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User-programmable process monitoring now in a low-cost package.

User-Programmable Process Monitoring Now in a Low-Cost Package

Computer-integrated manufacturing is based on real-time availability of manufacturing information. A supplier of CIM systems, Hunkar Laboratories Inc., Cincinnati, has addressed that basic need for information with product enhancements at both the top and bottom end of the price/performance scale. At the low end, a new programmable data-acquisition terminal provides unusual flexibility for evaluating a process at low cost. Hunkar has also upgraded its top-of-the-line CIM-1 system with new software features that provide additional "windows" on plant operations.

LOW-COST DATA ACQUISITION

P-DAT is the brand-new programmable version of Hunkar's Data Acquisition Terminal (DAT). It automatically receives and stores data from sensors on a processing machine or auxiliary equipment, and from serial devices such as bar-code readers, electronic calipers, and weigh scales. With the latter, data on product weights and dimensions can be automatically correlated with process data. Manual inputs of operator identification codes, reasons for downtime and rejects, and so forth can also be made with the keypad. This low-cost device, typically mounted on the processing-machine control cabinet, is the basic data-gathering "node" for Hunkar's CIM-1 plant network, but P-DAT can also be used on its own as a one-machine monitor. It can be programmed via an IBM-compatible personal computer, and can download information to the PC for convenient viewing and for statistical analysis, or to a plug-in portable printer.

The P-DAT hardware has been upgraded to accept up to 32 analog inputs plus 32 digital I/O's (vs. a max. of 8 + 8 for the basic DAT). Price range, complete with certified sensors (i.e., uniformly calibrated and checked for accuracy) and signal-conditioning equipment, is $5000-9000.

The most important new feature of the P-DAT is its programmable software. Although originally aimed mainly at injection, blow and transfer molding, programmability now makes the device "universally" user-configurable for batch or continuous manufacturing processes, according to company president Denes Hunkar. For example, it's now being used on a resin supplier's compounding line. Here's a rundown of the programmable features, which are geared especially to satisfying statistical process control (SPC) requirements:

* Text fields: All displays, definitions and alarms can be programmed by the user in any language.

* Data-acquisition logic: For example, the user can program it to "Measure temperature X when the process is at stage Y," or "Measure the difference between input A and input B at step C."

* Analog scaling: Define the range of measurement you're interested in to give higher resolution where it counts.

* Measurement definitions: Determine whether you want averages, medians, etc.

* SPC database: You decide how many and which variables will be monitored.

* SPC process qualification functions: You choose which of the monitored parameters are critical to your product quality, and designate which are to be the basis for good/bad product acceptance/rejection. You also set the upper and lower specification limits for these parameters.

* Process-control logic functions: This new feature turns the data collector into a "closed-loop SPC device," in Hunkar's words. If any designated parameter exceeds its preset SPC limits, an output signal can actuate a diverter flap or an alarm, or instruct the machine to shut down.

All these functions are programmed off-line on the PC and then downloaded to the P-DAT. "What you have is a monitor/controller that is not process-specific," says Hunkar. "If you change the process, you can change the logic." (CIRCLE 15)

FULL-BLOWN CIM UPGRADES

The software for Hunkar's CIM-1 plantwide monitoring system (see PT, April '88, p. 15 and March '89, p. 71), has also been enhanced with two new modules (see PT, Oct. '89, p. 13). One is the "Expert Analyzer," which automatically searches all machines and auxiliaries on the CIM-1 network for all variables that have exceeded specification limits during a preset production period. "There are no more stacks of printouts to plow through," says Hunkar; "the system looks only for faults and reports just the faults. Also, it prioritizes them, so you can see right away what's the worst problem to fix first."

An example of such an Expert Analyzer output is the accompanying "Process Performance Chart," a Pareto-type frequency distribution of significant deviations. A new feature in the SPC-PRO "expert" software in Hunkar's CIM-1 system allows the user to select what constitutes a "significant" deviation. The user can specify the acceptable boundaries of deviation as equal to the upper and lower specification limits (USL and LSL) -which are automatically set for each parameter by the expert software, based on statistical analysis of an initial run of good parts - or the user can select a degree of "offset" ([+ or -] 5-20%) from those standard limits.

The second new module in the CIM-1 software is the Event Manager, which logs discrete events that occur throughout a production period, such as when a machine was serviced and by whom; which individuals punched in or out of work, and when. You can search for a particular type of event via word-processing software. This is said to be useful for payroll purposes and employee productivity monitoring.

CALIBRATED FOR TYPES OF

INJECTION AND BLOW MOLDING

Among several other new enhancements of the CIM-1 system, it now can monitor up to 32 different types of processes - before it could monitor numerous machines performing the same process. Also, the SPC-PRO software, which automatically sets the USL and LSL for each quality-related parameter in the process, now can adjust those limits according to the particular type of molding being performed. Based on monitoring millions of shots from nearly 500 injection machines at customer locations, Hunkar has established a database of median performance of U.S. machines in different types of actual production.

Thus, you can select programs for setting USL's and LSL's according to "industry average performance" in: 1) semiautomatic injection molding, 2) automatic mode, or 3) close-tolerance injection molding.

For blow molders, another major target of the CIM-1 system, Hunkar now has three different programs for setting molding tolerances: 1) accumulator-type blow molding, 2) polyolefin extrusion blow molding, and 3) PVC extrusion blow molding.

In addition, SPC - PRO automatically performs statistical analysis of molding performance. Typical X-Bar and R charts have now been supplemented with additional "Process Performance Coefficients" that can be displayed for any SPC variable. The Process Capability Index (PCI) is the ratio of the specified process tolerance to the "natural variability" of that parameter, which Hunkar defines as "the variability independent of a process - or the ability of a sensor to repeat a measurement." In other words, PCI tells you how "capable" your process is, in terms of that particular variable, and provides a single numerical index to tell you whether your machine performance is getting better or worse in that regard.

The Process Performance Index (Cpk), a refinement of CPI, is an indicator of how well your process is able to remain within desired limits. Cpk is an index of the deviation of the process mean (X-Bar) from the midpoint between USL and LSL. Although Cpk is well known to SPC experts, Hunkar says it is unusual to apply that index to a process variable rather than a part dimension, and even more unusual to have process-variable Cpk's calculated automatically for you. Hunkar recommends the use of Cpk as a convenient yardstick for qualifying the performance capability of a new machine, and he supplies a portable machine-monitoring kit with SPC-PRO software that can be used for that purpose.

Two additional performance indexes that have been added to the SPC-PRO reports are Cpu and Cpl, which indicate the process performance relative to the USL and LSL. They tell you whether the distribution of data points is shifting toward one end of the range or the other; this feature often negates the need to plot conventional distribution charts. (CIRCLE 16)

PHOTO : Hunkar Laboratories' new Programable Data Acquisition Terminal (P-DAT) is a user-configurable SPC tool for monitoring process and production data from virtually any type of process.
COPYRIGHT 1990 Gardner Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1990, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Publication:Plastics Technology
Date:Feb 1, 1990
Words:1314
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