Italian machine builder hones its motion controls
04 January 2012
Following a review of its wide range of automated handling machines for the cookware, ceramics and tableware market, Italian machine builder CMC decide to replace motion controls based on induction motor/VSD combinations, opting instead for servo-drives and brushless servomotors
CMC, located in the heart of the Italian ceramic tile production area in and around Sassuolo in northern Italy, has for the last 30 years specialised in the design and development of production line machines – often tailor-made for its customers, particularly those in the ceramics industries. The company is a key supplier to the SACMI Group and has supplied machines for some of Europe’s most prestigious manufacturers of tableware – including Villeroy and Boch, Pozzi-Ginori and Tognana.
During a recent review of all of its machine designs, the company sought ways to enhance handling and throughput, and generally improve machine efficiency and performance. The first step was to reassess all motion controls using conventional induction motors, which formerly produced the movements of all axes under the control of variable-speed drives.
The brief was to improve efficiency, dynamic performance and accuracy, and it was decided that brushless servomotors would ensure high precision positioning and lower energy losses. These were subsequently fitted with Sin/Cos absolute encoders that store the position of each axis in permanent memory, dispensing with homing set-up procedures, which would otherwise have been necessary at each start-up.
For the servo drives, the choice came down to Control Techniques’ compact Digitax ST units, which are used in conjunction with centralised motion controllers. These can be connected using either digital or analogue networks to provide the movement control for each axis. Optional plug-in modules equip the servo-drives with dedicated servo networks – typically EtherCAT, Sercos or CANopen – while dedicated I/Os include high-speed ‘freeze’ input, high resolution analogue input and simulated encoder output to simplify connection with external controllers. A range of encoder signals are accepted by the drive, including Sin/Cos, Hiperface, Endat and SSI, enabling the most appropriate to be selected for any particular applications.
Digitax ST also features a ‘Safe Torque Off’ (STO) standard input that disables the power stage of the drive to ensure a high level of safety, for machine maintenance purposes. The integrated STO function reduces the cost of meeting compliance with machine safety standards EN 954 Cat.3.
Typical machine
A typical CMC machine might include an auxiliary system for use with a press for the production of aluminium pans. The system comprises a series of elements: a module for de-stacking and distribution of aluminium disc blanks, followed by transport, inspection and oiling of the blanks, which are then aligned and elevated to a take-up station that comprises a pair of straight bars with synchronised movements. A pan take-up and conveyor completes this unit.
Set-up is controlled via a selection of menus from the screen and requires minimal manual intervention. This particular machine achieves a high production rate of 16 cycles per minute while ensuring access to the press during die-change operations is both easy and safe. The machine is very flexible and easy to adapt to different products and has a very low maintenance requirement – and Digitax ST servo-drives control each of its key axes.
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