Futur e Wor k 

At the time of this writing, a life test of the mec hanism had bee n started. Th e test is an a mbient con dition  life test in which the me chanism will run contin uously for one mo nth, resulting in 300,00 0 full cycles of the   mechani sm at the nominal sp eed of 30 mm/s. This  test will charact erize wear  at the interface between the  piezo moto r fingers a nd th e ceramic strip, in the Ve spel rollers sliding ag ainst the steel pins, an d the   rolling contact between the Vespel rollers and the hard-anodi zed alum inum  sled. The t est will al so  characterize any chan ge in the fo rce require d to move the me chanism, p ositional e rror along the vel ocity  profile, and v elocity erro r over the life test. A seco nd life test will then be cond ucted for a two -week period  in a vacuum  cham ber. T his test will characteri ze the mechanism’ s perfor mance as well as heat  dissipatio n under vacuum condition s. 

It is pla nned that the next desi gn ite ration will  incorporate  a locking d evice to prote ct the mech anism  durin g launch vibratio ns. It will al so incorporate all of the o ptics on a single structu re and u se the  interferomete r reference laser a s the p rimary feedb ack device.  

Work to qu alify the piezo motor for space flight appli cation s will continue. Fu rther the rmal-vacu um testin g  will be conducted to better characteri ze the properti es of th e motor under these conditions, as well as  characterize the h eat di ssipation. Vib ration te sting will be condu cted to better un derstand  how the m otors  will re act to l aunch lo ad e nvironm ents.  The d rive el ectro nics will also be re-d esigned and qualified fo r  space flig ht. Once the se motors a re qualified they can easily b e incorp orate d into a new mechani sm  design witho ut the need to re-qu alify the motor at t he piece p art level. The motor is a  stand-alon e  comp onent that ca n be integrated  into a system to quickly an d cost effe ctively cre ate a li near or rotary  mech anism.   

Lesso ns Lea rned 

In orde r to redu ce the m ass as much  as po ssible  in the cu rrent desig n, the piezo motor was used to   prelo ad the kinem atic rail  system. Whi le this elim inated the need for a  fourt h roller and reduced the   overall syste m mass, it also reduced the stiffnes s of the system. Each o f the piezo element s are  prelo aded against the  ceramic strip with inde pendent spri ngs that  are soft when compared to the rest of  the syste m. This reduces t he natu ral frequen cy of the  system  and, in turn, reduces the  margin of stability   in the control loop. In future de signs an indep ende nt roller will be used to preloa d the rails, a nd the line of  action  of th e prelo ad force from  the piezo fingers will  act directly t hrough the center of the  dual spherical  rollers. Thi s will allow the mechani sm to have an adjustabl e preload inde pendent of the fi xed preload i n  the piezo motor finge rs.   

The u se of the piezo m otor to prelo ad the sy stem also p recluded te sting  of the rails and moto r  individually. The dra g force  of the rail system alon e could not be di rectly mea sured due to the necessity of  the pie zo motor to  comp lete the system an d the  associated  friction holdi ng force. While  combinin g  function ality of key comp onent s save s pa ckaging  spa ce and mass, it make s individua l compo nent  perfo rman ce characterization difficult. The addition o f independ ent preload rollers in the ne xt design will   slightly increase the mechanism s size but it w ill provi de the ability to better characteri ze the perform ance  of the rail sy stem at the sub -assembl y level and understan d its contri bution to the overall  mech anism  perfo rman ce.  

The ability to  quickly build  prototype s and conduct tests was inv aluabl e for t his type of d evelopme nt  proje ct. Whe n dealing with su ch stri ngent requi rements, ne w technolo gy, and complex sy stems, there i s  no substitute for te sting th e actual hardware. Duri ng the course  of the p rototype devel opme nt, more  than   ten mechani sms were b uilt and teste d using the inte rferometer setup. This g ave a tremen dous amo unt of  insight into the cau ses of velocity erro r over a broad freq uency rang e. Inevitably things t hat are not  accou nted fo r in the  design will show up in te sting, and the  soon er the mechanism can be tested, the   sooner d esign iteration s can be in corpo rated into the next hard ware desi gn.     

Having custom data red uction software to quickly quant ify and visually ch aracterize th e results of   perfo rman ce testing saved  a trem endous amou nt of time du ring the a ctual te sting of the mech anisms.  261