Printing apparatus

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printing apparatus for feeding ink to plates mounted peripherally of a plate cylinder, and transferring the ink through a blanket cylinder to printing paper wrapped around an impression cylinder.

2. Description of the Related Art

A known printing apparatus of the type noted above includes a plate cylinder for supporting a plurality of plates mounted peripherally thereof, a plurality of ink feeders for feeding different color inks to image areas on the plurality of plates mounted on the plate cylinder, respectively, and a single impression cylinder. Such a printing apparatus is capable of color printing by using the single plate cylinder and the single impression cylinder. Thus, the entire apparatus requires a reduced area for its installation and operation.

Japanese Patent Publication (Unexamined) H3-143634 (1991), for example, describes a printing apparatus for printing images on printing paper with two color inks. This apparatus includes a plate cylinder for supporting two plates mounted peripherally thereof, two ink feeders for feeding the different inks to the respective plates on the plate cylinder, a single dampening water feeder for feeding dampening water to each plate on the plate cylinder, and an impression cylinder having half a diameter of the plate cylinder. A sheet of printing paper is fed for every two rotations of the impression cylinder.

However, the printing apparatus described in the above patent publication always prints with two color inks, and is incapable of monochromatic printing.

SUMMARY OF THE INVENTION

An object of the present invention, therefore, is to provide a printing apparatus with a plate cylinder for supporting a plate mounted peripherally thereof, the plate having two image areas, for allowing images to be printed selectively with a single color ink and with two color inks.

The above object is fulfilled, according to the present invention, by a printing apparatus comprises a plate cylinder for supporting a plate as mounted peripherally thereof, the plate having two image areas, two ink feeders for contacting and feeding inks to the image areas on the plate mounted on the plate cylinder; a blanket cylinder equal in diameter to and contactable with the plate cylinder; an impression cylinder having a diameter n/2 (n being an odd number) of the diameter of the plate cylinder and the blanket cylinder, and contactable with the blanket cylinder; n printing paper holder(s) (each) having a gripper for holding an end of the printing paper to maintain n sheet(s) of the printing paper peripherally of the impression cylinder; a printing paper feeder for feeding the printing paper to the impression cylinder; a printing paper discharger for discharging the printing paper from the impression cylinder after a required printing process; and a printing paper holder control mechanism for controlling the printing paper holders to carry out selectively a first opening and closing operation once for every rotation of the impression cylinder, and a second opening and closing operation once for every two rotations of the impression cylinder.

In a preferred embodiment of the invention, the printing paper holder control mechanism comprises a fixed cam disposed laterally of the impression cylinder, the fixed cam being contactable with a cam follower attached to the gripper of the printing paper holder, to open the gripper, thereby opening and closing the printing paper holder once for every rotation of the impression cylinder; a movable cam disposed coaxially with the fixed cam, the movable cam being movable between an open/close prohibiting position for prohibiting the printing paper holder from opening and closing by action of the fixed cam, and an open/close permitting position for permitting the printing paper holder to open and close by action of the fixed cam; a movable cam drive mechanism for reciprocating the movable cam between the open/close prohibiting position and the open/close permitting position with rotation of the impression cylinder; and a movable cam stop mechanism for stopping the movable cam in the open/close permitting position regardless of the rotation of the impression cylinder.

Preferably, the movable cam drive mechanism comprises a cam rotatable synchronously with the blanket cylinder; and a link mechanism coupled to the movable cam, the link mechanism including a cam follower contactable with the cam rotating synchronously with the blanket cylinder, to be pivotable with the rotation of the blanket cylinder to reciprocate the movable cam between the open/close prohibiting position and the open/close permitting position.

The movable cam stop mechanism may comprise a stopper for prohibiting pivotal movement of the link mechanism.

In another aspect of the invention, a printing apparatus comprises a first and a second plate cylinders each for supporting a plate as mounted peripherally thereof, the plate having two image areas, two ink feeders for contacting and feeding inks to the image areas on the plate mounted on the first plate cylinder; two ink feeders for contacting and feeding inks to the image areas on the plate mounted on the second plate cylinder; a first blanket cylinder equal in diameter to and contactable with the first plate cylinder; a second blanket cylinder equal in diameter to and contactable with the second plate cylinder; an impression cylinder having a diameter n/2 (n being an odd number) of the diameter of the first and second plate cylinders and the first and second blanket cylinders, and contactable with the first and second blanket cylinders; n printing paper holder(s) (each) having a gripper for holding an end of the printing paper to maintain n sheet(s) of the printing paper peripherally of the impression cylinder; a printing paper feeder for feeding the printing paper to the impression cylinder; a printing paper discharger for discharging the printing paper from the impression cylinder after a required printing process; and a printing paper holder control mechanism for controlling the printing paper holders to carry out selectively a first opening and closing operation once for every rotation of the impression cylinder, and a second opening and closing operation once for every two rotations of the impression cylinder.

The printing apparatus according to the present invention provides a first and a second plate cylinders each for supporting a plate as mounted peripherally thereof, the plate having two image areas. This construction allows a selection between printing with one or two color inks and printing with four color inks.

In a further aspect of the invention, a printing apparatus comprises a plate cylinder for supporting a plate as mounted peripherally thereof, the plate having two image areas; two ink feeders for selectively contacting and feeding inks to the image areas on the plate mounted on the plate cylinder; a blanket cylinder equal in diameter to and contactable with the plate cylinder; an impression cylinder having n/2 (n being an odd number) of the diameter of the plate cylinder and the blanket cylinder, and contactable with the blanket cylinder; n gripper(s) each for holding an end of the printing paper on the impression cylinder; a printing paper feeder and discharger for feeding the printing paper to the impression cylinder and discharging the printing paper from the impression cylinder; and a control mechanism for controlling the gripper(s) and the printing paper feeder and discharger to carry out selectively a first operation once for every rotation of the impression cylinder when both images of the two image areas on the plate are the same image, and a second operation once for every two rotations of the impression cylinder when both images of the images areas on the plate are different images.

Other features and advantages of the present invention will be apparent from the following detailed description of the embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown.

FIG. 1

is a schematic side view of a printing apparatus according to the present invention;

FIGS. 2A and 2B

are explanatory views each showing an arrangement of image areas on a plate;

FIG. 3

is a schematic view showing two plates, each having a single image area, mounted peripherally of a plate cylinder;

FIG. 4

is a schematic view of a contact mechanism for acting on a first blanket cylinder;

FIG. 5

is a block diagram showing a principal electrical structure of the printing apparatus;

FIG. 6

is a flow chart showing an outline of prepress and printing operations of the printing apparatus:

FIG. 7

is a flow chart of a prepress process;

FIG. 8

is an explanatory view of the printing operation of the printing apparatus;

FIG. 9

is another explanatory view of the printing operation of the printing apparatus;

FIG. 10

is a further explanatory view of the printing operation of the printing apparatus;

FIG. 11

is a still further explanatory view of the printing operation of the printing apparatus;

FIG. 12

is a still further explanatory view of the printing operation of the printing apparatus;

FIG. 13

is a still further explanatory view of the printing operation of the printing apparatus;

FIG. 14

is a schematic view of a gripper control mechanism for opening and closing grippers;

FIG. 15

is another schematic view of the gripper control mechanism for opening and closing the grippers;

FIG. 16

is a further schematic view of the gripper control mechanism for opening and closing the grippers;

FIG. 17

is a schematic view showing the gripper control mechanism along with fixed cams and the grippers;

FIG. 18

is an explanatory view of a positional relationship among movable cams and fixed cams;

FIG. 19

is another explanatory view of the positional relationship among movable cams and fixed cams;

FIG. 20

is an explanatory view of a printing paper transfer operation;

FIG. 21

is another explanatory view of the printing paper transfer operation;

FIG. 22

is a further explanatory view of the printing paper transfer operation;

FIG. 23

is a still further explanatory view of the printing paper transfer operation;

FIG. 24

is a still further explanatory view of the printing paper transfer operation;

FIG. 25

is a still further explanatory view of the printing paper transfer operation;

FIG. 26

is a still further explanatory view of the printing paper transfer operation;

FIG. 27

is a still further explanatory view of the printing paper transfer operation;

FIG. 28

is a still further explanatory view of the printing paper transfer operation;

FIG. 29

is a still further explanatory view of the printing paper transfer operation;

FIG. 30

is a still further explanatory view of the printing paper transfer operation;

FIG. 31

is a still further explanatory view of the printing paper transfer operation;

FIG. 32

is a still further explanatory view of the printing paper transfer operation; and

FIG. 33

is an explanatory view of a printing apparatus in a different embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described hereinafter with reference to the drawings.

The construction and operation of a printing apparatus embodying the invention will be described first.

FIG. 1

is a schematic side view of the printing apparatus according to the present invention.

This printing apparatus records images on blank plates mounted on first and second plate cylinders

11

and

12

, feeds inks to the plates having the images recorded thereon, and transfers the inks from the plates through first and second blanket cylinders

13

and

14

to printing paper held on an impression cylinder

15

, thereby printing the images on the printing paper.

The first plate cylinder

11

is movable between a first printing position shown in a solid line and an image recording position shown in a two-dot chain line in FIG.

1

. The second plate cylinder

12

is movable between a second printing position shown in a solid line in FIG.

1

and the same image recording position.

Around the first plate cylinder

11

in the first printing position are an ink feeder

20

a

for feeding an ink of black (K), for example, to the plate, an ink feeder

20

b

for feeding an ink of magenta (M), for example, to the plate, and dampening water feeders

21

a

and

21

b

for feeding dampening water to the plate. Around the second plate cylinder

12

in the second printing position are an ink feeder

20

c

for feeding an ink of cyan (C), for example, to the plate, an ink feeder

20

d

for feeding an ink of yellow (Y), for example, to the plate, and dampening water feeders

21

c

and

21

d

for feeding dampening water to the plate. Further, around the first or second plate cylinder

11

or

12

in the image recording position are a plate feeder

23

, a plate remover

24

, an image recorder

25

and a developing device

26

.

The first blanket cylinder

13

is contactable with the first plate cylinder

11

, while the second blanket cylinder

14

is contactable with the second plate cylinder

12

. The impression cylinder

15

is contactable with the first and second blanket cylinders

13

and

14

in different positions. The apparatus further includes a paper feed cylinder

16

for transferring printing paper supplied from a paper storage

27

to the impression cylinder

15

, a paper discharge cylinder

17

with chains

19

wound thereon for discharging printed paper from the impression cylinder

15

to a paper discharge station

28

, and a blanket cleaning unit

29

.

Each of the first and second plate cylinders

11

and

12

is coupled to a plate cylinder moving mechanism not shown, and driven by this moving mechanism to reciprocate between the first or second printing position and the image recording position. In the first printing position, the first plate cylinder

11

is rotatable synchronously with the first blanket cylinder

13

. In the second printing position, the second plate cylinder

12

is rotatable synchronously with the second blanket cylinder

14

. Adjacent the image recording position is a plate cylinder rotating mechanism, not shown, for rotating the first or second plate cylinder

11

or

12

whichever is in the image recording position.

The plate feeder

23

and plate remover

24

are arranged around the first or second plate cylinder

11

or

12

in the image recording position.

The plate feeder

23

includes a supply cassette

63

storing a roll of elongate blank plate in light-shielded state, a guide member

64

and guide rollers

65

for guiding a forward end of the plate drawn from the cassette

63

to the surface of the first or second plate cylinder

11

or

12

, and a cutter

66

for cutting the elongate plate into sheet plates. Each of the first and second plate cylinders

11

and

12

has a pair of grippers, not shown, for gripping the forward and rear ends of the plate fed from the plate feeder

23

.

The plate remover

24

has a pawl mechanism

73

for separating a plate from the first or second plate cylinder

11

or

12

after a printing operation, and a conveyor mechanism

69

for transporting the plate separated by the pawl mechanism

73

to a discharge cassette

68

.

The forward end of the plate drawn from the feeder cassette

63

is guided by the guide rollers

65

and guide member

64

, and gripped by one of the grippers on the first or second plate cylinder

11

or

12

. Then, the first or second plate cylinder

11

or

12

is rotated by the plate cylinder rotating mechanism not shown, whereby the plate is wrapped around the first or second plate cylinder

11

or

12

. The rear end of the plate cut by the cutter

66

is gripped by the other gripper. While, in this state, the first or second plate cylinder

11

or

12

is rotated at low speed, the image recorder

25

irradiates the surface of the plate mounted peripherally of the first or second plate cylinder

11

or

12

with a modulated laser beam for recording images thereon.

On the plate P mounted peripherally of the first plate cylinder

11

, the image recorder

25

, records an image area

67

a

to be printed with black ink, and an image area

67

b

to be printed with magenta ink, as shown in FIG.

2

A. On the plate P mounted peripherally of the second plate cylinder

12

, the image recorder

25

records an image area

67

c

to be printed with cyan ink, and an image area

67

d

to be printed with yellow ink, as shown in FIG.

2

B. The image areas

67

a

and

67

b

are recorded in evenly separated positions, i.e. in positions separated from each other by 180 degrees, on the plate P mounted peripherally of the first plate cylinder

11

. Similarly, the image areas

67

c

and

67

d

are recorded in evenly separated positions, i.e. in positions separated from each other by 180 degrees, on the plate P mounted peripherally of the second plate cylinder

12

.

When this apparatus is used in monochromatic or two-color printing, as described hereinafter, an image is formed in the image areas

67

a

and

67

b

or image areas

67

c

and

67

d

to be printed with the same ink.

In the foregoing embodiment, two image areas

67

a

and

67

b

or

67

c

and

67

d

are provided on the single plate P mounted peripherally of the first or second plate cylinder

11

or

12

, in order to simplify the structure of the first or second plate cylinder

11

or

12

. Alternatively, the first or second plate cylinder

11

or

12

may include two sets of grippers, each set for holding the forward and rear ends of one plate P. Then, as shown in

FIG. 3

, each of the first and second plate cylinders

11

and

12

may support two plates P each having a single image area. As used herein, the term “holding a plate having two image areas” should be interpreted to include the case of holding a single plate having two image areas and the case of holding two plates each having a single image area. In the latter case also, the two plates P should be held as evenly separated on the first or second plate cylinder

11

or

12

, so that the image areas recorded on the respective plates are in evenly separated positions, i.e. in positions separated from each other by 180 degrees.

Referring again to

FIG. 1

, the ink feeders

20

a

and

20

b

are arranged around the first plate cylinder

11

in the first printing position, while the ink feeders

20

c

and

20

d

are arranged around the second plate cylinder

12

in the second printing position, as described hereinbefore. Each of these ink feeders

20

a

,

20

b

,

20

c

and

20

d

(which may be referred to collectively as “ink feeders

20

”) includes a plurality of ink rollers

71

and an inkwell

72

.

The ink rollers

71

of the ink feeders

20

a

and

20

b

are swingable by action of cams or the like not shown. With the swinging movement, the ink rollers

71

of the ink feeder

20

a

or

20

b

come into contact with one of the two image areas

67

a

and

67

b

formed on the plate P mounted peripherally of the first plate cylinder

11

. Thus, the ink is fed only to an intended one of the image areas

67

a

and

67

b

. Similarly, the ink rollers

71

of the ink feeders

20

c

and

20

d

are swingable by action of cams or the like not shown. With the swinging movement, the ink rollers

71

of the ink feeder

20

c

or

20

d

come into contact with one of the two image areas

67

c

and

67

d

formed on the plate P mounted peripherally of the second plate cylinder

12

. Thus, the ink is fed only to an intended one of the image areas

67

c

and

67

d.

The dampening water feeders

21

a

,

21

b

,

21

c

and

21

d

(which may be referred to collectively as “dampening water feeders

21

”) feed dampening water to the plates P before the ink feeders

20

feed the inks thereto. Of these dampening water feeders

21

, the water feeder

21

a

feeds dampening water to the image area

67

a

on the plate P, the water feeder

21

b

feeds dampening water to the image area

67

b

on the plate P, the water feeder

21

c

feeds dampening water to the image area

67

c

on the plate P, and the water feeder

21

d

feeds dampening water to the image area

67

d

on the plate P.

The developing device

26

is disposed under the first or second plate cylinder

11

or

12

in the image recording position. This developing device

26

includes a developing unit, a fixing unit and a squeezing unit, which are vertically movable between a standby position shown in two-dot chain lines and a developing position shown in solid lines in FIG.

1

.

In developing the images recorded on the plate P by the image recorder

25

, the developing unit, fixing unit and squeezing unit are successively brought into contact with the plate P rotated with the first or second plate cylinder

11

or

12

.

The first and second blanket cylinders

13

and

14

movable into contact with the first and second plate cylinders

11

and

12

have the same diameter as the first and second plate cylinders

11

and

12

, and have ink transfer blankets mounted peripherally thereof. Each of the first and second blanket cylinders

13

and

14

is movable into and out of contact with the first or second plate cylinder

11

or

12

and the impression cylinder

15

by a contact mechanism described hereinafter.

The first and second blanket cylinders

13

and

14

with the soft blankets mounted peripherally thereof are slightly reduced in diameter when in contact with the first and second plate cylinders

11

and

12

. As used herein, the term “the same diameter” allows for slight errors due to such changes in diameter. Further, as described hereinafter, the impression cylinder

15

, paper feed cylinder

16

and paper discharge cylinder

17

have half the diameter of the first and second plate cylinders

11

and

12

and the first and second blanket cylinders

13

and

14

. This also allows for slight errors due to changes in diameter.

FIG. 4

is a schematic view of the contact mechanism for acting on the first blanket cylinder

13

. The contact mechanism for the second blanket cylinder

14

is similar in structure to the contact mechanism shown in FIG.

4

.

The first blanket cylinder

13

is rotatably supported by a shaft

101

. An eccentric shaft

102

decentered from the shaft

101

is formed on a side thereof. The eccentric shaft

102

is surrounded by an eccentric bearing

103

decentered from the shafts

101

and

102

. Thus, as shown in

FIG. 4

, the axis

104

of the shaft

101

, i.e. the axis of the first blanket cylinder

13

, the axis

105

of the eccentric shaft

102

and the axis

106

of the eccentric bearing

103

are offset from one another.

The eccentric shaft

102

has a plate

107

fixed thereto, while the eccentric bearing

103

has a plate

108

fixed thereto. The two fixed plates

107

and

108

are interconnected by two coupling plates

111

and

112

forming a link mechanism. The forward end of a cylinder rod

114

of an air cylinder

113

is connected to a connection between the two coupling plates

111

and

112

. The air cylinder

113

has a cylinder body coupled to an end of a rotary plate

116

rotatable about a shaft

115

. The other end of the rotary plate

116

is coupled through a rod

117

to a plate

118

fixed to the eccentric bearing

103

.

The rotary plate

116

is coupled to a shaft

120

of an eccentric member

119

through two coupling plates

121

and

122

forming a link mechanism. The forward end of a cylinder rod

124

of an air cylinder

123

fixed to a main body of the apparatus is connected to a connection between the two coupling plates

121

and

122

. The eccentric member

119

has a worm wheel

125

connected thereto and meshed with a worm gear

127

rotatable by a motor

126

.

With the cylinder rods

114

and

124

of the air cylinders

113

and

123

extended as shown in

FIG. 4

, the surface of the first blanket cylinder

13

is spaced slightly from the surfaces of the first plate cylinder

11

and the impression cylinder

15

.

When the air cylinder

113

is driven to retract the cylinder rod

114

, the first blanket cylinder

13

is moved toward and into contact with the first plate cylinder

11

by action of the link mechanism formed of the two coupling plates

111

and

112

.

When the air cylinder

123

is driven to retract the cylinder rod

124

, the first blanket cylinder

13

is moved toward and into contact with the impression cylinder

15

by action of the link mechanism formed of the two coupling plates

121

and

122

. At this time, the rotary plate

116

also rotates clockwise about the shaft

115

, whereby the first blanket cylinder

13

moves not only toward the impression cylinder

15

but also toward the first plate cylinder

11

. Consequently, the first blanket cylinder

13

is maintained in contact with the first plate cylinder

11

.

Rotation of the eccentric member

119

results in a slight movement of its shaft

120

. Thus, the contact pressure of the first blanket cylinder

13

for contacting the impression cylinder

15

and the first plate cylinder

11

may be adjusted by driving the motor

126

to rotate the worm wheel

125

connected to the eccentric member

119

thereby to move the shaft

120

slightly. This enables adjustment of a printing pressure in time of printing with the first blanket cylinder

13

.

Referring again to

FIG. 1

, the blanket cleaning unit

29

disposed between the first and second blanket cylinders

13

and

14

cleans the surfaces of the first and second blanket cylinders

13

and

14

by feeding a cleaning solution to an elongate cleaning cloth extending from a delivery roll to a take-up roll through a plurality of pressure rollers, and sliding the cleaning cloth in contact with the first and second blanket cylinders

13

and

14

. The cleaning cloth may further be brought into contact with the surface of the impression cylinder

15

for cleaning the same.

The impression cylinder

15

contactable by the first and second blanket cylinders

13

and

14

has half the diameter of the first and second plate cylinders

11

and

12

and the first and second blanket cylinders

13

and

14

, as noted hereinbefore. Further, the impression cylinder

15

has a gripper

573

, which will be described later in regards to FIGS.

17

and

21

-

32

for holding and transporting the forward end of printing paper.

The paper feed cylinder

16

disposed adjacent the impression cylinder

15

has the same diameter as the impression cylinder

15

. The paper feed cylinder

16

has a gripper

574

, which will also be described later in regards to FIGS.

17

and

21

-

32

, for holding and transporting the forward end of each sheet of printing paper fed from the paper storage

27

by a reciprocating suction board

74

. When the printing paper is transferred from the feed cylinder

16

to the impression cylinder

15

, the gripper

573

of the impression cylinder

15

holds the forward end of the printing paper which has been held by the gripper

574

of the feed cylinder

16

.

The paper discharge cylinder

17

disposed adjacent the impression cylinder

15

has the same diameter as the impression cylinder

15

. The discharge cylinder

17

has a pair of chains

19

wound around opposite ends thereof. The chains

19

are interconnected by coupling members, not shown, having a plurality of grippers

575

which will also be described later in regards to FIGS.

17

and

21

-

32

arranged thereon. When the impression cylinder

15

transfers the printing paper to the discharge cylinder

17

, one of the grippers

575

of the discharge cylinder

17

holds the forward end of the printing paper having been held by the gripper

573

of the impression cylinder

15

.

With movement of the chains

19

, the printing paper is transorted to the paper discharge station

28

to be discharged thereon.

The paper feed cylinder

16

is connected to a drive motor through a belt not shown. The paper feed cylinder

16

, impression cylinder

15

, paper discharge cylinder

17

and the first and second blanket cylinders

13

and

14

are coupled to one another by gears mounted on end portions thereof, respectively. Further, the first and second blanket cylinders

13

and

14

are coupled to the first and second plate cylinders

11

and

12

in the first and second printing positions, respectively, by gears mounted on end portions thereof. Thus, a motor, not shown, is operable to rotate the paper feed cylinder

16

, impression cylinder

15

, paper discharge cylinder

17

, the first and second blanket cylinders

13

and

14

and the first and second plate cylinders

11

and

12

synchronously with one another.

FIG. 5

is a block diagram showing a principal electrical structure of the printing apparatus. This printing apparatus includes a control unit

140

having a ROM

141

for storing operating programs necessary for controlling the apparatus, a RAM

142

for temporarily storing data and the like during a control operation, and a CPU

143

for performing logic operations. The control unit

140

has a driving circuit

145

connected thereto through an interface

144

, for generating driving signals for driving the ink feeders

20

, image recorder

25

, developing device

26

, blanket cleaning unit

29

, the moving mechanisms for moving the first and second plate cylinders

11

and

12

, the contact mechanisms for the first and second blanket cylinders

13

and

14

, and so on. The printing apparatus is controlled by the control unit

140

to execute prepress and printing operations as described hereinafter.

The prepress and printing operations of the printing apparatus will be described next.

FIG. 6

is a flow chart showing an outline of the prepress and printing operations of the printing apparatus.

First, the printing apparatus executes a prepress process for recording and developing images on the plates P mounted on the first and second plate cylinders

11

and

12

(step S

1

). This prepress process follows the steps constituting a subroutine as shown in the flow chart of FIG.

7

.

The first plate cylinder

11

is first moved to a prepress position, i.e. the image recording position shown in a two-dot chain line in FIG.

1

. (step S

11

).

Next, a plate P is fed to the outer periphery of the first plate cylinder

11

(step S

12

). To achieve the feeding of the plate P, the pair of grippers, not shown, grip the forward end of plate P drawn from the supply cassette

63

, and the rear end of plate P cut by the cutter

66

.

Then, an image is recorded on the plate P mounted peripherally of the first plate cylinder

11

(step S

13

). For recording the image, the image recorder

25

irradiates the plate P mounted peripherally of the first plate cylinder

11

with a modulated laser beam while the first plate cylinder

11

is rotated at low speed by the cylinder rotating mechanism not shown.

Next, the image recorded on the plate P is developed (step S

14

). The developing step is executed by raising the developing device

26

from the standby position shown in two-dot chain lines to the developing position shown in solid lines in FIG.

1

and thereafter successively moving the developing unit, fixing unit and squeezing unit into contact with the plate P rotating with the first plate cylinder

11

.

Upon completion of the developing step, the first plate cylinder

11

is moved to the first printing position shown in the solid line in

FIG. 1

(step S

15

).

Subsequently, the printing apparatus carries out an operation similar to steps S

11

to S

15

by way of a prepress process for the plate P mounted peripherally of the second plate cylinder

12

(steps S

16

to S

20

). Completion of the prepress steps for the plates P mounted peripherally of the first and second plate cylinders

11

and

12

brings the prepress process to an end.

Referring again to

FIG. 6

, the prepress process is followed by a printing process for printing the printing paper with the plates P mounted on the first and second plate cylinders

11

and

12

(step S

2

). The operation of the printing apparatus in this printing process will be described in detail hereinafter.

Upon completion of the printing process, the plates P used in the printing are removed (step S

3

). To remove the plates P, the first plate cylinder

11

is first moved to the prepress position shown in the two-dot chain line in FIG.

1

. Then, while the first plate cylinder

11

is rotated counterclockwise, the pawl mechanism

73

separates an end of the plate P from the first plate cylinder

11

. The plate P separated is guided by the conveyor mechanism

69

into the discharge cassette

68

. After returning the first plate cylinder

11

to the first printing position, the second plate cylinder

12

is moved from the second printing position to the prepress position to undergo an operation similar to the above, thereby having the plate P removed from the second plate cylinder

12

for discharge into the discharge cassette

68

.

Upon completion of the plate removing step, the first and second blanket cylinders

13

and

14

are cleaned (step S

4

). For cleaning the first and second blanket cylinders

13

and

14

, the contact mechanisms as shown in

FIG. 4

separate the first and second blanket cylinders

13

and

14

from the first and second plate cylinders

11

and

12

and the impression cylinder

15

. The first and second blanket cylinders

13

and