Assisitve soft hand exoskeleton

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Graspex is an open-source soft robotic hand exoskeleton, intended to serve either as a rehabilitation device to regain hand mobility after an accident, or as an assistive device for those people with a permanent motor disability. The main objective of this project is to design a simple, lightweight, and comfortable device with the aim of improving the quality of life of those people that, because of their condition, cannot perform even the simplest activities of daily life.

I like to define this kind of device as an exomusculature, rather than as an exoskeleton. The support structure is made of fabrics and flexible materials, so there is no external rigid structure as in the case of conventional exoskeletons, and the actuation system consisting of a set of actuators connected to the fingers through a series or artificial tendons somehow mimics the musculotendinous system of the human hand.

As I already stated in another of my projects, Dextra, I consider the human hand the most versatile tool we use in our daily lives. We use our hands for almost every action we perform in a normal day. The problem I addressed with Dextra is what happens when you do not have one or both hands, and how can this problem be alleviated. But, what if you have both hands but you cannot move them? The problem still remains, you have to face your daily life with a serious limitation. And this situation is more common than it seems: cerebral vascular accident, or stroke, remains the leading cause of adult disability and it is estimated that there are nearly 800,000 stroke incidents in the United States annually. Nearly 80% of stroke survivors suffer hemiparesis of the upper arm and impaired hand function is reported as the most disabling motor deficit [1].

For the above reason, there is a need for some kind of device that serves as a means to either rehabilitate a person suffering from the disabling condition until he or she regains hand functionality, or if this is impossible to achieve, as a means to assist hand motion so that the person can carry out his or hers daily activities as normally as possible. To this end, exoskeletons, a subclass of wearable robotic devices, are being developed to help people mobilize their affected limbs.

However, conventional exoskeletons are often bulky and heavy, and suffer from a problem known as joint misalignment. This problem arises because the kinematic chain of the wearable robot overlaps that of the human body, and, as the latter is very complex and difficult to replicate, usually the differences between the two cause interaction forces, joint misalignment and motion restrictions, which ultimately cause discomfort and difficulties in controlling the device.

Soft exoskeletons, a new type of exoskeletons that have emerged in recent years from the conjunction of soft robotics and wearable robotics, get rid of most of the problems that conventional exoskeletons have. In a soft exoskeleton, the rigid frame of a conventional exoskeleton is replaced by textiles that transmit the forces generated by the actuators to the user’s limbs and provide support for the actuators, electronics and power sources. By getting rid of the rigid frame, a soft exoskeleton is usually lighter and also avoids problems related with joint misalignment that conventional exoskeletons usually have, providing a minimal impediment to the wearer’s motions. The downside of this approach is that, in the absence of a rigid structure, the user’s skeleton must withstand the external loads as well as the forces generated by the actuators. For this reason, soft exoskeletons are usually designed as rehabilitation/assistive devices and not as force augmentation devices.

Graspex is designed following this soft exoskeleton paradigm. The idea is to build a hand rehabilitation/assistive soft exoskeleton that will be completely open-source, so that it can be easily replicated and modified. To this end, all mechanical parts will be designed to be 3D printable, but because of the soft nature of the device, most of them will be made of flexible TPU filament. The actuation system will be based on compact DC motors connected to the fingers by means of artificial tendons. To prevent the wrist position from affecting force transmission, the output of the actuators will be connected to the palm of the hand through a Bowden transmission system. Control electronics will be based on an Arduino-like microcontroller (or a Raspberry Pi Zero if complexity increases), to widen the range of people that will be able to hack the device. Having a fully hackable hand exoskeleton will allow anyone to use the device not only as originally intended, but in many other ways, for example as a force feedback device for virtual reality.

Main features

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Palm piece

sla - 507.21 kB - 04/23/2018 at 08:22



Fingertip piece for the index finger

sla - 191.68 kB - 04/23/2018 at 08:22



Tendon routing ring for the middle phalanx of the index finger

sla - 39.93 kB - 04/23/2018 at 08:22



Tendon routing ring for the proximal phalanx of the index finger

sla - 41.10 kB - 04/23/2018 at 08:22


  • Soft matter(s)

    Alvaro Villoslada04/20/2018 at 15:27 0 comments

    For this year's Hackaday Prize I wanted to try something that has been little researched by the open source robotics community and, at the same time, that is related to my favorite field of robotics, wearable robotics, and has to do with what I think is one of the most amazing part of our body: the hand.

    There are plenty of open source robotic hands and hand prostheses out there (heck, even I designed my own :D) and some of them are truly outstanding. But, what about open source exoskeletons? To this day, exoskeletons are still mostly confined to research laboratories and some cutting-edge companies, but there are not so many examples of open source exoskeletons. Perhaps it is because these are complex devices that must be carefully designed from a mechanical and control point of view in order not to damage the user. Maybe it is because they are devices that have to be able to withstand high loads and exert great forces, especially in the case of arm and leg exoskeletons, so 3D printing is out of the question and other more expensive or not so easily available manufacturing methods have to be used.

    I think that these limitations apply to the devices that come to mind when we come across the word exoskeleton: those bulky and heavy power suits, built as chains of rigid links with powerful actuators that augment the force of their users. But there is a relatively new concept in robotics that, applied to the design of wearable robots, I believe has a huge potential for the emergence of a multitude of DIY exoskeleton projects: soft robotics.

    Essentially, soft robotics is based on the use of flexible, soft and compliant materials that replace the traditionally rigid bodies and actuators of robots, usually following a bio-inspired approach. This, when applied to the design of an exoskeleton, means that the complex and heavy rigid structure is no longer necessary, and materials such as textiles, polymers or other synthetic elements are used as the interface that transmits the motion of the actuators to those limbs that are mobilized by the device.

    Bio-inspired design also applies to the actuation system of a soft exoskeleton. If DC motors are used, these are not longer placed directly over the joints of the user's body. Instead, they are placed away from them, for example inside a backpack, and their motion is transmitted by a cables, mimicking the way muscles and tendons work. In addition, there are new actuators designed following the soft robotics approach: pneumatic artificial muscles, soft pressurizable elastomeric actuators, granular jamming actuators...

    All in all, I think soft exoskeletons are easier to design, as they don't involve complex mechanisms and a lot less moving parts are needed. Basically, you just need some kind of interface to transmit the motion of the actuators to the part of the body you want to mobilize. There is no need for a mechanical structure made of links and joints; the mechanical structure is your own skeleton. This, of course, is a drawback if you want to design a force augmentation device, but in the case of assistive or rehabilitation (and maybe also haptic) devices, I think this is a path worth exploring.

    That's why I've embarked on designing a soft hand exoskeleton. I chose the hand because, as I said, hands are amazing tools, and also because the requirements for moving the fingers and generating a grasping force similar to the natural one are easier to meet than in the case of the arms or legs. In addition, the required parts are smaller, making them easier to print. So I got down to business and started designing the pieces of the exoskeleton structure, testing with flexible materials for 3D printing. Below, you can see one of the first parts, an interface to connect the output of the motors with the palm of the hand:

    I think this will be a really challenging project, as it involves not only the design of the soft hand exoskeleton itself, but also the actuation...

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