JP2010139011A - Screw and driver bit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow a smooth screw tightening operation, without generating axial inclination of a screw, even when a slight deviation exists between axes of a screw driving hole and a tip part of a driver bit, when engaging those. <P>SOLUTION: This screw 1 is formed with the driving hole 4 engaged with a driving protrusion part of the driver bit, in a head part 2. The driving hole 4 is formed with three engaging grooves 41 radially from the screw center axis C1 with 120° of angle along a circumferential direction, in top view of the head part 2. A bottom face 411 of each engaging grooves 41 is a flat face, and each flat face is within the same face orthogonal to the center axis C1. A cylindrical center hole 42 is drilled coaxially with the center C1, in the center of the driving hole 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a screw having a driving hole in the head and a driver bit having a driving projection engaging with the driving hole.

Generally, as an industrial screw, a screw having a cross-shaped groove formed in the head (hereinafter referred to as “cross-shaped screw”) is often used.
FIG. 14A is a plan view of a head portion of a conventional cross groove screw 101, and FIG. 14B is a partially cutaway sectional view of the head portion.
As shown in FIG. 5A, the drive hole 110 of the head 102 of the screw 101 is formed with four engagement grooves 111 that form a 90-degree angle radially from the center. The bottom surface 112 of the joint groove 111 is inclined as shown in FIG. 2B, and the drive hole 110 becomes thinner as it becomes deeper.

The operator inserts and presses the tip end 121 of the driver bit 120 (see FIGS. 15A and 15B) having a shape similar to that of the drive hole 110 into the drive hole 110, thereby pressing the tip end. The engagement blade 122 of 121 is guided by the inclined surface of the bottom surface 112 of the engagement groove 111 so that the driver bit 120 and the screw 101 are coaxial, and a smooth screw tightening operation can be executed.
JP 2006-90456 A

However, according to the shape of the drive hole 110 of the cross groove screw 101 and the drive tip 121 of the driver bit 120 as described above, particularly when the screw tightening operation is performed using an automatic screw tightening machine, Problems arise.
That is, in the automatic screw tightening machine, what is called an adsorption method is often used in order to engage and hold the drive hole of the screw head with the tip end portion 121 of the driver bit 120.

In this adsorption method, a driver bit is inserted coaxially into a sleeve-shaped bit guide, and the inside of the bit guide is exhausted backward (in the direction opposite to the tip), so that the pressure at the tip of the bit is different from the atmospheric pressure. The head of the screw is configured to be sucked and held (see, for example, JP-A-8-19970).
According to the above suction method, if there is any error between the screw supply position of the device (part feeder) that supplies the screw to the automatic screw tightening machine and the position of the driver bit, the center axis of the screw and the driver bit is shifted. The screw is attracted to the tip of the driver bit.

When the screw is sucked in this state, in the case of the drive hole of the conventional cross groove screw, the center axis of the screw is held in an inclined state with respect to the center axis of the driver bit. ”), There is a possibility that the screw tightening operation cannot be performed accurately.
FIGS. 15A and 15B are diagrams for explaining this phenomenon of axis collapse. In both figures, the screw 101 is shown in a cross-section at the same position as in FIG. 14B so that the engagement relationship between the drive hole 110 of the screw 101 and the tip portion 121 of the driver bit 120 can be easily understood. For the driver bit 120, only the front engaging blade 122 is shown in cross section.

  When the drive hole 110 of the screw 101 and the tip end portion 121 of the driver bit 120 are fitted coaxially, the engagement groove 111 and the engagement blade 122 have the same center as shown in FIG. Engage at positions P1 and P2 that are symmetric with respect to the axis, but when the center axes of both are slightly shifted, the driver bit 120 is first shifted from the center axis of the engagement groove 111 as shown in FIG. The first contact is made with the inclined portion of the bottom surface 112 (point P3 in the figure), and due to friction, the screw is inclined by an angle δ in the direction of clearance with the contact point P3 as a fulcrum, and is contacted at the point P4. In this state, the screw 101 is sucked and held at the tip of the driver bit 120.

When manually tightening screws, it is relatively easy to align the center axis of the screw with the driver bit by adjusting the pressing force and driver bit direction appropriately. In the configuration in which the screw is sucked and held by force, the above-mentioned shaft collapse is difficult to be corrected.
Then, the screw 101 is rotationally driven while being tilted with respect to the central axis of the driver bit 120, and the position of the tip of the leg portion of the screw is not fixed, which hinders the screw tightening operation. There is even a risk of damaging the workpiece.

  The present invention has been made in view of the above problems, and when engaging the screw drive hole and the tip of the driver bit, even if there is a slight shift in the axial center of the screw, It is an object of the present invention to provide a screw and a driver bit that can perform a smooth screw tightening operation without causing shaft tilt.

  In order to achieve the above object, a screw according to the present invention is formed integrally with a head having a driving hole with which a driving projection of a driver bit is engaged, and has a thread on its peripheral surface. A screw having a formed leg, wherein the drive hole has at least three engagement grooves that are radial from the central axis of the screw when the head is viewed in plan, and Are formed at substantially equal intervals in the direction, flat surfaces are formed on at least a part of the bottom surfaces of the respective engaging grooves, and the flat surfaces are in the same plane perpendicular to the central axis. It is characterized by.

Here, it is desirable that there is no portion protruding from the flat surface on the bottom surface of each engagement groove.
Here, it is desirable that the pair of inner wall surfaces facing each other in the circumferential direction of each of the engagement grooves is formed so as to be substantially perpendicular to the same plane including the flat surface.
Furthermore, it is preferable that the inner wall surface located on the outer peripheral side of each engagement groove is formed to be substantially perpendicular to the same plane including the flat surface.

Further, a cylindrical recess may be formed coaxially with the central axis on the bottom surface of the drive hole where the engagement grooves meet.
The driver bit according to the present invention comprises a shaft portion and a drive projection formed at the tip thereof, and the driver bit operates by engaging the drive projection with a drive hole formed in the head of the screw. The driving protrusion includes at least three engaging blades that are radial from the central axis of the shaft in a plan view and are formed at substantially equal intervals in the circumferential direction; The engaging blade has a flat portion at a position substantially corresponding to the flat surface of the bottom surface of the engaging groove of the screw drive hole on the tip end surface thereof, and the surface of the portion of the flat portion facing the flat surface is It exists in the same plane orthogonal to the central axis of the said axial part, It is characterized by the above-mentioned.

Here, it is desirable that at least a side surface in the width direction of the portion inserted into the drive hole of the engagement blade is formed perpendicular to a plane orthogonal to the central axis of the shaft portion.
In addition, when a cylindrical concave portion is formed on the bottom surface of a portion where the engagement grooves of the screw drive hole meet, the drive projection is It is desirable that the base portion where the engaging blades meet is provided with a columnar protrusion formed coaxially with the central axis of the shaft portion and inserted into the cylindrical recess.

Here, it is preferable that the protruding amount of the cylindrical protrusion in the central axis direction is smaller than the depth of the cylindrical concave portion of the screw.
Here, it is preferable that the outer diameter of the columnar protrusion is larger than the width of each engagement groove of the screw.

  As described above, since the bottom surface of each engagement groove of the drive hole has a flat surface and they are on the same plane orthogonal to the central axis of the screw, If a flat portion is provided in a portion corresponding to the flat surface of the bottom surface of the engaging groove, and the surface of the flat portion is formed on the same plane orthogonal to the central axis of the driver bit, the drive hole and the drive protrusion When the parts are engaged, the flat surfaces perpendicular to the central axes of the two parts come into contact with each other, and the screw does not tilt with respect to the central axis of the driver bit. As a result, a good screw tightening operation is possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(1) Shape of screw FIG. 1 is a perspective view of a screw 1 according to an embodiment of the present invention.
As shown in the figure, the screw 1 includes a head 2 having a trident drive hole 4 formed on the upper surface, and a leg formed integrally with the head 2 and having a thread 5 formed on the peripheral surface thereof. Part 3.

FIG. 2A is a plan view of the head 2 of the screw 1.
As shown in this figure, the drive hole 4 has three engagement grooves 41 extending radially from the central axis C1 of the screw 1 and formed at equal intervals of 120 ° in the circumferential direction. It is composed of a cylindrical center hole (concave portion) 42 formed coaxially with the central axis C1.
Each engagement groove 41 includes a flat bottom surface 411, a pair of engagement inner walls 412 arranged to face each other in the circumferential direction, and an outer peripheral side inner wall 413 located on the outer peripheral side.

The depth of each engagement groove 41 is the same, and the flat bottom surface 411 is formed on the same plane orthogonal to the central axis C1. The bottom surface 411 is in contact with a flat portion at the tip of the driver bit 6 described later, so that the center axis of the driver bit and the screw 1 are parallel to prevent the shaft from collapsing.
Each pair of engaging inner walls 412 is a portion that receives the driving force by engaging with the engaging blade at the tip of the driver bit 6. In the present embodiment, the engaging inner walls 412 are perpendicular to the plane including the bottom surface 411. (Hereinafter, the state in which the inner wall or the side surface is formed perpendicular to a specific plane may be simply referred to as “upright”.) As a result, when a rotational torque is applied to the engagement groove 41 by the driver bit 6, a component force is generated that pushes back the driver bit 6, and the phenomenon that the tip of the driver bit 6 slides out of the drive hole 4 of the screw 1 (camout) It becomes possible to prevent.

The outer peripheral side inner wall 413 is also upright with respect to the plane including the bottom surface 411.
The pitch, height, and the like of the thread 5 are determined based on, for example, JIS (Japanese Industrial Standards) for the screw depending on the nominal diameter of the screw and the application.
(2) Tip Shape of Driver Bit The tip portion (hereinafter referred to as “engagement tip portion”) of the driver bit 6 used for tightening the screw 1 has a shape that matches the shape of the drive hole 4. ing.

FIG. 3 is a perspective view of the driving protrusion 8 formed at the tip of the shaft portion 7 of the driver bit 6 according to the present embodiment when viewed from the tip side.
As shown in the figure, the drive protrusion 8 is formed by three engagement blades 81 radially from the central axis C2 of the driver bit 6 and at 120 ° angles at equal intervals in the circumferential direction. In addition, a cylindrical center protrusion 82 is provided on the base 83 where the engagement blades 81 meet to be coaxial with the center axis C <b> 2 of the driver bit 6.

Each engagement blade 81 includes an end surface 811 in the extending direction of the shaft portion 7, a pair of engagement side surfaces 812 in the circumferential direction, and an outer peripheral side surface (hereinafter referred to as “outer peripheral side surface”) 813. .
The end face 811 of each engagement blade 81 is flat and is on the same plane perpendicular to the central axis C2. The pair of engagement side surfaces 812 and the outer peripheral side surface 813 are formed so as to stand upright with respect to the same plane including the end surface 811.

Further, the edge portion of the end surface 822 at the tip of the center projection 82 is chamfered to form a tapered portion 821.
(3) Relationship between the shape and dimensions of each part of the drive hole 4 and the drive projection 8 FIGS. 4A and 4B are a plan view of only the drive projection 8 of the driver bit 6, and the drive projection 8. The longitudinal cross-sectional view in the centerline of the engagement blade | wing 81 is shown.

As shown in FIG. 4A, the cross-sectional contours of adjacent engaging side surfaces 812 of each engaging blade 81 are such that their asymptotes 812a form a hyperbola 85 that forms an angle of 110 ° with each other. It is formed.
The outer diameter d of the center protrusion 82 (see FIG. 4B) is determined so that the inscribed circle of each hyperbola 85 becomes the contour of the center protrusion 82.

Here, m is the diameter of the circumscribed circle of the drive protrusion 8, and Wa is the width dimension on the outer peripheral side (the narrowest part) of the engaging blade 81 (unit is [mm], respectively). The unit of the code indicating the dimensions is [mm]).
Moreover, as shown in FIG.4 (b), the outline of the cross section of the end surface 811 of the engagement blade | wing 81 is orthogonal to the central axis C2. Although only one engagement blade 81 is disclosed in FIG. 4B, all three engagement blades 81 have the same shape, and the end surface 811 of each engagement blade 81 is the same orthogonal to the central axis C2. It is formed so that it lies on the plane.

Here, t is the amount of protrusion of the cylindrical center protrusion 82 from the end face 811 of the engaging blade 81, t ′ is the width of the tapered portion 821 in the direction of the central axis C2, and d is the outer diameter of the center protrusion 82. , D ′ represents the outer diameter of the finest detail on the tip side of the tapered portion 821.
On the other hand, FIGS. 4C and 4D show a plan view of only the drive hole 4 of the screw 1 and a longitudinal sectional view of the center line of one engagement groove 41, respectively.

As shown in FIG. 4C, the cross-sectional contours of the two engagement inner walls 412 of the adjacent engagement grooves 41 are continuous so that their asymptotic lines 412a form a hyperbola 45 that forms an angle of 106 ° with each other. Formed. Further, the diameter D of the center hole 42 (see FIG. 4D) is determined so that the inscribed circle of each hyperbola 45 becomes the outline of the center hole 42.
Here, M is the radius of the circumscribed circle of the drive hole 4, and Wb is the width dimension on the outer peripheral side (the narrowest part) of the engagement groove 41.

Moreover, as shown in FIG.4 (d), the outline of the cross section of the bottom face 411 of the engaging groove 41 is orthogonal to the central axis C1. Although only one engagement groove 41 is disclosed in FIG. 4D, all the three engagement grooves 41 have the same shape, and the bottom surface 411 of each engagement groove 41 is the same perpendicular to the central axis C1. It is formed so that it lies on the plane.
Here, H indicates the depth of the engaging groove 41, and T indicates the depth of the cylindrical center hole 42 from the bottom surface 411 of the engaging groove 41.

The following relationship is established between the dimensions of the drive hole 4 and the drive projection 8.
d ′ <Wb <d <D Condition (1)
Wa <Wb Condition (2)
m <M Condition (3)
t ′ <t ≦ T Condition (4)
(4) About the shape of the hyperbola 45, 85 In this embodiment, the angle formed by the two asymptotic lines 812a of the hyperbola 85 drawn by the engagement sidewalls 812 of the two adjacent engagement blades 81 in the drive projection 8 is θa, When the angle formed by the asymptotic line of the hyperbola 45 drawn by the engagement inner wall 412 of the adjacent engagement groove 41 in the drive hole 4 is θb, θa> θb (condition (5)) is satisfied (this embodiment) In the form, θa = 110 °, θb = 106 °).

FIGS. 5A and 5B are diagrams for showing the shapes of the hyperbolas 85 and 45 by equations in the xy coordinate system, respectively.
In general, a hyperbolic equation having a focal point on the x-axis, a positive x-intercept of a (> 0), and an angle formed by two asymptotes in a region where x> 0 is expressed by the following equation: It is.
x ² / a ² −y ² / (a · tan (θ / 2)) ² = 1 (Formula 1)
Further, the equation of each asymptote is y = ± x · tan (θ / 2).

As shown in FIG. 4A, in the case of the engagement blade 81 of the driver bit 6, θ = θa = 110 ° in Equation 1, and the x intercept a is an inscribed circle (outside the center projection 82). Is equal to the radius d / 2 of the diameter), and the hyperbola 85 is obtained when the center line in the direction in which the two adjacent engaging blades 81 extend is the x axis, the direction orthogonal thereto is the y axis, and the central axis C2 is the origin. ^{is, x 2 / (d / 2} ) 2 -y 2 / represented by the following formula ((d / 2) · tan55 °) 2 = 1 ( equation 2)
Similarly, in the case of the engagement groove 41 of the drive hole 4, in Equation 1, θ = θb = 106 °, and the x intercept a is equal to the radius D / 2 of the inscribed circle (the inner diameter of the center hole 42). Therefore, the hyperbola 45 is expressed by the following equation when the midline in the direction in which the adjacent engagement grooves 41 extend is the x axis, the direction orthogonal thereto is the y axis, and the central axis C1 is the origin.

x ² / (D / 2) ² −y ² / ((D / 2) · tan 53 °) ² = 1 (Formula 3)
In this embodiment, a screw having a nominal diameter of 1 [mm] is set to d / 2 = 0.18 [mm] and D / 2 = 0.2 [mm].
The hyperbola 85, 45 approaches the asymptotic line as it approaches the circumscribed circle, but the value of the x intercept a is smaller than that of the engaging groove 81 as described above, and the asymptotic line The angle θ / 2 with respect to the x-axis is made larger than that in the case where the engagement blade 81 has the engagement groove 41, so that the relationship of d <D in the above condition (1) and the condition (2) ( Wa <Wb) is also satisfied.

  The above equation 3 is an equation in which the center position of the hyperbola 45 coincides with the center axis C1 of the screw 1. However, the center position of the hyperbola 45 is offset from the center axis C1 of the screw by a predetermined amount (in the state as it is). The center may be shifted). In this way, the shape of the hyperbola 45 remains the same, the inner diameter D of the center hole 42 can be increased, and the degree of freedom in design increases. The same applies to the hyperbola 85 on the other engagement blade 81 side.

Furthermore, the hyperbolic curves 85 and 45 may have the same shape (that is, θa = θb in FIGS. 4A and 4C), and one center position may be shifted.
For example, in the equation 2 showing the hyperbola 85 on the engagement blade 81 side, the equation of the hyperbola moved in the x direction from the central axis by α (> 0) is:
(X−α) ² / (d / 2) ² −y ² / ((d / 2) · tan 55 °) ² = 1
(Formula 4)
This equation 4 may be applied as the equation of the hyperbola 45 on the engagement groove 41 side.

Even in this case, the relationship of d <D and Wa <Wb can be satisfied.
(5) Operational Effects According to the present embodiment, the following operational effects are obtained.
(5-1) Prevention of shaft collapse FIG. 6A is a diagram showing a state in which the drive projection 8 of the driver bit 6 is coaxially inserted into the drive hole 4 of the screw 1 in plan view. In the figure, the drive protrusion 8 is shown in a cross section at the portion of the engagement blade 81 in the direction of the central axis C2, and should be hatched originally. The main purpose is to show the relationship of the shape of the engagement blade 81, and the broken lines and the lead lines are difficult to understand, and therefore the hatched lines are omitted for convenience (FIGS. 7A, 8 and 8 below). 9 (a) (b), FIG. 10, FIG. 11 (a), FIG. 12 (a), FIG.

  As shown in FIG. 6A, each side surface of the engagement blade 81 of the drive projection 8 has a certain clearance (clearance) with respect to the inner walls 412 and 413 of the engagement groove 41. . Therefore, even if there is a slight shift between the screw 1 and the central axes C1 and C2 of the driver bit 6 during suction holding, the drive projection 8 of the driver bit 6 is not The drive hole 4 is smoothly inserted.

Thereby, in the conventional cross groove screw, it is possible to avoid the problem that the tip of the engagement blade of the driver bit is in contact with the inclined bottom surface of the engagement groove of the screw and the shaft is likely to be inclined.
This is an effect obtained mainly by satisfying the above conditions (2) and (3).
On the other hand, FIG.6 (b) shows the principal part in the BB arrow sectional drawing in Fig.6 (a). In this figure, the drive hole 4 is shown only by the outline of the cross section of the head 2 so that the engagement relationship between the drive protrusion 8 and the drive hole 4 can be easily understood. The hatched lines indicating this are not shown (the same applies to FIGS. 7 (b), 10 (b), 11 (a), 12 (b), 13 (b), etc.). .

As shown in FIG. 5B, the flat surface 811 at the tip of the engagement blade 81 abuts on the flat bottom surface 411 of the engagement groove 41, and these contact relationships are related to all the engagement blades 81. Since it occurs between the mating grooves 41, the screw 1 and the central axes C1 and C2 of the driver bit 6 are maintained in parallel, and the shaft collapse can be effectively prevented.
Further, when the center protrusion 82 is inserted into the center hole 42 (d <D in the condition (1)), the center axes C1 and C2 are substantially coincided with each other within the clearance between the center protrusion 82 and the center hole 42. Engage on the same axis for centering.

In particular, in the present embodiment, the engagement of the engagement groove 41 and the engagement blade 81 is performed at three locations around the central axis at equal intervals, so that rattling is unlikely to occur and the screw is stably There is an advantage that 1 can be attracted and held by the driver bit 6.
At this time, since the condition (4) is satisfied, the bottom surface 411 of each engagement groove 41 and the end surface 811 of the engagement blade 81 are securely connected without the tip of the center projection 82 interfering with the bottom of the center hole 42. It can be made to contact.

If the screw 1 is attracted and held by the driver bit 6, even if the positions of the engaging grooves 41 and the engaging blades 81 in the rotational direction do not coincide as shown in FIG. 6 (a) and 6 (b) can be shifted to the engaged state.
That is, since the screw 1 is normally attracted to the driver bit 6 in the automatic screw tightening machine, the upper surface of the head 2 of the screw 1 in the state shown in FIG. 7b, the end face 811 of each engagement blade 81 comes into contact with the upper surface of the head 2 as shown in the cross section of FIG. 7B. In this state, the central axis C1 , C2 is kept substantially parallel, and the driver bit 6 rotates.

  At this time, the screw 1 also rotates with the rotation of the driver bit 6 due to the frictional force at the contact surface between the head 2 and the engaging blade 81, but at the moment when both contact, the inertial force of the screw 1 Since the rotational speed is slower than the rotational speed of the driver bit 6, the rotational angles of the two differ, and when the positions of the engagement blades 81 and the engagement grooves 41 overlap, 7 (b), the engaging blades 81 and the center protrusion 82 of the driver bit 6 enter the engaging groove 41 and the center hole 42 of the screw 1 and are engaged smoothly. The

(5-2) Improvement of Durability FIG. 8 shows a state where the engagement blade 81 applies drive torque to the engagement inner wall 412 of the engagement groove 41 when the screw 1 is tightened by rotating the driver bit 6. It is a top view.
As shown in the figure, when the engagement blade 81 of the driver bit 6 is rotated clockwise about the central axis C2 (in the design of the present embodiment, the center line of the engagement blade 81 and the engagement groove 41). And the vicinity of the front end of the engagement side surface 812 abuts at the abutment positions S1 to S3 of the engagement inner wall 412 of the engagement groove 41 of the drive hole 4.

  Each engagement inner wall 412 and engagement side surface 812 are both upright and slightly curved in the same direction, and the elasticity of the material of the screw 1 (metal) is also helped, so that the engagement side surface 812 and the engagement inner wall 412 can be in surface contact with a relatively large area, and fretting wear hardly occurs between them. Therefore, the driving hole 4 is not easily crushed, and the driver bit 6 in the automatic screwing machine is less worn, so that it can be used for a long time without using a very expensive material, which is advantageous in terms of cost.

  The driving torque applied to the engagement inner wall 412 is, for example, the force F1 applied in the normal direction of the contact surface with the engagement side surface 812 and the length of the arm from the central axis orthogonal to the engagement position S1. As a result of the product of the length L1, both the engagement inner wall 412 and the engagement side surface 812 change in a hyperbolic shape in plan view as described above, and the engagement inner wall 412 has a smaller angle formed by an asymptote. For this reason (see condition (5)), the radius of curvature near the central axis is smaller on the engagement inner wall 412 than on the engagement side surface 812, and the engagement blade 81 and the engagement blade 41 are located at the root of the engagement groove 41 as shown in FIG. Thus, the engagement groove 41 and the engagement blade 81 do not come into contact with each other near the center axis, but can come into contact with each other at S1 away from the center axis.

As a result, the arm length L1 can be increased, and a large driving torque can be transmitted (the same applies to other portions S2 and S3).
Moreover, since the distance between the contact groove S1 and S3 in the vicinity of the outer periphery increases the distance to the engagement groove 41 adjacent to the rotation position at the contact position, the wall thickness of the engagement inner wall 412 can be increased. There is an advantage that it becomes larger and can withstand stronger rotational torque.

  Furthermore, when the number of the engagement grooves is an even number, especially in the case of a cruciform groove screw having four engagement grooves as in the prior art, when the center axis is shifted, only two engagement grooves that are inverted by 180 ° are used as engagement blades. In other cases, the engagement groove may not contribute to the transmission of the driving force, but in the case of a tridentate shape as in this embodiment, in addition to surface contact at each engagement location. Since the drive torque can be transmitted almost uniformly by always engaging at the three locations S1 to S3, the cam-out hardly occurs and the engagement groove 41 is not easily crushed.

(5-3) Improvement of centering function In addition to the function of the center hole 42 and the center projection 82, the number of the engagement grooves 41 is three and the condition (5) is satisfied. It is also possible to obtain an effect that becomes easier.
That is, when the screw is adsorbed, considering the case where the screw 1 is slightly shifted to the left and right with respect to the driver bit 6 within the clearance between the center hole 42 and the center projection 82 as shown in FIG. According to the condition (5), the radius of curvature near the center axis is smaller at the engagement inner wall 412 than at the engagement side surface 812. Therefore, the engagement groove 41 and the engagement blade 81 are first brought into contact with each other in the vicinity of the root S4. The rotation of 81 in the direction of the arrow causes the screw 1 to move relatively to the right due to the reaction T0 of the force applied from the engagement blade 81 to the engagement inner wall 412 at the position S4. The blade 81 and the engagement groove 41 come into contact with each other and receive reaction T1 to T3 at each contact position S1 to S3, and try to move the central axis C2 relatively in a direction where the force is weak. By such an adjustment function acting, the contact positions S1 to S3 of the three engagement grooves 41 and the engagement blades 81 are moved, and the reaction T1 to T3 from the engagement inner wall 412 at those positions is almost the same. It converges to an equal position, that is, a position where the central axes C1 and C2 substantially coincide as shown in FIG. 9B. Thereby, centering can be performed reliably.

Such a centering function can be obtained if it is a three-pronged drive hole, but it satisfies the condition (5) as in the present embodiment, and the engagement inner wall 412 and the engagement side surface. Since both of the shapes in the plan view of 812 are curved, the contact position between the engagement inner wall 412 and the engagement side surface 812 moves smoothly, and the centering can be performed more smoothly.
Further, in the present embodiment, the description has been given assuming that the shaft deviation is within the range of the positioning error between the automatic screw tightening machine and the parts feeder when the screw 1 is sucked and held. Even if the amount of axial deviation may be more than that, if it is smaller than the radius of the circumscribed circle of the drive hole 4 of the screw 1, centering is possible.

FIGS. 10A and 10B show the centering operation in this case.
That is, when the center axis C2 of the driver bit 6 is positioned in the middle of the engagement groove 41 of the drive hole 4 of the screw 1 as shown in FIG. From the relationship of d ′ <Wb <d <D in the previous condition (1), the outer diameter d of the cylindrical portion of the center protrusion 82 is larger than the width Wb of the engagement groove 41, so that it does not enter the groove. Since the diameter d ′ of the tip end portion of the taper portion 821 is smaller than the width of the engagement groove 41, a part of the tip end side enters the engagement groove 41 (see FIG. 10B). Since the edge is hyperbolic as described above and the groove width of the engaging groove 41 becomes wider toward the central axis), the driver bit 6 is urged toward the driver bit 6 side by suction. As the screw 1 is rotated, the screw 1 gradually moves relative to the central axis C2 direction of the driver bit 6. Go and centering are performed, finally enters the center hole 42 of the driving hole 4 of the center projection 82 screw 1 of the driver bit 6.

  Here, as shown in FIG. 4C, in the plan view of the drive hole 4, the contact point between the pair of engagement inner walls 412 of the engagement groove 41 and the inscribed circle (that is, the inner surface of the center hole 42) is E1. , E2, if the distance between both contacts is Wr, and the angle between the line connecting the central axes C1 and E1 and the x-axis is θr, the angle formed between the adjacent engaging grooves 41 is 120 °. θr is 60 °, which is a half angle.

Therefore, when the distance Wr is represented by the diameter D of the center hole 42,
Wr = 2 · (D / 2) sin60 °
As described above, in this embodiment, the nominal diameter is 1 [mm] and D = 0.4 [mm]. Therefore, when calculating as sin 60 ° = 1.73 / 2, Wr = 0. 346 [mm].

On the other hand, since the outer diameter d of the center projection 82 is 0.36 [mm], d> Wr. In this portion, the center projection 82 has not yet fallen into the engagement groove 41, and the center axis C2 is When approaching the center axis C1, the center protrusion 82 enters the center hole 42, and smooth centering is possible.
Therefore, if the range from the portion that intersects (in contact with) the inscribed circle to the circumscribed circle at the tip is defined as one engagement groove, the width of each engagement groove 41 is smaller than the outer diameter d of the center protrusion 82. More preferably, the width of the engagement groove 41 gradually increases as it moves from the circumscribed circle side (width Wb) to the central axis C1, and the width Wr of the root portion also has the outer diameter of the center projection 82. By making the shape smaller than d, the centering function can be sufficiently exhibited.

10 (a) and 10 (b), the driver bit 6 is shown to move for convenience of explanation, but actually, the central axis C1 of the screw 1 is centered on the central axis C2 of the driver bit 6. As the screw 1 rotates, the screw 1 moves to gradually reduce the distance between the central axes C1 and C2, and the centering is performed.
For the above purpose, the same effect can be obtained by forming an R portion having an appropriate curvature radius instead of the tapered portion 821 of the center protrusion 82.

In conventional cross groove screws, the tip of the driver bit is sharply pointed, and the engagement blade engages directly with the drive groove of the screw when the screw is attracted, so the position where the tip of the driver bit enters the engagement groove It is difficult to achieve smooth centering as described above.
However, according to the configuration of the screw 1 and the driver bit 6 according to the present embodiment, when the screw 1 is sucked and held by the driver bit 6 of the automatic screw tightening machine, both the central axes are slightly shifted. However, the shaft can be effectively prevented from being tilted, the centering can be performed efficiently, and the durability of the screw 1 and the driver bit 6 can be improved while ensuring the necessary tightening torque. It is something that can be done.

<Modification>
As described above, the present invention has been described based on the embodiment. However, the content of the present invention is not limited to the above embodiment, and for example, the following modifications can be considered.
(1) In the above-described embodiment, the bottom surface 411 of each engagement groove 41 is formed as a substantially flat surface except for the portion where the center hole 42 is formed. However, the bottom surface 411 is flat enough to prevent the shaft from collapsing. Therefore, it is not always necessary to form the entire bottom surface 411 in a plane.

FIGS. 11 (a) and 11 (b) respectively show a plan view when the screw 1 and the driver bit 6 according to such a modification are engaged, and a longitudinal sectional view of the main part thereof.
As shown in both figures, the bottom surface 411 of the engagement groove 41 is provided with a flat portion 411a at a position slightly protruding from the portion, and the top surface (engagement blade) of the flat portion 411a of each engagement groove 41 is provided. 81 is formed so as to be in the same plane orthogonal to the central axis C1 of the screw 1.

Since the end face 811 of the engaging blade 81 of the driver bit 6 that contacts this is in the same plane orthogonal to the central axis C2 of the driver bit 6, the shaft fall of the screw 1 is effectively prevented also in this modification. be able to.
Further, as shown in FIGS. 12A and 12B, a flat portion 811 a may be provided on a part of the end surface 811 of the engagement blade 81 of the driver bit 6.

As shown in both figures, the lower surface of the flat portion 811a of each engagement blade 81 (the contact surface with the bottom surface 411 of the engagement groove 41) is in the same plane orthogonal to the central axis C2 of the driver bit 6. In this modification, it is possible to prevent the shaft 1 from falling down.
Furthermore, the flat portions 411a and 811a may be provided at positions corresponding to both the bottom surface 411 of the engagement groove 41 and the end surface 811 of the engagement blade 81. In this case, even when the center axes C1 and C2 are displaced within the clearance between the center hole 42 and the center projection 82, the flat portions 411a and 811a are in contact with each other in any engagement groove 41. It goes without saying that setting is desirable.

In the case of the modification shown in FIGS. 11 and 12, there should be no portion protruding from the flat portions 411a and 811a. If there is, it will not be possible to make contact with each other on a flat surface in the same plane, so that it will not be possible to prevent the shaft from collapsing.
However, instead of projecting the partial flat portions 411a and 811a of the engagement groove 41 of the screw 1 and the engagement blade 81 of the driver bit 6 from the bottom surface 411 and the end surface 811 respectively, one side is retracted (recessed), If the other flat portion has a convex shape so that the flat surfaces can be secured in contact with each other, the same effect of preventing the shaft from collapsing can be obtained.

  (2) According to the above embodiment, the center protrusion 82 is inserted into the center hole 42 so that the screw 1 and the driver bit 6 can be easily centered. The center hole 42 of the engagement groove 41 and the engagement blade 41 are located within the minimum clearance between the engagement groove 41 and the engagement blade 81. The center protrusion 82 of 81 is not particularly required as shown in FIGS.

In this case, as shown in the longitudinal sectional view of FIG. 13B, the contact area between the flat surfaces of the bottom surface 411 of the engagement groove 41 of the screw 1 and the end surface 811 of the engagement blade 81 of the driver bit 6 is It becomes larger and the shaft collapse is more reliably prevented, and the processing of the drive hole 4 and the drive projection 8 is facilitated and the productivity is improved.
Further, when the screw 1 is viewed, the center hole 42 is eliminated, so that the strength of the screw is improved. When the driver bit 6 is viewed, the center protrusion 82 which is the most worn portion can be eliminated, so that the durability is improved. The maintenance cost can be further reduced.

Such a configuration is particularly effective for a screw (thin head screw) having a relatively small nominal diameter and a small thickness in the direction of the central axis C1 of the head 2.
Even in the case of this modified example, since there are three engaging grooves 41 and three engaging blades 81, there is no problem because centering is achieved based on the principle described in FIG. 9 without the center hole 42. .
(3) In the above embodiment, the cross-sectional shape of the engagement groove 41 of the drive hole 4 in the screw 1 and the cross-sectional shape of the engagement blade 81 of the driver bit 6 and the drive protrusion 8 draw the hyperbola 45 and 85, respectively. (Refer to FIGS. 4 (a) and 4 (c)), but it is not necessarily a hyperbola. Both or one of them is a curve that curves toward the central axis, and the radius of curvature becomes closer to the central axis. You may make it draw the curve which becomes small. Moreover, you may make it consist of a some straight line approximated to the said curve.

However, in the case of forming by approximating a plurality of straight lines, corner portions are generated and stress concentrates on the portions. From the viewpoint of increasing durability, the cross-sectional shape is related to a continuous curve. It can be said that it is more desirable to form the joint groove 41 and the engagement blade 81.
(4) In the above embodiment, the inner diameter D of the center hole 42 in the drive hole 4 of the screw 1 is an inscribed circle of the three hyperbolas 45 defining the shape of each engagement groove 41 in plan view. The outer diameter of the center protrusion 82 of the drive protrusion 8 of one driver bit 6 is smaller than D, and three hyperbolas 85 defining the shape of the end face of each engagement blade 81 in plan view. Was determined to be an inscribed circle.

  However, the position at which the engagement blade 81 of the driver bit 6 transmits the rotational torque to the engagement groove 41 of the screw 1 is finally located near the engagement blade 81 and the tip of the engagement groove 41 (see FIG. 8), even if the inner diameter of the center hole 42 is slightly larger than the diameter of the inscribed circle, there is no hindrance to the tightening operation, and the outer diameter d of the center projection 82 of the driver bit 6 is increased accordingly. It doesn't matter. This is because the durability of the driver bit 6 increases as the center protrusion 82 becomes thicker.

  On the other hand, as the inner diameter of the center hole 42 is increased, the strength of the screw 1 is reduced, and so-called “neck jump” may occur. Considering the nominal diameter of 1 and the strength of the material to be used and the torque required for tightening the target workpiece, a safe value that will not damage the screw 1 even if the required tightening torque is applied is obtained through experiments and calculations. Desired.

(5) In the above embodiment, the engagement inner wall 412 of the drive hole 4 of the screw 1, the outer peripheral side inner wall 413, the engagement side surface 812 of the engagement blade 81 of the drive protrusion 8 of the driver bit 6, and the outer peripheral side surface 813. Are made upright and have no inclined surface.
As a result, even if an axis shift occurs during screw suction, there is no inclined surface with which the tip of the drive projection 8 abuts, and an effect that the shaft collapse hardly occurs can be obtained.

  However, in the above embodiment, the clearance between the drive hole 4 and the drive projection 8 at the time of engagement is relatively large. Therefore, the engagement inner wall is within the range of positioning accuracy of the automatic screw tightening machine and the parts feeder. 412, the outer peripheral side inner wall 413, the engaging side surface 812, and the outer peripheral side surface 813 are provided with a slight inclination so that the one inclined surface does not first come into contact with the other part at the time of screw adsorption. Therefore, there is no risk of axis collapse. In this sense, the inner wall of the engagement groove 41 and the side surface of the engagement blade 81 need not all be upright.

However, from the viewpoint of preventing the cam-out phenomenon that the drive protrusion 8 slides out of the drive hole 4 during tightening, both the engagement inner wall 412 and the engagement side surface 812, particularly the regions that contact when tightening, are inclined. It is desirable to make it an upright shape without causing it.
As described above, the conventional cross groove screw is configured to achieve centering by tilting the bottom surface of the engagement groove and tapering the drive hole so that the tip of the driver bit and the drive hole are fitted. As in the embodiment of the present invention, a sufficient clearance cannot be provided at the time of engagement. Therefore, when the screws are held by suction, the inclined surface of the drive hole is always in the driver's inclined surface if there is a slight deviation between the central axes of both. It had to engage with the driving tip of the bit, and the shaft collapsed.

However, in the present invention, shaft tilting and centering are realized by a technical idea completely different from the conventional cross groove screw, so that a sufficient clearance is provided between the drive hole 4 of the screw 1 and the drive protrusion 8 of the driver bit 6. Thus, the screws 1 can be more easily engaged with each other when the screw 1 is sucked and held, which greatly contributes to automation of screw tightening of a screw having a small diameter.
<Others>
(1) The shape of the drive hole 4 of the screw 1 described above is particularly effective for a small screw (nominal diameter is 2.0 mm or less), but it can of course be applied even to a large screw. is there.

  (2) Further, the shape of the drive hole 4 of the screw 1 and the drive projection 8 of the driver bit 6 described above may not be dedicated to the automatic screw tightening machine but may be provided for manual operation.

  The present invention is suitable as a configuration of a screw and a driver bit that can prevent a screw shaft from collapsing when the screw driving hole is engaged with the tip of the driver bit and can perform a screw tightening operation smoothly.

1 is an external perspective view of a screw 1 according to an embodiment of the present invention. (A) and (b) respectively show a plan view and a partially cutaway sectional view of the screw 1. It is an external appearance perspective view of the front-end | tip part of the driver bit 6 which concerns on embodiment of this invention. FIGS. 4A and 4B are a plan view and a cross-sectional view showing the shape of the drive protrusion 8 of the driver bit 6, respectively, and FIGS. 4C and 4D are plan views showing the shape of the drive hole 4 of the screw 1, respectively. FIG. (A) (b) is a figure which shows the hyperbola 85 which shows the outline shape of the engagement blade 81 of the drive projection part 8, and the hyperbola 45 which shows the outline shape of the engagement groove | channel 41 of the drive hole 4, respectively. FIGS. 7A and 7B are a plan view and a cross-sectional view, respectively, when the drive protrusion 8 of the driver bit 6 is engaged with the drive hole 4 of the screw 1. (A) (b) is the top view and sectional drawing for demonstrating engagement operation when the rotation position of the engagement blade | wing 81 of the driver bit 6 and the engagement groove | channel 41 of the drive hole 4 differs, and is adsorb | sucked. is there. It is a figure for demonstrating a mode that rotational torque is provided to the engagement groove | channel 41 by the engagement blade | wing 81. FIG. (A) (b) is a figure for demonstrating a mode that even if an axial shift | offset | difference exists in both at the time of the adsorption | suction holding | maintenance of the screw 1 to the driver bit 6, it corrects. (A) and (b) show that when the screw 1 is held by suction to the driver bit 6, the engagement operation between the two is performed smoothly even when the axial displacement of both is larger than that in FIG. 9. It is a figure for demonstrating. (A) and (b) are the top views and sectional drawings for demonstrating the structure of the screw 1 and the driver bit 6 which concern on the modification of this invention. (A) and (b) are the top views and sectional drawings for demonstrating the structure of the screw 1 and the driver bit 6 which concern on another modification of this invention. (A) and (b) are the top views and sectional drawings for demonstrating the structure of the screw 1 and the driver bit 6 which concern on another modification of this invention. (A) and (b) are the top view and the partially cutaway sectional view for showing the shape of the conventional cross groove screw. (A) (b) is a figure for demonstrating the phenomenon of the axis fall in the said conventional cross groove screw.

Explanation of symbols

1 Screw 2 Head 3 Leg 4 Drive hole 5 Thread 6 Driver bit 7 Shaft 8 Drive protrusion
41 engaging groove 42 center hole 45, 85 hyperbola 411 bottom surface 411a flat part 412 engaging inner wall 413 outer peripheral side inner wall 412a asymptotic line 81 engaging blade 82 center projection 811 end face 811a flat part 812 engaging side face 813 outer peripheral side face 812a asymptotic line 821 Taper

Claims (10)

A screw having a head formed with a drive hole with which a drive projection of a driver bit is engaged, and a leg formed integrally with the head and having a thread formed on a peripheral surface thereof;
The drive hole has at least three engaging grooves formed radially from the central axis of the screw when the head is viewed in plan, and is formed at substantially equal intervals in the circumferential direction.
A screw characterized in that a flat surface is formed on at least a part of the bottom surface of each engagement groove, and the flat surfaces are in the same plane perpendicular to the central axis.   2. The screw according to claim 1, wherein a portion protruding from the flat surface does not exist on a bottom surface of each engagement groove.   The pair of inner wall surfaces facing each other in the circumferential direction of each of the engagement grooves are formed so as to be substantially perpendicular to the same plane including the flat surface. Screw as described in.   The inner wall surface located in the outer peripheral side of each said engagement groove is formed so that it may become substantially perpendicular | vertical with respect to the same plane containing the said flat surface, The any one of Claim 1 to 3 characterized by the above-mentioned. Screw as described in.   5. The cylindrical concave portion is formed on the bottom surface of the drive hole where the engagement grooves meet, and is coaxially formed with the central axis. 6. The described screw. A driver bit comprising a shaft portion and a drive projection formed at a tip thereof, wherein the drive projection is formed by engaging the drive projection with a drive hole formed in a screw head according to claim 1,
The drive protrusion includes at least three engagement blades that are radial from the central axis of the shaft in plan view and are formed at substantially equal intervals in the circumferential direction.
Each engagement blade has a flat portion at a position substantially corresponding to the flat surface of the bottom surface of the engagement groove of the screw drive hole on the tip end surface thereof,
The driver bit, wherein a surface of a portion of the flat portion facing the flat surface is in the same plane orthogonal to the central axis of the shaft portion.   The driver according to claim 6, wherein at least a side surface in a width direction of a portion inserted into the drive hole of the engagement blade is formed perpendicular to a plane perpendicular to the central axis of the shaft portion. bit. A cylindrical recess is formed coaxially with the central axis of the screw at the bottom surface of the portion where the engagement grooves of the screw drive hole meet.
The drive protrusion includes a columnar protrusion that is formed coaxially with a central axis of the shaft portion and is inserted into the cylindrical recess at a base portion where the engagement blades merge. Item 8. The driver bit according to Item 6 or 7.   9. The driver bit according to claim 8, wherein a protruding amount of the cylindrical protrusion in the central axis direction is smaller than a depth of the cylindrical concave portion of the screw.   The driver bit according to claim 8 or 9, wherein an outer diameter of the columnar protrusion is larger than a width of each engagement groove of the screw.

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