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Comparing induction motors, permanent-magnet motors, and servomotors

Designers and motor personnel advantage from discovering a supplier that’s an skilled resource of info to assist in pragmatic motor choice. Involve application specialists as early as you possibly can, as they are able to assist create prototypes, custom electrical and mechanical styles, mountings, and gearboxes. This also reduces expenses related with shorter lead occasions and rush delivery.

Servo motors can offer higher performance, faster speeds, and smaller sizes. PM synchronous motors offer advantages on high-energy- consuming and high-dynamic applications, compared to induction motors. Variable frequency drives used with asynchronous motors also can be used with synchronous delta servo motor, producing higher efficiencies than an asynchronous motor, using perhaps 30% less energy in positioning applications.Here recommend you delat servo motor.

Delta Electronics’ new high-performance, cost-effective ASDA-B2 series servo motors and drives meet the requirements for general-purpose machine tools and enhance the competitive advantage of servo systems.

The power rating of the ASDA-B2 series ranges from 0.1kW to 3kW. The superior features of this series emphasize built-in generic functions for general purpose applications and avoiding variable costs from mechatronics integration. Delta’s ASDA-B2 makes it convenient to complete assembly, wiring and operation setups. Switching from other brands is quick and easy due to the ASDA-B2′s outstanding quality and features, and complete product lineup. The ASDA-B2 satisfies the requirements of general-purpose machine tools. Customized solutions for different industries are available on request which is why the ASDA-B2 is popular and always in demand by customers in the field of industrial automation.

Induction motor systems (lower cost, rugged, reliable, and well known) can offer an alternative to mitsubishi servo motors systems (the traditional, established solution) for certain applications. This, of course, is based on similar electronic controls being used (with the latest technology and approximately the same cost), leaving the cost of motors the differentiating issue.

Overview of the pros and cons of each motor type

Induction motor

SPEEDLess speed range than PMAC motors • Speed range is a function of the drive being used — to 1,000:1 with an encoder, 120:1 under field-oriented control

EFFICIENCYEven NEMA-premium efficiency units exhibit degraded efficiencies at low load

RELIABILITYWaste heat is capable of degrading insulation essential to motor operation • Years of service common with proper operation

POWER DENSITYInduction produced by squirrel cage rotor inherently limits power density

ACCURACYFlux vector and field-oriented control allows for some of accuracy of servos

COST - Relatively modest initial cost; higher operating costs



PMAC

SPEEDVFD-driven PMAC motors can be used in nearly all induction-motor and some servo applications • Typical servomotor application speed — to 10,000 rpm — is out of PMAC motor range.

EFFICIENCY - More efficient than induction motors, so run more coolly under the same load conditions

RELIABILITY – Lower operating temperatures reduces wear and tear, maintenance • Extends bearing and insulation life • Robust construction for years of trouble-free operation in harsh environments

POWER DENSITY – Rare-earth permanent magnets produce more flux (and resultant torque) for their physical size than induction types

ACCURACY – Without feedback, can be difficult to locate and position to the pinpoint accuracy of servomotors

COST – Exhibit higher efficiency, so their energy use is smaller and full return on their initial purchase cost is realized more quickly

Servomotor

SPEED – Reaches 10,000 rpm • Brushless DC servomotors also operate at all speeds while maintaining rated load

EFFICIENCY – Designed to operate over wide range of voltages (as this is how their speed is varied) but efficiency drops with voltage

RELIABILITY – Physical motor issues minimal; demanding servo applications require careful sizing, or can threaten failure

POWER DENSITY – Capable of high peak torque for rapid acceleration

ACCURACY – Closed-loop servomotor operation utilizes feedback for speed accuracy to ±0.001% of base speed

COST – Price can be tenfold that of other systems

In the end, all industrial motor subtypes have strengths and weaknesses,plus application niches for which they’re most suitable. For example, many industrial applications are essentially constant torque, such as conveyors. Others, such as centrifugal blowers, require torque to vary as the square of the speed. In contrast, machine tools and center winders are constant horsepower, with torque decreasing as speed increases. Which motors are most suitable in these situations? As we will explore, the speed-torque relationship and efficiency requirements often determine the most appropriate motor.

What is a Servo Control System

A servo control system is one of the most important and widely used forms of control system. Any machine or piece of equipment that has rotating parts will contain one or more servo motor drive control systems. The job of the control system may include:

* Maintaining the speed of a motor within certain limits, even when the load on the output of the motor might vary. This is called regulation.
* Varying the speed of a motor and load according to an externally set programme of values. This is called set point (or reference) tracking.

Servo motors are brushed or brushless DC motors with feedback, typically encoder or resolver. They can be rotary or linear motors. They require a complex closed loop control algorithm (such as the classic PID method). Normally the control loop has to be tuned, and Delta servo motor dither can be a problem.. Due to the added control and feedback, typically servo systems are more expensive than stepper systems.

Servo motors typically have a peak torque of 3-10x the continuous torque, their torque curve is much flatter than the stepper curve, and the maximum speeds are much higher. Peak torque is a great thing; often, a system just needs extra power for a short time to accelerate, overcome friction, or such.

Our daily lives depend upon servo controllers. Anywhere that there is an electric motor there will be a servo control system to control it. Servo control is very important. The economy of the world depends upon servo control (there are other things to be sure – but stay with me on the control theme). Manufacturing industry would cease without servo systems because factory production lines could not be controlled, transportation would halt because electric traction units would fail, computers would cease because disk drives would not work properly and communications networks would fail because network servers use hard disk drives. Young people would become even more unbearable and they would complain more than they do now, because their music and games systems will not work without servo control.

Servo control systems are that important and it is vital to know about them. So pay attention and sit up straight – you are not on holiday and I am not writing this for the good of my health.

Basic Configurations of Gear Reducers

NMRV030Gear redcuers are categorized according to the orientation of the input and output shafts, right-angle or parallel-shaft reducers. These different arrangements use different typees of gearing. For mixer applications, both right-angle and parallel-shaft reducers have advantages and disadvantages. Right-angle reducers are typically shorter than parallel-shaft reducers, allowing them to fit better between floors and below roofs. Conversely, right-angle drives obstruct part of the top ot the tank, which can make piping connections difficult. Mounting and adjusting foot-mounted motors may be easier with right-angle drives than with parallel-shaft reducers.

Parallel-shaft gear reducers use one or more sets of parallel-shaft gears, such as helical gears, to make the necessary speed reduction. Some parallel-shaft reducers have the motor stacked above the worm gear motor to limit the overall diameter of the mixer drive system. Other parallel-shaft reducers have the motor mounted alongside the gear reducer to limit the overall height of th drive system. Generally, parallel-shaft reducers are easier than right-angle mixer drives to design and build. However, they do involve mounting and operating a verical electric motor, which can cause additional problems with large motors.

In-line reducers are usually a variation on parallel-shaft reducers. A properly designed double-reduction reducer with two sets of gearing having the same center distance can be arranged so that the input and output shafts are not only parallel, but in line with one another. Compared with parallel shaft reducers, in-line reducers usually trade greater height for smaller diameter and centered weight. Other types of gearing, such as plaetary planetary gear box, can make an in-line reducer. Whatever the basic configuration, well-designed gear reducers will provide good service in mixer applications.

Right-angle gear reducers must use at least one right-angle gear set, typically spiral bevel or worm gears. Both spiral-bevel and worm gears have unique advantages with respect to mixer applications. Spiral-bevel gears are some of the quietest and most efficient right-angle gears. Although less efficient than other gears, worm gears can make heat dissipation more difficult.

The Introduction of Planetary Gearbox

Planetary gears are very popular due to their advantages such as high power density, companctness, and multiple and large compact gear ratios and load sharing among planets. Gearing arrangement is comrised of four different elements that produce a wide range of speed ratios in compact layout. These elecments are, Sun gear, an extenally toothed ring gear co-axial with the gear train Annulus, an internally toothed ring gear coaxial with ghe gear train Planets, externally toothed gears with mesh with the sun and anulus, and Planet Carrier, a support structure for planets, co-axial with the train. Planetary gear reducer motor system as shown in Figure 1 is typically used to perform speed reduction due to serveral advantages over conventional parallel shaft gear systems.

Planetary gears are also used to advantages over conventional parallel shaft gear systems. Planetary gears are also used to obtain high power density, large reduction in small volume, pure torsional reactions and multiple shafting. Another advantage of the planetary gearbox arrangement is load distribution. If the number of planets in the system are more the ability of load shearing is greater and the higher the torque density. The planetary gear box arrangment also creats greater and the higher the torque density. The planetary gearbox arrangment also creates greater stability due to the even distribution of mass and increased rotational stiffiness.

In recent years, enhancement of interior quietness in passenger cars. Automobiles is an important factor for influencing occupant comfort. Planetary gear sets are essential components of automatic transmissions because of their compact size and wide gear ratio range. They produce high speed reductions in compact spaces, greater load sharing, higher torque to weight ratio, diminished bearing loads and reduced noise and vibration. A Despite their advantage, the noise induced by the vibration of planetary gear systems remains a key concern. Planetary gears have receive considerably less research attention than single mesh gear paris. This paper focus on the study o two PGTs with different phasing (angular positions) while keeping every individual set unchanged.

This figure shows that the basic layout planetary gear train in which there is one Sun gear. Three Planet gear and one ring gear. They can produce the high speed reduction in compact space and having greater load shearing capacity & high torque to weight ratio.

Planetary basics — ratios, helix angles, axial loads, crowning

A planetary gearhead takes a high-speed, low-torque input, say from an electric motor, then increases torque and reduces speed at the output by the gearhead ratio. This lets motors run at higher, more-efficient rpms in equipment that operates at low speeds. It also reduces inertia reflected back to the motor, increasing stability. And using a planetary gearhead often lets machine builders reduce the size and cost of motion-control hardware.

Planetary units with helical gears, rather than spur gears, have a larger contact ratio. The contact ratio is the number of teeth in mesh at any given moment. While typical spur gearing has a 1.5 contact ratio, helical gearing more than doubles it to 3.3. Benefits of higher contact ratios include:

• 30 to 50% more torque capacity than equivalent spur-type planetary gearing.
• Better load sharing, which increases life.
• Smoother and quieter operation.
• Backlash reduced by as much as 2 arc-min.

The gearhead’s helix angle also has a significant impact on performance because the greater the angle, the more teeth in the mesh at any one time. So increasing the helix angle from the typical 12° up to 15° raises torque capacity by 17 to 20%; and by as much as 40% over straight-cut spur gears. Gears with a 15° helix angle also emit less noise.

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DC Brush Motor

Choosing the right DC Motor (or DC gear motor) for a specific application can be a daunting task and many manufacturers only provide basic motor specifications. These basic specifications might not be sufficient for your needs. Listed below are ideal motor specifications and whenever possible, ways to approximate values.

A truly quiet DC worm gear motor is often needed in medical applications not only to reinforce the quality of the deployed medical devices but also to not be a contributing source to ambient noise where concentration and communication are vital. While that is a driving factor in the development of the new DCmind line of DC brush motors from Crouzet Motors, what is even more important is the significant increase in both lifetime and efficiency that accompany that engineering development.

Typical Specifications

For DC electric motors in Minnesota and around the country, there are common specifications needed to design a motor.

Nominal Voltage – For DC electric motors, it is important to know the nominal voltage of the drive motor. The designer also needs to know if a motor is to be operated outside of the nominal voltage range for any period of time.

Horsepower Rating – This is the rating of the nominal work that the worm gear reducer is expected to perform. The power rating can be expressed in horsepower or watts. This requirement can also be stated as a combination of torque and speed. We will also need to know if the motor will run at different load points, as either under loading or overloading the motor are detrimental to its service life.

Rated speed – The motor designer needs to know how fast the motor is required to run in the application. We also need to know if there are times when this speed would change, either by using a speed control to vary the voltage supplied to the motor or by increasing or decreasing the load on the motor.

Duty cycle – As a Permanent Magnet DC Motor runs, the current passing through the windings causes heat to be generated, raising the temperature of the motor as time passes. As the motor reaches its continuous running load point, the temperature should stabilizes within an hour or so. If the temperature does not stabilize, you need a higher horsepower rated motor.

Stall Torque – The maximum amount of torque provided by a motor with the shaft not rotating is known as stall torque. Keep in mind that if a motor is subjected to stall conditions for more than a few seconds, it likely will sustain irreparable damage.
Inrush Current – This is the current that a motor draws upon start up, whether or not it is under load. This current drops immediately as the motor’s speed increases, but in some cases any attached electronics can become seriously damaged by the extremely high current. Sometimes motor components can be damaged also. In those cases a current limiter would be recommended.

My conclusion is that DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets, and that induction drives will likely maintain dominance for the high-performance pure electrics. The question is what will happen as hybrids become more electrically intensive and as their performance levels increase? The fact that so much of the hardware is common for both drives could mean that we will see induction and DC brushless live and work side by side during the coming golden era of hybrid and electric vehicles.

The Type of Gear Reducers

Gear drives are also known as gear reducers or gearboxes. These are rugged mechanical devices desined to transmit high power at high operating efficiencies and have a long service life. The worm gear motor is an important component of the mixer drive systems, providing speed reduction and increasing allowable torque. Moreover, in some cases it provides support to the mixer shaft.

Helical gears are used in parallel shaft gear reducers. In helical gears, gear teeth are machined along a helical path with respect to the axis of rotation. Helical gears are commonly used with two-, three-, and in some cases even four-, five-, and six-stage speed reductions. In-line helical reducers are a variation of parallel shaft speed reducers configured such that the output and input shafts are in-line.

Spiral bevel gears are used when the input and output shafts of the gear reducers are required to be at right angles. The curve shape of the spiral bevel teeth makes gradual contacts, resulting in less noise during operation. Helical, parallel shaft, and helical bevel gear units have high operating efficiency, approximately 98% for each gear stage reduction.

Worm gears, are the most economical speed reducers, capable of providing a sizable speed reduction with a single gear set. The input and output shaft of these gears are at right angles to each other. However, becasue of the sliding contact between the worm pinion and the gear, the worm gear reducer is less efficient. The efficiency decreases as the speed redcution ratio increases. For example, at a speed reduction ratio of 10:1, the efficiency of the worm gearbox may be approximately 90%. However, at a redution ratio of about 50:1, the efficiency of the worm reducer drops to about 70%. Gearbox manufactures offer gear reducers in helical bevel and helical worm design.

Helical, spiral bevel, and worm gears are external gears with the teeth on the outer periphery of the gears. In planetary gears the teeth profile is on the inside of a circular ring with meshing pinion. Planetary gears consist of an internal gear with a small pinion, known as a sun gear, surrounded by multiple planetary gears. These gears can provide high speed reduction ratios and are relatively compact in size. Gear reducer manufacturers also offer geared-motor, that consists of a factory assembled motor with the gear unit. Figure 12.34 shows a variety of gear reducer with motor configurations.

NMRV worm gear series also available as compact and flexibility. NMRV worm gear series also available as compact integral helical/worm option, has been designed with a view to modularity: low number of basic models can be applied to a wide range of power ratings guaranteeing top performance and reduction ratios from 5 to 1000.


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