This section was edited by Associate Editor Alan S. Brown.
GRIPPER LIKE A HAND
“FLEXIBLE” IS A WORD NOT USUALLY ASSOCIATED WITH ROBOTIC GRIPPERS, AND FOR GOOD REASON. Robotic grippers can open and close their jaws and rotate all they want, but most are engineered to pick up only one specific part fixtured in one predefined orientation. No one would confuse this with a truly flexible gripper—your hand, for example—that can clasp and manipulate objects as diverse as a penny, a ball, or a fork.
Festo AG’s new FinGripper shows one new approach to changing this paradigm. The company put it on display at Germany’s Hanover Fair this past April. Despite being surrounded by swimming and flying robotic penguins, the FinGripper drew a large crowd of engineers.
Based on the flexible structure of a fish’s tail, Festo’s FinGripper is flexible enough to grasp a series of differently shaped light bulbs without damaging the glass.
What they saw were the three plastic “fingers” that made up FinGripper’s hand wrapping around each of three differently shaped light bulbs, and lifting and rotating them 90 degrees. The gripper had a touch so light it could manipulate the fragile bulbs without breaking any glass, and so flexible it could grasp one disparate shape after the other.
The key to FinGripper’s performance is the “Fin Ray” structure of its three “fingers,” which move like the flexible tail of a fish. (This is something Festo learned from studying how penguins and fish swim.)
Each FinGripper finger looks like an elongated isosceles triangle with a series of slats running between the two long sides. The slats are attached to the side with hinges, which act like bearings. When the triangular finger wraps around an object, such as a light bulb, the slats pivot to accommodate the motion while providing the reinforcement needed for a firm grip.
Festo made the grippers directly form CAD drawings using selective laser sintering, which fuses one layer of plastic at a time until the structure is complete. The company powers the three fingers with a pneumatic bellows.
“We haven’t optimized the design yet,” said Markus Fischer, a Festo designer who leads the company’s efforts to translate biological capabilities into industrial applications. “We thought it would break after 10,000 to 100,000 cycles, but so far it has lasted 5 million cycles.”
Like natural systems, Festo’s FinGrippers have evolved. “The grippers either worked as a system or not at all,” Fischer said. “The first ones we printed out were not so good. They needed thicker walls and bearings on the strips going across.”
Festo wants to use the technology for industrial robotics, said Fischer. Potential applications include aquaculture and agriculture, where the FinGripper could sort fragile objects like tomatoes.
A new way to make molds for injection molding promises to slash cycle times and scrap rates for complex parts. Creating conformal rather than straight-drilled cooling channels in molds removes heat faster and more evenly. While performance varies with part size and complexity, some companies have reduced cycle times by 60 percent and scrap by 50 percent, said Augustin Niavas. Niavas is a key account manager for Germany’s EOS GmbH Electro Optical Systems, which makes equipment to build the molds directly from CAD files.
Injection molding is the most widely used plastics processing technology. The process melts thermoplastics and forces them into a metal mold. After the plastics cool, the mold opens to reveal the finished part. To speed cooling, molders run liquid through cooling channels they drill into the mold.
Direct metal laser sintering builds molds with integral cooling channels layer by layer. Shaping the cooling channels to the part speeds cycle times and slashes scrap.
Cooling channels work great when molding parts with regular features. Add curves and irregular geometries, and manufacturers run into problems. Straight drilled channels cannot follow the contours of the part. As a result, they remove heat unevenly, so operators must wait until the material farthest away from the cooling channel cools before they remove it from the mold. No wonder cooling time can account for up to 70 percent of each injection molding cycle. Uneven cooling can also warp parts and increase scrap rates.
This is where EOS comes in. The company’s equipment produces molds from 3-D CAD data by direct metal laser-sintering, fusing metal powders into solids one layer at a time. The company’s equipment has no problem creating cooling channels that curve, arch, and branch to conform to any shape, because channels are built into the mold as it is formed, not drilled afterwards.
EOS application engineer Siegfried Mayer pointed to a German service bureau, LaserBearbeitungsCenter outside Stuttgart, which was having trouble molding long, thin, cylindrical lipstick caps. It was easy to remove heat from the outside of the part with standard cooling, but it was hard to build an effective cooling channel inside the mold’s core. This produced a hot spot on the cap of the tube. Using conformal cooling eliminated the hot spot and reduced cycle time by more than 60 percent.
Mayer also mentioned a filter housing that had a problem with warpage. “Its core was so thin, it was impossible to create a cooling channel,” he explained. “There were different cooling gradients within the mold. They had to keep the whole mold enclosed until the energy flowed out.” Even then, the processor had to scrap 50 percent of its output. Conformal cooling not only reduced cycle times, but also slashed scrap rates to nearly zero.
While direct metal laser sintering has been around for decades, it was not until 2007 that EOS developed a maraging steel that it could use to make molds durable to withstand mass production.
Conformal cooling also solves a problem that bedevils drilled cooling channels, flow blockage as gunk accumulates at right-angle turns. “We don’t have that problem because we have very regular paths,” said Niavas. “We can also build structures like bumps into the pathway to generate turbulence to clean the channel.”
MagneMotion Inc. of Devens, Mass., has introduced a smart, new linear synchronous motor called MagneMover Lite for moving payloads of up to 2 kilograms at speeds to 2 meters per second over virtually unlimited distances. Building on the company’s QuickStick system, the new MagneMover Lite includes a built-in controller that individually identifies and routes each puck, positioning it within 0.05 millimeter at any workstation along the line.
Because it has fewer moving parts to maintain and uses electricity efficiently, MagneMover Lite has a lower cost of ownership than conventional conveyor systems, according to MagneMotion’s vice president of sales and marketing, Peter Mattila.
The MagneMover controller keeps up to nine pucks in motion per meter of track. Pucks can also travel bidirectionally, so if a screw is not inserted at a workspace, the system can back up the individual pallet and repeat the operation instead of routing the pallet around the entire line a second time. Individual puck identification also supports the pharmaceutical industry’s track and trace requirements.
The system is based on a permanent magnet linear synchronous motor. It puts permanent magnets on the pucks, then runs a current through stationary coils (stators) under the track to generate an electromagnetic field. This pulls or pushes against the field created by the permanent magnets (which act like rotors) on the puck, propelling it forwards or backwards. MagneMotion has used the same technology to move larger loads as well as elevators for several years now.
Linear synchronous motors are similar to the propulsion systems used for magnetic levitation trains. Most other industrial magnetic systems are based on linear induction motors, which mount the magnetic coils on the puck and induce magnetic fields within copper or aluminum plates on the track. The coils require lots of current to induce magnetic fields and grow less efficient as tracks grow longer.
According to MagneMotion, linear synchronous motors can run long distances without large dropoffs in efficiency. It claims small systems typically achieve 50 percent efficiencies, while larger systems reach 85 percent or more. “We can build a line 300 meters or longer, compared to about 1 meter for induction systems,” Mattila said.
According to Mattila, the new MagneMover Lite is designed to compete with conventional conveyor systems on a cost-of-ownership basis. The system achieves higher speeds and throughputs, up to 2-4 meters/second compared with about 0.3 meter/second for high-speed conveyors, and there are no moving parts to wear out or replace. “The system is accurate to within a fraction of a millimeter without a pneumatic stop, so you can position parts for assembly without removing them from the puck,” he said.
PULTRUSION GOES 'ROUND IN CIRCLES
UNTIL NOW, PULTRUSION HAS BEEN USED TO MAKE STRAIGHT COMPOSITE PROFILES THAT GO INTO EVERYTHING FROM LADDERS AND SKI POLES TO INDUSTRIAL DECKING AND MILITARY ANTENNAS. The process looks a lot like extrusion, except it works by pulling rather than pushing. A gripper grabs the reinforcing fibers, pulls them through a vat of resin, and then through a die. The die shapes the profile while heating the resin so that it solidifies as it exits.
Pultrusion is cheap (for composites), fast, and produces a quality part—as long as it’s straight. Now, thanks to Thomas Technik+Innovation KG of Bremervörde, Germany, pultrusion can also make curved parts of almost any radius. Potential applications include lightweight spiral springs for automobiles, circular aircraft fuselage segments, arched windows, more expressive furniture, bridge beams, pipes, and storage tanks.
Radius pultrusion produces spiral composites for automotive springs, aircraft parts, arched windows, bridge beams, and other applications.
Composites bring advantages to the table in many applications. Take, for example, automobile suspension springs. Composites weigh significantly less than steel, and so improve gas mileage and handling. They also demonstrate excellent fatigue strength and resist corrosion. They may even have a cost advantage in shorter production runs.
The problem with conventional molds is that by the time the fiber and resin are about two-thirds through them, the materials have become too hard to bend.
The radius pultrusion process takes a different approach. Unlike conventional pultrusion, it is not a continuous pulling process. Nor does it pull the profile through a mold. Instead, the curved mold moves along the curved profile.
It works like this: After pulling fibers through the curved mold, the gripper stops and the mold moves from the gripper backwards along the fibers. As it moves, it dips the fibers in resin and heats the resin-coated fibers so that they harden. When it reaches the end of the segment, the gripper moves forward, grabs the newly hardened pultrusion, and pulls it along the planned curve. The mold then moves back to the gripper and repeats the dip-and-cure step again.
Clearly, radius pultrusion is not as fast as conventional continuous pultrusion. Yet Thomas believes the process is attractive for spirals with radii greater than 30 centimeters. It may also prove an alternative to batch production of smaller curved parts, since it is often faster and can produce hollow profiles with multiple channels without using core materials or silicone tubing.
DIAMOND IS A PIPE'S BEST FRIEND
DIAMONDS ARE NOT JUST BEAUTIFUL. They rank as the hardest and most lubricious of all natural materials. Over the past 25 years, several firms have learned to apply diamond and diamondlike coatings to the exterior of wear parts. Now Sub-One Technology Inc. of Pleasanton, Calif., has developed a low-cost way to apply diamondlike and silicon carbide (another very hard ceramic) to interior surfaces as well.
Diamondlike coatings protect the interior of downhole pipes from corrosion and wear, while lowering in-pipe friction significantly.
Offshore oil and gas companies have already begun to embrace Sub-One’s coatings for pipes, valves, and other downhole components. Known as InnerArmor, the coating has a hardness that stands up well to abrasive wear and erosion from the grit and sand entrained with oil and gas. The coating’s coefficient of friction is so low (down to 0.01), drillers may be able to narrow downhole pipe diameter without reducing flow. Moreover, the coatings are chemically inert, so they resist fouling and retain their lubricity even when exposed to saltwater and sulfates in gas and oil.
This gives engineers a new option for offshore drilling. In the past, they often chose high-alloy pipes, which handled extreme conditions but were costly and required expensive machining.
Or they could treat the surfaces of lesser alloys to handle the harsh offshore environment. Compared with polymer liners, InnerArmor is harder, more durable, and far more heat-resistant. It is easier to apply to a pipe interior than thermal spray coatings, and produces smoother surfaces without grinding and polishing. It uses environmentally friendlier chemicals than chrome plating does, requires less surface preparation, and produces a harder and more wear resistant coating.
Sub-One sees other potential applications from automotive piston rings, cylinders, and diesel exhaust recirculation systems to piping for high-pressure, high-temperature geothermal power systems.
Creating a practical diamondlike carbon coating has taken decades. The first diamondlike carbon films tended to adhere to themselves better than to the surfaces on which they were applied. When they were applied too thickly, a tap of a hammer would be enough to pop them off the surface. Sub-One solved the problem by creating a graded surface that gradually transitions from silicon to diamondlike coating, so there is no one transition point.
According to Dore Rosenblum, vice president of marketing for Sub-One, the company can produce coatings that range from 3 micrometers on an engine cylinder to 30 to 40 μm on the interior of a downhole pipe. The company’s deposition process applies the coating at about 0.5 μm per minute.