Lightweight construction for miniload cranes: Evolution or revolution?

RBG CheetahFor many years, the lightweight construction  for storage and retrieval cranes is driven by the requirements of performance and energy efficiency. There is a trade-off between operations and design in an automatic small parts store. A modern storage and retrieval crane has to provide a better performance without deteriorating the cost advantage and the storage capacity. An increase in the performance requires higher driving dynamics of the storage and retrieval crane, which requires a larger volume and a stiffer supporting structure to give a reduced calming time. This however leads to a deterioration of the approach dimensions and a reduced storage capacity. With the same volume of the supporting structure, the stability without changing the approach dimension can be implemented by an antipedalgear. This however leads to higher acquisition costs and reduced availability caused by an additional technical expense. Similarly the stiffness can be increased due to the lightweight construction with new materials, like Carbon Fibre Reinforced Plastic (CFRP). So the energy consumption as well as the stress of susceptible components will be reduced, what leads to a reduction of the operating costs and the availability. The acquisition costs will be significantly higher  using CFRP. The evolution of familiar concepts , which rely on the use of thin-walled, edged or rolled metal structures, are reaching their limits with an increase of dynamic. This shows, for example when there are problems with the fatigue strength and results in cracks in the metal. This is why GEBHARDT decided to go a revolutionary way and rely on composite materials. The result is the GEBHARDT Cheetah.

Up to now the implementation of a consistently lightweight construction with composite materials failed because of the high material- and manufacturing costs. That’s why the implementation of the Cheetah-mast is made of standard profiles of composite materials. The critical buckling of the large volume mast can be prevented with the use of profiles in the thrust range of the mast. The storage and retrieval crane is made of different materials, mainly steel, aluminum and composite materials. This material mix breaks down the previous problems with composite material concepts in storage technology.  Because the adhesive bonding has proved to be a good joining technology for different materials, a suitable surface pretreatment and  adhesive technique was developed. Equally the adhered materials were checked regarding their aging, to guarantee a permanent bond. Adhesive Bonding is especially advantageous in comparison to welding, because there is nearly no thermal deformation which has to be corrected. Also the adhesive is using the complete contact surface of the joining members – e.g. in comparison to spot-welding. Furthermore the adhesive gives a higher damping to the overall structure, so the storage and retrieval crane gets an improved calming time after slowing down. Besides the development of the new product, Gebhardt also had to implement new technologies for the manufacturing process. Up to now the multi material mix and especially the use of composite materials were used rarely in intralogistics. To check the operational stability and the operational safety of the new storage and retrieval crane, the mast was tested on a servo-hydraulic vibration test rig. It proved it’s stability even after a few millions of load change and showed no damage at all. Testing also included tens of thousands of collisions with the buffer and emergency stops. That’s how the test stand trials and aging test reflect the whole life cycle of the Cheetah.

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