Controlling 3 Steppers exactly

Question

Update

Here the update regarding the code I tried to program. I have a stepper with an attached disc with little holes every 45 degrees where a microswitch can rest into (hole is the exact size of the microswitch; and be in off position then). I would like the stepper to move 45 degree (until hole 1) and then (as a first step) wait for 3 seconds and then move another 45 degree to hole and stop etc.

As a next step I would like the same to be controlled via serial from another software. So I can send to serial a "move" command and then the same as described above will happen once the Arduino get the "move" command.

Below my attempt. It does do the homing, but not very smoothly and the next step (just moving 3 seconds) is a very rough movement. Here my qestions:

1. How can I make this move smoothly ?
2. How should I adapt this code to make the stepper stop once it is in the hole ?
3. How can I make the microswitch get out of the hole after it rests in there ?

Thank you very much for your help !

Code

#include "AccelStepper.h"

int M2dirpin = 4;  //Motor Y direction pin
int M2steppin = 5; //Motor Y step pin
int M2en=12;  //Motor Y enable pin
#define home_switch 9 // Pin 9 connected to Home Switch (MicroSwitch)

// AccelStepper Setup
AccelStepper stepperX(1, 5, 4);   // (1,2,3) = (Dedicated Board, STEP, DIR)
// Stepper Travel Variables
long initial_homing = -1; // Used to Home Stepper at startup


void setup() {

  pinMode(home_switch, INPUT_PULLUP);
  pinMode(M2dirpin,OUTPUT);
  pinMode(M2steppin,OUTPUT);
  pinMode(M2en,OUTPUT);
  digitalWrite(M2en,LOW);
  Serial.begin(9600);  // Start the Serial monitor with speed of 9600 Bauds
  stepperX.setMaxSpeed(50.0);      // Set Max Speed of Stepper (Slower to get better accuracy)
  stepperX.setAcceleration(50.0);  // Set Acceleration of Stepper

  // Start Homing procedure of Stepper Motor at startup
  Serial.print("Stepper is Homing . . . . . . . . . . . ");

  while (digitalRead(home_switch)) {  // Make the Stepper move CCW until the switch is activated
    stepperX.moveTo(initial_homing);  // Set the position to move to
    initial_homing--;  // Decrease by 1 for next move if needed
    stepperX.run();  // Start moving the stepper
    delay(20);
  }

  stepperX.setCurrentPosition(0);  // Set the current position as zero for now
  stepperX.setMaxSpeed(50.0);      // Set Max Speed of Stepper (Slower to get better accuracy)
  stepperX.setAcceleration(50.0);  // Set Acceleration of Stepper
  initial_homing = 1;

  while (!digitalRead(home_switch)) { // Make the Stepper move CW until the switch is deactivated
    stepperX.moveTo(initial_homing);
    stepperX.run();
    initial_homing++;
    delay(20);
  }

  stepperX.setCurrentPosition(0);
  Serial.println("Homing Completed");
  Serial.println("");

 // Move 10 steps forward from the limit switch (to get out of the switch)
  while (stepperX.currentPosition() != 10) 
  {
    stepperX.setSpeed(10);
    stepperX.run();

}
}
void loop()
{
stepper1();
}

void stepper1() 
{
  stepperX.move(22);
  unsigned long startMillis = millis();
  while( millis()-startMillis<3000 )
{
  stepperX.run();
}
}

Old question: I apologize for the high level, pseudo code question, but I am trying to understand conceptional how I can achieve the following:

I have 3 steppers (1 circular motion, 2 linear motion) which I would like to stop every time at the exact same position. The first stepper should rotate e.g. 45 degrees and stop, after which the second stepper should push down (like a linear actuator) stay at that position for a certain time and move back to the initial position, after that the 3rd stepper should also (linear motion) move to certain position and return. These three steps would than repeat for a very long time.

Do Steppers accumulate errors in position and if yes how can I make sure that this is not happening ?

I read abut "homing" and tried microswitches, but wasn't able to combine it with the three stepper setup. Also 3D printers should always stop exactly at the same place and therefore I assumed there must be a solution for this.

Is there a template code I can start from that is similar to the setup described ?

How can I make sure these steps are done strictly after each other.

Again I apologize for the high level question, but all my attempts so far to solve this failed.

Thank you !

Answer 1

About errors with stepper motors: Stepper motors introduce errors depending on the forces, that act upon them. For example: If your stepper does not have enough power to accellerate the attached weight, it will loose steps when trying (meaning that the rotor does not do a step despite the coils being controlled for the step). (The same of course also goes for deacceleration or moving against a barrier) Since you only know the position bei counting the steps, that you "send" to the motor, you get an error.

You have basically 2 options to prevent this from happening: 1. Choose the correct strength for motors for your application and don't overburden the motors at any moment in operation. 2. You can attach a rotary encoder to the rotor, so that you can check, if the rotor really moved the number of steps, that you instructed it to do. (Here be sure, that the numbers of steps for rotary encoder and motor match, or calculate correctly, if they don't). The position in your program would then only be updated based on the rotary encoder. This solution is more difficult, since you need extra parts and good code, that will not miss any of the rotary encoder pulses.

About Homing: Yes, this can be used to prevent the accumulation of errors during a longer operation. Also this is often used, so that the device does not have to constantly save it's current position to peristent storage. If the power is cut off, the device will forget it's position and calibrate it again after powered on again by using the end switches. Also this means, that in the powered off state it's not a problem, when the motor is moved away from it's position by outer forces.

It is unclear, how precise you need the application to be and what errors are really introduced. It may be sufficient for you to just get the position of the motors by homing, when you power your device on, and then simply letting it work. If that's not sufficient, you might do a homing cycle after every sequence. The same goes for the rotary encoder solution. It might be an overkill here, depending on the exact properties of the application.

Template code: I simply googled "Arduino stepper homing" and found some articles about it, which also contain example code. That should enable you to write code for your own application. Since you didn't really described, what your setup is, we cannot see, if this really fits your application. But Homing is the same everywhere.

Steps strictly after each other: You can just write your program to finish one part and then go on to the next (blocking code). Or, if you want it to be more elaborate and flexible, you can use non-blocking code (like in the BlinkWithoutDelay example of the Arduino library) with a finite state machine. The states could be the 3 parts of your program, or divided further. In each state you are doing only 1 thing and change to the next state, when finished. The code in each state should be non-blocking, so that it only does something, when it needs to, and else let's the program continue (for example: When moving a stepper at a certain speed, you are doing 1 step, then waiting a bit, then doing the next step and so on. While waiting you can do other things.)

You didn't mention, what your problems with the limit switches were, so we cannot help you with that. Thus this answer is as high level as your question. Hope, that helps.