JPH05127107A - Video clock signal generator - Google Patents

Abstract

PURPOSE:To obtain a proper threshold value, to make configuration simple and reduce cost, and to eliminate the loss of the quantity of light. CONSTITUTION:A linear scale 11 is provided with a pattern 13 for threshold value voltage setting reference which is wider than the diameter of spot light, and laser light is reflected by or transmitted through the pattern 13 and engraved stripes 10 to obtain a reference voltage and a voltage amplitude. The ratio of the reference voltage and voltage amplitude is calculated from the spot diameter of the laser light 51, the ratio of the width of the engraved stripes 10 and the width of the pattern 13 and constant, so the threshold value voltage is generated according to the reference voltage. Consequently, the threshold value voltage is determined according to this ratio to obtain the proper threshold value voltage even if the reference voltage varies owing to variation in the light output of a laser light source, variation in the photoelectric conversion efficiency of a detector 1, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to oscillate a laser beam to make it enter a linear scale, and to reflect or transmit the laser beam to a marking line formed on the linear scale so that the number of marking lines on the linear scale can be adjusted. The present invention relates to a video clock signal generator which outputs a corresponding pulse signal, and more particularly to determination of a threshold value when producing a video clock signal.

[0002]

2. Description of the Related Art As conventional video clock signal generators, there are those shown in FIGS. 6 and 7, respectively.

That is, the one shown in FIG. 6 determines a threshold value in advance from the optical output of laser light, the photoelectric conversion efficiency of the detector 1 for signal detection, etc., and the detection signal from the detector 1 is amplified by the amplifier circuit 2. The current-voltage conversion and amplification are performed, a predetermined threshold voltage is generated from the constant voltage generation circuit 17, and the comparison circuit 18 compares the threshold voltage with the amplified voltage.
The video clock signal is generated by performing a comparison process at.

In the structure shown in FIG. 7, the laser light is split and made incident not only on the detector 1 but also on the detector 19 for monitoring the light quantity, and the output from the detector 19 is calculated via the amplifier circuit 2. It is input to the circuit 20 and the threshold voltage is determined by the arithmetic circuit 20.

[0005]

However, in such a conventional video clock signal generator, in the former case, the optical output of the laser light source fluctuates, and the photoelectric conversion efficiency of the detector 1 fluctuates due to temperature changes and the like. However, there is a problem in that the predetermined threshold voltage may not be able to respond to these fluctuations, so that the original function may not be exhibited and the desired video clock signal may not be obtained. there were.

In the latter case, the detector 1 for detecting the signal and the detector 19 for monitoring the light quantity are required.
An optical system for distributing the laser light to each of the detectors 1 and 19 is required. Further, there is a loss of light quantity for distributing the laser light. Further, for example, when the photoelectric conversion efficiency of one of the two detectors 1 and 19 changes or there is a difference in the photoelectric conversion efficiency of the detectors 1 and 19, there is a difference. There is a problem in that the threshold voltage generated from is unsuitable.

The present invention has been made by paying attention to such a conventional problem, and has a simple structure using only one detector for signal detection, which reduces the cost and eliminates the loss of the light quantity. Another object of the present invention is to provide a video clock signal generator capable of obtaining an appropriate threshold voltage according to variations in the optical output of the laser light source.

[0008]

SUMMARY OF THE INVENTION The gist of the present invention for achieving such an object is that a linear scale (1
In the video clock signal generator, wherein the spot light is vibrated on the engraved line (10) of (1) to output a pulse signal according to the number of engraved lines (10),
0) is provided with a threshold voltage setting reference pattern (13) having a width wider than the diameter of the spot light on at least one of both ends in the pitch direction, and the threshold voltage setting reference pattern (13) is provided. ), A threshold voltage to be compared with the voltage obtained when the spot light is irradiated on the engraved line (10) is generated based on the reference voltage obtained when the spot light is irradiated. A video clock signal generator characterized by comprising a threshold voltage generating circuit (5).

[0009]

The laser light (51) from the laser light source vibrates and is incident on the linear scale (11), and the laser light (51) is used for the marking line (10) of the linear scale (11) and the threshold voltage setting reference. The pattern (13) is reflected or transmitted.

A pattern (1 for threshold voltage setting reference)
3) is wider than the spot light diameter, laser light (5
Depending on the relationship between the spot diameter of 1) and the scanning speed of the laser light (51), etc., the light quantity of the laser light (51) reflected or transmitted by the pattern (13) for threshold voltage setting reference, and the engraved line (10). The ratio of the amount of laser light reflected or transmitted by the light source is constant.

The ratio is constant regardless of the output of the laser light source, the photoelectric conversion efficiency of the detector (1), and the scanning speed.

That is, the laser beam (5
Voltage (P2) obtained when 1) is reflected or transmitted
Is a value obtained by proportionally dividing the reference voltage (P1) obtained when the laser light (51) is reflected or transmitted through the threshold voltage setting reference pattern (13), and according to the reference voltage (P1), If a threshold voltage is generated, the generated threshold voltage will always be appropriate.

Next, the threshold voltage and the marking line (10)
Compared with the voltage obtained when the laser light (51) is reflected or transmitted, the desired video clock signal can be obtained.

The reference voltage (P1) can be used as a reference for determining where the video clock signal is generated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the drawings.

1 to 4 show a first embodiment of the present invention.

As shown in FIG. 2, a scanner mirror 52 is provided which oscillates the laser light 51 from the laser light source and makes it enter the linear scale 11 via the lens 53. The laser light transmitted through the linear scale 11 is condensed on the detector 1 by the lens 55. The detector 1 has an SPD (silicone photo dio).
de) is commonly used.

FIG. 4 conceptually shows the linear scale 11. On the substantially rectangular substrate of the linear scale 11, engraved lines 10, 10 ... Are continuously provided at a constant pitch in the central portion in the longitudinal direction. The engraved lines 10 are formed so as to transmit the laser light, and the width of the engraved lines 10 in the pitch direction (scanning direction) is slightly smaller than the diameter of the spot light 12 of the laser light.
The space between the adjacent engraved lines 10 reflects or absorbs the laser light and is also slightly narrower than the diameter of the spot light 12.

At both ends of the linear scale 11, patterns 13 for threshold voltage setting reference are formed.

Pattern 13 for threshold voltage setting reference
Has the same optical characteristic as that of the engraved line 10 for transmitting the laser beam, and is formed sufficiently wider than the diameter of the spot beam 12 so that the entire spot beam 12 can be included in the pattern 13.

The scanner mirror 52 controls the amplitude of the spot light 12 so that the whole spot light 12 vibrates to a position where it enters the pattern 13 for threshold voltage setting reference at both ends.

As shown in FIG. 1, the detector 1 is connected to an amplifier circuit 2 for current-voltage converting and amplifying the detected signal, and the output terminal of the amplifier circuit 2 is connected to a peak voltage detecting circuit 3. There is. In the peak voltage detection circuit 3, the entire spot light 12 has the pattern 1 for the threshold voltage setting reference.
3 is to detect a reference voltage corresponding to the light amount of the laser light incident on the detector 1.

The peak voltage detection circuit 3 is provided with
It may be configured to be reset at appropriate intervals at the same timing.

The peak voltage detecting circuit 3 is connected to the threshold voltage generating circuit. The threshold voltage generation circuit is the first
It is composed of an arithmetic circuit 4 and a second arithmetic circuit 5. The first arithmetic circuit 4 is for calculating the threshold voltage Vth1, and the second arithmetic circuit 5 is for calculating the threshold voltage Vth2.

The threshold voltage Vth1 is set to a level at which only the signal based on the threshold voltage setting reference pattern 13 can be detected, and the threshold voltage Vth2 is set to a level at which the signal on the score line 10 can be detected.

The comparison circuit 6 and the comparison circuit 7 are connected to the output terminal of the amplifier circuit 2, and the comparison circuit 6 and the comparison circuit 7 are connected to the output terminal of the arithmetic circuit 5.

The comparison circuit 6 is a circuit for comparing the detection signal (the waveform is shown in FIG. 3) obtained when the linear scale 11 is scanned with the spot light 12 with the threshold voltage Vth1. Similarly, the comparison circuit 7 is a circuit that compares the detection signal with the threshold voltage Vth2.

The output terminal of the comparison circuit 6 is connected to the inverting gate 8. The output terminals of the inverting gate and the comparison circuit 7 are connected to the AND gate 9, respectively. The AND gate 9 is a circuit for digitally processing the signal a from the inverting gate 8 and the signal b from the comparison circuit 7. The AND gate 9 digitally processes the desired video clock signal c.

Next, the operation will be described.

When the laser light scans the linear scale 11, the detector 1 detects the transmitted light of the spot light 12 of the laser light.

At this time, the scanner mirror 52 is controlled so that the spot light 12 as a whole enters the pattern 13 for threshold voltage setting reference at both ends of the linear scale 11.

The detection signal detected by the detector 1 is shown in FIG.
The waveform becomes as shown in. The waveform of FIG. 3 has a large peak P1 generated corresponding to the pattern 13 for threshold voltage setting reference and a small peak P2 generated corresponding to the score line 10. The detection signal is current-voltage converted and amplified by the amplifier circuit 2, and then the reference voltage corresponding to the output level of the peak P1 of the detection signal is detected by the peak voltage detection circuit 3.

Based on the detected reference voltage, the first arithmetic circuit 4 and the second arithmetic circuit 5 obtain two threshold voltages.

The threshold voltage Vth1 is input to the comparison circuit 6 at a voltage value slightly lower than the reference voltage. Similarly, the threshold voltage Vth2 is input to the comparison circuit 7 at a voltage value lower than the threshold voltage Vth1 by a predetermined ratio.

The signal output from the comparison circuit 6 is inverted by the inverting gate 8 and the signal a is output from the inverting gate 8. In the signal a, the portion of the voltage higher than the threshold voltage Vth1 is represented by the L- level.

Further, the comparison circuit 7 outputs the signal b.

The threshold voltage Vth2 can be determined based on the reference voltage because the ratio of the reference voltage and the voltage obtained when the laser light is reflected or transmitted through the marking line 10 is constant. ..

At this time, if the peak voltage detection circuit 3 is reset at the same timing and at appropriate intervals, it is possible to appropriately respond to variations in the optical output of the laser light source, and as a result, appropriate The reference voltage can always be obtained.

Further, the signal a and the signal b are input to the AND gate 9 and digitally processed by the AND gate 9 to obtain the clock signal c.

FIG. 5 shows a second embodiment of the present invention.

In this embodiment, the linear scale detector 15 having a pattern in which reflection or transmission is opposite to that of the linear scale 11 is shown.

That is, the engraved line 14 and the threshold voltage setting reference pattern 16 are reflection or absorption patterns.

In the above embodiment, the linear scale 1
Although the patterns 13 and 16 for the threshold voltage setting reference are provided at both ends of 1 and 15, respectively, it is sufficient to provide the patterns 13 and 16 at at least one of both ends.

[0044]

According to the video clock signal generator of the present invention, the linear scale is provided with a threshold voltage setting reference pattern wider than the diameter of the spot light, and the laser beam is reflected or transmitted through the pattern. Since the threshold voltage is generated based on the reference voltage obtained at this time, it is possible to obtain an appropriate threshold voltage according to the change in the optical output of the laser light source. In addition, a simple configuration using only one detector for signal detection can reduce the cost and eliminate the loss of the light quantity.

[Brief description of drawings]

FIG. 1 is a block diagram of a video clock signal generator showing a first embodiment of the present invention.

FIG. 2 is an explanatory view showing an arrangement state of a linear scale showing the first embodiment of the present invention.

FIG. 3 is a waveform diagram of a detection signal showing the first embodiment of the present invention.

FIG. 4 is a front view of the linear scale showing the first embodiment of the present invention.

FIG. 5 is a front view of a linear scale showing a second embodiment of the present invention.

FIG. 6 is a block diagram of a video clock signal generator showing a conventional example.

FIG. 7 is a block diagram of a video clock signal generator showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Detector 2 ... Amplification circuit 3 ... Peak voltage detection circuit 4 ... 1st calculation circuit 5 ... 2nd calculation circuit 6, 7 ... Comparison circuit 8 ... Inversion gate 9 ... AND gate 10 ... Marking line 11 ... Linear scale 12 ... Spot Light 13 ... Threshold voltage setting reference pattern 52 ... Scanner mirror

Claims (1)

[Claims] 1. A video clock signal generator which oscillates spot light on a marking line of a linear scale and outputs a pulse signal according to the number of marking lines, wherein both end portions of the marking line in the pitch direction are provided. A pattern for threshold voltage setting reference having a width wider than the diameter of the spot light is provided on at least one side, and a reference voltage obtained when the pattern for threshold voltage setting reference is irradiated with the spot light. Based on the above, a video clock signal generator comprising a threshold voltage generating circuit for generating a threshold voltage to be compared with a voltage obtained when the spot light is irradiated on the marking line. ..