A Short History of Soft Grippers
During the past 50 years, the world has seen an enormous growth in robotic technology. From the creation of Unimate, the first industrial robot arm, to the introduction of the Roomba robotic vacuum cleaner, the field of robotics has expanded exponentially, creating highly versatile and efficient machines used in manufacturing, medical, industrial applications, and more. Such advancement has set the stage for certain technologies to flourish. Robotic mechanisms designed simply to grasp objects--or as they are more commonly known, grippers--are just one such technology. As robots have been applied to more and more fields, robotic gripper technology has diversified dramatically, leading the way for new approaches, such as soft grippers.
Soft grippers are just that: comprised of soft materials, as opposed to the strictly-hard grippers that the world has come to associate with robots. Soft grippers have been on the rise during the past few years, largely due to the need for robots that are versatile and can interact with a variety of environments. Applications such as medicine, food handling, autonomous robotics, and assistive robotics are all fields that demand compliant and delicate manipulation of objects. Soft grippers fit the needed criteria because through their inherent compliancy and a variety of other behaviors, they can accomplish feats that would be difficult for hard grippers to achieve. In this blog post, we hope to give you a solid understanding of the state of soft gripper technology through some of the notable grippers and developments made in the field. This will not be an exhaustive list; however, it will cover many well-known grippers as well as some lesser-known ones.
Pneumatic Soft Grippers
One of the most prominent categories is soft pneumatic grippers, which use pressurized gas in order to actuate some form of soft structure, often a finger-like mechanism. In 1989, prior to the creation of many of the grippers in this post, Koichi Suzumori, a researcher at Okayama University and professor at Tokyo Institute of Technology, developed extremely complex and intricate soft grippers. At the time, this was a largely unexplored field, making Suzumori’s work that much more pioneering. Soft Robotics Incorporated, an established company in the soft robotics field that grew out of the Whitesides Research Group at Harvard University in 2012, has also developed a number of pneumatic grippers. Soft Robotics’ grippers have been largely focused on applications like food handling, packaging, and factory settings. Their “adaptable grippers” are quite notable, since they were some of the first commercial soft robotic grippers that were designed to be retrofitted on a number of pre-existing robotics platforms. Other trailblazers in the field of grippers include Robert J. Wood, Ph.D., a professor of engineering and applied sciences at the Harvard SEAS, and David Gruber, CUNY marine biologist, who implemented soft grippers made of foam and silicone in existing aquatic ROVs from 2014 through 2016. Researchers Huichan Zhao, Kevin O’Brien, Shuo Li, and Robert Shepherd at Cornell have recently tackled the problem of sensing in grippers, publishing a paper in 2016 regarding a pneumatic soft gripper with optoelectronic sensing. This project was one of the first pairings of optical sensing with pneumatic actuators. Other developed grippers have even gone beyond the typical silicones and rubbers used: Many of the soft pneumatic grippers created by Pneubotics, for example, have consisted of heat-sealed bladders inside fabric structures.
Electrical Soft Grippers
Another category of soft grippers is electronic ones, or any soft gripper that directly uses electric current to actuate a grasping motion or contribute to gripping ability. Researchers of the DEA team from EPFL developed grippers in 2015 that illustrate this well. They have invented dielectric minimum energy structures, which can change shape when given electricity. These structures can be shaped so that they form a simple, yet elegant and precise gripper. The team has oriented the gripper for space applications concerning debris clean-up. Other electronic soft grippers utilize different means to hold an object: A gripper made by the same team in 2016 consisted of electrostatic pads that could wrap around a target and hold it in place, another unique innovation.
Cable-Driven Soft Grippers
Using cables and strings to move robotic mechanisms has been a technique employed for a great deal of time, and has led to the development of various cable-driven soft grippers. One such gripper is quite different from many of the others in this post, as it more resembles a tentacle than a hand. From The Octopus Project in 2016, an interdisciplinary initiative funded by the European Commission and coordinated by the Scuola Superiore Sant'Anna educational institute in Italy, it uses cables to make the appendage twist, move, and even wrap itself around a small object. To gain a further level of softness, researchers at Carnegie Mellon’s Soft Robotics and Bionics Lab led by Chris Atkeson over the past four years have made inflatable arms, structures, and of course, grippers. By combining inflationary structures with cable systems, the researchers achieved a greater degree of compliance and an extremely soft gripping system.
Other Notable Soft Grippers
As there is large breadth in the field of soft grippers, there are many more techniques and methods of gripping than have been categorized here. The granular jamming effect is yet another example and category of soft gripping technology. Empire Robotics has brought jamming into play with its VERSABALL grippers, which are designed to be enclosed units that can easily be fitted to existing robotic platforms and were first unveiled in 2012. Despite this innovation, Empire Robotics closed in early 2017 due to a struggle to commercialize their system. Sukho Song of the Max Planck Institute for Physical Intelligence in 2014 investigated using the fibrillar adhesion effect for gripping. Being a physical effect that has not been explored much at all, the use of it in soft gripping technology is certainly noteworthy.
The field of soft robotics has expanded greatly over the past three decades and will most likely continue to going forward. Although soft grippers are just a small subfield of this larger field, it has its own rich past of work and development to draw upon and build on. The recent advancement of soft gripper technology also says a great deal about the state of robotics as a whole. Humans have historically looked to themselves and nature for a starting-point of technology, which is why many of the grippers on this list have finger-like appendages, mimicking our hands. Despite this, in the past, robotics has to a great extent missed a fundamental fact of our hands: their softness. The rise of soft grippers is a massive step towards filling this informational gap, and supports the future of robotics as a whole.
By Aidan Leitch