Relays getting freeze suddenly - arduino-uno

Question

Hi all, I'v done a project for a factory which were needing a packing machine, so I made it with some pneumatic cylinders using arduino, relays, IR sensor.
I'm attaching my code and a picture how schema looks because sometimes my relays are freezing suddenly and they just need to power off then again power on and its OK.
Btw; I'm attaching schema only for one relay with all elements, code is for 4
relays.
Any idea about this please?
Picture of schema
int relay1 = 13;
int relay2 = 12;
int relay3 = 11;
int relay4 = 10;
int sensor1 = 5;
int sensor2 = 6;
int sensor3 = 3;
int sensor4 = 2;
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
pinMode(relay1, OUTPUT);
pinMode(sensor1, INPUT);
pinMode(relay2, OUTPUT);
pinMode(sensor2,INPUT);
pinMode(relay 3, OUTPUT);
pinMode(sensor3,INPUT);
pinMode(relay4, OUTPUT);
pinMode(sensor4,INPUT);
pinMode(LED_BUILTIN,OUTPUT);
}
void loop() {
digitalWrite(relay1, LOW);
delay(2000);
digitalWrite(relay1, HIGH);
delay(2000);
digitalWrite(relay2, LOW);
delay(2000);
digitalWrite(relay2, HIGH);
delay(2000);
digitalWrite(relay 3, LOW);
delay(2000);
digitalWrite(relay3, HIGH);
delay(2000);
digitalWrite(relay4, LOW);
delay(2000);
digitalWrite(relay4, HIGH);
delay(2000);
while(1){
delay(100);
if(digitalRead(sensor2) == LOW)
{
Serial.println("Eggs on");
digitalWrite(relay1,HIGH);
delay(350); // shpejtesia sensorit // sensor speed
}
else
{
Serial.println("No eggs");
digitalWrite(relay1,LOW);
delay(50); // sa mu kthy shpejt klipi mbrapa // speed of cylinder getting back
}
if(digitalRead(sensor1) == LOW)
{
Serial.println("Eggs on");
digitalWrite(relay2,HIGH);
delay(350); // shpejtesia sensorit // sensor speed
}
else
{
Serial.println("No eggs");
digitalWrite(relay2,LOW);
delay(50); // sa mu kthy shpejt klipi mbrapa // speed of cylinder getting back
}
if(digitalRead(sensor3) == LOW)
{
Serial.println("Eggs on");
digitalWrite(relay3,HIGH);
delay(350); // shpejtesia sensorit // sensor speed
}
else
{
Serial.println("No egs");
digitalWrite(relay3 ,LOW);
delay(50); // sa mu kthy shpejt klipi mbrapa // speed of cylinder getting back
}
if(digitalRead(sensor4) == LOW)
{
Serial.println("Eggs on");
digitalWrite(relay4,HIGH);
delay(100); // shpejtesia sensorit // sensor speed
}
else
{
Serial.println("No eggs");
digitalWrite(relay4 ,LOW);
delay(50); // sa mu kthy shpejt klipi mbrapa // speed of cylinder getting back
}
}

Answer 1

I design systems with relays operating in production plants. Sticking of the relays is a rare condition, but can occur in certain situations.
Relay Coil Voltage Stability ----
If the relay coil voltage is insufficient then the relays may fail to switch on. I would measure the voltage at coil switch on ensure that the relay coil voltage is stable. For best results I would supply the relay coils from a separately regulated (5 VDC) supply. That ensures that any loading affects of the relay coils on the supply voltage do not cause dropouts on the Arduino supply and stop the program.
Relay Contact Erosion due to inductive loads ----
Relay contacts can become eroded over time, occasionally sticking and eventually welding shut. The damage occurs when switching inductive loads off. The inductive load's energy discharges across the contacts and can generate an arc in the contact gap if the inductively generated voltage is sufficiently high. The plasma then erodes the contacts. A solution is to add a transorb across the contacts that is rated above the normal load voltage (e.g. above 24 VDC). This will absorb the inductive energy harmlessly. Another option is an RC filter. See the relay manufacturer's technical guidelines for more information on this subject.
Some issues that may be present in you system. The details are not apparent from the posted circuit diagram due to absence of some of the circuitry.
Isolation of Earths ----
Ensure that the earth voltages of the Arduino and 24V power are not connected. Otherwise there may be an Arduino earth voltage spike when you are swuitching on and off the solenoids. This could trip of the Arduino and halt the program. The Arduino power and the 24 VDC power sources should be independent and floating.
Relay Driver Isolation ----
Add optical isolators to the relay driver circuit so that there is at least a 1000 V barrier between the Arduino and the relay driver.
Relay Coil Voltage Suppression ----
Add a reverse polarity diode connected across the coil to absorb the inductive energy when the relay coil discharges. Otherwise that energy may cause damage to the arduino output pin.
Good luck with your system