Ink cartridge including a unit to sense a remaining amount of ink

An ink cartridge includes a residual ink sensing unit having a simple structure of an upper electrode plate and a lower electrode plate to accurately detect a capacitance between the upper and lower electrode plate. Therefore, data of a remaining amount of ink is reliably measured, there is less possibility that an ink bag is damaged when the residual ink sensing unit is installed in the ink bag, and damage to the ink cartridge and defective printing due to unstable supply of ink and the missing of the time for replacing the ink cartridge are prevented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No. 10-2005-0060283, filed on Jul. 5, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to an ink cartridge, and more particularly, to an ink cartridge including a residual ink sensing unit to sense an amount of ink remaining in an ink bag.

2. Description of the Related Art

Generally, an inkjet image forming apparatus includes a detachable ink cartridge to form an image by spraying ink to a printing medium. When the ink is exhausted, the ink cartridge is replaced by a new one. The ink cartridge includes a housing that houses the ink cartridge, a nozzle unit that sprays ink to the printing medium, an ink bag that contains ink to be supplied to the nozzle unit and flexibly shrinks according to ink consumption, and a meniscus that forms an ink path from the ink bag to the nozzle unit. When ink is sprayed from the nozzle unit, a negative pressure is generated, and ink contained in the ink bag is continuously provided to the nozzle unit due to the negative pressure.

When the ink contained in the ink bag is exhausted, the value of the negative pressure increases excessively, and consequently the nozzle unit and the meniscus can be damaged. To prevent damage to the nozzle unit and the meniscus and defective printing due to an unstable supply of ink, and to display the time for ink replacement, the ink cartridge includes a residual ink sensing unit.

FIG. 1is a cross-sectional view illustrating a conventional residual ink sensing unit. Referring toFIG. 1, the residual ink sensing unit includes an ink bag25, two terminals24aand24b, and an ink outlet23. The ink bag25includes two flexible sidefilms21and22. As an example, each sidefilm21and22is formed by three layers. An inner layer19of the ink bag25containing ink is easily attached to an intermediate layer18, and manufactured with a thin film made of, for example, a polyethylene (PE) material in order to suppress chemical changes of toner. The intermediate layer18is formed by an aluminum film in order to protect the toner against the outside air and moisture. An outer layer17of the ink bag25is made of a material having a higher melting temperature than that of the material of the inner layer19, and thus the outer layer17does not melt when the inner layer19is attached to the intermediate layer18by means of heat.

Both sidefilms21and22of the flexible ink bag25get closer to each other as the ink is consumed. At this time, a capacitance between the sidefilms21and22is changed, and a remaining amount of ink is sensed using a change of the capacitance. That is, electrodes18aand18b, formed by removing a part of the outer layer17and exposing a part of the intermediate aluminum layer18, are connected to the terminals24aand24b, respectively, and a voltage value between the terminals24aand24bis measured. If the sidefilms21and22acting as capacitors and a resistance element (not shown) are appropriately connected to each other to form an RC circuit the change of the capacitance according to the approach of the sidefilms21and22is measured by a voltage difference.

However, a part of the inner layer19of the very thin ink bag25may come off. Due to this, insulation of the ink bag25is deteriorated, and thus, a functional characteristic of the sidefilms21and22as the capacitor is lowered, and reliability of data which is measured using the terminals24aand24bis decreased. Moreover, there is a problem in that the sensitivity of the residual ink sensing unit is lowered since the voltage difference is not proportional to the ink consumption.

Meanwhile, a hole is created in the sidefilms21and22of the ink bag25by high heat because the sidefilms21and22are very thin, and thus an ink storage capacity of the ink bag25can be deteriorated. Furthermore, to expose the electrodes18aand18bfrom the thin sidefilms21and22, chemical materials or specific processes are needed, which make the manufacturing processes complicated.

SUMMARY OF THE INVENTION

The present general inventive concept provides an ink cartridge including a residual ink sensing unit that accurately senses a remaining amount of ink, has high data measurement reliability, does not damage an ink bag, and is manufactured with simple processes.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing an ink cartridge including a housing, an ink bag that contains ink, a first side supported by an inner portion of the housing, and a second side that approaches the first side according to an ink consumption, a residual ink sensing unit that includes a lower electrode plate fixed to the second side, an upper electrode plate opposite to the lower electrode plate and spaced-apart by a distance from the lower electrode plate, the distance being increased to generate a capacitance change according to the ink consumption, and that senses an amount of ink remaining in the ink bag using the capacitance change between the upper and lower electrode plates.

The residual ink sensing unit may further comprise a stopper that stops the movement of the upper electrode plate such that the distance between the upper and lower electrode plates starts to increase when a height of the ink bag reaches a predetermined level according to the ink consumption.

An air gap may be formed between the upper and lower electrode plates.

The ink bag may have a side portion which is Σ-shaped and may include a folded portion.

The residual ink sensing unit may further comprise an elastic member to press the upper electrode plate towards the lower electrode plate.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing an ink cartridge apparatus, including a housing, an ink bag disposed within the housing and containing ink, and a residual ink sensing unit having a first electrode formed on the ink bag and a second electrode formed between the first electrode and the housing to sense an amount of ink remaining in the ink bag according to a distance between the first electrode and the second electrode.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing an ink cartridge apparatus, including a housing, an ink bag disposed in the housing and containing ink' and a residual ink sensing unit having first and second electrodes having a distance therebetween to be increased according to an ink consumption, and to detect an amount of residual ink according to the increased distance.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing an ink cartridge apparatus, including a housing, an ink bag disposed in the housing and containing ink; and a residual ink sensing unit having a first and second electrode and a stopper, and to detect a first state of a first amount of the ink using the first and second electrodes, and a second state of a second amount of ink using the first and second electrodes and the stopper.

The foregoing and/or other aspects and utilities of the present general inventive concept may be achieved by providing method to sense ink remaining in an ink cartridge with a housing and an ink bag, including measuring a capacitance between a first electrode formed on the ink bag and a second electrode formed between the first electrode and the housing where the ink bag has a volume that reduces as ink leaves the cartridge, and increasing the distance between the first electrode and the second electrode at a predetermined volume of ink.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2is a cross-sectional view illustrating an ink cartridge according to an embodiment of the present general inventive concept. Referring toFIG. 2, the ink cartridge includes a housing110, an ink bag120, and a residual ink sensing unit. Since a stopper illustrated inFIGS. 5 through 9is not included in the ink cartridge illustrated inFIG. 2, the movement of an upper electrode plate130is not limited. The upper electrode plate130is attached to a first inner wall of the housing110, a lower electrode plate140is attached to the ink bag120, and capacitance changes at the start of ink consumption since a distance between the upper and lower electrode plates130and140increases according to the ink bag as it shrinks.

The housing110forms an external case of the ink cartridge, and includes an ink cartridge outlet111. The ink cartridge outlet111is connected to a nozzle unit of an image forming apparatus to form an image on a printing medium with the ink.

According to the present embodiment, the ink bag120contains ink, and includes an ink bag outlet112connected to the ink cartridge outlet111to draw ink out of the ink cartridge. The ink bag120includes a first side121and a second side122. The first side121of the ink bag120is fixed to a second inner wall of the housing110. The second side122of the ink bag120is free, and moves towards the first side121fixed to the housing110according to ink consumption. The ink bag120may be a film formed with a plurality of layers, for example, three layers. According to the present embodiment, an inner layer may be made of a polyethylene material, an intermediate layer may be may be made of an aluminium material, and an outer layer may be made of a polypropylene material.

According to the present embodiment, the residual ink sensing unit includes the upper electrode plate130and the lower electrode plate140. The upper and lower electrode plates130and140are made of conductive materials. The lower electrode plate140is attached to the second side122of the ink bag120, and moves towards the first side121of the ink bag120according to the ink consumption.

As illustrated inFIGS. 5 and 7, in an initial state where the ink bag120is filled with ink, the upper electrode plate130contacts the lower electrode plate140, and the upper and lower plates130and140being insulated from each other. Further, the upper electrode plate130moves while contacting the lower electrode plate140when a height of the ink bag120that decreases according to ink consumption is greater than a predetermined value. At this time, a capacitance between the upper and lower plates130and140is maintained at a maximum value. As illustrated inFIGS. 5 through 9, a difference of the height of the ink bag120between the initial state where the ink bag120is filled with ink and a final state where the ink is completely or almost exhausted is greater than an allowable maximum distance between the upper and lower electrode plates130and140. The capacitance does not change from the initial state where the ink bag120is filled with ink to an intermediate state where the height of the ink bag120reaches a predetermined level, but the capacitance begins to change when the height of the ink bag20is below a predetermined level.

It is possible that the upper electrode plate140may be spaced at a predetermined distance from the lower electrode plate130in the initial state where the ink bag120is filled with ink, and the upper and lower electrode plates130and140may move together while maintaining the distance therebetween, when the height of the ink bag120is greater than the predetermined level.

As illustrated inFIG. 2, the upper electrode plate140may be fixed to a top inner wall of the housing110in an initial state where the ink bag120is filled with ink, and the distance between the upper and lower electrode plates130and140may begin to change as soon as the ink is consumed.

FIG. 3is a graph illustrating a voltage difference between the upper and lower electrode plates130and140according to a distance d. Referring toFIG. 3, a horizontal axis d milimeter (mm) represents a distance between the upper and lower electrode plates130and140, and a vertical axis V volt (v) represents the voltage difference between the upper and lower electrode plates130and140volt (v). Although not illustrated in drawings, the upper and lower electrode plates130and140act as a capacitor and are connected to a resistance element to form an RC circuit, and capacitance changes according to an increase of the distance d between the upper and lower electrode plate130and140are measured by a voltage difference between the upper and lower electrode plates130and140. The capacitance between the upper and lower electrode plates130and140is in proportion to areas of the upper and lower electrode plates130and140and in inverse proportion to the distance d between the plates130and140. Since the distance between the upper and lower electrode plates130and140is increased as the ink is consumed, the capacitance is decreased. Due to the decrease of the capacitance, the voltage difference between the upper and lower electrode plates130and140is reduced in the RC circuit. The voltage difference varies according to a shape of the ink bag120, shape and material of each of the upper and lower electrode plates130and140, and an insulating material thereof.

According to the present embodiment, when a space between the upper and lower electrode plates130and140is insulated by air, the slope of the voltage difference is steep in a left range of a portion810where the distance d is about 4 mm. Therefore, the maximum distance between the upper and lower electrode plates130and140may be about 4 mm. In the left range of the portion810, when the distance d is between 0 mm and 4 mm, the upper and lower electrode plates130and140may be used as residual ink sensors. When the distance d is between 4 mm and 10 mm, because the capacitance is not sensitively changed, the upper and lower electrode plates130and140may not be used as residual ink sensors.

FIG. 4is a graph illustrating the voltage difference between the upper and lower electrode plates130and140according to a remaining amount of ink. The vertical axis represents the voltage difference volt (v) between the upper and lower electrode plates130and140. A horizontal axis represents the amount of ink remaining volume (cc) in the ink bag120. Since the distance d between the upper and lower electrode plates130and140is increased according to ink consumption, the capacitance is decreased, and thus the voltage difference between the upper and lower electrode plates130and140is reduced. When the remaining amount of ink is between 30 cc and 9 cc, the voltage difference between the upper and lower electrode plates130and140is slightly changed. In this section, the distance d between the upper and lower electrode plates130and140is 0 and the upper and lower electrode plates130and140move together as the ink is consumed. When the remaining amount of ink is between 0 and 9 cc, the voltage difference between the upper and lower electrode plates130and140is sensitively changed. In this section, the distance between the upper and lower electrode plates130and140is changed in proportion to the remaining amount of ink within 4 mm as illustrated inFIG. 3.

FIGS. 5 and 6are cross-sectional views illustrating an ink cartridge having a stopper in different states of remaining ink. Referring toFIGS. 5 and 6, stop projections150are formed in the housing110as the stopper. Since the upper electrode plate130moves downward in contact with the lower electrode plate140until it meets the stop projections150, which interrupt the movement of the upper electrode plate130, the capacitance between the upper and lower electrode plates130and140, which are insulated from each other, is maintained at the maximum value, and the voltage difference between the upper and lower electrode plates130and140is maintained at the maximum value, for example, approximately 4 V (FIG. 3), and not changed despite the consumption of ink.FIG. 6illustrates a state where the upper electrode plate130meets the stop projections150and thus the movement of the upper electrode plate130is stopped despite further ink consumption. As the ink is consumed, the lower electrode plate140continuously descends, and the distance d between the upper and lower electrode plates130and140is gradually increased. According to ink consumption, the voltage difference between the upper and lower electrode plates130and140is continuously reduced.

FIGS. 7 and 8are cross-sectional views illustrating an ink cartridge having a stopper in different states of remaining ink. Referring toFIGS. 7 and 8, stop rods160protruding from the upper electrode plate130are formed as the stopper. Since the upper electrode plate130moves downward in contact with the lower electrode plate140until the stop rods160meet an inner wall of the housing110, the capacitance between the upper and lower electrode plates130and140, which are insulated from each other, is maintained at the maximum value, and the voltage difference between the upper and lower electrode plates130and140is maintained at the maximum value, for example, approximately 4 V (FIG. 3) to and is not changed despite the ink consumption.FIG. 8illustrates a state where the stop rods160of the upper electrode plate130contact the inner wall of the housing110and the movement of the upper electrode plate130is stopped despite the ink consumption. As the ink is consumed, the lower electrode plate140continuously descends, and the distance between the upper and lower electrode plates130and140is gradually increased. The voltage difference between the upper and lower electrode plates130and140is continuously reduced according to the ink consumption.

FIG. 9is a cross-sectional view illustrating an ink cartridge having an elastic member700. Referring toFIG. 9, the elastic member700presses the upper electrode plate130towards the lower electrode plate140. The elastic member allows the ink bag120to perpendicularly shrink without sloping in any direction. The elastic member700may be a conic coil spring. Although not illustrated in drawings, the elastic member may also be a leaf spring, a cylindrical spring, or the like. The conic coil spring700may have a coil string diameter of 0.6 to 1.0 mm.

According to the present embodiment, a side portion124of the ink bag120may form a Σ shape (or an accordion shape) and has a folded portion125. The Σ shape of the ink bag120allows the ink bag120to perpendicularly shrink without sloping in any direction.

A look-up table (LUT) may be created to represent a relationship between the voltage difference between the upper and lower electrode plates130and140and the remaining amount of ink stored in the residual ink sensing unit. The residual ink sensing unit may acquire the voltage difference between the upper and lower electrode plates130and140, sense the remaining amount of ink using the relationship, and further include an additional displaying unit or an alarming unit to display the remaining amount of ink and time for replacing or refilling the ink the ink cartridge unit.

As described above, according to the present general inventive concept, an ink cartridge including a residual ink sensing unit having a simple structure of an upper electrode plate and a lower electrode plate to accurately detect a capacitance between the upper and lower electrode plate. Therefore, reliability of measurement data of a remaining amount of ink is ensured, there is less possibility that an ink bag is damaged when the residual ink sensing unit is installed in the ink bag, and damage to the ink cartridge and defective printing due to unstable supply of ink and the missing of the time for replacing ink are prevented.