Industrial Project Gary ANDRIEU Guillaume BLIN François GIRAULT Adriana SODRE DEL PRA NETTO
Development of a mechanical prosthetic hand In partnership with Association My Human Kit
Represented by Nicolas Huchet - BionicoHand
Industrial Project: Development of a mechanical prosthetic hand
Abstract Development of a mechanical prosthetic hand The Mecanicohand is a project create by Nicolas Huchet based in building a whole mechanical hand prosthesis that has to achieve some well defined goals: it must be easily repairable, replicable, esthetic, low-cost and the project must be open source. The main aim of it is conceive suitable prosthesis for every disable person in the world, so even the most needed can download, build and/or pay for their own hand. In this context, Nicolas established a partnership with fifth years from INSA Rennes to built this idea, with a satisfactory prosthesis as result, but that could have even better lock and thumb orientation system. In order to improve these areas, two new groups of students, this time from fourth year, developed, without testing, new systems. Now, our group’s tasks were to test the new ideas and to do bigger progress with the project. We worked on the lock and thumb orientation system, in order to enhance the systems of fourth years students, and also to make the prosthesis even more suitable to the defined goals. Improving the size and adapting components of the lock system, we were able to produce more hold strength with a lower force applied by the user and make it more robust. In the thumb context, we were able to perform a bigger aperture with a groove and a ball plunger and also to improve the lock position of it with help of magnets. Your results were really satisfactory, since they are easier to use and since they achieve all the defined goals.
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Industrial Project: Development of a mechanical prosthetic hand
Resumé Dévelopement d’une prothèse de main mécanique La main mécanique (ou Mecanicohand) est un projet créer par Nicolas Huchet basé sur l’élaboration d’une prothèse de main entièrement mécanique ayant pour but de remplir plusieurs objectifs : Elle doit être facilement réparable, reproductible, esthétique, son coût de production doit rester faible et le projet élaboré devra être Open Source. En outre, le principal objectif à terme, est de concevoir une prothèse pour toutes les personnes en besoin dans le monde. Ainsi chacun d’entre eux pourra télécharger le fichier élaboré, construire et/ou payer pour leur propre main. C’est dans cette optique que Nicolas a lié un partenariat avec des élèves de 5ème année de l’INSA de Rennes. Leur travail consistait à mettre en oeuvre la réalisation de cette main en se focalisant sur le système de blocage et sur l’orientation du pouce. Dans le but d’améliorer ces deux aspects, par la suite, deux groupes d’étudiant de 4ème année ont développé un nouveau système sans toutefois le tester. Cette tâche, ainsi que le perfectionnement des différents mécanismes, est revenue à notre groupe. Ainsi nous avons principalement travaillé sur le système de blocage et sur l’orientation du pouce dans la continuité du travail des 4èmes années. D’autres améliorations ont également pu être réalisées afin d’atteindre les différents objectifs de départ. En améliorant la taille et la forme des différents composants du système de blocage, nous avons pu augmenter considérablement la force de maintien tout en ayant une force d’application plus faible par l’utilisateur. Ce système est ainsi plus robuste et plus ergonomique qu’auparavant. Pour l’orientation du pouce, il est maintenant possible d’avoir une ouverture suffisamment grande grâce à l’utilisation dâune came. Le système d’indexation a quant à lui pu être réalisé avec des aimants. Toutes ces améliorations se sont retrouvées très satisfaisantes puisqu’elles permettent d’avoir une prothèse plus robuste, facile dâutilisation et qui remplit parfaitement le cahier des charges stipulé au départ.
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Industrial Project: Development of a mechanical prosthetic hand
Contents Introduction
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1 Project Overview 1.1 Presentation of Bionicohand/Mecanicohand . . . . . . . . . . . . . . . . . . . . . 1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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2 The Clem’hand 2.1 Fifth Year Project . . . . . . . . . 2.1.1 Lock System . . . . . . . . 2.1.2 Thumb Orientation System 2.1.3 Assembly . . . . . . . . . . 2.2 Fourth Year Project . . . . . . . . 2.2.1 Lock System . . . . . . . . 2.2.2 Thumb Orientation System
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3 System limiting the friction losses and increasing the closing force 3.1 First prototype: Last semesters innovations . . . . . . . . . . . . . . . . . . . . . 3.2 Second prototype: enlargement of the primary wheel . . . . . . . . . . . . . . . 3.3 Third prototype: guide for the rope . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Fourth prototype: pulley transmission for the thumb and alignment optimization of the secondary ropes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Fifth prototype: Final modifications . . . . . . . . . . . . . . . . . . . . . . . . .
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4 Thumb orientation 4.1 Modification before the first printing . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Second prototype: Increasing of the system’s dimension . . . . . . . . . . . . . . 4.3 Third prototype: Addition of the magnets for the indexing . . . . . . . . . . . . . 4.4 Fourth prototype: Improvement of the contact between the mobile part and the first phalanx of the thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Final prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5 Hand’s improvements 5.1 Locking system . . . . . . 5.2 Assembling of the primary 5.3 Choice of the elastic . . . 5.4 Choice of the magnets . . 5.5 Others elements related to 5.6 Finger control system . . 5.7 Enlargement of the fingers
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6 Project Management
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7 Study Of The Costs
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Conclusion
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Industrial Project: Development of a mechanical prosthetic hand
List of Figures
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Industrial Project: Development of a mechanical prosthetic hand
Introduction Between the industrial projects of the fifth year, we decided to participate in the improvement of a mechanical prosthetic hand. The project, created by Nicolas Huchet, is to optimize the work of the previous year, mainly the blocking system and the thumb indexing, respecting Nicolas requests: the hand should be easily repairable, replicable, and esthetic and have a low cost to manufacture. Our goal is, in the final end, having Nicolas approval to ours new systems. After studying past projects and look for other solutions, we have made the necessary changes and printed new prototypes of the hand. In this report, we describe all the stages of design the prototypes, explain the improvements of each one and compare them with the help of specifications. Finally, we will make the financial review of the project.
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Industrial Project: Development of a mechanical prosthetic hand
Chapter 1
Project Overview 1.1
Presentation of Bionicohand/Mecanicohand
The Bionicohand project is directed by Nicolas Huchet, who had his right hand amputated after an accident in 2002. The project consists in a prosthetic hand that must be adapted to the daily lives of people with disabilities. After his accident, Nicolas discovered the difficulty in finding a prosthesis that suits him. He now has a myo-electric hand that is relatively heavy, not practical for everyday life, unsightly and difficult to repair. Most modern implants have extremely high prices and are not reimbursed by social security, preventing its acquisition. In 2012, Nicolas met the makers of LabFab Rennes and discovers the open-source projects using 3D printers. With this new knowledge, he had the idea to produce an open source robot hand. In 2013, he developed the Bionicohand project to create his own prosthesis and offer it to other people with disabilities. In partnership with the LabFab Rennes, he downloads the robot hand InMoovof Gael Langevin (robot creator) that is fully available online and, via a 3D printer, produces a first hand. Latter, he fits this form of prosthesis to be controlled by muscle sensors which are connected on his arm. With his new conquest, Nicolas participated in several exhibitions, winning awards and became internationally known. In 2014, he created the association MyHuman Kit, which give the project a legal status and allow attract funding and collaborations with universities and research centers. Then, Nicolas has the idea of separating the project into two: a themed party for myo-electric prosthesis (Bionicohand) and other committed to the creation of a fully mechanical prosthesis (Mecanicohand). The first is controlled via muscle sensors placed on the arm and the second is controlled by a cable connected to a harness fixed to the body. The idea of developing a mechanical prosthesis is to become more robust and to have more strength, durability and less maintenance. As it would not have a motor, its weight and its costs will be minor, allowing access for people with limited financial resources or people who do not have social security coverage. Also in 2014, Nicolas entrusts to fifth graders from INSA Rennes the realization of the Mecanicohand project. They accomplished a prosthesis that meet all the objectives of the project, but that can be further improved. In this context, in 2015, two groups of fourth year have studied separately two different systems: the hand locking system and the thumb orientation system. Both have found good ideas for the project, however, they still need to be printed and tested on a prototype. Our part in this project is to improve the existing prosthesis, using the studies of fourth graders and seeking new changes. We must also continue to meet the goals of the Mecanicohand idea and ensure that the use of the hand is always easier and more comfortable for people with disabilities.
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Industrial Project: Development of a mechanical prosthetic hand
1.2
Objectives The main objectives of the project are:
• Technical Objective: improve and produce a mechanical prosthesis with several possibilities of movement. • Humanitarian objective: make the open source project to be broadcast internationally, with the help of NGOs, for the neediest. • Financial objective: to make a low-cost project in which the cost of the prosthesis must be less than 400e. • Social objective: enable the collaboration of professionals from several different areas and nationalities in the same project. • Personal Nicolas Goal: to have a new prosthesis that suits him and also suitable for others. The main reasons to seek improvements for previous projects are reduce the complexity of the locking system and the force that must be exerted to close the hand, and enable a greater opening of the thumb as well as having an easier system for the change of its positions. The idea of an open source project is letting the hand models being modify and improved by any person interested in the opportunity to participate in community development. This allows the collaboration of various professionals from different backgrounds, adding new techniques and new ideas to the project. This way, the progress is carried out as a volunteer, no financial return, while ensuring a low-cost project. Then, it ensure that a larger number of persons has access to the project and democratize the technology. In addition, it keeps the opportunity for Nicolas participation in the project, without the pressure for results related to large companies. Finally, the LabFabs, with its 3D printers, are beginning to spread all over the world. This helps to disseminate our project technology to a huge amount of people with disabilities who could never otherwise possess.
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Industrial Project: Development of a mechanical prosthetic hand
Chapter 2
The Clem’hand 2.1
Fifth Year Project
The Clem Hand project was developed last year for the fifth year students from INSA Rennes Benjamin Rapp, Julien Courgeon, Caillebotte and Quentin Thibault Roussel. They used the software CATIA to do the computer aided design (CAD) and the 3D printer to manufacture the prototypes. The final prototype of this project and its operation are described below. The hand is composed of 16 pieces: a palm, a hood, 5 phalanxes numbered 1 to 5 with nails corresponding to the fingertips, 5 phalanxes numbered 1 to 5 corresponding to the end of the fingers, a interface palm/thumb, a rivet, a carriage and a bar, all of which can be seen in the Picture 2.1 below.
Figure 2.1: Last year prototype
Inside of each finger there are two passages: the first is localizing above and is where pass the elastic cable; the second is located in the bottom and is attributed to the braided cable. The elastic cable helps the system to come back to the rest position and has shown to be a robust and fast solution, as well as esthetic solution, since the cable does not appear externally (Figure 2.2). The braided wire belongs to the blocking system, which will be soon described in the sub item below. In addition, the fingers have esthetics characteristics and have a more robust and precise kinematics, beside of being ergonomics. 4
Industrial Project: Development of a mechanical prosthetic hand
Figure 2.2: Diagram of the fingers
Finally, the palm and the hood have also assured their esthetic, their adaptation to the person amputee and also with the arm interface, their easy access to the lock system and the lightness.
Figure 2.3: Diagram of the palm and the hood
2.1.1
Lock System
The locking system consists of a rod and a carriage with stair notches. The purpose of this system is to provide a progressive block of the hand in different positions, generated by the rotation of the top of the rod, which remains above the hood, by the user. The braided cable of each finger is attached to the gray parts of the Figure 2.4, shown in the region 1, and there is a wire coming out of the carriage that goes into the hole 5 of the Figure 2.3. Thus, when the user pulls the wire, the hand closes and he can lock it in the desire position by turning the bar. This system has its effective confirmed with several locking positions, with an automatic locking, with its accessibility, it easy use (with the arrow at the end of the bar to indicate the active blocking) and its discretion, since only one small part of the rod can be seeing above the hood.
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Industrial Project: Development of a mechanical prosthetic hand
Figure 2.4: Lock System
2.1.2
Thumb Orientation System
Indexing of the thumb is done with the junction of the pieces of interface palm / thumb and the rivet. The interface parts possibility the rotation of thumb for different positions and the rivet is used to block it in each of the positions. This last piece is placed between the zones 2 and 3 of the Picture 2.5. The user must pull the rivet to unlock the thumb and conduct the rotation of the thumb to another desired position, where he/she can release the rivet to block once again. This system ensures less mechanical slack between the thumb and palm during movement and also ensures the robustness of this part besides a easy and accessible use of the rivet.
Figure 2.5: Diagram of the thumb
2.1.3
Assembly
In general, the prototype performance meets the majority of applications. It reach all the necessary positions, being them the rest position (open hand), the side pincer (closed hand with the thumb pivoted by 90 ◦ turn) and the large pincer (closed hand with the top of fingers together); lock and thumb indexing systems are functional; the effort required to close the hand is less than 70N; the hand adapts well to the interface element with the amputated arm; the prosthesis is esthetic and the project is low-cost (the overall cost was less than 300 ) and use easily replaceable standard parts. Yet, there are still some areas for improvement. The main ones are that the opening of the thumb must be improved in order to enable it to achieve a larger aperture and, in addition, the locking system is not sufficiently robust and convenient.
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Industrial Project: Development of a mechanical prosthetic hand
Figure 2.6: Final prototype
2.2
Fourth Year Project
With the objective of improving the project carried out for the fifth year, two student groups of the fourth-year searched alternatives for the prosthesis. The studies of the locking system and the thumb indexing system were made independently for each group, and, for that reason, they were not assembled or printed.
2.2.1
Lock System
The lock system was developed by the students Pierre-François Durbecq, Chloé Fauvel, Fanny Pernelle and Antoine Rioual. Their idea was to create a cylinder connect to the fingers by cables and crossed by an axis, so it could rotate. When it happens, the cylinder brings the cables in translation and the fingers move. As we can see, in the Picture 2.7 below, parts 1 are for the fingers, part 2 for the thumb, part 3 is attached to cable that is connect to the shoulder of the person and part 4 is a component of the lock system.
Figure 2.7: Cylinder from Lock system
The lock system works with the help of a switch, which fits in the toothed wheel on the cylinder. The main idea is, when the switch is pressed, he block the cylinder rotation and block the hand in one position. The contact between the switch and a cylinder tooth is maintained thanks to threads efforts, which create a tightening torque. It’s possible to see the lock system and the switch with the toothed wheel in details in the Pictures 2.8 and 2.9 respectively. 7
Industrial Project: Development of a mechanical prosthetic hand
Figure 2.8: Final lock system
Figure 2.9: Switch and the toothed wheel
The bascule and the tappet indicated in the Picture 2.10, helps to hold the switch in one position. The tappet is attached to the palm and to the bascule, which is connected to the switch. The tappet pressure pushes the bascule and the switch, and, in the lock position, the bascule is stopped by cylinder tooth, establishing a moment around the rotation axis and retaining it in position. In free position, the bascule is blocked by an abutting.
Figure 2.10: Lock system forces diagram
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Industrial Project: Development of a mechanical prosthetic hand
2.2.2
Thumb Orientation System
The group of the students Antoine Duvernay, Clément Ferrec, Paul Mulotand and FrançoisLouis Toulemonde worked at the movement system of the thumb. Their idea was create a groove to guide the thumb trough it positions, with the help of a ball plunger, as it’s possible to see in the Picture 2.11. In order to hold the positions and to ensure a good gripping ability of the thumb, they created ball housings, which can also be seeing in the Picture 2.11 .
Figure 2.11: Ball plunger (left) and the guide and ball housings (right) from the thumb orientation system
Finally, it’s possible to see the whole system below, in Picture 2.12.
Figure 2.12: Final lock system (left) and its details (right)
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Industrial Project: Development of a mechanical prosthetic hand
Chapter 3
System limiting the friction losses and increasing the closing force One of the main problem in the previous version of Clem’Hand was the required force to close the hand and to hold an object. As explained in the first part we had a single trolley that translated in one direction in order to perform the closing movement. The issue with this kind of actuator is due to the fact that a finger (the thumb) is in opposition with the four other. In addition to that there was no real device to change de direction of the force provided by the rope. This rope passed over a sharp angle and changed direction.
3.1
First prototype: Last semesters innovations
The first design is mainly based on the improvements studied by a team of INSA student last semester. These studies were never printed it were thus the first model that we printed. This developments have been explained in the first part of this report. They were the starting point of our work on Clem’Hand.
Figure 3.1
The picture below show the path followed by the rope on the first prototype we can still see a couple of sharp angle. On the other hand on the previous prototype there was only one angle now the changing of direction is made by two angles to make it smoother. The other problem that we immediately see is the incorrect winding around the secondary wheel. Indeed the rope axis is not perpendicular with the wheel axis. 3D printing this prototype made us realize that something could look great on Catia but turn out to be not as good as expected. We also figured out that it is necessary not to forget the mounting part of the work. A design has to be efficient but also easy to mount.
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Industrial Project: Development of a mechanical prosthetic hand
3.2
Second prototype: enlargement of the primary wheel
The aim of this prototype was to lower the required force to close the hand and so to increase the closing force developed by the hand. This finally aims for better control of holding an object. Based on the idea found on previous semester we choose to increase the diameter of the primary wheel to change the transmission ratio. Theoretically this increase the travel of the rope on the primary wheel and deceases the traction force. To make sure that the new wheel would fit in the housing we had to change the shape of the bottom of the palm. The transmission ratio is given by: Fs=(Rp/Rs)Fp Fp: Primary force (necessary) Fs: Secoundary force (produced) Rp: Primary radius Rs: Secondary raduis (4.5mm) In the first case we had Fs=1.3Fp (Rp=6mm) and we have Fs=1.9Fp (Rp=8.5mm) in the second case.
Figure 3.2
Finally the modification appears to be a real improvement indeed the required force has been approximately divided by two. Thanks to this we can hold bigger things. It also appears that we have a far better control of the hand, we can hold small objects as well. Theoretically we could even more increase the diameter of this wheel to lower the force but we are restricted by the size of the palm.
Figure 3.3
On this picture we can see that the bottom of the palm has been flattened to clear some space for the primary wheel.
3.3
Third prototype: guide for the rope
As explain previously we are restricted by the dimension of the housing and we can’t obtain a better transmission ration. Thus it is necessary to find a new improvement clue to increase the closing force. By observing carefully the prototype we realise that the thumb rope still passes over a sharp angle. This kind of configuration is really bad for the mechanism indeed it causes a lot of friction and friction means loss of force and wear on the angle. The first considered solution was adding a circular guide around the edge. 11
Industrial Project: Development of a mechanical prosthetic hand
Figure 3.4
As shows the picture above the rope is completely leaded by the guide. The previous prototype also shows us that sometimes the ropes doesn’t roll up correctly around the primary wheel. Indeed we can’t add flanges as on the sides of the secondary wheels to ensure the correct winding due to the lack of space. So it is decided to add another guide on the primary rope the ensure the correct winding.
Figure 3.5
This prototype shows usefulness of the different guides inside the palm. First the closing movement is even smoother and allows us to hold small items very easily. On the other hand the different rope are well guided and the inside of the palm is very clean.
3.4
Fourth prototype: pulley transmission for the thumb and alignment optimization of the secondary ropes
The concept of guide is interesting but we decided to go further in the design of this prototype to limit the friction losses for the thumbs rope. Next innovation consists in adding a pulley in the circular guide. We enjoy the fact that 3D Printing allows us to create this kind of complex structures. It works according to the returns of corner principle.
Figure 3.6
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Industrial Project: Development of a mechanical prosthetic hand
On this prototype we finally decided to better align the secondary ropes that actuates the fingers 1 to 4. Indeed we realized that this was a little problem of the previous version. We added small guides at the beginning of the secondary ropes and the shape of the secondary wheels have changed. This is no big change but everything has to be optimised to make the prototype very efficient. It also makes the palm cleaner because every rope is guided.
Figure 3.7
3.5
Fifth prototype: Final modifications
On this last prototype the aim is to optimize every aspect without changing the overall design. Thus there are only small modifications performed at this final step. The first thing is the sharp edge for the thumb articulation; once again the rope passes through an angle. We designed a curve with a maximum curvature radius to minimize the friction between the plastic and the rope.
Figure 3.8
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Industrial Project: Development of a mechanical prosthetic hand
The second optimization concerned the guides for the secondary ropes. On previous prototype the guide were not designed as straight lines as you can see on the first picture below. We design a straight path to limit the friction in these guides on prototype five. The main modifications are on the guides at extreme right and left.
Figure 3.9
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Industrial Project: Development of a mechanical prosthetic hand
Chapter 4
Thumb orientation As presented previously, we have begun from the work of the 4GMA students. The idea retained was to use a cam system to increase the opening of the thumb. The cam profile was designed with 3 grooves so that indexing the thumb in 3 different positions and the mobile part of the system was composed of 3 different parts: a 1.6mm diameter steel rod, a washer and a mechanical stop in order to add a spring to maintain the indexing ball on the cam profile.
Figure 4.1: Global view of the system, cam profile and mobile part of the system
4.1
Modification before the first printing
But the cam system was too small for the 3D printer. We decided to increase the dimension of the stem (from 1.6mm to 3mm) in order to completely 3D print the stem and to create a 2 parts unit for the stem composed of a monobloc unit which integrate the washer with the bar and an over part with the mechanical stop. We didnât modify the cam profile; we just increase the width to fit the rod diameter. The first prototype allow us to demonstrate that the cam system works quite well but was too small, with small parts not enough robust even with the first increase of the dimensions of the system. Moreover, the stop wasn’t really necessary for the functioning of the cam system. 15
Industrial Project: Development of a mechanical prosthetic hand
Figure 4.2: Mobile part of the system of the first prototype
About the indexing function, the 3D printer didnât allow us to have a good surface quality with precise groove for the cam profile. We discussed at this design step about the possibility to have a separation of the string in two after the wrist, one part for the thumb and the other one for the 4 last fingers. It could have allowed us to separate the closure force between the thumb and the 4 other fingers. But this idea was abandoned, because of the locked system, placed on the bar in the middle of the palm. Therefore, only one string had to be fixed to this bar in order to lock all the fingers at the same time.
4.2
Second prototype: Increasing of the system’s dimension
For the second prototype, we decided to increase again the dimension of the cam bar in order to have a more robust piece and to remove the mechanical stop which was useless. Moreover, the cam bar did not allow a maximal opening of the thumb. We also increase the depth corresponding to the last position of the thumb in order to increase the opening of the hand, the width of the cam profile and the diameter of the grooves for the indexing. Because of the increasing of the dimensions of the system, we had to reduce the number of indexing position from 3 to 2.
Figure 4.3: Mobile part of the system and cam profile of the second prototype
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Industrial Project: Development of a mechanical prosthetic hand
4.3
Third prototype: Addition of the magnets for the indexing
Despite the increase of the diameter of the groove for the indexing to the maximum size, the 3D printer didnât allow us to obtain a well indexing for the cam system. The thumb can stay in the 2 wanted position because of the assembly of the hand (crimping of the thumb with the palm), but this solution was not viable. We had to abandon this solution of indexing with groove. We have designed a solution of indexing with magnets which could be easy to assembly and simple to implement. 2 magnets are simply fixed in the palm and 2 other in the mobile part of the thumb with glue. This system allows the amputee to choose between the opened and the closed position of the thumb by switching between the 2 couple of magnets. We can also increase again the opening of the hand by increasing the depth of the cam profile. We decided to completely re-design the cam profile on the GSD workshop on CATIA because this realized by the previous students was designed for a small pieces and a small rod, we had reached the limit and it was not simple to modify and to increase again the dimension of the profile.
Figure 4.4: Complete orientation system of the thumb with magnets and zoom on the palm and the thumb on the third prototype
Because of the modification of the cam system rod shape, we had to modify the first phalanx of the thumb in order to fit the shape of the extremity of the rod. We created a small circular groove in the phalanx (in orange in the figure â). This system worked quite well but we noted some point to be improved. Firstly, the mobile part of the cam system was in contact with the elastic band of the thumb. It was a difficulty to assemble the prosthesis and it disturbed the functioning of the system. Moreover, we wanted to try the cam system without string as the mobile part was pressed again the cam profile by the elastic band. That is why we designed a new mobile part of the system (Figure â). 17
Industrial Project: Development of a mechanical prosthetic hand
Figure 4.5: Modification on the first phalanx of the thumb on the third prototype
4.4
Fourth prototype: Improvement of the contact between the mobile part and the first phalanx of the thumb
The addition of material on the first phalanx of the thumb was not satisfying, therefore we decided to design a bigger groove to enveloping the mobile part of the cam system (in orange on the picture â). The holes for the magnets were too small, we increased the diameter of the holes but because of the lack of space on the palm, we decided to add material on the edge of the palm in order to hide the magnets (in orange on the Figure â).
Figure 4.6: Modification on the mobile part, the first phalanx of the thumb and the palm on the fourth prototype
The mobile part of the system was really better with this new shape and the addition of material on the first phalanx of the thumb and on the palm was a success. But for the last prototype, we decided to improve the aesthetics of the hand by smoothing this addition of material. Moreover, we noticed a problem with the mobile part of the cam system. The washer included in the monobloc used to block the spring, also served to avoid the mobile part to leave his compartment. We decided to put back the washer on the mobile part but without adding a spring.
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Industrial Project: Development of a mechanical prosthetic hand
4.5
Final prototype
In this final prototype, we solved the last problems with the shape of the first phalanx of the thumb, the insertion of the magnets and the mobile part of the cam.
Figure 4.7: Last modifications on the thumb orientation
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Industrial Project: Development of a mechanical prosthetic hand
Chapter 5
Hand’s improvements In this part, we will detail all the improvements which were doing to the hand to make it most robust and ergonomic as possible to facilitate the assembly and the printing to.
5.1
Locking system
After printing the first prototype, we saw the leak of robustness in the locking system. Therefore we had the system grow as we can see below:
Figure 5.1: Locking system of the prototype 1
Figure 5.2: Locking system of the prototype 2
Thus, the printing and the assembly are easier than before.
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Industrial Project: Development of a mechanical prosthetic hand
5.2
Assembling of the primary wheel At the beginning, this assembly is made by crimping:
Figure 5.3: Primary wheel for the prototype 1
We could also note that the aesthetic of the hand at this place could be improved because the rod protrudes from both side of the palm. In order to solve this problem, we decided to create a groove as we can see below. Thus, it just needed to clip the primary wheel. The force are taken parallel to the surface, this solution is not a problem for the operation of the mechanism.
Figure 5.4: Primary wheel for the prototype 2
5.3
Choice of the elastic
The choice of the elastics was an important thing during the evolution of our hand. Indeed, they let to bring back the fingers at their initial position more or less quickly in function of the thickness, the stiffness and the type of the elastic. The first elastic used (at the right on the figure below) were not enough thick (1.5mm) and were surround by a tissue coating. Consequently the finger didn’t come back quickly. Then, for the third prototype, we have chosen the elastic at the left on the figure below. These were thicker and stiffer than before with a good resistance over time.
Figure 5.5: Comparison of the elastic
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Industrial Project: Development of a mechanical prosthetic hand
5.4
Choice of the magnets
For the third prototype, we decided to choice an indexing with magnets for the thumb. These magnets have respectively a diameter of 6mm and a thickness of 2mm. This choice was wise because the prototype after printing assured all the tasks asking. Nevertheless, it could be interesting to increase the thickness which will allow to increase the force.
5.5
Others elements related to the robustness and the assembly
During the building of the first prototype, we saw that the crimping damaged the finger. After studying of the cracked, we noted that it was due to the position of the layer of printing. Indeed, the choice of the orientation of the layer is important in order to avoid it:
Figure 5.6: Good and bad orientation of the layer
The layer must be perpendicular to the axle of the crimp rod in order to avoid the slipping of pieces after printing.
5.6
Finger control system
For the first and the second prototype, the control of the tension of the rope was assured by simply knots between the end of each finger and the primary wheel. It was very rough. Thatâs why we had the idea to put a cable ties at the end of each finger:
Figure 5.7: Before putting cable ties; prototype 2
Figure 5.8: After putting cable ties; prototype 3
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Industrial Project: Development of a mechanical prosthetic hand
Moreover, we decided to put the set screw in front of each nails in order to not damage the aesthetic of the hand:
Figure 5.9: Set screw in front of each nail
This system is very convenient because it allows to control easily the tension inside the rope.
5.7
Enlargement of the fingers
For the 5th prototype, we want to improve the robustness between palm and fingers. In order to do that, we decide to grow the attachment as we can see on the figure below.
Figure 5.10: Before and after the change
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Industrial Project: Development of a mechanical prosthetic hand
Chapter 6
Project Management The first thing that has to be done in this part is the Matrix WBS, that consist on separating the project in several parts and tasks, as it is possible to see in the Picture 6.1 above.
Figure 6.1: Matrix WBS
The next step is building a Gantt’s Diagram, with help of the software Excel, in order to plan the whole project developing. The first diagram done can be seeing at Picture 6.2. However, the progress of the project did not follow exactly this dates, so another diagram had to be done. The new Gantt’s Diagram are show at Picture 6.3 . The differences between both diagrams were basically because the group did more prototypes than first expected. Although the change in the planning, it has helped the group to explore and/or find several new improvements for the prosthesis, becoming possible to make better choices on materials and solutions. It also worth remembering on December 18t h, it
24
Industrial Project: Development of a mechanical prosthetic hand
Figure 6.2: Frist Gantt’s Diagram
Figure 6.3: Final Gantt’s Diagram
started the Christmas vacation, preventing the group to print the fourth prototype before January 6t h. In the end, the final date to deliver the project did not change excessively and this change has helped the group to develop a better prosthesis.
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Industrial Project: Development of a mechanical prosthetic hand
Chapter 7
Study Of The Costs We will now measure and quantify the work done as part of our project. In order to better organize it, we will divide it in three parts: the study cost, the print cost and the material cost. The first part consists in the hours of work of the group. Each student spent around 110 hours working in the project, counting the schedule work and the time spent at home. It give us a total of 440 hours. Then, to calculate the hourly rate of our mission, we searched that the average salary of a junior engineer is 38,000 egross for a total of 1,600 hours in a year. That means a tax of 23.75 efor hour. Adding the employer contributions at 40 %, we get 33.25 e. Finally, multiplying this for the total of hours, we get a total price of 440 hours x 33.25 eper hour = 14,630 e. The second part is the printing cost. The 3D printing cost at INSA Rennes is 1 e/cm3 , this including the price of the material and the support and also the price of the cleaning product. The total in cm3 of print material was 1,176.501 e, considering the 5 prototypes printed. In the end, the cost was 1 e/cm3 x 1,176.501 e= 1,176.501 e. The third part is the total cost of the materials that was around 24 e for the whole project (each prototype used around 6 efor the brass tube, cables, washer, rubber patch, spring etc). Lastly, the project total cost was 14,630 e+ 1,176.501 e+ 24 e= 15,830.501 e. Now, calculating the price for one CLEM’hand, we have 234.383 cm3 of printing material that give us a 1 e/cm3 x 234.383 cm3 = 234.383 ecost, and we have around 6 eof material (the detailed calculus of this part is shown in Annex ...). Finally, the total cost for one CLEM’hand is 258.42 e+ 6 e= 264.42 e.
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Industrial Project: Development of a mechanical prosthetic hand
Conclusion This report shows the improvements made this year on a long term project: Clem’Hand. The final prototype would not have been possible without the work of previous teams. This starting point for our studies has been explained at the beginning of this report. At the end of last year the external geometry of the hand was very interesting, we actually almost didnât changed it. This geometry was based on a tree-dimensional scan of a womanâs hand that makes it very close to the shape of a real hand. The main developments performed this year concerned the actuators of the fingers. In fact last yearâs prototype was almost unable to grab and hold an object. In this report are explained the different axis of amelioration on which we worked. Some of them are based on designs produced by a couple of team last semester. One of these designs is the complete change of the locking system that was not very efficient so far. The other one was a variable mechanical stop for the thumb. This system aims in indexing the thumb in two different positions and vary the maximum opening angle of this finger to make the hand look more human. The first prototype we printed showed us that these designs were interesting for the hand amelioration. Our work on the next prototypes was to make them easy to mount, reliable and optimize their efficiency. In the same time we developed some completely new ideas to make the hand easier to use. Some of this amelioration are very small but brought big improvements in the way you use this prosthetic hand. In fact this object is supposed to be low cost but also easy to build for everyone. During this part of the project we had to think the design on the use experience (UX) aspect. Indeed it is required that the prosthesis be adjustable with only one hand. For every prototype we had an immediate impression on the improvement as soon as we printed it. These phases of the project were very rewarding because they maintain a link between the theoretical design and the real object. As soon as a prototype was assembled we were able to know what we had to improve for the next one. The first conclusion of this project is that the prosthetic hand is really easier to use. Mainly we have done some real improvements concerning the closing force and precision. On that point the objective is reached, we can hold big object like a 1.5L water bottle but also tiny things such as a paperclip. Another objective for this prosthetic hand is to be low cost (less than 400e) and easy to mount. We can add that this objective is achieved, the global cost is indeed 250eif it is 3D printed but we can also imagine a mass production that could make it even cheaper. In addition the hand is quite easy to mount and contains only nineteen pieces. The material you need to build it is effortlessly findable in a DIY store or on the internet. Finally it is interesting to conclude concerning the project management aspect. It is important to say that working on this project was very rewarding for all of us. We improved skills on technical methods like computer design but also we developed our teamwork capacity. Indeed we found ways to divide the tasks even if we were working on the same CAD file. We divided the tasks in the way to best use each one’s skills. Therefore it was pleasant for all of us to work on this efficient and interesting project.
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Industrial Project: Development of a mechanical prosthetic hand
List of Figures 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11
Last year prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of the fingers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of the palm and the hood . . . . . . . . . . . . . . . . . . . . . . . . . . Lock System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagram of the thumb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Final prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cylinder from Lock system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Final lock system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Switch and the toothed wheel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lock system forces diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ball plunger (left) and the guide and ball housings (right) from the thumb orientation system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.12 Final lock system (left) and its details (right) . . . . . . . . . . . . . . . . . . . . 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9
10 11 11 12 12 12 13 13 14 15 16 16
4.7
Global view of the system, cam profile and mobile part of the system . . . . . . . Mobile part of the system of the first prototype . . . . . . . . . . . . . . . . . . . Mobile part of the system and cam profile of the second prototype . . . . . . . . Complete orientation system of the thumb with magnets and zoom on the palm and the thumb on the third prototype . . . . . . . . . . . . . . . . . . . . . . . . Modification on the first phalanx of the thumb on the third prototype . . . . . . Modification on the mobile part, the first phalanx of the thumb and the palm on the fourth prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Last modifications on the thumb orientation . . . . . . . . . . . . . . . . . . . . .
5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10
Locking system of the prototype 1 . . Locking system of the prototype 2 . . Primary wheel for the prototype 1 . . Primary wheel for the prototype 2 . . Comparison of the elastic . . . . . . . Good and bad orientation of the layer Before putting cable ties; prototype 2 After putting cable ties; prototype 3 . Set screw in front of each nail . . . . . Before and after the change . . . . . .
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Industrial Project: Development of a mechanical prosthetic hand
6.1 6.2 6.3
Matrix WBS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frist Gantt’s Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Final Gantt’s Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24 25 25
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Fiche prototype Nom du prototype/Version : Clem’Hand prototype1 Date : 07/11/15 Auteur : Guillaume Blin
Points positifs
Item
Description
Système de verrouillage
Les deux positions sont vraiment distinctes, le système est efficace et facile d’utilisation La force nécessaire a été considérablement diminuée grâce aux diamètres différents sur la « barre/bobine » Assemblage de la main relativement aisé
Force nécessaire à la fermeture
Assemblage
Amélioration
Item
Améliorations possibles
Système de ressort pour le verrouillage
Le piston/ressort s’est cassé, il sera nécessaire d’augmenter les dimensions pour plus de robustesse De système est inexistant sur ce modèle, il faudra l’intégrer dans les versions suivantes Les élastiques achetés sont trop faibles pour permettre un retour des doigts en position ouverte Le fonctionnement est valide mais les dimensions devront être augmentées pour plus de robustesse. Actuellement la butée ne permet pas une ouverture maximale du pouce, il sera nécessaire de repenser le chemin (plus profond ?) Ces objets devront être enlevés car inutiles. Modifier le trou du bouton de verrouillage (espace en avant pour la position verrouillé de 2mm et à droite pour laisser passer l’axe serti) Obtenir un meilleur alignement avec doigts des bobines d’enroulement (principalement l’index) Modifier la paume pour permettre d’augmenter le diamètre d’entrainement (meilleur rapport de transmission) L’huile utilisée attaque le plastique Trouver un type de rondelles et adapter les jeux pour faciliter la fermeture et l’ouverture
Indexation du pouce Elastiques de retour des doigts
Butée variable
Ergots sur le capot Capot
Barre/bobine
Huilage Rondelles pivots
Fiche prototype Nom du prototype/Version : Clem’Hand V2 prototype2 Date : 19/11/15 Auteur : Guillaume Blin
Points positifs
Item
Description Système de verrouillage
Les dimensions sont augmentées, les pièces sont plus robustes. L'assemblage est plus facile.
Force nécessaire à la fermeture
La force nécessaire a été considérablement diminuée grâce aux diamètres différents sur la « barre/bobine »
Barre de butée
Les dimensions ont été augmentés, on désormais une barre de gros diamètre plus robuste. Il faudrait augmenter la course de la butée. De plus il faudrait prévoir un espace pour le passage de l'élastique.
Elastiques de rappel
Les élastiques choisis sur ce prototype sont plus raides, le rappel des doigts en position ouverte est assez efficace. Il serait intéressant dans le prochain prototype d'essayer les élastiques de taille supérieure.
Amélioration
Item
Améliorations possibles Indexation du pouce
Le système est peu efficace sur ce modèle, il faudra le modifier dans les versions suivantes
Réglage des câbles
Le système de réglage des câbles par des noeuds utilisé sur ce prototype est difficile à mettre en oeuvre. l'idée sur le prototype suivant serait de pouvoir intégrer des serre câbles (dominos électriques) dans le bout des doigts.
Orientation du câble du pouce
Le câble du pouce passe par un angle vif sur une des arrêtes et ne vient pas s'enrouler correctement sur sa bobine. Il faudrait lui aménager un guidage afin de limiter les frottements et faciliter l'enroulement.
Barre/bobine Guidage du câble d'activation
Obtenir un meilleur alignement avec doigts des bobines d’enroulement (principalement l’index) Ajouter un guide
Fiche prototype 3 Nom du prototype/Version : Clem’Hand V2 prototype 3 Date : 02/12/15 Auteur : Gary ANDRIEUX
Points positifs
Items
Description Indexage avec les aimants
L'indexation est facile et simple d'utilisation. La force des aimants peut être augmentée en sélectionnant des aimants plus épais.
Modification de la came et du profil
La came épouse maintenant parfaitement la première phalange du pouce et l'augmentation de la profondeur du profil permet une ouverture plus importante.
Ajout des guides
Les guides permettent un bon guidage des fils et diminue la force nécessaire pour fermer la main. Les frottements au niveau du guide du pouce sont faibles et donc acceptables.
Serre câbles au bout des doigts
La mise en place des fils est simple et les différents réglages pour la fermeture de la main sont faciles.
Alignement des trous avec la tige
Les trous de la tige sont maintenant en face de ceux des doigts ce qui facilite la fermeture.
Améliorations
Items
Améliorations possibles Indexation du pouce
Serre câbles au bout des doigts
Fils au niveau des doigts
Course des doigts différentes
Pour le montage
La force d'indexation reste un peu faible. Possibilités : - augmentation de l'épaisseur des aimants - mise en place d'un indexage à bille - système avec un blocage complet
Faire en sorte de faire apparaître les vis de réglage au niveau des ongles (majeur et pouce). Regarder pour adapter des clips au niveau des ongles.
Attention à la sortie des fils au niveau des articulations lors de la fermeture de la main
La course du majeur est plus importante. Agrandir le diamètre d'enroulement du fil pourrait solutionner cela.
- Difficultés de montage de la barre au fond de la paume. - Diminuer les côtes sur CATIA plutôt que de limer les pièces une fois l'impression faite.
Gants
Mettre des gants plutôt que de coller des petits bouts de caoutchoucs.
Elastique pouce
Améliorer le passage de l'élastique au niveau du pouce (Tige, phalange).
Fiche prototype 4 Nom du prototype/Version : Clem’Hand V2 prototype 4 Date : 14/01/16 Auteur : Guillaume Blin
Points positifs
Items
Description Indexage avec les aimants
Les aimants sont mieux intégrés dans la paume et ne dépassent plus. En revanche il à été nécessaire d'agrandir les logements qui n'étaient pas adaptés aux aimants.
Poulie La poulie est un élément bien intégré dans la conception de la paume et facile de montage. Elle est utile on peut voir qu'au court de la fermeture elle effectue un quart de tours.
Serre câble D'un point de vue esthétique les vis de réglage sont mieux intégrées dans les doigts
Guides
Une série de petits guides permet un meilleur alignement des câbles des doigts vers la barre d'enroulement
Améliorations
Items
Améliorations possibles Came
Erreur d'impression
Le suiveur de came n'avait pas de butée sur ce prototype ce qui a pour conséquence une facilité de montage mais il peut se désolidariser de la main en position fermée.
Lors de l'impression du prototype un double fond à été créé sur la paume, nous ne connaissons à ce jour pas la cause de ce problème.
ASSEMBLY INSTRUCTION Summary I.
Tubes .............................................................................................................................................................. 4
II.
Locking system+pulley .................................................................................................................................... 5
III.
Fingers ............................................................................................................................................................ 7
IV.
Thumb .......................................................................................................................................................... 10
V.
Wires ............................................................................................................................................................ 11
This manual explains how to mount our Clem'hand named prosthetic hand. First the essential step to mount this hand is to have printed and washed (total dissolution of support) all the parts (19) necessary: Palm Cover Thumb base Finger tips: 1 to 5 finger phalanges: 1 to 5 Button Winding bar Piston: 2 tips Came shaft Pulley
In order to assemble the following hardware and tools are needed: Equipment: A 4mm diameter brass tube A 3mm diameter steel tube 20 washers 4mm inner diameter Braided wire diameter 1.2mm Round spring wire
