By Katrin Pudenz
Modular assembly means using a great number of small, separate workstations to enable highly flexible workflows. To this end, the routes between these stations must be flexible and well thought out. Driverless transport systems not only transport car bodies, but also move the parts required for production.
The driverless transport systems required for modular assembly are developed in Audi's "Technical Center for Production Assistance Systems" department. The principle of driverless transport systems is nothing new in automotive production - these systems have in fact been in use for many decades. The electrically powered transport robots convey components, containers and in some cases even entire car bodies. They follow guidance wires or RFID chips in the factory floor. The Technical Center for Production Assistance Systems has developed and set up two innovative concepts called "Audi Laser Tracking System" and "Audi AGV" (Automated Guided Vehicle). Fabian Rusitschka, CEO of arculus and mastermind behind modular assembly, explains that the new developments can be divided into two fleets. "One fleet transports the car bodies from one station to another, while the other delivers the parts - from screws to sliding roofs."
Paula takes care of transporting the parts
The AGVs in the first fleet of driverless transport systems are characterized by high autonomy. AGV stands for automated guided vehicle and is known internally as "Paula". Paula takes care of transporting the parts required for modular assembly.
The AGVs use navigation software developed by Audi on the basis of automotive software and automotive software development processes. This means that they can supply goods from the warehouse to the assembly line freely and autonomously. They recognize complicated traffic situations and react to them flexibly.
The navigation system allows a AGV to drive autonomously on a defined route, which is designed and simulated on the computer in advance. Alternatively, the AGV can learn a route on a manually controlled drive and store it. On the basis of this map, it moves freely within its radius – according to the principle of machine learning, it always searches for the optimal route.
Three on-board laser scanners
Paula is equipped with three on-board laser scanners - two at the front and one at the rear. Two of the scanners are specifically approved for personal protection, as the developers explain. They scan the hall and recognize solid objects such as shelves or moving objects such as people or forklifts. The third scanner points upwards and checks the space up to the hall ceiling in order to recognize objects hanging from the ceiling.
The sensors also serve to record measuring data - the computer of the AGV then compares that data with its own map data. At the same time, the navigation software compares the data measured by the laser scanners with the wheel revolutions, allowing exact localization.
Contours as characteristics
The driving strategy of the AGV is defensive. It recognizes an employee or an electric vehicle crossing its path and always gives them priority. Its speed is limited to 4.2 kilometers per hour. All braking is gradual and energy efficient. In calculating the braking, the engineers used similar algorithms to those used for controlling the adaptive cruise control (ACC) in cars.
With its laser scanners, the AGV recognizes the workpiece trailer from its contours. It drives up to it to the nearest millimeter, even if it is not standing in its predefined position. Parking over the charging plate takes place with the same precision.
The second fleet is the Audi Laser Tracking System, which can recognize and guide a group of driverless transport vehicles. Using a high resolution laser scanner, a powerful computer locates them by means of their reflectors and gives them maneuvering commands by radio, the developers explain. Each of the four wheels is individually driven by a step motor. This allows precise steering, which is important when driving around obstacles and when docking onto the large transport containers. The transport robots operate at walking pace, just under six kilometers per hour.
At today's level of development, the central computer can control the transport robots in a radius of twelve meters - individually or in trains. To cover a large hall, it would be necessary to have either several laser scanners or a computer with a laser scanner as a mobile unit that drives through the hall, guiding a group of driverless vehicles.
Self-driving robots at BMW
BMW also uses autonomous robots to transport car parts. In the hall of Supply Logistics, a self-driving robot maneuvers itself underneath a roller container with parts. Silently and with flashing lights, it picks up the container and begins to move. As BMW describes it, the logistics hall is complicated and extensive - and nobody can find their way around without a good sense of direction. But this is no problem for the transport robot. Flanked by radio transmitters and equipped with a digital map, it drives independently to the destination of the goods, as the BMW experts explain. When a tugger train crosses its path, a fitted sensor identifies the obstacle and stops the self-driving robot loaded with car parts weighing up to half a ton.
By measuring its distance to three radio transmitters, the robot is able to calculate its exact position and route. With the help of sensors, it identifies critical situations and can respond accordingly, sharing the route with people and other vehicles. For later series operation, the system is to be equipped with a 3D camera system to make navigation even more accurate.
VDMA expert Sascha Schmel says: "Further automation and improved flexibility is the motto of the day in production logistics. Sooner or later, automation will turn into autonomization. But this is a challenge the intralogistics sector will gladly take on. The association supports this trend on several levels, including through dialog platforms with customer sectors and its own assessments of the future."