| 摘要 |
A controller is disclosed for maintaining the width of a continuous web, for example the diameter of an extruded tubular film or bubble (16). A video camera (26) is used to observe the bubble or tube (16) at a point (20) thereof where it has hardened. The line sync pulses from the camera are counted to provide an enable pulse at the centre of the scanning field at which time clock pulses are counted during a period corresponding to the width of the video pulse, which count is stored in a working counter. The working count is updated once every field, and is compared with a reference count. Any deviations between the reference and working counts produces control signals which drive appropriate air solenoids (32) for modifying the air pressure within the tubular film or bubble (16) until the diameter of the bubble and, therefore, the width of the video pulse, are at their respective desired values. <IMAGE>
|
