Motion control improves accuracy and repeatability in laser microprocessing

May 11, 2017
Laser micromachining/microprocessing HMI software is a critical component or subsystem of the machine.

Software and laser control is critical

JASON GOERGES

When faced with a new potential project or application, laser microprocessing and micromachining system integrators and original equipment manufacturers (OEMs) can often provide a proof-of-concept demonstration on a "demo machine" with relatively little time and effort. However, once interest by the client(s) is shown, the difficult process of turning proof-of-concept into a robust machine solution begins, often dictated by a very aggressive schedule.

Delivering laser pulses to the workpiece with a high degree of accuracy and repeatability, along with developing and maintaining the human machine interface (HMI) software, are among the most complex and resource-intensive efforts associated with this process. As these efforts involve a variety of technologies and disciplines, there are many challenges to solve.

Thanks to new motion/computer numerical control (CNC) technologies in the marketplace, such as customizable HMI development platforms, advanced motion performance optimization features, and the laser control module, many of the aforementioned challenges are solved in an out-of-the-box manner. This allows the machine developer to minimize complexity and bring a machine to market faster, with improved process accuracy.

Laser micromachining/microprocessing HMI software is a critical component or subsystem of the machine, and typically falls into one of two classifications. One is a CNC-style HMI that imports and executes machine code programs (typically G-code) created by a computer-aided manufacturing (CAM) software post-processor. The other is an "integrated graphical" HMI that allows import and manipulation of CAD files, and provides integrated CAM/post processing functionality.

Some motion and CNC controller companies now offer customizable HMI development platforms for both types of HMIs. This allows a system integrator or OEM to take a new, less-resource-intensive approach to developing and maintaining their HMI software: building the HMI application with a customizable platform.

CNC-style HMI

Many laser micromachining and microprocessing systems are used in a machining or manufacturing environment alongside other traditional CNC machines, such as lathes, mills, and routers. Having commonality between the laser system HMI and the HMIs of the other machines is beneficial to the manufacturer, as it leverages existing knowledge and experience of the manufacturer's machinists and technicians.

A customizable CNC HMI development platform can be expected to provide many standard HMI features out of the box, including:

  • The ability to load, edit, and execute NC files with Standard RS-274 and user-defined G-codes (FIGURE 1);
  • Flexible CNC program flow control options such as stop, hold, abort, single-block run, block skip, and feed-rate hold;
  • Real-time monitoring of program execution, axis positions, feed rates, G-code modality, alarms, and faults; and
  • Multi-tiered user access login screens for operators, technicians, developers, and administrators.
FIGURE 1. An interface for loading, executing, monitoring, and modifying CNC programs.

The platform also solves many challenges associated with integration of the HMI host application and the motion/CNC controller, as it optimizes NC program download, compilation, and execution time; manages G-code modality to support mid-program start; and displays, handles, and logs machine fault and error conditions.

The competitive advantages of a laser microprocessing and micromachining system are often related to its application-specific functionality. As the name implies, a customizable CNC HMI development platform provides value to the machine developer by allowing application-specific HMI customization with relatively little effort. Simple examples of such customizations are custom tabs, buttons, or screens. More sophisticated customizations may involve process visualization or integration of other devices in the machine, such as cameras and laser displacement sensors.

Integrated graphical HMI

Laser microprocessing and micromachining systems used in applications such as flexible PCB drilling and cutting, glass and polymer display processing, semiconductor processing, precision optics manufacturing, and high-precision additive manufacturing are often used in high-tech research and production facilities. In such systems, an integrated graphical HMI is typically preferred over a CNC-style HMI, as the system operator is not a CNC machinist. The integrated graphical HMI can directly take in a CAD file from which a laser path is defined, and the corresponding machine code is then automatically generated and executed on the motion controller. In such cases, a separate CAM or post-processing software is not required.

A customizable integrated graphical HMI development platform, with built-in functions for specific processes such as laser marking, drilling, etching, cutting, and additive manufacturing, provides significant added value to the machine builder/integrator and end user by solving a number of development challenges out of the box:

  • A wide range of CAD files are natively supported (DXF, DWG, Gerber, NC Drill, STL, etc.) and can easily be manipulated to create motion recipes (such as scaling, rotation, and tiling);
  • Parameters for all motion axes can be configured and monitored from a single window/location;
  • Real-time monitoring and data collection of motion feedback and laser status;
  • Commonly used devices such as cameras and galvanometer scanners are natively supported and configurable within the HMI-new devices can be integrated as well, without the need to write new libraries from scratch; and
  • Full simulation capabilities allow the user to see the expected laser beam path and determine expected process duration (FIGURE 2).
FIGURE 2. 3D visualization and recipe planning for processing of 3D parts.

Similar to a CNC-style HMI development platform, an integrated graphical HMI development platform can be also customized for application-specific functionality.

Process improvements

For many laser microprocessing and micromachining applications, the motion performance is critical in determining the achievable accuracy and repeatability of the process. Motion performance is affected both by the profile generation (commanded motion path) and the servo performance (how well the actuators/stages follow the commanded motion path).

Today's sophisticated motion/CNC controllers provide advanced profile generation and servo performance optimization features, such as minimal energy profile generation; motion segment blending and corner smoothing (FIGURE 3); adaptive servo control algorithms; autotuning and performance characterization tools; and advanced PWM drive technologies.

FIGURE 3. Advanced motion performance optimization includes controller-based profile corner rounding.

In addition to motion performance, position-based output synchronization also has a significant impact on laser microprocessing and micromachining accuracy and repeatability. This task has traditionally been handled within the motion/CNC controller or drive that is physically connected to the machine actuators.

Recently, dedicated laser control modules have become available that provide additional flexibility and capabilities with respect to position-based output synchronization for laser triggering and gating. Once added on to a motion control network, the module can be configured (via software) to provide synchronized outputs based on motion of any combination of axes in the network. The laser control module can be configured to operate in various laser control modes, making it simple to implement a wide variety of applications (FIGURE 4).

FIGURE 4. A fixed-distance pulse triggering mode involves triggering the laser at precise positions with fixed-distance intervals independent of velocity.

For applications where the laser pulses are not triggered individually by an external control system, a gating mode can be used (FIGURE 5). In such applications, the gating signal is typically turned on and off precisely at the beginning or end of a motion segment or block, though it can also be done at arbitrary locations along a motion path.

FIGURE 5. Gating involves turning the laser on and off at precise locations in the motion path.

Digital modulation modes for power control are also possible, such as pulse width modulation (PWM) and frequency modulation (PFM). Operating modes can be combined simultaneously for even more advanced applications.

There are many challenges associated with the process of developing a robust and scalable laser micromachining or microprocessing machine platform, especially in optimizing accuracy and repeatability of laser control relative to motion, and HMI software development. Many of these challenges that were once up to each machine developer to solve with limited tools and support are now addressed by new technologies and offerings from motion/CNC controller providers, enabling better machine performance and reduced development effort.

JASON GOERGES ([email protected]) is the general manager of ACS Motion Control, Bloomington, MN; www.acsmotioncontrol.com.

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