Automated guided vehicles, or AGVs, cover a range of applications. Being automated, they occupy a waypoint between remotely controlled and fully autonomous. An AGV differs in this way from an autonomous mobile robot, or AMR.

In their form and function, AGVs and AMRs are similar, but while an AMR can direct itself around a working area using location and mapping technologies, an AGV will likely need to be told where it is, where it needs to go and, most importantly, how to get there.

What both AGVs and AMRs have in common is the ability to detect obstacles and take actions to avoid them. Sometimes that action will be to change course, other times it may simply be to stop and wait.

Object detection can be achieved in various ways, with varying resolution and accuracy. Detecting the distance to an obstacle, particularly with accuracy, raises the bar. The solutions are few and when size and power limitations are combined with the demands of the working environment, it makes the list even shorter.

What is time-of-flight sensing?

Time-of-flight (ToF) technology is one method used to detect distance. If the field of view is tuned to the application, it is an effective technology. ToF is widely used to provide guidance and collision avoidance in AGMs and AMRs, but ToF is used in many other applications.

Emitting a visible or infrared light pulse and measuring the time it takes for a reflection to be detected is one way of implementing ToF. As an example, optical ToF is now used to autofocus digital cameras in some mobile phones. The hardware needed for optical ToF can be small, which is one of its main advantages.

But optical ToF has some disadvantages, too. Because it uses light, it can be affected by ambient conditions as well as overall visibility. This means it may not work well in rain, fog or when there is a source of strong light in the field of view.

Ultrasonic ToF

Ultrasonic ToF uses sound instead of light. These miniature sonar devices emit sound at ultrasonic frequencies and listen for the subsequent reflections. The time it takes for the reflection to hit the sensor is measurable. That measurement is used to calculate the distance to the object.

An ultrasonic ToF sensor can operate in all conditions, including bright sunshine or total darkness. The technology is immune to most forms of interference found in various environments, including sound and light, dust or smoke. The technology is being used in land drones for collision avoidance as well as ground and ceiling detection in indoor flying drones. Thanks to its small size, low power and robustness, ultrasonic ToF can also be used in many other applications.

The SmartSonic™ time-of-flight platform from TDK InvenSense uses the ultrasonic approach. The devices in the SmartSonic family comprise ToF MEMS-based (microelectromechanical systems) sensors with integrated systems-on-chip (SoCs). SmartSonic devices are also ultra-low power. They consume as much as 100 times less power than an infrared optical ToF sensor. This puts the technology firmly into applications where size, weight and power are critical. This includes battery-powered systems and remote electronic devices that operate from energy harvested from the environment.

The attributes of ultrasonic ToF make it a good option when considering object detection and avoidance in AGVs and AMRs. But it can also be used to automate other functions, such as: