DE102008027831B4 - Measurement of the lens center thickness - Google Patents

Abstract

A lens to be tested (100) with an optical axis (104) is received on a pivot bearing (102) with an axis of rotation (106). The pivot bearing (102) with the lens (100) is rotated about its axis of rotation (106). A laser beam is aligned parallel to the axis of rotation (106) of the pivot bearing (102) and directed through the rotating lens (100). A spatially resolving light sensor detects the impact circle of the laser beam after it has passed through the rotating lens (100). The impact circle is visualized on a display. The lens (100) is aligned on the pivot bearing (102) in such a way that the size of the radius of the percussion circle visualized on the display is minimized, whereby the optical axis (104) of the lens (100) with the axis of rotation (106) of the pivot bearing ( 102) coincides. To measure the lens center thickness, an adjusted pair of calipers (210; 212) arranged in opposite directions is swiveled in such that the axes of the calipers (210; 212) coincide with the axis of rotation (106) of the pivot bearing (102) after swiveling. The thickness of the lens (100) on the axis of rotation (106) is then measured by probing with the feelers (210; 212).

Description

Field of the invention

The invention relates to the measurement of the lens center thickness at centered or uncentered lenses.

State of the art

The central linden thickness is a central optical property of a lens. The thickness of a lens in the center of the lens corresponds to the distance between the two lens surfaces in the region of the optical axis. The thickness of a lens in the center of the lens should be definable with an accuracy of <10 μm.

The principal problem in determining the thickness of a lens in the center of the lens (Lens Center Thickness) is determining the thickest or thinnest position on the DUT. Any lateral deviation from this leads to a measurement error that depends on the lens radii.

Common methods include clamping the lens with the aid of a central tensioner aligned with the measuring apparatus. This method has the disadvantage that it only works well enough for already centered lenses.

Another method is to determine the thickest or thinnest part of the lens with the aid of the measuring apparatus itself. In the case of tactile measurement, however, there is a great risk of damaging the test specimen itself. Non-contact measuring devices are very expensive and costly to operate with competitive accuracies compared to tactile measuring probes.

In the publication JP 57 108 610 A For example, a method for measuring the center thickness of a lens is described. In this case, a method for the required before the measurement of the center thickness centering of the lens to be measured is also disclosed.

A method for aligning a resting on a centering lens is also the DE 10 2004 030 896 A1 refer to. The document relates to a device for aligning an optical axis of a lens by means of two workpiece spindles which have on their front side in each case a centering bell for receiving a lens. A reference to the spindle axis axially offset from the centering arranged light source generates a coaxial with the workpiece spindle aligned light beam, which passes through the arranged between the centering lens. The centering bell opposite light detector is arranged, which is designed as a camera unit. The light detector has a sensor (CCD chip) which realizes the detection and evaluation of the light intensity generated by the light beam passing through the lens. The position of the lens can be automatically corrected by a special tool.

The further publication JP 56 160 631 A describes a method for simultaneously measuring the thickness and eccentricity of a lens by means of two autocollimators arranged opposite each other. In the middle between the autocollimators, the lens to be measured is rotatably mounted in a lens holder.

One in the publication DE 195 30 027 A1 The described method relates to the automatic measurement of lens parameters. In this case, the lens to be measured is penetrated by a front surface and a rear surface of a preferably monochromatic parallel beam. The light beam is hereby limited by an annular diaphragm in the immediate vicinity of the lens, the light beam ultimately falling onto a radiation receiver which is spatially resolving at least in one axis, which successively generates a plurality of measured signal values, on the basis of which the searched parameters of the lens, inter alia the center thickness, are determined become.

task

The object of the invention is to provide a method that allows the determination of the lens center thickness in a simple and accurate way.

solution

This object is achieved by the inventions having the features of the independent claims. Advantageous developments of the inventions are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into the content of this specification. The invention also includes all reasonable and in particular all mentioned combinations of independent and / or dependent claims.

In the following, individual process steps are described in more detail. The steps do not necessarily have to be performed in the order given, and the method to be described may also have other steps not mentioned.

In the method according to the invention for measuring the thickness of the lens center at centered and uncentered lenses, a lens to be tested having an optical axis is first recorded on a rotary bearing with an axis of rotation.

In a further step, the pivot bearing is rotated with the lens about its axis of rotation.

A laser beam is aligned parallel to the axis of rotation of the pivot bearing. The laser beam is directed through the rotating lens.

On the side facing away from the laser beam side of the lens, a spatially resolving light sensor is arranged such that it can detect a beat circle of the laser beam after passing through the rotating lens.

The beat circle of the laser beam is visualized on a display.

The lens is now aligned on the pivot bearing so that the size of the radius of the visualized on the display striking circle is minimized, whereby the optical axis of the lens coincides with the axis of rotation of the pivot bearing.

In a next step, an oppositely arranged adjusted probe pair is pivoted in such a way that the axis of the probe after pivoting coincides with the axis of rotation of the pivot bearing.

Subsequently, the thickness of the lens is measured on the axis of rotation by probing with the buttons.

After the lens to be tested has first been received by the rotary bearing of the measuring apparatus used, the laser beam aligned parallel to the axis of rotation of the rotary bearing is guided by the lens to be tested. After penetrating the lens, the laser beam strikes the spatially resolving light sensor, which was arranged on the side of the lens facing away from the laser beam. The sensor detects the beating circle generated by the laser beam after passing through the rotating lens. As a sensor, a position sensitive device (PSD) is advantageously used.

The beating circle generated on the sensor by the laser beam is visualized as an output signal of the sensor on a display (eg touch panel). The size of the radius of the striking circle is proportional to the size of the existing tilt of the optical axis of the lens with respect to the axis of rotation of the pivot bearing. The position of the lens is iteratively changed until the radius of the beat circle reaches a value close to or equal to zero. When this result is achieved, the conformity of the optical axis of the lens to be tested with the axis of rotation of the pivot bearing has been established, i. H. the lens was centered with regard to your position. This can be done the measurement of the thickness of the lens in the lens center.

In order to prevent the position of the lens on the pivot bearing during the subsequent measurement is changed unintentionally, the inclusion of the lens on the pivot bearing is designed so that the lens can be sucked by a vacuum pump and thus fixed in the centered position.

After centering the lens on the pivot bearing, the laser / PSD combination, via a suitable pivoting device, exchanged by a pair of buttons arranged in opposite directions.

The probes are used to measure the center thickness of the lens. The probe positions are calibrated (adjusted) before starting the measurement, ie. H. First, the position of the push-button is defined for touching stylus tips (stylus distance = zero). The buttons indicate their position by a digital signal. The accuracy of the probe should be <2 μm. For the measurement process, the probes are pivoted in and moved counter to the lens surfaces and positioned so that they touch the two lens surfaces in each case in the region of the optical axis of the lens.

In this position, the digital signals of both buttons are detected and offset against each other. The result of the offset of both probe signals defines the value of the thickness of the lens in the lens center, d. H. in the area of the optical axis of the lens.

It is particularly advantageous that the proposed method does not require knowledge of the lens data, so that unknown lenses can also be measured.

Furthermore, it is also advantageous that lenses can be measured which have a decentering. The decentering is a manufacturing error of a lens, in which the optically effective surfaces of the lens (lens surfaces) are tilted with respect to a reference edge (lens edge) or reference axis of the lens. As a reference axis in a single lens, the shape axis d. H. serve the axis of symmetry of the lens edge.

The invention advantageously makes it possible, with the aid of an inexpensive combination of laser and position diode, to align an unknown lens without contact for a subsequent tactile measurement by means of a likewise inexpensive tactile measuring apparatus.

It is also advantageous that the lens thickness measurement according to the invention can be carried out preferably on lenses with small radii and small diameters and a manufacturing technology Prior centering of the lens to be tested is not required. It should be noted, however, that the lenses to be tested must be transparent to the laser beam.

In an advantageous development of the invention, the positioning of the lens is performed by an actuator. The centered position of the lens to be tested on the pivot bearing of the measuring arrangement is realized iteratively. The process for producing a centered position of the lens can also be carried out manually.

In an advantageous embodiment of the invention, the probes are pneumatically (i.e., through the application of compressed air) movable together and positioned on the lens surface.

• a) mit einer Aufnahme für eine zu prüfende Linse (100), wobei die Linse eine optische Achse (104) hat und die Aufnahme auf einem Drehlager (102) mit einer Rotationsachse (106) gelagert ist;
• b) mit einem Motor (216), der das Drehlager (102) mit der Linse (100) um seine Rotationsachse (106) dreht;
• c) mit einem Laser (206), der einen Laserstrahl erzeugt, der parallel zur Rotationsachse (106) des Drehlagers (102) ausgerichtet ist;
• d) mit Mitteln, den Laserstrahl durch die sich drehende Linse zu lenken;
• e) mit einem ortsauflösenden Lichtsensor, wobei der ortsauflösenden Lichtsensor auf der vom Laserstrahl abgewandten Seite der Linse derart angeordnet ist, dass er einen Schlagkreis des Laserstrahls nach Durchtritt durch die sich drehende Linse erfassen kann;
• f) mit einem Display, auf dem der Schlagkreis visualisiert wird;
• g) mit Mitteln, die Linse so auf dem Drehlager auszurichten, dass die Größe des Radius des auf dem Display visualisierten Schlagkreises minimiert wird, wodurch die optische Achse der Linse mit der Rotationsachse des Drehlagers zusammen fällt;
• h) mit Mitteln, ein gegenläufig angeordnetes justiertes Tasterpaar derart einzuschwenken, dass die Achsen der Taster nach dem Einschwenken mit der Rotationsachse des Drehlagers zusammen fallen; und
• i) mit Mitteln, die es erlauben, anschließend mit den Tastern die Dicke der Linse auf der Rotationsachse durch Antasten zu messen.

The invention also includes a device for measuring the thickness of the lens center at centered and non-centered lenses with:

• a) with a receptacle for a lens to be tested ( 100 ), wherein the lens has an optical axis ( 104 ) and the inclusion on a pivot bearing ( 102 ) with a rotation axis ( 106 ) is stored;
• b) with a motor ( 216 ), the pivot bearing ( 102 ) with the lens ( 100 ) about its axis of rotation ( 106 ) turns;
• c) with a laser ( 206 ), which generates a laser beam parallel to the axis of rotation ( 106 ) of the pivot bearing ( 102 ) is aligned;
• d) means for directing the laser beam through the rotating lens;
• e) with a spatially resolving light sensor, wherein the spatially resolving light sensor on the side facing away from the laser beam side of the lens is arranged such that it can detect a beat circle of the laser beam after passing through the rotating lens;
• f) with a display on which the beat circle is visualized;
• g) means for aligning the lens on the pivot bearing so as to minimize the size of the radius of the beat circle visualized on the display, whereby the optical axis of the lens coincides with the axis of rotation of the pivot bearing;
• h) means for pivoting a pair of counterparts arranged in the opposite direction in such a way that the axes of the buttons coincide with the axis of rotation of the pivot bearing after pivoting; and
• i) with means that allow, then with the buttons to measure the thickness of the lens on the axis of rotation by probing.

In an advantageous development of the device according to the invention, the means are also provided for effecting the positioning of the lens by an actuator.

In a further advantageous embodiment, the device has the ability to drive together the probe with pneumatic means and to position on the lens surface.

Further details and features will become apparent from the following description of preferred embodiments in conjunction with the subclaims. In this case, the respective features can be implemented on their own or in combination with one another. The possibilities to solve the problem are not limited to the embodiments. For example, area information always includes all - not mentioned - intermediate values and all imaginable subintervals.

The embodiments are shown schematically in the figures. The same reference numerals in the individual figures designate the same or functionally identical or with respect to their functions corresponding elements. In detail shows:

1a a schematic diagram (schematically) of a non-centered on the pivot bearing lens;

1b a schematic diagram (schematically) of a centered on the pivot bearing aligned lens;

2 an overall perspective view (schematically) of the measuring device;

3 a partial perspective view (schematically) of the measuring device with an inside view of the base housing of the measuring device;

4 a partial perspective view (sectional view, schematically) of the measuring device; and

5 a schematic representation of the procedure for measuring the center thickness of a lens.

1a shows a schematic representation of a lens to be tested 100 before an executed centering. The Lens 100 is located on the lens mount of a pivot bearing 102 , The optical axis 104 the lens 100 is located in an undefined tilted or offset position with respect to the axis of rotation 106 of the pivot bearing.

1b shows that as a result of the iterative alignment of the position of the optical axis 104 the lens 100 in the course of Zentrierungsvorganges 100 a defined aligned position of the optical axis 104 in relation to the axis of rotation 106 of the pivot bearing was taken and thus the goal of centering has been achieved and the optical axis 104 the lens 100 and the rotation axis 106 of the pivot bearing 102 coincide. This condition is the prerequisite for carrying out the subsequent concrete tactile measurement of the lens center thickness.

An overall perspective view (schematic) of the measuring device 200 show the 2 , The measuring device 200 consists of a base housing 202 with the functional elements contained therein. Above on the base housing 202 is a fastening device 204 with the laser device 206 and the swivel device 208 for the buttons 210 and 212 (not shown) arranged. On the top cover 214 of the base housing 202 is the pivot bearing 102 with the lens holder. The rotational movement of the pivot bearing 102 is by a motor 216 causes the side of the base housing 202 is appropriate. The power transmission from the engine 216 to the pivot 102 via a V-belt 218 that drives the drive 220 of the motor 216 with the pivot bearing 102 combines.

3 shows a perspective partial view of the measuring device 200 an interior view of the base housing 202 the measuring device 200 , In addition to 2 are the bottom button 212 as well as parts 213 the device for the opposite approach of the button 210 . 212 on surfaces of the lens to be measured 100 shown. The for the centering of the lens 100 on the pivot 102 required position diode (not shown) is below the pivot bearing 102 arranged.

4 shows in a further perspective partial view of the measuring device also already in the 2 and 3 named functional elements. Explicit are in 4 additionally the probe heads 402 and 404 represented, which are driven up to the lens surfaces. After approaching the measurement is carried out.

In 5 the process steps according to the invention are shown schematically. In step 500 becomes first a lens to be tested 100 with an optical axis 104 on a pivot 102 with a rotation axis 106 added. In step 502 becomes the pivot bearing 102 with the lens 100 turned around its axis of rotation. A laser beam gets in step 504 aligned parallel to the axis of rotation of the pivot bearing and in step 506 through the rotating lens 100 directed. In step 508 becomes on the side of the lens facing away from the laser beam 100 on a location-resolving light sensor arranged there, the beat circle of the laser beam after passing through the rotating lens 100 detected. The beating circle will be in step 510 visualized on a display.

In step 512 (Decision) becomes the result of the alignment (centering) of the lens 100 on the pivot 102 rated.

If the centering has been done with the allowable tolerance ("Yes"), in which case the optical axis 104 the lens 100 with the rotation axis 106 of the pivot bearing coincides, then done in step 514 the execution of the tactile measurement of the lens center thickness with the stylus device (button 210 . 212 ).

Is the appropriate quality of the orientation of the lens 100 not yet reached ("no"), the lens becomes 100 in step 516 keep it up on the pivot 102 until the size of the radius of the beat circle visualized on the display is minimized.

LIST OF REFERENCE NUMBERS

100

lens

102

Swivel bearing with lens holder

104

Optical axis of the lens

106

Rotation axis of the pivot bearing

200

measuring device

202

base housing

204

fastening device

206

laser device

208

Swivel device for push buttons

210

button

212

button

213

Device for moving the buttons

214

upper cover plate base housing

216

engine

218

fan belt

220

Drive wheel of the motor

402

button head

404

button head

500

step

502

step

504

step

506

step

508

step

510

step

512

step

514

step

516

step

quoted literature

• JP 57 108 610 A
• DE 10 2004 030 896 A1
• JP 56 160 631 A
• DE 195 30 027 A1

Claims (6)

Method for measuring the thickness of the lens center at centered and non-centered lenses, comprising the following steps: a) a lens to be tested ( 100 ) with an optical axis ( 104 ) is on a pivot bearing ( 102 ) with a rotation axis ( 106 ) recorded; b) the pivot bearing ( 102 ) with the lens ( 100 ) is moved around its axis of rotation ( 106 ) turned; c) a laser beam is parallel to the axis of rotation ( 106 ) of the pivot bearing ( 102 ) aligned; d) the laser beam is transmitted through the rotating lens ( 100 ) directed; e) on the side of the lens facing away from the laser beam ( 100 ), a spatially resolving light sensor is arranged such that it forms a beat circle of the laser beam after passing through the rotating lens (FIG. 100 ) can capture; f) the beat circle is visualized on a display; g) the lens ( 100 ) is so on the pivot bearing ( 102 ) minimizes the size of the radius of the beat circle visualized on the display, whereby the optical axis ( 104 ) of the lens with the axis of rotation ( 106 ) of the pivot bearing ( 102 ) coincides; h) an oppositely arranged adjusted pair of probes ( 210 ; 212 ) is pivoted in such a way that the axis of the button ( 210 ; 212 ) after pivoting with the axis of rotation ( 106 ) of the pivot bearing ( 102 ) coincides; and i) then use the buttons ( 210 ; 212 ) the thickness of the lens ( 100 ) on the axis of rotation ( 106 ) measured by probing. Method according to the preceding claim, characterized in that the positioning of the lens ( 100 ) by an actuator. Method according to one of the preceding claims, characterized in that the buttons ( 210 ; 212 ) are pneumatically zusammenfahrbar and positioned on the lens surface. Device for measuring the thickness of the lens center at centered and non-centered lenses: a) with a receptacle for a lens to be tested ( 100 ), wherein the lens has an optical axis ( 104 ) and the inclusion on a pivot bearing ( 102 ) with a rotation axis ( 106 ) is stored; b) with a motor ( 216 ), the pivot bearing ( 102 ) with the lens ( 100 ) about its axis of rotation ( 106 ) turns; c) with a laser ( 206 ), which generates a laser beam parallel to the axis of rotation ( 106 ) of the pivot bearing ( 102 ) is aligned; d) with means, the laser beam through the rotating lens ( 100 ) to steer; e) with a spatially resolving light sensor, wherein the spatially resolving light sensor on the side facing away from the laser beam side of the lens ( 100 ) is arranged such that it forms a beat circle of the laser beam after passing through the rotating lens ( 100 ) can capture; f) with a display on which the beat circle is visualized; g) by means of the lens ( 100 ) so on the pivot bearing ( 102 ) to minimize the size of the radius of the beat circle visualized on the display, whereby the optical axis ( 104 ) of the lens ( 100 ) with the rotation axis ( 106 ) of the pivot bearing coincides; h) with means, an oppositely arranged adjusted pair of probes ( 210 ; 212 ) such that the axes of the probe after pivoting with the axis of rotation ( 106 ) of the pivot bearing ( 102 ) fall together; and i) with means that allow it, then with the buttons ( 210 ; 212 ) the thickness of the lens ( 100 ) on the axis of rotation ( 106 ) by probing. Device according to the preceding claim, characterized in that means are provided for positioning the lens ( 102 ) realized by an actuator. Device according to one of the preceding claims 4 or 5, characterized in that the buttons ( 210 ; 212 ) can be moved together by pneumatic means and positioned on the lens surface.

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