Micro PLCs, software make machines flexible

DN Staff

August 12, 1996

8 Min Read
Micro PLCs, software make machines flexible

Two different trends are emerging from the evolution in electronics, networks, and software, and both are adding value and flexibility to industrial machines. The first is the development of small programmable controllers (micro PLCs). The second is personal computer (PC)-based machine control. Industry experts say these trends are converging on a common point.

Regarding the first trend, inexpensive micro PLCs are cutting design time and giving engineers improved startup, configuration, run-time adjustments, programming/editing, monitoring, diagnostics, and other advantages, without a significant increase in overall size or cost.

Flexible manufacturing models. Just ask Telford, PA-based P.S. Group. The engineering firm recently got the nod to design and build dereelers, rereelers, and semi-auto-press and auto-press machines to manufacture I/O components for PLCs. To control the new machines, P.S. Group turned to Allen-Bradley. The reasons: time and money.

"Only two years ago we had a year or more to build an assembly machine for our customers. Now, they want the machine in ten to fourteen weeks," says P.S. Group President Terry McGinn. "With that amount of time, we can't afford to reinvent an assembly machine every time the product is redesigned," adds McGinn.

P.S. Group engineers opted for the Allen-Bradley MicroLogix 1000 micro PLC for its cost, speed, and simplicity.

The eleven machine process modules, developed in the last nine months, make up a flexible production line that can assemble various components without engineers having to redesign each module. "This flexibility cuts costs and design time, and improves our competitiveness in the market," says McGinn. "In fact it has cut our lead time and costs in half compared to two years ago."

The MicroLogix uses the same programming package as its bigger brother, the Allen-Bradley SLC500. "Our strategy is to develop a standard program for each particular module, then reuse this program in all similar modules. Daisychaining a family of programmed modules creates an assembly process," says McGinn.

The Allen-Bradley control system integrates the stepper-motor control and through-beam optical sensor inspection in the machines.

P.S. Group engineers designed new interconnection devices in house and mounted them on the circuit boards to eliminate large terminal strips. The synergy of the small MicroLogix (120x80x40 mm) with control-architecture redesign reduced the bulk of the controls from a 42 x30-inch area to a 12x12-inch area, McGinn reports. The implication: wiring and overall size reductions cut costs.

P.S. Group will use the same machines to assemble docking station components for notebook computers. "With only eight weeks to deliver, the engineers will be able to focus on tool design for the existing machines," says McGinn.

PC-centric automation. While P.S. Group engineers had speed and cost reduction at the top of their wish list, Palm Bay, FL-based GSMA Systems, Inc. faced another challenge: ease of use. GSMA engineers were designing controls for Cartesian robots that could be easily programmed by end users with varying degrees of expertise.

To get the ease of use, they followed the second major trend. GSMA engineers chose SIMATIC S7-214 micro PLCs in a PC-based control system from Alpharetta, GA-based Siemens Corp.

The challenge: development of a low-level communications protocol between the PC and multiple S7 micro PLCs over the two-wire RS-232 lines. The result: EZ-ScriptTM and PLC-ToolkitTM symbolic script software.

"Our customers require user-friendly software to prevent being at the vendor's mercy for program changes," says Paul Leppek, GSMA's director of software development. The use of PC-based script language eliminates the dedicated programmer, and enables the end user to write his/her own high-level script program with minimal knowledge of relay ladder logic (RLL) or statement lists.

"Although you can't beat the cost, reliability, and robustness of the PLC for I/O control, many engineers are more comfortable working on PCs," says Leppek.

GSMA chose the SIMATIC S7 micro PLCs primarily for the support and reputation of the firm. "The inexpensive I/O, flexibility, and availability of analog/expansion modules is what gave the S7 the edge over the competition," he adds.

"The S7 micro PLCs provide us with robust, remote, flexible I/O. For example, we can give our customers local I/O if they want it, then expand remote I/O as the customer requires," says Leppek.

The S7 micro PLCs controlthe machine and I/O not related to motion, while a high-end Delta Tau PMACTM motion controller handles servo-motor control.

The PMAC's DSP runs at 40 to 100 MHz. Servo-cycle time is in the 25- to55-msec range. It has built-in servo-motion algorithms to provide complex coordinated control of multiple axes, and connects to the PC via a standard ISA bus.

This flexible, open-architecture solution incorporates three dedicated control entities that form the triangular control configuration used in all GSMA Cartesian robots. "A PC, motion card, and remote PLC form the corners of the RoboWin(TM) controller," says Leppek. The RoboWinTM and PLC ToolKit(TM) GUI (graphical user interface) make the triangular control architecture transparent to the user, and enable control, programming, and monitoring of all machine functions.

A Pentium 486 100-MHz processor is the heart of the PC-based control system. "We'll probably run the 133-MHz processors next year when the price comes down," says Leppek. One advantage of PC-based control is that simple board swapping enables integration of the latest technology in the control system.

The PC supervises, provides operator interface functions, and networks to other PC-compatible peripherals. "Vision systems, bar-code readers, CAD data, and analog and digital feedback controls are just a few of the peripherals we have integrated for our customers," says Leppek.

The PC-controlled Cartesian robot built for 3-D conductor coil winding incorporates fully coordinated eight-axis servo-motion control with less than one thousandth of an inch total error for all eight axes, according to Leppek.

The PC impact.Design News talked with manufacturers at this year's IPC show in Detroit to find out how PC-centric automation solutions will impact PLCs.

PLC companies have entered the fight by forming alliances and by purchasing or developing software in-house.

"By including peripherals with PLCs, manufacturers can enhance their product," says Charlottesville, VA-based GE Fanuc engineer Jerry Corbell. PLC makers develop open, multiplexed I/O buses to incorporate programmers, operator interfaces, and third-party software into their own products.

For example, GE Fanuc has recently introduced a new line of its CIMPLICITY Monitoring and Control Products for Windows 95 and Windows NT. The PCIF-30 interface allows control of remote micro PLCs by open-architecture PCs.

Among other noteworthy examples:

- ORMEC, Rochester, NY, also offers a PC-based system controller. The OrionTM, built on the IBM-PC architecture, is a fully integrated motion controller offering DSP-based servomotor control and convenient interfaces to sensors and programmable limit switches, machine I/O, operator interfaces, and popular factory networks.

- Square D, Palatine, IL, says its upgraded Modicon TSX Quantum line delivers high-performance communications and tight controller-computer connectivity.

- Recently Cutler-Hammer, Milwaukee, WI, and Indramat, Hoffman Estates, IL, formed an alliance to co-develop, market, and support open-architecture application solutions for automotive manufacturing. Cutler-Hammer now offers the D700 series industrial PCs designed for easy maintenance and maximum uptime.

Among new micro PLCs that are penetrating broader applications such as vending machines and traffic lights:

- Omron Electronics, Schaumburg, IL, rolled out the CPM1. The CPM1 combines proportional-integral-derivative (PID) algorithms and process instructions with floating point and trigonometric analysis functions, a first for Omron.

- Aromat boasts that its FP10SH is the world's fastest PLC. The controller uses a customized 32-bit, five-level, pipe-line architecture RISC processor to increase its speed ten-fold over the FP10S. "The new processor eliminated the dual processors of the FP10S and reduced the cost by 25%," says Milton Navarro, senior engineer for Aromat. It offers 40 ns-per-step execution time, 30-120K program steps, expandable memory, and up to 8,196 I/O, all in a package measuring 6x1.5x4.5 inches. According to Navarro, scan time at 10,000 steps is 1 to 1.5 ms. Scheduled to be released soon, the FP10SH is for fast machine control. Applications include: chip taping, mounting, and insertion in the semiconductor industry; process control; and manufacturing.

- Mitsubishi Electronics America Inc., Mt. Prospect, IL, claims to have the world's smallest 14 I/O PLC. The FXOS-14MR-ES/UL measures 75x 60x90 mm and is for applications up to 30 I/O. The FXOS line features four models that integrate the CPU, I/O, and power supply in one small unit. Ac power ranges from 100-240V.

As PLCs continue to shrink in cost and size, engineers are sure to benefit from lower costs. The trend toward integration and open-architecture control solutions improves the flexibility of designs, enabling engineers to reduce costs and cut time to market.

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