Method and device for determining center hole of crankshaft

1. A method of determining a center hole of a material crankshaft that is obtained through molding with a first mold and a second mold, the method comprising using a computer and a shape measuring machine to:

obtain first shape data of a first portion of the material crankshaft molded by the first mold by measuring the first portion;

obtain second shape data of a second portion of the material crankshaft molded by the second mold by measuring the second portion;

compute a first misalignment amount of the first portion due to a misalignment between the first and second molds by comparing the first shape data with first designed data corresponding to the first mold;

compute a second misalignment amount of the second portion due to the misalignment between the first and second molds by comparing the second shape data with second designed data corresponding to the second mold;

obtain first revised designed data based on the computed first misalignment amount;

obtain second revised designed data based on the computed second misalignment amount;

adjust, based on the misalignment amount, data corresponding to the misalignment amount so as to reproduce actual shape data; and

determine, based on the actual shape data, a position of the center hole in the material crankshaft such that a rotation balance of the material crankshaft is within a predetermined range.

2. The method of determining a center hole of a crankshaft according to claim 1 , wherein

the obtaining of the first and second shape data includes obtaining two-dimensional shape data of the first portion molded by the first mold and two-dimensional shape data of the second portion molded by the second mold, with the first and second portions including each of a plurality of counterweights of the crankshaft material and excluding axial parts of the crankshaft material.

3. The method of determining a center hole of a crankshaft according to claim 1 , wherein

the obtaining of the first and second shape data includes obtaining the first and second shape data in at least four axial positions of the crankshaft material.

4. The method of determining a center hole of a crankshaft according to claim 1 , wherein

the computing of the first misalignment amount includes using a method of least squares to move and/or rotate the first designed data to a first position where the first designed data is most approximate to the first shape data,

the computing of the second misalignment amount includes using a method of least squares to move and/or rotate the second designed data to a second position where the second designed data is most approximate to the second shape data,

the first revised designed data corresponds to the first position, and

the second revised designed data corresponds to the second position.

5. The method of determining a center hole of a crankshaft according to claim 1 , wherein

the adjusting of the data includes,

when an overlapped section exists between the first portion and the second portion, removing data corresponding to the overlapped section to produce the actual shape data, and

when the first portion and the second portion are separated from each other with a gap, interpolating data into the gap to reproduce the actual shape data.

6. The method of determining a center hole of a crankshaft according to claim 1 , wherein

determining of the position of the center hole includes calculating a center line of inertia based on the actual shape data where products of inertia about the center line are zero.

7. The method according to claim 1 , further comprising

using a center hole boring machine to bore the center hole at the determined position.

8. A device adapted to determine a position of a center hole of a material crankshaft that is obtained through molding with a first mold and a second mold, the device comprising:

a shape measuring machine configured to detect shape data of the material crankshaft; and

a computer, the computer including

a shape data obtaining section configured to obtain first shape data of a first portion of the material crankshaft molded by the first mold by measuring the first portion, and obtain second shape data of a second portion of the material crankshaft molded by the second mold by measuring the second portion;

a misalignment amount computing section configured to compare the first and second shape data respectively with first and second designed data corresponding to the first and second molds, respectively, to compute a first misalignment amount of the first portion and a second misalignment amount of the second portion due to misalignment between the first mold and the second mold, and to obtain first revised designed data and second revised designed data based on the first and second misalignment amounts;

an actual shape data reproducing section configured to adjust, based on the misalignment amount, data corresponding to the misalignment amount so as to reproduce actual shape data; and

a center hole determining section configured to determine, based on the actual shape data, the position of the center hole in the material crankshaft such that a rotation balance of the material crankshaft is within a predetermined range.

9. The device according to claim 8 , further comprising

a center hole boring machine operatively coupled to the computer and configured to bore the center hole at the position determined by the center hole determining section.

10. The device according to claim 8 , wherein

the misalignment amount computed by the misalignment amount computing section corresponds to misalignment between the first mold and the second mold in at least one of an axial direction of the material crankshaft, a transverse direction of the material crankshaft, and a mold closing/opening direction.