A laser scanning system utilizing a MEMS scanner and Lissajous pattern generation was developed for measuring object distance and position. This system employs a Measurement Scanner Car Distance technique, enabling the detection of objects with varying reflectivity. The setup includes a laser diode, a 2D MEMS scanner, a Position Sensitive Detector (PSD), and an Avalanche Photodiode (APD). The scanner directs a laser beam onto the target object, and the reflected light is captured by the APD for intensity measurement. Simultaneously, the PSD tracks the beam’s position on the scan pattern, allowing for precise localization of the object.
System Components and Functionality for Measurement Scanner Car Distance
The core of the system lies in its ability to generate a 2D Lissajous scan pattern. This pattern is created by driving the MEMS scanner with sinusoidal inputs at different frequencies for the x and y axes. The resulting scan covers a wide area, allowing for comprehensive object detection. A 638 nm laser diode with 120 mW output power serves as the light source, while an electromagnetic 2D scanner with a 1.2 mm mirror diameter handles beam steering.
Fig. 2. Block diagram and optical setup of the distance measurement system.
The reflected beam is split, with half directed towards the PSD for position tracking and the other half towards the APD for intensity measurement. A large 5x5x5 cm beam splitter and a 5.08 cm diameter bi-convex lens are used to maximize light collection by the 1 mm diameter APD. The Lissajous scan pattern, approximately 8×8 cm, is captured at the image plane and reconstructed using the PSD signal. The x-axis scan frequency is 715 Hz, and the y-axis frequency is 520 Hz, with corresponding applied currents of 96 mA and 88 mA.
Fig. 3. Lissajous scan patterns: (a) actual pattern; (b) reconstructed pattern using PSD signal.
Synchronization and Distance Calculation
Accurate distance measurement requires precise synchronization between the APD and PSD signals. A time delay of approximately 0.524 ms was observed in the PSD signal compared to the APD signal. This delay is compensated for during signal processing to ensure accurate mapping of position and intensity data.
Fig. 4. LD input signal and corresponding output signals from the PSD and APD, illustrating the time delay.
By mapping the synchronized signals, the position and intensity of the reflected beam can be determined for each measurement point. The intensity data, represented by the PSD output voltage, correlates with the distance to the object.
Fig. 5. Typical output waveform of the APD sensor.
Experimental Results and Further Development
Experiments using a mirror and paper as target objects demonstrated the system’s ability to measure distance and position for materials with different reflectivity. While the current system utilizes a relatively slow scanner, resulting in a sparse scan pattern, the principles demonstrated can be applied to higher frequency scanners for improved resolution and frame rate. This measurement scanner car distance approach shows promise for various applications requiring accurate and efficient object detection. Future work could focus on refining the relationship between measured intensity and distance for different materials and implementing higher-frequency Lissajous scanning for enhanced performance.
Fig. 6. Measurement results for a mirror: (a) mirror position; (b) reconstructed scan pattern and intensity points; (c) intensity vs. xy position.
Fig. 7. Measurement results for paper: (a) paper position; (b) intensity vs. x position; (c) intensity vs. xy position.
