Robotic hands have many uses and can find application in multiple industries and scenarios, including manufacturing, surgery, bomb disposal and even nuclear decommissioning. However, developing a robotic hand with human-like fingers is no easy task, and often engineers have to give way and trade strength for dexterity and vice-versa.
Image Credit: Ruotolo, W., Brouwer, D. and Cutkosky, M., (2021) From grasping to manipulation with gecko-inspired adhesives on a multifinger gripper. Science Robotics, [online] 6(61). Available at: https://www.science.org/doi/10.1126/scirobotics.abi9773
Now, a team of engineers at the Department of Mechanical Engineering, Stanford University, California, have developed a robotic hand that is both dexterous and strong detailed in a paper published in the journal Science Robotics.
Inspired by gecko feet, the robot hands are coated with a grippy adhesive material based on the structure of gecko toes, creating a strong hold via microscopic flaps.
In addition to strength and dexterity the adhesive coatings do not feel sticky to the touch nor do they leave behind any residue on the objects that come into contact with. While anthropomorphic hands have attracted much attention in research circles for over 30 years, simple parallel grippers are still the norm in real-world and manufacturing applications as they provide powerful grips in a compact and lightweight package.
Gecko-inspired adhesives are a promising technology to span that gap in performance, but three key principles must be maintained for their efficient usage: high contact area, shear load sharing, and evenly distributed normal stress.
Wilson Ruotolo, Former Graduate Student in the Biomimetics and Dextrous Manipulation Lab at Stanford University
FarmHand
Called FarmHand, the engineers are now showing off their four-fingered robotic hand which has human-inspired dexterity combined with the gripping capabilities of geckos that build on previous models that have utilized this technology.
Previous gecko-inspired gripper designs have generally focused on pick-and-place applications where the gravity load tends to function in a single direction or in low-torque applications such as grasping smooth objects in outer space.
In fact, NASA has embraced the technology testing gecko-inspired adhesives in numerous applications, including having space robots on the space station conducting inspections and making repairs.
Behind this gecko-inspired phenomenon is a concept called van der Waals forces. A slight electrical field is generated because electrons encircling the nuclei of atoms are not spaced evenly, so there are both positive and negative sides to a neutral molecule. The positively charged part of a molecule attracts the negatively charged part of other molecules, which produces the “stickiness.”
However, to activate the van der Waals effect, the gecko-inspired adhesives must contact the surfaces in a very particular way. This is pretty straightforward when ranges of motion are simplistic, and the surface is relatively flat, but much more complex when using multiple gecko adhesives sections or pads on an articulate mechanism like FarmHand.
To overcome such challenges, the engineers fabricated a collapsible rib-like structure that buckles with a small application of force. This buckling effect ensures that equal forces are applied to the adhesive sections/pads of the FarmHand and activates the van der Waals effect.
Large real area of contact and evenly distributed normal stresses on contact patches are achieved by joint configurations and torque distributions that center contact patches on the phalange faces.
Wilson Ruotolo, Former Graduate Student in the Biomimetics and Dextrous Manipulation Lab at Stanford University
Additionally, the FarmHand also demonstrates the ability to perform a hyperextended pinch which is a result of the ‘tendons’, which mimics the human ability to pick an object up with the fingertips with the requisite force and dexterity.
This is a significant advancement as many robotic hands typically only pick objects up using a gripping ‘c-shape’ motion, or find it difficult to balance dexterity and strength.
The team refers to the issue at hand as the “heirloom tomato problem.” Conventional robotic hands in real-world applications are best suited to repetitive tasks such as picking up an object of a similar size in succession. However, in tests, FarmHand demonstrated the ability to pick up a wide variety of objects including basketballs, uncooked eggs, bunches of grapes, plates, among others.
The researchers are now considering commercial applications for the FarmHand and seeking ways to improve certain feedback features such as tracking how the hand is gripping and moving and how this could be improved in general use.
References and Further Reading
Ruotolo, W., Brouwer, D. and Cutkosky, M., (2021) From grasping to manipulation with gecko-inspired adhesives on a multifinger gripper. Science Robotics, [online] 6(61). Available at: https://www.science.org/doi/10.1126/scirobotics.abi9773
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