User Constants - YASKAWA SGM Series User Manual

The mechanical system will start to vibrate at the upper limits for the position and speed loop
gain. Do not exceed these limits. Generally position loop gain cannot be increased beyond the
characteristic frequency of the mechanical system.
Example: Articulated Robots
Using harmonic gears produces a mechanism with extremely low rigidity.
Characteristic frequency of the mechanical system: 10 to 20 Hz
Allowable position loop gain: 10 to 20 (1/s)
Example: Chip Mounters, IC Bonders, Precision Machine Tools
Characteristic frequency: 70 Hz or more.
Position loop gain: 70 (1/s) or more.
The response of the servo system (Controller, Servodriver, Servomotor, detector, etc.) is cru-
cial to the response requirements, but a highly rigid system is also needed as well.

5.9.2 User Constants

J Cn−0003: Load Moment of Inertia
The load moment of inertia specifies motor axis converted load moment of inertia.
Specify the load moment of inertia as a percentage of the motor's rotor moment of inertia (mo-
tor moment of inertia = 100%).
J Cn-0004: Speed Loop Gain
The Speed Loop Gain sets the speed loop response. The response is improved by setting this
user constant to the maximum value in a range that does not cause vibrations in the mechanical
system.
J Cn-0005: Speed Loop Integration Time Constant
The speed loop has an integration element that enables response to micro-inputs. Because this
integration element can produce a delay in the servo system, positioning set time increases and
response slows as the time constants increase. The integration time constant must be increased,
however, to prevent machine vibration if the load moment of inertia is large or the mechanical
system includes an element prone to vibration. The following equation can be used to calculate
a guideline value.
T ≧ 2.3 ×
i
Ti: Integration time constant [s]
Kv:Speed loop gain [Hz]
J Cn-0017, 0018: Torque Reference Filter Time Constant
When a ball screw is used, torsional resonance may occur that increases the pitch of the vibrat-
ing noise. This oscillation can sometimes be overcome by increasing the torque reference filter
1
2π × K
v
5 -21
5.9 Adjustments
5