ABSTRACT
Typical rovers with wheels equipped with conventional grousers are prone to getting stuck in unconsolidated sandy dune inclines as the wheels tend to sink into the sand. This phenomenon is caused by the motion of the grouser through the sand during the latter half of the rotation, in which the grouser pushes the sand from underneath the wheel upwards and towards the backside of the wheel. This creates a space that the wheel can sink into. To minimize sand movement and subsequent sinkage, we propose the concept of using an "assistive grouser", which is attached to the side of a conventional rover wheel. The assistive grouser is designed to be able to autonomously maintain a uniform angle relative to the rover body independent of the rotation of the wheels. Rotating the wheel causes the assistive grousers to automatically penetrate into the sand slope surface at a constant angle of attack, thereby acting as an anchor and providing traction for the wheel. Maintaining a uniform grouser angle as opposed to a rotating motion also assists in extracting the grouser out of the sand without moving the sand towards the back of the wheel. Moreover, the angle of the assistive grousers is held constantly by a single dedicated motor, meaning that the angle of the assistive grousers can be optimized to provide the least amount of sinkage for each slope angle. The experimental results showed that for slope angles of 0-30 degrees, the rover equipped with the proposed assistive grousers experienced significantly less sinkage and consumed less current compared to the rover equipped with conventional grousers.
ABSTRACT
PURPOSE: To demonstrate visually the change in the optical path of oblique incident rays in pseudophakic eyes with intraocular lenses (IOLs) of different shapes using a 3-dimensional, computer-simulated model eye with an aspherical corneal surface. SETTING: Department of Ophthalmology, Hamamatsu Red Cross Hospital, Hamamatsu, Japan. METHODS: A Gullstrand schematic eye was created using an optical design program (Zemax), and the anterior and posterior surfaces of the cornea were replaced by rotationally symmetrical, aspherical surfaces expressed as polynomial equations based on the corneal topography (Orbscan II, Bausch & Lomb). The lens was replaced by an IOL (anterior convex or posterior convex). The model eye was displayed 3-dimensionally, and an incident ray 45 degrees from the visual axis was projected. The astigmatic difference was compared by visually confirming the convergence profile of tangential and sagittal rays. Coma aberration was also compared by the shape of the spot diagram. RESULTS: The distance between the tangential and sagittal foci was larger with an anterior-convex IOL than with a posterior-convex IOL. Coma aberration markedly deformed the spot diagram at the retinal surface in the eye with an anterior-convex IOL. CONCLUSIONS: The optical characteristics of the oblique incident rays in a pseudophakic eye were visually represented with sufficient clarity. Aberrations in the oblique incident rays were larger in the eye with an anterior-convex IOL than in the eye with a posterior-convex IOL, making examination and retinal photocoagulation of the peripheral fundus difficult.
