JPS5829861B2 - load cell scale - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a load cell scale using a resistance strain gauge.

Generally, a load cell scale using a resistance strain gauge has a configuration as shown in FIG.

That is, 1 is a beam, and a pressure receiving part 2 for applying an external force is formed on the upper surface of one end of the beam 1, and a base part 3 at the other end is fixed to a frame body (not shown).

By forming an irregularly shaped hole 4 in which two elliptical holes are connected to each other on the side surface of the bent beam 1, two distorted parts 5, 6, 7.8 are formed on the upper side and two on the lower side. There is.

Resistive strain gauges 9 are fixed to the outer surfaces of these strained parts 5, 6, 7.8.

These resistance strain gauges 9 are connected to a resistance block 11 via a terminal plate 10 while forming a bridge circuit.

When the weight of the object to be measured is applied to the pressure receiving part 2, the beam 1 is deflected, and in response to the pressure, an electric signal is emitted from the bridge circuit to a digital readout (not shown) to measure the weight. It is something.

Here, conventionally, a resistor Ra is used as the resistive strain gauge 9 corresponding to the strained portions 5, 6, 7°8.

Basic bridge circuit consisting of Rb, Rc, and Rd (Figure 2)
A bridge circuit (Fig. 3) is provided in which a resistor Rs for sensitivity correction, a resistor Rst for temperature correction of sensitivity, a resistor RZ for zero balance correction, and a resistor Rzr for zero balance temperature correction are added. It is something that

Then, if the input is ■ (constant) and the output is Vo, becomes.

Here, conventionally, in order to set the output V o = O at the time of no load (i.e., W = 0) shown by equation (1), (1)
The right side of the equation is set to zero, and the resistance of each side is Ra = Rb =
Rc = R, d.

When a load W is applied to a bridge circuit consisting of resistors set in this way, the resistance value of each resistor increases or decreases by JR, so the resistance value of each side to which the load W is applied is "A"
If t RB t ROt RD, then RA=R,D
=Ra+ARsRB=Rc=Ra-AR.

The relationship between the input ■ and the output Vo at this time is as follows.

Here, AR is proportional to the applied load W, JR, = kW
Since the relationship is (k: constant), it becomes (2 equations), and the load W
If the horizontal axis is taken as the horizontal axis and the output Vo is taken on the vertical axis, a straight line passing through the origin as shown in FIG. 4 is obtained.

Here, electrical display of the load cell scale can be done by directly connecting it to a voltmeter or by using an AD converter, but according to Fig. 4, when there is no load, pressing W = o will change the output voltage. = O and passes through the origin, so when measuring the object to be measured, the initial load of the load receiver is displayed as the output Vo from the beginning and added to the weight of the object to be measured.
The load on the object to be measured cannot be directly displayed, and the load on the object to be measured is calculated by subtracting the initial load, making the output mechanism complicated.

Even if the output of the load cell scale is amplified by an amplifier, the input voltage range is limited because of the voltage corresponding to the initial load, and the amplifier cannot be used effectively.

This invention was made in view of these points, and when the output of a load cell scale is displayed with a voltmeter or an AD converter, the load of only the object to be measured is directly displayed, and the residual load of the amplifier is The purpose of this invention is to obtain a load cell scale that can effectively utilize the input voltage range.

In this invention, one of the gauge resistors has a resistance value of 4 so that the bridge consisting of the gauge resistors set with equal resistance values R1 on each side is balanced by the initial load W of the load receiver.
JR, (where ARl is the amount of change in resistance of the gauge resistor due to the initial load W1) is added, or the resistance value of the gauge resistor itself of the housing tobacco is set to 4JR1 above R0. be.

Therefore, in order to balance the bridge with the initial load of the load receiver, either add an external resistor with a resistance value of 4JR1 to one of the gauge resistors of the bridge, or change the resistance value of the housing or the gauge resistor itself to 4JR on R7. By setting this, the load of only the object to be measured can be directly displayed using a simple circuit, and the input voltage range of the amplifier can be effectively utilized.

An embodiment of the present invention will be explained based on FIGS. 5 and 6.

Similar to the bridge circuit shown in FIG. 3, the bridge circuit shown in FIG. 5 has gauge resistors Ra, Rb,
It has Rc and Rd.

Further, Rzr is a resistor for temperature correction of the output voltage when no load is applied, and Rz is a resistor for making the output voltage when no load is a constant initial bias voltage.

Assume that the bridge circuit is connected to a load cell scale as shown in FIG.

In such a bridge circuit, first each gauge resistance R
It is assumed that a, Rb, Rc, and Rd are set to the same resistance value R1, and an unknown resistance r is added as an external resistance to the gauge resistances R and b.

Then, the resistance value of each side connected to the load W is RA
, R.B.

When R, C, R, and D are assumed, the resistance value of each gauge resistor increases or decreases by AR due to the load W, and the relationship between the input ■ and the output Vo at this time is as follows.

Here, when the initial load W1 of the load receiver is applied (i.e., the resistance value change of the gauge resistance AR=, (R1)
When the output VO=O, equation (3) becomes as follows.

Note that an external resistance of r=4JR1 may be added only to the gauge resistance Rc.

Therefore, the resistance value of each gauge resistor is equal to the resistance value R1
and r=4JR1 for any one gauge resistance.
By adding an external resistance of , the output Vo due to the initial load W1 can be made zero.

In this case, the unloaded resistance of each side Ra = R, c = Rd = R0, R, b = R1 + 4a
The initial bias voltage is determined by this equation (6).

Also, when the load is W, equation (3) becomes, and a straight line passes through (Wl, O) shown in Fig. 6. Here, if the load of only the object to be measured is Wx, then The output Vo corresponding to the load Wx can be directly displayed.

Therefore, the output V due to the load Wx of this measured object alone
Since o can be measured simply by displaying it with a voltmeter and AD converter, there is no need to provide a correction mechanism such as subtraction of the initial load on the output side, making it simple.

In addition, when increasing or decreasing the output of a load cell scale using an amplifier, the input voltage range can be used effectively.

In the above embodiment, each gauge resistance was set to the same resistance R1, and the external resistances 4 and 11 were added only to the gauge resistance Rb (-! or R, c). The gauge resistors may be left with a resistance value of 1, and external resistors of 2JR1 may be added to the corresponding gauge resistors Rb and Rc, respectively.

In other words, if a load W is applied in this case, This is similar to equation (7) above.

Next, a case where the above-mentioned external resistance is included in the resistance of the gauge resistor itself will be explained.

1. If the resistance value of each gauge resistance is Ra=Rc=Ra'=R1, Rb-(R1+r') (where r' is the unknown resistance), then the resistance value of each gauge in relation to the load W is A t RB t RO+ RD becomes, and the relationship between the input ■ and the output Vo at this time is as follows.

Here, when the initial load is set to W1, the output V o = 0 is expressed by equation (8). Therefore, the unknown resistance molecule' is r':4, hRl(10) (', "R1>>, (R1, r '＞＞l r' )))
becomes.

Note that only the gauge resistance Rc is Rc=(R1+4 JR,
1) may be used.

In addition, when the resistance value of neither gauge resistor Rb or Rc is changed, the resistance value of only one of gauge resistors Ra and Rd is Ra=Rt 4JR1
(=Rd).

In this way, the resistance value of any one of the gauge resistors Ra, Rb, Rc, and Rd is set to R1±4. JR
,.

Even if it is set to , a straight line (FIG. 6) similar to that obtained when an external resistor 4JR is added is obtained.

In other words, the resistance value of each gauge resistor is Ra=Rd=Rt.

Rb=aa=(F,,+2JR1) or R,a=
It is also possible to set Rd=(R, -2JR1) and Rb=Rd=R1, and in this case, when the load W is added, the above-mentioned formula C71 is obtained.

As described above, this invention adds an external resistor with a resistance value of 4AR1 to one of the gauge resistors of the bridge, or increases the resistance value of the gauge resistor itself to R1 so that the bridge is balanced depending on the initial load of the load receiver. Since it is set to 4JR, 1, the load of only the object to be measured can be directly displayed with a simple output mechanism, and the input voltage range can be used effectively even when amplifying the output of the load cell scale with an amplifier. It has the effect of

[Brief explanation of drawings]

Fig. 1 is a perspective view of a load cell scale, Fig. 2 is a basic bridge circuit diagram showing a conventional example, Fig. 3 is its bridge circuit diagram, Fig. 4 is its characteristic graph, and Fig. 5 is an embodiment of the present invention. FIG. 6 is a graph showing its characteristics. Ra, R, b, Rc, Rd---Gauge resistance.

Claims (1)

[Claims] 1. One of the gauge resistors has a resistance value of 4AR0 (however, the bridge made of ← gauge resistors set for equal resistance values on each side is balanced by the initial load W1 of the load receiver). , JRl is the amount of change in resistance of the gauge resistor due to the initial load W), or the resistance value of the gauge resistor itself is set to R0±4JR1.