MLD-S Tech-FB Library Description - Bosch Rexroth

1-54 MLD-S Technology Library Rexroth MLD-S Tech-FB Library
1.10 Measuring Wheel Function Blocks
Introduction and Overview
The Measuring Wheel Technology Function Block (Tech-FB’s) enhance
the basic functionality of MLD-S by provide a prepackaged application
specific functionality that has been pre-tested and reduces the learning
curve for the user.
The Measuring wheel is the most common device used in a closed loop
servo system to compensate for material slippage in a feeder application.
For example as the material is fed into at machine/process slippage may
occur between the feed rolls and material due to an oily film or
containments on the material or fluctuations in back tension on the web or
in the case of a corrugated feeder where the rolls are serpentine and the
point of contact (pitch diameter) varies, these as well as many other
mechanical constraints can cause slippage to occur. BRC based systems
will overcome this by using the drive based measuring wheel operation
mode, this is a specialized drive positioning mode that compensates for
slippage or stretch by placing a measurement device directly on the
moving material, it is connected to the drives optional encoder port. This
signal is used to close the position loop to the drive so the actual length of
the commanded move profile can be monitored to assure the required
accuracy is maintained. The measuring wheel utilizes frictional forces
between the wheel and the material surface for engagement, it must be in
100% contact before the position control loop is closed via the measuring
wheel encoder, if not the system can oscillate or run away. Most feeder
system need to switch back between motor and measuring wheel
encoder to accommodate special operations like initial material threading,
run-out or roll-lift. To provide as means to easily switch between the two
feedback devices the MX_MeasuringWheel FB will be supplied.
Fig. 1-75:
Measuring Wheel Application
DOK-MLD-S*-TechFB*****-AW01-EN-D