Browse Prior Art Database

Deflection Servo Initialization

IP.com Disclosure Number: IPCOM000079762D
Original Publication Date: 1973-Aug-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 4 page(s) / 41K

Publishing Venue

IBM

Related People

Fillmore, GL: AUTHOR [+3]

Abstract

A technique is described for quickly estimating the proper initial conditions for a deflection servo system 3n an ink jet printer, at power on or When with power already on the stream is brought up after a period of inactivity.

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Deflection Servo Initialization

A technique is described for quickly estimating the proper initial conditions for a deflection servo system 3n an ink jet printer, at power on or When with power already on the stream is brought up after a period of inactivity.

In an ink jet printer having a deflection servo sensor and servo system, it is desirable to be able to quickly adjust drop deflection to its normal value regardless of the starting conditions at the time the ink stream is turned on. Whether it is a hot afternoon or a cool morning, it is desirable to move in to normal operating mode quickly.

Since the primary cause of deflection error is velocity change due to variation in fluid viscosity, one approach is to measure temperature and make a correction to the pump drive so that the initial deflection would be almost correct; then several additional correction cycles ensue, as required, since the settling time of a typical pump system, after a change is made, can be rather long, i.e., 2-10 seconds. The use of the temperature sensor scheme to make the first "rough" estimate of the correction required, leaves only one or two cycles necessary for a final adjustment.

Another factor to be considered, is the amount of overshoot allowable in the case where a drop is actually deflected above the proper height. Too much overshoot will send drops into the upper deflection plate causing contamination and probable failure. A minimum clearance above the nominal deflection path permits some overshoot. This should normally be kept small as it requires extra deflection plate clearance and extra deflection voltage. Fig. 1 illustrates a stream of ink drops 1 passing through a charge electrode 2 and between deflection plates 3a and 3b, toward a split deflection sensor 4 having a sensor gap 4a. Path B is the path followed by properly deflected drops. Drops that are too high take path A, while drops that are too low take a path such as C below the sensor gap.

A simpler approach can be developed using some logic and the D-A converter, normally provided in the printer. Basically, with a character matrix 24 wide by 40 high, for example, drop No. 40 (top drop) should pass by 4a in deflection sensor 4 and produce an electronic null in differential amplifier 5. When the machine is first turned on, it is possible that this will occur but it is also possible that the locale of the printer will be cool and smaller drops will be produced, which will thus be deflected above the sensor gap. Conversely, if the locale is hot, larger than normal drops will be produced and will not be deflected as high as the sensor gap.

By simply extending the range of the D-A converter (DAC), deflection can be corrected to the proper level by changing the charging voltage. The logic determines how many DAC steps different from the nominal position are necessary in order to correct deflection. Then an appropriate change to the pump drive is made. This change should very nearly corre...