Constant tape speed controller

An apparatus and method are disclosed for advancing a tape at a constant, high speed. Two detectors are provided for detecting values representative of the rotational periods of the reels at both low and high tape advance speeds. A calculator is included for determining particular arithmetic functions of these values. A comparator is also provided, which has a memory for storing a parameter dependent on a particular arithmetic function of values representative of low speed rotational periods of the reels. The comparator is provided for comparing the results of a particular arithmetic function of values representative of high speed rotational periods of the reels with the parameter and for outputting an error signal for adjusting the tape advance speed to maintain a constant, high speed.

FIELD OF THE INVENTION 
The present invention relates to a device for controlling the travel speed 
of a tape, such as within a magnetic tape recorder/playback device during 
a high speed search or fast feed. 
BACKGROUND OF THE INVENTION 
A conventional tape transport device, such as the tape transport device 
used in a magnetic tape recorder/player 10, is schematically depicted in 
FIG. 1. Tape 11, which is supplied from a supply reel 12, is fed between a 
capstan 13 and pinch roller 14 assembly to a take up reel 15. In the 
operation of the recorder/player, the tape 11 is fed at varying speeds 
between the reels 12, 15. For normal speeds, and speeds up to 
approximately twenty times normal, the tape 11 is advanced by a capstan 
motor 16 connected to the capstan-pinch roller assembly 13-14. Such speeds 
are considered low operating speeds. 
When using the capstan-pinch roller assembly 13-14 to advance the tape 11, 
the tape speed remains relatively constant. When it is desired to advance 
the tape 11 at a high speed, such as 100 to 200 times the normal speed, 
the capstan-pinch roller assembly 13-14 is not used. Rather, the tape 11 
is typically advanced at high speeds by a drive mechanism connected to one 
of the reels 12 or 15. 
In the prior art, the tape advance rate at high speeds was kept constant by 
maintaining a certain relationship between the rotational periods of the 
supply and take-up reels. In FIG. 2, a cross-sectional segment of the tape 
11 is shown having a thickness t. The tape itself has a total length L and 
L&gt;&gt;t. Assuming that the length L and thickness t are uniform and 
unchanging in FIG. 1, the tape has a fixed cross-sectional area of Lt. 
Further, this area must be constant at any given moment regardless of how 
much tape is wound on each reel. If at a particular moment, the outer 
radius of the supply reel is r.sub.S and the outer radius of the take up 
reel is r.sub.T (each reel having a minimum inner radius of r), then the 
following equation relates the areas of tape on each reel to the total 
cross-sectional area: 
EQU .pi.(r.sub.T.sup.2 -r.sup.2)+.pi.(r.sub.S.sup.2 -r.sup.2)=Lt(1) 
because the amount of tape between the reels is negligible. Further, if the 
rotational period of the take-up and supply reels are represented by 
T.sub.T and T.sub.S, respectively, then the following relationship is also 
true: 
##EQU1## 
where V.sub.T is the tape speed. Equations (1) and (2) can be combined to 
yield: 
##EQU2## 
An examination of the right hand side of equation (3) reveals that only 
the terms in the denominator vary as tape is transported from one reel to 
another. Hence, the prior art attempted to maintain the constancy of the 
high speed tape advance by maintaining a constant relationship between the 
sum of the squares of the rotational periods or the sum of the rotational 
periods of the reels. 
This solution proves problematic for the conventional tape player/recorder. 
As noted above, the speed of a particular tape is a function of both the 
thickness and length (e.g., 30, 60 90, 120, etc. minutes) of the tape. 
Since a conventional tape player/recorder accepts tapes with varying 
lengths and thicknesses, the constancy of higher advance speeds cannot 
easily be maintained universally for all tapes. 
It is therefore an object of the present invention to provide a high speed 
controller which maintains the tape advance at a constant rate. It is a 
further object to provide a constant tape speed controller which uniformly 
maintains a constant tape speed regardless of the length or thickness of 
the tape used in the playback/recorder. 
SUMMARY OF THE INVENTION 
These and other objects are achieved by the present invention which 
provides an apparatus and method for advancing a tape from a supply reel 
to a take-up reel at a constant high tape advance speed. First and second 
detectors are respectively connected to the supply and take-up reels for 
detecting a value representative of the rotational period of each reel. A 
calculator is provided for computing particular arithmetic functions of 
those detected values at both low and high tape advance speeds. The 
invention also has a comparator connected to the calculator. The 
comparator has a memory for storing a parameter dependent on a particular 
arithmetic function of the values which are representative of the detected 
low speed rotational periods. The comparator is provided for comparing the 
results of a particular arithmetic function of the values representative 
of the detected high speed rotational periods with the parameter. The 
comparator is also used for outputting an error signal for adjusting the 
tape advance speed in order to maintain a constant, high tape advance 
speed. 
In accordance with the invention, the parameter may illustratively be 
determined from equation (3). For a tape of any thickness, an arbitrary 
tape speed V.sub.T is related to the take-up reel and supply reel 
rotational periods by equation (3). A ratio V.sub.H.sup.* /V.sub.L may be 
formed between a low tape speed, represented by V.sub.L, and a desired 
high tape speed, represented by V.sub.H.sup.*. Substituting equation (3) 
into this ratio, the following relates the low speed take-up and supply 
rotational periods, represented by T.sub.LT and T.sub.LS to the desired 
high speed take-up and supply rotational periods, represented by 
T.sub.HT.sup.* and T.sub.HS.sup.* : 
##EQU3## 
This relationship may be used to determine the parameter which 
illustratively may be set equal to the left-hand side of equation (4b). 
More specifically, with a given desired ratio of V.sub.H.sup.* /V.sub.L 
and with the quantity T.sub.LT.sup.2 +T.sub.LS.sup.2 determined at low 
speed operation, the parameter which corresponds to a desired value for 
T.sub.HT.sup.*2 +T.sub.HS.sup.*2 may be obtained. 
Thus, in accordance with an illustrative embodiment of the invention, to 
use the present invention, the tape recorder/playback device is first 
operated at a low speed and T.sub.LS.sup.2 +T.sub.LT.sup.2 is determined. 
Using a desired ratio V.sub.L /V.sub.H.sup.* and T.sub.LS.sup.2 
+T.sub.LT.sup.2, a parameter representative of a desired value of 
T.sub.HS.sup.*2 +T.sub.HT.sup.*2 is determined. This parameter is stored. 
Then, the tape device is operated at a high speed. The actual value of 
T.sub.HS.sup.2 +T.sub.HT.sup.2 is determined and compared with the desired 
value stored in the memory and an error signal is generated to change the 
actual speed of the tape to try to change the actual value of 
T.sub.HS.sup.2 +T.sub.HT.sup.2 to be equal to the desired value. When the 
actual value of T.sub.HS.sup.2 +T.sub.HT.sup.2 is equal to the desired 
value, the desired speed V.sub.H.sup.* is achieved.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 3, a controller 20 according to one embodiment of the 
invention is depicted. The controller has a capstan servo 21 for low speed 
tape advances, a reel servo 25 for high speed tape advances and a 
processor 34 for controlling the servos 21, 25. The capstan servo 21 
includes a capstan frequency generator 22 (CFG) for determining the actual 
rotational period of the capstan 13. The CFG transmits a signal indicative 
of the actual capstan rotational period to a capstan speed controller 24 
which compares the actual capstan rotational period with a desired capstan 
rotational period. Preferably, the capstan speed controller 24 operates 
under the control of the processor 34 which may, among other things, set 
the desired capstan rotational frequency. The results of this comparison 
are transmitted from the capstan speed controller 24 to the capstan motor 
driver 23 which accordingly adjusts the speed of the capstan motor 16 to 
achieve the desired tape speed. 
The reel servo 25 comprises a supply reel frequency generator 26 (SFG) and 
a take-up reel frequency generator 27 (TFG) for respectively determining 
the rotational periods of the supply 12 and take-up 15 reels. Each 
frequency generator 26, 27 transmits a signal indicative of the rotational 
period of its respective reel to a respective period counter 28 or 29. 
The period counters 28, 29 convert the signal transmitted by the SFG 26 or 
TFG 27 to rotational periods. The rotational periods of each reel 12, 15 
are outputted to a calculator 30 which determines a particular arithmetic 
function of the periods which is useful for controlling the speed of the 
reels. Illustratively, the calculator outputs the value S.sub.L 
=T.sub.LT.sup.2 +T.sub.LS.sup.2 where T.sub.LT and T.sub.LS are the low 
speed rotational periods of the take-up 15 and supply 12 reels, 
respectively, and S.sub.L is the sum of the squares of those low speed 
rotational periods. The sum of squares value S.sub.L is transmitted to the 
processor 34. 
The processor 34 uses the calculated value S.sub.L to set a reel motor 
speed parameter which is stored in a speed parameter memory 33. The reel 
motor speed controller 32 compares the parameter stored in the speed 
parameter memory 33 and the calculated values of the calculator 30 to 
produce an error signal which reflects the difference between the two. 
This error signal is transmitted to a reel motor driver 31 which 
accordingly adjusts the reel speed to achieve a desired high tape advance 
speed. 
The operation of the invention is now discussed. Suppose it is desired to 
run the tape at a desired high speed V.sub.H.sup.*. Initially, the 
processor 34 engages the capstan servo 21 to drive the tape 11 at a 
particular low speed V.sub.L in order to determine the relative rotational 
periods of the reels 12, 15. For example, if V.sub.H.sup.* =128 times 
normal speed then the processor 34 illustratively causes the capstan servo 
to drive the tape at V.sub.L =16 times normal speed. 
As the capstan motor 16 spins the capstan 13 to advance the tape at a low 
speed V.sub.L, the CFG 22 continuously transmits a signal indicative of 
the rotational period of the capstan 13. The capstan speed controller 24 
receives this signal and a signal from the processor 34 indicative of the 
desired low tape speed V.sub.L (i.e., sixteen times the normal speed). An 
error signal is produced and transmitted to the capstan motor driver 23 
which adjusts the capstan motor 16 speed to achieve the desired low tape 
speed V.sub.L. 
Meanwhile, the supply and take-up reels 12, 15 rotate as tape 11 is 
transported from the former to the latter by means of the capstan-pinch 
roller assembly 13-14. In response to the rotation of the reels, the SFG 
26 and TFG 27 generate signals indicative of the periods of their 
respective reels 12 or 15 which reflect the speed of these reels 12, 15. 
These generated signals are respectively transmitted to the period 
counters 28, 29 where they are converted to the low speed take-up reel 
period T.sub.LT and the low speed supply reel period T.sub.LS. 
The calculator 30 receives, and computes an arithmetic function of, these 
periods. Illustratively, the following function is computed: S.sub.L 
=T.sub.LT.sup.2 +T.sub.LS.sup.2. Alternatively, the sum of the periods 
T.sub.LT +T.sub.LS may be computed. At this stage of the operation of the 
controller 20, the calculated sum of squares S.sub.L is transmitted to the 
processor 34. When the processor 34 receives the low speed sum of squares 
S.sub.L, it disengages the low speed tape advance of the capstan servo 21. 
Using S.sub.L, the processor 34 computes a parameter for use in maintaining 
a constant, high tape speed. Illustratively, the parameter is a desired 
sum of squares for a high speed tape advance designated S.sub.H.sup.* 
(where S.sub.H.sup.* =T.sub.HT.sup.*2 +T.sub.HS.sup.*2 and T.sub.HT.sup.* 
and T.sub.HS.sup.* are the desired high speed rotational periods of the 
take-up and supply reels, respectively) and is computed from the following 
equation which is derived from equations (4a)-(4b): 
EQU S.sub.H.sup.* =S.sub.L k.sup.2 (5) 
In equation (5), k is the ratio of the actually detected low tape advance 
speed V.sub.L to the desired high tape advance speed V.sub.H.sup.*, i.e., 
k=V.sub.L /V.sub.H.sup.*. In an alternative embodiment, where S.sub.L 
=T.sub.LS +T.sub.LT is calculated, S.sub.H.sup.* is set equal to S.sub.L 
k. S.sub.H.sup.* is the parameter which is loaded into the speed parameter 
memory 33. 
After storing the parameter S.sub.H.sup.*, the processor 34 engages the 
reel servo 25 so that one of the reels 12 or 15 drives the tape at a high 
speed. The SFG 26 and TFG 27, in conjunction with the period counters 28 
and 29, determine the actual high speed rotational periods T.sub.HS and 
T.sub.HT of the reels 12 and 15, respectively. The calculator 30 uses 
these periods to compute an arithmetic function. Continuing with the above 
example, the sum of the squares of the actual periods, i.e., S.sub.H 
=T.sub.HT.sup.2 +T.sub.HS.sup.2, is computed. Again, in an alternative 
embodiment, where S.sub.L =T.sub.LS +T.sub.LT and S.sub.H.sup.* =S.sub.L 
k, S.sub.H is computed as T.sub.HT +T.sub.HS. This time, the reel motor 
speed controller 32 receives the actual detected high speed sum of squares 
S.sub.H and compares it with the parameter stored in the speed parameter 
memory, i.e., the desired high speed sum of squares S.sub.H.sup.*. An 
error signal is produced reflecting the discrepancy between the actual 
detected sum of squares value S.sub.H and the desired sum of squares 
parameter S.sub.H.sup.* which is transmitted to the reel motor driver 31. 
The reel motor driver 31 adjusts the reel speed accordingly to achieve the 
desired tape transport speed V.sub.H.sup.*. 
It may be appreciated that the SFG 26 and TFG 27 continually transmit 
signals indicative of the rotational period of their respective reels. 
Thus, the high speed tape advance may be continually maintained at a 
desired, constant rate V.sub.H.sup.*. 
Turning now to FIG. 4, a second embodiment 40 according to the present 
invention is now discussed. The second embodiment 40 is similar to the 
first embodiment 20 with a few differences. Firstly, the speed parameter 
memory 45 is connected directly to the calculator 30 for receiving and 
storing a value directly from the calculator 30 under the supervision of 
the processor 44. The processor 44, need not be a micro-processor (i e., 
no longer requires a complicated arithmetic logic unit) but may be a 
simpler control unit. 
An oscillator 41 is provided which generates a signal with a constant 
period T and transmits this signal to a multiplexer 43 and to a frequency 
divider 42. The frequency divider 42 produces an output signal having a 
period nT which is a multiple n of the oscillator 41 period T. This signal 
is additionally inputted to the multiplexer 43. The multiplexer 43 
operates under the control of the processor 44 and selects the oscillator 
41 signal or the frequency divider 42 signal for output depending on a 
control signal transmitted from the processor 44. The signal outputted 
from the multiplexer 43 is inputted to each period counter 28 and 29 and 
serves as a base period for determining the rotation periods of the reels 
12, 15. Thus, the rotational period counters 28 and 29 do not output the 
rotational periods. Rather, the period counters 28, 29 output a base 
period factor which, when multiplied by the base period, yields the 
particular rotational period of the supply or take-up reel T.sub.S or 
T.sub.T. In other words, if the base period is T, the supply reel period 
counter 28 outputs a factor x.sub.S and the take-up reel period counter 
29 outputs a factor x.sub.T where T.sub.S =x.sub.S T and T.sub.T =x.sub.T 
T. 
The operation of the second embodiment is now briefly discussed insomuch as 
it differs from the operation of the first embodiment. By virtue of 
including a selectable base period of either T or nT, the required 
calculations for computing the desired high rotational period parameter 
may be simplified. Suppose that the base period T is used for high speed 
rotational period determinations and nT for low speed period 
determinations. Using the above relationships the sum of the squares of 
the low speed base period factors Y.sub.L, the sum of the squares of the 
actually detected high speed base period factors Y.sub.H and the sum of 
the squares of the desired high speed base period factors Y.sub.H.sup.* 
may be computed similar to S.sub.L, S.sub.H and S.sub.H.sup.*. Thus: 
EQU Y.sub.L =x.sub.LS.sup.2 +x.sub.LT.sup.2 (6a) 
EQU Y.sub.H =x.sub.HS.sup.2 +x.sub.HT.sup.2 (6b) 
EQU Y.sub.H.sup.* =x.sub.HS.sup.*2 +x.sub.HT.sup.*2 (6c) 
In equations (6a), (6b) and (6c), x.sub.LS is the base period factor of the 
supply reel detected at a low speed, x.sub.LT is the base period factor of 
the take-up reel detected at a low speed, x.sub.HS is the actual base 
period factor of the supply reel detected at high speed, x.sub.HT is the 
actual base period factor of the take-up reel detected at high speed, 
x.sub.HS.sup.* is the desired high speed base period factor of the supply 
reel and x.sub.HT.sup.* is the desired high speed base period factor of 
the take-up reel. Thus: 
EQU T.sub.LS =x.sub.LS nT (7a) 
EQU T.sub.LT =x.sub.LT nT (7b) 
EQU T.sub.HS =x.sub.HS T (7c) 
EQU T.sub.HT =x.sub.HT T (7d) 
EQU T.sub.HS.sup.* =x.sub.HS.sup.* T (7e) 
EQU T.sub.HT.sup.* =x.sub.HT.sup.* T (7f) 
Recalling that: 
EQU S.sub.H.sup.* =S.sub.L k.sup.2 (8) 
the period nT may be factored out of the right hand side and the period T 
out of the left hand side, or: 
EQU x.sub.HS.sup.*2 +x.sub.HT.sup.*2 =n.sup.2 k.sup.2 (x.sub.LS.sup.2 
+x.sub.LT.sup.2) (9) 
which reduces to: 
EQU Y.sub.H.sup.* =Y.sub.L n.sup.2 k.sup.2 (10) 
Equation (10) has one parameter, n, which may be set to any desired value. 
It may be appreciated from equation (10), that by setting the multiple n 
of the frequency divider 42 equal to V.sub.H.sup.* /V.sub.L, that the sum 
of the squares of the detected low speed base period factors Y.sub.L, will 
be equal to the sum of the squares of the desired high speed base period 
factors Y.sub.H.sup.*. In other words, by judicious selection of n (i.e., 
equal to V.sub.H.sup.* /V.sub.L), Y.sub.H.sup.* may be easily calculated 
directly from Y.sub.L without a multiplication step (i.e., since 
Y.sub.H.sup.* =Y.sub.L, no multiplication is required). 
Assume, as with the first embodiment 20, that it is desired to advance the 
tape at a desired high speed V.sub.H.sup.*. Initially, the capstan servo 
21 is engaged to drive the tape at a low speed V.sub.L. The processor 44 
causes the multiplexer 43 to select the signal of the frequency divider 
which has a base period nT, where n=V.sub.H.sup.* /V.sub.L. For instance, 
if V.sub.L =16 times normal speed and V.sub.H.sup.* =128 times normal 
speed, the rotational period counters 28 and 29 have a base period 8T. The 
period counters 28, 29 output the detected low speed base period factors 
x.sub.LS and x.sub.LT. The calculator 30 receives these factors and 
computes the sum of the squares of the detected low speed base period 
factors Y.sub.L =x.sub.LS.sup.2 +x.sub.LT.sup.2. This value is transmitted 
directly to the speed parameter memory 45. Once received, the control unit 
44 disengages the capstan servo 21. 
Next, the reel servo 25 is engaged to advance the tape at a high speed. The 
control unit 44 causes the multiplexer 43 to select the signal of the 
oscillator 41 as the base period of the period counters 28, 29. As 
discussed in detail above, the period counters 28, 29 thus have a base 
period of T which is used to determine the actual detected high speed base 
period factors x.sub.HS and x.sub.HT. These factors are fed to the 
calculator 30 which outputs the sum of their squares Y.sub.H 
=x.sub.HS.sup.2 +x.sub.HT.sup.2. This actual detected sum of the squares 
of the high speed base period value is transmitted to the reel motor speed 
controller 32, which compares it with the parameter stored in the speed 
parameter memory 45. As described in detail above, because the parameter 
Y.sub.L stored therein equals the sum of the squares of the desired high 
speed base period factors Y.sub.H.sup.*, it may be used to determine the 
discrepancy between the actual tape speed and the desired tape speed. 
Thus, by using two different periods T and nT as base periods for the 
period counters 28, 29, the same result is achieved as with the first 
embodiment without performing a multiplication. This is desirable in the 
preferred embodiment so that a less sophisticated and cheaper processor 44 
may be used. 
Finally, the aforementioned embodiments are intended to be merely 
illustrative. Numerous alternative embodiments may be devised by those 
ordinarily skilled in the art without departing from the spirit and scope 
of the following claims.