Chapter V Summery and conclusion - INFLIBNETshodhganga.inflibnet.ac.in/bitstream/10603/4027/13/13_chapter 5.pdfElectronic System Design for Tensometer Summery and conclusion - 203

Electronic System Design for Tensometer

Summery and conclusion - 203 -

Chapter V

Summery and conclusion

5.1 Thesis Summery

The work done under the title ‘Microcontroller Based System Design For

Tensometer’ is divided into the five chapters:

1) Microcontroller based embedded systems

2) Theoretical aspects of motion control systems

3) Microcontroller based system design approach

4) Virtualization of the system using object oriented features of MATLAB (Expert

system design in MATLAB)

5) Summery and conclusion

The chapter I gives brief account of embedded systems designed around

microcontrollers. It begins with the definitions of embedded systems, the abstraction of

all the definitions is as follows,

“Embedded electronic system is an embedded component of any other larger

application designed to satisfy specific needs of the application.”

The application may be accommodating more than one embedded components

each for different unique function. The embedded electronic system is generally wired

around a microcontroller, as it is better suitable for the dedicated function and also a

cheaper alternative when compared with microprocessor and VLSI technology.

Microcontrollers are now-a-days very popular, even a simple search for the word

‘microcontroller’ on google search produces results with millions of web-pages

consisting of microcontroller information. The range of microcontrollers include tiniest

4-bit chips suitable for toys, to mega 32-bit MIPS, pico power versions for multimedia

applications. The 8-bit microcontrollers have the major share of microcontroller usage



and applications. They are also better suitable for electronic control applications than the

others when compared at the hardware/software complexity and cost/performance ratio

level.

From the wide variety of 8-bit microcontrollers it is really hard to choose a

particular one. Thus major emphasis is given to the cost and availability of the

microcontroller chips and development tools, as well as the ease of programming. The

three microcontroller families shortlisted via the survey made are the Intel MCS51

family, the Atmel AVR family and the Microchip PIC family. All the three families show

close comparison on the hardware front, with the AVR being the fastest one. But when

compared at the software level the MCS51 family being CISC (complex instruction set

computing) provides large number of instructions and easier to program at assembly

language level. However at the higher language level e.g. C programming language level

all the microcontrollers show similar results about execution speed and code density.

Thus considering hardware simplicity, availability of chips and hardware/software

tools, and fastest time-to-market characteristics; the MCS51 family of microcontrollers

was chosen for initial prototype development. Practically any of the MCS51, AVR or PIC

microcontrollers can be used for stepper motor motion control.

5.1.1 Orientation of the research work:

Microcontroller based optical tracking system for tensometer:

A short introduction to the system designed as the outcome of the work done in

the area of ‘Embedded system design for tensometer’ has been included here. A

tensometer is a device used to evaluate the Young's modulus (how much it stretches

under strain) of a material and other tensile properties of materials, such as tensile

strength. It is usually loaded with a sample between two grips that are either adjusted

manually or automatically to apply force to the specimen. The machine works either by

driving a screw or by hydraulic ram. The latter have the great advantage of being able to

create much more complex loading patterns, such as the cyclical loads needed for

measurement of fatigue strength.



Fig 5.1: Typical stress-strain curve for non-ferrous alloys.

1: True elastic limit

2: Proportionality limit

3: Elastic limit

4: Offset yield strength, usually defined at e=0.2%

S: Engineering stress, e: Engineering strain, A: Undeformed cross-sectional area, P:

Uniaxial load, L: Underformed length, and l: Elongation.

The Universal-Testing-Machine is the other application for the similar work.

(UTM info.) These machines have an arrangement for applying tensity to an object under

test, and monitor its compression/expansion as well as in some cases the break point of

the object material. For the objects composed of metals, concrete and other hard materials

the compression/expansion is very small, limited to tens of microns to few millimeters.

This test gives the idea about the object’s strengths as well as deformation under the

stress conditions. Such tests are very useful and necessary in the industries like

construction, fabrication, metal forging, molding, etc.

The systems that involve electromechanical parts require extra care during the

design phase. A typical example is an embedded system designed around a

microcontroller for driving a linear motion control system. In such case a designer should

be aware of mechanical limits of the system, the electrical drive requirements and the

backend tactical intelligence. In short for working on such a system requires expertise in

electronics as well as mechanical fields. Otherwise an automated expert system needs to

be developed to assist the designers during application development.



The system designed does exactly the same job. The actual work has been divided

into two phases:

Phase 1: prototype design and development in the laboratory,

Phase 2: creating a virtual stepper motor object linked to the reference databases.

It was decided to base the prototype design on an ATMEL microcontroller

AT89S52, which would add intelligence to the system. The microcontroller was selected

to control the motion of linear motion control system, which in turn would keep track of

the moving arm of the tensometer or universal testing machine. Optical sensor

arrangement consisting of IR/laser R/T pairs was proposed for keeping track of moving

arm of the tensometer. By counting the number steps applied to the stepper motor for

moving the tracking arm from origin to track the current position of moving arm, the

system calculates the displacement.

In the second phase it was proposed to extend the work towards using a virtual

object of stepper motor for driving the linear motion control system. The software

platform identified for this purpose was MATLAB, so as to achieve rapid application

development by the use of MATLAB toolboxes. The GUI toolbox could provide the

frond-end for the user interface, while the database toolbox allow linking various

databases to the software. Two databases were proposed; one for linear motion control

system and the other for stepper motor. The software flow to begin with the selection of

linear motion control system of the required precision and length, followed by the

available stepper motors with suitable stepping angle and torque. On finalization of the

linear motion system components viz. screw drive mechanism and the stepper motor, the

system generates final driver specifications for the user reference.

During the initial phase an embedded system, a single board computer (SBC), has

been designed around the MCS51 family of microcontrollers. The SBC design

methodology was selected to make it as flexible as possible, to serve wide variety of

applications from simple monitoring applications to complex data loggers. The SBC

included an EEPROM, Real Time Clock, serial RS232 link and a very flexible CPU

solution. Primarily it supported cheaper solution with AT89S52 with 8 KB of code

memory for small applications. But considering complex data logging applications, the



same board has been upgraded to support AT89C51RD2 with 64KB code memory, a

wide variety of on-chip peripherals and double clock speeds. This SBC has been tested

for variety of applications, some remarkable applications are:

1. Mouse Signal Interpreter using AT89S52 microcontroller that is further reduced to

AT89C2051, a scaled down version of 8051 microcontrollers.[1]

2. Programmable power supply using AT89S52 microcontroller. [2]

3. AC mains power failure monitor using AT89S52

These applications helped in further rectifying the design and making the system

effective.

A linear motion control system designed with this SBC also contained a screw

driven angular to linear motion drive coupled with a 2 Kg.cm torque unipolar stepper

motor. The system tracks a motion of moving arm with optical arrangement formed using

IR R-T pairs. The infrared LEDs provide a tracking and lock with the moving arm. Once

locked the system can track the motion within the specified limits. Being optically

coupled the system has no loading effect on the moving arm, and thus eliminates errors

associated with it.

5.1.2 Motion control systems:

Chapter II explains basics of motion control systems; especially linear motion

controllers. Linear motion controllers are very much useful in robotics, as well as in the

packaging, printing, textile, semiconductor production, and assembly industries for

process automation. Linear motion controllers are categorized into two types: belt-drive

type linear motion controllers and screw-drive type linear motion controllers. The belt-

drive type being simple but less accurate, are useful for general purpose systems where

accuracy and precision are not much important. These drives are also hampered by

frequent maintenance as belts can lose tensioning over time and even skip teeth.

The screw-drive type linear motion controllers are better selected for precise and

accurate motion control. They adopt primarily two types of screws for driving the

movable table: lead-screw also known as power screw, and the ball-screw. While lead-



screw is a cheaper solution, the ball-screw provides much better precision, accuracy and

efficiency.

With the recent advances in the motor technology linear motors are now being

available with higher precision and rigid constructions. But the higher cost limits their

usage in specific applications, where cost-performance ratio is not of much importance.

5.1.3 Stepper motor selection and driver design:

Stepper motors provide comparatively cheaper solution with sufficiently higher

resolution required for motion controllers. Basically they provide angular motion as a

result of input pulses, but when coupled to the screw-drive mechanism the angular

motion gets converted to precise linear motion. Depending on the screw-drive mechanism

selected the stepper motor specifications change, typically the step angle, inertia, driving

torque and thus the required electric power required for the motor are dependant on the

screw-drive selection.

The stepper motor driver selection depends on the application requirements. The

prime requirement of the drive circuit is to provide a perfect square wave shaped pulses

to the motor winding. Thus the driver design complexity generally depends upon the

speed of stepper motor if the torque is considered to be constant. However for the

purpose of tensometer arm tracking, which generally moves at slow to moderate rates

depending upon the material tensile strength, the stepper motor driving speed is much

limited. Thus simple start-stop drive action is much more suitable for this application.

The driver circuit will mainly contain the switching devices which supply pulses

to the stepper motor windings in the predetermined sequence. The bipolar junction

transistors can be useful for this purpose if the stepping rate is higher. But the larger

driving current and increased power dissipation limit their usage. The MOSFET drive is

better suitable for the tensometer arm tracking application, because of its slow speed of

operation. The IRF540N MOSFET can be driven directly from the microcontroller port

outputs because of its low threshold voltage (VT). However for better reliability, isolation

is required between low power logical circuitry and high power switching circuitry.

Amongst the various isolation techniques the optical isolation is found to be better

suitable for driving MOSFETs.



The wave drive or half-step drive techniques are sufficient for low or medium

precision screw-drive mechanisms, with precisions upto few tens of micrometer. For

highly precise motion control stepper motor micro-stepping drive technique can also be

adopted if the screw-drive supports the required precision.

5.1.4 Design of microcontroller based system for tracking tensometer arm:

The third chapter mainly deals with the design and development of the specified

prototype. It prime focus is on the design of a single board computer (SBC-51), based on

the MCS51 family microcontroller. In addition it also covers the stepper motor driver and

sensor interfacing to the SBC-51, and the linear regulated power supply designed for

SBC51 and stepper motor driver.

5.1.4.1 Single board computer (SBC-51):

To be a full functional single board computer a microcontroller required majority

of peripherals on-chip, viz. CPU core, memory and I/O ports.[3] But for building an

application, human interface devices viz. display, keypads must also be added to the

system depending on the application needs. These are also called as standard I/O streams,

which are the default locations where the computer reads from or writes to.[4] By default

serial port of microcontroller acts as a standard I/O stream, which can be redirected

towards to a keypad and display for user convenience.

The microcontroller with limited on-chip memories might not prove useful for

data logging applications. Also most of the microcontrollers lack the on-chip real-time

clock (RTC) crucial for applications which need to maintain calendar information. These

deficiencies in cheaper microcontrollers like AT89S52 are filled up by the inclusion of

serial (I2C) EEPROM (ATMEL 24cXX) and Philips serial (I2C) RTC PCF8583P. The

MAX232, RS-232 transceiver is added to the board for converting TTL signals to RS232

signals required for communicating devices e.g. personal computer. All the port lines,

except four pins: two for RS232 serial bus and the other two for I2C serial bus, are

available for interfacing external peripherals such as keyboard, LCD module, ADC, etc.

A crystal frequency 11.0592 MHz allow the microcontroller to communicate with the

external world using standard RS232 communication baud rates.



5.1.4.2 Stepper motor driver:

Two stepper motor driver circuits have been developed and tested. The first

design incorporated BJT power transistor MJE3055, which formed a Darlington pair with

the internal output transistor of the opto-isolator 4N35. The other design was based on the

MOSFET IRF540 power stage. The optical isolation is still present similar to the bipolar

design. To improve speed of operation a push-pull arrangement is provided at the gate of

MOSFET, to charge/discharge the parasitic gate capacitance rapidly. Both the circuits

utilize the freewheeling diode to protect the active switching element.

5.1.4.3 Sensor arrangement:

The prototype made in our laboratory employed infra-red receive-transmit pairs

(IR-RT pairs) of diode/transistor. A total of three pairs are required for table movement to

track the tensometer arm: viz. a centre lock pair and two direction finders. In addition to

that two IR-RT pairs have been used as scope definitions. They define the scope within

which the table can track the tensometer arm.

5.1.4.4 Power supply:

The system utilizes two separate regulated power supplies: +5V/500mA for

microcontroller and other digital logic circuitry and the +12V/3A for stepper motor driver

stage. The three terminal positive voltage linear regulator IC’s LM7805 and LM7812 are

utilized for the voltage regulation purpose. For +12V power supply a series pass

transistor TIP2955 is used as a current booster for IC LM7812.

5.1.5 Firmware design:

The system firmware has been written in an Embedded C language using Keil C

compiler for 8051. The C programming language being high level language provides

direct constructs and operators for all sorts of human thinking. This is true for the

branching decisions as well as looping (iterating) decisions. It is thus the language for

rapid application development.

To simplify the software development process the entire program has been

divided into multiple files: sm_main.c the main program file, defines.h the hardware

definition file, drive.h stepper motor driver file, and lcd.h the driver for LCD module.



The final compiled firmware program size is no larger than 3 Kbytes for code and

65 bytes for data. Thus the firmware easily fits onto AT89S52.

5.1.6 Virtualization of the system using object oriented features of MATLAB:

(Expert system design in MATLAB)

Chapter IV describes the design of expert system design in MATLAB. Using the

prototype designed, one can have a range of applications in motion control with varying

specifications of accuracy and precision. In majority of applications the logic system and

the driver part remains the same. The only part of the system which needs to be changed

and tested is a linear motion controller and a suitable stepper motor required to drive it.

The expert system designed in MATLAB does exactly the same thing.

The MATLAB software has been divided into multiple files to simplify the

software design. MATLAB being object oriented language provides a stepper motor

object to which the parameters and drive methods can be applied. The system uses two

databases: a screw-drive mechanism database for screw specifications and a stepper

motor database. The expert system enables the used to select a screw-drive of required

characteristics and find the stepper motor suitable for the same. Once finalized the

stepper motor and screw-drive mechanism parameters have been calculated and displayed

for user convenience. The system also allows the user to drive the stepper motor object

virtually, and observe the performance of the system in terms of angular motion precision

and accuracy, as well as linear motion precision. Use can also use plots of angular/linear

displacement versus number of steps, for studying the overall system behavior for chosen

components.



5.2 Conclusions:

The microcontroller based system has been designed using two different

microcontrollers: AT89S52 for small system configuration and P89C51RD2 for large

system configuration.

The SBC configuration have been tested and used successfully for designing

various applications viz. programmable power supply, mouse signal interpreter, motion

controller for thin film pyrolysis system, web-server for environmental parameter

monitoring. The unique advantage of the SBC is low cost yet effective, automatic,

portable and standalone single board computing solution has been made available in

place of expensive computer systems used in applications. The SBC designed eliminates

the need of continuous human monitoring and process control in applications like motion

controller, programmable power supply.

Two stepper motor driver configurations have been designed and implemented for

SRI-SYN make 2 KG.CM stepper motor rated at 12V, 500 mA per phase. It was

observed that the MOSFET based power stage offers larger power handling capabilities,

the simulation results were observed closer to ideal for upto 10A load currents, as

discussed previously. The circuit and waveform are shown in fig. 3.15B,C.

The prototype model based on the custom made lead-screw and SRI-SYN

STM601 stepper motor was successfully able to track the tensometer arm within the

defined scopes defined for the screw drive linear motion controller.

The software developed using the Keil C compiler was very much compact in

comparison to the code developed for AVR platform (Approx 1939 bytes versus 4880

bytes) however the data memory requirements are slightly larger for Keil-MCS51, than

the WINAVR-AVR environment (approx 55 bytes and 2 bits versus 40 Bytes for AVR)

but can fit on an entry level microcontrollers such as AT89S52 with 8Kbytes of code and

256 bytes of internal data memory on-chip.

The same prototype model has been simulated using virtual stepper motor object

based on the object oriented features of MATLAB. The simulation results (table no. 4.6,



page 198) have been compared with the real prototype (table no. 3.7, page 104) and

found to be matching in functionality and performance.

Thus the expert system designed in MATLAB provides user a guideline for

revealing proper linkage between screw-drive linear motion controller and stepper motor

for a particular application. The software enables the user to combine and simulate

various screw-drives and stepper motors, before making final decision to actually procure

the components. The software provides choice of screw-drive linear motion controllers as

well as matching stepper motors for every screw-drive. The user has to select a screw-

drive with required precision and feed length. The system performs database search for

possible matches, and calculates and displays the specifications for the selected ones.

Based on the screw-drive linear motion controller selection, the software performs new

search in the stepper motor database for matching stepper motors. The user has to select

suitable stepper motor from the list of matching stepper motors. When both the screw-

drive and stepper motor have been finalized the software constructs stepper motor virtual

object coupled with the screw-drive mechanism and displays driving results for the

system. The MATLAB software also provides graphical representation of driving

sequence. The user finalizes the selection after simulating various linear motion control

configurations based on different screw-drive mechanisms and stepper motors.

5.3 Future scope:

The system basically makes use of stepper motors and screw-drive mechanisms.

For better precision and durability the system can also be configured around linear motor

to replace both the stepper motor and screw-drive mechanism.

The current system facilitates local monitoring using LCD module. It can be

extended for remote monitoring using embedded web server modules.

The data logging facilities could be added to the system for the applications which

require monitoring displacement variations for force or time variations.

An IP core integrating entire logical component can be implemented using VLSI

prototype based on FPGA/CPLD core.



References:

[1] P.A.Kadam, Pravin A.Kadam, B.J.Raut, G.G.Tengashe, S.R.Sawant, Mouse

Signal Interpreter Using Microcontroller 89C2051, J. Instrum. Soc. India 36(2)

101-112

[2] P. A. Kadam, G. G. Tengashe, S. R. Sawant, DESIGN OF

MICROCONTROLLER BASED DC PROGRAMMABLE POWER SUPPLY, J.

Instrum. Soc. India 37(2) 92-99

[3] John L. Hennessy et. al., Computer Architecture: A Quantitative Approach.

Morgan Kaufmann, 2006

[4] Sumitabha Das, Unix Concepts and Applications, Tata Mcgraw-hill, 2003

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Chapter V Summery and conclusion - INFLIBNETshodhganga.inflibnet.ac.in/bitstream/10603/4027/13/13_chapter 5.pdfElectronic System Design for Tensometer Summery and conclusion - 203