Smaller scanners for machine guarding - the factors that matter

The basic operation uses time-of-flight measurement. Light pulses are emitted from a scanner to create a two dimensional scan of its surroundings. If the emitted light strikes an object, it bounces back and is received by the scanner. A rotating mirror spreads the light pulses out in a fan shape over an angle of up to 270-degrees. Objects within a user configured area are thus detected by the scanner.

A smaller footprint means safety laser scanners are easier and less expensive to install. They can be mounted in space constrained areas with beam detection height as low as 35mm off ground, to be used for repeatable detection of workers’ shoes. Small scanners are ideal for applications such as Automated Guided Carts (AGCs) or safety mat replacement.

A triple field set can be programmed with one protective field and two warning fields. The safety and warning zones are freely programmable and can be changed dynamically or statically. Once an object is detected in the defined "warning zone,” the scanner can initiate an output signal – an audible or visible indicator. Triple field sets can be found in mobile applications by using a warning field output to slow the speed of a vehicle. Stationary applications can use a warning field output to reduce machine speed, which translates into a smaller required protective field.

A machine’s speed, braking time and position will drive the safety detection range and determine whether to use a scanner that has triple or dual fields. An application that travels faster will require a longer safety zone and possibly more slow-down options to prevent injuries.

Typically, a larger safety zone is needed to move machines or vehicles fast in order to compensate for a longer braking time. If the safety zone does not adapt to the changing environment of a machine, the vehicle cannot go around corners, or machines require a protective field to cover all possible hazard locations. In order to use fast speed in a condensed space, users need to be able to balance safety zones.

Safe zone switching

The simplest and safest way to switch zones on a vehicle is using encoders. This enables vehicles to do tight turns – with built-in tolerance functions. Speed signals are sent from the encoder into the scanner without any interaction with the vehicle control. But selecting zones safely and simply with a machine which has changing hazard zones does not always require encoders: instead, position signals can be sent from the machine directly to the scanner and used to monitor zones based on the current position of the machine.

Which scanner do you choose? There are many sizes and variants. The hazard, speed, design, environmental factors and size of the application will have a large impact on which scanner features are needed. Other factors which come into consideration include: safety detection range, scanner size, triple vs. dual fields, number of total fields required, contour mapping, and network connectivity. If more intelligent feedback is needed to manage the safety system, network connectivity can access the status and diagnostics of the safety system. Access can be given locally at the end user location, for faster troubleshooting and minimal downtime, or remotely to the support team.

Choosing a safety laser scanner that is immune to environmental factors will avoid false signals and minimise service costs.