JP2009279603A - Method and device for detecting load inflection point in press stage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a load inflection point at high precision in a press stage. <P>SOLUTION: The variation 17 of the inclination of a load is calculated and displayed together with a load profile 15 in a press stage b on a display device. The peak b of the variation 17 of the inclination is detected using two threshold values L1, L2 (L1&gt;L2), thus an inflection point is detected. At the point of time in which the variation 17 of the inclination exceeds the threshold values L1, L2 and is also made lower than the threshold value 2 after that, the peak b is determined as an inflection point. After the inflection point is determined, the press stage is finished. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method and apparatus for detecting a pressing process, and more particularly to a technique for detecting a load inflection point in a pressing process.

  2. Description of the Related Art Conventionally, a technique is known in which a load that changes with time or displacement in a pressing process is sampled at a predetermined sampling timing, and whether the pressing process is normal or abnormal is determined based on whether the sampling value is normal or abnormal. A technique for detecting a certain physical quantity and determining whether the detected value is normal is not limited to the pressing process. On the other hand, when pressing or press-fitting a soft material such as aluminum or a thin material, the material may break if an excessive load is applied. Therefore, it is necessary to terminate the press at a load near the inflection point of the load. is there.

  The definition of the load inflection point is generally the point at which the load change during the measurement period has become the maximum. In order to determine the inflection point before the end of measurement, the load or displacement value exceeds a specific value. It is necessary to detect a point. However, in this method, it is necessary to set the load and displacement value at the end of measurement for each press and press-fit condition. However, if the margin of the value is increased, an extra load is applied, and conversely if the margin is reduced. There is a problem that the measurement ends before the inflection point due to variation in values.

  In Patent Document 1, in the caulking method, an inflection point of a characteristic curve indicating a relationship between a stroke amount of a punch for caulking a housing and a caulking load applied to the punch is detected at the time of caulking. The sizing process is described in which the stroke amount is constant. As an inflection point detection method, the caulking stroke and the caulking load are sampled as needed, and the amount of change between the inclination at the time of sampling and the inclination at the sampling before and after that is calculated, and the calculation result exceeds a certain threshold value. The inflection point is described as the inflection point, or the inflection point is when the absolute value of the slope when sampling exceeds a predetermined threshold.

JP 2002-35864 A

  However, the inflection point cannot be detected with high accuracy simply by setting the inflection point when the amount of change exceeds a certain threshold value. The reason is that the amount of change in load varies in various ways due to the influence of noise or the like, and there are many cases where not only a single peak value but also a plurality of peak values are mixed in close proximity.

  The object of the present invention is to detect the load inflection point with high accuracy in the press (including press-fitting) process, and thereby, even when pressing a soft material such as aluminum or a thin material, the load near the inflection point is used. It is an object of the present invention to provide a method and an apparatus capable of reliably terminating a press.

The present invention is a method for detecting a load inflection point in a pressing process, the step of inputting a load value as a function of time or displacement detected during the pressing process, and a change amount of the inclination of the load value. A step of calculating, and a step of detecting a load inflection point from the calculated amount of change in the slope of the load value, wherein the second positive value is smaller than the first positive threshold value and the first threshold value. When the amount of change in the slope of the load value exceeds the first threshold value and the second threshold value and then falls below the second threshold value. Detecting the load inflection point by detecting.
In one embodiment of the present invention, the second threshold value is set with reference to the first threshold value.

  In another embodiment of the present invention, when the load inflection point is not detected, a third negative threshold is used, and the amount of change in the slope of the load value is the third threshold. Detecting an end point of the pressing step by detecting a time point below the value.

  Further, the present invention is an apparatus for detecting a load inflection point in a pressing process, a means for inputting a load value as a function of time or displacement detected during the pressing process, and a change in the inclination of the load value. Means for calculating an amount, and means for detecting a load inflection point from the calculated amount of change in the inclination of the load value, which is smaller than a first positive threshold value and the first threshold value. Using a second positive threshold, the amount of change in the slope of the load value exceeds the first threshold and the second threshold, and thereafter the second threshold is set to And a means for detecting the inflection point by detecting a time point below.

  According to the present invention, the load inflection point can be detected with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, the block diagram of the press process evaluation apparatus in this embodiment is shown. The apparatus 1 shown in FIG. 1 also functions as a digital indicator, and visually displays a load change or a displacement of the press machine in a press process as a graph display or a digital numerical value. The digital indicator is incorporated in the press process control mechanism that controls the press process, and the load signal from the strain gauge type transducer that measures the load during pressing, or the displacement meter (sensor) that measures the displacement of the press machine. Input the displacement signal.

  The device 1 according to the present embodiment includes an input / output interface I / F 10, a memory 12, a display device 14, a CPU 16, a ROM 18, and a RAM 20.

  The input / output interface I / F 10 inputs a load signal from a transducer or a displacement signal from a displacement meter.

  In accordance with the program stored in the ROM 18, the CPU 16 converts the input load signal into a digital signal using the RAM 20 as a working memory, holds the value of the digital signal (load value) at a predetermined timing, and stores it in the memory 12. To do.

  In addition, the CPU 16 displays the sequentially acquired load values on the display device 14 as a function of time or displacement. A load value as a function of time or displacement is called a load profile. The display device 14 is composed of a liquid crystal monitor or an organic EL monitor.

  FIG. 2 shows an example of the load profile 15 displayed on the display device 14. The horizontal axis X is time or displacement, and the vertical axis Y is a load value. The load profile 15 is shown as a curve in the XY coordinate system. The user can grasp the state of the pressing process by visually recognizing the load profile 15.

  In addition to the load profile 15, the CPU 16 calculates a change amount of the load inclination and sequentially stores it in the RAM 20 and displays it on the display device 14. The amount of change in load inclination is the amount of change between the load inclination at a certain sampling time and the load inclination at the sampling before and after that, and is a second-order differential value of the load profile. Then, the CPU 16 detects the inflection point of the load by comparing the change amount 17 of the load inclination sequentially calculated and stored in the RAM 20 with a threshold value. However, in this embodiment, the CPU 16 detects the load inflection point not by comparing the change amount of the load inclination with a single threshold value but with a plurality of threshold values.

  FIG. 3 shows a state in which the load profile 15 and the change amount 17 of the load inclination are displayed in parallel on the display device 14 in synchronization. In the upper part of the load profile 15, a change amount 17 of the load inclination is displayed in synchronization with the load profile 15. In the load profile 15, a section t0 is a section where the mold and the material are not in contact with each other, and the load gradient is also zero. A section t1 is a section in which the mold is in contact with the material and the material is deformed, and the load gradient has a certain finite value. At time d0, the amount of change in the load gradient also becomes a finite value, and peak a appears. A section t2 is a section in which the mold and the material are in contact with each other and the deformation of the material is finished, but the load continues to increase. Since the deformation of the material is completed at time d1, the inclination changes. The change point of the slope at this time d1 is the inflection point, and the peak b appears as the change of the slope. A section t3 is a section in which the load of the press machine reaches a set value and becomes a constant value, and the inclination is zero. Since the slope changes from finite to 0 at time d2, a negative peak c appears.

  Thus, peaks a, b, and c appear in the load change amount 17, and only the peak b corresponding to the inflection point needs to be detected from these peak peaks. As can be seen from FIG. 3, since the peak b is a positive peak and has a relatively large amplitude, the change amount 17 of the slope is compared with a positive threshold, and the portion exceeding the threshold is It may be detected as a load inflection point. However, various noises are mixed in the change amount 17 of the slope, and the peak b is often not a single peak waveform but a complex waveform in which a plurality of peaks are mixed. The purpose of detecting the load inflection point is that, as described above, when pressing or press-fitting a soft material such as aluminum or a thin material, the material may break if an excessive load is applied. This is to accurately detect the inflection point because it is necessary to terminate the press with a load in the vicinity of the inflection point. Simply comparing the magnitude 17 of the inclination change with the single threshold value, a plurality of peaks The true load inflection point cannot be accurately detected in the case of a waveform.

  For example, it is assumed that a noise peak exists immediately before the true peak corresponding to the load inflection point. In the process of detecting the load inflection point by comparing the change amount 17 of the slope with the threshold value, the noise peak immediately before is erroneously detected as the load inflection point, and the press may be terminated at this timing. There is. In this case, since the press ends without passing through the load inflection point, the press process does not end normally and becomes abnormal.

Therefore, in the present embodiment, the load inflection point is detected using a plurality of threshold values, specifically, the first threshold value L1 and the second threshold value L2 as shown in FIG. FIG. 4 is a partially enlarged view of the peak b in FIG. 3 and shows that a plurality of peaks are generated. The magnitude relationship between the first threshold value L1 and the second threshold value L2 is L1> L2. The load inflection point is detected according to the following criteria.
(1) When the first threshold value L1 is exceeded, peak hold is performed and the maximum value position is held.
(2) When the change amount 17 of the slope once falls below the threshold value L1 and again exceeds the maximum value position, the peak hold is performed again.
(3) The maximum position held when the second threshold value L2 is exceeded is determined as the load inflection point.

  Referring to FIG. 4, first, peak hold is started at the time (time) d3 when the change amount 17 of the slope exceeds the first threshold value L1, and the maximum is reached at the time (time) d3 ′ when the change is less than L1. The position P3 is stored. Next, when the value falls below the first threshold value L1 and again exceeds the first threshold value L1 (time) d4, the maximum position P3 is cleared, the peak hold is started again, and when the value falls below L1 (Time) The maximum position P4 is stored at d4 ′. Next, the load inflection point is determined at the time (time) d5 when the value falls below the second threshold value L2, and the maximum position P4 is detected as the load inflection point position. The maximum position P3 may be determined as the load inflection point position at the time d3 ′, but the certainty is ensured by considering that the pressing process is terminated when the load inflection point is detected. Therefore, the maximum position P4 is determined as the load inflection point position at time d5.

The second threshold value L2 can be set independently of the first threshold value L1, but is dynamically set in association with the change amount maximum value L1P exceeding the first threshold value L1. You can also That is, L2 = L1P−ΔTh may be set with ΔTh as a predetermined amount. FIG. 4 also shows the second threshold value L2 ′ set as L1P−ΔTh. When L2 ′ is used, the above (3) is
(3) 'The maximum position held when ΔTh is below the maximum value L1P of the amount of change held exceeding the first threshold value L1 is determined as the load inflection point.
In other words. At this time, P4 is determined as the load inflection point position at time d6. Whether to use (3) or (3) ′ can be determined by appropriately switching depending on the nature of the pressing process. This is the case where (3) is used when the peak can be expected to increase or decrease monotonously, and (3) ′ is used when the peak cannot be expected. By adjusting the magnitude of ΔTh and setting ΔTh to be larger as the fluctuation is larger, the load inflection point position can be determined by absorbing the peak fluctuation. Note that (3) ′ satisfies the condition of L1P> L2 only when the peak monotonously increases / decreases, even if the magnitude relationship between the first threshold value L1 and the second threshold value L2 is L1 <L2. If so, the inflection point can be determined correctly.

  FIG. 5 shows a load profile 15 and a change amount 17 of inclination in another pressing process. This is a case where there are two load inflection points. In this case, peaks a, b, c, and d appear in the change amount 17 of the slope. The peaks to be detected are the first load inflection point and the second load inflection point, and peaks b and d. The peak b can be detected based on the above criteria (1) to (3). Peak d can be determined as the next detected peak when peak b is detected. When the level of peak d is small and about the same as peak a, the level of peak d may not exceed the first threshold value L1. Therefore, in this case, when the peak b is detected, the level of the first threshold value L1 may be lowered to detect the peak d. Needless to say, when the first threshold value L1 is lowered, the second threshold value L2 or L2 'is also lowered simultaneously. Alternatively, the peak a may be excluded from detection by setting the first threshold L1 to a value sufficiently lower than the initial value and starting a size comparison after a predetermined time has elapsed since the start of pressing.

  On the other hand, some abnormality may occur in the pressing process, and a situation where the load inflection point cannot be detected may occur. In this case, in this embodiment, since the load inflection point is detected and the pressing process is terminated, a situation where the pressing process does not end indefinitely is assumed. Of course, it is conceivable to forcibly end the pressing process according to the elapsed time from the start of pressing, but it is preferable if it can be completed earlier. Therefore, as shown in FIG. 6, paying attention to the peak c of the change amount 17 of the inclination, this peak c is detected and the pressing process is terminated. The peak c is a negative peak, and the peak c can be detected by setting a negative threshold value L3 and determining whether or not the value is below the negative threshold value L3. When the peak b or the peak d cannot be detected and the load inflection point cannot be determined, and the peak c is detected, the pressing process may be terminated immediately. In short, the peak c can be used as a trigger for quickly ending the pressing process when the load inflection point cannot be detected.

  FIG. 7 shows still another load profile 15 and a change amount 17 of the inclination. This is a case where the load profile 15 has a maximum value and a minimum value in the section t1. In this case, peaks e and f also appear in the change amount 17 of the slope corresponding to the maximum value and the minimum value. Therefore, peaks a, e, f, b, and c appear in all. Also in this case, it is possible to detect the peak b by using the rules (1) to (3) or (3) ′ described above, to determine the load inflection point, and to end the pressing process. If the point cannot be determined, the pressing process can be terminated at peak c.

  In the present embodiment, the peak c is detected when the load inflection point cannot be detected. However, the peak c is detected regardless of whether or not the load inflection point has been detected or regardless of the inflection point detection. It is also possible to detect only c. The peak c may be detected in parallel with the load inflection point detection, and when the peak c is detected and the pressing process is still continued, the pressing process may be terminated uniformly. By detecting the peak c and terminating the pressing process, the pressing process can be terminated without receiving a stop signal from outside the apparatus.

It is a block diagram of embodiment. It is load profile explanatory drawing. It is explanatory drawing which shows the correspondence of a load profile and the variation | change_quantity of inclination. It is detection explanatory drawing of the peak b. It is explanatory drawing which shows the correspondence of another load profile and the variation | change_quantity of inclination. It is detection explanatory drawing of the peak c. It is explanatory drawing which shows the correspondence of another load profile and the variation | change_quantity of inclination.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Press process evaluation apparatus, 14 Display apparatus, 15 Load profile, 16 CPU, 17 Change of inclination.

Claims (5)

A method for detecting a load inflection point in a press process,
Inputting a load value as a function of time or displacement detected during the pressing process;
Calculating the amount of change in the slope of the load value;
A step of detecting a load inflection point from the calculated amount of change in the slope of the load value, the first positive threshold value and a second positive threshold value smaller than the first threshold value; By detecting the time point when the amount of change in the slope of the load value exceeds the first threshold value and the second threshold value and then falls below the second threshold value. Detecting the load inflection point;
A method of detecting a load inflection point in a pressing process, comprising: The method of claim 1, wherein
The method of detecting a load inflection point in a pressing process, wherein the second threshold value is set based on the first threshold value. The method according to claim 1, further comprising:
When the load inflection point is not detected, a third negative threshold value is used, and by detecting the time point when the amount of change in the load value inclination falls below the third threshold value, Detecting an end point; and
A method of detecting a load inflection point in a pressing process, comprising: An apparatus for detecting a load inflection point in a press process,
Means for inputting the load value as a function of time or displacement detected during the pressing process;
Means for calculating the amount of change in the slope of the load value;
A means for detecting a load inflection point from the calculated amount of change in the slope of the load value, the first positive threshold and a second positive threshold smaller than the first threshold. By detecting the time point when the amount of change in the slope of the load value exceeds the first threshold value and the second threshold value and then falls below the second threshold value. Means for detecting the inflection point;
A load inflection point detecting device for a pressing process, characterized by comprising: The apparatus of claim 4, further comprising:
Means for displaying the load value as a function of time or displacement, and for displaying the amount of change in the slope of the load value in synchronization with the load value;
A load inflection point detecting device for a pressing process, characterized by comprising:

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