Image registration in a can decorator
A can decorator having a blanket wheel and a plurality inking stations. Each of one or more of the inking stations comprises a rotatable shaft geared to the blanket wheel, a print cylinder mounted on the shaft for rotation with the shaft during printing operations, and an adjustment mechanism for adjusting the angular position of the print cylinder on the rotatable shaft during set-up and for fixing the angular position for printing operations. There is further provided a rotary encoder for determining the angular position of the print cylinder relative to the rotatable shaft during set-up and for providing an electrical signal indicative of the angular position to an operator interface device.
1 . A method of performing print registration in a can decorator having a blanket wheel and a plurality of inking stations, each inking station having a print cylinder and a rotatable shaft defining a cylinder portion that defines a constant diameter over the cylinder portion, the method comprising:
for each of one or more of the inking stations, performing a set-up procedure including using a rotary encoder to detect an angular position of the print cylinder relative to the rotatable shaft on which the print cylinder is mounted, and
adjusting the angular position of the print cylinder relative to the shaft using the detected angular position.
2 . The method according to claim 1 , wherein using the rotary encoder to detect the angular position of the print cylinder relative to the rotatable shaft comprises the step of measuring an angular position of the print cylinder relative to a location on the respective inking station.
3 . The method according to claim 1 , further comprising the steps of:
for one or more of the inking stations, using a linear position sensor to detect an axial position of the print cylinder relative to the rotatable shaft, and
adjusting the axial position of the print cylinder on the shaft using the detected axial position.
4 . The method according to claim 1 , wherein the rotary encoder is an induction encoder.
5 . The method according to claim 1 , wherein said step of adjusting the angular position of the print cylinder on the shaft using the detected angular position comprises displaying the detected angular position on a display whilst manually performing the adjustment.
6 . The method according to claim 1 , wherein the rotatable shaft is geared to the blanket wheel.
7 . The method according to claim 1 , wherein the rotary encoder comprises a first section and a second section, the first section being in a fixed position relative to a main body of the inking station and the second section being in a fixed position relative to the print cylinder.
8 . The method according to claim 7 , wherein the first section is attached to the main body of the inking station.
9 . The method according to claim 8 , wherein the second section is attached to the rotatable shaft.
10 . The method according to claim 7 , wherein the first section comprises active components and the second section comprises a passive device.
11 . The method according to claim 7 , wherein the rotary encoder is an induction encoder.
12 . The method according to claim 11 , wherein the induction encoder comprises a laminar construction comprising etched copper or printed coils.
13 . The method according to claim 11 , wherein said print cylinder is mounted on the rotatable shaft via a sleeve, wherein a second section of the induction encoder is fixed to the sleeve, opposed to but spaced apart from a first section of the induction encoder.
14 . The method according to claim 1 , further comprising the steps of measuring an axial position of the cylinder relative to the shaft and providing an electrical signal indicative of the axial position to an operator interface device by a linear position sensor.