Motion Control Resources
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Where Motion Control Meets Sustainability
by Ray Chalmers, Contributing Editor
Motion Control & Motor Association Posted 05/28/2019
Interest in green manufacturing (optimizing energy use, reducing carbon footprints, cutting greenhouse gas emissions, increasing sustainability) is growing. With new product designs and recent efficiency standards updates, motion control products such as motors, drives, gearboxes, and more are making demonstrable contributions.
The U.S. Energy Information Administration (EIA) conducts the Manufacturing Energy Consumption Survey (MECS) to collect detailed information on energy use, expenditures, and other data by U.S. manufacturing establishments. It estimates that manufacturing accounted for about 75% of total U.S. industrial sector energy consumption in 2016.
The EIA has conducted the MECS eight times since the initial MECS in 1985. The latest (2014) MECS sample size of approximately 15,000 establishments was drawn from a sample frame representing 97% to 98% of the national manufacturing payroll.
Every industry uses energy, but three industries account for most of the total U.S. industrial sector energy consumption. The EIA estimates that in 2017, the bulk chemical industry was the largest industrial consumer of energy, followed by the refining industry and mining. These three industries combined accounted for about 58% of total U.S. industrial sector energy consumption.
Where motors and motion control are concerned, the energy consumed is by and large electricity. The amount of electricity used by U.S. manufacturers has varied somewhat from the 1998 MECS to the 2014 MECS. However, electricity's share of annual energy use (excluding feedstocks) by manufacturers has been fairly consistent at about 17%. Most of the electricity consumed by manufacturers is purchased, but some manufacturers generate their own electricity onsite.
In fact, given the energy used compared to production output, the “energy intensity” of recent U.S. manufacturing has continued to decrease. According to the latest MECS, from 2010 to 2014, manufacturing fuel consumption grew by 4.7%. At the same time, real gross output increased by 9.6%—or more than twice that rate—resulting in a 4.4% decrease in energy intensity, from 3.016 thousand British thermal units (Btu) per dollar of output in 2010 to 2.882 thousand Btu in 2014.
|Manufacturing fuel consumption has fallen while output has risen, resulting in a falling “energy intensity.”|
This is not to say that energy conservation is unimportant or does not pay dividends. According to the Department of Energy’s Advanced Manufacturing Office, motor system optimization can typically achieve 10 to 20 percent in energy savings over conventional systems, and often as much as 50 percent. Such improvements can translate into huge potential savings in the U.S., where more than 20 million motor systems are currently in use in industrial locations.
In fact, energy bills attributable to motor-driven equipment total six times the equipment’s initial purchase price each year. The industry has proven that using a systems approach can improve not only motor system efficiency, but also plant productivity and reliability. Factors contributing to motor system efficiency include the efficiency of individual components, but also and more importantly, how these components are integrated into a complete system.
“If I’m running a plant, I’ve got a lot of things on my plate, but number one is reducing downtime. A robust power transmission plan is the top priority,” said John Malinowski who retired from Baldor (now ABB) and is in a position to know. For years he was senior manager of industry affairs for Baldor and was recently named a fellow of the IEEE (Institute of Electrical and Electronics Engineers) in recognition of his service on standards development.
“Conventional thinking was that electric bills were fixed costs, simply to be collected and processed. This is about as wrong as wrong can be,” added Malinowski.
He points out that using premium efficiency motors (for low voltage motors through 500 HP) in a multitude of industrial applications (conveyors, fans, equipment) is not just a good strategy to employ, it’s the law.
|A plant’s first priority is uptime, but unchecked energy bills can run six times the price of equipment per year.|
The U.S. Department of Energy (DOE) has been regulating energy efficiency for electric motors since 1997 when the Energy Policy Act went into effect. This required most 1- to 200-HP general-purpose motors to meet NEMA Energy Efficiency standards. Since then, DOE energy efficiency regulations have evolved, with the Energy Independence and Security Act (EISA) of 2007 upping efficiency requirements for 1- to 200-HP general-purpose motors to NEMA Premium Efficiency levels and adding the requirement for certain 201- to 500-HP motors to meet NEMA Energy Efficiency standards. In 2010, a motor coalition was formed in order to, “determine and document a plan to improve the efficiency of the greatest number of units, providing the greatest savings impact while reducing potential enforcement issues, and while maintaining full product utility for American industry.” As a result of this coalition’s work, the Amended Integral HP Rule was released in May of 2014 and was implemented in June of 2016 as the Integral HP Motor Final Rule. This Integral Horsepower Rule supersedes the EISA standard and specifies that nearly all motors covered must meet NEMA Table 12-12 at Premium Efficiency levels. More importantly, it closes the gaps and potential loopholes in the EISA standard and expands the scope of covered motors to those that meet the following criteria:
- Is a single-speed induction motor
- Is rated for continuous duty (MG 1) operation or for duty type S1 (IEC)
- Contains a squirrel-cage (MG 1) or cage (IEC) rotor
- Operates on polyphase alternating current (AC) 60-hertz sinusoidal line power
- Has 2-, 4-, 6-, or 8-pole configuration
- Is rated 600 volts or less
- Has a three- or four-digit NEMA frame size (or IEC metric equivalent), including those designs between two consecutive NEMA frame sizes (or IEC metric equivalent) or an enclosed 56 NEMA frame size (or IEC metric equivalent)
- Has no more than 500 horsepower, but greater than or equal to 1 horsepower (or kilowatt equivalent)
- Meets all the performance requirements of a NEMA design A, B or C electric motor or an IEC design N or H electric motor
Still, the Integral Horsepower Rule does not include all motors used in industrial applications. The most significant omissions from the rule, relevant to industrial motors and motion control include:
- Synchronous AC motors
- Permanent magnet AC motors
- Servo motors
But there’s a good reason these motors aren’t covered by the Integral Horsepower Rule. The DOE considers permanent magnet (PM) motors, switched reluctance (SR) motors, and synchronous reluctance (SynRM) motors to be “newly emerging” or “advanced” technologies that can achieve higher efficiency levels than premium efficiency. In fact, these motors may meet or exceed “super efficiency” standards. Specifically, NEMA recognizes that permanent magnet and switched-reluctance motors have both high-power density (torque-to-weight ratio) and high efficiency and it recommends that they be considered for many types of industrial applications, including:
- When the application requires speed control (i.e., when an adjustable speed drive is required for speed regulation)
- When driven equipment is in operation for over 2,000 hours per year
- When an old standard efficiency motor is driving a centrifugal load with throttled or damper flow control and can be replaced with a variable speed PM or SR motor and controller
- When operations involve frequent starts and stops (this is a good application due to the low inertia of PM and SR motors)
- When motors operate at partial load a good deal of the time
- When the PM or SR motor can be used in a direct drive configuration to displace a single or two-speed motor with gearbox (e.g., a cooling tower fan drive motor), a gear motor, or a belted power transmission system
- In vertical pump-mount applications where resonance frequencies must be avoided.
Now that the sale and use of premium efficiency motors are a matter of law, Malinowski affirms what’s important to note is the energy use of industrial systems. “Machines and systems are often sized for worst-case scenarios, but seldom run there,” he says. Again, a plant manager’s most important priority is uptime. Systems thinking requires looking at multiple components – motors, variable-speed drives, gearboxes – and see where upgrades make sense. A helical or helical-bevel gearbox, for example, may be an expensive upgrade but could operate with a smaller-size motor. Optimizing equipment does not always mean improving system efficiency, but can save impressive amounts of energy.
|EPA’s Energy Star has a tracking methodology and awards program for industrial plants.|
Large integrated manufacturing facilities often have energy management personnel with any number of projects underway, but guidance is available for plants of any size to set up and operate an energy savings program. The same Energy Star designation for household appliances from the US Environmental Protection Agency (EPA) is available to manufacturers through the EPA’s Energy Star Challenge for Industry. EPA’s Energy Star industrial program provides industry-specific energy benchmarking tools and other resources for 19 different types of manufacturing plants. This enables plants to compare energy performance to others in the same industry and establish meaningful energy performance benchmarks and goals. Only plants in the top 25 percent of energy performance nationwide can earn the Energy Star. Plants from the automotive, baking, cement, corn refining, food processing, glass manufacturing, pharmaceutical manufacturing, and petroleum refining sectors are among those that qualified in 2018.
Industry sites participate by committing to a goal of reducing energy intensity by 10 percent within five years or less. Seven steps are involved:
- Establish an energy intensity metric;
- Select an energy tracking method;
- Set a baseline and 10 percent improvement goal;
- Create a formal site file and plan for tracking data;
- Register for the EPA Energy Star Challenge;
- Track energy use and achieve the 10 percent reduction; and,
- Verify energy savings and apply for recognition.
Another way to obtain energy performance information is to work with your industrial distributor network. Often representing a wide range of plant technologies, distributors have a vested interest in the plant uptime priority and will employ dedicated energy service teams to assess compressed air, lighting, HVAC, and power quality in addition to mechanical systems and provide a complete report of performance efficiency and strategies for improvement.
Rexroth, the drives and controls company of Bosch Group, promotes what they call the 4E approach: Energy System Design, Efficient Components, Energy Recovery, and Energy on Demand.
- Energy System Design: In order to improve energy efficiency, it is critical that your system is viewed as a whole long before you start using it, Rexroth says. Mechatronic simulation optimally configures your machine or plant from the beginning. Existing concepts can also be improved with software solutions that help you analyze and reduce energy consumption and cycle time.
- Efficient Components: From highly-efficient servo motors, distributed drives and axial-piston variable pumps through to roller rail systems with low coefficients of friction, a diverse portfolio helps match energy-efficient components to system tasks.
- Energy Recovery: In one interesting example, highly efficient servo drive controllers enable braking energy, such as that in a machine tool’s headstock, to be recovered. Energy can be buffered, sent to other axes, or fed back into the mains.
- Energy on Demand: Situational pressure controls for all control principles, frequency converters for economic speed controls, variable-speed pump drives for reduced idle power, or on/off valves for energy switch-off during breaks are just some options for reducing energy costs.
Reduced electricity costs often provide efficient payback of a 4E program, according to the company. The company is not only a provider, it’s a user. Pilot projects in different Rexroth plants have shown that machine manufacturers and industrial operators can
achieve a much higher level of energy efficiency when the 4E approach is applied – without having to replace existing machinery.
Actual Position versus Commanded Position: Closing the Loop
Low-cost step motors (also called stepper motors) make them popular for automation applications such as indexing and positioning. Because traditional step motor systems run open loop, drive electronics constantly supply current to the motor windings, regardless of torque demand from the load. Configured to provide the motor’s rated current, the drive will do its best to power that rated current into the motor at all times, whether the motor needs it or not. Expending unnecessary energy during operation makes open-loop step motor systems inefficient. Excessive power consumption wastes money and step motors operate “hot” due to this excess of power.
Closing the loop makes a more efficient step motor system. By employing a common feedback device such as an encoder to monitor actual shaft position versus commanded position, closed-loop step motor systems automatically reduce current to the motor when torque is no longer demanded by the load. Only the amount of current needed to drive the load powers the motor. This saves energy, especially when the torque demand is low.
“This simple change to the stepper system is extremely powerful and greatly improves the efficiency of the step motor,” noted Eric Rice, director of marketing, Applied Motion Products, in a recent white paper. “A closed-loop stepper system will consume much less power than a traditional step motor system. Increasing motor efficiency while decreasing power consumption translates to lower energy bills and greener operations.”
|An integrated motor from Applied Motion Products combines the motor, encoder, drive and controller into a single package for closed-loop operation.|
In tests when turning a dynamometer at a fixed speed of 10 rev/sec (600 rpm) with a torque load of 50 oz-in, the open-loop system draws 0.73 amps and consumes on average 87.2 Watts of power. The closed-loop system draws 0.42 amps and consumes on average just 50.0 Watts of power. That’s more than a 40% reduction in power consumption with the closed-loop motor, which is doing the same amount of work as the open-loop motor.
In addition to increasing motor efficiency, a closed-loop stepper system operates more quietly. Step motors are known to make audible noise. This is due to the fact that open-loop step motors operate at full rated current regardless of load. Because the closed loop stepper system runs with less current, it operates more quietly, especially at speeds in the range of 0 to 20 revs/sec (0 to 1200 rpm).
“Closed-loop step motor systems may cost more initially, but reductions in energy consumption, heating, and audible noise, along with increases in torque and accuracy justify the switch from open-loop,” Rice adds. “The use of closed-loop step motor systems will reduce energy consumption and provide other long-term benefits in many applications.”
How much more energy-efficient can a sensor be when it powers itself? In a recent white paper, Posital and its parent company Fraba BV are undertaking extensive R&D efforts as to its acquisition of Wiegand Effect technology.
The “Wiegand effect” is a physical phenomenon discovered in the 1970s by John Wiegand, an American musician and inventor who became interested in the use of magnetic effects in audio equipment. Wiegand found that when a specially prepared piece of ferromagnetic alloy (“Wiegand wire”) is subject to a reversing external magnetic field, it will retain its magnetic polarity up to a certain point, then suddenly ‘flip’ to the opposite polarity. This change in magnetic polarity, which takes place over a few microseconds, can generate a pulse of current in a copper coil wrapped around the Wiegand wire.
Another main application for the Wiegand effect has been to provide power for rotation counters in water and gas meters and multi-turn rotary encoders used in industrial motion control applications. When the Wiegand effect is used for rotation counters, a short (15 mm) length of Wiegand wire is mounted on the sensor’s body, close to a rotating permanent magnet. As the magnetic field rotates, the magnetic polarity of the wire segment flips twice for each full turn (N-S to S-N, then S-N to N-S). These polarity changes generate current pulses in a fine copper wire wrapped around the Wiegand wire. The current pulse created with each polarity change (almost 200 nanojoules per pulse) is sufficient to energize a low-power counter circuit that records rotation count.
The special advantage of this arrangement is that the rotation counter is, in effect, self-powered. The instrument will maintain a reliable rotation count, even if motion occurs when external system power is unavailable. The counter system doesn’t need backup batteries, improving reliability and reducing maintenance requirements.
Add in the possibility of wireless data communications and we are approaching the idea of stand-alone sensors that won’t require wired connections for power or data communications. Such sensors would open the door to an enormous range of exciting applications.
With planning and keeping an eye out for motion control contributions, notably improved system energy savings contribute to both environmental sustainability and improved fiscal performance. Sustainability is good business.