JPH0560085B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optical scanning device that can be used, for example, in a laser printer, and in particular to an optical scanning device that prevents malfunctions due to noise in a synchronizing circuit for optical scanning. Regarding equipment.

(Prior Art) An optical scanning device that forms an image by scanning an object with a light beam using a rotating deflector is used in, for example, a laser printer. In such an optical scanning device, an optical sensor is provided outside the image recording area on the same line in the main scanning direction for synchronizing image writing, and after the optical sensor detects the light beam, A control method is adopted in which image writing is started after counting clocks for several pixels. However, if noise enters the transmission line of the photosensor output signal, the information output onto the object to be scanned will be out of synchronization, making the image unsightly. Therefore, a technology has been proposed that eliminates the above drawbacks by predicting the period at which the optical sensor output signal is obtained and blocking the incoming signal when a signal with a period other than the predicted period comes in. . Tokukai Akira
The one described in Publication No. 55-157723 is an example. More specifically, by setting the allowable range for light beam detection by the optical sensor in advance, and only when a detection signal is output from the optical sensor within this range, this is treated as a regular optical sensor output. This is to prevent malfunctions caused by noise.

(Objective) An object of the present invention is to provide a synchronization detection modulation signal that outputs a synchronization detection modulation signal from just before the light beam is incident on the optical sensor until the optical sensor detects the incidence of the light beam. By extracting the optical sensor output only when the synchronization detection modulation signal is output from the synchronization detection modulation circuit, that is, only when the unblanking signal is output, the optical sensor output signal line can be An object of the present invention is to provide an optical scanning device that can more reliably and easily prevent malfunctions caused by mixed noise.

(Structure) The present invention is an optical scanning device that scans an object with a light beam using a rotating deflector, and synchronizes the main scanning direction with the output of a photosensor provided outside an image scanning area. An image scanning clock generator that updates the image scanning clock with its output, and a synchronization detection device that outputs a modulation signal for synchronization detection from just before the light beam is incident on the optical sensor until the incidence of the light beam is detected by the optical sensor. It has a modulation circuit and an optical sensor output switching circuit that applies the optical sensor output signal to the image scanning clock generator and the synchronization detection modulation circuit only when the synchronization detection modulation signal is output from the synchronization detection modulation circuit. It is characterized by

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

In FIG. 3, a beam emitted from a laser light source 1 such as a semiconductor laser is made into parallel light by a collimator lens 2, and this parallel light is incident on a rotating deflector consisting of a rotating polygon mirror 3 and is deflected. It's summery. The deflected beam is configured to image a scanning spot on a photoreceptor 5, which is an object to be scanned, by an fθ lens 4. The laser beam is modulated by a recording signal and scanned over the surface of the photoreceptor 5 by a rotating polygon mirror 3 to form an electrostatic latent image. Sub-scanning is performed by rotating the photoreceptor 5 around its axis. Photoreceptor 5
A photosensor 6 is provided outside the image recording area, and when the photosensor 6 detects the light beam deflected by the rotating polygon mirror 3, it outputs a photodetection signal.

In the example shown in FIG. 4, a hologram disk 8 is used as the rotating deflector, replacing the rotating polygon mirror 3 in the example shown in FIG. A mirror 9 is added to guide the deflected light from the lens to the fθ lens 4, and the other configuration and operation are the same as the example shown in FIG.

Next, an example of an electrical control system used in the present invention will be described. In FIG. 1, the synchronization detection modulation circuit 11 lowers the synchronization detection modulation signal with the optical sensor output signal, and after a predetermined time after the fall, raises the synchronization detection modulation signal in preparation for the next line scan. This is then input to the image control circuit 13. The predetermined time from falling to rising of the synchronization detection modulation signal is the reference clock C0.
It may be made by counting or by using any other suitable timer. Image scanning clock generator 12
generates an image scanning clock and controls the image control circuit 1.
3, and the image scanning clock is updated by the photosensor output signal. The image scanning clock may be generated in fixed numbers based on the optical sensor output, or may be generated continuously. The character generator 14 is connected to the image control circuit 13
The image information signal for each main scanning line is transmitted in synchronization with the image scanning clock using a control signal from the main scanning clock. The image control circuit 13 receives the image information signal from the character generator 14, the synchronization detection modulation signal from the synchronization detection modulation circuit 11, and the positive and negative signals.
In the case of the PON process, the image end erase signal is output to the light source drive circuit 15 as a modulation signal. The light source drive circuit 15 is the image control circuit 1
When the light source is a semiconductor laser, the modulation signal input from 3 modulates the semiconductor laser, and when the light source is a gas laser, for example, a He-Ne laser, it modulates an acousto-optic element placed on the path of the laser beam. It's getting old.

The synchronization detection modulation circuit 11 requires an optical sensor output to control the fall and rise of the synchronization detection modulation signal, and the image scanning clock generator 12 requires an optical sensor output to update the image scanning clock. Output is required. This optical sensor output signal is transmitted to the AND circuit 1 as an optical sensor output opening/closing circuit.
6, the optical sensor output signal is ANDed with the synchronization detection modulation signal from the synchronization detection modulation circuit 11, and only when the synchronization detection modulation signal is being output, the optical sensor output signal is output from the image scanning clock generator 12 and the synchronization detection modulation signal. It is added to the circuit 11 to prevent malfunctions due to noise on the optical sensor output signal line.

Image scanning clock generator 12 may be configured as shown in FIG. 5, for example.
In FIG. 5, a reference clock oscillator 17 generates a reference clock C0 having a frequency equal to the clock frequency f0 for image scanning, and outputs a delay element 18.
It is now being added to Delay element 18
, generates clocks C1, C2, . The above clocks C1, C2,...
...Cn has the same width and is sequentially shifted by a certain amount of time. The latch circuit 19 latches the input clocks C1, C2, ...Cn according to the rising edge of the optical sensor output, and
are outputted and inputted to the clock selection circuit 20, and their inverted outputs 1, 2, . . . are also inputted to the clock selection circuit 20. The clock selection circuit 20 receives the output Q1 of the latch circuit 19 in the previous stage,
Using Q2,...Qn and 1, 2,...
The clock C1 is clocked by a signal of Qk・k+1 (k=1 to n-1; Qn・1 if k=n) or k・Qk+1 (k=1 to n-1; n・Q1 if k=n). , C2, . . . Cn and outputs it as an image scanning clock signal. Specifically, the clock selection circuit 20 includes six AND circuits 21, 22, 23, 24, 25, 26 and an OR circuit 27, where n=6, as shown in FIG. Each AND circuit receives one of the latched clocks and the inverted signal of the next latched clock as input, and also receives an unlatched clock corresponding to the third clock counted from the above one clock. The clock from the delay element 18 is input, and thereby the clocks C1, C2,...Cn
One of them is selected and outputted as an image signal clock through an OR circuit 27.

Next, the operation of the control system described above will be explained. The delay element 18 in FIG. 5 is based on the reference clock C0 from the reference clock oscillator 17.
As shown in the figure, clocks C1, C2, . . . have a constant width and are sequentially shifted in time.
...Generate C6. The latch circuit 19 latches the clocks C1 to C6 using the optical sensor outputs, and inputs the latch signals D1 to D6 and their inverted signals 1 to 6 to the clock selection circuit 20. As shown in FIG. 6, when there is an optical sensor output when clock C1 is "H" and clock C2 is "L", the current states of clocks C1 to C6 are latched, and the AND in FIG. circuit 2
1 opens the gate and the third clock C4 counting from clock C1 is selected as the image scanning clock. If there is an optical sensor output when clock C4 is "H" and clock C5 is "L", the AND circuit 24 opens the gate and the third clock C1 counting from clock C4 is selected as the image scanning clock. When the photosensor output signal is output in this way, the image scanning clock to be used for main scanning is determined, and at this time the image scanning clock is updated from the previous line image scanning clock. The number of image scanning clocks in one line scanning is determined to be a predetermined value, and when the final state is determined to be "L" or "H", the image scanning selected from the final state by the optical sensor output signal is performed. Updated on clock. This image scanning clock is input to the image control circuit 13 shown in FIG. Start writing. The clocks C1 to Cn are set so that the variation in the phase difference between the updated image scanning clock and the photodetection signal is approximately constant (1/N clock or less). This suppresses variations in image writing positions to 1/N dots or less.

FIG. 2 is a timing chart for explaining the operation of the control system shown in FIG. 1. In Figure 2,
To indicates the predetermined time from the fall of the modulation signal for synchronization detection to the rise of the modulation signal for synchronization detection when the optical sensor output signal is input, and T indicates the next line scan after obtaining the optical sensor output. This shows the scanning time for one line until the optical sensor output obtained with . This time T becomes approximately constant when the drive system of the rotary deflector rises to a predetermined rotation speed. Therefore, the pulse width of the synchronization detection modulation signal can be made as narrow as the division angle accuracy of the rotary deflector.
Further, the predetermined time To can be accurately controlled by counting the reference clock C0 as described above.

Now, suppose that the output from the optical sensor 6 in FIGS. 3 and 4 is directly transmitted to the synchronization detection modulation circuit 11 without using the AND circuit 16 in FIG.
and image scanning clock generator 12. In this configuration, if we consider the case where noise enters the optical sensor output line as shown by a in FIG. 2, the image scanning clock will be updated at the time when the noise a is introduced, and After the update, writing of image information starts after counting the same clock a predetermined number of times, resulting in variations in the image writing position.

However, according to an embodiment of the invention as shown in FIG.
is ANDed with the synchronization detection modulation signal by
The optical sensor output is transmitted to the image scanning clock generator 12 and the synchronization detection modulation circuit 1 only when the synchronization detection modulation signal is output from the synchronization detection modulation circuit 11.
1, even if noise enters the optical sensor output line when the synchronization detection modulation signal is not output, the image scanning clock will not be updated and the image writing position will not vary. It disappears. By narrowing the width of the synchronization detection modulation signal, the probability of malfunction can be further reduced.

In Fig. 2, modulation signal A indicates the case where there is a positive-positive process and an image edge erase signal, and modulation signal B indicates the case where there is a negative-positive process and there is no image edge erase signal. It shows.

Here, consider a case where the rotational speed of the rotary deflector has not risen to a predetermined rotational speed. In this case, the one-line scanning time T is longer than when the rotating deflector has risen to a predetermined rotation speed, so the pulse width of the synchronization detection modulation signal is adjusted so that the laser beam is detected by the optical sensor. It needs to be widened. In the illustrated embodiment, the synchronization detection modulation signal is output until the laser beam is detected by the optical sensor. Accordingly, the pulse width of the synchronization detection modulation signal becomes wider, and the optical sensor output can be reliably obtained. Furthermore, if the optical sensor output cannot be obtained within the time required to scan several lines, an error signal indicating an abnormal state may be output, and at this time, the modulation signal for synchronization detection may be reset. You can also do this.
When it is reset, the synchronization detection modulation signal is raised after a predetermined time To in consideration of when the abnormal state returns. However, the error signal is canceled when the optical scanning system returns to normal, that is, when the optical sensor output is obtained while the synchronization detection modulation signal is being set. Further, by processing the error signal by the CPU, it is possible to eliminate malfunctions at the start of rotation of the rotary deflector.

(Effects) According to the present invention, since the optical sensor output switching circuit is provided so that the optical sensor output signal is effectively output only when the synchronization detection modulation signal is output from the synchronization detection modulation circuit, the optical Malfunctions due to noise entering the sensor output signal line can be effectively prevented. Furthermore, since the optical sensor output opening/closing circuit may have a relatively simple circuit configuration, it is possible to provide an optical scanning device that can effectively prevent malfunctions due to noise despite having a simple configuration.
Furthermore, as long as the rotational speed of the rotating deflector is constant,
Even if the width of the synchronization detection modulation signal is narrowed, it is possible to extract the optical sensor output, and by doing so, malfunctions can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control system showing an embodiment of the present invention, FIG. 2 is a timing chart for explaining the operation of the same embodiment, FIG. 3 is a conceptual diagram showing an example of an optical scanning device, and FIG. The figure is a conceptual diagram showing another example of an optical scanning device, FIG. 5 is a block diagram showing a specific example of the image scanning clock generator in the above embodiment, and FIG. 6 shows the operation of the same image scanning clock generator. The timing chart of FIG. 7 is a circuit diagram showing a specific example of the clock selection circuit in the image scanning clock generator. 3... Rotating polygon mirror as a rotating deflector, 5...
Scanning object, 6... Optical sensor, 8... Hologram disk as a rotating deflector, 11... Modulation circuit for synchronization detection, 12... Image scanning clock generator,
16...AND circuit as a light sensor output opening/closing circuit.

Claims (1)

[Claims] 1. In an optical scanning device that scans an object with a light beam using a rotating deflector and synchronizes the main scanning direction using an optical sensor output provided outside the image scanning area, the image scanning clock is updated using the optical sensor output. An image scanning clock generator, a synchronization detection modulation circuit that outputs a synchronization detection modulation signal from just before the light beam is incident on the optical sensor until the optical sensor detects the incidence of the light beam, and a synchronization detection modulation circuit. An optical scanning device comprising an optical sensor output switching circuit that applies an optical sensor output signal to an image scanning clock generator and a synchronization detection modulation circuit only when a synchronization detection modulation signal is output from the circuit.