A research paper titled Biological Organisms as End Effectors explores the oddball approach of giving small animals jobs as grippers at the end of a robotic arm. Researchers show that pill bugs and chitons — small creatures with exoskeletons and reflexive movements — have behaviors making them useful as grippers, with no harm done to the creatures in the process. The prototypes are really just proofs of concept, but it’s a novel idea that does work in at least a simple way.
Pill bugs reflexively close, and in the process can grasp and hold lightweight objects. The release is simply a matter of time; researchers say that after about 115 seconds a held object is released naturally when the pill bug’s shell opens. While better control over release would be good, the tests show basic functionality is present.
Another test involves the chiton, a small mollusk that attaches to things with suction and can act as an underwater end effector in a similar way. Interestingly, a chiton is able to secure itself to wood and cork; materials that typical suction cups do not work on.
A chiton also demonstrates the ability to manipulate a gripped object’s orientation. Chitons seek dark areas, so by shining light researchers could control in which direction the creature attempts to “walk”, which manipulates the held object. A chiton’s grip is strong, but release was less predictable than with pill bugs. It seems chitons release an object more or less when they feel like it.
This concept may remind readers somewhat grimly of grippers made from dead spiders, but researchers emphasize that we have an imperative to not mistreat these living creatures, but to treat them carefully as we temporarily employ them in much the same manner as dog sleds or horses have been used for transportation, or carrier pigeons for messages. Short videos of both pill bug and chiton grippers are embedded below, just under the page break.
Soft robotic grippers have some interesting use cases, but the industrial options are not cheap. [James Bruton] was fascinated by the $4000 “bean bag” gripper from Empire Robotics, so he decided to build his own.
The gripper is just a flexible rubber membrane filled with small beads. When it is pushed over a object and the air is sucked out, it holds all the beads together, molded to the shape of the object. For his version [James] used a soft rubber ball filled with BBs. To create a vacuum, he connected a large 200cc syringe to the ball via a hose, and actuated it with a high torque servo.
It worked well for small, light objects but failed on heavier, smooth objects with no edges to grip onto. This could possibly be improved if the size and weight of the beads/BBs are reduced.
Among all the job-related problems wrought by the pandemic, here is another one that comes as the result of people generally staying home: there are hardly any backpackers to do traditional transient backpacker jobs like picking apples. Researchers at Monash University’s Department of Mechanical and Aerospace engineering found a way to fill in the gap by building a pneumatic robot arm that can harvest an apple every seven seconds at top speed.
A suite of cameras and algorithms look for fruit amongst the foliage and carefully remove it by gripping it gently and twisting, much like a human would. In order to do this, the robot must consider the shape of the fruit, the way it’s hanging, and where to separate it from the tree while keeping damage to a minimum. A suction system helps pull the apple into the soft, four-fingered grip and then the arm twists and turns to deposit the apple into the bin.
There are a lot of upsides to this robot, including the fact that it works in any lighting and weather conditions and can ID an apple in less than 200 milliseconds. The only problem is that this operation results in the occasional missing stem — a cosmetic problem that sounds nit-picky, but would definitely prevent some stores from buying the fruit. Well, that, and there only seems to be one of these robots so far.
There are two videos after the break — a short one that gives you the gist, and a much longer one that offers a view of the suction cup, which emerges from the middle of the fingers like a xenomorph’s little mouth.
In a recent International Conference on Robotics and Automation paper, [Shenli Yaun] and some others from Stanford discuss the design of a roller-based robot hand that has many features that mimic the human hand. The key feature is that each of the three fingers has a roller with a small geared motor.
The rollers allowed the hand to change an object’s orientation without losing its grasp. Of course, this works well with spherical objects like a ball. But the video shows that it can manipulate other items like a 6-sided die, a water bottle, or even a piece of paper. By spreading the fingers it can even hold large objects you wouldn’t expect at first glance.
A lot of great scientific breakthroughs come through imitating nature, but technology often runs up against limits in certain areas. This is particularly evident in robotics, where it takes a lot of effort (and cost) to build a robot which can effectively manipulate heavy objects but not crush others which are more delicate. For that, a research group has looked outside of nature, developing a robotic grasper which uses omnidirectional wheels to grab various objects.
The robot hand is composed of three articulating fingers with fingertips which are able to actively manipulate the object that the hand is holding. With static fingertips, it is difficult to manipulate an object in the hand itself, but with the active surfaces at the fingertips it becomes easier to rotate the object without setting it down first or dropping it.
The project is much more than designing the robot hand itself, too. The robot uses calculated kinematics to manipulate the objects as well, but a second mode was also tried where the robot was able to “learn” how to handle the object it was given. The video linked below shows both modes in operation, with interesting results. If you prefer more biologically-inspired robot arms, though, there are always novel designs based on non-humans.
It is an old movie trope: a robot grips something and accidentally crushes it with its super robot strength. A little feedback goes a long way, of course, but futuristic robots may also want to employ soft grippers. [Jessica] shows how to build soft grippers made of several cast fingers. The fingers are cast from Ecoflex 00-50, and use air pressure.
A 3D-printed mold is used to cast the Ecoflex fingers, which are only workable for 18 minutes after mixing, so it’s necessary to work fast and have everything ready before you start.
While robotic arms can handle a wide variety of tasks, the specific job at hand will have a major influence on the type of end effector used. For sorting ferromagnetic parts an electromagnet might be enough, while for more accurate location a mechanical gripper could be employed. If you’re working with particularly delicate objects or in concert with human beings, it may be desired to have a force controlled gripper to avoid damage. [James Bruton] has been whipping up a design of his own for just this purpose.
The basic gripper is 3D printed, with 3 fingers consisting of two joints each. Retraction of each finger is courtesy of bungee cord, while extension is via a servo attached to the finger through a spring. The position of each finger is measured with a resistive flex sensor. An Arduino Uno is employed to run the servos and read the attached sensors.
As force is applied by the servo, the spring begins to stretch. This leads to a greater difference between the servo position and the finger position as the applied force increases. By calculating this difference, it’s possible to determine the force applied by the fingers. This can then be used to limit the applied force of the gripper, to avoid breaking delicate objects or crushing soft, fleshy humans.
[James] notes that there are some drawbacks to the current design. The force required to move the fingers is inconsistent along their travel, and this interferes somewhat with accurate measurement. Overall though it’s a solid proof of concept and a good base for further revisions. Files are on Github for those who wish to tinker at home.