JPS60114071A - Device for generating light beam scan synchronizing signal - Google Patents

Abstract

PURPOSE:To distinguish noises from photodetecting signals of a photodetector and to prevent occurrence of malfunctions due to noise by outputting synchronizing signals for light beam scanning start only when signals are obtained, which are synchronized with falling of the signals outputted by the photodetector. CONSTITUTION:Counters 9A and 9B calculates by starting with the fall of a signal (b) outputted from a comparator 8 to determine the specified length of light scan beam J whenever the beam J is made incident to the photodetector, including a falling period of the allowable light-scan beam J. A pulse of signal H which is a correspondent output pulse is outputted by an AND circuit 12 only when a pulse of a signal (g) is outputted in synchronization with the fall of the signal (b) outputted from the comparator 8 by a fall detector 11, while a pulse of time width P of a signal (f) which is a specified fall period of the beam J from a flip-flop 10B, and this signal (h) pulse is made to a synchronizing signal for starting the light beam scan of the beam J.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to generation of a light beam scanning synchronization signal in an optical scanning device that scans an object to be scanned with a light scanning beam using a polarizer or the like to form an image, read information, etc. It is related to the device.

2. Description of the Related Art Structures and Problems Theretofore, an optical scanning device as shown in FIG. 1, which shows an electrostatic latent image forming section of a laser beam printer, has been proposed.

In FIG. 1, a light beam L outputted by a semiconductor laser 2 is collimated by a collimator lens 3, polarized in the axial direction of a photoreceptor drum 1 by a rotating polygon mirror 4, and then polarized by an f/θ lens 6. The image is formed on the photosensitive drum 1.

The light beam L output from the semiconductor laser 2 is modulated by an electric signal (not shown), and since the photoreceptor drum 1 is rotated at a constant speed in the direction of the arrow, there is no electrostatic charge on the photoreceptor drum 1. A latent image is formed two-dimensionally. Incidentally, a developing/transfer means of a well-known electrophotographic process is arranged around the photosensitive drum 1, and is used to visualize the electrostatic latent image described above on the recording paper.

Now, in such a configuration, the timing of modulation of the light beam in the axial direction S of the photoreceptor drum 1 is changed for each scan.
, and to adjust the position of the image, a reflecting mirror 6 and a light receiving element 7 are provided, and when the light beam enters the light receiving element 7, a light beam scanning synchronization signal is generated, and this synchronization signal causes the image of the semiconductor laser 2 to be adjusted. This synchronizes the timing of the start of signal modulation.

This light beam scanning synchronization signal is generally generated by comparing the output level of the light receiving element 7 with a predetermined reference level. As a result, the timing of image signal modulation can be determined accurately, regardless of the accuracy of the surface division angle of the rotating polygon mirror 4, uneven rotation speed, etc.
Therefore, the positions of the images can be accurately matched for each scan.

However, the above-described light beam scanning synchronization signal generation method has a problem in that when noise occurs in the light receiving element 7 and its signal transmission path, an incorrect synchronization signal is generated due to the noise, causing the device to malfunction. .

As a solution to this drawback, two light-receiving elements are arranged close to each other in the scanning direction at the scanning start part, and a synchronization signal is generated by two output signals from these two light-receiving elements.
A method has also been proposed to reduce malfunctions caused by noise generated during light beam scanning.

However, even with this method, if noise occurs between the generation of the output signal by the first light receiving element and the generation of the output signal by the second light receiving element, the same malfunction as described above will naturally occur. This method requires two light-receiving elements, and the processing circuit for processing the output signals of these light-receiving elements also becomes complicated, which poses problems such as not being economical.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides a light beam scanning synchronization signal generator that can prevent malfunctions caused by noise and generate an extremely accurate synchronization signal for starting light beam scanning. The purpose is to provide equipment.

Structure of the Invention The present invention detects the rise and fall timings of a signal output from a light receiving element disposed at a scanning start part where an optical scanning beam is incident, and outputs the signal from the light receiving element having a prescribed time width. The optical beam scan is performed only when a signal synchronized with the falling edge of the signal output from the light receiving element is obtained during the set falling period. By outputting a start synchronization signal, noise and a light reception signal of the light receiving element are distinguished from each other, thereby achieving the above-mentioned purpose.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a schematic configuration of a light beam scanning synchronization signal generating device according to an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

7 is a light-receiving element, such as a photodiode capable of high-speed response, on which the optical scanning beam J is continuously incident; 8 is a comparator that binarizes the signal a output from the light-receiving element;
9A and 9B are counters, 10A and 1oB are flip-flops, and these counters 9A, 9B and 10A,
10B determines a signal to be output from the light receiving element having a specified time width, and sets its falling period. A falling detector 11 outputs a signal q having a predetermined time width in synchronization with the falling of the signal S output from the comparator 8.

12 is an AND circuit which generates a light beam scanning synchronization signal of the light scanning beam E using the signal f having <Russe in the above-mentioned set falling period output from the 7 Rinobronop 10B and the signal q from the falling detector 11. This outputs the following.

Next, the operation of this embodiment will be explained with reference to the waveform diagram in FIG.

When the optical scanning beam ■ is incident on the light receiving element 7, the optical scanning beam ■ scans in the axial direction of the photoreceptor drum 1 in FIG. ,
Rising part t1. Constant output part t2. It exhibits a trapezoidal waveform with a falling portion t3. The time from the rising portion t1 to the falling portion t3 is determined by the scanning speed of the light beam J and the area of the light receiving portion of the light receiving element.

The signal a output from the light receiving element 7 is sent to the comparator 8.
A signal with a binarized time width is output, and one of the signals is branched to the counter 9A, and the other is input to the falling edge detector 11.

The counter 9A starts its operation in synchronization with the rise of the signal C output from the comparator 8, and outputs a pulse of the signal C after a predetermined time M. The pulse of the signal C is branched and one is input into the flip-flop 10A and the other is input into the 7-line log 1oB.
A separates the pulse of the signal C from the pulse of the signal d and inputs it to sBK. Counter 9B outputs a pulse of signal e after time N.

The pulses of the signal e output multiple times from the counter 9B and the pulses of the signal C output earlier from the counter 9A are input to the flip 70 knob 10B, and are input to the flip log 10B.
A signal f having a pulse having a time width P equivalent to the time N of the transfer signal e is output.

Here, the time width P of the pulse of the signal f indicates a prescribed falling period including the falling time of the pulse in the time width of the signal f output from the comparator 8.

The reason for this is that the time width of the pulse of the binarized signal output from the comparator 8 indicates the length of the optical scanning beam J at a certain point in time, but the optical scanning beam J is Due to uneven rotation of mirrors, etc., minute scratches occur every time each optical scanning beam (2) scans. Accompanying this minute fluctuation, the time width of the signal also shows a minute fluctuation.

Therefore, the time width P of the pulse of the signal f output from the flip 70 block 10B, which corresponds to the time N of the signal e output from the counter 9B, takes into account the minute fluctuation width that occurs every time the optical scanning beam E is scanned. This means the allowable falling period of the optical scanning beam I set as follows.

- Also, the rise of the signal S output from the comparator 8, the time M until the pulse of the signal C output from the counter 9A, and the rise of the pulse of the signal C output from the counter 9A, and the signal e output from the counter 9B. The sum of the time up to the pulse N and the time N indicates the specified length of the optical scanning beam.

In this way, the counters 9A and 9B calculate the optical scanning beam from the rising edge of the signal output from the comparator 8.
The specified length is set each time the optical scanning beam J is incident on the light receiving element, including the allowable falling period of the optical scanning beam J. Therefore, the time M of the signal C is set to be shorter than the time Kx of the pulse width of the signal S.

Now, from the flip-flop 10B, the above-mentioned optical scanning beam I
While a pulse of time width P of the signal f is being outputted during the specified falling period of Only when a pulse is output, a signal pulse, which is a coincidence output pulse, is output from the AND circuit 12, and this signal pulse is used as a synchronization signal for starting the light beam scanning of the optical scanning beam.

Here, the counter 9A is configured to operate only while the pulse of the signal having the time width K output from the comparator 8 is generated. Therefore, even if a signal due to noise enters the light-receiving element 7 or its transmission path, the waveform of the signal due to noise is generally shorter than the signal a, which is the output of the light-receiving element 7. Since a pulse similar to the pulse is not generated and it is clear that the counter 9B does not operate, an erroneous synchronization signal will not be generated.

Furthermore, there is a possibility that an erroneous signal may be generated if noise occurs immediately after the fall of the signal δ that is output multiple times from the light receiving element 7, but the time N indicating the specified fall time is extremely short. Since it is set short, the probability that noise will occur during this time N is extremely small, and even if it does occur, the shift in the synchronization signal will be extremely small and the effect on the image will be kept to a minimum. I can do it.

Although the present invention has been described above as an example of use in an electrostatic latent image forming section of a laser printer, it is not limited thereto, and can be used in other optical scanning devices as well.

As described in detail, according to the present invention, the output signal of the light receiving element is determined to have a predetermined time width from the rising edge of the output signal of the light receiving element to which the optical scanning beam is incident, and the falling period thereof is indicated. Generate a pulse with a specified time width, and while the pulse with the specified time width indicating this falling period is being generated,
The synchronization signal for starting the light beam scanning of the light scanning beam is generated only when a pulse output in synchronization with the falling edge of the output signal of the light receiving element is detected.
An accurate synchronization signal can be generated without being affected by noise at all, and therefore the possibility of malfunction can be effectively avoided and a high-quality image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of an electrostatic latent image forming section of a laser beam printer, FIG. 2 is a block diagram of a light beam scanning synchronization signal generator showing an embodiment of the present invention, and FIG. FIG. 3 is a waveform diagram showing signals at each output section in FIG. 2; 7... Light receiving element, 8... Comparator, 9A. 9B...Counter, 10A, 10B...
・Solinobu flop, 11... Fall detector, 1
2...AND circuit.

Claims (1)

[Claims] The output signal of the light receiving element placed at the scanning start part where the optical scanning beam that optically scans the object to be scanned by the polarizer is incident is 2.
A comparator for converting into a value, and a predetermined time period indicating the fall period of the binary output signal of the light receiving element, which has a predetermined rising time width for the output signal of the binarized light receiving element. falling period setting means for generating a pulse of a predetermined time width, falling detection means for generating a pulse of a predetermined time width in synchronization with the falling edge of the output signal of the binarized light receiving element; and an AND circuit that outputs a coincidence output pulse only when a pulse from the falling edge detection means is generated while a pulse with a prescribed time width indicating a falling period is generated from the period setting means. A light beam scanning synchronization signal generating device, characterized in that the coincidence output pulse is used as a synchronization signal for starting light beam scanning of the light scanning beam.