Patent Publication Number: US-6988724-B2

Title: Sheet-fed printing apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a sheet-fed printing apparatus for printing on sheets of printing paper and, more particularly, to a delivery section of the sheet-fed printing apparatus. 
   2. Description of the Background Art 
   A sheet-fed printing apparatus for printing on sheets of printing paper comprises a delivery section (or a paper discharge section) for receiving a stack of printed sheets.  FIG. 7  is a partial sectional view of a delivery section  110   d  and its surrounding parts in a conventional sheet-fed printing apparatus  110 . The delivery section  110   d  comprises a delivery table  102  for placing thereon a printed sheet pa discharged from a chain delivery  101  for transporting printed sheets. The printed sheet pa gripped by a gripper  103  carried around by the chain delivery  101  is released (or dropped) from over the delivery table  102 . At this time, the leading edge of the printed sheet pa is hit against a sheet-trapping element  104 , whereby the printed sheet pa falls upon the delivery table  102 . In this manner, such printed sheets pa are successively stacked in a fixed position, and are referred to as stacked printed sheets ps The delivery table  102  is provided with a vertical movement element  105  for moving the delivery table  102  gradually downwardly each time the number of stacked printed sheets ps increases. This is to provide a constantly fixed distance (or vertical spacing) between the printed sheet pa and the delivery table  102  or the stacked printed sheets ps when the printed sheet pa is discharged. 
   An operator of the sheet-fed printing apparatus  110  is required to take printed samples out of the stacked printed sheets ps during the printing operation. Since the judgment as to whether or not printed sheets are acceptable and the adjustment of the amount of ink supply are made based on a check of the printed samples, the operator must take out printed samples at suitable sampling intervals while the sheet-fed printing apparatus  110  is in operation. 
   To this end, the sheet-trapping element  104  in the conventional sheet-fed printing apparatus  110  is capable of an opening movement from a closed position  104   a  indicated by the dotted lines to an open position  104   b  indicated by the solid lines. In synchronism with the opening movement of the sheet-trapping element  104 , a temporary sheet-receiving element  106  pivots from an inoperative position not shown to an operative position shown in  FIG. 7 . Then, the printed sheet pa is discharged, with the leading edge thereof lifted up by the temporary sheet-receiving element  106 . A printed sheet pb indicated by a dotted line in  FIG. 7  is shown in such a lifted position. 
   Thus, the operator can pick one or some sheets out of the previously stacked printed sheets ps under the printed sheet pa lifted by the temporary sheet-receiving element  106 . After the printed samples are taken in this manner, the sheet-trapping element  104  is returned to the closed position  104   a  indicated by the dotted lines, and the temporary sheet-receiving element  106  accordingly returns to its inoperative position not shown. Then, the printed sheet pb received in the temporary sheet-receiving element  106  is discharged onto the delivery table  102 , and is additionally stacked on the previously stacked printed sheets ps. 
   With the above-mentioned arrangement, the operator can manually take out the printed samples with ease in principle. It is, however, actually difficult for the operator to take out the printed samples quickly from the sheet-fed printing apparatus  110  in high-speed operation. Additionally, the delivery section  110   d  is often provided with a cover thereon so that the operator cannot easily gain access to movable parts of the delivery section  110   d . As an example, the delivery section  110   d  may be an interlocked cover mounted thereon and is adapted to prevent the sheet-fed printing apparatus  110  from operating when the cover is open. In such a case, the operator cannot take out the printed samples during the printing operation, as discussed above. 
   SUMMARY OF THE INVENTION 
   The present invention is intended for a sheet-fed printing apparatus for printing on sheets of printing paper and, more particularly, for a mechanism for discharging printed sheets. 
   According to the present invention, the sheet-fed printing apparatus comprises: a) a delivery section capable of receiving a stack of printed sheets; b) a transport element for transporting a printed sheet to a release position to drop the printed sheet in the release position; c) shielding element for shielding the delivery section and the transport element from an external environment of the sheet-fed printing apparatus, the shielding element having an opening permitting the printed sheet to pass through; and d) a printed sheet discharge element capable of discharging at least a portion of the printed sheet dropped in the release position out of the sheet-fed printing apparatus through the opening. 
   Preferably, the shielding element comprises a first shielding element openable and closable for shielding the delivery section from the external environment of the sheet-fed printing apparatus, and a second shielding element for shielding at least the transport element from the external environment of the sheet-fed printing apparatus; and the printed sheet discharge element is capable of discharging at least the portion of the printed sheet out of the sheet-fed printing apparatus through the opening when the first shielding element is closed. 
   This allows an operator to obtain the printed sheet partially discharged by the printing sheet discharge element as a printed sample without the need to open the first shielding element to gain direct access to the delivery section while the first shielding element is closed and the sheet-fed printing apparatus is in operation. 
   Preferably, the release position includes a first release position and a second release position; the transport element is capable of selectively dropping the printed sheet in the first release position; and the printed sheet is forcedly dropped in the second release position when the printed sheet is not dropped in the first release position. 
   This provides different destinations to which the printed sheet is discharged, depending upon whether or not a printed sample is needed. If the printed sample is needed, the operator can easily obtain the printed sample without the need to gain direct access to the delivery section. 
   It is therefore an object of the present invention to provide a sheet-fed printing apparatus which allows an operator to obtain a printed sample easily even when the sheet-fed printing apparatus is in operation. 
   These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional side view of a delivery section and its surrounding parts in a sheet-fed printing apparatus according to a first preferred embodiment of the present invention; 
       FIG. 2  is a front view of the delivery section; 
       FIG. 3  is a view showing the construction of first and second sheet-trapping elements; 
       FIG. 4  is a sectional side view of the delivery section according to a modification of the first preferred embodiment; 
       FIG. 5  is a view showing the construction of the first and second sheet-trapping elements and their surrounding parts according to another modification of the first preferred embodiment; 
       FIG. 6  is a sectional side view of the delivery section according to a second preferred embodiment of the present invention; and 
       FIG. 7  is a sectional side view of a delivery section of a conventional sheet-fed printing apparatus. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Preferred Embodiment 
   A first preferred embodiment according to the present invention will now be described with reference to the drawings.  FIG. 1  is a sectional side view showing an example of a delivery section  1   d  of a sheet-fed printing apparatus  1  according to the present invention. As illustrated in  FIG. 1 , the delivery section  1   d  of the first preferred embodiment comprises a delivery table  2  for receiving successive printed sheets Pa transported theretoward by a chain delivery CD  1  serving as a transport element, to form a stack of printed sheets thereon; a delivery section cover  3  for covering the delivery section  1   d ; and a sheet-trapping mechanism  4  for positioning the leading edge of a discharged printed sheet Pa. 
   The chain delivery CD 1  is a known mechanism, and includes grippers  5  (only one of which is shown in  FIG. 1 ) each for gripping the leading edge of the printed sheet Pa, and a chain  6  for carrying the grippers  5  attached thereto around. A gripper  5  gripping the printed sheet Pa is caused to make an opening movement by the action of a cam mechanism not shown when it is over the delivery table  2 , thereby releasing (or dropping) the printed sheet Pa onto the delivery table  2  or onto stacked printed sheets Ps piled on the delivery table  2 . 
   The delivery table  2  is a table on casters for placing the stacked printed sheets Ps thereon, and is movable up and down by a vertical movement mechanism  7 . Specifically, the delivery table  2  is in a raised position near the gripper  5  at the commencement of printing, and is moved downwardly each time a new printed plate Pa is released and stacked, thereby to provide a constantly fixed distance that the printed sheets Pa fall from the grippers  5 . In some cases, the delivery table  2  is provided with a centering mechanism not shown for aligning the stacked printed sheets Ps in a direction perpendicular to the plane of the figure. 
   The delivery section cover  3  is a shielding member capable of opening and closing for covering the delivery section  1   d.  In conjunction with a fixed cover  8  provided also as a shielding member, the delivery section cover  3  prevents an operator from gaining access to the inside of the sheet-fed printing apparatus  1  during a printing operation. Specifically, a safety switch  9  for detecting whether the delivery section cover  3  is open or closed is provided in the closed position of the delivery section cover  3 . The operation of the safety switch  9  is always monitored by a controller  10  for controlling the operation of the sheet-fed printing apparatus  1 . When the safety switch  9  detects that the delivery section cover  3  is open, the controller  10  performs the process of, for example, stopping the operation of the sheet-fed printing apparatus  1  or actuating an alarm for alerting the operator and the like to a danger. 
     FIG. 2  is a view of the delivery section cover  3  as seen in the direction of the arrow A of  FIG. 1 . As shown in  FIG. 2 , a horizontally extending slit opening  11  is cut in an upper portion of the delivery section cover  3 . The opening  11  is located at a destination to which the gripper  5  drops the printed sheet Pa, and is sized to allow the printed sheet Pa to pass through. In this preferred embodiment, the opening  11  is positioned so that the printed sheet Pa discharged from the gripper  5  travels a predetermined flight path and then passes through the opening  11 . A pair of vertically extending openings  14  and a pair of vertically extending openings  15  which allow a pair of first sheet-trapping elements  12  and a pair of second sheet-trapping elements  13 , respectively, to be described later to pass through are formed between the delivery section cover  3  and the fixed cover  8 . Preferably, the openings  11 ,  14  and  15  are sized and shaped to prevent the operator from inserting his/her hand therethrough and gaining access to movable parts in the sheet-fed printing apparatus  1 . 
   The sheet-trapping mechanism  4  comprises the pair of first sheet-trapping elements  12  pivotable between an open position b indicated by the solid lines in  FIGS. 1 and 3  and a closed position c indicated by the dotted lines, and the pair of second sheet-trapping elements  13  pivotable between a closed position d indicated by the solid lines in  FIGS. 1 and 3  and an open position e indicated by the dotted lines. 
   The construction of the first and second sheet-trapping elements  12  and  13  will be described with reference to  FIG. 3 . Each of the first sheet-trapping elements  12  is an elongated plate-like member having a slightly bent forward end. The first sheet-trapping elements  12  are fixed to a rotary shaft  16  rotatably supported by a frame of the sheet-fed printing apparatus  1 , and are manually pivotable in a direction indicated by the double-headed arrow of  FIG. 3 . The pair of sheet-trapping elements  12  are arranged in a direction parallel to the leading edge of the printed sheet Pa, as shown in  FIG. 2 , and are integrally fixed to the rotary shaft  16 . 
   Each of the second sheet-trapping elements  13  is an L-shaped plate-like member, attached to a mounting metal piece  18 , supported by a rotary shaft  17 . The pair of sheet-trapping elements  13  are arranged in the direction parallel to the leading edge of the printed sheet Pa, as shown in  FIG. 2 , and are integrally fixed to the rotary shaft  17 . 
   Gears  19  and  20  are provided in coaxial relation with the rotary shafts  16  and  17 , respectively, and are in interlocking and meshing engagement with each other. Thus, the pivotal movement of the first sheet-trapping elements  12  drives the second sheet-trapping elements  13  to pivot in the opposite direction. More specifically, when the first sheet-trapping elements  12  are in the open position b, the second sheet-trapping elements  13  are in the closed position d. Conversely, when the first sheet-trapping elements  12  are in the closed position c, the second sheet-trapping elements  13  are in the open position e. 
   The closed position c of the first sheet-trapping elements  12  is inward of the sheet-fed printing apparatus  1  from the delivery section cover  3 . The first sheet-trapping elements  12 , when in the closed position c, can block the printed sheet Pa from passing through the opening  11 . The closed position d of the second sheet-trapping elements  13  is substantially level with the bottom of the opening  11 . When the second sheet-trapping elements  13  are in the closed position d, longitudinal flat portions  13   a  of the respective second sheet-trapping elements  13  project out over the stacked printed sheets Ps. The longitudinal flat portions  13   a  of the respective second sheet-trapping elements  13  in the closed position d are situated to guide the back surface of the printed sheet Pa to be discharged next for ease of the passage of the printed sheet Pa through the opening  11 . Bends  13   b  of the respective second sheet-trapping elements  13  are upright and are situated outside the delivery section cover  3  to function to stop the leading edge of the printed sheet Pa tending to pass through the opening  11 . Such an arrangement aligns the leading edges of printed sheets Pa successively discharged and then projecting outwardly of the opening  11 , and blocks the printed sheets Pa from passing through the opening  11 . 
   In the above-mentioned construction of the sheet-trapping mechanism  4 , when the first sheet-trapping elements  12  are maintained in the closed position c, discharged printed sheets Pa successively collide against the first sheet-trapping elements  12  and are stacked on the delivery table  2 . When an operator who wants to obtain printed samples manually opens the first sheet-trapping elements  12  to the open position b, the second sheet-trapping elements  13  pivot to the closed position d in synchronism with the first sheet-trapping elements  12 . In this state, the discharged printed sheets Pa pass through the opening  11 , but the leading edges of the printed sheets Pa are stopped by the bends  13   b  of the respective second sheet-trapping elements  13 . In other words, the printed sheets Pa are carried and held by the second sheet-trapping elements  13 , with the leading edges of the printed sheets Pa projecting outwardly of the delivery section cover  3 . Accessible printed sheets Pb shown in  FIG. 1  are in such a position. The operator takes a required number of printed samples out of the plurality of accessible printed sheets Pb carried on the second sheet-trapping elements  13 , thereby to obtain the printed samples while the delivery section cover  3  is closed. After taking out the printed samples carried on the second sheet-trapping elements  13 , the operator may return the first sheet-trapping elements  12  to the closed position c. 
   The first preferred embodiment is adapted so that the printed sheet Pa released from the gripper  5  is discharged directly through the opening  11  to the outside of the sheet-fed printing apparatus  1 . This eliminates the need to provide an additional transport driving source for discharging the printed sheet Pa. 
   Modifications of First Preferred Embodiment 
   (1) In the first preferred embodiment described above, the accessible printed sheets Pb which can become the printed samples are carried and held by the second sheet-trapping elements  13 . However, the second sheet-trapping elements  13  may be dispensed with.  FIG. 4  shows a discharge tray  21  provided in place of the second sheet-trapping elements  13 , as an example. The discharge tray  21  is a member mounted to the outer surface of the delivery section cover  3  and having a slide-down surface extending gently downwardly from the bottom of the opening  11  for receiving the accessible printed sheets Pb. In this modification, when the first sheet-trapping elements  12  are opened, the printed sheets Pa successively discharged out of the opening  11  are carried on the discharge tray  21  as the accessible printed sheets Pb completely slid down onto the discharge tray  21  or completely discharged outwardly of the sheet-fed printing apparatus  1 . A roller for guiding the back surfaces of the printed sheets Pa may be provided near the bottom of the opening  11  so that the printed sheets Pa completely slide down along the slide-down surface of the discharge tray  21  without making a stop at some midpoint. This roller may be adapted to always rotate, as required. 
   (2) The first and second sheet-trapping elements  12  and  13  are manually opened and closed in the first preferred embodiment, but may be opened and closed by a driving element such as a motor. In this case, the controller  10  preferably monitors the feed timing of the printed sheets Pa to cause the opening movement of the first sheet-trapping elements  12  to be timed with the feed of the printed sheets Pa. This allows the first sheet-trapping elements  12  to open in proper timed relation if the printing speed is high. 
   (3) In the first preferred embodiment, the opening  11  is cut in the upper portion of the delivery section cover  3  which is opened and closed. However, an opening may be formed in an intermediate portion of the delivery section cover  3  or formed in the fixed cover  8 . That is, an opening may be provided which permits the printed sheets Pa to pass through the cover placed forward of the falling path of the printed sheets Pa. 
   (4) So far as the scheme of taking out the printed samples is capable of taking the entire printed samples out of the sheet-fed printing apparatus  1  as described in Modification (1), this scheme may be combined with the scheme of Modification (2) to automate the taking out of the printed samples. For example, an input element is used to previously determine a required sampling interval and the required number of printed samples, and the operation of the first sheet-trapping elements  12  is controlled based on the number of printed sheets counted by a printed sheet counter. This allows the first sheet-trapping elements  12  to be held in the open position at the determined sampling intervals and for a length of time required to take out printed samples the number of which is previously determined, thereby achieving the automation of the taking out of a desired number of printed samples. 
   (5) In the first preferred embodiment, while the first sheet-trapping elements  12  are open, the printed sheet Pa is always discharged as the accessible printed sheet Pb to the second sheet-trapping elements  13 . Thus, a plurality of printed sheets Pa are discharged in some cases while the first sheet-trapping elements  12  are open during high-speed printing. If only a single printed sample is needed, a mechanism may be provided for stopping discharging subsequent printed sheets Pa to the second sheet-trapping elements  13 . 
     FIG. 5  shows such a modification which comprises a sensor  22  for detecting whether the first sheet-trapping elements  12  are open or closed, a sensor  23  for detecting whether or not a printed sheet Pa is discharged onto the second sheet-trapping elements  13 , and a temporary sheet-receiving element  24  insertable into a predetermined operative position (shown in  FIG. 5 ). 
   In this modification, when the first sheet-trapping elements  12  are opened and a printed sheet Pa is discharged as an accessible printed sheet Pb onto the second sheet-trapping elements  13 , the sensor  23  detects the presence of the accessible printed sheet Pb. The sensor  23  is, for example, an optical sensor capable of detecting the accessible printed sheet Pb through a through hole  13   c  formed in the second sheet-trapping elements  13 . 
   When the sensor  23  detects the accessible printed sheet Pb, the controller  10  causes a predetermined driving element to insert the temporary sheet-receiving element  24  from an inoperative position not shown into the operative position. For example, if the inoperative position is outward of a printed sheet discharge path in a direction perpendicular to the plane of the figure, the temporary sheet-receiving element  24  may be moved in the direction perpendicular to the plane of the figure by a slide movement mechanism such as a solenoid to enter the printed sheet discharge path. 
   After only the single accessible printed sheet Pb is discharged onto the second sheet-trapping elements  13 , a printed sheet Pa is carried as a temporarily carried printed sheet Pc on the temporary sheet-receiving element  24  even if the first sheet-trapping elements  12  are open. When the sensor  22  detects that the first sheet-trapping elements  12  are closed after the printed sample is removed from the second sheet-trapping elements  13 , the controller  10  returns the temporary sheet-receiving element  24  to its inoperative position. At the same time, the temporarily carried printed sheet Pc on the temporary sheet-receiving element  24  is transferred onto the delivery table  2 . This modification ensures the taking out of the single printed sample even at a high printing speed. 
   Second Preferred Embodiment 
   A second preferred embodiment according to the present invention will now be described with reference to  FIG. 6 .  FIG. 6  is a sectional side view showing a delivery section  30   d  of a sheet-fed printing apparatus  30  according to the second preferred embodiment. 
   As illustrated in  FIG. 6 , the delivery section  30   d  of the sheet-fed printing apparatus  30  comprises a chain delivery CD 2  for transporting printed sheets; a delivery table  31  for receiving successively discharged printed sheets to form a stack thereon; and covers  32  and  33  for covering said chain delivery CD 2  and the delivery table  31 . 
   The chain delivery CD 2  includes grippers  34  each for gripping a printed sheet Pd, and a chain  35  for carrying the grippers  34  attached thereto around. Each of the grippers  34  includes a cam follower  34   a , and a gripper finger  34   b  operated to open and close by the cam follower  34   a . The cam follower  34   a  is urged by a spring not shown in such a direction as to close the gripper finger  34   b.    
   In the path of movement of the grippers  34 , a movable cam  36  is provided at a first discharge point dp 1 , and a fixed cam  37  is provided at a second discharge point dp 2  downstream of the first discharge point dp 1 . Each of the movable cam  36  and the fixed cam  37  is provided with a cam plate. When each of the grippers  34  passes by the movable cam  36  or the fixed cam  37 , the cam follower  34   a  collides against the movable cam  36  or the fixed cam  37  to open the gripper finger  34   b , whereby the printed sheet Pd is dropped and discharged. The movable cam  36  is selectively movable between a lowered position in which the movable cam  36  collides against the cam follower  34   a  and a raised position clear of the cam follower  34   a , and is controlled by a controller  50 . The movable cam  36  is driven to move up and down, for example, by a solenoid  36   a , but may be so driven by a hand-operated lever. The fixed cam  37  is in a fixed location so as to constantly come in contact with the cam follower  34   a.    
   The delivery table  31  is provided under the first discharge point dp 1  and is disposed to receive a printed sheet Pe released by the gripper  34 . The delivery table  31  places thereon successively discharged printed sheets Pe as the stacked printed sheets Ps aligned by a sheet-trapping element  38 . The delivery table  31  is movable up and down by a vertical movement mechanism  39  to provide a constantly fixed distance that the printed sheets Pe fall from the grippers  34  onto the delivery table  31  or the stacked printed sheets Ps. 
   The covers  32  and  33  cover the chain delivery CD 2  and the delivery table  31 . The cover  33  is openable and closable so that the stacked printed sheets Ps on the delivery table  31  are taken out after the printing operation. The cover  32  is formed with an opening  40  near the second discharge point dp 2 . A printed sheet Pf discharged at the second discharge point dp 2  passes through the opening  40  and is received in a tray  41 . 
   In this preferred embodiment, the movable cam  36  is normally in the lowered position, and causes the gripper  34  to open at the first discharge point dp 1 . Thus, the discharged printed sheets Pe are successively stacked on the delivery table  31 . When an operator obtains a printed sample, the movable cam  36  is withdrawn to the raised position. This precludes the gripper finger  34   b  from making the opening movement at the first discharge point dp 1 . Hence, the printed sheet Pd is not discharged at the first discharge point dp but is discharged at the second discharge point dp 2 . The printed sheet Pf discharged at the second discharge point dp 2  passes through the opening  40  and is received as the printed sample into the tray  41 . 
   There is no need to open and close the covers  32  and  33  to obtain a printed sample also in the second preferred embodiment. Therefore, the operator can arbitrarily take out the printed sample during the printing operation even if the covers  32  and  33  are provided with an interlock for safety. 
   Preferably, the movement of the movable cam  36  is timed in synchronism with the printing speed. For example, a sampling interval at which the printed sample is taken out and the required number of printed samples are previously determined, and the controller  50  may control the vertical movement of the movable cam  36  in accordance with the determined conditions. This achieves the automation of the taking out of the printed sample. 
   In the second preferred embodiment, the delivery table  31  is disposed just under the first discharge point dp 1 . However, the delivery table  31  may be disposed just under the second discharge point dp 2 , whereas the opening  40  for taking out the printed sample therethrough be disposed at the first discharge point dp 1 . In this case, the movable cam  36  is normally in the raised or inoperative position, and may be moved to the lowered position only when the operator wants to obtain a printed sample. 
   While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention.