JP4479234B2 - Positive characteristic thermistor sorting method and sorting apparatus - Google Patents

Description

  The present invention relates to a screening method and a screening apparatus for a positive temperature coefficient thermistor that screens non-defective products and defective products based on an attenuation current waveform detected by applying a voltage.

  2. Description of the Related Art Conventionally, as a method for selecting ceramic elements, a selection method for determining whether a product is good or not based on an inrush current has been proposed (see Patent Document 1).

  However, the selection method according to the above prior art detects an inrush current with respect to the surface temperature, and sufficient determination accuracy cannot be obtained in the quality determination of the product.

  Therefore, in the positive temperature coefficient thermistor, a non-defective product and a defective product are selected by inspecting a characteristic in which a resistance value increases by self-heating when a voltage is applied.

In other words, in the conventional sorting method, a voltage is applied to the positive temperature coefficient thermistor, the change in the flowing current is captured by applying the voltage, current measurement is performed immediately before the voltage application is completed, and the quality of the product is judged. Had gone.
JP-A-9-92504

  In the conventional sorting method, the product quality is judged by applying a voltage to the positive temperature coefficient thermistor for 45 seconds, for example. As described above, since the voltage is applied for a long time, there is a problem in that the sorting operation is expensive.

  In addition, in order to ensure a long application time, the tester has many application terminals, and there is a problem that the equipment is complicated and long, and the equipment cost is increased.

  Further, in order to secure the application time, the operation is performed at a relatively low speed (for example, processing speed: 200 / min), and there is a problem that the sorting operation cannot be performed efficiently.

  An object of the present invention is to provide a screening method and a screening apparatus for a positive temperature coefficient thermistor that can reduce sorting work costs, equipment costs, and efficiency of sorting work by shortening the voltage application time.

  The positive temperature coefficient thermistor selection method of the present invention includes a step of applying a voltage to a plurality of positive temperature coefficient thermistors to be selected to obtain an attenuation current waveform, and an average value and a standard deviation value of the attenuation current waveform of the positive temperature coefficient thermistor. A step of calculating an upper limit value and a lower limit value from the average value and the standard deviation value using an average value ± n × standard deviation value (where n = 3 to 6), Determining whether the attenuation current waveform of the characteristic thermistor is within a determination range between the upper limit value and the lower limit value, and selecting those within the determination range as non-defective products.

  A screening device for a positive temperature coefficient thermistor according to the present invention comprises: a decay current detection means for detecting a current waveform obtained by applying a voltage to a plurality of positive temperature coefficient thermistors to be sorted; a decay current waveform of the positive temperature coefficient thermistor; Upper and lower limits for calculating an average value and a standard deviation value, and calculating an upper limit value and a lower limit value from the average value and the standard deviation value using an average value ± n × standard deviation value (where n = 3 to 6). A selection unit that determines whether the attenuation current waveform of each of the positive temperature coefficient thermistors is within a determination range between the upper limit value and the lower limit value, and selects those that are within the determination range as non-defective products It is equipped with.

  The average value and the standard deviation value are calculated using, for example, a plurality of moving averages of positive characteristic thermistors.

  Further, a configuration may be added in which the inrush current of the positive temperature coefficient thermistor is detected, it is determined whether or not the detected inrush current is within a standard range, and those within the standard range are selected as non-defective products.

  Furthermore, a configuration may be added in which an overcurrent of the positive temperature coefficient thermistor is detected and the positive temperature coefficient thermistor that has detected the overcurrent is selected as a defective product.

  According to the positive temperature coefficient thermistor selection method and apparatus of the present invention, the average value ± n × standard deviation value (where n = 3 to 6) is calculated from the average value and standard deviation value of the decay current waveform of the positive temperature coefficient thermistor. To calculate the upper limit value and the lower limit value, determine whether the decay current waveform of each positive temperature coefficient thermistor is within the judgment range between the upper limit value and the lower limit value, and determine that the product within the judgment range is a non-defective product Sort out. In this way, the dynamic characteristics possessed by the positive temperature coefficient thermistor are captured by the temporal change of the current, the difference in the degree of current attenuation is judged and the abnormal one is automatically judged, so by applying a short time voltage, The pass / fail judgment of the positive characteristic thermistor can be made.

  In addition, the determination range is set based on the average value and standard deviation value based on the moving average obtained by sampling, instead of using a predetermined determination range, so it is possible to accurately determine the difference between slightly different attenuation current waveforms. it can.

  Furthermore, in addition to detecting the decay current waveform of the positive temperature coefficient thermistor, more accurate determination can be made by performing selection by inrush current detection or overcurrent detection.

  According to the positive temperature coefficient thermistor sorting method and sorting apparatus of the present invention, it is possible to obtain an effect of reducing sorting work cost, equipment cost, and sorting work efficiency.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram of a screening device for a positive temperature coefficient thermistor, FIG. 2 is a schematic diagram of an automatic resistance measuring device, FIG. 3 is an explanatory diagram showing a method for extracting an attenuation current waveform, and FIG. FIG. 5 is a graph showing the decay current waveform of a different type positive thermistor, FIG. 6 is a graph showing the inrush current detection of the positive thermistor, and FIG. 7 is the positive characteristic. It is a graph which shows the mode of the burning detection of a thermistor.

  The positive temperature coefficient thermistor sorting device shown in FIG. 1 is mounted on the automatic resistance measuring device shown in FIG.

  1 and 2, 11 is an automatic resistance measuring device, 12 is an application power source, 13 is a computer, 14 is an application relay, 15 is a burnout detection circuit, 21 is a voltage application line, 22 is a current waveform extraction line, and 23 is a control. Signal line, 25 is a rail for transporting a positive temperature coefficient thermistor W as a product to be selected, and 26 is a simultaneous measurement of two positive temperature coefficient thermistors W at a maximum processing speed of 360 pieces / minute (2-pitch tact feed). Voltage application / measurement terminal 31, 31 is an automatic input unit, 32 is a resistance measurement unit, and 33 is a defective product extraction unit.

  The automatic resistance measuring device 11 has a conventional resistance selection function at room temperature (25 ° C.) and the function of the present invention (attenuation current measurement, inrush current detection or overcurrent detection). Resistance selection function → function of the present invention → defective product sampling. The automatic resistance measuring device 11 is a non-defective product when both of the resistance selection result and the selection result by the function of the present invention are good products.

  The application power source 12 is constituted by a DC constant voltage power source (0 to 60 V, 0 to 50 A, 750 W), and applies a constant voltage to the positive temperature coefficient thermistor W.

  The computer 13 includes an attenuation current detection unit that detects an attenuation current waveform with an A / D converter (converting analog data into digital data) and a determination range setting unit that sets a determination range based on the detection value. And a selection means for determining the degree of change in the attenuation current waveform and selecting those within the determination range as non-defective products, and sending the selection result to the automatic resistance measuring device 11. Further, it detects an inrush current that flows immediately after voltage application, functions as an inrush current detection means for selecting those within the standard range as non-defective products, and sends the selection result to the automatic resistance measuring device 11. The attenuation current waveform is measured by an A / D converter without using a current meter for speeding up the current measurement, and a reference connected in series to the positive temperature coefficient thermistor W as shown in FIG. This is done by measuring the voltage value across the resistor 27.

  The application relay 14 turns on / off the voltage application to the positive temperature coefficient thermistor W under the control of the computer 13. The relay is turned off and no voltage is applied to the positive temperature coefficient thermistor W determined to be defective by burnout detection (details will be described later) or inrush current detection (details will be described later) of the computer 13.

  The burnout detection circuit 15 monitors whether an overcurrent is flowing due to a short circuit of the positive temperature coefficient thermistor W while a voltage is being applied to the positive temperature coefficient thermistor W. When the overcurrent is detected, the immediate application relay 14 is turned off, and the voltage application to the positive temperature coefficient thermistor W is cut off. The overcurrent detection and voltage disconnection operations are directly performed by the burnout detection circuit (burnout detection means) 15 to increase the processing speed. The overcurrent detection information is sent to the automatic resistance measuring device 11 via the computer 13 and the positive characteristic thermistor W is selected as a defective product. The burnout detection circuit 15 may be configured to perform only overcurrent detection and the voltage disconnection operation may be performed by the computer 13 or may be configured to eliminate the burnout detection circuit 15 and perform the overcurrent detection and voltage disconnection operation by the computer 13. Good.

  A determination process in the computer 13 will be described.

  There are two judgment items performed by the computer 13; attenuation waveform detection and inrush current detection. Two positive characteristic thermistors W are processed simultaneously, and each judgment result is sent to the automatic resistance measuring device 11 to automatically The resistance measuring device 11 sorts out defective products.

  First, attenuation waveform detection will be described.

  The attenuation waveform detection is performed by determining whether or not the attenuation current waveform that flows when a voltage is applied to the positive temperature coefficient thermistor W is within the upper and lower limit value range (determination range) shown in FIG.

  FIG. 4 shows the decay current waveform of the positive temperature coefficient thermistor W. The horizontal axis is the voltage application time (seconds), the vertical axis is the current (A), the solid line is the average current, the broken line is the standard deviation, and the alternate long and short dash line is The upper limit and the two-dot chain line indicate the lower limit.

  The upper and lower limits of the decay current waveform are sampled at 25 points at intervals of 0.010 seconds or less during the voltage application time, the average and standard deviation of the current are calculated for each point, and the average value ± n × standard deviation The value is set (here, n = 3 to 6). Note that which value of n = 3 to 6 is determined in advance for each product name.

  In the example of FIG. 4, the sampling start position is 0.035 seconds, the sampling interval is 0.005 seconds, and the number of sampling points is 25. These values are determined in advance for each product name.

  The average value and the standard deviation value are calculated by a moving average of 50 positive characteristic thermistors W.

  Immediately after the start of the lot, the current value at each sampling point is accumulated, and when the number of measured positive characteristic thermistors W reaches 12, the average value and standard deviation value are obtained at 10 pieces excluding the maximum and minimum values. Is calculated. Upper and lower limit values are calculated based on the average value and the standard deviation value, and the twelve positive characteristic thermistors W are collectively determined. The determination result is sent to the automatic resistance measuring device 11, and defective products that deviate from the upper and lower limit values are automatically extracted.

  Until the number of measurement reaches 50, the average value and the standard deviation value are calculated with the number of measurement at that time. The upper and lower limit values are calculated based on the average value and the standard deviation value, and the positive characteristic thermistor W is determined. When the number of measured items reaches 13, the determination is first made with the previous upper and lower limit values (calculation results with N = 10), and in the case of a non-defective product, the average value is obtained with 11 items excluding the maximum value and the minimum value. Standard deviation values and upper and lower limits are calculated.

  When the number of measurement is 50 or more, the moving average of 50 is used. For example, when the number of measurement is 51st, 50 pieces from the second to the 51st are used, and when the number of measurement is 52nd, 50 pieces from the 3rd to the 52nd are used. The average value, standard deviation value, and upper and lower limit values are calculated and judged. Alternatively, for the 51st and subsequent items, the average value, the standard deviation value, and the upper and lower limit values are calculated and determined by dividing 50 items from the 51st to 100th items and 50 items from the 101st to 150th items. May be performed.

  In addition, only the positive characteristic thermistor W whose measurement result is a good product is used as the current value used for calculating the average value and the standard deviation value. For example, when the number of measurement becomes 13, the positive characteristic thermistor W that has become a defective product as a result of the determination in the determination range up to the 12th is excluded and calculated.

  In determining whether the product is non-defective or defective, a product that falls outside the range of the upper and lower limit values more than the specified number of times in the sampling region of the attenuation current is determined as a defective product. That is, in the positive temperature coefficient thermistor W, it is measured whether or not each sampling point is out of the range of the upper and lower limit values, and the number of out of sampling points and the specified number of times set in advance for each product name are determined. Compare. As a result of comparison, if the number of deviations is equal to or greater than the specified number, it is determined as a defective product. The attenuation current is measured within the work feeding tact time.

  A product having a low withstand voltage level (defective product) has a different attenuation current waveform as compared with a normal product, but a difference occurs in the deviation method depending on the level. That is, an attenuation current waveform is close to a normal product. In addition, there is a distribution in the withstand voltage level, and there is a range of normal products. Therefore, in the determination of defective products, there are very few points that deviate from the upper and lower limit values, and even products that can be determined to be almost normal products are determined to be defective products. In addition, even if the value fluctuates due to noise, there is a possibility that a normal product is determined as a defective product. Therefore, only those that deviate from the upper and lower limit values more than the specified number of times are determined to be defective. The specified number of times was determined by taking data.

  FIG. 5 shows a graph of the attenuation current waveform of different types of positive temperature coefficient thermistors. That is, it is possible to determine with higher accuracy by determining the detection of different types, which is incomplete with only the conventional resistance selection function, together with the attenuation characteristics. Here, the different varieties are those having the same resistance value at normal temperature and different attenuation characteristics (different inclinations of the graphs of the attenuation current waveform). Thus, even if the result of resistance selection is a non-defective product, it can be seen that the attenuation current waveform deviates from the lower limit value within the range surrounded by the dot-and-dash circle 51 as a result of the determination based on the attenuation characteristics. It can be determined as a defective product, and the determination accuracy is improved.

  Next, inrush current detection will be described.

  FIG. 6 shows the decay current waveform immediately after the voltage is applied to the positive temperature coefficient thermistor W. For inrush current detection, the upper and lower limits of the current value at the time of inrush (after 5 msec has elapsed since the voltage was applied to the positive temperature coefficient thermistor W. However, there is a variation of ± 1 msec) are determined. Here, 5 msec is the time until the applied relay is reliably turned on. During the time up to 5 msec after applying the voltage, only the burned-down product is detected.

  The purpose of setting the upper limit 62 is to protect the detection equipment from overcurrent and to detect a product defect (detection of a product having an abnormally high inrush current even if it does not burn out). The purpose of setting the lower limit 63 is detection without voltage application.

  That is, it is determined whether or not the inrush current measurement point 61 is between the upper limit value 62 and the lower limit value 63 (standard range). Defective products with only pressure resistance can be removed. The standard range is set in advance for each product name.

  A determination process in the burnout detection circuit 15 will be described.

  The burnout detection circuit 15 continuously monitors an overcurrent such as a short current with an electric circuit.

  FIG. 7 shows a current waveform when the positive temperature coefficient thermistor W burns out. In FIG. 7, 72 indicates a preset overcurrent detection level, and when the current value of the positive temperature coefficient thermistor W exceeds the overcurrent detection level 72 as indicated by a dashed line 71 in the figure. In the burnout detection circuit 15, the direct application relay 14 is operated to cut off the applied voltage of the positive temperature coefficient thermistor W. Thus, the cutting operation is speeded up by directly cutting the application relay 14 without using the computer 13. The overcurrent detection level 72 is determined in advance for each product name, and the value is set in the burnout detection circuit 15 by the computer 13.

  The overcurrent detection information is also sent to the computer 13, and further sent from the computer 13 to the automatic resistance measuring device 11, and the automatic resistance measuring device 11 selects the positive characteristic thermistor W from which the overcurrent is detected.

  Unlike the attenuation waveform detection and inrush current detection, this overcurrent detection continuously (always) monitors the current from the start to the end of voltage application to detect burned-out products and protect the sorting device from overcurrent.

  According to the positive characteristic thermistor W sorting method and sorting apparatus configured as described above, it is possible to shorten the application time without degrading the quality by capturing the change in the current in the decay process and determining whether the current is good or bad. That is, whether the positive temperature coefficient thermistor W is good or bad can be determined by a change in the attenuation process current of 0.1 seconds or less, so that the selection work cost can be reduced and the stress on the positive temperature coefficient thermistor W can be reduced.

  In addition, the application time can be shortened, so that the number of application terminals of the withstand voltage tester can be reduced, the equipment can be downsized and the equipment cost can be reduced. Due to the miniaturization, it is possible to mount on the high-speed automatic resistance measuring device 11 without taking up a mounting space.

  Further, by shortening the application time, it is possible to operate at a high speed (for example, processing speed: 360 pieces / minute), the sorting work efficiency can be improved, and the production period can be shortened.

  In addition, the determination range is set based on the average value and standard deviation value based on the moving average obtained by sampling, instead of using a predetermined determination range, so it is possible to accurately determine the difference between slightly different attenuation current waveforms. it can.

  Furthermore, in addition to detecting the decay current waveform of the positive temperature coefficient thermistor W, more accurate determination can be performed by performing selection by inrush current detection or overcurrent detection.

  It should be noted that the positive characteristic thermistor sorting method and sorting apparatus of the present invention need only perform at least attenuation waveform detection among attenuation waveform detection, inrush current detection, and burnout detection.

  The positive temperature coefficient thermistor selection method and apparatus of the present invention use a positive characteristic in which resistance increases as a result of self-heating by applying a voltage, and thermistors used for applications such as overcurrent suppression and temperature detection. It is useful as a sorting method and a thermistor sorting device.

The block diagram of the screening device of the positive temperature coefficient thermistor in the embodiment of the present invention Schematic diagram of automatic resistance measuring device in an embodiment of the present invention Explanatory drawing which shows the extraction method of the attenuation | damping current waveform in embodiment of this invention The graph which shows the mode of the setting of the judgment range used for selection by the attenuation | damping current waveform of the positive temperature coefficient thermistor in embodiment of this invention Graph of attenuation current waveform of positive temperature coefficient thermistor of different varieties in embodiment of the present invention The graph which shows the mode of the inrush current detection of the positive temperature coefficient thermistor in embodiment of this invention The graph which shows the mode of the burning detection of the positive temperature coefficient thermistor in embodiment of this invention

Explanation of symbols

11 Automatic Resistance Measuring Device 12 Power Supply for Application 13 Computer 14 Application Relay 15 Burnout Detection Circuit W Positive Characteristic Thermistor

Claims (8)

Applying a voltage to a plurality of positive temperature coefficient thermistors to be selected to obtain an attenuated current waveform;
Calculating an average value and a standard deviation value of the decay current waveform of the positive temperature coefficient thermistor;
From the average value and the standard deviation value, a step of calculating an upper limit value and a lower limit value using an average value ± n × standard deviation value (where n = 3 to 6),
Determining whether or not the decay current waveform of each positive characteristic thermistor is within a determination range between the upper limit value and the lower limit value, and selecting those within the determination range as non-defective products. Selection method for characteristic thermistors. The method for selecting a positive temperature coefficient thermistor according to claim 1, wherein the average value and the standard deviation value are calculated using a plurality of moving averages of the positive temperature coefficient thermistor. 2. A step of detecting an inrush current of a positive temperature coefficient thermistor, and a step of determining whether or not the detected inrush current is within a standard range, and selecting a product within the standard range as a non-defective product. Or the screening method of the positive temperature coefficient thermistor of Claim 2. 4. The method of selecting a positive temperature coefficient thermistor according to claim 1, further comprising a step of detecting an overcurrent of the positive temperature coefficient thermistor and selecting the positive temperature coefficient thermistor detecting the overcurrent as a defective product. Attenuating current detecting means for detecting an attenuating current waveform obtained by applying a voltage to a plurality of positive characteristic thermistors to be selected;
An average value and a standard deviation value of the decay current waveform of the positive temperature coefficient thermistor are calculated, and an upper limit is calculated from the average value and the standard deviation value using an average value ± n × standard deviation value (where n = 3 to 6). Determination range setting means for calculating a value and a lower limit;
Screening means for determining whether or not the decay current waveform of each of the positive temperature coefficient thermistors is within a determination range between the upper limit value and the lower limit value, and selecting those within the determination range as non-defective products Positive characteristic thermistor sorting device. 6. The screening apparatus for a positive temperature coefficient thermistor according to claim 5, wherein the average value and the standard deviation value are calculated using a plurality of moving averages of the positive temperature coefficient thermistor. 6. An inrush current detecting means for detecting an inrush current of a positive temperature coefficient thermistor, determining whether the detected inrush current is within a standard range, and selecting a product within the standard range as a non-defective product. Or the screening device of the positive temperature coefficient thermistor of Claim 6. 8. A screening device for a positive temperature coefficient thermistor according to claim 5, further comprising burnout detection means for detecting an overcurrent of the positive temperature coefficient thermistor and selecting the positive temperature coefficient thermistor detecting the overcurrent as a defective product. .

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