Contribution with pictures

Switzerland is at least as clean as it is beautiful. Behind it there is a lot of organization even more manual effort. Together with SBB, we were able to carry out a pilot project for digital waste management at train stations. Waste garbage cans are equipped with battery-powered sensors that record the fill level of the bins in real time. This enables a faster response to overflowing waste garbage cans with fewer control rounds.

Motivation for efficient waste management

SBB Facility Management employs 1200 people to ensure cleanliness on public transport. In addition to the trains, they clean 800 stations and empty over 6000 waste garbage cans. On a single platform at Zurich main station, there are 15 or more recycling stations. That alone amounts to 45 trash bags that are checked and emptied every few hours - a huge job. It depends very much on where a waste garbage can is located - depending on the number of people, the waste bags fill up at different rates. In an innovation project, we worked with SBB to find ways to optimize facility management processes. This led to the idea of equipping the waste garbage cans with sensors that measure the fill level of the garbage cans. We expect the following from this:

1. faster reaction to overfilled bins
2. fewer control rounds
3. optimization of routes and schedules for emptying waste garbage cans

Currently, bins are checked at regular, fixed intervals and emptied when necessary. If you know when a waste bin is full, you don't have to check it as often. In addition, the data collected can be used to optimize emptying intervals.

Realization of digital waste management

Our ultrasonic-based fill level sensor ax-dist was developed precisely for waste management. Thanks to Swisscom's energy-efficient LoRaWAN network, the sensor can monitor the fill level of containers for 2-4 years (depending on transmission interval and reception) with two normal AA batteries. However, the sensor is optimized for large waste bins and recycling containers. SBB waste garbage cans, whether square recycling stations or the classic round waste garbage cans, are quite small. The waste bag is often only 30-40cm in diameter. Ultrasound-based distance sensors have, due to their principle, too large a measuring angle to be able to measure in such narrow spaces.

Optical distance measurement

In cooperation with SBB we have developed a new optical sensor based on the ax-dist. Like the ax-dist, the new ax-opto is battery-powered and sends its data via LoRaWAN. Instead of using ultrasound to measure distance, we rely on an optical measurement method. Here, the distance is determined with the help of infrared light. Similar to a photo camera, we can evaluate different pixels (16×16) to influence the measurement range and angle. In this way, we can create a rough, three-dimensional image of a surface. In contrast to ultrasound-based measuring methods, even very small buckets can be measured.

For the first two objectives, the measurement method provides good data. However, it turns out that the waste garbage cans at train stations are often not full at all, but just clogged. For example, when a newspaper, an empty cardboard bag or a pizza box gets stuck in the opening. Often these items fall into the bag later or you are stuffed into the bag by SBB employees. But because the sack is not full, it is not taught. From the point of view of the distance sensor, however, it is not possible to distinguish whether the sack has been emptied or stuffed. This is problematic because in order to optimize the emptying process, it must be known how often the waste garbage can has been emptied in the past.

Detection of emptying

For this reason we have included an accelerometer. When the waste garbage cans are emptied, they are pulled out like a drawer to change the bag. With the acceleration sensor, we can detect this movement to change the waste bag and distinguish it from other vibrations. In this way, in addition to measuring the fill level, we also achieve detection of the empties. Now it can be reliably recorded how often a waste garbage can is emptied and an estimate can be made of how often inspection rounds are carried out unnecessarily. This data forms the basis for optimizing the cleaning processes.

Software

In a pilot project at the train station in Altstetten, we are testing the system and collecting data. SBB statisticians evaluate these with the aim of developing statistical models about the collection of garbage. We rely on our own ax-track cloud to visualize the data. The IoT platform displays the plans of the stations. On it, you can see the position and fill level of each bucket, and you can also access the history of the fill level. This way, the information is easily and quickly accessible everywhere. The fill levels are color-coded, showing at a glance where intervention is needed and where it is not.

Result of the pilot project

The sensors have now been in operation for several months and are showing good data. The project has shown how important it is for customers and developers to work closely together in IoT projects. This is the only way to find the right solution for an idea and implement it profitably. The pilot project shows that the technology is ready for the implementation of digital waste management. The next step is to integrate this technology into facility management work processes. The goal is to provide employees with a tool that facilitates their work without adding unnecessary complexity. Digital level sensors have great potential and many areas of application. Our ax-opto sensors as well as the ax-dist can be purchased from us - we are also happy to provide you with the matching IoT platform with ax-track.