Smart machine processes 10,000+ tulip bulbs per hour thanks to reliable wireless communication

ISO, Horti Innovators, automates complex and high-cycle processes in agriculture and horticulture with the help of robotics, vision, AI and machine learning. A key target group is tulip bulb growers. SMC's communication solutions help growers sort unprecedented numbers of tulip bulbs and place them in the picking bin. For this, ISO chose a wireless communication solution from SMC that is not only extremely reliable, but also allowed the company to solve a number of complex design problems.

Planting tulip bulbs is a complex process. Not only are very large numbers involved, but the bulbs must first be arranged in rows at certain intervals. In addition, each individual tulip bulb must be placed with the sprout (the first beginning of the tulip's stem) pointing upwards. An additional complication is that the tulip bulb must be secured in the pricking tray in such a way that the bulb remains in the correct position even during transport from the pricking tray. This is crucial to prevent damage to the shoot. ISO has developed a modular bulb planting system that can automate this entire process. Robots and cameras can therefore take on virtually all tasks and operations. "These are standard machines that are configurable to the customer's layout and specifications. Each machine is capable of processing all types and sizes of tulip bulbs for cut flowers," says Bastiaan Ophorst, mechanical engineer at ISO.

Smart process requires wireless vision system

How does this bulb planting machine work? Forklifts feed the tulip bulbs into cubic containers. The bulbs are then already sorted by size. This is because the size of the bulb determines which containers to use for pricking up. The cubic bin is emptied into a collection bin at the beginning of the line. The tulip bulbs end up several layers high in this. To achieve a neat row of bulbs that can be picked up by the grippers of the robotic arms, the bulbs are transported toward the loading station by vibrating plates. The vibrating plates ensure that the multiple layers of tulip bulbs are reduced to a single row. The vibrating plates also ensure that space is created between the individual bulbs. This spacing depends on the number of bulbs to be placed in pricking trays.

After the cameras and vision system have determined the position and orientation of the bulb on the belt, the bulbs are fed into the bulb planting machine in a neat line with the required spacing. This line generally consists of several modules (so-called
 'planting modules'). Usually there are four modules. Each module has one robotic arm. The information about the position and orientation of the bulb now determines how the grippers of the robotic arms pick up a series of bulbs and place them on a so-called stitching bridge. The number of positions on the stab bridge depends on the number of bulbs that can be placed in one row in the pricking tray. The robotic arm now places the bulbs on the stitching bridge in such a way that each bulb is precisely placed in a gripper. Each stab bridge has up to two times seven grippers arranged in two parallel rows 180 degrees opposite each other. When seven grippers are filled, the stabbing bridge rotates and the row of bulbs is placed in the pricking tray. Depending on the type of bulb, there is a small pin in the bottom of the container for each position for a tulip bulb. Mass is grown on water forcing, the more exclusive varieties on soil forcing. The stitching bridge gently presses the bulbs onto this peg or into the soil, fixing the position of the bulb. This keeps the bulbs positioned with the sprouts up even during transport. When the pricking tray is full, it is moved out of the module and its place is taken by a new, empty pricking tray. The bulb-filled pinch tray is then transported to a final station where a grower's employee makes a final visual check. 

After this, six cameras take an image of each individual tulip bulb. These six images are assembled into a 3D image. This shows the position of each bulb on the belt, the 3D geometry of the bulb and the location of the shoot. This information together determines how the gripper should later pick up each individual sphere. An optical health check of each bulb also takes place via the 3D camera to prevent an unhealthy bulb from being accidentally picked up. These so-called "sour bulbs" are not picked up by a gripper, but are marked by the machine's control system and removed at the end of the belt. The speed of the belt can be varied to achieve the desired spacing between bulbs. This can also prevent dunnage in the machine. 

Reliable wireless communication achieved

ISO faced a major technical challenge in designing this bulb planting machine: the rotational movement of the pitch bridges. In fact, this rotation is always in the same direction. However, communication must take place between the central control of the bulb planting machine, the robotic arms and the cutting bridges. Because of the rotational movement, a wired solution was very difficult to implement. Ophorst explains: "We looked at using slip rings, but that would have required very many contacts. There are more than thirty functions/detections in each slip ring. That can't be done via wiring. Therefore, we were quickly convinced that we had to go for wireless communication. But how do you do that in a reliable way?"

 "The solution came from SMC," says Bert Evertse, PLC programmer at ISO and responsible for the control of the bulb planting machine "We had already carried out some tests with a product from another brand, where the communication was via Bluetooth. That turned out to be quite sensitive to interference, which - especially with this type of high-speed line - is very undesirable. However, SMC came up with the right solution at exactly the right time. What SMC proposed to us as a solution was an industrial wireless network within the bulb planting machine. We now have a base module placed on the non-rotating part of the line, and a remote module on the pitch bridge. Data for controlling the cutting bridge are hereby sent from the base to the remotes via SMC Industrial Wireless Communication. The control data - about 60 bits per module plus some data for diagnostic purposes and the like - are transferred to the transmitter via serial communication (Ethernet/IP). The configuration of the base and remote is addressed once upon installation via NFC (Near Field Communication)."

The distances between the base module and the remote modules can vary. Depending on the number of modules that make up the bulb planting machine, it is 5 to 6 meters. A maximum radius of 10 meters is possible. The moving parts in each module - think of the servomotors of the robot arms - do not appear to have any impact on data transmission. "There is absolutely no question of interference," says Evertse. "Indeed, the communication is extremely reliable."