*2.2. Conveying Performance Bench Test*

When using the DCHs to harvest wheat, the length of the wheat stalk cut by the header and fed into the combine does not match the working parameters of the relevant DCH parts, which adversely affects the conveying performance. Therefore, to reduce the probability of congestion, a test was carried out on the threshing test bench to determine the best stalk feed length and working parameters by exploring the influence of the parameters of WCHs on the conveying performance, which can provide the basis for the structural design of the DCH.

#### 2.2.1. Test Equipment

The structure of the threshing test bench consists of a frame, a longitudinal axial flow threshing and separating device, a tangential flow threshing and separating device, an inclined conveyor, a screw conveyor, a material conveying platform, and a grain collecting box, as shown in Figure 3. The tangential flow threshing and separating device, inclined conveyor, and screw conveyor bring wheat stalks into the longitudinal axial flow threshing and separating device. In contrast, the tangential flow threshing and separating device completes some of the threshing tasks. Moreover, a 37 kW three-phase asynchronous motor and its supporting frequency converter are used simultaneously to drive the tangential flow threshing rotor, the inclined conveyor, and the screw conveyor and adjust their speeds. The longitudinal axial flow threshing rotor imposes a significant workload; a 75 kW threephase asynchronous motor and its supporting frequency converter are exclusively used for driving the threshing rotor, for which the angular velocity is also adjusted. The material conveying platform is 10 m long and feeds wheat stalks into the harvester. The frequency converter is used to adjust the rotational speed of the asynchronous motor to change the conveying velocity, thereby controlling the feed rate.

**Figure 3.** Structural view of the threshing test bench. 1. Frame; 2. Longitudinal axial flow threshing and separating device; 3. Tangential flow threshing and separating device; 4. Material conveying platform; 5. Inclined conveyor; 6. Screw conveyor; 7. Motor; 8. Grain collection boxes; 9. Frequency converter.

#### 2.2.2. Experimental Materials and Methods

The test wheat cultivar was Zhoumai 32, and its average plant height was 743 mm. The test used manually harvested wheat and a cutting height of 50 to 80 mm. The grain moisture content was identified as 14.2%.

Combining this with the requirements of Equipment for harvesting—Combine harvesters —Test Procedure (GB /T 8097-2008), conveying time was taken as the testing indicator for the performance of conveying. The conveying time refers to when the wheat is first conveyed by the conveying platform to the screw conveyor, then passes through the inclined conveyor and the tangential flow threshing rotor, and finally arrives at the longitudinal axial flow threshing rotor. An observation window is set on the side sealing plate of the tangential threshing device, and the NORPIX FR-1000 high-speed digital camera is used to photograph the movement of materials in the transition area of the tangential axial threshing device, as shown in Figure 4. In the test, the acquisition frame rate of the high-speed digital camera was set to 200 frames per second, and the image recording began when turning on the conveying platform. The time taken for the material conveying platform to deliver the wheat to the screw conveyor is *t*1. After the tests ended, Image-Pro Premier image analysis software was used to analyze the collected images. To avoid a small number of stalks remaining in the header frame and inclined conveyor during the later stage of material conveying from affecting the judgment of the end time, based on less than or equal to five stalks in five consecutive frames of images, the time corresponding to the first frame of the image was selected as the end time *t*<sup>2</sup> [27], as shown in Figure 5. The results of the experiments have shown that the number of images with

less than or equal to five stalks in succession is less than 10 frames, so the error in judging the conveying time of high-speed photographic images is less than 0.05 s. The conveying time *t* is:

$$t = t\_2 - t\_1 \tag{1}$$

**Figure 4.** Conveying performance experiment site. 1. Observation window; 2. High-speed digital camera; 3. Light source; 4. Computer.

**Figure 5.** Conveying time collection. (**a**) Image at the beginning of the experiment; (**b**) Image during the stalk conveying; (**c**) Image at the end of the stalk conveying.

Three factors and three levels of the Box–Behnken response surface analysis methods were used in the test [28]. The test factors, such as feed rate, feed length of stalk, and speed of the tangential threshing rotor, were expressed as A, B, and C, respectively, and the conveying time was the test indicator, which was expressed as Y. The coding table of test factors is shown in Table 1.


Adjust the speed of the axial threshing rotor to 900 r/min and the speed of the conveying bench to 1 m/s. Cut the harvested wheat stalks and keep the upper part of the stalks at 300 mm, 450 mm, and 600 mm, respectively. Weigh the materials with different lengths of 24 kg, 27 kg, and 30 kg by an electronic scale and lay them evenly on the rear 3 m conveying platform with the wheat ears toward the threshing test bench to achieve feeding speeds of 8 kg/s, 9 kg/s, and 10 kg/s.
