Medical fluid machine having solenoid control system with reduced hold current
View Patent ↗An electromechanical solenoid control system with reduced hold current includes an electromechanical solenoid including an armature and a coil; a voltage source; a resistor placed in an electrical line between the voltage source and the solenoid coil; a switching device configured to selectively apply power from the voltage source to the solenoid coil; and a control element connected electrically to the switching device, the control element operable to receive a signal from the electrical line and use the signal to control the switching device to selectively apply power from the voltage source to the solenoid coil.
1. An electromechanical solenoid control system comprising:
an electromechanical solenoid including an armature and a coil;
a voltage source;
a resistor placed in an electrical line between the voltage source and the solenoid coil;
a switching device configured to selectively apply power from the voltage source to the solenoid coil;
a control element connected electrically to the switching device, the control element operable to receive a continuous signal from the electrical line and use the signal to (i) determine when to switch from a solenoid activation state to a solenoid hold state and (ii) control the switching device to selectively apply power from the voltage source to the solenoid coil; and
wherein the control element is further operable to cause the switching device to (a) operate at a solenoid actuation level when, in the solenoid actuation state, the armature is to be moved within the coil and (b) to operate at a solenoid hold level when, in the solenoid hold state, the continuous signal indicates to the control element that the armature is moving or has moved within the coil.
2. The electromechanical solenoid control system of claim 1 , wherein the switching device includes a field effect transistor (“FET”).
3. The electromechanical solenoid system of claim 2 , wherein the control element is connected to a gate of the FET.
4. The electromechanical solenoid system of claim 1 , which includes at least one signal conditioning apparatus configured to perform at least one of: (i) amplification of the signal received by the control element; (ii) conversion of the signal from a differential form to one referenced to a ground; and (iii) filtering of the signal prior to the control element.
5. The electromechanical solenoid system of claim 1 , wherein the signal is a voltage signal across the resistor.
6. The electromechanical solenoid system of claim 5 , wherein the voltage signal is formed via a current flow through the resistor due to at least one of: (i) inductance of the coil and (ii) a recirculation diode connected electrically to the electrical line.
7. The electromechanical solenoid system of claim 5 , wherein the voltage signal is formed via a current flow through the resistor that varies as a function of a duty cycle of the switching device.
8. The electromechanical solenoid system of claim 1 , wherein the control element includes at least one attribute selected from the group consisting: (i) including a microprocessor; (ii) being configured to supply a voltage to the switching device; and (iii) being configured to control the switching device via pulse width modulation.
9. The electromechanical solenoid system of claim 1 , which is configured to be used to open and occlude tubing.
10. The electromechanical solenoid system of claim 1 , the control element configured to set the solenoid hold level to a level slightly above which the armature was released after the previous hold state.
11. The electromechanical solenoid system of claim 1 , the solenoid including a spring biased to expand to cause the armature to release from activation.
12. The electromechanical solenoid system of claim 1 , the solenoid including a spring biased to retract to cause the armature to release from activation.
13. The electromechanical solenoid system of claim 1 , the signal being a continuous signal, the control element configured to monitor the continuous signal and to determine that a solenoid fault condition is present if an expected change in the signal does not occur.
14. The electromechanical solenoid system of claim 13 , the fault condition being (i) an armature failing to activate condition or (ii) an armature failing to release from activation condition.
15. An electromechanical solenoid control system comprising:
an electromechanical solenoid including an armature and a coil;
a power source configured to power the coil; and
a control element configured to control power from the power supply to the coil, the control element receiving a signal from an electrical point between the power supply and the coil, the signal changing in a characteristic fashion when the armature upon activation begins to move or is moving within the coil, the characteristic change including a negative going current spike in the coil caused when the armature begins to move, the control element configured to sense this characteristic change and to thereafter reduce power from the power source to the coil.
16. The electromechanical solenoid system of claim 15 , wherein the power is reduced to a hold level.
17. The electromechanical solenoid system of claim 15 , wherein at least one of: (i) the power source is a voltage source; (ii) the control element includes a microprocessor; (iii) the control element controls a switching device to control power from the power source to the coil; (iv) the control element uses pulse width modulation to control power from the power source to the coil; (v) a resistor is placed between the power supply and the coil, the signal taken from across the resistor; (vi) signal conditioning is provided to condition the signal inputted to the control element; and (vii) the signal is aided by a recirculation diode.
18. The electromechanical solenoid system of claim 15 , wherein the control element is configured to reduce the power to a level determined in a prior release of the armature within the coil.
19. An electromechanical solenoid control system comprising:
an electromechanical solenoid including an armature and a coil;
a power source configured to power the coil; and
a control element configured to control power from the power supply to the coil, the control element receiving a signal from an electrical point between the power supply and the coil, the signal changing in a characteristic fashion including a positive-going current spike in the coil when the armature after an intentional release begins to move or is moving within the coil, the control element configured to sense the characteristic change and store the current level at which the change occurred.
20. The electromechanical solenoid system of claim 19 , the control element further configured to remove power from the coil upon sensing the characteristic change.
21. The electromechanical solenoid system of claim 19 , wherein the electromechanical solenoid includes a spring biased to release the armature.
22. The electromechanical solenoid system of claim 19 , wherein at least one of: (i) the power source is a voltage source; (ii) the control element includes a microprocessor; (iii) the control element controls a switching device to control power from the power source to the coil; (iv) the control element uses pulse width modulation to control power from the power source to the coil; (v) a resistor is placed between the power supply and the coil, the signal taken from across the resistor; (vi) signal conditioning is provided to condition the signal inputted to the controller; and (vii) the signal is aided by a recirculation diode.
23. The electromechanical solenoid system of claim 19 , the controller further configured to use the stored current level as a hold level when the coil is subsequently activated.
24. The electromechanical solenoid system of claim 23 , the controller still further configured to increment the stored current level or use a previously stored current level as the hold level if the stored current level is determined to be insufficient.
25. An electromechanical solenoid control method comprising:
intentionally releasing an armature of a solenoid;
sensing a power current level at which a positive-going current spike occurs in a coil of the solenoid;
updating an electrical current release level to be the sensed current level, which is indicative of the armature of a solenoid beginning to move or moving; and
setting an electrical current hold level for the solenoid to be the updated electrical current release level plus an increment.
26. The electromechanical solenoid control method of claim 25 , which includes performing the method of claim 25 individually for a plurality of solenoids used in a system.
27. An electromechanical solenoid control system comprising:
an electromechanical solenoid including an armature and a coil;
a voltage source;
a resistor placed in an electrical line between the voltage source and the solenoid coil;
a switching device configured to selectively apply power from the voltage source to the solenoid coil;
a control element connected electrically to the switching device, the control element operable to receive a continuous signal from the electrical line and use the continuous signal to (i) determine when to switch from a solenoid activation state to a solenoid hold state and (ii) control the switching device to selectively apply power from the voltage source to the solenoid coil; and
the control element further operable to monitor the continuous signal and to determine that a solenoid fault condition is present if an expected change in the signal does not occur.