Certified Machinery Safety Expert (TÜV NORD)
ABB Jokab Safety Products
When faced with a new or changed machine-safety risk, bolt-on solutions may seem like the easiest, cheapest approach. In most cases, it makes sense to consider a safety PLC, which can provide a far superior, lower-cost solution.
Back in 70s, young guys often “customized” their cars with a variety of bolt-on accessories. These hot- rodder wannabees screwed mud flaps, hood scoops, curb feelers, and more onto their cars. They may have looked cool for a while; but in the long run, most of these bolt-on additions did more harm than good.
The same is true for control panels. “Bolt-on solutions,” where people meet a new system requirement by attaching an additional piece of hardware or patch the software, usually deliver mixed results. Bolt-ons are typically fast and easy to install and usually meet the immediate need. But they often don’t offer the best long-term outcome. They seldom integrate fully with the existing systems fully, limiting functionality and effectiveness. And while they almost always cost less in the short run, actual lifecycle costs are usually higher.
“A great example is the recent call I got from a distributor who wanted to add a light-curtain muting controller on a production conveyor,” says Rich Gibson, marketing manager for ABB’s Jokab safety products. “This control allows product to pass through the curtain, while an arm or tool would create a trip. My response to him was, ‘Why would you want to add another control device when you already have the capability in your existing control panel?’ Bolting
on the necessary additional devices would have solved his problem, but I recommended a far better solution: the central, intelligent controller.”
In pre-digital days, every point of protection started with a sensor, whether a light beam, door switch, e-stop, or whatever. Between that sensor and the panel, was a dedicated controller mated to that sensor. The controller for a door stop was different than the controller for light beam. You also needed one or more relays. All these devices had to be hardwired together.
It was a classic case of the law of diminishing returns. As they addressed new risks by adding more hardware, they reduced overall system reliability. Each device and every connection created new, additional, potential points of failure.
It’s hard to overstate the benefits people are realizing as they transition to digital safety PLCs for machine- safety applications. The controllers are largely device agnostic, making it possible to directly connect most safety devices and sensors. Both for panel builders and owners, that simplifies systems and reduces the parts inventory.
All these advantages come with a price tag that’s typically smaller – significantly smaller – than add-on solutions. The cost of a programmable controller in any multi-safety-function panel is more than offset by the savings from eliminating dedicated controllers and relays. In applications with a simple door stop and estop, a digital controller might be overkill. But, as the number of safety functions grows, the cost benefits of digital technology quickly make it the better choice. Savings in the vicinity of 40% are common.
Some people have reasonable concerns about replac- ing multiple components with a single controller. It’s true you eliminate many potential points of failure, but instead you have all your safety-control-system eggs in one metaphorical basket. But offsetting that concern is the ease of troubleshooting and replace- ment when there’s a controller issue.
Rather than the frustration of running down problems in individual devices, diagnosing issues of all sizes is typically facilitated by the built-in diagnostics of a programmable controller. It’s possible to plug an HMI into a safety PLC and access a trove of system infor- mation. If there is a failure, swapping out the control- ler will probably be faster than the diagnosis and re- pair of relay-logic components. Controller programming is readily transferred to the replace- ment part.
“Rather than looking at safety control systems as a collection of individual safety components, take a more holistic approach,” Gibson suggests. “Start with a risk assessment of the machine or process to iden- tify all the tasks and hazards. This should include in- put from everyone who interacts with the machine. In- experienced people making assessments may do a tremendous job of identifying all the potential risks faced by an operator, but fail to consider how techni- cians perform maintenance or do changeovers.”
You can typically rely on your safety-controller provid- ers for a no-cost risk-reduction evaluation. Before in- viting them in to do an assessment, though, clarify what the deliverable will be. You don’t simply want a list of risks; you want a detailed set of solutions as well.
It’s reasonable to ask for the required wiring dia- grams to implement those solutions, but that may take them beyond what they are willing to provide for free. They may also offer installation services, providing a turnkey package. That level of service will definitely incur additional costs.
To ensure the quality of their assessment, it may be worthwhile to require they be credentialed in these systems. Your local pipe and wire distribu- tor can probably provide all of the necessary com- ponents, but it’s not likely they will be able to as- sess the machine-safety issues. It will be even less likely that they will be able to guide your installa- tion and maintenance. Certified Machine Safety Expert is one designation that indicates the indi- vidual has demonstrated capabilities in this area.
Turning over safety-control-system design and in- stallation to an expert may be the easiest ap- proach, but it’s probably not the best. Keeping your experts involved in the process will help them develop their skills and knowledge. That will give them skills and knowledge to update and fur- ther evolve the system over time. The initial tran- sition from analog to digital is a fairly large step, making modifications and maintenance on the system in the future much less intimidating.
For simple safety-control systems that require the addition of a basic function like a new door switch or safety mat, bolting on the components to pro- vide that new capability may be the best way to go. In most cases, though, a programmable safety controller will deliver superior results in terms of safety, functionality, and integration with both lo- cal and plant systems. It also lays the foundation of faster, easier modifications to safety systems, and provides all these benefits at a significantly lower cost.
Certified Machinery Safety Expert (TÜV NORD)
ABB Jokab Safety Products
First-generation safety interlocks, like the mechanical door switch, were the best available solution 50 years ago ‒ but were far short of perfect. Read how the technology evolved – not always smoothly – to today’s safer, more reliable sensors.
The most fundamental machine-safety device is probably the door switch or interlock. Open a door, fence, or shield, and a switch stops the mechanical motion of the machine. The technology has been around for about 50 years, and you can still find new equipment that relies on these mechanical door switches.
Over the years, newer and better devices were adopted and then actually rejected for a time before making a resurgence. Today, newer and far better technology has emerged that provides superior machine reliability and operator safety.
Before talking about the state of the art in safety sensors, let’s look at how this technology evolved.
The operating environment for the original safety switches was much different than today. Back then, relays provided the safety logic, making all the if/and/then decisions. There were no PLCs or logic or software, just panels full of relays clicking and clacking.
“Removing a key from the interlock on a machine door would actually cut the power to the contactors,” explains Rich Gibson, marketing manager for ABB’s Jokab safety products. “That would then stop the machine motion. The problem was that the relays were 115 VAC, which meant those switches had to break open higher-current AC contactors to de-energize the coils.”
Each time those relays clicked and clacked, every time they broke or made contact, there was arcing. Over time, that arcing would frequently result in the contacts welding together, which was the most common failure mode for relay-based systems.
When they failed in the open (machine stopped) position, that was a nuisance. When they welded shut in the closed (machine energized) position, it was a major safety hazard.
The solution they came up with to overcome contact welding was an improvement, but it came with a new weakness. They created a safety switch based on a mechanical linkage, an armature that increased the leverage on the contacts.
Now, when you removed the interlock key and opened the door, a cam mechanism would drive the armature that would force open the contacts, even if they were welded shut. Safety had been ensured, but at the cost of a more mechanically complex, and therefore inherently less-reliable, solution.
“Fast forward 20 or 30 years,” says Gibson. “The technology shifted from 115 VAC to 24 VDC. These DC safety relays combined with safety PLCs and safety controllers, all operating on lower current, eliminating the possibility of welded contacts. That simply wouldn’t happen.”
In addition, the older-style mechanical switches that relied on physical contact between the door and the frame were increasingly replaced with non-contact magnetic switches. The active side of the switch, the component with wires running back to the panel, typically relied on a reed switch. In its simplest form, the reed switch has two contacts that look like metal reeds. They are contained inside a glass envelope filled with nitrogen, making parallel contact along their entire surface. These magnetic switches brought a new level of reliability to safety switches.
“The same couldn’t be said for machine reliability, though,” Gibson says. “The problem was that the gap between the magnet and the switch was critical. As gates sagged, as doors got out of alignment or as fences bent, the magnets no longer reliably actuated the switches. The natural vibration of the machine was often all it took to separate the magnet and switch enough to bring the machine to a stop and start the frustrating and time-consuming search for the problem while the machine sat idle.”
The poor reliability of these types of safety systems and the resulting loss of production became a huge issue in the 1990s. Equipment owners had to choose between compromising on safety or reliability; they couldn’t have both. So many started gravitating back to the old mechanical switches.
“I think this issue gave safety a black eye because it created the impression – accurate at the time – that adding safety to the machine meant hampering production,” Gibson says.
Today’s non-contact safety sensors with coded magnetic switches overcome that problem. These more-powerful magnets are far less sensitive to alignment issues. The sensors are low voltage DC and have no mechanical wear, successfully combining both high safety-system integrity and machine reliability.
One of the added advantages of these sensors is that the magnets provide an added layer of safety by reducing the ability to spoof them.
“Machine operators and maintenance techs are very adept finding workarounds to safety systems,” Gibson observes. “In the past, you could outsmart some switches with a simple fridge magnet. Today’s magnets are uniquely coded, making that more difficult and, in most cases, impossible.”
The next big thing in safety sensors is radio frequency (RF) technology. Now, in addition to a non-contact, non-mechanical device, you eliminate the magnet and get a much higher tolerance for misalignment.
Each ABB Eden non-contact safety sensor includes one of about 100,000 potential codes. That makes it much less likely that someone can defeat the switch and cheat the doors. Gibson believes most safety-product manufacturers will move to these coded RF sensors in the next few years.
“Some industries, like packaging, have warmly embraced coded RF sensors,” Gibson says. “Their equipment has a lot of doors, so they were especially eager to overcome the pain of the previous generation of safety-sensor technology. In the manufacturing industry, though, they are still feeling that pain but are beginning to see a solution in coded safety sensors.”
It is also a step forward in predictive maintenance, because the sensor can transmit a warning if it is starting to get close to the threshold where it won’t make contact with its mating component. This raises the reliability considerably.
“It really has been an evolution,” Gibson says. “Those early safety switches were the best we could do at the time with the technology we had. But today, equipment makers have far superior options, and even better solutions are in the not-too-distant future.”
Product Marketing Manager – EPR, Pilot Devices, Limit Switches
ABB Electrification Products
In every assembly process, simplicity saves time and money. Two simple technologies that simplify panel making are push-in connections and compact pilot devices. Learn more about how they can help improve your assembly process.
Anyone who has been part of a Lean Six Sigma process-improvement team knows they typically rely on some very complex statistical methods. But not all of the improvements result from sophisticated tools like regression analysis, attribute agreement analysis, and t-Tests.
As someone who’s been part of a number of process-improvement projects, I know there are also a few simple but sure-fire ways to reduce errors and costs while accelerating a process. One of them is to reduce the number of process steps or activities. When it comes to panel building, there are two types of products that enable panel builders to easily simplify their process.
Push-in terminal connections are an increasingly popular wiring method on devices like contactors. Both solid-wire and ferrule connections are as easy as inserting the wire end into the cable hole, no tool required. For stranded wire, a flat-blade screwdriver is needed to open the terminal, but no torqueing or screwing is required.
It’s easy to see how this is much faster than tightening terminal screws, typically reducing assembly time by half. It also eliminates the time needed to carefully torque each connection. The push-in connectors are engineered to ensure the required torque. As a confidence check, installers can check connections with a simple tug test.
Unlike screw-in connections, push-in connections are vibration-proof. Wires won’t vibrate loose in transit or during use. You never have to retighten them, increasing the reliability of the panel and reducing maintenance. An added benefit in high-volume panel shops is that push-in connectors enable automated assembly; the feature is very robot-friendly.
Push-in connections aren’t a new concept. They have long been embraced by electrical-equipment manufacturers in Europe. In the US, acceptance has been slower but is accelerating as manufacturers become more confident in the technology and more aware of the benefits. Many major panel shops, eager to reduce costs and production time while increasing panel reliability, have adopted push-in connections as their preferred technology.
Another simple process-improvement tactic is to reduce the number of components required in an assembly. Fewer parts means fewer steps in the production area. One way panel builders are reducing their component count is with all-in-one pilot devices. Rather than building up the device by attaching contacts, the pilot device installs as one unit.
The all-in-one design also eliminates the need to sort through and find the correct contacts for the device, and eliminates the possibility of assembling the wrong contacts.
The speed benefit of this design is obvious. Perhaps less obvious, but just as important in terms of cost reduction, is the inventory aspect. The all-in-one pilot device reduces the need to stock a range of contacts for your panel shop.
Some shops prefer the ability to customize or configure pilot devices on a per-panel basis. For them, the all-in-one design may not be the right choice. But for most panel shops, and particularly higher-volume shops, building up pilot devices from multiple components makes little sense.
Almost every electrical and mechanical device made today is increasingly modular, manufactured from sub-assemblies rather than individual components. This speeds and simplifies production and reduces product failures. When maintenance is required, service often consists of a simple module swap. Those same benefits come with the all-in-one pilot device.
Technology like push-in terminals and all-in-one pilot devices won’t revolutionize your panel-building process. Instead, like most changes that result from continuous-improvement efforts, they will create incremental but measurable benefits. Still, saving 30 seconds on each connection in a panel can add up to significant savings.
Both push-in connections and all-in-one pilot devices will absolutely simplify and speed panel assembly while increasing reliability. These technologies typically are no more, or only slightly more, expensive than the alternatives, ensuring reduced panel-production costs.
Panel builders interested in a simple way to quickly enhance their production process should consider whether products like push-in connections and all-in-one pilot devices make sense for their shops.
ABB Customer World is a chance to learn, connect with peers, and find solutions. This year, it includes a remarkable simulation of the ABB Ability Electrical Distribution Control System, connecting devices throughout the showroom in working demo.
Market Development Manager-Americas – Renewable Energy & Power Generation
ABB Electrification Products Division
When selecting components for energy storage power control systems, traditional designs are the right choice in some cases. For automatic transfer switches and current monitoring systems, it’s a smart idea to consider today’s smarter digital devices.
Product Marketing Manager
ABB Jokab Safety Products
Actions to solve one problem often have other, unexpected consequences. Panel builders opt for digital components primarily to create more-compact panels. But they also discover other unexpected additional benefits of interest to both panel builders and buyers.