## 3 Results
### SolidWork Motion Analysis
#### 3.4.2 Lift Forces  
Using SolidWorks motion analysis, lift forces and torques were recorded for each design under gravitational loading with simulated motors. Linear and rotation motors were used to simulate the real-world motion of each device. Design 1: Rotational Lift  
Design 1 (rotational lift shown in Figure 4) employs five rotational motors for its lift mechanism, with four situated at the base facilitating upward rotation and another at the top controlling patient tilt. The motion analysis for the lift mechanism from 0 to 90 degrees over 30 s yielded force results as depicted in Figure 10.  
Figure 9: Tipping forces: (**a**) tipping forward results and (**b**) tipping backward results. Notably, all motor torque charts exhibit smooth motion without spikes, validating a seamless experience for the patient. The rear rotational motors at the base experience the highest torque at 859 Newton meters each, while the front rotational motors encounter the least torque at 32 N-m each. The unique V pattern observed in the tilt control motor's torque (making at 420 N-m) aligns with the device countering gravity during the initial 45 degrees and then working against gravity to position the patient upright. Design 2: Scissor Lift  
Design 2 (scissor lift shown in Figure 5) introduces a sophisticated mechanism involving two distinct motor techniques. The lower portion of the lift relies on a piston system, where extension lowers the lift, and retraction raises it. Simultaneously, the upper portion responsible for controlling the patient's tilt integrates two linear actuators on each side. The forces required for these linear actuators are depicted in Figure 11, revealing an equitable distribution of forces resulting in a maximum force of 3000 N at the initial movement phase. Notably, the motor force undergoes a shift of around 18 s, becoming  
Figure 10: Design 1 (rotational lift) torque results. (**Top**): torque on the top motor when moving from 0 to 90 degrees. (**Middle**): combined torque on the two front lower motors that control the lift. (**Bottom**): combined torque on the two back motors which control the lift mechanism. negative as the motor restricts the force of gravity rather than actively pushing against it. In contrast, the piston system exerts a maximum force of 4000 N, showcasing its robust lifting capacity. Design 3: Double Pivot Lift  
Design 3 (double pivot lift shown in Figure 6), a complex configuration involving four motors, presents a nuanced approach to the RWTD lift mechanism. Two motors are strategically positioned at the back, while the other two are situated on the front pivots. The motion is orchestrated in a counterclockwise direction towards the rear of the device, primarily focused on raising the RWTD. An integral aspect of this design is its concerted effort to maintain the center of gravity of the device in a consistent position throughout the lifting process. This attention to the center of gravity dynamics is pivotal for ensuring the stability and controlled motion of the device during elevation. As depicted in Figure 12, the left graph illustrates the lift torques experienced by the rear motors during the lifting operation. The maximum lift torque for each rear motor peaks at 174.4 Newton meters, a critical moment occurring around the 12-s mark when the tilt angle is near 45 degrees. This specific torque application is strategically timed to manage the transition phase of the device's tilt. Meanwhile, the right graph in Figure 11 details the lift torque on the front motors throughout the lift process. At the 90-degree tilt position, the front motors experience their maximum lift torque of 300.5 Newton meters. Post the 60-degree tilt position, the tilt angle becomes exclusively controlled by the front motors, effectively guiding the device to the precise upright position.