VIDEO PROJECTION APPARATUS CAPABLE OF OPERATING AT OPTIMUM RESONANT FREQUENCY AND ITS CONTROLLING METHOD

A video projection apparatus includes: a light source (22); an optical deflector (19) having a mirror (191) for reflecting light (L) to project a view field (F), an actuator (193a) for rocking the mirror (191) with an axis of the mirror (191) and a sensor (197a) provided in the vicinity of the actuator (193a); and a control unit (14, 15, 16). The control unit (14, 15, 16) generates a sine-wave voltage (V xa ) applied to the actuator (193a) and a cosine-wave voltage (V xa '); calculates a first convolution (X) between the sine-wave voltage (V xa ) and a sense voltage (V xsa ) from the sensor (197a); calculates a second convolution (Y) between the cosine-wave voltage (V xa ') and the sense voltage (V xsa ); converts an orthogonal coordinate formed by the first convolution (X) and the second convolution (Y) into a polar coordinate formed by a radius component (R) and an angle component ( ¸ ) and sweeps the frequency (f x ) of the first and second voltages (V xa , V xa ') so that the frequency (f x ) is defined as a resonant frequency (f r ) when the radius component (R) is maximum.