Mar 16, 2020 12:00:00 AM
Making it all run smoothly
Zimmer grippers automate a machine system for hardening the surface of battery terminals
The call from faraway Russia came in around noon – from a small town called Novoaltaisk near the border between Russia and Mongolia. The man on the other end of the line was interested in a gas-tight solution for the surface of battery terminals of his own design. These components had previously been obtained from China for the Russian market and produced by hand in a laborious process, recalls Ralf Löschner, founder of Wenaroll Tools and Systems GmbH. Mr. Löschner recommended the development of a roller burnishing tool, because in most cases costly processes such as grinding, reaming, lapping, honing and polishing can be replaced with roller burnishing technology. The surface achieved by this technology is distinguished by an outstandingly high contact ratio and significantly improved tribological properties. It has now been more than a year and a half since the initial conversation and what started with a mysterious phone call has blossomed into a stable German-Russian partnership marked by smooth collaboration.
Wenaroll is based in Solingen, Germany and has been a leading provider in the area of roller burnishing technology for metallic surfaces for over 35 years. Their core technological competency lies in developing and producing tools and machines. Furthermore, as the "Tools and Systems" part of the company name implies, Wenaroll is also an innovative and forward-thinking partner that implements application-specific solutions. The company`s long-standing international market and client base includes renowned companies from sectors such as commercial vehicles, construction machinery, aerospace technology, mechanical engineering, the automotive industry and many others.
German-Russian development project
The extensive development project, which is the result of German-Russian collaboration, is an automated machine system for hardening the surface of terminals. The system consists of components including a frame with a drive unit and machine base with various roller units, a gripper unit with four grippers, a control cabinet, a feeding and sorting unit and an operating panel. This machine, referred to as an automatic battery terminal burnishing tool, thus makes it possible to use roller burnishing to compress the surface of battery terminals made of lead alloys. Briefly explained, the process in the system works as follows: The battery terminals enter the machine through the feed unit. The gripper unit transports the terminals to the roller units where the actual processing takes place. For roller burnishing, the terminals are clamped and rotated. The roller units move together and the designated surfaces are hardened by the burnisher rolls with a defined amount of force. The roller burnishing process takes place at a maximum force of 255 newtons and a maximum speed of 400 rpm. The result is impressive: The terminals are now gas-tight and have a surface with a roughness depth of Rz < 1 µm. In addition to being gas-tight, it was particularly important to the Russian client for the machine to have an extremely high production speed. Thanks to this speed, the processing time is a maximum of 8 seconds per battery terminal.
Gripper as a central component of the system
The four parallel grippers, mounted on an aluminum frame, are one of the central components of the system. The client had very specific ideas when it came to the gripper design. The preference was for electric grippers with a single cable solution. The idea was for the grippers to feature the smallest possible gripping force to prevent damage to the delicate surface of the lead battery terminal. The gripper design had to ensure that no defects would be left behind on objects being gripped. A further requirement was the option to use long gripper jaws or gripper fingers. For certain gripped objects, the design required the option to insert the fingers deep into the device. Any high torques that occur are optimally absorbed by the long jaw guides in the gripper. This is made possible by the parallel offset arrangement of the gripper jaws, which at the same time allows long guide lengths despite a compact installation space. In addition, the goal was to make grippers with the ability to precisely detect various material thicknesses and sizes.
In their search for a suitable gripper, the development team led by their boss Ralf Löschner decided to go with Zimmer Group as its gripper specialist of choice. According to Löschner, the company from Rheinau in Baden, Germany, had "the best reputation in the region," not to mention excellent quality and availability that Löschner was looking for. Four models of the GEP2000 series (GEP2010IO-05-A) were specially selected for this application: electrically driven small-part grippers that are very easy to control and were primarily designed for handling small parts (such as battery terminals) as well as for assembly tasks. For these functions, the series offers adjustable gripping forces between 40 N and 500 N and jaw strokes between six and 16 millimeters.
Additionally, the grippers are equipped with a mechanical self-locking mechanism that prevents the loss of the battery terminals in the event of power failure. The superlative durability and reliability of the Zimmer grippers is another factor that led Wenaroll to consider them as an option. Their housings are made of hard-anodized aluminum and for the guides the developers rely on a flat guide that has been tried and tested for decades. This allows 10 million cycles to be handled without maintenance. However, the four individual grippers are not all that Zimmer Group delivered to Wenaroll. Zimmer’s in-house Systems Department also developed and fabricated the complete gripper unit including the frame structure, wiring, etc.
Zimmer Group supplied the complete gripper unit including the four grippers, frame structure, wiring, etc.
Thinking into the future
The designers of the system and the grippers were thinking ahead, including features that are useful for future considerations: The Zimmer Group GEP2000 grippers are equipped with an integrated control system and the version that was selected features 2 digital inputs in combination with an analog output for sensing the jaw positions. An integrated analog sensor outputs a voltage of between 0 and 10 volts, depending on the jaw position. This voltage can then be evaluated using an analog card in the higher-level control system, making it possible to determine the position of the gripper jaws.
The roller unit as a unique challenge
A special challenge in building the system was developing the roller unit. This unit had to map many functions simultaneously in order to precisely burnish or compress the surface of parts that have a large tolerance. The completed system, which is currently set up at Wenaroll in Solingen, has already been accepted and will be shipped to Russia very soon. “We are absolutely satisfied with the system. We have achieved our objectives with regard to quality, precision and process speed," says a visibly pleased Ralf Löschner. Future collaborative projects between Wenaroll and Zimmer Group are a definite possibility.
