Metalworking: Automation in Batch Size One
Batch size one and robot-assisted automation: This is a challenging combination, especially when, for each batch, plasma cutting tools must be positioned with high precision in a heavy-duty environment. Under these conditions, machines from HGG Profiling Equipment BV in Wieringerwerf, Netherlands, process steel profiles. Up to 10 axes, six provided by a Stäubli robot, enable the highest flexibility, while Stäubli´s uniVAL drive interface synchronizes the robot with the machine’s “heartbeat.”
Steel is a very strong and reliable but difficult-to-shape material in all sorts of industries, from shipbuilding to the process industry and structural steel construction. Welded and bolted connections between steel profiles require precise fitting and careful preparation to allow efficient assembly.
As the connections get more complex and regulations get stricter, it becomes nearly impossible to carry out these operations manually. The Dutch machine manufacturer HGG is on a mission to revolutionize the world of steel processing with the most accurate, versatile, and productive machines in the world.
Watching the result of this mission is impressive: A robot approaches a steel beam clamped in a compact cell. With a plasma cutting end-of-arm tool, the robot cuts diverse holes, in rectangular and round shapes, and also with tilted, bevel-shaped cuts, on all four sides of the beam. This takes just a few seconds – and it would be a typical metalworking process if the next beam were to be processed in the same way. But a beam (or profile or tube) with a completely different shape might be next, and it will be cut differently.
The heartbeat of the machine, synchronized with the robot
The machines developed and produced by HGG can process one-off, individual steel parts with high speed and precision. There are several types of machines, from the very compact RoboRail to the top model of the range, the RPC 1200. Both, and others as well, are designed to process 3D parts like beams, tubes, and profiles with up to 120 mm thickness. Most of them perform plasma cutting, and for about 25 years, Stäubli robots have been used to handle the plasma cutting heads.
Why did HGG opt for Stäubli robots? Robin Appel, Team Leader R&D, explains: “Robotic applications in our machines require a very high level of precision – in each axis and each individual cutting process. When you process series parts, you can optimize. But we have one-off pieces and need a very agile machine. For each part, we move multiple axes in order to apply complex cuts and have to synchronize these movements with the robot. If you don’t, you can run out of tolerances quickly.”
To avoid this, the engineers’ idea was to “generate a pulse from the main system that is like a heartbeat, and synchronize the external controller with the robot controller in this pulse to achieve constantly high precision,“ says Robin Appel. But this kind of synchronization was cumbersome and error-prone. Therefore, HGG needed a better solution.
They found one in the form of Stäubli’s uniVAL drive: a plug-and-play solution for driving Stäubli robots with standard, generic industrial motion controllers, which allows the precise synchronization HGG was aiming for.
As easy as it gets: Connecting external and robot axes
This is why HGG initially chose Stäubli robots, and has continued to use them for many years in different types and generations of machines. Robin Appel: “We link the axes of the robots with the external axes, which are controlled by B&R motion controllers, via Stäubli´s uniVAL drive. We connect the cable, start the uniVAL drive, and can control each joint of the robot. So we control 10 axes – six of the robot, and four external ones – in the same way.“
The physical process starts with the exact measurement of each part or project. Here, the target positions for the cutting head are defined. How does the robot “know“ where to cut? Klaas Slagter, R&D Software Engineer and Robot Expert: “We have our own work preparation software called ProCAM, which can read many formats, and we are able to calculate the next project while one is processed – in less than one minute. So there is no downtime during the calculation process.“
One might think that the cutting process of, say, a structural steel part for construction does not require utmost sub-millimeter precision. But this is wrong for one reason, as Robin Appel explains. “Multidimensional precision is crucial: If you cut under an angle, the distance from the cutting head to the profile is important. If it varies just a little bit, you might produce scrap. So we need a very good point cloud – and very precise robots.“ The Stäubli robots’ rigid joints and built-in-house gearboxes are essential for the results that users of HGG machines need to achieve.
Complicated cutting tasks with two additional axes
While the compact RoboRail, mainly designed for cutting tubes and smaller profiles, uses a TX2-60L with a plasma cutting head, the most advanced machine in the range, the RPC, is equipped with a larger TX2-90. It can process pipes (with an additional gripper), but is mainly used for cutting large beams and square tubes for structural steel construction, and is used worldwide, including in the USA and Australia.
This machine is designed for complex planning and cutting tasks. It often makes cuts with angles, and has an additional axis called the “translator.” This is basically an x/y table turned on its side that can go up and down and shift forward and backward. The Stäubli robot is mounted with its base to the translator, and with this extension or additional axis, it can reach virtually every point of the beam or profile. Because the robot arm and its travel paths are long, additional requirements arise. As Robin Appel explains, “Having a larger work area and having to rotate the robot to cut at all sides, it is much more of a challenge to get it accurate. We need utmost precision in each axis, otherwise the machine would multiply mistakes.“
Utmost precision under tough conditions – and calibration on-site
Apart from the precision and controllability, there is another important property that the robots in the HGG cells must possess. According to Klaas Slagter, “Each cut produces dust and smoke. The fine dust is very abrasive, and it gets everywhere. This is why sealing is very important, considering each axis, each arm, and each joint are moving.“ As a result, the robot has to be a fully encapsulated system – a requirement that Stäubli robots fulfil in very different industries, e.g., food and semiconductor manufacturing.
If any doubts remain about HGG’s expertise in selecting, operating, and programming robots, one fact can be added. Robin Appel: “We do not buy calibrated robots from Stäubli; we do this ourselves. We can even do that in the field because we have our own software to detect the parameters on-site. And with uniVAL drive, we can include the other axes in the calibration, too. We add all parameters in one system.”
This is quite unusual and serves another purpose, which is advantageous for the user: “If something hits the robot or falls onto the robot – remember, we are in the steel industry – we do not need to send it to Stäubli to see if it has to be readjusted. We just use the software to recalibrate it to the parameters within the tolerances.“
The user perspective: Shorter arms, fewer errors
From the perspective of HGG and, ultimately, the users of HGG machines, the combination of Stäubli robots with external axes offers clear advantages. Robin Appel: “In our opinion, longer robot arms tend to introduce less accuracy or more errors. We use the flexibility of the robots, offering the possibilities of tilted cuts, etc., and gain a long reach by means of the external axes. In the end, we get a very accurate and flexible system.“
With this goal in mind, Stäubli and HGG have gone far in close cooperation: “We had a lot of joint development with Stäubli, in close contact with the engineers, and we also make use of Stäubli’s standby services worldwide.“ And currently, further developments are ongoing.
About Stäubli
Stäubli is a global industrial and mechatronic solution provider with four dedicated Divisions: Electrical Connectors, Fluid Connectors, Robotics and Textile, serving customers who aim to increase their productivity in many industrial sectors. Stäubli currently operates in 28 countries, with agents in 50 countries on four continents. Its global workforce of 6,000 shares a commitment to partnering with customers in nearly every industry to provide comprehensive solutions with long-term support. Originally founded in 1892 as a small workshop in Horgen/Zurich, Switzerland, today Stäubli is an international Group headquartered in Pfäffikon, Switzerland.
About Stäubli Robotics
Stäubli Robotics’ unique product portfolio contains 4 and 6 axis industrial robots, cobots, mobile robotics and Automated Guided Vehicles. The powerful, high precision solutions allow clients in many demanding industries to tackle the challenges of Industry 4.0 under specific manufacturing conditions.
