JPS6316028Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a disk player that detects and reproduces information such as a video signal recorded on a disk (disc) using a capacitive pickup.

The cartridge section of the capacitive pickup used in conventional disk players of this type has a first
As shown in the figure, a cantilever 1 is provided, and a needle 3 is provided at the tip of a glass rod 2 attached to its tip. The cantilever 1 is rotatably supported by a rubber damper 4 in a cartridge case (not shown), has a magnet 5 at its rear end, and is tracked by a tracking coil (not shown).

The needle 3 is formed of a hard material such as diamond into a substantially pentagonal prism shape, has an electrode film on its side surface, and detects recorded information using changes in capacitance between the needle 3 and the disk 6 as a signal source. .

A fly lead 8 is connected between this needle 3 and a fly lead terminal 7 provided on a cartridge case (not shown).
The needle 3 is curved greatly backward and engaged, so that the needle 3 is lightly pressed against the disk 6 and serves as a lead wire from the needle 3.

The tip of the resonator rod 9 is brought into contact with the fly lead terminal 7, and the resonator rod 9 and the lead lines 10, 11 are connected to the side of the cartridge portion.
As a result, a detection section 12 is constructed which includes a resonant circuit Q shown in a lumped circuit constant system in FIG. 2, an oscillation coil _L1 , and a detection coil _L2 .

Then, a high frequency output of, for example, 915 MHz is input from the UHF oscillator 13 to the lead line 10, and the resonant frequency of the resonant circuit Q is changed by changing the capacitance Ca between the needle 3 and the disk 6, and slope detection is performed. generates an AM wave, which is connected to a diode.
AM detection circuit 14 consisting of D ₁ , capacitor C ₁ , and resistor R ₁ performs AM detection, detects information recorded in advance as an FM signal modulated on the disk as an FM wave, amplifies it with preamplifier 15, and outputs it. do.

When detecting recorded information using this capacitive pickup, if the stylus pressure is F, the spring constant is k, and the amount of stylus depression is x (see Figure 1), it is expressed as F=kx. When the needle sinking amount x changes by Δx due to accompanying vertical vibration, etc., a stylus pressure change of ΔF=kΔx occurs.

This stylus pressure variation affects the sensitivity of the above-mentioned signal detection circuit, and the level, that is, the amplitude of the reproduced FM wave changes. Its frequency is 15Hz, assuming the disk rotation speed is 900rpm.

This amplitude fluctuation makes the reproduced signal unstable,
When playing back a video signal, it adversely affects the screen and makes it unsightly.

Therefore, it is necessary to detect such stylus pressure fluctuations and correct the reproduced signal. For this purpose, a strain gauge is attached to the fly lead 8 shown in FIG. 1, and a change in the distance between the disk 6 and the bottom surface of the arm gauge 16 to which the cartridge with the needle 3 is attached is measured as shown in FIG. There are ways to detect it.

However, the former has the problem that special measures must be taken to attach the strain gauge to the fly lead, and furthermore, the damping system of the strain gauge itself must be considered.

Furthermore, the latter has the problem that different corrections must be made when the arm cage is near the outer periphery of the disk and when it is near the inner periphery.

Therefore, the present invention detects stylus pressure fluctuations with a simple configuration without causing the above-mentioned problems.
It is an object of the present invention to make it possible to perform correction to keep the output level of a reproduced signal constant.

Therefore, in the disk player according to the present invention, a metal piece having a width equal to or larger than the tracking width is attached above the part where the fly lead moves up and down as the needle of the capacitive pickup moves up and down. The above objective is achieved by providing a circuit that detects changes in capacitance between the fly lead and adjusts the gain of the preamplifier that amplifies the signal detected by the fly lead. be.

Hereinafter, embodiments of this invention will be described with reference to FIG. 4 and subsequent figures of the drawings.

FIG. 4 is a block circuit diagram showing an embodiment of this invention, together with the mounting positions of the metal pieces.

In this invention, the metal piece 20 is attached to the fly lead 8 by vertical movement of the capacitive pick-up needle 3.
It is attached above the part where the needle 3 moves up and down so as to have a width W that is equal to or larger than the tracking width (the maximum displacement width in which the needle 3 can move in the radial direction of the disk 6 by the tracking servo). Note that a specific example of the mounting state will be described later.

Fluctuations in stylus pressure are detected based on changes in capacitance Cb between the metal piece 20 and the fly lead 8.

That is, the oscillation output of the frequency d from the oscillator 21 drives the variable capacitance diode CD through the resistor _R2 , applies AM modulation by changing the capacitance Cb, and transmits it to the needle 3 and the disk 6. The input signal is input to a slope detection block 22 for detecting an information signal due to a change in capacitance Ca between.

In this case, the oscillation frequency d of the oscillator 21 is an odd multiple of 1/2 of the horizontal synchronization signal _fH in the case of a video signal, that is, d=(2n+1) _H /2, and is 100KHz to 300KHz, which does not affect the reproduced signal.
Select a frequency of approximately

For NTSC color video signal, _H = 15.75KHz x 99.9%, and d is, for example, 243.881KHz or 259.615KHz.
It is enough to do it to a certain extent.

Note that the slope detection block 22 is composed of a detection section 12, a UHF oscillator (oscillation frequency: 915MHz) 13, and an AM detection circuit 14, as in the conventional example shown in FIG. 2, and its operation is also the same as described above. Since they are similar, the explanation will be omitted.

The output of the slope detection block 22 is amplified by the preamplifier 23 to obtain an FM wave information signal output.As shown in FIG. signal) is superimposed with a signal of frequency d that is AM modulated with a 15Hz stylus pressure fluctuation signal.

This signal is passed through the FM demodulation circuit 24 to obtain a reproduced output of the information signal, and is also passed through the bandpass filter 25 having a passband of the center frequency d to generate a 15Hz stylus pressure fluctuation signal as shown in FIG. 5b.
Extract only the AM modulated signal b of frequency d.

This signal b is connected to diode D ₂ and capacitor C ₂
Detected by an AM detection circuit consisting of a resistor _R3 and a resistor R3, a 15Hz stylus pressure fluctuation signal c as shown in Fig. 5c is obtained.
get.

This stylus pressure fluctuation signal c is fed back to the preamplifier 23 and its gain is adjusted to control the output level of the preamplifier 23 to be constant regardless of the stylus pressure fluctuation.

Figure 6 shows this AGC (automatic gain
Although a specific example of the control circuit is shown, the preamplifier 23 is a known voltage-controlled variable gain amplifier (VCA), and detailed explanation thereof will be omitted.

FIG. 7 shows another embodiment of this invention, in which two preamplifiers are provided, and the first stage uses an ordinary preamplifier 15 as in the conventional example shown in FIG.
The output is further amplified by a second-stage preamplifier 23 using a VCA, and then output to an FM demodulation circuit 24.

On the other hand, the output of the first-stage preamplifier 15 is passed through a band-pass filter 25 to extract a signal with frequency d, which is subjected to AM detection to detect a 15Hz stylus pressure fluctuation signal as in the previous embodiment. Preamplifier 2
3 to adjust the gain and control the output to a constant value.

8 to 10 show specific mounting states of the metal piece 20. FIG.

The metal piece 20 is attached to a U-shaped attachment piece 31 that protrudes inward from the side surface of the cartridge case 30, and is attached to the oscillator 21 shown in FIGS. 4 and 7.
A contact portion is provided which is connected to a circuit such as a variable capacitance diode via a contact rod 32.

As explained in the embodiments above, according to this invention, by simply attaching one metal piece to the cartridge of a capacitive pick-up, changes in the capacitance between this metal piece and the fly lead can be applied. As a result, fluctuations in stylus pressure can be easily detected, and the playback signal level can be kept constant by adjusting the gain of the preamplifier that amplifies the signal detected by the stylus.

Therefore, it is easy to install, and there is no need to adversely affect the reproduction of information signals or to make corrections depending on the position of the pickup, and the influence of fluctuations in stylus pressure can be reliably eliminated.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing the cartridge section of a capacitive pickup used in a conventional disk player, FIG. 2 is a circuit diagram showing the configuration for reproducing information signals, and FIG. FIG. 4 is an explanatory diagram of vertical vibration accompanying the rotation of the disc, and FIG. 5 is a block circuit diagram showing an embodiment of this invention.
c is a signal waveform diagram of each part used to explain the operation of the embodiment of FIG. 4, FIG. 6 is a circuit diagram showing a specific example of the preamplifier in the embodiment of FIG. 4, and FIG.
A block circuit diagram showing another embodiment of this invention, FIG. 8 is a perspective explanatory view showing a cartridge portion of a capacitive pickup according to this invention, and FIG. 9 is a block circuit diagram showing another embodiment of this invention.
FIG. 8 is a schematic side view taken from the direction of arrow A in FIG. 8 with the front side plate removed. FIG. be. 1... Cantilever, 3... Needle, 6... Disk, 8... Fly lead, 9... Resonator rod, 10, 11... Lead line, 12... Detection section, 13... UHF oscillator, 14... ...AM detection circuit, 15, 23 ... Preamplifier, 20 ... Metal piece, 21 ... Oscillator, 22 ... Slope detection block, 24 ... FM demodulation circuit, 25 ... Bandpass filter, 30 ... Cartridge case .

Claims (1)

[Scope of utility model registration request] In a disk player that detects and reproduces information recorded on a disk using a capacitive pickup, the needle of the capacitive pickup is held between the needle and the cartridge case by vertical movement. A metal piece having a width equal to or larger than the tracking width is attached above the part where the fly lead moves up and down, and a change in capacitance between the metal piece and the fly lead is detected, and the needle What is claimed is: 1. A disc player comprising: a circuit for adjusting the gain of a preamplifier that amplifies a signal detected by a stylus, and the output level of a reproduced signal is kept constant regardless of fluctuations in stylus pressure.