Abstract: The presence of a photoconductor drum in a laser printer may be determined by making electrical measurements without directly sensing drum presence. In some embodiments, this may be done without using any added printer components.

Abstract: A printing machine includes a charge neutralizing system for neutralizing static charge on sheets of material fed therethrough. The charge neutralizing system includes a grounded wire (47) located in proximity to the sheets for neutralizing charge on the sheets. The charge neutralizing system further includes a grounded conductive brush (81) mounted on a sheet deflector (61) so that one end of the brush (77) contacts sheets as they traverse a first sheet feed path (71) and the other end of the brush (79) contacts sheets are they are routed by the deflector to a second alternative sheet feed path (63). The grounded brush (81) further serves to decelerate the sheet as it exits the printing machine over the second sheet feed path (63).

Abstract: A pressurized ink jet stream is broken up into droplets spaced substantially uniform distances by application of a predetermined frequency to the stream. When the velocity of the stream is to be determined, a frequency perturbation is placed in the predetermined frequency to produce a gap in the stream of droplets at a selected distance from the perturbation application point. The presence of the gap is optically sensed at the selected distance by determining when the time period between adjacent droplets at the selected distance exceeds a predetermined period of time. The velocity of the stream is determined in accordance with the time that it takes from the perturbation of the gap until the gap is sensed at the selected distance because of the time period between adjacent droplets exceeding the predetermined period of time.

Abstract: The application of the voltage on a charge electrode to selectively charge droplets of a pressurized conductive ink stream is synchronized with the break off of the droplets from the stream so that the break off occurs in the third quarter of the time period during which the charge voltage is placed on the charge electrode. To determine in which quarter that break off is occurring, the charge voltage is placed on the charge electrode at the same time for two adjacent quarters of a cycle during each of the two adjacent cycles in which a disturbance is placed on the stream by drive means such as a transducer, for example, to produce two droplets. During the next application of the charge voltage on the charge electrode, the charge voltage is applied for the last of the prior two adjacent quarters and the next adjacent quarter during two adjacent droplet producing cycles.