Measuring tool, encoder and producing method of encoder

Details Measuring tool, encoder and producing method of encoder Measuring tool, encoder and producing method of encoder

2003-05-19

2004-12-28

Bennett, G. Bradley (Department: 2859)

Geometrical instruments

Distance measuring

Scale reading position sensor

C033S784000

Reexamination Certificate

active

06834439

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a measuring tool, an encoder used for the measuring tool and a producing method of the encoder.
2. Description of Related Art
Various measuring tools for measuring distance, length and angle have been conventionally known. For instance, a caliper gauge is used as a measuring tool for measuring length. A caliper gauge has a main beam having a first measuring jaw, and a slider capable of slide movement along the longitudinal direction of the main beam and having a second measuring jaw to be in contact with a workpiece together with the first measuring jaw.
Maintaining measurement accuracy for a long time is of great importance for such a caliper gauge, and the main beam and the slider may preferably be made of material capable of minute processing and enduring repeated slide movement. Accordingly, the main beam and the slider of a caliper gauge are made of anti-frictional thermally treated metal having low linear expansivity such as stainless.
However, great amount of time and cost are required for machining metal down into a desired shape. In order to obtain good slidability between the main beam and the slider, the slide surface of the main beam and the slider has to be accurately machined by lapping etc. Such machining is also required for accurate measuring tool other than a caliper gauge. Since such measuring tool experiences many accurate processing during production process, the production line becomes complicated and production cost can be increased.
In order to maintain the measurement accuracy, linear expansion has to be kept within a predetermined range. In a general measuring tool, the error caused by the linear expansion is restrained by maintaining the temperature during measurement at twenty degrees Celsius, for instance. However, the measurement error by the linear expansion inevitably occurs in a severe measuring environment under hot and low temperature.
Further, when the measuring tool is grasped by hand, different linear expansion occurs on account of different temperature distribution by hand, which results in measurement error.
Further, a measuring tool having a slide mechanism such as a caliper gauge is likely to be worn after repeated use. Lubricant has to be used for reducing friction to maintain smooth slide movement, which is likely to cause adhesion of dust etc.
Digital measuring tool such as digital caliper gauge and digital micrometer has an encoder for detecting the movement of the movable member relative to the fixed member between the slide surface of the main beam and the slider.
As shown in
FIG. 13
, the encoder has a main scale
15
having an electrode pattern in which an electro-conductive portion
141
and an insulative portion
142
are alternately arranged along the longitudinal direction of a main beam
11
at a predetermined pitch, and a detector head
125
provided on a slider
12
to be electrostatically coupled with the main scale
15
to detect relative movement of the slider relative to the main beam.
The main scale
15
has an insulator
161
such as glass and polycarbonate and the electro-conductive portion
141
provided on the surface of the insulator
161
at a predetermined pitch. The insulator
161
is fixed (i.e. adhered) on the main beam
11
through a bonding layer
162
.
The detected value of the detector head
125
is outputted to an electric circuit
126
to be arithmetically processed and displayed on a non-illustrated display as a measurement value.
However, since the main scale
15
is bonded on the main beam
11
, the main scale
15
may be curved or the main scale
15
may be peeled off from the main beam
11
, which can result in error in the detected value.
Further, linear expansion of the main scale
15
and uneven heat distribution by the heat of hand also occur as in a normal measuring tool.
The above problem is not restricted to a digital caliper gauge but also occurs in a measuring tool having an encoder for detecting relative movement of a movable component relative to a fixed component such as a digital micrometer and a digital dial gauge.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a measuring tool which has high performance and can be easily produced, thus overcoming the conventional problem.
In order to attain an object of the present invention, a measuring tool according to an aspect of the present invention has a component at least a part of which is formed by a synthetic resin containing a nanoscale compound.
The measuring tool refers to a tool for measuring physical quantity such as length, distance and angle, which may be a caliper gauge, micrometer, a dial gauge etc. The component refers to a member constructing the measuring tool such as a main beam of a caliper gauge, a frame and a spindle of a micrometer, and a case body, a gear and a spindle of a dial gauge etc.
Though synthetic resin in general is fragile and has great linear expansion coefficient, advantages such as enhancement in rigidity, restrained linear expansion, improvement in anti-frictional properties, decrease in friction coefficient, improvement in thermal conductivity, and application of electro-conductivity or insulative performance can be obtained by adding nanoscale compound (e.g. carbon nanofiber) into base material of synthetic resin (e.g. polystyrene) and defining various conditions. It is not precisely clear why such advantages can be obtained, but it is thought that such advantages are based on a network of the nanoscale compound within the synthetic resin.
Accordingly, since the linear expansion coefficient can be reduced in a measuring tool having a component made of synthetic resin containing nanoscale compound such as a caliper gauge having a main beam and a slider composed of synthetic resin containing nanoscale compound, error on account of linear expansion can be eliminated and an accurate measurement can be conducted. When the linear expansion coefficient is low, accurate measurement is possible without being influenced by measurement temperature under severe condition of high and low temperature.
Since the anti-frictional properties can be improved, no abrasion is caused on the measuring tool after repeated use, thereby maintaining measurement accuracy.
Since the friction coefficient is low, excellent slidability can be obtained and slide mechanism can be used without lubricant, thus preventing stain or dust on the measuring tool.
Since excellent thermal conductivity can be obtained, heat of hand instantaneously disperses even when the measuring tool is grasped for measurement, so that partial expansion difference can be eliminated. Accordingly, measurement error on account of hand heat can be eliminated for a hand-tool type measuring tool which is grasped in use, thus enabling accurate measurement.
Since the rigidity is enhanced, the deformation of the measurement tool can be restrained. Especially, the deformation caused by pressing force applied on a measuring tool which sandwiches a workpiece for measurement such as a caliper gauge and a micrometer can be restrained, thus enhancing measurement accuracy.
Since the rigidity is enhanced, the thickness and size of the component can be reduced while maintaining a predetermined strength.
Since the measuring tool is made of synthetic resin, the weight of the measuring tool can be reduced. Further, since synthetic resin is used, the measuring tool is more easily fitted to hand than metal without causing metal allergy.
The component at least a part of which is made of synthetic resin containing nanoscale compound may preferably be formed by injection-molding.
When the synthetic resin containing nanoscale compound is injection-molded, no machining is necessary and the measuring tool can be easily produced. Accordingly, production line and production process can be simplified and production cost can be lowered. Since the synthetic resin containing nanoscale compound has excellent moldability and pattern transferability, accurate components can be

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