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Electric motors

on Jan 14, 2012

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Electric motorsPresentation Transcript

• ELECTRIC MOTORS An Introduction to DC and Stepper Motors
• Electric Motors
• Electric motors are everywhere!
• In your house, almost every mechanical movement that you see around you is caused by an AC or DC electric motor.
• Direct Current Motors
• overall plan of a simple 2-pole DC electric motor
• A simple motor has 6 parts, as shown in the diagram
• Direct Current Motors
• Direct Current Motors
• Brushed DC Motor
• The brushed DC motor is one of the earliest electric motor designs
• Easy to understand design
• Easy to control speed
• DC STEPPER MOTORS
• Stepping motors are electric motors without commutators
• Commutation is handled externally by the motor controller
• Controller charges opposite coils attracting the center rotor magnets
• DC STEPPER MOTORS
• DC STEPPER MOTORS
• Voltage Rating
• provides desired torque
• Resistance-per-winding determines
• the current draw of the motor
• Maximum operating speed
• Degrees per Step
• Sets the number of degrees the shaft will rotate for each full step
• UNIPOLAR STEPPER MOTOR
• Relatively easy to control
• simple 1-of-'n' counter circuit can generate the proper stepping sequence
• 1 transistor per winding
• UNIPOLAR STEPPER MOTOR
• two center-tapped coils
• represents the connection of a 4 -phase unipolar stepper motor
1 2 1a 1b 2a 2b 2a 1b
• UNIPOLAR STEPPER MOTOR
• 6 wires with a center tap on each of two coils
• IDENTIFYING WIRES
• Check make and model to see if wire colour code is available
• Observe the wires to see if you can identify groups of 3 wires
• Measure resistance between wires
• Wire with lowest resistance is power wire
• IDENTIFYING WIRES
• 6 wire motors
• Groups of 3 wires
• 1 power & 2 signal
• 5 wire motors
• 1 power & 4 signal wires
• power wire has lowest resistance to the others
• CONTROL PROGRAM
• Once wires identified and connected to the circuit: a program is needed to run the motor
• Example Turing Program:
• loop
• parallelput (1)
• delay (500)
• parallelput (2)
• delay (500)
• parallelput (4)
• delay (500)
• parallelput (8)
• delay (500)
• end loop
• STEPPER MOTOR CONTROL
• 4 signal wires fired in the correct sequence will turn the motor