Innenzahnsegment, zylindrischer Gegenstand mit Innenzahnsegment sowie Formen für solche und Verfahren zur Herstellung von solchen

摘要

A rotatable internal gear, for use in zooming a camera lens, has a helical inner gear 12d, an adjacent helical relief groove 12e and helical lead grooves 12c. The gear is moulded in plastic using a mould (Figures 10 to 15, not shown) having an outer cylindrical mould part also forming gear 12a and thread 12b, and having a two-piece internal mould part. To remove a moulded gear, a first internal mould piece bearing helical projections defining grooves 12c, 12e is unscrewed from the moulded gear. The second internal mould piece has a helical array of teeth, defining gear 12d, which lie in a helical slot in the first mould piece, and which are left in the moulded gear with the unscrewing. The second internal mould piece is then pulled axially to move the mould teeth into the moulded relief groove 12e, whereupon the second piece is rotated so that the helical mould teeth can be unwound along the moulded groove 12e. The outer mould part may be split. An alternative mould (Figures 16 to 29, not shown) has a teeth- and groove- defining mould core comprising segments which can be cammed radially inwards to allow axial seperation of mould and moulded gear. Alternate segments are moved radially at different rates. A formula is given relating the numbers of teeth and segments, and the tooth form is chosen to allow radial segment movement. In the camera lens (Figures 1 to 8, not shown), axial movement of an outer lens barrel is caused by rotation of a groove 12c, and rotation of gear 12d causes axial movement of a threaded internal lens barrel while the seperation of lenses carried thereby is varied by the rotation. <IMAGE>