In motion control units, traversing commands are executed consecutively. The command parameters include, for example, the target coordinates, the traversing velocity, the acceleration and the target velocity (velocity in the target coordinate).
The board APCI-8008 have a Look-ahead mode, which allows you to combine multiple commands with one another and thus to optimise both velocity and acceleration, or depending on the axes, to limit drives. Consequently, automated velocity changes between traversing profiles can be adjusted.
Look-Ahead mode: das principle
The Look-ahead mode enables a contour, which includes several interpolation profiles, to be accelerated to the trajectory velocity and decelerated to the target position in a controlled manner. Here, the acceleration and braking ramps may be part of several traversing profiles as well.
If multiple spooled move commands, whose target velocities do not equal 0, are programmed consecutively, the target velocity of the profile entered last in the spooler is set to 0 (by the system software). Afterwards, the target velocities of the profiles entered before are temporarily set in a way so that the programmed trajectory acceleration can be used for deceleration at the end of the whole contour. This means that when a profile is programmed, the target velocities of the previous profiles are automatically adjusted (Look-ahead).
Maximum permitte velocity jump
With this mode, it is possible to define a maximum permitted velocity jump (MDVEL) for each axis. In case this velocity jump is exceeded with an axis, the target velocity of the corresponding profile (and of the adjacent profiles) will be automatically limited. Hence, the maximum permitted velocity jump is adhered to, and irrespective of the traverse distance of the programmed profiles, all target velocities can be reached with the programmed acceleration.