Configure the Gripper Footprint
From your chosen form of interface, you'll need to construct the framework or footprint for the grippers, allowing them to reach various securing points of a blank or part. First, determine stability and flexibility of the work piece, what obstructions are present during pick-up, what secondary operations are needed and method of drop-off. Critical is the part weight, cell layout, robot payload capacity and reach. Recommended is a lightweight, modular, aluminum framework easily adjustable to accommodate changes required during trial runs. Construct the framework with various brackets and connectors configured to the outside dimension of your part to allow for securing all sides of the part. Once EOAT is refined and proven, any extra framework can be reduced or eliminated.

Mount Clamps, Brackets and Extensions
With your framework complete, choose adjustable clamps and brackets for mounting to all sides of the partframe profile. This provides maximum flexibility. Then choose tubular arms or extensions that allow for height and angle adjustments to reach every possible area of the part for optimal gripping. Whatever type of gripper you choose, incorporate the proper types of mounting mechanisms-mechanical adapters, brackets or manifolds-for that gripper.

Select the Part-Securing Method-Grippers or Fingers 
This describes the actual mechanical means-pneumatic grippers, pliers or fingers-by which your newly constructed part handler contacts the part. Grippers normally are required for heavy and very flexible parts or when a large pulling force is necessary. Grippers also find use on parts or sheet with holes or porosity, making vacuum-cup usage impractical. For most applications, however, vacuum-cup securing is most cost-effective. Most surfaces, even textured, can be secured by specifying the proper type and size of vacuum cup. At times, vacuum cups are the initial and primary means of part pick-up, then gripper fingers flip behind the part for added support while moving parts overhead or at high speeds. 

Select the Right Vacuum Cup 
Some common vacuum-cup shapes include oval, flat, 11/2-bellows, and 21/2-bellows. Oval cups are useful when the work piece is long and narrow or if the work piece has raised ribs or edges. Flat vacuum cups (Fig. 1) are used for flat work pieces with smooth to slightly textured surfaces. They hold up best to shear when a horizontal load is applied and offer a faster response time than bellows-styled cups. 

The 11/2-bellows vacuum cups (Fig. 2) provide a flexible sealing lip for work pieces with irregular, smooth or contoured surfaces. In addition, they work well with slightly flexible surfaces. The bellows provide dampening and help protect sensitive work pieces. The 21/2-bellows vacuum cup (Fig. 3) is used for maximum part compliance and dampening. Vacuum cups are made from a variety of materials, each with specific properties. (See table for characteristics of each.) For high abrasion and wear resistance, choose polyurethane. For higher heat applications, choose silicone or Viton. Nitrile provides good overall performance in a variety of conditions. Once you've chosen the style and material based on environmental and work piece conditions, you can size your vacuum cups and determine the lift capacity using the following basic formulas. An irregularly shaped work piece or one subjected to high accelerations can adversely affect lift capacity.

Sizing Vacuum Cup Diameter
Diameter of vacuum cup (cm) = D = 2 x v(A ÷ p) where:
A = Vacuum cup area (cm2) = [(m ÷ n) x 10 x S] ÷ P
m = Mass (N)
n = Number of vacuum cups
P = Vacuum pressure (kPa)
S = Safety factor (use 1 for theoretical,
8 for horizontal lift and 4 for vertical lift)

For example:
Workpiece mass = m = 50 lb. = 50 x 4.45 = 222.5 N
P = -80.6 kPa
n = 4
S = 1
A = [(222.5 ÷ 4) x 10 x 1] ÷ 80.6 = 6.9 cm2
D = 2 x v(6.9 ÷ p) = 2.96 cm = 29.6 mm
29.6 mm is the theoretical minimum
vacuum-cup diameter.

Lift Capacity of Vacuum Cups
Theoretical lift per pad (N) = [(P x A) ÷ 101] x S x 10.13 where:
P = Vacuum pressure (kPa)
A = Area of vacuum cup (cm2)
S = Safety factor (use 1 for theoretical,
8 for horizontal lift and 4 for vertical lift)

For example:
Vacuum pressure = P = -80.6 kPa
Area of vacuum cup = A = 176.7 cm2 (for a 150-mm-dia. cup)
Safety Factor = S = 1
Lift = [(P x A) ÷ 101] x S x 10.13 = [(-80.6 x 176.7) ÷ 101] x 1 x 10.13 = 1428 N
1428 N ÷ 4.45 = 321 lb.

These formulas are based upon actual test data. Due to varying accelerations of the workpiece, they should be used for reference only.

Put It All Together
With these basics of modular tooling construction, the next step is sourcing individual components or gripper kits, which simplify EOAT configuration by providing preselected parts and requiring minimal layout or machining. If time and resources are short, select a provider to build the robotic tool built. This option is best for more complex applications. Then, plan for the actual tooling installation, ideally in a period of scheduled machinery shutdown. Assemble all vital parties such as the press supplier, the tool-and-die maker, robot supplier, gripper supplier and maintenance personnel who will be responsible for keeping the line running. MF