The basic definition for servo motors is an automatic device that uses an error-correction routine to correct the motion of the servo motors. The general term servo can be applied to systems other than servo motors that use a feedback mechanism such as an encoder or other feedback device to control the motion parameters. Typically when the term servo is used it applies to 'servo motors' but this term is also used as a general control term with the meaning of a feedback loop to position whatever the item is including servo motors.

Servo Motors are different from other controlled motors in that it is controlled by a time-based derivative commonly referred to as the PID loop. Servo motors that are used to control position must be capable of changing the velocity of the output shaft because the time-based derivative, or the rate of change of position, is velocity.

There are two main types of servo motors - Rotary and Linear.

Rotary Servo Motors
Rotary servo motors are what most people think of when they think of servo motors. The three types of rotary servo motors are: AC Servo Motors, Brush DC Servo Motors, and Brushless DC Servo Motors. The motion of rotary servo motors is often converted into linear motion by the use of a screw thread (ball screw or leadscrew), or with the use of belts and pulleys.

Rotary AC Servo Motors are an AC type motor that is used with a feedback device. These are typically only used in smaller application because large AC Servo Motors are typically too inefficient when compared to its DC or Brushless counterparts.

Linear Servo Motors
Linear servo motors are flattened out servo motors where the rotor is on the inside, and the coils are on the outside of a moveable u-channel. Both types of servo motors are becoming more popular as the prices for servo motors continue to come down.

Servo Motors are considered one of the more expensive motors when compared to AC, Brushless, DC, Stepper, and other motor types. The reason for the expense of Servo Motors is the precision required to make the servo motors and the expensive components that go along with servo motors.

Generally speaking servo motors are intended to be a very precise positioning or speed control device. The motion of servo motors should be smooth and very precise. To accomplish these features, servo motors are manufactured under very tight control parameters. Along with the cost of the servo motors are the case, bearings, connectors, and feedback devices. The case is usually industrial grade, often sealed to achieve an IP65 rating or better. The bearings are high quality to make sure that the servo motors can run at the speeds desired and can handle the appropriate axial and radial loads. The connectors are typically mil-style connectors that can be detached at the servo motors themselves, but are still very reliable and industrial grade. The Feedback devices are typically differential encoders and or resolvers. The devices are very expensive and add cost to servo motors.

There are two options for feedback controls on Servo Motors. These options include either a servo encoder or a servo resolver. A servo encoder and a servo resolver provide the same solution in many applications, but are vastly different. They are both used to sense speed, direction, and position of the output shaft on servo motors.

The resolver on servo motors uses a second set of rotor and stator coils called the transformer to induce rotor voltages across an air gap. The resolver does not use any electronic components, therefore it's very robust with a high temperature range, and is inherently shock resistance due to its design. A resolver is mostly used in harsh environments.

The optical encoder on servo motors uses a rotating shutter to interrupt a beam of light across an air gap between a light source and a photodetector, over time the wear associated with the rotating shutter reduces the longevity and reliability of the encoder.

The application will determine whether a resolver or an encoder is needed. Encoders are more accurate and are easier to implement so they should be the first choice for any application. The only reason to choose a resolver is if environmental and longevity requires it.

Anaheim Automation provides many different accessories for our servo motors. These accessories include a brake, encoder, connector, cable and a handheld interface unit.

The brakes for our servo motors are a 24vdc system. The brakes used with the servo motors are perfect for any holding applications. They are available on all of the servo motors Anaheim Automation has to offer, and are already attached to the rear of the servo motors. The brakes for the servo motors have a low voltage design for applications that are susceptible to weak batter, brown out, or long wiring runs. When electric power is applied to the brake of the servo motors the armature is pulled by the electromagnet force in the magnet body assembly, which overcomes the spring action. This allows the friction disc to rotate freely. When electrical power is interrupted, the electromagnetic force is removed and the pressure spring mechanically forces the armature plate to clamp the friction disc between itself and the pressure plate.

Anaheim Automation's servo motors are designed with a 2500 counts per revolution quadrature encoder, with a resolution of 10,000 pulses per revolution.

Anaheim Automation's servo motors come with all the necessary connectors to connect to another company's servo driver or an Anaheim Automation servo driver. These connectors for servo motors can also be purchased separately if they are lost. Please refer to the user's guide for a specific part number.

The cables for servo motors can be made with the supplied servo motor connector, or can be purchased from Anaheim Automation. The cable for use with servo motors comes with a standard length of 5M but can be adjusted to any length required.

Anaheim Automation offers a variety of options to customize servo motors. This list includes, but is not limited to: shaft, brake, oil seal for an IP65 rating, mounting dimensions, speed, torque, and voltage. Please give Anaheim Automation a call for any custom applications where servo motors are used.

The steam engine governor is considered the first powered feedback system that used a gain value so it is considered the first servo mechanism. The word servo motors comes from the French phrase "Le Servomoteur" or the "slave motors". The first known record of its use was by JJL Farcot in 1868 to describe steam engines and hydraulics for use in steering a ship.