Back to top

Acceleration limits in the S300/S600/S700 drives

There are three parameters in the S300, S600, and S700 drives that define the acceleration limits, or maximum acceleration ramp and deceleration ramp.  ACC and DEC are the acceleration and deceleration limits in the velocity loop.  They are labeled in DriveGUI software as "Acc. Ramp" and "Dec. Ramp".  In the Drive.exe software for the S600, the labels are "Setp. Ramp +" and "Setp. Ramp -".  When the drive is in velocity mode, these are the only acceleration limits that apply.  They are user defined and specific to each individual application.

However, when the drive is in position mode (closing position loop for motion tasking, electronic gearing, or analog position), there is a third acceleration limit that applies.  PTMIN is the acceleration limit in the position loop.  It also defines the deceleration limit in the position loop.  When the drive is in position mode, the position and velocity control loops are active.  Therefore all three acceleration and deceleration limits apply.

Since there is an acceleration limit applied in the position loop, the limits in the velocity loop are not needed.  But they are still active.  It is important to set the velocity loop acceleration and deceleration limits to a high (fast) ramp (or short time) so that they do not cause a delay in the velocity loop.  If the velocity loop limits are set to a slow ramp, then they will cause a delay in the velocity loop, translating into a long, slow oscillation.  The motor will appear to "run away" slowly, or drift, but in fact will be following a long, slow reversing motion.

The acceleration units are important to understand to prevent this situation.  The units can either be in speed per second, position per second squared, or in time (milliseconds to reach max speed).  The first two units are speed based, meaning a high value causes a fast ramp.  The time based unit means that the motor will take the specific number of millisecond to reach maximum speed.  A high value is a slow ramp.  Make sure to understand these units and set the acceleration limits appropriately in order to prevent the velocity loop delay and oscillation.