A Photoelectric Film Tachometer

It is often required to know the linear speed of motion-picture film. When a sprocket-drive machine is utilized, it is a relatively simple operation to install a tachometer generator and indicator. However, in the case of friction-drive machines, a simple monitoring of the machine motor gives only an approximate speed, due to film slippage and machine overdrive. One method to indicate speed on a friction-drive machine is to use a metering spool in conjunction with a pinch roller and a tach generator; however, this approach is not too safe or reliable. In an attempt to overcome these problems, a “skip-tooth” sprocket has been designed which is free wheeling and does not place any drag on the film. To this sprocket a slotted disc is attached which acts as a chopper for a reflected light beam. The chopped beam is then converted to an electric current which is displayed on a meter calibrated to read directly in feet per minute of film travel.

Print ISSN

0361-4573

Published

1970-02

Content type

Original Research

DOI

10.5594/J10742