JPS6316432A - Focus error detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a focus error detection device for an optical head in a device that optically records and reproduces information, such as an optical disk device.

Conventional Technology The modern era is called the information age, and the technology development of high-density, large-capacity memory, which forms the core of the information age, is actively being carried out.

In addition to the above-mentioned high density and large capacity, the capabilities required of memory include high reliability and high speed access, and optical disk memory is attracting the most attention as a device that satisfies all of these requirements. An optical disk memory is a device that optically records information on a recording medium, and recently, a lot of research has been conducted on magneto-optical disks that can also erase recorded information.

A major feature of optical disk memory is that it does not damage the information recording medium because it uses a non-contact recording/playback method. Servo system is required. The optical head requires a function to detect a focus error between the information recording medium and the objective lens, and an objective lens actuator to drive the objective lens and perform focus servo. It is related to.

In the past, many reports have been made regarding techniques related to focus error detection.Hereinafter, an example of a conventional focus error detection device will be described with reference to the drawings.

FIG. 3 shows a schematic diagram of a conventional focus error detection device. Note that for convenience, the four-split photodetector 7 is also shown in a view as viewed from arrow G.

In Fig. 3, 1 is a light source, 2 is an objective lens, 3 is an information recording medium, 4 is a No.-7 mirror, 5 is a convex lens, 6 is a reflective optical element, 4 is a 4-split photodetector, 8 is a differential It's an amplifier. The reflective optical element 6 is located in the convergent light beam produced by the convex lens 6, and consists of two reflective planes having the same reflectance and having a step so as to spatially divide the convergent light beam into two and reflect it in approximately the same direction. ing. Figure 4 shows a convex lens 5,
6 is a perspective view of the reflective optical element 6 and the 4-split photodetector 7. The optical system pace 9 has a positioning block H for fixing the reflective optical element at a predetermined position.

As shown in FIG. 4, the reflective optical element e consists of two reflective surfaces, a reflective surface E and a reflective surface F. In FIG. 3, when the accuracy of each component and the mounting accuracy on the optical system base are obtained as designed, when the objective lens 2 is focused on the information recording medium 3, the convex lens 5 The converged luminous flux is reflected by the reflective surfaces E and F of the reflective optical element 6 positioned and fixed on the optical system pace 9.
After the division, the light is reflected with an optical path difference and connects to a focal point P and a focal point Q, respectively. The light receiving surface of the 4-split photodetector 7 is installed approximately perpendicular to the incident optical axis at an intermediate position between the focal point P and the non-focal point. As a result, two congruent semicircular light spots are formed on the four-split photodetector T. 4-split photodetector 7
For example, the position within the light receiving surface is adjusted so that the four light receiving areas receive uniform light. Here, the 4-split photodetector 7
Among the electrical signals generated in the four light receiving regions, the electrical signals of the diagonally located light receiving regions are summed, and the difference is obtained by a differential amplifier 8 to obtain a focus error signal.

The operation of the conventional focus error detection device configured as described above will be explained below. As in the case of FIG. 3, FIG. 5 shows the positional relationship between the convex lens 5, the reflective optical element 6, and the 4-split photodetector 7 when the objective lens is focused. FIG. 5B is a view taken along arrow G in FIG. 5, and the same applies to FIGS. 6 and 7 below. At this time, two light spora (S and T) are formed on the 4-split photodetector 7 in a semicircular shape, congruent, in the same direction, and with the same amount of light, and the amount of light incident on the four light receiving areas is Since they are set to be equal, the output of the focus error signal obtained by the differential amplifier 8 is zero.

FIG. 6 shows that the information recording medium 3 in FIG. 3 is the objective lens 2.
5 shows a case in which the light is displaced in a direction away from the convex lens 5, and converged light enters the convex lens 5 compared to the case shown in FIG. As a result, the two convergence points formed by the convex lens 6 are both shifted toward the reflective optical element 6, and the light spots S and T as shown in the 0-arrow view of FIG. is formed. At this time, the output of the differential amplifier 8 is unbalanced, and a positive focus error signal can be detected.

FIG. 7 shows that the information recording medium 3 in FIG. 3 is the objective lens 2.
This shows the case where the convex lens 6 is displaced in a direction approaching .
, more diverging light than in the case of FIG. 3 is incident.

As a result, the two convergence points formed by the convex lens 5 are both shifted in the direction away from the reflective optical element 6, and an optical spora (S) as shown in the view of arrow G in FIG. and T are formed. At this time, a negative focus error signal can be detected from the output of the differential amplifier 8.

Figure 8 shows the information recording medium 3 as in Figures 3 and 6.
2 shows a case where the 4-split photodetector 7 is slightly displaced in the direction of the arrow J while the objective lens 2 is in focus. Reference numeral 11 indicates a dividing line in one direction of the four-split photodetector 7, and reference numeral 13, indicated by a broken line, indicates a dividing line before the dividing line 11 is displaced. When the convergent light flux incident on the reflective optical elements and the position of the reflective optical element 6 fixed to the positioning block HK of the optical system base 9 are as designed, the light spots S and T have congruent shapes, the same direction, and the same direction. Hato becomes. Therefore, before the displacement, the light receiving area a of the 4-split photodetector 7.

The amounts of light received at b, c, and d are all equal. However, after the displacement, it decreases in the light receiving areas a and b, and increases in the light receiving areas c and d. At this time, the amount of light that has decreased in the light-receiving area a, that is, the amount of light that has increased in the light-receiving area d, is equal to the amount of light that has already decreased in the light-receiving area, that is, the amount of light that has increased in the light-receiving area C. Both the sum and the sum of the electrical signals detected in the light receiving areas S and D do not change compared to before the minute displacement of the 4-split photodetector 7, and the focus error signal obtained by the differential amplifier 8 is zero. hand,
It is not affected by the displacement of the 4-split photodetector 7.

Problems to be Solved by the Invention However, with the above configuration, it is difficult to obtain the same amount of light from the two light spoilers (T and S) obtained on the four-split photodetector 7, There was a problem in that the amount of light received in the area was not uniform. The reasons for this are, firstly, that the optical axis of the convergent light beam incident on the reflective optical element 6 is tilted and has parallel misalignment.

This is caused by variations in the precision of the light source 1 and various optical elements, the positioning precision of each, and the precision of the optical system base.

Second, accuracy of the reflective optical element 6 1 Due to the positioning accuracy when fixing the reflective optical element 6 to the optical system base 9 using the positioning block H, the optical axis of the convergent light beam does not match the stepped surface of the reflective optical element. It is. Therefore, in the explanation of the conventional focus error detection device shown in FIGS. 3 to 8, the accuracy and positioning accuracy of each component are obtained as designed, and the light spot T and The case where S is the same amount of light is used. Photospora) T and S
The effect when the same amount of light is not obtained will be explained with reference to the drawings. Figure 9 is similar to Figure 8,
When the objective lens 2 is focused on the information recording medium 3, the optical axis of the convergent light beam does not match the step surface of the reflective optical element, so the convergent light beam is spatially uniform due to the reflective optical element 6. Two light spots T and S on the 4-split photodetector 7, which are not divided into two with the same light intensity but in the same direction.
Although they are in the same direction, they do not have the same shape or the same amount of light, so the amount of light received in the four light receiving areas is not uniform.

Even in the state shown in FIG. 9, if the position of the 4-split photodetector 7 is adjusted within the light-receiving surface and the dividing line 11 is positioned, the amount of light received in each of the light-receiving areas a, b, c, and d will be different. It is possible to make the output of the differential amplifier 8 zero. Therefore, the focus error signal can be obtained by the differential amplifier 8.

Let us now consider the case where the dividing line is slightly displaced due to temperature drift or the like, as discussed in FIG. In FIG. 9, when the dividing line 11 is slightly displaced in the direction of arrow J, the amount of light received decreases in the light receiving areas a and b, and increases in the light receiving areas a and a. At this time, the amount of light that has decreased in the light-receiving area a, that is, the amount of light that has increased in the light-receiving area d, is not equal to the amount of light that has already decreased in the light-receiving area, that is, the amount of light that has increased in the light-receiving area C.

That is, if the position of the 4-split photodetector 7 is slightly displaced due to factors such as temperature changes, the output of the differential amplifier 8 will become zero even when the objective lens 2 is focused on the information recording medium 3. Therefore, it is not possible to obtain an accurate focus error signal. However, it has the disadvantage that it is impossible to record and reproduce information stably.

The present invention has been made in view of the above-mentioned conventional interlayer points, and is a focal point that can suppress the deterioration in the ability to detect focus error signals caused by the fact that the optical axis of the convergent light beam and the stepped surface of the reflective optical element do not coincide. The object of the present invention is to provide an error detection device.

Means for Solving the Problems In order to achieve the above object, the focus error detection device of the present invention includes a convex lens that receives reflected light from an information recording medium, the convex lens, and a focus error detection device located in a convergent light beam by the convex lens, a reflective optical element consisting of two reflecting planes having the same reflectance and having a step, which spatially divides the convergent light beam into two and reflects the same in substantially the same direction; and the objective lens is focused on the information recording medium. is located at an intermediate position in the optical axis direction between the two focal points formed by the convex lens and the reflective optical element, and has a substantially cross-shaped dividing line, and one of the dividing lines is in the same plane as the step surface of the reflective optical element, and is installed to receive the light intensity of two light spots in four light receiving areas; at least the four-divided photodetector and the reflective optical element; The optical system pace that fixes the element is electrically connected to the light receiving areas at diagonal positions among the four light receiving areas of the 4-split photodetector, and the sum is calculated, and each electrical signal of the sum is calculated. It is comprised of a differential amplifier that takes the difference, and an installation device in which the reflective optical element is installed on the optical system base at a position where the light intensities of the two light beams divided by the reflective optical element are approximately the same. .

Effect of the Invention With the above-described configuration, the present invention uses an installation device to locate the position where the light intensities of the two light beams divided by the reflective optical element are approximately the same, that is, the optical axis of the convergent light beam and the stepped surface of the reflective optical element coincide. A reflective optical element is installed on the optical pace at a position where Therefore, when the objective lens is focused on the information recording medium, it is possible to form two semicircular light spots of the same size and in the same direction.

In this state, if you adjust the dividing line position of the 4-split photodetector so that the four light-receiving areas receive the same amount of light,
As mentioned in the explanation of the operation of the conventional focus error detection device, even if the 4-split photodetector is displaced in either direction of the dividing line due to environmental temperature changes, light will be received by the 4 light-receiving areas of the 4-split photodetector. The amount of light that is generated does not change if you take the sum of the electrical signals generated from the light-receiving areas located at diagonal positions, and the output of the differential amplifier obtained by taking the difference between the summed electrical signals, that is, the focus error signal is This means that stable detection ability is always maintained.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view schematically showing the main parts of a focus error detection device in an embodiment of the present invention. Since the overall configuration of the focus error detection device is the same as that of the conventional example shown in FIG. 3, the installation device for positioning the reflective optical element will be mainly described here. In FIG. 1, 5 is a convex lens, 6 is a reflective optical element, 7 is a 4-split photodetector, and 9 is an optical system base, which are the same as those of the conventional example.

The operation of the focus error detection device configured as described above will be described below.

The installation device provides the optical system base 9 with a guide surface M of the installation guide 21 and a guide surface N of the optical system base 9 (in this embodiment, the upper surface of the optical system base 9 is used).
This is a means that allows sliding in directions on two surfaces 4 of the respective surfaces of the reflective optical element e that are substantially perpendicular to the stepped surface formed by the reflective surfaces E and F.

When the objective lens is focused on the information recording medium, the guide surfaces M and N are placed at a position where the stepped surface of the reflective optical element 6 coincides with the optical axis of the convergent beam formed by the convex lens 6. The reflective optical element 6 is positioned and fixed by sliding two surfaces substantially perpendicular to the stepped surfaces of the reflective optical element 6 in the direction of .

At this time, the convergent light beam is spatially divided into two by the reflective optical element 6 and reflected in approximately the same direction with approximately the same amount of light, so that two congruent semicircular light spots appear on the 4-split photodetector 7. is formed. The four-division photodetector 7 is positioned and connected within the light-receiving surface so that the four light-receiving areas receive uniform light. Therefore, the focus error signal obtained by the differential amplifier 8 becomes a drop. Furthermore, the focus error signal generated by the positional fluctuation of the information recording medium 3 is the same as the operation of the conventional example described in FIGS. 6 and 7.

As described above, according to this embodiment, an installation device is provided on the two guide surfaces of the optical system base, which is a means for making two surfaces of each surface of the reflective optical element that are substantially perpendicular to the step surface slidable. By providing this, it is possible to align the optical axis of the convergent light beam with the stepped surface of the reflective optical element.
No matter which direction of the dividing line the divided photodetector is displaced, the focus error signal can always maintain a stable detection ability.

Moreover, providing two guide surfaces on the optical system base does not increase the cost of the reflective optical element positioning and fixing block described in the conventional example, so the installation device can be easily configured without increasing costs. It also has the unique effect of being achievable. It goes without saying that any means may be used for the flat part on which the reflective optical element slides and the means for fixing it in the installation device.

Other embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a perspective view schematically showing the main parts of a focus error detection device in another embodiment of the present invention. Here, as in the case of FIG. 1, the installation device will be mainly explained.

In FIG. 2, 5 is a convex lens, 6 is a reflective optical element, and 7 is a convex lens.
1 is a 4-split photodetector, 9 is an optical system, and these components are the same as those of the conventional example. 12 is a mounting member to which the reflective optical element 6 is fixed.

The operation of the focus error detection device configured as described above will be described below.

The installation device includes a mounting member 12 for fixing the reflective optical element 6 and guide surfaces P and Q on the optical system pace 9, so that the reflective optical element 6 can be fixed on each surface of the mounting member 12.
It is constituted by means that allows two surfaces substantially perpendicular to the stepped surface formed by the reflective surfaces E and F to be slid in the direction.

When the objective lens is focused on the information recording medium, the guide surfaces P and Q are placed at positions where the stepped surface of the reflective optical element 6 coincides with the optical axis of the convergent beam formed by the convex lens 6. The mounting member 12 to which the reflective optical element 6 is fixed is positioned and fixed by sliding the two surfaces of the mounting member 12 that are substantially perpendicular to the step surface of the reflective optical element e in the direction. In this state, two congruent semicircular light spots are formed on the four-split photodetector 7, as in the embodiment shown in FIG. , the focus error signal becomes zero. Furthermore, the focus error signal generated by the positional change of the information recording medium 3 is the same as the operation of the conventional example described in FIGS. 6 and 7, which is the same as in the embodiment shown in FIG.

As described above, according to this embodiment, the mounting member for fixing the reflective optical element and the two guide surfaces of the optical system pace are provided with two guide surfaces of the mounting member that are substantially perpendicular to the step surface of the reflective optical element.
By providing an installation device consisting of means that allows the surface to slide, the focus error signal can always maintain stable detection ability.

Moreover, since the reflective optical element is fixed to a mounting member and this fixed member is slid, no external force is applied to the reflective optical element during positioning. Therefore, it also has the unique effect of not damaging the optical characteristics of the reflective optical element. It goes without saying that any means may be used for sliding or fixing the mounting member in the installation device.

Effects of the Invention The present invention is a focus error detection device that uses a convex lens and a reflective optical element to detect 4 images using reflected light from the information recording medium when the focus of the objective lens is on the information recording medium.
The configuration forms two semicircular light spots on the split photodetector, and further includes a setting device that allows the reflective optical element to slide against the two guide surfaces of the optical system. υ, the shapes of the two light spots can be jointly made to have approximately the same -light, quantity. Therefore, by setting the 4-split photodetector, it is possible to equalize the amount of photoelectricity received by the 4 light-receiving areas, so it is possible to detect a stable focus error signal that is not affected by minute displacements of the 4-split photodetector using a simple configuration. This can be achieved using a setting device that does not increase costs.

Furthermore, by configuring the installation device with a mounting member that fixes the reflective optical element and a means that allows the mounting member to slide with respect to the two guide surfaces of the optical system pace, the optical characteristics of the reflective optical element are impaired. Therefore, it is possible to realize an excellent focus error detection device that can stably detect a focus error signal without causing any problems.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing the main parts of a focus error detection device according to an embodiment of the present invention, FIG. 2 is a perspective view of main parts of another embodiment, and FIG. 3 is a configuration of a conventional focus error detection device. Figure, 4th
The figure is a perspective view of the main part, and FIGS. 5, 6, 7, 8, and 9 are plan views for explaining the operation of the conventional photodetector. 1...Light source, 2...Objective lens, 3.
... Information recording medium, 4 ... Half mirror
16...Convex lens, 6...Reflecting optical element, 7...4-split photodetector, 8...Differential amplifier, 9... Optical system pace, 11.13...
...Dividing line. Name of agent: Patent attorney Toshio Nakao and one other person f.
- Maruhara 2゛-r Ding Torenshi゛3----J tribute? 10,000 (Nikozo tg body 8-Shi difference v〃Anof〃Fig. 4 9-Ekin thread 1゛-^ Fig. 5 (8) Fig. 6' Fig. 7 Fig. 8 Fig. Φ f59 Fig.

Claims (3)

[Claims] (1) a light source; an objective lens that focuses light from the light source onto an information recording medium to form a minute light spot; , a means for separating the light transmitted through the objective lens, a convex lens for converging the light separated by the separating means, and a convex lens located in the convergent light beam by the convex lens, spatially dividing the convergent light beam into two. a reflective optical element consisting of two reflective planes having the same reflectance and having a step that reflects the light in approximately the same direction; and when the objective lens is focused on the information recording medium, the convex lens and the reflective optical element is located at an intermediate position in the optical axis direction of two focal points formed by and has a substantially cross-shaped dividing line, and one of the dividing lines is in the same plane as the step surface of the reflective optical element. an optical system base on which at least the four-split photodetector and the reflective optical element are positioned and fixed; and a differential amplifier that electrically connects diagonally located light receiving areas among the four light receiving areas of the four-split photodetector to calculate the sum, and calculates the difference between the summed electric signals; A focus error detection device comprising: an installation device in which the reflective optical element is installed on the optical system base at a position where the light quantities of the two light beams divided by the reflective optical element are approximately the same light quantity. (2) The installation device is placed on the two guide surfaces of the optical system base.
2. The focus error detection device according to claim 1, wherein the focusing error detecting device is a means that allows sliding on two surfaces substantially perpendicular to the step surface among the surfaces of the reflective optical element. (3) The installation device includes a mounting member for fixing the reflective optical element, and two guide surfaces of the optical system base, of which two surfaces of the mounting member are substantially perpendicular to the step base surface of the reflective optical element. 2. The focus error detection device according to claim 1, further comprising a means for making sliding possible.