Patent ID: 7518626

Claim:
A light beam synchronization detector comprising: a first photoelectric converter section and a second photoelectric converter section; a comparison output section which receives inputs of a first output signal outputted from the first photoelectric converter section and a second output signal outputted from the second photoelectric converter section, compares the first output signal with the second output signal and generates and outputs a light beam detection signal on the basis of a result of the comparison; and a control section which receives inputs of the first output signal outputted from the first photoelectric converter section and the second output signal outputted from the second photoelectric converter section, outputs a first control signal to the comparison output section when at least one of the first output signal and the second output signal exceeds a prescribed threshold value to put the comparison output section into an operative state and outputs a second control signal to the comparison output section when both the first output signal and the second output signal are equal to or lower than the threshold value to put the comparison output section into an inoperative state, wherein the first photoelectric converter section comprises: a first photoelectric converter and a first signal converter section that converts a first current signal outputted from the first photoelectric converter into a first voltage signal and outputs the first voltage signal as the first output signal; the second photoelectric converter section comprises: a second photoelectric converter and a second signal converter section that converts a second current signal outputted from the second photoelectric converter into a second voltage signal and outputs the second voltage signal as the second output signal; and the threshold value is set to be smaller than an absolute value of both the first voltage signal and the second voltage signal when a quantity of light incident on either the first photoelectric converter section or the second photoelectric converter section is not greater than half of the quantity of light needed for normal operation of the light beam detector.