JV502 INDUSTRIAL ROBOTS AUTOMATION

CHAPTER 5:SENSOR IN ROBOTS AUTOMATION

Learning Outcomes:Upon completion this chapter, student

should be able:-1. State the categories of sensor2. Explain the velocity sensors, acceleration

sensors and the position sensors.3. Explain the application of robot sensor in

industries

Contents1. Introduction of robot sensor2. Velocity and acceleration sensors3. Position sensors4. Application of robot sensor in industries

Introduction of robot sensorSensors are devices that can sense and

measure physical properties of the environmente.g. temperature, luminance, resistance to touch,

weight, size, etc.

A robot needs sensing to be an active participant in the environment.

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 camera

General sensor classification

Sensor Characteristics 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 input signal. 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 SensorVelocity sensors:

Used for medium to low frequency (1 to 1000 Hz) measurements.

Act as a low-pass filter (reduce high frequency signals)Traditional velocity sensors employ an

electromagnetic sensor to pick up the velocity signalAcceleration sensors:

Used for the highest frequencies (100 Hz and up)Three types of accelerometers:

piezoelectric strain gage ( piezoresistive) servo accelerometer

Tachometer A DC tachometer works in a similar fashion

to the Linear Velocity Transducer, except magnet is fixed (“stator”) “coil” of wire rotates inside the magnetproduces a voltage proportional to the angular

velocity

Incremental EncodersTwo 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 (Channel B).

Position Sensors Potentiometer Resolver Optical Encoders

Relative position Absolute position

Linear variable differential transformers (LVTD)

Potentiometer Resistance changes with the position of the

dialpotentiometers (“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

Resolver sensorHas 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 encoders Optical sensing of

encoder position is used

A light source (LED or light-emitting diode) is placed on one side of the encoder disk

A light detector (phototransistor) is on the other side

Optical encoders Detecting absolute position

Linear variable differential transformers (LVTD)LVDT measures linear motion traveled as a

voltage signalThe 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 either side

Application of robot sensor in industriesVarious Types of Sensors for Robot Arc

Welding Stations:

Figure 5(a) shows a contact type sensorA gas nozzle, or a finger, is used as a probe to

detect contact with the work pieceThe nozzle senses the existence, location, and

orientation, and, thereby, the location of the weld seam.

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 process

This type of sensor is appropriate for welding of bigger pieces with weaving when penetration control is not necessary.

Group DiscussionTopic Industry

Application of robot sensor in industriesa. Types interfaces and groups of sensors used in

industrialb. Primary simple contact sensor commonly found

in robots automation systemc. State non-contact sensor used in industrial

systemd. Difference between the simple sensor and

complex sensor interface

• Automotive• Semiconducto

r• Food

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