Dynamic information storage or retrieval – With servo positioning of transducer assembly over track...
Patent
1986-11-04
1988-12-27
Richardson, Robert L.
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
360 7702, 369 44, G11B 700
Patent
active
047945796
DESCRIPTION:
BRIEF SUMMARY
The invention concerns circuitry for an audio or video disk player in accordance with the preamble to Claim 1.
Carrying out the requisite servo track readjustment by means of coarse-drive and precision-drive mechanisms, whereby the coarse-drive mechanism is always activated once and briefly once a prescribed threshold attained by integration of a radial error signal has been attained, is known for a track-guidance system for players for playing back audio and/or video disks. The function of the precision-drive mechanism is to rapidly control radial fluctuations in the track up to specific amplitudes.
Since the transducers in precision-drive mechanisms have characteristics that differ due to manufacturing tolerances, it is absolutely necessary in order to avoid errors in scanning to position the operating point of the particular precision-drive mechanism in the linear vicinity of the transmission curve. Known precision-drive mechanisms that integrate the radial error signal to activate the coarse-drive mechanism, however, involve the drawback that the operating point can migrate when the audio or video disk has different radial eccentricities.
The object of the invention is to provide a circuit wherein the optimum operating point of the radial precision-drive mechanism will be maintained while taking the various amplitudes of the radial eccentricity into consideration.
This object is attained by the invention recited in claim 1. Practical embodiments and developments of the invention are recited in the subsidiary claims.
The invention will now be specified with reference to the drawings, wherein
FIG. 1 shows the transmission curves of a known precision-drive mechanism,
FIG. 2 shows the effects of radial eccentricity on the operating point,
FIG. 3a illustrates a threshold device in the form of a comparator,
FIG. 3b shows a radial-error signal without guidance for the coarse-drive system,
FIG. 3c shows the corresponding sequence of pulses at the computer output terminal, and
FIG. 4 illustrates the control circuitry for a coarse-drive system by way of example.
FIG. 1 shows by way of example of a typical precision-drive mechanism the curve v=f(u), whereby v is the amplitude of motion and u is the voltage at the precision-drive mechanism. Due to the non-linearity of curve v=f(u), operating point A must not be selected at U=0 in this precision-drive mechanism. Unobjectionable scanning cannot occur until U=U.sub.1.
FIG. 2 shows the effect of a displacement of the operating point. In precision-drive systems with a threshold-detector circuit and a threshold S as specified in the applicants' own Application No. P 35 08 422.7 (T-PA 522) different radial-eccentricity amplitudes have the drawback of displacing operating point A. With small radial eccentricities X.sub.A operating point A(X.sub.A) is displaced only slightly, whereas the displacement is extensive with large radial eccentricities X.sub.b.
FIG. 3a illustrates the system for activating a coarse-drive mechanism 3 with a comparator 10 as threshold detector known from No. P 35 08 422.7 (T-PA 522). A radial-error signal U.sub.R is supplied by input terminal 8 through an RC stage 12 and 13 to the non-inverting input terminal of a comparator 10. The inverting input terminal of comparator 10 is connected to reference-voltage level by an adjustable resistor 11 that controls the threshold of comparator 10. When the threshold of comparator 10 is exceeded, the output signal U.sub.K from comparator 10 starts coarse-drive mechanism 3 up through an operational amplifier 14, and the mechanism immediately starts moving due to the complete operational voltage derived from amplifier 14. The coarse-drive mechanism continues rotating until radial-error signal U.sub.R drops below the threshold of comparator 10.
FIG. 3b illustrates radial-error signal U.sub.R at the input terminal of comparator 10 for a situation in which coarse-drive mechanism 3 is to be prevented from moving. A track advance delivered by precision-drive mechanism 2 occasions a slow increase in radial-error signa
REFERENCES:
patent: 4142209 (1979-02-01), Hedlund et al.
patent: 4658389 (1987-04-01), Kuehn
patent: 4703467 (1987-10-01), Elliott
Deutsche Thomson-Brandt GmbH
Fogiel Max
Richardson Robert L.
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