Although modern PLCs are equipped with microcontrollers, they can not deny their descent from electromagnetic, relay-based devices. Therefore, their use in flexible automated systems is often complicated. Especially in times of high demand fluctuations and individualized products – keyword lot size 1 – reveals their decisive disadvantage: their programming is cumbersome and requires experts. The consequence: The automation of many production steps does not pay off since the adjustments of the control program and the retrofitting of the systems are far too expensive. But PLCs are not the only way to automate tasks. Collaborative Robots ( Cobots) can be an effective and easy to program alternative to the PLC for many applications. For example, the use of collaborative robots in small, specialized work cells is worthwhile, for example for testing and testing applications as well as for feeding machines with workpieces.
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More than just a stupid production assistant
Cobots are designed to work with employees to perform monotonous, dangerous or unergonomic tasks. While traditional industrial robots are tightly installed and sealed off for months or years, Cobots can easily move from one task to another.
At the same time, Cobots has the potential to be more than just a simple production helper: it enables companies to make informed decisions in real time through data collection and analysis. When companies have their production data in the view, they can react flexibly to errors and thus save costs. But the collection and evaluation of this data do not take place at all, especially in small and medium-sized companies – because too complicated and too expensive to set up with constantly changing production batches. When information is collected, it is usually done manually, by sampling or through standalone systems. This, in turn, makes fast analysis and leads to long reaction times. Also, the data collection and analysis requires appropriate expertise.
Example: Cobot collects and processes data
At the Rethink Robotics headquarters in Boston, a good example is an application where a Cobot replaces a PLC. Here, a Sawyer-type Cobot serves three machines in quality assurance and at the same time evaluates their data. The Setup: At first a part arrives at the Cobot and he hands it over to a tester. If the component passes this test, the robot transports it to a second test bench and then to a third test bench. Only if all three tests were successful, the Cobot puts the part in the container for good parts. But why does it make sense to use a cooperative robot in this work cell? The reason is that the testers work with microcomputers. A PLC would only let the testers know when to start or stop. The robots automated by the PLC could only tell if a part was successfully or incorrectly tested. So far that sounds easy. However, an engineer would have to program one or even three controllers (the test equipment) as well as a robot – at least in two different languages. In contrast, the Cobot can process the measurement data of the test equipment and make decisions based on it – similar to a PLC. This is made possible by the operating system Intera 5.2. The robot then processes the data that it evaluates with its sensors, such as the control lamp of the tester. The Cobot controls the work cell and tells the devices when to start or stop. But he also decides – according to the input, he receives from the test systems – whether a part passed the test or not. The advantage: the entire process can be programmed without having to learn a programming language. Instead, the behavior tree principle of the Intera software is sufficient.
Programming: Gaming industry as a role model
Initially, the concept of behavior trees came from the gaming industry because specialized programmers are expensive and rare in the industry. Also, game designers often lack programming skills but need to program complicated behavioral patterns for video game characters. The Behavior Tree principle can not only be applied to Cobots, but in law also to the entire work cell.
Rethink Robotics has developed the collaborative robot Sawyer for flexible use along the entire production line. The easy-to-use user interface and the train-by-demonstration (teach-in mode) enable operators to teach the Cobot new tasks without the need for special programming skills.
The fact is: the demand for individualized applications is increasing. This also increases the number of work cells in which the use of Cobots instead of PLCs is offered. However, the collaborative robots will not replace all classic controllers whose strength is undisputed in the automation of large-volume systems. PLCs better control production lines that only produce a single product in the long run or move heavy parts. There it does not need the flexibility of a Cobot and the investment in an SPS pays off due to the duration and consistency of the use. But if more flexible production lines are needed, the use of Cobots is worthwhile.