Blog # 3

 The Wheelchair Lifting Aid Progress

    Over the work period of April 22-29, Team 8 has finished the 3D cad assembly of the final design of the wheelchair system, its stress analysis for the lifting procedure, and the static analysis of the reaction forces during the lifting procedure. The 3D CAD assembly was conducted through SOLIDWORKS, and includes the key components in action such as the linear actuator and its corresponding connecting parts. Figure 1 below is a short video which demonstrates the linear actuator in action and how the team plans to angularly translate the wheelchair seat. 

Figure 1: Wheelchair Lifting Aid in action

    The Team's final design concept has been carried out as previously discussed, however small modifications have been made. For instance, for the intermediate part which will connect the linear actuator to the wheelchair seat, its dimensions and design have been slightly altered. Figure # below illustrates the new intermediate part which has dimensions (INSERT DIMENSIONS) and is to be constructed of aluminum. The team believes this intermediate part to be a key feature to the overall design, as it will be increasing the surface contact area between wheelchair seat and linear actuator, resulting in a greater region for the center of gravity of the patient to stay within and thus providing more stability during the lifting process. 

Figure #: New Intermediate Part

    Within our final design, the team has officially concluded that the stroke length of 10 inches from the linear actuator has allowed the seat to achieve an angle of 68 degrees from the horizontal. Figure # below illustrates with the usage of trigonometric functions and the built in dimensions from SOLIDWORKS, by sin^(-1)[6.3/6.8] = 68 degrees the wheelchair seat's angle was able to be calculated when the linear actuator was fully extended. One of the team's primary goal was for this angle to be at least 65 degrees, and although this goal has been achieved the team will further work to continue to increase this angle. The larger the angle from the horizontal of the wheelchair seat, the smaller the angle of inclination the caregiver will have to undertake when lifting the patient off of the elevated wheelchair seat. To angle can be increased by experimentally positioning the linear actuator at different positions within the newly created bottom platform.

       Figure #: Seat Angle created from the horizontal 

   

         

Figure #: Stroke Length of the Linear Actuator 

    Initially the team planned to conduct the stress analysis of the lifting procedure through COMSOL, however due to licensing issues that platform has become unavailable and the team opted to instead conduct the analysis through SOLIDWORKS. The stress analysis conducted has allowed the team to highlight the highest areas of stress experienced on the wheelchair system during the lifting procedure. Figure # below illustrates that the highest areas of were at the connecting point between the linear actuator and wheelchair seat, the linear actuator and the platform, and between the U-brackets and the bottom platform.  To minimize these induced stresses, the team plans to continue experimenting with the geometry, dimensions, and material of the connecting parts. 

Figure #: Stress Analysis on wheelchair (specific part) 

    As for the static reaction force analysis, the team has conducted this analysis to analyze the worst case scenario for the lifting process. This worst case scenario for the lifting process has been determined to be a slippery (wet) surface for the wheelchair wheels on ceramic tile. A friction coefficient of 0.6 was used. Figure # below illustrates the reaction forces on the wheelchair system. 

Figure #: Static reaction force analysis on wheelchair system 

Figure #: Force Vs Seat Angle

    To continue preparing for the execution phase, the team plans to utilize the summer period to test the fitment and motional clearance of the connecting parts within the wheelchair system as the linear actuator extends. In order to save money on materials, the parts will be 3D printed. The team will 3D print the mounting U-brackets, the bottom platform, and the intermediate mounting part which connects to the wheelchair seat. Although the stresses will not be able to be analyzed, the team will primarily focus on experiment with the positioning of these connecting parts. Refraining from placing a load on the seat will allow the team to study the motion of the wheelchair seat whenever the 3D parts are connected with the linear actuator and wheelchair frame.