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Review

Research Status and Prospects of Automatic Leveling Technology for Orchard Machinery

by
Guangyu Xue
1,2,
Jiwen Peng
1,2,
Haiyang Shen
1,2,
Gongpu Wang
1,
Wenhao Zheng
1,2,
Sen Huang
1,2,
Zihan Huan
1,2,
Lianglong Hu
2,* and
Wenqin Ding
1,*
1
Nanjing Institute of Agricultural Mechanization, Ministry of Agriculture and Rural Affairs, Nanjing 210014, China
2
Graduate School of Chinese Academy of Agriculture, Beijing 100083, China
*
Authors to whom correspondence should be addressed.
Sustainability 2025, 17(12), 5297; https://doi.org/10.3390/su17125297
Submission received: 7 May 2025 / Revised: 30 May 2025 / Accepted: 6 June 2025 / Published: 8 June 2025
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Abstract

China’s orchards cover vast areas, predominantly located in hilly regions where the terrain is complex, making mechanized operations difficult to implement effectively. This results in a low comprehensive mechanization rate in the fruit planting industry, severely restricting the development of agricultural mechanization in China’s hilly areas. This article first explains the principles of automatic leveling technology, summarizing the characteristics and suitable application scenarios of different leveling technologies in the context of actual work in hilly orchards. It then provides an overview of the research progress in automatic leveling machinery for orchards from the perspectives of power machinery, operation platforms, and operating tools, analyzing the leveling control schemes of various orchard operation machinery equipped with automatic leveling features tailored for hilly orchard work. This article explores key technologies for chassis leveling, summarizes universal leveling mechanisms and control algorithms, analyzes the numerous challenges faced by the current development of automatic leveling technology for orchard machinery, and offers targeted development suggestions.

1. Introduction

China is a major fruit-growing country [1]. As of 2023, the area of orchards in China has reached 12,738.06 thousand hectares [2], with high-quality orchards mainly distributed in hilly regions such as the central Sichuan, Shandong, Guangdong–Guangxi, and Shaanxi–Gansu [3,4,5]. Hilly orchard terrain is complex, with poor working environments and certain slopes, making it difficult for traditional agricultural machinery to operate effectively. The 2022 National Agricultural Mechanization Development Statistical Bulletin indicates that the comprehensive mechanization rate for crop farming in China has reached 73.11% [6]. However, there are nearly 46,667 thousand hectares of hilly mountainous cropland where mechanization development is significantly lagging behind that of plain areas, with a comprehensive mechanization rate for farming that is 20 percentage points lower than the national average [7]. In recent years, rapidly developing orchard picking robots and spectral information collection equipment for orchards, among other precision agriculture equipment, have high requirements for the ground environment of orchards. When these devices operate in complex terrain, it is easy for the calibration relationship between the onboard equipment’s base coordinate system and the geodetic coordinate system to become misaligned, and errors can be transmitted through the motion chain to the end effector, reducing its positioning accuracy and work efficiency. The application of automatic leveling technology can alleviate these issues to some extent.
Automatic leveling technology achieves real-time monitoring and precise control of equipment posture by integrating sensor systems and automatic control algorithms, ensuring stable operation of equipment in complex terrain conditions. In the field of orchard machinery, with the introduction of precision agriculture and sustainable development concepts, the requirements for the accuracy of orchard machinery operations have significantly increased; the application of automatic leveling technology allows for operational equipment to flexibly respond to changes in slope and terrain, significantly improving the work efficiency and safety of machinery in hilly orchards, ensuring precise execution of operations, reducing pesticide and fertilizer pollution, protecting soil and water resources, and promoting the sustainable development of precision smart agriculture. This provides strong support for the high-quality and stable development of the fruit industry and is of great significance in promoting the mechanization and modernization process of hilly orchards and sustainable agricultural development.
This article focuses on the mechanized operation scenarios of hilly orchards, aiming to improve the precision of orchard mechanization. It analyzes the research progress of automatic leveling technology for orchards in countries with a high proportion of hilly terrain. First, it introduces the basic control principles of automatic leveling technology and categorically discusses the characteristics and application scenarios of different leveling technologies. It also summarizes the research progress of automatic leveling machinery from three aspects: power machinery, operating platforms, and working tools. Furthermore, it analyzes key leveling technologies for chassis that have potential application prospects in the field of orchard machinery, points out the challenges faced by research on automatic leveling technology for orchard machinery, and puts forward targeted development suggestions.

2. Overview of Automatic Leveling Technology

2.1. The Basic Principle of Automatic Leveling Technology

Automatic leveling technology is a key technology that ensures mechanical equipment, vehicles, or tools maintain a level or specific angle on uneven terrain or in dynamically complex environments [8]. Automatic leveling technology is based on a feedback control system, which uses attitude sensors to obtain the tilt angle and position information of the equipment. The controller processes and calculates the adjustment amount, driving the actuator for attitude adjustment, enabling the equipment to achieve a level state, ensuring the stability and safety of equipment operation. A typical control loop of an automatic leveling system is shown in Figure 1.

2.2. Composition and Classification

The automatic leveling system generally includes three main modules: sensors, control systems, and actuators. The control system is the core of the entire automatic leveling system, responsible for receiving signals from sensors and issuing commands to drive the actuators to perform corresponding actions. Based on the configuration of the actuator’s movement branches, it can be divided into two types: series type and parallel type [9]. In the series type automatic leveling mechanism (as shown in Figure 2a), there is only one movement chain, with each leg independently controlled, providing high flexibility, and the components in the movement chain are connected end to end in a series arrangement. In contrast, the parallel automatic leveling system (as shown in Figure 2b) has a shorter movement chain, with multiple movement chains acting together in the working space, offering excellent stability and overturning resistance. The advantages and disadvantages of the two types of actuators are summarized in Table 1. In orchard mechanization operations, parallel automatic leveling systems have been applied in high-load scenarios such as fruit transportation, automatic leveling of manned platforms, and leveling the chassis of working machines due to their outstanding stability and load-bearing capacity. With the continuous in-depth research on parallel mechanisms and the ongoing development of kinematic solution algorithms for parallel mechanisms [10,11], parallel automatic leveling mechanisms are gradually being widely adopted.
In the hardware structure of the automatic leveling system, it can be divided into “static plane”, “dynamic plane”, and “support” based on its relative motion to the ground. The “static plane” remains relatively stationary with respect to the ground (or the moving carrier). In some automatic leveling systems, the ground itself serves as the “static plane”, while the “dynamic plane” is connected to the “static plane” through the “support”. The “support” in an automatic leveling system is mainly classified into rigid, semi-rigid, and elastic support [13]. Rigid support includes various support methods such as three-point support, four-point support, and six-point support. Rigid support can provide maximum structural strength and minimum deformation, but it is relatively expensive and complex to install, usually applied in scenarios that require extremely high stability and precision [14], such as precision instrument platforms or heavy machinery; elastic support has good shock absorption performance, which helps reduce the impact of external vibrations on the equipment, improving the operational stability and service life of the equipment [15]. However, its structural strength and stability are not as good as rigid support, mainly applied in scenarios that need to absorb vibrations and shocks, such as vehicle suspension systems or certain special mechanical devices; semi-rigid support combines characteristics of both rigid and elastic support, which can ensure stability while enhancing the adaptability and durability of the system [16], providing certain structural strength and being able to absorb vibrations and shocks to a certain extent, suitable for scenarios with medium precision requirements. The specific classification characteristics and application scenarios are shown in Table 2.
In the control algorithm of automatic leveling systems, the classic PID control structure is simple and easy to implement, but its parameters are fixed, making it difficult to effectively cope with nonlinear factors such as terrain changes and load fluctuations, resulting in response lag and insufficient accuracy. With the introduction of modern control theory, various improvement strategies have emerged: Feedforward-PID control integrates a feedforward compensation mechanism to anticipate and offset major disturbances, enhancing the system’s response speed and anti-interference capability. Fuzzy PID control utilizes a fuzzy logic rule base to dynamically adjust PID parameters based on real-time errors and their rates of change, without relying on precise mathematical models, thus exhibiting stronger robustness. Neural network PID control leverages the powerful nonlinear mapping and learning capabilities of neural networks to adaptively optimize controller parameters. The characteristics and application scenarios of various control algorithms are shown in Table 3.

3. Research Status of Automatic Leveling Machinery in Orchards

There is a variety of orchard operation machinery, covering all aspects from planting, management to harvesting. Common types of orchard operation machinery mainly include power machinery, work platforms, and other implements such as mowers, sprayers, pruning machines, fertilization machines, and soil tillage equipment.

3.1. Power Machinery

Power machinery plays a vital role in orchard machinery, serving not only as the core driving force for mechanized operations in orchards but also as a key factor in improving production efficiency, reducing labor intensity, and cutting costs. Currently, various operational processes in orchards mainly rely on tractor-drawn schemes, connecting corresponding operational equipment to complete the work in each phase [17]. There remains a high demand for power machinery in orchard mechanization.

3.1.1. Research Progress in Power Machinery in China

To address the issues of traditional tractors being prone to tipping over in complex terrains, as well as poor adaptability and chassis stability, the Yang Fuzeng team from Northwest A&F University designed a hydraulic differential system based on traditional tracked tractors. They developed a mini remote-controlled hillside tracked tractor, which adjusts the vehicle’s posture by driving the differential system through hydraulic cylinders controlled by solenoid valves. The cylinders are equipped with limit switches internally, allowing for real-time detection of the piston position to form a closed-loop control system [18,19,20,21,22]. The leveling system of this tractor uses a PID algorithm for control, which is simple and user-friendly; however, the change in the center of gravity during the leveling process can affect the overall longitudinal stability of the tractor. Building on the aforementioned research, Sun Jingbin et al. further designed a remote-controlled omnidirectional leveling hillside tracked tractor (as shown in Figure 3), proposing a lateral leveling scheme based on a parallel four-bar linkage and a longitudinal leveling scheme based on a double-frame mechanism. This tractor can achieve lateral and longitudinal leveling on slopes from 0° to 15° laterally and 0° to 10° longitudinally [23,24], with adjustable ground clearance and good passability, demonstrating excellent maneuverability.
Shanxi Agricultural University researchers Sun Qiankun et al. designed a tractor chassis with a three-point automatic leveling mechanism (as shown in Figure 4) [25]. This chassis controls frame balance through a leveling cylinder, with a leveling angle range of −25° to 25°. Jian Hongliang et al. addressed the issues of easy tipping and poor passability in hilly and mountainous tractors by designing an adaptive hilly and mountainous tractor. They used virtual prototyping technology to analyze the lateral stability and obstacle-crossing performance of the chassis model based on actual operational requirements. The results showed that the maximum lateral stability angle of the chassis is 37.5°, which exceeds the standard [26] requirement of 35° and meets the operational requirements for hilly and mountainous areas [27].
In the field of tractor body posture control in hilly and mountainous areas, Qi Wenchao et al. from Shanghai Jiao Tong University designed a posture active adjustment system based on a double closed-loop fuzzy PID control algorithm. The tractor equipped with this system is shown in Figure 5a, which adjusts the tractor’s posture using two sets of oscillating mechanisms with eccentric wheels mounted on the rear drive axle (as shown in Figure 5b). This system employs a fuzzy PID algorithm for control, combined with angle sensors and body tilt sensors installed on the left and right oscillating mechanisms to form a double closed-loop control, effectively reducing overshoot and leveling time. In harsh working conditions, the system can control the body tilt angle within ±3° [28,29,30]. Based on this active adjustment system for tractor posture, Zhang Jinhui et al. further designed a synchronous control system for the posture of the tractor body and implement based on a neural network PID control algorithm, addressing issues such as the poor posture adjustment accuracy and reliability of existing tractors. The control effect is better than that of conventional PID control algorithms [31,32]. On a fixed-gradient surface, the adjustment error does not exceed 1°, and on a randomly graded surface, the maximum lateral tilt angle error of the body is 2.874°, demonstrating good control accuracy and stability.

3.1.2. Research Progress in Power Machinery Abroad

Abroad, leveling technology began to be applied in the agricultural machinery field as early as the mid-20th century [33]. Researchers primarily focused on the dynamic stability of tractors and posture control in complex scenarios. Zhen Li et al. [34] studied the dynamic stability of tractors and concluded that the suspension system stiffness and tire characteristics are key factors affecting lateral stability, and appropriately adjusting these parameters can significantly improve the safety of tractors on random road surfaces. The evaluation method proposed in this study can effectively predict the lateral stability of tractors and is of great guiding significance for tractor design and performance optimization.
To address the issues of control and stability of tractors moving on steep slopes, Behrooz Mashadi et al. [35] designed a two-layer controller consisting of a fuzzy upper controller and a PI lower controller to control the stability of the tractor. The structure of the controller is shown in Figure 6, consisting of an inner loop and an outer loop control circuit. The outer loop controller is mainly used for roll control, outputting the target hydraulic force based on the tractor’s roll angle and roll rate, while the inner loop controller is mainly used for force tracking control of the hydraulic system, avoiding overshoot and instability phenomena caused by the nonlinear regulation exhibited by the hydraulic system due to residual structural damping and back pressure generated during operation. Iman Ahmadi [36] studied the effects of forward speed, ground slope, and wheel–ground friction coefficient on the lateral stability of tractors under the presence of position disturbances, proposing that to improve the overall stability of tractors, priority should be given to increasing the stability index derived from slip dynamics.

3.1.3. Summary of Automatic Leveling Technology for Power Machinery at Home and Abroad

Power machinery is an important part of mechanized operations in orchards. Domestic researchers have mainly made innovations in leveling mechanisms and leveling schemes, proposing hydraulic differential high-type and parallel four-bar leveling mechanisms. In terms of leveling algorithms, there are dual closed-loop fuzzy PID control algorithms and neural network-based PID control algorithms. Foreign researchers have mainly focused on the relationship between multi-parameter collaborative control and the stability of power machinery, providing theoretical references for the collaborative control of power machinery posture. A comparison of various technical characteristics and leveling performance is shown in Table 4.

3.2. Operation Platform

The orchard work platform is the core of orchard mechanization, serving as a universal mechanical platform that participates in the comprehensive management and operations of the orchard. It plays a key role in reducing labor intensity and improving production efficiency during the process of mechanized production in orchards. In recent years, high-altitude work platforms introduced in the market are typically equipped with an automatic leveling system [37].

3.2.1. Research Progress in Operation Platform in China

Zou Daqing et al. from Jiangsu New Energy Vehicle Research Institute Co., Ltd. (Yancheng, China) collaborated with Jiangsu University to propose a hydraulic omnidirectional leveling scheme based on a point–line composite support “three-layer frame” in response to the agricultural machinery operation needs in hilly areas [38]. They designed an omnidirectional leveling tracked working machine (as shown in Figure 7), which can achieve a maximum leveling angle of 20° [39].
In response to the high-altitude operation requirements of orchards, Chongqing Xinyuan Agricultural Machinery Co., Ltd. (Chongqing, China) and Ding Xiaobing et al. designed a versatile lifting work platform for hilly orchards with leveling function (as shown in Figure 8a). Its leveling mechanism is driven by hydraulic cylinders [40], making it easy to operate and highly practical in actual work (as shown in Figure 8b).
Yu Yongchao et al. [41,42] from Beijing Forestry University designed a high-level automatic leveling platform for apple orchards in hilly and mountainous areas for heavy work such as flower thinning, fruit thinning, bagging, and picking. It uses an incremental PID controller for control and has good anti-overturning ability. This platform uses an incremental PID controller for control and has good anti-tipping capability. Jin Sheng from Hunan Agricultural University also designed an electric operation platform for fruit picking and transportation, which uses hydraulic rods to achieve horizontal and vertical leveling. The dynamic leveling error of the cargo box was less than 1° when unloaded and maintained within 1.5° when fully loaded [43].
The aforementioned orchard operation platforms all have a fixed chassis, with the upper platform executing leveling function control logic. In contrast, the upper platform only performs lifting movements, while the chassis-leveling operation platform control logic, such as the all-terrain orchard operation platform invented by Lu Zemin et al. from Jiangsu University, is based on chassis leveling [44] (as shown in Figure 9). This operation platform’s chassis achieves real-time leveling through the actuation of electric cylinders, adapting to the orchard road conditions and reducing the likelihood of overturning. The design has a simple structure and good passability, but its adaptability to specific complex terrains still needs further validation.
Li Zeao et al. from Huazhong Agricultural University designed a multifunctional working platform for orchards with four independent drive wheels to address the complex structure and poor maneuverability of traditional working platforms. This working platform [45], as shown in Figure 10, uses hub motors to achieve four-wheel independent drive and steering. It detects the tilting angle of the platform using angle sensors, which in turn drive two electric push rods to automatically adjust and achieve leveling of the working platform. The leveling angle range is from 0° to 10°, with an angle error of ±1°.
Professor Fan Guiju et al. from Shandong Agricultural University designed a hill area orchard operation platform, which utilizes a static hydraulic triangular leveling mechanism to achieve automatic leveling and rotation of the working platform [46]; Gao Longwei et al. from Chang’an University designed an automatic leveling system [47,48], where the moving platform is connected to the static platform via a universal joint and a flexible transmission cable. The moving platform has leveling degrees of freedom around the X and Y axes. By analyzing the telescopic length of the flexible cable and the tilt angle of the moving platform, leveling of the platform can be achieved. This system has a simple structure and compact size, but it can only perform automatic leveling under static conditions, which does not meet the needs for dynamic leveling.

3.2.2. Research Progress in Operation Platform Abroad

Fruit orchards in European and American countries are mostly distributed in plains, and the research on leveling technology for orchard operation platforms is relatively little; on the other hand, East Asian countries like South Korea and Japan, where orchards are mainly located in hilly and mountainous areas, have accumulated more research results in the field of mechanical leveling technology for mountain orchards [49]. The earliest countries to produce orchard lift platforms were mainly the United States, Australia, and Japan. The lift platforms from the United States and Australia are mainly suitable for large orchards, while the orchard lift platforms produced in Japan are compact, flexible, and equipped with automatic leveling functions, making them suitable for hilly areas.
Due to its unique national conditions and terrain, Japan began researching machinery suitable for steep slope operations in mountainous orchards as early as the early 1990s. Masao Nozawa [50] designed a self-propelled operating platform for orchards with leveling function, which is suitable for both standard and tree-type orchards, and can operate normally on slopes of 15°. Yamada et al. [51] designed a mobile lifting work platform for high-altitude operations such as thinning flowers, thinning fruit, thinning leaves, pruning, and harvesting in orchards. This device consists of an omnidirectional steering system combined with a lateral stability control device, and its horizontal control device can adjust the seat direction based on the ground slope, ensuring level operation. The design of this device is compact and highly maneuverable, allowing for flexible operation in narrow orchard environments.
Sang-Sik Lee et al. from Korea’s Gyeongdong University [52,53] designed an automatic leveling system to address potential safety issues related to orchard aerial work machinery operating on unpaved roads and slopes. The working principle involves installing lateral hydraulic rods on both sides of the chassis, using lateral tilt angle sensors to measure posture information, which is processed by a controller to drive the lateral hydraulic rods’ extension and retraction, thereby controlling the automatic leveling of the work platform. The Jang team from Kyungpook National University [54] developed a tracked automatic leveling lift platform (as shown in Figure 11), which utilizes a hybrid power system, with a maximum lifting height of 2500 mm, and a maximum adjustable working width of 2900 mm. Even when the machine’s body tilts at angles of ±20°, the work platform can still accurately maintain within a frame angle range of ±0.5°. The response time is only 1 s, greatly enhancing stability and work efficiency in complex environments.
Crendon Machinery [55] of Australia produces a series of self-propelled all-terrain lift platforms, which use the principle of a parallel four-bar mechanism to ensure that the upper working platform remains parallel to the ground at all times. Tecnofruit [56] of Italy produces a fruit harvesting auxiliary platform (as shown in Figure 12). This platform features two working surfaces; the front platform can be raised to 3 m, while the rear platform is fixed at a height of 1 m. The platform is equipped with a fork-like lifting device with an inclined angle to facilitate the loading and unloading of boxed fruits. In addition, the platform has a lateral leveling function, allowing for it to operate stably in hilly and sloped areas.

3.2.3. Summary of Automatic Leveling Technology for Domestic and International Work Platforms

Currently, orchard work platforms primarily focus on improving work efficiency and safety in hilly and mountainous areas. The mainstream equipment in the market mostly adopts hydraulic or electric drive leveling. Domestic research emphasizes mechanism optimization and algorithm control, while foreign countries such as Japan and South Korea focus on highly mobile integrated technology. Europe, the United States, and Australia emphasize the stability control of large work platforms. A comparison of various technical characteristics and leveling performance is shown in Table 5. In terms of leveling logic, work platforms are mainly divided into the mainstream mode of “fixed chassis + upper leveling” and the emerging “chassis leveling + upper lifting” scheme. The latter simplifies the structure, but its terrain adaptability requires further experimental validation.

3.3. Construction Machinery and Tools

In addition to power machinery and multifunctional orchard operation platforms, there are various types of machinery used in orchard mechanization, such as mowers, sprayers, pruners, fertilizer applicators, and soil cultivation equipment. With the introduction of the concepts of precision agriculture and sustainable development, researchers have begun to study orchard mechanization tools with automatic leveling functions in recent years.

3.3.1. Research Progress in Construction Machinery and Tools in China

In the field of orchard picking operations, in order to improve the degree of mechanization and reduce labor costs, Zheng Hang et al. from the Zhejiang Academy of Agricultural Sciences invented a picking device with an automatic leveling function [57] (as shown in Figure 13). This device uses an angle sensor fixed to the vehicle body to detect the vehicle’s posture, and the controller drives the leveling mechanism to achieve leveling of the picking platform.
In response to the precise plant protection operation requirements in orchards, Zhang Xueguo et al. from Shandong Yongjia Power Co., Ltd. (Linyi, China) invented a gantry-type orchard spraying mechanism to address the issue of uneven spraying in hilly terraced fields with traditional sprayers [58]. This mechanism is designed with a rotation mechanism and a leveling mechanism to adapt to the terraced operational mode. Its leveling mechanism controls the adjustment of the spray rod’s level through a set of pull wire slider devices connected to a counterweight. The mechanical structure is simple, but it cannot automatically level itself.
In order to solve the problem of traditional lawn mowers being unable to adapt to the complex and uneven terrain of hilly areas, Yang Fuzeng et al. from Northwest Agriculture and Forestry University invented a suspension-type, disc-shaped obstacle-avoidance mowing device for hilly orchard operations. This device can maintain the knife disc parallel to the slope by relying on hydraulic cylinders and a set of parallel four-bar mechanisms combined with a pressure spring floating mechanism, even on uneven ground. It features a compact structure, quick response, and neat cutting [59,60].
In the field of information collection and precision operations in orchards, to address the issues of high labor intensity and poor collection results in traditional spectral information gathering, Nie Zhaocheng et al. [61] designed an omnidirectional self-leveling platform suitable for spectral data collection in hilly and mountainous orchards (as shown in Figure 14). This machine can automatically level itself during both dynamic movement and static fixation without the need for secondary leveling operations, ensuring that the spectrometer mounted on the platform can effectively collect spectral data.

3.3.2. Research Progress in Construction Machinery and Tools Abroad

HAUN et al. [62] invented a leveling device for lawn mowers that ensures that the mower deck remains level at all times, significantly improving the mower’s balance performance. However, this device adjusts the vehicle’s posture manually, requiring the operator to continuously monitor and respond promptly to changes in the vehicle’s tilt, which places higher demands on the driver’s reaction speed. Additionally, due to the relatively simple structure of the manual adjustment system and the lower hardware sensitivity, there are certain limitations in practical applications.
To address the issue of agricultural vehicles operating in complex terrain being unable to predict rollover risks using conventional methods, Denis et al. from Clermont University in France proposed an online adaptive observer based on lateral load transfer (LLT) estimation. The transfer process is shown in Figure 15. This method mainly relies on the coupling between intermittent measurements and stability assessment, combined with changes in the vehicle’s center of gravity height and mass to assess and avoid the rollover risk of grape harvesters when working in complex terrain, thus driving the hydraulic leveling system (as shown in Figure 16) to control the posture of the harvester body [63]. Due to the reliance of this algorithm on the online adjustment of the dynamic model, its robustness and accuracy mainly depend on the accuracy of the model and its real-time adjustment capability.
In terms of orchard pest control and soil cultivation, the John Deere R4038 self-propelled sprayer (as shown in Figure 17) produced by John Deere in Ankeny, Iowa, USA features a “field cruising” operation function. Its four wheels are equipped with an airbag shock absorption system, independent suspension, and air spring, allowing for automatic adjustment of balance during operation [64]. HOEHN et al. [65] studied a leveling system applied to tillage machinery that can adjust the height of the tillage equipment relative to the ground in real time, helping to maintain consistent soil cutting depth [66].

3.3.3. Summary of Domestic and International Automatic Leveling Operation Machinery

The characteristics and performance parameters of various types of automatic leveling machinery used in orchards are compared in Table 6.

4. Key Technology of Chassis Leveling

The chassis, as the basic support platform for agricultural machinery, serves as a bridge connecting the power source and the working device. It not only directly affects the overall stability and mobility of agricultural machinery but also determines the adaptability and working efficiency of the equipment to complex terrains. An excellent chassis design and automatic leveling technology can ensure smooth operation of agricultural machinery in complex working environments, reduce operational errors caused by uneven terrain, and enhance working precision. The complex working conditions in orchards impose higher requirements on chassis design and leveling technology.
Gansu Province Mechanical Science Research Institute Co., Ltd. (Lanzhou, China), Lu Fengyu et al. [67] designed an omnidirectional attitude adjustment tracked chassis for agricultural machinery that features lateral and longitudinal leveling functions. The chassis’ lateral leveling mechanism employs a parallel four-bar suspension design, adjusting the height of the tracks on both sides through hydraulic cylinder drives to keep the chassis horizontally level (as shown in Figure 18a). The longitudinal leveling mechanism is installed between the frame and the chassis beam, connected using a hinged four-bar mechanism to two sets of lifting hydraulic cylinders symmetrically fixed on the front and rear transverse beams of the chassis. The controller regulates the elevation of the cylinders to maintain the chassis level longitudinally (as shown in Figure 18b). This chassis utilizes posture angle leveling and a fuzzy PID control algorithm, providing high passability and good stability advantages.
South China Agricultural University, Wu Weibin et al. invented a lightweight tracked chassis with adaptive adjustment for sloped terrain that can achieve chassis leveling in four modes based on actual work needs using a height adjustment mechanism and a horizontal adjustment mechanism. The lateral adjustment of the chassis is shown in Figure 19a and the longitudinal adjustment in Figure 19b. Due to the use of multiple retractable rods and mobile bridge designs, this chassis can achieve a larger leveling angle, and the chassis height is adjustable [68].
Liu Pingyi et al. from China Agricultural University designed a type of adaptive leveling suspension and a corresponding adaptive leveling chassis for agricultural use in hilly areas (as shown in Figure 20a). When working on rugged terrain, the suspension springs of the chassis can absorb and release energy in real time according to changes in the terrain. By changing the angle of a Y-type adjustable suspension (as shown in Figure 20b), the height of the chassis can be altered, achieving dynamic adaptive leveling of the chassis [69]. To further improve the chassis leveling response speed, Liu Pingyi et al. proposed a pre-detection active leveling method for agricultural chassis in hilly areas that utilizes height measuring sensors to detect the ground conditions ahead of travel. Based on the acquired ground information and the traveling state of the chassis, they calculated the required adjustment for each independent suspension, achieving real-time dynamic active leveling through pre-detection [70]. This method employs a four-wheel independent suspension leveling system that provides strong passability.
Similar to the adaptive leveling chassis, a legged wheeled robotic chassis designed by Jacek Bałchanowski [71] is shown in Figure 21. This chassis is a hybrid system that combines the ability to walk effectively on flat terrain with the capability to traverse obstacles while walking.
Xiaolong Zhao et al. [72] studied the leveling control technology for three-wheeled agricultural robot chassis. To address the issue of easy imbalance of the three-wheeled chassis on complex terrain, they proposed a hierarchical leveling method based on active suspension and an adaptive dual-loop composite control strategy (ADLCCS-SLM). The control principle is illustrated in Figure 22. This method achieves rapid leveling of the chassis by sequentially adjusting one or two suspension systems, avoiding the complicated scenario of simultaneous linkage of all three suspension systems.
To improve the obstacle-crossing capability of wheeled vehicles, J. Pijuan et al. [73] analyzed a dual-axle vehicle model with an active balancing system and adjustable weight distribution, exploring how to redistribute the load on each wheel by adjusting the height of the suspension system and applying active torque between the bogie and the chassis. The study indicates that the use of an active bogie system can enhance the vehicle’s obstacle-crossing performance regardless of the position of obstacles and the angle of the terrain.
In summary, the characteristics and performance parameters of various chassis leveling technologies with application prospects in the orchard machinery field are compared as shown in Table 7. Research on chassis leveling systems and control technologies is moving towards efficiency, integration, and intelligence. The current research focus mainly includes enhancing the obstacle-crossing ability and adaptability of the chassis system, utilizing efficient control algorithms to optimize leveling accuracy and response speed, and continuously exploring new leveling actuators and control schemes to improve the overall performance of automatic leveling chassis. This provides a solid practical reference and theoretical basis for the development of universal automatic leveling technology for orchard automatic leveling machinery.

5. Challenges Faced

With the rapid development of intelligent orchard machinery, automatic leveling technology provides strong support for further improving production efficiency and operational quality in hilly orchards. However, research on automatic leveling machinery for orchards still faces numerous challenges, manifested in the following aspects:

5.1. The Working Environment in the Orchard Is Complex

Chinese orchards are mainly distributed in hilly and mountainous areas, where orchards commonly face issues such as steep slopes, complex and varied terrain, high planting density, and rough management practices, bringing many challenges to the research of automatic leveling machinery for orchards. The complex and variable operating environment in orchards requires that automatic leveling machinery has good adaptability and can operate stably under different slope and terrain conditions. In the current stage of research, solutions that adopt posture perception, data processing, and active compensation are often used. In addition, the existing automatic leveling machinery for orchards has relatively single functions, only meeting the specific operational needs of certain fixed terrain production processes, resulting in low equipment utilization rates. Currently, there is a lack of research on universal automatic leveling chassis for orchard mechanization both domestically and internationally, and there is insufficient technical reserve for universal automatic leveling technology in orchards, making it difficult to adapt to the different operational needs of various working tools in complex working environments.

5.2. The Combination of Agricultural Machinery and Agronomy Is Difficult to Achieve Effectively

The effective integration of agricultural machinery and agronomy is an important means to promote the modernization of agriculture. Good agronomic standards provide direction and design basis for the research and development of new agricultural machinery. Currently, some orchards in China lack standardized management in terms of management methods and planting models, resulting in a significant disconnect between agronomic practices and supporting machinery. As an important component of modern agricultural equipment, automatic leveling machinery for orchards requires deep integration of technology innovation and optimization with the physiological characteristics of fruit trees, soil conditions, climate environment, and other multidimensional agronomic technical needs. However, relevant research is still insufficient. In practical operations, mechanical equipment faces issues of low efficiency and poor effectiveness, unable to fully realize its potential in orchard production. There is an urgent need to strengthen the deep integration of agricultural machinery for orchards and planting agronomy, through interdisciplinary collaboration, to deeply study the growth patterns of fruit trees and the mechanics of mechanized operations, and to customize the development of automatic leveling machinery suitable for different orchard environments.

5.3. The Leveling Performance Needs to Be Improved

The leveling performance of automated leveling machinery primarily refers to factors such as leveling accuracy, response speed, and anti-interference capability [74]. Currently, both domestic and international automated leveling machinery for orchards faces multiple challenges in further improving leveling performance. Due to the complex and variable terrain in orchards, there are numerous obstacles and irregular topographies in the operating environment that require the leveling system to possess high perception capabilities and precise control algorithms to quickly identify subtle terrain changes and make accurate adjustments. Secondly, because the working environment in orchards often changes rapidly, factors such as wind strength and soil moisture can affect leveling effectiveness, necessitating a leveling system with high response speed to monitor environmental changes in real time and react promptly. Finally, the enhancement of anti-interference capability for automated leveling machinery in orchards cannot be overlooked. Potential electromagnetic interference and mechanical vibrations in orchards can impact the stability of the automated leveling system, which requires that the design of the system adequately considers potential interference factors and implements appropriate shielding and filtering measures to ensure the reliability and stability of the automated leveling system.
The cost issues that arise while improving leveling performance also need to be considered. The enhancement of leveling performance comes with increased research, manufacturing, and maintenance costs, which may limit the application of this technology to large-scale orchards. Therefore, researchers and related companies need to coordinate the balance between leveling performance and application costs in order to promote the use of automatic leveling technology in orchard mechanization.

6. Outlook

After examining the many challenges facing the development of automatic leveling machinery in orchards, this article further discusses the future development directions. The complexity of the working environment, the difficulties in integrating agricultural machinery with agronomy, and the limitations of leveling performance are the core bottlenecks restricting the development of automatic leveling machinery in orchards that urgently require breakthroughs through innovative research.

6.1. Apply Interdisciplinary Integration Methods to Conduct In-Depth Research on the Characteristics of Orchard Working Environments

Research on automatic leveling machinery for orchards should focus on a comprehensive analysis and systematic clustering of the complex terrains in different orchards. By extracting, classifying, and modeling detailed terrain features, it is possible to refine widely applicable strategies and technical pathways. This process requires researchers to have a strong interdisciplinary knowledge background in agricultural engineering, mechanical engineering, and computer science, while closely aligning with the practical needs and agronomic characteristics of the orchard industry, providing a solid and systematic theoretical foundation and practical guidance for the development of universal automatic leveling technology for orchards.

6.2. Applying Systemic Thinking at All Stages of Orchard Management Combines the Agricultural Machinery Research and Development Process with the Requirements of Planting Agronomy

The research and development of autonomous leveling machinery for orchards must closely follow agricultural processes. In the early stages of orchard establishment, it is necessary to accurately plan the row spacing and plant spacing of fruit trees based on the characteristics of agricultural machinery operations, and to design planting modes such as terraced, contour, or fish-scale pits based on the biological characteristics of fruit trees. This includes organizing work slopes, improving complex terrain conditions, and reducing machinery energy consumption and operational errors. In the mid-term management of the orchard, a data sharing and feedback mechanism should be established, as well as developing a joint operation system that allows for real-time sharing of agricultural data and various operational machinery during orchard management. Additionally, a universal autonomous leveling chassis that can be equipped or switched with multiple types of working tools should be developed to enhance the operational efficiency and equipment utilization rate of agricultural machinery in orchards. Throughout the entire process of mechanized operation in orchards, the operational parameters of supporting agricultural machinery should be precisely controlled according to the morphology and agronomic characteristics of fruit trees. By applying new sensors, adaptive algorithms, and developing advanced autonomous leveling machinery, the growth stages of fruit trees can be sensed and the operation parameters of machinery optimized in real time to prevent damage to the trees and improve operational effectiveness.

6.3. Comprehensively Improve Leveling Performance

6.3.1. Improve Mechanical Structure Design

Automatic leveling machinery for future orchards can utilize a deformable and adaptive chassis architecture, considering biomimetic design that imitates the joint structures of insects or crawling animals. This will lead to the design of leg components capable of flexibly adjusting height and angle, ensuring stable passage even on steep slopes and in uneven areas. At the same time, lightweight and high-strength materials should be employed to reduce the machine’s weight while maintaining structural rigidity, lowering energy consumption and enhancing response speed, and minimizing leveling errors caused by mechanical vibrations or deformations.

6.3.2. Optimize Control Algorithms

Based on machine learning and artificial intelligence technologies, deep integration of IoT and 5G technology can be used to develop intelligent control algorithms that can perceive the environment in real time and make autonomous decisions. By deep learning from a large amount of orchard terrain data, combining IoT and 5G technology, the machine can predict terrain changes, proactively plan leveling strategies, and reduce oscillations and overshoot during the leveling process. By combining the advantages of fuzzy control and PID control, the system addresses both gentle slopes and sudden terrain changes in the orchard, with fuzzy control managing large deviations and nonlinear scenarios, while PID control performs precise fine-tuning, ensuring high-precision leveling under all working conditions, thereby improving the work quality and efficiency in fruit harvesting and crop protection operations.

6.3.3. Strengthen the Application of Sensor Technology

The development of the orchard automatic leveling machine utilizes new sensors such as laser radar and millimeter-wave radar. Laser radar can perform high-precision mapping of the orchard’s three-dimensional terrain, providing detailed information on slope and height differences. Millimeter-wave radar has strong penetration abilities through dust and water mist, ensuring continuity in terrain monitoring under harsh conditions. At the same time, a multi-sensor fusion system is established to comprehensively analyze the data collected from gyroscopes, accelerometers, inclination sensors, and radar. By using data fusion algorithms, information from different sensors is processed in a comprehensive manner, allowing for mutual calibration and supplementation. This enables accurate and all-weather understanding of the machine’s posture and orchard terrain, providing a data foundation for precise leveling and improving leveling performance.

6.4. Strengthen Policy Support

The development of automatic leveling technology for agricultural machinery in hilly orchards should be promoted at the policy level. Management departments can reduce the cost of technology promotion by establishing a special subsidy fund for agricultural equipment and implementing a tiered differential tax reduction policy for agricultural machinery purchases in hilly areas. Regional leading agricultural enterprises can be guided to establish intelligent agricultural machinery sharing centers to dilute fixed costs through large-scale operations. Automatic leveling technology could be incorporated into the mandatory technical standards system for agricultural machinery in hilly areas to drive industrial upgrading through technical specifications, while establishing a patent cross-licensing system to reduce the sunk costs of innovation for enterprises. Ultimately, through the synergistic empowerment of policies and markets, the iterative upgrade of automatic leveling technology for agricultural machinery in hilly orchards towards high precision, low energy consumption, and low cost should be promoted, and a sustainable intelligent operation system should be built.

Author Contributions

Conceptualization, L.H. and W.D.; methodology, W.D. and G.W.; software, G.X. and J.P.; validation, H.S., J.P. and Z.H.; formal analysis, L.H. and W.D.; investigation, G.X. and W.Z.; resources, G.X. and S.H.; data curation, G.X.; writing—original draft preparation, G.X.; writing—review and editing, G.X.; visualization, G.W. and J.P.; supervision, L.H.; project administration, W.D.; funding acquisition, L.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Basic Research Funds of Chinese Academy of Agricultural Sciences, grant number S202308; The industry prospect and key core technology of science and technology projects in Jiangsu province, grant number BE2021016-2; Jiangsu agricultural machinery R & D manufacturing promotion and application integration pilot project, grant number JSYTH01; Jiangsu agricultural science and technology independent innovation fund project, grant number CX(24)1023; National Key Research and Development Program of China, grant number 2023YFD2000303.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic diagram of automatic leveling system control circuit.
Figure 1. Schematic diagram of automatic leveling system control circuit.
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Figure 2. (a) Schematic of the series leveling mechanism; (b) schematic of parallel leveling mechanism.
Figure 2. (a) Schematic of the series leveling mechanism; (b) schematic of parallel leveling mechanism.
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Figure 3. Remote-controlled omnidirectional leveling tracked tractor.
Figure 3. Remote-controlled omnidirectional leveling tracked tractor.
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Figure 4. Schematic diagram of the three-point automatic leveling mechanism: 1. left drive wheel; 2. front steering drive axle; 3. vehicle body; 4. leveling cylinder; 5. fixed hinge support; 6. swing support seat; 7. frame fixed support; 8. right drive wheel.
Figure 4. Schematic diagram of the three-point automatic leveling mechanism: 1. left drive wheel; 2. front steering drive axle; 3. vehicle body; 4. leveling cylinder; 5. fixed hinge support; 6. swing support seat; 7. frame fixed support; 8. right drive wheel.
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Figure 5. (a) Remote-controlled omnidirectional leveling tracked tractor prototype. (b) Schematic diagram of the attitude active adjustment mechanism: 1. left wheel; 2. left final drive assembly; 3. left swinging mechanism; 4. right axle sleeve; 5. right final drive assembly; 6. right wheel; 7. right swinging mechanism; 8. rear drive axle; 9. left axle sleeve.
Figure 5. (a) Remote-controlled omnidirectional leveling tracked tractor prototype. (b) Schematic diagram of the attitude active adjustment mechanism: 1. left wheel; 2. left final drive assembly; 3. left swinging mechanism; 4. right axle sleeve; 5. right final drive assembly; 6. right wheel; 7. right swinging mechanism; 8. rear drive axle; 9. left axle sleeve.
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Figure 6. Overall structure of the dual-layer controller.
Figure 6. Overall structure of the dual-layer controller.
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Figure 7. Omnidirectional leveling crawler-type working machine.
Figure 7. Omnidirectional leveling crawler-type working machine.
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Figure 8. (a) Orchard elevation leveling platform: 1. operation platform system; 2. lifting and leveling system; 3. hydraulic chassis system. (b) Orchard experiment.
Figure 8. (a) Orchard elevation leveling platform: 1. operation platform system; 2. lifting and leveling system; 3. hydraulic chassis system. (b) Orchard experiment.
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Figure 9. All-terrain orchard operation platform based on chassis leveling.
Figure 9. All-terrain orchard operation platform based on chassis leveling.
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Figure 10. Four-wheel independent drive multifunctional operating platform for orchards.
Figure 10. Four-wheel independent drive multifunctional operating platform for orchards.
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Figure 11. Track-type automatic leveling lift platform.
Figure 11. Track-type automatic leveling lift platform.
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Figure 12. Fruit auxiliary picking platform.
Figure 12. Fruit auxiliary picking platform.
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Figure 13. Harvesting device with automatic leveling function.
Figure 13. Harvesting device with automatic leveling function.
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Figure 14. Omnidirectional self-leveling platform.
Figure 14. Omnidirectional self-leveling platform.
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Figure 15. Schematic of lateral load transfer in tilt risk assessment.
Figure 15. Schematic of lateral load transfer in tilt risk assessment.
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Figure 16. Hydraulic leveling system.
Figure 16. Hydraulic leveling system.
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Figure 17. John Deere 4038 sprayer.
Figure 17. John Deere 4038 sprayer.
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Figure 18. Omnidirectional attitude adjustment crawler chassis: (a) schematic diagram of horizontal leveling; (b) schematic diagram of longitudinal leveling.
Figure 18. Omnidirectional attitude adjustment crawler chassis: (a) schematic diagram of horizontal leveling; (b) schematic diagram of longitudinal leveling.
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Figure 19. Lightweight tracked chassis: (a) schematic diagram of horizontal leveling; (b) schematic diagram of longitudinal leveling.
Figure 19. Lightweight tracked chassis: (a) schematic diagram of horizontal leveling; (b) schematic diagram of longitudinal leveling.
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Figure 20. Pre-detection active leveling chassis: (a) Schematic diagram of horizontal leveling. (b) Schematic diagram of longitudinal leveling: 1. rear frame; 2. chassis tilt angle status sensor; 3. front frame; 4. height distance sensor; 5. Y-type adjustable suspension; 6. wheel.
Figure 20. Pre-detection active leveling chassis: (a) Schematic diagram of horizontal leveling. (b) Schematic diagram of longitudinal leveling: 1. rear frame; 2. chassis tilt angle status sensor; 3. front frame; 4. height distance sensor; 5. Y-type adjustable suspension; 6. wheel.
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Figure 21. Wheeled-legged robot chassis.
Figure 21. Wheeled-legged robot chassis.
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Figure 22. Double-ring composite control structure: ωA—front left wheel road excitation; ωB—front right wheel road excitation; ωC—rear wheel road excitation; α—roll angle; β—pitch angle; Xv—valve core displacement.
Figure 22. Double-ring composite control structure: ωA—front left wheel road excitation; ωB—front right wheel road excitation; ωC—rear wheel road excitation; α—roll angle; β—pitch angle; Xv—valve core displacement.
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Table 1. Comparison of advantages and disadvantages of series and parallel auto-leveling mechanisms.
Table 1. Comparison of advantages and disadvantages of series and parallel auto-leveling mechanisms.
TypeAdvantagesDisadvantageApplication
Series typeIt has a large workspace, each joint can be controlled independently, and it is easy to conduct kinematic analysis.The structural strength is low, making it unsuitable for heavy load operations, and the accumulation of errors leads to a decrease in the positioning accuracy of the end effector.Camera gimbal
Parallel typeNo cumulative error, with high positioning accuracy and strong load capacity.The workspace is small, making forward kinematics analysis quite difficult.Stewart platform [12], motion simulator, wave compensation device
Table 2. Classification characteristics and applications of leveling systems.
Table 2. Classification characteristics and applications of leveling systems.
Classification MethodTypeCharacteristicsApplication
Power source typeManual adjustmentRelying on the operator to observe the level instrument and manually adjust the leg height. It takes a long time to adjust, has poor leveling precision, and is difficult to operate.Simple crane
Hydraulic driveUsing a hydraulic system as an actuator, it has a small volume, light weight, and compact structure; it features good dynamic performance and high response frequency; with high stiffness, it is suitable for large-tonnage leveling systems. However, it is sensitive to temperature and prone to leakage.Aerial fire truck
Electromechanical DriveUsing servo control systems and sensor technology, with a simple structure, high precision, easy maintenance, and strong environmental adaptability.Radar antenna
Supporting structureRigid supportThe supporting structure is stable and not easily deformed, but it is costly and complex to install [14].Radar antenna
Semi-rigid supportIt can ensure a certain degree of structural strength while also absorbing vibration and impact to some extent [16].Vehicle leveling system
Elastic supportIt has good shock absorption performance, but it may sacrifice some structural strength and stability [15].Earthquake rescue vehicle
Number of support pointsThree-point supportThe structure is simple, but its anti-overturning ability is relatively poor.Radar antenna
Four-point supportStrong anti-tipping ability, at most generating one virtual leg that is relatively easy to eliminate.Crane
Six-point supportGreater anti-tipping ability, but prone to multiple virtual legs, requiring more complex control strategies to eliminate virtual legs.Heavy crane
Table 3. Characteristics and applications of leveling control algorithms.
Table 3. Characteristics and applications of leveling control algorithms.
NameCharacteristicsApplication
PID controlSimple structure and determined parameters, achieving error correction through linear combinations of proportion, integration, and differentiation.Flat terrain and stable load static working scenario
Feedforward-PID ControlThe integration of feedforward channel pre-compensation can measure interference, providing good dynamic response and anti-interference capability.Known interference environment or operational scenarios that require quick response during dynamic driving.
Fuzzy PID ControlDynamically adjusting PID parameters based on a fuzzy rule base, without relying on precise mathematical models, offers strong robustness.Complex operational scenarios with significant terrain fluctuations and loads that change over time.
Neural Network PID ControlUtilizing the self-learning capability of neural networks to fit nonlinear relationships and adaptively optimize parameters during the leveling process.Nonlinear systems or precision leveling operations in strongly coupled, multi-degree-of-freedom scenarios
Table 4. Comparison of characteristics of automatic leveling technology for power machinery and leveling performance.
Table 4. Comparison of characteristics of automatic leveling technology for power machinery and leveling performance.
Research and Development InstitutionsTechnical NameCharacteristicsLeveling Performance
Northwest A&F University [23]Omnidirectional leveling mechanismIncluding a lateral leveling device based on a four-bar linkage mechanism and a longitudinal leveling device based on a double frame mechanism.Satisfy leveling on horizontal slopes from 0° to 15° and vertical slopes from 0° to 10°
Shanxi Agricultural University [25]Three-point leveling mechanismDesign a swing support seat and leveling hydraulic cylinder on the front steering drive axle, forming a three-point leveling mechanism with the swing support seat of the rear steering drive axle.Meet slope leveling from −25° to 25°
Shanghai Jiao Tong University [28]Posture Adjustment SystemThe active adjustment of the tractor’s posture is achieved through the left and right eccentric wheel swinging mechanisms attached to the rear drive axle.It takes ≤7.5 s to level the ±10° slope, with an error of <0.5°
Iran University of Science and Technology [35]Dual-level leveling controllerThe two-layer controllers use fuzzy logic control and proportional-integral (PI) control, ensuring that the actual force generated is as close as possible to the target force set by the upper-layer controller./
Table 5. Comparison of technical characteristics and performance of automatic leveling technology for work platforms.
Table 5. Comparison of technical characteristics and performance of automatic leveling technology for work platforms.
Research and
Development Institution		NameFeaturesPerformance Parameters
Jiangsu University/Jiangsu New Energy Vehicle Research Institute Co., Ltd. (Xuzhou, China) [39]Omnidirectional leveling tracked work machineThe omnidirectional leveling solution is based on a “three-layer frame” structure, with a distributed hydraulic system between the frames. The leveling is ensured through the extension and compression of hydraulic cylinders to keep the omnidirectional body level.Satisfies leveling on horizontal slopes from 0° to 20° and vertical slopes from 0° to 25°, with leveling times of 2.8 s for horizontal and 3.2 s for vertical on-site.
Chongqing Academy of Agricultural Sciences/Chongqing Xinyuan Agricultural Machinery Co., Ltd. (Chongqing, China) [40]General lifting operation platform for fruit orchards in hilly areasThe leveling system outputs high-pressure oil through a gear pump and controls the left and right or front and back bi-directional balance valves via a valve spooling seat and an electromagnetic reversing valve, achieving automatic leveling of the platform.Lifting height ≥ 1.5 m, maximum load capacity ≥ 1 t
Beijing Forestry University [41]High-level automatic leveling platformThe platform achieves automatic leveling using a folding arm scissor pitch leveling mechanism and a lateral tilt leveling mechanism.The minimum value of the limit overturning slope is 25.29°
Hunan Agricultural University [43]Electric working platformUsing hydraulic rods to drive the platform for horizontal and vertical leveling.Satisfies leveling on horizontal slopes from 0° to 12° and vertical slopes from 0° to 20°
Huazhong Agricultural University [45]Four-wheel independent drive multifunctional operating platform for orchardsThe leveling of the working platform is achieved by using two electric actuators placed in the front–back and left–right directions on the leveling platform.Meet slope leveling of 0° to 10°, with an error of ≤1°
Kyungpook National University [54]Crawler-type automatic leveling lift platformInstall two hydraulic cylinders on both sides of the vehicle to achieve automatic leveling of the platform.Meet leveling for slopes of 0° to 20°, with an error of ≤0.5° and a time of ≤1 s
Crendon Machinery [55]Self-propelled all-terrain aerial platformUsing multiple hydraulic cylinders in combination to achieve automatic leveling of the lifting platform.Satisfies leveling on a horizontal slope of 0°~12.5° and a vertical slope of 0°~15°
Table 6. Comparison of automatic leveling technology for construction machinery.
Table 6. Comparison of automatic leveling technology for construction machinery.
Research
Institution		NameFeaturesPerformance
Parameters
Zhejiang Academy of Agricultural Sciences [57]Harvesting device with automatic leveling functionUsing an installed angle sensor on the vehicle body to detect the horizontal status of the vehicle body, driving the oil cylinder to achieve automatic leveling of the vehicle body./
Northwest A&F University [59,60]Hanging disc-type hilly orchard obstacle-avoidance contour mowing deviceAdjust the cutter head to maintain parallelism with the slope by relying on a hydraulic cylinder and a set of parallel four-bar mechanisms combined with a spring float device./
Southwest University [61]Omnidirectional self-leveling platformThe current attitude angle of the platform is collected through sensors. After parsing and calculating by the microcontroller, commands are sent to the actuator to drive the push rod motor for platform leveling.Satisfies leveling of slopes from 0° to 18°, with static error < 0.3°, dynamic error < 3°
Clemson University [63]Online adaptive observer for anti-rolloverUpdate the vehicle’s dynamic model parameters through intermittent LLT (lateral torque) measurements and a sensitivity gradient search algorithm, allowing the hydraulic leveling system to automatically adjust in real time.Meet the leveling requirements for slopes of 0° to 16.5°
Table 7. Comparison of technical characteristics and performance parameters of chassis automatic leveling technology.
Table 7. Comparison of technical characteristics and performance parameters of chassis automatic leveling technology.
Research InstitutionNameCharacteristicsPerformance Parameters
Gansu Institute of Mechanical Science Co., Ltd. (Lanzhou, China) [67]Omnidirectional attitude adjustment agricultural machine track chassisAdjust the height of the tracks on both sides by driving the hydraulic cylinders to keep the chassis horizontally level, connecting two sets of lifting hydraulic cylinders that are symmetrically fixed on the front and rear cross beams of the chassis through a hinged four-bar mechanism, controlling the work of the cylinders to keep the chassis longitudinally level.Satisfies horizontal leveling from 0° to 15° and vertical leveling from 0° to 30°, with an error ≤ 15°
South China Agricultural University [68]Lightweight tracked chassis with slope adaptive adjustmentAchieve chassis leveling in four ways through the combination of height adjustment mechanism and horizontal adjustment mechanism./
China Agricultural University [69]Adaptive leveling chassis for agricultural use in hilly areasChange the chassis height by adjusting the angle of the Y-shaped adjustable suspension, achieving dynamic adaptive leveling of the chassis.Compared to a four-wheel rigid chassis, the sum of the roll angle and pitch angle is reduced by 54.86%
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Xue, G.; Peng, J.; Shen, H.; Wang, G.; Zheng, W.; Huang, S.; Huan, Z.; Hu, L.; Ding, W. Research Status and Prospects of Automatic Leveling Technology for Orchard Machinery. Sustainability 2025, 17, 5297. https://doi.org/10.3390/su17125297

AMA Style

Xue G, Peng J, Shen H, Wang G, Zheng W, Huang S, Huan Z, Hu L, Ding W. Research Status and Prospects of Automatic Leveling Technology for Orchard Machinery. Sustainability. 2025; 17(12):5297. https://doi.org/10.3390/su17125297

Chicago/Turabian Style

Xue, Guangyu, Jiwen Peng, Haiyang Shen, Gongpu Wang, Wenhao Zheng, Sen Huang, Zihan Huan, Lianglong Hu, and Wenqin Ding. 2025. "Research Status and Prospects of Automatic Leveling Technology for Orchard Machinery" Sustainability 17, no. 12: 5297. https://doi.org/10.3390/su17125297

APA Style

Xue, G., Peng, J., Shen, H., Wang, G., Zheng, W., Huang, S., Huan, Z., Hu, L., & Ding, W. (2025). Research Status and Prospects of Automatic Leveling Technology for Orchard Machinery. Sustainability, 17(12), 5297. https://doi.org/10.3390/su17125297

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