Elasto-optic device for spot wobble in a video disc player

• US 3,985,952 A
• Filed: 01/27/1975
• Issued: 10/12/1976
• Est. Priority Date: 02/04/1974
• Status: Expired due to Term

• Current Assignee: Zenith Radio Corporation (LG Corporation)
• Original Assignee: Zenith Radio Corporation (LG Corporation)
• Inventors: Adler, Robert
• Primary Examiner(s): Konick, Bernard
• Assistant Examiner(s): Faber, Alan
• Application Number:
  US05/544,250
• Time in Patent Office: 624 Days
• Field of Search: 178/6.6 R, 178/6.6 DD, 178/6.7 A, 179/100.3 B, 179/100.3 V, 250/235, 250/202, 350/6, 350/161, 350/285, 360/77, 340/173 LS
• US Class Current: 369/44.13
• CPC Class Codes: G02F 1/0128 based on electro-mechanical, magneto-mechanical, elasto-optic effects
• CPC Class Codes: G11B 7/09 with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
• CPC Class Codes: G11B 7/0953 to compensate for eccentricity of the disc or disc tracks

Abstract

An elasto-optic device for providing periodic lateral displacement in a radial tracking servo system for a video disc player. A transparent prism is vibrated in either a flexural or a second harmonic extensional mode by a thin piezoelectric ceramic platelet attached to a side of the prism and energized by an oscillatory signal. Vibration occurs at a natural mechanical resonant frequency of the prism, and a linear strain distribution is established in the prism at its intersection with the path of the optical beam used for reading the record track. The substantially linear strain distribution effects a corresponding localized periodic change in the index of refraction of the prism material to provide lateral optical beam deflection without the use of moving parts.

Claims

1. A radial tracking servo system for an optical-pickup video disc player of the type comprising means for producing a light beam and means for causing said beam to read a record track on a rotating record disc, which servo system comprises:

an elasto-optic light beam deflector including a transparent prism interposed in the path of said beam and an electromechanical transducer mechanically coupled to said prism and adapted to establish vibration therein in a mechanically resonant vibration mode;

a reference signal oscillator including said elasto-optic light beam deflector as its frequency-determining element, for causing periodic lateral deflection of said light beam relative to said record track;

means including a photoreceptor responsive to said light beam for developing an output signal including an amplitude modulation component representative of deviations of said periodically laterally deflected light beam from a centered relationship to said record track;

a quadrature phase corrector coupled to said reference signal oscillator for developing a phase-shifted reference signal;

means coupled to said photoreceptor for deriving said amplitude modulation component;

and a synchronous detector coupled to said phase corrector and to said last-mentioned means and responsive to said phase-shifted reference signal and to said amplitude modulation component for developing a radial tracking error correction signal.

2. A radial tracking servo system according to claim 1, in which said vibration mode is a flexural mode and the frequency of said vibration is substantially equal to 1.024 V_ext (W/L²), where V_ext is the velocity of extensional acoustic waves in the material of said prism, and L and W are the length and width, respectively, of said prism in a plane perpendicular to said beam path.

3. An elasto-optic device according to claim 2, in which said electromechanical transducer comprises a thin platelet of piezoelectric ceramic material attached to one side of said prism on a face parallel to and in a location substantially centered with respect to said beam path.