Method of and device for detecting amount of ink in ink fountain

Information

  • Patent Grant
  • 6772690
  • Patent Number
    6,772,690
  • Date Filed
    Monday, July 1, 2002
    21 years ago
  • Date Issued
    Tuesday, August 10, 2004
    19 years ago
  • CPC
  • US Classifications
    Field of Search
    • US
    • 073 304 R
    • 073 304 C
    • 073 290 R
    • 101 116
    • 101 119
    • 101 120
    • 101 3491
    • 101 363
    • 101 364
    • 101 484
    • 101 491
    • 137 386
    • 347 7
    • 118 694
  • International Classifications
    • B41F3102
    • B41F3300
    • G05D900
Abstract
The amount of ink in an ink fountain in a printer is detected on the basis of change of oscillation. The oscillation frequency is changed on the basis of dielectric constant information on the dielectric constant of the ink.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




This invention relates to a method of and a device for detecting the amount of ink in the ink fountain in a printer such as a stencil printer, and more particularly to such a method and a device in which the amount of ink is detected on the basis of the oscillation frequency.




2. Description of the Related Art




There has been known a printer such as a stencil printer in which ink is supplied to an ink fountain in a printing drum by an ink pump from an exchangeable ink container. In such a printer, the amount of ink in the ink fountain is detected by an ink sensor and when the ink in the ink fountain is consumed to a predetermined amount, the ink pump is operated to replenish the ink fountain with the ink from the ink container in order to keep constant the amount of ink in the ink fountain. (See, for instance, Japanese Unexamined Patent Publication No. 60(1985)-193687)




As a method of detecting the amount of ink, there has been proposed a method in which the tip of a needle antenna connected to an oscillator is dipped in the ink and the amount of the ink is detected on the basis of the oscillation frequency of the oscillator which varies with the depth to which the antenna is dipped in the ink. (See, for instance, Japanese Unexamined Patent Publication No. 58(1983)-62520) With this method, since as the depth to which the antenna is dipped in the ink increases, the electrostatic capacity around the antenna increases and the oscillation frequency of the oscillator lowers, the amount of ink in the ink fountain can be kept constant by replenishing the ink fountain with the ink so that the oscillation frequency detected becomes constant.




However, the oscillation frequency also depends upon the dielectric constant of the ink, and when the ink is small in dielectric constant, change of the oscillation frequency is small, which makes it difficult to detect change of the oscillation frequency with change of the amount of ink in the ink fountain. To the contrast, when the ink is large in dielectric constant, unnecessary radiation increases and the accuracy in detecting the change of the oscillation frequency is deteriorated. When detection of change of the oscillation frequency with change of the amount of ink in the ink fountain is difficult or the accuracy in detecting the change of the oscillation frequency is deteriorated, it becomes impossible to keep constant the amount of ink in the ink fountain and as a result, quality of the printed image deteriorates.




SUMMARY OF THE INVENTION




In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and a device for detecting the amount of ink which can properly detect change of the oscillation frequency irrespective of the dielectric constant of the ink.




In accordance with a first aspect of the present invention, there is provided a method of detecting the amount of ink in an ink fountain in a printer on the basis of change of oscillation frequency wherein the improvement comprises




the step of changing the oscillation frequency on the basis of dielectric constant information on the dielectric constant of the ink.




The dielectric constant information may represent the dielectric constant of the ink itself, or may represent other factors such as the viscosity of the ink, the color of the ink, the time for which the ink is left to stand and the date of production of the ink on the basis of which the dielectric constant of the ink can be calculated.




The dielectric constant information may be obtained by measuring the dielectric constant of the ink or may be obtained from an information storage means attached to the ink bottle for supplying ink to the ink fountain.




As the information storage means, for instance, a nonvolatile memory (e.g., an EEPROM) which can hold data for a predetermined time interval without supplying power. This applicant has proposed a system for variously controlling a printer on the basis of information stored in such an information storage means attached to consumables like an ink bottle. See Japanese Unexamined Patent Publication No. 2001-18507.




Further the dielectric constant information may be input through an input means.




In accordance with a second aspect of the present invention, there is provided a device for detecting the amount of ink in an ink fountain in a printer on the basis of change of oscillation frequency wherein the improvement comprises




a frequency changing means which changes the oscillation frequency on the basis of dielectric constant information on the dielectric constant of the ink.




The frequency changing means may be arranged to obtain the dielectric constant information by measuring the dielectric constant of the ink and to change the oscillation frequency on the basis of the dielectric constant information thus obtained.




Further, the frequency changing means may be arranged to change the oscillation frequency on the basis of dielectric constant information provided from an information storage means attached to the ink bottle for supplying ink to the ink fountain.




The device may further comprises an input means so that the frequency changing means changes the oscillation frequency on the basis of the dielectric constant information input through the input means.




In accordance with the present invention, since the oscillation frequency is changed on the basis of the dielectric constant information, the change of the oscillation frequency can be easily detected by increasing the oscillation frequency when the ink is small in dielectric constant and, unnecessary radiation can be suppressed and the accuracy in detecting the change of the oscillation frequency can be improved by decreasing the oscillation frequency when the ink is large in dielectric constant, whereby change of the oscillation frequency can be accurately detected and the amount of ink in the ink fountain can be accurately detected irrespective of the dielectric constant of the ink, which makes it feasible to keep constant the amount of ink in the ink fountain and to obtain high quality images.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic view showing an important part of a stencil printer employing an ink amount detecting device for detecting the amount of ink in accordance with a first embodiment of the present invention,





FIG. 2

is a block diagram showing the structure of the ink amount detecting device of the first embodiment,





FIG. 3

is a circuit diagram showing a specific circuit of the ink amount detecting device of the first embodiment,





FIG. 4

is a flow chart for illustrating operation of the ink amount detecting device of the first embodiment,





FIG. 5

is a block diagram showing the structure of an ink amount detecting device in accordance with a second embodiment of the present invention, and





FIG. 6

is a flow chart for illustrating operation of the ink amount detecting device of the second embodiment.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




In

FIG. 1

, a stencil printer comprises a printing drum


1


around which a master


2


is wound. An ink coater roller


3


is disposed inside the printing drum


1


to rotate about a rotary shaft


4


in the direction of arrow A in contact with the inner peripheral surface of the printing drum


1


, thereby supplying ink to the printing drum


1


. A doctor roller


5


is disposed in the vicinity of the ink coater roller


3


to control the amount of ink supplied to the outer peripheral surface of the ink coater roller


3


. The doctor roller


5


is provided with respect to the ink coater roller


3


with a space t intervening therebetween. An ink fountain


7


is formed at the contact area of the ink coater roller


3


and the doctor roller


5


. An ink supply mechanism


6


supplies ink to the ink fountain


7


by a ink supply pump (not shown).




When passing through the space t between the ink coater roller


3


and the doctor roller


5


in response to rotation of the ink coater roller


3


, the ink in the ink fountain


7


adheres to the outer peripheral surface of the ink coater roller


3


to form an ink layer


8


of a uniform thickness. As the ink coater roller


3


rotates, the ink layer


8


is conveyed to the contact area of the ink coater roller


3


and the printing drum


1


and transferred to the inner peripheral surface of the printing drum


1


. Further, the ink transferred to the inner peripheral surface of the printing drum


1


passes through the printing drum


1


under the pressure of the ink coater roller


3


and is transferred to a printing paper


9


through the master


2


.




The amount of ink in the ink fountain


7


is detected by an ink amount detecting device


10


in accordance with a first embodiment of the present invention. As shown in

FIG. 2

, the ink amount detecting device


10


comprises an oscillator circuit


11


, a receiver circuit


12


, a detector circuit


13


, an amplifier circuit


14


, a comparator circuit


15


, a detecting circuit


16


and an antenna


17


.




With reference to also

FIG. 3

, the oscillator circuit


11


is an LC resonance circuit having a winding and a capacitor and the oscillation frequency from the antenna


17


can be controlled by changing the bias of a variable capacitance diode


11


A. The control signal for changing the bias of the variable capacitance diode


11


A is input from the detecting circuit


16


.




The receiver circuit


12


is a kind of tuning circuit and generates a harmonic signal when it receives a signal of a particular frequency and is tuned.




Since ink is larger than air in dielectric constant, the electrostatic capacity of the capacitor of the oscillator circuit


11


increases as the amount of ink in the ink fountain


7


increases, and vice versa. Accordingly, in order to keep the amount of ink in the ink fountain


7


constant at a predetermined amount, the bias of the variable capacitance diode


11


A of the oscillator circuit


11


is controlled so that a signal of a frequency corresponding to the predetermined amount is oscillated, and the receiver circuit


12


is set to be tuned to the frequency of the oscillator circuit


11


.




The detector circuit


13


converts the frequency signal generated by the receiver circuit


12


to a DC voltage.




The amplifier circuit


14


amplifies the DC voltage output from the detector circuit


13


.




The comparator circuit


15


compares the value of the signal output from the amplifier circuit


14


with a reference value. When the value of the signal output from the amplifier circuit


14


is not smaller than the reference value, the comparator circuit


15


generates an ON-signal to turn on a switching circuit


20


. Whereas when the value of the signal output from the amplifier circuit


14


is smaller than the reference value, the comparator circuit


15


generates an OFF-signal to turn off the switching circuit


20


. The switching circuit


20


is for controlling the ink supply pump (not shown) and only when the switching circuit


20


is on, the ink supply pump supplies ink to the ink fountain


7


.




The detecting circuit


16


reads out information representing the kind of ink stored in a memory


32


attached to the ink bottle


31


, and generates a control signal for setting the bias of the variable capacitance diode


11


A of the oscillator circuit


11


with reference to a table


16


B (

FIG. 2

) representing the relation between the kind of the ink and the bias of the variable capacitance diode


11


A (based on the dielectric constant according to the kind of ink). Bias of the variable capacitance diode


11


A to cause the oscillator circuit


11


to oscillate at a frequency optimal to the dielectric constant of the ink is calculated in advance for each of a plurality of kinds of ink and the kind of ink is related to the calculated bias in the table


16


B.




The detecting circuit


16


is provided with a connector


16


A which is connected to a circuit board


33


on which the memory


32


is mounted and reads out the kind of the ink stored in the memory


32


. When the ink bottle


31


is set in the stencil printer and the circuit board


33


is connected to the connector


16


A, the kind of the ink stored in the memory


32


is readout. The detecting circuit


16


is also connected to a display panel


41


and determination in processing performed by the detecting circuit


16


is displayed on the display panel


41


.




Operation of the stencil printer will be described, hereinbelow.

FIG. 4

shows the processing to be performed by the detecting circuit


16


. The detecting circuit first determines whether an ink bottle


31


has been set in the stencil printer. (steps S


11


and S


12


) When it is determined in step S


12


that an ink bottle


31


has been set in the stencil printer, the detecting circuit


16


reads out ink information representing the kind of the ink in the ink bottle


31


from a memory


32


attached to the ink bottle


31


. (step S


14


) When it is determined in step S


12


that an ink bottle


31


has not been set in the stencil printer, a display to call upon the operator to set an ink bottle


31


is made on the display panel


41


. (step S


13


) Steps S


11


to S


13


are repeated until an ink bottle


31


is set.




After reading out the ink information, the detecting circuit


16


refers to the table


16


B and determines whether the kind of the ink read out is in the table


16


B. (step S


15


) When it is determined in step S


15


that the kind of the ink read out is in the table


16


B, the detecting circuit


16


gets bias of the variable capacitance diode


11


A corresponding to the kind of the ink from the table


16


B (step S


16


), and outputs a control signal corresponding to the bias to the oscillator circuit


11


(step S


17


). Whereas when it is determined in step S


15


that the kind of the ink read out is not in the table


16


B, an error message such as “The kind of ink is not good” is displayed on the display panel


41


(step S


18


) and the bias is set to a default value (step S


19


). Thereafter, the detecting circuit


16


proceeds to step S


17


. Then the oscillator circuit


11


sets the oscillation frequency according to the bias represented by the control signal. (step S


20


)




The oscillator circuit


11


oscillates at an oscillation frequency thus set. When ink exists in the ink fountain


7


and the tip of the antenna


17


is in contact with the ink, the dielectric constant of the ink increases the electrostatic capacity and the oscillation frequency at which the oscillator circuit


11


actually oscillates becomes lower than the oscillation frequency set by the control signal from the detecting circuit


16


. At this time, since the receiver circuit


12


is not tuned to the oscillation frequency of the oscillator circuit


11


, the output voltage from the receiver circuit


12


becomes lower than when the receiver circuit


12


is tuned to the oscillation frequency of the oscillator circuit


11


. Accordingly, the value of the signal output from the amplifier circuit


14


is smaller than the reference value and the comparator circuit


15


generates an off signal, whereby the switching circuit


20


is turned off. In this state, the ink supply pump is not operated and no ink is supplied to the ink fountain


7


.




To the contrast, when the ink in the ink fountain


7


is consumed and the tip of the antenna


17


comes to be away from the ink, the oscillator circuit


11


oscillates at the oscillation frequency set by the control signal from the detecting circuit


16


. At this time, the receiver circuit


12


is tuned to the oscillation frequency of the oscillator circuit


11


and outputs a harmonic signal at a high voltage. Accordingly, the value of the signal output from the amplifier circuit


14


is not smaller than the reference value and the comparator circuit


15


generates an on signal, whereby the switching circuit


20


is turned on. In this state, the ink supply pump is operated and ink is supplied to the ink fountain


7


from the ink bottle


31


.




Then, when the amount of ink in the fountain


7


is increased and the antenna


17


is brought into contact with the ink again, the ink pump is stopped, whereby the amount of ink in the ink fountain


7


is kept constant during printing.




In the stencil printer, since the oscillation frequency of the oscillator circuit


11


is changed according to the kind of the ink or the dielectric constant of the ink, the change of the oscillation frequency can be easily detected by increasing the oscillation frequency when the ink is small in dielectric constant and, unnecessary radiation can be suppressed and the accuracy in detecting the change of the oscillation frequency can be improved by decreasing the oscillation frequency when the ink is large in dielectric constant. Accordingly, change of the oscillation frequency can be accurately detected and the amount of ink in the ink fountain can be accurately detected irrespective of the dielectric constant of the ink, which makes it feasible to keep constant the amount of ink in the ink fountain


7


and to obtain high quality images.




Though, in the first embodiment described above, the table


16


B represents the relation between the kind of ink and the bias of the variable capacitance diode


11


A, the table


16


B may be arranged to represent the relation between the dielectric constant of ink and the bias of the variable capacitance diode


11


A when the ink information stored in the memory


32


represents the dielectric constant of the ink. Further, when the ink information stored in the memory


32


represents another factor such as the viscosity of the ink, the color of the ink, the time for which the ink is left to stand or the date of production of the ink which can affect the dielectric constant of the ink, the table


16


B may be arranged to represent the relation between such a factor and the bias of the variable capacitance diode


11


A.





FIG. 5

is a block diagram showing the structure of an ink amount detecting device


10


′ in accordance with a second embodiment of the present invention. The ink amount detecting device


10


′ of this embodiment differs from the ink amount detecting device


10


of the first embodiment in that a control circuit


51


which measures the dielectric constant of the ink and outputs a control signal for changing the oscillation frequency of the oscillator circuit


11


according to the measured dielectric constant of the ink is provided in place of the detecting circuit


16


.




The control circuit


51


outputs a control signal which sets the bias of the variable capacitance diode


11


A of the oscillator circuit


11


so that the value of the signal output from the amplifier circuit


14


becomes equal to a reference value and the oscillator circuit


11


oscillates at the frequency at which the value of the signal output from the amplifier circuit


14


becomes equal to the reference value. Since the output signal of the amplifier circuit


14


is an analog signal, the control circuit


51


is provided with an A/D convertor.




Operation of the second embodiment will be described with reference to the flow chart shown in

FIG. 6

, hereinbelow. In the second embodiment, the depth to which the antenna


17


is dipped in the ink fountain


7


is set to a predetermined default value. A control signal for setting the bias of the variable capacitance diode


11


A of the oscillator circuit


11


to an initial value is first output to the oscillator circuit


11


. (step S


31


) This causes the oscillator circuit


11


to oscillate at the default oscillation frequency, whereby the receiver circuit


12


outputs an output signal and the amplifier circuit


14


amplifies the output signal and inputs the amplified output signal into the control circuit


51


. (step S


32


) Then whether the output signal is equal to the reference value is determined. (step S


33


) When it is determined in step S


33


that the output signal is equal to the reference value, the control signal is set to provide the bias at that time. (step S


34


) Otherwise, the control signal is changed to change the bias of the variable capacitance diode


11


A of the oscillator circuit


11


(step S


36


) and then step S


32


and S


33


are repeated until the output signal becomes equal to the reference value. Steps S


36


, S


32


and S


33


are repeated until the output signal becomes equal to the reference value in a predetermined time interval (step S


35


). When the output signal does not become equal to the reference value in the predetermined time interval (step S


35


). an error message to the effect that it is impossible to detect the amount of ink is displayed on the display panel


41


(step S


37


).




Though the oscillation frequency of the oscillator circuit


11


is changed by setting the bias of the variable capacitance diode


11


A of the oscillator circuit


11


by the detecting circuit


16


in the first embodiment and by the control circuit


51


in the second embodiment, the oscillation frequency may be changed by manually inputting a desired oscillation frequency through a keyboard or a control panel.



Claims
  • 1. A method of detecting an amount of ink in an ink fountain of a printer, comprising:determining the amount of ink in the ink fountain based on a change of oscillation frequency of an oscillator coupled to an antenna dipped in the ink fountain; obtaining dielectric constant information associated with the type of ink in the ink fountain; and applying a bias to the oscillator based on the obtained dielectric constant information, wherein the dielectric constant information is obtained by measuring the dielectric constant of the ink.
  • 2. A device for detecting an amount of ink in an ink fountain of a printer, comprising:means for determining the amount of ink in the ink fountain based on a change of oscillation frequency of an oscillator coupled to an antenna dipped in the ink fountain; means for obtaining dielectric constant information associated with the type of ink in the ink fountain; means for applying a bias to the oscillator based on the obtained dielectric constant information of the ink, wherein said means for obtaining measures the dielectric constant of the ink.
  • 3. An ink level sensor configured to detect an amount of ink in an ink fountain of a printer, comprising:an oscillator coupled to an antenna and configured to sense the amount of ink in the ink fountain based on a change of oscillation frequency of the oscillator when the antenna is dipped in the ink fountain; and a circuit configured to apply a bias to the oscillator based on dielectric constant information of the ink associated with the type of ink in the ink fountain, wherein the dielectric constant information is obtained by measuring the dielectric constant of the ink.
Priority Claims (1)
Number Date Country Kind
2001-200918 Jul 2001 JP
US Referenced Citations (4)
Number Name Date Kind
5103728 Barney Apr 1992 A
5699731 Hara Dec 1997 A
5898308 Champion Apr 1999 A
6530519 Suzuki Mar 2003 B1
Foreign Referenced Citations (3)
Number Date Country
58-062520 Apr 1983 JP
60-193687 Oct 1985 JP
2001-18507 Jan 2001 JP