SYNCHRONIZATION SYSTEM 477 



Discussion 



During the development of the control system, one of the first 

 difficulties encountered was hunting of the controlled motor. The 

 problem of hunting, of course, becomes more difficult of solution the 

 greater the precision of speed regulation desired and the greater the 

 moment of inertia of the load connected to the motor, the latter state- 

 ment applying only to controlled systems of the synchronous type. 

 Since the moment of inertia of the scanning disc is large relative to 

 that of the motor armature, it is seen that the conditions for securing 

 stable rotation would be unfavorable in both the above mentioned 

 respects if the scanning disc were mounted directly on the motor shaft. 

 The hydraulically damped type of coupling above described was, 

 therefore, inserted between the motor shaft and the scanning disc. 

 It was found, however, that hunting still occurred. A further analysis 

 of the problem showed that the axis of the field flux of the motor was 

 shifting back and forth across the pole faces. The damping winding 

 shown in Fig. 4 was then added with a marked improvement. It was 

 also observed that a strong series field on the motor assisted in secur- 

 ing stability and it was, in fact, necessary to employ all three ex- 

 pedients to secure satisfactory performance. In the system as finally 

 developed the television image, if disturbed by a momentary load 

 such as the pressure of the hand against the disc, would come back to 

 rest within approximately one second, there being two oscillations 

 during this interval. In actual operation, it was found that the 

 normal fluctuations in line voltage occurring on the commercial power 

 supply produced no transients of sufficient magnitude to cause any 

 objectional instability in the received image. 



In conclusion, it should be pointed out that this type of control 

 system could be equally well employed with larger motors for other 

 applications requiring precise speed regulation. While the circuit 

 described is applicable only to a direct current motor, a similar system 

 may be applied to an alternating current motor substituting a saturat- 

 ing reactor in place of the regulating field winding in the manner 

 described by the author in his paper ^ presented before the Society of 

 Motion Picture Engineers, September, 1928. 



2 S. M. P. E. Transactions, Vol. 12, No. 35, page 696. 



