JP2001162548A - Screw fastening device and foreign matter bite-in judging method for the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent drop of the thrust force after screw fastening by accurately sensing inclusion of foreign matter into a seat surface and screw part generated in the screw fastening process. SOLUTION: If a screw bites in any foreign matter when screw is to be fastened, the fastening torque will rise above the first reference torque (from A to B) because screw fastening is performed while the foreign matter is deformed. After the end of the deformation of foreign matter, the drive torque rises only with the torque required to fasten the screw (from B to C). According to this foreign matter bite-in judging method for a screw fastening device, the torque required for the foreign matter to make deformation is determined from the angle difference between A-D or the area surrounded by ABD through utilization of the approximation straight line for the rise of the torque required to fasten the screw between B and C and the obtained torque value is compared with the preset threshold to serve accurately sensing the bite-in of foreign matter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw tightening device for tightening screws, bolts, nuts and the like to a specified torque by external power. Furthermore, the present invention relates to a method for determining whether a foreign matter is caught when a screw or the like of a screw tightening device is tightened.

[0002]

2. Description of the Related Art When two members are fixed using screws, bolts or the like, in order to obtain an appropriate tightening force, the rotation of a drive source is adjusted so that the tightening torques thereof become a reference value. Is controlled. As the management of the tightening torque, in the prior art, as described in Japanese Patent Application Laid-Open No. 63-237874, it is determined whether tightening is appropriate based on the required time and angle until a certain torque value of 1-2. This is a very simple method of detection and management, but the variation in product accuracy is so large that angle detection is difficult, it is difficult to set an appropriate threshold, and high-precision determination cannot be performed. There is.

[0003] Another prior art is disclosed in Japanese Patent Laid-Open No. 6-9 / 1994.
As disclosed in Japanese Patent No. 9322, there is an apparatus that detects a bite of a foreign substance and a screw failure based on a time and an angle until seating. In this regard, most of the tightening machines use several gears in order to increase the reduction ratio, and backlash is a problem. In addition, there is also a problem that before the tightening by the tightening machine, the position to which the screw is tightened in advance largely depends on the variation.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to reduce the axial force after fastening in the tightening process of screws, bolts, etc. Another object of the present invention is to provide a screw tightening device and a method for determining whether a foreign matter has been caught by the screw tightening device, so that foreign matter such as cutting chips can be detected with high accuracy in a process.

[0005]

According to the present invention, as a means for solving the above-mentioned problems, there is provided a screw tightening device as described in the claims and a method for judging a foreign object from being caught by the device. I do. In the screw tightening device according to claim 1, the screw corresponding to the first reference torque when the screw tightening completion point C is reached with a rising gradient of the torque required only for the actual screw tightening after the foreign matter deformation. The tightening angle is defined as a virtual screw tightening start point D, the screw tightening angle when the first reference torque is reached is defined as a torque increase start point A, and the torque required for deformation of the foreign matter is the angle difference between points A and D. Therefore, when the angle difference is equal to or more than a predetermined value, it is determined that a foreign object has been caught, and the foreign object can be detected with high accuracy. If it is determined that foreign matter has been caught, remove the screw and remove the caught foreign matter.
Alternatively, if the external thread, internal thread, and seating surface are damaged by foreign matter, it is possible to replace the damaged one. Then, the screws may be tightened again.

The screw tightening device according to the first aspect determines whether a foreign object is caught by using the angle difference between the point A and the point D. From the difference between the torque increase curve from the torque increase start point A to the screw tightening completion point C and the approximate approximate straight line from the virtual screw tightening start point D to the screw tightening completion point C, the work required for deformation of the foreign matter is calculated. However, if this value is equal to or more than a predetermined value, it is determined that foreign matter has been caught, and the foreign matter can be detected with high accuracy. That is, the torque required for the deformation of the foreign matter corresponds to the area surrounded by points A, B, and D, which is the amount of work, and therefore, is based on a value that exceeds the fluctuation range due to variations when screwing is performed normally. As a value, a bite of a foreign substance is detected by comparing the area with its reference value. The point B is a point at which the gradient of the actually detected torque rise curve is inflected, and becomes substantially constant from the inflection point to the point C. According to a third aspect of the present invention, the screw gripper is driven to rotate at a constant speed during the screw tightening period. Thus, when a foreign object is caught, the torque required to deform the foreign object can be detected with high accuracy.

[0007] The method for judging the entry of foreign matter by the screw tightening device according to claims 4 and 5 corresponds to the screw tightening device according to claims 1 and 2, respectively, and the invention of a product is a method invention. The effect is substantially the same as that of the device according to claims 1 and 2. That is, this method can accurately detect foreign matter being caught, and prevent a decrease in axial force after screw fastening and a worst case screw breakage.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a screw tightening device according to an embodiment of the present invention; FIG. 1 shows a screw tightening device of the present invention. In the figure, reference numeral 1 denotes a motor for driving an adapter (screw gripper) 4 to the head of a screw 5, and a rotary shaft 6 of the motor. A torque detector 3 such as a torque transducer for detecting a rotation torque and a rotation angle detector 2 such as an encoder for detecting a rotation angle are attached. Motor 1
During the screw tightening period, the drive power controlled by the motor drive circuit 8 so as to rotate at a constant speed is supplied from the power supply. Further, during the screw tightening period, the tightening torque and the tightening angle at regular intervals are detected by the torque detector 3 and the rotation angle detector 2, respectively, and the data is read into the ECU 7. In FIG. 1, the rotation angle detector 2
Although the torque detector 3 and the torque detector 3 are provided separately, it is also possible to integrate them and perform the detection with an externally mounted sensor. Further, a fluid motor using hydraulic pressure or pneumatic pressure may be used as a drive source of the motor.

The ECU 7 determines the presence or absence of a foreign substance based on the read data according to a foreign substance detection algorithm shown in FIG. This algorithm will be described with reference to FIGS. Data reading is started, and in step 701, a point at which the detected torque reaches the first reference torque as shown in FIG. When the screw is fastened to the member to be tightened without being caught by a foreign object, the head of the screw (the head has a larger diameter than the screw body) until the bearing surface contacts the member to be tightened. The tightening torque of the screw is sufficiently small, and the first torque for detecting the torque increase starting point A in the graph of FIG.
Does not rise to the reference torque of. However, once the seating surface of the head of the screw abuts against the member to be tightened, the tightening torque starts to increase due to the frictional force between the seating surface and the member to be tightened.

When the torque rises to a predetermined value, it is determined that the tightening of the screw has been completed, and the tightening is stopped. This is the screw tightening completion point C in step 702.
Is the detection of However, during the screw tightening period, the drive motor is rotating at a constant speed, and even after instructing to stop the tightening, the screw tightening ends with a slight delay due to the inertia of the mechanism inside the motor. Therefore, the second reference torque for determining the completion of tightening is set in consideration of the delay.

If the screw bites a foreign substance when the screw is tightened, the screw is tightened while deforming the foreign substance. Therefore, the tightening torque for deforming the foreign substance is increased as shown in FIG. At the tightening angle position (point A) before the tightening angle position in the case of tightening, the torque increases above the first reference torque, and the tightening torque increases in a rising curve until the deformation of the foreign matter is completed ( A point → B point). The deformation of this foreign matter is finished,
When the screw tightening is no longer affected, thereafter, the tightening torque increases with only the torque necessary to tighten the screw (point B → point C). That is, from the point B to the point C, the tightening torque increases with an approximately straight line and an approximate straight line.

In step 703, the end point B of the foreign matter deformation is detected. The point B can be determined as a point at which the gradient is inflected in the actually detected torque rise curve and the gradient becomes substantially constant from the inflection point to the point C. Next, in step 704, a tightening torque curve (points A to C) when the screw is actually tightened is obtained.
2), an approximate curve of the torque from point A to point B is obtained as shown in FIG. Further, in step 705,
An approximate straight line of the torque from point B to point C showing a substantially constant rising gradient of the torque required only for the tightening of the screw is obtained, and the approximate straight line is extended as shown in FIG. A screw tightening angle corresponding to the first reference torque for determination is determined as a virtual screw tightening start point D.

In step 706, as shown in FIG. 2, an approximate curve between points A and B, which is an actual tightening rise curve, the approximate straight line determined above, and the torque value of the first reference torque The area enclosed by is calculated as the amount of work consumed for foreign matter deformation (loss of the tightening work viewed from the tightening work side). That is, from the difference between the approximate torque increase curve from the torque increase start point A to the screw tightening completion point C and the approximate increase curve from the virtual screw tightening start point D to the screw tightening completion point C, the work required for deformation of the foreign matter is determined. Calculate the quantity.

Further, at step 707, an angle difference between the screw tightening angle at the torque increase start point A and the screw tightening angle at the virtual screw tightening start point D is calculated.

Next, in step 708, step 70
The two parameters of the amount of work consumed for the foreign matter deformation and the arrival angle from the point A to the point D calculated by the CPU 6,707 are compared with a preset threshold to determine the presence or absence of the foreign matter. I do. This threshold value is set as a reference value that exceeds a fluctuation range due to variation when screwing is performed normally. Since the torque required for deformation of the foreign object corresponds to both the angle difference between the points A and D or the area surrounded by the points A and B and the point D, either one of the calculations in steps 706 and 707 is performed. May be performed to determine the bite of a foreign object by using the obtained one parameter.

Further, when the tightening torque is equal to or more than a predetermined value, the deformation of the foreign matter is completed, and thereafter, it is confirmed by a test that the torque is used only for screw tightening.
In step 703, the point B may be set in advance to a fixed value equal to or more than the predetermined value.

In the screw tightening device according to the present invention, the use of the above-described algorithm is used to determine whether or not foreign matter has been caught. If it is determined that foreign matter has been caught, the screw is removed, and the caught foreign matter, etc. If the external thread, internal thread, or seat is damaged by foreign matter, replace the damaged one, and then re-tighten the screw. it can. Further, according to the present invention, the torque required for deformation of the foreign matter can be accurately obtained from the difference from the actual torque rise curve based on the approximate line of the increase in the torque required only for tightening the screw. Can be determined with high accuracy. That is, as shown in, for example, Japanese Patent Application Laid-Open No. 63-237874, the torque pattern data when the screw is tightened normally without biting foreign matter is stored,
Even if an attempt is made to determine whether a foreign object is caught by comparison with the stored pattern data, highly accurate determination is impossible. This is because, for example, when oil or the like is interposed between the screw and the member to be tightened, the frictional force between the two decreases, and the gradient of the torque rise becomes smaller than the stored data. is there. According to the present invention, when the screw is actually tightened, the gradient of the increase in torque required only for the tightening of the screw is detected from the torque increase gradient between points B and C. When the torque reaches the point C with this rising gradient, the screw tightening angle corresponding to the first reference torque is set to D.
Find as a point. As a result, it is possible to accurately determine the curve of the increase in torque required only for tightening the screw. Therefore, the torque required for the deformation of the foreign matter can be accurately obtained from the difference from the actual torque rise curve with reference to the rise curve.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a screw tightening device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating an operation of a method for determining whether a foreign object is caught by the screw tightening device according to the embodiment of the present invention.

FIG. 3 is a flowchart of a method for judging foreign matter getting caught by the screw tightening device according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Drive motor 2 ... Rotation angle detector 3 ... Torque detector 4 ... Adapter 5 ... Bolt

Claims (5)

[Claims] A rotary power source for driving the screw gripper; a torque detecting means for detecting a driving torque by which the rotary power source drives the screw gripper; and a rotation for detecting a screw tightening angle of the screw gripper. Angle detection means; and a rise start point setting for setting a screw tightening angle when the torque detected by the torque detection means becomes a first reference torque for determining a start of increase in torque as a torque increase start point. Means for setting the screw tightening angle when the torque detected by the torque detecting means becomes the second reference torque corresponding to the screw tightening completion as a screw tightening completion point; An ascending gradient detecting means for detecting an ascending gradient of torque accompanying an increase in the screw tightening angle after the deformation, and an ascending gradient detected by the ascending gradient detecting means,
Virtual screw tightening start point setting means for setting a screw tightening angle corresponding to the first reference torque as a virtual screw tightening start point when the screw tightening completion point is reached; and a screw tightening angle at the torque increase start point. And a judging means for judging that a foreign substance is caught when the angle difference between the screw tightening angle at the virtual screw tightening start point and the virtual screw tightening start point is equal to or larger than a predetermined value. 2. A rotary power source for driving a screw gripper, torque detecting means for detecting a driving torque by which the rotary power source drives the screw gripper, and rotation for detecting a screw tightening angle of the screw gripper. Angle detection means; and a rise start point setting for setting a screw tightening angle when the torque detected by the torque detection means becomes a first reference torque for determining a start of increase in torque as a torque increase start point. Means, and a torque detected by the torque detecting means, a screw tightening completion point setting means for setting a screw tightening angle when the second reference torque corresponding to the completion of screw tightening as a screw tightening completion point, An ascending gradient detecting means for detecting an ascending gradient of torque associated with an increase in the screw tightening angle after the foreign matter deformation, and an ascending gradient detected by the ascending gradient detecting means,
Virtual screw tightening start point setting means for setting a screw tightening angle corresponding to the first reference torque as a virtual screw tightening start point when the screw tightening completion point set by the screw tightening completion point setting means is reached; From the difference between the approximate torque rise curve from the torque increase start point to the screw tightening completion point and the approximate rise curve from the virtual screw tightening start point to the screw tightening completion point, the work required for deformation of the foreign matter is calculated. A screw tightening device comprising: a calculating unit that performs the calculation; and a determining unit that determines that a foreign object is caught when the work amount calculated by the calculating unit is equal to or more than a predetermined value. 3. The screw tightening device according to claim 1, wherein the rotary power source rotationally drives the screw gripper at a constant speed. 4. A step in which a rotational power source detects a driving torque for driving the screw gripper and a screw tightening angle of the screw gripper at regular intervals, and the detected torque is used to determine the start of torque increase. The step of setting the screw tightening angle when the first reference torque becomes the torque increase start point, and the detected torque becomes the screw tightening angle when the second reference torque corresponding to the screw tightening completion is obtained. A step of setting a screw tightening completion point; a step of obtaining an approximate straight line in which the slope of the detected torque rise curve is inflected and having a substantially constant slope from the inflection point to the screw tightening completion point; Is obtained to the first reference torque, and this is set as a virtual screw tightening start point. The angle difference between the screw tightening angle at the torque increase start point and the screw tightening angle at the virtual screw tightening start point is Above a certain value Biting determination method of foreign substances and determining steps and biting of the foreign matter, become more threaded fastening device when that. 5. A step of detecting a driving torque for driving the screw gripper and a screw tightening angle of the screw gripper at regular time intervals by the rotary power source, and detecting the detected torque to determine a start of torque increase. The step of setting the screw tightening angle when the first reference torque becomes the torque increase start point, and the detected torque becomes the screw tightening angle when the second reference torque corresponding to the screw tightening completion is obtained. A step of setting a screw tightening completion point; a step of obtaining an approximate straight line in which the slope of the detected torque rise curve is inflected and having a substantially constant slope from the inflection point to the screw tightening completion point; Is obtained as a virtual screw tightening start point, a torque rise curve from a torque increase start point to a screw tightening completion point, and a screw tightening from the virtual screw tightening start point. Complete Calculating a work amount required for deformation of the foreign object from a difference from the ascending approximate straight line up to the point; and determining that the foreign object is caught when the calculated work amount is a predetermined value or more. A method for determining the entry of foreign matter into a screw tightening device.