Case Studies

This note covers:

• On-the-fly disengagement and re-engagement of the follower motion
• Modulo counting of the ECAM table offset entry
• Modulo counting of the slave reference and feedback
• Modulo counting of the master feedback

The basic assumptions are that:

• The master moves at any speed
• The slave performs a constant trajectory over the master location
• The slave disengages the follower after each cycle

The slave is a roller driven by the Cornet Servo Drive (MIS), and contains two matrixes that perform the printing on the box. The roller completes one cycle each two boxes. After printing, the roller stops following the master conveyer and returns to its homing location. This location is actually the beginning of the next motion (start of the ECAM table). The roller begins following again after the fast input is sensed and the follower is re-engaged. Problems Encountered

• The slave (roller) linear speed must be adjusted to the conveyer speed while printing.
• The slave rolling each cycle can cause a loss of synchronization between the master reference and the slave feedback.
• The slave must HOME each cycle regardless of the fact that the reference is an auxiliary reference.
• The slave must adjust the absolute position after each consecutive cycle in order to prepare for the next cycle.
• The master must roll over without losing synchronization with the follower referencing.
• The slave trajectory is repetitive regardless of the master location.
• Two boxes can arrive at the roller at the same time. In this case, the captured location of the first box can be lost because the captured location of the master is ambiguous.

• To accelerate the roller speed in order to synchronize with the conveyer belt at the printing area, an ECAM table is used. The trajectory of the slave is nonlinear. The ECAM table assures that the linear speed of the roller exactly matches that of the conveyer belt when the load reaches the printing location. (Refer to The Recorded Slave Trajectory.)
• To overcome this, the MIS offers a smooth modulo count when it exceeds the slave position limits. The smoothness is achieved by maintaining the velocity command regardless of the change in the slave feedback indication for each modulo rollover.
• The position command to the controller is built from the auxiliary reference (in this case the master reference) and any software command. The HOME location can be achieved by giving the absolute location of HOME or, as in this case, using the modulo rollover location that is half of the roller cycle.
• A position-relative command is applied on-the-fly as a software command. The relative position command adjusts the software position command to the starting location of the next cycle; that is, the next box to be printed.
• The master continues to count practically to the limit of the position register. When it is rolled, the slave does not follow and no interference is made to the slave movement. The reference to the ECAM table is taken after an offset from the master. Since this offset is modulo, the actual reference to the slave is always within the limits of the ECAM trajectory.
• By using an automatic capture routine that interrupts the internal user program, the location of the conveyer is captured each box regardless of the location of any prvious box. Each box is allowed only after a previous one passes the fast input switch. Since this is a very short interrupt routine, several boxes can be marked almost immediately. This application requires only two captures at the same time.