Students: Jelle van Leeuwen, Stephan de Reus, Irene Stolk, Stef Nibbelink.
The Scindapsus is a plant that consists out of long strings with leaves. In figure 1 is the Scindapsus we work with in the project. To get new plants a leaf with 1.5 cm to 2 cm stem around the leave has to be potted. After 3 weeks the cutting should get roots and grow into a new plant.
In the current situation mother plants are growing in a greenhouse. Employees will cut strings off these plants. After collecting enough strings they will go to another workstation. Here they cut the Scindapsus strings into cuttings. Thus a leaf with 1.5 cm to 2 cm around the leaf. The bits of stem and leaves which cannot meet these requirements will be thrown away. The last bit of the string is also thrown away. The leaves are too small to let the cutting grow out into a plant. After the cuttings are made the employees will pot these cuttings into a pot. The cuttings will be potted in a certain pattern.
The goal of this project is to automate the cutting of a Scindapsus string. The strings itself will be cut and placed in a rack. The system of this project will pick up these strings and cut them into cuttings. Later these cuttings will be potted. The potting will not be included in this project and in this situation, will still be done by employees.
The system exists out of a guiding system, vision system and cutting system. The guiding system will guide the Scindapsus string towards the cutting system. A photo will be taken and analyzed. The cutting position will be determined with the photo.
The Guidance system
The strings have a set location on the rack, in the Scindapsus clips (2)( Figure 2). This way robot knows all the positions of these strings.
The Universal Robot(1) will move the strings of Scindapsus through the setup. So the string will be picked up from point 2. It will be moved through the funnel (3). This will prevent the plant from being damaged. This is also needed to guide the string into the PVC tube (4). The robot will move the Scindapsus string trough the tube with a slim end of arm tool. In the side of the tube is a slit for this tool. The string is guided through a tube to keep it in place without being held by the robot.
The Vision system
The camera will be triggered to make a photo by the robot. This photo is processed by Halcon code. The picture will be simplified. From this a skeleton will be made of the silhouette of the string. With this skeleton the armpits can be found. These are the branches with leaves. This can be seen at A of figure 3. Based on this armpit the correct distance will be calculated and send to the robot. The robot will move the string the correct distance through the cutting system.
If there is no plant the vision system will send a signal to the robot. The robot will pick up the next string from the next fixed place of the rack.
The cutting system
In figure 4 is an close up of the cutting system and end of arm tool(6). The cutting blade is not shown in this picture. The cutting tool (7) will contain the cutting blade. On the other side is a similar tool to keep the string in the middle and to cut the plant. The end of arm tool will be holding the string underneath the cutting tool. Both parts of the cutting tool will go to the middle by pneumatic cylinders (10). This cutting tool will stay closed. By staying closed it will hold the rest of the string in place. The end of arm tool will have the cutting. This cutting can be moved to a crate and let go. In a later situation this cutting could be placed in a pot. After the end of arm tool has let go of the cutting the next cutting will be made. Again a photo will be analyzed. The robot will pick up the string just above the cutting tool. The cutting tool will open and the robot will pull the string down again. This will continue until the vision system gives the signal to get a new string.
Conclusion and recommendations
With the solution as described in this article we can accurately cut the strings in pieces of the correct size. The problem that occurred with this design is that the leafs are often (partially) cut off. In the time period set for this project a solution for this problem has not been found. This is due to very little and misshapen test material. The test plants we had access to were not grown in greenhouses but were poorly maintained in wrong environments. Because of this the amount of testing was very limited and the results of tests were inaccurate. Solutions that failed on the test plants could have possibly worked on well-maintained Scindapsuses or while working with well-maintained Scindapsuses good solutions would most likely have come up.
For a recommendation it is advised to look into the following possible solutions. While guiding the plants the leafs could possibly be guided simultaneously towards a certain position to keep them out of the way when the plant reaches the cutting tool.
The leafs could also be guided away at the cutting tool. A redesign of a the cutting tool and/or the end of arm tool could possibly guide the leafs away from the blade.
At last air could be integrated in the system. Air blowing on the leafs from one or several directions could maybe blow the leafs away for long enough to make a clean cut.
These solutions have not been tested due to a lack of time and resources (mainly test plants).
Jelle van Leeuwen, Stef Nibbelink, Stephan de Reus, Irene Stolk.