Pneumatic-photoelectric transducer in a magnetic tape unit

Claim 2

A pneumatically responsive photoelectric transducer for use with the pneumatic buffer of a web transport to provide an electrical output signal indicating the position of the web loop in the buffer, the transducer comprising: a closed housing having a cavity including a generally flat wall and an oppositely disposed curved wall, a first air-flow port connecting the flat wall of said cavity to ambient pressure, a second air-flow port connecting the curved wall of said cavity to a wall of said buffer which selectively communicates with ambient pressure on one side of the web loop or a differential pressure on the opposite side of the web loop, in accordance with the position of the loop, a flat, air-impervious movable member in saiD cavity and movable from a preferred flat position adjacent said first port to an unstable curved position adjacent said second port when the position of the web loop establishes a pressure differential at said second port, said member when in said unstable position substantially sealing said second port to thereby restrict airflow through said housing, and a photoelectric couple controlled in accordance with the position of said member to provide an output signal indicating the position of the web loop.

Claim 3

A transducer as defined in claim 1 wherein at least a portion of said member includes a light-reflective surface, and means including said surface completing said photoelectric couple only when said member is in one of its two positions.

Claim 4

A transducer as defined in claim 1 wherein said differential pressure is established by a vacuum force which pulls said web into said buffer to form a loop therein and said member is forced into said unstable curved position adjacent said second port when said second port is subjected to the vacuum force below said loop.

Claim 5

A transducer as defined in claim 3 wherein said movable member includes a reflective surface, and wherein said reflective surface is operable to complete said photoelectric couple only when said member is in said curved position.

Claim 6

In a magnetic tape unit having at least one pneumatic column buffer which buffers a variable length loop of magnetic recording tape as the tape travels between a reel and a tape processing station, an improved transducer for sensing the length of the tape loop in the buffer and servo controlling the rotation of said reel, comprising: a housing including a closed cavity having a generally flat wall and an oppositely disposed curved wall, first air-flow means continuously connecting said flat wall to ambient pressure, second air-flow means connecting said curved wall to a wall of said buffer which communicates with ambient pressure on one side of the tape loop and a differential pressure on the opposite side of the tape loop, in accordance with the length of the loop, a flat, flexible air-impervious movable member positioned in said cavity in a manner to be moved from a stable flat position adjacent said first air-flow means to an unstable curved position conforming to said curved wall adjacent said second air-flow means and closing the same to substantially prevent airflow through said housing when the length of the tape loop establishes a negative pressure differential at said second air-flow means, a photoelectric couple including at least a portion of said member controlled in accordance with the length of the tape loop, and reel control servo means controlled by said photoelectric couple.

Claim 7

In a magnetic tape unit having at least one pneumatic column buffer which buffers a variable length loop of magnetic recording tape as the tape travels between a reel and a tape processing station, an improved transducer for sensing the length of the tape loop in the buffer and servo controlling the rotation of said reel, comprising: a housing including a closed cavity having a generally flat wall and an oppositely disposed curved wall, first air-flow means continuously connecting said flat wall to ambient pressure, second air-flow means connecting said curved wall to a wall of said buffer which communicates with ambient pressure on one side of the tape loop and a differential pressure on the opposite side of the tape loop, in accordance with the length of the loop, a flat, flexible air-impervious movable member positioned in said cavity in a manner to be moved from a stable flat position adjacent said first air-flow means to an unstable curved position conforming to said curved wall adjacent said second air-flow means and closing the same to substantially prevent airflow through said housing when the length of the tape loop establishes a negative pressure differential at said second air-flow means, a photoelectric couple including at least a portion of said member controlled in accordance with the length of the tape loop, and reel control servo means controlled by said photoelectric couple.

Claim 8

A magnetic tape unit as defined in claim 5 wherein, said buffer includes at least one opaque wall and at least one transparent wall, and said second air-flow means is connected to the opaque wall of said buffer.

Claim 9

A magnetic tape unit as defined in claim 6 wherein, said buffer is connected to a vacuum source to thereby maintain an extended tape loop by virtue of vacuum force, and said housing is opaque said first cavity wall is a generally flat wall and said second cavity wall is a generally curved wall, said movable member is a thin flexible member having a stable flat condition when adjacent said first air-flow means, and being forced to assume an unstable curved position by vacuum pressure at said second air-flow means, in accordance with the length of the tape loop.

Claim 10

A magnetic tape unit as defined in claim 5 wherein, at least a portion of the surface of said movable member which faces said curved wall is a reflective surface, said photoelectric couple includes light source means and photocell means mounted in noncommunicating relation at said curved wall, and said movable member when in said unstable position effects communication between said light source means and said photOcell means by virtue of said reflective surface.

Claim 11

A magnetic tape unit as defined in claim 8 wherein, the portion of said curved cavity wall which supports said movable member at said unstable position includes a recessed surface such that said movable member is supported without physical contact to that portion of said reflective surface which is relied upon to effect said communication between said light source means and said photocell means.