Hershey Chocolate North America packages up to 200 units/min with the MPI-400 parallelogram robot-cartoner from IASE, Branchburg, N.J. One Indramat CLC multi-axis control synchronizes fives axes. These axes control the infeed speed and spacing of wrapped candy, and all actions of the robot’s three-stage product accumulator. The robot uses two digital servos for positioning and one for the robot hand, which tracks the moving cartoner discharge belt, so that the robot’s product placement matches the speed of the belt. The system coordinates all motion through the Sercos network.

Automation technology has progressed exponentially in a short time as packaging machine builders adopt digital motion control technology. Digital electronic accuracy is true accuracy, unlike conventional machine calibration which often came down to how much error an operator was willing to tolerate. Here, trial-and-error adjustments frequently led to compromise mid-range operating parameters that inevitably drifted as the machine picked up speed. Digital control, though, achieves perfect axis coordination and repeatable performance, even while operating at the fastest available drive speed.

Knowing that accuracy won’t be sacrificed, production can run machines at their maximum possible speed. This benefit is most dramatic when old machines are retrofit with electronic control. A Hershey Chocolate North America plant, for example, had the gears and chains gutted from one packaging line, then retrofit the frames and mechanics with digital ac servo drives linked through a Sercos network to a multi-axis control card. Now the line wraps Reese’s Crunchy Cookie Cup candy bars at more than double the speed with greater uptime and fast changeover. “When refurbishing older machines, it’s not uncommon for a mechanical-to-digital conversion to increase flow wrapping production from 350 to 750 candy bars per minute,” says Wade Latz, manager of packaging systems engineering at Hershey.

Digital-based devices are easy to change and upgrade. Often, installing a new chip or new software code is all that’s needed. And it doesn’t come at the expense of axis count, wasted hardware, speed, accuracy, or uptime. In short, digital control can optimize packaging production for every level of machine complexity — from single-axis applications, to simple sequenced multi-axis packaging, to highly complex lines with multiple coordinated motion functions.

Single-axis packaging

Because early digital controls and drives provided high capability at high cost, single-axis packaging systems usually stayed loyal to the economy of analog control. When industry first offered less expensive digital drives, proprietary interfaces limited users’ options to upgrade or use the drives in a larger system.

The latest group of open digital servo drive systems, however, integrate multiple functions — such as motion control, amplifier, power supply, and axis inputoutput (IO) tasks — into a single control unit that’s adaptable to new applications. These drives are becoming common on simple point-to-point applications like auger fillers, single-axis sweeps, and random infeeders.

Sequenced multi-axis motion

The demand for accuracy at high speeds inspired a new generation of digital controls that need minimial integration to precisely sequence multiple motions. Such controls are so flexible that it no longer makes sense to purchase packaging machines for immediate needs without serious consideration of future needs.

The most flexible packaging controls are PC-based with an open-architecture. Various cards or printed-circuit boards for multiple axes of motion control, logic, and IO plug into the control backplane, integrating all into one unit. Such tightly integrated controls frequently use intelligent digital drives with internal digital signal processors. The drives handle much of the master control’s traditional functions — closing the position, velocity, and torque loops. In many cases, the integrated PC-based control can execute motion and logic functions without separate PLC hardware and the associated costs.

Consider the benefits of a motion controller and intelligent digital drives for a typical 10-axis high-speed cartoner. Previous systems might consist of three proprietary 4-axis controls, or 10 single-axis controls, sequenced by an external logic control. This scheme requires extensive wiring and programming to smoothly sequence multiple motion controls with separate processors, and to coordinate them with a separate logic program.

With digital technology, that same 10- axis cartoner is controlled by one motion control processor with integrated logic. It communicates in real time along a fiber-optic ring, in a daisy-chained network between all 10 axis drives. The packager purchases only one control, significantly reducing the time and cost of integration and wiring. In addition, such a system is flexible enough for new programs and process changes. Accuracy is high because all axes work on the same processor clock, and the fiber-optic network is noise immune. One packaging machine builder, Klockner-Bartelt, Sarasota, Fla., says that start-up for such a cartoner usually takes just two days.

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