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


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


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.

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Moving servo motors

Servo motor is an engine that controls the operation of mechanical components in the servo system.Servo motor can make the control speed, position accuracy is very accurate, can be converted to torque and speed voltage signals to drive the control object. Servo motor rotor speed by the control signal input, and can respond quickly, in automatic control system that is used for the implementation of components, and has small electromechanical time constant, high linearity, initiating voltage characteristics, the received signal is converted into the motor shaft angular velocity or displacement output. DC and AC yaskawa servo motor is divided into two major categories, the main feature is that when the signal voltage is zero without rotation, speed with the increase of torque and uniform decline.

Telling a servo motor to move to specific angle is easily accomplished using write(). The Arduino will do all the nessary caculation;determining the length of the pulse to generate and sending the pulse on time:


The angle parameter is an integer number,from 0 to 180, and represents the angle in degrees.

If you require precision, you can specify the length of the pulse by using the writeMicroseconds () function. This eliminates the need for calcuation by the Arduino and specifies the exact pulse length, an integer, expressed in microsenconds:

servo.write Microseconds (microseconds);

It does not matter what the original position waw, the servo motor ASD-B2-0421-B automatically adjusts its position. The Arduino does not need to calculate this either; all the intelligence is embedded inside the motor assembly. It does, however, keep the last angle that it was instructed to use, and this value can be feched with read();

int angle *

Remember that servo motors can receive only instructions and not return information. The value returened by read() is the value inside the Arduino. When connecting a servo motor, there is no way to know what position it was in initially. It can be helpful to set a servo motor to a default position before starting your application. (For exapmle, a remote-controlled car should probably have the wheels turn so that they are at 90 degrees; withoust adjusting the steering, the owner would expect the car to go straight and not at an angle.)

Servo motors and other physical objects take time to get to where you want them to be, so it’s considered good practice to give your motor a bit of time to get where it wants to go. Some motors move faster than others, if you’re unsure of how much time you’ll need, it’s best to check your motor’s documentation.

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The Brief Introduction of DC Servo Motor

What is the meaning of servo?

In modern usage the term servo or servo-mechanism is restricted to a feedback control system in which the controlled variable is mechanical position or time derivatives of position such as velocity and acceleration.

A servo is a device, electrical, mechanical or electro mechanical, that upon receipt of a stimulus or input, will employ feedback for velocity and/or position control, creating a closed loop.

A feedback system is a control system which tends to maintain a prescribed relationship between a controlled quantity and a reference quantity by comparing their functions and using the difference as a means of control

There are mainly two types of servo-motors

1)AC Servo motor
2)DC Servo-motor

AC servo-motors are generally preferred for low-power use. And for high-power use DC servo-motors are preferred because they operate more efficiently than comparable to AC servo motors.

Unlike large industrial motors, dc servomotors are not used for continuous energy conversion. The basic operating principle is same as other electromagnetic motors.


1.It has construction as same as dc motor. It is consist of stator and rotor and controlling parts.2.It has feedback generator for generating feedback for controlling the speed & torque.
3.It has two ports one for dc supply and other for controlled dc supply.
Field Controlled DC Servo Motor Theory:

The figure below illustrates the schematic diagram for a field controlled DC yaskawa servo driver. In this arrangement the field of DC motor is excited be the amplified error signal and armature winding is energized by a constant current source.

The field is controlled below the knee point of magnetizing saturation curve. At that portion of the curve the mmf linearly varies with excitation current. That means torque developed in the DC motor is directly proportional to the field current below the knee point of magnetizing saturation curve.

Armature Controlled DC Servo Motor Theory:

The figure below shows the schematic diagram for an armature controlled DC panasonic servo motor. Here the armature is energized by amplified error signal and field is excited by a constant current source.

The field is operated at well beyond the knee point of magnetizing saturation curve. In this portion of the curve, for huge change in magnetizing current, there is very small change in mmf in the motor field. This makes the servo motor is less sensitive to change in field current. Actually for armature controlled DC servo motor, we do not want that, the motor should response to any change ofPerformance Specifications:

DC servomotors share many performance specifications that are applicable to all types of?DC motors. To properly size a motor, these specifications must be matched according to the load requirements of the application.

Shaft speed (RPM) defines the speed at which the shaft rotates, expressed in rotations per minute (RPM). Typically, the speed provided by the manufacturer is the no-load speed of the output shaft, or the speed at which the motor’s output torque is zero.

Terminal voltage refers to the design voltage of the DC motor. Essentially the voltage determines the speed of a DC motor,and speed is controlled by raising or lowering the voltage supplied to the motor.

Torque is the rotational force generated by the motor shaft.The torque required for the motor is determined by the speed-torquecharacteristics of thevarious loads experienced in the targetapplication.

Starting torque – The torque required when starting the motor,which istypically higher than the continuous torque.
Continuous torque – The output torque capability of the motor under constant running conditions.

Some ratings of dc servo-motor available:

Shaft Speed:

Less than 1,610 rpm

1,610 to 3,187 rpm
3,187 to 4,700 rpm
4,700 to 7,090 rpm
7,090 rpm and up

Terminal Voltage:

Less than 20 VDC
20 to 50 VDC
50 to 100 VDC
100 to 180 VDC
180 VDC and up

Continuous Current: 

Less than 1 amps
1 to 4 amps 4 to 8 amps
8 to 17 amps
17 amps and up

Continuous Torque:

Less than 0.45 Nm
0.45 Nm to 1.70 Nm
1.70 Nm to 5 Nm
5 Nm to 17 Nm
17 Nm and up

Continuous Output Power:

Less than 0.4 HP
0.4 to 1 HP 1 to 2 HP
2 to 6 HP
6 HP and up


  • High output power relative to motor size and weight.Encoder determines accuracy and resolution.
  • High efficiency. It can approach 90% at light loads.High torque to inertia ratio.It can rapidly accelerate loads.
  • Has ”reserve” power. 2-3 times continuous power for short periods.
  • Has ”reserve” torque. 5-10 times rated torque for short periods.
  • Motor stays cool. Current draw proportional to load.
  • Usable high speed torque.
  • Maintains rated torque to 90% of NL RPM
  • Audibly quiet at high speeds.Resonance and vibration free operation.


  • Requires ”tuning” to stabilize feedback loop.Motor ”runs away” when something breaks. Safety circuits are required.
  • Complex. Requires encoder.Brush wear out limits life to 2,000 hrs. Service is then required.
  • Peak torque is limited to a 1% duty cycle.Motor can be damaged by sustained overload.
  • Bewildering choice of motors, encoders, and servo-drives.
  • Power supply current 10 times average to use peak torque.
  • Motor develops peak power at higher speeds. Gearing often required.
  • Poor motor cooling. Ventilated motors are easily contaminated.


DC servomotors finds its applications in various domain. Some of them are given below:

  • For very high voltage power systems, dc motors are preferred because they operate more efficiently than comparable ac servomotor.
  • It has also find its application in inkjet printers and RC helicopters.
  • To drive conveyors used in Industrial manufacturing and assembling units to pass an object from one assembly station to another.
  •  It is also used in solar tracking system.DC servomotors are widely used in robots, toy cars and other position controlled devices.
  • Widely used in radars, computers, robots, machine tools tracking system, process controllers etc.

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The Hybrid Servo Motor Technologies

In terms of their basic operation, the step motor and the brushless servo motor are identical. They each have a rotating magnet system and a wound stator. The only difference is that one has more poles than the other, typically two or three pole-pairs in the brushless servo and 50 in the stepper. You could use a brushless servo as a stepper – not a very good one, since the step angle would be large. But by the same token, you can also use a stepper as a brushless servo by fitting a feedback device to perform the commutation. Hence the“hybrid servo”, so called because it is based on a hybrid panasonic servo motor (Fig. 1.44). These have also been dubbed ‘stepping servos’and‘closed-loop steppers. We prefer not to use the term‘stepper’at all since such a servo exhibits none of the operating characteristics of a step motor.

The hybrid servo is driven in precisely exactly the same style because the brushless motor. A two-phase drive offers sine and cosine present waveforms in response to signals in the feedback device. This device might be an optical encoder or perhaps a resolver. Because the nema 23 stepper motors has 50 pole pairs, there will probably be 50 electrical cycles per revolution. This conveniently permits a 50-cycle resolver to become constructed in the exact same rotor and stator laminations because the motor itself.

A hybrid servo generates approximately the same torque output as the equivalent step motor, assuming the same drive current and supply voltage. However, the full torque capability of the motor can be utilized since the system is operating in a closed loop (with an open-loop step motor, it is always necessary to allow an adequate torque margin). The hybrid servo system will be more expensive than the equivalent step motor systems, but less costly than a brushless servo. As with the step motor, continuous operation at high speed is not recommended since the high pole count results in greater iron losses at high speeds. A hybrid servo also tends to run quieter and cooler than its step motor counterpart; since it is a true servo, power is only consumed when torque is required and normally no current will flow at standstill. Low- speed smoothness is vastly improved over the open-loop full step motor.

It is worth noting that the hybrid servo is entirely different from the open-loop step motor operated in‘closed loop’ or ‘position tracking’ mode. In position tracking mode, an encoder measures the load movement and final positioning is determined by encoder feedback. While this technique can provide high positioning accuracy and eliminates undetected position loss, it does not allow full torque utilization, improve smoothness or reduce motor heating.

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The Main Threen Types of Servo Motor

Servomotors are utilized in every thing from toys and drones to household products like DVD players. They are available in a number of configurations (probably the most typical kinds are listed beneath); understanding the variations will be the trick to figuring out that is correct for the project.

In easy terms, servos are standalone electric motors that push and rotate components in machines wherein a particular job and position have to be defined. When a Leadshine DM542 is offered a command, it moves to a position and holds there with resistive force. A servo utilizes either a rotary actuator or perhaps a linear actuator to manage angular or linear positions via acceleration and velocity. They usually operate in between four.5V¨C6V, which run via energy, ground, and manage wires.

servo motor and drive

AC Servo Motor

Two phase, reversible, induction motors with high resistance rotor winding. This provides a nearly linear speed-torque for accurate control.Similar stator winding configuration to a split phase AC, single phase, motor. The two stator winding are at right angles to each other.

AC motors can also incorporate gearing to increase torque output, reduce speed, and simplify motor design. There are a number of different gear assemblies that can be used:


Specific advantages that gearmotors offer to a servo application include:

Operation of the motor over its optimum speed range
Minimizing motor size by multiplying torque
Minimizing reflected inertia for maximum acceleration
Providing maximum torsional stiffness

Leadshine Servo Motor manufacturer has specialized in manufacturing ASD-B2-0221-B over 47 years experience. All of our industrial servo motor is exacting design of advanced technology, innovation, classic quality and featuring low vibration, low noise, smooth run and proper torque. Our industrial servo motors have been evidenced with major international certifications-as zero-defect products that fulfill the customers’ satisfaction and requirements. Which are mainly applied in the power unit of machine tool, precise and electrical machine. Leadshine’s AC servo motors feature is stable, compact, low noise, low vibration.

DC Servo Motor

Because of the low armature inductive reactance these motors provide very fast and accurate response to start/stop command signals.Normally used in Computerized Numerically Controlled machines and similar equipment.

Brushless DC Servo Motor

Named Brushless DC Servo Motor since they are comparable to a DC motor turned inside-out, they’re not DC at all. They’re supplied with three phase energy towards the startor making a rotating magnetic field just as is carried out for an AC induction motor.

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The Advantages and Disvantages of Servo Motors

Servo motors are somewhat more expensive than steppers — perhaps double the price, or more. They are generally just as accurate, if maintained in a proper state of tune, however they rely on encoders to provide positioning information back to the computer. Thus the complexity of the system is at least doubled, with no accuracy advantage, greater initial cost, and more maintenance issues. The ”closed loop” rhetoric that some manufacturers play up sounds convincing to the uninitiated, but provides no benefit over a simpler and more reliable stepper system.

Servo motors are available in larger sizes than stepper motors, and powerful ac servo motor are generally used on heavy machines with gantry carriages in the 500 to 1,000 lb range. They offer no advantage whatsoever on lighter machines, such as Torchmate and its competitors.

Servo motor design

A servo by definition is any device with feedback. Servo motors have coils on their stator which are energized in sequence by a brushless servo motor or amplifier, causing rotation (spinning) of the magnetic rotor. In order for the controller to determine what winding to energize next, it must know the current position of the rotor.This sensing is done using either hall sensors or a dual-function encoder.

Servo motor system components

The block diagram of a servo system is identical to the block diagram of a step motor system,although the technology of the components is different.The servo amplifier is the functional equivalent of the step motor drive. As with step motors, functions are often combined by manufacturers.

Advantages of Servo Motors

For applications where high speed and high torque is needed, servo motors shine. Stepper motors peak around speeds of 2,000 RPM, while servo motors are available many times faster. Servo motors also maintain their torque rating at high speed, up to 90% of the rated torque is available from a servo at high speed. Servo motors are also more effecient than stepper motors with efficiencies between 80-90%. A servo motor can supply roughly twice their rated torque for short periods, providing a well of capacity to draw from when needed. In addition, servo motors are quite, available in AC and DC drive, and do not vibrate or suffer from resonance issues.

Some of the advantages of servo motors over stepper motors are as follows:

High intermittent torque
High torque to inertia ratio
High speeds
Work well for velocity control
Available in all sizes

Servo motors are capable of delivering more power than stepper motors, but do require much more complex drive circuitry and positional feedback for accurate positioning. Servo motors are also much more expensive than stepper motors and are often harder to find. Servo motors often require gear boxes, especially for lower speed operation. The requirement for a gearbox and position encoder make servo motor designs more mechanically complex and increase the maintenance requirements for the system. To top it all off, servo motors are more expensive than stepper motors before adding on the cost of a position encoder.

Servos have inherent disadvantages:

• More complex system than step motors
• Motors must be tuned for optimal performance
• More costly system than step motors
• Less torque at lowest speeds compared to step motors
• Non-standard mounting geometries (vary by manufacturer) and shaft diameters
• Less torque than comparably sized step motors at low speeds


Selecting the best motor for your application depends on a few key design criteria for your system including cost, positional accuracy requirements, torque requirements, drive power availability, and acceleration requirements. Overall, servo motors are best for high speed, high torque applications while stepper motors are better suited for lower acceleration, high holding torque applications.

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