Browse Prior Art Database

Optical Drop Servo Scheme

IP.com Disclosure Number: IPCOM000051799D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 5 page(s) / 100K

Publishing Venue

IBM

Related People

Bishop, CA: AUTHOR [+3]

Abstract

In a continuous stream ink jet printer some form of ink stream servo is required to compensate for the day to day (sometimes hour to hour) environmental changes. The servo chosen should include a sensor which is capable of detecting when the ink pump is at the correct pressure. The optical sensor which normally outputs a string of Pulses as drops past the sensor is described in the servo system of U.S. Patent 4,217,594. In this patent, a perturbation is imposed on the stream which creates a gap therein which may be detected at the detector. Inasmuch as the distance from the nozzle to the sensor is a constant, and since the time from perturbation to detection can be easily measured, the drop velocity may be determined. and the pump pressure adjusted to correct for incorrect. drop velocity.

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Optical Drop Servo Scheme

In a continuous stream ink jet printer some form of ink stream servo is required to compensate for the day to day (sometimes hour to hour) environmental changes. The servo chosen should include a sensor which is capable of detecting when the ink pump is at the correct pressure. The optical sensor which normally outputs a string of Pulses as drops past the sensor is described in the servo system of U.S. Patent 4,217,594. In this patent, a perturbation is imposed on the stream which creates a gap therein which may be detected at the detector. Inasmuch as the distance from the nozzle to the sensor is a constant, and since the time from perturbation to detection can be easily measured, the drop velocity may be determined. and the pump pressure adjusted to correct for incorrect. drop velocity.

ln the embodiment illustrated and described herein, a detectable pattern is imposed on the ink stream, a digital logic being described which allows the pattern to be detected. In the described embodiment, two perturbations are imposed on the stream with a constant number of drops between them.

Crystal drive perturbation logic places two perturbations on the crystal drive signal separated by an adjustable time delay. The time delay will determine the number of drops between perturbations, and each perturbation will cause a gap. The gap detector decodes the gaps created by the crystal drive perturbation logic by looking at the output of the optical drop detector. Each time the drop detector output goes low, it fires a single-shot. If another drop does not pass by the optical sensor before the single-shot times out, a second single-shot will be fired, indicating the presence of a gap.

The control and flight time counting logic more fully described below causes the crystal drive to be perturbated and then counts the time that passes before the gaps pass the optical sensor. This "flight time" will be proportional to the velocity of the ink drops.

The control and flight time counting logic, along with suitable timing diagrams, are illustrated in Figs. 1-5. Referring first to Fig. 1, there are four input signals to the logic; SERVO, SYN 3, XTAL CLK and RESET. SERVO indicates that a servo cycle should begin. SYN 3 is a system signal used to synchronize the start of the servo with the crystal drive signal (XTAL CLK). XTAL CLK is the clock signal that drives the crystal in the ink jet drop generator, while RESET is the servo system reset signal. XTAL DR IN (Figs. 2,3 and 6) is the crystal drive input.

When the SERVO signal goes low and then back to high, a "1" will be clocked through the flip-flop 1, and the signal RDY will be a "1". When SYN 3 goes high, the data on the RDY line is clocked through the second flip-flop 2. The SYN 3 pulse also causes a pulse to appear at the output of AND gate 3 as well as in the output of OR gate 4. The output of OR gate 4 is a signal called BEGIN that is applied to the crystal perturbation logic....