The present invention relates generally to ink jet printers. More particularly, the present invention relates to ink level sensing for printers utilizing ink jet cartridges and ink reservoirs.
An operational consideration for printers utilizing ink reservoirs and cartridges is the level of ink in the cartridges. Sensing the ink level is performed so that the printer does not attempt to print without ink. Operation of ink jet and other types of printers without ink can damage the printer""s print head.
In thermal ink jet printers, printing is performed by boiling ink and shooting the ink through very small nozzles hundreds or even thousands of times per second. Printing without the ink, the print headxe2x80x94a complex electro-mechanical system containing hundreds of nozzles, heating elements, barriers, ink flow channels, and underlying circuitsxe2x80x94would be irreparably damaged.
In the past, printing without ink was not a pressing concern because useful life of the print heads was short. By the time the ink was depleted, the print head usually needed to be replaced. After depletion of the ink, the entire cartridge, including the print head, was discarded. Thus, the old ink jet cartridges were built as disposable units.
More recently, however, the print heads are being built as reusable units. The print heads are able to last beyond the depletion of the ink. Because the print head is relatively expensive as compared to the ink, it is becoming increasingly common to replenish the ink rather than to discard the print head. For this reason, printing without ink should be avoided so as to avoid damaging the print head.
Additionally, operation of a printer with a depleted ink supply may lead to loss of important information. For example, a printer printing a facsimile message may receive the transmitted information and operate as if the received information is being printed. If the ink is depleted, the information is never printed. Unless the receiver can ask the sender to retransmit the fax, the information is irretrievable.
Knowing the exact ink level of the ink cartridge may be important under other considerations. For instance, before beginning a large print job, it would be useful to know whether the remaining ink is sufficient to finish the print job. If the amount of ink is insufficient, the ink cartridge can be replaced or replenished to avoid wasting time, paper, and effort of unsuccessfully attempting to print the large print job.
The ink level of foam-filled ink containers may be sensed by measuring the opacity of an open area within the foam. The measurement is made with a light source and a photodetector. The ink level is sensed at only one location within the reservoir. Therefore, ink level above or below the sensing point cannot be determined. Additionally, this optical technique depends upon the ink level changing within the foam in a known manner, and gives erroneous readings in some circumstances. For example, a partially full cartridge stored for some time on its side may provide erroneous readings.
There is a need to detect the level of ink remaining in the ink reservoir.
According to one aspect of the invention, an ink cartridge for a printer includes a housing defining an ink reservoir; a first electrode proximal to the reservoir; and a second electrode proximal to the reservoir. The electrodes are spaced apart for ink level measurement of the reservoir.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.