JPS5994016A - Load detection mechanism - Google Patents

Abstract

PURPOSE:To improve the load detection accuracy by arranging arms of a shaft support plate spirally in an axial symmetry while a flexure easy to bend is provided parallel almost at the right angle of the length thereof near both ends thereof. CONSTITUTION:As a measuring load displaces a shaft 22 in the Z axis direction, flexures 30 and 31 of arms 42 (42a-42d) bends so readily to incline the arms 42 slightly from the level. At the same time, the center 41 is displaced in the Z axis direction while turning slightly clockwise as indicated by the arrow. When the width W of the flexure 30 is very limited, there is little resistance against rotation of the center 41 at a fine angle associated with the Z-axis-wise displacement. This requires no force for the displacement of the detection mechanism itself when loaded, the measuring load given is wholly applied to a load cell 23 thereby improving the load detection accuracy with such a simple construction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to a load detection mechanism that reliably and precisely measures loads on upper plate materials and the like.

In general, the conditions required for a load detection mechanism are that only the force in the measurement direction can be faithfully determined, and even if a force in the perpendicular direction is applied, the resistance of the mechanism is strong and does not affect the measured value, especially at -1 m In the case of weighing plates, it is necessary that so-called four-corner errors do not occur in response to unbalanced loads applied to positions offset from the center of the weighing pan.

A typical example of a conventionally used load detection mechanism for upper plate material is shown in FIG. In FIG. 1, a weighing pan (not shown) is placed on top of the pan holder l, and gravity acting in the Z-axis direction is applied to this mechanism as a measurement load. The plate support 1 is further extended downward as a support 2, the lower end 3 of which is connected to a load cell 5 on a substrate 4. As the load cell 5, strain gauge type, electromagnetic force balance type, piezoelectric element,
Any suitable load-bearing electrical transducer with relatively small displacement, such as a tuning fork vibrator, vibrating string, or gyroscope, is commonly used.

Two further pillars 6.7 are planted on the board 4,
Two V-shaped arms 8.9, arranged vertically and in parallel, forming a donkey pal mechanism are supported by these columns 6.7 and shaft 2, and the figure 7 of these arms 8.9 base 8a,
9a is fixed to the shaft 2, the tips 8b, 8c, 9b, and 9c of the branches are fixed to the pillars 6.7, and a reinforcing bar IO is attached between the upper ends of the pillars 6.7. The V-shaped arm 8.9 itself is made to have sufficient rigidity, but near its base and outer end there are flexible parts, flexi+11a,
llb, llc, 12a, 12b, and 12c are provided, and these portions can be bent relatively freely. However, the conventional detection mechanism shown in FIG. 1 has the following drawbacks.

(a) The strength against undesirable horizontal forces applied to the pan receiver l is relatively weak, and the degree of influence differs depending on the direction. Mechanism is likely to be twisted.

(b) Regarding the groove directions of the -y reflex mills 11c, 12a to 12C, if the Yl and Y2 directions and the Yl' and Y2' directions are not parallel, a four-corner error will occur due to an unbalanced load in the Y1 direction.

(C) If the branches of the arms 8 and 9 are not sufficiently parallel to each other, errors at the four corners will occur mainly due to unbalanced loads in the X direction.

(d) Since axis 2 performs arc interlocking while maintaining verticality, axis 2
When the load cell 5 is displaced in the vertical direction, it is also slightly displaced in the horizontal direction, and an undesirable horizontal force is also applied to the load cell 5, causing a measurement error.

The present applicant proposed a detection mechanism as shown in FIG. 2 in order to solve the above-mentioned drawbacks of the prior art.

In this mechanism, the lower end of a shaft 22 that is integrally constructed with a plate holder 21 is connected to a load cell 23, and around the shaft 22, holding cylindrical bodies 24 and 25 are arranged concentrically connected in two stages, upper and lower. . Between the shaft 22 and the negative end of the upper holding cylinder 24 and between the shaft 22 and the upper end of the lower holding cylinder 25 are axisymmetric cross-shaped four-pronged arms 26a to 26d, 27a to 27d.
Shaft support plates 28 and 29 made of thin metal plates are provided so that the arms 26 and 27 are oriented parallel to each other, and the shaft 22 is supported by these shaft support plates 28 and 29. Each arm 26a to 26 of the shaft support plate 28.29
d, near the axis 22 of 27a-27d and the retaining cylinder 24.
The arm 26 is formed by rolling or cutting near the fixed part of the arm 25.
．． Flexure 3 consisting of a flexible portion that facilitates bending of 27
0.31 is formed perpendicular to the radial direction.

In such a detection mechanism, when a load is applied to the pan holder 21 in the Z-axis direction coaxial with the pan holder 21 and the shaft 22, the load is transmitted to the load cell 23 via the shaft 22. This operating state will be explained with reference to the operating principle diagram shown in FIG. 3, which is simplified on the xz plane or the YZ plane. When a load W is applied on the shaft 22, the shaft support plate 28.
Since the four-pronged arms 26 and 27 of No. 29 are arranged axially symmetrically, the il+ 22 descends correctly on the axis in a straight line without being deviated in the horizontal direction unlike the conventional mechanism, and the load cell 23 is aligned with the broken line. At the same time, each arm 2
6.27 will also be transformed to the state shown by the broken line.

In this case, there are the following three types of drag on the detection mechanism when the detection mechanism causes displacement or deformation in response to the load W.

■ Load cell 23 pressure 1? i=varies depending on the type and rating of the load cell, but in general the amount of displacement of the load cell is proportional to the magnitude of the applied load, so it is desirable to have as large a resistance to the load as possible, that is, to have high rigidity with little displacement deformation.

- Extension of arms 26, 27: In order for the shaft support plates 28, 29 to move from the horizontal state shown in solid lines in FIG. 3 to the inclined state shown in broken lines, the arms 26, 27 themselves must be extended. Therefore, tension acts on each arm 26, 27, and the sum of the component forces in the vertical direction, that is, the Z-axis direction is the load W.
acts as a drag force against It is preferable that the magnitude of this drag force be as small as possible compared to the compression drag force of the load cell 23.

■ Bending of flexure 30.31: With proper design and engineering, the drag force of flexure 30.31 is much smaller than that caused by I and ■ above and can be ignored.

1; The only peculiar point in the operation of the detection mechanism shown in FIG. 2 that differs from the conventional mechanism shown in FIG. Fig. 4 is an explanatory diagram for calculating the elongation A general case is assumed in which the center has already deviated downward by d from the horizontal state perpendicular to the axis 22 at the zero point, and a displacement δ due to the load W occurs from this state as a reference point. Here, since the displacements d and δ are proportional to the length ρ of the arm 26 and are extremely small, the following formula (1) % Formula % (1) Assuming the length g of the arm 26 to be 50 mm, the displacement assumed to be within the practical range. Table 1 shows the calculation of the extension X of the arm 26 in terms of d and δ.

Table 1 Relationship between axial displacement δ and elongation X d\δ 5
10 20 50 1000 0.000
25 0.001 0.004 0.025 0.11
00 0.01025 0.021 0.044 0.
125 0.3200 0.02025 0.041
0.084 0.225 0.5 However, all units are g
m (0, OO1mm) As is clear from the values in Table 1, even in the maximum case in Table 1, the elongation X of the arm 26 is 0.
．． It can be seen that it is only 5 gm (0,0005 mm).

Next, the tension T of the arm 26 based on the elongation X will be determined. As is well known, the relationship between tension T and elongation X is given by the following equation (2).

T = a x E / ρ ... (2) where, T is tension Kg, 11 is length mob, a is cross-sectional area ml112, X is elongation mm, E is Young's modulus Kg/m
It is l112.

Similarly to the above, the length g of the arm 26 is set to 50111111.
, the width is 10 mm, the thickness is 0.2 mm (the cross-sectional area a is 2 mm
2), Young's modulus E = 2X l 04Kg/mm
If steel material No. 2 is used, I#1. m(0,00
Tension Tot±800g/for elongation X per 1mm)
It is given by the river m.

Next, the lengthwise direction of the arm 26 is
Find the component forces in 11 directions. Taking into account that there are a total of 8 arms 26 in the load inspection DJ machine cabinet shown in Figure 2 (this means a total of 80 tons of component force in the axial direction), calculate from the following equation (3). can.

8Tx (d+δ)/1' -=・(3) In equation (3), p is exactly the force (β+X), so X is omitted in the calculation. Therefore, To=800 (
g/#Lm) as the first table number ('+1 indicated displacement d
, δ, the sum of the axial component forces corresponding to the elongation
The results calculated based on the formula are expressed as the second table number.

Table 2 Total axial component force d\δ 5 10 20” 50 10
00 0.0001B 0.0013 0.010
0.1B 1.3100 0.14 0.30'
0. f38 2.4 7.7200 0.53
1.1 2.4 7.2 19 However, the units of displacement d and δ are pm (0, OO1 mm ), the middle of the numbers in Table 2 is g, and the numbers are rounded to three significant digits or less.

The sum of the axial component forces shown in Table 2, J (i14) means that the arm 26, 27 holds the support for that part of the measured load W, and the load cell 23 (not reached) This is a measurement error (I'm not saying this at all, but compared to the measured load W+/]\\\\\It is certain that the smaller the better, the better).-For example, at the rated load. When the displacement δ of the load cell 23 is 5 gm,
At the zero point I/), temporarily (this arm 26.27 is 0, 2+
Even if it is tilted by 50 mm/nm/50 mm, the sum of the axial component forces based on the tension T of the arm 26.27 caused by the load A + (direct + 10.53 g), so the weight is 5
In the case of Kg, it is only 1/10,000 of t, and even if that l
O% force 111 Even if it changes due to some reason other than constant load, the measurement error that occurs is 1/1000 of the weighing weight and 4 yoke (calibration).Load cell 23
Even if the change of 4<1δ is slightly large, 207z, m,
The inclination of the arm 26.27 at the zero point is O, l turIl/
If it is assembled within 50mm, the total value of the axial component force will be 0.68g, which will give almost the same result.

As is clear from the explanation given above, in the load detection mechanism shown in FIG. It will be seen that when it is relatively small, it can be almost ignored from the standpoint of All-determined error.

Further, the plate support rod 21 and the support 22 in this load detection mechanism are supported by a shaft support plate 28.29 which is arranged at approximately equal angles from the center and has an axisymmetric cross-shaped four-pronged arm 26.27. Because ti! Words that have extremely strong resistance to undesirable external forces applied to the movable part in the direction perpendicular to z22, that is, in the horizontal direction, and that have almost no difference in resistance to external forces in the X-axis direction, Y-axis direction, or any horizontal direction between the two. It is structurally very easy to understand.

Next, let's look at the fifth reason why the four-corner error that occurs when an unbalanced load is extremely small according to the load detection mechanism shown in Figure 2.
This will be explained using figures. Consider a case where the arms 26 and 27 are both not horizontal and not parallel to each other due to manufacturing errors or assembly errors, which is an extremely poor condition. When a load W is applied to the end of the weighing pan 32 on the pan cup 21, at a position away from the center, each arm 26.27 receives a tension force F1, F2' and a compression force Fl through the shaft 22. ', F2
is applied to each arm 26.2 as a reaction force on the shaft 22.
From 7, a force is applied in the opposite direction to the arrow. however,
The magnitudes of forces F1, Fl', F2, and F2' are equal, and F
Since the sum of the axial component forces of l and Fl' is 0, and the sum of the axial components of F2 and F2' is also 0, it has no effect on the load cell 23, and in the end, the four-corner error due to the unbalanced load It has an outstanding advantage both in principle and in practice: it does not occur. Even if the detection mechanism is installed at a slight incline, the sum of the axial component forces will be O in the same way, and no four-corner errors will occur.

The basic condition of this detection mechanism, which has a four-corner error of O, is that each arm 26, 27 is arranged in an axially symmetrical position 11, so that it corresponds to the top and bottom like the conventional mechanism in Fig. There is no requirement that the arms 8.9 be parallel. The conditions for the arms 26 and 27 to be axially symmetrical are as follows:
Mainly (the 24.25 inch of the Kuji cylindrical body has two parallel electric numbers).
The easy processing method of Tsutomu°, which is manufactured by Tsutomu, allows the parallelism of the plane perpendicular to the cylinder axis to the height of the cylindrical axis to be achieved. Error force (detection mechanism force that almost never occurs is considered to be the easy side and 4. However, the holding cylinder body 24.25
Even if several pillars of equal height were used instead, the basic advantages of this load inspection mechanism would be undermined.
,%.

The load detection mechanism shown in FIG. 2 solves the problems of the prior art and has the above-mentioned advantages. -mu 26
．． 27 I edge elongation force <'A: flill,
The arm tension due to this elongation in the X-axis direction or tY tAI
Due to the presence of a component force in the + direction, even a small force) and c±1. )
There is a problem that part of the 411 constant load is not transmitted to the load cell 23.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a load detection mechanism that can realize extremely high-precision load detection. two shaft support plates that have at least three thin plate-shaped arms arranged axially symmetrically and at equal intervals and support the upper and lower parts of the shaft; and a holding member that holds the outer ends of the arms of these shaft support plates. Each arm of the shaft support plate is arranged in a spiral shape so that its longitudinal center line does not pass through the axis, and near both ends of each arm there are easily bendable holes that are approximately perpendicular to the longitudinal direction of the arm and parallel to each other. It is characterized by having a flexure.

The present invention will be explained in detail based on the embodiment shown in FIG. 6 and below. In these drawings, the same reference numerals as in FIG. 2 indicate the same members.

FIG. 6 is a plan view showing an embodiment of the detection mechanism, in which two shaft support plates 40 made of F-shaped metal plates are arranged in an axisymmetric spiral shape around a center portion 41 and at equal intervals. Arm 42
a to 42d, the central part 41 supports the shaft 22, and the outer end of the arm 42 is fixed to the holding cylinder 24.25. That is, the center line of the arm 42 in the longitudinal direction passes tangentially near the center portion 41 and the shaft 22 through which the shaft 22 passes. In reality, the two shaft support plates 40 support a part and the lower part of the support 22, as in the case of the detection mechanism shown in FIG. 2, except for the shaft support plate 40. The other mechanisms are the same as in the case of FIG. A flexure 30.3 is provided near both ends of each arm 42.
1 are provided substantially perpendicularly to the longitudinal direction of the arm 42 and parallel to each other, and the direction in which the flexure 30 on the center portion 41 side is formed is determined in the direction passing through the axis of the shaft 22. Each arm 42 is formed with an extremely narrow width W near the center 41,
The flexure 30 provided here has reduced bending resistance in both horizontal and vertical directions.

In FIG. 6, when the shaft 22 is displaced in the Z-axis direction perpendicular to the plane of the paper due to the measured load, the flexures 30, 31 of each arm 42 are bent relatively easily, and each arm 42 is slightly inclined from the horizontal. At this time, since the length of the arm 42 projected on the horizontal plane becomes shorter, the center portion 41 is displaced in the Z-axis direction and at the same time rotates slightly in the clockwise direction of the arrow.

For the sake of simplicity, consider the case where the width W of the flexure 30 provided on the arm 42 on the side of the center part 41 is very narrow, and there is almost no resistance force against the small angle rotation of the center part 41 due to displacement in the Z-axis direction. Since it does not exist, if the bending drag of the flexure 30 is ignored, the force required to displace the detection mechanism itself when loaded is O, and the ideal characteristic is that all of the given I11 constant load type O is applied to the load cell 23. is obtained. In the actual case where the ideal assumption conditions are not satisfied, in other words, even if the flexure 30 has a bending drag force and the width W of the flexure 30 is not O, the implementation shown in FIG. In the example, it is clear that the drag force of the detection mechanism accompanying the axial displacement during loading is extremely small, and is within a negligible range compared to the drag force of the load cell 23 itself.

In this case, since the amount of change in the length of the arm 42 projected on the horizontal plane is equivalent to the elongation X obtained by equation (1), the first
The maximum value in the table is 0.5 pm, and the center of the flexure 30 on the center 41 side of the arm 42 is 1011 degrees from the axis.
Taking as an example the case where the shaft support plate 40 is provided at a position of 1 m, the rotation angle between the center portion 41 of the shaft support plate 40 and the shaft 22 is 0.5 pm.
/ l OII + m = only 1/20000, and it can be seen that there is no problem in measurement at all.

Regarding the load detection mechanism using this axially symmetrical spiral shaft support plate 40, the force in the direction perpendicular to the shaft 22 and the resistance against unbalanced loads are qualitatively the same in principle and effect as in the explanations from FIG. 2 onwards. has. Furthermore, when the shaft 22 attempts to displace in the horizontal direction, the bending force in the horizontal plane that acts on any of the arms 42 is caused by mutually axially symmetrical arms, for example 42a and 42.
Since C acts almost integrally through CJgR41, the axis 22 is stronger than that shown in FIG.
The horizontal displacement of can also be small. A further advantage is that in the actual case where the coefficients of thermal expansion of the shaft support plate 40 and the holding cylinder 24,25 are not equal, the temperature change ratio
Even if the arm 42 expands and contracts relative to each other, the shaft 22 and the center 41 of the shaft support plate 40 can easily rotate through the required small angle and escape, so no tensile or compressive stress is generated between the arms 42 and the temperature changes. (Regardless of this, extremely stable measurements are possible.

As described above, the structure shown in FIG. 6 allows relatively large axial displacement while maintaining the basic advantage of the present invention of being extremely strong against forces in the direction perpendicular to the axis and unbalanced loads. , the numerical range number in Table 1 does not stop, load cell 23
Since the displacement δ is larger, for example, 1 mm, and the permissible range of the zero point displacement d from the horizontal state can be further widened, the range of application and practical use is significantly expanded.

Further, when an unbalanced load W is applied as shown in FIG. 5, the shaft 22 will be slightly inclined.

One way to reduce this inclination is to increase the radial rigidity of the arms 26 and 27 to reduce the amount of expansion and contraction based on the unbalanced load W, but other effective measures include The aim is to increase the width and strengthen the horizontal bending rigidity. From this point of view, it is preferable to increase the width of the outer part of the arm 42 on which a strong bending moment acts, as in the embodiment, to seek rationality in terms of material mechanics. In this case, for example, when the plate support rod 21 tries to deviate in the X-axis direction due to an unbalanced load in the This acts to reduce the horizontal displacement of the cup 21.

Although the explanation has been made assuming that the shaft support plate 40 is manufactured as a single piece by punching or the like, the load detection mechanism of this embodiment is not necessarily limited to this, and can be manufactured using two punched plates. can be formed by orthogonal to each other. Since these plates are overlapped in the center to support the shaft 22, it is impossible to assemble them on the same horizontal plane unless special work is done, but as already explained in FIG. 5, each arm 42 supports the shaft 22. As long as the basic condition of symmetrical arrangement is satisfied, there is no problem in measurement even if all the arms 42 are not on the same horizontal plane. Although the diagram shows the case of 4 trees, if the load is light and the unbalanced load is not so large as shown in Figure 7, the load detection mechanism can be configured with three arms. . That is, FIG. 7 shows the trifurcated arm 43.
a, 43b, and 43c are arranged in a spiral shape toward the center portion 41, and are formed by punching out a thin sheet metal base. The flexures 30, 31 are provided with sufficient flexibility by providing notches 44 on both sides of the arm 43, or by forming punched portions 45 between these notches 44. On the other hand, for applications involving large loads or large unbalanced loads, the load detection mechanism may be configured using a shaft support plate with five or more pronged arms.

In addition, in order to simplify the explanation, in the embodiment, the load cell 23
Although the case where a compression type load cell 23 is used has been explained as an example, it is of course possible to use a tension type load cell 23 by changing the force transmission mechanism.

As explained above, the rJ heavy detector of the present invention is 1/
'1 With a simple configuration, it is possible to
It is extremely resistant to undesirable external forces in the direction, and when used in -, +-mt scales, there is almost no error force at the four corners of the counter, making highly accurate load measurement possible. There are huge advantages.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional load detection mechanism, Figure 2 is a structural diagram of another detection mechanism, Figure 3 is a diagram of the basic operation principle of 1, and Figure 4 is a diagram of the arm's seasonal changes when a load is applied. An explanatory diagram, Fig. 5 is an overview of the movement when an unbalanced load is applied, Figs. 6 and 7 are an example of the present invention (6? It is a structural diagram. Reference numeral 21 is a plate support rod, 22 +thdl+, 2] load cell, 24.25 is a holding cylinder, 26.27.42.4
3 is arm, 28.29.40t @11 branch temple board, 3
0.31 is a flexure, 441 is a cutting base b, and 45 is a punching part. Figure 1 Figure 3 Figure 4 Figure 5 Teitouri Neichisho (self-proposal) December 17, 1980 Director General of the Patent Office Kazuo Wakasugi 1, Indication of the Case 1988 Patent Application No. 205284 2. Name of the invention Load detection mechanism 3. Relationship with the person making the amendment Patent applicant address 3-9-11 Yushima, Bunkyo-ku, Tokyo Name Shinko Denshi Co., Ltd. Representative Yuzuru Nishiguchi 4, Agent address 121 Tokyo Address: C-104 Umejima High Town, 2-17-3 Umejima, Adachi-ku, Tokyo 18th year, month, day 6, Detailed explanation of the invention in the specification subject to amendment 7, Contents of the amendment (1) Page 9 of the specification "T" in the 10th line is corrected to "To". (2) "X-axis direction or Y-axis direction" on page 13, line 19 of the same page is corrected to "X-axis direction."

Claims (1)

[Claims] 1. A shaft that receives a load, and two arms that support the upper and lower parts of the shaft, each having at least three thin plate-like arms that are axially symmetrical and spaced apart from the center that supports the shaft. and a holding member that holds the outer ends of the arms of these shaft support plates, each arm of the shaft support plate is arranged in a spiral shape such that its longitudinal center line does not pass through the axis, A load detection mechanism characterized in that near both ends of each arm, easy-to-bend flexures are provided that are substantially perpendicular to the longitudinal direction of the arms and parallel to each other. 2. The load detection mechanism according to claim 1, wherein the width of the arm is narrowed near the center to reduce the bending resistance in both the horizontal and vertical directions of the flexure provided in this part. 3. The load measuring mechanism according to claim 1, wherein the arm becomes wider toward the outer end.