JPH11126351A - Parts for digital disk signal reader, signal reader using the same as well as method for stabilizing servo characteristic of reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide parts for a reader which has a gain allowance of >=20 dB of a servo circuit and is less or is entirely free of reading errors in spite of widening a servo band and a reader using the same as well as a method for stabilizing the servo characteristics of the reader. SOLUTION: Liquid crystal polymers satisfying the following conditions: loss coefft. x modulus of elasticity >70 MPa and (modulus of elasticity/sp. gr.)<1/2> >70 MPa<1/2> , thermoplastic resins, such as polyphenylene sulfide resins, polyester resins and polycarbonate resins, or their composite resins or thermoplastic resin compsns. prepd. by adding glass fibers, glass beads, carbon fibers or inorg. fillers to these resins are used as the materials of the parts, such as lens holders, bearings, bobbins, sliding shafts and/or actuator bodies, constituting the signal reader of a digital disk driving device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal reading apparatus for a digital disk drive characterized in that servo characteristics are stabilized by using a specific thermoplastic resin, composite resin or thermoplastic resin composition.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable increase in the capacity and speed of information handled by digital disk drives. For example, increasing the disk rotation speed of a CD-ROM,
Increasing the recording information density due to the development of VD.
For example, when reading using a laser beam, the disk of the digital disk drive device may have a focal point of the laser beam and the information to be read on the disk when reading the information on the disk due to eccentricity, runout, rotational vibration, etc. Reading errors may occur due to relative displacement. In order to prevent this, conventionally, a shift amount is corrected by a servo circuit.

However, the frequency band (hereinafter referred to as "servo band") of a servo circuit has been widened due to the increase in the capacity and speed of information handled by a digital disk drive in recent years. Then, the gain margin in the servo circuit for correcting the deviation is reduced, and it has become difficult to design a stable servo circuit. The gain margin in the servo circuit is defined as the product of the gain of the pickup and -1 at the frequency at which the phase of the pickup control force and the movement of the pickup with respect to that force are delayed by 180 degrees (that is, the gain is given a minus sign). (Hereinafter referred to as a gain margin). The larger this value is, the more stable the servo circuit can be obtained. The force for controlling the pickup is a force applied to the pickup for correcting the lens to a target position according to the deviation, and the pickup is normally controlled by a magnetic force. The force for controlling the pickup and the phase of the movement of the pickup are closely related to the natural frequency of the pickup. Generally, at the same frequency of the pickup, the phase has a characteristic that the phase is delayed by 180 degrees on the high frequency side as compared with the low frequency side. If there are two natural frequencies, the phase is delayed by a total of 360 degrees. However, at the primary resonance point, which is the lowest resonance frequency, the delay can be compensated for by the phase compensation circuit. Most are. Therefore, the phase is usually 1 near the secondary resonance point.
80 degrees late. Therefore, in general, the servo circuit 2
The gain margin at the peak of the next resonance point often indicates a measure for stabilizing the servo circuit. In general, the primary resonance point is often a natural frequency of a metal spring, a resin hinge, or the like that elastically supports an objective lens (also referred to as a lens for simplicity). The secondary resonance point is a lens holder,
It is often the natural frequency of a bearing, bobbin, sliding shaft, actuator body, or the like.

The frequency of the secondary resonance point mostly depends on the natural frequency of the above components of the signal reader. Recently, using a material with a large (elastic modulus / specific gravity) ^1/2 ,
Attempts have been made to increase the natural frequency of the signal reader, increase the frequency of the secondary resonance point of the servo circuit, and increase the gain margin. However, this method alone is required to design a sufficiently stable servo circuit. Was difficult.

The fact that the natural frequency can be increased by increasing the (elastic modulus / specific gravity) ^1/2 of a material used for a signal reading device for a digital disk drive,
It is generally known and described in, for example, P104 of "Introduction to Vibration Engineering" supervised by Mr. Shinji Yamada (Power Corporation).
Recently, there has been an attempt to design a stable servo circuit in consideration of a loss coefficient in addition to (elastic modulus / specific gravity) ^1/2 .
Even in consideration of this method, it has been difficult to design a sufficiently stable servo circuit.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reading device component having a gain margin of a servo circuit of 10 dB or more and having little or no reading error even when the servo band is widened, and a reading device using the same. And a method for stabilizing the servo characteristics of the reading device.

[0007]

The inventors of the present invention have conducted intensive studies to design a servo circuit that is stable even if the servo band is widened, and as a result, have found a new material selection method, and have found a new material selection method. It has been found that a reading device having a stable servo circuit can be obtained by applying the method to material selection of a signal reading device of the device, and the present invention has been completed.

That is, the first aspect of the present invention is that the following conditions are used for the material of the components constituting the signal reading device of the digital disk drive: loss coefficient × elastic modulus> 70 MPa, and (elastic modulus / specific gravity) ^1/2 The present invention relates to a signal reading device using a thermoplastic resin or a thermoplastic resin composition satisfying> 70 MPa ^1/2 . A second aspect of the present invention relates to the signal reader component according to the first aspect, wherein the component is a lens holder, a bearing, a bobbin, a sliding shaft, and / or an actuator body.
A third aspect of the present invention relates to the signal reading device component according to any one of the first to second aspects of the present invention, wherein the thermoplastic resin is a liquid crystal polymer, a polyphenylene sulfide resin, a polyester resin, a polycarbonate resin, or a composite resin thereof. Things. A fourth aspect of the present invention is the thermoplastic resin composition according to any one of the first to third aspects of the present invention, wherein the thermoplastic resin is obtained by adding glass fiber, glass beads, carbon fiber, and / or an inorganic filler to the thermoplastic resin. The present invention relates to a component for a signal reader. The fifth aspect of the present invention is the first aspect of the present invention.
The present invention relates to a signal reading device incorporating the signal reading device component according to any one of the above (1) to (5). Sixth Embodiment
Is a loss coefficient × elastic modulus> 70 MPa, and uses a thermoplastic resin or a thermoplastic resin composition which satisfies (elastic modulus / specific gravity) ^1/2 > 70 MPa ^1/2 for a digital disk drive device. The present invention relates to a method for stabilizing servo characteristics of a signal reading device. A seventh aspect of the present invention is that the components are a lens holder, a bearing, a bobbin,
The present invention relates to a method for stabilizing servo characteristics of a signal reading device according to the sixth aspect of the present invention, which is a sliding shaft and / or an actuator body. An eighth aspect of the present invention is the servo characteristic of the signal reading device according to any one of the sixth to seventh aspects of the present invention, wherein the thermoplastic resin is a liquid crystal polymer, a polyphenylene sulfide resin, a polyester resin, a polycarbonate resin, or a composite resin thereof. It relates to a stabilization method. A ninth aspect of the present invention is the thermoplastic resin composition according to any one of the sixth to eighth aspects of the present invention, wherein the thermoplastic resin is obtained by adding glass fiber, glass beads, carbon fiber, and / or an inorganic filler to the thermoplastic resin. The present invention relates to a method for stabilizing the servo characteristics of a signal reading device.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
A digital disk drive is a device for mounting and rotating a digital disk, a device for irradiating a rotating digital disk with laser light, etc., and a position where the irradiated laser light stores desired information on the digital disk. The device comprises a device for adjusting the focus so as to focus on, and a device for receiving the reflected light from the surface of the digital disk. The present invention relates to a signal reading device (pickup) that adjusts the speed of the signal. FIG. 2 shows an example of the signal reader. 1 is an objective lens, 2 is a lens holder, 3 is a bearing, 4 is a bobbin around which a coil is wound, 5 is a sliding shaft (a rod at the center in the figure), 6 is an actuator body, and 7 is a magnetic circuit. In the example of FIG. 2, a lens holder 2 provided with an objective lens 1 for focusing a laser beam at a target position, and a bobbin 4 wound with a coil for rotating the lens holder 2 in accordance with a shift in focus. An actuator body 6 for mounting and fixing a bearing 3 and a sliding shaft 5 for rotating and moving the objective lens up and down in order to make the objective lens follow a target position, and provided on a plane of the actuator body 6. It comprises a magnetic circuit 7. The objective lens 1 is made of inorganic glass or organic glass such as acrylic resin. Bobbin 4
For example, a tracking coil and a focusing coil are wound. The bobbin 4 is fixed by fitting the bearing 3 and the sliding shaft 5, and the magnetic circuit 7 rotates or moves the lens holder 2 up and down according to the displacement, and supports the weight of the lens holder and the like. The sliding shaft 5 is vertically mounted on the actuator body 6 and fixed. In accordance with the displacement, a rotating force and a vertical moving force are generated on the bobbin 4 on which the tracking coil and the focusing coil are wound by the magnetic circuit 7, the lens holder 2 is rotated and moved up and down, and the lens 1 The laser beam focuses on the position. In FIG. 2, the laser light is irradiated from below the objective lens,
Through the objective, focus on the digital disk surface above the objective. The components for a signal reader according to the present invention are not limited to this example.
Those described on page 45 are also included.

[0010] Even if the servo band of the signal reading device is widened, in order to manufacture a device that stabilizes the servo characteristics and has little or no reading error, a signal having a gain margin of 10 dB or more, and moreover, a signal having a gain margin of 20 dB or more. It is necessary to make a reader. For this purpose, the physical properties of the material used for the signal reader are determined by the following equation: loss coefficient × elastic modulus> 70 MPa
And (Elastic modulus / specific gravity) ^1/2 > 70 MPa ^1/2 is a necessary condition, and preferably, a loss coefficient ×
Elastic modulus> 200 MPa, and (elastic modulus / specific gravity) ^1/2 > 80 MPa ^1/2 , more preferably, loss coefficient × elastic modulus> 400 M
Pa, and (elastic modulus / specific gravity) ^1/2 > 100 MPa ^1/2 . Here, the elastic modulus is measured by a method described in ASTM D790, and the loss coefficient is Jls G0.
602. The loss coefficient means a value obtained by dividing a loss elastic modulus by a storage elastic modulus in a complex dynamic elastic modulus of a solid. If a material that does not satisfy either one of the conditions is used, the frequency of the secondary resonance point of the servo circuit is lowered or the amplitude is increased, and the servo circuit becomes unstable.

The material used for the signal reading device for a digital disk drive is a resin or a resin composition. As the resin, a liquid crystal polymer, polyphenylene sulfide, polyester resin, polycarbonate resin, or a composite resin thereof is used. By using a composite resin, the value of loss coefficient × elastic modulus and (elastic modulus / specific gravity) ^1/2 may be improved in some cases. For example, a composite resin can be obtained by blending polycarbonate and a liquid crystal polymer. The method of compounding the resin is not particularly limited, and may be any method that satisfies the above conditions. As the composite resin, a resin having a compounding amount of the liquid crystal polymer to the polycarbonate of 2 to 50% by weight is preferable. It is preferable that the compounding amount of the liquid crystal polymer is 2 to 50% by weight with respect to polyphenylene sulfide or polyester resin.

As the resin composition, glass fibers (GF) and carbon fibers (C
What added F), glass beads, and / or an inorganic filler is used. The inorganic filler is mica, potassium titanate, calcium carbonate, or the like, and these can be used as a mixture. The amount of the inorganic filler is preferably 2 to 80% by weight based on the resin composition after the compounding.

In the present invention, known additives and / or fillers and other polymer materials can be added to the resin and the composite resin as required. For example,
Mainly composed of various stabilizers, antioxidants, lubricants, nucleating agents, plasticizers, mold release agents, lubricity-imparting agents, antistatic agents, other polymeric materials or granular, powdery glass, metals and metal oxides And the like.

Depending on the type of the resin or the resin composition, the above condition of (loss coefficient × elastic modulus)> 70 MPa and (elastic modulus / specific gravity) ^1/2 > 70 MPa ^1/2 may not be satisfied. , Just selecting the resin,
Care must be taken when using as a resin composition.
For example, care must be taken because a material obtained by merely filling glass fiber with approximately 20% by weight of polycarbonate does not satisfy the above conditions. In addition, in this invention, the addition amount of an inorganic filler shows weight%.

[0015]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. The test method of the material and the reader is shown below. The method of measuring the loss coefficient of the material was performed in accordance with the central support steady vibration method of Jls G0602 (FIG. 1). Test specimen shape: 130 mm x 13 mm x 3.2 mm

Using the materials selected above, a reader as shown in FIG.
The gain margin in the frequency gain of the positioning servo circuit of the ROM reader was evaluated. Here, the gain margin indicates a difference between the peak gain at the secondary resonance point and 0 dB (see FIG. 3). Also, the number of reading errors that occurred when reading one CD-ROM into a personal computer was investigated.

Examples 1 to 7 and Comparative Examples 1 to 3 Loss coefficients (η) near the secondary resonance frequency of the various materials shown in Table 1, the same loss coefficient (η) × elastic modulus (E),
Table 1 shows (elastic modulus (E) / specific gravity (ρ)) ^1/2 , and the secondary resonance point frequency, the gain margin, and the number of read errors of the reader manufactured using these materials.

[0018]

[Table 1]

The gain margin is preferably 10 dB or more from the viewpoint of stabilizing the servo circuit.
It is shown that the gain margin of 10 dB or more is achieved for all the resins using the resin satisfying the condition of elastic modulus> 70 MPa and (elastic modulus / specific gravity) ^1/2 > 70 MPa ^1/2. I understand from 1. As for those which do not satisfy at least one of the conditions, none of them can achieve a gain margin of 10 dB or more, and the number of read errors is large. Further, if both conditions are not satisfied, the gain margin 10
dB or more could not be achieved, no deviation could be corrected by the servo circuit, and no information could be read.

[0020]

As it is conventional, according to the present invention, and only the loss factor, (elastic modulus / specific gravity) only ^1/2 and loss factor and also selects the material taking into account the (elastic modulus / specific gravity) ^1/2 Although it was difficult to manufacture a signal reading device having a sufficient gain margin, according to the present invention, the loss coefficient × elastic modulus> 70 MPa and (elastic modulus / specific gravity) ^1/2 > 70 MPa ^1/2 By making a signal reading device using a certain material,
When the gain margin is 10 dB or more, furthermore, 20 dB or more,
A device without any reading errors could be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a loss factor measuring method used in the present invention.

FIG. 2 is a diagram showing a signal reading device used in the present invention.

FIG. 3 is a diagram illustrating an example of a frequency-gain measurement result according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 2 Lens holder 3 Bearing 4 Coil wound on bobbin 5 Sliding shaft 6 Actuator body 7 Magnetic circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G11B 7/135 G11B 7/135 A

Claims (9)

[Claims] 1. A heat source which satisfies the following conditions as a material of a component constituting a signal reading device of a digital disk: loss coefficient × elastic modulus> 70 MPa and (elastic modulus / specific gravity) ^1/2 > 70 MPa ^1/2. A component for a signal reading device, characterized by using a thermoplastic resin or a thermoplastic resin composition. 2. The components are a lens holder, a bearing, a bobbin,
The component for a signal reading device according to claim 1, which is a sliding shaft and / or an actuator body. 3. The thermoplastic resin is a liquid crystal polymer, a polyphenylene sulfide resin, a polyester resin, a polycarbonate resin or a composite resin thereof.
3. The component for a signal reader according to any one of 2. 4. The signal reading device according to claim 1, wherein the thermoplastic resin composition is obtained by adding glass fiber, glass beads, carbon fiber, and / or an inorganic filler to the thermoplastic resin. Parts. 5. A signal reading device incorporating the signal reading device component according to claim 1. 6. The loss coefficient × elastic modulus> 70 MPa,
And a method for stabilizing servo characteristics of a signal reading device for a digital disk, wherein a thermoplastic resin or a thermoplastic resin composition satisfying (elastic modulus / specific gravity) ^1/2 > 70 MPa ^1/2 is used as a material. 7. The parts are a lens holder, a bearing, a bobbin,
7. The method according to claim 6, wherein the method is a sliding shaft and / or an actuator body. 8. The thermoplastic resin is a liquid crystal polymer, a polyphenylene sulfide resin, a polyester resin, a polycarbonate resin, or a composite resin thereof.
7. The method for stabilizing servo characteristics of a signal reading device according to any one of claims 7 to 7. 9. The signal reading device according to claim 6, wherein the thermoplastic resin composition is obtained by adding glass fibers, glass beads, carbon fibers, and / or an inorganic filler to the thermoplastic resin. Servo characteristics stabilization method.