Motion Control Instructions The robot tool moves at the constant speed of 0.75 inch per second through each location defined in the array path[]. In the next example, the robot tool is to be moved along a circular arc. However, the path is not prerecorded-it is described mathematically, based on the radius and center of the arc to be followed. The program segment below assumes that a real variable radius has already been assigned the radius of the desired arc, and x.center and y.center have been assigned the respective coordinates of the center of curvature. The variables start and last are assumed to have been defined to describe the portion of the circle to be traced.
Finally, the variable angle.step is assumed to have been defined to specify the (angular) increment to be traversed in each incremental motion. (Because the DURATION instruction is used, the program moves the robot tool angle.step degrees around the arc every 0.5 second.) When this program segment is executed, the X and Y coordinates of points on the arc are repeatedly computed. They are then used to create a transformation that defines the destination for the next robot motion segment.
DURATION 0.5 ALWAYS FOR angle = start TO last STEP angle.step x = radius*COS(angle)+x.center y = radius*SIN(angle)+y.center MOVE TRANS(x, y, 0, 0, 180, 0) END Timing Considerations Because of the computation time required by eV+ to perform the transitions between motion segments, there is a limit on how closely spaced commanded locations can be. When locations are too close together, there is not enough time for eV+ to compute and perform the transition from one motion to the next, and there will be a break in the continuous-path motion. This means that the robot stops momentarily at intermediate locations.
The minimum spacing that can be used between locations before this effect occurs is determined by the time required to complete the motion from one location to the next. Straight-line motions can be used if the motion segments take more than about 32 milliseconds each. Joint-interpolated motions can be used with motion segments as short as about 16 milliseconds each. NOTE: The standard trajectory generation frequency is 62.5 Hz. With an optional software license, trajectory frequencies of 125 Hz, 250 Hz, and 500 Hz are possible. The minimum motion times for joint and straight-line motions must be greater than or equal to the configured trajectory cycle time.
As a convenience, if they are set to be less than the configured trajectory cycle time (for example 0), the trajectory cycle time is used as the minimum motion time. eV+Language User's Guide, v2.x, 18318-000 Rev A Page 120