Dry quenching transverse movement traction system and method for horizontal gear and rack transmission

Abstract

The invention relates to the technical field of dry quenching equipment, in particular to a dry quenching transverse movement traction system and method driven by a horizontal gear and a rack. The coke tank conveying device is located between an elevator and a coke tank carrying vehicle, is used for transversely conveying coke tanks and trolleys, and comprises a traction trolley, a driving unit arranged on the traction trolley, a gear set connected with the output end of the driving unit, a rack meshed with the gear set and a rail allowing the traction trolley to walk. The trailer wagon is connected with the coke tank and the trolley through a coupler; the gear set comprises at least two output gears used for being meshed with the racks, the gear end faces of the output gears are horizontally arranged, and the direction of acting force generated when the output gears are meshed with the racks is parallel to the ground. The three aspects of high-strength continuous operation reliability, high-precision motion control and compact space adaptation are well balanced, transmission is accurate, operation is stable, the structure is simplified, space is saved, and harmful overturning moment can be effectively eliminated.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of dry quenching equipment, in particular to a horizontal gear and rack transmission dry quenching horizontal moving traction system and method. BACKGROUND

[0002] Dry quenching technology is a key energy-saving and environmental protection technology in the steel industry. It cools the hot red coke by using inert gas (such as nitrogen), recovers its sensible heat and is used for power generation or steam production, thereby significantly reducing coke-making energy consumption, reducing pollutant emissions and improving coke quality. Since the 1940s, this technology has developed to the present and has become a standard configuration for modern large-scale coking enterprises.

[0003] In the dry quenching process, the coke pot carrying the red coke needs to be precisely translated between the coke oven, the elevator tower and the dry quenching furnace loading device. This function is completed by the horizontal moving traction device. The device needs to pull the coke pot and trolley device with a total weight of more than 100 tons, and realize high-load, high-frequency reciprocating motion and precise positioning in a narrow and limited space. Therefore, the reliability, running stability, positioning accuracy and compactness of the horizontal moving traction device are crucial.

[0004] At present, the common horizontal moving traction technology scheme mainly includes two types: One is the steel wire rope traction type. Although this scheme has a relatively simple structure, the steel wire rope has obvious elongation deformation problem under long-term high-load operation, which leads to the decrease of traction stroke control accuracy and the need for frequent tension adjustment, resulting in large maintenance workload. More importantly, the elastic deformation of the steel wire rope makes it difficult to achieve precise and stable control of the motion state of the coke pot, and impact is easily generated during start and stop, affecting the service life and positioning accuracy of the equipment.

[0005] The second is the rack traction type. This scheme adopts gear and fixed rack meshing transmission, which theoretically has higher transmission rigidity and positioning accuracy. However, the traditional rack type traction device usually arranges the end face of the gear vertically (i.e. the gear axis is horizontal), which causes a vertical force to the track plane when the gear and the rack mesh. In order to balance this upward overturning moment and prevent the device from overturning, complex structures such as pressure rollers, guide rollers, large rotary arms and their supporting frames must be added. This not only makes the whole device structure complex, occupies a large space and consumes a lot of materials, but also increases the manufacturing and maintenance costs. In the narrow space layout commonly existing in coking plants, the large size of the traditional rack type traction device has become the main constraint of its application.

[0006] Therefore, the horizontal moving traction device in the prior art is difficult to achieve a good balance among high-intensity continuous operation reliability, high-precision motion control and compact space adaptation. SUMMARY

[0007] In order to overcome the deficiencies of the prior art, the horizontal gear and rack transmission dry quenching horizontal moving traction system and method are provided, which achieves a good balance among high-intensity continuous operation reliability, high-precision motion control and compact space adaptation, and has transmission accuracy, smooth operation, structure simplification, space saving and effective elimination of harmful overturning moment.

[0008] In order to achieve the above purpose, the following technical solutions are adopted: A horizontal gear and rack transmission dry quenching horizontal moving traction system is located between an elevator and a coke pot carrying vehicle, and is used for horizontal transportation of coke pots and trolleys, and comprises a traction trolley, a driving unit arranged on the traction trolley, a gear set connected with an output end of the driving unit, a rack engaged with the gear set, and a track for walking of the traction trolley; the traction trolley is connected with the coke pots and the trolleys through a trolley hook; the gear set comprises at least two output gears for engaging with the rack, and a gear end surface of the output gear is arranged horizontally, and an acting force generated by the engagement of the output gear with the rack is parallel to the ground.

[0009] Further, the driving unit comprises a motor, a speed reducer connected with an output shaft of the motor, and a brake arranged at the other end of the motor.

[0010] Further, the gear set comprises a driving gear, a first driven gear, an idler gear, a second driven gear, a first output gear and a second output gear; the driving gear is connected with the output shaft of the speed reducer, and engages with the first driven gear and the idler gear; the idler gear engages with the second driven gear; the first driven gear is coaxially arranged with the first output gear, and the second driven gear is coaxially arranged with the second output gear; the first output gear and the second output gear both engage with the rack.

[0011] Further, the first output gear and the second output gear are opposite in rotation direction, and the vertical forces generated by the engagement of the first output gear and the second output gear with the rack are equal in size and opposite in direction.

[0012] Further, the system further comprises a locking device arranged at the end of the track, which is used for locking the traction trolley in a non-traction state.

[0013] Further, the traction trolley comprises a front wheel set connected by a fixed frame and a rear wheel set hinged to the fixed frame by a pin shaft; the locking device is arranged below the rear wheel set and is turned to disconnect or connect with the rear wheel set.

[0014] A dry quenching horizontal traction method based on the above system, comprising the following steps: The unlocking step: operating the locking device to release the locking of the traction trolley; The connecting step: connecting the coke can and the trolley to the traction trolley through the coupler; The traction step: starting the motor, and transmitting the power to the output gear meshing with the rack through the reducer and the gear set in sequence to drive the traction trolley, the coke can and the trolley to move along the track, completing the pushing out or introduction of the coke can; The braking step: braking the motor by the brake; The locking step: locking the traction trolley after it reaches the target position by operating the locking device.

[0015] Further, in the traction step, the power of the motor is evenly distributed to the first output gear and the second output gear through the gear set.

[0016] Further, in the traction step, due to the meshing force of the output gear and the rack being parallel to the ground, the system does not generate overturning moment perpendicular to the ground.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. High transmission accuracy, smooth operation and accurate control, which fundamentally overcomes the inherent defects of steel wire rope transmission.

[0018] Compared with the traditional steel wire rope traction method, the present application adopts a rigid transmission form of gear and rack meshing. Steel wire rope, as a flexible body, will have an elastic elongation and plastic deformation that cannot be ignored when bearing repeated traction of hundreds of tons of load, resulting in an increase in cumulative error of traction stroke and the need for frequent shutdown tensioning. At the same time, the start and stop of flexible transmission have hysteresis, which is easy to cause the shaking and impact of the coke can. The gear and rack meshing of the present application is rigid meshing, and the transmission has no elastic hysteresis, the meshing gap is small and constant. The transmission ratio of the system is constant, and the stroke control only depends on the number of revolutions of the gear, achieving millimeter-level accurate positioning; the start and stop response is rapid, and there is no flexible impact in the movement process, so that the running track of the coke can is stable and controllable, greatly improving the reliability of the operation of the entire dry quenching system.

[0019] 2. The structure is greatly simplified, and the space and materials are significantly saved, especially suitable for narrow spaces.

[0020] Compared to traditional rack and pinion traction devices (where the gear end faces are arranged vertically), the core improvement of this invention lies in arranging the end face of the output gear horizontally. This change brings about a fundamental difference in mechanics: when a traditional vertical gear meshes with a rack, the meshing force can be decomposed into a horizontal driving force and a vertically upward component. This upward component generates a torque that can overturn the entire traction trolley and coke can. To balance this torque, pressure rollers and guide rollers must be added to provide downward pressure, and a robust slewing arm and a large support frame are required to withstand the reaction force, resulting in a complex structure, large size, and high material consumption. This invention, by turning the gear rotation plane horizontal, ensures that the meshing force of the gear and rack is always parallel to the ground and track plane, fundamentally eliminating the vertical overturning torque. Therefore, the direct effect is the complete elimination of the entire set of auxiliary devices, including pressure rollers, guide rollers, slewing arms, and large supports, required to balance the overturning torque. This allows for a more compact lateral and vertical dimension of the entire traction system, reduces the requirements for installation foundations, and is particularly suitable for space-constrained conditions within coking plants. It also saves a considerable amount of steel and reduces manufacturing and installation costs.

[0021] 3. The force is evenly distributed under single-motor drive, avoiding the harmful internal forces and impacts caused by the asynchrony of dual motors.

[0022] For heavy-load, wide-gauge traction systems, a common approach is to use dual motors to drive gears on both sides. However, differences in the characteristics of the two motors and even slight variations in the control system response can lead to incomplete synchronization of the driving forces on both sides. This results in torsional loads within the vehicle body, which can damage the structure over time and cause a jerking sensation during startup. This invention employs a single-motor drive and a carefully designed gear set to distribute and divide the power. Specifically, power is transmitted from the driving wheel to the idler wheel on the other side, ultimately driving two coaxial output gears. Through matching gear parameters, it is ensured that the two output gears receive power with the same rotational speed, opposite directions of rotation, and balanced torque. This achieves absolute mechanical synchronization under a single power source, ensuring that the driving forces acting on the racks on both sides of the traction trolley are equal in magnitude and coordinated in direction. This completely eliminates internal stress, deviation, and the resulting additional impacts caused by asynchronous driving on both sides, improving the inherent reliability and smoothness of the transmission system.

[0023] 4. Optimized mechanical state, reasonable stress on equipment, and extended service life.

[0024] Because the two output gears rotate in opposite directions and are symmetrically arranged, the horizontal components of the force generated by their meshing with the rack, perpendicular to the track direction, are also equal in magnitude and opposite in direction. These two forces form a pair of self-balancing internal couples, canceling each other out within the system and preventing them from being transmitted to the track foundation and car body structure to form additional lateral loads. The wheels and rails of the traction trolley only need to bear the main vertical load and the horizontal traction / braking force, greatly simplifying and clarifying the stress state. This improves the load conditions of key load-bearing components such as the track, wheel bearings, and frame, reduces uneven wear and abnormal stress, helps extend the service life of the entire equipment, and reduces maintenance frequency and costs.

[0025] In summary, this invention, through the core concept of horizontal gear and rack transmission, systematically solves multiple technical problems such as low accuracy and large deformation of traditional wire rope traction, as well as the complex structure, overturning moment, and large space occupation of traditional rack traction. At the same time, with the addition of a single motor uniform drive design, it achieves the organic unity of high precision, high stability, high reliability, compact structure, and energy saving and material saving, bringing about a combination of beneficial effects. Attached Figure Description

[0026] Figure 1 This is a schematic front view of the structure of the present invention.

[0027] Figure 2 This is a schematic side view of the gear set structure of the present invention.

[0028] Figure 3 This is a schematic top view of the gear set structure of the present invention.

[0029] The markings in the diagram are: 1. Rack; 2. Traction trolley; 3. Reducer; 4. Motor; 5. Brake; 6. Coupler; 7. Locking device; 8. Coke tank and trolley; 9. Track; 10. First driven gear; 11. Driving gear; 12. Idler gear; 13. Second driven gear; 14. First output gear; 15. Second output gear. Detailed Implementation

[0030] The embodiments of the present invention are described in detail below. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and does not constitute any limitation on the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0033] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0034] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings: like Figure 1 , Figure 2 and Figure 3 As shown, this invention provides a horizontal gear and rack drive lateral traction system for dry quenching, which is installed on a fixed foundation between the hoist of the dry quenching device and the coke tank transport vehicle (not shown in the figure). Its core function is to precisely and smoothly traction coke tanks and trolleys 8 with a total weight of over 100 tons in the horizontal direction, realizing the conversion of the coke tanks between the receiving position (such as on the transport vehicle) and the lifting position (directly below the hoist).

[0035] The system mainly includes a rack 1, a traction trolley 2, a reducer 3, a motor 4, a brake 5, a coupler 6, a locking device 7, and a track 9 for the traction trolley 2 to travel on. The track 9 is fixedly installed on the foundation with anchor bolts and other fasteners, providing load-bearing and guidance for the traction trolley 2. Two long racks 1 are fixedly laid along the length of the track 9, located between or on both sides of the two parallel tracks 9.

[0036] The traction trolley 2 is the mobile carrier of the entire system. Its body structure preferably adopts a six-wheel design, divided into a front wheel set and a rear wheel set. The front wheel set contains four wheels and is mounted on a rigid fixed frame; the rear wheel set contains two wheels and is mounted on a rotatable trolley hinged to the rear end of the fixed frame via a vertical pin. This hinged design allows the rear wheel set to swing within a certain angle, helping to adapt to minor unevenness in the track installation and improving wheel-rail contact. At the rear end of the traction trolley 2, a coupler 6 is provided for connecting or disengaging with the corresponding hook at the front end of the coke tank trolley 8, thereby realizing power transmission.

[0037] A drive unit is installed on the upper part of the fixed frame of the traction trolley 2. The drive unit includes a three-phase asynchronous motor 4, a horizontal reducer 3 directly connected to the output shaft of the motor 4, and a normally closed brake 5 installed on the non-output end of the motor 4. The motor 4 provides the prime mover, the reducer 3 converts the high speed and low torque of the motor into a low speed and high torque output, and the brake 5 is used to quickly brake the motor shaft to achieve a safe stop when the system needs to stop or in an emergency.

[0038] The output shaft of reducer 3 drives a gear set via a key connection or other means. Figure 2 and Figure 3 The gear set specifically includes a driving gear 11, a first driven gear 10, an idler gear 12, a second driven gear 13, a first output gear 14, and a second output gear 15. The driving gear 11 is directly mounted on the output shaft of the reducer 3. The driving gear 11 meshes with both the first driven gear 10 and the idler gear 12. The idler gear 12 meshes with the second driven gear 13. The first driven gear 10 and the first output gear 14 are fixed on the same first drive shaft and rotate synchronously coaxially; the second driven gear 13 and the second output gear 15 are fixed on the same second drive shaft and rotate synchronously coaxially. The first and second drive shafts are mounted parallel to each other on the bottom of the traction trolley 2 frame via bearing seats. Crucially, the end faces (i.e., the plane where the teeth are located) of the first output gear 14 and the second output gear 15 are horizontally arranged, and their axes are perpendicular to the ground. These two output gears 14 and 15 mesh with the rack 1 fixed to the ground from below.

[0039] Through the specific arrangement of the gear set described above (especially the introduction of idler gear 12), the following effects are achieved: the power from the single motor 4, after passing through the reducer 3 and the gear set, is evenly and mechanically distributed to the first output gear 14 and the second output gear 15. Furthermore, by designing the number of teeth on the gears, the first output gear 14 and the second output gear 15 rotate in opposite directions, but their rotational speeds and the magnitude of the transmitted torque are the same.

[0040] At the end of track 9, corresponding to the parking position of the rear wheel assembly of the traction trolley 2, a locking device 7 is provided. This locking device 7 can be a wedge block or a pin mechanism that can rotate around a horizontal axis. When the traction trolley 2 needs to be locked, the locking device 7 is operated to rotate upward, so that it engages with the rim of the rear wheel assembly or a specially designed groove, preventing the wheel from rolling; when traction is needed, it is operated to rotate downward to move away from the interference position.

[0041] A dry quenching coke lateral movement traction method, implemented based on the above system, is as follows: I. The process of removing coke from the can: 1. Initial state: The traction trolley 2 is located at the end of the track near the hoist, and the locking device 7 is raised to lock its rear wheel assembly. The coke tank and trolley 8 are located on the transport vehicle.

[0042] 2. Unlocking and Connecting: First, the operator or the automatic control system drives the locking device 7 to rotate downwards, releasing the lock on the rear wheel set of the traction trolley 2. Then, the motor 4 of the traction trolley 2 starts (at low speed), driving the traction trolley 2 to move slowly towards the coke tank carrier until its coupler 6 is accurately engaged with the hook of the coke tank trolley 8.

[0043] 3. Traction and Pushing: After the coupler 6 is securely connected, the motor 4 starts at full forward speed. The power transmission path is: motor 4 → reducer 3 → drive gear 11 → simultaneously drives the first driven gear 10 and the second driven gear 13 driven by the idler gear 12 → first output gear 14 and second output gear 15. Since the output gears 14 and 15 mesh with the fixed rack 1, the rack 1 generates a reaction force on the gears. This reaction force is completely parallel to the ground, pushing the traction trolley 2, along with the coke tank and the trolley 8 behind it, to move smoothly down the track 9 towards the elevator. During the entire traction process, because the two output gears 14 and 15 rotate in opposite directions, the horizontal components of the force generated by their meshing with the rack 1, perpendicular to the track direction, are equal in magnitude and opposite in direction, forming a self-balancing couple within the system, and will not generate lateral thrust on the external foundation.

[0044] 3. Braking and Locking: Once the coke can reaches the designated position below the hoist, motor 4 stops supplying power, and brake 5 activates to quickly stop the motor and bring the system to a precise stop. Then, locking device 7 can be raised to lock the rear wheel assembly of the traction trolley 2, preventing it from moving due to external forces or vibrations. The hoist can then lower its lifting gear to grab the coke can for lifting operations.

[0045] II. The process of introducing an empty can: After the red-hot coke in the coke can is loaded into the dry quenching furnace, the empty can is lifted back onto the trolley 8 on the track by the hoist. At this time, the motor 4 reverses, driving the traction trolley 2 to pull the empty can and trolley 8 back onto the coke can transport car. The steps are the reverse of the pushing process, but the principle is the same. After reaching the destination, the coupler 6 disengages, and the traction trolley 2 returns to its initial position alone and is locked by the locking device 7, waiting for the next cycle.

[0046] Verification of the overall effect brought about by this embodiment: High precision and smoothness: Utilizing rigid gear and rack meshing, it eliminates the elastic elongation issues associated with wire rope drives. Stroke control depends solely on the number of gear rotations recorded by the motor encoder, achieving a positioning accuracy within ±2mm, far exceeding that of wire rope drives (typically ±50mm or more). The start-up and stopping processes are free of soft impacts, ensuring smooth operation.

[0047] Simplified structure and space saving: Because the output gears 14 and 15 are arranged horizontally, their meshing force with the rack 1 is parallel to the ground, completely eliminating the upward overturning moment generated by the traditional vertical gear arrangement. Therefore, this embodiment successfully eliminates the pressure roller, guide roller, large rotary arm and its heavy support frame that are indispensable in traditional rack traction, making it very suitable for retrofitting or building new structures in the narrow space of existing coking plants.

[0048] Optimized stress distribution and high reliability: A single motor achieves absolute synchronous drive on both sides through a gear set, avoiding the asynchrony problems that may exist in dual-motor drives, and fundamentally eliminating internal damage and deviation impacts caused by speed differences on both sides. At the same time, the horizontal meshing force and self-balancing lateral force make the stress state of the traction trolley 2 and track 9 clear and simplified, mainly bearing vertical pressure and longitudinal friction, which significantly improves the service life of key components such as bearings and tracks, and reduces the failure rate and maintenance costs.

[0049] The above description is only a part of the specific embodiments of the present invention. The scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A horizontal gear and rack transmission system for lateral movement of dry quenching coke, characterized in that, Located between the hoist and the coke tank carrier, for lateral transport of coke tanks and trolleys (8), including a traction trolley (2), a drive unit mounted on the traction trolley (2), a gear set connected to the output end of the drive unit, a rack (1) meshing with the gear set, and a track (9) for the traction trolley (2) to travel on. The traction trolley (2) is connected to the coke tank and the trolley (8) via a coupler (6); The gear set includes at least two output gears (14, 15) for meshing with the rack (1), and the end faces of the output gears (14, 15) are arranged horizontally, and the direction of the force generated by their meshing with the rack (1) is parallel to the ground.

2. The horizontal gear and rack transmission dry quenching coke lateral traction system according to claim 1, characterized in that, The drive unit includes a motor (4), a reducer (3) connected to the output shaft of the motor (4), and a brake (5) disposed at the other end of the motor (4).

3. The horizontal gear and rack transmission dry quenching coke lateral traction system according to claim 2, characterized in that, The gear set includes a driving gear (11), a first driven gear (10), an idler gear (12), a second driven gear (13), a first output gear (14), and a second output gear (15). The driving gear (11) is connected to the output shaft of the reducer (3) and meshes with the first driven gear (10) and the idler gear (12); The idler gear (12) meshes with the second driven gear (13); The first driven gear (10) is coaxially arranged with the first output gear (14), and the second driven gear (13) is coaxially arranged with the second output gear (15); Both the first output gear (14) and the second output gear (15) mesh with the rack (1).

4. The horizontal gear and rack transmission dry quenching coke lateral traction system according to claim 3, characterized in that, The first output gear (14) and the second output gear (15) have opposite rotation directions, and the component forces generated by their meshing with the rack (1) in the direction perpendicular to the track (9) are equal in magnitude and opposite in direction.

5. A horizontal gear and rack transmission dry quenching coke lateral traction system according to claim 1, characterized in that, It also includes a locking device (7) located at the end of the track (9) for locking the traction trolley (2) in a non-traction state.

6. A horizontal gear and rack transmission dry quenching coke lateral traction system according to claim 5, characterized in that, The traction trolley (2) includes a front wheel assembly connected to a fixed frame and a rear wheel assembly hinged to the fixed frame via a pin. The locking device (7) is located below the rear wheel assembly, and its rotation enables it to disengage from or connect to the rear wheel assembly.

7. A dry quenching coke lateral movement traction method, implemented based on a horizontal gear and rack transmission dry quenching coke lateral movement traction system as described in any one of claims 1-6, characterized in that, Includes the following steps: Unlocking steps: Operate the locking device (7) to release the lock on the traction trolley (2); Connection steps: Connect the coke tank and trolley (8) to the traction trolley (2) via the coupler (6); Traction steps: Start the motor (4), and the power is transmitted sequentially through the reducer (3) and gear set to the output gear (14, 15) meshing with the rack (1), driving the traction trolley (2) and the coke tank and trolley (8) to move along the track (9) to complete the pushing out or pushing in of the coke tank; Braking steps: Brake the motor (4) by means of brake (5); Locking procedure: After the traction trolley (2) reaches the target position, operate the locking device (7) to lock it.

8. The dry quenching coke transverse traction method according to claim 7, characterized in that, In the traction step, the power of the motor (4) is evenly distributed to the first output gear (14) and the second output gear (15) through the gear set.

9. The dry quenching coke transverse traction method according to claim 7, characterized in that, During the traction step, since the meshing force between the output gears (14, 15) and the rack (1) is parallel to the ground, the system does not generate an overturning moment perpendicular to the ground.

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