5 th International & 26 th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12 th –14 th , 2014, IIT Guwahati, Assam, India 547-1 DEVELOPMENT OF SPM FOR AUTOMATION IN SHEET-METAL DISC TEETH CUTTING OPERATION Chetan Mahatme 1* , Sachin Mahakalkar 2 , Jayant Giri 3 1* YeshwantraoChavan COE,Nagpur, 440010, E-Mail: [email protected]2 YeshwantraoChavan COE,Nagpur, 440010, E-mail: [email protected]3 YeshwantraoChavan COE, Nagpur, 440010, Email:[email protected]Abstract This paper discusses the development of an automated loading and unloading system for sheet-metal disc teeth cutting operation on a power press. Presently the operation under consideration is manual. The worker manually picks the disc from the input bin and places it onto a press bed for teeth cutting and after completion, removes the disc and places it into an output bin. Because of such repetitive task, the worker is prone to various musculoskeletal disorders (MSDs) and cumulative trauma disorders (CTDs). If the cycle time is further reduced, there will be gain in production quantitatively, but the efficiency of the worker will further reduce and there will be chances of fatal injuries. For studying the ergonomic conditions of the worker, a detailed RULA and REBA analysis of the worker is carried out. On the basis of ergonomic analysis results, an alternative to the manual operation, a more sophisticated automated loading and unloading system is suggested. The viability of the suggested system is checked through simulation and FEM analysis. A scaled prototype model of proposed system is also developed and tested. The software used for RULA analysis, CAD model development and simulation is CATIA V5R19. For REBA analysis REBA assessment worksheet is used. Keywords:- RULA, REBA, Modelling, Simulation 1. Introduction Material handling is a necessary, but wasteful and expensive activity in manufacturing and distributing. Insufficient material handling accounts for additional costs in two main ways: idle time and cost of labour. Effective material handling solutions can reduce a production or distribution facility’s cost by significant amounts. The aim of the work described in this paper was to ergonomically analyze the working condition of the worker for a sheet-metal disc handling tasks, specifically for picking, transferring and placing, which have been identified as the most frequently encountered tasks in a number of industrial sectors and are currently performed manually. Their analysis and providing the alternative would greatly improve the productivity and cost effectiveness of these industries. In the context of industrial jobs, manually transferring an object from one point to another (pick- and-place or hand transfer tasks) occurs frequently in the retail trades, manufacturing, and production assembly and is a common component for many machine-paced tasks. The time available to do one transfer (pick then place) will be referred to as cycle time (CT). There are certain effects and physical demands of speeding up the demands of the job by reducing the CT [3]. It results in mainly workers, muscle pain and tenderness of the neck and shoulder areas, and forearm extensors. Neck and shoulder complaints are also common in repetitive tasks, if the CT is reduced. An MIDC, Hingna based steel industry named Bajaj Steel Private Ltd. is the leading manufacturer of the cotton ginning and pressing machinery in India. The sub-part of that machinery is an Impact Cleaner Machine which is used for cleaning the raw cotton. In that machine saw blades in the form of teethed disc are required for freeing the raw cotton. The teeth cutting on the disc is done on the power press. The pick-transfer-and-place operation of the disc on power press is presently being done manually by the worker. This paper suggests on the basis of an ergonomic analysis that an automated material handling system for that operation will perform efficiently and productivity gain can be obtained. The present system is shown in the figurebelow: Figure 1 Present system 2. Literature Review For carrying out the ergonomic analysis a detailed literature survey has been carried out. It shows effects of bad postural working conditions on
Transcript
5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT Guwahati, Assam, India
547-1
DEVELOPMENT OF SPM FOR AUTOMATION IN SHEET-METAL DISC
This paper discusses the development of an automated loading and unloading system for sheet-metal disc teeth cutting operation on a power press. Presently the operation under consideration is manual. The worker manually picks the disc from the input bin and places it onto a press bed for teeth cutting and after completion, removes the disc and places it into an output bin. Because of such repetitive task, the worker is prone to various musculoskeletal disorders (MSDs) and cumulative trauma disorders (CTDs). If the cycle time is further reduced, there will be gain in production quantitatively, but the efficiency of the worker will further reduce and there will be chances of fatal injuries. For studying the ergonomic conditions of the worker, a detailed RULA and REBA analysis of the worker is carried out. On the basis of ergonomic analysis results, an alternative to the manual operation, a more sophisticated automated loading and unloading system is suggested. The viability of the suggested system is checked through simulation and FEM analysis. A scaled prototype model of proposed system is also developed and tested. The software used for RULA analysis, CAD model development and simulation is CATIA V5R19. For REBA analysis REBA assessment worksheet is used.
Keywords:- RULA, REBA, Modelling, Simulation
1. Introduction
Material handling is a necessary, but wasteful and expensive activity in manufacturing and distributing. Insufficient material handling accounts for additional costs in two main ways: idle time and cost of labour. Effective material handling solutions can reduce a production or distribution facility’s cost by significant amounts. The aim of the work described in this paper was to ergonomically analyze the working condition of the worker for a sheet-metal disc handling tasks, specifically for picking, transferring and placing, which have been identified as the most frequently encountered tasks in a number of industrial sectors and are currently performed manually. Their analysis and providing the alternative would greatly improve the productivity and cost effectiveness of these industries. In the context of industrial jobs, manually transferring an object from one point to another (pick-and-place or hand transfer tasks) occurs frequently in the retail trades, manufacturing, and production assembly and is a common component for many machine-paced tasks. The time available to do one transfer (pick then place) will be referred to as cycle time (CT). There are certain effects and physical demands of speeding up the demands of the job by reducing the CT [3]. It results in mainly workers, muscle pain and tenderness of the neck and shoulder areas, and forearm extensors. Neck and shoulder complaints are also common in repetitive tasks, if the CT is reduced.
An MIDC, Hingna based steel industry named Bajaj Steel Private Ltd. is the leading manufacturer of the cotton ginning and pressing machinery in India. The sub-part of that machinery is an Impact Cleaner Machine which is used for cleaning the raw cotton. In that machine saw blades in the form of teethed disc are required for freeing the raw cotton. The teeth cutting on the disc is done on the power press. The pick-transfer-and-place operation of the disc on power press is presently being done manually by the worker. This paper suggests on the basis of an ergonomic analysis that an automated material handling system for that operation will perform efficiently and productivity gain can be obtained. The present system is shown in the figurebelow:
Figure 1 Present system
2. Literature Review
For carrying out the ergonomic analysis a detailed literature survey has been carried out. It shows effects of bad postural working conditions on
DEVELOPMENT OF SPM FOR AUTOMATION IN SHEET
human body. The bad postures and anthropometric data mismatch had contributed to musculoskeletal disorder problems. For designing the worksnecessary to obtain the relevant informatiotask performance, equipment, working posture and environment. In developing an industrial workstation, the designer should take into account workstation height. When the workstation is too high results in cramp in shoulder of worker whereas when the workstation is too low this may result in backache. Also as the operator is a highly paid skilled worker and machine time is very expensive the reduction in performance has far-reaching consequences for the user organisations. Material handling system and ergonomics go hand by hand. There is a link between ergonomics and material handling work which underlines the necessity to analyse and classify the manufacturing system layout configuration in relation to both technologicalenvironmental parameters. The prevalence and incidence of work-related musculo-skeletal disorders (WMSDs) among industrial workers have been well recognized [3]. There have been documented workrelated problems in the manufacturing industries such as electronics assembly, materials picking and assembly tasks, parts assembly, cashiering, laminate industry, and garment sewing and printingthese jobs involve grasping and moving objectsUS Bureau of Labour Statistics reported that repetitive placing, grasping, and moving objects accounted for 31% of non-fatal occupational injuries in private industry workplaces that were associated with repetitive movement. Of these cases, 65% affected the fingers, hands, and the wrists and 11% make up shoulder-related complaints. Thusenvironment for workers is needed at the workplace.
3. Methodology
Firstly, present working condition is studiedThe work-piece under consideration is sheetdisc having following specifications:
3.1. Subject
The object to be handled is a sheet-metal disc having: Outer Dia. 40.64cm Inner Dia. 18cm No. of teeth 330 Thickness 1mm approx. Material Spring Steel Figure 2 Disc
3.2 RULA Analysis
RULA stands for Rapid Upper Limb Assessment
which is used for rapid assessment on neck and upper limb loading in mainly sedentary tasks (repetitive tasks).It was developed to investigate the exposure of individual workers to risks associated with work
DEVELOPMENT OF SPM FOR AUTOMATION IN SHEET-METAL DISC TEETH CUTTING OPERATION
human body. The bad postures and anthropometric data mismatch had contributed to musculoskeletal disorder problems. For designing the workstation it is necessary to obtain the relevant information or data on
equipment, working posture and environment. In developing an industrial workstation, the designer should take into account workstation
too high results in cramp in shoulder of worker whereas when the workstation is too low this may result in backache. Also as the operator is a highly paid skilled worker and machine time is very expensive the reduction in
reaching economical consequences for the user organisations. Material handling system and ergonomics go hand by hand. There is a link between ergonomics and material
derlines the necessity to e and classify the manufacturing system layout
figuration in relation to both technological and he prevalence and
skeletal disorders (WMSDs) among industrial workers have been well
]. There have been documented work-ems in the manufacturing industries such
as electronics assembly, materials picking and assembly tasks, parts assembly, cashiering, laminate
and garment sewing and printing. Many of these jobs involve grasping and moving objects. The
r Statistics reported that repetitive placing, grasping, and moving objects
fatal occupational injuries in private industry workplaces that were associated with repetitive movement. Of these cases, 65%
ands, and the wrists and 11% related complaints. Thus, safe
environment for workers is needed at the workplace.
Firstly, present working condition is studied. piece under consideration is sheet-metal
Figure 2 Disc
Rapid Upper Limb Assessment which is used for rapid assessment on neck and upper limb loading in mainly sedentary tasks (repetitive tasks).It was developed to investigate the exposure of individual workers to risks associated with work-
related upper limb disorders. The RULA analysis examines the following risk factors: number of movements, static muscle work, force, working posture, and time worked without a break. All these factors combine to provide a final score that ranges from 1(Good) to 7(Worse).
3.3Parameters Used for RULA Analysis
1) Posture: Intermittent 2) Repeat Frequency: Fewer than 4 times per3) Worker’s posture: A) Arms are working across midline B) Check balance 4) Load: 750 gm. Divided to 375 gm. on each arm.5) Manikin: Japanese (Asian, closely resembling to Indian (Not listed in software)), male, weight 65 kg and height 170 cm approximately. According to above parameters, a manikin is built under human builder module in CATIA as shown in figure 2. The load of the disc is shown by downward green arrows. The posture of the manikin is equivalent to the worker.
Figure 3Manikin
3.4 Scores Obtained
The RULA analysis is carried out for each posture of the worker for generating its individual score. The scores obtained from these analysis are then compared with that of REBA analysis scores. There postures are: 1.Disc pick-up from input bin 3.Disc placing on indexing machine 3.Finished disc placing in output bin. 1. Disc pick-up from stack
Figure 4(a) LHS Score Figure 4(b) Tube view
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related upper limb disorders. The RULA analysis examines the following risk factors: number of movements, static muscle work, force, working posture, and time worked without a break. All these factors combine to provide a final score that ranges
Parameters Used for RULA Analysis
equency: Fewer than 4 times per minute
4) Load: 750 gm. Divided to 375 gm. on each arm. 5) Manikin: Japanese (Asian, closely resembling to Indian (Not listed in software)), male, weight 65 kg
According to above parameters, a manikin is built under human builder module in CATIA as
f the disc is shown by downward green arrows. The posture of the manikin
The RULA analysis is carried out for each posture of the worker for generating its individual
obtained from these analysis are then compared with that of REBA analysis scores.
Figure 4(b) Tube view
5th International & 26th All India Manufacturing Technology, DesigIIT Guwahati, Assam, India
Figure 5(a) RHS Score Figure 5(b) Tube view
2. Disc placing on indexing machine
Figure 6(a) LHS Score Figure 6(b) Tube view
Figure 7(a) RHS Score Figure 7(b) Tube view
3. Finished disc placing in output bin Figure 8(a) LHS Score Figure 8(b) Tube view
All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12
Figure 5(a) RHS Score Figure 5(b) Tube view
(b) Tube view
(b) Tube view
(b) Tube view
Figure 9(a) RHS Score Figure 9(b) Tube view
3.5 What these RULA scores suggest ?
These scores suggest that the present working conditions are not suitable for the worker changes are required soon. The detail score analysis for RHS and LHS shows the effect of working conditions on workers forearm, wrist, upper arm, neck and trunk. Also, the disc to be handled has sharp edges which causes minor injuries and bruises. To avoid these problems an automated material handling system is the best solution available.
3.6 REBA Analysis
It stands for Rapid Entire Body Assessment. Its purpose is to develop a postural analysis system sensitive to musculoskeletal risk in variety of jis based on body segment specific ratings within specific movement planes, using a scoring system for muscle activity including static, dynamic, rapidly changing or unstable postures, and provide a benchmark for urgency of action. It considers MSDRisk Factors which are awkward postures,load/force, coupling, activity level. Body regions considered are trunk, neck, legs, knees, upper and lower arms, wrists. Inter-observer reliability was found to be 6214 users of REBA Analysis. (S. Hignett L.Mc.Atammey) REBA scoring is carried out as shown in figurebelow:
Figure 10 Procedure Adopted for REBA Scoring
n and Research Conference (AIMTDR 2014) December 12th–14th, 2014,
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(b) Tube view
suggest ?
These scores suggest that the present working conditions are not suitable for the worker and changes are required soon. The detail score analysis for RHS and LHS shows the effect of working conditions on workers forearm, wrist, upper arm, neck and trunk. Also, the disc to be handled has sharp edges which causes minor injuries and bruises. To void these problems an automated material handling
It stands for Rapid Entire Body Assessment. Its purpose is to develop a postural analysis system sensitive to musculoskeletal risk in variety of jobs that is based on body segment specific ratings within specific movement planes, using a scoring system for muscle activity including static, dynamic, rapidly changing or unstable postures, and provide a benchmark for urgency of action. It considers MSD Risk Factors which are awkward postures,load/force, coupling, activity level. Body regions considered are trunk, neck, legs, knees, upper and lower arms, wrists.
observer reliability was found to be 62-85% for Analysis. (S. Hignett and
REBA scoring is carried out as shown in figure10
Figure 10 Procedure Adopted for REBA Scoring
DEVELOPMENT OF SPM FOR AUTOMATION IN SHEET
3.7 Scores Obtained
A detailed REBA Analysis is carried out on the worker postures. The scores of each body region are calculated and are assembled with load, coupling and activity scores. The final scores are obtained for comparing with RULA scores. 1. Disc pick-up from input bin
Figure 11 REBA Sheet for disc pick
i/p bin 2. Disc placing on indexing machine
Figure 12 REBA Sheet for disc placing on
indexing m/c
3. Finished disc placing in output bin
Figure 13 REBA Sheet for disc Placing in o/p bin
DEVELOPMENT OF SPM FOR AUTOMATION IN SHEET-METAL DISC TEETH CUTTING OPERATION
A detailed REBA Analysis is carried out on the worker postures. The scores of each body region are
and are assembled with load, coupling and activity scores. The final scores are obtained for
REBA Sheet for disc pick-up from
REBA Sheet for disc placing on
REBA Sheet for disc Placing in o/p bin
3.8 Results from Ergonomic Analysis
Table 1 RULA and REBA analysis score comparison
As these scores suggests that there is a need of change in the present manual material handling system, a conceptual automated material handling system is suggested.
4.Conceptual CAD Model
Software Used for CAD model development is CATIA V5R19. The CAD model is developthen virtually tested by simulation for clash detection.
Figure 14 Conceptual CAD Model
5. FEM Analysis of Gripper Plates
The FEM analysis of gripper plates of both vertical as well as horizontal gripper is carried out using Workbench 14.0. The CAD model of gripper plate is imported in ANSYS in .igs format.considered is Aluminium. Element selection is automatic.The meshing is carried out refinement factor of 3 for selective dense meshing load is applied on the gripper platelocations. Fixed supports and standard earth gravity is specified. The results are obtained for Vonstress and total deformation.
5.1 Vertical Picker Gripper Plate Analysis
5.1.1 Total Deformation:
The Max. total deformation obtained is 0.20132mm (fig.15) which is less than provided.(Near about 10mm). Hence, it
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Results from Ergonomic Analysis
Table 1 RULA and REBA analysis score comparison
As these scores suggests that there is a need of change
handling system, a conceptual automated material handling system is
for CAD model development is model is developed and
by simulation for clash detection.
Conceptual CAD Model
The FEM analysis of gripper plates of both vertical as rried out using ANSYS
Workbench 14.0. The CAD model of gripper plate is .igs format. The material
Element selection is The meshing is carried out with maximum
refinement factor of 3 for selective dense meshing and ad is applied on the gripper plate at respective
Fixed supports and standard earth gravity is The results are obtained for Von-Mises
Analysis
eformation obtained is 0.20132mm allowable gap it’ssafe.
5th International & 26th All India Manufacturing Technology, DesigIIT Guwahati, Assam, India
Figure 15 Total Deformation
5.1.2 Von-Mises Stress:
The Max. Von-Mises stress value is 4.8385MPa(fig.16)which is less that Syt of AluminMPa).Hence, its safe.
Figure 16 Von-Mises Stress
5.2 Horizontal Gripper Plate Analysis
5.2.1 Total Deformation:
The Max. Total Deformation obtained is 0.53211mm (fig.17) which is less than allowable gap provided.(Near about 10mm). Hence, it
Figure 17 Total Deformation
5.2.2 Von-Mises Stress:
The Max. Von-Mises stress value is 5.8052MPa18)which is less that Syt of AluminMPa).Hence, it’s safe.
Figure 18 Von-Mises Stress
All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12
Total Deformation
Mises stress value is 4.8385MPa Aluminium (413
Mises Stress
5.2 Horizontal Gripper Plate Analysis
The Max. Total Deformation obtained is 0.53211mm less than allowable gap
it’s safe.
Total Deformation
Mises stress value is 5.8052MPa (fig. Aluminium (413
Mises Stress
6. Scaled Prototype
Figure 19 Scaled Prototype Model
Figure 20 Microcontroller Board
7.Working of Prototype
The conceptual model in fig.19material handling system proposed for disc handling operation. There is a vertical picker equipped with gripper system to which end effectors in the form of two bars are attached (5). The end effectors have slots one on each bar for mounting the electromagnetic coil. There will be a limit switch attached to the end gripper assembly which will detect the disc after touching and reverses the motor movement. Vertical stacker is placed concentrically with the two bars of end effector. Vertical stacker has a key slot in which the discs with key will be stacked so as to maintain their orientation with respect to indexing machine key slot. The horizontal support will be consists of two gripper systems having two bars each and the bars can be moved vertically when requiredeach bar two electromagnetic coils will be mounted [4]. The vertical and horizontal movements to the gripper systems will be transferred by electric motors with the help of lead screw. A disc holder is attached to the press body which carries a thick metal disc and can be placed over the sheet-metal disc when clamping of the disc is required. The thick metal disc can be moved vertically with the help of a mechanism attached to a motor. There is another stacker serving as output bin in which the finished teethed disc will be placed. The vertical gripper system will be placed slightly above the horizontal gripper system. The operation will be carried out as follows:
n and Research Conference (AIMTDR 2014) December 12th–14th, 2014,
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Scaled Prototype Model
The conceptual model in fig.19 depict the material handling system proposed for disc handling operation. There is a vertical picker equipped with gripper system to which end effectors in the form of
. The end effectors have slots e electromagnetic
coil. There will be a limit switch attached to the end gripper assembly which will detect the disc after
movement. Vertical stacker is placed concentrically with the two bars of
er has a key slot in which the discs with key will be stacked so as to maintain their orientation with respect to indexing machine key
The horizontal support will be consists of two gripper systems having two bars each and the
ically when required (2). On each bar two electromagnetic coils will be mounted [4]. The vertical and horizontal movements to the gripper systems will be transferred by electric motors with the help of lead screw. A disc holder is attached
y which carries a thick metal disc and metal disc when
clamping of the disc is required. The thick metal disc can be moved vertically with the help of a mechanism attached to a motor. There is another stacker serving
bin in which the finished teethed disc will be placed. The vertical gripper system will be placed slightly above the horizontal gripper system.
The operation will be carried out as follows:
DEVELOPMENT OF SPM FOR AUTOMATION IN SHEET-METAL DISC TEETH CUTTING OPERATION
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1) The vertical gripper system will move downwards, the motion will be transmitted from motor to the lead screw and ultimately to the end effector. As the end effector touches the disc in the stack the bottom limit switch gets pressed and the current to the electromagnetic coil is passed which will create electromagnetism in the coil and the disc will be picked from the stack (8). The current to the electromagnetic coil will be sent as per the magnetic strength required to lift one disc at a time. 2) The vertical gripper carrying the disc will travel to its original top position which is restricted by another limit switch at top. While going to top position the horizontal gripper will be crossing the vertical gripper the electromagnetic coils in the horizontal gripper will be energized also at the same time current polarity in electromagnetic coils of vertical gripper will be reversed so as to lose its electromagnetism. Thus the horizontal gripper will be carrying the disc at this time. 3) Now the horizontal gripper will travel to its right with the disc attached to the end effector. The motion to the gripper will be transferred from motor to the lead screw and lead screw to the end effector. When the gripper will be above the indexing machine the limit switch present at the end of horizontal system will get pressed and the motor motion will stop and end effector will place the disc on the indexing machine by losing the electromagnetism in electromagnets. 4) During the disc cutting operation the leftmost gripper will travel to its original position and will grab another disc from the vertical gripper. 5) When the teeth cutting will be completed onto the disc, the disc platform will get slightly upward motion and the disc from the indexing machine will stick to the horizontal gripper electromagnet. It will carry the disc to the output vertical stacker, during which the leftmost horizontal gripper will place another disc onto the indexing machine. This cycle will go on and on until the discs in the stack are finished.
8. Conclusion and Future Scope
The RULA & REBA analysis are carried out on the present worker conditions and their results have shown the need of change in the present material handling system which is manual. Thus the development of automated material handling system is justified. The development of working prototype of the model is done. The suggested Material Handling System is an economical option available instead of dedicated Robotic Systems available in the market. After implementing the proposed model the cycle time of the operation will be reduced and labour cost will also be reduced. The proposed model can work continuously without much downtime so that significant productivity gain can be obtained. This system requires low maintenance and it’s easy to install. Further development in the system can be
done such as incorporating dual gripping mechanism i.e. magnetic as well as suction gripper so that the disc picking will be more precise (1)(9).By using various sensors such as proximity sensors, force/pressure sensors proper gripper positioning can be done.Gripper adjustment option can be incorporated so that variable diameter discs can be handled.In-Line manufacturing system (9) can be developed for producing various parts from same sheet-metal disc.
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