Packaging Machinery: Filling and Sealing Positioning

Displacement measurement on packaging machinery concentrates on two places, dosing and sealing. On the dosing side are filling-piston and metering-cylinder stroke, which directly determine the volume accuracy of each pouch or bottle. On the sealing side are closing and positioning of the sealing dies, pillow-pack cut-off knife and case-packer jaws, which determine seal quality and line cycle time. Food and pharmaceutical packaging also require washdown, so the protection-rating requirement is higher.

Dosing side: filling volume is determined by stroke

The core formula of piston filling is “volume = cross-sectional area × piston stroke”. Displacement feedback reads the piston absolute position; the controller converts stroke to volume and realises volumetric filling. Accuracy depends on repeatability (typically of the order of ±0.002 mm; see the three accuracy terms) and the resolution grade; 5-20 μm is recommended. Non-linearity must be read together with measuring range (of the order of <0.02% FS; a short range can be better), otherwise the small-volume section is easily misjudged. After a power loss absolute position is retained, so re-zeroing is unnecessary after a batch change and line flush (see absolute vs. incremental position).

Sealing side: die closing and knife positioning

Die closing affects seal strength and appearance; knife position affects pouch length and cut neatness. Displacement feedback is used for closing-position control, synchronisation monitoring on multi-lane machines, and hold-position during dwell. A high-speed line should check whether the refresh rate keeps up with the control cycle (see matching response time to the control cycle). If the drive is a pneumatic or hydraulic cylinder, the selection framework is given in why hydraulic cylinder position control uses magnetostrictive sensing.

Typical measuring-point layout on packaging machinery

Installation points for washdown and food-grade environments

Food and pharmaceutical packaging often have high-pressure hot-water or disinfectant washdown, requiring IP69K protection (for the meaning of each rating see IP protection ratings). Series 13 mobile hydraulic offers IP69K, 25 g vibration and 100 g shock, and is suited to wet areas and vibrating stations; for ordinary dry-area positioning specify Series 18 profile type. Cables and connectors must use food-grade resistant materials and be routed downwards. Installation practice is covered in installing and commissioning in practice.

Interfaces and line integration

Filling and sealing are often multi-lane in parallel. Position feedback may be a fieldbus type for unified management, or SSI for a highly deterministic position loop (Series 192 SSI digital interface). Synchronous sampling on a high-speed line should use a fieldbus that supports distributed clocks (see the practical fieldbus guide). Robot load/unload and positioning can be compared with industrial robots: seventh-axis and vertical-axis position.