This device has to perform three important tasks during a winding operation:
- shift the cone belt corresponding to the increase in bobbin diameter;
- reverse the direction of movement of the bobbin rail at the upper and lower ends of the lift stroke;
- shorten the lift after each layer to form tapered ends on the bobbins.
The required moment for each change-over and the magnitude of the adjustment both depend upon the roving hank and the material, and must therefore be adapted to the prevailing conditions by means of change gear positions. In the following sections, a short description of a builder motion for a roving frame will be given. In this arrangement, most of the movement changes are effected electro-pneumatically.