High-Order Filter for TOF Distance Measurement
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Solution Overview
Problem
Current electro-optical distance measurement devices, particularly those using the sampling time of flight measurement method, face challenges in achieving high accuracy due to limitations in signal representation, dependency on lookup tables, and susceptibility to environmental changes, which restrict their use in applications requiring sub-millimeter precision like geodetic equipment.
Innovation Solution
The introduction of a high-order filter in the signal path allows for exact reconstruction of the signal, fulfilling the Nyquist-Shannon theorem, enabling accurate time-position evaluation and reducing aliasing effects, thus improving measurement accuracy without relying heavily on lookup tables or complex calibration processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If sampling time of flight measurement is used, then measurement speed is improved, but measurement precision deteriorates due to quantification errors from low-resolution ADC
Solution Approach 1:
The patent applies dynamic resampling of the captured signal waveform at multiple time points with different time offsets. Instead of using a single static sampling point, the system dynamically evaluates multiple potential time positions and selects the optimal one, thereby achieving sub-quantization precision without requiring higher sampling rates or resolution ADCs
Solution Approach 2:
The patent transitions from single-point time sampling to multi-dimensional signal evaluation by capturing the entire waveform and analyzing it across multiple time dimensions. This allows the system to extract precise time-of-flight information from the waveform shape itself rather than relying solely on discrete sampling points, effectively adding temporal dimensionality to the measurement process
2Measurement precision
If lookup tables and complex calibration processes are used to improve accuracy, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent implements a self-calibrating evaluation method where the system automatically determines optimal time offsets and evaluates waveform characteristics directly from the captured signal. The microcontroller autonomously performs the complex calculations and selections without requiring external calibration data or lookup tables, making the system self-sufficient and reducing operational complexity
Solution Approach 2:
The patent replaces traditional mechanical/calibration-based precision methods with computational signal processing. Instead of using pre-calibrated lookup tables or physical reference standards, the system uses digital waveform analysis and mathematical evaluation to achieve high precision, substituting computational complexity for physical calibration complexity
3Reliability
If signal amplification is increased to detect weak reflected signals, then sensitivity is improved, but aliasing effects increase reducing measurement accuracy
Solution Approach 1:
The patent extracts the essential time-of-flight information from the amplified signal waveform by analyzing its shape and characteristics rather than directly measuring the amplified voltage. By focusing on the waveform's temporal features (rise time, peak position, zero-crossing points) rather than its amplitude, the system can use signal amplification to improve detection of weak signals while avoiding the aliasing and distortion problems that would otherwise corrupt precision measurements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy of distance measurements to sub-millimeter ranges, making devices more robust and tolerant to environmental changes, while using affordable ADCs with moderate sampling rates, and allows for higher measurement precision in time and amplitude.
Implementation Method 1
reducing aliasing effects
Implementation Method 2
fulfilling the Nyquist-Shannon theorem
Implementation Method 3
an optoelectronic device for turning the optical signal to an electrical signal
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
Highly accurate electro-optical time of flight distance measuring device for determining a distance to a target. It is comprising at least a transmitter for sending out a pulse shaped optical radiation to the target, in particular as a pulse modulated laser beam from a laser diode, as well as a receiver for an optical signal, which signal is comprising parts of the optical radiation scattered back from the target, built for turning the optical signal to an electrical signal, in particular as a photodiode or avalanche photodiode, and a filter with a transfer-function for filtering the electrical signal, in particular an analog lowpass or bandpass filter whereby the filter is built in such a way that its transfer-function is of at least 4th order, in particular 5th or 7th or higher order, so that aliasing is suppressed. Further a waveform-sampler, as an analog-to-digital- converter, for digitalizing the pulse shape from the filtered electrical signal as time- and value-quantized digital data, and a computation means for a numerical evaluation of the distance according to the pulse shape or a pulse shape representing numerical signature from the digital data, in particular with a resolution in time being orders of magnitude better than the time-quantisation interval of the waveform sampler is comprised.