Comparing Laser Scanner Applications

By Scott Orlosky

Contributed By Digi-Key's North American Editors

Lasers — an acronym for light amplifying by stimulated emission of radiation — are electronics that emit one or more beams of coherent light. Coherent indicates electromagnetic waves of identical frequency and waveform and constant phase difference. Lasers can be used for:

  • Cutting, etching, welding and slicing applications — as in precision engraving, drilling, semiconductor finishing, mechanical resurfacing, and (in the medical field) LASIK eye surgery
  • Imaging and projecting — as in holographics, confocal microscopy, high-definition surveying (for the creation of point clouds), laser spectroscopy
  • Data transmission — as in barcode readers as well as fiber-optic and DVD technologies
  • Positioning — as in work-cell safety systems, 3D printing, and light detection and ranging (LiDAR) systems

Laser scanning — the use of swept or deflected laser-beam arrays — is core to many of these applications. This article will review several laser-scanning applications that are most common in industrial automation.

In its simplest embodiment, a laser signal is generated as a point source and is then swept through an active angle by reflection off a precisely controlled internal mirror. An internal light detector reads the reflected signal. Because the laser beam’s projection angle and time-of-flight (ToF) are known, the scanner’s electronics can use the returned signals to create a detailed map of structures within the scanner range.

Simple in concept, there were a host of development challenges that had to be overcome to make laser-scanning technology work in the real world. Among the more challenging were variations in ambient light, platform movement, calibration of light sources for consistent output, and withstanding dust and dirt usually found in industrial environments.

Solutions have been found to these technical challenges; and now some of the most sophisticated applications are those in autonomous ground vehicles (AGVs) employing 3D scans over a 360˚ range. Today it’s also commonplace to see self-leveling laser scanners used in construction for precision hanging of sheetrock or floor leveling. Yet another laser-scanner application is in surveyor transits, which help civil engineers plan road grades to a resolution of millimeters. These are examples of purpose-built laser-scanning devices for specialized functions — though the real versatility of laser scanners is on the factory floor.

Laser scanners for industrial safety

Consider one essential laser-scanner application in automation — guarding dangerous work cells. In basic installations, a laser scanner is placed in a fixed position while the laser scans across a single plane. Such scanners are light curtains that serve as safety-monitoring systems. A light curtain is located so as to guard a specific piece of potentially dangerous equipment — and it monitors for any interruption of the light beam. In response to an interrupt, it slows or stops the piece of critical equipment or provides an alarm signal.

The scanner must be located and the beam geometry consistent with the ability to monitor any potential entry point for an operator. As implied by the response modes mentioned above, a scanner is often used in conjunction with other safety equipment (guards, alarms and shutoff switches) to ensure that no harm comes to an operator as they approach the equipment.

Prior to the existence of optical-scanning technologies, mechanical interlocks were employed to safeguard dangerous work cells. During maintenance, electricity to the work cell would be disabled and lockout-tagout procedures would be in place. Humans are notoriously unreliable, and people have been known to bypass safeguards. Optical interlocks are more reliable — especially along with a hard reset or a two-operator panel to ensure that no single operator can initiate a restart. Read more about this in the Digi-Key article “Safety Laser Scanners to Safeguard Human Operators.”

Image of Banner SX5-Series safety laser scannerFigure 1: This SX5-Series safety laser scanner allows OEMs or end users to define up to six safety zones and two warning zones using a PC. (Image source: Banner)

Note on Time-of-Flight (ToF) Technologies: Using ToF enables precise mapping of the location of objects based on polar coordinates: angle of the light beam and distance to an object in the area being observed. This information can be used to create a map of the observable area of the scanner into zones. This is critical when considering the next special case of working with collaborative robots (cobots).

Cobots by design are intended to work alongside human operators in collaborative activities. This requires close proximity and attendant risks. A scanner programmed with a map of the workspace can control allowable movements by the cobot depending on their location and movement of the coworker. This is a fairly new area of growth in the robotic as well as the scanner market, so new applications are constantly evolving.

Laser Scanners for AGVs and Locating Tasks

Now consider the benefits and drawbacks of light detecting and ranging (LiDAR) based on laser scanners using ToF on a moving platform. Used in autonomous ground vehicles (AGVs), such systems rely on internal maps of the AGV location so all object detections have context. This ability is called simultaneous localization and mapping or SLAM. This adds to the system complexity because position location errors directly impact mapped location of obstacles or targets. Use of local transponders, teach-programming, or floor embedded tracks help alleviate this issue.

Image of IDEC 270° SEL-H05LPC safety laser scannerFigure 2: This is a 270° SEL-H05LPC safety laser scanner for use in AGVs, forklifts, robots, and other moving equipment found in industrial facilities. (Image source: IDEC)

Scanning technologies are subject to changes in the signal-to-noise ratio (SNR) based on changes to ambient light. The worst case being full sunlight where the light can be several orders of magnitude greater than the scanning illumination. There are several potential solutions available including modulation of the source, structured scanning, and use of narrow frequencies along with filtering. Fortunately, AGVs mostly work in light-controlled warehouses, which don’t need these techniques. For vehicles intended to work outside, there is currently intense study and research being done for solutions.

Laser scanners by definition are line-of-sight devices. This means they are limited to the view directly in front of them. If facing head-on a column of pillars, the scanner will only see the lead pillar in the row. Change of perspective is needed for the scanner to detect additional pillars, assuming they are within range.

LiDAR on mobile vehicles can be quite valuable — especially when that LiDAR combines with other sensors to respond to real-time changes in warehouse environments. Here LiDAR helps boost delivery rates, reduce personnel requirements, and minimize accidents.

Choosing the right scanning capabilities in a LiDAR system means specifying the linear range, the angular scan window, and both the linear and angular resolution for these measurements. Bandwidth or update rate is another critical element as that can limit the operating speed of the AGV. Lastly, but importantly, the power consumption will set the time between recharging and also the number of units that can be deployed at any given time.

Image of AGVs on the market today use LiDAR to navigate their factoryMany AGVs on the market today use LiDAR to navigate their factory or automated-warehouse environment. (Image source: Gettyimages)

Electrical and mechanical considerations for LiDAR in AGVs

LiDAR is continuing to evolve, driven largely by the autonomous vehicle market. Consequently, there are a wide range of capabilities, functions, and price points. It also means that no mounting or connectivity standard has yet emerged. When contemplating the use of AGVs in an application, the process would be to match existing offerings to the system requirements and specify the physical structure from there. Several companies execute system engineering and offer completed or customizable LiDAR systems. Depending on the requirements, a pre-engineered solution may just be the starting point toward a more optimized solution.

The National Institute of Standards and Technology (NIST) has taken the lead in establishing safety standards for AGVs. At present these are focused primarily on the issue of collisions including:

  • Collapsible bumpers: Mostly in older models, the intent is that bumpers will include force sensing and will initiate a stop when they hit an obstacle, limiting the contact force.
  • Non-contacting methods: Modern AGVs are expected to detect objects and stop without causing a collision. Test shapes approximating the human form have been used, though more human-like shapes and poses are proposed for future testing.
  • Sudden obstacles: The unexpected appearance of an obstacle within the safety zone. The AGV is expected to initiate an emergency stop, however collision avoidance isn’t expected.
  • Anticipation of occluded obstacles: These obstacles include equipment or people near the AGV drive path. The expectation is that there will be designated slow zones where there’s less than 0.5 m of clearance from the AGV drive path.

In anticipation of future AGV use, they are also working with robot safety standards to begin development of test methods involving the use of a robotic arm secured to an AGV base.

One of the dominant trends in LiDAR is the push to reduce the size, weight and cost of LiDAR without sacrificing performance. Progress has been made in the last decade, reducing these attributes by an order of magnitude. Mentioned earlier, SLAM, or localization is getting more attention. The idealized solution will allow an AGV to start from anywhere and develop its own internal map of the world in which it operates. Such operation relies on the integration of LiDAR with other sensor types — including GPS, wheel-speed sensors, and cameras.

Laser scanners for data communications

The concept of a linear barcode reader is simple: A combination of lines and spaces creates a sort of Morse code which can be directly read by:

  • Measuring light from the scanner as it’s reflected back off the barcode
  • Measuring ambient light as it’s reflected back

There are nine varieties of linear barcode in regular use globally, dependent on the application. Though laser scanners are the norm for barcode scanning, barcodes don’t necessarily need the precision of a laser light source, with some exceptions noted below. In most cases the reading and translation of the barcode content is all done within the scanner. Typically, the barcode scanner passes decoded values directly to a database.

A few areas demand the fine resolution of a barcode laser. For places with space constraints, the standard barcode stripes are held to a narrower physical standard. This requires a fine resolution reader and laser scanners do quite nicely. A similar situation exists when the barcode is further away (on the shelf in a warehouse for example), which effectively reduces the angular size of the code.

Sometimes ambient light isn’t enough to ensure good contrast between the bars and the spaces. In this case, a known light source like a laser is suitable to light up the code and make it easily readable.

Even consumers who frequent grocery stores are familiar with handheld scanners at self-checkout lanes. Because barcode scans can be presented in an infinite number of orientations, scanners in these settings must produce a tight matrix of crossing laser scan lines. This ensures that no matter how the barcode presents, at least one of the scan lines will intercept the entire code.

Image of MikroElektronika MIKROE-2913 barcode-scanner boardFigure 4: This MIKROE-2913 barcode-scanner board can read 1D and 2D barcodes adherent to various protocols. It includes a micro-USB port to work as a standalone device or with other boards. (Image source: MikroElektronika)

Barcode 2D Scanners: Two-dimensional (2D) codes differ from the linear codes mentioned above. They’ve grown in popularity due to their high information density, error checking, and readability even if damaged. The complexity of 2D barcodes means that they are not suitable for use with laser scanners and rely on cameras for decoding. There are four types of 2D barcodes in common use, though most consumers will be familiar with the quick-response (QR) code, which is easily read by most smartphones.

When machine builders and end users weigh barcode and scanner options, there are three main aspects to consider:

  1. Where will the scanner be used? Is it for inventorying in a warehouse, tracking of production parts on a manufacturing line, or point-of-sale use?
  2. How much data is needed and what is the physical space available on the item to place the barcode?
  3. On what surface will the barcode be printed — and what print resolution is that surface capable of retaining?

Once these three questions have been answered, there should be a number of viable alternatives from which to choose.

Image of Code Reader 950 (CR950) barcode laser scanner from Brady CorporationFigure 5: This Code Reader 950 (CR950) barcode laser scanner from Brady Corporation has a wide-area image sensor for easier scanning. The result is omnidirectional reading of 1D and 2D barcodes — even those on shiny surfaces. (Image sources: Brady Corporation)

Other Reader and Camera-Based Alternatives: Most variations on the barcode scanner have been covered above. Worth mentioning is that some barcode scanners will use a long row of LEDs to illuminate the code in conjunction with a matching row of charge-coupled device (CCD) detectors to detect the reflected light. These are called LED readers.

There are also camera systems specifically designed and configured to effectively and quickly read 2D codes.

Conclusion on Laser Scanner Applications

The proliferation of laser-based devices and uses since the invention of the laser in 1960 has been mind boggling. Though the barcode predates the laser by 11 years, the use of coherent-light scanning to read information has become the gold standard. Laser-based position tracking and detection scanning have also become go-to solutions in industrial settings. Whether designing a system from scratch, or augmenting an existing process, there’s a good chance that some variation on a laser-scanning approach has value for most industrial manufacturing or tracking applications. Considering how far the technology has come, odds are good that if the exact configuration isn’t available today, something suitable is on the horizon.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Scott Orlosky

Throughout his 30-year career, Scott Orlosky has designed, engineered, developed, marketed, and sold sensors and actuators for industrial and commercial industries. He is coinventor on four patents for the design and manufacturing of inertial sensors. Orlosky is also a coauthor of Encoders for Dummies and produced the BEI Sensors industrial newsletter for nearly 15 years. Orlosky holds a master’s degree in Manufacturing and Control Theory from the University of California, Berkeley.

About this publisher

Digi-Key's North American Editors