JPH0654267B2 - Weight detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load transmission function of a weight detection device such as a weight detection function-added heat device and a digital electronic scale.

2. Description of the Related Art A conventional weight detection device detects a weight by using a load-capacitance conversion element having a structure in which two alumina diaphragms having electrodes printed on the surfaces thereof are opposed to each other with a minute gap. . FIG. 6 shows a configuration diagram of the weight detection element, and FIG. 7 shows a cross-sectional view of a main part of a conventional weight detection device.
The respective alumina substrates 1 on which the electrodes 2 are printed face each other with their electrodes facing each other, and a sealing glass 3 holds a minute gap to form a laminated capacitor. When a pressure or a local load is applied on the alumina substrate 1 of the weight detecting element 7, the alumina substrate 1 changes the distance between the deflection electrodes 2 and the capacity of the weight detecting element 7 changes. The weight is detected by applying a predetermined signal processing to this capacitance.

When measuring the pressure of gas or liquid, the diaphragm of the alumina substrate 1 is only exposed to the environment to be measured, and no special configuration is required. The configuration is as shown in the figure. 5 is a sensor bed for mounting the weight detecting element 7, 6 is a sensor cover for electrically shielding the weight detecting element 7, and 8 is a leaf spring. A damper for preventing the weight detection element 7 from being applied and a lead wire 9 for extracting the capacitance of the weight detection element 7 to the outside. 4 is a weight detecting element 7 for measuring the applied load.
It is a load transmission member that transmits to. The load W is applied to the pressure point 4 via the damper 8. Since the pressing point 4 is in surface contact with the surface of the alumina substrate 1, the load W presses the weight detecting element 7 with a constant pressing area defined by the contact area of the load transmitting member.

The capacitance of the weight detecting element 7 at this time is calculated by a theoretical formula as follows. FIG. 8 is a diagram for explaining the principle of weight detection of a conventional weight detection element, and the dimensions of each part are also noted. Here, the deflection amount δ when a load of W is applied to the alumina substrate is: 0 ≦ r ≦ b ・ When b ≦ r ≦ a Becomes However, ν; Poisson ratio, E; Young's modulus, t;
Plate thickness, b; load transmission member diameter. In FIG. 8, assuming that a donut-shaped area having a radius r and a minute diameter dr is S, S = 2πrdr (3) The electrostatic capacitance dC at that portion is dC = εS / (d−δ). ……………… (4) ε; Permittivity between electrodes, d; Initial gap Here, by substituting equations (1) to (3) into equation (4) and integrating r from 0 to a ₀ , weight detection The capacitance C of the element 7 can be calculated by the following equation.

This equation almost agrees with the actually measured value, and there is a correlation shown in FIG. 10 between the load transmission member diameter b and the sensitivity [pf / kg], and the weighing characteristic greatly changes depending on the load transmission member diameter, that is, the pressing area. I understand.

Problems to be Solved by the Invention It is desirable to make the pressing area uniform in order to obtain a more uniform weighing characteristic in such a load transmitting member having a flat contact surface. For that purpose, it is necessary to increase the flatness of the contact surface of the load transmitting member. That is, if the contact surface of the load transfer member is rough and uneven, point contact may occur, or the weight detection element may be pressed by a part of the contact surface, and the pressurizing area accurately defined by the diameter of the load transfer member can be obtained. This is because the characteristics vary without being able to do so. It will be explained how difficult it is to accurately obtain the flatness of the contact surface by taking a processing method as an example. There are various methods for processing the load transmitting member, but cutting is considered to be optimal considering the flatness of the pressure surface and mass productivity. In the case of cutting, however, as shown in Fig. 9 (a), the rotating metal material 24 is sent to the center by sending a cutting tool 25 to shave the flatness, but as the cutting tool 25 moves toward the rotation axis, the angular velocity is increased. As the feed rate of the cutting tool 25 is not gradually decreased, the central part is shown in Fig. 9 (b).
It becomes a convex bulge like. However, no matter how the processing method is modified, the angular velocity of the rotating shaft is 0 in reality.
Therefore, it is unavoidable that a protrusion is formed in the central portion. Further, the output of this protrusion also varies depending on the material, the state of the cutting tool 25, and the like during processing. In this way, when the load transmission member has a protrusion, what kind of effect it has on the weighing characteristics is as follows: (1) Point contact with the weight detection element at light load and surface contact at heavy load The linearity of the load is different.

(2) Since the point contact is made, the pressure direction to the weight detection element is unstable and the repeatability is reduced.

(3) The point contact part wears due to repeated application of load and the characteristics change over time.

Various problems occur. Here, the cutting process is taken as an example, but it is very difficult to strictly process the flatness in consideration of mass productivity and cost. The present invention solves such conventional problems, and provides a weight detection device excellent in accuracy, repeatability, and durability performance thereof.

Means for Solving the Problems A weight detecting device of the present invention has a structure of a load transmitting means for applying a load to a load detecting element in a constant pressurizing area, and a center portion is engraved with respect to a contact surface with the load detecting element. It has a concave shape.

In the weight detecting device of the present invention, since the load detecting means is indented in the central part and is in contact with the diaphragm surface of the load detecting element in a concave shape, the load is applied at a constant pressing area defined by the outer ring which is just concave. Can be applied to the weight detection element. Therefore, there is no variation in weighing characteristics, that is, variation in accuracy due to non-uniformity of the pressing area of the weight transmission means, which has been seen in the past. Especially in the case of such a shape,
Since there is no need for rigorous processing to obtain flatness of the pressing area as in the past, the weighing characteristics similar to those of a flat load transmission member can be obtained, which is a great advantage in terms of productivity, workability, and cost. Therefore, it is extremely advantageous in practical use.

Embodiment Hereinafter, a weight detection device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a sectional view of the main part from the side, and FIG. 4 shows a perspective view. Descriptions of parts common to those in FIG. 7 are omitted. Reference numeral 4 denotes a load transmitting member, which has a concave shape with a dented central portion. 11 parallel holding metal fittings, 12 fixed holding metal fittings and 13 parallel motion fittings are four connecting focus 1
Each connecting portion connected by 0 is slidable with an appropriate clearance.
This is a Roberval mechanism which is well known in the field of scales, and by this function, the parallel movement metal fitting 13 can freely move in the thrust direction of the table shaft 14. The load is transmitted to the weight detecting element 7 through the leaf spring 8 attached to a part of the parallel motion fitting 13, and protects the alumina porcelain which is easily broken against impact load. With respect to the excessive static load, a part of the parallel motion fitting 13 comes into contact with the sensor mount 18 due to the effect of the leaf spring 8 and acts as an excessive load limiter.

Reference numeral 17 denotes a bottom plate to which the fixed holding metal fitting 12 is attached.
Reference numeral 16 is a rubber foot, and 15 is a table on which an object to be measured is placed. The weight of the object to be measured placed on the table 15 is applied to the load transmitting member 4 via the leaf spring 8. The relationship between the load and the capacitance at that time is as shown in Fig. 11 from the equation (5).

FIG. 3 shows a block diagram of a circuit of the present weight detection device. 1
Reference numeral 9 is a C-F converter circuit in which the pulse frequency changes depending on the capacitance. 20 is a microcomputer, 21
Is a display section for displaying weight and the like, 22 is a key input section,
Reference numeral 23 is a power supply unit for supplying electric power to the microcomputer 19 and the C-F converter circuit. Here, the capacitance of the weight detection element 7, which changes depending on the weight, is converted by the CF converter circuit 19 into a frequency that can be discriminated by the microcomputer 20. Microcomputer 20
Is a configuration in which the number of pulses output from the C-F converter circuit 19 is counted for a predetermined period of time to detect the frequency, and the weight is calculated from a predetermined frequency-weight correlation (first-order or second-order power series approximation formula). Has become. The calculated weight is displayed on the display unit 21. Power ON and O with key input unit 22
Select FF, tare (reset), etc.

1 (a) and 1 (b) are structural views of the load transmission member, and FIG. 2 (a) to FIG.
A process drawing is shown in (e). The surface A serves as a contact surface with the weight detection element 7. In this step, first, the metal material 2 which is the base material
After cutting the center part of the A surface of 4 with the drill 26, the tool is fed along the A surface in the B axis direction while rotating the base material at a high speed around the B axis perpendicular to the A surface. Become. In the completed structure, as shown in FIG. 1, the contact portion with the weight detection element 7 becomes a donut-shaped portion shown by black coating which is left uncut by a drill (C portion), and 26 is a contact surface recess cut by the drill. Is.

By doing so, the load is transmitted to the weight detecting element 7 by contact with the doughnut-shaped portion of the C portion, so that the characteristics equivalent to those of the flat load transmitting member having the pressing area πr ² can be obtained. . Therefore, it is possible to remarkably reduce problems such as poor linearity with respect to load, deterioration of repeatability, and change with time of weighing characteristics, which are caused by variations in flatness of the contact surface as in the conventional case. From the point of view of the present invention, it is more desirable to reduce the area of the contact portion of the portion C to make line contact.

EFFECTS OF THE INVENTION As described above, in the weight detecting device of the present invention, the structure of the load transmitting means for receiving a load and applying the load with a constant pressing area on the diaphragm surface has a concave shape in which the central portion of the diaphragm contact surface is dented. The shape, that is, the structure does not press the diaphragm by the surface, but presses the diaphragm by the line of the outer ring of the surface. Therefore, it is possible to easily obtain a constant pressurizing area equal to the area surrounded by the line without requiring a special processing method, and the pressurizing area due to the flatness variation found in the conventional flat load transmitting means. Since there is almost no variation in the pressure applied area and a change in the pressing area due to the load condition, the weighing accuracy can be significantly improved. Further, since the pressurizing area does not change due to wear of the contact surface under repeated load application, it is very advantageous in durability.

[Brief description of drawings]

1 (a) and 1 (b) are a sectional view and a front view of a load transmitting member of a weight detecting device according to an embodiment of the present invention, and FIGS.
(e) is a process drawing of the load transmitting member, FIG. 3 is a side view of the same, FIG. 4 is a partially cutaway perspective view of the same, FIG. 5 is a block diagram of the same control circuit, and FIG. FIG. 7 is an exploded perspective view of the weight detecting element, FIG. 7 is a sectional view of a main part of a conventional weight detecting device, FIG. 8 is an explanatory view of the principle of the weight detecting element, and FIG. Fig. 9 (b) is a sectional view of the main part of the same member, Fig. 10 is a characteristic diagram showing the relationship between the size of the contact surface and the sensitivity of the conventional load transmitting member, and Fig. 11 is the application of the same weight detecting element. It is a characteristic view which shows the relationship between load and capacity. 1 ... Alumina substrate (diaphragm), 2 ... Electrode, 3
...... Seal glass, 4 ...... Load transmission member (load transmission means), 7 ...... Weight detection element.

Claims (1)

[Claims] 1. A load detecting element whose physical quantity changes depending on the amount of deflection of the diaphragm due to the load applied to the diaphragm surface, and a load which receives the load and applies a constant pressure area to the diaphragm surface of the load detecting element. And a load transmitting means for storing the weight, and the load transmitting means has a shape in which a central portion of a contact surface with the load detecting element has a concave shape.