High-Speed Microscale Optical Tracking Using Digital Frequency-Domain Multiplexing

Abstract

Position-sensitive detectors (PSDs), or lateral-effect photodiodes, are commonly used for high-speed, high-resolution optical position measurement. This paper describes the instrument design for multidimensional position and orientation measurement based on the simultaneous position measurement of multiple modulated sources using frequency-domain-multiplexed (FDM) PSDs. The important advantages of this optical configuration in comparison with laser/mirror combinations are that it has a large angular measurement range and allows the use of a probe that is small in comparison with the measurement volume. We review PSD characteristics and quantitative resolution limits, consider the lock-in amplifier measurement system as a communication link, discuss the application of FDM to PSDs, and make comparisons with time-domain techniques. We consider the phasesensitive detector as a multirate DSP problem, explore parallels with Fourier spectral estimation and filter banks, discuss how to choose the modulation frequencies and sample rates that maximize channel isolation under design constraints, and describe efficient digital implementation. We also discuss hardware design considerations, sensor calibration, probe construction and calibration, and 3-D measurement by triangulation using two sensors. As an example, we characterize the resolution, speed, and accuracy of an instrument that measures the position and orientation of a 10 mm × 5 mm probe in 5 degrees of freedom (DOF) over a 30-mm cube with 4-μm peak-to-peak resolution at 1-kHz sampling.

State estimation and feedforward tremor suppression for a handheld micromanipulator with a Kalman filter

“…By actuating these motors, the instrument tip is able to move with respect to the handle in a 2x2x1 mm range of motion to cancel tremor, snap to virtual fixtures [8], apply grids of laser burns [9], or perform other intelligent behaviors [10]. High-rate positioning information is achieved with low-latency optical tracking hardware named ASAP [14]. Using three pulsed LEDs on the tip of the instrument and one on the handle, two Position Sensitive Detectors (PSDs) at a 60° angle triangulate the frequencymodulated LEDs at 2 kHz for full 6 DOF positioning of the tip and handle with <10 µm RMS error.…”

“…Assuming the set-point velocity is negligible ‫(‬ ሶ ≫ ‫‬ ௦ ሶ ), our error ݁ ிி reduces to hand velocity ‫‬ ሶ and feedforward control ‫ݑ‬ ிி can be integrated into the system with a PID controller similar to (14):…”

Autoregressive modeling of physiological tremor under microsurgical conditions

“…Two LEDs mounted to the instrument inside diffuse spheres pulse square waves, one at 2 kHz and the other at 3 kHz. The two signals are sensed by orthogonal position-sensitive detectors (PSD's) (DL10, UDT Sensors Inc. Hawthorne, CA, USA) and demodulated to measure the tip position with an error of less than 10 µm RMS (root mean square) [8].…”

A micro motion sensing system for micromanipulation tasks

“…To address the above issues, motion sensing systems which can sense microsurgical instrument motion in micro scale are developed based on a passive tracking method [20][21][22], or an active tracking method [23][24][25]. Although systems based on active tracking method (active tracking systems) can provide high resolution due to high intensity light reception at the sensors, the light sources have to be fixed on the instrument to be tracked, requiring electronics and wires on the instrument.…”