JPH08292264A - Laser doppler speed measuring equipment and color image forming equipment using the same - Google Patents

Abstract

PURPOSE: To measure the speed of a continuous substance to be measured, by judging whether the light reception level of a light-receiving means is within the allowable limits or not and by controlling the quantity of light of a light source so as to make the level be within the limits when it is outside the limits. CONSTITUTION: A beam LB of a laser light source l is divided in two, beams LB1 and LB2 , by a half mirror 2 and the same point on a substance 7 to be measured is irradiated by direct transmitted light and by reflected light via a mirror 3, a crossing angle θ being formed by them. Scattered light 9 from the point is passed through a lens 4 and detected by a photosensor 5. The photosensor 5 is connected with a light reception level discriminating circuit 6 discriminating light reception levels on the basis of an output of the sensor and with a conversion circuit 8 converting cycles of the light reception level and a reference value thereof into current values. When the light reception level of the sensor 5 is outside the allowable limits, the quantity of light of the light source l is controlled by the circuit 8 so that it be kept within the limits. The output of the sensor 5 is passed through an amplifier 10 and subjected to heterodyne detection by BPF 11, a Doppler signal is detected therefrom and the speed of the substance 7 is determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a plurality of laser beams onto an object to be measured, and detects the frequency shift of scattered light that is Doppler-shifted according to the speed of the object to be measured, in a non-contact state. The present invention relates to a laser Doppler velocity measuring device for measuring the moving velocity of an object to be measured and a color image forming device using the same.

[0002]

2. Description of the Related Art Conventionally, as the non-contact type speed measuring device, for example, a device adopting a laser Doppler system has been used. FIG. 9 shows the measuring principle of a speed measuring device adopting the laser Doppler method. A He-Ne laser or a semiconductor laser is often used as the light source 101 of the laser Doppler type speed measuring device. In the laser Doppler type speed measuring device, the laser beam LB emitted from the laser light source 101 is divided into two by the beam splitter 102, and one laser beam LB
Is transmitted through the beam splitter 102 to directly irradiate the object to be measured 107, and the other laser beam LB is reflected by the mirror 103 to irradiate the object to be measured 107, so that the two laser beams LB intersect each other at an intersection angle θ. Then, the object to be measured 107 is irradiated. Then, the scattered light scattered by the object to be measured 107 moving at a certain speed v is collected by the condenser lens 1.
The light receiving sensor 105 formed of a photoelectric conversion element or the like passes through an optical system 04 and the like, the detection signal of the light receiving sensor 105 is amplified by an amplifier 108, and heterodyne detection is performed via a band pass filter (BPF) 109 to obtain Doppler. Get the signal. The Doppler frequency of the Doppler signal detected at this time is expressed by the following equation. f _D = (2v) sin (θ / 2) / λ where f _D is the Doppler frequency and v is the DUT 107.
, Λ is the wavelength of the laser light, and θ is the beam crossing angle.

Doppler frequency f in the above equation
_{Since D} is proportional to the speed v of the object 107 to be measured, this laser Doppler speed measuring device measures the speed v of the object 107 to be measured by extracting the Doppler signal and performing a predetermined signal processing. You can do it.

By the way, in the speed measuring device adopting the laser Doppler system constructed as described above, the output from the light receiving sensor 105 is the above formula in which the reflected light (DC component) from the object to be measured 107 is the Doppler frequency. Signal (AC
Ingredients) are included. Further, the reflected light (DC component) 110 from the object to be measured 107 is, as shown in FIGS. 10 and 11, two laser beams LB which are irradiated to the object to be measured 107 at a predetermined angle θ. Signals that are lower than the Doppler frequency called the pedestal component due to the fact that they interfere with each other as shown in FIG.
1 is also included. Furthermore, random noise of many frequencies is superimposed on the output signal of the speed measurement device adopting the laser Doppler method.

In the case of the laser Doppler type speed measuring device, the speed v of the object 107 to be measured can be measured by the wavelength λ of the laser beam and the beam crossing angle θ.
Since the position of the object to be measured 107 is changed or the type of the object to be measured 107 is changed,
When the reflectance (or the transmittance) of 07 changes, there is a problem that the velocity v of the object 107 to be measured may become impossible to measure. Further, in the case of the laser Doppler type speed measuring device, as shown in FIG.
If the distribution of scattered light amount is different due to the difference in the measurement surface of 7,
There is a problem that the amount of reflected light incident on the light receiving sensor 105 changes, and the light receiving level decreases or rises, and the velocity v of the DUT 107 may become unmeasurable.

Therefore, as a technique for removing the noise contained in the Doppler signal, for example, Japanese Patent Laid-Open No. 55-
Some are disclosed in Japanese Patent No. 51379. Since the Doppler velocity measuring apparatus according to Japanese Patent Laid-Open No. 55-51379 divides the scattered light into two in the optical path for receiving the scattered light from the object to be measured which is subjected to the Doppler effect by using the laser light, And a subtraction circuit for taking the difference between the electric output of the photoelectric conversion element and the photoelectric conversion element for respectively receiving the scattered light divided by the optical means, and the output to be measured from the subtraction circuit. A means for detecting the speed of the body is provided, the light scattered by the measured object is divided into two, each divided light is acquired by a separate photoelectric conversion element, and the two photoelectric conversion elements are differential amplifiers. The DC component is removed by an arithmetic circuit such as to obtain a Doppler frequency signal having a good SN ratio.

Further, as a technique for avoiding an unmeasurable state of the velocity v of the object 107 to be measured, for example, JP-A-4-151588 and JP-A-62-299778 are available.
Japanese Patent Application Laid-Open No. 4-25788 and Japanese Patent Application Laid-Open No. 4-2.
The one disclosed in Japanese Patent No. 5787 has already been proposed.

In the devices disclosed in Japanese Patent Laid-Open No. 4-151588 and Japanese Patent Laid-Open No. 62-299778, a probe or a probe is received according to the distance information from the probe including the light receiving sensor to the object to be measured and the level information of the light receiving sensor. The structure for moving the converging lens is adopted to prevent the measurement from becoming impossible. Further, in the above-mentioned Japanese Patent Laid-Open No. 25788/1992, the position of the light receiving sensor is made variable so as to prevent the measurement from being disabled due to a decrease in the light receiving level. Further, in the above-mentioned Japanese Patent Application Laid-Open No. 4-25787, measurement is performed at a plurality of points from a plurality of sets of incident optical system and light receiving system, the velocity is obtained from a signal output from at least one light receiving system, and measurement is impossible due to a decrease in light receiving level. It prevents the occurrence of a condition.

To further describe the technique according to the above proposal, the laser Doppler velocimeter according to Japanese Patent Laid-Open No. 4-151588 discloses a laser generating means for outputting light of a specific wavelength and an output beam of the laser generating means. A beam splitter that divides the beam into two, a plurality of mirrors that can irradiate the moving object with the directions of the two divided laser beams intersecting each other, and a Doppler shift according to the speed of the moving object for each of the two irradiation beams. Lens system for receiving the scattered light caused by the above, a photodetector for electrically converting the scattered light including the Doppler signal received by the lens system, an optical base for accommodating all the above components, and the photodetection An amplifier for amplifying the output of the container, a Doppler frequency detecting means for detecting the Doppler frequency from the signal amplified by the amplifier,
In a laser Doppler velocimeter equipped with a velocity calculator that calculates the velocity of a moving object from the Doppler frequency that is the output signal of the Doppler frequency detecting means, the velocity of the received light is modulated near the coupling point of the lens system. A vibrator with a pinhole that vibrates for that purpose, and a distance fluctuation detecting means for detecting a distance fluctuation between the moving object and the optical base from a velocity modulation signal by the vibrator with a pinhole obtained at the output of the photodetector. The control means controls the distance variation detection signal of the distance variation detecting means so that the distance between the moving object and the optical base is always constant.

The laser Doppler velocimeter disclosed in Japanese Patent Laid-Open No. 62-299778 irradiates the surface of an object to be measured with a laser beam passing through a beam splitter and a converging lens, and measures scattered light from the surface. For moving a converging lens by using a photodetector composed of a plurality of light receiving elements in an apparatus for condensing on a detection surface of a photodetector by a lens for processing and processing a signal of the photodetector by a signal processor Is provided, and the actuator is controlled based on the change in the ratio of the light intensity received by each light receiving element.

Further, the Doppler velocimeter according to the above-mentioned Japanese Patent Laid-Open No. 25788/1992 makes an irradiation light beam of wavelength λ incident on a moving object at a predetermined incident angle θ, and shifts the frequency of scattered light from the moving object. In the velocimeter for detecting the velocity information of the moving object based on the above, the incident light flux is changed so that the incident angle θ changes in accordance with the change of the wavelength λ of the irradiation light flux and sin θ / λ becomes substantially constant. It has an optical system for making it incident on a moving object, and has an adjusting means for adjusting the detection area on the moving object surface to be variable in a direction different from the moving direction when detecting scattered light from the moving object. It is configured as follows.

Further, the Doppler velocimeter according to the above-mentioned Japanese Patent Laid-Open No. 25787/1992 makes an irradiation light beam of wavelength λ incident on a moving object at a predetermined incident angle θ, and shifts the frequency of scattered light from the moving object. In the velocimeter for detecting the velocity information of the moving object based on the above, the incident light flux is changed so that the incident angle θ changes in accordance with the change of the wavelength λ of the irradiation light flux and sin θ / λ becomes substantially constant. An optical system having an optical system for making it incident on a moving object is provided, and an optical means for making the irradiation light incident on a plurality of positions different from the moving direction of the moving object surface is provided, and scattered light from the plurality of positions is respectively detected by a plurality of detecting means. It is configured to detect and use the output signal from at least one of the plurality of detecting means to obtain the moving speed of the moving object.

[0013]

However, the above-mentioned prior art has the following problems. That is, the apparatus disclosed in Japanese Patent Laid-Open No. 55-51379 according to the above proposal divides the light scattered by the object to be measured into two, obtains each divided light by separate photoelectric conversion elements, and obtains two photoelectric conversion elements. Is configured to remove a DC component by an arithmetic circuit such as a differential amplifier to obtain a Doppler frequency signal having a good SN ratio. In this case, the Doppler frequency signal is detected from the photoelectric conversion element. Even if the noise generated during the process can be removed, there is a problem that the noise included in the scattered light from the object to be measured cannot be effectively removed.

Further, Japanese Patent Laid-Open No. 4-1515 related to the above proposal
In the case of the devices of JP-A-88, JP-A-62-299778, JP-A-4-25788, and JP-A-4-25787, even if the position of the object to be measured changes, measurement is performed from the probe. Depending on the distance information to the object and the level information of the light receiving sensor, the probe or the focusing lens is moved, or multiple points are measured from multiple sets of the incident optical system and the light receiving system, and output from at least one light receiving system. By obtaining the speed from the signal, it is possible to avoid to some extent the occurrence of the unmeasurable state due to the decrease in the light receiving level.

However, in the apparatus according to the above-mentioned Japanese Patent Laid-Open No. 4-151588, for example, a plurality of image forming means for forming images of different colors are arranged in parallel with each other, and a plurality of these image forming means are formed. A color image forming apparatus that forms a color image by sequentially transferring a plurality of images of different colors sequentially formed by a transfer unit onto a transfer medium that is held on a transfer belt that is controlled to cyclically move at a predetermined speed. In the case of application, since the object to be measured 107 is a member such as a transfer sheet or a translucent transfer belt that conveys the transfer sheet in a sucked state, the reflectance of the object to be measured 107 ( Or, the transmittance) and the surface state greatly differ depending on the type of the object 107 to be measured. On the other hand,
In the above laser Doppler type speed measuring device, the measurable speed v of the measured object 107 is determined by the wavelength λ of the laser light, the beam crossing angle θ, etc., and therefore the reflectance (or transmittance) of the measured object 107 is determined. ) Etc., there is a problem that the speed v of the object to be measured 107 cannot be measured. When measuring the speeds of both objects to be measured, such as the above-mentioned transfer paper or translucent transfer belt, which have different reflectance (or transmittance), when measuring one after measuring the other It is necessary to change the settings of the laser beam light quantity, the position of the light receiving sensor, the angle of the light receiving sensor, etc., and the measured values may be interrupted over time. There was also the problem that it could not be measured.

Further, in the case of the Doppler velocimeter disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 4-25788, the incident angle θ changes according to the change of the wavelength λ of the irradiation light beam so that sin θ / λ becomes almost constant. An optical system for causing the irradiation light flux to enter the moving object, and when detecting scattered light from the moving object, a detection area on the moving object surface is variable in a direction different from the moving direction. Although it is configured to have an adjusting means for adjusting, when the sensor probe composed of an optical system for making the irradiation light beam enter the moving object by the adjusting means is inclined and the measurement is attempted, the level of the reflected light amount decreases and the measurement is performed. There is a problem that it becomes impossible.

Therefore, the present invention has been made in order to solve the above-mentioned problems of the prior art. The object of the present invention is to effectively remove the influence of noise and to measure the object to be measured. Laser Doppler velocity measuring device capable of continuously measuring the velocity of an object to be measured with a relatively simple structure without changing the settings even when the reflectance or surface condition is different, and a color image formation using the same To provide a device.

[0018]

A laser Doppler velocity measuring apparatus according to claim 1 of the present invention separates one laser beam having a wavelength λ into two or more laser beams on an object to be measured. An illumination optical system for irradiating the same position on the object to be measured, the scattered light scattered at the irradiation position on the object to be measured is received by the light receiving means, and the Doppler signal is detected from the received light signal to be measured. In a laser Doppler velocity measuring device for measuring the speed of an object, when the light receiving level of the light receiving means is outside the allowable range, and a determining means for determining whether the light receiving level of the light receiving means is within the allowable range. Is provided with a light quantity control means for controlling the light quantity of the laser light source so that the light receiving level of the light receiving means falls within an allowable range.

Further, in the color image forming apparatus according to the second aspect of the present invention, a plurality of image forming means for forming images of different colors are arranged in parallel with each other, and the plurality of image forming means successively perform the image forming means. An apparatus for forming a color image by sequentially transferring a plurality of formed images having different colors to a transfer medium held on a transfer belt controlled to circulate at a predetermined speed. The transfer belt or the transfer medium having an illumination optical system for separating one laser beam having a wavelength λ into two or more laser beams and irradiating the same position on the transfer belt on the transfer belt holding the transfer belt. A laser dopp that receives the scattered light scattered at the irradiation position above by the light receiving means and detects the Doppler signal from the received light signal to measure the moving speed of the transfer belt or the transfer medium. -In a color image forming apparatus using a speed measuring device, a determining means for determining whether or not the light receiving level of the light receiving means is within an allowable range and a light receiving level of the light receiving means is outside the allowable range. Is provided with a light quantity control means for controlling the light quantity of the laser light source so that the light receiving level of the light receiving means falls within an allowable range.

[0020]

The laser Doppler velocity measuring apparatus and the color image forming apparatus using the same according to the above-mentioned claim 1 and claim 2, and a discriminating means for discriminating whether or not the light receiving level of the light receiving means is within an allowable range. When the light receiving level of the light receiving unit is out of the allowable range, the light receiving unit is configured to include a light amount control unit for controlling the light amount of the laser light source so that the light receiving level of the light receiving unit falls within the allowable range. So
When the reflectance or surface condition of the object to be measured is different and whether the light receiving level of the light receiving means is within the allowable range is determined by the determining means, and the light receiving level of the light receiving means is outside the allowable range, The reflectance (transmittance) of the object to be measured is controlled by controlling the light quantity of the laser light source by the light quantity control means so that the light receiving level of the light receiving means falls within the allowable range.
Even when the value changes significantly or the surface condition of the DUT changes, the effect of noise can be effectively eliminated by the received light signal that is within the allowable range, and the continuous measurement can be performed without changing the setting. It is possible to measure the speed of the measurement object.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments.

FIG. 4 shows an embodiment of a color image forming apparatus to which the laser Doppler velocity measuring device according to the present invention is applied.

In this color image forming apparatus, as shown in FIG. 4, a black image forming section 51 for forming a black (K) color image.
a, a yellow image forming portion 51b that forms a yellow (Y) image, a magenta image forming portion 51c that forms a magenta (M) image, and a cyan that forms a cyan (C) image. The color image forming section 51d is provided with four image forming sections, and these four image forming sections 51a, 5a,
1b, 51c and 51d are horizontally arranged at a constant interval. Further, the four image forming portions 51a, 51 for the black, yellow, magenta and cyan colors are provided.
Below the b, 51c, and 51d, the transfer paper 53 conveyed by the paper feed roller 55 is electrostatically adsorbed, and the transfer paper 53 is transferred to the transfer positions of the image forming units 51a, 51b, 51c, and 51d. A transfer belt 52 is arranged as an endless transfer material carrier to be conveyed. The transfer belt 52 is formed of a semi-transparent synthetic resin or the like into an endless belt shape, and includes a plurality of rollers 57 and 58 including drive rollers.
It is possible to move in a circular fashion.

The above four image forming portions 51a, 51b, 51c, 5 for black, yellow, magenta and cyan are provided.
1d has the same configuration, and black, yellow, magenta, and cyan toner images are sequentially formed on these four image forming portions 51a, 51b, 51c, and 51d, respectively, as described above. Is configured. The image forming units 51a, 51b, 51c of the respective colors,
51d includes a photoconductor drum 59. A toner image of a predetermined color is formed on the surface of the photoconductor drum 59 through a charging process, an image exposure process, and a developing process.
The toner images of a predetermined color formed on the transfer belt 52 are sequentially transferred onto the transfer paper 53 electrostatically held on the transfer belt 52 in a state of being superimposed on each other. And black, yellow,
The transfer paper 53 on which the magenta and cyan toner images have been multi-transferred is separated from the transfer belt 52 and then subjected to a fixing process by a fixing device 56 to form a color image.

In the color image forming apparatus constructed as described above, the black, yellow, magenta, and magenta colors formed by the respective image forming units are formed on the transfer paper 53 electrostatically held on the transfer belt 52. A color image is formed by sequentially transferring a cyan toner image. Therefore, in order to prevent color deviation of the toner images of the respective colors and form a high-quality color image in the color image forming apparatus, it is necessary to accurately control the moving speed of the transfer belt 52 to a predetermined value. It is necessary to accurately detect the rotation speed of the transfer belt 52. Therefore, in the vicinity of the transfer belt 52, a laser Doppler speed measuring device 54 capable of accurately detecting the moving speed of the transfer belt 52 in a non-contact state is arranged.

FIG. 1 shows an embodiment of a laser Doppler velocity measuring device applied to the above color image forming apparatus.

In FIG. 1, reference numeral 1 denotes a laser light source which emits a laser beam LB. The laser beam LB emitted from the laser light source 1 is divided into two by a half mirror 2 and two laser beams LB1 and LB2,
The laser beam LB1 that has passed through the half mirror 2 is directly irradiated onto the DUT 7, and the laser beam LB2 reflected by the half mirror 2 is reflected again by the mirror 3 to the same point on the DUT 7. Are irradiated so as to form a crossing angle θ with the other laser beam LB1.
The scattered light 9 reflected by the DUT 7 is
A plurality of light receiving sensors 5 are simultaneously detected. The scattered light 9 reflected from the object 7 to be measured, that is, in the direction orthogonal to the surface of the object 7 to be measured is condensed by the condenser lens 4 and is incident on the light receiving sensor 5.

Although a signal having a Doppler frequency is present in the output of the light receiving sensor 5, the bias component (DC component) changes depending on the amount of scattered light reflected from the DUT 7. As shown in FIG. 2, if the bias component (DC component) of the output of the light receiving sensor 5 is within the allowable range, the speed of the DUT 7 can be continuously measured.
When the value deviates from the allowable range due to the extreme decrease or increase of the reflectance of the object, the change of the surface condition, or the like, it becomes difficult to obtain a good Doppler frequency signal and the influence of noise becomes large.

Therefore, in this embodiment, when the bias amount of the light receiving sensor 5 deviates from the allowable range, the amount of deviation from the reference value is converted into the light amount of the laser light source and fed back to the current source of the laser light source, and the light receiving sensor. The output is controlled to be within the reference value range.

That is, as shown in FIG. 1, the light receiving sensor 5 detects the output of the light receiving sensor 5 and judges the light receiving level, and the light receiving level reference value and the current light receiving level. A conversion circuit 8 for converting the difference into a current value is connected. Then, the output of the light receiving sensor 5 is amplified by the amplifier 10 via the light receiving level determination circuit 6, and the band pass filter (BP)
F) 11 performs heterodyne detection to detect a Doppler signal. In addition, the band pass filter (B
The Doppler signal detected by the PF) 11 is subjected to predetermined signal processing by a counter and an analyzer (not shown) to measure the velocity v of the DUT 7.

The output of the light receiving sensor 5 is, as described above, the amplifier 10 and the band pass filter (BPF) 1.
1 and a counter and an analyzer (not shown) perform predetermined signal processing to convert the signal into a speed including a Doppler frequency. The Doppler frequency is represented by the following equation, as described above. f _D = (2v) sin (θ / 2) / λ where f _D is the Doppler frequency, v is the moving speed of the DUT 7, λ is the wavelength of the laser beam LB, and θ is the beam crossing angle.

FIG. 3 shows a concrete circuit configuration of the light receiving level determining circuit 6 and the converting circuit 8 for converting the difference between the light receiving level reference value and the current light receiving level into a current value.

In FIG. 3, reference numeral 5 denotes the light receiving sensor, and the output of the light receiving sensor 5 is input to one input terminal of each of the two comparators 61a and 61b and corresponds to the light receiving sensor 5. Two comparators 61a, 6
Two threshold values corresponding to the upper limit and the lower limit of the light receiving level allowable range are input to the other input terminal of 1b. An "H" level signal is output from the comparators 61a and 61b when the output from the light receiving sensor 5 is less than or equal to the upper limit threshold value of the light receiving level allowable range and greater than or equal to the lower limit threshold value. It is supposed to be done. Further, an AND circuit 62 for discriminating whether or not the light receiving level is within an allowable range is connected to the output terminals of the two comparators 61a, 61b corresponding to the light receiving sensor 5, and from this AND circuit 62, 2 The "H" level signal is output only when the outputs of the two comparators 61a and 61b are both at the "H" level.

The output from the AND circuit 62 is input to the ROM 81 which constitutes the conversion circuit 8 for converting the difference between the light-reception level reference value and the current light-reception level into a current value. This R
For the OM 81, a lookup table for converting the deviation amount between the light reception level reference value and the current light reception level into the laser light source light amount is stored in advance. The laser light source light amount converted from this deviation amount is used as a laser light source. Other configurations may be used as long as they feed back to the current source of the light source 1. As the contents written in advance in the ROM 81, for example, the output from the AND circuit 62 is "
In the case of the L ″ level, that is, when the light receiving level of the light receiving sensor 5 is outside the allowable range, the difference between the output of the light receiving sensor 5 and the reference value of the light receiving level is obtained by the subtractor 82, and the output of this light receiving sensor 5 is obtained. Depending on the difference between the received light level and the reference value,
What determines the increase value of the light amount of the laser light source 1 is used so that the light receiving level of the light receiving sensor 5 becomes equal to the reference value. The output from the ROM 82 is added to an initial set current value by an adder 83, and the light amount of the laser light source 1 is increased via a laser oscillation driver 84.

With the above structure, the laser Doppler velocity measuring apparatus according to this embodiment can effectively eliminate the influence of noise as follows.
Even if the reflectance or surface state of the measured object is different, the speed of the measured object can be continuously measured without changing the setting. That is, in the laser Doppler velocity measuring device, as shown in FIG.
The laser beam LB emitted from the laser beam is divided into two by the half mirror 2 into two laser beams LB1 and LB2,
The light is transmitted through the half mirror 2 or reflected by the half mirror 2 and the mirror 3 to irradiate the same point on the DUT 7 so as to form a crossing angle θ with each other. Then, the DUT 7
The scattered light 9 reflected by is detected by the light receiving sensor 5 via the condenser lens 4, the Doppler signal is detected based on the output from the light receiving sensor 5, and the moving speed v of the DUT 7 is measured. It

By the way, in the color image forming apparatus to which the laser Doppler velocity measuring device is applied, as shown in FIG. 4, the transfer sheet 53 is conveyed while being held on the transfer belt 52, and the transfer sheet 53 is held. Transfer belt 52
By measuring the moving speed of the sheet and the moving speed of the transfer sheet 53 by the laser Doppler speed measuring device 54,
The moving speed of the transfer belt 52 is controlled to be equal to a predetermined speed.

However, the transfer belt 5 which is the object to be measured 7 is
Since 2 is made of a semitransparent synthetic resin film, its reflectance (transmittance) is significantly different from that of the transfer paper 53, and the transfer belt 52 and the transfer paper 53, which are the DUTs 7, are as shown in FIG. , The surface condition is different. Therefore, the amount of reflected light incident on the light receiving sensor 5 becomes lower than the allowable range, and in this state as it is, the influence of noise becomes large, and it may not be possible to measure the speed of the DUT 7.

In this embodiment, as shown in FIG. 6, the output of the light receiving sensor 5 is monitored by the circuit shown in FIG. 3 (step 1). Next, it is judged whether or not the light receiving level of the light receiving sensor 5 is within the reference value range (step 2). If the light receiving level of the light receiving sensor 5 is within the reference value range, the light is received as it is. A Doppler frequency signal is output based on the output of the sensor 5 (step 3). That is, the output from the light receiving sensor 5 is, as shown in FIG. 3, a comparator 61 in which the upper and lower threshold values of the allowable range of the light receiving level are input to one input terminal.
If the light receiving level of the light receiving sensor 5 is not within the allowable range, the output of one or both of the two comparators 61a and 61b becomes the "L" level. Therefore, the above two comparators 6
In the AND circuit 62 to which the outputs of 1a and 61b are input,
It is determined whether the received light level is within the allowable range, and if the output of either one of the two comparators 61a and 61b is at the "L" level, it is determined that the received light level is outside the allowable range, and "
An L "level signal is output.

When the light receiving level of the light receiving sensor 5 is not within the reference value range, the light receiving sensor 5
The difference between the received light level and the reference value of the
A current value that increases or decreases from the calculated light amount is determined by the ROM 81 (step 4). Next, the current value determined by the ROM 81 is added to the initial set current value by the adder 83 (step 5). Then, a current obtained by adding the current value determined by the ROM 81 to the initially set current value is supplied to the laser light source 1 through the laser oscillation driver 84, and the light amount of the laser light source 1 changes, It is determined whether or not the output of the light receiving sensor 5 is within the reference value range (step 6), and when the output of the light receiving sensor 5 is within the reference value range, the process returns to step 1. If the output of the light receiving sensor 5 does not fall within the reference value range, an error message is displayed and the current source is stopped (step 7).

At this time, the rising characteristics of the laser light amount of the semiconductor laser used as the laser light source 1 are shown in FIG.
As shown in, there is almost no rise delay time,
Even when the laser light amount of the laser light source 1 is controlled during measurement of the moving speed of the DUT 7, there is no problem in the operation of measuring the moving speed of the DUT 7.

As described above, in the above embodiment, it is determined whether or not the light receiving level of the light receiving sensor 5 is within the allowable range, and if the light receiving level of the light receiving sensor 5 is outside the allowable range. Is configured to include a conversion circuit 8 for controlling the light amount of the laser light source so that the light receiving level of the light receiving unit falls within an allowable range. Differently, whether or not the light receiving level of the light receiving sensor 5 is within the allowable range is determined by the light receiving level determining circuit 6, and when the light receiving level of the above light receiving sensor 5 is out of the allowable range, the light receiving sensor 5 concerned.
Laser light source 1 so that the received light level of
Even if the reflectance (transmittance) of the DUT 7 changes greatly or the surface condition of the DUT 7 changes, the received light signal within the allowable range can be controlled by controlling the light amount of The influence of noise can be effectively removed, and the velocity of the object to be measured can be continuously measured without changing the setting.

FIG. 8 shows a second embodiment of the present invention. The same parts as those in the above-mentioned embodiment are designated by the same reference numerals. In this embodiment, the light quantity of the laser light source 1 is changed. Even during the control, the measurement value of the moving speed of the DUT 7 is configured so as not to be missing.

That is, in this embodiment, the light receiving sensor 5
Is provided with a hold circuit 85 for interpolating the output signal of the light receiving sensor 5 and a selector 86 for switching the output signal of the light receiving sensor 5, and when the output of the light receiving sensor 5 is out of the allowable range, R
While the light quantity of the laser light source 1 is controlled by the operation of the OM 81, the output signal of the light receiving sensor 5 immediately before the control which is temporarily stored in the hold circuit 85 is output to measure the moving speed of the DUT 7. It prevents the omission.

The other structure and operation are the same as those of the above-mentioned embodiment, and the description thereof will be omitted.

[0045]

EFFECTS OF THE INVENTION The present invention has the above-mentioned structure and operation, and can effectively remove the influence of noise, and can be set even when the reflectance or surface condition of the object to be measured is different. It is possible to provide a laser Doppler velocity measuring device capable of continuously measuring the velocity of an object to be measured without changing the above and a color image forming device using the same.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a laser Doppler velocity measuring device according to the present invention.

FIG. 3 is a graph showing the output of the light receiving sensor.

FIG. 3 is a block diagram showing an output level determination circuit and a light amount control circuit of a light receiving sensor.

FIG. 4 is a configuration diagram showing a color image forming apparatus to which an embodiment of the laser Doppler velocity measuring device according to the present invention is applied.

5 (a), (b), and (c) are explanatory views respectively showing a light scattering state due to a surface state of the object to be measured.

FIG. 6 is a flowchart showing the operation of an embodiment of the laser Doppler velocity measuring device according to the present invention.

FIG. 7 is a graph showing changes in the light amount of a laser light source.

FIG. 8 is a main part configuration diagram showing a second embodiment of the laser Doppler velocity measuring device according to the present invention.

FIG. 9 is a configuration diagram showing a conventional laser Doppler velocity measuring device.

FIG. 10 is a graph showing an output signal of the laser Doppler velocity measuring device.

FIG. 11 is a graph showing an output signal of the laser Doppler velocity measuring device.

FIG. 12 is an explanatory diagram showing a laser beam with which an object to be measured is irradiated.

[Explanation of symbols]

1 laser light source, LB1, LB2 laser beam, 2
Half mirror, 3 mirror, 4 condenser lens, 5a, 5
b, 5c, 5d, 5e light receiving sensor, 6 light receiving level determination circuit, 7 DUT, 8 conversion circuit.

Claims (2)

[Claims] 1. An illumination optical system for separating one laser beam having a wavelength λ into two or more laser beams and irradiating the same position on the object to be measured is provided on the object to be measured. In a laser Doppler velocity measuring device that receives scattered light scattered at an irradiation position on an object by a light receiving means and detects a Doppler signal from the light receiving signal to measure the speed of the object to be measured, the light receiving level of the light receiving means And a laser light source so that the light receiving level of the light receiving unit falls within the allowable range when the light receiving level of the light receiving unit is out of the allowable range. A laser Doppler velocity measuring device comprising a light amount control means for controlling the light amount of the laser. 2. A plurality of image forming means for forming images of different colors are arranged in parallel with each other, and a plurality of images of different colors sequentially formed by the plurality of image forming means are provided at a predetermined speed. A device for forming a color image by sequentially transferring to a transfer medium held on a transfer belt which is controlled so as to circulate with a transfer belt, which has a wavelength of λ on the transfer belt holding the transfer medium. Has an illuminating optical system that splits the laser beam into two or more laser beams and irradiates the same position on the transfer belt, and scatters light scattered at the irradiation position on the transfer belt or the transfer medium by the light receiving means. In a color image forming apparatus using a laser Doppler speed measuring device that receives light and detects the Doppler signal from the received light signal to measure the moving speed of the transfer belt or the transfer medium, If the light receiving level of the light receiving means is outside the permissible range, the light receiving level of the light receiving means is within the permissible range. As described above, a color image forming apparatus using a laser Doppler velocity measuring device provided with a light amount control means for controlling the light amount of a laser light source.