New Protocol:

Easy-to-Use Servo System Offers
Maximum Control and Flexibility

SAMCOP aims to simplify motion control while integrating both hard and soft PLCs

-- By Frances Richards

Motion control has always been one of the key challenges facing automation. Imagine an automotive assembly line with materials and components moving from cell to cell, speedily advancing along a complex network of synchronized conveyors, with a myriad of functions taking place at what seems the speed of light -- pressing, drilling, positioning, assembling, welding, painting and more.

Historically, motion such as this was driven first by stand-alone systems using "hard" PLCs (programmable logic controllers), and more recently by "soft" PLCs, specialized software on a PC to coordinate motion control. Hard PLCs began to be used in the automotive industry, circa 1960, and have spread to almost all other industries during the 1980s and '90s. Rather than physically unwiring and rewiring hard PLC systems of the past, the trend has moved toward logic-controlling software that is run on PCs.

A new protocol, developed by Star Micronics, Knoxville, TN, as their entry into the North American motion control industry, is the advanced line of SAMCOP Servo Peripherals. This servo system can be treated like a standard PC peripheral device while significantly improving the performance of motion control systems, offering maximum control and flexibility.

"This product line offers ease-of-use seen in very few of the competitive systems, and buying fewer components saves money for manufacturers," says Fred Martin, product market manager for Star Micronics.

Major feature -- mix and match technology

A major feature differentiating SAMCOP from traditional servo systems is the new Termi-BUS technology, which offers unified control of mix-and-match brushless and/or stepping motors. This allows for either simple or high-performance actuators to be driven by a single command controller, eliminating the need for separate controllers for each actuator.

In addition to decreasing the cost of servo systems by eliminating controllers, SAMCOP has the ability to connect with up to 16 axes. When upgrading or servicing the system, costs are less because there are fewer pieces to address. Distributed intelligence at the amplifier level eliminates the need for a specific PC motion card, which also saves money.

"The ability to store up to 16 different profiles on one axis, and to have this ability for up to 16 axes offers both flexibility and ease-of-use, which we believe will help open some niche markets," states Lev Barshay, systems integrator at Pyramid Industries, Inc., New Milford, CT, a manufacturer of small programmable controllers and custom boards.

Another improvement in the SAMCOP system is the SMAP programming software developed by Star, which provides the capacity for programming and supervision for any point-to-point (PTP) motion control system. SMAP operates in Microsoft's Win32 environment, with a built-in Human Machine Interface (HMI) and library that allow for easy high-level servo control via a graphic screen. Star offers three series of servo motors within the SAMCOP family, to provide support for any application. Both the R and the RC series are well-suited for use in closed-loop systems for stepping motors. The R series offers a separately placed motor and an amplifier, while the RC series saves space by combining the two, for applications requiring a compact servo motor. Both the R and RC series feature outputs up to 200W and are capable of operating at speeds in excess of 4500 RPM. The B series is designed for high-speed, medium power applications, and features a rated output between 200W and 1500W, depending on the motor selected. This third series consists of brushless servo motors for closed-loop control systems, with absolute or incremental encoders available for use.

Star also provides the CTA-1, a handheld programming tool designed to indicate command data for individual points as well as to edit common data in the nonvolatile memory that is built into the servo amplifier. Using the CTA-1 linked through the Termi-BUS SIO, data stored in the servo amplifiers can be edited up to the maximum 16 axes.

To market, to market -- ease of use and pricing seen as critical issues

This new technology is already being used in various applications in Japan, with markets being identified and developed in the US. Small space requirements and high speed movements (down to 80 W) are a niche market served by this new protocol. Lower pricing for these smaller systems does not sacrifice any of the sophisticated software features of the more powerful systems. Further, lower power units can be mixed with higher power units, since up to 16 axes, with 16 positions per axis, may be controlled via SAMCOP. In competing systems, mixing of light and heavy movements can be problematic -- not so with SAMCOP, whose distributed intelligence at the amplifier level eliminates the need for a motion card, which also saves money.

Market research by Star Micronics has led to two conclusions regarding new motion control systems -- most important to manufacturers are ease-of-use and price. SAMCOP has addressed these concerns with an ability to integrate existing hard and soft PLCs, compatibility with several PC-based systems and "mix and match" capabilities, which can combine motion control with other on/off functions. The ability to mix movement commands with other types of on/off controls makes SAMCOP a truly unified system, especially appropriate for 1500 W-and-under applications. Automation synchronized by sophisticated motion control systems such as SAMCOP brings a new generation of protocols to the wide-ranging world of automation applications.

For more information, contact Star Micronics America, Inc, 790-531 North Cedar Bluff Rd, Knoxville, TN 37923. 423-693-7700.
Circle 715.

The PC versus PLC Debate

- Frank Severance
Western Michigan University

Controllers usually reside in one of three areas. Some are standalone devices, but it is most common for the controller to be physically on a card and placed in a personal computer (PC) or programmable logic controller (PLC) to be run as part of the overall control system. Enter the great debate -- should the host be a PC or should it be a PLC? As in many arguments of this sort, a religious fervor many times seems to cloud the issues. Even so, there are good reasons for choosing one device over the other

Personal computers tend to be popular since many engineers are already familiar with them from desktop or academic experience. They are part of the popular culture. In contrast, the PLC tends to seem somewhat reclusive and therefore less familiar to many engineers. However, this characteristic is in reality its strong suit. While the PC tends to be user friendly and operator oriented, the PLC tends to be operator indifferent and task oriented. This is because the PC is designed with the extra layers of a user interface (Windows, most often) and responds immediately to keyboard strokes and mouse clicks. It also spends an inordinate amount of time updating screen displays. Since these user interface functions are given top priority, other tasks are delayed.

On the other hand, a PLC has no real need for sophisticated user interfaces and extra layers of operator oriented software. It concentrates almost totally on the logical and communications tasks at hand. Therefore, PLCs tend to excel in input/output processing, data stream handling and real time event-critical tasks. This, of course, is the stuff of dedicated control systems and is the reason why PLCs tend to be so popular in industrial control environments.

Structurally there is not much difference between PCs and PLCs. Both have motherboards with expansion slots, processors, memory and input/output. However, in the expansion slots of a typical PLC reside controllers, drivers, serial and parallel I/O and digital/analog converters and other engineering-based cards. A good PLC will be able to communicate via GPIB buses to standard engineering instrumentation. Add to this, industrial hardening of the enclosures and the ability to download programs from your PC to your PLC, and it is hard to imagine a better control environment.

When it comes to control, there is little that a PLC cannot do that a PC can. However, the debate will not go away quickly. As long as engineers like their personal computers, they will try to adapt Windows NT and 95 to real time computing environments. The real question is not so much which is better, but whether or not the PC is up to the task at hand.