Hello everyone,
I couldn't find any solution to my problem when searching the forum, so I hope its fine if I post it here. 
I am working on a project where I wanna use an Arduino Uno in combination with a CNC shield and 4 NEMA17 stepper motors (currently I am using only 2 of them).
In our little company, we wanna automate a paper feed in for a lasercutter. That means, we do have setup a homemade construction from aluminium and want to use two servos to shift some sort of an "infinite paper roll" into the lasercutter. It works like this: The lasercutter cuts its job into the paper. Afterwards the stepper should move the paper by a certain amount >into< the lasercutter fo the next lasercutting job and so on.
We do have a processing GUI with buttons that allow me to trigger the Arduino to rotate the steppers by a certain amount (example below "-700"). I attach you a shortened code version here for clarity.
#include <AccelStepper.h>
#include <MultiStepper.h>
// Define the stepper motor and the pins that is connected to
AccelStepper stepper1(1, 2, 5); // (Typeof driver: with 2 pins, STEP, DIR)
AccelStepper stepper2(1, 3, 6);
AccelStepper stepper3(1, 4, 7);
MultiStepper steppersControl; // Create instance of MultiStepper
long gotoposition[3]; // An array to store the target positions for each stepper motor
void setup() {
Serial.begin(9600); // opens serial port, sets data rate to 9600 bps
stepper1.setMaxSpeed(800); // Set maximum speed value for the stepper
stepper2.setMaxSpeed(800);
stepper3.setMaxSpeed(800);
// Adding the 4 steppers to the steppersControl instance for multi stepper control
steppersControl.addStepper(stepper1);
steppersControl.addStepper(stepper2);
steppersControl.addStepper(stepper3);
}
void loop() {
int CurPosLCServosFront = 0; // Initialise PositionServo variable of both Servos (mirrored)
int rotateNextCard = -700; // single movement of Arduino after button click
int counter = 1; // counts number of movements of servos
while (counter<100) {
[...]
moveServos(CurPosLCServosFront+rotateNextCard);
CurPosLCServosFront = CurPosLCServosFront+rotateNextCard;
delay(1500);
[...]
}
void moveServos(int positionServosLCFront) {
// Store the target positions in the "gotopostion" array
Serial.println("Start rotating Servos...");
gotoposition[1] = positionServosLCFront; // Servos in Feed-In
steppersControl.moveTo(gotoposition); // Calculates the required speed for all motors
steppersControl.runSpeedToPosition(); // Blocks until all steppers are in position
Serial.println("Finished!");
}
So when starting up the Arduino, the servos has a position "0" and after each click it rotates (always in the same direction!) by "-700" (a few round trips of the servo). Afterwards the current position variable of the stepper gets updated and on the next movement another "-700" are added.
Therefore the steppers move always in one direction and aquire over time a pretty big value for its position. What happens is that after about 10-20 movements the stepper rotates a lot back in the other direction throwing the paper out of the lasercutter. To me it looks like the servo would get the command from the Arduino to go to a positive position (for which it needs to rotate all the way back). But from my code I simply cant understand where is the problem.
So I wanted to ask if someone could help me out, had a similar problem already or maybe knows a solution i could try?
Thank you very much and cheers from Austria
PS: I should maybe add. After that problem happened, I restart the Arduino and everything works fine from the beginning until that problem appears again).
