Browse Prior Art Database

Two Level Ink Jet Deflection Control System

IP.com Disclosure Number: IPCOM000081001D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Buehner, WL: AUTHOR [+4]

Abstract

This ink jet printer has precision deflection control using a solid-state heater/cooler control system to minimize temperature effects, and a deflection sensor/pump pressure control loop to reduce other effects.

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Two Level Ink Jet Deflection Control System

This ink jet printer has precision deflection control using a solid-state heater/cooler control system to minimize temperature effects, and a deflection sensor/pump pressure control loop to reduce other effects.

Short term - i.e., drift - variations are encountered in ink jet printing systems. One method of solving this problem involves a sensor 1 to indicate when test droplets 2 are at the proper height, control logic 3, and an electrically controlled adjustable-pressure pump 4. Deflection height adjustments are made by adjusting pump pressure.

The table lists all of the known factors affecting (short-term) deflection. The present control algorithm, within its resolution limits, corrects for pump pressure drift, viscosity versus temperature and batch-to-batch viscosity variation. All of these effects cause jet velocity to change and this system simply changes pressure to force jet velocity back to the proper value. Since the deflection height sensor cannot distinguish among the various causes of deflection height drift, all of the other effects are also corrected by changes in velocity. However, these changes are made away from the desired nominal operating velocity.

As shown in the table, these other effects amount to a +/-6.2% deflection variation which is corrected by a +/-3% velocity change. This is a significant drawback of this type of control scheme, as preliminary data suggests that control system-induced velocity changes can have a significant adverse impact on correction factors. The actual estimates are of relative drop placement errors of 2 to 4 mils - which is quite large compared to an assumed objective, for example, of +/-0.5 mil.

An alternative control scheme is described in an article in the IBM Technical Disclosure Bulletin, Vol. 16, No. 10, March 1974, page 3295, entitled "Viscosity Control Circuit". This involves utilizing a solid-state crystalline (bismuth telluride, for example) device as a heat pump 5 with a temperature sensor 6 and control logic 7, in order to maintain the liquid horn 8 assembly at a constant temperature. As shown in the table 1, such a system allows near perfect control of all of the fluid parameters which vary with temperature, density and viscosity, etc. The jet diameter vs. temperature effect is eliminated as well as the charge electrode edge effect. The temperature control unit only needs to control the temperature of the nozzle and the ink in the cavity with the crystal, so it can be a relatively low-powered device.

This system can operate full time and be a true "servo; rather than a "sampled data" control system like the deflection measuring scheme. However, as can be seen from the table, some +/-5.% of the total drift effects are not included in the control loop of this sort of system. Thus character height variation of that magnitude would occur and make the system inadequate to meet objectives of +/-2%, as an example. However, a lower...