Introduction to the Robot Cell

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Nov 13, 2013 (3 years and 8 months ago)

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Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
1



Manufacturing Systems Laboratory

Introduction to the Robot Cell

The robot cell in the Manufacturing S
ystems laboratory contains two industrial robotic arms
made by Kuka Roboter which
are designed for use in the automobile assembly industry. The
cell also contains tools
, equipment
, conveyors
,

sensors and controllers which are connected
to work with these two arms. These arms are used for teaching and student projects,
including projects

on prototyping and control systems.


The following documentation is intended as an introduction to the Kuka robot cell. More
detailed documentation is available including a user guide, a tutorial guide, programming
manuals and hardware specification shee
ts.

It is intended for distribution to staff, students and the general public.





Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
2


Contents.

Introduction to the Robot Cell



Page 1

Safety in the Kuka Robot Cell



Page 3

Size and Capacity of the robot Cell


Page 4

C
ontrollers

for the robot cell.



Page 5

Emergency Stop System




Page 5

Robot TCP Controllers

and
Cell Control Panel.

Page 7

R
obot inputs and outputs



Page 8

Tool Power s
upplies

and Grippers


Page 9

C
onveyors





Page 10

Program Setup





Page 11

Tutorials

User Programming




Page 13

Cartesian
Co
-
ordinate Programming


Page 15

Sensor Examples




Page 16

Advanced Programming T
echniques


Page 19

Auxiliary Control




Page22








Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
3



Safety in the Kuka Robot Cell

The Kuka robotic arms are heavy, powerful machines capable of inflicting serious harm by
crushing or l
aceration. The machines each weigh

around 250kg and draw a peak power of
around 10 kilo
-
Watts. The robot cell is prot
ected by a light gate rated by appropriate
or
ganisations for safety applications

which triggers an emergency stop whenever an
yone
enters the cell, this prevents anyone from accidentally moving into the path of a moving
robot.

It is essential that any operators are fully familiar with the safety requirements in the User
Guide before operation the system. Only authorised people wh
o have a
n adequate level of
training are permitted to

use the system.



It’s Big and

Powerful!!!

Keep out of the robot cell

when in operation
.





Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
4



Size and Capacity of the Robot Cell

Each
of the robotic arms measures 2.2

metres in height when fully extended vertically and
has a horizontal reach of 1.6 metres. Payload is up to 15 kilos and maximum speed is 2
metres per second with linear movement or a 180 degree rotation in 2 seconds with point
to point movement.

The robot

arms each weigh in at around 250kg and draw up to
10kWatts
of power at peak operation.





The robot cell measures 6 metres by 3.5
metres with the range of the two arms
overlapping slightly. Conveyors with a
capacity of up to 50kg allow work pieces
to be t
ranslated between the two arms
while a turntable with a similar capacity
is located in the overlapping workspace.

Communication with the cell is through
USB ports or re
-
writable CDs using plain
text files. These can originate from
scanner packages, graphic

design or
mathematical computer packages.

Communication with sensors and
auxiliary motors and valves takes place
through a Devicenet serial
communication module.




Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
5



C
ontrollers

for the robot cell.

Power
is distributed through a controlling cabinet which contains motor drivers, PLC logic for
monitoring position and computers for the human
-
machine interface.


Control
Cabinet

for KR16 . . . . and KR15

The cell
also
requires a 240V AC supply for a numbe
r of features, most essentially the emergency
stop system
, but also tools, conveyors and other auxiliary systems
.
The cell also uses compressed air
for grippers and some tools.








Emergency Stop System

The emergency stop system for the
robot cell is configured
to trip an emergency stop on both of the
robotic arms if any person enters the cell or reaches through the window.

The triggering mechanisms consist of a 40 beam SICK C4000 light gate
rated for finger detection
operating across the

cell window and a 3 beam SICK M4000 light gate across the do
or plus a keyed
stop with remov
able key on the control panel.

Any one of these can trigger a stop.


3 Beam light gate for the door to the cell.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
6








40 Beam Sick light gate covering the
window of the cell







Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
7



Robot
TCP
C
ontrollers

The robot controllers
can be monitored

from the

LCD screen of the

controlling hand held TCP unit or
from auxiliary screens or projections.





Cell Control Panel
.

The cell control panel allows switching of

the emergency stop system, conveyors
, pneumatics and
auxiliary 240V.

I
ndicator lights and two LCD displays
provide feedback in addition to the two TCP
controllers.






Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
8



Robot Inputs and Outputs

A number of digital inputs and o
utputs are available on all
robots to allow them to detect the results
of sensor processing and to communicate in a simple manner with one another.

There are also two
analogue inputs available for the Kr16 KrC2 controller.

Inputs and outputs for the Kr16 controller are handled by a D
evicenet communication module which
is located outside of the control cabinet and communicates with the robot computer through a five
wire serial bus.
Most sensors are processed by

a
PLC logic

module

which is capable of doing
analogue to digital assessment
s, pulse counting, and frequency measuring
.
Outputs from the K
uka
controllers also go

to PLC logic which can be configured to do a number of tasks

including the
switching of motor controllers, solenoids and relays
.

Video.

Cameras which include a miniature

borescope camera are available to allow close up observation of
processes from outside the cell.







Wide angle camera on the scorbot robotic arm


Borescope camera on Kr16 robot




Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
9


Tool Power Supplies.

A switchable AC 240V power supply exists
inside the cell for the powering of tools that may be
mounted in the robot cell. This can be switched from switches on the cell control panel

including the
auxiliary emergency stop
.

240 Volt outlet



A 12 Volt, 8 Amp DC power supply is mounted on the shoulder of each robot arm and is intended for
the powering of DC powered tools.
There are also switchable compressed air supplies.

G
rippers

The pneumatic grippers attached to the wrist of each robotic arm

are intended to allow for a quick
changeover of tools without the need to unscrew bolts or other mechanisms.
W
hen the air pressure
is applied the grippers have a holding force in excess of 15 kilograms and therefore secure any tool
that the robot can han
dle.

Gripper ope
n and closed
.



Tools n
eed to have a baseplate with four

notches which fit into lugs on the gripper. The baseplate is
secured front and rear by lapping plates
on the gripper
to prevent any possibility of it falling out.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
10




Baseplate

of tool





Mounted on the gripper

In addition to attaching the tool it will also be necessary to make any electrical power and
communication connections and pneumatic connections.

Conveyors

Two conveyors and a turntable are available within the robot cel
l for the manoeuver of work pieces
relative to the robotic arms. Each can be controlled from the

control panel and each can be reached
by both of the arms. They all have a maximum payload of 50kg.


Turn

table and straight conveyor for mould making.





The loop
conveyor allows work pieces to be moved to the robots in a continuous cycle, which is
often used to repr
esent a production process or to bring different work pieces to the robotic arms.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
11






Program Setup

Base Frames of
Reference.

Frames of reference can be established for the robotic arms to align their movement with the
conveyors and tables within the cell

and with the other machine, they

allow both arms to be aligned.

An example of this is the mould making frame of ref
erence
.

For the Kr 16 t
his has the following offsets: X 1000, Y 0, Z 950, A 29, B 0, C
-
1.


For the Kr15 this has offsets: X 600, Y
-
950, Z 950, A
-
90, B 0, C 0.



This allows both machines to work
on the same piece with the same data.



Y

X

Z

Z

X

Y



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
12



Tool Definition

Tool definitions can be defined to allow orientation to take place about a point in space relative to
the tool tip.

Tool 3 Grinder

This is intended for use with the pneumatic grinder.




USB
Connection

The controlling computer for each of the KrC robot controllers have a number of USB ports available,
which can take memory sticks.

It is possible to provide some ( but not all ) of the programming for the robots source files from a
text ( .txt )

file on a memory stick

or CD
. This can be produced on any PC using a wide variety of
programs. A thorough knowledge of expert programming is required to do this.

Tools

Tools need to be custom built for specific applications. However a number of tools exis
t in the lab
including an electric router, a pneumatic grinder, DC powered hot wire for cutting polystyrene and
vacuum suction pads.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
13



A few of the robot tools


Tutorials

The tutorials and examples described

in
the following pages are used

to introduce st
aff and
students to the programming and control of the system. Those wishing to do a ‘project’
within the cell will probably need to spend 20 hours in the laboratory familiarising
themselves with the system before starting the project. Those that wish to d
o ‘research’ will
need to spend in excess of 100 hours.

See the
T
utorial
G
uide for the details of each tutorial.

Pr
ogramming manuals written by Kuka Roboter are available within the laboratory in paper
and software versions. All programming must start with

User programming even when more
sophisticated routines will be included. Advanced programming will require Expert level
programming and use of the editor.

The manuals available in the lab total 630 pages in 9 volumes in addition to this document.



Use
r Programming


programming at the simplest level.

This tutorial is designed to introduce staff and students to programming of the Kuka robots at

the
simplest level
.

The tutorial is designed to familiarise

the user with control of the robotic arms through
the TCP
controller.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
14




Tasks include reseting the emergency stop system, jogging the robot , starting a program and
entering moves into a program.







The intended program
should contain at least one point to point, one linear and one circular move.
It
should contain some continuous and non
-
continuous functions. Linear speeds should be around
0.3 m/sec and point to point should be around 30% but make changes to these values to suit the
program. Acceleration should be around 30% and feel free to include s
ome tool definitions.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
15




Circular

move with orientation change
.





Cartesian Co
-
ordinate Programming


cutting a model car.

The model car cutting exercise is intended to familiarise staff and students with the cartesian co
-
ordinate system in the kuka

robot and the method of programming designs into the system which
can then be cut automatically.

Hotwire cutting of polystyrene is one of our quickest and simplest processes
,

o
nce students are
familiar with this they can move on to more complex systems wi
thin the robot cell.

Syntax
Example

; X
-
Z profile for a Aston Martin DB4

LIN { X
-
35.0, Z 0.}

LIN { X
-
35.0, Z 31.0}

CIRC { X
-
32.0, Z 34.5},{ X
-
27.0, Z 36.0}

…………

LIN { X 35.0, Z 0.}


; Y
-
Z profile of Aston Martin DB4



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
16


LIN { Y 0.0, Z 10.}

LIN { Y 14.0, Z
10.}

…………….

CIRC { Y 138.0, Z 44.0},{ Y 168.0, Z 33.0}

LIN { Y 168.0, Z 17.0}















Sensor E
xamples

Non
-
contact sensors in the lab include infrared, ultrasonic and inductive sensors. These need to be
installed for specific applications and
connected to the appropriate robot controller inputs if they are
to trigger automatic reactions.

Infra
-
red Sensors

Two

tutorial examples are available
using infra
-
red reflactive sensors. These cover sensors mounted
on the conveyor and on a tool, to detect

the arrival of a pallet and whether a path is clear or
blocked.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
17






Infra
-
red Sensor

on the conveyor


and three on a tool

Pallet in position

with inputs 3 and 4 True.











Infra
-
red sensors preventing a collision with a mag
wheel and

two

2 meter range sensors.

Ul
trasonic sensors

The two ultrasonic range finders located in the cell monitor the loop conveyor and can be used to
locate the position of

items on the conveyor. The sensors are connected to analogue input channels
1 and 2 on the Kr16 controller.

U
ltrasonic rangefinder
s monitoring a

mag wheel.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
18






Laser Referencing

Laser referencing is used to establish tool offsets and to provide
accurate alignment

of frames of
reference to known lines. It uses a laser diode and light receiver to create a through beam with the
reciever connected to the robot inputs.





Laser beam

masked by

a tool tip.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
19






Light reciever








Laser Diode


Advanced Programming Techniques

Inverse Kinematics

The Inverse Kinematics example is intended as a simple display of how to derive complex
relationships between axes. This program takes known angles of three of the
robot
axes and uses
these values to deriv
e the three equations which will establish a straight line in space parallel to one
of the conveyors.

Curve Fitting

In this example a smoothly curved surface is created from a number of known points. The first

example is in two dimensions ho
wever it is rel
atively easy to expand the system out to three
dimensions.

The example which we

use is an aircraft wing with the cross sectional profile shown
below:

Cross sectional curve of aircraft wing


The cutting part of the program is shown below.


I=0

WHILE I<4

POSITION.X=STARTX+(12*I*I)

POSITION.Z=STARTZ+(18.67*I)
-
(2.0*I*I)
-
(0.67*I*I*I)

POSITION.A=5
-
(1*I*I)

LIN POSITION C_VEL

I=I+0.1

ENDWHILE





Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
20










This is a fairly simple two dimensional example with
an orientation in the A co
-
ordi
nate to produce a
tapered wing.

More complex arrangements are possible to create three dimensionally curved surfaces. Examples
that have been done in the robot cell include ‘Spitfire’ wings with the curved plan view and cross
section, yacht hull models, fan blades and aerod
ynamic cockpit canopys
.


Downloading D
ata
A
rrays

Data from a variety of sources including scanners, design packages and mathematical software can
be loaded into the robot for operational purposes.


Rapidform computer graphic model

For this example
Rapidform w
as used to create the model and

ASCI Point files
are used to pass the
point data to the robot controller.

Cutting the wax mould



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
21





A program is written to cut a mould from the data points available. This mould was then used to
create a
fibreglass part.






The finished piece
































Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
22














Auxiliary Control

I/O for auxiliary control

Connection to all of the auxiliary systems within the robot cell is done via the I/O system which
consists of a Devicenet
communication module which is wired to a Programmable Logic Controller.
The PLC recieves signals from the robot programming and from control panel switches and can
switch on output relays to start other units.

Three Phase AC Motors

Three phase motors are driven from a controller which provides forward/reverse, on/off and speed
and acceleration control. The example here is made by Telemecanique and uses a 240 Volt single
phase supply.






Three phase motor controll
er with the control panel open
.

Our example motor is a 360W motor being driven by 240V from the motor control unit. Also
attached to the motor are an inductive sensor which detects the passing of a lug on the shaft of the
motor and an incremental sensor u
nit which is attached via a belt drive to the shaft and gives 500
pulses per revolution of the shaft. Both the incremantal sensor and the inductive unit are connected
to the controlling PLC with the incremental sensor connected to a fast counter and the in
ductive
sensor connected to a normal counter.

The three phase motor used in our example



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
23






Inductive sensor

Connection to controller




Incremental sensor

Although the system always requires significant amounts of tunin
g it is possible to have
auxili
ary

systems such as tools
,

conveyors and turntables operating in this manner.

Much more sophisticated

versions of these systems are also available.




Pneumatics

Pneumatics are frequently used for grippers, reciprocating systems and some linear
actuation. The
y

are controlled by the electronic switching of solenoid valves from the robot controller.

Solenoid triggered pneumatic valve.



Restrictor valve.







Pneumatic Cylinders
r
etracted

wit
h the electrical limit switches.



Manufacturing Systems Lab. Robot Cell


Author: Ken Snow


2012


Page
24




H
ydraulics

Hydraulic systems are generally used for high load operations involving payloads of hundreds or
thousands of kilos.
Pumps are driven by three phase electric motors, while directional valves are
switched electronically with solenoid valves.

Hydraulic pump


Return


Out

Solenoid valves





25mm and 40mm cylinders with a 300mm stroke.