JP2013088406A - Distance measuring device including range-finding sensor and distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measuring device for improving range finding accuracy within a distance range requested to a device and realizing output value-distance conversion for which individual variation of a sensor is corrected, a distance measuring method, and a display device including the distance measuring device.SOLUTION: The distance measuring device includes: an adjustment part 21 for performing offset correction according to an output value at the longest distance within the distance range requested to the device, in a PSD sensor 20 in which the output value and the distance have inversely proportional relation; an amplification part 22 for performing gain correction according to an output value at the shortest distance in the distance range requested to the device; and a calculation part 23 for measuring an output value at the middle distance, obtaining a characteristic curve intrinsic to a range-finding sensor on the basis of the output values at three points of the longest distance, the shortest distance and the middle distance, and calculating a distance to a measuring object by applying the output value of the PSD sensor 20 to the characteristic curve.

Description

  The present invention relates to a distance measuring device including a distance measuring sensor having an inversely proportional relationship between an output value and a measurement distance, a distance measuring method, and a display device including the distance measuring device.

  FIG. 2 is a schematic diagram of an optical analog output type triangulation type distance measuring sensor using an infrared LED (Light Emitting Diode) and a position detecting element PSD (Position Sensitive Detector). Infrared light output from the infrared LED is irradiated onto the front measurement object with a sufficiently sharp directivity angle by the light projection lens, and the light incident on the light receiving lens among the reflected light diffusely reflected by the measurement object is displayed on the PSD. The spot light incident position (light intensity barycentric position) is electrically detected, and the spot light incident position changes according to the distance from the distance measuring sensor to the measurement object. Measure distance.

At this time, the spot light incident position is a right triangle formed by the distance (variable d) from the light projecting lens (front surface of the distance measuring sensor) to the measurement object and the pitch between the light projecting lens and the light receiving lens (design value p). From the similarity relationship of the right triangle formed by the distance between the light receiving lens and the PSD (design value f) and the amount of displacement of the spot light incident position on the PSD (variable x), the design values p and f of the sensor are set as constants. For example, d and x change in conjunction with each other, and the relationship is inversely proportional as shown in the following equation.
d / p = f / x
Ｄ d = (p * f) / x

Here, the variable x is a spot light incident position when the measurement object is at infinity, that is, a position of light perpendicularly incident on the PSD from the center of the light receiving lens, and a spot when the measurement object is at the measurement distance. This represents the difference from the light incident position. The PSD can detect the spot light incident position as a photocurrent, and can measure the variable x by converting the photocurrent into a voltage and taking it out. If the design value p and the design value f are known, the above equation is obtained. Can be used to measure the variable d.

The basic characteristics of the analog output type triangulation distance measuring sensor, that is, the characteristics in which the output voltage of the sensor is inversely proportional to the distance to the object to be measured are satisfied as long as the geometrical relationship shown in FIG. 2 is maintained. . However, due to these basic characteristics of the analog output type triangulation type distance measuring sensor, as the measurement object moves away from the analog output type triangulation type distance measuring sensor, the resolution of the distance measurement value becomes lower and the distance measurement is reduced. There arises a problem that accuracy is lowered.

  Therefore, an optical distance measuring sensor that can prevent the measurement accuracy of the distance from decreasing as the measurement object moves away has been proposed (see, for example, Patent Document 1).

JP 2007-10556 A

  However, no matter how much the measurement accuracy of individual sensors (especially the measurement accuracy at a long distance) is improved, there are actual variations in electrical sensors, structural variations, physical properties, etc. Due to individual variations, output voltage characteristics vary among individual sensors. FIG. 3 shows a conceptual diagram of voltage-distance conversion in the distance measuring sensor. It can be seen from FIG. 3 that different output voltages Vo and V′o are associated with each sensor for an arbitrary measurement distance do.

  For this reason, when using a distance measuring sensor, a calibration process (voltage-distance conversion) is required in which the output voltage V and the distance d to the measurement object are associated with each other in a one-to-one relationship in advance. It is.

As a method of voltage-distance conversion, conventionally, a plurality of output voltages V1, V2, V3,... At each measurement distance d1, d2, d3,. There is known a method (linear interpolation method) for approximating a characteristic curve. Table 1 shows a conceptual diagram of a voltage-distance conversion table by a linear interpolation method.

However, as apparent from the line indicating the relationship between the output voltage V of the sensor α in FIG. 3 and the measurement distance d, this method cannot be increased in accuracy unless the number of measurement points is increased. There were problems such as requiring a lot of measurement time.

  In addition, a guaranteed range of measurement distance is defined as a specification for the distance measuring sensor, and accuracy of distance measurement outside the range is not guaranteed. Therefore, when a distance measurement device equipped with a distance measurement sensor is used to measure the distance, the measurement range having a sufficiently wide measurement distance guarantee range compared to the measurement range required for the distance measurement device. It is necessary to use a distance sensor. When the measurement range is determined in advance, the output voltage range of the distance measuring sensor is also within a certain range.

Here, the output voltage V of the sensor is ADC (Analog-to-Digital).
However, since the input voltage range and input resolution of the ADC are limited, in order to increase the distance resolution, the measurement range required for the corresponding distance measuring device is used. It is desirable to make the dynamic range as large as possible. Accordingly, the output voltage V of the sensor is not directly input to the ADC, but the output voltage range of the distance measuring sensor in the measurement range required for the distance measuring device is estimated in advance, and an amplifier circuit or the like is based on the estimation result. It is effective to input to the ADC after optimizing the voltage range so as to match the input voltage range of the ADC.

FIG. 4 shows the relationship between the input voltage range of the ADC and the output voltage range of the distance measuring sensor. The output characteristic γ is an example in which the output voltage V of the sensor is directly input to the ADC. The output characteristic δ is an example in which the voltage range is appropriately optimized and then input to the ADC. Although FIG. 4 shows a case where the signal is input to a 4-bit ADC, it can be clearly seen that the output characteristic δ has a higher distance resolution (number of plots) within the measurement range.

Conventionally, in order to estimate the output voltage range of a distance measuring sensor in the measurement range required for the corresponding distance measuring device, it has been necessary to consider the individual variation of the sensor. There is a problem that a large design margin must be taken to allow variation, and as a result, the dynamic range is impaired because the design voltage cannot be sufficiently adjusted to the input voltage range of the ADC.

The present invention has been made in view of the above points, and with respect to the measurement range required for the corresponding distance measurement device, the distance measurement accuracy (distance resolution) within the range is improved, and individual variations in the characteristic curve of the sensor are achieved. It is an object of the present invention to provide a distance measuring device, a distance measuring method, and a display device including the distance measuring device capable of performing voltage-distance conversion corrected for the same at the same time in a short time with high accuracy.

The invention described in claim 1
A distance measuring sensor having an inversely proportional relationship between the output value and the distance to the measurement object;
A calculation unit that calculates a distance from the distance measurement sensor to a measurement object based on an output value of the distance measurement sensor;
The calculation unit determines an output value of the distance measuring sensor based on a distance from the distance measuring sensor to at least three arbitrary measurement points and an output value of the distance measuring sensor at the measurement point. The distance from the distance measuring sensor to the measurement object is calculated by applying a characteristic curve relating to the distance from the distance measurement sensor to the measurement object and the output value of the distance measurement sensor.

The invention according to claim 2
A distance measuring sensor having an inversely proportional relationship between the output value and the distance to the measurement object;
An adjustment unit for performing offset adjustment on the output value of the distance measuring sensor;
An amplifying unit for amplifying the output value of the distance measuring sensor adjusted for the offset;
A calculation unit that calculates a distance from the distance measurement sensor to a measurement object based on the amplified output value of the distance measurement sensor;
The calculation unit outputs the amplified output value of the distance measurement sensor, the distance from the distance measurement sensor to at least three arbitrary measurement points, and the output value of the amplified distance measurement sensor at the measurement point Is applied to a characteristic curve related to the distance from the distance measuring sensor to the measurement object and the amplified output value of the distance measurement sensor determined on the basis of the distance from the distance measurement sensor to the measurement object. The distance is calculated.

The invention described in claim 3
A method for converting an output value of a distance measurement sensor having an inversely proportional relationship between an output value and a distance to a measurement object into a distance from the distance measurement sensor to the measurement object,
The distance from the distance sensor to the object to be measured and the output of the distance sensor based on the distance from the distance sensor to at least three arbitrary measurement points and the output value of the distance sensor at the measurement point Determining a characteristic curve for the value;
Calculating the distance from the distance measuring sensor to the object to be measured by applying the output value of the distance measuring sensor to the characteristic curve.

The invention according to claim 4
A method for converting an output value of a distance measurement sensor having an inversely proportional relationship between an output value and a distance to a measurement object into a distance from the distance measurement sensor to the measurement object,
Performing offset adjustment on the output value of the distance measuring sensor;
Amplifying the offset adjusted output value of the distance measuring sensor;
The distance from the distance measurement sensor to the measurement object and the amplification based on the distance from the distance measurement sensor to at least three arbitrary measurement points and the amplified output value of the distance measurement sensor at the measurement point Determining a characteristic curve related to the output value of the distance measuring sensor,
A step of calculating a distance from the distance measuring sensor to a measurement object by applying the amplified output value of the distance measuring sensor to the characteristic curve.

A fifth aspect of the present invention is a display device comprising the distance measuring device according to any one of the first to second aspects.

  According to the present invention, a method for obtaining a plurality of unknown coefficients (for example, l, m, n) by paying attention to a basic characteristic of a distance measuring sensor in which an output value and a measurement distance have an inversely proportional relationship (an unknown coefficient method) By adopting, high-accuracy output value-distance conversion without error due to interpolation can be performed for individual sensors with all individual variations. Further, when the output value of the distance measuring sensor is a voltage or an analog output value (such as current) that can be converted into a voltage, at the same time, based on the result of the high-accuracy output value-distance conversion, the dynamics of the ADC The output range of the distance measuring sensor in the measurement range required for the corresponding distance measuring device can be optimized so that the range can be maximized. Furthermore, since only three measurement points are required, the measurement time required for adjusting individual variations can be greatly shortened.

It is a block diagram which shows the structure of the liquid crystal display device which concerns on this invention. It is a schematic diagram of an optical analog output type triangulation type distance measuring sensor using an infrared LED and a position detection element PSD. It is a conceptual diagram of voltage-distance conversion in the distance measuring sensor. It is a conceptual diagram which shows the relationship between the input voltage range of ADC and the output voltage range of a ranging sensor. It is a conceptual diagram which shows the variation of unknown coefficient l, m, n. It is a circuit diagram which shows an output voltage optimization circuit. It is a conceptual diagram which shows two characteristic curves before and behind offset correction. It is a conceptual diagram which shows optimization of the characteristic curve of a sensor by offset correction and gain correction. It is a conceptual diagram which shows the change of the characteristic curve when a measurement range is changed.

[Basic Principle of the Present Invention]
First, the basic principle of the present invention will be described as a premise.

    As described above, in the present invention, a method for obtaining a plurality of unknown coefficients (unknown coefficient method) is used by paying attention to the basic characteristics of a distance measuring sensor in which the output value and the measurement distance are inversely proportional to each other. Table 2 shows a conceptual diagram of a voltage-distance conversion table by the unknown coefficient method.

As is apparent from the line indicating the relationship between the output voltage V of the sensor β in FIG. 3 and the measurement distance d, it is possible to perform highly accurate voltage-distance conversion without error due to interpolation by using the unknown coefficient method. .

  The basic characteristics of the analog output type triangulation type distance measuring sensor (hereinafter referred to as a characteristic curve) are described using a standard form equation of an inversely proportional curve. The equation representing the characteristic curve is the following equation (1).

In Expression (1), do is an arbitrary measurement distance, Vo is an output voltage at do, and l, m, and n are unknown coefficients.

The solid lines in FIGS. 5A to 5C depict the characteristic curve of the sensor represented by Expression (1). The point (m, n) in FIG. 5 is the center of the characteristic curve, and represents that the characteristic curve is asymptotic to V = n and d = m.

Also, the broken lines in FIGS. 5A to 5C depict changes in the characteristic curve when the unknown coefficients l, m, and n are changed with respect to the solid line in FIG.

The unknown coefficient l can be regarded as a variation of (p * f) in FIG. 2, that is, a structural variation, and is a coefficient that determines a deviation in the oblique direction of the characteristic curve. The change of the unknown coefficient l is shown in FIG. The change of the unknown coefficient l appears as a variation along the straight line V = (dm) + n of the characteristic curve.
= (D-m) + n is the largest change near the intersection (√ (l + m), √ (l + n)) (near the top of the characteristic curve), and affects the measurement accuracy over the entire measurement distance .

The unknown coefficient m has a dimension of distance and can be regarded as a variation in the optical path from the infrared LED to the PSD in FIG. 2, and is a coefficient that determines the deviation of the characteristic curve in the horizontal axis direction. The change of the unknown coefficient m is shown in FIG. Factors that cause variations in the optical path include, for example, lens decentration, sensor body distortion and asymmetry, or a cover material that is attached to the front surface of the sensor for protection and blinding of the sensor. When the measurement distance d is sufficiently long, the influence of the unknown coefficient m on the characteristic curve of Equation (1) becomes relatively small. In addition, due to the nature of the inverse proportional curve, the smaller the measurement distance d, the smaller the change in the measurement distance d with respect to the change in the output voltage V. Therefore, the change in the unknown coefficient m affects the distance measurement accuracy on the short distance side of the characteristic curve. give.

The unknown coefficient n has a voltage (output value) dimension and can be regarded as variations in the offset voltage when the measurement object is at infinity, and is a coefficient that determines the deviation in the vertical direction of the characteristic curve. The change of the unknown coefficient n is shown in FIG. Factors that cause variations in offset voltage include, for example, variations in PSD die-bond positions, PSD position detection errors, and photocurrent-voltage conversion variations. When the measurement distance d is sufficiently small, the influence of the unknown coefficient n on the characteristic curve of Equation (1) is relatively small. Further, due to the nature of the inversely proportional curve, the change in the measurement distance d with respect to the change in the output voltage V increases as the measurement distance d increases. Therefore, the change in the unknown coefficient n affects the distance measurement accuracy on the far side of the characteristic curve. give.

By obtaining these three unknown coefficients l, m, and n for each sensor, a characteristic curve including individual variations is obtained, and highly accurate voltage-distance conversion becomes possible.

In order to specify the unknown coefficients l, m, and n, it is necessary to actually measure at least three output voltages at different measurement distances. If the sensor is manufactured with sufficiently high accuracy, the unknown coefficients l, m, and n may be considered to be within a certain range.

  Next, embodiments of the present invention will be described with reference to the accompanying drawings.

  In the present embodiment, the distance measuring device according to the present invention is applied to a liquid crystal display device.

  FIG. 1 is a block diagram showing a configuration of a liquid crystal display device 1 according to the present embodiment.

  In the figure, a liquid crystal display device 1 is a display device including a liquid crystal panel 17 as a display device, and displays an image on the liquid crystal panel 17 based on an image signal input from the PC 3.

The liquid crystal display device 1 includes a control unit 10, a RAM (Random Access Memory) 11, a RAM (Random
Access
Memory) 24, ROM (Read Only Memory) 12, ROM (Read Only Memory) 25, operation unit 13, input unit 14, image processing unit 15, panel driving unit 16, liquid crystal panel 17, light driving unit 18, and backlight 19 , A PSD sensor 20, an adjustment unit 21, an amplification unit 22, a calculation unit 23, and the like.

Specifically, the control unit 10 is a CPU (Central Processing).
Unit) or an MPU (Micro Processing Unit) or the like, and various processes can be performed by reading and executing a control program stored in the ROM 12. The control unit 10 performs various control processes for displaying an image on the liquid crystal panel 17 by exchanging information with each unit in the liquid crystal display device 1 and controlling operations of these units.

  The RAM 11 is configured by a data rewritable memory element such as SRAM (Static RAM) or DRAM (Dynamic RAM), and can store temporary data. For example, the RAM 11 temporarily stores data generated in the calculation process of various control processes performed by the control unit 10.

  The RAM 24 is also composed of a data rewritable memory element such as SRAM (Static RAM) or DRAM (Dynamic RAM), and can store temporary data. In the present embodiment, the RAM 24 stores the detection result of the PSD sensor 20 and data (details will be described later) such as the amplifier output voltage Vamp output based on the detection result.

  The ROM 12 is configured by a nonvolatile memory element such as an EEPROM (Electrically Erasable Programmable ROM) or a flash memory, for example, and includes a control program necessary for the operation of the control unit 10 and other various data (not shown). Stored in advance.

  The ROM 25 is also constituted by a nonvolatile memory element such as an EEPROM (Electrically Erasable Programmable ROM) or a flash memory. In the present embodiment, values of variation components (constants) A, m, and B (details will be described later) constituting a characteristic curve used for calculating the distance from the PSD sensor 20 to the measurement object are stored in the ROM 25 in advance. The calculation unit 23 reads out these data and performs processing.

  The operation unit 13 includes various function keys for the user to operate the liquid crystal display device 1. For example, for setting the display characteristics of the liquid crystal display device 1 such as a key for changing the brightness (brightness) of the image display of the liquid crystal panel 17 or a key for changing the color balance of the image display. A setting key is provided on the operation unit 13. The operation unit 13 accepts user operations on these function keys and notifies the control unit 10, and the control unit 10 can control the operation of each unit in response to the notification from the operation unit 13.

  The input unit 14 has a connection terminal connected to an external device such as the PC 3 via a signal cable, acquires an image signal input from the PC 3, and provides the image signal to the image processing unit 15. The image processing unit 15 performs various image processing such as brightness adjustment or color balance adjustment on the image signal given from the input unit 14 under the control of the control unit 10, and outputs the image signal after the image processing. It gives to the panel drive part 16. When the panel driving unit 16 drives the liquid crystal panel 17 in accordance with the image signal given from the image processing unit 15, the liquid crystal display device 1 can perform image display based on the image signal from the PC 3.

  The liquid crystal panel 17 has a structure in which a pair of glass substrates are opposed to each other, and a liquid crystal layer, which is a liquid crystal substance, is formed in a gap therebetween. One glass substrate is provided with a plurality of pixel electrodes and TFTs (Thin Film Transistors) each having a drain connected to the pixel electrode, and the other glass substrate is provided with a common electrode. The gate and source of each TFT are connected to a gate driver and a source driver (not shown) of the panel drive unit 16, and drive signals are input from the panel drive unit 16, respectively.

  The panel drive unit 16 outputs a drive signal for driving the liquid crystal panel 17 in accordance with the image signal given from the image processing unit 15. Specifically, the gate driver of the panel driving unit 16 selectively applies a voltage to the gates of a large number of TFTs included in the liquid crystal panel 17 according to a given image signal, and similarly, the source of the panel driving unit 16 The driver applies a voltage to the source of the TFT with a voltage value corresponding to the input video signal. As a result, the liquid crystal panel 17 controls the on / off of the TFT of each pixel by the voltage applied from the gate driver of the panel drive unit 16, and outputs the output voltage (to the liquid crystal panel 17) input from the source driver of the panel drive unit 16. Is applied to the TFT of each pixel, the light transmittance determined by the electro-optical characteristics of the liquid crystal substance is controlled, the light transmission from the backlight 19 is adjusted, and a desired image is obtained. Gradation can be displayed. Each pixel of the liquid crystal panel 17 is further composed of sub-pixels for a plurality of colors such as RGB, and color display is possible by arranging a color film in the light transmission direction.

  The backlight 19 is disposed on the back side of the liquid crystal panel 17 in the display device 1 and is driven by an output voltage supplied from the light driving unit 18. The light driving unit 18 adjusts the output voltage to the backlight 19 according to the control of the control unit 10. Thus, for example, the brightness of the backlight 19 can be adjusted by causing the light driving unit 18 to adjust the output voltage according to the brightness setting set by the user operating the operation unit 13.

  The PSD sensor 20 is provided in a front portion of the casing of the liquid crystal display device 1 (for example, a surrounding frame portion surrounding the liquid crystal panel 17), detects a distance to an object existing on the front side of the liquid crystal display device 1, and detects the distance. As a result, a signal having a voltage value corresponding to the distance is output to the adjustment unit 21. The PSD sensor 20 is used in combination with, for example, an infrared LED, receives reflected light from an object of infrared light emitted from the infrared LED, and a signal having a voltage value corresponding to a light receiving position or a light receiving angle at this time. Is output. For this reason, the distance to the object can be calculated by the triangulation method based on the voltage value of the signal output from the sensor. The PSD sensor 20 outputs a signal having a higher voltage value as the distance to the measurement object is shorter, and outputs a signal having a lower voltage value as the distance to the object is longer.

  The adjustment unit 21 to which the output signal from the PSD sensor 20 is given adjusts (corrects) this signal based on an instruction from the calculation unit 23 by a method described later.

The offset adjusted (corrected) signal is amplified by the amplifying unit 22 based on an instruction from the calculating unit 23 by a method described later. As will be described later, in the present embodiment, the adjusting unit 21 and the amplifying unit 22 are provided in the same output voltage optimization circuit 4 (FIG. 6), and the offset adjustment (correction) in the adjusting unit 21 is an output. It is executed in the amplifier A2 and the amplifier A1 that constitute the voltage optimization circuit 4, and the amplification (gain correction) in the amplifier 22 is executed in the amplifier A1. Note that the offset correction and the gain correction are executed almost in real time.

The calculation unit 23 calculates the distance from the PSD sensor 20 to the measurement object by applying the amplified signal to a characteristic curve obtained by a method described later. The calculation unit 23 acquires the voltage value Vamp of the amplified signal as digital information by A / D conversion (not shown).

Based on the distance information to the measurement object calculated by the calculation unit 23, the control unit 10 determines whether a detection object (for example, a person) is present in front of the liquid crystal display device 1 (within the detection range of the PSD sensor 20). A control process is performed to determine whether or not to display / hide the liquid crystal panel 17 according to the determination result. That is, when it is determined that there is a person, the control unit 10 displays an image input from the PC 3 on the liquid crystal panel 17, and when it is determined that there is no person, the control unit 10 stops displaying the image on the liquid crystal panel 17. To do. The image display may be stopped by, for example, stopping the output of drive signals by the panel drive unit 16 and the light drive unit 18, and for example, the power supply to each unit from the power supply circuit (not shown) is stopped. This may be done by other methods.

Next, details of offset adjustment (correction) executed in the adjustment unit 21 and amplification (gain) correction executed in the amplification unit 22 will be described.

FIG. 6 shows an example of the output voltage optimization circuit 4 that performs offset adjustment (correction) and amplification (gain) correction. The output voltage optimization circuit 4 corresponds to the adjustment unit 21 and the amplification unit 22 illustrated in FIG. As described above, the offset adjustment (correction) in the adjustment unit 21 is performed in the amplifier A2 and the amplifier A1 that constitute the output voltage optimization circuit 4, and the amplification (gain correction) in the amplification unit 22 is performed in the amplifier A1. The

The output voltage optimization circuit 4 is composed of two stages of differential amplifiers A2 and A1, and is provided with an offset correction voltage Voffset input from an external DAC or the like to the first stage amplifier A2, and a temperature provided by a forward voltage of a diode, etc. When the compensation voltage Vtemp is input, differential amplification is performed with a gain G2 (not shown) determined by the resistance ratio R2 / R1, and a correction voltage Vcomp is generated. The correction voltage Vcomp and the sensor are supplied to the amplifier A1 at the next stage. When the output voltage Vo is input, differential amplification is performed with a gain G1 (not shown) determined by the resistance ratio R4 / R3 to obtain an amplified voltage Vamp. The amplified voltage Vamp is input to an ADC (not shown).

The amplified voltage Vamp can be expressed by the following equation (2) using the gain G1 of the amplifier A1, the gain G2 of the amplifier A2, the offset correction voltage Voffset, and the temperature compensation voltage Vtemp. Equation (2) can also be expressed as Equation (2) ′ using the correction voltage Vcomp.

The temperature compensation voltage Vtemp and the gain G2 of the amplifier A2 are set in advance from the temperature characteristics of the sensor. In the analog output type triangulation type distance measuring sensor, when the expansion or contraction of the mechanical material or the change of the electric characteristic occurs due to the change of the ambient temperature, the above-mentioned unknown coefficient changes and an error occurs in the characteristic curve.

The temperature characteristics of the characteristic curve vary depending on the sensor design.For example, if the output voltage of the sensor has a linear temperature characteristic, a reference voltage is applied to an element having the same linear temperature characteristic, such as a silicon diode or a Zener diode. Is input to the amplifier A2 as a temperature compensation voltage Vtemp to give a temperature characteristic to the correction voltage Vcomp, and by setting the gain G2 so that the temperature characteristic of the correction voltage Vcomp becomes equal to the temperature characteristic of the sensor, When the amplifier A1 differentially amplifies the correction voltage Vcomp and the sensor output voltage Vo, the temperature characteristic of the sensor can be canceled. The temperature compensation voltage Vtemp and the gain G2 may be set in consideration of the offset correction voltage Voffset and the temperature characteristics of the amplifiers A1 and A2.

[Offset correction]
The offset correction voltage Voffset is a DAC (Digital-to-Analog
This is a variable DC voltage supplied from a converter, etc., and is set according to the longest distance dmax in the measurement range required for the corresponding distance measuring device.

The offset correction voltage Voffset does not necessarily have to be set according to the longest distance dmax in the measurement range required for the corresponding distance measuring device, and can be set according to an arbitrary distance d. . That is, it may be set according to a distance longer than the longest distance dmax, or conversely, may be set according to a distance shorter than the longest distance dmax. However, when it is set according to a distance shorter than the longest distance dmax, it is necessary to prevent the measurement distance from being saturated within the measurement range required for the corresponding distance measurement device.

Hereinafter, a case where the offset correction voltage Voffset is set according to the longest distance dmax in the measurement range required for the corresponding distance measuring device will be described. This is because offset correction can be performed most efficiently and with high accuracy.

FIG. 8 is a conceptual diagram showing optimization of the characteristic curve of the sensor by offset correction and gain correction.

First, the amplified voltage Vmin at the longest distance dmax in the measurement range required for the corresponding distance measuring device is actually measured.

Next, offset correction is performed by adjusting the offset correction voltage Voffset so that the Vmin approaches the minimum value of the input voltage range of the ADC. When Vmin is brought close to the minimum value of the input voltage range of the ADC, it may be made to coincide with the minimum value, but a margin may be provided so as not to fall below the minimum value due to secular change or the like. The initial value of the offset correction voltage Voffset may be an arbitrary voltage.

In addition, for example, the initial value of the offset correction voltage Voffset is set equal to the temperature compensation voltage Vtemp to cancel the correction voltage Vcomp, or the tendency of individual variations in the sensor is investigated in advance, and the individual variation near the center is determined. The time required for offset correction can be shortened by a method in which the offset correction voltage Voffset optimized for the characteristic curve of the sensor is used as an initial value.

[Gain correction]
The gain G1 of the amplifier A1 is set according to the shortest distance dmin in the measurement range required for the corresponding distance measuring device after performing the offset correction described above.

The gain G1 of the amplifier A1 does not necessarily have to be set according to the shortest distance dmin in the measurement range required for the corresponding distance measuring device, but can be set according to an arbitrary distance d. it can. That is, it may be set according to a distance longer than the shortest distance dmin, or conversely, may be set according to a distance shorter than the shortest distance dmin.

Hereinafter, a case where the gain G1 of the amplifier A1 is set according to the shortest distance dmin in the measurement range required for the corresponding distance measuring device will be described. This is because the gain can be corrected most efficiently and with high accuracy.

First, the amplified voltage Vmax at the shortest distance dmin in the measurement range required for the corresponding distance measuring device is actually measured.

Next, gain correction is performed by adjusting the gain G1 so that the Vmax approaches the maximum value of the ADC input voltage range.

When Vmax is brought close to the maximum value of the input voltage range of the ADC, the maximum value may be made to coincide with the maximum value, but a margin may be provided so as not to exceed the maximum value due to secular change or the like. Further, since the amplified voltage Vmin at the longest distance dmax in the measurement range changes by changing the gain G1, the offset correction is performed again, the gain correction is performed again, and this is repeated to increase the voltage range with higher accuracy. May be optimized. Note that the initial value of the gain G1 is set so as not to exceed the input voltage range of the ADC in the output voltage range of the distance measuring sensor in the measurement range required for the corresponding distance measuring device.

If the input resolution of the ADC is sufficiently large and sufficient distance resolution can be obtained without changing the gain G1 of the amplifier A1 to make the dynamic range of the ADC as large as possible, it is required for the corresponding distance measuring device in advance. The gain G1 may be set to a fixed value so as not to saturate even in a characteristic curve of a sensor having an individual variation with the widest output voltage range in the measurement range.

As described above, as shown in FIG. 8, the offset characteristic and gain correction result in the sensor characteristic curve passing through the output voltage optimizing circuit so that the output voltage range of the distance measuring sensor in the desired measurement range becomes the input voltage range of the ADC. It is optimized together.

The output voltage optimization circuit 4 shown in FIG. 6 performs offset correction and gain correction, and the characteristic curve of the sensor of the output voltage Vo at an arbitrary measurement distance do becomes the characteristic curve of the amplified voltage Vamp at an arbitrary measurement distance do. Even if converted, the characteristics of the characteristic curve of the analog output type triangulation type distance measuring sensor do not change. Hereinafter, this point will be described.

By substituting the characteristic curve of the distance measuring sensor shown in the above formula (1) into the above formula (2) and putting it into the following formulas (3) and (4), formula (5) is obtained. Note that Expression (4) can also be expressed as Expression (4) ′ using the correction voltage Vcomp.

Here, since the gain G1 and the unknown coefficient l in Expression (3) are constants, the coefficient A is a constant. Similarly, since the gains G1 and G2, the unknown coefficient n, the offset correction voltage Voffset, and the temperature compensation voltage Vtemp in Expression (4) are constants, the coefficient B is a constant. Therefore, the amplified voltage Vamp and the measurement distance do in equation (5) are in an inversely proportional relationship. That is, the output voltage optimization circuit 4 in FIG. 6 performs offset correction and amplification (gain correction) on the characteristic curve of the sensor output voltage Vo at an arbitrary measurement distance do, and the amplified voltage Vamp at an arbitrary measurement distance do. The characteristic curve of the analog output type triangulation type distance measuring sensor does not change even if it is converted to the characteristic curve of FIG. it can. In other words, equation (5) is a voltage-distance conversion equation for associating the amplified voltage Vamp at an arbitrary measurement distance do, and by obtaining the coefficients A, m, and B for each sensor, the individual characteristic curve of the sensor is obtained. Variations can be corrected.

The above-described offset correction corresponds to setting the coefficient B in the equation (5) as represented by the equations (4) and (4) ′.

FIG. 7 shows two characteristic curves before and after offset correction. Even when any coefficient B is set, that is, when any offset correction voltage Voffset is set, the characteristic curve before and after the offset correction only translates in the V-axis direction. Here, the coefficient B can be selected regardless of the unknown coefficients A and m by treating the change in the amplification voltage Vamp due to the change in the arbitrary measurement distance do as a relative value with respect to any one point on the characteristic curve. it can. Therefore, the coefficient B may be set to a desired value in accordance with hardware requirements, that is, the ADC input voltage range.

Further, in the above-described gain correction, since the gain G1 applied to the coefficients A and B is changed as expressed by the equations (3), (4), and (4) ′, an arbitrary measurement distance in the equation (5) is obtained. The amplification voltage Vamp at do increases or decreases, and the slope of the characteristic curve changes as indicated by the gain correction arrow in FIG.

[Distance calculation method]
Next, details of a method for calculating the distance from the PSD sensor 20 to the measurement object in the calculation unit 23 will be described.

After performing the above-described offset correction and gain correction, the amplified voltage Vmid at the intermediate distance dmid in the desired measurement range is actually measured.

The intermediate distance dmid may be arbitrarily selected between the longest distance dmax in the measurement range required for the corresponding distance measuring device and the shortest distance dmin in the measurement range required for the corresponding distance measuring device. By examining the tendency of individual variation and setting the intermediate distance dmid near the apex of the characteristic curve of the sensor having the individual variation near the center, the correction accuracy of the individual variation of the sensor can be increased.

The three measurement points (dmax, Vmin), (dmid, Vmid), and (dmin, Vmax) obtained in the above process are expressed by the following equations (6) and (7) using equation (5), respectively. And can be represented by the formula (8).

Equation (6) is obtained from Equation (6) and Equation (8), Equation (10) is obtained from Equation (9), Equation (7), and Equation (8), and coefficient is obtained from Equation (9) and Equation (10). A and m are obtained as shown in equations (12) and (13).

Expression (11) is obtained from Expression (5) and Expression (8), and coefficient B is eliminated. When Expression (11) is summarized for an arbitrary measurement distance do, Expression (14) is obtained.

When formula (8) is summarized for coefficient B, formula (15) shown below is obtained, so formula (14) can be expressed as formula (16). Equation (16) is equivalent to an equation that summarizes Equation (5) for an arbitrary measurement distance do. The variation coefficient A, m, B of the sensor is calculated using the equations (12), (13), and (15), and the individual variation of the sensor characteristic curve is corrected by using the equation (16). Voltage-distance conversion is possible.

According to the present embodiment, the process of performing offset correction according to the longest distance dmax and gain correction according to the shortest distance dmin in the measurement range required for the corresponding distance measuring device, that is, the dynamic range of the ADC In the process of optimizing the output range of the PSD sensor 20 in the measurement range required for the corresponding distance measuring device (output voltage optimization circuit 4), two of the three measurement points are obtained. Since the point measurement is completed, the characteristic curve of the PSD sensor 20 can be obtained very efficiently.

Based on the coefficients A, m, and B calculated in the above process, the unknown coefficient l and the unknown coefficient n can be back-calculated from the expressions (3) and (4), respectively. Three unknown coefficients l, m, and n that determine the characteristic curve of the sensor before passing can be obtained.

And the characteristic curve of a sensor can be specified from Formula (1) using the calculated unknown coefficients l, m, and n. Therefore, when changing the measurement range required for the corresponding distance measuring device, offset correction and gain correction are performed based on the desktop calculation using the characteristic curve of the sensor specified above, and a new coefficient B ′ And the gain G1 ′ can be set to match the ADC input voltage range and the range sensor output voltage range without re-measurement. By such adjustment, even if the measurement range required for the corresponding distance measuring device is changed, the output range of the distance measurement sensor can be optimized so that the dynamic range of the ADC can be maximized. It is possible to perform a highly accurate output value-distance conversion. FIG. 9 shows a characteristic curve obtained by changing the measurement range required for the corresponding distance measuring device.

In the present embodiment, a description will be given by taking as an example a configuration in which a distance measuring device provided with a voltage output optical analog output type triangulation type distance measuring sensor using LED and PSD is mounted on the liquid crystal display device 1. However, the application of the present invention is not limited to the liquid crystal display device 1. The distance measuring sensor constituting the distance measuring device of the present invention may be any sensor as long as the output value of the sensor has an inversely proportional relationship with the distance to the object to be measured. The output value may be a current, a numerical value, digital data, or the like, and is not limited to an optical distance measuring sensor, and may be, for example, an electrostatic sensor, a luminance sensor, a temperature sensor, or the like. The distance measuring device according to the present invention can also be applied to a display device other than a liquid crystal display device, such as a plasma display, an organic EL display, or a CRT display.

Furthermore, the distance measuring device according to the present invention is not limited to the display device, and various electric devices that perform various controls (for example, power on / off control) based on the distance to the measurement object (for example, a person). For example, it can be applied to an air conditioner, a lighting device, a crime prevention facility, and the like.

As apparent from the first aspect, the distance measuring device according to the present invention may be configured without the adjusting unit 21 and the amplifying unit 22. That is, a configuration in which the above-described offset correction and gain correction are not performed may be employed. In this case, the measurement points may be arbitrary three points, and the longest distance dmax and the shortest distance dmin are not necessarily included in the measurement points.

1. Liquid crystal display device (display device)
3 ... PC
4. Output voltage optimization circuit (adjustment unit and amplification unit)
10: Control unit 11: RAM
12 ... ROM
13. Operation unit 14 Input unit 15 Image processing unit 16 Panel drive unit 17 Liquid crystal panel 18 Light drive Section 19 Backlight 20 PSD sensor (ranging sensor)
21 ...... Adjustment unit (adjustment unit)
22 …… Amplifier (amplifier)
23... Calculation unit (calculation unit)
24 ... RAM
25 ... ROM

Claims (5)

A distance measuring sensor having an inversely proportional relationship between the output value and the distance to the measurement object;
A calculation unit that calculates a distance from the distance measurement sensor to a measurement object based on an output value of the distance measurement sensor;
The calculation unit determines an output value of the distance measuring sensor based on a distance from the distance measuring sensor to at least three arbitrary measurement points and an output value of the distance measuring sensor at the measurement point. A distance measuring apparatus that calculates a distance from the sensor to the measurement object by applying a characteristic curve relating to a distance from the distance measurement sensor to the measurement object and an output value of the sensor. A distance measuring sensor having an inversely proportional relationship between the output value and the distance to the measurement object;
An adjustment unit for performing offset adjustment on the output value of the distance measuring sensor;
An amplifying unit for amplifying the output value of the distance measuring sensor adjusted for the offset;
A calculation unit that calculates a distance from the distance measurement sensor to a measurement object based on the amplified output value of the distance measurement sensor;
The calculation unit outputs the amplified output value of the distance measurement sensor, the distance from the distance measurement sensor to at least three arbitrary measurement points, and the output value of the amplified distance measurement sensor at the measurement point Is applied to a characteristic curve related to the distance from the distance measuring sensor to the measurement object and the amplified output value of the distance measurement sensor determined on the basis of the distance from the distance measurement sensor to the measurement object. A distance measuring device that calculates a distance. A method for converting an output value of a distance measurement sensor having an inversely proportional relationship between an output value and a distance to a measurement object into a distance from the distance measurement sensor to the measurement object,
The distance from the distance sensor to the object to be measured and the output of the distance sensor based on the distance from the distance sensor to at least three arbitrary measurement points and the output value of the distance sensor at the measurement point Determining a characteristic curve for the value;
And a step of calculating a distance from the distance measuring sensor to a measurement object by applying an output value of the distance measuring sensor to the characteristic curve. A method for converting an output value of a distance measurement sensor having an inversely proportional relationship between an output value and a distance to a measurement object into a distance from the distance measurement sensor to the measurement object,
Performing offset adjustment on the output value of the distance measuring sensor;
Amplifying the offset adjusted output value of the distance measuring sensor;
The distance from the distance measurement sensor to the measurement object and the amplification based on the distance from the distance measurement sensor to at least three arbitrary measurement points and the amplified output value of the distance measurement sensor at the measurement point Determining a characteristic curve related to the output value of the distance measuring sensor,
And a step of calculating a distance from the distance measuring sensor to a measurement object by applying the amplified output value of the distance measuring sensor to the characteristic curve.   A display device comprising the distance measuring device according to claim 1.

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