Pneumatics: New Key to Human-Robotic Actuation

By Paul J. Heney, Editorial Director

New HMI solution may play important role in industrial environments

When the future doesn’t pan out quite the way that movies or television envisioned it, people often complain about the absence of items available today—from flying cars to wristwatch TVs to lifelike robotics. While Ford has yet to announce the 2014 Floating Taurus and Apple hasn’t quite perfected the wearable iTV, automation technology expert Festo Corp. has been doing some fascinating, futuristic things in robotics. And maybe the future isn’t as far off as we thought.

Valves with a basic poppet design feature few sliding seals, and are pressure unbalanced.

Over the past few years, Festo’s German R&D team has developed some very buzz-worthy inventions. The ultralight SmartBird flight model was inspired by a herring gull and is extremely aerodynamic and agile—it certainly wowed audiences at the 2011 Hanover Fair. Other designs have played off the natural ideas of elephant trunks, jellyfish and geckos.

The latest such product to come out of this futuristic think tank is the ExoHand, a pneumatically operated robotic assistance system that will, the company says, create a more humane working environment in production—and extends people’s scope of action even as they age—by functioning as an assistance system for assembly tasks in production.

Presented for the first time at the Hanover Trade Fair 2012, the ExoHand will potentially expand future human-machine cooperation in industrial environments based on soft robotics. As a force-feedback system, it can extend people’s scope of action in production environments. The system can also be used as a platform for the development of new applications in service robotics, as well as in personal assistance systems.

Pneumatic gripping and touching
The ExoHand is an exoskeleton that is individually adapted to the human hand. The fingers can be actively moved and their strength amplified. The user’s hand movements can be registered and transmitted to the robotic hand in real time. The exoskeleton structure supports the human hand externally and simulates the physiological degrees of freedom of the hand.

The hardware of both ExoHands—the ‘wearable’ one that is called the active orthosis and the robotic hand—is exactly the same. Each uses the same actuators and valves. On the robotic hand, the company simply added a molded silicon hand.

Eight pneumatic actuators move the exoskeleton. Sensors record the forces, angles and distances. Servo pneumatic open- and closed-loop control algorithms allow precise movement of the individual finger joints. The device supports the various possibilities for gripping and touching that a human hand can create. The pneumatic components allow highly flexible and ergonomic control of the individual finger joints. High forces can thus be transmitted precisely in a small space and with a low weight—without the system becoming rigid and restrictive. This flexibility is crucial in human-machine interaction, as it minimizes the risk of injury.

The actuators are Festo type DFK-10 pneumatic cylinders, each with a stroke of approximately 40 mm and a force of 40 Newtons. Compressed air at 6 bar is used, along with piezovalves.

Dipl.-Des. Elias Knubben, Head of Corporate Bionic Projects at Festo, explained that pneumatic technology was chosen because the actuators are lightweight, robust and powerful—and also because they are especially safe for the interaction between man and machine.

Knubben said that the pneumatic drive system comprises some dominant nonlinearities which come from the flow rate characteristic of the valves and the friction of the cylinders.

“Each finger of the artificial robotic hand is moved by using a position control loop. The algorithm compensates for the nonlinearities. The pressures of each cylinder is gauged and indicates the gripping force,” said Knubben. “This gripping force is reflected to the ‘wearable’ hand. So the pressure—not the position—of the cylinders is controlled in order to realize the gripping force. The cylinder strokes of the ‘wearable’ hand form the reference positions for the mentioned artificial robotic hand.”

Boosting power in assembly
Despite a high level of automation, there are still many assembly tasks in industry that can only be performed by humans. Many of these are repetitive tasks that cause fatigue and can be particularly challenging for older members of the workforce. The ExoHand helps operators to remain working longer without incurring permanent physical damage. It can be used as an assistance system, providing enhanced strength for assembly tasks.

When used for remote manipulation of a robotic hand in an industrial environment, the ExoHand allows complex activities in dangerous or hazardous environments to be carried out from a distance. Because all joints and their actuators exist in the form of an exoskeleton outside of the actual hand, the ExoHand can be worn over a human hand or an artificial hand made from silicone. It performs two functions here—acting firstly as an interface between the operator and the control system and secondly as a robotic hand. This allows the control of a complete artificial hand with virtually all of the relevant degrees of freedom.

Thus, with a single system, it is possible to design a scenario combining robotics with orthotics. Forces can be transmitted to the hand as force feedback from another environment, creating an ability to feel shapes. This technology offers enormous potential not only for remote manipulation, but also for navigation in the virtual world.

Synergies in service robotics and rehabilitation
When the ExoHand is used in combination with a robot in medical environments, human-like characteristics are absolutely essential. In stroke therapy, for example, the hand orthosis can be used to help treat the first signs of paralysis in patients. The ExoHand can be used together with a brain-computer interface to create a closed feedback loop. It can help stroke patients who are showing the first signs of paralysis to restore the missing connection between brain and hand. An electroencephalography signal (EEG) from the brain indicates the patient’s desire to open or close the hand. The active hand orthosis then performs the movement. The result is a training effect, which over time helps patients to move their hand again without any technical assistance. Festo is working together with the Centre for Integrative Neuroscience at the University Hospital Tübingen on this project.

Knubben explained that there were a lot of small changes during the development, such as the significant change of switching from a rotational to a linear position measuring system.

“The design process is an ongoing development from the beginning to the end.”

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