Die guide of wire electrical discharge machine

Abstract

A die guide (28) for a wire electrical discharge machining machine (10) comprises: a first guide section (44) that has a first hole (56) that is larger than the cross-sectional area of a wire electrode; and a second guide section (48) that has a second hole (62) that is larger than the cross-sectional area of the wire electrode. The first hole is formed in the first guide section so as to restrict the movement of the wire electrode in a first direction that is orthogonal to a feed direction. A second hole is formed in the second guide section so as to restrict movement in a second direction that is orthogonal to the feed direction and is on the opposite side to the first direction, by being in contact with the wire electrode at at least two points in a cross-section that is orthogonal to the feed direction.

Description

Technical Field

[0001] The present invention relates to a die guide of a wire electrical discharge machining machine.

Background Art

[0002] Japanese Patent Laid-Open No. 2000-5935 discloses a die guide of a wire electrical discharge machining machine. In a wire electrical discharge machining machine, a pair of die guides are arranged above and below a workpiece to be machined. A hole through which a wire electrode passes is formed in the die guide. The upper die guide supports the wire electrode sent from the wire feeding section to the workpiece to be machined. The lower die guide supports the wire electrode sent from the workpiece to be machined to the wire recovery section.

Summary of the Invention

[0003] In a wire electrical discharge machining machine, cutting of a wire electrode and connection of the wire electrode are performed. The tip of the cut wire electrode may be thicker than the diameter of the wire electrode. For this reason, it becomes difficult for the tip of the wire electrode to pass through the hole of the die guide.

[0004] When the hole of the die guide is large, it is relatively easy to insert the tip of the wire electrode into the hole. However, when the hole of the die guide is large, the wire electrode easily moves in a direction orthogonal to the feeding direction of the wire electrode inside the hole of the die guide. For this reason, the positioning accuracy of the wire electrode in a plane orthogonal to the feeding direction of the wire electrode decreases. As a result, the accuracy of wire electrical discharge machining decreases.

[0005] An object of the present invention is to solve the above-described problems.

[0006] Aspects of the present invention relate to a die guide of a wire electrical discharge machining machine that supports a wire electrode so as to be capable of being fed in the feeding direction of the wire electrode, including a first guide portion having a first hole through which the wire electrode passes and that is larger than the cross-sectional area of the wire electrode, and a second guide portion having a second hole through which the wire electrode passes and that is larger than the cross-sectional area of the wire electrode. The first hole is formed in the first guide portion so as to restrict movement of the wire electrode in a first direction orthogonal to the feeding direction, and the second hole is formed in the second guide portion so as to restrict movement of the wire electrode in a second direction orthogonal to the feeding direction and opposite to the first direction by contacting the wire electrode at at least two points in a cross-section orthogonal to the feeding direction.

[0007] According to the present invention, it becomes easier to insert the wire electrode into the die guide, and displacement of the wire electrode can be reduced. As a result, it is possible to suppress a decrease in the accuracy of wire electrical discharge machining.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0009] [1 First Embodiment] FIG. 1 is a diagram schematically showing a partial configuration of a wire electrical discharge machining machine 10. In the embodiments described below, for convenience of explanation, the vertical direction is defined. Specifically, at the position of the workpiece 12 to be machined by the wire electrical discharge machining machine 10, the feeding direction of the wire electrode 14 is downward. However, the feeding direction of the wire electrode 14 does not have to be downward.

[0010] The wire electrical discharge machining machine 10 machines the workpiece 12 by generating a discharge between the wire electrode 14 and the workpiece 12 (between the electrodes). The wire electrical discharge machining machine 10 includes a wire electrode 14, a table 16, a wire feeding unit 18, a wire recovery unit 20, a voltage supply unit 22, a drive unit 24, a control device 25, and a pair of wire guides 26.

[0011] The wire electrode 14 is formed in a linear shape. The table 16 supports the workpiece 12. The wire electrode 14 is movable in the X direction and the Y direction. The X direction and the Y direction are perpendicular to each other and perpendicular to the vertical direction. Further, the wire electrode 14 can be inclined with respect to the table 16. Note that instead of the wire electrode 14, the table 16 may be movable and tiltable. Also, both the wire electrode 14 and the table 16 may be movable and tiltable.

[0012] The wire feeding unit 18 feeds the wire electrode 14 toward the workpiece 12 on the table 16. The wire feeding unit 18 includes a roller for feeding the wire electrode 14 wound around a wire bobbin toward the workpiece 12, a motor for driving the roller, and the like. The wire recovery unit 20 recovers the wire electrode 14 from the workpiece 12 on the table 16. The wire recovery unit 20 includes a roller for recovering the wire electrode 14, a motor for driving the roller, and the like.

[0013] The voltage supply unit 22 supplies a pulse voltage between the wire electrode 14 and the workpiece 12 on the table 16. The voltage supply unit 22 has pulse power supplies connected to the wire electrode 14 and the table 16 respectively. The drive unit 24 drives each of the table 16, the upper wire guide 26-1, and the lower wire guide 26-2 individually. The drive unit 24 has a plurality of motors and a plurality of power transmission mechanisms.

[0014] The control device 25 controls the voltage supply unit 22 according to a machining program. Specifically, the control device 25 controls the pulse power supply of the voltage supply unit 22 to cause a discharge between the wire electrode 14 and the workpiece 12. Also, the control device 25 controls the drive unit 24 according to the machining program. Specifically, the control device 25 controls the drive unit 24 so that at least one of the table 16 and the two die guides 28 is driven based on the machine coordinate system. Further, the control device 25 controls the drive unit 24 so that the motors of the wire feeding unit 18 and the wire collecting unit 20 are driven.

[0015] The pair of wire guides 26 includes an upper wire guide 26-1 and a lower wire guide 26-2. The upper wire guide 26-1 and the workpiece 12 are relatively movable in the X and Y directions. The upper wire guide 26-1 is located between the wire feeding unit 18 and the workpiece 12. The lower wire guide 26-2 and the workpiece 12 are relatively movable in the X and Y directions. The lower wire guide 26-2 is located between the workpiece 12 and the wire collecting unit 20.

[0016] Each wire guide 26 has a die guide 28. The die guide 28 of the upper wire guide 26-1 is also referred to as the die guide 28-1. The die guide 28 of the lower wire guide 26-2 is also referred to as the die guide 28-2. The die guide 28-1 is held at a predetermined position within the upper wire guide 26-1 by a guide block (not shown). The die guide 28-2 is held at a predetermined position within the lower wire guide 26-2 by a guide block (not shown).

[0017] FIG. 2 is an enlarged cross-sectional view of the tip 34 of the die guide 28-1 according to the first embodiment. The die guide 28-1 has a guide body 30 and a wire insertion hole 32 formed in the guide body 30. The tip 34 of the die guide 28-1 is located at the position closest to the object to be processed 12 (the lower side in FIG. 2) among the die guide 28-1.

[0018] The wire insertion hole 32 penetrates the guide body 30 in the vertical direction. The wire electrode 14 is inserted into the wire insertion hole 32 from above. A guide portion 40 is accommodated in the wire insertion hole 32 located at the tip 34.

[0019] The guide portion 40 guides the wire electrode 14 in the feeding direction of the wire electrode 14. The guide portion 40 supports the wire electrode 14 so as to be able to be fed in the feeding direction of the wire electrode 14. Further, the guide portion 40 restricts the movement of the wire electrode 14 in a direction orthogonal to the feeding direction of the wire electrode 14.

[0020] The guide portion 40 has a first auxiliary member 42, a first guide portion 44, a second auxiliary member 46, a second guide portion 48, a tapered guide portion 50, and a third auxiliary member 52. Each of the first auxiliary member 42, the second auxiliary member 46, and the third auxiliary member 52 is made of, for example, ceramics. Each of the first guide portion 44, the second guide portion 48, and the tapered guide portion 50 is made of, for example, diamond.

[0021] The first auxiliary member 42 is located at the uppermost part of the guide part 40. The first guide part 44 is located below the first auxiliary member 42. The upper surface of the first guide part 44 abuts against the lower surface of the first auxiliary member 42. The second auxiliary member 46 is located below the first guide part 44. The upper surface of the second auxiliary member 46 abuts against the lower surface of the first guide part 44. The second guide part 48 is located below the second auxiliary member 46. The upper surface of the second guide part 48 abuts against the lower surface of the second auxiliary member 46. The tapered guide part 50 is located below the second guide part 48. The upper surface of the tapered guide part 50 abuts against the lower surface of the second guide part 48. The third auxiliary member 52 is located below the tapered guide part 50. The upper surface of the third auxiliary member 52 abuts against the lower surface of the tapered guide part 50. The third auxiliary member 52 is located at the lowermost part of the guide part 40.

[0022] The first auxiliary member 42 has a first auxiliary hole 54 that penetrates in the vertical direction. The first auxiliary hole 54 communicates with the upper wire insertion hole 32.

[0023] The first guide part 44 has a first hole 56 that penetrates in the vertical direction. A first throttling part 58 is formed between the upper opening and the lower opening of the first hole 56. The diameter of the first hole 56 becomes smaller from the upper opening of the first hole 56 toward the first throttling part 58. Also, the diameter of the first hole 56 becomes larger from the first throttling part 58 toward the lower opening of the first hole 56. That is, the diameter of the first throttling part 58 is the smallest among the diameters of the first hole 56. The first hole 56 communicates with the first auxiliary hole 54. The diameter of the upper opening of the first hole 56 is equal to or larger than the diameter of the lower opening of the first auxiliary hole 54. For this reason, it is easy to insert the wire electrode 14 into the first hole 56 from above.

[0024] The second auxiliary member 46 has a second auxiliary hole 60 that penetrates in the vertical direction. The second auxiliary hole 60 communicates with the first hole 56.

[0025] The second guide part 48 has a second hole 62 that penetrates in the vertical direction. The diameter of the second hole 62 becomes smaller as it goes downward. The diameter of the second hole 62 may be substantially constant at the lower part of the second guide part 48. The diameter of the second hole 62 may become larger as it goes downward at the lower part of the second guide part 48. The portion with the minimum diameter in the second hole 62 is referred to as the second throttling part 64. The second hole 62 communicates with the second auxiliary hole 60. The diameter of the upper opening of the second hole 62 is equal to or larger than the diameter of the lower opening of the second auxiliary hole 60. Therefore, it is easy to insert the wire electrode 14 into the second hole 62 from above.

[0026] The tapered guide part 50 has a tapered guide hole 66 that penetrates in the vertical direction. The tapered guide part 50 regulates the inclination angle of the wire electrode 14 during the taper processing. A third throttling part 68 is formed between the upper opening of the tapered guide hole 66 and the lower opening of the tapered guide hole 66. The diameter of the tapered guide hole 66 becomes smaller as it goes from the upper opening of the tapered guide hole 66 toward the third throttling part 68. Also, the diameter of the tapered guide hole 66 becomes larger as it goes from the third throttling part 68 toward the lower opening of the tapered guide hole 66. That is, the diameter of the third throttling part 68 is the smallest among the diameters of the tapered guide hole 66. The tapered guide hole 66 communicates with the second hole 62. The diameter of the upper opening of the tapered guide hole 66 is equal to or larger than the diameter of the lower opening of the second hole 62. Therefore, it is easy to insert the wire electrode 14 into the tapered guide hole 66 from above.

[0027] The third auxiliary member 52 has a third auxiliary hole 70 that penetrates in the vertical direction. The third auxiliary hole 70 communicates with the tapered guide hole 66.

[0028] In the die guide 28-1 of the upper wire guide 26-1, the wire electrode 14 passes through the first auxiliary hole 54, the first hole 56, the second auxiliary hole 60, the second hole 62, the tapered guide hole 66, and the third auxiliary hole 70 in this order. The feeding direction of the wire electrode 14 substantially coincides with the downward direction.

[0029] FIG. 3 is a diagram showing the relationship between the wire electrode 14 and the first guide portion 44 and the second guide portion 48. FIG. 4A is a diagram showing a cross section taken along line IVA-IVA in FIG. 3. FIG. 4B is a diagram showing a cross section taken along line IVB-IVB in FIG. 3. Hereinafter, the "feeding direction of the wire electrode 14" is simply referred to as the "feeding direction". In FIG. 3, the feeding direction is downward. Here, the directions orthogonal to the feeding direction are defined as the first direction, the second direction, the third direction, and the fourth direction. The second direction is the opposite direction of the first direction. The third direction is the opposite direction of the fourth direction. The first direction and the second direction are orthogonal to the third direction and the fourth direction.

[0030] As shown in FIG. 4A, the cross-sectional area of the first constriction portion 58 is larger than the cross-sectional area of the wire electrode 14. In the present embodiment, the cross-sectional shape of the first constriction portion 58 is circular. That is, the diameter of the cross section of the first constriction portion 58 is larger than the diameter of the cross section of the wire electrode 14. For example, it is preferable that the diameter of the first constriction portion 58 is twice or more the diameter of the wire electrode 14. However, if the wire electrode 14 can easily pass through the first constriction portion 58, the diameter of the first constriction portion 58 may be larger than the diameter of the wire electrode 14 and less than twice the diameter of the wire electrode 14. Around the first constriction portion 58, the first inner peripheral surface 74 of the first guide portion 44 is located. In a cross section orthogonal to the feeding direction, the first inner peripheral surface 74 and the outer peripheral surface 72 of the wire electrode 14 are in contact at one point. This point is referred to as the first contact point 76. Note that the cross-sectional shape of the first constriction portion 58 may be an annular shape. Therefore, the cross-sectional shape of the first constriction portion 58 may be an elliptical shape.

[0031] As shown in FIG. 4B, the cross-sectional area of the second aperture portion 64 is larger than the cross-sectional area of the wire electrode 14. For example, the cross-sectional shape of the second aperture portion 64 is such that the hole becomes narrower as it goes in the second direction. For example, it is preferable that the length of the second aperture portion 64 in the second direction is twice or more the diameter of the wire electrode 14. However, if the wire electrode 14 can easily pass through the second aperture portion 64, the length of the second aperture portion 64 in the second direction may be larger than the diameter of the wire electrode 14 and less than twice the diameter of the wire electrode 14. Around the second aperture portion 64, the second inner peripheral surface 78 of the second guide portion 48 is located. In a cross-section orthogonal to the feeding direction, the second inner peripheral surface 78 and the outer peripheral surface 72 of the wire electrode 14 are in contact at two points. These two points are referred to as second contact points 80-1 and 80-2.

[0032] Here, regarding the positions of the respective contact points, an explanation will be given using the tangent line 82 of the wire electrode 14 at the first contact point 76, the virtual line 84, and the normal line 86 of the wire electrode 14 at the first contact point 76. The tangent line 82 extends along a cross-section orthogonal to the feeding direction. The virtual line 84 is parallel to the tangent line 82 and passes through the position of the diameter center 88 of the wire electrode 14. The normal line 86 extends along a cross-section orthogonal to the feeding direction. Of the outer peripheral surface 72 of the wire electrode 14, the outer peripheral surface 72 located in the first direction with respect to the virtual line 84 is referred to as the first outer peripheral surface 72-1. Of the outer peripheral surface 72 of the wire electrode 14, the outer peripheral surface 72 located in the second direction with respect to the virtual line 84 is referred to as the second outer peripheral surface 72-2.

[0033] The first contact point 76 is located on the first outer peripheral surface 72-1. Each of the second contact point 80-1 and the second contact point 80-2 is located on the second outer peripheral surface 72-2. Further, the second contact point 80-1 is located in the third direction with respect to the normal line 86. The second contact point 80-2 is located in the fourth direction with respect to the normal line 86. That is, with respect to the line direction of the virtual line 84, the first contact point 76 is located between the second contact point 80-1 and the second contact point 80-2.

[0034] With respect to the line direction of the normal line 86, the position of the diameter center 88 of the wire electrode 14 in the second throttle portion 64 is displaced with respect to the position of the diameter center 88 of the wire electrode 14 in the first throttle portion 58. For example, the position of the diameter center 88 of the wire electrode 14 in the first throttle portion 58 and the position of the diameter center 88 of the wire electrode 14 in the second throttle portion 64 are separated by a distance D.

[0035] The first guide portion 44 regulates the movement of the wire electrode 14 in the first direction by contacting the wire electrode 14 at the first contact point 76. The second guide portion 48 regulates the movement of the wire electrode 14 in the second direction by contacting the wire electrode 14 at the two second contact points 80-1 and 80-2. Further, the second guide portion 48 regulates the movement of the wire electrode 14 in the third direction by contacting the wire electrode 14 at the second contact point 80-1. Further, the second guide portion 48 regulates the movement of the wire electrode 14 in the fourth direction by contacting the wire electrode 14 at the second contact point 80-2. In this way, each of the first guide portion 44 and the second guide portion 48 reduces the displacement of the wire electrode 14.

[0036] Among the first holes 56, the cross-sectional area of the smallest first throttle portion 58 is larger than the cross-sectional area of the wire electrode 14. Among the second holes 62, the cross-sectional area of the smallest second throttle portion 64 is larger than the cross-sectional area of the wire electrode 14. Among the tapered guide holes 66, the cross-sectional area of the smallest third throttle portion 68 is larger than the cross-sectional area of the wire electrode 14. Also, the cross-sectional area of the smallest portion of the first auxiliary hole 54, the cross-sectional area of the smallest portion of the second auxiliary hole 60, and the cross-sectional area of the smallest portion of the third auxiliary hole 70 are each larger than the cross-sectional area of the wire electrode 14. Therefore, the wire electrode 14 can easily pass through each hole.

[0037] Note that the die guide 28-2 of the lower wire guide 26-2 also includes a first auxiliary member 42, a first guide portion 44, a second auxiliary member 46, a second guide portion 48, a tapered guide portion 50, and a third auxiliary member 52. The shape of the die guide 28-2 of the lower wire guide 26-2 is slightly different from the shape of the die guide 28-1 of the upper wire guide 26-1. Also, the shapes of the respective guide portions 40 are different. However, both die guides 28 are common in that the first guide portion 44 contacts the wire electrode 14 at one point and the second guide portion 48 contacts the wire electrode 14 at two points.

[0038] [2 Second Embodiment] FIG. 5 is an enlarged cross-sectional view of the tip portion 34 of the die guide 28-1 according to the second embodiment. The guide portion 40 of the second embodiment does not have a tapered guide portion 50. Except for the absence of the tapered guide portion 50, the die guide 28-1 of the second embodiment is the same as the die guide 28-1 of the first embodiment. The same applies to the die guide 28-2.

[0039] [3 Other Embodiments] Three auxiliary members are provided in the guide portion 40 of the first embodiment. However, the number and shape of the auxiliary members provided in the guide portion 40 are not limited.

[0040] In addition to the first guide portion 44 and the second guide portion 48, the guide portion 40 may have one or more members that restrict the movement of the wire electrode 14.

[0041] In the guide portion 40, the second guide portion 48 may be provided at the position of the first guide portion 44, and the first guide portion 44 may be provided at the position of the second guide portion 48.

[0042] In the second constriction portion 64, the second inner peripheral surface 78 may contact the wire electrode 14 at three or more points.

[0043] In a cross-section orthogonal to the feeding direction, the peripheral portions of the second contact points 80-1 and 80-2 that contact the wire electrode 14 may be linear or curved.

[0044] The above-described embodiments may be combined with each other.

[0045] [Invention Obtained from Embodiment 4] The invention that can be grasped from the above embodiments will be described below.

[0046] An aspect of the present invention is a die guide (28) of a wire electrical discharge machining machine (10) that supports a wire electrode (14) so as to be capable of being fed in the feeding direction of the wire electrode, the wire electrode passes through, and a first guide portion (44) having a first hole (56) larger than the cross-sectional area of the wire electrode, and the wire electrode passes through, and a second guide portion (48) having a second hole (62) larger than the cross-sectional area of the wire electrode, the first hole is formed in the first guide portion so as to restrict the movement of the wire electrode in a first direction orthogonal to the feeding direction, and the second hole is formed in the second guide portion so as to restrict the movement in a second direction orthogonal to the feeding direction and opposite to the first direction by contacting the wire electrode at at least two points in a cross section orthogonal to the feeding direction.

[0047] In the present invention, the first hole restricts the movement in the first direction by contacting the wire electrode at one point in a cross section orthogonal to the feeding direction, and is parallel to a tangent line (82) of the wire electrode at a first contact point (76) where the wire electrode contacts the first hole in a cross section orthogonal to the feeding direction, and a virtual line (84) passing through the diameter center position of the wire electrode, and the second hole may contact the wire electrode at at least two points on a semi-peripheral surface (72-2) of the wire electrode on the side opposite to the first contact point.

[0048] In the present invention, with respect to the line direction of the virtual line, the first contact point may be located between two second contact points (80-1, 80-2) where the second hole contacts the wire electrode.

[0049] In the present invention, in a cross section orthogonal to the feeding direction, the first hole may be circular.

[0050] In the present invention, in a cross-section orthogonal to the feeding direction, the second hole may have a shape in which the hole becomes narrower as it goes in the second direction.

[0051] In the present invention, in a cross-section orthogonal to the feeding direction, with respect to the line direction of the normal line (86) of the wire electrode at the first contact point, the diameter center position (88) of the wire electrode in the second hole may be offset with respect to the diameter center position (88) of the wire electrode in the first hole.

[0052] In the present invention, a tapered guide portion (50) may be provided closer to the workpiece (12) to be machined by the wire electrical discharge machine than the first guide portion and the second guide portion.

Explanation of reference numerals

[0053] 10... Wire electrical discharge machine 12... Workpiece 14... Wire electrode 28... Die guide 44... First guide portion 48... Second guide portion 50... Tapered guide portion 56... First hole 62... Second hole 72-2... Second outer peripheral surface (half peripheral surface) 76... First contact point 80-1, 80-2... Second contact points 82... Tangent line 84... Virtual line 86... Normal line 88... Diameter center (diameter center position)

Claims

1. A die guide of a wire electrical discharge machining machine that supports the wire electrode so as to be capable of being fed in the feeding direction of the wire electrode, a first guide portion having a first hole through which the wire electrode passes and having a cross-sectional area larger than that of the wire electrode, a second guide portion having a second hole through which the wire electrode passes and having a cross-sectional area larger than that of the wire electrode, comprising: the second guide portion is located on the tip side of the die guide relative to the first guide portion, the first hole is formed in the first guide portion so as to restrict movement of the wire electrode in a first direction orthogonal to the feeding direction, the second hole is formed in the second guide portion so as to restrict movement in a second direction orthogonal to the feeding direction and opposite to the first direction by contacting the wire electrode at at least two points in a cross-section orthogonal to the feeding direction, further comprising a taper guide portion that is located closer to a workpiece to be machined by a wire electrical discharge machining machine than the first guide portion and the second guide portion and restricts the inclination angle of the wire electrode during taper machining, the taper guide portion has a taper guide hole that penetrates along the feeding direction and through which the wire electrode passes, a throttle portion is formed between a first opening that is one opening of the taper guide hole and a second opening that is the other opening, A die guide of a wire electrical discharge machining machine, wherein the diameter of the taper guide hole becomes smaller from the first opening toward the throttle portion and becomes larger from the throttle portion toward the second opening.

2. The die guide of the wire electrical discharge machining machine according to claim 1, the first hole restricts movement in the first direction by contacting the wire electrode at one point in a cross-section orthogonal to the feeding direction, In a cross-section orthogonal to the feeding direction, the second hole contacts the wire electrode at at least two points on the semi-peripheral surface of the wire electrode on the side opposite to the first contact point, with respect to a virtual line that is parallel to the tangent line of the wire electrode at the first contact point where the wire electrode contacts the first hole and passes through the center position of the diameter of the wire electrode. The second hole is a die guide of a wire electrical discharge machining machine that contacts the wire electrode.

3. A die guide of a wire electrical discharge machining machine according to claim 2, A die guide of a wire electrical discharge machining machine, wherein the first contact point is located between two second contact points where the second hole contacts the wire electrode, with respect to the line direction of the virtual line.

4. A die guide of a wire electrical discharge machining machine according to any one of claims 1 to 3, A die guide of a wire electrical discharge machining machine, wherein in a cross-section orthogonal to the feeding direction, the first hole is circular.

5. A die guide of a wire electrical discharge machining machine according to any one of claims 1 to 4, A die guide of a wire electrical discharge machining machine, wherein in a cross-section orthogonal to the feeding direction, the second hole has a shape in which the hole becomes narrower as it goes in the second direction.

6. A die guide of a wire electrical discharge machining machine according to claim 2, A die guide of a wire electrical discharge machining machine, wherein in a cross-section orthogonal to the feeding direction, with respect to the line direction of the normal line of the wire electrode at the first contact point, the center position of the diameter of the wire electrode in the second hole is shifted with respect to the center position of the diameter of the wire electrode in the first hole.

Images