Motor Feedback Systems and Encoders

Motor feedback is at the center of modern automation. Whether you’re building a servo-controlled robot arm or synchronizing a CNC spindle, accurate feedback ensures the entire system runs smoothly, efficiently, and safely. Below is a deeper, more comprehensive explanation of how motor feedback works and how various encoder technologies align with different applications.

What Is Motor Feedback?

Motor feedback, also called closed-loop motor control or feedback control, uses a mechanism to monitor and adjust a motor’s output as shaft movement to an angular position, providing torque or controlled rotational speed. It utilizes encoders to measure the motor’s active output versus its desired output. A motor controller can then adjust the input to get the desired value.

The encoder essentially acts as the motor’s “sensor”, providing real-time information such as:

• Position (both relative and absolute)
• Speed
• Direction of rotation
• Multi-turn counts (for applications requiring tracking over many revolutions)

Benefits of Feedback Control

A properly designed closed-loop system offers several advantages:

• High Accuracy: Corrects for load changes, friction, and system variability.
• Consistency & Repeatability: Essential for manufacturing, robotics, and precision automation.
• Stability: Reduces drift and helps maintain performance over time.
• Reliability: Detects errors early and enables safer machine behavior while continuously providing accurate and repeatable measurements under specified operating conditions for a long service life..

It’s important to acknowledge trade-offs: closed-loop systems increase complexity, cost, and introduce slight processing delays since feedback must be measured and processed.

Why Absolute Encoders?

As mentioned, encoders are leveraged in most feedback control systems. This is because they can convert mechanical motion into precise electrical signals. These signals are then sent to a controller where they are analyzed and used to make continuous adjustments. In applications that require accurate torque, precise stops, or consistent motion, encoders ensure that is possible.

For a deeper dive into encoder technologies, types, and applications, explore the Knowledge Center.

Motor Feedback and Motor Type

Different motors require different feedback technologies. The type of motor usually dictates the encoder needed in the application.

DC Motors

• Typically pair with incremental encoders for speed and basic positioning.
• Ideal in simpler motion systems or cost‑sensitive applications.

AC Motors / Induction Motors

• Often use incremental or absolute hollow‑shaft encoders.
• Common in elevators, conveyors, and industrial machinery.

Servo Motors

• Requireprecise control with absolute, sine‑wave, or multi‑turn encoders.
• Resolver may be used in harsh environments due to their rugged construction.

Regardless of your motor type, Hengstler engineers can help identify the correct encoder technology, mechanical configuration, shaft interface, and signal protocol for your system.

Closed Loop Motor Control Applications

Robotics, CNC machinery, packaging, medical devices, and elevators are all common applications where feedback control systems can be found. Whether the application needs high precision, is in constant motion, or requires a high level of accuracy, encoders will continue to be a staple in the motor feedback industry.

Robotics and Absolute Encoders

Robotic systems demand precise joint positioning and reliable homing behavior. Absolute encoders excel in these environments because:

• They output a unique digital position value at every shaft location, eliminating the need for homing after power loss.
• Multi‑turn absolute encoders can track complete revolutions, even if power is removed.
• Improved safety: robots won’t “snap” to a default home position when powered on.
• Higher repeatability leads to more accurate picking, welding, assembly, and inspection operations.

CNC Machinery and Incremental Encoders

CNC machines require accurate, real‑time position feedback for coordinated motion control. Both encoder types can be used, but each has trade-offs:

Incremental Encoders

• Generate pulses proportional to shaft movement.
• Cost-effective and widely used in CNC spindles, stages, and axes.
• Require a homing routine at startup.
• Provide excellent resolution but not absolute position retention.

Absolute Encoders

• Provide direct position value without homing.
• Offer better accuracy and reduced downtime.
• Increasingly preferred in advanced CNC equipment.

ACURO AC58 Absolute Encoder	ACURO AD58 Absolute Encoder	ACURO AC36 Absolute Encoder	ACURO AD37 Absolute Encoder

Packaging and Encoders

Packaging applications depend on timing, synchronization, and speed tracking:

Absolute Encoders

• Enable precise positioning in sealing, cutting, filling, and sorting equipment.
• Reduce errors and improve consistency across large production batches.

Incremental Encoders

• Ideal for tracking conveyor speed or distance.
• Cost-effective with simple integration.

Medical Devices and Absolute Encoders

In medical environments, feedback devices must deliver reliable, repeatable performance:

• Absolute encoders retain position through power cycles, critical for imaging, robotic surgical systems, and automated dispensing.
• High precision improves diagnostic accuracy and enhances patient safety.
• Their reliability supports strict compliance standards.

ACURO AC36 Absolute Encoder	ACURO AD36 Absolute Encoder	ACURO AC58 Absolute Encoder

Elevators and Hollow-Bore Incremental Encoders

Elevators rely on feedback for speed control and smooth travel. Incremental hollow-bore encoders are typically chosen because:

• They measure velocity accurately and reliably.
• Hollow-bore designs simplify installation on motor or brake shafts.
• They are a cost-efficient solution for vertical transport systems where absolute multi‑turn position tracking is not always required.
• Allows to add a wheel behind the encoder for manually moving the motor shaft in terms of power loss.