Spiral bevel gears transmit motion between intersecting shafts and are produced on machines whose tooth-flank geometry depends on a set of cutting adjustments rather than on a single tool profile. On a CNC generator, values such as cradle angle, roll ratio, horizontal wheel position and vertical wheel position must reach the part program as numerical data, together with auxiliary settings such as saddle infeed/withdrawal time, indexing time and cutter spindle speed. A standard SINUMERIK Operate interface exposes these values as generic R parameters or program variables. Changing to another gear therefore requires locating and editing the correct variables in one or more programs—an operation that is slow, indirect and prone to error.
A dedicated human–machine interface (HMI) can hide this variable-level complexity behind gear-specific labels. In the implementation described here, an EasyXML configuration is used on a Siemens SINUMERIK 828D-controlled spiral bevel gear cutting machine; the same approach is applicable to the 840D sl when the required number of controlled axes makes it appropriate. The HMI provides three functions: entry and viewing of cutting parameters, management of parameter files, and live display of machining data. Its purpose is not to replace the CNC kernel but to organize the parameter set that the NC program consumes and to generate the machining program from that set without manual editing of R variables.
Gear-specific parameters as the interface contract
The cutting adjustment data for a spiral bevel gear are defined by the generating process. Cradle angle and roll ratio determine the relative generating motion, while horizontal and vertical wheel positions locate the gear blank relative to the cutter. Auxiliary values control non-cutting and support motions: saddle infeed and withdrawal, indexing between teeth, and cutter spindle speed. In the CNC program, these quantities are represented by R parameters. The HMI maps each operator-facing field to a defined address, so that a named parameter on screen is always the same numerical location in the control.
Typical bindings used in the interface include nck/Channel/Parameter/R[153] for roll ratio, nck/Channel/Parameter/R[112] for cutter spindle speed, and nck/Channel/GeometricAxis/actProgPos[1] for the current X-axis position. The first two belong to the process-parameter layer; the third belongs to the machining-status layer. This separation is important. Process data should be stable and deliberate, whereas position and speed data must refresh continuously during cutting.
XML form controls support both behaviors. A field can be declared read-only with a fixed numeric format, or made editable for a file-modification screen. A control marked with a hot link follows changes in the referenced NC value without requiring a separately compiled polling application. The HMI is therefore a presentation and parameter-management layer over the control’s existing numerical model.
EasyXML project structure
EasyXML projects are built from configuration files stored in the manufacturer area of the CNC file system, under the SINUMERIK HMI directory. The startup file xmldial.xml defines the main menu, the initial form, and the soft keys that open subordinate screens. Other dialog XML files are brought into the project through INCLUDE declarations. Dialog definitions are placed in the appl directory, while bitmap images in BMP or PNG format are placed in the ico directory. When the configuration is placed in the designated manufacturer directory, the control compiles and displays the new interface automatically.
This file-based structure separates screen presentation from machine logic. A soft key definition contains a caption, a position in the menu, and a navigation target. A form definition contains the window caption, the positions and sizes of controls, and the variable path to which each control is bound. The main menu can therefore expose “Machining,” “Process Parameters” and “File Management” as operator-level functions while the underlying NC variable names remain hidden. The same project can also include images for the startup screen or for process illustrations without changing the NC program.
Functional modules and operator workflow
| Module | Purpose | Implementation basis |
|---|---|---|
| Process parameters | Display cutting adjustments and auxiliary values using gear-specific names rather than raw R-parameter numbers | Read-only XML controls bound to NC R parameters; the active parameter file determines the displayed set |
| File management | Create, modify, delete and upload parameter files for different gears or process variants | Built-in text-file read, write and remove functions; semicolon-delimited values are split and converted to numeric fields |
| Machining | Show current axis coordinates and cutter spindle speed during production | Hot-linked read-only controls bound to channel and axis variables |
The operator workflow follows the module boundaries. A parameter file is first selected or created in file management. The cutting and auxiliary values are then reviewed on the process-parameter screen. Uploading the selected parameter set causes the CNC system to generate the machining program according to the corresponding R parameters. During cutting, the machining screen displays live axis and spindle data. In this arrangement, the file preserves a reusable process recipe, the R parameters provide the live connection to the NC program, and the HMI controls what the operator can see or change at each stage.
File management and parameter persistence
The file-management screen is opened from the main menu and is implemented in rcp_manage.xml. Its parameter files are text files whose fields are separated by semicolons. Reading a file calls doc.readfromfile, splits the returned string at the separator, converts the selected fields to floating-point values, and assigns them to interface variables. This allows the screen to show a structured parameter list instead of a line of raw program text. The path of the current configuration file is held as a variable, so the same dialog can operate on different files without redesigning the screen.
Modification uses a related dialog in recipe_modify.xml. The field type is changed from read-only to editable, and a Save soft key writes the edited content back with doc.writetofile. Deletion is handled inside the management dialog by doc.remove. A new file is created through recipe_new1.xml; the default file name is defaultpara.txt, and the initial values are taken from the parameters of the associated program. The operator can then replace them with the values required for the next gear and save the file.
This approach gives parameter files a practical role as part-level process records. A file can hold the cutting adjustments and auxiliary settings for a particular gear or process variant, allowing changeover to begin from a known set rather than from an empty variable table. Because the file operations use the control’s built-in document functions, the HMI does not require a separate database or an external file server.
Process parameter display and NC program generation
The process-parameter screen is opened through xmldial.xml and is implemented in canshu.xml. It presents the selected file’s adjustment values as read-only fields. Roll ratio, for example, is bound to R[153] and formatted as an integer in the interface definition; cutter spindle speed and axis-position fields use a %6.3f format where finer display resolution is needed. The read-only setting protects the process view from accidental changes: deliberate modification takes place through the file-modification path, not by touching a value on the monitoring screen.
The Upload soft key connects the parameter layer to program generation. The CNC system generates the machining program from the R parameters corresponding to the values shown on the process-parameter screen. The interface therefore does not require the operator to open the part program and rewrite individual variable assignments. It supplies an organized, gear-oriented parameter set; the generation and execution of the machining program remain functions of the CNC system and its associated background program.
This distinction is technically significant. The HMI is not a gear-design calculation engine and does not replace the generating theory embedded in the process. Its contribution is to make the required machine settings visible in the language of the gear-cutting process and to ensure that the same settings are transferred consistently to the control. The result is a shorter editing chain and fewer opportunities for a wrong variable to be changed.
Machining screen and live machine data
The machining screen is intended for production monitoring rather than parameter entry. It displays the current coordinates of the machine axes and the cutter spindle speed. The X-axis value is read from nck/Channel/GeometricAxis/actProgPos[1]; the spindle-speed field is bound to the relevant channel R parameter. Both controls are read-only and hot-linked, so the displayed values follow the machine state during the cycle.
The interface definition also sets numeric formats and refresh behavior for these fields. Position and speed values use a %6.3f display format, and the axis-position control uses a high refresh setting so that the coordinate display remains responsive during feed motion. This is a modest but useful function: the operator can confirm axis motion and spindle speed without leaving the dedicated gear-cutting interface or opening a generic diagnosis page.
Engineering scope and deployment
The configuration is intended for Siemens 828D and 840D sl systems, with the choice governed by the number of controlled axes and the machine architecture. Its main technical advantage is that a gear-specific HMI can be created through XML configuration and built-in file and variable functions, without modifying the CNC kernel. Screen layout, soft-key navigation, parameter labels and data bindings are all held in the manufacturer file area, while the control continues to execute standard NC programs and motion functions.
The same property defines the engineering constraint. Each control is bound to an explicit NC variable path, and each file-management function depends on a defined directory and file format. If the machine configuration, R-parameter assignment or controller software changes, the bindings and file paths must be checked against the new configuration. The HMI also assumes that the manufacturer directory and parameter files are protected against unauthorized editing, since they directly influence the values used for program generation.
The described interface has been deployed commercially at scale on spiral bevel gear cutting machines. Its significance lies less in a novel control algorithm than in the organization of an existing CNC data model: gear-cutting parameters are presented as named process values, parameter sets are stored and reused as files, and live machine data are kept separate from editable process data. For small and medium-sized gear manufacturers, this is a practical route to a dedicated machine interface while retaining the standard Siemens control platform.