Dynamic magnetic information storage or retrieval – Converting an analog signal to digital form for recording;...
Reexamination Certificate
1998-07-10
2001-04-24
Faber, Alan T. (Department: 2753)
Dynamic magnetic information storage or retrieval
Converting an analog signal to digital form for recording;...
C360S073040, C360S073140, C360S008000, C242S334400, C356S028000, C250S231140
Reexamination Certificate
active
06222690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tape speed sensor which detects a tape travel speed and a phase in a tape recording/reproducing apparatus or the like and which may correct an error signal caused by a deviation inherent in the tape speed sensor itself, a control circuit using this tape speed sensor and a method of controlling a tape speed sensor by using this control circuit.
2. Description of the Prior Art
FIG. 13
is a diagram showing a rotary encoder according to the prior art.
A rotary encoder
1
shown in
FIG. 13
is for use with a tape recording/reproducing apparatus or the like without a capstan, for example, and a rotary shaft
2
of the rotary encoder is rotated as a tape is transported.
The rotary encoder
1
comprises a rotor
3
secured to the rotary shaft
2
and a stator
4
partly opposed to the rotor
3
. The rotor
3
has slits
6
which comprise light-passing areas and light-shielding areas alternately formed on a circumference like a bar code. The stator
4
is shaped as a fan having slits partly defined thereon. The slit
6
may coincide with the slit
5
formed on the stator
4
when the rotor
3
is rotated.
A light-emitting diode (LED), for example, or the like is used as a light-emitting element
7
, and a photodiode (PD) or the like is used as a light receiving element
8
. Light emitted from the light-emitting element
7
is passed through the slits
5
,
6
defined on the rotor
3
and the stator
4
and detected by the light receiving element
8
, thereby being converted into an electrical signal (envelope signal). A rotation speed of a rotor and a phase displacement can be detected by processing this envelope signal with an electrical means not shown. Thus, the tape recording/reproducing apparatus is able to control a running speed, wow or flatter or the like by feeding these detected values back to a reel motor which controls a tape travel.
In the prior-art rotary encoder
1
, since the information indicating that the slits
5
,
6
are opposed to each other (envelope signal) is the representative detected value which results from detecting only a part of the whole of the slits
6
defined on the rotor
3
, the envelope signal is low in signal level and has much noises so that it is not high in accuracy. Also, to increase the accuracy of the envelope signal, assemblies such as slits have to be finished with a high accuracy and also have to be assembled with a high accuracy. In addition, the semiconductor laser (LD) or the PD of high sensitivity is used as a light source to receive light. There is then the problem that the manufacturing cost increases extremely.
Further, when the shafts of the rotor
3
and the rotary shaft
2
are deviated from each other, an eccentricity occurs in the rotation of the rotor
3
. Consequently, the detected value is such one that an error component that the rotary encoder
1
itself contains is superimposed upon the tape running speed and the wow and flatter detected by the rotary encoder
1
.
However, since the conventional rotary encoder
1
cannot eliminate the error component contained in the rotary encoder
1
itself, the rotary encoder cannot obtain a more. accurate speed and cannot reduce the wow and flatter. Also, even when the encoder itself can be manufactured with a high accuracy, the wow and flatter cannot be eliminated completely. Further, even though the tape speed is controlled by directly accelerating or decelerating the rotation speed of the reel motor, the wow and flatter cannot be eliminated from a standpoint of a delay of a responsiveness of a mechanism system or a standpoint of ability of assembly.
Furthermore, in order to solve the above-mentioned problems and to make the rotary encoder
1
become high in accuracy, the prior art attaches importance to the standpoint of the structure and seeks after the finished accuracy of each assembly and the assembly accuracy. There is then a limit upon reduction of the manufacturing cost.
SUMMARY OF THE INVENTION
In view of the aforesaid aspect, it is an object of the present invention to provide a tape speed sensor in which an accurate cycle of an envelope signal can be detected with a high accuracy and a rotation speed and a phase can be detected with a high accuracy by using a trigger signal obtained from the rotation of a rotor as an envelope signal which results from simultaneously detecting information of slits formed on the whole circumferences of the rotor and the stator.
It is another object of the present invention to provide an inexpensive tape speed sensor in which a manufacturing cost can be suppressed without considering a finished accuracy and an assembly accuracy of each assembly of a tape speed sensor from a structure standpoint.
It is a further object of the present invention to provide a control circuit for a tape speed sensor in which an error component contained in a rotary encoder itself can be eliminated electrically.
It is yet a further object of the present invention to provide a tape speed sensor in which wow and flatter can be theoretically eliminated from reproduced data by modulating the reproduced data by an error signal detected from a tape speed sensor and a control method using such control circuit.
According to the present invention, in a tape speed sensor including a rotor whose outer circumferential surface contacts with a running tape and which has a translucent cylindrical portion, a supporting member for pivotally supporting this rotor, a light-emitting element for introducing light into the rotor, slits formed around both of an end face of the rotor and the supporting member opposed to this end face along a circumference direction at a predetermined pitch and a light-receiving element for a rotation speed detection for receiving light passed through the rotor and passed through the slits, the tape speed sensor is characterized in that partial pass bands for partly passing light emitted from the light-emitting element to the outside from the outer peripheral surface of the rotor or non-pass bands for partly shielding light passed to the outside from the outer peripheral surface of the rotor are formed on the rotor and a second light-receiving element for rotation phase detection for detecting light passed through the pass bands or the shielding of light by the non-pass bands is provided on the outer peripheral portion of the rotor.
There is further provided a reflection portion for reflecting light irradiated from the light-emitting element radially from the rotation center side of the rotor and wherein a reflection surface for reflecting radially reflected light in the direction of the slits from the cylindrical portion is formed on the rotor in a peripheral fashion, a part of the peripheral reflection surface formed on the rotor is made as a non-reflection shape and the non-reflection shape portion is formed as the pass band.
There is further provided a reflection portion for radially reflecting light irradiated from the light-emitting element from the rotation center side of the rotor to the cylindrical portion of the rotor and wherein a reflection surface for reflecting the radially reflected light from the cylindrical portion to the slit direction and which passes a part of light is formed on the rotor in a peripheral fashion, a shielding portion for partly shielding light passed through the peripheral reflection surface and which is emitted to the outer peripheral direction is formed on the rotor, and this shielding portion is formed as the non-pass band.
A control circuit using a tape speed sensor comprises a motor servo system for controlling a rotation of a tape by feeding back an output from the tape speed sensor, a PLL loop for generating a control clock from the output from the tape speed sensor, a signal delay unit for delaying a reproduced signal from a head, an A/D converter for A/D-converting a head output signal from the signal delay unit by using the control clock, a memory controller for controlling the A/D-converted digital signal, a memory f
Tanaka Masanobu
Yamashita Tatsumaro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Faber Alan T.
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