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//! A small PID controller library. //! //! This crate implements the classic independent PID formulation. //! //! # Introduction //! //! PID controllers are an integral part of control systems, and provide a way to //! perform error correction. It's used to control things like throughput or //! resource allocation: as the resource approaches capacity, the returned //! correction decreases. And because it is aware of a time factor, it can deal //! with rapid changes as well. //! //! # Loop Tuning //! //! However PID controllers are not a silver bullet: they are a tool in a wider //! toolbox. To maximally benefit from them they need to be tuned to the //! workload. This is done through three parameters: `proportional_gain`, //! `integral_gain` and `derivative_gain`. Automated algorithms exist to tune //! these parameters based on sample workloads, but those are out of scope for //! this crate. //! //! [Read more on loop tuning](https://en.wikipedia.org/wiki/PID_controller#Loop_tuning). //! //! # No-std support //! //! `#[no_std]` support can be enabled by disabling the default crate-level //! features. This disables the `Controller::update` method which automatically //! calculates the time elapsed. Instead use the `Controller::update_elapsed` //! method which takes an externally calculated `Duration`. //! //! # Examples //! //! ```no_run //! use pid_lite::Controller; //! use std::thread; //! use std::time::Duration; //! //! let target = 80.0; //! let mut controller = Controller::new(target, 0.25, 0.01, 0.01); //! //! loop { //! let correction = controller.update(measure()); //! apply_correction(correction); //! thread::sleep(Duration::from_secs(1)); //! } //! # fn measure() -> f64 { todo!() } //! # fn apply_correction(_: f64) { todo!() } //! ``` #![forbid(unsafe_code)] #![deny(missing_debug_implementations, nonstandard_style)] #![warn(missing_docs, future_incompatible, unreachable_pub, rust_2018_idioms)] use core::time::Duration; #[cfg(feature = "std")] use std::time::Instant; /// PID controller /// /// The `target` param sets the value we want to reach. The /// `proportional_gain`, `integral_gain` and `derivative_gain` parameters are all /// tuning parameters. /// /// # Examples /// /// ```no_run /// use pid_lite::Controller; /// use std::thread; /// use std::time::Duration; /// /// let target = 80.0; /// let mut controller = Controller::new(target, 0.5, 0.1, 0.2); /// /// loop { /// let correction = controller.update(measure()); /// apply_correction(correction); /// thread::sleep(Duration::from_secs(1)); /// } /// # fn measure() -> f64 { todo!() } /// # fn apply_correction(_: f64) { todo!() } /// ``` #[derive(Debug)] pub struct Controller { target: f64, proportional_gain: f64, integral_gain: f64, derivative_gain: f64, error_sum: f64, last_error: f64, #[cfg(feature = "std")] last_instant: Option<Instant>, } impl Controller { /// Create a new instance of `Controller`. /// /// # Examples /// /// ``` /// # #![allow(unused_assignments)] /// use pid_lite::Controller; /// /// let target = 80.0; /// let mut controller = Controller::new(target, 0.20, 0.02, 0.04); /// ``` pub const fn new( target: f64, proportional_gain: f64, integral_gain: f64, derivative_gain: f64, ) -> Self { Self { target, proportional_gain, integral_gain, derivative_gain, error_sum: 0.0, last_error: 0.0, #[cfg(feature = "std")] last_instant: None, } } /// Get the target. /// /// # Examples /// /// ``` /// # #![allow(unused_assignments)] /// use pid_lite::Controller; /// /// let target = 80.0; /// let mut controller = Controller::new(target, 0.20, 0.02, 0.04); /// assert_eq!(controller.target(), 80.0); /// ``` pub const fn target(&self) -> f64 { self.target } /// Set the target. /// /// # Examples /// /// ``` /// # #![allow(unused_assignments)] /// use pid_lite::Controller; /// /// let target = 80.0; /// let mut controller = Controller::new(target, 0.20, 0.02, 0.04); /// controller.set_target(60.0); /// assert_eq!(controller.target(), 60.0); /// ``` pub fn set_target(&mut self, target: f64) { self.target = target; } /// Push an entry into the controller. /// /// # Examples /// /// ``` /// # #![allow(unused_assignments)] /// use pid_lite::Controller; /// /// let target = 80.0; /// let mut controller = Controller::new(target, 0.0, 0.0, 0.0); /// assert_eq!(controller.update(60.0), 0.0); /// ``` /// /// # Panics /// /// This function may panic if the `time_delta` in millis no longer fits in /// an `f64`. This limit can be encountered when the PID controller is updated on the scale of /// hours, rather than on the scale of minutes to milliseconds. #[cfg(feature = "std")] #[must_use = "A PID controller does nothing if the correction is not applied"] pub fn update(&mut self, current_value: f64) -> f64 { let now = Instant::now(); let elapsed = match self.last_instant { Some(last_time) => now.duration_since(last_time), None => Duration::from_millis(1), }; self.last_instant = Some(now); self.update_elapsed(current_value, elapsed) } /// Push an entry into the controller with a time delta since the last update. /// /// The `time_delta` value will be rounded down to the closest millisecond /// with a minimum of 1 millisecond. /// /// # Examples /// /// ``` /// # #![allow(unused_assignments)] /// use pid_lite::Controller; /// use std::time::Duration; /// /// let target = 80.0; /// let mut controller = Controller::new(target, 0.5, 0.1, 0.2); /// let dur = Duration::from_millis(2); /// assert_eq!(controller.update_elapsed(60.0, dur), 16.0); /// ``` /// /// # Panics /// /// This function may panic if the `time_delta` in millis no longer fits in /// an `f64`. This limit can be encountered when the PID controller is updated on the scale of /// hours, rather than on the scale of minutes to milliseconds. #[must_use = "A PID controller does nothing if the correction is not applied"] pub fn update_elapsed(&mut self, current_value: f64, elapsed: Duration) -> f64 { let elapsed = (elapsed.as_millis() as f64).min(1.0); let error = self.target - current_value; let error_delta = (error - self.last_error) / elapsed; self.error_sum = self.error_sum + error * elapsed; self.last_error = error; let p = self.proportional_gain * error; let i = self.integral_gain * self.error_sum; let d = self.derivative_gain * error_delta; p + i + d } /// Reset the internal state. /// /// # Examples /// /// ``` /// # #![allow(unused_assignments)] /// use pid_lite::Controller; /// use std::time::Duration; /// /// let target = 80.0; /// let mut controller = Controller::new(target, 0.0, 0.0, 0.0); /// let dur = Duration::from_secs(2); /// let correction = controller.update_elapsed(60.0, dur); /// /// controller.reset(); /// ``` pub fn reset(&mut self) { self.reset_inner(); } #[cfg(feature = "std")] fn reset_inner(&mut self) { self.error_sum = 0.0; self.last_error = 0.0; self.last_instant = None; } #[cfg(not(feature = "std"))] pub fn reset_inner(&mut self) { self.error_sum = 0.0; self.last_error = 0.0; } } #[cfg(test)] mod test { use super::*; #[test] fn base_correction() { let target = 80.0; let mut controller = Controller::new(target, 0.5, 0.1, 0.2); let dur = Duration::from_millis(2); assert_eq!(controller.update_elapsed(60.0, dur), 16.0); } #[test] #[cfg(feature = "std")] fn no_correction() { let target = 80.0; let mut controller = Controller::new(target, 0.0, 0.0, 0.0); assert_eq!(controller.update(60.0), 0.0); } }