JPS6125363A - Beam position detector - Google Patents

Abstract

PURPOSE:To obtain an accurate picture recording start position with no adjustment by measuring a pulse width after waveform shaping and using a time when a 1/2 time of the pulse width measured before is elapsed as a picture recording start time after a prescribed time is elapsed from the said measurement. CONSTITUTION:An input signal subjected to beam detection 5 is pulse-waveform- shaped by an amplifier/waveform shaping circuit 6 and the pulse is measured by a counter 20 based on the rise of an output pulse Vp. The pulse Vp is inputted to a pulse width measuring device 21 at the same time to obtain the pulse width and a 1/2 of the pulse width is inputted to the counter 22. Then the counter 20 outputs a start signal to the counter 22 after the time Tc. Thus, the counter 22 starts the measurement of 1/2 of the measured pulse width and transmits a picture recording start signal to a picture recording controller at the same time when the measurement is finished to start the write of a picture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a beam position detection device used when recording an image by main-scanning a laser beam with a rotating polygon mirror, and for determining the timing to start recording an image.

In a device that records images by main scanning with a rotating polygon mirror,
Since the division angle of each surface of the rotating polygon mirror is not necessarily constant due to manufacturing precision, etc., it is necessary to accurately know when to start beam scanning for each surface. For this purpose, a beam detector is provided on the scanning line, and this detection signal is amplified and waveform-shaped and used as a synchronization pulse, and this synchronization pulse operates a timer to determine when to start image recording.

To explain this example with reference to FIG. 1, a laser beam emitted from a laser oscillator 1 is main-scanned by a rotating polygon mirror 2, passes through an f-0 lens 3, and records an image on a recording surface 4. Further, a beam detector 5 is placed on the main scanning line on the scanning start side, and the signal detected thereby becomes a synchronizing pulse signal S through an amplification and waveform shaping circuit 6. FIG. 2 shows a detailed diagram of the amplification/waveform shaping circuit 6. When a laser beam is incident on the beam detector 5, a photoelectric current proportional to the amount of incident light is generated from the beam detector 5, and this current is passed through the operational amplifier 7 and the resistor. The voltage is converted into a voltage by a current-voltage conversion circuit constituted by R1 and input to the comparator 8. Further, this voltage is compared with a voltage level determined by resistors R2 and R3, and a synchronized pulse signal S is obtained after pulse shaping.

By the way, the angle of inclination of the rotating polygon mirror 2 is generally not constant on each side, and the current output from the beam detector 5 is not constant due to dust in the air, fluctuations in laser power, etc.
For this reason, the voltage input to the comparator 8 will fluctuate, and the synchronization pulse signal S will also fluctuate, making it impossible to accurately detect the position.

FIG. 3 shows this situation, where S1 and S2 are the input voltage waveforms of the comparator 8, and the waveform S1 has stronger light incident thereon. Note that L is a voltage comparison level determined by resistors R2 and R3 in FIG.

As is clear from FIG. 3, the synchronous pulse signal S has a waveform S
The widths are different between 1 and S2, and if the synchronizing pulse signal S generated thereby is used, there is a drawback that the image recording start time fluctuates by Δt and the image quality deteriorates.

In order to eliminate this drawback, for example, JP-A-58-130
A method disclosed in Japanese Patent No. 69 is known. Figure 4,
To explain this method with reference to FIG. 5, the signal detected by the beam detector 9 is amplified by the amplifier 10, and this amplified signal passes through the first delay circuit 11 and becomes the signal Va shown in FIG. is input. Also, the amplifier l
The signal amplified by O is also input to the signal inversion circuit 13,
The output of this signal inversion circuit 13 passes through a signal attenuation circuit 14 and becomes a signal vb, which is input to an adder 12. At the same time, the output vb of the signal attenuation circuit 14 is input to the second delay circuit 15, and its output is input to the adder 12 as the signal Vc.

The adder 12 combines these three signals and outputs it as a signal v3 to the waveform shaping circuit 16, and the combined signal is waveform-shaped and becomes the synchronizing pulse signal S.

This method is intended to narrow the pulse width of the wide input waveform Va by inverting and attenuating the signal itself, and further adding it, thereby reducing the influence of variations in the input signal. The adjustment is complicated and delicate, and when the input voltage level changes significantly, the delay time is constant, so the fluctuation cannot be completely suppressed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a beam position detection device that eliminates the drawbacks of the conventional example described above and makes it possible to accurately determine the image recording start point of a laser beam without any adjustment. , when recording an image by main scanning a laser beam modulated by an image signal with a rotating polygon mirror, a light detection means for detecting the start time of image recording, and comparing the detection signal with a predetermined reference value. means for shaping a waveform, means for measuring a pulse width that depends on the amount of incident light after the waveform shaping, means for measuring a certain period of time from the time when the pulse is detected, and a pulse measured after the elapse of the certain period of time. and a means for measuring a half cycle of the pulse width, and is characterized in that the image recording start time is set at the time when the sum of a certain time from the time when the pulse is detected and the half cycle of the measured pulse width has elapsed. It is something.

The present invention will be explained in detail based on the embodiment shown in FIG. 6 and below.

6 and 7 are detailed explanatory diagrams of the present invention. As shown in FIG. 6, it has been confirmed that even if the laser power is varied variously, the peak time to of the signal waveform does not change. Therefore, if the synchronization pulse starts at a time with a pulse width of 1/2 of the amplified and waveform-shaped pulse, it is possible to always find a constant image recording start point.

FIG. 7 shows the principle of the present invention, in which (a) shows a case where the amount of incident light is strong, and (b) shows a case where the amount of incident light is weak.

T1. T2 is the pulse width when shaping the input signal waveform based on the reference voltage, and Tc is the theoretical time width from the time of beam detection to the start of image recording, as is clear from the explanation of Fig. 6. Although the time width Tc is always a constant value, the pulse width T1. T2 varies depending on the amount of incident light. In order to determine the image recording start time TO under such conditions, first a means for measuring the waveform-shaped pulse width is provided. On the other hand, a counter is activated to measure a certain period of time Tc from the rising edge of the waveform-shaped pulse Vp. 1/2 of the measured value of the pulse width from the end of measurement of this counter
For example, in the case of Fig. 7 (a), T1/2, (b)
In this case, a second counter set to T2/2 is activated.

It can be easily understood from FIG. 7 that the time point at which the measurement by the second counter ends is the image recording start time point TO. In this way, even if the level of the input waveform varies, it is possible to always obtain a constant image recording start time TO.

Next, specific block circuit configuration diagrams for realizing the present invention are shown in FIGS. 8 to 10, where 5.6 is the first
This is the beam detector and amplification waveform shaping circuit shown in FIG. Based on the rise of the pulse Vp whose waveform has been shaped by the amplification reference waveform shaping circuit 6, the first counter 20 that measures a certain period of time Tc starts measuring. At the same time, pulse V
p is input to the pulse width measuring device 21 to find the pulse width, and 1/2 of this pulse width! , 2 is input to the counter 22. The first counter 20 outputs a start signal to the second counter 22 after time Tc. As a result, the second counter 22 starts measuring 172 of the measured pulse width, and at the same time as the measurement ends, it sends an image recording start signal to an image recording controller (not shown) to start writing the image.

FIG. 9 shows an example of a fixed time counter, where CP is a reference clock pulse signal and has sufficient frequency resolution for the accuracy of the image recording start time TO. The pulse Vp whose waveform has been shaped by the amplification Φ waveform shaping circuit 6 is connected to the J input of the JK flip-flop circuit 23, and the Q output of the JK flip-flop circuit 23 becomes high level at the rise of the pulse vp.

This Q output is connected to the count enable terminal E% of the N-ary programmable counter 24, and the N-ary programmable counter 24 is set to a time Tc by a count number setting device 25 constituted by a digital switch or the like. At the same time that the count enable terminal EN becomes high level, the N-ary programmable counter 24 starts counting, and after the elapse of time Tc, the timeout output v1 becomes the zero level. This output Vl is connected to the input of the JK flip-flop circuit 23, and at the same time as the output Vl goes high, the Q output goes low, causing the N-ary programmable counter 24 to complete counting. At the same time, the output v1 also serves as a start signal for the second counter 22, and the output v1 is connected to the reset terminal RS of the programmable counter 24 to clear the contents of the counter 24 and prepare for the next measurement.

FIG. 10 shows a pulse width measuring circuit and a 172 pulse width measuring circuit, the waveform-shaped pulse VP is connected to the enable terminal EH of the M-ary binary counter 26, and the clock pulse CP is based on the reference shown in FIG. It is the same as a clock pulse. The counter 26 counts during one bell when the pulse Vp goes high, and as a result, the output terminals Q1~
An initial value with a pulse width of l is output to the Q intestine. These outputs are connected to program terminals A1 to A (Peng-1) of the M-adic programmable binary counter 27. It should be noted that the program terminal LSB (L
ow 51gn1ficantbit) The terminal Q2 is input to the terminal AI, the terminal Q3 is input to the terminal A2, etc., shifted by one bit. This means that 1/2 of the pulse width is automatically programmed into the counter 27 because executing 172 in binary corresponds to shifting one bit to the right.

The timeout output Vl of the fixed time counter shown in FIG. 9 is connected to the J input of the JK flip-flop circuit 28. When the output v1 rises, the output Q of the JK flip-flop circuit 28 becomes high level, and the counter 27 is started. Since the counter 27 is programmed to be 1/2 of the measurement pulse time as described above, the timeout output v2 is output when 172 of the measurement pulse time has elapsed. Since this output v2 is connected to the terminal of the JK flip-flop circuit 28, the terminal Q becomes low level at this point, and counting by the counter 27 ends. At the same time, the output v2 clears the contents of the counters 26 and 27 in preparation for the next measurement. The output v2 is also input to an image recording controller (not shown) and starts recording 1547 minutes of images.

As explained above, according to the beam position detection device according to the present invention, at the same time as measuring the pulse width after waveform shaping, a certain period of time from the rise of the pulse after waveform shaping is measured, and after a certain period of time elapses, the measurement is performed first. By setting the time when 1/2 of the pulse width has elapsed as the image recording start point, it is possible to determine the image recording start point accurately without any adjustment.
High quality images can be obtained.

[Brief explanation of the drawing]

#IF5! J is an explanatory diagram of the beam detector placed on the scanning line, WIJ2 is a circuit diagram of the amplification/waveform shaping circuit, Fig. 3 is an explanatory diagram of the case where the synchronization pulse shifts depending on the incident scene, and Fig. 4 is an explanatory diagram of synchronization depending on the amount of incident light. A conventional block circuit configuration diagram for correcting pulse deviation, FIG. 5 is a waveform diagram thereof, FIG. Its principle explanatory diagram, Fig. 8 ~ M1
FIG. 0 is a block circuit configuration diagram. Reference numeral 5 is a beam detector, 6 is an amplification waveform shaping circuit, and 20
is the first counter, 21 is the pulse width measuring device, and 22 is the second counter.
counter, 24 is an N-ary programmable counter, 26
is an M-ary binary counter, and 27 is an M-ary programmable binary counter. Patent applicant: Canon Co., Ltd. Figure 1 Figure 13 Figure 4 Figure 5f! 1 Xf-m- C Shi-m Figure 6 Figure 8

Claims (1)

[Claims] 1. In the case of recording an image by main scanning a laser beam modulated by an image signal with a rotating polygon mirror, a light detection means for detecting the start time of image recording, and the detection signal means for shaping a waveform by comparing it with a predetermined reference value; means for measuring a pulse width that depends on the amount of incident light after said waveform shaping; means for measuring a certain period of time from the time when said pulse is detected; and a means for measuring a half cycle of the pulse width measured after a period of time has elapsed, and the image recording start time is set at the time when the sum of the fixed time from the time when the pulse was detected and the half cycle of the measured pulse width has elapsed. A beam position detection device characterized by: 2. The beam position detection device according to claim 1, wherein the measuring means is a counter that counts clock pulses.