Autonomous asparagus harvesters minimise labour

How do you like yours? As a regular vegetable, perhaps, roasted, grilled or simply blanched, or perhaps served in its most delicate form bathed on the plate in a buttery Hollandaise sauce.

Laboured process of visual selection and hand cutting

However you like your asparagus, getting this popular and highly seasonal food from field to plate typically involves a laboured process of visual selection and hand cutting, and multiple passes through the crop during the harvesting period.

With fewer people willing to undertake this work, and those that are commanding higher wages due to market forces or minimum wage legislation, the race is on to develop efficient, effective, reliable and affordable machines to do the work instead.

Harvesters that minimise labour

Some growers have already turned to harvesters that minimise labour but take every asparagus spear with each pass, resulting in a significant proportion that do not meet minimum length and quality standards.

The ideal solution is a harvesting technique that mimics hand cutting in the sense that it selects and cuts only those spears that are ready for consumption.

Sparter harvesters for ‘white’ asparagus

Dutch tech company Cerescon believes it has the answer with its Sparter harvesters for ‘white’ asparagus, a delicacy mainly grown in Europe in raised beds or dams under cover to maintain its blanched appearance.

In 2017, the company introduced two- and three-row tractor-operated versions for harvesting 35 to 50 hectares (85 to 125 acres) of asparagus during the short season.

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This autonomous single-row harvester from Cerescon has joined the tractor-powered two- and three-row models with the promise of slashing costs by 70% compared with hand-cutting. – Photo: Cerescon

Last year, the single-row self-propelled autonomous version for around 30 hectares (75 acres) was unveiled with a price tag of € 350,000. “With this machine, the harvest costs per hour are reduced by up to 70% compared to manual harvesting,” says Thérèse van Vinken of Cerescon. “Just one person is needed to collect the harvested asparagus into crates and due to the compact dimensions smaller fields can be harvested with less headland loss.”

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Technology detects and cuts mature asparagus

Output and quality gains are also claimed for the Sparter thanks to patented technology that detects and cuts mature asparagus spears before they emerge in the bed, which can result in purple tip discolouration, and by minimising the ‘collateral damage’ caused during hand cutting to nearby spears that have yet to emerge.

The patented detection system passes a signal through the soil dam to make the asparagus ‘visible’ to feelers passing through the bed that rapidly retract after a spear has been detected and its position calculated.

The cutting and lifting mechanism that follows is deployed vertically and remains stationary in relation to the ground as the harvester continues to move forwards at a constant speed.

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Minimal collateral damage to nearby spears is claimed for the cutting and lifting mechanism – here the asparagus spear is uncovered for illustration. – Photo: Cerescon

Two cutters per row

There are two such cutters per row to achieve the capacity required, which for the single-row autonomous Sparter is around 0.3 hectare/hr (0.75 acre/hr). Picked asparagus spears are placed on a conveyor belt and transported to a basket, while the hole in the bed is repaired to promote straight and even growth for maximum yield of ‘A’ class produce during the next harvesting pass.

Yield mapping data

A bonus is that the detection system also provides yield mapping data enabling growers to use precision farming techniques for better yield prediction and inputs management.

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Harvesting ‘green’ asparagus

The need to change from hand- to machine-harvesting of ‘green’ asparagus by larger growers is just as pressing as for its ‘white’ counterpart, says Matthias Kinzel of Strauss Verpackungsmaschinen, a leading manufacturer of machinery to support manual harvesting operations.

“For many growers, it is increasingly difficult to get people of the right calibre to do this seasonal work, and then the logistics involved in providing accommodation and welfare, and organising everyone into an efficient team every day, is a big challenge,” he says. “The additional labour-sourcing and safeguarding issues created by the Covid-19 virus have highlighted the dangers of relying completely on manual harvesting using seasonal labour.”

Geiger Manufacturing trailed and Haws self-propelled harvesters

At present, selective harvesting solutions are limited to the Geiger Manufacturing trailed and Haws self-propelled harvesters developed in the United States, which both use optical sensors to select individual asparagus stems by height.

Air driven spears

The $ 99,000 Geiger-Lund Pickit harvester deploys air driven spears to cut through the stems, which are then plucked by rotating rollers and deposited on a conveyor, while the Haws harvester (see video below), which is not yet in series production, has a complex mechanism of multiple cutting and lifting arms to achieve the same end.

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However, research projects based in Germany and New Zealand aim to use modern computer vision and control systems to produce lighter, simpler and more agile mechanical systems to be deployed. Strauss is the main commercial partner in projects part-funded by the European Union for both green and white asparagus.

“Both methods of production present significant software and hardware challenges for automated selective harvesting,” says Matthias Kinzel of Strauss. “The project for green asparagus with the University of Bremen now has priority because this product is most widely grown worldwide and it’s a little easier to locate, measure, cut and transfer the asparagus when you have the whole spear above ground.”

“In the next stage we aim to improve the speed and accuracy of the image-based selection system and the cutting and transfer mechanism, and also to improve the stability of the lightweight robotic platform in the field to achieve consistent accuracy.”

Harvester by University of Waikako and RoboticsPlus

A project led by the University of Waikato in New Zealand has NZ tech start-up RoboticsPlus among its partners. “The harvester works via a computer vision system that detects the asparagus spears, and then computes their corresponding base location,” says the University’s Dr Shen Hin Lim, project leader. “The robotic arm goes to that location at a calculated time to cut and gently grip the asparagus, then transfer and release it into a basket.”

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California growers who have seen the proof-of-concept prototype working in their crops are enthusiastic about its potential, pointing out that legislated minimum wage increases and working hour changes make finding ways of harvesting with less labour in less time an urgent need.

Dr Lim says the team’s focus is now on achieving a three-fold increase in the speed of the cutting and picking mechanism to make the system, currently in a tractor-trailed format, more commercially viable.

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Green asparagus picking robots in greenhouses

While those projects work towards automated selective harvesting on a field scale, commercial use of green asparagus picking robots in greenhouses is already underway in Japan.

Each of the 65kg tracked vehicles developed by tech start-up Inaho is just 1.25m long and 39cm wide, has an infra-red detection system, and uses a manipulator arm with a combined cutter and gripper to transfer individual spears to a basket.

The robot signals when the basket is full via a smartphone app that is also used to set harvesting parameters and the vehicles move between greenhouses following white marker lines.

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Inaho’s asparagus harvesting robot uses an infra-red detection system and a manipulator arm to cut and handle individual asparagus spears. – Photo: Inago

Inaho supplies harvester on lease basis

Inaho currently supplies the machines on a lease basis according to the crop market price and volume harvested; the first one went to a horticultural enterprise in the Saga prefecture on the island of Kyushu.

Asparagus and cucumber grower Kotaro Ando says harvesting accounts for 50-60% of his work so the robot releases productive time for other activities such as sales promotion. Yutaka Hishiki, CEO of Inaho, said: “We have received a lot of feedback from local farmers that they want to introduce robots quickly.”

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Asparagus harvesting machines by Kirpy and Christiaens

Harvesting machines that take the whole asparagus crop with each pass reduce labour requirements and expenses at the cost of wastage of spears that do not meet length and quality standards.