final report 1_ _1_

Page No.1

College OF Engineering Pune

CHAPTER 1 INTRODUCTION 1.1 INTRODUCRION

Due to any major injury if any person loses his or her major working arm then it

becomes very difficult for a person to live normal life. Some times person becomes inactive

and depressed.

To overcome this problem, We are developing a Mechatronics system which will

aesthetically looks like normal human hand and will be able to perform basic operations like

gripping, holding, placing of object etc. for this purpose, currently a prosthetic hand is

available in which each finger is actuated using brain signals and operations are carried out.

Since cost of the system is very high we are planning to develop a low cost and much simpler

system.

1.1. Physiology of hand[15]

The amputee person is having muscles and tissues but the activity is depending on muscles

stimulation. In our design, muscle activity of forearm will be sensed and it will be responsible

for finger motions. Muscle activity is sensed by the surface electrodes and sensing circuitry

will give output signal to the controller board. The controller will control the direction of the

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motor, thus in term controlling motion of the fingers. Soft material fingers are closed or

opened like an umbrella. The whole system is run by rechargeable battery inside. Life of

active battery depends upon the motion of the fingers. The assembly can be easily mounted

and removed from the amputee region for charging period. The assembly is fully covered

with gloze which gives real skin effects.

Cost of the projects is comparatively less and economical. As there are very less mechanical

parts the maintenance is also less. Some of the major safety aspects are also considered to

avoid damages and accidents. Environmental effects persons comfort is taken under

consideration throughout the development.

In this survey, average hand size and average palm size information including hand size

charts segmented by both hand length and width. Data regarding average female and male

hand size is illustrated, accurate as of 2012 and 2013. Hand is made up of two major parts, 1)

the Palm, and 2) the Fingers. The combination of all parts makes the hand - and the addition

of the two dimensions yield an average hand size! As you may have guessed, average hand

size varies heavily by gender - the following charts identify average hand sizes.

Average Hand Size(width) Average Hand Size (Length)

Male Female Male Female

189 mm

(7.44 inches)

172 mm

(6.77 inches)

84 mm

(.30 inches)

74 mm

(2.91 inches)

The kinematics, robotics and mechanism design are relevant in two separate areas of this

project:

1. Identification of the hand motion. This is necessary as input data for the

system identification of the myoelectric signals, in order to relate the electrical

impulse to a certain motion. The signals will differ, besides physiological

variables (environment, patient history etc.), mainly by the motion to perform

and the exerted force implied in the action. These two are always coupled, and

a system to identify and separate the effects of each of them is needed. This

implies the need of a system to track hand motion and another sensory system

to track contact and maybe also internal forces, to account for the fact that the

same motion can be performed with “relaxed” or with “tense” muscles.

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2. Development of an artificial prosthetic hand. The final hand prosthesis has a

strong mechanical component, in which the advances of robotic artificial

hands need to be paired with the results of the signal identification and

constrained by desired user specifications: similarity to the real human hand

(weight, size and complexity, surface), comfortable body interface, human like

performance and adequate sensory feedback. The design of the prosthetic hand

is Mechatronics and multidisciplinary in nature.

1.2 NEED OF PROJECT

Upper limb amputation with hand loss is extremely devastating. The role of the hand

in human life is not limited to physical/functional movements, but, rather, is intimately

intertwined with psychosocial roles including gestures, caressing, communication, and

sensation. Thus, successful rehabilitation after upper limb amputation requires a multi-

dimensional, interdisciplinary approach. Selection of the appropriate prosthetic device that

provides the best prehension and functional movement is an important goal of rehabilitation.

The amputee‘s physical and cognitive capacity (e.g. amputation level, stump muscle

capacity); functional, recreational and vocational needs, psychosocial acceptance, availability

of resources (e.g. health care system, insurance coverage), accessible medical/technical

support for prosthetic fitting and follow up (e.g. living in rural or urban areas) influence the

prosthetic choice. For example, a study by LeBlanc comparing prosthetic use in different

countries shows the effect of cultural and psychosocial factors along with functional needs on

prosthetic choices. According to this study, 72% of upper limb prosthesis users in the US

preferred hooks as a terminal device; whereas in three European countries this percentage

was lower, varying between 12-30%.

1.3 AIM OF POJECT

Design and develop low cost alternative for existing prosthetics hands for five Finger

operations with muscle actuation. To enable patient to perform basic operations like gripping

and holding of simple objects. There are some research objectives considered for detailed

overlook.

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Research Objectives:

� Design of artificial fingers, palm and actuation mechanism under mechanical aspects.

� Design of muscle actuation sensing system, finger actuation system under electronic

aspects.

� Safety aspects for gripping, holding of objects.

� Aesthetically, ergonomically and environmentally satisfying design.

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CHAPTER 2

BACKGROUND AND LITERATURE REVIEW

The prosthetic hands are commonly used in artificial limb replacement area. It is

merely medical related term. The existing techniques for amputee are spring operated hand

which is actuated by movement of shoulder of the body. These hands are mainly use to hide

the amputee area and use for minimum daily work. Below are the few artificial prosthetic

hands.

2.1 Upper limb prostheses

Upper limb prosthetic devices are either passive or active. Passive prostheses, with no

moving parts, are generally used for cosmetic purposes. Active prostheses may be body-

powered or externally-powered. Hybrids of these two systems are also available. A body-

powered prosthesis usually employs a harness and cables. A variety of terminal devices

(hooks, hands) can be attached. According to LeBlanc (1988), 28% of prehensors in use in

the US were hands (both passive and active); whereas in the UK, West Germany and Sweden

the percentage of hand prehensors were 76%, 88%, and 70%, respectively[2]. The advantages

of body-powered prostheses include: simple operational mechanisms with intrinsic skeletal

movement (which voluntarily opens/closes a terminal device), silent action, light weight,

moderate cost, durability and reliability, and rough sensory feedback about the positioning of

the terminal device. They are utilized more often in less-developed countries with scarce

medical and rehabilitation infrastructure and technical resources. As Bhaskaranand points

out, prosthetic rehabilitation of patients with financial constraints requires durable and low

cost prostheses[1]. Body-powered prostheses are also preferred by amputees living in rural

areas (far from prosthetic centres), as well as by workers who are in labour-intensive manual

and outdoor occupations. In general, prostheses used at challenging work environments are at

a higher risk of exposure to corrosive materials, water or heat.

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2.1.1 Spring operated hand:-

In this technique, the hand is operated by spring tension. Normally these fingers are in ideal positions as shown above in fig. The spring is connected to shoulder by some mechanical strings.

Fig.2.1 Spring operated prosthetic hand. [16]

Whenever patient jerks the oulder, strings pull the spring and accordingly fingers are opened.

Main fact is, only three fingers are in actual operation. The little finger and ring finger are

dummy and used only for aesthetically sound design.

When person actuates the fingers trough cable from shoulder, the three fingers opens and

closes immediately releases the tension. Silent control of fingers is not possible because of its

structure. The system is made up of metallic parts cause heaviness.

Cost of the system is less and economical for poor peoples. Comparing to operation and cost,

it is very ideal product.

2.1.2 Myoelectric prostheses

Myoelectric technology uses electromyographic (EMG) activity, a form of electrical

signal, from the voluntary movements of the stump muscles. EMG signals, which control the

flow of energy from the battery to the electric motor, are captured through surface electrodes.

The amplitude of the EMG signal is generally proportional to the contraction of the residual

muscle. After amplification and transmission, the myoelectric control system activates the

electric motor to operate the terminal device. Surface electrodes can be affected by donning,

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or by surface conditions such as perspiration. As well, during the journey from the muscle to

the skin‘s surface, EMG signals may encounter noise and interference from other tissues. One

option to increase signal control is needle/implant electrodes inserted into active muscle

fibres. However, this approach is not immune to many technical issues and introduces its own

pros and cons. More information about implantable electrodes can be found elsewhere. The

motion of the wrist and terminal device are controlled by myoelectric sensors located either

at a single site (muscle) or dual sites. Switching between the two different modes (wrist or

terminal device) is usually directed by proportional control (fast or slow muscle contraction)

or simultaneous control (muscle co-contraction) [upp/55][59]. In proportional control, the

power of the muscle determines the speed or force of the prosthetic device[upp/60].

Advanced sockets (integrating sensors and metal connections within silicone) and

elastomeric liners have helped improve EMG signal acquisition[upp/55]. The incorporation

of programmable microprocessors in myoelectric prostheses increases the adjustment range

for EMG signal characteristics and the modification of prosthetic control parameters. Using

microprocessors, EMG signals are filtered and a real-time signal analysis is provided.

Microprocessors also accommodate pattern recognition-based control, which increases

functionality of the prosthesis with higher involvement/input of the user and, in return,

decreases the cost and time involved during initial fitting

2.1.1 Commercially available hand:-

Fig.2.2 Commercial Myoelectric hand [6]

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In this technique, each finger is actuated separately with separate mechanism. These fingers

are operated by small dc motors with the sensing of brain signals. The intermediate system is

very complex and bulky. The EEG signals from the brain are sensed and processed using

high capacity filters and electronic circuits. These fingers motions are aesthetically same as

real human fingers. The cost of the hand is very high.

2.2 Review of literature

- Analyzing and comparing incidence and prevalence rates of amputations is

frequently unreliable. Data collection methods vary across countries and even across

jurisdictions within the same country.30

- Frequently, studies on patients with upper limb prostheses have limited numbers of

study subjects. Study teams from different prosthetic rehabilitation centers would do well to

collaborate to maximize sample size and enhance the validity of their research. A lack of

standard outcome measures frequently restricts this integration and limits the comparison of

findings from individual studies [3].

- The majority of the studies on upper limb myoelectric prostheses have used

questionnaire surveys only [5]. Other authors have employed questionnaires in addition to

other study methods [6] while a number were either clinical/comparative studies or were

chart reviews without questionnaires [4]

- Occasionally, studies compare control systems of various prosthetics without

keeping terminal devices constant across compared groups [7].

- Prosthetic studies performed in laboratory settings usually have results based on

optimal conditions, rather than real life conditions [8]. Many of the published studies on

myoelectric prostheses are based on experimental hands or prosthetic features being studied

in research laboratories of the manufacturers/universities.

Page No.9


CHAPTER 3

SYSTEM OVIERVIEW

3.1 BLOCK DIAGRAM

Fig.3.1 System Design

From Fig.3.1 this block diagram, we can know the whole project outline. Muscle

sensing circuitry is giving signals to the microcontroller. Microcontroller rotates the motor to

operate the fingers. Gripping or holding is done by the fingers which give feedback through

feedback system to the controller. Controller will decide to stop or start the motor.

The system design consists of mechanical gripper actuated by electronic circuit. The

design is fabricated in aluminium material. It is designed with real human hand dimensions.

These various aspects like palm, length of fingers, thickness of the finger, are take from the

human hand dimensions. These five fingers are actuated with a lead screw assembly. The

lead screw is rotated by DC motor accordingly. All fingers are actuating by single motor.

Human forearm muscles are main sensing element of the system. This muscle actuation is

sensed by FSR. Whenever human is picking or gripping fingers, forearm muscles are

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actuating. FSR are mounted on the human forearm of amputee person where maximum

muscle motion is available. These signals are processed by microcontroller. These fingers

are actuated to hold or release the objects. We can pick 10kg of weight in the hand with any

shape. There are three strain gauges coupled with alternate fingers and thumb as feedback

sensing in terms of the vibration to the patient muscles. These feedback signals confirm

patient that objects is gripped by fingers perfectly. These feedbacks are given to the patient

through vibration motor (pager motor). The feedback response is analogue in nature which is

relative to the intensity of vibration to the muscles.

3.2 DESIGN ASPECTS

In the designing aspects three main parameters are included which defines the whole

system. In Mechatronics design system, designer should always think on mechanical,

electronics aspects. Here the project falls in medical engineering collaboration with

Mechatronics touch. It is very necessary to consider aesthetic, ergonomics, environmental

situations, user comfort for this prosthetic hand. The design is based on all above parameter

considerations. The detail design aspects are discussed below with specifications.

3.2.1 MECHANICAL DESIGN:-

In this aspects the material, size, shape, weight, strength, suitability,

maintenance etc various parameters are discussed and a well satisfying system is designed.

As these components are having some irregular shapes, these components are fabricated by

laser cutting operation. Autocad drawing files were given as input for the sheet metal cutting.

It was very cost effective and accurate machining.

Fig. 3.2 shows detailed mechanical design of the hand. It consists of 7 main sub parts.

Assembly of the all these parts gives collective performance of the hand. Details of the parts

are discussed below;

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Fig.3.2. Skeleton of Hand

1. Base:-The body is fabricated by cutting of 3mm aluminium sheet by laser cutting

techniques. 2D shapes are cut through sheet and then sandwiched by grubs. Outer

diameter of the upper part of base is 90 mm and lower part i.e. base mounting is 30

mm with offset distance of 40 mm for free motion of the pinion. The distance

between base plate and the bearing is maintained by 3 ribs which affect a cage like

structure. It is collectively known as Base. The bearing mounting is having through

holes to hold the “Mounting” of the hand. The upper part of the base is sliced in three

sections. It is made only for clamping of the finger pins. These slices are fastened by

3*10 mm grubs.

Finger

Base

Link Pin Pinion

Mounting

Lead Screw Bearing

Motor

Clamp pin

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Fig.3.3 Base

2. Fingers:-It is main part of the assembly. These fingers are light weight. The very

important aspect considered while designing is its strength. As the gripping, holding

of an object is done by fingers; its strength is maintained more. Shape of the finger is

kept such that all fingers can meet at a point when closed. It has good capacity to

hold, grip partial heavy objects also. The finger has two holes at lower end to hinge

itself and the link pin. Finger is pushed or pulled by the pinion through “Link pin”.

These are fabricated in pieces of three by laser cutting and then sandwiched by grubs

as shown in the fig. Strain gauges are bonded on the fingers by adhesive.

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Fig.3.4 Finger

3. Link Pin:-It is aluminium material pin with 3 mm thick, 24 mm in length and 5 mm in

width. It has two holes at its both ends in 2 mm diameter. It is assembled to connect

finger with “Pinion”.

Fig 3.5 Link pin

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4. Pinion:-It is same as base but slight small in diameter. It has slots inside to mount

pins. It is made up of light material aluminium. The dimensions of the part are, outer

dia. is 30 mm, 6 mm thick, 12 mm inner diameter with threaded nut of M6 inside

having pitch 1mm. It is freely slides over the “Stud” with forcing the link pin upward

and pulling downward.

Fig 3.6 Pinion

5. Lead Screw:-It is 50mm in length with external threading of 1mm pitch. It is passing

through bearing mounted on the base. Stud is actual rotating by motor through gear.

One end is fixed with “motor”, while another is just supported to the base. To and fro

motion of “Pinion” is achieved by this stud rotation. It is made up of MS material.

6mm outer diameter lead screw is machined on lathe to get specific diameters for

mounting on bearings.

Fig.3.7 Lead screw

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6. Clamp Pin:-It is MS pin in 2mm diameter used in base, finger and pinion for hinge

and clamp mechanism. These pins are fabricated on lathe machine. A 3mm rod is cut

into small pieces as shown here in fig. 3.8. Special purpose small lathe machine is

used for fabrication.

Fig 3.8 Clamp pin

7. Mounting:-It is supportive to mechanical and electronic components. It is very

essential for fixing the hand over the amputee.

Fig 3.9 Mounting

It is made up of reformed plastic material. Shape and size of this mounting is depending

on the amputee persons size of forearm. Synthetic material is cushioned inside for

comfort. The base is fixed with one end of the mounting. This mounting has two sections

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separated by a diaphragm. At the closed end circuit board, strain measurement board,

motor and battery are placed. These components are separated by diaphragm. On the end,

amputee hand is placed. This part is covered with some cushion material to feel soft for

patient. This mounting is light weighted and has good strength to bear the load. In the

open end of the mounting two FSRs and pager motor is coming out for connection with

the patient.

8. Bearing: - It is standard size bearing used in 2 nos. to support the lead screw at its both

ends. It has 5mm inner diameter, 19 mm outer diameter and 6mm width. It is fixed into the

bearing slots designed on base component.

Fig. 3.10 Bearing

It is ball type bearing in steel material. These bearings are minimizing the friction between lead screw and motor which will help to operate the assembly smoothly.

3.3 ELECTRONIC DESIGN

In any Mechatronics system, electronics has always same importance in designing.

Similarly here in the prosthetic hand designing, sensing part is achieved by the electronics

circuitry. This circuitry is mounted on the Mountings of the hand shown in mechanical

design. Size of the circuit is designed in compact size so that it can be easily fitted in

mountings. It is protected from external environment also. The detailed design is discussed

below;

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Strain Gauge (BF AA series )

Fig.3.11 Strain gauge [10]

Karma material is a nickel chromium alloy which can be used for strain sensing. The

characteristics of the alloy compared with standard constantan alloy strain gages are as

follows:

• Improved fatigue life.

• Excellent Stability over a wide temperature range.

• A much flatter thermal output curve which provides for more accurate

Thermal correction over a wider temperature range.

• A higher resistivity which enables higher resistance strain gages for

The same size or same resistance in a smaller size.

Karma gages are available with temperature characteristics matched to stainless steel or

aluminum. Karma is known to be difficult to solder, even with special flux. OMEGA is

offering ribbon leads or copper plated solder pads, so that standard soldering techniques can

be used, making wiring easier [10].

Creep compensation is available for Karma strain gages. It may be necessary in transducer

design to match the strain gage transducer creep characteristics to the spring element. Karma

strain gages are labeled with a letter code which identifies a creep code value. The creep

characteristics of a strain gage pattern can be modified by varying the length of the end loops

and the limb or strand width. Creep codes are a ratio of the end loop length to the limb width.

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An increasing ratio will give a longer end loop and a more positive creep characteristic.

OMEGA will work with you to develop the custom creep value needed for your application.

K-Series strain gages are suggested for static strain measurement over a wide temperature

range from -75 to 200°C (-100 to 392°F) due to their good linearity over this wide

temperature range.

K-Series strain gages are often used for fatigue-rated transducer designs. The fatigue life of

Karma alloy tends to be much better than constantan, and so transducers using Karma strain

gages provide good fatigue life. You will notice if you compare the fatigue specifications that

Karma is rated at ±1800 micro strain, >10,000,000 cycles, and constantan is rated at SGD

series is rated at ±1500 micro strain, >10,000,000 cycles. A transducer designed at ±1500

micro[11].

Fig3.12 Strain Gauge Specification [11]

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3.3.1 Force Sensing Resistor FSR

A force-sensing resistor is a material whose resistance changes when

a force or pressure is applied. They are also known as "force-sensitive resistor" and are

sometimes referred to by the initialize "FSR".

Force-sensing resistors consist of a conductive polymer, which changes resistance in a

predictable manner following application of force to its surface. They are normally supplied

as a polymer sheet or ink that can be applied by screen printing. The sensing film consists of

both electrically conducting and non-conducting particles suspended in matrix. The particles

are sub-micrometre sizes, and are formulated to reduce the temperature dependence, improve

mechanical properties and increase surface durability. Applying a force to the surface of a the

sensing film causes particles to touch the conducting electrodes, changing the resistance of

the film. As with all resistive based sensors, force-sensing resistors require a relatively simple

interface and can operate satisfactorily in moderately hostile environments. Compared to

other force sensors, the advantages of FSRs are their size (thickness typically less than

0.5 mm), low cost and good shock resistance. However, FSRs will be damaged if pressure is

applied for a longer time period (hours). A disadvantage is their low precision: measurement

results may differ 10% and more [12].

Fig3. 13 FSR Sensor [12]

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PARAMETER VALUE NOTES

Specifications:

• Size Range

– Max = 20” x 24” (51 x 61 cm) , Min = 0.2” x 0.2” (0.5 x 0.5 cm) Any shape

• Device thickness:

– 0.008” to 0.050” (0.20 to 1.25 mm) Dependent on materials

• Force Sensitivity Range:

– < 100 g to > 10 kg Dependent on mechanics

• Pressure Sensitivity Range:

– 0< 1.5 psi to > 150 psi(< 0.1 kg/cm2 to > 10 kg/cm2)

• Part-to-Part Force Repeatability:

– 15% to 25% of established nominal resistance with a repeatable actuation system

• Single Part Force Repeatability:

– 2% to 5% of established nominal resistance with a repeatable actuation system

• Force Resolution:

– Better than 0.5% full scale

• Break Force (Turn-on Force):

– 20 g to 100 g (0.7 oz to 3.5 oz) Dependent on mechanics and FSR build

• Stand-Off Resistance:

– > 1M Unloaded, unbent

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3.3.2 Microcontroller Atmega8 (Atmel)

The Atmel®AVR® ATmega8 is a low-power CMOS 8-bit microcontroller based on

the AVR RISC

Architecture. By executing powerful instructions in a single clock cycle, the ATmega8

achieves

Throughputs approaching 1MIPS per MHz, allowing the system designer to optimize power

consumption versus processing speed [13].

Features

• High-performance, Low-power Atmel®AVR® 8-bit Microcontroller

• Advanced RISC Architecture

– 130 Powerful Instructions – Most Single-clock Cycle Execution

– 32 × 8 General Purpose Working Registers

– Fully Static Operation

– Up to 16MIPS Throughput at 16MHz

– On-chip 2-cycle Multiplier

• High Endurance Non-volatile Memory segments

– 8Kbytes of In-System Self-programmable Flash program memory

– 512Bytes EEPROM

– 1Kbyte Internal SRAM

– Write/Erase Cycles: 10,000 Flash/100,000 EEPROM

– Data retention: 20 years at 85°C/100 years at 25°C

– Optional Boot Code Section with Independent Lock Bits

• Peripheral Features

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– Two 8-bit Timer/Counters with Separate Presales, one Compare Mode

– One 16-bit Timer/Counter with Separate Presales, Compare Mode, and Capture

• Eight Channels 10-bit Accuracy

– 6-channel ADC in PDIP package

• Six Channels 10-bit Accuracy

Fig3.14. Atmega8 microcontroller[13]

– Byte-oriented Two-wire Serial Interface

– Programmable Serial USART

– Master/Slave SPI Serial Interface

– Programmable Watchdog Timer with Separate On-chip Oscillator

– On-chip Analog Comparator

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3.3.3 DC Motor

These motors are light weight, high speed, moderate torque and low cost depending

on requirement. In the design of this system DC motor is selected because of these versatile

properties. The whole system is operated on the dc power bank i.e. battery. The system

design is well suitable for 5V dc supply and minimum power consumption. The selected dc

motor is therefore well suitable in power consumption; torque required and speeds in rp.

Fig3.15.DC Motor

Specification:

Body Diameter: 15.5 mm

Body Length: 20mm

Shaft Orientation: Inline

Rated Operating Voltage: 5V

Rated Torque: 0.5mNm

Rated Speed: 9000rpm

Typical Max Output Power: 910mW

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3.3.4 Vibration Motor

These tiny and feisty motors have offset weights that make them vibrate when they

spin. They're normally called "pager motors" because they're the type found in pagers and

cell phones that have a "vibrate" feature.

What to do with them? Well for starters, they're the perfect thing for making Bristle bots,

vibrobots, BEAM bots, and other tiny robots. They have wire leads attached that are color

coded and pre-stripped on the ends. These motors can be driven with 3 V coin cells like the

CR2032. Each one comes in a removable rubber boot that has one flat side for easy mounting

[14].

Fig.3.16 Pager motor [14]

Specifications:

Nominal voltage: 3 V

Operating voltage: 2.5 ~ 3.5 V

Rated current: 85 mA

Nominal speed: 12000 RPM

Diameter: 5mm

Length: 8mm

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3.3.5 Power source

Fig. 3.17 Power bank

This power source is 5V, 2 amp rating. Power source is main device in the electronic

section. This battery source is rechargeable and tiny in shape. This battery is fixed in

the mounting of the device. Life of battery is depending upon usage of the device. If

the battery is unable to produce current required to run the motor, it is supposed to

charge by adapter.

Page No.26


CHAPTER 4

HARDWARE IMPLIMENTATION

Hardware implementation consists of measurement system board and its peripherals. Main

controller board and strain gauge board are discussed below.

4.1 Measurement System

Fig.4.1 Controller board

This board is consisting of various electronic parts like controller, motor driver, switches,

variable resistors, zener diode and input/output Berge pin connectors. The circuit board is

designed for compact size and shape so that it can be fitted in the mounting of the hand. The

measurement board is fabricated by PTH technology with dual side tracks. Each input pin has

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connected with variable resistor to adjust the amplification of input signal. Two FSR and two

strain gauges are input for board. There are two output relimate connectors for DC motor and

pager motor. Board is separately powered by a battery.

Fig. 4.2 Strain measurement

Sensor mounting circuit is shown above. It is mainly for strain gauge input signal. Strain

gauges are normally connected with a arm of bridge. In this circuit strain gauges mounted on

the fingers are connected to the measurement board through this bridge circuit. Variable

resistors are used to adjust the change in resistance i.e. strain developed. When fingers are

gripping object, at maximum gripping, strain will develop. This strain is in terms of change in

resistance. This change is sensed by the circuit and signals are given to the measurement

board.

4.2 Mechanical System

The fig. 4.2.1 is showing that how FSR are mounted on the forearm of amputee person.

These FSR are having force ranges from 10 gms to 10 kg. Sensors are firmly mounted on the

forearm such that some minimum force can be applied on it. These sensors are placed on the

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maximum stimuli muscle region to get maximum output. These sensors are mounted on the

amputee area before mounting of the assembly on the amputee. It is having long flexible

cables such that fsr can hold better

Fig. 4.3 FSR mounting

.

Fig.4.4 Strain gauge Mounting

Fig. 4.2.2 is showing strain gauge mounted on the finger. These gauges are bonded by epoxy

adhesive Loctite 416. Two strain gauges are bonded on two fingers. These mounting of

sensors are covered.

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4.3 Algorithm of the system

Fig. 4.5 Algorithm of system

Prosthetic hands are normally operated by EMG signals for the smoother operations. These

signals are captured by placing electrodes. The signal conditioning and processing is quite

difficult and which increases overall cost of the system. Here in this system very simple

concept is adopted. The forearm muscle motions are responsible for finger actuations. As the

muscles are contracted or relaxed, fingers are closed or opened. The patient has amputee in

below elbow region. It means that forearms muscles are present and working finely. These

active muscles are our main sensing elements. These muscles are sensed by FSR i.e. Force

Sensing Resistor. These FSR are mounted on the well active muscles in amputee area. The

signal sensed by the FSR is processed in the controller. The controller is programmed such

that there are two modes of operations, Teach and Run. During teach mode patient is setting

only two positions of fingers with respect to muscle highest contraction and relaxation. These

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positions are achieved by user with his skills. LEDs are used as indicators for position

recording. As two positions are recorded, user will shift the Teach mode into Run mode. In

the teach mode, user has to record two levels for motor actuation. To grip and release the

object in fingers, motor has to rotate in clockwise and anticlockwise directions. In the teach

mode user will relax his amputee muscles at his maximum and this level of muscle is stored

in controller. Similarly by contracting the muscle at his highest, another level is stored. When

user has to open his fingers in Run mode, he has to keep his muscles level to highest

maximum relaxes, which is stored previously. To close the fingers, user has to keep muscles

level to highest contraction, also stored in memory. Any intermediate position, if not stored

previously, treated as stop for motor rotation. In the controller user can store maximum 8

positions for very smoother operation. It gives only gripping actuation and dose not confirm

that object is perfectly held by fingers. To overcome this problem, strain gauges are mounted

on three fingers. If the gripping of fingers continues it will exert strain on fingers. The response of these strain gauges is directly synchronized with vibrator motor. These vibrations

are nothing but the response for perfect gripping. The patient will cope up with this response

after few days, months by successive use of the system. To limit the pinion motion, two

micro switches are mounted on the base of the device. For both maximum limit of the pinion

those switch becomes NC, which are already NO. This will directly stops the motor

actuation. Power bank is used as power source for the system and can be charged. It is small

in size, better life, cheap.

Fig.4.6 Hand Image Covered.

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4.4 Cost Estimation

As we have discussed earlier, the aim behind this development was to reduce the cost of the

product and make available the system for Indian rural persons who have their amputee.

Current available highly developed products are very much costlier to afford common person.

Here in this development of the system we have purposely tried to reduce the cost.

Electronic costing product wise is listed below,

Component Description Quantity Unit cost

Rs. Total cost

Rs.

Atmega 32 Micro controller on

board 1 140 140

FSR force sensing sensor 2 500 1000

strain gauge strain sensing sensor 2 180 360

Variable resistors 100k ohm variable

resistors 11 5 55

Switch buttons Push type ON/OFF

button 8 2.25 18

Resistors Smd resistors 10k ohm 20 0.25 5

Zener diode Diode for

measurement board 1 5 5

IC base IC mounting base 1 5 5

L293D Motor driver ic 1 45 45

Relimate connectors Output pin connectors 2 5 10

Berge pin connectors ------ 50 ----- 50

Variable resistors 20 ohm for bridge 4 5 20

INA114 Strain gauge bridge IC 2 400 800

Pcb Circuit board manufacturing

1 1000 1000

Page No.32


Mechanical costing product wise is listed below,

Components Description Quantity Unit

cost Rs. Total cost

Rs.

Aluminum sheet

3mm thick 200*200 sheet 1.5 kg 230/kg 345

Laser cutting Aluminum laser cutting for better shape

and size 1 1200 1200

Grub screws Fastening of components 30 3 90

Plastic mounting

For mounting on forearm 1 40 40

Foam 6mm foam sheet 1 50 50

Stud 6*50mm, 1mm pitch stud 1 20 20

Bearings 5*17*6mm bearing 2 50 100

Gloves To wrap over fingers 1 100 100

Total 1945

Total product cost = electronic cost + mechanical cost = 5837/- ~ 6000/-

The combination of the both costing is nothing but the cost of the individual product in experimental basics, in the bulk manufacturing this cost will fall down drastically.

Dc motor 5V dc motor 1 150 150

Pajor motor 1.5V vibration motor 1 80 80

Wires, solder metal, Wax,

------ ----- ------ 150

Total 3892

Page No.33


CHAPTER 5

EXPERIMENTAL SETUP AND RESULTS

In detail of systems, it consists of mechanical gripper and electronic circuits. Before

going to the experiments we know that the Patient with below elbow amputee has some part

of well stimulated muscles. Maximum stimuli part of the muscles is observed to decide the

fixing of FSR for better results. After getting well stimulated locations, a capping of cloth is

designed. These capping are having cavities to place FSR which after wrapped around the

amputee, achieve the desired location of stimuli. Then controller is put on TEACH mode by

user. User has now freedom to record suitable intermediate positions. In this mode as user

pushes first button controller will store its first position. Slowly he will move his muscles and

motor will star rotation. As he finds another intermediate position again, this is stored.

Similarly patient can store maximum 8 no. of positions. Now here teaching task is completed.

Now user will shift to RUN mode and autonomous actuation is starting. This can be said as

Level Sensing. Now user starts to do routine tasks with these mechanisms. When muscles are

actuated, respective finger gripping is achieved. If the object is picked in the hand by user

then also motor is still running in same direction. This will create strain on the fingers and

same is reflected to the user muscles in terms of vibrations. This method is repeated multiple

times by patient for better command n the gripping.

5.1 Experiment conducted

In the experiment of the hand operation FSR are mounted on forearm. By selecting

Teach mode operation both contraction and relaxing levels of force are stored in the

controller. Controller is then punt on Run mode to operate continuously. After successful

mounting of the whole assembly I contract and relaxed the muscles. Similarly the fingers of

the assembly are actuated as shown in fig. 5.1 and 5.2. Same procedure is repeated for

multiple times to confirm the successful operation. At the highest gripping state pager motor

started to vibrate. These vibrations are sensed by the human muscles, as the brain is very

much adoptive to cope up with vibration as successful gripping.

Page No.34


Fig. 5.1 muscle contracted to closed position

Fig 5.1 shows the muscles are contracted in the forearm region, results in the gripper is closed. As we know that, there are two muscle positions are stored in the controller; this is highest contraction of the muscle. This sensing is given by the FSR and gripper motor starts rotating which in actuation closing fingers.

Fig.5.2 muscle relaxed to open position

Page No.35


Fig 5.2 shows the muscles are relaxed in the forearm, results in the gripper is opened fully.

This is highest relaxing muscle position stored in the controller. Similarly any intermediate position sensed by the FSR is resulting stop of the motor.

Findings

� Fingers can be actuated according to muscle motions.

� Fingers can grip objects in the hand.

� Strain is developed in the fingers gives vibration to the pager motor.

Page No.36


CHAPTER 6

EXPERIMENTAL SETUP AND RESULTS

6.1 Conclusion

1. Mechanical design of the five figures operated prosthetic hand is developed in solid

works and it is fabricated in aluminium.

2. Measurement system required for the sensing the muscle actuation has been

developed on board had been fabricated.

3. System has been developed with low cost application.

6.2 Future Scope

1. Mounting material is designed for user comfort.

2. Feedback system design for safety.

3. Environmentally sound design.

4. System design for intermediate position of fingers.

5. Limit switches are mounted for safely to control the max and min finger motions.

6.3. Advantages

1. Amputee persons can perform his minimum task.

2. Aesthetically it will look like a real hand which hides its amputee.

3. Low cost comparatively.

4. Rechargeable battery operated.

5. Picking, holding, gripping of objects, writing by pens can be possible.

Page No.37


REFERANCES

[1]. 43. Bhaskaranand K, Bhat AK, Acharya KN. Prosthetic rehabilitation in traumatic upper limb

amputees (an Indian perspective). Arch Orthop Trauma Surg. 2003 Sep;123(7):363-6.

[2]. LeBlanc M. Use of prosthetic prehensors. Prosthet Orthot Int. 1988 Dec;12(3):152-4.

[3]. Biddiss EA, Chau TT. Upper limb prosthesis use and abandonment: a survey of the last 25

years. Prosthet Orthot Int. 2007 Sep;31(3):236-57.

[4]. Kyberd PJ, Beard DJ, Morrison JD. The population of users of upper limb prostheses

attending the Oxford Limb Fitting Service. Prosthet Orthot Int. 1997 Aug;21(2):85-91.

[5]. Biddiss E, Chau T. Upper-limb prosthetics: critical factors in device abandonment. Am J Phys

Med Rehabil. 2007 Dec;86(12):977-87.

[6]. Datta D, Kingston J, Ronald J. Myoelectric prostheses for below-elbow amputees: the Trent

experience. Int Disabil Stud. 1989 Oct-Dec;11(4):167-70

[7]. Weaver SA, Lange LR, Vogts VM. Comparison of myoelectric and conventional prostheses

for adolescent amputees. Am J Occup Ther. 1988 Feb;42(2):87-91.

[8]. Hacking H. Long-term outcome of upper limb prosthetic use in the Netherlands European

Journal of Physical Medicine and Rehabilitation 1997;7(6):179-81.

[9]. A. L. Window Strain Gauge Technology, 1992 :Elsevier Applied Science

[10]. Strain gauge BF AA 350 10 (online) available on http://www.omega.com/techref/strain-

gage.html

[11]. Strain gauge manual (online) available on

http://www.omega.com/manuals/index.html?s=all

[12]. FSR details (online) available on http://www.instructables.com/id/FSR-Tutorial/

[13]. AVR atmega 32 microcontroller (online) available on

http://www.atmel.com/products/microcontrollers/avr/default.aspx

[14]. Pager motor details (online) available on

http://shop.evilmadscientist.com/productsmenu/partsmenu/131-pagermotor

[15]. Hand palm anatomy available (online) http://ittcs.wordpress.com/2010/10/31/notes-on-

anatomy-and-physiology-the-hand-and-the-tigers-mouth/

[16]. Spring operated hand paper by M.C. CARROZZA R. LAZZARINI M.R. CUTKOSKY The SPRING

Hand: Development of a Self-Adaptive Prosthesis for Restoring Natural Grasping Autonomous

Robots 16, 125–141, 2004_c 2004 Kluwer Academic Publishers. Manufactured in The

Netherlands