Toying with an Idea

Matthew Holm
September 01, 1995

If you visit Kathryn Lilly in Penn State's Powder Injection Molding Lab, she won't tell you that her student, Ed Pinger, is playing with toys. "We're designing specialized robot end effectors," she says, but it's easy to misunderstand.

An end effector is nothing more than a tool in this case, one fitted onto the end of a robotic arm. Pinger, inspired by a toy he found last year, has built one to retrieve parts from an injection molding machine.

Powder injection molding (PIM) begins with powdered metal and powdered plastic. The two are mixed, and then forced into a mold, much like packing sand into a bucket for building sand castles. The powders are heated, and the plastic binds the metal together to form a solid, die-cast object.

Up until 10 years ago, a human hand had to retrieve the molded part from the die an inefficient step in the manufacturing process. So, engineers tried to incorporate robots into the process, originally with a simple grasping claw to pull parts from the machine.

"Unfortunately, the pieces are very brittle," says Lilly, snapping a fresh part as easily as she would a chocolate bar. They don't become strong until the plastic binder is leached out with solvents and then cooked in a furnace a process called sintering. Sintering leaves behind only the metal, which constricts to form a perfect, reduced-scale replica of the original mold, like a sort of industrial Shrinky-Dink.

But first, the part has to be moved from the die to the furnace. Star Automation a member of the consortium funding the Penn State PIM lab supplied a robotic arm, and the PIM lab's engineers began to design new end effectors. Their goal was a tool that could be as delicate and adaptable as a human hand: able to maneuver in the tight space around the die, retrieve small and irregularly shaped pieces, and avoid breaking the "green" (nonsintered) parts. Grasping claws couldn't always get small or rounded objects, and pneumatically-powered suction cups lacked fine control. "Pneumatics are pretty much either on or off," says Lilly. "It's what we call a bang-bang control situation."

Lilly is one of several faculty associates that work with the PIM lab, helping in areas, such as robotics, that lie outside of injection molding. Lilly had been working on the retrieval problem herself before Pinger began his graduate work in Spring 1995. Since then, Pinger, Lilly, and engineers in the PIM lab have tackled the problem as a team, incorporating Lilly's and Pinger's ideas into the design that was born last December in a toy store.

Pinger's inspiration was 3-D pin art. The toy has a bed of nails (or pins) that rest in a network of holes drilled through the base. They slide freely along their length, stopped in the downward direction by the head of the pin and in the upward direction by a clear plastic plate resting an inch or so above the base, atop four corner supports. When the pins are pushed away from the base by an object such as a hand, they show, point by point, the shape of that object.

Pinger wondered what would happen if he attached an electromagnet to such a toy, or rather, tool. Since most of the PIM products are metallic (and ferrous), a magnetic retrieval system would work. So, he built his own pin art device, using steel pins, a plastic base and top plate, and four solenoids to support the top plate. By applying current to the solenoids, he surrounded the pins with a magnetic field and effectively magnetized them.

Pinger's tool is a "universal" end effector, because it conforms to many different geometries. The pin art can make contact with the entire exposed surface of a molded part and pull it free of the die with its magnetic grasp. "It can't crush or damage parts like other tools," Pinger says, "and for a more delicate touch, we could easily develop a denser array of smaller pins."

In fact, the simplicity of this tool is its greatest advantage. It's cheap and easy to produce (Pinger spent the most time drilling the pinholes, but even that only took a few hours by hand), and even easier to put to use. Pinger and Lilly avoided trying to replicate a human hand exactly, as MIT and Stanford have done, because the controls are incredibly complex. In contrast, the pin art only needs to be moved into contact with an object and turned on a child could do it. The tool is compact, lightweight, easily maneuvered, and has low power requirements. "It's elegant," says Pinger. "We've found that elegant designs are often the most efficient."

His next step is, naturally, more simplification. The four solenoids on the corners are not very efficient field- generators, so he plans to do away with them entirely. "I just had the solenoids on hand," he says. Instead, he will use the pins themselves as a core, wrapping the magnet wire around the base to create a much stronger magnetic field.

After that, he and Lilly plan to investigate manufacturing methods so the tool can be mass-produced for industry. "We're hoping to patent the design," says Lilly. "And, who knows?" she laughs. "Maybe Ed will start his own company." She doesn't say if she means a toy company.

Kathryn Lilly, Ph.D., is assistant professor of mechanical engineering in the College of Engineering, 232 Reber Building, University Park, PA 16802; 814-863-7273. Edmund Pinger is a graduate student in mechanical engineering, seeking a master's degree in controls/robotics. This project is funded in part by the Consortium on Advanced Processing via Powder Injection Molding, directed by Dr. Karl F. Hens of the Particulate Materials Center, 118 Research Building West, University Park, PA 16802-6809; 814-863-8207. Additional funding will come from the Leonhard Center for the Enhancement of Engineering Education, and from Penn State's Department of Mechanical Engineering.

Last Updated September 01, 1995