The reasons why pneumatic grippers dominate electrical grippers are obvious. Pneumatic grippers are more reliable, they offer a wide variety of sizes, much faster actuation times, they have the ability to produce considerably more force than electric grippers within the same footprint, the cost is much lower and they’re simple to control.
Pneumatic grippers are the most common type of end effector found in virtually every industry, from industrial production to cleanroom environments. Pneumatic grippers are compact, lightweight, and offer a high force-to-weight ratio that is ideal for high-speed assembly machines and robots. Compressed shop air is readily available in most plants and pneumatic grippers don’t have the added weight of motors and drive mechanisms, so they can fit into limited space. Gripping force can be easily adjusted using a regulator (FRL) and speed is controlled via metering outflow controls. Pneumatic grippers can also be stalled in any position for unlimited time without over heating like electric units and do not have limitation on duty cycles (rest period) between actuation.
There are two standard types of grippers: parallel and angular—the latter refers to the jaw movement in relation to the gripper body.
Parallel grippers are the most common, due to the ease of tooling, their adaptability to various part sizes without the need to change the tooling finger. Their also suited for synchronous where both jaws move at the same time or non-synchronous use, which allows the jaws to comply and shift to the work piece centerline.
Angular gripper jaws swing in an arc that can be adjusted to reduce the opening swing; usually they are dedicated to picking up one size part. They are useful where vertical space is limited and fail safe part handling is needed. Once the jaws are two degrees past parallel the jaws are toggled locked so even if air pressure is lost the part is held firmly.
Specialized grippers that do not fit the traditional two jaw parallel and angular gripper categories include O-ring grippers, single jaw, three jaw parallel or angular, bladder grippers that inflate against the part O.D or I.D, and magnetic grippers. Adaptive grippers “blind to shape” or “dexterous manipulation” are the newest being developed. This type of robotic gripper wraps around and adapts to different size parts.
Knowing the fundamentals of grippers and design guidelines can help engineers narrow their choices, speed the machine design process, and boost reliability, productivity and throughput.
The following items are tips on increasing pneumatic gripper reliability:
- Minimize tooling finger length and weight. Longer tooling will deflect as well as put excessive moment torque on bearing, increasing friction and reducing gripping force.
- Build in compliance to reduce stress on the actuator and machine.
- Design in smooth deceleration and acceleration via programming or shock absorbers.
- Design tooling fingers with an encompassing grip for a secure and precise placement of the part.
- Never use WD-40, “Water Displacement, 40th formula.” this is a penetrating oil “very low viscosity” and water-displacing spray, it will cause seal and bearing failure.
Next we focus on increasing productivity. Below are tips for achieving this:
- Design tooling jaws to limit space between the tooling jaws and work piece; this improves the cycle time of actuation.
- Select the proper material for tooling jaws to prevent deflection; look up the coefficient of friction between the work piece and tooling to prevent slippage.
- Use a lockout regulator to prevent tampering of air pressure and avoid damaging the part being handled.
- Realign the gripper to the work piece after changing venders or molds since the tolerance may be different, causing jams or crashes.
- Use a standard off-the-shelf gripper; custom units will halt production until a new one is manufactured.