Design of plastic spur gears using virtual reality

48 Int. J. Computer Aided Engineering and Technology, Vol. 6, No. 1, 2014

Copyright © 2014 Inderscience Enterprises Ltd.

Design of plastic spur gears using virtual reality

O.T. Laseinde* and S.B. Adejuyigbe College of Engineering, Federal University of Agriculture Abeokuta, P.M.B. 2240, Abeokuta Ogun State, Nigeria E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] *Corresponding author

Abstract: The research is a study into the design process of plastic spur gears using virtual reality (VR). It is aimed at developing a functional model and further validating the model for the production of plastic spur gears. It involves the development of a software application which will automatically generate gear design parameters. At the conclusion of the research, a flawless simulated computer model for the calculation of all parameters of plastic spur gears was developed in both DOS environment and in an enhanced interface using macromedia flash. The complete plastic spur gear profile was generated upon feeding in the major gear designing parameters. In conclusion, virtual reality can be applied as a useful teaching tool for the improvement of engineering learning processes especially in areas with limited access to required learning infrastructure.

Keywords: computer-aided design; CAD; computer model; plastic mould; plastic spur gears; simulation; virtual reality; VR.

Reference to this paper should be made as follows: Laseinde, O.T. and Adejuyigbe, S.B. (2014) ‘Design of plastic spur gears using virtual reality’, Int. J. Computer Aided Engineering and Technology, Vol. 6, No. 1, pp.48–61.

Biographical notes: O.T. Laseinde is a Mechanical/Production Engineering Professional with PhD in Mechanical Engineering from the Federal University of Agriculture, Abeokuta Ogun State Nigeria. He is proficient in the use of computer-aided design (CAD) applications for 2-D and 3-D solid designs, virtual reality, artificial intelligence and expert systems. He consults widely for numerous national and international organisations in areas of design and maintenance of power infrastructure, steel structures, building mechanical services and design of HVAC systems.

S.B. Adejuyigbe is currently the Dean in Federal University of Agric, Abeokuta Nigeria. He is the author of over 100 journals and books. His research interest covers computer-aided engineering (CAD/CADD/CAM/CAPP/CIM); manufacturing engineering; ergonomics and human factor engineering; materials processing and foundry engineering; machine tools; production/ operations management; knowledge-based expert system; artificial intelligence; and entrepreneurship. He is a member of numerous local and international engineering bodies. He has served as a peer reviewer on several local and international journals of engineering.

Design of plastic spur gears using virtual reality 49

1 Introduction

Development in engineering methods has improved on conventional ways of solving problems. Enhanced teaching aids useful for demonstrating the operational techniques of computer driven devices have been made possible using virtual reality (VR). VR is defined as simulation in reality. It has been defined in so many different ways by various authors but summarily, it is seen as the act of simulating a real life event. It is generally agreed that the essence of VR lies with computer-based three-dimensional (3-D) environments.

Often termed ‘worlds’, they represent real world or conceptual environments that can be navigated through, interacted with and updated in real-time. VR is an artificial intelligence tool otherwise called artificial reality or virtual environment (VE). It involves manipulation of objects using sensor data and real time control.

However, VR has a much broader definition and can be experienced in several different ways. Stone (1998) defines VR as an artificial environment which is experienced through sensory stimuli as sight, sound, touch provided by a computer and in which one’s action partially determine what happens in the environment.

Another probably more easily understood definition is that VR is a computer generated simulation of a real or imaginary environment with which the user can interact and manipulate (Warwick et al., 1993).

VR can also be seen as a way for humans to visualise, manipulate and interact with computers and extremely complex data. The visualisation part refers to the computer generating visual auditory or other sensual outputs to the user of a world within the computer. This world may be a computer-aided design (CAD) model, a scientific simulation or a view into a data base. The user can interact with the world and directly manipulate object within the world as in the case of animated scripts.

Interaction with the virtual, at least with near real time control of the view point is a critical test for a VR. Therefore, the specific objective of the research is to develop a design model which can be used for the production of plastic spur gear using VR.

2 Review of literature

VR is a major aspect amongst the five major subjects of artificial intelligence. They are all interrelated depending on their area of application. VR can be divided into two basic types – text-based and graphical-based. Text-based VE are created by two or more networked users in multi user domains (MUD) over the internet (Dieterle and Clarke, 2006).

In general, people are more familiar with graphics based VR. In graphics-based systems, the VE is created to visually simulate a real or imaginary world. Technically, these environments can either be two-dimensional (2-D) or 3-D; however 3-D environments are more immersive, they are used more frequently to create virtual worlds. Virtual 3-D environment can be created using real-world photographic process, by computer graphics or possibly even a combination of the two (Stone, 1998).

Head mounted displays, data gloves, special rooms and other devices can be used with graphics-based environments to make them completely immersive giving the users a sense of actually being inside the virtual world. However, these devices are expensive, cumbersome and uncomfortable. The most widely used form of VR in use today is

50 O.T. Laseinde and S.B. Adejuyigbe

desk-top VR. In these systems VR worlds run on users’ desk-top computers and are displayed on a standard monitor and navigated using a mouse, 3-D space ball, keyboard and similar input devices.

Desk-top VR systems can be distributed easily via the World Wide Web or on storage devices and users need little skill to install or use them. Generally all that is needed to allow this type of VR to run on a standard computer is a single piece of software in the form of a viewer. Most VEs meant to be experienced by both general public are presented through the user’s computer monitor.

Recently, the two types of environments, text-based and graphics-based have been combined to create online virtual world where users develop or choose a character (called an avatar) which then can navigate the 3-D VEs and interact visually and through role, play or chat with other user on line communities (Jeffrey, 2001).

It is evident from so many reports however that there has been an early realisation of the advantage a simulated graphics work can present but getting it on the format seen and felt had rather been difficult.

2.1 Uses of VR

There are several areas of applications of VR. They fall into the main categories of training, education, simulation, visualisation, conceptual navigation, design and entertainment but there is much overlap between these categories:

• Training applications include allowing users to practise a process repeatedly in a no-risk environment. For example, users might dig an archaeological site, trying out different strategies without the risk of destroying important evidence (Barcelo et al., 2000).

• Educational applications include virtual visits and simulations (Whitelock et al., 1994). For example, a virtual visit to a museum that is too far away to visit or does not exist in the real world. Historic battles may be simulated allowing users to see what really happened (Witmer et al., 1996).

• Visualisation examples include an architect’s design for a building or the reconstruction of ancient buildings from archaeological evidence. Such models also allow users to explore things too large or too small to explore in reality and can bring historical time-lines to life (Stone, 1998).

• Applications of VR for conceptual navigation enable, for example, users of a library or archive to find the information they need at a logical or physical level.

• VR allows designs to be visualised and tested. For example, a design application might allow a choreographer to see a dance in action.

• Entertainment applications include virtual art galleries and games. VR may also be considered as an art form in its own right (Goodrun, 1994).

• Collaborative virtual environments (CVEs) allow users to interact with each other in a virtual world allowing the development of virtual communities, thus adding a new dimension to VR.


Practically, everything needed to make gears turns up from standard pressure angles to uniform tooth shapes have been handled and can be bought off the shelf. The science of plastic gearing is still undergoing development. Making plastic gears require high precision of cutting when compared to materials such as metal. Plastic gears can melt at temperatures where metal hardly deform but plastic gears can also run dry without lubricants. They can be moulded in unusual shapes and large enough lots, inexpensively.

Despite many advances in plastics gear technology, users of metal gear have not begun trading in all their current lots for plastic version. That is not to say making plastics gear is any small matter. The main concern in moulding them is that they will shrink upon cooling, throwing off any chance of obtaining accurate geometry in the final form. A big road block to producing a precise plastic gear is the distortion from shrinkage during the injection moulding process. The distortion results in an inconsistent gear tooth profile and low gear accuracy. The generic moulding solution cavity correction method was developed for producing high precision moulded gear.

According to Koller et al. (1995), direct gear design works ideally for plastic gears because it provides total design flexibility that is not achievable using the traditional gear design and production process. Direct gear design compensates plastic low strength to the bending stresses, reducing the bending stress concentration, minimising and balancing specific sliding velocities resulting in maximum efficiency and minimum heat generation.

Today moulders go through number of tool cavity corrections until they get it right just to obtained a high precision part. The shape of a moulded part is the result of a combination of factors including the tool geometry, material properties, moulding process parameter to mention but a few. These factors are the genetic moulding blue print of a part, much like deoxyribo-nucleic acid (DNA) as explained by Katkov et al. (2006); in the genetic blue print of living organism genetic moulding solution technology is based on the mathematical prediction software which defines the transformation functions between initials cavity profile and the resulting part profile. These methods do not depend on plastic material properties, part shape or moulding process parameters. This technology allows going from initial tooling cavity to final tooling cavity in one straight process.

2.2 VR development

VR has been described as a “multidisciplinary effort covering everything from mechanical engineering to psychophysiology” (Rosenblum, 1999). The briefest of examinations into the applications of VR will support this idea. The potential uses of the technology are boundless, but there are essentially two approaches to current VR development: modelling the real world and abstract visualisation.

2.2.1 Modelling the real world

Some of the more obvious applications of VR are those where a computer permits simulations of the real world in a safe, controlled or more economical environment. This approach also makes the modelling of reality possible in ways that would be intractable in the real world; for example, space or deep sea travel, or even a system for examining social interaction within a family of animals (Allison et al., 1997). It also permits the sort of model so frequently encountered in television archaeology, where long-since


destroyed buildings are ‘rebuilt’ and presented in a synthetic environment (Lombard and Ditton, 1997).

2.2.2 Abstract visualisation

The other most commonly found approach to development of VR application is in those areas where large quantities of abstract data need to be manipulated, examined or accessed. Such visualisations range from common datasets such as maps, to micro and macro structures such as molecular architecture or social networks (Carson et al., 1999). By combining VR with geographical information systems (GIS), geographical information can be explored in three dimensions (Koller et al 1995) or the information contained within a computer database can be visualised and navigated as a solid, tangible entity (Freeman et al., 1998).

Almost any situation that requires interaction with information, even mathematical algorithms can benefit from virtual visualisation according to Hibbard et al. (1999). Users are able to visualise and interact with information through multi-dimensional graphical representations (combined with text clues). Such representations increase users’ ability to analyse the underlying data by negating the need for them to construct their own mental image of the data structure (Stanney and Salvendy, 1995).

3 Materials and methods

The first phase in a successful VR project is deciding whether it is in fact the best option to achieving research aims and Objectives. VR may not be suitable if the target audience do not have access to the technology needed to view it or lacks the computer skills necessary to manipulate the model. Hence, a well-planned, well-documented and detailed work plan was put in place towards achieving the research objectives

The research involved the following stages namely:

1 analysis of the user requirements of the VR application to be developed

2 definition of the objects, textures, animations and sounds that will make up the world

3 documentation for the design of the model and how it works within the chosen system

4 definition of platforms which the world will run on

5 determining the programming language suitable for developing the gear calculations simulation software.

The following high level languages were adopted namely: AutoCAD/Pro Engineer; 3-D studio max (3-Ds-Max); macromedia flash and Q-basic.

The basic application process was broken down into an input processor, a simulation process, a rendering process, and a world database. The time required for processing was carefully put into consideration since every delay in response time degrades the feeling of ‘presence’ and reality of the simulation (Sato et al., 1997).


The process design was drafted out using AutoCAD in conjunction with pro-engineer (Pro-E). Macromedia flash and Pro-E were utilised for the final gear parameter calculator. To start with, Q-basic was employed for the computation of gear parameters such as addendum, dedendum and diametral pitch. Macromedia flash software was adopted to facilitate effective interaction and enhance appearance since interactivity is an important feature that enhance reality in simulations (Encarnacao and Fruhauf, 1994).

Figure 1 Basic rack of the 20-degree tooth form

Figure 2 Two meshing spur gears with terms and pressure angle description

3.1 Gear calculation

The required formulas, parameters and relationships which would be needed for the process of calculation of plastic spur gears were clearly itemised. These were programmed into the applications backend using Q-basic. It yielded good result but the user interface was not so attractive. As earlier explained, the beauty of every VR work is the users perception towards the application which is directly corresponding to how interactive and how attractive the front end application looks. Further research work eventually led to the use of a better interface which is designed to generate required spur


gear calculations. Three spur gear tooth forms are generally used with pressure angles of 14 1/2, 20, and 25 degrees. The 14 1/2 degree tooth form is being replaced and made obsolete by the 20 and 25 degree forms (Figure 1). Figure 2 illustrates two meshing gears with description of terms. The larger pressure angle makes teeth with a much larger base, which makes these teeth much stronger and also allows the production of gears with fewer teeth. Any two gears in mesh with each other must be of the same pressure angle (Maryland Metrics, 2002). When gear tooth measurements are to be made with gear tooth callipers, the chordal tooth thickness and the chordal addendum must be calculated. The application was developed such that it matches the imputed variables with the standard spur gear formulas already built into the application thereby generating accurate results for addendum (a), pitch diameter (D), outside diameter (Do), tooth thickness (t), whole depth (ht), clearance (c), centre distance (C), working depth (hk), diametral pitch (P) and chordal addendum (ac). Table 1 Spur gear terms and definition

Addendum The radial distance from the pitch circle to the outside diameter.

Dedendum The radial distance between the pitch circle and the root diameter.

Circular thickness The distance of the arc along the pitch circle from one side of a gear tooth to the other.

Circular pitch The length of the arc of the pitch circle from one point on a tooth to the same point on the adjacent tooth.

Pitch diameter The diameter of the pitch circle.

Outside diameter The major diameter of the gear.

Root diameter The diameter of the root circle measured from the bottom of the tooth spaces.

Chordal addendum The distance from the top of the tooth to the chord connecting the circular thickness arc.

Chordal thickness The thickness of a tooth on a straight line or chord on the pitch circle.

Whole depth The total depth of a tooth space equal to the sum of the addendum and dedendum.

Working depth The depth of engagement of two mating gears.

Clearance The amount by which the tooth space is cut deeper than the working depth.

Backlash The amount by which the width of a tooth space exceeds the thickness of the engaging tooth on the pitch circles.

Diametral pitch The number of gear teeth to each inch of pitch diameter.

Pressure angle The angle between a tooth profile and a radial line at the pitch circle.

Centre distance The distance between the centres of the pitch circles.


Table 2 Spur gear formula table

To find 14 1/2 degree pressure angle 20 and 25 degree pressure angles

Addendum, a 1.0aP

= 1.0aP

=

Dedendum, b 1.157b

P= 1.157b

P=

Pitch diameter, D NDP

= NDP

=

Outside diamete, Do 2

oND

P+

= 2o

NDP+

=

Number of teeth, N N = D × P N = D × P

Tooth thickness, t 1.5708t

P= 1.5708t

P=

Whole depth, ht 2.157

thP

= 2.257th

P=

Clearance, c .157c

P= .257c

P=

Centre distance, C 1 2

2N NC

P+

=×

1 2

2N NC

P+

=×

Working depth, hk 2

khP

= 2kh

P=

Chordal tooth thickness, tc 90 degreessinct D

N⎛ ⎞= ⎜ ⎟⎝ ⎠

90 degreessinct DN

⎛ ⎞= ⎜ ⎟⎝ ⎠

Chordal addendum, ac 2

4cta aD

= + 2

4cta aD

= +

Diametral pitch, P NPD

= NPD

=

Centre distance, C 1 2

2D DC +

= 1 2

2D DC +

=

Note: The formula table was utilised for developing the back end of the gear calculator

4 Results

4.1 The developed computer model for plastic spur gear calculations

An application was designed by the researcher to handle the generation of required gear parameters seamlessly. The front end interface is shown in Figure 3. The calculations are for a 20 degree pressure angle spur gear with module 5, 20 teeth and gear ratio 6.


Figure 3 (Test 1) Spur gear calculation user interface (see online version for colours)

Notes: Data input: module = 5, number of teeth = 20, gear ratio = 6.




4.2 The flow chart showing the sequential process of gear modelling

The flow chart in Figure 7 represents the gear design parameter generator. Certain criterion was set such that the application will not generate a computer model of the gear except certain requirement is met. The minimum number of teeth set to be imputed was seven (7).

Figure 7 Gear modelling

NO

YES

Z = no. of teeth

NO

YES

Start

Are parameters

ok?

Input no. of teeth (Z)

Is Z > 7?

End

Gear input parameters

Generate gear model

4.3 Result validation

The results obtained using the developed VR application was compared with that obtained when using manual computation.

4.4 Benefits of the developed tool

• Delivers correct tool cavity geometry for high precision plastic parts.

• Eliminates the expense of repetitive cavity correction.

• Cuts process development and delivery time.

• Increase precision of moulded parts.


Table 3 Comparing between manually calculated and computer generated parameters

Test

1

Test

2

Test

3

Test

4

Para

met

ers

Com

pute

r res

ult

Man

ual r

esul

t

Com

pute

r res

ult

Man

ual r

esul

t

Com

pute

r res

ult

Man

ual r

esul

t

Com

pute

r res

ult

Man

ual r

esul

t

Mod

ule

(M)

5 5

5

5

10

10

10

10

N

o. o

f tee

th (N

) 20

20

10

10

20

20

10

10

Gea

r rat

io (r

) 6

6

5 5

10

10

10

10

Add

endu

m (a

) 5

5

5 5

10

10

10

10

Ded

endu

m (b

) 6.

25

6.24

6.25

6.

25

12

.5

12.5

12.5

12

.5

Pitc

h di

amet

er (D

) 10

0 10

0

50

50

20

0 20

0

100

100

Out

side

dia

met

er (D

o)

110

110

60

60

220

220

12

0 12

0 To

oth

thic

knes

s (t)

7.85

4 7.

854

7.

854

7.85

4

15.7

04

15.7

04

15

.708

15

.708

W

hole

dep

th (h

t) 11

.25

11.2

11.2

5 11

.25

22

.5

22.5

22.5

22

.5

Cle

aran

ce (c

) 1.

25

1.25

1.25

1.

25

2.

5 2.

5

2.5

2.5

Cen

tre d

ista

nce

(C)

350

350

15

0 15

0

1100

11

00

55

0 55

0 W

orki

ng d

epth

(hk)

10

10

10

10

20

20

20

20

Cho

rdal

add

endu

m (a

c) 5.

0981

75

5.09

8

5.19

635

5.19

635

10

.196

35

10.1

9635

10.3

927

10.3

927

Dia

met

ral p

itch

(P)

0.2

0.2

0.

2 0.

2

0.1

0.1

0.

1 0.

1


5 Conclusions and recommendation

The aim of VR is to have a simulation in reality capable of achieving predefined objectives. Indeed, one of the stated aims of the research work was to develop a computer model for the design of plastic spur gears using VR. This was achieved and the results obtained have been validated. The research has also revealed various techniques of achieving the set goals. Such discovery was the implementation of macromedia flash when it was difficult to achieve the expected reality when using Q-basic computer language. We eventually achieved a better enhanced application simply by utilising flash which we integrating into the application during the design process. Haven completed a VR model for plastic spur gear generation, results obtained using the CAD approach have been compared with those generated manually.

Major benefits of applying VR includes reduction in time and resources, cost saving, provision of unlimited access to expensive unavailable equipment, enhancement of practice under hazardous conditions and an improvement in safety to mention but a few. As a recommendation, the industries should explore the economic benefit of applying VR in processes concept development.

In conclusion, the use of VR is highly recommended by researchers involved in modelling real life applications.

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Design of plastic spur gears using virtual reality

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