Sausage casing machine

Source: CAN Newsletter December 2005

Sewing machines for sausage casings are not immediately associated with high-tech. However, the development of an automatic sewing machine manufactured by Beckmann Maschinenbau for a sausage-producing customer posed quite some control-technological challenges. After all, a motion control solution had to be devised for seven real axes and one imaginary axis. And the complexity of the motions with resect to the axes is comparable to that typical of CNC path control systems. The task and the method of the sewing machine are relatively easy to describe: the starting product is a fabric tape (textile casing) of 200-mm width, which is folded to form a two-layer tape of 100-mm width and conveyed close to the two sewing heads by means of a toothed belt. The task of the sewing heads is to sew the contours of various sausage models into the tape according to given geometric data. In this way an endless tape of sewed sausage casings is produced, which are separated from one another in the subsequent course of processing.

Demanding application

Each of the two sewing heads has three axes:

  • the needle stroke,
  • the linear motion along the x-axis perpendicular to the direction in which the fabric tape is conveyed, and
  • the tangential slaving of the heads during the process of sewing and, in particular, separating (cutting).

The sewing heads are located at the right and left edge of the fabric tape and they are out of line to ensure freedom of motion. The seventh axis is associated with the control of the speed of the material conveyor belt.
From a control-technological point of view, this is a typical motion control application. The relation between the three axes of each sewing head is well defined so as to coordinate the respective motions. In addition, the two groups of axes have to be coordinated with the motion of the conveyor belt (7th axis). A virtual (8th) axis is used to implement a look-ahead function for speed monitoring. Moreover, typical PLC functions are required, for example, the optical thread break detector, emergency stop buttons, light barriers, etc.
The end users from food production imposed very high productivity and quality requirements. In order to meet these, the control solutions had to provide sufficient computing power and comprehensive programmability.

The embedded controller has, as default, an Ethernet interface, an RS-232 interface for loading the application software and two CAN interfaces. For all of these products, the CANopen communication protocol provides device profiles. The controller implements CiA 401, CiA 402, and CiA 405. The fieldbus modules implement CiA 401.

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