Considering the Driving Motor

When selecting a driving motor required to rotate the ball screw, normally take into account the rotational speed, rotational torque, and minimum feed amount.

When Using a Servomotor

Rotational Speed

The rotation speed required for the motor is obtained using the equation (52) based on the feed speed, ball screw lead and reduction ratio.

Required Resolution

Resolutions required for the encoder and the driver are obtained using equation (53) based on the minimum feed amount, ball screw lead, and reduction ratio.

Motor Torque

The torque required for the motor differs between uniform motion, acceleration, and deceleration. To calculate the rotational torque, see "Considering the Rotational Torque" .

Maximum torque
The maximum torque required for the motor must be equal to or below the maximum peak torque of the motor.
T_max ≦ Tp_max
T_max: Maximum torque acting on the motor
Tp_max: Maximum peak torque of the motor
Effective torque value
The effective value of the torque required for the motor must be calculated. The effective value of the torque is obtained using equation (54).

The calculated effective value of the torque must be equal to or below the rated torque of the motor.

T_rms≦ T_R
T_R: Rated torque of the motor (N･mm)

Inertial Moment

The inertial moment required for the motor is obtained using equation (55).

(It is normally between 3 to 10. However, it varies depending on the motor and the driver. Check the specific value in the motor manufacturer's catalog.)
The inertial moment of the motor must be equal to or above the calculated J_M value.

When Using a Stepping Motor (Pulse Motor)

Minimal Feed Amount (per Step)

The step angle required for the motor and the driver is obtained using equation (56) based on the minimum feed amount, ball screw lead, and reduction ratio.

Pulse Speed and Motor Torque

Pulse speed: The pulse speed is obtained using equation (57) based on the feed speed and the minimum feed amount.
Torque required for the motor: The torque required for the motor differs between the uniform motion, the acceleration, and the deceleration. To calculate the rotational torque, see "Considering the Rotational Torque".

Thus, the pulse speed required for the motor and the required torque can be calculated in the manner described above. Although the torque varies depending on the motors, normally the calculated torque should be doubled to ensure safety. Check if the torque can be used in the motor’s speed-torque curve.