Grippers are available to suit just about any application, such as this parallel design used to handle DVDs.

Identifying the best gripper for the application can be a daunting task given the thousands of different combinations, part numbers, and variation in gripper names. Yet there are only three basic types of grippers. Knowing the fundamentals of each can help engineers narrow their choices and speed the design process.

Paging through a gripper supplier's parts catalog or searching for parts on the Internet can lead a design engineer to an overwhelming selection of components. To find the right gripper for the application as quickly and accurately as possible, this article provides some helpful tips.

Start with the basics

Adjustable angle gripper.

The majority of grippers are variations of three fundamental designs: Parallel, three-finger, and angled grippers. Parallel grippers are just what their name implies — two slides either closing parallel to the workpiece to grip its outside edges, or opening out to put pressure on inside walls. Parallel grippers are by far the most commonly applied design.

Three-finger grippers are used to center the workpiece between the fingers, which are offset by 120°. The three fingers slide the workpiece to the gripper's center, holding the object snugly.

Another option is angled grippers, which approach the sides of the workpiece from various angles, for example, 30°, 40°, or 80° — visualize mechanical fingers coming out at an angle to hold a basketball. Many standard angled grippers can be adjusted to various angles according to the workpiece. Angled grippers are suitable for holding larger workpieces and those with odd shapes. They're also used where space is too tight for a parallel gripper to open wide enough to hold the workpiece. A variation of the angled gripper is the radial gripper: The fingers open a full 180° — useful where vertical space is limited. Fully open radial fingers can rest just above or below the workpiece and close when it is in position.

This flexible gripper from Festo is based on the mechanics of a fish fin.

Parallel, three-finger, and angled grippers come in a host of sizes for varying degrees of gripping force, which can range from 20 N to more than 6,300 N for high-force models. Closing times can vary from 0.1 to less than 0.001 sec for standard parts with repetition accuracy an average of ± 0.01 to ± 0.05 mm. What's more, suppliers often work with design engineers on custom solutions not accommodated by standard parts.

Specialty grippers

Beyond the traditional parallel, three-finger, and angular types, other styles of grippers exist. For example, bellows grippers are used for internal gripping on the inside walls of fragile workpieces, such as bottles or jugs. The flexible bellows expand, pressing against the workpiece.

A new generation of adaptive grippers is also being developed, such as one gripper based on the mechanics of a fish fin. This robotic gripper's fingers effectively wrap around and adapt to different shapes with flexibility up to 360°. The end effector has an exceptional range of motion and may not need to be changed when different products come down the line. That said, these specialized grippers have fairly limited applications compared to the traditional gripper designs.

Pneumatic versus electric designs

All three of the basic gripper styles are available in either pneumatic or electric versions. Pneumatic grippers are generally less expensive upfront, simpler, lighter, and offer higher gripping forces than electric versions, but electric grippers are somewhat less expensive to operate than their pneumatic counterparts. Even so, today's pneumatic systems offer diagnostic features that help maintenance personnel and machine operators identify air pressure loss, which contributes to higher energy costs in pneumatic systems.