Stepper Motor Tutorial

Transcription

1 UG108: Praxis II January 2013 Asian Institute of Technology Undergraduate Program Handout: Stepper Motor Instructor: Chaiyaporn Silawatchananai, Matthew N. Dailey Stepper Motor Tutorial Introduction: In this tutorial we will learn how to run and control motion of a stepper motor using Arduino Uno Rev3. By using stepper motor we can control the position or velocity of motor or rotational mechanic without using any feedback sensors (open loop control). Hardware Summary Stepper Motor: is a motor that runs in step, its rotor turns through a specific number of degrees and then stops. It converts electronic digital signals into mechanical motion in fixed increments. Each time an incoming pulse is applied to the motor, its shaft turns or steps a specific angular distance. The shaft can be driven in either direction and operated at low or very high stepping rates. Therefore the stepper motor has the capability of controlling the velocity, distance, and direction of a mechanical load. It also produces a holding torque at standstill to prevent unwanted motion or disturbance. One attractive feature of the stepper motor is that it responds to digital signals. It can be controlled by computers or a computer peripheral device. The stepper motor is typically used in an open-loop system which position is determined by counting pulses. They are used in many practical applications such as printer, CD players, floppy discs and X-Y positioning tables. There are two types of stepper motor: unipolar motor and bipolar motor. We can distinguish bipolar motors from unipolar motors by measuring the coil resistance. In bipolar motors we can find two wires with equal resistance. Alternatively 4-wire steppers are strictly Bipolar, while 5 and 6 wire motors with center-taps are Unipolar. Unipolar motor contains centre tapped windings. Usually centre connection of coils are tied together and used as the power connection. By using this arrangement a magnetic poles can be reversed without reversing the direction of current. Thus the commutation circuit can be made very simple. This ease of operation makes Unipolar Motor popular among electronics hobbyists. Figure 1: Unipolar Stepper Motor Windings, reproduced from edu/design_ref/actuators/stepper_intro.html Bipolar motors have no center tap connections. Current through a winding should be reversed to reverse the magnetic poles. So the driving circuit should be more complicated. We can solve this by using a H-bridge connection or by using IC-chips such as L293D or L298. A Bipolar motor is capable of higher torque since entire coil(s) may be energized, not just half-coils. 1

2 Figure 2: Bipolar Stepper Motor Windings, reproduced from edu/design_ref/actuators/stepper_intro.html The control sequences are shown below, using + and - symbols to indicate the polarity of the power applied to each motor terminal: Terminal 1a Terminal 1b Terminal 2a Terminal 2b ULN2003 IC: is a high-voltage high-current Darlington transistor arrays. Each consists of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The collector-current rating of a single Darlington pair is 500 ma. Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers, and logic buffers. This IC-chip has a bunch of transistors embedded in a single housing. It allows the connection of devices and components that need much higher current than the ones that the our Arduino board can offer. Simple stepper motor control Components required 1. Arduino UNO R3 2. Proto-board 3. Jumper (Connecting wires) 4. IC ULN2003A 5. IC L293D 6. Stepper motor V DC power supply Arduino pin numbers pin 8 as output for motor pin A pin 9 as output for motor pin B pin 10 as output for motor pin C pin 11 as output for motor pin D 2

3 (a) Diagram generated by Fritzing (b) Schematics generated by Fritzing Figure 3: Bipolar Stepper motor with Arduino (a) Diagram generated by Fritzing (b) Schematics generated by Fritzing Figure 4: Unipolar Stepper motor with Arduino 3

4 You can connect the circuit as in the Figure 3 for bipolar stepper motor control or Figure 4 for unipolar stepper motor control. We will use 4 outputs pins from the Arduino to control the motion of stepper motor. Code-1: Write your program to make the motor spin and control the direction by using serial communication, the code given below is not complete, you should be able to write a complete working code. Pin assignments int motorpin1 = 8; int motorpin2 = 9; int motorpin3 = 10; int motorpin4 = 11; int delaytime = 10; The setup function pinmode(motorpin1, OUTPUT); pinmode(motorpin2, OUTPUT); pinmode(motorpin3, OUTPUT); pinmode(motorpin4, OUTPUT); Serial.begin(9600); The loop function byte val; if(serial.available()){ val = Serial.read(); switch(val){ case 'A':moveForward(); break; case 'D':moveBackward(); break; case 'W':delayTime--;Serial.println(delayTime); break; case 'S':delayTime++;Serial.println(delayTime); break; The moveforward function digitalwrite(motorpin1, HIGH); digitalwrite(motorpin2, LOW); digitalwrite(motorpin3, LOW); digitalwrite(motorpin4, LOW); digitalwrite(motorpin1, LOW); digitalwrite(motorpin2, HIGH); digitalwrite(motorpin3, LOW); digitalwrite(motorpin4, LOW); digitalwrite(motorpin1, LOW); digitalwrite(motorpin2, LOW); digitalwrite(motorpin3, HIGH); digitalwrite(motorpin4, LOW); digitalwrite(motorpin1, LOW); digitalwrite(motorpin2, LOW); digitalwrite(motorpin3, LOW); digitalwrite(motorpin4, HIGH); 4

5 Conclusion and results: After download the compiled program on your Flash memory. Press A to command stepper motor rotate and Press B to move in oppositive direction. When we send command once, the stepper motor rotates for 4 steps according to moveforward function. So we can find the number of steps per revolution. To change direction, change the control sequence. We can adjust the speed by Press W or S which the delay time of each sequence is increased or decreased. Code-2: Write your program to control the motor shaft to absolute position by using serial communication, the code given below is not complete, you should be able to write a complete working code. Pin assignment and defined variable int motorpins[] = {8,9,10,11; //working variable int delaytime = 10; int steps = 200; //number of steps per rev int gear = 1; int step_counter = 0; The setup function int i = 0; for(i=0; i<4; i++){ pinmode(motorpins[i], OUTPUT); Serial.begin(9600); Define the function to tell motor to move a certain angle void moveangle(float angle){ int i; int howmanysteps = angle/stepangle(); if(howmanysteps<0){ howmanysteps = -howmanysteps; if(angle>0){ for(i = 0;i<howmanysteps; i++){ Forward(i%4); else{ for(i=0;i<howmanysteps;i++){ Backward(i%4); void movetoangle(float angle){ moveangle(angle-actualangle()); // actual stepper motor angle float actualangle(){ return step_counter*stepangle(); // angle made by each step 5

6 float stepangle(){ return (360.0)/(steps*gear); // backward step void Backward(int coil){ int i; int count2[] = {1, 2, 4, 8; for(i=0; i<4; i++){ digitalwrite(motorpins[3-i], count2[coil]>>i&0x01); step_counter--; // forward step void Forward(int coil){ int i; int count2[] = {1, 2, 4, 8; for(i=0; i<4; i++){ digitalwrite(motorpins[i], count2[coil]>>i&0x01); step_counter++; The loop function byte val; if(serial.available()){ val = Serial.read(); switch (val) { case 'A': movetoangle( 0); break; case 'B': movetoangle( 45); break; case 'C': movetoangle( 90); break; case 'D': movetoangle(135); break; case 'E': movetoangle(180); break; case 'F': movetoangle(225); break; case 'G': movetoangle(270); break; case 'H': movetoangle(315); break; case 'W': delaytime--; break; //increase speed case 'S': delaytime++; break; //decrease speed Serial.print(val); Assignment: Write Arduino Program to rotate stepper motor for 30 degrees in every 1 seconds. References Industrial Control Electronics: Devices, Systems & Application by - Terry Bartelt. 6