The present invention relates in general to pulse generators for variable speed drives, and in particular, to a new and useful pulse generator for sewing machine drives comprising a shaft rotating in synchronism with the main shaft of a machine having a pulse disc thereon with light and dark zones. The pulse disc is mounted for rotation with a casing which is provided with axial and radial bearing surfaces on either side of the pulse disc for centering the pulse disc as it rotates and for functioning as a shield and seal against exterior dust, oil and the like.
In prior art pulse generators of this kind, the casing accommodating the light transmitting and light receiving modules is mounted unilaterally on a shaft carrying the pulse disc. Since the pulse disc is partly provided with light-dark zones which are very narrow, the position of the light transmitting and light receiving modules must be adjusted and maintained during operation with an extreme accuracy, to ensure a quite satisfactory function of the modules. Known arrangements, therefore, require an expensive mounting to prevent the casing from executing any undesirable oscillatory motion during rotation of the pulse disc which might unfavorably affect the function of the pulse generator. Such arrangements also require a complicated design and their assemblage is expensive if a reliable operation of the pulse generator is desired.