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Integrating electric drives, pneumatics and I/O through one controller using Codesys programming, Festo introduces the CPX-CEC  to the legacy CPX family of products. Programmed with Codesys embedded controller in accordance with IEC 61131-3, the CEC simplifies logic development, visualization, and commissioning. This new controller has a standard CANOpen Master Port, cycle times of up to 1 ms, and a modular I/O system with up to 512 input/output connections. Included are built-in Codesys libraries for easy motion programming using electric drives and diagnostics libraries for preventive maintenance and monitoring functionality. Festo company officials said the CPX multifunctional platform allows integration of motion control, safety, and diagnosis for applications in factory and process automation. The hybrid controllers reduce cycle times by up to 30% and reduce air consumption by up to 50%. Faster troubleshooting with integrated diagnostics can reduce downtime by 35%. Extensive functional integration with pneumatic, electrical and motion to reduce system cost by up to 20% and installation time by up to 60%, a company official said. The CEC supports most fieldbus options, servo-pneumatics applications, and decentralized installations. Included are built-in Codesys libraries for easy motion programming using electric drives and diagnostics. Festo supplies automation components, including drives, controllers, sensors, visualization, programming, system design and implementation. www.festo.com/cms/en-us_us/9791_9802.htm Festo Corp. www.festo.com/usa Also read: Report from Hannover: Flying penguin, innovations, efficiency; Control Engineering Machine Control channel; and the Control Engineering Machine Control newsletter?

Piezoceramic motors and actuators have fewer mechanical component parts to wear out and service, and have ability to provide more accurate positioning, attractive attributes for medical device manufacturers. Different piezo actuators and motor types are available. The most common ones are: A) “Simple” piezo actuator—expands proportionally to voltage. Motion is proportional to drive voltage. Sub-groups include:

• Stacked actuator is the most common type, with high force, fast response, and short travel;
• Shear actuator has fast lateral motion, and XY systems are available. They can have high force and very high frequency, though travel typically limited to 20 µm;
• Tube actuator is mostly for microdispensing applications and atomic force microscopy (AFM) scanners; and
• Bender actuator has long travel (deflection) to several mm, but low force and low frequency.

B) Flexure-guided, piezo actuator has frictionless flexures, and motion amplifiers provide longer travel, and extremely straight motion. Motion is proportional to drive voltage.

• Integrated multi-axis systems are available;
• Motion range up to 2 mm and above; and
• Frictionless, without wear and tear.

C) Ultrasonic friction motors

• Based on high frequency oscillation of a piezo plate (stator);
• Unlimited motion, high speed, fast response (10 to 10s of millisecs);
• Oscillation is transferred to a slide or rotor via friction; and
• Due to friction, resolution is limited to typically 50 nm.

D) Piezo stepping motors

• Basically unlimited motion range;
• Based on accumulation of small controllable steps;
• Picometer resolution dither mode (direct piezo actuation);
• Compact and high force to 155 lb. (for off the shelf units); and
• Fast response (less than 1 millisec). Very high stiffness.

E) Ultrasonic transducers

• Plate or disk-driven with a high frequency at resonance; and
• Used as sensors or transmitters, and in nebulizers.

Also see: A piezo stepping linear motion animation, a 17-second video, courtesy of Physik Instrumente; Piezo motors, actuators streamline medical device performance; 11 ways piezoelectric motors improve equipment performance; and Control Engineering Machine Control Channel. Physik Instrumente L.P. (PI) manufacturers nanopositioning, linear actuators, and precision motion-control equipment for photonics, nanotechnology, semiconductor, and life science applications; www.pi-usa.us. Jim McMahon writes about instrumentation technology for Zebra Communications; jim.mcmahon@zebracom.net. Edited by Mark T. Hoske, Control Engineering, www.controleng.com.

Failures in industrial safety systems can cause death and destruction; integrating safety during the design process can save time, money, and lives, and avoid daily headlines. An environmentally devastating oil spill off the Louisiana Gulf Coast continues to dominate the news, a disaster resulting from a deadly explosion on an offshore drilling rig that took 11 lives. Not a month before, an underground explosion caused by methane gas killed 29 in a West Virginia mine. Dramatically different in many ways, these tragic events share a common thread: somewhere, somehow, an industrial safety system failed. Manufacturing takes safety seriously—and thankfully these tragedies are the exception and not the rule—but the fact remains that if safety procedures and systems falter for even an instant, catastrophe can occur. Systems must be fail-safe; and the need to integrate safety into manufacturing equipment and operations early in the design process has never been more apparent than in these days of technological sophistication and fragile economies. While integrating safety into manufacturing design is simpler, more efficient, and more cost-effective than adding it later, more importantly it helps avoid loss of property and life. Safety approached as an afterthought becomes very difficult to retrofit into an existing machine, process, or system. To illustrate the wisdom of incorporating it upfront, Control Engineering asked leading manufacturers, vendors, and integrators to explain how they have integrated safety into manufacturing systems and the benefits of doing so. The following examples describe the application of a variety of safety functions. Use the links provided for expanded discussions of each, see links below to additional articles at www.controleng.com. Automated material handling system cuts injuries, labor By automating a material handling system, Wisconsin-based CNC Solutions helped a customer streamline its operation, reduce the labor involved, and produce a more consistent product more quickly than the previous manual system. The integrator, who focuses on using technology to provide plant automation solutions for machine and process controls, believes automation is the key to staying competitive, providing safety, and achieving a fast return on investment. Any injury affects downtime, increases workers’ compensation and insurance rates, and impacts the bottom line. In this case, the size and weight of sheet metal blanks led to material handling issues. The customer’s manual operation was labor intensive, requiring two people to handle the product. Sharp sheet metal edges created safety hazards and caused multiple compensation claims. CNC Solutions sought to reduce the amount of material handling required and have just one person operate the system in a safe manner. CNC Solutions accomplished this by reducing the number of times the product was physically touched during the process from eight to zero, says the integrator involved. Under the new system, a robot moves the product from its previous operation directly into the work cell in a stacked form. The multi-station robotic system processes parts as needed and stacks them for use in the next operation. The automated system delivers uninterrupted production, virtually eliminating human-related downtime and repetitive motion injuries. One operator enters a part number in the human-machine interface (HMI) and moves the stacked parts in and out of the cell on wheeled carts, significantly reducing injury incidence. Perimeter guarding with access gates and door interlocks increases safety even further. PLCs get safety up and running fast System integrators at D&D Automation, Stratford, Ontario, Canada, say all safety circuits should be in place before any device is operable. During the design phase of a project, it may be impossible to cover everything from a safety integration standpoint, but having as many bases covered as possible is still best. For a body shop start-up project for a car assembly plant, the first step D&D Automation took on all framing lines was to establish communication and network connections using a Pilz safety PLC (programmable logic controller). “Any safety bus or device issues needed to be resolved before moving on,” says the integrator involved. “Once we had all our safety communications and networks up, we could start flagging the safety I/O. In most cases, a safety PLC is a luxury as you can tailor your safety logic and make modifications according to your needs without having to rewire relays. This is not to say that hardwired safety circuits are commissioned any differently. The commissioning steps still apply. However, the ability to modify safety logic in a safety PLC is also its disadvantage. To prevent improper edits or tampering, be sure to password-protect your work!” In this case, heavy traffic in and out of the cell and the timeframe required for tooling adjustments made it imperative to get as much safety running as soon as possible. E-stops, gates, and light curtains needed to be functional to protect workers within or around the cell. Programmable safety PLCs gave the integrator the ability to almost completely tailor safety functionality to its needs. The controls department at the facility was able to create its own modular function blocks. The integrator then worked with the controls department to develop and implement a combination light curtain/safety gate block. When gates are open and the plane of the light curtains is broken, the system generates a safety stop in the adjacent work cell. The group also customized a safety synchronization feedback from the shop robots via their respective safety bus nodes. Dual-channel outputs from the robot node are activated after the robot completes its own safety routine and are used within the safety program for motor interlocks to indicate the robot is within its safe working envelope. Programmable safety PLCs also help reduce troubleshooting time. The ability to monitor safety programs enables missing input conditions to be found quickly without needing a multimeter or having to sort through drawing sets. Make safety integration a job for experts Safety automation projects present challenges that go beyond the typical project. Legal requirements must be met, and the application must be validated (sometimes by a regulatory agency) to ensure associated risks are at acceptable levels given various application scenarios. For example, will safe conditions be maintained if misuse occurs or equipment fails? Integrating safety technology into a project requires extensive knowledge, application expertise, and years of experience, insists Juergen Bukowski, Sick safety program manager. Safety programming relies extensively on the abilities of the PLC programmer, who must get the equipment up and running, adapt it for the environment, and make changes “on the fly.” Consider, says Bukowski, a typical safety application in which material must exit the machine but no person or material may be allowed in. “This can be accomplished by ‘muting’ a light curtain with additional sensors. Muting automatically temporarily suspends operation of the safety device. When the sensors detect a pallet, the safety light curtain is muted,” he says. A safety PLC can do the job, notes Bukowski; a safe, pre-certified muting function block ensures safe suspension of the light curtain (see diagram). Assume the muting sensor is a reflector switch for which the output is HIGH when it sees a reflector and LOW when an object is in the light path. “The muting function block needs to be HIGH on the sensor input to mute the light curtain,” Bukowski adds. “An inexperienced integrator might see this as no problem and say, ‘Let’s negate the signal by using a NOT function block.’ ” Though such a solution may work fine and appear safe, continues Bukowski, what if the common power supply for the two sensors breaks down? “Both sensors will switch off,” he says. “It will appear to the safety PLC that both sensors see the object and result in the suspension of the light curtain. An unsafe situation may easily occur by adapting a safe concept (function block) to a real-world scenario,” he warns. “In this case, use of active HIGH sensors in combination with additional control signals or time monitoring functions would be necessary.” Manufacturers carefully select qualified integrators for their automation projects. They must do the same with the safety portions of those projects. Keep them separate, suggests Bukowski. “Leave safety to the experts,” he says. “Experienced safety integrators will reduce the likelihood of safety risks during all phases of a project. Making use of simple, easy-to- use tools for design, simulation, and testing also helps validate safety functions throughout the life cycle of the machine or project.” Safety PLCs over safety Ethernet harness the power of one wire Incorporating safety functions during the initial design process is the far better option, agree Siemens and solutions partner Advanced Engineering, Franklin, TN. Even starting small is beneficial, because most safety capabilities can accommodate a growing system. In a recent project, Advanced Engineering saw how specifying a safety PLC as early as possible in the planning process saves time and money when designing the wiring and planning functionality. Using safety Ethernet to do start/stop, speed references, and safety over the same wire turned out to be “a big savings,” says Jim Neufeldt, president of the firm. “Soon everything will have safety Ethernet. Plug up to a device, and you’ll get control, diagnostics, and safety. You can set up zones and reset the device. With smart devices, such as a drive, other functions are available as well.” The company works extensively in the automotive industry and has installed many safety systems with more than 200 I/O safety points. “Typically, that requires a great deal of wiring,” says Neufeldt. “However, distributing the I/O points using Profinet and a Siemens Simatic S7-300F processor significantly reduces the wiring and enhances operator safety.” In one case, an automaker setting up zones for robots and stamping presses sought to safeguard the zones. The effort would require a great number of safety relays, and the manufacturer was concerned about cost. The integrator suggested instead a design with safety PLCs and safe I/O. It included guarding zones between presses and determining which functions to shut down for each zone so that the operators could enter a zone safely. Using relays would have cost approximately $100,000. The safety PLC design was installed for about $60,000. The automaker has since modified the system, making changes that would have been nearly impossible with relays. Ultimately, says Neufeldt, using a safety PLC is more productive than relays. They are more flexible, offer diagnostics, require few wires, and can accommodate distributed I/O without downtime. Safety controller integration at GM Greater emphasis on integrating safety also can increase throughput and save millions of dollars. More than 15 years ago, General Motors embarked on a journey to make its safety record among the world’s best. The program it launched cut the incident rate in its North American facilities dramatically, taking its lost workday case rate from 4.5 per 100 to 0.14 between 1993 and 2008. The automaker did it by “making safety—and our commitment to safety—visible to everyone at every level,” says Mike Douglas, the company’s senior manager and consultant, Global Health & Safety, Design, Standards, and Technologies. GM executives and union representatives partnered to integrate safety from the shop floor to the top floor. Among the efforts were establishing safety task forces and creating a risk assessment program to help identify potential hazards, determine safety automation needs, and ensure machines and equipment met applicable code requirements. In one project, safety controls from Rockwell Automation were installed for tasks routine and integral to production, a move that saved GM several million dollars annually across five plants and helped reduce downtime. In fact, the safety features boosted plant throughput by four additional vehicles every five hours, which in turn increased GM’s bottom line. That risk assessment process also led to integrating safe and standard control to streamline hardware, wiring, and productivity costs. GM focused on programmable controllers to reduce the cable and labor costs associated with the hardwiring required with safety relays. Then, it worked with Rockwell Automation to develop and implement what became the Allen-Bradley GuardLogix controller. The controllers, with a SIL (safety integrity level) 3 functionality rating, integrate safe and standard control. They are part of the Rockwell Automation Integrated Architecture system, which helps improve information-sharing, provide multi-disciplined control, reduce training costs, and accelerate programming and commissioning. The automation system’s operational intelligence and diagnostics also improve equipment productivity and lifespan, while reducing downtime. Using the controllers instead of traditional safety relays helped GM reduce installation and debugging time for new body shop equipment. Previously, wiring for a typical five-robot cell required 640 wires/cables. The new system reduced wiring to one five-wire cable. “Plug and play” functionality and debug features also reduced installation and maintenance time and costs. The GM safety journey continues as the automaker and its partner, Rockwell Automation, implement additional safety automation solutions that help trim costs, increase production, and, most importantly, keep people safe. When someone asks who’s responsible for safety at GM, Douglas says: “It’s simple—everybody is.” Integrating functional safety, motion control Integrators with motion control expertise are often asked to retrofit servo controlled motion to an existing machine or process. Servo control may offer a number of benefits, but whenever new motion is added, says Gary Thrall, senior product support engineer, Bosch Rexroth Corp., the functional safety of the machine must be considered. Functional safety is best applied as part of the overall machine design process rather than as an add-on at the end, he says. A high-production automotive airbag assembly manufacturer improved cycle time by connecting a light curtain at the access to the load/unload station to the forward overtravel limit input of the servo drive. The servo moves the bag folding arms. If the operator reaches through the light curtain while the machine is still moving toward the unload station, the axis would stop. Moving away after releasing the completed airbag, motion would be allowed even though the operator’s hands were through the curtain. By using a standard (non-safety) input without redundancy or diagnostics, says Thrall, a single failure could possibly cause a loss of stopping function and allow rapid motion toward the operator’s hands—the hazard the company was trying to avoid. The standard servo drive overtravel limit input is a circuit designed with normal good practice, but it is not a safety-rated redundant control-reliable circuit, he says. Among scores of machines, none has failed to a hazardous condition, but those involved chose to lower the risk. Thrall suggests the plant consider the drive feature Safe Direction, as defined in IEC EN 61800-5-2. Safe Direction provides safety certified monitoring of the axis motion that reduces the axis to no torque if the axis moves more than a configurable distance in the "wrong" direction. Once configured, monitoring can be turned off and on with redundant complementary safety inputs to the drive—in this case, from the light curtain outputs. In many retrofits, Thrall continues, the original system may not be up-to-date on basic guarding and interlocking. Often a simple single-channel non-redundant emergency stop to remove power is all that was provided. Adding proper guarding and door interlocking that drops power to servo drives may result in new errors and sequence restart issues. Dropping input power contactors also stresses bus capacitors, wastes energy from discharging and recharging, and decreases production cycle time. Dave Stuber of Custom Controls Solutions, St. Charles, IL, suggests use of Safe Stop 2 functionality, as defined in standard IEC EN 61800-5-2, which protects the operator should a drive start up unexpectedly. It allows a drive to maintain torque and hold position while stopped. All axes in a complicated system can maintain position and synchronization while doors are opened for setup adjustments. The safety function monitors for motion and shuts down to no torque if there is motion beyond a determined safe limit. Power cycling stress, contactor wear, time delay, errors, and additional logic for mid-cycle restart are avoided. Integrated safety means security as well Safety instrumented systems (SIS) require advanced integrator skills. An integrator must demonstrate the competency and qualifications to do SIS work and be able to deliver a system proven to meet client requirements for the safety integrity level (SIL) of each safety instrumented function (SIF), says Neil Crompton, managing director of UK-based Trinity Systems Ltd. Most safety systems need to have their communications functions integrated into the DCS communications infrastructure safely and securely, he says. To do this, the integrator must be able to configure and deploy the communications capabilities of the SIS and DCS. Integrators must harden the communications integration by providing highly secure and robust systems. Cyber security is increasingly critical. Without it, an integrator could deliver a system that could potentially experience a loss of view or, worse, a loss of real-time data between the SIS and the DCS they are integrating. Meeting this challenge requires integrators to leverage the cyber security features of SIS and DCS, develop new tools, and develop new skill sets. Systems must have communications and security solutions flexible enough to collaborate with third-party DCS and easy enough to deploy to deliver the needed safety functions. SIS functions must be partitioned appropriately from the DCS functions so that a loss of communications or integrity will not prevent the safety system from performing its designed function, which is to keep the processes that require protection in a safe state. Some SIS systems self-police communications access. In one case, Invensys Operations Management collaborated with Byres Security, a cyber security firm, to add an OPC firewall to its Tricon Communications Modules (TCM). The firewall enabled a layer of defense-in-depth that lets integrators enjoy the flexibility and integration benefit of OPC Classic without worrying about security systems once associated with DCOM-based systems. Often the integrator must develop tools to augment vendor-supplied functionality. In one case, Trinity Systems developed a remote viewer that takes advantage of the communications security features of the Triconex TCM and Triconex Firewall. The viewer provides a simple and reasonably priced window into the SIS from a business or a primary control network, while the Triconex Tofino Firewall and the Triconex Communication Module’s on-board User Access Security Model ensure that it is a read-only window that can never impact safety functionality. “Processors and manufacturers are continuously threatened by new and increasingly dangerous cyber attacks, which require greater vigilance and security,” said Joe Scalia, portfolio architect, Invensys Operations Management. “An OPC firewall mitigates those risks by managing the traffic to and from the communications module, providing further assurance that a cyber incursion will not compromise integrated communications between the safety and critical control systems and supervisory HMI or distributed control systems.” Jeanine Katzel is a contributing editor to Control Engineering. Reach her at jkatzel@sbcglobal.net. Find automation system integrators specializing in safety and security systems, machine build/retrofits, machine design/control, manufacturing engineering, and others at www.controleng.com/integrators. For more on the vendors and integrators mentioned in this article, visit their websites: www.adveng.com (Advanced Engineering) www.bosch-rexroth-us.com www.cncsolutionsllc.com www.ddauto.com (D&D Automation) www.gm.com www.iom.invensys.com www.pilz.com www.rockwellautomation.com www.sea.siemens.com www.sickusa.com www.tofinosecurity.com (Byres Security) www.trinitysystems.com ONLINE extras - read more about each application above and see additional photos. Applying programmable safety PLCs: D&D Automation Integrating safety requires attention to cyber security issues as well: Trinity Systems Ltd. Leave it to the experts: Integrating safety in automation requires specialized knowledge - Sick Inc. Providing safety through systems integration: CNC Solutions Safe journey: GM program strives to make safety everyone’s job - Rockwell Automation Safety from a System Integrator Perspective: Bosch Rexroth Corp. Using a common wire: Safety PLCs with safety Ethernet - Advanced Engineering Also read... Machine Safety blog System Integration Channel on Control Engineering System Integration newsletter

For the purposes of feedback control, stability refers to a control loop’s ability to reduce errors between the measured process variable and its desired value or setpoint. A stable control loop will manipulate the process so as to bring the process variable closer to the setpoint, whereas an unstable control loop will maintain or even widen the gap between them. With the exception of explosive devices that depend on self-sustained reactions to increase the temperature and pressure of a process exponentially, feedback loops are generally designed to be stable so that the process variable will eventually achieve a constant steady state after a setpoint change or a disturbance to the process. Unfortunately, some control loops don’t turn out that way. The problem is often a matter of inertia – a process’s tendency to continue moving in the same direction after the controller has tried to reverse course. Consider, for example, the child’s toy shown in the first figure. It consists of a
weight hanging from a vertical spring that the human controller can raise or lower by tugging on the spring’s handle. If the controller’s goal is to position the weight at a specified height above the floor, it would be a simple matter to slowly raise the
handle until the height measurement matches the desired setpoint. Doing so would certainly achieve the desired objective, but if this were an industrial positioning system, the inordinate amount of time required to move the weight slowly to its final height would degrade the performance of any process that depends on the weight’s position. The longer the weight remains above or below the setpoint, the poorer the performance. Moving the weight faster would address the time-out-of-position problem, but moving it too quickly could make matters worse. The weight’s inertia might cause it to move past the setpoint even after the controller has observed the impending overshoot and begun pushing in the opposite direction. And if the controller’s attempt to reverse course is also too aggressive, the weight will overshoot the other way. Fortunately, each successive overshoot will typically be smaller than the last so that the weight will eventually reach the desired height after bouncing around a bit. But as anyone who has ever played with such a toy knows, the faster the controller moves the handle, the longer those oscillations will be sustained. And at one particular speed corresponding to the resonant frequency of the weight-and-spring process, each successive overshoot will have the same magnitude as its predecessor and the oscillations will continue until the controller gives up. But if the controller were to become even more aggressive, those oscillations would grow in magnitude until the spring reaches its maximum distention or breaks. Such an unstable control loop might be amusing for a child playing with a toy spring, but it would be disastrous for a commercial positioning system or any other application of closed-loop feedback. One solution to this problem would be to limit the controller’s aggressiveness by equipping it with a speed-sensitive damper such as a dashpot or a shock absorber as shown in the second figure. Such a device would resist the controller’s movements more and more as the controller tries to move faster and faster. The
derivative term in a PID controller serves the same function, though too much derivative damping can actually make matters worse. See “Understanding Derivative in PID Control,” Control Engineering, February 2010. See Tutorials Channel at www.controleng.com/tutorials. Vance VanDoren, Ph.D., P.E., is Control Engineering consulting editor, at controleng@msn.com. www.controleng.com

Safety systems today are growing bigger and more intricate. As they do, so, too, grows the importance of keeping costs down while working faster. Specifying a safety PLC upfront in planning makes it possible to save significant time and money when designing the wiring and planning functionality of a project. A systems integrator in Franklin, TN, and a Siemens Solutions Partner, Advanced Engineering and its technicians have designed and installed many systems with more than 100 safety I/O points. Using Ethernet allows them to do start/stop, speed references, and safety all over the same wire. In the estimation of Advanced Engineering, the day is coming when everything will have safety Ethernet. Simply plug up to a device to obtain control, diagnostics, and safety from it. In addition, zones can be set up, and the device reset. In smart devices, such as a drive, other functions are available as well. The integrator works extensively in the automotive industry and has installed safety systems with more than 200 I/O safety points. Typically, that number of I/O points requires a great deal of wiring. However, by distributing the I/O over Profinet using a Siemens Simatic S7-300F processer, wiring is reduced and operator safety enhanced significantly. In one case, an automaker was setting up zones for robots and stamping presses. The original specification to safeguard the zones called for many safety relays. However, the automaker was concerned with the cost for a relay based system. The suggestion was made for a design using safety PLCs and safe I/O up front that included the guarding zones between the presses. The design also determined which functions to shut down for each zone to make it safe for the operators to enter a zone. In this instance, the quote for using safety relays reached $100,000. Done with a safety PLC, the cost was reduced to about $60,000. In addition, the automaker has since modified the system, which would have been nearly impossible with relays and which would require costly downtime. With the safety PLC system, the automaker simply added new zones into the safety PLC logic, similar to programming a normal PLC. Ultimately, using a safety PLC is more productive than relays. For example, one company installed a safety relay system on a line of machines. It estimated that unplanned downtime caused a 20% drop in productivity. In fact, the company’s production charts revealed that as each machine was fitted with safety relays, productivity dropped 20% on average. On the other hand, safety PLCs are flexible, offer diagnostics, require few wires, and can accommodate distributed I/O points without the downtime. If safety is approached as an afterthought, if becomes very difficult to retrofit it into an existing machine. However, incorporating safety into the design at the beginning of the process has shown time and again to be cost effective. Whether an integrator or a plant, it is possible to start small. For example, Siemens offers a small PLC with distributed ET200S I/O; the heads of the I/O have safety capabilities. As the system grows, it can accommodate a central processor that can control these remote heads and allow zones to be set up. www.adveng.com www.sea.siemens.com - Jim Neufeldt is president, Advanced Engineering, Franklin, TN; Edited by Jeanine Katzel, Control Engineering consulting editor. www.controleng.com. Also read: Integrated Safety and Motion; Safety Sensors Rise to New Heights . 

Medium-voltage (MV) ac drives produce hundreds of times greater power output than their smaller, more numerous low-voltage (LV) cousins—enabling control of huge, multi-megawatt electric motors that power the largest of industrial loads found in mines, power stations, or metal processing plants. MV drives operate at higher supply voltages to obtain lower losses and use smaller cables that add up to better overall drive efficiency, hence lower system cost. MV drives offer more than just size and not all models are of gigantic size. Other factors also influence their choice for specific applications and users—for example, control architectures that incorporate harmonics mitigation. The definition of “medium voltage”  varies widely by industry. For motor drives, the range above 600 V to 15 kV represents some consensus; Europe regards 1 kV as the MV threshold. However, few actual drive products exist below 2.3 kV. Common MV drive inputs are 2.3 and 4.16 kV in the Americas, while Europe and the rest of the world prefer 3.3 and 6.6 kV. (See link at end of article.) Power, voltage, current: P = VI
A major advantage of MV over LV drives is lower current flow for a given power output, as seen from the basic electrical engineering relationship: power equals voltage x current (P=VI). To illustrate, Tim Russell, senior system engineer at TM GE Automation Systems (TMEIC GE), compares two units rated at 1,000 hp (746 kW): the MV drive operating from 4,160 V supply carries only 125 amps or so, while the LV drive running on 460 V must carry 1,130 amps! “MV cable construction is a bit more expensive, due to insulation requirements, but copper content is much lower due to lower amperage,” Russell says. This translates into much smaller cables and lower voltage drops. Overall cable cost favors MV technology. (TMEIC GE designs and develops advanced automation, large ac machines, and variable-frequency drives based on the combined heritage of Toshiba, Mitsubishi Electric, and General Electric.) More costly power cabling needs of LV drives are well recognized at Rockwell Automation. Comparing 480 V and 4.16 kV drive systems at the same power load, Fred Jason—PowerFlex 7000 portfolio manager, Rockwell Automation Canada—arrives at the same approximate current requirements: LV drives draw about nine times the current compared to MV drives. It means larger and more LV cables per phase (see “drive-to-motor cabling” table), larger and heavier cable tray or conduit, and more costly cable installation, according to Jason. At ABB Inc., use of smaller gauge cable for the same output is likewise seen as an advantage for MV drives. “It’s first seen in reduced copper cost, but also in less labor cost to pull the cable, as well as in the number and size of conduit pipes,” says Paul Nolden, program manager, MV drives. “This becomes increasingly important in applications with long input and motor cable lengths, as in remote lift stations, deep wells, and mining.” Siemens Industry Inc. also notes the lower cost of physically smaller MV cabling and switchgear. “Still, this is a ‘hard sell’ to customers who seem to attach little credit to the cable benefit,” says Scott Conner, manager, large drives sales applications engineering. “Sometimes customers don’t want to pull the bigger LV cables, but it’s more an installation complexity issue for them rather than just cost savings.” Better economy above 500 hp
Although MV drives provide the only practical choice at some power demand level, a wide output range exists over which they can be a “better economic solution.” TMEIC GE puts this range between 500 to 1,500 hp, depending on the application and industry (see “relative cost” diagram). Other reasons to select MV drives given by TMEIC GE include applications where:

• Synch-to-line is required and the utility feeder is medium voltage;
• Utility capacity at low voltage is inadequate for the drive load (for example, due to large inrush currents for motor starting that MV drives avoid); and
• Long cable runs (>300 ft/92 m) exist from drive to motor—and cable size, cost, and voltage drop become substantial.

Siemens notes an overlap for medium- and low-voltage drives in the 300 to 2,000 hp range. In Europe, LV drives tend to range higher due to use of voltages like 690 V. Based on Siemens’ end users’ experience, selecting MV drives becomes an “easier decision” around 1,000 hp, where they start to be size competitive and use of an MV motor often becomes a necessity, Conner explains. “LV drives become cumbersome to implement at high power outputs, including the need to parallel power semiconductors. At some output point, MV switching devices provide operational and packaging advantage but not necessarily cost. However, for MV drives overall, cost per horsepower has come down in recent years,” adds Conner. Rockwell Automation’s Jason thinks an MV drive can be “extremely cost competitive” with an LV drive at higher power levels. To make the decision, a total installed cost analysis is necessary. “It’s important to evaluate operating costs over the project life cycle, including system efficiencies, input power factor, cable costs, air conditioning needs, and maintenance requirements,” says Jason. Cost of additional system components required for an LV system, such as input and/or output transformers, must be factored in. ABB also recommends that choice of MV or LV drive be based on total installation cost. Converter to converter, LV may have lower cost to power ratio (up to some point), but other required system add-ons can quickly overcome that advantage, explains Nolden. For example, a step-down transformer is always required for an LV drive, but not so for an MV drive (see transformerless design). Moreover, any harmonic filtering added to an LV drive leads to lower system efficiency and higher cost, he notes. “Besides efficiency, cost of material and installation labor is less for medium-voltage drives, mainly due to the smaller cable conductor size,” says Rick Hoadley—principal consulting applications engineer, MV drives—at ABB. Moreover, amperage rating of available semiconductors and high current density seen throughout the drive makes designing LV drives in the 1,000–3,000 hp range increasingly difficult, according to Hoadley. “There is a point where packaging of multiple power devices in parallel becomes too large and too costly,” he adds. Handling harmonics
Variable-frequency drives (VFDs), either low- or medium-voltage type, are prone to generate unwanted voltage/current harmonics. Because MV-VFDs operate closer to distribution voltages and represent large power sources, they’re more often compelled to include harmonics reduction in their designs. Hoadley suggests that perhaps 20% of LV drives specifically incorporate harmonic mitigation, while almost all MV drives employ it. Low harmonic distortion then becomes a further attraction. Traditional MV drive design depends on a multi-pulse transformer to limit harmonics. Hoadley notes that the input transformer works together with the drive’s multi-pulse rectifier section (18, 24, 36, or even higher pulses), which produces cancelling waveform patterns to minimize line-current harmonics. “Harmonic cancellation” is typically part of the basic design, according to TMEIC GE’s   Russell. It comes from common use of multi-winding, phase-shifted transformers that shape output waveforms and provide input isolation. “Harmonic cancellation then results from the configuration of the rectifier circuits and windings,” Russell says. Moreover, for high-performance applications with dynamic loads, MV drives include an active front end to provide harmonic control. While either of these techniques could be applied to low-voltage drives, they don’t require transformers for output wave configuration, and the additional cost is usually not warranted, he explains. Yet LV drives typically require additional harmonic filtering. “Adding harmonic cancelling filters and/or transformers to LV drives often has them approaching the cost of comparable MV drives,” Russell states. ‘Transformerless’ design
Transformers represent a major investment in large, heavy equipment. The premise of eliminating the input transformer in medium-voltage drives is clear: it enables dramatic cuts in unit size and weight, as well as cost reduction. “Transformerless” MV drive operation is not new, but real product practicality has come only with modern designs. These MV drives rely on an active front end (AFE) rectifier plus power electronics advances to obtain beneficial functions normally provided by the isolation transformer. Rockwell Automation, a strong advocate of transformerless MV drives, enthusiastically promotes that option in its PowerFlex 7000 product line—along with the traditional design. Navid Zargari, manager of R&D at Rockwell Automation Canada, cites weight and volume reductions of 67% and 59%, respectively, for transformerless versus traditional MV drives in otherwise comparable 950-kW systems. Rockwell’s transformerless design, trademarked “Direct-to-Drive” technology, combines an AFE rectifier—to minimize line-side harmonics via its switching pattern—and a special dc link inductor, which virtually eliminates common-mode voltage stresses harmful to motor winding insulation, explains Zargari, who had a major role in the company’s Direct-to-Drive development. Power-switching devices, in this case, symmetrical gate-commutated thyristors (SGCTs), also help to limit harmonics and reduce filtering requirements for voltage transients. “Output current and voltage waveforms are near sinusoidal, resulting in virtually no voltage stress on the motor winding, even if connected through long cables,” Zargari adds.

Transformerless MV drives are especially attractive to limited space applications. Of course, suitable supply (or utility) voltage must be available for implementation; otherwise a step-down transformer is still needed at the drive input. Actually, this kind of “correct MV bus” may already exist in some industrial facilities (see related article). Other manufacturers have not neglected the transformerless drive approach. ABB offers such an option (which it calls “direct-to-line”) in its ACS 2000 and ACS 6000 MV drives; and TMEIC GE’s TM-30 and TM-50/70 drives with active source converter can operate without a transformer given the “proper utility voltage.” Find further perspective on transformerless MV drives in a related article. As their cost to power ratio continues to improve over time, medium-voltage ac drives—of either traditional or transformerless design—can expect wider application by informed users with energy efficiency in mind. Frank J. Bartos, P.E., is Control Engineering consulting editor. Reach him at braunbart@sbcglobal.net. For more information, visit:
www.abb.us/drives www.geindustrial.com www.mitsubishielectric.com www.rockwellautomation.com www.siemens.com www.tmeicge.com www.toshiba.com ONLINE extras

• What’s medium voltage? It depends on application, industry
• Transformerless medium voltage drives perspective
• Inverter topologies: Voltage-source or current-source

Other MV drives information worth reading The following sources represent worthwhile reading and are recommended for more in-depth knowledge about medium-voltage ac drive technology:  1)    Bill Horvath, PE, “Medium Voltage Drives Overview, Evolution & Application,” TM GE Automation Systems (Nov. 2004)   2)    Rolf-Dieter Klug and Norbert Klaassen, “High Power Medium Voltage Drives—Innovations, Portfolio, Trends,” Siemens AG, Large Drives Division (2005)   3)    Joable Andrade Alves, Gilberto da Cunha and Paulo Torri, “Medium Voltage Industrial Variable Speed Drives,” WEG Automation, Brazil (2009)

In a typical automation project, maximum efficiency is key. However, undertaking a safety automation project presents additional challenges. First, legal requirements must be met. Second, care must be taken to ensure and validate that the application is truly safe. For example, is safety ensured if the equipment is misused or fails? Many people—including health and safety engineers, consultants, and safety equipment suppliers—are involved in performing a risk assessment and creating a safety plan. Fewer have a role in determining, commissioning, and implementing safety technology. In fact, often it is up to the integrator alone. During typical automation projects, PLC programmers must adapt the system to the real-world environment and makes changes “on the fly” to get the project up and running. They often use “OR” function blocks (parallel contacts in ladder logic) and active low sensors. Both are highly critical when doing safety programming. Consider, for example, a safety application where material has to get out of a machine, but neither a person nor any material is allowed in. This arrangement can be accomplished by “muting” a light curtain using additional sensors. Muting refers to an automatic, temporary suspension of the safety device. When the sensors detect a pallet, the safety light curtain is muted. This configuration can be done with a safety PLC. A safe and pre-certified muting function block ensures safe suspension of the light curtain (see the diagram). Assume that the muting sensor is a reflector switch where the output is “HIGH” when it sees a reflector and “LOW” when an object is in the light path. The muting function block needs to be “HIGH” on the sensor input to mute the light curtain. An inexperienced integrator might see no problem with this situation, saying, “Let’s negate the signal by using a ‘NOT’ function block.” Although such a solution works well and appears safe, what happens if the common power supply for the two sensors breaks down? Both sensors will switch off and it will appear to the safety PLC that they both see the object. As a result, the light curtain will be suspended. An unsafe situation can occur easily by adapting a safe concept (function block) to a real-world scenario. An integrator needs to know his/her determination methods will influence the application. In this case, use of active “HIGH” sensors in combination with additional control signals or time monitoring functions would be required. Integrating safety technology in a practical way requires extensive knowledge, application expertise, and many years of experience. Just as you would carefully select a qualified integrator for an automation project, make sure to do the same for the safety portion of the project by keeping them separate. This approach will ensure that safety is left to the experts. Experienced safety integrators will reduce the likelihood of safety risks during all phases of a project. Making use of simple and easy-to- use tools for design, simulation, and test also will help validate the safety functions throughout the life cycle of a machine or project. - Juergen Bukowski is safety program manager, Sick Inc., Minneapolis, MN. Edited by Jeanine Katzel, consulting editor, Control Engineering, www.controleng.com www.sickusa.com Also see the Control Engineering: Machine Safety blog Machine Control Channel System Integration Channel

Wago Corporation's updated 758 Series industrial PCs combine CoDeSys V2 software, Linux OS, IEC programming languages, and multiple onboard fieldbus protocols for real-time control applications. Characterizing this design as a PC and PLC hybrid, Wago says the 758 Series offers a robust, scalable solution and network connectivity. Models in the series include traditional PC interfaces like compact flash, USB, RS-232, and DVI ports. Independent Ethernet ports provide fieldbus connectivity, supporting Profibus and CANopen protocols. Wago adds that the PCs permit direct connection to the more than 400 specialty, analog, and digital modules in its Wago I/O System. CoDeSys V2 enables development of IEC 61131, C, or C++ user-defined function blocks, protecting intellectual property in secure, organized code. The company says that using Linux maximizes control and programming capabilities within a stable, open system. Four variants within the series provide up to 256 MB of RAM and up to 512 MB flash memory for large system programs and extensive data logging. CoDeSys visualization tools and the unit’s DVI port provides users with an effective local HMI solution. Wago says it designed the 758 Series' Web-based management system to enable simple system configuration and project commissioning. The 758 series industrial PCs offer passive cooling and non-rotating data storage media. The 758-875 variant operates in temperatures from -20 to 60 °C. All four models carry UL 508 and CE listings. Peter Welander, pwelander@cfemedia.com
Control Engineering Visit the Control Engineering Information Control Channel.

National Instruments (Nasdaq: NATI) today at its NIWeek conference and show announced new AKD Servo Drives and AKM Servo Motors, designed so engineers and scientists can more easily build scalable, distributed motion control systems. The new products simplify setup and configuration for deploying custom motion applications to any NI real-time controller supporting NI EtherCAT technology, including NI CompactRIO, PXI real-time controllers and NI industrial controllers, the company said. National Instruments also is releasing the NI LabVIEW 2010 NI SoftMotion Module that provides support for NI EtherCAT drives for simplified motion application development. The new AKM brushless servo motors are said to provide superior dynamic performance in four different frame sizes, with high torque, density and speed ranges. The motors use low-inertia rotors and feature low-cog, low-harmonic distortion magnetic design. The motors also are perfectly matched with NI servo drives and provide plug-and-play configuration with integrated Smart Feedback Device (SFD) technology and simplified cabling. The new AKD Servo Drives feature simplified setup and configuration through EtherCAT technology and integration with the LabVIEW project, a feature in LabVIEW software that engineers use to group LabVIEW and third-party files, create build specifications for executables, and deploy or download files to hardware targets. The new drives update torque loops in 0.67 μs, and velocity and position loops at 62.5 μs and 125 μs. Applications include basic torque-and-velocity applications to indexing to multi-axis programmable motion, using graphical system design. The LabVIEW NI SoftMotion Module delivers graphical development for custom motion control applications, to configure motion axis settings, test configuration, tune motors and quickly develop a custom motion application. The module features an updated interactive configuration and a high-level function block API for increased ease of use. It makes the execution of motion applications on a Windows-based system possible. In addition, the new module easily connects to the new drives and motors as well as third-party drives and motors using NI C Series drive interface hardware. Learn more at www.ni.com/motion. See also the NI Motion Control Bundle on www.ni.com to quickly and easily assemble a full motion control system. Also read: NIWeek: New Ethernet data acquisition platform NIWeek: NI LabVIEW 2010 optimizes compiler for faster code execution NIWeek 2010: Explore technologies, gain competitive advantages - Edited by Mark T. Hoske, Control Engineering, www.controleng.com.

As U.S. manufacturing roars back to life, resolving engineering challenges and maximizing return on investment were among goals of Siemens Automation Summit and the Siemens Answers for Industry Conference, in Charlotte, NC, June 8-10, 2010. Opening statements at the summit from Raj Batra, president, Industry Automation Division, Siemens Industry Inc., covered “Driving Technology and Innovation Together. The events, held regionally last year to help with travel budgets, moved again to a national format, “a sign that the U.S. Manufacturing recovery is taking hold. After the most severe downturn in more than 80 years, this is a welcome sign to all of us,” Batra said in an opening welcome. As of early June 2010, Batra said, U.S. manufacturing marked its tenth successive month of growth; productivity increased in first-quarter 2010 by more than 6%, consumer spending increased (2 million iPads sold in less than 60 days after launch), housing starts and existing home sales were up, and the U.S. economy grew 3% (in real gross domestic product, GDP) in first-quarter 2010, all proof of economic resiliency. A year ago, U.S. auto industry was on life support and one-third of manufacturing capacity was standing still. We’ve had a tremendous bull run, he said, pleased that recovery has arrived now, rather than years from now, as some had feared. Innovation matters, and the U.S. is the best source global source for innovation, Batra said. Citing statistics from a Plant Engineering magazine survey of 1,000 plant engineers, the “Changing world of the plant engineer,” there’s a war underway for high-technology talent. Top concern registered by the respondents was the state of the economy. The second largest concern was job security and globalization, including outsourcing to markets where the labor costs are lower. The third largest concern was finding employees with the right skills to replace workers expecting to retire in the next few years. These changes offer great opportunities, since innovation represents the greatest opportunity for anyone in manufacturing or industrial jobs today, Batra noted.  Industrial-strength opportunities Opportunities for manufacturing are many, including:

• A Siemens wind blade manufacturing plant in Fort Madison, Iowa, that created 600 clean energy jobs.
• Siemens technology is driving four of the five largest U.S. solar installations. Solar photovoltaics in the U.S. provides 340 MW of power, growing to 2,700 MW in five years. For polysilicon production globally, 34% is in the U.S.
• Adding smart grid functions will help manage power flow and reduce power outages, which cost the U.S. $150 billion a year. Grid R&D has lagged behind other industries’ modernization in the past 50 years. Industry, which consumes two-thirds of all energy, has a vital role to play in defining how the smart grid manages functions, interconnecting more than 9,200 electric generating units, 1 million megawatts of capacity over 300,000 miles of transmission lines.

Intense investments are required • $1.3 billion in venture capital invested between 2005-2009; • $11 billion in the American Reinvestment and Recovery Act; and • $1.5 trillion (forecast) over next 20 years according the Brattle Group. Investments will help energy sources become more reliable, efficient, secure, and sustainable, with more emphasis on two-way communication to the grid, plant-wide asset management, and effective data use. Efficiency, sustainability Energy efficiency efforts include support of the Profinet extension, called PROFIenergy, which helps monitor and control energy use by putting unused loads in sleep mode, Batra said. Because industrial equipment can consume up to 60% of the energy during idle periods as it does during production, a lower-power standby mode is desirable. The PROFIenergy extension triggers standby, power down and wake up from a central location. Working with Siemens, Mercedes Benz piloted PROFIenergy technology, reducing energy costs during non-productive periods (such as nights and weekends) by 75%.  Siemens sustainability efforts in place since 1971 have resulted in the largest portfolio of green products globally, worth $32 billion last year, Batra said, adding that the company has abated 210 million tons of C02 for customers, as a result. As a company, Batra said, Siemens aims to use its technologies to help reduce:

• Energy consumption by 20%;
• C02 emission by 20%;
• Water consumption by 20%; and
• Waste production by 15%.

Product life cycle management Effective product lifecycle management adds efficiency to the supply chain, and 75% of all manufacturing costs are pre-determined in the product design phase, Batra said. Adding to the company’s product lifecycle management (PLM), Siemens recently acquired Comos, a supplier of PLM systems for process industry plants. At the Comos user conference in Brazil in May, Petrobras representatives talked about integrating Comos into its process control system, Batra said, noting that two engineers in charge of commissioning said they completed a year’s worth of work in two weeks. Siemens is the only company offering PLM solutions for discrete and process industries, Batra added. Siemens User Advisory Board Integration: The Siemens User Advisory Board expressed preference in co-locating Siemens Automation Summit and the Siemens Answers for Industry Conference “to expand the available seminar content, showcase demos, and pool of attendees available for potential recruitment into the user community,” said Dennis Inverso, chairman, Siemens User Advisory Board, in a printed welcome statement. Inverso is principal consultant, DuPont Electrical & Instrument Control Systems Group. Those involved in the UAB include, along with Siemens staff, AE Solutions, Air Products, Cargill, Dow Chemical, DMC Inc., DuPont, and Sony DADC. The co-located event was said to include more than 90 seminars, feedback sessions and roadmap discussions along with a solutions showcase. Also see the Control Engineering sustainable engineering channel. Related links include: www.sea.siemens.com www.siemens.com/PLM www.siemens.com/smartgrid www.siemens.com/sustainability www.usa.siemens.com/solutionpartner www.sea.siemens.com/us/Products/Process-Automation/Pages/UserComm_Landingpage.aspx - Mark T. Hoske, Control Engineering content strategist, www.controleng.com, part of CFE Media, www.cfemedia.com.