Sheet feeding apparatus and method of detecting double feed

Abstract

A sheet feeding apparatus includes a stacker for stacking a sheet; a feeding device for feeding the sheet on the stacker to a predetermined processing position; a drive device for driving the feeding device; a double feed detection device having a sending element and a receiving element arranged at a downstream side of the feeding device for detecting a double feed of the sheet; a sensitivity adjustment device for comparing a detected value of the receiving element with a predetermined reference value for adjusting an output of the sending element; and a control device for controlling a transport speed of the feeding device. The sensitivity adjustment device adjusts the output of the sending element when the control device controls the drive device to stop the sheet or to decelerate the sheet at a predetermined speed.

Description

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a sheet feeding apparatus for sequentially separating sheets such as originals on a stacker into a single sheet and feeding the sheet to a processing platen for reading in other processes. More particularly, the present invention relates to a sheet feeding apparatus provided with a double feed detection function for detecting a double feed of sheets in a path from the stacker to a processing platen.

A conventional sheet feeding apparatus feeds sheets such as originals to a processing platen. A reading apparatus for reading images on the sheets at the processing platen is widely known as a scanner, copier, or a facsimile machine. An apparatus for printing at a processing platen is widely used as a printer.

It is necessary to accurately separate the sheets into a single sheet and to feed the sheet to the processing platen with proper positioning. Particularly, when sequentially reading a series of originals, it is possible that the sheet is not fed to the platen, i.e., a non-feed, or two or more sheets are fed to the platen, i.e., a double feed, thereby causing an improper process at the processing platen. When printing a series of originals at the processing platen, an incorrect process may occur at the platen due to the non-feed or double feed.

Accordingly, it is necessary to stop a process when the double feed or non-feed is detected while feeding the sheet from the stacker to the processing platen. For example, a sensor is provided for detecting the sheet prior before the processing platen (at an upstream side). When the sheet does not reach a predetermined position for a predetermined amount of time after the sheet is fed from the stacker, it is determined that the non-feed occurs and the process at the platen stops.

It is difficult to accurately detect the double feed of the sheets, and a detection element and a judgment circuit are expensive. In a system in which scanners or copiers are linked through a network, the double feed of the sheets can cause a serious system error. Accordingly, it is necessary to accurately detect the double feed with low cost.

Japanese Utility Model (Kokoku) No. 06-49567, and Japanese Patent Publications (Kokai) No. 2000-95390 and No. 2003-176063 disclose devices for detecting the double feed using a pair of ultrasonic wave sensors. In the devices, a pair of ultrasonic wave sensors is arranged at opposing positions to sandwich a sheet in a sheet transport path. A sensor on a wave receiving side (wave receiving element) detects ultrasonic waves emitted from a wave sending side (wave sending element) to detect the double fed through attenuation of the ultrasonic waves permeating the sheet.

FIG. 2 shows an example of a widely known ultrasonic wave sensor for detecting the sheet. A piezoelectric diaphragm is embedded in a metal case covering the sensor. A high-frequency voltage is applied to an electrode formed on the piezoelectric diaphragm, thereby generating ultrasonic waves from a surface of the case. The case is filled with a plastic 13. A wave receiving element has a structure same as that of the wave sending element and receives the ultrasonic waves to oscillate a surface of the case. As a result, the piezoelectric diaphragm fixed to the case also oscillates to output electrical energy to an external source.

The piezoelectric diaphragm may have a variance in a dimension and a shape thereof, and the metal case may have a variance in a characteristic frequency. Accordingly, in a manufacturing process, it is necessary to combine the wave sending and wave receiving elements within a tolerable range to achieve accurate detection. Therefore, conventionally, characteristics of each of the elements are measured in the manufacturing process, so that only the elements within a tolerance level are used to produce the ultrasonic wave sensor.

The elements of the conventional ultrasonic wave sensor for detecting the double-feed of the sheets are measured in the manufacturing process as described above, thereby increasing cost of the elements. When an ambient temperature fluctuates or the sensor is deformed upon receiving an impact, it is possible to cause an erroneous detection. Accordingly, it is necessary to select the detection elements with similar characteristics within a specific range for the wave sending side and the wave receiving side, so that the sensors detect the sheets without an influence of a temperature or deformation. Accordingly, the apparatus tends to be expensive and durability may be compromised.

In view of the problems described above, an object of the present invention is to provide a sheet handling apparatus capable of accurately detecting a double feed of sheets fed from a stacker to a processing platen, thereby eliminating an erroneous process at the processing platen. In the sheet feeding apparatus, detection elements for detecting the double feed of the sheets are adjusted in a state that the detection elements are disposed in a transport path, so that a variance in characteristics between the detection elements at sending and receiving sides is adjusted.

Further objects and advantages of the invention will be apparent from the following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to the invention, a sheet feeding apparatus includes a stacker for holding sheets; a feeding device for kicking a sheet from the stacker to a predetermined processing position; and a sending element and a receiving element disposed at a downstream side of the feeding device for detecting a double feed of the sheets. The sending and receiving elements are composed of a wave sending element and a wave receiving element of an ultrasonic wave sensor, and are arranged to face each other on opposite sides of the sheet. A sensitivity adjustment device is provided for comparing a detected value of the wave receiving element with a predetermined reference value to adjust an output of the wave sending element. A control device of a drive device is provided for driving the feeding device.

The sensitivity adjustment device adjusts the output of the wave sending element when the drive device is stopped or decelerated at a predetermined speed. The sensitivity adjustment device compares the output value of the wave receiving element with the predetermined reference value. According to a result of the comparison, the sensitivity adjustment device increases or decreases, for example, amplitude of high frequency power in a case of the ultrasonic sensor to change electrical energy supplied to the wave sending element. Accordingly, it is possible to obtain a predetermined output from the wave receiving element. It is possible to stably detect the double feed of the sheets even if detection sensitivity of the wave sending element and the wave receiving element is degraded due to a temperature change or aging.

According to the present invention, first and second transport devices may be arranged between the stacker and the predetermined processing position with a gap therebetween. The double feed detection device having the sending element and the receiving element is arranged between the first and second transport devices. The sensitivity adjustment device is disposed for comparing the detected value of the sending element to a predetermined reference value and adjusting the output of the sending element. A sheet sensor is disposed for detecting that the sheet from the stacker reaches a downstream side of the first and second transport devices to send a sheet leading-edge detection signal. According to the sheet leading-edge detection signal, the sensitivity adjustment device adjusts the output of the sending element. Also, according to the sheet leading-edge detection signal from the sheet sensor, the first and second transport devices stop. After the sensitivity adjustment device completes the sensitivity adjustment, the first and second transport devices restart to discharge the sheet at a high speed.

According to the present invention, a method of detecting a double feed includes a transport step for transporting a sheet from a stacker to a predetermined sheet processing position; a double feed detection step for detecting the double feed of the sheets with an ultrasonic wave sensor comprising a sending element and a receiving element and arranged between the stacker and the sheet processing position; a sensor sensitivity adjustment step for changing an output of the sending element by stopping the sheet traveling between the stacker and the sheet processing position or decelerating the sheet at a predetermined speed; and a discharge step for moving the sheet after the sensor sensitivity adjustment step or discharging the sheet at a speed higher than the predetermined speed. In the sensor sensitivity adjustment step, the sheet is nipped by at least two transport devices arranged at upstream and downstream sides in a transport direction of the sheet.

In the invention, the sending element and the receiving element of the ultrasonic wave sensor are arranged in a path for transporting the sheets. When detecting the double feed of the sheets, the sensitivity adjustment device compares the output of the receiving element with the predetermined reference value for adjusting the output of the sending element. Accordingly, it is possible to accurately detect the double feed through the adjustment of the output of the sending element even if a fluctuation occurs due to a variance in characteristics of the sending and receiving side elements, mounting positions of the elements, or an ambient temperature.

Accordingly, even when the ultrasonic wave sensor has characteristics changing easily, a tolerable range of characteristics is widened, thereby reducing manufacturing cost. Further, the output of the wave sending side is adjusted when transport of the sheet such as a test sheet is stopped or the sheet is decelerated to a predetermined speed. Accordingly, it is possible to accurately obtain the output of the wave sending element without an influence of a variance in a sheet transport speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a sheet feeding apparatus according to the present invention;

FIG. 2 is a schematic view showing a double feed detection device composed of an ultrasonic wave sensor;

FIGS. 3(a) and 3(b) are block diagrams showing a control circuit of the sheet feeding apparatus shown in FIG. 1, wherein FIG. 3(a) shows a control circuit for double-feed detection, and FIG. 3(b) shows a sensitivity adjustment circuit;

FIGS. 4(a) and 4(b) are graphs showing waveforms of output signals from the ultrasonic wave sensor shown in FIG. 2, wherein FIG. 4(a) shows a single feed and FIG. 4(b) shows a double feed;

FIG. 5 shows a block diagram showing the control circuit of the sheet feeding apparatus shown in FIG. 1;

FIG. 6 is a flow chart showing an operation of adjusting sensitivity of the sheet feeding apparatus shown in FIG. 1;

FIG. 7 is a flow chart showing an operation of detecting the double feed of sheets in the sheet feeding apparatus shown in FIG. 1;

FIG. 8 is a schematic view of an image reading apparatus and an image forming apparatus with the image reading apparatus as a unit according to the present invention;

FIG. 9 is a view showing a sheet feeding unit of the image reading apparatus shown in FIG. 8;

FIG. 10 is a perspective view showing a paper feed stacker of the image reading apparatus shown in FIG. 9;

FIGS. 11(a) and 11(b) are views showing a drive mechanism of the image reading apparatus shown in FIG. 9, wherein FIG. 11(a) shows a sheet feeding unit, and FIG. 11(b) shows a transport unit; and

FIGS. 12(a) to 12(e) are views showing an operation of feeding a sheet in the image reading apparatus shown in FIG. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, preferred embodiments of the present invention will be explained with reference to the accompanied drawings. The invention applies to an apparatus and a method for detecting a double feed of two or more overlapped sheets before reaching a processing position when the sheets stacked on a stacker in a sheet feeding unit of an image reading apparatus such as a copier, or printer are separated and transported one by one to the processing position such as an image reading platen, or printing platen.

FIG. 1 is a schematic view of a sheet feeding mechanism according to an embodiment of the present invention. FIG. 2 is a schematic view of a double feed detection device composed of an ultrasonic wave sensor. FIGS. 3(a) and 3(b) are circuit diagrams of a control circuit.

As shown in FIG. 1, the sheet feeding apparatus is equipped with a stacker 1 for storing sheets; a sheet guide 3 for guiding the sheets from the stacker 1 to the processing platen 2; at least two transport devices, i.e. first and second transport devices 4 and 5, arranged on the sheet guide 3; and a double feed detection device 6 arranged between the first transport device 4 and the second transport device 5 for detecting a double feed of the sheets. A separating device separates the sheets stacked on the stacker 1 into a single sheet, and the first and second transport devices 4 and 5 feed the sheet to a processing position (platen 2). Predetermined processes such as reading images, printing, stamping or stapling are performed at the processing position. Then, the sheet is discharged to a discharge stacker 9.

The stacker 1 is composed of a tray for stacking the sheets. An empty sensor S1 for detecting the presence of sheets, and a size sensor S2 for detecting a length of the sheets can be mounted according to specifications required by the apparatus. The separating device for sequentially separating the uppermost or the lowermost sheets for feeding is disposed at the leading end of the stacker 1.

A combination of a first transport roller 4a and a friction pad 4b as shown in the drawing, or a combination of a forward drive roller and a reverse drive roller, or the combination of a feed roller and separating claw (corner separator) are widely known and used as the separating device. Depending on the apparatus, even a vacuum separation can be used. The present invention allows for the use of either of these methods for separating sheets into single sheets. The drawing provided shows a configuration for the separating device that employs a first transport roller 4a (although a belt is also perfectly acceptable) for rotating in a direction to feed the sheet, and a friction pad 4b that prevents a double feed of sheets. The transport device 4 transports the separated sheet toward the platen 2. A resist roller 5a for temporarily idling a sheet in the transport path between the separating device and the platen 2, and a transport roller 8a are disposed for continuing to transport a sheet from the first transport roller 4a to the platen 2.

At least two transport devices of the first and second transport device between the stacker 1 and the processing platen 2 are provided. As shown in the drawing, the first transport roller 4a is set as the first transport device; and the resist roller 5a is set as the second transport device. The first and second transport devices 4a and 5a are disposed with a spacing that is shorter than the shortest size sheet length. Note that the resist rollers 5 employ a known configuration. A pair of rollers 5a and 5b in mutual contact forms a curve in sheets fed from the transport roller 4a to correct any skewing in the sheet. Then, at a predetermined timing, the rollers 5a and 5b feed the sheet to the platen 2.

A double feed detection sensor 6 and the sheet sensor 7 for detecting a leading edge of a sheet are arranged between the first and the second transport rollers 4 and 5. The double feed detection sensor 6 is configured by arranging a pair of a wave sending element 6a and a wave receiving element 6b at opposite positions with the sheet moving therebetween along the sheet guide 3. The sheet sensor 7 is configured by arranging a pair of a light emitting element 7a and a light receiving element 7b to oppose each other. The double feed detection sensor 6 shown in the drawing is an ultrasonic wave sensor. The wave sending element 6a and the wave receiving element 6b have a same structure of a piezoelectric diaphragm. Note that the symbol 8a in the drawing represents a transport roller and is disposed at the sheet guide 3 for controlling the feeding of the sheet to the platen at a predetermined speed.

The double feed detection sensor 6 is composed of an ultrasonic wave sensor. The wave sending element 6a and the wave receiving element 6b are disposed at opposite positions. Both the wave sending element 6a and the wave receiving element 6b are composed of a piezoelectric diaphragm having a same structure, as shown in the example of FIG. 2. In each of the ultrasonic wave sensors, a piezoelectric diaphragm 11 such as a piezoelectric diaphragm ceramic plate is embedded in and connected to cylindrical external frame cases 10 made of a metallic material such as an aluminum alloy. The case 10 is filled with a resilient plastic 13. Electrodes are formed on the front and back surfaces of the piezoelectric diaphragms 11. One of the lead wires 12 is connected to the piezoelectric diaphragm 11 and the other is connected to the case to provide electrical grounding. When the high-frequency power is applied to the lead wire 12, the piezoelectric diaphragm 11 oscillates at a predetermined frequency. Then, electromotive force generated by the excited piezoelectric diaphragm 11 on one side is transmitted outside along the lead wire 12.

The wave sending element 6a is electrically connected to a high frequency power source. The following will describe the electrical connection in reference to FIG. 3(a). The power 14 is connected to the high frequency oscillating circuit 15. The oscillating circuit generates high frequency voltages of between 30 KHz and 40 KHz. An amplifier circuit 16 amplifies and supplies that to the wave sending element 6a. When this occurs, the piezoelectric diaphragm 11, whose inherent oscillating frequency is set to a predetermined frequency, generates ultrasonic waves from the case 10 at that frequency. Note that the amplifier rate of the amplifier circuit 16 is set by the control CPU. Instruction signals from the CPU undergo D/A conversion and are then relayed to the amplifier circuit 16.

The ultrasonic waves generated from the wave sending element 6a are transmitted to the wave receiving element 6b passing through the sheet S on the sheet guide 3. The ultrasonic waves that travel through the sheet cause the case 10 to oscillate in the wave receiving element 6b, thereby causing the piezoelectric diaphragm 11 that is mounted to the case 10 also to oscillate. The electromotive force generated by the oscillation of the piezoelectric diaphragm 11 is led to the lead wire 12 from the electrode. The current is output as a detected value proportional to the amplitude of the piezoelectric diaphragm 11.

The wave receiving element 6b is connected to an amplifier circuit 18 for amplifying the detecting current. The amplifier circuit 18 amplifies the detected current generated by the piezoelectric diaphragm 11. The amplifier circuit 18 is connected to a smoothing circuit 19 composed of an integrated circuit. The detected current of the amplified wave is averaged by the smoothing circuit 19 and sent to the comparator circuit 20. At the comparator circuit 20, the current from the smoothing the circuit 19 is compared to a preset reference value. The reference value is determined in the following way.

FIGS. 4(a) and 4(b) show the output values (analog voltage) of the smoothing circuit 19. FIG. 4(a) shows the output value when a single sheet is fed through the transport path. FIG. 4(b) shows the output value when two sheets are fed. A sheet kicked from the stacker 1 is transported from the first transport roller 4a to the second transport roller 5a. In FIG. 4(a), the symbol A represents the output value when the leading edge of the sheet is moving from the first transport roller 4a toward the second transport roller 5a. In that span of time, the waveform is unstable. In the same drawing, the symbol B represents the output value when the sheet is nipped and held by the first transport roller 4a and the second transport roller 5a. During the span of time, the waveform is stable. In the same drawing, the symbol C is the output value when the trailing edge of the sheet, still held by the second transport roller 5a, is released from the first transport roller 4a. At this time, the waveform becomes unstable again.

It is clear that the levels of the output values are different in the region B representing the stable waveforms in the drawing when there is a single sheet or two sheets. Specifically, when the ultrasonic waves pass through the sheet, the degree of attenuation is smaller when there is one sheet, which means there is a higher detected electrical current. Conversely, when there are two or more sheets, the degree of attenuation of the ultrasonic waves increases, thereby reducing the amount of detected electrical current. In other words, the detected current output from the smoothing circuit is higher than the detected current when there is one sheet between the pair of transport rollers 4a and 5a, and it is lower than the detected current when there are two or more sheets when compared to the stable reference value. Note that the thicknesses of paper or the quality of paper used can differ. Therefore, it is necessary to experiment using a variety of different paper types to find the appropriate reference value for of the machine specifications.

Comparison data received from the comparator circuit 20 is then transferred to the control CPU (control circuit) 21. Size sensors S2 and S3 arranged on the stacker 1, a sheet sensor 7, and a discharge sensor, not shown, arranged on the sheet guide 3 are connected to the control CPU21. The sheet sensor 7 is arranged between the first transport roller 4a and second transport roller 5a for transmitting the timing for the arrival of the leading edge of a sheet to the control CPU21.

The control CPU is connected for transmitting instruction signals to the motor driver circuit 22 of the drive motor M for driving the first and second transport rollers 4a and 5a. Power 25 is connected to a pulse generator 23 for supplying pulse currents to the motor driver circuit 22. The drive motor M, which receives energy from the power 25, is composed of a stepping motor. The pulse generator 23 is connected to a counter 24. The counter 24 calls the number of pulse currents that are supplied to the drive motor M, and is connected to the control CPU 21.

An operation for detecting a double feed of sheets on the apparatus having the configuration of FIG. 1 will be explained with reference to the flowchart in FIG. 7. The control programs on the CPU 21 are configured as described below for the transport control unit 28. When the power 14 to the apparatus is turned on, the CPU 21 judges whether there is a sheet on the stacker 1 according to the status signals received from the empty sensor S1 (F1). If a sheet is present, the CPU 21 issues a start signal to the motor drive circuit 22. Receiving the signal, the motor driver circuit 22 begins supplying pulse power from the power 25 to the drive motor M via the pulse generator 23. At the start up of the drive motor M (F2), the first transport roller 4a that is connected to the drive motor M rotates in the clockwise direction of FIG. 1 to kick a sheet from the top of the stacker 1.

The friction pad 4b separates the sheets into a single sheet when the first transport roller 4a kicks several sheets from the stacker 1. The single sheet advances along the sheet guide 3, and the leading edge of the sheet arrives at the second transport device 5 passing between the double feed detection sensor 6, then the sheet sensor 7. The second transport device 5 is in a stopped state at this time. Therefore, when the leading edge of the sheet enters a nipping point (where the rollers are in contact with each other) between the second transport rollers 5a and 5b, the sheet forms a corrective loop shape. When the leading edge of the sheet arrives at the sheet sensor 7, the transport control unit 28 starts the timer (F3) by receiving the detection signal from this sheet sensor 7. The drive motor M stops after the time T1 (F4).

Next, the CPU 21 receives processing start signal from the main apparatus such as an image reading device or printer as a paper feed signal (F5), then restarts the drive motor M with that signal. The drawing shows a transmission mechanism configured of a one-way clutch, so that the forward drive of the drive motor M rotates the first transport roller 4a and the reverse drive rotates the second transport roller 5a (selectively).

Therefore, when the drive motor M restarts, it rotates the second transport roller 5a, and the first transport roller 4a remains in a stopped status. The second transport roller 5a then feeds the sheet toward the transport roller 8a (F6). Simultaneous to this, the transport control unit 28 of the CPU 21 restarts a timer T2 (F7). The timer T2 is set to a value where T1<T2, so that the loop in the sheet (curved in a registration loop) can be released. When a predetermined amount of time passes for the timer T2, the CPU 21 issues a double feed detection instruction signal (F8). Upon receiving the signal, the detection signal/reference value comparator 29 inside the CPU 21 receives the double feed comparison data (see FIG. 3(a)) and judges whether there is a double feed of sheets (F9). To detect a double feed (or judge the double feed), values detected from the wave receiving element 6a are compared with predetermined reference values (LVO in FIG. 2) at the comparator circuit 20. If the detected value is lower than the reference value, the system judges that there has been a double feed of two or more sheets. [0037]

Changes in the ambient environment or other conditions can cause erroneous detections to occur in the detection signal/reference value comparator unit 29 of the configuration shown in the drawings. To prevent erroneous detections in the detected value of the wave receiving element 6b, the sheet is formed into a registration loop by the second transport device 5, and an air layer is formed between the two or more sheets. Then, the double feed detection is performed when the registration loop is released. Also, the sheet is detected while nipped by both the first transport roller 4a and the second transport roller 5a. As the sheet is being transported, the system judges with the average value detected for a predetermined distance (length).

The detection signal/reference value comparison unit 29 executes a double feed process (F10) when a double feed of sheets has been judged. In the double feed process, the apparatus stops and the operation panel displays that there has been a double feed in the system. In this case, an operator may either take a sheet out of the sheet guide 3 and reset it on the stacker 1, or discharge the sheet to a discharge stacker 9 without any processing at the processing platen 2. When the detection signal/reference value comparison unit 29 has determined that the feeding of a sheet is normal (that there has not been a double feed), the second transport roller 5a and the transport roller 8a feed the sheet to the processing platen where a predetermined process is applied to the sheet (F12). When the trailing edge of the sheet passes over the sheet sensor 7, the CPU 21 detects the status signal to drive the drive motor M (F2) to cause a next sheet to be kicked from the stacker 1 in the same way.

Note that the transport roller 8a is linked to a drive motor that is different from the drive motor M mentioned above. However, it feeds the sheet to the processing platen 2 at a predetermined speed. The sheet having undergone the predetermined process at the processing platen 2 is sequentially fed and stored in the discharge stacker 9. A discharge sensor disposed on the edge of the sheet exit on the discharge stacker 9 detects that a sheet has been stored (F13). At the status signal from the empty sensor S1 for detecting whether there are sheets on the stacker 1, the CPU 21 determines whether to continue the series in the job or to end the series (Fl4). When the empty sensor S1 detects a next original on the stacker 1, the CPU 21 issues a paper feed instruction signal (F5) to feed the next sheet to the processing platen 2.

The operation described above relates to conventional sheet feeding steps. If the apparatus is a scanner device for reading images sequentially on a sheet at the processing platen 2, the transport control unit 28 which is executed in the CPU 21, described above, controls the speed of the drive motor M in the following way.

The transport control unit 28 sets the transport speed of the first transport device 4 and the transport roller 8a according to the sheet processing conditions at the signals from the scanner device. The transport speed is determined according to the reading conditions of images by the scanner device. The conditions include color, or black-and-white, high or low reading resolutions. Therefore, the transport speed can vary according to the conditions. Generally, color and high resolution readings are performed at a low speed, whereas black-and-white and low resolution readings are set to a high speed. Therefore, the transport speed is set to a variety of high or low speeds according to the reading conditions.

FIG. 3(b) shows a sensitivity adjustment circuit (means) 35 embedded in the CPU 21. The detective value from the wave receiving element 6b is amplified by the amplifier circuit 18. The smoothing circuit 19 smoothes this value, and the comparator circuit 20 compares it to the reference value. In this circuit configuration, first the amplifier rate is transmitted as an analog voltage value from the sensitivity adjustment circuit 35 of the CPU 21 to the amplifier circuit 16, which supplies high-frequency power to the wave sending element 6a, via the D/A converter 17. The amplifier circuit 16 supplies high-frequency voltage to the wave sending element 6a at the amplitude of the amplifier rate that was set. On the other hand, detected currents from the wave sending element 6a passes through the amplifier circuit 18, and the output value (detected value) from the smoothness circuit 19 is converted into digital values by the A/D converter 36. The values are then sent to the sensitivity adjustment circuit 35.

The sensitivity adjustment circuit 35 compares the output value of the wave receiving element 6b to the predetermined reference value (at the output value/reference value comparator unit 37) and judges the output value according to the complete results of the comparison (output value judgment unit 39). The amplifier rate is set (amplifier rate setting unit 38) according to the results of the judgment of the output value judgment unit 39. A gain is used to set the amplifier circuit 16 via the D/A converter 17.

A preset amplifier rate reference value 41 is read, for example, from ROM to set the amplifier circuit 16 gain to generate the ultrasonic waves from the wave sending element 6a. The wave receiving element 6b detects ultrasonic waves passing through a test sheet (reference sheet) and outputs that to the A/D converter 36 from the smoothing circuit 19 via the amplifier circuit 18. The output value (an analog voltage value) is compared to the reference value. If the output value matches the reference value (in a constant range), the amplifier rate is stored in an amplifier rate memory 40. If the output voltage does not meet the reference value, the output value judgment unit 39 sets the amplifier rate, so that the output value (the analog voltage) rises to predetermined amount such as 0.1 V. (the amplifier rate setting unit 38)

The amplifier rate is increased by a predetermined amount, and the output value/reference value comparison unit 37 compares that again with the output value of the wave receiving element 6b. If they match, the amplifier rate is stored in the amplifier rate memory 40. If the output value does not meet the reference value, the amplifier rate is increased further by the predetermined amount. The same adjustments are repeated. If the amplifier rate setting reaches a maximum value 42 for the preset amplifier rate, the CPU judges that there has been a system error in the double feed detection of the wave sending element 6a and the wave receiving element 6b. It may display an error message on the control panel for example to prompt an operator to repair or to continue the sheet processing on the system without using the double feed detection function.

Note that according to the embodiment of the present invention, if the output value from the smoothness circuit 19 is within a range of 3.5V to 4.0V, a correct (normal) amplifier rate is judged. Also, the reference value for adjusting the amplifier rate in the invention is set to a value wherein the output value (an analog voltage value) after smoothing does not exceed a maximum of the minimum increment (for example 0.1 V) of an amp rte even when the element (or device) in use is combined with a highly sensitive component.

The following will explain adjusting the sensitivity of the amplifier rate on the apparatus of FIG. 1 while referring to the flow chart of FIG. 6.

First, the sensitivity adjustment mode is entered (F20). The mode can be entered either by an operator using a switch on the control panels, or the main apparatus such as an image reader or printer can automatically enter the mode at the same time as it is initializing the system. When entered, the CPU 21 judges whether there is a sheet on the stacker 1 according to the status signals received from the empty sensor S1. In this case, the CPU 21 judges whether there is a test sheet placed on the stacker 1. If there is a test sheet, it starts the drive motor M.

The drive speed of the drive motor M is set to the same speed as when processing a sheet, as described above. The sheet on the stacker 1 is kicked by the drive of the drive motor M. The leading edge of the sheet passes through (F22) the ultrasonic wave sensor (double feed detection device) to start the feeding of the test sheet (F23). When the leading edge of the sheet arrives at the sheet sensor 7 (F24), the timer T1 starts with a signal from the sheet sensor 7 (F25). After a predetermined amount of time has passed on the timer T1 (F26), the drive motor M stops, thereby stopping the first transport roller 4a (F27).

Next, the drive motor M drives in the reverse direction, thereby starting a drive of the second transport roller 5a (F28). At the same time that the drive motor M starts, the counter 24 connected to the pulse generator 23 counts the number of pulses. The CPU 21 uses this to judge whether a predetermined length of the sheet has been transported by the second transport roller 5a. The predetermined amount for the sheet to be transported is set so that the sheet will be straightened from the registration loop by the second transport roller 5a.

Just about the time that the registration loop is released, the transport control unit 28 of the CPU 21 stops the drive motor M or decelerates it to a predetermined speed. The drive motor is stopped to prevent the variations in the ultrasonic sensor detection value caused by the movement of the sheet for the sensitivity adjustment that follows thereafter. The deceleration to a predetermined speed is set to an optimum speed for the amount of time for the sensor adjustment that follows to be completed when changing the detection value according to the transport speed and in the transport of the sheet. Normally, the speed for sensitivity adjustment is set to a speed slower than the minimum speed for the predetermined process that occurs on a sheet at the processing platen 2.

Sensitivity adjustments are conducted as described below while the sheet is traveling at a low speed or decelerating. First, the sensitivity adjustment circuit 35 supplies high frequency power to the wave sending element 6a at the gain set by the amplifier rate reference value 41 (F36). The output value (an analog voltage) from the wave receiving element 6b passes through the A/D converter 36 and is compared. If the results match, the amp value is stored in the amplifier rate memory 40 to complete the sensitivity adjustment. If the comparison results do not matched, the output value judgment unit 39 increases the amplifier rate by the predetermined amount. When the amplifier rate setting unit 38 does not exceed a maximum value (which is set to a range wherein the gain of the amplifier circuit is not saturated) of the amplifier rate, power is supplied from the amplifier circuit 60 to the wave sending element 6a.

If the amplifier rate from the output value judgments unit 39 exceeds the maximum value, the CPU 21 issues a failure signal to the main apparatus (F38). The transport control unit 28 drives the transport roller 8a at high speed to discharge the test sheet to the discharge stacker 9 (F39). Having been notified of the failure signal at the main apparatus, the operator can then select whether to process the sheet without using the double feed detection function (the non-detection operating mode) (F40), or to repair the double feed detection device (F42) (by stopping machine operations). If the operator selects the non-detection operating mode, a message indicating that it is possible to feed the sheet but not to perform the double feed detection is displayed on the control panel. Then, the sheet can be processed as described above (F41).

After adjustments are completed for the appropriate sensitivity from the wave receiving element 6b (F32), the transport roller 8a drives at a high speed to discharge the sheet on the sheet guide 3 into the discharge stacker 9 (F33) The control panel of the main apparatus displays a message indicating that the adjustments are completed (F34). The adjustment mode is exited and the system is prepared for processing a next sheet (F35). Then, the appropriately adjusted amplifier rate is stored in the amplifier rate memory 40 and is used at the gain setting up of the amplifier circuit 16 when feeding a sheet.

An image reading apparatus according to an embodiment of the present invention will be explained next. FIG. 8 shows an image reading apparatus A and an image forming apparatus B mounted with the image reading apparatus A as a unit. FIG. 9 shows a sheet feeding unit in the image forming apparatus B.

The image forming apparatus B mounted with the image reading apparatus A is embedded with a print drum 102 inside the casing 100; a paper feed cassette 101 that feeds paper to the print drum 102; a developer 108 that forms images using toner on the print drum 102; and a fixer 104. A print head 103 such as a laser forms latent images on the print drum 102. Paper fed from the paper feed cassette 101 is sent by the transport rollers 105 to the print drum 102, and the images formed by the print head 103 are transferred to the sheet and then fixed thereupon by the fixer 104. The sheet with images is stored in the discharge stacker 121 from the discharge roller 107.

The image forming apparatus B is widely known as a printer, and is composed of a paper feed unit, a printing unit, and a discharge storage unit. Their functions are various and are not limited to the structure described above. For example, it is perfectly acceptable to employ an inkjet printer, or a silkscreen printer.

A data control circuit 109 is electrically interlocked to the print head 103 to sequentially transfer image data that is accumulated by the memory apparatus 122 such as a hard disk for accumulating image data to the print head. On the upper portion of the image forming apparatus B, the image reading apparatus A is mounted as a unit. The image reading apparatus A is mounted with the platen 112 on the casing 110. An optical mechanism 114 and a photoelectric converting element 113 are arranged to read the original through the platen. A CCD is widely known and used for the photoelectric converting element 113.

As shown in FIG. 9, the sheet feeding apparatus C is installed on the platen 112. Above the platen 112 are arranged a paper feed stacker 115 and a discharge stacker 116 above each other on the sheet feeding apparatus C. The sheets from the paper feed stacker 115 are guided to the discharge stacker 116 via the U-shaped transport path 134 traveling over the platen 112.

Arranged on the paper feed stacker 115 are an empty sensor 117 for detecting the sheets on the stacker, and a size sensor 132. As shown in the drawing, a side guide 133 aligns the side edges of the sheets. The size sensor 132 and the side guide 133 are described in further detail below with reference to FIG. 10.

Arranged at a downstream side of the paper feed stacker 115 are a separating roller 119 and a stationary roller 120 in contact with the roller. A kick roller 118 is mounted on the bracket 119b mounted on the rotating shaft 119a of the separating roller 119. When the rotating shaft 119a rotates in the clockwise direction, the kick roller 118 lowers to above the paper feed stacker 115. Conversely, when the rotating shaft 119a rotates in a counterclockwise direction, the kick roller 118 rises to a state shown in the drawing. The mechanism is described in further detail below.

At a downstream side of the separating roller 119 are the double feed detection sensor 123 that detects the double feed of the sheets, and a sheet edge detection device 124 that detect the leading edge and the trailing edge of the sheet. These are arranged in the transport path 134. Also, equipped in order on the transport guide 134 are the resist rollers 125a and 125b; feed rollers 127a and 127b; a transport roller 129; and a pair of discharge rollers 130a and 130b. These are sequentially arranged to transport the sheets from the paper feed stacker 115 to the discharge stacker 116.

As shown in the drawing, a lead sensor 126 detects the leading edge of the sheet. A guide 128 supports the sheets at the platen 112 position. A circulating path 131 circulates the sheets from the platen 112 to the resist rollers 125a and 125b through a path switching gate 131a.

Next, the side guide 133 and the size sensor 132 will be explained. A pair of side guides 133 (133a and 133b) is disposed on the left and right of the paper feed stacker 115 to control the side edges of the sheets. The side guides are movably mounted in the width direction of the sheets. The racks 135 and 136 are integrally mounted to the left and right guides 133a and 133b. These mate with the pinion rotatably fixed to the paper feed stacker 115.

The left and right guides 133a and 133b are moved in the opposite directions for the same amount by a pinion 137. The detection piece 139 composed of a protrusion at a position that corresponds to the size of the sheets is disposed on one of the racks 136. The position of the detection piece 139 is detected by the position sensor 138 mounted to the bottom of the stacker 115. The position sensor is composed of a slidac volume and can detect the position of the side guide 133 by detecting the variation in the resistance value varying with the length of engagement with the detection piece 139. Furthermore, size sensors 132 are disposed in plurality on the stacker 115 to detect the trailing edge of the sheet.

The position sensor 138 detects the width direction of sheets on the stacker 115, and with the judgment by the size sensor 132 for sheets having the same width, the size of the sheet on the stacker 115 is detected.

FIGS. 11(a) and 11(b) show a drive mechanism for the separating roller 19 and the resist rollers 125. The paper feed drive motor 140 capable of both forward and reverse rotations drives the kick roller 118, the separating roller 119, and the resist rollers 125. The transport drive motor 141 drives the paper feed roller 127, the transport out roller 129, and the discharge roller 130. With the forward rotation, the paper feed drive motor 140 drives the kick roller 118 and the separating roller 119. With its reverse drive, it drives the resist roller 125. Simultaneously, the paper feed drive motor 140 controls the rising and lowering of the kick roller 118. Force from the paper feed drive motor 140 is transmitted to the resist rollers by a one-way clutch 142 via the belts B1 and B2 only in one direction of rotation. At the same time, the paper feed drive motor is connected to a rotating shaft of the separating roller 119 by the one-way clutch 143 to transmit drive relatively with the one-way clutches 142 and 143.

The bracket 119b is supported on the rotating shaft of the separating roller 119 via the spring clutch 144. Drive is transmitted to the kick roller 118 mounted on the bracket 119b by the transmission belt B3. When the paper feed drive motor 140 rotates in the forward direction, rotating drive is transmitted to the separating roller 119 and the kick roller 118. Simultaneously, the spring clutch 144 is released so that the bracket 119b becomes free and lowers from an idled and raised position shown in FIG. 9 and the kick roller 118 touches the sheet on the stacker. Rotating the paper feed drive motor 140 in the reverse direction transmits drive to the resist rollers 125. Simultaneously, the spring clutch 144 contracts, thereby raising the bracket 119b to return to the idled position shown in FIG. 9.

The transport unit drive motor 141 is connected to the feed rollers 127, transport rollers 129, and discharge rollers 130 via the belts B5, B6 and B7. The feed rollers 127 and transport rollers 129 always rotate in one direction with the forward and reverse rotations of the motor with the one-way clutch. The discharge rollers 130 rotate forward and reverse with the forward and reverse rotations of the motor.

Sensors for detecting the leading edge of the sheets are arranged in the transport path 134. Their functions will be explained. The size sensors 132 that detect the size of the sheets set on the paper feed stacker 115 are arranged in plurality. These detect the size of the sheets to control sheet transport. The empty sensor 117 is disposed on the leading edge of the paper feed stacker 115 to detect the sheets on the stacker. This detects the transport of the final sheet and sends a signal to the processing apparatus, such as the image reading apparatus A. At a downstream side of the separating roller 119 are disposed the double feed detection sensor 123 described above and the sheet edge detection sensor 124.

A lead sensor 126 is disposed in front of the paper feed roller 127. This relays the leading edge of the sheet to the image reading apparatus for reading images and calculates the starting line for printing. Simultaneously, if the sheet is not detected after a predetermined amount of time from the paper feed instruction signal from the resist roller 125, the drive motor stops because of a jam and issues a warning signal. At a downstream side of the transport rollers 129 is disposed the discharge sensor 145 to judge jams by detecting the leading-edge and the trailing-edge of the sheets.

The following will outline an operation of the apparatus described above. The power to the apparatus is turned on, and sheets are placed in the paper feed stacker 115. By setting the sheets, the empty sensor 117 detects the sheets and starts the paper feed drive motor 140. With the rotation of the paper feed drive more 140, the kick roller 118 and separating roller 119 separate the sheets and kick them out. They are fed to the transport guide 128 between the separating roller 119 and the transport rollers 125. The sheet edge detection means 124 (hereinafter referred to as sensor 124) detects the leading edge of the sheets (ST101). The timer T1 activates after the detection signal of the leading edge of the sheet (see FIGS. 4(a) and 4(b)) to stop the motor 140 after a predetermined amount of time (ST102).

According to the operations as shown in FIG. 12(a), the sensor 124 detects the leading edge of the sheet and activates the timer T1. Next, in FIG. 12(b), the leading edge of the sheet strikes the resist rollers 125 and a loop is formed in the sheet. In this state, a set amount of time for the timer T1 ends and the motor 140 stops.

When the paper feed instruction signal is generated from the control unit of the image reading apparatus A, the motor 140 starts rotating again in the reverse direction. Also, with the paper feed instruction signal, the timer T2 is activated. With the timer T2, the registration loop is removed and the sheet is supported between the separating roller 119 and the resist rollers 125 for transport in a straight line as shown in FIG. 11(c).

Next, as shown in FIG. 11(d), until the trailing edge of the sheet is released from the separating roller 19, the double feed detection sensor 123 detects the double feeding of the sheets. The trailing edge of the sheet transported in that way is detected by the sensor 124. Approximately about the time when the trailing edge of the sheet is detected, the lead sensor 126 detects the leading edge of the sheet and the feed roller 127 feeds the sheet toward the platen 112.

When the leading edge of the sheet is detected by the lead sensor 126 and the sheet reaches the platen 112, the reading process is executed as electrical signals by the optical mechanism 114 and the photoelectric converting element 113. After the sheet has been read, it is discharged to the discharge stacker 116 by the transport rollers 129 and the discharge rollers 130. The discharge of the sheet is detected by the discharge sensor 145.

The double feed detection device is composed of the ultrasonic wave sensor arranged in a path leading to the resist rollers 125 at a downstream side of the separating roller 119 (feeding device). The sensitivity adjustment circuit 35 explained with reference to FIG. 3(a) is disposed on the wave sending element of the ultrasonic wave sensor. A smoothed output value (analog voltage) is compared to a reference value. If a test sheet is placed on the stacker 115 and the sensor sensitivity adjustment mode is selected using the control panel of the apparatus, the output of the wave sending elements is adjusted to the appropriate conditions as described in the operation flowchart shown in FIG. 7.

The disclosure of Japanese Patent Application No. 2004-170395, filed on Jun. 8, 2004, is incorporated in the application.

While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.

Claims

1. A sheet feeding apparatus comprising:

a stacker for stacking sheets;

a feeding device for feeding the sheets on the stacker to a predetermined processing position;

a drive device for driving the feeding device;

a double feed detection device arranged at a downstream side of the feeding device for detecting a double feed of the sheets and having a sending element and a receiving element;

a control device for controlling a transport speed of the feeding device; and

a sensitivity adjustment device for comparing a detected value of the receiving element with a predetermined reference value for adjusting an output of the sending element, said sensitivity adjustment device adjusting the output of the sending element in a condition such that the control device controls the drive device to stop the sheet or to decelerate the sheet at a predetermined speed.

2. A sheet feeding apparatus according to claim 1, wherein said sending element includes an ultrasonic wave sending element and said receiving element includes an ultrasonic wave receiving element, said sensitivity adjustment device having an amplifier device for increasing or decreasing amplitude of the ultrasonic wave sending element.

3. A sheet feeding apparatus, comprising:

a stacker for stacking sheets;

a feeding device for separating the sheets on the stacker into a single sheet and feeding the sheet to a predetermined processing position;

first and second transport devices arranged between the stacker and the sheet processing position with a predetermined distance therebetween;

a double feed detection device arranged between the first and the second transport devices for detecting a double feed of the sheets, and having a sending element and a receiving element disposed oppositely;

a control device for controlling transport speeds of the first and second transport devices;

a sheet sensor for detecting that the sheet fed from the stacker reaches a downstream side of the first and second transport devices; and

a sensitivity adjustment device for comparing a detected value of the sending element with a predetermined reference value for adjusting an output of the sending element so that the sensitivity adjustment device increases or decreases the output of the sending element according to a sheet leading edge detection signal from the sheet sensor.

4. A sheet feeding apparatus according to claim 3, wherein said control device stops the drive device according to the sheet leading edge detection signal from the sheet sensor, and restarts the drive device after the sensitivity adjustment device increases or decreases the output of the sending element.

5. A sheet feeding apparatus according to claim 3, wherein said control device drives the drive device at a predetermined speed according to the sheet leading edge detection signal from the sheet sensor, and drives the drive device at a speed higher than before after the sensitivity adjustment device increases or decreases the output of the sending element.

6. A sheet feeding apparatus according to claim 3, wherein said first and said second transport devices have a first operation mode to transport the sheet to the sheet processing position at a first speed to perform a specific process, and a second operating mode to transport the sheet to the sheet processing position at a second speed without performing the specific process, said first speed being higher than the second speed.

7. A method of detecting a double feed of sheets transported from a stacker, comprising:

a transport step for transporting the sheet on the stacker to a predetermined processing position;

a double feed detection step arranged between the stacker and the sheet processing position for detecting the double feed of the sheets with an ultrasonic wave sensor having a sending element and a receiving element;

a sensor sensitivity adjustment step for changing an output of the sending element while the sheet is stopped or is decelerated at a predetermined speed between the stacker and the sheet processing position; and

a discharging step for discharging the sheet by restarting the sheet or moving the sheet at a speed higher than the predetermined speed after the sensor sensitivity adjustment step.

8. A method according to claim 7, wherein said sensor sensitivity adjustment step is executed when the sheet is nipped by at least two transport devices arranged at an upstream side and a downstream side in a direction that the sheet is transported.