Lecture 2-6-13, Power Point [PPTX]

taupeselectionMechanics

Nov 14, 2013 (3 years and 11 months ago)

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Anatomy

Similar to human torso, shoulder, arm, and wrist in
construct, movement, and reach.










Joints



Enables rotation of connected members.




Provides the axes of rotation for adjoining members.


Links



Rigid members between two joints.


Robot Joints & Links
Groover

Fig. 8.1
-
8.2


Joints

-

Enables linear or rotational movement of adjoining members.


Number of joints = Degrees of freedom



Linear


(L)



Orthogonal

(O)


Rotational


(R)


Revolving


(V)


Twisting


(T)







Lab SCARA
:


Revolving
-

Rotational
-

Orthogonal


Twisting

Lab Cartesian
: Linear


Linear


Orthogonal


Twisting

Articulated Robot
: Twisting


Rotational
-

Rotational


Gripper Joints


Yaw (Z rotation), Pitch (Y rotation), Roll (X rotation)

Robot Joint Types
(
Groover

Fig. 8.2
Find an error
)








Linear





Orthogonal









Rotational






Revolving




Twisting



Jointed Arm (Articulated) Robot


Robot Configurations
Groover

Fig. 8.3
-
8.7


Polar coordinate (T
-
R
-
L joints)


Cylindrical (L
-
R
-
R or L
-
V
-
R joints)


Cartesian (Rectilinear) (L
-
L
-
O joints)

Reversal:


Articulated (Rotational, Jointed Arm) (T
-
R
-
R joints)


SCARA (V
-
R
-
O
-
T)

Reversal:


Tool Configuration
: Rotation on Tool XYZ coordinates


Yaw


Y axis

Pitch


X axis

Roll


Z axis


Robot Configuration




Articulated


(Rotational)



Cartesian



SCARA


Robot Configuration



Polar





Cylindrical


Applications & Set up Location

Applications


Primary uses
: Part pick & place, part presentation,





transferring, visual inspection.


Solutions for
: Hazardous conditions, tedium, ergonomic





issues, positional accuracy, and precision.


Economic life:
General purpose machine. Extension of useful





life with attachment of a new end effecter.

Set up Location


Fixed (Robot centered, In
-
line, Off
-
line).


On
-
track (Floor or Ceiling). Ex. Robotic clamp in press work.


Free roaming.


Robot Kinematics

Degrees
of Freedom



Same as number of joints

4
-
axes for
assembly

robots:



SCARA (
x, y, z, r
)

6
-
axes for
material

handling

robots:
Articulated

arm robot

Base, links
-

θ
1
, θ
2
, θ
3.


Wrist
: y,
p, r (
yaw
, pitch, roll)


Positioning

Lead screws for linear move or belt
-

or direct
-
drive servo motors
for joint rotation.


Drive Power



Electric, hydraulic, pneumatic.




Motor type: open loop (stepper) or closed loop (servo).


Motion Control



Servo motor for rapid rotation of the upper joints.


Stepping motor for precision movement of the lower joints.


Robot Kinematics

Coordinate Systems

-


Cartesian (World)
-

X, Y, Z.





Polar (Joint)
-

θ
1
, θ
2
, θ
3
. Tool


(
y, p, r
)


Wrist

Assembly



Typical
, 3
degrees of freedom (Fig. 8.8).





Keyed flange for gripper connection.


End Effecter (Gripper)


Electric, pneumatic, vacuum, magnetic.






May have a separate coordinate controller.


Movement Path



PTP, Straight or curved motion under robot control.


Linear/circular interpolation under program control.


Absolute vs. Relative
(Cartesian: ΔX, ΔY, ΔZ; Rotational: Δ θ
1
, Δ θ
2
, Δ θ
3
)



Set P1 = Trans (x, y, z, y, p, r);


r: Gripper angle on X
-
Y



Set P2 = P1: Trans (
dx
,
dy
,
dz
, , ,
dr
); Δ offsets from P1

R
-
R Robot: Polar to X
-
Y Conversion


Length/height:




L
0

= Shoulder, L
1
= Upper arm, L
2
= Elbow


Angles (Relative):



θ
0

= Base pivot, θ
1
= Upper arm , θ
2

= Elbow



r = L
1

Cos θ
1
+ L
2

Cos (θ
1
+ θ
2
)

X = r Sin θ
0

Y = r Cos θ
0

Z = L
0

+ L
1

Sin θ
1
+ L
2

Sin (θ
1
+ θ
2
)


Exercise:
Develop an extension for a R
-
R
-
R robot.

θ
0

θ
1

θ
2

L
2

L
1

L
0

x

y

z

(X, Y, Z)

Z

r


X

Y

(X, Y, 0)


T

R


R

Polar and Cartesian coordinates of T
-
R
-
R Robot




r = L
1

Cos θ
1
+ L
2

Cos (θ
1
+ θ
2
)





2
< 0 for left elbow]

X = r Cos θ
0

Y = r Sin θ
0

Z = L
0

+ L
1

Sin θ
1
+ L
2

Sin (θ
1
+ θ
2
)

Robot Operation
-

Features


Programming Tool


Teach (Lead
-
through path), Program
code, Simulator/Code generator



Signal Interface



I/O ports for exchanging signals with
other in
-
line equipment



Vision Guidance



Positioning, Gripper orientation,
Gaging
, Shape recognition, Part ID, OCR inspection



Safety Interlock



E
-
stop, motor stall sensor, light curtain,
pull cord, enclosure


Work Envelope

The 3
-
D space reachable by end effecter
-

Sweep area.

Safety Envelope


Additional 12” around the work envelope.


Lab 550 Robot


Plan View






Steps for constructing SCARA work envelope



for Problem 6


1.

With the lower arm fully opened, draw the path of the wrist
from zero
to the maximum rotation of the upper arm.

2.

Repeat Step 1 with the lower arm fully closed.

3.

With the upper arm fully opened, draw the path of the wrist
from zero to the maximum rotation of the lower arm.

4.

Repeat Step 3 with the upper arm fully closed.







Θ
1

= [0, 180
°
]



Θ
2 = [0, 135
°
]


L1

L2



SCARA Work Envelope Construction

C.R., Accuracy, Repeatability

Linear Positioning System


Control Resolution



Distance between two adjacent addressable points



C.R. determined by mechanical limit


Repeatability

±

3
σ


(
σ
: mechanical error)


Accuracy



½ of C.R.
±

3
σ




Ex
.
Lead screw mechanism with gear driven by stepping motor



XY bench on CNC machine, Z
-
axis drive on SCARA robot.


Extension to XYZ rectilinear and
θ
1
θ
2
θ
3

angular reach space.