Re-design of a packaging machine employing linear servomotors: A description of modelling methods and engineering tools

Position-controlled servo-systems mostly make use of electric rotary motors and gearboxes and, if necessary, a transmission mechanism to convert rotary into linear motion. Even so, especially in the field of automatic machines for packaging, it should be highlighted that most of the required movements are usually linear, so that Linear Electric Motors (LEM) should somehow represent a more convenient solution for designers. LEM can directly generate the required trajectory avoiding any intermediate mechanism, thus potentially minimizing the number of linkages/mechanical parts and, therefore, the undesired backlash and compliance that come along. On the other hand, particularly within small-medium enterprises, LEM may be rarely employed despite obvious advantages, mostly due to their high-cost as compared to rotary actuators and the lack of knowledge of the achievable performance. In light of these considerations, the present paper reports an industrial case study where an automatic machine for packaging, comprising distributed actuation and several tasks requiring a linear motion, has been completely redesigned employing different kind of LEM (i.e. iron-core and iron-less). Such machine architecture is compared to a “traditional” design where brushless gearmotors are coupled to linkage systems. The paper mainly focuses on the selection criteria for the LEM system and on the engineering tools employed during the different design stages. Qualitative and quantitative conclusions are finally drawn, which may provide useful hints for designers that are willing to actually employ LEM-based solutions in an industrial scenario.