Measuring and testing – Dynamometers – Responsive to force
Reexamination Certificate
1997-12-02
2001-01-16
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Dynamometers
Responsive to force
Reexamination Certificate
active
06173619
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a load detecting apparatus using a load cell type load detector (hereinafter simply referred to as “load cell”), and more particularly to a load detecting apparatus using a load cell in which the temperature compensation is effected for variations of a zero point of the load cell caused by temperature changes.
(2) Description of the Related Art
It has been known that, in a load detecting apparatus using a load cell, the zero point of the load cell varies depending on the temperature changes of the load cell itself caused by changes in an environment temperature. For the compensation of the variations of the zero point caused by the temperature changes, a prior art disclosure is found in each of Japanese Patent Application Kokai Publication No. Sho 54-55474 and Japanese Patent Application Kokai Publication No. Hei 1-152317.
The method with which the measured value is compensated by taking the temperature changes into consideration has a problem in that the method is very complicated. Also, the method in which the influence from temperature changes is attempted to be reduced by adding such an element as a temperature compensation element to a circuit such as a bridge circuit has a problem in that, when there is a large extent of temperature changes, the temperature compensation of the measured values to within a limited value not only involves technical difficulties but also complicates the circuit concerned, thus increasing the cost involved.
The Japanese Patent Application Kokai Publication No. Sho 54-55474 discloses a technique which, with a comparatively simple arrangement and with an object of ensuring to overcome the influence of temperature changes, attempts to maintain a constant temperature of a load cell by providing heat sources and heat sensitive elements in the neighborhood of the periphery of a case of the load cell and controlling temperatures of the heat sources by the heat sensitive elements.
In the arrangement disclosed in the Japanese Patent Application Kokai Publication No. Hei 1-152317 and shown in
FIG. 1
, the load cell
22
supported on the mounting base is covered by a cover
20
and there are provided a plurality of air conditioning means
21
for adjusting the temperature in the spaces formed by the cover
20
and a plurality of temperature measuring elements
23
for measuring the temperatures of the load cell
22
, the mounting base, etc. This technique disclosed in the Japanese Patent Application Kokai Publication No. Hei 1-152317 attempts to realize a load detecting apparatus with which errors caused by a temperature drift is reduced by controlling the air conditioning means
21
such that the respective temperatures measured by the temperature measuring elements
23
become constant. This technique is to prevent the changes in the voltages outputted from the load cell which occur when the temperatures of the load cell are changed in the state wherein the constant load is being applied. The arrangement disclosed in the Japanese Patent Application Kokai Publication No. Hei 1-152317 attempts to prevent the temperature drift by maintaining a constant temperature higher than environment temperature changes in order to eliminate the influence of such environment temperature changes.
In both the above prior art techniques, it is attempted to compensate the changes in the measured values due to the temperature changes by controlling the temperatures of the load cell, and it is made possible to make the compensation only by the temperature control so that the compensation in this way is simpler than the compensation of the measured values themselves as practiced before.
However, in the arrangement disclosed in the Japanese Patent Application Kokai Publication No. Sho 54-55474, it is necessary that the load cell and the strain element which serves as a detecting element for the load cell be positioned in the space surrounded by an outer case, thermal insulating materials, etc. Also, in the arrangement disclosed in the Japanese Patent Application Kokai Publication No. Hei 1-152317, in addition to the necessity to position the load cell in the space surrounded by the cover, it was necessary to provide the air conditioning means. This means that, for purposes of the temperature compensation, a specific load cell must be manufactured so that the cost is high and its use becomes limited. Thus, there was a demand for a temperature compensation technique which provides an arrangement in which a general use load cell can be used as it is and which does not require any special or added installation.
SUMMARY OF THE INVENTION
An object of the invention is to overcome the problems existing in the prior art, and to provide a method and apparatus for effecting temperature compensation in a load cell formed with a strain gauge attached to a deflectable body or a sensing element.
According to one aspect of the invention, there is provided a method for effecting temperature compensation in a load cell type load detector formed with a strain gauge attached to a deflectable body, the method comprising the steps of:
providing a pair of thermally conductive thermal source blocks so as to be directly in contact with the deflectable body and be disposed respectively at two symmetric metric positions with respect to a center of the deflectable able body; and
temperature-controlling a temperature of the deflectable able body by the thermal source blocks such that the temperature of the load cell type load detector is not affected by environment temperature changes and is maintained at a constant temperature.
According to a second aspect of the invention, there is provided an apparatus for effecting temperature compensation in a load cell type load detector in a load detecting apparatus having a mount base, a deflectable body provided on the mount base, a strain gauge attached to the deflectable body, and a load generating section for receiving a flow of objects to be measured, the apparatus for effecting temperature compensation comprising:
a pair of thermally conductive thermal source blocks provided so as to be directly in contact with the deflectable body with the thermal source blocks being disposed respectively at two symmetric positions with respect to a center of the deflectable body, and having thermal elements in or on the thermal source blocks; and
a pair of temperature sensors provided respectively to the thermal source blocks;
a control means for controlling the thermal elements based on temperatures detected by the temperature sensors such that a temperature of the load cell type load detector may be maintained at a predetermined constant temperature.
Where the thermal source blocks are positioned in symmetric positions with respect to a center portion of the strain gauge attached to the deflectable body of the load call, the deflectable body is heated or cooled by both the symmetrically positioned thermal source blocks so that, because of the internal thermal conduction within the deflectable body, the temperature of the overall load cell, particularly that of the deflectable body having the strain gauge at its center portion, can always be controlled to a constant temperature. Also, by providing the thermal source blocks respectively between load generating portions such as between the deflectable body and a load cell mounting portion and between the deflectable body and a hopper, the thermal conduction (heat radiation) from the deflectable body is only to the ambient air so that no unbalanced heat radiation develops. Because the balance is attained between the heating or cooling by thermal source blocks provided in the symmetric positions and the heat radiation of the heat to the ambient air between the thermal source blocks, it is made possible to control the temperature of the overall load cell to a constant temperature and to provide an apparatus which is easy to handle and low cost.
REFERENCES:
patent: 4198868 (1980-04-01), Runyan
patent: 4365520 (1982-12-01), Zaghi
patent
Maeda Hiroki
Satake Satoru
Fish & Richardson PC
Fuller Benjamin R.
Satake Corporation
Thompson Jewel V.
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