Numerical control apparatus of machines

A numerical control machine tool comprising:

• a table upon which a workpiece is mounted as a processing object;
• a spindle axis to which is mounted a tool that performs a required processing to said workpiece;
• first and second drive shafts having axial directions horizontal and at right angles to each other, and a third drive shaft having an axial direction vertical and at right angles to said first and second drive shafts, respectively, said first, second and third drive shafts three-dimensionally moving said table;
• and
• first, second and third drive shaft control means, provided for said first, second and third drive shafts, respectively, for controlling positions of said first, second and third drive shafts, respectively, said first, second and third drive shaft control means comprising:
• first, second and third servo motor means, respectively, for driving said first, second and third drive shafts, respectively, to move said table in three dimensions in response to first, second and third position instructions, respectively, provided by an external instruction apparatus,
• first, second and third reversal detection means, respectively, for receiving said first, second and third position instructions, respectively, from said external instruction apparatus, detecting, from said first, second and third position instructions, respectively, first, second and third reversal instructions indicating reversal of said first, second and third drive shafts, respectively, and outputting first, second and third reversal detection signals, respectively, in response thereto,
• first, second and third storing means, respectively, each for storing first, second and third data, said first, second and third data each comprising at least two types of compensation amounts, respectively, said at least two types of compensation amounts of each of said first, second and third data each including:
• first, second and third proper compensation amounts, respectively, for compensating for position errors of said spindle axis caused by backlash of said first, second and third drive shafts, respectively, when said first, second and third drive shafts are reversed, respectively, and
• first, second and third first-relative compensation amounts, respectively, for compensating for influences on said first, second and third drive shafts, respectively, by reversal of another one of said first, second and third drive shafts when reversal of said another one of said first, second and third drive shafts has been detected by one of said first, second and third reversal detection means of said another one of said first, second and third drive shaft control means,
• first, second and third means for selecting first, second and third error compensation amount signals, respectively, said first, second and third selecting means determining, in accordance with said first, second and third reversal detection signals provided by said first, second and third reversal detection means, respectively, whether said first, second and third proper compensation amounts stored in said first, second and third storage means are to be included in said first, second and third error compensation amount signals, respectively, and determining, in accordance with said another one of said first, second and third reversal detection signals provided by said another one of said first, second and third reversal detection means, respectively, whether said first, second and third first-relative compensation amounts stored in said first, second and third storage means are to be included in said first, second and third error compensation amount signals, respectively,
• first, second and third position detection means for detecting positions of said first, second and third servo motor means, respectively, and outputting first, second and third position detection signals, respectively, and
• first, second and third servo control means for generating first, second and third position compensation signals from said first, second and third position detection signals, respectively, in accordance with said first, second and third error compensation amount signals, respectively, to compensate a position of said spindle axis, generating first, second and third position compensation instruction signals from said position instruction provided by said external instruction apparatus in accordance with said first, second and third position compensation signals, respectively, and controlling driving of said first, second and third servo motor means in accordance with said first, second and third position compensation instruction signals, respectively.