Precision indexing angle measuring method and system for machine tools

A measuring system for measuring the precision in indexing the angle of a table of a machine tool, said angle indexing precision measuring system for machine tools comprising:

• a relative angle measurement apparatus having two separate parts and capable of measuring a change in relative angle between said two parts over a given range of measurable angles;
• a rotating mechanism that is fixed to a portion of said machine tool independent of the rotation of said table and rotates with the axis of rotation of said table as a center;
• and
• a control unit for processing a value measured by said relative angle measurement apparatus and controlling said machine tool and rotating mechanism,
• wherein in a state in which one of said two parts of said relative angle measurement apparatus is fixed to said table, the other part is attached to said rotating mechanism, and said two parts are set so that the relative angle between them can be measured,
• within a range of angles within which the relative angle between said two parts reaches one limit of a range of set angles equal to or smaller than the given range of measurable angles,
• said control unit repeats an operation of reading the relative angle between said two parts, which is output from said relative angle measurement apparatus, after rotating said table by a unit angle by controlling said machine tool;
• after the relative angle between said two parts reaches one limit of the range of set angles, said control unit controls said rotating mechanism so as to rotate the other one of said two parts until the relative angle between said two parts reaches the other limit of the range of set angles;
• and
• said control unit carries out the above operations repeatedly over a whole range of angles at which the precision in indexing an angle is measured,
• wherein said two parts are a laser interference unit and a dual corner cube unit having two corner cubes juxtaposed, said relative angle measurement apparatus measures a change in relative angle between said laser interference unit and dual corner cube unit by detecting a change in interference fringes resulting from interference of laser light rays output from said laser interference unit and reflected from said two corner cubes after irradiated,
• wherein said relative angle measurement apparatus includes a laser light source for supplying laser light to said laser interference unit, a fringe counter for counting the number of changes in interference fringes, an optical fiber over which laser light is supplied from said laser light source to said laser interference unit, and an optical fiber over which the resulting laser light is transmitted from said laser interference unit to said fringe counter.