Doctor device

In a doctor device comprising a doctor blade which is applicable to a plate cylinder of a printing press and is located in a doctor holder, the holder is pivotally connected to a beam parallel thereto by at least one leaf spring. A plurality of piston-cylinder units disposed on the beam in a row have their piston rods applied directly or indirectly by way of pressure bolts to the holder or a part connected thereto. The piston-cylinder units are fed by a pressure medium at an adjustable basic pressure. Each piston-cylinder unit is associated with a separately adjustable fine regulating valve by way of which an additional pressure can be superimposed on the basic pressure by introducing additional pressure medium.

The invention relates to a doctor device comprising a doctor blade which is 
applicable to a plate cylinder, is located in a doctor holder and is 
provided with means for setting its application pressure which is 
differently variable over its length. 
In a doctor device of this kind known from DE-PS No. 11 42 877, there is a 
row of spindles of which the front ends are supported directly on the 
doctor blade and which are axially displaceable but non-rotatable in 
rotatably mounted rings. To turn the spindles, endless belts are provided 
which pass about direction-changing rollers by means of a remote control 
and which, with the aid of magnetically or pneumatically controlled 
pressure rollers, can be pressed against the surfaces of the rings so as 
to be carried along thereby under friction. For the purpose of manual 
actuation, the spindles carry actuating buttons at their rear ends. The 
known device not only has a complicated construction but is also difficult 
to manipulate to provide reproducible results and does not permit 
sufficiently fine adjustment of the pressure means for acting on the 
doctor blade at a different pressure. 
It is therefore the problem of the invention to provide a doctor device of 
the aforementioned kind which is simple to construct, easier to manipulate 
and permits the reproducible setting of different pressing forces over the 
length of the doctor blade. 
According to the invention, this problem is solved in that the holder for 
the doctor blade is pivotably connected to a beam parallel thereto by at 
least one leaf spring, that a plurality of piston-cylinder units disposed 
on the beam in a row have their piston rods applied directly or indirectly 
by way of pressure bolts to the holder or a part connected thereto, that 
the piston-cylinder units are fed by a pressure medium at an adjustable 
basic pressure, and that each piston-cylinder unit is associated with a 
separately adjustable fine regulating valve by way of which an additional 
pressure can be superimposed on the basic pressure by introducing 
additional pressure medium. The pivotable mounting of the holder of the 
doctor blade by means of leaf springs in accordance with the combination 
of the invention permits a flexible adaptation of the doctor blade to the 
plate cylinder because there is no undesirable stressing in rigid bearings 
that would otherwise have to be taken up by the flexibility of the doctor 
blade. The piston cylinder units disposed at intervals over the length of 
the holder of the doctor blade first of all act on the holder with equal 
pressing forces which, however, can be varied in sections over the length 
of the doctor blade in the desired manner by means of the fine regulating 
valve. The sectional fine adjustment can be carried out by hand through 
remote control or automatically according to a predetermined programme. 
Finally, the pressing force of the doctor blade on the plate cylinder can 
be measured by suitable converters and the fine regulating valves can be 
controlled according to the measured values. The pressure medium is 
preferably air but could also be hydraulic liquid. 
Mounting a holder for a doctor blade on leaf springs is known per se from 
DE-AS No. 19 64 118. However, this known mounting is not a pivot mounting 
but merely serves for the low-friction support of the holder at 
right-angles to the doctor movement, the back of the holder being 
supported in the direction of the doctor movement on a pressure measuring 
device which is secured to the doctor table. 
GB-PS No. 13 16 105 discloses a rocker bearing for the holder of a doctor 
blade about an axis parallel to the plate cylinder axis, inflatable 
flexible tubes being disposed at both sides of the bearing between the 
holder and the beam for mounting same. By inflating the tubes, one can 
vary the pressure exerted by the doctor blade on the plate cylinder. 
Finally, DE-PS No. 20 57 689 discloses a doctor device in which, for the 
purpose of applying and withdrawing the doctors to and from the plate 
cylinder, provision is made for piston-cylinder units which are connected 
to the doctor carriers and have stepless pistons. The larger piston ring 
area is impinged by a pressure medium which controls the application and 
withdrawal motions. A smaller piston area divided off by seals can be fed, 
independently of the means for controlling the application and withdrawal 
motions, with a pressure medium for the simultaneous and uniform fine 
adjustment of the doctors. With the aid of the two last-mentioned doctor 
devices, it is not possible to exert a different pressure over the length 
of the doctor blade. 
According to a development of the invention, the leaf spring carries at the 
end opposite to the holder a clamp member which is insertable in a 
complementary recess of the beam and held therein by a locking device 
actuated by at least one piston-cylinder unit. To exchange the doctor 
holder with doctor blade, it is merely necessary to withdraw the doctor 
blade from the plate cylinder, actuate the piston-cylinder unit and 
replace the doctor holder with another. Replacement can be carried out 
particularly rapidly and simply if the piston-cylinder unit is fed. The 
apparatus according to the invention thus not only permits a desired 
different pressure of the doctor blade over its length but the holder with 
blade can also be particularly simply and rapidly exchanged for a new one, 
the pressure conditions for the doctor blade being simply reproducible.

Applied to a plate cylinder 1 there is a doctor knife 2 with supporting 
doctor 2.1 of a doctor which is held between a doctor beam 3 and a bar 4. 
A leaf spring 5 connected to the bar 4 is perpendicular to the doctor beam 
3. The lower free end of the leaf spring 5 which extends over the entire 
length of the doctor is clamped between two bars 6 and 7 of equal length. 
The bars 6 and 7 are disposed in a groove 8 of a rail 9 which has the same 
length as the doctor. Four pressure cylinders 10 are secured to the rail 9 
and a pressure member 11 having an oblique face 12 is seated on their 
piston rod. The bar 7 has an oblique angle complementary to the oblique 
face 12. In FIG. 1, the piston of the pressure cylinder 10 is shown in the 
projected condition so that the pressure member 11 pushes the bars 6, 7 
into the corner of the groove 8 diametrally opposite the oblique face 12. 
In front of the piston of the pressure cylinder 10 there is a compression 
spring 13 which pushes the piston to the right when the pressure of the 
pressure medium is switched off. In the unpressurised condition, the bars 
6, 7 are free so that the doctors can be readily removed from their 
operative position by means of the handle 14. A bar 15 fixed to the rail 9 
is secured on the doctor carrier (not shown) with which the side plates 
15.1 disposed on the right and left-hand sides as well as the defecting 
plate 15.2 are also connected and on which the five pressure cylinders 16 
are arranged, of which the piston rod acts on the underside of the doctor 
beam 3 by way of a pressure bolt 18 guided in a guide member 17. When a 
pressure medium acts on the pressure cylinder 16, a force is exerted on 
the doctor beam 3 that presses the doctor blade 2 against the plate 
cylinder 1 while bending the leaf spring 5. The size and location of these 
pressure forces are freely selectable. so that, for example, the two 
left-hand pressure cylinders 16 can exert a strong force and the others 
merely a weak force. 
The pneumatic circuit diagram of FIG. 4 shows a control for the pressure 
cylinders 16. The control consists of five fine regulating valves 21 one 
for each pressure cylinder 16, and a fine regulating valve 22 with which a 
basic value is set for the pneumatic pressure to the regulating valves 21. 
The pressure of the pressure medium can be turned on and off by means of a 
control slide valve 23. The control slide valve 23 is preceded by a slide 
valve 24 with which there are connected a pressure medium source 25 with a 
conduit 26 for the pressure cylinders 16 and with conduits 27 which lead 
to the pressure cylinders 10. The fine regulating valves 21 are fed with 
pressure medium through conduits 28, 29, 30. By means of a set screw 31 on 
the fine regulating valve 21, one can add pressure to the pressure 
cylinders 16 through the conduits 32. The fine regulating valve 22 feeds 
pressure medium through conduits 33, 34, 35 into the fine regulating 
valves 21 and into conduits 32 and this pressure in conduits 32 is 
superimposed on by the pressure from conduits 30 as controlled by valves 
21. Thus, a basic pressure is preselected by the fine regulating valve 22 
and it can be increased individually in each pressure cylinder 16 by the 
addition of fluid by means of the set screws 31. The force of the doctor 
can thus be adjusted at will in sections. 
On replacing the doctor blade, the blade is first of all withdrawn with the 
slide valve 23 and the lock is then released with the slide valve 24. 
After replacement and renewed application of the blade, the previous 
pressure conditions will again obtain.