Fail-safe lamp control for photocopier - with time delay circuit to switch off lamp if normal exposure time exceeded

摘要

The photocopier has a scanning optic system whose movement is controlled by microswitches, with the speed of the scan controlled to achieve a set exposure level. The machine is fitted with fail-safe controls to monitor paper feed blockages and an additional timing circuit coupled to the lamp supply. The timing circuit switches off the lamp if a reasonable exposure time is exceeded i.e. the scanner stops, and prevents the copy paper charring. Any additional detected defect also immobilises the machine as added fail-safe.