Semi-submersible vehicle for shallow coastal waters

emi-submersible vehicles have hollow shaft angle sensors to maximise space.

ASV Ltd is 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 300kg for sonars, computers, sensors, winches and camera equipment. Its diesel propulsion systems allows a range of 400miles at 4knots.

The relatively shallow submersion requirement for the ASV 6000 meant that actuators specifically for sub-sea use, operational at much greater depths, were massively over-engineered and consequently very expensive.

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 340° electrical range to the ASV designed control system. With independent linearity to +/-0.25 per cent, 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 one-piece assembly is housed in an anodised aluminium casing with a slotted ball bearing for maximum support.

Variohm EuroSensor Limited is based in Towcester, Northants, UK. www.variohm.com