Robotics Safety Tests for new ISO standard

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Robotics Safety Tests for new ISO standard

• Samson Phan

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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

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Can we reduce the number of injury criterias?
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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?

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Proposed Model

• Quasi-static
• Stress wave traversal (Timoshenk Goodier, 1951)
• Inconsequential skin
• Thickness of layer ltlt 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-gtKE -gtdeflection-gt
pressure-gtshear stress
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Quasi-static Assumption?
Material Youngs 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
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Inconsequential skin thickness?

• Skin thickness 2-4.5 mm
• Bone thickness (skull) 4-10 mm
• Muscle thickness

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Sliding Contact
q(x,y)µ p(x,y)
Bhushan 2001
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Tangential velocity inclusion

• Assume sufficient tangential velocity to induce
  sliding

Vx µ Vz
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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

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Model Development

• 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-v12)/E1 (1-v22)/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
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Contact Mechanics

• Combine eq (2) (3)
• Equate with eq (1)
• Solve for p0

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• Failure criteria

• Assumptions

• Von Mises Yield at surface for u gt0.3

• Spherical rigid manipulator
• quasi-static
• negligible plane orientation change
• negligible skin thickness (doesnt affect contact
  dynamics)

Hamilton 1983
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Onset of Yield
Wassink et al
µ 0.4
µ 0.8
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Kind of like boxing
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Another approach

• Allowable amount of soft tissue damage?
• OSHA mandated levels?
• Same set of equations to visualize volume

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How about non spherical impactors?
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Impedance as a performance and safety parameter
Impedence (m,E,w)
m
s
w
60 Hz
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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

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Dropping Stuff
N10
N4