# A Vision Servo System for Automated Harvest of Sweet Pepper in Korean Greenhouse Environment
## 2 Material and Methods  
### Hardware Composition  
As shown in Figure 1, the manipulator used in this study is the cylindrical robot which has three axes, namely a rotation axis, a horizontal axis, and a vertical axis, and is appropriate for a narrow space. The cylindrical robot is controlled by height L1, angle \(\theta\)2, and radius L3 like Figure 1a. The robot can carry out works in a narrow space, like a sweet pepper greenhouse, efficiently and easily move to horizontally. It has three independent degrees of freedom, and its vertical and horizontal joints cross each other. If the degree of freedom of horizontal orientation is ignored, it is a rotating and horizontally moving L2-\(\Theta\)2 manipulator as shown in Figure 1b. The rotation angle \(\theta\)1 is defined as horizontal X-axis, and L2 can be defined as the distance from the rotation axis to the endpoint of the end-effector. Depending on the environmental characteristics of the sweet pepper farming analyzed by [PERSON] et al. [21] and [PERSON] [22], the working area was set up at 350-600 mm from the center of the system and 1000 mm vertically. The planting interval of sweet pepper was 1000 mm and the rail intervals were 500-600 mm. The working area was set up after considering these conditions. In order for the manipulator to be able to transport horizontally and vertically two linear actuators were used. As for the linear actuator, which is in charge of vertical transportation: its stroke is 1000 mm; the lead of its ball thread is 10 mm; its maximal vertical load(weight) is 18 kg; its maximal transportation speed is 500 mm\(\cdot\)s\({}^{-1}\); and its repetitive transfer accuracy is 0.005 mm. As for the linear actuator which oversees horizontal transportation: its stroke is 500 mm; its maximal load (weight) is 25 kg; and other specifications are the same with the linear actuator which oversees vertical transportation. The cylindrical robot is made of duralumin, an alloy of aluminum with excellent corrosion resistance, in consideration of a greenhouse's hot and humid working environment. Figure 2 presents the manipulator with three axes, namely a rotation axis, a vertical axis, and a horizontal axis. Since the motor of the manipulator must work under the high temperature and humidity of the planting environment of sweet pepper, this study used Panasonic Minas a5 (Panasonic, Kadoma, Japan). Figure 1: Coordinate relationship of the manipulator used in this study: (**a**) three axes (rotation, horizontal, vertical); (**b**) two axes ignoring vertical orientation. Figure 3 presents the end-effector. The end-effector drops a fruit from below and makes the peduncle of the fruit positioned in its cutting portion through pose control, thus making its pneumatic cylinder harvest the fruit. The cutting part of the end-effector is designed to be carried out vertically, thus preventing damage to the stem of the sweet pepper. The end-effector was designed according to the characteristics of sweet peppers cultivated in South Korea with reference to the studies of [PERSON] et al. [23], Ministry of Agriculture, Food and Rural Affairs (MAFRA) [24] and [PERSON] et al. [25]. The horizontal length of the end-effector is set up at 120 mm, and 150% of the sweet pepper's average diameter 80.92 mm. On the other hand, its vertical length is set up at 140 mm, and 150% of the sweet pepper's average length 92.15 mm. The entrance size of the cutting portion is set at 16 mm, in consideration of the average diameter of a sweet pepper's peduncle, thus preventing the peduncle's escape from the entrance. The entrance is set up at 10 mm initially, at a relatively narrower size, thus making it controlled elasticity by a spring. In the front of the end-effector, a pneumatic cylinder for cutting was installed, and in order to catch the stem of sweet pepper, a guide of 35 mm thickness is designed. For the stem of sweet pepper to be located in the guide, the guide has a 60\({}^{\circ}\) angle. In addition, the vertical guide is designed to be 59\({}^{\circ}\).