Fig.: Product and search parameters ("ProductParameters")
The "ProductParameters.DistanceToSensor" input specifies the distance between the registration mark sensor and the standstill position of the sealing/cutting axis. Any difference between the standstill position and interval starting position can be compensated using "ProductParameters.StartOffset". The standstill position and interval starting position can be different in order to protect the material during standstill (e.g. influence of heat, etc).
The first expected position of the registration mark is calculated with basic mode mcACT_CFG using the following values of input structure "ProductParameters":
•StartOffset
•Length
•DistanceToSensor
•RegMarkPosition
FirstRegMarkPosition = ((Length - (DistanceToSensor mod Length) + RegMarkPosition) mod Length) + StartOffset
The value of the "PositionError" output is determined as follows during operation:
PositionError = ActPosition – RegMarkPosition
Fig.: "PositionError"
The user can use the definition of the product length ("ProductParameters.Length") to simultaneously determine the ideal (desired) distance between two seal/cut points and the distance between two registration marks. If the product length is specified incorrectly, then the function block is not able to recover the registration mark in the next product interval.
The value of the "LengthError" output is determined as follows during operation:
LengthError = ActLength – Length
Fig.: "LengthError"
A length tolerance (as a percentage of "Length") must be specified for the function block using "ProductParameters.LengthTolerance" in order to correctly output the determined values. The function block then checks if its events are within a plausible range. The value used should not be selected too low since this could cause valid trigger events to be rejected.
Typical values: 5 - 10%
If the registration mark is outside of a configured trigger window during operation, then the function block can still search for it. For example, the point at which the search for the registration mark should resume again depends on the subsequent parameters of the "ProductParameters" input structure:
•SearchMode
•LengthChange
•MissedTriggerCount
For further details, please refer to Retrieving a lost registration mark.