Servos versus induction motors: Look at performance, costs

Choosing between servos and induction motors depends on the level of performance required by the application and costs. Induction motors are simple, low-cost, and straightforward. Servos can offer higher performance, faster speeds, and smaller sizes.

09/12/2012


An advanced feature of the Beckhoff AM8000 servomotor is “one cable-technology.” With this technology, the power and process data are transmitted in one standard motor cable instead of two cables. It has a low rotor moment of inertia, very high overload cThe decision to use servos versus induction motors ultimately depends on the level of performance required by the application and costs. The principal strengths of induction motors are that they are simple, low-cost, and represent a very mature technology. Induction motors are also comparatively affordable, straightforward in terms of on/off control, simple to wire, and offer a wide variety of product selection with many vendors able to deliver. In terms of drawbacks, these motors offer limited position control and are typically larger in size.

Higher performance, smaller size

Servos, on the other hand, are more dynamic motors that include a feedback device, such as an encoder or resolver, to control speed and position accuracy. The main strengths of servomotors include much higher performance, the ability to deliver higher speeds, smaller size, and a wide variety of supplementary components. Of course, servos are slightly higher in cost due to the more advanced technology in play. High speeds and torque performance can be limited occasionally by servo drive update time.

Typical squirrel-cage induction motors represent a low-cost choice for velocity control for applications, such as constant speed conveyors, sorters, or similar transmission systems that have reasonable constant loading.  Because induction motor torque is generated by percentage of slip, they tend to have a limited flat torque region based on speed when compared to servos.

Common three-phase induction motor applications include machine tools, cranes, pumps, fans, robot applications, and others. In such applications, a synchronous servomotor could be “overkill” relative to the costs involved. However, both solutions clearly have their place. Depending on the application, servos may still be required based on other performance criteria, such as repetitive robust indexing with repeatable positioning and/or higher velocity accuracy. Other instances of where servo positioning systems are necessary include applications that require a range of supply voltages (such as 115 V ac to 480 V ac).

Accuracy justifies cost

As requirements for accurate positioning, higher speeds, and robust indexing moves with limited dwell time become more critical, it’s easier to justify the additional cost for servos to achieve more accurate positioning control. Typical servomotor applications include higher performance machinery for packaging, metal forming, CNC, woodworking, robotics, and more.

Advanced servomotors available today feature a low rotor moment of inertia and a very high overload capacity. Salient pole-wound technology gives rise to a high copper space factor, which helps attain high continuous torques. Very small end turns result in a small overall length. Fully potted stator provides for a thermally ideal binding of the winding to the motor housing. Potting also mechanically protects winding wires against vibrations.

One-cable technology is another advanced feature where power and process data are transmitted in one standard motor cable instead of two cables. Encoder data, rotor position, multi-turn information, and the status of the thermal conditions in the motor are transmitted reliably and free from interference via a digital interface. The benefits here include significant cost savings, since plug connectors and cables are eliminated at the motor and the controller ends.

- Bob Swalley is motors and drives specialist, Beckhoff Automation. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering and Plant Engineering, mhoske@cfemedia.com.

www.beckhoffautomation.com/drivetechnology  



The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers. Vote now (if qualified)!
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Maximize ROI with integrated control system approach; Microcontrollers vs. PLCs; Power quality; Accelerate and rewire IIoT; Traits for excellent engineers
HMI effectiveness; Distributed I/O; Engineers' Choice Award finalists; System Integrator advice; Inside Machines
Women in engineering; Engineering Leaders Under 40; PID benefits and drawbacks; Ladder logic; Cloud computing
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. As we know, PLCs aren’t the only option for making decisions in a control loop, but they are likely why you’re here.
This digital report explains how plant engineers and subject matter experts (SME) need support for time series data and its many challenges.
This article collection contains several articles on how advancements in vision system designs, computing power, algorithms, optics, and communications are making machine vision more cost effective than ever before.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers. Vote now (if qualified)!
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Maximize ROI with integrated control system approach; Microcontrollers vs. PLCs; Power quality; Accelerate and rewire IIoT; Traits for excellent engineers
HMI effectiveness; Distributed I/O; Engineers' Choice Award finalists; System Integrator advice; Inside Machines
Women in engineering; Engineering Leaders Under 40; PID benefits and drawbacks; Ladder logic; Cloud computing
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. As we know, PLCs aren’t the only option for making decisions in a control loop, but they are likely why you’re here.
This digital report explains how plant engineers and subject matter experts (SME) need support for time series data and its many challenges.
This article collection contains several articles on how advancements in vision system designs, computing power, algorithms, optics, and communications are making machine vision more cost effective than ever before.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by Control Engineering subscribers. Vote now (if qualified)!
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Maximize ROI with integrated control system approach; Microcontrollers vs. PLCs; Power quality; Accelerate and rewire IIoT; Traits for excellent engineers
HMI effectiveness; Distributed I/O; Engineers' Choice Award finalists; System Integrator advice; Inside Machines
Women in engineering; Engineering Leaders Under 40; PID benefits and drawbacks; Ladder logic; Cloud computing
Programmable logic controllers (PLCs) represent the logic (decision) part of the control loop of sense, decide, and actuate. As we know, PLCs aren’t the only option for making decisions in a control loop, but they are likely why you’re here.
This digital report explains how plant engineers and subject matter experts (SME) need support for time series data and its many challenges.
This article collection contains several articles on how advancements in vision system designs, computing power, algorithms, optics, and communications are making machine vision more cost effective than ever before.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Control room technology innovation; Practical approaches to corrosion protection; Pipeline regulator revises quality programs
Cloud, mobility, and remote operations; SCADA and contextual mobility; Custom UPS empowering a secure pipeline
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me