OPTICAL SAFETY DEVICE FOR PRESS BRAKES, PRESS BRAKE, AND OPTICAL MONITORING METHOD

In the present invention, an assessment unit (70) assesses, on the basis of the light reception state of a photodiode (564) positioned nearest an upper die (12), whether or not a shadow of the upper die (12) cast by a laser (B) projected on an optical receptor (52) side has expanded to the photodiode (564). A deactivation unit (72) deactivates the photodiode (564) positioned nearest the upper die(12) if it is determined that the shadow of the upper die (12) has expanded to said photodiode (564). A detection unit (74) detects the presence or absence of foreign matter between the upper die (12)and a lower die (14) on the basis of the light reception state of a plurality of active photodiodes (56) while an upper table (26) is descending. 本发明的判定部(70)基于位于离上模具(12)的最近的光电二极管(564)的受光状态，判定因向受光器(52)侧投影的激光(B)而形成的上模具(12)的影是否扩大到该光电二极管)(564)。在判定为上模具(12)的影扩大到位于离上模具(12)的最近的光电二极管(564)的情况下，无效化部(72)将该光电二极管(564)无效化。检测部(74)在上部工作台(26)的下降动作中，基于有效的多个光电二极管(56)的受光状态来检测上模具(12)与下模具(14)之间有无异物。