**2. Materials and Methods**

#### *2.1. Automatic Apple Grader Design*

The structure of the automatic apple grader designed in this paper is shown in Figure 1. It consists of Feeding and material handling lifting mechanism, turnover detection conveyor, visual inspection and automatic grading control system, and graded actuators. The design is based on a two-level layout to reduce the space required.

**Figure 1.** Structure of the automatic apple grader.

(1) Feeding and material handling lifting mechanism. The Feeding and material handling lifting mechanism is a scraper elevator, as shown in Figure 2. The scraper elevator consists of a funnel-shaped storage tank and a vertical conveyor belt, where the funnel-shaped storage tank includes the back plate of the hopper and the support plate, the three-dimensional conveyor belt includes the guide plate and the curved scraper, and the whole mechanism is placed at an inclination of 45◦. The scraper elevator moves the conveyor belt by means of an AC motor driven by a frequency converter, which organizes the disordered apples into an orderly quadruple queue, transporting them from the bottom upwards and conveying them into the Turnover detection conveyor.

**Figure 2.** Scraper elevator. (1—hopper, 2—support plate, 3—guide plate, 4—curved scraper).

(2) Turnover detection conveyor. The Turnover detection conveyor is shown in Figure 3 and consists of sprockets, chains, sponge rollers, and motors. The apples are lifted by the scraper elevator into the turnover detection conveyor. The turnover detection conveyor uses pairs of double-tapered rollers to turn the apples axially, and a CCD industrial camera mounted on top of the lampshade collects images of the tumbling apples several times to obtain complete surface information about the apples in a moving position.

**Figure 3.** Turnover detection conveyor. (1—sprockets, 2—chains, 3—sponge rollers, 4—motor).

(3) Visual inspection and automatic grading control system. The visual inspection and automatic grading control system are shown in Figure 4 and consist of a CCD industrial camera and automatic grading control system. The visual inspection and automatic grading control system determines the grading of apples according to the information collected by the CCD industrial camera on the whole surface of the apples and finally sends the grading results to the graded actuators.

**Figure 4.** Visual inspection and automatic grading control system structure diagram.

(4) Graded actuators. The graded actuator is shown in Figure 5 and consists of a Trigger grading mechanism, sprocket chain drive, grading fruit cup, grading channel, and a motor. The grading fruit cup is shown in Figure 5b and consists of a cup body, a drop door, and rollers. The grading actuator receives the grading results from the image detection and automatic grading system and allows the apples to reach the corresponding grade position and then open the cups and fall into the corresponding grade storage bin.

**Figure 5.** Graded actuators. (**a**) Grading actuator; (**b**) Detail of grading fruit cup. (1-Trigger grading mechanism; 2-Sprocket chain drive; 3-Grading fruit cup; 4-Grading channel; 5-Motor).
