Introduction to robots, classification of robots, Kinematics of robot manipulator, Introduction to a mobile robot, kinematics of mobile robot, sensors used in robots, microcontrollers for robots

1. Nikhil Shrivas
Assistant professor
Department of Mechatronics Engg.
Manipal University Jaipur
AN I NTRODUCTI ON TO ROBOTICS
Classification, Kinematics and hardware

2. Contents
1) Why robotics?
2) Types of robots.
3) Robot Manipulator
4) Mobile Robots
5) Sensors and actuators.

3. Introduction
Random House Dictionary: A machine
that resembles a human being and
does mechanical routine tasks on
command.
Robotics Association of America: A
robot (industrial robot) is a
reprogrammable, multifunctional
manipulator designed to move
materials, parts, tools, or specialized
devices, through variable programmed
motions for the performance of a
variety of tasks.

4. Types of Robot
Robot Manipulators Mobile Robots
Figure 1. Examples of robot Manipulators. Figure 2. Examples of Mobile Manipulators.

5. Legged robots
Underwater robots
Wheeled mobile robots
Aerial Robots
• Locomotion
Figure 2. Examples of Mobile robots.

6. Robot Manipulator
Figure 4. robotic frame relative to world co-ordinate. Figure 5. Different robot frames.

7. Two frames kinematic relationship
There is a kinematic relationship
between two frames, basically a
translation and a rotation.
This relationship is represented by a
4 × 4 homogeneous transformation
matrix.
Figure 6. Two frames with kinematics representation .

8. Homogeneous transformation
Rotation matrix
R is orthogonal ⇔
independent entries, e.g., Euler
angles
3
T
R R I
 
Revolute Prismatic
Figure 7. Manipulator Joints.

9. Open kinematic chain
In manipulator robotics, there
are two kinematic tasks:
Direct (also forward) kinematics
– Given are joint relations
(rotations, translations) for the
robot arm.
Task: What is the orientation and
position of the end effector?
Inverse kinematics – Given is
desired end effector position and
orientation.
Task: What are the joint rotations
and orientations to achieve this? Figure 8. Open Kinematic chain.

10. Direct kinematics Inverse kinematics
For a kinematic mechanism, the
inverse kinematic problem is difficult to
solve.
The robot controller must solve a set
of non-linear simultaneous algebraic
equations.
Source of problems:
• Non-linear equations (sin, cos in
rotation matrices).
• The existence of multiple solutions.
• The possible non-existence of a
solution.
• Singularities.
Figure 9. Direct kinematics of a manipulator
(representation of frames).

11. Types of mobile robot
The types are classified based on the actuation, locomotion and wheel configurations.
Figure 10. Different types of mobile robots
Mobile robot
Holonomic
3-wheel 4-wheel
Nonholonomic
Differential
2-wheel
Caster support
Inverted
pendulum
4-wheel
Steering
Tri-cycle
Ackerman
steering
unicycle

12. Holonomic mobile robot
The motion along all the axes are unrestricted, i.e. having higher maneuverability.
Also called omnidirectional (w.r.t. ground) robot.
The wheels are having free to slide along the axis of
Rotation.
X
Y
Y’
X’
𝜃
O(0 0 0)
O’(𝑥 𝑦 𝜃)
Figure 12. 3-wheel Omnidirectional mobile robot
Figure 11. Omnidirectional mobile robot

13. Cont.
◦ The three wheeled robot in figure 3 are capable of linear motion along infinite possible direction
from its current position as depicted in figure 2.
◦ These motions are obtained by utilizing the property of vector summation of the velocities produced
by all three wheels along their tangents.
◦ The other omnidirectional robot is based on the special mechanism-based wheel, known as
mecannum wheel.
13
Figure 13. mecanum wheel Figure 14. Design of mecanum wheel

14. cont.
The rollers in the wheel are at 45
degrees from axis of rotation of the
wheel, thus producing a lateral
motion.
The robot and its motion is shown in
figures below.
The net direction of resultant vector
is responsible for
The omnidirectional motion
Figure 15. Omnidirectional design based on wheel vectoring

15. Nonholonomic mobile robot
The motion of the robot along one of its axes is restricted,
also known as nonholonomic constrain.
In the figure, the wheels can rotate in same
direction with equal speed to produce a
pure linear motion along X-axis.
The changing the direction of rotation while
Keeping speed same gives pure rotation about
Z-axis.
The difference in speed (hence differential) is
produced to obtain a curved trajectory.
However, the motion along Y-axis is restricted,
hence called nonholonomic mobile robot.
Figure16. Nonholonomic wheeled mobile robot

16. Differential mobile robot
Based on the utility and power requirement, the number of actuators can be increased or decreased.
The most common are 2-wheel and 4-wheel differential drive robots.
The inverted pendulum design based on 2-wheel is an unstable system known as Segway platform.
Figure 19. Differential (4-wheel)
drive
Figure 17. Differential (2-wheel) with
caster wheel
Figure 18. Differential (2-wheel)
Segway

17. Unicycle
The complexity of this robot is greater than every
other types of mobile robot.
The motion are restricted in two directions i.e. pure
rolling about Z-axis and the linear motion along the Y-
axis.
However, the change in the center of mass plays
important role in maneuvering.
Figure 20. Unicycle robot

18. Steering based robot
The steering can be applied to single front wheel (in tri-cycle), double front wheel
(Ackerman steering).
The robot’s curved motion is obtained about a point in the plane also known as
instantaneous Centre of curvature/rotation (ICC/ICR).
Figure 21. tri-cycle robot Figure 22. Ackerman steering robot

19. Mobile Robot Maneuverability
 The maneuverability of a mobile robot is the combination
 of the mobility available based on the sliding constraints
 plus additional freedom contributed by the steering
 Three wheels is sufficient for static stability
 additional wheels need to be synchronized
 this is also the case for some arrangements with three wheels
 It can be derived using the equation seen before
 Degree of mobility
 Degree of steerability
 Robots maneuverability
m
s
M m s

20. The basic types of 3-wheel robot
Based on different designs, the robot’s ability to perform motion i.e. its maneuverability is
obtained for tri-cycle robot.
Figure 23. Maneuverability of tricycle mobile robot with different designs

21. Locomotion of mobile robot
The locomotion is defined by the number of actuators, types of wheels and
design of the robot.
 Assumptions in wheels
 Movement on a horizontal plane
 Point contact of the wheels
 Wheels not deformable
 Pure rolling (vc = 0 at contact point)
 No slipping, skidding or sliding
 No friction for rotation around contact point
 Steering axes orthogonal to the surface
 Wheels connected by rigid frame (chassis)
 .r
v
YR
XR

P
YI
XI
Figure 24. Mobile robot in 2-D plane

22. Kinematics of Differential drive
1) Specify system measurements
2) Consider possible coordinate
systems
3) each wheel must be traveling at the
same angular velocity around the
ICC
4) Determine the robot’s speed around
the ICC and then linear velocity
5) Determine the point (the radius)
around which the robot is turning.
w(R+d) = VL
w(R-d) = VR
Thus, w = ( VR - VL ) / 2d
R = 2d ( VR + VL ) / ( VR - VL )
So, the robot’s velocity is V = wR = ( VR + VL ) / 2
Figure 25. ICC“ instantaneous center of
curvature”
x
y
VR
VL
2d
ICC
R
w
V

23. Figure 26. Nomad 200
• Wheel velocities are linearly related with actuators
speed.
• Have to obtain position and orientation w.r.t. given
velocities
Vrobot = Vwheels
wrobot = wwheels
x(t) =  Vwheels(t) cos((t)) dt
y(t) =  Vwheels(t) sin((t)) dt
(t) =  w(t) dt
position
velocity
y
x
 w
Vwheels
ICC at 
Forward kinematics, velocity and position

24. Inverse kinematics: differential drive
Key question: Given a desired position or velocity, what can we do
to achieve it?
Figure 27(a). starting
position
Figure 27 (b). final
position
x
VR(t)
VL (t)
y
𝑃𝑖

25. Turn so that the wheels are parallel to the line between the original and final position
of the robot origin i.e. line connection the robot and desired point.
Drive straight until the robot’s origin coincides with the destination.
Rotate again in order to achieve the desired final orientation.
Usual approach: decompose the problem and control only a few DOF at a time
-VL (t) = VR (t) = Vmax
VL (t) = VR (t) = Vmax
VL (t)
t
VR (t)
-VL (t) = VR (t) = Vmax
Figure 28. set of motion of actuators

26. Inverse kinematics: four-wheel robot (Ackerman Steering)
VBL
VBR
VFR
VFL
x
y
ICC
aR
aL • Similar to a tricycle-drive robot
wg
r
g
d
d
VFR
=
sin(aR)
r =
g
tan(aR)
+ d
determines w
Figure 28. Four-wheel robot
•The other wheel velocities are
now fixed!
wg
VFL
=
sin(aL)
aL = tan-1(g / (r + d))
w(r - d) = VBR
w(r + d) = VBL

27. cont.
After finding out the front and real wheel velocities, the net velocities for the differential mode
can be obtained as
𝑉𝐿 𝑡 = 𝑉𝐹𝐿 + 𝑉𝐵𝐿
and
𝑉𝑅 𝑡 = 𝑉𝐹𝑅 + 𝑉𝐵𝑅
The obtained left and right velocities can be converted to respective wheels angular velocities.
With the help of proper actuation and control, the robot can be maneuvered easily to obtain
desired position.
Inverse kinematics: four-wheel robot (Ackerman Steering)

28. Sensors and
Actuators
 There are various types of sensors
needed for robot’s positioning and
control.
 For example, the position of the
robot can be tracked using Optical
encoders, motion camera, GPS etc.
 For collision avoidance and
maneuvering, Ultrasonic sensor,
Lidar, IR based proximity sensor
and radar are used.
LIDAR
RADAR
GPS
ULTRASONIC

29. Cont…
 For path detection and
environmental mapping, a camera
pair is used to imitate human eye.
 For providing power to the wheels
i.e. locomotion, mainly three types
of motors are used. The DC motor,
Stepper motor and AC motor.
AC motor
DC motor
Stepper motor
Camera pair eye

30. Driver
 For various types of actuators, we need
drives to control the motion.
 Among actuators, DC motor is controlled
easily, but AC motor is most difficult to
control.
 The control of Stepper motor is
moderate.
AC motor Driver
DC motor Driver
Stepper motor Driver

31. Brain/Controller
 Most general way to control robot is using microcontroller. However, some
simple tasks can also be executed without programming, using the logic gate
arrays.
 The programming is inversely proportion to the hardware.
 Some of the most common controllers are shown in the following figures.
 The common communication protocols are Serial, I2C, UART, CAN Bus, TCP/IP,
UDP etc.
Arduino Uno
Xilinx FPGA Spartan 6
AVR ATMega32 Raspberry Pi 4
NI Compact Rio

32. Thank you