JPH04303714A - capacitive load cell - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 in a load transducer for an electronic scale.

0002

[Prior Art] A typical load converter is a strain gauge type load cell in which resistance gauges R1 to R4 are attached to a load cell body 1 and the resistance gauges R1 to R4 are connected to a bridge circuit as shown in FIG. It has been known.

One end A of the load cell 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, R3, a compressive force acts on the resistance gauges R2, R4, and the output signal of the bridge circuit changes according to the load W.

[0004] In this strain gauge type load cell,
Since the change in the output signal of the bridge circuit with respect to the change in the load W is small, a capacitive load cell as shown in FIG. 4 has been developed.

[0005] This is because the first electrodes 3 face each other in the direction of displacement due to elastic deformation of the load cell body 1 [direction of arrow Y].
A and a second electrode 3b are arranged, the first electrode 3a is connected to the one end A side of the load cell main body 1, and the second electrode 3b
is connected to the other end B side of the load cell main body 1, and the first
The capacitance change between the electrode 3a and the second electrode 3b is detected by the capacitance-load converter 4 and is used as a weighing signal. Metal plates are used as the first electrode 3a and the second electrode 3b. 5 is an insulator interposed between the load cell body 1 and the electrode.

FIG. 5 shows a structure for attaching the electrodes 3a and 3b, which are attached to the surface of an insulator 5 attached to the load cell body 1 by tightening bolts 6.

[0007]

Problem to be Solved by the Invention In such a capacitive load cell, when the temperature of the atmosphere changes, the electrode 3a
The difference in linear expansion coefficient between electrode 3b and insulator 5, and the difference in linear expansion coefficient between electrode 3b and insulator 5
Due to the difference in the coefficient of linear expansion between the first electrode 3a and the second electrode 3b, the electrodes 3a and 3b warp as shown by the imaginary line in FIG. There is a problem that the distance changes and the weight value fluctuates.

[0008] An object of the present invention is to provide a capacitance type load cell that can reduce warpage of an electrode due to a difference in linear expansion coefficient between the electrode and an insulator.

[0009]

[Means for Solving the Problems] The capacitive load cell of the present invention has a load cell main body that is attached to a fixed side at one end and elastically deforms in response to a load applied to the other end, in the direction of displacement of the elastic deformation. A first electrode and a second electrode are arranged opposite to each other, the first electrode is connected to the one end side of the load cell main body, and the second electrode is connected to the other end side of the load cell main body. , in a capacitive load cell that detects a change in capacitance between a first electrode and a second electrode as a change in a weighing signal, an electrode is provided on the one end side of the load cell main body or on the other end side of the load cell main body. It is characterized in that it is attached by being pressed by the biasing force of an elastic body.

0010

[Operation] According to this structure, the electrode is pressed against the insulator by the biasing force of the elastic body, and as the temperature of the atmosphere rises, the biasing force of the elastic body becomes weaker. Therefore, even if the electrodes warp due to differences in linear expansion coefficients of the materials,
The degree of this warping can be reduced compared to when it is firmly restrained with a constant force regardless of the temperature of the atmosphere, and fluctuations in weight values due to changes in the temperature of the atmosphere can be reduced.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be explained based on FIGS. 1 and 2. Components having the same functions as those in FIG. 4 showing the conventional example will be described with the same reference numerals.

FIG. 1 shows the mounting structure of the first electrode 3a and second electrode 3b in the capacitive load cell of the present invention. Since both the electrodes 3a and 3b have the same mounting structure, the case of the electrode 3a will be described here as an example.

The electrode 3a is placed on the insulator 5 attached to the load cell body 1, and the threaded part 7 of the bolt 6 is screwed onto the insulator 5, so that the electrode 3a is connected between the head 8 of the bolt 6 and the electrode 3a. A compression spring 9 as an elastic body is interposed therein.

With this structure, the electrode 3a is pressed against the upper surface of the insulator 5 by the biasing force of the compression spring 9. The biasing force of the compression spring 9 decreases as the ambient temperature rises, so if the electrode 3a is about to warp due to the difference in linear expansion coefficient between the electrode 3a and the insulator 5, the biasing force of the compression spring 9 will decrease. In contrast, slippage occurs between the electrode 3a and the insulator 5, and the warpage is eliminated.

Therefore, even if the ambient temperature fluctuates, the warpage of the first and second electrodes 3a, 3b can be reduced and the stability of the weight value signal can be improved. Note that in this embodiment, ceramic is used as the insulator 5,
The first and second electrodes 3a and 3b are formed by plating gold on a ceramic base material.

In the above embodiment, a coil-shaped compression spring 9 was used as the elastic body, but this is designed so that the electrodes 3a, 3b are pressed against the insulator 5 by a leaf spring 10 as shown in FIG. The same is true even if the configuration is configured as follows.

[0017]

As described above, according to the present invention, the capacitance change between the first electrode and the second electrode, which face each other in the direction of the elastic deformation of the load cell body, can be used as a weighing signal change. In the capacitive load cell to be detected, the electrode is attached to the load cell body side by pressing it with the biasing force of the elastic body. As the temperature of the atmosphere rises, the biasing force exerted by the elastic body weakens, and even if the electrodes warp due to differences in the coefficient of linear expansion of the materials, the degree of warpage remains firmly constant regardless of the temperature of the atmosphere. The weight can be reduced compared to those that are restrained by force, and stable weight measurement can be achieved even when the ambient temperature changes.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of an electrode mounting structure of a capacitive load cell according to the present invention.

FIG. 2 is a longitudinal cross-sectional view of an electrode mounting structure according to another embodiment.

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

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

FIG. 5 is a longitudinal cross-sectional view of a conventional electrode mounting structure in a capacitive load cell.

[Explanation of symbols]

1 Load cell body 3a First electrode 3b Second electrode 5 Insulator 6 Bolt 9 Compression spring [elastic body] 10 Leaf spring [elastic body]

Claims (1)

[Claims] 1. A load cell body having one end attached to a fixed side and elastically deforming in response to a load applied to the other end has a first electrode and a second electrode disposed facing each other in the direction of displacement of the elastic deformation. A first electrode is connected to the one end side of the load cell main body, a second electrode is connected to the other end side of the load cell main body, and the electrostatic charge between the first electrode and the second electrode is reduced. In a capacitive load cell that detects a change in capacitance as a change in a weighing signal, an electrostatic capacitor is attached to the one end of the load cell body or the other end of the load cell body by pressing an electrode with the biasing force of an elastic body. Capacitive load cell.