Example explanation: How to choose the appropriate servo motor

Example explanation: How to choose the appropriate servo motor
The following is a detailed process of selecting a suitable servo motor through specific examples:

1、 Example background

A robotic arm on an automated production line needs to drive a 50kg disk to rotate, with a diameter of 500mm and a high-speed requirement of 60rpm. Now we need to choose a suitable servo motor and reducer for this disc.

2、 Selection steps

1. Calculate the moment of inertia of the disc

We need to calculate the moment of inertia of the disk. The moment of inertia is a physical quantity that describes the magnitude of an object's inertia during rotation. For a disk, the formula for calculating its moment of inertia is:

JL=MD²/8

Among them, M is the mass of the disk, and D is the diameter of the disk. Substitute the known values into the formula to obtain:

JL=50 × (500/1000/2) ㎡× π× 8 ≈ 15625kg · cm ² (here, to simplify the calculation, the influence of π is ignored, and accurate values should be used in actual calculations)

Note: The calculation result here is an approximate value, and more accurate formulas and values should be used in actual calculations.

2. Determine the load inertia ratio

When selecting a servo motor, it is necessary to ensure the matching relationship between the load inertia and the motor inertia. It is usually recommended that the load inertia be less than three times the motor inertia to ensure the dynamic response performance of the system. However, in practical applications, this ratio still needs to be adjusted according to specific load characteristics and action modes.

3. Choose servo motors and reducers

Assuming there are two different power servo motors to choose from, namely 400W and 500W. The rotor inertia and high speed parameters of these two motors are known. Now it is necessary to select suitable motors and reducers based on these parameters.

For a 400W motor, assuming its rotor inertia is 0.277kg · cm ² and high speed is 3000rpm. If choosing this motor, it is necessary to calculate the required reduction ratio R of the gearbox, so that the load inertia converted to the motor shaft is less than 3 times the motor inertia. According to the formula:

15625/R²<3×0.277

Understood: R²>18803， That is, R>137 (taking integer solutions here, more accurate values should be used in actual calculations). However, at this time, the output speed of the motor is 3000/137 ≈ 22rpm, which is lower than the high speed of 60rpm required by the disc, so this motor does not meet the requirements.

For a 500W motor, assuming its rotor inertia is 8.17kg · cm ² and high speed is 2000rpm. Similarly, calculate the required reduction ratio R of the gearbox so that the load inertia converted to the motor shaft is less than three times the motor inertia. According to the formula:

15625/R²<3×8.17

Understood: R²>637， That is, R>25 (taking integer solutions here, more accurate values should be used in actual calculations). At this time, the output speed of the motor is 2000/25=80rpm, which is greater than the high speed of 60rpm required for the disc, so this motor meets the requirements.

In summary, by calculating the moment of inertia of the disc, determining the load inertia ratio, and selecting servo motors and reducers, we can conclude that for the robotic arm on this automated production line, choosing a 500W servo motor and corresponding reducer is a suitable choice. This motor can meet the torque and speed requirements for disc rotation, while ensuring the dynamic response performance of the system.

Please note that the above selection process is a simplified example, and in the actual selection process, more factors need to be considered, such as the accuracy, reliability, cost, and maintenance of the motor. Therefore, in practical applications, it is recommended to collaborate with professional servo motor suppliers or engineers to ensure the selection of servo motors that are suitable for your application.