Question

我正在将400 PPR编码器与Arduino一起使用以测量编码器值。我能够让编码器读取值0-400（正向旋转）和0到-400（负向旋转），并在编码器完成一整圈旋转后将其重置为0。我的代码的这一部分有效，我遇到的问题是将这些位置值转换为RPM。

我的方法是这样的：我正在使用millis（）函数来跟踪整个程序时间，并使用一个变量time_now来存储该值。我有一个if语句，每次millis（）变得比time_now大REFRESH_RATE（在我的情况下，它定义为1 mSec），因此每1毫秒运行一次。

我的下一个方法是每毫秒采样两个样本。 pointSample1和pointSample2之间的差异应为我提供编码器以1毫秒为单位移动的滴答声的数量。这有点复杂，因为它实际上是一个400度的圆，因此，例如，如果pointSample1为395度，pointSample2的读数为5度，我们需要采用编码器分辨率和pointSample1之差，然后将其加到pointSample 2或（PPR- pointSample1）+ pointSample2。

同样，这应该给我每毫秒的滴答声，然后可以轻松转换为RPM。

#define REFRESH_RATE 1 //sets the refresh rate for tracking RPM (in mSec)

volatile float temp, counter = 0;    //This variable will increase or decrease depending on the rotation of encoder
int revsTotal = 0;
int pulseInitial = 0;
int PPR = 400;                      //Equal to the number of ticks per revolution of your encoder

unsigned long time_now = 0;         //time since program start
int pulseDifferential = 24;         //number of ticks per mSec for desired RPM
float pointSample1 = 0;             //first tick sample
float pointSample2 = 0;             //second tick sample
float pulsemSec = 0;                //the amount of ticks the encoder is reading every millisecond
float RPM = 0;                      //RPM of the motor

void setup() {

  pointSample1 = counter;

  Serial.begin (4800);

  pinMode(2, INPUT_PULLUP); //sets pin mode for pin 2

  pinMode(3, INPUT_PULLUP); //sets pin mode for pin 3
//Setting up interrupt
  //A rising pulse from encoder activated ai0(). AttachInterrupt 0 is DigitalPin nr 2 on most Arduinos.
  attachInterrupt(0, ai0, RISING);

  //B rising pulse from encoder activated ai1(). AttachInterrupt 1 is DigitalPin nr 3 on most Arduinos.
  attachInterrupt(1, ai1, RISING);
  }

  void loop() {

  // Send the value of counter
  if( counter != temp ){                        //if change is detected in the encoder, print the positional data values
  Serial.println ("Positional Data: ");
  Serial.println (counter);
  temp = counter;

    if( counter >= PPR or counter <= -PPR){ //This if statement resets the counter every time the encoder does a full revolution, protecting from reset after memory becomes filled
      counter = 0;
    }
  }
  if(millis() > (time_now + REFRESH_RATE) or millis() == 0){         //should run once every time the refresh rate is met (refresh rate = 1mSec, if statement runs once every mSec). millis() = 0; is for varibale overflow protection
    pointSample2 = counter;                       //sets pointSample2 to the encoder position, pointSample1 starts at 0. This allows the difference between the two to be taken to determine the rotation per mSec
    if(pointSample1 - pointSample2 < 0){          //conditional if / elseif statement checks the sign (positive or negative) of the ticks between samples, and makes sure that the pulses per mSec is always positive
      pulsemSec = pointSample2 - pointSample1;
    }
    else if (pointSample1 - pointSample2 > 0){
      pulsemSec = (PPR - pointSample1) + pointSample2;
    }
    RPM = (((pulsemSec / PPR) * 1000) * 60);      //pulsemSec / PPR = revs per msec; revs per msec * 1000 = revs per sec; revs per sec * 60 = RPM
    pointSample1 = pointSample2;                  //changes pointSample1 for the next cycle
    time_now = millis();                          //sets time_now to the amount of time since program start
    Serial.println ("pulsemSec: ");
    Serial.println (pulsemSec);
    Serial.println ("RPM: ");
    Serial.println (RPM);
  }
  }

  void ai0() {
  // ai0 is activated if DigitalPin nr 2 is going from LOW to HIGH
  // Check pin 3 to determine the direction
  if(digitalRead(3)==LOW) {
  counter++;
  }else{
  counter--;
  }
  }

  void ai1() {
  // ai0 is activated if DigitalPin nr 3 is going from LOW to HIGH
  // Check with pin 2 to determine the direction
  if(digitalRead(2)==LOW) {
  counter--;
  }else{
  counter++;
  }
  }

在测试过程中，我使用数字转速表测得的电机转速约为473 RPM。根据Arduino的输出，这转换为我的代码测得的RPM为13,350 RPM，这是一个更高的数字。我认为PulsemSec变量的测量存在问题，而不是转换为RPM的方法存在问题，但是我不确定问题出在什么地方。

Answer 1

每毫秒更改一次，您写入大约30个字节。 4800波特时30字节为30/480 * 1000毫秒= 62毫秒。因此，一旦缓冲区已满，它将阻塞。但是您假设计算中只经过了1毫秒。

计算脉冲的方式也偏斜：

// ai0 is activated if DigitalPin nr 2 is going from LOW to HIGH
// Check pin 3 to determine the direction

// ai[1] is activated if DigitalPin nr 3 is going from LOW to HIGH
// Check with pin 2 to determine the direction

因此，如果我们使用偏移编码，则每个脉冲周期将获得两个计数器增量：

pin 2   ________********________********

pin 3   ****________********________****


                !ai0            !ai0
                    !ai1            !ai1
                counter++       counter++
                    counter++       counter++

所以您可能将计数器增加一圈800倍。

使用Arduino将位置编码器值转换为RPM的问题

1 个答案: