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High throughput: Two work tool heads move simultaneously and independently of each other onto two rails positioned one behind the other
Asparagus is grown in many different countries, which means the environmental conditions are quite diverse (it can be hot or cold, dusty and wet). This was another reason why the engineers decided on HepcoMotion as the system can withstand the rough environmental conditions. “The V-guide principle ensures Hepco’s
bearings are virtually self-cleaning,” says Völkers. “During the carriage’s journey, the bearings push the dirt off the rail.” In addition, unlike bearing circulation systems, there is no need for greasing as all the components are corrosion- resistant. The asparagus therefore never comes into contact with rust. “This is one of the basic requirements that needs to be fulfilled in the food industry,” he adds.
The driving force comes from an AC geared motor with a worm gear, located on the side of the linear guide rail. “The motors of the DLS system can have a power of up to 1.1 kW, this gears a reduction of 5:1 up to 75:1, explains Mark Völkers, area manager field sales, North Germany, at HepcoMotion. “This allows driving forces up to 750 Newtons and speeds of up to 1.4m per second, with special motors it is possible to achieve five metres per second.” The harvesting robot works with two
tool heads simultaneously, which can move on two rails positioned one behind the other independently of each other – enabling a high throughput.
RING SEGMENTS FROM HEPCOMOTION ALLOW A SWIVEL MOVEMENT WITH ONLY ONE DRIVE As soon as the tool head is positioned, it swivels a gripper arm from the back downwards. For this movement the engineers have used another HepcoMotion system: PRT2. The solution involves a spectrum of stainless steel rings and ring segments. They can be linked by straight guide rails to a diversity of open and closed stretches of rail. With the asparagus robot there are 90˚ bends on both sides of the tool head fitted with attached straight pieces. The gripper arm is screwed onto a carriage with V-guide bearings, which are arranged concentrically and eccentrically. These rollers engage from above and below with the induction- hardened V track of the ring segment.
The movement is affected by means
of a timing belt which pulls the carriage and gripper arm across the 25mm wide rail, thus producing a pivotal movement. The motor is mounted on the outer side of the tool head. “The special feature
“The basis of the harvester robot is a
is that thanks to the rail system a linear movement and rotation of the gripper are achieved with only a space- saving drive,” says Lasse Langstädtler, research assistant of the Bremen Institute for Structural Engineering and Production Equipment (bime), in the faculty of Production Engineering at the University of Bremen. “The roller guide also allows the gripper arm to lower relatively quickly, and thanks to the combination of a linear movement and rotation when lowering, it is possible to fit in a small distance between the stalks of two asparagus.” A slower movement would have to start
chassis with four wheels and a front-wheel drive. In the centre between the wheels there is a camera system installed, which films the green asparagus stems as it goes past”
FIELD TESTS The engineers together with their project partner from England, C. Wright & Son have tested the asparagus harvest machine in real conditions. “Among other things with this field test we wanted to find out how long the batteries can supply the machine with energy,” says Strauss. One of the challenges is also the speed of the harvesting tools. Up to now they have been no faster than human harvesters,
but if they had a sufficient supply of energy, they could work in the fields for 24 hours without any problems. This could
make harvesting in the future more economic and make asparagus cheaper.
earlier which could cause the gripper arm to damage any immature asparagus stems which are not yet ready for harvest. As soon as the gripper arm is lowered, a pneumatic cylinder is triggered to drive a shearing off action and simultaneous gripping of the asparagus while the robot continually moves forwards at 0.5m a second. The whole tool head then travels to the side and deposits the asparagus on a conveyor belt.
The tool head for harvesting the asparagus stems moves across the whole width of the vehicle via a HepcoMotion
belt-driven carriage and a Hepco SL2 linear guide rail
HepcoMotion T: 01884 257000
www.hepcomotion.com
DESIGN SOLUTIONS | NOVEMBER 2016
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