JP2006181662A - Device and method for measuring and polishing large-sized optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for measuring and polishing a large-sized optical element, measuring and polishing a large-sized segment lens or mirror with a diameter of 1 to 3m with high accuracy, and comparatively lowering the manufacturing cost. <P>SOLUTION: This measuring and polishing device includes: an element positioning device 10 holding a large-sized optical element 1 substantially horizontally with a surface 2 to be polished up; a non-contact measuring device 20 for measuring an error from the target value of the surface to be polished in non-contact state; a self-running polishing device 30 moved along the surface to be polished to partially polish the surface to be polished; and a polishing control device 40 for giving a command for a polishing position to the self-running polishing device according to the measurement result of the non-contact measuring device, wherein the surface to be polished is polished while being measured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a measurement polishing apparatus and method for measuring and polishing a large optical element with high accuracy.

  By observing light falling from outside the earth (especially infrared light), measuring the intensity, wavelength, energy, etc. of the light, analyzing the origin of light and the universe, analyzing the celestial body that emits the light, identifying the distance, Information on Earth planetary exploration by imaging, identification of reactions such as biomaterial synthesis in outer space, etc. can be obtained.

  For this purpose, the "Subaru Telescope" has already been manufactured and installed in Hawaii, USA. The “Subaru Telescope” is a reflective telescope having a large primary mirror (mirror) having a diameter of about 8.2 m. This primary mirror is obtained by welding and integrating a plurality of glass mirrors and finishing them with a large polishing apparatus. However, such a manufacturing means has a problem that it requires a large processing chamber (for example, deep underground) with little temperature change and requires a long time for processing.

Patent Documents 1 to 3 have been proposed as processing means for large optical elements (for example, reflection mirrors).
Further, hologram interference has been conventionally known as means for performing aspheric measurement in a non-contact manner (for example, Non-Patent Documents 2 and 3).

  In recent years, large-diameter telescopes having a diameter exceeding 30 m have been planned in various countries. For example, two projects with a diameter of 50 m and 100 m are progressing in Europe, and a project with a diameter of 30 m is progressing in the United States (Non-patent Document 1). In Japan, a large-aperture telescope project with a diameter of about 30 m is also being studied.

Paul Shore, "Production Challenge of the Optical Segments for Extra Large Telescopes", International Progress on Advanced Optics and Sensors. 25-30 2003. Koji Tenjinbayashi, “Hologram Interferometer”, Optical Technology Contact, Vo. 25. No. 10 (1987). Toyohiko Yadagai, “Aspherical measurement using computer generated hologram”

JP 2001-353648 A, "ELID Mirror Grinding Apparatus and Method for Large Diameter Workpiece" Japanese Patent Application Laid-Open No. 2002-11656, “Machining and Measuring Apparatus and Method for Large Ultraprecision Aspherical Surface” International Publication WO 03/047833 A1, “Manufacturing method and apparatus for large curved double-sided Fresnel lens”

  An optical element (for example, a primary mirror (mirror)) used in the above-described large-aperture telescope having a diameter exceeding 30 m is considered to be configured by combining many segment lenses having a diameter of, for example, 1 to 3 m. In order to reduce the influence of thermal expansion, each segment lens uses a special glass having a very low thermal expansion coefficient (for example, “Zerodure” (registered trademark) of Schott, Germany), and is arranged independently while being separated from each other. .

However, even in the case of such a configuration, when the shape of the segment lens is a hexagon having a major diameter of 1 m, about 30 × 30 = 900 or more segment lenses are required in the case of the aperture of 30 m.
In the case of the "Subaru Telescope", it takes several months to make a primary mirror with a diameter of about 8.2m. In addition, even if a hexagonal segment lens having a major diameter of 1 m is manufactured by means of Patent Documents 1 to 3, at least one week is required from grinding until polishing and measurement are completed. More than 900 segment lenses It takes 900 weeks = 17 years or more to produce.
In addition, a large grinding apparatus capable of processing a hexagonal segment lens having a major diameter of 1 m requires a manufacturing cost of several hundred million yen. For example, when it is attempted to reduce the number of production years to about two years, a dozen large grinding apparatuses are manufactured. Therefore, since the cost of several billion yen is required, the feasibility is low.
Therefore, with one or several large grinding machines, segment lens grinding (for example, ELID grinding) is carried out with high efficiency, and polishing and measurement are performed simultaneously using a large number of inexpensive large grinding measuring machines. It is being considered.

  The present invention has been developed to meet such a demand. That is, an object of the present invention is to measure and polish a large segment lens or mirror having a diameter of, for example, 1 to 3 m with high accuracy, and to measure and polish a large optical element with a relatively low manufacturing cost. Is to provide.

According to the present invention, an element positioning device that holds a large optical element almost horizontally with a surface to be polished facing upward,
A non-contact measuring device for measuring an error from the target value of the polished surface in a non-contact manner;
A self-propelled polishing apparatus that moves along the surface to be polished and partially polishes the surface to be polished;
Provided with a measuring and polishing apparatus for large optical elements, comprising a polishing control device for instructing a polishing position to a self-propelled polishing device based on a measurement result of a non-contact measuring device, and polishing while measuring a surface to be polished Is done.

  According to a preferred embodiment of the present invention, the non-contact measuring device is an interference measuring device that measures the surface to be polished using laser light from above the surface to be polished, the lower end of which is fixed to the element positioning device.

  Further, the self-propelled polishing apparatus includes a polishing tool for partially polishing a surface to be polished, a tool lifting / lowering device for lifting / lowering the polishing tool, and a surface to be polished for moving the tool lifting / lowering device to a desired position. It consists of a possible self-propelled carriage and a receiving and transmitting device that receives and transmits the polishing position by the polishing tool in a non-contact manner.

  The polishing tool includes a rigid member having high rigidity attached to a tool lifting / lowering device so as to be movable up and down, a flexible thin polishing member having a lower surface capable of following the surface to be polished, a rigid member, and thin polishing. It is preferable that it consists of an elastic container sandwiched between members and containing a viscoelastic medium inside.

  Moreover, it is preferable that the said polishing tool consists of a magnetic field generating member attached to the tool lifting / lowering device and a magnetic abrasive agent interposed between the magnetic field generating member and the surface to be polished.

Further, according to the present invention, an element positioning step for holding the large optical element almost horizontally with the surface to be polished facing upward,
A non-contact measurement step of measuring an error from the target value of the polished surface in a non-contact manner;
A partial polishing step of partially polishing the surface to be polished;
And a polishing control step for determining the polishing position of the partial polishing step based on the measurement result of the non-contact measurement step, and a polishing method for measuring a polished surface is provided. The

According to the apparatus and method of the present invention, since the element positioning device and the non-contact measuring device (for example, the interference measuring device) are provided, the polished surface of the large optical element faces upward in the element positioning step and the non-contact measuring step. An error from the target value of the surface to be polished can be measured in a non-contact manner while being held almost horizontally, and even a segment lens or mirror having a large diameter can be measured with high accuracy in a short time.
In addition, since the self-propelled polishing apparatus and the polishing control apparatus are provided, the polishing position is determined based on the measurement result of the non-contact measuring apparatus in the partial polishing step and the polishing control step, and the polishing position is commanded to the self-propelled polishing apparatus. The running polishing apparatus can be moved along the surface to be polished to partially polish the surface to be polished, and the surface to be polished can be polished with high accuracy. In addition, when measurement accuracy falls with an abrasive | polishing agent, you may perform a measurement and grinding | polishing alternately.
Furthermore, even if these devices are large optical elements having a diameter of, for example, 1 to 3 m, they do not require numerical guides or sensors for large-scale and high accuracy, so that the manufacturing cost can be kept relatively low. Can do.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected and used for the common part in each figure.
In the following example, the large-sized optical element 1 is a segment mirror that constitutes a reflecting mirror whose aperture exceeds 30 m, for example. Each segment mirror is a hexagonal mirror having a diameter of, for example, 1 to 3 m, and the reflecting surface thereof is ground by a large grinding device using ELID grinding or the like in advance on different aspheric surfaces so as to constitute a reflecting mirror as a whole. Is done.
The aspherical shape required for each segment mirror varies depending on the distance from the center of the reflecting mirror, and when the reflecting mirror having a diameter of 30 m is constituted by a hexagonal mirror having a diameter of 1 m, there are about 30 types.
With advanced grinding technology that combines ELID method with ultra-precision / nano-precision / large-scale grinding equipment and on-machine measurement method, large optical elements over 30cm can be processed efficiently with nano-level roughness and sub-micron shape accuracy. Necessary types and number of segment mirrors can be ground in a short time.
As the pre-processing of the present invention, ultra-precision grinding by ELID grinding is powerful and effective, but with the improvement of roughness and shape accuracy, the processing damage by grinding does not become zero, so that damage is reduced to the limit Since there is a need, the polishing process according to the present invention is extremely important. In particular, in a state where grinding damage remains, there is a concern that grinding damage may gradually develop (due to secular change due to vibration, temperature change, etc.) in the use environment such as an astronomical telescope, and the present invention becomes important.
The reflection surface 2 of the large optical element 1 (segment mirror) that has been previously ground into an aspheric shape in this way is hereinafter referred to as a “surface to be polished”.

  FIG. 1 is an overall configuration diagram of a large optical element measuring and polishing apparatus according to the present invention. In this figure, the large optical element measuring and polishing apparatus of the present invention includes an element positioning apparatus 10, a non-contact measuring apparatus 20, a self-propelled polishing apparatus 30, and a polishing control apparatus 40.

The element positioning device 10 holds the large optical element 1 substantially horizontally with the above-described polished surface 2 facing upward. Further, in the grinding process (e.g., ELID grinding) as a pre-process, the work surface 2 can be ground while being mounted on a grinding apparatus as it is, and operations such as rotation, indexing, and swinging can be added. After work, it can be removed from the grinding machine and used independently.
The non-contact measuring device 20 is an interference measuring device that has a lower end fixed to the element positioning device 10 and measures the surface 2 to be polished from above the surface 2 to be polished using the laser beam 3. The error from is measured without contact.
The self-propelled polishing apparatus 30 moves along the surface 2 to be polished and partially polishes the surface 2 to be polished.
The polishing control device 40 commands the polishing position to the self-propelled polishing device 30 based on the measurement result of the non-contact measuring device 20.

FIG. 2 is an overall configuration diagram of a non-contact measuring apparatus according to the present invention. As shown in this figure, the non-contact measurement device 20 is an interference measurement device, and includes a laser device 21, an irradiation optical system 22, a reference element 23, a reflection optical system 24, an interference fringe observation device 25, and the like.
The laser device 21 oscillates the laser beam 3, the irradiation optical system 22 irradiates the laser beam 3 toward the surface to be polished 2, and the reflected light 4 is imaged on the interference fringe observation device 25 by the reflection optical system 24. The reference element 23 is a lens having a reference surface or a computer generated hologram, and the interference fringe 5 corresponding to an error from the target value of the polished surface 2 is observed by the interference fringe observation device 25.

In this example, the reference element 23 is a lens having a reference surface, and the position can be finely adjusted by a piezo device (not shown).
The interference fringe observation device 25 includes a CCD and a monitor, and inputs the observation image to the polishing control device 40.

  The polishing control device 40 is an arithmetic device (for example, a computer) that stores an image processing program, processes an input observation image, calculates an error from the target value of the surface 2 to be polished, and selects a position where the error is large. The self-propelled polishing apparatus 30 is commanded as a polishing position.

FIG. 3 is an overall configuration diagram of a self-propelled polishing apparatus according to the present invention. In this figure, the self-propelled polishing apparatus 30 includes a polishing tool 32, a tool lifting / lowering apparatus 34, a self-propelled carriage 36 and a receiving / transmitting apparatus 38.
The polishing tool 32 has a function of rotating the tool center 33 around the axis by a tool motor 33 to partially polish the surface 2 to be polished.
The tool lifting / lowering device 34 is an actuator (for example, a pneumatic cylinder) attached to the self-propelled carriage 36 so that the center of rotation of the polishing tool is in contact with the surface 2 to be polished at a predetermined angle. Has the function of
The self-propelled carriage 36 includes, for example, a pair of crawler devices 36a and a control device (not shown), travels and moves on the surface 2 to be polished, and moves the tool lifting device 32 to a desired position.

The receiving / transmitting device 38 is, for example, a wireless transmitter installed in the vicinity of the polishing position of the polishing tool, and detects the polishing position by the polishing tool in a non-contact manner.
The self-propelled polishing apparatus 30 has a plurality of sensors (not shown) for obtaining signals (for example, radio waves used in a wireless LAN or the like, infrared rays or ultrasonic waves) detected by the transmission / reception apparatus 38, and from the detected signals. The polishing position by the polishing tool is detected in a non-contact manner, and the self-propelled polishing apparatus 30 is controlled based on the data while collating with a command value from the polishing control apparatus.

Using the apparatus described above, the method of the present invention comprises an element positioning step, a non-contact measurement step, a partial polishing step, and a polishing control step. Each step is preferably performed in this order, but the order may be changed or repeated as necessary.
In the element positioning step, the large optical element is held almost horizontally with the surface to be polished facing upward.
In the non-contact measurement step, an error from the target value of the surface to be polished is measured in a non-contact manner.
In the partial polishing step, the surface to be polished is partially polished.
In the polishing control step, the polishing position of the partial polishing step is determined based on the measurement result of the non-contact measurement step.

FIG. 4 is a first embodiment of a polishing tool according to the present invention. In this example, the polishing tool 32 is an elastic polishing tool, and includes a rigid member 52, a thin polishing member 54, and an elastic container 56.
The rigid member 52 is, for example, a metal plate having high rigidity, and is attached to a lifting member (for example, a lower end of a cylinder rod) of a tool lifting device 34 (for example, a pneumatic cylinder) via a spherical joint 51 and can be lifted and lowered. It is configured to be possible.
The thin polishing member 54 is a flexible polisher having a lower surface that can follow the surface 2 to be polished.
The elastic container 56 is sandwiched between the rigid member 52 and the thin polishing member 54 and contains a viscoelastic medium 57 (for example, fluid) therein.
With this configuration, by lowering the polishing tool 32 toward the surface 2 to be polished, an isotropic pressure is applied to the thin polishing member 54 (polisher) via the isotropic viscoelastic medium 57, and the lower surface of the polisher. Can follow the surface 2 to be polished, and the surface 2 to be polished can be polished with a constant pressure while being accompanied by abrasive grains.

FIG. 5 is a diagram showing a second embodiment of the polishing tool according to the present invention. In this example, the polishing tool 32 is a magnetic fluid tool, and includes a magnetic field generating member 62 and a magnetic abrasive 64.
The magnetic field generating member 62 is attached to an elevating member (for example, the lower end of the cylinder rod) of the tool elevating device 34 (for example, a pneumatic cylinder), and generates a magnetic field that attracts the magnetic material to the lower surface.
The magnetic abrasive 64 is made of magnetic powder (for example, iron powder, cobalt powder), abrasive grains (for example, diamond abrasive grains), and a polymer or oil that imparts an appropriate viscosity.
With this configuration, the magnetic abrasive 64 can be adsorbed to the lower surface of the magnetic field generating member 62 and the surface to be polished 2 can be polished with the abrasive grains contained therein.
In the present invention, when any polishing tool is used, it is desirable to use a small-diameter abrasive grain (for example, submicron) as compared with the abrasive grain size used in the grinding process as the pre-processing. As the abrasive grains, for example, diamond, cerium oxide, silica, CG, alumina and the like are desirable.

According to the apparatus and method of the present invention described above, since the element positioning device 10 and the non-contact measuring device 20 (for example, an interference measuring device) are provided, the surface to be polished of the large optical element 1 in the element positioning step and the non-contact measuring step. 2 can be held almost horizontally and the error from the target value of the polished surface 2 can be measured in a non-contact manner. For example, even a large segment lens or mirror having a diameter of 1 to 3 m can be measured in a short time. Can be measured with high accuracy.
Further, since the self-propelled polishing device 30 and the polishing control device 40 are provided, the polishing position is determined based on the measurement result of the non-contact measuring device 20 in the partial polishing step and the polishing control step, and the polishing position is set in the self-propelled polishing device 30. The self-propelled polishing apparatus 30 can be moved along the surface to be polished to partially polish the surface to be polished, and polishing can be performed with high accuracy while measuring the surface to be polished. In addition, when measurement accuracy falls with an abrasive | polishing agent, you may perform a measurement and grinding | polishing alternately.
Furthermore, even if these devices are large optical elements having a diameter of 1 to 3 m, for example, they do not require large-sized and highly accurate guides and sensors for numerical control, so that manufacturing costs can be kept relatively low. Can do.
According to the present invention, the average roughness (for example, Ra and rms) of the surface of the large optical element is aimed at 1 nano to sub-nano level, and the shape of the entire segment is aimed at an accuracy around 100 to 300 nm.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously, unless it deviates from the summary of this invention.

1 is an overall configuration diagram of a large optical element measuring and polishing apparatus according to the present invention. 1 is an overall configuration diagram of a non-contact measuring apparatus according to the present invention. 1 is an overall configuration diagram of a self-propelled polishing apparatus according to the present invention. It is 1st Embodiment figure of the grinding | polishing tool by this invention. It is 2nd Embodiment figure of the grinding | polishing tool by this invention.

Explanation of symbols

1 Large optical element (segment mirror), 2 surface to be polished (reflection surface),
3 Laser light, 4 Reflected light, 5 Observation image (interference fringe),
10 element positioning device, 20 non-contact measuring device,
21 laser device, 22 irradiation optical system, 23 reference element,
24 reflection optical system, 25 interference fringe observation device,
30 self-propelled polishing equipment, 32 polishing tools,
33 Tool motor, 34 Tool lifting device,
36 self-propelled carriage, 36a crawler device, 38 receiving and transmitting device,
40 Polishing control device (computer),
51 spherical joint, 52 rigid member, 54 thin abrasive member,
56 elastic container, 57 viscoelastic medium,
62 Magnetic field generating member, 64 Magnetic abrasive

Claims (6)

An element positioning device for holding the large optical element almost horizontally with the surface to be polished facing upward;
A non-contact measuring device for measuring an error from the target value of the polished surface in a non-contact manner;
A self-propelled polishing apparatus that moves along the surface to be polished and partially polishes the surface to be polished;
A measuring and polishing apparatus for a large optical element, comprising: a polishing control apparatus that commands a polishing position to a self-propelled polishing apparatus based on a measurement result of a non-contact measuring apparatus, and polishing while measuring a surface to be polished.   2. The non-contact measurement apparatus according to claim 1, wherein the non-contact measurement apparatus is an interference measurement apparatus in which a lower end is fixed to the element positioning device and the surface to be polished is measured using laser light from above the surface to be polished. Measuring and polishing equipment for large optical elements.   The self-propelled polishing apparatus is capable of moving on a polishing tool that partially polishes a surface to be polished, a tool lifting device that lifts and lowers the polishing tool, and a surface to be polished that moves the tool lifting device to a desired position. The measuring and polishing apparatus for a large optical element according to claim 1, comprising a self-propelled carriage and a receiving and transmitting apparatus that receives and transmits a polishing position by a polishing tool in a non-contact manner.   The polishing tool includes a rigid member having high rigidity attached to a tool lifting / lowering device so as to be movable up and down, a flexible thin member having a lower surface capable of following the surface to be polished, and a rigid member and a thin member. 4. The measuring and polishing apparatus for a large optical element according to claim 3, comprising an elastic container sandwiched between members and containing a viscoelastic medium therein.   4. The large-sized optical device according to claim 3, wherein the polishing tool includes a magnetic field generating member attached to a tool lifting device and a magnetic abrasive interposed between the magnetic field generating member and a surface to be polished. Element measuring and polishing equipment. An element positioning step for holding the large optical element almost horizontally with the surface to be polished facing upward;
A non-contact measurement step of measuring an error from the target value of the polished surface in a non-contact manner;
A partial polishing step of partially polishing the surface to be polished;
And a polishing control step for determining a polishing position of the partial polishing step based on the measurement result of the non-contact measurement step, and polishing while measuring the surface to be polished.

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