The challenge is to make the science of ‘defectology’ truly innovative by doing it during production so as to avoid intervention after significant damage has already been done. Hence the Sacmi Imola PET Division’s development of high-performance vision systems. The PVS systems are not only able to detect any kind of defect in the pre-form but can also interact with the line to prevent reproduction of the error immediately. The latest Sacmi-developed model is the PVS 2, which offers the great advantage – with respect to the tried and tested PVS 1 – of installation on the line, next to the press: able to analyse up to 2,000 preforms per hour, it uses a sampling system, picking pre-forms at set time intervals and returning them to the production cycle where free of defects. Otherwise, the PVS 2 warns the operator, who can then intervene to stop production.
Among the detectable defects: contamination and dirt, crystalline formations, container warping, cratering and holes at the injection point, bubbles and opacity, colour variations. While these are the same as those detected by the PVS 1, which can boast an analysis rate of up to 40,000 pre-forms per hour, the latter nevertheless operates in “stand alone” mode only; this means that analysis is carried out when the production cycle is already over and, consequently, the amount of damage already done to the pre-form batch may be significant. A key factor in the development of the PVS 2 was the finding that pre-form defects tend to progress “tangentially”; in other words, when the machine drifts outside the optimal range for one or more parameters, it tends to do so to an ever-greater extent: hence the effectiveness of line sampling. All PVS models can flexibly manage different pre-form formats and diameters.
Recently, the Sacmi Imola PET Division also developed the PVS 3, a system designed to be installed not at the converter but at the bottler upstream from the blowing machine; this unit can analyse up to 36,000 oriented pre-forms an hour and reject them before they are sent for blowing. Yet it is from the innovative PVS 2 - the first system of its kind on the market - that Sacmi expects the best sales performance: cheaper than the PVS 1, the PVS 2 intervenes in the production process exactly as and when required: the other two models, instead, only function when the “damage has been done”. And, bearing in mind the costs of PET, the relevant diseconomies are far from negligible. In addition to the basic software, the three PVS models also share the same set-up system. Quality standards are decided by the operator on a case-by-case basis: a pre-form judged to be good is ‘captured’ by the PVS camera and acceptable tolerances for individual parameters are set according to customer-specific requirements.