Case Study: Engineering a Competitive, High-Capacity Medical Treatment Chair ⚕️

1. Overview & Challenge: The Product Development Mandate

Client: Leading Australian Medical Treatment Chair Manufacturer (Confidential)

My Role: Lead Mechanical Design & Prototyping Engineer

The Core Problem: The client faced intense market pressure from lower-cost international manufacturers. Their existing chair line was expensive to produce and lacked the ergonomic versatility modern hospitals demand. The mandate was two-fold:

1. Redesign for DFM (Design for Manufacture): Achieve a 15% reduction in material and assembly costs to be market competitive.

2. Elevate Versatility & Safety: Design a single platform chair capable of safely supporting both standard and bariatric patients (up to 300 kg) while improving patient access and staff efficiency.

2. Process & Design Thinking: Engineering for 300 kg Capacity

To meet the competing goals of high capacity and lower cost, the design focus was on structural optimization and component consolidation:

• Structural Redesign for 300 kg: The primary engineering challenge was reinforcing the column and base to handle the 300 kg load factor without increasing bulk or cost. We transitioned from a custom welded base frame to a monocoque column design utilizing FEA (Finite Element Analysis) in SolidWorks. This allowed us to optimize wall thickness and geometry, achieving the required 3:1 safety factor while using 10% less material than the previous design's custom weldment.

• Access & Ergonomics: To improve patient entry/exit, the column was redesigned to reduce the lowest seat height by 15 cm. This involved rerouting internal electrical componentry and designing a new low-profile actuator mount to maximise clearance.

• The Pivoting Mechanism: The integrated footrest and pivoting armrests were developed to move fluidly with the patient, minimising strain. This required designing a 3-bar linkage mechanism that could be easily fabricated, focusing on standard bearing sizes and minimizing complex machining operations to maintain a competitive BOM (Bill of Materials).

3. Prototyping & Iteration: Testing the Limits

The prototype development process was highly iterative, with a clear focus on safety and durability validation:

• Proof-of-Concept (V1): A scaled, 3D-printed prototype was created to validate the ergonomics of the armrest pivot and footrest deployment. This allowed for quick adjustments to the rotation axes and stop points before committing to expensive tooling.

• Functional Prototype (V2): Full-scale prototypes were fabricated using production-intent materials (powder-coated reinforced steel for the base) and subjected to extensive load and durability testing.

  • The 300 kg Load Test: The initial column prototype showed unacceptable stress concentrations around the actuator attachment points under maximum load. Iteration: I redesigned the mounting plate geometry, increasing the fillet radii and distributing the load across a larger surface area, successfully passing the static 300 kg test with minimal deformation.

• DFM Validation: The final iteration included a simplified, two-piece leg rest design and standardized castor attachment points. This simplification was directly validated with the manufacturing team, confirming the goal of significantly easier assembly and reduced labour time.

4. Solution & Impact: Quantifiable Results

The final design successfully met all original project objectives, resulting in a superior product that is driving market advantage for the client:

• Cost Reduction: The optimized structure and component consolidation achieved a 17% reduction in overall manufacturing costs, beating the initial 15% target.

• Improved Efficiency: Simplified assembly and maintenance features (like the leg rest and castor system) are projected to reduce hospital M & E (Maintenance and Engineering) costs by 12% over the chair's lifetime.

• Versatility & Safety: A single design now accommodates patients up to 300 kg, streamlining hospital inventory and guaranteeing equitable, high-quality care.

• Hygiene & Space Optimization: All electrical components are concealed and the chair utilizes smooth, sealed surfaces for 100% sanitisation accessibility. The design’s compact footprint and 15 degree floor clearance allowance ensures seamless integration into standard hospital room layouts.

5. Conclusion & Lessons Learned

This project was a prime example of how structural engineering and design for manufacture can directly solve market competition challenges. The key takeaway was the need for early and rigorous FEA validation on load-bearing components. By front-loading the stress analysis on the 300 kg column design, we saved multiple costly iterations in physical prototyping, ensuring the client launched a highly competitive, New Standard product on time and under budget.