Patent ID: 7810864

Claim:
An opening and closing device comprising: an electrically conductive fixed body that defines an opening portion therein; a movable body that is displaceable between a full closed position and a full open position, wherein: the movable body closes the opening portion of the fixed body at the full closed position; and the movable body opens the opening portion of the fixed body at the full open position; a drive motor that drives the movable body to open and close the opening portion of the fixed body; a speed control device that controls a rotational speed of the drive motor to change a speed of displacement of the movable body; a detection assembly that includes a sensor electrode, which is located on an end portion of the movable body toward the full closed position, wherein the detection assembly detects a change of a capacitance formed between the sensor electrode and an electrically conductive object adjacent to the sensor electrode; and a determining device that computes, as a detection value, a change amount of the capacitance at the sensor electrode per a predetermined constant measuring time based on the change of the capacitance detected by the sensor electrode, wherein: the determining device compares the detection value with a constant threshold value, which is used for determining whether the object exists between the movable body and a periphery of the opening portion; the determining device determines whether the object exists between the movable body and the periphery of the opening portion based on the comparison result, and the threshold value is determined based on an actual change of the capacitance detected in advance by the sensor electrode in a condition, where the object is absent between the movable body and the periphery of the opening portion during a closing operation of the movable body.