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PROJECT REPORT: (ASME FormatMEL421: Medical Devices & Equipments

Submitted on: 12-07-2014

JAIPUR HAND

Nihal Chaudhary

Mithlesh Kumari*School of Mechanical Materials & Energy Engineering

Indian Institute of Technology RoparRupnagar 140001, Punjab, INDIA

*Corresponding author:Tel: (+91)7814328262; E-mail: nihal@iitrpr.ac.in

ABSTRACTHand amputation is an extremely traumaticexperience for a patient; it has been observed that

patients that experience the loss of a limb havedeveloped mental and emotional disorders. In order toimprove the overall quality of life for hand amputeepatients, a number of prosthetic devices are availableon the market today. Many of these devices fail toapproach the level of dexterity possible of the humanhand. Jaipur Hand, on the contrary, uses an adaptivegrasp system and an innovative finger link design.The natural appearance and motion characteristic ofthe human hand were modeled as closely as possible.

INTRODUCTIONMutilating hand injuries have been shown to result in

stress and anxiety disorders, major depression, pain

syndromes and adjustment problems. It has been

found that up to 94% of the individuals with a severehand injury experience symptoms associated with one

of these disorders. Their symptoms commonly

include; nightmares, flashback memories, moodswings, cognitive difficulties, concerns regarding

disfigurement, phantom limb sensation and the fear of

dying. It is obvious that losing a hand in an accident

is severely traumatic for a person, and can negativelyaffect their self-image which will be directly

disruptive of their overall enjoyment of life. In cases

where hand replantation is not possible due to theextent of injury, the patient must consider the possible

use of a hand prosthesis in order to be able to return

to some of their normal activities with greater

dexterity.

ANATOMY OF HUMAN HANDThe human hand itself is extremely difficult to modelwhen attempting to duplicate the high dexterity of

actions it can perform, one truly learns to appreciatethe subtle complexities of human structure shown infigure. These bones have a system of tendons thatconnect to the base of each of the phalanges whichserve to curl the fingers to form a hand gesture.

Source: http://en.wikipedia.org/wiki/File:Scheme_human_hand_bones-en.svg

When in contraction the muscle will pull on thetendons, which in turn will curl the fingers. Thesemuscles will be unaffected during a hand amputationand the nerve enervation pathways will remain intactmeaning that the patient will still be able to contractthe flexor digitorum normally. As the muscle will stillreact when the brain commands it tooElectroMyoGram (EMG) signals can be extracted

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from this muscle, and potentially be used to control aprosthetic device in order to allow the user to feel likethey have more natural, instinctive control over theirprosthetic.

DESIGN CONSIDERATIONS Fit It should fit the less-active patients andcomfortable with a 'total contact' fit.

Rotation ease of changing direction Weight maximizing comfort, balance and

speed. AestheticsIt should look like a natural hand. CostIt should be inexpensive. The exterior should be water proof and

durable.

It should made of locally available materials.

DESIGNThe four fingers and thumb have the ability toindependently conform to the shape of an object in itsgrasp; the adaptive grasp system. There are threefeatures of the hand that allow for adaptive grasp,firstly the finger are able to curl during flexion, givingthe prosthetic finger flexion characteristics similar tothe human hand. Secondly, the fingers are able to flexindependently of each other during closing, with theuse of a parallel spring mechanism within the palm.

Finally, the thumb is able to adduct (rotate inwards)and abduct (rotate outwards) as well as to flex andextend.

Thumb DesignThe thumb is designed so that it can be actuated withthe same linear actuator as the fingers. When designthe linkages, the same consideration for biologicalaccuracy was taken into account.

The thumb of the prosthetic hand has two

degrees of freedom. It is able to flex andextend like the fingers, however it is also ableto adduct and abduct about the thumbrotational axis.

To perform flexion and extension, the distalportion of the thumb uses four links. Thisallows only the two outer segments to flex andextend.

The base segment cannot flex or extend butcan only adduct and abduct.

Source: http://www.emeraldinsight.com/journals.htm?articleid=1937104

The thumb is constructed with four links; two links

that make up two segments mimicking the humanthumb, and two links that connect the first two linkstogether and are responsible for curling the thumbFlexion of the thumb is achieved with a drive cableconnected between the final link of the assembly andthe force plate. Whereas extension is achieved with anextension spring positioned against a flange on thefinal link which will extend the thumb when tension

on the drive cable is released.

Source: http://www.emeraldinsight.com/journals.htm?articleid=1937104

Finger DesignIn order to mimic the real finger, the three segmentsmake up the prosthetic finger for a total of six linksLinks 1, 2, and 3 correspond to the three segments ofthe human finger and have been dimensioned to be thesame size as the average human finger. Whereas link

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4, 5, and 6 are the connecting joints that drive thecurling motion of each finger. At link 6, the endlinkage is attached to the linear actuator that will pullon the finger and curl the finger. The curling trajectoryhas been as design to be as universally adaptable as

possible, along with the adaptive grasp system, a largevariety object can be held with the fingers.

a) Disassembled fingerb) Assembled finger

A form of independent flexion of the fingers isachieved through the adaptive grasp system. During

finger flexion, each finger will flex around an object,

however, the final position of each finger will berelative to the others based on the shape of the object

in its grasp. The design that allows for adaptive graspis a piston system; all of the fingers are acted upon by

a single linear actuator connected to a force plate. Theforce plate is then connected to a set of four pistons

(cylinder springs); a piston per finger, the end of each

finger is then connected to the end of link 6 on eachfinger. When the force plate is forced downwards by

the linear actuator the fingers begin to follow their

natural curling motion until they become obstructed

by the object in its grasp. At this point the spring inthe pistons initial compressive force will be

overcome and begin to compress. The unobstructedfingers will continue to follow along their natural pathuntil they too become obstructed by the object in its

grasp. Meanwhile, the fingers that came into contact

with the object initially will tighten their grip around

the object relative to the stiffness coefficient andamount of compression of the piston spring. This

unique design overcomes the potential for imbalance

in the grip and stabilizes the grip ensuring that the

object will be grasped securely.

Source:http://mechanicaldesign.asmedigitalcollection.asme.org/article.aspx?articleid=1743166

Illustration of finger flexion

The overall design of the JAIPUR HAND is

unique and allows for a great amount ofdexterity and grip adaptability.

The natural appearance and motioncharacteristic of the human hand weremodeled as closely as possible.

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ADAPTIVE GRASP SYSTEMThe most interesting and unique feature of thisprosthetic hand is the adaptive grasp system. Theadaptive grasp system allows for the fingers toindependently conform about an object within its

grasp. The main structure of the system is constructedwith a force plate and an array of piston springs whichconnect to the fingers.The system is comprised of three basic components;the force plate, the pistons and the motor drive shafts.The force plate simply a long rectangular piece ofaluminum to which each of the pistons will beattached. The motor drive shaft is threaded bolt, whendriven by the motor it will make the force platetranslate along the drive shafts main axis. Therebyeither pushing or pulling on the attached piston

springs. The piston spring is the heart of the adaptivegrasp system.

The pin hole will connect to the end of link 6 of the

finger and threaded end would connect to the force

plate creating a connection for the transfer of motion

between the two components. However, the design ofthe piston spring is such that as the finger are being

curled should one of the fingers become obstructed by

an object in its path, the force plate can continue alongits motion path curling the other unobstructed fingers.Meanwhile the obstructed finger will be pressed

against the object and instead the spring inside thepiston spring will be compressed with the continuedmotion of the force plate. This effectively will tightenthe grip around the object until all of the fingers havereached their maximum flex points or they haveconformed around the object forming a stable,conformed grasp.

The drive system of the prosthetic hand is composedof two DC rotary motors, each with a threaded boltfixed to their drive shaft. The two motors spin inunison to allow for even translational motion of theforce plate and allow for a high grip force to be

achieved. When the force plate is driven in theopposite direction, in order to extend the fingers, thepiston will be forced against the end of the pistonspring cylinder and will allow for extension of thefingers.

F igure a: Fingers and thumb fully extended andpiston springs are fully extended as fingers are not

obstructed by objects

F igure b:As fingers and thumb curl to close around

object one of the fingers comes in contact with the

object while the in obstructed fingers continue along

their curl trajectory. Note that the spring has begun tocompress and exert a force on the object proportional

to the stiffness value of the spring.

MATERIAL USEDThe rest of the hand is filled with cushion rubbercompound which is lighter and has more resiliencethan the tread compound. The rubber is reinforcedwith rayon cord dipped in rubber gum. The hand iscovered with skin colored rubber compound.

COSTThe Jaipur Foot is quite cheap and costs only $ 20 (Rs

1200) as compared to other artificial hand available inthe USA which cost around more than $10,000.

ADVANTAGES The design is simple effective not requiring

any sensors, or electronic processing.

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Conventional prosthetic hands have limitedmechanical function while Jaipur hand has the

ability to perform passive adaptive grasp.

Jaipur hand is much smaller in size and is notheavy. (around 500 grams)

The cosmetic appearance of the hand is good

CONCLUSIONJaipur hand is efficient in providing light weight,comfortable, durable, artificial hand for rehabilitationof the physically challenged and the handicapped.Jaipur hand is time tested and has been proved on thegrounds of material properties like hardness, abrasion,tensile strength, relative density, resilience.Also, a major research is going to make the modelfunctionally more efficient in Stanford University in

collaboration with Bhagwan Mahavir VikalangSahayata Samiti (BMVSS),the largest organisationin the world for the handicapped in terms of fitmentof artificial limb, callipers etc,

REFERENCES

http://www.emeraldinsight.com/journals.ht

m?articleid=1937104

http://www.rehab.research.va.gov/jour/2013/505/belter505.html

http://jaipurfoot.org/what_we_do/prosthesis/

artificial_hand.html#.UoqnrcSmb2Y

http://www.researchgate.net/publication/222

283408_Multiple_finger_passive_adaptive_

grasp_prosthetic_hand

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