Upon completion this chapter, student should be
1. State the categories of sensor
2. Explain the velocity sensors, acceleration sensors
and the position sensors.
3. Explain the application of robot sensor in
1. Introduction of robot sensor
2. Velocity and acceleration sensors
3. Position sensors
4. Application of robot sensor in industries
Introduction of robot sensor
Sensors are devices that can sense and measure
physical properties of the environment
e.g. temperature, luminance, resistance to
touch, weight, size, etc.
A robot needs sensing to be an active participant in the
Each sensor is based on a transduction principle, i.e. a
conversion of energy from one form to another.
Classification of sensors
Proprioceptive (“sense of self”, internal state):
Measures values internally to the system (robot), e.g.
battery level, wheel position, joint angle, etc.
Exteroceptive (external state): Observations of robot
environment, objects in it.
Active: emit energy in environment
More robust, less efficient
Passive: passively receive energy from environment
Less intrusive, but depends on environment e.g. light for
Dynamic range: Ratio between lower and upper
limits, usually in decibels.
Range: Difference between min and max.
Resolution: Minimum difference between two values.
Linearity: Variation of output signal as function of the
Bandwidth or frequency: The speed with which a sensor
can provide a stream of readings.
Sensitivity: Ratio of output change to input change.
Error/Accuracy: Difference between the sensor’s output
and the true value.
Velocity and Acceleration Sensor
Used for medium to low frequency (1 to 1000 Hz)
Act as a low-pass filter (reduce high frequency signals)
Traditional velocity sensors employ an electromagnetic sensor
to pick up the velocity signal
Used for the highest frequencies (100 Hz and up)
Three types of accelerometers:
strain gage ( piezoresistive)
A DC tachometer works in a similar fashion to the
Linear Velocity Transducer, except
magnet is fixed (“stator”)
“coil” of wire rotates inside the magnet
produces a voltage proportional to the angular velocity
Two sensors (usually optical) are mounted such that
one is halfway blocked by the "solid" area (Channel A)
while the other is in the middle of the "clear" area
Linear variable differential transformers (LVTD)
Resistance changes with the position of the dial
potentiometers (“pots”) are electrical resistance
elements made in both linearly & rotary form
a mechanical motion of the wiper changes the output
voltage in proportion to the wiper displacement
Has a similar function principle as a stepper motor.
It is a rotary electrical transformer basically
implemented for calculating the degrees of rotation.
Wheel / motor encoders
Measure position, speed, direction
of revolution of the wheel.
Odometry - wheel movements can
be integrated to get an estimate of
the robots position.
Typical resolutions of 2000
increments per revolution.
Optical sensing of encoder
position is used
A light source (LED or
light-emitting diode) is
placed on one side of the
A light detector
(phototransistor) is on the
Detecting absolute position
Linear variable differential
LVDT measures linear motion traveled as a voltage
The sensor is based on the physical properties of
transformers and electromagnetic induction
The transformer coil construction consist of a
primary winding between a pair of secondary coils on
Application of robot sensor in
Various Types of Sensors for Robot Arc Welding
Figure 5(a) shows a contact type sensor
A gas nozzle, or a finger, is used as a probe to detect
contact with the work piece
The nozzle senses the existence, location, and
orientation, and, thereby, the location of the weld
Figure 5(b) shows a non-contact type sensor referred
to as a through-the-arc sensor
This sensor detects changes of welding parameters
while the torch is weaving during the arc welding
This type of sensor is appropriate for welding of bigger
pieces with weaving when penetration control is not
Application of robot sensor in industries
a. Types interfaces and groups of sensors used in industrial
b. Primary simple contact sensor commonly found in
robots automation system
c. State non-contact sensor used in industrial system
d. Difference between the simple sensor and complex