US 2013/0271995 A1Published application

Autofocus mechanism

AssigneeMitutoyo Corporation

InventorShohei Udo

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Abstract

A computation & control unit defines, as first and second voltages, A+B_signal voltages at distances which give the maximum and minimum voltages of an S_signal voltage, respectively. The unit further defines the higher one of the first and second voltages as an S_signal validity determination voltage and defines a distance at which the S_signal voltage takes on an in-focus determination voltage. The unit defines first and second lower limit voltages, defines the higher one of the first and second lower limit voltages as a lower limit voltage, and defines, as an upper limit voltage, an A+B_signal voltage at a distance which gives an in-focus determination voltage between the maximum and minimum positions of the S_signal voltage. An input and output unit outputs the upper and lower limit voltages as the upper and lower limit values of a settable range of the S_signal validity determination voltage.

Claims6

Dependent claims

An autofocus mechanism, comprising:

an objective lens that collects a laser beam to irradiate a measurement workpiece therewith;
a beam splitter that splits light reflected from the measurement workpiece through the objective lens;
a first light amount restricting element disposed in front of a focal position of one split beam of the reflected light;
a first light-receiving element that receives the reflected beam having passed through the first light amount restricting element;
a second light amount restricting element disposed behind a focal position of the other split beam of the reflected light;
a second light-receiving element that receives the reflected beam having passed through the second light amount restricting element;
and
a processing unit that converts signals output from the first and second light-receiving elements into an A_signal voltage and a B_signal voltage, respectively, so as to determine an A+B_signal voltage and an S_signal voltage, which are expressed by Equations (1) and (2) below, wherein
the processing unit includes:
first & second voltage computing means that defines, as a first voltage and a second voltage, A+B_signal voltages at distances between the objective lens and the measurement workpiece, the first voltage and the second voltage being indicative of the maximum voltage and the minimum voltage of the S_signal voltage, respectively;
S_signal validity determination voltage computing means that defines a higher one of the first voltage and the second voltage as an S_signal validity determination voltage serving as a threshold voltage which determines, as valid, an in-focus determination voltage, the in-focus determination voltage being equal to the S_signal voltage obtained when the distance is equal to a focal distance of the objective lens;
and
focal distance computing means that defines, as the focal distance of the objective lens, a distance at which the S_signal voltage takes on the in-focus determination voltage, the distance being given by the A+B_signal voltage equal to or greater than the S_signal validity determination voltage,
A
+
B_signal


voltage
=
A_signal


voltage
+
B_signal


voltage
,
(
1
)
S_signal


voltage
=
(
A_signal


voltage
-
B_signal


voltage
)
(
A_signal


voltage
+
B_signal


voltage
)
.
(
2
)

61 more elements

An autofocus mechanism, comprising:

an objective lens that collects a laser beam to irradiate a measurement workpiece therewith;
a beam splitter that splits light reflected from the measurement workpiece through the objective lens;
a first light amount restricting element disposed in front of a focal position of one split beam of the reflected light;
a first light-receiving element that receives the reflected beam having passed through the first light amount restricting element;
a second light amount restricting element disposed behind a focal position of the other split beam of the reflected light;
a second light-receiving element that receives the reflected beam having passed through the second light amount restricting element;
and
a processing unit that converts signals output from the first and second light-receiving elements into an A_signal voltage and a B_signal voltage, respectively, so as to determine an A+B_signal voltage and an S_signal voltage, which are expressed by Equations (1) and (2) below, wherein
the processing unit including:
first lower limit voltage computing means that defines a first lower limit voltage so as to reduce a distance between the objective lens and the measurement workpiece from a maximum position indicative of a maximum voltage of the S_signal voltage, the first lower limit voltage being defined as the A+B_signal voltage at a distance at which the sum of an in-focus determination voltage and an allowable voltage is the S_signal voltage, the in-focus determination voltage being the S_signal voltage obtained when the distance is equal to the focal distance of the objective lens, the allowable voltage being set to be less than a voltage obtained by subtracting the in-focus determination voltage from the maximum voltage;
second lower limit voltage computing means that defines a second lower limit voltage so as to increase the distance from a minimum position indicative of a minimum voltage of the S_signal voltage, the second lower limit voltage being defined as the A+B_signal voltage at the distance at which a difference between the in-focus determination voltage and the allowable voltage is equal to the S_signal voltage;
lower limit voltage computing means that defines a higher one of the first and second lower limit voltages as a lower limit voltage;
upper limit voltage computing means that defines, as an upper limit voltage, the A+B_signal voltage at the distance which gives the in-focus determination voltage between the maximum position and the minimum position of the S_signal voltage;
and
output means that outputs the upper limit voltage and the lower limit voltage as an upper limit value and a lower limit value of a settable range of an S_signal validity determination voltage, the S_signal validity determination voltage being a threshold voltage for determining, as valid, the in-focus determination voltage at the distance at which a voltage obtained by subtracting itself from the A+B_signal voltage is equal to or greater than zero,
A
+
B_signal


voltage
=
A_signal


voltage
+
B_signal


voltage
,
(
1
)
S_signal


voltage
=
(
A_signal


voltage
-
B_signal


voltage
)
(
A_signal


voltage
+
B_signal


voltage
)
.
(
2
)

63 more elements

Dependencies are inferred from the claim text.