Asynchronous Stepper Motor Position Control

Controlling 4 stepper motors with 1 Arduino Mega by using 16 bit timers

1. Hardware

• Arduino Mega - ATmega2560 MCU based on AVR Architecture

• Enable to control 4 Stepper Motors, Syringe pumps asynchronously

• Enable to control 6 Stepper Motors, Syringe pumps synchronously

• Stepper motor position is set based on optical homing sensor and PWM signal on STEP pin of motor driver IC during moving

• DRV8711 - Texas Instruments Motor Driver IC Module (Polulu)

• Support microstepping

• Support for 6 hardware, X and Y (Motor A and B HBOT), Z1, Z2, Syringe Pump, and more

• Mega Pin Map - Pin is matched with Arduino Mega pin map

_STEP = A0;

_DIR = A1;

_SS = 31;

_SLEEP = 39;

_STLFLT = 22;

_HOME = A8;

_RESET = 48;

2. Important Notice

• Assigned pin number of Arduino Mega is based on my configuration. User can change the pin assignment.
• _STEP, _DIR, _SS, _SLEEP, _STLFLT, _HOME, and _RESET are should be assigned.

3. Class Declaration

ASMC(int MotorNumber, float MotorCurrent, unsigned int max_speed, unsigned int min_speed, unsigned int home_speed, int microstepping, float lead,
            int sample_time_BEMF = 7, int stall_detection_count = 3, int stall_detection_threshold = 0, bool newboard=false);

• Motor Current should be checked by motor specification
• Based on MotorNumber, pre-assigned pins are chosen. Please refer to the ASMC.cpp
• Based on max_speed and min_speed, the library automatically calculates middle speed.
• microstepping is calculated as 2^microstepping. If you want to choose 8 microstepping, you can put 3.
• lead is the unit number for changing revolution to linear acutation.

4. SPI Communication

• Through SPI communication, Arduino Mega can set motor driver, DRV8711. The SPI communication is based on pre-set pins of Arduino Mega. You can refer to the Arduino Website for SPI communication.
• Register_DRV8711.h file shows what you can program
• Important Notice: To avoid unexpected current flow at the beginning, when you write register in DRV8711, you should write 0 ENABLE register in CTRL area first. After finishing all set-up of register in DRV8711, you can write 1 on ENABLE register. By using this methodology, you can protect your circuit board and motor from unexpected current draw from power source. Please refer to SPI_DRV8711.cpp.

5. Stall/Fault Detection

• There are three main parameters of Stall and Falut detection.

1. Sampling Time of Back EMF - 0: 50us, 1: 100us, 2: 200us, 3: 300us, 4: 400us, 5: 600us, 6: 800us, 7: 1000us
2. Stall Detection Count by Inside Counter in DRV8711 (Please look at the page 23 in '/source/drv8711.pdf'.) - 0: Count 1, 1: Count 2, 2: Count 4, 3: Count 8
3. Stall Detection Threshold - 0 to 255 -> higher value, more sensitive to stall