Servos, advanced controls, and modern communication strategies team up to boost packaging productivity
"Yes, sir, we have apple, grape, strawberry, and raspberry in small, medium, and large cartons or bottles." Though statements like this delight consumers, they give fits to packagingequipment designers.
“Packagers want more types of products to be run on the same machine and at higher rates,” says Mike Seitel of Norwalt Design. “Everyone wants more machine versatility.” Norwalt manufactures assembly machinery for consumer products such as deodorant, hair coloring, orange juice, and toothpaste.
The demand for flexibility is driven by the Just-In-Time (JIT) scheduling used by processors of packaged goods. The goal of JIT is to minimize inventory. For packaging machine operators, this means many low-volume runs instead of a few high-volume runs.
“Quick changeovers are a paramount issue,” says Matthew Piercy, chief engineer at Asgard Inc. “We also build in a lot of control flexibility for what users are going to do down the road. We don’t look at a machine as dedicated. We try to give the customer flexibility.”
Designers accommodate needs
Packaging machine manufacturers use advanced motion-control technologies to boost the productivity of a variety of packaging systems — from machines that fill and close bags, bottles, or cans to those that add labels and pack the filled containers into cartons. Here are the major technologies, as described by Doug Burns, program manager, packaging initiative at Allen-Bradley Co., Milwaukee:
• Adjustable-speed drives, especially servos, are becoming more common for positioning products faster and with greater precision.
• Plant-wide communication networks are linking and coordinating machines on the packaging line.
• Interfacing between operators and machines is becoming closer. This means more comprehensive monitoring of machine operations, more effective response to variations in machine parameters, and less disruptive maintenance or repair.
• The merging of programmable logic controllers (PLCs) and personal computers (PCs) means higher performance and greater data handling in a dependable industrial platform.
• Reducing, if not eliminating, the need for programming expertise simplifies the adaptation of PLCs to frequently changing packaging requirements.
Servo positioning systems are replacing mechanical systems for both machine setup and control. Servos provide highspeed, precise motion control and they can be programmed to provide specific motion profiles. They give packagers the flexibility to rapidly change a machine setup from one product to another. Changing the motion profile requires only an operator’s key stroke, rather than shutting down the machine to adjust stops, cams, and other components.
Krones Inc., a Franklin, Wis. manufacturer of labeling and filling machines, uses an adjustable-speed (A-S) drive on the main drive motor of each machine, and on several conveyor motors that must be synchronized with the main motor. “A remote I/O communication network links the A-S drives to a PLC,” says Cary Lindauer, mechanical project engineer, labeling machines. “The PLC sends instructions to each drive so that they all run at the same speed.”
Operators may program the PLC to nudge the speed of a supply conveyor slightly higher than that of a labeling machine. This applies enough pressure between the boxes or bottles entering the machine to prevent gaps in the line.
Other A-S drive uses include adjusting the feed rate of a supply hopper, smoothing the acceleration of bottles on a conveyor during a stop to prevent them from tipping over, or diverting items from a single line to multiple lines. For example, plastic bottles made on a blow molder must be arranged in rows and columns before they go into a packing box.
The ability to provide more monitoring and diagnostic information is becoming increasingly important to packagers. With this information, operators monitor machine components and, when performance parameters fall below acceptable limits, take appropriate action. For example, the control system may alert operators to an unusual bearing-temperature rise or dirt accumulating on an optical sensor so they can schedule maintenance and avert a failure and consequent downtime.
On a machine, device-level controls monitor production functions. In some cases, smart devices monitor and report their own performance. Signals are sent to a controller — either a programmable controller, dedicated controller, or an industrialized personal computer — that performs real-time control of packaging operations. The controller is often networked into a supervisory-level system that links the plant floor with management.
The trend is to distributed I/O, with many small controls linked by communication cables (over DeviceNet or Profibus networks, for example), rather than having a large central control for an entire plant. You can also put a lot of sensors on a single pair of cables that connect to a control, which saves a lot of wiring.
Advanced human-machine interfaces — usually an industrially-hardened PC with high-definition graphics — let the operator monitor operations, make control decisions, and issue commands to a controller to adjust machine parameters.
These interfaces also provide operators with a wealth of support information at their fingertips. For example, the operator can access an entire machine operating manual on the interface terminal.
PLCs and PCs
Many equipment builders rely on PLCs to control their machines. One of them, R.A. Pearson Co., Spokane, Wash., makes machines that put consumer products, like cereal or ketchup, into boxes or trays. PLCs achieve fast changeover between different package sizes in these machines. This is typically done with a motor, PLC, and proximity switch, explains Don Parker, electrical project engineer. “To change from 16-oz to 32-oz bottle pack patterns, you simply push a button and the PLC causes the machine’s configuration to adjust to the new pattern. The proximity switch sends data to the PLC that counts from a home position.” For more precise operations, an encoder or resolver replaces the switch. In this way, a step motor changes the stroke of a load ram to push different length bottles into a case.
“Most of the packaging lines we put together have decentralized control,” states Larry Luciano of Luciano Packaging. “Usually they come from different vendors. We bring them together and install a centralized control package. We now have a machine with a 12-axis servo system that has very sophisticated control. The motor control system has cards that go into a VME rack, which makes the system more flexible and convenient. There’s less wiring and a smaller panel. The motor controls plug right into the PLC, so there’s faster communication between motor and PLC.”
If you’re thinking about adapting PCs to control packaging operations, proceed with caution. PLCs can perform real-time machine control and provide built-in diagnostics, fault handling, and watchdog capabilities. But adapting a PC to machine control puts the burden of providing these safeguards on the software code writer. In a control application, the consequences of a software glitch are more severe and costly than in a typical datamanipulating PC application.
Moreover, some machine builders are skeptical about PC reliability in severe factory environments. One reason: they have seen failures of computer-based operator interfaces.
So-called “open-controller” systems are emerging that combine the control capabilities of a PLC with the data-handling characteristics of a PC. With an open-controller, packagers can take advantage of the PC’s ability to collect, analyze, and present data generated during machine operations.
Machine controls are not limited to PLCs and PCs. “Programmable limit switches (PLSs) control machine operations that require timing or counting, such as engaging a cylinder or releasing a label at a specific point in the operating cycle,” states Randy Schwanke, electrical engineering administrative manager at Krones Inc.
The Ranpak Corp., Painesville, Ohio, manufactures machines that make cushioning materials for packages. According to Paul Guth, vp of manufacturing, they are moving away from relays, switches, and timers, toward software on a microprocessor chip, which is imbedded in the machine. These microprocessors control machine operation with the aid of condition- monitoring sensors.
Packaging engineers and operators want to spend their time optimizing operations, not developing and debugging control system software. Not only are these system configuration and operation chores time-consuming, but every custom routine that is written carries with it the risk of an error.
Using familiar software application packages simplifies and reduces the time required to develop PLC control. Through pretested functions — such as creating database tags and communication routines — this software reduces the need for machine-level (ladder logic) programming. Packagers can configure PLC control systems for their machines through a simple, fill-in-the-blanks procedure requiring minimum programming experience.
Packagers are constantly pushing for smoother, more reliable, and more efficient operation, plus better communication. These demands require more electrical components in packaging machines — more A-S drives, but fewer clutches and brakes.
The increasingly complex electrical systems will, in turn, boost the need for diagnostics. Packagers want the equipment to work like copy machines that provide instructions on how to fix a jam. Diagnostics is becoming a larger, more difficult part of the control system, which requires larger software programs for operator interfaces and PLCs.
Packaging companies will probably require fewer, but better trained, machine operators, as well as knowledgeable troubleshooters to ensure reliability.
Servomotors will be used in many more applications. For this reason, Don Parker would like to see more use of PLCs to change servomotor parameters using only one software package. You write a control program on the PLC, then enter a number on a keypad to change the servomotor’s acceleration rate, for example.
The trend toward distributed I/O will continue — with devices communicating over coaxial cable to a large central PLC controller. A human controller can access this information and determine operating problems such as a machine being out of glue, or needing bearing lubrication.
Krones is moving towards linking components on a DeviceNet network so that if container fillers slow down or speed up, the machines downstream know what’s happening and adjust accordingly. This will require more sophisticated controls — PLCs and A-S drives — that are smaller and less expensive.
Machine builders that use PLC controls may eventually move toward PCs because they are less expensive, distribute more I/O, and allow more operator interface.
Ranpak wants to see motors, controls, and sensors that easily tie to a microprocessor. They also want more reliable drive components to support their lifetime warranty on packaging machines.