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Global Institute of Technology, Jaipur ITS-1, IT Park, EPIP, Sitapura Jaipur 302022 (Rajasthan)

Solution VII sem University Examination 2019

Subject Code_5ME3-01 V Semester/3rd Year

RTU Paper Solution

Branch – Mechanical Engineering

Subject Name – MECHATRONIC SYSTEMS

Paper Code –5ME3-01

Date of Exam – 14/11/2019




Part-A

1. MECHATRONICSYSTEM

Actuators: Solenoids, voice coils, D.C. motors, Stepper motors, Servomotor, hydraulics,

pneumatics.

Sensors: Switches, Potentiometer, Photoelectric, Digital encoder, Strain gauge,Thermocouple

etc

Input signal conditioning and interfacing: Discrete circuits, Amplifiers, Filters, A/D, D/D.

Digital control architecture: Logic circuits, Microcontroller, SBC, PLC, Sequencing and

timing,

Logic and arithmetic, Control algorithm, Communication.

Output signal conditioning and interfacing: D/A D/D, Amplifiers, PWM, Power transistor,

Graphical displays: LEDs, Digital displays.

2. An electrical resistance strain gauge with a resistance of 100 Ω and a gauge factor of 2.0.

change in resistance of the gauge when it is subject to a strain of 0.001 The fractional change

in resistance is equal to the gauge factor multiplied by the strain, thus



Subject Code_5ME3-01 V Semester/3rd Year 4. PVDF Tactile sensor

In general, tactile sensors are used to sense the contact of fingertips of a robot with an object.

They are also used in manufacturing of ‘touch display’ screens of visual display units

(VDUs) of CNC machine tools. Figure shows the construction of piezo-electric

polyvinylidene fluoride (PVDF) based tactile sensor. It has two PVDF layers separated by a

soft film which transmits the vibrations. An alternating current is applied to lower PVDF

layer which generates vibrations due to reverse piezoelectric effect. These vibrations are

transmitted to the upper PVDF layer via soft film. These vibrations cause alternating voltage

across the upper PVDF layer. When some pressure is applied on the upper PVDF layer the

vibrations gets affected and the output voltage changes. This triggers a switch or an action in

robots or touch displays.

5.




Part-B

1. There are many situations where control is exercised by items being switched on or off at

particular preset times or values in order to control processes and give a step sequence of

operations. For example, after step 1 is complete then step 2 starts. When step 2 is complete

then step 3 starts, etc.

The term sequential control is used when control is such that actions are strictly ordered in a

time- or event-driven sequence. Such control could be obtained by an electric circuit with sets

of relays or cam-operated switches which are wired up in such a way as to give the required

sequence. Such hard-wired circuits are now more likely to have been replaced by a

microprocessor-controlled system, with the sequencing being controlled by means of a

software program. As an illustration of sequential control, consider the domestic washing

machine. A number of operations have to be carried out in the correct sequence. These may

involve a pre-wash cycle when the clothes in the drum are given a wash in cold water,

followed by a main wash cycle when they are washed in hot water, then a rinse cycle when

they are rinsed with cold water a number of times, followed by spinning to remove water

from the clothes. Each of these operations involves a number of steps. For example, a

prewash cycle involves opening a valve to fill the machine drum to the required level, closing

the valve, switching on the drum motor to rotate the drum for a specific time and operating

the pump to empty the water from the drum. The operating sequence is called a program, the

sequence of instructions in each program being predefined and ‘built’ into the controller used.

An example is an elevator, which uses logic based on the system state to perform certain

actions in response to its state and operator input. For example, if the operator presses the

floor n button, the system will respond depending on whether the elevator is stopped or

moving, going up or down, or if the door is open or closed, and other conditions.

3. Operational Amplifier is a basic and an important part of a signal conditioning system. It is

often abbreviated as op-amp. Op-amp is a high gain voltage amplifier with a differential

input. The gain is of the order of 100000 or more. Differential input is a method of

transmitting information with two different electronic signals which are generally

complementary to each other. Figure shows the block diagram of an op-amp. It has five

terminals. Two voltages are applied at two input terminals. The output terminal provides the

amplified value of difference between two input voltages. Op-amp works by using the

external power supplied at Vs+ and Vs- terminals.




In general op-amp amplifies the difference between input voltages (V+ and V-). The output

of an operational amplifier can be written as

Vout = G * (V+ - V-)

where G is Op-amp Gain

Figure shows the inverting configuration of an op-amp. The input signal is applied at the

inverting terminal of the op-amp through the input resistance Rin. The non-inverting terminal

is grounded. The output voltage (Vout) is connected back to the inverting input terminal

through resistive network of Rin and feedback resistor Rf. Now at node a, we can write,

I1 = Vin/R1

The current flowing through Rf is also I1, because the op-amp is not drawing any current.

Therefore the output voltage is given by,

Vout = –I1 Rf = –Vin Rf/R1 =-(5.5V1+10V2+4) Rf/R1

Thus the closed loop gain of op-amp can be given as,

G = Vout/Vin = –Rf/R1

The negative sign indicates a phase shift between Vin and Vout.



Subject Code_5ME3-01 V Semester/3rd Year 5. Brushless DC motor

A brushless DC motor has a rotor with permanent magnets and a stator with windings. The

rotor can be of ceramic permanent magnet type. The brushes and commutator are eliminated

and the windings are connected to the control electronics. The control electronics replace the

commutator and brushes and energize the stator sequentially. Here the conductor is fixed and

the magnet moves (Fig).

The current supplied to the stator is based on the position of rotor. It is switched in sequence

using transistors. The position of the rotor is sensed by Hall effect sensors. Thus a continuous

rotation is obtained.

• More precise due to computer control

• More efficient

• No sparking due to absence of brushes

• Less electrical noise

• No brushes to wear out

• Electromagnets are situated on the stator hence easy to cool

• Motor can operate at speeds above 10,000 rpm under loaded and unloaded conditions

• Responsiveness and quick acceleration due to low rotor inertia

Disadvantages of brushless DC motor:

• Higher initial cost

• Complex due to presence of computer controller



Subject Code_5ME3-01 V Semester/3rd Year • Brushless DC motor also requires additional system wiring in order to power the electronic

commutation circuitry

6. Pressure sensor

Fluid pressure

Chemical, petroleum, power industry often need to monitor fluid pressure. Various types of

instruments such as diaphragms, capsules, and bellows are used to monitor the fluid pressure.

Specially designed strain gauges doped in diaphragms are generally used to measure the inlet

manifold pressure in applications such as automobiles. A typical arrangement of strain

gauges on a diaphragm is shown in figure. Application of pressurized fluid displaces the

diaphragm. This displacement is measured by the stain gauges in terms of radial and/or

lateral strains. These strain gauges are connected to form the arms of a Wheatstone bridge.

Capsule is formed by combining two corrugated diaphragms. It has enhanced sensitivity in

comparison with that of diaphragms. Figure shows a schematic of a Capsule and a Bellow. A

stack of capsules is called as ‘Bellows’. Bellows with a LVDT sensor measures the fluid

pressure in terms of change in resultant voltage across the secondary coils of LVDT. Figure

shows a typical arrangement of the same.




TEMPERATURE SENSORS:

Bimetallic Strips: A Bimetallic thermostat consists of two different metal strips bounded together and they

cannot move relative to each other.

These metals have different coefficients of expansion and when the temperature changes the

composite strips bends into a curved strip, with the higher coefficient metal on the outside of

the curve.

The basic principle in this is all metals try to change their physical dimensions at different

rates when subjected to same change in temperature.

This deformation may be used as a temperature- controlled switch, as in the simple

thermostat.



Subject Code_5ME3-01 V Semester/3rd Year Resistance Temperature Detectors (RTDs): The materials used for RTDs are Nickel, Iron, Platinum, Copper, Lead, Tungsten, Mercury,

Silver, etc.

The resistance of most metals increases over a limited temperature range and the relationship

between Resistance and Temperature is shown below.

The Resistance temperature detectors are simple and resistive elements in the form of coils of

wire

The equation which is used to find the linear relationship in RTD is

Thermistors: Thermistor is a semiconductor device that has a negative temperature coefficient of resistance

in contrast to positive coefficient displayed by most metals.

Thermistors are small pieces of material made from mixtures of metal oxides, such as Iron,

cobalt, chromium, Nickel, and Manganese.

The shape of the materials is in terms of discs, beads and rods.

The thermistor is an extremely sensitive device because its resistance changes rapidly with

temperature.

The resistance of conventional metal-oxide thermistors decreases in a very non-linear manner

with an increase in temperature.




Part-C

1.

the hydraulic system shown in Figure, relationships can be derived which describe how the

heightsof the liquids in the two containers will change with time. With this model inertance is

neglected.

Container 1 is a capacitor and thus




2. The mechatronic system is multi-disciplinary, embodying four fundamental disciplines:

electrical, mechanical, computer science and information technology. The mechatronic

design methodology is based on a concurrent, instead of sequential, approach to discipline

design, resulting in products with more synergy. Starting with the basic design, and

progressing through the manufacturing phase, mechatronic design optimizes the parameters

at each phase to produce a quality product in a short cycle time. Mechatronics uses the

control systems in providing a coherent framework of component interactions for system

analysis. The integration within a mechatronic system is performed through the combination

of hardware (components) and software (information processing). Hardware integration

results from designing the mechatronic system as an overall system and bringing together the

sensors, actuators, and microcomputers into the mechanical system. Software integration is

primarily based on advanced control functions. The first step in the focused development of

mechatronic systems is to analyze the customer and the technical environment in which the

system is integrated. Complex technical systems designed to solve problems tend to be a

combination of mechanical, electric, fluid, power, and thermodynamic parts with hardware in

digital and analog form coordinated by complex software. Typical mechatronic systems

gather data and information from their technical environment using sensors. The next step is



Subject Code_5ME3-01 V Semester/3rd Year to use elaborate ways of modeling and description methods to cover all subtasks of this

system in an integrated manner. This includes an effective description of necessary interfaces

between subsystems at an early stage. The data are processed and interpreted, leading to

action carried out by actuators. Mechatronic systems result in shorter developmental cycles,

lower costs, and higher quality. They also provide additional influence through the

acquisition of information from the process.

The mechatronic design methodology is concerned not only with producing high quality

products but with maintaining them as well, an area referred to as life cycle design.

Several important life cycle factors are described below.

• Delivery: Time, cost, and medium

• Reliability: Failure rate, materials, and tolerances.

• Maintainability: Modular design.

• Serviceability: On board diagnostics, prognostics, and modular design.

• Upgradeability: Future compatibility with current designs.

• Disposability: Recycling and disposal of hazardous materials

A typical program for such a robot might be:

1 Close an upright gripper on a component hanging from an overhead feeder.

2 Contract the arm so that the component is withdrawn from the feeder.

3 Rotate the arm in a horizontal plane so that it points in the direction of the workpiece.

4 Extend the arm so that the gripper is over the workpiece.



Subject Code_5ME3-01 V Semester/3rd Year 5 Rotate the wrist so that the component hangs downwards from the gripper.

6 Release the gripper so that the component falls into the required position.

7 Rotate the gripper into an upright position.

8 Contract the arm.

9 Rotate the arm to point towards the feeder.

Hydraulic and pneumatic rams are widely used to drive robot arms since they can easily be

controlled to move limbs at a relatively slow speed, while electric motors would need to

operate through a gearbox. The positions of the arm and gripper are determined by limit

switches. This means that only two positions can be accurately attained with each actuator

and the positions cannot be readily changed without physically moving the positions of the

switches. The arrangement is an open-loop control system. In some applications this may not

be a problem. However, it is more common to use closed-loop control with the positions of

an arm and gripper being monitored by sensors and fed back to be compared in the controller

with the positions required. When there is a difference from the required positions, the

controller operates actuators to reduce the error. The angular position of a joint is often

monitored by using an encoder

3.(a) (i) Accumulator The accumulator is 8-bit register (can store 8 bit data). It is a part of

arithmetic/logic unit (ALU). In general, after performing logical or arithmetical operations,

result is stored in accumulator. Accumulator is also identified as Register A.

(ii) Status-The status register is a hardware register that contains information about the state

of the processor. Individual bits are implicitly or explicitly read and/or written by

the machine code instructions executing on the processor. The status register lets an

instruction take action contingent on the outcome of a previous instruction.

(iii) Memory address register- In a computer, the Memory Address Register (MAR) is

the CPU register that either stores the memory address from which data will be fetched from

the CPU, or the address to which data will be sent and stored.

In other words, MAR holds the memory location of data that needs to be accessed. When

reading from memory, data addressed by MAR is fed into the MDR (memory data register)

and then used by the CPU. When writing to memory, the CPU writes data from MDR to the

memory location whose address is stored in MAR. MAR, which is found inside the CPU,

goes either to the RAM (Random Access Memory) or cache.

https://en.wikipedia.org/wiki/Hardware_register

https://en.wikipedia.org/wiki/Central_processing_unit

https://en.wikipedia.org/wiki/Machine_code



Subject Code_5ME3-01 V Semester/3rd Year (iv) A program counter is a register in a computer processor that contains the address

(location) of the instruction being executed at the current time. As each instruction

gets fetched, the program counter increases its stored value by 1. After each instruction is

fetched, the program counter points to the next instruction in the sequence. When the

computer restarts or is reset, the program counter normally reverts to 0.

3.(b) A microcontroller is a small and low-cost microcomputer, which is designed to perform

the specific tasks of embedded systems like displaying microwave’s information, receiving

remote signals, etc.

The general microcontroller consists of the processor, the memory (RAM, ROM, EPROM),

Serial ports, peripherals (timers, counters), etc.

CPU

CPU is the brain of a microcontroller. CPU is responsible for fetching the instruction, decodes it,

then finally executed. CPU connects every part of a microcontroller into a single system. The

primary function of CPU is fetching and decoding instructions. The instruction fetched from program memory must be decoded by the CPU.

Memory

The function of memory in a microcontroller is the same as a microprocessor. It is used to store

data and program. A microcontroller usually has a certain amount of RAM and ROM (EEPROM, EPROM, etc) or flash memories for storing program source codes.

Parallel input/output ports

https://whatis.techtarget.com/definition/register

https://whatis.techtarget.com/definition/processor

https://whatis.techtarget.com/definition/instruction

https://searchsqlserver.techtarget.com/definition/fetch



Subject Code_5ME3-01 V Semester/3rd Year Parallel input/output ports are mainly used to drive/interface various devices such as LCD’S,

LED’S, printers, memories, etc to a microcontroller.

It is a microprocessor-based system. It implements the functions of a computer and a controller

on a single chip. Generally microcontroller is programmed for one specific application and it is

dedicated to a specific control function. Microcontrollers find applications in automobiles, aircraft, medical electronics and home

appliances. They are small in size and can be embedded in an electromechanical system without

taking up much space. Thus we can have a system with its functions completely designed into a

chip. However microcontrollers have very little user programmable memory. Various types of

microcontroller chips available in market are: Motorola 68HC11, Zilog Z8 and Intel MCS51 and

96 series.

3.(C) Electrically actuated systems are very widely used in control systems because they

are easy to interface with the control systems which are also electric and because

electricity is easily available unlike fluid power which require pumps and compressors.

The advantages of electric systems are

Electricity is easily routed to the actuators; cables are simpler than pipe work.

Electricity is easily controlled by electronic units

Electricity is clean.

Electrical faults are often easier to diagnose.

1. A.C. MOTORS

A.C. motors are mainly used for producing large power outputs at a fixed speed.

Typically these are 1420 or 2900 rev/min. Such motors are controlled by switching them

on and off.

Increasingly, speed control is being used with A.C. motors on applications such as

pumps where it is found to be more economical to control the flow rate by changing

speed rather than by opening or closing a pipe line valve. Speed control is achieved

electronically by varying the frequency or by chopping the power supply.

2. D.C. MOTORS

Direct current motors are more widely used in control applications and they are usually

referred to as SERVO MOTORS. These are covered in detail later in the tutorial. The

development of more powerful magnets is improving the power to weight ratio but they

are still not as good as hydraulic motors in this respect. Servo motors usually have a

transducer connected to them in order to measure the speed or angle of rotation. The

diagram shows a typical arrangement.

3. STEPPER MOTORS

Basically a stepper motor rotates a precise angle according to the number of pulses of

electricity sent to it. Because there is confidence that the shaft rotates to the position

requested, no transducer is needed to measure and check the position and so they are

common on open loop systems. There are 3 types of stepper motor in common use and



Subject Code_5ME3-01 V Semester/3rd Year these are

Figure

1. The PERMANENT MAGNET TYPE. 2. The VARIABLE RELUCTANCE TYPE. 3. The HYBRID TYPE.

4. LINEAR ELECTRIC ACTUATORS

Figure

In recent years, a range of linear electric actuators have been developed to perform

functions similar to hydraulic and pneumatic cylinders. These are based on a motor

driven lead screw. The motors may be AC or DC. The speed of the motor is reduced

with a compact gear box before driving the lead screw. Actuators have been developed

with thrusts up to 15 kN and strokes up to 3 metres.

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