Hydraulic drive for pull through doctor blade transfer system

In a pull through doctor blade transfer system wherein a coiled blade is payed off one rotatable reel while simultaneously being taken up on another rotatable reel, with an intermediate portion of the blade between the reels being supported in a blade holder arranged to apply the blade to a moving surface to be doctored, each reel is driven by a hydraulic motor. In operation, hydraulic fluid discharged from the motor driving the take up reel is fed to the motor connected to the pay off reel. This fluid is pumped to a high pressure by blade induced rotation of the pay off motor, thus creating a braking torque.

BACKGROUND OF THE INVENTION 
This invention relates to doctoring apparatus wherein flexible elongated 
doctor blades are advanced longitudinally across the surfaces being 
doctored. 
U.S. Pat. No. 4,691,406, the disclosure of which is herein incorporated by 
reference in its entirety, discloses a doctoring apparatus of the 
above-mentioned type. The doctor blade has a length greater than the width 
of the surface being doctored. A blade holder applies an intermediate 
portion of the blade to the surface being doctored. The blade is movable 
longitudinally through the blade holder, and has continuing portions which 
extend in opposite directions beyond the ends of the holder to 
hydraulically driven pay off and take up reels. Hydraulically actuated 
clamps act on the continuing blade portions and are adjustable between 
closed settings preventing relative movement between them and the blade, 
and open settings permitting such relative movement. A hydraulic drive 
reciprocates the blade holder. The clamps are opened and closed in timed 
sequence with reciprocation of the blade holder to achieve longitudinal 
shifting of the blade in a selected direction across the doctored surface, 
from one to the other of the reels. This type of "pull through" blade 
transfer system maximizes efficiency by eliminating lost production time 
normally associated with the changing of conventional "cut to length" 
blades. 
It is extremely vital to the optimum performance of the above-described 
pull through blade transfer system that the blade be kept under proper 
tension both on the pay off and take up runs between the reels and the 
clamps. Too little tension can result in uncontrolled expansion of the 
coils being removed from or accumulated on the reels, whereas excessive 
tension can have a damaging effect on the transfer equipment and/or the 
blade itself, in extreme cases causing blade breakage. 
SUMMARY OF THE INVENTION 
A general objective of the present invention is the provision of a pull 
through blade transfer system having the capability to closely control and 
maintain appropriate tension in the blade stock being payed off and taken 
up on the reels. 
A more specific objective of the present invention is to provide a pull 
through blade transfer system wherein the hydraulic motors used to operate 
the reels are hydraulically interconnected in a manner permitting them to 
alternatively serve as drives or as dynamic brakes, depending on whether 
blade stock is being taken up on or payed off from their respective reels. 
Other objects and advantages of the present invention will become more 
apparent as the description proceeds with reference to the accompanying 
drawings, wherein:

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT 
Referring initially to FIG. 1, a pull through doctor blade transfer 
apparatus is shown doctoring a rotating cylinder 10. A doctor blade holder 
12 is mounted on a doctor back 13 and is positioned adjacent to the 
cylinder 10. The doctor back is adapted to be reciprocated to and fro in 
the direction of arrow 14 by a double acting piston-cylinder unit 16. The 
doctor back is rotatably adjusted by means of another pistoncylinder unit 
(not shown) to urge the holder 12 towards the cylinder 10, thus applying 
the working edge -8 of an elongated flexible doctor blade 20 to the roll 
surface. The doctor blade has a bottom edge 22 which is parallel to the 
working edge 18 and which is supported in the holder 12. 
The doctor blade 20 is adapted to be wound into coil form. A cartridge 23 
containing a fresh blade coil is mounted on a reel driven by a first 
hydraulic motor 24. The leading blade end is threaded through a first 
clamp 26, the blade holder 12, a second clamp 28, and is then connected to 
an empty cartridge 29 mounted on another reel driven by second hydraulic 
motor 30. 
During the doctoring operation, the doctor back 13 and the holder 12 are 
reciprocated by the piston-cylinder unit 16, and one or the other of the 
clamps 26,28 is employed in timed sequence with this oscillation to shift 
the blade longitudinally across the cylinder surface, with blade stock 
being gradually paid off from the cartridge of one reel and taken up on 
the cartridge of the other reel. A more detailed description of this 
procedure is provided in the previously referenced U.S. Pat. No. 
4,691,406. 
When the trailing end of one blade length leaves a spent cartridge, that 
cartridge is replaced by another cartridge containing a fresh coil. The 
leading end of the fresh coil is then advanced to a position directly 
adjacent to the preceding trailing end, and the two ends are detachably 
interconnected. This having been accomplished, the doctoring operation is 
momentarily interrupted, the clamps are released, and the reels are 
speeded up to rapidly traverse the interconnected ends across the cylinder 
10. Then, the doctoring operation is continued, and the blade ends are 
disconnected to allow the cartridge containing the spent coil to be 
replaced by an empty cartridge to which the fresh leading end is then 
connected. 
The hydraulic drive system used to operate the pull through apparatus of 
FIG. 1 will now be described with further reference to FIG. 2. A pump 36 
driven by motor 38 withdraws hydraulic fluid from a reservoir 40 and 
discharges the same as a pressurized flow to line 42. Typically the pump 
discharge will be at an elevated pressure of about 2000 p.s.i. Line 42 
communicates at junction 44 with lines 46,48, and continues on through a 
two-way solenoid valve 50. The continuing portion of line 42 feeds a "Reel 
Drive Circuit". Branch line 48 feeds an "Oscillation Circuit", and branch 
line 46 feeds a "Blade Transfer Circuit." The operation of each of these 
circuits will now be separately described in greater detail. 
OSCILLATION CIRCUIT 
Branch line 48 leads through a pressure reducing valve 52 and then to a 
four-way solenoid valve 54. Valve 52 drops the line pressure down to a 
lower level of for example 300-400 p.s.i. Valve 54 communicates with two 
lines 56,58 which each lead through flow control needle valves 60 before 
respectively communicating with the cylinder chambers 16,16b on opposite 
sides of the piston in piston-cylinder unit 16. Pressure switches 62,64 
communicate respectively with lines 56,58 to sense pressure build up at 
each end of the piston stroke in unit 16. The signals from pressure 
switches 62,64 are fed to a controller 66 which in turn is connected to 
the solenoid 54a of valve 54. 
In the illustrated setting of valve 54, hydraulic fluid is being fed to 
chamber 16b of piston-cylinder unit 16, causing the doctor back 13 to be 
moved to the left as viewed in the drawings. When pressure switch 64 
senses a pressure build up indicating that the piston has reached the end 
of this stroke, a signal is fed to controller 66 which in turn signals the 
solenoid 54a of valve 54 to shift to its opposite setting. Hydraulic fluid 
is then fed to chamber 16a, causing the doctor back to shift in the 
opposite direction until pressure switch 62 senses a pressure build up, 
again signalling controller 66 and resulting in another reversal In this 
way, the doctor back is reciprocated to and fro, with exhaust fluid from 
the piston-cylinder unit being bled back through valve 54 and line 68 to 
the reservoir 40. 
BLADE TRANSFER CIRCUIT 
Branch line 46 leads through another pressure reducing valve 70 to a double 
ended solenoid valve 72. Valve 70 reduces line pressure to about 1500 
p.s.i.. Lines 74,76 lead from valve 72 to the blade clamps 26,28, and 
another line 78 communicates with reservoir 40. The solenoids 72a,72b of 
valve 72 are controlled by controller 66 in response to signals received 
from the pressure switches 62,64. Thus, during a shifting of the blade 
stock from cartridge 23 to cartridge 29, when the doctor back 13 is being 
shifted to the left, both clamps 26,28 are open, and fluid is being bled 
from valve 72 via line 78 to the reservoir 40. At the end of the driving 
piston stroke of unit 16, as signalled by pressure switch 64, the 
controller 66 will energize the solenoid 72b of valve 72 to apply brake 
28. When the doctor back 13 is shifted in the opposite direction, the 
blade will be prevented from moving with it, thus shifting the blade 
relative to the doctor back. At the next leftward stroke of the doctor 
back, the brake 28 will be released, thus allowing the frictional 
resistance between the blade and holder to pull the blade with the doctor 
back. In this way, the blade is incrementally shifted longitudinally 
across the cylinder 10 from cartridge 23 to cartridge 29. Blade shifting 
in the opposite direction, i.e., from cartridge 29 to cartridge 23, can be 
achieved in a similar manner by allowing brake 28 to remain open and by 
employing brake 26 in timed sequence with doctor back shifting, again in 
response to signals from the controller 66. 
REEL DRIVE CIRCUIT 
Line 42 continues from junction 44 through two-way solenoid valve 50, and 
through junction 80 to a four-way solenoid valve 82. Lines 84,86 
respectively lead from valve 82 through pressure reducing valves 88,90 
before being rejoined at junction 92 and continuing as a common line 94 
through two-way solenoid valve 96 to a four-way solenoid valve 98. 
The hydraulic motors 24,30 are each respectively provided with high 
pressure ports 24a,30a and low pressure ports 24b,30b. The low pressure 
ports 24b,30b are interconnected by a low pressure line 100. Lines 102,104 
respectively connect high pressure ports 24a,30a to valve 98. 
Pressure reducing valve 88 serves to reduce line pressure to about 400 
p.s.i., whereas pressure reducing valve 90 reduces line pressure to about 
1400 p.s.i.. 
Line 106 branches from junction 80 through a pressure reducing valve 108 
before joining low pressure connecting line 100 at junction 110. Valve 108 
reduces line pressure to about 200 p.s.i. and insures that an appropriate 
back pressure is applied to both motors 24,30 in order to avoid 
cavitation. A relief valve 112 is connected by line 114 to line 106 at 
junction 116. 
Another line 118 branches from junction 80 through a pressure reducing 
valve 120 and through a three-way solenoid valve 122 to valve 98. Valve 
122 also communicates with reservoir 40. A pressure relief valve 123 
communicates with reservoir 40 and with line 118 at junction 124. 
The Reel Drive Circuit may be operated in any one of the following modes: 
a. Blade Tensioning 
In this operational mode, the reel drive circuit operates in conjunction 
with the Blade Transfer Circuit and the Oscillation Circuit to insure that 
appropriate tension is maintained in the blade stock as it is uncoiled 
from one reel and coiled onto the other reel. Valve 50 is adjusted to 
direct fluid through junction 80 to valve 82. Valve 82 is adjusted to 
direct fluid through pressure reducing valve 88, thereby feeding fluid at 
a reduced pressure of approximately 400 p.s.i. to valve 96. Valve 96 is 
adjusted to direct fluid to valve 98 which in turn is adjusted to direct 
fluid to the motor operating in a "drive" mode to take up blade stock 
being received from the reciprocating doctor back 13. In the condition 
illustrated in FIG. 2, motor 24 is being operated in the "drive" mode to 
take up blade stock being shifted in the right hand direction as viewed in 
FIG. 1. The discharge fluid from motor 24 is exhausted through low 
pressure port 24b and fed via line 100 to the low pressure port 30b of 
motor 30, the latter being in a "pay off" mode. As the blade stock is 
payed off from reel 29 by the reciprocation of doctor back 13 acting in 
conjunction with brake 26, the motor 30 is rotated in a direction opposite 
to its drive direction, thereby pumping the fluid received from motor 24 
via line 100. This pumping action is opposed by the pressure of the fluid 
in line 104, in this case approximately 400 p.s.i. Thus, motor 30, when in 
this pumping mode, operates as a dynamic brake to maintain an appropriate 
level of tension in the blade stock being payed off from cartridge 29. 
When blade stock is being advanced in the opposite direction, i.e., from 
cartridge 23 to cartridge 29, valve 98 is shifted to its opposite setting, 
thereby causing motor 30 to operate in the drive mode while motor 24 
operates in the pumping or dynamic brake mode. 
b. Rapid Traverse 
Situations will arise where it becomes necessary to interrupt the doctoring 
operation while blade stock is rapidly traversed from one reel to the 
other. This might be required, for example, when traversing the detachably 
interconnected ends of spent and fresh coils. Under these circumstances, 
valve 72 is adjusted to dump fluid back to the reservoir 40, thereby 
allowing both clamps 26,28 to remain open. Also, valve 54 is adjusted to 
dump fluid back to reservoir 40, thereby interrupting reciprocation of the 
doctor back 13. Under these conditions, valve 82 is adjusted to direct 
fluid through pressure reducing valve 90 in order to feed higher pressure 
fluid through valves 96 and 98 to the motor operating in the drive mode. 
The higher fluid pressure will result in a higher volume of fluid being 
fed to the motor, which in turn will produce a more rapid blade traverse. 
c. Initial Threading 
Under certain conditions, when threading the front end of a fresh coil 
through the apparatus, or when locating the front end of a fresh coil next 
to the trailing end of a spent coil in preparation for connecting the two 
together, it will be necessary to slowly drive one reel while allowing the 
other reel to remain stationary. Assume for example that one wishes to pay 
off blade stock from the reel driven by motor 30 while allowing the reel 
driven by motor 24 to remain stationary. Valve 96 is adjusted to block 
flow to valve 98. This allow fluid to flow from junction 80 through 
pressure reducing valve 108 and then on through low pressure line 100 to 
low pressure port 39b. This will produce reverse rotation of motor 30 with 
a resulting pay off of blade stock. Exhaust fluid will continue through 
port 30a, line 104 and energized solenoid valve 122 back to reservoir 40. 
Motor 24 will remain stationary because through flow is blocked by the 
closure of valve 96. 
Reverse rotation of motor 24 with motor 30 remaining stationary can be 
achieved by simply shifting valve 98 to its opposite setting. 
In light of the foregoing, it will now be appreciated by those skilled in 
the art that the hydraulic drive system of the present invention is 
extremely versatile, allowing easy selection of various operational modes 
in response to various needs of the doctoring operation. The motors 24,30 
can act as drives, or alternately they can serve as effective dynamic 
brakes.