Why use intelligent drives with integrated motion control for wafer machines?

The world-renowned, domestic machine builder of production systems for wafers, biscuits and confectionery had already used VLT® drives from Danfoss under its former company name FHW Franz Haas Waffelmaschinen for many years - and remains true to this tradition even under the flag of the Bühler Group. Due to the increasing need to synchronize and position, the machine drives have recently been gradually converted to servo technology.

When Danfoss launched the Integrated Motion Control (IMC) functionality in 2017, Haas - as it was known at that time - asked whether the new control technology would also be a practical alternative to servo controls for its machines. Advantages were particularly expected from the associated free choice of motor, the technology independence and the simple system optimization through automatic motor adaptation

The IMC function can be used universally, since it can position absolutely, relatively and with sensor. In absolute position, the position reference refer to a defined machine zero point. This is determined at the start of the machine by the so-called homing run. If an optional feedback system with absolute position is used, this is not necessary because the zero point is set by the encoder. A typical application for this in Leobendorf is “downstream” of the cone oven with an absolute positioning of linear axes. The task here is to place paper in front of the continuously moving candy cones in order to be able to slide them into each other in the next step. The motors used are PM motors that are operated in open loop. The advantage of IMC: The rotary encoder can be eliminated, thus eliminating the costs for the encoder as well as for cabling, evaluation and work time for installation and commissioning. The use of the VLT® AutomationDrive (with IMC) itself also brings savings, because the purchase and installation costs of standard drives are significantly lower compared to a corresponding servo system.

Synchronization means creating an angle-synchronous synchronization of two or more axes. The gear ratio of the two axes to each other can be continuously adjusted. The reference signal for position and speed is either picked up by an external encoder, generated by a PLC as a pulse signal or specified via a virtual master signal. This virtual master signal is a pulse signal from which the direction of rotation, speed and position can be derived.

The reference for the master drive is either carried out in the traditional way via an analog signal or via a setpoint on the fieldbus. This master drive then converts the signal into a virtual master signal, which serves as a reference value for the follower drives as well as for the master itself.

The Leobendorf wafer machine specialists use synchronization with a master signal, for example in the follower drives of the cone oven. In the subsequent processes, up to eight axes each move at an angle synchronous to one another. A pulse signal from the PLC is used as the master signal. Before starting the drives, all are moved to a reference position (homing). The PM motors used in open loop with gearbox achieve angle-synchronous synchronization despite different gearboxes and different motors, via exact adjustment of the gear ratio. This removes the need for the complete encoder system for the eight axes and the servo controllers. In addition, the ovens can be started up much faster and the engineering has been simplified