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FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY ASPARAGUS HARVESTING BREAKS


NEW GROUND High precision sensors, RFID and fieldbus technology from Turck have been specified for a


machine specifically designed to harvest white asparagus


and manufacturing team. So when developing its machine – the AvL Compact S1560 – for the fully autonomous selective harvesting of white asparagus, Dutch startup AvL Motion decided it needed an ultrasonic sensor for height control. Looking into the solutions available, the company chose the IO-Link compatible RU40U from Turck for the machine. As a result of the collaboration, however,


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more sensor technology was integrated in the vehicle – including miniature inductive proximity switches, precise encoders, and LE550 laser sensors from Banner Engineering, and the robust Li500-Q25 linear position sensor. AvL also uses the TN-Q14 RFID read/write head for the identification of harvesting modules, while the TBEN-S2-4IOL compact I/O module transfers IO-Link signals to the PLC. AvL Motion uses two of the ultrasonic sensors RU40U with IO-Link to measure the distance between the asparagus bed and the pneumatically controlled internal frame of the machine. In spite of the partly dusty or rain-slicked subsoil, the sensors enable stable measurement of the height, which users can set on an HMI.


HARVESTING Unlike the models offered by the competition, farmers do not have to attach the AvL Compact S1560 to a tractor. The harvesting process of the machine is, however, very dynamic. Once the machine is positioned and set in motion, the surface of the soil is scanned, and the precise location of an asparagus tip is detected by the main controller through the use of laser sensors, together with an additional optical process. A variable number of harvesting modules move in the process round a circular track inside the robot. At present, this consists of twelve of them around 25cm high cassettes. These are adjusted to the speed of the robot and control the entire process of inserting, cutting and gripping. The controller not only needs the coordinates of the selected asparagus spears to fine tune the harvesting process, but also a continuous flow of


18 DESIGN SOLUTIONS JUNE 2024


hen developing machinery, careful specification of the right components is an essential process for the design


Farmers do not have to attach the AvL Compact S1560 to a tractor


information on the position and movement of the modules. This starts with the query of how many cassettes are currently located in the buffer, i.e. how many are in park position, and those currently detecting an asparagus shoot in the circuit. For this, AvL uses the tiny BI3-M08K inductive sensors. The exact identification of the harvesting modules is implemented with RFID – using the TN-Q14 HF read/write head, which reads the individual code of each cassette. Added to this is the position detection provided by a rotary encoder.


CONTROL Once a harvesting machine starts its circuit, this passes a type NI10U-M12 uprox proximity


switch, which sets the running of the timer for the harvesting process in the PLC. As the asparagus spears don’t grow in tidy rows, the harvesting modules can also move left or right in addition to their movement round the circular track. This is driven with compressed air and is therefore always delayed by a few tenths of a second. To ensure the correct alignment of the cassettes, the PLC obtains information about the distance between the initial and target position of the modules, measured with LE550 laser sensors from Turck’s optoelectronics partner Banner Engineering. An external control module is used by the


operator to control the speed and the hydrostatic steering of the harvesting machine, with two Turck encoders measuring the wheel revolutions. AvL uses an inductive linear position sensor to measure the wheel position and, for this, the positioning element of the LI500-Q25 sensor is linked with the piston of the steering cylinder. In this way, the main controller calculates the angle of both wheels using only one value – and operators can turn the machine easily with a joystick.


Turck Banner www.turckbanner.co.uk/en


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