Transcript Feasibility Study of Replacing an Industrial Hydraulic

Feasibility Study of Replacing an
Industrial Hydraulic Lift System with
an Electro-Mechanical Lift System
Critical Design Review
Thursday, 21 September 2000
Professors:
Students:
Dr. Ram & Dr. Buckner
Jeremy Bridges & David Herring
Overview
 Problem
Statement
 Potential Candidate Designs
 Selecting Candidate Designs
 Finalizing Design Solution
 Proposed Design Implementation
 Conclusion
 Questions & 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 electromechanical 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.
2.
3.
4.
Accurate lifting with little drift
Smooth operation
Compact system
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
Average
Weight
Ball Screw Jac
Machine Screw Jac
Rack & Pinion
Cam/Cylinder Lift
Chain/Cable Lift
Electric Cylinder Linear Actuator
Scissor Truss (Car Jack)
Cost
0.05
6
6
7.5
7.5
9
1.5
9
Safety Performance Reliability
0.4
0.2
0.35
7
9
9
9.5
8.5
8.5
3.5
7.5
4
3
6.5
3.5
3
7
4
7
9.5
9.5
8
5.5
6.5
Scale: 1 = poor
5 = neutral
10 = best
Rank
1
7.65
8.975
3.875
3.4
3.65
7.6
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
Safety
Ease of
Assembly
Rank
0.3
0.45
0.1
0.1
0.05
1
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
Weight
Ball Screw Jac
Scale: 1 = poor
5 = neutral
10 = best
Ball Screw Jac
Clevis (2)
Aluminum
Housing
Drive shaft
Ball Screw Jac - Space Issue
Fork support unit
Ball Screw Jac
Interference w/
Drive Unit
Machine Screw Jac
Drive Shaft
Aluminum
Housing
Clevis (2)
Machine Screw Jac
Lower Mounting Option 1
Upper Linkage
Bracket
welded to
existing
chassis
Fork Unit Support
Machine Screw Jac
Lower Mounting Bracket
(Option 1)
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 Bracket
Option 1
 Will require additional hole drilled in
fork unit support and filling of
existing hole
 May allow additional undesired
degrees of freedom
Upper Mounting Bracket
Option 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
Mounting
Bracket
Fork Unit
Support
Upper linkage
Machine Screw Jac
Lower
Mounting
Bracket
Motor Information
Brake 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:
AC or DC Motor:
Limit Switches:
Fabrication:
DC-AC Inverter:
Misc. Hardware:
Estimated Total Cost:
$500
$600-$1200 (depending on HP requirements)
$100-$200
$200 (if needed)
$200-$300 (if needed)
$50
--------------$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???
Web Site:
http://www.mae.ncsu.edu/courses/mae586/buckner/index.html