1 Software Concept of the Simulators

The CNC Simulators are employed in production as well as in vocational training and further education. We have made every effort to meet the complex requirements in both these fields of application by including appropriate new functions in the current Version 6.2 of our software, which makes the MTS Simulators one of the most efficient systems on the market today. This high performance is accompained by increased clarity and convenience of operation, due to the new user interface and function keys.

1.1 Performance Characteristics

Since the MTS Simulators can simulate all aspects of a CNC machine tool, they can also test NC programs for actual production; this includes checking for possible collisions as well as establishing workpart geometries (including thread geometries and roughness depths) based on the actual state of machining. No complicated changes of programming or control systems are necessary. Finally, a generalized postprocessor serves to translate NC programs into the programming code of any given CNC control system, so that they can be transmitted to the actual machine tool. 

The main performance characteristics of MTS Simulators are:

• open system qualities, in order to adapt the Simulators to different machine tools and control systems,
• configurable programming code based on the German Standard DIN 66025 and offering the full range of commands common to modern CNC control systems (including all standard machining cycles, contour strings, tool tip and cutter radius compensation),
• convenient NC programming with four different input modes available for specific tasks,
• dynamic update of the body lines of the workpart are dynamically updated during the machining simulation, achieved by a mathematical model of the workpart which allows even complex tool geometry; moreover, the theoretical roughing depth of each contour is generated from the given tool geometry, the course of the contour and the feedrate,
• collision tests, accounting for the geometry of elements in the entire working space (spindle, chuck, clamping device, tailstock, tool, turret/magazine) as well as for the actual machining, according to the tool motions programmed,
• measuring of the turning part, display of intersections and 3D-representations,
• storage and documentation of work results by easily handled NC program, workpart and status administration,
• convenient overall operation including such features as a setup form for automatic setup, an operating concept for Workshop-Oriented Programming (WOP) and a distinctly organised operation flow which corresponds to largely the actual handling of production machines and controls.

These characteristics make the Simulators a very effective means of support in industrial production; program errors can be avoided at an early stage and machine down times are reduced. Furthermore, the Simulators can be integrated into a complete CAD/CAM system environment, which helps minimise internal communication problems and ensures smooth production. 

In professional CNC training this objective is attained through a process of various stages. The MTS Simulators are not customised for a single learning path, but support a range of training concepts, offering a variety of possible solutions in NC programming and providing extensive information and help on every level.

• training system with all typical characteristics but not restricted to a specific control system, 
• full information on the actual state of machining, in every program function,
• comprehensive error indication and correction facilities,
• a range of learning levels,
• opportunities for independent work.

The MTS Simulators keep the user continuously informed on the actual state of the machine, with all operational functions supported by user dialogues. Collision monitoring and error messages means that NC programscan be corrected instantly. Convenient programming aid is available at any time on graphic help screens. 

From a didactic point of view an important advantage of working with CNC Simulators, as compared with employing a real production machine for training purposes, is the possibility to reduce complex operational procedures to a number of simple operations at the beginning. Complexity can then be re-established with each successful step in the learning process. With the four different programming modes provided by the MTS Simulators (NC Editor; Interactive Programming; Workshop-Oriented Programming; Teach In) NC programs can be generated step by step, while each NC command programmed is immediately executed by the machine tool. This concept offers an easy way to understand the abstract programming language. The system's additional features, such as adaptation to specific machines, real time simulation and precise collision monitoring inclusive of technology data, add up to a comprehensive representation of CNC technology. Experience has shown that the simulators provide an effective but nevertheless gentle introduction to CNC technology, taking away the fear of making mistakes.

The MTS Simulators are designed to permit CNC training independent of specific control systems or specific manufacturer's products. One main educational objective of this training is to give qualified skilled workers a profound basic knowledge, along with the ability to adapt their skills to varying machine and control configurations. The voide range of CNC control systems available, increasingly with integrated CAD functions, demand highly-skilled, versatile operators. Versitility in this context is above all the ability to adapt to different machine configurations, which is precisly the ability promoted by the MTS Simulators. Several years of practical evaluation at AEG's CNC training centre in Berlin have proved the undeniable value of this approach.

For purposes of CNC training the PAL programming code is also available, since it is this which is used by the chambers of industry and commerce in examinations qualifying for a certificate of proficiency.

In addition MTS offers a choice of more than seventy postprocessors for the translation of specific DIN-based controls. These are linked to the Transmission Program which allows variable configuration of interfaces as well as the definition of control characters for data transmission.

INCAD constitutes an Integrated NC and CAD System, functioning both as a full-range CAD system and as a very convenient NC programming system. Among its outstanding features are a uniform user interface, serving both programs, and a direct link to the Generalized Postprocessor, facilitating the adjustment to workshop conditions.

The CAD system of INCAD offers a number of very effective and user-friendly functions for the generation, modification and documentation of design drawings. Exchange of geometry data with other CAD systems is realised through data communication in the IGES, resp. DXF formats.

The NC programming system features separate tool and technology administration, which can be generated and edited by the user. Automatic generation of NC programs (which includes contour strings as well as all current machining cycles) is established through a process of reducing a design to single contours and subsequently assigning technology data and machining methods. A graphically supported interactive dialogue guides the user through this procedure. The reproduction of specific machine and control configurations in the CNC simulators means that NC programs for turning and milling can be tested and optimized before being sent to a real production machine.

All in all the MTS software modules add up to a fully integrated CAD/CAM package, offering practice-oriented and customised solutions for production and training.

Main machining modes available are the following:

• Setup Mode,
• Automatic Mode,
• NC Programming.

The uniform WOP operating concept applies to each of the CNC Simulators, and includes function keys, menu guidance and program dialogues. Auxiliary functions to facilitate program generation and optimisation are measuring, zooming, display of intersections and 3D-representation as well as a number of programming- and controlling aids.

Realistic simulation of the machine tool and its controls is an important precondition for flexibility of application; with MTS Simulators provide the user can define the geometry of the working space and the various machine elements such as spindle, chuck, fixtures, tools, turret, tailstock etc. These parameters are considered in the simulation and computation of the workpart geometry which, with an accuracy of 1 µm , is based on the actual machining, not on the programmed address values. Exact collision checks, taking all machine components into account, are carried out during program execution; errors are denoted in plaintext messages.

• Machine configuration: specifications of the machine tool (machine parameters) including geometry data and technical specifications.
• Control system configuration: definition of the programming code, specific default settings concerning the logic of controls, such as execution of subprograms, machining cycles, modal commands etc.
• Computer hardware configuration: specifications of the hardware employed, interfaces, periphery, graphic mode etc.

Each configuration is stored in a separate configuration file, which allows quick and convenient alternation between different default settings.

• The NC Editor supports direct entry or editing of NC blocks via its programming interface, especially suited for NC programs. Each NC block entered is subject to an automatic syntax check ("syntax" in this context being the internal structure of the NC blocks). There is also a check to ensure that the values entered fall within the permitted ranges.
• The Interactive Programming Mode, constituting a reciprocal completion of the Automatic mode and the Editor, is the easiest and most effective way to start on NC programming. During program generation each NC block entered is immediately executed in the simulation, including collision tests.
• Teach-In is a special kind of interactive programming. While the workpart is tooled manually, as in the Setup Mode, the tool paths generated in this way are automatically converted into G-commands (corresponding to DIN 66025) and inserted into the NC program.
• Using the WOP interface, complex contours can be programmed without any further aid. A dialogue system serves to query the geometry data given in the drawing: in addition to co-ordinate values the input of lengths, angles or tangential transitions is possible. Every unequivocally defined partial contour is graphically displayed; if various solutions are possible, they will be offered for selection. Chamfers and roundings can be inserted into a contour string by entering the chamfer width or the radius. All contours generated in the WOP mode can be measured and zoomed.

A new feature of the system is the so-called "Setup Form Interpreter". A setup form contains all information necessary to set up the machine automatically for a specific NC program. At the same time a setup form can be automatically generated from any machine status.

In addition to these applications the CNC Simulators provide a number of special functions designed for convenience of operation. Among these are:

• re-chucking (flipping) the workpart,
• display of sections and 3D - representation,
• measuring and zooming,
• display of traverse paths,
• a variety of programming aids.

• working space,
• information field,
• function keys.

• current tool co-ordinates,
• spindle speed, feedrate, active tool and compensation register,
• cutting speed,
• coolant and spindle engine status,
• increment or in automatic mode, the leght (min.) of the NC program run,
• blank dimensions (resp. in the automatic mode: the modal commands).

The keys <F1> to <F8> at the bottom of the screen serve to control the applicable functions of the CNC Simulator.

In automatic mode the line above is used to display the NC block being executed.

The colours used in the display can be edited at will (depending on the graphic card employed), e.g. to match the display of a given CNC machine tool.

Other CNC control foils may be used instead of the original MTS foil as long as the allocation of symbols, characters and digits is appropriately configured for each overlay. The user can then work with a variety of keyboard layouts at comparatively low cost. 

Concurrent use of different input media is also possible.

All configuration data (with machine, control and hardware parameters grouped separately) are stored in configuration files to be named by the user. This allows convenient "switching" between different configurations. The configuration files can be password-protected against unauthorised access.

The current Version 5.3 of the system offers considerably extended configuration possibilities, especially with regard to the components of the machine working space. This further increases the practical applicability of the simulators:

In the Simulator for Milling the workpart can be held either by a magnetic chuck, by a vice or by any number of gripping jaws.

A similar procedure applies to the Simulator for Milling; standard tools already defined are universal, angular, spherical and T-slot cutters and drills.

Appropriate error messages will appear if invalid blank dimensions have been entered, if the spindle is active, or if tool or tailstock are too close to the workpart.

Instead of defining a blank, prefabricated parts (e.g. castings) can be selected from a "parts file" to be inserted as a blank or a semi-finished part for further machining. Geometry data of such parts will automatically be read from the parts file. Conversely each semi-finished part can be stored in a file to be re-loaded at a later point in time.

The set of tools can of course be modified in the setup mode. All tools mounted will be graphically displayed; the same applies to the total set of tools in the tool file (cf. above, Ch. 4 ).

The predefined ("gauged") offset values of each tool can be read in from the tool file. When a "reference tool" has been defined, the offset values can alternately be established by "touching" the workpiece. Faulty offset values will of course lead to inaccurate machining or even collisions. At the same time it is possible as in general practice to create finishing allowances by entering slightly different offset values.

As well as normal program termination, the automatic run can be temporarily suspended to invoke such functions as measuring, zooming or 3D representation. The program run can also be terminated to call up a different machining procedure.

When the test run function is activated, the machining simulation is of course much faster than the actual machining would be in fact the speed of the simulation also depends on the performance of the Personal Computer employed. This does not however impede the exact calculation of machining times during the test run.

When the system is reset to the setup mode after program execution, the established feed times of the respective tools (cf. above Ch. 4) can be displayed.

With any NC program the traverse paths can be displayed, with feed motion and rapid traverse marked in different colours.

The programming code (the syntax) of the MTS Simulators has therefore been conceived as an open system: it is not fixed but can be edited or redefined by employing the "Free Definition Programming Code" to create a "Cross-Reference File". Thus the user can generate his own programming code, orientated on the DIN blocks, on which his subsequent NC programming will be based.

As all further generation of programming codes is based on the standard command code supplied with the MTS Simulators, this code is designed to provide a most comprehensive syntax. Among its commands are the following:

¹ cf. Ch.11 for a detailed description of the "Freely Configurable Programming Code"

² "Syntax" means here and in the following the formal structure of NC commands, i.e. the selection and assignation of parameters and the signs to the specified values.

2. Different programming codes (esp. the PAL code, cf. below, Ch.7.5) can be used in the training to point out the peculiarities of these codes and to make the trainees acquainted with their application.

The MTS control system provides programming of multiple-point contour strings and open contours, including sequences of "undefined" spans (entities). The "intermediate points" will be computed by the system (see Diagr.). Even contours of high geometric complexity can therefore be programmed easily, starting out from the design drawing of the part. No special mathematical knowledge or further aid is necessary. The process can be further facilitated by employing the "WOP-Interface" (see Ch. 7.4) which is specially designed for segment contour programming and offers convenient user guidance.

Extract from a Program

N021: Activation of cutter radius compens. to the right of the contour, with semicircular approach;

N023: circular arc (counterclockwise), 1st entity of an open four-point contour string, with absolute centre co-ordinates (P070); choice of alternate solutions (P001);

N025: tangential transition (P000) onto clockwise circular arc, 2nd entity of the open four-point contour string, with radius B specified only;

N027: tangential transition (P000) onto counterclockwise circular arc , 3rd entity of the open four-point contour string, with absolute centre co-ordinates (P070), radius specification; choice of alternate solutions.

In the following this entity is treated as the 1st entity of a closed four-point contour string;

N029: tangential transition (P000) onto counterclockwise circular arc , 2nd entity of the closed four-point contour string, with radius only;

N031: tangential transition (P000) onto counterclockwise circular arc , 3rd entity of the closed four-point contour string, with absolute (P070) centre co-ordinates and end co-ordinate in X, radius B specified and choice No.2 of alternate solutions (P002);

N033 Deactivation of cutter radius compensation, with semicircular retreat.

In the CNC Simulator for Milling the invocation of G41 or G42 allows cutting along the programmed contour with the appropriate cutter radius compensation (CRC). Additionally the approach and retreat movements of the tool can be programmed with the applicable NC commands: G45 (contour parallel approach / retreat), G46 (semicircular approach / retreat), G47 (quadrant approach / retreat).

As a special feature, the number of contour segments anticipated in the computing of the cutter radius compensation can be configured (only anticipation of the next span is a standard with CNC controls).

In the following overview most of the common standard cycles available as well as some complex machining procedures are listed:

Extract from a Program

N105: Rectangular pocket cycle, with specification of finished size, depth of pockets, corner radius and tool adjustments;

N110: Repeated cycle for machining along a straight line, with co-ordinates for the first execution, specification of angles, of distances between and number of pockets;

N115: Circular pockets cycle, with specification of radius and depth of pockets, the clearance plane and the tool adjustments;

N120: Single cycle, with specification of co-ordinates;

N125: Tool change, tool adjustment and machining data;

N130: Deep drilling cycle, with chip breaking, specification of drilling depth; 1st drilling level, dwell times and degression;

N135: Tool adjustment in X;

N140: Cycle for machining along circular arcs, with arc centre co-ordinates and radius, specification of cycle start angle, difference angles between starting positions of subsequent invocations, number of repetitions.

Tool Tip Compensation

Cutter Radius Compensation with Approach / Retreat Statement

Drilling Patterns:

Pocket Cycles:

• tapping

• boring
• reaming
• on a straight line (cycle)
• on a circular arc (cycle)
• rectangular pocket

Thread Cycles:

• standard threads
• tapered threads
• special threads

Each of these modes is designed to meet specific requirements, and with their clear layout and error messages they all offer convenient user guidance during program generation. It is possible to switch from one mode to another at any time during programming, and so to exploit the advantages of the different input systems.

1. a plaintext error message appears (e.g. "Collision")

The user can undo the machining effected by the faulty block by striking any key. Immediate correction in the respective program line is possible, then the simulation can be re-activated.

In this case the Simulator has successfully executed the programmed machining. It is now up to the programmer to decide (in the course of an interactive entry sequence) whether to accept the result. If approved, the NC block is adopted as part of the program being created and the system will be ready for input of the next program line. If the user discards the result, the machining effected by this block will be undone (as in the case of errors) where cycles are concerned, this may amount to a considerable number of cancelled movements.

The immedeate simulation of NC command execution and the direct correction of input errors has been widely approved in the practice of CNC training. Interactive Programming provides a clear, application-oriented introduction to programming, which is a perfect learning aid. In addition, it can be used alongside "Workshop-Oriented Programming", whenever the programming of complex contour geometries is required.

The WOP interface provided by MTS has all of these features plus some additional capabilities for convenience fo use:

• The MTS WOP interface can easily be installed to function with the CNC Simulators. Consequently, it is possible different programming modes to switch through, so as to make full use of the respective advantages of each system.

• In the course of NC programming the generated contour and the generating NC block are displayed together on the screen. That means, that the results of programming can be checked immedeately and the input correct if necessary. Geometry definitions are directly linked to the program generation.

• Conversely all programmed contours can be read in to be ready for editing by the functions of the WOP interface.

• The MTS programming code allows for programming of multiple-point contour strings and open contours, including sequences of "undefined" spans (entities). The user is relieved of extensive calculations, as the programming system confines the dialogue to prompts concerning a selection of valid parameters, inclusive of rounding and chamfering data. Thus the programmer can be certain of the contour being unequivocally defined and of its being executed on the workpart. In addition to this, auxiliary diagrams are available to help with the parameter input.

WOP programming generally starts out with the definition of a contour segment (entity) as a straight line or a circular arc (clockwise or counterclockwise) with either a tangential or non-tangential transition. The system then offers a choice of geometry input possibilities, including a check on the mathematical validity of inputs. If the contour entered is sufficiently determined, it will be graphically displayed online.

• Magnification of details: zooming,
• Measuring (especially dimensioning of threads),
• Accounting for roughing depths,
• Display of intersections,
• 3D-representation.

The zoom function is also available with Workshop-Oriented Programming and Measuring.

• entity dimensioning specifies all geometry data (start and end point, transition angles, lengths, circle centres etc.) of contour segments (straight lines or arcs), 
• point dimensioning establishes the distances of contour points from a definable dimension zero (with an accuracy of 1/1000 mm). 

During dimensioning the zoom or magnifying function can be activated for separate dimensioning of a workpart detail. Repeated magnification is possible, the maximum being a detail of 6/1000 mm by 8/1000 mm magnified to fill the screen.

Therefore, for each basic G function the area covered by the cutting edge is computed and brought to coincidence with the actual workpart contour - i.e. integrated into the internal mathematical model of the workpart. A theoretical roughing depth, established from the cutting edge geometry and the feed motion, is attributed to each contour span.

It follows from this calculation, that the only linkage between the generated geometry and the NC program data is the resulting tool motion. Furthermore this data model allows the graphic representation of body lines (true and apparent edges), relieve cuts, thread geometries and roughing depths, as well as a variety of intersections through the workpart. As a rule internal machining is displayed in half or full section, while external machining is displayed either in half section or in external view.

The (dynamically updated) motion of the cutter (with its spindle) can be viewed in a further overlay window, inserted in the intersection display. In this way the user always has three views of the machining process, which means convenient and precise control of the NC program execution.

Finally, the screen display as described above can be complemented by screen representations of freely definable intersections through the workpart. This mode of display allows free movement of section areas in the X and Y axes, independent of the cutter centre position. Once more the intersection display is dynamically updated. A line (which of course can be edited) indicates the Z plane.

The transmission program is designed to transmit NC programs without any changes of format or syntax. Certain control characters, such as for encoding program start and program end or line feed can be defined by the user. To facilitate the interface configuration and to ensure a perfect interconnection, the transmission program allows the link between the Simulator and the target machine control to be tested before it is actually established.

The postprocessors change the MTS-coded programs into basic NC blocks which correspond to the DIN standard and whose syntax is compatible with the dialect of DIN used in the target control. At present more than seventy postprocessors are available. 

The most economic solution for the translation of NC programs is the Generalized Postprocessor, which enables the user to determine cross-references of commands in the translation. Provided that these features are supported by the target control system, the performance characteristics of the Generalized Postprocessor are the following:

• Addresses are changed if necessary,
• Formats of values of the addresses are adapted to the control,
• Subroutines are kept during the translation,
• Parameters are retained or added,
• Cycles are transformed into the respective cycles of the target control,
• Segment contour programming is kept while being translated into G-functions.

The capabilities of the target control system as well as of the MTS software are used to the full in the translation. With its user-defined command references between the source and the object code, the Generalized Postprocessor is a powerful and universal tool which can adapt the MTS software to a wide variety of CNC control systems.

In addition to the MTS and PAL programmings codes we also offer a software module, which allows the application of any other NC syntax in the CNC Simulators. Provided you have the "Free Definition Programming Code" license, NC blocks of the foreign syntax can be assigned to the respective MTS syntax blocks. In this way a foreign command code can be used to generate NC programs in the CNC Simulators.

A definable programming code file serves to convert the various NC commands. The comprehensive "command standard" of the MTS programming code means that even NC commands from a foreign programming code can be assigned to MTS-coded commands. The "translation" of single NC blocks is then carried out, based on there cross-references.

Each new programming code file is generated with the help of a special editor, which can be invoked from the configuration program. Programming codes which are already part of the configuration can easily be selected or edited for use with a task in one of the CNC Simulators.

¹ For a description of the MTS Programming Code cf. above. Ch.7.

Once the help function has been activated, any number of help windows can be called up. The user can browse through sub-headings, e.g. to compare related commands, or jump from subject to subject to obtain wider information. During interactive programming or program generation with the NC Editor the programming level can be re-activated alongside the help function, and an NC block corrected or entered directly.

The programming aids are designed to support the basic didactical concept of the CNC Simulators. On one level, the user is provided with immediate answers to any questions he may have, while on another level, help windows providing information on wider aspects of programming are available. The reputation of the MTS Simulators for learner-friendliness is due in no small way to there extensive help facilities.

Hardware requirements for running the MS-DOS Version 5.3 of the MTS CNC Simulator package are as follows:

• 4 MB of RAM
• a 80386, 80486 or pentium processor
• 8 MB to 10 MB of available storage capacity on hard disk, depending on the extent of the software employed
• a floppy disk drive (5 ¼" or 3 ½")
• a serial interface, if a graphic tablet or mouse is to be used
• a parallel interface to connect the software protection module (hardlock); this interface can also be used to connect a printer
• one of the video cards listed in the following:

- HVGA (1024 x 768 pixels)
- SVGA (800 x 600 pixels)
- VGA (640 x 480 pixels)

For use with 80386-processors
• a mathematical coprocessor is not required but highly recommendable (because of the extensive mathematical calculations necessary)

Optional enhancements of the systems are:
• additional interfaces for peripheral devices (e.g. tape reader/ puncher, plotter, mouse-devices [Microsoft, Genius etc.]) or a direct connection to a CNC machine tool.