GB2312080A

GB2312080A - Automatic tape remaining system with only one reel mounted sensor

Info

Publication number: GB2312080A
Application number: GB9607704A
Authority: GB
Inventors: Thor Itt Chiam; Li Yang Lee
Original assignee: Thomson Multimedia SA
Current assignee: Vantiva SA
Priority date: 1996-04-13
Filing date: 1996-04-13
Publication date: 1997-10-15
Anticipated expiration: 2016-04-13
Also published as: GB2312080B; GB9607704D0

Abstract

An automatic tape remaining (ATR) system that only requires one additional sensor, located at the take up reel 6, to be added to a tape device. Rotations of the capstan 4 are also counted using a sensor that is normally already present in conventional tape devices. To determine the amount of tape remaining the ATR system searches forward for three turns of the take up reel 6 and records the number of capstan 4 pulses in each rotation of the take up reel 6. The tape 1 is then fast rewound for the same number of take up reel 6 turns, back to the original position, and the number of capstan 4 pulses are again counted. Since the capstan 4 is connected to the supply reel 2 via a transmission 8-11 during the rewind operation its rotations at this time give a measure of the rotation of the supply reel 2. From these measurements the tape type and the amount of tape remaining can be calculated.

Description

Automatic Tape Remain System for a Tape Device The invention relates to an automatic tape remain system used in a tape device such as a video cassette recorder (VCR) or an audio tape recorder. Such an automatic tape remain system, in short "ATRS", automatically detects the cassette type (tape type) and the tape remain time in a VCR or an audio tape recorder.

US Patent Nr. 4,280,159 discloses an ATR-system which uses two separate rotation sensors, wherein one sensor is provided at the supply reel and one at the take-up reel, for the measurement and the detection of the cassette type and the tape remain time. In the known system, the tape inserted is transported at a predetermined velocity from the supply reel to the take-up reel by a capstan drive. The rotations of the respective reels are simultaneouly sensed by the two sensors and the rotational periods T5 and Tt of the supply and take-up reel, respectively, are detennined using the measurement signals of the sensors. It can be shown that the rotational periods T5 and Tt are functions of the temporary radiens Rs and Rt of the supply and take-up reel, respectively. Because the overall tape length is constant it can be shown that (RS2 + Rt2) is constant and a function of the tape used. In consequence, the function (to2 + Tt2) is indicative of the type of tape used. Using a look-up table for the different type of tapes, i.e for the different possible values of the function (T52 + Tt2), it is possible to determine the type of tape with the simultaneous measurement of the rotational periods of the supply and take-up reel, respectively. Because of the constant overall tape length and the constant capstan velocity during the normal playback mode, measurement theory further shows that the rotational periods Ts and Tt further comprise information on the approximate amount of tape left on the supply, respectively the approximate amount of tape already wound on the take-up reel. In other words, the remaining tape time or recording time of the supply reel can be approximately calculated and, for example, displayed. The complete measurement process includes transporting an amount of tape of an inserted cassette for a predermined amount of time in the forward direction and measuring the amount of pulses delivered by the rotational sensors of the supply and take-up reel, respectively, for the calculation of the rotational periods, and winding the tape back to its original position.

But the known ATR system needs two separate sensors, one for each tape reel. These additional components of e.g. a consumer tape device results in higher costs in comparision with a tape device without an ATR system.

It is therefore an object of the present invention to provide a ATR system with the same accuracy as known systems but lower production costs.

This object is solved by the features of claim 1.

Preferred embodiments are subject of the dependent claims.

The ATR system according to this invention uses for the calculation of tape type and tape remaining time signals from a single rotation sensor which is preferably provided at the take-up reel, and signals from a capstan rotation sensor, which must be provided even in known systems.

The rotational periods of the supply and the take-up reel are determined by first measuring the rotational period of the take-up reel for a predetermined amount of rotations of the take-up reel at the normal playback speed in terms of capstan rotations. Then the tape is rewound to the original position with the fast rewind mode. Because in this mode the capstan drive is connected to the supply reel by a transmission with a fixed and known gear ratio, the rotational period of the supply reel can be expressed in terms of capstan rotations. Because the predetermined amount of forward rotations of the take-up reel is chosen appropriatly, the deviation in the rotational period from one measuring rotation of the takeup reel to the next one can be neglected. Therefore the rotational periods of the supply reel measured through the fast rewind mode is the period corresponding to the previous measured rotational period of the take-up reel.

Preferably the rotational periods of the supply reel and the take-up reel are expressed in terms of capstan pulses per one rotation of the take-up reel. With these rotational periods and appropriate calculations, the tape type can be identified.

Accordingly one sensor can be saved compared to the known ATR systems, which decreases production costs of consumer tape devices without decreasing the accuracy of the detection of the tape type and the tape remain time. Further the overall measurement time is the same as in the known system, because the tape is also wound back to the original position in the known system.

Preferably the bobby rotation sensor is located at the take-up reel and the first mesurement is done during a forward run at normal playback speed, or a multiple of said speed, e.g. 7 times the normal playback speed. and the second measurement is done during a fast rewind mode. During the fast rewind mode the supply bobby is connected to the capstan drive through a transmission with a fixed and known gear ratio.

Preferably the predetermined length corresponds to k full rotations of the take-up reel, k being a natural number. An amount of k = 3 rotations of the take-up reel is sufficient under normal conditions for the determination of the tape type and remain time.

As already has been mentioned, it is necessary for the determination of the rotational period of the supply reel to use a fixed gear ratio when the capstan drive is connected to the supply reel during the fast rewind mode.

Preferably the gear ratio equals 2.5.

To facilitate the calculations, the rotational periods of the supply and the take-up reel are expressed in terms of capstan rotations, i.e. in terms of capstan pulses per one reel rotation.

Therefore one take-up reel rotation corresponds to m reel pulses and one capstan rotation corresponds to n capstan pulses, wherein preferably n = 360 and m = 12.

To enhance the accuracy of the ATR system, m can be chosen as 13.

Preferred embodiments of the invention are now described with reference to the accompanying drawings, wherein: Fig. 1A shows the ATRS in the search forward phase, Fig. 1B shows the ATRS in the fast rewind phase, Fig. 2 shows a schematic of the tape wound around the capstan, Fig. 3 shows a schematic of the bobby with tape, and Fig. 4 shows a reel pulse disk generating 13 pulses.

Fig. 1 shows a schematic of the ATR system with a tape 1 inserted, comprising a supply reel 2 (left bobby), a reading/writing drum 3 around which the tape 1 is wound, a capstan drive 4 with a pinch roller 5 for transporting the tape 1, and a take-up reel 6 (right bobby) provided with a reel sensor 7. In the preferred embodiment one reel rotation of the right bobby 6 with its reel sensor 7 corresponds to 12 reel pulses of the rotation sensor 7. Further one capstan rotation of the capstan 4 corresponds to 360 capstan pulses. During the search forward phase of the first measurement phase the ATR system the right bobby 6 is rotated for three full turns in clockwise direction as indicated by the arrow B. In other words, the capstan 4 rotates in the direction of an arrow A. During this first phase, as depicted in Fig. 1A, the number of capstan pulses is measured as a function of the three full rotations of the take-up reel, which corresponds to 36 pulses of the rotation sensor in the first embodiment wherein one full rotation of the take-up reel corresponds to 12 pulses.

Fig. 1B shows the fast rewind phase or reverse phase of the ATR system, wherein the tape 1 is rewound for three turns of the take-up reel with a transmission comprising a rubber band 8 rotated by the capstan 4, a gear 9 and a gear 10 with a fixed gear ratio of 2.5 wherein the gear ratio depends on the VCR used. Like in Fig. 1A one capstan rotation corresponds to 360 capstan pulses and one reel rotation of the take-up reel 6 with its real sensor 7 corresponds to 12 reel sensor pulses. In this measurement phase, the capstan rotates in a direction C, the supply reel in the direction D, and the take-up reel in the direction E.

According to the amount of tape 1 wound on each bobby 2, 6, the bobbies 2, 6 are rotating at different angular speeds. If the cassette inserted does not activate the end of tape sensor and the user does not enter any command, ATRS will start to search forward without a picture for three turns of the right bobby 6. The number of capstan pulses in one rotation of the right bobby 6 is recorded. Then a fast rewind is done with the exact same number of rotations of the take-up reel back to the original position and the number of capstan pulses in one rotation of the right bobby 6 is recorded. From these measurements either the ratio of the circumference of the take-up reel 6 to the circumference of the supply reel 1 is calculated, which is indicative of the tape type used, and/or the sum of the squares of the rotational periods is calculated. These circumferences correspond at the constant capstan velocity (playback mode) to the rotational periods of the repective bobbies 1, 6. Using the speed to distance relation and the gear ratio between the capstan and the right bobby 6 the tape time and the remain time can be calculated.

Further if the cassette inserted activates the end of sensor right away before entering the ATRS routine, it will be rewound for a few rotations first before ATRS takes over. If the cassette inserted activates end of sensor before ATRS gets the tape type, no ATRS determination is performed.

Further, if the user enters a command, for example play, record, search and fast rewind, during or before the ATRS is performed, then ATRS must be performed first before carrying out said command.

In the following some equations for the calculations are given. For these equations first the definitions of the variables and constants are presented: dC = diamater of capstan (fixed) = 3.53 mm - dB = thickness of tape (assumed 19 zm first and normalized later) VB = net linear tape speed (23.39 mm/s) n/fg) = &num; of CFg pulses per reel rotation (measured by capstan Fg detection cct. and supply reel pulses) RiFg = &num; of CFg pulses per right reel rotation in search forward (measured by capstan Fg detection cct and supply reel pulses) LeFg' = It of CFg pulses per right reel rotation in fast rewind (measured by capstan Fg (frequency generator) detection cct (circuit) and supply reel pulses) - LeFg = It of CFg pulses per left reel rotation (variable, calculated) Tree1 = time for 1 reel rotation (variable, calculated) CFg = Fg pulses per capstan rotation (360 pulses) - W = &num; of reel turns (variable, calculated) - WL* = &num; of left reel turns (variable, calculated) WR* = It of right reel turns (variable, calculated) Wleftabs = number of turns on left reel according to preceding calculation Wleftrel = relative number of turns on left reel, changing according to process mode Tband = tape time (variable, calculated) TreSt = remain tape time (variable, calculated) Tsum = total tape time (variable, calculated) Tbandleft = tape time of left bobby (variable, calculated) Tbandright = tape time of right bobby (variable, calculated) Tbobby = time equivalent of small/large bobby (26/62 mm) TSb = total tape time inclusive of Tbobby (variable, calculated) - k2 = speed constant (constant), (wherein Fg = frequency generator and cct = circuit).

Normally, as it is shown for example in Fig. 1A and Fig. 1B, one full right bobby circumference is only a portion of one full left bobby circumference. Assumed that during fast rewind of the ATRS, one round of the right bobby 6 corresponds to approximately 2,5 rounds of the capstan.

Then the ratio of circumference of right bobby over left bobby is: (RiFg * dC * Pi/360)/(LeFg * dC * Pi/360) = LeFg'/(360 * 2.5) Therefore: LeFg = RiFg * 360 * 2.5/LeFg'. 1) With reference to Fig. 2, the diameter of the capstan axis de equals 3,53 mm. The tape partly contacts the capstan 4 axis and is driven with a velocity vg. The total tape 1 that passes by the capstan in one round of the supply bobby equals the number of capstan turn * dc * Pi (mm).

Since n(Fg) / CFg = number of capstan turns and Speed * Time = Dist, it follows: VB * Treel = (n(Fg)/CFg) * dC * Pi. 2) Therefore: Treel = n(Fg) * d0 * Pi/(CFg * Vg). 3) With reference to Fig. 3, the circumference of a bobby with a tape diameter of 2 * W * dB is (2 * W * d3 * Pi). Because Speed = Dist/Time, it follows: VB = 2 * Pi * d3 * W / Treel, and: W = Treel * Vg/(2 * Pi * dB). 4) Substituting 3 into 4 results in: W = n(Fg) * dc/ (2 * dB * CFg). 5) Define: k2 = dB * Pi/VB.

Then: Tband=W*W*k2, 6) Tbandleft = Wleft * Wleft * k2, 7) Tbandright = Wright * Wright * k2, 8) Tsb = Tbandleft + Tbandright, 9) Tsum = T5b - Tbobby, 10) and Trest = (Wleftabs + Wleftrel)**2 2 k2 11) The consequence of the construction is, that the accuracy of the ATRS depends on the diameter of the bobby with reel. As the tape type is getting bigger (for example T160, T200), the reel thickness becomes smaller. Hence, it is possible that T160 with a tape thickness of 19 llm has a diameter which equals the diameter of a T200 tape with a thickness of 15 ;jm. With the approximative formulas described above, it is possible that ATRS will misdetect a T200 as T160. Another reason of misdetection is due to hardware tolerance and also by the nature of the formulas because they are only an estimation. Also the ATRS system can only detect C~type cassette at its tape start due to the physical construction of such a cassette.

To further improve the accuracy of the ATRS the existing 12 reel pulse disk 12 of the sensor 7 the right bobby 6, as it has been described in the above embodiment, can be replaced by a 13 reel pulse disk 13, shown in Fig. 4. This would reduce the error of approximately 30 windings in the worst case of the 12 reel pulse disk 12 to theoretically approximately 10 windings. Such a tape is shown in Fig. 4. The 13 reel pulse disk 13, as it is shown in Fig. 4, shows equal spaces between each pulse except between the first and 13th pulse.

Claims

1. Automatic tape remain system for a tape device using sensors for measuring the rotational periods of the supply and take-up reel, characterized in that the system comprises one reel rotation sensor (7) measuring the rotational period of a respective reel (2, 6) relative to the capstan (4) rotation for a run of a predetermined length in one direction and measuring the rotation of the capstan (4) connected to the other reel (2, 6) through a transmission (8, 9, 10) with a known gear ratio during a run in the direction opposite to the first direction for the predetermined length.

2. System according to claim 1, wherein the reel rotation sensor (7) is located at the take-up reel (6).

3. System according to claim 1 or 2, wherein the first measurement is done during a forward run at normal playback speed or a multiple of said speed and the second measurement is done during a fast rewind mode.

4. System according to one of preceding claims, wherein the predetermined length corresponds to k full rotations of the take-up reel (6), n being a natural number.

5. System according to claim 4, wherein k equals 3.

6. System according to one of the preceding claims, wherein the gear ratio of the transmission (8, 9, 10) equals 2.5.

7. System according to one of the preceding claims, wherein the rotational periods of the supply and the take-up reel (2, 6) are expressed in terms of capstan rotations.

8. System according to one of the preceding claims, wherein one takeup reel (6) rotation corresponds to m reel pulses and one capstan (4) rotation corresponds to n capstan pulses.

9. System according to claim 8, wherein n = 360 and m = 12.

10. System according to claim 8, wherein m = 13.