Servo motors are often used as a high-performance alternative to a stepper motor. Stepper motors, by comparison, have an inherent ability to control position as their motion is based on output steps from a step & direction signal. This allows the stepper motor to be used in open-loop position control applications without any feedback device since the signal from their stepper drive specifies the number of steps & direction to rotate per shaft revolution. However, the lack of position feedback limits their performance since the stepper motor can only drive a load that is well within its torque capacity. Missed steps under load usually lead to positioning errors or a stall condition when no closed-loop feedback is in place. Additionally, load–to-motor inertia matching is absolutely critical when using a stepper motor, but less so when using a servo motor.
Servo Motor Types
Servo motors come in two main types: brush and brushless. Both servo motor types operate in a continuous torque range as well as a peak torque range. Peak torque can be much higher than continuous torque, but can only be achieved for short periods of time. By comparison, continuous torque can be reached throughout the regular operation of a servo motor.
The brush type motor is an older technology that can be run with simple motor controls, such as 2 or 4 quadrant servo drives, but have parts (graphic or precision metal brushes) that require maintenance. Todays preferred servo motor is brushless. The brushless servo motor has no component maintenance but does require a servo drive that can electronically commutate the motor. This is normally done with a primary feedback device like Halls Sensors. A brushless servo motor will normally have an encoder or resolver for accurate position feedback that can be used used to control both position and/or velocity.
Brushless servo motors can be rotary, linear or frameless in construction. They can perform very simple motion or be used in highly dynamic requirements. Applications include: robotics, CNC machinery, laser cutting, packaging, printing, material handling and many other automated manufacturing processes.
DC Motor/Brushed MotorsView More
DC Brushed Motors that have winding in the rotor and permanent magnets on the stator. Carbon brushes and a mechanical commutator provide a current path through the windings to achieve motor torque. A DC motor will continuously rotate if a DC power source is applied across its terminals. DC motors require simpler drives but require higher maintenance, and are larger in size for the same output power.
There are two types of brushed permanent magnet DC motors: iron core and moving coil rotor.
Moving Coil Rotor Motors feature:
- High acceleration due to a low mass inertia
- Low electromagnetic interference
- Low inductance
- High efficiency
- Linearity between voltage/load & speed, and load & current
- Small torque ripple
Iron Core Rotor Motors feature:
- High torque-to-inertia ratio
- High starting torque
- Low thermal resistance
- Low current consumption
- High inertia for improved load-to-motor inertia matching
- Low cost
Brushless Servo MotorsView More
Brushless Servo Motors that have windings in the stator and permanent magnets attached to the rotor. No brushes are used. Motor rotation is achieved by means of electrical commutation performed by the drive. Brushless servo motors provide high acceleration, high torque, and no maintenance. Brushless Servo Motors offer the highest torque-to-weight ratio and are commonly used in the highest throughput, precision and demanding applications.
There are two types of brushless servo motors:
Slotted Motors feature:
- Better accel/decel capabilities
- Better load to rotor inertia ratio
- Lower rotor inertia
- Lower cost vs. slotless motors
Drawbacks of slotted motors include: cogging, high speed operation and lower efficiency vs. slotless design.
Slotless (coreless) Motors feature:
- Zero cogging
- Smooth operation
- Increased heat dissipation
- Ability to withstand high peak torque
- High power density
- Lowest electrical time constant
- Low inductance
Drawbacks of slotless motors include: low inductance, low moment of inertia, cost and lower accel/decel capabilities vs. slotted design.
Linear Servo MotorsView More
A linear motor provides direct linear motion (rather than rotary). Electromagnetic force is utilized to produce thrust directly, eliminating the need for rotary to linear conversion. Advantages include: high speeds, high precision, fast response, stiffness, zero backlash and maintenance free operation. Disadvantages include: higher cost, required higher bandwidth, larger footprint and heat. Types: Iron core, air core, and slotless.
Pancake Servo MotorsView More
Available in both Brush and Brushless varieties, these flat disc armature motors feature:
- Low inertia
- Low axial profile
- High-pulse torque capability
- No cogging even at low operating speeds
Drawbacks of pancake servo motors include: cost, delivery, customization, low inductance and low inertia.
Direct Drive Rotary MotorsView More
Direct Drive Rotary Motors are brushless motors with high resolution encoders or resolvers, plus optional radial bearings that turn the table top or integral coupling which is directly attached to the load. Key benefits include high accuracy and torque in a package that does not have a gear reducer.
The key disadvantages include high system cost, larger size, and the requirement of using a specific motor control system, one designed for that specific rotary motor.
Search our Servo Motors by Supplier:
- Akribis Systems
- Applied Motion Products
- Applimotion, Inc.
- ElectroCraft, Inc.
- Galil Motion Control
- Harmonic Drive® LLC
- ITT Torque Systems
- JVL Industri Electronik
- Maxon Motor AG
- MCG, Inc
- Nippon Pulse America
- QuickSilver Controls Inc.
- Tecnotion B.V.
Search our Servo Motor Products by subcategory at the links below:
Harmonic Drive® Servo Motor Actuators feature zero backlash, high accuracy & are available in a range of sizes & hollow shaft designs.
Learn About Servo Motor Actuators - AC & DC Servo Actuators »
AC Servo Motor + Drive Systems
Preconfigured Motor+Drive Systems feature plug & play operation, a range of sizes & multiple fieldbus connectivity options.
Learn About AC Servo Motor + Drive Systems »
Brush and Brushless Mini Gearmotors
Gearmotors are available with either Spur & Planetary Gearheads in a variety of sizes with reductions ranging from 2:1 to over 9000:1.
Learn About Brush & Brushless Mini Gearmotors - Miniature Gearmotors »
Brush Mini Motor
Moving Coil Rotor DC brush motors from 0.3 W to 250 W output, in sizes Ø 6 mm – 65 mm. Imperial & metric varieties.
Learn About Small DC Brushless Motor - Maxon DC Mini Motors »
Brush Servo Motors, NEMA and Metric Frame
Multiple frame/stack combinations. Tpk to 27.1 Nm (240 lb-in). Speeds to 6,500 RPM. 2-pole & 4-pole designs with many winding options.
Learn About DC Brushed Servo Motors - Metric & NEMA 23, 34, 42 & 56 Brush Servo Motors »
Brushless Mini Motors
Electronically commutated DC brushless motors from 0.2 W to 480 W output, in sizes Ø 4 mm – 90 mm. Includes cylindrical & flat varieties.
Learn About Brushless DC Mini Motors - Small Brushless Motors »
Brushless Servo Motors, Metric Frame
8 frame sizes with 28 frame/stack combinations. Tpk to 668 Nm (5912 lb-in). Speeds to 8,000 RPM. 75 VDC; 120, 240 & 480 VAC windings.
Learn About Brushless Servo Motors, Metric Frame »
Brushless Servo Motors, NEMA Frame
Multiple frame/stack combinations. Tpk to 668 Nm (5912 lb-in). Speeds to 8,000 RPM. 24, 75 & 160 VDC; 120, 240 & 480 VAC windings.
Learn About Brushless Servo Motors for NEMA 17, 23, 34, 42, 56 Frames »
Direct Drive Motors
Direct Drive & Torque Motors providing 0.7 Nm to 339 Nm continuous torque and speed ranges from 190 rpm to 6918 rpm.
Learn About Direct Drive Servo Motor Supplier - Torque Motor Supplier »
Explosion Proof, Washdown, and Food Grade Motors
Specialty motors for Washdown, Class I, Division 1, Group C & D Hazardous Location, Explosion-proof, Food Grade & ATEX certified applications.
Learn About Explosion Proof, Washdown, & Food Grade Servo Motors »
Direct Drive Frameless Motors in sizes 20 - 533 mm include: slotted, slotless, 3phase ring type, low profile & large through hole types.
Learn About Direct Drive Frameless Motor Supplier - Frameless Torque Motors »
Integrated Servo Motors
Integrated Servo Motors are constructed to include the motor, driver, encoder and associated electronics into a single package.
Learn About Integrated Servo Motors »
Ironcore, Ironless & Linear Shaft Motor models available in continuous force outputs from 0.29N to 780N .
Learn About Linear Servo Motors - Nippon Pulse & Tecnotion Linear Motor Supplier »
Electronically commutated DC brushless flat/pancake motors from 0.2 W to 100 W output, in sizes Ø 9.2 mm – 90 mm.
Learn About Pancake Motors - Brush & Brushless Flat Servo Motors »
Voice Coil Motors
Direct drive, zero cogging, and zero backlash Voice Coil Motors and Voice Coil Position Actuators. Cylindrical or rectangular shape.
Learn About Voice Coil Motors - Voice Coil Actuators »