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visual3d:documentation:kinematics_and_kinetics:inverse_dynamics [2024/07/17 15:22] – sgrangervisual3d:documentation:kinematics_and_kinetics:inverse_dynamics [2024/11/20 17:04] (current) – [Inverse Dynamics Calculations in Visual3D] wikisysop
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 Inverse Dynamic calculations are usually represented by [[Visual3D:Documentation:Visual3D_Signal_Types:LINK_MODEL_BASED_Data_Type|Model_Based_Items]]. Inverse Dynamic calculations are usually represented by [[Visual3D:Documentation:Visual3D_Signal_Types:LINK_MODEL_BASED_Data_Type|Model_Based_Items]].
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-=== Inverse Dynamics === 
  
 Biomechanical movement analysis provides a quantitative record of motion, and thereby allows objective comparison of performance across different conditions and patient groups. Biomechanical movement analysis typically involves several discrete steps. First, the motion of tracking targets attached to the subject is recorded using cameras. Second, a biomechanical model is defined to represent selected characteristics of the subject such as the number and type of segments (inertial properties), the joint properties (number of degrees-of-freedom (dof)), and the kinds of actuators that move the segments. Third, the kinematics of the model are calculated by determining the transformation from recorded tracking markers to the pose of each segment of the biomechanical model. The definition of the biomechanical model can be a crucial determinant of the reliability of the transformation between tracking markers and model pose and for interpreting specific movement disorders. Fourth, inverse dynamics analysis is applied to the kinematics of the biomechanical model and to the location, magnitude, and direction of externally applied forces (e.g., ground reaction forces acting on the foot). Biomechanical movement analysis provides a quantitative record of motion, and thereby allows objective comparison of performance across different conditions and patient groups. Biomechanical movement analysis typically involves several discrete steps. First, the motion of tracking targets attached to the subject is recorded using cameras. Second, a biomechanical model is defined to represent selected characteristics of the subject such as the number and type of segments (inertial properties), the joint properties (number of degrees-of-freedom (dof)), and the kinds of actuators that move the segments. Third, the kinematics of the model are calculated by determining the transformation from recorded tracking markers to the pose of each segment of the biomechanical model. The definition of the biomechanical model can be a crucial determinant of the reliability of the transformation between tracking markers and model pose and for interpreting specific movement disorders. Fourth, inverse dynamics analysis is applied to the kinematics of the biomechanical model and to the location, magnitude, and direction of externally applied forces (e.g., ground reaction forces acting on the foot).
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 In [[Visual3D:Documentation:Kinematics_and_Kinetics:Six_Degrees_of_Freedom|6 DOF]] tracking there is no explicit linkage (or joint) connecting the segments. Visual3D explores the collection of segments and considers any two segments in proximity (the distal end of one segment and the proximal end of another segment within the radius of the segment ends) to be "linked" and references a **//Joint//** between them. The **//Joint//** does not constrain the segments, but is rather a bookkeeping tool that keeps track of which segments are assumed to have an equal and opposite Joint Reaction Force acting between their endpoints and an equal and opposite Joint Moments acting on the adjacent segments. In [[Visual3D:Documentation:Kinematics_and_Kinetics:Six_Degrees_of_Freedom|6 DOF]] tracking there is no explicit linkage (or joint) connecting the segments. Visual3D explores the collection of segments and considers any two segments in proximity (the distal end of one segment and the proximal end of another segment within the radius of the segment ends) to be "linked" and references a **//Joint//** between them. The **//Joint//** does not constrain the segments, but is rather a bookkeeping tool that keeps track of which segments are assumed to have an equal and opposite Joint Reaction Force acting between their endpoints and an equal and opposite Joint Moments acting on the adjacent segments.
  
-=== Inverse Dynamics Calculations in Visual3D ===+====== Inverse Dynamics Calculations in Visual3D ======
  
 Kinetics is the study of the forces and moments that cause motion of a body. For human movement, biomechanics attempt to determine the forces that result from muscle contractions and the torques that are produced, which together bring about the movement of the segments and thus of the whole body. Kinetics is the study of the forces and moments that cause motion of a body. For human movement, biomechanics attempt to determine the forces that result from muscle contractions and the torques that are produced, which together bring about the movement of the segments and thus of the whole body.
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 An advantage of this recursive formulation is that the approach is generalizable because there is substantially less bookkeeping required to keep track of the external forces and torques. An advantage of this recursive formulation is that the approach is generalizable because there is substantially less bookkeeping required to keep track of the external forces and torques.
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 +=== Sampling Rate ===
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 +Many people collect analog data at a higher rate than their motion capture data, which is the point rate. 
 +This is fine, as long as the higher rate is an integer multiple of the point rate. 
 +When force data are applied to a model, the resulting Link_Model_Based data are at point rate. 
 +This is because forces applied to segments cannot be calculated where the segment location is unknown (between point frames), 
 +i.e. there are no target data to generate segment locations for the ‘extra’ analog frames. 
 +However, the FORCE data retain the analog data rate. 
 +These ‘extra’ sample points are displayed as SUB frames within the point rate. 
 +The first subframe is synchronized with the point data, and it is this first subframe that is used for Inverse Dynamics calculations.
 +Other Link_Model_Based data, which are based on segments, are also sampled at the point rate, since segmental data can only ever be calculated at point rate.
  
 === Center of Mass of the Model === === Center of Mass of the Model ===
visual3d/documentation/kinematics_and_kinetics/inverse_dynamics.1721229751.txt.gz · Last modified: 2024/07/17 15:22 by sgranger