JP2608637B2 - Capacitive load cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitive load cell used for a load transducer of an electronic balance.

[0002]

2. Description of the Related Art As a general load converter, as shown in FIG. 3, resistance gauges R1 to R4 are attached to a load cell body 1 and these resistance gauges R1 to R4 are connected to a bridge circuit. It has been known.

[0003] One end A of the load cell main body 1 is attached to the fixed side 2, and a load W acts on the other end B. The load cell body 1 is elastically deformed according to the load W,
Due to the deformation, a tensile force acts on the resistance gauges R1 and R3, and a compressive force acts on the resistance gauges R2 and R4, so that the output signal of the bridge circuit changes according to the load W.

In this strain gauge type load cell,
Since the output change of the output signal of the bridge circuit with respect to the change of the load W is small, a capacitive load cell as shown in FIG. 4 has been developed.

This is because the first electrodes 3 opposed to each other in the direction of the elastic deformation of the load cell body 1 (in the direction of arrow Y).
a and the second electrode 3b, the first electrode 3a is connected to the one end A of the load cell body 1, and the second electrode 3b
Is connected to the other end B side of the load cell main body 1 so that the first
A change in capacitance between the electrode 3a and the second electrode 3b is detected by the capacitance-load converter 4 and used as a weighed signal. Metal plates are used as the first electrode 3a and the second electrode 3b. Reference numerals 5 and 6 denote insulators interposed between the load cell body 1 and the electrodes.

[0006]

However, even if there is no displacement in the deformation of the load cell body 1, when the temperature and humidity of the atmosphere change, the dielectric constant between the first electrode 3a and the second electrode 3b is changed. Changes, and the first electrode 3a and the second electrode 3b
Since the capacitance changes during the period, it is required to strictly control and stabilize the atmosphere.

The present invention provides a first electrode 3a and a second electrode 3b.
It is an object of the present invention to provide a capacitance type load cell capable of automatically correcting a change in capacitance caused by a change in atmosphere during the period.

[0008]

A capacitive load cell according to the present invention comprises a load cell body having one end attached to a fixed side and elastically deforming in response to a load applied to a movable side at the other end.
A fixed-side electrode having a base end attached to the fixed side; and a movable-side electrode opposed to the fixed-side electrode and having a base end attached to the movable side, wherein an electrostatic force between the fixed-side electrode and the movable-side electrode is provided. In a capacitive load cell that detects a change in capacitance as a weighing signal change, a sensor electrode group that opposes each other and has both base ends attached to the fixed side and whose electrode spacing does not change due to the load applied to the movable side of the load cell body is provided. The capacitance between the fixed side electrode and the movable side electrode is corrected based on the capacitance of the sensor electrode group and output as weighing information.

[0009]

According to this configuration, since the capacitance of the sensor electrode group does not change due to the load applied to the movable side of the load cell body, only a change in the atmosphere can be taken out as a change in the capacitance of the sensor electrode group. The weighing signal based on the capacitance between the fixed side electrode and the movable side electrode is corrected by the capacitance of the sensor electrode group, and a weighing signal in which a change in atmosphere is compensated is output.

[0010]

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. It is to be noted that, in the claims, the fixed side electrode is composed of the first electrode 3a, the movable side electrode is composed of the second electrode 3b, and the sensor electrode group is composed of the first electrode 3a and the third electrode c. This will be described in detail below.

As shown in FIG. 1, the first
A third electrode 3a facing the first electrode 3a
And the capacitance between the first electrode 3a and the third electrode 3c is measured by the capacitance-load converter 8. The measured value of the capacity-load converter 8 is the first
And a correction unit 9 connected to the output of the capacitance-load conversion unit 4 for measuring the capacitance between the electrode 3a and the second electrode 3b.

More specifically, the dielectric constant between the first electrode 3a and the second electrode 3b and the first electrode 3a and the third electrode 3c
Is the same as the dielectric constant between the first electrode 3a and the third electrode 3c. And the second electrode 3
The measured weighing value obtained from the capacitance value during b
And outputs a weighing signal corrected in a weight value decreasing direction by a ratio corresponding to the amount of change from the reference value of the capacitance value between the electrode 3a and the third electrode 3c.

In this embodiment, ceramics are used for the insulators 5 to 7, and the first to third electrodes 3a are used.
3c, the base material is ceramic and is formed by gold plating thereon.

With such a configuration, the first electrode 3a
Even if the atmosphere of the second electrode 3b fluctuates, if the load W is constant, the weight value signal output from the correction unit 9 can be maintained constant.

In the above embodiment, the first electrode 3a and the second
The correction unit 9 is provided separately from the capacitance-load conversion unit 4 for measuring the capacitance between the electrodes 3b. The operation of the capacitance-load conversion unit 4 is directly performed by the output of the capacitance-load conversion unit 8. The same applies to a configuration in which correction is made to The same applies to a case where the input stage of the capacity-load converter 4 is configured as shown in FIG. 2 without providing the capacity-load converter 8 and the correction unit 9.

Assuming that the capacitance between the first electrode 3a and the second electrode 3b is C2 and the capacitance between the first electrode 3a and the third electrode 3c is C1, the capacitance shown in FIG. In the load converter 4, the output voltage Vi of the signal source 11 is applied to the inverting input terminal (-) of the differential amplifier 10 via the capacitance C2,
A capacitance C1 is interposed between the inverting input terminal (−) of the differential amplifier 10 and the output of the differential amplifier 10,
, A voltage V0 corresponding to the corrected weight value is obtained.

[0018]

As described above, according to the present invention, apart from the fixed side electrode and the movable side electrode which oppose each other in the direction of the elastic deformation displacement of the load cell main body and the distance between the electrodes changes according to the load, the sensor is provided. An electrode group is provided, and the capacitance between the fixed-side electrode and the movable-side electrode is corrected based on the capacitance of the sensor electrode group and output as weighing information to automatically correct fluctuations due to changes in atmosphere. As a result, stable weight measurement can be realized. Furthermore, since the capacitance of the sensor electrode group does not change due to the load applied to the movable side of the load cell body, only a change in the atmosphere can be taken out as a change in the capacitance of the sensor electrode group. Fluctuations of the capacitance between the fixed side electrode and the movable side electrode due to the change in atmosphere can be automatically corrected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a capacitive load cell of the present invention.

FIG. 2 is a configuration diagram of a specific electric circuit of another embodiment.

FIG. 3 is a configuration diagram of a strain gauge type load cell.

FIG. 4 is a configuration diagram of a conventional capacitive load cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Load cell main body 3a 1st electrode 3b 2nd electrode 3c 3rd electrode 4 Capacity-load conversion part

Claims (1)

(57) [Claims] 1. One end is attached to a fixed side and the other end is movable.
The load cell body to elastically deform in response to load applied to the side, the fixed-side electrode having a base end is attached to the stationary side,
The base end was attached to the movable side facing the fixed side electrode
A movable-side electrode is provided, and static between the fixed-side electrode and the movable-side electrode is provided.
Capacitance type b that detects capacitance change as weighing signal change
And the base ends are on the fixed side.
To the load acting on the movable side of the load cell
Therefore, a sensor electrode group that does not change the electrode spacing is provided and fixed
The capacitance between the side electrode and the movable side electrode is
A capacitive load cell that corrects based on capacitance and outputs it as weighing information .