YASKAWA 16-bit Rated Output 100W Absolute Encode SGMAH-01AAA4C AC SERVO MOTOR RPM: 3000

The displacement angle is determined by the following relationship:
X = (Z ÷ 2π) × sin(Ta ÷ Th) where:
Z = rotor tooth pitch
Ta = Load torque
Th = Motors rated holding torque
X = Displacement angle.

Therefore if you have a problem with the step angle error of the loaded motor at rest you can improve this by changing the “stiffness” of the motor. This is done by increasing the holding torque of the motor. We can see this effect shown in the figure 5.
Increasing the holding torque for a constant load causes a shift in the lag angle from Q2 to Q1.
Step Angle Accuracy One reason why the stepper motor has achieved such popularity as a positioning
device is its accuracy and repeatability.
Typically stepper motors will have a step angle accuracy of 3 – 5% of one step. This error is also noncumulative from step to step. The accuracy of the stepper motor is mainly a function of the mechanical
precision of its parts and assembly. Figure 9 shows a typical plot of the positional accuracy of a stepper motor.

 

Step Position Error
The maximum positive or negative position error caused when the motor has rotated one step from the previous holding position.
Step position error = measured step  angle - theoretical angle

Positional Error
The motor is stepped N times from an initial position (N = 360°/step angle) and the angle from the initial position