Vacuum System Overview - Vacuum Cups

By John M. Westbeld, Design Manager >SAS< Automation, LLC

Vacuum cups often are the best solution for workpiece handling in robotic or automation applications. Typical applications include removing injection-molded plastics from molds, sheet metal transfer, palletizing of workpieces, nesting fixtures and assembly fixtures.

Typical materials that are handled include plastic, sheet metal, glass, wood, cardboard, paper and electronic components. Choosing the right vacuum cups for the application depends on several characteristics of the workpiece and environment. Vacuum cups come in different forms, sizes and materials to accommodate working conditions.

Some of the forms of vacuum cups can take include, but are not limited to, oval, flat, 1.5 bellows and 2.5 bellows. Oval cups are useful when the workpiece is long and narrow or if the workpiece has raised ribs or edges. Flat vaccum cups are used for flat workpieces with smooth to slightly textured surfaces. In general, they have a wide range of diameters for different-sized workpieces. They also hold up best to shear when a horizontal load is applied and have faster response time than the bellows-style cups. The 1.5 bellows vacuum cups provide a flexible sealing lip for workpieces with irregular, smooth or contoured surfaces. They also work well with slightly flexible surfaces. The bellows provide dampening and help protect sensitive workpieces.

Vacuum cups are made of different materials, including nitrile, silicone, polyurethane and viton, and the environmental and workpiece characteristics will determine what material is best suited for your application. Polyurethane, for example, is the choice for high abrasion and wear resistance, silicone or viton for higher heat applications and nitrile for good overall performance in a wide variety of conditions.

Once you have chosen the style and materials, you can size your vacuum cups and determine the lift capacity using the following basic formulas. If the workpiece is irregularly shaped or is subject to high accelerations, the lift capacity can be adversely affected.

Lift Capacity of Vacuum Cups: theoretical lift per pad (N) = [(PxA)/101] x S x 10.13, where P=vacuum pressure (kPa); A=area of vacuum cup (cm2); and S= safety factory (use 1 for theoretical, 8 for horizontal lift and 4 for vertical lift).

Once the vacuum cups are chosen for a specific application, the task of mounting the cups can be made easier with an adjustable, modular system of clamps, connectors and gripper arms. You can use extruded aluminum framework for flatplate design. Just mount the clamps or connectors to the framework, then mount the vacuum cups directly into the connectors or mount the vacuum cup into a gripper arm, which in turn is mounted into a clamp. The gripper arms can be spring-loaded for part compliance or to be used as spring buggers. The gripper arms also have an option to adjust the angle of the vacuum cup to meet workpiece contours.

John Westbeld is Design Manager for SAS Automation. He can be reached at 937/372-5255.

Reprinted with permission from RoboticsWorld, March 2002. Published by Douglas Publications,