This feature was designed to allow the SST servo drive to excel in three application areas:  
  1. To allow axes to position accurately to a point and then become compliant ("allow itself to be pushed around" within user-defined limits), typically when a pin is engaged for mechanical registration.
  2. When used with axes that have compliant drive mechanisms and high static friction, this feature eliminates motor overheating and shutdowns that normally occur with other servo systems, and
   3. MoveDone Torque Fold-back provide a convenient, automatic method to clamp (apply a fixed force) at the end of a move.

The MoveDone torque fold-back feature reduces the torque available to the servo automatically once it detects that the move is complete (see MoveDone Output... directly above).
You can see how this feature is useful when you have to allow the endpoint of an axis to be compliant or when you want to clamp something with the axis under control at the end of the move without complicated software and encoder processing. It’s not immediately obvious why, however, it would help with axes that would otherwise have motor overheating or shutdown problems, so let’s expand on this:
It is not uncommon for inexpensive mechanics or long-travel axes to have significant compliance in the drive train and significant stiction (break-away friction) at the load. This will happen with heavy cantilevered loads run by belts or, when a worm gear box is driven with a compliant coupling, etc. In these situations, the load will periodically stop very near (close enough for the application), but not at the commanded position and then "stick" there (because, for example it has plain linear bearings under a large load.) A typical servo system responds by adding torque until the motor is at the exact position commanded, but often this torque is not enough to free the stuck load so, instead of moving the load it just winds-up the compliant mechanics (stretches the belt, etc.) The motor uses torque continuously to do this and heats up, reducing its continuous output capability and often intermittently shutting down because its ratings are exceeded. Using MoveDone Torque Fold-back in these situations will drastically increase the system reliability because this bad behavior is actively suppressed by limiting the torque at the end of the move to some low value. In addition, the motor will run cooler or be able to be reduced in size, and wear on the axis due to chronic wind-up (tension) is reduced.
With other digital servo drives, the only way around this problem is an expensive mechanical retrofit that is not required for the application, it is just required to keep the servo system "happy". Alternately, complicated software workarounds have to be employed with traditional servo control boards. The SST servo drive’s MoveDone Torque Fold-back feature eliminates the need for either of these expensive solutions, helping you keep you keep your material costs low while simplifying your control software development and enhancing your design flexibility.
In existing open-loop stepper motor applications where the mechanics exhibit this behavior, this effect is likely to go unnoticed until you try to drop-in a servo system. MoveDone Torque Fold-back eliminates the risk of this problem when an SSt servo system is dropped into your existing stepper motor applications.
The MoveDone Torque Fold-back feature (together with the RAS, Hard Stop Homing, Limits Switch Homing, Torque/Force Fold-back input feature and flexible input resolution) helps enable the use of simple low cost controls, that lack encoder feedback, even in machines that have less than perfect mechanics or where automatic endpoint clamping is required.