Motors - Motion Control Tips

New high-speed, compact brushless motors from Portescap

March 19, 2019 By Miles Budimir Leave a Comment

Portescap has expanded its Ultra ECTM range of brushless dc slotless motors with the introduction of the new 35ECS motor. This 2-pole motor offers ultra high speed and power (up to 330 W, max continuous) without compromising on the smooth operation and long life offered by Portescap’s brushless slotless motors.

The new 35ECS motor is available in two lengths: the 35ECS60 and the 35ECS80. The 35ECS60 and 35ECS80 motors feature Portescap’s patented Ultra EC coil technology which provides unparalleled torque and power density with limited core losses over a wide range of working speeds without friction and brush wear. These motors feature a patented high-speed rotor design as well to sustain speeds up to 40,000 rpm. The 35ECS80 is unique and opens new areas for slim/long package with impressive torque capabilities at high speeds, while the 35ECS60 allows high speed capabilities at low voltages. Thanks to its rugged design, the 35ECS can sustain peak torque during 2 sec up to 1.1 Nm (35ECS60) and 2.0 Nm (35ECS80).

The 35ECS motors can be used in a range of applications, including industrial applications, enhancing the life and reliability of a device without compromising on power and machine throughput and saving energy. The new 35ECSs are an ideal choice for applications such as battery-operated hand tools (industrial tightening devices or drills), factory automation equipment (large fans or vacuum pumps), and also for applications with diameter constraints.

The new 35ECS motors feature a laser-welded front flange to ensure the strongest housing to sustain high torque reaction. A temperature probe on the coil head ensures an optimized control of motor performances in heavy duty applications. These motors are offered with hall sensors and a total of six different coils to match speed and voltage requirements. Upon request, Portescap can also provide options for customization including gearboxes, encoders, coil variations and mechanical interface modifications.

For more information, visit www.portescap.com.

What is Space Vector Pulse Width Modulation (SVPWM)?

March 14, 2019 By Danielle Collins Leave a Comment

One common, modern method for controlling three-phase induction motors and permanent magnet synchronous motors (aka BLAC or PMAC motors) is field oriented control, which independently controls the magnetizing and torque-producing components of the stator current. This allows the torque-producing component to be kept orthogonal to the rotor flux, maximizing torque production.

Space vector pulse width modulation (SVPWM) is a technique used in the final step of field oriented control (FOC) to determine the pulse-width modulated signals for the inverter switches in order to generate the desired 3-phase voltages to the motor.

Field oriented control with space vector pulse width modulation.
Image credit: Texas Instruments

The following is a summary of how FOC with SVPWM operates:

1) Measure two of the three motor phase currents and feed them into a Clarke transform to convert them from a three-phase system (i_a, i_b, i_c) to a two-dimensional orthogonal system (i_α, i_β). Note that it’s not necessary to measure all three currents, since the sum of the three must equal unity (0). So the third current must be the negative sum of the first two.

2) Apply a Park transform to convert the two-axis stationary system (i_α, i_β) to a two-axis rotating system (i_q, i_d), where the d axis current is aligned to the rotor flux and the d axis current (the torque-producing component) is orthogonal to the rotor flux.

3) The stator current flux and torque are controlled independently, typically by PI controllers. Voltages to be applied to the motor, V_dand V_q, are determined from the PI controllers.

4) Next, an inverse Park transform converts the two-axis rotating system (V_sqref, V_sdref) back to a two-axis stationary system (V_s_αref, V_s_βref). These are the components of the stator voltage vector and are the inputs for the SVPWM, which generates the 3-phase output voltage to the motor. (Note that the use of SVPWM eliminates the need for an inverse Clarke transform to obtain the three-phase output voltages.)

Field oriented control transforms a three-phase system time-dependent system into a two-coordinate (d and q), time-invariant system. SVPWM is used in the final step to determine the PWM signals to be applied to the motor.
Image credit: Freescale Semiconductor

The details behind SVPWM

Voltage is delivered to the motor by a three-phase inverter with six transistors (two on each leg of the output). Each of the three outputs can be in one of two states (top transistor closed and bottom transistor open, or vice-versa), giving eight (2³) total states for the output. These are referred to as base vectors.

For each leg of the inverter output, either the top transistor will be open and the bottom closed, or vice-versa. Therefore, there are eight total states (2³) for the inverter output.
Image credit: switchcraft.org

The eight base vectors are plotted on a hexagonal star diagram. Each vector makes up a spoke of the star, with 60 degrees phase difference between adjacent vectors. The two vectors (V₀ and V₇) that contain outputs which are either all plus or all minus are referred to as null vectors and are plotted at the center (origin) of the star.

Each base vector makes up one segment of a hexagonal star, with the null vectors (V₀ and V₇) plotted in the center.

The goal of SVPWM is to produce a “mean vector” during the PWM period (T_PWM) that is equal to the desired voltage vector (V_out).

The location of V_out is determined on the star diagram, and the base vectors that constrain that sector (V₁ and V₃, for example), along with one of the null vectors, are used to synthesize the desired voltage. This is done by applying V₁for a specified time (T₁), V₃for a specified time (T₃), and the null vector for the amount of time necessary (T₀) to provide a resultant vector equal to V_out.

The values of T1, T3, and T₀ can be determined with the following equations:

The simulation of V_out can then be expressed as:

Compared to standard field oriented control, using FOC with space vector pulse width modulation enables more efficient use of the DC supply voltage, provides lower harmonic distortion — which improves power factor — and reduces torque ripple.

New 200-W high-torque brushless servo motor from maxon

March 12, 2019 By Miles Budimir Leave a Comment

The new EC-i 52XL 200-W brushless servo motor from maxon features a flux collector rotor which provides outstanding torque performance compared to the existing EC-i 52 180-W high torque motor. Especially on the industrial automation front, when space is limited but high torque and dynamics are required, the maxon EC-i 52XL motor with its extended length (80 to 110 mm) is the ideal motor choice.

Its extra power can be even more significant at relatively low speed which makes it a powerful fit to a variety of industrial applications including material handling and transport systems.

Because of its optimized magnet ring, the brushless EC-i 52XL motor with an iron winding offers a high torque density and a low cogging torque. The multi-pole internal rotor is extremely dynamic. Its solid design, with a steel flange and steel housing, makes this motor a robust solution for industrial applications.

Other features include 24, 36 and 48 Vdc windings, 8 pole pairs, and optional gearheads, encoders and drive electronics.

For more information visit www.maxonmotorusa.com.

SureStep IP65 rated stepper motors from AutomationDirect

March 7, 2019 By Miles Budimir Leave a Comment

AutomationDirect has added motors designed for washdown environments to its stepper systems product line. SureStep IP65 rated high-torque stepping motors are completely protected from solids and dust ingress and from low pressure water jets from any direction, making them suitable for many washdown applications.

These fully sealed, single-shaft motors are available with industry-standard NEMA 17, 23, and 34 mounting flanges and provide holding torque from 61 to 1,288 oz-in. The motors use 2-phase technology with 200 full steps per revolution or 1.8 degrees per full step.

The square-frame or “high-torque” style of these stepping motors is the latest in bipolar motor technology, resulting in the best torque to volume ratio. Waterproof white epoxy coating on the motor laminations and special bearings and seals keep moisture out of the motor.

IP65 motors are available in single-shaft configurations and have a 1-ft. cable and locking connector. Extension cables with mating IP65 connector are available in 6, 10 and 20 ft lengths. The stepper motors are CE compliant and have a 1-year warranty.

To learn more, visit www.automationdirect.com/ip65-stepper-motors.

Torque motor from ETEL now with integrated cooling system

March 5, 2019 By Miles Budimir Leave a Comment

In order to simplify the implementation of liquid cooling with torque motors and ease the mounting into direct-drive machine applications, ETEL announces that their TMB+ torque motor can now be ordered with a closed cooling jacket pre-built around it.

For over a decade, ETEL has been producing high quality frameless torque motors that are used in thousands of machines around the world. Still, several industries have not fully embraced the use of torque motors, and with ETEL’s pre-integrated closed cooling jacket now available in North America through HEIDENHAIN CORPORATION, building a torque motor into a machine is easier than ever.

In the past, the cooling channels outside of a torque motor required that the user design a jacket around it and a number of factors would complicate this procedure such as locations of the liquid inputs and outputs, water tightness, rustproof/non-porous material, etc. Now that ETEL offers a closed cooling jacket for all 62 of its TMB+ torque motor sizes, the design process is simplified and makes direct drive easier than ever as this option allows greater flexibility with the location of the motor. Easier implementation also allows direct drive to expand to many more industries, giving more OEMs the ability to take advantage of its many features.

Each TMB+ motor that comes with a cooling jacket is the exact same model as if it were ordered without which means it offers the same performance as previously listed on its datasheets. It also allows for all varieties of windings, cables, sensors, and bridges along with two output options of an axial or radial output to accommodate any machine design.

For more information, visit www.etel.ch.

What is plugging for electric motors?

February 26, 2019 By Danielle Collins Leave a Comment

There are generally three types of electrical braking for motors: regenerative braking, dynamic braking, and plugging. Of the three methods, plugging provides the fastest stop, but it can be harsh on both the electrical and mechanical components. Because of this, it’s the least commonly used method of braking, but it is appropriate for some applications.

Plugging can be more harsh on electrical and mechanical components, but it provides a faster stop than dynamic braking methods.
Image credit: secs.oakland.edu

Plugging — sometimes referred to as “reverse current braking” — is possible on both DC motors and AC induction motors. For DC motors, plugging is achieved by reversing the polarity of the armature voltage. When this happens, the back EMF voltage no longer opposes the supply voltage. Instead, the back EMF and the supply voltage work in the same direction, opposing the motor’s rotation and causing it to come to a near-instant stop. The reverse current produced by the combined supply voltage and back EMF is extremely high, so resistance is placed in the circuit to limit the current.

DC motor circuits for regular motoring operation (left) and for plugging (right). Notice that for plugging operation, the armature voltage is reversed and resistance is added to the circuit.

For AC induction motors, the stator voltage is reversed by interchanging any two of the supply leads. The field then rotates in the opposite direction and the motor’s slip (the difference between the speed of the stator’s rotating magnetic field and the speed of the rotor) becomes greater than unity (s > 1). In other words, the rotor spins faster than the rotating magnetic field in the stator. Torque is developed in the opposite direction of the motor’s rotation, which produces a strong braking effect.

Slip, which is the difference between the speed of the stator’s rotating magnetic field and the speed of the rotor, is a fundamental property of AC induction motors. In normal motoring operation, the rotor spins at a slower rate than that of the stator’s rotating magnetic field.

When the motor speed reaches zero, if it is not disconnected from the supply, it will begin to reverse, or rotate in the opposite direction. In some applications, reversal of the motor’s direction is the goal. But when plugging is used to brake the motor, a zero-speed switch or plugging contactor is used to disconnect the motor from the supply when its speed reaches zero.

One of the potential problems with plugging as a braking method (especially when the braking time is short) is that it can be difficult to brake the motor at exactly zero speed. Another drawback to plugging is that it can induce high mechanical shock loads on the motor and connected equipment, due to the abrupt stop that it causes. Plugging is also a very inefficient method of stopping and, therefore, generates significant heat.

Despite these drawbacks, plugging is used in equipment such as elevators, cranes, presses, and mills, where a rapid stop of the motor (with or without reversal) is required.

Integrated servo motor offers design benefits for mobile robotic applications

February 19, 2019 By Miles Budimir Leave a Comment

Applied Motion Products’ new series of integrated servo motors combine a high torque density, low inertia servo motor with an on-board drive and controller to save on space, wiring, and cost over conventional servo systems with separate motor and drive components. The MDX Integrated Servo Motors provide greater design modularity and simplicity for a wide range of applications including automated guided vehicles and autonomous mobile robots in the accurate positioning of drive and lift axes.

The motors house control electronics at the back, near the feedback device. No other external electronics package is required to drive or control the motor. The back of the motor also contains connectors for power, communications, and I/O. The MDX on-board controllers use the same command interfaces as external motor controllers including CANopen, RS-485, Modbus, and Ethernet as well as discrete I/O interfaces like pulse and direction. Command signals from a robot or machine’s central processing unit can be wired directly to the integrated servo motor.

Eliminating the need to connect motor power and feedback cables to an external motor controller, MDX Integrated Servo Motors free space in a robot or machine to accommodate other critical components, such as material handling mechanisms, sensors, additional axes of motion, or operator-interface components. Robot designers can focus less on controller placement and wiring and more on non-motor system components for faster design iterations. MDX Integrated Motors benefit the robot designer in many areas by reducing the number of components in the system, eliminating cables or wire harnesses, freeing valuable space, simplifying the bill of materials, enabling faster design cycles, and saving money.

MDX Integrated Servo Motors also provide a better solution to brushed dc and ac induction motors in serving as the main drive motors for forward/reverse motion and the material handling axes for accurate lifting, clamping, and engagement of the payload during transfer to different locations. In addition to providing more accurate speed and positioning than ac induction motors, MDX Integrated Servo Motors do not have motors brushes that wear out.

Every MDX Integrated Servo Motor can run stored programs created with Q Programming that incorporates commands for various kinds of motion, I/O control, and machine sequencing, as well as math functions that let users create complex motion profiles and control algorithms. Two environmental ratings are available including IP65 and IP20. The most popular IP65 rated motor includes M12 connectors for all connection points. IP20 rated motors feature pluggable connectors that save cost in high volume, price-sensitive applications.

For more information visit www.applied-motion.com.

When do tubular linear motors outperform traditional iron core and ironless designs?

February 15, 2019 By Danielle Collins Leave a Comment

In a recent post, we looked at traditional iron core and ironless linear motors, both of which have a flat-type construction. But another type of linear motor, often referred to as a “tubular linear motor,” is also gaining traction in industrial applications. This is especially true in the packaging and medical industries, where tubular linear motors have proven an ideal replacement for pneumatics, with a similar form factor but much better efficiency and reliability.

Like their flat counterparts, tubular linear motors have two main parts: permanent magnets and a stator that houses windings. But in the tubular linear motor design, the magnets are not laid out on a flat track; instead, disc-shaped magnets are embedded in a tube (often referred to as a thrust rod), and the stator (also referred to as a forcer) surrounds the thrust rod.

Tubular linear motors can be iron core or ironless types. They offer an alternative to pneumatic and ball screw actuators, with both high speed and high thrust force capabilities.
Image credit: LinMot USA, Inc.

The tubular design has several key benefits over flat linear motors. First, all the magnetic flux from the permanent magnets is harnessed to generate force. And, according to the Lorentz force principle, the force generated by the interaction of the thrust rod magnets and the stator coils is perpendicular to both the magnetic field and the current — in the direction of travel. These two attributes give tubular linear motors extremely high efficiency. This higher efficiency means less heat is generated, so there is less expansion and contraction of components due to thermal effects, and less heat is transferred to the external load. The end result of higher efficiency and less heat generation is better positioning accuracy.

Force production for tubular designs is a linear function of drive current, because the air gap between the stator and thrust rod is non-critical. This means that even if the air gap varies over the length of the stroke, the motor’s force production will remain the same.

Another benefit of tubular designs over flat linear motors is their compact footprint. And tubular linear motors can operate with either the stator (forcer) moving and thrust tube stationary, or with the thrust tube moving while the stator is held stationary. The ability to have the trust tube moving is one of the attributes that makes tubular linear motors a good replacement for pneumatic cylinders, which often operate with an extending and retracting rod, for pushing or pressing operations.

With a tubular linear motor, the thrust rod can move while the forcer is stationary, or the forcer can move while the thrust rod is held stationary.
Image credit: Parker Hannifin Corp.

Like their flat counterparts, tubular linear motors can use iron in the stator surrounding the coils, or they can be constructed with ironless stators. Ironless types produce less force, but don’t experience cogging, so they can achieve very smooth motion, even at low speeds.

Tubular designs with iron in the stator have an ease-of-use benefit over their flat, iron core counterparts because the cylindrical design effectively balances the attractive and repulsive forces between the stator and the thrust rod, so assembly is not as difficult for iron core tubular designs as it is for iron core flat designs. But, like their flat counterparts, tubular iron core linear motors do experience cogging.

New low-profile, direct-drive motor from Mitsubishi Electric

February 5, 2019 By Miles Budimir Leave a Comment

The new TM-RG2M/TM-RU2M low-profile direct- drive motors from Mitsubishi Electric Automation, Inc. are designed to let machine designers have direct control of a load without traditional transmission components.

Built with speed and precision in mind, they provide a smaller footprint and allow for more compact, efficient, and precise machines than those typically built using rotary servo motors. Applications that are well suited for the new motor include coating and vapor deposition systems, index tables, tool changers, rotary material handling robots, and rotary axis on XYθ inspection positioning systems.

Unlike rotary servo motors that are coupled to a load with a mechanical transmission such as a gear, coupling, or belt, the TM-RG2M/TM- RU2M low-profile direct-drive motor is coupled directly to a load, resulting in greater positioning accuracy, reduced energy use and less maintenance. It is ideal for use in industries such as semiconductor / LCD manufacturing, machine tool, material handling and inspection.

The new direct-drive motor allows users to reduce installation space, while combining direct control with the accuracy of a servo motor. It also allows for flexibility when sizing by allowing for compatibility with larger- capacity servo amplifiers such as Mitsubishi Electric’s MR-J4-40B (-RJ) with the TM-RG2M/TM-RU2M 004E30 to further increase torque. It features two installation methods – flange type with pilot and table type with positioning pinholes.

“The TM-RG2M / TM-RU2M Low-Profile Direct Drive Motor reduces the complexity of traditional mechanical power transmission systems which increases the machine efficiency and reduces downtime/maintenance by eliminating mechanical components,” said Dan Zachacki, Senior Product Marketing Engineer at Mitsubishi Electric Automation, Inc. “It provides customers with the all advantages of a servo motor in a compact package that is capable of supporting and driving a load directly.”

For more information, visit https://us.mitsubishielectric.com/fa/en.

Get your motor running… efficiently

January 29, 2019 By Miles Budimir Leave a Comment

A few tips for design and selection of induction and permanent magnet ac electric motor systems will make them more energy efficient.

Gabriel Venzin
ABM Drives Inc., ABM Greiffenberger U.S. Subsidiary

Efficiency in motor designs is a more relevant concern than ever. With electric motors providing over 60% of all industrial power, efficiency is a key design parameter. Here we’ll look at some general requirements as well as more specific ones for permanent magnet ac (PMAC) motors, which hold for common industrial applications in a limited power range.

To start, efficiency is defined as the ratio of delivered mechanical power to the supplied electrical power. An electrical motor that is 85-percent efficient converts 85 percent of electrical energy into mechanical energy. The remaining 15 percent dissipates as heat.

Exploded view rendering of an ac induction motor illustrating the housing, bearings and fan components.

Energy efficient electric motors use high-quality materials and optimized designs to achieve higher efficiencies. For example, more aluminum in the rotor and better slot-filling factor in the stator reduce resistance losses. Optimized rotor configuration and rotor-to-stator air gap reduce stray-load losses. Improved cooling fan design provides motor cooling with a minimum of windage loss. Higher quality and thinner steel laminations in the rotor and stator cores allow operation with substantially lower magnetization losses. Finally, reduced friction losses result from higher-quality bearings.

Selection points for both induction and PMAC motors

Optimizing the dimensions of rotor/stator laminations and the quality of steel used is key to improving performance
Hysteresis and eddy current losses together are called core losses. Around 20 percent of total losses are caused by eddy currents and magnetic core saturation.

Eddy currents induced in laminations moving relative to a changing magnetic field cause significant power losses. Laminated stator cores reduce eddy current losses and are based on the quality, resistivity, density, thickness, frequency and flux density of the iron. Eddy current losses can be minimized with a higher number of laminations.

Hysteresis losses are caused in the magnetic circuits when the flux is continually changing. The majority of flux-carrying material used in electric motors is steel used for stator and rotor cores.

Minimize the flux density and core losses by reducing the thickness of laminations. Hysteresis losses are reduced by annealing better grades of steel for laminations to change the grain structure for easy magnetization.

Reduce eddy current losses by increasing the resistivity of the steel with silicon, but silicon content increases die wear during stamping because it increases steel hardness. Steel crystals damaged during stamping severely degrade the magnetic quality of the affected volume.

Annealing flattens the laminations and recrystallizes the crystals damaged during stamping, which extends one sheet thickness into the lamination.

The special design of ABM’s Sinochron motor rotor with internal magnets leads to an almost ideal sine distribution of the magnetic flux. It’s designed for sensor-less control mode, making it an alternative to servo drives.

Use bath impregnation process for lamination, versus drip for optimum thermal management
Impregnating stators strengthens stator winding electrical insulation, protects against chemicals or harsh environments, and enhances thermal dissipation. Thermoset plastics including epoxies, phenolics, and polyesters are used for impregnating stators. ABM uses the bathing method whereby stators are immersed in resin for an extended period of time to assure optimum penetration and protection. Another impregnation method is called vacuum-pressure, which uses a tank that is evacuated first and then pressurized to achieve penetration into the stators. Driving out air pockets from the electric winding enhances the thermal conductivity of the winding.

Design slots in the stator to maximize the volume of copper that can be inserted
Low stator winding mass causes up to 60 percent of total losses, so to reduce them the mass of stator winding must be larger which reduces electrical resistance. Electric motors that are highly efficient contain more than 20-percent extra copper compared to standard efficiency electric motors. The stator’s insulated electrical windings are placed inside the slots of the steel laminations. The cross-sectional area must be large enough for the power rating of the motor.

In general, open or semi-closed stator slots are employed in induction motors. In semi-closed slots the slot opening is much smaller than the width of the slot, and winding is more difficult and time consuming to manufacture compared to open slots. However, the air gap characteristics are better compared to the open type.

The number of stator slots must be selected at the design stage because this number affects the weight, cost, and operating characteristics. The advantages of more slots are reduced leakage reactance, reduced tooth pulsation losses, and higher overload capacity. The disadvantages of more stator slots are increased cost, increased weight, increased magnetizing current, increased iron losses, poorer cooling, increased temperature rise, and reduction in efficiency.

SINOCHRON PMAC motor efficiency is more than twice compared to standard asynchronous motors under partial-load. It’s made possible by a continuously excited synchronous motor, which operates with practically no rotor losses.

Use high grade/pure aluminum in the rotor die casting
Custom designed rotors can maximize starting torque, reduce conductor resistance and increase efficiency. Most induction motor rotors are squirrel-cage designs. They are rugged, simple in construction and less expensive, but they have a low starting torque. Copper rotors increase efficiency but are difficult and expensive to manufacture.

Tightening manufacturing tolerances allows optimum air gap between rotor and stator
The air gap is the radial distance between the rotor and stator in an electric motor for standard radial motors. An optimum air gap needs to be maintained for design efficiency. Air gap dimension involves the design of stator, rotor, motor housing, and bearings. All these affect the exact alignment of the stator and rotor axes.

Use copper windings that meet DIN EN 13601 and UL Norm standards
The European standard DIN EN 13601 specifies copper and copper alloys for general electrical purposes including dimensions and tolerances, tensile test, hardness test, bend test, electrical resistivity test. It also specifies characteristics of coppers for electrical purposes including the preference for oxygen-free or deoxidized coppers which may be heat-treated, welded or brazed without the need for special precautions to avoid hydrogen embrittlement which causes cracking.

For global compliance, UL determines that magnet wire complies with IEC 60317. Magnet or enameled wire is an electrolytically refined copper or aluminum wire that has been fully annealed and coated with one or more layers of insulation. ABM, for example, uses wires with a total of 12 insulation coats. Typical insulating films in order of increasing temperature range are polyvinyl, polyurethane, polyester, and polyimide up to 250 °C. Thicker rectangle or square magnet wire is wrapped with a high-temperature polyimide or fiberglass tape.

Use of more copper, larger conductor bars and conductors increases the cross-sectional area of stator and rotor windings. This lowers resistance of the windings and reduces losses due to current flow. A high-efficiency electric motor will usually have 20 percent more copper in the stator winding.

General selection guidelines
The motor selection process involves some basic considerations. For starters, verify the application requirements. Then, what torque and speed is needed when and how often? What is the duty cycle? What are the ambient conditions such as temperature and pressure? Even the most efficient motor will not perform to its utmost efficiency if used for the wrong application.

Many of the electric motors discussed here are used for gearmotors, a combination of a gear reducer and an electrical motor. A gearmotor delivers high torque at low speed. In short, gearmotors take motor power and reduce its speed while magnifying its torque.

Gearmotor duty cycles do not only impact the motor performance rating, e.g., a continuous duty cycle
S1 motor will provide a higher output if it’s used at an S3 intermittent duty cycle, but also especially for gearboxes used in extraordinary applications where torque peaks and system shocks are possible. For such situations, it’s critical to carefully determine what duty cycle and what peaks/shocks per a specific time period are experienced so the engineering team of the motor/gearbox OEM can select and recommend a suitable drive system.

A good start is to review data on past extreme temperature and or pressure conditions in which the application will be operating and any other unique conditions that may be relevant to the design. Always inform the motor OEM if your application is being used in extreme conditions – this can be a game changer.

Design housing for best cooling
The electrical efficiency of motors has improved so much that the power drawn by cooling fans has become a larger percentage of the total losses. Optimization of cooling fan dimensions involves using the minimum power for the fan, while providing adequate cooling. The optimal fan design may result in a 65 percent reduction in fan power requirements. An important design feature is the clearance between the blade and the housing. The space between the housing and the fan blade should be as small as possible to prevent turbulence and decrease backflow.

A cool motor runs more efficiently. To obtain the best airflow, optimize the cooling fan and fan shroud design. Assuring a tight bond between the stator and motor housing provides the best cooling performance.

Select low-friction bearings suited for operating speeds
Ball or roller bearings are used in high-efficiency electrical motors. They consist of an inner and outer race and cage containing steel or ceramic rollers or balls. The outer race is attached to the stator and the inner race to the rotor. When the shaft rotates, the element also rotates and the friction of the shaft rotation is minimized. They have a long life and maintenance costs are low. High precision application allows the smallest air gap possible. Thermal contraction and expansion can affect shaft and housing fits as well as internal bearing clearances.

Power output governs shaft size and bearing bore. Load magnitude and direction determines bearing size and type. Consider additional forces such as unsymmetrical air gaps causing magnetic pull, out-of- balance forces, pitch errors in gears, and thrust loads. For bearing-load calculations consider the shaft as a beam resting on rigid, moment-free supports. Ball bearings are more suitable for high-speed applications than roller bearings. High-speed factors include cage design, lubricant, running accuracy, clearance, resonance frequency, and balancing.

Knowing the ambient temperature range and the normal operating temperature range will help determine the most effective lubrication method for the bearing: oil or grease. Normal operating temperatures for gearmotors considered here range from -25 to 40 °C. Synthetic grease has good performance properties over a wide range of temperatures. Grease allows simplified maintenance, cleanliness, fewer leaks, and contaminant protection.

Bearings need a minimum load, so rolling elements rotate and form a lubricant film rather than skidding, which raises operating temperatures and degrades lubricants. Allow a minimum load equal to about 0.01 times the dynamic radial-load rating for ball bearings. It’s especially important when bearings are approaching 70 percent of recommended ratings.

Use a quality balancing machine, high standards and balance at the operational speeds of the motor application
Noise and vibration can result when the center of mass does not co-exist with the axis of rotation. Balancing has limited effect on efficiency but impacts operating noise and life expectancy that is also important for maximum use of resources.

Bearing vibration readings are normally taken on three planes – vertical, horizontal and axial. Vertical vibration may indicate a mounting problem. Horizontal vibration may mean a balance problem, whereas axial vibration may indicate a bearing problem. Balancing at operational speeds is important because unbalance can also be caused by centripetal forces at the bearings.

Additional design criteria for PMAC motors

PMAC motors are a growing alternative to ac induction motors, which for decades have been the workhorse of almost any electrical motor application. PMAC motors preserve the reliability and simplicity of the ac induction motor while offering higher efficiency, synchronous operation, and the opportunity to use a smaller frame size.

PMAC motors replace the magnetic field induced in the conductors in the rotor with permanent magnets, usually made from alloys of rare-earth metals, giving them much lower electric resistive losses than ac induction motors because no electric current is induced in the rotor. In place of mechanical commutation, a control system is required to determine which coils are supplied with current to produce the maximum torque. Magnetic fields generated by rare-earth PMAC motors can deliver the same torque as ac induction motors with a smaller, lighter motor.

This illustration shows the special design of the SINOCHRON PMAC motor rotor laminations and the imbedded magnets that allow a sinusoidal motor motion.

Select PMAC motor size to allow operation in partial load area for best efficiency
Energy savings from PMAC motors depend on the number of service hours, motor size, and motor loading. PMAC motors nearly always maintain higher efficiency – no matter the speed or torque compared to ac induction motors and makes them an attractive alternative to induction motors in variable-speed applications. By substituting existing line-powered three-phase electric motors with PMAC motors, energy savings of 20 to 35 percent can be expected.

Optimize design of rotor laminations to show a sinusoidal magnetic field
For example, ABM synchronous motors with high-performance permanent magnets come with a sinusoidal flux distribution as well as Electro- Motive-Force. Stator windings, for distributed windings, are normally identical to asynchronous motor windings. It results in lowered vibration, noise and maintenance cost as well as increased overall performance.

Selection of rare earth versus ferrite (ceramic) magnets
Neodymium rare earth, samarium cobalt magnets or ferrite (ceramic) magnets are used in PMAC electric motors. Rare earth magnets are two to three times stronger than ferrite or ceramic permanent magnets but are more expensive. Samarium cobalt magnets are optimal for high-temperature applications because of their high energy density, 250 to 550 °C temperature resistance, small decrease of parameters due to temperature increase, and oxidation protection.

The selection of samarium cobalt or neodymium as an electric motor magnet is
based on operating temperature, corrosion resistance and required performance. A low-grade neodymium magnet may begin to lose “strength” if heated above 80 °C. High-grade neodymium magnets operate at temperatures up to 220 °C.

Ferrite or ceramic magnets have won wide acceptance due to their strong resistance
to demagnetization, exceptional corrosion resistance, and low price. Magnetic losses occur when operating at temperatures above 250 °C, but are recovered when the magnet is brought down to a lower temperature. Cold temperatures of -40 °C may result in permanent losses of magnetic strength unless the circuit has been designed for such extremes.

PMAC motors require inverters
PMAC inverter drive units can be loss-free in no-load operation/standstill. New motor design combinations offer advantages in powering conveying equipment, escalators, spooling machines, compressors and traction drive units. By substituting existing line-powered three-phase drive units, energy savings of up to 30 percent can be expected.

The characteristic profile of PMAC drive units makes them well suited to drive pumps and fans that operate continuously. No additional components, like encoders, are needed. Up to 25 percent smaller footprint allows machine designs to be more compact. The motors have excellent control behavior and combined with a sensorless drive controller unit, have excellent true running even at low speeds and impressive dynamics at impulse load and speed variations.

Select an inverter that can provide sensorless operation
Standard PMAC drives can “self-detect” and track the rotor’s permanent magnet position. This is critical for a smooth motor start and also allows for optimum torque production, which results in optimum efficiency. Lack of position or speed sensor reduces the cost and increases reliability of a drive system.

Programming and optimization of inverter
The importance of programming the controller settings for a specific motor to attain optimum efficiency is becoming more and more important with the ever- increasing efficiency regulations.

Choosing manufacturing partners
When choosing partners during a machine build, remember that there are two methods for choosing an electric motor source. Either pick a standard motor that might or might not fit a specific application or choose a competent motor partner to engineer and manufacture a motor that fits the application exactly.

Standard motor solutions are suitable if a design engineer doesn’t have the time or engineering resources to have a custom version engineered — or if it needs a quick setup. New modular approaches to design and construction let manufacturing engineers get reasonably priced custom motors even in modest volumes.

No matter the approach to motor selection, be sure to continually improve the design/drive system by comparing predictions of performance with measurements. Then use the result of the analysis to improve the next iteration.

ABM Drives
www.abm-drives.com