Exam 1 Flashcards
know
What is an example of a common obstacle we
encounter in inverse kinematics problems
Inverse kinematics problems often have more than one solution, and the system of equations is nonlinear. When solving for a combination of acceptable angles, we often will find a combination that is physiologically
impossible/improbable.
Need to use Fsolve
When solving an underdefined system of equations (common in biomechanics) using the
pseudo inverse in MATLAB, what additional assumption is used to select a combination of
forces from the infinite available possibilities?
Pinv() minimizes the solution vector. This aligns with the idea that we will select the most efficient combination of muscle forces..
When dealing with multiple unknown muscle forces, it is possible to link them all back
to a single variable dependent on the relative muscle geometry. Briefly list the assumptions
associated with this approach
we assume that 10 muscles exert a unifrom maximum pressure and that 2) all muscles will engage the same percentage of their maximum force. This allows us to write theri ration of forces as a function of their ratio of cross-sectional areas.
Provide an example of an activity where quasi-static equilibrium would likely
be a poor choice for estimating the forces involved
Running or anything where you are moving with speed/ the force you exert depends on the quickness of the motion you are performing
What is the relationship between the pressure applied by the weight of an
object on ground and the resulting normal force? Where should the normal
force be applied ?
Normal force is equal to the integrated pressure in opposite direction under statics. It should align with the center of gravity of the object.
mechanics
nehavior of physical bodies when subjected to mechanical disturbances such as forces or displacements and the subsequent effect of the bodies of their environment
bio-mechanics
concerned with the application of classical mechanics to biology. It combines engineering mechanics wiht biophysics
assumptions and fators for making a model
recognize its limits, simplify it, the more detailed the harder to solve.
common limits for engineering models
small deformations, linear stress-strain behavior, negligible dynamic effects
what do forces represent
load distributed over an area (pressure)
coplanar system
forces acting on a 2d plane or surface
colinear
if all forces have a common line of action
magnitude of moment
Equal to the force times the shortest difference to the pt. M=Fxd
external forces
forces applied to an object externally
internal forces
forces that hold the body togetehr when the body is under the effect of externally supplied forces
well defined
has as many equations as unknowns
underdefined
has more unknowns than equations
overdefined
has more eqautions than unknowns
multiple muscle groups solving
- assuming single muscle group activated
- assuming the muscles are equally activated
- optimization of expenditure
optimization
we solve this by assuming the lowest energy necessary for completing the motion( high efficiency)
pinv() or isqnonneg()
direct kinematics
calculate the end pt given all other measurments
danvit harten berg matrix
vector based-approach to solve kinematics and range of motion
inverse kinematics
calculates joint angles and positions given an end point, nonlinear, multiple solutions, fsolve
Fsolve
needs sys of eqs paramaters and initial guesses
