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

Mechanics

Nov 14, 2013 (4 years and 5 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.

Rigid members between two joints.

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

-

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

-
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

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.