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Off-the-shelf cell control.

Off-the-shelf cell control

Cell control has evolved backwards. It began with customized minicomputers capable of providing second-tier supervisory control of the flexible cell's complex array of CNC machines and work-handling systems. As cell technology caught on, it evolved to simpler control forms based on modifying the lone CNC in more elementary single-machine cells. Now, the development of high-powered engineering workstations is creating an opportunity to leap forward to fill in the control gap between these two extremes: applications more complex than a simple cell but less than one requiring significant vendor-supplied custom engineering.

Simple cells

The simplest form of cell control is based solely on material-handling automation: how you choose to move material in and out of the cell. The simplest cell situation is a single machine with its own local pallet pool. Take an existing CNC machine, put eight pallet-storage areas in front of it, and you've created a one-machine cell. To control that cell, simply add I/O capability to the CNC to enable it to shuttle multiple pallets. The next step up in complexity is adding a more challenging workhandling system: a rail-guided vehicle. That will require redoing the CNC's software because a rail-guided vehicle is essentially a two-axis device: one axis for linear movement and the other for the Y motion of pushing pallets on and off stations. Yet, even this is relatively easy to do, and a lot of users have successfully adapted their CNCs to handle this level of cell control. Machine-tool suppliers can provide relatively simple ways to do this. For example, a CNC can be used to do the basic servo control, with a PC with color graphics tacked on to the CNC to handle the monitoring functions. There are also a lot of shop-floor management-information systems that provide cell-monitoring functions, but stop short of full cell control.

Workstations

A much bigger leap is to wean yourself from the CNC and employ a separate cell computer to provide more sophisticated system functions. This represents a big step in both price and functionality. Once you get away from the CNC-type controller, you jump to minicomputer-level cell control - a separate-station hierarchy that ties several CNCs in the cell together and adds work-scheduling and tool-management functions. This is how the more complex cells have been handled in the recent past. Enter the workstation. With the latest workstation technology, a Micro VAX or VAX-based computer can now handle cell control very nicely. Theoretically, users can do this in-house by buying a high-tech workstation and developing the software themselves. However, the reality is few have the time or inclination to attempt this much automation and software development on their own. The same holds true if you go outside for cell control. Because most system suppliers have developed custom cell controllers based on minicomputers, not newer workstations, that's where their expertise lies. That's what they've been working with for the past decade as cell technology evolved. Minicomputer cell control remains the custom solution for most major cells developed by the systems integrators. The low-level do-it-yourself approach came in four years ago, as an alternative to reinventing the wheel each time you needed to integrate workhandling into an elementary cell.

Commodity approach

The first to take advantage of this opportunity to tailor the latest workstation technology to mid-range cell control is Cincinnati Milacron. They introduced their Synchron cell controller at IMTS-90. Its intent is to be commodity cell controller, in effect, a shop-floor, user-friendly CNC for cells that can be adapted to a given application by the manufacturing engineer and machine operator without major outside help from either Milacron or a systems integrator. Says Milacron's Chris Edwell, division manager, Advanced Manufacturing Systems, "The primary benefits are improved process control and coordination of resources, which ultimately maximize spindle-utilization time. The cell controller monitors resource availability within a cell and executes the simultaneous processing of multiple work orders. Fixtures, tooling, and part programs are all resident in the cell and managed by the cell controller. Transporting and refixturing of parts can be eliminated, reducing process variability." The specific functions performed by Synchron include:

Work-order management - assisting you in determining what work to put on what pallets and tracking their progress through the cell. You prioritize the work and the cell controller executes your prioritization through automatic production scheduling.

Tool management - helping you determine which tools will be needed for a given job, and making sure those tools are available when the parts arrive.

Machine management - up-loading and down-loading part programs to the CNC, and the ability to review programming and make programming modifications at the cell controller.

Training - touch-sensitive help screens walk the user through the learning process and are a key-stroke away to assist with trouble-shooting problems that develop.

Status monitoring - color graphics that depict the present condition of every element in the system, and alarms that alert the operator when something goes awry. Event logging, diagnostics, and error recovery procedures also help speed problem analysis and corrective action.

Transitional benefits

Mark Adkins, Milacron's product manager for Synchron, is excited about how Milacron has positioned this control. "By using the new RISC workstation, we can offer a much more gradual transition to full cell control. You don't have to start with a very simple cell controller and then jump to an expensive minicomputer system. We can offer something in between. The bottom line is that you are enhancing the productivity of the machine tool. That's what the cell controller is all about. Keeping work in front of the machine, so that it operates at maximum efficiency." What's your involvement in a typical startup? Is this really a commodity that users can simply plug in, define their parameters, and start up quickly by themselves without a need for customizing services? "The goal of our original design concept," relies Adkins, "was to provide an off-the-shelf commodity cell controller. It has sufficient documentation and an ease of training that it can be operational in a week or less. Yet, it can also be customized, and there are users that will insist on special features that we can provide. For examples, some want to use multiple material-handling systems within a single cell; i.e., they might want both AGVs and rail-guided vehicles, and the standard Synchron doesn't handle this." What would that involve - additional hardware and software? "We would first write the software, and then look at its performance requirements which might then require a bigger computer. Another nice feature of these new workstations is their ability to easily plug-in more MIPS (millions of instructions per second) capability - computer horsepower. The software and appearance of the product don't change; the screens and cabinets stay the same; it's just a bigger CPU."

Cost?

Where does the cost of the Synchoron fit into the spectrum of cell-control options? "For comparison," replies Adkins, "our pallet-sequencer product on the low end is available for as little as $15,000, but we don't consider that true cell control. On the high end, the customized minicomputer approach starts at $250,000 and goes up from there. "The basic Synchron cell controller starts at $55,000, and that can run up to $150,000 for large cells involving five or six machines and requiring all of our standard options; i.e., additional CRTs, staging terminals, etc. The capability limit for the standard Synchron is eight machines, but we can go beyond that on a custom basis." Adkins points out that there are other savings beyond the basic cost of the cell controller. "We're providing shop-floor functionality of a minicomputer that typically demands a separate computer room to function in. Visit any such installation and ask to see the cell controller, and they take you to an air-conditioned room." In contrast, Milacron's system doesn't require hiring a veteran systems programmer and putting him or her up in expensive housing. "Ours is a shop-floor product, right at the cell. That systems-programming support function is now gone. The operator can develop and run the system, just as he can the CNC. There's no need for anyone else, other than the normal metalcutting CNC-program-generating functions, however they're being handled."

Retrofits?

What about retrofitting situations? Does it make sense to come in at a later time and add a cell controller to an existing system? "Yes," says Adkins, "that's a migration strategy that some people have, and we're doing that in a number of cases. We're working with customers who have a number of our machines set up in a row, running in a standalone mode, and we're adding a rail-guided vehicle in front of those machines and connecting the cell controller to each CNC. This is a particularly good application for a free-standing, packaged controller. It takes less time to install, and there's less need for custom-engineering time purchased from Milacron, and there's less production disruption because the installation is much quicker.

"Although it would be less expensive, generally, to do the cell and its automation all at once," he admits, "some users are deciding that they aren't ready to go to full automation immediately. So, they put the machines in, get the tooling, fixturing, and part programming going, get their people comfortable with the cell, and then we will come back six months later and add the material-handling equipment and cell controller. Instead of leaping to a totally integrated cell initially, they have a chance to get used to the key cell elements first, and then move to cell integration when their people are really ready."

PHOTO : System diagram for the Synchron cell controller.

PHOTO : Example of a typical window-format video display: Upper left is a plan view of all cell components, color-coded with their present status (active, idle, fixtured, alarmed, etc). Upper right window contains four ions for further details on various subsystems: pallets (PAL), material-handling systems (MHS), staging terminal (STG), and machine-tool condition (MTC). Lower left is a help screen, and lower right is a window for editing NC programs.
COPYRIGHT 1990 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Author:Sprow, Eugene
Publication:Tooling & Production
Date:Nov 1, 1990
Words:1658
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