Overview of Inverter Selection Selecting the Motor Capacity Select a motor before selecting the Inverter. Calculate the load inertia in the application, calculate the motor capacity and torque required to handle the load, and select an appropriate motor. ● Calculating the Motor Shaft Conversion Inertia Use the following equations to calculate the inertia of all of the parts and convert that to the motor shaft conversion inertia. J w = J 1 + J 2 = M 1 D 2 8 + M 2 D 2 ■ Simple Selection Method (Calculation of the Required Output) J w J w : Inertia (kg m 2 ) J 1 : Inertia of cylinder (kg m 2 ) J 2 : Inertia due to object (kg m 2 ) 4 x 10 -6 (kg m 2 ) D: Diameter (mm) M 1 :
Mass of cylinder (kg) M 2 : Mass of object (kg) With this method, you select the motor based on the output (W) required when the motor is rotating at a steady rate. This method does not include the involved calculations for acceleration and deceleration, so add some extra capacity to the calculated value when selecting the motor. This is a simple way to calculate the size of motor needed in equipment that operates at a steady rate for long periods, such as fans, conveyors, and mixing machines. This method is not suitable for the following kinds of applications:
•Applications requiring sudden start-ups •Applications where the equipment starts and stops frequently •Applications where there is a lot of inertia in the transmission system •Applications with a very inefficient transmission system J w = J 1 + J 2 + J 3 + J 4 = M 1 D 2 8 + M 2 D 2 8 x 10 -6 (kg m 2 ) 1 2 + D 2 D 2 1 + M 3 D 2 4 1 + M 4 D 2 4 1 J w : Inertia (kg m 2 ) J 1 : Inertia of cylinder 1 (kg m 2 ) J 2 : Inertia of cylinder 2 (kg m 2 ) J 3 : Inertia due to object (kg m 2 ) J 4 : Inertia due to belt (kg m 2 ) D 1 : Diameter of cylinder 1 (mm) D 2 : Diameter of cylinder 2 (mm) M 1 : Mass of cylinder 1 (kg) M 2 : Mass of cylinder 2 (kg) M 3 :
Mass of object (kg) M 4 : Mass of belt (kg) J 1 D 1 Roller 1 J w = J 1 + D 1 D 2 2 J 2 + M D 2 1 4 x 10 -6 (kg m 2 ) J w M D 2 J w : Inertia of entire system (kg m 2 ) J 2 : Inertia of roller 2 (kg m 2 ) J 1 : Inertia of roller 1 (kg m 2 ) Roller 2 J 2 D 1 : Diameter of roller 1 (mm) D 2 : Diameter of roller 2 (mm) ● Linear Motion: Steady Power P O (kW) W m • W • V M: Effective mass of workpiece (kg) Motor µ P0 = 6120 • η Load J L = J 1 + G 2 (J 2 + J w ) (kg m 2 ) η V µ : Friction coefficient W: Weight of moveable load (kg) V : Speed of moveable load (m/min) h: Efficiency of reduction mechanism (transmission) Gear J L : Motor shaft conversion load inertia (kg m 2 ) J w :
Load inertia (kg m 2 ) Motor J 2 : Load gear inertia (kg m 2 ) J 1 : Motor gear inertia (kg m 2 ) ● Rotational Motion: Steady Power P O (kW) T Z 1 : Number of gear teeth on motor side Z 2 : Number of gear teeth on load side η 9535 • η N P0 = T • N Gear ratio G = Z 1 /Z 2 Motor T N η : Load torque at load axis (N m) : Speed of load axis (r/min) :
Efficiency of reduction mechanism (transmission) ● Calculating the Motor Shaft Conversion Torque and Effective Torque Calculate the total combined torque required for the motor to operate based on the acceleration torque due to the motor shaft conversion load inertia (calculated above) and the load torque due to friction force and the external force applied to the load. ■ Detailed Selection Method (R.M.S. Calculation Method) With this method, you calculate the effective torque and maxi- mum torque required in the application's operating pattern. This method provides a detailed motor selection that matches the operating pattern.
• Acceleration Torque Speed (rotational) Acceleration Torque (T A ) T A = 2 π N 60t A J M + J L η (N m) η N T A : Acceleration Torque ( N m) J L : Motor shaft conversion load inertia ( kg m 2 ) J M : Inertia of motor itself ( kg m 2 ) η : Gear transmission efficiency N: Motor speed (r/min) Time t M Acceleration time (s) A • Motor Conversion Load Torque (External and Friction) 2 D D: Diameter (mm) T W = F x 10 − 3 (N m) F: External torque (N) Friction force in general: TW: Load torque (N m) F = µ W µ : Friction coefficient W: Weight of moving parts η G T L = Tw (N m) η : Gear transmission efficiency Z 1 : Number of gear teeth on motor side Z 2 :
Number of gear teeth on load side T L : Motor shaft conversion load torque (N m) T w : Load torque (N m) M Gear (reduction) ratio G = Z 1 /Z 2 58 Overview of Inverter Selection