28 • Chapter 6 Programming Motion DMC-2X00
VELOCITY
(COUNTS/SEC)
20000
10000
5000
15000
20 40 60 80
TIME (ms)
100
A axis velocity profile
B axis velocity profile
C axis velocity profile
0
Figure 6.1 - Velocity Profiles of ABC
Notes on fig 6.1: The A and B axis have a ‘trapezoidal’ velocity profile, while the C axis has a
‘triangular’ velocity profile. The A and B axes accelerate to the specified speed, move at this constant
speed, and then decelerate such that the final position agrees with the command position, PR. The C
axis accelerates, but before the specified speed is achieved, must begin deceleration such that the axis
will stop at the commanded position. All 3 axes have the same acceleration and deceleration rate,
hence, the slope of the rising and falling edges of all 3 velocity profiles are the same.
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.