Vacuum handling is used extensively for automated parts handling in manufacturing and production systems, particularly in the automotive sector and for packaging tasks. Experience shows that around 20 percent of industrially generated compressed air - which is proven to be responsible for at least ten percent of total industrial electrical energy consumption in the European Union - is used to generate vacuum for robot-assisted handling tasks in production. For large-scale industrial handling applications, compressed air-based vacuum generation is typically realized by ejectors due to their fast and wear-free operation and direct integration into gripping systems. In view of the typical efficiency of air compression and pneumatic vacuum generation, only a fraction of the electrical energy originally invested can ultimately be used for the vacuum-based handling process, meaning that even a small amount of energy saved on the process side can lead to a significant reduction in the amount of electrical energy required. The aim of the IWF in the BMWi-funded BiVaS research project is to achieve a significant increase in the energy efficiency of vacuum handling processes by means of intelligent operating strategies.

The ability of industrial suction pads to adapt to complex surfaces and to provide both the sealing required to generate the suction force and the force transmission due to external loads has hardly been investigated to date. The lack of detailed knowledge about the mechanical processes involved in the evacuation of suction pads and external loads is usually taken into account with safety factors that are used in system and process design. However, the use of safety factors greatly oversizes both the vacuum generation system and the gripper system.

Depending on the suction pad model, an axial load results in radial constriction and thus a loss of the effective suction surface. © TU Braunschweig, IWF

Comparability through automated test procedure
In order to eliminate the need for oversizing, an automated test procedure was developed at the IWF that makes the performance of any suction pads visible using defined test objects and load cases. The test objects differ not only in their geometry - convex and concave primitive geometries such as cylinders, pyramids or rounded edges were parameterized and manufactured in different forms. The material and surface roughness are also varied in order to maximize the information content of the test trials. In this "gripper course", a fully automated robot-supported process, the test cycles are triggered centrally by a programmable logic controller (PLC). A 6D force-torque load cell records the relevant loads on the suction cup and, in addition to these measured values, also stores the applied pressure difference as well as the compressed air and vacuum volume flow. Thanks to full automation, a large number of different suction cups and load cases can be tested with the necessary statistical validation in a short time and with little manual effort. Long-term tests are also planned for future investigations in order to determine whether newly manufactured suction pads are subject to initial conditioning and from which number of cycles reproducible behavior can no longer be determined.

Using the results for process planning
With knowledge of the capabilities and limitations of the characterized suction pads, new design methods can be developed for gripping system and process planning. This begins with the positioning of the individual suction pads on the workpiece to be handled. Whereas previously the requirements were adequate mass distribution and gripping surfaces that were as flat as possible, it is now possible to prove, based on reliable test results, that a curved surface may offer a more advantageous force transmission for the specific application than a flat surface. Taking this idea even further, these findings can also be transferred to component design in the sense of Design for Handling (DfH) and specific elements can be incorporated into the component to enable more efficient handling. The trajectory planning for the robot movement can also be expanded with new boundary conditions using the findings from the gripper course. For example, the process planner can significantly reduce conservative safety factors by optimizing the trajectory according to the maximum permissible loads for the application-specific combinations of suction gripper and component surface geometry.

F.Gabriel/as

Scientific Society for Assembly, Handling and Industrial Robotics (MHI e.V.) © MHI e.V.

Briefly explained: The MHI e.V.
The Wissenschaftliche Gesellschaft für Montage, Handhabung und Industrierobotik e.V. (MHI e.V.) is a network of renowned university professors - institute directors and chair holders - from German-speaking countries. The members conduct both fundamental and application-oriented research on a wide range of current topics in the fields of assembly, handling and industrial robotics. Further information on the society, its members and activities: www.wgmhi.de.

Institute for Machine Tools and Production Engineering (IWF) at the Technical University of Braunschweig. © IMF

Briefly explained: The IWF
The Institute for Machine Tools and Production Engineering (IWF) at the Technische Universität Braunschweig is jointly headed by Prof. Dr.-Ing. Klaus Dröder and Prof. Dr.-Ing. Klaus Dröder focuses on technological and automation-related issues along current and future manufacturing process chains. The focus is on the implementation of future manufacturing strategies that enable the flexible production of functionalized products in terms of quantities and variants with maximum efficiency. The research areas range from assembly and production automation to the machining and processing of metallic materials, wood and composite materials and new production technologies for the integrated production of material-hybrid functional structures. Novel tool concepts and technologies are also considered.