Tài liệu Dc motorcontrol for robot

DC MOTOR CONTROL SYSTEMS FOR ROBOT APPLICATIONS By: Rick Bickle 11/7/2003 Motor control questions „ „ „ „ Why do we need speed control? How is DC motor speed controlled? How is motor direction controlled? What circuits can be used? Reasons for accurate speed control „ „ Motor speed should be independent of load. Differential drive platforms need to synchronize wheel speed to go in a straight line. Speed control with PWM „ Pulse Width Modulation Simple PWM circuit U1A 74HC14A 1 U1B 2 3 4 74HC14A D1 DIODE MG1 1 U1C 5 6 1 2 2 74HC14A D2 DIODE 3 R2 POT MOTOR DC U1D 9 C1 CAP NP 8 74HC14A U1E 11 10 74HC14A U1F 13 12 74HC14A H-Bridge motor driver circuit CIRCUIT INPUTS A B C Output 0 0 0 N Channel Brake 1 1 0 P Channel Brake 1 0 0 Forward 0 1 0 Reverse V+ R2 4.7K R1 4.7K S X X 1 Motor Off S Q1 IRF9510 G Q2 IRF9510 G D D M1 +5 +5 DC Motor D Input A R3 4.7K 1 G S 14 S Q5 2N2222 3 2 7 Q4 IRF510 Q3 IRF510 G 14 D R4 4.7K U1B 74HC08 4 Input B 6 Q6 2N2222 5 U1A 74HC08 7 V+ +5 +5 R5 D 14 U1C 74HC08 9 Q7 IRF510 G 14 R6 4.7K S 8 Q8 2N2222 10 U1C 74HC08 4.7K 9 8 10 7 7 PWM Input Optical encoder circuit 11 U27E 74HC14 10 13 U27F 74HC14 12 R11 C14 10K 0.001uF U27A 74HC14 2 L. Motor R6 4.7K 1 9 U6A 8 1 Tach Input A 3 R7 4.7K 3 U27B 74HC14 4 2 U6C 74HC86 74HC86 Tach Input B R10 D3 5V 10 D4 5V C15 10K 0.001uF U27C 74HC14 6 R. Motor R8 4.7K 5 13 U6B 11 4 Tach Input A 6 R9 4.7K 9 Tach Input B D5 5V D6 5V U27D 74HC14 8 12 5 74HC86 U6D 74HC86 Motor control diagram PROCESSOR H-BRIDGE CIRCUIT DC MOTOR ENCODER Control systems „ „ „ „ What is a control system? What are some examples? What are the types of control systems? How are control systems represented? Open loop control systems „ „ „ The output of the plant does not affect the input. (No feedback) Less common today than closed loop control systems. Examples include: „ „ Stereo volume control Electric drill speed control Open loop control system INPUT GAIN PLANT OUTPUT = INPUT X GAIN Closed loop control systems „ „ Use a measurement of output to control the input (Feedback) Examples include: „ „ Air conditioning thermostat Automobile cruise control Closed loop control system INPUT SUM GAIN PLANT FEEDBACK OUTPUT = (INPUT – OUTPUT) X GAIN Motor control diagram PROCESSOR H-BRIDGE CIRCUIT DC MOTOR ENCODER PID Closed loop control system „ „ PID controls the gain portion of the closed loop control system. PID algorithms adjust the gain to the plant based on several characteristics of the feedback, not just the current value. PID control system diagram P GAIN INPUT SUM I GAIN SUM PLANT D GAIN FEEDBACK OUTPUT = (INPUT – OUTPUT) X (P GAIN + I GAIN + D GAIN) Sample PID output chart „ „ „ „ „ „ „ Set point Rise time Overshoot Settling time Peak time Overdamped Underdamped PID implementation „ „ „ „ What is the mathematics of PID? How is it programmed? What are some common problems? How is the PID behavior optimized? PID variables „ „ „ „ Error term P – Proportional gain I – Integral gain D – Derivative gain Error term „ „ The error term is derived by subtracting the feedback (motor speed) from the set point (set speed). This is the error in terms of a number of encoder counts per unit time. P GAIN INPUT SUM I GAIN SUM D GAIN FEEDBACK PLANT