TECHNOLOGY

ADVANCED ULTRASONIC SENSORS

WHAT MAKES THEM DIFFERENT?

In general, ultrasonic sensors are sensors that make use of the characteristics of high-frequency sound for a range of applications such as distance measurement, non-destructive testing of materials, or medical applications.

For distance measurement, a typical ultrasonic sensor uses a transducer to periodically send out ultrasonic pulses in the air. These pulses get reflected from objects in the detection area of the sensor and are received back by the sensor. By measuring the time it takes an ultrasonic pulse to travel to the object and get reflected back to the sensor, the distance to the object can be calculated. This principle is called time-of-flight measurement.

In addition to measuring the distance to an object, Advanced Ultrasonic Sensors can also calculate the horizontal and vertical position of an object relative to the sensor itself (i.e. they provide 3D coordinates for detected objects). The localization of objects in three-dimensional space also allows an advanced ultrasonic sensor to detect multiple objects in a single scan. In that sense, the principle behind our 3D ultrasonic is similar to echolocation, as applied for example by bats. In comparison, a typical ultrasonic sensor, as described in the previous section, will normally only give the distance to the nearest object. Because of this, a limited opening angle is usually applied for this type of sensor. In contrast, our sensors systems allow for opening angles of up to 160°.

BENEFITS OF AN ADVANCED ULTRASONIC SENSOR

LOW-POWER

SMALL SIZE

PROCESSING POWER

PRIVACY

PRECISION

RELIABILITY

HOW DOES THE TECHNOLOGY WORK?

Our sensor technology only detects an object only at the strongest points of reflection. This explains why there are less points (i.e. the point cloud is sparse) for Advanced Ultrasonic Sensors compared to other sensors, which scan a grid (i.e. Lidar or 3D cameras).

The limitations of our sensors are mainly based on the physical properties of ultrasound and the respective reflection characteristics of objects. For the sensor to detect an object, the sent out ultrasonic pulses have to be reflected by the object and received back by the sensor. The reflection characteristics of an object depend on its properties, such as the object’s surface size, orientation, and the material characteristics of the object, as well as the relative position of the object to the sensor.

The surface size of an object plays a pivotal role in reflecting the ultrasonic wave that is sent out by the transducer. An object, for which only a small surface faces the sensor, has a lower chance of detection.

The orientation of an object determines which part of the ultrasonic pulse gets reflected to the sensor. At an adverse angle (= surface not perpendicular to sensor), a smaller proportion of the pulse is received by the sensor, in which case the object has a lower chance of detection.

Ultrasonic pulses are attenuated in air, which limits the detection range that can be achieved by Advanced Ultrasonic Sensors. The further away an object is from the sensor, the lower its chance of detection becomes.

Material characteristics of an object also determine which part of the ultrasonic pulse gets reflected to the sensor. For weakly reflecting or sound absorbing materials, such as foam, the chance of detection decreases.

Generally, the output of our sensors are a list of detected reflections for each frame, with each frame containing the output of one full measuring cycle. A graphical representation of the sensor output is a sparse point cloud.

The information put out by the sensor for each detected reflection contains the 3D coordinates of the origin of the reflection and its relative signal strength. A marker is added to each frame in case it is registered as “noisy”, meaning that the level of ambient noise affected the accuracy of the measurement. The number of reflections and their strengths depend on the reflection characteristics of the object.

ULTRASONIC 3D ECHOLOCATION SENSOR

At the beginning of each measurement cycle, a transducer on the sensor sends out an ultrasonic pulse. This pulse is reflected by surrounding objects and received by an array of microphones on the sensor. Based on the different times of when echoes arrive at the individual microphones, the origins of the echoes are calculated as 3D coordinates. These 3D coordinates are put out at the end of each measurement cycle.

BEACON BASED 3D TRACKING SYSTEM

Toposens 3D Tracking System is based on an extension of our current ultrasonic sensors and a radio interface used for data transmission. It therefore provides X,Y,Z coordinates for detected objects using a single sender and receiver couple.

The 3D Trackng System makes use of a sending and receiving unit, i.e. the ultrasonic pulses sent out by one senor are received by the others which transmit their received data back to the central sending unit.

Toposens 3D Tracking System is designed to provide precise (5 – 10 mm) location data to autonomous robots, AGVs and industrially used vehicles (e.g. forklifts). It can also be used to track humans and other objects with a mobile beacon installed on them, for example, pallets in warehouses or other assets that require constant monitoring.