EP0142995A2

EP0142995A2 - Registration control method and device for rotary press

Info

Publication number: EP0142995A2
Application number: EP84308036A
Authority: EP
Inventors: Tsunehiko Imamoto; Toshiki Sugimoto
Original assignee: Dai Nippon Printing Co Ltd
Current assignee: Dai Nippon Printing Co Ltd
Priority date: 1983-11-22
Filing date: 1984-11-20
Publication date: 1985-05-29
Anticipated expiration: 2004-11-20
Also published as: JPS60110454A; EP0142995B1; EP0142995A3; DE3484005D1

Abstract

A registration error is detected by reading register marks printed on a printing medium in the preceding unit and the succeeding unit of a multi-color rotary press and in response to a detected registration error, gains Kp and K_o in PD control are optimized based on (1) a pass length between the plate cylinders, (2) pass length between a plate cylinder and a position at which a register mark is detected, (3) the radius of a plate cylinder and (4) either of the displacement velocity of a compensator roller or the printing speed to that the position of the shaft of the compensator roller which is interposed between the adjacent units is displaced, whereby register marks are registered with respect to each other.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a multicolor rotary press such as a gravure rotary press and more particularly to a registration control method and device therefor.
From the standpoint of control theory, registration control in a multicolor rotary press is extremely complicated so that it is difficult to provide a control device with excellent response and stability which are demanded in general as control performance. That is, in order to reduce spoilage to a minimum, fast response is needed. Then, hunting results so that stability is adversely affected. Therefore, the question is how to adjust in the case of registration error.

'SUMMARY OF THE INVENTION

In view of the above, the present invention was made and has for its object to provide a registration control method and device for automatically calculating optimum correction values depending upon the construction of a printing press and in response to printing conditions when registration errors are detected and correcting registration errors quickly in response to the calculated correction values, thereby reducing spoilage to a minimum.
To the above and other ends, according to the present invention, the optimized gains Kp and K in PD control are obtained in response to the pass length (1₁) between the adjacent plate cylinder units, the pass length (1₂) between the plate cylinder and the position at which a register mark is to be detected, the radius (r) of the plate cylinder, the compensator roller displacement velocity (v) and/or the printing speed (V) on the assumption that the correct registration control can be effected by using some of various factors affecting the registration control which can be correctly analyzed and in response to the optimized gains, the position of the shaft of a compensator roller is displaced, thereby accomplishing registration.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a view used to explain the construction of a multicolor rotary press to which the present is applied;
Figs. 2 - 7(a) and 7(b) show experimental results which confirm validity of the registration control method in accordance with the present invention;
Fig. 2 shows a standard case;
Fig. 3 shows a case in which only the printing speed is varied with other factors or parameters remained unchanged;
Figs. 4(a) and 4(b) show the characteristic curves prior to and after the adjustment in accordance with the present invention when the pass length between the adjacent units is varied;
Figs. 5(a) and 5(b) show characteristic curves when the pass length between a plate cylinder and a position at which a register mark is to be detected is varied;
Figs. 6(a) and 6(b) show characteristic curves when the compensator roller velocity is varied;
Figs. 7(a) and 7(b) show characteristic curves when the radius of a plate cylinder is varied;
Fig. 8 shows characteristic curves when the tension exerted to printing paper is varied; and
Fig. 9 shows characteristic curves when the elongation coefficient of printing paper is varied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Prior to the description of preferred embodiments of the present invention, a prior art registration control device will be briefly described so that the problems or defects thereof become more apparent.
Fig. 1 shows a prior art registration control device. In Fig. 1, only plate cylinder units 11 and 12 with impression cylinders 21 and 22 of a multicolor rotary press are shown. A printing paper of the like is transported from the plate cylinder unit 11 to the plate cylinder unit 12. Guide rollers 23 and a compensator roller 20 are interposed between the plate cylinder units 11 and 12. The deviation between a register mark printed by the preceding plate cylinder and a register mark printed by the succeeding plate cylinder can be made zero by shifting the shaft of the compensator roller 20.
In order to control the shift of the shaft of the compensator roller 20, the output pulses from a pulse generator PG of the preceding plate cylinder 11 and the output from a scanning head SH disposed adjacent to the succeeding plate cylinder 12 are applied to a mis-registration detection circuit 21. The output of the detection circuit 31 is applied through a PD control circuit 32 to a register motor drive circuit 33 so as to drive a register motor M for shifting the shaft of the compensator roller 20.
In this case, the control of the displacement of the shaft of the compensator roller 20 is effected by the so-called PD control. That is, a registration error E derived from the detection circuit 31 and its derivative dE/dt are substituted in the following equation (1) so that the drive time At and direction of rotation of the register motor M are obtained. In response to thus obtained drive time and the direction of rotation, the compensator roller is shifted by Δt.
where Kp: proportional gain (constant) K_D: differential gain (constant) In general, the proportional gain Kp and the differential gain K are constant and depending upon the construction of a printing press and printing conditions such as pass length between units, the position of a scanning head, the velocity of a compensator roll, a printing speed, circumferential lengths of cylinders and so on, hunting results and response is considerably degraded.
Therefore according to the prior art, frequency corrections such as one correction per rotation of a plate cylinder have not been employed, but a method is employed in which one correction is effected for from two to ten rotations of a plate cylinder or in which feedback gains (that is, both Kp and K_Dare adjusted simultaneously) are changed in order to avoid hunting.
However, according to the above-described methods, an operator must adjust the number of correction times and gains so that the printing operation becomes very complicated. Furthermore, the adjustment is made in such a way that gains are set at considerably lower levels so as to avoid hunting under any conditions. Therefore, the above-described method is not excellent in view of controllability of response, stability and so on. In other words, that one correction is made for two or more rotations of a plate cylinder merely attains a result inferior to the case in which one correction is made per rotation. As a result, many spoilages occur.
In order to overcome the above-described problems, control response must be improved, but in the case of registration control, the improvement of response results in unstability. The reason is that the analyses of various factors affecting the registration control have not yet been sufficiently made so that it has been difficult to find out an optimum point at which response and stability requirements are satisfactorily attained. There are many various factors which cannot be correctly analyzed. For instance, they are rotary speeds and sizes of various rollers of a printing press in addition to the timing deviation between the operation of a device and its detection when the position at which a register mark is detected is located behind a plate cylinder and the elongation of printing paper or the like.
In view of the above, so far the registration control has been improved only in a trial-and-error manner so that no satisfactory result has not been obtained.
Referring again to Fig. 1, the construction of a multicolor rotary press will be described in more detail.
A printing paper is guided by a guide roller 23 and passes between the preceding unit comprising the plate cylinder 11 and the impression cylinder 21 so that a first color image is printed on the printing paper. Thereafter the printing paper is transported through guide rollers 23 and the compensator roller 20 to the succeeding unit comprising the plate cylinder 12 and the impression cylinder 22 so that a second color image is printed. Thereafter the printing paper is transported to the succeeding unit through guide rollers or to a discharge unit.
In the preceding unit, a first register mark is printed and in the succeeding unit, a second register mark is printed. These register marks are detected by the scanning head SH disposed behind the position at which the plate cylinder 12 is made into contact with the impression cylinder 22 and the output of the scanning head SH is applied to the mis-registration detection circuit 31. The output signal from the scanning head SH represents a time deviation ATe between the first and second register marks.
Meanwhile, pulse signals representative of the rotational speed of the plate cylinder 11; that is, the pulse signals representative of the transport speed v of printing paper is applied from the pulse generator PG of the plate cylinder 11 to the mis-registration detection circuit 31. (The pulse generator PG generates gate signals for detecting the register marks.) Then, in response to the pulse signals and the output signal from the scanning head SH, the detection circuit 31 calculates a mis-registration or registration error E. That is,
where n: the rotational speed of the plate cylinder 11 and r: the radius of the plate cylinder.
The registration error E is applied to a PD control circuit 32 so that the register motor drive signal is generated by PD calculation. The register motor M which is rotated at a constant speed is driven by a register motor drive circuit 33 so that the position of the shaft of the compensator roller 20 is controlled. Thus, the registration operation is carried out.
When the register motor M which displaces the position of the shaft of the compensator roller 20 is of a constant speed type, the displacement of the position of the shaft of the compensator roller 20 is in proportion to the drive time of the register motor M. Therefore the PD control circuit 32 calculates a drive time in accordance with the general PD control equation. That is, a drive time At is given by the following equation:

where Kp: proportional gain,
K_D: differential gain,
E_k: registration error detected this time, and
E_k-1: registration error detected in the preceding detection.

Extensive studies and experiments were made by the inventor and it was found out that Kp and K_D in Eq. (3) can be obtained by the following equations:

where 1₁: the pass length between the adjacent plate cylinder units,
1₂: the pass length between the plate cylinder and the position at which the register mark is detected,
v : the velocity of the compensator roller, and
r : the radius of the plate cylinder. f₁ and f₂ are functions of l₂ and f₃ is a function of r. All the function f₁, f₂ and f₃ are monotonously reducing function and have positive values. That is,

Validity of Eqs. (4) and (5) can be confirmed from experimental results.as shown in Figs. 2 - 7(a) and 7(b).

Fig. 2 shows that various factors used in registration control of a multicolor rotary press are all optimized. Experimental results shown in Figs. 3 - 7(a) and 7(b) are compared with those shown in Fig. 2 and evaluated. The optimized conditions as shown in Fig. 2 can be obtained as follows:

Parameters

Unless otherwise stated, the parameters of a multicolor rotary press are as follows:

(1) Tension:
- The tension T₁ of printing paper which is fed to the preceding unit is constant and is 15 kg while tension of printing paper fed into the succeeding unit is 15 + AT₂ k^g.
(2) Velocity of printing paper V: 100 m/min = constant
(3) The radius of plate cylinders r: 0.14 m
(4) The pass length 1₁ between the adjacent units: 7.8 m
(5) The length 1₂ between a plate cylinder and the position at which a register mark is detected:
0.48 m
(6) The velocity V of the displacement of the shaft of the compensator roller:
0.5 mm/sec.
(7) Other parameters:
- The variation in tension Δt₂; the change in position of the compensator roller Δc; and the registration error E represent only deviations from the above-described parameters and initial values.

Explanation of Characteristic Curves

If the deviation of the register mark is detected 0.5 mm in Fig. 2, then the compensator roller is shifted for At calculated on the base of 0.5 mm/sec. As a result, the compensator roller is displaced by +0.67 mm at the most from the initial position and remains at the position ±0.25 mm.
In response to the change Δc in the position of the compensator roller, the tension applied to printing paper between the adjacent units is 15 + 0.66 kg at the maximum, 15 - 0.02 kg at the minimum and becomes 15.00 kg finally.
Because of the operations carried out in the manner described above, the registration error E is reduced in time and becomes 0.00 mm finally. Thus, registration is accomplished.

Fig. 3 shows the characteristic curves when the printing velocity V is varied. In this case, registration control can be carried out relatively rapidly and smoothly as compared with the standard case as shown in Fig. 2. That is, it has been confirmed that the above equations (4) and (5) do not include the printing speed V and that even when the printing speed varies, registration control is not affected.
Figs. 4 (a) and 4(b) - 7 (a) and 7(b) show experimental results of factors contained in the above equations (4) and (5).
Fig. 4(a) shows the characteristic curves when the gains Kp and K_D remain unchanged while the pass length 1₁ between the adjacent units is increased from 7.8 m to 14 m. In this case, the control of the position of the compensator roller is carried out for At obtained by calculation. The gain Kp and K_D, however, are different from those in Eqs. (4) and (5) so that hunting results.

On the other hand, in Fig. 4(b), the gains Kp and K_D are optimized by Eqs. (4) and (5) so that hunting can be substantially suppressed.
Fig. 5(a) shows the characteristic curves when the gain Kp and K_D are maintained at the standard values while the pass length 1₂between the plate cylinder and the position at which the register mark is detected is increased from 0.48 m to 0.88 m. In this case, hunting results.
On the other hand, in Fig. 5(b), the gains Kp and k_D are optimized according to Eqs. (4) and (5) so that hunting is suppressed.
Figs. 6(a) and 6(b) show characteristic curves when the compensator roller displacement velocity v is varied from 0.5 mm/sec to 1 mm/sec while the gains are maintained at the standard values (Fig. 6(a)) and gains are calculated from Eqs. (4) and (5). It is seen that hunting can be suppressed by adjusting the gains Kp and K_D.
Figs. 7(a) and 7(b) show characteristic curves when only the gain K_D is adjusted; that is, when the radius r of the plate cylinder is changed from 0.14 m to 0.08 m. As is clear from Eqs. (4) and (5), the radius r of the plate cylinder is only contained in Eq. (5) and is not included in Eq. (4). Therefore, when the radius r of the plate cylinder is changed, only the gain K_Dis changed but the gain Kp remains unchanged. In this respect, the radius r of the plate cylinder is fundamentally different from the pass length 1₁between the adjacent units, the pass length 1₂between the plate cylinder and the position at which the register mark is detected and the compensator roller displacement velocity v explained above with reference to Figs. 4(a) and 4(b) - Figs. 6(a) and 6 (b) .
Validity of Eqs. (4) and (5) are confirmed from the above-described explanation in conjunction with the characteristic curves as shown in Figs. 2 - 7(a) and 7(b). Furthermore, it should be noted that Eqs. (4) and (5) constitute only the essential factors which can be correctly analyzed in registration control. The gains Kp and K_D obtained from Eqs. (4) and (5) can better cope with various conditions which are expected to occur in registration control so that it can be said that the registration control system can be remarkably consolidated.
So far with reference to Figs. 2 - 7, it has been described how the factors which can be correctly analyzed in registration control can be processed.
Figs. 8 and 9 show characteristic curves obtained when the influence on registration control of other factors such as variations in tension of printing paper, an elongation coefficient of printing paper (which is dependent upon the quality of paper) and so on. Fig. 8 shows the characteristic curves when the tension T of printing paper is changed from 15 kg to 30 kg. The characteristic curves as shown in Fig. 8 are substantially similar'to those shown in Fig. 2. Fig. 9 shows the characteristic curves when the elongation coefficient of printing paper is changed from 0.00022 1/kg to 0.00005 1/kg. The characteristic curves as shown in Fig. 9 are also substantially similar to those as shown in Fig. 2.
That is, it can be said that in response to variations in tension and quality of printing paper, it is not needed to adjust the gains in registration control.
It follows therefore that in registration control it suffices to adjust the gains Kp and K_D of the PD control in response to the pass length (1₁) between the adjacent plate cylinder units, the pass length (1₂) between the plate cylinder and the position at which the register mark is detected, the compensator roller displacement velocity (v) and the radius (r) of the plate cylinder.
In the above-described embodiment, it has been assumed that the compensator roller velocity v be constant. However, depending upon types of printing presses, there are compensator rollers whose displacement time is constant (the rotational period T of the plate cylinder) and whose displacement velocity is variable. In this case, instead of the equations (3), (4) and (5), the following equations (3)', (4)' and (5)' are used:

where Kp': proportional gain,
K_D': differential gain,
E_k: registration error at present,
E_k-1: registration error prior to one rotation of the plate cylinder,
1, : pass length between adjacent units,
L₂ : pass length between the plate cylinder and the position at which the register mark is detected,
v : the displacement velocity of the compensator roller,
V : printing speed, and
r : the radius of the plate cylinder.
f₁', f₂', ^f ₃': monotonously reducing function.

As described above, in the case of registration in a multicolor rotary press by PD control, in response to the _pass length (1₁) between the adjacent units, the pass length (1₂) between the plate cylinder and the position at which the register mark is detected, the compensator roller displacement velocity (v), the radius (r) of the plate cylinder and the printing speed (V), the gains Kp and K are optimized so that registration control can be carried out with excellent response and stability. As a result, as compared with the conventional registration control system, spoilage can be much reduced.

Claims

1. A registration control method for a rotary press of the type in which a registration error is detected by reading register marks printed on a printing medium in a preceding unit and a succeeding unit of a multi- color rotary press and in response to a detection signal, a compensator roller is displaced so as to change a pass length between the adjacent units, thereby correcting registration errors between colors on said printing medium, characterized in that: in response to a detected registration error, a PD operation is executed based on the following equation so as to find out a drive time At of said compensator roller,

where K_P : proportional gain,

K_D : differential gain,

E_k : registration error at present,

E_k-1 : registration error prior to one rotation of a plate cylinder,

l₁ : pass length between the adjacent units,

l₂ : pass length between a plate cylinder and a position at which a register mark is detected,

v : displacement velocity of a compensator roller,

r : the radius of a plate cylinder, f₁,f₂,f₃: monotonously decreasing functions, f_1,f₂,f₃>0,

T : rotation period of a plate cylinder; and in response to a calculated value, the compensator roller is displaced at a predetermined velocity v so as to change the pass length between the adjacent units.

2. A registration control method for a rotary press of the type in which a registration error is detected by reading register marks printed on a printing medium in a preceding unit and a succeeding unit of a multicolor rotary press and in response to a detection signal, a compensator roller which is interposed between said preceding and succeeding units is displaced so as to change the pass length between the adjacent units, thereby correcting registration errors between colors on said printing medium, characterized in that:

in response to a detected registration error, a PD operation is executed based on the following equation so as to find the displacement velocity v of said compensator roller,

where K'_P : proportional gain,

KID: differential gain,

E_k : registration error at present,

E_k-1 : registration error prior to one rotation of a plate cylinder,

l₁ : pass length between the adjacent units,

V : printing speed,

r : the radius of a plate cylinder, _f1',_f2',f₃': monotonously decreasing functions, f₁',f₂'.,f₃'>0; and

in response to a calculated value, said compensator roller is displaced for a predetermined time during the rotation period T of a plate cylinder so as to change said pass length.

3. A registration control device of the type in which a registration error is detected by reading register marks printed on a printing medium in a preceding unit and a succeeding unit of a multicolor rotary press and in response to a detection signal, a compensator roller which is interposed between said preceding and succeeding units is displaced so as to change the pass length between the adjacent units, thereby correcting registration errors between colors on said printing medium, characterized by comprising:

calculation means for, in response to a detected registration error, executing a PD operation based on the following equation so as to find out a displacement time At of said compensator roller,

where Kp : proportional gain,

KD differential gain,

E_k : registration error at present, E_k-1 : registration error prior to one rotation of a plate cylinder,

l₁ : pass length between the adjacent units,

v : displacement velocity of a compensator roller,

r : the radius of a plate cylinder, ^f _l,^f ₂,f₃: monotonously decreasing functions, f₁,f₂,f₃>0

T : rotation period of a plate cylinder; and

means for, in response to a calculated value, displacing said compensating roller at a predetermined velocity v.

4. A registration control device for a rotary press of the type in which a registration error is detected by reading register marks printed on a printing medium in a preceding unit and a succeeding unit of a multicolor rotary press and in response to a detection signal a compensator roller which is interposed between said preceding and succeeding units is displaced so as to change the pass length between the adjacent units, thereby correcting registration errors between colors on said printing medium, characterized by comprising:

calculation means for, in response to a detected registration error, executing a PD operation based on the following equation so as to find out a displacement velocity v of said compensator roller,

where K'p : proportional gain,

KID: differential gain,

E_k : registration error at present,

E_k-1 : registration error prior to one rotation of a plate cylinder,

1₁: pass length between the adjacent units,

1_{2 :} pass length between a plate cylinder and a position at which a register mark is detected,

V : printing speed, r : the radius of a plate cylinder, f₁',f₂',f₃': monotonously decreasing functions,

f₁',f₂',f₃'>0; and

means for, in response to a calculated value, displacing said compensating roller for a predetermined period during the rotation period T of a plate cylinder.