Çizgi izleyen robot sadece sola dönüyor

#include <QTRSensors.h>


#define NUM_SENSORS   8    
#define TIMEOUT       2500
#define EMITTER_PIN   QTR_NO_EMITTER_PIN 


QTRSensorsRC qtrrc((unsigned char[]) {2, 4, 5, 6, 7, 8, 9,10},NUM_SENSORS, TIMEOUT, EMITTER_PIN);
unsigned int sensorValues[NUM_SENSORS]; // array with individual sensor reading values
unsigned int line_position=0;

int pwm_a = 3;
int pwm_b = 11;
int dir_a = 12; 
int dir_b = 13; 


int calSpeed = 85; 


float error=0;
float PV =0 ; 
float kp = 1; 
int m1Speed=0;
int m2Speed=0;


void setup()
{

  pinMode(pwm_a, OUTPUT);
  pinMode(pwm_b, OUTPUT);
  pinMode(dir_a, OUTPUT);
  pinMode(dir_b, OUTPUT);


  analogWrite(pwm_a, 0);
  analogWrite(pwm_b, 0);
   


  delay(2000);


  for (int i = 0; i <= 100; i++)  // begin calibration cycle to last about 2.5 seconds (100*25ms/call)
  {
   


    if (i==0 || i==60) 
    {
       digitalWrite(dir_a, LOW);
       analogWrite(pwm_a, calSpeed);
       digitalWrite(dir_b, HIGH);
       analogWrite(pwm_b, calSpeed);  
    }
   
    else if (i==20 || i==100)
    {
       digitalWrite(dir_a, HIGH);
       analogWrite(pwm_a, calSpeed);
       digitalWrite(dir_b, LOW);
       analogWrite(pwm_b, calSpeed);  
    }
   
    qtrrc.calibrate();
   
  }

 
  line_position = qtrrc.readLine(sensorValues);

  while (sensorValues[6] < 200)
  {
    line_position = qtrrc.readLine(sensorValues);
  }
 

  while (line_position > 4350)
  {
    line_position = qtrrc.readLine(sensorValues);
  }


  analogWrite(pwm_b, 0);
  analogWrite(pwm_a, 0);


  delay(1000);

}



void loop() // main loop
{


  unsigned int line_position = qtrrc.readLine(sensorValues);
 
 
  follow_line(line_position);

}








void follow_line(int line_position)
{



  switch(line_position)
  {
     
    // Line has moved off the left edge of sensor
    // This will make it turn fast to the left
    case 7000:
           digitalWrite(dir_a, HIGH);
           analogWrite(pwm_a, 200);
           digitalWrite(dir_b, LOW);
           analogWrite(pwm_b, 200);
    break;



    case 0:    
           digitalWrite(dir_a, LOW);
           analogWrite(pwm_a, 200);
           digitalWrite(dir_b, HIGH);
           analogWrite(pwm_b, 200);
    break;



    default:    
      error = (float)line_position - 3500;

 

      PV = kp * error;


      if (PV > 55)
      {
        PV = 55;
      }

      if (PV < -55)
      {
        PV = -55;
      }
     


      m1Speed = 200 - PV;
      m2Speed = 200 + PV;
   

      digitalWrite(dir_a, LOW);
      analogWrite(pwm_a, m1Speed);
      digitalWrite(dir_b, LOW);
      analogWrite(pwm_b, m2Speed);
      break;
  }

}