How are Servo Motors controlled?

Servo motors operate on negative feedback, meaning that the control input is closely compared to the actual position via a transducer. If there is any variance between physical and wanted values, an error signal is amplified, converted, and used to drive the system in the direction necessary to reduce or eliminate error. Servo motors are controlled by a pulse of variable width that is sent from a micro-controller output pin to the servo motor’s control wire. The shaft angle is determined by the duration of the pulse, also known as pulse width modulation (pwm). This pulse has to have specific parameters such as; minimum pulse, a maximum pulse, and a repetition rate. Given these constraints, neutral is defined to be the position where the servo has exactly the same amount of potential rotation in the clockwise direction as it does in the counter clockwise direction. It is important to note that different servo motors will have different constraints on their rotation, but they all have a neutral position, and that position is always around 1.5 milliseconds (ms).

Anaheim Automation offers AC and DC Servo Drives providing high speed DSP. These servo motors are equipped with auto disturbance rejection control and speed observation control algorithm, in addition to compensation servo delays, forward feed control, and reference smoothing techniques. Anaheim Automation Servo Drives are equipped with a range of dynamic features:

High Overload Capacity

Kinco Servo Drives can handle up to three-fold the rated power of the unit for instantaneous load requirements.

Communication Interface

Standard CAN bus interfaces are available in the FD AC Servo Driver, simplifying the integration process. Based on Modbus protocol via RS485 interface, up to 31 servo motors can be connected together. When RS485 interface is used, the transmission distance can reach up to 4,000 feet. Fieldbus and EtherCAT modules are also available. Anaheim Automation AC Servo Drivers can also communicate with a PLC, VFD, another servo drive, HMIs, touch screens, and more.

Kinco Servo+ Communication Software

Anaheim Automation software is capable of the following:

Servo Motor Types

There are two main types of Servo Motors: Rotary and Linear.

Rotary Servo Motor
A Rotary Servo Motor is what most people think of when they think of a
Servo Motor. There are many types of Rotary Servo Motors: AC Servo Motor,
Stepper Servo Motor, Brush DC Servo Motor, Permanent Magnet
Synchronous Servo Motor, and Brushless DC Servo Motor. The motion of
a rotary Servo Motor is often converted into linear motion by the use of a
screw thread (ball screw or lead screw), or with the use of belts and pulleys.

Any motor that has a closed loop feedback device that responds to disturbances in the motion profile classifies as a Servo Motor. Typically, Servo amplifiers (or drivers) are coupled with Permanent Magnet Synchronous Motors that feedback speed and position through an encoder mounted to the shaft. The amplifier can also receive a feedback signal from an encoder mounted elsewhere in the application, such as on the lead screw or drive pulley, to close the loop on the motion profile. The feedback signal changes the amount of current that the motor receives from the amplifier so that more current is delivered when the motor requires more torque and less current is delivered when the motor does not require it. In torque control mode, the servo motor will increase and decrease voltage to maintain speed and always deliver a specified torque.

Linear Servo Motor

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

Servo Motor Cost

A Servo Motor is considered one of the more expensive motors when compared to AC, Brushless, DC, Stepper, and other motor types. The reason for the expense of a Servo Motor is the precision required to make a Servo Motor, and the added components that go along with a Servo Motor. Generally speaking, a Servo Motor is intended to be used as a precise positioning or speed control device. The motion should be smooth and very precise. To accomplish these features, the Servo Motor is manufactured under very tight control parameters. In addition to the cost of the Servo Motor 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 ensure that the Servo Motor can run 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 Motor, but are very reliable and industrial grade. The feedback devices are typically differential encoders and or resolvers. These devices are very expensive and add cost to the Servo Motor.

Servo Motor Feedback

There are two types of servo systems: open-loop and closed-loop. In an open-loop system, the input signal, which may be either analog or digital, travels through amplifiers to produce the correct output before then passing out of the system. Open-loop systems have no feedback, so the input must be returned to zero before the output can return to zero. A closed-loop system is "self-adjusting." Rather than data flowing in only one direction, it may route back to the start of the system from a specific amplifier, such as velocity or position, instructing the system to adjust itself accordingly as necessary. The velocity and current position data modify the output and position at a consistent, predetermined rate. There are two options for Servo Motor feedback controls, 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 Servo Motor output shaft.

The resolver on the Servo Motor 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 is very robust with a high temperature range, and is inherently shock-resistant due to its design. A resolver is mostly used in harsh environments.

The optical encoder on the Servo Motor 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 environmental concerns and longevity requirements.

Servo Motor Accessories

Anaheim Automation provides many different accessories for its Servo Motor product line. These accessories include brakes, encoders, connectors, cables and a handheld interface unit, as well as a full line of servo motor drives.

The Servo Motor brake is a 24VDC system. These Servo Motor brakes are perfect for holding applications and are available for Anaheim Automation Servo Motors. They can be purchased separately or are attached to the rear of the Servo Motor. The Servo Motor brakes 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 Servo Motor brake, 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 Motor is designed with a 2500 counts per revolution quadrature encoder, with a resolution of 10,000 pulses per revolution.

Anaheim Automation's Servo Motor comes with the necessary connectors to connect to another company's servo drive or an Anaheim Automation servo drive. These Servo Motor connectors can also be purchased separately should they become lost. Please refer to the servo motor user's guide for a specific part numbers.

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

NOTE: Anaheim Automation strongly recommends the purchasing of the cables with servo motors and drives to ensure cable integrity. These cables are perfectly matched and a stable form of connection.

Servo Motor History

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 Motor comes from the French phrase "Le Servomoteur" or the "slave motor". 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.

Servo Motor Customization

Anaheim Automation was established in 1966 as a manufacturer of "turnkey" motion control systems. Its' emphasis on R&D has ensured the continued introduction of advanced motor drivers and controllers, such as the Servo Motor product line. Today, Anaheim Automation ranks among the leading manufacturers and distributor of motion control products; a position enhanced by its excellent reputation for quality products at competitive prices. The Servo Motor product line is no exception to the Company's goal.

Anaheim Automation offers a wide variety of standard Servo Motor products. Occasionally, OEM customers with mid to large quantity requirements prefer to have a Servo Motor that is custom or modified to meet their exact design requirements. Sometimes the customization is as simple as a shaft modification, brake, oil seal for an IP65 rating, mounting dimensions, wire colors, or simple label requirement. Other times, a customer might require that a Servo Motor meet an ideal specification such as, speed, torque, and/or voltage. Engineers appreciate that Anaheim Automation's Servo Motor product line can answer their desire for creativity, flexibility and system efficiency. Buyers appreciate the simplicity of the "one-stop shop," and the cost savings of a custom Servo Motor design, while engineers are pleased with Anaheim Automation's dedicated involvement in their specific servo motor system. Note: There are minimum purchase requirements for all special/custom orders.

Anaheim Automation's standard Servo Motor product line is a cost-effective solution; they are known for their rugged construction and excellent performance. This is a result of dedicated engineering, friendly customer service and professional application assistance, often surpassing the customer's expectations for fulfilling their custom requirements. Anaheim Automation takes pride in its standard stock base located in Anaheim, California, USA. To make customization of a Servo Motor affordable, a minimum quantity and/or a Non-Recurring Engineering (NRE) fee is required. Contact the factory for details, should you require a custom Servo Motor in your design.

All Sales for a customized or modified Servo Motor are Non-Cancelable, Non-Returnable, and an NCNR Agreement must be signed by the customer, per each request. All Sales, including a customized Servo Motor, are made pursuant to Anaheim Automation's standard Terms and Conditions, and are in lieu of any other expressed or implied terms, including but not limited to any implied warranties.