**2. Design Scheme and Working Principle of the Underactuated Broccoli-Picking Manipulator**

In this paper, 300 mature Zhejiang 'Tai Lu' series were selected for studying broccoli's biological character data statistics. The physical characteristics of suitable broccoli were analyzed, as shown in Figure 1. The suitable characteristics were a flower ball diameter Φ of 14–18 cm, a plant height *h*<sup>1</sup> of 45–50 cm, a stem diameter Φ<sup>1</sup> of 0.34–0.46 cm, a flower ball height *h* of 7–9 cm, and a harvested plant height *h*<sup>3</sup> of 12–15 cm.

**Figure 1.** Planting patterns and biological characteristics of broccoli.

A single-stepper motor driven by an underdrive manipulator with two degrees of freedom, which was designed based on a compact underdrive structure, fewer drive actuators, a simple and efficient motion control system, broccoli physical characteristics, and low-loss picking agricultural requirements, can achieve the low-loss enveloping of flower balls with different diameters. The structure of the manipulator is shown in Figure 2.

**Figure 2.** Schematic diagram of manipulator structure: 1 stepper motor; 2 lift platforms composed of worm-and-nut; 3 drive-rod; 4 frame bottom plates; 5, 6 linkage; 7, 9 rockers; 8 clamp guard plates; 10 swing-rod; 11 cutting-blade.

The manipulator is composed of a set of symmetrical underactuated clamping mechanisms, clamping guard plates, cutting blades, and a single-stepper motor, which is picked by a clamping–cutting method. The working principle is shown in Figure 3. The manipulator moves directly above the broccoli and enters the picking area (Figure 3a). Under the action of drive rod force, the clamp guard plates (8) envelope the flower ball (Figure 3b) while the rocker (7) remains motionless. At this time, the rocker (9) drives the swing-rod (10) on the cutting blade (11) to allow the closure of the cutting blades and complete the stem cutting (Figure 3c). Finally, the manipulator driven by the motor picks the flower ball (Figure 3d).

**Figure 3.** Working principle diagram of picking manipulator: (**a**) The manipulator enters the area to be picked, (**b**) Envelope flower ball, (**c**) Clamp–cut flower ball, and (**d**) Release flower ball.
