CA2189284A1 - Ink jet short detection circuit - Google Patents
Ink jet short detection circuitInfo
- Publication number
- CA2189284A1 CA2189284A1 CA 2189284 CA2189284A CA2189284A1 CA 2189284 A1 CA2189284 A1 CA 2189284A1 CA 2189284 CA2189284 CA 2189284 CA 2189284 A CA2189284 A CA 2189284A CA 2189284 A1 CA2189284 A1 CA 2189284A1
- Authority
- CA
- Canada
- Prior art keywords
- circuit
- detection
- ink
- electrodes
- charge
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
- B41J2/01—Ink jet
- B41J2/07—Ink jet characterised by jet control
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
- B41J2/01—Ink jet
- B41J2/07—Ink jet characterised by jet control
- B41J2/125—Sensors, e.g. deflection sensors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
- B41J2/01—Ink jet
- B41J2/17—Ink jet characterised by ink handling
- B41J2/18—Ink recirculation systems
- B41J2/185—Ink-collectors; Ink-catchers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
- B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
- B41J2/01—Ink jet
- B41J2/17—Ink jet characterised by ink handling
- B41J2/18—Ink recirculation systems
- B41J2/185—Ink-collectors; Ink-catchers
- B41J2002/1853—Ink-collectors; Ink-catchers ink collectors for continuous Inkjet printers, e.g. gutters, mist suction means
Abstract
A detection technique comprises a plurality of closely spaced, continuous detection electrodes placed immediately below and along the length of a charge plate in an ink jet printing system. The detection electrodes typically comprise parallel conductors. A circuit is provided for monitoring the conductivity between the electrodes.
The electrodes are electrically isolated from one another when properly placed on the catcher surface.
If the conductivity, as measured by the circuit, rises above a predetermined threshold level it is an indication that some amount of unwanted ink is present at the location of the conductors. This signals improper print head operation requiring a print head shut-down and/or clean cycle.
The electrodes are electrically isolated from one another when properly placed on the catcher surface.
If the conductivity, as measured by the circuit, rises above a predetermined threshold level it is an indication that some amount of unwanted ink is present at the location of the conductors. This signals improper print head operation requiring a print head shut-down and/or clean cycle.
Description
218928~
INK JET SHORT DETECTION CIRCUIT
Technical Field s The present invention relates to planar charging and deflection print heads that require a means of detecting unwanted ink on a charge plate during 6tart-up and printing and, more particularly, to improved detection of misplaced ink in the charge plate region of such printing system6.
Backqround Art In continuou8 ink jet printing, ink is supplied under pressure to a manifold region that distribute6 the ink to a plurality of orifices, typically arranged in a linear array(s). The ink discharges from the orifices in filaments which break into droplet stream~. The approach for printing with these droplet ~treams is to selectively charge and deflect certain drops from their normal trajectories.
In the field of ink jet printer~, it is desirable to be able to detect unwanted ink on the charge plate during start-up and printing. The unwanted ink may be a mist build-up on or near the charge leads, but i~ usually an accumulation of ink on or near the charge leads caused by a crooked jet or improper start-up. The unwanted in~ on the charge plate causes an electrical short between the charge leads and ground, causing print defects and physical damage to the charge plate due to unwanted current flow.
Existing charge lead short detect schemes rely on a mea6urement of the current drawn from the charge plate voltage supply by conductive ink 218~8~
bridging a charge lead to some nearby ground. Thi~
requires the current measurement to take place during the nonprint state when the charge lead voltages are all nonzero. There are several problems with the present short detect scheme.
One problem with the pre6ent short detect scheme is that timing the current measurements with non-print times can be tedious to perform on long arrays, eepecially with possible segmented phasing.
Another problem i8 that if the amount of ink bridging the charge leads to ground i8 small enough, then the current drawn from the charge lead power supply can be below the threshold needed to signal an improper condition due to high ink path resistance. Therefore, the threshold current for detecting a ~short n mu~t be made as 6mall as possible. This i8 limited greatly by the externally induced noise created by the charge driver ~witching slew rates. This allows Rmall, high resistance ink paths to exist without ~eing detected for some amount of time, causing ink build-up and charge lead deplating to take place until a more catastrophic failure occurs. Additionally, if a jet is in the beginning phases of cra6hing where ink is only being placed at the lower portion of the charge plate region, without actually electrically contacting the charge lead, it i6 not detected and the print head i9 allowed to function even though a print problem may exist, or until a much more damaging condition is created from ink accumulating in the charge plate area.
It is seen then that there i6 a need for an improved means of detecting unwanted ink on the charge plate during start-up and printing.
21892~
Summarv of the Inv~ntion This need is met by the short detect technique according to the present invention, wherein misplaced ink in the charge plate region is detected, without regard to print pulse timing or charge lead short circuit to ground.
In accordance with one aspect of the present invention, a detection means comprises a set of closely spaced, continuous parallel conductors placed immediately below and along the length of the charge plate, as short detection electrodes.
Additionally, a circuit i~ provided for monitoring the conductivity between the electrodes. The electrodes are electrically isolated from one another when properly placed on the catcher surface.
If the co~ ctivity, as measured by the circuit, rises above a predetermined threshold level it is very likely that some amount of ink is present at the location of the conductors. This i~ an indication of i~ o~er print head operation and should signal a print head 6hut-down and/or clean cycle.
Accordingly, it i8 an advantage of the present invention that it continuously monitors for ink accumulation in the charge plate area. It is a further advantage of the present invention that the electrically isolated monitoring circuit does not depend on current being drawn by the charge lead potential for detection. The circuit can also be made very ~ensitive to the pre~ence of ink without being greatly affected by the electrical noiRe produced during printing. It i9 an object o~ the present invention that a jet impacting on the charge plate below the charge leads i8 as readily detected as a jet impacting on the charge leads.
21~9284 Other objects and advantages of the invention will be apparent from the following description, the accompanying drawing and the appended claims.
Brief Descri~tion of the Drawinq Fig. 1 illustrates a short detection circuit, according to the present invention;
Fig. 2 is a side view of a continuous ink jet system of the type suitable for use with the short detection circuit of Fig. 1;
Fig. 3 illustrates the location of short detection electrodes as~ociated with the short detection circuit of Fig. 1;
Fig. 4 illustrates a flex circuit for - fabricating the short detection electrodes of Fig.
3;
Fig. S illustrates an alternative fabrication method for the short detection electrodes of Fig. 3;
Figs. 6, 7, and 8A and 8B illustrate various alternati~e embodiments of the short detection circuit of Fig. 1, in accordance with the present invention; and Fig. 9 illustrates voltage produced across a sensing resistor during a print head start-up si~ulation.
Detailed DescriDtion of the Preferred ~hoA;mPnts This preeent invention allows for detection of misplaced ink in the charge plate region, without regard to print pulse timing or charge lead contact with the ink. Detection electrode~ 10, as illustrated in Fig. 1, detect the presence of ink on or close to charge leads 16. If 218928~
ink i9 present on or very close to the lead~, there i9 a problem with the printhead which needs to be corrected. The detection electrode6 10 are 6ituated inside box 12. Out~ide box 12 is illustrated a S detection circuit 14 used for monitoring conductivity between charge leads 16. Voltage source Vs and a6sociated internal impedance Zi provide an oscillating potential between leads 10.
The conductivity between the leads i8 monitored by IO measuring the voltage drop across resistor Rs with voltmeter circuit Vac. When the conductivity decreases between the detection leads due to the presence of a conductive fluid, ~uch as ink, an increase in the current through Rs is pro~lc~, yielding an increase in the voltage mea6ured by Vac.
The pre~ent invention relates to the type of continuous ink jet system illustrated in Fig. 2.
A plurality of jet~ i8 created at high 6patial resolution by a drop generator, which ~timulates the natural break-up of jets into uniform streams of droplets. A plurality o~ conducting elements, or charge leads 16, are located on a planar charge plate 18. A plurality of streams of drops 20 are supplied by drop generator 22. A plurality of independently switchable sources 24 of electrostatic potential are supplied to the plurality of charge leads 16. A catcher 26 intercepts the slightly deflected stream~ of drops. The plurality of streams of drops impacting on the catcher forms a film of ink 30, which in turn form~ a flow of ink 28, sucked away from the face of the catcher by a vacuum. Reference number 32 represents the area on the catcher at which the deflected drops impact the catcher and merge together to form a film of ink on the catcher face. The undeflected ink drops then 218~Z8~
print the image on 6ubstrate 34.
The present invention comprise~ a set of closely spaced, continuous parallel conductors placed immediately below and along the length of the charge plate 18, to operate as 6hort detection electrodes 10. Fig. 3 shows the location of short detection electrodes 10, situated just below and along the entire length of charge plate 18. The electrodes can be any suitable electrodes, such a6 2 mil diameter copper wires. The electrodes may be secured by any suita~le means, such as epoxy, at each end of the array.
The electrodes can be fabricated a6 a flex circuit 36 that is attached as a 6eparate co~ronent to the catcher/charge plate as~embly with an appropriate attachment means 38, such as epoxy, as in Fig. 4. The flex circuit 36 of Fig. 4 comprises detection electrodes 10 as two flat conductive ele~ents fixed on a thin dielectric substrate, with connections for the external sensing circuit.
Fig. 5 shows an alternative fabrication method comprising a dielectric 40 sandwiched ~etween electrodes 10, which comprise two thin conductive plates. The edges of the plates form the sensing electrodes. This structure is inserted between the catcher 26 and the charge plate 18 during charge plate bonding, with connection electrodes provided at any point convenient ~or the sub~equent electronics to access. The flex circuit sandwiched dielectric-type configurations allow a relatively small potential difference to be used between the sensing electrodes by the sensing circuit, producing a greatly reduced electrochemical reaction between the ink and the electrodes (when ink is present) as compared with that obtained by currently used short detect circuits.
Another emho~i mPnt of the detection circuit 14, illustrated in Fig. 6, has the electrodes 10 connected to either terminal of one set of w; n~i n~s of a transformer 42. This e~bodiment is novel in that the conductivity sensing circuit eliminates a direct electrical connection of the detection leads lo to conductivity measuring circuitry. When operating properly, the winding of transformer 42 would be an open circuit. When ink bridges the detector electrodes 10, this circuit would be co~pleted, which could be sensed by an impedance measuring circuit 44 connected to the second 6et of winding~. A6 will be obvious to those skilled in the art, any suitable impedance measuring mean~, such a~ an impedance bridge circuit comprised of inductors, capacitors, and resistors, could be used, as well as various known sophisticated integrated circuit versions of the impedance bridge.
Fig. 7 shows another embodiment of circuit 14 wherein the detection relies on a battery-like response caused by ink 46 bridging dissi~ilar metals, referenced a~ detection leads 10' and lOn. When ink join9 the detection electrodes lO' and 10l', a voltage is produced which can be detected. Hence, in Fig. 7, the detector electrodes 10' and lo~ are dissimilar metals which, when bridged by an alkali or acidic ink 46, would produce an emf in a battery-type chemical reaction. This emf is then detected by a voltage sensing circuit 48. A~ will be obvious to those skilled in the art, any suitable voltage sensing mean6 could be used, such as a st~n~rd operational amplifier circuit configured with resistors and capacitors as a high 218928~
input impedance voltage measuring device.
Alternatively, the emf sensing device could be a single integrated circuit chosen for the specific purpose of measuring small voltages. The advantage of the circuit embo~im~nt illustrated in Fig. 7 is that it doe6 not require a test voltage to be placed on the detector electrodes, allowing a completely passive input circuit de~ign.
Yet another embodiment of the short detect circuit 14, according to the present invention, i8 illustrated in Fig~. BA and 8B. The circuit 14 o~ Figs. 8A and 8B utilizes a single electrode 10 in place of the pair of electrodes illustrated in Fig~. 1, 6 and 7. This ~ingle electrode 10 iB placed, by means of a voltage divider or equivalent circuit, at a potential between ground (catcher face potential) and the charge plate lead 16 potential. By noting the polarity of the current generated in the circuit connected to the lead, it can be ascertained whether the ~isplaced ink i6 bridging the electrode and charge plate or electrode and catcher. This i9 in addition to the somewhat simplified implementation obtained from using only a single lead.
Fig. 9 show~ the voltage produced (Vac) across sensing re6istor Rs of Fig. 1 during a print head start-up simulation on a print head test stand.
The sequence of events recorded in Fig. 9 are as follows. Initially, there was cross flu6h of the print head where ink i8 flowing from the orifice plate, over the charge plate and down the face of the catcher.- In this 6tate, ink iB also flowing over the ~hort detect electrodes, resulting in a relatively high con~l~ctivity between the wires.
This produces a relatively high voltage across Rs, ~l8g28~ ' as indicated by the signal in region A of Fig. 9.
Region B of Fig. 9 shows the signal voltage across Rs produced when the print head has been taken out of the cro~s flush state and into the jetting and charge plate drying state. Here, jets have been started ~y closing the outlet valve and the catcher heater has been turned on. At about t=2 minutes, a very sharp decrea~e in Vac occurs, indicating the conductivity between the sen~ing electrodes has decreased dramatically. This is due to the ink in the area of the sensing electrodes running of f /drying, producing the low conductivity state.
~t approximately t=3.3 minute6, the print head alignment was disturbed in a way to produce one to two jets just beg;nn;n~ to impact on the lower portion of the charge plate. This, in turn, caused a small amount ink to run down the ~urface of the charge plate/catcher and over the sensing electrodes. The presence of ink ;~e~;ately raises the conductivity between the electrodes, as is indicated in part C of Fig. 9. This abrupt increase in Vac indicates an improper condition on or near the charge plate and can be used to signal that a shut down condition exists.
After the "short" is detected, the print head alignment is changed to eliminate the crashing jet condition. At about t=3.8 minutes, vac decreased to near zero. This obtain~ from the runoff/drying of the ink which accumulated during C.
Therefore, the circuit recovers when an abnormal condition is Le,.,uved.
The present invention comprises detection lead or leads positioned i~me~;~tely below the charge plate on which a portion of any unwanted ink ~18928 1 will likely be deposited; and an electrical circuit which monitors the conductivity of the area between the detection electrodes. The circuit monitors the conAllctivity between the electrodes 10. The electrodes are electrically i601ated from one another when properly placed on the catcher surface.
If the conductivity, as measured by the circuit, rises above a predetermined threshold level, it is very likely that some amount of ink is present at the location of the conductors. This is an indication of improper print head operation and should signal a print head shut-down and/or clean cycle.
In a preferred ~hoA;~nt of the present invention, the circuit for monitoring the conductivity between the electrodes i8 isolated (floating) from the charge driver potential so that in the case of a large mass of ink bridging the charge leads and short detect electrodes, no large currents are produced in either the charge lead(s) or the sensing electrodes.
The sen~ing circuit of the pre6ent invention can be, but i8 not re6tricted to, an ac signal with a frequency and amplitude chosen to provide ~Y;~llm short detect sensitivity with high noise rejection. For example, a circuit functioning in a manner similar to a lock-in amplifier would reject all signals at frequencie6 other than that used for monitoring the conductivity between the sensing electrodes. Various embodiments of the circuit are illustrated in Figs. 1, 6, 7, 8A and 8s.
However, it will be obvious to those skilled in the art that various other circuit configurations may be used without departing from the scope of the invention. The specific circuit selected for any given application typically depends on the electrical co~ ctivity of the fluid.
Industrial A~licability and Advantaaes The present invention i8 useful in the field of ink jet printing, and has the advantage of continuously monitoring for ink accumulation in the charge plate area. The present invention has the further advantage of providing an electrically isolated monitoring circuit which i6 not dependent on current being drawn by the charge lead potential for detection. It i8 a further advantage that the circuit can be made very sensitive to the pre~ence of ink, without being greatly affected by the electrical noise produced during printing. Finally, it is an advantage of the present invention that a ~et impacting on the charge plate below the charge leads is detected as readily as a jet impacting on the charge leads.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that modifications and variations can be effected within the spirit and scope of the invention.
INK JET SHORT DETECTION CIRCUIT
Technical Field s The present invention relates to planar charging and deflection print heads that require a means of detecting unwanted ink on a charge plate during 6tart-up and printing and, more particularly, to improved detection of misplaced ink in the charge plate region of such printing system6.
Backqround Art In continuou8 ink jet printing, ink is supplied under pressure to a manifold region that distribute6 the ink to a plurality of orifices, typically arranged in a linear array(s). The ink discharges from the orifices in filaments which break into droplet stream~. The approach for printing with these droplet ~treams is to selectively charge and deflect certain drops from their normal trajectories.
In the field of ink jet printer~, it is desirable to be able to detect unwanted ink on the charge plate during start-up and printing. The unwanted ink may be a mist build-up on or near the charge leads, but i~ usually an accumulation of ink on or near the charge leads caused by a crooked jet or improper start-up. The unwanted in~ on the charge plate causes an electrical short between the charge leads and ground, causing print defects and physical damage to the charge plate due to unwanted current flow.
Existing charge lead short detect schemes rely on a mea6urement of the current drawn from the charge plate voltage supply by conductive ink 218~8~
bridging a charge lead to some nearby ground. Thi~
requires the current measurement to take place during the nonprint state when the charge lead voltages are all nonzero. There are several problems with the present short detect scheme.
One problem with the pre6ent short detect scheme is that timing the current measurements with non-print times can be tedious to perform on long arrays, eepecially with possible segmented phasing.
Another problem i8 that if the amount of ink bridging the charge leads to ground i8 small enough, then the current drawn from the charge lead power supply can be below the threshold needed to signal an improper condition due to high ink path resistance. Therefore, the threshold current for detecting a ~short n mu~t be made as 6mall as possible. This i8 limited greatly by the externally induced noise created by the charge driver ~witching slew rates. This allows Rmall, high resistance ink paths to exist without ~eing detected for some amount of time, causing ink build-up and charge lead deplating to take place until a more catastrophic failure occurs. Additionally, if a jet is in the beginning phases of cra6hing where ink is only being placed at the lower portion of the charge plate region, without actually electrically contacting the charge lead, it i6 not detected and the print head i9 allowed to function even though a print problem may exist, or until a much more damaging condition is created from ink accumulating in the charge plate area.
It is seen then that there i6 a need for an improved means of detecting unwanted ink on the charge plate during start-up and printing.
21892~
Summarv of the Inv~ntion This need is met by the short detect technique according to the present invention, wherein misplaced ink in the charge plate region is detected, without regard to print pulse timing or charge lead short circuit to ground.
In accordance with one aspect of the present invention, a detection means comprises a set of closely spaced, continuous parallel conductors placed immediately below and along the length of the charge plate, as short detection electrodes.
Additionally, a circuit i~ provided for monitoring the conductivity between the electrodes. The electrodes are electrically isolated from one another when properly placed on the catcher surface.
If the co~ ctivity, as measured by the circuit, rises above a predetermined threshold level it is very likely that some amount of ink is present at the location of the conductors. This i~ an indication of i~ o~er print head operation and should signal a print head 6hut-down and/or clean cycle.
Accordingly, it i8 an advantage of the present invention that it continuously monitors for ink accumulation in the charge plate area. It is a further advantage of the present invention that the electrically isolated monitoring circuit does not depend on current being drawn by the charge lead potential for detection. The circuit can also be made very ~ensitive to the pre~ence of ink without being greatly affected by the electrical noiRe produced during printing. It i9 an object o~ the present invention that a jet impacting on the charge plate below the charge leads i8 as readily detected as a jet impacting on the charge leads.
21~9284 Other objects and advantages of the invention will be apparent from the following description, the accompanying drawing and the appended claims.
Brief Descri~tion of the Drawinq Fig. 1 illustrates a short detection circuit, according to the present invention;
Fig. 2 is a side view of a continuous ink jet system of the type suitable for use with the short detection circuit of Fig. 1;
Fig. 3 illustrates the location of short detection electrodes as~ociated with the short detection circuit of Fig. 1;
Fig. 4 illustrates a flex circuit for - fabricating the short detection electrodes of Fig.
3;
Fig. S illustrates an alternative fabrication method for the short detection electrodes of Fig. 3;
Figs. 6, 7, and 8A and 8B illustrate various alternati~e embodiments of the short detection circuit of Fig. 1, in accordance with the present invention; and Fig. 9 illustrates voltage produced across a sensing resistor during a print head start-up si~ulation.
Detailed DescriDtion of the Preferred ~hoA;mPnts This preeent invention allows for detection of misplaced ink in the charge plate region, without regard to print pulse timing or charge lead contact with the ink. Detection electrode~ 10, as illustrated in Fig. 1, detect the presence of ink on or close to charge leads 16. If 218928~
ink i9 present on or very close to the lead~, there i9 a problem with the printhead which needs to be corrected. The detection electrode6 10 are 6ituated inside box 12. Out~ide box 12 is illustrated a S detection circuit 14 used for monitoring conductivity between charge leads 16. Voltage source Vs and a6sociated internal impedance Zi provide an oscillating potential between leads 10.
The conductivity between the leads i8 monitored by IO measuring the voltage drop across resistor Rs with voltmeter circuit Vac. When the conductivity decreases between the detection leads due to the presence of a conductive fluid, ~uch as ink, an increase in the current through Rs is pro~lc~, yielding an increase in the voltage mea6ured by Vac.
The pre~ent invention relates to the type of continuous ink jet system illustrated in Fig. 2.
A plurality of jet~ i8 created at high 6patial resolution by a drop generator, which ~timulates the natural break-up of jets into uniform streams of droplets. A plurality o~ conducting elements, or charge leads 16, are located on a planar charge plate 18. A plurality of streams of drops 20 are supplied by drop generator 22. A plurality of independently switchable sources 24 of electrostatic potential are supplied to the plurality of charge leads 16. A catcher 26 intercepts the slightly deflected stream~ of drops. The plurality of streams of drops impacting on the catcher forms a film of ink 30, which in turn form~ a flow of ink 28, sucked away from the face of the catcher by a vacuum. Reference number 32 represents the area on the catcher at which the deflected drops impact the catcher and merge together to form a film of ink on the catcher face. The undeflected ink drops then 218~Z8~
print the image on 6ubstrate 34.
The present invention comprise~ a set of closely spaced, continuous parallel conductors placed immediately below and along the length of the charge plate 18, to operate as 6hort detection electrodes 10. Fig. 3 shows the location of short detection electrodes 10, situated just below and along the entire length of charge plate 18. The electrodes can be any suitable electrodes, such a6 2 mil diameter copper wires. The electrodes may be secured by any suita~le means, such as epoxy, at each end of the array.
The electrodes can be fabricated a6 a flex circuit 36 that is attached as a 6eparate co~ronent to the catcher/charge plate as~embly with an appropriate attachment means 38, such as epoxy, as in Fig. 4. The flex circuit 36 of Fig. 4 comprises detection electrodes 10 as two flat conductive ele~ents fixed on a thin dielectric substrate, with connections for the external sensing circuit.
Fig. 5 shows an alternative fabrication method comprising a dielectric 40 sandwiched ~etween electrodes 10, which comprise two thin conductive plates. The edges of the plates form the sensing electrodes. This structure is inserted between the catcher 26 and the charge plate 18 during charge plate bonding, with connection electrodes provided at any point convenient ~or the sub~equent electronics to access. The flex circuit sandwiched dielectric-type configurations allow a relatively small potential difference to be used between the sensing electrodes by the sensing circuit, producing a greatly reduced electrochemical reaction between the ink and the electrodes (when ink is present) as compared with that obtained by currently used short detect circuits.
Another emho~i mPnt of the detection circuit 14, illustrated in Fig. 6, has the electrodes 10 connected to either terminal of one set of w; n~i n~s of a transformer 42. This e~bodiment is novel in that the conductivity sensing circuit eliminates a direct electrical connection of the detection leads lo to conductivity measuring circuitry. When operating properly, the winding of transformer 42 would be an open circuit. When ink bridges the detector electrodes 10, this circuit would be co~pleted, which could be sensed by an impedance measuring circuit 44 connected to the second 6et of winding~. A6 will be obvious to those skilled in the art, any suitable impedance measuring mean~, such a~ an impedance bridge circuit comprised of inductors, capacitors, and resistors, could be used, as well as various known sophisticated integrated circuit versions of the impedance bridge.
Fig. 7 shows another embodiment of circuit 14 wherein the detection relies on a battery-like response caused by ink 46 bridging dissi~ilar metals, referenced a~ detection leads 10' and lOn. When ink join9 the detection electrodes lO' and 10l', a voltage is produced which can be detected. Hence, in Fig. 7, the detector electrodes 10' and lo~ are dissimilar metals which, when bridged by an alkali or acidic ink 46, would produce an emf in a battery-type chemical reaction. This emf is then detected by a voltage sensing circuit 48. A~ will be obvious to those skilled in the art, any suitable voltage sensing mean6 could be used, such as a st~n~rd operational amplifier circuit configured with resistors and capacitors as a high 218928~
input impedance voltage measuring device.
Alternatively, the emf sensing device could be a single integrated circuit chosen for the specific purpose of measuring small voltages. The advantage of the circuit embo~im~nt illustrated in Fig. 7 is that it doe6 not require a test voltage to be placed on the detector electrodes, allowing a completely passive input circuit de~ign.
Yet another embodiment of the short detect circuit 14, according to the present invention, i8 illustrated in Fig~. BA and 8B. The circuit 14 o~ Figs. 8A and 8B utilizes a single electrode 10 in place of the pair of electrodes illustrated in Fig~. 1, 6 and 7. This ~ingle electrode 10 iB placed, by means of a voltage divider or equivalent circuit, at a potential between ground (catcher face potential) and the charge plate lead 16 potential. By noting the polarity of the current generated in the circuit connected to the lead, it can be ascertained whether the ~isplaced ink i6 bridging the electrode and charge plate or electrode and catcher. This i9 in addition to the somewhat simplified implementation obtained from using only a single lead.
Fig. 9 show~ the voltage produced (Vac) across sensing re6istor Rs of Fig. 1 during a print head start-up simulation on a print head test stand.
The sequence of events recorded in Fig. 9 are as follows. Initially, there was cross flu6h of the print head where ink i8 flowing from the orifice plate, over the charge plate and down the face of the catcher.- In this 6tate, ink iB also flowing over the ~hort detect electrodes, resulting in a relatively high con~l~ctivity between the wires.
This produces a relatively high voltage across Rs, ~l8g28~ ' as indicated by the signal in region A of Fig. 9.
Region B of Fig. 9 shows the signal voltage across Rs produced when the print head has been taken out of the cro~s flush state and into the jetting and charge plate drying state. Here, jets have been started ~y closing the outlet valve and the catcher heater has been turned on. At about t=2 minutes, a very sharp decrea~e in Vac occurs, indicating the conductivity between the sen~ing electrodes has decreased dramatically. This is due to the ink in the area of the sensing electrodes running of f /drying, producing the low conductivity state.
~t approximately t=3.3 minute6, the print head alignment was disturbed in a way to produce one to two jets just beg;nn;n~ to impact on the lower portion of the charge plate. This, in turn, caused a small amount ink to run down the ~urface of the charge plate/catcher and over the sensing electrodes. The presence of ink ;~e~;ately raises the conductivity between the electrodes, as is indicated in part C of Fig. 9. This abrupt increase in Vac indicates an improper condition on or near the charge plate and can be used to signal that a shut down condition exists.
After the "short" is detected, the print head alignment is changed to eliminate the crashing jet condition. At about t=3.8 minutes, vac decreased to near zero. This obtain~ from the runoff/drying of the ink which accumulated during C.
Therefore, the circuit recovers when an abnormal condition is Le,.,uved.
The present invention comprises detection lead or leads positioned i~me~;~tely below the charge plate on which a portion of any unwanted ink ~18928 1 will likely be deposited; and an electrical circuit which monitors the conductivity of the area between the detection electrodes. The circuit monitors the conAllctivity between the electrodes 10. The electrodes are electrically i601ated from one another when properly placed on the catcher surface.
If the conductivity, as measured by the circuit, rises above a predetermined threshold level, it is very likely that some amount of ink is present at the location of the conductors. This is an indication of improper print head operation and should signal a print head shut-down and/or clean cycle.
In a preferred ~hoA;~nt of the present invention, the circuit for monitoring the conductivity between the electrodes i8 isolated (floating) from the charge driver potential so that in the case of a large mass of ink bridging the charge leads and short detect electrodes, no large currents are produced in either the charge lead(s) or the sensing electrodes.
The sen~ing circuit of the pre6ent invention can be, but i8 not re6tricted to, an ac signal with a frequency and amplitude chosen to provide ~Y;~llm short detect sensitivity with high noise rejection. For example, a circuit functioning in a manner similar to a lock-in amplifier would reject all signals at frequencie6 other than that used for monitoring the conductivity between the sensing electrodes. Various embodiments of the circuit are illustrated in Figs. 1, 6, 7, 8A and 8s.
However, it will be obvious to those skilled in the art that various other circuit configurations may be used without departing from the scope of the invention. The specific circuit selected for any given application typically depends on the electrical co~ ctivity of the fluid.
Industrial A~licability and Advantaaes The present invention i8 useful in the field of ink jet printing, and has the advantage of continuously monitoring for ink accumulation in the charge plate area. The present invention has the further advantage of providing an electrically isolated monitoring circuit which i6 not dependent on current being drawn by the charge lead potential for detection. It i8 a further advantage that the circuit can be made very sensitive to the pre~ence of ink, without being greatly affected by the electrical noise produced during printing. Finally, it is an advantage of the present invention that a ~et impacting on the charge plate below the charge leads is detected as readily as a jet impacting on the charge leads.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that modifications and variations can be effected within the spirit and scope of the invention.
Claims (11)
1. A detection means for detecting ink formed on a charge plate of a printhead in an ink jet printing system having a catcher, the charge plate having associated charge leads, the detection means comprising:
at least one detection electrode placed below and approximately along a length of the charge plate; and a circuit for monitoring electric loading of the at least one detection electrode.
at least one detection electrode placed below and approximately along a length of the charge plate; and a circuit for monitoring electric loading of the at least one detection electrode.
2. A detection means as claimed in claim 1 wherein the at least one detection electrode comprises at least one closely spaced continuous parallel conductor, closely spaced to the charge electrodes.
3. A detection means as claimed in claim 1 wherein the at least one detection electrode comprises at least one short detection electrode.
4. A detection means as claimed in claim 3 wherein the at least one short detection electrode is situated on a catcher surface.
5. A detection means as claimed in claim 1 wherein the at least one detection electrode comprises a first detection electrode and a second detection electrode.
6. A detection means as claimed in claim 5 wherein the circuit for monitoring conductivity comprises a circuit for monitoring conductivity between the first and second electrodes.
7. A detection means as claimed in claim 5 wherein the second detection electrode comprises a printhead component.
8. A detection means as claimed in claim 7 wherein the printhead component comprises a conductive catcher face of the catcher.
9. A detection means as claimed in claim 8 wherein the catcher is metal.
10. A detection means as claimed in claim 5 wherein the second detection electrode comprises an external charge plate heater.
11. A detection means as claimed in claim 10 wherein the external charge plate heater is located under the charge leads.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US55095895A | 1995-10-31 | 1995-10-31 | |
| US08/550,958 | 1995-10-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2189284A1 true CA2189284A1 (en) | 1997-05-01 |
Family
ID=24199263
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2189284 Abandoned CA2189284A1 (en) | 1995-10-31 | 1996-10-31 | Ink jet short detection circuit |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0771655B1 (en) |
| JP (1) | JP3946800B2 (en) |
| CA (1) | CA2189284A1 (en) |
| DE (1) | DE69623907T2 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6805435B2 (en) | 1998-10-16 | 2004-10-19 | Silverbrook Research Pty Ltd | Printhead assembly with an ink distribution arrangement |
| EP1013426B1 (en) * | 1998-12-14 | 2007-12-19 | Eastman Kodak Company | Short detection for ink jet printhead |
| EP1129854A1 (en) * | 2000-03-03 | 2001-09-05 | Domino Printing Sciences Plc | Flash-over detector |
| US7144103B2 (en) | 2004-05-05 | 2006-12-05 | Eastman Kodak Company | Beveled charge structure |
| US8777364B2 (en) | 2010-07-30 | 2014-07-15 | Hewlett-Packard Development Company, L.P. | Short circuit detection in an inkjet printhead |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4631550A (en) * | 1985-08-15 | 1986-12-23 | Eastman Kodak Company | Device and method for sensing the impact position of an ink jet on a surface of an ink catcher, in a continuous ink jet printer |
| JP2724998B2 (en) * | 1985-10-14 | 1998-03-09 | セイコーエプソン株式会社 | Ink drop detector |
| US4928113A (en) * | 1988-10-31 | 1990-05-22 | Eastman Kodak Company | Constructions and fabrication methods for drop charge/deflection in continuous ink jet printer |
| US4994821A (en) * | 1989-09-18 | 1991-02-19 | Eastman Kodak Company | Continuous ink jet printer apparatus having improved short detection construction |
| US5381099A (en) * | 1993-03-02 | 1995-01-10 | Unisys Corporation | Streak detection for ink-jet printer with obnically connected segment pairs |
| DE69609248T2 (en) * | 1995-05-26 | 2001-03-08 | Scitex Digital Printing Inc | Process for the production of charge electrodes |
-
1996
- 1996-10-30 DE DE1996623907 patent/DE69623907T2/en not_active Expired - Lifetime
- 1996-10-30 EP EP19960307865 patent/EP0771655B1/en not_active Expired - Lifetime
- 1996-10-31 JP JP28996296A patent/JP3946800B2/en not_active Expired - Fee Related
- 1996-10-31 CA CA 2189284 patent/CA2189284A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| EP0771655A3 (en) | 1998-09-16 |
| EP0771655A2 (en) | 1997-05-07 |
| EP0771655B1 (en) | 2002-09-25 |
| DE69623907D1 (en) | 2002-10-31 |
| DE69623907T2 (en) | 2003-08-07 |
| JP3946800B2 (en) | 2007-07-18 |
| JPH09201974A (en) | 1997-08-05 |
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Legal Events
| Date | Code | Title | Description |
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| FZDE | Dead |
Effective date: 20031031 |