Optical: systems and elements – Optical modulator – Light wave directional modulation
Reexamination Certificate
2002-04-25
2003-09-16
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave directional modulation
C359S814000, C359S813000, C359S822000, C369S044150, C369S044220
Reexamination Certificate
active
06621618
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an optical scanning device for apparatuses for recording and/or reproducing information on optical recording media, which is suitable in particular for recording and/or reproducing information at high speed, such as, for example, the scanning of a DVD at a twelve-fold speed.
Optical scanning devices for recording media in laser disc and compact disc players are generally known. The design and function of such scanning devices, also referred to as pick-up, are described in Electronic Components & Applications, Vol. 6, No. 4, 1984, pages 209-215. Such scanning devices have a so-called actuator on which there is arranged an objective lens which is provided for tracking and for focusing the light beam or laser beam on the optical recording medium. In principle, optical scanning devices can be distinguished by the way in which the objective lens is suspended. Thus, the objective lens mount is fastened to a frame for example by means of four parallel leaf springs in the case of a known leaf-spring actuator or via articulated joints or hinges in the case of an actuator of the articulated-joint or hinge type, respectively. Disadvantages are that such arrangements have an undesirable tendency to oscillate, require a high level of assembly complexity and have relatively high reaction times inter alia due to the mass to be moved. A further way of elastically supporting the objective lens mount is to use four wires which connect the lens holder to the actuator baseplate. In comparison with optical scanning devices with a leaf spring or articulated joint, so-called wire pick-ups can be produced more cost-effectively and allow shorter access times. However, they are particularly sensitive relative to other parallel guides with regard to resonance phenomena, tilting of the objective lens and thermal loads. On the other hand, in particular for high-speed applications and in order to achieve short access times, high currents are necessary in the track and focus coils, which currents heat the lens holder and lead to undesirable oscillation of the lens holder and to tilting of the objective lens. The scanning of optical recording media at a multiple of the speed which is necessary for reading or recording on an audio, video or data CD or DVD at single speed increases the requirements made of optical scanning devices with regard to uniformity of the response characteristic. The frequency response and phase angle of the optical scanning device should have as uniform a profile as possible over a wide frequency range and not be disturbed by free oscillations. It is demanded, for example, that resonance phenomena occur only above 40 kilohertz and they have a level reduction or attenuation of 45 decibels in comparison with attenuation at a frequency of 1 kilohertz, in order to be able to scan a DVD at a twelve-fold speed.
SUMMARY OF THE INVENTION
The object of the invention is to provide an optical scanning device for optical recording media which to the greatest possible extent avoids the disadvantages of known optical scanning devices with regard to oscillation properties, speed and thermal load ability, meets the requirements in the course of reading or recording at high speed and can be produced with a low degree of complexity.
This object is achieved by means of features which are specified in the main claims. Advantageous designs and developments are specified in subclaims.
One aspect of the invention involves avoiding to the greatest possible extent the disadvantages of so-called wire pick-ups relative to other parallel guides with regard to tilting of the objective lens, asymmetrical guidance properties, natural resonance behaviour and thermal load ability for high-speed applications, and nevertheless producing the optical scanning device with a low degree of complexity.
To that end, an optical scanning device for high-speed applications is provided which has a lens holder which is formed by a hollow body and whose side walls are arranged such that they run at an angle to a connecting point with its elastic support. The lens holder has a hexagonal form which is formed with the side walls which run at an angle to a connecting point with its elastic support. As a result of the hexagonal shape of the lens holder, air chambers are formed between lens and coils of the actuator, the distance between lens and coils of the actuator is enlarged and the stability or rigidity of the lens holder formed by a hollow body is increased. For this purpose, the side walls or side areas of the lens holder are preferably arranged such that they deviate at an angle of from 3 to 10 degrees from a straight line. The angle at which the side walls of the lens holder are arranged with respect to one another is chosen in such a way that, in the event of maximum deflection of the lens holder from its neutral position, contact occurs neither before nor after the connecting point with the wires which support it.
The lens holder formed by a hollow body is of integral design and preferably constructed symmetrically. The configuration as hollow body with air chambers further improves the thermal properties of the optical scanning device since additional cooling and heat dissipation are achieved by actuator movements. Moreover, the heat dissipation can be increased further by giving the surface of the lens holder a dark configuration. Furthermore, the wires which elastically support the lens holder are arranged at an angle which, in the neutral position of the lens holder, deviates by more than two degrees from a perpendicular to the lens holder, in order to ensure little or no tilting of the lens over the entire deflection range of the actuator for tracking. With the angle, a change is made to the rigidity of the support of the actuator on its baseplate and, as a result, also to the resonance behaviour in a targeted manner for a direction of action. By virtue of the angle at which the wires which elastically support the lens holder for tracking are brought up to the lens holder, there is an advantageous influence both on the guidance properties in the event of deflection of the lens for the purpose of following the recording track, on account of the lens tilting to a lesser extent, and on the natural resonance behaviour of the optical scanning device. Since the ends of the wires, which ends project freely beyond the connecting point with the lens holder, may, as a result of the mounting process or during separation, deviate from the original direction in which they were brought up to the lens holder, the side walls of the lens holder are arranged at an angle which is preferably greater than or equal to the angle at which the wires are brought up to the lens -holder in its neutral position. The wires which elastically support the lens holder for tracking on the baseplate are brought up to the lens holder in punctiform fashion. This enlarges the lateral distance between wire and lens holder in the vicinity of the soldering or connection point, with the result that, on the one hand, the process of bringing up the wires is facilitated and, on the other hand, an adverse effect on the guidance properties which is based on burr on the parts or on residues of soldering agent is avoided. Furthermore, it may be assumed that reduced resonance phenomena deep into the kilohertz range can also be attributed to the fact that oscillations proceeding from the lens holder are prevented from propagating by the angle between wire and side wall of the lens holder.
The side walls which are arranged at an angle to one another have the effect of achieving, despite a compact structure of the lens holder, a larger distance between the lens and the windings, which are heated by high currents in high-speed applications.
A depression for accommodating the focus coil is provided in the side walls of the lens holder, the said depression forming webs on which there is fixed, after the application of the focus coil, a circuit board, preferably formed by a printed circuit board. The circuit board advantageo
Kaaden Jürgen
Oldermann Klaus
Suzuki Tsuneo
Davenport Francis A.
Fried Harvey D.
Thompson Tim
Thomson Licensing S. A.
Tripoli Joseph S.
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