Screw Fastening System

Abstract

To precisely control thrust generated by a screw fastening device and perform pushing against a screw using minimal thrust not causing come-out.SOLUTION: A screw fastening system 1 includes: a drive board which is driven so as to move linearly along a driving shaft; and a screw fastening device which is coupled to the drive board via a coupling device 40 and moves along a screw fastening shaft parallel to the driving shaft. The coupling device 40 includes: a first block 41 provided fixed to the drive board; a second block 42 provided fixed to the screw fastening device; a linear guide 50 for supporting the second block so that it is movable relative to the drive board along the screw fastening shaft only; and a load detector 43 which is provided between the first block and the second block in order to detect a load acting along the screw fastening shaft therebetween.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a screw tightening system for tightening or loosening screws, bolts, self-tapping screws, nuts, and the like. [Background technology]

[0002] Screw tightening devices, sometimes called "nut runners," have been used to tighten screws on workpieces in factory production lines. To reduce labor on production lines, industrial robots such as Cartesian robots or SCARA robots are often used. The industrial robot moves a screw tightening device to the position of the workpiece and causes the screw tightening device to tighten or loosen the screw.

[0003] In the assembly process of electronic devices, cross-recessed screws (cross-recessed bolts) are often used to secure printed circuit boards and other components to frames and housings. When tightening cross-recessed screws, a certain amount of thrust must be applied to prevent cam-out during tightening. However, if the thrust is too great, the printed circuit board or frame may bend, resulting in poor tightening or even damage. Furthermore, if an excessive amount of thrust is applied between the time the screw contacts the workpiece, such as the printed circuit board, and the screw head seats, there is a risk of damage to the threads of the machine screw.

[0004] Therefore, from the time the screw comes into contact with the workpiece until the screw head is seated, it is necessary to apply the lowest possible thrust to the screw fastening device, and after the tightening torque has been generated, apply the minimum thrust within the range that does not cause cam-out, and press the screw using the screw fastening device.

[0005] For this reason, as shown in Patent Document 1, it has been proposed to provide a torque sensor between a ball screw for applying thrust (pressing force) to the screw fastening device and a motor that rotates the ball screw, and to correct the thrust based on the torque detected by the torque sensor, thereby preventing the occurrence of cam-out. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 1994-304827 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the above-mentioned Patent Document 1, the output of the torque sensor includes not only the frictional force and inertial force associated with the lifting and lowering movement of the screw fastening device, but also the frictional force associated with the rotation of the ball screw and power transmission, which poses a problem that the actual thrust force of the screw fastening device cannot be accurately detected.

[0008] Therefore, it is not possible to precisely control the thrust force of the screw tightening device, and it is difficult to control the thrust force to the minimum required to prevent cam-out and damage to the screw threads.

[0009] Furthermore, even if the load is determined from the motor current value and controlled, it is difficult to precisely control the thrust force of the screw tightening device, and similar problems arise.

[0010] The present invention has been made in consideration of the above-mentioned problems, and aims to enable precise control of the thrust force of a screw tightening device, making it possible to press against a screw with the minimum thrust force that does not cause cam-out. [Means for solving the problem]

[0011] The device of the present invention is a screw fastening system having a drive board that is driven to move linearly along a drive axis, and a screw fastening device that is connected to the drive board via a connecting device and moves along a screw fastening axis parallel to the drive axis, wherein the connecting device comprises a first block fixedly provided on the drive board, a second block fixedly provided on the screw fastening device, a linear guide that supports the second block so that it can move only along the screw fastening axis relative to the drive board, and a load detector that is provided between the first block and the second block and detects the load acting along the screw fastening axis between them.

[0012] Preferably, the load detector is attached to the second block with a clearance therebetween.

[0013] Preferably, a forward stopper is provided between the first block and the second block to limit the relative distance between the first block and the second block so that the load applied to the load detector when tightening a screw with the screw tightening device does not exceed its allowable value.

[0014] Preferably, the load detector is a beam-type load cell, and the beam-type load cell is arranged on a plane perpendicular to the screw-tightening axis between the opposing surfaces of the first block and the second block, with one end fixed to the surface of the first block via a first base and the other end attached to the surface of the second block via a second base.

[0015] Preferably, the forward movement stopper is formed by a bridge block fixed to the surface of the first block abutting against the surface of the other end of the beam-type load cell.

[0016] Preferably, a backward stopper is provided between the first block and the second block to limit the relative distance between the first block and the second block so that the load applied to the load detector when loosening a screw with the screw tightening device does not exceed its allowable value.

[0017] Preferably, the linear guide has a guide member attached to the drive board and a guide shaft portion attached to the second block and sliding through a guide hole provided in the guide member, and the reverse stopper is formed by a set collar attached to the guide shaft portion abutting against the end face of the guide member.

[0018] Preferably, The aforementioned The device has a control device for controlling the motor that drives the drive substrate, and the control device has a thrust control unit that controls the thrust when the screw fastening device fastens a screw based on the load detected by the load detector.

[0019] Preferably, the control device Load detector The motor has a stop control unit that controls the motor to stop when the load detected by the load detection unit exceeds an allowable set value.

[0020] Preferably, the drive substrate is attached to the distal arm of a scalar robot. [Effects of the Invention]

[0021] According to the present invention, the thrust force of the screw tightening device can be precisely controlled, and it is possible to press the screw with the minimum thrust force that does not cause cam-out. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a front view of a screw tightening system according to an embodiment of the present invention. [Figure 2]2 is a diagram showing a screw fastening device and a connecting device of the screw fastening system of FIG. 1 as viewed from the left side. [Figure 3] 2 is a cross-sectional view of the screw fastening system taken along line AA-AA in FIG. 1. [Figure 4] 3 is a cross-sectional view of the screw fastening system taken along line BB-BB in FIG. 2. [Figure 5] FIG. 3 is a cross-sectional view of the coupling device in FIG. 2. [Figure 6] FIG. 1 is a perspective view for explaining the operating principle of a beam-type load cell. [Figure 7] FIG. 10 is a front view of a screw tightening system according to another embodiment of the present invention. [Figure 8] FIG. 2 is a block diagram of a control device that controls the screw tightening system. DETAILED DESCRIPTION OF THE INVENTION

[0023] FIG. 1 is a front view of a screw fastening system 1 according to an embodiment of the present invention, FIG. 2 is a view showing a screw fastening device 20 and a connecting device 40 as seen from the left side of the screw fastening system 1 of FIG. 1, FIG. 3 is a cross-sectional view of the screw fastening system 1 taken along line AA-AA in FIG. 1, and FIG. 4 is a cross-sectional view of the screw fastening system 1 taken along line BB-BB in FIG. 2.

[0024] 1 to 3, a screw fastening system 1 includes a lifting drive device 10, a screw fastening device 20, and a connecting device 40.

[0025] The lifting drive device 10 includes a frame 11, a motor 12 attached to the upper end of the frame 11 so as to rotate forward and backward and whose rotational speed is controlled, a ball screw shaft 13 attached between an upper plate 11a and a lower plate 11b of the frame 11 and driven to rotate by the motor 12, a ball nut box 14 that is threadedly engaged with the ball screw shaft 13 and driven to move linearly along the drive shaft 5 by the rotation of the ball screw shaft 13, and a drive base plate 15 that is fixed to the ball nut box 14 with a bolt 16 and moves integrally therewith.

[0026] The screw tightening device 20 is connected to the drive board 15 via a connecting device 40, and moves up and down along a screw tightening shaft 6 that is parallel to the drive shaft 5. The screw tightening device 20 is, for example, an electric servo nut runner that can control the torque angle by control, and has the function of performing high-speed rotation control, determining whether the bolt is seated by detecting the torque, and switching to a low speed to tighten up to the target torque while detecting the torque.

[0027] That is, the screw fastening device 20 has a motor 21 that rotates forward and backward and whose rotational speed is controlled, a reduction gear 22, a torque sensor 23, an output shaft 24, a bit 25, etc. The bit 25 rotates as the motor 21 is driven to rotate, and the screw or nut engaged with the bit 25 rotates, thereby performing fastening or loosening. The rotational torque applied to the bit 25 is detected by the torque sensor 23. The reduction gear 22 may include an impact generating device, in which case the screw fastening device 20 can operate as an impact-type screw fastening device.

[0028] In addition, a plate 42 corresponding to the second block of the present invention is fixed to the screw fastening device 20 by a screw or the like on the side of the output shaft 24 of the torque sensor 23, that is, on the load side.

[0029] 4 and 5, the connecting device 40 includes a first block 41 fixedly attached to the drive substrate 15, the aforementioned plate 42 fixedly attached to the screw fastening device 20, a linear guide 50 that supports the plate 42 so that it can move only along the screw fastening shaft 6 relative to the drive substrate 15, and a load detector 43 that is provided between the first block 41 and the plate 42 and detects the load acting along the screw fastening shaft 6 between them.

[0030] A forward stopper 48A is provided between the first block 41 and the plate 42 to limit the relative distance between the first block and the plate 42 so that the load applied to the load detector 43 when tightening a screw with the screw tightening device 20 does not exceed its allowable value.

[0031] The load detector 43 is a beam-type load cell, which is arranged on a plane perpendicular to the screw-tightening axis 6 between the opposing surfaces of the first block 41 and the plate 42, with one end fixed to the surface of the first block 41 via a first base 44 by a bolt 45, and the other end attached to the surface of the plate 42 via a second base 46 by a bolt 47 and a washer member 47 with a play clearance 9.

[0032] That is, the second pedestal 46 is cylindrical with a step on its outer circumferential surface, and a play clearance 9 is provided in the diameter direction between the outer circumferential surface of the second pedestal 46 and the inner circumferential surface of the hole in the plate 42, and in the axial direction between the step portion of the second pedestal 46 and the front surface of the plate 42, so that no force acts on the load detector 43 except in directions along the guide axes 7a and 7b that are parallel to the screw tightening axis 6. The plate 42 is provided with a hole 42a for attaching and detaching the bolt 45.

[0033] The linear guide 50 consists of two linear guides 50a and 50b, each with the same structure, one on the left and one on the right. Each linear guide 50a, 50b has a guide member 51 attached to the drive board 15 with a bolt 54 and a positioning pin 55, a bushing member 52 fitted into the inner peripheral surface of the guide member 51, and a guide shaft portion 61 attached to the plate 42 and sliding through a guide hole 52a provided in the guide member 51. The guide hole 52a is actually the inner peripheral surface of the bushing member 52. A set collar 63 is attached to the end of the guide shaft portion 61 by tightening it with a bolt.

[0034] In this embodiment, the set collar 63 has an annular shape, is cut off at one point on the circumference, and is fastened by tightening a bolt to the cutoff portion, thereby tightly gripping and fixing the inner peripheral surface of the guide shaft portion 61. However, various other configurations can be used. For example, a set screw may be provided in the radial direction of the annular collar and pressed against the outer peripheral surface of the guide shaft portion 61, or a step may be formed integrally with the end of the guide shaft portion 61 and used as a stopper. Various other configurations are possible as long as they function as a stopper.

[0035] The linear guide 50 is capable of moving the guide member 51 and the guide shaft portion 61 relatively along the guide shafts 7a and 7b within the range in which the load detector 43 deflects when a load is applied to it. This allows the load detector 43 to accurately detect the thrust force when the screw fastening device 20 is fastening a screw, and to maintain high accuracy over a long period of time without being subjected to lateral loads, torsional loads, etc.

[0036] Furthermore, a forward stopper 48A and a backward stopper 63A are provided so that an excessive load is not applied to the load detector 43 in the direction along the guide shafts 7a and 7b.

[0037] The forward stopper 48A is formed when the bridge block 48, fixed to the surface of the first block 41 by bolts 49, abuts against the other end of the beam load cell (43), i.e., the surface on the side of the second pedestal 46. A clearance 8a is provided between the bridge block 48 and the beam load cell (43) in a free state, i.e., when no load is applied, and when the beam load cell (43) is within the allowable load range or at the maximum load detection value, the clearance 8a becomes zero, causing the bridge block 48 to abut and stop in this state.

[0038] The backward movement stopper 63A is formed when, when the first block 41 and the plate 42 move relatively apart, the guide member 51 and the guide shaft portion 61 move relatively, and the set collar 63 attached to the guide shaft portion 61 abuts against the end face of the guide member 51. A clearance 8b is provided between the set collar 63 and the end face of the guide member 51 in the free state, and when the beam-type load cell (43) is within the allowable load range in the negative direction (reverse direction) or at the maximum load detection value, the clearance 8b becomes zero, causing the set collar 63 to abut against the end face and stop in this state.

[0039] The size of the clearances 8a and 8b in the free state is, for example, about 0.4 mm to 1 mm, and may be designed to be a fixed value depending on the specifications of the beam-type load cell (43), or may be adjustable on site.

[0040] As shown in FIG. 5, the beam-type load cell (43) is provided with a detection portion 43a to which a strain gauge is attached and from which lead wires are drawn, and a hole 43b for adjusting the detection load.

[0041] FIG. 6 shows a perspective view for explaining the operating principle of a beam-type load cell.

[0042] 6, beam-type load cell 80 is, for example, a rod with a rectangular cross section, and has a plurality of strain gauges 81 attached to its front and back surfaces, connected in a bridge configuration, for example. When one end of the load cell is fixed to base 82 with bolts 83 and a load F is applied to the other end, beam-type load cell 80 bends within its elastic range, strain gauge 81 changes according to the amount of bending, and a signal corresponding to the load F is output from the lead wire.

[0043] In the screw fastening system 1 described above, the screw fastening device 20 is supported by the lifting drive device 10 that simply drives it up and down, but it may also be supported by a robot or manipulator that performs various other operations. Examples are shown below.

[0044] FIG. 7 shows a screw tightening system 1B according to another embodiment of the present invention.

[0045] In FIG. 7, a screw fastening system 1B includes a scalar robot 10B, a screw fastening device 20, and a connecting device .

[0046] The scalar robot 10B is a robot that can drive the screw fastening device 20 attached to its tip to move parallel to the X, Y, and Z axes. In other words, the screw fastening device 20 can be moved to any position within a predetermined space by the scalar robot 10B, and can fasten or loosen a bit according to the screw that is the workpiece.

[0047] As shown in Figure 7, the scalar robot 10B has a base fixed to a base not shown, a first arm 11Ba that can be rotated about a first axis relative to the base, a second arm 11Bb that is supported by the first arm 11Ba and can be rotated about a second axis 4, an elevator shaft 14B that is supported by the second arm 11Bb and driven up and down along a drive shaft 5 by a motor 12B, and a drive board 15B attached to the lower end of the elevator shaft 14B.

[0048] The screw fastening device 20 is connected to the drive board 15B via a connecting device 40, and is moved up and down along the screw fastening shaft 6 parallel to the drive shaft 5 in the same manner as described above.

[0049] FIG. 8 shows a block diagram of a control device 100 that controls the screw tightening systems 1 and 1B.

[0050] In FIG. 8, a control device 100 includes a screw tightening control unit 101, a thrust force control unit 102, a stop control unit 103, a robot control unit 104, and the like.

[0051] The screw fastening control unit 101 controls the motor 21 of the screw fastening device 20. For example, based on an input signal from a torque sensor 23 or the like, the motor 21 of the screw fastening device 20 is controlled so that the bit rotates at a predetermined rotation speed.

[0052] The thrust control unit 102 controls the thrust when the screw is tightened by the screw tightening device 20, based on the load detected by the load detector 43. At this time, for example, control is performed so that the thrust is as low as possible from the time the screw contacts the workpiece until the screw head is seated, and so that the thrust is the minimum within a range that does not cause cam-out after tightening torque is generated.

[0053] The stop control unit 103 controls the motors 12 and 21 to stop when the load detected by the load detector 43 exceeds a set allowable value. At this time, the stop control unit 103 may control the entire scalar robot 10B to stop. By appropriately performing the control operation of the stop control unit 103, it is possible to prevent the forward stopper 48A and the backward stopper 63A from actually coming into contact with each other and operating.

[0054] The robot control unit 104 controls the scalar robot 10B and the lifting drive device 10 as a whole.

[0055] The control device 100 can be realized using various hardware and software such as electrical components, electronic devices, electronic circuits, integrated devices, and computers.

[0056] As described above, in the screw fastening systems 1 and 1B, the screw fastening device 20 is supported by the nearest connecting device 40, and the thrust applied to the screw fastening device 20 is detected by the load detector 43 provided on the connecting device 40, so the thrust can be detected with high accuracy and the thrust by the screw fastening device 20 can be precisely controlled. This makes it possible to press against the screw with the minimum thrust that does not cause cam-out, which can contribute to improving production efficiency.

[0057] Furthermore, since one end of the load detector 43 is supported with a play clearance 9 relative to the plate 42, no unnecessary forces act in directions other than those of the guide shafts 7a and 7b, allowing for accurate detection of thrust and preventing damage and deterioration.

[0058] Furthermore, since forward stopper 48A and backward stopper 63A are provided in the direction of guide shafts 7a and 7b, excessive load exceeding the allowable load is not applied to load detector 43, and damage and deterioration of load detector 43 are prevented.

[0059] Further, the forward stopper 48A and the backward stopper 63A have a simple structure yet operate reliably.

[0060] Furthermore, when controlling the thrust, by taking into consideration the load applied to the load detector 43, such as the screw tightening device 20, in relation to the load detected by the load detector 43, it is possible to accurately control subtle thrust.

[0061] Furthermore, by constantly monitoring the load detected by the load detector 43, if the thrust falls below the command value when the screw is fed at high speed, the pressing speed is increased to improve the robot's tracking ability, and if the thrust rises above the command value, the pressing speed is decreased to return to the command value.By performing feedback control, it is possible to press the screw with a minimum amount of thrust and yet be able to adequately track even when the screw is fed at high speed.

[0062] In the embodiment described above, an example in which the screw tightening device 20 is attached to the scalar robot 10 has been shown, but it can also be attached to and used with robots that perform various other operations.

[0063] In the above-described embodiment, the structure, shape, dimensions, material, number, connection method, etc. of each part or the entire structure of the lifting drive device 10, the screw tightening device 20, the connecting device 40, the linear guide 50, the screw tightening system 1, 1B, etc. can be changed as appropriate in accordance with the spirit of the present invention. [Explanation of symbols]

[0064] 1,1B screw tightening system 5 drive shaft 6 Screw-tightening shaft 7a, 7b Guide shaft 8a, 8b clearance 9 Play Clearance 10 Lifting drive device 10B Scalar Robot 11Bb Second arm (tip arm) 12, 12B motor 15 Drive board 20 Screw tightening device 40 Coupling device 41 First Block 42 Plate (Second Block) 43 Load detector 44 First pedestal 46 Second pedestal 48 Piece Block 48A Forward stopper 50 Linear guide 51 Guide member 52A guide hole 61 Guide shaft 63 Set Color 63A Reverse stopper 100 control device 102 Thrust control unit 103 Stop control unit

Claims

1. A screw fastening system including a drive board that is driven to move linearly along a drive axis, and a screw fastening device that is connected to the drive board via a coupling device and moves along a screw fastening axis that is parallel to the drive axis, The coupling device is a first block fixedly provided on the drive substrate; a second block fixedly provided to the screw fastening device; a linear guide that supports the second block so that the second block can move only along the screw fastening shaft relative to the drive board; a load detector that is provided between the first block and the second block and detects a load acting along the screw fastening shaft between them, an advance stopper is provided between the first block and the second block to limit the relative distance between the first block and the second block so that the load applied to the load detector when the screw is fastened by the screw fastening device does not exceed its allowable value; the load detector is a beam-type load cell, the beam-type load cell is disposed on a plane perpendicular to the screw fastening axis between the opposing surfaces of the first block and the second block, one end of the beam-type load cell being fixed to the surface of the first block via a first pedestal, and the other end of the beam-type load cell being attached to the surface of the second block via a second pedestal; the forward movement stopper is formed by a bridge block fixed to the surface of the first block abutting against the surface of the other end of the beam-type load cell. A screw tightening system characterized by:

2. A screw fastening system including a drive board that is driven to move linearly along a drive axis, and a screw fastening device that is connected to the drive board via a coupling device and moves along a screw fastening axis that is parallel to the drive axis, The coupling device is a first block fixedly provided on the drive substrate; a second block fixedly provided to the screw fastening device; a linear guide that supports the second block so that the second block can move only along the screw fastening shaft relative to the drive board; a load detector that is provided between the first block and the second block and detects a load acting along the screw fastening shaft between them, a backward movement stopper is provided between the first block and the second block to limit the relative distance between the first block and the second block so that the load applied to the load detector does not exceed its allowable value when the screw is loosened by the screw fastening device; The linear guide is a guide member attached to the drive substrate; a guide shaft portion attached to the second block and sliding through a guide hole provided in the guide member, The reverse stopper is formed by a set collar attached to the guide shaft portion abutting against an end surface of the guide member. A screw tightening system characterized by:

3. The load detector is attached to the second block with a clearance therebetween. The screw tightening system according to claim 1 or 2.

4. Between the first block and the second block, there is provided an advance stopper that limits the relative distance between the first block and the second block so that the load applied to the load detector when the screw is fastened by the screw fastening device does not exceed its allowable value. The screw tightening system according to claim 2 .

5. the load detector is a beam-type load cell, the beam-type load cell is disposed on a plane perpendicular to the screw fastening axis between the opposing surfaces of the first block and the second block, one end of which is fixed to the surface of the first block via a first pedestal, and the other end of which is attached to the surface of the second block via a second pedestal; The screw tightening system according to claim 4.

6. a backward movement stopper is provided between the first block and the second block to limit the relative distance between the first block and the second block so that the load applied to the load detector does not exceed its allowable value when the screw is loosened by the screw fastening device; The screw tightening system according to claim 1 .

7. The linear guide is a guide member attached to the drive substrate; a guide shaft portion attached to the second block and sliding through a guide hole provided in the guide member, The reverse stopper is formed by a set collar attached to the guide shaft portion abutting against an end surface of the guide member. The screw tightening system according to claim 6.

8. A control device for controlling a motor that drives the drive substrate, The control device a thrust control unit that controls the thrust when the screw fastening device fastens a screw based on the load detected by the load detector; The screw tightening system according to claim 1 or 2.

9. The control device a stop control unit that controls the motor to stop when the load detected by the load detector exceeds an allowable set value; The screw tightening system according to claim 8.

10. The drive substrate is attached to the distal arm of a scalar robot. The screw tightening system according to claim 1 or 2.

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