JPH04204774A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain stable vertical line width without being vanished or made big due to printing density by switching the adjusting time of a modulating time according to the printing density. CONSTITUTION:AND of the output of a selector 4 and a printing signal outputted from a controller 1 is turned into the output signal of an AND circuit 5, and inputted into a laser device 6. Then, the output of the AND circuit 5 is turned into the AND of the printing signal (g) and a signal (h), and the signal (i) of the modulating time 20ns. At this time, the adjusting time of the modulating time of laser light is varied according to the printing density, as well. Thus, the stable vertical width without being vanished or made big due to printing density is obtained only by adding a simple circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a scanning optical system for a laser printer or the like.

[Background of the invention]

The prior art will be explained using FIG. 3. In a laser printer or the like, the laser group W6 is moved once by a print signal sent from a control device II.

The laser beam 7 emitted from the laser device is rotated through a polygonal boundary 8.
By scanning along the same straight line in the direction of the axial force on the photosensitive drum 9 and gradually rotating the photosensitive drum,
A latent image of characters or figures is formed on the surface of the photosensitive drum. Switching of printing density in laser printers, etc. is performed using a rotating multi-sided interface 8.
This is done by changing the rotational speed of the printer and the modulation time of the print signal. The higher the print density, the shorter the print signal modulation time. The modulation time of the print signal is closely related to the line width of a straight line, that is, a vertical line, perpendicular to the direction of the rotation axis of the photosensitive drum. In other words, as shown in FIG. 5, if the width of the vertical line drawn with the modulation time t of the print signal is d, then if the modulation time is set to t2, which is half of tl, the width of the vertical line will be approximately d. It becomes d2 which is half. Therefore, a method has conventionally been used in which the vertical line width is adjusted by adjusting the modulation time of the print signal. Figure 3 shows delay circuit 2. Switch 3, A
Vertical 1 composed of ND circuit 10! @An example of an adjustment circuit is shown. When printing at a print density in which the print signal modulation time is 40 ns, the fourth
A print signal a having a modulation time of 40 ns in the signal diagram shown in the figure is input to an AND circuit 10 and a delay circuit 2. The delay circuit 2 responds to the input signal by 5ns to 30ns in steps of Sns.
Outputs a delayed signal. If 4-4' of switch 3 is connected as shown in Figure 3, it will take 20ns for print signal a.
The delayed output signal of the delay circuit 2 is input to the AND circuit 10, and the logical product of the print signal a and the signal 1) is input to the AND circuit.
This becomes the output signal C of O. By driving the laser device 6 with this signal C, a vertical line width is finally obtained that is shorter by an amount corresponding to 20 ns compared to the print signal a having a modulation time of 40 ns. Next, when the print density is doubled, the modulation time of the print signal d sent from the control device M1 is generally 20 ns, which is half of the print signal a. Therefore, the input of the AND circuit 10 is 20 ns for the print signal d and the print signal d.
Since the signal e is delayed, the output of the AND circuit 10 is the signal f.
As shown in FIG. 3, the modulation time becomes O, and the laser group w6 cannot be driven. In other words, if the printing density is doubled, printing becomes impossible. Modulation time adjustment time '120
If the printing density is reduced from ns to 51 S, printing is possible even if the printing density is doubled or doubled, but there is a problem that the vertical line width becomes too thick because the adjustment time is short.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the prior art and provide a stable vertical line width that corresponds to the print density even when the print density is changed.

[Summary of the invention]

The present invention focuses on the fact that the modulation time of the laser beam changes depending on the printing density, and the adjustment time of the modulation time of the laser beam is also variable according to the printing density. Never stable
Embodiment of the Invention FIG. 1 shows an embodiment of the invention. The delay circuit 2 outputs a signal delayed by 5 ns to 30 ng in Sns increments with respect to the input signal, and the switch 3 selects the output of the delay circuit 2 to set the modulation time adjustment time. SE1/Q4 is SEL
A/B is logic 0, output Y1. Y2. Human power Al, A2, and A3 are output to Y3, and when SEL A/B is set to logic 1, input B is output to output Y1, Y2, and Y3, respectively.
l.

B2 and B3 are output. The logical product of the output of the selector 4 and the print signal output from the control device 1 becomes the output signal of the AND circuit 3I5, and the output signal is the laser group! 6 is input. This will be explained below using the signal diagram shown in FIG. When printing at a print density in which the modulation time of the print signal is 40 ns, the modulation time 40 ns sent from the control device 1
The print signal g of ns is input to an AND circuit 5 and a delay circuit 2. If the settings of switch 3 are as shown in Figure 1, connecting 2-2' and 4-4' and leaving the others open, the print signal g
A signal delayed by Ions is input to A2 of the selector 4, and a signal delayed by 20 ns is input to Bl of the selector 4. At this time, if SEL A/B is set to logic 1, a signal will be output to the output Y1 of the selector 4, and Y2 and Y
3 is input Bl.

Since B2 is open, it becomes logic 1. Therefore, AND circuit 5
The output is the logical product of the print signal C and the signal 11, and becomes a signal i with a modulation time of 20 ns. By driving the laser family W6 with the signal i, a vertical line width corresponding to 20 ns, which is half of the print signal with a modulation time of 40 ns, is obtained. Next, when the printing density is doubled, the control device Wi1
A print signal i with a modulation time of 20 ns is sent out from. At this time, if SEL A/B of selector 4 is set to logic O, 10 ns of the output of delay circuit 2 for print signal j
The delayed signal becomes the Y2 output of the selector 4 and is input to the AND circuit 5, and the Yl and Y3 outputs are input to the input A1. , A3
becomes logic 1 because it is open. Therefore, the input of the AND circuit 5 is the print signal j and the other signals are logic 1, so
The output of the AND circuit 5 is the signal 1 with the modulation time Ions], which drives the laser device 6, thereby producing the print signal j
For a modulation time of 20 ns, a vertical line width equivalent to half 1 ounce is obtained. As described above, by switching the adjustment time of the modulation time according to the print density, the vertical line width can be adjusted according to each print density, and stable vertical lines can always be obtained.

〔Effect of the invention〕

According to the present invention, since the changeover time adjustment time is changed according to the printing density, it is possible to obtain a stable vertical line width that does not disappear or become thicker depending on the printing density.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the scanning optical system of a laser printer which is an embodiment of the present invention, Fig. 2 is a signal diagram in Fig. 1, Fig. 3 is a diagram showing the prior art, and Figs. 4 and 5 are 4 is a signal diagram in FIG. 3; FIG. In the figure, 1 is a control device, 2 is a delay circuit, and 3 is a control device.
4 is a switch, 4 is a selector, 5 is an AND circuit, 6 is a laser device, 7 is a laser beam, 8 is a rotating multifaceted surface, 9 is a photosensitive drum, and 10 is an AND circuit. Name of patent applicant Hitachi Koki Co., Ltd.

Claims (1)

[Claims] An electrophotographic apparatus having a switching means for controlling light emission/non-emission of light from a light source, a scanning means for scanning light from the light source, and a means for switching the scanning speed of the scanning means and the modulation time of a printing signal according to printing density. An electrophotographic apparatus comprising: a print signal modulation time adjustment means corresponding to each print density; and a print signal modulation time adjustment value that changes depending on the print density.