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Servo systems consist of four main components — motor, drive, controller, and feedback. In some cases, a standalone controller determines required motor moves and prompts the drive to supply the necessary electrical energy to make those moves happen. In other cases, drive and controller are integrated into one component. Either way, the drive core controls torque or velocity or position ... although in servo systems, the most common command parameter is torque. That control is via a torque-mode amplifier or linear drive function.

Note that servo drives are also sometimes called amplifiers because they take control signals from the controller and amplify them to deliver some voltage and current to the motor. These are not to be confused with integrated designs (including motor, feedback, controller, and drive) also sometimes called drives for their axis-driving function.

Types •  Servo-Loop •   Architecture •  Servo System

What are servo drive loops?

What is distributed architecture for servo drives?

Why are servo drives also called servo inverters, amplifiers, and controllers?

What is a servo drive?

Servo drives, also called amplifiers in the motion-control industry, take a command signal for position, velocity, or current and adjust the voltage and current applied to the servomotor based on closed-loop feedback.

There are several types of servo drives. A common variation is the torque-mode amplifier. These convert the command signal from the controller into a specific amount of current to the motor. 

Traditional servo-system architecture consists of a power supply, a motion controller, and servo drives all housed in one location that is typically a control cabinet located away from the machine.

Let’s start with the term servo drive. Here’s what a drive does in a servo system: It basically takes an input signal from a controller and amplifies that signal which is then sent to the motor. 

The basic idea is easy to understand. An integrated motor-drive system combines a motor and a drive (at the very least) and can also include other components such as controllers or encoders. Sometimes these integrated motion subsystems are simply called drives.

Tuning a servo system is a complex and iterative process. It typically requires tuning multiple control loops, each with its own gains (proportional, integral, and/or derivative) to be adjusted. In addition, tuning a servo drive usually requires adjustments to additional parameters including acceleration and velocity feed-forward gains and filters to reduce oscillations.

Application •  Linear vs PWM •   Analog •  Digital

When do you need a linear amplifier versus a PWM drive?

Where are analog servo drives used?

Where are digital servo drives used?

Selecting a servo drive: 9 things you need to know

For applications that require extremely smooth motion, no audible noise, and little or no EMI, linear servo drives — commonly called linear amplifiers — are preferred over PWM drives.

The purpose of a servo drive is to convert low-power signals from the controller to high-power signals to the motor, instructing it to produce the desired torque or velocity.

The original servo drives are analog types that operate on ±10-Volt inputs. In contrast, digital servo drives operate over fieldbus networks that now dominate the market.

Sizing a motor for a servo application requires evaluating the move profile and torque requirements to determine the mechanical demands of the system

Functional safety standards EN/IEC 62061 and EN/ISO 13849-1 ensure safety via electronic solutions, unlike traditional safety systems, which used electromechanical components to achieve safety. And while functional safety applies to a machine and its control system (not to individual components), the drive lies at the heart of the safety implementation.

This comprehensive collection with illustrations and descriptions, includes formulas, terms, and explanations for the calculations concerning drive systems. 

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