Method and apparatus for adjusting the velocity of ink drops in an ink jet printer

In an ink jet printing apparatus, the combination comprising

• jet forming means for projecting a continuous stream of ink drops along a path toward a print medium,
• pump means connected to said jet stream forming means for supplying a liquid ink under pressure to said jet forming means, and
• control means for adjusting the velocity of said ink drops including
• means for determining the direction of any velocity error in said stream,
• and means for correcting any velocity error determined by said error detection determining means including,
• means for making coarse incremental adjustments in said pump pressure in the sense opposite to said velocity error until a first reversal in the direction of said velocity error occurs,
• means for causing said coarse adjustment means to toggle about a null point velocity of said stream, and
• means operative after a predetermined number of toggling operations of said coarse adjustment means for making one or more incremental fine adjustments in said pump pressure whereby said velocity is set at substantially said null point.