Notes Mect

7/28/2019 Notes Mect

1/4

UNIT 1

INTRODUCTION TO MECHATRONICS SYSTEMSMechatronics is the synergistic combination of Mechanical engineering, Electronic engineering,Computer engineering, Control engineering, and Systems Design engineering in order to design, and

manufacture useful products. The term mechatronics is defined as a multidisciplinary engineering

system design, that is to say it rejects splitting engineering into separate disciplines.

A mechatronics engineer unites the principles of mechanics, electronics, and computing to generate a

simpler, more economical and reliable system. Mechatronics is centered on mechanics, electronics,

computing, control engineering, molecular engineering (from nanochemistry and biology), and

optical engineering, which, combined, make possible the generation of simpler, more economical,

reliable and versatile systems. The portmanteau "mechatronics" was coined by Tetsuro Mori, the

senior engineer of the Japanese company Yaskawa in 1969. An industrial robot is a prime example of

a mechatronics system; it includes aspects of electronics, mechanics, and computing to do its day-to-

day jobs.

The development of mechatronics has gone through three stages: The first stage corresponds to the

years around the introduction of word mechatronics. During this stage, technologies used in

mechatronics systems developed rather independently of each other and individually.With start of

eighties a synergic integration of different technologies started taking place.A notable example is

opto-electronics, an integration of optics and electronics. The concept of hardware/software co-

design also started in this year. The third stage, which is considered as start of Mechatronics Age,

starts with the early nineties. The most notable aspect of this stage are more and more integration of

different engineering disciplinesand increased use of computational intelligence in the mechatronics

products and systems.Another important development in the third stage is the concept of

micromechatronis, i.e., start of miniaturization the components such as microactuators and

microsensors.Design of such products and processes, therefore, has to be the outcome of a multi-


2/4

disciplinary activity rather than an interdisciplinary one. Hence mechatronics challenges the

traditional engineering thinking, because the way it is operating, is crossing the boundaries between

the traditional engineering disciplines.

SENSORS

A sensor is a device which receives and responds to a signal. A sensor's sensitivity indicates how

much the sensor's output changes when the measured quantity changes. For instance, if the

mercury in a thermometer moves 1 cm when the temperature changes by 1 C, the sensitivity is

1 cm/C (it is basically the slope Dy/Dx assuming a linear characteristic). Sensors that measure very

small changes must have very high sensitivities. A good sensor obeys the following rules:

Is sensitive to the measured property

Is insensitive to any other property likely to be encountered in its application

Does not influence the measured property

Characteristics of sensor

The sensitivity may in practice differ from the value specified. This is called a sensitivity error, but

the sensor is still linear.

Since the range of the output signal is always limited, the output signal will eventually reach a

minimum or maximum when the measured property exceeds the limits. The full scale range defines

the maximum and minimum values of the measured property.

If the output signal is not zero when the measured property is zero, the sensor has an offset or bias.

This is defined as the output of the sensor at zero input.

If the sensitivity is not constant over the range of the sensor, this is called nonlinearity. Usually this

is defined by the amount the output differs from ideal behavior over the full range of the sensor, often

noted as a percentage of the full range.

If the deviation is caused by a rapid change of the measured property over time, there is a dynamic

error. Often, this behaviour is described with a bode plot showing sensitivity error and phase shift as

function of the frequency of a periodic input signal.

If the output signal slowly changes independent of the measured property, this is defined as drift

(telecommunication).

Long term drift usually indicates a slow degradation of sensor properties over a long period of

time.

Noise is a random deviation of the signal that varies in time.

Hysteresis is an error caused by when the measured property reverses direction, but there is some

finite lag in time for the sensor to respond, creating a different offset error in one direction than in the

other.

If the sensor has a digital output, the output is essentially an approximation of the measured

property. The approximation error is also called digitization error.


3/4

If the signal is monitored digitally, limitation of the sampling frequency also can cause a dynamic

error, or if the variable or added noise noise changes periodically at a frequency near a multiple of

the sampling rate may induce aliasing errors.

The sensor may to some extent be sensitive to properties other than the property being measured.

For example, most sensors are influenced by the temperature of their environment.

DISPLACEMENT AND POSITION SENSORS

Displacement Measurement

Measurement of displacement is the basis of measuring:

Position

Velocity

Acceleration

Stress

ForcePressureProximity

Thickness

Displacement Sensors types

Potentiometers displacement sensors

Inductive displacement sensors

Capacitive displacement sensors

Eddy current displacement sensors

Piezoelectric displacement sensors

Ultrasonic displacement sensors

Magnetostrictive displacement sensors

Optical encoder displacement sensors

Strain Gages displacement sensors

Resistive displacement sensors: An electrically conductive wiper that slides against a fixed resistiveelement. To measure displacement, a potentiometer is typically wired in a voltage divider

configuration.


4/4

A known voltage is applied to the resistor ends. The contact is attached to the moving

object of interest The output voltage at the contact is proportional to the displacement.

Documents

Notes Mect