In apparatus for sensing information recorded on a medium in the form of lateral displacements along the length of at least one of the boundaries between an elongate zone of said medium having particular properties with respect to reflecting light radiations and regions of said medium laterally adjacent said zone having different properties than said zone with respect to reflecting light radiations, wherein said apparatus includes:
- pickup means, including means for directing light radiations along a transmission path, means for receiving light radiations along a collection path, and means for mounting said directing means and said receiving means in positions relative to each other for angularly converging intersection of said transmission and collection paths, said intersection defining a locale in spaced relationship to said pickup means within which substantially optimized reflection of light radiations from said transmission path to said collection path can occur;
- support means for respectively supporting said pickup means and said medium for relative movement therebetween, said pickup means and said medium being relatively movable in a translational sense along the length of said zone of said medium for directing light radiations in said transmission path successively toward a plurality of portions of said medium disposed along the length of said zone and each including a longitudinal stretch of said zone and parts of said regions laterally adjacent to said stretch, said pickup means and said medium also being relatively movable in a spacing sense toward and away from each other for altering the positioning of said locale relative to coincidence with the portion of said medium toward which light radiations in said transmission path are being directed, said pickup means and said medium also being relatively movable in a tracking sense transversely to the length of said zone of said medium for altering the positioning of said portion of said medium toward which light radiations in said transmission path are being directed relative to laterally centered relationship with said zone of said medium;
- drive means operably coupled with said support means for producing relative movement between said pickup means and said medium in said translational sense along the length of said zone of said medium;
- spacing adjusting means operably coupled with said support means for producing relative movement between said pickup means and said medium in said spacing sense toward or away from each other;
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- tracking adjusting means operably coupled with said support means for producing relative movement between said pickup means and said medium in said tracking sense transversely to the length of said zone of said medium;
- the improvement of which apparatus comprises means for controlling the spacing and tracking of said pickup means relative to said medium without any necessity for mechanical engagement between relatively moving parts of said apparatus and said medium, said controlling means including:
- spacing sensing means operably associated with said receiving means, responsive to light radiations and disposed to receive a first pair of components of light radiations being reflected along said collection path from different sections of said portion of said medium toward which light radiations in said transmission path are being directed for producing spacing signals corresponding in a predetermined manner to said first pair of light radiation components being respectively reflected from said sections of said portion of said medium, said spacing sensing means including a pair of spacing sensors, said first pair of components of light radiations received by said spacing sensing means being respectively reflected along said collection path from a pair of sections of said portion of said medium toward which said radiations in said transmission path are directed that are offset from each other in the general direction of the length of said zone of said medium and being respectively applied to said spacing sensors;
- a first pair of angularly offset mirrors in operable association with said collection path disposed for separating said first pair of radiation components reflected from said sections from each other and further reflecting the same respectively toward said spacing sensors;
- means for operably coupling said spacing sensing means with said spacing adjusting means for operating the latter in accordance with said spacing signals to relatively move said pickup means and said medium in said spacing sense toward and away from each other as required to maintain said locale within which substantially optimized reflection of light radiations from said transmission path to said collection path can occur in substantial coincidence with said portion of said medium toward which light radiations in said transmission path are being directed;
- tracking sensing means operably associated with said receiving means, responsive to light radiations and disposed to receive a second pair of components of light radiations being reflected along said collection path from different segments of said portion of said medium toward which light radiations in said transmission path are being directed for producing tracking signals corresponding in a predetermined way to said second pair of light radiation components being respectively reflected from said segments of said portion of said medium, said tracking sensing means including a pair of tracking sensors, said second pair of components of light radiations received by said tracking sensing means being respectively reflected along said collection path from a pair of segments of said portion of said medium toward which said radiations in said transmission path are directed that are offset from each other in a direction generally transverse to the length of said zone of said medium and being respectively applied to said tracking sensors;
- means for operably coupling said tracking sensing means with said tracking adjusting means for operating the latter in accordance with said tracking signals to relatively move said pickup means and said medium in said tracking sense transversely to the length of said zone of said medium as required to maintain the positioning of said portion of said medium toward which light radiations in said transmission path are being directed in substantially laterally centered relationship with said zone of said medium;
- a second pair of angularly offset mirrors in operable association with said collection path disposed for separating said second pair of radiation components reflected from said segments from each other and further reflecting the same respectively toward said tracking sensors;
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- information sensing means operably associated with said receiving means, responsive to light radiations and disposed to receive at least a third component of light radiations being reflected along said collection path from at least one part of said portion of said medium toward which light radiations in said transmission path are being directed for producing information signals corresponding in a predetermined fashion to said recorded information to be sensed from said medium.