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Error in Control Systems

In a control system, you are likely to encounter the concept of "Error" in one form or another. The concept of error in control systems is different from its ordinary language meaning (e.g., “your solution to #5 on the midterm has an error in it”).

What is Error?

Error is basically the difference between the current state and the desired state of a control system. The goal is to minimize the error, often using control algorithms such as:

  • PID (Proportional-Integral-Derivative)
  • Pure Pursuit
  • Stanley

Examples Where Error is Important

1. A car’s position relative to its goal

  • The error is the distance between the current position of the car and the target position.

  • EThe Ackermann Drive Program demonstrates using PID to correct position-based error.

2. A car’s steering angle

  • If you want to turn right but are currently going straight, the error is:
    error = desired steering angle - current steering angle

  • If the car is going straight, the current steering angle is 0°.

3. A car’s speed

  • If you want to maintain the speed limit, the error is:
    error = current speed - speed limit

Summary of Examples

In each case, a different control system is needed to correct each type of error. For example, when using PID control to manage both position and steering angle, you would need:

  • One PID controller for position control
  • Another PID controller for steering angle control