With crop protection in mind, sprayers rely on magnetostrictive position sensors to control innovative electrohydraulic steering system.
Self-propelled sprayers from Bargam SpA, Imola, Italy, treat plants gently and ensure flexibility during treatment of crops planted in rows. Bargam’s MAC XL machine series can easily be adapted to particular field requirements. The boom width spans up to 118 ft (36 m) and is suitable for spraying plants up to 712 ft (2.3 m) tall. Changing wheel track width from 6 to 10 ft (1.8-3 m) for different crops is accomplished right from the cab by controlling the machine’s electrohydraulic system.
Light on its wheels
The heart of the sprayer is a hydraulic steering system that allows the MAC XL boom sprayers to drive quickly and safely on the road, yet to also move forward gently and effectively in the field. The steering system ensures precise control even on difficult terrain and minimizes plant damage as the machine travels through a field. Three settings for the steering system are selectable from the cab: two-wheel front steering; four-wheel, and coordinated (crab) steering.
The MAC XL defaults to manual front-wheel steering for travelling on roads. In this mode, the machine can accelerate safely up to a maximum speed of 25 mph. During field operation, the operator can switch to four-wheel steering, a mode in which steering is controlled by the electronics. With this setting, it features a small turning radius of only 18 ft (5.5m) for quick and nimble maneuvering. Moreover, four-wheel steering ensures that plant damage due to track deviations (caused by stones, tree roots, etc.) are minimal because it improves the traction of the individual wheels.
To make corrections and to stay on the track when traveling across a hillside, the crab steering option can be selected. This mode can be used to improve the approach to field edges or to maneuver up to the next plant row. Using a combination of these steering and drive modes, the vehicle can be maneuvered forwards and sideways simultaneously, while the sprayer boom always remains oriented perpendicular to the plant rows.
To perform all three steering mode combinations, the self-propelled MAC sprayer is equipped with another important feature. The position of the front axle can be changed by the driver, while the rear axle is adjusted electronically according to the front axle position. Four hydraulic cylinders position the wheels of the front and rear axles to set them to the correct steering angle. Two in-cylinder position sensors adjust the rear wheels in accordance with the setting of the front axle.
| Bargam’s MAC XL Series sprayers feature multifunctional electrohydraulics, including a closed-loop steering system with Temposonics model MH magnetostrictive transducers for providing reliable and repeatable position feedback of steering cylinders for versatile two-wheel, allwheel, and crab steering. |
The steering controller uses a signal from the front wheel position sensor as the main feedback and a signal from a sensor in the rear axle cylinder as secondary feedback to synchronize the position of both wheels in a closed-loop control circuit. This enables the sprayer to maintain the ideal track without damaging plants.
The linear position sensors integrated into the MAC XL sprayers’ hydraulic cylinders are supplied by MTS Sensors, Cary, N.C. If position sensors had been mounted externally, the position signal could have easily been corrupted by environmental influences. In a farming environment, process-related influences beyond control must be taken into account, such as shocks, stones, various weather conditions, and electric and magnetic fields from overhead power lines. Embedding the sensors inside the cylinder protects them from extreme weather conditions and provides a better signal quality without noise.
The Temposonics Model MH series position sensors used for steering control on Bargam machines from MTS Sensors were designed to be integrated into the hydraulic cylinders on off-highway machines. The sensors’ compact design allows easy integration, and a non-contact measurement principal allows wear-free position measurement, ensuring that no maintenance is necessary.
Easy does it
Hydraulic cylinders with integrated displacement measurement improve performance of the sprayers. Furthermore, the Model MH sensors are easy to install because they come with a universal Temposonics prefabricated connector system based on a M12x1 connector. During installation, the contact socket is brought out from the cylinder through the terminal hole. The contact socket is then snapped into a custom flange that is part of the package. Four standard screws then fasten the connector system to the cylinder. The compact connector sizes enable cylinder installation even in work areas.
Another advantage of the Temposonics connector is the fact that when used with a molded M12x1 cable, the connection is protected against environmental influences according to IP69K. This protects the cylinder and position sensor not only against environmental influences, such as dust and water, but it also withstands the force of pressure washing the machine.
Based on magnetostrictive technology, Temposonics sensors help guarantee highly accurate and reliable measurement. Based on linear, direct determination of the piston movement, the sensor provides a highly repeatable measure of the steering angle of the machine’s wheels.
The sensors are protected from high-frequency interference up to 200 V/m. They also tolerate vibration up to 25 G, shock to 100 G, and operate in temperatures from –40° to 221° F. Measurements are temperature compensated, so changes in hydraulic oil temperature during operation do not affect the measurement process. The sensors also feature high immunity to EMI and RFI, have almost infinite resolution, and operate with hysteresis better than ±100 μm and non-linearity of less than ±0.04% full scale.
For Bargam, the high reliability offered by Temposonics Model MH sensors was of great importance during their decision. “Our target is to make our sprayers absolutely failure-proof. Once installed, the MTS sensors provide reliable and precise operation over decades, which is completely in line with our fit-and-forget principle,” says Bargam engineer Ottavio Barigelli.
Users, therefore, can take full advantage of the benefits of a steering system with precise wheel positioning and reliable track guidance — thereby improving productivity.