INDENTATION TYPE HARDNESS METER

PURPOSE:To measure a hardness value accurately without manual operation by performing the binary coding of digital image signals, selecting picture elements corresponding to the four sides of an indentation other than the elements in the vicinities of the corner parts of the four sides of the indentation, and performing specified operations and the like. CONSTITUTION:A quadrangular-pyramid pressing piece 2 is compressed on the surface of a test piece 1 with a specified load in a testing machine 4, and an indentation 3 is formed. Optical image data 7 of the indentation 3 which is formed on an image setting device 6 undergoes AD conversion in an AD converter 8. An autofocus part 10 is controlled with the obtained digital signal. An adjusted digital image signal 12 undergoes binary coding in a binary coding part 13. A digital image processing part 15 selects picture elements corresponding to the four sides of the indentation other than the elements in the vicinities of the four sides based on the binary coded image signals 14. A computing part 16 classifies the picture elements for every side and imparts coordinate points. The linear approximations of the four sides of the indentation are obtained. The coordinates of the intersections of the four regression expressions are computed. The two diagonal lines of the square which is obtained by connecting the coordinates of the four intersections are obtained with an indentation-size measuring part 17. The hardness is operated and outputted based on the average value of the lengths of the two diagonal lines of the indentation and the compressing load of the compressing piece with a hardness computing part 18.