JPH0625660B2 - Tilt sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tilt sensor for detecting a tilt angle of a rotating disk having a high regular reflectance.

[Prior Art] FIG. 5 shows a conventional tilt sensor. This tilt sensor includes an LED 2 that irradiates the rotating disk 1 with light.
Then, in order to receive the reflected light, a pair of photo diodes 3 and 3 arranged on both sides of the LED 2 are provided (FIG. 4A). In this case, the lens 4 can be interposed between the rotating disk 1 and the photodiodes 3 and 3 to make the incident angle of the lens 4 substantially perpendicular (FIG. 11B).

The light emitted from the LED 2 is reflected by the rotating disk 1 and enters the photodiode 3. For example, the rotating disk 1 is Δθ
When tilted in the B direction at an inclination angle of (see (a) in the figure), the amount of light incident on the left photodiode 3 increases and the amount of light incident on the right photodiode 3 decreases. Since the increase / decrease in the amount of light can be electrically detected as the increase / decrease in photocurrent, if the photocurrent value for the tilt angle is experimentally obtained in advance, the tilt angle of the rotating disk 1 can be calculated from the obtained photocurrent value. Can be detected.

[Problems to be Solved by the Invention]

However, in the conventional tilt sensor, a positional deviation occurs when the LED chip and the substrate are die-bonded, and the position of the LED is determined with reference to the substrate, which causes a problem that the optical axis is displaced. It was

FIG. 6 shows causes of variations in directivity.
For example, when the light emitting element, which should originally be fixed at the position a, is fixed at the position b, the optical path goes leftward after passing through the lens. Also, when the light emitting element is fixed at the position of c,
The optical path goes to the right after passing through the lens. in this case,
The directional characteristics are not symmetrical with respect to the optical axis and are biased rightward or leftward.

FIG. 7 shows an example of the directional characteristics of an LED whose directional characteristics are biased. As described above, when an LED having a biased directional characteristic is used, an error occurs in the measured value, and the error must be adjusted by the optical system. in this case,
Since the optical axis shift occurs at a two-dimensional level, it is desirable to use an adjustment mechanism that can be optically adjusted in two directions. However, the use of a two-way adjustment mechanism makes the sensor expensive, and the use of an inexpensive one-way adjustment mechanism makes the adjustment very difficult.

Therefore, an object of the present invention is to provide a tilt sensor that does not require an optical system adjustment mechanism.

[Means for Solving the Problems]

In order to achieve the above object, the present invention achieves a tilt sensor that includes a slit light source, a position detection element, and a calculation unit, and that detects a tilt angle of a rotating disk having a high regular reflectance. Here, the slit light source irradiates the rotating disk with slit light along the radial direction of the rotating disk, and the position detecting element extends in the tangential direction of the rotating disk to receive the reflected light of the slit light. The calculation means detects the tilt angle of the rotating disk based on the position of the reflected light on the light receiving surface.

[Action]

Since the present invention is configured as described above, the slit light emitted from the slit light source and reflected by the rotating disk is:
It is projected in a direction orthogonal to the direction in which the light receiving surface of the position detection element extends. The computing means detects the tilt angle of the rotating disk by comparing the reference position such as the projection position when the rotating disk is not tilted with the projected position when the rotating disk is tilted.

〔Example〕

A tilt sensor according to an embodiment of the present invention will be described below with reference to the accompanying drawings. In the description, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a perspective view showing a tilt sensor according to this embodiment. This tilt sensor is basically configured to include a slit light source 5, a position detection element 6, and a calculation processing section (calculation means) (not shown).

The slit light source 5 is configured by including an elongated slit 5a on an LED (not shown). In this case, since the slit 5a is provided between the LED and the rotary disk 7, the light emitted from the LED is slit-shaped in the rotary disk 7.
Is projected to. The rotating disk 7 is provided at least at a position facing the slit light source 5 with a reflecting surface (not shown) having a large regular reflectance in the circumferential direction. The position detecting element 6 is a PSD (Position-Sensitive Detectors) 6a as a light receiving surface.
And the PSD head amplifier 6b are included, and the projection position can be detected from the slit light projected on the PSD 6a. Specifically, when the slit light is incident on the light receiving surface 6a, electric charges proportional to the light energy are generated at the incident position. The generated charges pass as a photocurrent through a resistance layer (not shown) and are output from the electrodes. Since this resistance layer is made to have a uniform resistance value over the entire surface, the photocurrent is divided in inverse proportion to the distance (resistance value) to the electrode and taken out from the electrode. By calculating the difference or ratio of the currents extracted from the electrodes by the arithmetic processing unit, the incident position of light can be calculated regardless of the incident light energy. The arithmetic processing unit is composed of, for example, an IC incorporating an arithmetic processing circuit, and can output a voltage value V1 corresponding to the slit light projection position. The LED driver 8 is connected to the LED via a driver transistor 9 and a current setting resistor 10.

FIG. 2 is a side view showing the basic principle of the present invention. The slit light emitted from the slit light source 5 is applied to one surface of the rotary disk 7 along the radial direction of the rotary disk 7 and projected on the light receiving surface 6 a of the position detection element 6. Therefore, for example, a perpendicular line drawn in a direction orthogonal to the plane of the rotating disk 7 is irradiated with an inclination angle of θ2.

For example, the PSD 6 when the rotating disk 7 is not tilted
With the position of the slit light projected on a as the reference, when the rotating disk 7 is tilted by θ1, the positional deviation amount on the PSD 6a is ΔX. Here, if the distance from the slit light source 5 to the rotating disk 7 is L (see FIG. 1), ΔX = L · tan 2θ1 (1) holds. Here, assuming that the length of the PSD 6a in the longitudinal direction is C and the voltage value when the total photocurrent is converted into a voltage is V0, the relational expression with ΔX is V1 = V0 (0.5−ΔX / C) ... (2) By substituting the equation (1) into the equation (2), V1 = V0 (0.5-L · tan 2θ1 / C) is obtained. Therefore, the tilt angle θ1 of the rotating disk 7 can be calculated from the voltage value V1 corresponding to the projection position of the slit light.

The error on the die bond in PSD 6a is ΔX
Instead of, the error can be taken into account and corrected by using (ΔX ± α). In this case, the output voltage value V1 is given by V1 = V0 (0.5-L · tan 2θ1 / C) ± 0α / C, and therefore the PSD may be adjusted by ± V0α / C by the offset. Therefore, no optical adjustment is required, and the tilt sensor can be easily manufactured.

FIG. 3 is a plan view showing an arrangement example of the tilt sensor with respect to the rotating disk 7. What is important here is that the longitudinal direction of the slit 5a substantially coincides with the radial direction so that the slit disk is irradiated with the slit light along the radial direction of the rotary disk 7, and the longitudinal direction of the reflected light. This is the point where the extending direction of the light receiving surface 6a and the tangential direction substantially coincide with each other so that the extending direction of the light receiving surface 6a is orthogonal.

FIG. 4 shows the directional characteristics of an LED with an aspherical lens. By using the LED chip 12 having an aspherical lens 11 such as a cylindrical lens as a slit light source in combination with a slit, a lens optical system becomes unnecessary. In an ordinary LED, scattering occurs when light is emitted from the package, and the light that hits the DUT does not serve as a point light source, which makes designing difficult. However, if an LED with an aspherical lens is used, a point light source can be easily realized, the spot size can be predicted, and the design becomes easy. In this case, the size of the LED 12 is 1, the distance of the LED 12 to the aspherical lens 11 is L ′, and the aspherical lens 11 is
From L to the non-measurement object, the spot size of the LED 12 is given by (L / L ') l.

The present invention is not limited to the above embodiment. For example, in this embodiment, the tilt angle can be detected, but since the moving distance of the slit light is detected in principle, the amount of surface blur can be detected. Therefore, it can also be used as a distance sensor.

Further, although the PSD is used as the position detecting element, a two-divided photodiode or the like can be used.

〔The invention's effect〕

Since the present invention is configured as described above,
It is possible to provide a tilt sensor that does not require adjustment of the optical system.

Further, this tilt sensor can eliminate the influence of the reflectance of the rotating disk.

[Brief description of drawings]

FIG. 1 is a perspective view showing a tilt sensor according to an embodiment of the present invention, FIG. 2 is a side view showing the basic principle of the present invention, and FIG. 3 is a plan view showing an arrangement example of the tilt sensor with respect to a rotating disk. FIG. 4 is an explanatory diagram showing the directional characteristics of an LED with an aspherical lens, FIG. 5 is an explanatory diagram showing a tilt sensor according to the prior art, and FIG. 6 is an explanatory diagram for explaining the cause of the variation in directivity. FIG. 7 is an explanatory diagram schematically showing directional characteristics of LEDs. 1, 7 ... Rotating disk, 2 ... LED, 3 ... Photodiode, 4 ... Lens, 5 ... Slit light source, 6 ... Position detection element, 8 ... LED driver, 9 ... Driver transistor, 10 ... Resistor for setting current, 11 ... Aspherical lens, 12 ... LED chip.

Claims (1)

[Claims] 1. A tilt sensor for detecting a tilt angle of a rotating disk having a high regular reflectance, comprising a slit light source having a longitudinal direction along a radial direction of the rotating disk and irradiating the rotating disk with slit light. A position detecting element having a light receiving surface extending in a tangential direction of the rotating disk for receiving the reflected light of the slit light, and a tilt angle of the rotating disk is detected based on the position of the reflected light on the light receiving surface. A tilt sensor configured to include a computing unit.