## 1 Introduction  
Plastic film mulching is an important agricultural production technology [1] that has the functions of maintaining fertilizer, increasing temperature and reducing crop diseases [2]. However, with the wide application of plastic film, plastic film that has not been recycled in time changes the physical structure of the soil, hinders the normal transportation of soil water and nutrients, and even causes crop yield reduction and destroys sustainable agriculture production [3, 4]. In the face of the increasingly serious problem of residual film (residual film can be explained as mulch film that was not been recovered in time in farmland), the Ministry of Agriculture and Rural Affairs and others jointly issued \"opinions on accelerating the prevention and control of agricultural film pollution\" in 2019, and the Ministry of Agriculture and Rural Affairs again launched \"management measures for agricultural film\" in 2020 [5, 6]. The problem of residual film pollution is highly valued by government departments and urgently needs to be solved [7]. In foreign countries, the plastic film thickness is greater than 0.020 mm and the film has strong damage resistance [8], so it is easy to recover. However, the plastic film thickness used in China is generally less than 0.008 mm, which can easily be torn in the process of mechanical recovery [9], the recovery of residual film is a difficult problem. At this stage, the methods of residual film recovery include manual recovery, the use of degradable film, and mechanized recovery [10]. Among them, the cost of manual recovery is too high; As degradable film technology is not particularly mature and difficult to process [11], it is not suitable for China's national conditions. Therefore, mechanized recovery is the main trend at present [12]. The recovery of residual film before sowing is the main recovery method [13]. The residual film is mostly fragmented and distributed on the surface and shallow soil, so the recovery of residual film is difficult, and the recovery effect is not ideal [14,15]. To solve the problem of residual film recovery before sowing, China has developed a variety of residual film recovery machines [16]. The film removal device is not only the core working part of the residual film recovery machine, but also the main difficulty in the development of residual film recovery machines [17]. At this stage, there are relatively few studies on film removal devices, mainly including the pneumatic type [18], telescopic rod tooth type [19] and stripping blade type [20]. The structure of the pneumatic stripping device is relatively simple. The main working component is the fan. During operation, the film removal mainly depends on the force of the air flow on the residual film, but the film removal effect is not good [21,22]; the telescopic rod tooth removal device mainly depends on the expansion and contraction of the elastic teeth on the eccentric roller to pick up and remove the film. It has high development cost and low reliability [23]; the stripping blade type removal device mainly adopts a method in which the rotating direction of the working part of the film removal device is the same as that of the film picking device, the film removal rate is not high and the film wrapping phenomenon easily occurs on the film stripping blades [24]. Addressing the problems of a low film removal rate and serious film wrapping phenomenon in the film removal device of residual film recovery machines before sowing, this paper designs a film removal device composed of a vane type film removal roller and a diversion shell, according to the film picking principle of an arc-toothed residual film recovery machine. The film removal device combines the advantages of mechanical stripping and pneumatic stripping. Therefore, it is named \"Mechanical + airflow\" combined film removal device [25]. Through theoretical analysis, a film removal blade, which is the key working part of a film removal device, is designed, and its parameters are determined.