What goes around

Even though the market for industrial motor control is growing, stricter safety standards, calls for more reliability and flexibility, and demand for increased communications in connected factories are all factors placing greater pressure on hardware and software developers. On top of that, motor control systems need to be more intelligent, producing data that can be analysed, sometimes in real time, so that processes can be adjusted and made more efficient. This is important, as in some cases motors can account for between half and two-thirds of the power consumed in a plant. Analysing the data also helps with the reliability of the motors; it enables regular diagnostics allowing potential problems to be spotted before there is a serious breakdown. Knowing how a motor is running means that maintenance need only be scheduled when it’s needed, rather than to a fixed schedule.
“You can monitor motors over time and thus spot if the figures show a drift over time,” said Jeff Smoot, Vice President of Motor Control at CUI. “This can show problems with the encoder, or something else such as the bearings going or temperature problems. You can get an engineer to sort that before it becomes a catastrophic failure.”
Due to their higher efficiency, there is a general trend to move away from brushed motors to brushless DC motors, but these need more complex algorithms to control them. “The algorithm requires a lot more computation and a feedback loop to monitor the current of the motor and adjust it,” said Rufino Olay, Business Development Manager at Intersil. “But we are seeing a lot of companies moving over from brushed motors to brushless.” Heinz Oyrer, marketing manager at Austria Microsystems, added: “Brushless DC motors are more reliable and more efficient. There is a big trend to replace brush motors with them and they are gaining in popularity rapidly.” However, given the extra electronics needed to control them, brushless motors are dearer to buy, but Oyrer reckons that as they become more popular, economies of scale will take effect, meaning this is only a temporary situation.

Meeting the standards
Even though IEC60730 is mainly for household appliances, the safety aspects do apply to some industrial motors, such as found in ventilation systems, vacuum pumps and so on. They can also be found in industrial boilers. “Any supplier today who wants to sell in Europe needs to comply with this,” said Vincent Mignard, Segment Marketing Manager for Renesas. “The software must be able to detect motors that are too fast or burning.” He said this type of software could take three to four months to develop and then needs to be tested on the target hardware. The documentation has to be written and approved which, he said, sounded simple but was ‘a pain in the neck’.
What is crucial is that if there is a failure, the microcontroller will put the whole system in a safe mode. Then there is IEC61508, which is the industrial functional safety standard for electrical and electronic equipment. Again, software and hardware needs to be tested and proven to detect any failures. “This applies to industrial motors,” said Mignard. “These could be, say, robot arms that need tight resolution such as in automotive manufacturing. Or they could be in warehouses for moving stock. Some use stepper motors. They could be opening and closing doors.” Here he said it was even harder as the standard required more tests on the CPU itself, on the core and on the instruction sets.
“When we develop the software, we have to prove that we tested the instruction sets on the microprocessor,” he said. “All the cells of the RAM have to be tested. We have to do the same for the flash and the key peripherals.” This, he said, could be 12 months of work just to design the software, test it and get it approved; the approval process itself can take three to four months. IEC61508 also calls for redundancy to guarantee safety and reliability, and Olay believes one way round this to make life easier for the designer is to use a digital module for the power management side: “You need to reduce the areas of failure,” he said. “By using modules you have more integration and thus fewer components. Redundancy increases the number of components by a factor of two, so a module can help you reduce that number.”

Communications
As factories become more automated, there is an increased need for communications that are reliable in what is a very electrically noisy environment. “Anywhere you have an inductive load that is turning or you have relays, it is extremely noisy,” said Mignard. There are various techniques to protect the electronics, such as putting diodes on each port to guard against high current or voltage. Filters can be used to control incoming signals. Buffers can isolate signals. There can be complete noise cancellation circuits. “All of this costs a lot of time and money,” said Mignard.
The cost factor of the communications is also a factor for more sophisticated real-time control of the factories. “Everyone wants real time,” said Chris Clearman, Marketing Manager at Texas Instruments. “They would have real-time communications built into every drive if the price was right. But we are seeing a demand for premium products with real-time communications, low latency and all the safety features. This will push the price down as they become more used.”
He said that the future would see growing demand for capturing as much data as possible to keep efficiency under control. “They want more performance and more software and analytics on the data,” he said. “They want to do things more efficiently. And they want the system costs lower. And all this means more integration, so we are looking at the whole system to see what else can be integrated.”
But Jason Chiang, Senior Marketing Manager at Microsemi, believes companies should look at the total cost of ownership rather than just the upfront price: “The complexity of the motor does go up but this makes the motor more efficient,” he said. “The customer has to factor this in. You would think that it would increase the cost, but the total cost of ownership could be lower because the motors are running more efficiently. It can be a difficult idea to sell.”

Capturing data
There are different ways to capture information such as direction, position, speed and acceleration about a rotating shaft, and there are advantages or disadvantages for each type of sensor used in rotary encoders. The most popular are magnetic, optical and capacitive. Magnetic works well in greasy environments but does not have the accuracy of optical. Optical does not do as well in some harsh environments as airborne contaminants and grease can affect the encoder accuracy. Optical is also more fragile. Capacitive falls somewhere between these two. It is not as prone to oil, dust and dirt, and is rugged, but does not have the accuracy of optical. It is also more susceptible to electromagnetic interference.
“Optical encoders also cost ten times more than magnetic,” said Oyrer. “You also have to position them very accurately. With magnetic, you have a wider range.” He said magnetic position sensors were more popular for stepper motors, such as found in industrial sewing machines, still a big market in Asia. They are also used for wafer handling, printing, scanning and in elevators.
As factories fall more under the scope of the so-called internet of things, the motors that make up the bulk of the power consumption are being looked at more closely. Being able to control these motors so they can respond to changes in load and environmental factors means that they can be made to run more efficiently. But communications in a factory as well as sensor technology provide their own challenges in buildings that are often electrically noisy and physically dirty. On top of all this, strict safety standards have to be met.
There are still debates about which technologies best serve this market, and these are debates that have yet to run their course. That said, with the money savings that more efficient and connected factories can bring, electronic motor control will continue to be a big and growing market.