JPH0452662Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention relates to a force measuring device, and particularly to one that prevents zero point fluctuations due to temperature changes in the usage environment.

<Prior art> The applicant of this invention applied for a force measuring device as shown in Figs.
issue). This has a main elastic body 1 and a secondary elastic body 2 as shown in FIG. A string 5 is provided between the parts, a magnetic field generator 6 is provided around the string 5, and an amplifier 7 as shown in FIG. 4 is connected to the string 5.

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.

The tension P is measured by the string 5, the magnetic field generator 6, the amplifier 7, etc. In other words, the string 5 has a magnetic field generator 6
, a magnetic field is applied perpendicular to the length direction of the string 5, and when the string 5 is slightly bent in a direction that cuts the magnetic field due to the tension P, a current flows through the string 5 according to Fleming's right-hand rule. flows. This current is supplied via a capacitor 8 to an amplifier 7 where it is amplified, and its amplified output is supplied to the string 5 via a resistor 9. This output flows in the direction of further bending the string 5 in the same direction, and 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 returns in the opposite direction. This causes string 5
A current flows in the opposite direction to that before, and this 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, which is the opposite direction to that before. Flex string 5 in the direction. Thereafter, this is repeated, and the string 5 vibrates at the same frequency. 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,
In addition, a crystal sensor, a tuning fork sensor, a semiconductor sensor, etc. can be used, and by changing the position of the auxiliary elastic body, it is also possible to measure compressive force instead of tension.

In such conventional force measuring devices, an initial load is applied to the force detector in order to improve measurement accuracy. For example, the effective length l of the string 5 is made shorter than the center axis distance of the main elastic body 1 and the secondary elastic body 2, and the secondary elastic body 2 is bent downward to give an initial load, that is, an initial tension (actual (See Application No. 58-139731). Note that since the elastic coefficient K1 of the main elastic body 1 is selected to be larger than the elastic coefficient K2 of the secondary elastic body 2, the secondary elastic body 2 bends downward, but the main elastic body 1 hardly bends.

<Problems to be solved by the invention> The above force measuring device had a problem in that the zero point also changed when the temperature of the usage environment changed. That is, there is a relationship between the load W and the string tension B as shown in equation (1).

P=Δl ₀・K1・K2/K1+K2+WK2/K1+K2 ...(1) However, Δl ₀ is the effective length l of the string 5 and the principal elastic body 1 which is longer than this in order to give initial tension to the string 5. This may be the difference in distance between the elastic body 2 and the secondary elastic body 2. The first of equation (1)
The term is the initial tension, and the second term is when the load W is the main elastic body 1
The tension is shared by the ratio of the elastic coefficients of the elastic body 2 and the secondary elastic body 2, and in the case of a practical example, when the second term is 1, the value of the initial tension is 4 to 6. Here, if the temperature coefficients of K1 and K2 are α1 and α2, the tension P is P=Δl ₀ K1(1+α1・T)・K2(1+α2T)/K1(
1+α1・T)・K2(1+α2T) +WK2(1+α2・T)/K1(1+α1・T)・K2(
1+α2・T) ...(2) If both elastic bodies 1 and 2 are made of the same material, α1 = α2 = α, and the tension P is P = Δl ₀ K1・K2 (1 + αT) ² / (K1 + K2) (
1+αT)+WK2(1+αT)/(K1+K2)(1+αT) =Δl ₀ K1・K2(1+αT)/(K1+K2)+WK2
/K1+K2...(3). Equation (3) can be replaced with P=A(1+αT)+WB...(4). However, A=Δl ₀ K1·K2/K1+K2, B=K2/K1+K2. Therefore, as shown in Figure 5, the ambient temperature
When changing to T1, T2, T3, the initial tension becomes S1, S2,
Changes with S3. In this way, the initial tension changes due to changes in the usage environment, which causes a large change in the zero point. In order to prevent this and maintain a predetermined accuracy, temperature control is required, which is disadvantageous in terms of use.

<Means for solving the problem> A means for solving the above problem is to use the force measuring device described above to generate a force that cancels the change in the initial load caused by the temperature change, that is, AαT, that is, − A temperature change member that applies AαT to the force detector is provided between both elastic bodies.

<Operation> According to such means, a force of -AαT is applied to the force detector even if the temperature changes, so the tension P is: P=A(1+αT)+WB−AαT=A+WB...(5 ), and the initial load does not fluctuate due to temperature changes.

<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
2 is a structure applying a Roberval mechanism, in which a cavity 12a is formed so that the side shape is a parallelogram frame, and the four corners of the cavity 12a are strain-generating parts 12b.
is formed. These main elastic body 12 and sub-elastic body 14 are
93326), it is manufactured by machining the same material, for example, an aluminum alloy, as one piece. The base portion 16 of the main elastic body 12 and the secondary elastic body 14 which are integrated is connected to a fixed base 18
is fixed. At the force application point of the main elastic body 12,
A platform (not shown) is coupled across the secondary elastic body 14, and by placing an article on this platform, a downward load is applied to the main elastic body 12.

A string 20 is selected between the point of action of the main elastic body 12 and the point of action of the auxiliary elastic body 14 . The effective length L of the string 20 is selected to be shorter than the distance between the central axes of the main elastic body 12 and the secondary elastic body 14 in a no-load state. Therefore, if the elastic modulus of the main elastic body 12 is selected to be larger than the elastic coefficient of the secondary elastic body 14 by attaching the string 20, almost only the secondary elastic body 14 will bend, and the initial tension will be applied to the string 20. is applied. Although not shown in the figure, a magnetic field generator is provided around the string 20 as in the conventional case, and the string 20 is connected to a circuit as shown in FIG. 4.

A mounting portion 22 is provided on the upper surface of the main elastic body 12, and a base end portion of a bimetal 24 provided parallel to the secondary elastic body 14 is adhered to this mounting portion 20. Further, the tip of the bimetal 24 contacts the tip of a conical contact portion 26 provided on the lower surface of the auxiliary elastic body 14 at one point. The attachment part 24 is the main elastic body 1
It can be formed integrally with the main elastic body 12, or it can be formed separately and adhered to or fitted into the main elastic body 12. Similarly, the contact portion 24 can also be formed integrally with the secondary elastic body 14, or can be formed separately and adhered to or fitted into the main elastic body 12.

In the force measuring device configured in this way, the string 20 is initially
Initial tension is applied to . However, as the temperature rises, the elastic coefficients of the main elastic body 12 and the secondary elastic body 14 become smaller, and the reaction force caused by tilting the secondary elastic body 14 downward tends to decrease. At this time, the bimetal 24 bends upward, and the secondary elastic body 14
push upwards. At this time, bimetal 24
The material, effective length, thickness, width, etc. of the main elastic body 12
If the material of the auxiliary elastic body 14 is appropriately selected after taking into account the material, etc., it is possible to cancel out the fluctuations in the initial tension due to temperature changes.

The second embodiment has a contact portion 2 as shown in FIG.
6 is provided at the tip of the bolt 28 and fixed to the secondary elastic body 14 with a nut 30, and the bimetal 2
4 is connected to the main elastic body 12 via the mounting portion 22 with a bolt 31. Reference numeral 32 denotes a long hole for bolt insertion, which is drilled in the auxiliary elastic body 14, and by using this, the effective length of the bimetal 24 can be adjusted. 34 is a driver insertion hole bored in the auxiliary elastic body 14.

In the second embodiment, the bimetal 24 is coupled to the main elastic body 12 together with the attachment portion 22;
The bimetal 24 may be coupled to the main elastic body 12 with a bolt, and the bimetal 24 may be attached to the mounting portion 22 with another bolt.

<Effects> As described above, according to this invention, temperature changes in initial tension can be offset by a temperature change member such as a bimetal, so zero point fluctuations due to temperature changes can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a side view of a first embodiment of a force measuring device according to this invention, FIG. 2 is a partially omitted cutaway sectional view of the second embodiment, and FIG. 3 is a side view of a conventional force measuring device. FIG. 4 is a circuit diagram of a conventional force measuring device, and FIG. 5 is a diagram showing changes in initial tension due to temperature changes in the conventional force measuring device. 12... Main elastic body, 14... Secondary elastic body, 20...
... String (force detector), 24... Bimetal (temperature change member).

Claims (1)

[Scope of utility model registration request] A main elastic body whose base is fixed and has a force application point, and when the force application point receives a force in a predetermined direction, the point of application causes an elastic displacement proportional to the force, and a secondary elastic body made of the same material as the main elastic body, which generates a reaction force smaller than the force corresponding to the displacement when displacement is applied to its point of action;
a force detector attached between the main elastic body and the secondary elastic body, the force detector having a length dimension shorter than the distance between the attachment points between the two elastic bodies before the force detector is attached. In the force measuring device to which an initial tension is applied, a temperature change member that changes strain in a direction that changes the tension of the force detector as the temperature changes is interposed between the two elastic bodies. A force measuring device characterized in that the temperature characteristic of the deformation of the temperature change member is selected to a value that can offset the temperature change in the initial tension.