JP2007065524A - Imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens capable of securely imaging an image of a component irrespective of variation in the component, in the imaging lens applied to a recognition camera of a mounting machine or the like. <P>SOLUTION: The imaging lens includes, from an object side to an imaging surface side, a first lens 1 having a positive refractive index and having the biconvex shape with convex surfaces directed to the object side and the imaging surface side, a second lens 2 having a positive refractive index and having a meniscus shape with a convex surface directed to the object side, a third lens 3 having a negative refractive index and having a biconcave shape with concave surfaces directed to the object side and the imaging surface side, an aperture diaphragm SD having a prescribed diameter, a fourth lens 4 having a negative refractive index and having a biconcave shape with concave surfaces directed to the object side and the imaging surface side, and a fifth lens 5 joined to the concave surface of the fourth lens 4 at the imaging side and having a biconvex shape with convex surfaces directed to the object side and the imaging surface side. Thus, the working distance can be made large while achieving reduced size, and telecentric properties at the object side are secured. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging lens used in a recognition camera for recognizing an electronic component or the like in a mounting machine that mounts the electronic component or the like on a substrate, and more particularly to an imaging lens having telecentricity on the object side.

In the process of mounting electronic components on the board, in order to accurately determine each electronic component at a predetermined position, the electronic component picked up by the pick-up nozzle of the mounting machine is imaged by a recognition camera and the obtained image data is calculated. By processing and finely adjusting the position of the suction nozzle, a slight positional deviation of the electronic component is also corrected.
As an imaging lens applied to this recognition camera, when recognizing an object such as an electronic component, the object side has telecentricity so that the size of the captured image does not change even if the distance between the object and the lens changes. It is preferable to have it. Furthermore, since related parts such as illumination are arranged in the vicinity of the lens barrel of the imaging lens, it is necessary to make the working distance relatively long.

By the way, the conventional imaging lens includes a front lens group having a positive refractive power, a diffractive optical element having a diffractive optical surface, and a rear lens group having a positive refractive power, and the front lens group includes three positive lenses. And one negative lens, and the rear lens group is composed of one negative lens and three positive lenses, and is applied to an optical system for a scanner (for example, Patent Documents). 1).
When this imaging lens is applied for recognition of electronic components and the like in the mounting process, the working distance (distance between the object such as the electronic component and the lens closest to the object) is shortened. For example, a specification requirement of 80 mm or more is required. I can't meet.
Further, in this imaging lens, since the principal ray from the object and the optical axis are slightly inclined, the telecentricity on the object side is not sufficient.

JP 2004-252100 A

  The present invention has been made in view of the above-described prior art, and the object thereof is to ensure the telecentricity on the object side and to sufficiently secure the distance between the object and the lens, that is, the working distance, An object of the present invention is to provide an imaging lens that is small in size, low in cost, has high optical performance, and is suitable for a mounting process of electronic components.

The imaging lens of the present invention includes a first lens having a positive refractive index and a convex surface facing the object side and the image plane side, arranged in order from the object side to the image plane side, and a positive lens. A second meniscus lens having a refractive index and having a convex surface facing the object side; a third lens having a negative refractive index and having a concave surface facing the object side and the image surface; and a predetermined aperture An aperture stop having a negative refractive index and being cemented to a concave surface on the image plane side of the fourth lens and a biconcave fourth lens having a negative refractive index and a concave surface facing the object side and the image plane side, And a cemented lens composed of a biconvex fifth lens having a convex surface facing the image surface side.
According to this configuration, since the outer diameter of the first lens can be kept small, it is possible to arrange components such as illumination around the first lens while reducing the overall size. In addition, the first to third lenses on the front side of the aperture stop have a positive refractive power, and the cemented lenses (the fourth lens and the fifth lens) on the rear side of the aperture stop have a negative refractive power. In this way, the working distance from the object to the first lens can be increased (for example, about 80 mm). Furthermore, by using a cemented lens in which the fourth lens is bonded as a biconcave lens and the fifth lens as a biconvex lens, it is possible to cope with visible light for recognition, that is, a white light source, and chromatic aberration can be corrected well. .
In addition, since the first lens is a biconvex lens, the light beam of the object that has spread is rapidly bent and the amount of light is secured, and the angle between the principal ray from the object and the optical axis is as close as possible to 0 degrees, that is, a parallel light beam. The telecentricity on the object side can be ensured. Furthermore, the spherical aberration generated in the first lens can be favorably corrected by the second lens and the third lens, and high resolution can be obtained.

In the above configuration, when the radius of curvature of the concave surface on the object side of the third lens is R5 and the radius of curvature of the concave surface on the image surface side of the third lens is R6, the following equation (1):
(1) | R5 | = R6
A configuration that satisfies the above can be adopted.
According to this configuration, when the expression (1) is satisfied, the manufacturing cost of the third lens can be reduced, and mistakes before and after assembly, that is, incorrect assembly can be prevented.

In the above configuration, when the radius of curvature of the convex surface on the object side of the fifth lens is R9 and the radius of curvature of the convex surface on the image side of the fifth lens is R10, the following equation (2):
(2) R9 = | R10 |
A configuration that satisfies the above can be adopted.
According to this configuration, when the expression (2) is satisfied, the manufacturing cost of the fifth lens can be reduced, and mistakes before and after assembly, that is, erroneous assembly can be prevented.

In the above configuration, the first lens and the second lens may be formed of the same glass glass material.
According to this configuration, the cost of the entire imaging lens can be reduced.

In the above configuration, the third lens and the fifth lens may be formed of the same glass glass material.
According to this configuration, the cost of the entire imaging lens can be reduced.

In the above configuration, when the conjugate length from the object to the image plane is TT, the working distance from the object to the front surface of the first lens is WD, and the back focus from the rear surface of the fifth lens to the image plane is BF, the following formula ( 3),
(3) 2.05 × WD> TT = 160 mm, BF> 30 mm
A configuration that satisfies the above can be adopted.
According to this configuration, by satisfying the expression (3), an imaging lens suitable for a recognition camera in a mounting machine such as an electronic component can be obtained.

  According to the imaging lens having the above configuration, the telecentricity on the object side can be ensured, and the distance between the object and the lens, that is, the working distance can be sufficiently secured, and the optical performance is high in size, low cost, high electronic performance, etc. A suitable imaging lens can be obtained in the mounting process or the like.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
1 to 5 show an embodiment of an imaging lens according to the present invention. FIG. 1 is a lens configuration diagram, FIG. 2 is an optical path diagram, and FIG. 3 is a partial optical path diagram from an object to the first lens. FIG. 4 is a cross-sectional view showing a lens barrel provided with an imaging lens, and FIG. 5 is an aberration diagram.
As shown in FIG. 1, the imaging lens includes a first lens 1 having a positive refractive index, a second lens 2 having a positive refractive index, and a negative lens, which are arranged in order from the object side to the image plane side. A third lens 3 having a refractive index; a fourth lens 4 having a negative refractive index; and a fifth lens 5 which is cemented to the fourth lens 4 and has a positive refractive power. 4 has a four-group, five-lens configuration including an aperture stop SD having a predetermined aperture between four. An imaging plane P of an image sensor such as a CCD is disposed behind the fifth lens 5.

  Incidentally, in the first lens 1 to the third lens 3, the aperture stop SD, the fourth lens 4 and the fifth lens 5, as shown in FIG. 1, each surface is Si (i = 1 to 10), The curvature radius of the surface Si is Ri (i = 1 to 10), the refractive index of the first lens 1 to the fifth lens 5 with respect to the d line is Ni (i = 1 to 5), and the Abbe number is νi (i = 1 to 5). ). Further, the distance (thickness, air interval) on the optical axis L from the first lens 1 to the image plane is Di (i = 1 to 10), and the distance on the optical axis L from the object OBJ to the first lens 1 is set. Represented by D0. Further, the distance from the object OBJ to the image plane P, that is, the conjugate length is TT, the distance from the object OBJ to the front surface S1 of the first lens 1, that is, the working distance is WD, and the air from the rear surface S10 of the fifth lens 5 to the image plane P The conversion distance, that is, the back focus is represented by BF.

The first lens 1 is a biconvex positive lens made of a glass material and having a convex surface S1 on the object side and a convex surface S2 on the image surface side.
The second lens 2 is a positive meniscus lens made of a glass material and having a convex surface S3 on the object side and a concave surface S4 on the image surface side.
The third lens 3 is a biconcave negative lens made of a glass material and having a concave surface S5 on the object side and a concave surface S6 on the image side.
The fourth lens 4 is a biconcave negative lens made of a glass material and having a concave surface S8 on the object side and a concave surface S9 on the image surface side.
The fifth lens 5 is a biconvex positive lens made of a glass material and having a convex surface S9 on the object side and a convex surface S10 on the image surface side.
The fourth lens 4 and the fifth lens are bonded to each other on the surface S9 and formed as a cemented lens having a negative refractive power as a whole.

  Further, as shown in FIG. 4, the first lens 1 to the fifth lens 5 and the aperture stop SD are fitted and fixed inside the lens barrel 10 in a state of being sequentially arranged in the optical axis direction L. ing. The aperture stop SD is integrally formed as a part of the lens barrel 10. The lens barrel 10 is incorporated as a part of a recognition camera included in the mounting machine.

According to the imaging lens having the above-described configuration, the outer diameter of the first lens 1 can be kept small. Therefore, while reducing the overall size, illumination or the like is provided around the first lens 1, that is, near the tip of the lens barrel 10. Parts can be placed.
In addition, the first lens 1 to the third lens 3 positioned in front of the aperture stop SD have positive refractive power, and are cemented lenses (fourth lens 4 and fifth lens) positioned in the rear side of the aperture stop SD. By forming 5) to have a negative refractive power, the working distance WD from the object OBJ to the first lens 1 can be increased (for example, about 80 mm) as shown in FIG.
Furthermore, by using the cemented lens in which the fourth lens 4 is bonded as a biconcave lens and the fifth lens 5 as a biconvex lens, it is possible to cope with visible light for recognition, that is, a white light source, and correct chromatic aberration well. Can do.
Further, since the first lens 1 is a biconvex lens, as shown in FIG. 2, the light ray of the object that has spread is rapidly bent and the amount of light is secured, and as shown in FIG. 3, the principal ray from the object OBJ. Can be as close as possible to 0 degrees, that is, parallel rays, and the object side telecentricity can be ensured. Furthermore, the spherical aberration generated in the first lens 1 can be favorably corrected by the second lens 2 and the third lens 3, and high resolving power can be obtained.

Here, in the imaging lens having the above-described configuration, the curvature radius R5 of the concave surface S5 on the object side of the third lens 3 and the curvature radius R6 of the concave surface S6 on the image plane side of the third lens 3 are preferably expressed by the following formula (1). ,
(1) | R5 | = R6
It is formed so as to satisfy.
Thereby, the manufacturing cost of the 3rd lens 3 can be reduced, and the mistake before and behind at the time of an assembly | attachment, ie, an incorrect assembly, can be prevented.

In the imaging lens having the above-described configuration, the curvature radius R9 of the convex surface S9 on the object side of the fifth lens 5 and the curvature radius R10 of the convex surface S10 on the image plane side of the fifth lens 5 are preferably expressed by the following formula (2):
(2) R9 = | R10 |
It is formed so as to satisfy.
Thereby, the manufacturing cost of the 5th lens 5 can be reduced, and the mistake before and behind at the time of an assembly | attachment, ie, an incorrect assembly, can be prevented.

In the imaging lens having the above-described configuration, the first lens 1 and the second lens 2 may be preferably formed of the same glass glass material. Thereby, the expense of glass material can be reduced and the cost as the whole imaging lens can be reduced.
Similarly, the third lens 3 and the fifth lens 5 may be preferably made of the same glass glass material. Thereby, like the above-mentioned, the expense of glass material can be reduced and the cost as the whole imaging lens can be reduced.

Further, in the imaging lens having the above-described configuration, the conjugate length TT from the object OBJ to the image plane P, the working distance WD from the object OBJ to the front surface S1 of the first lens 1, and the rear surface S10 to the image plane P of the fifth lens 5. Is preferably the following formula (3):
(3) 2.05 × WD> TT = 160 mm, BF> 30 mm
It is formed so as to satisfy.
As a result, an imaging lens suitable for a recognition camera capable of imaging components with high accuracy in a mounting machine such as an electronic component while achieving downsizing and cost reduction can be obtained.

  Specific examples of the imaging lens having the above configuration will be described below. Here, main specification specifications, various numerical data (setting values), and values of the conditional expressions (1) to (3) in this embodiment are as follows. Further, spherical aberration, astigmatism, distortion, and longitudinal chromatic aberration are as shown in FIG. In the astigmatism shown in FIG. 5, S represents the aberration on the sagittal plane, and M represents the aberration on the meridional plane.

<Specification specifications>
Working wavelength = 440 nm, focal length = 30.13 mm, imaging range = φ3.6 mm, aperture aperture SD aperture = φ5.9 mm, brightness (NA) = 0.09, conjugate length (object to image plane) (TT) = 166 mm, imaging magnification = 2.4, outer diameter of the first lens 1 = 20 mm, outer diameter of the second lens 2 = 16 mm, outer diameter of the third lens 3 = 12 mm, outer diameter of the fourth lens 4 Dimensions = φ7 mm, outer diameter of fifth lens 5 = φ8 mm, working distance (WD) = 82 mm, back focus (BF) = 30.06 mm

<The curvature radius Ri (mm) of the 1st lens 1-the 5th lens 5>
R1 = 2.682 mm, R2 = −78.792 mm, R3 = 20.280 mm, R4 = 78.270 mm, R5 = −30.484 mm, R6 = 30.484 mm, R7 = ∞, R8 = −7.324 mm, R9 = 16.351 mm, R10 = -16.351 mm

<Surface spacing (mm)>
D0 (WD) = 82.0 mm, D1 = 4.0 mm, D2 = 2.5 mm, D3 = 6.0 mm, D4 = 2.4 mm, D5 = 5.0 mm, D6 = 10.0 mm, D7 = 16.8 mm , D8 = 3.0 mm, D9 = 4.0 mm, D10 = 30.4 mm
<Refractive index Ni (d line) of the first lens 1 to the fifth lens 5>
N1 = 1.62041, N2 = 1.62041, N3 = 1.84666, N4 = 1.71736, N5 = 1.84666
<Abbe number νi of the first lens 1 to the fifth lens 5>
ν1 = 60.3, ν2 = 60.3, ν3 = 23.8, ν4 = 29.5, ν5 = 23.8

<Conditions (1) to (3)>
(1) R5 = -30.484 mm R6 = 30.484 mm
(2) R9 = 16.351 mm R10 = −16.351 mm
(3) 2.05 × 82 mm = 168.1 mm> 166 mm = TT BF = 30.06 mm

  In the above embodiment, the brightness (NA) is 0.09, the conjugate length TT is 166 mm, the working distance WD is 82 mm, the back focus BF is 30.06 mm, and the object is ± 0.2 mm back and forth with respect to the reference plane. When deviated, the captured image is 98.8% of the captured image on the reference plane, and the imaging lens suitable for the recognition camera of the mounter in which the image fluctuation is small and various aberrations are corrected well. Obtained.

  As described above, the imaging lens of the present invention can secure the telecentricity on the object side, can sufficiently secure the distance between the object and the lens, that is, the working distance, and can obtain high optical performance with a small size and low cost. Therefore, as long as it is a field that captures and recognizes objects with slight fluctuations, it is not limited to the mounting field and can be used for other recognition or imaging, as well as being applicable to imaging of mounting devices such as electronic components. It is also useful in lens optical systems.

It is a schematic block diagram of the imaging lens which concerns on this invention. FIG. 2 is an optical path diagram of the imaging lens shown in FIG. 1. FIG. 2 is a partial optical path diagram from an object to a first lens in the imaging lens shown in FIG. 1. It is sectional drawing which shows the lens-barrel incorporating the imaging lens shown in FIG. FIG. 2 is an aberration diagram showing spherical aberration, astigmatism, distortion, and longitudinal chromatic aberration in the embodiment of the imaging lens shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st lens 2 2nd lens 3 3rd lens 4 4th lens 5 5th lens L Optical axis TT Conjugation length WD Working distance BF Back focus R5 Curvature radius R6 of object side surface of 3rd lens Image of 3rd lens Radius of curvature R9 of the surface side surface radius of curvature R10 of the object side surface of the fifth lens curvature radius of the surface of the fifth lens image side

Claims (6)

Arranged in order from the object side to the image plane side,
A biconvex first lens having a positive refractive index and having a convex surface facing the object side and the image surface side;
A meniscus second lens having a positive refractive index and a convex surface facing the object side;
A biconcave third lens having a negative refractive index and having a concave surface facing the object side and the image surface side;
An aperture stop having a predetermined aperture;
It has a negative refractive index and is cemented to a biconcave fourth lens having a concave surface directed toward the object side and the image plane side, and a concave surface on the image plane side of the fourth lens, and convex to the object side and the image plane side A cemented lens composed of a biconvex fifth lens facing
An imaging lens comprising: 2. The following equation (1) is satisfied, where R5 is a radius of curvature of the concave surface on the object side of the third lens and R6 is a radius of curvature of the concave surface on the image side of the third lens. The imaging lens described.
(1) | R5 | = R6 The following equation (2) is satisfied, where R9 is a radius of curvature of the convex surface on the object side of the fifth lens and R10 is a radius of curvature of the convex surface on the image surface side of the fifth lens. The imaging lens described.
(2) R9 = | R10 | The first lens and the second lens are formed of the same glass glass material,
The imaging lens according to any one of claims 1 to 3. The third lens and the fifth lens are formed of the same glass glass material,
The imaging lens according to claim 1, wherein: When the conjugate length from the object to the image plane is TT, the working distance from the object to the front surface of the first lens is WD, and the back focus from the rear surface of the fifth lens to the image plane is BF, the following equation (3) The imaging lens according to claim 1, wherein the imaging lens is satisfied.
(3) 2.05 × WD> TT = 160 mm, BF> 30 mm

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