Page 751 - Mechatronics with Experiments

PROGRAMMABLE MOTION CONTROL SYSTEMS 737
axis reading may not be accurate. The registration mark provides us with a positive sensing
mechanism for the actual web length passed.
From an electronic gearing motion coordination point of view, the registration mark
requirement adds one more motion coordination problem. That is, the tool must be in correct
positional phase relative to the mark in order to cut it at the right offset location. Assuming
that there is no slip or variation in registration mark location, once the tool and paper are in
phase, they will stay in phase for a fixed cycle length. However, to ensure accuracy in every
cycle against web slippage or variations in web registration mark location, the tool-web
position phase is checked and corrected if necessary.

Motion Coordination Algorithm: Rotating Tool (Cutting Knife,
Print Head, Seal Head) with Registration Mark Application:
Main Program
{
while (TRUE)
{
Initialize the rotating knife with registration mark
application algorithm
Verify HOME motion sequence is done
Check Task 1
Check Task 2
.....
Check Print Phase and Registration Mark
{
When Enterered Contact Phase, execute
Contact_Phase Function once
When Entered Noncontact Phase, execute
Non_Contact_Phase Function once
When Registration mark is received, excecute
Registration_Mark_Phase_Adjustment
}
}
}

Algorithm Initialize:
web_cycle_length = ... % web length per cycle
tool_circumference = .... % pi * diameter
contact_percentage = ..... % 0 to 100
gear_ratio_contact_num = 1
gear_ratio_contact_den = 1
gear_ratio_noncontact_num = web_cycle_length *(100-
contact_percent)/100
gear_ratio_noncontact_den = tool_circumference *(100-
contact_percent)/100

define desired position phase for tool on registration
mark
setup fast position capture (actual or commanded) of
tool axis on registration mark

Return
Contact_Phase:
change gear ratio of tool (slave) to web (master) to
ratios defined by
z = gear_ratio_contact_num / gear_ratio_contact_den
Return