Putting the Muscle in Fluid Power

Festo’s Airic’s_arm robot foreshadows the industry’s mechatronic future

by Mike McLeod | March 6, 2008

Capable of human-like dexterity, Festo's Airic’s_arm is composed of more than 30 artificial muscles controled by 72 servo-pneumatic, piezo-actuated proportional valves.

At Hannover Fair last year, and again at Motek, the international trade show for assembly and handling technology held in Stuttgart, Germany, Festo International rolled out the Airic’s_arm, a technology demo created in the labs of Festo’s Switzerland-based Bionic Learning Network. Complete with human-like bones, more than 30 artificial muscles and a full range of motion due to its articulated shoulder joint, the robot weighs only 6.3 kg and can hold up to 3 kg when full extended.

While Airic’s_arm looks like something out of an Isaac Asimov novel or a “show off” piece intended to entice trade show attendees, such mechatronic initiatives are critically important for the automation giant. Not only will Festo maintain the double-digit growth it experienced last year but also confront competition from increasingly capable and inexpensive electronic components. At an international press conference held late last year in Stuttgart, the company announced it would be upping its R&D budget to 7.5 percent of 2006 revenues.

“The research performed at facilities like the Bionic Learning Network illustrates Festo’s continued commitment to innovative drive concepts and advanced technical training,” says Dr. Eberhart Veit, director of product and technology management and spokesman of the management board of Festo AG. “In cooperation with universities, institutes and development enterprises, Festo is promoting ideas which extend beyond its core competence of automation and didactics, and which could become interesting areas of practical application.”

Boiling the Bones

In many ways, that time has already come for Festo, as the core technologies that comprise the pneumatic arm have made their way into the company’s product line and production processes. For example, the robot’s metal human-like bones—including radius, ulna, metacarpals and finger bones, as well as shoulder joint and blade—were all made using a laser sintering process in which layer after layer of powdered steel is melted to create the finished product.

At Festo’s Test & Technology department, the company used the same process to prototype the mechanical stops for its expanded line of pneumatic DGC rodless slide drives and new DGSL pneumatic mini slides, both of which debuted at the Motek show.

According to the company, the mechanical stop prototypes performed 30 million dynamic load cycles in continuous operation or the equivalent of receiving an impact of 400 N every 1.25 seconds for a year and a half. More importantly, the use of advanced prototyping reduced construction time by three to five hours per item thus reduced time-to-market by 25 percent.

“At Festo, we use generative techniques to produce samples in only days that can withstand dynamic load cycles and are impervious to air and gas pressures up to 16 bar. The result is a better product for our customers that gets to market that much faster,” says Klaus Muller-Lohmeier, a Festo technology manager.

The Muscle of Fluid Power

Driving the rapid prototyped bone structure of Airic’s_arm are the robot’s most distinctive feature, 30 artificial or “fluidic” muscles that actuate everything from the overall arm movement down to the curling of the fingers. Festo’s improvement of the 50-year-old McKibben artificial muscle, these unique pneumatic actuators are essentially elastomer tubes reinforced with aramide fibres. When compressed air is forced into the elastic chamber, the tube’s diameter increases and shortens, simulating the kinematics of real muscle. Consequently, these actuators have almost instantaneous reaction times at frequencies up to 100 Hz and can exert 6,000 N of force when filled to a pressure of 6 bar.

Rick Sauer, product manager of core products for Festo Canada, says the company’s fluidic muscles are finding their way into more and more industrial applications.

“They can be used in environments that aren’t typically friendly to other types of actuators, such as rod-type air cylinders where you have an exposed piston rod,” he says. “They are ideal for conveyor tracking, mining operations or any wet and dirty environment because contaminants can’t get dragged inside the mechanism.”

Brains Behind the Brawn

Of course, the muscle of Airic’s_arm would be little more than a novel application of conventional “bang-bang” fluid power technology without sophisticated mechanisms to control them. For this, the robot integrates 72 servo-pneumatic, piezo-actuated proportional valves, eight valve modules, 32 pressure sensors and six length sensors to measure the tensile forces and contraction of the individual muscles. In addition, a mechatronic unit regulates the pressure distribution throughout the system.

According to Sven Zybell, general manager of Festo’s Switzerland-based Advanced Micro Technology AG unit, R&D projects like Airic’s_arm wouldn’t be possible without the miniaturization technologies Festo is increasingly integrating into its products.

“With the microtechnology found in our piezo valves, we can create components that perform better, take up less space and use less energy than standard mechanical systems,” he says.

Festo’s new HGPPI two-fingered gripper features six 5-mm 3/2-way piezo valves, a pressure sensor in each chamber and an integrated controller, allowing the unit an overall gripping force from 5 to 60 N with position control as fine as ±0.1 mm and force to ±2.5 N.

While piezo valves, as a stand-alone product, have yet to enter the market, they do comprise the key component of Festo’s new HGPPI two-fingered gripper. Its six 5-mm 3/2-way piezo valves give independent control of both movement and pressure. Featuring a pressure sensor in each chamber and an integrated controller, the unit allows for an overall gripping force from 5 to 60 N with position control as fine as ±0.1 mm and force to ±2.5 N. According to Jörg Tertünte, Festo marketing concepts for the Americas, its biggest benefit is its flexibility.

“If you have a normal parallel gripper and you want to pick something up, it has to be centred,” he says. “With the HGPPI, both fingers move independently. When a finger moves, its possible to define what that force should be; when you reach that force level, it stops and the next finger moves. This way, it’s possible to grip different work pieces with the same gripper.”

On the Bus

At present, the HGPPI only communicates over Profibus DP, but the company says the other protocols will become available in the future. Mark Hoyland, regional sales manager for Festo Canada, says providing an open platform is central to the company’s automation strategy.

“We aren’t married to any one fieldbus technology,” Hoyland says. “Festo is worldwide player, so we need to be on board with all the main bus networks.”

As an example, the HGPPI integrates with the company’s CPX platform, a modular electrical terminal that communicates with most major protocols including Profinet, Profibus, DeviceNet, Ethernet/IP, ModBus/TCP, InterLink and CANOpen.

Tertünte says the platform’s modular nature also allows centralized and decentralized pneumatic/electrical components to be placed side by side in the same system, yielding higher cycle rates and lower wiring costs. “And, by combining the CPX platform with our CPI subsystem, we can control up to 512 additional inputs and 512 outputs, which reduces the costs for the fieldbus technology by 2/3rds,” he says.

As for Airic’s_arm, the company says it will continue to extend the robot’s functionality with cameras and tactile sensors as well as building other parts of its body including back, hips and neck. Whatever the end result, Festo’s R&D projects will continue to pave the way for the company’s, and the industry’s, future.
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