Vegetable grafting technique, a vital way toguarantee stable and high yield of plants, has been widely adopted around the world. Since vegetable grafting strongly depends on timing, a time window that is suitable for grafting is usually very short and precise grafting techniques areoften required. Manual grafting can hardly satisfy these requirements due to the low efficiency, intense work loads, and low survival rates of grafted seedlings. To counteract these problems, a grafting robot has been designed to implementautomatic vegetable grafting operations, to improve the grafting efficiency, reduce labor intensity, improve the survival rates of grafts, and to facilitate the vegetable production scale and industrialization [1Y. Osamu, and F. Akiko, "Growth adjustment technique of seedling optimal for grafting by seedling storage for cucumber full-automatic machine grafting", Tokyo Agricultural Research, vol. 55, pp. 201-202, 2002.-10J.Z. Lou, J.P. Li, P.A. Zhu, and G. Lü, "Design and test of stock clamping mechanism for vegetable grafting", Transactions of the Chinese Society of Agricultural Engineering, vol. 29, pp. 30-35, 2013.]. For solanaceae, the grafting methods include cleft grafting, attached grafting and parallel grafting. Among these, the cleft grafting method was mostly applied in practical production due to the simplicity in operation. In the past, many reports for solanaceae grafting robot were focused on the attached and parallel grafting methods [11X. Li, J.P. Li, Z.B. Chen, P. Zhu, and J. Qiu, "Design and test of key mechanism of beveling pin-grafting machine", Journal of Zhejiang University: Agricultural & Life Science, vol. 39, pp. 663-667, 2013., 12K. Jiang, W. Zheng, Q. Zhang, and Q. Feng, "Development and experiment of vegetable grafting robot", Transactions of the Chinese Society for Agricultural Engineering, vol. 28, pp. 8-14, 2012.]. Despite the wide utilization in growing seedling, the cutting process of cleft grafting is relatively complicated and there are still few reports about cleft grafting techniques [13Y. Zhao, Q. Sun, and T.Z. Zhang, "Mechanical system design of grafting robot for nutritional bowl eggplant seedlings", Transactions of the Chinese Society for Agricultural Machinery, vol. 38, pp. 94-97, 2007., 14K. Liu, Y.L. Yang, K. Li, Q. Chu, and L. Zhong, "Experimental study on rootstock cutting mechanism of pipeline grafting machine for solanaceae", Transactions of the Chinese Society for Agricultural Engineering, vol. 28, pp. 23-28, 2012.]. Y. Zhao [13Y. Zhao, Q. Sun, and T.Z. Zhang, "Mechanical system design of grafting robot for nutritional bowl eggplant seedlings", Transactions of the Chinese Society for Agricultural Machinery, vol. 38, pp. 94-97, 2007.] reported horizontal shoot apical meristem and vertical cleft grafting operation part with complicated design. S.B. Tian [15S.B. Tian, J.F. Yang, R.L. Wang, D. Xu, and T. Li, "Optimiza-tion experiment of operating parameters on vibration sorting-clip device for vegetable grafting machine", Transactions of the Chinese Society for Agricultural Engineering, vol. 30, pp. 9-16, 2014.] reported a kind of semiautomatic grafting machine based on multi-station pipeline system for mechanical grafting. However, the automation of this grafting machine still needs to be improved. In order to solve these problems, an automatic grafting robot for solanaceae was designed. Using this robot, holding, carrying, position-setting, cutting, jointing and seedling discharging for rootstock and scion have been successfully achieved.

This paper demonstratesa grafting robot based on cleft grafting technique. Furthermore, it also provides a new approach for enhancing the efficiency of grafting solanaceae vegetables. The average rootstock cutting success rate, average scion cutting success rate and average conjugation success rate were 98.7%, 99.0% and 59.6% respectively.

First, use a purchased grafting clip to arrange seedlings in order, and then carry this grafting clip to the push clamp position and hold seedlings by the clamping device. The automatic sorting device of the grafting clip is an electromagnetic vibration disc, consisting of a vibration plate, an electromagnet, an armature, a spring piece, a mounting seat, and a damping rubber pad. The pulse current produced by a controller has the same natural frequency as the system and can excite the electromagnet. The system is then led to resonance so that the armature and vibration plate will be quickly pulled to the magnet [15S.B. Tian, J.F. Yang, R.L. Wang, D. Xu, and T. Li, "Optimiza-tion experiment of operating parameters on vibration sorting-clip device for vegetable grafting machine", Transactions of the Chinese Society for Agricultural Engineering, vol. 30, pp. 9-16, 2014.].

The function of the push and clamp mechanism was to push the grafting clip, while the clip is open, from its original position to the position that the scion and rootstock are to be fitted. Then the clip is closed to bite the fitting parts of rootstock and scion. Finally, the push and clamp mechanism is reset. The movement of the clip should be gentle in order to protect the grafted seedling. Therefore, the mechanical device should meet the requirements as follows: the grafting clip remains open with the largest angle which forms the original position to the position that the scion and rootstock are fitted; a buffer device is needed to reduce the impact caused by the close operation of the grafting clip. According to the requirements of the function of the push and clamp device, the design of the push and clamp mechanism includes the following aspects:

Fig. (6) Schematic of the scion cutting mechanism.

4.2. The Push Rod and the Seat

The function of the push rod was to push the grafting clip to the clamping position carefully and return to the original position. Due to the sharpness of the grafting clip, the thrust of the push rod only depends on the spring coil of the grafting clip and the cutting groove.

Fig. (7) Diagrammatic sketch of the push clamping device.

In order to convey grafted seedlings, a mechanism to discharge grafted seedlings was needed. A flat belt conveyor was employed as the conveying mechanism. The prime motor was 24V DC stepping motor, veins were needed for increasing the friction force between roller and belt core. The belt core was made of canvas. The width of the belt was decided by the diameter of the nutritional pot, while the coefficient of friction was decided by the speed of DC motor and the mass of the nutritional pot. With the driving chain, the power was conveyed to the driving roller. Fig. (8) shows the diagrammatic sketch of the discharging device.

Fig. (8) Diagrammatic sketch of the device for discharging grafted seedlings.

The experiment used 100 of Beinong eggplant as rootstock and 100 of Seven leaves eggplant as scion, all in their suitable grafting time. Then the samples were randomly divided into 10 groups with 10 per group. The standard of success:

• (1). rootstock and scion bonding well-rootstock and scion centring, pieced together well without deviation;
• (2). rootstock and scion bonding moderate-rootstock and scion centring, pieced together moderately with some deviation;
• (3). rootstock and scion bonding poor-rootstock and scion centring, pieced together badly with major deviation. It can be seen as successful grafting with “good” or “moderate” comment. Fig. (11) exhibits the prototype of grafting robot.

Fig. (10) Flow diagram of stock processing main control module.

Fig. (11) The prototype of grafting robot.

The results of grafting experiments are shown in Fig. (12). The Results of grafting experiments indicate that the average rootstock notch and the average scion notch with a high rate of success. Due to the winding joint and the individual difference between rootstock and scion, a deviation is ineluctable for alignment of the rootstock and scion.

Fig. (12) Results of grafting experiments.

To summarize, a grafting robot for Solanaceous vegetables has been designed according to the manual operation rules of cleft grafting. Furthermore, it also provided a new approach for enhancing and standing Solanaceous vegetables grafting efficiency. The average rootstock cutting success rate, average scion cutting success rate and average conjugation success rate were 98.7%, 99.0% and 59.6% respectively.

The authors confirm that this article content has no conflict of interest.