Patent ID: 8028990

Claim:
A paper thickness detecting apparatus for detecting a thickness of a piece of paper conveyed through a conveyance path from a change in electrostatic capacitance of a sensor having opposing electrodes, the sensor being arranged such that the conveyance path of the paper passes between the electrodes, the paper thickness detecting apparatus comprising: a first sensor including a first applying electrode and a first detecting electrode that are arranged on opposite sides of the conveyance path, the first sensor being coupled to a first electric current detection circuit for detecting electric current in the first detecting electrode; a second sensor including a second applying electrode and a second detecting electrode that are arranged on opposite sides of the conveyance path, the second sensor being coupled to a second electric current detection circuit for detecting electric current in the second detecting electrode, the first applying electrode and the second applying electrode being arranged on opposite sides of the conveyance path; and a thickness detecting unit configured to obtain a first response signal detected by the first electric current detection circuit of the first sensor and a second response signal detected by the second electric current detection circuit of the second sensor, and to detect a change in the thickness of the paper due to a foreign object from a result of comparing the first response signal with the second response signal.