JP4736597B2 - Medium detection device - Google Patents

Description

  The present invention relates to a medium detection apparatus and an image forming apparatus including a sensor that reflects light emitted from a light emitting unit toward a conveyance path of a medium so as to straddle the conveyance path and takes in the light reception unit.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a sensor is arranged on a conveyance path of a sheet material (paper, OHP film, etc.) serving as a medium, and a medium passing through the conveyance path is detected by the sensor to determine the timing of subsequent processing. Adjustments have been made.

  Although there are a contact type and a non-contact type as this sensor, a non-contact type sensor that does not give unnecessary resistance to the medium is often used. As a non-contact type sensor, an optical sensor is mainly used, and a light amount change due to transmission or reflection of light emitted from a light emitting unit to a light receiving unit is captured by the light receiving unit to detect passage or non-passage of a medium.

  In recent years, a light-emitting unit and a light-receiving unit are arranged on one side of a medium conveyance path, and a reflector such as a right-angle prism is provided on the other side to fold the light back and guide the light to the light-receiving unit across the medium conveyance path. A type sensor is also considered (for example, see Patent Document 1).

JP 2003-40486 A

  However, in the detection of a medium using such a retroreflective sensor, the conventional image forming apparatus simply detects the presence or absence of the medium on the conveyance path, and the medium type (for example, plain paper, tracing paper, OHP, etc.) The type is not determined. Therefore, there is a problem that it is not possible to perform control such as discriminating the type of medium using the regressive reflection type sensor and adjusting the subsequent processing.

The present invention has been made to solve such problems. That is, the present invention relates to a sensor that reflects light emitted from a light emitting unit substantially perpendicularly toward a medium conveyance path so as to straddle the conveyance path a plurality of times and takes it in a light receiving unit, and a level change of an output signal by the sensor A step of determining a type of the medium according to a step-like level change generated in the output signal of the sensor according to the number of times the light emitted from the light emitting unit straddles the transport path. The medium detecting device is characterized by determining means for determining the type of the medium based on the next level change when the predetermined level has not been reached .

  In the present invention as described above, the medium detection using a sensor that reflects the light emitted from the light emitting portion substantially perpendicularly toward the conveyance path of the medium so as to cross the conveyance path a plurality of times and captures the light at the light receiving portion, that is, a regressive reflection type sensor. In this case, since the type of the medium is determined using the level change of the output signal of the sensor, the type of the medium can be accurately determined.

  The determination unit can also calculate the medium transport speed in accordance with at least two level change timings among the step-like level changes in the output signal of the sensor.

  In the present invention, such a medium detection apparatus is applied to an image forming apparatus, and the image forming conditions on the medium are adjusted based on the type of the detected medium, or the processing timing at the later stage is determined according to the detection timing of the medium. And the image forming conditions can be adjusted according to the calculated conveyance speed of the medium.

  Therefore, according to the present invention, the type of the medium can be accurately determined by the regressive reflection type sensor, and accurate image formation can be performed by adjusting the image forming condition according to the type of the medium and correcting the processing timing. Is possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating a medium detection device according to the present embodiment. That is, the medium detection device according to the present embodiment is provided in the conveyance path of the medium P mainly for detecting the sheet-like medium (paper etc.) P, and reflects the light so as to cross the conveyance path a plurality of times. And a determination unit 3 that determines the type of the medium according to the level change of the output signal of the sensor S.

  The sensor S is a retroreflective sensor, and has a configuration in which the light emitting unit 1 and the light receiving unit 2 are provided on one side of the conveyance path, and the first reflection unit 11 and the second reflection unit 12 are provided on the other side of the conveyance path. It has become. In addition, as the 1st reflection part 11 and the 2nd reflection part 12, a right angle prism and a reflector are used.

  In the retroreflective sensor S, light is emitted from the light emitting unit 1 substantially vertically toward the conveyance path, and the light is reflected at a substantially right angle by the first reflection unit 11 provided on the other side of the conveyance path. The light is further reflected at a substantially right angle by the reflecting portion 12 so as to be returned to one side of the transport path and sent to the light receiving portion 2.

  With such a configuration, the light emitted from the light emitting unit 1 travels through the conveyance path once in a direction toward the first reflecting unit 11 and once in a direction from the second reflecting unit 12 toward the light receiving unit 2. It will be in a state to straddle. Therefore, when the arrangement of the light emitting unit 1 and the light receiving unit 2 and the arrangement of the first reflection unit 11 and the second reflection unit 12 are arranged along the conveyance direction of the medium, the medium passes through the optical path twice along with the conveyance of the medium P. It will be in the state to block. As a result, the level change of the output signal at the light receiving unit 2 appears in two stages. Here, among the optical paths straddling the transport path, the optical path from the light emitting unit 1 to the first reflecting unit 11 is defined as a first optical path, and the optical path from the second reflecting unit 12 to the light receiving unit 2 is defined as a second optical path.

  2A and 2B are diagrams for explaining the change in the output level of the sensor accompanying the conveyance of the medium. FIG. 2A is a schematic diagram showing the passage state of the medium viewed from the upper side of the sensor, and FIG. 2B is the detection accompanying the passage of the medium. It is a figure which shows the change of a timing and an output level. Note that the output level shown in FIG. 2B is larger as the amount of received light is smaller.

  First, when the front end P1 of the medium P is in front of the light emitting unit 1, almost all of the light emitted from the light emitting unit 1 is captured by the light receiving unit 2, so that the output level becomes the lowest value (FIG. 2B). (See Part A). Next, when the front end P1 of the medium P is placed on the light emitting unit 1, the medium P gradually blocks the first optical path as the medium P is transported. As a result, the amount of light captured by the light receiving unit 2 is gradually reduced, and the output level is gradually increased (see part B in FIG. 2B). When all of the medium P is placed on the light emitting unit 1, the light capturing amount in the light receiving unit 2 is constant, and the output level is also constant (see part C in FIG. 2 (b)).

  Next, when the leading end P1 of the medium P is placed on the light receiving unit 2, the second optical path is gradually blocked by the medium P as the medium P is conveyed. At this time, since the medium P also blocks the first optical path, the amount of light taken in by the light receiving unit 2 is further reduced, and the output level is increased again (refer to part D in FIG. 2B). ). When all of the medium P is placed on the light receiving unit 2, the amount of light taken in by the light receiving unit 2 is constant, and the output level is also constant (see part E in FIG. 2B).

  As described above, by using the regressive reflection type sensor, the change in the output level at the light receiving unit 2 is stepped with the passage of the medium P, so that the change in the light transmittance of the medium P appears remarkably. (1) to (3) shown in FIG. 2B show changes in the output level when the media P of different types (light transmittance) are detected. In the present embodiment, since the medium P blocks the two optical paths, the difference in light transmittance appears to be doubled.

  In the present embodiment, the difference in the amount of light transmission caused by the difference in the type (light transmittance) of the medium P is regarded as the level change of the output signal at the light receiving unit 2, and the determination is made based on the difference in the level change of the output signal. The unit 3 determines the type of the medium P. FIG. 3 is a schematic diagram illustrating a medium determination method based on a difference in output level change. Here, an example will be described in which the type of medium is determined using the level change at the B portion of the signals (1) and (2) shown in FIG.

  As described above, the amount of light transmitted to the light receiving unit 2 varies depending on the type (light transmittance) of the medium P, and thus the level change of the output signal in the light receiving unit 2 is different. The detection timing until reaching a predetermined level (threshold) set in advance is measured, and the type of the medium P is determined based on the detection timing.

  For example, the signal (1) reaches a certain level at the detection timing T1, and the signal (2) reaches a certain level at the detection timing T2. That is, as the transmittance of the medium P is lower, the change rate of the signal level is larger, and therefore reaches a certain level at an early timing. Using this, when the output level changes from the timing T0 at which the output level starts to reach a certain level at the detection timing T1, it is determined that the medium P is of the type corresponding to (1), and the level is fixed at the detection timing T2. When it reaches, it can be determined that the medium P is of the type corresponding to (2).

  If the signal does not reach a certain level in the first change interval (B portion shown in FIG. 2B) of the output level, detection is made until the next change interval (D portion shown in FIG. 2B). When the timing is detected, the type can be determined even for the medium P having a high light transmittance. Thereby, in this embodiment, it is possible to discriminate the type from plain paper having a low light transmittance to tracing paper or an OHP film having a high light transmittance.

  Moreover, in this embodiment, although it comprised so that the light radiate | emitted from the light emission part 1 using the 1st reflection part 11 and the 2nd reflection part 12 might straddle a conveyance path twice, more than 3 times using more reflection parts You may comprise so that a conveyance path may be straddled. Thereby, the number of steps of the change of the output level in the light receiving unit 2 increases according to the number of times of straddling, and even a medium having a higher light transmittance can be detected.

  FIG. 4 is a schematic diagram illustrating a method for calculating a conveyance speed by the determination unit. That is, as described above, since the output level of the light receiving unit 2 changes stepwise with the conveyance of the medium P, the conveyance speed of the medium P is calculated using the detection timing of the stepwise change. Can do.

  For example, when the tip P1 of the medium P shown in FIG. 2 starts to pass over the light emitting unit 1, the output level starts increasing at the detection timing t1 shown in FIG. 4, and the medium P completely covers the light emitting unit 1. The output level becomes constant at the detection timing t2. When the medium P further advances and the leading edge P1 begins to pass over the light receiving unit 2, the output level rises again at the detection timing t3. When the top of the light receiving unit 2 is completely covered, the output level becomes constant at the detection timing t4. It becomes.

  Among these, for example, when the time from the detection timing t2 to the detection timing t4 is counted, the time from when the medium P covers the light emitting unit 1 to the light receiving unit 2 is known, and the interval between the light emitting unit 1 and the light receiving unit 2 ( The transport speed of the medium P can be calculated from the distance) and this time.

  The determination unit 3 detects the level change of the signal output from the light receiving unit 2, counts the time between the detection timings t2 and t4, and sets the preset distance value between the light emitting unit 1 and the light receiving unit 2. Using this, the conveyance speed of the medium P is calculated. When the transport speed of the medium P is calculated, it is possible to adjust the timing of subsequent image forming processing.

  In the above example, the conveyance speed of the medium is calculated based on the detection timings t2 and t4. However, even if another detection timing is used, the same calculation can be performed using a distance corresponding to the detection timing. is there. However, the conveyance speed can be calculated with higher accuracy when the detection timing and the corresponding distance are separated to some extent (for example, about 5 mm to 50 mm).

  FIG. 5 is a schematic diagram illustrating a configuration example when the medium detection device of the present embodiment is applied to an image forming apparatus. In this image forming apparatus, the medium detection apparatus according to the present embodiment is applied to the conveyance path (see the broken line in the figure) from the storage tray of the medium P to the transfer drum 51 and the transfer roll 52. In this example, as the retroreflective sensor, three sensors, sensor S1 immediately after the conveyance roll pair 55, sensor S2 immediately after the pre-registration roll pair 54, and sensor S3 immediately before the registration roll pair 53, are arranged.

  Outputs from the sensors S1 to S3 are sent to the determination unit 3, where medium detection timing, type determination, and conveyance speed calculation are performed. The medium detection method by each of the sensors S1 to S3 is the same as that described above, and various detections are performed using output levels that change stepwise.

  For example, the medium sent by the conveyance roll pair 55 is detected by the sensor S1, and the medium type and the conveyance speed are calculated here. The determination unit 3 sends the detected medium type and transport speed to the adjustment unit 4. The adjustment unit 4 adjusts the image forming conditions according to the type of medium sent from the determination unit 3.

  Here, since the timing at which the type of medium can be determined differs depending on the type of medium (light transmittance), the determined timing shift is reflected in the subsequent processing. Specifically, in the case of a medium having a high light transmittance, since the detection timing tends to be delayed, the detection is corrected in a direction to advance the timing for detecting the leading edge of the medium P in the subsequent processing. As a result, it is possible to perform highly accurate image processing in which the detection timing shift is corrected.

  Further, in all of the sensors S1 to S3, the medium transport speed when the sensors S1 to S3 are passed through is calculated by the determination unit 3 and passed to the adjustment unit 4 so as to sequentially correspond to the change in the medium transport speed. Subsequent processing timing can be determined. As a result, it is possible to perform highly accurate image formation corresponding to the type of the medium P and the transport speed by determining the type of the medium P and calculating the transport speed.

  Here, in the medium detection device of the present embodiment, it is desirable to use an LED light source as the light emitting unit 1 of the sensor S and perform pulse phase width control (PWM) with a constant amount of current on the LED light source. . In the PWM control, the output level can be adjusted stably and accurately with respect to the LED light source. In addition, when the medium is not passing through, light is emitted from the light emitting unit toward the light receiving unit, and the reference level is sequentially taken in, so that even if there is a change in the surrounding environment, it can be offset, and a medium with higher accuracy Detection can be performed.

  By using the medium detection device of the present embodiment as described above, the sensor S that detects the type of the medium P on which image recording is performed can also be used to measure the conveyance speed, thereby reducing costs and saving space. Is possible.

  The sensor S includes a light emitting unit 1 and a light receiving unit 2 and detects the type of the medium P based on the light transmission amount of the medium P. Therefore, the light transmittance is different between plain paper, an OHP sheet, tracing paper, and the like. Even various media can be detected with high accuracy. In addition, the sensor S returns the light vertically transmitted from the light emitting unit 1 to the medium P by the reflection unit (the first reflection unit 11 and the second reflection unit 12) attached with the medium P interposed therebetween. Since the light is guided to the light receiving unit 2 with P interposed therebetween, a plurality of times of light passes through the medium P, and even a medium with high transmittance (such as a transparent OHP sheet) has a large gain in the amount of light received. Can be obtained.

  Further, when the leading edge P1 of the medium P is detected by the sensor S, the detection timing of the leading edge P1 of the medium P in the latter stage is corrected according to the amount of light transmission, so that the medium leading edge detection accuracy in the latter stage can be improved. The alignment performance of the image formed on P can be improved.

  Further, in the present embodiment, a stable output level is obtained by PWM control in which the light emitted from the light emitting unit 1 when the medium P is not passing is captured by the light receiving unit 2 and the light amount captured by the light emitting unit 2 is fed back. Thus, the detection accuracy of the type of the medium P and the detection accuracy of the front end P1 of the medium P can be improved.

  Further, the sensor S arranges the light emitting unit 1 and the light receiving unit 2 in the passing direction of the medium P, detects each time the medium P passes through the optical path, and compares the output level of the light receiving unit 2 to thereby compare the medium P. This type of detection accuracy and the detection accuracy of the tip P1 of the medium P can be improved.

  In the above embodiment, an image output apparatus such as a copying machine or a printer has been described as an example of the image forming apparatus. However, the present invention is not limited to this, and can be applied to an image input apparatus such as a scanner. It is.

It is a schematic diagram explaining the medium detection apparatus which concerns on this embodiment. It is a figure explaining the output level change of the sensor accompanying conveyance of a medium. It is a schematic diagram explaining the judgment method of the medium by the difference in the change of an output level. It is a schematic diagram explaining the calculation method of the conveyance speed by a judgment part. It is a schematic diagram showing a configuration example when the medium detection device of the present embodiment is applied to an image forming apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light-emitting part, 2 ... Light-receiving part, 3 ... Judgment part, 4 ... Adjustment part, 11 ... 1st reflection part, 12 ... 2nd reflection part, 51 ... Transfer drum, 52 ... Transfer roll, 53 ... Registration roll pair, 54 ... Pre-registration roll pair, 55 ... Conveying roll pair, P ... Medium, P1 ... Tip, S ... Sensor

Claims (1)

A sensor that reflects light emitted from the light emitting unit substantially vertically toward the conveyance path of the medium so as to straddle the conveyance path a plurality of times and takes in the light receiving unit;
Steps for determining the type of the medium in accordance with a level change of an output signal from the sensor, which is generated in the output signal of the sensor in accordance with the number of times the light emitted from the light emitting unit straddles the transport path A medium detecting device comprising: a determination unit configured to determine the type of the medium based on a next level change when the level has not reached a predetermined level among the level changes .

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