Soft Stop
Reducing the output gradually over a set time instead of zeroing it at once when the command is removed. In a sudden stop the inertia of the load hits the mechanics as an impact and suspended loads swing; a gradual stop spreads this energy over time. The ramp time is typically set from the same pot as the start ramp (RMP on the PT500).
A sudden stop has three consequences: shock in the mechanics, pendulum motion in a suspended load, and the sudden release of the energy the motor produces. A soft stop relieves all three.
- Mechanical life: Gears, chains and rope connections are strained most at the moment of a sudden stop; gradual deceleration noticeably lowers this peak force.
- Positioning accuracy: Because a soft stop reduces the speed while approaching the target, it improves the repeatability of the actual stopping point. Conversely, an overly long stop ramp increases the overtravel distance.
- Energy: In gradual deceleration the energy produced by the motor is spread over time; the voltage rise on the supply line is reduced to the same degree.
The limit of a soft stop is that it cannot hold the load in the air. If the load can fall back under gravity, a mechanical brake or a self-locking gearbox is required regardless of the stop ramp.
On automatic gates and barriers, a soft stop reduces the closing impact and so lowers both the noise and the hinge load.
The context in which this term is used: DC Motor Driver Selection Guide