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 CurrentInput Voltage Range

Power Range

LCD Display 2mA 5V 10mW

MCU 10mA 5V-6V 500mW-600mW

Pressure 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

TOTAL792.1mW-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 Supplier

Keypad 16 key customize 1 $28.68 $28.68 1 week Digi Key

LED display 1 $24.68 $24.68 1 week Allied Electronics

Control Panel Enclosure 1 $58.98 $58.98 1 week OKW Enclosures, Inc

Pressure 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 weekJameco Inc.

PCB circuit wiring red (100 ft roll) 1 $7.95 $7.95

1 weekJameco Inc.

PCB circuit wiring white (100 ft roll) 1 $7.95 $7.95

1 weekJameco Inc.

6-PIN Wiring connector 1NA $8.90 1 week Allied Electronics

6-PIN Wiring connector recept 1NA $8.90 1 week Allied Electronics

AC-DC power supply 1 $11.86 $11.86 1 week Digi Key

Microcontroller Unit 1 $7.70 $7.70 7 weeks Digi Key

Printed Circuit Board 1 $30.58 $30.58 2 weeks Sunstone CircuitsAMP Panel mount connectors/mate 5 $1.08 $5.40

1 weekAllied Electronics

Card 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?