EP2106563A1

EP2106563A1 - Three-dimensional scanning method using a telecentric beam

Info

Publication number: EP2106563A1
Application number: EP07802513A
Authority: EP
Inventors: Stephen Hastings; Stephen Coles
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-08-06
Filing date: 2007-08-06
Publication date: 2009-10-07
Also published as: WO2009018856A1

Abstract

This invention relates to a method of laser beam targeting and apparatus for laser beam targeting. In particular, the invention relates to three-dimensional lase.r beam targeting and focusing where the laser beam exiting the apparatus is maintained perpendicular to the target area. In other terms, the output beam is telecentric.

Description

THREE-DIMENSIONAL SCANNING METHOD USING A TELECENTRIC BEAM

Field of the Invention

This invention relates to a method of laser beam targeting and apparatus for laser beam targeting. In particular, the invention relates to three-dimensional laser beam targeting and focusing where the laser beam exiting the apparatus is maintained perpendicular to the target area and correcting an optical production and subsequent complex mirror scanning problem originally incorporated within DE10343080 Device for steering and focusing a laser beam in tbe direction of a target object comprises a focusing unit for focusing the laser beam, a rotating X-mirror, a rotating Y -mirror, and a stationary field mirror for receiving the deviated beam (Hastings, 21 April 2005).

Background of the Invention

Current laser beam scanning techniques involve two-dimensional targeting and focusing with standard X and Y deflection technology, where the third dimensional Z movement is controlled using a Z positional table to move the target closer and further away from the targeting and focusing apparatus and therefore to control the position of the focused laser beam energy or spot in the Z direction through a range of target planes on a three- dimensional target. Current laser beam scanning techniques also use telecentric focusing lens technology to improve the perpendicularity of the laser beam at the target plane.

While telecentric lens technology remains relatively expensive, the additional requirement to position the focused laser beam or spot in the Z direction through a telecentric lens arrangement remains optical difficult and limited.

In the first of the aforementioned systems the laser beam is directed onto a first or X direction galvano motor controlled mirror that then deflects the laser beam onto a second or Y direction galvano motor controlled mirror that in turn deflects the laser beam towards the two-dimensional target plane. The X and Y galvano motors each comprise a central spindle that is held within a magnetic field and onto which a deflecting mirror is affixed. By sending a signal to increase or decrease the magnetic field the spindle can be rotated clockwise and anti-clockwise at high speeds and with high accuracy and repeatability.

By controlling an X and a Y galvano motor in combination with switching of a laser source an image can be scanned onto the target plane. An f-Theta or pre-objective scanning lens can be used to focus the laser energy to a spot at a two-dimensional target plane while the Z movement of the target plane is controlled by moving the target closer and further away from the targeting apparatus to change the position of the two- dimensional targeting in the third or commonly known as Z axis.

Disadvantageously, the method of laser beam targeting as described in the first of the aforementioned systems does not correct for the combined rotation of the X and Y direction galvano motor controlled mirrors and so the beam entering the target area will not be perpendicular at all points and the circularity or ellipticity and therefore the energy density of the focused laser beam or spot will be constantly changing over the entire field area.

In the second of the aforementioned systems the laser beam is passed through a set of optics of which one will be under positional control and usually via a third or Z direction controlling galvano motor mechanically adapted to produce lineal movement from said galvano motor's rotational movement. With this arrangement it is possible to control the position of the laser beam or spot at a three-dimensional target within a third or Z-axis.

However maintaining perpedicularity at said three-dimensional target may only be achieved by using a further complicated and expensive set of telecentric delivery optics.

Disadvantageous^/, the method of laser beam targeting as described in the second of the aforementioned systems is complicated and limited and does not allow for relatively large three-dimensional field areas without increasing the diameters of the elements of the telecentric lens arrangement.

Furthermore, and also disadvantageous^/, the previous method as described in DEl 0343080 Device for steering and focusing a laser beam in the direction of a target object comprises a focusing unit for focusing the laser beam, a rotating X-mιrror, a rotating Y -mirror, and a stationary field mirror for receiving the deviated beam (Hastings, 21 April 2005) details a special Y direction mirror controlled and rotated by a second galvano motor. Said special Y direction mirror deflecting a laser beam onto a fixed special Z mirror and it is this special Y direction mirror controlled and rotated by a second galvano motor that is difficult to manufacture when required to be mounted to said galvano motor and difficult to balance on the rotational axis of said galvano motor thus generating moment of inertia and maximum rotational speed issues.

Summary of the Invention

According to the present invention there is provided a method for targeting a laser beam over a three-dimensional area whereby the perpendicularity of said laser beam entering the target area is maintained by the use of a flat or piano X or first galvano motor controlled mirror deflecting the laser beam onto a specially shaped and statically fixed intermediate mirror in turn deflecting said laser beam onto a flat or piano Y or second galvano motor controlled mirror deflecting said laser beam onto a specially shaped and statically fixed Z mirror.

The position of the focused laser beam or spot at the target is controlled in the X or first direction by the signals and commands inputted to the X or first direction galvano motor rotating the flat or piano X or first deflection mirror. The position of the focused laser beam or spot at the target is controlled in the Y or second direction by the signals and commands inputted to the Y or second direction galvano motor rotating the flat or piano Y or second deflection mirror.

The position of the focussed laser beam or spot at the target is controlled in the Z or thrird direction by the signals and commands inputted to the Z or third direction galvano motor or linear motor linearly moving one single optic or multiple optics within a set of focusing optics.

The exact geometry of the spacing between all components, the number and specifications of the elements within the set of focusing optics and the curvature or curvatures of the mirrors may be altered depending on the exact three-dimensional field size, the wavelength of said laser beam, the required focused laser beam or spot size at the three-dimensional target and the input laser beam size.

Advantageously, the method described in the present invention allows for optical correction of the laser beam to maintain constant or near constant perpendicularity and circularity of the focused laser beam or spot in the entire three-dimensional field area.

Advantageously, the method described in the present invention allows for focusing of the laser beam energy or spot in the three-dimensional target field in the Z or third direction without the use of complicated transmissive optics.

Advantageously, the method described in the present invention allows for a wide range of laser energy wavelengths to be utilised depending upon the materials and coatings used in manufacturing the set of focusing optics the flat or piano X or first direction mirror the specially shaped and statically fixed intermediate mirror the flat or piano Y or second direction mirror and the specially shaped and statically fixed Z mirror.

Advantageously, the method described in the present invention allows for control of the laser beam energy or spot in the three-dimensional target depending upon the curvatures and geometries of the delivery optics and especially the specially shaped and statically fixed intermediate mirror and the specially shaped and statically fixed Z mirror. Advantageously, the method described in the present invention allows for non-circular X and Y scanning areas by changing the size and/or shape and/or curvature of the specially shaped and statically fixed intermediate mirror and the specially shaped and statically fixed Z mirror.

Advantageously, the method described in the present invention allows for the use of the apparatus in the reverse direction where a two-dimensional or three-dimensional area is required to be scanned so that the optical information is passed through the system from the target field via the specially shaped and statically fixed Z mirror the flat or piano Y or second direction scanning mirror the specially shaped and statically fixed intermediate mirror and the flat or piano X or first direction scanning mirror and the set of focusing optics into a reading apparatus, for example a CCD camera.

Brief Description of the Drawings

Figure 1 is a simple single elevation cross-sectional diagram depicting one embodiment of the layout of the apparatus described within the invention and showing a beam expanded and then focused through a post-objective lens telescope so that the laser beam exiting the final optical element of said post-objective lens telescope focuses in a required three- dimensional target area through deflection off a rotating flat or piano X or first direction mirror attached to an X or first direction galvano motor and deflection off a specially shaped and statically fixed intermediate mirror and deflection off a rotating flat or piano Y or second direction mirror attached to an Y or second direction galvano motor and deflection off a specially shaped and statically fixed Z mirror.

Figure 2 is an isometric diagram depicting a repeat of the apparatus as described in Figure 1 above.

Detailed Description of the Invention

As depicted in Figure 1, in a method of three-dimensional laser beam scanning targeting where the laser beam exiting the apparatus remains perpendicular to a three-dimensional target area a laser beam (1) passes through a set of focusing optics (2) and (3) to a flat or piano X or first direction mirror (4) controlled and rotated by an X or first direction galvano motor (5) and said flat or piano X or first direction mirror (4) deflects the laser beam (1) onto a specially shaped and statically fixed intermediate mirror (6) and said specially shaped and statically fixed intermediate mirror (6) deflects said laser beam (1) onto a flat or piano Y or second direction mirror (7) controlled and rotated by a Y or second direction galvano motor (8) and said flat or piano Y or second direction mirror (7) deflects the laser beam (1) onto a specially shaped and statically fixed Z mirror (9) and said specially shaped and statically fixed Z mirror (9) deflects said laser beam (1) to a three-dimensional target area (10) whilst always maintaining the laser beam (1) perpendicular to said target (10).

By altering the distance or distances between the set of focusing optics (2) and (3) the exact focus of said laser beam (1) in the Z or third direction at the target (10) can be finely controlled.

The laser beam (1) under focus control through the apparatus by the actions of moving one or more elements of the set of focusing optics (2) and (3) and commonly the smaller first or expander optic (2) is then deflected off the flat or piano X or first direction mirror (4) and scanned along the length of a specially shaped and statically fixed intermediate mirror (6) and said specially shaped and statically fixed intermediate mirror (6) having a curvature to control the profile of the laser beam (1) and maintain perpendicularity in one single direction deflecting towards a flat or piano Y or second direction mirror (7) and said flat or piano Y or second direction mirror (7) accepting the laser beam (1) arriving perpendicular to its axis of rotation from said specially shaped and statically fixed intermediate mirror (6) in turn deflects said laser beam (1) to a specially shaped and statically fixed Z mirror (9) and said specially shaped and statically fixed Z mirror (9) having a curvature to control the profile of the laser beam (1) and maintain perpendicularity of the laser beam (1) entering an entire three-dimensional target field area (10).

Because in raster processing one galvano driven flat or piano mirror is performing the high speed side-to-side scanning whilst the other galvano driven flat or piano mirror performs the incremental advance scanning this method of having a small X or first direction mirror (4) and a larger and heavier Y or second direction mirror (7) is not detrimental to overall processing speeds.

Likewise, in relatively slow vector scanning speed applications, for example plastic welding or liquid crystal display hole drilling, the additional weight of the Y or second direction mirror (7) is also not detrimental to overall processing speeds.

Furthermore, the addition of a specially shaped and statically fixed intermediate mirror (6) followed by a flat or piano Y or second direction galvano driven mirror (7) addresses problems and production, balance, speed and targeting capability issues when using a galvano motor driven complex special Y direction mirror as described in DE10343080 Device for steering and focusing a laser beam in the direction of a target object comprises a focusing unit or focusing the laser beam, a rotating X-mιrror, a rotating Y -mirror, and a stationary field mirror for receiving the deviated beam (Hastings, 21 April 2005).

Claims

1. A method of controlling and positioning a laser beam wherein a three-dimensional area may be targeted with a laser beam to maintain perpendicular entry of said laser beam into said three-dimensional area and said method comprising a set of focusing optics, an X or first direction mirror controlled and rotated by a galvano motor and deflecting the laser beam onto a specially shaped and statically fixed intermediate mirror in turn deflected onto a Y or second direction mirror controlled and rotated by a second galvano motor and deflecting the laser beam onto a a specially shaped and statically fixed Z mirror deflecting said laser beam to said three-dimensional area.

2. A method according to Claim 1 , wherein one or more elements of said set of focusing optics is/are moved linearly to the incoming laser beam to allow for fine focus of the laser beam entering the three-dimensional target area perpendicularly to position said focus anywhere within the X or first, Y or second and Z or third directions within said three-dimensional target area.

3. A method according to claims 1 and 2, wherein said apparatus may be used for either targeting laser energy through the apparatus to the three-dimensional target area or used for collecting information at the three-dimensional target area and reading said information with a reading device at the usual laser beam input side of the apparatus.

4. A method according to claims 1-3, wherein said apparatus may target to or collect information from a two-dimensional target plane.

5. A method according to claims 1-4, wherein said apparatus may be designed in a way so that improvements in perpendicularity may be achieved with a smaller special fixed Z direction mirror than the X or first and Y or second directional size/s of the target area.

6. A method according to claims 1-5, wherein said laser beam exiting said specially shaped and statically fixed intermediate mirror is not perpendicular to said laser beam entering said specially shaped and statically fixed intermediate mirror.

7. A method according to claims 1-6, wherein said laser beam exiting said specially shaped and statically fixed Z mirror is not perpendicular to said laser beam entering said specially shaped and statically fixed Z mirror.

8. A method according to claims 1-7, wherein said target may be active or moving and where said targeting apparatus may follow or track said movements to target said laser beam relative to said movements.