Multi-sensor Doppler radar for machine tool collision detection

Abstract

Abstract. Machine damage due to tool collisions is a widespread issue in milling production. These collisions are typically caused by human errors. A solution for this problem is proposed based on a low-complexity 24 GHz continuous wave (CW) radar system. The developed monitoring system is able to detect moving objects by evaluating the Doppler shift. It combines incoherent information from several spatially distributed Doppler sensors and estimates the distance between an object and the sensors. The specially designed compact prototype contains up to five radar sensor modules and amplifiers yet fits into the limited available space. In this first approach we concentrate on the Doppler-based positioning of a single moving target. The recorded signals are preprocessed in order to remove noise and interference from the machinery hall. We conducted and processed system measurements with this prototype. The Doppler frequency estimation and the object position obtained after signal conditioning and processing with the developed algorithm were in good agreement with the reference coordinates provided by the machine's control unit.

Extended Kalman Doppler tracking and model determination for multi-sensor short-range radar

“…The observed noise voltage of the down-converted, digitized IQ-signal at the mixer output typically has a variance of less than 1 µV 2 , with Gaussian probability distribution. The following frequency estimator based on FFT and spectral peak detection (Wächter et al, 2014(Wächter et al, , 2015 attains the Cramer-Rao lower bound (CRLB) for signal-to-noise ratios (S/N) larger than 0 dB. The frequency estimation uncertainty is Gaussian distributed with variances of less than 1 Hz 2 , dependent on the S/N and the length of the observation interval kT s .…”

“…An even more sophisticated task is the prediction of future machine states and of temporary and instantaneous production steps, such as processes in milling machines. This leads to the notion of collision avoidance in automated machine tools in order to prevent damages and downtimes, which cause high maintenance and material costs (Wächter et al, 2014).…”

“…In this contribution, the approach of a predictive 24 GHz Doppler surveillance and collision avoidance radar is described. Extensions and continuations of the fundamental investigations in Wächter et al (2015), Azodi et al (2013) and Azodi et al (2014) are merged. A new signal processing stage for nonlinear target tracking based on Doppler shift estimates is introduced.…”

Sparse representation discretization errors in multi-sensor radar target motion estimation

“…A very fine grid results in a highly coherent sensing matrix which not only causes more computational complexity, but also increases the ambiguity in the reconstruction process. In radar applications, such as collision avoidance radars (Azodi et al, 2014;Wächter et al, 2014), assuming a very fine discretization is not even practical as out-bound targets 1 considerably enlarge the solution domain. Targets, whose true motion states lie offside the grid points of the discretized solution domain, are commonly referred to as off-grid targets (Tan and Nehorai, 2014;Nielsen et al, 2012;Tang et al, 2012;Gurbuz et al, 2013).…”

A study of compressed sensing based collision avoidance by multi-sensor CW radar data

“…These collisions, which usually occur during the tool-change operation of the machine, dramatically increase the maintenance costs [7]. Therefore, an automated system for protecting the machine from these collisions is needed.…”