EXPERT SYSTEMS AND SOLUTIONS

Email: expertsyssol@gmail.comexpertsyssol@yahoo.comCell: 9952749533

www.researchprojects.info PAIYANOOR, OMR, CHENNAI

Call For Research Projects Final year students of B.E in EEE, ECE, EI, M.E (Power Systems), M.E (Applied

Electronics), M.E (Power Electronics)Ph.D Electrical and Electronics.

Students can assemble their hardware in our Research labs. Experts will be guiding the

projects.

The International Organization for Standardization gives a definition of robot in ISO 8373: "an automatically controlled, reprogrammable, multipurpose, manipulator programmable in three or more axes, which may be either fixed in place or mobile for use in industrial automation applications." This definition is used by the International Federation of Robotics, the European Robotics Research Network (EURON), and many national standards committees.

"A robot is a reprogrammable, multi-functional manipulator designed to move material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks." (Robotics Institute of America)

• Fanuc Robotics (Japan)• Kuka (Germany)• ABB  (1988 through merger of ASEA of Sweden

and Brown, Boveri & Cie of Switzerland)• Stäubli (Switzerland)• Adept  (USA)• Yskawa Motorman (Japan)

Robots are used in almost any industry where repetitive tasks are involved, or the task is difficult manually, or dangerous, such as

welding, painting, or surface finishing in the aerospace or automotive industries

electronics and consumer products assembly and inspection inspection of parts by robot assisted sensors or in the form of a Coordinate Measurement Machine (CMM)

underwater and space exploration hazardous waste remediation in government labs, nuclear facilities, and medical labs

Cartesian or gantry robot: Cartesian robots have three linear joints that use the Cartesian coordinate system (X, Y, and Z). They also may have an attached wrist to allow for rotational movement. The three prismatic joints deliver a linear motion along the axis.

Cylindrical robot : The robot has at least one rotary joint at the base and at least one prismatic joint to connect the links. The rotary joint uses a rotational motion along the joint axis, while the prismatic joint moves in a linear motion. Cylindrical robots operate within a cylindrical-shaped work envelope.

Spherical Robot Scara : Commonly used in assembly application, this selectively

compliant arm assembly is primarily cylindrical in design. It features two parallel joints that provide compliance in one selected plane.

Articulate: All joints are revolute. Most industrial robots are of this type.

Parallel Link: example Stewart’s platform, spider from Adept

Cartesian (PPP)Cylindrical (RPP)

Spherical (RRP) Spherical (RRP)

Robot consists of rigid links connected to one another by joints which allow relative motion of neighboring links

Links Joints

Prismatic: Sliding joint Revolute: rotation

End effector:

A the free end of the link chain (normaly wrist) is the end-effector. Gripper Welding torch Electro magnet Or any other tool

Payload is the maximum load the that robot can carry with out compromising its speed and accuracy.

Always specified at some distance from wrist.

Auxiliary payload: The load which can be put on other arms Normally much higher then actual payload

Number of independent variables used to define the configuration of the robot Number of motors used gives the dof of

robot In 3-D space the robot must have 6 dof

to position and orient the tool▪ 3-dof for positioning▪ Another 3-dof for orientation of the tool

Two types of work volume Dextrous : is that volume of space

which the robot end-effector can reach with all orientation

Reachable work volume: that volume of space which the robot can reach with at least one orientation

A taught point is one that the robot is moved to physically, and then the joint position recorded/stored

Points are taught using teach pendent

Repeatability is the precision by which the robot can be positioned at its taught point

The precision with which the computed points can be attained is called accuracy.

Computed point are points which the robot has to reach but were never taught to it. For example point coming from camera or directly programmed Accuracy is lower bounded by repeatability Accuracy is affected by the precision of

parameters appearing in the kinematic equations. E.x. Error in DH parameters

Real time i/o cards (analog and digital) can be attached

to robot controller i/o signals are read in real time and action taken There is a upper limit to the maximum number

of i/o the robot can access Non-real time

Cannot be used to generate interrupts Cannot be used modify the motion all ready

started OPC, serial communication etc, (manufacturer

dependent)

The orientation of an object can be defined by attaching a coordinate system to the object and then describing it with respect to some reference coordinate system

Tool coordinate system attached to the tool or end effector

Wrist coordinate system Attached to the wrist of the robot. Fixed during

manufacturing. Tool C.S is defined w.r.t this Base coordinate system

Attached to the work piece or table etc Global / world coordinate system

A fixed coordinate system w.r.t the robot. All other coordinate system gets calibrated with respect to this.

Actuator coordinate system

Translation: when origin one coordinate system (C.S.) is displaced w.r.t a ref. C.S. The axis remain parallel

Rotation: When one C.S. is rotated about any axis in some ref. C.S. This is described by a 3x3 rotation matrix.

Transformation = rotation and translation

To completely describe a tool with respect to some C.S we need to know both the Position of the origin of tool C.S And Orientation of the tool C.S

Frame includes both position and orientation of an object

Mapping between frames is carried out using Homogeneous transformation. It is a 4X4 matrix

Roll pitch yaw

anglean by Zabout rotate then and . anglean by

Yabout then , anglean by Xabout {b} rotate{A}.First

frame referanceknown a with coincident {B} frame thetart with

A

AA

S

Z-Y-X Eural angle

Z-Y-Z Eular angle

angleby Xabout rotate theand , anglean by Yabout

rotate then , anglean by Zabout {B} rotateFirst

{A}. frameknown with consident {B} frame Start with

BB

B

angleby Zabout rotate theand , anglean by Yabout

rotate then , anglean by Zabout {B} rotateFirst

{A}. frameknown with consident {B} frame Start with

BB

B

Equivalent angle axis

rule

handright the toaccording , anglean by K vector aabout {B} rotateFirst

{A}. frameknown with consident {B} frame Start withA

Forward kinematics Given the joint find the configuration

(orientation + position) of the Tool Coordinate Point (TCP) w.r.t world or base frame

Solution easy Use in coordinate measuring machine

Inverse kinematics Given the configuration of TCP find the

joint angle

A system is solvable if some algorithm exist to find all joint angles, given the end-effector position and orientation

Equation are nonlinear- difficult to solve Multiple solutions may exist Method of solution

Closed form solution▪ Pieper showed that robots having 6dof and 3

consecutive intersect at a point can have closed form solution

Numerical solution

For kinematic point a link is described by two attribute Link length “ai-1”

▪ Directed from axis “i-1” to “i”

Link twist “i “▪ As per rigahd rule

thumb along “ai-1” Each link is numbered

starting from zero for the ground link or Base link

When is “ai-1” not defined uniquely ? Axis intersects Axis are parallel

When is “i “ not defined uniquely?

Choose what ever suits you.

When one link is described w.r.t another link two more parameters come into picture Link offset “di” Joint angle “i”

Either of to is variable Prismatic d is variable Revolute is variable

These four parameter ai-

1,i, di,i is called Denavit-Hartenberg parameter

“d” and “” What is the direction of “d” and

Pointing from axis “i-1” to “I” For use right hand rule

Now will fix coordinate system to each link

Axis specific motion PTP the fastest motion

Path related motions Linear Circular Spline

Multiple solution is a problem for PTP motion only

How multiple solution is help full ?Obstacle avoidanceOccurs only in case of PTP motion

Orientation control: The orientation of a tool can be different at the start

point and end point of a motion. There are several different types of transition from the start orientation

to the end orientation.Types of control

Slandered Wrist PTP constant

The orientation of the tool changes continuously during the motion. The orientation is achieved by rotating and pivoting about the TCP.

The CP motion is broken down into several small PTP motions by the robot controller.

This excludes the possibility of a singularity occurring in the case of Wrist PTP. The robot can deviate slightly from its path, however.

Wrist PTP not suitable if the robot must follow its path exactly, e.g. in the case of laser welding.

The orientation of tool remains constantStart position orientation is fixedEnd position orientation is disregarded

Needs 3 pointsDraws only half circle (specific to KUKA)

Singularity comes from matrix inversionone to one correspondence between

joint C.S and Cartesian C.S. is lotSingularity is a configuration of the

robotOne or more degree of freedom is lostSmall change in Cartesian coordinate

results in large change joint motion.

For articulate 6 dof robot 3 types of singularity exists ( for example KukaR6) Overhead: the wrist root point (intersection of axes A4,

A5 andA6) is located vertically above axis 1.

Extended: the wrist root point (intersection of axes A4, A5 and A6) is located in the extension of axes A2 and A3 of the robot. The robot is at its limit of work volume

Wrist : In the wrist axis singularity position, the axes A4 and A6 are parallel to one another and axis A5 is within the range ±0.01812°

It is a multidimensional form of derivative Relates joint velocity with Cartesian co-

ordinate. It is square matrix called J J is a function of joint angles When the Jacobian becomes singular i.e.

det(J) = 0, under certain configuration the, the robot is said to be in singular position

SCARA Robot Kinematics A 4-axis SCARA (Selective Compliance Assembly Robot Arm) robot has

parallel shoulder, elbow, and wrist rotary joints, and a linear vertical axis through the center of rotation of the wrist. This type of manipulator is very common in light-duty applications such as electronic assembly.

Mechanism Description In this example, the upper-arm length (L1) is 400 mm, and the

lower-arm length (L2) is 300 mm. The shoulder joint (S), the elbow joint (E), and the wrist joint (W) have resolutions of 1000 counts per degree. Rotation in the positive direction for all 3 joints is counter-clockwise when viewed from the top. The vertical axis (V) has a resolution of 100 counts per millimeter, and movement in the positive direction goes up. When the shoulder, elbow, and wrist joints are at their zero-degree positions, the two links are both extended along the X-axis and the tool orientation C is at zero degrees. When the vertical axis is at its home position, it is 250 mm above the Z-axis zero point. Due to wiring constraints, rollover of the rotary axes is not permitted.

Forward Kinematics

Inverse Kinematics Limiting ourselves to positive values of the elbow (E) angle, producing

the right-armed case (done by selecting the positive arc-cosine solutions), we can write our inverse kinematic equations as follows:

Vz

WESC

EESLSESLSLy

EESLSESLSLx

)cos()}cos()cos({

)sin()}sin()sin({

221

221

Velocity of tool point w.r.t joint speed

Or in matrix form

1000

0111

00)cos()cos()cos(

00)sin()sin()sin(

*

1000

0111

00)cos()cos()cos(

00)sin()sin()sin(

221

221

221

221

ESLESLSL

ESLESLSL

J

V

W

E

S

ESLESLSL

ESLESLSL

z

c

y

x

0

0

)(21

E

JwhenySingulatit

ESinLLJ