Extrusion International USA 1-2019

57 Extrusion International 1/2019 wrapping, or lengthening processes. Mathematically, winded material forms an Archimedes spiral (Picture 2). The ma- terial is wound or unwound with a spe- cific tensile force that depends on the material properties, thickness, or diam- eter. Every wound material places differ- ent and sometimes very high demands on the winding drive. So it is very impor- tant that the material not be damaged at any time during the winding process. To make things even more difficult, the weight and diameter of the wound ma- terial becomes continually larger as the diameter increases. Frictional forces of the bearing and themoment of inertia of the woundmass increase as well. On central winders, the drive acts on the center of the wound material. The motor torque is transferred through the drive train, drive shaft, and a core to themateri- al web. Theweb then transfers the torque from the inner layers to the outer layers. The size of the motor is determined by its torque. For central winders, themaximum torque occurs at the largest winding di- ameter, which coincides with the slowest speed. For this reason, the installed type output (corner power) of central winder drive systemsmust be significantly greater than the process output. Although high speeds and high torques do not occur si- multaneously, the drive must be able to produce both; in this context drive engi- neers refer to applications with a constant output curve or applications with a linear reciprocally decreasing load torque curve. Electric motors with a high drive output are used in these situations, but their power cannot be fully exploited. The use of converters permits operation of motors in thefieldweakening rangeandexpands thewinding drive’s speed range. Central winders with defined material tractive forces are dimensioned predomi- nantly for stationary operating condi- tions. Inmost cases, the dynamic reserves of the converter are adequate to brake the drive, even in emergency situations. However, when torque is very high and braking paths are short, it may be neces- sary to use braking torque as the relevant variable for dimensioning. On winders with intermittent operating modes, the dynamic drive torque determines proper dimensions. When winding/unwinding thicker material sheets, bendingmoment must also be considered for deformation. The hand-sling principle – the future of drive engineering? Picture 3 shows themechanical drive train of a patent-applied drive system fromKa- bel.Consult.Ing, which includes a plane- tary gearboxwhose sun gear and annulus gear are each driven by identical rotary- current servo motors. The output sides of thedrivespassthroughthebearingsofthe planetary gears. The mechanical portion of the drive system is characterized by the planetary gearbox’s annulus gear, which is driven by a high-performance toothed belt with Kevlar/carbon fiber drawing el- ements. The toothed belt attaches firmly to the outside of the annulus gear and provides for a zero-clearance draw/slack connection. Using the same principle, the entire system may be coupled modularly to additional drive units of the same type. Picture 4 shows a formulamatrixwith two power splits and three drive motors with variables for rotor adjustment range, field weakening range, torque, speed, and output. The drive speed of the modularly coupled drive system is calculated according to the expanded Willis formula. According to the formula, motors are operated in the field weakening range when require- ments are low. As torque requirements in- creasewithin the“classic rotor adjustment range”, the motors operate preferably as single drives. If even higher output or a higher torque is required, this is achieved by connecting additional motors (using a principle exemplified by the hand-sling) that had been blocked. Picture 5 shows a block diagram of a complete drive system for a constant-speed application. Kabel.Consult.Ing Reststrauch 55 , 41199 Mönchengladbach, Germany www.kabelconsulting.de Each of the drive trains shown on the dia- gram has two drive motors. Depending on the purpose of the application, the individual driveshafts may be subject to various speeds/torques or performance curves. In contrast to a conventional “one-motor” design, this new drive con- cept consists of at least two servo ampli- fiers (double module) and rotary current servo motors plus a planetary gearbox comprised of high-performance toothed belts. It has the advantage of significantly higher overall efficiency and allows in- stallation of smaller-output motors with lower operating costs. The complete drive system has the general benefits as- sociated withmodularity: - For designers: lower development costs, economical production with unit-price degression, several series of identical de- sign, and consistent and straightforward assembly processes. - For users: exchangeable modules make repairs fast and economical. Compat- ibility and use of shared parts reduce the need to hold spare parts to a minimum. Consistentmodularitygreatlyexpands the benefits for both themanufacturer (sales, assembly, spare parts service) and users (purchasing, operation, repairs). The new drive system is SIGNO-funded and is also part of a funding initiative by Germany’s Ministry of Economic Affairs and Energy. Author: Juan Carlos González Villar, development engineer and process optimizer at Kabel.Consult.Ing in Mönchengladbach (Germany) Picture 5: TheMadisonmethod (two-man teams) – the future of drive engineering? (Source: Sercos e.V.) Picture 6: Telescoping L-output with two drives and three “hand-slings” (Source: Kabel.Consult.Ing)