Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-03-30
2001-04-17
Hindi, Nabil (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S247100, C369S075110
Reexamination Certificate
active
06219315
ABSTRACT:
PRIOR ART
The invention is based on a method for controlling the focusing and guidance of a light beam as generically defined by the preamble to the main claim. From International Patent Disclosure WO 92/04712, a method is already known in which an optical scanner, whose objective lens focuses a light beam onto a rotating compact disk or CD by means of a focusing control circuit, outputs the data signal to an amplifier. The optical scanner also generates the actual value for a track controller and the actual value for the focus controller. The track controller furnishes a track error signal to the optical scanner, in order to guide the light beam along the data tracks of the CD. The focus controller generates a focus error signal for the optical scanner, in order to focus the light beam onto the disk by means of the objective lens.
ADVANTAGES OF THE INVENTION
The method according to the invention having the characteristics of the main claim has the advantage over the prior art that because of the adaptation of the mechanical oscillation behavior to the capabilities of the applicable control circuit and the suppression of amplitudes that exceed a predetermined value, spring means and damping means can be economized on since vibration of the housing that affects the control devices can be better compensated for. In this way, production and assembly expenses are saved, and the space needed and the weight are reduced.
By means of the provisions recited in the dependent claims, advantageous refinements of and improvements to the method defined by the main claim are possible.
It is especially advantageous that the masses, spring constants and damping values of the scanner, the recording medium, the fundamental substrate, and the at least one housing are selected such that the frequencies at which the amplitudes of the relative motion of the recording medium relative to the scanner and the accelerations acting on the scanner are maximal exceed a value of approximately 60 Hz. In this way, the frequencies at which the amplitudes of the relative motion of the recording medium with respect to the scanner and the accelerations acting on the scanner are maximal are outside a range from 10 Hz to 30 Hz, in which the spectral density of the vibration spectrum is motor vehicles is maximal. Thus the effects on the aforementioned amplitudes and accelerations of the vibration acting on the motor vehicle are reduced considerably.
It is also advantageous to select the time constants of a differentiator in the respective control circuit in such a way that the width of the applicable frequency band for the control is adapted to the frequency range having the maximal values of the amplitudes, and the predetermined stability reserve is adhered to. In this way, the control circuits can also be tuned to the coupled mechanical oscillator, which makes improved resistance to vibration possible.
The use of an integrator in the applicable control circuit whose time constants are selected such that the amplification in the applicable frequency band for the control is increased to a first predetermined value, and the predetermined stability reserve is adhered to is also especially advantageous. In this way, the applicable control deviation can be reduced, above all in the low-frequency range. Since the vibration spectrum has especially high amplitudes at low frequencies, a major improvement in vibration resistance is obtained precisely in this range.
The use of a proportional amplifier with which an increase in amplification and bandwidth of the frequency range for the control, in each case to a second predetermined value, is performed is also advantageous. In this way, the adaptation of the control loops to the coupled mechanical oscillator is improved further, and the control deviation is reduced further, once an amplification resulting in improved resistance to the vibration.
By increasing the amplification at the points in the applicable frequency band for the control where the effects of vibration on the motion of the recording medium relative to the scanner are maximal, the control deviation is advantageously reduced still further in a targeted way by means of an additional amplifier, and thus the resistance to the vibration is further increased. It is also especially advantageous, in the assembly of the coupled oscillator, to not allow a predetermined frequency value to undershoot the natural frequency of the fundamental substrate and/or by the natural frequency of the at least one housing. In this way, the space needed for the oscillations of the fundamental substrate in the at least one housing can be reduced, since the amplitude of oscillation of the fundamental substrate becomes less. As a result, special damping means for damping the fundamental substrate in the at least one housing are no longer necessary, either. Expense, effort, space and weight are thus saved.
Another advantage is obtained by the choice of the natural frequency of components of the coupled mechanical oscillator above 60 Hz. In this way, the frequencies at which the amplitudes of the relative motion of the recording medium with respect to the scanner and the accelerations acting on the scanner are maximal can be placed especially simply in a range that is outside the maximum spectral density of the vibration spectrum.
Another advantage is that a particular predetermined value for the amplification factors, in a frequency range of maximum spectral density of the vibration spectrum, is not undershot; the value is predetermined such that a predetermined control precision of the control circuits is adhered to. In this way, position errors in scanning the recording medium, which result from vibration of the motor vehicle in the range of the maximum spectral density of the vibration spectrum between 10 Hz and 30 Hz, can be better compensated for by the control circuit. The choice of the rotary speed of the recording medium in such that the frequencies of interference signals, which occur because of defects in the recording medium, are located in a frequency range in which in which an intended damping by the applicable control circuit is not undershot is especially advantageous. In this way, it is possible to increase the error tolerance of the reader to defects in the recording medium.
It is especially advantageous to fasten the recording medium between a first and second plate in such a way that its natural frequency is within a predetermined range; a bell-like fastening of the recording medium has proved to be especially favorable. In this way, the motions of the recording medium relative to the scanner that are dictated by the vibration of the at least one housing can be kept especially slight. The resistance to vibration is thus improved still further.
It is also advantageous to use a damping material for the first plate that is flexible at right angles to the plane of the plate. The amplitude of oscillation of the recording medium fastened between the first and second plates is thus reduced, making it easier to control the position of the scanner.
REFERENCES:
patent: 5255254 (1993-10-01), Watanabe et al.
patent: WO 92/04712 (1992-03-01), None
Baas Dieter
Buchs Willy
Cochard Roland
Jeannin Pierre
Hindi Nabil
Robert & Bosch GmbH
Striker Michael J.
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