Skip to main content
blog | Applications Sizing - Part 1: Getting Started Sizing Servos |
|
2 minute read

Never sized a servo before? Well, we want to share with you some of the best practices we have found over the years. Over the next few months, we will continue this series with a variety of tidbits that will help you become more comfortable with the job of sizing a servo. In this post, we’ll start with the basics of good preparation.

It begins by understanding the different components that make up a servo motor and drive system. Servos are closed loop systems because they regulate some desired function by incorporating feedback – much like the cruise control in your car. You set the desired speed and the cruise control determines how much throttle is required to keep the car moving at the desired speed. In the servo systems we deal with, a feedback device provides constant feedback between motor and drive in order to precisely regulate the speed and/or torque of the motor being driven. Most often these are highly dynamic systems involving rapid load accelerations and decelerations. They operate in all 4 quadrants, meaning they control torque and speed whether positive or negative.

Four Quadrant Operation

Sizing a servo requires a system solution. The system includes a definition of the mechanical load, motion profile including positioning requirements, the servo motor characteristics, and the environment in which the motor and other components are placed. 

Let’s begin with an understanding of the implications of the mechanical load and motion requirements. Basic Newtonian physics teaches us that force (or torque in rotary terms) is proportional to the mass (rotary inertia) times the acceleration rate, whether positive or negative. Therefore, it’s important to accurately define the mechanics, specifically the masses in motion, and the required motion profile. Along with the motion profile it’s important to understand the actual positioning requirements of the load in terms of resolution, accuracy and repeatability (something we’ll touch on in a future blog post). This will be directly affected by the feedback device selection, but also any lost motion such as backlash or compliance in the mechanical system.

Unless a direct drive motor system is being considered, the mechanism will include one or more mechanical transmissions. A linear to rotary transmission might be accomplished by a pulley driven belt or screw based mechanism like a ballscrew - just as a couple of examples.

Servo Mechanisms

Rotary transmissions include gearboxes or belt driven reducers providing speed reduction by means of different size pulleys. In some applications the part being moved makes a significant contribution to the total moving mass. A changing mass as in the case of robotic systems, must also be understood since the amount of total load change can be a factor in the tuning of the servo drive.

The components in motion need to have their inertias summed and reflected back to the motor shaft. In addition to the inertia, external forces, friction and inefficiencies need to be taken into consideration.  All of this will determine the speed/torque characteristics required to meet the performance criteria of your application.

So that's quite a bit to take in for our first venture into sizing, but hang in there, it will all make sense as we tie this together.  Before we close this post, let's quickly review some of the key elements to consider:

  1. Understand your mechanical load and how it will connect to the servo motor
  2. Motion profile and positioning requirements
  3. The characteristics of the servo motor technology being considered
  4. The environment all this will operate in
 
Try out Kollmorgen’s MOTIONEERING Online Sizing tool and learn about what parameters you need to run through a sizing exercise.

Consult an Expert

AKMA Servo Motors

The lightweight AKMA servo motor is designed for harsh environments like food and beverage processing, and delivers performance and reliability.
Learn More

Engineer the Exceptional

Learn how to engineer exceptional machines, robots and vehicles with the highest-performing, most reliable motors, drives, automation solutions and more.

Learn More

Related Resources

Accelerating the Development of Next-Generation Prostheses and Exoskeletons >

Learn how Kollmorgen servo technology is helping OEMs accelerate the design of next-generation prostheses and exoskeletons.

Stop, hold and go safely: Motion tuning for vertical loads >

When designing motion for applications such as vertical gantries and hoists, you need to take special care to ensure operator safety and operational efficiency. Let’s discuss best practices for meeting the particular challenges involved.

What are the Five Major Components of a Brushless Servo Motor >

Servo motors are used in numerous markets to power machines, instruments, robots, and other factory automation applications. This blog addresses five major elements of a conventional brushless DC servo motor: the rotor, stator, bearings, feedback and…
What is considered a low voltage motor?

What is Considered a Low Voltage Motor? >

The Low Voltage Directive defines low voltage from 50 – 1000 Vac, or 120 – 1500 Vdc, which is based on the mains voltage used to power the electrical system and ties in with specific IEC regulations on safety and risk of shock and arcing. When low…
Servo Motor Design Considerations for Hazardous Environments

Servo Motor Design Considerations for Hazardous Environments >

While servo motors and drives are prevalent in a wide variety of industrial applications, what should be considered when they operate in extreme or hazardous environments? In many cases, the motor itself operates in the extreme environment, while the…

What are the basic elements of a servo system? >

Working with motion control experts like Kollmorgen makes selecting a servo system easier and faster, resulting in an optimal system for the application.

How to Customize a Servo Motor - Standard vs Custom >

When and how to customize a standard servo motor depends on the predicted benefits derived from the customization that should include a solution tied to form, fit, and function. Learn more.

The Big Debate – Stepper vs Servo >

What is the best motor technology to use in a motion control application? There are numerous technologies to create motion, from hydraulic to pneumatic or electromechanical. In the world of precision motion control, many machine designers face a…

Bandwidth, Gain and Phase Margin in Servo Systems: What is Phase Margin? >

Phase margin is a measurement in the frequency domain, taken from a Bode plot, that calculates the amount of phase lag above -180 degrees at the point on the amplitude plot that crosses 0dB (gain cross over frequency).