JP4424105B2 - Sheet separation device - Google Patents

Description

  The present invention relates to a sheet separating apparatus suitable for a copying machine or a printer.

  2. Description of the Related Art A copying machine, a printer, and the like are provided with a sheet separating device that takes out sheets one by one from a bundle of sheets stacked in multiple stages and supplies them to an image forming apparatus. FIG. 13 shows an example of this type of sheet separating apparatus. In FIG. 13, a sheet bundle is stacked on the tray 201. The pickup roll 202 rotates while being pressed against the sheet bundle, thereby feeding the leading end of the uppermost sheet to the nip portion between the sheet feeding roll 203 and the separation roll 204. The paper feed roll 203 rotates in the same direction as the pickup roll 202 and sends out a sheet sent from the pickup roll 202 to a conveyance path toward the image forming apparatus.

In order to feed the sheets one by one from the sheet bundle loaded on the tray 201 through the nip portion, it is necessary to apply an appropriate torque to the separation roll 204. The reason is as follows. FIG. 14 is a schematic diagram illustrating a state in which two sheets of the sheet P1 and the sheet P2 are double fed to the nip portion between the sheet feeding roll 203 and the separation roll 204. Assuming that the separation torque _Tr is applied to the separation roll 204 in a direction perpendicular to the paper surface (from the paper surface upward), a blocking force F _r acts on the sheet P2 in the left direction of the paper surface (here, the separation roll 204). If r _r is r _r , then T _r = F _r · r _r ). Further, the sheet P2, the frictional force F _f by the friction between the sheet P1 acts rightward on the paper surface. Therefore, the conveying force for the separation torque T _r is too small attempts conveying the frictional force F _f That sheet P2 acting on the seat P2 rightward on the paper surface is, the sheet P2 exceeds the blocking force F _r is conveyed with the sheet P1 The That is, a double feed state is caused. Conversely, if the separation torque _Tr is too large, the blocking force _Fr becomes too large and the sheet P1 is conveyed in the reverse direction. That is, a conveyance failure occurs.

  FIG. 15 is a diagram illustrating a configuration of a sheet separating apparatus according to the related art. The stepping motor 301 is a motor for driving the separation roll 204. The stepping motor 301 is connected to the separation roll 204 via the torque limiter 303. The torque limiter 303 has a function of limiting the separation torque applied from the stepping motor 301 to the separation roll 204. With such a mechanism, a constant separation torque can be applied to the separation roll 204.

  However, various forces acting on the above-described sheet differ depending on, for example, the material of the sheet or roll, the position of the roll, or the like. Furthermore, these forces also change with the aging of the material of the sheet or roll or the position of the roll. Therefore, it is desirable that the separation torque applied to the separation roll 204 is not constant but can be controlled.

As a sheet separating apparatus having such a torque variable mechanism, for example, there are technologies described in Patent Document 1 and Patent Document 2. The technique described in Patent Document 1 detects the rotation speed of the separation roll and switches the torque of the motor when the rotation speed becomes a predetermined speed or less. The technique described in Patent Document 2 changes the torque applied to the separation roll in accordance with the double feed state, temperature, or humidity.
JP 2000-44076 A JP 2000-264489 A

By the way, the technique described in Patent Document 1 employs a DC motor instead of a stepping motor by directly connecting the motor and the separation roll without providing a torque limiter between the motor and the separation roll. Since the DC motor is directly connected to the separation roll in this way, it becomes possible to change the output torque from the motor by controlling the input current to the DC motor, but the inertia moment of the entire system increases and double feed At times, there is a problem that the reaction time until the separation motor rotates in the reverse direction becomes long.
In addition, the technique described in Patent Document 2 is provided with a sheet number detector for detecting the number of sheets in order to detect a double feed state, and there is a problem that the configuration becomes complicated.
Also, in any of the techniques disclosed in any of the documents, the roll rotation speed when the separation roll is reversely rotated varies depending on conditions such as the type of sheet, and depending on the conditions, the separation roll does not reversely rotate, causing double feeding, or On the other hand, there was a problem that jam occurred because the reverse rotation speed was too high.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sheet separating apparatus capable of appropriately controlling the torque applied to the separating roll and the reverse rotation speed of the separating roll with a simple configuration.

  In order to achieve the above-described object, the present invention provides a transport roll, a separation roll disposed so that an outer peripheral surface thereof is in contact with the transport roll, and transport that rotates the transport roll in a certain direction. Conveying torque generating means for applying torque; means for applying a separating torque in the same direction as the conveying torque to the separating roll, the separating torque generating means capable of controlling the magnitude of the separating torque; and rotation of the separating roll A speed measuring means for measuring the speed, a first storage means for storing the target rotational speed of the separation roll, and a difference between the rotational speed measured by the speed measuring means and the target rotational speed stored in the storage means. Based on the control means for outputting the first control signal for controlling the separation torque generating means and the separation torque generated by the separation roll driving means. Torque limiting means for limiting the first control signal so as not to exceed a value, and a first drive signal for driving the separated torque generating means based on the control signal output from the torque limiting means. A sheet separating apparatus having a first separation driving unit is provided.

  In a preferred embodiment, the sheet separating apparatus includes a speed change measuring unit that measures a change amount of the rotation speed of the separating roll before and after a certain time interval, and the separation roll driving based on a measurement result by the speed change measuring unit. Second separation drive means for outputting a second drive signal for controlling the means, and drive signal addition means for adding the first drive signal and the second drive signal and outputting an added drive signal. Further, the separation torque generating means generates the separation torque based on the addition drive signal.

  In another preferred embodiment, the sheet separating apparatus includes: a second storage unit that stores a plurality of threshold values of the separation torque; and a selection unit that selects one threshold value from the plurality of threshold values. The selecting means selects the first threshold value based on an instruction input by a user.

  In another preferred embodiment, the sheet separating apparatus includes a parameter measuring unit that measures a physical parameter of a sheet introduced into the sheet separating apparatus, a second storage unit that stores a plurality of threshold values of the separation torque, The apparatus further includes a selection unit that selects one threshold value among the plurality of threshold values based on the physical parameter measured by the parameter measurement unit.

  According to the present invention, it is possible to obtain a sheet separating apparatus capable of controlling the separation torque and the reverse rotation speed for separating sheets. By appropriately controlling the separation torque and the reverse rotation speed, it is possible to prevent poor conveyance and double feeding. Further, according to the present invention, it is possible to configure a torque variable mechanism with high responsiveness. When the second sheet is introduced into the nip portion from the state of conveying one sheet, it is possible to prevent a conveyance failure and double feeding by generating a necessary torque at a high speed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<1. First Embodiment>
<1-1. Configuration>
FIG. 1 shows the configuration of a copying machine using a sheet separating apparatus according to the first embodiment of the present invention. Similar to a general copying machine, the copying machine includes an image reading device 1 that reads an image from a document, an image forming device 2 that records an image read by the image reading device 1 on a sheet, and a user's man It has an operation display unit 3, which is a machine interface, a storage unit 4, and a control unit 5 for controlling the whole.

  The sheet separating apparatus according to the present embodiment is an apparatus that takes out sheets one by one from a sheet bundle stacked on the tray 10 and conveys the sheets toward the image forming apparatus 2. As in the above-described FIG. 13, the sheet separating apparatus has a pickup roll 202, a paper feed roll 203, and a separation roll 204. The pressing force generation unit 11 is a device that generates pressure to press the pickup roll 202 against a sheet bundle supported by the tray 10 as a sheet support. In the present embodiment, the bearing of the pickup roll 202 and the bearing of the paper feed roll 203 are connected, and the pressure generated by the pressing force generator 11 is applied to both the pickup roll 202 and the paper feed roll 203. It has become. The pressing force generation unit 12 is a device that presses the separation roll 204 from below to a sheet feeding roll 203 as a sheet support, and generates a nip pressure between both rolls. The rotation driving units 21, 22, and 23 are devices that generate torque for rotating the pickup roll 202, the sheet feeding roll 203, and the separation roll 204, respectively.

  The control unit 5 has a function of controlling the roll pressure and the nip pressure by the pressing force generation units 11 and 12 and a function of controlling the torque generated by the rotation driving units 21 to 23 as main control functions corresponding to the sheet separating apparatus. have. The above is the overall configuration of the copying machine using the sheet separating apparatus according to the present embodiment.

Subsequently, a conveying system of the sheet separating apparatus according to the present embodiment will be described. FIG. 2 is a diagram illustrating a configuration of a conveyance system (rotation driving units 22 and 23, a sheet feeding roll 203, and a separation roll 204) of the sheet separating apparatus according to the present embodiment. The separation roll 204 is connected to the DC motor 32 via a one-way clutch 31 and gears 35a and 35b that are used when the sheet is pulled out in the reverse rotation direction at the time of jamming. The motor driver 33 outputs a drive current for driving the DC motor 32 under the control of the control unit 5. In addition, a current limiting circuit 34 is connected to the output side of the motor driver 33, and the drive current output from the motor driver 33 is limited to a limit current value I _max or less specified by a control signal from the control unit 5. can do. An encoder 36 for measuring the rotation speed of the separation roll is attached to the rotation shaft of the separation roll 204. The signal from the encoder 36 is output to the control unit 5. The control unit 5 outputs a signal for controlling the DC motor 32 to the motor driver 33 based on the rotation speed of the separation roll 204 measured by the encoder 36. The rotation drive unit 21 that drives the separation roll 204 is not limited to the DC motor 32, and may be a motor of another system such as a brushless motor or a stepping motor as long as it is a rotation drive device capable of controlling torque. Further, the encoder 36 may be attached not to the rotation shaft of the separation roll 204 but to the rotation shaft of the DC motor 32 or the rotation shaft in the drive system from the DC motor 32 to the separation roll 204.

  The paper feed roll 203 is connected to the stepping motor 37 via gears 38, 39, 40 and 41. The stepping motor 37 generates a conveyance torque on the paper feed roll 203 in accordance with a control signal from the motor driver 42. As a result, the sheet feed roll 203 rotates in the direction of discharging the sheet to the discharge side.

ここで、Ｍは分離ロール２０４の慣性モーメントに各ギアやモータの慣性モーメントをそれぞれのギア比に応じて補正した慣性モーメントを加えた、分離ロール駆動系全体の分離ロール２０４の軸上からみた慣性モーメントである。ｒ_gはＤＣモータ３２が生成するトルクを分離ロール２０４に伝えるギアのギア比、Ｔ_rはモータが生成するトルクの大きさ、ｒは分離ロール２０４の半径、Ｆは分離ロール２０４と接するシートに作用する搬送力である。 <1-2. Principle of operation>
Next, the operation principle of the sheet separating apparatus according to this embodiment will be described. The equation of rotational motion of the separation roll 204 is as follows.

Here, M is the inertia viewed from the axis of the separation roll 204 of the whole separation roll drive system, which is obtained by adding the inertia moment obtained by correcting the inertia moment of each gear or motor according to the gear ratio to the inertia moment of the separation roll 204. It is a moment. r _g is the gear ratio of the gear that transmits the torque generated by the DC motor 32 to the separation roll 204, T _r is the magnitude of the torque generated by the motor, r is the radius of the separation roll 204, and F is the sheet in contact with the separation roll 204. It is the conveying force that acts.

F is ± μ _rr · N for 1 sheet so that the sheet feeding roll 203 follows a predetermined conveying speed when the number of sheets sandwiched in the nip portion is 0 or 1; Is a force having a magnitude in the range of ± μ _pr · N. Here, μ _rr is a coefficient of friction between the sheet feeding roll 203 and the separation roll 204, μ _pr is a coefficient of friction between the separation roll 204 and the sheet, and N is a contact pressure between the sheet feeding roll 203 and the separation roll 204. The resistance due to friction of the motor, gear, and shaft was ignored.

ここで、記号「ｌｉｍｉｔ」は、後続する括弧内の数式の最大値が、ｌｉｍｉｔ記号の下に記載された値であることを示す。すなわち、Ｔ_rの最大値はＴ_r ^maxである。また、Ｋ₁は比例定数、Ｖ_p／ｒは分離ロール２０４が逆回転する際の目標逆回転速度である。Ｔ_r ^maxは、通常状態（シートが０枚あるいは１枚の状態）のときに給紙ロール２０３から与えられる搬送トルクの最大値Ｔ_f ^maxよりも小さく、重送状態（ニップ部にシートが２枚以上ある状態）のときに給紙ロール２０３から与えられる搬送トルクＴ_fよりも大きな値に設定される。すなわち、

である。ここで、Ｔ_f＝ｒ・Ｆである。なお、本明細書においては、分離ロール２０４がシートを出力側に排出する回転方向を正回転方向、シートを入力側に戻す回転方向を逆回転方向と定義する。分離ロール２０４の回転角θおよび目標逆回転速度Ｖ_p／ｒもこの定義に従って正負が定義される（Ｖ_p／ｒは逆回転の目標速度であるので負の値である）。また、トルクは本来ベクトルであるが、以上の記述から明らかなように、搬送トルクＴ_fと分離トルクＴ_rの向きは同一である。したがって、以下の説明ではトルクの大きさのみについて議論する。 In the drive system shown in FIG. 2, the torque _Tr generated by the DC motor 32 is given by the following equation.

Here, the symbol “limit” indicates that the maximum value of the mathematical expression in the parentheses that follows is the value described under the limit symbol. That is, the maximum value of T _r is T _r ^max. K ₁ is a proportionality constant, and V _p / r is a target reverse rotation speed when the separation roll 204 rotates reversely. T _r ^max is smaller than the maximum value T _f ^{max of the} conveyance torque given from the sheet feeding roll 203 in the normal state (the state where the sheet is 0 sheet or 1 sheet), and the double feed state (the sheet is 2 in the nip portion) It is set to a value larger than the transport torque _Tf given from the paper feed roll 203 when there are more than one sheet). That is,

It is. Here, T _f = r · F. In this specification, the rotation direction in which the separation roll 204 discharges the sheet to the output side is defined as the normal rotation direction, and the rotation direction in which the sheet is returned to the input side is defined as the reverse rotation direction. The rotation angle θ of the separation roll 204 and the target reverse rotation speed V _p / r are also defined as positive or negative according to this definition (V _p / r is a negative value because it is the reverse rotation target speed). The torque is originally a vector, but as is clear from the above description, the directions of the transport torque _Tf and the separation torque _Tr are the same. Therefore, only the magnitude of torque will be discussed in the following description.

By solving the differential equation obtained by substituting Equation 2 into Equation 1, the transport torque _Tf applied from the sheet feeding roll 203 is changed from the normal state (the state of 0 sheets or 1 sheet) to the double feed state (sheets). The time change of the rotational speed dθ / dt of the separation roll 204 can be obtained when a step response is made in the state of two or more sheets.

FIG. 3 shows the time change of the rotational speed dθ / dt obtained in this way and the time change of the torque generated by the DC motor 32. As can be seen from Equation 2 and FIG. 3, according to the sheet separating apparatus according to this embodiment, the maximum value T _r ^max of the separation torque for preventing double feeding and the speed at which the separation roll 204 is rotated in reverse during double feeding. Can be controlled independently.

<1-3. Operation>
Next, details of the operation of the copying machine using the sheet separating apparatus according to the present embodiment will be described. FIG. 4 is a schematic diagram illustrating a state in which a sheet is conveyed to the nip portion between the sheet feeding roll 203 and the separation roll 204 and the sheet is output from the nip portion to a subsequent conveyance system. FIG. 5 is a timing chart showing the operation of the sheet separating apparatus. Hereinafter, an operation when two sheets conveyed to the nip portion are separated by the sheet separating apparatus according to the present embodiment and discharged one by one from the nip portion will be described.

  When the user inputs a copy instruction by operating the operation display unit 3, the control unit 5 outputs a signal instructing the motor driver 33 and the motor driver 42 to drive the separation roll 204 and the paper feed roll 203. When the user inputs an instruction, the operation display unit 3 displays a list of sheets usable in the copying machine. The user selects a sheet to be used from the displayed list. In the storage unit 4, an identifier for identifying one tray 10 among the plurality of trays 10 and a maximum value (limit torque) of the separation torque optimum for the paper set in the tray 10 are recorded in association with each other. The limit torque table is stored. The control unit 5 reads the limit torque value associated with the identifier of the sheet selected by the user from the limit torque table stored in the storage unit 4. The control unit 5 stores the read value in the storage unit 4 as a limit torque value. The limit torque table is stored in the storage unit 4 in advance, for example, when the user inputs the parameters of the sheet by operating the operation display unit 3 when setting the sheet. The limit torque may be determined using a conversion table or function for converting the parameter to the limit torque and recorded in the limit torque table.

The storage unit 4 stores a function f that converts torque into a drive current for the motor driver 33. The control unit 5 reads the function f from the storage unit 4, converts the limit torque value to the limit current value I _max. The control unit 5 outputs a control signal indicating the limit current value thus obtained to the current limit circuit 34. The storage unit 4 further stores a target reverse rotation speed V _p / r of the separation roll 204. The target reverse rotation speed V _p / r is a fixed value set individually for each apparatus.

ここで、ａ、ｂはモータの特性により定められる定数であり、その値は記憶部４に記憶されている。 In the present embodiment, the DC motor 32 is a motor having a characteristic that generates a torque _Tr according to the following equation with respect to the drive current _Idr .

Here, a and b are constants determined by the characteristics of the motor, and the values are stored in the storage unit 4.

から算出される出力電流Ｉ_OUTをＤＣモータ３２に出力することにより、制限トルクＴ_r ^maxを無視した場合の分離トルクＴ_rに相当する電流を発生させることができる。なお、数５において、ｃ＝１／ａ、ｄ＝−ｂ／ａである。すなわち、制御部５は、エンコーダ３６から信号、記憶部４に記憶されている目標逆回転速度Ｖ_p／ｒ、および数５に基いて、電流Ｉ_OUTを出力させる制御信号をモータドライバ３３に出力する。モータドライバ３３は、制御部５からの制御信号に従って電流Ｉ_OUTを後段の電流制限回路３４に出力する。電流制限回路３４は、電流Ｉ_OUTが制限電流値Ｉ_maxを超える場合には、電流値をＩ_maxとし、駆動電流Ｉ_drとしてＤＣモータ３２に出力する。Ｉ_maxは制限トルクＴ_r ^maxに相当する電流値であるため、ＤＣモータ３２は制限トルクＴ_r ^maxを超えないよ範囲で分離トルクＴ_rを発生する。このようにして、ＤＣモータ３２は、分離ロール２０４の回転速度ｄθ／ｄｔに対して数２に基いて制御された分離トルクＴ_rを発生させることができる。 Therefore, if the separation torque limit value T _r ^max is ignored from Equations 2 and 4, the rotational speed dθ / dt of the separation roll 204 output from the encoder 36 will be described.

The output current I _OUT calculated from by outputting the DC motor 32, it is possible to generate a current corresponding to a separation torque T _r of the case of ignoring the limit torque T _r ^max. In Equation 5, c = 1 / a and d = −b / a. That is, the control unit 5 outputs a control signal for outputting the current I _OUT to the motor driver 33 based on the signal from the encoder 36, the target reverse rotation speed V _p / r stored in the storage unit 4, and Equation 5. To do. The motor driver 33 outputs the current I _OUT to the subsequent current limiting circuit 34 in accordance with the control signal from the control unit 5. When the current I _OUT exceeds the limit current value I _max , the current limit circuit 34 sets the current value to I _max and outputs the drive current I _dr to the DC motor 32. Since I _max is a current value corresponding to the limit torque T _r ^max , the DC motor 32 generates the separation torque T _r within a range that does not exceed the limit torque T _r ^max . In this way, the DC motor 32 can generate the separation torque _Tr controlled based on the equation 2 with respect to the rotational speed dθ / dt of the separation roll 204.

  Further, the control unit 5 outputs a signal for driving the paper feed roll 203 to the motor driver 42. The motor driver 42 outputs a control signal to the stepping motor 37.

FIG. 4A is a diagram illustrating a state where the sheet is not conveyed to the nip portion (normal state) in the sheet separating apparatus according to the present embodiment. A conveyance torque T _{f that} is rotated in the direction of arrow A in FIG. In a state where no sheet is conveyed to the nip portion, T _f = r · μ _rr · N. Based on the output current from the motor driver 33, the DC motor 32 outputs a separation torque _Tr that rotates the separation roll 204 in the same direction as the conveyance torque, that is, in the direction of arrow B in FIG. Therefore, on the contact surface between the paper feed roll 203 and the separation roll 204, that is, the nip portion, the outer peripheral portions of the paper feed roll 203 and the separation roll 204 are operated to rotate in opposite directions. However, in the present embodiment, since the maximum value T _r ^max of the separation torque is set to be smaller than the conveyance torque T _f (see Equation 3), the separation roll 204 is fed on the contact surface in the normal state. It rotates in the same direction as the outer periphery of the roll 203 (the direction of arrow C in FIG. 4A). At this time, since the torque T _r and the torque T _f are constant, the rotational speed dθ / dt of the separation roll 204 is constant (this constant speed is referred to as “conveying speed”).

FIG. 4B is a diagram illustrating a state in which one sheet P1 is conveyed to the nip portion (this is also a normal state). Except for the point that T _f = r · μ _pr · N, it is the same as the case of FIG. That is, the paper feed roll 203 and the separation roll 204 rotate in the directions of arrows A and C in FIG. 4B, respectively, and output the sheet P1 to the subsequent transport system. A section I in FIG. 5 corresponds to the normal state in FIG. 4A or 4B.

FIG. 4C is a diagram illustrating a state where two sheets of the sheet P1 and the sheet P2 are conveyed to the nip portion. At this time, the sheet P <b> 1 in contact with the paper feed roll 203 is conveyed in the conveyance direction by the frictional force with the paper supply roll 203. On the other hand, a frictional force with the sheet feeding roll 203 acts on the sheet P2, but since the frictional force between the sheets is small, slip occurs between the sheets. Here, the separation roll 204 is acted on by the separation torque _Tr that tries to rotate the separation roll 204 in the direction B, that is, in the direction opposite to the direction in which the separation roll 204 rotates. Decrease (FIG. 5, section II).

When the rotation speed of the separation roll 204 decreases, the drive current I _dr output from the motor driver 33 according to Equation 5 decreases. That is, the separation torque _Tr decreases. However, when the value of the separation torque T _r calculated by Equation 4 is larger than T _r ^{max, the} drive current I _dr is limited by the current limiting circuit 34, so that T _r = T _r ^max is constant. While _Tr is constant, as can be seen from Equation 1, the rotational acceleration d ² θ / dt ² of the separation roll 204 is constant. Therefore, while _Tr is constant, the rotational speed dθ / dt of the separation roll 204 decreases with a constant slope (FIG. 5, section II).

As the rotation speed dθ / dt of the separation roll 204 decreases, the value of the separation torque _Tr calculated by Equation 4 also decreases. If the value of T _r is less than T _r ^max, separation torque T _r begins to decrease from the predetermined value. As the separation torque _Tr decreases, the rotational acceleration d ² θ / dt ^{2 of} the separation roll 204 also decreases. That is, the rotational speed dθ / dt of the separation roll 204 decreases while the inclination gradually decreases, and gradually approaches the target reverse rotation speed (section III in FIG. 5).

  In this way, the conveyance speed of the sheet P2 decreases, and further, the sheet P2 is fed back to the input side by the reverse rotation of the separation roll 204 (FIG. 4D). When the sheet P1 passes through the nip portion, the normal state is resumed, the separation roll 204 starts to rotate again in the direction of arrow C in the figure, and the sheet P2 is conveyed to the output side.

As described above, according to the sheet separating apparatus according to the present embodiment, the maximum value T _r ^max of the separation torque for preventing double feeding and the speed for reversely rotating the separation roll 204 at the time of double feeding are independent of each other. Can be controlled. Thereby, conveyance failure and double feeding can be prevented.

<2. Second Embodiment>
When two sheets are conveyed to the nip part, the separation roll 204 that has been rotating in the forward direction decelerates due to the action of the separation torque _Tr and eventually rotates backward, but the two sheets are introduced into the nip part. After that, it takes a finite time until the separation roll 204 actually starts reverse rotation (time t _{1 to} t _{2 in} FIG. 5). That is, even though the speed is reduced, the second sheet is conveyed to a certain degree in the conveyance direction and is returned therefrom by reverse rotation. This is mainly due to the moment of inertia of the drive system, but if this time is too long, the reaction rate becomes slow, which is a problem. Therefore, in this embodiment, the separation roll 204 is given a separation torque exceeding the limit torque T _r ^max during double feeding, and the separation roll 204 is reversed at high speed.
Hereinafter, the configuration, operation principle, and operation of the present embodiment will be described, but the description of the same matters as those of the first embodiment will be omitted.

<2-1. Configuration>
FIG. 6 shows the configuration of a copying machine using a sheet separating apparatus according to the second embodiment of the present invention. The same components as those in the sheet separating apparatus according to the first embodiment are denoted by the same reference numerals. The speed change measuring unit 51 calculates the amount of change in the rotational speed per certain time interval based on the signal from the encoder 36. Based on the signal from the speed change measurement unit 51, the control unit 5 outputs to the motor driver 43 a control signal that outputs a current for generating torque that accelerates reverse rotation of the separation roll 204. The current adding circuit 52 adds the currents output from the motor driver 43 and the current limiting circuit 34 and outputs the result to the DC motor 32 as a drive current.

ここで、Ｋ₂は駆動系の慣性モーメント以下の定数であり、ω_a、ω_bはそれぞれ時刻ｔ_a、ｔ_bにおける分離ロール２０４の回転速度である（ｔ_a＜ｔ_b）。 <2-2. Principle of operation>
In the drive system shown in FIG. 6, the separation torque _Tr generated by the DC motor 32 is given by the following equation.

Here, K ₂ is a constant equal to or less than the moment of inertia of the drive system, and ω _a and ω _b are the rotational speeds of the separation roll 204 at times t _a and t _b , respectively (t _a <t _b ).

The first term of Equation 6 is the same as the torque defined by Equation 2. That is, the maximum value is limited by the limit torque T _r ^max . In the present embodiment, the second term is added to this. Here, since the constant K ₂ is set to be equal to or less than the inertia moment of the drive system, the torque according to the second term is canceled by the inertia moment of the drive system. That is, when the separation roll 204 is rotated in reverse, the torque of the second term can eliminate the inertia moment of the drive system, and the limit torque of the first term can be applied quickly.

  FIG. 7 is a diagram illustrating an operation principle of the present embodiment. In short, the sheet separating apparatus according to the present embodiment generates a strong torque exceeding the limit torque when double feeding occurs, and reversely rotates the separation roll 204 at high speed.

<2-3. Operation>
Next, details of the operation of the copying machine using the sheet separating apparatus according to the present embodiment will be described. FIG. 8 is a timing chart showing the operation of the sheet separating apparatus according to this embodiment. Hereinafter, using FIG. 4 and FIG. 8, as in the first embodiment, the two sheets conveyed to the nip portion are separated by the sheet separating apparatus according to the present embodiment, one by one from the nip portion. The operation at the time of discharging will be described.

  When the user inputs a copy instruction by operating the operation display unit 3, the control unit 5 outputs a signal instructing the motor driver 33 and the motor driver 42 to drive the separation roll 204 and the paper feed roll 203. When the user inputs an instruction, the operation display unit 3 displays a list of sheets usable in the copying machine. The user selects a sheet to be used from the displayed list. The storage unit 4 stores a limit torque table in which an identifier for specifying a sheet that can be used in the copying machine and an optimum separation torque for the sheet are recorded in association with each other. The control unit 5 reads the value of the separation torque associated with the identifier of the sheet selected by the user from the limit torque table stored in the storage unit 4. The control unit 5 stores the read separation torque value in the storage unit 4 as a limit torque value.

In addition, the storage unit 4 stores a function f for converting torque into a drive current for the motor driver 33 and a function g for converting torque into a drive current for the motor driver 43. The control unit 5 reads the function f from the storage unit 4, converts the limit torque value to the limit current value I _max. The control unit 5 outputs a control signal indicating the limit current value thus obtained to the current limit circuit 34.

The control unit 5 outputs to the motor driver 33 a control signal for outputting the current I _{OUT according} to _Equation 5. The motor driver 33 outputs the current I _OUT to the subsequent current limiting circuit 34 in accordance with the control signal from the control unit 5. When the current I _OUT exceeds the limit current value I _max , the current limit circuit 34 sets the current value to I _max and outputs it as the output current I _dr1 to the current addition circuit 52. The output current I _dr1 corresponds to the drive current that generates the torque of the first term of _Equation 6.

なお、数７は数６の第２項および数４から導出される。 In order to generate the drive current corresponding to the second term of Equation 6, the control unit 5 outputs a control signal for outputting the output current I _dr2 by the following equation to the motor driver 43.

Equation 7 is derived from the second term of Equation 6 and Equation 4.

The motor driver 43 outputs the output current I _{dr2 according} to _Equation 7 to the current addition circuit 52 in accordance with the control signal from the control unit 5. The current addition circuit 52 adds the output currents I _dr1 and I _dr2 output from the motor driver 33 and the motor driver 43, and outputs the result to the DC motor 32 as the drive current I _dr . That is, I _dr = I _dr1 + I _dr2 . In this manner, the DC motor 32 can generate the separation torque _Tr controlled based on Equation 6 with respect to the rotational speed dθ / dt of the separation roll 204.

  Further, the control unit 5 outputs a signal for driving the paper feed roll 203 to the motor driver 42. The motor driver 42 outputs a control signal to the paper feed roll 203.

In the normal state of FIGS. 4A and 4B, similarly to the first embodiment, the sheet feeding roll 203 is given a conveyance torque Tf that is rotated by the stepping motor 37 in the direction of arrow A in the figure. Yes. Based on the output current I _dr from the current addition circuit 52, the DC motor 32 outputs a separation torque _Tr that rotates the separation roll 204 in the same direction as the conveying torque, that is, in the direction of arrow B in the drawing. As described in the first embodiment, the separation roll 204 rotates in the same direction as the outer periphery of the paper feed roll 203 (in the direction of arrow C in the figure) on the contact surface in a normal state. At this time, since the torque T _r and the torque T _f are constant, the rotational speed dθ / dt of the separation roll 204 is constant at the conveyance speed. Section I in FIG. 7 corresponds to the normal state in FIG. 4 (a) or FIG. 4 (b).

In the double feed state of FIG. 4C, slip occurs between sheets. Here, the separation roll 204 is acted on by the separation torque _Tr that tries to rotate the separation roll 204 in the direction B, that is, in the direction opposite to the direction in which the separation roll 204 rotates. Decreases (FIG. 7, section II).

When the rotation speed of the separation roll 204 is decreased, the drive current I _dr1 output from the motor driver 33 according to _{Equation 5} is decreased. However, the output current is limited to I _dr1 = I _max while I _dr1 > I _max . On the other hand, since the rotation speed of the separation roll 204 is reduced, that is, acceleration is generated, the output current I _dr2 output from the motor driver 43 to the current addition circuit 52 increases according to _Equation 7. Therefore, the drive current I _dr output from the current adding circuit 52 to the DC motor 32 exhibits a characteristic of increasing after exceeding I _max and then decreasing. That is, the separation torque _Tr generated by the DC motor 32 also exhibits similar characteristics (FIG. 8, section II).

As described above, when the two sheets are conveyed to the nip portion and the separation roll 204 starts to decelerate from the forward rotation due to the slip between the sheets, the DC motor 32 is in a direction to accelerate the deceleration of the separation roll 204, that is, the reverse rotation. A strong torque exceeding the limit torque T _r ^max is generated. Therefore, the separation roll 204 is reversely rotated at a high speed, and a responsive sheet separation process is realized.

As the rotational speed dθ / dt of the separation roll 204 decreases and approaches the target reverse rotational speed, the speed change amount Δω (= ω _b −ω _a ) decreases, and I _dr2 gradually approaches the minimum value. Accordingly, I _dr also asymptotically _{approaches the} minimum value, and the rotational speed dθ / dt of the separation roll 204 gradually approaches the target reverse rotational speed (FIG. 7, section III).

According to the present embodiment, the DC motor 32 generates a torque that eliminates the inertial moment of the drive system, as compared with the first embodiment, so that it is possible to realize a sheet separating apparatus with good responsiveness. . In this embodiment, the DC motor 32 generates a torque that is equal to or greater than the limit torque T _r ^max while the rotation speed of the separation roll 204 is changing, but this excessive torque reduces the rotation speed of the separation roll 204. Since it is spent for changing, the torque acting on the seat is equal to or less than the limit torque T _r ^max . Therefore, according to the present embodiment, it is possible to realize a sheet separating apparatus that can control both the separation torque that prevents double feeding and the reverse rotation speed during sheet separation and that has high responsiveness.

<3. Modification>
The present invention is not limited to the above-described embodiment, and various modifications can be made. For example, in the above-described embodiment, the paper (sheet) to be used is determined by the user's instruction input, and the limit torque value is determined according to the paper to be used. However, the embodiment is applied to the designated copying process. The method of determining the limit torque value to be performed is not limited to this. For example, a parameter meter that measures physical parameters such as sheet thickness may be installed, and the limit torque value may be determined based on the physical parameters measured by the parameter meter.

  In the above-described embodiment, the example in which the motor driver 33 and the current limiting circuit 34 are configured as separate circuits has been described. However, instead of these two circuits, a motor driver incorporating a current limiting circuit is used. Also good. Furthermore, in the second embodiment, the example in which the motor driver 33, the motor driver 43, the current limiting circuit 34, and the current adding circuit 52 are configured as separate circuits has been described. The circuit summarized in (1) may be used.

Further, in the above-described embodiment, the configuration in which the current limiting circuit 34 is installed in the subsequent stage of the motor driver 33 (FIGS. 2 and 6) has been described. It is good also as a structure installed in.
FIG. 9 is a diagram illustrating a configuration of a conveyance system of a sheet separating apparatus according to a modification example of the first embodiment. The separation roll 204 is connected to the DC motor 32 through gears 44 and 45 and a shaft 46. The control unit 5a includes a maximum value limiting circuit 34a and a speed control circuit 53a. The speed control circuit 53 a outputs a control signal corresponding to a term in the limit of Formula 2 based on the target reverse rotation speed V _p / r stored in the storage unit 4 and the signal from the encoder 36. The maximum value limiting circuit 34a limits the control signal from the speed control circuit 53a in order to limit the maximum value of torque to T _r ^max . The controller 5a outputs the control signal generated as described above to the motor driver 33. As a result, the motor driver 33 outputs a drive current for generating the torque _Tr shown in Equation 2 to the DC motor 32. Other configurations and operations are the same as those in the first embodiment.

FIG. 10 is a diagram illustrating a configuration of a conveyance system of a sheet separating apparatus according to another modification of the first embodiment. The control unit 5 b calculates a rotation speed of the separation roll 204 based on a signal from the encoder 36, a rotation speed of the separation roll 204, and a target reverse rotation speed V _p / r stored in the storage unit 4. In order to limit the maximum value of torque to T _r ^max , a subtracting circuit 59b that outputs a control signal based on the difference between them, an amplifying circuit 55b that amplifies the control signal output from the subtracting circuit 59b by K ₁ times A maximum value limiting circuit 34b for limiting the control signal output from the amplifier circuit 55b is incorporated. The object and effect of the present invention can also be achieved by such a configuration.

FIG. 11 is a diagram illustrating a configuration of a conveyance system of a sheet separating apparatus according to a modification of the second embodiment. The operations of the speed control circuit 53c and the maximum value limiting circuit 34c are the same as those of the speed control circuit 53a and the maximum value limiting circuit 34a of FIG. That is, the maximum value limiting circuit 34c outputs a control signal corresponding to the first term of Equation 6. Acceleration control circuit 56c, based on a signal from the encoder 36, and outputs a predetermined time the amount of change in the rotational speed of the separation roll 204 before and after (corresponding to the second term of number 6) K ₂ multiplied by the control signal . The adding circuit 52c adds the control signal output from the maximum value limiting circuit 34c and the control signal output from the acceleration control circuit 56c, and outputs the result to the motor driver 33. As a result, the motor driver 33 outputs a drive current for generating the torque _Tr shown in Equation 6 to the DC motor 32. Other configurations and operations are the same as those of the second embodiment.

FIG. 12 is a diagram illustrating a configuration of a conveyance system of a sheet separating apparatus according to another modification example of the second embodiment. The operations of the speed calculation circuit 54d, the subtraction circuit 59d, the amplification circuit 55d, and the maximum value limiting circuit 34d are the same as those of the speed calculation circuit 54b, the subtraction circuit 59b, the amplification circuit 55b, and the maximum value limiting circuit 34b of FIG. The acceleration calculation circuit 57d outputs a signal corresponding to the amount of change in speed based on the signal from the encoder 36. Amplifier 58d amplifies the signal outputted from the acceleration calculation circuit 57d _doubled K. The adder circuit 52d adds the control signal output from the maximum value limiting circuit 34d and the control signal output from the amplifier circuit 58d, and outputs the result to the motor driver 33. The object and effect of the present invention can also be achieved by such a configuration.

  In addition, the signal processing in the control unit 5 in the above-described embodiment and each modification may be realized by software processing instead of hardware by a combination of circuits.

1 is a diagram illustrating a configuration of a copying machine using a sheet separating apparatus according to a first embodiment of the present invention. It is a figure which shows the structure of the conveyance system of the sheet separation apparatus which concerns on the same embodiment. It is a figure explaining the principle of operation concerning the embodiment. FIG. 6 is a diagram illustrating a state in which a sheet is introduced into a nip portion and output to a subsequent conveyance system. 6 is a timing chart showing the operation of the sheet separating apparatus according to the embodiment. It is a figure which shows the structure of the copying machine using the sheet separation apparatus which concerns on 2nd Embodiment of this invention. It is a figure explaining the principle of operation concerning the embodiment. 6 is a timing chart showing the operation of the sheet separating apparatus according to the embodiment. It is a figure which shows the structure of the conveyance system of the sheet separation apparatus which concerns on the modification of 1st Embodiment. It is a figure which shows the structure of the conveyance system of the sheet separation apparatus which concerns on another modification of 1st Embodiment. It is a figure which shows the structure of the conveyance system of the sheet separation apparatus which concerns on the modification of 2nd Embodiment. It is a figure which shows the structure of the conveyance system of the sheet separation apparatus which concerns on another modification of 2nd Embodiment. 1 shows an example of a sheet separating apparatus according to the prior art. It is a schematic diagram which shows a mode that two sheets were double-fed to the nip part. It is a figure which shows the structure of the sheet separation apparatus which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image reading apparatus, 2 ... Image forming apparatus, 3 ... Operation display part, 4 ... Memory | storage part, 5 ... Control part, 10 ... Tray, 11 ... Pressing force generation part, 21 ... Rotation drive part, 31 ... One-way clutch, 32 ... DC motor, 33 ... motor driver, 34 ... current limiting circuit, 35 ... gear, 36 ... encoder, 37 ... stepping motor, 38 ... gear, 42 ... motor driver, 43 ... motor driver, 51 ... speed change measuring unit, 52 ... Current adding circuit, 201 ... Tray, 202 ... Pickup roll, 203 ... Feeding roll, 204 ... Separating roll, 301 ... Stepping motor, 303 ... Torque limiter.

Claims (4)

A transport roll;
A separation roll disposed so that the outer circumferential surface is in contact with the transport roll; and
Conveying torque generating means for applying a conveying torque for rotating the conveying roll in a certain direction to the conveying roll;
A means for giving a separation torque in the same direction as the conveying torque to the separation roll, and a separation torque generating means capable of controlling the magnitude of the separation torque;
Speed measuring means for measuring the rotational speed of the separating roll;
First storage means for storing a target rotational speed of the separation roll;
Control means for outputting a first control signal for controlling the separation torque generating means based on the difference between the rotational speed measured by the speed measuring means and the target rotational speed stored in the storage means;
Torque limiting means for limiting the first control signal so that the separation torque generated by the separation roll driving means does not exceed a certain threshold;
Possess a first separation driving means for outputting a first driving signal for driving the separation torque generating unit based on the control signal outputted from the torque limiting means,
The target rotation speed is a target rotation speed when the separation roll rotates in the same direction as the conveyance roll . Speed change measuring means for measuring the amount of change in the rotational speed of the separating roll before and after a certain time interval;
Second separation drive means for outputting a second drive signal for controlling the separation roll drive means based on a measurement result by the speed change measurement means;
Drive signal adding means for adding the first drive signal and the second drive signal and outputting an added drive signal;
Further comprising
The sheet separating apparatus according to claim 1, wherein the separation torque generating unit generates the separation torque based on the addition drive signal. Second storage means for storing a plurality of threshold values of the separation torque;
Selecting means for selecting one threshold value among the plurality of threshold values;
The sheet separating apparatus according to claim 1, wherein the selection unit selects the first threshold value based on an instruction input by a user. Parameter measuring means for measuring physical parameters of the sheet introduced into the sheet separating apparatus;
Second storage means for storing a plurality of threshold values of the separation torque;
The sheet separating apparatus according to claim 1, further comprising: a selecting unit that selects one threshold among the plurality of thresholds based on a physical parameter measured by the parameter measuring unit.

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