Patent ID: 8469496

Claim:
A method of ejecting liquid drops comprising: providing liquid under pressure sufficient to eject a liquid jet through a nozzle of a liquid chamber; modulating the liquid jet to cause portions of the liquid jet to break off into a series of drop pairs traveling along a path using a drop formation device, each drop pair separated in time on average by the drop pair period, each drop pair including a first drop and a second drop; providing a charging device including: a charge electrode associated with the liquid jet; and a source of varying electrical potential between the charge electrode and the liquid jet, the source of varying electrical potential providing a waveform, the waveform including a period that is equal to the drop pair period, the waveform including a first distinct voltage state and a second distinct voltage state; synchronizing the charging device with the drop formation device to produce a first charge state on the first drop and to produce a second charge state on the second drop; varying a relative velocity of a first drop and a second drop of a selected drop pair using a drop velocity modulation device to control whether the first drop and the second drop of the selected drop pair combine with each other to form a combined drop, the combined drop having a third charge state; and causing the first drop having the first charge state to travel along a first path, causing the second drop having the second charge state to travel along a second path, and causing the combined drop having a third charge state to travel along a third path using a deflection device.