When a robot grasps a cylinder block weighing 50 kilos and approaches a saw or milling cutter, any vibration or sliding motion must be avoided. But deviations from target production data make it difficult for the robots to grasp. August Mössner GmbH & Co. KG in Germany, manufacture specialized machinery for the foundry and aluminum industries along with saws for the widest possible variety of materials as well as equipment for the dismantling of nuclear power stations has found a solution for this problem. As well as tailor-made manipulators for robots manufactured with the aid of the ZEISS T SCAN, the programming of the equipment is optimized with flexible laser scanning.
The two robot arms rigidly stretch their necks into the air, their movements appear frozen. One of them holds a cylinder block in suspension, weighing at least 50 kilos. Only in a few weeks’ time, when the entire plant has been completed, will they start moving and saw off disturbing feeder and sprue systems and mill off casting flashes on engine blocks coming from a foundry. To do this, they heave the parts to saws and milling machines that protrude from the wall and look like giant dentist drills.
Here at August Mössner in Eschach is not where they will be put to work, however, but rather at engine plants of well-known automobile manufacturers. The processing stations are designed and put into trial operation at August Mössner who has a reputation in the automotive industry for delivering automated production lines with dozens of robots on schedule and perfectly functional.
Deviations of Several Millimeters
Christian Kunz’s team plays an important role when it comes to deviations. The 20 employees of his robotics, research and development department are responsible for planning the precise, safe and efficient operation of the processing lines. But the devil is in the details. One of these details are the contour parts with which the robots grip the cylinder block. They are as small as a hockey puck, but must be able to grip the casting precisely and hold it in position during processing, against the forces that occur. For this purpose, the contour parts have recesses that fit exactly over the bulges of the castings. However, this is initially not the case.
Kunz holds a contour part to the rough casting of a gearbox-housing, at the point where the robot is later to pick up the component. But no matter how the mechatronic engineer turns and tilts the fitting, the parts do not fit together. “When car manufacturers send us castings, they often deviate from the target design by a few millimeters,” explains Kunz.
This is no wonder, since most of them are so-called start-up parts for new engine types.
The tolerances are still large when series production starts and are not shown in the CAD models of the castings. Kunz and his team have found a solution in which ZEISS T-SCAN is of central importance. Using a hand-held laser scanner, the engineers measure the surface contour of the casting – for example of an engine block or a transmission housing – and compare the data set generated by this with the target CAD data supplied by the car manufacturer. On the one hand, this serves to document the actual state and on the other hand, the measurement is the basis for adapting the contour parts to the casting and for subsequent programming of the robot. In this way, the engineers can quickly see where there are deviations and can immediately initiate reworking of the contour parts. The contour part is reworked by hand, then scanned and can thus be documented and converted into CAD data.
Significant Time Svings
The decision to purchase the ZEISS T-SCAN was taken in 2017. The free handling within the measuring field was particularly convincing, says Kunz: “With the ZEISS T-SCAN we can also capture large and very heavy parts from all four sides and from above without having to laboriously move the part.”
Such a flexible measuring process would not have been possible with the stationary solution of a competitor. Furthermore, ZEISS T-SCAN is a portable system with a high degree of user-friendliness. This means that, if required, components can be measured directly at the customer’s premises after processing in the robot cell. This saves valuable time, especially when starting up a new system.
“It takes only 10 minutes to set up,” says Kunz, “and together with the customer we can quickly check the result of the processing. Since the modular system does not require a physical connection to a measuring table, data acquisition is easy and effortless even in hard-to-reach areas.
In the meantime, ZEISS T-SCAN has more than paid off for Mössner and above all for the automation specialist customers. “Depending on the plant, we can reach acceptance or commissioning of the plant up to two weeks earlier thanks to the ZEISS T-SCAN,” says Christian Kunz, head of robotics, research and development. For small systems with two robots, this means almost half the time. In larger systems with dozens of robots, commissioning can take up to a year, so two weeks does not seem so important. However, such plants often build several duplicates for parallel production lines. Then the time saved quickly adds up to months. The car manufacturer, for example, can start series production correspondingly faster, and the sooner the end customers get their cars.
Ideal Zero Point
Also the programming, the so-called teaching of automated production facilities has been optimized with a time saving of 80%. Thanks to ZEISS T-SCAN and Christian Haase, among other factors. The 25 year-old is studying industrial management at the University of Aalen and is building a modular robot cell at Mössner as part of his master thesis. Haase also completed his bachelor thesis in mechatronics at August Mössner.
Christian has concentrated on how to optimize the programing of robots. In order to minimize the tolerances between the virtually programmed trajectories and the real trajectories, a selected master part is scanned and provided with a Wiest system, in this case balls. The Wiest system is named after the Wiest AG in Neusäß, which offers systems for the calibration of robots. In Haase’s bachelor’s thesis, this was done on the engine block for which the automated processing station is currently built.
The balls serve as reference points for an ideal coordinate system that is in the middle of the engine block. After measurement with ZEISS T-SCAN and a falsecolor comparison in the intuitive ZEISS software, which among other things, illustrates where oversize or undersize exists, the reverse engineering software and a robot simulation program make the optimum trajectories available a few work steps later – even for other castings with different deviations. The zero point of the coordinate system is always at the same position.
This results in considerable time savings when it comes to programming the robots. “Without ZEISS T-SCAN, this would not be possible, and my bachelor thesis would not have been possible either,” emphasizes Haase.
For more information: www.zeiss.com/metrology