Chapter 3 Reverse Engineering

Definition: Reverse Engineering

Reverse engineering is opposite to forward engineering. Works with existing product to create CAD model and modify or reproduce

the design aspect of the product. Can also be defined as duplicating an existing product by capturing its

physical dimensions. Reverse engineering is also defined as the process of obtaining a geometric

CAD model from 3-D points acquired by scanning/digitizing existing parts/products.

Reverse engineering helps in redesigning a component for better

maintainability and also to reproduce a system without access to its design documents.

Introduction

Companies are exploring ways to reduce lead times for new product development.

Reverse engineering is now

considered among the technologies that provide business benefits in shortening the product development cycle.

Reverse engineering allows

the possibilities of closing the loop between what is “designed” and “ actually manufactured”.

What is Reverse Engineering ?

Engineering is the process of designing, manufacturing, assembling and maintaining products & systems.

Forward engineering : is the traditional process of moving from logical designs to the manufactured and assembled systems. In some situations, may be product are available without any technical details e.g. drawing, bills of material or without engineering data.

Reverse engineering : process of duplicating an existing part, subassembly, or product, without drawings, documentation is known as reverse engineering.

Reverse Engineering a Solution

As products become more organic in shape designing in CAD becomes more challenging without any guarantee that the CAD design will replicate the sculpted model exactly.

Reverse engineering can be considered as an optimal solution to the above problem.

The physical model is the source of information for the CAD in the reverse engineering.

Reverse engineering also helps in compressing the product development lead time.

The process is also referred as physical to digital process. Example: injection molding companies explore ways to reduce the design

development time of tool and die. Reverse engineering helps in transferring a physical product or clay mock

up in digital form. Digital form can be easily remodeled and exported for rapid prototyping or rapid manufacturing.

Why Use Reverse Engineering ?

The original manufacturer no longer exists, but a customer needs the product, e.g. , aircraft spares required typically after an aircraft has been in service for several years.

The original manufacturer of a product no longer produces the

product, e.g. , the original product has become obsolete. The original product design documentation has been lost or

never existed. Creating data to refurbish or manufacture a part for which there

are no CAD data, or for which the data have become obsolete or lost.

Inspection and/or Quality Control–Comparing a fabricated part

to its CAD description or to a standard item.

Cont……

Some bad features of a product need to be eliminated e.g. , excessive wear might indicate where a product should be improved.

Strengthening the good features of a product based on long-term usage.

Analyzing the good and bad features of competitors’ products.

Exploring new avenues to improve product performance and features.

Creating 3-D data from a model or sculpture for animation in games and movies.

Cont…… Creating 3-D data from an individual, model or sculpture to

create, scale, or reproduce artwork.

Architectural and construction documentation and measurement.

Fitting clothing or footwear to individuals and determining the anthropometry of a population.

Generating data to create dental or surgical prosthetics, tissue engineered body parts, or for surgical planning.

Documentation and reproduction.

Reverse Engineering Strategy

Reason for reverse engineering a part

Number of parts to be scanned–single or multiple

Part size–large or small

Part complexity–simple or complex

Part material–hard or soft

Part finish–shiny or dull

Part geometry–organic or prismatic and internal or external

Accuracy required–linear or volumetric

Majors Steps in R.E.

Reverse Engineering: The Generic Process

R.E. is a 3 phase process

i. Scanning

i. Point processing

i. Application specific geometric model development

Scanning Phase Selection of correct scanner. Preparing the part to be scanned. Scanning to capture geometric details e.g. steps, slots, pockets

and holes. 3D scanners for scanning part geometry, producing clouds of

points to define surface profile. Two types of scanners.

i. Contact ii. Non-contact

Data Acquisition Techniques

Contact Scanner

Contact probes automatically follow contours of a physical surface.

Probe devices are based on CMM technologies, tolerance range 0.01-0.02mm

Speed of scanning is function of size of part, generally slow for large parts.

Tactile device probes must deflect to register a point, a degree of contact pressure is required.

Restrictions with contact pressure limits the use of this technology for soft materials.

Non Contact Scanners

Based on lasers, optics and charge couple devise sensors.

Tolerance limit in the range of ± 0.025 to

0.2mm. Problem in scanning surface parallel to axis of

laser. Shiny surfaces needs to be treated with fine

powder before scanning. Employed when the accuracy of the

information generated is secondary to the speed.

Output of scanning phase id point cloud data.

Laser Triangulation

Location & angles between light source & photo sensing devices to configure position coordinates.

Light is focused at a predefined

angle on the surface. Photosensitive device captures the

reflected light & using geometric triangulation the coordinates of surface is recorded.

Light source and photosensitive

device is normally mounted on moving platform to enable multiple scans.

Accuracy of scan depends on the

resolution of the photosensitive device & the distance between the surface & scanner.

Interferometry

Measure the coordinates of any point/ feature in terms of wavelengths using interference patterns.

Considered as very accurate, since

light has a wavelength in the order of nanometers, while R.E. applications are in the range of cm to m.

Generally, a monochromatic beam

of light is employed both to probe the object and for a reference beam for comparing with the reflected light.

Structured Lighting

A popular method is shadow Moire, where an interference pattern is projected onto a surface producing lighted contour lines.

These contour lines are captured

in an image and is analyzed to determine the distances between the lines.

Distance between interference

lines is proportional to the height of the surface at the point of interest & coordinates of surface points can be deduced.

Stereo Image Analysis Relative locations of landmarks in multiple images are related to

position coordinates of points of interest. Method is similar structured lighting method. Image frames are analyzed to determine coordinate data. Analysis does not rely on projected patterns, but, stereo pairs are used

to infer information to determine coordinates. Referred as passive method, as no structured light is employed. Correlation of image pairs & landmarks with the help of images is

considered as a complex procedure hence active methods have preference.

Other Methods ACOUSTIC Sound is reflected from a surface. Essentially the same as time of flight Distance between surface & source is measured with known speed of

sound.

MAGNETIC FIELD Involves sensing the strength of magnetic field source. Magnetic touch probes are employed of sensing the location and

orientation of a stylus within the field.

HYBRID Combination of contact & non-contact systems.

Non Contact Scanners: Advantages

No physical contact.

Fast digitizing of substantial volumes.

Good accuracy and resolution for common applications.

Ability to detect colors.

Ability to scan highly detailed objects, where mechanical touch probes may be too large to accomplish the task.

Non-Contact Scanning : Challenges

Calibration

Accuracy

Accessibility

Occlusion

Fixture (placement)

Multiple views

Noise and incomplete data

Statistical distributions of parts

Surface finish

Point Processing Phase Importing the point cloud data,

reducing the noise in the collected data & also reducing # of points.

Tasks were performed using a range of filters.

Also allows to merge multiple scan data sets.

Good datum planning for multiple scanning will reduce the effort required in the point processing and avoid errors from merging multiple scan data.

Output is a clean, merged point cloud data set.

Application Geometric Model Development Phase

Generation of CAD models from point data is probably the most complex activity.

Surface fitting algorithms are

required to create surface to represent 3D information described within the point cloud data set.

Most CAD systems are not

capable to display and process large amount of point data, as a result discrete software packages are required for point processing.

Point cloud Triangulated surface

Steps for Multiple Overlapping Scan

Is Project Suitable for R.E. ? How will the team perform the investigation? What constraints have to be dealt with in analyzing the artifact? What plan will best unravel the artifact’s function and design

features? What types of plots or graphical displays will best communicate

discoveries about the object’s function? How was it manufactured? What is the consumer population? Are design improvements possible? What kind of an ad or commercial will be suited for the object?

Reverse Engineering: Applications

Frisbee Aluminum can Wind-up toy robot Disposable camera Stapler Climbing rope Coffee maker Thermos

Ski binding

Water gun

Lighter

Match

Bicycle light system

Audio speakers

Shock absorber

Aluminum Can : Procedure

i. Measured dimensions

ii. weight

iii. flow

iv. rates (wide mouth, narrow mouth),

v. force (required to open)

vi. load (to deform and to explode).

vii. The deformation force defines the critical axial buckling load.

Aluminum Can : Results/Conclusion

Requires 550 to 600 pounds to deform.

Requires 725 to 790 pounds to explode.

Wide mouth takes 8.3 seconds to empty.

Narrow mouth takes 13.6 seconds to empty.

Ease of recycling is a big advantage.

617 cans can be stacked high without damaging the bottom can. This is important for storage and shipping.

The Match : Procedure

i. Studied history.

i. Measured the burn time of matches of different lengths as a function of angle.

i. The critical angle to hold a match in the wind (a fan was used).

i. The striking force and match angle (an air track was used).

The Match : Results/Conclusion

Held horizontally, a short match burned about 1.7 inches in 30 seconds.

Held at 45°, a short match burned about 1.4 inches in 12 seconds.

In wind, it is best to point a match straight down.

The best striking angle was between 35 - 40° from the surface.

The Toaster : Procedure

i. Dissected object.

i. measured dimensions.

i. Measured temperature and time at each setting.

i. Measured electrical resistance.

The Toaster : Results/Conclusion

The time for toasting ranges with settings from 20 to 34 seconds, if the toaster is cooled between tests.

The time for toasting ranges with settings from 4.7 to 11.7 seconds, if the toaster is not cooled between tests. Hence, for a quick response, let the toaster go through a heat cycle before initially toasting.

The toast compartments taper in width from top to bottom. The team theorized that this permits smaller, thicker items to be toasted without falling to the bottom of the toaster.

R.E. : Project Report Background:

Describe what need the device fulfills. Give a brief history of the

design. Include any accompanying literature as an appendix.

Project Goals:

List the goals for performing the reverse-engineering study; i.e.,

what will be learned from the study?

Test and Analysis Procedures:

Describe the procedures used to address the above goals. How was

the device and its components evaluated? Document test data

obtained.

Dissection Details:

Describe (using drawings, photos and/or video where appropriate)

the key components and how they function.

Results:

Describe what was learned about this device’s design and

functionality. Provide suggestions for changes that would improve its

function or make it more cost effective to produce. Provide

suggestions for any changes that would make it “greener” or more

universally available.

Marketing:

Include either an advertisement (in print) or a video or radio

commercial, marketing this artifact to an identified target group of

potential customers.