Turbines housed in aircraft engines are subjected to some of the roughest conditions imaginable. They are pieces of mission-critical equipment that must perform flawlessly at speeds of 30,000 RPM in temperatures greater than 800°C for hours at a time. Therefore, engine manufacturers fully understand that even small surface defects can reduce performance, increase maintenance costs and reduce the useful life of an aircraft engine. They need to inspect turbine blades very carefully to maintain the efficiency and reliability that the air transport industry requires. One particular North American manufacturer inspected its blades by hand and human eye. The highly trained inspectors would measure hundreds of features and check for surface defects at depths in the order of thousandths of an inch. Manual inspection was not only costly, in terms of time and labour, but it was subjective as well. Results were variable and even differed between inspectors. Finally, because manual inspection was so time consuming, there was no systematic inspection of every blade; only a sampling of blades would be inspected. Clearly, the manufacturer required an approach that would allow systematic inspections of the blades, save time, and yield consistent and repeatable results. That was when they approached Orus Integration Inc. in Laval, Que., to design an automated turbine inspection system. Project manager Louis Dicaire says that early on in the project, the development team learned that flexibility, repeatability and precision were absolutely necessary for success. During development, the Orus engineering team relied on their previous experience — they designed vision-based metrology systems for the Canadian military and aerospace industry. They also worked closely with Genik Automation in St. JérÃ´me, Que., for part handling and mechanical engineering of the machine. Orus calls the system the INL-1900x2T. A single enclosure houses two stations that perform the inspections. The metrology station features two Basler GigE cameras at 1920x1080, each fitted with a large field of view telecentric lens (non-perspective lens) and two collimated LED blue (520 nm) lights. The surface inspection station uses four Basler GigE cameras; the resolution of the first camera is 1920x1080 for the surface inspection, and the remaining three offer a 640x480 resolution for surface inspection of areas that are hard to reach with a single camera. Two CCS diffuse on-axis lights and one CCD diffuse backlight illuminate the surface station. A Fanuc six-axis LR Mate 200iC robot and 4U controller and Omron PLC round out the hardware components. The software is based on the Matrox Imaging Library 9.0 with Processing Pack 1. The blade’s journey The INL-1900x2T has three inspection roles to fill: verify several hundred metrology features of the blade, inspect both sides of the turbine blade and other critical surfaces for defects, and validate the part’s character markings. The entire inspection procedure takes 15 seconds per part. To perform a batch inspection, an operator first scans the barcode on the job sheet with a scanner and loads the pocket wheel with the carousel that holds the parts. Then the wheel indexes the first part while a height detector validates its y position to ensure the part was properly loaded. Then the robot picks up the part by its blade section and carries it to the metrology station, which is illuminated by the two collimated lights. With the camera’s telecentric lenses, and the four-inch slab of granite to absorb heat and vibrations, the INL-1900x2T enjoys a very stable optical system. “Under these conditions, the contrast of the round sections of really shiny objects appear super sharp,” Dicaire explains. Precision is extremely important. “The robot is very repeatable, but cannot place the blade with the precision that we need, which is smaller than 10 microns,” he says. Orus’s solution was to rotate the part and acquire the images at high speed. Depending on the feature that needs measuring, the software minimizes or maximizes a specific feature. When an image of a particular reference point, called the datum, matches the original CAD drawing, the software identifies it as the reference image. Then the metrology software measures the part’s parallelism, length, radius, angles and other feature. Since there are many datums to optimize, this step is performed more than once. The software records results for hundreds of features and 50 tolerances. After the software records the metrology results for all of the blade’s features, the robot places the blade in a three-pronged gripper that is mounted on a Y-Theta station. The clamp rotates the blade 360 degrees to inspect both sides for surface defects. Then the software verifies the part’s character markings: first by stitching together several images to form a complete image and then by passing the OCR algorithms that determine the character. When the inspections are complete, all the results for the part are logged; all data is retrievable for reporting. If the part passes inspection, the robot puts the part in a good-parts chute. If a feature has failed, the part is held in the clamp and information is displayed on the screen so the operator knows what to correct on that specific part. Then the gripper releases the part into a reject chute. The wheel turns, indexes the next part and the process repeats for all parts in the carousel. MIL power Orus has used Matrox Imaging Library (MIL) for almost nine years. “This is probably the project where we dug deepest inside the library,” Dicaire says. One of the implemented algorithms features an adaptive threshold: the algorithm dynamically locates bright spots in dark areas and dark spots in bright areas. For other operations, the developers at Orus used the GUI interfaces for several MIL modules: OCR, Edge Finder, Geometric Model Finder, and of course Metrology. The metrology software was almost exclusively developed with the GUI so the system could learn the parts. Indeed, the INL-1900x2T’s flexibility means the system can accommodate several different parts, even new parts that are still under development. “With the GUIs,” Dicaire explains, “we can build a system that lets our clients be more autonomous with the final product. We find that, with the level of complexity of our projects, MIL’s ease-of-use, performance, flexibility, and the great support from [Matrox Imaging’s] Vision Squad team are the reasons we continue to develop with MIL.” Measuring up Dicaire says the challenges involved in designing metrology machines are always the same: repeatability, precision and linearity. To get the system to return predictable, repeatable results, the software must exhibit fine sub-pixel accuracy; the machine shows ±3 sigma under five microns. Of course, an image is only as good as its lighting, and Dicaire notes that the system required a stable and high-performance optical system. To achieve the required precision, Orus used a military-grade calibration target to calibrate both cameras at the same time. Though the INL-1900x2T saves thousands of hours of labor, its main advantage is its ability to perform very complex analyses while offering a simple interface and a very easy-to-use concept for the operators. “This project uses an array of field-proven technology: robot, axis, vision library. All of this enables the machine to grow and adapt to the client’s future needs. Except for the mechanical design, almost all components are off the shelf.” “This machine is a mix of technologies that are all dedicated to make the vision system work in optimal conditions,” Dicaire says. “It’s a great example of what we can do.” Sarah Sookman is a media relations specialist with Matrox Imaging in Montreal.
A custom integrator of turnkey automated inspection machines for quality control, Cincinnati Automation "saw the light," adopting a new LED backlit conveyor to convert automotive part gauging from a step-by-step to continuous process, more than tripling throughput. The AccuVision conveyor from Conveyor Technologies Ltd. features a grid of high-intensity LED lights beaming up through a translucent urethane conveyor belt. "The backlit conveyor let us change gaging to a continuous operation for faster processing, and with less complex systems engineering," says Phillip Smith, Cincinnati Automation president. "For gaging operations, backlighting is positively preferred," he notes. "You get a silhouette of the part with crisp edges, sharp contrast and no shadows for precise dimensional inspection against the programmed master." In the past, the Erlanger, Ky., company would have processed the parts on a stationary backlight table, he says. "To gauge overall geometry and edge geometry, which we're doing here, we'd use a pick-and-place system for part transfer and a walking beam to advance parts to the first station for top inspection and on to the second station for side inspection," Smith explains. "We’d have to move parts to the inspection station, then move them off, so doing backlighting on the conveyor itself is a great advantage in speed and simplicity." Pick-and-place backlit gaging was limited to about 10 parts per minute, compared to 36 a minute for the new continuous conveyor system. And, that higher processing speed is governed by the speed of the part loading system, he notes. He believes a backlit system could easily handle parts at 60 to 120 a minute, depending on part size/configuration and faster loading capabilities. "A high-speed vision system can process a part in less than 100 milliseconds, so theoretically a system could process up to 600 parts a minute, provided you get the parts on the belt that fast," Smith adds. The continuous gaging system is configured to run 40 different part numbers for the automotive supplier, ranging from five up to eight inches OD. Robot grippers load the parts three at a time on the 66-by-12-inch translucent belt. Parts advance along the belt to the LED light field, where each is visually gauged by an overhead Keyence digital camera with an 8.5-inch field of view. At the end of the conveyor, a second Keyence camera with a 0.5" field of view gages the side geometry, catching the lead edge just as it extends beyond the conveyor. Parts then pass off the conveyor to an incline slide with a diverter flap. Failed parts drop through a slot in the incline. The flap lowers for good parts, covering the slot and allowing parts to pass down to the next station. Delivering two mega-pixel imaging, the Keyence cameras in the CA system provide 0.006-inch pixel resolution for overall part gaging and 0.0003-inch pixel resolution for edge gauging, based on the respective fields of view. The machine control shows images of each part being gaged, with both views tiled on the screen at the same time along with read-out results. Gauging data can be recorded as a text file to the system's PC for SPC quality control. Integrating backlighting with the conveyor enabled a highly compact design, with the entire machine measuring just 96 inches long by 36 iches wide by 70 iches tall. "This is a very space-efficient, Lean solution for plants," Smith stresses. The conveyor is mounted 55" off the floor, giving plenty of space for stacking parts for conveyor loading and for a scrap bin inside the machine to catch rejects. The bed of the Conveyor Technologies conveyor is only 2.28 iches deep, even with the LED light module mounted inside, for space savings and application versatility. "Backlit conveyors are still relatively new, but we were fortunate in finding a source almost in our backyard," Smith says. Cincinnati Automation specified a 10-by-12-inch light field. AccuVision light fields are available in six widths (two to 12 inches) and five lengths (six to 30 inches). The backlit conveyors can be ordered in belt widths from 2.5 to 24 inches. Made of translucent urethane, the conveyor belt "has really good diffusion properties, a good even light for the camera," Smith says. "The light is bright enough that it washes out imperfections from dirt build-up or smudges on the belt." Cincinnati Automation selected white LED light for the conveyor so that dirt on the belt would be more obvious, to aid in routine cleaning, he explains. Conveyor Technologies also offers red LEDs, which would work just as well for the Keyence cameras, he notes, but have less contrast for the human eye in monitoring against dirt build-up. The conveyor's array of LEDs provides a more even light than fluorescents, notes Smith. "With fluorescents you typically wind up with hot spots where the bulbs are. To minimize that effect, we would locate the bulbs further away and install diffuse panels, maybe even a couple of panels. It's more difficult to get uniformity across the light panel. The way Conveyor Technologies does it, they have rows of high-intensity LED light distributed evenly under the belt and the belt itself is the diffuse panel." Freedom from frequency oscillation makes LEDs ideal for high-speed digital cameras. Fluorescent "flicker" — oscillating cycles of bright/dim — usually aren't visible to the naked eye, but will be captured by the camera and are readily apparent on the control's monitor screen. "The LEDs may cost more than fluorescents at the component level, but are more effective, operate far longer, and are just easier to work with when you consider everything involved," Smith says. The gauging machine is fitted with dark tinted panels on sides and top to control against ambient light. Located almost dead-center along the I-75 corridor (and only about a quarter-mile off the inter-state), Cincinnati Automation gets a good 50 percent of its work from the automotive industry, typically Tier 2 and 3. After automotive, its key customer industries come from medical device manufacturing, also strong regionally, followed by packaging and label inspection. Conveyor Technologies uses modular design and engineering innovation to provide performance-enhancing and space-saving solutions to part conveying. The AccuVision Internal Backlight Conveyor is part of a patented, modular product concept from Conveyor Technologies that is foundation to 15 different low-profile conveyor types. www.cincinnatiautomation.com www.conveyortechltd.com
Downtime due to problems with the quality of electric power can be costly. With rising levels of automation and computerization in manufacturing facilities, voltage sag lasting just a few milliseconds can bring an automated factory floor to a halt. Power disturbances are bound to occur, and while some may only briefly interfere with sensitive equipment, others could result in the total loss of power for days. Most international standards define power quality as the physical characteristics of the electrical supply provided under normal operating conditions that do not disrupt or disturb the customer’s processes. (The quality of power supply implies voltage quality and supply reliability.) Therefore, a power quality problem exists if any voltage, current or frequency deviation results in a failure or in a bad operation of equipment. Voltage quality problems relate any failure due to deviations of the line voltage from its normal characteristics, and the supply reliability is characterized by its adequacy (ability to supply the load), security (ability to withstand sudden disturbances) and availability (focusing especially on long interruptions). When power is generated, it has very predictable characteristics. It energizes all electrical equipment equally and satisfactorily. However, as the power travels through the wires and energizes the equipment, the various pieces of equipment can change its quality, making it less suitable for the next application. These changes are especially common in large industrial complexes and include increases and decreases in voltage, momentary power outages and noise on the electrical system; at its most extreme, poor power quality can even cause equipment to malfunction. This can cause business problems such as lost productivity, idle people and equipment and lost data. Voltage sags Voltage sag, or “undervoltage,” is a momentary decrease in voltage outside the normal tolerance, typically caused by the starting of heavy loads, lightning and power system faults. A good example is the starting of a motor. Motors draw more current when they are starting than when they are running at their rated speed. Consequently, the starting of a motor causes voltage sag while it accelerates to its rated speed. Excessive load changes may also cause sags. Computer equipment and controllers may power down depending on the duration and magnitude of the voltage sag. In addition, voltage sags cause loss of data. One way of reducing damage would be to connect sensitive electronic devices to circuits other than the ones large motor-driven appliances are on, try to lighten the load on the affected circuit. If a sag lasts longer, it is classified as undervoltage and is usually caused by circuit overloads, poor voltage regulation and intentional reduction by the utility. The impacts of undervoltages include equipment shutdowns, and the overheating of motors. Voltage swells A voltage swell, or “overvoltage,” is a momentary increase in voltage outside the normal tolerance. Voltage swells are caused by sudden decreases or the turning off of heavy loads and can damage equipment by breaking down insulation. If voltage swells last longer, they are classified as overvoltage, frequently caused by poor voltage regulation. For instance, shunt capacitors designed to improve upon the voltage profile might supply excessive reactive power and cause overvoltages. Periodic loads, such as pumps, cause periodic increases and decreases of amplitude (sags and swells); this is referred to as voltage modulation. Outages Outages, or blackouts, simply occur when power completely drops off line for anywhere between brief moments to several hours. Power outages can be caused by many circumstances, such as storms, which can be accompanied by heavy wind, ice, precipitation and lightning. Momentary outages, which are seen as a dimming or flickering of lights or even a brief loss of power, are caused by short circuits. Short circuits happen when something, such as a tree limb, comes into contact with power lines or when the lines touch each other. When a short circuit occurs, a breaker automatically de-energizes the circuit and interrupts the flow of power. Electrical equipment is designed to quickly open and close the breaker two or three times automatically attempting to clear the problem. An uninterruptible power supply or generator could help mitigate the drop in power in both instances. Harmonics For most of the 20th century, the predominant use of electricity for business and industry was to power motors, lights and heating devices. These uses have little effect on the 60 Hz (cycles per second) sine waveform of the electricity delivered to them from their utility. They are referred to as linear loads, because the current rises and falls in proportion to the voltage wave. A few industries, such as steel mills and aluminum smelters, used electricity to power arc furnaces, which distorted the sine waveform because the current flow was not proportional to the voltage. These loads are referred to as non-linear loads. Non-linear loads cause waveforms that are multiples of the normal 60 Hertz sine wave to be superimposed on the base waveform. These multiples are called harmonics. In the last 20 years, there has been an explosion of microprocessor-based equipment, which are also non-linear loads. Equipment widely used in offices and manufacturing not only creates harmonic issues but are also susceptible to harmonic disorders. These include are computers, monitors, adjustable-speed drives, welding equipment, transformers, etc. The list goes on and on. The invention of all these sophisticated electronic gadgets and circuitry has increased the problems associated with harmonics immensely. Transients Transients can be defined as sudden, brief increases in current or voltage in a circuit that can damage sensitive components and instruments. These disturbances are shorter than sags or swells, and are caused by sudden changes in the power system. Two main categories of transients based on their duration are switching surge and impulse spike. Switching surges are caused as a result of resonating circuits with switching devices. Large capacitor bank switching can cause resonant oscillations, leading to surges causing tripping or even damaging protective devices. Electronically controlled industrial motors are particularly susceptible to these transients. Impulses are very short spikes, in the order of a few microseconds. They are mainly caused by lightning strikes, arcing and insulation breakdowns. Most power systems are protected from surges and spikes using a transient voltage surge suppressors (TVSS) device and by surge dividers and arc-gaps at high voltages and avalanche diodes at low voltages. If these disturbances are encountered by monitoring systems, depending on the magnitude of the spike, it may saturate or damage the monitoring sensors. Furthermore, TVSS systems are an effective first step toward power quality management. They’re generally specified to protect the incoming AC power at the service entrance, the branch panels and individual sensitive loads. Additionally, signal and control circuit conductors are also protected to eliminate any activity from coming in the “back door.” It should be considered mandatory where there are safety-to-live and public safety considerations involved. Applications include water and wastewater treatment plants, manufacturing systems, industrial robots, power system controllers, and controllers in food-processing and petrochemical plants. Power-quality monitoring is extremely important: it provides a continuous health check of a facility’s power system to see, diagnose and avert looming problems. Harshad Singh is a technical sales specialist with Gescan Ontario in Milton, a division of Sonepar Canada.
Through the ’90s and the past decade, PCs became indispensable to every business, and naturally, many people and vendors started looking at using them to control machines and processes on the factory floor. Now, some automation vendors and systems integrators are saying PCs can be used for machine and process control in an increasing number of applications. For example, in 2004, McCain Foods of New Brunswick implemented a PC-controlled refrigeration system in its new frozen foods plant in Maine to precisely control temperature and optimize energy consumption of multiple compressors. Systems integrator TechCold International, based in Keswick Ridge, N.B., wrote a sophisticated control system in a computer language easily processed by a PC but not by even a top-of-the-line PLC. The software also communicates with almost every PLC from every manufacturer on the market, and developing interfaces and drivers is relatively straightforward — not true for PLCs. Not only does the system reduce costs, energy consumption and greenhouse gas emissions, says TechCold president Ernie Adsett, it also can be duplicated in McCain’s other plants around the world. The project attracted a lot of attention in the automation world. In the ’90s, Siemens, a longtime player in the PLC and automation field, brought out “soft PLCs,” software that runs on a Windows PC and emulates sophisticated PLCs. Its Simatic line reduces control costs by 20 to 30 percent compared to traditional PLCs, says product manager Ehab Rofaiel. The idea of using a PC to drive automated systems was originally met with considerable skepticism. PCs, after all, crash, which could lead to production downtime and critical data loss. Siemens’ solution was its RTX real-time operating system, an OS that runs alongside Windows in the PC that keeps going even if Windows stops for some reason. Siemens has been demonstrating it in operation for years and is making headway in convincing the market that it’s viable. “Every month, we see more acceptance of PC-based controls in the market,” Rofaiel says. Some, however, maintain that PCs just aren’t cut out for real-time manufacturing automation control. Very early on, some manufacturers noticed PCs weren’t always performing as quickly or reliably as their old-fashioned PLCs. “Some customers who switched from PLCs to PC control have gone back to PLCs,” says Bill Black, controller product manager with GE Fanuc, a major supplier of PLCs. “They’ve found that it’s more difficult to get support for PC control.” One reason is that regular updates to the operating system or control software often requires updates to all the drivers. And costs of PLCs have fallen recently, as well. “Controllers have gotten more sophisticated, faster and able to handle larger programs today,” he says. Today, manufacturers who want to automate can choose between PLCs, PCs and a hybrid of the two to control processes and machines, monitor factory floors and ensure safety. But how do they choose? Strengths and weaknesses PLCs were developed specifically for the manufacturing plant: dedicated to a limited set of tasks, they’re rugged, resistant to the rigours of the factory floor, such as vibration, heat and dust. “PLCs are reliable. They do their job well,” TechCold’s Adsett says. A PLC’s main advantage, though, is not so much that it’s fast — today’s PCs have processing speeds that are orders of magnitude faster — but that its simple operating system (OS) means its main processing power is always available for the unit’s main task, explains Nicolas Arel, a systems integrator based in Montreal. Windows, the most popular PC operating system, demands priority on the central processing unit’s attention. In other words, if the machine that the computer controls sends a signal at the same time that the OS sends a routine instruction to the CPU, the OS instruction will be processed first, forcing the machine’s signal to wait. If you’ve ever been frustrated by the hourglass symbol when you’re doing fairly simple work on your PC, imagine if that happens when a critical alarm signal from a manufacturing operation has to wait for the OS to refresh. Worse, conflicts for computer processing cycles from different processes can cause the computer to crash, which can halt production lines or critical operations and even put people at risk if the system is controlling a safety-related process. Because PLCs have been around for more than 40 years, their use is well known in manufacturing settings; programming them is relatively simple, and in most manufacturing plants, electricians know how to set them up and troubleshoot them. But their functions are limited, like their programming language. They can handle input and output, but complex tasks are difficult to program using ladder logic. Setting up different responses to a wide range of circumstances that might occur is far easier in one of the richer, more modern programming languages used in personal computers. Another limitation is that PLCs are proprietary systems; while manufacturers can choose from a wide range of suppliers, Allen-Bradley’s PLCs are not compatible with Omron’s or Siemens’. This limits the manufacturer’s choice and flexibility. The personal computer, however, is (if anything) flexible. A multi-purpose device, it’s well suited to handling a wide range of tasks and integrating data in a way that’s easy to understand. And while PLCs are well accepted and widely understood on the factory floor, PCs are equally well understood in the office. PCs are good at linking information from the factory to the front office. They’re often used for monitoring efficiency and displaying activity to management. Today’s PCs use very powerful computers with extremely high data speeds compared to PLCs. They can handle images at high speeds and can be made compatible with many other computers, networks and even PLCs. And because they’re so widely known, there are a lot of people available who know how to program them. But PCs are not typically rugged systems; they’re susceptible to heat, dust and vibration and have to be “hardened” or “ruggedized” for use on the factory floor. They’re also susceptible to computer viruses (something PLCs don’t have to worry about) and being hacked. And worst of all, they’re prone to crashing. This can lead to loss of data, which can be a huge problem and cause expensive delays when the PC is controlling critical manufacturing operations. “PLCs are good for interlocking operations, and fast decisions. They’re not so good with high-speed data collection or complex programs,” Adsett says. “PCs are better suited to monitoring, optimization and analysis — making sure you’re getting out of a process what you should be.” The hybrid approach However, PCs and PLCs are not an either-or choice. Almost every systems integrator advocates using them side by side. Even Simatic’s Rofaiel says PCs cannot completely replace PLCs. “PLCs are best suited, for example, in fault-tolerant applications, where you have two PLCs running side by side so that if one goes down, the second kicks in instantly,” he says. Systems integrator Arel says there is a place for both PLC and PC control systems. “The PLC’s computer power is not as good as a PC’s,” he says. “Their speed is limited.” He worked on an installation for a printing company that prints numbered lottery tickets. Quality control is essential, so the company needed a fast and precise way to track all production and any wasted paper or tickets due to paper breaks or other production problems. Managers also wanted to link all the different equipment for a real-time, accurate picture of productivity in their plant. “Printing goes at 1,000 feet per minute, and they want to take it up to 2,000 feet per minute,” he says. That means they need very fast data exchange between the plant floor and the front office systems. “The amount of data is humongous.” The solution was using PLCs on the equipment for tracking of lottery numbers, with a PC system on top of that for the data exchange and quality control applications. TechCold’s Adsett agrees with this hybrid approach. “When we go into a customer’s plant, we don’t say, ‘You have to replace all your PLCs with PCs.’ Instead, we add a layer of control on top of the PLC system.” PC in a PLC Luckily, manufacturers don’t really need to choose between PLCs and PCs anymore. “The evolution of the programmable automation controller (PAC) has removed the barriers between PCs and PLCs,” says GE Fanuc’s Black. PACs combine PCs and PLCs, adding the newest high-speed and flexible microprocessors to the rugged, reliable operation of PLCs and using newer, reliable, customized operating systems. Combining the two types of controllers means PACs are being used not only for process and machine control but also data acquisition, machine vision and remote monitoring. They can handle multiple communications protocols, including PC protocols from TCP/IP to OLE for process control (OPC), and PLC Fieldbus networks such as Profibus, RS-485 and others. They can also have USB ports and Ethernet connections. “PACs can use more sophisticated programming languages like structured text, which makes programming them for math functions more intuitive. And they can handle tasks that can’t be programmed with ladder logic,” Black adds. Simply put, choosing a side is not a necessity. With ever-evolving technologies and hybrid approaches, it’s just a matter of settling on an approach that fits the application. Scott Bury is a freelance writer based in Kanata, Ont.
Researchers from the Ishikawa Komuro Laboratory at the University of Tokyo presented the video of a high-speed robotic hand at the 2009 IEEE International Conference on Robotics and Automation. The laboratory's website has many more videos related to this project, called Sensor Fusion. PLAY High-Speed Robot Hand The video shows the manipulator dribbling a ping-pong ball, spinning a pen, throwing a ball, tying knots, grasping a grain of rice with tweezers, and tossing and catching a cellphone. "These videos show that high-speed sensor-motor fusion has great potential to produce new control strategy and new robotic skills," the narrator says.
Pistons and hydraulics systems lay at the heart of ceramic tile equipment in a process that has undergone huge changes from original operations a thousands years ago in the city of Foshan in Guangdong Province, China.Today, Trelleborg Sealing Solutions provides the seals for a large proportion of the ceramic presses built in China and supplies all of China’s main ceramic press manufacturers. The largest of these is Foshan Henglitai Machinery (HLT), which was established in 1957 and produced China’s first hydraulic ceramic press in 1988. The company currently has the largest market share and exports to numerous countries.Advanced technology, according to Trelleborg, ensure smooth, efficient operation for hours on end, all year round in machines that can measure up to 10 metres (or 33 feet) high and four metres (or 13 feet) wide, exerting a force of thousands of tons, as the tiles are mass produced. A powder consisting mainly of clay and feldspar is pressed into a mold using a piston. Then another piston pushes the tiles out of the mold and away for drying, glazing and firing in a kiln."Our seals are critical components for these machines," says Elton He, application engineer with Trelleborg in southern China. "We supply all the seals used in the cylinders, and since these provide the power used to press the tiles, they are of crucial importance to the functioning of these machines. Most of the cylinders move at a rate of about ten or 15 cycles per minute and the machines normally operate about 20 hours a day."They might only be shut down at the end of the year to perform maintenance, so these are very tough operating conditions."High-tech materials are crucial for the demanding conditions under which they must perform, an example would be HLT’s biggest ceramic press which exerts a maximum pressing force of 72,000 kN and contains between 100 and 150 Trelleborg Sealing Solutions seals, ranging in size from just 50 mm (or two inches) to 1.6 metres (or five feet, three inches). These include many high-performance Turcon-based PTFE seals – engineered thermoplastic compounds that offer low friction to reduce power loss and minimize wear over a long life. Orkot wear rings are also used, which are composite bearing materials that incorporate advanced polymer technologies. Trelleborg offers 100-plus seals can be divided into four basic types:• Piston seals, such as those installed on the groove of the pistons that press the actual tiles• Turcon seals, such as patented Glyd Ring T, Stepseal 2K and Excluder• Orkot and Turcite wear rings• Large-diameter O-Rings, which function as static seals on all the cylinders and flanges in the ceramic pressThe seals have to be durable to seal in the mineral oil-based hydraulic oil as well as strong, wear-resistant and capable of handling pressures up to 35 MPa / 5,075 psi and withstanding temperatures in the range of 60Â°C to 80Â°C.
Manufacturer G&W Products has found itself well positioned to weather the current economic storm, thanks to recent expansions in technology that increased capabilities while maximizing productivity. For the last five years, Lincoln Electric Automation has been a key partner in contributing to this effort.Despite the worldwide slowdown in manufacturing activity, the Fairfield, Ohio-based company is on track to achieve year-over-year growth between 2008 and 2009. Automated welding plays a big role in the company’s growth plan, says CEO Gary Johns."There is no question robotic integration has allowed G&W to be more competitive in the marketplace," Johns notes. "It has allowed us to swiftly complete medium-to-large-volume welding work. It also has allowed us to realize significant gains in the consistency and quality of overall productivity. Automation and other initiatives have allowed G&W’s business to grow approximately 35 percent over the last three years while maintaining nearly the same number of employees." G&W, which employs 120 workers on three shifts, offers a full range of fabrication services for such industries as material handling, military hardware, retail displays, power distribution and construction equipment.The company produces metal stampings and fabricated metal parts to customer prints and specifications. Its engineering department also works closely with customers to turn concepts into manufactured parts, and assemblies.In addition to MIG, TIG and spot welding, G&W provides a full range of manufacturing capabilities, including laser cutting, stamping, metal forming, tool and die manufacturing, and even powder coating. This gives customers a total solution of value-added production options in a competitive marketplace. These services take the concept of traditional job shop operations to a higher level.In the past four years, the use of robotic welding systems has become firmly integrated into the company’s list of well-established capabilities. At G&W Products, automation is not just a passing fancy; it’s now an important part of the company’s production process and a strong contributor to its competitive bottom line."There are many jobs we have quoted that are ideally suited for robotic welding and often it is an advantage when we are competing with companies without this capability," explains the company’s vice president of sales, Randy Sagraves. "More importantly, this technology has fit in well with our value-added operations. As customers come to us for welding requirements, they are introduced to many other areas that can add value to their purchase. Evidence to our success with robotic welding is introduction of four additional Lincoln systems in the past two years."Ahead of the curveG&W Products offers its customers more than 2,500 available welding hours each week in MIG, TIG and spot welding in both stationary and portable environments. Five Lincoln Electric robotic welding systems help the company keep pace with higher volume MIG welding demands, particularly in light of the well-documented shortage of skilled welders in the United States.Reports from the American Welding Society (AWS) say this shortage, combined with the drive for higher productivity and reduced costs, will continue to boost the popularity of automated welding systems on shop floors. In fact, the market for welding robots is growing at a higher rate than any other industrial market. The industrial sector, as a whole, boasts sales of more than 15,000 robots a year, including welding robots. A report released in June 2008 from the International Federation of Robotics notes the supply of robotic welding systems in use in both North and South America increased 42 percent over the previous year. That’s not to say manual welding performed by the G&W’s highly skilled team of 20 welders doesn’t have its place in the company’s production process. The size of a job plays a determining role, allowing the company to employ the substantial skills of its manual welding team more efficiently – where they are most needed."Most items we are welding robotically can be manually welded, as well. The factors driving us to robotic welding are related to cost and capacity, rather than capability," Sagraves says. "Volume is the most important variable in determining a fit for robotics. With some parts, we make several hundred pieces of a particular item each month, so it makes sense to robotically weld it. This allows us to be cost effective by spreading the cost of the equipment and the fixturing over the cost of the job and while involving our highly skilled welders with jobs of varying volumes or items that are too large or complex for the robotic cells."Integrated systemThe robotic welding area at G&W features three System 50HP Dual Headstock Robot Cells, a System RCT TurnTable Robot Cell and a System 40 TurnTable Robot Cell, all from Lincoln Electric Automation. The company produces more than 20,000 parts on its robotic systems each month, some of which can be welded six times faster than they could be welded manually."Our robotic line handles MIG welding of aluminum parts, high-tensile-strength steel and weldment geometries that require creative fixturing," says Doug Keehn, G&W’s director of advanced manufacturing. "Once the fixture is proven out and the programming is completed to meet these challenges, the production and quality are quite consistent."Pre-engineered, the System 50HP units are dual-headstock workstations designed for medium-sized parts that can be welded using the flexibility of reorientation – something that fits well with G&W customers’ varied parts orders, which can include structural, plate, tubing, sheet metal extrusions and even special shapes."These cells can handle our larger, more complex parts," Keehn explains. "Its rotary design also helps us more effectively process aluminum parts."The System 40 TurnTable Robot Cell, another pre-engineered solution, provides short delivery times and reduced variable costs to enhance standard parts production. Its indexing, two-position turntable workstation works well with G&W’s small- to medium-sized parts that can be welded without re-orientation. For higher volume jobs involving medium-sized production parts, programmers at G&W rely upon Lincoln’s System RCT, a flexible turntable robotic welding and cutting workcell. This unit features a patented, center-mounted positioner design that maximizes the robot work envelope by bringing it closer to the workpiece."Both of these units are versatile and can handle some of the simpler parts we have at a higher volume, delivering increased cost effectiveness," Keehn says.All of the robotic systems, which are equipped with fume exhaust hoods and Fanuc RoboticsÂ® arms, deliver superior weld quality and consistency, a plus in medium-to-large volume parts production. The other most notable benefits come in setup and programming, particularly if the weld isn’t too complex, Keehn points out."If a part requires only a few welds, we can get sets of eight to 10 parts completed in two minutes," he says. "What’s more, every robotic cell has two stations. While one station is welding, we can load the other side with the same part, or a completely different part, provided the filler metal and gas are the same. This allows nearly uninterrupted production."Programmers behind the productionThe fixturing of the robotic systems are critical to the success of each product. They must be accurately designed and programmed to hold critical tolerances; easy to load and unload; designed to hold as many parts as possible; and robust enough to withstand the rigors of consistent use. G&W management relies on its team of specially trained programmers to oversee this crucial element of its robotic operations.Some members include journeyman welders, while others on the team are experts in automation and know how to run the equipment and program it for maximum weld quality, consistency and speed. Those who were not welders by trade have received welding training so that they can know how to recognize good weld penetration and quality. Two senior operators oversee the operation and programming of all the cells, but all of those on the robotics team have been trained in the proper operation of the units. All operators attend Lincoln’s Welding School, and the senior operators have also attended Lincoln’s Advanced Training program. The team also participates in regular internal training sessions on welding and weld inspection.""Our programmers’ backgrounds are varied. When we identify who is best suited to run the robots, we realize they might require additional welding training, or they might need training on the equipment and how to run it," Keehn says. "It requires both skills. You don’t necessarily need to have a welding background, but you do need to have a strong knowledge of good welding and programming and know how to manage those cells to deliver a superior quality weld. We’re not just welding sheet metal. Our work involves many different aspects of welding."This move towards automation was driven by the desire for higher volume weldments and also the desire to increase value-added capabilities as a competitive advantage, Sagraves notes. He stresses that robotics isn’t just for large fabricators. Making the move to robotics has helped reshape and strengthen G&W Products’ business, despite the challenges of a struggling economy. Johns says he believes adding robotic welding to the shop’s service offerings was one of the best strategic moves the company management has made. He says they only wish they had integrated them sooner."Integrating automation into our operations reflects our company’s overall direction and growth plans," Johns says. "Efficiency is an overall theme. We’re looking to become leaner, more flexible and more competitive. Robotic welding fits perfectly into this plan. Robotics is more than a fad in this industry. It’s an ingredient to a plan to stand above the competition."www.gandwproductsinc.comwww.lincolnelectric.ca
JÃ¤germeister has, behind its modern image, a very long and traditional history. The company Mast-JÃ¤germeister AG has been producing its signature alcoholic beverage since 1935, and it is enjoyed in more than 80 countries around the world.The drink is made from a total of 56 herbs, blos soms and roots and has always been produced and bottled in WolfenbÃ¼ttel, Germany. More recently, Mast-JÃ¤germeister AG opened production sites in Kamenz, and Wittmar, near WolfenÂbÃ¼ttel. The company says that its continuously rising sales figures prove that JÃ¤germeister is a market success with more than 81 million bottles being filled in 2007 alone."Quality is one of the key factors to the brand's success. "Quality assurance is an extremely important subject in the JÃ¤germeister production," explains Jens RieÃŸen, head of the Kamenz plant. "Due to our strong brand reputation, we are committed to making sure that our customers will always get the very best quality." At the Kamenz site in Saxony, over 20 million litres of JÃ¤germeister is bottled per year – and since this modern facility commenced production, the company has been relying on checkweighers from Mettler Toledo Garvens.Mettler Toledo Garvens supplied the "dynamic" weighing technology for "completeness" checking in the end-of-line packaging process where the weight of cartons filled with either "1 litre" or "0.04 litre" bottles is verified. This ensures that incomplete cartons or those containing bottles with too little content are detected and rejected, preventing them from leaving the factory. Moreover, the weight check ensures that damaged bottles with leaks are immediately detected."Garvens checkweighers can be integrated in near to every production line as their design can be easily adapted to the given technical requirements of any production line. An example of this is where two weighing terminals of two separate E Series checkweighers, integrated into different production lines, were installed side by side, allowing for easy operation of both checkweighers from one position. This solution, according to the company, was appreciated by the staff operating the JÃ¤germeister production lines.An XE3 checkweigher weighing 60 cartons per minute is also in use. In this application, the XE3 can weigh products up to 6,000 grams with an accuracy within one gram. The XE3 automatically rejects underweight cartons by means of a pusher, enabling the line staff to check the carton and replace bottles where necessary. This method ensures that only full bottles reach the end consumers. ca.mt.com
Whether running a small operation lights out to keep costs down or operating a large corporation that produces custom products, manufacturing already runs on tight profit margins and have narrow margins for error. When a process is implemented, it is done with care and precision; that line must run with a minimum of input and maintenance, and certainly no unexpected surprises. After the considerable engineering it takes to link together machinery, conveyors and stations, it is expected (and rightly so) that everything will simply hum along.Meanwhile in the front office, new clients are sought and landed, and new business is solicited from existing clients. Either one likely means a new process or production runs. The orders make their way over to the engineers, who then must work within slim budgets to add in or change existing lines. With traditional conveyors, this can mean extensive downtime as the new equipment is installed and lines rearranged. Where it can break down is in taking apart and reconfiguring conveyors; for the most part, they never go back together the same way again, necessitating the ordering of whole new systems. Although it appears that the conveyor industry has solved most integration issues and addressed the issue of inflexible systems that are costly to alter, most conveyors touted as "modular" have not technologically advanced to current industry needs.Taking an analogy, if someone owns a "modular" home and decides a few months or even a year down the road that they want the bathroom on the other side of the house, or want to expand the kitchen, they can’t just snap in a module and rearrange their home. In a similar way, most conveyor systems that are labeled "modular" require some type of extensive construction or deconstruction that can entail cutting and welding–and what’s to be done with parts that are cut away? They simply become very expensive waste as they cannot be used again. This is even true when only small changes are made, such as adding a corner or changing an angle.Even the smallest task of cleaning a belt, let alone removing, changing or altering belts can also be a major issue. Even today, most belts are normally made in fixed lengths, and if they must be changed in any way, "fixes" must be arrived at with which sections of belt can be fitted together in such a way that the line can continue to run. It’s either that or ordering a whole new belt; obviously not a cost-effective solution.In industries such as pharmaceuticals, in which processes must be maintained at a certain level of cleanliness, ease of manipulating conveying systems is also a serious issue. In cases in which areas can’t be easily reached for cleaning, belts must be removed or other parts must be taken off." If conveyors are not specifically built to accommodate these measures, it is a labor-intensive activity when it comes to putting it all back together again; the few dollars saved on initial cost is lost on backend maintenance.An Adaptable "Snap in Place" ApproachHenry Tamangi, Maintenance Manager, with Comar Inc., a company that manufactures packaging and liquid dispensing solutions for the pharmaceutical industry, has found a reconfigurable modular conveyor system that opens up whole new vistas in "changing on the fly." Because The product line Comar produces is so diverse, those new processes being ordered by the front office are not such problems after all.Comar’s processes consist of three departments: blow molding, injection molding and a secondary operations department that performs offset printing, hot stamping, silk screening and assembly of all molded components. The parts are molded, go through finishing in secondary operations and are then shipped out. Comar integrates their processes and departments using DynaCon reconfigurable conveyor systems, produced by Dynamic Conveyor Corporation of Muskegon, Mich. "What is so nice about them is that they are modular," Tamangi said. "You can take them apart shorten them, lengthen them, change the angles, or change the drive motors to be constant speed or variable speed. You can change the configuration of them quite easily."Reconfigurable modular conveyors are used to connect different machines. For example, if a molding machine is connected to a printing machine, the conveyor is used to connect the two so there is an inline process; parts do not need to be placed in a box and physically moved. In two different applications, a molding machine, an offset printer, an assembly machine and a wrapper have all been linked. Tamangi estimates there are 50 reconfigurable conveyor systems throughout his facility. "We’ve tried other conveyers that were touted as similar, but I wouldn’t say that they are modular like the DynaCons. We have so many because we have good success with them," he says.Because these systems are specifically made to be pulled apart and reassembled as needed, maintenance is quite easy. "Because we serve the pharmaceutical industry, the systems have to be cleaned and doing that with the DynaCon system is very easy," Tamangi said. "We just clean them from time to time when needed." We can pull the conveyors apart, take the belts outside, and power wash them. Each conveyor gets power washed once or twice a month, depending on the job."Although they are dreaded, malfunctions do occur in from time-to-time in every manufacturing process. Recently, Comar experienced a substantial water leak on a 550-ton press and had to roll the conveyor out. But because the conveyor system was so easily removed and put back in place, the event was much less dramatic than it might have been. "Because it was a DynaCon conveyor, the cleaning time was cut at least in half," Tamangi reported. "We just rolled it away from the press" power washed, cleaned, and sanitized the entire conveyor and put it back in service. With metal conveyors you really can’t power wash them down, so a lot of hand wiping would take place; a lot of elbow grease."Another company in a similar industry utilizing the same conveyor technology had an instance of having to move an entire process to a different floor. The process utilized three conveyors, but once it was moved to its new location and rearranged for the new work area, the flow had been reduced to two conveyors and there were considerable leftover parts. With traditional conveyor technology, those parts would have gone to waste, but because of the versatile nature of these conveyors the parts were able to be re-utilized for an entire new system in another area of the plant.Versatility of BeltsThis same company had a problem with belts on previous systems, specifically with diagonal vulcanized seams that were damaged or came loose, causing the belt to come apart. Attempts to repair the belts created seams causing uneven product flow, pinching and part damage. "DynaCon systems utilize interlocking belt systems that are formed in links allowing the belt to be taken apart and reassembled easily, every inch. Maintenance and repair are never a problem. Ideal for Today’s OperationsSuch conveyor systems are ideal for operations with frequent layout changes or those who need to quickly change process lines, but also ideal for operations that are competing with larger corporations with greater budgets. For example, Air Support Medical Company, manufacturer of parts for anesthetic and respiratory circuits, wanted the ability to run their molding machines 24X7, but that was challenge for the small corporation. "To do that would we would have needed two operators on at night, but then you need to have supervisors and it gets to be financially difficult." said Kathy Walters, Air Support Medical Company’s owner. The solution has been to evolve lights-out operations at night, using a simple video surveillance system, similar to one used in a convenience store, and the internet to monitor the molding machines. However, before discovering the DynaCon modular conveyor system, the company’s ability was limited. "Sometimes if we had small parts, we might run it in a Gaylord, but it had to be something that wouldn’t make a lot of parts because we couldn’t get it away from the machine fast enough. The DynaCon gave us the ability to run a lot of the parts and be able to control the flow of parts that came off of it," said Walters. Being able to quickly set up and reconfigure conveyor systems has been a major source of help for them. "We just bought our fifth conveyor system," said Walters. "The flexibility is great; you can move them around, or you can add parts to go higher or remove them if you need a lower conveyor. They give us the cost-effective ability to run and control the flow of the parts during lights-out operations."Their formula has worked; in a declining economy, they are expanding and having to hire additional personnel. To remain competitive in today’s tough markets, manufacturers should take every measure possible to ensure they can replace, change or add new processes "on the fly" with technologies such as reconfigurable modular conveyor systems.Bruce Boyers is a freelance writer based in Glendale, Calif.
This online version has been modified from the print version to include a solution to harmful VFD currents: the shaft grounding ring.With the rising cost of energy, the use of variable frequency drives (VFDs) is growing. By optimizing the frequency of a three-phase alternating-current (AC) induction motor's voltage supply, a VFD controls the motor's speed and torque, while providing energy savings. These savings can be quite substantial - 20 percent or more - making VFDs a "green" solution as well as a wise money-saving investment.To be truly "green," however, a technology must be sustainable as well as energy efficient. Yet the currents induced on motor shafts by VFDs can wreak havoc with motor bearings, dramatically shortening motor life and severely diminishing the reliability of systems. To mitigate these currents and realize the full potential of VFDs, a cost-effective method of shaft grounding is essential.Whether used to save energy or increase the accuracy of process control, VFDs only achieve their full potential when carefully matched to the application and installed with appropriate safeguards. Safeguards will eliminate the need for expensive repairs and enable VFDs to fulfill their promise of energy and cost savings.Energy-saving potentialIn today's typical VFD, a rectifier converts the AC utility feed to direct current (DC), a filter smoothes the current's waveform and then a pulse-width modulation (PWM) inverter turns it back to AC in variable form using insulated gate bipolar transistors (IGBTs). Typical output frequency is two to 12 kHz, or 2,000 to 12,000 on/off cycles per second. VFDs may be used to directly drive one or more motors in constant-torque applications, to ensure that they do not use any more power than necessary. With encoder feedback, a VFD can also be used to control the speed of a motor by modulating the voltage and frequency of power to the motor according to programmed parameters. In the field of flow control, the potential for increased efficiency with VFDs is especially dramatic. Many centrifugal fans and pumps run continuously, but often at reduced loads. Because the energy consumption of such devices correlates to their flow rate cubed, the motors that drive them will use less power if controlled by a VFD. In fact, if a fan's speed is reduced by half, the horsepower needed to run it drops by a factor of eight. With rising energy costs, restricting the work of a motor running at full speed through the use of dampers and other throttling mechanisms seems needlessly wasteful.In constant-torque applications where the main objective is more accurate process control, a VFD can be programmed to prevent the motor from exceeding a specific torque limit. This protects the motor, and in some cases associated machinery and products, from stress and damage. If a machine jams, for instance, the motor that powers it will, without the moderating influence of a VFD, draw excessive current until its overload device shuts it down.Regardless of the application, the VFD must be compatible, not only with the motor, but also with every other system component. Potential problemsBecause the waveform from a VFD is generated by pulse-width-modulated switching, it has high-frequency components that are capacitively induced onto the motor shaft and discharged through the bearings. These are not pure sine waves; they contain high-frequency currents and voltages called harmonic content, the potential effects of which are many. And even when the motor is designed for inverters, it is vulnerable to bearing failure from VFD-induced currents.Motor shaft currents induced by VFDs can damage motor bearings. Although best addressed in the design stage of a system, these currents can usually be mitigated by retrofitting previously installed motors. Without some form of mitigation, shaft currents discharge to ground through bearings, causing pitting, fusion craters and "fluting." This unwanted electrical discharge machining (EDM) leads to excessive bearing noise, premature bearing failure and subsequent motor failure.Motors are never fully compatible with the VFDs that drive them unless these shaft currents are addressed and mitigated. Various other negative effects can also manifest themselves if the driven motor is not designed for use with a VFD, or if either the motor or the VFD is not rated properly for the application or the load. For example, when required to maintain a constant torque, a motor tends to lose some efficiency, running hotter at lower speeds but hotter still when controlled by a VFD. If such a motor must be operated at less than 30 percent of its maximum speed, it may need extra cooling or thermal protection. Similarly, a VFD-controlled motor's capability to produce torque drops more quickly at lower motor speeds than a motor using pure sine wave power. For constant-torque loads, a VFD should be rated for 60 seconds at 150 percent of the load. A VFD's current rating also limits the load-acceleration rate.Another rule of thumb is that the cable connecting a VFD with a motor should not be more than 50 feet long, or else two different wave types could meet at the motor terminals and in effect double the voltage received by the motor. If a longer cable is required, extra line filtering is recommended to protect the motor and other sensitive equipment nearby from harmonic content and radio frequency interference (RFI). RFI can also be reduced by enclosing motor leads in a rigid conduit. Regardless of its length, the cable between a VFD and the motor or motors it regulates can be enclosed in a corrugated aluminum sheath or another kind of grounded, low-impedance shielding.VFDs may also not be appropriate for systems that must maintain high pressure. During periods of low flow, a VFD-controlled pump motor may not be able to slow down enough without reducing pressure. For systems that require dynamic braking, VFDs are available with an optional power load resistor that can shunt excess energy from the DC bus.A closer look at bearing damageEvery VFD-controlled AC motor develops a parasitic capacitance between the stator and rotor. Short of dismantling the motor, there are two main ways to check for bearing damage from induced shaft currents - by measuring vibration and voltage. Both are best used to establish a baseline early on, so that trends can be monitored later. Neither method is foolproof.By the time vibration tests confirm bearing damage by identifying particular energy spikes in the range of two to four kHz, the damage has usually reached the "fluting" stage. Likewise, the main benefit of voltage tests may be the relief they provide when the results indicate no bearing damage. If a baseline voltage measurement is taken right after a VFD has been installed, successive tests may provide early warning of harmful current loops, but there are many variables. Induced shaft currents can be measured by touching an oscilloscope probe to the shaft while the motor is running. These voltages repeatedly build up on the rotor to a certain threshold, then discharge in short bursts along the path of least resistance, which all too often runs through the motor's bearings to the frame (ground). Serious bearing damage is thought to be more likely in systems that operate with high carrier frequencies, a constant speed or inadequate grounding.A high carrier frequency means a high discharge rate. For this reason, it is advisable to purchase a VFD that permits fine tuning of the carrier frequency in increments no larger than one kHz. There is no doubt that inadequate grounding significantly increases the possibility of electrical bearing damage in VFD-driven motors. Without proper grounding, VFD-induced electrical discharges can quickly scar the race wall. During virtually every VFD cycle, these induced currents discharge from the motor shaft to the frame via the bearings, leaving small fusion craters in ball bearings and the bearing race wall. These discharges are so frequent that before long the entire bearing race becomes riddled with pits known as frosting. The damage eventually leads to noisy bearings, but by the time such noise is noticeable, bearing failure is often imminent. Since many of today's motors have sealed bearings to keep out dirt and other contaminants, electrical damage has become the most common cause of bearing failure in VFD-controlled AC motors.Mitigating bearing damageElectrical damage to AC motor bearings often begins at startup and grows progressively worse. As a result of this damage, the bearings eventually fail. To guard against such damage and thus extend motor life, the induced current must be diverted from the bearings by means of mitigation technologies, such as insulation, shielding and/or an alternate path to ground. Insulating motor bearings is a partial solution that more often than not shifts the problem elsewhere. Blocked by insulation, shaft current seeks another path to ground. Attached equipment, such as a pump, often provides this path and it frequently winds up with bearing damage of its own. In addition to being expensive, insulation is subject to contamination. Worse yet, some types of insulation can be totally self-defeating. In certain circumstances, the insulating layer has a capacitive effect on high-frequency VFD-induced currents, allowing them to pass right through to the bearings it was supposed to protect.A Faraday shield can be created by installing grounded conductive material, such as copper foil or paint, between the stator and rotor. If built to the proper specifications for the motor, this can block most of the harmful currents that jump across the motor's air gap. However, this mitigating measure is often expensive and difficult to implement, and attached equipment could still be vulnerable to deflected currents.Likewise, nonconductive ceramic ball bearings divert currents from the main motor's bearings but leave attached equipment open to damage of its own. Ceramic bearings can be costly and usually must be resized to handle mechanical static and dynamic loadings.Yet another mitigation attempt comes in the form of conductive grease, which, in theory, bleeds off harmful currents by providing a lower-impedance path through the bearings. In practice, however, the conductive particles in the grease increase mechanical wear.Metal grounding brushes certainly help. They contact the motor shaft to provide alternate paths to ground. Unfortunately, they also wear out and corrode, thus requiring regular maintenance.Alternate discharge paths to ground, when properly implemented, are preferable to insulation because they neutralize shaft current. Techniques range in cost and sometimes can only be applied selectively, depending on motor size or application. The ideal solution would provide an effective, low-cost, very-low-resistance path from shaft to frame, and could be broadly applied across all VFD/AC motor applications, affording the greatest degree of bearing protection and maximum return on investment.Avoid damage with a shaft grounding ringA shaft grounding ring (SGR), such as the AEGIS SGR from Electro Static Technology (www.est-aegis.com), meets all these criteria–the company's patent-pending Electron Transport Technology uses the principles of ionization to boost the electron-transfer rate and promote extremely efficient discharge of the high-frequency shaft currents induced by VFDs. Without some form of mitigation, VFD-induced shaft currents can cause considerable motor/bearing damage.It's scalable to any NEMA or IEC motor regardless of shaft size, horsepower or application. The company says these grounding rings have been successfully applied to power generators, gas turbines, AC traction and break motors, cleanrooms, HVAC systems and a long list of other industrial and commercial applications.For VFD-equipped motors of less than 100 HP (75 kW) with shaft diameters of less than two inches (50 mm), a single SGR on the drive end of the motor shaft is typically sufficient to divert harmful shaft currents.Large AC motors (100 HP/75 kW or more) and even large DC motors, especially those with shaft diameters of more than two inches (50 mm), are more likely to have high-frequency circulating currents (as well as EDM-type discharges) that can damage bearings. Motors with roller bearings are also more vulnerable to damaging circulating currents because roller bearings have a greater surface area and their lubricant layer is usually thinner. Such motors benefit from the combination of an shaft grounding ring on the drive end and insulation on the non-drive end to break the circulating current path." This may also be the solution in situations where installing an SGR on the non-drive end would be impractical because of encoders, fans, or other special circumstances. For most large motors, the best bearing protection may be obtained by installing an SGR on the drive end of the shaft and insulation on the non-drive end.This is also a common solution for motors above 500 HP (375 kW), and most manufacturers already take this approach." However, when insulation on the drive end is not designed into the motor or cannot be easily installed, two SGRs are recommended – one on the drive end (DE) and one on the non-drive end (NDE).In critical applications where motors with two ceramic bearings are specified, at least one SGR should be used to ensure that shaft voltage does not pass down the line to attached equipment such as gearboxes, pumps, encoders, pillow block bearings or break motors.The AEGIS SGR is available in two versions–a continuous ring for most NEMA- and IEC-frame motors and a split-ring design, which allows installation in the field, around larger shafts, without the need to disassemble attached equipment.Adam Willwerth is the development manager for Electro Static Technology.
Like many manufacturers, S&C Electric Canada is looking for ways to tighten its belt during the economic downturn.
Digital Industry USA
September 10-12, 2019
EMO Hannover 2019
September 16-21, 2019
Autonomous Mobile Robot Conference
September 17, 2019
Weidmuller Open House
September 17, 2019
International Metrology Congress
September 24-26, 2019
CMTS: Canadian Manufacturing Technology Show
September 30-3, 2019