PID Controller for Rust ![Latest Version] ![Documentation] ![Build Status]

A proportional-integral-derivative (PID) controller.

Features

• Visibility into individual contribution of P, I, and D terms which often need to be logged for later analysis and parameter tuning.
• Output limits on a per term basis.
• Mitigation of integral windup using integral term limit.
• Mitigation of derivative kick by using the derivative of the measurement rather than the derivative of the error.
• On-the-fly changes to kp/ki/kd.
  • Mitigation of output jumps when changing ki by storing the integration of e(t) * ki(t) rather than only e(t).
• Generic float type parameter to support f32 or f64.
• Support for no_std environments, such as embedded systems.

Example

```rust extern crate pid; use pid::Pid;

fn main() { // Set only kp (proportional) let mut pid = Pid::new(10.0, 0.0, 0.0, 100.0, 100.0, 100.0); // Set our target pid.updatesetpoint(15.0); // Fake a measurement of 10.0, which is an error of 5.0. let output = pid.nextcontroloutput(10.0); // Verify that kp * error = 10.0 * 5.0 = 50.0 asserteq!(output.output, 50.0); // Verify that all output was from the proportional term asserteq!(output.p, 50.0); asserteq!(output.i, 0.0); assert_eq!(output.d, 0.0);

// Verify that the same measurement produces the same output since we
// aren't using the stateful derivative & integral terms.
let output = pid.next_control_output(10.0);
assert_eq!(output.p, 50.0);

// Add an integral term
pid.ki = 1.0;
let output = pid.next_control_output(10.0);
assert_eq!(output.p, 50.0);
// Verify that the integral term is adding to the output signal.
assert_eq!(output.i, 5.0);
assert_eq!(output.output, 55.0);

// Add a derivative term
pid.kd = 2.0;
let output = pid.next_control_output(15.0);  // Match the desired target
// No proportional term since no error
assert_eq!(output.p, 0.0);
// Integral term stays the same
assert_eq!(output.i, 5.0);
// Derivative on measurement produces opposing signal
assert_eq!(output.d, -10.0);
assert_eq!(output.output, -5.0);

} ```

Assumptions

• Measurements occur at equal spacing. (t(i) = t(i-1) + C)
• Output limits per term are symmetric around 0 (-limit <= term <= limit).

Formulation

There are several different formulations of PID controllers. This library uses the independent form:

where: - C(t) = control output, the output to the actuator. - P(t) = process variable, the measured value. - e(t) = error = S(t) - P(t) - S(t) = set point, the desired target for the process variable.

kp/ki/kd can be changed during operation and can therefore also be a function of time.

If you're interested in the dependent form, add your own logic that computes kp/ki/kd using dead time, time constant, kc, or whatever else.

Todo

• [ ] Three-term output limit: MAX(p + i + d, global_limit).
• [ ] Helper for (auto-)tuning by detecting frequency & amplitude of oscillations.