| 摘要 |
PURPOSE:To enable detection with high reliability and to space and retreat a probe device from a steel plate by connecting three sensors to a majority logic circuit, and enabling judgement from the result of the detection with the other two sensors even if any one of the sensors makes a wrong detection. CONSTITUTION:The output terminal of a memory M1 is connected to the respective 1st input terminals of ANDs 11, 12, and the output terminal of a memory M2 is connected to the 2nd input terminal of the AND 12 and the 1st input terminal of the AND 13. The output terminal of a memory M3 is connected to the 2nd input terminal of the AND 11 and the 2nd input terminal of the AND 13. The 3rd input terminals of the ANDs 11-13 are commonly connected to a detector for steel plate, and the signal of a ''1'' is applied thereto if the steel plate exists. Therefore none of the ANDs opens the gates and produces output unless the same outputs are produced from any two photodetector. On the other hand, if >=2 light beams are interrupted by the steel plate and the output of a ''1'' is generated from an inverter, the output of the memory goes to a ''1'' and the ANDs 11-13 open the gate, thereby producing the output of a ''1'' and making OR gate ''1''. The presence of abnormality in the way how the steel plate is fed is thus known. |
