Plastic bottle compactor - PIETRO MINCUZZI

In 2012 for 2 years, with a team of 3 experts, I studied and developed new types of compactors for plastic bottles and metal tins.

New rules

Around 2012 several countries in Europe started introducing new regulations to foster the collection of plastic bottles and containers for recycling. The regulations introduced incentives to reward the consumer for each item or weight unit collected.

a plastic bottle compactor with no reward

Plastic collection equipment was already in place to receive and store temporarily plastic containers such as drinks bottles and other containers fro household fluids.

A new requirement was to reliably measure the quantity inserted by each consumer and handle proper financial transactions for the reward processing.

Challenge

A company in Italy was making equipment for plastic collection. They were selling and leasing equipment to local collection handling companies.

They asked help to cope with the new costly requirements without going out of market with too expensive equipment. That was a very interesting challenge:

measure in a reliable and certifiable way the quantity introduced
keep and release proper accounting statements
maintain the cost of collection per unit at the same level or less despite the new requirements

I was working at the time with a small international engineering team in China on advanced automation projects, but we had spare capacity and resources and we accepted the challenge. So we provided an effective solution to the problem.

The solution

First of all we considered that in order to keep the cost of the equipment low in relation to the amount of plastic collected we had to concentrate the collection per unit of equipment, passing thus from simple storage to the more space effective compacting.

If a unit of equipment can handle a much larger quantity before being full and require intervention from the handler then the cost of equipment and handling per unit of plastic is much lower.

Compacting bottles

We studied different method of compacting. The challenge here is that plastic bottles and containers are made for the large majority in Polipropylene or PP which is cheap but extremely difficult to deform permanently by simply crashing it.

Heating might work, but it is an option that we had to rule out for safety and energy efficiency reasons.

Cutting might work but the technology is expensive and equipment may require frequent maintenance which would increase the operating costs.

Other more exotic option such as freezing and breaking or vacuum packing may have been interesting but already the cost of study and development was beyond the budget.

We then opted for a more traditional method based on mechanical compression. We achieved a high degree of compacting by compressing in two stages the material and tightening it in a bale constrained by strips. The automation for such a solution was simple, durable and very reliable.

Counting bottles

Then we solved the first problem posed by the challenge, to measure the quantity of plastic introduced.

We studied different options, such as scanning the bar-codes on the containers to identify them and account them basing on a database of known products.

The scope and cost of handling such a product database would have limited the applicability and increased the cost. It would also have exposed to frauds without some video surveillance system which in turn would have exposed the operators to plenty of legal constrains and liabilities.

Mechanical unit counting based on individual introduction of each item and then using some sort of light barrier to measure shape and size was an option, but apart of the cost it would have implied unacceptable processing time for the user to dispose a number of bottles.

Luck helped us: the requirement in our case was to simply weight the quantity of scrap plastic introduced.

We implement a simple weighed loading bay in our machine where the user drops the whole quantity of scrap plastic and has it weighed at once when the bay is closed. We used standard load cells and easy to certify, cost effective equipment.

Accounting rewards

The last remaining problem was easy to solve.

We were based in China which is the land of smart payments. All goes by bar-codes, phones and smart cards in China and already in 2012 cash transaction was being substituted by cashless payments.

The technology was reliable and already very affordable and accessible.

Considering a certain conservatism of the European market we opted for well established Contactless smart cards to stay with each user and contain the records. Then we used standard financial methods and algorithms to maintain local and central ledger files.

An extra bonus

We went an extra mile and we also equipped the compactor with a general purpose large display to use as bulletin board or ad panel. This offered the opportunity for the plastic collection handling company to get additional revenue from advertisement and propagate service messages, news, or other contents.

The compactor

We completed three units, two specialised for plastic bottles and other fluid containers and the third one for aluminium tins.

The units work independently each having a loading bay, a display to guide the user during operations or show contents during idle time, a printer for paper receipts and a slot for the user to apply their contact-less smart card.

The loading bay door normally closed but unlatched is lifted open by a user who then drops a load of plastic scrap of the proper type or aluminium tins. Then the user closes the door that gets automatically latched and the process starts. Immediately the display shows the weight of the scrap loaded and transfers a credit bonus to the smart card.

The user can leave then while the machine completes the process in less than one minute and prepares for the next user.

The machines could also be equipped with an interface to connect via WiFi to a local hot spot and communicated to the handling company when they require emptying or maintenance.

The maintenance operations are minimal consisting in final compacting with bale forming and extraction when the machine is full, some simple cleaning in case of fluids spillage from the scrap containers, and software or content update, simply executed connecting a USB pendrive for a few seconds.

GUI and Automation based on Raspberry PI

A bunch of technologies

For the prototype implementation we relied on a simple single board PLC connected via Mitsubishi MELSEC protocol to a Raspberry PI unit, a weighing unit equipped with load-cell connected via RS485 serial line and a simple protocol, a Contactless smart cart read/write unit connected via USB, a receipt printer, also connected via serial RS232 line, and finally a display unit, or a large screen, via HDMI port.

Every time the user loads plastic craps and closes the loading bay door the PLC unit runs the sequence for locking the bay door, measuring and first stage compacting. Periodically the PLC executes the second stage compression.

For the operator of the collection handler the PLC executes the final compression and bale forming, the bale unloading, and some maintenance sequences.

The Raspberry PI coordinates the PLC sequences waiting for user actions and processing them.

It handles measurement, accounting, registration of quantity loaded. It then communicates to the central server via internet channels. It also runs diagnostics and provide instructions and information to the user as well as a service interface for the service personnel.

The entire Grapic User Interface, the main sequences and the communication protocols are controlled via the HMI-SCADA package Proview, of which my team is a competence center in China.

A work in progress

The project completed with the deployment in Caserta, South Italy, of 3 prototype units specialised in collecting respectively plastic bottles for drinks, other larger plastic containers for household fluids, and aluminium tins.

The whole study and materials were then handed over to the client company for further development, while we started new studies for improved versions and new technologies.