JPH0453555Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial field of application> This force measuring device is used to measure force and weight, and is designed to prevent fluctuations in the zero point due to temperature changes in the usage environment. It is.

<Prior art> The applicant of this invention previously applied for a force measuring device as shown in Figs. 4 and 5 (Japanese Patent Application No. 1982-
No. 175456). As shown in FIG. 4, this has a main elastic body 1 and a secondary elastic body 2, and these elastic bodies 1, 2
One end of is fixed on the fixing base 4 via the member 3,
A string 5 is provided between the other ends, and a permanent magnet 6 is placed around the string 5.
An amplifier 7 is connected to the string 5 as shown in FIG.

In this force measuring device, when a load W is applied downward to the other end of the main elastic body 1, a deflection Δl1 proportional to the load W is generated in the main elastic body 1, as shown in FIG. Pull the bottom edge of the The tension P applied to the string 5 acts on the other end of the auxiliary elastic body 2, causing the other end to bend downward Δl2. Here, the elastic modulus of the main elastic body 1 is K1, and the elastic modulus of the secondary elastic body 2 is K2.
If we ignore the elongation of string 5, P=Δl2・K2 holds true, and Δl1=Δl2=Δl, so W=Δl(K1+K2) P=W・K2/(K1+K2), and the tension P is the load. It is proportional to W, and by measuring P, the load W can be measured.

Tension P is measured by string 5, permanent magnet 6 and amplifier 7. In other words, a magnetic field is applied to the string 5 by a permanent magnet 6 perpendicular to its length direction, and when the string 5 bends slightly in a direction that cuts the magnetic field due to the tension P, Fleming's right-hand rule applies. A current flows through the string 5 according to . This current is supplied to an amplifier 7 via a capacitor 8 and amplified, and the amplified output is supplied to the string 5 via a resistor 9. This output flows in a direction that causes string 5 to further bend in the same direction,
The string 5 is further bent in the direction of cutting the magnetic field. The string 5 is bent to a position where the energy applied from the amplifier 7 and the bending stress of the string 5 are balanced, and then returns in the opposite direction. As a result, a current flows in the opposite direction to the string 5, and the reverse current is supplied to the amplifier 7 via the capacitor 8 and amplified, and the amplified reverse current is supplied to the string 5. , bend string 5 in the opposite direction. After that, repeat this to make the frequency oscillate. This frequency is is required. However, n is the harmonic number of vibration, l
is the effective length of the string 5, g is the gravitational acceleration, and r is the mass per unit length of the string 5. Therefore, by measuring the number of changes in the output of the amplifier 7, the frequency can be measured, thereby the tension P can be measured, and naturally the load W can be measured.

The string 5 acts as a force detector, but in addition to these, a crystal sensor, a tuning fork sensor, a semiconductor sensor, etc. can be used, and there are also forms of use that measure not only tension but compressive force.

In such conventional force measuring devices, the force detector is given an initial load to improve measurement accuracy. For example, an initial tension is applied to the string 5 by flexing the auxiliary elastic body 2 by a certain amount and stretching the string 5 (Utility Model Application No. 139731/1982).

<Problems to be solved by the invention> The conventional force measuring device has a problem in that the zero point also changes when the temperature changes. That is, there is a relationship between the load W and the tension P of the string 5 as shown in equation (1).

P=Δlо・K1・K2/K1+K2+WK2/K1+K2...(1) However, since Δlо gives the initial tension to string 5,
This is the difference between the effective length l of the string 5 and the distance between the main elastic body 1 and the auxiliary elastic body 2, which are longer than that. The first term in equation (1) is the tension when the secondary elastic body 2 is bent by Δlо at its tip, that is, the initial tension, and the second term is the load W which is the elasticity of the main elastic body 1 and the secondary elastic body 2. This is the tension that is shared by the ratio of the coefficients, and in the case of the one that is in practical use, if the second term is set to 1, the value of the initial tension is 4 to 1.
It is 6. Here, the temperature coefficients of K1 and K2 are α1 and α2
Then, the tension P is P=Δlо・K1(1+α1・T)・K2(1+α2・T)/K
1(1+α1・T)・K2(1+α2・T)+WK2(1+α2
・T)/K1(1+α1・T)+K2(1+α2・T)……(2
). If the main elastic body 1 and the secondary elastic body 2 are made of the same material, α1 = α2 = α, and the tension P
is, P=ΔlоK1・K2(1+αT) ² /(K
1+K2)(1+αT)+WK2(1+αT)/(K1+K2)(
1+αT) =ΔlоK1・K2(1+αT)
/K1+K2+WK2/K1+K2...(3). From equation (3), temperature changes in the elastic modulus affect the initial tension, which causes a large zero point change. For example, the symbols a, b, and c in Fig. 8 show the relationship between the deflection of the secondary elastic body 2 and the tension P when the temperatures are T1, T2, and T3. Even if a deflection of Δlо is applied to the secondary elastic body 2, when the temperature changes from T1, T2, T3, the initial tension also decreases.
It changes from S1, S2, S3. In order to prevent such a change in the initial tension, that is, a change in the zero point, and maintain a predetermined accuracy, temperature control is required, which is disadvantageous in terms of use.

<Means for Solving the Problems> In order to solve the above problems, the present invention has a fixed base and a force application point, and receives a force in a predetermined direction at the force application point so that the application point is A main elastic body that produces an elastic displacement proportional to the direction of the force, and a reaction force that is smaller than the above force corresponding to that displacement when a displacement is applied to its own point of action in the same direction as the displacement of the point of action of the main elastic body. a secondary elastic body made of the same material as the main elastic body, and having a length dimension equal to the distance between the points of action of each of the elastic body and the secondary elastic body, and is attached between both the elastic bodies. , in a force measuring device equipped with a force detector in which elongation due to displacement of the main elastic body and the secondary elastic body can be ignored, the elasticity between the two elastic bodies in the vicinity of the force detector is almost constant even when there is a temperature change. A constant modulus spring having a constant modulus of elasticity is placed in a state where it is strained to apply an initial tension to the force detector.

<Operation> According to the present invention, since the initial tension is applied by a spring whose elastic modulus hardly changes, the tension P
is P=Δl・K+W・K2/(K1+K2)...(4). However, Δl is the amount (displacement) by which the spring is bent in order to provide it between both elastic bodies, and K is the spring constant of the spring.

Since the elongation of the force detector can be ignored,
When a force is applied to the main elastic body, the amount of deflection of the main elastic body and the amount of deflection of the secondary elastic body are equal, and the distance between both elastic bodies does not change. As a result, Δl does not change,
Even if a force is applied to the principal elastic body, the initial tension is not affected.

Also, since the elongation of the force detector can be ignored, by providing a spring between both elastic bodies,
Even if an initial tension is applied to the force detector, no deflection occurs in either elastic body, and even if there is a temperature change, the initial tension is not affected by the temperature change. That is, the initial tension is always Δl·K. Therefore, the relationship between the tension P and the deflection of the secondary elastic body changes as the temperature changes from T1, T2, and T3, as shown by symbols A, B, and C in FIG. 8, but the initial tension Sо (= Δl·K) is always constant and the zero point does not fluctuate.

<Example> The first example has a main elastic body 12 and a sub elastic body 14, as shown in FIG. This main elastic body 1
Reference numeral 2 has a structure applying a Roberval mechanism, in which a cavity 12a is formed so that the side surface shape is a parallelogram frame, and the four corners of the cavity 12a are formed as strain-generating parts 12b. The main elastic body 12 and the auxiliary elastic body 14 are manufactured by machining the same material as one body, similar to that disclosed in Japanese Patent Application No. 58-201543. The base portion 16 of the main elastic body 12 and the secondary elastic body 14 that are integrated is connected to a fixed base 18
is fixed. At the force application point of the main elastic body 12,
A platform 19 is connected across the secondary elastic body 14, and by placing an article on the platform 19,
A downward load is applied to the main elastic body 12. Note that the elastic modulus of the main elastic body 12 is set larger than that of the secondary elastic body.

The point of action at the tip of the main elastic body 12 and the secondary elastic body 1
A string 20 is stretched between the point of action of 4 and the point of action of 4. The effective length L of this string 20 is selected to be equal to the distance between the central axes of the main elastic body 12 and the auxiliary elastic body 14, and the elongation can be ignored as in the conventional one. Therefore, unlike conventional ones, the effective length of the string 20 is made shorter than the length between the center axes of the main elastic body 12 and the secondary elastic body 14, and the secondary elastic body 14 is bent downward by a certain amount to apply initial tension to the string 20. I haven't put any money on it. Although not shown in the figure, a magnetic field generator is provided around the string 20, similar to the conventional one, and the string 20 is connected to a circuit as shown in FIG. .

A saucer 22 is coupled to the lower surface of the auxiliary elastic body 14 so as to be in contact with it at one point. Further, a saucer 24 is coupled to the upper surface of the main elastic body 12 so as to face the saucer 22 . This tray 24 also contacts the upper surface of the main elastic body 12 at one point. A constant-elasticity spring 26 whose elastic modulus is not easily changed by temperature is fitted into or bonded to these trays 22 and 24. The constant elasticity spring 26 is a commercially available product made of, for example, nickel, chromium, iron, or titanium alloy, which has been heat-treated to obtain high mechanical properties and has a constant elastic modulus in the temperature range of -45°C to +65°C. be.
This constant elasticity spring 26 is formed in the shape of a cylindrical compression coil spring, and its length is originally the same as that of the saucer 22.
A piece longer than the distance between the trays 24 is compressed by pressing and is fitted or bonded between the saucers 22 and 24. Therefore, the constant elasticity spring 26 applies its acting force to the lower surface of the auxiliary elastic body 14, and the initial tension is applied to the string 20 by this acting force.

In this force measuring device, when a force is applied to the main elastic body 12, the elongation of the string 20 can be ignored, so the amount of deflection of the main elastic body 12 and the secondary elastic body 14 is the same. Therefore, since the spring 26 is provided between the main elastic body 12 and the auxiliary elastic body 14, the amount of displacement of the spring 26 does not change, and the initial tension depends on the deflection of the main elastic body 12 and the auxiliary elastic body 14. It does not change depending on.

Also, since the elongation of string 20 can be ignored,
Even if an initial tension is applied to the string 20 by providing a spring 20 between the main elastic body 12 and the auxiliary elastic body 14 in the vicinity of their points of action, the main elastic body 12 and the auxiliary elastic body 14 do not bend. Therefore, the elastic coefficients of the main elastic body 12 and the secondary elastic body 14 are not related to the initial tension, and the initial tension does not change even if the temperature changes.

In the second embodiment, as shown in FIG. 2, a screw hole 28 is cut through the main elastic body 12 in the vertical direction, and a male screw body 30 is screwed into the screw hole 28. A saucer 24 is provided in the same manner as in the first embodiment, and an operating section 32 is provided on the lower surface. The rest of the structure is the same as that of the first embodiment.

With this configuration, the initial tension applied to the string 20 can be adjusted by inserting a driver or the like into the operating section 32 and changing the screwing position of the male threaded body 30 with respect to the screw hole 28.

In the third embodiment, as shown in FIG. 3, the main elastic body 12 and the secondary elastic body 14 have insertion holes 34,
36, and insert the tip of the constant elastic spring 26 into the set screws 42, 44 provided in passages 38, 40 bored from the side so as to communicate with these insertion holes 34, 36. Therefore, the constant elastic spring 26 is fixed. The rest of the structure is the same as that of the first embodiment.

In the fourth embodiment, as shown in FIG. 6, the secondary elastic body 14 is arranged in the cavity 12a of the main elastic body 12,
The base of this secondary elastic body 14 is fixed to the base of the main elastic body 12. Then, the vicinity of the point of action of the auxiliary elastic body 14 and the vicinity of the point of action of the main elastic body 12 are pulled upward by a constant elastic spring 26a serving as a tension spring, so that the string 20 is Initial tension is applied.

This embodiment also uses a tension spring 24a, but when force is applied to the main elastic body 12, the elongation of the string 20 can be ignored, so the deflection of the main elastic body 12 and the secondary elastic body 14 are equal. , tension spring 24a
The amount of displacement does not change, and the initial tension does not change due to the application of force. Further, since the elongation of the string 20 can be ignored, neither the main elastic body 12 nor the sub elastic body 14 is bent when applying the initial tension to the string 20. As a result, the elastic coefficients of the main elastic body 12 and the secondary elastic body 14 are not related to the initial tension, and the initial tension does not change even if the temperature changes.

The fifth embodiment, as shown in FIG. The right end portion is fixed to the tip end side of the main elastic body 12, that is, to the point of action side. And the secondary elastic body 14
A string 20 is provided between the left end in the figure and the base side of the main elastic body 12, and this string 20 is pulled downward by a tension spring 26a.

Also in this force measuring device, when a force is applied to the main elastic body 12, the main elastic body 12 bends, and the right side portion of the secondary elastic body 14 in the figure bends accordingly. At this time, since the elongation of the string 20 can be ignored, the position of the left end of the auxiliary elastic body 14 does not change, and the tension spring 2
6a is not displaced. Therefore, the initial tension does not change due to the force being applied to the main elastic body 12.
Further, since the elongation of the string 20 can be ignored, neither the main elastic body 12 nor the sub elastic body 14 is bent when applying the initial tension to the string 20 by the tension spring 26a. Therefore, the main elastic body 12, the secondary elastic body 1
The elastic modulus of 4 does not affect the initial tension, and the initial tension does not change even if the temperature changes.

In the first and second embodiments, the saucers 22 and 24 are provided, and the constant elastic spring 26 is provided between them so that the acting force is applied to one point.
Either one of these may be omitted, or in some cases both may be omitted. In each embodiment, the constant elasticity springs 26 and 26a are formed into cylindrical coil springs, but conical, claw-shaped, or barrel-shaped coil springs may also be used.

<Effects> As described above, in this invention, the initial tension is applied using a constant elastic spring, so even if there is a temperature change, the zero point hardly fluctuates.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway side view of the first embodiment of the force measuring device according to this invention, Fig. 2 is a partially omitted side view of the second embodiment, and Fig. 3 is a portion of the third embodiment. 4 is a side view of a conventional force measuring device, FIG. 5 is a circuit diagram of the same device, FIG. 6 is a side view of the fourth embodiment, and FIG. 7 is a side view of the fifth embodiment. Side view,
FIG. 8 is a diagram showing the relationship between the deflection of the auxiliary elastic body and the tension of the string in the conventional force measuring device and the force measuring device according to the present invention. 12... Main elastic body, 14... Secondary elastic body, 20...
... String (force detector), 26, 26a... Spring.

Claims (1)

[Scope of utility model registration request] A main elastic body whose base is fixed, has a force application point, receives a force in a predetermined direction at the force application point, and the point of application causes an elastic displacement proportional to the direction of the force; and the displacement of the application point of the main elastic body. A secondary elastic body made of the same material as the main elastic body, which produces a reaction force smaller than the force corresponding to the displacement when a displacement in the same direction is applied to its point of action, and the main elastic body and the secondary elastic body. a force detector having a length dimension equal to the distance between the points of application of each of the two elastic bodies, the force detector being installed between the two elastic bodies, and capable of ignoring elongation due to displacement of the main elastic body and the secondary elastic body; In the device, a constant elastic modulus spring having a substantially constant elastic modulus even when temperature changes is placed between the two elastic bodies in the vicinity of the force detector, and is strained to a state that applies an initial tension to the force detector. A force measuring device characterized in that it is installed with the