GB2312283A

GB2312283A - Inductive ink level detection mechanism

Info

Publication number: GB2312283A
Application number: GB9706535A
Authority: GB
Inventors: Steven B Elgee; James M Cameron
Original assignee: Hewlett Packard Co
Current assignee: HP Inc
Priority date: 1996-04-17
Filing date: 1997-04-01
Publication date: 1997-10-22
Anticipated expiration: 2017-04-01
Also published as: GB9706535D0; KR970069343A; GB2312283B; KR100384915B1; DE19642899A1; JPH1044469A

Description

TECHNICAL FIELD 1 2312283

2 This invention relates to ink level detection mechanisms, and more 3 particularly, to an inductive ink level detection mechanism for detecting an amount 4 of residual ink within an ink container of an ink-jet pen.

6 BACKGROUND OF THE INVENTION

7 An ink-jet printer is a type of non-impact printer which forms characters 8 and other images by controllably spraying drops of ink from a print head. One 9 conventional type of ink-jet print head consists of a replaceable cartridge or pen io which is removably mounted to a movable carriage. The pen controllably ejects 11 liquid ink through multiple nozzles in the form of drops which travel across a 12 small air gap and land on a recording media.

13 Ink droplets are ejected from individual nozzles by localized heating. A 14 small heating element, typically in the form of a thermal resistor, is disposed at is each nozzle. An electrical current is passed through the element to heat it up. The 16 heated element vaporizes a tiny volume of ink which is ejected through the nozzle. 17 The heating elements are commonly formed on a single silicon wafer chip, which 18 make the replaceable pen easy to assemble and inexpensive to produce. 19 A reservoir of ink is held in a container that forms part of an independent 20 cartridge separate from the pen. The pen draws ink from the container during 21 printing. The container can be configured as a rigid chamber, or a flexible bag. 22 As the pen uses ink, the ink supply in the container is slowly depleted. Printers are 23 often designed to detect the level of residual ink in the container and to inform the 24 user when it is time to replace or refill the pen. Depending upon the construction, 25 2_ either the entire pen or the ink container of the pen is replaced. The exhausted pen 2 or container is disposed or recycled.

3 There are essentially three different types of prior art techniques for

4 detecting the level of residual ink in ink containers: capacitance sensing, 5resistance sensing, and magnetic sensing. U.S. Patent No. 4,415,886 describes a 6 residual ink detection mechanism for detecting the amount of residual ink in an ink 7 container using capacitance sensing. The container is formed as a flexible bag 8 having an upper and lower sheet. A metal thin film layer is disposed on each of 9 the upper and lower sheets to form a pair of spaced capacitor electrodes. A pulse o generating circuit applies pulses to the capacitor electrodes and the electrostatic 11 capacitance between the electrodes is measured. When the ink container is full, 12 the capacitance of the electrode pair is small. As the ink is depleted, the 13 capacitance of the electrode pair increases. The drawback associated with this 14 type of capacitance sensing device is that it does not work well when used in Is conjunction with conductive inks. To achieve adequate perforTnance with 16 conductive ink supplies, a very large frequency signal (on the order of several 17 NMz) must be passed through the capacitor. Generating a large frequency signal 8 is not a desirable operating condition for an ink-jet printer.

19 U.S. Patent No. 4,700,754 describes an ink level detector for a collapsible ink container which also employs capacitance sensing. Instead of using two 21 electrodes formed on the bag, however, the '754 patent measures the capacitance 22 between the liquid ink and an electrically conductive coating formed on the ink 23 container. This capacitance sensing technique has a drawback in that it functions 24 as a switch-like warning detector that is either off or on depending upon whether the ink supply is depleted to a certain level. The measured capacitance is 2 proportional to the area of ink covering the layer with the electrode. As ink nears 2 depletion, the capacitance decreases very rapidly forming a level transition for 3 on/off detection. The capacitance ink level detector does not function as a gauge 4 which continuously monitors changing levels of residual ink.

U.S. Patent No. 4,202.267, No. 4,551,734, No. 4,719,475, No. 5,289,211, 6 and No.5.488,395 all describe techniques for monitoring the residual ink level in 7 an ink container by measuring change in electrical resistance between a pair of 8 electrodes.

9 Japanese Application No. 60-92861 describes an ink bag having a magnetic o sheet on one surface of the bag and a proximity lead switch positioned underneath i i an opposing surface. As the ink is depleted, the bag collapses to a point where the 12 lead switch triggers to indicate that the ink level is low. This technique is limited 13 in that it is only a bi-state sensor, in that the switch is either on or off. There is no 14 ability to measure or detect gradual changes in the ink supply.

is The inventors have developed an improved ink level detection mechanism 16 that continuously monitors the ink level within an ink container.

17 18 SUMMARY OF THE UWENTION

19 An ink level detection mechanism has a flexible ink container for storing an ink supply used by an ink-jet pen. The ink container has opposing sides which 21 move relative to one another depending upon an amount of ink held therein. In 22 one implementation, the ink container is formed as a flexible plastic bag.

23 The ink level detection mechanism also has a pair of electrically conductive 24 coils formed on the opposing sides of the ink container. In one implementation, the coils are printed as thin metal film traces on the container sides. In this 3 4.

manner, the coils move relative to one another in conjunction with the movement 2 of the opposina sides of the flexible container.

3 An ink level sensing circuit is connected to the coils. The ink level sensing 4 circuit generates a signal which induces an electro-magnetic field between the pair s of coils. The ink level sensing circuit then senses an ink level within the ink 6 container by detecting change in the field as the coils are moved relative to one

7 another. The field strength increases as the coils are moved closer together.

8 The inductive ink level detection mechanism is advantageous over prior art

9 systems in that the field grows stronger as the ink is depleted from the container, io enabling more accurate measurement of the ink level as the container nears empty.

11 In addition, the inductive ink level detection mechanism can be employed with 12 conductive inks.

13 14 BRIEF DESCRIPTION OF THE DRAWINGS is Fig. 1 is a diagrammatic illustration of an ink-jet pen. 16 Fig. 2 is a diagrammatic illustration of an ink level detection mechanism for 17 an ink-jet pen constructed according to an aspect of this invention. is Fig. 3 is a circuit representation of the ink level detection mechanism.

19 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

21 Fig. 1 shows a replaceable ink-jet supply cartridge 10 for supplying ink to 22 an ink-jet pen used in an ink-jet printer. Cartridge 10 is a self- contained, 23 disposable supply container having a rigid housing 12 and an ink level detection 24 mechanism 14 held within the housing 12. The ink supply cartridge 10 also includes a fluid port 15 which permits output of the liquid ink for use by the print 4 head. In other implementations, however, the ink level detection mechanism 14 2 might itself form part of an ink-jet pen. As used herein, the terms "pen" and "print 3 head" are substantially interchangeable.

4 Fig. 2 shows the ink level detection mechanism 14 constructed according to s an aspect of this invention. The ink level detection mechanism 14 has a flexible 6 ink container 16 in the form of a flexible, collapsible bag. The ink bag 16 defines 7 an ink reservoir chamber 18 which holds liquid ink. In one implementation, the 8 ink bag 16 is constructed using multi-layer plastic sheets which are sealed about 9 their periphery to form the ink reservoir chamber 18. The ink bag 16 is preferably io sized and constructed for use with a replaceable ink-jet pen.

11 The ink bag 16 has opposing sides 20 and 22 which move relative to one 12 another depending upon an amount of ink held in the chamber 18. The ink bag 16 13 has at least one tubular outlet port 15 in fluid communication with the chamber 18 14 through which the liquid ink is transferred to the nozzles for ejection.

Is The ink level detection mechanism 14 has a pair of electrically conductive 16 coils 30 and 32 which are provided on opposing sides 20 and 22, respectively, of 17 the ink container 16. Conductors 34 and 36 interconnect the coils 30 and 32 to an 18 ink level sensing circuit 50, which is described below in more detail.

19 In the illustrated implementation, the coils 30, 32 and conductors 34, 36 are formed directly on the sides 20, 22 as thin film metallic traces. The traces can be 21 formed on the inside, outside, or within the multi-layer side walls forming the bag 2216. The thin film traces forming the coils 30 and 32 can be printed on the plastic 23 bag using photolithographic techniques, or mounted to the bag using adhesives.

24 The coils 30, 32 move relative to one another in conjunction with 25 movement of the sides 20, 22. As noted above, the bag sides 20, 22 move relative (0 to one another depending upon the amount of residual ink left in the ink bag 16.

2 When the ink bag 16 is full, the coils 30, 32 are spaced a maximum distance apart. 3As ink is withdrawn from the ink bag 12 during printing, the coils 30, 32 move 4 toward one another.

The ink level sensing circuit 50 generates a signal which induces an electro- 6 magnetic field between the pair of coils 30, 32 and senses an ink level within the

7ink container 16 by detecting change in the field as the coils 30, 32 are moved

8 relative to one another. The ink level sensing circuit 50 is connected to the coils 930, 32 via respective conductors 34, 36. The ink level sensing circuit 50 can be lo constructed as part of the replaceable ink cartridge, in which case it outputs an ink 11 depletion signal to the ink-jet printer. Alternately, the ink level sensing circuit 50 12 can be constructed separately from the replaceable ink cartridge as part of the 13 permanent control circuitry of the printer. In this latter case, the conductors 34, 36 14 are terminated by contacts which are positioned to connect to conductive receiving pads when the pen is installed in the printer to thereby electrically couple the coils 16 30, 32 to the remotely located ink level sensing circuit 50.

17 Fig. 3 shows a circuit representation of the ink level detection mechanism 18 10. The ink level sensing circuit includes a current generator 52, a sensor 54, and g an ink level monitor 56. The current generator 52 generates and applies a current to coil 30. The current signal can be applied in any type of alternating waveform, 21 with examples being a square wave or a sinusoidal wave. The current signal is 22 oriented through the coil 30 to induce an electro-magnetic field between the two

23 coils 30, 32. The field is directed along an axis running transverse to the sides of

24 the bag 16. The strength of the field varies according to the distance of the gap

6 7 between the two coils 30 and 32. The gap begins wide and then narrows as the ink 2 bag is depleted from a full ink supply to an empty ink supply.

3 The sensor 54 detects a voltage across the second coil 32 which is induced 4 by the field. The voltage is an indication of the field strength. The ink level s monitor 56 uses the sensed voltage from sensor 54 to derive a value indicative of 6 the residual ink level. When the value computed by the ink level monitor 56 7 reaches a point indicative of a low or near empty ink supply, the ink level sensing 8 circuit 50 outputs a control signal to the ink-jet printer control unit indicating that 9 the ink level is low. The ink-jet printer can then inform the user to replace the pen o or refill the ink reservoir.

11 In the illustrated implementation, the current generator 52 generates the 12 current signal from a voltage source. This input voltage is sent to the ink level 13 monitor 56. The output voltage measured by sensor 54 is likewise sent to the ink 14 level monitor 56. The ink level monitor 56 computes a ration of the output voltage is to the input voltage to produce a value indicative of the residual ink level in the ink 16 chamber.

17 The inventors simulated the ink level detection mechanism using 3/4" coils, 18 each having ten turns. A sinusoidal current signal having a frequency of 1 Nfliz 19 and a root mean square amperage of approximately 100 mArms was generated using a sinusoidal voltage source that produced an input voltage of 1.2 VinrMs.

2, The current was applied to the first coil 30. A voltage sensor was coupled to the 22 second coil 32 to measure an output voltage Voutrms. The inventors dynamically 23 changed the gap distance between the coils and measured the distance at various 24 points representative of ink depletion within the ink bag. A ratio of the output 7 8 voltage Voutrms to the input voltage Virirms was computed at each of the points.

2 Table 1 gives the results.

3 4 Table 1

Gap (mm) Strengib Ratio 6 11.5 0.15 7 9.2 0.21 8 6.9 0.28 9 4.6 0.38 2.3 0.59 11 0 1.00 12 13 As shown in the results of table 1, the signal strength increased as the gap 14 narrowed. This is beneficial because the inductive ink detection mechanism is becomes increasingly more accurate at detecting changes in the volume of residual 16 ink as the ink supply is depleted. This accuracy enables the printer to more 17 accurately sense when the ink level is low and timely inform a user that the ink is cartridge or pen needs to be replaced.

19 In the above implementation, one coil is driven with a current or voltage source and the induced voltage on the other coil is measured. In another 21 implementation, the coils 30 and 32 are connected in series. The same signal is 22 passed through the serial connected coils 30, 32 to induce an electro-magnetic field 23 between them. If the coils are wound in the same direction, the field strength 24 increases as the ink is depleted from the ink bag. Conversely, if the coils are 25 counter-wound, the field strength decreases as the ink is depleted from the bag.

8 11 In compliance with the statute, the invention has been described in language 2 more or less specific as to structure and method features. It is to be understood, 3 however, that the invention is not limited to the specific features described, since 4 the means herein disclosed comprise exemplary forms of putting the invention into s effect. The invention is, therefore, claimed in any of its forms or modifications 6 within the proper scope of the appended claims appropriately interpreted in 7 accordance with the doctrine of equivalents and other applicable judicial doctrines.

8 9 10 11 12 13 14 Is 16 17 18 19 21 22 23 24 25 9

Claims

c) CLAIMS

2 1. An ink level detection mechanism (14), comprising: 3 a flexible ink container (16); and 4 a pair of electrically conductive coils (30, 32) provided on opposing sides s (20, 22) of the ink container (16), the coils (30, 32) moving relative to one another 6 depending upon an amount of ink held in the ink container (16). 7 8
2. An ink level detection mechanism as recited in claim 1, wherein the 9 ink container (16) comprises a flexible bag.
3. An ink level detection mechanism as recited in claim 1, wherein the 12 conductive coils (30, 32) are formed on the ink container (16).

13 14
4. An ink level detection mechanism as recited in claim 1, wherein the is conductive coils (30, 32) are connected in series.

16 17
5. An ink level detector, comprising:

is a pair of electrically conductive coils (30, 32) which are arranged on g opposing sides of an ink reservoir and move relative to one another in conjunction with an ink level of the ink reservoir; and 21 an ink level sensing circuit (50) connected to the coils to induce a field 22 between the pair of coils (30, 32) and to sense an ink level of the ink reservoir by 23 detecting change in the field as the coils move relative to one another.

24
6. An ink level detector as recited in claim 5, wherein the signal is 2 applied to a first coil (30), and a voltage is induced at a second coil (32) by the 3 field.

4
7. An ink level detector as recited in claim 5, wherein the coils (30, 32) 6 are connected in series.

7 8
8. An ink level detector as recited in claim 5, wherein the field has a 9 strength which increases as the coils (30, 32) are moved closer together.

11
9. An ink supply cartridge comprising an ink level detector as recited in 12 any one of the claims 1-8.

13 14
10. An ink-jet pen comprising an ink level detection mechanism as recited in any one of the claims 1-8.

16 17 18 19 20 21 22 23 24 25