Zero Servo is a position control function that stops and holds the motor shaft. The drive safeties the stopped motor and an external force will not move the motor.
When you enable the Zero Servo function, the drive will save the home position. The drive can correct the motor position and put the motor into the home position when the load rotates the motor.
To enable Zero Servo, set H1-xx = 72 [MFDI Function Selection = Zero Servo]. The drive starts Zero Servo when the MFDI terminal set for Zero Servo [H1-xx = 72] activates and the motor speed decreases to less than the value set in b2-01 [DC Injection/Zero SpeedThreshold]. The drive stops and holds the motor in the Zero Servo start position. When Zero Servo is enabled, the drive will hold the motor in position when the frequency reference increases to more than the value set in b2-01. When Zero Servo is enabled, the drive will hold the motor in position when the frequency reference increases to more than the value set in b2-01.
Note:
Zero Servo is available when A1-02 = 3, 7 [Control Method Selection = Closed Loop Vector, PM Closed Loop Vector].
Figure 1. Zero Servo Time Chart
Monitor U6-22 [ZeroServoPulse Move] shows the difference between the position of the motor shaft and the Zero Servo start position when Zero Servo is enabled. To find the difference, divide the number of pulses shown in U6-22 by 4.
When the position of the motor shaft is in the range of “Zero Servo start position ± b9-02 [Zero Servo Completion Window]”, the drive will activate an MFDO set for Zero Servo Complete [H2-xx = 33].
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Do not let the Zero Servo function hold 100% load for long periods of time. When the application must use Zero Servo to hold 100% load for long periods, operate in less than 50% of the drive rated output current or use a larger capacity drive.
If Zero Servo holds the load for too long in 50% or more of the drive rated output current, it will cause damage to the drive.
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Note:
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When you use the Zero Servo function, keep the Run command ON. If the Run command is OFF, the drive will not hold the motor shaft in position.
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When you turn oFF the Zero-Servo command, the terminal set for Zero Servo Complete will deactivate.
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If A1-02 = 7 [PM Closed Loop Vector] and an external force rotates the motor during Zero Servo, the drive will detect dv4 [Inversion Prevention Detection]. To prevent dv4 detection, increase b9-01 [Zero Servo Gain] or increase the number of pulses set in F1-19 [Deviation 4 Detection Selection].