Mark Williamson, STEMMER IMAGING
Many scanning applications require shape data for 360º of a part, including portioning applications in the food industry. This can now be achieved quickly and easily by networking multiple 3D line profile sensors in a ring configuration. These are used for the creation of a 3D point cloud of the complete circumference of the part in a common co-ordinate system, for full cross sectional visualisation and measurement.
This process has been simplified by the introduction of Firmware 5.0 for the Gocator 3D line profile sensors from LMI Technologies. The Gocator series of 3D line profilers bring advanced 3D smart imaging capabilities to a wide market, providing factories with a comprehensive range of tools to improve efficiencies in product validation. Laser line measurements of cross-sectional shapes of parts and materials surfaces can be collected to create 3D point clouds for volumetric measurements. Built-in measurement tools make 3D measurement reliable, repeatable, and easy, and there is no need to send 3D point cloud data to 3rd-party software.
Setting up the system
Two conveyor belts are used. The gap between them allows the Gocators to be networked in a ring around the part with a clear line of view of it as it passes from one conveyor to the next. As the part moves through the sensor ring, a 3D point cloud of the entire circumference is acquired with full data preservation on object sides and any overhanging areas. Data is “stitched” into a complete 3D model to provide accurate volume measurement. All of the sensors in the ring network are aligned to a common coordinate system in order to determine relative position using a known calibration piece. Setting this up is done by a new enhanced 6 degrees of freedom simple alignment process. A known polygon calibration target is passed through the ring. Each angular corner is aligned between the sensors so the smart sensor can then calculate each sensor’s position and transform data into a common coordinate system. This transformation is carried out automatically for every 3D point produced by the sensor.
Measurements can be made using the new Profile Closed Area tool provided in Firmware 5.0. This allows cross sectional area measurements to be made on profiles as the object moves through the sensor ring, from which the volume can be calculated by multiplying the area by length. For portioning applications where the target object must be cut according to its total weight, the weight of the object can be determined from its volume and density. Scripting can be used to accumulate the areas from the profiles acquired as the object moves through the sensor ring and trigger downstream control decisions to activate cutters when the target weight is reached.
Other multi-sensor configurations
For added versatility, it is possible to have a number of other Gocator multi-sensor networking configurations. Two or more sensors can be mounted side by side to measure large objects that are wider than a single sensor’s field of view. Sensors mounted opposite each other can determine true object thickness when the object cannot be referenced to a known surface like a conveyor. Sensors mounted at an angle to an object can eliminate shadowing effects.
Author: Mark Williamson, STEMMER IMAGING, The Old Barn, Grange Court, Grange Road, Tongham GU10 1DW UK. Tel: +44 1252 780000