Soft robots, or those made of materials such as rubber, gels, and cloth, have advantages over their bulkier, heavier counterparts, especially when it comes to tasks that require direct human interaction. Robots that can safely and gently help people with limited mobility shop, prepare meals, get dressed, or even walk will undoubtedly change their lives.
but, Soft robots You currently lack the power to perform these kinds of tasks. This long-standing challenge — making soft robots stronger without compromising their ability to interact gently with their environment — has limited the development of these devices.
With the relationship between strength and smoothness in mind, a team of Penn Engineers has created a new electrostatically controlled device cling That enables the soft robotic hand to lift 4 pounds — about the weight of a sack of apples — 40 times more than the hand could lift without the gripper. Additionally, the ability to perform this task that requires a soft touch and power has been achieved using only 125 volts of electricity, one-third the voltage required for existing clutches.
Their safe, low-energy approach could also enable soft, wearable robotic devices that would simulate the sensation of grasping. tangible thing in augmented and virtual reality environments.
James Pickall, Assistant Professor of Mechanical Engineering and Applied Mechanics (MEAM), and Kevin Turner, Professor and Chair of MEAM with a minor appointment in Materials Science Engineering, Ph.D. The students, David Levine, Gokulanand Iyer, and Daelan Roosa, publish a study in Robotics science describe a new fracture mechanics-based paradigm for electro-adhesive grippers, a mechanical architecture that can control the stiffness of soft robotic materials.
With this new model, the team was able to realize a gripper 63 times stronger than the current electric adhesive gripper. The model not only increased the force capacity of the clutch used in soft robots, but also reduced the effort required to operate the clutch, making soft robots stronger and safer.
Today’s soft robotic hands can hold small objects, like an apple for example. Because it is soft, the robotic hand can accurately grasp objects of various shapes, understand the energy required to lift them, and become stiff or tense enough to grab an object, a task similar to how we grasp and hold objects with our hands.
An electric gripper is a thin device that promotes a change of stiffness in a material allowing a robot to perform this task. A clutch, similar to a clutch in a car, is the mechanical connection between the moving objects in a system. In the case of electrical adhesive grippers, two electrodes covered with a dielectric material are attracted to each other when a voltage is applied. The attraction between the electrodes creates a coil Friction force At the interface that prevents the two panels from sliding over each other. The electrodes are attached to the flexible material of the robot hand.
By actuating the gripper with an electrical voltage, the electrodes stick together, and the robotic hand carries more weight than it did previously. Turning off the clutch allows the plates to slide over each other and relax in the hand, so that the body can be released.
Traditional models of clutches are based on the simple assumption of Coulombic friction between two parallel plates, where friction prevents the two clutch plates from sliding over each other. However, this model does not capture how mechanical stress They are irregularly distributed in the system and, therefore, do not expect a good clutch force capacity. Nor are they strong enough to be used to develop stronger clutches without the use of high voltages, expensive materials, or extensive manufacturing processes. A robotic hand with a clutch built using a friction model might be able to pick up an entire bag of apples, but it requires high voltages which makes it unsafe. human interaction.
“Our approach deals with the force capacity of the clutches at the model level,” says Pikul. “And our model, the one based on fracture mechanics, is unique. Instead of creating parallel plate clutches, we based our design on lap joints and examined where fractures occur in these joints. The friction model assumes that stress on the system is uniform, which is not realistic. In fact, it is concentrated The pressure is at different points, and our model helps us understand where those points are. The resulting clutch is stronger and safer because it requires only a third of the effort compared to conventional clutches.”
“The fracture mechanics framework and model has been used in this work to design connections and structural components for decades,” Turner says. “What is novel here is the application of this model to the design of electrical contact grippers.”
The researchers’ improved gripper can now be easily integrated into existing hardware.
“The model based on fracture mechanics provides insight into the workings of the electro-adhesive gripper, helping us to understand it more than the friction model could ever do,” says Pecol. “We can already use the model to improve existing clutches just by making very small changes to the geometry and thickness of the materials, and we can continue to push boundaries and improve the design of future clutches with this new understanding.”
To prove the strength of their gripper, the team attached it to a pneumatic toe. Without the researchers’ gripper, the finger was able to hold the weight of a single apple while blowing into a curled-up position; With that said, a finger could hold an entire bag of them.
In another demonstration, the gripper was able to increase the strength of the elbow joint to be able to support the weight of a mannequin arm at a low power demand of 125 V.
Future work that the team is happy to go into involves the use of this new clutch Model To develop augmented and virtual wearable devices.
“Conventional clutches require about 300 volts, a level that can be unsafe for human interaction,” Levine says. “We want to continue improving the grippers, making them smaller, lighter and less energy efficient to bring these products into the real world. Ultimately, these grippers can be used in wearable gloves that simulate the manipulation of objects in a virtual reality environment.”
“Existing technologies provide feedback through vibrations, but simulating physical contact with a virtual object is limited by today’s devices,” says Picul. “Imagine having both a visual simulation and the feeling of being in another environment. Virtual and augmented reality can be used for training, teleworking, or just simulating touch and motion for those who lack those experiences in the real world. This technology brings us closer to those possibilities.”
Improving human-robot interactions is one of the main goals of the Pikul Lab and the direct benefits this research offers fuel their research passion.
“We haven’t seen a lot of soft robots in our world yet, in part because of their lack of strength, but now we have one solution to this challenge,” Levine says. “This new way of designing grippers could lead to applications of soft robotics that we can’t imagine right now. I want to create robots that help people, make them feel good, and enhance the human experience, and this work brings us closer to that goal. I’m really excited to see where we go next.”
David J. Levine et al., A mechanics-based approach to realizing high-capacity electrostatic adhesives for robots, Robotics science (2022). DOI: 10.1126/scirobotics.abo2179
University of Pennsylvania
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