Weighing scales – Computer – Electrical
Reexamination Certificate
1998-10-05
2001-08-07
Gibson, Randy W. (Department: 2859)
Weighing scales
Computer
Electrical
C177S025180, C177S185000, C702S101000, C702S085000
Reexamination Certificate
active
06271484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a weighing apparatus for measuring the weight of articles to be weighed and, more particularly, to the adjustment of a filter used in the weighing apparatus for removing a vibratory component contained in a weight signal.
2. Description of the Prior Art
Of the weighing apparatuses for measuring the weight of articles to be weighed, a combination weighing apparatus is known in which a combination calculation of respective weights of the articles to be weighed which have been supplied into a plurality of weighing hoppers is performed to provide a product having a predetermined weight. In this combination weighing apparatus, since the natural vibration peculiar to a weighing mechanism itself having an associated weighing hopper and an external vibration brought about mainly by vibration of the floor tend to be imposed as a vibration component on a weight signal outputted from each of the weighing hoppers, the use of a filter (a low-pass filter) in association with each of the weighing hoppers is necessitated to remove the vibration component to secure a weighing accuracy. In general, the frequency of the natural vibration is higher than that of the external vibration.
The filter of the kind described above is of a nature that once the filter constant determinative of the filter characteristics (cut-off frequency and/or damping characteristic) is determined, a filter response time can be fixed. In other words, if the capability of damping vibrations is increased by lowering the cut-off frequency, the response time can be increased, but if the capability of damping vibrations is lowered by increasing the cut-off frequency, the response time can be reduced. In view of this, the filter that can be employed in the weighing apparatus of the kind referred to above is required to be of a type having such a filter characteristic capable of damping the vibration component down to a level which will no longer affect the weighing accuracy and also having a short response time.
However, since the vibration component of the weight signal varies depending on weighing conditions of the weighing apparatus and/or conditions under which the weighing apparatus is installed, the solution hitherto taken is to install the weighing apparatus at a site of installation, to conduct a series of tests through trial and error with the filter characteristic being varied while articles to be weighed are actually supplied into the weighing apparatus and finally to select one of filters which has a vibration damping capability effective to secure the weighing accuracy and also having a short filter response time. Accordingly, an adjustment of the filter was a time-consuming work. Since the combination weighing apparatus requires the use of a plurality of weighing mechanisms, adjustment of the filter is required for each of the weighing mechanisms, resulting in extremely timeconsuming and complicated procedures.
SUMMARY OF THE INVENTION
The present invention has been devised to substantially eliminate the above discussed problems and is intended to provide an improved weighing apparatus having an automatic filter adjusting capability, which is effective to secure a weighing accuracy and wherein the filter characteristic of the filter having a short response time can be adjusted in a short time.
In order to accomplish this object, one aspect of the present invention provides a weighing apparatus having an automatic filter adjusting capability which comprises a weighing cell for outputting a weight signal indicative of a weight of an article to be weighed which has been loaded thereon, a variable filter having a predetermined filter characteristic, for filtering the weight signal to provide a filtered weight signal, and a filter adjusting device for adjusting the filter characteristic of the variable filter to the predetermined filter characteristic. The filter adjusting device includes a vibration component detecting means for detecting a vibration component from the filtered weight signal, a level setting means for setting a permissible level of the vibration component of the filtered weight signal, a comparator for comparing the vibration component of the filtered weight signal with the permissible level, and a filter characteristic changing means operable based on a result of comparison performed by the comparator to adjust the filter characteristic of the variable filter to allow the vibration component to attain a magnitude approximating to the permissible level, but not exceeding the permissible level.
With this weighing apparatus, the filter characteristic is automatically adjusted, based on a result of comparison of the vibration component of the filtered weight signal with a permissible level of the vibration components, so that the vibration component of the filtered weight signal can attain a value approximating to the permissible level, but not exceeding the permissible level. In this way, by damping the vibration component down to a value within the permissible level, the weighing accuracy can be secured and, on the other hand, by damping the vibration component down to a value approximating to the permissible level, the filter characteristic in which the response time is reduced as short as possible can be obtained quickly in a short time.
The present invention according to a second aspect thereof provides a combination weighing apparatus having an automatic filter adjusting capability, which comprises a plurality of weighing cells for outputting respective weight signals indicative of weights of articles to be weighed which have been loaded thereon, a variable filter having a predetermined filter characteristic, for filtering the weight signals to provide corresponding filtered weight signals, a combination calculating means for selecting a combination of the articles to be weighed based on the respective filtered weight signals outputted from the variable filter to thereby calculate the combination which is approximating to a target value within a predetermined allowance, a filter adjusting device for adjusting the filter characteristic of the variable filter to the predetermined filter characteristic. The filter adjusting device used therein includes a vibration component detecting means for detecting a vibration component from each of the filtered weight signals, a level setting means for setting a permissible level of the vibration component of each of the filtered weight signals, a comparator for comparing the vibration component of each of the filtered weight signals with the permissible level, and a filter characteristic changing means operable based on a result of comparison performed by the comparator to adjust the filter characteristic of the variable filter to allow the vibration component to attain a magnitude approximating to the permissible level, but not exceeding the permissible level.
With the combination weighing apparatus according to the second aspect of the present invention, the filter characteristic is automatically adjusted, based on a result of comparison of respective vibration components of filtered weight signals with a permissible level of the vibration components, so that the respective vibration components of the filtered weight signals can attain a value approximating to the permissible level, but not exceeding the permissible level. In this way, by damping the vibration components down to a value within the permissible level, the weighing accuracy can be secured and, on the other hand, by damping the vibration components down to a value approximating to the permissible level, the filter characteristic in which the response time is reduced as short as possible can be obtained quickly in a short time.
The present invention furthermore provides, in accordance with a third aspect thereof, a combination weighing apparatus having an automatic filter adjusting capability, which comprises a plurality of weighing cells for outputting respective weight signals indicative of weights
Gibson Randy W.
Ishida Co. Ltd.
Staas & Halsey , LLP
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