JP2003262782A - Position detector, auto-focus apparatus and image recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position detector and an auto-focus apparatus which can be realized by simple and inexpensive structure and to provide an image recorder which records an image corresponding to an image signal in a recording material by using these position detector or auto-focus apparatus. <P>SOLUTION: Light beams which form an image in the neighborhood of the surface of an object is emitted from a light source, and reflected light scattered on the surface of the object is caught by an optical detection element to obtain the current signal of a current value. This current signal is converted to the voltage signal of a voltage level according to the current value, the maximum value and the minimum value per a unit time of the voltage signal are respectively detected to calculate the voltage of the difference between the maximum value and the minimum value of the voltage signal. Then, the voltage of the difference is compared with a reference value. According to the compared result, it is discriminated whether the object exists within a prescribed range decided by the reference value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device for determining whether or not an object is within a predetermined range, so that a light beam emitted from a light source forms an image near the surface of the object. The present invention relates to an autofocus device that controls the position of a lens of an image optical system, and an image recording device that records an image corresponding to an image signal on a recording material using the position detection device or the autofocus device.

[0002]

2. Description of the Related Art Conventionally, when determining whether a distance to an object is within a predetermined range, the principle of triangulation is used to measure the distance to the object, and the result is a reference value (range). Upper and lower limits).

For example, in an image recording apparatus, when it is determined whether or not a recording material such as a printing plate as an object is within a predetermined range near an image forming position of a light beam emitted from an exposure light source, the position is determined. A light beam is emitted from the light source for detection to the recording material, and a part of the reflected light scattered on the surface of the recording material is captured by the optical sensor via the condenser lens, and the one-dimensional light spot imaged on the optical sensor. The distance to the recording material was calculated by obtaining the desired position with the arithmetic device, and the result was compared with the reference value.

Hereinafter, referring to the conceptual diagram shown in FIG.
A conventional position detecting device will be described.

As shown in FIG. 7, a conventional position detecting device 8
At 0, a light beam is emitted from the light source 82 for position detection to the object 98 via the imaging lens 100, and a part of the reflected light scattered on the surface of the object 98 passes through the condenser lens 102 to 1 It is captured by the dimensional light position detecting element 84. The one-dimensional light position detecting element 84 outputs two current signals having different current values according to the distance X between the light source 82 and the surface of the object 98, and the current-voltage converter 86 and the amplifier 88, respectively.
Are converted and amplified into two voltage signals (analog signals) V1 and V2.

The two voltage signals V1 and V2 are supplied to the arithmetic circuit 9
At 0, the distance X from the light source 82 to the surface of the object 98 is calculated based on the calculation formula (V1-V2) / (V1 + V2). After that, the distance X calculated by the arithmetic circuit 90 is compared with the upper and lower limits of the reference value by the comparators 92 and 94, respectively, and the AND gate 9
By taking the AND of the comparison results by 6,
It has been determined whether or not the distance X from the light source 82 to the object 98 is within a predetermined range indicated by the upper limit and the lower limit of the reference value.

Therefore, in the conventional position detecting device 80,
Two current-voltage converters 86 and two amplifiers 88 are required, respectively, and further, an analog operation circuit for adding, subtracting, and dividing the two amplified analog signals V1 and V2, or a digital operation for this operation. A to do
/ D (analog-digital) converter and advanced control IC (integrated circuit) for computing converted digital data
Was needed. Therefore, there is a problem that the device becomes complicated and expensive.

Further, when the surface of the object has irregularities, when the surface is irradiated with a coherent light beam having a small spot diameter, the reflected lights scattered on the surface of the object 98 interfere with each other, resulting in interference called a speckle pattern. A fringe is created on the one-dimensional optical position detecting element 84. This interference fringe is
The intensity of the entire light passing through the condenser lens 102 changes randomly with time because it changes randomly with a slight displacement of the surface of the object 98, and as a result, it affects the measurement result of the position of the object 98. .

On the other hand, when the spot diameter of the light beam with which the object 98 is irradiated is large, the interference of the reflected light scattered on the surface of the object 98 is averaged with each other, and the interference fringes become finer. The temporal change in the intensity of the entire light passing through 102 tends to be small. Therefore, generally, in order to avoid the influence of the interference fringes, measures such as increasing the spot diameter of the light beam with which the target object 98 is irradiated and irradiating the target object 98 with a non-coherent light beam are taken. Has been taken.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems based on the above-mentioned prior art, and to realize a position detecting device and an autofocus device which can be realized with a simple and inexpensive structure, and these position detecting devices. Another object is to provide an image recording device that records an image corresponding to an image signal on a recording material by using an autofocus device.

[0011]

In the present invention, the interference pattern produced by the reflected light scattered on the surface of the object is utilized,
It is determined whether the position of the object is within a predetermined range. That is, when a coherent light beam is irradiated to a predetermined position near the object surface, when the spot diameter of the light beam on the object surface is small, the temporal change in the intensity of the entire light transmitted through the condenser lens becomes large, On the other hand, when the spot diameter of the light beam on the surface of the object is large, the fact that the temporal change of the intensity of the entire light transmitted through the condenser lens becomes small is used.

Specifically, a light beam is emitted from a light source, reflected light scattered on the surface of an object is captured, the maximum value and the minimum value per unit time of a voltage signal corresponding to the light intensity are obtained, and the If the voltage difference is greater than the reference value,
Since the change in the light intensity per unit time is large, it is determined that the object is within the predetermined range. On the other hand, when the difference voltage in the unit time is smaller than the reference value, the change in the light intensity per unit time is small, so it is determined that the object is not within the predetermined range.

That is, in order to achieve the above object, the present invention provides a light source for emitting a light beam which forms an image near the surface of an object, and a light beam emitted from the light source scattered on the surface of the object. The photodetector element that captures the reflected light and outputs a current signal having a current value corresponding to the light intensity, and the current signal output from the photodetector element is converted into a voltage signal having a voltage level corresponding to the current value. A current-voltage converter for conversion,
Maximum value detecting means and minimum value detecting means for detecting the maximum value and the minimum value per unit time of the voltage signal output from the current-voltage converter, and output from these maximum value detecting means and minimum value detecting means A difference detector for calculating a voltage difference between the maximum value and the minimum value of the voltage signal, and a difference voltage output from the difference detector and a reference value are compared, and a comparison result is output. And a position detector that determines whether the object is within a predetermined range determined by the reference value according to a comparison result output from the comparator. To do.

Further, the present invention is an autofocus used in an apparatus equipped with an image forming optical system for controlling a light beam emitted from a first light source so as to form an image near the surface of an object through a lens. A device for capturing a light source that emits a light beam that forms an image near the surface of the object, and a light beam emitted from the second light source that captures reflected light scattered on the surface of the object. A photo-detecting element that outputs a current signal having a current value corresponding to the light intensity, and a current-voltage conversion that converts the current signal output from the photo-detecting element into a voltage signal having a voltage level corresponding to the current value And a maximum value detecting means and a minimum value detecting means for detecting the maximum value and the minimum value per unit time of the voltage signal output from the current-voltage converter, respectively, and the maximum value detecting means and the minimum value detecting means. means Difference detector for calculating the difference voltage between the maximum value and the minimum value of the voltage signal output from the differential detector, and displacement for calculating the displacement amount of the object based on the difference voltage output from the difference detector. Based on the amount calculation means and the displacement amount of the object calculated by the displacement amount calculation means, the light beam emitted from the first light source is imaged near the surface of the object, An autofocus device is provided, which is provided with an image forming position adjusting means for controlling the position of the lens of the image forming optical system.

Further, the present invention is an image recording apparatus for recording an image corresponding to an image signal on a recording material, wherein an exposure light source of the recording material and a light beam emitted from the exposure light source form a lens. Via the imaging optical system for controlling so as to form an image near the surface of the recording material through the imaging light system and the light beam emitted from the exposure light source through the imaging optical system in the main scanning direction and the main scanning direction. A scanning exposure unit that scans and exposes the recording material with a light beam emitted from the exposure light source based on the image signal while relatively moving in a sub-scanning direction that is substantially orthogonal to the scanning direction. And a position detection device, the position detection device,
Recording an image corresponding to the image signal on the recording material while determining whether or not the recording material is within a predetermined range in the vicinity of the imaging position of the light beam emitted from the exposure light source. A characteristic image recording apparatus is provided.

Further, the present invention is an image recording apparatus for recording an image corresponding to an image signal on a recording material, wherein an exposure light source of the recording material and a light beam emitted from this exposure light source pass through a lens. Via the imaging optical system for controlling so as to form an image near the surface of the recording material through the imaging light system and the light beam emitted from the exposure light source through the imaging optical system in the main scanning direction and the main scanning direction. A scanning exposure unit that scans and exposes the recording material with a light beam emitted from the exposure light source based on the image signal while relatively moving in a sub-scanning direction that is substantially orthogonal to the scanning direction. An autofocus device is provided, and the light beam emitted from the exposure light source is imaged near the surface of the recording material based on the displacement amount of the recording material by the autofocus device. While controlling the position of the urchin the lens, to provide an image recording apparatus and recording an image corresponding to the image signal onto the recording material.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The position detecting device, autofocus device and image recording device of the present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings.

FIG. 1 is a schematic perspective view of an embodiment of the image recording apparatus of the present invention. The image recording device 10 shown in FIG.
While determining whether the recording material A such as a printing plate is within a predetermined range near the image forming position of the light beam emitted from the exposure light source by using the position detecting device (not shown) of the present invention, An image corresponding to an image signal is recorded on the recording material A, and includes a light source unit 12, a scanning exposure unit 14, and an image forming optical system 16.

In the illustrated example, the fiber array 24 of the light source section 12 and the imaging optical system 16 are fixed to a predetermined position on one moving support 38 to form an imaging unit 36.

In the image recording apparatus 10, first, the light source section 12 emits a multi-beam composed of a plurality of light beams arranged in a line at a predetermined interval.
A plurality of semiconductor lasers 18 and these semiconductor lasers 1
8 is provided with a plurality of optical fiber cables 20 provided in a one-to-one correspondence, and a connector array 22 and a fiber array 24 for bundling the central portion and the end portion of these optical fiber cables 20 at one place. .

Here, the plurality of semiconductor lasers 18 are arranged in a line on the heat sink 26 at a predetermined interval in the sub-scanning direction (direction of arrow c in the figure).
It is kept at a predetermined temperature by 6. A light beam for exposing the recording material A is emitted from each semiconductor laser 18. In the case of the illustrated example, one light beam is emitted from each semiconductor laser 18, and a multi-beam composed of a plurality of light beams in total is emitted.

The optical fiber cable 20 is connected at its incident end face at the starting end to the corresponding emitting part of the light beam of the semiconductor laser 18. In addition, the connector array 22 bundles the central portion of the connector array 22 on the support plate 28 at a time.
The fiber array 24 allows the multi-beams emitted from the emission end face of the terminal end of the optical fiber cable 20 to be arranged on the recording material A at a predetermined interval in the sub-scanning direction so as to be arranged in a row by the support member 30. It is arranged.

The light beams emitted from the respective semiconductor lasers 18 pass through the corresponding optical fiber cables 20, and are emitted from the emission end face of the terminal end arranged in a line by the supporting member 30 of the fiber array 24.

Subsequently, in the image recording apparatus 10 shown in FIG. 1, the scanning exposure section 14 performs the scanning exposure of the recording material A in the outer drum (outer surface drum) system, and the outer drum 32 and this. The outer drum 32 is provided with a rotation driving means (not shown) and a sub-scanning means 34.

Here, the outer drum 32 has a recording material A such as a PS plate (PreSensitized plate) on the outer peripheral surface thereof.
Is mounted and is rotated at a predetermined constant speed in the main scanning direction (the rotation direction of the outer drum 32) by a rotation driving unit (not shown) during scanning exposure.

The sub-scanning means 34 is for moving the image forming unit 36 and the outer drum 32 relatively in the sub-scanning direction, and includes a moving support base 38 which is a base of the image forming unit 36 and a ball screw ( A driving screw) 40, a rotation driving means (not shown) for the ball screw 40, and a base 42.

Here, a V-shaped protrusion extending in the sub-scanning direction is formed in the lower portion of the movable support base 38, and a ball screw extending in the sub-scanning direction is formed in the center of the protrusion. Four
A female screw threaded with 0 is formed. Also, the base 42
Is formed with a V-shaped groove 44 that fits with the V-shaped protrusion of the movable support base 38 and extends in the sub-scanning direction. The movable support base 38 is rotationally driven (not shown). It is configured to be movable in the sub-scanning direction by the rotation of the ball screw 40 by the mechanism.

As shown in FIG. 1, the heat sink 26 of the light source section 12 and the connector array 22 are also mounted on the upper surface of the base 42.

Subsequently, in the image recording apparatus 10 shown in FIG. 1, the image forming optical system 16 forms an image of the multi-beam emitted from the light source section 12 on the recording material A of the scanning exposure section 14 with a predetermined spot diameter. The reduction optical system includes a collimator lens 46 and an imaging lens 48.

Here, the collimator lens 46 is arranged on the downstream side of the fiber array 24 in the light traveling direction,
All the multi-beam light beams emitted from the fiber array 24 are collimated light (parallel light). The imaging lens 48 includes the collimator lens 46 and the outer drum 3.
The light beam, which is disposed between the recording material A and the recording material A mounted on the outer peripheral surface of the second light beam and is emitted through the imaging lens 48, is imaged on the recording material A with a predetermined spot diameter.

In the perspective view of FIG. 1, the position detecting device of the present invention is not shown in order to avoid complication of the drawing, but the position detecting device is as shown in the conceptual diagram of FIG. ,
The recording material A, which is an object, is arranged while being separated from the recording material A for a certain period of time. This position detecting device may be fixed at a predetermined position on the base 42, for example, or may be fixed on the moving support 38 of the imaging unit 36 and moved in the sub-scanning direction at the same time during the sub-scanning. It may be configured to do so.

In the image recording apparatus 10, during scanning exposure, while the outer drum 32 is rotated in the main scanning direction at a predetermined constant speed, the sub-scanning unit 34 causes the imaging unit 36 to move in the sub-scanning direction at a predetermined constant speed. Be moved. As a result, the recording material A is two-dimensionally scanned and exposed by the multi-beam imaged on the recording material A through the semiconductor laser 18, the optical fiber cable 20, and the imaging optical system 16, and an image corresponding to the image signal is formed. It is recorded on the recording material A.

At this time, as will be described in detail later, by the position detecting device of the present invention, the recording material A is provided at a predetermined position near the image forming position of the light beam emitted from the semiconductor laser 18 through the image forming optical system 16. While judging whether it is within the range,
An image corresponding to the image signal is recorded on the recording material A.
Then, as a result of the determination, when the recording material A is not within the predetermined range, it is determined that the recording material A is lifted or peeled off, and the recording is stopped as necessary.

The image recording apparatus of the present invention is not limited to the one using the position detecting apparatus of the present invention, and may use the autofocus apparatus of the present invention. Further, the configuration of the image recording apparatus is not limited to that shown in the drawings, and the present invention is
The present invention can be applied to any image recording apparatus having a conventionally known structure including at least an exposure light source, an imaging optical system, and scanning exposure means. The recording material is not limited to a printing plate such as a PS plate, and any conventionally known recording material can be used.

Next, the position detecting device of the present invention used in the image recording device 10 of the present invention shown in FIGS. 1 and 2 will be described.

FIG. 3 is a conceptual diagram of the configuration of an embodiment of the position detecting device of the present invention. The position detection device 50 shown in FIG.
For example, it is determined whether or not the recording material such as a printing plate as the object 68 is within a predetermined range near the image forming position of the light beam emitted from the light source through the image forming optical system. A light source 52 for detection, a light detection element 54, a current-voltage converter 56, an amplifier 58, and a maximum value detection means 60.
And a minimum value detecting means 62, a difference detector 64, and a comparator 66.

Here, the light source 52 for position detection is arranged at a position separated from the object 68 for a predetermined period of time, and a predetermined distance in the vicinity of the surface of the object 68 via the imaging lens 70. The light beam that forms an image at the position is output. The light source 52 has a wavelength that does not affect the object 68 by the light beam output from the light source 52. The light beam emitted from the light source 52 uses coherent light having a relatively small spot diameter.

Similarly, the photo-detecting element 54 is also disposed at a position separated from the object 68 for a predetermined period of time, and the reflected light scattered on the surface of the object 68 is captured via the condenser lens 72, and its light intensity is changed. The current signal of the corresponding current value is output. Also,
The current-voltage converter 56 converts the current signal output from the photodetector element 54 into a voltage signal having a voltage level according to the current value. The voltage signal output from the current-voltage converter 56 is further amplified and output by the amplifier 58.

The maximum value detecting means 60 and the minimum value detecting means 62 detect the maximum value and the minimum value of the voltage signal per unit time of the voltage signal amplified and output from the amplifier 58, respectively. Further, the difference detector 64 calculates the voltage difference between the maximum value and the minimum value of the voltage signals detected by the maximum value detecting means 60 and the minimum value detecting means 62, respectively. The comparator 66 compares the difference voltage output from the difference detector 64 with the reference value, and outputs the comparison result.

The reference value is a threshold value for determining whether or not the object 68 is within a predetermined range. For example, the light amount of the light source 52, the photoelectric conversion rate by the light detecting element 54,
It is determined based on the conversion rate of the current-voltage converter 56, the amplification rate of the amplifier 58, and the like. By tightening the reference value, it is possible to tighten the criterion for determining whether or not the object 68 is within the predetermined range, and conversely, by loosening the reference value, the criterion can be relaxed.

In this position detecting device 50, first, the light source 5
From 2 through the imaging lens 70, the object 68 is irradiated with a light beam that forms an image at a predetermined position near the surface of the object 68.

The irradiated light beam is reflected and scattered on the surface of the object 68, and a part of the reflected light scattered on the surface of the object 68 is condensed by the photodetector 54 via the condenser lens 72. It The photodetector element 54 outputs a current signal having a current value corresponding to the intensity of the entire collected light, and the current signal is a voltage signal having a voltage level corresponding to the current value of the current signal by the current-voltage converter 56. The voltage signal is further converted into the output signal and is amplified and output by the amplifier 58.

After that, the maximum value detecting means 60 and the minimum value detecting means 62 respectively calculate the maximum value and the minimum value of the voltage signal per unit time, and the difference detector 64.
The voltage of the difference between the maximum value and the minimum value is detected by. Then, the comparator 66 compares the voltage difference and the reference value, and outputs the comparison result. Therefore, according to the comparison result, the object 6
It can be determined whether 8 is within a predetermined range.

As described above, when the surface of the object 68 is irradiated with a coherent light beam having a small spot diameter, the reflected lights scattered on the surface of the object 68 interfere with each other. When the object 68 moves in the in-plane direction, the object 68
Since the unevenness of the surface changes, the interference pattern changes, and the intensity of the entire light condensed via the condenser lens 72 changes with time.

Therefore, when the surface of the object 68 is irradiated with a coherent light beam having a small spot diameter and the object 68 is near the image forming position of the light beam, the spot diameter of the light beam on the surface of the object 68 is Remains small,
The temporal change in the intensity of the entire collected light becomes large. On the other hand, as the object 68 moves away from the image forming position of the light beam, the spot diameter of the light beam on the surface of the object 68 increases, whereby the interference of the reflected light scattered on the surface of the object 68 averages each other. As a result, even if the object 68 moves in the in-plane direction, the temporal change in the intensity of the entire condensed light becomes small.

Therefore, when the voltage of the difference between the maximum value and the minimum value of the voltage signal is larger than the reference value, the change in the light intensity per unit time is large, and the spot diameter of the light beam on the surface of the object 68 is relatively large. Since it is considered to be small, it can be determined that the object 68 is within the predetermined range. On the other hand, when the difference voltage is smaller than the reference value, the change in light intensity per unit time is small and the spot diameter on the surface of the target object 68 is considered to be relatively large. It can be determined that there is no.

Here, the maximum value and the minimum value of the voltage signal will be described as an example. FIGS. 4A and 4B are graphs of one example showing the time change of the voltage signal in the vicinity of the image forming position and the position away from the image forming position, respectively.
The horizontal axis in the figure represents the passage of time. The horizontal axis is 2 per memory
msec, and 20 msec on the entire horizontal axis of the graph. The vertical axis represents the voltage level of the voltage signal. The vertical axis represents 100 mV per memory.

First, as shown in the graph of FIG.
When the object 68 is near the imaging position, the difference voltage between the maximum value and the minimum value of the voltage signal is about 56 mV. on the other hand,
As shown in the graph of FIG. 6B, when the object 68 is located away from the image formation position, the difference voltage between the maximum value and the minimum value of the voltage signal is about 28 mV. In this way, the voltage of the difference between the maximum value and the minimum value of the voltage signal is
Is larger as it is closer to the image forming position, and is smaller as it is farther from the image forming position.

Further, by changing the converging angle of the light beam emitted from the light source 52 by the image forming lens 70, it is possible to adjust the criterion for judging whether or not the object 68 is within the predetermined range. For example, in the example of FIG. 5A, since the light beam has a narrow converging angle, the amount of change in the spot diameter of the light beam is small even if the amount of movement of the target object 68 is large, and therefore the judgment criterion is loose (the OK range is wide On the contrary, if the converging angle is widened as in the example of FIG.
The K range can be narrowed).

As described above, in the position detecting device 10, unlike the conventional method, the surface of the object 68 is not evaluated based on the result of measuring the distance to the surface of the object 68, but
It is directly detected whether or not it is within a predetermined range near the image forming position of the light beam.

Thus, according to the present invention, the object 68
In order to capture the reflected light scattered on the surface, the light detecting element 54
It is possible to use a general optical sensor such as, and only one current-voltage converter 56 and one amplifier 58 are required. Further, the arithmetic circuits such as the maximum value detecting means 60 and the minimum value detecting means 62, the difference detector 64, and the comparator 66 can also be realized by using inexpensive analog circuit elements. Therefore, since the structure is simple, there are advantages that the reliability of the device is improved and the cost is low.

The position detecting apparatus 50 of the present invention is used in the image recording apparatus 10 shown in FIG.
Can be used only for determining whether or not the object 68 is within a predetermined range near the imaging position of the light beam, and it is necessary to determine whether or not the object 68 is within a predetermined range. It is applicable to all known devices.

Next, the image recording apparatus 1 of the present invention shown in FIG.
The autofocus device of the present invention used in No. 0 is described.

FIG. 6 is a conceptual diagram showing the construction of an embodiment of the autofocus device of the present invention. The autofocus device 74 shown in the figure calculates, for example, the amount of displacement of a recording material such as a printing plate that is an object 68, and based on this amount of displacement, from the light source of the device including the imaging optical system to the imaging optical system. The position of the lens of the image forming optical system of this apparatus is controlled so that the light beam emitted via the lens forms an image near the surface of the object 68.

The autofocus device 74 is shown in FIG.
Compared with the position detection device 50 shown in FIG. 2, the comparator 66 is not provided, and only the displacement amount calculation means 76 and the imaging position adjustment means 78 are provided. The same reference numerals are given to the constituent elements, and detailed description thereof will be omitted.

Here, the displacement amount calculating means 76 determines the object 6 based on the difference voltage output from the difference detector 64.
The displacement amount of 8 is calculated. Although not limited thereto, when the displacement amount of the target object 68 and the differential voltage do not linearly correspond to each other, for example, data indicating the relationship between the differential voltage and the displacement amount of the target object 68 is displayed. It is preferable to provide in the form of a look-up table and use this look-up table to obtain the displacement amount of the object 68 from the voltage difference.

Further, the image forming position adjusting means 78 targets the light beam emitted from the light source of the apparatus having the image forming optical system based on the displacement amount of the object 68 calculated by the displacement amount calculating means 76. The position of the lens of the imaging optical system of this apparatus is controlled so that an image is formed near the surface of the object 68.

In the autofocus device 74, the operation until the difference voltage is detected by the difference detector 64 is exactly the same as that of the position detecting device 50 shown in FIG. After that, the displacement amount calculation means 76 calculates the displacement amount of the object 68 based on the voltage difference, and the imaging position adjustment means 78 includes an imaging optical system based on the displacement amount of the object 68. The position of the lens of the imaging optical system of this device is controlled so that the light beam emitted from the light source of the device forms an image near the surface of the object 68.

In the image recording apparatus 10 shown in FIG. 1, when the autofocus device 74 of the present invention is adopted, the image forming lens 4 of the image forming optical system 16 according to the displacement amount of the recording material A.
8 is moved, and the image forming position of the light beam emitted from the semiconductor laser 18 through the image forming optical system 16 is controlled so as to coincide with the surface of the recording material A. As a result, the image forming position of the light beam emitted through the image forming optical system 16 is always adjusted to the surface position of the recording material A, so that a high quality image can be recorded.

The autofocus device of the present invention is
In the image recording apparatus 10 shown in FIG. 1, the image recording apparatus is not usable only for automatically adjusting the image forming position of the light beam emitted from the exposure light source to the vicinity of the surface of the recording material A. The present invention can be applied to all conventionally known devices that require autofocus control.

The position detecting device, the autofocus device and the image recording device of the present invention are basically as described above. The position detection device, the autofocus device, and the image recording device of the present invention have been described above in detail.
The present invention is not limited to the above embodiments, and it goes without saying that various improvements and modifications may be made without departing from the spirit of the present invention.

[0062]

As described in detail above, according to the present invention, since the structure is simple, it is possible to improve the reliability of the device, and it is possible to realize it by using inexpensive parts. Is possible.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an embodiment of an image recording apparatus of the present invention.

FIG. 2 is a conceptual diagram of an embodiment of an image recording device to which the position detecting device of the present invention is applied.

FIG. 3 is a conceptual diagram showing the configuration of an embodiment of the position detecting device of the present invention.

FIG. 4A and FIG. 4B are graphs of an example showing a time change of a voltage signal at a position near an image forming position and a position apart from the image forming position, respectively.

5A and 5B are conceptual diagrams of an example showing a case where the light beam converging angles are different from each other.

FIG. 6 is a conceptual diagram of the configuration of an embodiment of the autofocus device of the present invention.

FIG. 7 is a structural conceptual diagram of an example of a conventional position detecting device.

[Explanation of symbols]

10 Image recording device 12 Light source 14 Scanning exposure unit 16 Imaging optical system 18 Semiconductor laser 20 optical fiber cable 22 connector array 24 fiber array 26 heat sink 28 Support plate 30 Support member 32 outer drum 34 Sub-scanning means 36 Imaging unit 38 Moving support 40 ball screw (drive screw) 42 base 44 groove 46 Collimator lens 48 Imaging lens 50,80 Position detection device 52,82 light source 54 Photodetector 56,86 current-voltage converter 58,88 amplifier 60 Maximum value detection means 62 minimum value detection means 64 difference detector 66,92,94 comparator 68,98 Target 70,100 Imaging lens 72,102 Condensing lens 74 Auto Focus Device 76 Displacement amount calculation means 78 Image forming position adjusting means 84 One-dimensional optical position detector 90 arithmetic circuit 96 AND gate

Claims (4)

[Claims] 1. A light source that emits a light beam that forms an image near the surface of an object, and a light beam that is emitted from this light source captures the reflected light scattered on the surface of the object and determines the intensity of the light. A photodetector element that outputs a current signal of a current value, a current-voltage converter that converts the current signal output from the photodetector element into a voltage signal of a voltage level according to the current value, and the current-voltage converter Value detecting means and minimum value detecting means for detecting the maximum value and the minimum value per unit time of the voltage signal output from the detector, and the voltage output from the maximum value detecting means and the minimum value detecting means. A difference detector that calculates the voltage difference between the maximum value and the minimum value of the signal, and a comparator that compares the difference voltage output from this difference detector with a reference value and outputs the comparison result , The comparator A position detecting device which determines whether or not the object is within a predetermined range determined by the reference value according to a comparison result output from the device. 2. An autofocus device used in a device including an imaging optical system for controlling a light beam emitted from a first light source so as to form an image near the surface of an object through a lens. A second light source that emits a light beam that forms an image in the vicinity of the surface of the object, and a light beam emitted from the second light source that captures the reflected light scattered on the surface of the object, and its light intensity A photo-detecting element that outputs a current signal having a current value corresponding to, a current-voltage converter that converts the current signal output from the photo-detecting element into a voltage signal having a voltage level corresponding to the current value, and Maximum value detecting means and minimum value detecting means for detecting the maximum value and the minimum value per unit time of the voltage signal output from the current-voltage converter, and the maximum value detecting means and the minimum value detecting means are output. Before A difference detector for calculating a voltage difference between the maximum value and the minimum value of the voltage signal, and a displacement amount calculating means for calculating the displacement amount of the object based on the difference voltage output from the difference detector. And the imaging optics so that the light beam emitted from the first light source forms an image near the surface of the object based on the displacement of the object calculated by the displacement calculating means. An image forming position adjusting means for controlling the position of the lens of the system. 3. An image recording apparatus for recording an image corresponding to an image signal on a recording material, wherein an exposure light source of the recording material and a light beam emitted from the exposure light source are recorded through a lens. An imaging optical system that controls to form an image near the surface of the material, a light beam emitted from the exposure light source through the imaging optical system, and the recording material in the main scanning direction and in the main scanning direction. The scanning exposure unit that scans and exposes the recording material with a light beam emitted from the exposure light source based on the image signal while relatively moving in the sub-scanning direction orthogonal to each other, and the position detection according to claim 1. An apparatus, the position detecting device, on the recording material while determining whether the recording material is within a predetermined range in the vicinity of the imaging position of the light beam emitted from the exposure light source. Image recording apparatus and recording an image corresponding to the serial image signal. 4. An image recording apparatus for recording an image corresponding to an image signal on a recording material, wherein an exposure light source of the recording material and a light beam emitted from the exposure light source are recorded through a lens. An imaging optical system that controls to form an image near the surface of the material, a light beam emitted from the exposure light source through the imaging optical system, and the recording material in the main scanning direction and in the main scanning direction. 3. A scanning exposure unit that scans and exposes the recording material with a light beam emitted from the exposure light source based on the image signal while moving relatively in a sub-scanning direction orthogonal to each other, and the autofocus according to claim 2. And a device for causing the light beam emitted from the exposure light source to form an image near the surface of the recording material based on the displacement amount of the recording material by the autofocus device. While controlling the position of the lens, an image recording apparatus and recording an image corresponding to the image signal onto the recording material.