Switching detector

Claim 2

An electrostatographic reproducing apparatus comprising: an electrostatographic surface adapted to have formed thereon a powder image for transfer to a transfer material applied to said surface, pickoff means for removing said transfer material from said surface after transfer of said image thereto; cleaning means positioned above said surface at a point beyond said pickoff means and including an AC electrode and a DC electrode, a source of AC potential coupled to said AC electrode for applying an electrostatic charge to said surface, and a device connected to said DC electrode for detecting failure of removal of said transfer material from said surface after transfer of said image to said material, said device including a source of DC potential and a detector, said detector responsive to provide a first condition in response to a first current flow between said DC and said AC electrode caused by the absence of transfer material at said position and a second condition in response to a second current flow between said DC and said AC electrode caused by the presence of transfer material at said position.

Claim 3

The combination of claim 1 wherein said second current flow is a reversal of said first current flow, and said detector includes means for distinguishing between said first and second current flows.

Claim 4

The combination of claim 1 wherein said cleaning means includes insulating shield walls surrounding said AC electrode, said DC electrode forming the interior of one of said walls, said walls being spaced to permit air to circulate therein.

Claim 5

The combination of claim 1 wherein said detector includes a first diode poled in a first direction and a second diode poled in the other direction, said second diode including an indicator means connected in series therewith, said second diode and indicator connected in parallel with said first diode, said parallel circuit being connected between an output means for sensing the condition of said detector and said source of DC potential.

Claim 6

An electrostatographic reproducing apparatus comprising an electrostatographic surface adapted to have formed thereon a powder image for transfer to a transfer material applied to said surface, pickoff means for removing said transfer material from said surface after transfer of said image thereto, cleaning means positioned above said surface at a point beyond said pickoff means, said cleaning means including an AC electrode and a DC electrode, said AC electrode surrounded by insulating walls with air venting spacing, a source of AC potential coupled to said AC electrode for applying an electrostatic charge to said surface, a source of DC potential having an adjustable valve coupled to said DC electrode, a detector coupled to said DC potential source, a utilization load coupled between said detector and a reference point, said detector including a first diode poled in the same direction as said DC potential source and connected between said utilization load and said DC potential source, a second diode poled in a direction opposite to said first diode and connected in series with a threshold ignition device, the series connection of said second diode and said threshold ignition device being connected in parallel with said first diode, said DC potential source being adjustable such that in the absence of transfer material between said cleaning means and said surface a first current flow insufficient to ignite said threshold device is provided in said utilizatIon load, and in the presence of transfer material between said cleaning means and said surface a second current flow sufficient to ignite said threshold device is provided in said utilization load.

Claim 7

An electrostatographic reproducing apparatus comprising an electrostatographic surface adapted to have formed thereon a powder image for transfer to a transfer material applied to said surface, pickoff means for removing said transfer material from said surface after transfer of said image thereto, cleaning means positioned above said surface at a point beyond said pickoff means, said cleaning means including an AC electrode and a DC electrode, said AC electrode surrounded by insulating walls with air venting spacing, a source of AC potential coupled to said AC electrode for applying an electrostatic charge to said surface, a source of DC potential having an adjustable valve coupled to said DC electrode, a detector coupled to said DC potential source, a utilization load coupled between said detector and a reference point, said detector including a first diode poled in the same direction as said DC potential source and connected between said utilization load and said DC potential source, a second diode poled in a direction opposite to said first diode and connected in series with a threshold ignition device, the series connection of said second diode and said threshold ignition device being connected in parallel with said first diode, said DC potential source being adjustable such that in the absence of transfer material between said cleaning means and said surface a first current flow insufficient to ignite said threshold device is provided in said utilizatIon load, and in the presence of transfer material between said cleaning means and said surface a second current flow sufficient to ignite said threshold device is provided in said utilization load.