JP7120535B2 - POSITION DETECTION DEVICE AND POSITION DETECTION METHOD USING REFLECTIVE PHOTOSENSOR - Google Patents

Description

The present invention relates to a position detection device and position detection method using a reflective photosensor, and more particularly to a position detection device and position detection method for detecting the position and movement amount of a moving object in a device such as a camera.

Conventionally, for example, in digital still cameras, camcorders, surveillance cameras, etc., various actuators are used to drive lenses, and position detection devices are used to perform position sensing of the movable lenses and the like.

Such position detection devices are roughly classified into those using magnetic sensors and those using optical elements. Comparing the two, the magnetic sensor has problems of demagnetization and magnetic fogging, and it may be advantageous to use an optical element that does not have these problems.

Various position detection devices using optical elements have been conventionally proposed. For example, light emitted from a light source is transmitted through a scale having a repetitive light-transmitting pattern, the transmitted light is received by a light-receiving element, and the amount of movement is detected by counting the number of times the light is received. There is an example (Patent Document 1) in which the resolution is increased by causing the emitted light to pass through a plurality of slits to generate interference fringes. However, in the latter transmissive type, the light source and the light receiving element must be separated and opposed to each other with a plurality of slits between them. .

On the other hand, when a reflective photosensor is used, the light emitting element and the light receiving element that serve as the light source are arranged in the same package, and are opposed to a scale having a repetitive reflection pattern so that the light emitted from the light emitting element is reflected by the scale. Since the light is received by the light-receiving element, for example, a reflective photosensor can be fixed in the apparatus, and a scale can be simply attached to the moving frame of the lens barrel at a position facing the photosensor. .

FIG. 5 shows a camera module showing such an example. The lens barrel 51 is of a so-called collapsible type, and the zoom lens 52 can be projected by a cam mechanism (not shown) as the moving frame 53 rotates. The moving frame 53 rotates in conjunction with the rotation of the shaft of the motor 54 . A reflective photosensor 1 is fixed to a substrate 55 by a support (not shown). A scale 2 having a reflection pattern in which the reflection surface sa and the non-reflection surface sb are repeated in stripes is attached to the outer wall of the moving frame 53 so as to face the reflection type photosensor 1 . The scale 2 may be formed by coating the surface of the outer wall of the moving frame 53, or may be formed by attaching a sticker having a reflective pattern formed by metal vapor deposition. A position detection device of this type is disclosed in a previous application (Patent Document 2) filed by the applicant of the present application.

In a conventional position detection device, a plurality of light receiving elements of a reflective photosensor are provided, and a plurality of signals with different phase differences from the plurality of light receiving portions are arithmetically processed to calculate the amount of movement.

In the position detection device disclosed in Patent Document 2, three light-receiving units are provided, and output signals of two photosensors that are 180 degrees out of phase are arithmetically processed to obtain a midpoint potential, and this midpoint potential is used as a reference. offset correction is performed on the output signals of the two photosensors having phases different from each other by 90 degrees, and the post-correction signals are arithmetically processed to detect the amount of movement.

In other conventional position detection devices, a plurality of light-receiving elements of a reflective photosensor are provided, and a plurality of signals having different phase differences from the plurality of light-receiving portions are arithmetically processed to obtain a midpoint potential. A rectangular wave obtained by comparing a plurality of signals with different phase differences is output to an arithmetic circuit to calculate the direction and amount of movement. By converting into a rectangular wave before inputting to the arithmetic circuit in this way, it is possible to reduce the processing amount of the arithmetic circuit.

Specifically, the output signals of two photosensors whose phases differ by 180 degrees are arithmetically processed to obtain the midpoint potential, and the midpoint potential and the output signals of the two photosensors whose phases differ by 90 degrees are compared by a comparator. Then, two rectangular wave outputs are obtained, the direction of movement is discriminated from the phase angle of the two rectangular wave outputs, and the amount of movement is calculated by counting the period of "H" level of the rectangular wave output.

At this time, if the midpoint potential is correct, the duty ratio of the rectangular wave output is 50%. However, if there is an error in the midpoint potential, the duty ratio of the rectangular wave will not be 50%, and an error will occur between the movement amount of the scale 2 and the calculated movement amount.

Also, the DC offset and signal amplitude fluctuate depending on various conditions such as the sensitivity of the photosensor, the amount of light emitted by the light emitting element, the distance and material of the reflecting surface of the scale 2, and the midpoint of the output signal of the photosensor fluctuates. Furthermore, the DC offset and signal amplitude also fluctuate depending on ambient light and temperature characteristics, and the midpoint of the output signal of the photosensor fluctuates in real time depending on the operating state. Therefore, in order to obtain an accurate duty ratio, it is necessary to correct the midpoint as needed.

Therefore, the applicant of the present application, in Patent Document 2, provided a light receiving unit with a phase difference of 180 degrees, IV-converted the output currents thereof by an operational amplifier, digitized by an A / D converter, processor (arithmetic circuit) A technique is disclosed in which a midpoint potential is calculated by a numerical calculation using .

JP-A-4-009712 JP 2014-002077 A

By the way, in the conventional method, when the offset correction of the output signal of the photosensor is performed, the electric signal obtained from the light receiving section is digitized, the digitized numerical value is temporarily stored in the memory, and then the numerical value is read out from the conversion table. , an A/D converter, a memory, and a digital signal processing circuit are required. Since the offset correction is performed based on the calculated midpoint potential, a D/A converter is also required, which increases the circuit scale. In addition, quantization errors also occur in these analog-to-digital conversions and digital-to-analog conversions. Furthermore, since numerical calculation takes time and offset correction is delayed, there is a problem that it is difficult to accurately correct the output signal of the photosensor that fluctuates in real time.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide a position detection device using a reflective photosensor that can reduce the circuit scale and can perform midpoint correction with little error in real time. do.

In order to achieve the above object, the invention according to claim 1 comprises: a reflecting section in which a reflecting surface and a non-reflecting surface are alternately arranged in a moving direction of a moving body; and a light emitting element that emits light to the reflecting section. and a light-receiving element for receiving reflected light from the reflecting part of the light emitted from the light-emitting element, and two signals having a phase difference of 180 degrees from the plurality of light-receiving parts of the light-receiving element. , calculates a midpoint value from these signals, and corrects the midpoint of the output signals of the plurality of light receiving units based on the midpoint value. A plurality of first current mirror circuits to which a signal from the light-receiving part or a signal having a phase difference of 180 degrees with respect to the signal is applied, and outputs the signals after inverting the polarity thereof, and output signals of the plurality of first current mirror circuits. and a second current mirror circuit to which the output signal of the analog addition circuit is applied and which has a mirror ratio of halving the output signal value of the analog addition circuit. and an analog 1/2 circuit that outputs the output value of the second current mirror circuit as the midpoint value.

The invention according to claim 2 comprises: a reflecting portion in which a reflecting surface and a non-reflecting surface are alternately arranged in a moving direction of a moving body; a light emitting element that emits light to the reflecting portion; Using a reflective photosensor having a light receiving element for receiving light reflected from the reflecting part of light, two signals with a phase difference of 180 degrees are output from the plurality of light receiving parts of the light receiving element, and these signals and correcting the midpoint of the output signals of the plurality of light receiving units based on the midpoint value, wherein the calculation of the midpoint value is performed by calculating the midpoint value of the plurality of light receiving units are input to the first current mirror circuit, the currents are combined in the first current mirror circuit, the output signal is output to the second current mirror circuit, and the output signal is output to the second current mirror circuit. and halving the output signal value of the first current mirror circuit to obtain the midpoint value .

According to the present invention, midpoint correction can be performed in real time with a small circuit scale and little error by using an analog circuit to correct the output signal of the reflective photosensor as it is as a current signal.

It is a figure which shows the Example of this invention. FIG. 4 is a diagram showing an example of a reflective photosensor used in the present invention; Fig. 10 shows an output according to an embodiment of the invention; FIG. 4 shows an analog adder circuit and an analog 1/2 circuit of the present invention; FIG. 10 is a diagram showing a camera module using a reflective photosensor;

The present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a position detecting device using a reflective photosensor, which is an embodiment of the present invention. It comprises a scale 2, an analog adder circuit 3, an analog 1/2 circuit 4, comparators 5a and 5b, and an arithmetic circuit (MPU) 6, which are provided facing each other.

The reflective photosensor 1 includes one light-emitting element 11 made of an LED and a light-receiving element 12 made of a photodiode. Since the reflective photosensor shown in FIG. 1 faces the scale 2, these light emitting/receiving elements are essentially invisible, but are shown for explanation.

The light-receiving element 12 is formed with three light-receiving portions 12a, 12b, and 12c that are divided into different areas in the moving direction 100 of the scale 2. As shown in FIG. The three light receiving portions 12a, 12b, and 12c adjust the size, shape, arrangement, and width of each of the reflecting surface sa and the non-reflecting surface sb of the scale 2, so that the three signal outputs from the reflective photosensor 1 are , is designed to be out of phase with the desired. In the embodiment, when the output A of the light receiving section 12a is taken as a reference (0 degrees), the phase angle of the output B from the light receiving section 12b is 90 degrees and the phase angle of the output C from the light receiving section 12c is 180 degrees. I am designing.

FIG. 2 is a diagram showing an example of a light-receiving element pattern of a reflective photosensor used in this embodiment. FIG. 2(B) shows another configuration example in place of the embodiment shown in FIG. 1 (FIG. 2(A)). The light receiving sections 102a, 102b, and 102c are arranged in a direction perpendicular to the moving direction 100 in a state where they partially overlap each other. The light receiving sections 12a, 12b, 12c and the light receiving sections 102a, 102b, 102c may be provided with a light shielding and reflecting film 13 as shown in FIGS. 2(C) and 2(D). The light-shielding reflective film 13 has the function of approximating the output signal of the light-receiving section to a sine wave.

The scale 2 has a repeating reflection pattern similar to that shown in FIG.

The analog addition circuit 3 outputs a signal obtained by adding the output signals of the light receiving sections 12a and 12c having a phase difference of 180 degrees among the three light receiving sections 12a, 12b and 12c.

An analog 1/2 circuit 4 receives the signal synthesized by the analog addition circuit 3 and halves it. This half value is the midpoint value of the light receiving portions 12a and 12c, and this midpoint value is output to the inverting input terminals of the comparators 5a and 5b.

Comparators 5a and 5b receive output signals from the light receiving portions 12a and 12b having a phase difference of 90 degrees among the three light receiving portions 12a, 12b and 12c. A value is inputted to an inverting input terminal and compared in magnitude, and a rectangular wave output A and a rectangular wave output B having a phase difference of 90 degrees are output to an arithmetic circuit (MPU) 6 from the respective output terminals.

An arithmetic circuit (MPU) 6 calculates the movement distance and the movement direction from the rectangular wave outputs A and B, which are the outputs of the comparators 5a and 5b and are different by 90 degrees. Since one cycle of the outputs of the comparators 5a and 5b corresponds to the sum of the widths (0.25 mm) of the reflecting surface sa and the non-reflecting surface sb of the scale 2, the cycles of the output signals of the comparators 5a and 5b are counted. The moving distance can be calculated by In addition, since the phase angles of the output signals from the light receiving sections 12a and 12b differ by 90 degrees, and the phase angle relationship is reversed depending on the traveling direction of the scale 2, the movement direction can be calculated from the order of the rising edges of the rectangular wave.

Specifically, the results shown in FIG. 3 are obtained. When the scale 2 moves in the direction of the arrow in FIG. 3A, the light receiving portions 12a, 12b, and 12c of the reflective photosensor 1 produce outputs A, B, and C, which are current signals. As shown in FIG. 3B, the output A, output B, and output C are sine wave (sin) or cosine wave (cos) signals, and the phase angle of output B is shifted by 90 degrees with respect to output A. , the phase angle of the output C is shifted by 90 degrees with respect to the output B.

Next, a specific example of adding the output A and the output C of the light receiving sections 12a and 12c and obtaining the half value midpoint value will be described. FIG. 4 shows an example of a circuit configuration for obtaining the midpoint value of output A and output C. An analog addition circuit 3 and an analog 1/2 circuit add the output currents of the light receiving sections 12a and 12c and halve the value. 4 is specifically realized. Npn type bipolar transistors Q1, Q2, Q5 and Q3, Q4, Q6 constitute a first current mirror circuit, respectively, and pnp type bipolar transistors Q7, Q8, Q9, Q10 constitute a second current mirror circuit. Q5, Q6 and Q10 are transistors for base current compensation.

The output signal A of the light receiving section 12a input to the terminal 41 is input as the collector current of Q1, and is output as the collector current of Q2 which is current-mirror connected. Similarly, the output signal C of the light receiving portion 12c input to the terminal 42 is input as the collector current of Q3, and is output as the collector current of Q4 which is current-mirror connected. Here, by setting the emitter area ratios of Q1 and Q2 and Q3 and Q4 to 1:1, it is possible to change only the polarity and output to the node 43 without changing the signal level of the input light receiving section.

The collector currents of Q2 and Q4 are then summed at node 43 and input as a collector current to Q7 forming a second current mirror circuit. The collector current of Q7 is output as the collector current of Q8 and Q9 which are current-mirror connected. The signal reaching the terminal 44 through Q8 is outputted to the inverting input terminal of the comparator 5a, and the signal reaching the terminal 45 through Q9 is outputted to the inverting input terminal of the comparator 5b. Here, by setting the emitter area ratios of Q7 and Q8 and Q7 and Q9 to 2:1, the magnitude of the current synthesized at node 43 is halved and output from terminals 44 and 45 to the next-stage comparators, respectively. 5a and 5b. Thus, the analog addition circuit 3 and the analog 1/2 circuit 4 can be realized.

In the comparators 5a and 5b, the midpoint values of the outputs A and B of the light receiving sections 12a and 12b and the outputs A and C of the light receiving sections 12a and 12c obtained by the analog adding circuit 3 and the analog 1/2 circuit 4 are calculated. are compared, and rectangular wave output A and rectangular wave output B are output to the arithmetic circuit (MPU) 6 as shown in FIGS. 3(C) and 3(D).

An arithmetic circuit (MPU) 6 calculates the moving distance and the moving direction from the rectangular wave output A and the rectangular wave output B which are the outputs of the comparators 5a and 5b. The period of rectangular wave output A and rectangular wave output B in FIGS. Therefore, the moving distance is calculated as 1.25 mm. Further, the rectangular wave output B in FIG. 3(D) has a waveform that leads the rectangular wave output A in FIG. 3(C) by 90 degrees. direction can be determined.

Here, in the above configuration, signals from the output of the reflective photosensor 1 to the output of the analog 1/2 circuit 4 are processed as currents without being converted into voltages. Since the comparators 5a and 5b that output rectangular waves process voltage signals, an IV conversion circuit is required between the analog 1/2 circuit 4 and the comparators 5a and 5b. Omit explanation.

As described above, according to the present invention, when calculating the midpoint value of the signal of the light receiving portion of the light receiving element, the signal from the light receiving portion is processed as a current signal by a simple analog circuit without IV conversion. This eliminates the need for an A/D converter, a D/A converter, a memory, or a digital signal processing circuit, so that the midpoint correction of the output signal of the reflective photosensor can be performed with a small circuit scale, less error, and This can be done in real time. In particular, the effects of factors that change in real time depending on operating conditions, such as ambient light and temperature, are extremely small.

Although the embodiments have been described above, the present invention is not limited to this, and various modifications are possible. Instead of emitting light, a fine light-shielding slit pattern may be provided on the surface of the LED. Also, a laser diode may be used instead of the LED. Since these light sources emit coherent light, a high resolution can be obtained by using a reflective diffraction grating for the scale 2 and providing a large number of light receiving portions so that the generated interference fringes are imaged on each light receiving portion. . In addition, when using such interference fringes, it is necessary to pay attention to the assembly error of the distance between the light source and the scale, the operating temperature range, and the like. Unlike industrial equipment such as machine tools that require precise position control, the above-mentioned cameras are often positioned as home appliances that require production efficiency on the premise of mass production. It is more suitable to use scattered light.

Further, the scale 2 may be a reflective diffraction grating as described above instead of the striped pattern (also referred to as a zebra pattern), and may be formed by repeatedly intermittently forming a three-dimensional engraving to reflect light toward the light-receiving element. may

1: Reflective photosensor 2: Scale 3: Analog addition circuit 4: Analog 1/2 circuit 5a, 5b: Comparator 6: Arithmetic circuit (MPU)
11: light-emitting element 12: light-receiving elements 12a to 12c: light-receiving part sa: reflecting surface sb: non-reflecting surface

Claims (2)

A reflecting section in which a reflective surface and a non-reflecting surface are alternately arranged in a moving direction of a moving body, a light-emitting element that emits light to the reflecting section, and the light emitted from the light-emitting element is reflected from the reflecting section. a reflective photosensor having a light-receiving element for receiving light, outputting two signals with a phase difference of 180 degrees from a plurality of light-receiving parts of the light-receiving element, calculating a midpoint value from these signals, A position detection device using a reflective photosensor that performs midpoint correction of output signals of a plurality of light receiving units based on a midpoint value,
a plurality of first current mirror circuits to which a signal from the light-receiving unit or a signal having a 180-degree phase difference with respect to the signal is respectively applied, and outputs the signals after inverting the polarity thereof; and outputs of the plurality of first current mirror circuits. and a second current mirror to which the output signal of the analog addition circuit is applied and which has a mirror ratio of halving the output signal value of the analog addition circuit. and an analog 1/2 circuit for outputting the output value of the second current mirror circuit as the midpoint value. A reflecting section in which a reflective surface and a non-reflecting surface are alternately arranged in a moving direction of a moving body, a light-emitting element that emits light to the reflecting section, and the light emitted from the light-emitting element is reflected from the reflecting section. Using a reflective photosensor having a light-receiving element for receiving light, outputting two signals having a phase difference of 180 degrees from a plurality of light-receiving parts of the light-receiving element, calculating a midpoint value from these signals, A position detection method for correcting the midpoint of output signals of a plurality of light receiving units based on the midpoint value,
The midpoint value is calculated by inputting two current signals having a phase difference of 180 degrees from the plurality of light receiving portions into a first current mirror circuit, combining currents in the first current mirror circuit, and outputting an output signal as a second current signal. A position using a reflective photosensor characterized by outputting to a current mirror circuit and halving the output signal value of the first current mirror circuit in a second current mirror circuit as the midpoint value . Detection method.

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