# Investigation of a Precise Control Scheme for Rice Quality
## 1 Introduction  
Rice, being one of the fundamental staple crops, ranks third in global production. Over half of the world's population relies on it as a dietary mainstay [1; 2]. Due to seasonal and weather influences, the moisture content of rice harvested from fields often exceeds safe storage requirements, particularly in southern China where heavy rainfall is frequent. Rice with excess moisture will deteriorate due to infestation and mildew [3; 4]. Therefore, it is imperative to conduct efficient drying treatment in order to ensure subsequent safe storage. Grain drying is a complex and dynamic process involving mass and heat transfer. Currently, hot air drying is the predominant method used in industrial settings [5]. However, the moisture content of grains and various parameters of drying air (e.g., temperature, velocity, and relative humidity) are critical factors that can limit both efficiency and quality outcomes for operators [6]. If the operation relies solely on experience, improper treatment during the drying process may cause rice to crack. The kernel's tensile strength can be exceeded due to moisture and temperature gradients, inducing stress that leads to cracking. Cracked rice is typically the result of mechanical damage incurred during milling, which can negatively impact both on its taste and nutritional quality, ultimately leading to a decrease in economic value [7]. Therefore, it is imperative to ensure the quality of drying while reducing the moisture content of rice. Several studies have been carried out to enhance the quality and efficiency of drying. [PERSON] et al. [8] found that increases in temperature and air evaporation accelerated desiccation, resulting in an increase in cracked kernels and a decrease in head rice yield (HRY). Additionally, a moisture content reduction of more than 3% in a single drying stepcould have negative effects on the overall kernel yield. [PERSON] et al. [1] observed a similar relationship between drying rate and crack percentage while investigating the impact of air-drying parameters, such as temperature, velocity, and relative humidity, on rice during deep-bed drying. For grain drying, a tempering stage is often incorporated as a processing method, wherein the supply of hot air is halted after a period of drying to facilitate internal water equilibrium through heat and moisture gradients [9]. This leads to enhanced drying efficiency in the subsequent stage, resulting not only in reduced drying time and energy consumption but also guaranteed drying quality. [PERSON] et al. [10] discovered that tempering at 60 \({}^{\circ}\)C could significantly reduce drying time, decrease the incidence of cracking, and enhance HRY. [PERSON] et al. [11] demonstrated that the internal water gradient and cracking of rice were significantly affected by both tempering temperature and duration. Compared to tempering at 20 \({}^{\circ}\)C, tempering at 50 \({}^{\circ}\)C resulted in a reduction in rice crack percentage ranging from 32% to 50%. In addition to the aforementioned experimental findings, researchers have also endeavored to establish models for further regulating and optimizing grain drying. [PERSON] and [PERSON] [12] utilized a combined model of partial differential equation and two-step intermittent thin-layer drying equation for rough rice to simulate the drying characteristics of a dryer with intermittent circulation under various conditions, including different drying temperatures, absolute air humidities, drying times, and tempering durations. This study offers valuable insights for the operation and design of circulating grain dryers. [PERSON] et al. [13] developed mathematical models to optimize the intermittent drying of rice in two stages by studying the drying and tempering processes. Different from a single empirical or theoretical model, [PERSON] and [PERSON] [14] developed a drying-breakage model by integrating an empirical breakage model with a theoretical drying model, thereby enabling the prediction of drying time and the estimation of HRY. [PERSON] et al.