1. Robotics Safety Tests for new ISO standard
Samson Phan

3. Conclusions
HIC
CLI
WAM “human safe” robot shows less high HIC number for collisions
HIC numbers for all tests too low for serious damage
Neck Constraint Matters
Bimodal distributtion shows CLI too insensitive for robot-human collision
R2 =
0.3871

5. Can we reduce the number of injury criterias?

6. Elimination of other scenarios
Unconstrained scenarios
All energy goes into deformation or plastic yielding instead of acceleration of the target.
Eliminate very sharp planforms
Designers are competent
Care given to not give knives
How sharp is “sharp?”

7. Proposed Model Quasi-static Inconsequential skin
Stress wave traversal (Timoshenk & Goodier, 1951)
Inconsequential skin
Thickness of layer << contact length
Hertzian pressure distribution
Coupling between tangential and normal forces based only on friction, not deformation (q (x)=u p(x))
Pressure distribution p0(1-x2/a2) (hertz pressure)
Friction induced tangential forces
Collision Parameter->KE ->deflection-> pressure->shear stress

8. Quasi-static Assumption?
Material
Young’s Modulus
Density
Wavespeed
Skin
4.2E5
1750 kg/m3
1600
Muscle
126E3
1060 kg/m3
10.9
Bone
18E18
1500 kg/m3
1.8974E8 m/s
Hunter 1956 said this.
Muscle
Skin
[agache] skin

9. Inconsequential skin thickness?
Skin thickness: mm
Bone thickness (skull): 4-10 mm
Muscle thickness
Stapp Car Crash J Nov;45:
The effects of skull thickness variations on human head dynamic impact responses.
Osullivan and king

10. Sliding Contact
Q/µP
q(x,y)=µ p(x,y)
Bhushan 2001

11. Tangential velocity inclusion
Assume sufficient tangential velocity to induce sliding
Vx ≥ µ Vz
Table 1 UCSF

12. Model Development Energy (Before collision) Energy (After Collision)
Tangential Velocity
Vertical Velocity
Limiting case
Vx = µ Vz
Velocity (Vx, Vy)
Deflection in robot (Erobot)
Deformation of tissue

13. Model Development mi = mass matrix of robot
Kinetic Energy of Robot to Tissue deflection (for solids of revolute)
Hertzian Theory of Contact for Solids of revolution
(sphere)
mi = mass matrix of robot
vi = velocity matrix of robot
R = relative curvature (1/R)=(1/R1 + 1/R2)
1/E* = (1-v1^2)/E1 + (1-v2^2)/E2
p0 = max pressure at given instance
d = deflection
P = total load compressing solid
Neglect dissipative losses (sound, heat, etc) and Erobot for worst case scenario

14. Contact Mechanics Combine eq (2) & (3): Equate with eq (1):
Solve for p0

15. Von Mises Yield at surface for u >0.3 Spherical rigid manipulator
Failure criteria
Assumptions
Von Mises Yield at surface for u >0.3
Spherical rigid manipulator
quasi-static
negligible plane orientation change
negligible skin thickness (doesn’t affect contact dynamics)
Hamilton 83?
Explicit equations for the stresses beneath a sliding
spherical contact
Hamilton 1983

16. Onset of Yield Wassink et al µ = 0.4 µ = 0.8
Material property function: E, v
Conclusion: reduce friction to
Wassink based on maximum tension
Mine based on von mises stress

17. Kind of like boxing… Boxing Shadows
 W. K. Stratton, Anissa (CON) Zamarron
Combat Sports Medicine Springer-Verlag London  / _11 Professional Athlete
Margaret Goodman1  and Edwin Homansky
(1) 

18. Another approach… Allowable amount of soft tissue damage?
OSHA mandated levels?
Same set of equations to visualize volume

19. How about non spherical impactors?
4:1
Exceed certain value of
Sphere on sphere, can it be generalized?
Pg 97 johnson, have to get fairly eccentric in order for it to be significant deviation
1:4

21. Impedance as a performance and safety parameter
Impedence (m,E,w) m s w
60 Hz

22. Epidermis spinosum Weakest shear layer in skin.
Blistering and abrasions: layer that separates.
Shear layer failure may be more predictive of injury than tension or Von Mises yield criterion

25. Dropping Stuff…
N=10
N=4