Laser Self-Mixing Velocimeter for Motion Encoding
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Solution Overview
Problem
Existing input devices face limitations in accurately measuring rotational and linear movement due to noise, precision issues, and cost constraints associated with potentiometers, optical imaging, and laser Doppler velocimetry, particularly in low-cost and endlessly rotatable controls.
Innovation Solution
A laser self-mixing velocimeter is used to encode direction and speed of rotation by measuring power fluctuations caused by the self-mixing effect, with optional phase locked loop, zero point control, and bias current modulation to enhance accuracy and reduce noise, particularly suitable for low-speed measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser Doppler velocimetry is used to measure rotational and linear motion, then measurement precision and accuracy are improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts only the essential self-mixing effect from complex laser Doppler velocimetry systems, eliminating the need for separate reference beams, complex optics, and sophisticated signal processing circuits. By using a single laser diode where the reflected light mixes with the laser's own output, the system achieves high measurement precision while dramatically reducing device complexity and cost.
Solution Approach 2:
The laser diode serves dual functions: it generates the measurement beam and simultaneously provides the reference beam through its own output. The reflected light from the target object mixes with the laser's output within the same device, eliminating the need for separate reference light sources and complex optical paths. This self-mixing approach reduces system complexity while maintaining high measurement accuracy.
2Measurement precision
If optical imaging arrays are used to track motion, then measurement precision is improved, but cost increases
Solution Approach 1:
The patent replaces complex optical imaging arrays with a simple laser-based self-mixing velocimeter. Instead of using cameras or imaging sensors to track motion, the system uses laser light interference patterns generated by the self-mixing effect to directly measure velocity and position with high precision. This substitution eliminates expensive imaging hardware while achieving comparable or superior measurement accuracy.
3Device complexity
If potentiometers are used to measure rotation, then device cost is reduced, but measurement precision and reliability deteriorate
Solution Approach 1:
The patent replaces mechanical potentiometers with an optical measurement system based on laser self-mixing. Instead of using resistive contact that wears and generates noise, the system uses non-contact optical interference to measure motion. This substitution eliminates mechanical wear and contact noise while achieving superior measurement precision and reliability, all at a lower cost than traditional optical encoders.
4Adaptability or versatility
If traditional optical encoders are used for endless rotation, then adaptability is improved, but measurement precision is limited
Solution Approach 1:
The patent uses the frequency and phase of the laser interference pattern to encode rotation information. By measuring changes in the frequency and phase of the self-mixing signal, the system can detect both the direction and magnitude of rotation continuously, enabling endless rotation measurement with high precision. The parameter-based encoding allows for unlimited rotation range without the mechanical constraints of traditional encoders.
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
The solution provides accurate and repeatable measurements of rotational and linear motion with expanded dynamic range and reduced noise, suitable for low-cost input devices, addressing the limitations of existing technologies.
Implementation Method 1
As light from that beam is reflected back into the emitting cavity of the laser, the beam power output fluctuates because of the self-mixing effect
Implementation Method 2
If the laser's beam is reflecting from a moving target back into its emitting cavity, the laser's power output will vary in a periodic manner. These power fluctuations, or 'beats,' have a frequency which corresponds to the Doppler shift associated with movement of the reflecting target
Data Source
AI summary
An input device encodes motion using a laser self-mixing velocimeter. The laser beam is directed at a disk or other moving member. As light from that beam is reflected back into the emitting cavity of the laser, the beam power output fluctuates because of the self-mixing effect and generates a beat signal. The beat signal frequency is used to determine the speed of the member's motion. The direction of motion is also determined based on the beat signal. A difference frequency analog phase locked loop filters the beat signal. A zero-point control disables motion detection when the average beat signal amplitude falls below a threshold. A triangle modulator generates a triangle wave for the laser bias current, with the triangle wave frequency being a submultiple of the beat signal frequency.