## 1 Introduction  
Shipborne helicopters refer to helicopters that can land on aircraft carriers or other ships. Shipborne helicopters have played an indispensable role in modern naval warfare since the 21 st-century [1; 2; 3] with the reform of modern warfare and the wide application of new UAVs (Unmanned Aerial Vehicles). In modern naval warfare, shipborne helicopters are required to land not only on aircraft carriers but also on medium-sized and small ships. Unlike aircraft carriers, the rolling and pitching range of medium-sized and small ships is large, and the area of the landing platform on the ships is small. These problems make the landing difficulty of shipborne helicopters increase exponentially [4; 5]. Various schemes have been introduced since 1971 to improve the landing ability of shipborne helicopters on medium-sized and small ships, ensure the attendance rate in high sea conditions, and enhance safety and reliability. The shipborne helicopter landing assistance system, considered adequate and widely used, includes Harpoon Assist Landing System, Recovery Assist Secure and Traverse System, and Aircraft Ship Integrated Secure and Traverse System (ASIST). ASIST, as the third-generation shipborne helicopter landing assistance system, is considered the development direction in the future with its unique design scheme and excellent functional characteristics [6,7]. As shown in Figure 1, according to the landing action of the shipborne helicopter and the task execution sequence of ASIST, the process can be divided into five stages [6]. * Approach stage: The shipborne helicopter approaches the ship from a distance. * Hover stage: The shipborne helicopter hovers above the deck. * Capture stage: The shipborne helicopter is captured by ASIST. * Secure stage: The shipborne helicopter is secured to the deck by ASIST. * Traction stage: The shipborne helicopter is towed to the designated position by ASIST. Many scholars have researched the different landing stages, which involve aerodynamics, structural dynamics, system reliability, speed trajectory planning, traction path planning, and many other aspects. In the approach stage, [PERSON] et al. [8] studied the task of the shipborne helicopter approaching the ship and proposed an approach guidance method. In the hover stage, [PERSON] et al. [9-11] thoroughly studied the influence of airflow between the shipborne helicopter and the deck. [PERSON] et al. [12] further investigated the effect of the interaction between the shipborne helicopter and the deck when two shipborne helicopters hover over the deck simultaneously. In the secure stage, [PERSON] et al. [13,14] studied the collision process between the tire and the deck when the shipborne helicopter landed on the ship and established the corresponding collision model. [PERSON] et al. [15] evaluated the secure reliability of the shipborne helicopter through the analytic hierarchy process. [PERSON] et al. [16,17] studied the ship-helicopter dynamic system and showed the dynamic model. However, few studies have been conducted on the capture and traction stage of the shipborne helicopter, or few people have paid attention to the problems of large impact force and the cumbersome traction process existing in ASIST [6]. The former made the ASIST incompatible with small shipborne aircraft, while the latter made the traction operation inefficient. It is imperative to seek a more reasonable, cleaner, and environmentally friendly design scheme based on the original ASIST to solve the deficiencies existing in ASIST [18,19]. Because asynchronous motors have the advantages of high power-density, high-energy transmission efficiency, and strong environmental adaptability [20,21], they are very suitable for the ship environment where ASIST is located. It is very convenient to use the asynchronous motor as the power source of ASIST with an appropriate speed control algorithm to solve the above problems.