Lighthouse Localization of Wireless Sensor Networks for Latency-Bounded, High-Reliability Industrial Automation Tasks

Abstract

We present the results of a latency-bounded, high-reliability conveyor belt control system for a cart containing a self-localizing wireless sensor node. The node is equipped with an ARM Cortex-M3 microprocessor, 802.15.4 transceiver, 9axis inertial measurement unit (IMU), and an infrared-sensitive photodiode which allows the wireless node to localize itself using a high-precision localization system for small, resource-constrained, low-cost wireless sensor nodes known as “lighthouse” localization. The cart moves across the conveyor belt, and upon reaching a specified position sends a wireless signal to a set of receiving nodes attached to the conveyor belt’s motor to reverse direction. Using an extended Kalman filter (EKF) running on-board the cart’s wireless sensor node to estimate the position and velocity of the cart, we are able to achieve 3ms response latency, equivalent to the response latency of industrial photoelectric sensors used in a related implementation. We also show the lighthouse system used in this implementation has no outlier measurements outside the $\pm 1 mm$ error range when stationed 3 meters away from the conveyor belt. This, in addition to use of the EKF, enables high-reliability control with strong occlusion tolerance. We show the wireless sensor node is able to continue estimating its position along the conveyor belt when occluded from the lighthouse base station with a median standard deviation reported by the EKF of 0.875mm after 10 cm of occlusion compared to a median 0.109mm standard deviation of the position estimate when not occluded.