Offset printer having power transmission shut off mechanism

An offset printer includes a drive motor, an impression cylinder gear, a paper feed cylinder, a paper feed cylinder gear, a paper discharge portion, a paper discharge gear, a blanket gear, a plate cylinder gear, an ink reciprocation roller, a mechanism for rotating the ink reciprocation roller, a mechanism for reciprocating the ink reciprocation roller, and first through fourth electromagnetic clutches. Rotation of the drive motor is transmitted to the paper feed cylinder gear and the paper discharge gear through the impression cylinder gear. The rotation force of the impression cylinder gear is also transmitted to, in the order of, the blanket cylinder gear, the plate cylinder gear, and the rotation and reciprocation mechanisms. Driving connection between the paper feed cylinder gear and the paper feed cylinder is selectively disconnected by the first clutch. Driving connection between the paper discharge gear and the paper discharge portion is selectively disconnected by the second clutch. Driving connection between the plate cylinder gear and the ink reciprocation roller is selectively disconnected by the third and fourth clutch.

BACKGROUND OF THE INVENTION
 The present invention relates to an offset printer, and more particularly,
 to a digital offset printer in which rotation of a drive motor is
 transmitted to a paper feed mechanism and a paper discharge mechanism
 through an impression cylinder, and also transmitted to an ink
 reciprocation roller through the impression cylinder, a blanket cylinder
 and a plate cylinder.
 Japanese Patent Application Publication No. 9-510410 discloses an offset
 printer capable of performing offset printing with four different colors
 of inks. The printer includes a single impression cylinder, a single paper
 discharge mechanism, a single paper feed conveyer, a single transfer drum,
 two blanket cylinders, two plate cylinders and, ink rollers for the four
 colors. The paper feed conveyer and the transfer drum are adapted for
 delivering a paper to a surface of the impression cylinder. The paper is
 mounted on the surface of the impression cylinder. The paper discharge
 mechanism is adapted to discharge the paper from the impression cylinder.
 The blanket cylinder is pressed against the paper mounted on the
 impression cylinder.
 The impression cylinder is rotated about its axis by the drive motor.
 Further, two blanket cylinders have their axes extending in a direction
 parallel with the axis of the impression cylinder, and the two blanket
 cylinders are in contact with the impression cylinder and are rotated upon
 rotation of the impression cylinder. The paper feed conveyer, the transfer
 drum and the paper discharge mechanism are also driven or rotated by the
 rotation of the impression cylinder.
 Each plate cylinder has a peripheral surface provided with a thin plate
 where an image to be printed is formed. The two plate cylinders have their
 axes extending in a direction parallel with the axes of the blanket
 cylinders. Each plate cylinder is in contact with each blanket cylinder,
 and each plate cylinder is rotated upon rotation of each blanket cylinder.
 Each peripheral surface of the plate cylinder is divided into two
 segments. One of the segments is formed with an image with a single color,
 and remaining segment is formed with an image with a different color.
 Accordingly, the two plate cylinders form images of four colors.
 The ink roller is adapted for supplying an ink to the plate of the plate
 cylinder. To this effect, two ink rollers are provided in contact with
 each plate cylinder so that two different colored inks can be supplied to
 each plate. Accordingly, totally four ink rollers are provided for four
 different colors. Axes of the ink rollers extend in parallel with the axis
 of the plate cylinder. The ink rollers are rotated upon rotation of the
 plate cylinder.
 In the digital offset printer, the plate cylinders must be rotated about
 their axes so as to form images on the plates. This is similar to a laser
 printer in which a photo-sensitive drum is rotated so as to form an
 electro-static latent image on an outer peripheral surface of the drum.
 The drive motor, which is a single drive source, is driven to rotate the
 plate cylinder.
 SUMMARY OF THE INVENTION
 However, in the conventional digital offset printer, driving force of the
 motor must be transmitted to the plate cylinder by way of the impression
 cylinder and the blanket cylinders in order to rotate the plate cylinder
 for image formation thereon. Accordingly, the paper feed conveyer, the
 transfer drum and paper discharge mechanism are also rotated or driven by
 the rotation of the impression cylinder. Further, the ink rollers are also
 rotated upon rotation of the plate cylinders. However, the paper feed
 conveyer, the transfer drum, the paper discharge mechanism and the ink
 rollers make no contribution for forming images on the plate cylinders.
 Reduction in time period requiring for the image formation is one of the
 factors in reduction in time period requiring for entire printing
 operation. In order to reduce the image forming period, the rotation speed
 of the plate cylinders must be increased. However, the rotation of the
 plate cylinders also causes rotation or driving of the other components
 which are not necessary for image formation on the plate. Therefore, high
 speed rotation of the plate cylinders may not be provided, and otherwise
 loss in rotation force may be increased, and the main body of the offset
 printer may be vibrated due to the concurrent rotations or driving.
 It is therefore, an object of the present invention to provide an offset
 printer capable of shutting off the power transmission to components
 during a process for forming an image on the surface of the plate
 cylinder, the components being nothing to do with the image formation
 during this process.
 This and other objects of the present invention will be attained by an
 offset printer including a frame, a drive motor supported on the frame, a
 drive gear for outputting a rotation force of the drive motor, an
 impression cylinder, a paper feed mechanism, a paper discharge mechanism,
 a blanket cylinder, a plate cylinder, an ink supplying mechanism, and a
 power transmission shut off mechanism. The impression cylinder has an
 impression cylinder gear provided coaxially and integrally rotatable
 therewith. The impression cylinder gear is meshedly engaged with the drive
 gear for rotating the impression cylinder upon rotation of the output
 gear. The paper feed mechanism includes a paper feed cylinder gear
 meshedly engaged with the impression cylinder gear, and a paper feed
 cylinder rotatable coaxially with the paper feed cylinder gear upon
 rotation of the impression cylinder gear for feeding a paper to a surface
 of the impression cylinder. The paper discharge mechanism includes a paper
 discharge gear meshedly engaged with the impression cylinder gear, a paper
 discharge portion rotatable coaxially with the paper discharge gear, and
 an endless chain mounted on the paper discharge portion and circularly
 movable on the paper discharge portion for removing the paper from the
 impression cylinder. The blanket cylinder is in contact with the surface
 of the impression cylinder and has a blanket cylinder gear meshedly
 engaged with the impression cylinder gear. The blanket cylinder gear is
 rotatable integrally with the blanket cylinder gear upon rotation of the
 impression cylinder gear. The plate cylinder has a plate cylinder gear
 meshedly engaged with the blanket cylinder gear. The plate cylinder is
 rotatable integrally and coaxially with the plate cylinder gear upon
 rotation of the blanket cylinder gear and in contact with a surface of the
 blanket cylinder for forming an image on a surface of the plate cylinder.
 The ink supplying mechanism is driven by the rotation of the plate
 cylinder for supplying an ink to the surface of the plate cylinder. An
 inked image is formed on the surface of the plate cylinder by the supplied
 ink based on an image formed on the surface of the plate cylinder, and the
 inked image on the plate cylinder is transferred to the surface of the
 blanket cylinder, and the impression cylinder presses a paper against the
 surface of the blanket cylinder for transferring the inked image on the
 blanket cylinder to the paper. The power transmission shut off mechanism
 is adapted for preventing the rotation force of the drive motor from being
 transmitted to at least one of the paper feed mechanism, the paper
 discharge mechanism and the ink supplying mechanism at least during image
 formation process on the surface of the plate cylinder.
 With the structure, because the transmission of rotation force from the
 drive motor to at least one of the paper feed mechanism, the paper
 discharge mechanism and the ink supplying mechanism is shut off during the
 image forming process on the surface of the plate cylinder, it becomes
 possible to avoid idle driving of at least one of the above described
 mechanisms which driving is unnecessary for the image formation. For
 example, if the power transmission from the drive motor to the paper feed
 mechanism is shut off, the power transmission to the paper feed cylinder
 can be shut off. If the power transmission from the drive motor to the
 paper discharge mechanism is shut off, the rotation force is not
 transmitted to the paper discharge portion, thereby reducing unnecessary
 rotation of the paper discharge portion. If the power transmission from
 the drive motor to the ink supplying mechanism is shut off, idle driving
 of the ink supplying mechanism can be obviated, which driving is
 unnecessary for the image formation. In any case, rotation or driving of
 the mechanisms which are unnecessary for forming an image on the surface
 of the plate cylinder can be dispensed with. Accordingly, high speed
 rotation of the plate cylinder results, and in other words, the plate
 cylinder can be rotated with lesser power. Thus, image forming process can
 be efficiently performed. Further, unwanted vibration of the mechanism due
 to unwanted operation or driving of the mechanism(s) can be eliminated,
 thereby improving durability of the offset printer and prolonging service
 life thereof.
 In a preferred embodiment, the power transmission shut off mechanism
 includes an electromagnetic clutch positioned between the paper feed
 cylinder gear and the paper feed cylinder for selectively coupling the
 paper feed cylinder gear and the paper feed cylinder. Further, a first
 rotation preventing member having a first locking projection engageable
 with the paper feed cylinder is provided for preventing the paper feed
 cylinder from being rotated with respect to the frame when the
 electromagnetic clutch disconnects the paper feed cylinder gear from the
 paper feed cylinder. The first locking projection is disengageable from
 the paper feed cylinder for allowing the paper feed cylinder to be
 rotatable with respect to the frame when the electromagnetic clutch
 couples the paper feed cylinder gear to the paper feed cylinder. An outer
 surface of the paper feed cylinder has a paper feed cylinder pawls with
 which the paper is held.
 With this arrangement, in OFF phase of the electromagnetic clutch, the
 paper feed cylinder gear is disconnected from the paper feed cylinder, so
 that the transmission of rotation force from the paper feed cylinder gear
 to the paper feed cylinder is shut off. In this instant, by the locking
 engagement of the first locking projection with the paper feed cylinder,
 free rotation of the paper feed cylinder can be prevented. Accordingly,
 paper feed cylinder pawls can be stably positioned away from the surface
 of the impression cylinder, to thereby preventing the pawls from being
 obstacles against the rotation of the impression cylinder.
 Further, in the preferred embodiment, the power transmission shut off
 mechanism includes an electromagnetic clutch positioned between the paper
 discharge gear and the paper discharge portion for selectively coupling
 the paper discharge gear and the paper discharge portion. Further, a
 second rotation preventing member having a second locking projection
 engageable with the paper discharge portion is provided for preventing the
 paper discharge portion from being rotated with respect to the frame when
 the electromagnetic clutch disconnects the paper discharge gear from the
 paper discharge portion. The second locking projection is disengageable
 from the paper discharge portion for allowing the paper discharge portion
 to be rotatable with respect to the frame when the electromagnetic clutch
 couples the paper discharge gear to the paper discharge portion. The
 endless chain is provided with paper discharge grippers.
 With this arrangement, in OFF phase of the electromagnetic clutch, the
 paper discharge gear is disconnected from the paper discharge portion, so
 that the transmission of rotation force from the paper discharge gear to
 the paper discharge portion is shut off. In this instant, by the locking
 engagement of the second locking projection with the paper discharge
 portion, free rotation of the paper discharge portion can be prevented.
 Accordingly, paper discharge grippers can be stably positioned away from
 the surface of the impression cylinder during the image formation process,
 to thereby preventing the grippers from being obstacles against the
 rotation of the impression cylinder.
 Further, in the preferred embodiment, the power transmission shut off
 mechanism includes a clutch positioned between the plate cylinder and the
 ink supplying mechanism for selectively shutting off transmission of
 rotation force of the plate cylinder to the ink supplying mechanism.
 With this arrangement, in OFF phase of the clutch, rotation force from the
 plate cylinder cannot be transmitted to the ink supplying mechanism.
 Normally, the ink supplying mechanism includes an ink reciprocation roller
 rotatable about its axis and reciprocally movable in its axial direction
 thereof. And therefore, in the OFF phase, the rotation and reciprocation
 of the ink reciprocation roller does not occur. In other words, any
 driving force for rotating and reciprocating the ink reciprocation roller
 is not required in the image formation process, which motion is
 unnecessary therefor. Accordingly, the plate cylinder can be rotated at
 high speed to enhance image forming efficiency on the plate cylinder.
 Further, surplus vibration does not occur, to enhance durability of the
 offset printer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 An offset printer according to one embodiment of the present invention will
 be described with reference to FIGS. 1 through 7. FIG. 1 shows an entire
 arrangement of the offset printer 1. The offset printer 1 has a frame 11
 (FIG. 2) to which a motor (not shown) is fixed. The motor has an output
 shaft (not shown) on which a drive gear 2 is mounted. The printer 1 also
 includes a generally cylindrical impression cylinder 3 having an
 impression cylinder gear (not shown) provided coaxially and integrally
 therewith. The drive gear 2 is meshedly engaged with the impression
 cylinder gear. Thus, the rotation of the motor is transmitted to the
 impression cylinder 3 through the drive gear 2 and the impression cylinder
 gear.
 The printer 1 also includes a generally cylindrical paper feed cylinder 4
 adapted for supplying a paper to a surface of the impression cylinder 3. A
 paper feed cylinder gear 41 (FIG. 2) is provided coaxially with the paper
 feed cylinder 4 and independently rotatable with respect to the paper feed
 cylinder 4. The paper fed cylinder gear 41 is meshedly engaged with the
 impression cylinder gear. A paper feed pile 42 is provided where a stack
 of papers are accommodated. A feeder board 43 and an infeed portion 44 are
 provided between the paper feed pile 42 and the paper feed cylinder 4. The
 feeder board 43 is in the form of a belt conveyer for delivering the paper
 from the paper feed pile 42 toward the paper feed cylinder 4. The infeed
 portion 44 is adapted for precisely and smoothly infeeding the paper to
 the paper feed cylinder 4. The infeed portion 44 is provided with a
 registration mechanism (not shown) including rollers for moving the paper
 to its correct position. A driving mechanism (not shown) driven by the
 rotation of the paper feed cylinder gear 41 is provided in the
 registration mechanism for rotating the rollers. Further, the driving
 force of the feeder board 43 for moving the paper from the paper feed pile
 42 to the infeed portion 44 is transmitted to the feeder board 43 from the
 driving mechanism of the registration mechanism. The paper feed cylinder 4
 has a peripheral surface provided with a paper feed pawl 4a adapted for
 fixing the paper to the paper feed cylinder 4 and delivering the paper to
 the impression cylinder 3. The paper feed pawl 4a is movable in a circular
 path together with the rotation of the paper feed cylinder 4. A
 combination of the paper feed cylinder 4, the paper feed pile 42, the
 feeder board 43 and the infeed portion 44 constitutes a paper supplying
 mechanism.
 A generally cylindrical paper discharge portion 6 is provided for
 discharging the paper from the surface of the impression cylinder 3. A
 paper discharge portion gear 61 (FIG. 4) in meshing engagement with the
 impression cylinder gear is provided coaxially and integrally with the
 paper discharge portion 6. Therefore, the paper discharge portion 6 is
 rotatable upon rotation of the impression cylinder 3. An endless chain 62
 is mounted between the paper discharge portion 6 and a sprocket 63 spaced
 away from the paper discharge portion 6. A plurality of paper discharge
 grippers 62a are provided to the endless chain 62 so as to grip the paper
 on the impression cylinder 3 and to remove the paper therefrom. Below the
 sprocket 63A, a paper discharge pile 64 is provided where each paper
 gripped and delivered by the gripper 62a and the endless chain 62 is
 stacked successively. The paper discharge portion 6, the endless chain 62
 and the sprocket 63 are driven by the rotation force transmitted from the
 impression cylinder gear through the paper discharge portion gear 61. A
 combination of the paper discharge portion 6, the endless chain 62, the
 paper discharge grippers 62a, the sprocket 63, and the paper discharge
 pile 64 constitutes a paper discharge mechanism.
 The offset printer 1 also includes two blanket cylinders 8 each in contact
 with the impression cylinder 3 and provided with blanket cylinder gear
 (not shown) provided coaxially and integrally with associated blanket
 cylinder 8. These blanket cylinder gears are in meshing engagement with
 the impression cylinder gear. During printing operation, the paper
 supplied to the surface of the impression cylinder 3 is pressed against
 the blanket cylinder 8 by the impression cylinder 3. The rotation force of
 the impression cylinder 8 is transmitted to the blanket cylinder 8 through
 the impression cylinder gear (not shown) and the blanket cylinder gear
 (not shown).
 Two plate cylinders 9 are provided each in contact with each blanket
 cylinder 8 and each provided with a plate cylinder gear 90a (FIG. 6)
 coaxially and integrally with each plate cylinder 9. Each plate cylinder
 gear 90a is in meshing engagement with each blanket cylinder gear (not
 shown). Thus the rotation force of the blanket cylinder 8 is transmitted
 to the plate cylinder 9 through the blanket cylinder gear (not shown) and
 the plate cylinder gear 90a. A thin plate (not shown) is mounted on a
 surface of the plate cylinder 9. The thin plate is sectioned into two
 segments, i.e., a first segment 9a where an image for a specific color is
 to be formed, and a second segment 9b where an image for a different color
 is to be formed. That is, one plate cylinder 9 forms two images with two
 different colors, and totally four images of four different colors are
 formed on the two plate cylinders 9.
 Two sets of ink supply units 15 are disposed adjacent to each plate
 cylinder 9 for supplying inks of different colors to the segments 9a and
 9b. Each ink supply unit 15 includes an ink reciprocation roller 151 (FIG.
 6) and an ink supply portion (not shown). The ink reciprocation roller 151
 has a gear 151a (FIG. 6) provided coaxially and integrally therewith. As
 described later, the ink reciprocation roller 151 is rotatable about its
 axis and reciprocally movable in the axial direction. As shown in FIG. 6,
 the gear 151a is driven by the plate cylinder gear 90a by way of a gear
 train including a plurality of gears 94, 96, 97, 98 and 99. Therefore, the
 rotation force of the plate cylinder 9 is transmitted to the ink
 reciprocation roller 151 through these gears.
 Next, a mechanism around the paper feed cylinder 4 will be described with
 reference to FIGS. 1 through 3. The paper feed cylinder gear 41 has a disc
 shape formed with a central circular through hole 41a in which a bearing
 46 is disposed. A paper feed cylinder shaft 45 extends through the through
 hole 41a through the bearing 46. The paper feed cylinder 4 (FIG. 1) is
 concentrically disposed over the paper feed cylinder shaft 45 and provided
 integrally therewith. Thus, the paper feed cylinder 4 is rotatable
 together with the rotation of the paper feed cylinder shaft 45. On the
 other hand, the paper feed cylinder gear 41 is rotatable about the paper
 feed cylinder shaft 45 by way of the bearing 46. In FIG. 2, beside the
 paper feed cylinder gear 41a, a generally cylindrical rotation force
 transmission member 47 is provided coaxially with and integrally rotatable
 with the paper feed cylinder shaft 45 which extends through a center
 portion of the transmission member 47.
 An electromagnetic clutch 48 is provided between the paper feed cylinder
 gear 41 and the rotation force transmission member 47. If the
 electromagnetic clutch 48 is rendered ON, the paper feed cylinder gear 41
 becomes integrally rotated with the transmission member 47 in coaxial
 fashion. If the electromagnetic clutch 48 is rendered OFF, the paper feed
 cylinder gear 41 is rotatable with respect to the transmission member 47.
 Because the transmission member 47 and the paper feed cylinder 4 are
 provided coaxially and integrally with each other, the paper feed cylinder
 4 is rotated together with the rotation of the paper feed cylinder gear
 41, i.e, the paper feed cylinder 4 and the paper feed cylinder gear 48 are
 connected together, during ON phase of the electromagnetic clutch 48, and
 the paper feed cylinder 4 is rotatable against the paper feed cylinder
 gear 41, i.e., these are disconnected from each other during OFF phase of
 the clutch 48. By switching the electromagnetic clutch 48 to OFF phase,
 the rotation force transmitted from the impression cylinder 3 to the paper
 feed cylinder gear 41 through the impression cylinder gear (not shown) is
 not transmitted to the paper feed cylinder 4. Accordingly any driving
 force requiring for rotating the paper feed cylinder 4 can be dispensed
 with, the rotation of the paper feed cylinder 4 being unnecessary for the
 purpose of only forming an image on the plate of the plate cylinder 8.
 In FIG. 2, the right end portion of the paper feed cylinder shaft 45 is
 provided with an annular locking member 49 concentrically with and
 integrally rotatable with the paper feed cylinder shaft 45 and the paper
 feed cylinder 4 (FIG. 1). The annular locking member 49 has an outer
 peripheral surface formed with a locking depression 49A (FIG. 3) recessed
 radially inwardly. As shown in FIG. 3, a first locking lever 50 is
 positioned in confrontation with the outer peripheral surface of the
 annular locking member 49. The locking lever 50 has a central portion
 rotatably supported by a pivot shaft 51 fixed to the frame 11, so that the
 locking lever 50 is pivotally movable about the pivot shaft 51. The
 locking lever 50 has one end portion provided with a first locking
 projection 50a engageable with the locking depression 49A, and another end
 portion provided with a spring securing pin 50b. The frame 11 also has a
 spring securing pin 11a, and a tension spring 52 is bridged between the
 spring securing pins 50b and 11a, so that the tension spring 2 urges the
 first locking lever 50 to pivot about the pivot shaft 51 in a
 counterclockwise direction in FIG. 3. That is, the tension spring 52 urges
 the first locking projection 50a to move into the locking depression 49A.
 As shown in FIG. 3, a pneumatic cylinder 53 and a limit switch 54 are
 provided above the tension spring 52. The pneumatic cylinder 53 has one
 end fixed to the frame 11, and another end pivotally connected to the
 other end of the first locking lever 50 at a position above the spring
 securing pin 50b. Upon actuation of the pneumatic cylinder 53, the first
 locking lever 50 is pivotally moved in a clockwise direction against the
 biasing force of the tension spring 52 as shown by a two dotted chain line
 in FIG. 3, so that the first locking projection 50a is disengaged from the
 locking depression 49A. The limit switch 54 is fixed to the frame 11. The
 limit switch 54 has a sensing element in contact with the first locking
 lever 50 as shown by a solid line in FIG. 3 when the first locking
 projection 50a is engaged with the locking depression 49A. That is,
 detection of abutment of the limit switch 54 onto the first locking lever
 50 implies a detection of the locking engagement between the locking
 projection 50a and the locking depression 49A.
 The engagement of the first locking projection 50a with the locking
 depression 49A prevents the paper feed cylinder 4 integral with the
 annular locking member 49 from being rotated. Therefore, the positions of
 the paper feed pawls 4a provided at the periphery of the paper feed
 cylinder 4 can be fixed to a predetermined circularly moving position.
 Consequently, rotation of the impression cylinder 3 is not affected by the
 accidental abutment of the paper feed pawls 4a onto the impression
 cylinder 3 due to unwanted free rotation of the paper feed cylinder 4,
 while the driving connection between the paper feed cylinder gear 41 and
 the paper feed cylinder shaft 45 is shut off in the OFF phase of the
 electromagnetic clutch 48 during image forming process.
 Next, the paper discharge mechanism 6 and its ambient arrangement will be
 described. As shown in FIG. 4, a disc shaped paper discharge gear 61
 formed with a central circular through hole 61a is provided, and a bearing
 66 is disposed in the through hole 61a. A paper discharge shaft 65 extends
 through the bearing 66. Thus, the paper discharge gear 61 is provided
 coaxilly with and rotatable with respect to the paper discharge shaft 65
 through the bearing 66. The paper discharge portion 6 is rotatable
 coaxially and integrally with the paper discharge shaft 65. In FIG. 4, a
 generally cylindrical rotation force transmission member 67 is positioned
 at right side of the paper discharge gear 61. The transmission member 67
 has a center portion through which the paper discharge shaft 65 extends,
 and is coaxially and integrally with the paper discharge shaft 65. An
 electromagnetic clutch 68 is disposed between the paper discharge gear 61
 and the rotation force transmission member 67. If the electromagnetic
 clutch 68 is rendered ON, the transmission member 67 and the paper
 discharge gear 61 are coupled together, so that these are rotated
 together. If the clutch 68 is rendered OFF, the paper discharge gear 61
 becomes rotatable coaxially with respect to the transmission member 67.
 Because the transmission member 67 and the paper discharge portion 6 are
 coaxially and integrally rotatable together, the paper discharge portion 6
 is integrally rotated with the paper discharge gear 61, i.e., the paper
 discharge portion 6 and the paper discharge gear 61 are connected
 together, if the electromagnetic clutch 68 is rendered ON, and the paper
 discharge portion 6 becomes rotatable with respect to the paper discharge
 gear 61, i.e., the paper discharge portion 6 is disconnected from the
 paper discharge gear 61, if the clutch 68 is rendered OFF.
 In OFF phase of the electromagnetic clutch 68, the rotation force
 transmitted from the impression cylinder 3 through the impression cylinder
 gear (not shown) and the paper discharge gear 61 is not transmitted to the
 paper discharge portion 6. Accordingly, a driving power for rotating the
 paper discharge portion 6 is unnecessary during image formation on the
 plate of the plate cylinder. Thus, power saving results.
 In FIG. 4, a disc shaped locking member 69 is provided at a leftmost end of
 the paper discharge shaft 65 integrally and coaxially therewith. The
 locking member 69 is formed with a radially inwardly recessed locking
 depression 69A (FIG. 5). Further, a second locking lever 70 is pivotally
 movably positioned in confrontation with an outer peripheral surface of
 the locking member 69 as shown in FIG. 5. The second locking lever 70 has
 an intermediate portion pivotally supported to a pivot shaft 71 fixed to
 the frame 11 (FIG. 4), a one end portion having a second locking
 projection 70a engageable with the locking depression 69A, and another end
 portion having a spring securing pin 70b. The frame 11 also has a spring
 securing pin 12a, and a tension spring 72 is bridged between the spring
 securing pins 12a and 70b, so that the tension spring 72 urges the second
 locking lever 70 to pivot about the pivot shaft 71 in a direction to
 provide engagement between the second locking projection 70a and the
 locking depression 69A as best shown in FIG. 5.
 In FIG. 5, a pneumatic cylinder 73 and a limit switch 74 are provided below
 the tension spring 72. The pneumatic cylinder 73 has a base end fixed to
 the frame 11, and a free end pivotally connected to the second locking
 lever 70 at a position below the spring securing pin 70b. Upon actuation
 of the pneumatic cylinder 73, the second locking lever 70 is pivotally
 moved about the pivot pin 71 in a clockwise direction in FIG. 5 as shown
 by a two dotted chain line against the biasing force of the tension spring
 72, so that the second locking projection 70a is disengaged from the
 locking depression 69A. The limit switch 74 is fixed to the frame 11. When
 the second locking projection 70a is engaged with the locking depression
 69A, one end of the limit switch 74 is in abutment with the second locking
 lever 70 as shown by a solid line in FIG. 5. That is, abutment of the
 limit switch 74 onto the second locking lever 70 implies a detection of
 locking engagement between the second locking projection 70a and the
 locking depression 69A.
 The engagement between the second locking projection 70a and the locking
 depression 69A prevents the paper discharge portion 6 integrally rotatable
 with the disc shaped locking member 69 from being rotated. Therefore,
 during image forming process on the plate of the plate cylinder, the paper
 discharge grippers 62a (FIG. 1) provided to the endless chain 62 can be
 maintained at their fixed positions. Accordingly, rotation of the
 impression cylinder 3 is not affected by the paper discharge grippers 62,
 because accidental abutment of the gripper onto the surface of the
 impression cylinder 3 can be prevented.
 Next, a mechanism for rotating an ink reciprocation roller 151 will be
 described with reference to FIG. 6. As described above, the plate cylinder
 gear 90a is provided coaxially and integrally rotatable with the plate
 cylinder 9, and the rotation force of the blanket cylinder gear (not
 shown) is transmitted to the plate cylinder 9 through the plate cylinder
 gear 90a. A plate cylinder shaft 91 is provided integrally with the plate
 cylinder 9, and is rotatably supported by the frame 11, 12 through bearing
 92. The plate cylinder shaft 91 has one distal end portion coaxially
 provided with an extension portion 91a whose radius is smaller than that
 of the plate cylinder shaft 91. Further, at left side of the plate
 cylinder shaft 91 in FIG. 6, a generally cylindrical rotation force
 transmission member 93 is provided coaxially and integrally rotatably with
 the plate cylinder shaft 91. The transmission member 93 has a radius
 greater than that of the plate cylinder shaft 91.
 A sub frame 12B is fixed to the frame 12 by a stud 12A and extends in a
 direction parallel with the frame 12. The extension portion 91a is
 rotatably supported by the sub frame 12B through a bearing. The above
 described gear 94 of the gear train is positioned between the power
 transmission member 93 and the sub frame 12B. The gear 94 has a central
 portion formed with a through hole 94A through which the extension portion
 91a extends via a bearing 95. Thus, the gear 94 is coaxially rotatable
 about the extension portion 91a. Further, the above described gears 96,
 97, and 98 of the gear train are rotatably supported to the sub frame 12B.
 The gear 94 is meshedly engaged with the gear 96 meshedly engaged with the
 gear 97. The gear 97 is meshedly engaged with the gear 98 provided
 coaxially and integrally rotatable with the gear 99. These gears 98 and 99
 are coaxially and integrally mounted on a shaft 100 having one end
 rotatably supported to the frame 12 through a bearing 101A, and another
 end rotatably supported to the sub frame 12B through a bearing 101B. In
 FIG. 6, a gear 151a in meshing engagement with the gear 99 is coaxially
 and integrally rotatable with the ink reciprocation roller 151 at a left
 end thereof. Because the ink reciprocation roller 151 is reciprocally
 movable in its axial direction, the gear 99 has a sufficient axial length
 capable of maintaining meshing engagement with the gear 151a in spite of
 the reciprocal movement of the gear 151a in its axial direction.
 An electromagnetic clutch 102 is disposed between the gear 94 and the
 rotation force transmission member 93. If the clutch 102 is rendered ON,
 the gear 94 and the transmission member 93 is coupled together, and if the
 clutch 102 is rendered OFF, the gear 94 is rotatable with respect to the
 transmission member 93. In other words, in ON phase of the electromagnetic
 clutch 102, rotation force of the plate cylinder 9 can be transmitted to
 the gear 151a through the rotation force transmission member 93, and the
 gears 94, 96, 97, 98 and 99. Therefore, upon rotation of the plate
 cylinder 9, the ink reciprocation roller 151 is rotated about its axis. On
 the other hand, in OFF phase of the electromagnetic clutch 102, rotation
 force transmission from the transmission member 93 to the gear 94 is shut
 off. Therefore, the ink reciprocation roller 151 is not rotated about its
 axis in spite of the rotation of the plate cylinder 9.
 With the OFF phase of the electromagnetic clutch 102, the rotation force
 transmitted to the plate cylinder gear 90a through the impression cylinder
 gear (not shown) and the blanket cylinder gear (not shown) is not
 transmitted to the ink reciprocation roller 151 but is shut off at the
 gear 94. Consequently, in the image forming process, a driving power for
 driving the ink supplying device 15 including the ink reciprocation roller
 151 can be dispensed with, the power being unnecessary for forming an
 image on the plate of the plate cylinder 9.
 Next, a mechanism for reciprocating ink reciprocation rollers 151, 161, 171
 in their axial direction will be described with reference to FIGS. 6 and
 7. In FIG. 6, the plate cylinder shaft 91 has a right end provided with a
 pulley 91b coaxially and integrally therewith, and an endless belt 103
 (FIG. 7) is mounted on the pulley 91b. A sub frame 11B is fixed to the
 frame 11 by studs 11A and extends in parallel with the frame 11. An
 intermediate rotation force transmission member 104 and a pulley 107 are
 positioned between the frame 11 and the sub frame 11B. More specifically,
 a rotation shaft 104a extends between the frame 11 and the sub frame 11B
 and is rotatably supported thereto through bearings 105. The transmission
 member 104 is provided integrally and coaxially with the shaft 104a. The
 pulley 107 is positioned at right side of the transmission member 104 in
 FIG. 6, and is formed with a central through hole 107A, through which the
 rotation shaft 104a extends via a bearing 106. Thus, the pulley 107 is
 coaxially rotatable about the rotation shaft 104a. The endless belt 103 is
 mounted on the pulley 107, so that the rotation force of the pulley 91b
 can be transmitted to the pulley 107 by way of the endless belt 103.
 An electromagnetic clutch 118 is disposed between the intermediate rotation
 force transmission member 104 and the pulley 107. If the clutch 118 is
 rendered ON, the transmission member 104 and the pulley 107 are coaxially
 and integrally rotatable. If the clutch 118 is rendered OFF, the
 transmission member 104 is rotatable with respect to the pulley 107. That
 is, in ON phase of the clutch 118, the rotation force of the plate
 cylinder 9 can be converted into reciprocally moving force of the ink
 reciprocation rollers 151, 161, 171, and in OFF phase of the clutch 118,
 the power transmission from the plate cylinder 9 to the ink reciprocation
 rollers 151, 161, 171 is shut off.
 In FIG. 6, a disc shaped rotation member 104b is provided coaxially and
 integrally rotatable with the rotation shaft 104a at a rightmost end
 thereof. The rotation member 104b is rotatably supported to the sub frame
 11B. A rod support portion 104c is provided on the rotation member 104b at
 an eccentric position with respect to the rotation shaft 104a. Further,
 one end 108a of a rod 108 is rotatably connected to the rod support
 portion 104c through a bearing 108b.
 A bracket 109 extends from the frame 11, and a reciprocation drive member
 110 is supported by the bracket 109. The reciprocation drive member 110
 includes a support portion 110, a pair of arm portions 113, 112 and a
 lever 110A. The support portion 110 is rotatably supported by the bracket
 109 and extends in a direction parallel with the frame 11. The pair of arm
 portions 113, 112 extend from the support portion 110 in opposite
 directions and perpendicular to a rotation axis of the support portion
 110a. The lever 110A has one end connected to the support portion 110 and
 another end pivotally connected to another end of the rod 108. The arm
 portion 113 has a free end to which one end of the rotation shaft of the
 ink reciprocation roller 151 is pivotally connected.
 To be more specific, as shown in FIG. 6, a rightmost end 109a of the
 bracket 109 is in a hollow cylindrical shape, through which the support
 portion 110a of the reciprocation drive member 110 extends in a direction
 perpendicular to a sheet of drawing. The right end of the lever 110A is
 formed with a through hole 11B, and the other end of the rod 108 is also
 formed with a through hole (not shown). A pivot shaft 111 extends through
 these through holes, so that the rod 108 is pivotally connected to the
 lever 11A.
 As best shown in FIG. 7, the pair of arm portions 112, 113 integrally
 extend from the support portion 110a in such a manner that one arm portion
 112 extends upwardly, and the other arm portion 113 extends downwardly in
 FIG. 7. Free ends of the arm portions 112, 113 are provided with ink
 reciprocation roller securing nuts 112a, 113a, respectively. As shown in
 FIG. 6, nut holding flanges 151b, 151c are provided at right side of the
 ink reciprocation roller 151 for interposing therebetween the nut 112a.
 Similarly, at right side of the ink reciprocation roller 161, nut holding
 flanges 161b, 161c are provided for interposing therebetween the ink
 reciprocation roller securing nut 113a.
 As shown in FIG. 7, a pivot shaft 114 is provided on the frame 11 (FIG. 6).
 and an intermediate portion of a reciprocation force transmission arm 115
 is pivotally supported to the pivot shaft 114. The arm 115 has free ends
 where ink reciprocation roller securing nuts 116, 117 are provided,
 respectively. The nut 116 is connected to one end of the shaft of the ink
 reciprocation roller 161 in cooperation with the ink reciprocation roller
 securing nut 113a. That is, the nut 116 is interposed between the nut
 holding flanges 161b and 161c which interpose therebetween the nut 113a.
 Further, the end portion of the shaft of the ink reciprocation roller 171
 is provided with nut holding flanges 171b, 171c, and the ink reciprocation
 roller securing nut 117 is interposed between the flanges 171b and 171c.
 Next, power transmission from the plate cylinder 9 will be described for
 performing reciprocal motion of the ink reciprocation rollers 151, 161,
 171. Assuming that the electromagnetic clutch 118 is ON phase, when the
 plate cylinder 9 is rotated, the pulley 91b is integrally rotated, so that
 the pulley 107 is rotated by way of the endless belt 103. Since the pulley
 107 is rotatable together with the rotation of the intermediate power
 transmission member 104, the rotation shaft 104a and the rotation member
 104c in ON phase of the electromagnetic clutch 118, the rotation member
 104b is also rotated, so that the rod support portion 104c is
 eccentrically rotated.
 The eccentric rotation of the rod support portion 104c is converted into
 reciprocating motion of the rod 108, which in turn pivotally moves the
 lever 110A about an axis of the support portion 110a. Thus, the support
 portion 110a of the reciprocation drive member 110 is angularly rotated to
 and fro about its axis. By the reciprocal angular rotation of the support
 portion 110a, the arm portions 113, 112 are pivotally moved about the axis
 of the support portion 110a to and fro, i.e., rightwardly and leftwardly
 in FIG. 6. Consequently, the ink reciprocation rollers 151,161 are axially
 reciprocatingly moved through the associated nuts 112a, 113a and nut
 holding flanges 151b, 151c, 161b, 161c. By the axially reciprocating
 motion of the ink reciprocation roller 161, the ink reciprocation roller
 171 is also reciprocally moved in its axial direction by way of the
 transmission arm 115, the nut 117 and the flanges 171b, 171c. Thus,
 totally three ink reciprocation rollers 151, 161 and 171 are concurrently
 reciprocally moved in their axial direction, whereby ink on the surface of
 the plate of the plate cylinder 9 can be kneaded. It should be noted that
 FIG. 6 shows an open developing view for better understanding the power
 transmission mechanisms at positions outside the frames 11 and 12. In
 reality, the ink reciprocation roller 151 should be delineated to be in
 contact with the plate cylinder 9 for kneading.
 If the electromagnetic clutch 118 is turned OFF, the pulley 107 becomes
 rotatable with respect to the intermediate power transmission member 104.
 Therefore, even though the rotation of the pulley 91b is transmitted to
 the pulley 107 via the belt 103, the rotation force of the pulley 107 is
 not transmitted to the ink reciprocation rollers 151, 161, 171.
 Accordingly, axially reciprocal motion of these rollers does not occur.
 With the OFF state of the electromagnetic clutch 118, the rotation force
 transmitted to the plate cylinder gear 90a through the impression cylinder
 gear (not shown) and the blanket cylinder gear (not shown) is not
 transmitted to the ink reciprocation rollers 151, 161, 171 by way of the
 reciprocation mechanism. Accordingly, during image forming process,
 reciprocating motion of the ink reciprocation rollers can be prevented,
 which motion is unnecessary for forming an image on the plate.
 While the invention has been described in detail and with reference to the
 specific embodiments thereof, it would be apparent to those skilled in the
 art that various changes and modifications may be made therein without
 departing from the spirit and scope of the invention.
 For example, in the illustrated embodiment, the drive gear 2 of the motor
 is positioned below the impression cylinder 3 as shown in FIG. 1. However,
 any position is available as long as the drive gear 2 is in meshing
 engagement with the impression cylinder gear for rotating the impression
 cylinder 3.
 Further, in the above described embodiment, during image formation process
 on the plate cylinder 9, driving operation of the paper feed mechanism,
 the paper discharge mechanism and the ink supplying mechanism are
 suspended. However, driving operation of at least one of the mechanisms
 can be suspended during the image formation process.
 Further, number of ink colors is not limited to four ink colors, but any
 other numbers of colors can be used for multiple color printing.
 Further, in the above embodiment, the image is formed on the thin plate
 mounted on the surface of the plate cylinder 9. However, the image can be
 directly formed on the outer peripheral surface of the plate cylinder
 without employment of the thin plate.
 Further, the above described embodiment is available for any types of
 offset printer other than the digital type offset printer.