The 3B: Laser Power + Beam Diameter & Position

Finally a cost effective, simple to use, precise industrial tool for measuring 3 beam parameters, all relevant in laser processing: the laser beam power, its diameter and its variations, the beam position and its changes. The value of laser power is provided by heads that come with NIST/PTB calibration; diameter and displacement are given with 100μm resolution. All from the same instrument.

This instrument is also totally safe and environment friendly since there is absolutely no emission of toxic fumes, as it happens when burning plexi sheets on similar applications. What achieves all this is the 3B , another goal from LaserPoint technological developments.

The 3B is a monitoring system that measures, displays, stores and logs data of the above fundamental parameters of a laser beam. It’s integration within machine control systems, offers new and unique diagnostic possibilities to system integrators, end user and service engineers.

Examples of 3B applications are:

• Alignment of machine’s complete beam lines, from laser source to focussing lens.
• Check of displacement of focus height over the entire working area (e.g. in flat bed laser cutting or welding applications) by mapping, with off-focus diameter measurements, the area of interest.
• Monitoring of welding processes by linking diameter variations to the corresponding shifts of focal positions.
• Map ping of laser beam diameters for applications using adaptive optics.

3B: THE SYSTEM

The 3B is a semi-automatic system composed by the following sub-assemblies:

• the 3B Detector head which faces the laser beam and absorbs the complete power up to 6KW. A major advantage of spanning to the maximum of laser power, is monitoring at the same beam conditions used in the working application.
• the 3B Electronics box hosting microprocessor controlled electronics units with high reading accuracy and resolution for data collection, analysis and display and data logging. The data logger has a large memory and a fast offload speed .
• SW packages: one for data measurement and visualization with PC and the 3B Data Logger Software to save/access memorized data .

The 3B can work either associated to a PC or as a Stand Alone unit. Operation with a PC allows Alignment operations, Live and Long Term Monitoring, and Quick Measure of Laser Parameters; this latter operation can also be made when working Stand Alone , in which case an external PC is only used to download stored data. Three working modes are switch selectable from the 3B electronics housing:

• StandAlone: the 3B measures and internally stores data without communicating with a PC
• PC « 3B: In this operating mode the 3B is controlled by a PC, via the supplied 3BSoft.
• DL « PC: in this mode the Data-Logger is in communication with a PC, via an RS232 serial port, to download measured data gathered and stored in the Stand Alone mode.

The 3B readout and data logger electronics are embedded in robust, IP65 rated cases.

Initial References: Set-Up and Alignment

To maintain, over time, a constant quality for the running process it is necessary to set the acceptable tolerance for each of 3B’s working parameters (e.g. set the Min and Max power ).

Alarms signals will be generated each time the defined limits are overtaken, whichever operational mode of the 3B has been selected. The handling of these signals will be managed by, e.g., the machine’s PLC to switch-on alarms or stop the process.

Values of alarm settings will be automatically saved and stored within the 3B internal memory . At the initial stage, prior to any measurement, the 3B head has to be perfectly aligned and positioned to be centred onto the system optical axis.

Alignment and fixing alignment parameters are very preliminary operations, necessary to have information which will be used as references for next measurements. Any further occurring change will be then referred to those reference values.

With a perfectly aligned beam, X and Y will be at 0; nevertheless, if the application can accept some tolerances, X or Y can be slightly shifted, e.g., by 0.1mm. These values will be the references and any successive variation will be thus referred to 0 (or 0.1).

For alignment purposes, the 3B detector has to be located in a fixed position and its electronics connected to a PC; the laser beam is moved looking for the sensor centre, until the screen shows the X and Y values = 0; alternatively, a carefully pre-aligned (e.g. mechanically) 3B head can be finely moved facing the laser beam until X and Y go to 0.

After the set-up procedure and the system alignment , the 3B can be used either for Live Monitoring, typical for continuous measurements that run over long periods, or for Quick Measures that last a few seconds .

3B OPERATIONAL MODES

The Stand Alone Operation

T  he Stand Alone Operation is provided for periodic and quick overlooks of laser parameters in environments where PCs are not directly available on the process site. A PC is only needed for the initial alignment and set-up.

The Stand Alone Operation is used to verify that beam behaviour remains constant , at least within pre-fixed limits, over a period which can be days or weeks. Each of these periodic checks only lasts some seconds after which beam data are stored within an internal memory to be, anytime later, downloaded to a spreadsheet (e.g. into an Exel file) by means of the datalogger.

The max number of acquisitions is 1552, which permits, for example, to monitor laser parameters every ½ hour over a period of 1 month before the need of downloading! This feature provides a tracking of working parameters unavailable up to now. There is no screen visualization of data but, for the safety of the process, should Power, Diameter or Displacement exceed their pre-set acceptable working range, alarms will be however generated.

In Stand Alone operation when laser power is above a starting threshold, the LED corresponding to MEASURE blinks and, at the same time, the “ Measurement in Progress” contact will close on the AUX I/O connector. As the measurement is over, acquired data will be stored within the 3B electronics and the contact will open.

The 3B internal memory will be continuously filled to its limit of 1552 acquisitions after which a download of data to PC is necessary Should any of laser parameters be out of the pre-set band, the corresponding LED will light and the corresponding contact will be closed.

The DB25 Aux I/O connector is used for the trigger input and connections with external alarm relays to start alarm lamps, stop the process , etc.

PC Operation and the 3B Soft (PC < > 3B)

When the 3B is connected to a PC (PC < 3B), the 3B Software screen will display a multi-function page that bears several, easy to use, operational boxes and displays to give access to the set-up page, the alignment function, live or periodic monitoring.

Long Term, Live Monitoring

The main page shows, in real time, measured values and whether modifications of the laser beam are occurring .

• Power: the beam power value is displayed in Watts.
• Diameter: shows the beam diameter with 100μm resolution.
• X Centre and Y Centre: are the calculated centroid position along the X and Y axis. Any displacement is shown in real time with 100μm resolution.
• Centroid & Diameter: two black circles define the Min and Max acceptable beam diameter which have been preset in the Set-Up page . When the laser is switched on, a third ring (blue) simulates the laser beam with its average diameter and position. If the blue ring location remains within the limit rings, its centroid (red dot) shows how far the beam is from the alignment position (e.g. X=0 and Y=0).
• Behaviour of Power, Diameter and X-Y Pos. with Time: 3 boxes display the evolution of laser power, beam diameter and beam positions vs time over a period from 1 min up to 12 h. Values are continuously updated. The 2 horizontal lines within the boxes show the alarm limits previously selected; the graph and the exceeded limit line will display an alarm message by changing colour.
• Print: prints a screenshot of the complete window. This print can be used as a calibration/alignment document available for the customer or for report files of service engineers .

During operation some error messages may be displayed:

• Overload: the actual laser power is above the maximum limit permitted by the head.
•  Diameter is Not Available (N/A): the actual value of the beam diameter is larger or smaller than limits acceptable by the head. (e.g. when laser warms-up).
• Align: the actual position of laser beam exceeds the limits set by user.

Periodic , Quick Measure of Laser Parameters

Whenever long term measurements are not necessary, the 3B can alternatively be used to make periodic controls or monitoring (every few hours, per day or week depending on the application necessity) to verify that the laser process is still done at the originally set parameters. Similarly to Stand-Alone operation, but with information shown on a PC screen, the Measure key on the main page opens a page for this type of quick measurements.

Each measure only lasts a few seconds and takes a picture of the beam situation in that moment. This other way of using the 3B is also straightforward: shortly after the laser has hit the detector, measurements automatically start and the period to go appears on a countdown box ( “Run X”, down to “Run 0”, where X stays for the remaining number of seconds ).

Measured data will be displayed as histograms in order to provide an immediate view of stability or evolution for each parameter . The max number of measurements displayable on each frame is 30, after which histograms will scroll .

Again, each frame contains the alarm thresholds (shown as continuous horizontal lines): when these values are overtaken, the lateral LED corresponding to the parameter above the limit will light on, while a mark will be added to the corresponding histogram.

Parameter scales can be expanded or reduced by acting on 2 lateral sliding windows. A “Print” key is available to print a screenshot of this window.

In any case all data collected during the measurement session are automatically stored in a file and can be read with a text editor program or imported into a spreadsheet, e.g.Excel.

Datalogging (DL < > PC)

    Communication between data logger and the 3B electronics is enabled by the front panel switch (DL < PC) and through the serial communication port RS232.

For data downloading, a specific, exhaustive Software is included in the package. Once the EXE program has been launched, some initial instructions like the serial port selection (COM X) and Connect are provided on the screen. Initial configuration also includes an EraseEeprom and Set Time/Date; once they have been set, a simple click on the Send Command key will store data.

Specific requests can be asked the 3B: for example Read How Many Bytes Are In EEPROM, in case it is necessary to verify if the memory is empty and avoid to mix up new data with others from a previous measurement session.

The Erase EEPROM function from the Command box and Send Command will clear the memory, if necessary.

Other commands are also available:

• Stop Time: brings the clock in stand-by mode, blocking an internal clock.
• Read Current Status: gives information on the Datalogger status, like:
  • Command Error
  • Ext. Memory Overflow
  • PIC EEPROM error
  • Ext Memory is empty
  • Status Ok

Controlling the status reports about wrong or illegal commands, informs if the external memory is full or whether errors have occurred within the microprocessor non-volatile memory; another error message tells when configuration or memorized data are read but memory is void. Status OK is for normal operation .

When data are downloaded they will be located on a new page, containing various fields like Frame No ( frame number), Time/Date (day and hour of acquisition), Power and its Status, XPosition and its Status, Y Position and its status Status, Beam Diameter and its Status).

A status bar shows the % of filling of the table and unless the bar does not reach 100%, data will not be displayed. The Save Data function permits to save data in a text file (which can be read by most of electronic sheets).

Download 3B Data Sheet here

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