αSTEP/Stepper Motor Specifications

Description of Specification Items

Maximum Holding Torque

Maximum holding torque (holding force) the motor has when power is supplied (at rated current) but the motor is not rotating. (With geared types, the value of holding torque considers the permissible strength of the gear.)
Depending on the product, the value may decrease due to automatic current cutback function during motor standstill.
For the actual value, check the holding torque at motor standstill.

Rotor Inertia

This refers to the inertia of the rotor inside the motor. This is necessary when the required torque (acceleration torque) for the motor is calculated.

Rated Current

The rated current is determined by the motor temperature rise. It is the current value that can flow to the motor windings continuously at motor standstill. As a general rule, the current setting of the driver must be the rated current.

Basic Step Angle

The angular distance (in degrees) that the motor moves upon input of one pulse signal to the driver. It differs depending on the motor structure and excitation mode.

Gear Ratio

This is the ratio of the rotation speed between the input speed from the motor and the speed of the gearhead output shaft. For example, a gear ratio of 10 indicates that when the input speed from the motor is 10 r/min, the gearhead output shaft speed is 1 r/min.

Permissible Torque

The permissible torque represents the maximum value limited by the mechanical strength of the gearhead output shaft when operated at a constant speed.
For the types other than the TS geared, PS geared, PN geared, HPG geared, and harmonic geared types, the total torque including acceleration and deceleration operation torque should not exceed the permissible torque.

Maximum Instantaneous Torque (TS geared, PS geared, PN geared, HPG geared, and harmonic geared type)

The maximum torque that can be applied to the gearhead output shaft during acceleration and deceleration operation such when a load inertia is started and stopped.

Holding Torque at Motor Standstill

While Power is ON: Holding torque when the automatic current cutback function is active (factory setting).
Electromagnetic Brake: Static friction torque when the electromagnetic brake is activated at standstill. (Electromagnetic brake is power off activated type.)

Speed Range

This is the range of the operable rotation speed on the gearhead output shaft.

Backlash

This is the play of the gearhead output shaft when the motor shaft is fixed.
When positioning in bi-direction, the positioning accuracy is affected.

Power Supply Input

The current value of the power input is the maximum input current value of the driver. (The input current varies according to the rotation speed.)

Excitation Mode

The driver has a function that can change the motor's step angle.
The step angle value at which the motor can be driven when setting is shown in the table. (The step angle value for microsteps is explained separately.)

Setting Speed Range

The range of rotation speeds that can be set with the combination of the motor and the driver.

Speed Accuracy

The degree of error in operating speeds due to individual differences in drivers, temperature, and aging.

How to Read Rotation Speed-Torque Characteristics

The characteristics diagram shows the relationship between the speed and torque when a motor is operated.
The required speed and torque is always used when selecting a motor. On the graph of characteristics, the horizontal axis expresses the speed at motor output shaft while the vertical axis expresses the torque.

The speed - torque characteristics are determined by the motor and driver, so they vary greatly based upon the type of the driver used.

① Maximum Holding Torque

Maximum holding torque (holding force) the motor has when power is supplied (at rated current) but the motor is not rotating.
Depending on the product, the value may decrease due to automatic current cutback function during motor standstill.
For the actual value, check the holding torque at motor standstill.

② Pullout Torque

Maximum torque that can be generated at each rotation speed.
When selecting a motor, be sure that the required torque falls within this curve.

• *The figure below shows the pullout torque when no clean damper or inertial load is installed (for reference).

③ Maximum Starting Frequency (fs)

This is the maximum pulse speed at which the motor can start and stop instantaneously (without acceleration/deceleration time) when the frictional load and load inertia of the motor are 0.
Driving the motor at a pulse speed of this rate or more will require a gradual acceleration/deceleration. This frequency drops when there is a load inertia on the motor.

Load Inertia - Starting Frequency Characteristics

The figure below shows the speed - torque characteristics of the RKII Series stepper motor.