Screw fastening machine

Abstract

To provide a screw fastening machine in which a screw fastening tool can easily fit to a screw.SOLUTION: A screw fastening machine 10 has: a screw fastening tool 28 which rotates by receiving drive of a rotary drive source 26, and can reciprocate back and forth; a chuck unit 30 comprising a pair of chuck claws 32, 32 in which a holding hole 321 capable of holding a screw S supplied onto a movement path of the screw fastening tool 28 with a tip is formed, and which are so split as to be capable of opening and closing; and a closing mechanism 37 which forcibly closes the chuck claws 32, 32. The closing mechanism 37 has contact members 39, 39 which are arranged on both side faces of the chuck claws 32, 32, and can reciprocate back and forth. The contact members 39, 39 do not contact both side faces of the chuck claws 32, 32 at an advance position, and on the other hand, contact both side faces of the chuck claws 32, 32 at a retreat position, and forcibly close the chuck claws 32, 32.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] A known screw driver includes a screw tightening tool that rotates when driven by a motor and a chuck unit that holds screws pressure-fed from an external supply device along the movement path of the screw tightening tool, as shown in Patent Document 1. The chuck unit of this screw tightening tool includes a pair of chuck jaws arranged on the axis of the screw tightening tool, a chuck body having a support groove that swingably supports the chuck jaws, a mounting screw that penetrates the groove wall of the support groove and the chuck jaws and pivotally supports the chuck jaws, and a supply pipe that supplies screws to the chuck jaws. The chuck jaws have a separate holding hole formed on the surface facing the paired chuck jaws that can communicate with the supply pipe. With this structure, screws supplied from a supply device pass through the supply pipe and are delivered to the holding hole of the chuck jaws. Then, as the screw tightening tool rotates and moves forward, the screw tightening tool engages with the head of a screw waiting in the holding hole. This engagement between the screw tightening tool and the screw allows the screw to be fastened to a workpiece. However, when the above-mentioned screw tightening machine engages the screw and the tightening tool inside the chuck unit, friction occurs between the head surface of the screw and the tip surface of the tightening tool, causing the screw to rotate along with the tightening tool, making it impossible to engage the screw with the tightening tool.

[0003] Therefore, Patent Document 2 discloses a screw tightening machine in which a wedge-shaped protrusion is formed on the underside of the chuck jaw (the surface opposite the supply pipe), a pressing part is formed with a recess that engages with the protrusion of the chuck jaw, and an air cylinder moves the pressing part back and forth. When the pressing part of this chuck unit is driven by the cylinder and moves forward, it engages with the protrusion of the chuck jaw and closes the chuck jaw, so that the chuck jaw clamps the shank of the screw. As a result, the screw can be fitted into the screw tightening tool without co-rotating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Utility Model No. 2544183 [Patent Document 2] Japanese Utility Model Application Publication No. 05-029639 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional screw tightening tools, the support groove has a groove width greater than the thickness of the chuck jaws to allow the chuck jaws to oscillate, resulting in a gap between the support groove and the chuck jaws. When the protrusions on the underside of the chuck jaws are pressed with a gap between the support groove and the chuck jaws, as in the screw tightening tool disclosed in Patent Document 2, the pressure can cause the chuck jaws to shift within the support groove or tilt perpendicular to the plane of the chuck jaws' oscillation. When the chuck jaws shift within the support groove, the shift is greatest near the guide hole, which is farthest from the mounting screw that supports the chuck jaws. This can cause new problems, such as the screw held in the guide hole tilting and being unable to be fitted into the screw tightening tool.

[0006] Therefore, an object of the present invention is to provide a screw driving machine that can prevent improper fitting between a screw and a screw driving tool. [Means for solving the problem]

[0007] In order to achieve this object, the present invention provides a screw tightening tool that rotates when driven by a rotary drive source and can reciprocate back and forth, a chuck unit having a pair of chuck jaws that are formed with a holding hole that can hold a screw at its tip end supplied on the movement path of the screw tightening tool and that are divided so as to be able to open and close, and a closing mechanism that forcibly closes the chuck jaws, wherein the chuck unit has chuck jaws with tapered side surfaces, and the closing mechanism has abutment members that are arranged on both side surfaces of the chuck jaws and can reciprocate back and forth, and the abutment members are configured to allow the chuck jaws to be open without abutting against both side surfaces of the chuck jaws in the advanced position, but to abut against both side surfaces of the chuck jaws in the retracted position, thereby forcibly closing the chuck jaws. It is preferable that the contact member is a cam follower. It is also preferable that the contact member is disposed so as to contact the center of the chuck jaw in the thickness direction. [Effects of the Invention]

[0008] According to the above invention, the abutment member abuts against the outer side surfaces of the chuck jaws, forcing the chuck jaws into a closed state, which has the advantage that the chuck jaws do not shift within the support groove and that poor fit between the screw tightening tool and the screw is prevented. Furthermore, since the contact member is a cam follower, friction that occurs when the chuck jaws come into contact with the contact member is reduced, making it easier to move the contact member to a desired position. Furthermore, since the contact member contacts the center of the chuck jaw in the thickness direction, the chuck jaw is less likely to shift position. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side view showing the structure of a screw driver according to the present invention. [Figure 2] 1 is an enlarged side view showing the main structure of a screw fastener according to the present invention. FIG. [Figure 3] 1 is an enlarged cross-sectional view showing the main structure of a screw fastener according to the present invention; [Figure 4] FIG. 4 is a front view of the cross section AA of FIG. [Figure 5] 4 is an enlarged cross-sectional view of a main part showing a state transitioning from the state of FIG. 3 to the next state. FIG. [Figure 6] FIG. 6 is a cross-sectional front view taken along line BB in FIG. 5. [Figure 7] FIG. 6 is an enlarged cross-sectional view of a main part showing a state transitioning from the state of FIG. 5 to the next state. [Figure 8] FIG. 8 is a cross-sectional front view taken along line CC in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described below with reference to Figures 1 to 8. In Figure 1, reference numeral 10 denotes a screw driver that fastens a screw S into a workpiece W. This screw driver 10 has a moving means 20, a driver unit 24 that moves as it is driven by the moving means 20, and a chuck unit 30 that holds the screw S supplied from an external supply device on the movement path of the driver unit 24, and the driving of the moving means 20 and the driver unit 24 is controlled by a control unit (not shown).

[0011] The movement means 20 has a ball screw 21 extending in the front-rear direction, a servo motor 22 (hereinafter referred to as the movement motor 22) that rotates the ball screw 21, and a movement block 23 that is threadedly engaged with the ball screw 21 and moves forward or backward as the ball screw 21 rotates, and the driver unit 24 is connected to the movement block 23. Therefore, the driver unit 24 is driven by the movement motor 22 and can move forward and backward together with the movement block 23.

[0012] As shown in FIG. 1, the driver unit 24 has a hollow cylindrical housing 25, which is connected to the moving block 23. At the rear of the housing 25, an AC servo motor 26 (hereinafter referred to as the screw tightening motor 26) is held with its output shaft (not shown) inserted into the housing 25, and a shaft coupling 27 is connected to the output shaft of the screw tightening motor 26 so as to be rotatable integrally therewith. A box bit 28 is connected to the tip of the shaft coupling 27, and a fitting hole 281 that fits with the head of the screw S is formed in the tip surface of the box bit 28. Therefore, the box bit 28 is driven by the moving means 20 and can move in the forward and backward directions indicated by the two-dot chain arrow a in FIG. 4. The fitting hole 281 has an air vent 282 formed at the bottom thereof that continues to the rear end of the shaft coupling 27, and the air vent 282 is connected to a hose fitting 251 attached to the housing 25. An intake hose (not shown) is connected to this hose joint 251, and this intake hose continues to an external intake means such as a vacuum generator. Therefore, when the intake means is driven, negative pressure is created in the shaft joint 27 and the ventilation hole 282 of the box bit 28, and the screw S can be sucked and held in the fitting hole 281 of the box bit 28.

[0013] 3 and 4, the chuck unit 30 has a chuck body 31 fixed on the movement path of the box bit 28. A guide hole 311 having a diameter larger than the maximum diameter of the box bit 28 is formed through the chuck body 31, and the box bit 28 is configured to be freely inserted into the guide hole 311 in the axial direction. A pair of support grooves 312, 312 are formed on both side surfaces of the chuck body 31 so as to sandwich the guide hole 311. A pair of chuck jaws 32, 32 are supported in a swingable manner by the support grooves 312, 312. The chuck jaws 32, 32 are configured to be swingable about mounting screws 313, 313 that penetrate the groove walls of the support grooves 312 as support axes, and their tips are constantly biased to close by pawl springs 33, 33 compressed between the support grooves 312 and the bottom surfaces of the support grooves 312, 312. A holding hole 321 is formed on the opposing surface of the tip of each of the chuck jaws 32, 32, and is continuous with the guide hole 311 on an extension line of the guide hole 311. The holding hole 321 is formed with a hole diameter larger than the head diameter of the screw S, and is connected to the front of the holding hole 321 with a guide hole 322 having a hole diameter slightly smaller than the shank diameter of the screw S. The chuck jaws 32, 32 are configured with tapered outer diameters with tapered side surfaces.

[0014] A hose mounting bracket 34 is installed on the chuck body 31 at an angle relative to the guide hole 311 so that their extension lines intersect. The hose mounting bracket 34 is a cylindrical member configured to allow the screw S to pass therethrough, and a supply hose 62 extending from the supply device is connected to its end. The supply pipe 35 is installed between the hose mounting bracket 34 and the chuck jaws 32. Like the hose mounting bracket 34, the supply pipe 35 is also a cylindrical member configured to allow the screw S to pass therethrough, and is attached to the chuck body 31 so that it can swing in a direction away from the swinging surfaces of the chuck jaws 32, 32, with a setscrew 36 provided on the chuck body 31 as a support shaft. The supply pipe 35 communicates with the hose mounting bracket 34, and is constantly biased by a compression spring 351 so that its tip connects to the rear end of the holding hole 321 of the chuck jaws 32, 32. A jump-out prevention portion 352 is detachably connected to the tip of the supply pipe 35. The jump-out prevention portion 352 is a plate-shaped member with bifurcated engaging claws 353, 353 at its tip. When the supply pipe 35 is positioned on the extension line of the guide hole 311, the engaging claws 353 are positioned outward in the swing direction of the chuck jaws 32, 32, preventing the chuck jaws 32, 32 from opening beyond a predetermined angle. This predetermined angle is set so that the gap in the guide hole 322 is slightly wider than the shank diameter of the screw S. This prevents the screw S, which is pressure-fed by the supply device, from being pushed open by the chuck jaws 32, 32 due to the force of pressure and jumping out. This structure holds the supplied screw S with its shank inserted into the guide hole 322 and its head seat abutting the boundary between the retaining hole 321 and the guide hole 322. Furthermore, the engaging claws 353, 353 are sized so that they can be disengaged from the chuck claws 32, 32 before the chuck claws 32, 32 are pushed open by the box bit 28, as shown in FIG. 5, and so that they do not come into contact with the abutment members 39, 39 described later, as shown in FIG. 2.

[0015] The chuck unit 30 is also provided with a closing mechanism 37 that forcibly closes the chuck jaws 32. The closing mechanism 37 has an air cylinder 38, which is an example of a closing drive source. The air cylinder 38 is fixed to the surface of the chuck body 31 opposite the supply pipe 35 so that its piston rod 381 reciprocates in a direction parallel to the shaft coupling 27. A pair of abutting members 39 are fixed to the piston rod 381 of the air cylinder 38 via a connecting plate 382. The abutting members 39 are arranged to be reciprocable in front of the chuck jaws 32 when driven by the air cylinder 38. In this embodiment, the abutting members 39 are cam followers configured to rotate when in contact with the outer side surfaces of the chuck jaws 32. The abutting members 39 are arranged to abut against the centers of the chuck jaws 32 in the thickness direction. As a result, when the abutting members 39, 39 abut against the chuck jaws 32, 32, a force is applied to the entire outer side surfaces of the chuck jaws 32, 32, making it difficult for the chuck jaws 32, 32 to slip out of position.

[0016] When the air cylinder 38 retracts the piston rod 381 in the direction of the dashed-dotted arrow c as shown in FIG. 6, the abutment members 39 abut against the outer side surfaces of the chuck jaws 32, 32, and urge the chuck jaws 32 toward each other. When the piston rod 381 contracts, the abutment members 39 can press the chuck jaws 32 inward in the swinging direction, preventing the chuck jaws 32 from shifting within the support groove 312. On the other hand, when the air cylinder 38 advances the piston rod 381 in the direction of the dashed-dotted arrow b as shown in FIG. 8, the abutment members 39 release the chuck jaws 32, 32 so that they can swing freely and are in an open state. This allows the screw S and the box bit 28 to pass between the chuck jaws 32, 32.

[0017] The chuck jaws 32 are provided with a spring plunger 323 as an example of a biasing member that biases the chuck jaws 32 in an opening direction toward the tip side of the mounting screw 313. The spring plunger 323 includes a pressing pin 324 and a push-out spring (not shown) that biases the pressing pin 324 in a direction to push it out, housed inside a cylindrical housing. The pressing pin 324, biased by the push-out spring, presses the bottom surface of the support groove 312, thereby biasing the chuck jaws 32 in an opening direction. As shown in FIG. 4 , the spring plunger 323 is configured such that the pressing force of the pressing pin 324 is exerted only at a slight angle set within a range in which the opposing surface of the guide hole 322 is slightly wider than the shank of the screw S and the outer side surfaces of the chuck jaws 32 do not abut against the fitting jaws 353, and at this slight angle, the pressing pin 324 biases the chuck jaws 32 more strongly than the jaw springs 33. Therefore, when the closing mechanism 37 does not interfere with the chuck jaws 32, 32, the chuck jaws 32, 32 are held in a slightly open state. As a result, when the air cylinder 38 advances the piston rod 381 in the direction of the two-dot chain arrow b as shown in Figure 4, the chuck jaws 32, 32 can hold the screw S pressure-fed from the feed device in a state where the shank of the screw S enters the guide hole 322 and the head seating surface abuts on the boundary portion between the holding hole 321 and the guide hole 322.

[0018] Next, the operation of the screw driver 10 configured as described above will be described. When a start signal is input to the screw fastener 10, the control unit sends a drive signal to the component supply device to pressure-feed the screw S toward the chuck unit 30. At the start of the drive, the air cylinder 38 is on standby with the piston rod 381 extended, as shown in FIG. 4. Therefore, the chuck jaws 32 are held slightly open by the spring plunger 323, and the pressure-fed screw S is held inside the chuck jaws 32 so that its shank enters the guide hole 322 and its head seat engages with the boundary between the guide hole 322 and the retaining hole 321. At this time, the engaging claws 353 of the jump-out prevention unit 352 are arranged on the outer side in the swing direction of the chuck jaws 32, and the swing of the chuck jaws 32 is restricted, preventing the screw S from jumping out.

[0019] When the screw S is fed into the chuck jaws 32, 32 as described above, the control unit drives the air cylinder 38 to retract the abutting members 39, 39, as shown in FIG. 6. This causes the abutting members 39, 39 to abut against the outer side surfaces of the chuck jaws 32, 32, and press the chuck jaws 32, 32 inward in the swinging direction. As a result, the chuck jaws 32, 32 can clamp the shank of the screw S inserted into the guide hole 322. At this time, the abutting members 39, 39 press the chuck jaws 32, 32 in the swinging direction, preventing the chuck jaws 32, 32 from shifting. This has the advantage that the screw S is clamped between the chuck jaws 32, 32 without tilting. Furthermore, because the abutting members 39, 39 are cam followers, friction generated when the abutting members 39, 39 and the chuck jaws 32, 32 abut against each other is reduced. This has the advantage that the chuck jaws 32, 32 and the abutment members 39, 39 are less likely to wear even after long-term use, and that the abutment members 39, 39 are prevented from being unable to move to the desired position due to friction between the chuck jaws 32, 32 and the abutment members 39, 39.

[0020] After the cylinder is driven as described above and the chuck jaws 32, 32 clamp the screw S, the control unit drives the movement motor 22 in the forward direction to move the driver unit 24 forward. At the same time, the control unit drives the screw tightening motor 26 to rotate the box bit 28 and drives the vacuum generator to suck air through the fitting hole 281 of the box bit 28. When the driver unit 24 starts to move forward as described above, the box bit 28 swings the supply pipe 35 and enters the holding hole 321. As a result, the box bit 28 engages with the head of the screw S. At this time, because the screw S is clamped between the chuck jaws 32, 32, it engages without rotating together with the box bit 28. Furthermore, the screw S engaged with the box bit 28 in this way blocks the fitting hole 281 of the box bit 28, creating a negative pressure inside the box bit 28, and the screw S can be attracted and held in the fitting hole 281.

[0021] When the box bit 28 suction-holds the screw S as described above, the control unit advances the air cylinder 38 in the direction of the dashed-dotted arrow b, as shown in FIG. 8 . As a result, the chuck jaws 32, 32 are released from the abutment members 39, and the control unit restarts the moving motor 22. As a result, the chuck jaws 32, 32 are pushed open by the box bit 28, as shown in FIGS. 7 and 8 , and the box bit 28 advances again toward the workpiece W. Thereafter, when the tip of the screw S reaches a position just before contacting the workpiece W, the control unit switches the rotation of the moving motor 22 to low-speed driving. By advancing at a low speed while rotating in this manner, the screw S can be fastened to the workpiece W with a predetermined screw tightening torque. During the screw tightening process, when the screw tightening motor 26 outputs a predetermined tightening torque, the control unit stops the screw tightening motor 26 and drives the moving motor 22 in the reverse direction to retract the moving block 23 and driver unit 24 to their standby positions.

[0022] The specific configurations of the components of the present invention are not limited to those described above and may be modified in various ways without departing from the spirit of the invention. For example, the box bit 28 is an example of a screwdriver tool for fastening the screw S, and other fastening tools such as a driver bit may be used. The biasing member is not limited to the spring plunger 323 and may be modified as needed as long as it can hold the chuck jaws 32, 32 slightly open as described above. Furthermore, while the above embodiment is configured such that the jump-out prevention member 352 is fixed to the supply pipe 35, it is also acceptable to use a swing restriction plate that swings in conjunction with the supply pipe 35, as disclosed in Japanese Patent Application Laid-Open No. 2013-107158 by the present applicant. [Explanation of symbols]

[0023] 10...Screw tightening machine 20...Transportation 24...Driver unit 26 ... Screw tightening motor 27... Shaft coupling 28... Screw tightening tools 281... Fitting hole 30...Chuck unit 31... Chuck body 311... Guide hole 312… Support groove 313... Mounting screw 32...Chuck jaws 321…Retaining hole 322... Guide hole 33 ... Claw spring 35...supply pipe 352... Protrusion prevention part 353... Interlocking claws 36 ... Set screw 37 … Closing mechanism 38...Air cylinder 39 ... Contact member S...screw

Claims

1. a screw tightening tool that is rotated by the drive of a rotary drive source and is capable of reciprocating back and forth; a chuck unit having a pair of chuck jaws formed in a holding hole capable of holding a screw at its tip end supplied on a movement path of the screw tightening tool and split so as to be able to open and close; A screw tightening machine having a closing mechanism for forcibly closing the chuck jaws, The chuck unit has a tapered outer shape in which the side surfaces of the chuck jaws are tapered, The closing mechanism has abutment members arranged on both sides of the chuck jaws and capable of reciprocating back and forth, and the abutment members are configured to allow the chuck jaws to be open without abutting on either side of the chuck jaws in the forward position, but to abut on either side of the chuck jaws in the retracted position to forcibly close the chuck jaws.

2. 2. The screw driver according to claim 1, wherein the contact member is a cam follower.

3. 2. The screw tightening tool according to claim 1, wherein the contact member is disposed so as to contact the center of the chuck jaw in the thickness direction.

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