The invention relates to an electro-optical scanning device comprising a movable lens having an optical axis, which lens is movable in a focussing direction to form at least one radiation spot on a surface to be scanned and in a tracking direction oriented transversely of the focussing direction, in order to follow a recording track in said surface, and comprising a stationary section with a magnetic circuit and with an air gap extending in a plane defined by the focussing direction and the tracking direction, and a section which is movable relative to the stationary section and comprising said lens, which movable section comprises at least one focussing coil and at least one tracking coil for driving the lens, which coils extend into the air gap.
Such a scanning device is known from U.S. Pat. No. 4,321,701 (herewith incorporated by reference). The known electro-optical scanning device comprises a stationary section with a single magnetic air gap and a vertically disposed movable section. The movable section, which is guided relative to the stationary section via an intermediate body, comprises a plate-shaped body which extends in the air gap and, secured to this body, a holder for a lens and any other optical elements. The holder is positioned in such a way relative to the plate-shaped body that the optical axis of the lens is situated in the plane of the plate-shaped body. Vertical current conductors serving as tracking coils are arranged at two opposite edges of the plate-shaped body. A focussing coil mounted on the plate-shaped body and having a coil axis oriented transversely of the optical axis of the lens is arranged between said conductors.
A drawback of the known scanning device is that, as a result of the presence of the vertically disposed plate-shaped body and as a result of the unfavourable arrangement of the plate-shaped body and the lens holder relative to each other, the movable section has a large dimension viewed along the optical axis of the lens. Therefore, the prior-art scanning device has a substantial overall height, which renders the device unsuitable for use in modern optical disc players of small height. Another disadvantage of the prior-art scanning device is the comparatively intricate method of manufacturing the composite plate-shaped body. Moreover, it has been found that in practice the mutual arrangement of the lens and the coils is inconvenient and imposes undesirable constructional limitations.
USPTO Backgrounds
USPTO Backgrounds