DYNAMICS OF PARALLEL MANIPULATOR...KINEMATICS OF PARALLEL MANIPULATORS Moreover, since the only...
Transcript of DYNAMICS OF PARALLEL MANIPULATOR...KINEMATICS OF PARALLEL MANIPULATORS Moreover, since the only...
DYNAMICS OF PARALLEL
MANIPULATOR
PARALLEL MANIPULATORS
6-degree of Freedom Flight Simulator
BACKGROUND
Platform-type parallel mechanisms
6-DOF MANIPULATORS
INTRODUCTION
Under alternative robotic mechanical systems we
understand here:
Parallel Robots;
Multifingered hands;
Walking Machines;
Rolling Robots.
Parallel manipulators are
composed of kinematic
chains with closed subchains.
KINEMATICS OF PARALLEL
MANIPULATORS
General six-dof parallel manipulator
KINEMATICS OF PARALLEL
MANIPULATORSWe can distinguish two platforms:
One fixed to the ground โฌ One capable of moving arbitrarily within its
workspace โณ.
The moving platform is connected to the fixed platform
through six legs, each being regarded as a six-axis serial
manipulator whose base is โฌand whose end-effector is โณ.
The whole leg is composed of six links coupled through
six revolutes.
KINEMATICS OF PARALLEL
MANIPULATORS
Six-dof flight simulator: (a) general layout; (b) geometry of its two
platforms
KINEMATICS OF PARALLEL
MANIPULATORSIn this figure, the fixed platform โฌ is a regular hexagon,
while the moving platform โณ is an equilateral triangle.
Moreover, โฌ is connected to โณ by means of six serial
chains, each comprising five revolutes and one prismatic
pair. Three of the revolutes bear concurrent axes, and
hence, constitute a spherical joint, while two more have axes
intersecting at right angles, thus constituting a universal
joint.
It is to be noted that although each leg of the manipulator
has a spherical joint at only one end and a universal joint at
the other end.
KINEMATICS OF PARALLEL
MANIPULATORS
A layout of a leg of the manipulator
KINEMATICS OF PARALLEL
MANIPULATORSWe analyze the inverse kinematics of one leg of the
manipulator. The Denavit-Hartenberg parameters of
the leg shown in this figure are given in table:
i ai bi ฮฑi
1 0 0 90ยฐ
2 0 0 90ยฐ
3 0 b3 0ยฐ
4 0 b4 (const) 90ยฐ
5 0 0 90ยฐ
6 0 b6(const) 0ยฐ
KINEMATICS OF PARALLEL
MANIPULATORSIt is apparent that the leg under study is a decoupled
manipulator. In view of the DH parameters of this
manipulator, we have:
๐1๐2 ๐3 + ๐4 = ๐where c denotes the position vector of the center C of
the spherical wrist and, since frames โฑ3 and โฑ4 of the
DH notation are related by a pure translation, Q3 = 1.
Upon equating the squares of the Euclidean norms of
both sides of the foregoing equation, we obtain:
๐3 + ๐4๐ = ๐ ๐
KINEMATICS OF PARALLEL
MANIPULATORSWhere, by virtue of the DH parameters of Table:
๐3 + ๐4๐ = b3 + b4
2
Now, since both b3 and b4 are positive by
construction, we have:
b3 = ๐ โ b4 > 0
Note that the remaining five joint variables of the leg
under study are not needed for purposes of inverse
kinematics, and hence, their calculation could be
skipped.
KINEMATICS OF PARALLEL
MANIPULATORSWe derive three scalar equations in two unknowns, ฮธ1
and ฮธ2, namely,๐3 + ๐4 = ๐ฅ๐๐1 + ๐ฆ๐๐ 1
โ(๐3 + ๐4 = ๐ง๐0 = ๐ฅ๐๐ 1 โ ๐ฆ๐๐1
in which ci and si stand for cosฮธi and sin ฮธi, respectively
ฮธ1 is derived as: ๐1 = tan๐ฆ๐
๐ฅ๐
which yields a unique value of ฮธ1 rather than the two lying
ฯ radians apart, for the two coordinates xC and yC
determine the quadrant in which ฮธ1 lies.
KINEMATICS OF PARALLEL
MANIPULATORSOnce ฮธ1 is known, ฮธ2 is derived uniquely from the
remaining two equations through its cosine and sine
functions, i.e.,
๐2 =๐ง๐
๐3 + ๐4๐ 2 =
๐ฅ๐๐1 + ๐ฆ๐๐ 1๐3 + ๐4
With the first three joint variables of this leg known, the
remaining ones, are calculated as described in foregoing
chapter.
Therefore, the inverse kinematics of each leg admits two
solutions, one for the first three variables and two for the
last three.
KINEMATICS OF PARALLEL
MANIPULATORSMoreover, since the only actuated joint is one of the
first three, which of the two wrist solutions is chosen
does not affect the value of b3, and hence, each
manipulator leg admits only one inverse kinematics
solution.
While the inverse kinematics of this leg is quite
straightforward, its direct kinematics is not. Below we
give an outline of the solution procedure for the
manipulator under study
KINEMATICS OF PARALLEL
MANIPULATORS
Equivalent simplified mechanism
KINEMATICS OF PARALLEL
MANIPULATORSWe can replace the pair of legs by a single leg of length li connected
to the base plate โฌ by a revolute joint with its axis along AiBi. The
resulting simplified structure is kinematically equivalent to the
original structure.
Now we introduce the coordinate frame โฑi with origin at the
attachment point Oi of the ith leg with the base plate โฌ and the
notation below:
For i=1,2,3
Xi is directed from Ai to Bi
Yi is chosen such that Zi is perpendicular to the plane of the
hexagonal base and points upwards.
Oi is set at the intersection of Xi and Yi and is designated the
center of the revolute joint;
KINEMATICS OF PARALLEL
MANIPULATORSNext, we locate the three vertices S1, S2 and S3 of the
triangular plate with position vectors stemming from
the center O of the hexagon. Furthermore, we need to
determine li and Oi.
Referring to Figures and letting ai and bi denote the
position vectors of points Ai and Bi respectively, we
have:
๐๐ = ๐i โ ๐i
KINEMATICS OF PARALLEL
MANIPULATORS
๐๐ =๐๐2 + ๐๐๐
2 โ ๐๐๐2
2๐๐
๐๐ = ๐๐๐2 โ ๐๐
2
๐ฎi =๐i โ ๐idi
for i = 1,2,3, and hence ui is
the unit vector directed
from Ai to Bi.
KINEMATICS OF PARALLEL
MANIPULATORSMoreover, the position of the origin Oi is given by
vector oi, as indicated below:
๐จi = ๐i + ๐๐๐ฎi For i= 1,2,3
Furthermore, let si be the position vector of Si in
frame โฑi (Oi, Xi, Yi, Zi), then:
๐ฌ๐ =
0โ๐๐๐๐๐ ๐๐
๐๐๐ ๐๐๐๐
For i= 1,2,3
KINEMATICS OF PARALLEL
MANIPULATORSNow a frame โฑ0 (O, X, Y, Z) is defined with origin at
O and axes X and Y in the plane of the base hexagon,
and related to Xi and Yi as depicted in figure. When
expressed in frame โฑ0, si takes on the form:
๐ฌi 0 = ๐จi 0 + ๐i 0๐ฌi For i=1,2,3
Where [Ri]0 is the matrix that rotate โฑ0 to frame โฑi,expressed in and given as:
๐i 0 =cos๐ผ๐ โsin๐ผ๐ 0sin๐ผ๐ cos๐ผ๐ 00 0 1
KINEMATICS OF PARALLEL
MANIPULATORS
Referring to Figure:
cos๐ผ๐ = ๐ฎi โ ๐ข = ๐ขixsin ๐ผ๐ = ๐ฎi โ ๐ฃ = ๐ขiy
KINEMATICS OF PARALLEL
MANIPULATORSAfter substitution we obtain:
๐ฌi 0 = ๐จi 0 + li
๐ข๐๐ฅcos๐๐
โ๐ข๐๐ฆcos๐๐
sin๐๐
For i=1,2,3
Since the distances between the three vertices of the
triangular plate are fixed, the position vectors s1, s2,
and s3 must satisfy the constraints below:๐ฌ2 โ ๐ฌ1
2 = ๐12
๐ฌ3 โ ๐ฌ22 = ๐2
2
๐ฌ1 โ ๐ฌ32 = ๐3
2
KINEMATICS OF PARALLEL
MANIPULATORSAfter expansion, equations take the forms:๐ท1๐๐1 + ๐ท2๐๐2 + ๐ท3๐๐1๐๐2 + ๐ท4๐ ๐1๐ ๐2 + ๐ท5 = 0 (1)
๐ธ1๐๐2 + ๐ธ2๐๐3 + ๐ธ3๐๐2๐๐3 + ๐ธ4๐ ๐2๐ ๐3 + ๐ธ5 (2)๐น1๐๐1 + ๐น2๐๐3 + ๐น3๐๐1๐๐3 + ๐น4๐ ๐1๐ ๐3 + ๐น5 = 0 (3)
where c(ยท) and s(ยท) stand for cos(ยท) and sin(ยท), respectively,
while coefficients ๐ท๐ , ๐ธ๐ , ๐น๐ 15 functions of the data only
and bear the forms shown below:
๐ท1 = 2๐1 ๐จ2 โ ๐จ1T๐๐ฎ๐
๐ท2 = 2๐2 ๐จ2 โ ๐จ1T๐๐ฎ๐
๐ท3 = โ2๐1๐2๐ฎ๐๐๐ฎ๐
KINEMATICS OF PARALLEL
MANIPULATORS๐ท4 = โ2๐1๐2๐ท5 = ๐จ๐
2 + ๐จ๐2 โ 2๐จ๐
๐๐จ๐ + ๐12 + ๐2
2 โ ๐12
๐ธ1 = 2๐2 ๐จ๐ โ ๐จ๐๐๐๐ฎ๐
๐ธ2 = โ2๐3 ๐จ๐ โ ๐จ๐๐๐๐ฎ๐
๐ธ3 = โ2๐2๐3๐ฎ๐๐๐ฎ๐
๐ธ4 = โ2๐2๐3๐ธ5 = ๐จ๐
2 + ๐จ๐2 โ 2๐จ๐
๐๐จ๐ + ๐22 + ๐3
2 โ ๐22
๐น1 = 2๐1 ๐จ๐ โ ๐จ๐๐๐๐ฎ๐
F2 = โ2๐3 ๐จ๐ โ ๐จ๐๐๐๐ฎ๐
๐น3 = โ2๐1๐3๐ฎ๐๐๐ฎ๐
๐น4 = โ2๐1๐3๐น5 = ๐จ๐
2 + ๐จ๐2 โ 2๐จ๐
๐๐จ๐ + ๐12 + ๐3
2 โ ๐32
KINEMATICS OF PARALLEL
MANIPULATORSOur next step is to reduce the foregoing system of three
equations in three unknowns to two equations in two
unknowns, and hence, obtain two contours in the plane of
two of the three unknowns, the desired solutions being
determined as the intersections of the two contours.
Since the first equation is already free of ฮฆ3, all we have to
do is eliminate it from the other equations.
The resulting equations take on the forms:
๐1๐32 + ๐2๐3 + ๐3 = 0
๐1๐32 +๐2๐3 +๐3 = 0
KINEMATICS OF PARALLEL
MANIPULATORSWhere k1, k2, and k3 are linear combinations of s2, c
2, and 1. Likewise, m1, m2, and m3 are linear
combinations of s1, c1 and 1, namely,
๐1 = ๐ธ1๐๐2 โ ๐ธ2 โ ๐ธ3๐๐2 + ๐ธ5๐2 = 2๐ธ4๐ ๐2
๐3 = ๐ธ1๐๐2 + ๐ธ2 + ๐ธ3๐๐2 + ๐ธ5๐1 = ๐น1๐๐1 โ ๐น2 โ ๐น3๐๐1 + ๐น5
๐2 = 2๐น4๐ ๐1
๐3 = ๐น1๐๐1 + ๐น2 + ๐น3๐๐1 + ๐น5
KINEMATICS OF PARALLEL
MANIPULATORSWe proceed now by multiplying each of the above equations
by ฯ3 to obtain two more equations, namely.
๐1๐32 + ๐2๐3
2 + ๐3๐3 = 0๐1๐3
2 +๐2๐32 +๐3๐3 = 0
Further, we write equations in homogeneous form as:๐ฝ๐๐ = ๐
with the 4 x 4 matrix ฮฆ and the 4-dimensional vector ฯ3
defined as:
๐ฝ =
๐1 ๐2 ๐3 0๐1 ๐2 ๐3 00 ๐1 ๐2 ๐30 ๐1 ๐2 ๐3
๐๐ =
๐33
๐32
๐31
KINEMATICS OF PARALLEL
MANIPULATORSMoreover, in view of the form of vector ฯ3, we are interested
only in nontrivial solutions, which exist only if det(ฮฆ)
vanishes. We thus have the condition
det ๐ฝ = 0 (4)Equations (1) and (4) form a system of two equations in two
unknowns 1 and 2 . Moreover for ๐3:๐ธ4๐ ๐2 ๐ธ2 + ๐ธ3๐๐2
๐น4๐ ๐1 ๐น2 + ๐น3๐๐1
๐ ๐3
๐๐3=
โ๐ธ1๐๐2 โ ๐ธ5โ๐น1๐๐1 โ ๐น5
Knowing the angles 1 , 2 and 3 allows us to determine the
position vectors of the three vertices of the mobile plate s1, s2
and s3. Since three points define a plane, the pose of the EE is
uniquely determined by the positions of its three vertices
CONTOUR-INTERSECTION
APPROACHWe derive the direct kinematics of a manipulator analyzed
by Nanua et al. (1990). This is a platform manipulator
whose base plate has six vertices with coordinates expressed
with respect to the fixed reference frame โฑ0 as given below,
with all data given in meters:
A1 = (-2.9, -0.9), B1 =(-1.2, 3.0)
A2= ( 2.5, 4.1), B2 =( 3.2, 1.0)
A3 = ( 1.3, -2.3), B3 = (-1.2,-3.7)
The dimensions of the movable triangular plate are, in turn,
a1 = 2.0, a2 =2.0, a3 = 3.0
CONTOUR-INTERSECTION
APPROACHDetermie all possible poses of the moving plate for the six
leg-lenghts given as:
q1a = 5.0, q2a =5.5, q3a = 5.7
q1b = 4.5, q2b =5.0, q3b = 5.5
SOLUTION: After substitution of the given numerical
values:61.848 โ 36.9561๐1 โ 47.2376๐2 + 33.603๐1๐2 โ 41.6822๐ 1๐ 2 = 0
โ28.5721 + 48.6806๐1 โ 20.7097๐12 + 68.7942๐2 โ 100.811๐1๐2
+ 35.9634๐12๐2 โ 41.4096๐2
2 + 50.8539๐1๐22 โ 15.613๐1
2๐22
โ 52.9786๐ 12 + 67.6522๐2๐ 1
2 โ 13.2765๐22๐ 1
2 + 74.1623๐ 1๐ 2โ 25.6617๐1๐ 1๐ 2 โ 67.953๐2๐ 1๐ 2 + 33.9241๐1๐2๐ 1๐ 2 โ 13.202๐ 2
2
โ 3.75189๐1๐ 22 + 6.13542๐1
2๐ 22 = 0
CONTOUR-INTERSECTION
APPROACH
THE UNIVARIATE
POLYNOMIAL APPROACHReduce the two equations above, to a single monovariate
polynomial equation.
SOLUTION:
We obtain two polynomial equations in ฯ1, namely,
๐บ1๐14 + ๐บ2๐1
3 + ๐บ3๐12 + ๐บ4๐1 + ๐บ5 = 0
๐ป1๐12 +๐ป2๐1 + ๐ป3 = 0
No . 1 (rad) 2 (rad) 3 (rad)
1 0.8335 0.5399 0.8528
2 1.5344 0.5107 0.2712
3 -0.8335 -0.5399 -0.8528
4 -0.5107 -0.5107 -0.2712
THE UNIVARIATE
POLYNOMIAL APPROACHWhere:
๐บ1 = ๐พ1๐24 + ๐พ2๐2
2 + ๐พ3๐บ2 = ๐พ4๐2
3 + ๐พ5๐2๐บ3 = ๐พ6๐2
4 + ๐พ7๐22 + ๐พ8
๐บ4 = ๐พ9๐23 + ๐พ10๐2
๐บ5 = ๐พ11๐24 + ๐พ12๐2
2 + ๐พ13๐ป1 = ๐ฟ1๐2
2 + ๐ฟ2๐ป2 = ๐ฟ3๐2๐ป3 = ๐ฟ4๐2
2 + ๐ฟ5
THE UNIVARIATE
POLYNOMIAL APPROACHMultiplying the first equation by H1 and the second by
G1ฯ1 and subtract the two equations thus resulting, which
leads to a cubic equation in ฯ1 , namely,๐บ2๐ป1 โ ๐บ2๐ป2 ๐1
3 + ๐บ3๐ป1 โ ๐บ1๐ป3 ๐12 + ๐บ4๐ป1๐1 + ๐บ5๐ป1 = 0
Likewise multiplying the first by H1 ฯ1 and the second
one by G1 ฯ13+G2 ฯ1
2 and the equations thus resulting are
subtracted from each other, one more cubic equation in
ฯ1 is obtaines :๐บ1๐ป3 โ ๐บ3๐ป1 ๐1
3 + ๐บ4๐ป1 + ๐บ3๐ป2 โ ๐บ2๐ป3 ๐12
+ ๐บ5๐ป1 + ๐บ4๐ป2 ๐1 + ๐บ5๐ป2 = 0
THE UNIVARIATE
POLYNOMIAL APPROACHMoreover, multiplying the second equation by ฯ1, a
third cubic equation in ฯ1 can be derived:
๐ป1๐13 +๐ป2๐1
2 +๐ป3๐1 = 0
Now the foregoing equations constitute a
homogeneous linea system of four equations in the
firt four powers of ฯ1 which can be cast in the form:
๐๐๐ = ๐
Where ๐๐ = ๐13 ๐1
2 ๐1 1
THE UNIVARIATE
POLYNOMIAL APPROACH
๐ =
๐บ2๐ป1 โ ๐บ2๐ป2 ๐บ3๐ป1 โ ๐บ1๐ป3 ๐บ4๐ป1 ๐บ5๐ป1
๐บ3๐ป1 โ ๐บ1๐ป3 ๐บ3๐ป2 โ ๐บ2๐ป3 + ๐บ4๐ป1 ๐บ4๐ป2 + ๐บ5๐ป1 ๐บ5๐ป2
๐ป1 ๐ป2 ๐ป3 00 ๐ป1 ๐ป2 ๐ป3
To admit a nontrivial solution, the determinant of its coefficient
matrix must vanish:
det (H)=0
and this can be expanded in the form:
det(H) = H11 + H22 + H33
THE UNIVARIATE
POLYNOMIAL APPROACHWhere:
ฮ2 = ๐๐๐ก
๐บ2๐ป1 โ ๐บ2๐ป2 ๐บ4๐ป1 ๐บ5๐ป1
๐บ3๐ป1 โ ๐บ1๐ป3 ๐บ4๐ป2 + ๐บ5๐ป1 ๐บ5๐ป2
๐ป1 ๐ป2 0
ฮ2 = ๐๐๐ก
๐บ2๐ป1 โ ๐บ2๐ป2 ๐บ3๐ป1 โ ๐บ1๐ป3 ๐บ5๐ป1
๐บ3๐ป1 โ ๐บ1๐ป3 ๐บ3๐ป2 โ ๐บ2๐ป3 + ๐บ4๐ป1 ๐บ5๐ป2
๐ป1 ๐ป2 0
ฮ2 = ๐๐๐ก
๐บ2๐ป1 โ ๐บ1๐ป2 ๐บ3๐ป1 โ ๐บ1๐ป3 ๐บ4๐ป1
๐บ3๐ป1 โ ๐บ1๐ป3 ๐บ3๐ป2 โ ๐บ2๐ป3 + ๐บ4๐ป1 ๐บ4๐ป2 + ๐บ5๐ป1
๐ป1 ๐ป2 ๐ป3
VELOCITY ANALYSES OF
PARALLEL MANIPULATORSThe inverse velocity analysis of this manipulator consists in
determining the six rates of the active joints, ๐๐ 1
6given the
twist t of the moving platform. The velocity analysis of a
typical leg leads to a relation of the form of equation
namely,
๐๐ฝ ๐ฝ๐ฝ = ๐ญ๐ฝ J= I,II,โฆ, IV
Where JJ is the Jacobian of the Jth leg, is the 6-d joint-rate
vector ๐ฝ๐ฝof the same leg and tj is the twist moving platform
โณ with its operation point defined as the point CJ
VELOCITY ANALYSES OF
PARALLEL MANIPULATORSWe thus have:
๐๐ =๐๐ ๐๐ ๐ ๐๐ ๐๐ ๐๐
๐34๐๐ ร ๐๐ ๐34๐๐ ร ๐๐ ๐๐ ๐ ๐ ๐
๐ญ๐ =๐ ๐๐, ๐34 = ๐3 + ๐4
it is apparent that
๐๐ = ๐ฉ โ ๐ ร ๐ซ๐
with rJ defined as the vector directed from CJ to the
operation point P of the moving platform.
VELOCITY ANALYSES OF
PARALLEL MANIPULATORSMultiplying the left side of the equation by IJ
T
Where: ๐JT = [ ๐T ๐3
T]
We obtain:
๐JT ๐๐ฝ ๐ฝ๐ฝ = ๐๐ฝ
On the other hand we have:
๐JT๐ญJ = ๐J
T ๐J
Upon equating the right-hand sides of the foregoing
equations we have: ๐๐ฑ = ๐๐ฑ๐ป ๐๐ฑ
VELOCITY ANALYSES OF
PARALLEL MANIPULATORSWe obtain the relations between the actuated joint rates
and the twist of the moving platform, namely
๐๐ = (๐Jร ๐ญj)๐ ๐J
T ๐ ๐= ๐ค๐ฝ
๐๐ญ
We have the desired relation between the vector of
actuated joint rates and the twist of the moving platform,
namely. ๐ = ๐๐ญ
With the 6-d vectors b and t defined as the vector of joint
variables and the twist of the platform at the operation
point, respectively. Moreover, the 6 x 6 matrix K is the
Jacobian of the manipulator at hand.
VELOCITY ANALYSES OF
PARALLEL MANIPULATORSThese quantities are displayed below:
๐ =
๐๐ผ๐๐ผ๐ผโฎ๐๐ผ๐
๐ญ =๐ ๐ฉ ๐ =
๐I ร ๐ซIT ๐I
T
๐II ร ๐ซIIT
โฎ๐VI ร ๐ซVI
T
๐IIT
โฎ๐VIT
ACCELLERATION ANALYSES OF
PARALLEL MANIPULATORSThe acceleration analysis of the same leg is
straightforward. Indeed, upon differentiation of both
sides of equation with respect to time, one obtains ๐ = ๐ ๐ญ + ๐๐ญ
Where ๐ takes the form:
๐ =
๐ฎ๐ผ๐ ๐๐ผ
๐
๐ฎ๐ผ๐ผ๐ ๐๐ผ๐ผ
๐
โฎ๐ฎ๐๐ผ๐
โฎ ๐๐๐ผ๐
ACCELLERATION ANALYSES OF
PARALLEL MANIPULATORSuJ is defined as: ๐ฎJ = ๐J ร ๐ซ๐
Therefore: ๐ฎJ = ๐J ร ๐ซJ + ๐J ร ๐ซJ
Now since the vector rj are fixed to the moving platform, their
time-derivatives are simply given by:
๐ซ๐ = ๐ร ๐ซ๐
On the other hand, vector ej is directed along the log axis, and
so, its time-derivative is given by:
๐J = ๐J ร ๐J
with ฯJ defined as the angular velocity of the third leg link:
๐๐ฝ = ๐1๐1 + ๐2๐2 ๐ฝ
ACCELLERATION ANALYSES OF
PARALLEL MANIPULATORSIn order to simplify the notation, we start by defining
๐๐ = ๐1 J ๐ J = ๐2 J
Now we write the second vector of the equation
๐๐ฝ ๐ฝ๐ฝ = ๐ญ๐ฝusing the foregoing definitions, which yields:
( ฮธ1)J๐๐ ร bJ + b4 ๐j + ( ฮธ2)J๐ J ร bJ + b4 ๐j + bJ๐j = ๐J
where b4 is the same for all legs, since all have
identical architectures. Now we can eliminate
( ฮธ2)Jfrom the foregoing equation by dot-multiplying
its two sides by g j , thereby producing
ACCELLERATION ANALYSES OF
PARALLEL MANIPULATORS
( ๐1)J๐ ๐ ร ๐J โ ๐๐ฝ + ๐4 ๐j + ๐ JT ๐j๐J
T ๐J = ๐ T ๐J
Now it is a simple matter to solve for ( ๐1)J from the
above equation, which yields:
( ๐1)J=๐๐ฝ๐ 1 โ ๐๐ฝ๐๐ฝ
๐ ๐๐ฝ
โ๐ฝ
Where: โ๐ฝ= ๐๐ฝ + ๐4 ๐j ร ๐J โ ๐ ๐
ACCELLERATION ANALYSES OF
PARALLEL MANIPULATORSMoreover, we can obtain the above expression for
( ๐1)J in terms of the platform twist by recalling
equation which is reproduced below in a more
suitable form for quick reference:
๐J = ๐J๐ญ
where t is the twist of the platform, the 3 x 6 matrix
Cj being defined as:
๐J = [๐j ๐]
In which RJ is the cross-product matrix of rJ
ACCELLERATION ANALYSES OF
PARALLEL MANIPULATORSTherefore the expressione sought for ( ๐1)J takes the
form:
( ๐1)J=1
โ๐ฝ๐ ๐ฝ๐ 1 โ ๐J๐J
T ๐J๐ญ
A similar procedure can be followed to find ( ๐2)Jthe
final result being
( ๐2)J=1
โ๐ฝ๐๐ฝ๐ 1 โ ๐J๐J
T ๐J๐ญ
PLANAR AND SPHERICAL
MANIPULATORSThe velocity analysis of the planar and spherical
parallel manipulators of figures are outlined below
PLANAR MANIPULATORS
๐๐ฝ ๐ฝ๐ฝ = ๐ญ๐ฝ J= I,II, III
Where JJ is the Jacobian matrix of this leg while ๐ฝ๐ฝ is the
3-D vectore of joint rates of this leg:
๐ฝ๐ฝ =1 1 1
๐ธ๐๐ฝ1 ๐ธ๐๐ฝ2 ๐ธ๐๐ฝ3 ๐๐ฝ =
๐๐ฝ1 ๐๐ฝ2 ๐๐ฝ3
We multiply both sides of the said equation by a 3-D
vector nj perpendicular to the second and the third
columns of JJ.
PLANAR MANIPULATORS
This vector can be most easily determined as the cross product of
those two columns, namely, as
๐ง = ๐ฃJ2 ร ๐ฃJ3 =โ๐ซJ2
T๐๐ซJ3๐ซJ2 โ ๐ซJ3
Upon multiplication of both side of the equation by njT, we obtain:
โ๐ซJ2๐๐ซj3 + ๐ซJ2 โ ๐ซJ3T๐๐ซJ1 ๐๐ฝ1 = โ ๐ซJ2๐๐ซJ3 ๐ + ๐ซJ2 โ ๐ซJ3
T ๐
And hence we can solve directly reriving:
๐๐ฝ1 =โ ๐ซJ2๐๐ซJ3 ๐+ ๐ซJ2โ๐ซJ3
T ๐
โ๐ซJ2๐๐ซj3+ ๐ซJ2โ๐ซJ3T๐๐ซJ1
PLANAR MANIPULATORS
The foregoing equation can be written in the form:
๐๐ฝ ๐๐ฝ1 = ๐คJT๐ญ J=I,II, III
With jJ and kJ defined:
๐๐ฝ = ๐ซJ2 โ ๐ซJ3T๐๐ซJ1 โ ๐ซJ2๐๐ซj3
๐คJ = [๐ซJ2T๐๐ซJ3 ๐ซJ2 โ ๐ซJ3
T]T
If we further define: ๐ = [ ๐๐ผ1 ๐๐ผ๐ผ2 ๐๐ผ๐ผ๐ผ3]
And assemble all three foregoing joint-rate-twist relation we
obtain: ๐ ๐ = ๐๐ญ
PLANAR MANIPULATORS
๐ ๐ = ๐๐ญ
Where J and K are the two manipulator Jacobians
defined as:
๐ = diag ๐I, ๐II, ๐III , ๐ =
๐คIT
๐คIIT
๐คIIIT
Expressions for the joint accelerations can be readily
derived by differentiation of the foregoing expressions
with respect to time.
SPHERICAL MANIPULATORThe velocity analysis of the spherical parallel
manipulator can be accomplished similarly. Thus, the
velocity relations of the Jth leg take on the form:
๐J ๐J = ๐ J=I,II,III
Where the Jacobian of the Jth leg JJ is defined as:
๐ฝ๐ฝ = ๐๐ฝ1 ๐๐ฝ2 ๐๐ฝ3
While the joint-rate vector of the Jth ๐Jleg is defined
exactly as in the planar case analyzed above.
An obvious definition of this vector is, then:
๐งJ = ๐J2 ร ๐J3
SPHERICAL MANIPULATORThe desired joint-rate relation is thus readily derived
as:
๐๐ฝ ๐๐ฝ1 = ๐คJT๐
where jJ and kJ are now defined as:
๐๐ฝ = ๐J1 ร ๐J2 โ ๐J3๐คJ = ๐J2 ร ๐J3
The accelerations of the actuated joints can be
derived, again, by differentiation of the foregoing
expressions. We can then say that in general, parallel
manipulators, as opposed to serial ones, have two
Jacobian matrices.