Xenus Plus User Guide 16-01344 Rev 06
Copley Controls 20
2.2.4: Current Mode and Current Loop
Current Loop Diagram
As shown below, the “front end” of the current loop is a limiting stage. The limiting stage accepts a
current command, applies limits, and passes a limited current command to the summing junction.
The summing junction takes the limited current command, subtracts the actual current
(represented by the feedback signal), and produces an error signal. This error signal is then
processed using the integral and proportional gains to produce a command. This command is then
applied to the drive’s power stage.
Current Loop Inputs
• The drive’s analog or PWM inputs.
• A network command, CAN, EtherCAT or RS-232 Serial.
• A CVM control program.
• The drive’s internal function generator.
In velocity or position modes, the current command is generated by the velocity loop.
Offset
The current loop offset is intended for use in applications where there is a constant force applied to,
or required of, the servomotor and the system must control this force. Typical applications would be
a vertical axis holding against gravity, or web tensioning. This offset value is summed with the current
command before the limiting stage.
Limits
The current command is limited based on the following parameters:
Maximum amount of time that the peak current can be applied to the motor before it must
be reduced to the continuous limit or generate a fault.
For more details, see I
2
T Time Limit Algorithm (p. 139).
Note: Although the current limits set by the user may exceed the drive's internal limits, the
drive operates using both sets of limits in parallel, and therefore will not exceed its own
internal limits regardless of the values programmed.
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