Robotic Tactile Sensor System

8/2/2019 Robotic Tactile Sensor System

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Robotic Tactile Sensor System 1

Department of Electronics and Communication, CEMP

CHAPTER 1

INTRODUCTION

This paper presents a tactile sensor system for a robot manipulator and an

active-sensing technique to realize 3-D object recognitions concerning object shape,

object surface normal, and object edge tracing with experimental results. The

proposed tactile sensor units implemented on the robot hand consist of three thin

sheets of force-sensitive resistors arranged triangularly with the peripheral circuits.

One potential application of the proposed techniques is to realize an effective human

robot cooperation to move an object together by utilizing the control of a hand pose to

keep the direction of the hand normal to the object surface in three dimensions, which

is often necessary when pushing an object. Another is a 3-D object edge tracing. The

proposed techniques can be employed in industrial processes such as welding and

inspection to eliminate manual teaching procedures for searching the object edge

automatically before doing the welding process. In these applications, information

about the object shape or orientation is not required in advance.

Through this project we are aiming to create a robot which can mimic our

hand actions, i.e. it will do the jobs by our hand directions. We are doing the

simplified version of ROBOTIC TACTILE SENSOR SYSTEM AND

APPLICATIONS; KITTI SUWANRATCHATAMANEE, IEEE TRANSACTIONS

ON INDUSTRIAL ELECTRONICS, VOL. 57, NO. 3 MARCH 2010.

We are replacing the robot which was created by Mitsubishi with servo motor

robot.


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CHAPTER 2

BLOCK DIAGRAM

Fig 2.1 Block Diagram of base section

Fig 2.2 Block Diagram of control station


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CHAPTER 3

BLOCK DIAGRAM DESCRIPTION

3.1 ROBOTIC ARMThe robotic arm we use consists of servo motors, with 4 degrees of motion.

The robotic arm motions are controlled by the combined operation of both flex

sensors & accelerometer.

3.2 SERVOMOTORSA servomotor (servo) is an electromechanical device in which a PWM

input determines the position of the armature of a motor.

3.3 FLEX SENSORS

Flex sensors are passive resistive devices that can be used to detect

bending or flexing. We are using flex sensors for detect the hand motion.

3.4 ACCELEROMETER

An accelerometer simply measures acceleration, either due to motion

or due to gravity. Acceleration is measured in m/s2.

3.5 PIC

For our project we are using PIC micro-controller. PIC is a family of

Harvard architecture micro-controllers made by Microchip Technology. The name

PIC initially referred to "Peripheral Interface Controller". PICs are popular with both

industrial developers and hobbyists alike due to their low cost, wide availability, large

user base, extensive collection of application notes, availability of low cost or free

development tools, and serial programming capability. PIC 168F77A is used here.

3.6 KEYS

Keys are used for the control the movement of the Robotic ARM.


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3.7 ZIGBEE:-

For wireless communication we are using ZigBee module. ZigBee is a

specification for a suite of high level communication protocols using small, low-

power digital radios based on an IEEE 802 standard for personal area networks.Applications include wireless light switches, electrical meters with in-home-displays,

and other consumer and industrial equipment that requires short-range wireless

transfer of data at relatively low rates. The technology defined by the ZigBee

specification is intended to be simpler and less expensive than other WPANs, such as

Bluetooth. ZigBee is targeted at radio-frequency (RF) applications that require a low

data rate, long battery life, and secure networking.


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CHAPTER 4

ROBOTIC ARM

A robotic arm is a robotic manipulator, usually programmable, with similar

functions to a human arm .Servo motor is used for joint rotation. It has about same

number of degree of freedom as in human arm. Humans pick things up without

thinking about the steps involved. In order for a robot or a robotic arm to pick up or

move something, someone has to tell it to perform several actions in a particular order

from moving the arm, to rotating the wrist to opening and closing the hand or

fingers. .So, we can control each joint through computer interface.

4.1 SALIENT FEATURES

The arm has four servos which are controlled through the use of only onemicrocontroller.

The arm could grab things approximately in a hemisphere of 50cm and isrobust made completely with an aluminium sheet of 2.5mm.

The arm is very user friendly because of the computer interface developed byus, even layman could operate it.

They could lift objects up to weight of 200 gm. Enabling the base rotation without the help of any gears or ball bearing, also

using only low torque servo motors and three castor wheels for rotating the

whole body.

Keeping the design of robotic arm gripper simple, as well as implementingthe gripping mechanism without using gears and with one servo motors.

4.2 WHAT ARE SERVO MOTORS?

Servo refers to an error sensing feedback control which is used to correct the

performance of a system. Servo or RC Servo Motors are DC motors equipped with a

servo mechanism for precise control of angular position. The RC servo motors usually

have a rotation limit from 90 to 180. But servos do not rotate continually. Their


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rotation is restricted in between the fixed angles. A servo is a mechanical motorized

device that can be instructed to move the output shaft attached to a servo wheel or arm

to a specified position. Inside the servo box is a DC motor mechanically linked to a

position feedback potentiometer, gearbox, electronic feedback control loop circuitry

and motor drive electronic circuit.

4.3 WHERE ARE SERVOS USED?

The Servos are used for precision positioning. They are used in robotic arms

and legs, sensor scanners and in RC toys like RC helicopter, airplanes and cars.

4.4 SERVO MOTOR WIRING AND PLUGSThe Servo Motors come with three wires or leads. Two of these wires are to

provide ground and positive supply to the servo DC motor. The third wire is for the

control signal. These wires of a servo motor are colour coded. The red wire is the DC

supply lead and must be connected to a DC voltage supply in the range of 4.8 V to

6V. The black wire is to provide ground. The colour for the third wire (to provide

control signal) varies for different manufacturers. It can be yellow (in case of Hitec),

white (in case of Futaba), brown etc.

Futaba provides a J-type plug with an extra flange for proper connection of the

servo. Hitec has an S-type connector. A Futaba connector can be used with a Hitec

servo by clipping of the extra flange. Also a Hitec connector can be used with a

Futaba servo just by filing off the extra width so that it fits in well.

Hitec splines have 24 teeth while Futaba splines are of 25 teeth. Therefore

splines made for one servo type cannot be used with another. Spline is the place

where a servo arm is connected. It is analogous to the shaft of a common DC motor.

Unlike DC motors, reversing the ground and positive supply connections does

not change the direction (of rotation) of a servo. This may, in fact, damage the servo

motor. That is why it is important to properly account for the order of wires in a servo

motor.


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Fig 4.1 Servo motor

4.5 SERVO CONTROLA servo motor mainly consists of a DC motor, gear system, a position sensor

which is mostly a potentiometer, and control electronics. The DC motor is connectedwith a gear mechanism which provides feedback to a position sensor which is mostlya potentiometer. From the gear box, the output of the motor is delivered via servospline to the servo arm. The potentiometer changes position corresponding to thecurrent position of the motor. So the change in resistance produces an equivalentchange in voltage from the potentiometer. A pulse width modulated signal is fedthrough the control wire. The pulse width is converted into an equivalent voltage thatis compared with that of signal from the potentiometer in an error amplifier.

The servo motor can be moved to a desired angular position by sending PWM(pulse width modulated) signals on the control wire. The servo understands thelanguage of pulse position modulation. A pulse of width varying from 1 millisecondto 2 milliseconds in a repeated time frame is sent to the servo for around 50 times in a

second. The width of the pulse determines the angular position.For example, a pulse of 1 millisecond moves the servo towards 0, while a 2milliseconds wide pulse would take it to 180. The pulse width for in between angularpositions can be interpolated accordingly. Thus a pulse of width 1.5 milliseconds willshift the servo to 90.

It must be noted that these values are only the approximations. The actualbehavior of the servos differs based on their manufacturer.

A sequence of such pulses (50 in one second) is required to be passed to theservo to sustain a particular angular position. When the servo receives a pulse, it canretain the corresponding angular position for next 20 milliseconds. So a pulse in every20 millisecond time frame must be fed to the servo.

Fig 4.2 Pulse train


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Fig 4.3 Servo Motor System

The required pulse train for controlling the servo motor can be generated by a timerIC such as 555 or a microcontroller can be programmed to generate the requiredwaveform. Here we use PIC 16F877A microcontroller for it.

4.6 APPLICATION OF ROBOTIC ARM The robotic arm can be designed to perform any desired task such as welding,

gripping, spinning etc., depending on the application. For example robot arms

in automotive assembly line perform a variety of tasks such as wielding andparts rotation and placement during assembly.

In space the space shuttle Remote Manipulator System have multi degree offreedom robotic arms that have been used to perform a variety of tasks such asinspections of the Space Shuttle using a specially deployed boom withcameras and sensors attached at the end effector.

The robot arms can be autonomous or controlled manually and can be used toperform a variety of tasks with great accuracy.The robotic arm can be fixed ormobile (i.e. wheeled) and can be designed for industrial or home applications.Robotic hands often have built-in pressure sensors that tell the computer howhard the robot is gripping a particular object. This keeps the robot from

dropping or breaking whatever it's carrying. Other end effectors includeblowtorches, drills and spray painters.this improves their performance.

In medical science: "Neuroarm" uses miniaturized tools such as laser scalpelswith pinpoint accuracy and it can also perform soft tissue manipulation, needleinsertion, suturing, and cauterization.


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CHAPTER 5

FLEX SENSORS

Flex sensors are sensors that change in resistance depending on the amount ofbend on the sensor. They convert the change in bend to electrical resistance - the morethe bend, the more the resistance value. They are usually in the form of a thin stripfrom 1"-5" long that vary in resistance from approximately 10 to 50 kilohms. Theyare often used in gloves to sense finger movement.

There are two main brands of flex sensors that are affordable and easilyavailable: SpectraSymbol Flex sensors and the Gentile-Abrams sensor, available fromJameco (part #150551 for $12.95). There are variations on the typical flex sensor suchas the FlexPoint Bend Sensor which measures force as well and has a wider resistance

range. Interlink is another brand that senses force as well. The FlexPoint sensorsrange in price from $3-$7 depending on length (1"-3"). They also add on a plasticconnect or casing for $0.75. Here we use SpectraSymbol Flex sensors.

Fig 5.1 Flex sensor


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5.1 HOW THEY WORKFlex sensors are analog resistors. They work as variable analog voltage

dividers. Inside the flex sensor are carbon resistive elements within a thin flexiblesubstrate. More carbon means less resistance. When the substrate is bent the sensorproduces a resistance output relative to the bend radius. With a typical flex sensor, a

flex of 0 degrees will give 10K resistance will a flex of 90 will give 30-40 K ohms.The Bend Sensor lists resistance of 30-250 K ohms.

5.2 ELECTRICAL CHARACTERISTICSSize: approx. 0.28" wide and 1"/3"/5" longResistance Range: 1.5-40K ohms depending on sensor.Lifetime: Greater than 1 million life cyclesTemperature Range: -35 to +80 degrees CelsiusHysteresis: 7%Voltage: 5 to 12 V

5.3 SCHEMATICSFlex sensors can be used in a variety of ways:

5.3.1 BASIC CIRCUITFlex Sensor as Voltage Divider - Output voltage increases with the bend.

Fig 5.2 Basic Flex Sensor Circuit

The impedance buffer in the circuit above is a single sided operationalamplifier, used with these sensors because the low bias current of the op amp reduceserror due to source impedance of the flex sensor as voltage divider. Suggested opamps are the LM358 or LM324.

5.3.2ADJUSTABLE BUFFERA potentiometer can be added to the circuit to adjust the sensitivity range.

Fig 5.3 Adjustable Buffer Circuit


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5.3.3 VARIABLE DEFLECTION THRESHOLD SWITCHAn op amp is used and outputs either high or low depending on the voltage of

the inverting input. In this way you can use the flex sensor as a switch without goingthrough a microcontroller.

Fig 5.4 Variable Deflection Threshold Switch

5.3.4 RESISTANCE TO VOLTAGE CONVERTERUses the sensor as the input of a resistance to voltage converter using a dual

sided supply op-amp. A negative reference voltage will give a positive output. Shouldbe used in situations when you want output at a low degree of bending.

Fig 5.5 Resistance to Voltage Converter

5.4 APPLICATIONSFlex sensors are used in gaming gloves, auto controls, fitness products,

measuring devices, assistive technology, musical instruments, joysticks, and more.


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5.5 FLEX GLOVEAn ergonomic hand-attachable controller (flex glove) for providing command

signals to control movement of at least one object responsive to hand movement. Theergonomic hand-attachable controller includes a base with a top surface configured tosupport a palm of a user's hand. A plurality of planar finger members may be

provided which incorporate at least one finger pad which is operable to controlmovement of a remote object. At attachment member is provided to secure a hand of auser with the top surface of the controller. Electronics within the ergonomic hand-attachable controller convert movement of a user's hand and fingers to commandsignals for controlling the movement of a remote object.

Fig 5.6 Flex glove


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CHAPTER 6

ACCELEROMETER

An accelerometer measures acceleration (change in speed) of anything that it'smounted on. Inside an accelerator MEMS device are tiny micro-structures that benddue to momentum and gravity. When it experiences any form of acceleration, thesetiny structures bend by an equivalent amount which can be electrically detected.Today, accelerometers are easily and cheaply available, making it a very viable sensorfor cheap robotics.

6.1 PRINCIPLES OF OPERATION

Most accelerometers are Micro-Electro-Mechanical Sensors (MEMS). Thebasic principle of operation behind the MEMS accelerometer is the displacement of asmall proof mass etched into the silicon surface of the integrated circuit andsuspended by small beams. Consistent with Newton's second law of motion (F = ma),as an acceleration is applied to the device, a force develops which displaces the mass.The support beams act as a spring, and the fluid (usually air) trapped inside the ICacts as a damper, resulting in a second order lumped physical system. This is thesource of the limited operational bandwidth and non-uniform frequency response ofaccelerometers.

The accelerometer will detect the 3 dimensional motions and generate force

which will create resistance variations in the flux sensor.

6.2 APPLICATIONS FOR ACCELEROMETERS

Accelerometers are very important in the sensor world because they can sensesuch a wide range of motion. They're used in the latest Apple Powerbooks (and otherlaptops) to detect when the computer's suddenly moved or tipped, so the hard drivecan be locked up during movement. They're used in cameras, to control imagestabilization functions. They're used in pedometers, gait meters, and other exerciseand physical therapy devices. They're used in gaming controls to generate tilt data.They're used in automobiles, to control airbag release when there's a sudden stop.

There are countless other applications for them.

Possible uses for accelerometers in robotics:

Self-balancing robots Tilt-mode game controllers Model airplane auto pilot Alarm systems Collision detection Human motion monitoring Leveling sensor, inclinometer

Vibration Detectors for Vibration Isolators G-Force Detectors


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Typical accelerometer applications: Tilt / Roll Vibration / Rough-road detection

o Can be used to isolate vibration of mechanical system from outsidesources

Vehicle skid detectiono Often used with systems that deploy smart braking to regain control

of vehicle Impact detection

o To determine the severity of impact, or to log when an impact hasoccurred

Input / feedback for active suspension control systemso Keeps vehicle level

6.3 AVAILABILITY AND COSTThe MEMS IC's are easily available and very affordable. However they all

require support circuitry and come as surface mounts.

6.4 WIRING REQUIREMENTSAny accelerometer package will have a power and ground line, and a single

output analog pin for each axis of acceleration. Some of the sensors come withadditional features/pins.

Fig 6.1 A 3 axis accelerometer board


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CHAPTER 7

PIC 16F877A MICROCONTROLLER

PIC is a family of Harvard architecture microcontrollers made by MicrochipTechnology, derived from the PIC1650 originally developed by General Instrument'sMicroelectronics Division. The name PIC initially referred to "Peripheral InterfaceController.

PIC 16F877 (Microchip Technology, Inc.) 8-bit microcontroller will be usedfor the controller. This microcontroller has a 25 MHz processor (the current compilerruns the processor at 20 MHz), 33 input/output (I/O) pins, (8K*14words) of EnhancedFLASH program memory, (368*8bytes) of RAM, (256*8bytes) of data EEPROM.The PIC does not have an operating system and simply runs the program in itsmemory when it is turned on.

Fig 7.1 Pin diagram

The analog voltage signal generated due to the resistance variations in fluxsensor are converted to digital using the Analog to Digital Converter (ADC) in thePIC microcontroller. The microcontroller will use these signals to generate the PWMsignal required to drive the four servomotors in the robotic arm.

7.1 ANALOG-TO-DIGITAL CONVERTER (A/D) MODULE

The Analog-to-Digital (A/D) Converter module has five inputs for the 28-pindevices and eight for the 40/44-pin devices.


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The conversion of an analog input signal results in a corresponding 10-bitdigital number. The A/D module has high and low-voltage reference input that issoftware selectable to some combination of VDD, VSS, RA2 or RA3.

The A/D converter has a unique feature of being able to operate while the

device is in Sleep mode. To operate in Sleep, the A/D clock must be derived from theA/Ds internal RC oscillator.

The A/D module has four registers. These registers are:

A/D Result High Register(ADRESH)

A/D Result Low Register (ADRESL)

A/D Control Register 0 (ADCON0)

A/D Control Register 1 (ADCON1)

The ADCON0 register controls the operation of the A/D module. TheADCON1 register configures the functions of the port pins. The port pins can beconfigured as analog inputs or as digital I/O.

Fig 7.2 A/D Block Diagram


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7.2 PWM MODULE

The PWM signal is generated by the Capture/Compare/PWM (CCP) moduleof the microcontroller. Each Capture/Compare/PWM (CCP) module contains a 16-bitregister which can operate as a:

16-bit Capture register

16-bit Compare register

PWM Master/Slave Duty Cycle register

Both the CCP1 and CCP2 modules are identical in operation, with theexception being the operation of the special event trigger.

7.2.1 CCP1 MODULE

Capture/Compare/PWM Register 1 (CCPR1) is comprised of two 8-bitregisters: CCPR1L (low byte) and CCPR1H (high byte). The CCP1CON registercontrols the operation of CCP1. The special event trigger is generated by a comparematch and will reset Timer1.

7.2.2 CCP2 MODULE

Capture/Compare/PWM Register 2 (CCPR2) is comprised of two 8-bitregisters: CCPR2L (low byte) and CCPR2H (high byte). The CCP2CON register

controls the operation of CCP2. The special event trigger is generated by a comparematch and will reset Timer1 and start an A/D conversion (if the A/D module isenabled).

7.2.3 PWM MODE (PWM)

In Pulse Width Modulation mode, the CCPx pin produces up to a 10-bitresolution PWM output. Since the CCP1 pin is multiplexed with the PORTC datalatch, the TRISC bit must be cleared to make the CCP1 pin an output.

The PWM period is specified by writing to the PR2 register. The PWM period

can be calculated using the following formula:

PWM Period = [(PR2) + 1] 4 TOSC (TMR2 Prescale Value)

PWM frequency is defined as 1/ [PWM period].

When TMR2 is equal to PR2, the following three events occur on the nextincrement cycle:

TMR2 is cleared

The CCP1 pin is set (exception: if PWM duty cycle = 0%, the CCP1 pin willnot be set)


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The PWM duty cycle is latched from CCPR1L into CCPR1H

The PWM duty cycle is specified by writing to the CCPR1L register and to theCCP1CON bits. Up to 10-bit resolution is available. The CCPR1L contains theeight MSbs and the CCP1CON contains the two LSbs. This 10-bit value is

represented by CCPR1L:CCP1CON. The following equation is used tocalculate the PWM duty cycle in time:

PWM Duty Cycle = (CCPR1L:CCP1CON) TOSC (TMR2 Prescale Value)

The maximum PWM resolution (bits) for a given PWM frequency is given bythe following formula.

Fig 7.3 Simplified PWM Block Diagram


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Fig 7.4 PWM Output


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CHAPTER 8

ZIGBEE MODULE

ZigBee is an established set of specifications for wireless personal areanetworking (WPAN), i.e. digital radio connections between computers and relateddevices. This kind of network eliminates use of physical data buses like USB andEthernet cables. The devices could include telephones, hand-held digital assistants,sensors and controls located within a few meters of each other.

WPAN low rate or Zigbee provides specifications for devices that have lowdata rates, consume very low power and are thus characterized by long battery life.

Zigbee makes possible completely networked homes where all devices are able tocommunicate and be controlled by a single unit.

ZigBee is one of the global standards of communication protocol formulatedby the relevant task force under the IEEE 802.15 working group. The fourth in theseries, WPAN Low Rate/ZigBee is the newest and provides specifications for devicesthat have low data rates, consume very low power and are thus characterized by longbattery life. Other standards like Bluetooth and IrDA address high data rateapplications such as voice, video and LAN communications.

8.1 ARCHITECTURE

Though WPAN implies a reach of only a few meters, 30 feet in the case ofZigBee, the network will have several layers, so designed as to enable intrapersonalcommunication within the network, connection to a network of higher level andultimately an uplink to the Web.

The ZigBee Standard has evolved standardized sets of solutions, calledlayers'. These layers facilitate the features that make ZigBee very attractive: low cost,

easy implementation, reliable data transfer, short-range operations, very low powerconsumption and adequate security features.

1. Network and Application Support layer: The network layer permits growth ofnetwork sans high power transmitters. This layer can handle huge numbers of nodes.This level in the ZigBee architecture includes the ZigBee Device Object (ZDO), user-defined application profile(s) and the Application Support (APS) sub-layer.

The APS sub-layer's responsibilities include maintenance of tables that enablematching between two devices and communication among them, and also discovery,the aspect that identifies other devices that operate in the operating space of anydevice.

The responsibility of determining the nature of the device (Coordinator / FFD

or RFD) in the network, commencing and replying to binding requests and ensuring asecure relationship between devices rests with the ZDO (Zigbee Define Object). The


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user-defined application refers to the end device that conforms to the ZigBeeStandard.

2. Physical (PHY) layer: The IEEE802.15.4 PHY physical layer accommodates highlevels of integration by using direct sequence to permit simplicity in the analog

circuitry and enable cheaper implementations.

3. Media access control (MAC) layer: The IEEE802.15.4 MAC media access controllayer permits use of several topologies without introducing complexity and is meantto work with large numbers of devices.

Fig 8.1 ZigBee Stack Architecture

8.2 DEVICE TYPES

There are three different ZigBee device types that operate on these layers in any self-organizing application network.

These devices have 64-bit IEEE addresses, with option to enable shorteraddresses to reduce packet size, and work in either of two addressing modesstar andpeer-to-peer.

1. The ZigBee coordinator node: There is one, and only one, ZigBee coordinator ineach network to act as the router to other networks, and can be likened to the root of a

(network) tree. It is designed to store information about the network.

2. The full function device FFD: The FFD is an intermediary router transmitting datafrom other devices. It needs lesser memory than the ZigBee coordinator node, andentails lesser manufacturing costs. It can operate in all topologies and can act as acoordinator.

3. The reduced function device RFD: This device is just capable of talking in thenetwork; it cannot relay data from other devices. Requiring even less memory, (noflash, very little ROM and RAM), an RFD will thus be cheaper than an FFD. Thisdevice talks only to a network coordinator and can be implemented very simply in star

topology.


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8.3 ZIGBEE CHARACTERISTICS

The focus of network applications under the IEEE 802.15.4 / Zigbee standardinclude the features of low power consumption, needed for only two major modes(Tx/Rx or sleep), high density of nodes per network, low costs and simple

implementation.

These features are enabled by the following characteristics:

2.4GHz and 868/915 MHz dual PHY modes. This represents three license-free bands: 2.4-2.4835 GHz, 868-870 MHz and 902-928 MHz. The number ofchannels allotted to each frequency band is fixed at sixteen (numbered 11-26), one(numbered 0) and ten (numbered 1-10) respectively. The higher frequency band isapplicable worldwide, and the lower band in the areas of North America, Europe,Australia and New Zealand.

Low power consumption, with battery life ranging from months to years.Considering the number of devices with remotes in use at present, it is easy to see thatmore numbers of batteries need to be provisioned every so often, entailing regular (aswell as timely), recurring expenditure. In the ZigBee standard, longer battery life isachievable by either of two means: continuous network connection and slow but surebattery drain, or intermittent connection and even slower battery drain.

Maximum data rates allowed for each of these frequency bands are fixed as

250 kbps @2.4 GHz, 40 kbps @ 915 MHz, and 20 kbps @868 MHz.

High throughput and low latency for low duty-cycle applications (


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Fig 8.3 Protocol Stack

8.4 TRAFFIC TYPES

ZigBee/IEEE 802.15.4 addresses three typical traffic types. IEEE 802.15.4MAC can accommodate all the types.

1. Data is periodic. The application dictates the rate, and the sensor activates,

checks for data and deactivates.

2. Data is intermittent. The application, or other stimulus, determines the rate,as in the case of say smoke detectors. The device needs to connect to the network onlywhen communication is necessitated. This type enables optimum saving on energy.

3. Data is repetitive, and the rate is fixed a priori. Depending on allotted timeslots, called GTS (guaranteed time slot), devices operate for fixed durations.

ZigBee employs either of two modes, beacon or non-beacon to enable the to-and-fro data traffic. Beacon mode is used when the coordinator runs on batteries and

thus offers maximum power savings, whereas the non-beacon mode finds favourwhen the coordinator is mains-powered.


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In the beacon mode, a device watches out for the coordinator's beacon thatgets transmitted at periodically, locks on and looks for messages addressed to it. Ifmessage transmission is complete, the coordinator dictates a schedule for the next

beacon so that the device goes to sleep'; in fact, the coordinator itself switches to

sleep mode.

While using the beacon mode, all the devices in a mesh network know whento communicate with each other. In this mode, necessarily, the timing circuits have tobe quite accurate, or wake up sooner to be sure not to miss the beacon. This in turnmeans an increase in power consumption by the coordinator's receiver, entailing anoptimal increase in costs.

The non-beacon mode will be included in a system where devices are asleep'nearly always, as in smoke detectors and burglar alarms. The devices wake up andconfirm their continued presence in the network at random intervals.

On detection of activity, the sensors spring to attention', as it were, andtransmit to the ever-waiting coordinator's receiver (since it is mains-powered).However, there is the remotest of chances that a sensor finds the channel busy, inwhich case the receiver unfortunately would miss a call'.

8.5 APPLICATIONS

Industrial & commercial Consumer electronics Toys & games

PC & peripherals Personal health care home/building automation


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CHAPTER 9

CIRCUIT DIAGRAM

Fig 9.1 Basic Circuit Diagram (Without ZigBee Module)


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Fig 9.2 Circuit Diagram of Glove Section

Fig 9.2 Circuit Diagram of Base Section


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CHAPTER 10

CIRCUIT EXPLANATION

The flex glove which constitutes accelerometer and the flex sensor is used for

the sensing purpose. The accelerometer will detect the 3 dimensional motions

generated by our hand. These tiny micro-structures can only measure force in a single

direction, or axis of acceleration. This means with a single axis measured, we can

only know the force in the X, Y, or Z directions, but not all. The hand motions will

create resistance variations in the flux sensor which can be used to drive the robotic

arm.

The controlling of robot arm is done by using the PIC microcontroller, PIC

16F877A.The analog voltage signal generated due to the resistance variations in flux

sensor are converted to digital using the Analog to Digital Converter (ADC) in the

PIC microcontroller. The microcontroller will use these signals to drive the four

servomotors in the robotic arm.

The servo motor can be moved to a desired angular position by sending PWM

(pulse width modulated) signals on the control wire. The servo understands thelanguage of pulse position modulation. A pulse of width varying from 1 millisecond

to 2 milliseconds in a repeated time frame is sent to the servo for around 50 times in a

second. The width of the pulse determines the angular position. This PWM signal is

provided by the microcontroller.

In this circuit LM293D stepper motor diver is used to drive the stepper motors

with the PIC microcontroller. Thus the robotic arm can be moved according to themovement of our hands. The movement of robotic arm is generated using the

resistance variations in flex sensors.

The connections in this system are made wireless by using the ZigBee module

which provide wireless communication.

The power supply stage requires an output voltage of 5V for the PIC and the

flex glove and an output of 3.3V for the ZigBee module. It is implemented using the

voltage regulator ICs KA7805 for the 5V supply and LM317T for the 3.3V supply.


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CHAPTER 11

APPLICATIONS

In medical field for doing surgery by robot. In industries for doing jobs which are risky for humans. To realize an effective humanrobot cooperation. 3-D object edge tracing.


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CHAPTER 12

FUTURE WORKS

However, the proposed sensing unit works sufficiently in all the applications,

as the motion of the robot arm is slow enough. Various applications and experimental

results were introduced, such as object surface angle and object shape measurement,

surface normal following for humanrobot interactions, object edge recognition, and

object edge finding and tracing.

The experimental results show that the proposed tactile sensing system can be

used practically for obtaining the active object information. Accordingly, future worksshould include the application of the proposed sensor unit to actual welding and

interactive tasks. The welding task is one potential application for 3-D object

recognition. The researchers aim to develop a novel robot with an actual sensing and

welding torch. Hence, future works should include other trajectories and error

reduction to realize the efficient automatic welding task. Another potential application

is humanmachine cooperation. The researchers would also like to implement the

proposed system on humanoid robot feet to control the foot pose motion and to

maintain the balance of the whole body to make more stable biped walking in an

unstructured environment to support the human in his/her daily working tasks.


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CHAPTER 13

CONCLUSION

A tactile sensor system for a robot manipulator and an active-sensingtechnique is realized here. The proposed tactile sensor units implemented on the flexglove and robot arm allows us to attain a good humanrobot interaction. Onepotential application of the proposed techniques is to realize an effective humanrobotcooperation to move an object together by utilizing the control of a hand pose to keepthe direction of the hand normal to the object surface in three dimensions, which isoften necessary when pushing an object. Another is a 3-D object edge tracing. Theproposed techniques can be employed in industrial processes such as welding andinspection to eliminate manual teaching procedures for searching the object edge

automatically before doing the welding process. In these applications, informationabout the object shape or orientation is not required in advance.


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REFERENCES

1.

Robotic Tactile Sensor System and Applications; Kitti Suwanratchatamanee,Student Member, IEEE, Mitsuharu Matsumoto, Member, IEEE, and ShujiHashimoto, Member, IEEE: IEEE TRANSACTIONS ON INDUSTRIALELECTRONICS, VOL. 57, NO. 3, MARCH 2010

2. www.Tekscan.com3. www.spectrasymbol.com4. www.microchip.com5. www.digi.com6. www.datasheetcatalog.org7. www.tutorial-reports.com
http://www.tekscan.com/http://www.tekscan.com/http://www.spectrasymbol.com/http://www.spectrasymbol.com/http://www.microchip.com/http://www.microchip.com/http://www.digi.com/http://www.digi.com/http://www.datasheetcatalog.org/http://www.datasheetcatalog.org/http://www.tutorial-reports.com/http://www.tutorial-reports.com/http://www.tutorial-reports.com/http://www.datasheetcatalog.org/http://www.digi.com/http://www.microchip.com/http://www.spectrasymbol.com/http://www.tekscan.com/


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APPENDIX

Robotic Tactile Sensor System

Documents

Transcript of Robotic Tactile Sensor System