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# Servomotors / Servo Drivers

Servomotors and Servo Drivers are provided for the purpose from replacing stepping motors to high-speed, high-precision control. Models with MECHATROLINK II communications are also provided. Concerning Servomotors/Servo Drivers, OMRON offers different products in different areas. So please click on the banner "Products links" in the top right corner to reach the country website nearest you.

 Overview Features Principles Classifications Engineering Data Further Information

Servo Motor Selection Flow Chart

 Explanation References Determine the size, mass, coefficient of friction, andexternal forces of all the moving part of the ServoMotor the rotation of which affects. --- Determine the operating pattern (relationshipbetween time and speed) of each part that must becontrolled.Convert the operating pattern of each controlledelement into the motor shaft operating pattern. Operation Pattern Formula The elements of the machine can be separated sothat inertia can be calculated for each part thatmoves as the Servo Motor rotates.Calculate the inertia applied to each element tocalculate the total load inertia of the motor shaftconversion value. Inertia Formulas Calculation of Friction TorqueCalculates the frictional force for each element,where necessary, and converts it to friction torquefor a motor shaft.Calculation of External TorqueCalculates the external force for each element,where necessary, and converts it to externaltorque of a motor shaft.Calculates the total load torque for the motor shaftconversion value. Load Torque Formulas Select a motor temporarily based upon the motorshaft converted load inertia, friction torque, externaltorque and r.p.m of a motor. --- Calculate the Acceleration/Deceleration Torquefrom the Load Inertia or Operating Pattern. Acceleration/DecelerationTorque Formulas Calculate the necessary torque for each part of theOperating Pattern from the Friction Torque, ExternalTorque and Acceleration/Deceleration Torque.Confirm that the maximum value for the Torque foreach operating part (Maximum Momentary Torque)is less than the Maximum Momentary Torque of themotor.Calculate the Effective Torque from the Torque foreach Operating part, and confirm that it is less thanthe Rated Torque for the motor. Calculation of MaximumMomentary Torque,Effective Torque Calculate Regenerative Energy from the Torque ofall the moving parts. Please see the usermanual of eachproductfor the detailson calculation of theregenerative energy. Check if the the number of encoder pulses meetsthe system specified resolution. Accuracy of Positioning Check if the calculation meets the specifications ofthe temporarily selected motor.If not, change the temporarily selected motor andre-calculate it. The following table
 Specialized Check Items Check Items Load Inertia Load Inertia ≤ Motor Rotor Inertia x ApplicableInertia Ratio Effective Torque Effective Torque < Motor Rated TorquePlease allow a margin of about 20%. * Maximum Momentary Torque Maximum Momentary Torque < MotorMaximum Momentary TorquePlease allow a margin of about 20%. *For the motor Maximum Momentary Torque,use the value that is combined with a driverand the one of the motor itself. Maximum Rotation Speed Maximum Rotation Speed ≤ Rated RotationSpeed of a motorTry to get as close to the motor's ratedrotations as possible. It will increase theoperating efficiency of a motor.For the formula, please see "Straight-lineSpeed and Motor Rotation Speed". Regenerative Energy Regenerative Energy ≤ Regenerative EnergyAbsorption of a motorWhen the Regenerative Energy is large,connect a Regenerative Energy AbsorptionResistance to increase the Absorptioncapacity of the driver. Encoder Resolution Ensure that the Encoder Resolution meetsthe system specifications. Characteristics of a Positioner Check if the Pulse Frequency does notexceed the Maximum Response Frequencyor Maximum Command Frequency of aPositioner. Operating Conditions Ensure that values of the ambient operatingtemperature/humidity, operating atmosphere,shock and vibrations meet the productspecifications.

*When handling vertical loads and a load affected by the external torque, allow for about 30% of capacity.

Formulas

Formulas for Operating Patterns

Inertia Formulas

Load Torque Formulas

Acceleration/Deceleration Torque Formula

Calculation of Maximum Momentary Torque, Effective Torque

Positioning Accuracy

Straight Line Speed and Motor Rotation Speed

Sample Calculations

(1) Machinery Selection

(2) Determining Operating Pattern

(3) Calculation of Motor Shaft Conversion Load Inertia

(4) Load Torque Calculation

(5) Calculation of Rotation Speed

(6) Motor Temporary Selection [In case OMNUC U Series Servo Motor is temporarily selected]

*Note that this value changes according to the Series.

(7) Calculation of Acceleration/Deceleration Torque

(8) Calculation of Maximum Momentary Torque, Effective Torque

(9) Result of Examination

Note:This example omits calculations for the regenerative energy, operating conditions, or positioner characteristics.

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