JP2011225335A - Sheet conveying device, document reading apparatus, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveying device, along with a document reading apparatus and an image forming apparatus, capable of reducing power consumption required for paper feeding assist control.SOLUTION: The sheet conveying device detects a time from start of a paper feeding motor until detection of a document tip by a skew amount sensor as a document conveyance time (S501). If the document conveyance time is longer than a prescribed document conveyance time (S502: YES), a prescribed current amount (large) is selected (S503) as a total current amount to be supplied at the paper feeding assist control time, and if the document conveyance time is shorter (S502: NO), a current amount (small) is selected. Then, a document skew amount is detected (S505), and if the result is larger than a prescribed document skew amount (large) (S506: YES), a current amount having a prescribed ratio (large) is distributed to the paper feeding motor from the total current amount (S507), and if the result is smaller than the document skew amount (small) (S508: YES), paper feeding assist control is omitted, or otherwise the paper feeding assist control is executed with a ratio (middle) (S509).

Description

  The present invention relates to a sheet conveying apparatus, a document reading apparatus, and an image forming apparatus, and more particularly to a technique for solving a thermal problem at the time of so-called skew correction while reducing costs and saving power.

  In the field of copying machines, improvement in image reading speed is required in parallel with improvement in image forming speed. For this reason, for example, a back side reading unit may be provided so that both sides of a document can be read with a single sheet passing. The existing scanner reads the document from the lower side, whereas the back surface reading unit reads the document from the side opposite to the existing scanner, that is, the upper side. As a result, the number of sheet passing in the case of double-sided reading can be halved.

However, while the back side scanning unit must be disposed above the document transport path, it is necessary to avoid increasing the height of the automatic document reading device as much as possible because it leads to an increase in cost due to packaging and transportation. is there.
For this purpose, for example, the positions of the back surface reading unit and the roller for conveying the document are shifted so as not to overlap in the height direction. However, in this case, it is necessary to lengthen the document transport path from the document table tray on which the document is placed to the registration roller that corrects the skew of the document. For this reason, it is necessary to add a transport roller (hereinafter referred to as “paper feeding intermediate roller”) so that a small-size document can be transported even if the transport path becomes long.

FIG. 2 is a diagram showing a configuration of an automatic document feeder provided with a back surface reading unit. As shown in FIG. 2, a sheet feeding intermediate roller 207 is provided on the conveyance path from the document table tray 201 to the registration roller 210 in addition to the feeding roller 202 and the separating roller 206.
When the back side reading unit 218 is not provided, when correcting the skew of the original, the original is abutted against the stopped registration roller 210 to form a loop, and then the registration roller 210 is rotationally driven to skew. Transport the corrected document. In this case, since the separation roller 206 is composed of only one roller, the load resistance for pulling out the document held by the separation roller 206 is sufficiently smaller than the conveying force of the registration roller 210. Will not occur.

On the other hand, when the back surface reading unit 218 is provided, it is necessary to use three rollers as the sheet feeding intermediate roller 207 in order to reduce skew. For this reason, in the case of a long document, when the document is conveyed by the registration roller 210, it is sandwiched by the paper supply intermediate roller 207 in addition to the separation roller 206, so that the load resistance for pulling out the document increases.
For this reason, when the skew is large to some extent, when the document is conveyed by the registration roller 210, a loop is first canceled only at one end portion of the document, and a loop remains at the other end portion. In this state, if the registration roller 210 continues to convey the document, the load resistance due to the separation roller 206 and the paper feeding intermediate roller 207 is large, and therefore the document slips on the registration roller 210 and the skew is sufficiently large. It will not be resolved.

To solve such a problem, it is conceivable to pull out the original by improving the conveying force of the registration roller 210. However, there is a limit to increasing the frictional resistance between the registration roller 210 and the original, Since it causes an increase in power, it is not practical.
For this reason, paper feed assist control has been proposed in which the paper roller 206 and the paper feed intermediate roller 207 are rotationally driven along with the document conveyance by the registration rollers 210 (see Patent Document 1). Employing the paper feed assist control reduces the load resistance for pulling out the original from the separating roller 206 and the intermediate paper supply roller 207, thereby eliminating the skew of the original.

JP 2008-30937 A

  FIG. 9 is a timing chart showing the difference in operation between the sheet feeding motor 208 and the registration motor 213 depending on the presence / absence of sheet feeding assist control. FIG. 9A shows the operation when there is no sheet feeding assist control, and FIG. Indicates the operation when there is paper feed assist control. As shown in FIG. 9A, when the paper feed assist control is not performed, the paper feed motor 208 stops when the original is abutted against the registration roller 210 and a loop is formed, and the next original is fed. Does not work until paper starts.

On the other hand, when the paper feed assist control is performed, as shown in FIG. 9B, the paper is fed from the registration motor 210 rotating the registration roller 210 until the registration is stopped until the registration is stopped. Since the paper feed motor 208 operates for assist control, the corresponding power is consumed (901).
In this case, since the paper feed motor 208 also rotates the intermediate paper feed roller in addition to the rolling roller 206, the torque has to be increased, so that the power consumption of the paper feed motor 208 also increases in that sense. To do.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet conveying apparatus, a document reading apparatus, and an image forming apparatus that reduce power consumption required for sheet feeding assist control. .

  In order to achieve the above object, a sheet conveying apparatus according to the present invention is a sheet conveying apparatus that performs skew correction by abutting and bending a sheet against a stopped registration roller, and a registration motor that rotationally drives the registration roller. A sheet feeding roller that strikes the sheet against the registration roller, a sheet feeding motor that rotationally drives the sheet feeding roller, a total current amount determining unit that determines a total current amount used for sheet conveyance, and a sheet that strikes the registration roller A skew amount detecting means for detecting the skew amount at the time, and the sheet feeding roller is rotated in synchronism with the rotation of the registration roller so that the bending of the sheet is maintained in the sheet conveyance path from the sheet feeding roller to the registration roller. A paper feed assist control means, and the paper feed assist control means comprises a resist motor driving current and a paper feed motor drive. The resist motor drive current and the paper feed motor drive current are set so that the sum of the current and the total current amount is equal, and the proportion of the drive current of the paper feed motor decreases as the detected skew amount decreases. It is characterized by determining.

In this way, since the total amount of current corresponding to the seat is determined, power consumption can be reduced. Further, since the total amount of current is distributed to the sheet feeding motor and the registration motor according to the skew amount, it is possible to prevent the occurrence of skew after the registration is started.
In this case, the stopped registration roller is provided with a time measuring unit that measures a conveyance time required for the sheet feeding roller to abut the sheet, and the total current amount determining unit calculates the total current amount from the measured conveyance time. You may decide. In this case, a plurality of sensors for detecting the leading edge of the sheet may be provided upstream of the registration roller in the sheet conveying direction, and both the skew amount detecting means and the time measuring means may be used.

  Further, prior to conveying the sheet by the registration roller, an acquisition unit that acquires at least one of the thickness and hardness of the sheet is provided, and the total current amount determination unit includes the acquired thickness and hardness of the sheet. The total amount of current may be determined from at least one of the above. Since the skew amount of the original can be estimated from the thickness and hardness of the original, the amount of current required for sheet conveyance may be determined based on these.

  Further, in order to detect the skew amount, the skew amount detecting means includes a plurality of sheet leading edge detection sensors arranged on the upstream side of the registration roller in the sheet conveyance direction and disposed along the rotation axis of the registration roller. Further, the skew amount may be detected from a time difference in which the plurality of sheet leading edge detection sensors detect the leading edge of the sheet, and before the sheet is conveyed by the registration roller, at least the size, thickness, and hardness of the sheet are detected. Acquisition means for acquiring one may be provided, and the skew amount detection means may determine the skew amount from at least one of the acquired size, thickness, and hardness of the sheet.

  The document reading apparatus and the image forming apparatus according to the present invention include the sheet conveying apparatus according to the present invention. Even if it does in this way, the effect of the present invention can be acquired.

1 is a diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a diagram illustrating a configuration of a document reading unit 100. FIG. 5 is a plan view showing an arrangement of a skew amount sensor 212. FIG. 3 is a block diagram illustrating a main configuration of a control unit 112. FIG. It is a flowchart which shows the determination procedure of the paper-feed assist control time which concerns on embodiment of this invention. 6 is a timing chart showing rotation speeds of a sheet feeding motor 208 and a registration motor 213. 10 is a timing chart showing operations of the paper feed motor and the registration motor 213 when the document conveyance time is shorter than a predetermined time (S502: NO). 10 is a timing chart showing the operation of the paper feed motor and registration motor 213 when the document conveyance time is longer than the predetermined time (S502: YES). 5 is a timing chart showing the difference in operation between the sheet feeding motor 208 and the registration motor 213 depending on whether or not the sheet feeding assist control is performed, where (a) shows the operation when there is no sheet feeding assist control, and (b) shows the sheet feeding assist. The operation when there is control is shown.

Hereinafter, embodiments of a sheet conveying device, a document reading device, and an image forming apparatus according to the present invention will be described with reference to the drawings.
[1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.
FIG. 1 is a diagram illustrating a main configuration of the image forming apparatus according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a document reading unit 100, an image forming unit 110, and a paper feeding unit 120. The document reading unit 100 optically reads a document and generates image data. The configuration of the document reading unit 100 will be described later.

The image forming unit 110 includes image forming units 111Y to 111K, a control unit 112, an intermediate transfer belt 113, a secondary transfer roller pair 114, a fixing device 115, a paper discharge roller 116, a paper discharge tray 117, and a cleaner 118.
The image forming units 111Y to 111K form toner images of Y (yellow), M (magenta), C (cyan), and K (black), respectively, under the control of the control unit 112, so that the toner images of the respective colors overlap. Then, electrostatic transfer (primary transfer) is performed on the intermediate transfer belt 113. The intermediate transfer belt 113 is an endless rotating body, and rotates in the direction of arrow A to convey the toner image to the secondary transfer position.

The paper feeding unit 120 includes a plurality of paper feeding cassettes 121 that store recording sheets S for each type, and supplies the recording sheets S to the image forming unit 110. The supplied recording sheet S is conveyed to the secondary transfer position in parallel with the intermediate transfer belt 113 conveying the toner image.
The secondary transfer roller pair 114 electrostatically transfers (secondary transfer) the toner image on the intermediate transfer belt 113 to the recording sheet S. The recording sheet S to which the toner image is transferred is conveyed to the fixing device 115.

The fixing device 113 is an electromagnetic induction heating type fixing device, and heats the toner image and fuses it to the recording sheet S. The recording sheet S to which the toner image has been fused is discharged onto a paper discharge tray 117 by a paper discharge roller 116.
[2] Configuration of Document Reading Unit 100 FIG. 2 is a diagram illustrating a configuration of the document reading unit 100. As shown in FIG. 2, the document reading unit 100 includes an automatic document feeder unit (ADF: Automatic Document Feeder; hereinafter referred to as “conveying unit”) 200 and a document reading unit (hereinafter referred to as “reading unit”) 230. It has. The transport unit 200 is attached to the reading unit 230 by a hinge mechanism (not shown) so as to be opened and closed. When the front portion of the transport unit 200 is rotated upward, the upper surface of the reading unit 230 is exposed. The operator can place the original manually.

  The reading unit 230 includes platen glasses 231 and 232 and sliders 233 and 234. When reading a document supplied by the transport unit 200, the slider 233 stops at a sheet through position (image reading position) below the platen glass 232. The slider 233 includes a light source 235 and a mirror 236, illuminates the original passing through the platen glass 232 with the light source 235, and further reflects the reflected light with the mirror 236.

  The slider 234 includes mirrors 237 and 238, and sequentially reflects light reflected by the mirror 236 and guides it to the reduction lens 239. The light transmitted through the reduction lens 239 enters a CCD (Charge Coupled Device) line sensor 240. The CCD line sensor 240 includes a large number of photoelectric conversion elements arranged in the main scanning direction, and generates image data by repeatedly photoelectrically converting incident light. When reading a document placed on the platen glass 231, the entire document is read by moving the sliders 233 and 234 in the arrow A direction.

The transport unit 200 includes a document feed tray 201 on which a document to be transported is placed, and indicates that the document is placed on the document feed tray 201 in a state where the leading end of the document is abutted against the positioning unit 202. It is detected by a set sensor (not shown). The document regulating plate 203 is used for positioning the document in the width direction.
When reading of the original is started, the push-up plate 204 pushes up the original and presses it against the feed roller 205. A feed roller 205 feeds the original to the roller 206. The separating roller 206 is composed of a pair of upper and lower rollers, and conveys the uppermost one of the fed documents to the sheet feeding intermediate roller 207. The sheet feeding intermediate roller 207 also includes a pair of upper and lower rollers.

  The feed roller 205, the separating roller 206, and the paper feed intermediate roller 207 are driven to rotate by a paper feed motor 208. Note that the rotation of the paper feed motor 208 is transmitted to the feed roller 205 and the separating roller 206 via the paper feed clutch 209. For example, a stepping motor may be used as the paper feed motor 208. The stepping motor can increase or decrease the torque while maintaining the rotation speed by increasing or decreasing the current amount while maintaining the duty ratio.

  The intermediate sheet feeding roller 207 conveys the document toward the registration roller 210 in a stopped state. A conveyance path from the sheet feeding intermediate roller 207 to the registration roller 210 is formed by a pair of guide plates. Further, immediately before the registration roller 210 on the conveyance path, a loop storage unit 211 that stores a loop formed by a document that is abutted against the registration roller 210 by the paper supply intermediate roller 207 is provided.

The registration roller 210 is rotationally driven by a registration motor 213. As the registration motor 213, for example, a stepping motor may be used.
A skew amount sensor 212 is disposed on the upstream side of the registration roller 210 in the document conveyance direction. FIG. 3 is a plan view showing the arrangement of the skew amount sensor 212. As shown in FIG. 3, the skew amount sensor 212 includes three sub sensors 212 a to 212 c, and the three sub sensors 212 a to 212 c are arranged along the axial direction of the registration roller 210.

For example, each of the sub-sensors 212a to 212c includes a pair of LED light sources and a photo sensor, and detects the timing when the light emitted from the LED light sources is blocked by the document D. Then, it is determined that the skew amount increases as the detection time difference between the sub sensors 212a to 212c increases.
After a predetermined time has elapsed since the sub sensors 212a to 212c detected the leading edge of the document D, the registration roller 210 is rotated by the registration motor 213. In synchronization with this, the paper feed motor 208 rotationally drives the paper feed intermediate roller 207 (paper feed assist control). Note that the sheet feeding clutch 209 may be disconnected during the sheet feeding assist control, and the feeding roller 205 and the separating roller 206 may be stopped.

As a result, the document advances to the reading roller 214. The reading rollers 214 to 216 are rotationally driven by a reading motor 217. One side of the original is read by the reading unit 230 when it passes over the platen glass 232 by the reading rollers 214 and 215.
Thereafter, the original is conveyed by the reading rollers 215 and 216, and the other side is read when passing under the back side reading unit 218. The back surface reading unit 218 includes a linear light source that illuminates the document surface, and a contact line sensor (CIS: Contact Image Sensor) that receives reflected light from the document surface. Both the linear light source and the contact type line sensor are arranged so that the longitudinal direction thereof is orthogonal to the document conveying direction.

  After being read by the back side reading unit 218, the document is discharged onto the discharge tray 220 by the discharge roller 219. The paper discharge roller 219 is rotated by a paper discharge motor 221. A cleaning member 222 is disposed over substantially the entire length of the platen glass 232 in the longitudinal direction, and the surface of the platen glass 232 is cleaned by rotating about an axis substantially parallel to the platen glass 232. Similarly, a cleaning member 223 is disposed over substantially the entire length of the reading surface of the back surface reading unit 218, and the surface of the reading surface is cleaned by rotating about an axis substantially parallel to the reading surface. .

[3] Configuration of Control Unit 112 Next, the configuration of the control unit 112 will be described.
FIG. 4 is a block diagram illustrating a main configuration of the control unit 112. As shown in FIG. 4, the control unit 112 includes a CPU (Central Processing Unit) 401, a ROM (Read Only Memory) 402, and a RAM (Random Access Memory) 403, and the CPU 401 stores a control program recorded in the ROM 402. And the program is executed using the RAM 403 as a working storage area.

  As a result, the CPU 401 controls the paper feed motor 208 and the paper feed clutch 209 to rotationally drive the feed roller 205, the separating roller 206, and the paper feed intermediate roller 207. Further, the CPU 401 controls the registration motor 213 to rotationally drive the registration roller 210 and controls the reading motor 217 to rotationally drive the reading rollers 214 to 216 to adjust the conveyance speed when reading the document.

The paper feed motor 208 and the registration motor 213 are supplied with power from a common power supply device 404. The CPU 401 controls the amount of current that the power supply device 404 supplies to the paper feed motor 208 and the registration motor 213, respectively.
Further, by controlling the paper discharge motor 221, the paper discharge roller 219 is driven to rotate, and the document that has been read is discharged. When the CPU 401 abuts against the registration roller 210, the CPU 401 detects the skew amount by comparing the time during which the leading edge of the document passes through the plurality of skew amount sensors 212. Prior to document conveyance, the document is pressed against the feed roller 205 by the push-up plate 204.

[4] Operation of Control Unit 112 Next, the operation of the control unit 112 when determining the amount of current to be supplied to the paper feed motor 208 and the registration motor 213 will be described.
FIG. 5 is a flowchart showing the operation of the control unit 112. As shown in FIG. 5, the control unit 112 detects the time from when the paper feed motor 208 is activated until the leading edge of the document is detected by the skew amount sensor 212 (hereinafter referred to as “document transport time”) (see FIG. 5). S501). If the document transport time is longer than the predetermined document transport time (S502: YES), the total amount of current supplied to the paper feed motor 208 and the current supplied to the registration motor 213 during paper feed assist control is summed up. A predetermined current amount (large) is selected as the current amount (S503).

  Generally, thick paper has a large torque required for conveyance, so that the document conveyance time is long, and plain paper tends to be short because it is small. Based on this knowledge, in the present embodiment, the paper type is determined based on the length of the document conveyance time, and the current amount is selected so that the document can be conveyed with an appropriate torque. That is, when the detected document conveyance time is long, the amount of current is increased so as to increase the torque, and when it is short, the amount of current is decreased.

Therefore, when the detected document conveyance time is shorter than the predetermined document conveyance time (S502: NO), the amount of current supplied to the sheet feeding motor 208 and the amount of current supplied to the registration motor 213 during sheet feeding assist control. Is selected as a total current amount (small) (S504).
Next, the control unit 112 detects the document skew amount (S505). The document skew amount is obtained by multiplying the document conveyance speed (v) obtained from the document conveyance time detected in step S501 by the detection time difference (t) between the sub sensors 212a to 212c.

  When the detected document skew amount is larger than the predetermined document skew amount (large) (S506: YES), the ratio of the current amount to be distributed to the paper feed motor 208 out of the total current amount selected as described above is predetermined. (S507). This is to increase the torque of the paper feed motor 208 in order to prevent the occurrence of skew due to the load resistance of the feed roller 205 or the like when the document skew amount is large.

For the above reason, when the detected document skew amount is smaller than the predetermined document skew amount (large) (S506: NO) and larger than the predetermined document skew amount (small) (S508: NO). ), The ratio of the amount of current distributed to the paper feed motor 208 is set to a predetermined ratio (medium) (S509).
When the detected document skew amount is smaller than the predetermined document skew amount (small) (S508: YES), the ratio of the current amount distributed to the paper feed motor 208 is set to a predetermined ratio (small) (S510). ), Reducing the amount of current that is supplied to the paper feed motor 208. This is because, when the document skew amount is small, the occurrence of skew due to the load resistance of the feed roller 205 or the like is small, and skew correction by document conveyance can be expected.

When the ratio of the current amount is set to a predetermined ratio (small), the document skew amount is small, and there is a possibility that document skew may occur even if the sheet feeding assist control is not performed using the separation roller 206 or the sheet feeding intermediate roller 207. Therefore, re-feeding by the registration roller 210 is performed without feeding assist control (S511).
On the other hand, when the ratio of the current amount is set to a predetermined ratio (large) or (medium), the control unit 112 executes paper feed assist control when re-feeding with the registration roller 210 (S512). ).

The document skew amount may be determined to be large when, for example, the ratio of the document skew amount (vt) to the length in the document transport direction is greater than 0.5%. If this ratio is smaller than 0.3%, it may be determined that the document skew amount is small.
Also, regarding the length of the document transport time, for example, when the time required for transporting plain paper exceeds 1.3 times, it may be determined that the document transport time is long, otherwise it may be determined to be short.

Regarding the distribution of the amount of current between the paper feed motor 208 and the registration motor 213, for example, in the case of thick paper having a long document conveyance time, it may be as follows. That is, when the document skew amount is larger than 0.5%, the ratio of the current amount If of the paper feed motor 208 and the current amount Ir of the registration motor 213 is set as If: Ir = 0.5: 0.5 = 1: 1.
When the document skew amount is smaller than 0.5% and larger than 0.3%,
If: Ir = 0.25: 0.75 = 1: 3
If the document skew amount is less than 0.3%,
If: Ir = 0: 1
It is also good.

Document skew is more likely to occur when a thicker sheet or the like requires higher torque. Therefore, the occurrence of document skew can be suppressed by increasing the ratio of the paper feed motor 208.
In the case of plain paper with a short document conveyance time, the following may be used. That is, when the document skew amount is larger than 0.5%, the ratio of the current amount If of the paper feed motor 208 and the current amount Ir of the registration motor 213 is set as If: Ir = 0.4: 0.35 = 8: 7.
When the document skew amount is smaller than 0.5% and larger than 0.3%,
If: Ir = 0.2: 0.55 = 4: 11
If the document skew amount is less than 0.3%,
If: Ir = 0: 1
It is also good.

In this way, since the amount of current supplied to the registration motor 213 can be suppressed, the power consumption required for the paper feed assist control can be reduced.
FIG. 6 is a timing chart showing the operations of the paper feed motor 208 and the registration motor 213 when the original skew amount is small when the original is abutted against the registration roller 210 (S510: YES). In the drawing, the vertical axis of the timing chart indicates the rotational speed of the motor (the same applies to FIGS. 7 to 9).

  As shown in FIG. 6, when the skew amount of the document is small, there is no possibility that the document skew is generated again when the registration motor 213 transports the document after the registration is started. Regardless, that is, regardless of whether the original is plain paper or thick paper, the paper feed motor 208 is not driven. Therefore, useless paper feed assist control can be omitted, and power consumption is reduced.

  Note that the ratio of the amount of current supplied by the registration motor 213 to the amount of current supplied to the paper feed motor 208 during the document conveyance time (denoted as “1” in FIG. 6) is determined when the document is determined to be thick paper ( “S” is “1”, and when it is determined to be plain paper (S 502: NO), it is “0.75” because torque is not required as in the case of transporting thick paper. Conventionally, the ratio of the supply current amount of the registration motor 213 is “1” regardless of the paper type of the document. However, according to the present invention, it is possible to further power consumption.

In this embodiment, since the paper type of the original cannot be determined during the original conveyance time, the amount of current supplied to the paper feed motor 208 during this period generates a torque sufficient to convey the thick paper. It is always “1” so that
FIG. 7 is a timing chart showing the operations of the paper feed motor and the registration motor 213 when the document conveyance time is shorter than the predetermined time (S502: NO). If the document transport time is shorter than the predetermined time, it is determined that the document is plain paper. In this case, if the skew amount of the original is medium (S508: NO) or large (S506: YES), it is necessary to prevent the recurrence of skew after the resist is activated, and as shown in FIG. Assist control is performed.

The amount of current supplied to the paper feed motor 208 during the paper feed assist control is “0.2” if the skew amount is moderate with respect to the current amount “1” supplied to the paper feed motor 208 during the document conveyance time. (S509), if larger, “0.4” is set (S507). In this way, it is possible to reliably prevent the occurrence of skew after resist activation.
Further, during the paper feed assist control, the current amount supplied to the registration motor 213 is set so that the total current amount of the current amounts supplied to the paper feed motor 208 and the registration motor 213 is “0.75”. Determine (S504). That is, if the skew amount is medium, “0.55” is set (S509), and if the skew amount is large, “0.35” is set (S507).

  During the paper feed assist control, the total current amount is set to “0.75” while the current amount “1” is a current amount necessary for conveying a thick original, while the current amount “0. This is because “75” is an amount of current sufficient to convey a plain paper document. Conventionally, even during the paper feed assist control, an amount of current sufficient to transport thick paper is supplied regardless of the paper type. In this way, power consumption can be reduced.

  FIG. 8 is a timing chart showing the operations of the paper feed motor and the registration motor 213 when the document conveyance time is longer than the predetermined time (S502: YES). If the document transport time is longer than the predetermined time, it is determined that the document is thick paper. Even in this case, when the skew amount of the document is medium or more, the sheet feeding assist control is performed in order to prevent the recurrence of the skew after the registration is activated.

  When the original is thick paper, the torque required for conveyance is larger than when the original is plain paper, so the total current amount is set to “1” (S503). If the document skew amount is large (S506: YES), both the amount of current supplied to the sheet feeding motor 208 and the amount of current supplied to the registration motor 213 are set to “0.5” in order to prevent the occurrence of skew after registration activation. (S507).

If the document skew amount is medium (S508: NO), the amount of current supplied to the paper feed motor 208 is set to “0.25”, and the amount of current supplied to the registration motor 213 is set to “0.75” ( S509).
[6] Modifications Although the present invention has been described based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .

(1) In the above embodiment, the case where the skew amount is detected by the skew amount sensor 212 has been described. However, it goes without saying that the present invention is not limited to this, and the following may be used instead. good.
For example, the image forming apparatus 1 receives an operation input from the user by paying attention to the fact that the skew of an original document occurs more frequently on special paper, large-size paper, thick paper, and the like, but hardly occurs on A4 plain paper. It is also possible to provide a panel, accept the paper type (hardness), size, and paper thickness of the document to be read from the operation panel, and determine the paper feed assist control time from the skew amount estimated from these. Further, the paper type (hardness), size, and paper thickness of the document may be detected using an appropriate sensor, and the paper feed assist control time may be determined from the detection result.

As described above, when the paper type is determined before the document is fed, the amount of current supplied to the paper feed motor 208 during the document conveyance time may be determined according to the paper type. That is, if the original is thick paper, the amount of current may be increased, and if it is plain paper, it may be reduced.
(2) In the above-described embodiment, the case where the sheet feeding assist control is performed by the control unit 112 provided in the image forming unit 110 has been described. However, the present invention is not limited to this, and instead of this. Needless to say, the same effect can be obtained by performing the paper feed assist control by the control unit provided in the document reading unit 100 or the control unit provided in the transport unit 200.

  (3) In the above embodiment, the case where the current amount distribution ratio is switched to three stages according to the skew amount has been described, but it is needless to say that the present invention is not limited to this. May be switched to four or more levels. Further, it may be increased or decreased continuously according to the skew amount. In either case, the effects of the present invention can be obtained.

  (4) It goes without saying that the distribution ratio of the current amount shown in the above embodiment is merely an example, and other ratios may be adopted. However, it is desirable to increase the ratio of the amount of current supplied to the paper feed motor 208 as the torque required for document conveyance increases. The effect of the present invention is the same even if another reference value is adopted for the document conveyance time for determining whether the document is plain paper or thick paper.

  The sheet conveying apparatus, the document reading apparatus, and the image forming apparatus according to the present invention are useful as a technique for reducing the cost and power consumption of so-called skew correction.

1 …………………… Image forming apparatus 100 …………………… Document reading unit 200 ……………… Automatic document transport unit 201 ………………… Document feed tray 202… ……………… Positioning unit 203 ……………… Document restriction plate 204 ……………… Push-up plate 205 ……………… Feed roller 206 ……………… Separation roller 207 ……………… Feeding intermediate roller 208 ……………… Feeding motor 209 ……………… Feeding clutch 210 ……………… Registration roller 211 ………… ... Loop housing part 213 ................ Registration motor 212 ........... Skew sensor 212a to 212c ... Sub sensor

Claims (7)

A sheet conveying device that corrects skew by striking and bending a sheet against a stopped registration roller,
A registration motor that rotationally drives the registration roller;
A paper feed roller that strikes the sheet against the registration roller;
A paper feed motor that rotationally drives the paper feed roller;
A total current amount determining means for determining a total current amount for sheet conveyance;
A skew amount detecting means for detecting a skew amount when the sheet is abutted against the registration roller;
A sheet feeding assist control means for rotating the sheet feeding roller in synchronization with the rotation of the registration roller so that the bending of the sheet is maintained in the sheet conveyance path from the sheet feeding roller to the registration roller,
The paper feed assist control means is configured such that the sum of the resist motor drive current and the paper feed motor drive current coincides with the total current amount, and the smaller the detected skew amount, the more the feed motor drive current ratio is. A sheet conveying apparatus that determines a driving current of a registration motor and a driving current of a sheet feeding motor so as to reduce the number. A timing means for measuring the conveyance time required for the sheet feeding roller to abut the sheet on the stopped registration roller is provided.
The sheet conveying apparatus according to claim 1, wherein the total current amount determining unit determines the total current amount from the measured conveying time. Prior to conveying the sheet by the registration roller, the image forming apparatus includes an acquisition unit that acquires at least one of the thickness and hardness of the sheet,
The sheet conveying apparatus according to claim 1, wherein the total current amount determining unit determines the total current amount from at least one of the acquired thickness and hardness of the sheet. Provided on the upstream side of the registration roller in the sheet conveying direction, and includes a plurality of sheet leading edge detection sensors arranged along the rotation axis of the registration roller,
The sheet conveying apparatus according to claim 1, wherein the skew amount detecting unit detects a skew amount from a time difference in which a plurality of sheet leading edge detection sensors detect the leading edge of the sheet. Prior to conveying the sheet by the registration roller, the image forming apparatus includes an acquisition unit that acquires at least one of the size, thickness, and hardness of the sheet,
The sheet conveying apparatus according to claim 1, wherein the skew amount detecting unit determines the skew amount from at least one of the acquired size, thickness, and hardness of the sheet. An original reading apparatus comprising the sheet conveying apparatus according to claim 1. An image forming apparatus comprising the sheet conveying device according to claim 1.

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