Printing apparatus

Printing apparatus is disclosed comprising a rotatably mounted hub, a plurality of carriages circumferentially spaced around the hub, each carriage being adapted to support a printing blanket. Each carriage is movable with respect to the hub upon actuation to retract its respective blanket radially out of its operative printing position.

The present invention is applicable to printing apparatus and, in 
particular, provides an improvement in apparatus for continuously printing 
onto each of a series of articles. 
One application for the present invention is in apparatus such as that 
disclosed in the specification of our U.S. Pat. No. 4,055,142 which 
illustrates apparatus which can be used to perform successive coating and 
printing functions on a series of extruded tubes located on concentric 
arrays of mandrels on a rotating turret. The disclosure in U.S. Pat. No. 
4,055,142 is included herein by way of reference. It will be appreciated, 
however, that while the present invention may be well suited to this 
particular application, it is not limited to this field. 
When printing on a succession of articles in applications such as that 
illustrated in U.S. Pat. No. 4,055,142, it is frequently necessary to 
avoid a print application if, for example, one of the articles is damaged 
or absent from the series. 
In the past, it has been known to retract the entire printing drum or to 
stop its rotation entirely. Both of these methods have encountered 
substantial problems with mechanical inertia. In high speed operations 
such as can-making, where articles are processed at some 800 per minute, 
the retraction or stopping of the drum frequently allows a significant 
number of articles to avoid the printing function unnecessarily to simply 
to accommodate one defective or absent article. Furthermore, if one or 
more printing cycles is omitted, the printing blanket generally builds up 
an excess quantity of ink with the result that subsequent printing may be 
initially unsatisfactory. 
The present invention provides a simple solution to these problems by 
mounting one or more printing blankets on retractible carriages such that 
the blanket is radially retractible relative to the printing drum. The 
printing blanket can then be retracted out of printing engagement for one 
cycle if required, without stopping or retracting the drum itself. 
According to the invention there is provided printing apparatus comprising 
a rotatably mounted hub, a plurality of carriages circumferentially spaced 
around said hub, each carriage being adapted to support a printing blanket 
thereon, each said carriage being movable with respect to said hub upon 
actuation to retract its respective blanket radially out of its operative 
printing position.

Referring to the drawings, a hub 10 is rotatably mounted to a shaft 11 by 
bearings 12 and 13. The hub is rotatably driven by a gear 14 fixedly 
secured to it. Spaced around the periphery of the hub are four carriages 
15 each of which is axially radially slidable relative to the hub along 
inclined slideways 16. Each carriage includes a pair of brackets 17 for 
securing a printing blanket (not shown) to the carriage. Thus the 
individual blankets can be removed and replaced as required. 
As best shown in FIG. 2, each carriage is provided with a double acting 
pneumatic cylinder end 18 having a ram end 19 rigidly connected to the 
gear 14. A constant source of air pressure is applied to passages 20 in 
the shaft 11 from which they communicate to the individual cylinders by 
pneumatic control valves 21 individual to each carriage. The air pressure 
within each cylinder 18 urges its respective carriage in a direction away 
from the gear 14 along its slide into a position of maximum radial 
extension as shown. In this position, an abutment face 22 on each carriage 
comes into contact with an adjustable stop 23. Individual screw adjustment 
of these stops ensures that the maximum radial displacement of each 
printing blanket can be accurately set to a predetermined datum reference 
such as circle 24. This individual adjustment facility ensures that any 
individual blanket can be removed from its carriage, replaced and adjusted 
without disturbing the accurate setting of the remaining blankets. 
Clearly, one or more new blankets can be installed and accurately 
positioned quite independently of the remaining ones. 
Where it is required to retract one of the printing blankets to omit a 
specific printing function, a cam 25 is moved in the direction indicated 
by the arrow in FIG. 2, causing the respective pneumatic control valve 21 
to alter the fluid supply to its cylinder 18 which then draws the required 
carriage 15 down its inclined slide towards the gear 14, thereby to 
retract the printing blanket radially inward towards the axis of the hub 
and out of printing engagement with the article stream. The printing 
blanket in question is then unable to apply ink to the damaged article or 
vacant mandrel as the case may be and only a single print application is 
lost. As the printing hub continues to rotate, the cam 25 is retracted to 
reverse the procedure and restore the printing blanket to its operative 
position once the damaged or absent article has been traversed. The amount 
of radial retraction required for the carriage may only be of the order of 
3 or 4 mm. 
Each carriage is held securely in its operative position by an elastomeric 
insert 26 supplied with air along a passage 27 communicating with each 
pneumatic control valve 21. Air pressure within the passage 27 causes the 
elastomeric element 26 to expand against the adjacent carriage slide 16, 
thereby to hold the carriage securely in position. 
Although the invention has been described with reference to a specific 
example, it will be appreciated by those skilled in the art that the 
invention may be embodied in many other forms.