OpenBionics Affordable Prosthetic Hands

Description

We present a technical report, intended to serve as a step by step tutorial for the replication of the prosthetic hands. The guide contains illustrated instructions, carrying the user over all assembly steps and providing practical advice on any details that require attention.

Figure 1. Tools required to build all hand components.

Illustrations of all required parts (see for example Fig. 2 for a table of illustrated palm components), components, tools and materials (see Fig.1) are included, while comprehensive Parts Reference tables are provided (see for example a table containing all palm parts in Table 1).

Table 1. The parts required to assemble the palm.

Figure 2. Parts required to build the palm.

The assembly is divided into two main sections: 1) Fingers Assembly and 2) Hand assembly, with the latter containing instructions on how to build and attach all the hand components on the palm.

Figure 3. Attaching a flange on the assembled hand.

Hand Design

Following the design of the OpenBionics robotic hands [1], the Prosthetic hand [2] was designed to be affordable, lightweight and intrinsically-compliant. Its design is structurally and kinematically anthropomorphic. In particular, its sizing is parametrically determined by hand anthropometry studies [3], allowing for personalization and adjustment to the needs of each individual. Moreover, its kinematic model is derived by optimizing an index of anthropomorphism [4]. Finally, the prosthetic hand bears a novel differential mechanism based on the whiffletree mechanism [5] that allows the user to execute various grasping postures with a single actuator. Switching between the different postures or gestures is easy and intuitive. Simple locking buttons can independently block the motion of each finger. The proposed hands can be easily fabricated using low-cost, off-the-shelf materials and rapid prototyping techniques (e.g., 3D printing). The prosthetic hands assembly guide can be found here.

References

[1] A. Zisimatos, M. Liarokapis, C. Mavrogiannis and K. Kyriakopoulos, “Open-Source, Affordable, Light-Weight, Underactuated Robot Hands”, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Chicago, IL, USA, 2014.

[2] G. Kontoudis, M. Liarokapis, A. Zisimatos, C. Mavrogiannis and K. Kyriakopoulos, “Open-Source, Anthropomorphic, Underactuated Robot Hands with a Selectively Lockable Differential Mechanism: Towards Affordable Prostheses”, IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Hamburg (Germany), 2015.

[3] B. Buchholz, T. J. Armstrong, and S. A. Goldstein, “Anthropometric data for describing the kinematics of the human hand,” Ergonomics, vol. 35, no. 3, pp. 261–273, 1992.

[4] M. Liarokapis, P. Artemiadis, and K. Kyriakopoulos, “Quantifying Anthropomorphism of Robot Hands,” in IEEE International Conference on Robotics and Automation (ICRA), vol., no., pp.2041-2046, 6-10 May 2013.

[5] L. Birglen and C.M. Gosselin, “Force analysis of connected differential mechanisms: application to grasping,” The International Journal of Robotics Research, vol. 25, no. 10, pp. 1033–1046, 2006.

Introduction

Our initial method of creating fingers for robot and prosthetic hands was very simple and it didn't require any complex tools (silicone sheets were stitched onto the rigid phalanges with simple needles). The main disadvantages of this method are: 1) the process isn't automated, 2) the aesthetic aspect of the finger is not optimal (i.e., it doesn't feel like a product), 3) the finger cannot easily accommodate extra parts (e.g., sensing elements or other electronics). For these reasons we searched different fabrication methods for developing hands based on flexure joints.

Recently Ma et al [1] proposed a new methodology that is called hybrid deposition manufacturing (HDM). HDM combines additive manufacturing (AM) with multi-material deposition and embedded components in order to produce robotic, mechatronic, and other articulated mechanisms.

Design

Using the HDM approach for our prosthetic fingers we can embed inside them a wide range of electronics, like force sensors, flex sensors or even NFC tags that will facilitate interactions with other electronic devices. Of course the new design has the disadvantage that it requires more complex tools and is slightly more expensive.

Figure 1. The mold and the 3D printed finger base.

Figure 2. The mold opened. The new finger design is also depicted.

Figures 3. Fingers created with the HDM technique using different colors. As it can be noticed the proximal is now a pin joint, in order to reduce the effect of the torsional forces in the finger configuration and the out of plane motion of the finger.

The proposed design can be based on the human hand model. For now we use a ready model in SolidWorks. In the future we plan to use a 3D scanner (e.g., kinect, project soli, etc.) to reconstruct the intact hand of amputee, derive the mirror hand and build a personalized prosthesis.

To use this new design in SolidWorks, you can download the files form here. When you open the .sldASM files, SolidWorks will ask for the missing parts. These parts can be found in the following 3D model. A future direction of ours is to make the HDM design parametric and migrate it to FreeCAD, as we did for the initial design.

It must be noted that the new fingers are completely modular. We want amputees to constantly use our hands and we hope that they will break them. We expect that the most frequent damages will happen to the fingers that can be easily replaced. After all the design is so affordable that each user may have several spare parts. In the following figure we present a preliminary design of the new palm, that will accommodate the new HDM fingers (the differential mechanism has not been incorporated yet).

Figure 4. A preliminary version of the HDM design palm.

Materials and Tools Required

As depicted the build of materials are:

* paint of the desired color

* liquid polyurethane (PMC 780)

* cotton swabs

* paper tape

* NFC tags

The necessary tools are:

* a weighting scale

* a vacuum chamber

* plastic cups to mix the two liquid silicone parts.

The prices of the different hand components can be found here. The NFC tags cost 15.50$ (for 25 tags).

Figure 5. Some of the tools required for the replication of the HDM based prosthetic fingers. A weighting scale, the NFC tags, paints of different colors, cottons swabs (that are used for the tubes), packages of polyurethane (PMC 780) and plastic cups are depicted.

NFC Ready Fingers

As we have already mentioned, with the HDM process we are able to embed inside the finger various electronics like a set of NFC tags. We had the idea to do this, when we read a Hackaday article regarding near field communications.

Figure 6. The left part of the mold, the 3D printed finger base, the low-friction tubes and the NFC tags are depicted. One NFC tag is used for each phalanx of the finger.

The NFC ready fingers can be programmed to interact with various electronic (NFC ready) devices. For example the amputee may touch his smartphone with the index finger of the prosthetic hand to open a specific application or with the middle finger to tune the radio to his favorite station. More details on how to program NFC applications for android based devices can be found here.

Experiments

The new finger design performing unconstrained flexion, can be found at the following video:

Exemplar applications of the NFC ready fingers, can be found at the following video:

[1] Raymond R. Ma, Joseph T. Belter and Aaron M. Dollar, "Hybrid Deposition Manufacturing: Design Strategies for Multi-Material Mechanisms via 3D-Printing and Material Deposition", Journal of Mechanisms and Robotics, 2015.

To put the OpenBionics project into perspective, we present the current status of the Prosthetics Market and compare indicative commercially available solutions with the OpenBionics prosthetic hands in terms of cost.

The current status of the Prosthetic Hands Market

According to a study of 2010 by McGimpsey and Bradford [1], featured in the website of the National Institute of Standards and Technology (www.nist.gov) of the United States, the state of the market of the hand prosthetics can be summarized as follows:

• Nonfunctional cosmetic hands cost[1] between $3000 and $5000.
• Functional “split-hook” devices cost around $10000.
• Cosmetically realistic myoelectric hands with just open/close functionality cost between $20000 and $30000.
• Sophisticated neuroprosthetic hand systems might reach a total cost of more than $100000.
• Yearly third party health insurance caps on prosthetic services range from $500 to $ 3000 and lifetime restrictions range from $10,000 to one prosthetic device during a person's lifetime. This observation becomes really important given the fact that prosthetic devices are known to require frequent repairs and replacements. For reference, a study featured in the website of the U.S. department of Veteran Affairs [2] reports that the average lifetime cost for prosthetics and medical care for loss of a single arm for a veteran of the Iraq or Afghanistan wars was $823,299.

A simple online search supports the aforementioned observations. According to Wikipedia, the cost of the Otto Bock Michelangelo Hand exceeded $70000 in 2013 [3], while recent press results report that the prosthetic hands of Bebionic and Touch Bionics exceed the cost of $100000 (costs for fitting, training and programming) [4-5].

At the same time according to user studies [6], amputees express their disappointment for the increased weight of existing solutions and the difficulties they face with repairs, while in fear of damaging their device, they choose to use simple hooks for their every day life tasks. Another interesting finding of the same study is that the prosthesis acceptance[2] significantly increases (about 8 times) when the amputees are involved in the selection / preparation of the prosthesis (e.g., replication of an open-source design). These results led us to the conclusion that what amputees really need is a highly functional, personalized, affordable and lightweight prosthesis that can be easily and affordably developed, maintained and repaired.

The OpenBionics Prosthetic Hands: Affordable Dexterity

Aiming at addressing the aforementioned needs of amputees, a significant amount of effort at the design stage was devoted to selecting materials and tools that can be easily and affordably found in hardware stores around the world. In this section, we present detailed indicative costs for all materials required for the assembly of our prosthetic hand, along with total[3] costs for a few different hand setups.

Prosthetic hand actuated with surface EMG electrodes.

It is evident that the majority of the cost corresponds to the servo motor. Cheaper motors can also be used without compromising the efficiency of the proposed design. This observation led us to explore also alternative solutions for actuation. We focused on providing a fully motor-less system.

In particular, we have already developed a design that makes use of a custom-made body-powered, tendon driven actuation/transmission system (that can be built with ABS filament), drastically reducing the total cost of the system.

Body-Powered prosthetic hand

Body-Powered Actuation Mechanism

References

[1] McGimpsey, G., & Bradford, T. (2010). Limb prosthetics services and devices. Worcester, MA: Bioengineering Institute Center for Neuroprosthetics, Worcester Polytechnic Institution. Retrieved from http://www.glb.nist.gov/tip/wp/pswp/upload/239_limb_prosthetics_servic es_devices.pdf

[2] Blough DK, Hubbard S, McFarland LV, Smith DG, Gambel JM, Reiber GE. Prosthetic cost projections for servicemembers with major limb loss from Vietnam and OIF/OEF. J Rehabil Res Dev. 2010;47:387–402. doi: 10.1682/JRRD.2009.04.0037.

[3] https://en.wikipedia.org/wiki/Michelangelo_Hand

[4] http://www.cnn.com/2013/02/01/tech/bionic-hand-ilimb-prosthetic/

[5] http://www.wwltv.com/story/news/health/2015/05/28/girl-finally-gets-her-dream-prosthetic-hand/28130005/

[6] D. Edeer and C. W. Martin, “Upper limb prostheses - a review of the literature with a focus on myoelectric hands,” 2013. [Online]. Available: www.worksafebc.com/evidenc

[1] The aforementioned costs involve technological costs but also customization costs, since each device has to be adapted to the needs of the user.

[2] The prosthesis acceptance corresponds to the average amount of time that an amputee spends using a prosthetic device for everyday life tasks.

[3] It should be noted that the actual total cost is even lower than that reported on the tables (e.g., we don’t need 1Kg ABS filament to build a hand. With this amount we can build at least 3 hands with their harnesses).

The Idea

An old and reliable method of controlling prosthetic devices is by using a harness-socket actuation system in a body powered manner [1]. In order to further reduce the cost of our prosthetic hands omitting any kind of electronics and servos, we designed a body powered actuation system that an amputee can use as an interface to control a prosthetic hand. The proposed system is inspired by the classic harness-socket actuation systems but is designed as an exosceleton. The system consists of modular parts. Depending on the user's arm length an appropriate number of intermediate modules can be printed together with the end-effector and the tendon routing entry part.

Description

The proposed body powered actuation system, consists of:

• modular 3D-printed parts
• pins, dowels or shafts
• Velcro tape
• an elastic arm sleeve
• Dyneema thread

The mechanism can be replicated and assembled quite easily, as depicted in the picture below. Moreover, the proposed system with a prosthetic hand attached at the end-effector, can be used as a body powered prosthesis simulator for non-amputees that want to experience how functional a prosthesis is (e.g., kin that want to experience what amputees - family members feel). The cost of the system is less than 25$ and the weight 250 gr. Enjoy!

References:

[1] R. J. Pursley, "Harness patterns for upper-extremity prostheses", ArtifIcial Limbs, 2(3):26-60, Sep 1955.

Background

Nowadays most artificial (i.e., robotic or prosthetic) arms and hands are described as anthropomorphic without really evaluating their level of humanlikeness. The notion of Anthropomorphism comes from the Greek word anthropos that means human and the Greek word morphe that means form and according to Epley [1] its essence “is to imbue the imagined or real behavior of nonhuman agents with human-like characteristics, motivations, intentions and emotions”.

In the robotics literature, Mason et al. [2] discussed that the main reasons that researchers tend to be inspired by the human hand are the following:

• An anthropomorphic design interfaces well with human-centric environments (e.g., the objects and the environments surrounding us have been crafted for the human-hand).
• Human-likeness of robot hand designs provides intuitiveness for teleoperation studies.
• A humanlike design facilitates comparisons between biomechanical and robotic studies.
• A humanlike design is aesthetically advantageous for certain applications and environments (e.g., in prosthetic and entertainment oriented applications).
• For the simplest reason that the human hand, as an outcome of thousands of years of evolution is definitely a “good design”.

Motivation

Moreover, the last decade, anthropomorphism has received increased attention and has been a desired characteristic of robots for a plethora of Human - Robot Interaction applications for two main reasons:

• Robots need to establish solid social connections with humans and anthropomorphism is of paramount importance for this goal. After all it is well-known that the more humanlike a robot is in terms of appearance, motion and/or perceived intelligence, the more easily will manage to socially interact with humans, inducing them empathetic reactions.
• Anthropomorphism guarantees also safety of possible interactions between humans and robots (e.g., during a collaborative assembly task), as human-like motion can be more intuitively perceived by humans, which can comply their activities and/or motion, to avoid possible injuries.

The Toolbox

This repository contains a MATLAB toolbox for the quantification of structural anthropomorphism of artificial arms and hands. The toolbox is based on computational geometry and set theory methods and is distributed under an open-source license (GPLv3). For doing so, it compares human and artificial workspaces proposing a series of metrics that assess their relative coverages. For human and artificial arms the toolbox assesses anthropomorphism of the upper-arm, forearm and wrist / hand workspaces. For human and artificial hands the toolbox evaluates the anthropomorphism of the workspaces of the finger bases frames and the workspaces of the finger phalanges. Various methods for the computation of the workspaces volumes are also presented. The final score of anthropomorphism is derived as a weighted sum of the sub-scores of the independent workspaces metrics proposed and always ranges from 0 (for non-anthropomorphic artifacts) to 1 (for human-identical artifacts). Τhe toolbox can be used for design optimization of anthropomorphic prosthetic and robotic devices. More details for the quantification of anthropomorphism of artificial arms and hands, can be found in [3] and [4] respectively.

Fig. 1. Workspaces points and the corresponding convex hulls for the phalanges of the human index finger.

Fig. 2. Workspaces comparisons between human (black convex hulls) and two artificial arms (red convex hulls), for actual links lengths and normalized link lengths. Letter X denotes those cases for which no comparisons between the human and the artificial workspaces can be conducted (i.e., score of anthropomorphism is zero).

Fig. 3. Comparison of finger workspaces between a robot hand (black convex hulls) and the human hand (red convex hulls).

The toolbox is constantly under-development and the newest version can always be found in the OpenBionics/Anthropomorphism GitHub repository. We plan to eventually migrate the toolbox to Octave, R and/or Python (for people that do not have access to a MATLAB license). The toolbox has 3 main folders named: “Arm”, “Hand” and “Examples”. The first two folders contain the functions for the quantification of anthropomorphism of artificial arms and hands respectively, while the third folder contains examples of the implemented methods. Up to now (October 2015), the toolbox contains 55 functions and 3 examples. Should you have any questions or suggestions, feel free to contact us. Enjoy!

References

[1] N. Epley, A. Waytz, and J. T. Cacioppo, “On seeing human: a three-factor theory of anthropomorphism.,” Psychol. Rev., vol. 114, no. 4, pp. 864–886, 2007.

[2] M. T. Mason, A. Rodriguez, S. S. Srinivasa, and A. S. Vazquez, “Autonomous manipulation with a general-purpose simple hand,” The International Journal of Robotics Research, vol. 31. pp. 688–703, 2012.

[3] M. Liarokapis, P. Artemiadis, and K. Kyriakopoulos, “Quantifying Anthropomorphism of Robot Hands,” in IEEE International Conference on Robotics and Automation (ICRA), vol., no., pp.2041-2046, 6-10 May 2013.

[4] C. Mavrogiannis, M. V. Liarokapis, and K. J. Kyriakopoulos, “Quantifying Anthropomorphism of Robot Arms,” in IEEE/RSJ International Conference on Intelligent Robots and Systems, 2015.

Introduction

As we have already mentioned here, we are in the process of migrating our designs to FreeCAD in order to be freely accessible to all and because we believe in fully open source solutions! The new designs can be found here.

Up to now we have designed the palm with the differential and the thumb abduction / adduction mechanisms. Prosthetic fingers (the easy part) will follow as we are in the process of improving their design. We have also redesigned some parts for better performance (e.g., the bars of the differential mechanism are changed).

Differential Mechanism Update

As depicted, we reduced the radius of the button axle and the radius of the holes of the bars. This change, makes the coupled fingers (e.g., index and middle) more independent when one of them is locked. The radius is now 3 mm. When one finger is locked and the other moves, the locked finger tendon will move a distance of 3 mm*angle_of_bar. For example, if the angle_of_bar = PI/4 then the tendon moves a distance of ~2.35 mm.

Tendon Routing Update

We also modified the tendon routing. As you can see in the picture below the tendon comes out from the side of palm in order to be connected with the body harness for body powered prosthetic hands. With this configuration you can also put the servo motor in the same position (currently under development).

Thumb Mechanism Idea

A new thumb mechanism was also tested. As depicted in the picture below, we tried to add friction with a rubber layer (blue arrow) that needs appropriate tuning in order to resist the force of the tendon.

Stay tuned for more updates!!!

Until now our designs were prepared in Solidworks 2014 (Dassault Systems). Since Solidworks is not an open-source software and a lot of people do not have access to a Solidworks license, we decided to start migrating our designs to an open-source alternative and more precisely to FreeCAD.

We have already designed 2 versions in Solidworks 2014. The first version was fabricated using acrylic (Plexiglas) in a laser cutter as we mentioned in a previous log. You can find the appropriate files here.

The second version was fabricated using ABS in a 3D Printer as we mentioned in a previous log. You can find the appropriate files here.

More details can be found in our GitHub repository:

OpenBionics GitHub Repository | Prosthetic | FreeCAD Files

Introduction

We present the development of a breakout board for controlling our prosthetic hand. It is a PCB (printed circuit board) with pin headers to accomodate two different servo motors (standard servo and herkulex). It can have both analog inputs (e.g., EMG signals) and digital inputs (e.g., buttons for RobotHandExtension). An I2C bus can also be used in order to connect sensors like the takktile or other servos such as the openservo. The breakout board has also external pins for development.

The main microcontroller we currently use is an Arduino Micro Pro, equipped with an ATmega32U4 core. The PCB can be powered by an external power supply or a battery.

The board is currently under testing. Pictures of the board and its development process can be found below.

Pinout

The Pin Mapping of the breakout board.

Board Development

The development of the breakout board was done using the facilities of the Athens Hackerspace (Thanks!!!). Some photos of the development process and the final result.

The OpenBionics Electronics Library can be found here.

Arduino Firmware

In order to evaluate the capabilities of our prosthetic hand, we developed a simple firmware for Arduino using this library for Herkulex DRS-0201.

We modified the library in order to control the motor with an Arduino Micro Pro.

Next Steps

We plan on controlling our prosthetic hands with different interfaces, such as these or EMG sensors.

A schematic depicting the high-level control architecture of our prosthetic hands can be found below.

Introduction

The OpenBionics initiative (www.openbionics.org) was founded back in 2013 with the scope of providing open-source, affordable, light-weight robot and prosthetic hands. Our first hands were non-anthropomorphic 2, 3 and 4 fingered robot hands. In this log, inspired by the fact that in every day life tasks most amputees use simple hooks, we present simple, non-anthropomorphic robot hands that can serve as hook alternatives. These hands cost less than 100$ and weigh less than 200 gr.

Bioinspired Robot Fingers

The design is based on the same simple but yet effective idea: to use agonist and antagonist forces to implement flexion and extension of robot fingers, following a bioinspired approach. In this design steady elastomer materials (silicone sheets) are used to implement the human extensor tendons, while cables driven through low-friction tubes implement the human flexor tendons .

The structure of one robot finger is presented. The elastomer materials appear at the lower part of the image (white sheets), while the low-friction tubes (used for tendon routing) appear at the upper part of the image (white tubes) together with the rigid phalanges.

Modular Fingers Basis

Each robot hand has a modular fingers basis equipped with 5 slots that can “accommodate” a total of four fingers. Hands with various geometries of finger base frames, can be developed. Line and 2D polytope geometries are easily created, while for 3D polytope geometries finger bases with different heights have to be used (to create vertical offsets).

Disk Shaped Differential Mechanism

A disk-shaped differential mechanism was developed, in order to connect all the independent finger cables with the single actuator. The differential mechanism allows for independent finger flexions in case that one or multiple fingers have stopped moving, in case e.g., that they are already in contact with the object surface.

For the assembly of the robot fingers we use once again fishing line and needles in order to stitch the silicone sheets onto the rigid links (the links have appropriate holes by design).

Experimental Validation

In this section we present an experimental validation of the proposed simple robot / prosthetic hands. Most of the videos focus on robotics applications that demonstrate the robustness of grasps under object position and orientation uncertainties, but an EMG based control paradigm is also provided.

The first video presents a series of possible applications for the proposed hands. Among them, a three-fingered robot hand is used as a myoelectric prosthesis (by an able-bodied person) and the subject grasps using the myoelectric activations of his forearm muscles, two different objects.

The second video presents autonomous anthropomorphic grasp planning experiments using a four fingered hand. The robot hand efficiently grasps, a series of everyday life objects, even under position uncertainties.

The third video presents a three fingered robot hand mounted on a KUKA YouBot.

The forth video presents the Grebenstein test, where a user hits the robot hand fingers with a hammer in order to prove their robustness again impacts.

Tutorial

A tutorial for the replication of our hands, can be found here!

CAD Files

In this section we provide the cad files (Solidworks .sldasm, .sldprt and .dwg, .dxf, .stl), for the replication of the design.

A new version of our design is under development and can be found in our GitHub repository:
OpenBionics GitHub Repository

Description

Recently, we presented a methodology based on computational geometry and set theory methods for quantifying anthropomorphism of robot hands [1]. The idea was simple, to use the human hand as a reference for assessing the humanlikeness of robot and prosthetic hands in terms of both motion capabilities and morphology. This study was motivated by the fact that the objects and the environments surrounding us have been crafted in order to be used by the human hand, nature's most versatile and dexterous end-effector.

For this project we chose to design our prosthetic hand to be as anthropomorphic as possible, in order to maximize also its ability to grasp everyday life objects. For doing so, we used the index of anthropomorphism that we proposed in [1] and which provides a normalized score of human-likeness that ranges between 0 (non-human-like) and 1 (human-identical), together with parametric models derived from hand anthropometry studies [2]. Thus, we managed to conclude to a design that is considered human-like in terms of: 1) the selected finger phalanges lengths and 2) the positioning of the finger base frames.

In the following figure, the finger base frames workspaces are depicted for the human and different robot hands.

Another approach / methodology that can be used for the quantification of anthropomorphism of robot and prosthetic hands has been proposed by Feix et al and can be found in [3].

More details can be found at the following URL:

OpenBionics Affordable Prosthetic Hands: Anthropomorphism

References

[1] M. V. Liarokapis, P. K. Artemiadis, and K. J. Kyriakopoulos, “Quantifying anthropomorphism of robot hands,” in IEEE International Conference on Robotics and Automation (ICRA). IEEE, 2013, pp. 2041–2046.

[2] B. Buchholz, T. J. Armstrong, and S. A. Goldstein, “Anthropometric data for describing the kinematics of the human hand,” Ergonomics, vol. 35, no. 3, pp. 261–273, 1992.

[3] T. Feix, J. Romero, C. H. Ek, H. B. Schmiedmayer, and D. Kragic, “A metric for comparing the anthropomorphic motion capability of artificial hands,” IEEE Trans. Robot., vol. 29, no. 1, pp. 82–93, 2013.