• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • Advertise
  • Subscribe

Motion Control Tips

Automation • Motion Control • Power Transmission

  • News
    • Industry News
    • Editor Blogs
  • Controls
    • HMIs
    • PC-Based Controllers
    • PLCs + PACs
    • Stand-Alone Controllers
    • Software
  • Drives
    • Servo Drives
    • Stepper Drives
  • Encoders
    • Absolute Encoders
    • Incremental Encoders
    • Rotary Encoders
  • Mechanical
    • Bearings
    • Brakes + Clutches
    • Belt + chain
    • Couplings
    • Gears + Gearing
    • Lubrication
    • Shock + Vibration Mitigation
    • Springs + Rings + Seals
  • Linear
    • Actuators
    • Linear Motors
    • Linear Encoders
  • Motors
    • AC Motors
    • DC Motors
    • Brushless Motors
    • Gearmotors
    • Piezo Motors
    • Servo Motors
    • Stepper Motors
  • Systems
    • Conveyors + linear transport systems
    • Gantries + Stages
    • Rotary Tables
    • Grippers + End Effectors
    • Robotics
  • Networks
    • Connections + Sliprings
    • Fieldbuses
    • I/O
    • Sensors + Vision
  • Resources
    • FAQs
      • Motion Casebook
      • Motion Selection Guides
    • Suppliers
    • Video
You are here: Home / FAQs + basics / FAQ: What are servo feedback gains, overshoot limits, and position error limits?

FAQ: What are servo feedback gains, overshoot limits, and position error limits?

March 22, 2016 By Danielle Collins Leave a Comment

Servo tuning can be accomplished by several methods, but the most common way is to use a PID algorithm. The PID algorithm uses three feedback gains—proportional gain, integral gain, and derivative gain—to compare the commanded position (or velocity) with the actual value and issue commands to correct errors between the two.

Feedback Gains
Image credit: Thorlabs, Inc.

Feedback gains determine how hard the servo tries to correct or reduce the error between the commanded position and the actual position. Proportional gain is dependent on present error, integral gain is dependent on past error, and derivative gain is dependent on predicted future error.


Feedback gains

Proportional gain (Kp) determines the amount of restoring force (generated by the command voltage) that is applied to overcome the position error. The term “proportional gain” is used because its value is directly proportional to the positioning error. For example, if the proportional gain is 1.2 volts per encoder count, and the motor is 10 encoder counts from the commanded position, the command voltage will be 12.0 volts.

Proportional gain is the most important component of the PID algorithm, but a Kp value that is too high can cause the system to oscillate, to become under-damped, or to become unstable.

Often, as the servo controller works to decelerate the motor by reducing the command output, system friction overcomes the command voltage and causes the motor to fall short of the target.

Integral gain (Ki) overcomes this by producing a command that “pushes” the system to zero positioning error at the end of the move. The term “integral gain” is used because its command increases over time at the end of the move.

If sufficient positioning accuracy is achieved with the proportional gain, then integral gain may not be necessary. However, it is useful when steady-state (static) positioning is difficult to hold due to system disturbances, or when constant velocity motion is required.

Derivative gain (Kd) determines the restoring force that is proportional to the rate of change (derivative) of the positioning error. It works in conjunction with proportional gain to dampen the system response and reduce overshoot and oscillations.

Servo instability can occur if the derivative gain value is calculated too frequently, as it will begin to work against, rather than with, the proportional gain. To avoid this, the derivative sampling period can be increased.

Feedback Gains
The use of derivative gain in conjunction with proportional gain reduces settling time and overshoot.
Image credit: PMC Corporation

Overshoot limits

Derivative gain is used to set the overshoot limit, or the acceptable amount by which the servo can exceed the target position. While perfectly accurate positioning is desirable in theory, in real world applications, an overshoot limit that is too small will likely cause the system to be over-damped. Conversely, a very high overshoot limit gives good system response, but can lead to oscillations.

Feedback Gains
Each parameter of a PID loop affects the servo response differently, but in the end, they work together to minimize position error and overshoot.
Image credit: Thorlabs, Inc.

Position error limits

The principle behind servo control is the comparison of the system’s actual value versus the commanded value, and the difference between the commanded and actual position is the position error (also referred to as the “following error). As seen above, the purpose of feedback gains is to reduce the position error. The position error limit, however, is used to indicate a problem with the servo or with the tuning algorithm. The position error limit should be set to a value that would not be seen during normal operation, and the controller response should be programmed to stop the axis when this limit is reached or exceeded.

 

You Might Also Like

Filed Under: Controls, FAQs + basics, Motors, Servo Drives, Servo Motors Tagged With: feedback, feedback limit, overshoot limit, PID, servo gain, servo tuning

Reader Interactions

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

LEARNING CENTER

Design World Learning Center

Motion Control Handbook

“mct
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for Design Engineering Professionals.

RSS Featured White Papers

  • Robotic Automation is Indispensable for the Logistics Industry’s Continued Growth and Success
  • Reliable Linear Motion For Packaging Machines
  • Polymers Outperform Metals In Precision Gearing

Footer

Motion Control Tips

DESIGN WORLD NETWORK

Design World Online
The Robot Report
Coupling Tips
Linear Motion Tips
Bearing Tips
Fastener Engineering.
Wire and Cable Tips

MOTION CONTROL TIPS

Subscribe to our newsletter
Advertise with us
Contact us
About us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy | RSS