In wine and liquor bottling machines a film is shrunk over the bottleneck and the cork or cap, a so-called bottle cap. Two different modes of operation are used to cut the film to the desired length. The first method advances the reel-fed band by a fixed distance after a starting signal. Then, a digital signal activates a pair of scissors cutting the band. The second method uses a marking on the band which is detected by an optical reader and initiates a relative position move. Again, the scissors are activated. The selection of the mode of operation is set at the beginning by a digital signal.

The filling machines have an expected life of several decades if properly serviced and maintained. During the life cycle faulty modules and sub functionalities may be replaced, improved and modernized. This is made easier by a basic modular conception of the machine. Traditionally, a stepper drive controlled by the main PLC was used to cut the shrink-film. A redesign of this function uses a programmable maxon compact drive MCD EPOS P. The underlying goal is to put the modularization one step further by transferring intelligence to the local drive.

Another important aspect is to reduce the outer dimensions of the drive and at the same time achieve a higher force. The requirements are at least three working cycles per second. These conditions are optimally fulfilled with the use of a brushless dc motor as found in the MCD EPOS combined with a maxon ceramic gearhead GP 32 C (reduction ratio 18:1), to help provide higher life expectancy. The MCD is smaller than the existing controller and fits perfectly below the feeding roll with the gearhead. A toothed belt transmits the torque from the gearhead to the roll with an additional reduction of 2:1.

The local PLC functionality is built into the programmable MCD EPOS P 60W and controls the complete cutting operation. The drive receives a digital signal from the main PLC defining the mode of operation. Upon the starting signal, the complete process is controlled locally. This means the signals of the optical sensor and the state of the scissors are read, the position moves with the motor executed and the scissors activated. The digital outputs are used as well to provide error signals and to activate the inputs.

In addition, motor, encoder and motion controller are all integrated into an aluminum housing allowing protection up to IP54. All internal connectors are vibration proof and suitable for a harsh industrial environment. The brushless dc servo motor impresses by the high power density and the long life expectancy. Due to the high starting torque, an excellent dynamic behavior is obtained. The slotless winding allows smooth operation without cogging even at the lowest speed. This is further supported by the sinusoidal electronic commutation scheme of the controller. The digital incremental encoder with 1000 counts per turn results in 4000 positions of one motor revolution or a nominal resolution of 0.09°. Combinations with gearheads are foreseen to increase the torque.

The motion controller used is a member of the maxon EPOS family, a modular positioning system with CANopen filed bus interface. It can be used as a speed, torque and position controller. The motion controller is integrated in the slim and compact housing without increasing the outer dimensions of the drive with any protruding parts. The sophisticated heat management of the power stage is made with a printed circuit board specially mounted on an aluminum support. This allows keeping the electronics small and yet get the full rated power from the motor. The power stage is optimally adapted to the power requirements of the motor.

Due to the opto-coupled configurable inputs and outputs all kind of signals from the drive periphery can directly be connected, i.e. end switches or reference switches.

Urs Kafader is a technical trainer at maxon motor, Switzerland.
www.maxonmotorusa.com