Transcript lecture15
بسم هللا الرحمن الرحيم The Islamic University of Gaza Faculty of Engineering Electrical Engineering Department Microprocessor and Microcontroller Based Systems EELE 4315 — Fall 2010 Instructor: Eng.Moayed N. EL Mobaied Lecture 15 Actuators for Robots Actuators are used in order to produce mechanical movement in robots. In this lecture we will present: Actuators types Control method for: DC motor AC motor Stepper motor Servos motor Actuator Types Electrical Actuator DC Motor AC Motor AC Motor Stepper Motor Stepper Motor Servos Motor Hydraulic Actuators Hydraulic Actuators Pneumatic Actuators Pneumatic Actuators Other Actuators DC motor control • Controller H-bridge • PWM control DC motor control H-Bridge • DC motors only have two leads. The direction it spins is determined by which terminal has power applied and which is connected to ground. • An H-bridge consists of four switches (in our case BJTs) and depending on which two are closed, allow the motor to operate in either direction • We chose to use an L298 chip from STMicroelectronics because it has two H-bridges in one package. DC motor control PWM control • A pulse-width modulated signal is a rectangular waveform with a varying duty cycle. • A longer duty cycle means the voltage is on for longer and the average voltage applied to the motor is higher and vice versa. • Will be implemented using the PWM generator on our microcontroller. Pulse-Width Modulation Stepper Motor (uni-polar) Stepper Motor 1000 0100 0010 0001 Stepping Sequences for Single Coil Excitation Only one coil is active at a given instant of time Stepper Motor Single Coil Excitation Stepper Motor (Single Coil Excitation) Stepper Motor (Double Coil Excitation) 1100 0110 0011 1001 Stepping Sequences for Double Coil Excitation Two coils active at any given instant of time Stepper Motor (Double Coil Excitation) Stepper Motor (Driver circuit) Stepper Motor (Driver circuit) Stepper Motor (sequence) Stepper Motor (sequence) Servos motor Servos motor Do not confuse “servos” with “servo motors” Servos Motor Motors and Encoders Feedback measurement “optical encoder” - direction - resolution • Relative position light sensor light emitter grating decode circuitry Optical Encoders mask/diffuser light sensor decode circuitry light emitter grating A diffuser tends to smooth these signals Ideal Real Optical Encoders • Relative position light sensor light emitter grating decode circuitry - direction - resolution Optical Encoders • Relative position light sensor light emitter - direction - resolution decode circuitry grating A A A lags B B B Optical Encoders • Relative position light sensor - direction - resolution decode circuitry light emitter grating Phase lag between A and B is 90 degree A B A leads B Design problems Design # 1 ( Stepper motor) Design controller for stepper motor Switch for on/off Switch for right/left rotation with single coil excitation method. Switch for right/left rotation with double coil excitation method. Switch for speed (1,2) selection.