JPH10198174A - Paper kind detector and image forming device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect the kind of paper at the top, in a cassette where a plain paper and an OHP sheet are mixed by setting the arrangements of light emitting and receiving elements with respect to a paper sheet, within specific angles. SOLUTION: This paper kind detector provided with a reflective type sensor is constituted of the light emitting and receiving elements 1 and 2. Then, the arrangement angles of the light emitting and receiving elements 1 and 2 with the paper sheets are set 15 deg.-30 deg.. Even in one plain paper or plural plain papers laid one on top of another, almost the same reflectance is shown. On the other hand, when one OHP sheet exists on the plain paper or as the number of sheets laid one on top of another is larger, the reflectance is higher. In other words, the arrangement angles of the light emitting and receiving elements 1 and 2 are set 15 deg.-30 deg., so that in light projected from the light emitting element 1, the light passing through the OHP sheet becomes extremely little and most of incident light becomes regular reflected light. Therefore, even if one OHP sheet exists on the plain paper, the upper sheet is hardly influenced by the lower sheet and the kind of paper at the top in the cassette can be discriminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet type detecting device and an image forming apparatus provided with the device.

[0002]

2. Description of the Related Art In image forming apparatuses such as printers and copiers, plain paper and OHP sheets are used as paper for printing image data. These sheets have different characteristics from each other, and there are optimal printing conditions corresponding to the sheets. For example, in an image forming apparatus using an electrophotographic technique, when transferring a toner image to a sheet, the value of a high voltage applied to plain paper and an OHP sheet is changed, or the heat is sufficiently transferred to the OHP sheet in the fixing process to transfer toner. In order to increase the degree of melting of the paper and increase the transparency, control is performed such as reducing the paper conveyance speed. Therefore, the user who uses the image forming apparatus must set the print mode at the same time as setting the paper. If the print mode suitable for the paper is not executed, an error such as a paper jam occurs in the image forming apparatus or the quality of the output image deteriorates. In order to solve such a problem, various techniques have been invented for automatically determining the type of paper set in the image forming apparatus. Most of these inventions use an optical sensor.
As described in JP-A-6-56313 and JP-A-2-56375, a reflection type sensor is provided by providing one light emitting element and two or more light receiving elements. In addition, a sensor using a transmission sensor or a sensor configured by combining a transmission sensor and a reflection sensor can be easily considered.

[0003]

The reflection type sensor comprising one light emitting element and two or a plurality of light receiving elements, which is known in the art, is:
One of the light receiving elements is set at an angle symmetrical to the incident angle of the light emitting element to the paper, and the other light receiving elements are set at an angle asymmetrical to the incident angle of light. When light is irradiated and reflected on a sheet, the former receives specularly reflected light and the latter receives irregularly reflected light. Incidentally, the light irradiation angle of the light emitting element is generally about 45 ° with respect to the sheet.
The characteristics of the reflected light vary depending on the state of the paper surface. OHP sheets reflect specularly most of the light, whereas plain paper generates many irregular reflections in addition to specular reflection due to the surface roughness. That is, the known invention detects the paper type by paying particular attention to the presence or absence of diffusely reflected light. Considering a case where one sheet of OHP sheet is superimposed on plain paper in the paper type detection device having such a configuration, the OHP sheet transmits light, and thus the reflected light of the OHP sheet and the reflected light of plain paper are used as reflected light. The reflected light is mixed. In such a case, the known invention in which the determination is performed by paying particular attention to the irregularly reflected light has a problem that the top sheet type in the cassette to be detected at present cannot be detected. The image forming apparatus operates under printing conditions different from the paper type, and may cause an error such as paper jam or the like, and may cause deterioration in the quality of an output image.

In the case of using a transmission type sensor, since one sheet is symmetrical for detection, the problem of the reflection type sensor can be solved even if different types of papers are mixed. Paper must not overlap. Accordingly, the timing of the detection requires a function such as picking up the top sheet a little before the sheet is being conveyed or for detection. When the detection is performed during the paper transport, the determination of the paper type is performed at the end of the sequence, so that the image forming apparatus having a short paper path has a problem that the printing conditions of the final process cannot be determined in a timely manner. Although the latter can solve the former problem, the number of unnecessary operations increases during a series of processes of the image forming apparatus, which may become a bottleneck in increasing the printing speed of the apparatus.

SUMMARY OF THE INVENTION An object of the present invention is to provide a paper type detecting method for correctly detecting the top paper type in a cassette which is symmetrical to be detected even when plain paper and OHP sheets are mixed in a cassette containing paper. Is to provide.

[0006]

[Means for Solving the Problems] To solve the problems,
An arrangement angle θ of each element with respect to a sheet is set between 15 ° and 30 ° in a sheet type detection device provided with a reflection type sensor composed of a light emitting element and a light receiving element. By setting the angle, the light emitted from the light-emitting element by the OHP sheet has a very small amount of light transmitted through the sheet, and most of the incident light is specularly reflected light. Therefore, even if there is one OHP sheet on plain paper, it is less likely to be affected by the lower sheet, and it is possible to determine the type of the uppermost sheet in the cassette, that is, the type of sheet to be detected. In addition, since the reflectance of plain paper does not change with respect to the angle, there is an advantage that the difference in the specular reflection light between the OHP sheet and the plain paper increases.
To further increase the detection accuracy, another pair of reflection sensors is provided to constitute a paper type detection device. In the second reflection type sensor, the arrangement angle θ of each element with respect to the sheet is set to 45 ° or more. In this case, more light passes through the OHP sheet, and almost no regular reflection occurs with one sheet. In plain paper, the change in reflectance with respect to the angle is small.

In an image forming apparatus provided with a first sheet type detecting device constituted by two types of reflection sensors, a first output judging unit and a second output judging unit for judging each output, and each output By providing the determination result calculation means for performing a logical operation on the result of the determination means, it is possible to execute the printing process set for each paper type according to the type of paper obtained from the calculation processing result.

In the above-described first paper type detecting means, the light emitting element and the light receiving element are provided in each of the two pairs of reflection type sensors, but as another method, the second sheet comprising two light emitting elements and one light receiving element is used. Paper type detecting device can be considered. In this case, the image forming apparatus stores light emitting element on / off means for turning on / off the two light emitting elements, one output determining means for determining an output from the light receiving element, and a determination result of the output determining means. By providing the determination result storage means and the determination result calculation means for performing a logical operation on each determination result, it is possible to execute the printing process set for each paper type according to the paper type obtained from the calculation processing result as described above. Can be.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

FIG. 1 schematically shows a configuration of a first reflection type sensor in a first paper type detection device of the present invention. Actually, there is a plastic molded part (not shown) around each element, and the device is formed by fixing the element and forming a light path. In the present embodiment, the angle of each element of the first reflective sensor with respect to the sheet is set to 20 ° as shown in the figure. Similarly, the setting angle of the second reflective sensor shown in FIG. 2 is 45 °. What is common to the two sensors is that both focus only on specular reflection. The graphs shown in FIGS. 4 and 5 show the reflectance characteristics of the paper assuming the paper storage state in the cassette with these reflection sensors. In the figure, PPC indicates plain paper, OHP indicates an OHP sheet, and Blank indicates a black base (no paper). It can be seen that the plain paper shows almost the same reflectance regardless of which reflective sensor is used, even if one sheet or a plurality of sheets overlap. In the OHP sheet, the reflectance of the first reflective sensor having a smaller angle is higher, and the reflectance is higher as the number of overlapping sheets is larger. Focusing on the case where there is one OHP sheet on plain paper near the center of the graph and the case where only one OHP sheet is used, when θ = 45 °, the reflectance of one OHP sheet is smaller than that of plain paper. ing. When there is one OHP sheet on plain paper, the reflectance is greatly increased, and it can be seen that the reflection is affected by the lower sheet. As can be seen from the graph, it is difficult to accurately distinguish plain paper from OHP sheets. Next, when looking at the case of θ = 20 °,
The reflectances of one OHP sheet alone and one OHP sheet on plain paper have similar values. That is, it can be seen that the specular reflection is increased in the OHP sheet and that the reflection is dominant on the paper surface. As can be seen from the graph of FIG. 5, a clear separation point can be found between the plain paper and the OHP sheet. It is based on an experiment for an angle of θ = 20 °. OHP sheet and plain paper can be distinguished from each other at about θ = 30 °.
Considering the arrangement of the elements, the lower limit of the range is about θ = 15 °.

FIG. 3 shows a configuration of a reflection type sensor in the second paper type detecting device. In the configuration in which two reflection sensors are combined, two light emitting elements and one light receiving element are shared. In this case, means for controlling the energization of the light emitting element is required.

An embodiment of a control method in an image forming apparatus provided with the above-described paper type detecting device will be described. FIG.
FIG. 5 is a block diagram showing a control configuration of a sheet detection portion. Here, an image forming apparatus provided with a first sheet type detecting unit will be described. Paper type detector 6
The outputs from the respective reflective sensors are connected to output determination means 7 and 8 in the image forming apparatus 10, and the output is
It is input to PU9. The CPU has a function of a logical operation unit that performs a logical operation on each output determination result. Table 1 shows the output determination results of each sensor in the state where the paper is stored in the cassette. Based on the outputs of the two types of reflection sensors, it is possible to detect the state of plain paper, OHP sheet, and absence of paper. Therefore, the image forming apparatus can surely set the printing conditions suitable for the paper.

[0013]

[Table 1]

In this embodiment, the output determining means is provided as a peripheral circuit of the CPU.
Input to the A / D conversion port. By using the A / D conversion, it is possible to freely change the reference value for output determination to some extent. If the image forming apparatus can operate the reference value changing means from an operation panel or the like, there is an advantage that even if a sheet that cannot be distinguished at the time of standard setting is used, it can be handled by changing the reference value.

[0015]

According to the present invention, the paper type can be automatically detected in the cassette. It should be noted that the present paper type detection device can correctly detect the type when an OHP sheet and plain paper are mixed in the cassette, for example, even when there is one OHP sheet on plain paper. Therefore, in the image forming apparatus provided with the present paper type detecting device, it is possible to give optimum printing conditions to the paper, and the performance and reliability of the image forming device are improved. Also, when a system is constructed using the present image forming apparatus, it is possible to notify in advance if the paper is different from the paper designated by the host,
Avoid unnecessary printing.

[Brief description of the drawings]

FIG. 1 shows a first paper type detecting apparatus according to a first embodiment of the present invention.
FIG. 4 is an explanatory diagram of a reflection sensor.

FIG. 2 shows a second paper type detecting apparatus according to the first embodiment of the present invention.
FIG. 4 is an explanatory diagram of a reflection sensor.

FIG. 3 is an explanatory diagram of a reflection sensor in a second paper type detection device of the present invention.

FIG. 4 is a graph showing a reflection characteristic of a sheet by a first reflection sensor.

FIG. 5 is a graph showing a reflection characteristic of a sheet by a second reflection sensor.

FIG. 6 is a control block diagram of an image forming apparatus including a first sheet type determination unit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light emitting element, 2 ... Light receiving element, 3 ... Paper, 4, 5 ... Reflection type sensor, 6 ... Paper type detection apparatus, 7, 8 ... Output determination apparatus, 9 ... CPU, 10 ... Image forming apparatus.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // B41J 11/42 B41J 11/42 M (72) Inventor Kazuhiro Wakamatsu 1-1-1 Higashitaga-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd.Electrical Equipment Division Taga Division

Claims (6)

[Claims] 1. A paper type detection device comprising a light emitting element and a light receiving element, irradiating light from the light emitting element to a sheet to be detected, and detecting reflected light from the sheet with the light receiving element. A paper type detection device, wherein an arrangement angle [theta] of the light emitting element and the light receiving element with respect to the paper is set between 15 [deg.] And 30 [deg.]. 2. A paper type detection device comprising: a light emitting element and a light receiving element, irradiating light of the light emitting element to a sheet to be detected, and detecting reflected light from the sheet by the light receiving element. There are two types of reflective sensors composed of a light emitting element and the light receiving element. One of the light emitting element and the light receiving element has an arrangement angle θ between 15 ° and 30 ° with respect to the paper, and the other light emitting element and the light receiving element A sheet type detection device, wherein the element has an arrangement angle θ with respect to the sheet set to 45 ° or more. 3. The output determination means according to claim 2, wherein the first output determination means and the second output determination means determine respective outputs of the first reflection type sensor and the second reflection type sensor of the paper type detection device. An image forming apparatus comprising: a determination result calculation unit that performs a logical operation on a result of the determination unit, and executes a printing process set for each paper type according to a paper type obtained from the calculation processing result. 4. A paper type detection device, comprising: a light emitting element and a light receiving element, irradiating light from the light emitting element to a sheet to be detected, and detecting reflected light from the sheet with the light receiving element. Two light emitting elements and one light receiving element are provided. One of the light emitting elements has an arrangement angle θ with respect to the paper between 15 ° and 30 °, and the other has an arrangement angle θ with respect to the paper of 45 ° or more. The light emitted from each of the light-receiving elements is arranged to be reflected by a sheet to be detected and to be incident on the one light receiving element; A paper type detection device, wherein the devices are arranged at a predetermined angle so as to efficiently receive light from the elements. 5. The on / off means for controlling on / off of the one light emitting element, the other on / off means for controlling on / off of the other light emitting element, An output determination unit that determines an output from the light receiving element; a determination result storage unit that stores a determination result of the output determination unit; and a determination result calculation unit that performs a logical operation on each determination result. An image forming apparatus that executes a printing process set for each paper type according to the paper type obtained from the processing result. 6. An image forming apparatus according to claim 3, further comprising a criterion value setting means for changing the setting of the criterion value of said output determining means.