JPS6052369B2 - Screw axial force measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Since loosening of the screw cannot be essentially avoided in screw fastening, it is very important to consider the loosening of the screw when manufacturing and using the screw.

Currently, there are many screws with various locking mechanisms on the market, but if they are used without fully understanding their locking effect, accidents may occur without realizing that the screws are loosening. It is often seen. Therefore, when tightening screws, even if measures are taken to prevent loosening, it is necessary to accurately grasp the tightening axial force. By the way, there is no known device for measuring the axial force of a screw in which a strain gauge is attached to the outer peripheral surface of a pressure washer, and the tightening axial force of the screw acting on the washer is converted into compressive strain of the washer. It is being

(See US Pat. No. 3,461,715). but,
The axial force measuring device according to the above US patent has a configuration in which one or several foil-shaped strain gauges are arranged on the outer peripheral surface of the pressure washer parallel to the screw axis, so that the thickness of the pressure washer itself Not only is it necessary to make the pressure washers considerably thicker, but the electrical connections between each strain gauge are complicated.Furthermore, flat washers must be placed above and below the pressure washers to prevent them from bending or locally sinking when tightening the screws. They have to be used in combination, and the entire measuring device is very large, so even if it can be used in a laboratory, it is impossible to put it to practical use.

The purpose of the present invention is to solve the above-mentioned problems and to provide a screw axial force measurement method that is a simple device that can be used alone in the same way as a normal washer, and that can easily and at any time measure the axial force of a screw. The goal is to provide equipment.

In order to achieve the above object, the device of the present invention attaches a strain gauge in the form of a lead wire in a headband shape along the outer periphery of a washer in the shape of a disc spring, and leads out the lead wires at both ends to the outside. The present invention is characterized in that the axial force is converted into an elongation in the circumferential direction of the outer periphery of the washer and measured.

An embodiment of the present invention will be described below based on the drawings.

1 is a washer in the shape of a disc spring, made of spring steel with relatively high elasticity, and has a U-shaped cross-sectional annular groove 2 on its outer periphery.
is provided.

It is desirable to provide a flat surface 3 on the upper inner circumference of the washer 1 so that the tightening axial force of a bolt or nut used in combination with the washer 1 acts as evenly as possible over the entire circumference of the washer 1. Reference numeral 4 denotes a strain gauge in the form of a lead wire, which is fitted into the annular groove 2 of the washer 1 via a synthetic rubber or other electrically insulating fixing agent 6 and attached to the outer periphery of the washer 1 in a headband shape. A leader line 5 is led out to the outside.

7 is an auxiliary washer, and when washer 1 receives a load in the axial direction,
The washer 1 is provided to ensure that the outward displacement in the radial direction is as uniform and smooth as possible.
It has a conical slope 8 on which the back side of the washer 1 slides, and is hardened to have higher hardness than the washer 1.

The washer of the present invention having the above structure is used for screw fastening by being fitted under the neck of the port 10 in the same way as a normal washer, as shown in FIG. 4, for example.

When the washer 1 is displaced radially outward due to the axial tightening force during screw tightening, the outer periphery of the washer 1 elastically stretches, and the strain gauge 4 also stretches accordingly.

Since the elongation of this strain gauge 4 is proportional to the fastening axial force, the fifth
As illustrated in the figure, a change in the fastening axial force can be easily detected by connecting the leader wire 5 to a measuring device 11 and measuring the change in electrical resistance caused by the elongation of the strain gauge 4. Further, if the proportional relationship between the elongation of the strain gauge and the fastening axial force is set numerically in advance, it is also possible to immediately measure the magnitude of the axial force. As explained above, the measuring device of the present invention
A strain gauge in the form of a lead wire is attached in a headband shape along the outer periphery of a washer shaped like a disc spring, and the tightening axial force of the screw acting on the washer is converted into expansion of the outer periphery of the washer in the circumferential direction. Since the washer itself can be made relatively thin and can be used alone like a normal washer, it is very advantageous in terms of use and handling.

In addition, compared to conventional measuring devices of this type using strain gauges, the structure is simple and easy to manufacture, and it has the advantage that it can be mass-produced and provided at low cost. Note that if the auxiliary washer 7 is used in combination as in the above embodiment, even large axial forces can be accurately measured.

[Brief explanation of the drawing]

Fig. 1 is a plan view of a washer with an axial force detection device according to the present invention, Fig. 2 is a front view of the center longitudinal section, Fig. 3 is an enlarged sectional view of the main parts, and Fig. 4 is a front view showing the same usage state. FIG. 5 is a plan view showing a coaxial force measurement state. 1... Washer, 2... Annular groove, 3...
... Flat surface, 4 ... Strain gauge, 5 ...
・Leader line, 6... Fixing agent, 7... Auxiliary washer, 8... Conical slope.

Claims (1)

[Claims] 1. A strain gauge 4 in the form of a lead wire is attached in a headband shape along the outer periphery of the washer 1 in the shape of a disc spring, and the lead wires 5, 5 at both ends thereof are led out to the outside, so that it A screw axial force measuring device characterized in that the axial force is measured by converting the axial force into an elongation in the circumferential direction of the outer peripheral edge of the washer 1. 2 A conical slope 8 that slides into contact with the conical slope on the back side of the washer 1
The screw axial force measuring device according to claim 1, characterized in that an auxiliary washer 7 having the following is combined with the washer 1.