JPH0718740B2 - Weight detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weight detection device that has a rotating weighing platform and detects a weight change of an object placed on the weighing platform.

For example, there is a heating cooker that effectively utilizes the change in weight. Particularly in microwave ovens, attempts have been made for a long time to determine the degree of cooking by measuring the weight loss of the food placed on the rotary table during heating.

2. Description of the Related Art Conventionally, in a weight detection device having a rotary mounting table of this type, a positioner difference (measurement error due to a difference in mounting position of an object) occurs due to a weighing mechanism. Therefore, an average value during one rotation of the weighing table is calculated. By measuring or measuring the weight at the same point for each rotation, the difference in position and position was removed to detect the weight change.

As a method of measuring the amount of change in weight, it is common to measure the differential weight from the initial weight measured at the start of measurement as needed (Japanese Patent Laid-Open No. 60-111404).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described weight detection device, only one piece of data regarding the detected weight can be collected during one rotation of the rotary mounting table. For example, when considering application to a microwave oven, it often takes 10 to 12 seconds to make one rotation of the mounting table, and the reaction to weight change is extremely slow. In other words, even if the weight changes, the amount of change cannot be detected until the mounting table makes one rotation, which is a major issue in terms of measurement agility.

In addition, when a disturbance is added during measurement and a discontinuity point is generated in the absolute weight, a fatal error occurs in the method of obtaining the weight change based on the initial weight. Fig. 2 is an external view of a weight detection device using a Roberval mechanism that is already known in the field of scales, and Fig. 11 (a) is a weight measurement when an impact is applied from the outside while measuring absolute weight with this weight detection device. It is a characteristic. About 110
It can be seen that the impact is applied in the vicinity of the second and the absolute weight is reduced by 6 to 7 g. However, the weight change during this measurement is only 2 to 3 g, and the pulsation during the measurement is different from the actual weight change because it is due to the position error during rotation of the rotary mounting table. When such discontinuity occurs, the initial weight becomes completely meaningless data.

Generally, the weight detection device has a mechanical friction hysteresis because a mechanism system for transmitting the weight of the object to be measured to a sensor for weight detection is interposed. It is considered that such a phenomenon occurs due to the state transition caused by external impact or vibration. Even in abnormal cases, this phenomenon occurs even when the DUT moves due to shock or vibration during measurement. Conventionally, in measuring the weight change during rotation of the mounting table, it has been extremely difficult to accurately measure the weight change in such an abnormal case.

The present invention solves such a conventional problem, and provides a weight detection device capable of immediately detecting a weight change of an object during rotation of a mounting table even if there is a positional error due to a weighing mechanism. is there.

Means for Solving the Problems In order to solve the above problems, the present invention relates to a weight detection device, a rotary mounting table for mounting an object, a weight detecting means for detecting the weight of the object, and a rotary mounting table per rotation. A differential weight detecting means for sampling a plurality of weights n at equal intervals and obtaining a differential weight of each measured weight from a previous measured weight, a differential weight averaging means for averaging the differential weights over the past n times, and a differential weight. The weight change detecting means for measuring the weight change of the object by cumulatively adding the measurement signals from the averaging means is provided. Further, the difference weight averaging means sets the output signal to the previous output signal or the average value of the output signals at least two times before if the output signal deviates from a predetermined range.

Operation The weight detection device of the present invention measures the weight of an object at regular intervals n times during one rotation of the mounting table, and except for one time immediately after the start of measurement, the weight difference between the previously measured weights is measured for each weight measurement thereafter. To measure. From the (n + 1) th measurement after the start of measurement, the weight change is measured by sequentially adding and averaging the differential weights of the past n times and cumulatively adding the results.
As a result, it is possible to detect an accurate weight change at a time interval of (rotation period / n) and by removing the position error. Further, the output of the difference weight averaging means obtained by adding the difference weight over the past n times represents the accurate weight change rate without the influence of the position difference. Therefore, when this output shows an abnormal value that cannot be the weight reduction rate in measurement, it means that the above-mentioned abnormality due to shock, vibration, etc. (data discontinuity, jump, etc.). Detecting this, the output signal to the weight change detection means is set to the previous output signal or at least the previous two
By adopting the past weight reduction rate as the average value of the output signals of the times, the weight change amount can be instantly measured without time loss even in the case of an abnormality. As a method of detecting such an abnormality, there is also a method of monitoring the output of the weight detection means or the differential weight detection means, but the weight during rotation of the mounting table or the differential weight is affected by the position difference as in this example. Since it fluctuates greatly, it is extremely difficult to distinguish abnormality from normality. From such a point, it is understood that the present invention is very effective as a means for detecting an abnormality at the time of measurement and responding to the abnormality.

Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. Reference numeral 7 is an object to be measured, 1 is a rotary mounting table on which the object 7 is mounted, and 2 is a motor for rotating the rotary mounting table 1, which is a synchronous motor synchronized with a power supply cycle. Reference numeral 3 is a weight detecting means for exchanging the weight of the object 7 for receiving the rotary mount 1, the object 7 and the motor 2 into a predetermined physical quantity, and 4 is a weight detecting means 3
The difference weight detecting means 5 outputs the difference between the weight obtained by exchanging the detected signal to the weight at a constant interval and 3 times per one rotation of the motor 2 and the weight, and the weight obtained last time A differential weight averaging means for receiving the output of the weight detecting means 4 and further adding a total of three signals of the past two times of signals, and outputting a signal of a constant interval outputted from the differential weight detecting means 4 for the past two times. It also stores the past two output values of itself. 6
Is a weight change detecting means for cumulatively adding the signals output from the difference weight averaging means 5. The difference weight detecting means 4, the difference weight averaging means 5, and the weight change detecting means 6 are constituted by a microcomputer 8. FIG. 2 shows the main part of the weight detecting means and shows the principle of weight detection. Reference numeral 12 is a leaf spring, and each leaf spring is attached in parallel with the leaf spring spacer 11 inserted. This is known as a Roberval mechanism already known in the field of scales, and is a leaf spring spacer 11
One end is attached to the Roberval mechanism fixing metal fitting 13 fixed to the main body base to be a fixed end, and the other end is a free end, which is movable in the vertical direction. With this mechanical function, the load is accurately transmitted in the vertical direction no matter where the object is placed on the rotary mounting table 1. Now, when an object is placed on the rotary mounting table 1, the elasticity of the plate spring 12 causes a change according to the weight of the object, and the gap between the sheet metal electrodes 9 attached to the free end side and the fixed end side of the Roberval mechanism is reduced. It changes and the capacitance between the electrodes changes. The principle is that the weight is measured by detecting this. The circuit diagram is shown in FIG. Reference numeral 9 denotes a sheet metal electrode, which is equivalently represented by an electric circuit and serves as a capacitor, which is converted by the oscillation circuit 10 into a rectangular wave signal whose frequency changes depending on the electrostatic capacity and output to the microcomputer 8.

Reference numeral 14 is a power supply synchronizing signal generation circuit which outputs a rectangular signal having the same frequency as the commercial power supply to the microcomputer 8.

A method of detecting a weight change during rotation of the rotary mounting table 1 having the above-described configuration will be described. FIG. 4 shows a timing chart of each signal in the microcomputer 8. The weight detecting means 3 obtains a signal at a constant interval such as ..., and the number of three is just one revolution. The management of this timing relationship is realized by counting the pulse signals from the power supply synchronization signal generation circuit 14 a predetermined number of times. For this purpose, it is essential that the motor 2 is a power supply synchronous motor. Further details regarding this will be described later. The weights obtained in this way are in the form of the difference from the weight previously measured by the difference weight detecting means 4, and ′ = −,
Subsequent subtractions such as ′ = − ……. Further, the difference weight averaging means 5 outputs the output of the difference weight detecting means 4 for the past three times to "="'+' + ', "=" +.
It is added sequentially such as '+', .... Further, the output of the difference weight averaging means 5 is sequentially accumulated by the weight change detecting means 6 as "," + "," + "+", ....

Next, an algorithm of a program when this signal processing is performed using a microcomputer will be described based on the flowchart of FIG. Step when starting measurement
At 15, the register i which stores the current number of data is initialized to 1. In step 16, the pulse signal output from the power supply synchronizing signal generation circuit 14 is monitored, and if a falling edge is detected, the process proceeds to step 17, otherwise step 16 is repeated. In step 17, the number of times of falling is counted, and when the predetermined number of times n ₁ is reached, the process proceeds to step 16, and otherwise, the process returns to step 16. In steps 16 and 17, the data acquisition interval is accurately determined. For example, in the case of a power supply synchronous motor having a rotation cycle of 10 seconds, the count number n of power supply synchronization signals corresponding to the rotation cycle of the motor.
Is n = 3 × n ₁ = 10 / (1/60) = 600, and the same count number n ₁ corresponding to the interval when sampling 3 data items per rotation is n ₁ = n / 3 = 600 / 3 = 200. As a result, even if the power supply frequency fluctuates, data can be accurately collected at intervals that divide the rotation cycle into three equal parts.

Next, at step 18, the output signal of the weight detecting means 6 which is detected is exchanged for the weight W. When the number of measurements i is 1 in step 19, the process returns to step 16 and waits for the next data acquisition synchronization. In other cases, the difference weight DW is calculated in step 20 by DW (i-1) = W (i) -W (i -1) is calculated. Where i in () represents the number of measurements
If it is DW (i-1), it means the difference weight DW of the number of times of measurement (i-1). If the number of measurements i is 3 or less in step 21, return to step 16 to repeat the above process,
Otherwise, in step 22, the difference weight DW is added and averaged over the past three times and the averaged difference weight ADW is calculated as ADW (i) = DW (i) + DW (i-1) + DW (i-2). This calculation result is compared with predetermined abnormal levels l ₁ and l _{2 in} step 23 and l ₁ ≧ ADW (i) or l ₂ ≦ ADW
If (i), ADW (i) = (ADW (i-1) + ADW (i-2)) / 2, otherwise proceed to step 25. In step 25, the weight change CW is CW (i) = It is calculated as CW (i-1) + ADW (i). In step 26, the number of times of measurement is incremented, and if the measurement is not completed in step 27, the process returns to step 16 and repeats the processing. In the case of the first embodiment described below, steps 23 and 24 are omitted, and FIG. 5 shows the second embodiment. Figure 5 and steps below
FIGS. 6 to 9 show characteristic diagrams of respective outputs in an example in which the weight change is measured while actually rotating the motor using the algorithm omitting 23 and 24.

(Embodiment 1) FIG. 6A shows the output of the weight detecting means 3 in terms of weight value, and the motor rotation cycle is 10 seconds. In this way, the weight value fluctuates within a width of about 10 g with rotation due to the influence of the mechanical positioner difference. Therefore, it is well understood that in this state, a minute weight change of a few g cannot be measured at all. FIG. 6 (b) shows the output of the differential weight detecting means 3, which also has a very large pulsation due to the rotation. However, by passing through the difference weight averaging means 5, as shown in FIG. 7 (a), most of the pulsation is removed and the averaged difference weight can be detected.
Then, by cumulatively adding this data, only the weight change can be taken out as shown in FIG. 7 (b). However, since three pieces of data are added by the difference weight averaging process (step 22), the apparent weight change is output in the form of being amplified three times. Actually, the weight loss of about 12g is about 36g
Has become. With this method, the weight change amount of the object, which was output only at 10-second intervals of the conventional motor rotation cycle, can be immediately detected every 10/3 seconds and the influence of the positioner difference related to the weighing mechanism occurs at all. do not do. This is extremely advantageous in the application of instantaneously measuring a minute weight change of an object while the mounting table is rotating. Further, since three data are added and averaged by the difference weight averaging process (step 22), it is expected that fluctuations due to noise will be smoothed and reduced.

(Embodiment 2) FIG. 8 (a) is a weight W obtained by converting the output of the weight detecting means 3 into weight. Since the measurement is performed 3 times per one rotation of the motor, the measured value is pulsating with a swing width of about 5 g due to the influence of the positional difference. At the time of about 100 seconds and about 130 seconds, an external shock was applied to the weight detection device, and pulse-shaped jumping of data occurred. Then, the weight change started from around 80 seconds and finally decreased by about 3g. FIG. 8 (b) shows the detection means 4
Is the characteristic of the differential weight DW of the output of. FIG. 9 (a) shows the characteristics of the averaged differential weight ADW of the output of the differential weight averaging means 5, which is the result of the past three additions, that is, the physical average value of one rotation. ) Has the characteristic of removing pulsation by rotation. As a result, it is possible to instantly obtain the weight change rate by removing the influence of the positional difference due to the rotation. Since this output does not contain a pulsating component, it can be said that it is an optimum signal for detecting an abnormality in the measured value, and it can be easily and instantaneously discriminated whether it is normal or abnormal.
That is, looking at the outputs of the weight detecting means and the differential weight detecting means, it is extremely difficult to distinguish the pulsation width and the abnormal level of weight because the pulsations are superimposed on both. In particular, when a heavy object is placed on the end of the rotary mounting table, this pulsation tends to become larger and the discrimination becomes more difficult. If the abnormality detection levels l ₁ and l ₂ are l ₁ = 3.0 g and l ₂ = −3.0 g, 1
Four abnormalities at the time of 00,110,126,136 seconds can be easily determined. The output CW of the weight detecting means when this abnormality is detected and the processing of step 24 in FIG. 5 is performed becomes as shown in FIG. 9 (b), and the influence of the impact hardly appears. Moreover, by averaging the outputs of the differential weight averaging means for the past two times, the weight change can be continuously measured while the data is corrected at the normal weight reduction rate immediately before the abnormality occurs even during the abnormality, so that it is possible to prevent the disturbance. Has extremely excellent characteristics and the accuracy is remarkably improved. Figure 10 shows the cumulative addition of ADW as it is without this process, and there is a high possibility of malfunction due to the data being disturbed by the impact. Here, although the actual weight reduction is about 3 g, the output of the weight change detecting means is about 9 g. This is a phenomenon that occurs because the difference weights of the past three times are added in the process of averaging the difference weights, and the actual weight reduction amount is 1/3 thereof. It is desirable that the abnormality detection levels l ₁ and l _{2 be} set with an appropriate margin with respect to the limit value of the weight change rate of the object to be measured.

Other measurement examples are shown in Figs. The characteristic of the measurement example is that a stable point of the data jumps due to an external impact and a discontinuous point occurs. Figure 11 (a)
Is the output of the weight detection means and is discontinuous around 110 seconds. Despite the fact that the weight has changed by only about 3g, the output has decreased by about 7g, which is clearly a false measurement. FIG. 11 (b) shows the output of the difference weight detecting means, and FIG. 12 (a) shows the output of the difference weight averaging means.
If the abnormality detection levels l ₁ and l ₂ are set to the same level as in the case of the previous example, discontinuities can be easily detected.
When the process of is executed, the output of the weight change change detection means is
As shown in Figure (b), it is possible to accurately measure only about 3 g of the change in weight of the object (9 g, which is triple the display) while maintaining continuity.
Note that FIG. 13 shows a case where the process of step 24 is not executed.

EFFECTS OF THE INVENTION (1) As described above, the weight detecting apparatus of the present invention as set forth in claim 1 samples a plurality of weights n per revolution of the rotary mounting table at equal intervals, and averages each difference weight over the past n times. Further, the weight change amount is detected by cumulatively adding it, and the influence of the position error of the weighing mechanism can be removed, and the weight change can be detected at a high speed (rotation cycle / n).

(2) Since the addition and averaging is always performed n times, the degree of influence is reduced to 1 / n even for instantaneous noise.

Further, in the weight detecting device of the present invention as set forth in claims 2 and 3, a plurality of n weights per rotation of the rotary mounting table are sampled at equal intervals, and the respective differential weights are averaged over the past n times, and the averaged differential weight is the first. When the specified abnormality level l ₁ or more of the above or the second predetermined abnormality level l ₂ or less is regarded as an abnormality in the measured value, the previous change, or at least the previous two results are cumulatively added to change the weight. It detects the amount, and (1) it can detect minute changes in weight by eliminating the influence of positioning error due to the weighing mechanism.

(2) The weight change excluding the influence of the position / position difference due to the weighing mechanism can be sampled at intervals of 1 / n of the rotation cycle, and the measurement speed is dramatically increased.

(3) Even if an abnormality such as a sudden change or jump occurs in the data due to external disturbance such as shock, vibration or noise, it can be detected easily and instantly, and the weight change can be corrected and measured during the abnormality. The measurement speed and accuracy are significantly improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a weight detecting device according to an embodiment of the present invention, FIG. 2 is a side view of an essential part of a weight detecting means, FIG. 3 is a circuit diagram, and FIG. 4 is a timing chart of each output signal. FIG. 5 is a flowchart showing a signal processing algorithm, FIG. 6 (a) is an output characteristic diagram of the weight detecting means in one example of measurement in the first embodiment, and FIG. 6 (b) is an output characteristic diagram of the differential weight detecting means. FIG. 7 (a) is an output characteristic diagram of the same differential weight averaging means, FIG. 7 (b) is an output characteristic diagram of the same weight change detecting means, and FIG. 8 (a) is an example of measurement in the second embodiment. FIG. 8 (b) is an output characteristic diagram of the weight detection means of the example, FIG. 9 (a) is an output characteristic diagram of the difference weight detection means, FIG. 9 (a) is an output characteristic diagram of the difference weight averaging means, and FIG. 9 (b). Is the output characteristic diagram of the weight change detection means that processed the abnormality detection signal. Output characteristic diagram of weight change detecting means, the
FIG. 11 (a) is an output characteristic diagram of the weight detecting means in other cases of measurement, FIG. 11 (b) is an output characteristic diagram of the difference weight detecting means, and FIG. 12 (a) is the difference weight averaging means. FIG. 12 (b) is an output characteristic diagram of the weight change detecting means that has performed the signal processing of the abnormality detection, and FIG. 13 is an output characteristic diagram of the weight change detecting means when the processing is not performed. 1 ... Rotary mounting table, 2 ... motor, 3 ... weight detection means, 4 ... difference weight detection means, 5 ... difference weight averaging means, 6 ... weight change detection means, 8 ... microcomputer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenzo Ochi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP 63-200020 (JP, A) Actual development Sho 62- 14206 (JP, U)

Claims (3)

[Claims] 1. A rotary mounting table for mounting and rotating an object, weight detection means for detecting the weight of the object, and the rotary mounting table 1.
Differential weight detection means for sampling the weights n times a predetermined number of times at equal intervals and for obtaining the differential weight of each measured weight from the previous measured weight, and differential weight averaging means for averaging the differential weights over the previous n times. And a weight change detecting means for measuring the weight change of the object by cumulatively adding the measurement signals from the difference weight averaging means. 2. The output signal of the difference weight averaging means is the first signal.
2. The weight detection device according to claim 1, wherein the output signal is used as the previous output signal of the difference weight averaging means when the output signal is less than or equal to the predetermined value of or above the second predetermined value. 3. When the output of the difference weight averaging means is less than or equal to the first predetermined value or more than the second predetermined value, the output signal is averaged at least twice before the output signal of the difference weight averaging means. The weight detection device according to claim 2, wherein the value is a value.