Thursday 6 May 2010

Semi-submersible vehicles angle sensors

ASV Ltd is a leading designer and constructor of unmanned marine vehicle systems for commercial and military applications, providing cost effective solutions for time consuming or dangerous maritime tasks such as hydrographic surveys, surface surveillance, gunnery training and mine-hunting. When optimising the design of its new ASV 6000 coastal class semi-submersible vehicle, ASV selected Novotechnik GL series hollow shaft potentiometric angle sensors from Variohm EuroSensor to provide rotary position feedback as an intrinsic part of in-house designed actuators used for the steering and ride stabilisation control system

The ASV 6000 was developed for hydrographic survey and surveillance work in shallow coastal waters and is operated remotely via a continuous GPS communications link. With an overall length of six metres, the semi submersible operates just below the water surface and carries a payload capacity of 300 kg for sonars, computers, sensors, winches and camera equipment. Its diesel propulsion systems allows a range of 400 miles at 4 knots.

The relatively shallow submersion requirement for the vehicle meant that actuators specifically for sub-sea use, operational at much greater depths, were massively over-engineered and consequently very expensive. Other commercially available actuators either did not provide angle position feedback or were not waterproof.

As well as drive the costs down for this important component, the decision to build the actuators in-house also allowed ASV to manage the design within a considerably space-restricted area on the vessel, freeing up valuable real estate that could be used for payload equipment. The hollow shaft GL series angle sensor is fitted directly on the actuator motor shaft, significantly reducing the overall assembly length compared to rear shaft mounted variants with couplings.

ASV chose commercially available brushless servo motor technology for the steering and ride control actuators and fitted a sealed waterproof casing around each complete assembly, encasing the motor and angle sensor, and including connectors for motor power, commutation and sensor feedback.

The GL series angle sensors' high resolution potentiometric output presents the steering and pitch angular positions as a proportional voltage output through a zero to 340º electrical range to the ASV designed control system. With independent linearity to ±0.25%, the steering and ride stabilisation capability for the vehicle is more than sufficient.

The robust and durable shaft mounted GL sensor has a long pedigree of challenging angle position feedback applications such as autosports, construction equipment and agricultural machinery. The range is supplied in four nominal sizes, suitable for shaft diameters from 6 mm to 30 mm. The compact one-piece assembly is designed for easy installation and fully housed in an anodised aluminium casing with a slotted ball bearing for maximum support. The conductive plastic resistance element and precious metal multi-finger wiper assembly combine for an extremely long life of over 10 million movements.

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