Actuators in Automatic Control System

Actuators in Automatic Control System

Measurement & Control Systems Transducers Measurement Process Actuators Data processing Requirement analyses Decision making Control actions

CONTROL action requires MANIPULATING INPUT PARAMETERS to the PROCESS. ACTUATOR is a device that converts the control signal into physical ACTION.

What are some of the ACTUATORS? RELAY TRANSISTOR TRIAC SOLENOID Electric MOTOR Pneumatic / Hydraulic VALVES..

Types of Actuators 1. Electrical actuators Electric motors DC servomotors AC motors Stepper motors Solenoids 2. Hydraulic actuators Use hydraulic fluid to amplify the controller command signal 3. Pneumatic actuators Use compressed air as the driving force

Current State of Actuators All three types of actuators are in use today Electric actuators are the type most commonly used Hydraulic and pneumatic systems allow for increased force and torque from smaller motor There are some dual function actuators i.e. rotation and translation

Used for all Automation Actuators are used everywhere there is automation robot, conveyor system, etc. Linear Actuator Rotary Electric Motor Actuator

Where Used Electric motors used for high precision Precise robot applications such as automotive and pharmaceutical Now up to 10,000 lbf Hydraulic actuators used for increased torque High force and torque applications up to 32,000 lbf High precision achievable Pneumatic actuators are used for lower cost and lower precision applications

Stepper motor and Servomotor

Stepper Motor Stepper Motors DC pulses result in fixed angular motion Pairs of coils activated Lower speed (to avoid ringing) Lower power & holding torque 3/4/2014 IENG 475: Computer-Controlled Manufacturing Systems 10

Stepper Motors Step angle is given by: : α = 360 n s where n s is the number of steps for the stepper motor (integer) Total angle through which the motor rotates (A m ) is given by: where n p = number of pulses received by the motor. A m = n p α ω = 2πf n Angular velocity is given by: where f p = pulse frequency s p Speed of rotation is given by: N = 60 f n s p

Servo Motor

RELAY Works as the bridge between two mutually exclusive power supply systems. A switch controlled by an electromagnet works as an isolated circuit. A DC voltage is used to activate or deactivate the solenoid. Can be used along with a transistor, OPAMP, any other semiconductor actuator. A rectifier is usually required to protect the semiconductors from induced emf in the coil.

RELAY A switch that can be used to turn ON/OFF large loads that use AC or DC power. Electro magnet can be activated by 6 ~ 12 V (d.c).

RELAY Use of a Transistor to activate a Relay

THYRISTOR (SCR : Silicon Controlled Rectifier) Construction:

TRIAC Construction: Symbol:

TRIAC

Timer / Controller TRIAC Example use Fan Motor AC.. AC Mains supply

Example A stepper motor has a step angle = 3.6. (1) How many pulses are required for the motor to rotate through ten complete revolutions? (2) What pulse frequency is required for the motor to rotate at a speed of 100 rev/min?

Solution α = 360 n s A m = n p α N = 60 f n s p (1) 3.6 = 360 / n s ; 3.6 (n s ) = 360; n s = 360 / 3.6 = 100 step angles (2) Ten complete revolutions: 10(360 ) = 3600 = A m Therefore n p = 3600 / 3.6 = 1000 pulses Where N = 100 rev/min: 100 = 60 f p / 100 10,000 = 60 f p f p = 10,000 / 60 = 166.667 = 167 Hz

Example2 What is the angle resolution of the stepper motor with 1024 pulses per revolution? Solution Resolution = 360 o /1024 = 0.351 o /pulse

To be continued

SOLENOID VALVE This is an electrical actuator used to control water and / air flow. A plunger moved by a hollow electromagnet is coupled to a mechanical gate to open or close the water or air flow path. Can be activated using transistor driven relays, other semiconductor relays. Operates on 12 Vdc or 230 Vac.

Water level control using a SOLENOID VALVE Design a system which will activate a solenoid valve to fill a water tank once the level drops below a minimum mark. The tank should be filled upto a maximum limit before the solenoid is turned off. Given: BC 107 transistors, relays (SPDT), DC 12 V operated solenoid valve, contact sensors, other electronic hardware as required. MINI PROJECT! Control Circuit

Other data: Contact sensor resistance (with water) Contact sensor resistance (without water) Solenoid valve activation current: 300 ma.??

PIR Sensor Passive Infrared Detects a changes in the IR pattern of the scene in front of the sensor lens. The actual sensor on the chip is made from natural or artificial pyroelectric materials, usually in the form of a thin film, out of gallium nitride (GaN), caesium nitrate (CsNO3), polyvinyl fluorides, derivatives of phenylpyrazine, and cobalt phthalocyanine. (See pyroelectric crystals.) Lithium tantalate (LiTaO3) is a crystal exhibiting both piezoelectric and pyroelectric properties.