3.8 design example - philadelphia

Dr. Tarek A. TutunjiEngineering Skills, Philadelphia University

3.8 Design Example

Dr. Tarek A. Tutunji

Philadelphia University, Jordan


Preview In the previous sequences, seven design steps were

discussed.

In this sequence, a design example: overhead crane model will be presented to show the seven steps


1. Define the Problem The objective is to build a system that can translate a

weight in three dimensions by manual joystick.

Specifications:

Load = 5 kg

Speed = 0.11 m/s

Constraints

Time 8 months

Budget: $800


2. Gather Information Types of cranes

Tower

Truck Mounted

Overhead

Travelling bridge

Gantry

Jib

Monorail


2. Gather information An overhead crane is a crane where the hook-and-line

mechanism runs along a horizontal beam that itself runs along two widely separated rails.

Also a hoist is used to lift the items, the bridge, which spans the area covered by the crane, and a trolley to move along the bridge.

Its purpose is to move objects automatically between two locations in a factory


2. Gather Information


2. Gather Information Main Components

Bridge

Rail

Trolley

Beam

Hook


2. Gather Information Electrical components

Motors

Electronics

Controller

Sensor

Mechanical components

Shafts

Gears


3. Propose Solutions Type of crane

Tower

Overhead

Type of actuators

Electric: DC, AC, or Stepper

Pneumatic

Type of sensors

Optical

Limit Switches

Type of controller

PC

Microcontroller

Analog


4. Study the Solutions Overhead crane works

better than Tower for our purpose

Microcontroller

Cheaper than PC

More accurate than analog

DC Motor

Cheaper than AC and easier to control

Easier than pneumatic

Sensors

Limit switch for linear end position

Optical encoder for motor position


4. Study the Solutions: Choose Single girder overhead crane with dimensions: 2 m

length, 1.2 m width, and 1 m height

Three DC motors for xyz-directions

PIC microcontroller

Limit switches, three positioning sensors, control and drive circuits

Keypad. The user can specify the desired position by entering the coordinates on the keypad


5. Analyze & Design: Block Diagram

ControllerPower Electronics

Interface

Limit Switch Sensors

Crane Plant Electrical Motors


Analysis: Weight Calculations

Motors weight = 1.5kg ×2 = 3kg

• Shaft and bearing =4kg

• U- Shape steel bar and steel sheet = 2kg

• Screws and roundels = 0.25kg

• Teflon wheels = 0.25 kg

• Other parts = 0.5 kg

Total weight of Trolley = 10 kg


Analysis: Power Calculations F = M × g F = 5 kg × 9.81 m/s² = 49.05 N

T = F × R T = 49.05 N × 0.025 m = 1.23 N.m

Pm = T × ω Pm = 1.23 N.m × 4.7 rad/s = 5.8 watt.

P actual = 5.8 watt × 1.6 = 9.6 watt

Pe = 9.6Watt /0.8 = 12 Watt

Pe = I × V

We chose DC motor with V = 12 V, I = 3 A.


Analysis and Design: Simulation


Design: Mechanical Drawings


Design: Flow Chart


Design: Schematic Diagram


Final Design The mechanical components were composed of the frame,

the girder, and the trolley.

The frame used bars of hot roll steel AISI 1020: two parallel tracks of 2m length, six vertical columns of 1m length, and sixteen side holding bars.

The girder consisted of two parallel girder tracks of 1.2 m length mounted to side rolling bases.

The trolley part had two 36 watt DC motors with internal worm gear assembly mounted to side rolling bases.


Final Design Actuators:

Three DC motors as: Hook motor to lift the load, trolley motor to move the trolley above the girder, and girder motor to move the girder above the bridges. Each dc motor (3 A, 12V) had internal gears in order to reduce the speed and increase the torque with a gear ratio 1/140.

Sensors:

Two linear optical encoders were used as displacement sensors for the x-y positioning with a resolution 1pulse/cm. The tracks were made from plastic and fixed to the frame. For the z-direction, rotational optical encoders were placed on the shaft of the pulley with a resolution of 20pulse/revolution.


6. Implement: PCB


Implementation: Mechanical


7. Evaluate The crane was tested in

the labs

Equipment used: Scopes and multi-meters

Different loads (up to 5 Kg) were used

Speed of movement was measured using stopwatch

Microcontroller was damaged during testing.

Limit switches were calibrated.

The load cable was re-packaged

Added support to the skeleton frame

Insulated the controller using the opto-coupler.


Final Prototype


Acknowledgement This work was the effort of two student design teams:

Team 1:

Abd Al-hafez Suleiman

Yosef Abo Hurira

Team 2:

Hassan Abu Zahra

Moafeq Alkhateeb

Fadi Darweesh


Conclusion A design example was provided to show the 7-

design steps

In this design project, students used the 7-step design process to build an overhead crane model

3.8 design example - philadelphia

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