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Description  |
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SPECIFICATION
The invention relates to a multiple drive for a printing press with a
plurality of printing units, wherein individual printing units or
printing-unit groups are mechanically decoupled from one another, each
printing unit or printing-unit group is associated with a drive motor, and
each printing unit or printing-unit group is associated with a device for
rotational-speed and/or angle-of-rotation determination.
In the field of printing, there are demands for both rationalization and an
improvement in quality. In order to produce high-quality multi-color
prints that are printed on both sides and possibly also varnished in one
passage through the printing press, it is necessary, particularly in
sheet-fed offset printing, to place a multiplicity of printing units one
behind the other. Such printing units must be highly coordinated with
respect to their mode of operation.
In order to guarantee the latter, the impression cylinders of the
individual printing units usually mesh with the transfer drum disposed
between two printing units and form a closed gear train. Through the use
of one or more motors, the power is fed into the gear train at one or more
points.
It becomes apparent in practice that, given an identical press speed, the
greater the number of mechanically interconnected printing units, the
greater the tendency of a printing press to vibrate. Such vibrations
result in mackling in the printed image, which has a negative effect on
the quality of the printed product.
In order to obviate the disadvantages arising from the rigid connection of
the printing units, a drive on a multi-color printing press has already
become known in which the individual mechanically decoupled printing units
or printing-unit groups are each driven by a separate drive motor. In this
case, the synchronization of the printing units is no longer achieved by
the rigid gear train, but instead by the electrical synchronization of the
individual drive motors.
One possible way of accomplishing such synchronization is described in
German Published, Non-Prosecuted Application DE 35 03 178 A1,
corresponding to British Patent No. 2 157 022. In order to ensure
compliance with the controlled-movement conditions and thus to ensure the
safeguarding of the quality parameters and the reduction of consequential
damage through operator errors or mishaps, the aforementioned publication
describes a process for the digital regulation or feedback control of n
parallel-connected drives. Each of the n drives is associated with a
subsidiary setpoint generator which determines the time-dependent or
state-dependent movement relationship of the drive and supplies the
drive-specific setpoint values. The subsidiary setpoint generators are
subordinate to a master setpoint generator, which processes all of the
influencing variables. In the case of the dynamic monitoring of the
drives, the difference between the largest and smallest deviations of the
n drives is constantly formed and compared with a maximum permissible
difference. If the difference exceeds the value specified by the master
setpoint generator, then, while maintaining the mutual movement
relationship, the speed level of all of the drives is lowered to the
specified limit according to any desired functional relationship.
The aim of the process, at all times, is to minimize the angular difference
between the individual drives. Both the control parameters and the control
structure are thus independent of the phase angles of the printing units.
It is accordingly an object of the invention to provide a multiple drive
for a printing press with a plurality of printing units, which overcomes
the hereinafore-mentioned disadvantages of the heretofore-known devices of
this general type and in which the sheet transfer between the individual
printing units is synchronized.
With the foregoing and other objects in view there is provided, in
accordance with the invention, in a printing press including a plurality
of mutually mechanically decoupled printing-unit groups each having at
least one individual printing unit, a drive for the printing press,
comprising drive motors each being associated with a respective one of the
printing-unit groups, devices each being associated with a respective one
of the printing-unit groups for at least one of rotational-speed and
angle-of-rotation determination, and an angle feedback control device
being connected to the drive motors and to the determining devices for
dimensioning a permissible angle-of-rotation deviation of the
printing-unit groups from a preselected angle setpoint value and for
ensuring that the deviation is minimal at least in an angle-of-rotation
position in which sheet transfer takes place.
The drive according to the invention guarantees a very high repeat accuracy
with regard to sheet transfer. This is of great importance in sheet-fed
offset printing, since irregularities in sheet transfer result in mackling
and thus in color displacements, which have an extremely negative effect
on the quality of the printed products.
In accordance with another feature of the invention, the permissible
angle-of-rotation deviation of the individual printing units or
printing-unit groups from a preselected angle setpoint value exhibits a
preselectable dependence on the angular position of the printing unit or
printing-unit group.
In particular, in accordance with a further feature of the invention, the
permissible angle-of-rotation deviation within a preselectable range about
the angle-of-rotation position in which sheet transfer takes place, is
smaller than at angle-of-rotation positions outside the range.
According to the invention, the drive is constructed in such a way that the
cylinders of the individual printing units or printing-unit groups have a
precisely defined angular position at sheet transfer in order to prevent
the aforementioned mackling effects. However, also within specified limits
outside this sheet-transfer range, a specified permissible
angle-of-rotation deviation must not be exceeded, because otherwise there
might be gripper collisions between the gripper bridges of the impression
cylinders and those of the transfer cylinders. Outside this critical range
about the defined angular position at sheet transfer, the requirements in
terms of the permissible angle-of-rotation deviations of the individual
printing units or printing-unit groups are less stringent.
According to an advantageous embodiment of the drive according to the
invention, for the synchronization of the printing units or printing-unit
groups, the same angle setpoint is specified for each drive motor. This
variant has the advantage of compensating for any deviations from the
angle setpoint at the point at which they occur.
According to an alternative embodiment, for the synchronization of the
printing units or printing-unit groups, an angle setpoint is specified for
a selected drive motor and the next drive motor receives the actual value
of the preceding drive motor as its setpoint.
The drive according to the invention is not based on the notion of
correcting angular differences at each angular position or at each point
in time, but instead of monitoring them so that a correct sheet transfer
is achieved. The aim is furthermore to prevent mechanical collisions
between the gripper bridges. Intervention in the printing process, and
thus the excitation of vibrations, is reduced by specifying a relatively
large tolerance band outside the range about the angular position for
sheet transfer. Intervention in the control structure is concentrated in
the range about the angular position at which sheet transfer takes place.
In order to minimize any angular differences between the individual
printing units or printing-unit groups, particularly in the range of sheet
transfer, an advantageous embodiment of the drive according to the
invention provides for a correction value n.sub.diff to be added to the
rotational-speed setpoint value n.sub.setpoint, with the correction value
n.sub.diff being dimensioned in such a way that the detected angular
difference between the printing units or printing-unit groups is just
compensated by the time sheet transfer takes place. For this purpose, the
angle regulation or feedback control computes the time to sheet transfer
from the rotational-speed setpoint value and the angle setpoint value at
which sheet transfer is to take place. On the basis of the
angle-of-rotation difference between the angle setpoint value and the
angular position of the respective printing unit or printing-unit group
and on the basis of the remaining time to sheet transfer, the regulation
or feedback control determines the rotational-speed difference which, when
added to the rotational-speed setpoint value, precisely compensates for
the existing angle-of-rotation difference, by the time of sheet transfer.
This calculated rotational-speed setpoint value is inputted into the
rotational-speed regulation or feedback control as the new setpoint value.
In accordance with an added feature of the invention, the angle feedback
control device has means for preselecting an angle setpoint value and for
determining the respective angle-of-rotation deviation of the
printing-unit groups with respect to the preselected angle setpoint value.
In accordance with an additional feature of the invention, the printing
units groups include a first printing unit group and following printing
units groups, and the angle feedback control device has means for
preselecting an angle setpoint value for the first printing unit group and
for determining the angle-of-rotation deviation of each of the following
printing units groups with respect to the angle-of-rotation position of
the preceding printing unit group.
In accordance with yet another feature of the invention, the angle feedback
control device has means for determining a time to sheet transfer from the
rotational-speed setpoint value and the angle setpoint value, the angle
feedback control device has means for continuing to compute a
rotational-speed difference n.sub.diff by which the rotational speed
n.sub.setpoint must be increased or reduced in order to minimize the
angle-of-rotation deviation in the remaining time to sheet transfer, and
the angle feedback control device has means for controlling a
corresponding one of the drive motors according to a calculated new
rotational-speed setpoint value n.sub.new =n.sub.setpoint +n.sub.diff.
According to an advantageous further development of the invention, it is
further provided that the angle-of-rotation deviations regularly occurring
during each revolution are stored as a function of the respective angular
position of the printing unit or printing-unit group and as a function of
the rotational speed. In particular, therefore, periodically occurring
fluctuations in torque and rotational speed, and the periodically
occurring deviations in angle of rotation that are connected with them,
are used in this case in order to compute and prepare in advance the
necessary changes in rotational speed as a function of the angular
position. For example, one of the causes of the periodic fluctuations in
torque is the cyclical movement of the gripper bridges.
In accordance with a concomitant feature of the invention, there is
provided a storage apparatus associated with the angle feedback control
device for storing the calculated rotational-speed setpoint values as a
function of the angle-of-rotation position of the printing unit groups and
as a function of the respective rotational speed of the printing press.
Other features which are considered as characteristic for the invention are
set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a
drive for a printing press with a plurality of printing units, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein without
departing from the spirit of the invention and within the scope and range
of equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be best
understood from the following description of specific embodiments when
read in connection with the accompanying drawings.
FIG. 1 is a diagrammatic and schematic view of a printing press with two
printing units, wherein each printing unit is associated with its own
drive motor;
FIG. 2 is a graph representing dependence of a permissible rotational-speed
deviation on an angular position of the printing unit in accordance with
an embodiment of the drive according to the invention;
FIG. 3 is a flowchart for the control of the drives in accordance with an
embodiment of the drive according to the invention;
FIG. 4 is a flowchart for the control of the drives in accordance with a
further embodiment of the drive according to to the invention;
FIG. 5 is a flowchart for the control of the drives in accordance with a
further embodiment of the drive according to the invention;
FIG. 6 is a block diagram of the motor control arrangement;
FIG. 7 is a block diagram of the control function for the control
arrangement;
FIG. 8 is a block diagram showing the circuit arrangement of the
incremental transmitters for generating the clock pulse trains;
FIG. 9 is a timing diagram showing the phase-shifted pulse trains A and B,
and the zero pulse 0; and
FIG. 10 is a block diagram showing details of the timer circuit and clock
circuits.
Referring now to the figures of the drawing in detail and first,
particularly, to FIG. 1 thereof, there is seen a diagrammatic and
schematic representation of two printing units or printing-unit groups 1,
1' of a printing press which is not further illustrated. Each of the two
printing units 1, 1' is associated with a respective drive or drive motor
2, 2'. Angle sensors 3, 3' which detect respective angular positions
.phi..sub.actual, .phi.'.sub.actual of the printing units 1, 1', are
disposed on single-revolution shafts of the respective printing units 1,
1'. The angular position .phi..sub.actual, .phi.'.sub.actual of the two
printing units 1, 1' is supplied to a microcomputer 4. The microcomputer 4
is furthermore connected to a setpoint-input device 5 from which it
receives a rotational-speed setpoint value n.sub.setpoint and an angle
setpoint value .phi..sub.setpoint at which a sheet transfer is to take
place. The microcomputer 4 computes torque setpoint values M.sub.setpoint,
M'.sub.setpoint on the basis of an angular difference .phi..sub.diff
between the preselected angle setpoint value .phi..sub.setpoint and the
angular positions .phi..sub.actual, .phi.'.sub.actual of the printing
units 1, 1'. The torque values M.sub.setpoint, M'.sub.setpoint are
dimensioned in such a way that a permissible angle-of-rotation deviation
of the individual printing units 1, 1' from the preselected setpoint value
.phi..sub.setpoint, i.e. the angular position at which sheet transfer
takes place, is minimal.
FIGS. 2 to 5 show embodiment examples of the drive according to the
invention.
FIG. 2 shows respective tolerable angle-of-rotation and rotational-speed
deviations .phi..sub.tol and n.sub.tol as a function of the respective
angular position .phi. of the printing units 1, 1'. This graph shows the
case in which sheet transfer takes place with the printing press in the
zero position (0.degree., 360.degree., 720.degree., . . . ). Ideally, the
drive according to the invention operates in such a manner that the
setpoint angular position .phi..sub.setpoint of the printing units 1, 1'
is reached precisely at the instant of sheet transfer. However, it is at
least necessary for any angular deviation to be kept so small that
mackling does not have an adverse effect on the quality of the printed
product.
Outside of this angular-position range at which sheet transfer takes place,
the requirements in terms of the tolerable angular deviations
.phi..sub.tol between the individual printing units 1, 1' are less
stringent. Nevertheless, it must be noted that, within a range about the
angular position at which sheet transfer takes place, the permissible
angle-of-rotation deviation is restricted by the gripper movement of the
cylinders. If, in this case, a preselectable angle-of-rotation tolerance
.phi..sub.tol is exceeded, there may be gripper collisions and thus damage
to the gripper bridges and cylinders. Outside this range, in which the
tolerable angular deviation .phi..sub.tol is restricted only by the
specific structure of the cylinders, the permissible angle-of-rotation
deviations .phi..sub.tol are greater.
Through the specification of an angle-of-rotation tolerance .phi..sub.tol
that is dependent on the respective angular position of the printing units
1, 1', major control interventions in the drives 2, 2' of the printing
units 1, 1' are concentrated around the range of the angular position
.phi..sub.setpoint at sheet transfer. Outside a narrow range about the
angular position
at which sheet transfer takes place, interventions are required only to a
minor extent, if at all.
FIG. 3 shows a flowchart for the control of the drives 2, 2' in accordance
with an embodiment of the drive according to the invention. The algorithm
is suitable for the general determination of manipulated variables, i.e.
for the determination of the torque M, M' with reference to FIG. 1.
In the following discussion, the determination of manipulated variables
according to the invention is always described for one printing unit 1,
1'.
The start of a sampling cycle begins at a point 6. Then, at a point 7,
using the rotational-speed setpoint value n.sub.setpoint and the angle
setpoint value .phi..sub.setpoint at which sheet transfer takes place, the
angle difference .phi.*.sub.diff to sheet transfer is determined. Using
the rotational-speed setpoint value n.sub.setpoint and the angle
difference .phi..sub.diff, a time t.sub.u to sheet transfer is computed at
a point 8. At a point 9 in the flowchart, the manipulated variable M, M'
is computed in such a way that the angle difference .phi..sub.diff is
compensated in the time t.sub.u remaining before sheet transfer. At a
point 10, the manipulated variable M, M' is suitably corrected. Following
the correction of the manipulated variable M, M', the program starts the
next sampling cycle at the point 6.
FIG. 4 shows a flowchart for the control of the drives 2, 2' in accordance
with a further embodiment of the drive according to the invention. This
flowchart shows an embodiment of the drive according to the invention with
secondary rotational-speed regulation or feedback control.
The program starts the sampling cycle at a point 11. At a point 12, as in
the previously described embodiment example, the angle difference
.phi..sub.diff between the angular position .phi..sub.actual,
.phi.'.sub.actual of the printing units 1, 1' and the preselected angle
setpoint value .phi..sub.setpoint is determined. Then, at a point 13, the
remaining time t.sub.u to sheet transfer is computed from the
rotational-speed setpoint value n.sub.setpoint and the calculated angle
difference .phi.*.sub.diff. Using the computed time t.sub.u, the
rotational-speed change n.sub.diff, is computed at a point 14, wherein the
rotational-speed change n.sub.diff is dimensioned in such a way that the
angle difference .phi..sub.diff is compensated precisely in the time
t.sub.u remaining before sheet transfer. At a point 15, the computed
rotational-speed change n.sub.diff is added to the rotational-speed
setpoint value n.sub.setpoint. A new rotational-speed setpoint value
n.sub.new is used as the basis for the rotational-speed regulation or
feedback control of the drives 2, 2'. Then, at the point 11, the program
starts the next sampling cycle.
A further advantageous embodiment for the control of the drive according to
the invention is shown in FIG. 5. In this embodiment example, use is made
of the fact that the torque fluctuations and thus also the
angle-of-rotation deviations at the individual printing units 1, 1' occur
as a function of the angular position .phi. of the printing units 1, 1',
if one disregards irregularly occurring, random fluctuations. The
regularly occurring fluctuations are repeated cyclically at each
revolution of the printing press. It should be noted in this respect that
the occurring torque fluctuations and thus also the angle-of-rotation
deviations between the individual printing units 1, 1' depend on the press
speed v and thus on the rotational speed n of the printing press.
The program starts at a point 16. Then, as in the previously described
embodiments, the angle difference .phi..sub.diff from the preselected
angle setpoint value .phi..sub.setpoint is determined. Furthermore, as is
likewise described with regard to the preceding examples, at a point 18,
the time t.sub.u to sheet transfer is computed from the rotational-speed
setpoint value n.sub.setpoint and the angle-of-rotation difference
.phi.*.sub.diff to sheet transfer. The angle-of-rotation difference
.phi..sub.diff of the printing unit 1 from the preselected angle setpoint
value .phi..sub.setpoint is stored at a point 19 as a function of the
current angle-of-rotation position of the printing unit 1. The previously
stored angle difference .phi..sub.diff (.phi.+.DELTA..phi.) is read at a
point 20. Then, in a part 21 of the program, a manipulated variable M is
computed which compensates for the angular deviation .phi..sub.diff in the
time t.sub.u remaining before sheet transfer, with use being made of the
knowledge of .phi..sub.diff (.phi.+.DELTA..phi.) from an earlier
measurement. In this case, therefore, an additional manipulated variable
is computed from the known angle difference .phi..sub.diff (.phi.) from a
previous revolution of the printing press, with the additional manipulated
variable taking account of the likely angular deviation. In order to
compute the additional manipulated variable, the angle difference
.phi..sub.diff is stored with the information on the angular position
.phi. during a revolution of the printing press. A kind of
rotational-speed trend is then computed for each stored value. This
computation of the additional manipulated variable therefore takes place
concurrently with the execution of the control algorithm.
FIG. 6 shows additional details of the mircoprocessor 4, shown in FIG. 1,
wherein a transputer 31 is connected to a data bus 32. The transputer 31
is structured as a conventional microproccesor chip, e.g. of type
T805-6255 manufactured by the firm INMOS. The data bus 31 receives
respective inputs A, B & 0 from angle sensors 3, 3' in FIG. 1. The angle
sensors 3, 3' are advantageously constructed as incremental transmitters
typically having three signal tracks A, B, & 0 imprinted therein. Tracks A
and B include, e.g. 1024 increment sectors per revolution, mutually phase
shifted 90.degree. as shown in FIG. 9. Track 0 generates a single zero
pulse for each revolution of the incremental transmitters 3, 3'. Each
incremental transmitter is rigidly coupled to a selected rotating
component of the respective printing unit 1, 1', such as, for example, the
blanket cylinder or the transfer drum which passes each sheet from one
printing unit to the next.
The incremental transmitters 3, 3' are manufactured e.g. by the firm Baumer
under type designation BDM 05.05A1024/K143.
The angle sensor outputs A, B and 0 are connected to tachometer interface
circuits IF1 and IF1', shown with respective reference numerals 33, 33'.
Details of the tachometer interfaces are shown in FIG. 8, as described in
more detail below. The interfaces 33, 33' communicate via data bus 32 with
the transputer 31. The interfaces 33, 33' are typically realized in the
form of a micro circuit chip of the type known as an ASIC (Application
Specific Integrated Circuit) manufactured by the firm Siemens.
The transputer 32 communicates via data bus 32 with a timer circuit 36 and
a parallel interface circuit 34. The timer circuit generates a pulse-width
modulated output signal PWM which represents the required current value
(or voltage value) to be delivered from the motor control unit 37 to the
drive motor 2, 2' for the respective drive units 1, 1' of the printing
press. The pulse width of the output signal PWM is modulated in width so
that the respective motor 2, 2' drives the printing unit with a respective
torque M, M' as required to maintain the printing unit angle .phi..sub.act
close to or equal to the setpoint value .phi..sub.set, such that the angle
difference .phi..sub.act -.phi..sub.set falls within the required
tolerance.
The parallel interface 34 generates on the basis of signals A, B from the
respective angle sensors 3, 3' a direction of rotation signal VZ to the
motor 2, 2' on the basis of whether signal A is shifted in phase
90.degree. angle ahead of or trailing signal B, as described in more
detail in connection with FIGS. 8 and 9.
The parallel interface 34 also generates a release signal FRG that operates
to release certain functions in the motor control unit 37.
FIG. 7 is a control function diagram in conventional LaPlace transform
notation of the phase angle controller, showing the steps performed in
controlling phase angle 0 of printing unit 1 in angular relation to the
phase angle 0' of printing unit 1'. Values n and n' represent the
respective rps value of units 1 and 1'. The box K.sub.B represents the
amplification factor for the angle controller. Box P(.phi.,tu) represents
amplification factor of the angle controller, which is a function of the
actual value of the angle deviation .phi. of the sheet-gripper at the
point of sheet transfer from one printing unit 1 to the next unit 1'.
The box K.sub.PI (1+T.sub.PI S)/S represents the rps controller; The box
K.sub.PR /(1+T.sub.PR S) represents the controlled unit, i.e. the
controlled printing unit, and box 2.pi./S is derived from the number of
revolutions n and the angular position .phi. of the printing unit.
T.sub.P3 is the time constant for the rpm controller. K.sub.PR is the
amplification factor controlling the angle deviation .phi., and T.sub.PR
is the time constant controlling the angle deviation .phi..
FIG. 8 is a block diagram showing the operation of the tacho interface
circuit 1, 1' connected with the incremental transmitter, i.e. the angle
sensor 3, 3', and FIG. 9 shows the three signals A, B and 0. Signals A and
B are two pulse signals from respective tracks on the incremental
transmitter 3, 3', which are mutually phase shifted 90.degree., with track
A trailing track B. Signals A and B are connected to respective inputs of
an exclusive OR-gate 38, the output of which is connected to a counter 39
of conventional construction, driven by the trailing edge of the output
signal from XOR gate 38. The XOR gate operates to double the clock rate of
signals A and B.
For each complete rotation the incremental transmitter 3, 3' generates on a
separate 0 track, a 0 pulse shown in FIG. 9. The 0 pulse resets, via reset
circuit 41, the counter 39 to its 0 position, after which it starts to
count again for a next complete rotation of the transmitter. The counter
39 has output leads D.sub.0 -D.sub.15, on which output signals represent
the state of the counter 39, in either binary or, for example, hexadecimal
notation. The count in counter 39 represents the rotational angle of the
respective printing unit 1, 1' in relation to the 0 pulse.
Leads D0-D15 are connected via the data bus 32 to the transputer 31,
wherein the signals are interpreted as angular position signals for the
respective printing units 1, 1', which can then be compared with each
other to generate any angular deviations between the printing units 1, 1'.
The angular deviations are converted in the transputer 3 by software
control, operating as shown in FIG. 7 to generate the signal input
required for the timer 36 to generate the pulse-width modulated signal
PWM, which in turn steers the motor control unit 37 to control the drive
motors 2, 2' so that the phase deviation between the respective printing
units 1, 1' will fall within the required tolerances.
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