MXPA00009510A - Optical scanning device having an improved response characteristic - Google Patents

Abstract

The invention relates to an optical scanning device having an improved response characteristic, for use in an apparatus for optically reading or writing information in one or more tracks on a recording medium. The object of the invention is to provide an optical scanning device which, without any electronic compensation means, very largely avoids resonance peaks and has an improved response characteristic. According to the invention, this object is achieved by a retaining plate which supports the objective lens of the scanning device via bearing elements and has at least one cutout, which separates the mounting points, in the surface which holds the bearing elements for the objective lens holder. The field of application of the invention is optical scanning devices having an improved response characteristic for use in equipment for reading or writing information on an optical recording medium, such as a CD, DVD, a CD or DVD which can be written to, or else a magneto-optical recording medium, for example.

Description

OPTICAL EXPLORATION DEVICE THAT HAS IMPROVED RESPONSE FEATURE DESCRIPTION OF THE INVENTION The invention relates to an optical scanning device having improved response characteristic, for use in an apparatus for optically reading or writing information in one or more tracks in a recording medium which may be, for example, a compact disc ( known as a CD), a digital versatile disk (known as a DVD), a CD or a DVD on which it can be written, or a means of magneto-optical recording. The scanning devices for optical recording means are generally known. The construction and operation of an optical scanning apparatus, of a so-called optical pickup, is described in Electronic Components S. Applications, Vol. 6, No. 4, 1984, pages 209-215. Such scanning devices have been referred to as actuators on which a target lens is placed, which is provided for tracking and for focusing the light beam or laser beam on the optical recording medium. In principle, the optical scanning devices can be differentiated by the manner in which the objective lens is suspended. For example, in the case of a known leaf spring actuator, the objective lens retainer is fixed by means of four parallel leaf springs in a frame, see EP-A-0 178 077. The disadvantages are that such arrangements of Spring have an undesirable tendency to oscillate and involve a high level of assembly complexity. A parallel guide of the objective lens retainer is also obtained by an actuator of the articulated or hinged type, as is known, for example, from EP-B 0 563 034. It has been found that an actuator with a parallel guide is relatively stable in terms of tilting the objective lens during deflection, but they involve a high level of adjustment complexity since it needs to be aligned exactly in terms of the directions of movement that are guided by the joints. Another type of objective lens retainer is the use of four cables which, as support elements, connect the objective lens retainer to the base plate of the actuator. The so-called cable catchers can be produced more cost-effectively compared to optical scanning devices having a leaf spring or a hinge. However, it has been found that they are not advantageous in comparison with other parallel guides, in terms of inclination of the objective lens and guide characteristics. One criterion of quality of the optical scanning devices is their response characteristic, in which case the response characteristic term means the reaction of the optical scanning device to controlling signals by means of which the scanning device is diverted for focused or tracking , in order to explore a specific point in the recording medium or to follow the movement of the recording medium. The movement of the optical scanning device is intended to follow very precisely the control signals applied. However, as a rule, the excitation of a mechanical system leads to an oscillation by resonance in the region of the resonant frequency and what is called a resonance peak which has a negative effect on the response characteristic and the reaction of the Optical scanning device to control signals. Since the resonant frequency is often in the range that is audible to the human ear, this effect is additionally evident in a negative manner as what is called a howl. US 4,477,755 has already described the use of a circuit arrangement for electronic compensation of optical and mechanical instabilities in the focus control and tracking loop in order to avoid mechanical resonances and howls. The circuit arrangement contains a model of the mechanical system, by means of which the reaction of the scanning device to the control signals is monitored, and the movement of the scanning device is stopped if a predetermined threshold value is exceeded. For this purpose, the circuit contains a filter and a variable gain amplifier in order to produce a control signal compensation component at a selected frequency in the region of the frequencies at which the mechanical resonances are significant. The object of the invention is to provide an optical scanning device which, without any electronic compensation means, largely avoids the resonance peaks and has an improved response characteristic. This object is obtained by the characteristics of the invention specified in the independent claims. Advantageous developments of the invention are specified in the dependent claims. One aspect of the invention is the design of an optical scanning device such that it follows the control signals applied as uniformly as possible and without any resonance spikes. It has been found that the phenomenon of resonance are significantly affected by the characteristics of the retaining plate on which a means for supporting the objective lens holder is fixed. It has been found that disadvantageous resonance peaks are avoided by means of retaining the objective lens holder which is held in a flexible manner. On the other hand, the options for selecting an oscillating cushion material for the retainer plate are limited since, on the one hand, the retainer plate must support the weight of the objective lens and the objective lens retainer and, on the other hand, is It is necessary to ensure that the actuator returns to its original position after it has been bent. This means that the retaining plate must not deform affected by force or temperature. These contradictory requirements of high flexibility and high strength are satisfied by a retaining plate in which those points on the retaining plate which retain the support elements for the objective lens holder are largely mechanically decoupled. The mechanical decoupling of these points on the retaining plate which retains the support elements for the objective lens retainer is obtained by a retaining plate which has notches or cutouts on the surface and which retains the support elements for the objective lens retainer. These grooves are provided in such a way that, on the one hand, the straight edges of the surface which retain the support elements are interrupted by grooves or openings in the form of grooves and, on the other hand, the cut-outs are provided inside of the surface to reduce the effective area between the mounting points for the objective lens support elements. In a version of the invention, the mounting points are designed as isolated surfaces which are connected via restrictions to the surface which supports it. This type of configuration for the retaining plate significantly improves the response characteristic of the optical scanning device, and resonance peaks are avoided. The term response characteristic means, in particular, the reaction of the optical scanning device to control signals, as reflected in the frequency response and in the relative phase, and in the transfer function of the control signals to the scanning system optics. The resonance peaks are avoided to a large extent without any means of electronic compensation. This effect is rather surprising because the assumption must be made that holding the objective lens support elements on a comparatively larger spring surface can lead to increased resonance peaks. The retainer plate is preferably combined with a second retainer plate to form a retention system, in which case, the second retaining plate makes it possible, in an advantageous manner, for the first retaining plate to be designed to be thinner, so that additional damping is ensured in the lower frequency range and, in addition, to limit the maximum deflection of the actuator. In the case of a configuration which is provided as a wired sensor, the cables which are provided as support elements are passed through openings in the second retaining plate and are fixed on the first retaining plate, for example , by a welding process. The intermediate space which then remains in the openings for the cable in the second retaining plate is then filled with a filling compound. Preferably it is used as the silicone filling compound in order to dampen the fact that resonance peaks occur in the low frequency range. Although the assumption has been made that embedding the wires used as silicone support elements in the second retaining plate can significantly dampen the resonance peaks, it has nevertheless been found that this is valid only to an insufficient extent. The desired response characteristic is obtained only in combination with the first retaining plate, according to the invention. The invention will be explained in greater detail in the following text using an exemplary embodiment and with reference to the drawings, in which: Figure 1 shows a contour drawing of a retention plate of an optical scanning device having a characteristic of improved response, figure 2 shows a contour drawing of a side view of an optical scanning device having an improved response characteristic, figure 3 shows a contour drawing of a plan view of an optical scanning device having an improved response feature, Figure 4 shows a contour drawing of a plan view of a second retention plate of an optical scanning device having a limiting means, Figure 5 shows a contour drawing of a front view of a second retaining plate of an optical scanning device having a limiting means, figure 6 shows a contour drawing of a side view of a second holding plate of an optical scanning device having a limiting means; Figure 7 shows a frequency response and a phase diagram of an optical scanning device having a plate known retention in the focusing direction, figure 8 shows a frequency response and a phase diagram of an optical scanning device having a retaining plate according to the invention in the focusing direction, figure 9 shows a response of frequency and a phase diagram of an optical scanning device having a known latch plate in the tracking direction, FIG. 10 shows a frequency response and a phase diagram of an optical scanning device having a latch plate. retention, according to the invention, in the tracking direction, figure 11 shows a contour drawing of a retainer of the objective lens which is fixed by wires on a known retaining plate, figure 12 shows a contour drawing in relation to the assembly of an objective lens retainer, which is fixed by wires on a known retention plate, to form an actuator, Figure 13 shows a contour drawing of the conductive side of an optical scanning device having a known retention plate. In all the figures the same reference symbols are used. Figure 11 shows a contour drawing of an OH retainer of the known objective lens, which is fixed by wires W on a known HP retention plate. Four cables, which are fixed on the HP retainer plate, hold an OH retainer of the objective lens, placed on top of which is the objective lens O which is provided for focusing and tracking the light beam or laser beam on a recording medium optical, and SP coils to deflect the lens OR objective. The cables, which are used as support elements, in this case form a flexible support for the OH retainer of the objective lens, and at the same time are used to supply electric power to the SP coils arranged on the OH retainer of the objective lens. The retaining plate HP on which the lens holder OH is held by the four wires W is formed by a rectangular surface which, corresponding to figure 12, is connected to a reinforcement S on a base plate G, reinforcement S which extends at right angles from the base plate G. Accordingly, corresponding to FIG. 12, the SP coils provided in the recesses in the OH retainer of the objective lens are moved to a position which allows interaction with the lens. MSI magnet reinforcements; MS2. Reinforcements of the magnet MSI; MS2 likewise extend at right angles from the base plate G and parallel to the network S to which the retaining plate HP is fixed, and form a magnetic field which, by interaction with the magnetic fields produced by the coils SP, allow the objective lens O to deviate in a desired manner from a resting position. The magnetic field that originates from the reinforcements of magnet MSI; MS2 is preferably produced by at least one permanent magnet M, which is fixed to the magnet reinforcement MSI. As already mentioned, electric power is supplied to the SP coils with the proviso that the OH retainer of the objective lens via the wires W by means of which the OH retainer of the objective lens is fixed on the HP retainer plate. In order to secure the wires W, an HP retainer plate illustrated in FIG. 13 has solder spots LP1, LP2, LP3 and LP4 which are provided as holes in the HP retainer plate designed as a printed circuit board. The wires W are passed through the holes and are soldered to the HP retainer plate on which welding contact zones are provided, for this purpose, in the region of the holes. The welding contact areas or welding points LP1, LP2, LP3 and LP4 are connected via conductor tracks to the AP points of connection, to which control signals are supplied to deflect the lens OR objective. In addition, bolt openings D01 are provided; D02 for alignment of the HP retainer plate on the reinforcement S, and a mounting opening BMO is provided for the positioning of the HP retainer plate. As determined by measurements, such optical scanning devices have the disadvantage that they do not unconditionally follow the applied control signals. The deflection of the OH retainer of the objective lens with the objective lens and the SP coils represents a mechanical excitation and carries, at critical frequency intervals, what is called a resonance peak, as illustrated in FIG. 7 and FIG. 9 by the characteristic response deviations of a profile that is as uniform as possible. Such resonance peaks not only have an unfavorable influence on the regulation characteristic control of the optical scanning device, but also, due to the oscillation in the audible frequency range, also lead to what is called a howling, in a little way. advantageous As a rule, the suppression of the resonance peaks requires additional measures in the provision of the control signals as can be obtained, for example, by equalization for linearization of the response frequency. In order to avoid disadvantageous features and in order to save an additional means for driving the optical scanning devices, an optical scanning device is provided which has improved response characteristic. This is characterized by a retainer plate HP1 as illustrated in FIG. 1, which has cutouts on the surface which hold the supporting elements for the OH retainer of the objective lens at the welding points LP1 ... LP4, cuts which separate the mounting points of the welding points LP1 ... LP4 from each other. The mounting points of the welding points LP1 ... LP4 are designed as isolated surfaces, which are connected via restrictions to the surface with which they are supported. The fact that the resonance peaks are avoided by the retaining plate HP1 designed in this way is rather surprising in the case of the optical scanning system according to the invention, since it is also possible to find the proposed effect using a system of retention corresponding to those of Figure 2 and Figure 3, comprising a first retention plate HPl and a second retention plate HP2. The optical scanning device illustrated in Figures 2 and 3 has a first HPl retainer plate and a second HP2 retainer plate., on which the wires W are supported, which are used as support elements for the OH retainer of the objective lens. The cables in this case form a flexible support for the OH retainer of the objective lens on which the objective lens O and a focusing coil F as well as tracking T coils are placed. The control signals are applied to the focusing coil F or to the tracking coils T, or both, to produce a magnetic field in these coils, magnetic field which interacts with a magnetic field produced by two permanent magnets Ml, M2 to allow that the lens OR objective deviates from its resting position. The wires W that are used as support elements are used to supply the control signals to the focusing coil F and the tracking coils T, and are connected to welding contact zones L with the OH retainer of the objective lens and the first HPl retention plate. The permanent magnets Ml, M2 are fixed on the magnetic reinforcements MSI, MS2 which project at right angles from the base plate G, and the first retaining plate HPl and the second holding plate HP2 are connected via a medium BM of fixing to a reinforcement S, which likewise projects at right angles from the base plate G. The first retaining plate HPl in this case aligned, by means of the bolt openings D01, D02 provided in the first HPl retainer plate, with the corresponding D pins in the second HP2 retainer plate.

In order to assemble the target lens retainer OH with the retention system comprising a first retention plate HPl and a second retention plate HP2, the base plate G and the OH retainer of the objective lens are fixed in a retention device. assembly, and the wires W which connect the retention system to the OH retainer of the objective lens are connected by welding, preferably with the pre-stretched W wires in the welding contact zones L, to the OH retainer of the objective lens and to the first HP plate retention. For this purpose, the wires W are placed over welding contact zones L on the target lens retainer OH and passed through holes D provided in the second retaining plate HP2. Figures 4 to 6 show three views of the second retention plate HP2. In Figures 4 and 5 the holes B are indicated, and have side openings SO corresponding to Figure 5. These side openings SO are provided in order to fill the interspace between the cable W and the second retaining plate HP2 with silicone after W cables have passed through it. The silicone which fills the intermediate space between the cable W and the second retaining plate HP2, in this case acts as a cushioning material, in order to counteract the phenomenon of resonance. A second mounting opening B02 is provided, which is indicated in Figure 5 and which corresponds to the first mounting opening BOl in the first retaining plate HPl, in the second retaining plate HP2 in order to secure the second plate. HP2 retaining the reinforcement S on the base plate G. The first retaining plate HPl is aligned with the second retaining plate HP2 during assembly, by the bolts D indicated in figure 4. In addition, the second retaining plate HP2 it has fixing braces BS which are indicated in figures 4 and 6, and limit the upward deflection of the retainer OH of the objective lens in an advantageous manner. The OH retainer of the objective lens is connected to the retainer system just via the four wires W and then can not be bent in an impermissible range by the action of high acceleration forces, for example those that occur if dropped, reach not permissible, which must avoid the automatic return to the original rest position due to the exceeding of the elastic limit of the system. The second retention plate HP2 in this manner performs numerous functions, which comprise a support for the first retention plate HPl, damping of the cables W and limitation of the deflection of the retention holder OH of the objective lens. Although the oscillations of the OH retainer of the objective lens and the W cables are actually damped by the silicon inserted into the gaps between the cable W and the second retainer plate HP2, it has been found that the response characteristic of the scanning device Optics is significantly altered by the first HPl plate retention. This becomes evident from the measurements that have been carried out, and whose results are shown in figures 7 to 10. Figure 7 shows a frequency response and a phase diagram of an optical scanning device having a HP retention plate known in the direction of focus, which shows the FREQRESP response sensitivity in decibels dB as well as the Phase phase angle in degrees (Deg), logarithmically plotted (Log) against the frequency F in Hertz Hz in a range of up to five kilohertz 5K. The subsequent frequency response and the phase diagrams use an equivalent scale. The diagram, shown in Figure 7 of an optical scanning device having a known HP retention plate shows considerable discrepancies with respect to a uniform profile in the range between 800 and 900 Hz, both in terms of FREQRESP responsive sensitivity as in phase angle terms Phase. It is found that these resonance peaks in an optical scanning device whose construction corresponds to the optical scanning device according to the invention and which is shown in Figures 2 and 3, but with the difference that the known HP retention plate is used as the HPl retention plate. The comparison with the diagram, illustrated in Figure 8 of an optical scanning device having an HPL retention plate according to the invention demonstrates the surprising effect that the unfavorable characteristics are avoided in terms of FREQRESP responsive sensitivity and in Phase phase angle with HPl retention plate under compliant conditions. The scanning device according to the invention and having the characteristics shown in FIG. 8 has an improved response characteristic, since both the frequency response and the phase response have a uniform profile and no resonance peaks occur. . Such an effect occurs not only in the focus direction but also in the tracking direction, as the following diagrams clearly show in Figure 9 and Figure 10. Figure 9 shows the frequency response and the phase diagram of the optical scanning device shown in Figures 2 and 3 having a known HP retainer plate, in the tracking direction and Figure 10 shows the frequency response and the phase diagram of the same optical scanning device having an HPl plate of retention according to the invention, in the tracking direction. Although the assumption has been made that the resonance peaks can be avoided by embedding the wires W in silicone in the second retainer plate HP2, it has been found to be appropriate only to an inadequate degree, since the first HPI retainer plate , according to the invention, shows that only its configuration leads to the desired success. The invention is not limited to the version of the optical scanning device described herein, but is generally applied to optical scanning devices in which the OH retainer of the objective lens is held on an HP retainer plate by support elements.

Claims (5)

1. An optical scanning device having improved response characteristic, comprising an objective lens retainer, which is supported by support elements at mounting points on the surface of a retaining plate, characterized in that, in order to avoid spikes of resonance, a retaining plate is provided which has at least one cutout between each of the mounting points, which separates the mounting points, on the surface which retains the support elements for the lens retainer objective. The optical scanning device, as described in claim 1, characterized in that the support elements of the objective lens retainer and the cables are connected at welding points to the retaining plate, and are connected to welding plates at the lens lens retainer. 3. The optical scanning device having improved response characteristic, comprising an objective lens retainer which is supported on support elements at mounting points on a surface of a retainer plate, wherein the retainer plate is a retaining system which is formed from a first retaining plate and a second retaining plate, characterized in that, in order to avoid resonance peaks, the first retaining plate has at least one cut-out between each of the retention plates. mounting points, which separates the mounting points on the surface which retains the support elements for the objective lens retainer. The optical scanning device, as described in claim 3, characterized in that the second retaining plate has a limiting means in order to avoid any deflection of the objective lens retainer. The optical scanning device, as described in claim 4, characterized in that the limiting means for limiting any deflection of the objective lens retainer are limiting reinforcements on the second retainer plate, which separates the mounting points, on the surface which retains the support elements for the objective lens retainer.