Robots are autonomous machines that can take over mind-numbing or heavy work from humans. In the production industry, they are now well established, but in agriculture and horticulture there is still much to be gained. This is also the case with the harvesting of asparagus, which is a heavy and labour-intensive process. Arno van Lankveld, founder of AVL Motion, saw an opportunity to automate the delicate harvesting process. He developed a tool carrier with an asparagus harvesting robot. The modular design of the vehicle means it can also be used for other tasks. Partly thanks to the motion control technology from Lenze, AVL Motion was able to achieve a labour reduction of over 80%. And that is substantial. Aandrijftechniek went to the border of Brabant and Limburg to see how they managed it.
Asparagus is the white gold that is harvested from April to June. Normally seasonal workers are used for this, often from the former Eastern Bloc. However, it is becoming increasingly difficult to find seasonal workers, and the Covid-19 situation added to this in 2020. In Germany last year 20 percent of the asparagus was not harvested. And this year too, many asparagus growers are at a loss for what to do. Time for automation. Arno van Lankveld thinks that in a few years time everything will be harvested by machines. “If we look at the harvesting of asparagus, the smaller plots will still be harvested manually at first, but it is just a matter of time before this will also be done by machines. For the larger plots the asparagus harvesting robot is already more advantageous. The longer the beds are, the more effective the asparagus harvesting robot is.”
Michael Huijgen, account manager Drives & Automation at Lenze complements him: “In addition, this machine can in principle harvest 24/7 and can simply continue on weekends. In warmer weather, the harvest time is also limited for seasonal workers. And the robot never falls ill and has no Sundays or public holidays.”
AVL Motion’s asparagus harvesting robot only requires one operator. Van Lankveld: “The man or woman on the machine only has to perform three actions. Inserting the foil at the beginning of an asparagus bed. Then, when the machine reaches the end of the row, it has to be moved to the next row, using the remote control, and the film has to be fed in again. The third task during harvesting is stacking full crates of asparagus on the platform.”
Delicate process
According to Van Lankveld, his asparagus harvesting robot can achieve a labour reduction of over 80 percent. But how do you achieve that? “The capacity of the asparagus harvesting robot is about 9,000 asparagus per hour. That makes it unique. Robotics often involves automating human actions. We have installed 12 harvesting modules in our machine, six on the left and six on the right, which carry out the same operation cyclically according to the gondola principle. In this way, we have developed a unique process, comparable to 12 hand harvesters but with extremely high speed. A hand cutter cuts around 300 asparagus per hour, our asparagus harvesting robot 9,000 per hour.”
Before the asparagus can be harvested, the foil has to be removed. At the beginning of a row of asparagus, the operator has to feed the foil into the machine. AVL Motion developed a patented principle for this, which automatically feeds the foil and also neatly places it back on the asparagus bed. “The machine follows the asparagus bed itself, 100 percent autonomously without touching the bed,” explains van Lankveld. “First the foil is picked up. Then the asparagus become visible. Meanwhile, the machine drives at a speed of 1 metre per second (3.6 km/h). With a smart camera, the asparagus is detected to then be harvested.”
How does the robot recognise that the asparagus is ready to be staked? According to van Lankveld the camera recognises the asparagus by contrast analysis in a dark ‘scanning chamber’. So no daylight is needed for harvesting. “In the past, say 20 years ago, the cracked earth was already a sign for cutting. But then there was no foil over the beds. The function of the foil is multiple. Besides preventing the asparagus from discolouring, the white side of the foil serves to lower the temperature in the bed or the black side to increase it and to condition the humidity. The camera that detects the asparagus is trained by machine learning to recognise multiple variants of how an asparagus emerges from the bed. This leads to a harvest signal even in cracked soil, where the head is still under the ground.”
Controlling harvesting modules
If the camera detects an asparagus, it sends a signal to the control unit. The 12 harvesting modules are waiting in the robot and, after receiving the signal, the software controls one of the harvesting modules to extract the relevant asparagus. Meanwhile, the machine continues to move. The harvesting module in question stands still above the asparagus, enters the ground, cuts the asparagus and grasps it. Then the harvesting module moves forward again and in the meantime releases the asparagus above a conveyor belt and is transported to the operator’s crate. According to Huijgen, the difficulty in doing this in a precision synchronised way is the movement of the harvesting modules while the machine is moving. “The machine keeps on moving, while the 12 harvesting modules stand still above the asparagus and harvest it. That’s when the piece of technology from Lenze comes into play.”
Each harvesting module has a number of functionalities and one of these is that the cutting module can move sideways over the bed. Van Lankveld: “When a module is sent to the right position, it does so in an X and Y direction. In our case, the Y direction is equal to the direction of travel and the X direction is the lateral movement. Once the X-Y coordinate of the asparagus is known to the camera, one of the 12 harvesting modules synchronises with the driving speed to the correct position and then cuts out the asparagus with the harvesting cassette. In addition, there is a difficulty in that this robot keeps steering itself along the asparagus bed. This can have consequences for the positioning of the harvesting module. But in the software we have arranged it in such a way that it corrects the position of the asparagus with any corrections made, so that the asparagus is harvested at exactly the detected location.”
Motion control
At a Dutch fair trade back in 2018, there was the first contact between AVL Motion and Lenze. Van Lankveld had problems with the synchronisation movement with the first prototype. “At the time, that was a hydraulic movement with a piece of pneumatics in it. That was not accurate enough at the time.” Huijgen contacted van Lankveld, because only if Lenze could make the synchronisation movement more accurate was there a follow-up discussion. “We solved that with two drives that had to run synchronously,” Huijgen explains. “We developed this further in very good cooperation and in the machine of last year AVL Motion mounted the 12 modules (loop system) with an X and Y movement. That is a piece of motion control that AVL developed together with Lenze.”
A zero series of two machines is currently being built. “In these machines there is a complete Lenze solution where we were also allowed to realise a piece of the logic and visualisation,” explains Huijgen. “Things like the connection with the camera, the positioning, the visualisation for the operator and even a connection to the cloud. This is currently the connection for service, but later it will also be used to extract data from the machine for, among other things, the harvest forecast.”
The list of Lenze components is long. The asparagus harvesting robot includes an x530 IoT gateway, a c550 CoDeSys PLC with Motion controller incl. FAST UI runtime, a v450 Web panel 15″, various I/Os of the System 1000 type, several i700 Multi-axis servo inverters, several g500/MF 120Hz asynchronous drives and several g500/MCS synchronous drives. Lenze also supplied all motor and encoder cabling.
Software modules
A complex machine needs complex software, as does this asparagus harvesting robot. The basis of the control of the modules was supplied by Lenze. AVL Motion has taken over, improved and adapted it to the machine. “Lenze is used to working with standard modules and building blocks in the software,” Huijgen explains. “If you look at the motion, for every movement there is a building block available that solves a whole part of the motion for you. But this machine has such a complex motion that we could not solve it with one building block. We have now combined two building blocks, the ‘smart track’ movement and the ‘flying saw’ movement. We have combined the two to create the motion cycle of a harvesting module. Our aim is to provide a basis on which the customer can continue on his own. We also provide training and support, so that AVL becomes ‘self supporting’ in the field of programming. Modularisation is already applied in mechanical engineering, but in software we still see a gap. Lenze has taken a huge lead in order to get it done better.
Priority on reliability
AVL Motion’s machine is built as an autonomous tool carrier. Currently it is equipped with a harvesting frame for white asparagus. “We have designed the machine in such a way that we can exchange the harvest frame with another harvest frame, so that you can use the machine for a different crop. This makes the machine usable for several months throughout the year. We want to be able to change the functionality,” says van Lankveld.
As an asparagus robot, the machine must be fully functional every day for three months of the year. And if it then replaces 18 people, you can’t take the risk of a machine standing still for a long time. “This is one of the reasons why we said goodbye to the hydraulics in the machine,” says van Lankveld. “We eliminated that completely and it was mainly because of the reliability. It was also not very accurate and it generated too much heat. But the main problem was the unreliability. If a hydraulic motor breaks down, it contaminates the entire system. That means a complete system clean-up, which can take up to two days. With an electric drive, you can simply change the drive, put in a new one, and the machine runs again. It is even possible to switch off a harvesting module and still continue harvesting with the machine.”
Needless to say, there are also a number of wear parts, especially those that come into contact with sand. “We have designed the blades and grippers in such a way that an operator can click them in without any tools. The machine itself detects the success rate of the harvesting module. If the success rate drops below a certain level, the machine will indicate this and the operator can decide whether to do something about it or to switch off the module in question. If he wants to solve the problem, he sends the module to the maintenance position and can replace the relevant harvesting module. Then he can continue harvesting. And you don’t have to be a scientist to do that. Someone who can drive a tractor and hitch up machines can easily do the job. Our customers are very sensitive to this. They don’t want a deep-tech machine that grinds to a halt because of every problem, but proven technology. We innovate mechanically supported by proven sub-systems of A-brands. That makes our machine reliable, partly thanks to Lenze,” concludes van Lankveld.
