Finisher for an image forming apparatus

A finisher for finishing papers sequentially driven out of an image forming apparatus includes a plurality of trays selectively movable to a single paper outlet. The finisher reduces a period of time necessary for designated one of the trays to reach the paper outlet, increases the number of papers which can be stacked on the trays, and determines the number of papers stacked with a simple configuration. Papers are prevented from returning from the tray to the paper outlet without complicating the configuration of the outlet. An outlet roller protrudes from the paper outlet, but does not interfere with the tray moving past the paper outlet. The trays protect the operator from injury and protect the structural elements of the finisher from damage despite their movement.

BACKGROUND OF THE INVENTION

The present invention relates to an electrophotographic copier, printer, facsimile apparatus or similar image forming apparatus and more particularly to a finisher for finishing papers driven out of an image forming apparatus.

A finisher for the above application is taught in, e.g., Japanese Patent Laid-Open Publication No. 8-26579. The finisher includes a single tray mounted on one side thereof. A staple mode and a shift mode are available with the finisher. In the staple mode, papers sequentially driven out of an image forming apparatus are stacked on a staple tray disposed in the finisher, stapled together, and then discharged to the tray. In the shift mode, papers are directly discharged to the above tray without being stapled. The tray may be constructed to be movable up and down in order to stack a great number of papers, as also proposed in the past.

The above finisher has a paper outlet where a drive roller and a driven roller are arranged in a pair. The driven roller is rotatably mounted on one end of a roller support member that is angularly movable about the other end. The driven roller is pressed against the drive roller due to its own weight. In the shift mode, the drive roller and driven roller are held in contact with each other for discharging the papers. In the staple mode, the roller support member is angularly moved to release the driven roller from the drive roller.

However, the problem with this type of finisher is that all the groups of papers or all the stacks of papers are loaded on the single tray and cannot be distinguished from each other. This is particularly true when a plurality of persons share the finisher. Moreover, an image forming apparatus with such a finisher is often used as a printer for a computer or an output device for a facsimile apparatus. As a result, copies and printings are apt to exist together on the tray. This makes the distinction between copies produced by different persons and between copies and printings extremely difficult.

In light of the above, the finisher may be provided with another paper outlet and another tray or proof tray in addition to the above tray. Even this kind of scheme has a problem that because the outlets and trays are provided in one-to-one correspondence, various functions including a sort mode and a staple mode available with the finisher are limited. Specifically, when the proof tray is selected, stapling or similar advanced function is not available.

Japanese Patent Laid-Open Publication Nos. 9-48567 and 9-48559, for example, each disclose a finisher including a plurality of trays arranged one above the other and capable of locating one of them at a paper outlet. This kind of finisher, however, has the following problems left unsolved. The trays selected and the trays not selected each are moved across the outlet while only the tray selected is located at the outlet. Therefore, to prevent papers stacked on any one of trays from returning into the outlet, a shutter or similar sophisticated device must be arranged in the outlet.

Moreover, the trays each have an end fence for positioning the trailing edges of papers stacked thereon. Because the end fence is implemented by the wall of the finisher where the outlet is formed, an outlet roller cannot overlap the wall. As a result, although the trailing edge of a paper may successfully move away from the outlet roller, the paper is apt to partly remain between the outlet roller and the wall of the finisher. The finisher therefore fails to surely discharge papers.

Japanese Patent Laid-Open Publication No. 9-110259, for example, proposes a finisher addressing the above problems. The finisher taught in this document includes an outlet roller disposed in a paper outlet formed in the wall of the finisher. The outlet roller is movable toward and away from the paper outlet. After the trailing edge of a paper has reached the above wall, the outlet roller is moved away from the wall so as to prevent the trailing edge of the paper from remaining between it and the wall. This, however, complicates the arrangement of the paper outlet.

The finisher of Laid-Open Publication No. 9-48559 mentioned earlier has another problem left unsolved. After a tray unit has been moved to locate a designated tray at the single paper outlet, papers are discharged to the tray. As a result, the operation for discharging the papers must be delayed by a period of time necessary for the particular tray to reach the paper outlet.

Japanese Patent Laid-Open Publication No. 7-228401, for example, proposes a finisher constructed to reduce the above period of time and adaptive to a high-speed image forming apparatus. This finisher includes two paper outlets and two trays associated one-to-one with the paper outlets. The trays are arranged one above the other and movable up and down independently of each other. When the upper tray is used as a mass paper tray, the lower tray is retracted downward as soon as the upper tray is lowered to a preselected position. However, the paper outlets each being associated with a particular tray are sophisticated.

Japanese Patent Laid-Open Publication No. 8-73107 teaches a sorter capable of moving a plurality of trays up and down at the same time and varying the distance between nearby trays. The sorter allows the number of papers to be stacked on each tray to be varied, as desired. Each tray is movable via a paper outlet and is returned to its home position when papers are removed therefrom. However, the problem with this sorter is that all the trays are connected together and limit the stroke available for mass paper discharge, i.e., a sufficient capacity is not available for mass paper discharge.

In the finisher of the type locating one of a plurality of trays at a paper outlet by driving it independently of the other trays, when an upper tray should be brought to the paper outlet, a lower tray must be retracted downward away from the paper outlet. Also, when the lower tray should be brought to the paper outlet, the upper tray must be retracted upward away from the paper outlet. When the lower tray is used as a mass paper tray, it should preferably be retracted away from the paper outlet as far as possible from the capacity standpoint. This, however, increases a distance that the lower tray should be brought to the paper outlet when selected later, slowing down the finishing operation.

Further, Japanese Patent Laid-Open Publication No. 8-119518 discloses a finisher including a plurality of trays arranged one above the other and at least one of which is movable up and down for mass paper discharge. When the movable tray is selected, it is moved from a stand-by position where papers have been removed to a paper outlet. That is, the finisher taught in the above document recognizes a position where papers have been removed as a stand-by position. In practice, however, the movable tray sometimes reaches its lower limit position in the event of mass paper discharge. It follows that a substantial period of time is necessary for the tray to move from the stand-by position (lower limit position) to the paper outlet. The lower limit position of the mass paper discharge tray is naturally close to the bottom of the finisher, so that the function of the tray can be made most of. This increases the period of time necessary for the tray to move from the lower limit position to the paper outlet and is therefore apt to lower the processing speed of the image forming apparatus. To solve this problem, the moving speed of the tray must be varied by sophisticated control, as needed.

When a paper jams the paper outlet in any one of the conventional finishers, the operator must put the operator's hand in the paper outlet and move outlet rollers provided in a pair away from each other, i.e., rotate a roller support member for removing the paper. At this instant, the tray moving upward via the paper outlet is apt to injure the operator and damage structural elements around the paper outlet. Although the shutter taught in Laid-Open Publication No. 9-48557 or 9-48559 may obviate such an accident, it sophisticates the configuration of the outlet and control.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide a finisher capable of moving a lower tray to a paper outlet in a short period of time without resorting to any sophisticated control.

It is a second object of the present invention to provide a finisher highly productive and easy to use.

It is a third object of the present invention to provide a finisher capable of stacking a great number of papers without scaling up a drive source and moving a tray to a paper outlet in a short constant period of time without resorting to any sophisticated control.

It is a fourth object of the present invention to provide a finisher capable of preventing papers from returning from a tray to a paper outlet without complicating the configuration of the outlet, or promoting sure positioning of papers without complicating the configuration of the outlet, or reducing the period of time necessary for a tray to reach the outlet.

It is a fifth object of the present invention to provide a finisher capable of reducing a paper discharging time with a plurality of trays sharing a single paper outlet, and implementing mass paper discharge.

It is a sixth object of the present invention to provide a finisher capable of receiving, with a relatively simple construction, papers with a plurality of trays without causing the papers from returning from the trays to a paper outlet.

It is a seventh object of the present invention to provide a finisher capable of obviating accidents ascribable to the movement of a tray with a relatively simple construction.

It is an eighth object of the present invention to provide a finisher capable of preventing trays from colliding with each other, and reducing the distance of movement of a tray to a paper outlet to thereby adapt to a high-speed image forming operation.

In accordance with the present invention, a finisher for an image forming apparatus includes a paper outlet for discharging papers. A plurality of trays are capable of being selectively located at the paper outlet and include at least an upper tray and a lower tray movable up and down independently of each other. A controller selectively locates either one of the upper tray and lower tray at the paper outlet. The controller moves the lower tray to a retracted position when locating the upper tray at the paper outlet. A stand-by position sensor senses the stand-by position of the lower tray which is a home position defined between the paper outlet and the retracted position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the finisher in accordance with the present invention will be described hereinafter.

First Embodiment

Referring toFIG. 1of the drawings, a finisher embodying the present invention and directed toward the first object stated earlier will be described. As shown, the finisher or paper stacking device, generally labeled F, receives a paper from a copier G at a transfer position J. The copier G belongs to a family of image forming apparatuses. An inlet sensor SN1and inlet rollers4are arranged around the transfer position J. A proof tray P is provided on the top of the finisher F. A paper received via the inlet rollers4is discharged to the proof tray P via an outlet E1, or discharged to an upper tray1or a lower tray2via an outlet E2without being stapled or after being stapled, depending on the operation mode. Mainly, the upper tray1is used to stack papers. The lower tray1is capable of stacking a great number of papers.

A path selector21is positioned downstream of the inlet rollers4in the direction of conveyance of papers and operated by a solenoid21a(see FIG.2). When the solenoid21ais turned off, the path selector21is brought to a position indicated by a solid line in FIG.1. In this position, the path selector21steers a paper being conveyed by the inlet rollers4toward the outlet E1. At this instant, rollers5aconvey the paper toward the outlet E1while outlet rollers7discharge the paper to the proof tray P. An outlet sensor SN2is located between the rollers5aand outlet rollers7, as illustrated. It is to be noted that the rollers5aand outlet rollers7, as well as other rollers, each are implemented as a drive roller and a driven roller cooperating with each other.

When the solenoid21ais turned on, it brings the path selector21to a position indicated by a dash-and-dots line in FIG.1. In this position, the path selector21steers the paper into a horizontal path. Another path selector20is positioned on the horizontal path downstream of the path selector21and operated by a solenoid20a(see FIG.2). When the solenoid20ais turned on, it switches the path selector21to a position indicated by a dash-and-dots line in FIG.1. As a result, the path selector21steers the paper to a vertical staple route A. When the solenoid20ais turned off, it switches the path selector21to a position indicated by a solid line in FIG.1and causes it to steer the paper to a non-staple route B.

Rollers5bare arranged on the non-staple route B for conveying the paper introduced into the route B. An outlet roller or drive roller8cooperates with a driven roller8afor discharging the paper to the upper tray1or the lower tray2. An outlet sensor SN4is positioned between the rollers5nand the outlet roller8. The trays1and2each are driven by a respective drive source. A controller100selectively locates either one of the trays1and2at the outlet E2.

On the staple route A, rollers6C convey the paper to a staple unit12. Papers stapled by the staple unit12are discharged to the tray1or2by the outlet roller8. An outlet sensor SN3is located on the staple route A.

Assume that the operator of the copier G selects a staple mode. In the staple mode, papers sequentially guided into the staple route A are stacked on a staple tray disposed in the finisher F by a discharge roller6. A tap roller9positions every paper in the vertical direction (direction of conveyance) while a jogger fence11positions every paper in the horizontal direction (widthwise direction). The controller100sends a staple signal to a stapler S between consecutive jobs, i.e., during interval between the last paper of one stack and the first paper of the next stack. A paper stack stapled by the stapler S is immediately conveyed to the outlet roller8by a belt10ahaving a catch10and driven out to the tray1or2located at the outlet E2by the roller8.

The tap roller9pivots about a fulcrum9aby being driven by return solenoid9b(see FIG.2). Every time a paper is driven onto the staple tray, the tap roller9acts on the paper and causes it to abut against a rear fence46. At this instant, a brush roller6acooperative with the discharge roller6prevents the trailing edge of the paper from returning toward the staple path A. The tap roller9is rotatable in the counterclockwise direction. A home position sensor SN8is responsive to the home position of the catch10.

As shown inFIG. 2, the controller100is implemented by a microcomputer including a CPU (Central Processing Unit)102and an I/O (Input/Output) interface104. A control panel, not shown, is mounted on the top of the finisher body and includes various switches (SW). Signals output from the switches and various sensors are input to the CPU102via the I/O interface104. In response, the CPU102controls a motor50assigned to the upper tray1, a motor51assigned to the lower tray2, the solenoids20aand21a,the return solenoid9b,a motor52assigned to the rollers5a,5band5c,a motor53assigned to the outlet rollers7and8, motors54and56assigned to the stapler S, a motor55assigned to the belt10a,a motor57assigned to the jogger fence11, etc. Pulse signals for driving the motor52assigned to the rollers5care input to the CPU102and counted thereby. The CPU102controls the return solenoid9bin accordance with the number of the pulse signals. Also shown inFIG. 2are a DM motor DCM and a stepping motor STMP.

Sensors SN5, SN6, SN9and SN7are sequentially arranged on the outlet E2side of the finisher body from the upper portion to the lower portion. The sensor SN5is retracted position sensing means for sensing a position to which the upper tray1is retracted when the lower tray2should be brought to the outlet E2. The sensor SN6is discharge position sensing means responsive to the tray1or2brought to the outlet E2. The sensor SN9is stand-by position or home position sensing means responsive to the stand-by position or home position of the tray2. The sensor SN7is retracted position sensing means responsive to the tray2brought to its retracted position. The outputs of the sensors SN5, SN6, SN9and SN7are input to the CPU102via the I/O interface104.

A desired operation mode and a desired tray are input on an operation panel, not shown, mounted on the copier G or a computer, not shown, connected to the copier G. When the staple mode is input despite that the proof tray P is selected, the staple mode is automatically canceled with priority given to the proof tray P.

A mechanism for moving the trays1and2up and down will be described with reference to FIG.3. As shown, the upper tray1is mounted on a base40affixed to opposite side walls39aand39b.Guide rollers44are mounted on the side walls39aand39bvia stubs not shown. The guide rollers44are rollable on and along the inner peripheries of guide rails30aand30beach having a generally U-shaped section. The guide rollers44are positioned by the assembly of the side walls39aand39band base40and prevented from slipping out of the guide rails30aand30bthereby. Two timing belts37each are passed over a pair of timing pulleys36. The motor50drives the timing belts37via a drive shaft33aand a driven shaft33bon which the timing pulleys36are mounted. The side walls39aand39beach are partly affixed to the adjoining timing belt37. In this configuration, the unit including the upper tray1is movable up and down.

The lower tray2, like the upper tray1, is mounted on a base43affixed to opposite side walls42aand42b.Guide rollers44are mounted on the side walls42aand42bvia stubs not shown. The guide rollers44are rollable on end along the inner peripheries of the guide rails30aand30b.The guide rollers44are positioned by the assembly of the side walls42aand42band base43and prevented from slipping out of the guide rails30aand30bthereby. Two timing belts35each are passed over a pair of timing pulleys34. The motor51drives the timing belts35via a drive shaft41aand a driven shaft41bon which the timing pulleys34are mounted. The side walls42aand42beach are partly affixed to the adjoining timing belt35. In this configuration, the unit including the lower tray2is movable up and down.

FIG. 4shows a mechanism for driving the lower tray2. As shown, the rotation of the motor51is transferred via a worm gear58to the last gear of a gear train mounted on the drive shaft41a.The worm gear58allows the tray2to be held at a preselected position. The upper tray1is driven by a similar mechanism. The sensor SN7mentioned earlier is located between the opposite runs of the timing belt35and turned on and off by a part of the side wall42aor42baffixed to one run of the timing belt35located at the discharge side. This is also true with the sensor SN5. The driven roller8ais not shown in FIG.4.

The sensor SN9is positioned around the center of a paper discharged and operable on a surface which the rear edge of the paper contacts, i.e., on a side wall or rear fence32. More specifically, as shown inFIG. 5, the sensor SN9implemented by a microswitch includes a portion62affixed to a stationary member60forming a part of the finisher body, and a movable piece64rotatably supported by the portion62at its one end. The movable piece64partly protrudes from the side wall32in the paper discharge direction and is actuated by the rear end of the tray2or the top of a paper stack. The other sensors SN5, SN6and SN7each have the same configuration as the sensor SN9. All the sensors may be implemented by either one of refection type sensors or transmission type sensors.

As shown inFIG. 1, in the illustrative embodiment, the outlet roller8protrudes from the side wall32in order to prevent the side wall32from catching a paper being discharged via the outlet E2. The outlet roller8, however, interferes with the upper tray1when the tray1is retracted upward. As shown inFIG. 6, to obviate such interference, the guide rails30aand30beach include a bent portion31.FIG. 6shows a condition wherein the upper tray1is located at the outlet E2while the lower tray2is retracted. As shown inFIG. 7, as the guide rollers44are displaced, the tray1is angularly moved and prevented from interfering with the outlet roller8. The distance L1between the guide rollers44of the tray1are greater than the length L of the bent portion31.

The angular movement of the tray1causes the tension acting on the timing belt37to vary. In light of this, as shown inFIG. 6, the lower timing pulley36is affixed to a movable bracket68to which a spring66is anchored.FIG. 8shows a condition wherein the lower tray2is located at the outlet E2while the upper tray1is retracted upward.

How the controller100controls the upper tray1and lower tray2will be described hereinafter.FIG. 9shows home positions at which the trays1and2are located on the power-up of the copier G. As shown, the sensor SN5senses the upper end of an end fence1aincluded in the tray1when the tray1is located at its home position. The sensor SN9senses the lower end of the tray2when the tray2is located at its home position.

Reference will be made toFIGS. 10 and 11for describing the initialization of the trays1and2, i.e., a procedure for locating them at the home positions. As shown, on the power-up of the copier G, initialization begins (step S1). Specifically, the controller100determines whether or not the sensor SN7is in an ON state (step S2). If the answer of the step S2is positive (YES), the controller100raises the tray2(step S3) and then determines whether or not the sensor SN9is in an ON state (step S4). If the answer of the step S4is YES, the controller100stops the elevation of the tray2(step S5). As a result, the tray2is caused to stop at its home position. To move the trays1and2up and down, the controller100drives the motors50and51.

Subsequently, the controller100determines whether or not the sensor SN5is in an ON state (step S6). If the answer of the step S6is YES, meaning that the tray1is located at its home position, the controller100ends the initialization. If the answer of the step S6is negative (NO), the controller raises the tray1(step S7) and determines whether or not the sensor SN5is in an ON state (step S8). The controller100stops the movement of the tray1as soon as the sensor SN5senses the upper end of the end fence1a(step S9).

If the answer of the step S2is NO, meaning that the sensor SN7is in an OFF state, the controller100lowers the tray2(step S10) and then determines whether or not the sensor SN9is an ON state (step S11). If the answer of the step S11is YES, the controller100stops the movement of the tray2(step S12). In this case, the tray2is moved downward toward the sensor SN9.

If the answer of the step S11is NO, i.e., if the sensor SN9is in an OFF state, the controller100determines whether or not the sensor SN7is in an ON state (step S13). If the answer of the step S13is YES, the controller100stops the movement of the tray2(step S14). Subsequently, the controller100raises the tray2(step S15) and then determines whether or not the sensor SN9is in an ON state (step S16). As soon as the sensor SN9senses the lower end of the tray2(YES, step S16), the controller100stops the movement of the tray2(step S17). In this case, the tray2is raised from a position between the sensors SN9and SN7. This is followed by the step S6.

The controller100may move the two trays1and2at the same time, if desired.

To locate the tray1at the outlet E2, the controller100once stops the movement of the tray1when the sensor SN6senses the upper end of the end fence1a,then raises the tray1by a preselected distance, and then stops it. To locate the other tray2at the outlet E2, the controller100once stops the movement of the tray2when the sensor SN6senses the upper end of the tray2, then lowers the tray2by a preselected distance, and then stops it.

Because the home position of the tray2corresponds to the position of the sensor SN7, the tray2is moved from the home position to the outlet E2when selected. This successfully reduces the distance and time of movement of the tray2, compared to a case wherein the above home position corresponds to the position of the sensor SN7.

The end fence1aof the tray1has its intermediate portion notched so as not to interfere with a push roller70(seeFIG. 4) although not shown specifically. The sensor SN6is therefore so positioned as to sense the end fence1a,the rear end of the tray2or the top of a paper stack. In this sense, the sensor SN6serve as a paper sensor at the same time.

FIG. 12shows a condition wherein the tray2is selected and has received a certain number of papers. Assume that the other tray1is selected in the condition shown in FIG.12. Then, as shown inFIG. 13, the tray2is retracted until the sensor SN7senses it, while the tray1is brought to the outlet E2.

FIG. 14shows a condition wherein the tray2is selected and has received a number of papers great enough to turn on both of the sensors SN6and SN9. In the illustrative embodiment, the tray2reached the condition ofFIG. 14is determined to be full. More specifically, the sensor SN9is capable of detecting the full state of the tray2alone. When the tray1is selected with the tray2being in its full state, the tray2must be retracted. However, the tray2should only be retracted by a distance equal to the height of a stack that the tray1can accommodate, i.e., a dimension H shown in FIG.14.

In light of the above, the sensors SN9and SN7are spaced by the distance H from each other. It follows that when the full tray2is retracted and the tray1is brought to the outlet E2, no wasteful space exists between the trays1and2, as shown in FIG.15.

As stated above, the optimal distance between the sensors SN9and SN7can be regarded as the height of a stack that the tray1can accommodate (dimension H). Therefore, considering the sensor SN9to be a reference, it is possible to determine the position of the sensor SN7in terms of the distance of movement of the tray2. This obviates the need for the sensor SN7.

A specific procedure for retracting the tray2without using the sensor SN7will be described with reference to FIG.16. As shown, the controller100lowers the tray2(step S1) and then determines whether or not the sensor SN9is in an ON state (step S2). If the answer of the step S2is NO, the controller100resets a counter, not shown, for counting the pulses of the motor51to zero (step S3). When the sensor SN9turns on (YES, step S2), the controller100starts counting the pulses of the motor51with the above counter (step S4). On counting a preselected number of pulses (YES, step S5), the controller100stops the movement of the tray2. As a result, the tray2is located at its retracted position.

A specific initialization procedure not using the sensor SN7will be described with reference toFIGS. 17 and 18. As shown, on the power-up of the copier G, the controller100starts initialization (step S1). The controller100determines whether or not the sensor SN5is in an ON state (step S2). If the answer of the step S2is YES, the controller100determines that the tray1is located at its home position, and then determines whether or not the sensor SN6is in an ON state (step S3). If the answer of the step S3is YES, the controller determines that the tray2is located at the outlet E2, and then lowers the tray2(step S4). As soon as the sensor SN9turns on (YES, step S5), the controller100stops the movement of the tray2. As a result, the tray2is located at its home position.

If the sensor SN6is in an OFF state, as determined in the step S3, the controller100once raises the tray2(step S7) and determines whether or not the sensor SN6is an ON state (step S8). If the answer of the step S8is YES, the controller stops the movement of the tray2(step S9). This is followed by the step S4.

If the answer of the step S2is NO, meaning that the sensor SN5is in an OFF state, the controller100raises the tray1(step S10) and then determines whether or not the sensor SN5is in an ON state (step S11). If the answer of the step S11is YES, the controller100stops the movement of the tray1(step S12). Consequently, the tray1is located at its home position. This is followed by the sequence of steps to be executed when the answer of the step S2is YES.

The above embodiment achieves various unprecedented advantages, as enumerated below.

(1) The stand-by position or home position assigned to the lower tray is higher in level than the retracted position. Therefore, when the lower tray is selected, it can move to the outlet in a short period of time.

(2) The home position sensing means bifunctions as means for sensing the full state of the lower tray. This obviates the need for extra means for sensing the full state and thereby reduces the cost of the finisher.

(3) The stand-by position or home position sensing means is positioned above the retracted position by the height of a stack that the upper tray can accommodate. This minimizes the distance of retraction of the full lower tray and thereby obviates a wasteful space.

(4) Because the retracted position is determined in terms of the distance of movement of the lower tray without using extra means, the cost is further reduced.

(5) The discharge position sensing means is so located as to operate on a surface which the trailing edge of a paper on the tray contacts. The sensing means can therefore sense both of the upper tray and lower tray as well as the top of a paper stack. This simplifies the sensing arrangement and reduces the cost of the finisher.

Second Embodiment

This embodiment is directed mainly toward the second object stated earlier. Because the second embodiment is similar to the first embodiment ofFIGS. 1-8in construction and operation. The following description will concentrate on differences. This is also true with the other embodiments to be described later.

A tray control procedure to be executed by the controller100and unique to this embodiment will be described with reference toFIGS. 19-25in addition toFIGS. 1-8. The sensor SN5senses the upper end of the end fence1aof the tray1when the tray1is located at its home position while the sensor SN9senses the upper rear end of the tray2when the tray2is located at its home position.

Reference will be made toFIGS. 19 and 20for describing the initialization of the trays1and2, i.e., a procedure for locating them at the home positions. As shown, on the power-up of the copier G, the controller100starts initialization and lowers the tray2(step S1). The controller100determines whether or not the sensor SN7is in an ON state (step S2). If the answer of the step S2is YES, the controller100determines whether or not the sensor SN9is in an ON state (step S3). If the answer of the step S3is YES, the controller100determines that the number of papers stacked on the tray2is so great, the tray1cannot be lowered. In this case, the controller100sets a tray1inhibition flag in the flag area of a RAM (Random Access Memory), not shown, to thereby inhibit the tray1from being used (step S4). Then, the controller100stops the movement of the tray2(step S5).

If the sensor SN9is in an OFF state, as determined in the step S3, the controller stops of the tray2, then raises it (step S6), and again determines whether or not the sensor SN9is in an ON state (step S7). If the answer of the step S7is YES, the controller100stops the tray2and again lowers it (step S8). As soon as the sensor SN9turns off (YES, step S9), the controller100stops the tray2. As a result, the upper surface of the tray2or that of a paper stack on the tray2is located at or below the home position of the tray2. Subsequently, the controller100determines whether or not the sensor SN6is in an ON state. If the sensor SN6is in an OFF state, the controller100lowers the tray1(step S11). As soon as the sensor SN6senses the upper end of the end fence1aof the tray1(YES, step S12), the controller100stops the tray1(step S13).

During the downward movement of the tray2or during the stacking of papers on the tray2, the controller100determines whether or not the tray1can be lowered in accordance with a subroutine program shown in FIG.21. For example, while papers are sequentially stacked on the tray2, the tray2is sequentially lowered for accommodating a great number of papers. However, it sometimes occurs that after the current job, the tray1is selected in place of the tray2without the stack of papers being removed from the tray2.

In the above situation, the tray2is lowered. Specifically, as shown inFIG. 21, the controller100determines whether or not the tray1inhibition flag is set (step S1). If the answer of the step S1is NO, the controller100determines whether or not the sensor SN9is in an ON state (step S2). If the answer of the step S2is YES, the controller100determines whether or not the sensor SN7is in an ON state (step S3).

Assume that the sensors SN9and SN6both turn on while the tray2is in downward movement. Then, the controller100determines that the top of the stack on the tray2may lie in the range to which the tray1should be lowered. In this case, the controller100sets the tray1inhibition flag (step S4) and sends a signal indicative of the inhibition to a controller, not shown, included in the copier G. In response, the controller of the copier G urges the operator to remove the stack from the tray2via, e.g., the operation panel.

Assume that the sensor SN9senses a paper during stacking of papers on the tray2and then turns off. Then, the controller100raises the tray2, determining that the operator has removed the stack from the tray2. This will be described specifically with reference toFIGS. 22 and 23. As shown, the controller100determines whether or not papers are being stacked on the tray2(step S1). If the answer of the step S1is YES, the controller100determines whether or not a sense flag relating to the sensor SN9is set (step S2). If the answer of the step S2is YES, the controller100determines whether or not the sensor SN9is in an ON state (step S3). If the answer of the step S3is YES, the controller100sets the sense flag relating to the sensor SN9(step S4).

Subsequently, the controller100determines whether or not the sensor SN9is in an OFF state (step S5). If the answer of the step S5is YES, the controller100raises the tray2and clears the sense flag relating to the sensor SN9(step S6). As soon as the sensor SN6senses the tray2being raised (YES, step S7), the controller100stops the tray2(step S8). Thereafter, the controller100lowers the tray2(step S9) and then stops it as soon as the sensor SN6turns off (step S11). This successfully locates the tray2at the adequate position for receiving papers via the outlet2. Even when some papers are left on the tray2, the top of the papers is located at the adequate position.

FIGS. 24 and 25demonstrate a procedure for canceling the inhibition of the tray1. As shown, the controller100determines whether or not the tray1inhibition flag is set (step S1). If the answer of the step S1is YES and if the sensor SN9turns off later (YES, step S2), the controller raises the tray (step S3) and then stops it (step S5) as soon as the sensor SN9turns on (YES, step S4). As a result, the tray2is located at the home position or stand-by position. The controller100again determines whether or not the sensor SN7is in an OFF state (step S6). If the answer of the step S6is YES, the controller100clears the tray1inhibition flag (step S7) while sending a signal indicative of the cancellation to the controller of the copier G. In response, the controller of the copier G cancels the inhibition relating to the tray1.

As stated above, the second embodiment achieves the following advantages.

(1) The stand-by position or home position assigned to the lower tray is higher in level than the retracted position. Therefore, when the lower tray is selected, it can move to the outlet in a short period of time.

(2) The retracted position sensing means senses the upper surface of the lower tray or the top of papers stacked on the lower tray. The lower tray can therefore wait at a preselected position without regard to the number of papers stacked thereon. This is successful to render the removal of the paper stack stable and the period of time necessary for the lower tray to reach the outlet constant.

(3) Because the stand-by position sensing means is located in the range of movement of a paper of minimum size available with the lower tray, the above advantages (1) and (2) are achievable with papers of all sizes.

(4) By simply adding the stand-by position sensing means, it is possible to prevent the upper tray from interfering with the lower tray when moved downward. This reduces the down time of the entire system including the finisher while promoting safety operation.

(5) Even when the paper stack is abruptly removed, the stand-by position sensing means allows the lower tray to be located at the adequate discharge position without fail. It follows that a wasteful space above the lower tray is obviated.

Third Embodiment

This embodiment is directed mainly toward the third embodiment stated earlier. This embodiment is also similar to the first embodiment except for the tray control procedure to be executed by the control means. A first tray control procedure available with the third embodiment will be described with reference toFIGS. 26-30in addition toFIGS. 1-8. Again, the sensor SN6senses the end fence1aof the tray1when the tray1is in its home position while the sensor SN9senses the upper rear end of the tray2when the tray2is in its home position.

As shown inFIGS. 26 and 27, on the power-up of the copier G, the control means100starts initialization (step S1). Specifically, the control means100determines whether or not the sensor SN7is in an ON state (step S2). If the sensor SN7is in an OFF state (NO, step S2), the controller lowers the tray2, determining that the tray2is positioned above the sensor SN7(step S3). Then, the controller100determines whether or not the sensor SN9is in an ON state (step S4). If the answer of the step S4is YES, the controller100stops the movement of the tray2(step S5). As a result, the tray2is located at its home position.

Subsequently, the controller100determines whether or not the sensor SN6is in an ON state (step S6). If the answer of the step S6is NO, the controller100lowers the tray1, determining that the tray1is positioned above the sensor SN6(step S7). The controller100again determines whether or not the sensor SN6is in an ON state (step S8). As soon as the sensor SN6senses the upper end of the end fence1a(YES, step S8), the controller100stops the movement of the tray1(step S9).

If the answer of the step S2is YES, the controller100raises the tray2(step S10) until the sensor SN9turns on (YES, step S11). Then, the controller100stops the movement of the tray2(step S12).

When the tray2is located between the sensors SN7and SN9, the sensor SN9remains in an OFF state, as determined in the step S4. In this case, the controller100determines whether or not the sensor SN7is in an ON state (step S13). If the answer of the step S13is YES, the controller100stops the movement of the tray2(step S14) and then raises the tray2(step S15). As soon as the sensor SN9turns on (YES, step S16), the controller100stops the movement of the tray2(step S17).

As stated above, in the first tray control procedure, the tray1is located at the paper discharge position. Therefore, when the tray1is selected, neither the tray1nor the tray2is moved. This promotes the efficient use of the tray1when the tray1is frequently used.

When the tray2is selected, the tray1is elevated until the sensor SN5senses it. The tray2is raised from its stand-by position until the sensor SN6senses it. The elevation of the tray1and that of the tray2may be effected at the same time, if desired.

Because the tray2is moved from its stand-by position to the outlet E2, a period of time necessary for the tray2to reach the outlet2is shorter than when the tray2is moved from its retracted position (lower limit position) defined by the sensor SN7.

A second tray control procedure available with the illustrative embodiment is as follows. As shown inFIG. 28, the sensor SN5senses the upper end of the end fence1aof the tray1when the tray1is in its home position while the sensor SN9senses the upper rear end of the tray2when the tray2is in its home position. Initialization of the trays1and2will be described with reference toFIGS. 29 and 30.

As shown, on the power-up of the copier G, the controller100starts initialization (step S1). Specifically, the control means100determines whether or not the sensor SN7is in an ON state (step S2). If the sensor SN7is in an OFF state (NO, step S2), the controller lowers the tray2, determining that the tray2is positioned above the sensor SN7(step S3). Then, the controller100determines whether or not the sensor SN9is in an ON state (step S4). If the answer of the step S4is YES, the controller100stops the movement of the tray2(step S5). As a result, the tray2is located at its home position.

Subsequently, the controller100determines whether or not the sensor SN5is in an ON state (step S6). If the answer of the step S6is NO, the controller100raises the tray (step S7) and then determines whether or not the sensor SN5is in an ON state (step S8). If the answer of the step S8is YES, meaning that the sensor SN5has sensed the upper end of the end fence1a,the controller100stops the movement of the tray1(step S9). If the answer of the step S6is YES, the controller100ends the initialization, determining that the tray1is held its home position.

If the sensor SN7is in an ON state, as determined in the step S2, the controller100raises the tray2(step S10) and then determines whether or not the sensor SN9is in an ON state (step S11). If the answer of the step S11is YES, the controller100stops the movement of the tray2(step S12). If the sensor SN9is in an ON state, as determined in the step S4, the controller100determines whether or not the sensor SN7is in an ON state (step S13). If the answer of the step S13is YES, the controller100stops the movement of the tray2(step S14). Subsequently, the controller100raises the tray2(step S15). As soon as the sensor SN9senses the upper rear end of the tray2(YES, step S16), the controller100stops the movement of the tray2(step S17). In this case, the tray2has been positioned between the sensors SN9and SN7before.

While the above specific procedure moves the tray1after the tray2, the trays1and2may be moved at the same time, if desired.

To bring the tray1to the outlet E2, the tray1is stopped when the sensor SN6senses the upper end of its end fence1a.To bring the tray2to the outlet E2, the tray2is once stopped when the sensor SN6senses its upper rear end, then lowered by a preselected distance, and then brought to a stop.

Because the home position of the tray2corresponds to the position of the sensor SN9, the tray2is moved from the home position to the outlet E2when selected. This successfully reduces the distance and time of movement of the tray2, compared to the case wherein the home position is located below the position of the sensor SN7.

The end fence1aof the tray1has its intermediate portion notched so as not to interfere with the push roller70,FIG. 4, although not shown specifically. The sensor SN6is therefore so positioned as to sense the end fence1a,the rear end of the tray2or the top of a paper stack. In this sense, the sensor SN6serves as a paper sensor at the same time.

As stated above, in the finisher shown inFIG. 28, the distance between the trays1and2held in their stand-by positions is greater than in the finisher ofFIG. 1, facilitating the removal of a paper stack from the tray2. It follows that the stand-by position of the tray2defined by the sensor SN9can be selected in consideration of easy removal of a paper stack also.

The third embodiment shown and described has the following advantages.

(1) The stand-by position of the lower tray is located above the lower limit position of the same. This reduces a period of time necessary for the lower tray to reach the paper discharge position when selected.

(2) Because the home position of the upper tray corresponds to the paper discharge position, the finisher can be efficiently used when the upper tray is frequently used.

(3) Because the stand-by position of the upper tray is coincident with the retracted position above the outlet, the distance between the upper tray and the lower tray can be increased to facilitate the removal of a paper stack from the lower tray.

Fourth Embodiment

This embodiment is directed mainly toward the fourth object stated earlier. This embodiment differs from the previous embodiments in that the sensor SN9responsive to the retracted position or home position of the tray2is absent and in that the controller100controls the trays1and2in a unique way. The fourth embodiment will be described with reference toFIGS. 31-40in addition toFIGS. 1-8.

The sensor SN5senses the upper end of the end fence1aof the tray1when the tray1is in its home position. The home position of the tray2is lower than the position where the sensor SN6senses it by a preselected distance.

FIG. 31demonstrates initialization for locating the trays1and2at their home positions. As shown, on the power-up of the copier G, initialization begins (step S1). The controller100determines whether or not the sensor SN5is in an ON state (step S2). If the answer of the step S2is NO, the controller100raises the tray1(S3), determining that the tray1is positioned below the sensor SN5. As soon as the sensor SN5senses the tray1(YES, step S2), the controller100stops the movement of the tray1(step S4).

Subsequently, the controller100determines whether or not the sensor SN6is in an ON state (step S5). If the answer of the step S5is NO, the controller100raises the tray2(step S6). When the sensor SN6senses the tray2, the controller100stops the tray2at a position where the sensor SN6has not sense it. If the answer of the step S5is YES, the controller100lowers the tray2(step S7), determining that the tray2has overrun. Then, the controller determines whether or not the sensor SN6is in an ON state (step S8), and stops the tray2when the sensor SN6stops sensing the tray2(step S9).

Assume that the operator selects the tray1on the operation panel of the copier G or the computer connected thereto. Then, the controller100first determines whether or not the sensors SN5and SN6each are in an ON state in order to see the positions of the trays1and2. Patterns A-D shown below are representative of the possible combinations of the ON/OFF states of the sensors SN5and SN6and the positions of the trays1and2.

As shown inFIG. 32, as for the above pattern A, the controller100first lowers the tray2(step S1) while determining whether or not the sensor SN6is in an ON state (step S2). When the sensor SN6stops sensing the tray2(NO, step S2), the controller100further lowers the tray2by a preselected distance of (L3+L4) (step S3) and then stops its movement. As shown inFIG. 33, the distance (L3+L4) is great enough for the tray1to move to the paper discharge position and for the operator to pick up a paper stack from the tray2. Specifically, the distance L3is a height that the tray1occupies when brought to the paper discharge position. The distance L4is a height for implementing a tray gap L5necessary for the operator to pick up a paper stack from the tray2. To set the distance (L3+L4), a pulse counter, not shown, counts pulses for driving the motor51assigned to the tray2after the sensor SN6has stopped sensing the tray2.

Subsequently, the controller100lowers the tray1(step S5) and determines whether or not the sensor SN6has sensed the upper end of the end fence1a(step S6). If the answer of the step S6is YES, the controller100stops the movement of the tray1(step S7).

As shown inFIG. 34, as for the pattern B, the controller100once raises the tray2(S1) and determines whether or not the sensor SN6is in an ON state (step S2). If the answer of the step S2is YES, the controller100stops the movement of the tray2(step S3). Subsequently, the controller100lowers the tray2(step S4) and determines whether or not the sensor SN6is in an ON state (step S5). If the answer of the step S5is NO, the controller100lowers the tray2by the distance (L3+L4) (step S6) and then stops it (step S7). Thereafter, the controller100lowers the tray1(step S8) and determines whether or not the sensor SN6has sensed the upper end of the end fence1a(step S9). If the answer of the step S8is YES, the controller100stops the movement of the tray1.

As for the pattern C, the controller100does not execute any tray control and allows a job to be executed immediately.

As for the pattern D, the controller100determines that the position of the tray1is unusual, executes initialization, and then sets up the pattern B.

When the operator selects the tray2on the operation panel of the copier G or the computer connected thereto, the controller100also determines the statuses of the sensors SN5and SN6first in order to see the positions of the trays1and2.

Specifically, as shown inFIG. 35, as for the pattern A, the controller100first lowers the tray2(step S1) and determines whether or not the sensor SN6is in an ON state (step S2). When the sensor SN6stops sensing the tray2(NO step S2), the controller100stops the movement of the tray2(step S3).

As shown inFIG. 36, as for the pattern8, the controller100once raises the tray2(step S1) and determines whether or not the sensor SN6is in an ON state (step S2). As soon as the sensor SN6senses the tray2(YES, step S2), the controller100stops the movement of the tray2(step S3). Subsequently, the controller100lowers the tray2(step S4) and then stops it (step S6) as soon as the sensor SN6stops sensing it (NO, step S5).

As shown inFIG. 37, as for the pattern C, the controller100first raises the tray1(step S1) and determines whether or not the sensor SN5is in an ON state (step S2). If the answer of the step S2is YES, the controller100stops the movement of the tray1. Subsequently, the controller100lowers the tray2(step S4) and then stops the tray2(step S6) as soon as the sensor SN6stops sensing it (NO, step S5).

As shown inFIG. 38, as for the pattern D, the controller100first raises the tray1(step S1) and determines whether or not the sensor SN5is in an ON state (step S2). If the answer of the step S2is YES, the controller100stops the movement of the tray1(step S3). Subsequently, the controller100raises the tray2(step S4) and determines whether or not the sensor SN6is in an ON state (step S5). If the answer of the step S5is YES, the controller100stops the movement of the tray2(step S6). Thereafter, the controller100lowers the tray2and then stops the tray2(step S9) as soon as the sensor SN6stops sensing it (NO, step S8).

As shown inFIG. 39, the sensor SN7is positioned such that the tray2having been sensed by the sensor SN7can further move downward by a preselected distance. Stated another way, a preselected distance is available between the bottom of the finisher and the sensor SN7responsive to the lower limit position.FIG. 39shows the tray2in its full state. Specifically, as a great number of papers are stacked on the tray2, the tray2is sequentially lowered. When the sensors SN7and SN6sense the tray2and the top of the paper stack on the tray2, respectively, the controller100determines that the tray2is full.

When the tray2is full, the controller100lowers it to a position below the lower limit position by a preselected distance L6(see FIG.40). The distance L6is selected to be greater than the distance (L3+L4), FIG.33. Therefore, even when the tray2is left in its full state, the tray1can be located at the paper discharge position. The distance L6, like the distance (L3+L4), is determined in terms of the number of pulses for driving the motor51.

As stated above, the above embodiment achieves the following advantages.

(1) The end fence of the tray movable via the outlet is capable of preventing papers stacked on the tray from returning to the outlet without complicating the configuration of the outlet. The papers do not contact the structural elements of the outlet and are therefore free from disturbance and contamination.

(2) The upper tray is movable outward in the paper discharge direction via the outlet. This allows the papers to be neatly positioned without complicating the configuration of the outlet.

(3) The retracted position of the lower tray can be determined without resorting to extra sensing means which would increase the cost of the finisher. Because the retracted position is located above the lower limit position and because the lower tray can be moved from the retracted position, a period of time necessary for the lower tray to move to the paper discharge position is reduced when the lower tray is selected.

(4) The preselected distance is such that the upper tray can move to the paper discharge position and a paper stack can be picked up from the lower tray. This not only guarantees easy removal of a paper stack, but also reduces the tray switching time (moving time).

(5) Even when the lower tray is full, it can be lowered to allow extra papers to be stacked.

(6) Even when the lower tray is held in its full state, the upper tray can be lowered to the paper discharge position. This promotes the effective use of a paper discharge space available at the side of the finisher.

Fifth Embodiment

This embodiment is directed mainly toward the fifth object stated earlier. This embodiment also differs from the previous embodiments in that the sensor SN9responsive to the retracted position or home position of the tray2is absent and in that the controller100controls the trays1and2in a unique way. The fourth embodiment will be described with reference toFIGS. 41-50in addition toFIGS. 1-8.

In the illustrative embodiment, the home position of the tray1is a position which the upper end of the end fence1areaches when raised by a preselected distance (amount) after being sensed by the sensor SN6. The home position of the tray2is a position where the tray2is sensed by the sensor SN7.

On the power-up of the copier G, the controller100determines whether or not the sensor SN7responsive to the lower limit position is in an ON state. If the sensor SN7is in an OFF state, the controller100lowers the tray2via the motor51, determining that the tray2is positioned above the sensor SN7. As soon as the sensor SN7senses the tray2, the controller100stops lowering the tray2. Subsequently, the controller100determines whether or not the sensor SN5is in an ON state. If the sensor SN5is in an OFF state, the controller100once raises the tray1via the motor50and then lowers the tray1as soon as the sensor SN5senses it. When the sensor SN6senses the upper end of the end fence1a,the controller100raises the tray1by a preselected distance and then stops it. Further, if the sensor SN5is in an ON state, the controller100lowers the tray1, then raises it by the preselected distance when the sensor SN6senses the tray1, and then stops the tray1.

A first tray control procedure available with the illustrative embodiment will be described with reference toFIGS. 41 and 42. As shown, the discharge of papers from the copier G begins in the staple mode input on the copier G or the computer connected thereto (step S1), the controller100determines whether or not the tray1is selected by the operator (step S2). At the same time, the controller100determines whether or not the sensor SN7is in an ON state. If the sensor SN7is in an OFF state, the controller100lowers the tray2(step S3), determining that the tray2is positioned above the sensor SN7. The controller100again determines whether or not the sensor SN7is in an ON state (step S4) and then stops the movement of the tray2(step S5). Thereafter, the controller100lowers the tray1(step S6) and determines whether or not the sensor SN6is in an ON state (step S7). If the answer of the step S7is YES, the controller100stops the movement of the tray1(step S8). Then, the controller100raises the tray1by a preselected distance (amount) (step S9) and then stops it (step S10). As a result, the tray1is located at the paper discharge position.

When a paper is discharged to the staple tray of the finisher, the controller100determines whether or not stapling has ended (step S12). If the answer of the step S12is YES, the controller100causes a stapled paper stack to be driven out to the tray1(step S13).

Assume that the tray2is selected via the copier G or the computer connected thereto. Then, the controller100first determines whether or not the sensor SN5responsive to the retracted position is in an ON state. If the sensor SN5is in an OFF state, the controller100raises the tray1(step S14) and again checks the sensor SN5(step S15). When the sensor SN5turns on (YES, step S15), the controller100stops the movement of the tray1(step S16), then raises the tray2(step S17), and then determines whether or not the sensor SN6is in an ON state (step S18). If the answer of the step S18is YES, the controller100once stops the movement of the tray2, then lowers the tray2by a preselected distance (amount) (step S20), and then stops it (step S21). As a result, the tray2is located at the proper discharge position.

When a paper is discharged to the staple tray of the finisher (S22), the controller100determines whether or not stapling has ended (step S23). If the answer of the step S23is YES, the controller100causes a stapled paper stack to be driven out to the tray2(step S24).

The tray1or2is located at the outlet E2beforehand in response to information received from the copier G or the computer connected thereto. This successfully reduces a period of time relating to the movement of the tray1or2. Stated another way, the trays1and2are not moved relative to the outlet E2independently of each other, but are moved in parallel by staple processing within a necessary period of time. The finisher can therefore complete its operation in a shorter period of time than the conventional finishers.

After the tray1or2has been located at the outlet E2, papers are sequentially stacked on the tray1or2. When the sensor SN6senses the top of a paper stack on the tray1or2held at the outlet E2, the tray1or2is lowered by a preselected distance. Such a procedure is repeated to allow a great number of papers to be stacked on the tray1or2. This is also true with the other embodiments to be described later.

In the non-staple mode, the operator is allowed to select desired one of the proof tray P, upper tray1and lower tray2; the trays1and2each are capable of accommodating a great number of papers. The proof tray P, upper tray1and lower tray2may be respectively assigned to a facsimile apparatus, a copier or a printer, and a printer or a copier, as desired. The finisher is therefore adaptive to a multifunction image forming apparatus.

A second tray control procedure available with the illustrative embodiment will be described with reference toFIGS. 43-46. The procedure to be described prevents the trays1and2from interfering with each other when moved independently of each other.

As shown inFIGS. 43 and 44, when the controller100receives a paper output request from the copier G or the computer connected thereto (step S1), it sends an answer representative of a stand-by state to the copier G or the computer (step S2). The controller100determines whether or not the tray1is selected (step S3) and determines whether or not the sensor SN7is in an ON state. If the sensor SN7is in an OFF state, the controller100determines that the tray2is positioned above the sensor SN7, and lowers the tray2which would obstruct the positioning of the tray1at the outlet E2(step S4). Then, on the elapse of a preselected period of time (about 0.1 second to 0.5 second in the illustrative embodiment), the controller100lowers the tray1(step S6). As soon as the sensor SN7turns on (YES, step S7), the controller100stops the movement of the tray2.

Subsequently, the controller100determines whether or not the sensor SN6is in an ON state (step S9). When the sensor SN6turns on (YES, step S9), the controller100once stops the movement of the tray1(step S10), then raises the tray1by a preselected distance (amount) (step S11), and then stops it (step S12). The tray1is now ready to receive papers via the outlet E2. Thereafter, the controller100sends a signal representative of the cancellation of the stand-by state to the copier G or the computer (step S13). In response, a paper is transferred from the copier G to the finisher (step S14) and therefrom to the tray1(step S15).

If the answer of the step S7is NO, meaning that the sensor SN7is in an OFF state, the controller100determines whether or not the sensor SN6is in an ON state (step S16). When the sensor SN6turns on (YES, step S16), the controller once stops the movement of the tray1(step S17), then relates the tray1by a preselected distance (amount) (step S18), and then stops it (step S19). As a result, the tray1brought to the outlet E2. Further, the controller100determines whether or not the sensor SN7is in an ON state (step S20). If the answer of the step S20is YES, the controller stops the movement of the tray2(step S21). This is followed by the step S13.

Assume that the tray2is selected. Then, as shown inFIGS. 45 and 46, the controller100determines whether or not the sensor SN5is in an ON state. If the sensor SN5is in an OFF state, the controller100raises the tray1which would obstruct the positioning of the tray2at the outlet E2(step S1). Then, on the elapse of a preselected period of time (about 0.1 second to 0.5 second in the illustrative embodiment) (step S2), the controller100raises the tray2(step S3). As soon as the sensor S57turns on (YES, step S4), the controller100stops the movement of the tray1(step S5).

Subsequently, the controller100determines whether or not the sensor SN6is in an ON state (step S6). When the sensor SN6turns on (YES, step S6), the controller100once stops the movement of the tray2(step S7), then lowers the tray2by a preselected distance (amount) (step S8), and then stops it (step S9). The tray2is now ready to receive papers via the outlet E2. Thereafter, the controller100sends a signal representative of the cancellation of the stand-by state to the copier G or the computer (step S10). In response, a paper is transferred from the copier G to the finisher (step11) and therefrom to the tray2(step12).

If the answer of the step S4is NO, meaning that the sensor SN5is in an OFF state, the controller100determines whether or not the sensor SN6is in an ON state (step S13). When the sensor SN6turns on (YES, step S13), the controller once stops the movement of the tray2(step S14), then lowers the tray2by a preselected distance (amount) (step S15), and then stops it (step S16). Thereafter, the controller determined whether or not the sensor SN5is in an ON state (step S17). If the answer of the step S17is YES, the controller100stops the movement of the tray1(step S18). As a result, the tray2brought to the outlet E2. This is followed by the step S10.

A third tray control procedure available with the illustrative embodiment will be described with reference toFIGS. 47-50. Should the trays1and2each be moved at a particularly timing in order to avoid collision, the total period of time necessary for the movement of the trays1and2would be increased. This embodiment is capable of solving this problem.

As shown inFIGS. 47 and 48, when the controller100receives a paper output request from the copier G or the computer connected thereto (step S1), it sends an answer representative of a stand-by state to the copier G or the computer (step S2). The controller100determines whether or not the tray1is selected (step S3) and determines whether or not the sensor SN7is in an ON state. If the answer of the step S3is YES and if the sensor SN7is in an OFF state, the controller100determines that the tray2is positioned above the sensor SN7, and lowers the tray2at a first speed1(step S4). At the same time, the controller100lowers the tray1at a second speed2(step S5). The speed1is selected to be higher than the speed2, i.e., the tray to be retracted is moved at a higher speed than the tray to be brought to the outlet E2. This is done by controlling the motors50and51that are implemented by stepping motors.

Subsequently, the controller determines whether or not the sensor SN7is in an ON state (step S8), and stops the movement of the tray2as soon as the sensor SN7turns on (step S7).

Subsequently, the controller100determines whether or not the sensor SN6is in an ON state (step S8). When the sensor SN6turn on (YES, step S6), the controller100once stops the movement of the tray1(step S9), then raises the tray1by a preselected distance (amount) at the speed2(step S10), and then stops it (step S11). The tray1is now ready to receive papers via the outlet E2. Thereafter, the controller100sends a signal representative of the cancellation of the stand-by state to the copier G or the computer (step S12). In response, a paper is transferred from the copier G to the finisher (step S13) and therefrom to the tray1(step S14).

If the answer of the step S6is NO, meaning that the sensor SN7is in an OFF state, the controller100determines whether or not the sensor SN6is in an ON state (step S15). When the sensor SN6turns on (YES, step S15), the controller once stops the movement of the tray1(step S16), then raises the tray1at the speed2by a preselected distance (amount) (step S17), and then stops it (step S18). Further, the controller100determines whether or not the sensor SN7is in an ON state (step S19). If the answer of the step S19is YES, the controller stops the movement of the tray2(step S20). This is followed by the step S12.

Assume that the tray2is selected. Then, as shown inFIGS. 49 and 50, the controller100determines whether or not the sensor SN5is in an ON state. If the sensor SN5is in an OFF state, the controller100raises the tray1at the speed1(step S1) while raising the tray2at the speed2(step S2). Then, the controller100determines whether or not the sensor SN5is in an OFF state (step S3), and stops the movement of the tray1when the sensor SN5turns on (YES, step S5).

Subsequently, the controller100determines whether or not the sensor SN6is in an ON state (step S5). When the sensor SN6turns on (YES, step S5), the controller100once stops the movement of the tray2(step S6), then lowers the tray2at the speed2by a preselected distance (amount) (step S7), and then stops it (step S8). The tray2is now ready to receive papers via the outlet E2. Thereafter, the controller100sends a signal representative of the cancellation of the stand-by state to the copier G or the computer (step S9). In response, a paper is transferred from the copier G to the finisher (step10) and therefrom to the tray2(step11).

If the answer of the step S3is NO, meaning that the sensor SN5is in an OFF state, the controller100determines whether or not the sensor SN6is in an ON state (step S12). When the sensor SN6turns on (YES, step S12), the controller once stops the movement of the tray2(step S13), then lowers the tray2at the speed2by a preselected distance (amount) (step S14), and then stops it (step S15). Thereafter, the controller determined whether or not the sensor SN5is in an ON state (step S16). If the answer of the step S16is YES, the controller100stops the movement of the tray1(step S17). As a result, the tray2brought to the outlet E2. This is followed by the step S9.

As stated above, the fifth embodiment achieves the following advantages.

(1) A tray selected is brought to the outlet during finish processing. This reduces a period of time relating to the movement of the trays end therefore the entire finishing time.

(2) A plurality of trays each are brought to the outlet independently of each other. This implements a mass paper discharge function with a single outlet.

(3) The tray that would obstruct the tray selected is retracted first. The trays are therefore prevented from colliding with each other.

(4) The tray to be retracted is moved at a higher speed than the tray to be located at the outlet. This, coupled with the fact that the two trays start moving at the same time, obviates a wasteful time otherwise required to prevent the trays from colliding with each other.

Sixth Embodiment

This embodiment is directed toward the sixth object sated earlier. The operation of the control means100unique to this embodiment will be described with reference toFIGS. 51-53in addition toFIGS. 1-8.

Referring again toFIG. 1, the controller100, i.e., CPU102of the illustrative embodiment sets up any one of the following four different paper conveyance modes:

(1) conveyance along a first route A1(corresponding to the non-staple route B)

(2) conveyance along a second route A2(corresponding to the staple route A)

(3) conveyance along a third route A3

(4) paper discharge to either one of first and second trays selected

In the conveyance mode (1), when the sensor S1senses a paper, the path selectors20and21are switched to steer the paper to the outlet E2.

In the conveyance mode (2), when the sensor SN1senses a paper, the path selector21is switched to steer the paper to the second route A2. The roller6, brush roller6aand tap roller9are caused to operate. As soon as the sensor SN3senses a number of papers expected to be stapled together, the jogger fence11positions the edges of the papers, and then the stapler S staples the papers. Subsequently, the belt10awith the catch10is driven to convey the stapled paper stack to the outlet E2.

In the conveyance mode (4), one of the first and second trays is selected on the basis of a command received from, e.g., the computer connected to the copier G. The tray selected is brought to the outlet E2. Specifically, in response to the above command, the CPU102determines the current positions of the trays1and2, returns the trays1and2to their home positions, and then locates the tray selected at the outlet E2.

As shown inFIG. 51, on the power-up of the copier G, the controller100moves each of the trays1and2to the respective home position. The home position of the tray1is a position that the end fence1areaches when raised by a preselected distance after being sensed by the sensor SN5. The home position of the tray2is a position where the sensor SN7senses the tray2.

InFIG. 51, on the power-up of the copier G, the controller100determines whether or not the sensor SN7is in an ON state, i.e., whether or not it has sensed the tray2(step S1). If the answer of the step S1is NO, the controller100lowers the tray2via the motor51(step S2), determining that the tray2is located above the sensor SN7. The controller100turns off the motor51as soon as the sensor SN7senses the tray2, thereby stopping the movement of the tray2(step S3). As a result, the tray2is brought to its home position.

Subsequently, the controller100determines whether or not the sensor SN5responsive to the tray1is in an ON state (step S4). If the answer of the step S4is NO, the controller100raises the tray1via the motor50(step S5). As soon as the sensor SN5senses the tray1(YES, step S4), the controller100stops the movement of the tray1and then lowers it (step S6). When the sensor SN6senses the tray1being lowered (YES, step S7), the controller100stops the movement of the tray1, then raises the tray1by a preselected distance, and then stops it (step S8). As a result, the tray1is located at its home position and ready to stack papers thereon. In this manner, in the conveyance modes (1) and (2), the tray1serves as a main tray for stacking papers sequentially driven out of the copier G.

When the tray1is selected via, e.g., the computer, the controller100executes a sequence of steps shown in FIG.52. As shown, the tray1is brought to the outlet E2by a procedure similar to the procedure described with reference to FIG.51.

On the other hand, when the tray2is selected, the controller100executes a sequence of steps shown in FIG.53. As shown, the controller100determines whether or not the sensor SN5is in an ON state, i.e., whether or not it has sensed the tray1(step S1). If the answer of the step S1is NO, the controller100raises the tray1via the motor50(step S2). As soon as the sensor SN5senses the tray1, the controller100turns off the motor50and thereby stops the movement of the tray1(step S3).

Subsequently, the controller100raises the tray2via the motor51(step S51). When the sensor SN6senses the tray2(YES, step S5), the controller100turns off the motor51, then lowers the tray2by a preselected distance (step S6), and then causes papers to be stacked on the tray2. Every time the sensor SN6senses a paper (step S7), the controller100repeatedly lowers the tray2by a preselected amount (step S8). In this manner, the top of a paper stack on the tray2is constantly held at a height where other papers sequentially coming out via the outlet E2can be stacked on the tray2.

As stated above, when either one of the two layers1and2is selected, papers can be sequentially stacked on the tray selected. Moreover, because the tray2has its end fence implemented the wall of the finisher, it allows the trailing edges of papers to be positioned over a broader range than the tray1and can therefore accommodate a great number of papers. The procedure shown inFIG. 52or53is continuously executed until the number of papers indicated by, e.g., the computer have been stacked, although not shown specifically.

In the above embodiment, the tray1or2is selected in accordance with a command received from, e.g., a computer. Alternatively, an arrangement may be made such that when an interrupt mode, for example, is selected in a copy mode, the controller100selects a tray other than one being used and causes papers output in the interrupt mode to be stacked; the tray may even by the proof tray.

As stated above, the sixth embodiment achieves the following advantages.

(1) At least one of a plurality of trays has an end fence and a stacking surface movable up and down in synchronism with each other. In addition, one tray has an end fence implemented by the wall of the finisher body. The trays can therefore be selectively located at the paper discharge position. The tray whose end fence is implemented by the side wall of the finisher is capable of accommodating a great number of papers with a simple configuration.

(2) The trays each are driven by a respective drive source and can therefore be freely arranged. This successfully prevents the finisher from increasing in size.

(3) The trays share common guide rails. This reduces the cost and size of the finisher while simplifying the construction of the finisher.

(4) The tray having the end fence and stacking surface movable up and down in synchronism has its capacity determined by the end fence. Such trays can be arranged at a constant pitch. Therefore, by driving a plurality of trays with exclusive drive sources, it is possible to divide the trays into a group that can be arranged at the above constant pitch and the other group. This obviates an increase in cost ascribable to an increase in the number of drive sources.

(5) The guide rails each include a bent portion for preventing the end fence of the tray from interfering with the paper discharging means. This allows the paper discharging means to overlap the wall of the finisher and therefore to prevent the trailing edges of papers from returning to between the discharging means and the wall of the finisher.

(6) The bent portion of each guide rail has a length smaller than the pitch of guide means arranged on the tray. This reduces the tilting angle of the tray moving along the guide portion and thereby prevents a paper stack from dropping from the tray.

(7) Because the drive means for up-and-down movement are so located as not to interfere with each other, the belts forming part of the drive means can be arranged in parallel to each other. It follows that the finisher body can be reduced in size in the direction perpendicular to the parallel belts.

(8) The tray whose end fence is implemented by the wall of the finisher is located below the other trays. Therefore, a space below the lowermost tray can be used with priority, so that a great number of papers can be stacked on the lowermost stray.

(9) Because the tray selected is brought to the paper discharge position independently of the other trays, it allows papers to be stacked thereon without effecting the other trays.

Seventh Embodiment

This embodiment is directed mainly toward the seventh object stated earlier. This embodiment also differs from the previous embodiments in that the sensor SN9responsive to the stand-by position of the tray2is absent.

As shown inFIG. 54, a roller support member84is supported at its rear end in the paper discharge direction and angularly movable up and down. The driven roller8acooperative with the drive roller8is rotatably supported by the other or free end of the roller support member84. A microswitch or limit switch86(seeFIGS. 56-60) is mounted on a bracket, not shown, above the roller support member84and turned on or turned off by the displacement of the roller support member84. Such an arrangement will be described more specifically later.

A shift mode is available with the illustrative embodiment. In the shift mode, papers are directly discharged to the tray1or2by way of the non-staple route B,FIG. 1. Ashift signal is generated between consecutive jobs, i.e., between the last paper of a stack and the first paper of the next stack. In response, a shift motor88(seeFIG. 2) is energized to shift the tray1or2in the direction of thrust, i.e., the direction perpendicular to the direction of paper discharge in a horizontal plane, preparing the tray for the next stack of papers. Consequently, consecutive paper stacks are offset from each other on the tray1or2.

The essential part of the mechanism for moving the tray2up and down in the illustrative embodiment will be described with reference toFIGS. 4 and 55. As shown inFIG. 4, the output power of the motor51is transferred to a gear64mounted on the drive shaft41avia a worm wheel60and an intermediate gear62. The mechanism includes a safety measure for coping with the unusual downward movement of the tray2, as follows. As shown inFIG. 55, a gear66coaxial with the worm wheel60is positioned at the rear of the worm wheel60. The worm wheel60is held in mesh with the worm gear58by a spring68. One of the worm wheel60and gear66is formed with a recess while the other of them is formed with a lug. The recess and lug are capable of meshing with each other in the direction of rotation, but capable of separating from each other in the axial direction. The recess and lug allow the worm wheel60and gear66to mesh with each other and rotate in synchronism so long as the torque remains in a preselected range.

When the tray2moves downward in an unusual manner or loaded with an excessive number of papers, the above recess and lug move away from each other with the result that the worm wheel60moves to a position indicated by a dash-and-dots line inFIG. 55against the action of the spring68. Consequently, the worm gear58and worm wheel60are released from each other, causing the tray2to stop moving. Such a mechanism is also applied to the other tray1.

A tray control procedure particular to this embodiment will be described hereinafter. In the illustrative embodiment, the home position of the tray1is a position that the upper end of the end fence1areaches when raised by a preselected distance after being sensed by the sensor SN6. The home position of the tray2is a position where the sensor SN7senses the tray2. On the power-up of the copier G, the controller100determines whether or not the sensor SN7is in an ON state. If the sensor SN7is in an OFF state, meaning that it has not sensed the tray2, the controller100lowers the tray2via the motor51, determining that the tray2is positioned above the lower limit position. The controller100stops lowering the tray2when the sensor SN7senses the tray2.

Subsequently, the controller100determines whether or not the sensor SN5responsive to the retracted position is in an ON state. If the sensor SN5is in an OFF state, the controller100once raises the tray1via the motor50and then stops the tray1as soon as the sensor SN5senses it. The controller100again lowers the tray1until the sensor SN6senses the upper end of the end fence1a,then raises the tray1by a preselected distance, and then stops it.

Assume that the operator selects the tray1on the copier G or the computer connected thereto. Then, the controller100first determines whether or not the sensor SN7is in an ON state. If the sensor SN7is in an OFF state, the controller100lowers the tray2via the motor51, determining that the tray2is positioned above the lower limit position. The controller100stops the movement of the tray2when the sensor SN7senses the tray2. Subsequently, the controller100determines whether or not the sensor SN6is in an ON state. If the sensor SN5is in an OFF state, the controller100once raises the tray1via the motor60and then stops the tray1when the sensor SN5senses it. The controller again lowers the tray1until the sensor SN6senses the upper end of the end fence1a.Thereafter, the controller100raises the tray1by a preselected amount.

When the sensor SN5is in an ON state, the controller100lowers the tray1until the sensor SN6senses the upper end of the end fence1a.Subsequently, the controller100raises the tray1by a preselected distance and then stops it. In this condition, papers are sequentially stacked on the tray1.

When the tray2is selected on the copier G or the computer connected thereto, the controller100first determines whether or not the sensor SN5is in an ON state. If the sensor SN5is in an OFF state, the controller100raises the tray1until the sensor SN5senses it. Subsequently, the controller100raises the tray2until the sensor SN6senses it, and then lowers the tray2by a preselected distance. In this condition, papers are sequentially stacked on the tray2. Every time the top of the stack on the tray2is sensed by the sensor SN6, the controller100lowers the tray2by a preselected distance in order to stack a great number of papers on the tray2. The controller100determines that the tray2is full when the sensor SN7senses the tray2and when the sensor SN6senses the top of the stack.

The arrangement including the roller support member84,FIG. 54, and the safety measure unique to the illustrative embodiment will be described more specifically. As shown inFIG. 56, the roller support member84is rotatable up and down about a fulcrum84a.The driven roller8ais pressed against the drive roller or outlet roller8due to its own weight and the weight of the roller support member84. The underside84of the roller support member84serves as a paper guide and forms an outlet path92in cooperation with a guide90associated with the drive roller8.

As shown inFIG. 57, when papers are discharged in the form of a stack, the roller support member84is angularly moved in accordance with the thickness t of the stack. As a result, the driven roller8ais moved away from the drive roller8.

When, the roller support member84moves upward over an angle slightly greater than one corresponding to the maximum thickness t of papers or paper stack, the roller support member84contacts the microswitch86and turns it off. In the illustrative embodiment, the maximum thickness t is assumed to be the thickness of a stapled stack of fifty papers. It follows that when the operator's hand or similar object whose thickness is greater than the thickness t is put between the roller8and8a,the microswitch86turns off.

Specifically, as shown inFIG. 58, a diode92is connected in parallel between the motor50assigned to the tray1and the microswitch86. When the thickness of the papers or paper stack discharged is less than t, the microswitch86remains in its ON state. In this condition, the tray1is movable up and down, as needed.

Assume that an object having a thickness greater than the thickness t is put between the rollers8and8a,moving the roller support member84by more than the preselected angle corresponding to the thickness t. Then, as shown inFIG. 59, the upper surface of the roller support member84presses the contact of the microswitch86and thereby turns off the microswitch86. As a result, a current stops flowing through the elevation side of a motor driver, causing the tray1to stop rising.

More specifically, as shown inFIG. 60, when the operator's hand or similar object94is put between the rollers8and8awhile the tray1is retracting upward from the paper discharge position, the tray1stops rising. This protects the operator from injury and protects the finisher from damage ascribable to the object and tray1otherwise hitting against each other.

As stated above, the illustrative embodiment achieves the following unprecedented advantages.

(1) When the thickness of papers or paper stack discharged by the outlet roller pair is greater than the preselected thickness, the tray is inhibited from moving, e.g., upward. This protects the operator from injury and protects the finisher from damage.

(2) Because the roller support member has a paper guide surface, an extra paper guide is not necessary.

(3) The switch means is actuated at a position exceeding the thickness that the finisher itself can discharge. It follows that optimal safety matching with the finisher is achievable.

Eighth Embodiment

This embodiment is directed mainly toward the eighth object stated earlier. This embodiment is identical with the seventh embodiment as to the shift mode operation and the construction and movement of the tray2. As shown inFIGS. 61-63, this embodiment differs from the previous embodiments as to the positions of the sensors SN5and SN7. Again, the tray1expected to retract upward away from the outlet2includes the end fence1ain order to obviate the need for a sophisticated shutter mechanism otherwise arranged in the outlet E2.

A tray control procedure unique to the eighth embodiment will be described hereinafter. As shown inFIG. 9, the home position of the tray1is a position where the sensor SN5responsive to the retracted position senses the upper end of the end fence1a.The home position of the tray2is a position where the sensor SN9responsive to the retracted position senses the lower rear end (lower end hereinafter) of the tray2in the direction of paper discharge.

FIGS. 64 and 65demonstrate how the controller100locates the trays1and2at their home positions. The controller100may cause the trays1and2to start moving at the same time, if desired. As shown, on the power-up of the copier G, initialization begins (step S1). The controller100determines whether or not the sensor SN7is in an ON state (step S2). If the sensor SN7is in an OFF state (NO, step S2), the controller100lowers the tray2via the motor51(step S3), determining that the tray2is positioned above the lower limit position. Then, the controller100determines whether or not the sensor SN9is in an ON state (step S4). If the sensor of the step S4is YES, the controller100stops moving the tray2(step S5) and again raises it (step S6). Subsequently, the controller100determines whether or not the sensor SN9is in an OFF state (step S7), and stops the tray2(step S8) when the sensor SN9turns off (YES, step S7). As a result, the lower end of the tray2is located at the stand-by position or home position to which the sensor SN9is responsive.

If the answer of the step S2is YES, meaning that the tray2is located at the lower limit position, the controller100raises the tray2(step S9) and determines whether or not the sensor SN9turns on (step S10). When the sensor SN9turns on (YES, step S10), meaning that it senses the upper end of the tray2), the controller100continuously determines the status of the sensor SN9(step S11). As soon as the sensor SN9turns off (YES, step S11), the controller100stops raising the tray2. Consequently, the lower end of the tray2is located at the stand-by position.

When the tray2is located between the lower limit position and the stand-by position, i.e., if the sensor SN9is in an OFF state in the step S4, the controller100determines whether or not the sensor SN7is in an ON state (step S13). If the answer of the step S13is YES, the controller stops the tray2(step S14) and then raises it (step S15). Subsequently, the controller199determines whether or not the sensor SN9is in an ON state (step S16). If the answer of the step S16is YES, meaning that the sensor S16has sensed the upper end of the tray2, the controller determines the status of the sensor SN9(step S17). When the sensor SN9turns off (YES, step S17), the controller100stops moving the tray2(step S18). Consequently, the lower end of the tray2is located at the stand-by position.

After the step S18, the controller100determines whether or not the sensor SN5is in an ON state (step S19). If the answer of the step S19is NO, the controller100raises the tray1via the motor50(step S20) and continuously determines the status of the sensor SN5(step S21). When the sensor SN5turns on (YES, step S21), the controller100stops moving the tray1(step S22).

Reference will again be made toFIG. 12showing a specific condition wherein papers are sequentially stacked on the tray2while the tray1is held in its retracted position. The position of the tray2for receiving the papers via the outlet E2is coincident with the position where the sensor SN6secures the upper end of the tray2or the top of papers stacked thereon. As shown inFIG. 13, when papers are sequentially stacked on the tray1while the tray2is held in its retracted position, the tray2is held in its lower limit position in order to prevent papers stacked thereon from contacting the tray1.

In the condition shown inFIG. 12, when the sensor SN6senses the top of sheets stacked on the tray2, the controller100lowers the tray2by a preselected distance. The controller100repeats this operation when a great number of papers are stacked on the tray2. The controller100determines that the tray2is full when the sensor SN9senses the lower end of the tray2and when the sensor SN6senses the top of papers stacked on the tray2, as shown in FIG.14.

The controller100detects the full state of the tray2when the tray2is positioned above the lower limit position, so that the tray can be switched from the tray2to the tray1without the papers being removed from the tray2. In the illustrated embodiment, the sensor SN9responsive to the stand-by position serves to sense the full state of the tray2at the same time.FIG. 15shows a specific condition wherein the full tray2is retracted to its lower limit position while the tray1is brought to the outlet E2.

The full tray2must be retracted by an amount great enough for the tray1to be located at the position for receiving papers from the outlet E2. Therefore, as shown inFIG. 14, the above amount is determined by the amount of papers that can be stacked on the tray1, i.e., the height H1of the end fence1a.More specifically, if the sensor SN9is positioned above the sensor SN7by a distance H (between the stand-by position and the lower limit position) greater than the height H1, the sensor SN9can play the role of a tray2full sensor (full sensing means) and a stand-by position sensor at the same time. However, the prerequisite is that the distance H1between the sensors SN6and SN9(overall height of the full tray2including papers) be greater than or equal to the distance H.

Assume that papers should be discharged to the tray1when the trays1and2each are held in the respective home position. Then, as shown inFIGS. 66 and 67, the controller100lowers or retracts the tray2(step S1). When the sensor SN7responsive to the lower limit position turns on (YES, step S2), the controller100stops lowering the tray2(step S3) and lowers the tray1(step S4). Subsequently, when the sensor SN6turns on (YES, step S5), meaning that it has sensed the lower end of the tray1, the controller100continuously determines the status of the sensor SN6. When the sensor SN6turns off (YES, Step S6), the controller100stops lowering the tray1(step S7).

After the step S7, the controller100determines whether or not the sensor SN9is in an OFF state (step S8). If the answer of the step S8is YES, the controller100raises the tray2to the retracted position (step S9), determining that the number of papers on the tray2is small. As soon as the sensor SN9turns on, i.e., senses the upper end of the tray2(YES, step S10), the controller100continuously determines the status of the sensor SN9(step S11). When the sensor SN9turns off (YES, step S11), the controller stops raising the tray2(step S12). As a result, the lower end of the tray2is located at the retracted position.

When the tray2is selected in place of the tray1later, the tray2moves from the above stand-by position closer to the outlet E2than the lower limit position, or original retracted position, to the outlet E2. This reduces a period of time necessary for the tray2to reach the outlet E2.

Assume that the number of papers stacked on the tray2is small when papers are being discharged to the tray1. In this condition, the trays1and2must be prevented from colliding with each other even when the tray2is raised to the position where the sensor SN9senses the lower end of the tray2(stand-by position). To meet this requirement, the illustrative embodiment is so configured as to satisfy relations of H3≧H1and H1≧H2+H3, as shown in FIG.68.

Reference will be made toFIGS. 69 and 70for describing a tray control procedure to be executed when the trays1and2each are held at the respective home position, when papers should be discharged to the tray1, and when papers are removed from the tray2. As shown, the controller100lowers or retracts the tray2(step S1). As soon as the sensor SN7senses the tray2and turns on (YES, step S2), the controller100stops lowering the tray2(step S3) and lowers the tray1(step S4). Subsequently, the controller100determines whether or not the sensor SN6is in an ON state (step S5). If the answer of the step S5is YES, the controller100continuously determines the status of the sensor SN6(step S6). When the sensor SN6turns off (YES, step S6), the controller100stops lowering the tray1(step S7).

Subsequently, the controller100determines whether or not the sensor SN9is in an OFF state (step S8). As shown inFIG. 71, when the papers are removed from the tray2, the sensor SN9turns off. If the answer of the step S8is YES, the controller100raises the tray2so as to use the stand-by position as the retracted position (step S9), determining that the number of papers on the sheet2is small. When the sensor SN9turns on (YES, step S10), the controller continuously determines the status of the sensor SN9(step S11). When the sensor SN9turns off (YES, step S11), the controller100stops raising the tray2(step S12). Consequently, the lower end of the tray2is located at the stand-by position, as shown in FIG.72.

When the tray2is selected in place of the tray1later, the tray2moves from the above stand-by position closer to the outlet E2than the lower limit position, or original retracted position, to the outlet E2. This reduces a period of time necessary for the tray2to reach the outlet E2.

While the above embodiment includes a single tray1, it is similarly practicable with a plurality of trays1. The finisher may, of course, be constructed integrally with the copier G or similar image forming apparatus. If desired, the number of papers stacked on the tray2may be calculated by using the thickness of each paper and the number of papers.

As stated above, the illustrative embodiment achieves various advantages, as enumerated below.

(1) When the number of papers stacked on the lower tray is small, the stand-by position of the lower tray above the lower limit position is used as the retracted position. This reduces the period of time necessary for the lower tray to move to the outlet and thereby enhances rapid operation.

(2) The stand-by position sensing means determines the number of papers stacked on the lower tray. The decision is therefore easy and accurate.

(3) When the stand-by position sensing means assigned to the lower tray turns off due to the removal of papers from the lower tray, the stand-by position is used as the retracted position. This also reduces the period of time necessary for the lower tray to reach the outlet.

(4) When the retracted position of the lower tray is used as the stand-by position, the upper and lower trays are surely prevented from colliding with each other.

(5) The stand-by position sensing means plays the role of the full sensing means at the same time and therefore eliminates the need for extra full sensing means which would sophisticate the construction and increase the cost.