MACHINE BUILDING, FRAMEWORKS & SAFETY FEATURE
HARVESTING THE BENEFITS of electromechanical actuators
When developing a new harvesting machine that would help get product to market faster and more efficiently, Tribine selected smart electromechanical actuators from Thomson Industries
A
lthough developments over the years have enabled agricultural harvesters
to reap more field crops, their contribution to farm profitability has been constrained by limitations on their ability to get harvested product to market efficiently. With traditional combine harvesters, for example, product is unloaded from onboard storage bins into grain carts pulled by tractors running alongside. When full (around 800 bushels), the grain cart is hauled off the field to a semi- truck, before being delivered to market. However, the combine storage bins can
only hold around 350 bushels, so the grain cart needs to be pulled for extended distances. As a result, the tractor either needs to return quickly to the combine once unloaded or multiple tractor-grain cart combinations are needed. So, to help, Tribine Harvesters built a new machine.
THE DESIGN The Tribine cuts crop through the feeder house to a rotating cylinder or rotor which, at 38in in diameter, is larger than most combines. The three curved ‘concave’ segments that encircle the lower 270˚ of the rotor’s circumference help separate the grain from other material. Adjusting the concaves for various types of product or conditions requires modifying the speed of the rotor, and the gap between the rotor and concaves, according to the condition of the crop at harvest time. The company needed to adjust from approximately zero clearance up to a 2in gap, where the crop is threshed against itself to separate from the MOG (material other than grain). For this, an actuator assembly with advanced measurement and lock-in-place capabilities was needed. “We had to be able to measure the exact
distance between the concave and the rotor. We also needed a way of making sure that the concaves locked in place so they don’t change during harvesting unless commanded by the operator. And, because of the large size of our rotor cage, we needed actuators with enough force to enable fine adjustments to the concave positions to maximise threshing
performance,” said Russell Secrest, Tribine Harvester control systems engineer. Having looked into the solutions
available, the company decided Thomson Industries’ heavy duty, smart, electromechanical actuator with onboard electronics would be up to the task. So, three of the Electrak HD actuators,
which provide maximum control over the entire length of travel as they open and close the concaves around the rotor, were specified. As the actuators allow for scaling, the operator will know the current position and, because of inherent braking and force capability, will be able to adjust the concaves easily and lock in place. The Thomson actuators use only
four wires: two to provide low-power connections to the communications bus and two to connect to the power supply. This simple architecture enables the Tribine Harvester design team to communicate across a J1939 CAN bus communication network. “CAN communication has allowed for
quick and easy implementation,” said Secrest. “A nice thing about the HD actuators is that once you supply power to them, they exist on the communications side. You can set and forget.” The CAN bus networkability and built-in positional awareness of each actuator helped Secrest overcome some mechanical and linkage issues in building the actuator assembly. To close the gap between the rotor and concaves, two actuators have to be extending while the third is retracting. But when the gap needs to open, two actuators would be retracting, while the other is extending. “We don’t want any actuators to get
more than 10-12mm out of sync with each other,” explained Secrest. “Each actuator provides feedback of its position or faults over the communication bus in real time, allowing a controller to track position and status and, therefore, synchronising position within 5-10mm.” Once the grain is separated, a folding bin-fill auger transfers the cleaned grain
Concaves surrounding the rotor are adjusted by the electromechanical actuators depending on the threshing conditions required
to a 1,000-bushel grain bin – a size made possible with extension doors on the top. To synchronise the grain bin door operation, four HD actuators are used on the sides of the bin and one in the augur, each of which is programmed to deliver feedback on the position of the grain door across the CAN network and can be reset as needed. The feedback provides operators with the information they might require to resynchronise the augur and grain door operations to avoid blockage or increase output.
A SUCCESS Vehicles with this design are now being
shipped. The ability to move two actuators in one direction while another is actuating in the opposite direction has proven successful.
Actuators on the grain bin have contributed to the proven ability of the Tribine to meet its goal of unloading 1,000 bushels in only two minutes
Furthermore, the HD actuators have the force necessary to keep the actuators locked in place, while the network and onboard intelligence provide reliable information on the actuator’s position. Likewise, actuators on the grain bin
have contributed to the proven ability of the Tribine to meet its goal of unloading 1,000 bushels in only two minutes.
Thomson Linear
www.thomsonlinear.com
DESIGN SOLUTIONS | JUNE 2018 13
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