JPH068074A - Screw fastening device - Google Patents

Abstract

PURPOSE:To provide a screw fastening device capable of preventing the galling of screws by keeping pressing force, imparted to the screws during fastening, constant. CONSTITUTION:After a socket 42 is fitted to a bolt 50, an articulated robot 20 is operated by the operation of a control unit 10, and a nut runner 26 is moved by the specified distance in the X-axis direction, so that the socket 42 is pressed to the bolt 50 with the specified pressing force in the X-axis direction. When the socket 42 is rotated by a built-in driving motor 30 to start fastening, the screw-in quantity (x) is computed by a control unit 10 from the screw pitch P and the rotating speed N of the socket 42, and the nut runner 26 is moved by the distance (x) in the X-axis direction by the articulated robot 20. As a result, the nut runner 26 advances by the advance part of the socket 42 in association with the fastening of the bolt 50, so that a coil spring 38 always maintains the specified contraction quantity, and thus pressing force imparted to the socket 42 is kept to the specified grade.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw tightening robot for automatically tightening bolts, nuts and the like.

[0002]

2. Description of the Related Art Various screw tightening devices have been developed and used for automatically tightening bolts, nuts, screws, etc. in a machine assembling process. For example, a screw tightening device having a structure in which a nut runner is attached to a unit that can be moved three-dimensionally by an articulated robot is used. In this screw tightening device,
By fitting the nut runner socket to the bolt head etc. and rotating the socket with the drive motor,
Bolts are automatically tightened. In such a screw tightening device, it is necessary to perform tightening while applying a pressing force in order to prevent the socket from coming off from the bolt head or the like due to a reaction force when the socket rotates.

As a method for this, for example, Japanese Unexamined Patent Publication No. Hei 2
There is an invention of a screw tightening method disclosed in Japanese Patent Publication No. 284833. In the technique described in this publication, tightening is performed while applying a constant pressure to the screw member, and the screw tightening head is moved along with screwing. However, since such a movable pressing force control mechanism complicates the device, a method of applying a pressing force with a spring is used as a simpler mechanism.
That is, the socket portion of the nut runner is slidable, and the socket portion is axially biased by the spring. Due to the pressing force of this spring, the socket is rotated while being pressed against a bolt or the like, and tightening is performed. By adopting such a system, the moving mechanism and the pressurizing mechanism as in the technique described in the above publication are not required, and therefore, there is an advantage that the configuration is simple and the device is inexpensive.

[0004]

However, it has been found that when the above-mentioned spring pressing method is used for tightening, screwing is frequently caused. Due to such frequent occurrence of galling of screws, it is necessary to stop the screw tightening device and replace the member in which galling has occurred each time, so the efficiency of the automatic tightening process of screws is significantly reduced. There was a problem. Therefore, the inventors of the present invention have diligently studied the occurrence of galling of the screws, and as a result, it has been found that most of the galling of the screws generated during tightening is caused by the change in the pressing force of the spring. did. That is, in the above method, the urging force of the spring gradually weakens as the socket advances and the spring extends as the screws such as bolts are tightened. As a result, the pressing force during tightening is not constant and changes over time. It was found that when the pressing force changes in this way, galling frequently occurs. In particular, in order to apply the necessary pressing force up to the final stage of tightening, it is necessary to apply an excessively large pressing force at the initial stage of tightening, and galling is particularly likely to occur at the initial stage of tightening. In view of this, the present invention provides a screw tightening device capable of preventing galling of screws by maintaining a constant pressing force applied to screws during tightening with a simple structure using spring means. The purpose is to do.

[0005]

In order to solve the above problems, the present invention provides a socket mounted axially slidably on a socket support portion,
A screw provided with a nut runner, which is fitted between the socket and the socket support portion and has a spring means for applying a pressing force to the socket in the axial direction and a socket rotating means for rotating the socket around an axis. In the tightening device, the screw-in amount calculating means for calculating the screw-in amount from the screw pitch and the number of rotations of the socket, and the nut runner by the distance corresponding to the screw-in amount calculated by the screw-in amount calculating means. A screw tightening device having a nut runner moving means for moving the socket in the axial direction has been created.

[0006]

According to the screw tightening device of the present invention having the above structure, the screws are automatically tightened as follows. First, the socket is fitted to a head such as a screw (bolt head, nut, etc.). Then, the nut runner main body is moved in the axial direction by a predetermined distance, and the spring means fitted between the socket and the nut runner main body is contracted. As a result, a predetermined pressing force is applied to the socket in the axial direction, and the socket is pressed against the head of screws or the like. From this state, the socket rotating means rotates the socket around the axis, and tightening of screws is started. During this tightening, the screw-in amount calculating means calculates the screw-in amount from the screw pitch and the number of rotations of the socket. Then, the nut runner moving means moves the nut runner in the axial direction of the socket by a distance corresponding to the calculated screw-in amount. As a result, the nut runner also follows and moves as much as the socket advances as the screws are tightened. As a result, the spring means fitted between the socket and the nut runner body always maintains a predetermined amount of contraction, and the pressing force applied to the socket by the spring means is maintained at a predetermined magnitude. In this way, with a simple structure using the spring means, it is possible to prevent galling of the screws by keeping the pressing force applied to the screws constant during tightening.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment embodying the present invention will be described with reference to FIGS. 1 is a diagram showing an embodiment of a screw tightening device according to the present invention.
(A) is a figure which shows the whole structure of the screw fastening device of a present Example. Further, FIG. 1B is a cross-sectional view showing the structure of the nut runner that constitutes the screw tightening device. Figure 1
As shown in (A), the screw tightening device 2 of the present embodiment includes an articulated robot 20 and the articulated robot 20.
The two nut runners 26A and 26B are fixed to each other via a nut runner mounting plate 28.

The nut runner mounting plate 24 is fixed to the tip of the articulated robot 20 and can be moved three-dimensionally by the operation of the articulated robot 20. The operation of the articulated robot 20 and the nut runners 26A and 26B is controlled by the control unit 10, and the control signal for this is input from the control unit 10 to the articulated robot 20 and the nut runners 26A and 26B. . On the other hand, a signal indicating the operation of the articulated robot 20 and the nut runners 26A and 26B is output to the control unit 10 by the operation signal output line 14. The control unit 10 is a CPU
(Central processing unit) and RAM, ROM memory, etc.
These are computer systems connected by a bus so that data can be transferred freely. In this control unit 10, the articulated robot 2 transmitted through the operation signal output line 14
0, information regarding the operation of the nut runners 26A, 26B is processed, and signals for controlling these operations are output.

The nut runners 26A and 26B are
The nut runner base portions 28A and 28B are fixed to the nut runner mounting plate 24. On the nut runner base portions 28A and 28B, the nut runner main body portions 34A and 34B, the cylinders 36A and 36B, and the socket members 40A and 40B are attached. The structure of the nut runners 26A and 26B will be described in detail with reference to the sectional view of FIG. Two nutrunners 26
Both A and 26B have the structure shown in FIG. As shown in FIG. 1B, a drive motor 30 and a torque transducer 32 are built in the nut runner base portion 28. Drive motor 30
Is a motor for driving a nut runner that rotates the socket member 40 by rotating the cylinder 36. Further, the torque transducer 32 is a torque measuring device for measuring the torque when the drive motor 30 rotates. The drive motor 30 has a control signal input line 1
2 is branched and connected, and the operation signal output line 14 is branched and connected to the torque transducer 32.

As shown in FIG. 1 (B), a cylinder 36 is attached to the nut runner main body 34 so as to be rotatable about its axis. A cylinder hole 36a is provided inside the cylinder 36.
A socket member 40 is fitted in the socket. Cylinder hole 36
The small diameter portion 36b is formed on the right side of "a".
The socket member 40 is prevented from coming off by the piston portion 46 provided at the rear end of 0 abutting on the step of the small diameter portion 36b. Spline teeth are provided on the inner wall of the small diameter portion 36b, while spline teeth corresponding to the spline teeth are provided on the outer periphery of the socket member 40. With the above structure, the socket member 40 and the cylinder 36 are spline-coupled so as to be slidable in the axial direction and relatively non-rotatable around the axis. A large-diameter socket portion 42 is provided at the tip of the socket member 40, and the socket portion 42 is provided with a hexagonal fitting hole 44 that is fitted to the outer circumference of the bolt head or the nut. Further, the coil spring 3 is provided between the socket portion 42 and the cylinder 36.
8 is inserted. The coil spring 38 is a spring unit that applies a pressing force to the socket member 40 to the right in FIG.

Next, a method of controlling the position of the nut runners 26A and 26B by the articulated robot 20 will be described with reference to FIG. FIG. 2 (A) is a front view showing a bolt as an example of screws, and FIG. 2 (B) is an explanatory view showing changes over time in the position of the nut runner in the X-axis direction.
Bolts 50A, 50 by nut runners 26A, 26B
The rotation speed of B, that is, the rotation speed N of the socket members 40A and 40B per unit time is determined by the control signal transmitted from the control unit 10 through the control signal input line 12. At the same time, in the control unit 10, the value of this rotation speed N and the bolt 5 shown in FIG.
From the pitch P of 0 and the tightening elapsed time t, FIG.
As shown in (B), the traveling distance of the bolt 50, that is, the screw-in amount x is calculated. As will be described later, a control signal based on this calculation result is transmitted from the control unit 10 to the articulated robot 20 via the control signal input line 12. The control signal operates the articulated robot 20 to move the nut runner 30 in the X-axis direction by the same distance x as the screw-in amount.

Now, automatic tightening of screws by the screw tightening device 2 of the present embodiment having the above configuration will be described with reference to FIGS. 1 to 3 by taking bolt tightening as an example. First, as shown in FIG. 1, the sockets 42A and 42B are fitted to the heads 52A and 52B of the two bolts 50A and 50B temporarily fastened to a member (not shown). Then, the articulated robot 20 is operated by the control of the control unit 10, and the nut runner mounting plate 24 is moved by a predetermined distance in the X-axis direction of FIG. This predetermined distance is equal to this nut runner 2
The elastic force of the coil springs 38A, 38B contracted by the movement of 6A, 26B causes the sockets 42A, 4
The pressing force applied to 2B is predetermined so as to have a predetermined magnitude. This allows the socket 42
A predetermined pressing force is applied to the A and 42B in the X-axis direction, so that the sockets 42A and 42B are attached to the bolts 50A and 50B.
B heads 52A and 52B are pressed.

From this state, the socket 42 is rotated around the axis by the socket rotating means 30 and the bolt 5 is rotated.
The tightening of 0 is started. Here, as described above, in the control unit 10, the value of the screwing amount x / t per hour is calculated and stored from the screw pitch P and the number of rotations per hour N of the socket. During the tightening of the bolt, the timer counter in the control unit 10 calculates the elapsed time t from the start of rotation of the drive motor 30. From this elapsed time t and the screw-in amount x / t per time stored in the control unit 10, the screw-in amount x is calculated. Then, the articulated robot 20 moves the nut runner 26 in the X-axis direction by a distance corresponding to the calculated screw-in amount x. As a result, the nut runner 26 also follows and moves as much as the socket 42 advances as the bolt 50 is tightened. As a result, the coil spring 38 fitted between the socket 42 and the nut runner body 36 always maintains a predetermined contraction amount, and the pressing force applied to the socket 42 is maintained at a predetermined magnitude.

The result is displayed in the graph of FIG. FIG. 3 is a graph showing the change over time in the pressing force of the screw tightening device. The horizontal axis in Fig. 3 is the elapsed tightening time (units / second), and the vertical axis is the pressing force (units / second).
N). In FIG. 3, a curve 62 formed by connecting white circles is
It shows the change over time in the pressing force by the conventional screw tightening device, and the curve 64 in which black circles are connected is by the screw tightening device 2 of this embodiment. In the conventional screw tightening device, as shown by the curve 62, when the socket advances as the screws are tightened, the spring extends and the pressing force gradually weakens. For this reason,
In order to secure the minimum required pressing force in the final stage of tightening, it is necessary to apply an excessive pressing force in the initial stage of tightening, and in particular, galling is likely to occur in the initial stage of tightening. On the other hand, in the screw tightening device 2 of the present embodiment, the pressing force applied to the screws during tightening can be kept constant as indicated by the curve 64. Moreover, it is not necessary to apply an excessive pressing force in the initial stage of tightening. As a result, it is possible to prevent galling of screws.

By the way, as described above, most of the shavings caused by the automatic tightening using the nut runner is caused by the change in the pressing force. However, in the actual process, screw shaving may occur rarely due to other causes. The screw tightening device 2 of this embodiment is provided with a mechanism for detecting the occurrence of galling in such a case. The mechanism for detecting this galling will be described with reference to FIGS. 1, 4 and 5. As shown in FIG. 1B, the torque transducer 32 is attached to the drive motor 30 in the nut runner base portion 28. The torque of the drive motor 30 during rotation is measured by the torque transducer 32, and a detection signal corresponding to the torque value is output from the operation signal output line 14 to the control unit 10. The occurrence of galling is detected using the value of the rotational torque of the drive motor 30.

Theoretically, if the pressing force applied to the screws is constant, the change over time of the tightening torque during tightening of the screw tightening device always follows a constant curve.
The graph of FIG. 5 shows the change over time of the torque, where the horizontal axis represents the tightening elapsed time t and the vertical axis represents the tightening torque T. Curve T shown in FIGS. 5 (A) and 5 (B)
₀ (t) is the theoretical tightening torque curve described above.
Here, in the section of TA on the horizontal axis of FIG. 5 (A), the nut runner is reversed. This is as shown in the section TA of FIG. 5 (A) at the time when the tips of the screws are screwed into the mouths of the female threads when the tips of the screws are reversed with the female threads abutting. A curve T ₀ (t) shows a peak at. By utilizing this, the tips of the screws are securely screwed into the female screw mouth. Next, in the TB section, the nut runner is normally rotated at a low speed, and again shows a peak as shown in FIG. 5 (A) to establish screwing of screws, and then the nut runner is rotated at a high speed in the TC section. The screw is rotated normally and the tightening of screws is completed.

FIG. 5A shows the theoretical torque curve.
As shown in the horizontal axis t is divided into small time until t ₁ ~t _n, the value of T at each time interval t _n of the curve T ₀ (t) is stored in the memory of the control unit 10 ing.
On the other hand, the rotational torque of the drive motor 30 measured by the torque transducer 32 is
It is converted to the actual tightening torque value T _r (t). This actual torque value T _r (t) is compared with the above-described theoretical torque value T ₀ (t) for each time segment to determine whether or not galling occurs. When galling occurs, the curve showing the change over time of the actual torque is the curve T _r shown in FIG. 5 (B).
It looks like (t). Therefore, the difference between the actual torque value T _r (t) and the theoretical torque value T ₀ (t) is calculated for each time segment t _n , and when the cumulative value L of this difference exceeds a predetermined value, for example, ,
It will be determined that a scraping has occurred.

A specific procedure for determining the occurrence of galling in the control unit 10 will be described with reference to FIG.
FIG. 4 is a flowchart showing a procedure for determining the occurrence of galling. The determination program is started in step S10 of FIG. 4, the nut runner is first operated, and the tightening of the bolt is started by the rotation of the drive motor (step S12). Then, for each time segment t _n during tightening, the actual torque value T _r (t) and the theoretical torque value T ₀
The difference from (t) is calculated. Where the actual torque value T
_{When r} (t) is larger than the theoretical torque value T ₀ (t), that is, when T ₀ (t) −T _r (t) <0 continues for a predetermined time C ₁ or more, galling occurs. It is determined (step S14). In this case, the value of the rotation speed is corrected to N ₂ (reverse rotation and low speed rotation), and the articulated robot 20 is retracted while the nutrunner is rotated in the reverse direction (step S).
16).

Meanwhile, when it is determined as NO in step S14, the process proceeds to step S18, the cumulative value L of the difference shown in FIG. 5 (B) whether exceeds a predetermined value C ₂ is determined. Then, if L> C ₂ , it is also determined that galling has occurred, and the articulated robot 20 is moved backward by the distance x ₂ given by x ₂ = (L−C ₂ ) / M (step S20). . Note that M is an empirically obtained constant, and it is clear from many experimental data that the galling phenomenon is eliminated by retracting the nut runner by the distance x ₂ given by the above formula and re-tightening. It has become.

On the other hand, if "NO" is determined in the step S18, the process proceeds to a step S22, and it is determined whether the tightening torque of the nut runner at the present time is a predetermined value or more, and whether the nut runner's current tightening torque is a predetermined value or more. It If both reach the predetermined value, it is determined that the tightening is completed, the operation of the nut runner is stopped, and the program ends (step S24). Step S22
If the determination is NO, the tightening has not been completed, so the process returns to step S12 and the tightening is continued. In this way, in the screw tightening device 2 of the present embodiment, even if a galling phenomenon occurs due to a cause other than the change over time in the pressing force, it is possible to immediately detect this and correct the tightening.

In this embodiment, the articulated robot 20 is used.
Although two nut runners are attached to the tip of the above, the number of nut runners may be one or other. Further, the above-mentioned mechanism for detecting the occurrence of galling is not essential for constituting the present invention. Further, the shapes and sizes of the socket member 40, the coil spring 38 and the like are merely examples, and various shapes and sizes other than the above can be used. The structure, shape, size, material, number, arrangement, etc. of the other parts of the screw tightening device are not limited to those in this embodiment.

Further, as an effect unique to this embodiment, the drive motor 30 measured by the torque transducer 32 is used.
Since the configuration is such that the occurrence of galling can be detected by using the rotational torque of No. 1, even if a galling phenomenon occurs due to a cause other than the change over time of the pressing force, it is possible to immediately detect this and correct the tightening.

[0023]

According to the present invention, the screw-in amount calculating means for calculating the screw-in amount from the screw pitch and the number of rotations of the socket, and the nut runner are moved in the axial direction of the socket by a distance corresponding to the screw-in amount. Since the screw tightening device having the nut runner moving means is created, the pressing force applied to the screws by the spring means during the tightening can be kept constant, and galling of the screws can be prevented. As a result, a practical screw tightening device capable of dramatically improving the efficiency of the automatic tightening process with a simple structure using the spring means is provided.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram and a partial sectional view showing an embodiment of a screw tightening device according to the present invention.

FIG. 2 is an explanatory diagram showing a method of controlling a position of a nut runner in the screw tightening device.

FIG. 3 is a diagram showing a change over time in pressing force in the screw tightening device.

FIG. 4 is a flowchart showing a procedure for determining the occurrence of galling in the screw tightening device.

FIG. 5 is a diagram showing a change in tightening torque with time in the screw tightening device.

[Explanation of symbols]

 2 screw tightening device 10, screw-in amount calculating means 20, 24 nut runner moving means 26 nut runner 30 socket rotating means 36 socket support 38 spring means 42 socket

Claims (1)

[Claims] 1. A socket mounted slidably in an axial direction with respect to a socket support part, and a socket fitted between the socket and the socket support part, for applying a pressing force to the socket in the axial direction. A screw tightening device comprising a nut runner having a spring means and a socket rotating means for rotating the socket around an axis, comprising: a screw-in amount calculating means for calculating a screw-in amount from a screw pitch and a rotation speed of the socket. And a nut runner moving means for moving the nut runner in the axial direction of the socket by a distance corresponding to the screw-in amount calculated by the screw-in amount calculating means.