Final Design
Adjustable Chair for Measuring Blood Pressure in Children
Complete Chair Assembly (Left to Right): Front Left View, Front View, Front Right View, Back View
360 Degree View of Complete Chair Assembly
Major Components:
Backrest Adjustment:
A 4-bar linkage with a dual sliding lock mechanism made using 80/20 compatible parts and 3D printed parts was used for adjustment of the backrest, which controls the seat depth of the chair. This design was chosen due to its ease of use, robustness, and price. The 4-bar linkage mechanism allows for lower friction and being less prone to jamming compared to a linear slider, while also allowing the backrest height to be adjusted simultaneously with the seat depth. The dual sliding lock with knob adjustment was used due to the added safety against mechanism malfunctioning compared to a ratchet and pawl and to address issues of meshing with 3D printed gears. Compared to previous designs, this provides a very secure lock up while still being easy to adjust. The backrest surface was made using a modified school chair replacement.
Functional Requirements:
• Forward and back adjustment to accommodate patient
• Simple adjustment process for operator
• Safe for both operator and patient
• Locking so that it serves as a rigid backrest
Functional Requirements:
• Height adjustment to allow patient’s right arm to rest at heart level
• Allow space for patient to sit down
• Relatively easy to adjust
• Safe for both operator and patient
Armrest Adjustment:
A linear slider made using 80/20 compatible parts, constant force spring, and hand break locking mechanism was used for the vertical adjustment of the armrest, and a 90 degree hinge was included to allow the armrest to flip up, helping the patient get in/out of the chair. This design was chosen because it uses commercially available parts and allows for the armrest to be adjusted continuously throughout its range of motion. The constant force spring allows for the effective weight of the armrest to reduced, which helps during adjustment and improves safety by reducing the danger from the armrest slipping or falling under gravity. The armrest desk was cut out of plywood and the corners were rounded to avoid injury.
Footrest:
A stationary footrest was included to help reduce the minimum seat height to 9 to 10 inches. A stationary design was chosen over an adjustable design due to its simplicity and stability while being used as a foot stool. Additionally, the vertical height of the seat is already adjusted by the pneumatic piston in the chair base, making adjustability a redundant feature that would likely increase the time to fully adjust the chair. The mounts of the footrest are 3D printed in PLA and secured to the chair base using screws, and the platform was cut out of plywood and secured with screws. The corners of the footrest were also rounded to avoid injury. When not needed, the chair base can be rotated counterclockwise to move the footrest out of the way.
Functional Requirements:
• Reduce the minimum seat to platform (footrest/ground) height to 9-10”
• Removable/stowable when not in use
• Safe to use as foot stool when needed
Self-Breaking Casters:
Functional Requirements:
• Easy to mount other components onto
• Provide seat height adjustment
• Portable
Chair Base:
A standard office chair base with pneumatic piston was used for seat height adjustment and the bottom half of the chair. This was chosen due to ease of use and reliability, while also fitting the needs of the team the best. The footrest fits over two spokes on the base and the 80/20 framing of the upper half attaches to the standard mounting plate. The original casters were replaced with self-breaking casters to improve safety while in use.
Self-breaking casters were used for the wheels on the chair base because they add additional safety to the chair when in use by preventing the chair base from moving while a patient is sitting in the chair, while still allowing the chair to be easily moved when not in use.
Functional Requirements:
• Prevent movement of chair base while patient is in chair
• Maintain chair portability when not in use
• S
Functional Requirements:
• Easy to assemble
• Sturdy
• Secure mounting
Structural Framing:
Aluminum 80/20 parts were used for the structural framing of the upper half of the chair due being highly customizable and sturdy. This allows everything to be easily assembled and securely attached in place.
Final Performance:
The final chair design features three main mechanisms that allow for the required adjustments of seat depth, seat height, and arm height. This allows the user to adjust the chair to the appropriate position for children from 3 to 10 years old. The mechanisms are easy to adjust, reducing the total adjustment time to around 30 seconds.
The approximate duration for complete chair adjustment is about 30 seconds, although the actual duration may vary due to adjustments needed and cooperation of child.
Since the goal of this project was to provide a quick, easily adjustable chair to assist our sponsors in measuring children's blood pressure, we designed the final design of the chair to achieve all necessary adjustments in a safe, reliable, intuitive, and efficient manner. The three adjustment mechanisms were designed to have a large range of adjustment to best fit the variety of sized children that this chair will encounter during its usage, while remaining easy and intuitive to use by the operator of the chair. The adjustment mechanisms are adjusted using easily accessible knobs and handles.
Although the range of motions of these mechanisms and adjustments work as we expected, the final design may not be as entirely refined as we had hoped. While supplying a secure, reliable lockup of the backrest, the dual sliding locking mechanism can sometimes slightly jam if the backrest is pushed in a particular way, although this is uncommon. Additionally, to prevent the footrest from hinging off when stepping on it from the front, it can no longer be removed, and the chair must be rotated in a particular direction (counterclockwise) to avoid hitting it and prevent proper function of the armrest.
Regarding safety, the design has many elements built into it that successfully minimize hazards that may be present. These include panels mounted on each side of the backrest, reducing exposure to pinch points within the movement of the backrest; end caps and rail covers on the 8020 framing, covering potentially sharp edges on these components; sanding/finishing and rounding the corners on all wood platforms, preventing injury from splintering or sharp corners; permanently securing the footrest to the chair base, preventing injury from the footrest falling off; and constant force spring on the armrest sliding mechanism, reducing the danger from the armrest falling under gravity. Additionally, friction also helped in the safety of the design by resisting the motion of components and slowing down their travel.
Regarding cost, the design meets its requirements, costing approximately $720. This amount is less than 50% of the given budget and only includes the cost of materials used, not the cost of tools. Many design choices were made to account for cost, such as the backrest using a 4-bar linkage over a linear slider.