1. Field of the Invention
The present invention relates to a load cell-type electronic balance, and more particularly to a load cell-type electronic balance formed by attaching a plurality of strain gauges on an elastomer.
2. Description of Related Art
In the current load cell-type electronic balance, the following measures are taken to deal with the creep phenomenon: preparing a plurality of strain gauges with slightly different patterns, and particularly, preparing a plurality of strain gauges with different tab ratios; measuring the creep, and meanwhile, changing any one of four strain gauges or changing all the strain gauges into different patterns, so as to seek for an optimal combination of the strain gauges.
In the strain gauge-type load cell, a plurality of strain gauges is generally attached on an elastomer that is elastically deformed due the effects of a load, so as to form a Wheatstone bridge by the strain gauges, and an output of the Wheatstone bridge serves as a detecting output for the magnitude of the load applied to the elastomer.
In the above configuration, any one of the pillars 11 and 12 is fixed, for example, the pillar 11 is fixed. When the load is applied to the other pillar 12, the resistance of each of the strain gauges S1-S4 is changed due to the elastic deformation of each flexible part; thus, a voltage signal in proportion to the load is generated from the output end V of the Wheatstone bridge.
The load cell is used as, for example, a load unit for an electronic balance. When it is required to detect the load correctly, the creep phenomenon that the measurement values shown in
The current load cell has the following problems. In order to adjust the creep, not only the preparation of a plurality of strain gauges is required, it is also time consuming and labor intensive for determining the optimal combination of strain gauges.
Moreover, it is substantially difficult to adjust the creep phenomenon after the strain gauges are adhered. Therefore, when the strain gauges are used as load sensors for an electronic balance, the high resolution of the electronic balance becomes a problem. Furthermore, the following problem also exists, i.e., a cell for correcting the non-uniformity between the creeps of the same electronic balance does not exist. For example, in Japanese Patent Publication No. 2003-322571, a load cell is disclosed for solving the problems. As shown in
Patent document 1: Japanese Patent Publication No. 2003-322571
The current load cell-type electronic balance is formed through the manners described above, in which the creep characteristics will be greatly changed due to the environment in which the electronic balance is being used, particularly, due to temperature and humidity. Therefore, if the load cell-type electronic balance is formed through the following two methods, it is difficult to eliminate the creep error in all the environments in which the electronic balance is being used, and one method includes: preparing a plurality of strain gauges with slightly different tab ratios, and measuring the creep, and meanwhile, changing one of the strain gauges S1-S4 or changing all the strain gauges into different patterns, so as to seek for an optimal combination of the strain gauges; and the other method includes forming a plurality of Wheatstone bridges by attaching a plurality of strain gauges S1-S8 on an elastomer. The subject of the present invention is to reduce the creep error in accord with the using environment of the electronic balance. The present invention is developed in view of the above content and aims at providing a load cell-type electronic balance that is capable of reducing the creep error regardless of the using environment of the electronic balance.
Accordingly, the present invention is directed to a load cell-type electronic balance. In the load cell-type electronic balance of the present invention, a load cell formed by attaching a plurality of strain gauges on an elastomer serves as a load detection section, and includes: a creep storage unit, for measuring a creep corresponding to a magnitude and a load time of a load on a tray in a using environment and storing the creep measurement data; and a creep correction calculation/storage unit, for calculating a creep correction in the using environment according to the creep measurement data and storing the creep correction data, and then adding the measured load with the creep correction so as to correct a creep error.
Furthermore, the load cell-type electronic balance of the present invention includes a built-in weight, a weight changing device for increasing or reducing the built-in weight, and a control section for controlling the weight changing device, to apply the built-in weight in a predetermined time, so as to correct a creep error. The load cell-type electronic balance of the present invention is formed in said manner above and can reduce the creep error in the using environments.
The load cell-type electronic balance of the present invention stores the creep characteristics in a certain environment in which the electronic balance is used, and performs a correction calculation process; thus, the creep characteristics corresponding to the temperature and humidity in the using environment can be properly corrected.
In order to make the aforementioned and other objects, features, and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
The load cell-type electronic balance of the present invention has the following characteristics. The first characteristic of the load cell-type electronic balance lies in that a load cell formed by attaching a plurality of strain gauges on an elastomer serves as a load detection section, and the load cell-type electronic balance includes: a creep storage unit, for measuring a creep corresponding to a magnitude and a load time of a load on a tray in a using environment and storing the creep measurement data; and a creep correction calculation/storage unit, for calculating a creep correction in the using environment according to the creep measurement data, and storing the creep correction data, and adding the measured load with the creep correction so as to correct a creep error. The second characteristic of the load cell-type electronic balance lies in that a built-in weight, a weight changing device for increasing or reducing the built-in weight, and a control section for controlling the weight changing device are included to apply the built-in weight in a predetermined time, so as to correct the creep error. Therefore, the basic structure of the most preferred implementation aspect has both the first and second characteristics.
Hereinafter, the load cell-type electronic balance of the present invention is illustrated in detail below with reference to the following embodiments.
The calculation/control section 3 is formed by taking a microcomputer as a main body, which includes a central processing unit (CPU) 31, a read only memory (ROM) 32, a random access memory (RAM) 33, an interface 34, and an input device 35 with a creep correction key 35a, wherein the creep correction key 35a is used for inputting to correct the creep error. A general measurement and display program is written into the ROM 32, and additionally, a temperature correcting program and a creep correcting program are also written therein. The temperature correcting program is used to obtain a correction value that is used to eliminate the load detection error caused by the difference between the reference temperature and the detection temperature T; and the creep correcting program is used to obtain the following creep characteristics and to correct the creep. Furthermore, the RAM 33 has a region or working region for storing the digital conversion data from the load detection circuit 1b, and further has a region for storing the creep correction formula obtained by the creep correcting program.
Next, the load W1 on the tray and the corrected value ±ΔW1 are added and converted into a load W on the tray (S5). A series of processing is performed during each sample period A till the time duration t lasted from the very beginning reaches a total time B. The total time B is predetermined to be a time at which the load W on the tray becomes stable. As a result, the creep characteristics shown as black dots in
Y(t)=Wb−C(t) (1).
Furthermore, Wb indicates a load on the tray at time B.
w=w1±ΔW1(w1/W1) (2).
Next, after reading the creep correction formula Y(t) from the RAM 33, the creep correction value Y(t) (w1/W1) is calculated, and then the creep correction value Y(t) (w1/W1) and the load on the tray w are added and converted into a load on the tray wo shown by the formula (3) (S13). Then, the load w0 on the tray is multiplied by a weight conversion coefficient, and the weight measurement value is displayed on the display 6 (S14).
wo=w+Y(t)(w1/W1) (3).
The load cell-type electronic balance of the present invention obtains the creep characteristics in proportion to the magnitude and the load time of the load, converts the creep characteristics into a time function and derives a creep correction formula, and then corrects the creep characteristics by using the correction formula. The load cell-type electronic balance of the present invention is not limited to those described in the embodiments. For example, a plurality of lines can be used to approximate the time function. Additionally, the correction weight can also be used as the built-in weight 8.
The present invention is applicable for a high-precision electronic balance, in which the creep characteristics influenced by temperature and humidity cannot be ignored.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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2005-166895 | Jun 2005 | JP | national |
This application claims the priority benefit of PCT application serial no. PCT/JP2006/311311, filed on Jun. 6, 2006, and which claims Japanese patent application no. 2005-166895, filed Apr. 25, 2005. The entirety of each of the above-mentioned patent applications is incorporated herein by reference and made a part of this specification.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2006/311311 | 6/6/2006 | WO | 00 | 11/12/2007 |