JPS634647B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a weight measuring device, and more particularly, to a weight measuring device that is capable of alternately detecting the weight of an object to be measured applied to both ends of a strain rod whose substantially central portion is fixed to a support by a single detection circuit. This invention relates to a measuring device. For example, powder and granules such as cement, sugar, and salt;
A liquid such as oil or drinking water is first supplied to one of two containers arranged side by side, and when the weight of one container reaches a certain value, the cement, etc. is supplied to the other container. Then, when the weight of the other container reaches a certain value, cement is added to the empty container. A weighing device suitable for use in a metering and feeding device that continuously supplies cement, etc. to a large number of containers, such as bags, without stopping the flow by repeating the process of re-feeding cement, etc. The purpose of the present invention is to provide a weight measuring device that is highly sensitive and accurate. BACKGROUND OF THE INVENTION Conventionally, powder and granular materials such as cement have been supplied to containers using a metering and feeding device as shown in FIG. This weighing and feeding device has two weighing scales 1A and 1B arranged adjacently on one base 2.
The weights W _A and W _B of the two containers 3A and 3B can be measured at the same time, and the discharge end of the discharge pipe 4 that discharges cement, etc. without interruption is moved back and forth in the horizontal direction to supply cement, etc. It is provided with a switching mechanism 5 for switching the destination. This switching mechanism 5 receives an output from a control circuit (not shown) and operates a drive unit 7 that operates to pull the discharge end of the discharge pipe 4 toward the container 3B by means of a plunger 6.
and a spring 8 that biases the discharge end of the discharge pipe 4 so that it is located on the container 3A side,
The drive unit 7 and the spring 8 are arranged so as to be located on opposite sides of the discharge pipe 4. Reference numeral 9 denotes a wire connected between the tip of the plunger 6 of the drive unit 7 and the tip of the spring 8, and a fitting ring portion 10 into which the discharge end of the discharge pipe 4 is fitted is provided in the middle of the wire. There is. This wire 9 transmits the force from the drive part 7 and the spring 8 to the discharge end of the discharge pipe 4. 11 is the discharge pipe 4
This guide device receives the cement etc. discharged from the container at the upper socket 12 and guides the cement etc. to the containers 3A and 3B through bifurcated branch guide tubes 13A and 13B. The supply of cement or the like to the container by this supply device is carried out as follows. That is, this supply device is configured such that the drive unit 7 does not pull the end of the discharge pipe 4 when the weight W _A of the container 3A does not reach a predetermined value W _S ; The end of the container 4 is positioned closer to the container 3A by the contraction force of the spring 8. As a result, the cement etc. discharged from the discharge pipe 4 are supplied into the container 3A through the branch guide pipe 13A of the guide tool 11.
Then, when the weight _WA of the container 3A reaches a predetermined value W _S , a signal is transmitted from the weight scale 1A to the control circuit, and the drive section 7 is operated by the control circuit. Then, the end of the discharge pipe 4 is connected to the spring 8
is moved to the container 3B side against the contraction force of
Cement and the like discharged from the discharge pipe 4 are supplied into the container 3B via the branch guide pipe 13B. At that time, the container 3A is removed from the weighing scale 1A and the empty container 3A is placed on the weighing scale 1A. And weight scale 1B
When the weight W _B of the upper container 3B reaches a predetermined value W _S , a signal is transmitted from the weight scale 1B, and as a result, the control circuit stops outputting the signal that had been operating the drive unit 7, and the drive unit 7 The end of the discharge pipe 4 is not pulled. Therefore, the end of the discharge pipe 4 is moved toward the container 3A by the contracting force of the spring 8, returning to the state shown in FIG. After that, this kind of thing is repeated. In this manner, the metering and feeding apparatus shown in FIG. 1 allows a constant weight of cement, etc. to be fed into the container without stopping the flow. However, such a dosing device requires two scales to measure the weight of two containers. Therefore, there was a problem that the structure of the device became complicated and the cost of the device became extremely high. The present invention was made in view of the above-mentioned problems.
For example, it is ideal for a metering and feeding device that performs a continuous feeding operation, such as supplying powder, granular materials, liquid, etc. to one of two containers and then feeding it to the other container when a predetermined weight is reached. The purpose is to provide a simple and low-cost weight measuring device. That is, the present invention is characterized by fixing a substantially central portion of the straining rod to a support so that the weight of the object to be measured is applied to both ends of the straining rod, and One or more strain gauges that detect strain occurring on one side from the center and one or more strain gauges that detect strain occurring on the other side from the center are respectively attached, and both strain gauges are attached to the strain gauge. A single detection circuit is constructed, and the detection circuit alternately detects the weight applied to one end of the strain rod and the weight applied to the other end. Hereinafter, the present invention will be described in detail according to embodiments shown in the accompanying drawings. FIG. 2 is a front view schematically showing the structure of an embodiment in which the weight measurement device according to the present invention is applied to the above-mentioned metering and feeding device for powder and granular materials. In the figure, reference numeral 14 denotes a straining rod made of a straining material that can generate strain when subjected to a load, and its substantially central portion is thickened, and a bolt insertion hole 15 is bored in the thickened portion. . A bolt 16 is inserted into the bolt insertion hole 15, and the tip of the bolt 16 is screwed into a screw hole 18 provided in the strain rod support 17.
As a result, the center portion of the straining rod 14 is rigidly fixed to the straining rod support 17 and kept horizontal.
Reference numerals 19, 19, 19, and 19 denote gauge attachment grooves provided on both the upper and lower surfaces of the strain rod 14 at positions adjacent to the thick part at the center of the strain rod 14, and strain gauges SGa, SGb, and SGc, SGd
is attached. In this way, gauge attachment groove 1
9, 19, ...... are provided by reducing the wall thickness of the portion of the strain rod 14 where the strain gauges SGa to SGd are installed to increase the strain generated for the same load, thereby improving measurement sensitivity and measurement. This is to improve accuracy. Reference numerals 20 and 20 are small-diameter suspension shafts for suspending the containers 3A and 3B, the upper ends of which are bent into a U-shape, and the tips of the U-shaped portions 20a and 20a are bent downward to create strain. It is adapted to come into contact with the upper surface of both ends of the rod 14. 21, 21 has one end connected to the hanging support shaft 20, 2
0, the levers 21, 2
1 is supported so as to be rotatable about fulcrums 22, 22. 23, 23 are weights suspended from the other ends of the levers 21, 21. l ₁ is the distance between the fulcrum 22 of the lever 21 and the end connected to the hanging support shaft 20, and l ₂ is the distance between the fulcrum 22 of the lever 21 and the end where the weight 23 is suspended. Since the weight 23 is connected to the suspension shaft 20 via the lever 21, a force acts in a direction to reduce the weight of the containers 3A, 3B. That is, if the weight of the weight 23 is W ₀ , the force is W ₀ ×l ₂ /l ₁ , and therefore, the weights W _A and W _B of the containers 3A and 3B are approximately equal to or less than this force. When it is smaller, no weight is applied to the end of the strain rod 14. Also, the weight of containers 3A and 3B
When W _A and W _B are larger than the force (W ₀ · l ₂ / l ₁ ), there is a force at the end of the strain rod 14 that is smaller than W _A and W _B by W ₀ · l ₂ / l ₁ . Weights W _A ′ and W _B ′ are added. A bending moment M due to the weights W _A ′ and W _B ′ acts on the strain rod 14 . The magnitude of this bending moment M is determined by the weight W _A ′ acting on the end of the strain rod 14;
It is the product of W _B ' and the length from the end of the strain rod 14 to the gauge attachment (applied) part. The bending moment M causes strain in the strain rod 14, and the strain is detected by strain gauges SGa, SGb or SGc, SGd attached to the strain rod 14. Therefore, the strain gauge SGa
It is possible to measure the weights W _A ′, W _B ′ acting on the ends of the strain rod 14 due to the strain detected by ~SGd, and the weights W _A , W _B of the containers 3A, 3B. can. These four strain gauges SGa~
For example, the third
A bridge circuit as shown in the figure is constructed. E _P
is the bridge power supply applied to the bridge circuit, e ₀ is the output voltage of the bridge circuit, and T _X and T _Y are the output terminals. Note that the structure of the switching mechanism 5 and the guide tool 11 in the metering and feeding device is the same as that used in the metering and feeding device shown in FIG. 1, so the explanation thereof will be omitted. Next, the operation of this metering and feeding device will be explained. The initial state of this device is as shown in FIG. 2, and the discharge end of the discharge pipe 4 is initially located on the branch guide pipe 13A side. In addition, since the resistance values of the resistances Ra to Rd made up of the strain gauges SGa to SGd are the same when there is no strain, they are the same as the output terminals T _X of the bridge circuit shown in Figure 3.
There is no potential difference between T _Y and the output voltage e ₀ is zero. When discharge of cement and the like is started from the discharge pipe 4, the cement and the like are supplied to the container 3A through the branch guide pipe 13A. Therefore, the weight W _A of the container 3A,
Then, the weight W _A ′ acting on the left (left side in FIG. 2) end of the strain rod 14 gradually increases, and the moment M caused by the weight W _A ′ causes the strain rod 14 to move downward. bend. Then, since the strain gauge SGa receives strain, the output e ₀ of the Wheatstone bridge shown in FIG. 3 is generated only by Ra and Rb. On the other hand, the strain gauge SGc attached to the right side,
In SGd, the center part of the strain rod 14 is rigidly fixed and does not receive any strain, so no output is generated by W _B at the output e ₀ of the Wheatstone bridge, and the weight W _A ′ A voltage e ₀ of a magnitude corresponding to is output from the bridge circuit. This output voltage e ₀ increases as the weight W _A ' increases. Therefore, if it is made possible to detect, for example, with a comparator, that the voltage e ₀ has reached the reference voltage e _s corresponding to a certain reference weight W _S ′, cement, etc. will be in a predetermined amount in the container 3A. When it gets old, it can be detected. and,
At this time, the switching mechanism 5 is operated to move the discharge end of the discharge pipe 4 toward the branch guide pipe 13B. Then, cement etc. are supplied to the container 3B. Immediately thereafter, the container 3A filled with cement or the like is removed from the suspension support shaft 20, and a new empty container 3A is suspended. As a result, the output voltage e ₀ of the bridge circuit returns to its original value, that is, approximately zero. On the other hand, the weight W _B of the container 3B gradually increases and the right side of the strain rod 14 bends downward, so the strain gauge
SGc and SGd are subjected to strain, and the Wheatstone bridge generates an output e ₀ corresponding to W _B. Since the resistance values of the strain gauges SGa and SGb on the left side _of the strain rod 14 do _not change, a potential difference is generated between the output terminals _T e ₀ is output. This output voltage e ₀ gradually increases, and the weight of the container 3B side increases.
When W _B reaches the reference weight W _S , the output voltage e ₀ becomes the reference voltage
e _s , it is detected and the switching mechanism 5
The supply destination is returned to the container 3A side, and the container 3B is immediately replaced with an empty container 3B. After that, repeat the above operation. By the way, in the above-mentioned embodiment, a so-called end weight method is used in which a weight reduction mechanism consisting of a lever and a weight is provided so that the weight of the object to be measured is reduced by a certain amount and applied to the end of the strain rod. There is. According to this fractional amount method, the measurement sensitivity, measurement accuracy, and other performances of the weight measuring device can be significantly improved. Incidentally, a table comparing each characteristic between the case where the fractional method is not used and the case where the fractional method is used is shown below. Incidentally, when the fractional amount method is used, the fractional amount coefficient K (K=W _A /W _A ′=W _B /W _B ′)=30.

[Table] Total accuracy at=√ ₁ ² + ₂ ² + ₃ ² + ₄ ² +
a ₅ ² + a ₆ ² + a ₇ ² . As is clear from the table above, by using the fractional method, the characteristics of the strain gauge section and the characteristics of the amplifier can be significantly improved. Even if the weight measuring device is simply coated (waterproofed), it is possible to obtain a weight measuring device with very good performance. For example, according to a simple coating, the equivalent insulation resistance when connected in parallel to each gauge SG of a bridge consisting of strain gauges SG is not ∞ but 50 m.
As a result, an error of 7×10 ^-6 distortion will occur.For example, if the rated output is 4000×10 ^-6
If it is a strain, the effect of the reduction in insulation in the bridge cannot be ignored as shown by the figure of 0.175% FS. However, if the fractional amount method is used as in the present invention, the effect can be reduced to 1/K, that is, 0.0058% FS according to the numerical example described above, and an error of this degree does not become a problem. As mentioned above, with such a metering and feeding device, it is possible to continuously feed cement, etc. into a large number of containers one after another without stopping the flow, realizing a highly efficient metering and feeding operation of the contents. be done.
Then, strain gauges are attached to both sides of a strain rod whose approximately central portion is fixed, and one detection circuit consisting of both strain gauges alternately measures the weight of the two containers that are applied to both ends of the strain rod. This eliminates the need for two weighing scales like in the weighing and feeding device shown in Figure 1, and the structure of the weighing device is significantly simpler than that of conventional weighing devices. The manufacturing cost can also be significantly reduced. Moreover, since one weight measuring device is configured to measure the weight of two objects, the accuracy of each measuring device becomes a problem when using two weight measuring devices.
There is no need to worry about differences due to temperature effects, the initial unbalance adjustment of the weight measuring device and other adjustment operations only need to be performed once, and the same measurement result can always be obtained no matter which side of the strain rod is measured. It will be done. It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made. For example, in the embodiment shown in FIG. 2, the weight 23 is connected to the suspension shaft via the lever 21 in order to reduce the weight of the object to be measured by a certain amount, but one end of the spring is connected to the suspension shaft 20. , the other end of the spring is configured to be supported by a support plate provided on the device fixing part, and the suspension support shaft 2
0, the same effect can be obtained even if the spring force is applied in the direction opposite to the direction in which the weight W _A (W _B ) of the containers 3A, 3B is applied (that is, upward). Further, the straining rod 14 does not have to be a straight rod when viewed from its upper surface, and may be, for example, in a dogleg shape, a U shape, or the like. Furthermore, although the embodiment shown in FIG. 2 shows a structure in which the container containing the object to be measured is suspended from both ends of the strain lever, it is also possible to place the container above both ends of the balance. good. In this case, in order to avoid overturning the container and measurement errors due to eccentric loads, it is preferable to use a so-called Roberval parallel motion mechanism. Furthermore, in the above embodiment, the strain gauges were attached to both the upper and lower surfaces of the gauge attachment groove in order to obtain a larger strain output, but the strain gauges may be attached only to either the upper surface or the lower surface. Furthermore, in the above embodiment, the weights of the two containers were measured by the fractional method that is equipped with a weight reduction mechanism, but it is not always necessary to do so. The weight may be applied directly to the strain rod. As described in detail above, according to the present invention, both ends of the strain rod can be easily fixed to the support body by fixing substantially the center portion of the strain rod to which a strain gauge constituting one detection circuit is attached. It is possible to provide a low-cost weight measuring device that can alternately measure the weight of an object to be measured.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a conventional weighing and feeding device, FIG. 2 is a schematic front view showing an example of a weighing and feeding device using a weight measuring device according to the present invention, and FIG.
The figure is a circuit diagram showing an example of a detection circuit according to the present invention in which a bridge circuit is configured with a strain gauge. 3A, 3B... Container, 4... Discharge pipe, 5... Switching mechanism, 6... Plunger, 7... Drive unit, 8
... Spring, 9 ... Wire, 11 ... Guide tool, 13A, 13B ... Branch guide tube, 14 ... Strain rod, 16 ... Bolt, 17 ... Support body, 19 ...
... Gauge attachment groove, 20 ... Hanging support shaft, 20a ... U-shaped part, 21 ... Lever, 22 ... Fulcrum, 23 ...
Weight, SGa, SGb, SGc, SGd...Strain gauge, Ra, Rb, Rc, Rd...Resistance.

Claims (1)

[Scope of Claims] 1. A substantially central portion of the straining rod is fixed to a supporting body so that the weight of the object to be measured is applied to both ends of the straining rod, and the straining rod is One or more strain gauges for detecting the strain occurring on one side and one or more strain gauges for detecting the strain occurring on the other side from the center are respectively attached, and one detection is performed by both strain gauges. 1. A weight measuring device comprising a circuit which alternately detects weight applied to one end of a strain rod and weight applied to the other end by the detection circuit. 2. The weight measuring device according to claim 1, wherein the weight of the object to be measured is reduced by a certain amount and applied to each of both ends of the strain rod.