Zhi DongXi (public number: zhidxcom)
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On December 16, a new achievement by Stanford University engineers was released in Science Robotics, a sub-journal of science, the top international academic journal. Inspired by the gecko's toe grip, the researchers developed a robotic hand "farmHand" with both dexterity and steady grip, which can smoothly grasp objects such as eggs, grapes, and basketballs.
Unlike many of our common manipulators, the multi-knuckles of this manipulator can be expanded and closed in a wider range like a human hand, as shown in the figure below, and can grasp eggs, basketballs and even objects larger than themselves in a similar way to "picking".
▲ Grab the egg
Some robots can deftly grasp eggs, and some can grasp basketballs smoothly, but unlike human hands, few robots have both skills.
Wilson Ruotolo, 21, a former graduate student at Stanford's Biomimetics and Dexterous Operations Laboratory, said: "You'll see robotic hands do strong grips and precise grips and then hint that they can do anything. What we wanted to solve was how to create a robot that was both dexterous and powerful. ”
Rotorlo and Dane Brouwer, graduate students at Stanford's Biomimicry and Dexterous Operations Laboratory, published a paper on robotics on manipulators on Dec. 15 in the journal Science Robotics.
link:
https://www.science.org/doi/10.1126/scirobotics.abi9773
First, the original intention is to help farmers, picking fruits and holding basketballs
The researchers combined an adhesive based on the gecko's toe grip principle with a custom manipulator to create a robotic hand that can grasp with subtle force and achieve a wide range of unfolding and closing similar to a human hand.
The researchers designed it as a robotic agricultural aid, using a robotic hand to gently manipulate the fruit. As a versatile manipulator capable of efficient use of dry bonding technology, it maintains the gentleness and dexterity of picking eggs from cartons and grapes from vines.
▲ Grasp the grapes
It can spread the "palm" widely and manipulate larger objects, such as basketballs, can-shaped drinks, etc.
▲ Grab the basketball
This manipulator can also use force to control heavy objects that are many times larger than itself.
▲Manipulate larger objects
In addition, the robot can also grasp two objects at the same time.
▲ Grasp two objects at the same time
"The first application of gecko adhesives has been associated with climbing robots, climbers or grasping very large, very smooth objects in space. But we've been thinking about using them for more practical applications. "But it turns out that gecko adhesives are actually very picky." ”
The first use of gecko adhesives on a polydypic manipulator is a challenge, which requires special attention to control the tendons of the robotic fingers and the design of the finger pads under the adhesive.
Second, the use of intermolecular force to achieve a stable grip
One advantage of the parallel manipulator over the more anthropomorphic multi-fingered manipulator is that it has the potential for high grip, so a single precision finger can be used to gain strength, while the multi-finger manipulator farmerHand provides more grip with gecko adhesives.
The manipulator benefits from two biological inspirations. The first was the human hand, which has many jointed fingers but only four fingers, and the second was the gecko, inspired by the gecko's toes grasping the ground, and under the leadership of mark Cutkosky, one of the paper's authors and A Fletcher Jones Professor at stanford University School of Engineering, the research team developed a gripping but non-stick gecko adhesive that was applied to the fingers of the manipulator.
▲Robot schematic
Just like the toes of a gecko, a robotic hand that applies gecko adhesive can be fixed to an object through tiny flaps. When in full contact with the surface, these flaps produce van der Waals forces (intermolecular interaction forces), caused by subtle differences in the position of electrons outside the molecule. As a result, the adhesive requires only a small amount of force to firmly grip objects. Another benefit of this adhesive is that they do not stick or leave residue on the touch.
After applying the gecko adhesive, the gripper relies on the front of the finger rather than the tip to grasp the object, which provides more usable contact area. To explore the trade-offs, the researchers increased the torque of the manipulator brake by eliminating the constraint of a fixed final link length.
Third, increase the rib structure and expand the grip area
The crux of the matter is that the gecko adhesive must come into contact with the surface of the object in a specific way to activate van der Waals force. When the gecko adhesive is applied to a flatter surface, it is easier to control the way it comes into contact with the object. But when it is necessary to rely on multiple fingers with gecko adhesives to grip objects and touch objects at different angles, that is, when using farmHand to grasp, the control of gecko adhesives is even more difficult.
To solve this dilemma, the researchers added a layer of finger pads to the manipulator under the adhesive. This layer of paper pads is made of a foldable rib-like structure that bends with minimal force. Regardless of the position or angle of contact, the ribs are bent to ensure equal forces on the bonding pad and to prevent any premature slippage that causes the object to fall.
▲Finger pad design of the manipulator
"If you move these ribs, no matter where you start, the ribs produce a similar force." "It's a simple physical behavior that can even be deployed in spaces outside of robotics, such as a shoe upper or an all-terrain tire," Brower said. ”
The tendons of the human hand are important and can be expanded and contracted over a wide range. However, many manipulators and clips are designed to be "C" shaped, as if picking up things with only the fingertips, but this manipulator is based on the tendon principle of the human hand, achieving a larger grip area and installing a cushion at the end of the finger, which also provides more surface area for the gecko adhesive.
Another problem with designing flexible and powerful manipulators is that existing computer simulations are difficult to predict the true performance of soft objects, so getting the design right is particularly difficult. But the researchers have benefited greatly from 3D printing and testing many hard and soft plastic components, which has also accelerated their research process. They even said, "If five years ago, this study would have been unlikely to be successful, or at least much slower." ”
Further improvements to the manipulator may come in the form of feedback features that will help users understand how it grips and how to grip better when using the robotic.
Conclusion: Flexible and robust, it promotes commercialization
Multi-finger manipulators are more flexible than parallel manipulators, but if they want to be used in real life, they also need to have the robust functions of parallel manipulators. The Stanford researchers combined the flexibility and stiffness of the manipulator to grab eggs, watermelons, etc., as well as objects larger than themselves.
Secondly, the original robot farmHand prototype is low-cost, which also provides conditions for its upgrade. The researchers say that in the future, higher performance motor torque will achieve higher tendon tension, and the use of harder ribs can also improve the overall stability of the manipulator. The researchers are also considering further commercializing the manipulator.
Source: Stanford University website, Science Robotics