Article strapping arrangement with a synchronous motors connected to a frequency converter

#The present invention concerns a package strapper. Three motor-driven mechanisms, specifically a strap feed, a strap stretcher, and a strap-end fastener, are mounted on a strap track. The track loops around the package. The feed includes at least two wheels, each forced against one side of the strap by a spring. The motor that drives the feed can be reversed. The strap-stretcher wheel is between the feed and the track and is partly loosely surrounded by a strap guide. One end of the guide opens into the track.

#To ensure high performance on the part of the package strapper, the incoming strap rapidly occupies the entire loop of the track. The strap-feed motor turns off in accordance with a known principle when the leader, the forward end of the strap, that is, encounters a switch at the end of the track. The motor's inertia, however, allows it to feed enough extra strap to jam the track. The motor must accordingly also be mechanically lifted away from the feed wheels by an expensive magnetic clutch, which eventually wears out and must be replaced. Another drawback is that the leader tends to rebound off the switch and buckle the length of strap behind it.

#The tensions in the looped strap are evened out in accordance with a known principle. Specifically, the strap-stretcher motor is loosely mounted and, as its reaction increases, forces a spring back slightly against a bearing and engages a switch. The switch turns off the motor and engages a magnetic clutch, which immediately disengages the still spinning motor from the drive. The tension on the spring can be adjusted, and hence the tension in the strap as well. The strap-tension motor accordingly also requires an expensive clutch that wears out. Finally, the spring's bearing against the switch is also complicated.

#One embodiment of the invention will now be specified by way of example with reference to the accompanying drawing, wherein

#FIG. 1 illustrates the strap feed, the strap stretcher, a supply reel, and the strap track and

#FIG. 2 is a block diagram illustrating the motors, their power supply, and their controls.

#Strap 1 is extracted from a reel 2. The leader is threaded into a track 3 by hand until it arrives in the nip 4 between strap-feed wheels 5 and 6. An unillustrated spring gently forces wheel 5 against wheel 6. At least one of the wheels is driven. The wheels feed the leader into a guide 7. Once through guide 7, the leader is intercepted by a strap-stretcher wheel 8 and introduced into a track 10, represented by a solid line in FIG. 1, that loops entirely around a package 11. Strap 1 continues in the direction indicated by the arrow 12 until it completely occupies track 10. The wheel 8 is loosely surrounded by a strap guide 9 having one end opening into the track 10.

#Strap-feed wheel 6 rotates rapidly, and track 10 is soon completely occupied by strap. Just before arriving at the end or entry point, the leader travels past a sensor 13 in the form for example of a light barrier, its beam interrupted by strap 1.

#Sensor 13 notifies a data processor 15 that the leader has passed. Processor 15 is accommodated in and controls a frequency converter 14. The processor instructs converter 14 to considerably decrease the frequency of the electricity powering a motor 16 that drives the strap feed. A distance gauge comprising a light barrier 17 that shines through several perforations 18 distributed around a circle in strap-feed wheel 6 is now engaged. A pulse is transmitted to processor 15 every time the beam from light barrier 17 penetrates one of the perforations 18 in the rotating wheel. The intervals of arc can be much finer if the gaps between the cogs in one of the wheels in the drive are exploited instead of perforations 18 for the light to shine through.