intro to opensim
TRANSCRIPT
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Components of an OpenSim Model
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What is a musculoskeletal model?
1.
Skeleton:
Bones are rigid bodies
Joints permit motion between bodies
Constraints limit motion
2.
Muscles : Specialized forces
3. Other forces:
PrescribedForce BushingForce
CoordinateActuator
Contact
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OpenSim Model File
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Tree Topology of Multibody Models
Each body is connected by ONE joint to create a chain or open tree structure.
Body
Ground
BodyTorso
FreeJoint
Body
RightHand
PinJoint
Body
LeftHand
PinJoint
BodyHandle
WeldJoint
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5.00
0.0 0.0 0.00.1...
0.0
Defining a Body and its Joint
BP
Bo
Po
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childbody B
Boparentbody P
Po
BP
Joint
Body and Joint Reference Frames
B specified by joint locationand orientation
P specified by joint locationInParentand orientationInParent
Joint coordinates specify the kinematics of B relative to P
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Defining a Body and its Joint
ground
0.0 0.0 0.0
0.0 0.7853981633974483 0.0 0.0 -0.1 0.0 0.0 0.7853981633974483 0.0
translational 0.00000000-10 10false
...
B
P
Bo
Po
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Tree Topology of Multibody Models
Each body is connected by ONE joint to create a chain or open tree structure.
Body
Ground
BodyTorso
FreeJoint
Body
RightHand
PinJoint
Body
LeftHand
PinJoint
Constraint is required to form a closed loop
BodyHandle
WeldJointWeldConstraint
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Kinematic Constriants
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Available Joints and Constriants
: No qs, adds body frame to parent
: One q, rotation about common Z
: One q, translation along common X
: Three qs, rotation about body-fixed X, Y, Z
: Six qs, rotations like Ball and 3 translations
: User-defined SpatialTransform,1 to 6 qs
: frames on two bodies are fixed
: points on two bodies are fixed
: qdep= F(qind)
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Types of Forces in OpenSim
Force
Ligament Bushing Actuator
PointActuator
TorqueActuator
CoordinateActuator
Muscle
Prescribed ...
function of time function of state
function of control
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Muscle Actuator Example
-0.00240000 -0.15330000 0.00710000humerus_r
0.00000000 0.03100000 -0.00530000r_ulna_radius_hand
...
972.000000000.08580000
0.053000000.000000.010000000.0400000010.00000000
...
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Adding a joint to the model increases/decreasesthe number of degrees of
freedom. Adding a constraint increases/decreases
the number of system equations.
How are actuators different from other
types of OpenSim forces?
Hands On Example:Add a Body and Actuator to the Model