Hello and welcome to my second instructable, the creation of a 3D scanned and printed prosthetic hand, named 'Scand'. I decided to submit this project for the Make it Real 3D competition so I would be very grateful if you could please vote for me! This was a real mechanical prosthetic hand prototype, designed for a real amputee as part of MY university final major project, it was not a group project. In this instructable, I hope to show you briefly how I made it and I hope that you like what you see... :) please vote
Scand, designed by Scott Allen, is a piece of functional body art for consumers with single upper-body amputations. Scand aims not only to enhance the user's quality of life through added functionality but also to blow disproportionate, semi-fake prostheses out of the water with dimensionally accurate yet honest styling that allows users to express their personalities and increase social acceptance by completing their body profiles (Marr's computational Theory of perception, 1988) and by reducing the occurrence of the 'Uncanny Valley Phenomena'; the sense of 'repulsion' caused by one discovering that a limb, you thought was real, being in fact a fake (Mori, 1970).
Existing designs of prostheses can be ugly, disproportionate, heavy, expensive and have low levels of social acceptance, particularly prosthetic hooks. Despite this, prosthetic hooks are favoured by many due to their higher levels of functionality. In an effort to retain this vital functionality, Scand incorporates this very mechanism, albeit a modified version.
First, however, a cast is made of the user's existing hand using a environmentally friendly, seaweed based Alginate formula and Cystacal-D Dental stone. Next a 3D scan of the cast is taken to produce a 3D CAD model. The CAD model is mirrored, shelled and then further manipulated, by the designer, to encompass the internal mechanism, fixing points, rubber sleeve and a cavity in the top for interchangeable push-fit objects such as a clock, compass or electronic device. The CAD data is then sent to a 3D printer where the new prosthesis is printed very slowly, layer by layer using a fine powder. The thumb and finger grip are printed in a different, rubberised material for maximised grip. An Aluminium sand cast mechanism with elasticated tension, enables the rubberised thumb to open and close with variable gripping force, permitting the user to grasp objects. The thumb mechanism is actuated by a conventional body worn harness and cable system; moving the opposite shoulder increases/releases the cable's tension. Retaining operational familiarity will help many users in the transition from older designs to the new Scand design.
This particular prototype was designed specifically for a Client, a Transradial amputee who lost his left hand to Cancer, aged 21. Scand's design has significantly improved this user's quality of life allowing him to grip fine objects such as food sachets, snooker cues and spice jars, objects that he was unable to pick up with his existing prosthesis. Additionally, Scand is lightweight and more balanced to the user's natural hand weight than his existing heavy prosthesis, easing day to day use and fatigue. The client felt that the individuality and proportional accuracy of Scand, coupled with its ability to reinstate functionality, would benefit many new amputees during rehabilitation. Consumer's will be able to commission their prosthesis styling, including colours, materials, inlays and a choice of insertable push-fit objects enabling them to proudly express their personalities, not mask their disabilities.
View the designer's website: www.scottallendesign.co.uk
Scand, designed by Scott Allen, is a piece of functional body art for consumers with single upper-body amputations. Scand aims not only to enhance the user's quality of life through added functionality but also to blow disproportionate, semi-fake prostheses out of the water with dimensionally accurate yet honest styling that allows users to express their personalities and increase social acceptance by completing their body profiles (Marr's computational Theory of perception, 1988) and by reducing the occurrence of the 'Uncanny Valley Phenomena'; the sense of 'repulsion' caused by one discovering that a limb, you thought was real, being in fact a fake (Mori, 1970).
Existing designs of prostheses can be ugly, disproportionate, heavy, expensive and have low levels of social acceptance, particularly prosthetic hooks. Despite this, prosthetic hooks are favoured by many due to their higher levels of functionality. In an effort to retain this vital functionality, Scand incorporates this very mechanism, albeit a modified version.
First, however, a cast is made of the user's existing hand using a environmentally friendly, seaweed based Alginate formula and Cystacal-D Dental stone. Next a 3D scan of the cast is taken to produce a 3D CAD model. The CAD model is mirrored, shelled and then further manipulated, by the designer, to encompass the internal mechanism, fixing points, rubber sleeve and a cavity in the top for interchangeable push-fit objects such as a clock, compass or electronic device. The CAD data is then sent to a 3D printer where the new prosthesis is printed very slowly, layer by layer using a fine powder. The thumb and finger grip are printed in a different, rubberised material for maximised grip. An Aluminium sand cast mechanism with elasticated tension, enables the rubberised thumb to open and close with variable gripping force, permitting the user to grasp objects. The thumb mechanism is actuated by a conventional body worn harness and cable system; moving the opposite shoulder increases/releases the cable's tension. Retaining operational familiarity will help many users in the transition from older designs to the new Scand design.
This particular prototype was designed specifically for a Client, a Transradial amputee who lost his left hand to Cancer, aged 21. Scand's design has significantly improved this user's quality of life allowing him to grip fine objects such as food sachets, snooker cues and spice jars, objects that he was unable to pick up with his existing prosthesis. Additionally, Scand is lightweight and more balanced to the user's natural hand weight than his existing heavy prosthesis, easing day to day use and fatigue. The client felt that the individuality and proportional accuracy of Scand, coupled with its ability to reinstate functionality, would benefit many new amputees during rehabilitation. Consumer's will be able to commission their prosthesis styling, including colours, materials, inlays and a choice of insertable push-fit objects enabling them to proudly express their personalities, not mask their disabilities.
View the designer's website: www.scottallendesign.co.uk
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Signing UpStep 1: Creating the mould for a hand cast
To create the CAD model for the 3D printer we will need to use a hand-held 3D scanner as trying to accurately reverse engineer an organically shaped individual's hand would be virtually impossible, however the scanner does not scan actual body parts as well as it does models, objects and casts. For this reason, as well as not having to always have the client/person's hand available to re-scan (should you need to), it makes more sense to scan a stone cast.
It took me three attempts to get an ideal cast, so learn from my mistakes
- first I used a lemonade bottle as the casting container, however this dictated the position of my clients hand so much that it was in a less than ideal position to house the internal mechanism I intended to build, so I redid it using a wider container (a 5L water bottle), although I ended up using more alginate.
This step shows how to make the mould for the stone cast.
To create this mould you need several things, some of which you could improvise on, but ideally:
Alginate impression material - such as that made by Hydrogum (available online)
A casting container - such as a 5L water bottle with the top cut off.
A mixing stick of some kind - wooden spoon, scrap wood etc
Luke warm water
Your own hand or client's hand
Scissors
A mixing bowl/scrap container
1. Take the top off you casting container using scissors, you want it deep enough to pass the wrist by a could of inches.
2. Mix one part alginate with two parts water (or as specified on your packet)
3. Stir well with your mixing stick and work into a thick paste, work quickly as it sets quickly too!
4. Now quickly pour the mixture into your casting container/ 5L bottle
5. Now slowly insert the hand you intend to cast into the casting container and wait for about 10minutes until completely set.
6. Try to peel a gap at the wrist to release the vacuum within, now heave and tug to loosen the hand from the mould, you'll most likely need two people, once loosened carefully pull the hand from the mould, do not wriggle fingers within the mould.
It took me three attempts to get an ideal cast, so learn from my mistakes
- first I used a lemonade bottle as the casting container, however this dictated the position of my clients hand so much that it was in a less than ideal position to house the internal mechanism I intended to build, so I redid it using a wider container (a 5L water bottle), although I ended up using more alginate.
This step shows how to make the mould for the stone cast.
To create this mould you need several things, some of which you could improvise on, but ideally:
Alginate impression material - such as that made by Hydrogum (available online)
A casting container - such as a 5L water bottle with the top cut off.
A mixing stick of some kind - wooden spoon, scrap wood etc
Luke warm water
Your own hand or client's hand
Scissors
A mixing bowl/scrap container
1. Take the top off you casting container using scissors, you want it deep enough to pass the wrist by a could of inches.
2. Mix one part alginate with two parts water (or as specified on your packet)
3. Stir well with your mixing stick and work into a thick paste, work quickly as it sets quickly too!
4. Now quickly pour the mixture into your casting container/ 5L bottle
5. Now slowly insert the hand you intend to cast into the casting container and wait for about 10minutes until completely set.
6. Try to peel a gap at the wrist to release the vacuum within, now heave and tug to loosen the hand from the mould, you'll most likely need two people, once loosened carefully pull the hand from the mould, do not wriggle fingers within the mould.
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