Geometrical instruments – Distance measuring – Opposed contacts
Reexamination Certificate
1998-12-22
2001-01-30
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Distance measuring
Opposed contacts
C033S703000, C033S704000, C033S815000
Reexamination Certificate
active
06178658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micrometer. More specifically, the present invention relates to a micrometer of which frame deformation in accordance with temperature change in using environment can be restrained as small as possible.
2. Description of Related Art
Conventionally, as shown in
FIG. 3
, an ordinary micrometer has a U-shaped frame
1
, an anvil installed on one end of the frame
1
, a feeding mechanism
3
(ordinarily, such as a feed screw) installed on the other end of the frame
1
and a spindle
4
to move forward and backward to the anvil
2
.
The micrometer is ideally fixed to a stand or the like under an environment of a standard temperature (20° C., for example) in measuring a workpiece. However, the micrometer is often used under environments outside the standard temperature being held by hand. In other words, while holding the frame by one hand, the spindle
4
is advanced to the anvil
2
by handling the feeding mechanism
3
to hold the workpiece W between the spindle
4
and the anvil
2
. At this state, the moving displacement amount of the spindle
4
is read from the scale (or graduation)
5
.
When the micrometer is held by hand under an environment outside the standard temperature, the frame
1
is thermally deformed and the spindle is stretched or contracted by the circumambient temperature and heat of the hand, thereby deteriorating measurement accuracy.
As an instant case, the micrometer is held by one hand under an environment lower than the standard temperature. When the micrometer is thermally stabilized in advance to adjust the mechanical origin under an environment of standard temperature, the frame
1
has a configuration shown in double-dotted line in FIG.
4
.
When a U-shaped bent portion
6
is held by hand to measure the workpiece, a temperature distribution of the frame
1
is changed to deform the frame
1
as shown in a solid line in
FIG. 4
, causing a frame deformation error of &Dgr;x. Furthermore, the spindle
4
is contracted to cause additional error to magnify an entire error.
To solve above disadvantage, a material having an extremely small linear thermal expansion coefficient may be employed to both of the frame
1
and the spindle
4
. However, it is not practical in view of production cost or the like.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a micrometer adapted to maintain measurement accuracy under an environment of widely changing temperature and to enhance usability, while being manufactured economically.
A micrometer according to the present invention has a frame having a U-shaped configuration; an anvil provided on an end of the frame; and a spindle provided on the other end of the frame to advance and retract relative to the anvil. The micrometer is characterized in that the frame is made of a material of which a linear thermal expansion coefficient is smaller at an inside of the U-shaped configuration than an outside thereof.
According to the above arrangement, since the inside of the U-shaped configuration of the frame has a smaller linear thermal expansion coefficient than the outside thereof, a displacement amount of an end of the frame relative to the other end can be decreased as compared to a conventional micrometer by virtue of a “bimetal effect” (thermal deformation effect like a bimetal).
In other words, when a distribution of temperature applied to the frame is changed, for example, when the temperature of the frame is lowered below a standard temperature, the inside of the U-shaped configuration is less contracted than the outside of the U-shaped configuration. Accordingly, a frame deformation to make one end of the frame approach the other end is decreased so that an error caused by the deformation of the frame is made smaller than the conventional micrometer.
When the temperature of the frame is raised higher than the standard temperature, the inside of the U-shaped configuration is less stretched than the outside of the U-shaped configuration. Accordingly, a deformation which causes one end of the frame to move away from the other end is restrained to make the error caused by the deformation of the frame smaller than the conventional micrometer.
Accordingly, measurement accuracy of the micrometer can be maintained under a widely changing temperature to allow freer usage. Furthermore, since the frame is not required to be made of an extremely small linear thermal expansion coefficient, the micrometer can be manufactured economically.
In the above arrangement, to make the linear thermal expansion coefficient of the inside of the U-shaped configuration smaller than the outside, the frame is preferably made as follows.
The frame preferably includes an outer member disposed on the outside of the U-shaped configuration and an inner member unitedly provided on an inner surface of the outer member, the inner member being made of a material having a smaller linear thermal expansion coefficient than the outer member.
Accordingly, the outer member and the inner member can be separately made of a material having a different linear thermal expansion coefficient, e.g. cast iron and alumina ceramics, to be integrally connected, for example, bonded. Accordingly, the micrometer can be manufactured economically.
Another member having an intermediate linear thermal expansion coefficient may be sandwiched between the outer member and the inner member to make multi-layered structure of more than two layers.
Alternatively, the frame may be made of a material of which the linear thermal expansion coefficient gradually decreases from the outside of the U-shaped configuration to the inside thereof. In the above, the frame may be made of a material comprising zirconium oxide and nickel of which a mixing ratio varies gradually from the outside of the U-shaped configuration to the inside thereof, for example. The linear thermal expansion coefficient may be inclined to change consecutively, or alternatively, may be changed step-wise at an optional phase.
Accordingly, since no attaching of the outer member and the inner member is necessary, the manufacture can be simplified.
In the above arrangement, the spindle is preferably made of a material of a smaller linear thermal expansion coefficient than the material of the frame such as Invar of which the linear thermal expansion coefficient is approximately 1.2×10
−6
/° C.
Accordingly, an error caused by a stretch and a contraction of the spindle due to temperature change can also be diminished, so that the measurement accuracy can be maintained over more widely changing temperature to improve usability.
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Bennett G. Bradley
Mitutoyo Corporation
Oliff & Berridg,e PLC
Verbitsky Gail
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