JP2003014565A - Calibration curve automatically preparing apparatus for bolt axial tension - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for automatically preparing a calibration curve of a bolt axial tension necessary to be previously obtained in the case of measuring the bolt axial tension using an ultrasonic measuring method. SOLUTION: The calibrating curve automatically preparing apparatus measures a propagating time of an ultrasonic wave by transmitting and receiving the wave by an ultrasonic sensor 6 mounted at a bolt head 13 while an automatic clamping work of a hexagon head bolt 11 is executing by a nut runner 1 included in the sensor 6 at a distal end. The apparatus automatically forms the relationship between the propagating time of the wave and the bolt axial tension as the calibration curve by detecting the actual bolt axial tension by a load washer 14 engaged with a bolt clamping part. The bolt axial tension can be managed by measuring the propagating time of the wave by using the curve.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a calibration curve of a bolt axial force which must be prepared in advance when measuring a bolt axial force using an ultrasonic measuring method. To an apparatus for automatically creating a file. 2. Description of the Related Art An ultrasonic measuring method is known as a method for measuring a bolt axial force. In this method, after the ultrasonic wave transmitted from the ultrasonic sensor placed on the bolt head reaches the bolt tip,
The reflected echo wave is received, and the propagation time during this period is detected, and the axial force of the bolt is measured based on the difference in the propagation time. For that purpose, it is necessary to measure the relationship between the axial force of the bolt and the propagation time of the ultrasonic wave in advance to obtain a relational expression. FIG. 2 is a conceptual diagram showing the calibration curve data. For a bolt having a thread pitch of M10 and M12, the relationship between the propagation time of ultrasonic waves and the axial force of the bolt is represented as shown in this figure. FIG. 3 shows an example of a conventional method for preparing a calibration curve. A hexagonal bolt 1 is attached to a material 12 having a threaded hole.
1 is screwed. A load washer 14 is fitted between the bolt head 13 and the material 12, and the ultrasonic sensor 6 is mounted on the bolt head 13 in a state fixed by an adhesive or the like. The load on the load washer 14 is
It can be known from the axial force indicator 3. The measurement control and data analysis of the ultrasonic sensor 6 are performed by the ultrasonic measuring device 9. A method for preparing a calibration curve using such a conventional measuring device is as follows. First, the hexagonal bolt 11 is set to the tightening start state, and the propagation time of the ultrasonic wave 16 transmitted, reflected and returned in a state where the axial force is zero is measured. Next, while the hexagonal bolt 11 is additionally tightened with a spanner or the like, the measurement of the axial force by the load washer 14 and the propagation time of the ultrasonic wave 16 are measured at that time. Axial force should be determined to be slightly larger than the axial force used. A relational expression between the axial force of the bolt and the propagation time is calculated based on the measurement data, and the calculated expression is added to the axial force measurement program. FIG. 4 shows another example of a conventional method for preparing a calibration curve, and the same parts as those in FIG. 3 are denoted by the same reference numerals. Hex bolt 11 is inserted into the through hole of material 12,
The tip is fastened by a nut 17. Nut 1
7 is configured such that a tensile load is applied by a hydraulic pressure 18, and the load data is displayed on a hydraulic / tensile force display 19. Then, a relational expression between the axial force of the bolt and the propagation time is obtained according to the same procedure as above, and a calibration curve of the axial force of the bolt is created. [0006] In the above-described conventional method for preparing a calibration curve, the relationship between the axial force and the propagation time is recorded every time a bolt is tightened and an axial force is applied. Must be kept, which can lead to measurement errors. It takes a lot of man-hours to create a calibration curve, and it takes time and effort. By attaching / detaching the ultrasonic sensor and manually tightening it using a spanner, the variation in data becomes large. In order to obtain a highly accurate calibration curve, it is necessary to increase the number of data. However, since the conventional method requires a lot of time, a calibration curve is created with limited and small data, and the accuracy is reduced. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and performs an automatic bolt fastening operation using a nut runner having a built-in ultrasonic sensor at the tip. At the same time, the propagation time of the ultrasonic wave transmitted and received from the ultrasonic sensor toward the bolt, and the bolt axial force detected in real time by the load cell fitted to the bolted portion, the bolt axial force, An automatic calibration curve creation device for bolt axial force, which automatically creates a calibration curve. [0008] The present applicant has disclosed Japanese Patent Application Laid-Open No. 2000-141241.
As disclosed in Japanese Patent Application Publication, the ultrasonic wave transmitted from the ultrasonic sensor built into the socket tip of the nut runner, the echo pulse reflected from the bolt tip and returned is received, and the propagation time is measured. By doing so, a bolt fastening machine that calculates the bolt axial force has already been completed. The present invention can be realized only by using the above-described device, and data of both the axial force of the bolt and the propagation speed of the ultrasonic wave generated by the tightening by the nut runner are sent to the bolt fastening controller in real time and recorded. The calibration curve indicating the relationship between the two is continuously and automatically created. Next, an embodiment of the present invention will be described with reference to the drawings. The apparatus for automatically preparing a calibration curve for bolt axial force illustrated in FIG. 1 includes a nut runner 1, a bolt automatic fastening control device 2, and an axial force indicator 3. The nut runner 1 includes a motor 4, a socket 5, and an ultrasonic sensor 6 as main components, and an electric wire 7 extending from the ultrasonic sensor 6 extends outside via a slip ring 8, and is connected to a bolt automatic fastening control device 2. It is connected with the ultrasonic measuring instrument 9 in the inside. The motor 4 is controlled by a bolt fastening controller 10 in the automatic bolt fastening controller 2. The bolt to be measured is a hexagon bolt 11 in this embodiment, and is screwed into a screw hole formed in the material 12. A load washer 14 is fitted between the material 12 and the bolt head 13 as a load cell. The load washer 14 is connected to the axial force indicator 3, and the axial force indicator 3 is also connected to the ultrasonic measuring device 9 so that axial force data is sent to the ultrasonic measuring device 9. The ultrasonic sensor 6 is incorporated in a hexagonal hole at the tip of the socket 5 provided so as to engage with the bolt head 13, and comes into contact with the upper surface of the bolt head 13 when the socket 5 is set. In such a state as to be biased. At the time of actual measurement, the maximum axial force is input and instructed to the automatic bolt tightening control device 2 in advance. Simultaneously with the start of the automatic tightening by the nut runner 1, the axial force data from the load washer 14 and the propagation time data by the ultrasonic sensor 6 are collected, and are continuously performed until the specified maximum axial force is reached. When the tightening operation is completed, the ultrasonic measuring device 9 calculates a calibration curve representing the relationship between the bolt axial force and the ultrasonic wave propagation time. The axial force of the bolt is determined by the size, pitch,
Since it differs depending on various factors such as the material of the bolt and the state of the mating material, once the calibration curve is obtained by the above-described device for each condition, a simple device including only the ultrasonic sensor 6 and the ultrasonic measuring device 9 can be used. Thus, a target bolt axial force can be obtained only by monitoring the ultrasonic wave propagation time. In this case, the bolts may be tightened manually by a spanner or by an automatic fastening machine such as a nut runner. According to the present invention, the apparatus for automatically preparing a calibration line for a bolt axial force according to the present invention is capable of calibrating an automatic bolt tightening control device using an ultrasonic sensor and an axial force display obtained from a load cell in conjunction with each other. The line creation time can be completed in a few seconds, and the time can be greatly reduced as compared with the related art.
Since there is no need to attach and detach the ultrasonic sensor and the bolt is tightened by an automatic machine, data with little flapping can be obtained. Compared with the related art, since the data of the axial force to be measured and the propagation time can be continuously acquired in a close form, a highly accurate calibration curve can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing an embodiment of the present invention, in which a nut runner includes a partial cross section. FIG. 2 is a conceptual diagram for explaining a calibration curve. FIG. 3 is a conceptual diagram of a conventional calibration curve creating apparatus using a load washer. FIG. 4 is a conceptual diagram of a conventional calibration curve creating apparatus using hydraulic pressure. [Description of Signs] 1 Nut runner 2 Bolt automatic fastening control device 3 Axial force indicator 6 Ultrasonic sensor 11 Hexagon bolt 14 Load washer

Claims (1)

Claims: 1. A nut runner having a built-in ultrasonic sensor at a tip portion performs an automatic bolt fastening operation,
The calibration curve of the bolt axial force is calculated by using the propagation time of the ultrasonic wave transmitted and received from the ultrasonic sensor toward the bolt and the bolt axial force detected in real time by the load cell fitted to the bolted portion. Automatic creation of calibration curve for bolt axial force, characterized by automatic creation.