`Soft Motion' Follows Nontraditional Paths
M otion control finds itself, increasingly, an intimate part of the overall machine or process control system. As such, motion control is often associated with PC-based control that relies heavily on software functions. Soft motion is an emerging subset of PC-based control-similar to the development of soft logic-where motion control functions execute in software, entirely on the CPU of the industrial personal computer.
Soft motion is characterized by the absence of proprietary hardware or motion control boards. This methodology integrates all the necessary software components into an industrial PC-usually on a single CPU. With motion control as a PC-based function, integrating all parts of a control system can become a reality. These other functions include logic control, operator interface, supervisory control, data acquisition, communication, and system diagnostics. Application software aspects of soft motion, such as motion path generation, remain the same as in a standard motion control implementation.
Real-time control, interface requirements
Reliability and processing power of the operating system has been a restraint on the growth of soft motion. Availability of real-time extensions to the operating system, particularly to Microsoft Windows NT, is propelling the use of soft motion. While some motion applications can work with Windows NT (or other) operating system, critical, high-throughput applications require a real-time operating system (OS). Some refer to an OS with such capability as 'hard real-time.' Operating systems that provide hard real-time capability without extensions will bring on the next growth phase for soft motion.
More manufacturers are offering real-time extension for operating systems. Examples include Nematron (Ann Arbor, Mich.-HyperKernel), Radisys (Hillsboro, Ore.-Intime) now marketed by TenaSys (Beaverton, Ore.), and VenturCom (Cambridge, Mass.-RTX). See the article in Control Engineering (Sept. 2000; pp. 70-72, 85-89) for more about operating systems and these companies . For its part, Microsoft (Redmond, Wa.) has just recently introduced Windows CE version 3.0, an embedded operating system with hard real-time.
A further enabler for implementing soft-motion is the interface protocol between the motion controller and motor drive. SERCOS (Serial Real-time Communication System) is very often associated with soft motion control because of its digital motion system origins and its status as an international standard (IEC 61491). Today some 120 controller and drive vendors support SERCOS with compatible products. See main soft motion article for more on SERCOS.
FireWire (IEEE 1394) is another network interface making itself known in motion control and servo-drive applications. Credentials of this digital serial bus for PCs include rapid data transmission rates up to 400 Mbit/sec and its association with the IEEE standard. The origins of FireWire are in computers and consumer electronics.
Other network interfaces-including proprietary ones-are also in use, as mentioned in connection with a sampling of soft motion products and companies below.
Beckhoff's TwinCat Software System unifies soft motion with PC-based control.
Companies going 'soft' on motion
PC-based motion control made its debut in the machine tool sector. More recently, soft motion methods are starting to see play in general motion control (GMC), robotics, and factory automation.
Beckhoff Automation LLC (Minneapolis, Minn.) now offers its PC-based control solutions-including software-based motion control-in the U.S. The parent company, Beckhoff Industrial Electronics (Verl, Germany), claims 15 years of expertise in PC-based control, along with being a notable developer of PC-based hardware and software products. Among its hardware products are industrial computers, control panels, fieldbus components, and I/O systems.
Beckhoff's main product line is TwinCat, a purely software-based offering, in which software processing replaces all traditional PLC and NC tasks. TwinCat, for 'Total Windows Control and Automation Technology' is a real-time control software package for PCs that incorporates I/O access for 11 fieldbuses and TCP/IP, programming tools, and HMI interfaces. Its software PLC is IEC 61131-3 compliant, and a motion control package is included for point-to-point and interpolation control.
TwinCat supports up to 256 motion axes for various types of drives-such as servo (electric and hydraulic), variable frequency, and stepper drives. All major feedback sensor types are also supported. TwinCat version NC PTP offers point-to-point axis positioning calculated on the PC processor. It replaces traditional positioning modules and numerical controllers. TwinCat version NC I includes continuous path control via a G-code interpreter, along with 2-D and 3-D interpolation of geometric curves-also done on the PC. Electronic gearing and camming, programmable limit switch, and flying shears are some motion functions incorporated into the software control.
Architecture of TwinCat consists of run-time systems (servers) for real-time control program execution and programming environments for system or user programming, analysis, and configuration, says the company. Extensive software display tools aid the user with all aspects of system operation from startup to maintenance and visualization. TwinCat I/O supports numerous field bus networks and drive interfaces, among them SERCOS, Profibus-DP and -MC (motion control), and Lightbus. The latter bus is Beckhoff's own high-speed fiber-optic I/O system created for fast machine and motion control via PCs. Lightbus claims cycle times of less than 1 msec.
'Our real-time extension to the operating system was developed in-house; it's not a third-party product,' says Gerd Hoppe, president of Beckhoff Automation. The real-time extension works under Windows 2000, Embedded NT, and NT. It ensures that Windows NT processes important tasks during hard real-time usage without affecting or restricting NT properties.
Beckhoff cites numerous TwinCat applications controlling large numbers of motion axes from a single industrial PC. These applications include metal stamping, continuous laminate presses, injection molding machines, and rubber tire production (with 19 servo axes controlled from one IPC).
AML Soft Motion Controller for Windows NT was introduced by Automation Intelligence in 1999.
Automation Intelligence (Duluth, Ga.) introduced AML, its software-based motion control in 1992. The latest version of AML for Microsoft Windows NT includes VenturCom's real-time extension (RTX) operating system and SMS-PCI, a passive SERCOS interface board from Sanyo Denki. AML also supports a large variety of communication interfaces and interface standards, such as Ethernet, DeviceNet, Profibus-DP, and RS-232/422/485. Because AML runs on Windows NT, there is additional support for popular standards like OPC, ActiveX, and DDE. Automation Intelligence is a subsidiary of Sanyo Denki of Japan. (For more on AML, see 'Soft Motion' article .)
Manufacturing Data Systems Inc. (MDSI, Ann Arbor, Mich.) has for some time specialized in software-based CNC (computer numerical control) systems. Its core product, called OpenCNC, allows numerous types of machine tools to have a common motion control method. Because the all-software technology is reconfigurable, the soft motion control can be customized for lathes, mills, grinders, single- and multi-spindle precision drills, routers, gear hobs, and other machine tools, according to MDSI.
A SERCOS digital-drive interface is among standard features of OpenCNC Version 5.0. The latest version of the product (OpenCNC 5.1) now makes soft motion control Internet-enabled as well. This added capability on the factory floor helps bring more access to real-time machine data from business and execution systems located throughout an enterprise.
MDSI has shown that sophisticated multiaxis CNC machine tools and other motion control applications can be controlled entirely from software, running on a single processor and using a single operating system, Microsoft Windows NT.
Just announced by MDSI is the selection of OpenCNC software as a standard control for a new line of Wissner Gamma 303 high-speed cutting machines. Wissner GmbH (Göttingen, Germany) is an original equipment manufacturer of machine tools.
In an earlier announcement, MDSI reported a joint technology partnership with Advantech Automation Corp. (Taipei Taiwan), a manufacturer of PC-based industrial automation solutions, including panel PCs, industrial PCs, workstations, embedded PCs, and data acquisition and control devices. Advantech intends to incorporate MDSI's soft motion control into a new product solution for the general motion control and industrial automation markets, through its Industrial Automation Group, located in Cincinnati, Ohio.
From Baker Motion Control (Seekonk, Mass.) comes a related product called MotionSoft. This state-logic, icon-based motion sequence programming tool allows users to program a large variety of motion control cards without the need to know native code or special languages associated with the cards. MotionSoft is said to be completely motion-card independent.
MotionSoft is not a text editor. The software tool provides a series of fill-in-the-blanks-type forms that simplify description of complex motion-control sequences and other application variables. Many common applications are preprogrammed and the user only has to define specific data. According to Baker Motion Control, 'MotionSoft does for motion programming what Visual Basic did for [Microsoft] Windows programming.'
Another company in this arena is Soft Servo Systems Inc. (Waltham, Mass.), focusing on the development and manufacture of PC-based servo controllers and software for machine tools and factory automation. The company's 'soft motion' products run on Windows NT, with essentially all functions-such as current feedback, NC path generation, plant monitoring, communication, user interface, etc.-done on a single host CPU.
Field-programmable gate array (FPGA) technology serves as an economic tool to reprogram the servo control for diverse applications. For example, the servo interface can work with many different servo motors and encoders because FPGA methods permit the resident chip to be reconfigured. It is only necessary to download particular software files to handle differences in the hardware protocols. A proprietary 20 Mbit/sec fiber-optic link is used to transmit information for setup, control, and maintenance.
Still ahead, users' views
Soft motion is still a developing technology. To fully succeed, it must compete head-on with well-established, traditional motion control methods and their large inventory of installed products. Also, users need to be more informed about the benefits of this newer alternative technology. Very limited (unscientific) feedback received from users indicates that not many are aware of the full potential of soft motion.
Here are some things that users (or potential users) like. Motion control through software and intelligent drives; reduced commissioning time to hold down overall system costs, even at a 'slight premium for the SERCOS interface;' and one motion control solution usable for various applications, saving the need to learn to operate hardware from different manufacturers are among favorable points.
At the same time, users still worry about PC operating system performance, enough computing power for other associated tasks, and the potential of crashes. One general remark in answer is that personal computers advocated for soft motion are industrial personal computers, not the lowest-priced units available at the nearest computer store, intended for home and office use. Some user concerns are being answered by more real-time extensions to operating systems, newer operating systems that include hard-real time, control, and other developments, as discussed in this Online Extra and the accompanying September 2000 Control Engineering article on PC-based, software motion control. However, the most practical demonstration of soft motion's capabilities comes from the growing number of successful applications.
Although soft motion follows nontraditional paths, these are two-way paths. Potential users need to learn more of what's out there, while suppliers of the technology need to be more informative.
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