< Topic >When the foreign material whose detection is difficult has mixed into measurement object ones, the foreign material detection device which precision well can detect is offered. We calculate the reflectance ratio of measuring object ones in just above direction light absorbent element 11 vis-a-vis the reflectance ratio which does not have abbreviation difference being sought, making use of slanted direction light absorbent element, 12 when the detection difficult foreign material has mixed, we are possible, add, to calculate the reflectance ratio which is difference we calculate reflectance ratio making use of just above direction light absorbent element 11 in regard to the region which calculated reflectance ratio with slanted direction light absorbent element 12, (slanted directional reflectance/just above directional reflectance) seek and the foreign material have not mixed (slanted directional reflectance/just above directional reflectance) with by comparison the foreign materialWe are possible we judge the presence of mixture, when simply reflectance ratio of measuring object ones is compared comparing, precision well to detect the foreign material.< Selective figure >Figure 1【課題】検出が困難な異物が計測対象物に混入している場合であっても精度良く検出することができる異物検出装置を提供する。直上方向受光素子11では略相違のない反射率が求まってしまうのに対し、斜方向受光素子12を用いて測定対象物の反射率を求めており、検出困難な異物が混入している場合であっても相違ある反射率を求めることができ、加えて、斜方向受光素子12で反射率を求めた部位に関して直上方向受光素子11を用いて反射率を求め、(斜方向反射率/直上方向反射率)を求めて異物の混入していない(斜方向反射率/直上方向反射率)と比較して異物の混入の有無を判断しており、単に測定対象物の反射率を比べる場合と比して精度良く異物を検出することができる。【選択図】図1
