Apparatus And Method For Detecting Ink In A Reservoir Using An Overdriven Thermistor And An Electrical Conductor Extending From The Thermistor

• US 20110221802A1
• Filed: 03/09/2010
• Published: 09/15/2011
• Est. Priority Date: 03/09/2010
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Ottum, Marie E., Sabanovic, Mirza
• Granted Patent: US 8,562,091 B2
• Time in Patent Office: Days
• US Class Current: 347/7
• CPC Class Codes: B41J 2/17566 Ink level or ink residue control
• CPC Class Codes: G01F 23/246 thermal devices

Abstract

A method detects the level of ink in a print head reservoir by monitoring the power drawn by a thermistor positioned within the print head reservoir by an electrical conductor. The method includes dissipating heat in a thermistor positioned within an ink reservoir, the thermistor having an electrical conductor that extends from the thermistor, a length of the electrical conductor extending through at least a portion of the ink reservoir, providing electrical power through the electrical conductor to the thermistor to maintain the thermistor at a predetermined temperature that is a fixed differential above a temperature of the ink reservoir, measuring a parameter that corresponds to the heat dissipated from the thermistor and the length of the electrical conductor extending through the portion of the ink reservoir, and correlating the measured parameter to a predetermined value corresponding to an ink level in the ink reservoir to detect a position of the ink level in the reservoir continuously along the length of the electrical conductor and the thermistor.

Claims

1. A method for monitoring an ink level in an ink reservoir comprising:

dissipating heat in a thermistor positioned within an ink reservoir, the thermistor having an electrical conductor that extends from the thermistor, a length of the electrical conductor extending through at least a portion of the ink reservoir;

providing electrical power through the electrical conductor to the thermistor to maintain the thermistor at a predetermined temperature that is a fixed differential above a temperature of the ink reservoir;

measuring a parameter that corresponds to the heat dissipated from the thermistor and the length of the electrical conductor extending through the portion of the ink reservoir; and

correlating the measured parameter to a predetermined value corresponding to an ink level in the ink reservoir to detect a position of the ink level in the reservoir continuously along the length of the electrical conductor and the thermistor.

2. The method of claim 1 wherein the provision of electrical power to the thermistor and the length of the electrical conductor enables the thermistor and the length of the electrical conductor to reach a temperature that is a fixed differential above a temperature of the ink reservoir.

3. The method of claim 2, the provision of electrical power to the thermistor and the length of the electrical conductor further comprising:

initiating a first predetermined time period during which a measurement current is coupled to the thermistor through the electrical conductor;

initiating a second predetermined time period upon expiration of the first predetermined time period;

comparing a voltage across the thermistor to a threshold voltage during the second predetermined time period;

providing electrical power to the thermistor and the length of the electrical conductor upon detection of the thermistor voltage exceeding the threshold voltage during the second predetermined time period; and

decoupling the electrical power from the thermistor and the length of the electrical conductor upon expiration of the second predetermined time period.

4. The method of claim 3 wherein the measured parameter is a time period during which the electrical power is coupled to the thermistor through the electrical conductor.

5. The method of claim 1, the measured parameter correlation further comprising:

using the measured parameter as an index into a look up table to identify the ink level.

6. The method of claim 3 further comprising:

initiating the first predetermined time period upon the expiration of the second predetermined time period to form a periodic sequence of first and second predetermined time periods.

7. The method of claim 1, the dissipation of heat from the thermistor and the length of the electrical conductor further comprising:

detecting a temperature of the thermistor and the length of the electrical conductor; and

adjusting the dissipation of heat from the thermistor and the length of the electrical conductor in response to a comparison of the detected thermistor temperature to the fixed differential above the temperature of the ink reservoir.

8. The method of claim 7 wherein the dissipation of heat from the thermistor and the length of the electrical conductor and the detection of the temperature of the thermistor and the length of the electrical conductor occur sequentially.

9. The method of claim 8, the detection of the temperature of the thermistor and the length of the electrical conductor further comprising:

detecting a voltage drop across the thermistor and the length of the electrical conductor while a measurement current is flowing through the thermistor and the length of the electrical conductor.

10. The method of claim 9, the adjustment of the dissipated heat further comprising:

providing electrical power to the thermistor and the length of the electrical conductor upon the detected voltage drop exceeding a threshold voltage; and

decoupling electrical power from the thermistor and the length of the electrical conductor at a subsequent predetermined time.

11. The method of claim 10 wherein the measured parameter that corresponds to the dissipated heat is a measured time period during which electrical power is coupled to the thermistor through the length of the electrical conductor.

12. An ink level detection system for use in a printer comprising:

a thermistor positioned with an electrical conductor within an ink reservoir of a printer, the electrical conductor being thermally exposed within the ink reservoir to enable the electrical conductor to dissipate heat into the ink reservoir;

a switch configured to couple a voltage to the thermistor through the thermally exposed electrical conductor in response to a control signal being received at the switch;

a comparator having one input coupled to a voltage across the thermistor and another input coupled to a threshold voltage, the comparator generating the control signal received by the switch; and

a digital controller coupled to the comparator and configured to measure a parameter corresponding to a dissipation of heat from the thermistor and the thermally exposed electrical conductor during a predetermined time period and to correlate the measured parameter to a predetermined value that corresponds to an ink level in the ink reservoir to detect a position of the ink level continuously along a length of the thermally exposed electrical conductor and the thermistor.

13. The system of claim 12, the digital controller being further configured to ground the control signal electrically and turn off the switch for a first predetermined time period and, following expiration of the first predetermined time period, to measure a heating time period that commences in response to the voltage across the thermistor exceeding the threshold voltage and that terminates upon the expiration of a second predetermined time period, the second predetermined time period commencing in response to the first predetermined time period expiring, the heating time period being the measured parameter that corresponds to the dissipation of heat from the thermistor and the thermally exposed electrical conductor.

14. The ink level detection system of claim 13 further comprising:

a reference thermistor, the reference thermistor configured to generate a voltage corresponding to an operating temperature of the ink reservoir; and

the digital controller being further configured to generate the threshold voltage by converting a sum of a predetermined temperature differential and the operating temperature of the ink reservoir to a voltage.

15. The ink level detection system of claim 14 further comprising:

a memory configured to store a plurality of known heating time periods; and

the digital controller being further configured to use the measured heating time period as an index to identify a known heating time period stored in the memory to identify the position of the ink level continuously along the thermally exposed electrical conductor and the thermistor.

16. The ink level detection system of claim 12 wherein the measured parameter is a measured time period during which the voltage is coupled to the thermistor through the thermally exposed electrical conductor by the switch.

17. The ink level detection system of claim 16, the digital controller being further configured to average a predetermined number of measured time periods and to correlate the averaged time period to the predetermined value.

18. The ink level detection system of claim 12 further comprising:

a second thermistor coupled to the ink reservoir to enable the second thermistor to detect an operating temperature of the ink reservoir; and

the digital controller being coupled to the second thermistor and further configured to generate the threshold voltage with reference to the operating temperature by the second thermistor.

19. A thermistor probe for measuring a thermally conductive fluid level in a reservoir comprising:

a probe body;

an electrical conductor extending from the probe body; and

a thermistor electrically connected to the electrical conductor, the electrical conductor and the electrical conductor being external to the probe body to enable the thermistor and the electrical conductor to dissipate heat into a reservoir in which at least a portion of the electrical conductor and thermistor are positioned.

20. The thermistor probe of claim 19 wherein the electrical conductor extends from the thermistor in opposite directions.

21. The thermistor probe of claim 19, the electrical conductor further comprising:

a pair of parallel wires that are separated from one another by a predetermined distance.

22. The thermistor probe of claim 19, the probe body further comprising:

an opening; and

a member at least partially surrounding the opening that is configured to protect the thermistor and electrical conductor from contact.

23. The thermistor probe of claim 19 further comprising:

a connector, the electrical conductor being electrically connected to the connector.