Locking mechanics

Where we are Z=0 locking point Edge mounting mechanics (5 per stave) Edge mounting points Mould exists for parts 1, 2, 3. Adding 4 to another mould for other project. 4, 5, and 6 have been made on 5-axis machine so far. Materials used are PEEK and LCP. End locking points have to be machined completely (5-axis). Full characterization of the edge locking point under way. Started to provide input to full structure FEA, but has become much more detailed.

Setup Goal: Understand friction factor for FEA under longitudinal load. Designed setup so that other load directions can be measured as well. Locking force set with torque limited screw driver at 0.15Nm. Calculate the resulting radial force at ~44N. ~44N ~44N

Longitudinal load - results Fig 5-2 Test #1 Lock 1 result – fully unlocked No evidence of initial stiction Finger disengaged (not pressing on Bracket barrel) Load -- displacement curve when unlocked Test No: Force @ Peak (N) 1 8.898 2 8.468 Pull force required when locked up to ~20N. ~9N when unlocked. Resulting friction factor ~0.4 (for low loads) Is this the right unlocked/locked ratio? finger disengaged (not pressing on Bracket barrel) Load -- displacement curve when locked Fig 5-3 Test #1 Lock 1 result – fully locked Initial stiction Friction due to finger springiness Finger disengaged (not pressing on Bracket core) Test No: Force @ Peak (N) 1 20.082 2 19.843

Fig 6-b Test #2 – Side Push test – away from the datum faces Side pull test Fig 6-a Test #2 – Side Pull test – against the datum faces Curves A Curves B Lock tightness does not change the gradient much Fig 6-b Test #2 – Side Push test – away from the datum faces y = 16.0x Gradient decreases with reduced lock tightness Locked force/displacement curve similar for both directions. Stave mass provides ~2N per locking point.

Torque load Actually an off-center load

Torque load 2N Stave mass translates into about 8N at 20mm per locking point. Measured displacement is about 40μm, scaled to far edge gives about 200μm. This seems large. Need to understand cause Is it stiffness of bracket? Will make Al bracket to cross-check. Is it geometrical tolerance?

Summary I think this study is excellent work. A few things still need to be understood In particular torsion stiffness. Will give us the input needed for FEA. Can think about optimization. It would be good to see something similar for US mounting system.