Myoelectric Exiii hand

 
Tutoriel
Make an Exiii HACKberry myoelectric right hand
  • Difficulty : Difficile
  • Duration : 2-3 weeks
  • Budget : 700 €
 

Foreword

Bionico project consists of the self-making of a myoelectric prosthesis (electrical hand prosthesis equipped with muscle sensors on the arm for control)

Since 2013, technological innovation have seen projects emerge such as Open Bionics (Bristol, England) or Exiii Hackberry (Japan) with the same target.
These actors on the new scene of 3D printing develop bionic hands. These prototypes are still limited for a daily use compared to models on the market, but they have the following features:

• The total cost of the prosthesis is less than 1,000 euros (10,000 to € 70,000 on the market)

• Items (fingers, palm and socket) are made of plastic with a 3D printer

• Plans of parts, list of materials and manufacturing tutorial are online in order to make the prosthesis and help develop it by sharing the results (open source)

From the GitHub link, we have made the Exiii hand at Fab Lab Berlin.

The total cost for all the pieces is about 700 euros, but if you have a 3D printer, you can reduce the total cost to 150 euros.

Here we summarize how we proceeded and hope it will encourage you to do the same. This project is difficult, you may need people around to help you, do not hesitate to go to a fablab and ask someone to join you.

& most important, have fun!

 

Bionico at Fab Lab Berlin

Video about:
- Nicolas Huchet's 3 months residency program at Fab Lab Berlin
- Decision to make the Exiii project
- Help from Makea Industries and consulting from Ottobock
- 2 versions of the project: Fablab and hybrid version

 

Summary

1- GitHub, what is it?

2- The components

3- 3D print hand elements

4- Wrist assembly

5a- Middle finger assembly set

5b- Middle finger assembly set (video)

6- Index assembly instruction set

7- Installation of 4 fingers on the palm

8- Motors protection

9- Thumb assembly instruction set

10- Set the thumb on the palm

11- Index’s motor assembly set up

12- Coupling 3 fingers + servomotor

13- Soldering components

14- Solder muscle sensor/mini jack

15- Voltage regulator adjustment

16- Insert electronic components in the hand

17- Upper limb 3D scan

18- Socket modelling

19- 3D print the socket

20- Wirst & socket assembly set up

21- Solder battery cable

22- Upload the arduino code

23- Final assembly

24- Fablab or hybrid version ?

25- Wrist disconnector assembly set up (hybrid version)

26- Electrical wiring (hybrid version)

27- Fablab version Vs Hybrid version

Conclusion

 

1- GitHub, what is it?

We are in 2016, Github is the social network that definitely changes our way to work. Follow the steps to get started, download the files and feel like a geek!!

 

2- The components

The material list inside the unzipped folder is in the file : HACKberry_BOM_v1.xls
As It was hard to find some of the components in Europe, we decided to buy them directly from the HACKberry team to save time.
To buy the components, send an e-mail to:
Genta Kondo: genta.kondo(at)exiii.jp

 

3- 3D print hand elements

We started to use 3D print softwares such as Simplify, Maker Bot or Cura and desktop 3D printers such as I3 Berlin and Maker Bot but we did not reach the required quality. We ended up using a Stratasys -Dimension- 3D printer and its associated software to make sure to get higher quality, especially for the small parts such as the finger ones.
This step explains the basic set up of a 3D print software such as Simplify.

 

4- Wrist assembly

First of all, screw the wirst on the palm base because once the elements are assembled on the hand (fingers, components), it becomes impossible to do it.

 
 

5a- Middle finger assembly set

This step explains how to make the 3 last fingers (middle, ring, little finger). Repeat the same operation 3 times is a good exercise to start. You can also find the official vidéo from Exiii HERE

Let's go!
- Adjust the holes that will receive the pins with 1.8mm drill (up to 1.9mm)
- Insert axes
- Put together the components as shown from left to right, reading from top to bottom
- Tighten all the components with screws

 
 

5b- Middle finger assembly set (video)

 

6- Index assembly instruction set

- Enlarge holes with 1.8mm drill (up to 1.9mm max)
- Insert the pin with the spring
- Assemble elements step by step as shown on the fllowing pictures (read from left to right, top to bottom)

You can find a video of this assembly made by Exiii HERE

 
 

7- Installation of 4 fingers on the palm

1)
- Adjust axes of the palm with 1.8mm drill, adjust to 1.9 max if the axe does not fit
- Place little & ring finger with 2 axes for each fingers
- Adjust, insert & screw HbShaftStopperB04 to secure the 2 fingers

2)
- Place the middle finger with his 2 axes
- Place index finger with his 2 axes
- Insert and screw HbShaftStopperA04

 
 

8- Motors protection

The 3 motors the hand must be protected be protected to protect from overheat.
This step explains how to weld the resettable fuse (PTC) on each servomotor.

There is:

2 RXEF050 fuse for servos ES08MD
1 RXEF040 fuse for servo S03N

IMPORTANT: THE 2 SIMILAR PTC (RXEF050) MUST BE BE SOLDERED ON THE 2 SMALL SERVOS (ES08MD)

- Prepare the soldering equipment (soldering iron, tin, heat shrink tubing)
- Using a mini screwdriver, open the engine
- Cut the red thread as shown with cutting pliers
- Strip each end, slide the sleeve (0.5mm long), tin with iron and tin
- Reduce the length of PTC legs, tin the ends of the PTC
- Solder the 2 parts together (the direction does not matter)
- Protect soldering by sliding sheath
- Close the motor

REPEAT THE OPERATION FOR THE 2 OTHER MOTORS

 
 

9- Thumb assembly instruction set

- Check all components and prepare material (3 screws + spring)
- Follow the steps indicated on the pictures, left to right, top to bottom
- Assemble the elements with the ScrewM2L10
- Screw the servo ES08MD on the thumb (after the PTC is soldered on the servo)

You can also follow the video tutorial made by Exiii HERE

 
 

10- Set the thumb on the palm

- Insert the mini ball-bearing in the palm as indicated on picture 2
- Place and screw 1 servo ES08MAII in the thumb (the PTC fuse must be soldered before)
- Insert servo's axis in the mini ball-bearing
- Follow the instructions as indicated using 2 screws
- Make sure to fold the cable as indicated, the index motor will be placed above

 
 

11- Index's motor assembly set up

This step explains how to place index's motor in the palm with the axis in the right angle

 

12- Coupling 3 fingers + servomotor

This step explains how to link the 3 fingers together and how to link them to the servomotor

 

13- Soldering components

This slides explain:
- What the components are made for
- How to solder the components on the main PCB

 

14- Solder muscle sensor/mini jack

The original Exiii version uses 1 pressure sensor to open the hand:
- When the muscle is contracted, the diameter of the forearm changes, so the pressure on the sensor too.

This version uses a Myoware:
- When the muscle is contracted the sensor detects it and convert it into electricity

We have not tried the version with the pressure sensor and cannot say if the muscle sensor is more precise/reliable/friendly user compared to the muscle sensor

 

15- Voltage regulator adjustment

Thanks to the voltage regulator, the right power is delivered to the PCB and arduino, this step explains how to set up the power going out of the regulator

 

16- Insert electronic components in the hand

This step explains how to integrate the PCB in the palm, remember the lenght of the servo's cable and try to hide them as possible, it will make the hand easier to close

 

17- Upper limb 3D scan

The residual limb has been 3D scanning with the silicone liner on the stump. In this configuration, the socket is fitted on the shape of the residual limb + the silicone liner to ensure a good grip between the body and the interface.

In this case, it is the silicone liner used in the daily life with a professionnal socket

Because each person has a particular need and different grip depending of the level of missing limb, the grip will be different.

The involvement of the user is important to understand his needs

For this 3D scan, we used

  • 1 Ipad
  • 1 scan 3D Structure Sensor adapted on the Ipad

During the scan, the Ipad is wifi connected to the computer and directly send the datas to Skanect software. The file is exported in .OBJ
This file is imported into Mudbox software to converts the triangles mesh into square mesh. The file is again exported in either .OBJ or .STL
The final file is imported into Fusion 360 CAD software to modelise the socket from the 3D scan of the residual limb

 

18- Socket modelling

The model of the socket was made with Fusion 360. This video is not a tutorial, but a short trailer of the modelling made from the 3D scan. You can choose to slow down the speed of the video clicking the little icon at the bottom right of the video.

- Get the input of a professionnal O & P (Ortho Prosthetist) regarding the inside volume of the socket, it is important to remember that a socket is made to fit on a human being and it is crucial to have a consulting from a professionnal
- Import the upper limb 3D scan into Fusion 360
- Integrate the existing elements from Exiii like the wirst and the battery support
- In this case Lazslo, the 3D modeler integrated 2 square holes which correspond to the wedges of my silicone linar in order to hold the socket my residual limb.

Both of us were surprised about how good fitted the socket after the 1st print. Laszlo had to reduce the inside volume a little bit and the placement of the wedges so, after the 2nd print, the socket fitted well

 

19- 3D print the socket

Import the .STL file of the 3D model made on Fusion into Stratasys Dimension software

 

20- Wirst & socket assembly set up

Follow this steps from left to right, top to bottom in order to assemble the wirst together and screw it on the 3D printed socket

 
 

21- Solder battery cable

- Solder the cable as shown
- check + and - between cable and battery
- Screw the battery holder on the socket
- Put the battery on the battery holder

 
 

22- Upload the arduino code

  • Install arduino on the computer and open it
  • In “Tools”, select “card type”, then “micro arduino”
  • In the folder “HACKbery software”, open “HACKBerry_v1.ino”
  • Plug the hand to the computer with a micro USB lead
  • Upload code

This is a tutorial if you never used arduino

 

23- Final assembly

Once the code is uploaded, place the buttons switch in place, tidy the cables and close the hand. The hand is ready to use.

- Stick the electrode close enough to the elbow, this is where the muscle contraction is usually the best.
- The middle button is the switch power, the hand will open when you move it
- Press the tact switch that is the closer to the index to launch calibration. The 3 fingers of the hand will close.
- Contract your muscle and release, the index will close, contract during 2 sec then release again, the index will close again. Repeat the operation until the 4 fingers open.
- Release your muscle, the hand will close, contract your muscle to open the hand, keep contracting to stay open
- When and only when the hand is open, you can change modes. Press the 3rd little button aligned with the calibration button, this will change the position of thumb
- Middle button is Reset
- Open the hand again and press the last button on the right, it will activate/deactivate the 3 fingers

 
 

24- Fablab or hybrid version ?

The hand itself is the same for both versions, the difference is into the human machine interface (socket, electrodes and wrist).

The Fablab version is entirely possible to make with a 3D printer
The hybrid version is supposed to be adapted on a professional wrist disconnector (not available in the market). This hybrid version was made in order to be able to plug the hand directly on my daily used socket.

This version was possible to make thanks to the consulting from a certified O & P (orthotist and prosthetist) who provided us the component. The special wrist disconnector is not available, but you can find an equivalent if you talk with a certified O & P.

- The fablab version is the closest to the original Exiii project using the mechanical design of the wrist, a 3D printed socket and affordable muscle sensors.
- The hybrid version is made to be adapted on a professional socket of a myoelectric hand using a wrist disconnector. The wrist is not available on the market, and only O & P certified can provide it. Nonetheless, this non open-source version allows to adapt the hand on a professional socket.

In this way, we can make sure the user is comfortable and can control the hand the same way he controls his everyday myoelectric prosthesis. Moreover, using professional muscle sensor will allow the user to focus on the mechanical reliability of the Exiii hand.

 

25- Wrist disconnector assembly set up (hybrid version)

The residency at Fab Lab Berlin and the consultation from Ottobock made possible the creation of an hybrid version. This model is about the adaptation of the Exiii hand on a professional socket.

These steps explains how we adapted a wrist disconnector on the Exiii hand. This special wrist is not available on the market, neither on a catalog but it is possible to find a similar model if you get in touch with a certified O & P.

 

26- Electrical wiring (hybrid version)

This step explain how to plug/solder the wires coming from the socket (battery/muscle sensor) into the PCB

 

27- Fablab version Vs Hybrid version

The initial plan was to make this hand available to anyone and possible to realize in a Fablab using standardized and worlwide available components. This is how we decided to work on a 3D printed socket but the complexity of the project makes difficult to mix standard components with quality.

The challenge of this residency program was also to find a balance between an open source project based on a community and a company focused on business.

During the process of fabrication, new ideas came along and we made the decision to change the plan a little bit during the learning process of making this hand. Because I wear a myolectric prosthesis averyday an allready have a socket, we decided to try to adapt the Exiii hand on my socket. This "hybrid" prosthetic hand is a symbol of the possibility to adapt ourself.

The hybrid version was not part of the initial plan regarding the non availability of the components (wirst, socket, electrodes) and because the focus was to make this prothesis available, but this hybrid version is a "first time" between a company such as Ottobock and Open Source. It really represents the possibility and also the difficulties between traditionnal (to follow the initial plan) and DIY (try everything).

It is a learning process, hard to accept sometimes and often with a lot of doubts because we don't really know where this will lead us.

It took:

1 week to print the hand parts
1 day to assemble the hand
1 day to solder the components
2 days to 3D scan, modelize and 3D print the socket
1 day to integrate, adjust, set up , upload the code and test the hand

Feedback:

Negative: As a myohand daily user, I tested the speed, force, control and usability of the Exiii hand. It is, from my point of view definitely not usable for a daily use because it is not enough strong, robust. It is also difficult to put on clothes because the hand can't grab the clothes strong enough. The servos heat very fast and stop working after about 15 min use. The hand must be stopped to cool down the servos, and each time the hand is turned on, the training mode takes about 5 sec to set up. Each time the hand is turned on, the training mode takes a little bit of time which does not really motivates to use the hand.

Positive: For the first time ever, it is possible to use a 3D printed open source bionic hand, which means, possible to grab objects such as cups, a smartphone or small objects such as a pen, a sheet of paper, a spoon, a cookie, even a cigarette for smokers. The different modes allow to switch between power grasp, precision grasp, or lateral grasp which give the sensation of doing more things. For the 1st time, I have seen myself using the Exiii hand instead of my Varie + speed Ottobock hand when it comes to tap on a laptop thanks to the index position.

 

Conclusion

It was difficult as an amputee and a non technician to make this project. I was really afraid not to succeed because this project is complicated and involves lots of dexterity and skills because of the small components and the electronics.

Thanks to the team work and the residency program, I was feeling more confident and slowly but surely started to use the machines such as 3d printers or iron solder. Thanks to both versions, we could benefit of the experience of the 1st hand to make this second version faster.

It was a learning experience to be part of the residency program at Fab Lab Berlin, to benefit of the help from Makea Industrie and consulting from Ottobock.

It made the project possible to make and proved how positive, creative and productive is open innovation. I am looknig forward to live such an experience again.

I want to thank all the people involved in this project that happened at Fab Lab Berlin from April to July 2016, especially Laszlo, Ahmad, Jair, Uli and Park (link to their mini bio HERE:-)