A standard apparatus for erecting box blanks comprises a supply holding a stack of flattened box blanks, a conveyor passing adjacent the supply and having a succession of box seats, and a planet carrier rotatable about a sun axis between the supply and the conveyor. Several planetary elements on the carrier offset from the sun axis have axially spaced inner and outer ends and are rotatable about a planet axis parallel to and offset from the sun axis. Grabs on the planetary-element outer ends are engageable with the blank in the supply and engageable in the conveyor seats. A planet drive gear fixed to the planetary-element inner end is rotatable with the planetary element about the planet axis.
According to German 42 24 897 a differential drive including a sun wheel rotatable about the sun axis and meshing with all of the planet gears moves the planetary element and the carrier such that the grabs follow a hypocycloidal path having for each grab a respective outer point. Thus each grab engages the end flattened blank in the supply, pulls it out, then swings it through an arc to deposit it in one of the seats or cells of the conveyor and then swings through a further arc to return to the starting position. During this movement the blank is opened up or erected into its three-dimensional shape.
The problem with such a system is that the large symmetrical paths followed by the plural grabs take up a great deal of space. Several grabs are needed, however, to keep up with production pace, since each grab moves through a long complex path between its actual end-point use positions. In addition resetting the machine to work with box blanks of different format is a fairly complex task that takes quite some time, as each of the grabs has to be adjusted and reset. The grabs driven from a common sun gear have to be set perfectly so that each does its function when it moves into position between the supply and the conveyor.
Accordingly U.S. Pat. No. 4,518,301 of Greenwell shows a system for taking flattened box blanks out of a supply and transferring them to a conveyor. The blanks are erected as they are moved between the supply and the conveyor by a system having several grabs whose angular positions are controlled by a complex cam system. Such an arrangement is also extremely difficult to reset when the size of the blanks being handled changes.