JP2001221611A - Range finder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the scanning speed of a range finder by reducing the moment of inertia of a scanning mirror. SOLUTION: A range finder, which projects in order pulsed light in a plurality of directions and measures the time required until the reflected pulsed light is received after the pulse light is transmitted in each direction, uses a light- receiving lens 21 having an effective area with a size w1 of the area in a first direction X being smaller than a size w2 in a second direction Y, crossing the first direction X at right angles and the lens 21 is arranged, so that the second direction Y becomes parallel to the rotating axis of the scanning mirror 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring apparatus for measuring the round trip propagation time of light to an object reflecting light as distance information.

[0002]

2. Description of the Related Art Time of flight (TOF) from transmission of a light pulse to reception of a pulse reflected back from an object.
ight), it is possible to determine the inter-object distance by applying a known light propagation velocity. It has been proposed that a distance measuring device using this technique incorporates a scanning mechanism for deflecting pulsed light and performs measurement in many directions at high speed.

FIG. 7 is a schematic diagram of an optical system of a conventional distance measuring device. The optical system 100 includes a scanning mirror 310 and an actuator 320 for rotating the scanning mirror 310 about an axis along the direction Y.
And

[0004] The pulse light emitted from the laser light source 110 passes through a light projecting lens 120 for adjusting the spread angle, and enters a scanning mirror 310 via a prism 130. The scanning mirror 310 deflects the pulse light in a direction corresponding to the angular position at that time. The pulse light P10 directed outward from the scanning mirror 310 is reflected on the surface of the object Q. As long as the object surface is not specular, its reflection will be diffuse. Therefore, at least a part of the reflected pulse light P20 goes to the optical system 100 even if the incidence on the object surface is not perpendicular incidence. The pulse light P20 returned to the optical system 100 is reflected by the scanning mirror 310 and proceeds to the light receiving lens 210. The light receiving lens 210 condenses the pulse light P20 on the light receiving surface of the photodetector 220.

FIG. 8 is a configuration diagram of a portion related to pulse reception in a conventional optical system. FIG. 8A is a front view, and FIG.
(B) is a side view. Conventionally, a light receiving lens 210 having a circular (axially symmetric) effective light receiving surface in plan view has been used. The light receiving lens 210 has an optical axis A2
0 is arranged to intersect at right angles with the rotation axis A10 of the scanning mirror 310.

When the light receiving lens 210 has a circular shape, the width in the direction Y of the light beam condensed by the light receiving lens 210 is w, and the width in the direction X orthogonal to the direction Y is also w. During the scanning operation, the reflection surface (front surface) of the scanning mirror 310 is inclined with respect to the optical axis A20, so that the length h in the rotation radial direction of the reflection surface must be larger than the width w of the light beam in the direction X. (H> w). If the inclination angle of the scanning mirror 310 is θ (0 <θ <π / 2), h = w / sin θ. Therefore, the outer dimension H in the rotation radial direction of the conventional scanning mirror 310 is larger than the outer dimension W in the rotation axis direction (direction Y).

[0007]

SUMMARY OF THE INVENTION Conventional scanning mirror 31
At 0, the moment of inertia around the rotation axis was large, and a large acceleration torque was required for starting and braking the rotation. Therefore, when an actuator having a relatively small output torque is used for rotational driving, the rotational speed cannot be increased, and there is a problem that the time required for scanning becomes longer. An actuator having a large output torque is disadvantageous in reducing the size and power consumption of the distance measuring device. Incidentally, Japanese Patent Laid-Open No. 5-25
Japanese Patent No. 7076 discloses a configuration in which received light is condensed by a fixed concave mirror, and a scanning mirror and a light receiver are integrally rotated near the center of curvature to deflect transmitted light. According to this, it is possible to reduce the movable part and reduce the moment of inertia, thereby speeding up the scanning.
However, since the effective range of the concave mirror at each point in time during scanning is narrow, a large concave mirror is required. Therefore, it is difficult to reduce the size of the entire device.

Further, in the related art, there is a problem that one end of the scanning mirror 310 in the rotation radial direction is a useless portion that does not contribute to transmission and reception. Hereinafter, this problem will be described.

FIG. 9 is a diagram showing a conventional arrangement relationship between a scanning mirror and a light receiving optical axis. FIG. 9 (a) and (b)
As described above, the scanning mirror 310 reciprocates in an angle range from θa to θb with respect to the optical axis A20.
The rotation axis A10 is set to coincide with the center of gravity of the scanning mirror 310 in order to balance the rotation. As long as a general scanning mirror 310 having a rectangular cross section and a uniform material is used, the rotation axis A10 is located at the center of the cross section. As described above, conventionally, the rotation axis A10 intersects the optical axis A20 of the light receiving lens.

[0010] With the rotation, the length of the area of the reflecting surface where the effective light beam directed toward the light receiving lens is incident is a10.
To a20, and the sizes of the portions (shaded portions in the drawing) 311, 313, 314 where no effective light flux enters are also changed. As is clear from FIG. 9, in the conventional configuration, an effective light flux does not always enter the portion 311 on one end side (upper side in the figure) in the rotational radial direction regardless of the deflection angle position. That is, a part of the scanning mirror 310 does not participate in the deflection. The presence of such a useless portion 311 unnecessarily increases the moment of inertia around the rotation axis of the scanning mirror 310, and increases the output torque required of the drive source during acceleration and deceleration when reversing the direction of the reciprocating rotation. However, since the useless portion 311 is biased toward one end, removing the useless portion 311 causes an imbalance in the weight distribution of the scanning mirror 310, which may cause vibration and noise and shorten the life of the apparatus. Therefore, the portion 311 has to be left even if it is optically useless.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the moment of inertia of a scanning mirror to speed up scanning.

[0012]

According to the present invention, a non-axially symmetric lens having dimensions different from each other in two directions perpendicular to each other is used as a light receiving lens, and its long direction is made parallel to the rotation axis of the scanning mirror. . Further, in the present invention, the optical axis of the light receiving lens and the rotation axis of the scanning mirror intersect with an offset.

By using a non-axisymmetric light receiving lens, a predetermined effective light receiving area can be ensured and measurement accuracy can be maintained, and the size of the scanning mirror in the rotation radial direction can be shortened to reduce the moment of inertia. it can.

If the moment of inertia is small, high-speed scanning by a small rotary drive source (actuator) having a small output torque becomes possible. That is, assuming that the scanning mirror is a rectangular parallelepiped-shaped object, the moment of inertia I when rotating around the axis is expressed by the following equation (1). I = ρ · W · H · T (H ² + T ² ) / 12 (1) ρ: Density W: Length in the rotation axis direction H: Length in the direction perpendicular to the rotation axis (H = W / sin θ,
θ: tilt angle) T: thickness From this equation, W affects the moment of inertia I to the first power, whereas H is approximately 3 when T is relatively small.
It can be seen that the power has an effect. In other words, the effect when W increases is small, and the effect of decreasing the moment of inertia I when H decreases is large. Assuming that the rotor inertia and the load torque of the actuator itself are sufficiently small, the acceleration torque required to start or reverse the rotation of the actuator is proportional to the inertia moment I of the object. Therefore, if the inertia moment I decreases, the motor can be rotated at high speed with a small torque.

The distance that can be measured by transmitting and receiving light is determined by the amount of light focused on the photodetector, and this amount is proportional to the effective area of the light receiving lens. The effective area of the light receiving lens is closely related to the size of the reflection surface of the scanning mirror. When the dimension H of the scanning mirror in the radial direction of rotation (direction perpendicular to the axis of rotation) is reduced to reduce the moment of inertia I, in order to secure a predetermined measurable distance, the area of the reflecting surface is reduced to the dimension H. What is necessary is just to increase the dimension W in the rotation axis direction so as not to be different from before. If the dimensions of the light receiving lens are set in accordance with the scanning mirror, there is no useless portion where light does not enter the light receiving lens.

On the other hand, by providing an offset in the positioning between the light receiving lens and the scanning mirror, it is possible to equalize the position of the portion where the effective light beam does not enter on the reflecting surface of the scanning mirror at both ends in the rotational radial direction. Therefore,
Without losing the balance of the weight distribution, the size of the scanning mirror in the rotation radial direction can be reduced so that the portion where no effective light beam enters is reduced as much as possible, thereby reducing the moment of inertia.

According to a first aspect of the present invention, there is provided an apparatus for emitting a pulse light, a scanning mirror for deflecting the pulse light, and condensing reflected pulse light reflected by an external object and returned to the scanning mirror. A light receiving lens, and a photodetector that receives the condensed reflected pulse light, sequentially projecting the pulse light in a plurality of directions, and a time from transmission of the pulse light to reception of the reflected light pulse in each direction. Wherein the dimension of the effective area of the light receiving lens in the first direction X is shorter than the dimension of a second direction Y orthogonal to the first direction X, and the light receiving lens is It is arranged so that the direction Y is parallel to the rotation axis of the scanning mirror.

In the distance measuring apparatus according to the present invention, the scanning mirror is rotated about the rotation axis, and the scanning mirror and the light receiving lens are rotated about an axis orthogonal to the rotation axis. It has two-dimensional scanning means.

According to a third aspect of the present invention, the light source and the photodetector rotate integrally with the scanning mirror and the light receiving lens about an axis orthogonal to the rotation axis.
In the distance measuring apparatus according to a fourth aspect of the present invention, the light receiving lens is disposed so that its optical axis intersects with the rotation axis of the scanning mirror at a fixed offset distance.

In the distance measuring apparatus according to a fifth aspect of the present invention, the value of the offset distance is defined by: a virtual plane including a reflection surface of the scanning mirror when the scanning mirror is disposed at the first deflection angle position; When the scanning mirror is disposed at the second deflection angle position, the optical axis of the light receiving lens intersects a line of intersection with the reflection surface of the scanning mirror.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a block diagram showing the overall configuration of a distance measuring apparatus according to the present invention, and FIG. 2 is a conceptual diagram of distance measuring.

The distance measuring apparatus 1 includes an optical system 10 for transmitting and receiving light pulses, a light emitting circuit 40 for driving a light source, a receiving circuit 50 for A / D converting and storing a photoelectric conversion signal, and a controller 60. The optical system 10 has a scanning mechanism 30 for performing measurement in multiple directions. The receiving circuit 50
The controller 60 converts the reception data Dt indicating the reception time t2 of the reflected pulse light according to the photoelectric conversion signal from the optical system 10 into the controller 60.
Send to The controller 60 sets the time when a certain time has elapsed from the output of the light emission instruction signal as the transmission time t1, and the light propagation time (flight time) from the transmission time t1 to the reception time t2.
Calculate Ta. Further, the controller 60 calculates the distance L to the object Q from the light propagation time Ta and the known light propagation speed (3 × 10 ⁸ m / s), and outputs the distance data DL to an external device (eg, a computer) not shown. . In addition,
The device configuration is not limited to the example. For example, the sampling data of the photoelectric conversion signal may be used as the output of the distance measuring device 1, and the distance may be obtained by an external computer.

FIG. 3 is a schematic diagram of an optical system, and FIG. 4 is a configuration diagram of a part related to pulse reception in the optical system. Optical system 1
The configuration of 0 is the same as the conventional example of FIG. 7 except for the shapes of the scanning mirror 31 and the light receiving lens 21. Pulse light emitted from a semiconductor laser 11 as a light source passes through a light projecting lens 12 for adjusting a divergence angle, and enters a scanning mirror 31 via a prism 13. The scanning mirror 31 is driven by an actuator 32, rotates about an axis A1 along the direction Y, and deflects the pulse light in a direction corresponding to the angular position.
The pulse light P1 that has traveled from the scanning mirror 31 to the outside is reflected on the surface of the object Q, and a part thereof (pulse light P20) travels to the optical system 10. The pulse light P20 returned to the optical system 10
Is reflected by the scanning mirror 31 and proceeds to the light receiving lens 21.
The light receiving lens 21 focuses the pulse light P20 on the light receiving surface of the photodetector 22. In the distance measuring device 1, the scanning mirror 31
By changing the angular position of the object Q, it is possible to measure the distance to a plurality of locations of the object Q without changing the installation position or posture of the device itself.

In the optical system 10, the width w2 of the light beam condensed by the light receiving lens 21 in the direction Y is larger than the width w1 in the direction X orthogonal to the direction Y. w2 is replaced by k (k>
1) times, that is, if w2 = kw, w1 = w / k
It is. The cross-sectional shape of such a light beam is
Can be realized by making the shape of (1) long in one direction with an aspect ratio of k: 1 / k (an oval shape, an elliptical shape, a rectangular shape, etc.). Specifically, an axially symmetric lens obtained by cutting both ends in one direction may be used, or a Fresnel lens or a hologram lens formed into an elliptical shape or a rectangular shape from the beginning may be used. Here, the cross-sectional shape of the received light beam is different from that of the conventional example of FIG. 7, but the same value as the conventional example can be ensured for the cross-sectional area. The cross-sectional area is kw · w / k =
It is proportional to D ^2.

The size required for the scanning mirror 31 corresponds to the direction Y in FIG.
Is kW, and the length H 'in the rotation radial direction orthogonal to the rotation axis A1 is H / k. The moment of inertia I 'around the rotation axis of the scanning mirror 31 having such a size is given by the equation (2). I ′ = ρ · H / k · kW · T [(H / k) ² + T ² ) / 12 = ρ · H · W · T [(H / k) ² + T ² ) / 12 (2) (2) ) equation from the equation (1), if may ignore the T ² sufficiently small thickness T is than the length H, holds the relationship ^{I '= I / k 2 ...} (3) . For example, the aspect ratio of the shape of the light receiving lens 21 is 1: 2, and the lengthwise direction is the scanning mirror 31.
If k = ^21/2 is set so as to be parallel to the rotation axis A1 of the above, I '= I / ( ^21/2 ) ² = I / 2 (4) Can be reduced to の. Since the acceleration torque required for the actuator 32 is proportional to the moment of inertia I ′, the expression (4) indicates that the required acceleration torque is １ ／. This is 2% when the actuator 32 having the same output torque as the conventional one is used.
It means that double acceleration can be given. Accordingly, the scanning mirror 31 can be driven at a high speed, and the time required for scanning the object Q can be greatly reduced.

FIG. 5 is a diagram showing an arrangement relationship between a scanning mirror and a light receiving optical axis. The rotation axis A1 of the scanning mirror 31 is set to coincide with the center of gravity of the scanning mirror 31 because it is necessary to secure a rotational balance. Then, unlike the conventional example, the optical axis A2 of the light receiving lens intersects with the rotation axis A1 at a fixed offset distance d.

As shown in FIG. 5A, the scanning mirror 31 has an inclination angle θa with respect to the optical axis A2 and an angle Δ
It reciprocates between the angular position of FIG. 5B inclined by θ. With the rotation, the length of the area of the reflecting surface where the effective light beam directed toward the light receiving lens is incident is from a1 to a2.
It varies in the range up to. In the example of FIG. 5, the dimension H ′ (H ′ = a ′) of the scanning mirror 31 in the rotation radial direction is set so that the entire reflecting surface is effective when the inclination with respect to the optical axis A2 is minimum.
1) is selected to the minimum. The dotted lines on both outer sides of the scanning mirror 31 in FIG. 5A indicate the scanning mirror dimensions when the offset distance d is not provided. That is, the dotted line portion is a portion that can be removed by applying the present invention. As shown in FIG. 5B, when the inclination with respect to the optical axis A2 is not the minimum, the portions where the effective light flux does not enter (the hatched portions in the figure) 31b, 3
1c results. However, these useless portions 31b, 31
Since c occurs almost equally at both ends of the scanning mirror 31,
Even if the dimension H ′ in the rotation radial direction is shortened to the minimum and the reflection surface is used to the maximum, the rotation balance is not lost.

Next, the setting of the offset distance d will be described. As is clear from the comparison between FIG. 5 and FIG. 9, the reason why the useless portion of the reflecting surface is biased toward one end is caused by the apparent rotation center f of the reflecting surface accompanying the rotation of the scanning mirror 310 in FIG. It was not coincident with the optical axis A20. Therefore, in the optical axis arrangement of FIG. 5, the value of the offset distance d is set such that the apparent center of rotation e of the reflecting surface coincides with the optical axis A2. The apparent rotation center e is a virtual plane including the reflection surface in the first state in which the scanning mirror 31 is disposed at the angular position in FIG. 5A [the reflection surface of the dashed-line rectangle in FIG. Corresponding to FIG. 5) and FIG.
It is a line of intersection with a reflective surface in the 2nd state arranged at the angle position of (b).

In FIG. 5, the rightward direction is the x-axis and the upward direction is the y-axis with the rotation axis A1 as the origin. The angle between the reflecting surface and the x-axis in the first state is θ1, and the angle in the second state is θ2. Further, the scanning mirror 31
Is T.

The straight line representing the reflecting surface in the first state is given by equation (5). y = tan θ1 · x + [1+ (tan θ1) ² ) · T / 2 (5) Similarly, a straight line representing the reflecting surface in the second state is given by Expression (6). y = tan θ2 · x + [1+ (tan θ2) ² ) · T / 2 (6) The x coordinate of the intersection of the two straight lines is x ₀ = − (tan θ1 + tan θ2) from the simultaneous equation of the equations (5) and (6). ) · T / 2 (7)

Accordingly, the offset distance d can be obtained by the following equation: d = | x ₀ | = | (tan θ1 + tan θ2) · T / 2 | (8) [Second Embodiment] FIG. 6 is a configuration diagram of a second example of the optical system. In this figure, the same components as those in the first example described above are denoted by the same reference numerals as in FIG.

The optical system 10B of the second example is a transmission / reception means obtained by adding a second actuator 33 to the optical system 10 of the first example of FIG. 3 in order to realize biaxial scanning. The actuator 33 rotates the scanning mirror 31 about a rotation axis A3 that has a crossing or torsional relationship with the rotation axis A1 of the scanning mirror 31. The rotation axis A3 is the optical axis A2 of the light receiving lens 21.
Matches.

The scanning mirror 31 is driven by an actuator 32 and rotates in a direction R1 to rotate the pulse lights P1 and P1.
2 deflect. Transmission and reception of pulsed light are performed at predetermined intervals of the deflection angle, and distances in multiple directions are measured by one-dimensional scanning. Further, the scanning mirror 31, the actuator 32, and the components (not shown) for holding and connecting these components are integrally driven to rotate in the direction R <b> 2 by the actuator 33. Transmission and reception of pulsed light are performed at every predetermined rotation angle of this rotation, and in combination with scanning by the actuator 32, distance measurement in two directions by two-dimensional scanning is realized.

In the optical system 10 B, the receiving lens 21 is also driven to rotate integrally with the scanning mirror 31 by the actuator 33. Thereby, the longitudinal direction of the receiving lens 21 is kept parallel to the rotation axis A1 of the scanning mirror 31, and the facing relationship between the scanning mirror 31 and the receiving lens 21 is always appropriate. It is not necessary that only the receiving lens 21 be rotated around the rotation axis A3, and the components including the entire receiving optical system or the transmitting optical system may be integrally rotated.

According to the configuration of FIG. 6, the moment of inertia around the rotation axis A3 is considerably larger than the moment of inertia around the rotation axis A1. The reason for this is that the size of the part that rotates integrally is large in the radial direction around the rotation axis A3, and the weight of the part that rotates integrally is large. But,
If a rotational drive around the rotation axis A1 is a main scan, and a rotational drive around the rotation axis A3 is a sub-scan, a control method in which the sub-scan is performed by one step every time a large number of main scans is performed is adopted. The sub-scan is driven at a much lower speed than the main scan, and the effect of the increase in the inertia moment is sufficiently reduced to solve the problem of the acceleration torque. Such a control method is sufficiently practical.

In the above-described embodiment, a common scanning mirror is used for light emission and light reception. However, separate scanning mirrors may be provided for light emission and light reception. In this case, in the scanning optical system for projecting light, the light projecting optical axis of the pulse light and the rotation center of the scanning mirror are shifted from each other, and the apparent rotation center of the reflection surface and the light projecting optical axis of the pulse light coincide with each other. With such a configuration, it is possible to reduce the size of the light projection scanning mirror.

[0037]

According to the first to fifth aspects of the present invention,
The speed of scanning can be increased by reducing the moment of inertia of the scanning mirror.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an entire configuration of a distance measuring apparatus according to the present invention.

FIG. 2 is a conceptual diagram of distance measurement.

FIG. 3 is a schematic diagram of an optical system.

FIG. 4 is a configuration diagram of a part related to pulse reception in the optical system.

FIG. 5 is a diagram illustrating an arrangement relationship between a scanning mirror and a light receiving optical axis;

FIG. 6 is a configuration diagram of a second example of the optical system.

FIG. 7 is a schematic diagram of an optical system of a conventional distance measuring device.

FIG. 8 is a configuration diagram of a portion related to pulse reception in a conventional optical system.

FIG. 9 is a diagram showing a conventional arrangement relationship between a scanning mirror and a light receiving optical axis.

[Explanation of symbols]

 Reference Signs List 1 distance measuring device (optical device) 11 semiconductor laser (light source) 31 scanning mirror Q object P1 pulse light P2 pulse light (reflected pulse light) 21 light receiving lens 22 photodetector w1 dimension in first direction X w2 in second direction X Dimension A1 Rotation axis A2 Optical axis 32,33

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Koichi Sanebe 2-3-113 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. 2F065 AA04 AA06 AA51 FF12 FF32 GG06 GG12 HH04 JJ01 JJ15 LL13 LL62 MM15 MM16 MM28 QQ03 UU01 2F112 AD01 BA05 CA12 DA10 DA15 DA25 EA05 FA03 FA07

Claims (5)

[Claims] A light source for emitting pulse light; a scanning mirror for changing a light receiving direction; a light receiving lens for collecting reflected pulse light reflected by an external object and returned to the scanning mirror; A light detector that receives the reflected pulsed light, and sequentially projects the pulsed light in a plurality of directions, and a distance measuring device that measures the time from transmission of the pulsed light to reception of the reflected light pulse in each direction. The dimension of the effective area in the light receiving lens in the first direction X is shorter than the dimension in the second direction Y orthogonal to the first direction X, and the light receiving lens has the second direction Y of the scanning mirror. A distance measuring device, which is disposed so as to be parallel to a rotation axis. 2. A two-dimensional scanning means for rotating the scanning mirror about the rotation axis and rotating the scanning mirror and the light receiving lens about an axis orthogonal to the rotation axis. 2. The distance measuring device according to 1. 3. The distance measuring apparatus according to claim 2, wherein the light source and the light detector rotate integrally with the scanning mirror and the light receiving lens about an axis orthogonal to the rotation axis. 4. A light source for emitting pulse light, a scanning mirror for changing a light receiving direction, a light receiving lens for collecting reflected pulse light reflected by an external object and returned to the scanning mirror, and a light collecting lens. A light detector that receives the reflected pulsed light, and sequentially projects the pulsed light in a plurality of directions, and a distance measuring device that measures the time from transmission of the pulsed light to reception of the reflected light pulse in each direction. A distance measuring device, wherein the light receiving lens is arranged such that an optical axis thereof intersects a rotation axis of the scanning mirror at a predetermined offset distance. 5. The method according to claim 5, wherein the value of the offset distance is defined by a virtual plane including a reflection surface of the scanning mirror when the scanning mirror is disposed at the first deflection angle position, and a second deflection angle by the scanning mirror. 5. The distance measuring apparatus according to claim 4, wherein the value is a value at which an optical axis of the light receiving lens intersects a line of intersection with the reflection surface of the scanning mirror when the lens is arranged at the position.