Grinding apparatus

A grinding apparatus for grinding a workpiece, comprising:

• a chuck table rotatable about a predetermined rotational axis, the chuck table having a holding surface for holding the workpiece thereon;
• a grinding unit that is disposed above the chuck table and has a spindle, wherein a grinding wheel is to be mounted on a lower end of the spindle and the grinding wheel includes an annular wheel base and a plurality of grindstones disposed on a lower surface of the wheel base circumferentially therealong;
• a moving mechanism for moving the chuck table and the grinding unit relatively to each other in predetermined directions to bring the holding surface and the grinding wheel closer to each other;
• a detector having a light emitter and a light detector, wherein the light emitter includes a lens and a light-emitting element and the light emitter can apply a web-shaped laser beam to at least one of the grinding stones and a portion of the lower surface of the wheel base that is adjacent to the at least one of the grindstones radially of the grinding wheel, the light detector including a light-detecting element for detecting a reflected laser beam reflected of the web-shaped laser beam from the at least one of the grinding stones and the portion of the lower surface of the wheel base;
• and
• a control unit for controlling the grinding unit, the moving mechanism, and the detector, the control unit having a processor and a memory,
• wherein the control unit includes
• a holding surface position storing section for storing a relative vertical position of the holding surface with respect to the grinding wheel along the predetermined directions,
• a first distance calculating section for calculating a first distance in one of the predetermined directions from the detector to a lower surface of the at least one of the grindstones, and
• a lower surface position calculating section for calculating a position of the lower surface of the at least one of the grindstones with respect to the holding surface on a basis of the relative vertical position of the holding surface stored in the holding surface position storing section and the first distance calculated by the first distance calculating section.