Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2000-09-28
2001-09-04
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S520000, C324S548000, C324S551000, C324S707000, C209S574000, C053S054000, C053S591000
Reexamination Certificate
active
06285193
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of measuring the insulation resistance of a capacitor and an apparatus for screening characteristics.
2. Description of the Related Art
In general, a capacitor is determined as good or defective by measuring the insulation resistance of the same. When a capacitor is not charged, the insulation resistance thereof can not be measured correctly because of the capacity of the capacitor. Under such circumstances, a method is commonly used wherein a DC voltage is first applied to the capacitor to precharge it and a leakage current (charging current) is measured thereafter to measure the insulation resistance of the capacitor. Obviously, a good part has a low leakage current.
Known conventional methods for measuring insulation resistance include the method of measurement defined in Japanese Industrial Standard JIS-C5102. However, since a current value must be measured on a capacitor which has been sufficiently charged according to this method, a charging time as long as approximately 60 sec. has been required. The need for electronic apparatuses at reduced cost and with improved reliability has resulted in a need for improvement on the production capacity and quality of electronic components such as capacitors. It is totally impossible to satisfy such a need using the conventional method of measurement that requires such a long charging time per capacitor.
It is therefore an object of the present invention to provide a method of measuring the insulation resistance of a capacitor wherein the insulation resistance of a capacitor can be quickly and accurately measured.
It is another object of the present invention to provide an apparatus for screening the characteristics of capacitors wherein a characteristics measuring step and a packing step can be linked to improve operational efficiency and to reduce the size and cost of the facility.
SUMMARY OF THE INVENTION
In order to achieve the above-described objects, according to a first aspect of the invention, there is provided the steps of: applying AC signals at two different frequencies to a capacitor to measure the impedance of the capacitor at each of the frequencies the frequency f
1
being higher than the frequency f
2
; obtaining series resistance Rs and capacity C of the capacitor from the impedance at the higher frequency; and obtaining insulation resistance Rp of the capacitor from the series resistance Rs, the capacity C and the impedance at the lower frequency.
The measurement of insulation resistance according to the prior art wherein a DC current is applied for a long time has encountered a phenomenon that the apparent capacitance is reduced depending on the type of the capacitor. For this reason, the prior art involves a thermal process referred to as “thermal recovery” performed on a good capacitor on which the measurement of insulation resistance has been completed to recover the initial capacitance. This has resulted in an additional process following the measurement and has reduced operational efficiency further. On the contrary, according to the present invention, since it is only required to apply AC signals for a very short period, the capacity of a capacitor is not reduced and the need for “thermal recovery” process is therefore eliminated.
Further, a conventional apparatus for screening characteristics employs a large turn table having retaining portions to retain capacitors because it requires a measuring time of about 60 seconds per capacitor and requires operations such as establishing a charging area that surrounds a major part of the turn table and stopping the turn table for a predetermined time for charging, which has resulted in very low operational efficiency. In addition, it is necessary to keep capacitors determined as good in an unloading container temporarily and to pick up the capacitors from the unloading container one by one using a parts feeder or the like to supply them to a taping device or the like. This has significantly slowed operations from the measurement of characteristics up to packing and has resulted in increases in the size and cost of the facility.
On the contrary, when an apparatus for screening characteristics is configured using the above-described method for measuring insulation resistance according to an aspect of the invention, processes from the measurement of characteristics up to packing can be linked to each other to improve operational efficiency and to reduce the size of the facility. Specifically, a capacitor supplied to a retaining portion of a transporting means by a supply means is transported to an impedance measuring portion as the transporting means is driven to measure two kinds of impedance. The insulation resistance is then calculated by a good/defective determination means based on the impedance. While the measurement of insulation resistance has required a precharging time as long as 60 seconds in the prior art, the present invention makes it possible to perform measurement within a very short period on the order of several tens of milli-seconds because insulation resistance is calculated from impedance at two frequencies. Capacitors are determined as to whether they are good or defective based on measured insulation resistance; capacitors determined as defective are ejected from a defective parts ejecting portion; and capacitors determined as good are supplied from good parts unloading portion to a packing means wherein they can be immediately packed in a tape, case or the like.
The transporting means may be a turn table having retaining portions for retaining capacitors provided on the circumference thereof at equal pitches or an endless belt having retaining portions for retaining capacitors provided at equal pitches.
The determination of good and defective capacitors is preferably carried out depending not only upon the insulation resistance but also upon the electrostatic capacity thereof. In this case, the good/defective determination means may determine good and defective capacitors from measured values of both the insulation resistance and electrostatic capacity.
REFERENCES:
patent: 3930993 (1976-01-01), Best et al.
patent: 4216424 (1980-08-01), Vette
patent: 4404636 (1983-09-01), Campbell, Jr.
patent: 5262729 (1993-11-01), Kawabata et al.
patent: 5793640 (1998-08-01), Wu et al.
patent: 6130101 (1994-05-01), None
“Test methods of fixed capacitors for use in electronic equipment”, JIS C 5102 (1994), pp. 16-17, Japanese Industrial Standards Committee.
Deb Anjan K
Metjahic Safet
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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