Computer Aided Engineering Applications 3. Advanced ...oscar/wp-content/uploads/2015/01/3A_Advanced... · Computer Aided Engineering Applications 3. Advanced Manufacturing ... •

Computer Aided Engineering

Applications

3. Advanced Manufacturing 3.1 CAM systems

3.2 Geometry of surfaces

Engi 6928 - Fall 2014

3.2 Geometry of surfaces

3.3 Product data exchange

3.4 Data Communication

3.5 Automated Manufacturing systems

3.6 Part programming

3.1 CAM systems3.1 CAM systems

Structure of an Automated manufacturing system

Product

descriptionCAM software MCU

Machine

Hardware

Data IO

SCADA


HardwarePDE NC

CODEControl

Commands

The presentation goes over the primary modules shown in this figure.

3.2 Geometry of curves and surfaces3.2 Geometry of curves and surfaces

• Polygon models only require vertices and lines and

planar surfaces for B-Rep representation.

• Complex models require curves and curved surfaces

to represent its geometry.

• Water tight surface – A combination of surfaces • Water tight surface – A combination of surfaces

which are connected to form a closed volume. Solids

are water tight surfaces.

• Analytic curve – Analytic curves are defined by an

algebraic equations. Ex: circle, ellipse, parabola,

hyperbola.


• Synthetic curve - A Free form curve defined by a set

of points or control points.

• Parametric polynomial curve – A curve which is

defined using a parameter u.

• Analytic curves are not good for free form design. For

design of shapes like car bodies, ship hulls, synthetic

curves are required.


Continuity between curve segments

• Position continuity

• Slope continuity

• Curvature continuity– Requires minimum of a cubic polynomial

– Higher degree polynomial fittings cause oscillations


Hermite cubic spline

– A spline that passes through two given end points with

two given slopes.

– Can connect multiple points in a similar manner with

curvature continuity.

– has global control.– has global control.


Bezier curves (P. Bezier 1962)

– Only control points are used. No tangent vectors.

– Can be manipulated using the control polygon.

– Each control point affects the final curve according to the

blending function.

– Degree of curve = highest power of blending polynomials = – Degree of curve = highest power of blending polynomials =

number of control points -1.

Blending function of a cubic Bezier A cubic Bezier


Bezier curves (P. Bezier 1962)

– Convex hull property

– The curve is tangent and touches the first and last control

points.

– Has global control, degree of curve increments with

control points

Rational Beziers – Each control point has an associated weight

. Results in more control.


NURBS – Non-uniform rational B-splines

– A generalization of Bezier. Multiple rational Beziers joined

with knots.

– Can represent any analytic/ synthetic curve, line or

surface. (conic sections, cubics, Beziers)

– Local control – control points and degree are separate. – Local control – control points and degree are separate.

Degree specifies how many neighbouring points are

affected.

Blending function of a NURBS Construction of NURBS

　"


– Defined by degree, control points, and knots.

– Degree 3 (cubic), 5 (quintic) NURBS often used.

– Control points (N) >= degree +1

– Exclusively used in almost all CAD programs to represent

geometry at the kernel level.

– Standardized.... Simplifies data exchange

NURBS

– Standardized.... Simplifies data exchange

– Kinks are knots in a NURBS where only positional

continuity is preserved.

Kinks in NURBSKinks in NURBS


NURBS surface modeling

• NURBS surfaces are rectangular patches with two parameters u, v.

• Iso-uv lines are NURBS curves.

• Solids are formed by a set of NURBS NURBS patch

• Solids are formed by a set of NURBS patches knit to from a water tight shells.

• Software dedicated to surface modelling handles NURBS well.

• Editing NURBS patches could result in leaks on the shell.

NURBS patch

Watertight NURBS model


• Recent developments

– Subdivision models (used in animation industry) to NURBS

model conversion.

– T-spline modeling

Surface modelling

Solid modelling


Control points

knots

Increasing weight of a control point from 1 to 5

Changing a control point of a degree 3 curve vs a degree 7 curve

3.3 Product data exchange3.3 Product data exchange

Four types of product Data

– Shape – geometry, topology

– Non shape – color, units, identifiers, annotations

– Design – Material, FEA, Factors of safety

– Manufacturing – tolerances, BOM, process plans– Manufacturing – tolerances, BOM, process plans

A good natural file format should allow standardized

storing of as much as product data as possible, for

archival or exchange purposes.


Translators – direct vs indirect

+ runs quickly

+smaller data size

-Require 2nC2

+ Require 2n

translators

+ eliminate -Require 2nC2

translators

+ eliminate

dependence

- Standardization ?


1. STL file

• A simple file type for 3D. Defines the solid using set

of triangular faces (facets)

• No inner loops. No edge definitions (linear).

• Facet normal points to the free space. CCW order of • Facet normal points to the free space. CCW order of

vertices serves as a redundancy check.

• ASCII and binary types.


STL file

• Mesh density controllable.

• Is an approximate polygon model.

So certain geometric data are lost

in translation.

Common STL errors

• Topology errors – non manifold models, not water tight. (holes, isolated triangles, duplicates, etc.)

• Model errors. i.e. Errors in the original model itself

• Normal inconsistencies. Surface normal errors.

• Open source tools for processing – MeshLab

STL errors – self intersecting triangles

detected in MeshLab


2. DXF\DWG – Drawing interchange format

• The native format in AutoCAD which is considered

the de facto standard for 3D parts.

• DWG is used for 2D drawings.

• Has shape and non shape data. The file structure:• Has shape and non shape data. The file structure:


• The main body of file has an entity list ,

followed by a list of parameters for each

entity.

• The entities have both shape and non-

3. IGES – Initial graphic exchange specification

• The entities have both shape and non-

shape data.

• The entities include NURBS

• Allows new entity definitions in file.

• Developed in 1980`s, new developments

are difficult to standardize using the

standard definitions.


ᣠΆ


• Ongoing project . Attempts to define a natural file for

all shape, non-shape, design and manufacturing

data. (Common data format for entire life cycle)

• Multiple application domains (Mechanical, electrical,

etc.)

4. STEP – ISO 10303

etc.)

• Shares data in the form of applications. Ex: AP203

defines geometric entities.

Application layer in STEPS


Rhino to SolidWorks workflow

Organic Freeform modelling using NURBS surfaces in Rhino

Solid modeling in Sold works., shelling, features, Assembling

Export IGES

Parent child

relationship

preserved in the

workflow

NURBS surface

geometry fully

exported

粠ҡ

3.1 Data Communication3.1 Data Communication

Structure of an Automated manufacturing system

Product


Machine

Hardware

Data IO

SCADA


HardwarePDE NC

CODEControl

Commands


• Data communication is used to transfer data to and

from manufacturing machines.

• These data are essential for process control, where

the efficiency and quality of the production line is

tracked and corrected as necessary. Also required for

factory automation, remote monitoring etc..factory automation, remote monitoring etc..

• The data is often displayed on SCADA (Supervisory

control and Data Acquisition) units, which can be a

panel or a GUI interface in a PC.

肐ҡ


Data coding (Data format)

• For data communication, the sender and receiver

should be aware of the way data is stored in the

payload bits (1`s and 0`s) received.

• Common methods include ASCII strings, binary data

structures (sequences of ints, floats, Booleans etc.) .structures (sequences of ints, floats, Booleans etc.) .

• Data encryption encodes the data so that it cannot

be decrypted without the decryption key/s.

Communication protocol

• A set of standardized rules for data exchange. i.e.

Data formats , Error detection, Flow control,

Acknowledgement, Routing, Addressing, Retries

ᣠΆ

Keywords to knowKeywords to know

sender

8. Communication

Medium

-RF

1. Data format

-digital vs analog

-encoding (data type)

2. Error checking

3. Flow control

-Acknowledgement

receiver

-RF

-wired

-Acoustic

9. Channel

10. Bandwidth

-Acknowledgement

4. Retries

5. Addressing

6. Routing

7. Encryption


1. Serial links-RS232

• Typically a +-13V digital serial signal.

• Data buffers are used to transmit and

receive data.

• The connection parameters: Baud rate, MAX 232

(Serial, USART)

• The connection parameters: Baud rate,

Parity, Start bit, Stop bit, COM port.

• Minimum requirements are the RX, TX ,

and Ground lines.

• Low power devices communicate serial

at much lower voltage signals (5V/

3.3V) which can be converted to RS232.

RS

23

2 +

-13

V

UA

RT

5V

MAX 232

ᣠҩ


1. Serial links- RS232

Minimum connection

• Example: ASCII communication.

Baud :9600 (104.1 us per bit)

RXRX

TXTX

GNDGND

RXRX

TXTX

GNDGND

PAYLOAD

Baud :9600 (104.1 us per bit)

Start bit :1, Data bits:8,

Stop bit:1, Parity: none

• Range of communication: ~10 m (depends of baud,

shielding)

鎠ҥ


1. Serial links- RS232

• Data reception and transmission are standard

operations in many languages. C, Matlab etc.

• Software like hyper terminal, cool term allows to

send and receive serial data.

• Hardware flow control would improve link quality.

s = serial('COM1'); //open COM port 1set(s,'BaudRate',4800); //set BAUDfopen(s); //open devicefprintf(s,‘TEST') //send ‘Test’out = fscanf(s); // receive and store to outfclose(s) // close serial port

փ


Example: RS232 (UART) communication with

Matlab.

instrreset

clear

clcclc

serialOne=serial('COM24', 'BaudRate', 9600);

fopen(serialOne);

%%

fprintf(serialOne,'ps2500')

fprintf(serialOne,'pp2500')

fprintf(serialOne,'ts2500')

fprintf(serialOne,'tp300')

ᣠҧ


2. Local Area Networks- LAN

• LAN is good for network of devices and allows much

higher data rates (100 Mbps)

• Confined to 10Km in distance.

• WLAN uses a wireless medium (2.4GHz RF). LAN • WLAN uses a wireless medium (2.4GHz RF). LAN

uses wired medium (twisted pair)

• LANs have well established protocols for networking,

traffic control, and error recovery.

• TCP/IP and UDP protocols are popular.


2. LAN/ WLAN

• LAN communicates packets of Data.

• Each device in the network is assigned an IP address.

• Different Ports can be used under the same IP address so

that many application can access the LAN.

• Applications can run as a client (A requesting machine) • Applications can run as a client (A requesting machine)

or a server (a responding machine)

• The packet header contains the data of source and

destination , error checking info.

• Error checking is performed using check sum. (a number

representing the addition of all data bits in the payload)

ᣠҧ


TCP and UDP are two different transport layer

protocols. The main differences:

Transmission Control Protocol User Datagram protocol

Requires a connection with the

host for data transfer.

No connection required.

Lower speed Higher speed

Highly reliable ( flow control

and acknowledgements)

Low reliability (no retries, no

flow control)


• Example 1: TCP communication with Matlab

clear

clc

instrreset

close all

t = tcpip(‘127.0.0.1',4012,'NetworkRole', 'client');

fopen(t)

clear

clc

close all

t = tcpip('0.0.0.0',4012,'NetworkRole', 'server');

fopen(t)

Client ApplicationServer Application

Remote IP

Remote Port

Remote IP

Local port

fopen(t)

pause(1)

fprintf(t,'G01 X1.00 Y1.00')

fclose(t)

fopen(t)

while(1)

if (t.BytesAvailable>0)

data = fscanf(t)

end

end

fclose(t)

Connect to server @ localhost

i.e. 127.0.0.1 PORT: 4012

ᣠҧ


• Example 2: Machine network Machine 3

Local IP : 192.168.1.103

MCU application

Protocol /Role: UDP

Local PORT : 3005

Remote IP /PORT: n/a

LAN

COM10 COM1

9600 Baud

Machine 1

Local IP : 192.168.1.101

MCU application

Protocol /Role: TCP Server

Local PORT : 1005

Remote IP/PORT : any

Machine 2

Local IP : 192.168.1.102

MCU application

Protocol /Role: TCP Server

Local PORT : 1005

Remote IP/PORT : any

Central computer

Local IP : 192.168.1.101

Central Application to

control machine 2

Protocol /Role: ?

Local Port: ?

Remote IP:?

Remote Port:?


• Example 3: UDP communication with Matlab

clear

clc

close all

hudpr =

dsp.UDPReceiver('RemoteIPAddress','0.0.0.0','LocalIPPort',2

5000,'MessageDataType','int8')

count=1;

clear

clc

close all

hudps = dsp.UDPSender('LocalIPPortSource',

'Auto','RemoteIPAddress','127.0.0.1','RemoteIPPort',250

00)

50

100

150

count=1;

while(count<360)

dataReceived = step(hudpr);

if ~isempty(dataReceived)

signal(count)=dataReceived;

count=count+1;

end

end

plot(signal)

release(hudpr)

for i=1:360

step(hudps,int8(sind(i)*128))

end

release(hudps)

Sender

Receiver

0 50 100 150 200 250 300 350 400-150

-100

-50

0

Note: here we used the DSP system toolbox , since the computer lab does not have the

instrumentation toolbox

Protocol /Role: UDP

sender

Local Port: Any

Remote IP: 127.0.0.1

Remote Port:25000

Protocol /Role: UDP

receiver

Local Port: 25000

Remote IP: Any

Remote Port: Any

Documents

Computer Aided Engineering Applications 3. Advanced ...oscar/wp-content/uploads/2015/01/3A_Advanced... · Computer Aided Engineering Applications 3. Advanced Manufacturing ... •