The jrk is designed to be part of a control system in which the output (usually a motor position or speed) is constantly adjusted to match a specified target value. To achieve this, it constantly measures the state of the system and responds based on the latest information. The information processing performed by the jrk is outlined in the diagram below:
In this diagram, each arrow represents a specific number measured or computed by the jrk, and the blue boxes represent the internal computations that each occur once per PID period. The PID period can be set in 1 ms increments and is one of about 50 configurable parameters that affect the behavior of the system. For more information about configuring the jrk, see Section 3. The jrk uses the following measurements to determine the output:
Every PID cycle, the jrk performs the following computations to determine the behavior of the motor (see Section 3.d for more information):
The resulting value becomes the duty cycle of the PWM (pulse width modulation) signal applied to the motor. A value of +600 corresponds to 100% duty cycle in the forward direction, a value of -600 corresponds to 100% duty cycle in the reverse direction, and a value of 0 corresponds to 0% duty cycle or off.
Various parameters and commands have an effect on the steps described above. For example, feedback may be turned off so that the jrk can become a simple speed controller; in this case the PID calculation is bypassed and the duty cycle target is just equal to the target minus 2048. In this mode, limits applied to the duty cycle continue to provide a useful way of preventing damage to the system. As another example, a command to turn the system off prevents the motors from being driven, but all measurements and calculations continue to occur normally.
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