Method and system for high-speed, high-resolution, 3-D imaging of an object at a vision station

Abstract

A method and system for high-speed, high-resolution, 3-D imaging of an object including an anamorphic magnification and field lens system to deliver the light reflected from the object to a small area position detector having a position-sensing direction. Preferably, an acousto-optic deflector together with associated lens elements scans a beam of modulated laser light across the object to produce a telecentric, flat field scan. The deflector has a feedback loop to enable uniform illumination of the object. The light scattered from the object is collected by a telecentric receiver lens. A combined spatial and polarization filtering plane preferably in the form of a programmable mask is provided to control the polarization and acceptance angles of the collected light. A reduction or focusing lens is positioned immediately behind the filtering plane and is utilized as a telescope objective. The lens system includes a negative cylinder lens having a relatively large focal length and a field lens having a relatively small focal length. The cylinder lens and the reduction lens magnify the image in the position sensing direction of the detector and the field lens delivers the magnified light to the detector. The detector is a photodetector such as a lateral effect photodiode or a rectangular lateral effect detector. A pre-amplifier provides a pair of electrical signals which are utilized by signal processing circuitry to compute the centroid of the light spot.

Description

TECHNICAL FIELDThis invention relates to a method and system for imaging an object at a vision station to develop dimensional information associated with the object and, in particular to a method and system for the high-speed, high resolution imaging of an object at a vision station to develop dimensional information associated with the object by projecting a beam of controlled light at the object.BACKGROUND ARTA high-speed, high resolution (i.e. approximately 1 mil and finer) 3-D laser scanning system for inspecting miniature objects such as circuit board components, solder, leads and pins, wires, machine tool inserts, etc., can greatly improve the capabilities of machine vision systems. In fact, most problems in vision are 3-D in nature and two-dimensional problems are rarely found.Several methods have been used to acquire 3-D data: time of flight, phase detection, autofocus, passive stereo, texture gradients, or triangulation. The latter approach is well suited for high resolutio...

AI Technical Summary

Benefits of technology

An object of the present invention is to provide an improved method and system for high speed, high resolution 3-D imaging of an object at a vision station wherein high speed and sensitivity can be obtained by using a flying spot laser scanner with a light deflect

Problems solved by technology

In fact, most problems in vision are 3-D in nature and two-dimensional problems are rarely found.

With linear arrays or area cameras there is severe trade off between shadows, light sensitivity and field of view.

The primary disadvantages of such a system are the very low speeds (typically 10,000 points/second) and, in the case of multiple projected lines in a single image, ambiguous interpretations of the data result from overlap of adjacent stripes and multiple scattered light between stripes.

The large area detectors have several limitations: low speed due to large detector capacitance, high dark currents, and a much higher noise floor than what is found with small area devices.

With typical triangulation-based images it is difficult to deliver light to a small area device without decreasing the field of view (and consequently the inspection speed).

These are severe limitations and impose undesirable trade-offs which limit the system performance.

These moving parts are often not desirable, particularly if the sensor is to be subjected to the type of acceleration found with x-y tables and robotic arms in industrial environments.

A dilemma exists with conventional triangulation imagers: it is desirable to use a small detector but unless moving parts are included the field of view becomes too small, the resolution too coarse, and the light gathering capability poor.

Even if the

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