Character Animation The Human Hand

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Character AnimationThe Human Hand

• Computer Animation SS2008

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Functions of the Hand

• Manipulate delicate fine motions
• Complete powerful grasp tasks
• Support or transfer force for changing positions
• Serve as an sensory organ for perception of the
  surroundings
• Help to express emotions

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Structure

• Exercise
• On a piece of paper, trace the outline of your
  left hand
• Identify the location of each joint in your hand
  by moving your fingers, including your wrist
• Note on our outline the location of each joint
• Connect the dots to create ones in your drawing

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Structure

• Here's a diagram of the human hand
• How did you do?

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Structure

• Which bones and joints would you include in a rig
  for a human-like hand?

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Structure

• Carpometacarpal (CMC)?
• DOF 2
• Metacarpophalangeal (MCP)?
• DOF 2
• Proximal interpalangeal (PIP)?
• DOF 1
• Distal interpalangeal (DIP)?
• DOF 1

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Functional Position

• MCP joint45º of flexion
• PIP joint30º of flexion
• DIP jointslight flexion

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MusclesDigital Flexor Pulley System

• Composed of 5 annular ligaments 3 cruciform
  ligaments
• Holds the underlying tendons at a fixed distance
  to the phalanges (constant moment arm)?

• Gliding mechanism of long flexors
• Digital tendons were wrapped by tendon sheath
  which contains synovial fluid
• Vaginal ligament serves as a pulley to fix tendon
  to joint surface and prevent bowstring phenomenon

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MusclesExtensor Assembly

• Synonym extensor assembly
• Extension hood
• Composed of the central tendon of the long
  extensor, the lumbricals, and the interosseus
  muscles
• Central slip to base of middle phalanx
• Lateral bands to distal phalanx

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Grasping

• There are several types of grasping behaviors
• Cylindrical grasp
• Spherical grasp
• Hook grasp
• Conoid gasp
• Power grip
• Precision grip

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Power versus Precision
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Cylindrical Grasp

• Entire palmar surface of the hand grasping around
  a cylindrical-shaped object
• Muscle involvedfinger flexors, intrinsic
  muscles, and thumb flexors and abductors
• e.g. grasping a baseball bat or a hammer

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Spherical Grasp

• Cupping the thenar and hypothenar eminences with
  varying degrees of finger flexion
• Muscle involved finger flexors, especially from
  4th or 5th digits, and interossei
• e.g. holding a ball

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Hook Grasp

• Gripping like a hook formed by flexed fingers
  without the thumb involvement
• Usually a static nature for a period of time
• Muscle involved flexor digitorum profundus
• e.g. carrying a suitcase

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Conoid Grasp

• Cone-shaped grasp with the apex at the ulnar side
  of the palm
• e.g. using a knife or other tools

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2- or 3-Jaw-Chuck

• Pad of the thumb opposes against one digit or
  both index and middle finger
• 80 of prehension uses this pattern
• e.g. picking up a block

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Examples
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Rigging

• A possible rig for a hand might look like this