RELAY ARMATURE REBOUND ANALYSIS 189 



Ho\ve\-er, it is felt that the approach and notation of the analysis 

 presented here is sufhciently j>;eneral to allow extension of the rebound 

 pattern anah'sis to the tlirce-degree-of-freedom case. At any rate, with 

 the assumption of the magnitudes of frictional forces, the basic equations 

 of Part n" may be used to plot any particular case. 



VIII. ARMATURE REBOUND MODEL 



In order to verify the formal analysis presented in Parts III, IV and 

 Y, a large model of a two-degree-of -freedom system was constructed. 

 It consisted essentially of a large bar constrained to move in a plane, 

 biased against two stops, and to the ends of which writing pens were 

 attached. As rebound conditions were simulated by releasing the bar 

 against its stops, chart paper moved at right angles to the bar motion 

 and thus produced a record of end displacement versus time. 



By changing spring members and attaching masses to the bar, it was 

 possible to vary the mass distribution and the biasing forces. 



The results obtained closely agreed with those suggested by the 

 analysis. The maximum rebound amplitudes were generally somewhat 

 lower probabl}^ due to frictional effects. 



IX. RELAY DESIGN CRITERIA RESULTING FROM ARMATURE REBOUND 

 ANALYSIS 



A. Limitation of Analysis 



The assumptions which this analysis is subject to have been described 

 under Part II. As applied to relays and probably the majority of mechani- 

 cal structures, one assumption is most frequently and severely violated. 

 The stops, which have been assumed to be stiff springs associated with a 

 definite coefficient of restitution are, in practice, massive bodies which 

 dissipate energy through excitation of high frequency modes of vibration. 

 Accordingly, the assumption that the stops are at rest is violated, 

 particularly if the mechanism is subject to repetitive (pulsing) im- 

 pacts and the stop vibration does not decay greatly in the repetition 

 period . 



However, mechanisms designed in accordance with this analysis have 

 performed well even under moderate pulsing conditions if the sensitive 

 phasing region was avoided. In addition, every effort should be made to 

 reduce the amount and duration of stop and mounting structure vibra- 

 tion by making them stiff, massive, and dissipative, if possible. 



