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PATH PLANNING OF ROBOT ASSISTED SHEET
METAL BENDING IMPROVE PRODUCTIVITY
Authors: Priyanka Sairam1, Dr.S.V.Prakash2, Hemavathy.S3
1 IV Sem M.Tech (CIM),Dept of Mechanical Engineering, M.S.Ramaiah Institute of Technology,Bangalore -54.
2 Professors, Dept of Mechanical Engineering, M.S Ramaiah Institute of Technology, Bangalore -54.
3Assistant Professor, Dept of Mechanical Engineering, M.S Ramaiah Institute of Technology, Bangalore -54.
Email: priyankasairamr11@gmail.com
Keywords: Sheet Metal Bending, Robot
Programming, Teach pendant, Productivity
Abstract
The handling of material is a high resource
consuming task in many different manufacturing
industries. Global demand for material-handling
products is projected to rise by 7.0 percent annually
until 2014. Advanced automation and robotics
technologies can enhance the productivity of this
process, guaranteeing at the same time the highest
level of safety for workers. The sheet metal
bending operation is very time consuming and
laborious process when done manually. Because
during the bending operation, the space for
maneuvering a sheet metal part is very small,
collisions between the part and bending tools are
likely to occur. When a robot is used to handle the
part, the role of an automatic path-planning tool
becomes more significant. In this study the robot is
programmed to bend the sheet metal part, which is
done by using teach pendant. With this teach
pendant the robot is first taught the optimum path
so that it can perform the required task within
minimal time for the handling as well as feeding
the part to the bending machine. The robot then
moves in the same path in the remote mode as it is
taught when the robot is interfaced with PLC using
human machine interference. Finally the robot
assisted bending was able to achieve an increased
productivity.The productivity results, throughput
rate, comparison between manual and automated
process results and cost savings are included.
1 Introduction
The sheet metal industry has focused on the
automation of punching, shearing and nesting
processes for sheet metal parts[3].With the
development of the manufacturing automation
technology, the sheet metal fabrication applies
CNC equipment such as a CNC press brake, which
enhances the productivity for small batch
manufacturing[4]. In such a system, a programmed
robot is often used to handle materials and/or parts
during the sheet metal bending process. In the
robot-assisted sheet metal bending, the most
difficult task is to plan the bending sequence. A
feasible bending sequence should ensure that the
robot grasps the sheet metal part and moves it to a
dedicated position without any collision with tools
between the bending operations or during the
feeding operations. During the robot-assisted sheet
metal bending process, the sheet metal part, which
attaches to a robot, should be able to move freely in
a constrained manufacturing environment. This
environment is constrained by the bending machine
stroke, the top tool (punch), the bottom tool (die),
and the robot[1-2]. In this study the focus is to
automate the manual bending process using six axis
manipulator, which is used to handle the sheet
metal part and feed it to the CNC bending press for
the bending operations. The figure1 shows the
layout of the automated line to which the robots are
programmed present at the bending station, and
thus the manual bending operation in which two
workers are required to handle the part is converted
to robot assisted bending process inorder to
improve productivity and to minimize the no. of
labors.
Figure1. Layout of the automated line
2 Industrial Robots
Robots are programmable machines with some
human like capabilities. They are made up of
mechanical components, a control system and a
computer. These elements can be arranged in
different ways and can vary in size and complexity
to perform different tasks. Robots are controlled by
a variety of hardware and software systems
[10].The more complex tasks usually require servo-
control systems,which use sensors and
microprocessors. The control system carries out the
functions, which govern the robot’s motion.
Robotic systems are used in a CIM environment
because of they have a number of economic and
performance advantages over human labor or hard
automation in many manufacturing applications,
particularly in batch manufacturing. The major
advantages are due to their re-programmability.
Robots can be programmed by several techniques.
Robot programs can be very simple or extremely
complex, depending on the nature of the tasks and
type of motion control involved. Robot
programming is often done in high-level languages
that provide functions for data processing,
computation, sensing and manipulation. Robot
manufacturers have developed different robot
languages.
•Robots can be built with performance
capabilities superior to those of human
beings in terms of strength, size, speed,
accuracy and repeatability.
•Robots are better than humans to perform
simple and repetitive tasks with better
quality and consistency.
•Robots can replace humans in performing
tasks that are difficult and hazardous
because of factors such as size, weight,
reach, precision or environment (e.g., heat
as in pressure die casting), dust (as in
foundries), chemicals (detection of mines),
nuclear radiation, and pollution).
2.1 Control System Of a Robot
The motions of a robot are controlled by a
combination of software and hardware that is
programmed by the user. There are two basic
types of robot control systems – servo controlled
and non-servo controlled[5].
Figure 2. Control System of a Robot
3 Robot Programming:
Robot programming can be done in two different
ways. On-line using the actual robot or off-line
using PC based software [6].
1. On-line programming
2. Off-line programming
3.1 On-line programming
The majority of material handling robots are
programmed on-line using a teach pendant. This
will feature a joy stick or a series of toggle keys to
select which way you wish to move the robot to an
intended position. You then record that position
with the appropriate instructions relating to the
accuracy of the position, the type of robot move
plus any additional process related information.
These instruction are easily selected from a pre-
defined list of commands. Robot programs can be
given logical names so it easy to select the correct
one afterwards. Whilst most robots will have their
own unique way of being programmed, the basic
principle is the same for all of them.
3.2 Off-line programming
All functions are available from teach pendant.
Commands are selected from a list and are very
easy to understand. The user does not have to
worry about machine codes or syntax. The only
function on the actual cabinet is a rotary on/off
switch. The layout is very simple and the user can
make selections on the colour touch screen and the
key pad. There are six toggle keys and these are
used to move the robot to the required programmed
position. The user can select in which way the
robot moves to this position, either in a polar
coordinate system moving each robot axis
individually or in a linear coordinate system
whereby the robot moves in X, Y and Z describing
a straight path at the Tool Centre Point[8]. The
later is an obvious requirement when programming
a straight joint for welding. When programming the
robot, "teach" is selected and this drops the robot
speed to safe levels of around 250 mm/sec. The
speed of the robot when a toggle key is pressed can
be altered to suit[6-7].The mode switch is rotated to
play mode to test the program at 100% speed or
remote to run the robot in automatic from an
operator panel. When the robot is run in remote
mode for production, the teach pendant can be
parked in a safe place.
3.2.1 Teach pendant
In this work the robot programming is developed
by means of teach pendant. All functions are
available from teach pendant. Initially the robot
motion is planned and taught to robot by means of
teach pendant. Figure 3 represents the teach
pendant of motoman robot. The manipulator
consists of NX 100 controller, the programming
pendant and manipulator cables[8].
Figure 3 Teach pendant
3.2.2 Different Moves for Robot
Programming
The robot programmer tends to only use three
commands to program robot movements, which are
joint move, linear move or circular move. On the
Motoman teach pendant these are identified as :
MoveJ VJ=25.00 - A joint move reaching the
programmed position at, in this case a velocity of
25 % of the set maximum speed. A joint move
moves the robot to the programmed position as
quickly as possible irrespective of path [8].
MoveL V=50 - A linear move reaching the
programmed position in a straight line, defining the
position at robot accuracy at, in this case 50
cm/min. This command would be used when the
robot is welding along a seam.
MoveC V=50 - A circular move. The robot can
interpolate a perfect circle with three positional
points that are programmed at roughly 120 degrees
intervals. In this case the robot moves a 50 cm/min.
The units for velocity can be selected to suit the
user, e.g. cm/min, mm/sec or inches/min. If no
change is made the robot will default to the last
move command with the same settings for that
move. It is very straight forward to make changes
and modify speeds, movement type and approach
accuracy levels.
4 Methodology To Automate Bending
Operation Using Robot
Bending workstation is equipped with a material
handling Robot. It is used to load the punched sheet
metal from the turret punching press to the
bending machine to perform bending. Once the
bending operation is performed the bent sheet is
then moved to the unloading reference table by the
robot .
The path planning of this robot is done in the
following sequence
The motion planning consists of two sub-systems
[4].
•The Gross Motion Planning: That
determines the transfer motion of the
robot.
•“Fine Motion Planning” that determines
the motion of the robot when the part is
inside the punch-die space, especially the
retraction of the part after it is bent.
List of Programs for a robot to perform a bending
operation
Master
Reset Inputs/outputs
Sub program for different sheet size
The figure shows in detail the logic of the robot
which handles the sheet metal part and also feeds
the part into the bending machine where the
bending takes place. The figure explains the
sequence of movements which the robot follows
inorder to perform the required task.
Figure4. Model of Automated Bending Machine
Cell
The program is checked and interfaced with HMI
to run in the remote mode and then the production
is carried out which has been recorded and there by
observed improvements in the throughput which
are included in the results.
Figure 4. Bent sheet using Robot
Figure 5. logic flow diagram – bending
Robot home position
Robot moves to TPP when the unload
signal is ON, to pick the sheet from TPP
Robot picks the sheet from the TPP
,once the clamp opens, and then hand
sheet sensor gets on once it comes in
contact with the sheet
Vacuum cups gets on and the sheet is
picked , robot then moves rapidly to the
bending station as its taught
Robot then moves the sheet fastly till it
reaches the bending Machine , once it
reaches the bending machine, it then
slowly feeds into the M/C till gauge
sensor is on
When the sheet touches the sensor ,Ram
sensor gets ON , which moves the ram to
touch the sheet , bending takes place
Robot then retracts the sheet back once the
bending is done on one end. Once out of
the bending M/C, the robot rotates so that
the other end is bought forward for the
bending to occur
Same steps is repeated so that other end is
also bent
Robot then moves the sheet to
unloading table and unload the sheet
and then returns to the Home Position
END
5 Results
Figure 6. Productivity parts/hr)
The graph shows a linear behavior of the
productivity in terms of (parts/hr).There is an
increase in productivity by 3 parts/hr when
compared with the line data before programming
the material handling robots
By automating material handling using robots
following benefits has been incurred which are as
follows:
•Total Variable cost per annum has been
reduced by 21.36%.
•Throughput rate has been increased by
59.72%.
•Productivity has been increased to 1.7
times the original.
6 Conclusion
From the above studies it can be concluded that the
path planning of material handling robots at
Bending Workstation yields the following points.
Due to the new programs which has been done to
handle the articles which were done manually
before has enhanced the line capacity, throughput
rate and also the productivity can be increased.
Another advantage is that the no. of man power
also can be reduced ,which there by minimized
labor cost and at the same time increasing the
throughput rate by 33%,thereby meeting the
customer demand on time .
References
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Proceedings of the1999 IEEE
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Process Planning and Resolve
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Hua Wang and David A. Bourne
Robotics- and Computer-Integrated
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