JPH0237033B2 - TEEPURYOKENSHUTSUSOCHI - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is applicable to a video tape recorder (VTR).
The present invention relates to a tape amount detecting device that can be used in the present invention and other tape transport devices.

Conventional structure and its problems Conventionally, in VTRs and tape recorders, the amount of tape used or remaining amount of tape was determined by visual inspection or by a tape counter proportional to the number of rotations of the reel shaft. Recently, a system 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.

Regarding the principle, a method for measuring the angular velocity of one reel is described in Japanese Patent Publication No. 56-47628, and Japanese Patent Application Laid-Open No. 50-92717 and Japanese Patent Application Laid-open No. 53-
A method of measuring the angular velocity of both reels is described in Japanese Patent No. 6004.

In other words, 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 l ₁ of the tape remaining on the supply reel 1 is determined by the following two equations. Find it either way.

l ₁ = v ₂ /4πθT _A ² −πγ ² /θ ………(1) 1/1+T _B ² /T _A ² {(L+2πγ ² /θ)−πγ ² /
θ}……(2) (v is the tape transport speed, θ is the tape thickness, γ
is the radius of the hub of both reels, T _A and T _B are the rotation periods of supply reel 1 and take-up reel 2, respectively, and L is the total length of the tape.) The method of equation (1) calculates the rotation period or angular frequency of one reel. The method of equation (2) requires detecting the rotation period or angular frequency ratio of both reels.

A method that has been put into practical use recently is a method in which a microcomputer measures the rotation period and calculates the amount of tape.

A typical method for measuring the rotation period of the reel will be explained. In Figure 2, a disk 5 as shown in the figure
is attached to the reel shaft 7, and 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 receive a signal as shown in Figure 3a.
Pulses as shown in (in this case, 8 pulses per revolution) are obtained. In addition to this optical method, 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 the optical type, the number of magnetic poles in the magnetic type) due to cost considerations, so to improve accuracy, the period rather than the pulse frequency is measured. Furthermore, unless the pattern for generating pulses on the disk (in the optical system, the shape of the blades of the disk in FIG. 2) is completely symmetrical, the individual pulse widths will not be the same. For this reason, a method is used in which the period of each pulse width during exactly one revolution of the reel is summed to absorb errors due to the above-mentioned causes. In other words,
In order to accurately measure the period, the time required for one rotation of the reel is required as the measurement time.

Furthermore, methods (1) and (2) are based on the assumption that the tape between the two reels is taut and its length is constant, but in reality this may not be the case. be. For example, in the case of a VHS-type VTR, a mechanical servo as shown in Figure 4 is installed near the supply reel.

Referring to FIG. 4, the tape 12 wound on the supply reel 11 is pulled out through the fixed post 13 and through the post 15 of the tension arm 14. Tension arm 14 moves with 15 as a fulcrum, and if the tape tension becomes weak, it will be pulled in the direction of the arrow by spring 16. At the same time, the brake belt 17 is pulled, tightening the reel stand 18 and trying to weaken its rotation. Conversely, when the tape tension becomes stronger, the tension arm 14 moves in the opposite direction to 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. Therefore, immediately after starting tape running for playback (or recording) from a stopped state,
Even after the tape feeding speed on the magnetic head surface reaches a constant level, the tension arm 12 oscillates and the rotation of the supply reel fluctuates, so it is necessary to wait until the tension arm stabilizes before starting to measure the period of the supply reel. Must be.

In the end, from the start of running to the time when the rotation period that can be used to calculate the amount of tape is determined, the tension arm 12 needs to make one rotation to stabilize, and then another rotation to measure the angular frequency, for a total of about two rotations. Is required. Converting this to time, it is the low speed mode (long time mode) of a VHS video tape recorder.
When used in the worst case, it will take about 45 seconds.

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.

Purpose of the invention The present invention improves the conventional drawbacks as described above,
It is an object of the present invention to provide a device capable of quickly and accurately detecting the amount of tape especially at the start of running by eliminating the influence of uneven rotation of a reel.

Structure of the Invention The tape amount detecting device according to the present invention has a rotation period T of at least one of a supply reel and a take-up reel.
means for generating a signal with a period t _i proportional to (or angular frequency), a means for generating a reference clock signal, and a means for performing arithmetic processing to calculate the tape amount using the signal with the period t _i and the reference clock signal. and detect the amount of change Δt _i of the signal with period t _i per constant rotation angle. Or, the tape amount is calculated using _i obtained by a similar recurrence formula, and thereby the tape amount can be detected quickly and accurately at the start of running.

DESCRIPTION OF EMBODIMENTS An example of the configuration of the present invention is shown in FIG. In this embodiment, the remaining amount of tape in a VTR 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 applied to the waveform shaping circuit 21, where it is shaped into the waveform shown in FIG.
The waveform is 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 25. counter 25
keeps counting the number of pulses, and the microcomputer 22 reads the output value c _i of the counter 25 at the rising timing c of the rotational pulse a, calculates the remaining tape time, and drives the display element 26 to display it. .

Next, the operation of the microcomputer 22 will be explained.

(1) Calculating the period of the rotational pulse The period t i of the pulse is calculated using the following formula from the counter value c _{i -1} at one pulse edge and the counter value _{c i} at the next edge.

t _i =1/f(c _i −c _i-1 ) ......(3) (f is the frequency of the reference clock pulse) From this and the fact that one rotation of the reel corresponds to 8 rotation pulses, the reel 1 period of rotation
T _K is calculated as follows: T _K = 1/f _8k 〓 ^i=8k-7 t _i (4) (i is an integer of 8 or more).

(2) Amount of change in the rotation period T _i ΔT _i The period T _K of one rotation of the reel and the previous one
Calculate the difference ΔT _i in the period of rotation T _i-1 .

ΔT _i =T _i −T _i-1 (5) This ΔT _i is proportional to the thickness of the tape.

To explain this, in Figure 1, a certain 1
The following equation holds regarding rotation.

T _i =2πR _i /v ………(6) ∴ΔT _i =T _i −T _i-1 =2π/v(R _i −R _i-1 ) Here, the tape thickness θ is θ=R _i − Since R _i-1 , θ=v/2πΔT _i (7).

Therefore, depending on whether ΔT _i is a constant value, it can be determined whether the reel rotation is smooth or unstable. Also, if the thickness of the tape is unknown, you can use this to calculate the thickness of the tape,
It is also possible to correct the deviation from the nominal thickness.

(3) Calculation of remaining tape time τ _i The remaining tape time τ _i is calculated from equation (1) as follows: τ _i =l ₁ /V=V/4πθT _i ² −πr ² /vθ (8) However, since all the right-hand sides are known, the remaining tape time τ _i can be calculated.

(4) When the amount of change in rotation period ΔT _i is not constant,
The average value _i of ΔT _i is calculated using the following formula.

The thickness θ of the tape is calculated using the following formula.

θ=v/2π _i ......(10) Replace T _i with _i obtained from the following equation.

T _i =T _i-1 +ΔT _i (i=2, 3,...) Substitute these θ and T _i into equation (8) to find the tape remaining time τ _i .

(5) Measurement at start-up Immediately after the tape starts running, the remaining tape time τ can be quickly determined as follows.

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

Δt _i =t _i −t _i-1 (i=2, 3, 4,...) Calculate by substituting _i = _i-1 + _i ( ₁ = t ₁ ) T _i =8 _i θ = 8v/2π· _i = 4v/π _i into equation (8). However, as long as i is small, the error is large; however, in the term after one rotation in which the rotation of the supply reel becomes stable, the variation in Δt _i up to that point is absorbed by the above calculation, and a value with a small error is obtained. Whether the rotation of the reel has stabilized is determined by whether Δt _i has become constant, and immediately after stabilization, τ with a small error has been found.

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

(1) The remaining amount of tape can be detected quickly and with less error, such as when a VTR tape starts running.

(2) Even in cases other than the above, when the tape running speed v is constant but the reel rotation is unstable due to slack or uneven thickness of the tape,
Errors can be suppressed.

(3) It automatically determines whether the reel rotation is stable and calculates the remaining amount of tape using the optimal method, reducing errors.

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 a small error.

[Brief explanation of drawings]

Figure 1 is a plan view showing the configuration of a general magnetic tape recording device, which is used to explain the principle of detecting the amount of tape, and Figures 2A and B are an example of a method for measuring the rotation period of a tape reel. FIGS. 3a, b, and c are waveform diagrams for explaining the operation of the tape amount detection device of the present invention. FIG. 4 is a mechanical diagram of a tape tension used in a video tape recorder. FIG. 5 is a plan view showing the servo mechanism and a block diagram of a tape amount detecting device in an embodiment of the present invention. 5... Bladed disc, 6... Photo sensor, 2
DESCRIPTION OF SYMBOLS 1... Waveform shaping circuit, 22... Microcomputer, 23... Crystal oscillator, 24... Reference clock oscillator, 25... Pulse counter, 26... Display element.

Claims (1)

[Scope of Claims] 1. Means for generating a signal with a period t _i proportional to the rotation period T or angular frequency ω of at least one of the supply reel and the take-up reel, and means for generating a reference clock signal; It is equipped with a means for performing arithmetic processing to calculate the tape amount using the signal with period t _i and the reference clock signal, and detects the amount of change Δt _i of the signal with period t _i per constant rotation angle. A tape amount detection device characterized in that the tape amount is calculated using Δt _i obtained by the recurrence formula.