Spectacle lenses reliably sorted for shipment worldwide



A denisort line built by Swiss company Ferag AG for ZEISS Vision Care automates the shipping process for this international ophthalmic optics manufacturer based in Aalen, in the German territory of Württemberg. The new sorting system claims just 85 square metres of floor space – less than its predecessor – and yet multiplies capacity several times over to more than 35,000 shipment units per day. It is also very gentle on the sorted goods, which are mainly spectacle lenses manufactured according to personal prescriptions. On top of that, the system is extremely quiet-running and hence easy on the ears of people at work in the hall.

“ZEISS is about customer success, innovation, precision and reliability. Our customers are opticians and the overarching goal is to make them more successful. They place orders and receive goods from production or inventory just a short while after. Crucial to this is a logistics chain capable of smoothly and speedily dispatching many thousands of individual shipments, day after day,” says Joachim Hug during a tour of the shipping department at Aalen in Germany’s Württemberg territory, where spectacle lenses have been developed and manufactured since 1956. Here the supply chain manager points out the new denisort conveyor, which has been working flawlessly for months now. Its trays are all but silently taking on board one shipping envelope after another in rapid succession. These contain premium-quality spectacle lenses, which ZEISS Vision Care mostly manufactures in pairs according to opticians’ personalized prescriptions. The lenses are tailored to spectacle wearers’ specific vision impairments and provide perfect compensation. Pre-manufactured lenses held as inventory represent a smaller portion of the goods passing through the Ferag conveyor’s three sorting loops. In addition to custom-made and ex-stock lenses, the denisort line processes a third flow of goods: lenses sourced from other plants but brought together, packaged and shipped from Aalen.

Standardization reduces packaging types

Stand in front of the denisort conveyor and examine the sorting process more closely, and you will notice there are “large” and “small” shipping envelopes. The former are prepared for direct delivery to opticians. Together with the pair of lenses, they contain a warranty certificate, a customer card, the delivery note and various marketing items where called for. The “small” packages are not destined for direct delivery as a rule, but rather waypoints abroad: here they might undergo further processing such as being trimmed to size for spectacle frames, or highly granular distribution within the supply chain. “As part of modernization we drastically scaled back on the types of packaging, but in a way that would still cover all use cases,” points out Hug.

Automatic transfer to the sorter

Trays simply wind their way up and down: the spiral is a core element of the conveyor.

Shipping envelopes both large and small wend their way from the packaging to the sorting system via an ascending belt and a two-stage conveyor bridge, both also supplied by Ferag. Meanwhile, packaging barcodes are scanned and linked to a sorting destination. Transfer and shoot-in take place more than two and a half metres above floor level, without any manual intervention. This leaves sufficient overhead clearance for workers to pass back and forth between the packaging system and the denisort zone, either for servicing or to operate an additional semi-automatic feeding system that is reserved for special cases. For ergonomic reasons its infeed station is positioned at a height of one metre; items taken on board here include products that originate from other manufacturing locations. A further use is to feed manually packed items into the denisort line. There is a barcode reader in action at this station too, meticulously scanning the shipping envelopes.


Fully automatic transfer: shipping envelopes are conveyed from the automatic packaging machine to the sorting trays without manual intervention.


Gentle sorting for sensitive goods: the shipping envelopes glide undamaged into containers at 192 sorting destinations

Space-saving conveyor design

While the sorting system was assembled rapidly and in parallel with full factory operation, what every visitor immediately notices is how little space it requires: the footprint is just 15.2 by 5.6 metres. Despite this compactness, Ferag managed to accommodate 192 sorting destinations. Each one represents either a hub, a particular waypoint for the logistics service providers under contract to ZEISS Vision Care, a specific country, or a major customer. All the receiving containers corresponding to one such destination are arranged without a gap on three ascending levels. Continuous control over each level demanded a spiral with very tight curve radii. The spiral carries custom-made denisort trays in close proximity, so to prevent pile-ups on bends or collisions with the spiral supports, the Swiss engineers opted for conically tapered side guides. The trays themselves measure 32 by 40 centimetres and always lean to the left on their clockwise travel through the loops. The chain speed is 0.6 metres per second and the energy required is minimal, because the entire system requires only one drive. There is in addition the compressed air used to eject individual packages at their destination chutes.

Ferag system also works as a buffer store

The trays each eject their load upon passing the destination designated at shoot-in. Should the receiving container be full or not present at that moment, the tray makes another round on the conveyor, which can thus also function as a buffer store. On top of that, persistently undeliverable items may be discharged to an overflow chute. The total chain length of the sorting loop is 115 metres.

Proven technology with smart error handling

Hug says that in the interests of smooth running, ZEISS Vision Care favoured the use of proven and almost maintenance-free technology for the automation of shipping processes in Aalen. Nevertheless, the project implementation did raise a challenge or two. One "must" for the installation supplier: to come up with an intelligent solution that would cover the eventuality of incorrect sorting. In this respect the supply chain manager has praise for the Swiss, who exactly fulfilled ZEISS Vision Care’s expectations. In the event of a sorting error, the intelligent, Industry 4.0-compliant denisort system immediately sends a warning to the system operator, who can then take corrective action. There are three light barriers monitoring each chute, so every product discharge is precisely tracked and controlled.

High flexibility and precision

Clever design details: conically tapered side guides and permanently left-leaning trays allow particularly tight curve radii.

Because the plastic spectacle lenses are not yet trimmed for mounting into frames, they must reach the opticians in flawless condition. This is why ZEISS Vision Care explicitly opted for a supplier with technology capable of handling sensitive goods. Moreover, each shipping envelope is unique: depending on the contents and weight, it will behave differently when set in motion. This demands a high degree of flexibility and precision from the conveying and sorting technology. As the global market leader for postpress processing, Ferag has exactly the in-depth know-how about paper handling that the ophthalmic optics manufacturer was looking for. Hug sums it up: “Automated sorting of spectacle lenses packed in paper bags is a non-trivial task. From our point of view, Ferag has it down pat.”

Joachim Hug, Head of Supply Chain Management at ZEISS Vision Care, explains the denisort system: