DC motor ramping function

Projects Programming
2

Here's an example that uses a Finite State Machine to do the ramping. It ramps up over 6 seconds, holds at full speed until count 25, and then ramps down over 6 seconds. You kick off a sequence by setting RampStartTime to millis(). When RampStartTime is zero the sequence is done.

#define DEBUG_RAMP
#define MAX_PWM 255

int PWM_val = 0;
unsigned long RampStartTime = 0;
unsigned long currentTime = 0;
const unsigned long RampInterval = 6000; // Ramp timing cycle at 6 seconds

int EncoderCount = 0;
const int StartDecelerationCount = 25;

void setup()
{
  // put your setup code here, to run once:
  Serial.begin(115200);
  delay(1000); //0 - 999 blocking count

  RampStartTime = millis(); // initiate ramp-up
}

void loop()
{
  // put your main code here, to run repeatedly:
  delay(500); //0 - 499 blocking count
  // top of loop statements
  EncoderCount += 1; // simulate encoder count

  Ramp_PWM();
}

enum RampStates {Idle, RampingUp, FullSpeed, RampingDown} RampState = Idle;

int Ramp_PWM()
{
  unsigned long currentTime = millis();
  unsigned long elapsedRampTime = currentTime - RampStartTime;

  switch (RampState)
  {
    case Idle:
      if (RampStartTime != 0)
      {
        EncoderCount = 0;
        PWM_val = 0;
#ifdef DEBUG_RAMP
        Serial.println(F("Starting Ramp Up"));
#endif
        RampState = RampingUp;
      }
      break;

    case RampingUp:
      if (elapsedRampTime <= RampInterval)
      {
        PWM_val = MAX_PWM *
                  (float(elapsedRampTime) / float(RampInterval));
      }
      else
      {
#ifdef DEBUG_RAMP
        Serial.println(F("Reached Full Speed"));
#endif
        RampState = FullSpeed;
      }
      break;

    case FullSpeed:
      PWM_val = MAX_PWM;
      if (EncoderCount >= StartDecelerationCount)
      {
        RampStartTime = currentTime;
#ifdef DEBUG_RAMP
        Serial.println(F("Start Ramping Down"));
#endif
        RampState = RampingDown;
      }
      break;

    case RampingDown:
      if (elapsedRampTime <= RampInterval)
      {
        PWM_val = MAX_PWM - MAX_PWM *
                  (float(elapsedRampTime) / float(RampInterval));
      }
      else
      {
        PWM_val = 0;
        RampStartTime = 0;
#ifdef DEBUG_RAMP
        Serial.println(F("End Ramping Down"));
#endif
        RampState = Idle;
      }
  }

#ifdef DEBUG_RAMP
  if (RampStartTime != 0)
  {
    Serial.print(F("Elapsed time: "));
    Serial.print(elapsedRampTime);
    Serial.print(F(", Encoder Count: "));
    Serial.print(EncoderCount);
    Serial.print(F(", PWM value: "));
    Serial.println(PWM_val);
  }
#endif

  return 0;
}