JPS6157579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotational speed detection device for detecting the rotational speed of a capstan or the like.

Conventionally, there has been a rotational speed detection device as shown in FIG. In FIG. 1A, 1 is a rotating shaft, 2 is a rotating disk, and a large number of fan-shaped reflecting parts 3 and absorbing parts 4 are arranged radially at regular intervals on the outer edge of one side, with the rotating shaft 1 as the center. It's rotating. Reference numeral 5 designates a light emitting element for projecting light, such as a semiconductor laser, whose light is turned into a circular spot light by a lens 6 and focused on the outer edge of the rotating disk 2.
When this spot light is located on the reflecting section 3, it is reflected and enters the photoelectric conversion element 7. The rotational speed is detected by photoelectrically converting the light incident on the photoelectric conversion element 7 and subjecting it to signal processing. Note that the reflecting section 3 and the absorbing section 4 are located at a distance R from the rotation center of the rotating disk 2. In FIG. 1B, the reflecting portions 3 and the absorbing portions 4 are arranged at equal pitches on the outer edge of the rotating disk 2, and a circular spot 8 is focused thereon. FIG. 1C is a further enlarged drawing of FIG. It is taking place. One point where the outer circumference of this spot light 8 intersects with the outer circumference of the reflecting part 3 is _O2 , the center point of the spot light 8 is _O1 , and the foot of the perpendicular line drawn from the center point _O1 to the outer circumference of the reflecting part 3 is _O3 . Then, ∠O ₂ O ₁ O ₃ = θ, the radius of the spot light 8 is r, _{1 3} = the width of the reflecting part 3 and the absorbing part is 2r,
If the pitch is 4r, and the area of the portion where the spot light 8 enters the region of the reflection section 3 is Sr, then Sr=r ² cos ^-1 /r-√ ² - ₂ (1). Here, if r=1, then from equation (1), Sr=cos ^-1 -√1- ₂ ...(2). When formula (2) is graphed, it becomes like the dotted line in FIG. 3, and as the spot light 8 is alternately crossed by the reflecting section 3 and the absorbing section 4, Sr increases and decreases in a sinusoidal manner. Now, it is assumed that the intensity of the light reflected by the reflecting section 3 is proportional to the area Sr, and if the photoelectric conversion by the photoelectric conversion element 7 is linear, the signal from the photoelectric conversion element 7 is also sinusoidal. The result is a wavy waveform. Converting this sinusoidal signal into a rectangular wave requires a complex signal processing circuit. However, even if the slice level is determined and the phase is detected, the rotating disk 2
The amplitude of the sinusoidal signal changes constantly due to the effects of surface wobbling and core wobbling of the rotating shaft 1, and the phase detection result using the slice level each time changes the phase regardless of the speed. It was hot.

The present invention has been made in view of the above points and to eliminate the above drawbacks, and by approximating the shape of the spot light to the shape of the reflecting and absorbing parts of the rotating disk, the rotational speed can be detected with high accuracy. An object of the present invention is to provide a rotation speed detection device.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 shows an embodiment of the spot and other parts of the rotational speed detecting device of the present invention, which is exactly the same device as FIG. 1A except for the shape of the spot light. Here, the width of the reflective part 3 and the absorbing part 4 is 2r each.
and let their pitch be 4r. Since the distance R from the center of the rotating disk 2 to the reflecting section 3 is R>>r, the shapes of the reflecting section 3 and the absorbing section 4 can be considered approximately rectangular here. Reference numeral 8' denotes a spot light according to the present invention, which has a rectangular shape similar to the shape of the reflecting section 3 and the absorbing section 4. This rectangular spot light 8'
has dimensions of width 2r and length L, and its center point is O′ ₁
Let the foot of the perpendicular line drawn from O' ₁ to the outer periphery of the reflecting section 3 be O' ₃ , and ' ₁ ' ₃ =. As a device for producing this rectangular spot light 8', a device in which a slit having a shape similar to this rectangle is interposed between a light emitting element for projection and the rotating disk 2 can be considered. If the area of the part where the rectangular spot light 8' created in this way enters the area of the reflecting part 3 is SL, then SL=L(r-)...(3) Here, r=1, L= If it is 1/2, then SL=1/2(1-)...(4), and when formula (4) is graphed, it looks like the dashed-dotted line in Figure 3. [Same as Sr] Here, it is assumed that the intensity of the light reflected by the reflecting part 3 is proportional to the area SL, and if the photoelectric conversion by the photoelectric conversion element receiving this reflected light is linear, the photoelectric conversion The signal from the element becomes a triangular wave.

FIG. 4A shows a signal processing circuit of a rotation detection device that processes the light incident on the photoelectric conversion element, and 7 is the photoelectric conversion element that receives the reflected light of the rectangular spot light, and the signal outputted from it. The waveform is a triangular wave. Reference numeral 9 denotes a differentiating circuit that inputs and differentiates the electric signal from this photoelectric conversion element, 10 a slice circuit that slices and detects the signal from this differentiator circuit 9 at a constant level, and 11 a circuit that detects the signal detected by the slice circuit 10. A phase detection circuit detects the phase, and detects and outputs whether there is a phase shift, that is, whether there is a change in the rotational speed of the rotating disk 2 with respect to a predetermined rotational speed. Figure 4B
The signal waveform shows the relationship between the output signal of the differentiating circuit 9 and the slice levels S and L of the slice circuit 10, and the relationship between the phase detection points. At this time, the rotational speed of the rotating disk is kept at a constant value.

The aforementioned rectangular spot light 8' is applied to the photoelectric conversion element 7.
The reflected light enters the photoelectric conversion element 7.
Upon photoelectric conversion, a triangular wave signal is output. When this triangular wave signal is differentiated by the differentiating circuit 9, it becomes a rectangular wave as shown in FIG. 4B. Here, if the amplitude of a normal rectangular wave is D, the amplitude changes due to surface wobbling of the rotating disk 2 and center wobbling of the rotating shaft as described above. This change in amplitude has almost no relation to time in the case of a rectangular wave, so even if the slice level point is detected at slice levels S and L by the slice circuit 10, it will not be affected by the change in amplitude. Furthermore, even if the slice levels S and L of the slice circuit 10 vary somewhat, there is no phase shift because the slice level points are taken at the rising and falling points of the rectangular wave. Therefore, the slice circuit 10
Even if the slice level point is taken at , and the phase is detected by the sampled phase detection circuit 11 , there is no phase shift, and if the rotational speed of the rotating disk 2 is constant, the phase can be detected correctly in a half period T. It can be detected that the speed is constant.

The present invention is not limited to this, and in the embodiment, when R≫r, the reflective part is approximated to a rectangle, but
When a rectangular shape cannot be approximated, the reflecting section becomes a fan shape, and by making the shape of the spot light similar to this fan shape, the same configuration and operation as described above can be achieved. In addition, since the width L of the rectangular spot light toward the center of the rotating disk can be made large (actually, if the spot light and the reflecting part are fan-shaped, L can take a value close to R), The area of the reflected light of the spot light can be increased, and therefore, when this reflected light is detected by a photoelectric conversion element, the detection voltage can be increased.

By configuring and operating the present invention as described above, it is possible to detect rotational speed without being affected by core wobbling of the rotating shaft or surface wobbling of the rotating disk, which are unrelated to rotational speed, and furthermore, it is possible to detect fluctuations in the slice level. Even if there is a rotational speed, this effect has no relation to the rotational speed detection, so the rotational speed can be detected with high accuracy. Furthermore, since the area of the spot light can be relatively larger than that of the conventional circular spot light, the detection voltage by the photoelectric conversion element can also be large, which has the effect of reducing the influence of noise such as external light.

[Brief explanation of the drawing]

Fig. 1 shows a conventional rotational speed detection device, Fig. 2 is an enlarged view showing the relationship between the reflecting part and the spot light, which is the main part of the present invention, and Fig. 3 shows the area where the spot light is located in the reflecting part. FIG. 4A is a block diagram of an embodiment of the signal processing circuit applied to the present invention, and FIG. 4B is a signal waveform diagram showing the relationship between the signals in the block diagram of FIG. 4A. be. 1; Rotating shaft, 2; Rotating disk, 3; Reflector, 4;
Absorption part, 5; Light emitting element for projecting light, 7; Photoelectric conversion element, 8'; Rectangular spot light, 9; Differential circuit, 1
0: slice circuit, 11: phase detection circuit.

Claims (1)

[Scope of Claims] 1. A large number of reflective parts formed of surfaces that reflect light and absorption parts formed of surfaces that absorb light are arranged radially at regular intervals on the outer edge of the rotating disk. , the rotational speed of the rotating disk is determined by shining a spotlight on the reflecting and absorbing sections of the rotating rotating disk, receiving the light reflected by the reflecting section with a photoelectric conversion element, and processing the photoelectrically converted signal. In the rotational speed detection device for detection, a slit having a shape similar to the reflecting surface of the reflecting part and allowing the spot light to pass through, interposed in the optical path between the light source and the reflecting part of the rotating disk, and a photoelectric conversion element. A rotational speed detection device comprising a signal processing circuit comprising a differentiating circuit for differentiating an output triangular wave signal and a phase detection means for detecting the phase of a rectangular wave signal output from the differentiating circuit.