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f+h Intralogistics 3/2014

Drive technology The

Drive technology The book on the subject The Handbook Timing Belts is available in both German and English. The chapters “transmission accuracy”, “stiffness” and “linear positioning drives” provide applicationoriented calculations. For interested readers, examples are included regarding belt drive geometries for applications in various sectors. Handbook Timing Belts. Principles, Calculations, Applications. Raimund Perneder and Ian Osborne. Springer-Verlag, Berlin, Germany. 269 pages, price: 106,95 Euros, ISBN 978-3-642-17754-5 03 The helical cut Eagle PU timing belt for polygon-free running is quieter than belts with a standard pattern Image 01 e shows a storage and retrieval system with a total of three timing belts. This concept does not require a broad mobile beam. Here, the rail guide is allocated only to one track wheel located above and below. The two belts in charge of horizontal motion take over the parallel guide of the entire device due to their combined shape. The most appropriate belt drive geometry depends on the task at hand. A common feature of these drive concepts is that the driveways always range from long to very long. Frequently, belt lengths can measure over 100 meters. The resulting belt sag is counteracted by the fact that the belt is simply placed on a suitable support structure. Whereas finite timing belts are used for the long x-y motions of storage and retrieval systems, endless timing belts are occasionally used for load handling devices. Image 02 shows the linear z motion in double-acting telescope mechanics. The illustrated kinematic configuration for driving the telescopic fork is taken from a concept study, which enables both sides of a shelf in an alley to be equally accessed. Naturally, an actual construction must be as narrow as possible in terms of structure and detail design and, above all, it must feature a version with limited height. Aspects of configuration Today, technical data concerning spring stiffness, tolerance and reversal errors are available for all timing belt brands. A detailed calculation is beyond the scope of this article. The Handbook Timing Belts (see info box) provides calculation algorithms for different operating modes and load conditions in order to verify the accuracy of positioning and repeatability for a given geometry. In storage and retrieval systems featuring the afore-mentioned drive technology, the polyurethane timing belt with a steel cord tension member, available by the meter, is a commonly used drive element. The steel cord tension members have high stiffness values and a constant length, allowing low-maintenance operation. Moreover, it is essential for the timing belt to be used either as a load handling device or just for control purposes. In the second case, lifting and acceleration forces are to be assigned to other suspension elements, e. g. ropes, whereas the timing belt is only used for feedback on the current speed and to establish the position. Consequently, the loads on the belts are low, and any variation in extension due to different payloads can be neglected. Vertically positioned timing belt linear gears build up potential energy when lifting. In addition to the functional design of motors and belts, the applicable regulations and standards must be observed, according to the risk potential and operating site. The risks for lifted loads are to be assessed based on the risk of personal injury. If necessary, the handling area is to be closed and equipped with entry barriers. The safety of rope capacity for passenger lifts is, for example, factor 12. Over the last ten years, standard timing belts have achieved greater power density and load capacity in the tension members, as well as improved running performance. The improvements in performance are also associated with more fail-safe documentation on technical limits. In this way, for example, the current delivery programme of Elatech timing belts provides optimised stretch-resistant tension members, as well as zero backlash combined shapes between belt and pulley teeth. These timing belts are sold by SIT Antriebselemente GmbH, based in Brakel, Germany, and completed by the company’s own toothed pulleys and component manufacturing. In addition to production and readiness for delivery, customer service for advice and drive designing are available for users. The production range of the belt manufacturer Elatech also includes the Eagle PU timing belt (Image 03), in which two teeth marks, with oblique positioning of the teeth, tooth into the corresponding pulley, thus eliminating a polygon effect. This gear cutting method also operates up to 18 dB(A) quieter than comparable belts with a standard pattern. Images: SIT 28 f+h Intralogistics 3/2014

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