Position Tracking - Galil Motion Control CDS-3310 User Manual

Position Tracking

The Galil controller may be placed in the position tracking mode to support changing the target of an
absolute position move on the fly. New targets may be given in the same direction or the opposite
direction of the current position target. The controller will then calculate a new trajectory based upon
the new target and the acceleration, deceleration, and speed parameters that have been set. The motion
profile in this mode is trapezoidal. There is not a set limit governing the rate at which the end point
may be changed, however at the standard TM rate, the controller updates the position information at
the rate of 1msec. The controller generates a profiled point every other sample, and linearly
interpolates one sample between each profiled point. Some examples of applications that may use this
mode are satellite tracking, missile tracking, random pattern polishing of mirrors or lenses, or any
application that requires the ability to change the endpoint without completing the previous move.
The PA command is typically used to command an axis or multiple axes to a specific absolute position.
For some applications such as tracking an object, the controller must proceed towards a target and have
the ability to change the target during the move. In a tracking application, this could occur at any time
during the move or at regularly scheduled intervals. For example if a robot was designed to follow a
moving object at a specified distance and the path of the object wasn't known the robot would be
required to constantly monitor the motion of the object that it was following. To remain within a
specified distance it would also need to constantly update the position target it is moving towards.
Galil motion controllers support this type of motion with the position tracking mode. This mode will
allow scheduled or random updates to the current position target on the fly. Based on the new target
the controller will either continue in the direction it is heading, change the direction it is moving, or
decelerate to a stop.
The position tracking mode shouldn't be confused with the contour mode. The contour mode allows
the user to generate custom profiles by updating the reference position at a specific time rate. In this
mode, the position can be updated randomly or at a fixed time rate, but the velocity profile will always
be trapezoidal with the parameters specified by AC, DC, and SP. Updating the position target at a
specific rate will not allow the user to create a custom profile.
The following example will demonstrate the possible different motions that may be commanded by the
controller in the position tracking mode. In this example, there is a host program that will generate the
absolute position targets. The absolute target is determined based on the current information the host
program has gathered on the object that it is tracking. The position tracking mode does allow for all of
the axes on the controller to be in this mode, but for the sake of discussion, it is assumed that the robot
is tracking only in the X dimension.
The controller must be placed in the position tracking mode to allow on the fly absolute position
changes. This is performed with the PT command. To place the X axis in this mode, the host would
issue PT1 to the controller if both X and Y axes were desired the command would be PT 1,1. The next
step is to begin issuing PA command to the controller. The BG command isn't required in this mode,
the SP, AC, and DC commands determine the shape of the trapezoidal velocity profile that the
controller will use.
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46 Chapter 6 Programming Motion CDS-3310