Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-04-26
2002-09-17
Hallacher, Craig A. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S019000, C347S089000
Reexamination Certificate
active
06450601
ABSTRACT:
TECHNICAL FIELD
This invention relates to an ink jet printer and a method of managing the ink quality of such printer.
BACKGROUND OF THE INVENTION
In an ink jet printer using the deflected continuous jet principle, the ink not used for printing is recycled. However, the recovered ink does not have the same properties as the ink emitted during the jet, mainly because of solvent evaporation.
Two documents, referenced as [1] and [2] at the end of the specification, describe methods of controlling ink quality drift. Indeed, solvent evaporation must be compensated by adding exactly the amount of evaporated solvent to keep ink quality constant. In order to ensure feedback control of this solvent addition without fluctuation (hunting), evaporation speed has to be taken into account.
In prior art, various types of feedback control (proportional, proportional-integral, proportional-integral-derivative, . . . ) can devise a solvent addition decision by affecting a weight distribution relating to:
the present situation, or instantaneous difference between the desired value and the present operating pressure (proportional term);
the past situation, e.g. by taking into account the differences recorded for recent operating hours (integral term);
the future situation, or rather the trend of the present situation (derivative term).
These various types of feedback control are well adapted for managing ink quality. In particular, a wise choice of the relative weights of the various terms allows to improve speed and stability while avoiding oscillation (or “hunting”). The control principle of such feedback controls is well known to those skilled in the art.
The document referenced as [1] takes into account the measurement of the time the ink jet takes for draining a calibrated volume. A temperature sensor allows to take into account the natural influence of temperature on ink quality. Indeed, temperature has an effect on the ink's viscosity and density. The implemented feedback control uses the draining curve as a function of temperature. A reference point is set when the machine is started to account for dispersions among the various applications envisaged. However, such a method is only a rough one. Indeed, the theoretical analysis performed in this document [1] presumes independence of the ink's viscosity and density parameters, which is not correct: in fact, 80% of a printer's operating pressure is associated with ink density, so that even a small variation of this density may not be neglected with regard to the evolution of the pressure term due to viscosity. In addition, to keep ink quality constant, this document [1] considers a constant operating pressure. However, such constant pressure does not ensure constant jet speed over a wide operating range. Therefore, this method is restricted to a limited range of temperature evolution at the calibration point. In practice, a float is placed inside the pressurized reservoir feeding the jet (accumulator). Drainage time measurement is subject to the vagaries of the float (jamming, sticking, oscillation, . . . ). The accuracy and the repeatability of this kind of measurement are not good. Moreover, the measurement rate is very low (about ten per hour), so much so that a feedback control built with this type of detector is neither accurate nor fast.
In the document referenced as [2], the utilized machine comes with a specific device (ball viscometer) allowing to find out the ink viscosity of the machine. A viscosity/temperature curve translates the desired operating value. However, ink density evolution is by no means accounted for. This method is independent of the ink jet and does not call upon operating pressure. This machine operates at constant pressure and does not ensure constant writing quality for a wide temperature range. Moreover, such an implementation is costly because it uses a solenoid valve, a calibrated tube, a calibrated ball, detectors, tubing, etc.
Another method is described in the document referenced as [3]. It is based on the evolution of the operating pressure as a function of ink temperature by imposing a constant jet speed. This method not only ensures ink quality feedback control, but also maintains ink quality regardless of temperature, due to constant jet speed. It also performs jet speed measurement. The characteristic curve, which is the desired ink quality value, takes into account both ink viscosity and density. However, the implementation of this method requires that the difference in level between the head and the machine be known. Any error in this respect, not checked by the machine, results in a difference in ink quality and a deterioration of printing quality. In addition, this method requires operator action, and setting the reference pressure is done by varying the operating temperature of reference machines.
It is the object of the invention to compensate for the various disadvantages of the known art documents by providing a method of managing the ink quality of an ink jet printer, which by itself devises the desired operating value without any operator action.
SUMMARY OF THE INVENTION
This invention describes a method of managing the ink quality in an ink jet printer, wherein information relating to ink pressure P, temperature T, and jet speed V, and a desired pressure value curve P
consigne
as a function of temperature T and speed V is available, of the type:
P
consigne
=a×&rgr;
n
(
T
)×
V
2
+b×&mgr;
n
(
T
)×
V+&rgr;
n
(
T
)×g×H
H being the difference in level between the print head and the pressure transducer, &rgr;
n
(T) and &mgr;
n
(T) characteristic curves of the nominal ink, a and b being characteristic values of the ink circuit and g gravity acceleration, characterized in that, when the machine is started, jet speed is varied at its nominal value and the resulting pressure P(T)=a×&rgr;(T)×V
2
+b×&mgr;(T)×V+&rgr;(T)×g×H is measured so as to determine the coefficients a, b, &rgr;(T), &mgr;(T), and H, and corrective action is taken for the ink quality to make &rgr;, &mgr;, and P close to &rgr;
n
, &mgr;
n
, and P
consigne
to the temperature T.
In a first operating mode, five independent values of the pair (P
fonct
, V) are used to determine the five characteristics a, b, &Dgr;P, &rgr;, and &mgr;, with P
fonct
a&rgr;V
2
+b&mgr;V+&Dgr;P, &Dgr;P representing the difference in level term taken to be constant.
In a second operating mode, using the jet speeds V
1
and V
2
, the straight line (P
fonct
(V
1
)−P
fonct
(V
2
))/(V
1
−V
2
) as a function of V
1
+V
2
is plotted using a linear regression, the coefficients (a×&rgr;) and (b×&mgr;) are obtained, then the average is calculated for the &Dgr;P's associated with the set of measurements:
&Dgr;P
stat
=1/
n×&Sgr;
1
n
(
P
fonct
(
Vi
)−
a×&rgr;×Vi
2
−b×&mgr;×Vi
).
Advantageously, the coefficients a and b are known beforehand with sufficient accuracy for a given machine configuration from measurements performed on a sample machine and are stored in the memory of each machine produced.
Advantageously, the information regarding the ink is stored in fixed memory, e.g. as the following relations, for operation at constant concentration:
&rgr;
n
(
T
)=&rgr;
n
(
T
0
)*(1+&agr;×(
T−T
0
))
&mgr;
n
(
T
)/&mgr;
n
(T
0
)=1/(1+&bgr;×(
T−T
0
))
with:
T: operating temperature
T
0
: any temperature within the operating range
&agr;: coefficient reflecting fluid dilatancy
&bgr;: coefficient reflecting fluid viscosity variation.
Advantageously, the values regarding &rgr;
n
(T) and &mgr;
n
(T) are tabulated as obtained from laboratory tests.
In a first alternative of a third operating mode, the ink circuit characteristics a and b are known, the parameters P
fonct
, V, and T are measured, and &Dgr;Pi=P
fonct
(i)−a×&rgr;(Td)×
Farlotti Laurent
Pagnon Alain
Hallacher Craig A.
Imaje S.A.
Pearne & Gordon LLP
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