Feasibility Study of Replacing an Industrial Hydraulic Lift System with an Electro-Mechanical Lift System
Critical Design Review
Thursday, 21 September 2000
Professors:
Dr. Ram & Dr. Buckner
Students:
Jeremy Bridges & David Herring
OverviewProblem StatementPotential Candidate DesignsSelecting Candidate DesignsFinalizing Design SolutionProposed Design ImplementationConclusionQuestions & Comments
Problem Statement
Hydraulic lift systems occasionally leak fluid. This raises environmental issues. A high number of NACCO’s customers are concerned with this issue and have expressed a willingness to pay a little more for an electro-mechanical lift system. NACCO now would like to research the feasibility of replacing this hydraulic lift system with an electro-mechanical lift system in the most cost effective way so the customer can justify the increased cost.
Potential Design Solutions
1. Ball Screw Jac
2. Machine Screw Jac
3. Electric Cylinder Linear Actuator
4. Cam/Cylinder Lift
5. Rack and Pinion
6. Cable/Chain Lift
7. Scissor Truss (Car Jack)
Ball Screw Jac 1. Accurate lifting with little drift 2. Smooth performance 3. Little horsepower required from motor (1/3 Torque needed
compared to Machine Screw Jac) 4. Compact system 5. Can operate at high speeds 6. Capable of lifting more than 2 tons that lift desires 7. Horizontal input with vertical output 8. Duty cycle can be extended longer than Machine Screw Jac 9. Corrosion resistant 10. Long predictable life 11. A motor needs to be added 12. Reasonable cost 13. Reasonable size that can work within space constraints
Machine Screw Jac 1. Accurate lifting with little drift 2. Smooth operation 3. Compact system 4. Self-locking during manual operation with no vibration when using
20:1 or higher gear ratio. 5. Will not back-drive during mechanical failure with 20:1 or higher ratio. 6. Corrosion resistant 7. Preferred for static vibration 8. Slower travel speed compared to hydraulic, ball screw, or electric
cylinder actuator 9. A motor needs to be added 10. Reasonable cost 11. Reasonable size that can work within space constraints
Electric Cylinder Linear Actuator
1. Extremely accurate
2. High cost
3. Smooth operation
4. Limit switches included
5. Requires input voltage rather than a shaft or other mechanical input
6. Integrated motor
7. Includes ball screw with long life
8. Recommended as ideal solution to hydraulic (per Nook Linear Motion Design Guide, pg. ajec-6)
9. Perfect size that can work within space constraints
Cam/Cylinder Lift 1. Smooth operation
2. Will back-drive without brake during mechanical failure
3. Medium cost
4. Relatively equal travel time compared to hydraulic system
5. Size that may cause problems within space constraints
Rack and Pinion
1. Best during manual operation
2. Mechanical brake preventing back-drive on pinion
3. Low cost
4. Fast travel cycle time
5. Reasonable size that can work within space constraints
Cable/Chain Lift 1. Requires new lift point for lift truck forks
2. High torque
3. Cable wrapping is potential problem
4. If cable or chain break there is a sudden and quick back-drive
5. Medium cost
6. Slower travel time compared to the hydraulic system
7. Reasonable size that can work within space constraints
Scissor Truss (Car Jack) 1. Will not back-drive
2. Can be operated manually
3. Needs large amount of space for mounting
4. Low cost
5. Slower travel time compared to the hydraulic system
6. Size not ideal to work within space constraints
Criteria for Decision Matrix Cost (5%): evaluated on single mechanism basis for
general price ranges
Safety (40%): evaluated on back driving risk during a mechanical failure
Performance (20%) : educated comparison against current hydraulic system
Reliability (35%): evaluated with expected life and risk for a mechanical failure
Candidate Design Selection
Scale: 1 = poor
5 = neutral
10 = best
Average Cost Safety Performance Reliability RankWeight 0.05 0.4 0.2 0.35 1
Ball Screw Jac 6 7 9 9 7.65Machine Screw Jac 6 9.5 8.5 8.5 8.975Rack & Pinion 7.5 3.5 7.5 4 3.875Cam/Cylinder Lift 7.5 3 6.5 3.5 3.4Chain/Cable Lift 9 3 7 4 3.65Electric Cylinder Linear Actuator 1.5 7 9.5 9.5 7.6Scissor Truss (Car Jack) 9 8 5.5 6.5 7.525
Candidate Design
1. Ball Screw Jac
2. Machine Screw Jac
3. Electric Cylinder Linear Actuator
Selecting Final Design Size (45%) : evaluate component size and spacing
requirements
Ultimate Cost (30%) : overall cost including additional hardware
Ease of Assembly (5%) : implementation of design
Performance (10%) : travel speed and load handling
Safety (10%) : ability to back-drive
Final Design Decision Matrix
Ultimate Cost
Overall Size
Performance SafetyEase of
AssemblyRank
Weight 0.3 0.45 0.1 0.1 0.05 1
Ball Screw Jac 6.75 3 4 7 6 4.2375
Machine Screw Jac 7 7 4 7.5 7 7
Electric Cylinder Linear Actuator
1 7 9 4 7 6.7
Hydraulic Cylinder 10 10 9 9 9 9.65
Scale: 1 = poor 5 = neutral 10 = best
Ball Screw Jac
Clevis (2)
Drive shaft
Aluminum Housing
Ball Screw Jac - Space Issue
Fork support unit
Ball Screw Jac
Interference w/ Drive Unit
Machine Screw Jac
Aluminum Housing
Drive Shaft
Clevis (2)
Machine Screw JacLower Mounting Option 1
Upper Linkage
Fork Unit Support
Machine Screw Jac
Lower Mounting Bracket(Option 1)
Bracket welded to existing chassis
Option 1:
Stress Analysis must be conducted to select appropriate geometry and ensure structural rigidity
Material must be cut away from interior flanges of fork unit support
Weld strength must be determined
Machine Screw Jac Lower Mounting (Option 2)
Upper Lift Linkage
Fork Unit Support
Machine Screw Jac
Lower Mounting Bracket(Option 2)
Welded to Chassis
Option 2:
Stress Analysis must be conducted in order to determine correct thickness and geometry of bracket
No material will need to be cut away from fork unit support
Strength will be main concern and testing must be conducted
Possible Interference with drive unit at maximum turn radius
Upper Mounting BracketOption 1
Will require additional hole drilled in fork unit support and filling of existing hole
May allow additional undesired degrees of freedom
Upper Mounting BracketOption 2
Additional hole will be drilled and existing hole will be used (No filling will be needed)
More rigid support than Option 1
Machine Screw Jac Assembly
Upper linkage
Fork Unit Support
Machine Screw Jac
Upper Mounting Bracket
Lower Mounting Bracket
Motor InformationBrake Motor
3-Phase, AC Induction 1.5-2 HP depending on desired speed 230/460 VAC Input Voltage NEMA 56-C Motor Size Recommended by Nook Industries (~$1000) Would require DC-AC Inverter (~$500)
Brush DC Motor 1.5-2 HP depending on desired speed 24 VDC Input Voltage Needs to be researched further
Note: More Motor Information will be provided later
Cost of Final Design (Prototype)
Machine Screw Jac: $500AC or DC Motor: $600-$1200 (depending on HP requirements)Limit Switches: $100-$200Fabrication: $200 (if needed)DC-AC Inverter: $200-$300 (if needed)Misc. Hardware: $50
---------------Estimated Total Cost: $1250-$2450 (depending on configuration)
Conclusion
We recommend the Machine Screw Jac as the electromechanical solution
Option 1 - Lower Mounting Bracket
Option 2 - Upper Mounting Bracket
We desire feedback from NACCO on the configuration we have selected before we proceed with prototyping
Questions or Comments???Questions or Comments???
Web Site:
http://www.mae.ncsu.edu/courses/mae586/buckner/index.html
Top Related