Raimo Ahola

A time-of-flight laser receiver for moving objects

The design of a time-of-flight laser receiver for measuring and analyzing the motion of moving objects is presented. The receiver detects a small fraction of the light reflected back from an object and forms an ECL-level pulse for measuring the light pulses time of flight. The timing errors caused by amplitude variations of the reflected light pulses are minimized by utilizing the special characteristics of the application. Measured timing errors are within ±7 ps over a dynamic range of amplitude variations of more than 1:10. The bandwidth of the preamplifier of the receiver is about 200 MHz and the input noise current density about 3 pA/√Hz.

A new method for measuring the time-of-flight in fast laser range finding

A new method for measuring the flight time in high speed, high resolution ranging applications is presented. The detailed theoretical consideration of the method shows that the method is well suited to these applications. Examples of practical constructions and their performance show that the method can be put into practice with a very small number of components with good results.

Applications Of Laser Diodes And Position Sensitive Detectors In Determining Mechanical Misalignments Of Linear Motions And Off-Line Compensation Performed By Cartesian Coordinate Robots

The determination of position and orientation errors made by large-scale cartesian coordinate robots using latest 3D-measurement methods has proved to be difficult in practise. A method has been developed to determine the mechanical inaccuracies of linear motions, perpendiculars, deflections, rotations and bends of a robot, relative to the common reference coordinates of the robot and the work area. The measurement method is based on the use of a laser diode and a position sensitive detector (PSD). A PSD is an optoelectronic sensor capable of providing position data about a light spot incident on its surface. The dual-axis, non-discrete PSD provides continuous analog X- and Y-axis information as the light spot transverses its active area. It senses the centroid of the light spot so that the position daa is indpendent of the focus of the spot. The PSD typically has an active area of - 1 cm - 20 cm , a resolution of 1/5000, nonlinearity of + 1% - + 15% and a fast response enabling accurate detection even of a rapidly moving light spot. The system developed consists of a laser diode transmitter, two beam splitters, a retro-reflective mirror, a PSD based receiver and a microcomputer unit for controlling the system and analysing the measured information. The divergence of the laser diode transmitter is - 0.1 mrad, it is small in size and lightweight (about 100 g), the direction of the laser beam of a fastened transmitter can easily be adjusted and it can be modulated electronically. The direction of the laser beam is not so sensitive to temperature variations as is for example an He-Ne-laser. The effective size of the PSD is enlarged with the aid of optics to have a diameter of 10 cm. Using a modulated laser beam the background light can be compensated. The position data from the PSD receiver to the memory of the microcomputer is gathered continuously and information is produced by a graphic printer in the form of graphs or numbers. This enables the measurement of the straightness of moving paths of machines such as robots, displacement and vibration measurements, optical position and angle sensing and surface flatness measurements. The performance of the system will be reviewed by considering the results of the practical measurements for determining mechanical misalignments of linear motions of cartesian coordinate robots.

Analysing The Dynamics Of Fast-Moving Objects Using A Pulsed Laser Diode

A new method is suggested for analysing the dynamics of fast-moving objects. The basic differences, compared with the optical rangefinders and radar equipment available, are the continuous measurement of the distance and the possibility of measuring the alteration in distance and of measuring the velocity and acceleration of the object continuously and simultaneously. The above mentioned characteristics are attained using the well-known time of flight method with an exceptionally high pulse repetition rate and with a new type of an analog time to amplitude converter (TAC). The velocity and acceleration voltages are formed by derivation from the continuous distance voltage in respect of time. Preliminary results with a simple prototype have proven the method to be highly usable in many applications, e.g. in sports training and printing technology.