Basic Programming Concepts violation condition exists. Also, if during the execution of a belt-relative motion or while the robot is tracking the belt, the destination moves outside the belt window for any reason, a window violation occurs. Depending upon the details of the application program, the program either prints an error message and halts execution or branches to a specified subroutine when a window violation occurs. In order to provide flexibility with regard to the operation of the window-testing mechanism, several modifications to the normal algorithms can be selected by modifying the value of the BELT.MODE system parameter.
To assist in teaching the belt window, the conveyor belt calibration program contains routines that lead the operator through definition of the required bounding transformations. Conveyor Terms Belt-Relative Motion Instructions To define a robot motion relative to a conveyor belt, or to define a relative transformation with respect to the instantaneous location of a moving frame of reference, a belt variable can be used in place of a regular transformation in a compound transformation. For example, the instruction MOVES %belt:loc_1 directs the robot to perform a straight-line motion to location loc_1, which is specified relative to the location defined by the belt variable %belt.
If a belt variable is specified, it must be the first (that is, leftmost) element in a compound transformation. Only one belt variable can appear in any compound transformation. Motions relative to a belt can be only of the straight-line type. Attempting a joint-interpolated motion relative to a belt causes an error and halts execution of the application program. Except for these restrictions, motion statements that are defined relative to a belt are treated just like any other motion statement. In particular, continuous-path motions relative to belts are permitted. eV+Language User's Guide, v2.x, 18318-000 Rev A Page 196