DRIVES AND CONTROLS 



225 



Capstan 



L| 1-2 Lj 



Genera for 



Capstan 

 motor 



-F/yer motor 



Capsfan Speed 



Fig. 448. — A wire-insulating machine requires a constant speed ratio between capstan motor 

 and flyer for starting and running. The capstan motor drives a frequency changer or transmitter 

 electrically connected to the synchronous motor of the flyer. The speed ratio between flyer and 

 capstan is constant at all times. 



Cutting _..» 

 tool ^ 



m 



Works 



-»- Platen 



y//////////w/y///y/yyyy//y/^wyyy/yyyyy' 



■'-Limit switches'-' 



Max. constant load 



Position ot work 



Position of platen 



^^^^^^^^^^m 



Fig. 449. Fig. 450. 



Fig. 449. — For high-speed cutting on a metal planer, the tool enters the work at a slow speed to prevent tool 

 breakage, cutting speed is then increased, and near the end of the cut the cutting speed is reduced to prevent breaknig 

 out at edge of work. This speed control is accomplished by limit switches which put full field on the motor before the 

 tool leaves work. After the return stroke, delayed acceleration keeps full field on motor until tool enters work; then 

 the fast cutting speed is resumed. 



Fig. 450. — To keep load constant on the cutter and spindle of a milling machine for maximum production, a relay 

 controlled by the armature circuit of the direct-current spindle motor regulates the field of direct-current feed motor. 

 This automatically controls the feed within limits to maintain a maximum constant load on the spindle motor. 



