JPH0336902Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a force measuring device, and particularly to one having two strain elastic bodies and a force detector provided between these elastic bodies.

Previously, the creator of this idea proposed a force measuring device as shown in Figures 1 and 2 (Patent Application 1983-
(See No. 175456). This has a main elastic body 1 and a secondary elastic body 2. One ends of both of these elastic bodies 1 and 2 are fixed onto a fixed base 4 via a member 3 with bolts 5 and 5. That is, both elastic bodies 1,
2 is fixed in a cantilevered manner. Note that 6 is an insulating material for insulating both the elastic bodies 1 and 2.

A string 7 is stretched between the other ends of both the elastic bodies 1 and 2, and the effective length l of this string 7 is made equal to the length l of the member 3. A magnetic field is applied by a magnetic field generator 8 perpendicularly to the length direction of the string 7. The string 7 is connected via a capacitor 10 to the input side of an amplifier 9 shown in FIG.
A portion of the output of this amplifier 9 is fed back to the string 7 via a resistor 11.

Here, a downward load W is applied to the other end of the main elastic body 1.
When this is applied, a deflection Δl1 proportional to the load W is generated in the main elastic body 1, and the string 7 is pulled downward. string 7
The tension P applied to the auxiliary elastic body 2 acts on the other end of the secondary elastic body 2, causing the other end to bend downward Δl2. The spring constant of the main elastic body 1 is K1, and the spring constant of the secondary elastic body 2 is K2
If we ignore the elongation of string 7, then P=∆l2・K2 holds true, and ∆l1=∆l2=∆l, so W=∆l(K1+K2) P=W・K2/(K1+K2), and the tension P is the load W. is proportional to. Therefore, if the tension P can be measured, the applied load can be obtained. Therefore, when measuring the tension P, when the string 7 is slightly bent in a direction that cuts the magnetic field due to the applied load, a current flows through the string 7 according to Fleming's right-hand rule. This current is amplified by an amplifier 9, and its amplified output is supplied to the string 7 via a resistor 11. This output flows in a direction that causes the string 7 to further bend in the same direction, and the string 7 further bends in a direction that cuts the magnetic field.
The string 7 is bent to a position where the energy applied from the amplifier 9 and the bending reaction force of the string 7 are balanced, and then returns in the opposite direction. As a result, a current flows in the opposite direction to the string 7, and the reverse current is supplied to the amplifier 9 via the capacitor 10 and amplified, and an amplified reverse current is supplied to the string 7. Flex string 7 in the opposite direction. After that, repeat this to vibrate at the same frequency. This frequency is It is expressed as However, n is the harmonic number of vibration, l
is the effective length of the string 7, g is the gravitational acceleration, and r is the mass per unit length of the string 7. Therefore, P can be obtained by measuring the frequency and performing arithmetic processing,
The load W can be obtained by further calculating this.

By the way, in such a force measuring device, it has been found that more accurate measurements can be made by applying an initial tension several times the tension applied to the string 7 in the measurement range. That is, when a certain tension is applied to the string 7, the string 7
causes a resonance phenomenon with the external equipment, and the string 7 causes unstable vibration as shown in FIG. There are multiple regions where such unstable vibrations occur, as shown in Figure 6, at frequencies that are integral multiples of the frequency of the resonance phenomenon described above, and the measurement range should not be set to avoid these unstable vibration regions. Since this causes a measurement error, an initial tension approximately several times the measurement range is applied as shown in FIG. 6 to bring the measurement range outside the unstable region. Therefore, when a load W is applied to the other end of the main elastic body 1, a mounting plate or the like (not shown) attached to the main elastic body 1 is made heavier, thereby increasing the weight applied to the main elastic body. In this case, when a force is applied by placing the article on a tray or the like, the tension applied to the string 7 further increases as shown in FIG. 6, and the applied force is measured. However, this method has the disadvantage that if the tension applied in the measurement range of the force measuring device is large, the weight of the entire force measuring device becomes heavy.

The object of this invention is to provide a force measuring device that eliminates the above-mentioned drawbacks.

Therefore, in this invention, the distance between the main elastic body and the auxiliary elastic body is configured to be longer than the length l of a force detector such as a string and set to l+Δl ₀ .

By connecting the main elastic body and the secondary elastic body with a force detector with length l, if the spring constant of the main elastic body is K1 and the spring constant of the secondary elastic body is K2, then the other end of the secondary elastic body (force detection The other end of the main elastic body (the part where the force detector is attached) bends downward by Δl ₀ ·K1/(K1+K2), and the other end of the main elastic body (the part where the force detector is attached) bends upward by Δl ₀ ·K2/. (K1+K2) is bent. Then,
An initial tension is applied to the force detector as the main elastic body and the secondary elastic body try to return to their original positions. The magnitude of the initial tension S is S=Δl ₀ K1·K2/K1+K2. Therefore, a predetermined initial tension S can be obtained by appropriately selecting Δl ₀ . Therefore, even when the tension applied in the measurement range is large, that is, even when the applied load is large, accurate measurement can be performed without making the mounting plate or the like heavy, and the weight of the entire force measuring device can be reduced.

This invention will be explained below based on two embodiments shown in FIGS. 3 to 5. A first embodiment is shown in FIGS. 3 and 4. In FIG. 3, 11 is a main elastic body, 12 is a secondary elastic body, and 13 is a liner. Both elastic bodies 11, 12 and liner 13 are integrally formed and mounted on a fixed base 14. The distance between the attachment positions of the string 17 at the other ends of both the elastic bodies 11 and 12 is longer than the length l of the string 17 and is l+l ₀ . Therefore, when the string 17 is attached, the secondary elastic body 12 moves downward as shown in _FIG .
The main elastic body 11 bends upward by Δl ₀・
Bending by K2/(K1+K2), initial tension S on string 17
It takes S=Δl ₀ K1・K2/K1+K2. Although omitted in the figure, the main elastic body 1
1 is naturally provided with a magnetic field generator, and a load is applied to the main elastic body 11.

In the second embodiment, the main elastic body 21 is a Roberval mechanism, and the internal space includes a secondary elastic body 22, a liner 23, an insulator 26, a string 27, and a magnetic field generator 28.
This embodiment differs from the first embodiment in that the stage 30 is provided on the side of the main elastic body 21.
In this embodiment, the distance between the string attaching portion 29 of the main elastic body 21 and the auxiliary elastic body 22 is longer than the length l of the string 27 and is l+Δl ₀ .

In both embodiments, the string 7 and the magnetic field generator 28 are used as force detectors, but a crystal type or tuning fork type force detector can also be used. In both of the above embodiments, the main elastic body and the secondary elastic body were formed so that they were parallel to each other without a force detector, but with the force detector attached, the main elastic body and the secondary elastic body were formed so that they were parallel to each other. may be configured. In the first embodiment, the main elastic body 11, the secondary elastic body 12, and the liner 13 were integrated;
They may be formed separately as in the conventional structure shown in the figure. Conversely, in the second embodiment, the main elastic body 2
1. The secondary elastic body 22 and the liner 23 may be formed integrally. Further, in the first embodiment, the secondary elastic body 2 was provided above the main elastic body, but it was provided below and the string 7
A compressive force may be applied to a force detector such as the above. In this case, according to the present invention, an initial tension is applied to the force detector that measures the compressive force, but when a force is applied by placing an article etc. on a tray, the initial tension is reduced as shown in FIG. Since the compressive force is applied to the force detector in the direction of decrease and the force is measured, there is no problem in measuring this force even if the initial tension is applied. Furthermore, although the secondary elastic body 22 is provided inside the main elastic body 21 in the second embodiment, it may be provided above or below the main elastic body 21.

[Brief explanation of the drawing]

Figure 1 is a side view of a conventional force measuring device, Figure 2 is a circuit diagram showing part of the electric circuit used in the force measuring device, and Figure 3 is a first embodiment of the force measuring device according to this invention. A side view of the elastic body used, Figure 4 is the same as Figure 1.
FIG. 5 is a side view of the second embodiment, and FIG. 6 is a diagram showing the relationship between compressive force and tension in the string and unstable vibration. 11, 21... Main elastic body, 12, 22... Sub-elastic body, 17, 18, 27, 28... Force detector.

Claims (1)

[Scope of utility model registration request] A main elastic body and a secondary elastic body are provided at intervals in the vertical direction so as to deform when receiving a force, and when the main elastic body deforms due to the force, the secondary elastic body also shares the force. a force detector provided between the two elastic bodies to balance the combined restoring force of the two elastic bodies with the force and detect the force applied to the secondary elastic body; A force measuring device characterized in that an interval before the force detector is attached is selected to be larger than a length dimension of the force detector.