Stopping Modes

Publish Date: Sep 06, 2006 | 2 Ratings | 3.00 out of 5 | Print
There are three different methods for stopping motors: the Halt method, the Decelerate method, and the Kill method.

Halt
The Halt method causes an abrupt, instantaneous stop at maximum deceleration. The motion controller brings the motion to as instantaneous stop as possible depending on the inertia of the system. For servo boards, motion is stopped immediately by the axis controller and PID loop, which sets the destination position value equal to the present position when the stop motion command is executed. For stepper boards, the board stops motion immediately by terminating the step pulse generation when the stop motion command is executed.

The Halt method could be used to implement an emergency stop mechanism, which would stop a system when the system must be stopped instantly to prevent damage to human life or machinery. The disadvantage of the halt method is the amount of jerk the motor experiences. Using the halt method too often can lead to excessive wear on the motor.

Decelerate
The Decelerate method decelerates motors in the same way they would normally decelerate if they were allowed to run to the end of the profile. This method uses the preprogrammed deceleration rate to stop the motor. If the deceleration rate is low, the motors will stop more slowly; if the deceleration rate is high, the motors will stop more quickly. This method is useful if you need to stop the motor but do not need to stop it particularly quickly. The benefit of this method is that it does not have the high jerk potential that the Halt method has.

Kill
The Kill method takes the longest amount of time to stop. In the other methods, the controller actively works to stop the motor. The Kill method however, simply cuts power to the motor. On servo boards, the board sets the motor drive signal to zero and a motor off condition occurs in the per-axis servo circuit. This mode turns off position tracking and allows the motor to freewheel. On stepper boards, the board stops motion immediately by terminating the step pulse generation and activating the inhibit output. On a motor with a large amount of inertia, the kill command would take a long time to stop the motor. The Kill method can also be used to allow the motors of a system to turn freely so that manual adjustments can be made.

The figure below shows these different stopping modes.





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