JPH01209871A - Printing timing detecting system for laser printer - Google Patents

Abstract

PURPOSE:To correctly detect a writing position in case of printing with the low quantity of light and to effectively maintain a printing quality by setting a laser beam to a high level only at the writing start position. CONSTITUTION:When a prescribed voltage is impressed to a transistor 3 from a driving voltage supply part 4, a current passes to a semiconductor laser 1 and the laser beam is emitted. A photodiode 2 incorporated in a laser 1 detects the quantity of laser beam, feeds back to the driving voltage supply part 4 through a level detecting part 5, a light output level deciding part 6 or 11, a light output control part 7 or 12 and a driver amplifier 8 to maintain the laser beam output to a constant value. During a period when the laser beam is projected on a photosensor (not shown) disposed correspondingly to the writing start position and the vicinity thereof, a timing signal B goes to H to change over switching means 10, 13 to (b) side and set the light output to a high level V2. Then, the output of the photosensor is increased to improve S/N, so that, the writing start timing can be correctly detected to effectively maintain the printing quality.

Description

[Detailed Description of the Invention] [1 Already Required] This invention relates to a timing detection method for a laser printer device that uses a semiconductor laser at low output, and in particular to a method for detecting the starting position at the left end of a sheet of paper, which prints at a low light intensity level. , and to provide a print timing detection method for a laser printer that does not deteriorate print quality, and is a method for detecting a timing signal at a writing start position at the left edge of a sheet of paper when a laser printer scans line by line. The inspection is configured by providing a means for controlling and switching the output light level of a semiconductor laser for a light source of a laser printer device to a high level only at the writing start position for each line, and to a low level in the other scanning areas.

[Industrial application field]

The present invention relates to a timing detection method for a laser printer device that uses a semiconductor laser at low output, and particularly to a method for detecting a starting position at the left end of a sheet of paper.

(Prior Art) In a laser printer device, the timing of the writing start position at the left end of the paper is usually detected by a signal obtained by receiving scanning light with an optical sensor installed in front of the writing start position.

FIG. 3 shows a block diagram of a laser light control system of a conventional laser printer device. This laser beam control method uses a normal feedback control method. In the figure, 1 is a semiconductor laser, 2 is a photodiode for monitoring laser light built into the semiconductor laser 1, 3 is a transistor for driving the semiconductor laser 1, R is a resistor, and 4 is a drive voltage supply section for the semiconductor laser 1. .

When a required voltage is applied from the drive voltage supply section 4 to the base of the transistor 3, the transistor 3 becomes conductive, and the voltage +V applied to the semiconductor laser 1 causes a current to flow through the semiconductor laser l through the resistor R, driving it. Voltage supply section 4
Laser light is emitted in an amount corresponding to the supply voltage. A current proportional to the amount of laser light flows through the photodiode 2 that receives this laser light.

Reference numeral 5 denotes a light output level detection section, which converts the current flowing through the photodiode 2 into a voltage to detect the amount of the emitted light, and this converted voltage is sent to the light output level determination section 6.
feed back to one input terminal of The optical output level determining section 6 is composed of a comparator, and the other input terminal is controlled to maintain the output level of the laser beam at a required low level (so that the output of the optical output level detecting section 5 becomes voltage V). A light output setting level v1, which serves as a reference for this purpose, is constantly applied. This light output setting level vI is a setting value that can be adjusted in accordance with the print density. The optical output level determination section 6 compares the re-input level and outputs a binary signal indicating whether it is higher or lower than the optical output setting level vI.

Reference numeral 7 denotes an optical output control section, one input terminal of which is connected to the output side of the optical output level determination section 6, and the other input terminal of which the timing signal A is input.

FIG. 4 is a time chart of each part of the third part, where the horizontal axis shows time, and the vertical axis shows level (however, only the light emitted from the semiconductor laser is shown).

FIG. 3 will be explained below with reference to FIG. 4.

Timing signal A is a pulse signal that is output for each line in order to detect the starting position of the left edge of the paper when the laser printer device scans each line, and this timing signal A has become an effective level. The light output control section 7 corresponds to the output of the light output level determination section 6 so that the output level of the laser beam (i.e., the output of the light output level detection section 5) becomes equal to the light output setting level ν only at that point in time. It has a function of performing level control by controlling the level, and continuously holding and outputting the controlled level only during the printing time of one line via the driver amplifier 8. VO and T shown in the driver amplifier output C of the time chart indicate the held level and the holding time, respectively.

Reference numeral 9 denotes a buffer amplifier, and the print signal P is inputted to the drive voltage supply section 4 via the buffer amplifier 9. The drive voltage supply unit 4 is a circuit that uses the print signal P as a trigger signal to supply an analog signal (voltage VO) output by the driver amplifier 8 to the base of the transistor 3, and includes, for example, an open collector logic circuit or an analog switch. used. It is assumed that the timing signal A is superimposed on the print signal P.

As a result of driving the semiconductor laser 1 as described above, the output light LD emits an optical signal indicating the writing start position at the left end of the paper in response to the timing signal A for each line as shown in the time chart. A waveform as shown in the time chart of the detection signal S is obtained from an optical sensor (not shown) that receives the optical signal, and a preset one-line printing time T can be determined based on this detection signal.

[Problems to be Solved by the Invention] In recent years, as laser printer devices have become lower in price and smaller in size, photoconductor drums have succeeded in increasing their sensitivity, and there has been a trend toward the use of low-output semiconductor lasers. However, as the amount of light used decreases, the level of the photoelectrically converted electrical signal also naturally decreases, making it difficult to distinguish between electrical noise and electrical signals. As a result, the printing start position fluctuates due to noise, which has the drawback of deteriorating printing quality.

The present invention has been made in view of the above-mentioned conventional drawbacks, and therefore, it is an object of the present invention to provide a print timing detection method for a laser printer that prints at a low light intensity level and does not deteriorate print quality.

[Means to solve the problem]

FIG. 1 is a block diagram showing the configuration of the present invention. This method detects a timing signal at the writing start position at the left end of a sheet of paper when a laser printer device scans each line, and the method uses a semiconductor laser l for a light source of the laser printer device.
Means (10, 13) are provided for controlling and switching the output light level of each line to a high level only at the writing start position and to a low level for the other scanning areas.

[For production]

A means for switching the light amount control loop of the semiconductor laser between low level and high level is provided, and at the writing start position at the left end of the paper, high level emitted light is output in synchronization with timing signal B, and the pulse of timing signal B By switching the emitted light to the conventional low-level control method during the printing time for one line other than the width, it is possible to improve the light reception level of the detection signal at the writing start position at the left end of the paper.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted.

FIG. 1 is a block diagram showing the configuration of the present invention.

In the figure, an analog switch 10 is provided as a switching means on the output side of the optical output level detection section 5, and an analog switch 13 is also provided on the input side of the driver amplifier 8. Each analog switch 10.13 has a timing signal B
It is interlocked and driven by.

Figure 2 is the time chart of the first answering section, and the second
FIG. 1 will be explained with reference to the drawings.

Timing signal B is a signal that rises at the fall of timing signal A as shown in the time chart, and is intended to obtain a high-level laser beam at the writing start position on the left edge of the paper in synchronization with this timing signal B. be. It is also assumed that timing signals A and B are superimposed on the print signal P'' shown in the time chart.

Reference numeral 11 indicates a light output high level determination section, and reference numeral 12 indicates a high output control section, each of which has a configuration similar to that of the conventional optical output level determination section 6. It is the same as the optical output control unit 7, but in the former, the voltage v2 applied as the optical output setting level is set to a required level value that is sufficiently higher than the voltage V, and in the latter, the timing signal B is applied. Ru. Hereinafter, for convenience of explanation, a conventional optical output level determination section 6. The light output control section 7 is connected to a light output control section 6, and a bell determination section 6. This will be changed to the optical low output control section 7.

First, when the analog switches 10 and 13 are respectively tilted toward the contact a side, this is the same as the conventional laser beam control method described in FIG. 3. Next, when the pulse of the timing signal B is input, the analog switches 10 and 13 fall to the contact side, and the optical output high level determination section 11 determines that the level fed back from the optical output level detection section 5 is the optical output setting level V. , outputs a binary signal of higher or lower value. Reference numeral 12 denotes a high output control section, one input terminal of which is connected to the output side of the optical output high level determination section 11, and the other input terminal of which receives the timing signal B.

The timing signal B is a pulse signal that is added to the timing signal A that is output for each line in order to detect the starting position of the left edge of the paper when the laser printer scans each line. The output level of the laser beam, that is, the optical output, is increased only when the signal B reaches a valid level.

The high output control section 12 performs level control so that the output of the level detection section 5 becomes equal to the optical output setting level v2, and causes the semiconductor laser 1 to output high-level emitted light via the driver amplifier 8.

When the timing signal B reaches the invalid level, the optical output control is stopped, and the analog switch 10° 13 is also switched to the contact a side, allowing the optical low output control to continue as before. Part 1 7
With the control voltage held at , the control voltage v0 is supplied via the driver amplifier 8 to the drive voltage supply unit 4 for only T0 within the printing time of one line, as shown in the time chart C'.

In other words, the time during which the light output control is performed at a high level is as short as the pulse width of the timing signal B, as shown in the time chart LD', and the high level output time is the time required to detect the writing start position at the left edge of the paper. It is adjusted to cover the period during which the detector is illuminated. When this high-level laser beam is received by an optical sensor (not shown), a detection signal with a good S/N ratio can be obtained as shown in the time chart "S", and this detection signal is used as a reference for the writing position at the left edge of the paper. It can be used as

By adopting this method, the semiconductor laser emits light at a low output level according to the print density during printing, and emits at a high output level at the writing start position at the left edge of the paper, so a detection signal with a good S/N ratio can be obtained. Since light output control is performed even when emitting light at a high output level, a stable detection signal can be obtained.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a stable detection signal can be obtained because the light intensity of the semiconductor laser at the writing start position at the left end of the paper is increased compared to the conventional method, and the light output is also increased at the portion where the light intensity increases. Since the control is performed, the amplitude of the detection signal is also constant, which has the effect of stabilizing the writing start position.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of the present invention, and Figure 2 is a block diagram showing the configuration of the present invention.
3 shows a block diagram of a laser beam control system of a conventional laser printer, and FIG. 4 shows a time chart of each part of FIG. 3. In FIG. 1, 1 represents a semiconductor laser, and 10 and 13 represent switching means, respectively. ga

Claims (1)

[Claims] A method of detecting a timing signal at a writing start position at the left end of a sheet of paper when a laser printer scans line by line, the method comprising: detecting a timing signal of a writing start position at the left end of a sheet of paper, the method comprising: A printing timing detection method for a laser printer, characterized in that means (10, 13) are provided for controlling and switching the level to a high level only at the writing start position and to a low level for the other scanning areas for each line. .