**2. Materials and Methods**

#### *2.1. Structure and Working Principles of the DCH*

A DCH was designed based on the horizontal screw conveyor header of WCHs, which has two layers of cutterbars, as shown in Figure 1a. The DCH is mainly composed of the frame, a reel, a screw conveyor, upper cutterbars, lower cutterbars, wobble boxes, a profiling mechanism, and a transmission system. Among them, the profiling mechanism consists of a fixed beam, support arms, a height-limiting connecting rod, a swing block, and the ground wheel of the upper cutter. The swing block, support arm, and connecting rod installed with a height-limiting block form a crank rocker mechanism, as shown in Figure 1b. The fixed beam is welded to the support arms on both sides, and the upper cutter and ground wheel are installed on the fixed beam. In the case of uneven terrain, the profiling mechanism can enable the lower cutterbars to fluctuate with the change in wheat field terrain, which ensures consistency of cutting height and protects the cutterbars from damage to some extent.

Before an operation, a hydraulic height adjustment handle on the DCH is used to lower the header. In lowering the header, the ground wheel is the first to come into contact with the ground. The height of the lower cutterbars no longer undergoes significant fluctuation, while the upper cutterbars continue to descend to the set height. A schematic representation of the DCH in service is shown in Figure 2. The plant height of wheat is *L*1; the upper cutterbars first cut the upper part of the wheat stalks, which can then be pulled into the screw conveyor under the effect of the reel. The cut part with a stalk length of *L*<sup>2</sup> is fed into the combine harvester; the middle part of the wheat stalks can be cut by the lower cutterbars and then scattered across the field. The length of the central part of wheat stalks is *L*3. The uncut part of the wheat stalks remains on the ground, forming stubble with a height of *h.* The fixed scale of the oil cylinder on the DCH can be adjusted to tune the length of stalks cut by the upper cutterbars to adapt to harvesting wheat plants with different heights.

**Figure 1.** Structure of the DCH. (**a**) Three-dimensional structural diagram of the DCH; (**b**) Structural diagram of the profiling mechanism. 1. Reel; 2. Screw conveyor; 3. Frame; 4. Inclined conveyor; 5. Height-limiting connecting rod; 6. Swing block; 7. Ground wheel; 8. Lower cutterbar; 9. Fixed beam; 10. Wobble box of the lower cutterbars; 11. Belt expansion device; 12. Support arm; 13. Wobble box of the upper cutterbars; 14. Upper cutterbar.

**Figure 2.** Operation diagram of the DCH.
