JPS60106094A - Detector of tape quantity - Google Patents

Abstract

PURPOSE:To detect tape quantity quickly and properly at the time of starting of a travel by measuring a rotational frequency of a supplying reel in order to detect a remaining amount of a tape in a VTR. CONSTITUTION:A rotational pulse from a photosensor 6 is added to a waveform shaping circuit 21, and a shaped waveform is inputted to a microcomputer 22. On the other hand, a crystal oscillator 23 and an oscillator circuit 24 output a reference clock pulse, and input it to a pulse counter 25. The counter 25 is counting the number of pulses, and the microcomputer 22 reads an output (ci) of the counter 25 according to a timing (c) of a rise of a rotational pulse (a), calculates tape remaining time and indicates it on a display element 26. A certain rotational frequency Tk and the difference DELTATi between the Tk and the previous rotational frequency is calculated. The DELTATi is proportional to thickness of the tape. Thus whether or not the rotation of the reel is stable is decided depending upon the constant value of the DELTATi, and a remaining amount of the tape is detected quickly and with little errors at the time of starting of a travel of the tape, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tape detection device that can be used in video tape recorders (VTRs) and other tape transport devices.

Conventional (111') structure and its problems Traditionally, tapes were used in VTRs and tape recorders.
Another option is to use a tape collar that is proportional to the number of rotations of the reel shaft, but recently, a method has been put into practical use that detects the angular velocity of the tape reel, calculates this using a microcomputer, etc., and directly displays the remaining amount of tape. has been done.

Regarding the principle, a method for measuring the angular velocity of one reel is described in Japanese Patent Publication No. 56-47628, by the father Ti.
:! , 4 Publication No. 92717/1983 and Japanese Patent Application Publication No. 1973-
A method of measuring the angular velocity of both reels is described in Japanese Patent No. 6004.

1. In FIG. 1, when the tape is being transferred from the supply reel 1 to the take-up reel 2 by the capstan 3 and the pinch roller 4, the length of the tape remaining on the supply reel 1 is 11f''i. Choose one of the two types.

(V is the tape transport speed, θ is the tape thickness, γ is the radius of the hub of both reels, TA and TB are the supply reel 1 and take-up reel 20 rotation periods, respectively, and L is the total length of the tape). The method requires detecting the rotation period or angular frequency of one reel (method A requires detecting the ratio of the rotation period or angular frequency of both reels.

A method that has been put into practical use recently is a method in which the rotation period is measured and the chirp stone is calculated using a microcomputer.A typical method for measuring the rotation period of the reel will be explained.

In FIG. 2, when a disk 5 as shown in the figure is attached to the reel shaft 7, as the reel rotates, the blades of the disk intermittently cut off the light from the light emitting diode 8, causing the photo sensor 9 to appear as shown in FIG. Pulses as shown in a (in this case, 8 pulses per revolution) are obtained. In addition to this optical type,
There is also a magnetic method in which a disk is magnetized with several magnetic poles or more and this is detected by a magnetic sensor. In any case, it is not possible to increase the number of pulses per rotation (the number of blades in an optical system, the number of magnetic poles in a magnetic system) due to cost considerations, so in order to improve accuracy, the period rather than the frequency of the pulses is measured. In addition, in terms of the butterfly method of disk pulse generation, if the shape of the disk blades in Figure 2) is not perfectly symmetrical, the individual pulse widths will not be the same. Therefore, the reel will be exactly 1. A method is used in which the period of each pulse width during rotation is summed and the error due to the above causes is absorbed by 1. In order to measure the period with high accuracy, the measurement time is the period during one rotation of the reel. It takes time.

Father, in the method (1) and (Gong), the tape between the two reels is stretched tightly, and its length is constant.
), but in reality this may not be the case. For example, in the case of a VH8 type VTR, a mechanical servo as shown in FIG. 4 is provided near the supply reel.

Referring to FIG. 4, the tape 12 wound on the supply reel 11 passes through the fixed post 13 and the tension arm 1
It passes through the post 16 of No. 4 and is pulled out. The tension arm 14 moves using the fulcrum 15, and if the tape tension becomes weak, it is pulled in the direction of the arrow by the spring 16. At the same time, the brake belt 17 is pulled,
An attempt is made to tighten the reel stand 18 to weaken the rotation. On the other hand, if the tape tension becomes stronger, the
moves in the opposite direction of the arrow, and the braking force becomes weaker. In this way, the tape tension is kept constant by the movement of the tension arm 14. For this reason, immediately after starting tape running for playback (or recording) from a stopped state, the tension arm 12 swings and the rotation of the supply reel fluctuates even after the tape feed speed of the magnetic head reaches a constant level. You must wait for the tension arm to stabilize before you begin measuring the period of the supply reel.

In the end, it takes a lot of tension,
Approximately 1 rotation is required for 12 to become stable, and then another rotation is required to measure the angular frequency, for a total of approximately 2 rotations. Converting this into time, II;% when used in the low speed mode (long time mode) of a VH8 video tape recorder will take about 45 seconds at worst.

Furthermore, even in a steady running state, errors are likely to occur in the detected tape amount due to uneven rotation of the reel and changes in tape thickness due to unstable running.

The present invention improves the above-mentioned conventional drawbacks, eliminates the influence of uneven rotation of the reel, and provides a device that can quickly and accurately detect the amount of tape at the start of running, in particular. The purpose is to

Structure of the Invention The tape amount detecting device according to the present invention provides at least one of the supply reel and the take-up reel with a period 1. providing means for generating a signal of
means for generating a reference clock signal; and said period 1. It is equipped with means for performing arithmetic processing to calculate the tape amount using the signal and the reference clock signal, and detects the amount of change Δt□ per constant rotation angle of the signal of period 11 (i is an integer of 2 or more) or similar. This method is characterized in that the tape amount is calculated using Δti obtained by the recurrence formula, and as a result, the amount of tape can be detected quickly and accurately.

DESCRIPTION OF THE EMBODIMENTS An example of the structure of the present invention is shown in FIG. This example is a VTR
The remaining amount of tape is detected by measuring the rotation period of the supply reel.

The method for detecting the rotation of the supply reel is the same as the method described above in FIG. 2.

The rotation pulse from the photo sensor 6 is sent to the waveform shaping circuit 21
Here, the shaped mino waveform h'' in FIG. 3 is manually input to the microcomputer 22.

On the other hand, a reference clock pulse (FIG. 3b) is generated by the crystal oscillator 23 and the oscillation circuit 24, and its output is input to the pulse counter 26. The counter 25 continues to count the number of regular Nihals, and the microcomputer 22 continues to count the number of rotation pulses a.
1, which describes the operation of the microcomputer 22, which reads the output value C1 of the counter 26 at the rising timing C of , calculates the remaining tape length between +j and 94j, and drives the display element 26 to display the data. 1) Calculating the period of the rotation pulse From the counter value 'i-1 at one pulse edge and the counter value C1 at the next edge, calculate the pulse period 1i using the following formula + 5-j (C1- '1-1) ・・・・噸(f is,
Frequency of reference clock pulse) Based on this and one rotation of the reel corresponds to eight rotation pulses, the period Tk of one rotation of the reel is divided by (1 is an integer of 8 or more).

(Sakaki Calculating the amount of change ΔTk in the rotation period Tk The period Tk of one rotation with the reel and the period Ti-1 of the previous one rotation
Calculate the difference ΔT.

ΔTi−Ti ”i −1 . . . ΔT is proportional to the thickness of the tape.

To explain this, in FIG. 1, the following equation holds true for one rotation.

, °, ΔTi-Ti-Tt-1= (Ri-Ri-1)
(2) Here, since the thickness θ of the tape is θ:R1-R1-1, it becomes 0-1ΔT, . . . (7) 2π 1 .

Therefore, although ΔT0 is a constant value, it is possible to determine whether the reel rotation is smooth or wobbling. Furthermore, when the thickness of the tape is unknown, the thickness of the tape can be calculated from this υ, and the deviation from the nominal thickness can be corrected.

(:31 Calculation of remaining tape time τ1 11 hours remaining on tape τi is calculated by formula (1), = 13
．． −． 27,2.

, v 4ytO, . . . (8) Since all the right-hand sides are known, the remaining tape time τi
'/J bow, I can count 1.

(→ When the amount of change ΔT in the rotation period is not constant, ΔT
Calculate 0 stilts 1 straight ΔTi using the following formula.

l〒--9 Nijisuishi: Nii5e...Ko(@(i=
2, 3, 4. ...) The JV depth θ of the tape is calculated using the following formula.

0-1 ΔT, (1o) 2π 1 T, tit in the following equation is replaced with mel.

Ti=Ti-1+ΔT.

(i=2.3....) and 00. Substitute T into equation (1) to find the tape remaining time τi.

(→ Immediately after the measuring tape starts running, the remaining tape time τ can be quickly determined by using the following settings.

The basic method is the same as (4), but calculation is performed for each rotation pulse period instead of one rotation period.

ti:ti-1i-1 (i = 2, 3, 4...) (11=1.) T・=8j・ 1. 1 8v -4V - θ=−・Δi, ==−Δt.

Calculate by substituting 2π 1 π 1 into (@formula. However, as long as i is small, the error will be large, but after one rotation when the rotation of the supply reel is stable, 7
In term 6, the variation of Δt0 up to that point is the above 111
It is absorbed by calculation and a value with small error is obtained. Whether the reel rotation is stable or not is determined by Δ1. Immediately after stabilization, τ with a smaller error than t is determined.
This means that you are holding back.

Effect of the invention According to the present invention, the following effects can be obtained.

(1) When the VTR tape starts running, the remaining tape: 11. can be detected quickly and with less error.

('4) Although the tape running speed V is constant even at times other than the above, errors can be suppressed even when the rotation of the reel is unstable due to slack or uneven thickness of the tape.

(31'J - It is automatically determined whether the rotation of the wheel is stable or not, and the remaining amount of tape is divided by the optimal method, so errors can be suppressed.

As described above, according to the present invention, the amount of tape such as the remaining amount of tape in a VTR or the like can be detected quickly and with small errors.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the configuration of a general magnetic tape recording device presented to explain the principle of detecting the tape amount;
2, B is a plan view and a side view showing an example of a method for measuring the rotation period of a tape reel, and FIGS. 3 a, b, and c are waveforms illustrating the operation of the tape amount detecting device of the present invention. figure,
FIG. 4 is a plan view showing a mechanical servo mechanism for tape tension used in a video tape recorder, and FIG. 6 is a block diagram of a tape amount detecting device in an embodiment V of the present invention. 5...Blade A;'' disk, 6...Fut sensor, 21...Waveform shaping circuit, 22...
... Microcomputer, 23 ... Crystal oscillator, 24 ... Reference clock oscillator, 25 ...
...Pulse counter, 26...Display element.

Claims (1)

[Scope of Claims] At least one of the supply reel and the take-up reel is provided with means for generating a signal with a period of 11 proportional to the rotation period T thereof, and means for generating a reference clock signal;
i signal and a reference clock signal to calculate the tape amount, and detect the number of changes Δ1i per constant rotation angle of the signal with the period t (1 is an integer of 2 or more) or similar. A tape amount detection device characterized in that the tape amount is calculated using Δt obtained by the acclimatization formula.