mirror is that the value stored in R12 is different for each surface even if the scanner motor rotates normally due to the variation in the surface division accuracy of the polygon mirror.
[0027]
As shown in the present embodiment, by performing each surface, even if the surface division accuracy is poor, it is possible to detect the rotation state without any influence at all.
[0028]
(Example 2)
In the next embodiment, an application example of the present invention in a case where the number of rotations of the scanner has an overshoot will be described. Since the hardware configuration is the same as the configuration shown in FIG. 1, it will be described with reference to FIG. The data stored in the register 12 is shown in FIG. 3 (32). The upper figure shows the data of a certain surface stored in R12 (in the case of a six-surface polygon mirror, the data latched in R12 is the data for every six times since the data from the first surface to the sixth surface are repeatedly latched) It is. On the vertical axis, the data value increases as going to the upper side, and the data value decreases as going to the lower side. That is, the upper side indicates that the BD cycle is long because the data value (the count value of the main scanning counter 13) is large. In other words, it can be considered that the rotation speed of the polygon mirror is low. The horizontal axis indicates time, and the time elapses toward the right. As shown in the figure, the data decreases as the rotation speed increases. The straight line 31 is a line indicating a data value when the polygon mirror is rotating at a specified rotation speed. Although the data decreases as the rotation speed of the polygon mirror increases, as shown in the upper diagram of FIG. 3, the data converges to the specified rotation speed after a slightly higher rotation speed after passing the specified rotation speed.
[0029]
On the other hand, the lower diagram shows the absolute value of the difference between adjacent data in the upper diagram. The line indicated at 35 indicates the value that the difference takes when the rotation becomes constant.
[0030]
As shown in the figure, during the acceleration of the rotation, the level shifts above the line, and then converges as shown in the figure. The broken line 34 is an allowable range for 35. If it is within this range, it indicates that the rotation is within the allowable range. When there is an overshoot in the rotation, as shown in 37, the difference data is shown as if the rotation was once once at a high rotation position. In order to prevent this, since the difference data once matches 35, it is not determined that the specified rotation has converged immediately, but rather that the data corresponding to the specified rotation has continued for a certain number of times. This makes it possible to prevent the erroneous determination. For example, if a sequence for judging convergence is made 10 times consecutively and the value of 35 is matched, a transient state like 37 can be ignored.
[0031]
(Example 3)
In the above embodiment, the CPU 16 is interrupted every time the BD signal 14 is generated, and the CPU 16 performs the above-described processing. The period at which the BD signal 14 is generated is on the order of several hundred μsec. When a CPU with a slow processing speed is used, or when there is another task that needs to be processed at a high speed, the processing time of the CPU is reduced. In some cases, it is necessary to reduce these burdens by hardware in order to divide. In the following embodiment, an example will be described in which a part of the functions described above is performed by hardware to reduce the load on the CPU. FIG. 4 shows the configuration. Components having the same functions as those in FIG. 1 described in the previous embodiment are denoted by the same reference numerals. Among these circuits, the part added for this embodiment is 41 BD signal divider circuits. The details of the BD signal dividing circuit will be described below. FIG. 5 is a configuration example of a BD frequency dividing circuit. FIG. 6 shows the waveform of each part of this circuit. The function of this circuit is not to send the BD signal generated plural times each time the polygon mirror makes one rotation to the CPU as it is, but to pay attention to a certain surface and interrupt the CPU only when the BD signal comes out from that surface. Multiply. This reduces the load on the CPU. In this embodiment, the case where the number of polygon faces is six is described. Accordingly, the BD signal 14 is generated six times by one rotation of the polygon mirror, and one of them is sent to the interrupt signal of the CPU 16.
[0032]
Then, the configuration will be described with reference to FIGS.
[0033]
The BD signal dividing circuit 41 is roughly divided into a wave forming circuit 53 for synchronizing a BD signal and a clock to form a waveform, a frequency dividing circuit 54 for generating one BD signal from six BD signals, and It comprises a flip-flop 55 for connecting these. After being initialized by the reset signal 42, these circuits operate in synchronization with the basic clock 43. When the BD signal 44 is input to the waveform shaping circuit 53, the BD signal has a constant waveform synchronized with the basic clock 43. (The interval between the BD signals shown in FIG. 6 is set short for the sake of space. In an actual laser beam printer, the low level time is much longer than this waveform. However, the operation of this circuit is as follows. Is the same as an actual laser beam printer.) This waveform-shaped BD signal 47 is input to a frequency divider 54 via a flip-flop 55. The frequency divider 54 uses a Johnson counter, the details of which are described in the waveforms 48 to 51. Reference numeral 52 denotes a frequency-divided BD interrupt signal. By inputting this signal to the interrupt terminal 8 of the CPU 16, the load on the CPU 16 can be reduced. Thereafter, as described in the previous embodiment, the difference is obtained, and when the steady rotation of the scanner motor is detected, the process proceeds to the next sequence for image formation.
[0034]
(Example 4)
In the previous embodiment, the description has been made in terms of how quickly the scanner motor reaches a certain number of rotations. In the following embodiment, a case will be described in which an abnormality of a scanner motor is detected with this hardware configuration. As shown in FIG. 3, if the rotation does not fluctuate even if the rotation speed does not reach the specified rotation speed, the difference value matches the target 35. However, if the rotation of the scanner motor becomes steady at a rotation speed other than the specified rotation speed due to a malfunction of the scanner motor, the system needs to process the failure as a failure. Therefore, it is possible to detect a failure by checking whether the value stored in R12 is a value within a predetermined range when the difference matches the target value. By doing so, it is possible to prevent the output of an abnormal image and to easily identify the abnormal part when a failure occurs in the scanner motor.
[0035]
According to the embodiment described above, it is possible to minimize the convergence waiting time of the scanner motor. Therefore, it is possible to reduce the time from when the user prints to when he obtains the printed matter .
[0036]
In addition, even when the scanner motor fails, there is another advantage that the failed part can be easily specified, and the serviceability is improved.
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the rotation state can be determined appropriately based on the amount of change of a rotary polygon mirror, for example, the timing which shifts to an image forming sequence can be optimized, and a user can obtain a printed matter as soon as possible. It is possible to provide a laser beam printer capable of performing the above.
[Brief description of the drawings]
FIG. 1 is a circuit diagram for explaining a first embodiment.
FIG. 2 is a flowchart for explaining a first embodiment.
FIG. 3 is a graph for explaining a second embodiment.
FIG. 4 is a circuit diagram for explaining a third embodiment.
FIG. 5 is a circuit diagram for explaining a third embodiment.
FIG. 6 is a timing chart for explaining a third embodiment.
FIG. 7 is a diagram illustrating a configuration of a laser beam printer.
FIG. 8 is a diagram for explaining signals in the main scanning direction.
FIG. 9 is a timing chart for explaining a first print time.
FIG. 10 is a diagram for explaining a rising state of a scanner motor.
[Explanation of symbols]
12 Register 13 Main scanning counter 14 BD signal 16 CPU
41 BD signal dividing circuit 102 Laser unit 104 Scanner motor 105 Rotating polygon mirror (polygon mirror)
108 Photosensitive drum 111 Photoelectric conversion element

Claims (7)

A rotating polygon mirror for scanning the laser beam onto the photoconductor,
Beam detection means for detecting a laser beam scanned by the rotating polygon mirror and generating a beam detection signal,
Counting means for counting a reference clock in synchronization with a beam detection signal generated by the beam detection means;
Acquisition means for acquiring the cycle information of the beam detection signal using the counting means,
Storage means for storing the cycle information acquired by the acquisition means,
Judgment for judging that the rotary polygon mirror is in the rotation convergence state when the difference between the current cycle acquired by the acquisition means and the past cycle stored in the storage means is equal to or less than a predetermined value. And a laser beam printer. 2. The laser beam printer according to claim 1, wherein the operation shifts to an image forming sequence based on the determination that the rotary polygon mirror is in the rotation converging state . 2. The laser beam printer according to claim 1, wherein the acquisition unit stores a count value of the counting unit when reset by the beam detection signal in a register. 4. A laser beam printer according to claim 3, wherein said judging means judges the rotation state of the rotary polygon mirror by comparing periodic information obtained by a beam detection signal on the same surface of the rotary polygon mirror. . 5. The laser beam printer according to claim 4, further comprising frequency dividing means for dividing the beam detection signal to generate an interrupt signal for said judging means. The determination unit determines that the difference between the cycle information acquired by the acquisition unit and the past cycle information stored by the storage unit is equal to or less than a predetermined value for a plurality of times. a laser beam printer according to claim 1, wherein the determining the rotation state of convergence polygon. When it is determined that the rotating polygon mirror is in a converged state, a failure determination unit that determines a failure based on whether or not the period information acquired by the acquisition unit is within a predetermined range is provided. The laser beam printer according to claim 1.

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