| 摘要 |
<p>PURPOSE:To prevent breakdown of blade by issuing an alarm signal when a timer signal preset to the time until a blade comes to contact with a table and a detector signal detecting contact between blade and table are not outputted simultaneously. CONSTITUTION:An output of a detector 21 which detects electrical connection between a sleeve 12, contact spring 20, blade 17 and table 10 is supplied to the one input terminal of a NAND circuit 25. Meanwhile, a timer 34 is operated by a start switch 23 which closes when the sleeve 12 starts to move downward and an output of such timer is supplied to the other input terminal of the NAND circuit 25. At this time, the timer is set to a time until the blade 17 comes to contact with the table 10 and ''1'' is output during this period. Thereby, if the spring 20 wears out and closed circuit is not obtained, a signal ''1'' from the detector 21 cannot be obtained and an output of the NAND circuit 25 becomes ''1'' and an alarm 27 sounds.</p> |
