The present invention relates to a stencil printing machine having a printing drum in which perforated stencil sheet is made to wrap on an outer circumferential surface thereof and which is driven to rotate.

There has been known a stencil printing machine having a printing drum in a cylindrical shape having the features of the preamble of claim 1. An explanation will be given of an example of a structure of the stencil printing machine. The printing drum of the stencil printing machine is provided with a porous and cylindrical supporting member and a mesh screen layer which is made to wrap on an outer circumferential surface of the supporting member. At an inner portion of the printing drum, there is provided ink supplying means for supplying ink onto an inner circumferential face of the printing drum. On an outer side of the printing drum, there is provided a press roller as pressing means in proximity to the printing drum. Stencil sheet is made to wrap on an outer circumferential surface of the printing drum. The printing drum and the pressing means are rotated and print sheet is supplied therebetween. Ink supplied to the inner circumferential face of the printing drum, is transcribed onto the print sheet after passing through opening portions of the supporting member, the mesh screen layer and perforations of the stencil sheet to thereby form an image.

According to the above-described machine, prior to printing operation, a reading apparatus reads image of original and converts the image into electric signals. In accordance with the signals, a stencil making apparatus having a heat generating element such as a thermal head or the like perforates the stencil sheet. Further, the perforated stencil sheet is made to wrap on the outer circumferential surface of the printing drum and thereafter, the printing operation is carried out as described above.

According to the above-described machine, generally, when there causes a shift between printed image and draft image, there is carried out image adjustment in the longitudinal direction and the lateral direction.

Correction of image shift in the longitudinal direction is disclosed in Japanese Patent Laid-Open No. 66308/1975. Correction of image shift in the horizontal direction (lateral direction) is disclosed in Japanese Patent Laid-Open No. 218435/1988.

Further, in an offset printing machine, an aluminum plate is used as a printing plate. The aluminum plate is used by fixing a front end portion thereof by a clamp apparatus and making the aluminum plate wrap on a plate cylinder. A used aluminum plate is provided with considerable strength. All of the face of the aluminum plate is not fixed by the plate cylinder. Hence, in order to adjust a shift of the printed image, the aluminum plate is directly moved by a meandering adjusting member by pivoting the clamp apparatus holding a front end portion of the aluminum plate or moving the aluminum plate in a circular arc shape or the like.

However, according to the above-described conventional stencil printing machine, there poses a problem in which although image shift in the longitudinal direction or the lateral direction can be adjusted, image shift in a skewed direction cannot be adjusted. Further, when the structure of the offset printing machine is applied to the stencil printing machine, the strength of the stencil sheet is extremely smaller than that of the aluminum plate and therefore, there causes a problem in which wrinkle is formed in the stencil sheet or the like.

Japanese Patent Laid-Open No. 344648/1994 discloses a technology for carrying out skew adjustment of image by twisting a printing drum on which stencil sheet is made to wrap. However, strength of the printing drum is small since there are formed a number of perforations for passing ink at a portion of a peripheral wall thereof. Therefore, when the printing drum is twisted as described above, unreasonable stress is generated in the printing drum and there causes a problem of destruction or the like.

US-A-3,111,052, DE-C-476 600, and US-A-5,660,107 are another prior art documents to the present application.

According to the present invention, the above-described problem is alleviated and image skew adjustment is carried out simply and without generating unreasonable stress in the printing drum.

According to a first aspect of the present invention, there is provided a stencil printing machine comprising a base member (15) having rigidity and rotable about a central axis line of its own, an ink-permeable member (2) wound around the base member along a rotational direction and forming a circumferential surface for attaching stencil sheet, and characterized by skew-angle adjusting means (30, 40) arranged to move the ink-permeable member to a skewed angle relative to the base member which is not parallel with either of the central axis line and the rotational direction.

The skew-angle adjusting means (30, 40) may be arranged to move a side of one end portion of the ink-permeable member (2) to a skewed angle.

The ink-permeable member may be pivotable relative to the base member (15) centering on a substantially central portion in the central axis line direction of a side of the one end portion of the ink-permeable member (2).

A side of other end portion of the ink-permeable member (2) may be made movable along a direction of the central axis line.

The skew-angle adjusting means (30, 40) may be arranged to move the side of the one end portion and a side of other end portion of the ink-permeable member (2) in the skewed direction in cooperation with each other.

The stencil printing machine may comprise a pair of circular plate members (16) arranged coaxially on a common central axis line the base member (15) having a first base member (connecting base plate 17) for connecting the pair of circular plate members and rotatable around the central axis line. Next, the stencil printing machine may be further provided with a second base member (clamping base plate 18) attached pivotally to the first member, clamping means (3) provided to the second base member, and an ink-permeable member (2). The ink-permeable member may be provided with one end portion attached to one end portion of the second base member, a pair of side edge portions which are made to wrap on the pair of circular plate members along a rotational direction of the base member and other end portion attached to other end portion of the second base member and forms a circumferential surface for attaching stencil sheet one end portion of which is fixed to the clamping means. Further, the stencil printing machine may be provided with the skew-angle adjusting means (30) provided to the circular plate member for moving the ink-permeable member to said skewed angle by pivoting the second base member relative to the first base member.

The stencil printing machine according to the sixth aspect further may comprise an engaging portion (25) formed at other end portion of the second base member (clamp base plate 18) along a direction of the central axis line, an elastic member (spring 34) for connecting the other end portion of the ink-permeable member (2) to the engaging portion, wherein when the second base member is moved in the skewed angle by the skew adjusting means (30), a side of the other end portion of the ink-permeable member is moved along the direction of the central axis line.

Further, the stencil printing machine may be provided with the skew-angle adjusting means (40) having a moving member (43) provided to the circular plate member to be pivotable around the central axis line and connected with a side edge portion of the second base member arranged to move the ink-permeable member to said skewed angle by pivoting the second base member relative to the first base member by moving the moving member.

The stencil printing machine may further comprise a first gear portion (51) formed at the other end portion of the second base member (clamping base plate 18), and a second gear portion (52) provided on a side of the other end portion of the ink-permeable member (2) and engaged with the first gear portion (52), wherein when the second base member is moved to the skewed angle by the skew adjusting means (40), the side of the other end portion of the ink-permeable member is moved to the skewed angle.

The stencil printing machine may comprise a base member in a cylindrical shape having a rigid peripheral wall having an ink-permeable opening area and rotatable around a central axis line of its own, an ink-permeable member mounted to an outer circumferential surface of a peripheral wall of the base member along a rotational direction of the base member and attached with stencil sheet.

• Fig. 1 shows a substantially central portion of a plane view of a first example according to the present invention;
• . Fig. 2 shows a right half portion of the plane view of the first example according to the present invention;
• Fig. 3 is a right side view of the first example according to the present invention;
• Fig. 4 is a sectional view viewed from a cutting line of Fig. 2;
• Fig. 5 is a view viewed from an arrow mark of Fig. 2;
• Fig. 6 shows a left half portion of a plane view of a second example according to the present invention;
• Fig. 7 shows a right half portion of the plane view of the second example according to the present invention;
• Fig. 8 is a right side view cutting a portion of the second example according to the present invention;
• Fig. 9 shows a right half portion breaking a portion of the plane view of the second example according to the present invention;
• Fig. 10 is a right side view of the second example according to the present invention;
• Fig. 11 is a view showing to enlarge a portion of a control panel in the examples according to the present invention; and
• Fig. 12 is a view showing a total constitution of the examples according to the present invention.

An explanation will be given of a first example of an embodiment according to the present invention in reference to Fig. 1 through Fig. 5 and Fig. 12.

As shown by Fig. 12, a stencil printing machine according to the example is provided with a printing drum 1. The printing drum 1 is driven to rotate around a central axis line of its own. A circumferential surface of the printing drum 1 is constituted by an ink-permeable member 2 which is ink-permeable and flexible and is elastically deformed outwardly when depressed from an inner side thereof. At the outer peripheral surface of the printing drum 1, there is provided clamping means 3. Perforated stencil sheet is held by the clamping means 3 at its front end and is made to wrap on the outer circumferential surface of the ink-permeable member 2. At an inner portion of the printing drum 1, there is provided a squeegee roller 4 liftably. The squeegee roller 4 is lowered at a predetermined timing in synchronism with rotation of the printing drum 1 and presses the ink-permeable member 2 outwardly. The squeegee roller 4 is driven to rotate in a direction the same as that of the printing drum 1 in cooperation with the printing drum 1 by a drive gear 5 of the printing drum 1, an intermediate gear 6 and a gear 7 of the squeegee roller 4. A doctor roller 9 is arranged to be spaced apart from the squeegee roller 4 by a predetermined interval. Ink is supplied to the inner portion of the printing drum 1 by an ink supply pipe 8 and a constant amount of ink is supplied to a circumferential surface of the squeegee roller 4 by the doctor roller 9.

A pressure drum 10 is arranged on the lower side of the printing drum 1. The diameter of the pressure drum 10 is substantially the same as the diameter of the printing drum 1. In a nonprinting state, there is provided a very small clearance between the printing drum 1 and pressure drum 10. The pressure drum 10 is driven to rotate in a direction reverse to the direction of the printing drum 1 in synchronism with the rotation of the printing drum 1. At an outer peripheral surface of the pressure drum 10, there is provided a hold claw 11 for holding a front end of print sheet openably and closably. At the outer circumferential surface of the pressure drum 10, there is provided a recess portion 12 to evade interference with the clamping means 3 of the printing drum 1.

The front end of supplied print sheet is held by the hold claw 11 of the pressure drum 10. Print sheet is carried in accordance with the rotation of the pressure drum 10. The printing drum 1 is rotated in synchronism with the pressure drum 10. The squeegee roller 4 is lowered at a predetermined timing to thereby press the ink-permeable member 2 outwardly. The ink-permeable member 2 and stencil sheet which are deformed outwardly, sandwich the print sheet between the pressure drum 10 and the ink-permeable member 2 as well as the stencil sheet. The print sheet is carried while being sandwiched between the deformed printing drum 1 and the pressure drum 10. While carrying the print sheet, ink supplied to the inner peripheral face of the ink-permeable member 2, passes through the ink-permeable member 2 and perforations of the stencil sheet and is transcribed onto the print sheet to thereby form an image in correspondence with perforated image of the stencil sheet.

Next, a further detailed explanation will be given of the structure of the printing drum 1 according to the example in reference to Fig. 1 through Fig. 4 and Fig. 12 as follows.

The printing drum 1 is provided with a base member 15. The base member 15 is provided with a pair of circular plate members 16 coaxially arranged on a common central axis line and a connecting base plate 17 as a first member for connecting the pair of circular plate members 16. A longitudinal direction of the connecting base plate 17 is in parallel with the central axis line of the circular plate member 16. The base member 15 is driven to rotate around the central axis line by driving means, not illustrated.

As shown by Fig. 1 and Fig. 2, the connecting base plate 17 is rotatably attached with a clamp base plate 18 as a second member. According to the example, a substantially central portion of the clamp base plate 18 with respect to the axis line direction of the base member 15, is pivotally connected to a substantially center portion of the connecting base plate 17 by a fulcrum shaft 19. A position of connecting the two base plates 17 and 18 may not necessarily be disposed at the substantially central portion.

The clamp base plate 18 is provided with the clamping means 3. The clamping means 3 is provided with a rotation fulcrum 20 attached to the clamp base plate 18, a rotating shaft 21 pivotally supported by the rotation fulcrum 20 and a clamp plate 22 made of a metal attached to the rotating shaft 21. The rotating shaft 21 is in parallel with the central axis line of the base member 15. The rotating shaft 21 is pivoted by a drive mechanism, not illustrated. At an upper face of the clamp base plate 18, there is provided a clamp base having magnetism on one side of the rotating shaft 21. The clamp base plate 22 is magnetically attached to the clamp base while pinching the front end of the stencil sheet to thereby fix the front end of the stencil sheet to the clamp base plate 18. The clamp base plate 22 made of a metal strongly holds the stencil sheet by magnetic force.

As shown by Fig. 2, one end portion of the clamp base plate 18 is attached with one end portion of the ink-permeable member 2. The one end portion of the ink-permeable member 2 is on the upstream side in the rotational direction of the printing drum 1. At least a portion of the ink-permeable member 2 is constituted by a material which is ink-permeable and flexible. The ink-permeable member 2 is made to wrap on the base member 15 such that a pair of side edge portions thereof are brought into slidable contact with the circumferential surfaces of the pair of circular plate members 16. Other end portion of the ink-permeable member 2 is fixed with a connecting plate 23 which is slender in the axis line direction. The other end portion of the ink-permeable member 2 is disposed on the downstream side in the rotational direction of the printing drum 1. The connecting plate 23 is attached to the other end portion of the clamp base plate 18 via a spring 24 which is an elastic member. In this way, the ink-permeable member 2 is pulled to the downstream side in the rotational direction by elastic force of the spring 24 and is made to wrap on the circumferential surfaces of the pair of circular plate members 16. Therefore, the ink-permeable member 2 constitutes a cylindrical shape as a whole. When the ink-permeable member 2 is depressed from the inner side, the ink-permeable member 2 is bulged outwardly while sliding on the circumferential surfaces of the circular plate members 16 and when the depressing force is removed, the ink-permeable member returns to the original state by the spring 24.

As shown by Fig. 2 and Fig. 5, an engaging portion 25 is formed at the other end portion of the clamp member 18. The engaging portion 25 is formed with a long hole 26 along the direction of the central axis line. The spring 24 attached to the connecting plate 23 of the ink-permeable member 2, is movably engaged with the long hole 26 of the engaging portion 25. Therefore, when the one end portion side (upstream side) of the ink-permeable member 2 is moved by skew-angle adjusting means, explained below, the other end portion side (downstream side) of the ink-permeable member 2 is moved along the axis line direction of the base member 15.

According to the example, the ink-permeable member 2 which is made to wrap on the base member 15 is moved in a skewed direction which is not in parallel with either of the direction of the central axis line (transfer direction) and the rotational direction (longitudinal direction). An explanation will be given of skew-angle adjusting means 30 achieving the function.

As shown by Figures 2, 3 and 4, a cam 31 is axially supported by one end portion of the connecting base plate 17. The cam 31 is provided with a cam portion 32 and a gear portion 33. The cam portion 32 is provided with a stepped difference formed in the thickness direction and the stepped difference is engaged with a side edge portion of the clamp base plate 18. A spring 34 is provided between the clamp base plate 18 and the circular plate member 16 and urges the clamp base plate 18 to the cam portion 32. Therefore, rotation of the cam 31 smoothly moves the clamp base plate 18 with no play between the clamp base plate 18 and the cam portion 32. A moving gear 35 is provided to the circumferential surface of the circular plate member 16 via an attachment plate. The gear portion 33 of the cam 31 is engaged with the moving gear 35. The moving gear 35 is connected with a drive shaft, not illustrated, as driving means as necessary. When the printing drum 1 is stopped at a predetermined position, the drive shaft approaches in a direction designated by an arrow mark (c) in Fig. 2 and is connected to the moving gear 35. The clamp base plate 18 is axially supported at its central portion and accordingly, when the rotating cam 31 moves a side edge portion of the clamp base plate 18, the clamp base plate 18 is rotated centering on the fulcrum shaft 19. The ink-permeable member 2 attached to the clamp base plate 18 and the stencil sheet attached to the ink-permeable member 2 are moved to the skewed angle on the base member 15.

Next, an explanation will be given of operation in the above-described constitution.

Perforated stencil sheet is mounted to the printing drum 1. That is, the front end portion of the stencil sheet is fixed onto the clamp base plate 18 by the clamp plate 22 and the stencil sheet is made to wrap on the ink-permeable member 2 in accordance with rotation of the printing drum 1. Thereafter, printing operation is carried out as described above.

After carrying out the printing operation, when provided image is shifted to a skewed angle relative to the print sheet, position of the image is adjusted by using the skew-angle adjusting means 30. By rotating the moving gear 35, the cam 31 in mesh with the moving gear 35 is rotated. As shown by an arrow mark (d) in Fig. 1, the clamp base plate 18 in contact with the cam 31 carries out circular motion centering on the fulcrum shaft 19. Thereby, the ink-permeable member 2 fixed to the clamp base plate 18 also carries out rotational motion centering on the fulcrum shaft 19. The perforated stencil sheet on the ink-permeable member 2 also carries out circular motion centering on the fulcrum shaft 19. As a result, the shift of the image in the skewed direction of the stencil sheet relative to the print sheet is adjusted. According to the example, the fulcrum shaft 19 of the clamp base plate 18 is disposed at the substantially central portion of the printing drum 1 in the central axis line direction and accordingly, reference in adjusting the image is clear and an adjustment width can be minimized. Further, in a normal case, an amount of moving the ink-permeable member in the skew adjustment, is about several millimeters at maximum in an amount of movement in the rotational direction at an end portion of the printing drum in the central axis line.

The ink-permeable member is made to wrap on the circular member 16 by the elastic force of the spring 24. Therefore, in the above-described skew adjustment, even when the upstream side in the rotational direction of the ink-permeable member is pivoted, the downstream side is not pivoted simultaneously. However, according to the structure of the example, when the one end portion side (upstream side) of the ink-permeable member 2 is pivoted, the connecting plate 23 on the other end portion side (down stream side) of the ink-permeable member 2 can be slid in the axial direction designated by an arrow mark (e) in Fig. 2. Therefore, unreasonable force is not exerted to the stencil sheet and wrinkle is not caused in the stencil sheet.

An explanation will be given of a second example of an embodiment according to the present invention in reference to Fig. 6 through Fig. 10.

As a whole, a constitution of a stencil printing machine according to the example is substantially the same as that in the first example. In the constitution of the printing drum 1 of the example, portions substantially the same as those of the first example in view of their functions are attached with notations the same as those in the first example and an explanation thereof will be omitted. In the following, an explanation will be given centering on skew adjusting means 40 for moving the ink-permeable member 2 in the skewed direction.

According to the example, on an inner face side of at least one circular plate member 41, a recess portion 42 in a shape of a fan is formed to open to an outer circumferential surface thereof. At the recess portion 42, there is provided a moving member 43 in a shape of a fan. The moving member 43 is pivotable around the central axis line of the base member 15. The side edge portion of the clamping base plate 18 is connected to an outer circumferential surface of the moving member 43. The moving member 43 connected with the clamping base plate 18 is pivoted by driving means.

As explanation will be given of driving means for moving the moving member 43.

As shown by Fig. 8, a gear portion 44 is provided at a portion of the moving member 43. As shown by Fig. 9, the circular plate member 41 is arranged with a first drive gear 45 in mesh with the gear portion 44. A central shaft 46 of the first drive gear 45 penetrates the circular plate member 41 and is projected to outside. An end portion of the central shaft 46 disposed at outside of the circular plate member 41, is supported by a fixing sheet 47. On an inner side of the fixing sheet 47, the central shaft 46 is attached with a second drive gear 48. Further, the fixing sheet 47 rotatably holds a first transmission gear 49 in mesh with the second drive gear 48 and the first transmission gear 49 is coaxially provided with a second transmission gear 50. The second transmission gear 50 is connected with an outside drive source, not illustrated.

When image is adjusted, drive force of an adjusting motor, not illustrated in the drawing, is transmitted in an order of the second transmission gear 50, the first transmission gear 49, the second drive gear 48 and the first drive gear 45 to thereby move the moving member 43 in the circumferential direction of the circular plate member 41. As a result, a phase in the rotational direction between the circular plate member 41 and the moving member 43 with respect to the central axis line, is changed and a positional relationship between the connecting base plate 17 and the clamping base plate 18 fixed to the both members is also changed. In this case, the clamping base plate 18 is rotatably supported by the fulcrum shaft 19 of the connecting base plate 17 at its substantially central point thereof. Therefore, the clamping base plate 18 carries out rotational motion centering on the fulcrum shaft 19 by a change in the phase between the moving member 43 and the circular plate member 41. The ink-permeable member 2 attached to the clamping base plate 18 and the stencil sheet attached thereto also carry out rotational motion centering on the fulcrum shaft 19. Thereby, the skew-angle adjustment of image can be carried out.

According to the example, when the upstream side of the ink-permeable member 2 is moved to the skewed-angle, in cooperation therewith, the downstream side of the ink-permeable member 2 is also moved to the skewed angle. Such an operation is achieved by the following mechanism. As shown by Fig. 6, a first gear portion 51 is formed at the other end portion of the clamping base plate 18. The first gear portion 51 is formed at proximity of the fulcrum shaft 19. Further, a second gear portion 52 is formed at the connecting plate 23 attached to the other end portion side of the ink-permeable member 2. The first gear portion 51 and the second gear portion 52 are in mesh with each other. Therefore, when the clamping base plate 18 is pivoted by the skew adjusting means 40, the connecting base plate 23 connected to the downstream side of the ink-permeable member 2 is also pivoted.

Fig. 11 is an enlarged view of a control panel 60 applied to the above-described examples. At a portion of the control panel 60, there are provided two of direction switches 61 and 62 indicating the rotational direction of the ink-permeable member 2 in the skew adjustment (meandering correction). Further, there are also provided display elements 63 and 64 indicating an amount of rotating the ink-permeable member 2 in the skew adjustment (meandering correction). The display element 63 at the center indicates a correction amount of 0. The display elements 64 aligned respectively by fours on the left and on the right indicate correction amounts each of 0.4 mm per piece. The correction amount indicates a movement amount in the circumferential direction at the side edge portion of the ink-permeable member 2. Therefore, a maximum of 2 mm of correction can be carried out in each of the two rotation directions. When such operating means and displaying means are provided at the control panel 60 of the printing machine, the skew adjustment of the ink-permeable member 2 can simply be carried out.

Further, the moving gear 35 and the second transmission gear 50 in the above-described embodiments, each is in mesh with a drive gear attached to a drive shaft of a motor which is driving means, not illustrated. Further, when the direction switch 61 or 62 of the control panel 60 is depressed, the motor is driven and the screen member 2 is pivoted in accordance with an amount of driving the motor. Thereby, the skewed direction of the printed image formed at the print sheet can be adjusted.

Further, in the above-described embodiments, when printing operation is carried out by using successive newly perforated stencil sheet, it is necessary to peel off the stencil sheet which is made to wrap on the outer circumferential surface of the printing drum 1 by discharging means, not illustrated, and abandon the stencil sheet to a discharge box or the like, not illustrated. In that case, the stencil sheet is peeled off while rotating the printing drum and therefore, when the stencil sheet on the screen member is brought into a state of being inclined to the rotational direction of the printing drum, normal discharging processing cannot be carried out. Therefore, prior to the discharging operation, there is carried out a control of returning the screen member 2 to a home position which is an initially set position. In that case, lighting states of the display elements 63 and 64 on the control panel 60 are checked by the controlling means, not illustrated. When the display element 63 is not lighted, that is, when the skew adjustment of the printed image is carried out and any one of the display elements 64 is lighted, the screen member 2 is driven to turn to the home position by driving the motor. Further, as timing of returning the screen member 2 to the home position, time point at which new perforating instruction is inputted from an operation panel or the like is preferable. When the screen member 2 is returned to the home position in the discharge operation, one end portion of successive newly perforated stencil sheet can firmly be held by the clamping means 3 in a predetermined state.

The stencil printing machine of the above-described example is provided with the printing drum in which the ink-permeable member is made to wrap on the pair of connected circular plate members by the elastic force of the springs. According to the machine having such a constitution, printing operation is carried out by deforming the ink-permeable member outwardly and sandwiching print sheet between the ink-permeable member and the pressure drum at outside thereof. However, the present invention is not applied only to the stencil printing machine having such a basic constitution. The present invention is applicable also to a stencil printing machine having a rotatable base member having rigidity and an ink-permeable member which is made to wrap on the base member. The structure of the base member is not particularly limited. For example, a base member in a cylindrical shape made of a metal may be used. In such a case, an ink-permeable opening area is formed at a peripheral wall thereof. The ink-permeable member is made to wrap around the cylindrical member made of a metal.

Embodiments of the present invention, can provide that adjustment can be carried out even in the case in which printed image is printed obliquely and printed image having excellent image quality can be provided,

When both end portions of the ink-permeable member cooperate with each other, printing operation can be carried out without exerting unreasonable force to the printing drum 1 or the stencil sheet and accordingly, shift or the like of the stencil sheet can be prevented;

When there is constructed the constitution in which the ink-permeable member is pivoted by the cam provided to the circular plate member, there is no concern in which the skew adjusting means is brought into contact with and destructed by other printing member (pressure drum or the like) arranged outside of the printing drum, and

When there is constructed the constitution in which the ink-permeable member is pivoted by the moving members pivoted coaxially with the circular plate member, essential portions of the skew adjusting means can be arranged on the side of the rotational center of the circular plate member and accordingly, inertia of the printing drum is reduced and a variation in load in operating the printing machine is reduced.