Contact detecting apparatus

A contact detecting apparatus (10, 60, 70, 80), comprising:

• an electrostatic sensor (7, 7A) for detecting contact of a conductor (51, 52), the electrostatic sensor (7, 7A) comprising an application electrode (21) to which an input voltage (Vin) that is a constant voltage is applied from a power source (41), a measurement electrode (22, 22A) which is disposed opposite to the application electrode and whose potential is measured, and a dielectric (23) which is disposed between the application electrode and the measurement electrode;
• a first bridge capacitor (12) connected in series between a first measurement position (29) of the measurement electrode and a ground potential (42);
• a charge/discharge switching element (13) connected in series between the measurement electrode and the ground potential and connected in parallel to the first bridge capacitor, and discharging the potential of the measurement electrode to the ground potential when in a closed state;
• a control device (14) executing a process (S1) of discharging the potential of the measurement electrode to the ground potential by setting a state in which the input voltage is not applied to the application electrode and setting the charge/discharge switching element to the closed state, and a process (S2) of charging the electrostatic sensor by setting the charge/discharge switching element to an open state and setting a state in which the input voltage is applied to the application electrode after the process of discharging;
• and
• a measuring instrument (15) acquiring a first potential (V1) between the first measurement position of the measurement electrode and the first bridge capacitor in the process of charging,
• wherein the electrostatic sensor is configured so that an electrostatic capacitance changes in response to at least one of an area of contact with the conductor and a distance from the conductor, and is configured so that a time constant (τ) changes due to an electrical resistance according to a distance from the first measurement position, and
• the measuring instrument detects a position where the conductor is in contact with the electrostatic sensor based on a first potential first sampling value (V11) and a first potential second sampling value (V12) in the process of charging, wherein the first potential first sampling value is the first potential acquired at a first sampling time point (ST1) after a predetermined time has elapsed since start of charging the electrostatic sensor, and the first potential second sampling value is the first potential acquired at a second sampling time point (ST2) after a predetermined time has elapsed since the first sampling time point.