US20050054265A1

US20050054265A1 - Method and apparatus for manufacturing trace performing parts with aspherical surfaces

Info

Publication number: US20050054265A1
Application number: US10/657,798
Authority: US
Inventors: Cheng hao Piao; Li Cai
Original assignee: Nifco Inc
Current assignee: Nifco Inc; Hool International LLC
Priority date: 2003-09-08
Filing date: 2003-09-08
Publication date: 2005-03-10

Abstract

A method and apparatus for aspherical manufacturing are disclosed using trace performing. On a cone, a section whose trace corresponds to that of a required curve is defined by mathematical calculation, i.e. the parameters of the section is defined. The cone is installed to a position that provides with a trace intersection, the trace intersection couples with a grinding wheel, the cone links with the part, the part is rotated and swung about a swing axis with the cone, the trace intersection fixedly connects to the grinding wheel. Whereby the curve trace intersected on the cone is accurately transferred to the part during the performing. The present invention can be used in performing parts with convex/concave conic and high-order aspherical surfaces and has advantage in general utility, precision, efficiency and costs.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method and apparatus for the machining of aspherical optical parts.
2. Description of the Related Art
The aspherical parts in optical systems have not been widely used because of the difficulty of machining and inspecting such parts, although the advantages of using them, rather than spherical parts, are considerable. And these advantages have led to extensive research on discovering a machining and inspection process, to speed up the development and application of aspherical surface technology.
The methods that have been excogitated out to machine aspherical parts so far are more than twenty kinds, which can be classified into four groups: according to the machining principle they employed, excision machining, appending machining, transmogrification machining and metamorphosing machining. Although there are so many different machining methods, except the conventional manual machining, or numerical control machining, most of them are aiming at an aspherical surface with a particular shape and dimension. None of these methods can achieve a high efficiency, machining precision and universality within the same process.
At present, excision machining is the method most commonly used to machine small-batch aspherical optics parts both in home and abroad. The process includes conventional manual milling and polishing or numerical control turning, or numerical control milling and polishing, or numerical control grinding. Although the conventional manual milling and polishing method can attain a high precision aspherical part, the operator must be rich experienced and highly skilled, in addition to poor quality in its repeat performance, long machining period, and its high cost, this method cannot meet the requirements of batch production. For a long time, in order to solve the problems of long production period and high cost, people have been exploring in field of locus shaping by mechanism or mould copying. Although such a machining method would be efficient and ensure attainment of a good surface quality, it is still difficult to obtained high precision aspherical parts because the figure shaped by the locus shaping method has a significant profile error. Furthermore, it cannot meet the need for the varying shapes and dimensions of aspherical optics parts machined because of the immobility of the locus shaped by mechanism or mould copying. Therefore, it can only be used in batch production of a certain fixed shape and dimension of aspherical optics part requiring low or medium-range precision.
With the development of numerical control technology, people abandon the method of locus shaping by mechanism or mold copying, and turn to method of numerical control technology to solve the problems in machining of aspherical parts. The essence of method of numerical control technology is to gradually approach the surface or figure of design by using numerical control milling and polishing method. Alternatively, the aspherical surface can be attained by numerical control turning or grinding to move the lathe tool or grinding-wheel according to the track orders programmed. Numerical control machining is a kind of flexible machining technique, so it can meet the needs of varying shapes and dimensions of aspherical optical parts machining. But high precision aspherical surfaces can be attained only after inspection and measurement has been completed and finishing and milling have been frequently repeated. Furthermore, the machining equipment is expensive, and because it belongs to an area of expert operational technology, the operational techniques are complicated. And even though it can be used to machine high precision aspherical surfaces, it cannot meet the need of batch production because of the long machine period and its high cost. At present, there is no a single type of high efficient machining technology that can be used in both machining individual aspherical optics parts and batch production of aspherical optics parts.
The history of methods of machining aspherical optics parts has been the development from conventional manual machining to locus shaping by mechanism or mould and die copying, then to numerical control machining. From this development renovation, we can see that the key question is how to get a method of obtaining an accurate locus of aspherical surface shaping and machining high precision aspherical parts accurately and efficiently.
There are many types of aspherical surfaces which can be used in a optical system. Most of them are axis symmetrical aspherical surfaces and their machining is very difficult. Most of the axis symmetrical aspherical surfaces are composed of curves such as ellipses, parabolas and hyperbolas, in addition, there are also some high order aspherical surfaces.

SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus for the machining of aspherical optics parts with locus shaping, to resolve the problems identified above, of meeting the need of varying shape and dimension aspherical optics parts production both individually and by batch production, in a high efficient and low cost way.
The invented method of machining includes a process of coarse grinding, finishing grinding and super-finishing grinding (or polishing) of convex or concave surfaces of conic and high-order aspherical type. Characterized in that, the specific steps for machining conical aspherical optics parts comprising:
In a first step, according to the conic equation given by the designer, the section parameters of α, φ and L on a cone that decide the accurate locus needed are deduced by mathematical calculation, Or the appropriate curve locus is decided by trial-machining;
In a second step, the locus is intercepted on a cone by a transversal intercept object, and the cone is fixed on apparatus for machining aspherical optics parts with locus shaping, so that the transversal intercept object is mounted, then the relative position between them is established in terms of the parameters deduced above;
In a third step, the part is swinging around a swing-axle with the cone while it is rotating, then the accurate locus curve intercepted on the cone is accurately transferred to the part during the machining and an aspherical surface is shaped, that is, the locus intercepted can be transferred accurately to the part during machining and conical aspherical optics parts are obtained; and convex or concave high-order aspherical optics part can be obtained as follows: an accurate plane outline template, with a high-order curve profile made by other methods, is used to replace the cone fixed on the apparatus, and that is, the high-order curve profile on the plane outline template can be transferred accurately to the part during machining, and high-order aspherical optics part will be obtained.
This invention, additionally, specifies the apparatus to be used for the machining method outlined above. The apparatus comprising: swing-table, thrust-block, thrust-parts, part-axis-drive-electromotor, cone-move-screw, guidance-seating, part-fixing-shaft, backstop-seating, grinding-wheel, buttress-rack, locus-intercept-object, cone, lathe-bed, swing-axle, swing-axle-electromotor and part-axle-box,

the grinding-wheel sits on the buttress-rack;
the forward-and-backward and up-and-down mobile locus-intercept-object is fixed on the buttress-rack;
the buttress-rack is fixed on the lathe-bed;
the cone, whose angle can be adjusted, sits on the backstop-seating;
the backstop-seating is fixed on the guidance-seating;
the guidance-seating can be slid along the guidance-orbit located in the bottom of the part-axle-box;
the swing-axle-electromotor drives the swing-table to swing around the swing-axle, the part is clamped on the forepart of the part-fixing-shaft, it swings around the swing-axle with half stretched angle of the part while it is rotating,
the thrust-block is fixed on the swing-table;
the thrust-parts are fixed between the thrust-block and the part-axle-box, so as to keep the cone in constant contact with the locus-intercept-object,
The axes of the part-fixing-shaft, cone, and swing-axle are required to be co-planar in the vertical plane. The axes of the part-fixing-shaft and grinding-wheel are required to be co-planar in horizontal plane.

This process can be used to machine aspherical optics parts or mechanical parts of glass, porcelain, crystal or metal.
This invention is the apparatus and method for machining aspherical optics parts, wherein using innovative principle of intercepting accurate locus defined by the designer's conic equation and innovative technology of accurately transferring the locus intercepted to the part during the machining and thus obtaining the aspherical optics part.
The benefits of this invention are as follows:
1. Universality: all the conic curves of different parameters we needed, such as circle, ellipse, parabola or hyperbola can be intercepted from the cone 13 and the intercepted curves are proper.
2. High precision: the accurate values of section parameters α, φ and L can be calculated by formula deduced according to the conic equation y²−ƒ(x) given by the designer. Thus, an accurate locus of the conic equation as given can be ascertained easily and precisely.
3. Simplicity and reliability of the locus transfer mechanism: By fine-tuning to adjust the value of φ and L, the surface profile error can be eliminated. As a result, the locus of the curve intercepted can be accurately transferred to part 9 and a high precision aspherical surface can be obtained.
4. High efficiency and low cost: Because the locus can be easily and accurately intercepted and it can be transferred accurately at the same time. Furthermore, the working procedures of coarse grind, finishing grind and super-finishing grind (or polishing) can be carried out within one load and clip.
5. Simple operation: It is not necessary to employ an expert to operate the apparatus, and there are few technical requirements for an operator, so it is easy to spread widely.
In conclusion, applying the technology of this invention to the machining of aspherical optics parts can resolve the difficult problems of machining mentioned hitherto. Its efficiency and costs will be close to that of current methods of machining spherical optics parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the intercept locus on a cone.
FIG. 2 illustrates the apparatus to machine a convex aspherical optics part.
FIG. 3 illustrates the apparatus to machine a concave aspherical optics part.
FIG. 4 illustrates the apparatus to machine a concave aspherical optics part using a cylindrical grinding-wheel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is illustration of intercepting locus on a cone, where the half-apex-angle of the cone is α, point A is the vertex of the cone, point D lies on a generatrix of the cone, while the distance between point A and point D is L. If the cone is intercepted by a plane denoted as a-a, and the angle between the plane and the axes of the cone is φ 1=90, a locus defined by circularity curve equation is obtained as a result. If intercepted by a plane denoted as b-b, and the angle is 90>φ2>α, a locus defined by elliptical curve equation is obtained as a result. If intercepted by a plane denoted as c-c, and the angle is φ3=α, a locus defined by parabola curve equation is obtained as a result. If intercepted by a plane denoted as d-d, and the angle is α>φ3>−α, a locus defined by elliptical curve equation is obtained as a result. In any case, as long as the relative section parameters of α, φ and L on a cone are deduced according to any locus defined by the designer's conic equation, the locus can be intercepted from the cone. By mathematical calculation, the values of α, φ and L can be fixed accurately, or the appropriate curve locus is decided by the method of trial-machining. In fact, the half-apex-angle of the cone α is invariant and decided when it is machined. So that, only φ and L are needed to calculated in order to intercepting a designed curve.
The detailed method and technology for intercepting accurate locus and accurately transferring locus to the part have been shown in FIGS. 2, 3 and 4. The position of cone 13 and locus-intercept-object 12 are accurately decided by the accurate values of α, φ and L deduced. And making the distance between the aspherical part 9 and the center of a circle minimum, and it is aligned with the axis of swing-axle 15, and the contact point D of locus-intercept-object 12 and cone 13 is aligned with the grinding face of the grinding-wheel to the same vertical line. And under a little thrust force, the cone 13 and locus-intercept-object 12 are contacting all the time. And then, swing-axle-electromotor 16 is started to drive the swing-table 1 to swing, in this way, the accurate locus can be lined out on the cone which is given by the designer's conic equation. On this base, starting the grinding-wheel 10 and part 9 turning, and let the part move a little to the grinding-wheel simultaneously. Then, the grinding-wheel grinds out the allowance of the part accurately according to the intercepted locus, after grinding many times, all allowance are grinded out, and then the intercepted locus will be accurately transferred to part 9. The high precision conic aspherical surface is obtained, which is identical with the locus given by the designer's conic equation.
FIG. 2 illustrates an apparatus to machine a convex aspherical optical part. It is made up of swing-table (1), thrust-block (2), thrust-parts (3), part-axis-drive-electromotor (4), cone-move-screw (5), guidance-seating (6), part-fixing-shaft (7), backstop-seating (8), grinding-wheel (10), buttress-rack (11), locus-intercept-object (12), cone (13), lathe-bed (14), swing-axle (15), swing-axle-electromotor (16) and part-axle-box (17). Part 9 is rotating around the part-fixing-shaft (7). While together with the cone (13), it swings around swing-axle (15) along with the swing-table (1) in the range of the half-vertex-angle of the part. Cone (13) is in tight contact with locus-intercept-object (12) under the action of spring thrust-parts (3), a part-axle-box (17) is set on this apparatus, it can slide lengthways along the swing-table (1). Between the thrust-block (2) fixed on swing-table (1), and part-axle-box (17), thrust-parts (3) is set. The thrust-parts (3) shown in FIG. 2 is a spring, which can be replaced by a heavy hammer. Locus-intercept-object (12) can be set on buttress-rack (11) or lathe-bed (14), which can be moved forward and backward, up and down. The end of locus-intercept-object (12) is aligned with the outer circle grinding face of grinding-wheel (10) in the vertical plane, to ensure that the locus will be intercepted and transferred to part (9) accurately. The grinding-wheel (10) is also set on buttress-rack 11, it is fixed with locus-intercept-object 12 as a whole, cone (13) is set on backstop-seating (8), the angle φ between axes of cone (13) and swing-axle (15) can be adjusted to attain a calculated one. Backstop-seating (8) is fixed on guidance-seating (6) which is fixed on the guidance in the bottom of part-axle-box (17). By means of rotating cone-move-screw (5), guidance-seating (6) can slide along the guide pulley, which moves cone (13) to and fro. When cone (13) moves backward, part-axle-box (17) moves forward. Then part (9) comes into contact with grinding-wheel (10), consequently the allowances of the part is removed, simultaneously the curve locus is transferred accurately to part (9) and a convex aspherical surface comes into being, which is intercepted from cone (13) with locus-intercept-object (12).
FIG. 3 and FIG. 4 illustrate the machining of a concave aspherical surface. The radius of grinding-wheel (10) is less than the radius of part (9). For a concave aspherical surface with a large radius curvature, a grinding-wheel with disc shape must be used as shown in FIG. 3. For a concave aspherical surface with a small radius curvature, a grinding-wheel with cylindrical shape must be used as shown in FIG. 4.
If a high order aspherical optics part is to be machined, the cone should be replaced by a concave or convex high order aspherical plane template.
FIG. 2 illustrates the machining of a convex aspheric surface, wherein the contact point D of cone (13) and locus-intercept-object (12) are on the right of the axes of swing-axle (15). FIG. 3 and FIG. 4 illustrate the machining of a concave aspherical surface, wherein the point D is on the left of axis of swing-axle (15), and it is possible to work only when the radius of grinding-wheel is less than the curvature radius of the part.
In this invention, the purpose can also be achieved if some changes are made in the apparatus as follows: grinding-wheel, set on swing-table 1, is swinging while it is rotating, part (9) is only rotating which is set on buttress-rack (11), the position of cone (13) and locus-intercept-object (12) are exchanged with each other.
The above preferred embodiment is merely exemplary and is not to be construed as limiting the present invention. The equivalent modifications or decorations of this invention in the scope of the claims are all protected.

Claims

1. A method for machining aspheric with locus shaping, comprising the machining of coarse grind, fine grind, and super-finishing grind (or polishing) to a convex or concave surfaces of quadratic and high-order aspheric; and characterized in that, the specific steps for machining conical aspherical optics parts comprising:

in a first step, according to the conic equation given by the design, deduce the section parameters of α, φ and L (see FIG. 1) on a cone to decide the accurate locus, or the appropriate curve locus is decided by trial-machining;

in a second step, the locus is intercepted on a cone by a transversal intercept object, and the cone is fixed on apparatus for machining aspherical optics parts with locus shaping, so that the transversal intercept object is mounted, then the relative position between them is established in terms of the parameters deduced above;

in a third step, the part is swinging around a swing-axle with the cone while it is rotating, then the accurate locus curve intercepted on the cone is accurately transferred to the part during the machining and an aspherical surface is shaped, that is, the locus intercepted can be transferred accurately to the part during machining and conical aspherical optics parts are obtained; and convex or concave high-order aspherical optics part can be obtained as follows: an accurate plane outline template, with a high-order curve profile made by other methods, is used to replace the cone fixed on the apparatus, and that is, the high-order curve profile on the plane outline template can be transferred accurately to the part during machining, and high-order aspherical optics part will be obtained.

2. The method of claim 1, characterized in that, a convex aspherical optics part is obtained when the contact points of the cone and locus-intercept-object axes are on the right of the swing-axle.

3. The method of claim 1, characterized in that, a concave aspherical optics part is obtained when the contact points of the cone and locus-intercept-object axes are all on the left of the swing-axle, and the radius of the grinding-wheel must be less than the curvature radius of the part.

4. The method of claim 1, characterized in that, when the position of the cone and the locus-intercept-object is decided, in order to remove the redundant area, the part is allowed to move towards the grinding-wheel. The contact point of the locus-intercept-object and cone mentioned here is aligned with the working face of the grinding-wheel to the same vertical line.

The method of claim 1, characterized in that, it can machine aspherical optics parts or mechanical parts of glass, porcelain, crystal or metal materials.

6. The apparatus of claim 1, characterized in that, comprising (see FIG. 2): a swing-table (1), thrust-block (2), thrust-parts (3), guidance-seating (6), part-fixing-shaft (7), backstop-seating (8), grinding-wheel (10), buttress-rack (11), locus-intercept-object (12), cone (13), lathe-bed (14), swing-axle (15), swing-axle-electromotor (16) and part-axle-box (17), and The grinding-wheel (10) sits on the buttress-rack (11), the locus-intercept-object (12), which can be moved forward and backward, up and down, sits on the buttress-rack (11), The cone (13), the angle of which can be adjusted, sits on the backstop-seating (8), The backstop-seating (8) sits on the guidance-seating (6), which can be slid along the guidance lay in the bottom of the part-axle-box (17), the part-axle-box (17) can be slid lengthways on the swing-table (1), the swing-axle-electromotor (16) drives the swing-table (1) to swing around the swing-axle (15), part (9) sits on the front part of the part-fixing-shaft (7), together with the cone (13), it swings around the swing-axle (15) along with the swing-table (1) in the range protracted by the half-apex-angle of the part, the thrust-block (2) is fixed onto the swing-table (1), the thrust-parts (3) are set between the thrust-block (2) and the part-axle-box (17) to keep the cone (13) and the locus-intercept-object (12) in constant contact.

7. The apparatus of claim 6, characterized in that, the grinding-wheel (10) can be a disk shape one or a cylinder shape one, and when convex aspherical parts are machined, the disk grinding-wheel can be made up of one, two or three disks.

8. The apparatus of claim 6, characterized in that, the axes of the part-fixing-shaft (7), the cone (13), and the swing-axle (15) are required to be co-planar in the vertical plane. The axes of the part-fixing-shaft (7) and the grinding-wheel (10) are required to be co-planar in horizontal plane.

9. The apparatus in claim 6, characterized in that, if the grinding-wheel (10), on the swing-table (1), swings while it is rotating, And part (9) only rotates when it is set on the buttress-rack (11), and the positions of the cone (13) and the locus-intercept-object (12) are exchanged, then the machining purpose of this invention can also be achieved.

10. The apparatus in claim 6, characterized in that, if a convex or concave plane outline template with high-order curve profile is substituted for the cone (13), then a convex or concave high-order aspherical part can be machined.