Technology inside: Bacon slicer motion control
To improve the performance of the bacon slicer, Titan Slicer executives called in an experienced control system integrator, Tui Technology of Rotorua and Whangarei, New Zealand. Tui’s engineer, Malcolm Jones, had worked with motion controllers made by Delta Computer Systems Inc. of Battle Ground, Wash., in the past and came up with a new control system design for the bacon slicing machine using a Delta RMC75 motion controller. A PLC was still used in the new design, but for less time-critical functions, such as issuing on/off controls for the blade motor.
The Delta motion controller is programmed to do closed-loop position control using encoder feedback from the servo drive that moves the bacon slab into the cutting blade. The RMC sends a +/- 10 V analog output to the servo drive that moves the bacon slab.
The RMC’s fast cycle time allows the cutting operation to produce repeatable results. At 1600 rpm, there is a 38 ms time window in which to decide whether the bacon slab is to be moved forward to set up for the next cut or backward to clear the blade. The 1 ms loop time in the RMC running the Advanced Gear Move instruction enables repeatable and accurate slice thickness.
The Advanced Gear Move is just one of a number of gearing functions supported by the RMC 75. Whereas simple linear relationships can be set up between master and slave (using the RMC’s Gear Absolute function), an Advanced Gear Move operation lets the user program a nonlinear relationship between master and slave. For example, Figure 4 shows an Advanced Gear Move operation where the motion of the slave is dictated using a fifth-order polynomial equation. Most of the RMC’s simpler gearing commands allow the designer to choose the exact gear ratio to be used by specifying a numerator and denominator when the motion step is programmed.
Malcolm Jones said, “Where the RMC pays for itself is in the control of the first slice to meet our critical design goal.”
To program and tune the motion, Malcolm Jones used Delta Computer Systems’ RMCTools software, which includes a Plot Manager that displays trend or capture plots for key motion parameters versus time. Figure 4 is a plot that was produced by the Plot Manager that shows the operation of the advanced gear move instruction. RMCTools software also includes a Tuning Wizard, which enables quick and easy setting of control loop parameter gains for optimizing motion. “Using the Delta tools, I was able to prove that the system had enough timing margin to handle the higher cutting speeds,” said Jones.
– Brad Smith is regional applications specialist, Delta Computer Systems Inc. Edited by Mark T. Hoske, content manager CFE Media, Control Engineering and Plant Engineering, email@example.com.