JPS62185656A - Detecting device for presence/absence of sheet - Google Patents

Abstract

PURPOSE:To detect whether there is a sheet or not surely, so as to prevent any false detection due to a color of the sheet, by photoelectrically converting reflected or transmitted light from a light source through a receiving element, and judging the existence of the sheet when a potential in the absence of the sheet differs from that in the existence thereof to an extent exceeding a predetermined value. CONSTITUTION:Optical sensors 22, 23 are provided for detecting whether there is a document 3 or not when the document 3 is fed in the direction of an arrow 21 along a guide 20. A first sensor 22 for detecting the document 3 is located near by the guide 20, and a second sensor 23 is provided on the outside area of the guide 20, where there is not any possible passing of the document 3. Photoelectrically converted outputs 22a, 23a of receiving elements of both sensors 22, 23 are inputted to a comparing amplifier 28 through level regulating amplifiers 26, 27 in a processor 30. If the amplifiers 26, 27 are previously adjusted to equalize the levels of both outputs 22a, 23a in the absent state of the document 3, the converted output 22a is increased by the existence of the document 3, and it is judged that there is a document 3 when a potential difference exceeds a predetermined value. Thereby, it is possible to surely detect whether there is the document 3 or not without the occurrence of any false detection due to a color.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a sheet presence/absence detection device for detecting whether or not a sheet such as an original or copy paper exists at a predetermined position in a copying machine or the like.

``Prior Art'' For example, in a copying apparatus, copy sheets are stored in several trays according to their sizes, selected as needed, and sent out to perform copying.

When starting copying, the operator presses a print start button, and if there is no copy paper at this time, a predetermined warning lamp or the like is generally turned on to display this.

In this case, optical sensors are widely used to detect the presence or absence of copy paper.

Further, if the copy paper stops in the first general feed path during copying, a warning lamp is lit to indicate that a so-called jam has occurred. Again, optical sensors are often used to detect stopped copy paper.

FIG. 5 shows a reflective optical sensor, and FIG. 6 shows a transmissive optical sensor.

In FIG. 5, when light 2 is emitted from a light source 1 consisting of a light emitting diode or the like, this light is reflected by the surface of a sort such as copy paper 3 and enters a light receiving element 4.

This light is photoelectrically converted and the processing device 5 detects the presence or absence of the sheet.

In the case of FIG. 6, the light source 1 is placed opposite the light receiving element 4, and when the sheet 3 passes between the light source 1 and the light receiving element 4, the light 2 entering the light receiving element 4 is blocked.

The processing device 5 detects the presence or absence of the sheet by photoelectrically converting the incident light at this time.

Such an optical sensor is also used to detect, for example, the presence or absence of a document placed on a platen glass of a copying machine, its size, etc.

FIG. 7 is a graph showing changes in the photoelectric conversion output 6 manually input to the processing device 5 shown in FIG.

In Fig. 5, if sheet 3 does not exist, the low level L
A photoelectric conversion output of 6 can be obtained, and when sort 3 exists, a high level H photoelectric conversion output can be obtained. Here, a reference level ■s is set in advance, and this voltage vs.
When the photoelectric conversion output is higher than this, it is determined that a sheet is present.

Also, the level of photoelectric conversion output differs depending on the paper quality of the sheet. FIG. 8 shows the change 1-hi, and shows that the quality of the sheet improves, the surface becomes smooth, and the level of the culm electrical conversion output increases.

"Problems to be Solved by the Invention" FIG. 9 shows a schematic vertical cross-sectional view of an automatic document feeder used in copying machines and the like.

This device feeds a document 3 onto a platen glass 8 of a copying device, automatically starts copying, and discharges the document 3 to a discharge tray 9 after copying is completed.

In this device, when a document 3 enters a paper feed section 10, an optical sensor 11 detects this and drives a conveyor belt 12 to feed the document 3.

This optical sensor 11 sends the photoelectric conversion output 6 to the processing device 5 when the original 3 enters directly below it. The processing device 5 is provided with a comparison amplifier 13, which outputs a reference level (seventh
(corresponding to ■S in the figure) and the photoelectric conversion output 6 are compared. Generally, the reference level (1) S is taken out from the center tap of the voltage dividing resistor 14 or the like.

In such a device, for example, if the device is not properly grounded, strong external light 16 may enter from the side. This external light 16 causes the optical sensor 11 to malfunction,
There are cases where it is determined that a sheet is missing even though it exists, or vice versa, causing a delay in copying work.

Further, for example, if the image drawn on the original 3 is almost black, the level of the photoelectric conversion signal may become lower than the reference voltage S shown in FIG. 7 and may become undetectable.

The present invention has been made with attention to the above points, and it is an object of the present invention to provide a sheet presence/absence detection device that can accurately and without error detect the presence or absence of a sheet and is not easily affected by external light. .

"Means for Solving the Problem" The sheet presence/absence detection device of the present invention is installed in a sheet withdrawal path, and detects the presence or absence of a sheet by photoelectrically converting reflected light or transmitted light emitted from a light source using a light receiving element. It consists of a sensor that detects the presence of the sheet, and a processing device that processes the detection signal of this sensor to determine the presence or absence of the sheet. The present invention is characterized in that it is determined that the sheet is present when the level difference between the sheet and the sheet absent state exceeds a predetermined value.

Here, a first light-receiving element is arranged in the existing region of the sheet, a second light-receiving element is arranged in the non-existing region of the sheet, and the processing device converts the photoelectric conversion output of the first light-receiving element into , and the photoelectric conversion output of the second light-receiving element.

Further, the processing device obtains a first photoelectric conversion output in the absence state of the sorting, and then obtains a second photoelectric conversion output in the presence state of the sheet, and the processing device combines the first photoelectric conversion output with the first photoelectric conversion output. , the level difference between the second photoelectric conversion output and the second photoelectric conversion output may be determined.

"Function" In this way, if the photoelectric conversion output of the light receiving element is compared between the presence state and the absence state of the sheet, and the presence or absence of the sheet is determined from the level difference, when compared with a constant reference voltage, The number of false positives can be significantly reduced.

In this case, two light-receiving elements are used, and the first light-receiving element is placed in the area where the sheet is hidden or passes through, and the second light-receiving element is placed in the area where the sheet is present, where the sheet may be present. It is preferable to place the photoelectric conversion output signals in a non-existing region and compare both photoelectric conversion output signals at the same time.

Another method is to obtain the first photoelectric conversion output in the absence of the sheet in a region through which the sheet passes, and obtain the second photoelectric conversion output in the presence of the sheet. The level difference between the two photoelectric conversion outputs obtained at different times may be taken.

In either case, if the level difference is above a certain level, it is determined that there is a sheet, and if it is below a certain level, it is determined that there is no sheet.

In this way, when external light enters the light receiving element, the level difference does not become large, and erroneous detection can be prevented. Furthermore, even if the level of the photoelectric conversion output decreases due to the presence of the sheet, it can be determined that the sheet is present.

Embodiment FIG. 1 is a schematic diagram showing an embodiment of the sheet presence/absence detection device of the present invention.

This device is provided with optical sensors 22 and 23 that detect the presence or absence of original documents 3 when documents 3 of various sizes are fed in the direction of arrow 21 along a guide 20. This is used in the paper feed section 10 of the automatic document feeder shown in FIG.

No matter what size the document 3 is as shown in the figure, it is fed along the guide 20, so the first optical sensor 22 for detecting this is sent along the guide 20 on the path of the document. is located near. Further, the second optical sensor 23 is provided outside the guide 20. This is an area where there is no possibility of the original passing through. The photoelectric conversion outputs 22a and 23a of the light receiving elements of both optical sensors 22 and 23 are inputted to the comparison amplifier 28 in the processing device 30 via amplifiers 26 and 27 that adjust the levels of these signals.

The output of the comparison amplifier 28 is inputted to a comparison amplifier 29 which compares it with a reference level ■S. This standard level ■S
is obtained from the center tap of the voltage dividing resistor 25.

The apparatus having the above configuration operates as follows.

First, in the absence of the document 3, the amplification factors of the amplifiers 26 and 27 are adjusted so that the photoelectric conversion output 22a of the first light receiving element and the photoelectric conversion output 23a of the second light receiving element are at the same level. Adjust it. This state is shown in FIG. In this graph, ■ indicates the photoelectric conversion output of the first light receiving element, and ■ indicates the photoelectric conversion output of the second light receiving element. The vertical axis represents voltage (V), and the initial state is at levels Ia and IIa.

Here, when the original 3 is inserted directly under the first light receiving element, its photoelectric conversion output 22a increases to the level shown in FIG. 2 Ib.

The output signals of the comparison amplifier 28 in FIG. 1 are Ib and I[ in FIG.
This corresponds to the level difference of a, and this is compared with the reference level, and the comparison amplifier 29 outputs the judgment result.

In this way, when the level difference between Ib and IIa in FIG. 2 is above a certain level, it is determined that there is a document present, and when it is below a certain level, it is determined that there is no document.

For example, suppose that external light enters both of the light receiving elements. At this time, both light receiving elements collectively increase the photoelectric conversion outputs 22a and 23a. In this case, there is no level difference in the surface output as shown in IC and IIc in FIG. Therefore, it is determined that there is no document in the circuit shown in FIG.

Second, consider a case where the surface of the original 3 is black.

In this case, for example, if there is no manuscript, IC, [
Assume that a photoelectric conversion output as shown in a is obtained.

Next, when the original 3 is sent directly below the first light receiving element,
Since the surface is black, the photoelectric conversion output 22a decreases to the level shown in FIG. 2 1d.

This also creates a level difference of a certain level or more between the levels Id and IIa, and it is possible to detect that a document is present.

FIG. 3 is an explanatory diagram showing another embodiment of the present invention.

In this embodiment, a sheet 3' such as an original or copy paper is used.
Only one light receiving element 31 is provided for detecting.

As shown in FIG. 3a, a photoelectric conversion output 31a is first obtained in the absence of the sheet 3'. and,
The level of this output is recorded in the processing device 30'. key. Next, the photoelectric conversion output 31'a obtained when the /-t 3' is sent is obtained, and compared with the previously stored photoelectric conversion output 31a at that time, the level difference is determined. In this way, it is possible to determine whether or not sorting is to be performed in the same manner as in Figure 2, which uses two light-receiving elements.

"Modification" The sheet presence/absence detection device of the present invention is not limited to the above embodiment.

For example, the present invention can be applied to various parts of a copying machine as shown in FIG.

In this apparatus, a copy sheet is sent out from a cassette 40, conveyed by a conveyance roller 41 between a photosensitive drum 42 and a transfer device 43, and then discharged onto an output tray 44 through there.

At this time, the presence or absence of copy paper in the cassette 40, the conveyance path 4
An optical sensor 50 is used to detect the passage of a copy sheet through the copy paper 5. The present invention can also be applied to these.

Furthermore, the automatic document feeder described above is placed on the platen glass 8.

An optical sensor 50 is used to detect the insertion of the original and to detect that the original is set at a predetermined position on the platen glass 8. Further, in order to detect the size of the document on the platen glass 8, a plurality of optical sensors 50 may be provided on the top or bottom surface of the platen glass 8. The present invention can also be applied to such sensors.

"Effects of the Invention" The sheet presence/absence detection device of the present invention described above can reliably detect the presence or absence of a sheet even when outside light has entered.
Furthermore, false detections do not occur depending on the color of the sheet.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the sheet presence detection device of the present invention, FIG. 2 is a graph showing changes in the photoelectric conversion output of the light receiving element, and FIG. 3 is a diagram showing another embodiment of the present invention. FIG. 4 is a longitudinal sectional view of a copying machine for explaining the parts to which the sheet presence/absence detection device of the present invention can be adopted; FIGS. 5 and 6 are configuration diagrams of an optical sensor; FIG. The figure is a graph showing changes in the photoelectric conversion output, Figure 8 is a graph showing changes in the photoelectric conversion output depending on the paper quality of the sheet, and Figure 9 is a longitudinal cross-section of the automatic document feeder to explain the operation of a conventional sheet presence/absence detection device. It is a front view. 3... Sheet, 22a... Photoelectric conversion output of first light receiving element, 2
3a...Photoelectric conversion output of second light receiving element, 30
・・・・・・Processing device. Applicant: Fuji Xerox Co., Ltd. Agent

Claims (1)

[Claims] 1. A sensor installed in a sheet conveyance path that detects the presence or absence of a sheet by photoelectrically converting reflected or transmitted light emitted from a light source using a light receiving element, and this sensor detects the presence of the sheet. and a processing device that processes a signal to determine the presence or absence of the sheet. A sheet presence/absence detection device characterized in that it is determined that the sheet is present when the value exceeds a predetermined value. 2. Arranging a first light receiving element in the existing area of the sheet,
A second light-receiving element is arranged in a non-existing area of the sheet, and the processing device converts the photoelectric conversion output of the first light-receiving element;
2. The sheet presence/absence detection device according to claim 1, wherein a level difference between the photoelectric conversion output and the photoelectric conversion output of the second light receiving element is determined. 3. Obtaining a first photoelectric conversion output in a state where the sheet is absent, and then obtaining a second photoelectric conversion output in a state where the sheet is present, and the processing device outputs the first photoelectric conversion output;
2. The sheet presence/absence detection device according to claim 1, wherein a level difference between the second photoelectric conversion output and the second photoelectric conversion output is determined.