Satellite turntable control device

Abstract

The application relates to a satellite turntable control device, which comprises a bottom plate, a coarse adjustment gear ring is horizontally rotationally connected to the bottom plate, a fine adjustment gear ring is coaxially arranged above the coarse adjustment gear ring, the coarse adjustment gear ring is rotationally connected with the fine adjustment gear ring, a first gear is meshingly connected to the coarse adjustment gear ring, a first driving element for driving the first gear to rotate is fixedly connected to the bottom plate, a second gear is meshingly connected to the fine adjustment gear ring, a second driving element for driving the second gear to rotate is fixedly connected to the coarse adjustment gear ring, a linkage structure is arranged between the coarse adjustment gear ring and the fine adjustment gear ring, and a supporting structure is further arranged on the fine adjustment gear ring. The application has the effects of facilitating the control of the rotation angle of the turntable and improving the precision of the turntable.

Description

Technical Field

[0001] This application relates to the field of spacecraft manufacturing, and in particular to satellite turntable control devices. Background Technology

[0002] Satellites are manufactured in a separate process. After the parts are produced, they are transported to the assembly workshop, where multiple parts are assembled and fixed to form a whole structure. Due to the high precision required for satellite assembly, turntable devices are generally used to allow operators to assemble and fix the parts.

[0003] Turntable devices are essential for satellite assembly and testing. They are closely related to the efficiency of satellite assembly and the safety of testing, and directly affect the satellite's development cycle.

[0004] Regarding the aforementioned technologies, the inventors believe that the rotation of current turntable devices is generally achieved by rotating a wheel located at the bottom of the turntable, resulting in poor overall rotation effect, difficulty in controlling the rotation angle, and low splicing accuracy. Summary of the Invention

[0005] In order to facilitate the control of the rotation angle of the turntable, improve the accuracy of the turntable, and thus improve the accuracy control of satellite assembly, this application provides a satellite turntable control device.

[0006] The satellite turntable control device provided in this application adopts the following technical solution:

[0007] A satellite turntable control device includes a base plate, on which a coarse adjustment gear ring is horizontally rotatably connected. A fine adjustment gear ring is coaxially disposed above the coarse adjustment gear ring, and the coarse adjustment gear ring and the fine adjustment gear ring are rotatably connected. A first gear is meshed on the coarse adjustment gear ring. A first driving member that drives the first gear to rotate is fixedly connected to the base plate. A second gear is meshed on the fine adjustment gear ring. A second driving member that drives the second gear to rotate is fixedly connected to the coarse adjustment gear ring. A linkage structure is provided between the coarse adjustment gear ring and the fine adjustment gear ring. A support structure is also provided on the fine adjustment gear ring.

[0008] By adopting the above technical solution, the first driving component drives the first gear to rotate, which in turn drives the coarse adjustment gear ring to rotate. The coarse adjustment gear ring then drives the upper support structure to rotate. The second driving component drives the second gear to rotate, which in turn drives the fine adjustment gear ring to rotate. This allows the fine adjustment gear ring to rotate relative to the coarse adjustment gear. When the fine adjustment gear ring rotates, it can adjust the rotation angle of the support structure. When the rotation directions of the coarse and fine adjustment gear rings are the same, it can increase the rotation speed of the support structure. When the rotation directions of the coarse and fine adjustment gear rings are opposite, it can adjust the rotation accuracy of the support structure. This facilitates the control of the rotation angle of the turntable and improves the accuracy of the turntable.

[0009] Optionally, the linkage structure includes a first locking tooth fixedly connected to the fine-tuning gear ring, the first locking tooth being coaxially arranged with the fine-tuning gear ring, a second locking tooth being vertically slidably connected to the coarse-tuning gear ring relative to the position of the first locking tooth, a limit block being fixedly connected to the second locking tooth relative to the position of the coarse-tuning gear ring, a limit groove being vertically formed on the coarse-tuning gear ring relative to the position of the limit block, the limit block being slidably connected up and down inside the limit groove, the first locking tooth and the second locking tooth engaging when the limit block is at the top of the limit groove, and the first locking tooth and the second locking tooth disengaging when the limit block is at the bottom of the limit groove, and a drive structure for driving the second locking tooth to move up and down is provided below the second gear.

[0010] By adopting the above technical solution, the second locking tooth is driven to move up and down through the drive structure. When the second locking tooth and the first locking tooth are meshed, the coarse adjustment gear ring can drive the fine adjustment gear ring to rotate relative to each other. When the first locking tooth and the second locking tooth are disengaged, the fine adjustment gear ring can rotate freely above the coarse adjustment gear ring.

[0011] Optionally, the driving structure includes a driving rod coaxially fixedly connected to the second gear, the second driving member driving the driving rod to rotate, a driving block fixedly connected to the side wall of the driving rod, a driving ring coaxially slidably connected to the outer side of the driving rod, a first driving groove opened in the driving ring relative to the driving block, the first driving groove being inclined, a second driving groove being provided on one side of the first driving groove, the first driving groove and the second driving groove being opened in opposite directions, a ring groove being horizontally opened at the top of the first driving groove, the ring groove completely penetrating the first driving groove and the second driving groove, a first elastic member being vertically arranged below the second locking tooth, a connecting plate fixedly connected to the side wall of the driving ring, and the end of the connecting plate opposite to the driving ring being fixedly connected to the second locking tooth.

[0012] By adopting the above technical solution, when the second driving member drives the driving rod to rotate, the driving rod drives the driving block to slide relative to each other inside the first driving groove. Then the driving block enters the annular groove from the inside of the first driving groove, and rotates relative to each other inside the annular groove, pushing the limiting ring to move downward and compressing the first elastic member. After the rotation is completed, the first elastic member pushes the limiting ring to move upward, and then the driving block enters the second driving groove from the inside of the annular groove, thereby performing a cyclic operation.

[0013] Optionally, a magnet is fixedly connected to the bottom end of the drive ring, and an electromagnet is coaxially fixedly connected to the drive rod below the drive ring. When the electromagnet is energized, the magnetic poles of the end of the electromagnet closest to the first magnet are opposite to the magnetic poles of the end of the first magnet closest to the electromagnet.

[0014] By adopting the above technical solution, when the drive ring is located at the bottom, the first elastic element is compressed, and at this time the electromagnet is energized, so that the electromagnet and the first magnet are attracted to each other, which makes it easier to fix the drive ring, reduces the upward movement of the drive ring by the first elastic element, makes it easier to fix the position of the drive ring, and makes it easier for the slider to rotate inside the ring groove.

[0015] Optionally, a caster wheel is rotatably connected to the bottom of the base plate, and a movable structure is also provided below the base plate.

[0016] By adopting the above technical solution, the casters rotate relative to the bottom plate, thereby moving the bottom plate and facilitating the operation of the operator.

[0017] Optionally, the movable structure includes multiple legs, each leg being fixedly connected to a screw rod, which is threadedly connected to the base plate.

[0018] By adopting the above technical solution, by rotating the screw, the screw drives the support leg to move up and down, and then the support leg extends from under the base plate. When the base plate is in place, by rotating the screw, the screw drives the support leg to move downward and support it on the ground for easy fixation.

[0019] Optionally, a sprocket is coaxially fixedly connected to the screw, and a chain is sleeved on the outer side of the plurality of sprockets. When one of the screws is rotated, the screw can drive the sprocket to rotate, which in turn drives the chain to rotate, and the chain drives the other sprockets to rotate, which in turn drives the other screws to rotate.

[0020] By adopting the above technical solution, rotating the screw causes the sprocket to rotate, which in turn causes the chain to rotate, and the chain causes other sprockets to rotate, thereby causing other screws to rotate synchronously, which facilitates the synchronous movement of the outriggers.

[0021] Optionally, the support structure includes a support rod vertically arranged on the fine-tuning gear ring, with multiple support rods arranged along the axis of the fine-tuning gear ring, and a receiving plate horizontally fixedly connected to the top of the support rod.

[0022] By adopting the above technical solution, the receiving plate is placed on the support rod, and the support rod is placed on the fine-tuning gear ring, so that the support rod can rotate with the fine-tuning gear ring, and the receiving plate can support the satellite.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] 1. The first driving component drives the first gear to rotate, which in turn drives the coarse adjustment gear ring to rotate. The coarse adjustment gear ring then drives the upper support structure to rotate. The second driving component drives the second gear to rotate, which in turn drives the fine adjustment gear ring to rotate. This allows the fine adjustment gear ring to rotate relative to the coarse adjustment gear. When the fine adjustment gear ring rotates, it can adjust the rotation angle of the support structure. When the coarse and fine adjustment gear rings rotate in the same direction, it can increase the rotation speed of the support structure. When the coarse and fine adjustment gear rings rotate in opposite directions, it can adjust the rotation accuracy of the support structure. This facilitates the control of the rotation angle of the turntable and improves the accuracy of the turntable.

[0025] 2. When the second driving member drives the driving rod to rotate, the driving rod drives the driving block to slide relative to each other inside the first driving groove. The driving block then enters the annular groove from the inside of the first driving groove, and rotates relative to each other inside the annular groove, pushing the limiting ring to move downward and compressing the first elastic member. After the rotation is completed, the first elastic member pushes the limiting ring to move upward, and the slider enters the second driving groove from the inside of the annular groove, thus performing a cyclic operation.

[0026] 3. When the drive ring is at the bottom, the first elastic element is compressed, and the electromagnet is energized at this time, so that the electromagnet and the first magnet attract each other, which makes it easier to fix the drive ring, reduces the upward movement of the drive ring by the first elastic element, makes it easier to fix the position of the drive ring, and makes it easier for the slider to rotate inside the ring groove. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the satellite turntable control device in the embodiments of this application;

[0028] Figure 2 This is a schematic diagram of the structure at the positions of the coarse adjustment gear ring and the fine adjustment gear ring of the satellite turntable control device in the embodiments of this application;

[0029] Figure 3 This is a cross-sectional view of the positions of the coarse adjustment gear ring and the fine adjustment gear ring of the satellite turntable control device in the embodiments of this application;

[0030] Figure 4 This is a schematic diagram of the location of the drive ring of the satellite turntable control device in the embodiments of this application;

[0031] Figure 5 This is a cross-sectional view of the drive ring position of the satellite turntable control device in the embodiments of this application;

[0032] Figure 6 This is a schematic diagram of the moving structure of the satellite turntable control device in the embodiments of this application.

[0033] Explanation of reference numerals in the attached drawings: 1. Base plate; 2. Rotating structure; 21. Coarse adjustment gear ring; 211. First rotating motor; 212. First gear; 213. Second locking tooth; 2131. Limiting block; 214. Limiting groove; 2141. Spring; 22. Fine adjustment gear ring; 221. Second rotating motor; 222. Drive rod; 2221. Drive block; 223. Second gear; 224. First locking tooth; 23. Drive ring; 231. First drive groove; 232. Second drive groove; 233. Ring groove; 234. First magnet; 235. Electromagnet; 236. Connecting plate; 3. Support structure; 31. Support rod; 32. Receiving plate; 4. Moving structure; 41. Universal wheel; 42. Screw; 43. Support leg; 44. Sprocket; 45. Chain; 46. Handwheel. Detailed Implementation

[0034] The following is in conjunction with the appendix Figure 1-6 This application will be described in further detail.

[0035] This application discloses a satellite turntable control device. (See also...) Figure 1 , Figure 2 The satellite turntable control device includes a horizontally arranged base plate 1, a rotating structure 2 above the base plate 1, and a supporting structure 3 above the rotating structure 2. The rotating structure 2 can drive the supporting structure 3 to rotate, thereby driving the satellite parts to rotate. A moving structure 4 is arranged below the base plate 1, and the moving structure 4 can drive the base plate 1 to move.

[0036] Reference Figure 2 , Figure 3 The rotating structure 2 includes a horizontally arranged coarse adjustment gear ring 21, which is rotatably connected to the base plate 1. A fine adjustment gear ring 22 is coaxially arranged above the coarse adjustment gear ring 21. The number of teeth on the coarse adjustment gear ring 21 is less than the number of teeth on the fine adjustment gear ring 22, and the fine adjustment gear ring 22 is rotatably connected to the coarse adjustment gear ring 21. A first rotating motor 211 is fixedly connected to the base plate 1 at a position relative to the coarse adjustment gear ring 21. A first gear 212 is coaxially fixedly connected to the motor shaft of the first rotating motor 211, and the first gear 212 meshes with the coarse adjustment gear ring 21. The first rotating motor 211 drives the first gear 212 to rotate, which in turn drives the coarse adjustment gear ring 21 to rotate.

[0037] A second rotary motor 221 is fixedly connected to the coarse adjustment gear ring 21. A drive rod 222 is coaxially fixedly connected to the motor shaft of the second rotary motor 221. A second gear 223 is fixedly connected to the top of the drive rod 222, and the second gear 223 meshes with the fine adjustment gear ring 22. A first locking tooth 224 is coaxially fixedly connected to the inner wall of the fine adjustment gear ring 22. The first locking tooth 224 has a ring structure, and its bottom end has a sawtooth structure. A second locking tooth 213 is coaxially fixedly connected to the inner wall of the coarse adjustment gear ring 21 at a position relative to the first locking tooth 224. The second locking tooth 213 has a ring structure, and its top end has the same sawtooth structure as the first locking tooth 224. When the first locking tooth 224 and the second locking tooth 213 are relatively close together, the bottom end of the first locking tooth 224 and the top end of the second locking tooth 213 can mesh with each other.

[0038] The outer wall of the second locking tooth 213 is fixedly connected to a limiting block 2131. The inner wall of the coarse adjustment gear ring 21 has a vertically formed limiting groove 214 relative to the position of the limiting block 2131, and the limiting block 2131 is located inside the limiting groove 214 and is slidably connected to it. Inside the limiting groove 214, at the bottom end of the limiting block 2131, a spring 2141 is vertically arranged. The bottom end of the spring 2141 is fixedly connected to the coarse adjustment gear ring 21, and the top end of the spring 2141 is fixedly connected to the limiting block 2131.

[0039] Reference Figure 4 , Figure 5 A drive ring 23 is coaxially sleeved on the drive rod 222. The drive ring 23 is slidably connected to the drive rod 222. A drive block 2221 is fixedly connected to the side wall of the drive rod 222. A first drive groove 231 is opened on the inner side wall of the drive ring 23 relative to the position of the drive block 2221. The first drive groove 231 is inclined, and the inclination direction gradually tilts towards the positive rotation direction of the drive ring 23 along the height direction from top to bottom. A second drive groove 232 is also opened on the inner side wall of the drive ring 23. The second drive groove 232 is inclined, and the inclination direction of the first drive groove 231 is opposite to the inclination direction of the second drive groove 232.

[0040] The drive ring 23 has a horizontally formed annular groove 233 at the top of the first drive groove 231. The annular groove 233 is a ring structure, and the first drive groove 231 and the annular groove 233 are in relative communication, as are the second drive groove 232 and the annular groove 233. The drive block 2221 slides relative to the first drive groove 231 and can enter the annular groove 233 as guided by the first drive groove 231. When the drive rod 222 rotates in the opposite direction, the drive block 2221 can enter the second drive groove 232 and slide relative to it.

[0041] The bottom end of the drive ring 23 is coaxially fixedly connected to the first magnet 234, and the drive rod 222 is located below the first magnet 234 and coaxially fixedly connected to the electromagnet 235. The electromagnet 235 is opposite to the first magnet 234. When the electromagnet 235 is energized, the magnetism of the opposite side of the electromagnet 235 and the first magnet 234 is opposite.

[0042] A connecting plate 236 is fixedly connected to the side wall of the drive ring 23. The connecting plate 236 is horizontally positioned, and one end of the connecting plate 236 facing away from the drive ring 23 is fixedly connected to the second locking tooth 213. When the drive block 2221 is inside the first drive groove 231, the drive rod 222 is rotated, and the drive block 2221 slides from the inside of the first drive groove 231 into the inside of the ring groove 233, pushing the drive ring 23 to move downward. The electromagnet 235 is energized, and the electromagnet 235 and the first magnet 234 attract each other, thereby driving the connecting plate 236 to move downward. The connecting plate 236 drives the second locking tooth 213 to move downward, compressing the spring 2141, so that the first locking tooth 224 and the second locking tooth 213 disengage relative to each other, and the fine-tuning gear ring 22 can rotate freely.

[0043] When the drive block 2221 is inside the annular groove 233, the spring 2141 pushes the positioning block upward, causing the drive block 2221 to face the second drive groove 232. The spring 2141 then forces the drive block 2221 from inside the annular groove 233 into the second drive groove 232. This causes the second locking tooth 213 to move upward, engaging the first locking tooth 224 and the second locking tooth 213, thus enabling the coarse adjustment gear ring 21 to drive the fine adjustment gear ring 22 to rotate synchronously.

[0044] When a low precision adjustment is required, the first locking tooth 224 and the second locking tooth 213 mesh with each other, and the first rotating motor 211 drives the first gear 212 to rotate, which in turn drives the coarse adjustment gear ring 21 to rotate, and the coarse adjustment gear ring 21 drives the fine adjustment gear ring 22 to rotate synchronously.

[0045] When rapid rotation is required, the first locking tooth 224 and the second locking tooth 213 disengage relative to each other, and the first rotating motor 211 drives the coarse adjustment gear ring 21 to rotate, while the second rotating motor 221 drives the fine adjustment gear ring 22 to rotate. The fine adjustment gear ring 22 rotates in the same direction as the coarse adjustment gear ring 21, thereby increasing the rotation speed of the fine adjustment gear ring 22.

[0046] Furthermore, when precise control is required, the first rotating motor 211 drives the coarse adjustment gear ring 21 to rotate, and the second rotating motor 221 drives the fine adjustment gear ring 22 to rotate in the opposite direction, thereby improving the adjustment accuracy.

[0047] Reference Figure 1 , Figure 6The support structure 3 includes a support rod 31 vertically arranged above the fine-tuning gear ring 22. Four support rods 31 are equidistantly arranged along the circumferential direction of the fine-tuning gear ring 22, and a receiving plate 32 is fixedly connected to the top of the support rod 31. The receiving plate 32 is horizontally arranged, has an arc-shaped structure, and is coaxial with the fine-tuning gear ring 22.

[0048] The movable structure 4 includes casters 41 located at the four corners below the base plate 1. The casters 41 are rotatably connected to the base plate 1, thereby moving the base plate 1. Each of the four corners of the base plate 1 has a vertically mounted screw 42, threadedly connected to the base plate 1. The bottom end of the screw 42 has a horizontally mounted support leg 43, which is fixedly connected to the screw 42. A sprocket 44 is horizontally mounted inside the screw 42 in the base plate 1, and pin-connected to the screw 42, allowing the sprocket 44 to rotate with the screw 42 and slide relative to it along the height of the screw 42. A chain 45 is mounted on the outside of the four sprockets 44, and the chain 45 is meshed with the four sprockets 44.

[0049] One of the screws 42 has a handwheel 46 fixedly connected to its top coaxially. By rotating the handwheel 46, the screw 42 is driven to rotate, which in turn drives the sprocket 44 to rotate, which in turn drives the chain 45 to rotate. The chain 45 drives multiple sprockets 44 to rotate synchronously, which in turn drives multiple screws 42 to rotate synchronously, thereby supporting the outrigger 43 on the ground.

[0050] The implementation principle of the satellite turntable control device in this application embodiment is as follows: the second rotating motor 221 drives the drive rod 222 to rotate, and then the drive block 2221 on the drive rod 222 enters the annular groove 233 inside the first drive groove 231. The drive block 2221 moves downward, and the drive block 2221 drives the connecting plate 236 to move downward. Then the connecting plate 236 drives the second locking tooth 213 to move downward, so that the second locking tooth 213 is relatively disengaged from the first locking tooth 224, and then the fine adjustment gear ring 22 can rotate freely above the coarse adjustment gear ring 21.

[0051] The first rotating motor 211 drives the coarse adjustment gear ring 21 to rotate relative to each other, and then the second rotating motor 221 drives the fine adjustment gear ring 22 to rotate relative to each other. When the coarse adjustment gear ring 21 and the fine adjustment gear ring 22 rotate in the same direction, the rotation speed of the support structure 3 can be increased. When the coarse adjustment gear ring 21 and the fine adjustment gear ring 22 rotate in opposite directions, the rotation accuracy of the support structure 3 can be improved.

[0052] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A satellite turntable control device, characterized in that: The device includes a base plate (1), on which a coarse adjustment gear ring (21) is rotatably connected horizontally. A fine adjustment gear ring (22) is coaxially arranged above the coarse adjustment gear ring (21). The coarse adjustment gear ring (21) and the fine adjustment gear ring (22) are rotatably connected. A first gear (212) is meshed on the coarse adjustment gear ring (21). A first driving member that drives the first gear (212) to rotate is fixedly connected on the base plate (1). A second gear (223) is meshed on the fine adjustment gear ring (22). A second driving member that drives the second gear (223) to rotate is fixedly connected on the coarse adjustment gear ring (21). A linkage structure is provided between the coarse adjustment gear ring (21) and the fine adjustment gear ring (22). A support structure (3) is also provided on the fine adjustment gear ring (22). The linkage structure includes a first locking tooth (224) fixedly connected to the fine-tuning gear ring (22), the first locking tooth (224) being coaxially arranged with the fine-tuning gear ring (22), a second locking tooth (213) being vertically slidably connected to the coarse-tuning gear ring (21) relative to the position of the first locking tooth (224), a limit block (2131) being fixedly connected to the position of the second locking tooth (213) relative to the position of the coarse-tuning gear ring (21), and a limit groove (2131) being vertically formed on the position of the coarse-tuning gear ring (21) relative to the position of the limit block (2131). 14) The limiting block (2131) is located inside the limiting groove (214) and slides up and down. When the limiting block (2131) is located at the top of the limiting groove (214), the first locking tooth (224) and the second locking tooth (213) are engaged. When the limiting block (2131) is located at the bottom of the limiting groove (214), the first locking tooth (224) and the second locking tooth (213) are disengaged. A drive structure for driving the second locking tooth (213) to move up and down is provided below the second gear (223).

2. The satellite turntable control device according to claim 1, characterized in that: The driving structure includes a driving rod (222) coaxially fixedly connected to the second gear (223). The second driving member drives the driving rod (222) to rotate. A driving block (2221) is fixedly connected to the side wall of the driving rod (222). A driving ring (23) is slidably connected to the outer side of the driving rod (222). The driving ring (23) has a first driving groove (231) at a position relative to the driving block (2221). The first driving groove (231) is inclined. A second driving groove (2221) is provided on one side of the first driving groove (231). 32) The first drive groove (231) and the second drive groove (232) are set in opposite directions. The top of the first drive groove (231) is provided with a horizontal annular groove (233). The annular groove (233) completely penetrates the first drive groove (231) and the second drive groove (232). A first elastic element is vertically arranged below the second locking tooth (213). A connecting plate (236) is fixedly connected to the side wall of the drive ring (23). The end of the connecting plate (236) away from the drive ring (23) is fixedly connected to the second locking tooth (213).

3. The satellite turntable control device according to claim 2, characterized in that: The bottom end of the drive ring (23) is fixedly connected to a first magnet (234), and the drive rod (222) is located below the drive ring (23) and is coaxially fixedly connected to an electromagnet (235). When the electromagnet (235) is energized, the magnetic poles of the end of the electromagnet (235) near the first magnet (234) are opposite to the magnetic poles of the end of the first magnet (234) near the electromagnet (235).

4. The satellite turntable control device according to claim 1, characterized in that: A caster wheel (41) is rotatably connected to the bottom of the base plate (1), and a movable structure (4) is also provided below the base plate (1).

5. The satellite turntable control device according to claim 4, characterized in that: The movable structure (4) includes multiple legs (43), and screws (42) are fixedly connected to the legs (43). The screws (42) are threadedly connected to the base plate (1).

6. The satellite turntable control device according to claim 5, characterized in that: A sprocket (44) is coaxially fixedly connected to the screw (42). A chain (45) is sleeved on the outer side of the multiple sprockets (44). When one of the screws (42) is rotated, the screw (42) can drive the sprocket (44) to rotate, and then the sprocket (44) drives the chain (45) to rotate. The chain (45) drives the other sprockets (44) to rotate, and then drives the other screws (42) to rotate.

7. The satellite turntable control device according to claim 1, characterized in that: The support structure (3) includes a support rod (31) vertically arranged on the fine-tuning gear ring (22). Multiple support rods (31) are arranged along the axis of the fine-tuning gear ring (22). A receiving plate (32) is horizontally fixedly connected to the top of the support rod (31).

Images