Fire-extinguishing system with servo motor-driven foam pump
Embodiments of the invention provide a fire-extinguishing system for injecting foamant into a stream of water. The system can include a flow meter determining a flow rate of the stream of water and a foam pump having an inlet coupled to a supply of foamant and an outlet coupled to the stream of water. The system includes a servo motor driving the foam pump. The servo motor includes a sensor used to determine a rotor shaft speed and/or a rotor shaft torque. A controller can control an operating speed of the servo motor using closed-loop control depending on the flow rate and the rotor shaft speed and/or the rotor shaft torque.
1. A fire-extinguishing system for injecting foamant into a stream of water, the system comprising:
a flow meter determining a water flow rate of the stream of water;
a foam pump having an inlet coupled to a supply of foamant and having an outlet coupled to the stream of water; and
a servo motor driving the foam pump,
the servo motor including a sensor to measure rotor position in order to determine at least one of a rotor shaft speed and a rotor shaft torque,
an operating speed of the servo motor being controlled by a controller using closed-loop control based on the water flow rate and at least one of the rotor shaft speed and the rotor shaft torque.
2. The fire-extinguishing system of claim 1 , wherein the fire-extinguishing system is one of a stationary system and a mobile system.
3. The fire-extinguishing system of claim 1 , wherein the operating speed of the servo motor is based on a foamant flow rate.
4. The fire-extinguishing system of claim 3 , wherein the foamant flow rate is measured by a second flow meter.
5. The fire-extinguishing system of claim 3 , wherein the foamant flow rate is calculated based on a displacement of the foam pump.
6. The fire-extinguishing system of claim 1 , and further comprising a selector valve positioned downstream of the outlet, the selector valve having a first position allowing foamant to enter the stream of water and a second position allowing the foamant to exit the fire-extinguishing system without being introduced into the stream of water.
7. The fire-extinguishing system of claim 6 , wherein the selector valve is automatically operated to purge air in order to prime the foam pump.
8. The fire-extinguishing system of claim 7 wherein the selector valve is an electric calibration injection valve.
9. The fire-extinguishing system of claim 1 , wherein the controller identifies a viscous property of foamant based on the motor shaft torque and calibration values.
10. The fire-extinguishing system of claim 1 , wherein the servo motor has a back electromagnetic force constant of at least about 3.5 volts root mean squared per kilo revolutions per minute for a direct current power source of about 12 volts.
11. The fire-extinguishing system of claim 1 , wherein the servo motor has a back electromagnetic force constant of at least about 46 volts root mean squared per kilo revolutions per minute for a direct current power source of about 160 volts.
12. The fire-extinguishing system of claim 1 , wherein a rotor shaft angle is used to compute the rotor shaft speed of the servo motor.
13. The fire-extinguishing system of claim 1 , wherein the foam pump is a positive displacement pump.
14. The fire-extinguishing system of claim 1 , wherein the foam pump includes a piston, and the controller modifies the operating speed of the servo motor based on the piston position of the foam pump.
15. The fire-extinguishing system of claim 1 , and further comprising a load dump protection circuit to help prevent damage to at least one of the controller and the servo motor from over-voltage peaks.
16. The fire-extinguishing system of claim 1 , wherein the servo motor is powered by one of a DC power source and an AC power source.
17. The fire-extinguishing system of claim 1 , wherein the servo motor is capable of being powered by at least one of a plurality of voltages and a plurality of power sources.
18. The fire-extinguishing system of claim 1 , and further comprising a power management system capable of substantially preventing over-heating of the servo motor.
19. The fire-extinguishing system of claim 18 , wherein the power management system provides a variable duty cycle to the servo motor.
20. The fire-extinguishing system of claim 18 , wherein the power management system includes tailored pulse shapes.
21. The fire-extinguishing system of claim 1 , and further comprising a water pump positioned in the stream of water.
22. The fire-extinguishing system of claim 21 , wherein the foamant is introduced one of upstream and downstream of the water pump.
23. The fire-extinguishing system of claim 1 , wherein the foam pump can be automatically started.
24. The fire-extinguishing system of claim 1 , wherein the controller can stop the servo motor when a condition is detected by the controller.
25. The fire-extinguishing system of claim 24 , wherein the condition detected by the controller includes at least one of a current fold back condition, an over-temperature condition, a stall condition, and a low foamant supply condition.
26. The fire-extinguishing system of claim 1 , wherein the sensor measures a current draw of the servo motor.
27. The fire-extinguishing system of claim 26 , wherein the rotor shaft torque is computed based on the current draw and a torque constant of the servo motor.
28. The fire-extinguishing system of claim 27 , wherein the torque constant is mapped to compensate for temperature variations.