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Major classes in IKBT

This will introduce some major classes which hold data used by IKBT solver nodes/leaves. These are collected and posted onto the BT blackboard for visibility to the leaves.

The classes will be described in a bottom up manner from lowest level to highest level. Only the most important or most widely used members of each class will be described here.

unknown

File: ikbtbasics/kin_cl.py

This class represents each unknown which must be solved for.

Highlights:

symbol          # sympy variable 
name            # string name
eqnlist         # list of kequations containing this unknown
eqntosolve      # kequation to solve for this unknown
readytosolve    # True/False
solved          # True/False
solutions       # list of solutions for this unk.
solutionNames   # list of names e.g. th_5s1
dependencies    # set() of solved unks upon which this unk's solution depends. 
versionNames    # list of versions e.g. th_5v3
LHSversionNames # sympy var's for the version names

# methods
details()                # print summary of this unk.
set_solved(R,unknowns)   # once a solver has cracked this unknown call this
                         # creates solutionNames, dependencies, VersionNames etc.

kequation

File: 'ikbtbasics/kin_cl.py`

This represents a single kinematic equation having a left hand and right hand side.

Highlights:

LHS             # a sympy expression for left  hand side
RHS             #     "       "          right hand side

#methods
LaTexOutput()     # return latex string for a kequation (option: align)

matrix_equation

File: ikbtbasics/kin_cl.py

An equation in which each side is a 4x4 matrix.

Highlights:

Td             # the left hand side: desired end effector configuration (known)
Ts             # the right hand side: symbolic FK equations containing unknowns

mechanism

File: ikbtbasics/kin_cl.py

Kinematic parameters and methods for a serial-chain mechanism.

Highlights:

DH              # the (modified/Craig style) Denavit Hartenburg Parameter Table (must have 6 rows)
vv              # variables vector (1 = rotary joint, 0 = prismatic joint)
params          # constant parameters (e.g. l_2, d_1)
jlims           # joint limits

# methods
forward_kinematics()     # compute the fk equations
get_mequation_set()      # derives mequations transformed into each link frame
scan_for_equations()     # get unsolved kequations from lists of matrix_equations and auxiliary
scan_Mequation()         # get list of kequations from a matrix_equation
sum_of_angle_transform() # identify and convert SOA terms in the mechanism

Notes:

  • DH, vv, params, jlims should be set in ikbtfunctions/ik_robots.py

Robot

File: ikbtbasics/ik_classes.py

Highest level class to represent a target robot for IK solution.

Highlights:

solutionSet             # each solution version is a tuple of unknown versions (its a set!)
solListMatrix           # rows: valid solution combinations, cols: unknown versions
FinalEqnMatrix          # generate a kequation for each entry in solListMatrix
mequation_list[]        # all 4x4 matrix FK equations (generated by get_mequation_set()?)
kequation_aux_list[]    # SOA definitions eg:  th_23 = th_2 + th_3
SOA_eqns                # a single matrix_equation containing up to 16 SOA equations 
Mech                    # the mechanism of the Robot

# methods
scan_for_equations()      # get unsolved equations having 1 or 2 unks.
sum_of_angles_transform() # identify sum of angles terms and create new variable and eqn
create_solution_set()     # create solutionSet and solListMatrix after completion
make_LHS_versions()       # create FinalEqnMatrix