Cycloid gears as key
Cycloid gears as key technologies in tooling machines DRIVE TECHNOLOGIES Martin Pointner With fast tool changes and highly dynamic machining cycles, machine tool manufacturers are constantly increasing the performance of their systems. A glance at the industry media shows: On a highly competitive market, it is not unusual for new generations of machines to enter the market with a performance boost of up to 30 percent. Sumitomo Drive Technologies is supporting this development with its Fine Cyclo gearbox series, which enables increased productivity thanks to its physical operating principle, and especially, its zero mechanical backlash and high moment stiffness. Zero backlash and moment stiffness are among the most significant factors in achieving a positive correlation between productivity and production quality in machine tools. Elements such as rotary tables, swing tables and turrets must provide high torsional and moment stiffness so that machine tools can manufacture components both quickly and accurately. Every small deviation that measurably offsets an active force, decreases the speed at which workpieces can be machined within narrowly defined tolerances for dimensional accuracy or surface quality. Thanks to zero backlash, cycloid gearboxes by Sumitomo Drive Technologies have increasingly become a key technology. The high torque density also ensures that single-stage and double-stage cycloid gearboxes can be space-efficiently integrated in the machine layout. The advantages of the cycloid principle — Sumitomo Drive Technologies offers the widest selection of single and double-stage cycloid gearboxes on the market — in comparison to conventional gearboxes will become clear from the following application examples. More productivity thanks to fast tool changes In addition to the precisely controlled movement of the tools and workpieces during machining, high dynamics and precision are extremely important during tool changes. Every increase in speed has a direct impact on the productivity of a machining centre, by reducing unproductive processing time. Disc and chain magazines provide the option to retain tools in a machine. The rotative drive Author: Dipl.-Ing. (FH) Martin Pointner is product manager MCD at Sumitomo (SHI) Cyclo Drive Germany GmbH in Markt Indersdorf/Germany axle has the task of positioning (usually between 40 and 120) tools in front of the removal unit with high precision and speed. On disc magazines, these tools are horizontally arranged on the outer radius of the rotative axis, and on chain magazines - as the name would suggest - along a driven chain. This design has two effects on the gearbox. On the one hand, the required speed in conjunction with the robust design enables acceleration torques of well over 3 000 Nm. On the other hand, the high bending moments must be taken into account in the gearbox design. These result from the 90-degree angle between the disc magazine and drive axle, or from the chain tension, if applicable. The high bending moments permitted by the gearboxes of Sumitomo Drive Technologies make it possible to achieve this challenging task without an additional bearing - and also delivers savings in space as well as further savings through the elimination of components. If bending moments are to be completely avoided in an application, the special design of the Fine Cyclo gearbox enables the output to be realised via the external housing. The load then sits directly between the two main bearings. In the Fine Cyclo series of cycloid gearboxes by Sumitomo Drive Technologies, even the single-stage version can deliver acceleration torques of up to 7610 Nm. The double-stage version can achieve up to 30,000 Nm. These values are the result of the special design of the cycloid drives. Conventional gearboxes have interlocking pinions, whereas cycloid gearboxes transfer the torque via an eccentric shaft, cycloid discs and ring gear housing. In contrast to conventional planetary gearboxes, in which a small number of teeth bear the entire load, on a cycloid disc gearbox the load is distributed across at least 30 percent of the area of the cycloid discs, of which two or three are installed per stage respectively. In practice, this principle makes Cyclo gearboxes extremely shock-resistant and torsionally stiff. Especially in applications in which heavy loads must be positioned quickly, accurately and with high repeat precision, the gearbox is the Achilles heel of the drive axle. Due to their design, toothed gearboxes must cope with peak loads on only a small number of teeth and limited bearing surfaces. As a result, there is a high risk of long teeth, which are prone to bending, becoming deformed, as well as a strong tendency towards high wear on the tooth flanks due to friction. In contrast, cycloid drives offer flat and broad cam motions, which can deal with even heavy loads without taking any damage. Friction generates heat - and this has an adverse effect on production quality, especially in machine tools, due to the expansion of materials which is difficult to control. In Cyclo gearboxes from the Fine Cyclo series by Sumitomo Drive Technologies, the trans- MDA Technologies 3/2016
About Sumitomo Sumitomo (SHI) Cyclo Drive Germany is a subsidiary of Sumitomo Heavy Industries within the Power Transmission Control business segment, as is their sister company Hansen Industrial Transmissions. In 2014, Sumitomo Heavy Industries achieved an annual revenue of more than 6 billion US dollars. Under the umbrella brand of Sumitomo Drive Technologies, Sumitomo Heavy Industries is the market leader for drive technology in Japan and continues to expand its global presence and market share. As a result, Sumitomo (SHI) Cyclo Drive Germany GmbH has sales, service and production facilities in many European countries and subsidiaries in France, Great Britain, Italy, Spain, Scandinavia, and Turkey, as well as India since 2016. mission of torque takes place via a rolling motion, generating only minimal friction in comparison to zero backlash planetary gearboxes - accordingly, thermal loads are also much lower, thanks to reduced heat loss and increased efficiency. A further advantage of Cyclo gearboxes in machine tools is that there is no self-locking effect in these units. As a result, they can be run both forwards and backwards with high precision, after surpassing a defined breakaway torque. This detail enhances 01 Two-stage UA-series for high gear ratios and uniform motion repeat accuracy, especially in reversing applications. „Rotary“ and „tilting“ tables in machine tools are an example of this. These units tend to have comparably high stiffness and torque requirements for purposes of material guidance. Rotary tables and tilting tables position the clamped workpiece to a machining spindle that operates predominantly in a vertical direction. The same applies to this process as to the disc magazines. The stiffer the tilting table holds its position and the more it follows a curve in the form of a coordinated path, the better the end result of the machining process. Every burr and chatter mark has time-consuming consequences — and thereby limits productivity. The Fine Cyclo gearboxes by Sumitomo Drive Technologies pave the way for fast machining processes, because the gearboxes allow high feed forces without evasive movement, thanks to their high stability. Both these advantages have a direct effect on repeat accuracy - a property that is important in machine tools, especially in turrets. The tables carry different tools and always position them in exactly the same place, for the purpose of drilling exactly perpendicular holes, for example. The tool is then replaced with another, which is drilled in turn. Individually tailored gearboxes for specific applications The examples listed above show that machine tool design always comes down to one thing: individually tailored drive solutions, based on a standard modular product concept. For gearbox manufacturers like Sumitomo Drive Technologies, the natural 02 The new Fine Cyclo Drive. Highly compact precision drive with large hollow shaft conclusion is that special solutions and unconventional requests can be realised as economically as possible. As a result, the company, whose European headquarters are in Markt Indersdorf near Munich, is increasingly becoming a development partner for manufacturers of machine tools. In addition to its assembly plant, the Markt Indersdorf site also has research and development facilities that enable customer-specific projects to be precisely tailored customer requirements. „We begin working with customers as early as the initial design phase — with the aim of creating a highly integrated solution that will later become a unique selling point to enhance the customer‘s competitiveness. This helps our customers save both development capacity and production costs during the production of the machine series“, remarks Peter Köhler, Senior Manager of the EMEA Sales Service (MCD) at Sumitomo (SHI) Cyclo Drive Germany GmbH. Against this background, the company will now place even more focus on developing complete drives as plug & play solutions and delivering them in ready-to-install condition, including the servo motor. To ensure a constant ready supply, there are three international plants for precision gearboxes in Germany, Japan and China. The possibilities of cycloid gearbox technology are generally considered to be so broad that even unconventional specifications can be realised, such as large hollow shafts or the use of input and output on the same side of the gearbox. Photographs: teaser Fotolia, 01 to 03 Sumitomo www.sumitomodrive.com 03 Sectional view of C-Series. Large hollow shaft, lubricated for life and completely sealed MDA Technologies 3/2016
