What is a Servo System?

A servo system is made up of two main components: a servo motor and a servo drive. The servo drive acts as the power source for the motor, delivering the right voltage and current while keeping an eye on feedback to ensure everything runs accurately. Inside a servo drive, you’ll typically find three control loops:

• 1. Current (Torque) Loop – Manages the motor’s torque output.
• 2. Velocity Loop – Controls the motor’s speed.
• 3. Position Loop – Ensures the motor moves to the exact position needed.

The type of control used depends on the task at hand. For example:

• Torque Control only needs the current loop.
• Velocity Control requires both the current and velocity loops.
• Position Control relies on all three loops to achieve precise movement.

How Do Servo Drives and Motion Controllers Differ?

In a torque-controlled setup, the device supplying power to the motor is called a servo drive (or servo amplifier). But a drive can’t work on its own—it needs instructions. That’s where the motion controller comes in. The motion controller decides how much torque, speed, or position change is required and sends the appropriate commands.

In a typical brushless DC servo system, the three control loops work in harmony:

• The current loop (always in the drive) manages the motor’s current.
• The velocity loop (in the drive or controller) adjusts the speed.
• The position loop (in the drive or controller) ensures accuracy.

Feedback sensors, like encoders, provide real-time data to these loops, helping maintain precise control over the motor’s movement.

The Role of Motion Controllers

A motion controller is essentially the brain of the operation. It’s a microprocessor-based device that generates Pulse Width Modulation (PWM) signals to guide the motor. The servo drive then takes these signals and translates them into actual motion by switching power transistors to regulate current and voltage.

But a motion controller does more than just sending commands. It also processes feedback, fine-tunes motor performance, and ensures safety. These controllers can be programmed using languages like BASIC, C++, VB, or languages specified in IEC 61131-3 standards, making them highly adaptable to specific needs.

In some systems, all the control electronics are housed in a single cabinet. In others, the motion controller stays in the cabinet while the servo drives are placed closer to the motors, communicating through motion fieldbuses.

Although motion controllers and servo drives may appear to have similar functions after a brief examination of their functions, there are distinctions between them. The motion controller is the strategist, providing the commands; the servo drive is the executioner, supplying power and executing those commands. Understanding their teamwork is one of the principles for designing efficient and accurate automation systems, ensuring seamless operation in many industrial applications.

Camming and Gearing in Motion Control

Two key techniques used in servo motion control are electronic camming and electronic gearing, both of which allow coordinated movement between multiple axes in a system.

Electronic Camming

Electronic camming is a motion control technique that synchronizes a slave axis with a master axis according to a predefined electronic cam table. This allows the slave axis to follow a specific motion profile relative to the master axis, mimicking the function of mechanical cams but with greater flexibility and precision. Electronic camming is commonly used in applications where precise synchronization is required, such as constant gap maintenance, rotary knife operations, and material filling.

Electronic Gearing

Electronic gearing is applied when the movement of a slave axis needs to be incrementally and proportionally controlled based on a gear master—typically the position or velocity of another axis. This method ensures that the slave axis maintains a defined relationship with the master axis, similar to how mechanical gears work but with the added benefit of digital control and programmability. Electronic gearing is essential in applications that require smooth, proportional motion adjustments.

Both camming and gearing techniques enhance motion control performance, making them valuable for OEM equipment designs that require high-speed, precise, and synchronized operations. These technologies are commonly found in industries such as packaging, aerospace, agriculture, and food & beverage, where motion accuracy and efficiency are critical.

Cognidel is a leading training provider specializing in industrial automation courses, offering hands-on learning in PLC SCADA, PLC programming, and related technologies. With a structured curriculum designed to meet industry demands, Cognidel equips students and professionals with practical skills in automation, control systems, and industrial software. By focusing on real-world applications and expert-led instruction, Cognidel helps learners build a strong foundation in industrial automation, making them job-ready for careers in manufacturing, process industries, and smart automation systems.