Inventors:
Carmichael, John M. (Lexington, KY)
West, Donald L. (Lexington, KY)
Williams, Robert A. (Lexington, KY)
Other References:
Ruddy, G. A.; Position And Synchronization Sensor For An INR Jet Printer; IBM Tec. Disc. Bulletin, Vol. 15, No. 9, February 1973, pp. 2785-2786. .
Naylor et al.; Differential Synchronization Sensor; IBM Tec. Disc. Bulletin, Vol. 16, No. 3, August 1973, pp. 776-777..
Claims:
What is claimed is
1. A sensor system for ink jet printers, particularly providing reduced noise and improved signal to noise ratio, comprising:
2. The apparatus of claim 1, wherein said sensor means comprises:
3. The apparatus of claim 1, wherein said sensor means comprises:
4. The apparatus of claim 1, further comprising:
5. The apparatus of claim 1, further comprising:
6. The apparatus of claim 1, further comprising:
Description:
CROSS-REFERENCE
The following case is hereby incorporated by reference:
U.S. Pat. application Ser. No. 313,886, having J. W. Woods, et al. as inventors, filed Dec. 11, 1972, and entitled "Ink Jet Printing Apparatus with Overrun of Printhead to Insure Better Visibility and Counter Control of Printing Locations."
BACKGROUND OF INVENTION, FIELD AND PRIOR ART
The present invention has particular utility in the field of ink jet printing. Various schemes have been proposed heretofore for printing with drops of ink that are generated at extremely high frequencies, such as in the range of 100 kilohertz, or higher. In systems of this nature, such as that set forth in the Woods, et al. application referred to above, it is extremely important that the drops of ink be checked in order to determine that their velocity is correct, that their placement is correct, etc. An inductive type sensor is described in the U.S. Pat. application Ser. No. 313,913, having John Ghougasian, et al. as inventors, filed Dec. 11, 1972, and entitled "Drop Charge Sensing Apparatus for An Ink Jet Printing System."
Also, another form of drop charge sensing is described in the U.S. Pat. application Ser. No. 389,290 filed Aug. 17, 1973, having Hugh E. Naylor, et al., as inventors, filed concurrently herewith, and entitled "Deflection Sensors for Ink Jet Printers."
SUMMARY
In accordance with the present invention, various ink jet drop charge sensor configurations are described having improved sensitivity and efficiency and enabling the sensing of a single drop of ink. In one embodiment, a sensor is provided comprising a plurality of plates arranged in laminated form through which the ink drops pass. The sensor is incorporated in a sensitive detection circuit for development of signals from drops that are sensed. In another form, a probe sensor is provided comprising cylindrical elements, such as an outer shield, and inner shields, separated by insulation. This sensor is also coupled to a detection circuit for developing signals from drops passing through the sensor.
OBJECTS
A prime object of the present invention is to provide improved sensor arrangements for ink jet printers, the sensors having greater efficiency, greater sensitivity, and improved signal to noise characteristics.
The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of various embodiments of the invention as illustrated in the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
In the Drawings
FIG. 1 illustrates a detection circuit incorporating a sensor, the sensor being shown in greater detail in FIGS. 2 and 3.
FIG. 4 illustrates a variation further comprising a probe sensor having an external shield that is grounded.
FIG. 5 is another variation using a planar sensor.
DESCRIPTION
Non-contact sensing of the charge on an ink stream provides for fast charge synchronization in an ink jet printer when sensitive sensors and detection circuits are provided as shown in FIGS. 1 and 4.
The circuit shown in FIG. 1 permits the use of a non-contact sensor shown in more detail in FIGS. 2 and 3 to sense the charge on a few drops or a single drop of ink. An ink stream 1 comprising a plurality of drops proceeds from left to right originating from a nozzle, such as that shown in the Woods, et al application. The stream passes through a charge electrode 2 that places a variable charge on each drop of ink in accordance with data signals, and the like. Just beyond charge electrode 2 is sensor 3 comprising a center conductor 3a and an inner-shield 3b, together with an outer shield 3c that is grounded. The variably charged ink drops proceed between a pair of deflection plates 5 and as is known in the art are deflected in accordance with the amount of charge placed thereon. Drops required for printing strike paper 6 while those not required are sent to a gutter 8. A Field Effect Transistor (FET) operational amplifier 10 connected as shown in FIGS. 1 and 4 to the center conductor 32 and the inner shield 3b of sensor 3 effectively reduces the input capacitance of the circuit to zero. A large value resistor 16 is connected as shown in FIGS. 1 and 4 to supply bias current to the FET operational amplifier. This results in the ability to sense one drop of charged ink with a charge per drop less than 3×10-14 coulombs and with a frequency of less than 2500 samples/second. The output of amplifier 10 is AC coupled to another amplifier circuit 11 and thereafter to a threshold circuit 12 with a signal ultimately provided on line 13. Such signal may be incorporated in various circuits to control synchronization in the system as discussed in the Woods, et al application.
As shown in FIGS. 2 and 3, the center conductor 3a and the inner shield 3b are protected by an outer (guard) shield 3c connected to ground to reduce the noise pickup of the sensor. In addition to the outer shield the threshold circuit is time strobed on line 15 to reduce the effects of any noise pickup. This strobing time isolates the main noise source which is the charge electrode, and the charge-sensor sense time, during which the charged drops are passing the sensor.
More details of the laminated sensor are shown in FIG. 3 wherein the layers of the sensor comprise alternate sheets of copper and Mylar* (*Registered Trademark of Dupont).
The configuration in FIG. 4 comprises a cylindrical member 3 with cylindrical elements 3a, 3b, and 3c serving functions similar to those previously described. This configuration is characterized as a probe-type sensor, rather than a laminar sensor.
The circuit in FIG. 1 and sensor configurations of FIGS. 2 and 3 or FIG. 4 can be used to detect the charge placed upon a drop of ink, thereby indicating when the charging time of the charge electrode is synchronized with the ink drop formation.
The configuration in FIGS. 5a and 5b represents a probe-type sensor 3 constructed on one plane, rather than as a cylinder like the sensor in FIG. 4. However, similar elements are similarly referenced. Additional applications:
1. Velocity
By placing two sensors along the stream of ink some distance apart, then measuring the time it takes a drop of charged ink to move the known distance, a velocity can be observed (v = distance/time). A package or a single drop of charged drops can also be used but with somewhat less resolution.
2. Deflection
By placing one or more sensors at a position by which the drop or drops of ink (charged ink) are to pass if properly charged and deflected. If proper deflection is not measured, then the various parameters of the system (ink stream control parameters) may be closed within the loop including the sensors.
3. Stream Running
The stream of ink that is unused can be charged enough to keep it in the gutter but still have enough charge on the drops for the non-contact sensor and circuit to sense if the stream is running. Loss of sensor output indicates stream failure.
While the invention has been particularly shown and described with reference to several embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention.