Optical scanners, or servo-controlled, limited-rotation motors with laser-beam steering mirrors, were first introduced 40 years ago by General Scanning. Since then, they have become the enabling technology behind many innovative products across many different industries, including medical imaging, industrial machining, product identification, biomedical research, automotive manufacturing, and many more.

The typical single-axis optical scanner system components include scanner motor, mirror, mount, and servo driver.
While optical scanner performance has improved dramatically, little has changed in the way systems are developed, manufactured, and supported since the introduction of this technology. Today, new systems are emerging that consist of three elements: innovative scanner motors, advanced digital electronics, and a comprehensive software toolset.

To put this advancement in perspective, it is useful to review past solutions and their strengths and weaknesses. The original optical scanning technology was based on bulky motors controlled by analog servo drivers. Performance tuning for a single- or multi-axis system was a labor-intensive and time-consuming manual procedure. But it was the only game in town.

Inertia Matching

The original limited-rotation motors were fairly large and prone to wear and drift from thermal changes. Advances in materials and manufacturing techniques resulted in smaller, faster, more accurate motors. While these newer motor designs perform dramatically better and are far more reliable than those of just a few years ago, performance improvements are reaching a practical limit. So how does one achieve any meaningful improvement in motor speed and accuracy? It is done through inertia matching.

Even though scanner motors are now smaller and more efficient, and mirrors have become lighter and stiffer, system performance often falls below its potential. The reason is because engineers don’t often address component synergy. When configuring a scanner motor, little attention was paid to the optimal inertial match between the total load (mirror and mount) and the motor’s rotor assembly. In fact, some manufacturers exacerbate the problem by specifying that the load inertia can be up to ten times larger than that of the rotor. It turns out that the inertial match between the load and the rotor is one of the most important criteria in achieving optimal motor performance.

Figure 1 illustrates this new understanding of optical scanner motors. Rather than viewing the scanner motor as a collection of discreet components, General Scanning’s new scanner motors are configured as integrated assemblies, and designed for loads that do not exceed three times the inertia of the rotor.

Digital Servo Driver

Optimized scanner motor design is one step toward reaching the performance limit of an optical scanner-based system, but actual system-level performance, as compared to scanner motor performance, is largely dependant on how well a servo driver controls the motor.

Figure 2 illustrates a typical system design. Until recently, optical scanning servo drivers were analog devices. Engineers needed extensive servo knowledge and considerable time to optimize system performance for a given application. “Tuning the servo” was a trial-and-error process aimed at achieving the best balance of speed and accuracy, while eliminating the system’s resonance-frequency. In a dual-axis system, keeping a pair of optical scanners in lockstep became increasingly difficult as speeds increased.

The advent of digital servo drivers improved servo tuning significantly, but even today’s digital drivers are still rather limited. Some will let engineers load pre-defined tune files or allow rudimentary “self-tuning” to compensate for the inherent variations in all scanner motors. Yet, no digital driver offered real control over the tuning process. And with dramatically different tuning requirements for applications such as marking, welding, cutting, and drilling, servo tuning is still a time-consuming manual process.

Figure 1: Inertia matching means matching the inertia of the scanner motor assembly to the inertia of the load. This yields the highest scanner motor performance.
General Scanning has developed a new approach to digital servo control as part of its Lightning Digital Scanner technology platform. This new digital servo driver addresses the quest for higher system performance in a number of ways. First, the signal-to-noise ratio has been significantly improved through the use of a 16-bit bus design for low noise and high accuracy. The new design uses a DSP processor to run sophisticated control algorithms, and multiple filters for frequency-response shaping. Lastly, it provides an interface that enables the driver to support a sophisticated software toolset that automates tuning and documents key performance parameters. General Scanning offers the TuneMaster Software Toolset for this purpose, reducing development time, lowering production costs, improving product support, and maintaining “like-new” system performance over a product’s service life.

Software Toolset

Figure 2: The basic optical scanner consists of a servo driver and a scanner motor with position detector for feedback. Tuning the servo loop with analog or digital servo drivers traditionally has been a time-consuming manual procedure.
TuneMaster consists of three interactive modules that provide tools for product development, production, and field support. One of the main challenges in servo control is tune development or balancing scanner system speed and accuracy for a given application. Today, engineers use either an oscilloscope to observe optical scanner performance in the time-domain, or a signal analyzer to perform sophisticated tuning in the frequency domain. Engineers observe the results and adjust the controls to shape the response of the system. In either case, scanner tuning is done using an intermediate indicator that is limited to a specific type of motion.

The approach taken by TuneMaster allows engineers to tune the optical scanner in the application domain, or in other words, the system is tuned while running its actual application, such as marking, welding, or cutting. Additional equipment that yields intermediate indicators of system performance is no longer required because the tuning process is software-controlled and automatic. As a result, the resulting development time for the application tune can be reduced up to 90%.

Tuning the servo with software rather than using external equipment also makes it easier to set up multiple servos for OEM manufacturers. Using the MatchTune Generator Module, the operator downloads a specific tune for a given application from the archive and automatically adjusts the system’s optical scanner set to the desired quality and throughput based on the original application requirements captured by the TuneMaster Creator module.

In addition to automated scanner optimization, full documentation is retained for quality assurance and traceability. For each system, the original TuneMaster, the resulting MatchTune, system performance at the time of production, and serial numbers are recorded in a production database and onboard the Lightning servo driver. This capability also eases field repairs and upgrades because TuneMaster’s Support Toolbox Module lets technicians replace only the failed component — a motor or a mirror — and restore the system to like-new performance through its automated software-tuning routines.

Ongoing maintenance or re-tuning a system to maintain optimal performance also can be automated. By linking the system based on Lightning technology to a computer, TuneMaster software can re-tune the system to match the original performance specification. Click the retune button on the Support Toolbox Module GUI and system performance is re-optimized in less than a minute.

Lightning Digital Scanner Technology and TuneMaster software are examples of the ongoing development of digital optical scanning solutions, bringing in a new era of digital hardware paired with advanced software tools that provide cost-effective, improved control of optical scanners and the systems that depend on them.

This article was written by Amit Shahar, market development manager, at General Scanning (GSI Group), llerica, MA. For more information, contact Mr. Shahar at This email address is being protected from spambots. You need JavaScript enabled to view it., or visit http://info.hotims.com/10960-200 .