Laser tracking measurement device

Abstract

The invention provides a laser tracking measurement device, comprising a support rod, a laser tracker is arranged on the top of the support rod, a base connected by a support tube is arranged at the bottom, a knob is rotatably arranged on the support tube, a traveling frame is arranged on both sides of the base, anti-skid wheels are arranged at both ends of the traveling frame, a mounting seat is rotatably arranged on the traveling frame, the mounting seat is arranged in the base in a liftable manner, a fixing mechanism connected with the knob is arranged on two groups of traveling frames, the rotation of the knob can be selectively converted into locking or unlocking the position of the traveling frame through the fixing mechanism, and a locking assembly connected with the knob and multiple groups of anti-skid wheels is arranged on the fixing mechanism. The laser tracker can be stably supported horizontally by the device when the ground conditions are relatively complicated, and the device as a whole will not move or shake after being fixed on the irregular ground, thereby effectively improving the measurement accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of laser tracking measurement, and in particular to a laser tracking measurement device. Background Art

[0002] Laser tracker is an optical measuring instrument that irradiates laser light onto a target that contacts the measurement target, and then the laser light reflected by the target returns to the light source, thereby determining the three-coordinate position of the target. The characteristic of laser tracker is that it can measure large measurement targets, even when there are light-shielding objects or larger objects need to be measured. Compared with traditional coordinate measuring machines, laser trackers generally have a measurement range of more than 10 meters. At present, laser trackers are widely used in aerospace and general manufacturing fields, such as tooling settings.

[0003] For example, the Chinese invention patent with patent number 202110599171.0 provides a mobile measuring trolley device for a laser tracker, which can smoothly and safely move the laser tracker to other measurement sites to start the next measurement operation without shutting down the laser tracker, and allows the laser tracker to be flexibly raised and lowered.

[0004] Most of the existing laser tracking measurement devices are placed on the measurement plane through a tripod or a mobile base, and the placement surface of the laser measuring instrument may be an irregular surface. The traditional laser tracking measurement device requires cumbersome adjustment of its supporting structure so that the tester can be stably placed on the measurement plane without shaking while ensuring the levelness, so as to reduce measurement errors, resulting in certain inconveniences in the use of the traditional laser tracking measurement device. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a laser tracking and measuring device to solve the technical problem raised in the above background technology that the traditional laser tracking and measuring device needs to perform cumbersome adjustments to its supporting structure so that the tester can be stably placed on the measuring plane without shaking while ensuring the levelness, so as to reduce measurement errors, thereby causing certain inconveniences in the use of the traditional laser tracking and measuring device.

[0006] To achieve the above object, the present invention provides the following technical solution: a laser tracking measurement device, comprising:

[0007] A support rod, the top of which is provided with a laser tracker, and the bottom of which is provided with a base connected through a support tube, and the support tube is rotatably provided with a knob;

[0008] A walking frame is provided with two groups and is respectively located on both sides of the base, and both ends of the walking frame are provided with anti-slip wheels, and a mounting seat is relatively rotatably connected to the middle position of the walking frame, and the mounting seat is liftably arranged in the base;

[0009] A fixing mechanism, disposed on the two sets of the walking frames and connected to the knob, so that the rotation of the knob can be selectively converted into locking or unlocking the position of the walking frame; and

[0010] A locking assembly is arranged on the fixing mechanism and connected to the knob and the plurality of groups of anti-skid wheels, so that the rotation of the knob can be selectively converted into locking or unlocking the position of the anti-skid wheels.

[0011] In a preferred embodiment, a connecting tube is provided on the walking frame, and the connecting tube is rotatably arranged in the mounting seat along its axis.

[0012] In a preferred embodiment, a positioning rod is provided in the base, an end of the positioning rod is fixedly connected to the base via an abutment seat, and a connecting sleeve is provided on the mounting seat, and the connecting sleeve is slidably mounted on the positioning rod.

[0013] In a preferred embodiment, a supporting spring is provided between the connecting sleeve and a group of the abutting seats at the top.

[0014] In a preferred embodiment, both ends of the walking frame are connected to the base via a tension spring, and the connecting end of the tension spring and the walking frame is higher than the connecting end of the tension spring and the base.

[0015] In a preferred embodiment, the fixing mechanism includes:

[0016] A driving wheel, rotatably disposed along its axis in the base;

[0017] A control assembly, disposed on the support cylinder and connected to the driving wheel, to drive the driving wheel to rotate and lock its position;

[0018] The friction discs are provided in two groups and are respectively arranged at the ends of the two groups of connecting tubes;

[0019] There are two sets of drive shafts, which are respectively inserted into the two sets of connecting tubes. A mounting plate is provided at one end of the drive shaft, and a fastening plate is detachably provided on the side of the mounting plate facing the friction plate; and

[0020] The propulsion assembly is provided with two groups, which are arranged on the driving wheel and respectively connected with the two groups of driving shafts to convert the rotation of the driving wheel into driving the driving shaft to slide along its axis.

[0021] In a preferred embodiment, the control component includes:

[0022] A transmission shaft is rotatably disposed in the support cylinder along its axis, and one end of the transmission shaft is coaxially fixedly connected to the driving wheel;

[0023] a worm gear, disposed on the transmission shaft; and

[0024] The worm is rotatably arranged in the support tube along its axis and meshes with the worm wheel. One end of the worm extends out of the support tube and is connected to the knob.

[0025] In a preferred embodiment, the propulsion assembly comprises:

[0026] A propulsion frame, on top of which a guide column perpendicular to the side of the base is arranged, and the guide column is slidably arranged on the base along its axis;

[0027] A card-joint frame is arranged on the mounting plate and is slidably card-jointed on the propulsion frame; and

[0028] A transmission arm has one end hinged to the driving wheel and the other end hinged to the propulsion frame.

[0029] In a preferred embodiment, the locking assembly includes:

[0030] A locking frame is arranged in the traveling frame in a lateral sliding manner, a first pressing plate is arranged at both ends of the traveling frame, a second pressing plate is arranged at both ends of the locking frame, and the anti-slip wheel is arranged between the first pressing plate and the second pressing plate;

[0031] an abutment plate, disposed on the driving shaft and located on one side of the locking frame; and

[0032] A tightening spring is arranged between the locking frame and the abutting plate.

[0033] In a preferred embodiment, a handle is provided on the support tube, and a level is provided on the handle.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The device performs measurement work through a laser tracker when in use, and can be supported and moved on the ground through multiple sets of anti-skid wheels during use. When the installation area is an irregular surface, the support cylinder can be moved to a state perpendicular to the horizontal plane, the walking frame can rotate along the mounting seat, and the mounting seat can be raised and lowered in the base, so that after the walking frame is tilted and raised and lowered, the multiple sets of anti-skid wheels are in contact with the ground, and then the knob is turned. The positions of the two sets of walking frames are locked by the fixing mechanism during the rotation of the knob, and the positions of the multiple sets of anti-skid wheels are fixed at the same time by the locking assembly. Even if the ground conditions are relatively complicated, the laser tracker can be stably supported horizontally by the device, and the device as a whole will not move or shake after being fixed on the irregular ground, effectively improving the measurement accuracy.

[0036] 2. When the device is in use and is moved to an irregular surface, the walking frame supports the base and the laser tracker installed on it through the cooperation of the support spring and the tension spring. In the initial state, some anti-skid wheels do not contact the bottom surface. When one set of anti-skid wheels on the walking frame contacts the ground, the support cylinder can be pressed downward to make the mounting seat rise and fall, and the walking frame as a whole rotates and tilts along the connecting cylinder, so that when the base is level, multiple sets of anti-skid wheels can contact the ground, and then the knob is turned to drive the worm to rotate. During the rotation process, the worm drives the driving wheel to rotate and the self- The cam is engaged with the locking cam and the locking cam is engaged with the locking cam, and the locking cam is engaged with the locking cam, so that the locking cam is engaged with the locking cam and the locking cam is engaged with the locking cam. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific implementation of the present invention, the following will briefly introduce the drawings required for use in the specific implementation. In all the drawings, each element or part is not necessarily drawn according to the actual scale.

[0038] Figure 1 A schematic diagram of the three-dimensional structure of a laser tracking measurement device provided by the present invention;

[0039] Figure 2 This is a front view of a laser tracking measurement device of the present invention;

[0040] Figure 3 A cross-sectional view of a laser tracking measurement device of the present invention;

[0041] Figure 4It is a bottom structural schematic diagram of a laser tracking measurement device of the present invention;

[0042] Figure 5 It is a schematic diagram of the installation structure of a traveling frame and parts above it in a laser tracking measurement device of the present invention;

[0043] Figure 6 It is a schematic diagram of the installation structure of a fastening sheet in a laser tracking measurement device of the present invention;

[0044] Figure 7 The present invention is a schematic diagram of the structure of a disassembled traveling frame in a laser tracking and measuring device.

[0045] Reference numerals:

[0046] 101, laser tracker; 102, support rod; 103, support tube; 104, handle; 105, level; 106, base; 107, positioning rod; 108, abutment seat;

[0047] 201, transmission shaft; 202, worm wheel; 203, worm; 204, knob; 205, driving wheel;

[0048] 301, mounting seat; 302, connecting sleeve; 303, supporting spring;

[0049] 401, connecting tube; 402, walking frame; 403, tension spring; 404, first pressing plate; 405, anti-skid wheel; 406, friction plate;

[0050] 501, locking frame; 502, second pressing plate; 503, fastening spring;

[0051] 601, driving shaft; 602, abutment plate; 603, mounting plate; 604, clamping frame; 605, fastening plate; 701, propulsion frame; 702, guide column; 703, transmission arm. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific implementation methods are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Technicians in this field can make some non-essential improvements and adjustments to the present invention based on the above application content.

[0053] Example:

[0054] like Figure 1 , 2As shown in Figure 3, the present invention provides a laser tracking measurement device, including a support rod 102, a laser tracker 101 is arranged on the top of the support rod 102, a base 106 connected by a support tube 103 is arranged at the bottom, and a knob 204 is rotatably arranged on the support tube 103. A walking frame 402 is arranged on both sides of the base 106, and anti-skid wheels 405 are arranged on both ends of the walking frame 402. A mounting seat 301 is connected to the middle position of the walking frame 402 so as to be relatively rotatable, and the mounting seat 301 is arranged in the base 106 so as to be liftable. A connecting tube 401 is arranged on the walking frame 402, and the connecting tube 401 is rotatably arranged in the mounting seat 301 along its axis. A positioning rod 107 is arranged in the base 106, and the end of the positioning rod 107 is fixedly connected to the base 106 through an abutment seat 108, and a connecting sleeve 302 is arranged on the mounting seat 301, and the connecting sleeve 302 is slidably sleeved on the positioning rod 107. A support spring 303 is provided between the connecting sleeve 302 and a group of abutment seats 108 at the top. Both ends of the traveling frame 402 are connected to the base 106 through the tension spring 403, and the connection end of the tension spring 403 and the traveling frame 402 is higher than the connection end of the tension spring 403 and the base 106.

[0055] The device is measured by the laser tracker 101 when in use, and can be moved on the ground through the anti-skid wheel 405. In the initial state, the walking frame 402 and the anti-skid wheel 405 are both in an active state, and the base 106 is supported by the walking frame 402, and the base 106 can be raised and lowered within a certain range under the action of the support spring 303 and the tension spring 403. When the device is located on an irregular ground, the walking frame 402 can rotate along the axis of the connecting tube 401, and the mounting seat 301 can be raised and lowered along the axis of the positioning rod 107, so that multiple groups of anti-skid wheels 405 can be kept in contact with the irregular ground. If the ground is relatively uneven, the base 106 can be pressed downward to make the anti-skid wheels 405 move downward until all the anti-skid wheels 405 are in contact with the ground, and finally the base 106 is controlled to be in a horizontal state. The walking frame 402 compresses the support spring 303 during the lifting process, and the walking frame 402 stretches one group of tension springs 403 during the rotation along the axis of the connecting tube 401. A handle 104 may be provided on the support tube 103 , and a level 105 may be provided on the handle 104 . The support tube 103 may be straightened by the handle 104 , and the level 105 may be used to keep it as vertical as possible with the horizontal plane, so as to improve the measurement accuracy of the laser tracker 101 .

[0056] like Figure 2 , 3As shown, in this embodiment, a fixing mechanism connected to the knob 204 is provided on the two sets of walking frames 402, and the rotation of the knob 204 can be selectively converted into locking or unlocking the position of the walking frame 402 through the fixing mechanism. The fixing mechanism includes a driving wheel 205 rotatable along its axis and arranged in the base 106, and a control component connected to the driving wheel 205 is provided on the support cylinder 103. The driving wheel 205 is controlled to rotate and its position is locked by the control component. The control component includes a transmission shaft 201 rotatable along its axis and arranged in the support cylinder 103, one end of the transmission shaft 201 is coaxially fixedly connected with the driving wheel 205, a worm wheel 202 is provided on the transmission shaft 201, and a rotatable worm 203 is provided in the support cylinder 103, the worm 203 is meshed with the worm wheel 202, and one end of the worm 203 extends out of the support cylinder 103 and is connected to the knob 204. The worm 203 can be driven to rotate by rotating the knob 204. During the rotation process, the worm 203 drives the worm wheel 202 to rotate and self-lock it by meshing with the worm wheel 202, thereby driving the driving wheel 205 to rotate and lock its position after rotation.

[0057] like Figure 4 , 5 As shown in Figure 6, in this embodiment, the fixing mechanism also includes two groups of friction disks 406, and the two groups of friction disks 406 are respectively arranged at the ends of the two groups of connecting cylinders 401. A driving shaft 601 is passed through the connecting cylinder 401, and a mounting disk 603 is arranged at one end of the driving shaft 601. A fastening sheet 605 is detachably arranged on the side of the mounting disk 603 facing the friction disk 406. Two groups of propulsion components respectively connected to the two groups of driving shafts 601 are arranged on the driving wheel 205, and the rotation of the driving wheel 205 is converted into controlling the driving shaft 601 to slide along its axis through the propulsion component. The propulsion assembly includes a propulsion frame 701, on which a guide column 702 perpendicular to the side of the base 106 is arranged, and the guide column 702 is slidably arranged on the base 106 along its axis. A clamping frame 604 is arranged on the mounting plate 603, and the clamping frame 604 is slidably clamped on the propulsion frame 701. Two sets of transmission arms 703 are hinged on the driving wheel 205, and one end of the two sets of transmission arms 703 is hinged to the propulsion frame 701.

[0058] The two groups of transmission arms 703 are arranged symmetrically along the axis of the driving wheel 205. The driving wheel 205 controls the two groups of propulsion frames 701 to move along the axis of the guide column 702 through the two groups of transmission arms 703 during the rotation process. When adjusting the position of the base 106, the driving shaft 601 can be raised and lowered in the base 106. During the lifting process, the driving shaft 601 drives the clamping frame 604 to slide on the propulsion frame 701, so that the fastening sheet 605 and the friction disk 406 can be lifted and lowered synchronously, and the friction disk 406 can be rotated to drive the traveling frame 402 to rotate and tilt. When the propulsion frame 701 moves along the axis of the guide column 702, it can drive the fastening sheet 605 to move until it contacts the friction disk 406, thereby quickly fixing the positions of the two groups of friction disks 406 at the same time, so as to fix the position of the traveling frame 402 after rotation, tilting and lifting, so that the device can stably support the laser tracker 101 on an irregular surface.

[0059] like Figures 4 to 7 As shown, in this embodiment, a locking assembly connected to the knob 204 and multiple groups of anti-skid wheels 405 is provided on the fixing mechanism, and the rotation of the knob 204 can be selectively converted into locking or unlocking the position of the anti-skid wheels 405 through the locking assembly. The locking assembly includes a locking frame 501 that can be laterally slidably arranged in the traveling frame 402, a first pressing disk 404 is arranged at both ends of the traveling frame 402, a second pressing disk 502 is arranged at both ends of the locking frame 501, and the anti-skid wheels 405 are arranged between the first pressing disk 404 and the second pressing disk 502. An abutment disk 602 is arranged on the driving shaft 601, and the abutment disk 602 is located at one side of the locking frame 501, and a fastening spring 503 is arranged between the locking frame 501 and the abutment disk 602.

[0060] In the process of controlling the sliding of the driving shaft 601, the abutment plate 602 is driven to move, and the abutment plate 602 squeezes the fastening spring 503, so that the locking frame 501 is subjected to the force applied by the fastening spring 503 and slides in the walking frame 402, so as to control the first pressing plate 404 and the second pressing plate 502 to close and clamp the anti-skid wheel 405. In some preferred embodiments, anti-skid grooves or anti-skid sheets can be added to the contact surfaces of the first pressing plate 404 and the second pressing plate 502 and the anti-skid wheel 405 to increase the friction force on the anti-skid wheel 405, so as to stably fix the anti-skid wheel 405 and prevent the device from moving on the ground, so as to support the laser tracker 101 on an irregular surface during the stabilization process of the device.

[0061] Among them, the locking of the anti-skid wheel 405 must be prior to the locking of the walking frame 402, so that the device can be installed and adjusted without rolling the anti-skid wheel 405, avoiding displacement of the device as a whole from the ground during position adjustment, thereby improving the convenience of position adjustment. Similarly, by rotating the knob 204 in the opposite direction, the locking of the anti-skid wheel 405 and the walking frame 402 can be quickly released, so as to facilitate the movement of the device on the ground and make multi-point measurement more efficient.

[0062] Specific usage and beneficial effects of the present invention:

[0063] When the device is in use, the laser tracker 101 is used for measurement, and the multiple groups of anti-skid wheels 405 are used for support and movement on the ground. When the installation area is an irregular surface, the support tube 103 can be moved to a state perpendicular to the horizontal plane, the walking frame 402 can be rotated along the mounting seat 301, and the mounting seat 301 can be raised and lowered in the base 106, so that after the walking frame 402 is tilted and raised and lowered, the multiple groups of anti-skid wheels 405 are in contact with the ground, and then the knob 204 is rotated. The knob 204 locks the positions of the two groups of walking frames 402 through the fixing mechanism during the rotation process, and the positions of the multiple groups of anti-skid wheels 405 are fixed at the same time through the locking assembly. Even if the ground conditions are relatively complicated, the laser tracker 101 can be stably supported horizontally by the device, and the device as a whole will not move or shake after being fixed on the irregular ground, thereby effectively improving the measurement accuracy.

[0064] When the device is in use, when it is moved to an irregular surface, the walking frame 402 supports the base 106 and the laser tracker 101 installed thereon by the cooperation of the support spring 303 and the tension spring 403. In the initial state, some anti-skid wheels 405 do not contact the bottom surface. When one set of anti-skid wheels 405 on the walking frame 402 contacts the ground, the support cylinder 103 can be pressed downward to make the mounting seat 301 rise and fall, and the walking frame 402 can be rotated and tilted along the connecting cylinder 401 as a whole, so that when the base 106 is level, multiple sets of anti-skid wheels 405 can all contact the ground, and then the knob 204 is turned to drive the worm 203 to rotate. During the rotation process, the worm 203 drives the driving wheel 205 to rotate and Self-locking, the driving wheel 205 pushes the propulsion frame 701 to slide in the base 106 through the transmission arm 703 during the rotation, so that the abutment plate 602 and the friction plate slide along the axis of the driving shaft 601 at the same time, and the abutment plate 602 pushes the locking frame 501 to move through the fastening spring 503 during the sliding process, and then the position of the anti-skid wheel 405 is fixed by closing the first pressing plate 404 and the second pressing plate 502, and the driving shaft 601 continues to slide and makes the fastening plate 605 fit with the friction plate 406 to fix the position of the connecting tube 401, thereby quickly fixing the position of the walking frame 402 and the anti-skid wheel 405, and the entire fixing process can be completed by one person, and the operation is convenient and quick, thereby improving the measurement efficiency.

[0065] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments. On the basis of the present invention, some modifications or improvements can be made thereto, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A laser tracking measurement device, characterized in that: Included are: A support rod (102) having a laser tracker (101) disposed on the top thereof and a base (106) connected via a support tube (103) disposed on the bottom thereof, wherein a knob (204) is rotatably disposed on the support tube (103); Two groups of walking frames (402) are provided and are respectively located on both sides of the base (106); both ends of the walking frames (402) are provided with anti-slip wheels (405); a mounting seat (301) is rotatably connected to the middle position of the walking frame (402); and the mounting seat (301) is movably arranged in the base (106); A fixing mechanism, arranged on the two sets of the walking frames (402) and connected to the knob (204), so that the rotation of the knob (204) can be selectively converted into locking or unlocking the position of the walking frame (402); and A locking assembly, arranged on the fixing mechanism and connected to the knob (204) and the plurality of groups of anti-slip wheels (405), so that the rotation of the knob (204) can be selectively converted into locking or unlocking the position of the anti-slip wheels (405); The walking frame (402) is provided with a connecting tube (401), and the connecting tube (401) is rotatably inserted into the mounting seat (301) along its axis; The fixing mechanism comprises: A driving wheel (205) is rotatably arranged along its axis in the base (106); a control assembly, arranged on the support cylinder (103) and connected to the driving wheel (205) to drive the driving wheel (205) to rotate and lock its position; The friction discs (406) are provided in two groups and are respectively provided at the ends of the two groups of the connecting tubes (401); Two groups of drive shafts (601) are provided and are respectively inserted into the two groups of connecting tubes (401); a mounting plate (603) is provided at one end of the drive shaft (601); a fastening plate (605) is detachably provided on a side of the mounting plate (603) facing the friction plate (406); and Two groups of propulsion assemblies are provided, which are arranged on the driving wheel (205) and are respectively connected to the two groups of driving shafts (601) to convert the rotation of the driving wheel (205) into driving the driving shaft (601) to slide along its axis; The locking assembly comprises: A locking frame (501) is arranged in the traveling frame (402) in a transversely slidable manner, a first pressing disk (404) is arranged at both ends of the traveling frame (402), a second pressing disk (502) is arranged at both ends of the locking frame (501), and the anti-slip wheel (405) is arranged between the first pressing disk (404) and the second pressing disk (502); an abutment plate (602) disposed on the driving shaft (601) and located on one side of the locking frame (501); and A fastening spring (503) is arranged between the locking frame (501) and the abutting plate (602).

2. A laser tracking measurement device according to claim 1, characterized in that: A positioning rod (107) is arranged inside the base (106), and the end of the positioning rod (107) is fixedly connected to the base (106) via an abutment seat (108). A connecting sleeve (302) is arranged on the mounting seat (301), and the connecting sleeve (302) is slidably sleeved on the positioning rod (107).

3. A laser tracking measurement device according to claim 2, characterized in that: A supporting spring (303) is provided between the connecting sleeve (302) and a group of abutment seats (108) at the top.

4. A laser tracking measurement device according to claim 1, characterized in that: Both ends of the walking frame (402) are connected to the base (106) via a tension spring (403), and the connection end between the tension spring (403) and the walking frame (402) is higher than the connection end between the tension spring (403) and the base (106).

5. The laser tracking measurement device according to claim 1, characterized in that: The control component includes: A transmission shaft (201) is rotatably disposed along its axis in the support cylinder (103), and one end of the transmission shaft (201) is coaxially fixedly connected to the driving wheel (205); A worm gear (202) is arranged on the transmission shaft (201); and The worm (203) is rotatably arranged along its axis in the support tube (103) and meshes with the worm wheel (202). One end of the worm (203) extends out of the support tube (103) and is connected to the knob (204).

6. The laser tracking measurement device according to claim 1, characterized in that: The propulsion assembly comprises: A propulsion frame (701) is provided with a guide column (702) perpendicular to the side of the base (106) on its upper side, and the guide column (702) is slidably arranged on the base (106) along its axis; A card-joining frame (604) is arranged on the installation plate (603) and is slidably card-joined on the propulsion frame (701); and The transmission arm (703) has one end hinged to the driving wheel (205) and the other end hinged to the propulsion frame (701).

7. The laser tracking measurement device according to claim 1, characterized in that: The support tube (103) is provided with a handle (104), and the handle (104) is provided with a level (105).

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