Achieving sub-millimetre precision with a solid-state full-field heterodyning range imaging camera

Abstract

We have developed a full-field solid-state range imaging system capable of capturing range and intensity data simultaneously for every pixel in a scene with sub-millimetre range precision. The system is based on indirect time-of-flight measurements by heterodyning intensity-modulated illumination with a gain modulation intensified digital video camera. Sub-millimetre precision to beyond 5 m and 2 mm precision out to 12 m has been achieved. In this paper, we describe the new sub-millimetre class range imaging system in detail, and review the important aspects that have been instrumental in achieving high precision ranging. We also present the results of performance characterization experiments and a method of resolving the range ambiguity problem associated with homodyne and heterodyne ranging systems.

Understanding and Ameliorating Non-Linear Phase and Amplitude Responses in AMCW Lidar

“…An alternative to discrete phase stepping is to integrate over a range of relative phases, also known as heterodyning [41]. This can be achieved practically with a small frequency offset between the sensor and illumination modulation signals, resulting in a beating waveform being sampled by the sensor; this beat waveform is essentially equivalent to the standard correlation waveform.…”

Design and Construction of a Configurable Full-Field Range Imaging System for Mobile Robotic Applications

“…Space constraints restrict a more detailed review of the theory and implementation of full-field ranging systems. The interested reader is referred to reviews of such systems in [5] or the more detailed descriptions of the techniques we employ in [6][7][8][9][10] or further theoretical treatment in [11]. FFRIS devices currently on the market include systems developed by PMDTechnologies [12], Mesa Imaging [13] and Cantesa [14], with two typical examples illustrated in Figure 5.…”

“…Subsequent improvements [8] included the introduction of an FPGA to provide laser level control and intensifier gain control. The FPGA was also configured to generate a shuttering signal to gate the photocathode of the intensifier to ensure it turned off during CCD frame transfer in order to limit image smear.…”

Development of a Real-Time Full-Field Range Imaging System

“…This is a consequence of phase wrapping where objects beyond the unambiguous range of c / 2f M = 3.75 m are measured incorrectly. It is possible to correct for this ambiguity [9] but this functionality is not currently incorporated into this system. The plot also shows an interconnecting slope between test pixels 3 to 5 where the paper towels roll towards the camera through these pixels.…”

“…The system employs a modulated light source and shutter set up in a heterodyning configuration [9] as described in Section 2. Sections 3 and 4 introduce the various hardware components of the system and the software and firmware used to process the image sequence in real-time and provide control by the user [10].…”