How to select Servo motors?

HOW TO SELECT SERVO MOTORS?

Easy steps to choose the perfect servo motor for your automation system

SERVO MOTOR SIZING AND SELECTION

When choosing a servo motor for a particular application, there are many elements to take into account, including the needed speed, torque or force, motion profile, physical envelope that is available, and environmental concerns. 

This means that the selected motor solution must deliver the necessary load torque and speed, fit in the available area, and function properly under the application’s particular environmental conditions.

A servo motor is a component of a larger mechanism that gives a load motion so that it can be moved, machined, lifted, examined, etc. 

The muscle that supplies the requisite torque, force, and speed (required load point) to carry out a certain duty is the servo motor. 

A motor sizing tool that calculates the load points needed by a motor and analyzes data on the load, transmission components, and motion profile to choose a motor from the motor database that matches the load parameters is the quickest and most accurate approach to find these needs.

The sizing tool checks for the best solution as the initial load points are established and narrows the available motor options based on the necessary torque, speed, inertial ratio, and associated margins learned from the motor ratings.

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HERE ARE THE STEPS FOR THE PROCESS OF SIZING FOR CORRECT SERVO MOTOR:

1. ESTABLISH THE NECESSARY VOLTAGE.

The equipment’s available power is the first and simplest consideration. Servos are compatible with single phase or three phase electricity and come in variants that operate at 100 VAC, 200 VAC, and 400 VAC.

2. DESCRIBE THE MOTION PROFILE FOR THE APPLICATION.

Plot the necessary motor speeds for a cycle on equipment that performs repetitive tasks. Because servomotors cannot change their speed in steps and are not magical, it is important to allow for acceleration and deceleration time.

 Determine the maximum speed and acceleration needed for non-repetitive activities like milling.

3. ESTABLISH THE REQUIRED TORQUE FOR THE MOTION APPLICATION.

The amount of “muscle” required to rotate a mechanism is known as its torque, which can be generated from three different sources: friction, the mechanism’s inertia being accelerated, and external forces like pressing against something or gravity.

 Although it is the most challenging to calculate precisely, this step in the selection process is also the most forgiving. 

Determine the system’s inertia for each component and add the results. On the Internet, you can easily get the formulas for determining the rotational inertia of different shapes.

To determine the load’s acceleration torque, multiply the acceleration by the load’s inertia. Calculate any external forces as well as the friction forces for sliding loads and the gravity forces for vertical loads. 

To compute the torque, multiply each force by the radius it is exerting force on (referred to as the “moment”).

In the worst-case situation, sum up all the torque figures to determine the peak torque. This is often when the machine is accelerating at its fastest rate or when it is carrying its heaviest load.

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Calculate the necessary continuous torque by adding the torque values from external forces, gravity, and friction.

The root-mean-squared (RMS) computation should be used to determine the continuous torque demand, however this is laborious without a software tool.

4. DETERMINE THE IDEAL INERTIA RATIO FOR THE MOTION SYSTEM.

Although it is sometimes disregarded by beginners to servo sizing, calculating inertia ratio is likely the most crucial step in assessing a servo system’s performance.

 The ratio of the inertia of the load to the inertia of the motor’s rotor divided by the square of the gear reduction is known as the inertia ratio.

5. MAKE A SERVO MOTOR CHOICE HESITANTLY.

Now that the essential standards for selecting a servo motor have been established, it is time to search the product selection guide for the motor that best satisfies these standards.

Find a motor and drive that has a rated speed, continuous torque, and peak torque rating greater than the figures determined above, and that matches the supplied voltage.

To discover a motor that satisfies the inertia ratio requirement for the servo drive you are using, look at the motor’s rotor inertia.

6. VERIFY THE APPROPRIATE SERVO GEARING.

Servo Motors can operate at zero rpm or many thousands of rpm and still deliver their full rated torque. A small number of machines can benefit from high speeds without gear reduction. 

The three methods that gear reduction adapts the servo to the load are by decreasing speed, increasing torque, and decreasing inertia ratio. The gear ratio lowers the inertia ratio by the square of the gear ratio, which is the most significant effect. 

The gear ratio also increases torque proportionally. It is simple to include in the gearbox inertia into the torque and inertia calculations because gearbox manufacturers list the inertia of the servo-grade gearboxes.

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7. THIS TIME, REALLY CHOOSE A MOTOR.

Most of the available motors were probably capable of much greater speeds than were required in Step 5 (tentative motor selection). To calculate the starting gear ratio, divide the motor speed by the needed speed and round down.

 To determine the new needed torque, divide the original required torque by the gear ratio. This will reduce the options to just a few motors.

Find a motor with a good inertia ratio next. Choose the motor with the lower inertia ratio if two motors appear to be equal. Repeat this step a few times using motors with various rated speeds because it’s likely that there are multiple workable solutions.

Check all your servo motors requirements by here.

8. ADD A SERVO DRIVE AND OTHER POWER-TRANSMISSION COMPONENTS TO COMPLETE THE DESIGN.

After deciding on a servo motor, pick a servo drive that is rated for the right input voltage and has enough output current to drive the servo motor.

Servo drives can be managed via a variety of interface types. These interfaces comprise analog control, pulse-and-direction digital control, and various servo networks.

 In comparison to alternative interfaces, a servo network offers faster control and feedback, less wiring, and better diagnostics capabilities.

Finally, make a decision on any options, including external braking resistors, shaft seals, holding brakes for vertical loads, and keyed motor shafts.

Practice makes perfect when it comes to choosing the optimum servo system for a certain application. Verify your findings with the manufacturer or distributor if you have any doubts. Contact Epoch Automation – A leading provider of all automation Solutions.

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