JPWO2011158385A1 - Gear grinding method and processing apparatus - Google Patents

Abstract

A gear grinding method for grinding a gear W having a curved tooth surface S using a machine tool 10 that can be indexed in the direction of a rotational feed axis, and on the tooth surface based on the shape data of the gear W to be ground. A setting procedure for setting the machining point P to the angle, a normal vector vτ extending in a direction perpendicular to the tooth surface S at the machining point P set in the setting procedure, and a rotation of the grindstone 14a attached to the machine tool 10 A calculation procedure for calculating the index data θA, θC so that the axis is parallel to the normal vector vτ, and a control for grinding the gear W by controlling the machine tool 10 based on the index data θA, θC calculated in the calculation procedure. Procedures.

Description

  The present invention relates to a gear grinding method and a machining apparatus for grinding a tooth surface of an involute gear or the like.

Conventionally, when a gear is ground by the rotation of a grindstone attached to an NC machine tool, the gear is moved along with the movement of the machining point along the tooth surface in order to avoid the wear of the grindstone from being concentrated on the outer periphery of the grindstone. On the other hand, a grinding method is known in which the rotational axis of the grindstone is linearly moved to change the length of the leg of the perpendicular line dropped from the rotational axis of the grindstone to the center of the gear (see, for example, Patent Document 1). .
However, in general, since the tooth surface of the gear is formed in a curved shape, the tooth surface at the machining point is configured in the configuration in which the rotational axis of the grindstone is linearly moved with respect to the gear as described in Patent Document 1 above. The contact direction of the grindstone with respect to does not match, and an ideal tooth profile cannot be formed.

JP-A-8-252721

The present invention relates to a gear grinding method for grinding a gear having a curved tooth surface by using a machine tool that can be indexed in the direction of the rotational feed axis, and on the tooth surface based on the shape data of the gear to be ground. The setting procedure for setting the machining point to the vertical axis and the normal vector extending in the direction perpendicular to the tooth surface at the machining point set in the setting procedure are calculated, and the rotation axis of the grindstone attached to the machine tool is the normal vector. A calculation procedure for calculating the index data to be parallel and a control procedure for controlling the machine tool based on the index data calculated by the calculation procedure and grinding the gears are included.
Further, the present invention is a processing apparatus for grinding a gear having a curved tooth surface with a grindstone, the moving means for moving the grindstone relative to the gear in the linear feed axis direction and the rotary feed axis direction, and a grindstone. A machine tool having a driving means for rotational driving; a setting means for setting a machining point on the tooth surface based on shape data of a gear to be ground; and a perpendicular to the tooth surface at the machining point set by the setting means A computing means for computing a normal vector extending in the direction and computing index data such that the rotation axis of the grindstone is parallel to the normal vector, and a machine for controlling the machine tool based on the index data computed by the computing means Control means.

FIG. 1 is a block diagram showing a configuration of a processing apparatus according to an embodiment of the present invention.
FIG. 2 is a side view showing a schematic configuration of the NC machine tool of FIG.
FIG. 3 is a diagram illustrating an example of a workpiece and a tool in a grinding state.
4 is an enlarged view of a main part of FIG.
FIG. 5 is a diagram showing a concept of a grinding process by the grinding apparatus according to the embodiment of the present invention.
6A, 6B, and 6C are views showing the posture of the tool and the position of the spindle at predetermined machining points, respectively.
FIG. 7 is an enlarged view of the main part of the workpiece showing an example of the processing point setting position.
FIG. 8 is a diagram illustrating an example of a tangent vector and a normal vector at a processing point.
FIG. 9 is a diagram showing the machining points before indexing in the machine coordinate system.
FIG. 10 is a diagram showing the processed points after indexing.
FIG. 11 is a diagram for explaining a correction amount calculation method for calculating the position of the spindle.
FIG. 12 is a diagram showing the positional relationship between the indexed machining point and the spindle reference point.

Hereinafter, with reference to FIGS. 1-12, embodiment of the processing apparatus by this invention is described. FIG. 1 is a block diagram showing a configuration of a processing apparatus according to an embodiment of the present invention. This processing apparatus includes a machine tool 10 for grinding a gear, an input device 20 for inputting various information for gear grinding, and a control device 30 for controlling the machine tool 10 based on a signal from the input device 20. Is provided. The control device 30 is calculated by the setting unit 31 for setting the machining point of the gear, the calculation unit 32 for calculating the machining point index data and the spindle position data corresponding to the machining point after the indexing, and the calculation unit 32. A machine control unit 33 for controlling the machine tool 10 based on the index data and spindle position data.
As the machine tool 10, for example, a 5-axis vertical machining center is used. FIG. 2 is a side view illustrating a schematic configuration of the machine tool 10. A column 12 is erected on the bed 11, and a spindle head 13 is supported on the column 12 so as to be movable in the vertical direction (Z-axis direction) and the horizontal direction (Y-axis direction) via a linear feed mechanism. . A grinding tool 14 is attached to the spindle head 13 downward via the spindle, and the tool 14 is rotationally driven by a spindle motor in the spindle head 13. A table base 15 is supported on the bed 11 so as to be movable in the horizontal direction (X-axis direction) via a linear feed mechanism. The linear feed mechanism includes, for example, a ball screw and a servo motor that rotationally drives the ball screw.
An inclination table 16 is attached to the table base 15 so as to be swingable in the A-axis direction around the rotation axis Lx in the X-axis direction via a rotary feed mechanism. A rotation table 17 is attached to the tilt table 16 via a rotation feed mechanism so as to be rotatable about the rotation axis Lz in the Z-axis direction in the C-axis direction, and a work W is fixed on the rotation table 17. The rotary feed mechanism is constituted by, for example, a direct drive motor or a servo motor. FIG. 2 shows a reference state in which the angle θA in the A-axis direction of the tilt table 16 is 0 °, and the angle θC in the C-axis direction of the rotary table 17 is 0 °.
FIG. 3 is a view showing an example of the workpiece W and the tool 14 in a grinding state, and FIG. 4 is an enlarged view of a main part of FIG. In the present embodiment, a bevel gear having a convex curved tooth surface S is used as the workpiece W. This bevel gear is after quenching, and a predetermined amount of grinding allowance is left on the tooth surface S for finishing. The workpiece W has a substantially symmetrical shape with the workpiece rotation axis Lw as the center, and the workpiece W is attached to the rotary table 17 with the workpiece rotation axis Lw aligned with the table rotation axis Lz of FIG.
The tool 14 is a substantially disc-shaped grinding wheel that rotates about the rotation axis L0 of the main shaft, and a substantially annular grinding wheel 14a is provided on the lower peripheral edge of the grinding wheel, and the bottom surface (the grinding surface 14b) of the grinding wheel 14a is It extends in the XY plane orthogonal to the rotation axis L0 of the main shaft. According to the configuration of the machine tool 10 described above, the tool 14 and the workpiece W are relatively movable in the three orthogonal axes (X, Y, Z directions), and around two axes (A, C) orthogonal to each other. Direction). Therefore, the workpiece W can be ground by tilting the abrasive surface 14b of the grindstone 14a three-dimensionally to an arbitrary angle with respect to the tooth surface S of the workpiece W.
FIG. 5 is a diagram showing a concept of a grinding process by the grinding apparatus according to the embodiment of the present invention. In the figure, L1 is a normal line extending in a direction perpendicular to the tooth surface S at the processing point P. In the present embodiment, the indexing angles θA and θC of the rotary feed shafts (A axis and C axis) are adjusted so that the rotation axis L0 of the main shaft is parallel to the normal line L1. Further, the feed amount in the three orthogonal directions is adjusted so that the rotation axis L0 of the main shaft intersects with a tangent line of a tooth profile curve (an involute curve described later) from the tooth root portion to the tooth tip portion of the gear.
FIG. 6 is a diagram showing a change in posture of the rotation axis L0 of the main shaft with respect to the workpiece W as the machining point P moves along the tooth surface S. FIG. Although the inclination of the rotation axis L0 of the main shaft is changed in the figure, the inclination of the rotation axis L0 of the main shaft does not actually change and the inclination of the workpiece W changes. As shown in FIGS. 6A to 6C, as the processing point P moves from the tooth base side to the tooth tip side, the inclination of the normal L1 at the processing point P changes. Following the change in the inclination of the normal L1, the relative posture of the rotation axis L0 of the main shaft with respect to the workpiece W is changed as shown in the figure.
The workpiece W is, for example, an involute gear having a tooth profile formed by an involute curve. The input device 20 shown in FIG. 1 receives workpiece W shape data, tool 14 shape data, and a machining start command for the machine tool 10 necessary for setting an involute curve. For example, the bevel gear module, pitch circle diameter, basic circle diameter, pitch cone angle, radius of the grindstone 14a, width in the radial direction of the grinding surface 14b, and workpiece origin O1 in the workpiece coordinate system and machining in the machine coordinate system Data representing a positional relationship with the origin O2, data representing a distance in the Z direction from the tool mounting portion of the spindle to the grinding surface 14b, and the like are input.
The workpiece origin O1 is set as the starting point of the pitch cone angle of the bevel gear, and workpiece coordinate systems are defined in the X-axis, Y-axis, and Z-axis directions with the workpiece origin O1 as a reference. The machining origin O2 is set on the rotation axis Lz of the turntable 17, and a machine coordinate system is defined in the X-axis, Y-axis, and Z-axis directions with the machining origin O2 as a reference. For this reason, the workpiece origin O1 is located on the Z axis of the machine coordinate system (see FIG. 9), and the input device 20 has a distance H between the two as data representing the positional relationship between the workpiece origin O1 and the machining origin O2. Entered.
The setting unit 31 in FIG. 1 sets a plurality of machining points P along the tooth surface S of the workpiece W based on a signal from the input device 20. The machining point P is set as three-dimensional coordinates (Xa, Ya, Za) in the workpiece coordinate system with the workpiece origin O1 as a reference. FIG. 7 is an enlarged view of the main part of the workpiece W showing an example of the setting position of the processing point P. The processing points P (P1 to P5) are set to only N points (five points in the figure) along each involute curve Ci after a plurality of involute curves Ci (dotted lines) are defined along the tooth trace direction as shown in the figure. To do.
The number N of machining points can be set manually by the user or automatically by the setting unit 31. When the automatic setting is performed, for example, the tangential angles φa and φb with respect to the involute curve Ci at the start point Pa and the end point Pb of the involute curve Ci shown in FIG. N can be calculated by the following formula (I).
N = (φb−φa) / Δφ (I)
The calculation unit 32 calculates machining point data after indexing in the machine coordinate system. In this case, first, as shown in FIG. 8, a unit vector (tangent vector) uτ that is in contact with the involute curve Ci at each machining point P and that is opposite to the rotation center of the workpiece W, and a tooth at each machining point P are used. A unit vector (normal vector) vτ extending in a direction perpendicular to the tooth surface S from the inside of the portion is calculated.
Here, the X, Y, and Z components of the tangent vector uτ are (Xu, Yu, Zu), respectively, and the X, Y, and Z components of the normal vector vτ are (Xv, Yv, Zv), respectively. At this time, these vector components Xu, Yu, Zu, Xv, Yv, Zv use the pitch cone angle of the bevel gear, the tangent angle φ with respect to the involute curve Ci, and the tangential angle with respect to crowning in the tooth trace direction. Each can be calculated.
Next, index angles θA and θC (index data) of the A axis and the C axis are calculated so that the normal vector vτ is parallel to the rotation axis L0 (Z-axis direction) of the main axis. The index angles θA and θC can be calculated by using the components (Xv, Yv, Zv) of the normal vector vτ, for example, by the following equations (II) and (III).
θA = tan ⁻¹ {Zv / (Xv ² + Yv ² ) ^1/2 } −π / 2 (II)
θC = −tan ⁻¹ (Xv / Yv) (III)
After indexing the A axis and the C axis, the rotation axis L0 of the main axis and the normal vector vτ are parallel, and the tangent vector uτ exists on the XY plane of the machine coordinate system. At this time, assuming that the angle formed between the tangent vector uτ after indexing and the X axis is θR, the angle θR is calculated by using the Z component (Zu) of the tangent vector uτ and the index angle θA, for example, by the following equation (IV). can do.
θR = sin ⁻¹ (Zu / sin θA) (IV)
Further, based on the position coordinates (Xa, Ya, Za) of the machining point P before indexing in the workpiece coordinate system and the index angles θA, θC of the A axis and C axis, in the machine coordinate system after indexing of the machining point P. Calculate position coordinates. FIG. 9 is a diagram showing the machining point P before indexing in the machine coordinate system. When the distance between the workpiece origin O1 and the machining origin O is H, the position coordinates (X0, Y0, Z0) of the machining point P before indexing in the machine coordinate system can be expressed by the following equation (V).
(X0, Y0, Z0) = (Xa, Ya, H-Za) (V)
This processing point P is determined by the index angles θA and θC of the above formulas (II) and (III). FIG. 10 shows a machining point Pm obtained by indexing the machining point P with the indexing angle θA and a machining point Pn obtained by further indexing the machining point Pm with the indexing angle θC. The position coordinates (Xm, Ym, Zm) of the machining point Pm and the position coordinates (Xn, Yn, Zn) of the machining point Pn can be calculated by the following equations (VI) and (VII), respectively.
Xm = (X0 ² + Y0 ² ) ^1/2 cos {tan ⁻¹ (Y0 / X0) −θC}
Ym = (X0 ² + Y0 ² ) ^1/2 sin {tan ⁻¹ (Y0 / X0) −θC}
Zm = Z0 (VI)
Xn = Xm
Yn = − (Ym ² + Zm ² ) ^1/2 cos {tan ⁻¹ (Ym / Zm) −θA}
Zn = (Ym ² + Zm ² ) ^1/2 sin {tan ⁻¹ (Ym / Zm) −θA}
(VII)
As described above, the calculation unit 32 calculates the machining point data after the indexing of the machining point P in the machine coordinate system, that is, the position of the machining point Pn after the indexing such that the normal vector vτ is parallel to the rotation axis L0 of the main shaft. Coordinates (Xn, Yn, Zn) are calculated.
Further, the calculation unit 32 calculates the position of the spindle such that the grinding surface 14b of the grindstone 14a contacts the machining point Pn after indexing. That is, since the grindstone 14a is located away from the center axis of the tool 14 (the rotation axis L0 of the main shaft), the distance W from the rotation axis L0 of the main shaft to the machining point Pn is calculated as a correction amount. In this case, the correction amount W is calculated so that the contact portion between the grindstone 14a and the tooth surface S does not concentrate on a part of the abrasive surface 14b in the radial direction but covers the entire radial direction of the abrasive surface 14b.
FIG. 11 is a diagram for explaining a method of calculating the correction amount W. In the figure, Ta and Tb are a point at the outermost diameter (machining start point) and a point at the innermost inner diameter (machining end point) of the grindstone 14a, respectively, Pa is a tooth root point that is the starting point of the involute curve Ci, Pb Is the point of the tooth tip that is the end point of the involute curve Ci. In the figure, WL is equivalent to the radial length of the grinding surface 14b, WR is equivalent to the radius of the grinding wheel, and Pw is the rotation axis L0 of the main shaft set on the same plane as the grinding surface 14b. Corresponds to the upper reference point. When the number N of machining points along the involute curve Ci calculated by the above equation (I) is used, the grindstone correction amount ΔW when the machining point P moves by one point can be calculated by the following equation (VIII).
ΔW = WL / N (VIII)
Therefore, the correction amount Wn from the machining start point Ta when the angle of the tangent to the involute curve Ci is φn is expressed by the following equation (IX).
Wn = ΔW · (φn−φa) / Δφ (IX)
The computing unit 32 computes the correction amount W from the rotation axis L0 of the main shaft by the following formula (X) using the relationship of the above formula (IX).
W = WR-Wn
= WR-WL. (Φn-φa) / (φb-φa) (X)
Using the correction amount W obtained as described above, the calculation unit 32 calculates the position of the reference point Pw. FIG. 12 is a diagram showing a positional relationship between the processed point Pn after indexing and the reference point Pw. The reference point Pw is set at a position away from the machining point Pn by the correction amount W on the extension line of the tangent vector uτ, using the angle θR formed by the tangent vector uτ calculated by the above formula (IV) and the X axis. The At this time, the position coordinates (XL0, YL0, ZL0) of the reference point Pw of the main axis can be calculated by the following equation (XI).
XL0 = Xn + WcosθR
YL0 = Yn + WsinθR
ZL0 = Zn (XI)
The control device 30 creates an NC program based on the data calculated by the calculation unit 32 and stores the NC program in the memory.
The machine control unit 33 receives the machining start command from the input device 20 and executes the NC program. The machining point P index data (θA, θC) calculated by the calculation unit 32 and the position of the machining point Pn after the indexing are calculated. The machine tool 10 is controlled based on the data (Xn, Yn, Zn) and the position data (XL0, YL0, ZL0) of the reference point Pw separated from the machining point Pn by the correction amount W. That is, a control signal is output to the servo motor of the rotary feed mechanism to determine the machining point P, and a control signal is output to the servo motor of the linear feed mechanism to control the relative position of the spindle with respect to the workpiece W.
As a result, the normal line L1 perpendicular to the tooth surface S at the machining point P and the rotation axis L0 of the main shaft are parallel to each other, and the grindstone 14a can be brought into contact with the tooth surface S in the direction perpendicular to the entire tooth surface S. For this reason, the contact direction of the grindstone 14a with respect to the tooth surface S is constant during grinding, the contact force of the grindstone 14a can be kept constant, and variations in machining accuracy can be suppressed. Further, since the grindstone 14a contacts the tooth surface S in the vertical direction, the contact force of the grindstone 14a can be prevented from being dispersed, and the contact force acting on the tooth surface S can be increased. As a result, the workpiece W can be efficiently ground, and the machining efficiency of the workpiece W can be increased.
At the time of grinding, the machining location is changed along the involute curve Ci. For example, the machining points are moved in the order of P1, P2,. At this time, the correction amount W between the machining point P and the rotation axis L0 of the main shaft changes according to the movement of the machining point P. That is, the correction amount W increases when the tooth base side is ground, and the correction amount W decreases when the tooth tip side is ground. For this reason, when grinding the tooth base side, the outer diameter side of the grinding surface 14b is in contact with the tooth surface S, and when grinding the tooth tip side, the inner diameter side of the grinding surface 14b is in contact with the tooth surface S. Thereby, the whole area of the grinding surface 14b can be used for grinding, the grinding wheel 14a is evenly worn, and the service life of the grinding wheel 14a can be extended.
Thus, when the contact position of the grindstone 14a changes over the radial direction of the grinding surface 14b, if the rotation speed of the main shaft is constant, the peripheral speed of the grindstone 14a at the processing point P increases as the diameter of the grindstone 14a increases. Get faster. That is, when grinding the tooth base side, since the diameter of the grindstone 14a is large, the peripheral speed of the grindstone 14a is faster than when grinding the tooth tip side. In order to avoid this, it is preferable that the machine control unit 33 controls the rotational speed of the spindle (spindle motor) so that the peripheral speed of the grindstone 14a at the processing point P is constant. Specifically, when processing the tooth base side, the rotational speed of the grindstone 14a is made slower than when processing the tooth tip side. Thereby, the dispersion | variation in the processing precision by the difference in the peripheral speed of the grindstone 14a can be suppressed, and the workpiece | work W can be ground with high precision, using the whole region of the grinding surface 14b.
In summary, in the gear grinding method according to the present embodiment, the setting unit 31 of the control device 30 sets a plurality of processing points P along the tooth surface of the workpiece W in the workpiece coordinate system (setting procedure). ), The calculation unit 32 calculates a normal vector vτ extending in a direction perpendicular to the tooth surface S at the machining point P, and the rotation axis of the grindstone 14a (the rotation axis L0 of the main shaft) is parallel to the normal vector vτ. The calculation data in the machine coordinate system is calculated (calculation procedure). Further, the position of the spindle is calculated so that the grindstone 14a contacts the machining point Pn after the indexing (calculation procedure), and the machine control unit 33 controls the machine tool 10 based on the calculated index data and spindle position data. Control (control procedure). Thereby, the grindstone 14a contacts the tooth surface S in the vertical direction, the contact force of the grindstone 14a acting on the machining point P can be made constant, and variations in machining accuracy can be suppressed.
Further, in the calculation unit 32, a position on the extension line of the tangent vector uτ at the machining point Pn after the index and separated from the machining point Pn by the correction amount W according to the diameter of the grindstone 14a is the position of the rotation axis L0 of the main shaft. Therefore, the grindstone 14a can be prevented from coming into contact with the workpiece W except at the machining point P, and the contact position of the grindstone 14a can be changed smoothly with the movement of the machining point P. Further, in the calculation unit 32, as the machining location changes along the tooth profile of the workpiece W, the correction amount W corresponding to the diameter of the grindstone 14a is changed and the spindle position data is calculated. The entire area of 14b can be used for grinding, and the grindstone 14a can be used without waste. In addition to this, the machine control unit 33 controls the rotation speed of the main shaft so that the rotation speed of the grindstone 14a becomes slower as the distance from the processing point P to the rotation axis L0 of the grindstone 14a becomes larger. Variations in machining accuracy due to differences in speed can be suppressed.
In the above-described embodiment, a 5-axis machining center capable of rotating and feeding in the A-axis direction and the C-axis direction is used as the machine tool 10, but the grindstone 14 a is moved with respect to the workpiece W in the linear feed axis direction and the rotary feed axis direction. As long as the relative movement is possible, the machine tool may have any configuration. For example, a 6-axis machining center or a machine tool other than the machining center may be used. In the setting unit 31 of the control device 30, the machining point P is set on the tooth surface based on the signal from the input device 20, but the configuration of the setting means is not limited to this, for example, CL data generated by CAM The processing point P may be set based on (cutter location data).
In the grinding method according to the present invention, the normal vector vτ extending in the direction perpendicular to the tooth surface S at the processing point P is calculated, and the index data θA is set so that the rotation axis of the grindstone 14a is parallel to the normal vector vτ. , ΘC is calculated, and the machine tool is controlled based on the index data. The calculation unit 32 as the calculation unit and the machine as the machine control unit are provided as long as this feature can be realized. The configuration of the control unit 33 is not limited to that described above. The shape of the grindstone 14a may be other than a substantially disk shape.
Although the case where the bevel gear is ground has been described above, the grinding method according to the present invention can be similarly applied to the case where other gears (for example, spur gears) are ground.
According to the present invention, since the rotation axis of the grindstone for grinding the tooth surface is parallel to the normal vector at the machining point, the contact force of the grindstone with respect to the tooth surface at the machining point becomes constant, resulting in variations in machining accuracy. Can be suppressed.

DESCRIPTION OF SYMBOLS 10 Machine tool 14a Grinding wheel 30 Control apparatus 31 Setting part 32 Calculation part 33 Machine control part

Claims (5)

A gear grinding method for grinding a gear having a curved tooth surface using a machine tool that can be indexed in the rotational feed axis direction,
A setting procedure for setting a processing point on the tooth surface based on the shape data of the gear to be ground;
The normal vector extending in the direction perpendicular to the tooth surface at the machining point set in the setting procedure is calculated, and the rotation axis of the grindstone attached to the machine tool is determined to be parallel to the normal vector. Calculation procedure for calculating data,
And a control procedure for controlling the machine tool based on the index data calculated by the calculation procedure and grinding the gear. The gear grinding method according to claim 1,
In the calculation procedure, the rotation axis of the grindstone further intersects the tangent line of the tooth profile curve from the tooth root part to the tooth tip part of the gear at the machining point, and is opposite to the rotation center of the gear from the machining point. Calculating the position data of the rotation axis of the grindstone that is located at a distance according to the diameter of the grindstone,
In the control procedure, a gear grinding method for controlling the machine tool based on the index data calculated in the calculation procedure and the position data of the rotation axis of the grindstone. In the gear grinding method according to claim 2,
In the calculation procedure, as the machining position of the gear changes between the tooth root part and the tooth tip part, the distance between the machining point and the rotation axis of the grindstone is changed so that the distance between the machining point and the rotation axis of the grindstone changes. A gear grinding method that calculates position data. In the gear grinding method according to claim 3,
In the control procedure, a gear grinding method of controlling the machine tool so that the rotation speed of the grindstone becomes slower as the distance from the machining point to the rotation axis of the grindstone increases. A grinding device for grinding a gear having a curved tooth surface with a rotating grindstone,
A machine tool capable of moving the grindstone relative to the gear in a linear feed axis direction and a rotary feed axis direction;
Setting means for setting a processing point on the tooth surface based on shape data of the gear to be ground;
Calculation for calculating a normal vector extending in a direction perpendicular to the tooth surface at the machining point set by the setting means and calculating index data such that the rotation axis of the grindstone is parallel to the normal vector Means,
A gear grinding apparatus comprising: machine control means for controlling the machine tool based on the index data calculated by the calculation means.

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