Threaded fastening system

Abstract

Provided is a threaded fastening system capable of performing high-torque threaded fastening without using a high-rigidity holding device. The threaded fastening system (100) includes an electric motor (41), a holding device (10) that holds the electric motor (41), a support member (30) that is attached to a drive shaft of the electric motor (41), a threaded fastening machine (20) that is supported by the support member (30) and is capable of performing a threaded fastening operation under pulse fastening control, and a motor control unit (502) that controls the electric motor (41) to reduce a fastening torque reaction force on the holding device (10) that is generated by the threaded fastening operation under pulse fastening control of the threaded fastening machine (20).

Description

Technical Field

[0001] This invention relates to a threaded fastening system. Background Technology

[0002] A thread-fastening system is known that mounts a thread-fastening machine (nut wrench) at the front end of a robot arm to perform thread-fastening operations (for example, see Patent Document 1). Patent Document 2 also describes a structural example of the thread-fastening machine.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2017 / 104027

[0006] Patent Document 2: Japanese Patent Application Publication No. 4-310332 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In threaded fastening systems, when the reaction force generated during thread tightening is large, the thread tightening machine needs to be kept in a high-rigidity device or robot capable of withstanding the large reaction force. High-rigidity devices or robots tend to be large and heavy, leading to increased equipment costs and limitations on installation space.

[0009] Methods for solving problems

[0010] One aspect of this disclosure is a threaded fastening system comprising: an electric motor; a retaining device that retains the electric motor; a support member mounted on the drive shaft of the electric motor; a threaded fastening machine supported by the support member and capable of performing a pulse-controlled threaded fastening action; and a motor control unit that controls the electric motor to reduce the tightening torque reaction force on the retaining device generated by the pulse-controlled threaded fastening action performed by the threaded fastening machine.

[0011] Invention Effects

[0012] According to the structure described above, high-torque thread fastening can be performed without the use of a high-rigidity retaining device, which can achieve advantages such as reduced equipment costs and elimination of installation location limitations.

[0013] These objects, features, and advantages of the invention will become more apparent from the detailed description of typical embodiments of the invention shown in the accompanying drawings. Attached Figure Description

[0014] Figure 1This is a diagram showing the device structure of a threaded fastening system according to one embodiment.

[0015] Figure 2 This is a diagram showing the general hardware structure of a robot control device.

[0016] Figure 3 This is a functional block diagram that mainly represents the functions of the robot control device in the threaded fastening system.

[0017] Figure 4 This is a graph used to illustrate the effect of reducing the reaction force of the clamping torque acting on the robot by setting a torque limit.

[0018] Figure 5 This is a diagram illustrating a first variation related to an electric motor.

[0019] Figure 6 This is a diagram showing a second variation related to an electric motor.

[0020] Figure 7 This is a diagram used to illustrate the action of returning the rotational position of the thread-fastening machine after rotation through the thread-fastening action.

[0021] Figure 8 This is a diagram showing other equipment structures of a threaded fastening system.

[0022] Figure 9A This is the first example of a diagram showing the controlled position and orientation of a robot's wrist flange.

[0023] Figure 9B This is the second example of a diagram showing the state in which the position and posture of the robot's wrist flange are controlled.

[0024] Figure 9C This is the third example of a diagram showing the controlled position and posture of the robot's wrist flange.

[0025] Figure 10 This is a structural diagram of a thread-fastening system, which is another example of a support component using a thread-fastening machine.

[0026] Figure 11 This is a structural diagram of a thread-fastening system using a straight-type thread-fastening machine. Detailed Implementation

[0027] Next, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the drawings, the same reference numerals are used to denote the same constituent parts or functional parts. The scales of these drawings have been appropriately altered for ease of understanding. Furthermore, the embodiments shown in the drawings are examples for carrying out the invention, and the invention is not limited to the illustrated embodiments.

[0028] Figure 1 This is a diagram illustrating the device structure of a threaded fastening system 100 according to one embodiment. (See diagram for example.) Figure 1 As shown, the threaded fastening system 100 includes: a robot 10 as an industrial machine; a retaining member 40 mounted on the movable part of the robot 10, namely the wrist flange 11; an electric motor 41 held in the retaining member 40; a support member 30 mounted on the drive shaft 41a of the electric motor 41; a threaded fastening machine 20 supported by the support member 30; and a robot control device 50 responsible for controlling the threaded fastening action in the threaded fastening system 100. Figure 1 The example described is the use of a vertical joint robot as robot 10, but other types of robots or other types of industrial machinery can also be used.

[0029] The robot control device 50 controls the robot 10 and is also connected to the electric motor 41 and the thread fastener 20, and is responsible for controlling the electric motor 41 and the thread fastener 20.

[0030] The retaining member 40 has a frame-shaped retaining frame 42 that houses and holds the electric motor 41 within its internal space. The drive shaft 41a side of the electric motor 41 ( Figure 1 The lower end face of the drive shaft 41a is fixed to the front wall of the retaining frame 42, and the drive shaft 41a passes through the through hole formed in the center of the front wall. Additionally, the rear wall of the retaining frame 42 is fixed to the front end face of the wrist flange 11 of the robot 10. With this structure, the robot 10 functions as a retaining device for the electric motor 41 (i.e., the retaining member 40), which supports the threaded fastener 20 (support member 30) so that it can rotate.

[0031] As an example, the thread fastening machine 20 is an angled thread fastening machine (nut wrench), and the axis of the tool 23 of the head 21 is perpendicular to the axis of the body 22 which has a thread fastening action drive source connected to the head 21 of the thread fastening tool.

[0032] As an example, the support component 30 of the support thread fastener 20 is as follows: Figure 1As shown, it has a U-shaped frame when viewed from the side. Other shapes of components can also be used as the support member 30. The support member 30 has: a bottom wall portion 31 that provides fixed support for the head 21 of the thread-fastening machine 20; an upper wall portion 32 that is fixed to the drive shaft 41a of the electric motor 41; and a side wall portion 33 that connects the bottom wall portion 31 and the upper wall portion 32. The head 21 of the thread-fastening machine 20 is fixed to the bottom wall portion 31 with its tool side facing vertically downward, so as to be housed within the internal space of the support member 30. The center of the upper surface of the upper wall portion 32 of the support member 30 is fixed to the drive shaft 41a of the electric motor 41. In this structure, when the electric motor 41 (rotation shaft) rotates, the thread-fastening machine 20 rotates together with the support member 30.

[0033] In addition, Figure 1 In the diagram, arrow R1 indicates the direction of the tightening torque reaction force generated by the thread fastener 20, arrow M indicates the direction of movement (thread feed direction) of the fastened component (threaded component), and arrow R2 indicates the direction of rotation of the drive shaft 41a of the electric motor 41 under the tightening torque reaction force. Figure 1 In this example, the thread feed direction M is oriented vertically. By configuring the thread fastener 20 to be mounted on the wrist flange 11 of the robot 10 in this way, thread fastening can be performed at the desired position and orientation.

[0034] As detailed below, the robot control unit 50 controls the electric motor 41 to reduce the tightening torque reaction force generated during the thread tightening action based on the pulse tightening control (described later) of the thread tightening machine 20, i.e., the tightening torque reaction force acting on the robot 10.

[0035] Figure 2 This is a diagram showing the schematic hardware structure of the robot control device 50. (Example) Figure 2 As shown, the robot control device 50 may also have a general computer structure, with a processor 51 responsible for various controls connected via a bus to a memory (ROM, RAM, non-volatile memory, etc.) 52, an input / output interface 53, an operation unit 54 containing various switches, etc.

[0036] Figure 3 This is a functional block diagram that mainly represents the functions of the robot control device 50 in the threaded fastening system 100. For example... Figure 3 As shown, the robot control device 50 includes: a motion control unit 501 that controls the motion of the robot 10 based on motion programs, etc.; a motor control unit 502 that controls the electric motor 41; and a torque limit setting unit 503 that sets the torque limit of the electric motor 41. The motion control unit 501 is also configured to control the thread tightening action of the thread tightening machine 20.

[0037] also, Figure 3 The functional block diagram shows a structure where the motor control unit 502 includes servo control functions for the electric motor 41. However, it is also possible to have a structure where the electric motor 41 is driven by an external motor control device equipped with motor control functions such as a servo amplifier. In this case, the motor control unit 502 within the robot control device 50 functions as a host device that sends commands (position commands, etc.) to the external motor control device. The thread fastening machine 20 includes: a control unit (processor) 201 that receives commands (target torque, operating mode, fastening start, etc.) from the motion control unit 501 and executes those commands; and a motor 202 that performs a rotational motion under the control of the control unit 201.

[0038] The torque limit setting unit 503 sets the torque limit of the electric motor 41. Here, the torque limit refers to limiting the maximum current of the electric motor 41. By setting the torque limit, the electric motor 41 is limited from generating torque exceeding the torque limit. In the thread tightening operation, the robot 10 positions the thread tightening machine 20 (i.e., the electric motor 41) at a predetermined rotational position and controls the rotational position of the electric motor 41 to be positioned and held at the predetermined rotational position. Then, the thread tightening machine 20 is operated to perform thread tightening. In such a thread tightening operation, by setting the torque limit of the electric motor 41 using the torque limit setting unit 503, if the tightening torque reaction force generated during the thread tightening operation performed by the thread tightening machine 20 exceeds the torque limit, the drive shaft 41a of the electric motor 41 (i.e., the thread tightening machine 20) rotates in the direction of the tightening torque reaction force. This avoids a large reaction force acting on the robot 10 during the thread tightening operation.

[0039] The motion control unit 501, for example, plans the robot's trajectory according to the motion program and controls the servo motors of each joint axis of the robot so that the wrist flange 11 of the robot 10 moves along the planned trajectory. Through this function, the robot control device 50 (motion control unit 501) can position the thread fastener 20 (thread feed direction M) at the desired position / posture. As an example, in... Figure 9A The diagram shows the state in which the wrist flange 11 is controlled by the motion control unit 501 to make the thread feed direction M horizontal (lateral). Additionally, in Figure 9B The diagram shows the state in which the wrist flange 11 is controlled by the motion control unit 501 to make the thread feed direction M obliquely downward. Additionally, in Figure 9CThe image shows the state where the position of the wrist flange 11 in the X-axis direction (horizontal direction) moves from position P10 to position P11 under the control of the motion control unit 501. Additionally, in Figures 9A to 9C For ease of explanation, the robot control device 50 has been omitted.

[0040] The torque limit setting unit 503 sets the torque limit of the electric motor 41. The torque limit setting performed by the torque limit setting unit 503 has, for example, the following structure:

[0041] (A1) A structure that automatically applies pre-existing torque limits.

[0042] (A2) A structure that accepts numerical input of torque limits based on user operation.

[0043] (A3) A structure that pre-stores a table of recommended values ​​for torque limits corresponding to the control values ​​of tightening torque, and accepts the selection of torque limits based on user operation from the table.

[0044] Furthermore, in cases where the torque limit is set via user operation as described in (A2) and (A3), the system may also be configured to connect an operating device (e.g., a teach pendant) for receiving user operations to the robot control device 50.

[0045] Figure 4 This is a graph used to illustrate the effect of reducing the clamping torque reaction force acting on a robot by setting a torque limit. Figure 4 In the diagram, the vertical axis represents the tightening torque reaction force acting on the robot, and the horizontal axis represents time. Let the set tightening torque (target torque) of the thread tightening machine 20 be 50 Nm. As for the torque control operation modes during thread tightening, the thread tightening machine 20 has, for example, normal tightening control with continuous torque application and pulse tightening control with pulsed torque application. Pulse tightening control has the following advantages: by supplying a pulsed and gradually increasing current to the motor within the thread tightening machine, the motor can generate a gradually increasing pulsed torque, thus reducing the tightening torque reaction force compared to normal tightening control with continuous torque application. Especially in the final stage of the thread tightening operation, the tightening torque reaction force increases, therefore the reduction effect of the tightening torque reaction force using pulse tightening control is greater. A representative example of normal tightening control is control that gradually increases the tightening torque from the start of the operation to reach the target torque. Pulse tightening control is a control that generates torque intermittently (e.g., periodically) in pulses from the start of the action, such that the peak value of each pulse gradually increases from the start of the action to reach the target torque. Furthermore, in this specification, when referred to as pulse tightening control, it includes all control methods that can reduce the tightening torque reaction force compared to ordinary tightening control by generating torque in pulses or instantaneously (one pulse).

[0046] exist Figure 4 In the diagram 63, the dashed curve represents the tightening torque reaction force applied to the robot 10 when the thread fastener 20 is directly installed in the robot 10 without using the electric motor 41, and the thread fastener 20 is used for normal tightening control. In this case, a tightening torque reaction force of 55 Nm is generated. Figure 4 In the figure, the dashed line curve 62 represents the tightening torque reaction force applied to the robot when the thread fastener 20 is directly installed in the structure of the robot 10 without using the electric motor 41, and the thread fastener 20 is subjected to pulse tightening control. In this case, the magnitude of the tightening torque reaction force is 43 Nm.

[0047] exist Figure 4 In the diagram 61, the solid line represents the tightening torque reaction force applied to the robot in the structure of this embodiment (i.e., the structure using the electric motor 41) when the thread fastener is pulse-tightened. In this case, by setting the torque limit of the electric motor 41 to an appropriate value, the magnitude of the tightening torque reaction force applied to the robot is 8 Nm. Furthermore, Figure 4 The graphs use negative values ​​to represent the polarity of the clamping torque reaction force. In this embodiment, it can be understood that by applying a torque limit to the electric motor 41, the clamping torque reaction force applied to the robot 10 (curve 61) can be significantly reduced compared to the cases of curves 62 and 63.

[0048] The torque limit is set to a value that limits the maximum current of the electric motor 41. When measuring the tightening torque reaction force, the measurement can be performed by placing a force sensor between the robot 10 and the thread tightening reaction force reduction device (holding member 40, electric motor 41, support member 30, and thread tightening machine 20).

[0049] The robot control unit 50 (motor control unit 502) may also store a numerical table in its memory (non-volatile memory) 52 that establishes a correspondence between torque limits and clamping torque reaction forces (measured values). Furthermore, it may be configured to display such a numerical table on a display device (e.g., the display panel of the robot control unit 50, or the display section of a teach pendant connected to the robot control unit 50) to allow the user to select the torque limits. In this case, the robot control unit 50 may also highlight a recommended value for the torque limits, prompting the user to select from the recommended value. Additionally, the recommended value for the torque limits may be, for example, a value where the clamping torque reaction force is sufficiently lower than the allowable torque of the holding device.

[0050] Figure 5 and Figure 6This is a diagram showing a variation related to the retaining component 40 and the electric motor 41. For example... Figure 5 and Figure 6 As shown, a gear mechanism can also be added to the electric motor 41. Figure 5 In the structure shown, the retaining member 40A that holds the electric motor 41 has a retaining frame 42A. A gear mechanism consisting of spur gears 141 and 142 is arranged inside the retaining frame 42A. Figure 5 The side view shown has a rectangular frame shape, whose internal space houses spur gears 141 and 142. Figure 5 For ease of explanation, only the wrist flange 11 is shown in the diagram concerning the mechanism on the side of robot 10. Figure 5 In the mechanism, the output-side spur gear 142 of the spur gears 141 and 142 constituting the gear mechanism is arranged such that the axis of the spur gear 142 is aligned with the center line C1 of the wrist flange 11 of the robot 10. The electric motor 41 is mounted on the upper surface of the upper wall of the retaining frame 42A with its drive shaft 41a facing downwards and its central axis C2 parallel to the center line C1. Figure 5 In this structure, the electric motor 41 can be positioned on the outside of the retaining frame 42A, making the retaining frame 42A thinner.

[0051] exist Figure 6 In the structure shown, the retaining member 40B that holds the electric motor 41 has a retaining frame 42B. A gear mechanism consisting of bevel gears 242 and 242 is arranged inside the retaining frame 42B. Figure 6 The side view shown has a rectangular frame shape, whose internal space houses bevel gears 242 and 242. Figure 6 For ease of explanation, only the wrist flange 11 is shown in the diagram concerning the mechanism on the side of robot 10. Figure 6 In the mechanism, the output bevel gear 242 of the bevel gears 241 and 242 constituting the gear mechanism is arranged such that the axis of the output bevel gear 242 is aligned with the center line C1 of the wrist flange 11 of the robot 10. The electric motor 41 is mounted on the outer side of the side wall of the retaining frame 42B with the central axis C2 of the drive shaft 41a perpendicular to the center line C1.

[0052] according to Figure 5 , Figure 6 The structure allows for adjustment of the effective value (external force) of the clamping torque reaction force returned to the electric motor 41 according to the gear ratio.

[0053] As described above, if the reaction force of the tightening torque generated by the thread tightening action exceeds the torque limit of the electric motor 41, then the electric motor 41 (thread tightening machine 20) will rotate in the direction of the reaction force of the tightening torque during or at the end of the thread tightening action. Figure 7 The upper section indicates that the thread-fastening machine 20 is rotated by an angle θ in the direction of the tightening torque reaction force, moving it to position P1, due to the tightening torque reaction force accompanying the thread-fastening action. Additionally, Figure 7 The images in the upper and lower sections are views of robot 10 from above.

[0054] like Figure 3 As shown, the robot control device 50 may also include a rotational position recovery unit 504. The rotational position recovery unit 504 obtains the rotational position of the thread-fastening machine 20, which rotates together with the support member 30 during the thread-fastening action, from the encoder output of the electric motor 41, and rotates the electric motor 41 to return the thread-fastening machine 20 (support member 30) to its initial position or a preset position. Figure 7 The lower section shows the state in which the rotational position recovery unit 504 returns the position of the threaded fastener 20, which has been rotated by an angle θ, to the initial position P0.

[0055] As explained above, according to this embodiment, high-torque thread fastening can be performed without using a high-rigidity retaining device, which can achieve advantages such as reducing equipment costs and eliminating limitations on installation location.

[0056] The present invention has been described above using typical embodiments. However, those skilled in the art will understand that changes, omissions, and additions can be made to the embodiments without departing from the scope of the present invention.

[0057] In the described embodiment, an example of using an industrial robot as a holding device for holding an electric motor is presented. However, various industrial machines with movable parts can be used as holding devices for holding electric motors. Figure 8 This describes a structural example of a threaded fastening system 100A, which includes a lifting mechanism 111 that moves the spindle head (equipped with a holding member 40, which holds the electric motor 41) up and down, and a holding device 121 that moves it horizontally. Additionally, in Figure 8 In the middle, to and Figure 1 Structural components with the same structure are labeled with the same reference numerals and descriptions are omitted.

[0058] Figure 8The holding device 110 shown can move along the track 112 in the vertical direction (arrow A1 direction) of the lifting mechanism 111, and in the horizontal moving mechanism 121, the lifting mechanism 111 can move along the track 122 in the horizontal direction (arrow A2 direction). The control device 150 has a... Figure 2 as well as Figure 3 The robot control device 50 shown has the same functional structure as the control device 110, the electric motor 41, and the thread fastening machine 20. In this case, the control device 150 can also be constructed, for example, by a PLC (Programmable Logic Controller).

[0059] The shape of the support member 30 in the described embodiment is an example, and the support member for supporting the threaded fastener 20 may also have other shapes. Figure 10 The structure of the thread-fastening system 100B is shown when the support member 30B is used as the support member for the thread-fastening machine 20. Additionally, in Figure 10 In the middle, to and Figure 1 Components showing the same elements are labeled with the same reference numerals and their descriptions are omitted. Support member 30B includes: a main support plate 31B, which is fixed at one end to the drive shaft of the electric motor 41 and... Figure 10 The configuration extends horizontally in the desired state; and fixed frames 32B and 33B are respectively connected to the central portion and the other end of the main support plate 31B. Fixed frames 32B and 33B fix the threaded fastener 20. In this structure, it is also possible to achieve... Figure 1 The implementation shown has the same functionality.

[0060] In the described embodiment, a structural example is presented where an angled thread fastener 20 is used as the thread fastener, but a straight thread fastener can also be used as the thread fastener. Figure 11 This illustrates a structural example of a thread-fastening system 100C using a straight-type thread-fastening machine 20C. Additionally, in... Figure 11 In the middle, to and Figure 1 Components showing the same elements are labeled with the same reference numerals and their descriptions are omitted. The thread-fastening machine 20C has a main body 22C having an actuation drive source for a head 21C that connects to and holds a tool 23, the axis of which is aligned with the axis of the tool 23 in the head 21C. The thread-fastening machine 20C is supported by a support member 30C. The support member 30C is in... Figure 11The side view (sectional view) shown has a rectangular frame shape, within which the thread fastener 20C is held. Specifically, the thread fastener 20C is fixed with its front end protrusion of head 21C embedded in a through hole 33C formed in the lower side wall 32C of support member 30C. The upper side wall 31C of support member 30C is fixed to the drive shaft of electric motor 41. Furthermore, the thread fastener 20C has the same function as the thread fastener 20 (pulse tightening control, etc.). According to this structure, the same function as when using thread fastener 20 is achieved (i.e., the function of avoiding a large reaction force on robot 10 during thread tightening action based on pulse tightening control). Moreover, when using a straight thread fastener 20C, the rotation of the thread fastener 20C does not need to be considered, thus the function of the rotation position recovery unit 504 in the above embodiment can be omitted.

[0061] In the described embodiment, an electric motor 41 is fixed to the wrist flange 11 of the robot 10 via a retaining member 40. However, various configurations can be used as the configuration for fixing the electric motor 41 to the wrist flange 11.

[0062] The thread-fastening action described in this embodiment can be performed on various workpieces, such as workpieces fixed to a fixture, workpieces flowing in a conveyor, or workpieces held by a robot (a robot different from robot 10), as well as various workpiece supply methods.

[0063] Figure 3 The functional blocks of the robot control device 50 shown can be implemented either by the processor 51 of the robot control device 50 executing various software stored in the storage device, or by a structure based on hardware such as ASIC (Application Specific Integrated Circuit).

[0064] Explanation of reference numerals in the attached figures

[0065] 10 robots;

[0066] 20, 20C thread fastening machine;

[0067] Support components for 30, 30B, and 30C;

[0068] 40, 40A, 40B retaining components;

[0069] 41 electric motors;

[0070] 41a drive shaft;

[0071] 42. Maintain the frame;

[0072] 50 robot control devices;

[0073] 51 processor;

[0074] 52 memory;

[0075] 53 Input / Output Interfaces;

[0076] 54 Operations Department;

[0077] 100, 100A, 100B, 100C threaded fastening systems;

[0078] 150 control device;

[0079] 201 Control Department;

[0080] 202 motor;

[0081] 501 Motion Control Unit;

[0082] 502 Motor Control Unit;

[0083] 503 Torque Limit Setting Unit;

[0084] 504 Rotational Position Restoration Section.

Claims

1. A threaded fastening system characterized by comprising: an electric motor; a holding device that holds the electric motor; a support member that is attached to a drive shaft of the electric motor; a threaded fastening machine that is supported by the support member and is capable of performing a threaded fastening operation of pulse fastening control; and a motor control section that controls the electric motor so as to reduce a fastening torque reaction force on the holding device that is generated by the threaded fastening operation of pulse fastening control performed by the threaded fastening machine.

2. The threaded fastening system according to claim 1, characterized in that: the motor control section comprises a torque limit setting section that sets a torque limit of the electric motor, in a case where a load torque generated by the fastening torque reaction force exceeds the torque limit set by the torque limit setting section, the drive shaft is rotated in a direction in which the fastening torque reaction force is applied, so as to reduce the fastening torque reaction force on the holding device.

3. The threaded fastening system according to claim 2, characterized in that: the torque limit setting section accepts numerical input of the torque limit based on user operation.

4. The threaded fastening system according to claim 2, characterized in that: the torque limit setting section accepts user operation of selecting the torque limit from a table of numerical values that represent recommended values of the torque limit.

5. The threaded fastening system according to any one of claims 1 to 4, characterized by further comprising a rotational position recovery section that acquires a rotational position of the threaded fastening machine that rotates together with the support member along with the threaded fastening operation from an encoder output of the electric motor, and rotates the electric motor so as to return the support member and the threaded fastening machine to an initial position or a position set in advance.

6. The threaded fastening system according to any one of claims 1 to 4, characterized in that: the holding device is a robot, the threaded fastening machine is attached to a wrist portion of the robot via the electric motor and the support member, the threaded fastening system further comprises a robot control device that controls a position and a posture of the wrist portion of the robot.

7. The threaded fastening system according to claim 6, characterized in that: the robot control device controls the position and the posture of the wrist portion so that a threaded feeding direction of the threaded fastening machine becomes a desired direction. ​ ​

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