Cam steering rear drive dolly with steering fine adjustment mechanism

Abstract

The utility model provides a kind of cam steering rear drive dolly with steering fine adjustment mechanism, solve the problem of skidding or rollover caused by double rear wheel drive, and the problem that deviation of actual walking track and theoretical walking track of dolly is caused by the modification and adjustment between cam and front wheel in background art cannot be carried out.Techincal scheme, set in the driven rear wheel and driven rear wheel of the rear part of the vehicle frame;Driving motor, it is transmission connection with the driven rear wheel;Steering front wheel assembly, including support rod and front wheel, the rotation of the support rod can drive the front wheel steering;Steering cam assembly, including rotatably arranged in the cam shaft of the vehicle frame and the cam fixed in one end of the cam shaft;Steering transmission assembly is used for driving the steering front wheel assembly steering according to the outer contour shape when the cam rotates, to control the movement track of dolly;The steering transmission assembly includes: the arrow mark for indicating its initial position is equipped on the cam.

Description

Technical Field

[0001] This utility model relates to the field of drive vehicle technology, specifically a cam-steering rear-drive vehicle with a steering fine-tuning mechanism. Background Technology

[0002] With the widespread application of intelligent electric vehicles in logistics, transportation, and educational robots, the high precision and adaptive capability of their steering mechanisms have become key technological challenges. Especially in complex scenarios, such as those with multiple obstacles or discontinuous paths, traditional steering mechanisms like four-bar linkages and Geneva mechanisms struggle to meet practical needs due to poor trajectory adaptability and low control precision. According to the "Notice on Pilot Programs for Access and Road Traffic of Intelligent Connected Vehicles" issued by the Ministry of Industry and Information Technology in 2023, high-precision steering control technology has been listed as a core research direction for intelligent driving, requiring the tracking error of the steering system under dynamic paths to be controlled within 5cm. Furthermore, the 2025 China Undergraduate Engineering Practice and Innovation Ability Competition, themed "The Spirit of the Long March," requires participating vehicles to complete high-precision path tracking tasks in a simulated Long March route scenario. These vehicles typically need to automatically drive according to a preset route and complete specific tasks, such as bypassing obstacles.

[0003] Chinese invention patent CN119097929A discloses a steerable drive vehicle and a cam design method for the drive vehicle. The publication date is December 10, 2024. Section 0045 of the specification describes a device with a housing on the top of a base, a frame on the base, and a rotatable rear axle extending from the rear end of the frame. Rear wheels are connected to both ends of the rear axle. A drive motor is located at the rear end of the frame, with a first gear at its output end and a second gear on the rear axle. The first and second gears mesh to allow the rear axle to rotate. However, the drive motor directly and synchronously drives both rear wheels via the rear axle. Because the turning radii of the two rear wheels are different when turning, the inner rear wheel, with a smaller turning radius than the outer rear wheel, may slip or even tip over due to its shorter travel path. This causes the dual-wheel drive trajectory tracking to fail.

[0004] Furthermore, paragraph 0044 of the aforementioned patent (CN119097929A) discloses that the steering mechanism includes a gear reduction mechanism and a cam. The second gear meshes with the input end of the gear reduction mechanism. A first rotating shaft is rotatably mounted on the front end of the frame. The two ends of the first rotating shaft are respectively connected to the output end of the gear reduction mechanism and the middle of the cam. A connecting block is provided at the top of the steering shaft, and a contact rod is connected to the connecting block. The contact rod is correspondingly arranged with the outer contour line of the cam. Specifically, the cam can control the direction, and the gear reduction mechanism reduces the rotational speed of the cam, effectively increasing the distance the car travels in one revolution of the cam. The steering of the car's front wheels is controlled by the contact rod corresponding to the outer contour line of the cam. However, it only discloses that the contact rod corresponds to the outer contour line of the cam. When the outer contour line of the cam moves away from or near the contact rod, the contact rod cannot consistently contact the cam. During the experiment, the applicant discovered that during the assembly process of the drive car or after a long period of time and movement, the cam's control of the front wheel through the contact rod would deviate, requiring correction and adjustment to ensure that the car travels along the predetermined trajectory. However, the patent application did not disclose any relevant modification or adjustment technical solutions. Therefore, due to issues such as the machining accuracy of parts and assembly deviations, the actual travel trajectory of the car deviated from the theoretical travel trajectory. Utility Model Content

[0005] To address the shortcomings of existing technologies, this utility model provides a cam-steering rear-drive trolley with a steering fine-tuning mechanism, which effectively solves the slippage or rollover problems caused by dual rear-wheel drive as described in the background technology, as well as the problem that the technical solutions in the background technology cannot modify and adjust the relationship between the cam and the front wheel, resulting in a deviation between the actual and theoretical travel trajectories of the trolley.

[0006] To achieve the above objectives, the present invention provides the following technical solution.

[0007] A cam-steering rear-drive vehicle with a steering fine-tuning mechanism, comprising a frame, characterized in that it further comprises: The active rear wheel and the driven rear wheel are located at the rear of the vehicle frame; A drive motor, which is connected to the active rear wheel drive; A front steering wheel assembly includes a support rod and a front wheel, wherein rotation of the support rod can drive the front wheel to steer; A steering cam assembly includes a camshaft rotatably disposed within the vehicle frame and a cam fixed to one end of the camshaft; A speed reduction mechanism is connected between the drive motor and the camshaft, and is used to reduce the output speed of the drive motor and then transmit it to the camshaft; A steering transmission assembly is used to drive the front steering wheel assembly to steer according to the outer contour shape of the cam when the cam rotates, so as to control the movement trajectory of the trolley; the steering transmission assembly includes: a) A fine-tuning swing arm fixedly installed on the support rod; b) A push rod shaft that can be linearly slidably disposed on the fine-tuning arm, the push rod shaft being able to move in a direction toward or away from the cam; c) A first spring is provided in the middle of the fine-tuning arm, with the other end of the first spring fixed, for applying an elastic force to the fine-tuning arm so that the push rod shaft always keeps in contact with the outer edge of the cam; d) An adjustment mechanism disposed between the fine-tuning swing arm and the push rod shaft, used to drive the push rod shaft to move in a direction closer to or further away from the cam, so as to calibrate the correspondence between the outer contour of the cam and the steering angle of the front wheel; The cam is provided with an arrow marking to indicate its initial position.

[0008] As a further step, a rear axle is rotatably mounted on the rear of the frame, the driving rear wheel is fixedly mounted on the rear axle, and the driven rear wheel is rotatably mounted on the rear axle.

[0009] As a further step, a first gear is mounted on the output shaft of the drive motor, and a second gear that meshes with the first gear is mounted on the rear wheel axle.

[0010] As a further step, the aforementioned front steering wheel assembly also includes: Rotary connection to the front wheel clamp at the bottom of the frame; The front wheel is rotatably mounted on the bottom of the front wheel bracket; The support rod is fixedly connected to the top of the front wheel clamp.

[0011] As a further step, the aforementioned deceleration mechanism includes: The first gear and the second gear; A third gear fixedly mounted on the rear wheel axle; A drive shaft is rotatably mounted within the frame, and a fourth gear that meshes with the third gear is fixedly mounted on the drive shaft; the fourth gear has more teeth than the third gear. The fifth gear is fixedly mounted on the drive shaft; A sixth gear is fixedly mounted on the camshaft, the sixth gear meshes with the fifth gear, and the sixth gear has more teeth than the fifth gear.

[0012] As a further adjustment mechanism, the adjustment mechanism is a micrometer head mounted on the fine-tuning arm, the end of which abuts against the push rod shaft.

[0013] As a further step, a second spring is provided between the fine-tuning arm and the push rod shaft to apply tension to the push rod shaft.

[0014] As a further feature, a solar power system is also included, with solar panels mounted on the top of the vehicle frame.

[0015] Further features include a support base for lifting the trolley and suspending it during commissioning.

[0016] As a further step, the aforementioned debugging support base includes: A base plate used for support on a flat surface; At least three non-collinearly arranged columns are installed on the base plate, each column comprising an upper section and a lower section, wherein the diameter of the upper section is smaller than that of the lower section; The bottom of the frame is provided with an adjustment hole that mates with the column. The diameter of the adjustment hole is larger than that of the upper section of the column but smaller than that of the lower section of the column.

[0017] The beneficial effects of this utility model are: 1. Achieved high-precision motion trajectory calibration and compensation: This invention creatively provides a means for fine adjustment in the linear direction by adding a steering fine-tuning mechanism consisting of a fine-tuning arm, a push rod shaft, and a differential head. This design can accurately and quantitatively correct deviations in the correspondence between the cam profile and the front wheel steering angle caused by part machining errors and assembly tolerances, thereby ensuring that the actual travel trajectory of the vehicle closely matches the theoretical trajectory. The application of the differential head allows the value of each adjustment to be accurately recorded and reproduced, effectively avoiding the problems of over-adjustment or under-adjustment that easily occur in traditional experience-based adjustments, greatly improving debugging efficiency and trajectory tracking accuracy.

[0018] 2. Fundamentally eliminates the risks of slippage and rollover associated with dual-wheel drive: This invention abandons the complex dual-wheel synchronous drive scheme and innovatively adopts a rear wheel structure with a single active wheel drive and a free driven wheel. In this design, the inner and outer rear wheels can naturally rotate at different speeds during turns, completely eliminating the hidden dangers of forced slippage, jamming, and even vehicle rollover caused by the different turning radii of the inner and outer wheels. This not only ensures the stability and reliability of the vehicle's operation, especially when cornering, but also simplifies the overall vehicle structure, reduces manufacturing costs and assembly complexity, and minimizes cumulative errors that may be introduced by assembling multiple components.

[0019] 3. Provides convenient and efficient debugging and initial positioning functions: This utility model features clear arrow markings on the cam, providing an intuitive visual basis for quickly and accurately positioning the cam's initial mechanical position, greatly facilitating post-installation debugging. Furthermore, the accompanying dedicated debugging support base stably supports and suspends the trolley, freeing the wheels from ground resistance. This allows the operator to safely and easily complete a series of debugging operations, such as setting the initial angle of the front wheels, calibrating the fine-tuning mechanism, and verifying the cam's running trajectory, under no-load conditions, further ensuring the accuracy and convenience of debugging.

[0020] 4. Excellent motion matching is achieved through an optimized reduction mechanism: This invention uses a reduction assembly containing multi-stage gear transmission to significantly reduce the high speed of the drive motor before transmitting it to the camshaft, allowing the cam to rotate one revolution for the vehicle to travel a longer distance. This range-extending effect makes the vehicle's trajectory control smoother and more precise, making it particularly suitable for scenarios requiring large-scale, long-distance, and complex trajectory tracking. Attached Figure Description

[0021] Figure 1 This is a perspective view of the present invention; Figure 2 This is a two-dimensional view of the present invention. Figure 3 This is a three-dimensional view of the present invention. Figure 4 This is a perspective view of the present invention mounted on the debugging support base; Figure 5 This is a perspective view of the debugging support base of this utility model; Figure 6 This utility model has a three-dimensional structure. Figure 1 ; Figure 7 This utility model has a three-dimensional structure. Figure 2 ; Figure 8 This utility model has a three-dimensional structure. Figure 3 ; Figure 9 To show the three-dimensional view of the front steering wheel assembly and steering transmission assembly. Figure 1 ; Figure 10 To show the three-dimensional view of the front steering wheel assembly and steering transmission assembly. Figure 2 .

[0022] Explanation of reference numerals in the attached figures: Frame 1; Active rear wheel 2; Driven rear wheel 3; Drive motor 4; Steering front wheel assembly 5, support rod 501, front wheel 502, front wheel bracket 503; Steering cam assembly 6, camshaft 601, cam 602, arrow indicator 603; The speed reduction mechanism 7 includes a first gear 701, a second gear 702, a third gear 703, a transmission shaft 704, a fourth gear 705, a fifth gear 706, and a sixth gear 707. Steering transmission assembly 8, fine-tuning swing arm 801, push rod shaft 802, first spring 803, adjusting mechanism 804, second spring 805; Rear axle 9; 10 solar panels; The test support base 11, base plate 1101, column 1102, and test hole 1103 are included. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0024] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0025] It should be noted that in the description of this application, the directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0026] It should be noted that the scope of the methods and apparatus in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions in a substantially simultaneous manner or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0027] For ease of description, the orientation in this utility model is as follows: Figure 1 As shown in the description, the X-axis is defined as horizontal and the Y-axis is defined as vertical.

[0028] As one embodiment, this utility model discloses a cam-steering rear-drive vehicle with a steering fine-tuning mechanism, which has a frame 1 for supporting the entire vehicle. The rear of the frame 1 is respectively equipped with a driving rear wheel 2 and a driven rear wheel 3. Figure 1 As shown, the driving rear wheel 2 and the driven rear wheel 3 are located on the same straight line in the Z-axis direction. In one embodiment of the specific installation of the driving rear wheel 2 and the driven rear wheel 3, a rear wheel axle 9 extending along the Z-axis direction is rotatably mounted at the rear of the frame 1. The driving rear wheel 2 is fixed to the left end of the rear wheel axle 9, and the driven rear wheel 3 is rotatably mounted to the right end of the rear wheel axle 9. The rear wheel axle 9 is driven by a drive motor 4. After the rear wheel axle 9 is driven to rotate, it drives the driving rear wheel 2 to rotate. Since the driven rear wheel 3 is rotatably connected to the rear wheel axle 9, it can rotate freely with the vehicle, thus solving the problem of slippage when turning when both rear wheels are fixed to the rear wheel axle, as described in the background art.

[0029] In this embodiment, a steering front wheel assembly 5 is installed at the middle of the front part of the frame 1. The steering front wheel assembly 5 includes a front wheel bracket 503 rotatably connected to the bottom of the frame 1, a front wheel 502 rotatably mounted to the bottom of the front wheel bracket 503, and a support rod 501 fixedly connected to the top of the front wheel bracket 503. The front wheel 502 serves as support for the front of the bracket 1 and for steering. By rotating the support rod, the front wheel 502 can be rotated via the front wheel bracket 503, thereby controlling the direction of travel of the vehicle.

[0030] In this embodiment, the output shaft of the drive motor 4 is connected to a first gear 701, and the first gear 701 meshes with a second gear 702 that is fixed on the rear wheel axle 9. The drive motor 4 drives the rear wheel axle 9 to rotate through the first and second gears, so as to drive the active rear wheel as the drive wheel to make the trolley move forward.

[0031] In this embodiment, the frame 1 is also provided with a cam assembly 6 for steering control of the vehicle and a steering transmission assembly 8. The cam assembly 6 includes a camshaft 601 rotatably connected to the frame 1 and a cam 602 fixed on the camshaft 601.

[0032] The steering transmission assembly 6 is used to drive the cam 602 and the support rod 501 on the steering front wheel assembly 5. The steering transmission assembly 6 has a fine-tuning arm 801, which is generally L-shaped. Figure 9 and 10 As shown, a connecting plate is fixed to the first cantilever of the fine-tuning arm 801, and the connecting plate is fixed to the support rod 501. A push rod shaft 802 parallel to the second cantilever is slidably connected to the fine-tuning arm 801. A pull shaft is fixed to the top of the first cantilever of the fine-tuning arm 801. A first spring 803 is connected between the pull shaft and the frame 1. The first spring 803 pulls the fine-tuning arm 801 toward the cam 602 with the support rod 501 as the rotation center, so that the push rod shaft 802 always abuts against the cam 602. The steering transmission assembly also includes an adjustment mechanism 804, which drives the push rod shaft 802 to move closer to or further away from the cam 602. Preferably, the adjustment mechanism 804 is a micrometer head, with its housing connected to the fine-tuning arm 801. The feed shaft of the micrometer head abuts against the push rod shaft 802. Adjusting the micrometer head allows its feed shaft to extend forward or retract backward, thereby adjusting the correspondence between the outer contour of the cam 602 and the rotation angle of the front wheel 502, thus providing more precise control over the trolley's forward direction. A second spring 805 connects the fine-tuning arm 801 and the push rod shaft 802. The second spring 805 has tension, keeping the push rod shaft 802 in constant contact with the micrometer head to ensure the accuracy of the micrometer head adjustment. In this embodiment, an arrow mark 603 is provided on the cam end face to mark the initial position of the cam 602, facilitating the location of the cam's initial position during installation and debugging.

[0033] In this embodiment, the vehicle also includes a reduction mechanism 7, which reduces the output speed of the drive motor 4 and transmits it to the camshaft 601. The cam can control the direction, and the gear reduction mechanism reduces the speed of the cam, effectively increasing the distance the vehicle travels in one revolution of the cam. The reduction mechanism 7 includes: a first gear 701 fixed to the drive motor 4, a second gear 702 fixed to the rear axle 9, a third gear 703 fixed to the rear axle 9, a drive shaft 704 rotatably mounted in the frame, a fourth gear 705 and a fifth gear fixed to the drive shaft 704, and a sixth gear 707 fixed to the camshaft 601. The first gear 701 and the second gear 702 mesh, the third gear 703 meshes with the fourth gear 705 and the third gear 703 has fewer teeth than the fourth gear 705, and the fifth gear 706 meshes with the sixth gear 707 and the fifth gear 707 has fewer teeth than the sixth gear 707. Through the transmission and reduction of multi-stage gears, the speed of the drive motor 4 is reduced and then transmitted to the camshaft 601. The camshaft 601 drives the cam 602 to rotate, so as to achieve the purpose of driving the front wheels to steer.

[0034] In this embodiment, a debugging support base 11 is provided to support the trolley and suspend it in the air during debugging. The debugging support base 11 has a base plate 1101 and three columns 1102 arranged in a triangle on the base plate 1101. Debugging holes 1103 that mate with the columns 1102 are provided at the bottom of the frame 1. The columns 1102 have shoulders, and the debugging holes 1103 are fitted onto the columns and supported on the shoulders.

[0035] In this embodiment, before using the trolley, it is first debugged. The trolley is suspended on the debugging support base 11 through the debugging hole 1103 and the column 1102. The initial position of the cam 602 is found by the arrow marker 603. The initial position of the cam 602 can be set when the arrow marker 603 points to the push rod shaft 802. Then, the angle of the front wheel 502 is adjusted by the micrometer head. In this embodiment, it is aligned with the front. After adjustment, the trolley is removed from the debugging support base 11 and can then travel on a fixed trajectory. During travel, the drive motor 4 drives the active rear wheel 2 to rotate, moving the trolley forward. At the same time, the rotation of the drive motor 4 is transmitted to the cam 602 through the reduction mechanism 7. The outer contour of the cam 602 is designed according to the travel trajectory. The rotation of the cam 602 drives the micro-adjustment swing arm 801 to rotate through the push rod shaft 802, and then drives the front wheel 502 to steer through the support rod 501. The first spring 803 ensures that the push rod shaft 802 always abuts against the cam 602 to ensure steering accuracy.

[0036] In this embodiment, a solar power supply system is also included, with solar panels 10 disposed on the top of the vehicle frame 1. The solar power supply system is used to power the vehicle.

Claims

1. A cam-steering rear-drive vehicle with a steering fine-tuning mechanism, comprising a frame (1), characterized in that, Also includes: The active rear wheel (2) and the driven rear wheel (3) are located at the rear of the frame (1). A drive motor (4) is connected to the active rear wheel (2) via a transmission. The steering front wheel assembly (5) includes a support rod (501) and a front wheel (502), wherein the rotation of the support rod (501) can drive the front wheel (502) to steer; The steering cam assembly (6) includes a camshaft (601) rotatably disposed within the frame (1) and a cam (602) fixed to one end of the camshaft (601). The speed reduction mechanism (7) is connected between the drive motor (4) and the camshaft (601) and is used to reduce the output speed of the drive motor (4) and transmit it to the camshaft (601). A steering transmission assembly (8) is used to drive the steering front wheel assembly (5) to steer according to its outer contour shape when the cam (602) rotates, so as to control the movement trajectory of the trolley; the steering transmission assembly (8) includes: a) A fine-tuning swing arm (801) is fixedly installed on the support rod (501). b) A push rod shaft (802) is linearly slidably disposed on the fine-tuning arm (801), the push rod shaft (802) being able to move in a direction toward or away from the cam (602); c) A first spring (803) is provided in the middle of the fine-tuning arm (801), the other end of which is fixed, for applying elastic force to the fine-tuning arm (801) so that the push rod shaft (802) always keeps in contact with the outer edge of the cam (602); d) An adjustment mechanism (804) disposed between the fine-tuning swing arm (801) and the push rod shaft (802) is used to drive the push rod shaft (802) to move in a direction closer to or further away from the cam (602) to calibrate the correspondence between the outer contour of the cam (602) and the steering angle of the front wheel (502); The cam (602) is provided with an arrow mark (603) for indicating its initial position.

2. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 1, characterized in that: The rear axle (9) is rotatably mounted on the rear of the frame (1), the driving rear wheel (2) is fixedly mounted on the rear axle (9), and the driven rear wheel (3) is rotatably mounted on the rear axle (9).

3. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 2, characterized in that: A first gear (701) is mounted on the output shaft of the drive motor (4), and a second gear (702) that meshes with the first gear (701) is mounted on the rear wheel axle (9).

4. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 1, characterized in that: The front steering wheel assembly (5) also includes: Rotary connection to the front wheel clamp (503) at the bottom of the frame (1); The front wheel (502) is rotatably mounted on the bottom of the front wheel bracket (503); The support rod (501) is fixedly connected to the top of the front wheel bracket (503).

5. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 3, characterized in that: The deceleration mechanism (7) includes: The first gear (701) and the second gear (702); The third gear (703) is fixedly installed on the rear wheel axle (9); A drive shaft (704) is rotatably mounted in the frame (1), and a fourth gear (705) that meshes with the third gear (703) is fixedly mounted on the drive shaft (704). The fourth gear (705) has more teeth than the third gear (703). The fifth gear (706) is fixedly installed on the drive shaft (704). A sixth gear (707) is fixedly mounted on the camshaft (601), the sixth gear (707) meshes with the fifth gear (706), and the sixth gear (707) has more teeth than the fifth gear (706).

6. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 1, characterized in that: The adjustment mechanism (804) is a micrometer head mounted on the micro-adjustment arm (801), and the end of the feed shaft of the micrometer head abuts against the push rod shaft (802).

7. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 6, characterized in that: A second spring (805) is also provided between the fine-tuning swing arm (801) and the push rod shaft (802) for applying tension to the push rod shaft (802).

8. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 1, characterized in that: It also includes a solar power system, with solar panels (10) mounted on top of the frame (1).

9. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 1, characterized in that: It also includes a debugging support base (11) for supporting the trolley and keeping it suspended during debugging.

10. The cam-steering rear-drive trolley with steering fine-tuning mechanism according to claim 9, characterized in that: The debugging support base (11) includes: Base plate (1101) used for support on a flat surface. At least three non-collinearly arranged columns (1102) are installed on the base plate (1101), each column (1102) comprising an upper section and a lower section, wherein the diameter of the upper section is smaller than that of the lower section; The bottom of the frame (1) is provided with an adjustment hole (1103) that cooperates with the column (1102). The diameter of the adjustment hole (1103) is larger than the upper section of the column (1102) but smaller than the lower section of the column (1102).

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