Tape feed control system

A capstanless tape feed control system of a reel-drive type is capable of accurately detecting the respective working radii of a supply reel and a take-up reel and the total length of the tape, of efficiently controlling tape speed and of preventing damage to the tape. The tape feed control system calculates the working radii of the supply reel and the take-up reel and the total length of the tape while the leading end of the tape is moving toward the take-up reel, and detects tape speed on the basis of data representing the total length of the tape and the radius ratio between the supply reel and the take-up reel. The tension of the tape and the reel driving torque are detected while the tape is being fed and the working radii of the supply reel and the take-up reel are calculated on the basis of the tension and the reel driving torque. A tape loading operation and a tape unloading operation are performed after the leading end of the tape has been pulled out from the take-up reel, with the supply reel being held stationary and a predetermined back tension being applied to the tape by the take-up reel.

BACKGROUND OF THE INVENTION 
The present invention relates to a tape feed control system for use in 
combination with a data recorder for recording and reproducing digital 
data and, more specifically, to a tape feed control system that causes a 
tape to travel directly between a supply reel and a take-up reel. 
Data recorders employing a helical-scan magnetic recording/reproducing 
apparatus using a tape cassette, such as digital audio tapes (DAT) and an 
8 mm video tape cassette, have been used as external storage apparatus for 
computers and the like in recent years. The helical-scan data recorder, as 
compared with a fixed-head data recorder, is capable of operating at a 
high transfer rate and has a large storage capacity. Generally, data 
recorders are provided with a reel motor to feed the tape at an increased 
feed speed to improve the ability for random access and the operability 
thereof. Such data recorders feed a tape using a capstan motor to control 
the tape speed with a high accuracy, when the tape needs to be fed at a 
low tape speed for recording or reproducing, and the tape is driven 
directly by a supply reel motor and a take-up reel motor, when the tape 
needs to be fed at a high tape speed for versing-up or rewinding. The reel 
motors are used for exerting a back tension on the tape, as well as for 
driving the tape for high-speed feed. 
When feeding the tape using a capstan motor, the tape is nipped between a 
capstan connected to the capstan motor and a pinch roller pressed against 
the capstan. Since the radius of the capstan is known, the tape speed is 
controlled with a high accuracy by controlling the rotating speed of the 
capstan motor for constant-speed operation. When controlling the speed of 
the tape driven by the supply reel and the take-up reel, the tape speed 
cannot be regulated at a fixed tape speed by controlling the rotating 
speeds of the reels because the working radii of the reels vary 
continuously. 
A system for controlling tape speed through control of the rotating speed 
of a reel, as disclosed in Japanese Patent Laid-Open No. Hei 4-307449 
(1992), detects the working radius of the reel continuously and regulates 
the product of the working radius of the reel and the rotating speed of 
the same to a fixed value. Systems disclosed in Japanese Patent Laid-Open 
Nos. Hei 2-301053 (1990) and Sho 61-198460 (1986) control the rotating 
speeds of reels so that the sum of the respective squares of the 
rotational periods of the reels is constant, based on the fact that the 
total length of a tape contained in a tape cassette loaded into the tape 
operating device, i.e., the sum of the length of the tape on the supply 
reel and that of the tape on the take-up reel, is fixed regardless of tape 
speed. Although these two systems of controlling tape speed through the 
control of the rotating speeds of the reels use different methods of 
calculation, respectively, to determine tape speed on the basis of the 
total length of the tape and the rotational periods of the reels, these 
two systems are based on the same principle. 
The prior art data recorder needs a tape feed system provided with a 
capstan motor for driving the capstan to feed the tape at a low speed with 
a high accuracy, and two reel motors for driving the reels to exert a back 
tension on the tape and to feed the tape at a high tape speed. The need to 
provide these three motors in the tape feed system is an impediment to the 
miniaturization of the data recorder and to the reduction of the costs of 
the data recorder. 
Efforts have been made for the improvement of the data recorder to increase 
the recording capacity of the tape cassette without increasing the size of 
the tape cassette. These efforts are intended to increase the recording 
capacity by employing short-wave recording techniques and narrow-track 
recording techniques and by reducing the thickness of the tape contained 
in the tape cassette to increase the total length of the tape contained in 
the tape cassette. Tapes having a reduced thickness have a low rigidity 
and are liable to be damaged. Therefore, in an apparatus that nips the 
tape between a capstan and a pinch roller to feed the tape, the 
dimensional accuracies and the assembling accuracy of the capstan and the 
pinch roller must be increased, which increases the costs of the parts of 
the mechanical systems and the manufacturing costs of the apparatus. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
inexpensive tape feed control system to be incorporated into a data 
recorder provided with a helical-scan magnetic recording/reproducing 
system, which is capable of controlling tape speed by using a supply reel 
which are driven and a take-up reel in a wide tape speed range from a low 
tape speed to a high tape speed, and which is reliable in preventing 
damage to the tape and is satisfactory in operability. 
First, the present invention provides a detecting device which is capable 
of quickly and accurately detecting the respective working radii of the 
supply reel and the take-up reel. Secondly, the present invention provides 
a damage preventing device which is capable of preventing damage to the 
thin tape when feeding the thin tape, loading the thin tape and unloading 
the thin tape. Thirdly, the present invention provides a protective device 
which is capable of protecting the tape and of quickly restoring the 
system to a normal condition when the tape feed control system is operated 
erroneously by the operator or when the tape feed control system is 
disconnected abnormally from the power source. 
A tape feed control system in a first aspect of the present invention 
comprises a tape loading completion detecting means for detecting the 
completion of a tape loading operation; a supply reel stopping means for 
stopping the rotation of the supply reel when the completion of the tape 
loading operation is detected; a torque generating means for causing the 
take-up reel to generate a predetermined take-up torque when the 
completion of the tape loading operation is detected; a tape loading means 
for winding the tape around a drum; a rotational angle detecting means for 
detecting the respective angles of rotation of the supply reel and the 
take-up reel; take-up reel radius calculating means for calculating the 
working radius of the take-up reel on the basis of data representing the 
angle of rotation of the take-up reel and a predetermined loading path 
length; a tape rewinding means for rewinding the tape at a tape speed 
corresponding to the calculated working radius of the take-up reel; a 
leading end detecting means for detecting the leading end of the tape; a 
tape feed means for feeding an appropriate length of the tape from the 
supply reel to the take-up reel after the leading end of the tape has been 
detected; a total tape length calculating means for calculating numerical 
data relating to the total length of the tape on the basis of data 
representing the respective angles of rotation of the supply reel and the 
take-up reel detected by the rotational angle detecting means when the 
appropriate length of the tape is fed, and data representing the radius of 
the hub of the take-up reel; a rotational period detecting means for 
detecting the respective rotational periods of the supply reel and the 
take-up reel; a tape speed detecting means for detecting the tape speed on 
the basis of the data representing the total length of the tape and the 
data representing the respective rotational periods of the supply reel and 
the take-up reel; and a tape speed control means for feeding back the 
difference between the detected tape speed and a desired tape speed. 
A tape feed control system in a second aspect of the present invention 
comprises, in addition to the components of the tape feed control system 
in the first aspect of the present invention, a tape tension detecting 
means disposed between the drum and the supply reel to detect the tension 
of the tape; and a tension storage means for storing tension data 
representing a tape tension detected at the start of a tape feeding 
operation for feeding the tape from the leading end of the tape. The tape 
feed control system uses data representing the angles of rotation detected 
by the rotational angle detecting means at a moment in which the 
appropriate length of the tape is fed and when the tension detected by the 
tape tension detecting means is equal to the tension represented by the 
tension data stored in the tension storage means. 
A tape feed control system in a third aspect of the present invention 
comprises a tape tension detecting means disposed between a drum and a 
supply reel to detect the tension of the tape; a torque generating means 
for causing the supply reel to generate a predetermined winding torque; a 
supply reel radius calculating means for calculating the working radius of 
the supply reel using the tape tension data provided by the tension 
detecting means and torque data representing the torque generated by the 
supply reel by the torque generating means; a rotating speed/rotational 
period detecting means for detecting the rotating speed or the rotational 
period of the supply reel; a rotating speed/rotational period detecting 
means for detecting the rotating speed or the rotational period of the 
take-up reel; a radius ratio calculating means for calculating the radius 
ratio between the supply reel and the take-up reel on the basis of data 
representing the rotating speeds or the rotational periods provided by the 
two rotating speed/rotational period detecting means; and a take-up reel 
radius calculating means for calculating the working radius of the take-up 
reel on the basis of the supply reel radius data provided by the supply 
reel radius calculating means and the radius ratio data provided by the 
radius ratio calculating means. 
In the foregoing and the following description, the following definition is 
submitted to avoid any possible misunderstanding of the terms, "supply 
reel" and "take-up reel." The term, "supply reel" designates a reel that 
feeds a tape in the forward direction, and the term, "take-up reel" 
designates a reel that takes up a tape traveling in the forward direction. 
In the tape feed control system in the first aspect of the present 
invention, the tape loading completion detecting means detects whether or 
not a tape has been loaded into the apparatus and provides a tape loading 
start trigger signal upon detection of the loading of a tape. The supply 
reel stopping means holds the supply reel stationary so as to make it 
possible to pull out the tape from only the take-up reel when loading the 
tape. The torque generating means exerts a moderate back tension on the 
tape to prevent the tape from loosening and deviating from a correct path 
when loading the tape. The tape is unwound from only the take-up reel when 
loading the tape for the following reasons. 
The data recorder records management data for managing the recorded data in 
a section near the leading end of the tape and, therefore, access to the 
leading end of the tape must be gained first for versing in recording data 
and reproducing data. Therefore, in the normal tape cassette loading 
operation and in the normal tape cassette ejecting operation, the tape is 
unwound leaving a length of the tape corresponding to a loading path 
length. When the tape is thus unwound, the working radius of the take-up 
reel is substantially equal to the radius of the hub of the take-up reel 
regardless of the length of the tape. Accordingly, the supply reel is held 
stationary, the tape is unwound only from the take-up reel when loading 
the tape, and the take-up reel is made to generate a fixed torque to exert 
a desired back tension on the tape during the tape loading operation so 
that the tape may not be damaged during the tape loading operation. 
The tape loading means winds the tape around a drum mounted with a head. 
The rotational angle detecting means detects the respective angles of 
rotation of the supply reel and the take-up reel. The take-up reel radius 
calculating means calculates the working radius of the take-up reel on the 
basis of the angle of rotation through which the take-up reel is rotated 
for tape loading and the length of the tape unwound for tape loading. The 
tape rewinding means rewinds the tape at a substantially fixed tape speed 
so that the product of the calculated working radius and the rotating 
speed of the take-up reel is constant. The leading end detecting means 
detects an empty state of the take-up reel. The tape feed means feeds an 
appropriate length of the tape from the leading end in the forward 
direction. The total tape length calculating means calculates the working 
radius of the fully loaded supply reel on the basis of the data 
representing the respective angles of rotation of the supply reel and the 
take-up reel, and data representing the radius of the hub of the take-up 
reel, and calculates the total length of the tape on the basis of the data 
representing the respective working radii of the supply reel and the 
take-up reel. 
The total tape length calculating means calculates the working radius of 
the supply reel with reference to a radius of a hub including a very small 
error and is capable of highly accurately calculating the total tape 
length. The rotational period detecting means detects the respective 
rotational periods of the supply reel and the take-up reel including 
information about the radius ratio between the supply reel and the take-up 
reel and information about tape speed during the tape feed operation. The 
tape speed detecting means detects the tape speed on the basis of the data 
representing the total tape length and the data representing the 
respective rotational periods of the supply reel and the take-up reel. The 
tape speed control means compares the detected tape speed and the 
predetermined desired tape speed, and feeds back the difference between 
the detected tape speed and the desired tape speed to the reel motor to 
regulate the tape speed at a fixed tape speed in a feedback control mode. 
Those actions of the components prevent damaging the tape when loading the 
tape, provide data accurately representing the respective radii of the 
supply reel and the take-up reel and the total tape length, and provide a 
highly accurate tape speed control operation. 
The tape feed control system in the second aspect of the present invention, 
when the tape feed control system is provided with a most generally used 
tension sensor that varies the tape path length according to the tension 
of the tape, enables highly accurate calculation of data representing the 
radii of the reels and the total tape length. The tape path length is the 
physical length of a path along which the tape travels from the supply 
reel to the take-up reel. The tape tension detecting means detects the 
tape tension for feedback tension control. The tension storage means 
stores the tension data representing the tension of the tape detected at 
the start of feeding the tape from the leading end of the tape. The total 
tape length calculating means uses the data representing the respective 
angles of rotation of the supply reel and the take-up reel detected by the 
rotational angle detecting means after the appropriate length of the tape 
has been fed and at a moment when the tension of the tape detected by the 
tape tension detecting means is equal to the tension represented by the 
tension data stored in the tension storage means for calculating data 
representing the working radius of the fully loaded supply reel. 
Since the working radius of the supply reel is calculated on an assumption 
that the length of the tape taken up by the take-up reel is equal to the 
length of the tape fed from the supply reel, the length of the tape taken 
up by the take-up reel differs from the length of the tape fed from the 
supply reel when the tape path length varies according to the variation of 
the tension, and hence accurate calculation is impossible. To solve such a 
problem, the calculation is carried out on the basis of data obtained when 
the length of the tape taken up by the take-up reel is equal to the length 
of the tape fed from the supply reel; that is, the data representing the 
angle of rotation of the supply reel and the data representing the angle 
of rotation of the take-up reel are obtained when the tension of the tape 
is equal to the tension represented by the tension data stored in the 
tension storage means so that the calculation will not be affected by the 
variation of the tape path length. 
The tape feed control system in the third aspect of the present invention 
is capable of preventing damaging the tape in an unsteady state. The 
unsteady state is a state in which the data representing the radii of the 
reels or the total tape length is lost during the tape loading operation. 
The unsteady state occurs, for example, when the tape feed control system 
is disconnected accidentally during the tape loading operation due to a 
power failure or an operator's erroneous operation. If a tape unloading 
operation is started immediately after the reconnection of the tape feed 
control system to the power source, an appropriate back tension cannot be 
exerted on the tape because the respective radii of the reels are unknown, 
which is very likely to result in damage to the tape during the unloading 
operation. The third aspect of the present invention determines the 
respective radii of the reels and the total length of the tape without 
loading or unloading the tape when the data representing the radii of the 
reels or the total length of the tape is lost. 
Therefore, in the third aspect of the present invention, the tape tension 
detecting means detects the tension of the tape, and the torque generating 
means causes the supply reel to generate a torque that urges the tape in 
the backward direction. The supply reel radius calculating means 
calculates the working radius of the supply reel by operating the tape 
tension data provided by the tape tension detecting means and torque data 
representing the torque generated by the supply reel made to generate the 
torque by the torque generating means. This calculation is based on the 
fact that the product of the tension of the tape tangentially acting on 
the reel and the working radius of the reel is equal to the driving torque 
of the reel. The radius ratio calculating means for calculating the radius 
ratio between the supply reel and the take-up reel determines the radius 
ratio on the basis of the data representing the respective rotating speeds 
or the respective rotational periods of the supply reel and the take-up 
reel which are provided by the rotating speed/rotational period detecting 
means. The working radius of the take-up reel is calculated on the basis 
of the radius ratio and the working radius of the supply reel. 
Thus, the object of the present invention can be achieved by the foregoing 
configuration and actions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, which shows a tape feed control system forming a 
preferred embodiment according to the present invention, there are shown a 
magnetic tape 1, a supply reel 2, a take-up reel 3, a tape tension pickup 
4 (pin), magnetic heads 5, a drum 6, a supply reel motor 7, a take-up reel 
motor 8, FG sensors 9 and 10 associated with the supply reel 2 
(hereinafter referred to as "SFG sensors"), an FG sensor 11 associated 
with the take-up reel 3 (hereinafter referred to as "TFG sensor"), a 
supply reel motor driver/amplifier 12 (SMDA) for driving the reel motor 7, 
a take-up reel motor driver/amplifier 13 (TMDA) for driving the take-up 
reel motor 8, a rotating direction detector 14, a tension detector 15, an 
FG sensor 16 associated with the drum 6 (hereinafter referred to as "DFG 
sensor"), a PG sensor 17 associated with the drum 6 (hereinafter referred 
to as "DPG sensor"), a drum control circuit 18, a drum motor 19, a supply 
reel period/angle position detector 20 for detecting the rotational period 
and the angle of rotation of the supply reel 2, a take-up reel 
period/angle position detector 21 for detecting the rotational period and 
the angle of rotation of the take-up reel 3, a radius calculator 22, a 
memory 23, a tape tension controller 24, a tape speed controller 25, a 
current detector 26, a supply reel torque controller 27, a take-up reel 
torque controller 28, adders 29 and 30, a system controller 31, a loading 
motor 33, a motor driver/amplifier 32 (MDA) for driving the loading motor 
33, a loading completion detector 34 and a photocoupler 35. The components 
in an area 36 demarcated by the dotted lines constitute a computer or the 
like. 
In FIG. 1, the tape feed control system is in a loaded state. FIG. 2 
typically shows the mechanism of the tape feed control system in the 
loaded state in which the magnetic tape 1 threaded into the tape feed 
control system along a tape loading path. Shown in FIG. 2 are a tape 
cassette 50, guide pins 40, 43, 44 and 47 and guide rollers 41, 42, 45 and 
46 defining a tape loading path, tape guides 48 and 49 included in the 
tape cassette 50, the magnetic tape 1, the supply reel 2, the take-up reel 
3, the tape tension pickup 4 and the drum 6. When the cassette 50 is 
loaded into the tape feed control system, the tape 1 is extended between 
the supply reel 2 and the take-up reel 3 as indicated by dotted line 1', 
and the tension pickup 4, the guide rollers 42 and 45 and the guide pins 
43 and 44 are received in the cassette 50 as indicated by dotted arrows in 
FIG. 2. 
Operations including a cassette loading operation and a tape feed control 
operation will be described hereinafter with reference to FIGS. 1 and 3. 
First, operations to be executed in steps 2 to 7 of FIG. 3 will be 
described. Upon the detection of complete loading of the tape cassette 50, 
the loading completion detector 34 gives a loading completion signal to 
the system controller 31, and then the system controller 31 sends control 
signals to the relevant circuits to start a tape loading operation. The 
supply reel system executes a supply reel restraining control operation, 
in which the supply reel torque controller 27 gives a control signal to 
the SMDA 12 to make the supply reel motor 7 generate a predetermined 
torque. The supply reel motor 7 starts rotating, and the SFG sensors 9 and 
10 generate frequency signals (SFG signals) proportional to the rotating 
speed of the supply reel motor 7. The SFG sensors 9 and 10 are disposed at 
slightly different positions, respectively, relative to the supply reel 
motor 7 so that the phase difference between the two SFG signals is about 
90.degree.. The two SFG signals are supplied to the rotating direction 
detector 14. 
The rotating direction detector 14 detects the rotating direction of the 
supply reel motor 7 from the relation in phase between the two SFG 
signals, and supplies a rotating direction signal indicating the rotating 
direction of the supply reel motor 7 to the system controller 31. Then, 
the system controller 31 recognizes the rotating direction from the 
rotating direction signal and applies a reversing command to the SMDA 12. 
The reversing command does not require the reverse tape feed, but demands 
rotation in a rotating direction reverse to the rotating direction 
detected by the rotating direction detector 14. Consequently, the supply 
reel 2 is rotationally oscillated and is held substantially stationary. 
Since a torque that urges the supply reel 2 in the tape feed direction 
acts on the supply reel 2 when loading the tape 1, the supply reel torque 
controller 27 provides a control signal that makes the supply reel motor 7 
generate a torque that urges the supply reel 2 in the winding direction to 
a greater extent than the torque urging the supply reel 2 in the feed 
direction. 
On the other hand, the take-up reel system operates to exert a 
predetermined back tension on the tape 1. The back tension exerted on the 
tape 1 by the take-up reel 3 is dependent on a back tension control signal 
given by the take-up reel torque controller 28 to the TMDA 1 3. Since it 
is assumed that the take-up reel 3 is virtually empty when loading the 
tape 1, the torque necessary for exerting the predetermined back tension 
on the tape 1 is equal to the product of the predetermined back tension 
and the working radius of the empty take-up reel 3, i.e., the radius of 
the hub of the take-up reel 3. 
The system controller 31 carries out the supply reel restraining operation 
and the back tension control operation, and gives a drive control signal 
to the MDA 32, and then the MDA 32 provides a drive signal to drive the 
loading motor 33 for rotation. The rotation of the loading motor 33 is 
transmitted by a transmission mechanism to a mechanism for shifting the 
guide rollers and the guide pins as indicated by the arrows in FIG. 2 for 
a tape loading operation. The completion of the tape loading operation is 
detected by the loading completion detector 34. 
Since the tape tension pickup 4 remains inoperative during the tape loading 
operation, the tape tension controller 24 does not provide any control 
signal, tape speed control is not executed and hence the tape speed 
controller 25 does not provide any control signal. 
The angle of rotation of the take-up reel 3 during the tape loading 
operation, necessary for the calculation of the working radius of the 
take-up reel 3 at the completion of the tape loading operation, is 
measured by the TFG sensor 11 and the take-up reel period/angle detector 
21. A TFG signal generated by the TFG sensor 11 is a frequency signal 
proportional to the rotating speed of the take-up reel motor 8 and has a 
number of pulses proportional to the angle of rotation of the motor 8. For 
example, when the TFG rate, i.e., the number of TFG pulses for each one 
turn of the take-up reel motor 8, is 720, half the measured TFG pulses is 
the angle (degree) of rotation. The take-up reel period/angle position 
detector 21 counts the number of pulses of the TFG signal and gives data 
representing the angle of rotation of the take-up reel 3 during the tape 
loading operation to the radius calculator 22. The radius calculator 22 
calculates the working radius of the take-up reel 3 at the completion of 
the tape loading operation according to a mode control signal given 
thereto by the system controller 31. 
The working radius of the take-up reel 3 is calculated by using: 
##EQU1## 
where Rt (mm) is the working radius of the take-up reel 3, Ltp (mm) is the 
difference between a path length of the tape 1 indicated by a continuous 
line and a path length of the tape 1' indicated by the dotted line in FIG. 
2, and NTFG (rad) is the angle of rotation of the take-up reel 3 during 
the tape loading operation. The completion of the tape loading operation 
is detected by the loading completion detector 34. 
Steps 8 to 15 shown in FIG. 3 will be described hereinafter. The working 
radius Rt of the take-up reel 3 calculated by the foregoing procedure is 
supplied to the system controller 31. The system controller 31 compares 
the working radius Rt with a predetermined reference radius Rtref. If 
Rt&gt;Rtref, the system controller 31 decides that the length of the tape 1 
on the take-up reel is greater than a predetermined length and provides 
control signals to the relevant components to execute operations in steps 
10 to 15 of FIG. 3 for rewinding the tape 1. If Rt.ltoreq.Rtref, 
operations in steps 16 to 23 of FIG. 3 are executed. 
In steps 10 to 15 of FIG. 3, the working radius Rs of the supply reel 2 and 
the total length S of the tape 1 are calculated for quick reverse tape 
feed, in which the tape 1 is reversed at a high tape speed. When the 
working radii Rt and Rs and the total length S of the tape 1 are known 
(step 9), a high-speed reverse tape feed operation is started immediately. 
The working radius Rs of the supply reel 2 can be determined on the basis 
of the rotational period ratio or the rotation angle ratio between the 
supply reel 2 and the take-up reel 3 when the tape 1 is fed. The tape is 
reversed at a low tape speed. Since the working radius Rs of the supply 
reel 2 and the total length S of the tape 1 are not known at this moment, 
the tape speed and the tension cannot be accurately controlled and, 
therefore, the tape 1 is reversed at a low tape speed. This low-speed 
reverse tape feed is necessary for determining the rotational period ratio 
or the rotation angle ratio between the supply reel 2 and the take-up reel 
3. Therefore, the tape speed controller 25 controls the take-up reel 3 for 
rotation at a fixed rotational period. The tension controller 24 controls 
the supply reel motor 7 in a feedback control mode so that the tension of 
the tape 1 detected by the tension detector 15 coincides with a 
predetermined value. 
Data representing the respective rotational periods or the respective 
angles of rotation of the supply reel 2 and the take-up reel 3 is obtained 
by the period/angle detectors 20 and 21 and is applied to the radius 
calculator 22. The radius calculator 22 calculates the working radius Rs 
of the supply reel 2 by using: 
##EQU2## 
where Tt is the rotational period of the take-up reel 3, Ts is the 
rotational period of the supply reel 2, k is the rotational period ratio, 
which is equivalent to the radius ratio, and Rt is the working radius of 
the take-up reel 3. 
The total length S of the tape 1, which is a reference value dominating the 
tape feed control operation using the reels, is calculated by using: 
EQU S=Rs.sup.2 +Rt.sup.2 (4) 
where Rs is the working radius of the supply reel 2 and Rt is the working 
radius of the take-up reel 3. The calculated total length S is stored in 
the memory 23. 
The relation between the total length S of the tape 1, the tape feed speed 
V, the working radius Rs of the supply reel 2 and the working radius Rt of 
the take-up up reel 3 will be explained hereinafter. The tape feed speed V 
is expressed by: 
##EQU3## 
and the respective working radii Rs and Rt of the supply reel 2 and the 
take-up reel 3 are expressed by: 
##EQU4## 
The tape speed controller 25 calculates the tape feed speed V by using the 
total length S of the tape 1 stored in the memory 23, and the data 
representing the respective rotational periods Ts and Tt of the supply 
reel 2 and the take-up reel 3 and provided by the period/angle detectors 
20 and 21. The same data is used by the radius calculator 22 for 
calculating the respective working radii Rs and Rt of the supply reel 2 
and the take-up reel 3. Thus, the tape feed speed V and the working radii 
Rs and Rt are determined. This data enables a high-speed reverse feed 
operation, and the tape 1 is rewound until the working radius Rt of the 
take-up reel 3 decreases to below the reference radius Rtref. Upon the 
detection of a decrease of the working radius Rt of the take-up reel 3 to 
below the reference radius Rtref, the system controller 31 provides 
control signals to relevant components to execute operations in steps 16 
to 23 of FIG. 3. 
In the reverse feed operation in step 16 and the following steps of FIG. 3, 
the tape 1 is rewound. The photocoupler 35 (FIG. 1) detects the leading 
end of the tape 1. The photocoupler 35 has a light-emitting device and a 
light-sensitive device disposed on the opposite sides, respectively, of 
the tape 1, and detects a transparent leader tape in the leading end of 
the tape 1. The tape 1 is fed forward after the leading end of the tape 1 
has been detected at a low feed speed to calculate the total length S of 
the tape 1 accurately. During the low-speed forward feed operation, the 
take-up reel 3 is controlled so as to rotate at a fixed rotating speed. 
The period/angle position detectors 20 and 21 detect the number of turns 
(=(angle of rotation)/360.degree.) of the supply reel 2 and the take-up 
reel 3 during the low-speed forward feed operation and give data 
representing the number of turns to the radius calculator 22. After a 
predetermined length Lref of the tape 1 has been fed forward, the full 
working radius Rs.sub.0, i.e., the working radius of the full supply reel 
2, is calculated by using: 
##EQU5## 
where ns is the number of turns of the supply reel 2, nt is the number of 
turns of the take-up reel 3, and Td is the thickness of the tape 1. 
Then, the total length S of the tape 1 is calculated on the basis of the 
working radius Rt.sub.0 of the empty take-up reel 3, i.e., the radius of 
the hub of the take-up reel 3, and the working radius Rs.sub.0 of the full 
supply reel 2 by using: 
EQU S=Rt.sub.0.sup.2 +Rs.sub.0.sup.2 (8) 
Since the working radius Rt.sub.0 of the empty take-up reel 3 is 
substantially equal to the radius of the accurately formed hub of the 
take-up reel 3, the total length S can be accurately calculated. Since the 
expression (7) for calculating the working radius Rs.sub.0 of the full 
supply reel 2 does not include any term representing the length of the 
tape 1 fed for determining the total length S, the management of the 
length of the tape fed for the calculation of the total length S may be 
simple. Although tapes contained in cassettes which differ from each other 
in recording capacity have different thicknesses, the thickness of the 
tape 1 can be known from the recognition hole of the cassette. Therefore, 
an accurate thickness Td is used for accurately calculating the working 
radius Rs.sub.0 of the full supply reel 2. 
Data representing a desired speed is set in step 23 of FIG. 3 for 
regulating the sum of the respective squares of the rotational periods of 
the supply reel 2 and the take-up reel 3 at a fixed value when it is 
difficult, in view of the processing ability of the tape feed control 
system, to execute the speed detecting calculation using expression (5) 
continuously for tape speed control. The desired speed data for the sum of 
the respective squares of the rotational periods of the supply reel 2 and 
the take-up reel 3 is calculated by using: 
##EQU6## 
The desired speed data calculating operation need be executed only once 
after the total length S of the tape 1 has been determined, which reduces 
the signal processing load. 
The foregoing control operations are carried out when the cassette 50 is 
loaded into the tape feed control system and the tape 1 is threaded into 
the tape feed control system. Operations for unloading the tape 1 when 
ejecting the cassette 50 from the tape feed control system will be 
described hereinafter. FIG. 4 shows a tape unloading procedure to be 
carried out by the tape feed control system of FIG. 1. In most cases, the 
tape 1 is rewound before unloading. In step 2 of FIG. 4, the leading end 
of the tape 1 is detected prior to the tape unloading operation. After the 
leading end of the tape 1 has been detected, steps 3 to 6 are executed. 
Operations in steps 8 to 10 are executed until the leading end of the tape 
1 is detected. These operations are substantially similar to those in 
steps 8 to 16 of FIG. 3 and hence the detailed description thereof will be 
omitted. When unloading the tape 1, the operations in steps 9 to 12 of 
FIG. 3 are omitted because, in most cases, the data representing the 
working radii of the supply reel 2 and the take-up reel 3 and the total 
length of the tape 1 are known. 
Referring again to FIG. 4, upon detection of the leading end of the tape 1, 
the supply reel 2 is stopped and the take-up reel 3 is controlled so as to 
generate a torque for applying a predetermined back tension to the tape 1. 
Then, the loading motor 33 is driven for reverse rotation to shift the 
guide rollers 42 and 45 and the guide pins 40, 43, 44 and 47 from their 
working positions to their retracted positions in the tape cassette, as 
indicated by the dotted arrows in FIG. 2, while taking up the thus 
slackened tape 1 using the take-up reel 3. Upon detection of the 
completion of the tape unloading operation by the loading completion 
detector 34, a cassette ejecting operation is started. In the tape 
unloading operation and the cassette ejecting operation, the length of the 
tape 1 necessary for the next loading of the tape 1 is wound on the 
take-up reel 3. Therefore, the working radius of the take-up reel 3 
examined in step 3 of FIG. 3 enables step 15 and the following steps of 
FIG. 3 for the accurate calculation of the total length of the tape 1 to 
be quickly started in the next tape loading operation, which facilitates 
the tape loading operation. 
The control of the rotation of the drum 6 provided with the magnetic heads 
5 shown in FIG. 1, i.e., the control of the operation of the drum motor 
19, will be briefly described. Referring to FIG. 1, a drum FG signal (DFG 
signal), i.e., a frequency signal proportional to the rotating speed of 
the drum 6, generated by the DFG sensor 16 and a drum phase signal (DPG 
signal) generated by the DPG sensor 17 and representing the phase of the 
drum 6, are supplied to the drum control circuit 18. The drum control 
circuit 18 determines the period of rotation of the drum 6 from the DFG 
signal, compares the period with a predetermined desired period, generates 
a speed error signal corresponding to the difference between the measured 
period and the desired period, compares the phase of the drum 6 
represented by the DPG signal with a reference phase represented by a 
reference phase signal, and generates a phase error signal corresponding 
to the difference between the measured phase and the reference phase. The 
speed error signal and the phase error signal are added to obtain a 
control signal, which is used for the feedback control of the drum motor 
19 to make the drum 6 rotate at a predetermined rotating speed with a 
correct phase. 
As mentioned above, the take-up reel 3 is substantially empty and the 
working radius of the take-up reel is substantially equal to the radius of 
the hub thereof during the normal cassette loading operation and the 
normal cassette ejecting operation. Therefore, a back tension can be 
applied to the tape 1 during the tape loading operation by holding the 
supply reel 2 stationary, unwinding the tape 1 from only the take-up reel 
3 and making the take-up reel 3 generate a fixed torque, so that the tape 
1 can be prevented from being damaged during the tape loading operation. 
Since the working radius of the full supply reel 2 is calculated on the 
basis of the data representing respective rotating speeds of the supply 
reel 2 and the take-up reel 3 when the leading end of the tape 1 is 
detected, as well as the data representing the radius of the hub of the 
take-up reel 3, and the total length S of the tape 1 is calculated on the 
basis of the data representing the working radius of the supply reel 2 and 
the data representing the radius of the hub of the take-up reel 3, the 
total length S of the tape 1 can be accurately calculated, and hence the 
speed can be accurately detected. 
The tape 1 is searched to determine the leading end during the tape loading 
operation and, if the leading end of the tape 1 has not been rewound from 
the take-up reel 3, the respective working radii of the supply reel 2 and 
the take-up reel 3 and the total length S of the tape 1 are calculated 
temporarily, and then a high-speed reverse feed operation is executed, 
which improves the operability of the tape feed control system. 
A tape feed control system in a second embodiment according to the present 
invention, capable of even more accurately calculating the total length S 
of the tape, will be described hereinafter. The performance of a tape 
tension detector is a factor that introduces errors in calculating the 
total length of the tape. A tension detector as shown in FIG. 5 is used 
prevalently. Shown in FIG. 5 are a tape 1, a tape tension pickup 4, a 
guide pin 40, a guide roller 41, a tension arm 51, a spring 52, a magnet 
53, a magnetic detector 54, such as a magnetoresistance device or a Hall 
device, and a pivot shaft 55. A moment of rotation produced by the spring 
52 connected to one end of the tension arm 51 and a moment of rotation 
produced by the tension of the tape 1 balance each other. The distance 
between the magnet 53 attached to the tension arm 51 and the magnetic 
detector 54 attached to a fixed part under the tension arm 51 varies 
according to the variation of the tension of the tape 1, and the magnetic 
detector 54 provides a tension signal representing the tension of the tape 
1. 
When the tension arm 51 turns on the pivot shaft 55 in response to a 
variation of the tension of the tape 1, the tape path length between the 
guide pin 40 and the guide roller 41 varies accordingly. The same problem, 
i.e. the variation of the tape path length according to the variation of 
the tension, arises even if a potentiometer is used for detecting the 
tension through the detection of the angular position of the tension arm 
51 instead of the combination of the magnet 53 and the magnetic detector 
54. The variation of the tape path length causes a difference between the 
length of the tape 1 taken up by the take-up reel and that of the tape 1 
fed out by the supply reel. Since the expression (7) used for the accurate 
calculation of the working radius of the full supply reel necessary for 
the calculation of the total length of the tape 1 is based on an 
assumption that the length of the tape fed out by the supply reel is equal 
to the length of the tape taken up by the take-up reel, the working radius 
of the full supply reel calculated by using expression (7) includes an 
error as a matter of course when the length of the tape fed out and that 
of the tape taken up are different from each other. To put it differently, 
the length of the tape fed out by the supply reel and that of the tape 
taken up by the take-up reel must be exactly equal to each other for the 
accurate calculation of the working radius of the supply reel. 
In the second embodiment, steps 1 to 7 of FIG. 6 are executed instead of 
steps 18 to 20 of FIG. 3 for the accurate calculation of the total length 
of the tape after the leading end of the tape has been pulled out from the 
take-up reel. Since the same output of the tension detector corresponds to 
the same tape path length, the tape tension controller 24 controls the 
tension of the tape so that the output of the tension detector at the 
start of measurement of the respective numbers of turns of the supply reel 
and the take-up reel and the end of the measurement of the same during the 
low-speed forward feed operation are equal to each other. 
Referring to FIG. 6, in step 1, a tension Tns.sub.0 detected by the tension 
detector 15 (FIG. 1) is transferred through the radius calculator 22 and 
is stored in the memory 23. In steps 2 and 3, a low-speed forward feed 
operation is started and a measurement of the respective numbers of turns 
of the supply reel and the take-up reel is started. Upon the detection of 
the feed of a predetermined length of the tape, the tension of the tape is 
detected and is compared with the tension Tns.sub.0 stored in the memory 
23, and the numbers of turns of the supply reel and the take-up reel at a 
moment when the tension coincides with the tension Tns.sub.0 is recorded. 
When the tension does not coincide with the tension Tns.sub.0, the desired 
tension for the tension controller 24 is changed slightly to adjust the 
tension to the tension Tns.sub.0. 
Thus, accurate data not including any error due to the variation of the 
tape path length, necessary for the accurate calculation of the working 
radius of the full supply reel and the total length of the tape, can be 
obtained in a state where the length of the tape fed out by the supply 
reel and that of the tape taken up by the take-up reel are equal to each 
other. Thus, even if the tape feed control system is provided with an 
ordinary tension detector in which the tape path length varies according 
to the variation of the tape tension, the working radius of the full 
supply reel and the total length of the tape can be accurately calculated 
and, consequently, accurate tape speed control and accurate tension 
control can be achieved. 
A tape feed control system representing a third embodiment according to the 
present invention will be described hereinafter. This tape feed control 
system is capable of preventing damage to the tape in an unsteady state in 
which data representing the respective working radii of the supply reel 
and the take-up reel and/or the data representing the total length of the 
tape is lost due to, for example, an abnormal disconnection of the tape 
feed control system due to a power failure or an operator's faulty 
operation. If the tape unloading operation is started immediately after 
the reconnection of the tape feed control system to the power source, an 
appropriate back tension cannot be applied to the tape because the 
respective working radii of the supply reel and the take-up reel are 
unknown and, consequently, the possibility of damaging the tape during the 
unloading operation increases. The tape feed control system in the third 
embodiment does not execute the tape loading operation or the tape 
unloading operation when the data representing the respective working 
radii of the supply reel and the take-up reel or the data representing the 
total length of the tape is lost accidentally, but measures the respective 
working radii of the supply reel and the take-up reel and the total length 
of the tape. 
Referring to FIG. 7, which shows the operation of the tape feed control 
system in the third embodiment, the output of the loading completion 
detector 34 (FIG. 1) is examined by the system controller 31 in step 3 to 
see whether or not the loading operation for loading the tape cassette 
into the tape feed control system and for loading the tape has been 
completed. If the tape is not loaded or the tape cassette is not loaded 
into the tape feed control system, a normal process A is executed in step 
14 corresponding to step 1 in FIG. 3. If the loading operation has been 
completed, step 4 and the following steps are executed. In step 4, the 
supply reel 2 and the take-up reel 3 are made to generate fixed torques in 
the winding direction to apply a moderate tension to the tape, and a 
tension feedback control system is actuated. Since the respective working 
radii of the supply reel 2 and the take-up reel 3 are unknown at this 
stage, the tensile force applied to the tape by the supply reel 2 and the 
tensile force applied to the tape by the take-up reel 3 do not necessarily 
balance each other and, some times, the tape moves. Therefore, the SFG 
signals indicating the rotating speed of the supply reel 2 and the TFG 
signal indicating the rotating speed of the take-up reel 3 are examined to 
see if the tape is stationary. 
If the tape is moving due to unbalanced tensile forces acting on the tape 
in opposite directions, the respective torques of the supply reel 2 and 
the take-up reel 3 are adjusted to stop the tape because the tape may be 
damaged if the tape moves at this stage. When it is found from the SFG 
signal and the TFG signal that the tape is stationary, operations for 
calculating the respective working radii of the supply reel 2 and the 
take-up reel 3 and the total length of the tape are started. First, the 
tension of the tape and the current supplied to the supply reel motor 7 
are determined from the respective outputs of the tension detector 15 and 
the current detector 26 (FIG. 1) to determine the working radius of the 
supply reel 2. The tension of the tape thus determined is measured at the 
tape tension pickup 4, and is different from the tension of the tape 
measured at a position near the supply reel 2. The ratio between the 
tensions of the tape measured at the tape tension pickup 4 and at the 
position near the supply reel 2 is a known design value dependent on the 
coefficient of friction between the tape and each of the guide pins, and 
the angle of contact between the tape and each of the guide pins. 
Therefore, the tension of the tape at the position near the supply reel 2 
can be determined by correcting the tension measured at the tape tension 
pickup 4. Since the torque constant, i.e., current-torque conversion 
coefficient, of the supply reel motor 7 is known, the torque of the supply 
reel motor 7 is the product of the driving current supplied to the supply 
reel motor 7 and the torque constant. Therefore, the working radius Rs of 
the supply reel can be calculated by using: 
##EQU7## 
where Tns is the tension of the tape at a position near the supply reel 2, 
I is driving current supplied to the supply reel motor 7, and K.tau. is 
the torque constant of the supply reel motor 7. 
Then, steps 10 to 12 of FIG. 7 are executed to determine the rotational 
period ratio between the supply reel 2 and the take-up reel 3 and to 
calculate the working radius Rt of the take-up reel 3 and the total length 
S of the tape. Then, a normal process B is executed in step 13 of FIG. 7. 
Step 13 corresponds to step 8 of FIG. 8. 
Thus, when the data representing the respective working radii of the supply 
reel 2 and the take-up reel 3 or the data representing the total length of 
the tape is lost accidentally during the tape loading operation, the tape 
unloading operation without knowing the working radii of the supply reel 
and the take-up reel is inhibited, and the tape feed control system is 
quickly restored to its normal condition by quickly detecting the 
approximate working radii of the supply reel 2 and the take-up reel 3 and 
the approximate total length of the tape. Accordingly, the reliability in 
preventing damage to the tape and the ease of use are improved. 
Although the invention has been described in terms of the functions of the 
hardware forming the tape feed control system, the tape feed control 
system need not necessarily be an assembly of those individual component 
parts, and the functions of those individual component parts may be 
replaced by software that is executed by a microcomputer having the 
functions of, for example, the component parts included in the area 36 
demarcated by dotted lines in FIG. 1. Although the foregoing embodiments 
operate to hold the supply reel stationary in an entirely electrical 
feedback control mode during the loading operation or the unloading 
operation, the supply reel may be held stationary by a mechanical braking 
mechanism. 
As is apparent from the foregoing description, the present invention 
provides an inexpensive tape feed control system to be incorporated into a 
data recorder provided with a helical-scan magnetic recording/reproducing 
system, which is capable of highly accurately controlling tape speed by 
using a supply reel and a take-up reel capable of operating in a wide tape 
speed range from a low tape speed to a high tape speed, which is reliable 
in preventing damage to the tape and which is satisfactory in operation, 
without employing a capstan driving system. First, the present invention 
is capable of quickly and accurately detecting the respective working 
radii of the supply reel and the take-up reel to accurately control tape 
speed. Secondly, the present invention is capable of preventing damage to 
the thin tape when feeding the thin tape, loading the thin tape and 
unloading the thin tape. Thirdly, the present invention is capable of 
protecting the tape and of quickly restoring the system to a normal 
condition when the tape feed control system is operated erroneously by the 
operator or when the tape feed control system is disconnected abnormally 
from the power source.