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Chapter 2. Prehension

Chapter 2. Prehension

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198 THE PHASES OF PREHENSION<br />

Obi& Task<br />

INTRINSIC<br />

- spatial density aspect of texture<br />

- fragility<br />

-weight<br />

- size<br />

- shape<br />

- aenterof mass<br />

- distribution of mass<br />

EXTRINSIC<br />

-orientation<br />

- distance<br />

- direction ?<br />

- motion<br />

0<br />

Aim<br />

Fit<br />

Grab<br />

Grasp<br />

Lift<br />

Place<br />

Place Precisely<br />

Point<br />

Tap<br />

Throw<br />

TUmSCRW<br />

AT REST ATPEAK'APERTURE - AT CONTACT<br />

HAND TRANSPORT<br />

Movement time<br />

Velocity<br />

- peak velocity<br />

- time to peak<br />

- time in deceleration phase<br />

Acceleration<br />

-peak acceleration<br />

-time to peak acceleration<br />

- peak deceleration<br />

- time to peak deceleration<br />

- time after peak deceleration<br />

Higher Derivatives<br />

GRASP CONFIGURATION<br />

Apeaure<br />

-peakaperture<br />

- time to peak aperture<br />

- time after peak aperture<br />

-rate of enclosing<br />

Hand Configuration<br />

-joint angles<br />

- Begment lengths<br />

Figure 5.34 The black box revisited. Objects have intrinsic and<br />

also extrinsic properties. At the environmentally-defined level,<br />

tasks include grasp, lift, and place. At the kinematic level,<br />

prehensile behavior can be measured by movement time, velocity,<br />

acceleration, etc. For grip evaluating, a key metric has been the<br />

grip aperture, or the thumb and index finger separation over time.

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