state of art of the prosthetic hand

7/27/2019 State of Art of the Prosthetic Hand

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The state of the art of Prosthesis Hand

A human hand is a complex structure having 21 degrees of freedom (DOF): four DOF per finger

which has three phalanges and one metacarpus ad five DOF for the thumb which has two phalanges

and one metacarpus. It can perform grasping, holding and pinching operations while manipulating

objects of various sizes, weights and shapes. It has 27 bones and a multitude of muscles and tendons, in

addition, each hand has an array of over 17000 tactile sensors.

It is doubtless the most widely versatile machine that has ever existed anywhere.

With existing technology it is near impossible to replicate anything mechanically similar. However,

advances in technology have enabled some considerable improvements in the functionality of aprosthetic hand with an increase in the number of degrees of freedom available through the use of

smaller and lighter motor.

There has been much research towards the creation of a robotic end effector that is similar in function

and appearance, to the human hand. Similarly, in the area of prosthesis design, research is being

conducted towards the creation of a lower arm prosthesis is more like the human hand. The field of

robotic end effector design and the field of lower arm prosthesis design have many parallels. However,

the requirements for producing a mechanical manipulator for use by a laboratory robot are differentthan those for use by an amputee.

A prosthetic hand design must encompass the following properties: Lightweight, any device is worn by the operator on the end of a closely fitting external socket,

hence the weight bears directly onto the skin of the stump. The lever-arm created is therefore large

and the weight can obstruct blood flow in the underlying skin and results in symptoms ranging

from discomfort to skin breakdown. The weight of a human hand is around 1 kg, therefore a

prosthetic hand should satisfy this specification. Compact, the user population varies widely in the length of their residual limb, so any device

should retain all its drives and power sources within as small an envelope as possible, preferably

within the hand profile. Modularity, the use of a modular solution ensures that the largest number of people can use the

device as well as providing simplicity of manufacture of both left and right hands. Low power consumption, to make efficient use of the limited battery energy. Quiet, the purpose of all prostheses is to provide the functional result without attracting undue

attention to the user. The sound of gears and motors or the escape of gas in a pneumatic system istherefore generally unwelcome.


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Appearance- Cosmetic, a hand is considered to be cosmetic in appearance if it is aesthetically

pleasing and looks like the limb its designed to replace in both its lines and colour. Both static and

dynamic cosmesis are important but dynamic one it is more difficult to achieve and can be

enhanced by preserving as much of the persons residual motion as possible. A device can be

considered to be functionally cosmetic if at a glance it is not immediately recognizable as an

artificial hand regardless of whether it is in motion or not or whether it is or is not handlike when

stationary. Price,any device must be useable by a wide range of possible wearers. The prosthetics field is very

price sensitive. This means the device must be produced at a cost that will allow the hand to be

priced competitively.1

In order to reduce the overall weight of the hand an underactuated solution is often used. In

underactuated hands, the number of motors is lower than the number of active joints, so that some

kind of joint motion coupling should be provided. Underactuated hands have the advantage of system

simplicity, i.e., the number of required actuators is reduced while preserving the number of active

joints. Underactuated mechanisms can be used to obtain an adaptive grasp that resembles human

grasping more easily than a hand with completely independent DOFs could achieve. Indeed, the human

hand is also underactuated, as the distal interphalangeal joints of the fingers are not independently

controllable. When applied to mechanical fingers, the concept of underactuation leads to self-

adaptability. Without complex control strategies, self-adaptive fingers will envelope the objects andautomatically adapt to their shape with only one actuator.

The literature shows two different types of underactuated hands, depending on whether a tendon or

link transmission is used. The tendon systems are generally adopted to minimize the transmission

dimensions but are limited to small grasping forces, while link systems are preferred for applications in

which large grasping forces are required.

The following pages present an overview of prosthetic hands, sorted by mechanism used and by date.

The i-Limb is the only hand that fulfils almost the properties described above; in fact is commercially

available while the other hands, described below, are just robotic hand or prototypes. In fact even if

some hands show some relevant innovation, these hands have bulky and heavy housing for the motor,

outside the palm, and so is not possible to consider them like a real prosthetic hand.

1 Some hands, described below, are just prototypes, so it is difficult to establish a price.


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I-Limb Hand (Mead, Shakeshaft, Waddell 2007)

The i-Limb is not only lightweight, but it works and

looks like a human hand. The hand is powered by internal

batteries, fitted in the patients socket, which drive the

five motors of the i-LIMB Hand for a complete day. It is

made from high-strength plastics, and the fingers are

covered by injection-moulded Zytel, a tough nylon that

withstands hot and chemically aggressive environments.

This makes it more realistic, and much more useful and effective in performing everyday tasks. Each i-

LIMB digit is individually powered by a precision direct current micro motor. The motor is short

enough to fit into the phalangeal section next to the knuckle. To make the fingers curve as they grip, a

polyurethane-covered Kevlar toothed belt links each knuckle

joint to the nearest interphalangeal joint. In the i-LIMB

Hand, the interphalangeal joint nearest the fingertip does not

move, but the one nearest the knuckle is controlled by the

motor to make the finger bend and grip.

Using a modular design, the company is able to build

complete hands or partial hands, of different sizes, with the

minimum number of component parts. Modularity alsomeans easy replacement of worn-out parts.

The total cost to the patient is about $50,000 this makes the prosthetic hand more expensive than

traditional myoelectric devices.

Following is a brief description of hands that use a different kind of linkage mechanism.

The Southampton REMEDI hand (Light, Kyberd and Chappell 1994-2001) This hand has six degrees of freedom. The hand

consists of six small electrical motors, two of which are

used to actuate the extension-flexion, and rotation

movements of the thumb with each of the remaining

four motors being assigned to individual fingers. The

modular thumb unit is reversiblein design, so that it

may be used for either a left or right handed

prostheses. Each finger is made from six bar linkages,


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which when extended or flexed curl in a fixed anthropomorphic trajectory, this was designed to

replicate the trajectory of the human finger during natural curling . To ensure a lightweightunit, the

linkage is machined from carbon-fibre epoxy composite and the housing from a polymer thermoplastic

which has a low coefficient of friction.

When the proximal phalanx makes contact with the object, the proximal phalanx stops, and the other

two phalanxes begin rotating and closing on the

object because of the effect of the underactuated

linkages mechanism. By means of the coupling

linkages, the middle phalanx and distal phalanx

rotate at the same time, and the ratio of rotation

angles of two coupling joints--the mid joint and

distal joint-- are about 1:1, which mimic natural human hand movements. Finally, the fingertip or mid

phalanx is in contact with the object and the finger has completed the grasp motion. It shows that the

underactuated linkages mechanism is able to adapt shape with a wide variety of objects.

To reduce the power requiredto hold an object, the fingers are driven via a worm wheel gear

configuration. This also has the additional advantage that it prevents the fingers being back driven after

power is removed from the motor.

The TBM Hand, Toronto/Bloorview MacMillan (Dechev, Cleghorn, Naumann 1999) The TBM hand has five fingers and use a rigid

linkage system for actuating the fingers; each one is

comprised of six links.

The rotation of the thumb is performed manually by

the user. The key to this thumb design is to keep the

drive cable coaxial with the thumb rotational axis so

no matter which angle the thumb assembly is rotated

to, the drive cable will always be able to flex the thumb without slipping off the thumb pulley.

The TBM hand uses a single motor to actuate all

the mechanisms and to do this a novel cylinder

springs is used. Each cylinder spring consists

of a compression spring within a cylinder and

they are linked between link 6 of a finger and a

force plate. When the force plate moves right

along the x-axis, it pulls on the five pistons

distributing the actuators force amongst them.


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HIT/DLR ARHand (Huang, Li Jiang, Y.Liu, Hou, Hegao Cai, Hong Liu 2006)

The HIT/DLR Prosthetic Hand was

developed with the underactuated linkage

based on four- bar linkage mechanisms, placed

between the base joint and the middle joint.

The coupling linkage is passive moving, which

has not been driven by motor, and is

employed between middle and distal joints.

When one of the three fingers touches object

and stops, the other two fingers will continue

moving, until contacting the object. Compared with the tendon transmission, the linkage transmission

has the advantages of high stiffness and

reliability.

The thumb uses a sophisticated transmission

mechanism. The spherical bearing is used which

tends to make the motion track of the thumb

move from the preliminary position to the final

position as a cone surface. Its actuation

mechanism includes the motor, the synchronous pulleys and harmonic gear.

In 2009 the same authors propose the AR III; this hand uses only three actuators to drive five

fingers (total 15 joints).

To reduce system cost and complexity, the

adduction/ abduction and flexion/extension motions

of the thumb are combined together. Furthermore,

the thumb metacarpal is intentionally angled 60 tothe axis of TM joint to make thumb move along with

a cone surface. This configuration gives the thumb

superior grasping ability.

For more humanoid properties, the design of the AR hand III considered the ring and little fingers and

made them move together with the middle finger. These three fingers were mounted parallel on the

base axis, and each is equipped with a torsion spring.


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The SPRING Hand (Carrozza, Massa, Dario, Lazzarini, Vecchi, Cutkosky 2004)

The Spring hand has eight DOFs but only one motor. The

underactuated mechanism includes three cables (for each phalange)

and two compression springs that allow the adaptive behaviour.

The three cables are pulled in unison by means of a linear slider,

the slider is the fundamental element of the transmission system: in

fact it is possible to get the flexion and the extension of the finger

thanks to its two way linear motions. The Spring hand weights

about 400 grams.

The CyberHand (Edin, Cappiello, Micera, Carrozza 2005)

In the CyberHand the three fingered

RTR2 hand has been redesigned; in order

to improve the hand grasp functionality

and its anthropomorphism, all the

phalanges have a cylindrical shape withoutsharp edges. The CyberHand has 16 DoFs

and 6 motors. To reduce the weightthe 5

motors for fingers flexion are housed in a

socket, and the palm is composed by an

outside shell, made of carbon fiber. In order to increase the compliance of the graspinga soft padding

made of silicon rubber can be mounted on the palm. Cable transmissions obviously make it possible to

relocate bulky actuation and avoid problems due to rigid transmissions in articulated mechanism. The

total weight of the hand is about 320 grams, excluding the motors in the forearm.


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The SmartHand (Cipriani, Controzzi, Carrozza 2008)

The 16 DoFs (three for each finger, plus one for the

thumb opposition axis) SmartHand prosthesis is driven

by 4 DC motors. Thumb and index are independently

actuated, whereas the middle, the ring, and the little

fingers are joined together. Another motor is used for

the thumb opposition axis movement, in order to allow

different prehension patterns.

Hiroses soft finger has been selected as underactuated

mechanism for the fingers: the motors by pulling the

tendons which are wrapped along the finger pulleys

located in the joints are employed in the flexion of the

fingers. The reasons for the employment of such a mechanism are: the need for just a single actuator to

allow simultaneous flexion of three phalanxes (thus reducing weight and volumeof the prosthesis), the

simplicity of the control to be implemented and the compliance of the mechanism (related to the

capability of automatically wrap-around objects, allowing multi-contact and therefore stable grasps).

In most research prosthetic hands, non-back-drivability is obtained by means of screw/lead screw pairs;

but its main drawback, is that it is a low mechanical efficiency mechanism. The innovative idea has

been that to develop a high efficiency non-back-drivable miniaturized clutch mechanism. Thismechanism allows the transmission of the rotational motion, when it is originated by the motor shaft,

blocking instead motions originated from the output shaft (connected to a capstan driving the finger

tendon). The capstan has been designed with an eccentric geometry, with the purpose to privilege

strength in the first phase of the grasp, and speed in the last part.

The Manus Hand (Pons, Reynaerts, Saro, Levin, Van Moorleghem 2004)

MANUS-HAND proposes aprosthesis having ten joints of

which three are independently

driven. The fourth and fifth

fingers are provided with a

martensitic structure, this allows a

much higher number of bending

cycles as compared to commonly

used materials, thus improving the

overall reliability of the hand.


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A prototype of ultrasonic motors has been developed with the advantage improved performance and

self braking capabilities in comparison with a commercial DC motor.

There is one single actuator for the thumb motion.

To this purpose, the movements are transformed into

a cycle by means of an intermittent mechanism, the

so-called Geneva wheel. In this cycle two movement

planes are defined: the first plane corresponds to

cylindrical and tip grasps, i.e., thumb is flexed in an

opposition pattern; the second plane, implements

hook and lateral grasps, i.e., thumb is flexed in a non-

opposition pattern. The key position in this cycle is

the neutral position, at which the movement can

change from one plane to the other. The Geneva

wheel is implemented as gear. While the teeth of both gears are engaged there exists a 1:1 coupling

between the two wheels. At a certain

point, the gears are no longer in contact,

but the following wheel is locked in its

position by means of a form closed lock.

The driving wheel can continue rotating and drive another axis while the axis

connected with the following wheel of the

Geneva mechanism is locked.

Two drive paths exist in the Geneva

mechanism: t he first one drives the first axis. It starts at the actuated axis and the motion is transmitted

by means of gear set 4-3

(transmission ratio 1) and

gear set 2-1. The second

drive path also starts at the

actuated axis. This means

that the second axis (lateral

plane) can be coupled to

the driven axis

(transmission ratio 1) or

can be locked. In the firstcase, the opposition axis and gears 2 and 3 rotate at the same speed. Because the first axis (cylindrical


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plane) is mounted on the second axis, there is no relative motion between gears 1 and 2 and the thumb

does not rotate about the first axis. Thus, the thumb moves in the lateral plane. In the second case, the

Geneva mechanism is locked and the second axis does not rotate. Because of this also the housing

stands still and there is a relative motion between gears 1 and 2.

The UB Hand III (Lotti, Tiezzi, Vassura, Biagiotti, Palli, Melchiorri 2005)

In this prototype each finger can have up to 4 degrees of

mobility, obtaining a total number of 20 degrees of mobility

hand, where 16 degrees of mobility are actively actuated

whereas the others are locked or coupled. The internal

articulated structure is designed according the compliant

mechanisms concept so that the mobility of the phalanges

is obtained by means of elastic joints. The compliant

elements are made with close- wound helical springs

that are subjected to bending under the action of

pulling tendons. The fingers obtained by plastic

moulding with inclusion of continuous steel springs.

The actuation tendons are routed across the coiled

springs which form at the same time hinges and therouting paths. This solution allows a simplified

designwith appreciable kinematical propertieslike a

rough kinematical decoupling of the joints. In the upper finger, the yaw joint and the flexural bending

of the proximal phalanges are obtained through two orthogonal single axis hinges, while the articulation

at the base of the thumb is obtained by a single two DOF helicoidal hinges. This last joint is actuated

by means of three cooperating tendons that allow the thumb to bend on a plane having variable

direction. The Brno Prosthetic hand (Zajdlik 2006)

This prosthesis hand has twenty DOFs and

three motors.

The main innovation is in the mechanism

used called "with string and springs". A force

is applied by a string which leads through two

sliders mounted on springs. The first motion

generated when the string is pulled in the


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MCP (metacarpophalangeal) joint. Other joints can be activated only if the slider is below the level of

the appropriate joint. The PIP (proximal interphalangeal) joint moves only when Slider 1 is under its

(PIP) joint and the IP (distal interphalangeal) joint only moves if Slider 2 is below the DIP joint.

Biomimetic Hand (Sung-yoon Jung, Sung-kyun Kang, Inhyuk Moon 2008)

This hand has five fingers

driven by the motor-wire

mechanism, and the degree of

freedom is six. To reduce the

hand weights the fingers

skeleton and the palm was

made of the epoxy resin. To

reduce the number of

actuators this hand has a single

phalange called distal-middle phalange (DMP), and use a link

mechanism between the MCP joint and the PIP joint. To

reduce the friction influence the joint mechanism uses a

small-size bearing between phalanges. In addition, the pulley

mechanism to enable to assist force in finger flexion was also introduced. The wire path betweenpulleys is S shape from the fixed point to the top of the pulley on the PP, and to the bottom of the

pulley on the MB. This wire connection in the pulley mechanism reduces the friction influence, and it

produces a positive force to the direction of the finger flexion.

V-U Hand (Dalley, Wiste, Withrow, Goldfarb 2009)

The V-U hand has 16 joints driven by five independent

actuators.Specifically, to utilizing underactuation to reduce weight, a

hollow structural elements in the hand was developed, and

a space-frame to house the actuation units in the forearm.

By ensuring an efficient transmission (i.e., minimizing

friction in the system) its possible to obtain a low noise

hand. Finally, an anthropomorphic design based on scalable skeletal characteristics of the human hand

has been utilized. In doing this, it is believed that the cosmetic appearance of the device will be as

natural as possible. The skeleton structural components employ a monocoque structure realized in

high-strength nickel coated thermoplastic.


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The underactuation is governed by moment isotropy,

the hand will reach a configurational equilibrium when

all joint moments are equal. This is achieved by a

combination of having the tendon span multiple joints,

and using a pulley differential to split the force of

actuator output equally into two tendons. This design

allows the fingers to move quickly and with sufficient

force.

The last two projects propose other forms of power, instead of the traditional electric motors.

FluidHand (Schulz, Pylatiuk,Bretthauer, Kargov, Werner 2001)

It is based on the so called flexible fluidic actuators. This

actuators are high flexibilitydesigned into their mechanical

construction, realize very complex movements, they are

lightweightand very low manufacturing costs. A single

actuator element consists of a feeding channel for the

pressurized air or liquid and a "chamber" which is connected

to the two movable parts of a joint. During the inflation of the actuator element by air/liquid the volume of the element

expands and the height of the element vertical to the flexible

wall of the chamber increases. By using many fluidic actuator

elements together structures with very complex flexibility can be created. So a total of 18 miniaturized

flexible fluidic actuators are integrated into the mechanical construction of the fingers and the wrist.

The advantage of this design is that the flexible fingers of the hand are able to wrap around objects of

different sizes and shapes; because of the elastic

properties of the actuators the contact force is

spread over a greater contact area. Moreover the

surface of the fingers is soft and the friction

coefficient is increased by the silicone-rubber glove

that covers the artificial hand. The result is a reduced grip force is needed to hold an object. As a side-

effect from the softness and elasticity of the hand it feels more natural when touched than a hard

robotic hand and the risk of injury in direct interaction with other humans is minimized.

Only lightweightmaterials are used for the mechanical construction of the fingers and the wrist so that

each finger weighs less than 20 grams. This makes possible to reduce the mass of a new artificial hand


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to 50% of the mass of a conventional prosthetic hand. The time for a complete flexion and extension

of a finger is less than 100 ms; this is 10 times faster than a conventional prostheses.

Another fluidic hand was developed recently, in 2008 by the same authors.

Eight flexible fluidic actuators of compact design are integrated in the finger joints. Some actuators are

coupled, like the base joints of fingers IVV and both

joints of fingers II and III. The current flexible fluidic

actuator consists of a reinforced flexible bellow which

forms a closed elastic chamber. The axial expansion of

the flexible bellow exerts a pulling force on the joint

fittings, as the actuator is inflated with the fluid.

Low weightand inherent complianceare two major

attractions of this actuator. These materials can

transmit

energy as

well as a cylinder, but they have a higher power-to-weight

ratio at the same pressure and volume. Moreover, the

modular construction allows for the independence of the

actuators, consequently, actuators can be interchangedor

the number of degrees of freedom can be changed. This may be useful when redesigning the endmanipulator for the special application without a reconstruction of the whole system.

Pneumatic Prosthesis Hand (Takeda, Tsujiuchi, Koizumi, Kan 2009)

This five-fingered prosthetic hand using pneumatic

actuator. The finger can operate flexibly because the

pneumatic actuator is implemented directly in the

prosthetic fingers. In the MP joint, there are two

pneumatic actuators for flexion and extension operations.

In the DIP and PIP joints, there are a pneumatic actuator

for extension operation and a rubber gum for flexion

operation. The thumb mechanism is a bit different from

the other fingers; to give the degree of freedom of palmer

adduction, the CM joint has three actuators to rotate the palm direction.

The actuator is composed of a rubber balloon, a net that covers the balloon, and a feeding channel that

injects compressed air into the balloon. Expanding the rubber balloon shortens the net in the


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longitudinal direction and generates force. The expansion

and contraction operations can be controlled by

adjusting the pressure in the rubber balloon.

Even though the hand is only driven by a low-volume of

compressed air, it can generate enough powerto hold an

object that weighs up to 500 g.

state of art of the prosthetic hand

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