By Brian Casey
Eden Prairie, Minn.
Edited by Miles Budimir
Manufacturers are under constant pressure to increase machine throughput and flexibility. That might mean designing single machines to handle numerous motion-control tasks on a variety of products.
Integrating motion and sequential control into a single multitasking controller platform leads to better system performance, faster application development, easier maintenance, and lower system costs. It also offers the flexibility to expand as needed and can be applied in different areas of control.
Out with the old
Kinetix, an integrated motion control package from Rockwell Automation, consists of Allen-Bradley's ControlLogix controller, servodrives, motors, and motion-application expertise, along with a Sercos interface and actuators from Rockwell Automation Encompass partners.
Traditional control systems require two separate controllers: one dedicated to logic and I/O, and the other for motion. Each requires its own software package, hardwiring, communications, and synchronization logic. To synchronize both requires as much as 25% of the program logic in the dedicated controller and 25% of the program logic in the motion controller.
Traditional systems also use different application-programming packages and languages for motion and sequential controllers. In addition, the application program in each controller is large and complex with a separatecontrollers approach because logic to link and synchronize the controllers is required.
In with the new
Integrating motion and sequential control eliminates these programming redundancies. For example, integrated control can be done with a single programming software package such as Allen-Bradley RSLogix 5000. This simplifies application programming and minimizes efforts to get access to important production information and process analysis.
With the ControlLogix controller, all control elements are in the same multiprocessor platform. Central, built-in instructions simplify motion and sequential programming, doing away with the traditional two-controller approach. Motion and sequential elements automatically synchronize with direct in-line execution of motion commands, thus decreasing modification programming and making troubleshooting easier.
Packaging OEMs, for example, can use Kinetix to create flexible, modular machinery. Machinery modules can be coupled together to create a variety of different machines. This design scheme lets users disconnect the machine in the center and add new function modules. The machine and the electrical wiring are split at interface points and additional function modules are added as needed. RSLogix 5000 code programmed into ControlLogix gives users a reconfigured machine that can run different packages.
Allen-Bradley servodrives integrate into the Logix platform through direct Sercos (Serial Real-time Communications System) digital interfaces. Sercos is an open controller-to-digital-drive interface for high-speed, real-time serial communications using noise-immune fiber-optic cables. Unlike analog terminal blocks, Sercos eliminates up to 18 discrete wires and 36 terminations per motion axis. The result is systems that are less expensive and easier to wire. Standard motion modules control up to 16 axes, and drives can be distributed up to 32 meters/segment with plastic and 200 meters/segment with glass fiber.
Kinetix's Smart Motor Technology identifies specific Allen-Bradley servomotors connected to the drive, thus reducing commissioning time and safeguarding against incorrect motor replacement.
Fill 'er up
One company that took advantage of the integrated approach is ProSys Innovative Packaging Equipment of Webb City, Mo. A request came in for a machine to fill containers with a heavy, viscous, room-temperature vulcanizing silicone at 150 parts/min. But current pneumatically driven machines peaked at 120 parts/min.
ProSys engineers faced several challenges. For starters, pneumatic cylinders have slow cycle speeds when placed under heavy loads, and filling could only be done at a 1:1 ratio. This means for every inch of movement at one end of the cylinder, there was one inch of movement at the opposite end. This required adjustable linkages and several sizes of metering cylinders to get the specified degree of movement.
Another problem involved metering cylinders that had to be the same size as the containers being filled when used to provide predose volumetric metering of the filling material. This required manually changing cylinders for a production run with different-sized containers. Changeovers took about half an hour. And several cylinder sizes would be stocked, one for each container size.
The solution was migrating from pneumatic controls to servocontrol. The ControlLogix integrated motion package replaced the pneumatic system. The package controls five servomotors and drives for five separate motion axes. The first axis indexes the containers as they move through the machine. Servo indexing moves the conveyor to a fine positioning point quickly and repeatedly. After indexing, the remaining four axes help fill the containers. Two servomotors lift empty containers from the conveyor to an initial filling point, and the two remaining servomotors control the volumetric dosing as the cylinders dispense product into the container. The equipment's electronic gearing ensures that containers drop away from the fill nozzle at an optimum, programmable ratio as they're filled, avoiding air pockets which spoil the product. The entire process takes about 2 sec.
Servocontrols also reduce setup time. With pneumatic machines, technicians had to climb over the machine with a fistful of wrenches to change metering cylinders. Machine operators can now change the fill volume, speed, and ratio electronically, right at the control panel. Also, the ControlLogix system eliminates the need to store various size dosing cylinders.