Engineering Education Scheme

Final Report

Notes: This report was written for the end of the Scheme, before most of the further work for the Young Engineer's entry. The name and other references to the sponsoring company have been removed for reasons of confidentiality. Many of the diagrams and appendices have been lost since they were not part of the electronic document I saved.

ACKNOWLEDGEMENTS

Many thanks go to all the people who helped us throughout the project, much assistance and guidance was given by [the management and our assigned engineer at the company]. We would like to thank the teachers at school especially Mr. J Weedon and Mr. T Griffin for all their help, time and encouragement at all times throughout the project, but most of all for their enthusiasm.

Finally we would like to express our appreciation to all the staff at Plymouth University for their much needed and valued help, especially the composite materials department for their assistance with combating the various problems associated with a nine metre long beam.

We would all like to thank the Engineering Education Scheme for giving us an insight to a possible career and for giving us a very enjoyable time, it has benefited us all.

SUMMARY

Unauthorized access frequently occurs at the company's factory, this needs to be combated without causing too much inconvenience to the staff and operations of the factory. The obvious solution is for some form of barrier to be used. Our task is to design a suitable solution to the problem. There are several constraints regarding what type of barrier or gate could be used, these are detailed later in this report. It is the intention of the company that the barrier should be automatic in its operation so a system will have to be devised that will accomplish this. The company would prefer to have remote key-fob style switches to open and close the barrier to cause as little disruption to access as possible.

The design process involved working with electronics (to control the operation of the gate), civil engineering (assessing the site) and mechanical engineering (to develop the barrier itself). In the design process both modelling and prototyping were carried out.

The potential benefits of the final design are the elimination of unauthorized entrance to the site. The automatic nature of the barrier would solve the problem of loss of time caused by stopping and having to manually raise a barrier when staff come and go and deliveries are made. A non-automatic barrier would not only cause the problem of loss of time but also of leaving vehicles standing in the narrow road for prolonged periods of time.

Our main recommendation to the company is that they install a barrier similar to that which we have designed, that being one which retracts into the bank the runs parallel to the road.

INTRODUCTION

At present, the only means of stopping others from entering the premises is a single chain which is suspended from either side of the entrance. The chain has no lock so can be moved by anyone. When closed the chain is hard to see, therefore it could quite easily be driven into.

Inside the entrance is a small car park with space for three cars and leading up from this is a short track to the back entrance, further parking and outbuildings.

The company do not want unauthorized persons taking up the few parking spaces.

The company have issued us with the following design specifications. The barrier must;

1. be remotely controlled.
2. be aesthetically pleasing.
3. not affect sight lines when turning out.
4. cause any obstructions to passing traffic.
5. not restrict access to car park or main entrance to building.
6. not move within a close proximity of the overhead power cables.
7. allow for livestock to be moved to get to the small field next to the factory.
8. function at all times including when a power failure occurs.
9. have a manual override in case of complete failure of the controlling device.
10. not be tempting for the local children to sit or swing on it as it is opposite a first school bus stop.
11. keep within a budget.

We followed the standard design process to come up with a solution, the main stages were as follows:

1. Initial discussion with company representatives regarding specifications and constraints.
2. Research into barriers already available.
3. Sketches and brainstorm of initial ideas.
4. Discussion of the merits and problems with each idea.
5. Selection of two possible solutions.
6. Meeting with company to decide on which idea to develop.
7. Development of chosen idea.
8. Making a model of the final idea.
9. Running tests on the model.
10. Further development culminating in a full size prototype.
11. Design of controlling device.
12. Construction of controlling device.
13. Testing of controlling device.
14. Setting up controlling device with prototype.
15. Testing of final solution.
16. Presentation of final solution to company.

RESEARCH

The following are some examples of barriers available on the market.

This information was obtained from Newgate Ltd., a major company with a very good reputation with the barrier building industry, they supply many major names such as: Ministry of Defence, British Steel, British Gas, HM Prisons, National Power, ICI, British Aerospace and GEC Marconi. They also supply more than 20 leading UK security companies which specify newgate access barriers in their project proposals to major customers.

SLIDING GATE

This will have no trouble in keeping out people from the site, and this idea could be used for the solution, a large problem is that the company has decided to run this gate on a 415 volt power source which would require a step up in voltage and would require specialist parts to operate at this voltage.

This gate can be operated manually if a power failure occurred but would be heavy to push. It is very strong and would keep out cars but it could be unnecessarily strong for the needs of the company. This design could be modified for our needs as it would fit all of the design specifications and would look very good and could be easily made.

RISING KERB BARRIER

This appears to be a new and innovative design but the problems arise in excavating the drive to house the barrier, also due to the unevenness of the drive further alterations would have to be made, for example leveling the drive.

The fact that the all the mechanical parts and the platform have to be totally housed so that dirt and leaves would not clog up the unit make it suitable for this type of drive. As animals regularly use the drive, there are certain problems associated with waste and mechanics, this would make a sealed unit suitable.

The barrier runs on hydraulic rams which would be expensive to buy on our budget it would not be suitable but the fact remains that it fits all of the design specifications and it is a very good idea it is just a shame that it would be very hard to make as it would take a lot of engineering know how to get it absolutely fault free.

RISING ARM BARRIER Heavy duty

This again is a good idea but must be immediately ruled out due to the fact that the three phase power cables over head of the site would not allow the barrier to raise to its limit and obviously it would be very dangerous and costly. The housing must not reduce the size or the drive way as the optimum size must be allowed for good access and this could be a problem, as the housing is too large to be mounted in the bank.

This design is most suitable for areas where large numbers of vehicles enter and exit every day therefore it is tough, reliable and extremely secure.

For a design like this the purchaser obviously pay extra for these properties, so I think that it would be more cost effective if a less expensive method was found to stop traffic getting through.

Also the fact remains that if this barrier would be about seven metres long, the motor and gear box would have to be very powerful.

ELECTRIC SWING GATE

This gate was designed with high security as one of the main design criteria, so it is too secure for our purposes but the design could be modified so that there was only a single pole instead of the large gates. This design does not meet the specifications as the car park space at the factory cannot be compromised in any way.

This design would also not be suitable for a countryside industry and would look more suitable in a city where it would complement the surroundings a lot better.

In the description of this barrier it states that this design has been taken up by the Ministry of Defence and other large warehouses and would be the "Ideal answer to large site access and security problems".

GATE DRIVE UNITS

These are units that can be added to existing gates simply for automation purposes. It is possible that one of these units could be adapted to be used at the factory. The main problem with these units are that the gates open inwards this is unsuitable for the specifications set out to us.

These rams do help us a little as they are an aesthetically styled product and would not look out of place anywhere.

RISING ARM BARRIER -manually operated

This design would be the only one that would meet any realistic budget as the other designs are obviously too extravagant, and are made to the specifications of the purchaser, this is a virtually maintenance free barrier that will stand the test of time and will not require and power source or drive unit, but it unfortunately fails all the specifications in many ways including the rising aspect and the automated aspect.

By keeping the design simple it will dramatically lower the cost of production and it will lower the chances of it going wrong at any given time.

The counter balance and the support pillar would not have to be a problem as it could be incorporated into the bank but this idea could not be used unless a solution could be found concerning the power cables.

An automated version of this is also available and is often seen in car parks all over the country and it is in demand from lots of industries and businesses, this is slightly cheaper than other designs as it uses a basic principle of operation and is powered by a simple motor and gear box.

ACCESSORIES

Newgate make accessories that either make the barrier more visible when it is blocking an entrance or to warn that it is operation or to control its operation.

It would be a good idea to investigate the visibility as the turning is very sharp and the sight lines are very bad so it would be sensible to have a warning system. The Newgate traffic lights are very suitable as they could be seen easily and they could not be mistaken for road traffic signals therefore the flow of traffic past the entrance will not be affected, the lights are small and well designed and would not look too out of place.

The barrier is very close to the main building so a light and siren system would not be appropriate as this would be distracting to workers and to the neighboring houses.

One accessory that could be a good idea is the intercom system as the road is the main one that goes through the village and it is only wide enough to let one car pass at one time, this means that an efficient way of noticing the delivery vans or vehicles quickly without disrupting traffic. An induction loop would be just as effective but it would require digging up the road.

ANALYSIS

During the development of the barrier it became apparent that some certain points would have to be taken into consideration, these are detailed below.

As the barrier will have to be next to the road, planning permission may have to be applied for.

Measurements of the site will be required as the exact dimensions of the drive are essential for designing the barrier.

The barrier may have to be driven by a large motor, as the weight of any such barrier will require quite a lot of force to move it, it will be necessary to experiment with several different motors. It may be possible to have one or more motors driving the barrier.

The barrier must be controlled by a Key Fob. An infra red transmitter is a lot cheaper to manufacture but is very susceptible to climatic conditions and other factors such as the windscreen of the car, as reflection, refraction and dispersion may occur. A radio transmitter is a lot more costly, as due to broadcasting regulations they can only be manufactured by a licensed company, this would mean having to purchase the items. Tests will have to be carried out to see how climatic conditions effect infra red beams as it was also planned to have some sort of break beam to prevent accidents with the barrier.

The barrier may prove costly to manufacture, we may have to find some ways of reducing costs so that we may remain within the estimated budget.

The barrier must have the facility to be overridden manually and the motor disengaged, this is necessary for replacing broken components and to make repair and access simpler. A solution will have to be found to effect the aforementioned problem.

It will be necessary to find a way of making the barrier stop if it closes when a vehicle is still in its way.

A gearbox may have to be designed and constructed, as all motors tested so far are spinning above 1000 RPM, and this is much to fast to drive a barrier.

A method of driving the barrier must be found, metal cogs and chains will require maintenance, and rubber may not grip in damp conditions.

A traffic survey may have to be completed to give us an idea of the volume of traffic that would be going through the barrier, this will be necessary so the barrier's motors can be tested to see if they will be able to manage the amount of use.

Several different ideas for the barrier were investigated and most found unsuitable. One idea was an inflatable barrier which used compressed air to stiffen the barrier to block the entrance. This idea was not deemed suitable because there may be many problems such as punctures, high winds and people driving into it and getting through.

Another idea was a telescopic pole that came out of one of the banks and across the entrance. The main problem associated with this is having to keep the pole lubricated which would be necessary because the sections would constantly be moving in and out of each other.

The 'scissors' idea was not chosen due to the large amount of sideways flex that may occur in the barrier and also due to the large amount of joints needing lubrication.

As a modification to the existing arrangement, a cable could suspended across the entrance with a motor drive to let it fall to the ground so vehicles could drive over it and then pull it tight to stop vehicles getting past, this is unacceptable as it is quite hard to see, anything hanging off it, to improve its visibility would clog up the way it worked and could jam it.

Of the ideas for barriers that are raised up, most are unsuitable because of the overhead power cables. The one idea which may have worked was a bar that as it lifted up, hinged in the middle to limit the height required. This may prove a problem with having to drive mechanism at two joints.

Any barrier would have to be driven by a motor or some other device, a barrier that required driving in a linear plane would be easier to drive than one that needed non-linear driving.

[Two further ideas...]

The first of these two ideas has two upright boxes at either side of the entrance. Each box has a chain loop driven by a motor. The barrier is attached to the chain at either end of its length, when the chains are moved, the barrier moves with the chains. When in its closed position, the barrier is raised off the ground and when opened it lowers to ground level so it can be driven over.

This idea has several advantages, it would not block the car park or building entrance. It would not be high enough to risk touching the power lines. The main problems with this method are the need to keep the chain lubricated, the reduction of width of the entrance due to the upright boxes, the difficulties associated with the unevenness of the drive surface and keeping the two motors at either end synchronised.

The second idea has a carriage mounted in one of the banks beside the entrance. A pole runs on this carriage and is driven out of the bank across the entrance. The carriage contains bearings for the beam to run on and some form of motor drive.

The advantages of this idea are as follows. When open, the barrier would not obstruct the entrance in any way, either reducing the width of the entrance or reducing the visibility. The barrier would not block the car park or building entrance. The barrier would be driven in a linear plane.

SELECTION OF CHOSEN SOLUTION

After much discussion, the decision was made on the final solution, it was decided that the barrier that retracts into the bank is most sensible decision. This seemed the most suitable for many reasons;

1. The unevenness of the drive made the raising barrier unsuitable as it would be required when lowered, to be level with the ground, the costs of making the ground level would be far beyond the budget. The chosen solution does not need level ground.
2. With the raising barrier a cable would have to be run to the far side of the entrance to supply power to the motor. Not only would this prove costly to install, it would also be inconvenient to keep maintained. The retracing barrier would not need any electrical connection to the far side of the entrance.
3. The chosen solution would not reduce visibility when turning out from the factory into the road.
4. Due to the barrier being completely retracted into the bank, the width of the entrance would not be reduced at all, which may restrict access for large vehicles.
5. The bank is an earth bank with a stone retaining wall which would not be very difficult to excavate. With the other solution, the opposite wall would have to be knocked down and rebuilt further back to prevent narrowing of the entrance, this would prove costly.
6. The chosen solution would only have one mechanical base unit which is less than the raising design, this means that there is less to go wrong.

The idea was discussed with representatives from the company and it was agreed unanimously that this idea should be developed.

The next point of discussion was what sort of beam to use on the barrier. This was an important decision because using the wrong type of beam over such a wide gap could cause major problems with sag. The two original proposals were to use either a hollow circular cross-section beam or a beam with a cross section similar in shape to a capital i. The latter would have strength in both the horizontal and vertical directions. The I-bar would be difficult to obtain in such a small width but with a large length as would be needed, this type of bar is usually used on a greater scale for girders in buildings. The hollow circular beam would have equal strength in all directions and would be easier to obtain. This type of beam is available in steel and aluminium, the aluminium version would be lighter so would be less likely to sag. It was decided to use a hollow circular cross-section aluminium beam.

With the help of the engineer from the company, a design was created on the computer for the carriage to run the beam on. The design was taken to the residential workshop a Plymouth University and a model was constructed. The model was approximately to scale, about a third actual size. The beam was simulated by a length of copper pipe. The beam was driven with an electric car window motor which had been removed from a scrap Rover car. The model used a spring in tension to hold the motor against the beam. Six bearing were used to allow the free movement of the beam, and support in all dimensions. The model worked well and the motor was found to be strong enough for driving the model pole and even the full size pole. Whilst at the university, advice was sought on how much sag a was to be expected from the type of beam being proposed. After a lot of calculations a figure of about 60cm was worked out. Obviously this would not be suitable so some form of strengthening would be required. An expert in composite materials was asked how much the cost of a similar bar made from carbon fibre would be. Unfortunately this cost would be way over budget so the idea was dropped. The only other way of reducing the sag is to strengthen the beam. Of the various ideas put forward, including welding flat beams to the sides of the circular beam, the best idea was to have two circular bars in a figure of eight shape, separated by regularly spaced upright struts which would be riveted tightly. The one point that was raised regarding this idea was the possibility of torsional twisting. The calculation to determine the sag in this design of bar would have proved extremely complicated to perform but a figure of about 6cm was estimated. This amount of sag is still quite a lot but would be more manageable, it must be considered that the gap to be spanned is nearly seven metres so any design of beam is bound to have a degree of sag.

Experiments were carried out to compare the sag in the two different types of beam, the circular and figure of eight. Miniature models were made and they were fixed at one end and masses were put on to the far end, the displacement of the end of the beam was measured for each mass. The results of these tests are shown fully in appendix 5. The results indicate that the figure of eight beam would be a lot stronger than the circular beam.

Despite the choice of beam, it was decided to carry on with the work on the single beam carriage which had already begun. With the help of [the company engineer], the CAD design was modified to accept the double beam.

The prototype carriage was constructed and the bearings and springs added. The upper bearings were sprung because of the chance of imperfections in the beam and stones and mud getting dragged in, the springs allow for this type of problem. When inserted into the carriage, the beam moved freely on the bearings, a little filing was necessary to avoid and fixed pieces of metal scraping on the moving bar.

It was decided to use two identical window motors to drive the beam. The proposed method of driving was to have two motors directly opposite each other on either side of the beam, each driving a wheel which in turn drove the beam. The motors need to be sprung, again to allow for imperfections and the like.

At the same time as the development of the mechanical side of the project, the electronic parts were being designed.

DESIGN OF CONTROL CIRCUIT

The circuit needed to control the motor(s) and locking mechanism of the barrier needs to deal with a number of inputs and outputs:

Inputs:

• Radio "open"
• Radio "close"
• Open limit switch
• Close limit switch
• Proximity detector Key switch

Outputs:

• Motor on/off
• Motor direction
• Lock/unlock

This could be done with logic but the number of inputs and outputs would mean a fairly complex circuit which could work out expensive and inflexible. It was decided that a microprocessor circuit should be used. The flexibility of this approach would mean that changes to the operation of the system would be easy to make by just reprogramming the unit. An 8 bit 8MHz processor was chosen, a faster chip or one with a wider data bus would be more expensive but would not improve the performance of such a simple task. The 8031 processor was chosen because I have had experience of using it in the past, it also has a pin compatible version with and internal ROM which could be used when the final program is ready. This chip also has 128 bytes of internal RAM, saving an extra chip. For development, the ROM-less version was used so that the program could easily be changed with the use of an EPROM. The same board could be used for the ROM version with just one change to one of the pins on a socket.

With 2 of the input/output ports used for addressing the ROM, a single 8 bit wide input/output port was left for all of the above signal lines. Clearly with 9 signals and 8 bits a small amount of logic was needed. The key-switch has the same effect as the radio control key-fobs so four NAND gates were used to combine the signals from the three sources and put them into 2 inputs.

The circuit was designed on Isis software and transferred to a PCB layout on Ares software. From this a double sided board was made up but because the facilities were not available for through hole plating, it was not used. The board was then redesigned on a CAD package at [the] factory to avoid the problem of unavailability of through hole plating. [The company] do not make their own PCBs so the designs were sent away to be made professionally. The next stage was the design of the software. At the time of writing, the printed circuit board had not arrived back so consequently the circuit has not been assembled to be tested. It is hoped that the control circuit will be completed along with its software in time for the presentation.

CONCLUSIONS AND RECOMMENDATIONS

Due to the fact that at the time of writing this report the printed circuit board is still being manufactured, detailed tests have not been carried on the prototype circuit.

Tests have been carried on the scaled beams. The findings of these tests concluded to the use of a double-bar beam. These results, coupled with the calculations that were done at Plymouth, prove that the double bar will drastically decrease the amount of flex experienced over such a length.

Before it came to the testing stage, it was decided that due to many problems, including climatic susceptibility, infra red would be unsuitable for any applications in our project, therefore it necessary for radio transmitters to be used to open and close the barrier.

As infra red break beams were deemed unsuitable, as stated earlier, some way of preventing closure of the barrier will be necessary. The most suitable method seems to be the use of proximity detectors.

After testing several types of motor found in various cars (using car components means that they are very easy to get hold of should there be a problem, it also means we can use a simple car battery to power our barrier) it was found that electric window motors from a Rover SD1 were ideal, they have a very suitable running speed, also due to their incorporated gear box a large amount of torque can be supplied to drive the beam.

To disengage the motors from the pole we shall have some form of lever with a cam that when turned will move the motors away from the beam, allowing free movement of the beam.

It was concluded by all that it would be most suitable to drive the beam directly with rubber wheels, this will prevent the problems associated when there is contact between metal and metal. This means that the wheels will have to be spring loaded to provide as much pressure on the beam as possible. Slippage of the beam may still occur, and to try and combat this it is likely that there will be some form of brush to wipe off excess water, leaves and other waste materials off the pole as it enters the carriage.

The final design for the carriage satisfies the following design criteria;

1. The barrier is not exposed to the risk of colliding with the overhead power lines, as it is only moving in a horizontal plane.
2. The barrier is remotely controlled, and can be operated from within a vehicle.
3. The barrier can be controlled from the office via another radio key-fob.
4. The motor drive can be disengaged from the pole, this allows the pole to be moved manually.
5. The barrier will not be able to collide with any obstructions due to the proximity detector mounted on the end of one of the bars.
6. The internal workings of the barrier will be mounted in the bank, and therefore will be shielded by the earth, and a constructed casing, this will be accessed via an inspection cover.
7. When fully retracted, the barrier will not obstruct either the front entrance to the factory, or the entrance to the bottom car park.
8. None of the components of the barrier or its casing will obstruct the entrance, and the sight lines onto the carriageway will not be affected.
9. The barrier will have battery back-up incase of power failure, this will be trickle charged from the mains power source.
10. The bolts holding the two beams together will protrude, this will deter children from sitting and swinging on the beam.
11. The barrier will be encased by the bank, and will not look obtrusive when the barrier is closed.
12. There is no parts mounted on the bottom of the drive, this means that once the barrier is retracted there will be no restrictions to the movement of livestock past the barrier.
13. The barrier does in no way protrude onto the carriageway, so the barrier will be no inconvenience to passing vehicles.