design of a robotic manipulator for a wheelchair 2000-2001 gateway coalition ohio state university...
TRANSCRIPT
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Design of a Robotic Manipulator for a
Wheelchair
2000-2001 Gateway Coalition
Ohio State University
Sinclair Community College
Wright State University
December 8, 2000
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2000-2001 Team Members
Ohio State University
Prof. Gary Kinsel
Corey Johnson
Tim Kocher
Curt O’Donnell
Michael Stevens
Aaron Weaver
Jeff Webb
Sinclair Community
College
Prof. Beth Johnson
Brad Cutting
Chris Shirkey
Tim Tarp
Wright State University
Prof. James Menart
Shawn Riley
Jason Ruge
Lawrence Thomas
Eric Yu
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Project Overview & History
• Program Background
• 1996-1997
• 1997-1998
• 1999-2000
• 2000 Graduate Design
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Program Background
• National Science Foundation
• Seven Institutions
• Advancement of Engineering Education
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1996-1997 Design
• Cables and Transmission Pulleys– Keeps motor on base
of robot
• Short comings– Inappropriate motors
– Large size
– High maintenance and manufacturing costs
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1997-1998 Design
• Addition of knuckle joint and rotating base
• Short comings– Expensive
– Not mounted to wheelchair
– One-directional gripper activation
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1999-2000 Design
• Six degrees of freedom
• Fully functional gripper
• Mounted on wheelchair
• Short comings– Heavy– Expensive– Difficult to
manufacture
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2000 Graduate Design
• Chris Fearson– Ohio State University
Graduate Student
• Totally enclosed design
• A little lighter• Short comings
– Very expernsive– Hard to mount
• Two-piece clamps
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2000-2001 Design Objectives
• 1.5 kg (~ 3 lb) Lift Capacity
• 0.5 m/s Maximum linkage Movement Speed
• Total Assembly Weight Less Than 30 lbs
• Total Manufacturing Cost
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Preliminary Design Calculations
• Estimated Moment Calculations– Initial calculations
• Shoulder moment ~ 500 in-lbs
• Elbow moment ~ 125 in-lbs
– Updated calculations• Shoulder moment = 473.8 in-lbs
• Elbow moment = 169.8 in-lbs
• Application factor = 1.5
• Weight to lift (load) = 3.3 lbs
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Complete Arm Design
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Design Characteristics
• Freedom of motion– Shoulder joint
• 360° of twist• Up to 200° of bend
– Elbow joint• 280° of bend
– Wrist• 360° of twist• ~300° of bend
• Both shoulder motors in the base– Reduces the weight of the
lower arm
• Length– Lower arm = 15.5 in.– Forearm = 13.65 in.– Full extension ~ 35.5 in.
• Width– Extends 3.25 in. beyond
wheelchair width.– Wheelchair width with arm =
27.75 in.– Typical Door Width = 34 in.
• Compact travel position– ~5 in. tall– 15.5 in. long
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Travel Position
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Full Extension
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Shoulder Assembly
• Design Limitations (clearance, gear size, bearing size)
• Mounting Brackets
• Motors & Placement
• Gearing
• Bearings
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Design Limitations
• Maximum distance from the side of the chair must be less than 6 inches– Limits the diameter of twist gear and width of
base plate– Also limits the size of the twist bearing
• Spacing of the mounting brackets governed by the current design of the wheelchair frame
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Mounting Brackets• Single-piece design
• Rubber lining to protect the finish of the wheelchair
• Close tolerances make installation easy
• Simple clamping technique; one person can secure entire arm to wheelchair
1999-2000 Mounting Bracket
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Motors and Placement
• Twist and bend motors placed on the base
• Design reduces weight in the lower arm
• Bend motor mounted to the twist gear– Rotates with the arm
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Gearing• Twist Gearing
– Simple spur gear design
– Gear size cannot be reduced due to shoulder bracket position
– Current large pinion gear is due to mounting and placement limitations
• Future investigation into use of a idler gear
• Bend Gearing– Bevel gear design
– Currently ~8:3 ratio
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Bearings
• Twist bearing– Large bearing
• 3.5 in. O.D.
• 3 in. I.D.
– Concerned with thickness
• Ideally: ~.5 in.
• Current findings: >2 in.
– Investigating Oil Impregnated
• Bend Bearings– Mounted in the
shoulder brackets
– 1 in. O.D.
– .5 in. I.D.
– Flanged
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Lower Arm Assembly
• 2.5 in. Square Aluminum Tubing
• Elbow Motor• Shaft• Bearing• Gear
1999-2000 Lower Arm Link
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2.5 in. Square Aluminum Tubing
• Creates an enclosed and clean design
• Structurally strong, yet fairly light weight
• Requires minimal machining
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Shoulder Shaft
• Diameter: .5 in.• Length: 3.625 in.• Snap-ring attachment
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Bearing and Gearing
• Bearings at elbow side of the lower arm to allow free rotation– Mounted in the square tubing– Same bearing used in the shoulder for the bend
motion
• Bevel gears used to move the elbow joint– Currently the ratio is approximately 8:3
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Elbow Joint
• Bracket Design– Elbow Bracket
• Bent 1/8 in Stock Aluminum Plate
• Snap-ring attachment
• Bolted to the forearm
– Degree of Movement• Design allows for 280°
of motion at the elbow
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Forearm Assembly
• Same assembly used in previous design– Last modified by Chris Fearson
• Components– 2.5 in. square tubing– Both wrist motors completely enclosed by
tubing– Mounting for the differential gearing at the
wrist
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Forearm Assembly Model
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Differential Gear Set
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Forearm Assembly Model
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Preliminary Finite Element Analysis
• Mounting Brackets
• Stationary Plate
• Lower Arm Tube
• Elbow Links
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FEA: Mounting Brackets
• Constraints– Front and top inner surfaces
fixed– Rear bolt hole fixed
• Loading– 100 lb load applied to top
surface of bracket
• Maximum Stress– Front: 272 psi
• Factor of Safety = 184
– Rear: 338 psi• Factor of Safety = 148
Front
Rear
100 lb
100 lb
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FEA: Stationary Plate
• Constraints– Fixed at mounting bolt
holes
• Loading– 100 lb load at bearing hole
– 500 lb*in moment at bearing hole
• Maximum Stress– 8000 psi
– Factor of Safety = 6.25
100 lb
500 lb*in
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FEA: Lower Arm Tube
• Constraints– Fixed at shoulder shaft hole
• Loading– 100 lb at elbow shaft hole
– 100 lb side load at end (to simulate side impact)
• Maximum Stress– 36057 psi
– Factor of Safety = 1.39
100 lb
100 lb
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FEA: Elbow Links
• Constraints– Fixed at elbow shaft hole
• Loading– 50 lb total load at
distributed over bolt holes
– 170 lb*in moment at forearm end
• Maximum Stress– 17808 psi
– Factor of Safety = 2.81
50 lb
170 lb*in
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Preliminary Bill of Materials
• Not a complete listing– No machining costs or estimates– Twist shoulder bearing still under investigation– Gears can not be found until motor data is
complete
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Part Description Manufacturer Product Number Unit Cost Net Cost
Front Base Mounting Bracket: 1/2" Aluminum (Machined)Back Base Mounting Bracket: 1/2" Aluminum (Machined)
Rubber Inserts For Mounting BracketStationary Plate: 7" x 5" x 1/8" (Machined)
Shoulder Brackets: 2.5" x 3.1" x 0.5" (Machined)Shoulder Spacer: 3" OD, 3/4" Thick (Machined)
Bend Motor Mounting Plate: 2" x 2" x 1/4" (Machined)Drill Motor: FireStorm 18.0 V Black & Decker HP932K-2 $149.00 $298.00
Drill Motor EncoderMotor Shaft Bearing: 1" OD, 7/16 ID, 5/16" Thick
Twist Pinion: 1" OD, 7/16" ID, 3/8" ThickTwist Motor Shaft: 1/4" x 1/2" Key, 7/16" OD, 1-5/16"
Total Length(Machined)
Twist Gear: 1/2" OD, 5/16" ThickTwist Bearing: 3-1/2" OD, 3" ID, 1/2" Thick
Bend Pinion: 3/4" Head OD, 45-Degree Bevel, 1/2" Total Length
Bend Motor Shaft: 1/4" x 1/2" Key, 7/16 OD, 2.56" Total Length
(Machined)
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Part Description Manufacturer Product Number Unit Cost Net CostAluminum Tubing: 2-1/2" x 2-1/2" x 18", 1/8" Wall
ThicknessElbow Motor Mount: 2-1/4" x 2-1/4" x 1/4" (Machined)
Flanged Bearing: 1/2" PIC Design E7-S3F $25.46 $101.84Bevel Gear: 2" OD, 1/2" ID, 45-Degree Bevel
Elbow Joint Shaft: 1/2" OD, 3-1/4" Long (Machined)Shoulder Joint Shaft: 1/2" OD, 3-5/8" Long (Machined)
Drill Motor: FireStorm 18.0 V Black & Decker HP932K-2 $149.00 $149.00Drill Motor Encoder
Elbow Motor Shaft: 1/4" x 1/2" Key, 7/16 OD, 1-1/16" Total Length
(Machined)
Elbow Motor Pinion: 3/4" Head OD, 45-Degree Bevel, 1/2" Total Length
Aluminum Tubing: 2-1/2" x 2-1/2" x 12-1/2", 1/8" Wall Thickness
$47.50
Wrist Pillow Block: 5/8" ID (Machined)Elbow Link (Machined)
Wrist BearingWrist Motor Pittman GM8724S027 $150.22 $300.44
Wrist Shaft: 3/16" x 4-1/4" SDP/SI A7X1-06042 $2.05 $2.05Wrist Shaft Coupling SDP/SI A5C9-0606 $5.66 $5.66
Wrist Shaft Ball Bearing: 3/16" SDP/SI S9912Y-E1850FS2 $10.18 $10.18Wrist Differential SDP/SI S9570A-TS3 $304.93 $304.93
Wrist Gear Boston Gear GSS486Y-G $23.30 $46.60Wrist Pinion Boston Gear GSS486Y-P $19.27 $38.54