Selective asparagus harvesting with autonomous robot

AvL Motion is breaking new ground – with a machine for the selective harvesting of white asparagus, 'garnished' with high precision sensors as well as RFID and fieldbus technology from Turck

The Dutch startup company AvL Motion put on the market a machine for the fully autonomous selective harvesting of white asparagus. In its search for an ultrasonic sensor for height control, the company came across the IO-Link compatible RU40U from Turck. Through the subsequent collaboration more sensor technology was integrated in the vehicle, including miniature inductive proximity switches, precise encoders as well as 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.

The AvL Compact S1560 pulls asparagus spears automatically from the soil
Six to twelve harvesting modules are located on the machine
AvL founder Arno van Lankveld uses Turck's IO-Link ultrasonic sensor RU40U
Thanks to its robust design, the Li500-Q25 sensor can also be fitted outside above the front axle
BI3-M08K miniature sensors in the buffer area detect the number of harvesting cassettes
When a cassette passes the NI10U-M12, the PLC starts the timer for a harvesting operation
Turck encoders report at which position of the buffer a harvesting module is currently available
On the driver's platform, a worker packs the asparagus into boxes and has control of the harvester
The TBEN-S2-4IOL multiprotocol device is used as an interface between sensors and PLC

Height control via ultrasonic sensor with IO-Link

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 a stable measurement of the height, which users can set on an HMI. “Turck impressed us with the outstanding quality and fast delivery of their product. We therefore stayed with the manufacturer for other components,” says AvL CEO Arno van Lankveld.

Optical process replaces trained eye

The harvesting process of the AvL Compact S1560 is very dynamic. Once the machine is positioned and set in motion, the surface of the soil is scanned. 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 the around 25 centimeter high cassettes. They are adjusted to the speed of the robot and control the entire process of inserting, cutting and gripping.

Fine tuning between target and harvesting module

The controller not only needs the coordinates of the selected asparagus spears to fine tune the harvesting process, but also a continuous flow of 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.

Inductive sensor triggers a timer

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 do not 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. In order to nevertheless 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.

Turning maneuver by joystick

Operators use an external control module to control the speed and the hydrostatic steering of the harvesting machine. Two Turck encoders measure the wheel revolutions; AvL uses an inductive linear position sensor to measure the wheel position. 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. Unlike the models offered by the competition, farmers do not have to attach the AvL Compact S1560 to a tractor.

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