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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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268 Chapter 8 Matrix algebra

Engineeringapplication8.1

Robotcoordinateframes

InChapter7wesawthatvectorsprovideausefultoolfortheanalysisoftheposition

ofrobots.Byassigningavectortoeachofthelinksthepositionvectorcorresponding

tothetipoftherobot canbecalculated (Figure8.1).Inpracticetheinverse problem

ismorelikely:calculatethelinkvectorstoachieveaparticularpositionvector.Usually

a desired position for the tip of the robot is known and link positions to achieve

this are required. The problem is made more complicated because the position of a

link depends upon the movements of all the joints between it and the anchor point.

Thesolutionofthisproblemcanbequitecomplicated,especiallywhentherobothas

several links. One way forward is to define the position of a link by its own local

set of coordinates. This is usually termed a coordinate frame because it provides a

frameofreferenceforthelink.Matrixoperationscanthenbeusedtorelatethecoordinateframes,thusallowingalinkpositiontobedefinedwithrespecttoaconvenient

coordinateframe.Acommonrequirementistobeabletorelatethelinkpositionsto

a world coordinate frame. If a robot is being used in conjunction with other machinesthentheworldcoordinateframemayhaveanoriginsomedistanceawayfrom

the robot. The advantage of defining link coordinate frames is that the position of a

linkiseasilydefinedwithinitsowncoordinateframeandthemovementofcoordinate

frames relative toeach other can be expressed by means ofmatrix equations.

b

c

d

a

p

p = a + b + c + d

Figure8.1

Arobotwithlinksrepresentedbyvectors

a, b, cand d.

8.4.1 Translationandrotationofvectors

An introduction to the mathematics involved in analysing the movement of robots can

be obtained by examining the way in which vectors can be translated and rotated using

matrix operations.

Consider the pointPwith position vector given by

⎛ ⎞

x

r = ⎝y⎠

z

In order to translate and rotate this vector it is useful to introduce an augmented vector

Vgiven by

⎛ ⎞

x

V = ⎜y

⎝z⎠ (8.1)

1

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