Machine Design

Air spring key to robot handler

Custom actuators, pneumatic clamps, and seal software are among the topics covered in the pneumatics reference guide.

A robotic arm developed by Luzenac America relies on air springs to grip and handle bags of talc.

Designing a robotic arm to handle 50-lb packages of talc powder was an engineer's nightmare. The system had to be flexible, compact, lightweight, and able to withstand harsh operating conditions. Luzenac America, a worldwide manufacturer of talc for industrial and cosmetic use, turned to 15-in.-diameter air springs from Firestone Industrial, Carmel, Ind., to resolve key system design issues.

According to Peter Rugheimer, the project design engineer, the air spring is a central component of the robotic fork hand because the ratio of collapsed height to extended length was extremely important. The application requires a 13-in. stroke, yet the air spring must collapse to a minimal height.

A metal-walled hydraulic cylinder simply could not handle the system requirements, says Rugheimer. "Another problem with a hydraulic cylinder is the seals. We run in a very harsh environment. Every time the cylinder retracts, it draws dirt into the seal," he says. An air spring, on the other hand, has no dynamic seals and eliminates this potential failure mode.

It operates at variable pressures to 20 psi, and linkages on the sides guide the air spring so the forks remain parallel to the gripper face. Even at low pressures, the unit provides adequate gripping force. This is especially helpful when loading bags in which loose materials have settled.

Plant air inflates the air spring, with an output from the robot actuating a solenoid valve. A vacuum generator evacuates the air to retract the spring. A triple-redundant system ensures air pressure does not exceed 20 psi. This consists of a pressure regulator, backed by spring-loaded pop-off valves that trigger at 20 psi, and a failsafe rupture disk.

The robot arm has an allowable weight capacity of 160 lb, and the complete system needs only a 10 10-ft footprint. Because the computer-controlled system can pick-and-place pallets, place slip sheets between pallets and bags, move the bags, and squeeze them for uniform packing, the system is suited for a variety of applications. In addition to talc, the designers envision use with cement and lime, and agricultural products such as sugar, flour, and cornmeal.

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