pid with test

tests/test_pid.py

@@ -0,0 +1,66 @@
+import unittest
+
+from cnc.pid import *
+
+
+class TestPid(unittest.TestCase):
+    def setUp(self):
+        self._environment_temp = 25
+        # Coefficients below were chosen by an experimental way with a real
+        # hardware: reprap heating bed and extruder.
+        self._bed_c = 0.00231  # bed cooling coefficient
+        self._bed_h = 0.25  # bed heating coefficient
+        self._extruder_c = 0.0039  # extruder cooling coefficient
+        self._extruder_h = 3.09  # extruder heating coefficient
+
+    def tearDown(self):
+        pass
+
+    def __simulate(self, target_temp, environment_temp, cool, heat):
+        # Simulate heating some hypothetical thing with heater(h is a heat
+        # transfer coefficient, which becomes just a delta temperature each
+        # second) from environment temperature to target_temp. Consider that
+        # there is natural air cooling process with some heat transfer
+        # coefficient c. Heating power is controlled by PID.
+        pid = Pid(target_temp, 0)
+        temperature = environment_temp
+        heater_power = 0
+        fixed_at = None
+        zeros_counter = 0
+        for j in range(1, 15 * 60 + 1):  # simulate for 15 minutes
+            # natural cooling
+            temperature -= (temperature - environment_temp) * cool
+            # heating
+            temperature += heat * heater_power
+            heater_power = pid.update(temperature, j)
+            if fixed_at is None:
+                if pid.is_fixed():
+                    fixed_at = j
+            else:
+                self.assertLess(abs(temperature - target_temp),
+                                pid.FIX_ACCURACY * target_temp,
+                                msg="PID failed to control temperature "
+                                "{}/{} {}".format(temperature, target_temp, j))
+            if heater_power == 0.0:
+                zeros_counter += 1
+        self.assertLess(zeros_counter, 20, msg="PID turns on/off, instead of "
+                                               "fine control")
+        self.assertLess(fixed_at, 600,
+                        msg="failed to heat in 10 minutes, final temperature "
+                            "{}/{}".format(temperature, target_temp))
+
+    def test_bed(self):
+        # check if bed typical temperatures can be reached in simulation
+        for target in range(50, 101, 10):
+            self.__simulate(target, self._environment_temp,
+                            self._bed_c, self._bed_h)
+
+    def test_extruder(self):
+        # check if extruder typical temperatures can be reached in simulation
+        for target in range(150, 251, 10):
+            self.__simulate(target, self._environment_temp,
+                            self._extruder_c, self._extruder_h)
+
+
+if __name__ == '__main__':
+    unittest.main()