JPS6398843A - Surface undulation measuring instrument - Google Patents

Abstract

PURPOSE:To indirectly measure the quantity of surface undulation of a recording medium by multiplying the gain G of a servo circuit system and the gain of a focus actuator with a focus error signal S so as to obtain the displacement of an objective lens. CONSTITUTION:The focus actuator 13 included in an optical pickup has a transmission characteristic whose movement slows down as the frequency is increased even with the same voltage applied thereto. The displacement delta of an objective lens is expressed as delta=SG1G2(mum), where S(mV) is an error signal, G1 (mV/mV) is the combined gain of a phase compensating circuit 15 and an actuator driving circuit 16 and G2(mu/mV) is the gain of the actuator 13. On the other hand, since the objective lens in the optical pickup 11 follows the surface undulation of an optical recording medium 4, the displacement delta of an objective lens is equal to the surface undulation of the recording medium within the residual error. Since the focus servo residual error is usually 0.5mum or below, highly accurate measurement is attained.

Description

[Detailed description of the invention] [Industrial field of application] The present invention focuses light such as a laser into a spot with a minute diameter,
This device is used to measure the surface runout hl of an optical recording medium used when recording and reproducing information.

[Conventional technology]

Figure 5 shows a schematic diagram of the surface runout measuring device for measuring υ. 1 is a light source such as a tlc-Nc laser, and 2 is a reflecting mirror that directs the laser beam toward the recording medium surface 4a. 3 is a condensing lens that condenses the laser beam onto the recording medium surface.

4 is an optical marking medium, and the surface 4a is the surface with recording marks (1).The laser beam is focused on this surface.The reflected light from the recording medium 4 is condensed by a condenser lens 5. The light enters the position sensor 6 q1. Now, as shown in the figure, the incident angle θ of the incident light beam is focused and recorded as The movement of the reflected light flux caused by the surface wobbling of the medium 40 becomes parallel to the 31Q medium surface, and the relationship between the moving distance on the sensor 6 and the amount of surface wobbling δ is t=2m5δ.

In this way, the surface displacement 6 can be measured from the displacement of the light spot on the sensor 6.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional technology, the medium surface tilts due to vertical vibration of the recording medium, which may cause a displacement of one beam of sunlight. It is also difficult to set the optical lens, position sensor, etc., and the optical system has a long optical path length, making it susceptible to changes over time.The present invention is intended to solve these problems. The purpose is to provide a surface runout measuring device d that is less affected by the inclination of the medium surface and has a simple configuration.

[Means for solving problems]

The surface runout measuring device of the present invention extracts a focus error signal from the optical pickup when the optical pickup that records and reproduces information on an optical recording medium performs focus servo, and adds the gain of the servo circuit system to this error signal S. G
IN is multiplied by the gain G of the focus actuator, and the amount of surface deviation δ=SG1G2 is measured.

[Effect]

According to the above configuration of the present invention, since the objective lens follows the surface runout of the optical recording medium by the focus servo, the displacement positions of the surface runout plate of the recording medium and the objective lens become equal. The displacement position of the objective lens is determined by multiplying the focus error signal S by the gain G of the servo circuit system and the gain G of the focus actuator, and the surface runout fit of the recording medium can be indirectly measured.

〔Example〕

FIG. 1 shows a schematic diagram of the surface runout measuring device of the present invention.
is an optical pickup and a spindle motor (not shown)
Information is recorded and reproduced on the optical recording medium 4 which is rotated by the optical recording medium 4 and the like. Reference numeral 12 denotes a focus error signal detection optical system included in the optical pickup 11; 2; As a means for detecting a difference signal, a known astigmatism method, critical angle method, or the like is used. Reference numeral 14 denotes an error signal generation circuit that generates a focus error signal by taking the difference signal from the error signal detection optical system 12. 15 is a phase compensation circuit, and 1G is an actuator drive circuit. The output of the actuator drive circuit 16 is transmitted to the focus actuator 13 to cause the objective lens in the optical pickup 11 to follow the surface deflection of the recording medium 4.

When the optical pickup 11 is performing a recording or reproducing operation, a focus error signal is extracted from A in FIG.
As shown in the figure. In Fig. 2, the horizontal 611 is the frequency (]-1
z), and the vertical axis is the error signal voltage (mV). From this figure, it is easy to see how much error signal is occurring at a certain frequency.

This signal is amplified by the phase compensation circuit 15 and the actuator drive circuit 1G to drive the focus actuator 13.

FIG. 3 shows the transfer characteristics of the focus actuator 13 included in the optical pickup 11, where the horizontal axis is frequency (H2) and the vertical axis is gain [μm/mV]. In this way, the actuator becomes more difficult to move as the frequency increases even if the same voltage is applied.

Now, the error signal is S (mV), the gains of the phase compensation circuit 15 and the actuator drive circuit 16 are combined (z
(mV/mV), and the gain of the actuator 13 is G, Cμm/mV), then the displacement position δ of the objective lens is δ=SGIG,Cμm).As mentioned above, the objective lens in the optical pickup 11 follows the vibration of the optical recording medium 4 for the focus servo operation, so the displacement j1δ of the objective lens becomes ff2 within the servo residual space.
0 is equal to the amount of surface runout of medium 4. The spectrum of the amount of surface runout of the optical recording medium obtained in this manner is shown in FIG. represent. Normally, the focus servo residual error is 0.5 μm or less, so the simple l:i configuration described above allows for highly accurate measurement of the difference δ′.

〔Effect of the invention〕

As described above, according to the present invention, since the optical pickup is used, the optical setting is easy, and it is resistant to changes over time. The measurement accuracy is due to focus servo error ff1 (0.5μ
The accuracy is extremely high compared to other devices.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the surface ta measurement device of the present invention, Fig. 2 is a diagram showing the power spectrum of the error signal, Fig. 3 is a transfer characteristic diagram of the actuator, and Fig. 4 is a diagram of the vibration plate of the recording medium. The spectrum diagram, FIG. 5, is a schematic diagram of a conventional surface *bleak measuring device. 1...Light source, 2...Reflection mirror, 3.5...Condensing lens, 4...Optical recording body, 6...Position sensor, 7...Recording medium 1. M stationary, 11... optical pickup, 12... focus error signal detection optical system, 1
3... Focus actuator! 4..., entertainment difference fM signal generation circuit, 15... phase compensation circuit, 16...
・Actuator drive times! :5,. Above is the difference between each country and the words 5 lies = pressure S [ynv] Din G Yu [
Voice over

Claims (1)

[Claims] When an optical pickup that records and reproduces information on an optical recording medium performs focus servo, a focus error signal is extracted from the optical pickup and the error signal S is
By multiplying by the gain G_1 of the servo circuit system and the gain G_2 of the focus actuator, the surface runout amount δ=
Surface runout measuring device characterized by measuring SG_1G_2