Добавил:
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз: Предмет: Файл:
Jack H.Integration and automation of manufacturing systems.2001.pdf
Скачиваний:
86
Добавлен:
23.08.2013
Размер:
3.84 Mб
Скачать

page 366

Find the Jacobian matrix for the matrix given below. This will give a matrix that relates tool velocity to joint velocities.The joint angles are 30° and 20° for joints 1 and 2, find the joint velocities if the tool velocity is 0.05 m/s

 

 

 

 

 

 

 

 

 

 

 

 

 

cos ( θ 1 + θ 2)

sin ( θ 1 + θ 2)

0

cos θ

1

+ 1.2 cos ( θ

1 + θ

2)

T0, T =

– sin ( θ 1 + θ 2)

cos ( θ 1 + θ 2)

0

sin θ

1

+ 1.2 sin ( θ

1 + θ

2)

 

 

0

0

1

 

 

0

 

 

 

 

 

0

0

0

 

 

1

 

 

 

12.3 SPATIAL DYNAMICS

• The basic principles of planar dynamics are expanded up for 3D spatial problems. The added dimension adds some complexity that should be addressed.

12.3.1 Moments of Inertia About Arbitrary Axes

• Moments of Inertia are normally found for a single axis of rotation. When the object is

page 367

rotating about another axis, we must recalculate the moments of inertia.

• If we take the moments of inertia for the original axes, and project these values onto new vectors, we can get new values,

We start by defining the vector equivalencies for rotated axes,

R' = R = iRx + jRy + kRz = i'R'x + j'R'y + k'R'k

We can project this vector to the other set of axes,

 

 

R'x

= ( i')

( iRx + jRy + kRk)

=

Rx cos θ

i'i + Ry cos θ

i'j + Rz cos θ

i'k

 

 

 

 

 

 

 

 

 

 

 

 

 

R'y

=

( j')

( iRx + jRy + kRk)

=

Rx cos θ

j'i + Ry cos θ

j'j + Rz cos θ

j'k

 

 

 

 

 

 

 

 

 

 

R'z

=

( k') •

( iRx + jRy + kRk)

= Rx cos θ

k'i + Ry cos θ

k'j + Rz cos θ k'k

 

 

 

 

 

 

 

 

 

 

 

 

 

Next we integrate for moment of inertia for the shifted x axis,

 

 

 

 

 

 

Ix'x'

= ( i' × R'x) • ( i' × R'x) dm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

= ( Rx cos θ

i'i + Ry cos θ i'j + Rz cos θ

 

i'k) 2dm

 

 

 

 

 

 

 

 

 

 

 

 

= ( Rx cos θ

i'i) 2 + ( Ry cos θ

i'j) 2 + ( Rz cos θ i'k) 2 + 2( Rx cos θ i'iRy cos θ i'j)

 

 

 

 

 

 

 

 

2( Rx cos θ

i'i( Rz cos θ

i'k) )

+ 2( Ry cos θ i'j( Rz cos θ

i'k) ) dm

 

 

 

 

I

x'x'

= I

xx

( cos θ

) 2

+ I

yy

( cos θ

)

2 + I

zz

( cos θ

) 2

+ 2I

xy

( cos θ

i'i

cos θ

)

 

 

 

 

 

 

 

i'i

 

 

 

 

i'j

 

 

 

i'k

 

 

 

 

i'j

 

 

 

 

 

 

 

 

 

2Ixz ( cos θ i'i cos θ i'k)

+ 2Iyz( cos θ i'j cos θ

i'k)

 

 

 

 

 

 

Similarly for the shifted y and z axes,

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I

y'y'

= I

xx

( cos θ

) 2

+ I

yy

( cos θ

)

2 + I

zz

( cos θ

) 2

+ 2I

xy

( cos θ

j'i

cos θ

)

 

 

 

 

 

 

 

j'i

 

 

 

 

j'j

 

 

 

j'k

 

 

 

 

j'j

 

 

 

 

 

 

 

 

 

2Ixz ( cos θ j'i cos θ j'k)

+ 2Iyz( cos θ j'j cos θ

j'k)

 

 

 

 

 

 

 

I

z'z'

 

= I

xx

( cos θ

 

) 2

+ I

yy

( cos θ

 

)

2 + I

zz

( cos θ

) 2

+ 2I

xy

( cos θ

k'i

cos θ

)

 

 

 

 

 

 

k'i

 

 

 

 

k'j

 

 

 

k'k

 

 

 

k'j

 

 

 

 

 

 

 

 

 

2Ixz( cos θ k'i cos θ k'k)

+ 2Iyz( cos θ k'j cos θ

k'k)

 

 

 

 

 

 

Next we integrate for the product of inertia for the shifted x and y axis,

 

 

 

 

Ix'y'

= ( i' × R'x) • ( i' × R'y) dm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

+

+

+

+

page 368

This will lead to,

 

 

 

 

 

 

 

 

Ix'y' = Ixx( – cos θ i'i cos θ j'i) + Iyy( cos θ i'j cos θ j'j)

+ Izz ( – cos θ i'k cos θ j'k) +

 

 

Ixy ( cos θ

i'i cos θ

j'j + cos θ

i'j cos θ

j'i) + Iyz( cos θ i'j cos θ j'k + cos θ

i'k cos θ

j'j)

 

Ixz( cos θ

i'k cos θ

j'i + cos θ

i'i cos θ

j'k)

 

 

 

Iy'z'

= Ixx ( – cos θ j'i cos θ k'i) + Iyy( cos θ

j'j cos θ k'j)

+ Izz( – cos θ j'k cos θ

k'k) +

 

 

Ixy( cos θ

j'i cos θ k'j + cos θ j'j cos θ k'i) + Iyz( cos θ j'j cos θ k'k + cos θ

j'k cos θ

k'j)

 

Ixz( cos θ

j'k cos θ k'i + cos θ j'i cos θ k'k)

 

 

 

Ix'y'

= Ixx ( – cos θ k'i cos θ i'i) + Iyy( cos θ

k'j cos θ i'j)

+ Izz( – cos θ k'k cos θ

i'k) +

 

 

Ixy( cos θ

k'i cos θ i'j + cos θ k'j cos θ i'i) + Iyz( cos θ k'j cos θ i'k + cos θ

k'k cos θ

i'j)

 

Ixz( cos θ

k'k cos θ i'i + cos θ k'i cos θ

i'k)

 

 

 

We can define the new coordinate system in terms of translated axes,

Rx''

=

Rx'

+ dx'

Ry''

= Ry' + dy'

Rz'' = Rz' + dz'

This can be integrated for the shifted x axis,

Ix''x'' = ( Ry''2 + Rz''2) dm = ( ( Ry' + dy') 2 + ( Rz' + dz') 2) dm

+

+

+

= ( Ry'2 + 2Ry'dy' + dy'2 + Rz'2 + 2Rz'dz' + dz'2) dm

= ( Ry'2 + Rz'2) dm + ( 2Ry'dy') dm + ( 2Rz'dz') dm + ( dy'2 + dz'2) dm

= Iy'z' + 2mRMy' dy' + 2mRMz' dz' + ( dy'2 + dz'2) m

page 369

This eventually leads to,

 

 

 

 

 

 

 

 

 

 

 

I

x''x''

= I

x'x'

+ 2mR

d

y'

+ 2mR

d

z'

+ m( d ) 2

+ m( d ) 2

 

 

 

 

My'

 

 

 

Mz'

 

y'

z'

I

y''y''

= I

y'y'

+ 2mR

d

x'

+ 2mR

d

z'

+ m( d ) 2

+ m( d ) 2

 

 

 

 

Mx'

 

 

 

Mz'

 

x'

z'

I

z''z''

= I

z'z'

+ 2mR

d

x'

+ 2mR

d

y'

+ m( d ) 2

+ m( d ) 2

 

 

 

Mx'

 

My'

x'

y'

Ix''y''

= Ix'y' + 2mRMx' dy' + 2mRMy' dx' + mdx'dy'

 

Iy''z''

= Iy'z' + 2mRMy' dz' + 2mRMz' dy' + mdy'dz'

 

Ix''z''

= Ix'z' + 2mRMx' dz' + 2mRMz' dx' + mdx'dz'

 

12.3.2 Euler’s Equations of Motion

• We can use Euler’s equations of motion to determine moments produced by angular velocities and accelerations.

MMijx = IMxx α x ( IMyy IMzzyω z MMijy = IMyy α y ( IMxx IMzzxω z

MMijz = IMzz α z ( IMxx IMyyxω y

• These can be used to examine rotating three dimensional masses. Consider the following,