1. Design of a Robotic Manipulator for a Wheelchair 2000-2001 Gateway Coalition Ohio State University Sinclair Community College Wright State University December 8, 2000

2. 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

3. Project Overview & History Program Background 1996-1997 1997-1998 1999-2000 2000 Graduate Design

4. Program Background National Science Foundation Seven Institutions Advancement of Engineering Education

5. 1996-1997 Design Cables and Transmission Pulleys –Keeps motor on base of robot Short comings –Inappropriate motors –Large size –High maintenance and manufacturing costs

6. 1997-1998 Design Addition of knuckle joint and rotating base Short comings –Expensive –Not mounted to wheelchair –One-directional gripper activation

7. 1999-2000 Design Six degrees of freedom Fully functional gripper Mounted on wheelchair Short comings –Heavy –Expensive –Difficult to manufacture

8. 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

9. 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

10. 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

11. Complete Arm Design

12. 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

13. Travel Position

14. Full Extension

15. Shoulder Assembly Design Limitations (clearance, gear size, bearing size) Mounting Brackets Motors & Placement Gearing Bearings

16. 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

17. 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

18. 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

19. 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

20. 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

21. Lower Arm Assembly 2.5 in. Square Aluminum Tubing Elbow Motor Shaft Bearing Gear 1999-2000 Lower Arm Link

22. 2.5 in. Square Aluminum Tubing Creates an enclosed and clean design Structurally strong, yet fairly light weight Requires minimal machining

23. Shoulder Shaft Diameter:.5 in. Length: 3.625 in. Snap-ring attachment

24. 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

25. 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

26. 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

27. Forearm Assembly Model

28. Differential Gear Set

29. Forearm Assembly Model

30. Preliminary Finite Element Analysis Mounting Brackets Stationary Plate Lower Arm Tube Elbow Links

31. 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

32. 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

33. 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

34. 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

35. 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