Rehabilitation Centre for Children: Analysis and Redesign of Pediatric Mechanical Prosthetic Wrist Units

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Dmitrowicz, Selena
Impey, Joel
Hill, Alicia
Wang, Tao
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At the request of the Rehabilitation Centre for Children, located in Winnipeg, MB, the design team was presented with a project to redesign a pediatric mechanical prosthetic wrist unit. Currently, prosthesis users are subjected to a limited range of wrist motion, as compared to an anatomical wrist. Children ages six to eight years old are forced to use bulky, heavy adult wrist units. In addition, the adjustment mechanisms are difficult to use and often require the assistance of a parent. In order to increase the children’s independence and capabilities, a ball and socket style wrist unit dubbed the “Lock Ball”, was developed. Main components of the design include a polyetheretherketone (PEEK) ball contained within an Aluminum 6061-T6 housing. A clamping collar, fashioned from PEEK with stainless steel locking hardware, applies a frictional force onto the ball to lock it in the desired position, which the user may adjust via a handle. Terminal device interfacing is provided via a quick release 316 Stainless Steel coupling; the male end affixed to the ball and the female end with a pull release attached to the terminal device. Finally, the wrist unit is screwed into the arm socket. The Lock Ball has a large range of motion and locking positions. Allowing 360° of pronation and supination and 45° of flexion, extension, radial deviation, and ulnar deviation, the Lock Ball increases the range of motion over current wrist units. The friction clamping collar used to secure the ball allows near infinite locking positions and can withstand an applied force of 1320 N without slip. The maximum stress found using finite element analysis was at the clamping edge of the collar, but remained well below the yield strength. Therefore this design is safe and is well suited for active children. Through material selection and finite element analysis optimization, the Lock Ball has an outer diameter of 46 mm and weighs 114 g without the quick release coupling and 245 g with, achieving a 6.5% decrease in size and up to 40% in weight savings over comparable wrist units available today. The Lock Ball costs $1038.22, which...