The EMNet computer program has been developed to overcome the difficulties and reduce the errors that, heretofore, have been encountered in transferring data from computer-aided design (CAD) systems to computer numerically controlled (CNC) machines. EMNet could improve operations in almost any industrial machine shop that uses CNC equipment.

The difficulties and errors in question arise because CNC output files (files of numerical control data generated by CAD postprocessing programs) have customarily been transferred either by use of floppy disks or by manual entry of data into CNC equipment. Sometimes these files are too large to fit on floppy disks. Even when floppy disks are used, data transfers often fail. Moreover, although some programs for transfer of data from CAD to CNC operations have been commercially available, those programs are expensive, are usable only by persons who have advanced computer skills, and have caused failures of computer networks.

EMNet was designed for use by machinists who have little or no computer experience and are responsible for entering numerical control data into CNC machinery, as needed, to produce machined parts. EMNet features an easy-to-use “point and click” graphical user interface, and is available in versions for the Windows 3.x, Windows 95, and Windows NT operating systems. EMNet offers a full complement of Windows-style help displays for both machinists and computerworkstation administrators.

A computer on which EMNet is executed communicates with CNC machines via RS-232 serial interfaces connected according to specifications of the manufacturers of the machines. EMNet is easily configurable, and can be executed on a personal computer connected to two CNC machines. Each CNC machine can be assigned a name, a communication port, a default directory for data files, and options for whether to transmit carriage returns, line feeds, or end-of-block characters to the machine. If two machines are connected to a computer, the communication protocol for each port can be configured for the corresponding machine, separately from the protocol for the other port and its machine. Both the machine options and the communication- port settings are protected by a password that can be changed by a computerworkstation administrator.

After EMNet has been configured, the interaction required by the machinist is minimal. To transmit numerical control data to a CNC machine, the machinist performs the following steps:

  1. Choose the machine by use of frontpanel option buttons in an EMNet display. EMNet automatically switches to the default directory for the machine and opens the respective communication port.
  2. Click the “File” button on the EMNet display and select the file to transfer.
  3. Prepare the CNC machine to receive the file.
  4. Click the EMNet “Send” button.

To receive numerical control data from a CNC machine by use of EMNet, the machinist performs the following steps:

  1. Choose “Settings,” “Transfer,” “Receive” from the EMNet menu.
  2. Click the “Receive” button.
  3. Send the data from the control panel of the CNC machine.

EMNet also offers the capability of performing a byte-by-byte comparison of two numerical-control-data files. This capability was added to ensure that the data received by a CNC machine are intact; that is, without errors or missing bytes. To initiate a byte-by-byte comparison, the machinist performs the following steps:

  1. Choose “File,” “Compare” from the EMNet menu.
  2. Select the “known good” (original) file.
  3. Select the file to compare (typically, a file transferred from a CNC machine back to the computer).
  4. Verify whether the CNC machine includes a “program number” in the downloaded data, and if so, the line where the program number resides (typically line 2).

EMNet then performs a byte-by-byte comparison of the two files and displays the results. If a data mismatch is encountered, the comparison is terminated and the line and byte location of the mismatch is displayed.

This work was done by W. David Smith of Rothe Joint Venture, L. P., for Johnson Space Center. For further information, contact the Johnson Technology Commercialization Office at (281) 483-3309. MSC-22986