Noncontact surface shape measuring method and apparatus thereof
Even if a return beam from a work to be measured does not agree with the center of a two-piece sensor, a correction value is calculated according to a voltage difference between two sensors of the two-piece sensor if the voltage difference is within a neighborhood range. The correction value is added to an actual position of an objective lens in an up-down direction, to calculate a movement amount of the objective lens up to a focused state (a state in which the return beam agrees with the center of the two-piece sensor).
1. A noncontact surface shape measuring method for carrying out autofocusing control by way of a laser probe in an up-down direction with respect to a surface of a work, continuously scanning the work in a horizontal direction, and measuring a surface shape of the work according to a displacement amount in the up-down direction of an objective lens in an autofocusing optical system that is controlled so that a return beam of the laser probe is received at the center of a two-piece sensor, the noncontact surface shape measuring method comprising:
detecting a voltage difference between two sensors of the two-piece sensor and detecting whether or not the detected voltage difference is within a neighborhood range in which a voltage difference is substantially proportional to a displacement from an in-focus position;
calculating, if the detected voltage difference is within the neighborhood range, a correction value for a position of an objective lens in the up-down direction with respect to the in-focus position; and
adding the correction value to an actual position of the objective lens in the up-down direction, to calculate a movement amount of the objective lens in the up-down direction.
2. The noncontact surface shape measuring method according to claim 1 , wherein if the detected voltage difference is not in the neighborhood range, the continuous scanning in the horizontal direction is stopped until the voltage difference comes within the neighborhood range.
3. The noncontact surface shape measuring method according to claim 1 , wherein the neighborhood range is expanded to a range in which the two-piece sensor is able to detect a potential difference and a detected potential difference is nonlinear with respect to a displacement from the in-focus position.
4. A noncontact surface shape measuring apparatus for carrying out autofocusing control of a laser probe in an up-down direction with respect to a surface of a work to be measured and measuring a surface shape of the work according to a displacement amount in the up-down direction of an objective lens in an autofocusing optical system, comprising:
a scanner configured to continuously scan the work in a direction that is horizontal with respect to an optical axis of the objective lens; and
a controller configured to control a movement amount of the objective lens in the up-down direction so that a return beam of the laser probe is received at the center of the two-piece sensor, wherein the controller:
detects a voltage difference between two sensors of a two-piece sensor and detects whether or not the detected voltage difference is within a neighborhood range in which a voltage difference is related to a displacement from an in-focus position;
calculates, if the detected voltage difference is within the neighborhood range, a correction value for a position of an objective lens in the up-down direction with respect to the in-focus position; and
adds the correction value to an actual position of the objective lens in the up-down direction, to calculate a displacement amount of the objective lens in the up-down direction.
5. The noncontact surface shape measuring apparatus according to claim 4 , wherein the neighborhood range is a range in which a detected potential difference has a linear relationship with respect to a displacement from the in-focus position.
6. The noncontact surface shape measuring apparatus according to claim 4 , wherein if the detected voltage difference is not in the neighborhood range, the continuous scanning in the horizontal direction is stopped until the voltage difference comes in the neighborhood range.
7. The noncontact surface shape measuring method according to claim 2 , wherein the neighborhood range is expanded to a range in which the two-piece sensor is able to detect a potential difference and a detected potential difference is nonlinear with respect to a displacement from the in-focus position.
8. The noncontact surface shape measuring apparatus according to claim 5 , wherein if the detected voltage difference is not in the neighborhood range, the continuous scanning in the horizontal direction is stopped until the voltage difference comes in the neighborhood range.