Shock absorber
Safety solutions for the seventh axis: structural and crash dampers
The seventh axis is used in manufacturing and production systems to make robots more agile and to increase their reach. As an additional traversing axis, this linear axis quickly brings robots into the workspace or guides them precisely to parallel path-controlled operations. To prevent accidents from destroying the increase in productivity, Expert-Tünkers GmbH has been cooperating with ACE Stoßdämpfer GmbH for years in protecting the end positions.
The requirements for speed and mobility of automation solutions are increasing. As a specialist for automated manufacturing processes and as a family-owned company in its second generation, the solutions of the Tünkers Group originate from its own production facilities and decades of experience. For solutions in the robot environment such as clamping, machining and transport, Tünkers is known worldwide among engineers and designers. The robust, low-maintenance modules are designed for extreme operating conditions in large-scale production in the automotive and supplier industries.
Innovation, reliability and precision in automation technology are also of central importance for the subsidiary Expert-Tünkers. Also operating worldwide, the portfolio focuses on rotary tables and transport technology, with customer-specific solutions increasingly being developed. One product that brings together both the proven and the new is the Seventh Axis from the company based in Lorsch in Hesse. This is an additional traversing axis. The Seventh Axis makes it possible to increase mobility and reach in robotics. For example, the solution not only enables the robots to move quickly to the respective workspace, but also to be guided precisely to parallel path-controlled operations. This means that a robot can perform multiple work steps at different locations, resulting in faster processes, more economical operation and conservation of resources.
Requirement: Current-independent end position safety device
Expert-Tünkers relies on a torsion-resistant modular design for the fast, precise traversing axes, which enables high process accuracy even at a length of 30 meters. The drive is provided by a helical toothed rack with hardened flanks, a robust, adjustable guide system and a servo gearmotor integrated into the carriage of the robot. In addition to ground-level applications, traversing geo-molds are also conceivable, and thanks to the expertise in roll turntables, the seventh axis can also be created as a curve. Regardless of whether with or without a curve, a crash in the end positions must be avoided in any case. Otherwise, there is a risk of costly downtime in addition to repairs to robots and the overall design.
For this reason, the design team of the traversing axis was on the lookout during the development phase for protection that would work independently of electricity. For the Expert-Tünkers team, only a company that met its own high quality standards could be considered as a supplier for the safety elements. At the same time, the solution had to be inexpensive. The designers found the fulfillment of this requirement at ACE Stoßdämpfer GmbH from Langenfeld: "From cooperations in the past, we knew that at ACE, besides the product quality, the service is often the decisive factor. In the course of the project, we were confirmed in this", Nuno Martins, International Engineering Coordinator at Expert-Tünkers, gives an insight. The design revealed that different key data had to be taken into account at the two ends of the travel path. For example, with a maximum drive torque of around 400 Nm, 2,500 kg had to be decelerated at 2 m/s on one occasion and 4,000 kg at 1 m/s on another. At the start of the project, TC134-146-S tube safety dampers were installed in both end positions.
Solution 1: Reversible and irreversible solid state dampers
All TC-S types from ACE combine high power absorption with an attractive price-performance ratio. Added to this are their compact shape with diameters from 64 mm to 176 mm and a variety that continuously covers energy absorption in ranges from 450 Nm to 17,810 Nm. The aforementioned type is designed to absorb kinetic energy from 7,310 Nm to 10,230 Nm. Expert-Tünkers was very satisfied with the work of these safety dampers. The design team was even more satisfied with the high operational safety of the seventh axis during the course of the project. Therefore, the wish arose to design the end position safety device even more economically. In the wide range of solutions offered by ACE, the first choice was a damper designed for use in crane systems. This is characterized by its unique dual concept, in which two reversible solid-state dampers are combined in one component. As a result, high spring rates and the above-mentioned values are achievable. After the design engineers shared with ACE the experience gained in the operation of the Seventh Axis with regard to securing the end positions, Tubus Product Manager Thorsten Kohnen and his team in Langenfeld took another look at the design data. They calculated the Tubus TI30-75-3 safety dampers as another suitable solution for the application with the higher speed of 2 m/s.
For case 2 with a travel speed of 1 m/s, they recommended those of type TI24-33-1. If the values of these components for the emergency stop are compared with the aforementioned TC-S type, it can be seen that they have been tailored even more precisely to the respective requirements with 7,683 Nm/stroke and 2,701 Nm/stroke respectively. The biggest difference, however, is that the Tubus TI types are equipped with bellows and a metal guide sleeve. As a result, they operate without rebound, unlike ACE's TC-S reversible safety dampers, which are made of co-polyester elastomer. With energy absorption of up to 96 percent, these TI components are irreversible and thus intended for single use. A circumstance that was accepted based on the experience that the emergency almost never occurs.
„ACE informed us early on that a new product series was about to be launched that promised an even more interesting price/performance ratio for our case.“
Nuno Martins, International Engineering Coordinator, EXPERT-TÜNKERS
Solution 2: New one-way crash absorbers for emergency stop
After the deliveries of these components, the protagonists remained in contact. Nuno Martins from Expert-Tünkers reports: "ACE informed us early on that a new product series is about to be launched, which promises an even more interesting price-performance ratio for our case." The talk is of ACE crash dampers. Like TI dampers, these machine elements from ACE are irreversible. Made of special aluminum or steel tubing, the machine elements fold into a designated shape during a crash. Thus, they protect structures like a crumple zone with uniform energy dissipation of 98%. Available in ten basic types with outer diameters of 87.5 mm in the aluminum versions or 63 mm and 38 mm in the steel versions, the
suitable components for the end positions of the seventh axis were quickly found. Depending on the type, their maximum stroke is between 45 mm and 160 mm. Low support forces of 13,000 to 70,000 N make a decisive contribution to securing the structures.
Another decisive advantage for users of machine tools, conveyor systems or, as in this case, robotics is the range of possible energy absorption between 670 Nm/stroke and 11,200 Nm/stroke. On the other hand, after an accident, the crash event can be reconstructed from the deformation of the disposable element and, in the best case, avoided in the future. As their replacement is very quick and easy, this application illustrates how specific customer requirements can be realized to the point by expanding the product range of ACE Stoßdämpfer GmbH. "For us, thanks to the cooperation with ACE, an end position safety solution for the seventh axle has been created that really fits in all respects," Expert-Tünkers draws a positive conclusion.
Author: Robert Timmerberg M. A., Specialist journalist, plus2 GmbH, Düsseldorf
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40764 Langenfeld
GERMANY
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