JP2013202705A - Screw fastening method, and screw fastening device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an accurate fastening torque to be managed by efficiently performing fastening while reducing reaction of a fastening torque even when fastening a soft body, in a screw fastening method using an electric motor as a drive source.SOLUTION: High-speed speed control of causing an output shaft to rotate at high speed by a continuous fastening torque is performed until fastening is started and a fastening torque T reaches a seating torque T, and thereafter low-speed speed control of causing the output shaft to rotate at low speed by the continuous fastening torque is performed until the fastening torque T reaches a switching torque T. After the fastening torque T reaches the switching torque T, pulse control of cyclically increasing and decreasing the fastening torque T is performed, and fastening is performed to a stipulated torque T. Thus, fastening time to a seating point S is shortened, and compression and deformation from the seating point S to a switching point SW when fastening a soft body are efficiently performed. After the switching point SW is reached, fastening is performed by the pulse control, and the reaction of the fastening torque is reduced.

Description

  The present invention relates to a screw tightening method and a screw tightening device for tightening screw parts such as bolts and nuts using an electric motor as a drive source.

  2. Description of the Related Art In an automobile assembly line or the like, a screw tightening device is used for tightening a large number of screw parts such as bolts and nuts with a prescribed torque. The screw tightening device uses the motor as a drive source to rotate the output shaft on which the screw tightening tool is mounted, tightens the screw parts, stops the motor when the tightening torque reaches the specified value, Alternatively, the tightening is completed by cutting off the driving force of the motor by the clutch mechanism.

  When the operator operates the screw tightening device by hand, the reaction force of the tightening torque becomes a problem. When tightening by rotating the output shaft continuously, the operator receives the reaction force of the tightening torque directly by hand. Not suitable. On the other hand, there is a pulse-type screw tightening device that periodically increases and decreases the rotation speed of the output shaft, intermittently generates a tightening torque, and performs tightening with an impact force. In such a pulse-type screw tightening device, the reaction force of the tightening torque can be absorbed by the rotational inertia of the screw tightening device, and the burden on the operator can be reduced.

  Patent Document 1 discloses a seating point at which the output shaft is continuously rotated at a high speed by an electric motor at the start of tightening, and then a screw component is screwed and seated on a member to be coupled and the tightening torque rises. A screw tightening device is disclosed in which the drive torque of the electric motor is intermittently generated by supplying a pulse current when switching reaches tightening by striking force. According to this screw tightening device, the tightening time can be shortened by the continuous high-speed rotation of the output shaft up to the seating point where no large tightening torque is generated. By switching to tightening by force, the burden on the operator due to the reaction force of the tightening torque can be reduced.

Japanese Patent Laid-Open No. 2002-1676

However, the one described in Patent Document 1 has the following problems.
If there are many intervening parts such as washers and bushes fastened by screw parts, or if the interstitial parts include an elastic body such as rubber, so-called soft body fastening is used, and these interpositions are reached after reaching the seating point The tightening torque fluctuates and becomes unstable until the part is compressed and deformed to some extent by the axial force caused by tightening the screw part. In addition, since the reaction force characteristic of the elastic body changes depending on the deformation speed, there is a case where sufficient deformation cannot be obtained by the pulse-type tightening with the impact force. For this reason, during tightening, the intervening part may rotate together with the screw part, and there is a problem that accurate tightening torque measurement becomes difficult.

  The present invention has been made in view of the above points. Even in soft body fastening, the tightening torque can be efficiently tightened while reducing the reaction force of the tightening torque, and accurate tightening torque management is possible. It is an object of the present invention to provide a screw tightening method device and a screw tightening device that are capable of performing the above.

In order to solve the above problems, a screw tightening method according to the present invention is a screw tightening method for tightening a screw component using an electric motor as a drive source,
After starting the tightening and reaching the seating point where the screw parts are seated and the tightening torque rises, until the predetermined switching point is reached, the tightening torque is continuously applied to control the rotation. Run,
After reaching the switching point, a pulse control for controlling rotation by applying a tightening torque that increases or decreases periodically is executed.
The screw tightening device according to the present invention is a screw tightening device for tightening screw parts using an electric motor as a drive source, and controls a torque sensor for detecting a tightening torque and rotation of the electric motor. And a control device that
The controller starts tightening and, after reaching the seating point where the screw component is seated and the tightening torque rises, continuously applies the tightening torque and rotates until reaching a predetermined switching point. Perform speed control to control,
After reaching the switching point, a pulse control for controlling rotation by applying a tightening torque that increases or decreases periodically is executed.

(Aspect of the Invention)
In the following, some aspects of the invention that can be claimed in the present invention (hereinafter sometimes referred to as “claimable invention”) will be exemplified and described. As with the claims, each aspect is divided into sections, each section is numbered, and is described in a form that cites the numbers of other sections as necessary. This is for the purpose of facilitating the understanding of the claimable invention, and is not intended to limit the combinations of the constituent elements constituting the claimable invention to those described in the following sections. In other words, the claimable invention should be construed in consideration of the description accompanying each section, the description of the embodiments, etc., and as long as the interpretation is followed, another aspect is added to the form of each section. In addition, an aspect in which constituent elements are deleted from the aspect of each item can be an aspect of the claimable invention. The following contents (1) to (10) correspond to claims 1 to 10.

(1) A screw tightening method for tightening screw components using an electric motor as a drive source,
After starting the tightening and reaching the seating point where the screw parts are seated and the tightening torque rises, until the predetermined switching point is reached, the tightening torque is continuously applied to control the rotation. Run,
After reaching the switching point, the screw tightening method is characterized in that pulse control for controlling rotation by applying a tightening torque that increases or decreases periodically is executed.
(2) In the configuration of (1), tightening is started, tightening is performed at a high speed until the seating point is reached, and after reaching the seating point, it is rotated at a low speed until the switching point is reached. A screw tightening method characterized by tightening with a screw.
(3) In the configuration of (1) or (2), when the tightening torque reaches a predetermined seating torque, the screw tightening method is switched from high speed rotation to low speed rotation.
(4) The screw tightening method according to any one of (1) to (3), wherein when the tightening torque reaches a predetermined switching torque, the speed control is switched to the pulse control.
(5) In the structure of any one of (1) to (3), when the rate of increase in tightening torque reaches a predetermined threshold value, the screw control is switched from the speed control to the pulse control. Method.
(6) A screw tightening device for tightening screw parts using an electric motor as a drive source, comprising: a torque sensor for detecting a tightening torque; and a control device for controlling the rotation of the electric motor;
The controller starts tightening and, after reaching the seating point where the screw component is seated and the tightening torque rises, continuously applies the tightening torque and rotates until reaching a predetermined switching point. Perform speed control to control,
After reaching the switching point, a screw tightening device that performs pulse control for controlling rotation by applying a tightening torque that increases or decreases periodically.
(7) In the configuration of (6), the control device starts tightening, performs tightening at a high speed rotation until reaching the seating point, and after reaching the seating point, at the switching point. A screw tightening device characterized in that tightening is performed at low speed until it reaches.
(8) In the configuration of (6) or (7), the control controller switches from high speed rotation to low speed rotation when the tightening torque reaches a predetermined seating torque.
(9) In the configuration of any one of (6) to (8), the control control device switches from the speed control to the pulse control when the tightening torque reaches a predetermined switching torque. Screw tightening device.
(10) In any one of the constitutions (6) to (8), the control device switches from the speed control to the pulse control when the rate of increase in tightening torque reaches a predetermined threshold value. Screw tightening device.

With this configuration, by performing speed control that continuously applies a tightening torque from the start of tightening to the switching point through the seating point, tightening to the seating point and soft body fastening Compression and deformation from the seating point to the switching point can be efficiently performed, and after reaching the switching point, switching to pulse control enables tightening with reduced reaction force of the tightening torque (( 1) and (5)).
By tightening at high speed from the start of tightening to the seating point, the tightening time can be shortened, and by tightening at low speed from the seating point to the switching point, compression and deformation during soft body fastening Can be performed efficiently ((2) and (7)).
Note that the rotation speed in the speed control (high-speed rotation and low-speed rotation) is not limited to a constant speed, and the speed may be appropriately adjusted at the start, at the stop, and the like. Further, the control may be switched without stopping the electric motor once or at the seating point or the switching point that becomes the control switching point.
Since the tightening torque rises at the seating point, the seating point can be detected by monitoring the tightening torque and detecting that the tightening torque has reached the predetermined seating torque ((3) and ( 8)).
In soft body fastening, the rate of increase (inclination) in tightening torque increases at the end of compression and deformation, so the tightening torque is monitored and it is detected that the tightening torque has reached a predetermined switching torque. Thus, the switching point can be detected ((4) and (9)). Further, the switching point can be detected by directly comparing the increase in the increase rate of the tightening torque with the threshold ((5) and (10)).

  According to the tightening device and the tightening control method of the present invention, even in soft body tightening, the tightening can be efficiently performed while reducing the reaction force of the tightening torque, and accurate tightening torque management is possible. It becomes possible.

It is a block diagram which shows roughly the structure of the screw fastening apparatus which concerns on 1st Embodiment of this invention. It is a graph which shows the screw fastening control by the control apparatus of the screw fastening apparatus shown in FIG. 3 is a flowchart for executing screw tightening control shown in FIG. 2. It is a graph which shows the relationship between the rotation angle of the screw components in a soft body fastening, and fastening torque. It is a flowchart which shows a part of control flow for performing the screw fastening control which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
A first embodiment of the present invention will be described with reference to FIGS.
The screw tightening device according to the present embodiment can be operated by an operator by hand, and is for screwing a member to be coupled by tightening a screw component such as a bolt or a nut with a specified torque. Further, this screw tightening device is particularly suitable for so-called soft body fastening, in which screw coupling is performed by interposing parts such as washers and bushes between the members to be coupled. Although the case where there is an intervening part will be described, the present invention can be applied to tightening a screw part regardless of the presence or absence of the intervening part.

  As shown in FIG. 1, the tightening device 1 according to this embodiment detects an electric motor 2 that is a drive source, a speed reduction mechanism 3 that decelerates the rotation of the electric motor 2, and torque of an output shaft of the speed reduction mechanism 3. A torque sensor 4 that is connected to the output shaft of the speed reduction mechanism 3, a socket 5 that engages and holds screw parts (not shown) such as bolts and nuts, and a control device that controls the rotation of the electric motor 2. 6 is provided.

  The electric motor 2 is an AC servo motor, and the rotation can be controlled by a drive current (control current) from the control device 6. The electric motor 2 may be of another type such as a DC servo motor as long as it can execute rotation control described later. The speed reduction mechanism 3 is for reducing the rotation of the electric motor 2 to obtain a necessary tightening torque, and a known speed reduction mechanism such as various gear mechanisms can be used. Further, when the required tightening torque can be obtained by the output of the electric motor 2, the speed reduction mechanism 3 may be omitted and the socket 5 may be directly driven by the electric motor 2. The socket 5 can be appropriately selected according to screw parts to be tightened such as bolts and nuts. The control device 6 includes a driver circuit that generates a drive current for driving the electric motor 2 that is an AC servo motor, and executes rotation speed control based on setting information and rotation control based on a torque signal from the torque sensor 4. To do.

The control of the electric motor 2 by the control device 6 will be described in further detail.
Screw parts such as bolts and nuts are screwed into the members to be coupled, such as washers and bushes, and the socket 5 is engaged with the screw parts and tightened by driving the electric motor 2. . The relationship between the rotation angle A of the screw component and the tightening torque T in this case is shown in FIG. With reference to FIG. 4, when tightening is started and the seating point S at which the head of the screw component comes into contact with the intervening component or the coupling member is reached at the rotation angle A1, axial force is generated in the screw component, and tightening is performed. Torque T rises. Thereafter, the tightening torque T increases with compression and deformation of the interposed components such as washers and bushes by tightening the screw components. Then, when the rotation point A2 (tightening torque Tsw) reaches the switching point SW where the compression and deformation of the interposed parts are finished (compression and deformation progress, and the axial force and tightening torque are stable), the tightening torque T Increase rate of change (slope) increases. Thereafter, as the rotation angle A increases, the tightening torque T increases, and reaches the specified tightening torque Tc at the rotation angle A3.

  With reference to FIG. 2, the control device 6 starts the rotation of the electric motor 2, and monitors the torque of the output shaft of the speed reduction mechanism 3, that is, the tightening torque T of the screw component, by the torque sensor 4. First, high-speed speed control (speed control) for rotating the electric motor 2 at a constant speed at high speed is executed. When the seating point S is reached at time t1, an axial force is generated in the screw component, and the tightening torque T rises. At this time, the seating point S can be detected when the detected value of the tightening torque T by the torque sensor 4 reaches a predetermined seating torque Ts. When the seating point S is reached, low speed control (speed control) is performed in which the rotational speed of the electric motor 2 is decreased and the electric motor 2 is rotated at a low speed at a constant speed.

  Thereafter, with the compression and deformation of the interposed part due to the tightening of the screw part, the tightening torque T rises, and at time t2, the compression and deformation of the interposed part is completed and reaches the switching point SW. At this time, when the detected value of the tightening torque T by the torque sensor 4 reaches a predetermined switching torque Tsw, the switching point SW can be detected. Then, when the switching point SW is reached, the control to the electric motor 2 is switched, and the pulse control for performing the tightening by generating the pulsed tightening torque by increasing / decreasing the rotation speed of the electric motor 2 at a constant cycle is executed. To do. When the tightening torque reaches the specified torque Tc at time t3, the electric motor 2 is stopped and the tightening is finished.

Next, a control flow for executing the above-described control by the control device 6 will be described with reference to FIG.
Referring to FIG. 3, tightening is started, and in step S1, high speed control is performed to rotate electric motor 2 at a high speed at a constant speed, and the flow proceeds to step S2. In step S2, it is determined whether or not the detected torque (tightening torque T) of the torque sensor 4 has reached the seating torque Ts. If the tightening torque T has not reached the seating torque Ts, the process returns to step S1, and if it has reached, the process proceeds to step S3.

  In step S3, the electric motor 2 is temporarily stopped, and the process proceeds to step S4. In step S4, low speed control for rotating the electric motor 2 at a constant speed is executed, and the process proceeds to step S5. In step S5, it is determined whether or not the detected torque (tightening torque T) of the torque sensor 4 has reached the switching torque Tsw. If the tightening torque T has not reached the switching torque Tsw, the process returns to step S4, and if it has reached, the process proceeds to step S6.

  In step S6, the electric motor 2 is temporarily stopped, and the process proceeds to step S7. In step S7, the control current to the electric motor 2 is switched, pulse control is performed to perform tightening while increasing or decreasing the rotation speed of the electric motor 2 at a constant period, and the process proceeds to step S8. In step S8, it is determined whether or not the detected torque (tightening torque T) of the torque sensor 4 has reached the specified torque Tc. If the tightening torque T has not reached the specified torque Tc, the process returns to step S7, and if it has reached, the process proceeds to step S9. In step S9, the electric motor S9 is stopped to complete the tightening, and the process proceeds to step S10. In step S10, a sampling inspection or a total inspection is performed as necessary, and the tightening torque T of the tightened screw component is measured to determine whether it is acceptable.

  In this way, the high-speed speed control is executed at the start of tightening, and the electric motor 2 is rotated at a high speed at a constant speed, whereby the tightening time can be shortened. Thereafter, from the seating point S to the switching point SW, the low-speed speed control is executed and the electric motor 2 is rotated at a low speed at a constant speed so that the interposed part includes a soft body including an elastic bush or the like. However, since an appropriate axial force can be continuously applied to the interposed component, the interposed component can be smoothly and sufficiently compressed and deformed without generating an excessive reaction force. The tightening torque T can be detected accurately and stably. Further, it is possible to suppress the joint rotation of the coupling parts accompanying the tightening. Then, at the switching point SW, the electric motor 2 is driven by switching from the low speed control to the pulse control, so that the tightening can be performed, and the burden on the worker due to the reaction force of the tightening can be reduced efficiently. Tightening can be performed.

Next, a second embodiment of the present invention will be described with reference to FIG.
In the following description, the same reference numerals are used for the same parts with respect to the first embodiment, and only different parts will be described in detail.
In the first embodiment, the control device 6 determines that the switching point SW has been reached when the tightening torque T has reached the predetermined switching torque Tsw, and executes switching from the low speed control to the pulse control. On the other hand, in this embodiment (step S5 in FIG. 3), in addition to this, the switching point SW is based on the increase rate (inclination) of the tightening torque T with respect to the rotation angle A of the screw part. It is possible to select the control for determining the arrival at

In the present embodiment, the control device 6 applies the control flow (B) shown in FIG. 5 instead of the control flow (A) consisting of steps S4 and S5 in the control flow of the first embodiment shown in FIG. To do.
Referring to FIG. 5, after the electric motor 2 is temporarily stopped in step S3, in the control flow (B), the process proceeds to step S3-1 to determine the selection of the switching point SW setting method (manual setting or automatic setting). To do. When the automatic setting is selected (Y), the process proceeds to step S4 ′, the low speed control similar to step S4 is executed, and the process proceeds to step S5 ′.

  Based on the tightening torque T detected by the torque sensor 4 in step S5 ′, the tightening torque T periodically measured for each fixed rotation angle of the screw component is compared with the measured value of the previous period, and the tightening torque Is calculated, and it is determined whether or not the tightening torque increase change rate ΔT has reached a rigidity change determination rate R that is a preset threshold value based on a prior evaluation or the like. When the increase rate ΔT of the tightening torque has not reached the stiffness change determination rate R, the process returns to step S4 ′. If the upper rate change rate ΔT of the tightening torque has reached the stiffness change determination rate R, it is determined that the switching point SW has been reached, and the process proceeds to step S6.

  Further, when manual setting is selected in Step S3-1 (N), Steps S4 and S5 are executed as in the first embodiment, and the tightening torque T reaches the switching torque Tsw. If so, go to step S6.

  As described above, the control of the electric motor 2 is switched based on the switching point SW set automatically or manually. By selecting the automatic setting, it is possible to automatically set the switching point SW for the tightening of screw parts with different conditions such as intervening parts, so that the versatility of the tightening device 1 can be improved. it can.

  DESCRIPTION OF SYMBOLS 1 ... Screw fastening apparatus, 2 ... Electric motor, 4 ... Torque sensor, 6 ... Control apparatus, S ... Seating point, SW ... Switching point, T ... Tightening torque

Claims (10)

A screw tightening method for tightening screw parts using an electric motor as a drive source,
After starting the tightening and reaching the seating point where the screw parts are seated and the tightening torque rises, until the predetermined switching point is reached, the tightening torque is continuously applied to control the rotation. Run,
After reaching the switching point, the screw tightening method is characterized in that pulse control for controlling rotation by applying a tightening torque that increases or decreases periodically is executed.   Tightening is started and tightening is performed at high speed until reaching the seating point, and after reaching the seating point, tightening is performed at low speed until the switching point is reached. The screw fastening method according to claim 1.   3. The screw tightening method according to claim 1, wherein when the tightening torque reaches a predetermined seating torque, the rotation is switched from high speed rotation to low speed rotation.   The screw tightening method according to any one of claims 1 to 3, wherein when the tightening torque reaches a predetermined switching torque, the speed control is switched to the pulse control.   4. The screw tightening method according to claim 1, wherein when the rate of increase in tightening torque reaches a predetermined threshold, the speed control is switched to the pulse control. A screw tightening device for tightening screw parts using an electric motor as a drive source, comprising: a torque sensor for detecting a tightening torque; and a control device for controlling the rotation of the electric motor;
The controller starts tightening and, after reaching the seating point where the screw component is seated and the tightening torque rises, continuously applies the tightening torque and rotates until reaching a predetermined switching point. Perform speed control to control,
After reaching the switching point, a screw tightening device that performs pulse control for controlling rotation by applying a tightening torque that increases or decreases periodically.   The control and control device starts tightening and performs tightening at high speed rotation until reaching the seating point, and after reaching the seating point, tightening at low speed rotation until reaching the switching point. The screw fastening device according to claim 6, wherein the screw fastening device is performed.   The screw tightening device according to claim 6 or 7, wherein the control control device switches from high speed rotation to low speed rotation when the tightening torque reaches a predetermined seating torque.   The screw tightening device according to any one of claims 6 to 8, wherein the control control device switches from the speed control to the pulse control when the tightening torque reaches a predetermined switching torque.   The screw tightening device according to any one of claims 6 to 8, wherein the control device switches from the speed control to the pulse control when a rate of increase in tightening torque reaches a predetermined threshold value. .

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