GB2102343A

GB2102343A - Image position adjuster for an offset printing press

Info

Publication number: GB2102343A
Application number: GB08218510A
Authority: GB
Inventors: Koji Ishii
Original assignee: Ryobi Ltd
Current assignee: Ryobi Ltd
Priority date: 1981-07-09
Filing date: 1982-06-25
Publication date: 1983-02-02
Also published as: JPS587653U; GB2102343B; DE3224649C2; DE3224649A1

Abstract

An impression cylinder 2 has a gear 4 thereon which is meshed with a gear 5 on a rubber blanket cylinder 3, the latter also having thereon a worm wheel which is coupled to an adjusting gear 6 by way of a transmission gear mechanism 10. In normal operation of the press, a gear 9 on a shaft 8 is disengaged from the gear 6: however, when it is desired to adjust the position of the image on the impression cylinder 2, the shaft 8 is moved axially to engage the gear 9 with the gear 6, and is turned so as to rotate the blanket cylinder 3 by way of the mechanism 10 and the worm wheel, such rotation also being transmitted to the impression cylinder 2 by means of the gears 4 and 5 so that relative rotation occurs between the two cylinders 2 and 3. <IMAGE>

Description

SPECIFICATION Image position adjuster for an offset printing press The present invention relates to an image position adjuster for an offset printing press.

In the field of offset printing, the demand for paper printing plates has recently increased following the development of paper plate manufacturing machines, because the manufacturing cost per plate is low and the plate can be automatically mounted on and removed from the plate cylinder. However, these paper printing plates suffer from the disadvantage that the position of an image on the plate often becomes shifted from the position of the original during the plate manufacturing process. The amount of shift depends partially on the accuracy of the plate manufacturing machine itself; however, the amount of shift also depends upon the operator's skill in positioning the image at a predetermined position on the plate. This is a very difficult operation in practice because the image is likely to shift for every plate.In fact, the operation is so difficult that a slight shift in the image is inevitable. Therefore, whenever a printing plate is replaced, it is necessary to re-adjust the image position because of the above-mentioned shift, in order to determine correctly the printing image position with respect to supplied sheets.

In an offset printing machine capable of printing on only one side, a plate cylinder, a rubber cylinder and an impression cylinder are coupled and driven by separate gears provided for this purpose. In an offset printing machine capable of printing on both sides, the plate cylinder and the rubber cylinder, which are paired for the front side of a printing sheet, and the plate cylinder and the rubber cylinder, which are paired for the rear side, are coupled and driven by gears provided therefor in such a manner that the cylinders are driven at the same circumferential speed and are maintained in a predetermined circumferential relation, i.e. with a constant angular relation. With this arrangement, the image position can be adjusted by changing the circumferential coincidence relation between the cylinders.

Figure 1 of the accompanying drawings shows a side view of a conventional image position adjusting device for a single-side printing machine, while Figure 2 shows a developed view taken along the line 2-2 in Figure 1. In the conventional device, a gear a' is detachably secured to a rubber cylinder a by means of a retaining screw b, and this gear is maintained engaged with a gear c' which is secured to an impression cylinder c at all times to establish a circumferential coincidence relation between the rubber cylinder a and the impression cylinder c. To adjust the image position, the retaining screw b is loosened by turning a knob d' which is provided at one end of the box wrench d to release the gear a' from the rubber cylinder a.Thereafter a gear g, which is fixedly mounted on a shaft supported by frames e and which is engaged with the gear a', is turned with a handle h provided at one end of the shaft f, thereby to turn the impression cylinder c by way of the gears a' and c'. As a result, the circumferential coincidence relation between the rubber cylinder a and the impression cylinder c is changed to achieve the image position adjustment. Thereafter, the retaining screw b is tightened with the box wrench dto fasten the gear a' to the rubber cylinder a.

In the above-described conventional device, after the screw b has been loosened, the impression cylinder c is manually turned to change the circumferential coincidence relation between the cylinder c and the rubber cylinder a to achieve the image position adjustment. In reality, the adjustment is achieved by trial dnd error, and thus it takes a long time for even a skilled person to accomplish the image position adjustment. In addition, when the screw b is tightened after the image position adjustment, the image position may again be shifted. Thus, the image position adjustment using the conventional device is low in accuracy, and accordingly it is often necessary to repeat the adjustment several times.

Moreover, the image position adjustment is carried out with the printing machine stopped.

Therefore, as the period during which the printing machine is stopped increases, the plate surface becomes dryer and dryer, causing ink to stick to parts of the plate other than the image part.

Therefore, when the printing operation could otherwise be restarted because the image position adjustment has been achieved, it is necessary to remove the excess dried ink by idling the machine.

In the case of a paper printing plate, if ink sticks to parts of the plate other than the image part, it is impossible to use the plate. again.

If the above-described conventional device is employed for a printing machien capable of printing on both sides, the accuracy decreases and the time required for image position adjustment increases.

It is an object of the prevent invention to overcome the problems described above.

According to the present invention, an image position adjuster for an offset printing press comprises a rubber blanket cylinder, an impression cylinder, a first gear fixed to the rubber blanker cylinder, a second gear fixed to the impression cylinder and meshed with the first gear, an adjusting gear, an adjusting shaft, a shaft gear fixed to one end of the adjusting shaft and releasably engaged with the adjusting gear, a worm wheel connected to the rubber blanket cylinder, and a transmission gear mechanism for transmitting turning movement of the adjusting shaft to the worm wheel.

In this way, front-side image position adjustment and rear-side image position adjustment can be accomplished readily and quickly without requiring a large amount of operator skill, and moreover the adjuster is easy to operate and results in a high-accuracy adjustment of the image position.

Preferably, the adjusting shaft is normally biased axially outward so that the shaft gear is disengaged from the adjusting gear. To adjust the image position, the adjusting shaft is pushed axially inward and rotated. This rotational movement is transmitted to the work wheel via the shaft gear, adjusting gear and the transmission gear mechanism, which causes the rubber blanket cylinder to rotate. Since the first gear on the rubber blanket cylinder is engaged with the second gear on the impression cylinder, the latter cylinder is also rotated so that the image position is adjusted appropriately. When the adjusting shaft is released, the shaft gear disengages from the adjusting gear; however, the rubber blanket cylinder is positively prevented from moving due to the engagement of the transmission gear mechanism with the worm wheel.

The invention will now be further described, by way of example only, with reference to Figures 3 and 4 of the accompanying drawings, which are respectively a side view and front view, partly in section, of an image position adjuster for an offset printing press according to the present invention.

In the adjuster shown in Figures 3 and 4, a rubber blanket cylinder 3 has a gear 5 which is in mesh with a second gear 4 on the impression cylinder 2. The gear 5 and an adjusting gear 6 are rotatably loose-fitted on the rubber blanket cylinder 3 by means of a bearing 13. The adjusting gear is mounted in a frame 1 for sliding movement in an axial direction and is releasably engaged with a gear 9 on an adjusting shaft 8. The adjusting shaft 8 is biased outwardly, in an axial direction, by a compression spring 7. A transmission gear mechanism 10 is supported on the gear 5 by a bracket 11, and transmits a turning force of the adjusting gear 6 to a worm wheel 12 which is fixed to the rubber blanket cylinder 3.

The adjusting shaft 8 is mounted in a hole 1 4a in a support member 14 fixed to the frame 1 for sliding movement in the axial direction. The gear 9 is provided at an inner end of the adjusting shaft 8, while an adjusting knob 1 5 is provided at an outer end thereof. The shaft 8 is supported at both ends by the support member 14 and is biased outwardly by the compression spring 7 mounted thereon to keep the gear 9 normally out of mesh with the adjusting gear 6.

The transmission gear mechanism 10 includes a spur gear 1 Oa and a helical gear 1 Ob which are supported and coaxially spaced apart on a rotatable shaft 1 Oc. An end of the shaft 1 Oc is supported by the gear 5 and the bracket 11, and the bracket 11 also supports a second helical gear 1 Od and a worm gear 1 Oe which are coaxially mounted on another shaft 1 Of. The shafts 1 Oc and 1 Of are substantially perpendicular to one another. The gears 1 Od and 1 Oe are locked by a nut 1 Oh through a thrust bearing 1 Og so that they will not move axially and can rotate smoothly. The helical gears 1 Ob and 1 Od are engaged with the adjusting gear 6.Finally, the worm gear 1 Oe is engaged with the worm wheel 12, and the worm wheel 12 is securely mounted by a bolt 1 6 on the side of the rubber blanket cylinder 3.

In order to adjust the position of an image, the adjusting knob 5 is pushed axially inward against the force of the compression spring 7 so that the gear 9, located on the inner end of the adjusting shaft 8, comes into mesh with the adjusting gear 6. If the knob 1 5 is then turned in this pushed-in position, the adjusting gear 6 is caused to turn.

Since the spur gear 1 Oa is in mesh with the adjusting gear 6, the spur gear 1 Oa turns, and the transmission gear mechanism 10 causes the worm wheel 12 to turn. Therefore, the rubber blanket cylinder 3, which is connected to the worm wheel 12, also turns. Hence, the gears 4, 5 and the impression cylinder 2 turn as well.

Since the impression cylinder 2 turns with the gear 4 relative to the rubber blanket cylinder 3, the relationship in the peripheral position between the impression cylinder 2 and the rubber blanket cylinder 3 is changed, thus adjusting the image position in relation to printing paper being fed between the cylinders 2 and 3.

After the above adjustment of the image position is completed, the adjusting knob 1 5 is pulled outward with the aid of the compression spring 7, which causes the gear 9 to be disengaged from the adjusting gear 6. Since the transmission gear mechanism 10 is in mesh with the worm wheel 12 of the rubber blanket cylinder 3, the rubber blanket cylinder 3 cannot change its position in relation to the gear 5 during printing.

The gears 9 and 6, when stopped in any position, can be meshed by pushing the adjusting shaft inward while the printing press is stopped.

Therefore, adjustment of the image position can be made easily and in a short time by a simple operation. Since the amount of movement of the image in relation to the angle of rotation of the adjusting shaft 8 can be decreased by setting an appropriate gear ratio of the various gears, the image position can be fine-adjusted with high accuracy. Furthermore, since the worm wheel 12, which is securely mounted on the rubber blanket cylinder 3, and the transmission gear mechanism 10 supported on the gear 5 are in constant mesh, the gear 5 and the rubber blanket cylinder 3 will not shift out of position during printing. Thus, the adjusted image position is maintained.

Claims

1. An image position adjuster for an offset printing press, comprising a rubber blanket cylinder, an impression cylinder, a first gear fixed to the rubber blanket cylinder, a second gear fixed to the impression cylinder and meshed with the first gear, an adjusting gear, an adjusting shaft, a shaft gear fixed to one end of the adjusting shaft and re!easably engaged with the adjusting gear, a worm wheel connected to the rubber blanket cylinder, and a transmission gear mechanism for transmitting turning movement of the adjusting shaft to the worm wheel.

2. An image position adjuster as claimed in claim 1, further comprising means for biasing the adjusting shaft and the shaft gear away from the adjusting gear in an axial direction thereof to disengage the shaft gear from the adjusting gear.

3. An image position adjuster as claimed in claim 2, further comprising a frame, and wherein the adjusting gear is supported by the frame for sliding movement in said axial direction.

4. An image position adjuster as claimed in claim 2 or 3, wherein the biasing means comprises a compression spring.

5. An image position adjuster as claimed in any preceding claim, further comprising a bracket which mounts the transmission gear mechanism on the first gear.

6. An image position adjuster as claimed in any preceding claim, wherein the transmission gear mechanism comprises first and second rotatable shafts disposed substantially perpendicular to each other, a spur gear and a first helical gear fixedly supported on the first shaft, the spur gear being engaged with said adjusting gear, and a second helical gear and a worm gear fixedly supported on the second shaft, the first and second helical gears being engaged with one another and the worm gear being engaged with said worm wheel.

7. An image position adjuster as claimed in claim 6, wherein the transmission gear mechanism further comprises a nut and a thrust bearing for locking the second helical gear and the worm gear to prevent axial movement thereof.

8. An image position adjuster for an offset printing press, substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.