Arduino PID DC Motor Position Control - arduino

Question

I'm doing a control engineering project, implementing a PID motor position control for automatic antenna tracking system. The system contain a dc motor, absolute encoder, and a motor driver.
Everything work as expected, but one thing. The motor cannot stop at set point value near 0 degree (350 - 359, 0 - 10 degree). The used code:
#include <PID_v1.h>
int RPWM = 5;
int LPWM = 6;
int L_EN = 7;
int R_EN = 8;
boolean pin_state[10];
byte input_pin[] = {1, 2, 3, 4, 9, 10, 11, 12, 13};
int dec_position = 0;
int dc = 0;
double kp = 50, ki = 45, kd = 2;
double input = 0, output = 0, setpoint = 0;
volatile long encoderPos = 0;
PID myPID(&input, &output, &setpoint, kp, ki, kd, DIRECT);
void setup() {
pinMode(L_EN, OUTPUT);
pinMode(R_EN, OUTPUT);
pinMode(RPWM, OUTPUT);
pinMode(LPWM, OUTPUT);
for (byte i = 0; i < 9; i++) {
pinMode(input_pin[i], INPUT);
}
TCCR1B = TCCR1B & 0b11111000 | 1;
myPID.SetMode(AUTOMATIC);
myPID.SetSampleTime(1);
myPID.SetOutputLimits(-255, 255);
digitalWrite(L_EN, HIGH);
digitalWrite(R_EN, HIGH);
}
void loop() {
if (Serial.available() > 0) {
String baca = Serial.readString();
setpoint = baca.toInt();
}
ReadEncoder();
input = dc;
myPID.Compute();
pwmOut(output);
}
void pwmOut(int out) {
if (out > 0) {
analogWrite(RPWM, out);//Sets speed variable via PWM
}
else {
analogWrite(LPWM, abs(out));//Sets speed variable via PWM
}
}
void ReadEncoder() {
// FOR READING ENCODER POSITION, GIVING 0-359 OUTPUT CORRESPOND TO THE ENCODER POSITION
for (byte i = 0; i < 9; i++) {
pin_state[i] = !(digitalRead(input_pin[i]));
}
dec_position = (pin_state[8] * 256) + (pin_state[7] * 128) + (pin_state[6] * 64) + (pin_state[5] * 32) + (pin_state[4] * 16) + (pin_state[3] * 8) + (pin_state[2] * 4) + (pin_state[1] * 2) + pin_state[0];
dc = map(dec_position, 0, 500, 0, 360);
}
When the set point is a value between 10 - 350 the sytem worked well. But when it is not, the motor never stop rotating.
I know the problem is due to a little position overshoot cause the encoder to read a very large error.
For instance, if the setpoint is 0 degree, the motor rotate to reach it. Motor rotation is slowing down as its "now" position approaching 0 degree, but the system is not overshoot free. Therefore, even 1 degree overshoot cause the error value is -359 (set point - now position) and the motor rotate again to reach the desired position.
Need help how to overcome this problem. Sorry for bad english.

Answer 1

Here's the solution
double error;
if (SP>PV) {
if (abs(SP-PV) < abs(-360 + SP - PV)) error = SP - PV;
else error = -360 + SP - PV;
}
else{
if(abs(SP-PV)< abs(360 - PV + SP)) error = SP - PV;
else error = 360 - SP + PV;
}
Instead off simple present value minus the set point for error. The code above return shortest path from present value to set point.

Answer 2

i didn't read your code yet. However, to reach "set point" (SV) you should give for "present value" (PV) an error allowance (EA)
For example: EA = SV - PV.
If EA = (-2,+2)degree then it reach "now position"
And, you should not use degree for angle, you should convert it to position (calculate by pulse)
Hope that concept can help you.