Machines for pharmaceutical inspection

Dicembre 2014

A choice of Motion in Farm & BeautyWe are often led to believe that the choice of motion control for an automatic machine is linked exclusively to the features that it possesses: ability to handle cams rather than special cinematic numerical control functions or those cut on the fly. This is correct in principle, but is not always the discriminating element of choice.In the experience we're going to relate, for example, the control architecture was decided by the "shape" of the machine rather than the motion capabilities. In pharmaceutical inspection systems, in fact, the "carousel" configuration of the machines has imposed the use of an electrical splice (model SRH-180 by Servotecnica) with a large diameter for the transmission of power and motion commands on board the carousel, where the drives are also located.The basic version of this machine automatically provides for twenty-four motors that move perfectly synchronously with each other and must be related to the angular position of the carousel (master encoder). To ensure synchronisation of the axes, an EtherCAT bus was employed, the fastest, standard and open bus available on the market today. The technical control was chosen precisely for its high speed.When transmitting high-frequency signals (the 100Mbit / s of EtherCAT or Gbit / s of a video signal) the impedance of the transmission element is fundamental. In our case the collector, being part of the chain transmission, also contributes to its impedance. A 180 mm diameter electrical joint has a high resistance, which does not allow the transmission of signals at 100Mbit / s in a reliable manner. For this reason we separated the control machine (located on the ground) from the motion (brought aboard the carousel) connecting them through an Ethernet network at 10Mbit / s, more suited to the shape of the collector (or its electrical impedance).In this way tight axis synchronization is guaranteed by the EtherCAT network of the machine, while the master encoder signal and the high level variables are passed via Ethernet using the fast ADS protocol.Another fundamental aspect in the choice of the control system was the extreme compactness of the drives and the controls used. For the large tube inspection machines, we used 200Watt brushless motors with Gold Whistle drives by Elmo, while for the smaller test tubes, we were able to use the 100Watt motor with integrated electronics from the Pegasus series by LS Mecapion. As for the motion control, we chose the Gold Master (G-MAS) by Elmo, unique for its compact size (115 x 75 x 25 mm).

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