Screw fastening machine

Abstract

To provide a screw fastening machine which can easily change pressing force applied to a fastening tool.SOLUTION: A screw fastening machine includes: a motor 32; a fastening tool 35 which receives driving of the motor 32 to drive rotationally and in which a screw may be engaged with its tip; and an air cushion mechanism which is fitted in a rear end of the fastening tool 35 and holds the fastening tool 35 in a cushioning manner. Further, the air cushion mechanism has a shaft joint 33 which connects a drive shaft of the motor 32 with the fastening tool 35. The shaft joint 33 is provided with a fitting hole 332 which connects a rear end of the fastening tool 35 in a state where the rear end may move in an axial direction. Vent holes are provided on a side wall of the fitting hole 332. Pressurized air is supplied to the inside of the fitting hole 332 through the vent holes and the inside of the fitting hole 332 is brought into a pressurized state to bias the fastening tool 35.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a screw fastener for fastening a screw into a workpiece. [Background technology]

[0002] Conventionally, as shown in Patent Document 1, there is known a screw fastening machine in which an elevation drive source elevates a screw fastening unit equipped with a driver bit and a motor. Such a screw fastening machine is provided with a compression spring that constantly urges the driver bit in a direction away from the motor, and the driver bit moves axially relative to the motor when the compression spring flexes. Therefore, when a screw fitted to the driver bit comes into contact with a workpiece, the compression spring flexes, and the shock caused by the contact is absorbed by the compression spring, which has the advantage of preventing damage to the workpiece and the screw. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-315071 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional screw fasteners were designed so that the compression spring biased the driver bit toward the workpiece, and so when changing the pressing force of the driver bit, it was necessary to disassemble the screw fastener and replace the compression spring.

[0005] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a screw fastener that allows the pressing force of a driver bit to be easily changed. [Means for solving the problem]

[0006] The present invention was created in consideration of the above problems, and is characterized by having a motor, a fastening tool that is rotationally driven by the motor and can engage a screw at its tip, and an air cushion mechanism that fits into the rear end of the fastening tool and cushions the fastening tool. In addition, it is preferable that the air cushion mechanism has a shaft coupling which connects the drive shaft of the motor and the fastening tool, and this shaft coupling is formed with a fitting hole which connects the rear end of the fastening tool in a state where it can move axially, and a vent hole is provided in a side wall of this fitting hole, and pressurized air is supplied into the fitting hole through this vent hole, thereby pressurizing the inside of the fitting hole and biasing the fastening tool. In addition, it is preferable that the air cushion mechanism is configured so that the amount of pressurized air that can be supplied varies depending on the relative position of the fastening tool with respect to the shaft coupling, and that the air cushion mechanism has a measuring means for measuring the amount of pressurized air supplied to the air cushion mechanism. In addition, the shaft coupling has an insertion hole that is continuous with the tip side of the fitting hole and covers the fastening tool so that it can move relatively in the axial direction, and the insertion hole has a leakage hole that can exhaust pressurized air supplied inside to the outside, and it is preferable that the leakage hole is provided within the movement range of the fastening tool that moves relatively inside the shaft coupling. It is also preferable that the device has a screw tightening unit equipped with the air cushion mechanism, a position control unit which moves the screw tightening unit, and a control unit capable of controlling the driving of the screw tightening unit and the position control unit, and that the control unit is configured to be able to detect the position of the fastening tool relative to the shaft coupling from the amount of pressurized air supplied to the air cushion mechanism measured by the measuring means. Effect of the Invention

[0007] According to the screw fastener of the present invention, the fastening tool is held in a cushioned manner by an air cushion mechanism and is biased by pressurized air, which has the advantage that the pressure acting on the fastening tool can be easily changed by changing the air pressure of the pressurized air without disassembling the screw fastener. In addition, since the amount of pressurized air that can be supplied to the air cushion mechanism varies depending on the position of the fastening tool relative to the shaft coupling, and a measuring means is provided for measuring the amount of pressurized air supplied to the air cushion mechanism, it is possible to detect the movement of the fastening tool relative to the shaft coupling 33. This has the advantage that it is possible to detect when the screw comes into contact with the workpiece, thereby enabling screw tightening to be performed without applying a load to the workpiece. In addition, since the control unit can control the position control unit based on the position of the fastening tool relative to the motor transmitted from the measuring means, there is also the advantage that screw tightening can be performed with less load placed on the workpiece. [Brief description of the drawings]

[0008] [Figure 1] 1 is a partially sectional side view showing the structure of a screw fastener according to the present invention. [Diagram 2] 1 is an enlarged, partially cutaway, sectional side view showing the structure of a main part of a screw fastener according to the present invention. [Diagram 3] FIG. 3 is an enlarged view of part A in FIG. 2. [Figure 4] 4 is an enlarged view of part A in FIG. 2, showing a state transitioned from FIG. 3 to the next state. [Diagram 5] 3 is an enlarged view of a portion A in FIG. 2 showing a second embodiment of a screw fastener according to the present invention. FIG. [Figure 6] 3 is an enlarged view of a portion A in FIG. 2 showing a third embodiment of a screw fastener according to the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In Fig. 1 and Fig. 2, reference numeral 10 denotes a screw fastener that fastens a screw (not shown), which is an example of a fastening part, to a work (not shown). This screw fastener 10 has a position control unit 20, a screw fastening unit 30 supported by this position control unit 20, and a control unit that controls the driving of the position control unit 20 and the screw fastening unit 30. The screw has a head and a leg, and a male thread is formed on the outer periphery of the leg.

[0010] The position control unit 20 includes a base member 21 extending in the vertical direction, and an upper plate 22 and a lower plate 23 extending in the horizontal direction are fixed integrally to the upper and lower ends of the base member 21. A guide rod 24 extending parallel to the base member 21 is provided between the upper plate 22 and the lower plate 23, and a tool table 25 configured to be slidable is attached to the guide rod 24 so as to be movable up and down. An AC servo motor 26 for lifting (hereinafter referred to as the lifting motor 26) is placed on the upper plate 22, and a ball screw 27 is connected to the drive shaft of the lifting motor 26 so as to be rotatable integrally. The ball screw 27 is provided between the upper plate 22 and the lower plate 23, and the tool table 25 is connected to the ball screw 27 via a drive nut (not shown) that moves up and down by the rotation of the ball screw 27. With these structures, the tool table 25 can be lifted and lowered along the guide rod 24 by receiving the rotational drive of the lifting motor 26.

[0011] The screw tightening unit 30 has a hollow cylindrical motor holder 31 disposed above the tool stand 25 of the position control unit 20 as shown in FIG. 2. A fastening AC servo motor 32 (hereinafter referred to as the fastening motor 32) is fixed to the motor holder 31 so that its drive shaft is inserted into the motor holder 31, and a shaft coupling 33 is connected to the drive shaft of the fastening motor 32 so as to be rotatable together with the motor. An insertion hole 331 having a circular cross section is formed on the lower surface of the shaft coupling 33, and a fitting hole 332 having a substantially rectangular cross section is formed continuously at the bottom of the insertion hole 331. An elongated sliding hole 333 extending in the axial direction intersects with the insertion hole 331. A connecting pin 34 configured to be movable up and down is inserted along the sliding hole 333, and a driver bit 35 is suspended from the connecting pin 34. The driver bit 35 is a generally cylindrical member having approximately the same size as the insertion hole 331, and has at its upper end a fitting portion 351 that fits into the fitting hole 332, while at its lower end a drive portion that fits into the head of the screw. Due to this structure, the driver bit 35 can rotate integrally with the shaft coupling 33 and the drive shaft of the fastening motor 32, and can move relatively to the shaft coupling 33 and the fastening motor 32 by the dimension that allows the connecting pin 34 to move along the slide hole 333.

[0012] The air cushion mechanism, which is a main part of the present invention, will now be described. As shown in FIG. 2, the motor holding part 31 has a through hole into which the hose joint 311 can be inserted, and the hose joint 311 is connected to an air supply hose (not shown) that continues to a compressor, which is an example of an air supply means. In addition, a plurality of vent holes are formed near the bottom of the side wall of the fitting hole 332, extending in a direction perpendicular to the fitting hole 332 and opening on the outer circumferential side of the shaft joint 33. A cylindrical seal part 36 that airtightly connects the hose joint 311 and the fitting hole 332 is provided between the motor holding part 31 and the shaft joint 33. The seal part 36 has a connection hole 361 that connects the hose joint 311 and the fitting hole 332, and the seal part 36, the motor holding part 31, and the shaft joint 33 are kept airtight by airtight packings 362, 363, 364, and 365 that are attached above and below the connection hole 361. In this embodiment, the airtight packings 362, 363 that keep the seal part 36 and the motor holding part 31 airtight are made of packings with a circular cross section, while the airtight packings 364, 365 that keep the seal part 36 and the shaft coupling 33 airtight are made of packings with a Y-shaped cross section that allow the shaft coupling 33 to rotate. Bearings 366, 367 that hold the shaft coupling 33 rotatably are disposed above and below the seal part 36, and these bearings 366, 367 hold the motor holding part 31 and the shaft coupling 33 together with a retaining ring. With the above structure, the pressurized air supplied from the compressor is supplied to the shaft coupling 33 through the hose coupling 311 and the connection hole 361 of the seal part 36, and enters through the air hole of the shaft coupling 33 to pressurize the inside of the fitting hole 332. As a result, the air cushion mechanism can bias the driver bit 35 toward the tip end and hold it in a cushioning manner.

[0013] In addition, a connecting hole 352 extending in the axial direction is formed on the upper end surface of the fitting portion 351 of the driver bit 35, and a plurality of through holes extending in a direction perpendicular to the connecting hole 352 and penetrating to the outer surface of the fitting portion 351 are formed at the bottom of the connecting hole 352. In addition, a plurality of leakage holes 334 penetrating to the outer periphery of the shaft coupling 33 are formed near the bottom of the insertion hole 331 in the shaft coupling 33. The leakage holes 334 are formed in a plurality of stages in the axial direction of the driver bit 35, and are configured so that the driver bit 35 closes the leakage holes 334 in order from the lowest stage when the driver bit 35 moves relative to the shaft coupling 33 and the fastening motor 32. In addition, the driver bit 35 has an annular groove on its outer periphery, and an airtight packing 353 that keeps the space between the driver bit 35 and the shaft coupling 33 airtight is accommodated in the annular groove. For this reason, the pressurized air supplied from the compressor does not flow out from anywhere other than the leak hole 334. With these structures, the pressurized air that is supplied from the compressor and urges the driver bit 35 downward passes through the connecting hole 352 of the driver bit 35 and reaches the insertion hole 331, and then is exhausted to the outside through the leak hole 334.

[0014] The compressor is provided with a measuring means for measuring the flow rate of the supplied air, and this measuring means is connected to the control unit and constantly notifies the control unit of the flow rate. This allows the control unit to constantly grasp the amount of air supplied by the compressor, i.e., the amount of exhaust air from the leak hole 334. As a result, when air is supplied at a constant pressure, the control unit can grasp the blocking state of the leak hole 334 by the driver bit 35, i.e., the relative positional relationship between the driver bit 35 and the shaft coupling 33, from the increase or decrease in the amount of exhaust air. In addition, the leak hole 334 is provided so that the lowest leak hole 334 is located near the boundary between the main part of the driver bit 35, which has a substantially cylindrical shape, and the fitting part 351 when the connecting pin 34 is in contact with the lowest part of the sliding hole 333 as shown in FIG. 3, and the lowest leak hole 334 is immediately blocked when the driver bit 35 starts to move relative to the shaft coupling 33.

[0015] Meanwhile, a hollow cylindrical guide member 37 is fixed below the tool base 25 of the position control unit 20 so as to cover the driver bit 35, and a screw guide 371 is suspended from this guide member 37 so as to be relatively movable in the axial direction. This screw guide 371 contains the driver bit 35 so as to be able to rotate and relatively move in the axial direction, and is constantly biased downward by a cushion spring 372 contained between the screw guide 371 and the tool base 25. A vacuum pump, which is an example of a suction means, is connected to the screw guide 371, and an accommodating section capable of accommodating the screw is formed at its lower end opening.

[0016] Also, a chuck unit 40 capable of temporarily holding a screw pressure-fed from an external component supply device is fixed to the lower plate 23 on an extension line of the screw guide 371 and the driver bit 35. This chuck unit 40, like the chuck unit 40 disclosed in JP-A-9-174349, includes a component supply hose 41 connected to the component supply device, and a pair of chuck jaws 42 capable of holding a screw that has passed through the component supply hose 41 on an extension line of the screw guide 371 and the driver bit 35. The chuck jaws 42 are configured to swing when pressed from above by the screw guide 371 or the driver bit 35, and to be able to retreat from the extension line of the screw guide 371 and the screw tightening unit 30.

[0017] The control unit is connected to the lifting motor 26 of the position control unit 20, the fastening motor 32 of the screw tightening unit 30, a compressor, a vacuum pump, and a parts supply device, and is configured to be able to control the driving of these.

[0018] Next, the operation of the screw fastener 10 configured as above will be described. When the drive signal is input, the control unit drives the component supply device to pressure-feed the screw toward the chuck unit 40, and the screw is held by the chuck jaws 42 through the supply hose. After the screw is held by the chuck unit 40, the control unit drives the compressor, the vacuum pump, and the lifting motor 26. As a result, the driver bit 35 is urged downward, and the screw tool, which is sucking air from the lower end opening of the screw guide 371, descends toward the chuck unit 40. During this movement, the screw guide 371 adsorbs the screw held by the chuck unit 40 and stores it in the lower end opening. After that, the screw tightening unit 30 descends while the tip of the screw guide 371 pushes open the chuck jaws 42. During this descent, the control unit drives the fastening motor 32 to rotate the driver bit 35.

[0019] As described above, the screw tightening unit 30 that adsorbs and holds the screw further descends, and when the lower end of the screw guide 371 comes into contact with the workpiece, only the screw guide 371 stops descending. Therefore, the driver bit 35 descends inside the screw guide 371 while deflecting the cushion spring 372. As a result, the driver bit 35 comes into contact with the screw held in the screw guide 371 and presses the screw toward the workpiece. At this time, since the driver bit 35 is rotating, the drive part of the driver bit 35 fits into the head of the screw. After that, the screw abuts against the workpiece and rotates together with the driver bit 35 to be fastened to the workpiece.

[0020] As described above, when the screw abuts against the workpiece and the descent of the screw and the driver bit 35 stops, the driver bit 35 rises relative to the shaft coupling 33 which continues to descend, and the driver bit 35 closes the lowest leak hole 334 as shown in FIG. 4. When the leak hole 334 is closed in this way, the amount of exhaust air flowing out from the leak hole 334 to the outside decreases, and the amount of air supplied from the compressor to the motor holding part 31 also decreases accordingly. Therefore, the measuring means of the compressor notifies the control unit of the decrease in the amount of air supply. The control unit, upon receiving this notification, determines that the screw has come into contact with the workpiece and reduces the descent speed of the position control unit 20. In this way, since it is possible to detect that the screw has come into contact with the workpiece, it is possible to perform screw tightening without being affected by the warping of the workpiece.

[0021] As described above, when a screw is fastened to a workpiece, the fastening motor 32 outputs a provisional fastening torque until the screw is seated on the workpiece, and then after the screw is seated on the workpiece, the fastening is performed with a final fastening torque that is greater than the provisional fastening torque. When the final fastening torque is output, the control unit stops driving the fastening motor 32 and drives the lifting motor 26 to raise the screw fastening unit 30. At this time, as the screw fastening unit 30 rises, the driver bit 35 is biased by the pressurized air and again descends relative to the shaft coupling 33. This returns the driver bit 35 and the shaft coupling 33 to the initial positional relationship shown in FIG. 3.

[0022] The screw fastener 10 configured as described above can freely change the thrust applied to the driver bit 35 by changing the pressure of the compressed air supplied from the compressor. This makes it possible to apply a thrust suitable for the screw to be fastened without disassembling the screw fastener 10. In addition, since the moment when the screw contacts the workpiece can be grasped from the decrease in the amount of air supplied as described above, when fastening a normal screw, the position where the screw contacts the workpiece and the amount of air supplied decreases (hereinafter referred to as the decrease position) can be taught in advance to the position control unit 20. By comparing the position where the amount of air supplied actually decreases during fastening with the decrease position set in advance, it is possible to check whether the screw to be fastened is a normal screw having a desired length. Furthermore, since the driver bit 35 is biased by the compressed air, the driver bit 35 can be constantly biased with a constant force regardless of the relative positional relationship with the shaft coupling 33. This allows the driver bit 35 to act as a brake from the moment when it contacts the workpiece. Therefore, even if the descending speed of the screw fastening unit 30 is faster than usual, the screw fastening unit 30 can be slowly decelerated, and the upper end of the sliding hole 333 of the shaft coupling 33 can be prevented from colliding with the connecting pin 34. As a result, damage to the workpiece loaded with the weight of the screw fastening unit 30 through the driver bit 35 and the screw can be prevented.

[0023] The screw driver 10 according to the present invention is not limited to the above, and various modifications are possible within the scope of the invention. For example, the air cushion mechanism may have a structure other than the above, as long as it can hold the driver bit in a cushioning manner by pressurized air. In the above embodiment, the leakage holes 334 are formed in multiple stages in the vertical direction, but as shown in FIG. 5, the leakage holes 334 may have different sizes. When the leakage holes 334 have different sizes, when a large leakage hole 334 is blocked, the change in the amount of exhaust also becomes large, which has the advantage that the control unit can easily grasp the position of the driver bit. In addition, the leakage holes 334 may be configured as elongated holes extending in the vertical direction as shown in FIG. 6. When the leakage holes 334 are configured as elongated holes in this way, the amount of exhaust from the leakage holes 334 changes intermittently as the driver bit 35 rises and falls in the insertion hole 331, so that the control unit can always grasp the approximate positional relationship between the driver bit 35 and the shaft coupling 33.

[0024] Also, there is no problem if the screw tightening unit 30 does not have the screw guide 371 and instead attracts and holds the screw by magnetic force. Furthermore, the driver bit 35 is an example of a fastening tool for fastening a screw, and there is no problem if a fastening tool other than the driver bit 35, such as a box bit or a socket, that can fit with the outer diameter of the head of a screw that is configured to have a non-circular shape, is used. [Explanation of symbols]

[0025] 10 … Screwdriver 20 … Position control unit 30 … Screw tightening unit 31 … Motor holder 311... Hose joint 32 … Fastening motor 33 ... Shaft coupling 331… Insertion hole 332… Fitting hole 333…Sliding hole 334... Leak 34 ... Connecting pin 35 ... Driver bit 351… Fitting part 352... Connection hole 36 ... Sealing parts 361... Connection hole 40 … Chuck unit

Claims

1. A motor; a fastening tool that is driven by the motor to rotate and has a tip end capable of engaging a screw; a fastening tool having an air cushion mechanism which fits into the rear end of the fastening tool and cushions the fastening tool.

2. The screw fastener according to claim 1, characterized in that the air cushion mechanism has a shaft coupling which connects the drive shaft of the motor and the fastening tool, and a fitting hole is formed in this shaft coupling to connect the rear end of the fastening tool in an axially movably manner, and a vent hole is provided in a side wall of this fitting hole, and pressurized air is supplied into the fitting hole through this vent hole to pressurize the inside of the fitting hole, thereby biasing the fastening tool.

3. The air cushion mechanism is configured to change an amount of pressurized air that can be supplied depending on a relative position of the fastening tool with respect to the shaft coupling; 3. The screw fastener according to claim 2, further comprising a measuring means for measuring the amount of pressurized air supplied to the air cushion mechanism.

4. an insertion hole is formed in the shaft coupling, the insertion hole being continuous with a tip end side of the fitting hole and covering the fastening tool so as to be movable in an axial direction relatively, and a leakage hole is formed in the insertion hole so that pressurized air supplied inside can be exhausted to the outside, 3. The screw fastener according to claim 2, wherein the leakage hole is provided within a range of movement of a fastening tool that moves relatively inside the shaft coupling.

5. a screw tightening unit having the air cushion mechanism, a position control unit for moving the screw tightening unit, and a control unit capable of controlling the driving of the screw tightening unit and the position control unit, 4. The screw driving tool according to claim 3, wherein the control unit is configured to be able to detect a position of the fastening tool relative to the shaft coupling from the amount of pressurized air supplied to the air cushion mechanism measured by the measuring means.

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