Modulation signal amplitude adjustment for an ink jet printer

Claim 3

A method according to claim 1, including identifying the amplitudes of the modulation signal at two or more of said characteristic point.

Claim 4

A method according to claim 2, including identifying the amplitudes of the modulation signal at (i) a first said point in the region of the boundary between a correct modulation signal amplitude range and an under-modulation signal amplitude range, and (ii) a second point in the region of the boundary between the correct modulation signal amplitude range, and where in said selecting of the operating amplitude comprises selecting an amplitude between the amplitudes identified at the first and second points.

Claim 5

A method according to claim 3, in which said selecting of the operating amplitude comprises selecting an amplitude substantially midway between the first and second voltages.

Claim 6

A method according to claim 1, wherein said selecting of the operating amplitude comprises selecting an amplitude which varies from said amplitude identified in said identifying step by a predetermined amount.

Claim 7

A method according to claim 1 wherein said selecting of the operating amplitude comprises selecting an amplitude which varies from said amplitude identified in said identifying step by a predetermined offset.

Claim 8

A method according to claim 1 wherein said selecting of the operating amplitude comprises selecting an amplitude which varies from said amplitude identified in said identifying step by a predetermined factor.

Claim 9

A method according to claim 1 wherein said selecting of the operating amplitude comprises selecting an amplitude which varies from said amplitude identified in said identifying step an amount of amplitude variation which results in a predetermined offset of said phase relationship.

Claim 10

A method according to claim 1, in which said identifying step comprises identifying the amplitude of the modulation signal at the point in the function of said phase relationship with the amplitude of the modulation signal at which, for continued increases in the amplitude of the modulation signal, the rate of change of the determined phase relationship with change in the amplitude of the modulation signal falls below a threshold level.

Claim 11

A method according to claim 1, in which said identifying step comprises identifying the amplitude of the modulation signal at the point in the function of said phase relationship with the amplitude of the modulation signal at which, for continued decreases in the amplitude of the modulation signal, the rate of change of the determined phase relationship with change in the amplitude of the modulation signal falls below a threshold level.

Claim 12

A method according to claim 1, in which said determining step comprises performing repeatedly a cycle comprising varying the amplitude of the modulation signal in a predetermined direction by a preset amount and then determining said phase relationship.

Claim 13

An ink jet printer comprising: an ink jet forming means for generating an ink jet and modulating it in accordance with a modulation signal to influence the break-up of the ink jet into drops; charging means for providing, in accordance with a charging signal, an electric charge on the ink jet as it breaks up into drops; detection means for detecting charged ink drops; and control means for: (i) varying the amplitude of the modulation signal, (ii) controlling, at each of a plurality of amplitudes of the modulation signal, the phase relationship between the modulation signal and the charging signal and determining from the output of the detection means the phase relationship between the modulation signal at that amplitude and the instants when successive drops separate from the ink jet, (iii) identifying the amplitude of the modulation signal at a predetermined point in the function of (a) the phase relationship between the modulation signal and the instants when successive drops separate from the ink jet with (b) the amplitude of the modulation signal, and (iv) controlling the amplitude of the modulation signal during a subsequent printing operation in accordance with the identified amplitude at the predetermined point, wherein the control means identifies the predetermined point from the magnitude of change of the phase relationship between the modulation signal and the instants when successive drops separate from the ink jet with change in the amplitude of the modulation signal.

Claim 14

An ink jet printer comprising: an ink jet forming means for generating an ink jet and modulating it in accordance with a modulation signal to influence the break-up of the ink jet into drops; charging means for providing, in accordance with a charging signal, an electric charge on the ink jet as it breaks up into drops; detection means for detecting charged ink drops; and control means for: (i) varying the amplitude of the modulation signal, (ii) controlling, at each of a plurality of amplitudes of the modulation signal, the phase relationship between the modulation signal and the charging signal and determining from the output of the detection means the phase relationship between the modulation signal at that amplitude and the instants when successive drops separate from the ink jet, (iii) identifying the amplitude of the modulation signal at a predetermined point in the function of (a) the phase relationship between the modulation signal and the instants when successive drops separate from the ink jet with (b) the amplitude of the modulation signal, and (iv) controlling the amplitude of the modulation signal during a subsequent printing operation in accordance with the identified amplitude at the predetermined point, wherein the control means identifies the predetermined point from the magnitude of change of the phase relationship between the modulation signal and the instants when successive drops separate from the ink jet with change in the amplitude of the modulation signal.