Eddy current detection of laser-dispersed markers as a new approach to determining the position of load supporting means

The logistic industry has a steady need for improved positioning of goods to keep commercial success. Next to high accuracy, a low maintenance system is needed to ensure the benefits of automation. While state of the art position determination is done by mechanical, optical, or hydraulic techniques, this research addresses a new approach using laser-dispersed position markers and contactless eddy current technology for detection. A fiber laser is used to create thin melt tracks on lifting profiles, and zirconium oxide powder is added to the melt to create a dispersed track as a position marker. The influence of the laser process parameters on the track width and surface topology is determined, as well as the influence on eddy current measurements. It has been found that increasing the laser power and the powder feed rate of zirconium oxide in the investigated range from 190 to 490 W and 1.16 to 3.6 g/min, respectively, increased the signal from the eddy current sensor unit. Positioning concepts are examined by moving the eddy current sensor above the lifting profile with speeds up to 4000 mm/min. The laser-dispersed markers are clearly recognizable in the sensor signal with a minimum distance of 2 mm from each other and an interspace of 0.8 mm from the lifting profile to the sensor head. The recognition error rate is quite low at around 0.0037%. However, the resolution, which can be derived from the eddy current sensor signal, is about 0.5 mm ± 0.11 mm. In order to gain insight into the suitability of the examined technology for forklifts, the eddy current sensor is mounted on the fork bracket and typical actions are simulated. Last, other applications for eddy current detection of laser-dispersed markers, such as storing and reading information for component identification, are demonstrated.