Button mushrooms deftly picked and neatly trimmed by robot

In a new study, the prototype, which is designed to be integrated with a machine vision system, showed that it is capable of both picking and trimming mushrooms growing in a shelf system.

The research is consequential, according to lead author Professor Long He, because the mushroom industry has been facing labour shortages and rising labour costs. Mechanical or robotic picking can help alleviate those problems.

"The mushroom industry in Pennsylvania is producing about two-thirds of the mushrooms grown nationwide and the growers here are having a difficult time finding laborers to handle the harvesting, which is a very labour intensive and difficult job," said He. "The industry is facing some challenges, so an automated system for harvesting like the one we are working on would be a big help."

The button mushroom (Agaricus bisporus) is an important agricultural commodity. A total of 404,000 tonnes of button mushrooms, valued at $1.13bn (£80m approximately), were consumed in the US from 2017 to 2018. Of this production, 91 per cent were for the fresh market, according to the US Department of Agriculture, and were picked by hand, one by one, to ensure product quality, shelf life and appearance. Labour costs for mushroom harvesting account for 15 per cent to 30 per cent of the production value, He pointed out.

Developing a device to effectively harvest mushrooms was a complex endeavour. In hand-picking, a picker first locates a mature mushroom and detaches it with one hand, typically using three fingers. A knife in the picker's other hand is then used to remove the stipe end. Sometimes the picker waits until there are two or three mushrooms in hand and cuts them one by one. Finally, the mushroom is placed in a collection box. A robotic mechanism had to achieve an equivalent picking process.

The researchers designed a robotic mushroom-picking mechanism that included a picking "end-effector" based on a bending motion; a "4-degree-of-freedom positioning" end-effector for moving the picking end-effector; a mushroom stipe-trimming end-effector, and an electro-pneumatic control system. The researchers fabricated a laboratory-scale prototype to validate the performance of the mechanism.

The team used a suction cup mechanism to latch onto mushrooms and conducted bruise tests on the mushroom caps to analyse the influence of air pressure and acting time of the suction cup.

The test results, recently published in the journal Transactions of the American Society of Agricultural and Biological Engineers, showed that the picking end-effector was successfully positioned to the target locations and its success rate was 90 per cent at first pick, increasing to 94.2 per cent after second pick.

The trimming end-effector achieved a success rate of 97 per cent overall. The bruise tests indicated that the air pressure was the main factor affecting the bruise level, compared to the suction-cup acting time, and an optimised suction cup may help to alleviate the bruise damage, the researchers noted. The laboratory test results indicated that the developed picking mechanism has potential to be implemented in automatic mushroom harvesting.

Button mushrooms for the study were grown in tubs at Penn State's Mushroom Research Center on the University Park campus. Fabrication and experiments were conducted at the Fruit Research and Extension Center in Biglerville. A total of 70 picking tests were conducted to evaluate the robotic picking mechanism. The working pressures of the pneumatic system and the suction cup were set at 80 and 25 pounds per square inch, respectively. The Penn State Mushroom Research Competitive Grants Program supported the research.

Agricultural robots are a fertile area for research, with the intense demands of growing and and harvesting ever-larger amounts of fruit and vegetables to feed the world's 'mushrooming' population. Soft produce poses particular problems, as the robots have to be ultra-precise and delicate in handling the crop so as not to spoil it.

In March this year, researchers at Shibaura Institute of Technology in Tokyo demonstrated a convenient method for measuring the ripeness of fruit, using laser-induced plasma shockwaves and the resulting vibrations on the surface of the fruit. In 2019, a small group of autonomous robots were set to work picking enough strawberries for the Wimbledon tennis championships, where visitors consume around 34,000kg of the soft fruit every year.

Elsewhere, a team of researchers from the National University of Singapore (NUS) has developed a solar-powered, fully automated device - dubbed SmartFarm - that can absorb air moisture at night and release it during the day for crop irrigation. The water harvesting and irrigation process can be fine-tuned to suit different types of plants and local climate for optimal cultivation.

The thorny dilemma of how to eradicate hunger in every part of the world, without farming and distribution logistics causing even greater environmental damage to the planet, is at the heart of global food production. Easy answers do not grow on trees.