Method and system for continuous feed printing systems
A method of measuring and correcting the Young's Modulus inline to eliminate its impact on image length variation during print runtime. The method includes intentionally perturbing the nominal operating condition of the web printing system which is controlled by the double reflex printing controller. The perturbation creates misregistration in a control target printed image that is detectable by in-situ sensors, from which Young's Modulus is estimated. Specifically, the web tension before the print zone is set differently from the web tension in the print zone to create misregistration. The error is detected by the inline sensors, and it is used to calculate the actual Young's Modulus. The implementation of the method consists of measuring the Young's Modulus at various frequencies. The correct Young's Modulus in then incorporated into the double reflex printing algorithm.
1. A method of registering images in an imaging device with at least two marking stations, the method comprising:
generating a first set of timing signals for printing a registration target on a web of print media, wherein the first set of timing signals is generated via a double reflex printing algorithm;
printing the registration target using the first set of timing signals;
sensing the printed registration target with an image sensing unit and generating a digital image of the registration target;
processing the digital image and computing a registration error growth rate for each marking station in the imaging device;
modifying one or more parameters in the double reflex printing algorithm to compensate for the registration error growth rate;
generating a second set of timing signals via the modified double reflex printing algorithm; and
reprinting the registration target using the second set of timing signals.
2. The method of claim 1 , wherein the registration target comprises a collection of short dashes printed by selected marking stations.
3. The method of claim 1 , wherein the image sensing unit comprises a full width array.
4. The method of claim 1 , wherein the first set of timing signals the timing signals are represented by t 1 (k) and t 2 (k) and are generated by processing the measurements v a , v b , T a and T b such that t 1 (k) and t 2 (k) satisfy the following equations (1) and (2):
h
2
-
h
1
=
1
1
+
T
b
(
t
2
(
1
)
)
/
EA
∫
t
1
(
1
)
t
2
(
1
)
(
1
-
h
1
L
)
v
a
1
+
T
a
/
EA
+
(
h
1
L
)
v
a
1
+
T
b
/
EA
ⅆ
t
(
1
)
d
=
∫
t
i
(
k
)
t
i
(
k
+
1
)
(
1
-
h
i
L
)
v
a
1
+
T
a
/
EA
+
(
h
i
L
)
v
a
1
+
T
b
/
EA
ⅆ
t
,
i
=
1
,
2.
,
k
=
1
,
2
,
3
,
…
(
2
)
where, d is the desired dot to dot distance, E is the Young's Modulus of the web, and A is the cross section area of the web.
5. The method of claim 4 , wherein parameters in the double reflex printing algorithm are set as follows:
Set T b =2 *T a
Choose EA min and EA max such that EA min <EA true <EA max
Set EA algorithm =( EA min +EA max )/2,
where EA min and EA max are estimated lower and upper bounds of the actual EA.
6. The method of claim 5 , wherein the registration error growth rate is positive if EA algorithm >EA actual and negative if EA algorithm <EA actual .
7. The method of claim 6 , further comprising:
adjusting the parameter EA algorithm according to the following rules:
IF (rate)>0
Set EA max =EA algorithm
Set EA algorithm =( EA min +EA max )/2
IF (rate)<0
Set EA min =EA algorithm
Set EA algorithm =( EA min +EA max )/2.
8. A method comprising:
creating detectable registration errors in a printed image by intentionally setting a differential web tension between a pre-print zone and a print zone in a web of print media having a given Young's modulus;
printing an image using a double reflex printing algorithm;
sensing the registration errors in the printed image and determining a registration error growth rate; and
adjusting the value of Young's Modulus in the double reflex printing algorithm until the registration error growth rate is no longer increasing or decreasing.
9. The method of claim 8 , wherein the double reflex printing algorithm comprises generating a set of timing signals represented by t 1 (k) and t 2 (k) by processing the measurements v a , v b , T a and T b such that t 1 (k) and t 2 (k) satisfy the following equations (1) and (2):
h
2
-
h
1
=
1
1
+
T
b
(
t
2
(
1
)
)
/
EA
∫
t
1
(
1
)
t
2
(
1
)
(
1
-
h
1
L
)
v
a
1
+
T
a
/
EA
+
(
h
1
L
)
v
a
1
+
T
b
/
EA
ⅆ
t
(
1
)
d
=
∫
t
i
(
k
)
t
i
(
k
+
1
)
(
1
-
h
i
L
)
v
a
1
+
T
a
/
EA
+
(
h
i
L
)
v
a
1
+
T
b
/
EA
ⅆ
t
,
i
=
1
,
2.
,
k
=
1
,
2
,
3
,
…
(
2
)
where, d is the desired dot to dot distance, E is the Young's Modulus of the web, and A is the cross section area of the web.
10. The method of claim 8 , wherein parameters in the double reflex printing algorithm are set as follows:
Set T b =2 *T a
Choose EA min and EA max such that EA min <EA true <EA max
Set EA algorithm =( EA min +EA max )/2,
where EA min and EA max are estimated lower and upper bounds of the actual EA.
11. The method of claim 10 , wherein the registration error growth rate is positive if EA algorithm >EA actual and negative if EA algorithm <EA actual .
12. The method of claim 11 , further comprising:
adjusting the parameter EA algorithm according to the following rules:
IF (rate)>0
Set EA max =EA algorithm
Set EA algorithm =( EA min +EA max )/2
IF (rate)<0
Set EA min =EA algorithm
Set EA algorithm =( EA min +EA max )/2.
13. An image processing system comprising:
a first control mechanism operative to generate a first set of timing signals for printing a registration target on a web of print media, wherein the first set of timing signals is generated via a double reflex printing algorithm;
an imaging device with at least two marking stations for printing the registration target using the first set of timing signals;
an image sensing unit operative to sense the printed registration target and generate a digital image of the registration target; and
a second control mechanism operative to:
process the digital image and compute a registration error growth rate for each marking station in the imaging device;
modify one or more parameters in the double reflex printing algorithm to compensate for the registration error growth rate; and
generate a second set of timing signals via the modified double reflex printing algorithm.
14. The system of claim 13 , wherein the registration target comprises a collection of short dashes printed by selected marking stations.
15. The system of claim 13 , wherein the image sensing unit comprises a full width array.
16. The system of claim 13 , wherein the first set of timing signals the timing signals are represented by t 1 (k) and t 2 (k) and are generated by processing the measurements v a , v b , T a and T b such that t 1 (k) and t 2 (k) satisfy the following equations (1) and (2):
h
2
-
h
1
=
1
1
+
T
b
(
t
2
(
1
)
)
/
EA
∫
t
1
(
1
)
t
2
(
1
)
(
1
-
h
1
L
)
v
a
1
+
T
a
/
EA
+
(
h
1
L
)
v
a
1
+
T
b
/
EA
ⅆ
t
(
1
)
d
=
∫
t
i
(
k
)
t
i
(
k
+
1
)
(
1
-
h
i
L
)
v
a
1
+
T
a
/
EA
+
(
h
i
L
)
v
a
1
+
T
b
/
EA
ⅆ
t
,
i
=
1
,
2.
,
k
=
1
,
2
,
3
,
(
2
)
where, d is the desired dot to dot distance, E is the Young's Modulus of the web, and A is the cross section area of the web.
17. The system of claim 16 , wherein parameters in the double reflex printing algorithm are set as follows:
Set T b =2 *T a
Choose EA min and EA max such that EA min <EA true <EA max
Set EA algorithm =( EA min +EA max )/2,
where EA min and EA max are estimated lower and upper bounds of the actual EA.
18. The system of claim 17 , wherein the registration error growth rate is positive if EA algorithm >EA actual and negative if EA algorithm <EA actual .
19. The system of claim 18 , wherein the second control mechanism is further operative to:
adjust the parameter EA algorithm according to the following rules:
IF (rate)>0
Set EA max =EA algorithm
Set EA algorithm =( EA min +EA max )/2
IF (rate)<0
Set EA min =EA algorithm
Set EA algorithm =( EA min +EA max )/2.