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	Figure 1: As the system's data collection device, Z·World's Ethernet-enabled BL2000 single-board computer (3.43" x 4.15" x 0.82") mounts inside a centrally located enclosure.

Each year, manufacturing companies lose untold sums in lost production hours and replacement and repair costs associated with tooling and parts failures on their machine tools and computer numerical control (CNC) machines. That's why more and more firms are now investing in state-of-the-art tool monitoring and control systems that protect capital equipment and ensure quality control of precision-crafted parts. These systems closely monitor cutting processes and provide valuable information that can be used to reduce cycle time, increase tool life, and improve the bottom line.

	By Rob Caron President Caron Engineering Wells, ME

For the past 15 years, Caron Engineering's Tool Monitoring and Control System (TMCS)-which is used by manufacturers of high-production components, such as General Electric, Ford, and General Motors-has relied on single-board computers from Z·World (Davis, CA) to perform its essential control functions.

This year, we at Caron looked to implement a major redesign that would improve system throughput, boost code capacity, and better integrate Ethernet communications. Our overriding design challenge was to find a controller that would provide these capabilities and more in one affordable package.

The solution we chose was the BL2000 Wildcat single-board computer from Z·World (Fig. 1). The controller features built-in Ethernet, a Rabbit 2000™ 8-bit microprocessor with 22 MHz clock, 128K of SRAM and 256K of Flash memory, and four serial ports. It also has up to 28 digital I/O, including 12-bit analog I/O.

Inner Workings of the TMCS
Caron's TMCS operates on the principle that the horsepower required to cut a part increases as the tool's cutting edges deteriorate. The system measures and displays true motor horsepower for spindle and/or feed axes, determines when a tool is worn or broken, and commands the CNC machine to take corrective action before tools or parts are destroyed.

System components (Fig. 2) include the BL2000 acting as the data collection unit, a display for user interface, a horsepower transducer, machine I/O, and charting software for data management. The transducer, connected in line with the spindle motor, allows the system to learn the peak cutting horsepower for each tool. The user can then program limits for extreme wear and undercut conditions.

The TMCS monitors spindle horsepower and compares it to the set limits. If horsepower exceeds a limit, the system can respond by issuing a feed hold, interrupting the cutting program, and calling a sub-program to retract the worn tool and replace it with a spare. For cutting processes that require utmost precision, a unique adaptive control option executes automatic feedrate control, maintaining a constant horsepower to optimize cycle times.

	Figure 2: System components include the BL2000 acting as the data collection unit, a display for user interface, a horsepower transducer, machine I/O, and charting software for data management.

Control Issues
As the system's controller, the BL2000 handles most of the parallel or serial machine interface, as well as Ethernet or RS-232 communications to the system's display side (either a PC-based application or Windows CE box). All cutting limits-for up to 500 tools and 7 sections per tool-are stored on the SBC, which also saves the last 300 alarms with time/date stamps via its real-time clock.

Data storage capacity is important because today's CNC machines carry large magazines that hold a wide variety of cutting tools, as well as some of redundant units. When the settings warn that a tool is becoming dull, the TMCS simply calls up a spare to replace the worn tool.

Data for on-screen calibration and a digital voltmeter also come from the BL2000. On-screen calibration can be done for both zero and gain, and the digital voltmeter displays analog motor inputs. To accommodate all the custom programming that we do, we have installed a number of algorithms on the SBC. For example, a fuzzy logic engine handles adaptive control, while a software-based infinite impulse response filter ensures a clean transducer signal. Most other TMCS programming functions are also performed on the BL2000.

Smooth Transition
Transitioning to the BL2000 allowed us to discard the external Ethernet modem we'd used for data logging in prior versions. The Wildcat's 10Base-T Ethernet port streams process data directly through an RJ-45 connector to the system's customized charting application, WinChart 2000™, which records and stores cutting horsepower, start/stop signals, alarms, spindle speed, and coolant flow during operations. This information can then be used to evaluate cutting conditions and diagnose problems with the machining process.

The BL2000 not only stores more code and processes data faster than our previous board, it also has a lower price tag and a smaller form factor (3.43 x 4.15 x 0.82 inches). Meanwhile, the Wildcat's multiple built-in analog-to-digital channels eliminate the need for a separate A/D board and improve our system's resolution and response time.

Developing Story
Developing Caron's new TMCS was easy for a couple of reasons. First, we already had an effective product on the market based on a Z·World SBC. We simply implemented the same functionality into the BL2000 system and tested in our standard fixture. Second, software development for the new Rabbit-powered BL2000 was simple using Z·World's Dynamic C® development system. This integrated C-language editor, compiler, loader, and debugger helped us quickly modify our existing software for the system.

Dynamic C eliminates the need for in-circuit emulators and provides a variety of device drivers and custom libraries, including royalty-free TCP/IP stack and the MicroC/OS-II RTOS (real-time operating system). We've made extensive use of the TCP/IP libraries to configure Ethernet communications, and the real-time kernel enables us to effectively manage multitasking on machine tools.

A Distinct Advantage
Upgrading Caron's Tool Monitoring and Control System with the BL2000 single-board computer helps us offer parts manufacturers an unprecedented degree of control over their cutting processes-reducing cycle times and increasing tool life, thereby providing a quick ROI.

About the Author
Rob Caron attended the University of Hartford. He worked at Pratt & Whitney Aircraft for several years in electronics, then started in the CNC industry in the early '80s, working first for a machine tool dealer where he designed add-on enhancements to CNC machine controls, including monitoring and measuring products. He started Caron Engineering in '86 and now has several engineers working for him. He is a registered PE in electrical engineering.

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