trchain

Compound SE(3) transforms from string

T = TRCHAIN(S) is a homogeneous transform (4×4) that results from compounding a number of elementary transformations defined by the string S. The string S comprises a number of tokens of the form X(ARG) where X is one of Tx, Ty, Tz, Rx, Ry, or Rz. ARG is an arbitrary MATLAB expression that can include constants or workspace variables. For example: matlab trchain('Tx(1) Rx(90) Ry(45) Tz(2)')

is equivalent to computing matlab transl(1,0,0) * trotx(90, 'deg') * troty(45, 'deg') * transl(0,0,2)

T = TRCHAIN(S, Q) as above but the expression for ARG can also contain a variable ‘qJ’ which selects the Jth value from the passed vector Q (1×N). For example: matlab trchain('Rx(q1)Tx(a1)Ry(q2)Ty(a3)Rz(q3)', [1 2 3])

[T,TOK] = TRCHAIN(S …) as above but return an array of tokens which can be passed in, instead of the string.

T = TRCHAIN(TOK …) as above but chain is defined by array of tokens instead of a string.

Options

Notes

• Variables used in the string must exist in the caller workspace.
• The string can contain arbitrary characters between the elements, for example space, +, *, . or even |.
• Works for symbolic variables in the workspace and/or passed in via the vector Q.
• For symbolic operations that involve use of the value pi, make sure you define it first in the workspace: pi = sym(‘pi’);
• The tokens are simply a parsed version of the input string and provide some efficiency for repeated calls on the same chain.

See also

trchain2, trotx, troty, trotz, transl, SerialLink.trchain, ets

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