EP0859289A2

EP0859289A2 - A sheet stacker for preventing missing pages and a printer using the sheet stacker

Info

Publication number: EP0859289A2
Application number: EP97307961A
Authority: EP
Inventors: Nobuo Fujita; Shoki Iwawaki
Original assignee: Fujitsu Ltd
Current assignee: Fujitsu Ltd
Priority date: 1997-02-14
Filing date: 1997-10-07
Publication date: 1998-08-19
Also published as: EP0859289A3; JPH10226448A

Abstract

A sheet stacker prevents a sheet remaining in a reversing path from falling inside the sheet stacker when an initializing operation is performed. The sheet stacker is used with a printer (11) ejecting a sheet having a printed surface. A sheet reversing mechanism (51) reverses the sheet by switching the sheet ejected from the printer (11) from a first side to a second side. The sheet is stacked on a table (52) with the printed surface facing downwardly. In the sheet reversing mechanism, a receiving path (62) receives the sheet ejected from the printer (11). A reversing path (63) is connected to the receiving path (62), and an ejecting path (64) guides the sheet ejected from the reversing path (63) to the table (52). The sheet stacker is further provided with a sheet purge table (54) and a sheet purge path (53) provided between a lower end of the reversing path (63) and the sheet purge table (54). A sheet remaining inside the sheet reversing mechanism is ejected onto the sheet purge table (54) through the sheet purge path (53) by an initializing operation performed after recovery from an abnormality of the printer (11).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a sheet stacker and, more particularly, to a large capacity sheet stacker used by being connected to a large scale printer.

The sheet stacker is for stacking a large number of printed sheets on a table. Since the large number of sheets are bound, if it is desired, a missing page cannot be allowed. Accordingly, it is required for the sheet stacker to take measures to prevent an occurrence of a missing page.

When the sheet stacker has a mechanism for reversing sheets, there is a higher possibility of occurrence of a missing page than a sheet stacker which dose not have a sheet reversing mechanism. Thus, it is particularly required for the sheet stacker to take measures to prevent an occurrence of a missing page.

2. Description of Related Art

FIG.1 shows a conventional large capacity sheet stacker 10. The sheet stacker 10 is operated by being mechanically and electrically connected to a large scale printer 11 as shown in FIG.2.

The printer 11 includes a sheet path 12. The end of the sheet path 12 is a sheet eject opening 13. A sheet 14 is fed from a sheet cassette 15, and a front surface of the sheet 14 is printed while the sheet 14 passes a photosensitive drum 17 on which a photostatic latent image is provided by an optical unit 16 and a fixing device 18. The sheet 14 being printed on the front surface is ejected from the sheet eject opening 13 by sheet feed rollers 19, and enters the sheet stacker 10.

As shown in FIG.1, the sheet stacker 10 comprises a main body 30, a sheet reversing mechanism 31 inside the main body 30 and a sheet table 32 extending from the main body 30.

A sheet is switched back by the sheet reversing mechanism 31 in the sheet stacker 10 so that the printed surface is directed downwardly (face down), and the sheet is stacked on the sheet table 32.

The lower end of a reversing path 33 which constitutes a part of the sheet reversing mechanism 31 is an opening 34 which responds to various sheet sizes.

The sheet stacker 10 stops its operation when an abnormality such as a paper jam occurs in the printer 11, and starts an initializing operation when a recovery of the abnormality is completed and a return command is provided. The initializing operation is performed so as to confirm whether or not a sheet is present in the sheet stacker 10. The initializing operation includes an operation to draw a sheet into the reversing path 33, and an operation to feed a sheet out of the reverse path 33.

If a time when a paper jam occurs in the printer 11 coincide with a time when a sheet just enters the reversing path 33, the following problem may occur.

That is, when the sheet stacker 10 performs the initializing operation after recovery from an abnormality is completed and the return command is provided, the sheet left in the reversing path 33 is fed further along the reversing path 33, and falls inside the sheet stacker 10 by passing through the opening 34 as indicated by reference numeral 35.

It is possible that an operator does not realize that this has occurred, that is, the operator may not realize that there is a page missing which was printed immediately before the occurrence of the paper jam, and the operator will bind the sheets stacked on the sheet table 32 without including the missing page.

SUMMARY OF THE INVENTION

It is an general object of the present invention to provide an improved and useful sheet stacker in which the above-mentioned problem is eliminate.

A more specific object of the present invention is to provide a sheet stacker which prevents a sheet remaining in a reversing path from falling inside the sheet stacker when an initializing operation is performed.

It is another object of the present invention to provide a sheet stacker which ejects a sheet remaining in a reverse path to a table outside the sheet stacker when an initializing operation is performed.

It is a further object of the present invention to provide a sheet stacker which detects a sheet that has fallen inside the sheet stacker when an initializing operation is performed.

It is another object of the present invention to provide a sheet stacker which returns a sheet remaining in a reverse path to an inlet opening of the sheet stacker.

In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a sheet stacker for use with a printer adapted to eject a sheet having a printed surface, the sheet stacker comprising:

a sheet reversing mechanism which reverses the sheet by switching the sheet ejected from the printer from a first side to a second side; and

a table on which the sheet reversed by the sheet reversing mechanism is stacked with the printed surface facing downwardly,
wherein the sheet reversing mechanism includes a receiving path for receiving the sheet ejected from the printer, a reversing path connected to the receiving path, and an ejecting path for guiding the sheet ejected from the reversing path to the table,
the sheet stacker further comprising:

a sheet purge table; and

a sheet purge path provided between a lower end of the reversing path and the sheet purge table,
wherein a sheet remaining inside the sheet reversing mechanism is ejected onto the sheet purge table through the sheet purge path by an initializing operation performed after recovery from an abnormality of the printer.

According to the above invention, the sheet stacker comprises the sheet purge table and the sheet purge path provided between the lower end of the reversing path and the sheet purge path, and the sheet remaining in the sheet reversing mechanism is ejected on the sheet purge table by passing through the sheet purge path. Thus, the sheet ejected from the sheet reversing mechanism is placed on the sheet table when the initializing operation is performed, that is the sheet is placed on the sheet purge table after the initializing operation has been completed. Thus, the operator will realize the sheet placed on the sheet purge table before binding the sheets stacked on the table. Accordingly, the operator will pick up the sheet on the sheet purge table, and insert the sheet in the right place in the stacked sheets before binding the sheets. Thus, binding of the sheets without realizing that a sheet is missing is effectively prevented.

Additionally, there is provided according to the present invention a sheet stacker for use with a printer adapted to eject a sheet having a printed surface, the sheet stacker comprising:

a sheet reversing mechanism which reverses the sheet by switching back the sheet ejected from the printer from a first side to a second side; and

a stopper member mounted to a portion of the reversing path corresponding to a size of the sheet,
wherein a sheet remaining inside the sheet reversing mechanism is ejected onto the table after being engaged with the stopper member by an initializing operation performed after recovery from an abnormality of the printer.

According to the above invention, the stopper member is mounted on a portion of the reversing path. A sheet remaining in the sheet reversing mechanism is ejected onto the table after being engaged with the stopper member by the initializing operation performed after recovery from an abnormality. Thus, when the sheets stacked on the table are bound, no pages are missing.

Further, there is provided according to another aspect of the present invention a sheet stacker for use with a printer adapted to eject a sheet having a printed surface, the sheet stacker comprising:

a movable stopper member provided in the middle of the reversing path; and

urging means for moving the stopper member after the stopper member has been moved downwardly, to an original position,
wherein a sheet remaining inside the sheet reversing mechanism is ejected onto the table after an end of the sheet contacts the stopper member and the stopper member is moved downwardly against a force of the urging means by an initializing operation performed after recovery from abnormality of the printer.

According to the above invention, the stopper member is movably provided in the downward direction at a portion in the middle of the reversing path. Additionally, an urging means for upwardly moving the stopper member to the original position is provided. A force generated by the urging means is set to be smaller than the force exerted by the end of the sheet being fed. Thus, the end of the sheet in the sheet reversing mechanism presses down the stopper member against the force generated by the urging means, and thereafter the sheet is ejected onto the table. Thus, a missing page can be prevented when the sheets stacked on the table are bound. Additionally, since the stopper member is movable downwardly, the sheet stacker can handle all size sheets. Accordingly, adjustment is not needed when the sheet size is changed, which is very convenient for use.

Additionally, there is provided according to the another aspect of the present invention a sheet stacker for use with a printer adapted to eject a sheet having a printed surface, the sheet stacker comprising:

a sheet receiver provided at a lower end of the reversing path; and

a sheet sensor, provided near the lower end of the reversing path, for detecting the sheet received by the sheet receiver,
wherein a sheet remaining in the reversing path is deposited on the sheet receiver and the sheet is detected by the sheet sensor by an initializing operation performed after recovery from an abnormality of the printer.

According to the above invention, the sheet receiver is provided at the lower end of the reversing path, and the sheet sensor is provided near the lower end of the reversing path so as to detect the sheet received by the sheet receiver. The sheet located in the sheet reversing mechanism is detected by the sheet sensor since the sheet falls on the sheet receiver by the initial operation performed after recovery from an abnormality. Accordingly, the operator can realize that the sheet that fell on the sheet receiver before binding the sheets stacked on the table. Thus, the operator will insert the sheet on the sheet receiver into the correct position, and then bind the sheets. Thus, binding without realizing that a page is missing can be effectively prevented.

Additionally, there is provided according to another aspect of the present invention a sheet stacker for use with a printer adapted to eject a sheet having a printed surface, the sheet stacker comprising:

means for controlling the sheet reversing mechanism to return the sheet remaining in the reversing path toward the receiving path at the beginning of an initializing operation performed after recovery of an abnormality of the printer.

According to the above invention, since the means for rendering the sheet reversing mechanism to return the sheet remaining in the reversing path toward the sheet at the beginning of the initializing operation performed after recovery from an abnormality of the printer, the sheet can be positively prevented from falling in the interior of the sheet stacker. Thus, a missing page when binding the sheets can be prevented.

Further, according to another aspect of the present invention, a printer can be provided having a sheet stacker device similar to one of the sheet stackers according to the present invention.

Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 is an illustration of a conventional sheet stacker;

FIG.2 is an illustration of the sheet stacker shown in FIG.1 in use;

FIG.3 is an illustration of a sheet stacker according to a first embodiment of the present invention;

FIG.4 is an illustration of a sheet stacker shown in FIG.3 in use;

FIG.5 is an illustration of a drive system of sheet feed rollers shown in FIG.3;

FIG.6 is a chart for explaining a regular operation of the sheet stacker;

FIG.7 is a flowchart of an operation of a microcomputer during a regular operation of the sheet stacker;

FIG.8 is a chart for explaining an initializing operation of the sheet stacker;

FIG.9 is a flowchart of an operation of the microcomputer when the sheet stacker performs the initializing operation;

FIG.10 is an illustration for shown in an initializing operation when s sheet is in a reversing path;

FIG.11 is an illustration of a sheet stacker according the a second embodiment of the present invention;

FIG.12 is a perspective view of a reversing path shown in FIG. 11;

FIG.13 is an illustration of an initializing operation performed in a state in which a sheet is in the reversing path;

FIG.14 is an illustration of a variation of the sheet stacker according to the second embodiment of the present invention;

FIG.15 is an illustration of a sheet stacker according to a third embodiment of the present invention;

FIG.16 is a perspective view of a reversing path shown in FIG. 15;

FIG.17 is an illustration of an initializing operation performed in a state in which a sheet is in the reversing path;

FIG.18 is an illustration of a sheet stacker according to a fourth embodiment of the present invention;

FIG.19 is an illustration of a sheet stacker according to a fifth embodiment of the present invention;

FIG.20 is an illustration of the a drive system of sheet feed rollers shown in FIG.19;

FIG.21 is a chart for explaining an initializing operation of the sheet stacker;

FIG.22 is a flowchart of an operation of a microcomputer when the sheet stacker performs the initializing operation; and

FIG.23 is an illustration of a printer according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIRST EMBODIMENT

FIG.3 shows a sheet stacker 40 according to a first embodiment of the present invention. The sheet stacker 40 is mechanically and electrically connected to a large scale printer 11 as shown in FIG.4. A sheet receiving opening 60 of the sheet stacker 40 faces a sheet eject opening 13 of the printer 11.

The printer 11 includes a sheet path 12. The end of the sheet path 12 is a sheet eject opening 13. A sheet 14 is fed from a sheet cassette 15, and a front surface of the sheet 14 is printed while the sheet 14 passes a photosensitive drum 17 on which a photostatic latent image is provided by an optical unit 16 and a fixing device 18. The sheet 14, having being printed on the front surface, is ejected from the sheet eject opening 13 by sheet feed rollers 19, and the sheet 14 enters the sheet stacker 10.

The sheet stacker 40 comprises a main body 50, a sheet reversing mechanism 51 inside the main body 50, a sheet table 52 extending from the main body 50, a sheet purge path 53, and a purge table 54.

The sheet purge path 53 is connected to the lower end of a reversing path 63, and extends in an oblique and downward direction. The lower end of the sheet purge path 53 is a sheet eject opening 55 which is located in a portion of the main body under the sheet table 52. The purge table 54 is provided directly under the sheet eject opening 55.

A description will now be given, with reference to FIG.5, of the sheet reversing mechanism 51.

The sheet reversing mechanism 51 switches the back and front of a sheet so as to turn the sheet with the printed surface facing downwardly. The sheet reversing mechanism 51 comprises a sheet receiving opening 60; a sheet eject opening 61; a receiving path 62 which extends from the sheet receiving opening 60 so as to receive a sheet ejected from the printer; a reversing path which extends from the receiving path 62 and extends in a vertically downward direction; an eject path 64 between a top portion of the reversing path 63 and the sheet eject opening 61; a sheet feed roller 65 provided in the receiving path 62; a sheet feed roller 66 provided in the reversing path 63; a first motor 68; a second motor 69; a guide member 70 in the receiving path 62; a first sheet passage sensor 72 provided in the receiving path 62 to detect passage of a sheet; and a second sheet sensor 73 provided in the eject path 64 to detect passage of a sheet.

The first motor 68 rotates the sheet feed roller 65 via a gear 74. The second motor 69 rotates the

sheet feed rollers

66 and 67 via a belt 75 engaged with the

sheet feed rollers

66 and 67 and a pulley of the second motor 69. Each of the

sheet feed rollers

65, 66 and 67 is pressed by a roller so as to make a pair of rollers with the corresponding

rollers

65, 66 and 67.

The sheet stacker 40 includes, in association with the sheet reversing mechanism 51, a microcomputer 80, a first motor drive circuit 81, a second motor drive circuit 82 and a plunger drive circuit 83.

Information from the printer 11 and

sheet passage sensors

72 and 73 is provided to the microcomputer 80 so that the microcomputer 80 outputs control signals to the plunger drive circuit 83 and the first and second

motor drive circuits

81 and 82. A plunger 71 is driven by the plunger drive circuit 83. The first motor 68 is driven by the first motor drive circuit 81, and second motor 69 is driven by the second motor drive circuit 82. The sheet stacker 40 operates in synchronization with an operation of the printer 11.

The sheet stacker 40 normally operates as shown in FIG.6.

When the printed sheet 14 is ejected from the printer 11, the first motor is rotated in a normal direction as shown in FIG.6-(B) and the second motor is also rotated in the normal direction as shown in FIG.6-(B). Thus, the

sheet feed rollers

65, 66 and 67 are rotated as shown in FIG.6-(E). The sheet 14, which was ejected from the printer 11 and entered the sheet stacker 40 through the sheet receiving opening 60, is fed to the receiving path 62 by the sheet feed roller 65. The sheet 14 is then fed to the reversing path 63 by the sheet feed roller 66.

When the rear end of the sheet 14 with respect to a feeding direction passes the first sheet passage sensor 72, the first sheet passage sensor 72 outputs a signal as shown in FIG.6-(C). The first and

second motors

68 and 69 continue to rotate from a time t1 when the signal is output until a predetermined time period T1 has passed so that the entire sheet 14 enters the reversing path 63. In this state, the sheet 14 is straightened due to its elasticity, and the rear end of the sheet 14 is directed to the eject opening 64.

Thereafter, the first motor 68 is stopped, and the second motor 69 is rotated in the reverse direction. Thereby, the

sheet feed rollers

66 and 67 are rotated as shown in FIG.6-(F). The sheet 14 in the reverse path 63 is fed upwardly by the sheet feed roller 66, and moves out of the reversing path 63 and enters the eject path 64. That is, the sheet 14 is switched back so that the printed surface is directed downwardly, and the sheet 14 is fed so as to be ejected from the sheet eject opening 61 by the sheet feed roller 67.

When the rear end of the sheet 14 passes the second sheet passage sensor 73, the second sheet passage sensor 73 outputs a signal as shown in FIG.6-(D). The second motor 69 continues to rotate from a time t2 when the signal is output until a predetermined time period T2 has passed. Thereby the entire sheet 14 is ejected from the sheet eject opening 61, and the sheet 14 is ejected and stacked on the sheet table 52 with the printed surface down.

The micro computer 80 operates as shown in a flowchart of FIG.7.

The microcomputer 80 first rotates the first motor 68 and the second motor 68 in the normal direction (step ST1). Then the microcomputer 80 stops the first motor 68 and the second motor 69 after the predetermined time period T1 has passed after the first sheet passage sensor 72 detects the passage of the sheet 14 (steps ST2, ST3 and ST4). When the passage of the sheet 14 is not detected by the first sheet passage sensor 72, an alarm is displayed (step ST9).

Thereafter, the second motor 69 is reversed (step ST5). The second motor 69 is stopped after the predetermined time period T2 has passed since the second sheet passage sensor 73 detects the passage of the sheet (steps ST6, ST7 and ST8). When the passage of the sheet is not detected by the second sheet passage sensor 73, an alarm is displayed (ST9).

A description will now be given of an operation of the sheet stacker 40 when an abnormality such as a paper jam occurs in the printer 11 while a printing operation is performed, and recovery form the abnormality.

When an abnormality such as a paper jam occurs in the printer 11 while a printing operation is performed, an alarm is displayed and the operations of the printer 11 and the sheet stacker 40 are immediately stopped. Thus, the sheets being processed remain in the printer 11 and the sheet stacker 40.

After the operator has completed recovery from the abnormality, a return command is output from the printer 11 and the sheet stacker 40 performs an initializing operation. The initializing operation is performed so as to check if a sheet is remaining in the sheet stacker 40. The initialising operation is performed in two steps.

(First Step) When the return command is output from the printer 11, the first motor 68 is rotated in the normal direction for a time period T3 as shown in FIG.8-(A). Simultaneously, the second motor 69 is rotated in the normal direction for the time period T3. Thus, the

sheet feed rollers

65, 66 and 67 are rotated as shown in FIG.8-(C). Accordingly, if there is a sheet remaining in the sheet stacker 40, the sheet is fed in a direction toward the inside of the reversing path 63.

(Second Step) Thereafter, the second motor 69 is reversed, as shown in FIG.8-(B), for a time period T4 so as to rotate the

sheet feed rollers

66 and 67 as shown in FIG.8-(D). Accordingly, if there is a sheet remaining in the reversing path 63, the sheet is fed in a direction toward the sheet eject opening 61.

The microcomputer 80 is operated as shown by a flowchart of FIG.9.

First, the first motor 68 and the second motor 69 are rotated in the normal direction (step ST10). Then, the first motor 68 and the second motor 69 are stopped after the predetermined time period T3 has passed (steps ST11 and ST12). Thereafter, the second motor 69 is stopped (step ST13). The second motor is stopped after the predetermined time period T4 has passed.

A description will now be given of a situation in which a paper jam occurs in the printer 11 while the sheet 14 is located in the reversing path 63 of the sheet stacker 40.

FIG.10-(A) shows the sheet stacker 40 in a state in which operations of the printer 11 and the sheet stacker 40 are stopped due to a paper jam in the printer 11. The sheet 14 has just entered the reversing path 63 of the sheet stacker 40.

After the operator has completed the recovery from the paper jam, the return command is output from the printer 11 and the sheet stacker 40 performs the above-mentioned initializing operation. By the initializing operation in the above-mentioned first step, the sheet 14 in the reversing path 63 is fed downwardly by the sheet feed roller 66 rotating clockwise. The above-mentioned time period T3 is set to a time period sufficient for drawing the sheet 14, which has slightly entered the receiving path 62, into the reversing path 63.

Accordingly, when a portion of the sheet 14 enters the reversing path 63, the rear end (the upper end in FIG.10-(A)) of the sheet 14 with respect to the feeding direction passes the position of the sheet feed roller 66. The sheet 14 passes through the sheet purge path 53 and is ejected onto the purge table 54 outside the main body 50 via the sheet eject opening 55. The initializing operation in the second step is performed irrespective of the sheet 14 being ejected onto the purge table 54. When the initializing operation is completed, the sheet 14 is still placed on the purge table 54. If the sheet 14 is placed on the purge table 54, the operator can easily realize the occurrence of a missing page.

Sheets which are printed in the resumed operation are stacked on the sheets which were already stacked on the sheet table 52 by the sheet stacker 40. The operator will realize the sheet 14 is on the purge table 54, and will pickup the sheet 14 from the purge table 54 and insert it in the correct position in the stacked sheets. Then, the operator can bind the sheets. Thus, a problem that sheets are bound without realizing a page is missing can be effectively prevented.

SECOND EMBODIMENT

FIG.11 shows a sheet stacker 40A according to a second embodiment of the present invention. The sheet stacker 40A includes a stopper member 90 instead of the purge sheet path 53 and the purge table 54 of the sheet stacker 40 according to the above-mentioned sheet stacker 40. In FIGS.11 and 12, parts that are the same as the parts shown in FIG.3 are given the same reference numerals, and descriptions thereof will be omitted. It is assumed that the printer 11 performs printing on A4 size print medium.

As shown in FIG.12, a portion of the reversing path below the sheet feed roller 66 has a construction in which a wall 91 forming a side of the reversing path 63 is rotated with respect to a hinge 92 so that the reversing path 63 can be opened, if necessary. Provided on the wall 91 are stopper

member mounting portions

93 and 94.

The stopper member 90 is secured to the upper stopper member mounting portion 93 by a screw 95 in response to the A4 size which is the size of the sheet in the printer 11. The stopper member 90 traverses the reversing path 63 as shown in FIG.11

A distance L1 between the stopper member 90 and the sheet feed roller 66 is slightly less than a longitudinal dimension C1 of the A4 size sheet provided in a cassette of the printer 11.

A description will now be given of a situation in which a paper jam occurs in the printer 11 while the A4 size sheet 14 is located in the reversing path 63 of the sheet stacker 40A.

FIG.13-(A) shows a state in which a paper jam occurs in the printer 11 and the operations of the printer 11 and the sheet stacker 40A are stopped. The A4 size sheet 14 is located in the reversing path 63 of the sheet stacker 40A.

After the operator recovers from the paper jam, the return command is output from the printer 11, and the sheet stacker 40A performs the above-mentioned initializing operation. The sheet 14 in the reversing path 63 is fed downwardly by the sheet feed roller 66 rotating clockwise, and the rear end (the upper end in FIG.10(A)) of the sheet 14 with respect the feeding direction passes the position of the sheet feed roller 66. Immediately before the rear end 14a of the sheet 14 passes the position of the sheet feed roller 66, the end 14b on the leading side of the sheet 14 with respect to the feeding direction contacts the stopper member 90. The sheet 14 is moved further downwardly while the downward movement of the end 14b is restricted by the stopper member 90 contacting the end 14 of the sheet 14. Thus, the sheet 14 is trapped between the stopper member 90 and the sheet feed roller 66 in a slightly bent state as shown in FIG.13-(B).

The end 14a of the sheet 14 is urged upwardly due to the high bending strength of the sheet 14, that is, the elasticity of the sheet 14 itself, and is pressed against a portion between the sheet feed roller 66 and the roller contacting the sheet feed roller 66.

Thereafter, the initializing operation in the above-mentioned second step is performed, and the sheet feed roller 66 is rotated clockwise. Since the end 14a abuts against the sheet feed roller 66 due to the elasticity of the sheet 14, the sheet 14 is fed upwardly when the sheet feed roller 66 rotates clockwise. FIG.11-(C) shows this state.

Then, the sheet 14 enters the eject path 64, and is fed by the sheet feed roller 67. The second sheet passage sensor 73 detects the passage of the sheet 14, and the sheet 14 is ejected from the sheet stacker 40A so that the sheet 14 is placed on the sheets stacked on the sheet table 52 with the printed surface facing downwardly.

Accordingly, there is no missing page occurrence in relation to recovery from a paper jam in the printer 11.

It should be noted that when the printer 11 uses A3 size sheets, the stopper member 90 is removed from the stopper member mounting portion 93 and is mounted to the lower stopper member mounting portion 94. The sheet stacker 40A is then in a state shown in FIG.14.

A distance L2 between the stopper member 90 and the sheet feed roller 66 is slightly less than a longitudinal dimension C2 of the A3 size sheet provided in a cassette of the printer 11. Thus, similar to the case of the A4 size sheet, the A3 size sheet is stopped by the stopper member 90, and does not fall inside the sheet stacker 40A and is ejected on the sheet table 52 from the sheet stacker 40A.

THIRD EMBODIMENT

FIG.15 shows a sheet stacker 40B according to a third embodiment of the present invention. The sheet stacker 40B is generally a variation of the sheet stacker 40A according to the above-mentioned second embodiment. In FIGS.15 and 16, parts that are the same as the parts shown in FIGS.9 and 10 are given the same reference numerals, and descriptions thereof will be omitted.

As shown in FIGS, 15 and 16, an elongated opening 100 is formed in a wall 91A, and guide members 101 and 102 are fixed on each side of the elongated opening 100. A stopper 103 is provided so that a stopper tab 103a protrudes into the elongated opening 100 and a side rod 103b fits into the guide members 101 and 102. A tension coil spring 105 which acts as a biasing means is bridged between the stopper member 103 and a lug 104 on the wall 91A. The characteristic of the tension coil spring 105 is set so that a spring force is far smaller than the bending strength of the sheet, and is far smaller than a feeding force of the sheet feed roller 66. This is to provide a normal operation of the sheet stacker 40B without problems. Due to the coil spring, the stopper member 103 is located at the highest position with respect to the guide rails.

A distance L4 between the stopper tab 103a and the sheet feed roller 66 is slightly shorter than the longitudinal dimension of the minimum size sheet used by the printer 11.

A description will now be given of a situation in which a paper jam occurs in the printer 11 while the A4 size sheet is located in the reversing path of the sheet stacker 40B.

FIG.17-(A) shows a state in which a paper jam occurs in the printer 11, and the operations of the printer 11 and the sheet stacker 40B are stopped. The A4 size sheet 14 is located in the reversing path 63 of the sheet stacker 40B. After the operator has completed recovery from the paper jam, the return command is output from the printer 11, and the sheet stacker 40A performs the initializing operation.

Accordingly, the sheet 14 in the reversing path 63 is fed downwardly by the sheet feed roller 66 rotating clockwise by the initializing operation in the above-mentioned first step. Thus, the end 14b of the sheet 14 abuts the stopper tab 103a, and presses the stopper member 103. The sheet 14 is further moved downwardly by moving the stopper member 103 by extending the tension coil spring 105, and the end 14a passes the position of the sheet feed roller 66.

The sheet 14 is set in a state in which the end 14a of the sheet 14 is pressed against a position between the sheet feed roller 60 and the roller contacting the sheet roller 60.

Thereafter, the initializing operation of the above-mentioned second step is performed, and the sheet feed roller 66 is rotated counterclockwise. Since the end 14a of the sheet 14 abuts against the sheet feed roller 66, the sheet 14 is fed upwardly when the sheet feed roller 66 rotates counterclockwise. FIG.17-(C) shows this state.

The sheet 14 enters the eject path 64, and is fed by the sheet feed roller 66. The second sheet passage sensor 73 detects passage of the sheet 14, and the sheet 14 is ejected from the sheet stacker 40B so that the sheet 14 is placed on the sheets stacked on the sheet table 52 with the printed surface facing downwardly.

Accordingly, there is no occurrence of a missing page in relation to recovery form a paper jam in the printer 11.

It should be noted that the stopper 103 is moved to a position lower than that shown in FIG.17-(B). Additionally, the present embodiment can be applied without change even when the size of the sheet 14 is changed. That is, no change with respect to the stopper is required when a sheet size is changed, and thus it is convenient for use.

FOURTH EMBODIMENT

FIG.18 shows a sheet stacker 40C according to a fourth embodiment of the present invention. The sheet stacker 40C has a construction in which the sheet purge path 53 and the purge table 54 are removed from the sheet stacker 40 according to the first embodiment shown in FIG.3 and, instead, the reversing path 63 is extended downwardly, a sheet receiver 120 being provided at the lower end of the reversing path 63, and an actuator type sheet sensor 121 is provided near the lower end of the reversing path 63.

The sheet sensor 121 and the sheet receiver 120 are provided below a level H0 of the sheet feed roller 66 as a reference level. A level H1 is a level distant from the level H0 by the length of a sheet having a maximum length Cmax. The sheet sensor 121 is located at a level H2. The level H2 is lower than the level H1. Accordingly, as long as the sheet is caught by the sheet feed roller 66, the sheet sensor 121 does not detect the sheet even if the sheet has the maximum length.

The sheet receiver 120 is located at the level H3. The level H3 is lower than the level H2. A distance L10 between the level H2 and the level H3 is less than the above-mentioned length Cmax. Accordingly, when the sheet moves off the sheet feed roller 66 and falls on the sheet receiver 120, the sheet sensor 121 positively detects the sheet even when if the sheet has a minimum length. Thus, the operator can recognize that the sheet moved from the sheet feed roller 66 and fell onto the sheet receiver by monitoring an output of the sheet sensor 121. Accordingly, the operator can realize that the occurrence of a missing page prior to binding the sheets stacked on the sheet table 52. This prevents the operator from binding the sheets without realizing that a page is missing.

FIFTH EMBODIMENT

FIG.19 shows a sheet stacker 40D according to a fifth embodiment of the present invention. In FIGS.19 and 20, parts that are the same as the parts shown in FIGS.3 and 5 are given the same reference numerals, and descriptions thereof will be omitted.

The sheet stacker 40D comprises, as shown in FIG.19 and also in FIG.20, the main body 50, the sheet reverse mechanism 51 in the main body 50 and the sheet table 52 extending from the main body 50.

A description will now be given of an operation performed when an abnormality such as a paper jam occurs and recovery from the abnormality.

When an abnormality such as a paper jam occurs while a printing operation is being performed, an alarm is displayed and the operations of the printer 11 and the sheet stacker 40D are stopped. After the operator has completed recovery from the abnormality, the return command is output from the printer 11 and the sheet stacker 40D performs an initializing operation. The initializing operation is performed so as to check if there is a sheet remaining in the sheet stacker 40D. The initializing operation includes the following three steps.

(First Step) When the return command is output from the printer 11, the first motor 68 is rotated in the reverse direction for a time period T10 as shown in FIG.21-(A). Simultaneously, the second motor 69 is also rotated in the reverse direction for the time period T10 as shown in FIG.21-(B). Additionally, the

sheet feed rollers

65, 66 and 67 are rotated as shown in FIG.21-(C). If there is a sheet in the sheet stacker 40D, the sheet is fed in the direction toward the sheet receiving opening 60. Thus, the sheet never falls inside the sheet stacker 40D. Additionally, if the first sheet passage sensor 72 or the second sheet passage sensor 73 detects the sheet 14, an alarm is displayed. When the alarm display is performed, the operator removes the sheet 14 from inside the sheet stacker 40D. Thus, the sheet does not remain within the sheet stacker 40D, and occurrence of a missing page is prevented.

(Second Step) Thereafter, the first motor 68 is rotated in the normal direction for a time period T11 as shown in FIG.21-(A). Simultaneously, the second motor 69 is rotated in the normal direction for the time period T11 as shown in FIG.21-(B). Additionally, the

sheet feed rollers

65, 66 and 67 are rotated as shown in FIG.21-(D). If a sheet remains in the sheet stacker 40D, the sheet is fed in the direction toward the inside of the reversing path 63.

(Third Step) The second motor 69 is rotated in the reverse direction for a time period T12 as shown in FIG.21-(B), and the

sheet feed rollers

66 and 67 are rotated as shown in FIG.21-(E). If a sheet remains in the reversing path 63, the sheet is fed in the direction toward the sheet eject opening 61. Additionally, if the second sheet passage sensor 73 detects the sheet 14, an alarm is displayed. When the alarm is displayed, the operator will remove the sheet 14 from the sheet stacker 40D.

The microcomputer 80 operates as indicated by a flowchart shown in FIG.22.

First, the first motor 68 and the second motor 69 are rotated in the reverse direction (step ST20). Then, the first motor 68 and the second motor 69 are stopped (steps ST21 and ST 22).

It is then determined whether the first sheet passage sensor 72 or the second sheet passage sensor 73 detects the sheet 14 (step ST23). If one of the first sheet passage sensor 72 and the second sheet passage sensor 73 detects the sheet 14, an alarm is displayed (step ST31). Thereafter, the first motor 68 and the second motor 69 are rotated in the normal direction (step ST24). Then, the first motor 68 and the second motor 69 are stopped after the predetermined time period T11 has passed (step ST25 and ST26). Thereafter, the second motor 69 is rotated in the reverse direction (step ST27). After the predetermined time period T12 has passed, the second motor 69 is stopped (step ST28 and ST29).

Finally, it is determined whether or not the second sheet passage sensor 73 detects the sheet 14. If the second sheet passage sensor 73 detects the sheet 14, an alarm is displayed (step ST31).

According to the present embodiment, there is no need to change software of the microcomputer 80.

SIXTH EMBODIMENT

FIG.23 shows a printer 130 according to a sixth embodiment of the present invention. The printer 130 has a structure in which a printer unit 131 and a sheet stacker unit 40E are integrated, the sheet stacker 40E having a structure the same as the sheet stacker 40 shown in FIG.3. The sheet stacker 40E may also have a structure the same as that of the

sheet stacker

40A, 40B, 40C and 40D shown in FIGS.11, 15, 18 and 19, respectively.

The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.

Claims

A sheet stacker for use with a printer (11) adapted to eject a sheet having a printed surface, said sheet stacker comprising:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printer (11) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printer, a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table (52),
said sheet stacker characterized by:

a sheet purge table (54); and

a sheet purge path (53) provided between a lower end of said reversing path (63) and said sheet purge table (54),
wherein a sheet remaining inside said sheet reversing mechanism (51) is ejected onto said sheet purge table through said sheet purge path (53) by an initializing operation performed after recovery from an abnormality of said printer (11).
A sheet stacker for use with a printer (11) adapted to eject a sheet having a printed surface, said sheet stacker comprising:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printer (11) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printer (11), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path to said table (52),
said sheet stacker characterized by:

a stopper member (90) mounted to a portion of said reversing path (63) which corresponds to a size of the sheet,
wherein a sheet remaining inside said sheet reversing mechanism (51) is ejected onto said table (52) after being engaged with said stopper member (90) by an initializing operation performed after recovery from an abnormality of said printer (11).
A sheet stacker for use with a printer (11) adapted to eject a sheet having a printed surface, said sheet stacker comprising:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printer from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printer (11), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table (52),
said sheet stacker characterized by:

a movable stopper member (103) provided in the middle of said reversing path (63); and

urging means (105) for moving said stopper member (103) upwardly after said stopper member (103) has been moved downwardly, to an original position,
wherein a sheet remaining inside said sheet reversing mechanism (51) is ejected onto said table after an end of the sheet contacts said stopper member (103) and said stopper member (103) is moved downwardly against a force of said urging means (105) by an initialising operation performed after recovery from an abnormality of said printer (11).
A sheet stacker for use with a printer (11) adapted to eject a sheet having a printed surface, said sheet stacker comprising:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printer (11) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printer (11), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table,
said sheet stacker characterized by:

a sheet receiver (120) provided at a lower end of said reversing path (63); and

a sheet sensor (121), provided near the lower end of said reversing path (63), for detecting the sheet received by said sheet receiver (120),
wherein a sheet remaining in the reversing path (63) is deposited on said sheet receiver (120) and the sheet is detected by said sheet sensor (121) by an initializing operation performed after recovery from an abnormality of said printer (11).
A sheet stacker for use with a printer (11) adapted to eject a sheet having a printed surface, said sheet stacker comprising:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printer (11) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printer (11), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table (52),
said sheet stacker characterized by:

means for controlling said sheet reversing mechanism to return a sheet remaining in said reversing path (63) toward said receiving path (62) at the beginning of an initializing operation performed after recovery from an abnormality of said printer (11).
A printer comprising:

a printing unit (131) which ejects a sheet having a printed surface; and

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printing unit (131) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printing unit (131), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table (52),
said sheet stacker characterized by:

a sheet purge table (54); and

a sheet purge path (53) provided between a lower end of said reversing path (63) and said sheet purge table (54),
wherein a sheet remaining inside said sheet reversing mechanism (51) is ejected onto said sheet purge table through said sheet purge path (53) by an initializing operation performed after recovery from an abnormality of said printing unit (131).
A printer comprising:

a printing unit (131) which ejects a sheet having a printed surface; and

a sheet stacker including:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printing unit (131) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printing unit (131), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path to said table (52),
said sheet stacker characterized by:

a stopper member (90) mounted to a portion of said reversing path (63) which corresponds to a size of the sheet,
wherein a sheet remaining inside said sheet reversing mechanism (51) is ejected onto said table (52) after being engaged with said stopper member (90) by an initializing operation performed after recovery from an abnormality of said printing unit (11).
A printer comprising:

a printing unit (131) which ejects a sheet having a printed surface; and

a sheet stacker including:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printer from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printing unit (131), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table (52),
said sheet stacker characterized by:

a movable stopper member (103) provided in the middle of said reversing path (63); and

urging means (105) for moving said stopper member (103) upwardly after said stopper member (103) has been moved downwardly, to an original position,
wherein a sheet remaining inside said sheet reversing mechanism (51) is ejected onto said table after an end of the sheet contacts said stopper member (103) and said stopper member (103) is moved downwardly against a force of said urging means (105) by an initializing operation performed after recovery from an abnormality of said printing unit (131).
A printer comprising:

a printing unit (131) which ejects a sheet having a printed surface; and

a sheet stacker including:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printing unit (131) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printing unit (131), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table,
said sheet stacker characterized by:

a sheet receiver (120) provided at a lower end of said reversing path (63); and

a sheet sensor (121), provided near the lower end of said reversing path (63), for detecting the sheet received by said sheet receiver (120),
wherein a sheet remaining in the reversing path (63) is deposited on said sheet receiver (120) and the sheet is detected by said sheet sensor (121) by an initializing operation performed after recovery from an abnormality of said printing unit (131).
A printer comprising:

a printing unit (131) which ejects a sheet having a printed surface; and

a sheet stacker including:

a sheet reversing mechanism (51) which reverses the sheet by switching the sheet ejected from said printing unit (131) from a first side to a second side; and

a table (52) on which the sheet reversed by said sheet reversing mechanism (51) is stacked with the printed surface facing downwardly,
wherein said sheet reversing mechanism (51) includes a receiving path (62) for receiving the sheet ejected from said printing unit (131), a reversing path (63) connected to said receiving path (62), and an ejecting path (64) for guiding the sheet ejected from said reversing path (63) to said table (52),
said sheet stacker characterized by:

means for controlling said sheet reversing mechanism to return a sheet remaining in said reversing path (63) toward said receiving path (62) at the beginning of an initializing operation performed after recovery from an abnormality of said printing unit (131).