News Column

Patent Application Titled "Positioning Device for an Optical Triangulation Sensor" Published Online

June 19, 2014



By a News Reporter-Staff News Editor at Computer Weekly News -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventor MONKS, Tim (Bristol, GB), filed on November 27, 2012, was made available online on June 5, 2014.

The assignee for this patent application is Third Dimension Software Limited.

Reporters obtained the following quote from the background information supplied by the inventors: "Optical measurement systems which use a laser triangulation sensor to obtain dimensional information about objects are known. For example, such systems may be arranged to determine the distance of objects from the sensor or the profile of objects within the field of view of the sensor.

"Referring to FIG. 1, a conventional laser triangulation measurement device 1 comprises a light source 2 e.g. laser which is arranged to project a planar beam 4 (e.g. sheet) of light. The planar beam 4 is incident as a line 8 on an object or objects 5, 6 which lie in the field of view 7 of the device 1. Light reflected from the incident line 8 is collected by an imaging device 3, which may be a camera (e.g. having a charge coupled device (CCD) or an active pixel sensor (CMOS) device).

"The images captured by the imaging device 3 are processed to determine a data representation of the physical geometry of the objects 5, 6. The processing may involved reference to a calibrated look up table or the like. Such processing is known.

"FIG. 2 depicts two dimensions that may be determined using the data representation. The separation (gap G) or planar misalignment (mismatch or flush F) between adjacent surfaces may be determined, e.g. by performing suitable mathematical operations (e.g. line/radius fitting).

"An example of a conventional optical triangulation sensor is the GapGun, manufactured by Third Dimension Software Limited.

"It is often desirable to measure accurately the diameter (or radius) or edge profile of a hole formed in a measurement surface. For example, it may be particularly useful for measuring the edge profile of a countersink (i.e. a hole whose opening is tapered to receive a conical screw head or the like). To perform measurements of this type using an optical triangulation sensor it is desirable for the measurement axis (i.e. the line formed on the measurement surface when the planar light beam is projected thereon) to lie across the centre of the hole (i.e. on a diameter). For accurate measurements, the axis of the hole preferably lies in the plane of the light beam.

"Often this is done by eye, e.g. relying on a user's judgement. This limits the accuracy and repeatability of measurements.

"US 2010/0195116, which is incorporated herein by reference, disclosed an optical triangulation sensor having a guide element for centering the planar light beam across a hole. The guide element comprises a body receivable in the hole, the body having contact surfaces for abutting the hole circumference, the contact surfaces lying on a virtual conical surface whose axis is in the plane of the light beam. A void is provided in the body at each intersection between the virtual conical surface and the plane of the light beam to define a path for the planar light beam from the light source to the edge of the hole.

"U.S. Pat. No. 7,542,135 discloses an alternative solution, in which the self centering device includes a conical cone-shaped member adapted to mate with the countersink, the conical cone-shaped member having a slot extending partially therethrough to allow the laser beam to pass across the countersink and hole."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventor's summary information for this patent application: "At its most general, the present invention provides a positioning device having an adjustable guiding element which is capable of locating an optical triangulation sensor at the same distance away from holes have a range of diameters. The known guide elements described above caused the sensor to be at different distances from the hole depending on the diameter of the hole. The invention may increase the range of hole sizes that can be accurately located in the measurable range of the sensor, and may generally provide a more consistent measurement position for the sensor.

"According to the invention, there is provided a positioning device for locating a planar light beam emitted by an optical triangulation sensor across a diameter of a hole formed in a surface of an object, the positioning device comprising: a platform that is securable to the optical triangulation sensor, the platform having a mounting portion for abutting the surface of the object and an aperture through which the planar light beam is transmittable; a guiding element mounted on the platform and movable with respect to the platform along an adjustment path that extends through the aperture, wherein the guiding element comprises a body which is insertable into the hole, the body having a pair of contact surfaces for contacting diametrically opposed portions of the hole, the pair of contact surfaces being opposed to each other in a direction orthogonal to the plane of the planar light beam.

"In use, the positioning device is placed on the surface having the hole to be measured so that the mounting portion of the platform contacts the surface. The positioning device can be moved over the surface until the body of the guiding element locates in the hole, whereby the pair of opposed contact surfaces abut opposite sides of the hole, i.e. parts of the edge or the inside wall of the hole diametrically opposite each other. This abutment resists further movement of the positioning device in the direction between the opposed contact surfaces. Since this direction is orthogonal to the plane of the planar light beam, the positioning device therefore fixes the position of the planar light beam across the hole.

"The guiding element may be slidable relative to the platform. For example, the guiding element may comprise a rail which is slidable through a cooperating aperture formed in the platform. Alternatively, the platform may comprise the rail and the guiding element may comprise the cooperating aperture. The guiding element may slidable along a straight linear path, whereby the adjustment path is a straight line. Alternatively, the guiding element may be pivotally mounted on the platform, e.g. via a hinge or pivot mount, whereby the adjustment path is a curve. In this arrangement, the body may move along an arc relative to the platform.

"The body may be a planar element having a tapered end. The plane of the planar element is preferably orthogonal to the planar light beam, whereby the pair of opposed contact surface are provided by opposite edges of the tapered end. The tapered end may be part of the planar element that can protrude below the mounting portion platform along the adjustment path. The tapering may be a decrease in distance between the contact surfaces along a line normal to the adjustment path along the planar element towards its end. The opposed edges of the tapering surface may be curved, e.g. in a concave, convex or linear manner. For example, the curved edges may curve outwardly as they extend away from the end of the planar element.

"Where the adjustment path is a straight line, the opposed contact surfaces are preferably symmetrical about the adjustment path. Where the adjustment path is curved, the contact surface may not display symmetry.

"One or both of the contact surfaces may have a convex profile, i.e. may present a laterally rounded surface that corresponds to the curvature of the edge of the hole. In one embodiment, the body may be a planar element and one of the pair of contact surfaces (e.g. the front contact surface) may be a convex surface extending laterally away from one edge of the planar element. The convex surface may thus resemble a beak-like structure on one edge of the planar element. The beak-like structure may be symmetric about the plane of the planar element. This configuration may assist in self-centering the body in the hole. It may be particularly useful when measuring countersunk holes because a reaction force from the sloped surfaces of the countersink on the convex surface may act to push the guide surface further into the hole.

"The positioning device may include a biasing element arranged to urge the guiding element along the adjustment path through the aperture. In use, the biasing element thus acts to push the guiding element into the hole to be measured, thereby assisting accurate location. The guiding element and/or the platform may include a stop portion for limiting the movement of the guiding element along the adjustment path, e.g. to prevent the guiding element from being pushed off the platform.

"The positioning device of the invention may be an integral part of or a detachable module for an optical triangulation sensor for measuring a hole formed in a surface of an object. An optical triangulation sensor having a positioning device as set out above may be an independent aspect of the present invention. The sensor may include a light source arranged to emit a planar light beam, and a detector located out of the plane of the planar light beam for detecting light from the planar light beam that is reflected at an angle to the plane of the planar light beam.

"The light source may include a laser. Any laser used in conventional optical triangulation sensor may be suitable. The laser may be class 3 or lower. For example, it may be a class 2M or 3R. The intensity of the laser may be adjustable (e.g. automatically adjustable) for different optical properties of surfaces to be measured. Alternatively, the light source may comprise one or more LEDs.

"The detector may be any suitable imaging device, e.g. a camera incorporating a charge coupled device (CCD) or an active pixel sensor (e.g. CMOS device).

BRIEF DESCRIPTION OF THE DRAWINGS

"Embodiments of the invention are described below with reference to the accompanying drawings, in which:

"FIG. 1 is a schematic diagram of a conventional laser triangulation sensor and is discussed above;

"FIG. 2 is a cross-sectional view of a junction between two components illustrated a gap and flush condition and is also discussed above;

"FIG. 3 is a perspective view of an optical triangulation sensor having a positioning device that is an embodiment of the invention;

"FIG. 4 is another perspective view of the optical triangulation sensor shown in FIG. 3;

"FIG. 5 is a partly cut away side view of the optical triangulation sensor shown in FIG. 3;

"FIG. 6 is a partly cut away side view of an optical triangulation sensor having a positioning device that is another embodiment of the invention;

"FIG. 7 is upward view from base of the optical triangulation sensor shown in FIG. 6; and

"FIG. 8 is a partly cut away front view of the optical triangulation sensor shown in FIG. 6."

For more information, see this patent application: MONKS, Tim. Positioning Device for an Optical Triangulation Sensor. Filed November 27, 2012 and posted June 5, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3826&p=77&f=G&l=50&d=PG01&S1=20140529.PD.&OS=PD/20140529&RS=PD/20140529

Keywords for this news article include: Third Dimension Software Limited.

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Source: Computer Weekly News


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