伺服电机收到任何传感器的信号后如何停止一段时间？

Question

I am working on a simple Arduino Uno based project called "Waste segregation system". For that I've used 3 different sensors (IR, Inductive Proximity and Raindrop) and 3 Micro servo motors. Basically what it does is, different servo motor rotates according to the type of object it detects from a moving conveyor (Like Non-metal, Wet or Metal). So, everything works fine but the only issue I face is, I can not hold servo motor for some time at the newer position after the sensor senses any object. It returns to it's initial position after when the object is no more in front of a sensor.

I tried using delay() function at different parts of the code but it's not working properly. Like if I use delay(3000); the servo also moves 3 seconds later after sensing an object which is not desirable.

I would be so grateful of you if you help me somehow. Thanks in advance :)

The code I used;

#include <Servo.h>
Servo tap_servo_1;
Servo tap_servo_2;
Servo tap_servo_3;  

// here No. 1 is for Inductive sensor, No.2 is for Raindrop sensor and No.3 is for IR sensor //  

int sensor_pin_1 = 4;
int tap_servo_pin_1 =5;
int sensor_pin_2 =2;
int tap_servo_pin_2 =3;
int sensor_pin_3 =8;
int tap_servo_pin_3 =9;


int val_1;
int val_2;
int val_3;


void setup()
{
 pinMode(sensor_pin_1,INPUT);
 tap_servo_1.attach(tap_servo_pin_1);
 
 pinMode(sensor_pin_2,INPUT);
 tap_servo_2.attach(tap_servo_pin_2);
 
 pinMode(sensor_pin_3,INPUT);
 tap_servo_3.attach(tap_servo_pin_3);
}

void loop()
{
  val_1 = digitalRead(sensor_pin_1);
  
  if(val_1==0)
  {tap_servo_1.write(10);
  }
  if (val_1==1)
  {tap_servo_1.write(70);
  Serial.println("Waste detected is: Non-Metal");
   
  }

  
  val_2 = digitalRead(sensor_pin_2);
  
  if(val_2==0)
  {tap_servo_2.write(0);
  }
 if (val_2==1)
 {tap_servo_2.write(75);
 Serial.println("Waste detected is: Wet");
 }

 
 val_3 = digitalRead(sensor_pin_3);
  
 if (val_3==0)
  {tap_servo_3.write(10);
 }
 if (val_3==1)
  {tap_servo_3.write(70);
  Serial.println("Waste detected is: Metal");
  
  }
 }   

Answer 1

Based on my comment, then:

You instead want the servo to stay at position 70 some time after the object is not detected anymore.

You need something that ignores the sensor value after an object is being identified. At the moment every loop iteration (which is way faster than the mechanics of your system) will check the sensor value so you'll see that the servo goes back to the initial position quite instantaneously. Let's add a refractory period of say 3seconds. In this period you don't want to check the val_x sensor.

The problem with sleep is that it's a blocking function and the entire program will hang. You instead want to "freeze" the time after detecting an object and check again after a determined amount of time has passed.

 
// Store time here - init at zero 
unsigned long non_metal_detect_time = 0;
unsigned long       wet_detect_time = 0;
unsigned long     metal_detect_time = 0;

unsigned long ms_from_detection_non_metal;
unsigned long ms_from_detection_metal;
unsigned long ms_from_detection_wet;

    void loop()
    {
      val_1 = digitalRead(sensor_pin_1);
      
      ms_from_detection_non_metal = millis() - non_metal_detect_time ;

      // we care about this value only if 3s have passed otherwise we
      // ignore the value from the sensor even if the object is not there
      if(val_1==0 && ms_from_detection_non_metal > 3000  )
      {
        tap_servo_1.write(10);
      }
      

      if (val_1==1)
      { 
        // save when it's detected
        non_metal_detect_time = millis();
        tap_servo_1.write(70);
        Serial.println("Waste detected is: Non-Metal");
       
      }
    
      // You can do the same modifications for the other sensors.      

     }   

Another idea would instead require a more sophisticated software but it will also make a better use of you hardware resources. I'll give you the idea.

You can trigger serveral interrupts from the GPIO with edge detection:

• 0 -> 1: object is detected. ISR gives the command to the servo. Stop timer.
• 1 -> 0: object has gone. ISR starts timer.

And then the timer.

• Timer overflow: time has passed after object was gone. Give command to the servo to come back to init.