JPS6352021A - Force measuring instrument - Google Patents

Abstract

PURPOSE:To remove the influence of hysteresis and creeping and to measure a force with high accuracy by making a main and a subordinate strain inducing elastic body of the same material and shaping those strain inducing parts so that they are strained equally. CONSTITUTION:The main strain inducing elastic body 1 and subordinate strain inducing elastic body 2 are provided, and their one-end parts are fixed on a fixed base through a member 3 with bolts. Both elastic bodies 1 and 2 are formed of the same material or materials which are equal in temperature coefficient in such a shape that flection parts (strain inducing part) are equal in maximum stress; and the other-end parts coupled by a string 7. Consequently, a downward load W is placed on the other end part of the elastic body 1, but hysteresis is left at the elastic bodies 1 and 2 after the load is removed. The strain is added to the flection values DELTAl1 and DELTAl2 of the elastic bodies 1, 2 to exert influence upon a tensile force P. The hysteresis, however, is canceled in the device constituted by forming the elastic bodies 1 and 2 so that the inflection parts using the same member are equal in stress. The creeping is the same.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a force measuring device, and particularly to a device that measures force by converting it into an electrical signal.

Conventionally, there is a so-called load cell as a force measuring device as described above. This method involves attaching a strain gauge to the surface of a strain-generating elastic body that distorts when subjected to force, and measuring the change in resistance of this strain gauge to measure the magnitude of the force. It is necessary to measure forces of various magnitudes by changing the force, or there are large errors due to the physical properties of the strain elastic body, such as hysteresis, creep, etc., and this must be compensated for, but this is technically difficult. Not only that, but the costs involved increased, making the product more expensive.

This invention can eliminate the effects of hysteresis and creep without providing any compensation circuit, and can achieve high accuracy in IPitr.
An object of the present invention is to provide a force measuring device that can measure force with an L configuration.

Hereinafter, the present invention will be explained in detail based on two illustrated embodiments. The first embodiment, as shown in FIG. It is fixed to the fixing base 4 via bolts 5.5. That is, both strain elastic bodies 1.
2 is of the cantilever type. Both strain elastic bodies 1.
2 is made of the same material or a material with the same temperature coefficient, and the bending portions (strain components) la and 2a are formed in a shape that gives the same maximum stress. Note that 6 is an insulating material for insulating both the elastic bodies 1 and 2.

The other ends of both elastic bodies 1 and 2 are connected by a string 7, whose effective length is equal to the length of the member 3 and has the same coefficient of linear expansion as the member 3. made of material.

When a load W is applied downward to the other end of the primary strain elastic body l, a deflection Δcross 1 proportional to the load W is generated in the primary strain elastic body l, as shown in FIG. Pull the servant downwards. The tension P applied to the string 7 acts on the other end of the secondary elastic elastic body 2, causing the other end to bend downward. Here,
If the spring constant of the primary strain elastic body 1 is Kl, the spring constant of the secondary strain elastic body 2 is 2, and the elongation of the string 7 is ignored, then P=Δcross2・Kl holds, and Δstand1=Δ Intersection 2; Since it is Δ intersection, W = Δ or (2 to K1+) P = W - K2/(Kj + Kl), and it can be seen that the tension P is proportional to the load W.

A magnetic field is applied to the string 7 at right angles to its length direction by a magnetic field generator 8 provided on the elastic elastic body 1.
Since it is connected to an amplifier 9 as shown in FIG. 3, the string 7 vibrates. In other words, when string 7 is slightly bent in a direction that cuts the magnetic field due to an applied load, a current flows through string 7 according to Fleming's right-hand rule, and this current flows through capacitor IO.
The 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 point t that balances the energy given by the amplifier 9 and the bending reaction force of the string 7, and 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 IO and amplified, and an amplified reverse current is supplied to the string 7. Flex the string 7 in the opposite direction. Thereafter, this is repeated to vibrate at the frequency f. This frequency f can be found. ta, n is the harmonic number of vibration, and the sentence is string 7
, g is the gravitational acceleration, and r is the mass per unit length of the string 7. Therefore, by measuring the frequency f, the tension P can be measured, and the load W can be determined from this. A circuit for measuring the frequency f is shown in FIG.

In the figure, 12 is an oscillator including the circuit shown in FIG. 3, 14 is a frequency counter, and 16 is a time gate, which controls the frequency counter 14. 18 is a calculation section,
Based on the counter output of the frequency counter 14, actual load calculation, zero adjustment, tare subtraction, etc. are performed. 20 is an actual load display section.

In the force measuring device configured in this way, the temperature coefficient of the primary strain elastic body 1 is αl, and the temperature coefficient of the auxiliary strain elastic body 2 is α2.
Then, the tension P is.

P = W-2(1◆α2)/1(1◆α1)÷2(1+α2). Since the materials of the main and 1 elastic bodies L and 2 are made of materials that have the same temperature change in coefficient of resistance, αl = α2, and both the main and 1 elastic bodies are 20 to 30 mm. Since the distance is the same, the temperature conditions are the same. Therefore, P becomes P=W·, 2/1+2, and temperature compensation is completely achieved.

Also, whether strain remains in the main and secondary elastic bodies l, 2 even after the load is removed (this is called hysteresis), and this strain is determined by the deflection Δ of the main and secondary elastic bodies l, 2, or 1, Since it is added to Δ22, g5 is given to the tension P, but the magnitude of hysteresis is the same regardless of the size of the shape, as long as the stress of the flexible portion is equal. Therefore, this force measuring device in which the main and sub strain elastic bodies 1 and 2 are formed using the same material so that the stresses applied to the deflections Fvla and 2a are equal, cancels out hysteresis. The same holds true for creep. In other words, the amount of creep is defined as a function of the stress applied to the elastic body and time, and is unique to each material and the internal structure after heat treatment. This is offset by forming the main and auxiliary strain elastic bodies 1 and 2 in shapes that have the same maximum stress.

Furthermore, since the effective length of the string 7 and the length of the member 3 are made the same, and both are made of materials with the same coefficient of linear expansion, the linear expansion is relatively the same, making the change in the tension P zero. ing. Note that even if the linear expansion coefficients are not the same, the member 3 may be made of a material and have a length such that the relative linear expansion is zero.

In the second embodiment, as shown in FIG. 5, a known balamegram type elastic body is used as the principal strain elastic body 1.
A measuring plate 22 is provided at the tip of the primary strain elastic body 1. Note that the same parts are given the same reference numerals and the description thereof will be omitted.

As described above, the force measuring device according to the present invention has a simple structure consisting of the main strain elastic body 1, the auxiliary strain elastic body 2, the string 7, etc., and the dimensions of the principal strain elastic body 1 can be changed. This makes it easy to measure loads of any size. Furthermore, the strings 7, the auxiliary strain elastic body 2, and the member 3 can be of the same size regardless of the magnitude of the load to be measured, so that standards can be unified. Furthermore, the primary strain elastic body 1, the secondary strain elastic body 2
Hysteresis and creep can be compensated for by using the same material or having the same temperature coefficient and the same temperature change, and in addition, by forming the shapes of the flexible parts 1a and 2a so that the stresses are equal.

Therefore, hysteresis and creep can be compensated for without providing any compensation circuit, and highly accurate force measurement can be realized at low cost.

In the above example, whether the tension P was measured by the string 7 or
Instead, any force sensing device may be used, such as a crystal sensor, tuning fork sensor, etc. In addition, the force detector may be configured to apply tension, or the positions of the primary strain elastic body 1 and the auxiliary strain elastic body 2 may be arranged so that pressure is applied to the force detector. Good too.

[Brief explanation of drawings]

FIG. 1 is a side view of the first embodiment of the force measuring device according to the present invention, FIG. 2 is a diagram of the principle of the first embodiment, and FIG. 3 is a diagram of the principle of string vibration in the first embodiment. FIG. 4 is a circuit diagram of the first embodiment, and FIG. 5 is a side view of the second embodiment. 1...Primary strain-elastic body, 2...Sub-strain elastic body,
3... Member, 4... Fixed part, 7.8... Force detector.

Claims (1)

[Claims] (1) A cantilever-type primary strain elastic body whose base end is fixed,
This main strain elastic body is a cantilever-type secondary strain elastic body that is arranged at intervals and has a fixed base end, and when the main strain elastic body deforms under force, the secondary strain elastic body is The elastic body is also connected to both strain elastic bodies so as to share the force, and the combined restoring force of both strain elastic bodies is balanced with the force to detect the force applied to the secondary elastic body, and also to detect the force. and a force detector that undergoes small deformation when subjected to force, both of the strain elastic bodies are made of the same material, and the strain-generating portions of both of the strain elastic bodies are shaped so that the respective stresses are equal. A force measuring device featuring: