Surface shape measurement device with slit plate and single photoelectric converter

A surface shape measurement device for measuring a surface shape of a measurement subject, said device comprising:

• scanner means for scanning said surface of said measurement subject with a light point;
• lens means for focusing an image of said light point on said surface of said measurement subject;
• a slit plate member arranged at a position of a focal plane of said light point and having a plurality of apertures on a locus of said image of said light point;
• photoelectric converter means arranged at a position to receive said light passing through said plurality of apertures for converting said light into a pulse signal;
• pulse generator means for generating a scanning commencement pulse when said scanner means commences scanning;
• signal processing means connected to receive said pulse signal from the photoelectric converter means and to receive said scanning commencement pulse from said pulse generator means for determining a position of said light point on said surface of said measurement subject based on a time-point of generation of said pulse signal and from a time of receiving said scanning commencement pulse, wherein said signal processing means includes:
• level detecting decision means connected to receive said pulse signal from said photoelectric converter means for generating an information signal to find said time-point of generation of said pulse signal;
• delay means connected to receive said pulse signal as an input signal thereof and for generating a delayed signal by delaying said input signal by a fixed time;
• comparison means for comparing said delayed signal with said information signal to generate a comparison signal indicating said time-point of generation of said pulse signal based on a comparison result;
• counting means for counting a time from a commencement of scanning by said scanner means up to said time-point of generation of said pulse signal to generate a count value indicating said time;
• and
• calculation means for determining said position of said light point on said surface of said measurement subject based on said count value;
• whereby said surface shape of said measurement subject being measured based on said position determined by said signal processing means.