Servo Motors Speed Up

Rapid and often dramatic technological advancements have given new dimension and substance to automation and control systems of late. Throughout this time of change, however, some components have stayed stable and steady. Case in point is the servo motor. Enhancements and accessories may benefit the application, but the product remains nearly ubiquitous in manufacturing, providing critical serv...
By Jeanine Katzel, Control Engineering January 1, 2008

Rapid and often dramatic technological advancements have given new dimension and substance to automation and control systems of late. Throughout this time of change, however, some components have stayed stable and steady. Case in point is the servo motor. Enhancements and accessories may benefit the application, but the product remains nearly ubiquitous in manufacturing, providing critical service in countless systems and processes, and meeting ever-more-demanding requirements with higher torque, smaller sizes, absolute positioning feedback, and tuning software.

To evaluate the impact of the latest developments on the selection and use of servo motors, Control Engineering and Reed Research Group ( ) asked subscribers in a recent email/online survey to share opinions and preferences about this product line. Following are some insights gleaned from their answers.

Patterns and use

Based on input from 385 respondents queried late in 2007, some 54% said they specify, recommend, and/or buy electric servo motors for in-plant requirements, 25% said they do so for OEM (resale) use, and 21% use them for both in-plant and original equipment manufacturer (OEM) requirements. These results varied only slightly from those in the previous survey, conducted in 2005.

Looking at use patterns in a bit more depth, the survey found that just over 57% of all servo motors were for new applications. Replacement applications accounted for just over 26%, while retrofits made up 16.5% of the total. These numbers also were similar to those in the previous survey, with the current breakdown showing a slight rise in new applications (from 52%) and a small decline in retrofits (from 22%). Replacement applications held steady at 26%.

When asked about their primary applications for servo motors, close to half of the respondents (45%) put motion control at the top. Other common uses included packaging machines, accounting for 12%; machine tools and CNC equipment coming in at 11%, and assembly lines and material handling equipment at 6%. Also named—but by less than 5% of respondents in each case—were automotive manufacturing; printing equipment; pulp, paper, and web processing; and automated on-vehicle systems. Some 9% of the respondents selected “other” as the primary application for this equipment. (See complete breakdown in the accompanying pie chart.)

Respondents were also probed about a variety of other servo motor preferences, including type, size, speed, and configuration. More than half of the survey participants (53%) said they preferred brushless servo motors, and nearly half (47%) put brushless ac (permanent magnet) units at the top of their list. Also noted as products of choice were stepper motors (by 36%); ac induction units (by 31%); and linear brushless, permanent magnet (by 22%). Rounding out preferred types were brush dc (17%), linear brush (7%), and switched reluctance (2%). Total equals more than 100% due to multiple selections.

Functions and features

Functional and performance features of this product line also were examined in detail in the survey. When respondents were asked to rate a variety of functional characteristics on a scale from very important to not important al all, price was cited by nearly all (97%) as very or somewhat important. Other features noted as very or somewhat important included type of mounting (95%), and standard size such as NEMA 23, 34, 42, etc. (91%). Also near the top were EMI/RFI protection (90%); construction: normal housing (87%); sealing, IP65 or higher (83%); and integral holding brake (80%).

When asked to rate performance features similarly, respondents found it more difficult to choose. Nearly all the characteristics listed were cited as very or somewhat important by more than 90% of all respondents. These included high toque/inertia ratio (96%), high torque at low speed (96%), high output torque (95%), software for setup/tuning (92%), high power density, output per volume (92%), wide speed range (92%), and low torque ripple (90%). On the other end of the spectrum, “different rotor inertias available in same rotor size” and “interior permanent magnet rotor design” were rated not important by nearly a quarter (23%) and by 17%, respectively. (See how a selection of performance features stacks up against previous surveys in the accompanying bar chart.)

Applications typically are more complex than mere features and functions, however. As one respondent commented, “Make sure you know exactly how much torque and power is required for the application when purchasing the equipment. Have a good relationship with the servo drive manufacturer and they will have a willingness to help you work out any problems with your application.”

Advancements, enhancements

Examining some of the more progressive aspects of servo motor applications, such as networking and controls, the survey found that 41% of those responding use these devices in a networked arrangement. Currently, the two most common protocols in use are EtherNet/IP and SERCOS. Nearly half of all respondents (49% in each case) indicated that they currently use, and will continue to use for the next 12 months, these networks. Other networks cited by significant numbers of respondents include DeviceNet (32%), Profibus (31%), and Modbus TCP/IP (22%). When asked about planned use of a network not presently installed for these applications, respondents targeted SERCOS III (19%), EtherNet/IP (14%), EtherCAT (12%), and Profinet (11%) as top choices.

When asked about servo motors packaged with controls, drive, and feedback within the motor housing, only about a third of the respondents (30%) said they use such equipment currently. Another 19%, however, noted that although they do not currently use servo motors in these configurations, they plan to do so in the next 12 months. Just over two-fifths (41%) said they use linear servo motors, with another 22% indicating they plan to add them in the next 12 months.

Although servo motor applications are more advanced than they were years ago, the means of applying them have advanced as well. Make sure the equipment is easy to setup and able to communicate with all types of PLCs, cautioned one respondent. Another survey participant advised, “Don’t be afraid of using servos. They are much easier to setup and use than they were 10 years ago.”

Now and future trends

Respondents far and away prefer to buy electric servo motors as a matched motor and drive (52%). About a fifth (21%) said they bought the motor and drive separately and 15% chose an integrated motor and drive; 12% said they had no preference. Regarding speed, most survey participants (76%) said they required up to 3,000 rpm. Only a small number (9%) needed speeds above 10,000 rpm. In between, 43% said they used servo motors with speeds from 3,001 to 4,000 rpm, 37% required units at 4,000 to 6,000 rpm, and 12% noted requirements between 6,001 and 10,000 rpm.

When asked what servo motor power and size ratings they use currently, and what ratings they expected to use in the future, most respondents (71%) said they used and planned to continue to use in the next 12 months units up to 1 kW. Somewhat more than half (56%) used and planned to continue to use units between 1 and 5 kW. Only a small number use and plan to continue to use servo motors rated more than 30 kW. Most (78%) indicated they neither used units above 30 kW, nor did they intend to use them in the next 12 months.

Overall, the servo market appears stable with about half the survey sample saying they plan to continue the same level of spending for this equipment in the next 12 months as in the past. More than a third (35%) plan an increase, while only 14% forecast a decrease. Spending levels in the past 12 months were at the $15,000-$36,000 level for about a fifth (21%) of those responding; 17% said put spending at $5,000-$14,999; another 17% were in the $37,000-$99,999 range. Perhaps surprisingly, some 18% said they had spent $100,000 or more on electric servo motors over the past 12 months.

When asked what they had learned about servo-motor applications over the years, a number of respondents were quick to offer advice. “Do your homework before startup,” stressed one, adding, “Always check wiring before you turn anything on.” Know your application, offered another, as “the wrong choice can lead to a lot of work and cost too much.”

Servo motor products

Control Engineering subscribers participating in this survey identified, from a list provided, the vendors included here as leading servo motor suppliers. Read this article online at under January 2008 for products and more photos, including:

Rockwell Automation

Allen-Bradley HPK motors

Baldor Electric

BSM132C brushless servo motor

Danaher Motion

Cartridge DDR rotary servo motors

Yaskawa Electric America

Sigma V servo motors

Siemens Energy & Automation

1FT7 series synchronous servo motors

GE Fanuc Automation

DSM324i motion controllers

Bosch Rexroth Corp.

IndraDyn T torque motors

Parker Hannifin

MPP230/MPP270 high torque motors


DS/CM series synchronous servo motors

ONLINE : Read the research report at / . For more manufacturers, visit . Find system integrators with related experience at .

ONLINE extra:

Analysis: Use of brushless motors continues to grow, according to Dan Jones, Incremotion Associates

More links, graphics, and other extra information about servo motors follows.

Servo System Application Tips
Electric servo systems provide the most advanced and precise motion control available for increasingly versatile industrial applications. Servos excel in two distinct working modes: rapid point-to-point load positioning and smooth, accurate trajectory control between points, as in surface contouring….

Servo Motors
They come in many shapes, sizes, and configurations—from large slow-speed, direct-drive rotary torque motors to sleek, compact units with low rotor-inertia for optimum acceleration and deceleration of loads, to frameless motors, to linear motors providing high thrust force under extreme acceleration and speed….

Control Engineering 03/01/2006

More advice about servo motors

More advice follows from those who answered the survey.

One respondent stressed the need for proper motor sizing to achieve the required efficiency and performance, adding that correct drive selection for the application, the method of control, tuning software, and proper rating are also important.

Another said simple programming is needed.

Another respondent observed, "Saving money is not always the best option in the end" if quality is the cost.

Additional graphics

Network use with servo motors


Products, additional photos

For more information on products listed here, visit the Web sites included with each listing.

HPK motors boost precision, throughput

Allen-Bradley HPK (high-power Kinetix) motors from Rockwell Automation are intended for material handling or web converting applications that require high power capacities. Series is said to give OEMs and end users servo motor precision and performance at the power ranges and prices of induction motor technology. According to the manufacturer, the HPK motor extends the normal power range of a traditional servo motor package to 150 hp, allowing machine builders to increase acceleration and improve positioning, precision and, overall system throughput as much as 25%. The company reports the optimized electrical winding design of the motor mimics the speed/torque curve of a conventional permanent magnet servo motor to deliver peak torque twice the continuous torque when running at base speeds. The motors are equipped with single- or multi-turn, high-resolution absolute feedback that is said to eliminate the need for time-consuming homing routines, improve velocity regulation, and expand the system’s inertia matching capacity. They are reportedly the first of their kind to offer positioning, acceleration, and productivity capabilities comparable to traditional permanent magnet servo motors.
Rockwell Automation

High-power brushless servo motors

New family of higher power brushless servo motors from Baldor Electric Co. expands the company’s product offering by a factor of three. BSM132C brushless servo motors reportedly give designers much higher power capabilities and provide peak torques from 1,400 lb-in. (160 Nm) to 3,320 lb-in. (375 Nm), which equates to 130 hp (96 Kw) at 2,500 rpm. BSM132C lets designers use the benefits of brushless technology: less maintenance, faster acceleration, and positioning. Typical applications include packaging, machine tools, new installation and original equipment manufacturers (OEM), material handling, and web converting. The motor is said to enhance machinery precision and accuracy by providing high overload capacities and wide speed capability and accuracy. It is available with variety of accurate feedback devices, including resolver, incremental, and absolute encoders, with BiSS feedback. Feedback device selected depends on application accuracy and environmental conditions. BSM132C Series includes a high insulation protection system as standard and meets UL, CSA, and CE standards. Baldor Electric Co.

DDR servo motors now in smaller sizes

Danaher Motion’s Cartridge DDR direct drive rotary servo motor line adds three smaller sizes to bring to five the number of available frame sizes ranging from 4.25 in. sq to 13.78 in. sq with four stack lengths per frame. The motors use a direct drive technology that features pre-engineered components; an integrated, factory-aligned, high-resolution feedback device; and a unique bearing-less design that facilitates maintenance-free, mount-and-run operation in less than 30 min. "Users will benefit from increased machine uptime, a 20 db noise reduction, and up to a 50% increase in accuracy and torque density compared with traditional servo systems," said Jeff Arnold, technology specialist for the company. Motors are said to be applicable for new machine designs in the converting, packaging, printing, semiconductor, and factory automation industries. The company notes that although the line has a slightly higher initial cost over conventional servo systems, it will reduce operating costs more than $10,000 on one axis of motion over a 5-yr period. Devices are CE marked, UL listed, and available with 240-V, 400-V, and 480-V ratings for maximum design flexibility and robust operation. They provide 4.57 to 510 Nm continuous torque, peak torque to 1,017 Nm, and speeds to 2,500 rpm.
Danaher Motion

Servo motors offer autotuning function

Sigma-V series servo motors from Yaskawa Electric America reportedly offer improved positioning accuracy a thousand times the industry standard and an autotuning function for such sophisticated applications as two axes in super-high performance machines. Features include powerful serial encoders, servo amplifiers with the latest microprocessor technology, and powerful ASICs (application specific integrated circuits). User-friendly SigmaWin+ software allows fast and easy servo motor selection and easy set-up of the servo amplifier. Servo amplifiers adjust automatically to a wide range of inertia ratios so that manual fine-tuning is no longer necessary. In addition, the ?-V series can communicate via several open and Ethernet-based fieldbus systems. Series has been completely redesigned, says the manufacturer. Number of parts has been reduced by about 30%. A new coupling between the motor and the encoder has increased vibration resistance by 100% to 5G. A new stator design, advanced winding technologies, and high-density magnets are said to increase efficiency and reduce size, cutting energy consumption up to 30%. Applications include machines in electronics, semiconductor, packaging, printing, machine tool, injection molding, and metal forming industries.
Yaskawa Electric America Inc.

Synchronous servo motors provide increased torque

1FT7 series of synchronous servo motors from Siemens Energy & Automation is up to 30% smaller than the 1FT6 series and offers users increased torque and a robust encoder attachment with convenient mounting options in a compact design. It is reportedly the first servo motor with an encoder that can be replaced in the field without adjustment. Designed to withstand vibrations, the encoder operates without oscillations and the encoder technology integrates with the company’s Simodrive and Sinamics drives. It is constructed with the flange on the drive end and the flat surface on the top to provide expanded mounting options. A medium inertia motor designed for general machine tool applications, the 1FT7 series has a higher overload at 4 x MO (self-cooled) up to frame size 100. The flange on the drive end is compatible with the 1FT6 series. Self-cooling 1FT7 motors also can be cooled through forced ventilation or water cooling through "cool jets" to lower motor temperature. The cooling water connection, water flow, and redirections are maintained exclusively in the end shield on the non-drive end. 1FT7 series offers IP64/IP65/IP67 protection.
Siemens Energy & Automation

High-voltage servos are reliable, accurate, small
DSM324i motion controllers from GE Fanuc Automation, a unit of GE Industrial, support six Alpha HVi series servo models for use in general machine automation. Alpha HVi series servos, called the flagship servo line by GE Fanuc for its CNC business, are high voltage models with ac voltage input range of 400-480 V ac, and include separately mounted shared power supply modules. Series reportedly extends significantly the motor speed and torque rating that the company offers in its general motion product portfolio. Said Paul Derstine, product manager for GE Fanuc’s motion products, "Mean time to failure is measured in decades, which translates to improved machine productivity and reduced replacement costs." Line is called highly effective in high-speed printing and packaging applications, reducing the amount of space needed in the cabinet. Alpha HVi Series servos extend the torque range of Beta i series servos and support higher motor speed ratings. The same range of Alpha servos will be supported by the PACMotion controller. GE Fanuc Automation

Direct drive torque motors are synchronous, frameless

IndraDyn T torque motors from Rexroth are synchronous frameless units that include a stator with three-phase winding and a rotor with permanent magnets. They feature maximum torque ratings to 3,500 ft-lb, rated speeds from 25 to 700 rpm, and maximum speeds to 1,200 rpm, and offer low torque ripple of &1%. These motors are designed for link circuit voltages to 750 V and are available with liquid or conventional cooling and include thermal encapsulation. Liquid-cooled IndraDyn T torque motors are kit motors optimized for high torques to 13,800 Nm. They offer full torque even at standstill, extremely high overload capacity, and ease of assembly. They also have no elasticity in power transmission, and the direct-drive devices eliminate the need for mechanical transmission elements.
Bosch Rexroth Corp., Electric Drives and Controls

High-torque motors for high-power applications

Two high-torque motors from Parker’s Electromechanical Automation Div join the company’s MaxPlusPlus (MPP) servo motor family. MPP230 and MPP270 are said to offer the torque users need for high-power applications such as press feeders, tube benders, and plastic extruders. Frame sizes increase the torque range of the existing MPP product line to 162 Nm of continuous stall torque, and a peak torque of 513 Nm. Standard options include a resolver and Stegmann single- and multi-turn absolute encoders, and a 24-V brake option and shaft seal. Motors are UL listed and CE marked. All can be equipped with features such as custom output shaft dimensions, various front end-cap mounts, or special windings. Designed for demanding applications, MPP motors offer lower inertia and higher power in a smaller package than conventional motors. They offer segmented lamination technology, which can yield up to 40% higher torque per unit size than conventionally wound servo motors. Potted stators improve heat transfer for better thermal efficiency, resulting in increased torque at the motor shaft. High-performance neodymium magnets provide higher acceleration rates. Parker Hannifin

Synchronous servo motors for multiple uses

DS/CM line of synchronous servo motors from SEW-Eurodrive are said to feature dynamic performance, precision, adaptability, and long service life for applications such as material handling, packaging, and crane and hoist control. Line covers a wide range of standstill torques from 1 to 68 Nm, with peak performance ratings to 238 Nm. The servo motors come in a sturdy housing with built-in convection cooling for reliable performance, quiet operation, and exceptional service life. Series features a modular design for an almost unlimited number of configurations for mounting directly on a machine or integrated with the gear unit. Servo motors are available with 24-V holding brakes for the DS series or servo brakes for the CM series. CM series covers a torque range between 5 and 68 Nm static torque and is equipped with high-energy magnets that deliver a high overload capacity of 400% standstill current as standard. For static torque of 1 to 4 Nm, the DS series is said to provide an ideal low-power option. All DS/CM servo motors come with standard thermal motor protection and resolver feedback for motor control. They are offered in three sizes, with three lengths for each size, and are UL and CSA approved.
SEW-Eurodrive Control Engineering

Control Engineering Buyer’s Guide contains additional servo motor manufacturers and distributors.

Control Engineering Automation Integrator Guide contains system integrators with experiences with servo motors and systems.

Control Engineering Resource Center (free with registration) includes research reports on servo motors.