A NEW MINIMALLY-INVASIVE BEDRIDDEN PATIENT WEIGHING SYSTEM

Group 16Emily JaegerAmy RosenthalNicole Typaldos

THE PROBLEM Current weighing techniques are

inadequate and often dangerous Lifts require suspension of patient over the

bed Uncomfortable for patient and time consuming

and difficult for nurses Built-in scales have low accuracy (1% of

patient weight) Beds with built in scales are expensive,

causing a low adoption rate

DESIGN REQUIREMENTS Weigh bedridden patients within 0.23 kg (0.5 lb)

and with minimal movement of patient. A single user with no additional training to operate

the device and obtain patient weight in less than 5 minutes.

Device will not interfere with normal patient care. Adult and obese patient weighing 22.7 kg to 453.6

kg (50 lb to 1000 lb) should remain comfortable. Automatic readout to display screen. The device will cost a maximum of $10,000.

A COMPARTMENTALIZED FLUID FILLED BLADDER The Bladder

Location of the weight sensing The Controller

Allows the user to interact with the device and stores all important data

The Cart Contains a pump and reservoir to fill, drain,

and store the fluid when not in use

ANALYSIS – THE BLADDER Smallest bed deck size: 90.2 cm x 203.2

cm Bladder dimensions selected to be 90 cm

x 200 cm to accommodate all bed sizes The bladder had to be thick enough to fit

the sensor while also minimizing the volume of water The internal thickness is 3 cm in order to

accommodate the sensor

ANALYSIS – THE BLADDER Maximum weight to be held is 453.6 kg

(1000 lb) Given the area, this translates to a

maximum internal pressure of 8.0 kPa

ANALYSIS – THE CONTROLLER Power Requirements for Each

Component

Component Input Current Input Voltage Range Power Range

LCD Display 2mA 5V 10mW

MCU 10mA 5V-6V 500mW-600mWPressure Sensors (4) 8mA 7V-8V 56mW-64mW x (4)

16- Key Keypad 1.8mA 4.5V-5.5V 8.1mW-9.9mW

Fluid level sensor 10mA 5V 50mW

TOTAL 792.1mW-925.9mW

ANALYSIS – THE CART Pump Selection

Needed to be able to overcome the maximum pressure within the bladder to refill if patient is present

Needed to fill within our set goal of 5 minutes

To pump up to 53 L (14 gallons) in 5 minutes, or 2.8 gallons per minute minimum

DETAILS – THE BLADDER Material: PVC Tarpaulin (5 mm thick) Dividers: High Density Polyurethane

(HDPE) (2 mm thick) Overall dimensions: 90 cm x 200 cm x 3

cm 4 compartments each with a pressure

sensor

DETAILS – THE BLADDER Pressure to Weight

Each compartment contains a pressure sensor

The tare value of each sensor is stored in the controller

Using the area of the specific compartment, the weight on that compartment is obtained

These pressures are then summed by the controller to output the patient’s weight

DETAILS – THE CONTROLLER Internal Components

LCD Display High contrast Displays desired 40 characters Minimizes glare in the hospital

setting MCU

Takes at least 10 inputs Can store information and still

obtain new information 16-key keypad

Numbers: 0 through 9 Function keys: Tare, Get weight,

Adjust, Units, Cancel, Yes

DETAILS – THE CONTROLLER External Components

4 Pressure Sensors (140PC Series, Honeywell)

Gauge input Linear within desired range

Fluid Level Sensor (eTape, Milone Technologies)

Varies resistance based on fluid level

DETAILS – THE CART Cart Frame

Constructed from alloy 6061 aluminum 2.5” and 2.0” extruded square tubing (1/4”

thick) 3/64” thick sheets for platforms 1.25” extruded circular tubing (1/16” thick)

Tiered design to minimize dimensions

DETAILS – THE CART Water Reservoir

Material: HDPE (1/16” thick) Volume

Maximum: 66.8 L To fill line: 57.4 L

Opening near base with fitting for connection to pump

Design allows for higher fill accuracy as volume lowers

DETAILS – THE CART The Pump

Rotary vane pump (McMaster-Carr) 19.7 L per minute (5.2 gallons per minute) Maximum pressure of 1.66 Mpa (241 psi)

DETAILS – SAFETY CONCERNS Cords and tubing pose a tripping risk High pressure produced by the pump,

requires safety labeling and careful usage Water spill risk due to the tubing Controller displays warnings and

confirmation screens when certain functions are called

Training required for nurses to ensure proper usage

PRODUCTION – THE BLADDER

ComponentQuantity Unit Price Total Cost Lead Time Supplier

PVC Tarpaulin (per square meter) 2 $15.00 $30.00

30 to 45 days

CTA Hi-Tech Textiles Co.

In order to seal the bladder, high frequency welding is used.

Production cost ~$100

PRODUCTION – THE CONTROLLERComponent Quantity Unit Price Total Cost Lead Time SupplierKeypad 16 key customize 1 $28.68 $28.68 1 week Digi Key

LED display 1 $24.68 $24.68 1 week Allied ElectronicsControl Panel Enclosure 1 $58.98 $58.98 1 week OKW Enclosures, IncPressure Sensor 4 $127.75 $511.00 1 week Jameco Inc.Keypad Encoder Chip 1 $5.19 $5.19 1 week Jameco Inc.3-PIN Sensor connector 4 $0.40 $1.60 1 week Allied ElectronicsPCB circuit wiring black (100 ft roll) 1 $7.95 $7.95 1 week Jameco Inc.PCB circuit wiring red (100 ft roll) 1 $7.95 $7.95 1 week Jameco Inc.PCB circuit wiring white (100 ft roll) 1 $7.95 $7.95 1 week Jameco Inc.6-PIN Wiring connector 1NA $8.90 1 week Allied Electronics6-PIN Wiring connector recept 1NA $8.90 1 week Allied ElectronicsAC-DC power supply 1 $11.86 $11.86 1 week Digi KeyMicrocontroller Unit 1 $7.70 $7.70 7 weeks Digi KeyPrinted Circuit Board 1 $30.58 $30.58 2 weeks Sunstone CircuitsAMP Panel mount connectors/mate 5 $1.08 $5.40 1 week Allied ElectronicsCard edge connector (connect keypad output to pcb) 1 $1.30 $1.30

1 weekAllied Electronics

Total $728.62

PRODUCTION – THE CONTROLLER OKW provides free prototype creation with

the purchase of controller housing products. The PCB printing and customization would

cost $30.58. (Sunstone Circuits) Circuit assembly and soldering could be

done by team members For mass production

Circuitry assembly would cost $158 Milling of the enclosure would cost $14

PRODUCTION – THE CARTComponent Quantity Unit Price Total Cost Lead Time Supplier

HDPE (48" x 48") 1 $20.23 $20.23 < 1 week US Plastics Corp

Female Tank Fitting 2 $12.46 $24.92 1 week McMaster-Carr

Black Hose (per ft) 12 $1.20 $14.40 1 week McMaster-CarrHose Male Fittings (set of 2) 2 $16.68 $33.36 1 week McMaster-Carr24" eTape Continuous Liquid Level Sensor 1 $49.99 $49.99 2 weeks Milone Technologies

12-24B-XD Wheel 2 $42.74 $85.48 1 week Darcor Casters

12-24-XD Wheel 2 $34.25 $68.50 1 week Darcor Casters5/16" Square Bolts, 1" length (25 ct) 1 $5.59 $5.59 1 week McMaster-Carr2.5" Square Tube Aluminum, 1/4" thick (8 ft) 1 $97.34 $97.34 1 to 2 weeks The Metal Store2.0" Square Tube Aluminum, 1/4" thick (6 ft) 1 $56.80 $56.80 1 to 2 weeks The Metal Store1 1/4" Circular Tube Aluminum, 1/16" thick (8 ft) 1 $37.30 $37.30 1 to 2 weeks The Metal Store

Rotary Vane Pump 1 $1,160.16 $1,160.16 3 days McMaster-Carr

Total $1,654.07

PRODUCTION – THE CART Aluminum components are welded

together Rate of ~$60 per hour For 2 hours of welding: $120

For prototyping, the tank is created through plastic welding of sheets of HDPE: ~$50 for fabrication Mass production would utilize injection

molding

PRODUCTION OVERALL Total cost of materials: $2,412.69 Total cost of manufacturing: $300.58

Total cost for a single prototype: $2713.27

CONCLUSIONS Attempted to solve the problem, but

many unforeseeable complications arose throughout the design process

Due to these complications, a patent was not pursued

LESSONS Communication and clear explanation

is critical when working in a team Even the smallest parts play a critical

role In preliminary design, all possible

calculations, even trivial ones, should be completed to avoid surprises later on

QUESTIONS?