US Patent No. 9,374,881


Patent No. 9,374,881
Issue Date June 21, 2016
Title Radiation Generator Including Cut-off Voltage Generator And Associated Detection Unit
Inventorship Shuji Aoki, Yokohama (JP)
Kazuyuki Ueda, Tokyo (JP)
Assignee Canon Kabushiki Kaisha, Tokyo (JP)

Claim of US Patent No. 9,374,881

1. A radiation generator comprising:
a radiation tube including:
a cathode heater configured to generate heat in response to a voltage being applied thereto,
an electron emitting cathode configured to emit electrons in response to the heat generated by the cathode heater,
a grid electrode configured to control an amount of electrons emitted from the electron emitting cathode,
a lens electrode configured to focus an electron beam passing through the grid electrode, and
an anode having a target configured to generate radiation in response to an electron irradiation from the electron emitting

a grid-voltage generating unit configured to apply an extraction voltage to the grid electrode in response to an external
request for radiation output;

a cathode heater driver configured to generate a cathode heater voltage;
a cut-off voltage generating unit configured to generate a cut-off voltage applied to the grid electrode so as to lower the
potential of the grid electrode relative to the potential of the electron emitting cathode when there is no external request
for the radiation output;

a lens electrode driver configured to generate a lens electrode voltage applied to the lens electrode; and
a detection unit including a primary switching circuit and a secondary switching circuit, the primary switching circuit configured
to turn off energizing to the cathode heater and configured to detect a decrease in the cut-off voltage with respect to the
electron emitting cathode, and the secondary switching circuit configured to turn off energizing to the lens electrode,

wherein, when the decrease in the cut-off voltage is detected, the primary switching circuit turns off energizing to the cathode
heater such that the target is not irradiated by the electrons.