Aerotech UNIDEX 600 Series, User Manual

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AerTune U600 User’s Guide
5-30
Aerotech, Inc.
Version 1.4
5.7. Tuning With Tachometer Feedback
The UNIDEX 600 Series controller configures easily for controlling motors with external
tachometers providing velocity feedback. To configure the controller for an external
tachometer based Velocity Loop, the inherent digital Velocity Loop operation within the
controller must be disabled. This is done by setting the digital servo loop proportional
gain (Kp) and the integral gain (Ki) to zero. The servo system’s Velocity Loop must be
adjusted by the potentiometers on the amplifier for the particular
motor/tachometer/amplifier/load combination.
When configured this way, the analog outputs of the UNIDEX 600 that normally provide
current commands to amplifiers now deliver velocity commands to amplifiers accepting
tachometer feedback.
In this configuration, the servo system has the following characteristics.
•
The amplifier is configured to accept tachometer based velocity feedback
•
The amplifier regulates the Velocity Loop of the servo system. Velocity
Loop regulation is accomplished by the Pre-amp section of the amplifier
•
The proportional (Kp) and integral (Ki) gain parameters in the UNIDEX
600 controller’s servo loop have been set to zero (0), disabling its digital
Velocity loop functionality
•
The controller is now commanding velocity to the amplifier instead of
commanding torque.
5.7.1. Vff - Velocity Feed Forward
The Following Error (position error) that occurs while the axis is moving may be reduced
significantly by setting the velocity feed forward gain to one. When the velocity feed-
forward function is enabled (i.e., Vff = 1), an added voltage is summed with the velocity
command to the amplifier. This signal is proportional to the Velocity Command.
5.7.2. VGain - Constant Velocity Gain
The Following Error (position error) that occurs while the axis is moving at a constant
velocity may be reduced by setting the VGain parameter to a non-zero value. This causes
the velocity command to be increased proportionally by the commanded velocity, which
is scaled by the VGain servo loop parameter.
5.7.3. Servo Parameter Setup for Tachometer Feedback
When configuring a servo loop containing external velocity feedback from a tachometer,
the servo gain values shown in Table 5-2 are used.