Page 746 - Mechatronics with Experiments

732 MECHATRONICS

Programmable
motion controller

Position
capture
channel Drive

Print head
motor
Registration
sensor
Master Encoder
encoder
Print
area

Web motion
Registration
mark
FIGURE 10.12: Web handling with registration application. A print head (or a cut head) follows
the master encoder in order to match the speed of the web. It makes phase adjustments to its
position based on a registration sensor. The position of the print head must be captured very
accurately when the registration sensor triggers ON. The registration sensor must have good
repeatability and fast response in order to have a good positioning accuracy for the print head.

needs to be cut at a certain length (cut length is programmable). During the position range
when the knife is in contact with the web, the linear motion speed of the knife must match
the linear motion of the web (gear ratio z ), and during the position range when the knife
1
is not in contact with the paper, the knife must speed up or slow down to a different gear
ratio (z ) to let the desired amount of web length move (Figures 10.12, 10.13b).
2
Gearing with Registration Printing, cutting, and sealing applications in web han-
dling processes require motion coordination which involves gearing plus registration. This
very common form of motion coordination involves the following (Figures 10.12, 10.13):

1. electronic gearing of a slave axis to a master axis with a certain gear ratio, and
2. for each cycle, after a sensor input condition (registration mark or registration signal)
is true, the slave axis must make an incremental move during a certain distance of
the master axis. This is called phase adjustment based on registration mark sensing.
A variation of this approach is to calculate a new gear ratio and change the gear ratio
in order to get the same amount of additional move.
There are many variations of the registration mark applications. The incremental
motion distance may be either a predefined length or calculated based on the difference
between the actual position captured when the registration sensor triggers and a desired
position. The keys to achieving high accuracy in registration applications are to capture
certain motion related conditions very quickly (i.e., less than 25 μs) and respond very
quickly (i.e., a few millisecond).