Cutting Edge Grippers

September 29, 2009
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It's one of the great contradictions in assembly. On the one hand, industrial robots are expected to be fast and powerful. On the other, they need to be incredibly precise and delicate-kind of like expecting Arnold Schwarzenegger’s Terminator character to do needlepoint between gun battles.



The technology that enables robots to do the incredible variety of things that they do is their end effectors. Long and thin grippers, short and wide grippers, vacuum grippers, or combinations of multiple gripping devices mounted at various points on a set of aluminum framing-robotics manufacturers and suppliers have created a dizzying array of technologies to handle everything from engines to delicate glass ampoules for the medical device industry.

What follows is a survey of some of the more creative, flexible and original end effectors available to today’s assemblers.

The demands of the solar panel industry have pushed end effector manufacturers to come up with new and better products, like this specialized solar cell gripper. Photo courtesy Schmalz Inc.

Lightening the Load

Often it is the demands of a particular technology or industry that drive innovation in end effectors, and nowhere has this been truer than in the fast growing solar power industry.

With their bulky frameworks and delicate photovoltaic wafers, solar panels present a number of challenges for manufacturing engineers. In addition, faced with competition from other solar power manufacturers, not to mention established low-cost energy sources like oil and coal, assemblers in this arena have no choice but to automate if they hope to survive.

With this in mind, vacuum and material-handling equipment manufacturer Schmalz Inc. has created the SWG Wafer Gripper for picking up and manipulating solar wafers and cells. Conventional vacuum-cup grippers can contaminate or damage the wafers. However, the SWG employs a high number of small suction openings across its entire gripping surface to minimize shearing forces and ensure no damage is ever done at its contact points.

“The grippers support the whole surface area, minimizing torsion forces and conchoidal fracture risk, so there are no pressure peaks,” says Schmalz senior applications engineer Markus Schmider. Schmider adds that the system’s high-flow, high-throughput vacuum generator provides a strong gripping force without putting undue strain on the product itself.

The SWG overcomes the problem of component contamination by employing a vacuum system in which both the air and any small particles it may contain are completely extracted from the work area. As a result, the gripper is fully compliant with even the most rigorous clean room conditions.

Finally, the system is fast, with a cycle time of one second-a major consideration given the number of wafers or cells that can be used to create even a midsized panel.

End effector manufacturers continue to push the robotics envelope by creating innovative end-of-arm tooling like this noncontact solar wafer gripper. Photo courtesy Schunk Inc.

No-touch Gripping

Another veteran robotics supplier that has taken up the challenge of handling delicate solar panel parts is Schunk Inc. Long known for its finger grippers and work-holding products, the company recently created a “gripper” that employs a combination of ultrasonic and vacuum technologies to grasp the workpiece without actually coming in physical contact with it.

The system employs a principle known as “near-field levitation,” in which an ultrasonic generator is used to hold the workpiece at a slight distance, at the same time it is being pulled toward the gripped with a vacuum. In operation, equilibrium is created between the vacuum and the pressure of the ultrasonic waves making it possible to secure even the thinnest substrate.

The system can safely handle wafers measuring 300 millimeters in diameter and as little as 0.6 millimeter thick. Smaller parts can be as thin as 100 microns.

When manipulating smaller components, the system’s fluid-mechanical effect also generates a centering force, which makes it possible to have fast accelerations or to turn the gripper without the component sliding off. To handle larger parts, assemblers can include a set of lateral stops to prevent the workpiece from slipping when the gripper moves.

Today’s robotic end effectors are also used to speed up such traditional tasks as O-ring installation. Photo courtesy AGI Automation Components

With This Ring

Although O-rings have been around for years, assemblers continue to struggle to find the quickest and best way to install them in their products.

It was with this in mind that AGI Automation Components developed its six-finger AGP-6 O-ring gripper. Originally created as a custom system for a customer that wanted to use a six-axis robot to install O-rings on automotive sensors, AGI has since created a larger eight-finger version as well, called the AGP-8.

Pneumatically operated, the gripper features two independent pistons along with a set of double-action spreading jaws and single-action ejectors. When air pressure is applied to the first piston, the gripper’s six or eight parallel jaws spread the O-ring into a hexagonal or octagonal shape. This opening stroke can be precisely adjusted with a setscrew to prevent overexpansion.

Once the expanded O-ring has been placed over the part, air pressure is applied to a second piston, which causes the ejector jaws to push forward. This, in turn, pushes the O-ring from the spreading jaws onto the part being assembled. According to AGI president Peter Farkas, the process is both faster and more reliable than manual installation.

Today’s end-of-arm tooling is more flexible than ever. This packaging gripper can be easily adjusted to handle multiple product types coming off an assembly line. Photo courtesy SAS Automation LLC  

Packaging on the Line

Robots have long excelled in packaging applications, and many manufacturers now use robots to prepare their products for shipment or sale as soon as they are assembled.

In the past, the end effectors used for this kind of work were often product-specific. Every time a new product came down the line, the robot would need a new end effector.

To solve this problem, SAS Automation LLC has created a fully modular end effector, equipped with 20 vacuum cups that can accommodate a variety of products with minimal adjustment. In addition to picking multiple products from a conveyor and then positioning them for packaging, this end-of-arm tool (EOAT) can be used with either deep or shallow containers.

It can be mounted on any kind of robot and incorporates a set of custom-designed springs for repositioning of the vacuum cup assemblies during product positioning. To reduce costs, the 20 cups are all powered by a single vacuum pump, located next to the robot base.

This gripper can be used to both lift and rotate products, providing enhanced functionality in a compact, easy-to-use package. Photo courtesy Techno-Sommer Automatic

Head Over Heels

It’s the simplest thing in the world: pick something up, flip it over and put it back down again. It’s done all the time in manufacturing. Specific examples include reorienting incorrectly positioned parts as they come off a vibratory feeder bowl or turning over a part or assembly at a visual inspection station.

For years, assemblers have combined grippers with separate swivel units to perform these kinds of tasks. However, the resulting end effector can be bulky and require some creative engineering in terms of routing things like compressed air. It can also get expensive having to purchase multiple pieces of equipment and then integrate them.

To solve this problem, Techno-Sommer Automatic has developed the DGP404 series of grip-and-rotate modules, specifically for picking and rotating parts. Each unit has separate pneumatic connections for its grip and rotate functions, allowing them to operate separately.

According to Techno-Sommer sales manager Costas Charalambous, each gripper costs less than a comparable EOAT comprised of separate gripper and rotate units. The new grippers are also more streamlined. “This, in turn, allows engineers increased flexibility with their application designs that will save both time and space,” Charalambous says.

This gripper includes a proprietary jaw guidance system that automatically compensates for wear. This ensures it maintains the same level of performance throughout its operating life. Photo courtesy PHD Inc.  

Long-term Precision

No matter what the gripper, engineers require precision to ensure their processes function correctly and assemble products that work correctly. Unfortunately, the nature of the world is such that things inevitably wear down over time through hard usage. Precision straight out of the box is one thing. Precision over the long term is another.

With this in mind, PHD Inc. recently created a high-precision gripper for a component assembly application that employs the company’s EGRK electric gripper to ensure precision operation for the life of the system.

Each EGRK gripper includes an extremely rigid set of jaws to provide gripping moment capacity and high repeatability. It also features a proprietary wear compensation jaw guidance system to ensure the system maintains the same level of performance throughout its operating life.

Finally, the grippers are comprised of robust internal components, such as a high-torque electric motor, which is combined with a preprogrammed dedicated controller and hardened steel cam driver. The result, says PHD creative services manager John Proegler, is a gripper that provides plenty of power in a compact package.

These vacuum cup grippers are equipped with a textured contact surface to ensure oily parts can be manipulated quickly and safely without slipping. Photo courtesy PIAB North America

No-slip Grip

Assemblers have long used suction cups to grip sheet metal and sheet metal assemblies. In the automotive industry, vacuum grippers are often used to tend the stamping machines that produce door and hood components. However, conventional suction cups often encounter problems when faced with materials coated with oil or other die lubricants.

In addition to the danger of dropped parts, cups can slip and cause the pressed part to be incorrectly placed, causing defects or requiring that the line be stopped so the part can reset manually. In some cases, assemblers have been forced to run their production lines much slower than they would otherwise, because their vacuum-style end effectors have been unable to hold on when starting and stopping at higher speeds.

To solve this problem, vacuum equipment manufacturer PIAB North America has created the Duraflex Friction Cup line, so that assemblers can reliably manipulate slippery metal components without worrying about slippage.

Each Duraflex cup includes a sharp and finely grooved pattern on its gripping surface-similar to that of a stud-free winter tire on a car-to resist lateral movement of the product. The result is a gripper that allows an automated system to move at maximum speed with a minimum of vacuum cups.

According to Ed McGovern, vice president of business development at PIAB, the new Duraflex line came as a direct result of discussions with a number of the company’s customers in the automotive sector. “One of the things that kept coming up was that customers just needed to be able to grip things more effectively,” he says. McGovern adds that the new vacuum cups are also helping manufacturers process stamped components in the white goods industry.

This lightweight, electric gripper is affordable and quick to implement. Photo courtesy De-Sta-Co

Less Is More

Finally, there is the case in which less is more. Recently, the gripper, automation and workholding company De-Sta-Co developed the E-Gripper line of small, 24-volt DC electric grippers to perform high-speed pick-and-place tasks in the electronics and medical device industries.

According to De-Sta-Co marketing director John Bubnikovich, the E-Gripper line fills the gap between traditional pneumatic grippers and high-end servo-driven systems. Specifically, it provides the ease of use and low cost of a traditional pneumatic system, without having to run air to the tooling.

“We spoke to a lot of medical device companies that had systems that were all electric except for the grippers,” Bubnikovich says, explaining the need for this kind of end tooling. “This gives them another option.”

In contrast to more complicated servo systems, E-Grippers require neither a controller nor a lot of programming to operate. Nonetheless, they are fast, energy-efficient and capable of handling delicate parts, such as those used in catheters and drug delivery assemblies. The grippers are also clean-room compatible and feature a lightweight, compact design for use in a crowded assembly or laboratory setting.

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