JPH0930686A - Sheet sensing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sense a sheet position correctly and quicken a response in sensing by constituting a specific relation of such factors as a region where the output of a photo-sensor in a light receiving window becomes unstable, the distance of sheet advancing during one sampling clock, and the frequency of sampling. SOLUTION: Output condition of a photo-sensor SP1 is checked and recognized by a CPU with sampling clocks. When the CPU senses a sheet position on the basis of the output of the photo-sensor SP1, a plurality of sampling runs are made for the sensor output. The relation N>=int(X/d)+1 should be established, where X in mm is the length crosswise of the unstable region in a light receiving window, (d) in mm is the distance of sheet P advancing in the region within the window during one sampling clock, and N is frequency of sampling while the foremost part of a black mark passes the length X in the unstable region, provided that int signifies the status obtained by cutting off below the decimal of X/d and taking only the orders of integer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet detecting device for detecting a sheet or marks attached to a sheet.

[0002]

2. Description of the Related Art Conventionally, for example, in a printer or the like,
When carrying out printing by feeding the paper pulled out from the paper container to the printing unit, it is necessary to recognize that the paper has been fed to the print start position. Further, when multicolor printing (color printing) is performed, a plurality of types of color inks are applied on a single sheet of paper, which complicates the sheet conveying operation.
For example, in the case of three colors, first the Y (yellow) image is printed, then only the paper is reversed and reset to the print start position, then the M (magenta) image is printed from above the yellow color. Repaint. Then, the paper is returned again and set to the print start position three times, and the C (cyan) image is applied over the above two colors to finish the printing. Further, in the case of a four-color configuration in which characters and the like are printed in black, the paper is further reversed, and the Bk (black) image is overlaid and the printing ends.

In this way, the paper is reciprocated to and from the printing unit, and
In the case of color printing that prints in four colors or four colors, it is necessary to perform not only the alignment in the first paper feeding but also the alignment to the print start position of the paper for each reciprocation of the paper on which the colors are applied. is there. Otherwise, misregistration occurs in the colors to be applied, blurring occurs in the gradation and outline, and an image with good image quality cannot be obtained. For example, even in a printer having a relatively low resolution such as a standard print dot density of 300 dpi (dots / inch), the print dot pitch is extremely fine at about 85 μm (microns), and therefore some positional deviation occurs. Even if there is, a misalignment will occur in the overlapping of colors, so a good image cannot be obtained.

Therefore, in order to correctly align the sheets, a specific mark is printed in advance at a predetermined position on the back surface of the sheet with black ink or the like, and the mark is reflected by a reflection type photo sensor or a transmission type photo sensor. A method is used in which the position of the paper is recognized by detecting it with a sensor or the like, and the paper is correctly positioned based on this recognition.

FIG. 8A schematically shows a reflection type photo sensor as an example of the photo sensor for detecting the position (mark) of the sheet as described above. Further, Fig. 2 (b) shows a side view of the photo sensor and the paper conveyed to the printing section, and Fig. 3 (c) shows the photo sensor and the paper as seen from the conveying direction. The figure shows

The photosensor 1 shown in FIG. 1 (a) is provided with a light emitting portion 1a composed of an LED (light emitting diode) and the like, and a light receiving window 1b composed of a phototransistor and the like integrally formed on the upper part thereof. Above the photo sensor 1, the paper (paper P shown in FIGS. 2 (b) and 2 (c)) is tilted from the upper left to the lower right as shown by the arrow A in FIG. From right)
When the sheet P is conveyed to the sheet, the light emitted from the light emitting portion 1a is reflected on the sheet P and enters the light receiving window 1b. The passage or the position of the paper P is recognized by the output of the phototransistor (output of the photosensor 1) that detects the incident light.

In general, the size of the light receiving window 1b of the photosensor 1 is about 0.5 mm square even in the case of the reflection type or the transmission type. When all the light enters within the size of the light receiving window 1b, the output of the phototransistor is completely turned on. That is, the output of the photo sensor 1 is on when the surface of the paper P is a white background. Further, if no light is incident within the size of the light receiving window 1b, the output of the phototransistor is completely turned off. That is, if the reflection surface of the paper P (the surface in the detection area of the photo sensor 1) is in black, the output of the photo sensor 1 is off.

By the way, the amount of light incident on the light receiving window 1b does not always enter the entire window, and the entire window is not always completely shielded. In the process in which the conveyance surface of the paper P on the photo sensor 1 changes from a white background to a black background such as a mark, the phototransistor of the photo sensor 1 may become semi-conductive due to the gradual reduction of light from the incident light over the window. .

The above-mentioned paper P is A4 size, A3 size.
Size, or B5 size, B4 size, etc. are standardized, and a certain size (size) is commonly used depending on the application, but the thickness is standardized by the weight per unit area. However, it is relatively arbitrarily selected based on user preference or paper price. Therefore, the figure (b)
The gap between the guide plates 2a and 2b for guiding the paper P shown in is formed relatively gently with respect to the paper P passing therethrough so as to correspond to the thickness of the paper P arbitrarily selected.
Therefore, in the gradual gap between the guide plates 2a and 2b, the paper P is fed to the paper P by the slight vibration of the main body device and the conveyance system (especially vibration is likely to occur at the initial stage of startup).
As shown by the position P1 or P2 indicated by the alternate long and short dash line in (c),
It is easy to cause vibration fluttering up and down.

When such vertical vibration occurs, the same figure
As shown in (c), the light emitted from the light emitting unit 1a of the photo sensor 1 to the paper P is farther than the original position to be reflected due to the upward and downward reflection points of the paper P. Change nearby (to the left or right). If the current reflection surface of the paper P is a white background, even if the reflection point is vertically displaced from the original position, the displaced position is also a white background, so that the reflected light always corresponds to a white background. Then, even if the center of the reflected light, which is reflected by the paper P and then folded back and reaches the light receiving window 1b, deviates from the center of the light receiving window 1b due to the movement of the reflection point, it spreads to the light incident on the light receiving window 1b. And the entire area of the spread corresponds to the white background of the paper P as described above. Therefore, since the photo sensor 1 outputs an output corresponding to the detection of the white background, no inconvenience occurs. If the current reflection surface of the paper P is a black background (mark),
In this case as well, even if the reflection point deviates from the original position to the left or right, the deviated position is also a black background, so the reflected light always corresponds to a black background. That is, in this case, the light is not always reflected even if the paper P fluctuates vertically. Therefore, since the reflected light does not enter the light receiving window 1b, the photosensor 1 outputs an output corresponding to the detection of the black background, and in this case, the detection result is not inconvenient.

However, if the current reflection surface of the paper P is at the boundary between the white background and the black background, the phototransistor is originally in a semi-conductive state, and the amount of reflected light is gradually reduced as the paper P is conveyed, and the phototransistor of the phototransistor is reduced. When it falls below the output threshold, it turns off, but in reality this is not the case and troublesome things occur. Hereinafter, this will be briefly described.

First, FIG. 9 (a) shows a basic circuit configuration of the photo sensor, and FIG. 9 (b) shows an example of the output of the photo sensor. As shown in FIG. 3A, the light emitted from the light emitting diode (LED) of the light emitting portion 1a hits the paper P and is reflected, and the phototransistor (Ptr) of the light receiving window 1b.
Incident on. If the reflection point of the paper P is a white background, there is incident light, the phototransistor (Ptr) becomes conductive, and the emitter output VI becomes "H". On the other hand, if the reflection point of the paper P is a black background, there is no incident light and the phototransistor (Ptr)
The collector output and emitter are blocked and the emitter output VI
Becomes "L".

In FIG. 1B, the emitter output VI is shown from the bottom to the top of the vertical axis, and the time t is shown from the left to the right on the horizontal axis. As shown in the "white area" on the left side of the horizontal axis in FIG. 7B, when the reflection point of the paper P is a white background, the output of the photosensor 1 (emitter output VI) is the power supply voltage VC.
Is almost the same level as "H". If the paper P advances and its reflection point becomes a black background, the output of the photosensor 1 is at a substantially ground level, as shown in the "black area" on the right side of the horizontal axis in FIG. Is "L".

When the paper P does not vibrate vertically, when the reflection point of the paper P changes from the white background to the black background, the amount of light incident on the light receiving window 1b of the photosensor 1 gradually decreases. That is,
In the "intermediate region" where the white background changes to the black background, the output of the phototransistor originally becomes "L" when the output gradually decreases as shown by the broken line in FIG.

[0015]

However, since the paper P often vibrates up and down as described above, the reflection point vibrates up and down around the reference position correspondingly. When the reflection point swings back and forth in this way, the center position of the reflected light that is reflected and enters the light receiving window 1b also swings left and right (see FIG. 8C). That is, the amount of light incident on the light receiving window fluctuates irregularly, such as a large amount of white and a large amount of black. That is, as shown by the solid line in the "intermediate region" at the center of the horizontal axis in Fig. 9 (b), the photosensor 1 irregularly repeats the output close to white background detection and the output close to black background detection. appear. From the output of the photosensor indicating such an unstable detection state, it cannot be correctly determined that the position of the paper, that is, the boundary between the white background and the black background (black mark) has reached the detection area.

In order to prevent the detection of the sheet position from becoming extremely unstable in this manner, the number of samplings for checking the output of the photosensor is usually increased. Then, the control unit can determine that the unstable detection period (the period in which the photo sensor detects the above-mentioned intermediate region) has elapsed, and therefore, it is possible to confirm that the output is stable after the unstable detection period has elapsed. By checking, the position of the paper can be recognized.

However, if the number of samplings is increased, it is determined that the unstable detection period has elapsed after a certain amount of time has elapsed since the stable detection period has been entered, and accordingly, the detection response is increased accordingly. Will be slowed down. Not only that, the sampled signal (the output of the photo sensor) must be saved until the unstable detection period elapses, and in addition,
Since the photosensors similar to the above are provided in each part of the main body device, a RAM (random access memory) having a large capacity corresponding to the photosensors must be provided, which increases the product cost. Problems also occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances,
It is an object of the present invention to provide a paper detection device that can detect a paper position correctly without malfunctioning and that has a quick detection response.

[0019]

According to the first aspect of the present invention,
The mark on the paper reflects, absorbs, or transmits the light from the light source, and the reflected, absorbed, or transmitted light is incident on the light receiving window of the photo sensor, and the state of the incident light is measured by the photo sensor. It is premised on a paper detection device for identifying the above mark by detecting.

In the paper detection device of the present invention, X is a region where the output of the photosensor becomes unstable in the light receiving window of the photosensor due to the amount of light incident on the light receiving window, and a sampling clock for sampling the output of the photosensor is used. It is configured such that N ≧ int (X / d) +1 (where int is a function for extracting only integers), where d is the distance traveled by the paper during one clock period and N is the number of times of sampling. The light source and the photo sensor are
For example, as described in claim 2, it is integrally configured, the light of the light source is transmitted through the paper, and the transmitted light is detected by the photo sensor. Further, for example, as described in claim 3, the light of the light source is reflected by the paper, and the reflected light is detected by the photo sensor.

Next, the invention according to claim 4 reflects, absorbs, or transmits the light from the light source by the mark provided on the paper, and the reflected, absorbed, or transmitted light is the light receiving window of the photosensor. It is applied to a sheet detection device for identifying the mark by making the mark incident on the sheet and detecting the state of the incident light with a photo sensor.

In the paper detecting device of the present invention, the paper running means runs the paper, the judging means judges the output state of the photosensor, and the control means operates the judging means after the operation of the paper running means. Further, for example, as described in claim 5, a time counting means which is activated after the operation of the sheet traveling means is further provided, and the judging means operates after the time measuring means measures a predetermined time.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view of a print processing unit of an image forming apparatus according to an embodiment. In the figure,
The print processing unit includes a print head 11 and a platen roll 12 facing the print head 11. The facing portion between the print head 11 and the platen roll 12 forms a print portion.
An ink ribbon 13 is stretched and interposed between the guide rolls 14a and 14b in the printing section. The ink ribbon 13 is held by the supply reel 15a and the take-up reel 15b, and the take-up reel 15b rotates in the clockwise direction shown by an arrow B in the figure, and the used ink ribbon 13 is used.
By winding up, the unused portion of the ink ribbon 13 fastened to the supply reel 15a is pulled out and supplied to the printing portion.

The ink ribbon 13 and the platen roll 1
A sheet P is interposed between the sheet P and the sheet 2. The paper P has a large number of label-like recording papers having adhesiveness arranged on the back surface in the longitudinal direction of a tape-like mount, and is formed in a roll shape as a whole to be fastened to the paper feed reel 16. Has been done. This paper P advances and retreats in the transport direction indicated by arrow C in the figure by rotation of the paper feed reel 16 in both forward and reverse directions.

Reflective photosensors SP1 and SP2 for detecting the position of the paper P are provided in the front and rear of the printing section, that is, in the downstream and upstream of the paper P and the conveyance direction of the ink ribbon 13.
Are arranged. In addition, an ink ribbon sensor SR is arranged near the guide roll 14b between the guide roll 14b and the take-up reel 15b.

The above-mentioned print head 11 has, at its tip,
A heating element corresponding to the maximum number of print pixels in the width direction of the paper P arranged in the width direction of the paper P is provided. The front end of the print head 11 rotates up and down around the support shaft 11-1 at the rear end as shown by a double-headed arrow D in the figure.

The print head 11 is rotated upward during printing, so that the paper P and the ink ribbon 13 are pressed against the platen roll 12. The paper P is sequentially transferred with the ink of the ink ribbon 13 in the printing portion by the rotation of the platen roll 12 in the counterclockwise direction, and is carried out in the transport direction indicated by arrow C in the figure. Further, in the case of multicolor printing, the paper P is printed on one side thereof, then is re-carried in (sent back) in the opposite direction, and ink of another color is applied again on the previously printed surface. That is repeated.

FIG. 2 shows a block diagram of the main circuit of the image forming apparatus. In the circuit shown in the figure, a CPU (central processing unit) 20, a memory 21, an AD converter 22, a head control circuit 23, and an IO port 24 are connected to a bus 25. A volume circuit 26 is connected to the AD converter 22, the print head 11 is connected to the head control circuit, and a sensor 28 (photosensors SP1 and SP2, and an ink ribbon sensor SR) is connected to the IO port 24. ing.

The CPU 20 is a ROM (not shown).
The program stored in the (read-only memory) is read out, and the above-mentioned units are controlled based on the program. The memory 21 is a RA that can be written and read freely.
M (random access memory), CPU 20
The data in the middle of calculation by, the input signal of the sensor 28, etc. are temporarily stored.

The AD converter 22 converts the analog image data input from the outside by a scanner or the like and the density of which has been set in the volume circuit 26 into digital data. The head control circuit 23 supplies a pulse voltage according to the image data,
It is adjusted according to the heat history and the like, and is selectively applied to the heating element of the head 11.

The IO port 24 outputs a control signal to a motor driver that drives a motor (not shown) that conveys the paper P and the ink ribbon 13. Further, the light emission drive signal is output to the sensor 28 and the output of the sensor 28 is input.

FIG. 3 shows a circuit configuration of the photo sensor SP1. The photo sensor SP2 has the same configuration. As shown in the figure, the photosensor SP1 is formed by adding a comparator 20, a reference voltage power supply 21 and the like to a circuit having a configuration similar to the basic circuit configuration of the photosensor shown in FIG. 9A. The inverting input terminal of the comparator 20 has an emitter output VI of the phototransistor SP1b.
Is input, and the reference voltage VN is input to the non-inverting input terminal of the comparator 20. This photo sensor SP
The external appearance of No. 1 is the same as that of the photo sensor shown in FIG.

When the sensor detection area of the sheet P is white (hereinafter, simply the sheet P is white), the emitter output VI of the photosensor SP1b input to the inverting input terminal of the comparator 20 is "H", and the comparator 20 outputs the same. Since it becomes higher than the reference voltage input to the non-inverting input terminal, the output of the comparator 20 is “L”. On the other hand, when the sensor detection area of the paper P is black (hereinafter, simply the paper P is black), the emitter output VI of the photosensor SP1b is "L", which is lower than the reference voltage, and thus the comparator 2
The output of 0 is "H".

In FIGS. 4 (a), (b) and (c), the photo sensor S is shown.
The relationship between the output of P1 and the position of the paper P is schematically shown. It is assumed that the paper P is conveyed from left to right in the figure as indicated by arrow E in FIG. There is a white background Pf in the front in the transport direction, and a black mark Pk follows in the rear. Now, the boundary 22 between the white background Pf and the black mark Pk is a circle mark 23 in the figure.
It is assumed that the photo sensor SP1 shown in FIG.

FIG. 3B shows the light receiving window SP1b-1 of the photosensor SP1b. This light receiving window SP1b-1
Is approximately 0.5 × 0.5 mm (millimeter). The amount of light at the reflection point incident on the light receiving window SP1b-1 decreases with the passage of time. That is, the black shadow expands from left to right as indicated by arrow G in the figure.

By the way, the tip of the black mark Pk (white background Pf
Even if the boundary 22) between the black mark Pk and the black mark Pk reaches the light receiving window SP1b-1, the light receiving area (light blocking area) corresponding to the black mark is larger than the certain range of the light receiving window SP1b-1 shown in the area F of FIG. 3) is narrow, that is, if the white area (light receiving area) is equal to or larger than the area J, this is sufficiently larger than the black area (light shielding area) is equal to or smaller than the area F. Since the emitter output VI of the phototransistor SP1b exceeds the reference voltage VN, the output of the photosensor SP1 is
It is "L" as shown in the output 24 of (c). That is, the paper P is recognized as white.

FIGS. 5 (a) and 5 (b) show the output of the phototransistor SP1b in a state where a certain period of time has elapsed after the conveyance of the sheet P has further progressed from the above state. For convenience of explanation, from the state shown in FIGS. 4 (b) and 4 (c), the state shown in FIG.
The state during the elapse of the state shown in (b) will be described later.

As shown in FIG. 5 (a), when the front end 22 of the black mark Pk is sufficiently conveyed and further enters into the above-mentioned region F of the light receiving window SP1b-1 by the region X or more, this time, FIG.
As shown in (a), the black area (light-shielding area) is greater than or equal to the area F plus the area X, and the white area (light-receiving area) is less than or equal to the remaining area R. Since the width is sufficiently wide, the emitter output VI of the phototransistor SP1b becomes lower than the reference voltage VN, and the output of the photosensor SP1 is as shown in the output 26 of FIG.
"H". That is, the paper P is recognized as black.

In the intermediate state from the state shown in FIG. 4 to the state shown in FIG. 5, an unstable state appears as described later. FIGS. 6 (a) and 6 (b) show an unstable state of the output of the photosensor SP1 which appears when the tip 22 of the black mark Pk of the paper P is at the intermediate position of the reflection point. The relationship between the output of the photo sensor SP1 or the transport distance of the paper P and the sampling clock is schematically shown.

As shown in FIG. 7A, the light receiving window SP1b-
While the leading edge 22 of the black mark Pk is passing through the above-mentioned area X of 1 (hereinafter, referred to as the intermediate area X or the unstable area X), the paper P vibrates up and down as described above.
The amount of light incident on the light receiving window SP1b-1 is not stable. In some cases, the amount of light is sufficiently large as shown in FIG. 4 (b), and in other cases, the amount of light is the reference as shown in FIG. 5 (a). It becomes less than the value and changes irregularly.

Therefore, the output of the photosensor SP1 is
During the passage period, that is, in the intermediate period from the "L" output during the detection of the white background Pf to the output "H" of the black mark Pk, the irregular change in the light amount is dealt with. For example, the outputs 25a and 25b of "H" in FIG.
And 25c and "L" outputs 25d, 25e and 25
As shown in f, the detection signals of "H" and "L" are output irregularly. Incidentally, the horizontal axis shown in FIG. 4B represents the time T and the transport distance D of the paper P.

In this embodiment, the CPU 20 shown in FIG. 2 checks and recognizes the output state of the photosensor SP1 by using the sampling clock. Then, in general, when the CPU attempts to detect the paper position based on the output of the photo sensor, the output of the photo sensor is checked (sampling) a plurality of times in order to prevent chattering and noise from being picked up. However, if you try to determine the position of the paper by checking with a normal method, for example, if the number of samplings is increased, the detection response will be slow, while if the sampling clock cycle is made fine, a large capacity memory will be required. As described above, the inconvenience of becoming a problem occurs.

In this embodiment, the cycle of the sampling clock is set appropriately as follows. That is, the lateral length of the unstable region X of the light receiving window SP1b-1 is represented by X (mm) by using the same coefficient name as the region name, and the paper P is fed to the light receiving window SP1b- during one sampling clock.
If the distance traveled in the area within 1 is d (mm), and the number of times the tip 22 of the black mark Pk is sampled while passing through the length X of the unstable area is n, then , Int (X / d) ≦ n ≦ int (X / d) +1. However, int is a function that rounds down the decimal places of X / d and extracts only the integer.

In order to detect the black mark Pk correctly, it is necessary to check the state of the photosensor output during the period until the tip 22 of the black mark Pk completely passes through the unstable region X. In order to prevent the black mark Pk from being erroneously detected, in other words, to correctly detect the black mark Pk, where N is the number of samplings, it is necessary that N ≧ int (X / d) +1.

Thus, in this embodiment, the light receiving window SP1
The number of times of sampling in the unstable region X of b-1 is specified in advance, and sampling is performed based on this number of times of sampling.

In designing, the above relationship is converted into the following relationship. That is, if the step rate of the motor that conveys the paper P is S (millimeter / step) and one step corresponds to one sampling clock, the paper P can be used at one sampling clock as described above.
Will be "S = d" because it is transported a distance d. Therefore, assuming that the cycle of the sampling clock is C (ms), the distance d (= S) is carried in one clock as described above, and therefore the sampling time t is t> N × S (ms). Therefore, the number of sampling times N is N> t / C.

In the example shown in FIGS. 6B and 6C, the unstable region X
The sampling clock C requires about 4 cycles for the output period (sampling period) t of the photosensor corresponding to. That is, from the above equation, the number of times N must be at least 5 times.

After setting the number of times N in this way, for example, at the cycle C1 of the sampling clock shown in FIG.
If it is assumed that the output 25a of the photosensor SP1 that has become "H" from the output that has been "L" until then is detected, this is the first time, and the sampling is continuously performed five times until the fifth cycle C5. The output "H" of the photosensor SP1 which repeats the above-mentioned irregular changes at every clock cycle.
Not to detect. For example, in the example of FIG.
In the second cycle C2 and the fourth cycle C4, the output of the photosensor SP1 is "L", and "H" is not detected. That is, if it is not "H" for five consecutive times, it can be determined that the photosensor SP1 causes chattering as shown in FIG. 6B or the output is changed due to noise.

That is, if the tip 22 of the black mark Pk is the sampling frequency N specified in correspondence with the period during which the black mark Pk is passing through the unstable region X, and the output of the photosensor SP1 is "H" continuously. For example, the tip 22 of the black mark Pk has passed through the unstable region X and is in the stable region R shown in FIGS. 5 (a) and 5 (b). Therefore, the detection of the black mark Pk in the state shown in FIGS. 5 (a) and 5 (b) can be confirmed by confirming that the output of the photosensor SP1 has become "H" continuously N times. That is, the detection of the black mark Pk is completed in 5 cycles of the sampling clock.

Next, the processing operation of the CPU 20 for accurately detecting the position (black mark) of the paper P at high speed based on the above configuration and algorithm will be described below. FIG. 7 is a flowchart illustrating the processing operation of the CPU 20. In this process, the counter CNT built in the CPU 20 is used. Further, this processing is not limited to the photosensor SP1 (or SP2), but can be commonly applied to photosensors having other configurations.

As shown in the flow chart of the figure, it is first determined whether or not the paper P is being conveyed (step S).
1). In this process, if the signal for driving the motor 27 is output from the IO port 24, it is determined that the paper P is being conveyed.

When the paper P is stopped (S
1 is N), the black mark detection process is not performed and the above determination is repeated to wait for the conveyance of the paper P. In this case, if the black mark is detected while the paper is stopped, when the tip of the black mark is just in the detection area, as described above, the vibration between the paper P and the photo sensor is caused by the vibration of the motor. The distance fluctuates slightly. That is, the input voltage VI of the comparator 20 is not stable. This unstable state does not change with the passage of time unless the sheet P is being conveyed, and therefore the sheet position cannot be detected by the algorithm described above in this process. When the paper P is stopped, the paper P is processed without performing the black mark detection processing.
This is the reason for waiting for the start of conveyance of.

Then, in step S1 described above, when the paper P is being conveyed (S1 is Y), it is determined whether or not the output OUT (see FIG. 3) of the photosensor SP1 is "H". Is determined (step S2). This process is a process of determining whether or not the black mark Pk of the paper P is in the detection area of the photo sensor SP1. In this determination, if the output OUT of the photosensor SP1 is not "H" (S2 is N), the white background portion of the paper P is in the detection area. Therefore, in this case, the output of the photosensor SP1. The above determination is repeated until OUT becomes “H” (see the states of FIGS. 4B and 4C).

Then, the output OUT of the photosensor SP1
If H becomes "H" (S2 is Y), it is judged that the tip 22 of the black mark Pk may have come to the unstable region X (Figs. 6 (a), (b), (c)). ), The “H” signal is stored in the memory 2
1 (RAM) (step S3), and then the value of the counter CNT is incremented by "1" (step S3).
4). As a result, the number of times the output OUT of the photosensor SP1 becomes “H” within the predetermined time is recorded.

Subsequent to the above, the value of the count CNT just incremented is referred to, and it is determined whether or not the value is "N" (step S5). This "N" is
The length X of the unstable region is the number of times of sampling corresponding to the period during which the paper P is transported.

If the value of the counter CNT is not "N" in step S (N in S5), then,
It is determined whether or not one sampling cycle "C" has elapsed (step S6). If one sampling cycle "C" has not elapsed (S6 is N), the above determination is repeated until the elapse.

When one sampling cycle "C" has elapsed (S6 is Y), the photosensor SP is read again.
It is determined whether the output OUT of 1 is "H" (step S7). If the output OUT is "L" (S7 is N), the output just changed from "L" to "H" again becomes "L" within a short period of one sampling cycle. It is judged that the output fluctuation is caused by chattering in the unstable region X or noise, and the value of the counter CNT is cleared to "0" and output "H".
The recording of the number of times is canceled (step S8).

Next, it is judged again whether or not one sampling cycle "C" has passed after the above output change (step S9), and if one sampling cycle "C" has not passed (S9 is N ), The above determination is repeated until the time elapses, and after confirming the elapse of one sampling cycle "C" (S9 is Y), the process returns to the step S2 and the processes of step S2 and thereafter are repeated. That is, from the beginning, the black mark Pk
Detect again.

As a result, it is possible to prevent erroneous recognition that the black mark Pk is detected due to output fluctuations due to chattering or noise in the unstable region X. Step S7 above
If the output OUT of the photosensor SP1 is still “H” in the determination of No. 2, it is determined that the detection of the black mark Pk (see FIGS. 5A and 5B) may continue in the stable region. Then, in this case, the process returns to the step S3, and the processes after the step S3 are repeated. As a result, the recording of the number of sampling times when the output OUT of the photosensor SP1 is “H” within the predetermined time is continued.

If the value of the counter CNT referred to in the above step S5 is "N" (S5Y), this means that the number of times is set in advance corresponding to the predetermined time, Output O of photo sensor SP1
Since the UT has become "H", it is judged that the detection of the black mark Pk continues in the stable area (states of FIGS. 5 (a) and 5 (b)), and Step S
In step 3, the contents of the output OUT of the photosensor SP1 (in this case, the “H” signal) stored in the memory 21 are output to a predetermined circuit to determine the output of the photosensor SP1 (step S10), and the process concerned. To finish.

Thus, at the sampling timing, the output of the photosensor SP1 (comparator 20
Output), if OUT is not "H" N times consecutively,
The process of determining the "H" signal (the process of step S10) is not performed. That is, as in the case of detection in the intermediate region shown in FIGS. 6A, 6B, and 6C, the comparator 20
In the state in which the output OUT of R changes irregularly such that the output OUT becomes "H" or "L", "H" signal is determined because "H" does not continue N times during the sampling during this period. No processing is done. As a result, it is possible to reliably prevent erroneous detection of the unstable intermediate region.

"N" has a side length of 0.5 m.
The black mark Pk is detected because the sampling is an extremely small number of times corresponding to the carrying rate S of the paper P that is carried in the unstable area X that is less than 1/2 of the light receiving window SP1-1 which is m. Photo sensor SP1 after entering the state
The response time until the output of is determined is extremely short.

When a white background is detected from the black mark detection state, the determination condition in steps S2 and S7 may be set to "OUT = L". Also, steps SS1 and S
It is also possible to provide a timer between 2 and measure a predetermined elapsed time, and wait for the traveling of the paper P after the start of conveyance to stabilize before performing the determination in step S2.

[0064]

As described above, according to the present invention,
Since the output of the photo sensor is sampled by specifying the number of samplings based on the range of the unstable area of the light receiving window of the photo sensor and the paper transport rate corresponding to the sampling clock, the photo sensor due to chattering or noise in the unstable area. The output that fluctuates irregularly is not determined and detected as an output, and therefore stable sheet position detection without malfunction can be performed. Also, since the number of times of sampling is specified corresponding to the unstable area of the photo sensor, the correct paper position can be determined in the shortest time corresponding to the characteristics of the photo sensor. Therefore, the response of the paper position detection in an extremely short time is possible. Is possible.

[Brief description of drawings]

FIG. 1 is a side sectional view of a print processing unit of an image forming apparatus according to an embodiment.

FIG. 2 is a configuration block diagram of a main circuit of the image forming apparatus.

FIG. 3 is a diagram showing a circuit configuration of a photo sensor.

4A, 4B, and 4C are diagrams showing the relationship between the output of the photosensor and the position of the paper.

5 (a) and 5 (b) are diagrams showing the output of the phototransistor in a state where a certain period of time has elapsed after the sheet conveyance further progresses.

6 (a) and 6 (b) are diagrams showing an unstable state of the output of the photo sensor that appears when the tip of the black mark on the paper is at the intermediate position of the reflection point, and FIG. 6 (c) is the output of the photo sensor. Alternatively, it is a diagram schematically showing a relationship between a sheet conveyance distance and a sampling clock.

FIG. 7 is a flowchart illustrating a processing operation of a CPU that detects a position of a sheet.

8A is a schematic view of a reflective photosensor, FIG. 8B is a side view of the photosensor and the paper, and FIG. 8C is a view of the photosensor and the paper as viewed from the conveyance direction. Is.

9A is a diagram showing a basic circuit configuration of a photosensor, and FIG. 9B is a diagram showing an example of an output of the photosensor.

[Explanation of symbols]

 1 Photosensor 1a Light emitting part 1b Light receiving window P Paper P1, P2 Paper vibrating position 11 Print head 11-1 Spindle 12 Platen roll 13 Ink ribbon 14a, 14b Guide roll 15a Supply reel 15b Take-up reel 16 Paper reel SP1 , SP2 Reflective photosensor SP1a Light emitting diode SP1b Phototransistor SP1b-1 Light receiving window SR Ink ribbon sensor 20 Comparator 22 White / black background boundary 23 Photosensor reflection point (detection area) 24, 25d, 25e, 25f “L” output 25a, 25b, 25c, 26 "H" output d Carrier distance / 1 clock X Unstable detection area C (C1, C2, C4, C5) Clock period

Claims (5)

[Claims] 1. A mark provided on a sheet reflects, absorbs, or transmits light from a light source, causes the reflected, absorbed, or transmitted light to enter a light receiving window of a photosensor, and In the paper detection device for identifying the mark by detecting the state by the photo sensor, an area where the output of the photo sensor becomes unstable in the light receiving window of the photo sensor due to the amount of light incident on the light receiving window is defined as X. , N is the distance traveled by the paper during one clock period of a sampling clock for sampling the output of the photo sensor, and N is the number of times of sampling, N ≧ int (X / d) +1 (where int is an integer Paper detection device, which is configured to be a function for taking out only the position). 2. The light source and the photo sensor are integrally configured, the light of the light source is transmitted through the paper, and the transmitted light is detected by the photo sensor. Paper detection device. 3. The light source and the photo sensor are integrally configured, the light of the light source is reflected by the paper, and the reflected light is detected by the photo sensor. Paper detection device. 4. A mark provided on a sheet reflects, absorbs, or transmits light from a light source, causes the reflected, absorbed, or transmitted light to enter a light receiving window of a photosensor, and In a paper detection device for identifying the mark by detecting the state by a photo sensor, a paper running means for running the paper, a judging means for judging the output state of the photo sensor, and the paper running means after the operation of the paper running means. A sheet detection device comprising: a control unit that operates a determination unit. 5. The time measuring means which is activated after the operation of the paper running means is further provided, and the judging means is operated after the time measuring means measures a predetermined time.
Paper detection device described.