Assign kinematic variables from the KinematicsSolver object as targets
assigns as target variables the kinematic variables listed in the
ks under the names given in the
Those that do serve as constraints to apply during analysis. Their values must be later
defined in order to run the analysis. The solver, when called, searches for a solution
compatible with the targeted joint and frame variables.
The output is an updated table with the target variables—both new and old—in rows. Each row gives the ID of a variable, the type and block path of the joint to which it belongs if a joint variable, the base and follower frames from which it spawns if a frame variable, and the unit for its numerical value. The variables rank in the order added.
Most variables can be assigned individually. A few must be assigned in groups—axis components alongside rotation angle in spherical primitives; bend angle alongside azimuth angle in constant-velocity primitives. (A bend angle can be assigned individually but the azimuth angle cannot.)
The figure shows the variables of a general
Target (T), guess (G), and
output (O) variables can be joint variables (J) or frame variables (F). The
same variable can serve as target and output, but if it serves as target, it cannot double
as guess. Assigning a guess variable as target clears it as guess.
As with position targets in joint blocks in regular Simulink models, target variables should not overconstrain the system they describe. An assembly is overconstrained if a kinematic loop within it has a target for every joint. Kinematic loops such as four-bars and crank-sliders are evident from the model. Others arise when formulating a kinematic problem to solve.
Kinematic chains such as robotic arms and other serial manipulators become kinematic loops when subject to closure constraints. A target for a frame variable between base and end effector frames adds the equivalent of such a constraint. If the closed chain is to be underconstrained, at least one of its joints must stay free of target variables.
Adding a target variable that overconstrains the assembly causes
addTargetVariables to fail with
an error. Consider initial guess variables for the last joint of a kinematic loop, if
necessary, to guide the joint into place without overconstraining the assembly. Use the
function to assign a kinematic variable as an initial guess.
ks— Kinematics solver object
KinematicsSolver object is the representation of a Simscape
Multibody model used for kinematic analysis.
Example: ks = simscape.multibody.KinematicsSolver('sm_double_pendulum')
ids— Identifiers of kinematic variables to use