Lesso ns Lea rned 

Lesso ns le arned in the developm ent of the launch latch me chanism inv olved issue s of materials  comp atibility, linkage de sign, optimizatio n, ergon omic s, and structu red optimi zation. The re sulting desig n  changes were inco rporated in the devel opment test u nit. 

Material and Surface Com patibility    The lau nch la tch de sign i s not friction -based, an d sliding co ntact of  heavily load ed memb ers is gen erally  avoided. Ho wever, some sliding contact doe s occur. Tit anium i s used as th e basic mate rial in the latch   mech anism, cho sen for its low weight a nd high stiffness.  The surface p ropertie s of titanium are n ot idea l  for highly stressed o r slidi ng conta cts, and therefor e surfa ce mod ification thro ugh anodi c coatings an d  lubricant film s was pursued. Tiodi ze surface conversi on treatment and Tiolub e lubricant films we re used.  The high est contact force s occur b etween the spri ng beam and the l ocking pi n and betwe en th e rolle r and  the spring beam. With the original untreated parts, some ga lling was observed at t hese int erfaces. After  the surfa ce treatme nt of t he titaniu m spring  beam and roller, and h ard chromium pl ating  of the  steel  locking pi n, no further g alling occu rred. 

Latch De sign  A perceived probl em with the locking ri ng aro se during develop ment testing. Al though the lo cking rin g is  loosely suspe nded on the cente r pivot base, an d the bear ing surfa ces are d ry film-lub ricated,  the simple   large  size of the b earing led to th e concern that th e locking ring might  be prevented  by friction  from   reaching its f ull unlat ched position. Thi s possibility was addressed both by t he application of dry film   lubrication to  the locki ng ring bea rings surfa ces, and to the addition of a se condary cam surface to the   pivoting latch  pawl. After triggeri ng of th e unlatching functio n- and after the high  force d emand on the hot   wax actu ator- continu ed travel of the pivoting pawl engag es the cam su rface with a mating follower ramp   on the arm of  the locki ng ring, insu ring it s full travel. 

Latch/ Reset Force   During devel opment te sting, the forc e required to re set the latch mech anism was found to be und esirably  high from th e stand point of operator e rgonomics. O perato r effort  was reduced, and ad equate latch ed  stiffness preserved, by mo difying the wi dth and thickness of  the spring b eam m embers. 

Upper Plate Deformation   Bending of the upp er plate , or outp ut member, of the  gimbal was observed  in testing, a s a result of th e  high fo rces a pplied to  the l ocking pins by the latc h mechanism. De sign changes to the pl ate were ma de to   increa se stiffness at the l ocking pi n mounting p oints, and thi s chang e elimin ated plate b endin g as a  probl em. 

Latch Point E ngag ement   Becau se of manufa cturing tolerances and th e curved m otion of  the spring beams,  some dimen sional  allowan ce must be mad e at the beam-t o-latch pin co ntact point. In the initial desig n, the allowa nce wa s  gene rous, and the holding ability of the l atch in the Z di rection was augmente d by frictional forces. In fact,   mating surfaces were tex tured by grit blastin g in order to  enhance fri ction. It was fou nd in  testing  that  texturing a ctually aggravat ed gallin g of the mating surface s, and th at desig n feat ure was delet ed. Smooth  surfa ces were use d inste ad, with su rface treatment for hardening. Tolera nces were tightene d, and it wa s  then po ssible to redu ce th e dimen sion of the pocket  in the spri ng beam in whi ch the lo cking pin se ats.  The upp er and lowe r sho ulders of the  pocket offer pos itive re straint of the locking pin which is n ot  depe ndent o n friction.  105