All the fun of the fair
Thrills without spills is the aim of control technology in fairgrounds.
Ah, don't you just love a day at the fair? The colourful sights, the smell of popcorn and hot dogs, and the sound of people screaming themselves silly. It all combines to engender a frisson of excitement that all too often is preserved only in the endless summers of youth.
But, unlike in my youth at least, when big dippers with wooden frames operating on a wing and a prayer seemed the order of the day, the modern funfair ride is a high-tech beast. You just know that rides with names such as Nemesis, Oblivion, Detonator and Colossus are going to deliver - how to put this? - a wholly different experience from the waltzers and flying jets that were popular when I went a-courting.
As a species we have become thrill junkies, so fairground rides these days have to up the adrenaline ante. But the trick is still to deliver those thrills without the spills, and that comes down to using control technology. And it's this dual aim that governs ride makers' design philosophy.
Dutch company KMG offers a typical example. It builds and operates its machines all over Europe, and when it designs a new ride it goes through a four-stage process. First is the mechanical design, from which comes the requirements for the electrical and control engineering; second is the engineering of the electrical hardware, where decisions are taken on which signals go where and which main drive unit sizes will be needed. Also at this stage come decisions on to whether to opt for a single electrical cabinet or to go for more decentralised electrical cabinets, and combine or split up signals.
The third stage is the design of the software for safety devices such as emergency stops, and the drive units, to control the actual movements using limit switches and motor encoders. The final stage is testing the electrical and software design on the actual machine.
Electrical engineer at KMG, Bas Derkink, explains the design approach thus: "The most important consideration for us is that the control technology is there to control the amusement ride in a safe and end-user-friendly way. On the one hand that means there have to be enough devices to cover the necessary safety for the users and of course passengers of the ride, but on the other hand we don't want to end up with a machine that's so complex that we would have to train up our customers to the extent that they'd have to be specialists. So the safety features are based mostly on common sense rather than high-tech computer controls.
"Also, no two types of machine are the same - some have more movements and therefore more drive controls. That means more logic control, which increases the size of the overall control system.
"So the number of movements also directly affects the choice of control technology. For example, a simple rotational movement of a merry-go-round might need only one emergency-stop relay, whereas our Freakout swing ride, say, uses a 74-I/O safety PLC."
He continues: "Before the PLC era, we used redundant relay circuits on manufactured printed circuit boards in combination with classic emergency-stop relays. But when programmable safety PLCs came in several years ago, we switched to those and have used them ever since.
"Our rides use AC current motors, and we control them using frequency inverters. And at the design stage we move all non safety-related logic to the memory of the frequency inverter applications module, and move all safety-critical logic to the safety device."
If the type of control technology used on a ride depends on the type of ride, so too does that principle apply to the way the safety PLCs are programmed. "Pretty much all programmable components use a different interface to program the logic," says Derkink.
"We've chosen to use Control Techniques drives, so we are tied to the three programming types - DPL, Ladder diagrams and function blocks - it uses in its application modules and drive unit on-board memory. DPL is the oldest language and is good for code that uses a lot of calculations. It's very similar to Pascal but uses some drive-related functions.
"When CT introduced a new programming platform on its SP drive units in 2004, however, that gave us the ability to program Ladder diagrams into the drive units, which made many logical operations a lot easier and more graphical. The overview is much better in this language and very easy to adapt. I can't comment on function block programming, as we've never used it."
Although KMG specialises in making funfair rides that are designed to be easy to set up and take down at temporary funfairs across mainland Europe, some of its rides do run in the UK.
Even the funfairs of Europe tend to be far more high-tech than in the UK, and there are also other marked differences.
A case in point here is the work of Pete Smith. He has been designing and building funfair rides since 1962, and is a director of BJP Rides, one of the few funfair ride makers still left in the UK.
He says: "We specialise in portable rides for the travelling community, so the machines are designed to be dismantled and put on the back of a trailer time and time again. They also have to be easy to re-assemble and set up in a short time with the minimum number of people - that's about 45 minutes for our Miami ride.
"Bear in mind that these kinds of fairground operators will be family firms, so assembly and disassembly will be done by a man and
They're not technical specialists, and remember too that these rides have to be serviced in the field - sometimes in a field! So our policy is to make rides that are simple and robust.
"So for control we tend to use electro-hydraulic drives powered by a portable generator and a three-phase motor, plus relays and microswitches. There's no point in putting sophisticated electronics into our rides - the power supply from the generators is never that smooth, and the electronics won't tolerate the inevitable spikes. And the rides are usually driven manually using a joystick."
But despite the comparatively basic nature of these rides, safety is just as important here as in the headline-grabbing machines in the big parks. As Smith points out: "In safety terms we work to the guidance in the Health and Safety Executive's HSG 175 document. So, for example, the control system itself has interlocks to prevent the ride starting while it's loading and all the ride's restraints have to be locked first as well.
"And the safety regime is just as strict for these travelling fairgrounds as it is for the amusement parks. Wherever they set up, they need a permit from the local council, and they can't get that without certificates of conformity. There's a good paper trail."
Naturally, it makes sense for the fairground and amusement parks industry to provide an experience that's as safe as it is enjoyable. After all, as with, say, airliner crashes, when there's an accident it's big news, and, aside from the overarching human tragedy, a fatality or serious injury can, on a practical level, close a funfair or amusement park for the season. So for some years now the industry has been regulated by the Amusement Device Inspection Procedures Scheme (ADIPS), which controls about 98 per cent of the rides in the UK.
ADIPS is the UK industry's safety inspection scheme, and its purpose is to promote and improve fairground and amusement park safety through rules and procedures relating to the annual inspection of the amusement rides. It is supported by industry associations, and these in turn make up the scheme's Amusement Device Safety Council (ADSC), which draws up the actual policies on safety, technical guidance and moves towards self-regulation in the industry.
The HSE is the enforcing agency here, and Barry Baker, one of its principal inspectors, heads up the fairground inspection team. He says, "ADIPS covers four types of inspection. There are three pre-use criteria - the design review, to ensure the actual design is sound; the conformity check, to ensure the ride is built to its design spec; and the initial test, to ensure the ride actually works - then there's an in-service annual inspection, a bit like the MoT on a car."
The design review is rather like the type approval system operated by car manufacturers - another parallel with the motor industry - where every part of the finished design has to be checked against the original engineering drawings, and structural components, electrics and materials must all match the specification laid down by the design engineers. The ADSC provides a publication, 'Safety of Amusement Devices: Design (2nd Edition)', which covers every aspects of a ride's design, including a section devoted to control systems.
Once this review is complete, the ride is checked by an independent engineer who will make sure the ride operates correctly, the safety systems operate as they should, the electrics have the required earths and circuit breakers fitted and so on. If the ride fails this check it is given an immediate stop order and cannot operate until it has been brought up to standard and retested.
But what is the 'standard'? Well, there are several - such as IEC 62061 (Safety of machinery. Functional safety of safety-related electrical, electronic and programmable electronic control systems), EN 954-1 (Safety of machinery. Safety-related parts of control systems, Part 1. General principles for design) and IEC 61508 (Functional safety of electrical/electronic/programmable electronic safety-related systems, Parts 1-7) - and that's just for the design stage.
And before the ride can be used by the public, other standards come into play, as Baker explains: "There isn't actually an EU directive for fairgrounds; instead we have adopted the European standard EN 13814 (Fairground and amusement park machinery and structures), but even so, here in the UK we still require any ride coming in to the UK to be checked according to the guidance laid out in HSG 175."
Since 95 per cent of the rides in the UK are imported, that can make for a lot of checking for conformity, and Baker says: "The most problematic part of my job tends to be that the HSE doesn't have a mechanism for informing ride makers abroad about UK safety standards at the design stage - that element is still beyond our control.
"But then the quality of the design is the key factor here - so long as a ride is properly designed then there's usually no problem. And it's not the big, Nemesis-type rides that can cause concern, as they take quite a bit of time and money to design and build; it's more the middling ones costing of the order of a few hundred thousand pounds, which can be built and imported quickly. Sometimes I'm concerned that aesthetics have held sway over safety."
So again it comes down to design. But designs, like tastes, change over time, and at the sharp end here, checking conformity comes down to people like Mark Wolstenholme, senior electrical inspection engineer at inspection body Leisure Technical Consultants Ltd. He tests rides of all sizes and ages, and points out: "The actual test varies according to the age of the device and the standards that were in place at the time of its manufacture.
"So for example, a ride that's 50 years old would not have any restraint monitoring, yet if my risk assessment brought up the need for that ride to have some sort of restraint mechanism fitted then I would stipulate that. Fuse technology is another example - it's come a long way in those 50 years and if the technology on a ride no longer met modern standards, that would have to be changed too," he says.
But Wolstenholme adds that there's a simple way around any possible lack of conformity with imported rides - visit the manufacturer. He says: "In the past we've accompanied people from, say, Alton Towers, to the US to carry out design reviews of rides they're looking to buy, to make sure they're up to standard before they're actually shipped - checking for things like 'blocking' systems on rollercoasters to maintain a minimum distance between the cars. And the manufacturer has been happy to make any changes to a machine that may have been needed before completing the sale."
Safety makes for good business, and ride safety is definitely higher now than in the past - you have only to look at the statistics. The HSE says the chances of being killed or seriously injured on a funfair ride is 1 in 83 million, and there is a greater chance of being struck by lightning than there is of being killed on a fairground ride.
And the HSE's Baker reveals something that may come as a disappointment to the white-knuckle nuts. "The thing about these rides is that they are designed to be potentially high hazard, but they are actually low risk - they give only the illusion of danger."
Future wish list
So what of the future? KMG's Derkink already has a wish list. "Drive units are growing in functionality so the distinction between drive unit and PLC is dissolving. Drives can already connect to industrial networks, but the most interesting development in this technology is in the field of wireless PLC controls, wireless connections between decentralised I/O modules and the logical control," he says.
"Since most of our signals are safety-related we are bound by hard-wired connections, so safe wireless connections would offer us many more opportunities in control as well as diagnostics."
There's also talk of what could prove to be the next big thing in fairgrounds - personalised rides. What has been named only as "a very popular amusement park" in the US is unveiling the first rollercoaster in the world to have onboard LED lighting and a sound system where passengers can choose any audio track they want. Each of the four
cars in the rollercoaster is decked out with 78 white LEDs, 18 speakers, nine MP3 players and nine 'guest interface' panels.
When riders board the car, each one is allowed to choose their own music track. Once the train leaves the boarding area, the audio cues up and the light show begins. During the ride the sensors in the cars are triggered and subsequently change the onboard light show.
Sounds pretty groovy, although for my part, next time I want to be reminded of the colour of my knuckles, I think I'll just stick to repeating my new mantra: "IEC 62061... EN 954-1... IEC 61508... HSG 175..."