Optical ranging sensor

Abstract

To widen a dynamic range and to stably use a device even when environmental temperature is changed.SOLUTION: The optical distance measuring sensor 101 includes a charge storage part 42 for storing electric charge for generating a pulse current to be given to a light emitting element 45, a setting part 21 for setting a target sensitivity of the optical distance measuring sensor, a pulse current control part 20 for generating a pulse current synchronously with a repetitive signal and pulse-driving the light emitting element, and adjusting the pulse current based on the target sensitivity, a light receiving element 35 for receiving reflected light, a first temperature sensor 33, a nonvolatile memory 32 for storing characteristic data of the individual light receiving element, a calculation part 2 for calculating a time from irradiation of light to an object to reception of reflected light based on a temperature measured by the first temperature sensor, the characteristic data and the target sensitivity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical distance measuring sensor. [Background technology]

[0002] There is a photoelectric sensor that detects workpieces by measuring the propagation time of light (see, for example, Patent Document 1). In the photoelectric sensor of Patent Document 1, detection light is repeatedly generated by a light-emitting element. A light-receiving element receives reflected light from the detection light and generates a light-receiving signal that indicates the amount of received light. The light-receiving signal is binarized and input to a delay line in which multiple delay circuits that delay a 1-bit logic signal by a fixed time are connected in series. Branch points are provided between each delay circuit, and the output of each delay circuit is input to multiple memory elements as a distributed binary light-receiving signal. As a result, waveform data that indicates the time change of the binary light-receiving signal is generated in the multiple memory elements. Two or more waveform data are integrated by matching the light-emitting timing of the light-emitting elements, and the presence or absence of a workpiece is determined based on the integrated waveform data. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-75453 Summary of the Invention [Problem to be solved by the invention]

[0004] The photoelectric sensor in Patent Document 1 determines whether or not a workpiece is present based on accumulated waveform data, but if the reflectance of the workpiece is low, the sensitivity is insufficient, making stable detection difficult.

[0005] Furthermore, when photoelectric sensors are used as sensors for FA (Factory Automation), they are required to operate stably over a wider range of environmental temperatures than general electrical equipment. To improve sensitivity, light-receiving elements with an amplification effect are sometimes used, but these light-receiving elements have poor temperature characteristics when the amplification factor is large. Therefore, to stabilize sensitivity over a wide temperature range, the amplification factor must be kept low.

[0006] Furthermore, photoelectric sensors are used not only to detect workpieces with low reflectivity, but also to detect workpieces with high reflectivity. In such cases, if the sensitivity is set too high, detection becomes difficult, so a function that allows the sensitivity to be flexibly adjusted to suit the properties of the detected object is required.

[0007] Therefore, an object of the present disclosure is to provide an optical distance measuring sensor that has a wide dynamic range and can be used stably even when the environmental temperature changes. [Means for solving the problem]

[0008] An optical ranging sensor according to one embodiment of the present invention is an optical ranging sensor that estimates the distance to an object by measuring the time between irradiating the object with light and receiving the reflected light, and includes: a charge accumulation unit that accumulates charge to generate a pulse current to be supplied to a light-emitting element; a setting unit that sets a target sensitivity of the optical ranging sensor; a pulse current control unit that generates a pulse current in synchronization with a repetitive signal and pulse-drives the light-emitting element, the pulse current control unit adjusting the pulse current based on the target sensitivity; a light-receiving element that receives the reflected light; a first temperature sensor; a non-volatile memory that stores characteristic data of individual light-receiving elements; a light-receiving element control unit that adjusts the multiplication factor of the light-receiving element based on the temperature measured by the first temperature sensor, the characteristic data, and the target sensitivity; and a calculation unit that calculates the time based on an output signal repeatedly obtained from the light-receiving element whose multiplication factor has been adjusted.

[0009] Thus, by storing electric charges in a charge storage unit as an energy source for generating a pulsed current, a high-intensity pulsed current can be generated based on the stored energy. Furthermore, by generating a pulsed current in synchronization with a repetitive signal and pulse-driving the light-emitting element, the time width of the light-projection pulse can be narrowed, and the peak power can be increased while maintaining the average power, thereby improving sensitivity. Furthermore, by adjusting the pulsed current based on the target sensitivity, not only high-intensity light-projection pulses but also low-intensity light-projection pulses can be irradiated onto the target. On the light-receiving side, by adjusting the multiplication factor of the light-receiving element based on the temperature measured by the first temperature sensor, characteristic data of the individual light-receiving element, and the target sensitivity, control can be optimized for the characteristics and environmental temperature of the light-receiving element. Therefore, each individual element can be operated at a high multiplication factor with reduced fluctuation, achieving stable high sensitivity. Furthermore, by adjusting the reverse bias of the light-receiving element, for example, it is possible to operate at a low multiplication factor with reduced fluctuation. Therefore, an optical distance measuring sensor with a wide dynamic range and stable operation even when the environmental temperature changes can be provided.

[0010] In the above aspect, the pulse current control section may adjust the pulse current by adjusting the amount of charge accumulated by the charge accumulation section based on the target sensitivity.

[0011] For example, when a high-intensity light projection pulse is irradiated onto a light-emitting element, a high current supply capacity is required for the power supply for the pulse current. According to this aspect, energy is stored in advance in the charge storage unit, which is a passive element, and a high-intensity pulse current can be generated based on the stored energy, so that a high-intensity light projection pulse can be irradiated onto the light-emitting element using a simple circuit. Furthermore, the intensity of the pulse current can be adjusted by adjusting the amount of charge stored in advance in the charge storage unit, so that adjustment of the intensity of the light projection pulse can be simplified.

[0012] In the above aspect, the pulse current control unit may adjust the amount of charge by controlling the voltage applied to the charge storage unit.

[0013] According to this aspect, an amount of charge proportional to the voltage applied by the control of the pulse current control unit is accumulated in the charge accumulation unit, which makes it easier to adjust the amount of charge and, in turn, makes it easier to adjust the intensity of the light projection pulse.

[0014] In the above aspect, the optical distance measuring sensor may further include a second temperature sensor and a heater for maintaining an operable temperature of the light emitting element based on the temperature measured by the second temperature sensor.

[0015] According to this aspect, even when the ambient temperature is not suitable for use of the light-emitting element, heat can be supplied to the light-emitting element by the heater, and the temperature of the light-emitting element can be made suitable for use, thereby expanding the temperature range in which the optical distance measuring sensor can be used.

[0016] In the above aspect, the heater, the first temperature sensor, the light emitting element, and the light receiving element may be mounted on the same substrate.

[0017] According to this aspect, heat can be easily transferred through the substrate, so that both the light-emitting element and the light-receiving element can be heated effectively by generating heat from the heater. Furthermore, the temperatures of both the light-emitting element and the light-receiving element can be measured effectively by the first temperature sensor. In other words, since the light-emitting element and the light-receiving element can be heated and their temperatures measured using one heater and one temperature sensor, the circuit size and manufacturing costs can be reduced compared to, for example, a configuration including two heaters and two temperature sensors for heating the light-emitting element and the light-receiving element, respectively.

[0018] In the above aspect, the first temperature sensor and the second temperature sensor may be shared.

[0019] According to this aspect, by using a common first temperature sensor for adjusting the multiplication factor of the light receiving element and a common second temperature sensor for maintaining the operable temperature of the light emitting element, it is possible to reduce the circuit size and manufacturing costs compared to a configuration having two separate temperature sensors.

[0020] In the above aspect, the characteristic data may include a breakdown voltage of the light receiving element, a temperature coefficient of the breakdown voltage, and a temperature at which the breakdown voltage was obtained.

[0021] In this way, the custom data includes the breakdown voltage, the temperature coefficient of the breakdown voltage, and the temperature at which the breakdown voltage was obtained, which are useful for adjusting the multiplication factor with suppressed fluctuations, so that the multiplication factor at a given temperature can be easily and appropriately adjusted from the temperature and characteristic data.

[0022] In the above aspect, the light emitting element may be a laser diode.

[0023] According to this aspect, it is possible to irradiate the object with high-intensity light with good directionality, thereby effectively increasing sensitivity. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide an optical distance measuring sensor that has a wide dynamic range and can be used stably even when the environmental temperature changes. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a block diagram showing the configuration of an optical distance measuring sensor 101 according to a first embodiment. [Figure 2] 2 is a block diagram showing the configuration of a light projecting unit 40 in the optical distance measuring sensor 101 according to the first embodiment. FIG. [Figure 3] 2 is a block diagram showing the configuration of a light receiving section 50 in the optical distance measuring sensor 101 according to the first embodiment. FIG. [Figure 4]FIG. 1 is a perspective view of an optical distance measuring sensor 101 according to a first embodiment. [Figure 5] FIG. 1 is a side view of an optical distance measuring sensor 101 according to a first embodiment. [Figure 6] FIG. 2 is a plan view of the sensing substrate 12 according to the first embodiment as viewed from the object side. [Figure 7] 2 is a plan view of the sensing substrate 12 according to the first embodiment as viewed from the operation unit side. FIG. [Figure 8] FIG. 10 is a block diagram showing the configuration of a correction system 301 according to a second embodiment. [Figure 9] FIG. 10 is a diagram showing an example of temperature change of the breakdown voltage VBR of the avalanche photodiode 53 according to the second embodiment. [Figure 10] 10 is a flowchart showing an individual parameter acquisition method executed by a correction system 301 according to a second embodiment. [Figure 11] FIG. 10 is a block diagram showing the configuration of a light projecting unit 140 in an optical distance measuring sensor 101 according to a third embodiment. [Figure 12] FIG. 10 is a block diagram showing the configuration of an optical distance measuring sensor 101 according to a fourth embodiment. [Figure 13] FIG. 10 is a block diagram showing the configuration of a light projecting unit 240 in an optical distance measuring sensor 101 according to a fourth embodiment. [Figure 14] FIG. 10 is a block diagram showing the configuration of a light projecting unit 340 in an optical distance measuring sensor 101 according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the embodiment described below is merely a specific example for carrying out the present invention and is not intended to limit the scope of the present invention. Furthermore, to facilitate understanding of the description, the same components in each drawing will be designated by the same reference numerals wherever possible, and duplicate descriptions may be omitted.

[0027] Each drawing may show an x-axis, a y-axis, and a z-axis. The x-axis, y-axis, and z-axis form a three-dimensional Cartesian coordinate system in a right-handed system. Hereinafter, the direction of the x-axis arrow may be referred to as the x-axis + side, and the direction opposite to the arrow may be referred to as the x-axis - side, and the same applies to the other axes. The z-axis + side and z-axis - side may be referred to as the "object side" and "operation unit side," respectively. The z-axis direction may also be referred to as the "ray direction." The planes perpendicular to the x-axis, y-axis, or z-axis, respectively, may be referred to as the yz plane, zx plane, or xy plane.

[0028] [First embodiment] Fig. 1 is a block diagram showing the configuration of an optical distance measuring sensor 101 according to the first embodiment. Fig. 2 is a block diagram showing the configuration of a light projecting unit 40 in the optical distance measuring sensor 101 according to the first embodiment. Fig. 3 is a block diagram showing the configuration of a light receiving unit 50 in the optical distance measuring sensor 101 according to the first embodiment.

[0029] As shown in Figures 1 to 3, the optical distance measuring sensor 101 includes a control unit 20 (an example of a "pulse current control unit"), a heating unit 31, a non-volatile memory 32, a temperature sensor 33 (an example of a "first temperature sensor" and a "second temperature sensor"), a communication unit 34, an operation unit 35, a display unit 36, a light-emitting unit 40, and a light-receiving unit 50.

[0030] The control unit 20 includes a setting unit 21, a charge amount adjusting unit 22 (an example of a "voltage control unit"), a pulse control unit 23, a light receiving element control unit 24, and a calculation unit 25. The control unit 20 is configured by, for example, a CPU (Central Processing Unit) and an FPGA (Field Programmable Gate Array).

[0031] The light projecting unit 40 includes a voltage amplifying unit 41, a switching control unit 43, and a pulsed light generating unit 44. The pulsed light generating unit 44 includes a charge accumulating unit 42, a laser diode 45 (an example of a "light emitting element"), and a transistor 46.

[0032] The light receiving unit 50 includes a reverse voltage control unit 51, an avalanche photodiode (APD) 53 (an example of a “light receiving element”), a current-voltage conversion unit 54, a signal amplification unit 55, and a dark current measurement unit 56.

[0033] Fig. 4 is a perspective view of the optical distance measuring sensor 101 according to the first embodiment. Fig. 5 is a side view of the optical distance measuring sensor 101 according to the first embodiment. Fig. 6 is a plan view of the sensing board 12 according to the first embodiment as seen from the object side. Fig. 7 is a plan view of the sensing board 12 according to the first embodiment as seen from the operation unit side.

[0034] 4 to 7, the optical distance measuring sensor 101 further includes a sensor housing 11, a sensing board 12, a light projecting lens 13, and a light receiving lens 14. The sensor housing 11 includes a light projecting window 11a, a light receiving window 11b, and a connector 11c.

[0035] The sensor housing 11 is a member that forms the case of the optical distance measuring sensor 101, and is made of resin, metal, or the like. In Figures 4 and 5, the side surface of the sensor housing 11 on the + side of the y axis has an opening, but this opening can be covered with a lid.

[0036] A sensing board 12, a light-projecting lens 13, and a light-receiving lens 14 are provided inside sensor housing 11. Two openings are formed along the x-axis on the side of sensor housing 11 facing the object. A light-projecting window 11a and a light-receiving window 11b are provided in the opening on the negative x-axis side and the opening on the positive x-axis side, respectively.

[0037] The sensing board 12 has a plate shape extending along a plane parallel to the xy plane. A heating unit 31, a laser diode 45, and an avalanche photodiode 53 are mounted on the surface of the sensing board 12 facing the object. A temperature sensor 33 and a charge storage unit 42 are mounted on the surface of the sensing board 12 facing the operation unit.

[0038] The laser diode 45 emits pulsed laser light in the positive direction of the z axis. The laser light passes through the projection lens 13 and the projection window 11a and is irradiated onto an object (not shown) located on the object side of the optical distance measuring sensor 101.

[0039] The light receiving lens 14 receives the laser light reflected by the object (hereinafter sometimes referred to as reflected light) through the light projection window 11a and focuses the light on the avalanche photodiode 53. The distance from the optical distance measuring sensor 101 to the object is measured based on the time from when the laser diode 45 irradiates the laser light to when the reflected light is received by the avalanche photodiode 53 (hereinafter sometimes referred to as propagation time).

[0040] 1 and 2, the nonvolatile memory 32 is a readable and writable nonvolatile storage device such as an EEPROM (Electrically Erasable Programmable Read-Only Memory), and stores an operation mode table and programs (codes). Note that the nonvolatile memory 32 may be another type of nonvolatile storage device such as a flash memory.

[0041] The program can be installed externally. The program is distributed in a state stored in a storage medium that can be read by the optical distance measuring sensor 101. The program may also be distributed over the Internet connected via a communication interface.

[0042] The target sensitivity of the optical distance measuring sensor 101 is, for example, the sensitivity for detecting the presence or absence of an object. In this embodiment, the target sensitivity can be set to, for example, five levels. Note that the target sensitivity may also be set to four levels or less or six levels or more.

[0043] The target sensitivity also serves as an index of the operation mode of the optical distance measuring sensor 101. In the operation mode table, the set values ​​of "LD power" and "APD multiplication factor" are associated with the target sensitivity.

[0044] The target sensitivity may be set manually or automatically. When the target sensitivity is set manually, the user can select one of five levels of target sensitivity. In detail, for example, when the user performs a predetermined operation on the operation unit 35 to select the target sensitivity, five levels of target sensitivity are displayed on the display unit 36. The user selects the target sensitivity by operating the operation unit 35 while looking at the display unit 36.

[0045] The setting unit 21 in the control unit 20 sets the target sensitivity of the optical distance measuring sensor 101 based on the operation of the operation unit 35, and stores target sensitivity information indicating the set target sensitivity in the nonvolatile memory 32.

[0046] On the other hand, when the target sensitivity is set automatically, for example, the procedure is to project the light spot onto the object whose detection presence or absence is to be determined and onto the background of the object, and then press a teaching button included in the operation unit 35. Based on the operation content of the operation unit 35, the setting unit 21 acquires measurement results when the light spot is projected onto the object and the background, and sets an optimal target sensitivity that allows discrimination between the object and the background based on the acquired measurement results. The setting unit 21 saves the set target sensitivity in the non-volatile memory 32.

[0047] The control unit 20 causes the charge amount adjustment unit 22 to adjust the pulse current to be supplied to the laser diode 45 based on the target sensitivity. The charge amount adjustment unit 22 adjusts the pulse current based on the target sensitivity. Specifically, the charge amount adjustment unit 22 adjusts the amount of charge accumulated by the charge accumulation unit 42 in the light-projecting unit 40 based on the target sensitivity information and the operation mode table. In this embodiment, the charge amount adjustment unit 22 controls the voltage to be applied to the charge accumulation unit 42 based on the target sensitivity information and the operation mode table.

[0048] In detail, the charge amount adjusting section 22 recognizes that the LD power corresponding to the target sensitivity indicated by the target sensitivity information is "low" or "high" based on the operation mode table.

[0049] The charge amount adjusting unit 22 adjusts the amount of charge by controlling the voltage applied to the charge storage unit 42. In this embodiment, the charge amount adjusting unit 22 outputs pulse waves with the same on-time but with different duty ratios depending on the operation mode to the light projecting unit 40 at a predetermined cycle. Here, the duty ratio is a value obtained by dividing the on-time of the pulse by the predetermined cycle.

[0050] Specifically, when the charge amount adjusting unit 22 recognizes that the LD power is “low”, it outputs a pulse wave of a predetermined duty ratio (hereinafter sometimes referred to as the first duty ratio) to the light projecting unit 40.

[0051] On the other hand, when the charge amount adjustment unit 22 recognizes that the LD power is "high", it outputs a pulse wave of a predetermined duty ratio (hereinafter sometimes referred to as the second duty ratio) that is greater than the first duty ratio to the light projection unit 40.

[0052] Voltage amplifier 41 (see FIG. 2) in light projector 40 amplifies the pulse wave received from control unit 20 and outputs the amplified pulse wave to charge storage unit .

[0053] In this embodiment, the voltage amplifier 41 includes a low-pass filter and an operational amplifier. The low-pass filter in the voltage amplifier 41 smoothes the pulse wave received from the control unit 20.

[0054] Specifically, when the low-pass filter receives a pulse wave with a first duty ratio from the control unit 20, it smoothes the pulse wave to generate a first DC voltage. On the other hand, when the low-pass filter receives a pulse wave with a second duty ratio from the control unit 20, it smoothes the pulse wave to generate a second DC voltage that is higher than the first DC voltage.

[0055] The operational amplifier non-invertingly amplifies the first DC voltage or the second DC voltage received from the low-pass filter at a predetermined amplification factor and outputs the amplified voltage to the charge accumulation unit .

[0056] The charge accumulation unit 42 accumulates charges for generating a pulse current to be supplied to the laser diode 45. In this embodiment, the charge accumulation unit 42 includes, for example, four capacitor elements 42a connected in parallel. The capacitor elements 42a are, for example, ceramic capacitors. The capacitor elements 42a may also be other types of capacitors, such as film capacitors or tantalum electrolytic capacitors. The charge accumulation unit 42 may also be configured to include three or less or five or more capacitor elements 42a connected in parallel.

[0057] The capacitor element 42a has one end connected to the output terminal of the operational amplifier in the voltage amplifier 41 and the anode 45A of the laser diode 45, and the other end connected to ground. A charge corresponding to the first DC voltage or the second DC voltage applied from the voltage amplifier 41 is accumulated in the capacitor element 42a.

[0058] Pulse control unit 23 (see FIG. 1) generates a pulse current in synchronization with a repeatedly supplied signal (hereinafter, sometimes referred to as a repeating signal), and pulse-drives laser diode 45. Specifically, pulse control unit 23 releases the charge accumulated in charge accumulation unit 42 in synchronization with the repeating signal, and pulse-drives laser diode 45.

[0059] In this embodiment, the repetitive signal is, for example, a periodic signal. The periodic signal is a signal with a period of several microseconds and is generated inside the optical distance measuring sensor 101. Note that the periodic signal may also be generated outside the optical distance measuring sensor 101. Note that the repetitive signal may also be a signal that is repeatedly supplied at random timing.

[0060] The pulse control unit 23 outputs a control signal synchronized with the periodic signal to the switching control unit 43 in the light projecting unit 40 .

[0061] The switching control unit 43 (see FIG. 2) functions as a driver of the transistor 46. Specifically, the switching control unit 43 drives the transistor 46 in the pulsed light generating unit 44 based on a control signal received from the pulse control unit 23.

[0062] More specifically, when the switching control unit 43 receives a control signal having a predetermined on-voltage or higher from the pulse control unit 23, it outputs a signal (hereinafter sometimes referred to as an on signal) to the transistor 46 that turns on the transistor 46.

[0063] In detail, the switching control unit 43 includes, for example, a bipolar transistor. The bipolar transistor has a collector to which a power supply voltage is applied, a base that receives a control signal from the pulse control unit 23, and an emitter that is connected to ground via a resistive element.

[0064] When a control signal exceeding a predetermined on-voltage is applied to the base, the bipolar transistor transitions from an off state to an on state, and current flows from the collector to the emitter. This current flows through the resistor element, causing the emitter voltage to rise. The raised emitter voltage becomes an on signal that turns on the transistor 46 in the pulsed light generator 44.

[0065] The transistor 46 is, for example, a field effect transistor, and has a drain connected to the cathode 45K of the laser diode 45, a gate connected to the switching control unit 43 through a resistor element, and a source connected to ground through a resistor element.

[0066] When an on signal is input from the switching control unit 43 to the gate of the transistor 46, the transistor 46 transitions from an off state to an on state, thereby closing a discharge circuit from one end of the capacitor element 42a in the charge storage unit 42 through the laser diode 45, the transistor 46, and the ground to the other end of the capacitor element 42a.

[0067] As a result, the charge stored in the charge storage section 42 is discharged, causing a pulsed discharge current to flow through the laser diode 45, causing the laser diode 45 to emit pulsed light.

[0068] 5 to 7, the charge accumulation section 42 is disposed near the laser diode 45. In this embodiment, four capacitor elements 42a in the charge accumulation section 42 are provided on the surface of the sensing board 12 on the operation section side.

[0069] The laser diode 45 is provided on the object side surface of the sensing substrate 12. The terminals of the anode 45A and the cathode 45K are provided on the surface behind the object side surface, that is, on the operation unit side surface.

[0070] On the surface on the operation portion side, the four capacitor elements 42a in the charge storage portion 42 are provided near the terminal of the anode 45A and the terminal of the cathode 45K.

[0071] Specifically, the distance between the capacitor element 42 a in the charge storage unit 42 and the terminal of the anode 45 A or the terminal of the cathode 45 K is shorter than the distance between the laser diode 45 and the avalanche photodiode 53 .

[0072] In this way, by configuring the charge storage unit 42 to be located near the laser diode 45, it is possible to quickly respond to the transition of the transistor 46 to the on state, and therefore it is possible to irradiate pulsed laser light (hereinafter sometimes referred to as a light projection pulse) with a narrow time width and a high peak intensity from the laser diode 45.

[0073] 1 and 4 to 7, the heating unit 31 maintains the operable temperature of the laser diode 45 based on the temperature measured by the temperature sensor 33. In detail, the heating unit 31 controls and maintains the ambient temperature of the laser diode 45 within the operable temperature range defined as the specifications of the laser diode 45 element.

[0074] In this embodiment, the heating unit 31 includes seven resistance elements (examples of "first heaters" and "second heaters") connected in series and a switch. In detail, the seven resistance elements and the switch are connected in series between a power supply voltage supply terminal and ground.

[0075] Three of the seven resistive elements are provided on the object-side surface of the sensing substrate 12 on the +y-axis side of the laser diode 45. The other four of the seven resistive elements are provided on the object-side surface of the sensing substrate 12 on the -y-axis side of the laser diode 45.

[0076] The temperature sensor 33 is provided near the avalanche photodiode 53. In this embodiment, the avalanche photodiode 53 and the temperature sensor 33 are provided on the object side surface and the operation unit side surface of the sensing board 12, respectively. When the operation unit side surface of the sensing board 12 is viewed in plan, the temperature sensor 33 is provided at a position overlapping with the avalanche photodiode 53.

[0077] In other words, the temperature sensor 33 is provided on the surface of the sensing board 12 on the operation unit side at a position facing the avalanche photodiode 53 with the sensing board 12 in between.

[0078] The temperature sensor 33 measures the temperature at predetermined intervals, and outputs temperature information indicating the measurement results to the control unit 20, for example.

[0079] The control unit 20 monitors the temperature indicated by the temperature information received from the temperature sensor 33, and when the temperature drops below a predetermined value (for example, -10°C), it turns on the switch in the heating unit 31. As a result, current flows through the seven resistance elements in the heating unit 31, causing the seven resistance elements to generate heat and increase the temperature of the laser diode 45, so that the ambient temperature of the laser diode 45 is maintained within the above-mentioned operable temperature range.

[0080] As shown in FIG. 3, when the avalanche photodiode 53 in the light receiving section 50 is irradiated with light in a reverse bias state, it is able to detect the light with high sensitivity due to the self-multiplication effect.

[0081] When the reverse bias voltage applied to the avalanche photodiode 53 is increased, the avalanche photodiode 53 can be operated at a high multiplication factor (hereinafter, sometimes referred to as gain).

[0082] The relationship between the reverse bias voltage and the gain is not linear, but rather the closer the reverse bias voltage is to the breakdown voltage of the avalanche photodiode 53, the greater the gain exponentially increases.

[0083] Furthermore, when the avalanche photodiode 53 is used with a high gain, the gain changes significantly with temperature, meaning that the temperature characteristics of the gain are poor.

[0084] The temperature characteristics of the breakdown voltage and gain of the avalanche photodiode 53 vary from one device to another, making it difficult to operate the avalanche photodiode 53 with a constant high gain over a wide temperature range simply by applying a constant reverse bias voltage to the avalanche photodiode 53.

[0085] As shown in FIGS. 1 and 3, in this embodiment, the nonvolatile memory 32 stores characteristic data of each avalanche photodiode 53.

[0086] The characteristic data is the breakdown voltage V of the avalanche photodiode 53. BR , the temperature coefficient of the breakdown voltage γ, and a certain breakdown voltage V BR The temperature T of the avalanche photodiode 53 when ref and temperature T ref is the reference temperature when performing correction during operation of the optical distance measuring sensor 101.

[0087] In this embodiment, the breakdown voltage V BR is the reverse bias voltage that should be applied to cause a predetermined value of dark current to flow through the avalanche photodiode 53. Specifically, the predetermined value is, for example, 100 microamperes. The temperature coefficient γ will be described in detail later.

[0088] The reverse bias voltage V for the avalanche photodiode 53 to have a gain of G R The correction formula to give, for example, f G (T, V BR , T ref , γ), where T is the temperature of the avalanche photodiode 53.

[0089] In the operation mode table, the target sensitivity indicated by the target sensitivity information is associated with an APD multiplication factor of "low" or "high."

[0090] In this embodiment, the nonvolatile memory 32 stores a low-gain correction formula to be used when the APD multiplication factor is set to "low" and a high-gain correction formula to be used when the APD multiplication factor is set to "high."

[0091] The correction formula for low gain is f GL (T, V BR , T ref , γ), and the reverse bias voltage V R Give.

[0092] The high gain correction formula is f GH (T, V BR , T ref , γ), and the reverse bias voltage V R Give.

[0093] The light receiving element control unit 24 adjusts the gain of the avalanche photodiode 53 based on the temperature T measured by the temperature sensor 33, the characteristic data, and the target sensitivity.

[0094] In detail, the light receiving element control unit 24 periodically or irregularly controls the reverse bias voltage V R is calculated, and the reverse bias voltage V R Generates.

[0095] Specifically, the light receiving element control unit 24 recognizes, based on the operation mode table, that the APD multiplication factor corresponding to the target sensitivity indicated by the target sensitivity information is "low" or "high."

[0096] Furthermore, the light receiving element control unit 24 recognizes the temperature T from the temperature information output from the temperature sensor 33.

[0097] When the light receiving element control unit 24 recognizes that the APD multiplication factor is "low", it calculates the low gain correction formula, the breakdown voltage V BR , temperature T ref and the temperature coefficient γ are acquired from the nonvolatile memory 32, and the low gain correction formula f GL (T, V BR , T ref , γ) to T, V BR , T ref By inputting γ, the reverse bias voltage V R Calculate.

[0098] On the other hand, when the light receiving element control unit 24 recognizes that the APD multiplication factor is "high", it sets the high gain correction formula, the breakdown voltage V BR , temperature T ref and the temperature coefficient γ are acquired from the nonvolatile memory 32, and the high gain correction formula f GH (T, V BR , T ref , γ) to T, V BR , T ref By inputting γ, the reverse bias voltage V R Calculate.

[0099] The light receiving element control unit 24 supplies the calculated reverse bias voltage V R Control is performed to generate the following.

[0100] The reverse voltage control unit 51 includes, for example, a boost circuit. The reverse voltage control unit 51 controls the reverse bias voltage V R and applies a reverse bias voltage V to the cathode of the avalanche photodiode 53. R is applied.

[0101] The avalanche photodiode 53 is driven by a reverse bias voltage V R When reflected light from an object is received while a voltage is applied, a current flows from the cathode to the anode.

[0102] The current-voltage converter 54 converts the current flowing through the avalanche photodiode 53 into a voltage and outputs it to the signal amplifier 55 .

[0103] In this embodiment, the current-voltage conversion unit 54 includes, for example, a transimpedance amplifier and a capacitor element. The transimpedance amplifier has an input terminal connected to the anode of the avalanche photodiode 53 through the capacitor element, and an output terminal connected to the signal amplification unit 55.

[0104] The AC component of the current flowing through the avalanche photodiode 53 is input to the input terminal of the transimpedance amplifier. A signal (hereinafter sometimes referred to as an output signal) having a voltage corresponding to the current is output from the output terminal of the transimpedance amplifier.

[0105] The signal amplifier 55 amplifies the output signal from the current-voltage converter 54 and outputs it to the control unit 20 .

[0106] The calculation unit 25 in the control unit 20 calculates the propagation time based on the output signal repeatedly obtained from the avalanche photodiode 53.

[0107] In this embodiment, the calculation unit 25 acquires time-series data based on the output signal received from the light receiving unit 50, for example, every time the pulse control unit 23 outputs a control signal.

[0108] Specifically, the calculation unit 25 binarizes the voltage of the output signal based on, for example, the magnitude relationship between the voltage of the output signal and a predetermined threshold value. The start time of the time series data is, for example, the time when a control signal is output from the pulse control unit 23.

[0109] The calculation unit 25 integrates a plurality of pieces of time series data to obtain the integrated time series data (hereinafter, sometimes referred to as integrated time series data). The integrated time series data includes peaks based on the reflected light received by the light receiving unit 52.

[0110] The calculation unit 25 acquires the time when the avalanche photodiode 53 receives the reflected light according to a predetermined detection threshold (hereinafter also referred to as the light reception time).

[0111] The calculation unit 25 acquires, for example, the time when the peak based on the reflected light in the integrated time series data exceeds the detection threshold as the light reception time.

[0112] The calculation unit 25 estimates the distance to the object as the value obtained by multiplying the propagation time from the start time of the time series data to the light reception time by the speed of light and dividing the result by 2.

[0113] Incidentally, it is preferable that the pulse current supplied to the laser diode 45 is designed so that the laser diode 45 satisfies the laser class 1 standard and the S / N ratio of the output signal obtained from the reflected light is high.

[0114] The standard for laser class 1 includes a provision for the average optical power, which must not exceed 0.39 mW.

[0115] When the optical power value, pulse width, and pulse period of the light projection pulse output from the laser diode 45 are Po (mW), Pw (ns), and T (ns), respectively, the above definition is expressed by the following equation (1). Po×Pw / T<0.39mW (1)

[0116] To increase the S / N ratio, it is necessary to increase Po and decrease Pw. When a pulse current is generated based on a clock signal, the minimum Pw is half the clock period.

[0117] To achieve a high clock frequency while keeping costs down, the clock frequency is generally 450 MHz or less. In other words, the minimum Pw is (1 / 450 MHz) / 2 ≒ 1.1 ns.

[0118] Transforming equation (1) to Po / T<0.39 / Pw (mW / ns) and substituting 1.1 ns for Pw yields the following equation (2). Po / T<0.35(mW / ns) (2)

[0119] In other words, it can be said that a desirable design is to determine Po and T so that Po / T is as large as possible while satisfying formula (2).

[0120] Specifically, for example, Pw, Po, and T may be set to 2.7 ns, 500 mw, and 4000 ns, respectively.

[0121] In this case, Po / T=0.125, and equation (2) is satisfied. Also, Po×Pw / T=0.34 mW, and equation (1) is also satisfied.

[0122] Similarly, Pw, Po and T may be set to 1.2 ns, 500 mw and 2000 ns, respectively.

[0123] In this case, Po / T=0.25, and formula (2) is satisfied. Also, Po×Pw / T=0.30 mW, and formula (1) is also satisfied.

[0124] If Po is made adjustable, T may be designed to change in conjunction with Po. For example, if Pw, Po, and T are set to 2.7 ns, 500 mW, and 4000 ns, respectively, and Po is adjusted to 250 mW, T may be changed to 2000 ns.

[0125] This configuration allows the number of measurements per unit time to be increased, which is expected to reduce noise through integration, and achieve the maximum S / N ratio while complying with the Laser Class 1 standard.

[0126] [Second embodiment] An optical distance measuring sensor 101 according to a second embodiment will be described. From the second embodiment onwards, descriptions of matters common to the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0127] The optical distance measuring sensor 101 according to the second embodiment differs from the optical distance measuring sensor 101 according to the first embodiment in that the characteristic data of the avalanche photodiode 53 is acquired under the control of the equipment 201 .

[0128] 8 is a block diagram showing the configuration of a correction system 301 according to the second embodiment. As shown in FIGS. 3 and 8, the correction system 301 includes an optical distance measuring sensor 101 and equipment 201.

[0129] The communication unit 34 in the optical distance measuring sensor 101 is, for example, an IO-Link PHY, and is a communication element that communicates with the equipment 201. The equipment 201 and the control unit 20 can communicate with each other via the IO-Link PHY 34.

[0130] The communication unit 34 is connected to the equipment 201 through the connector 11c, for example, during a shipping inspection after product assembly of the optical distance measuring sensor 101. The equipment 201 controls the optical distance measuring sensor 101 through the IO-Link PHY 34.

[0131] In this embodiment, the equipment 201 controls the control unit 20 in the optical distance measuring sensor 101 to measure the dark current of the avalanche photodiode 53 while changing the temperature of the avalanche photodiode 53, and calculates the breakdown voltage V BR , temperature T refand temperature coefficient γ.

[0132] The dark current measurement unit 56 in the light receiving unit 50 measures the dark current of the avalanche photodiode 53. In detail, the dark current measurement unit 56 measures the dark current when a reverse bias voltage is applied to the avalanche photodiode 53 in a state where no light enters the light receiving surface of the avalanche photodiode 53.

[0133] In this embodiment, the avalanche photodiode 53 is physically covered by a light-shielding member during dark current measurement. The dark current measurement unit 56 includes, for example, a resistive element, a low-pass filter, and an operational amplifier.

[0134] The resistance element in the dark current measurement unit 56 has one end connected to the anode of the avalanche photodiode 53 and the other end connected to the ground.

[0135] The dark current flowing through the avalanche photodiode 53 flows to ground through a resistor element. A voltage corresponding to the dark current (hereinafter sometimes referred to as a measurement voltage) is generated at one end of the resistor element. A capacitor element may be connected in parallel with the resistor element. This stabilizes the measurement voltage.

[0136] The operational amplifier non-invertingly amplifies the measurement voltage received from one end of the resistance element through the low-pass filter at a predetermined amplification factor and outputs the amplified voltage to the control unit 20 .

[0137] FIG. 9 shows the breakdown voltage V BR 1 is a graph showing an example of temperature change. The vertical axis represents the breakdown voltage V BR The horizontal axis represents the temperature T of the avalanche photodiode 53.

[0138] 3, 6, 8, and 9, the equipment 201 controls the control unit 20 to determine characteristic data based on the dark current value measured by the dark current measurement unit 56, and writes the determined characteristic data to the nonvolatile memory 32. The characteristic data is determined based on the dark current values ​​of the avalanche photodiode 53 at a plurality of ambient temperatures.

[0139] [How to obtain individual parameters] Next, a method for acquiring individual parameters of the avalanche photodiode 53 in the second embodiment will be specifically described in detail. Fig. 10 is a flowchart showing the method for acquiring individual parameters executed by the correction system 301 according to the second embodiment. As shown in Fig. 10, the method for acquiring individual parameters includes steps S102 to S112, and each step is executed by the equipment 201 included in the correction system 301.

[0140] First, the equipment 201 controls the control unit 20 to make the heating unit 31 generate heat. The heating unit 31 changes the ambient temperature of the avalanche photodiode 53 (step S102).

[0141] Specifically, the heat generated by the heating unit 31 is conducted to the avalanche photodiode 53 through the sensing substrate 12. This causes the temperature of the avalanche photodiode 53 and its surroundings to rise.

[0142] Next, the equipment 201 determines whether or not a predetermined condition for ending the individual parameter acquisition process is satisfied (step S104). The predetermined condition will be described in detail later.

[0143] When the equipment 201 determines that the predetermined conditions are not satisfied (NO in step S104), it controls the control unit 20 to adjust the reverse bias voltage applied to the avalanche photodiode 53 while monitoring the measured voltage from the dark current measurement unit 56 (step S106).

[0144] Specifically, the equipment 201 adjusts the reverse bias voltage applied to the avalanche photodiode 53 so that a predetermined value of dark current flows through the avalanche photodiode 53 .

[0145] Next, the equipment 201 controls the control unit 20 to calculate the reverse bias voltage when a predetermined value of dark current flows through the avalanche photodiode 53, i.e., the breakdown voltage V BR Then, a storage process is performed to store the temperature information output from the temperature sensor 33 (step S108).

[0146] Next, the equipment 201 determines whether a predetermined condition for terminating the individual parameter acquisition process is satisfied (step S104). The predetermined condition may be, for example, whether the storage process has been performed a predetermined number of times (two or more times) and whether the breakdown voltage V BR The measurement was carried out.

[0147] By performing the preservation process multiple times while continuing to heat the avalanche photodiode 53, the breakdown voltage V BR is saved.

[0148] When the equipment 201 determines that the predetermined condition is satisfied (YES in step S104), the equipment 201 stores the breakdown voltage V BR The temperature coefficient γ is estimated based on the above (step S110).

[0149] In detail, the breakdown voltage V BR The higher the temperature T, the higher the breakdown voltage V BR is approximately proportional to the temperature T.

[0150] The equipment 201 is a temperature T and a breakdown voltage V BR The relationship between the temperature and the temperature is approximated by a linear equation to obtain a line SL. Then, the equipment 201 estimates the gradient of the line SL as the temperature coefficient γ.

[0151] The equipment 201 controls the control unit 20 to calculate the estimated temperature coefficient γ and the temperature T ref Breakdown voltage V BR and temperature T ref and are written into the nonvolatile memory 32 as characteristic data of the individual avalanche photodiodes 53 (step S112).

[0152] [Third embodiment] The optical distance measuring sensor 101 according to the third embodiment will be described. The optical distance measuring sensor 101 according to the third embodiment differs from the optical distance measuring sensor 101 according to the first embodiment in that the capacitance of the charge amount adjusting unit 22 is adjusted to adjust the magnitude of the pulse current.

[0153] Fig. 11 is a block diagram showing the configuration of the light-projecting unit 140 in the optical distance measuring sensor 101 according to the third embodiment. As shown in Fig. 11, the light-projecting unit 140 includes a constant voltage supplying unit 241 and a pulsed light generating unit 144 instead of the voltage amplifying unit 41 and the pulsed light generating unit 44 of the light-projecting unit 40 shown in Fig. 2.

[0154] The pulsed light generating section 144 further includes a switch section 47 compared to the pulsed light generating section 44 shown in FIG.

[0155] 1 and 11, the charge amount adjusting unit 22 in the control unit 20 adjusts the capacitance of the charge storage unit 42 based on the target sensitivity information and the operation mode table. The constant voltage supplying unit 241 in the light projecting unit 140 supplies a substantially constant voltage from the output terminal.

[0156] The switch section 47 in the pulsed light generating section 144 includes switches 47a in the same number as the capacitor elements 42a included in the charge accumulating section 42. In this embodiment, the switches 47a include four switches 47a.

[0157] The four switches 47a are provided corresponding to the four capacitor elements 42a, respectively. Each switch 47a has a first end connected to the output terminal of the constant voltage supply unit 241 and a second end connected to ground via the corresponding capacitor element 42a.

[0158] The switch unit 47 is not limited to a configuration including the same number of switches 47a as the number of capacitor elements 42a included in the charge accumulation unit 42, but may be a configuration including a number of switches 47a less than the number of capacitor elements 42a included in the charge accumulation unit 42. In this case, some of the plurality of capacitor elements 42a are connected to the output terminal of the constant voltage supply unit 241 via the corresponding switches 47a, and the other are connected directly to the output terminal of the constant voltage supply unit 241.

[0159] An anode 45A of the laser diode 45 is connected to an output terminal of the constant voltage supply unit 241. The charge amount adjustment unit 22 adjusts the capacitance of the charge accumulation unit 42 by controlling the opening and closing of four switches 47a based on the target sensitivity information and the operation mode table.

[0160] In this embodiment, the charge amount adjusting unit 22 can open and close each of the four switches 47a by outputting a logic signal to the switch unit 47. When the charge amount adjusting unit 22 recognizes that the LD power is "low", it closes some of the four switches 47a and opens the remaining switches 47a. Hereinafter, the number of switches 47a that are closed when the LD power is "low" may be referred to as the "first number".

[0161] On the other hand, when the charge amount adjusting unit 22 recognizes that the LD power is "high", it closes all four switches 47a. Note that when the charge amount adjusting unit 22 recognizes that the LD power is "high", it is not necessary to close all of the switches 47a as long as it is configured to close more than the first number of switches 47a (hereinafter, sometimes referred to as the second number).

[0162] As a result, when the LD power is "low", the capacitance of the charge accumulation unit 42 is the sum of the capacitances of the first number of capacitor elements 42a (hereinafter, sometimes referred to as the first capacitance). On the other hand, when the LD power is "high", the capacitance of the charge accumulation unit 42 is the sum of the capacitances of the second number of capacitor elements 42a (hereinafter, sometimes referred to as the second capacitance).

[0163] When the LD power is "low" or "high", the charge accumulation section 42 is charged with a charge corresponding to the first capacitance or the second capacitance, respectively.

[0164] Since the second capacitance is larger than the first capacitance, the magnitude of the pulse current supplied to the laser diode 45 when the LD power is "high" is larger than the magnitude of the pulse current supplied to the laser diode 45 when the LD power is "low".

[0165] [Fourth embodiment] The optical distance measuring sensor 101 according to the fourth embodiment will be described. The optical distance measuring sensor 101 according to the fourth embodiment differs from the optical distance measuring sensor 101 according to the first embodiment in that the magnitude of the pulse current flowing through the laser diode 45 is adjusted by the voltage applied to the gate of the transistor 46.

[0166] Fig. 12 is a block diagram showing the configuration of an optical distance measuring sensor 101 according to the fourth embodiment. As shown in Fig. 12, the optical distance measuring sensor 101 according to the fourth embodiment includes a control unit 220 and a light-projecting unit 240 instead of the control unit 20 and the light-projecting unit 40 of the optical distance measuring sensor 101 shown in Fig. 1. The control unit 220 includes a pulse control unit 223 instead of the charge amount adjusting unit 22 and the pulse control unit 23 of the control unit 20 shown in Fig. 1.

[0167] Fig. 13 is a block diagram showing the configuration of a light-projecting unit 240 in an optical distance measuring sensor 101 according to the fourth embodiment. As shown in Fig. 13, the light-projecting unit 240 includes a constant voltage supply unit 241 and a switching control unit 243 instead of the voltage amplification unit 41 and the switching control unit 43 of the light-projecting unit 40 shown in Fig. 2.

[0168] As shown in FIGS. 12 and 13, one end and the other end of the capacitor element 42a are connected to the output terminal of the constant voltage supply unit 241 and the ground, respectively.

[0169] The switching control unit 243 includes, for example, an AC signal source that generates an AC signal. The AC signal source operates under the control of the switching control unit 243 and supplies the generated AC signal to the gate of the transistor 46. The generation cycle of the pulse current is adjusted by adjusting the cycle of the AC signal. The magnitude of the amplitude of the AC signal is adjusted by adjusting the magnitude of the pulse current.

[0170] The pulse control section 223 generates a pulse current in synchronization with the repetitive signal, pulse-drives the laser diode 45, and adjusts the pulse current based on the target sensitivity.

[0171] In this embodiment, the pulse control unit 223 adjusts the magnitude of the pulse current flowing between the drain and source of the transistor 46 by controlling the switching control unit 243 based on the target sensitivity information and the operation mode table.

[0172] In particular, the pulse control unit 223 recognizes that the LD power corresponding to the target sensitivity indicated by the target sensitivity information is "low" or "high" based on the operation mode table.

[0173] When the pulse control unit 223 recognizes that the LD power is "low", it controls the switching control unit 243 to set the amplitude of the AC signal supplied to the gate of the transistor 46 to a first value.

[0174] On the other hand, when the pulse control unit 223 recognizes that the LD power is “high”, it controls the switching control unit 243 to change the amplitude of the AC signal supplied to the gate of the transistor 46 to a second value greater than the first value.

[0175] Furthermore, the pulse control unit 223 adjusts the period of the AC signal supplied to the gate of the transistor 46 so as to synchronize with a periodic signal generated inside the optical distance measuring sensor 101, for example.

[0176] This allows the magnitude of the pulse current flowing through the laser diode 45 when the LD power is "high" to be greater than the magnitude of the pulse current flowing through the laser diode 45 when the LD power is "low".

[0177] [Fifth embodiment] The optical distance measuring sensor 101 according to the fifth embodiment will be described. The optical distance measuring sensor 101 according to the fifth embodiment differs from the optical distance measuring sensor 101 according to the fourth embodiment in that a current mirror circuit is used to adjust the magnitude of the pulse current flowing through the laser diode 45.

[0178] Fig. 14 is a block diagram showing the configuration of a light-projecting unit 340 in an optical distance measuring sensor 101 according to the fifth embodiment. As shown in Fig. 14, the light-projecting unit 340 includes a pulsed light generating unit 344 and a switching control unit 343 instead of the pulsed light generating unit 44 and the switching control unit 243 of the light-projecting unit 240 shown in Fig. 13.

[0179] 13, the pulsed light generating section 344 includes a transistor 346 instead of the transistor 46. The switching control section 343 includes a transistor 343a and a constant current source 343b.

[0180] The transistor 343a and the transistor 346 are NPN bipolar transistors. The collector, base, and emitter of the transistor 346 are connected to the cathode 45K of the laser diode 45, the base of the transistor 343a, and the ground, respectively.

[0181] The transistor 343a is diode-connected, with the collector and base connected to the constant current source 343b and the emitter connected to ground.

[0182] Since the voltage between the base and emitter of transistor 346 and the voltage between the base and emitter of transistor 343a are approximately the same, the current flowing between the collector and emitter of transistor 346 (hereinafter sometimes referred to as the output current) is approximately the same as the current flowing between the collector and emitter of transistor 343a (hereinafter sometimes referred to as the reference current).

[0183] As shown in Figures 12 and 14, in this embodiment, the pulse control unit 223 adjusts the pulse current flowing between the collector and emitter of the transistor 346 by controlling the constant current source 343b based on the target sensitivity information and the operation mode table.

[0184] In particular, the pulse control unit 223 recognizes that the LD power corresponding to the target sensitivity indicated by the target sensitivity information is "low" or "high" based on the operation mode table.

[0185] When the pulse control unit 223 recognizes that the LD power is "low", it controls the constant current source 343b to set the magnitude of the reference current to a first value.

[0186] On the other hand, when the pulse control unit 223 recognizes that the LD power is "high", it controls the switching control unit 243 to set the magnitude of the reference current to a second value that is larger than the first value.

[0187] Furthermore, the pulse control unit 223 causes the constant current source 343b to output a pulsed reference current in synchronization with a periodic signal generated inside the optical distance measuring sensor 101, for example.

[0188] This allows the magnitude of the pulse current flowing through the laser diode 45 when the LD power is "high" to be greater than the magnitude of the pulse current flowing through the laser diode 45 when the LD power is "low".

[0189] In the first to fifth embodiments, the laser diode 45 is used as the light emitting element, but the present invention is not limited to this. For example, a light emitting diode may be used as the light emitting element.

[0190] Furthermore, in the first to fifth embodiments, the avalanche photodiode 53 is used as the light receiving element, but the present invention is not limited to this. Any other type of light receiving element may be used as long as it has a self-amplifying effect.

[0191] Furthermore, in the first and third to fifth embodiments, the optical distance measuring sensor 101 is described as having a configuration including the communication unit 34 and the dark current measurement unit 56, but the present invention is not limited to this. The optical distance measuring sensor 101 may be configured without at least one of the communication unit 34 and the dark current measurement unit 56. Even with such a configuration, the object of the present invention can be achieved.

[0192] In the first to fifth embodiments, the temperature sensor 33 is described as having three uses: adjusting the multiplication factor of the avalanche photodiode 53, determining characteristic data, and maintaining an operable temperature of the laser diode 45. However, the present invention is not limited to this. The optical distance measuring sensor 101 may further include another temperature sensor (an example of a "second temperature sensor"), and the other temperature sensor may be used to determine characteristic data or to maintain an operable temperature of the laser diode 45.

[0193] Furthermore, in the first to fifth embodiments, the heating unit 31 has been described as having two uses, namely, maintaining an operable temperature of the laser diode 45 and changing the ambient temperature of the avalanche photodiode 53, but the present invention is not limited to this. The optical distance measuring sensor 101 may further include another heating unit (an example of a "second heater"), and the heating unit 31 (an example of a "first heater") and the other heating unit may have the uses of maintaining an operable temperature of the laser diode 45 and changing the ambient temperature of the avalanche photodiode 53, respectively.

[0194] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangement, materials, conditions, shapes, sizes, etc., are not limited to those illustrated and can be modified as appropriate. Furthermore, configurations shown in different embodiments can be partially substituted or combined with each other.

[0195] [Appendix 1] An optical distance measuring sensor (101) that estimates a distance to an object by measuring the time from when light is irradiated onto the object to when reflected light is received, a charge storage unit (42) that stores charges for generating a pulse current to be applied to a light-emitting element (45); a setting unit (21) that sets a target sensitivity of the optical distance measuring sensor; a pulse current control unit (20) that generates the pulse current in synchronization with a repetitive signal and pulse-drives the light-emitting element, the pulse current control unit adjusting the pulse current based on the target sensitivity; a light receiving element (53) that receives the reflected light; a first temperature sensor (33); a non-volatile memory (32) storing characteristic data of the individual light receiving elements; a light-receiving element control unit (24) that adjusts the multiplication factor of the light-receiving element based on the temperature measured by the first temperature sensor, the characteristic data, and the target sensitivity; a calculation unit (25) that calculates the time based on an output signal repeatedly obtained from the light-receiving element with the multiplication factor adjusted, Optical distance sensor. [Explanation of symbols]

[0196] 11...sensor housing, 11a...light projection window, 11b...light receiving window, 11c...connector, 12...sensing board, 13...light projection lens, 14...light receiving lens, 20...control unit, 21...setting unit, 22...charge amount adjustment unit, 23...pulse control unit, 24...light receiving element control unit, 25...calculation unit, 31...heating unit, 32...non-volatile memory, 33...temperature sensor, 34...communication unit, 35...operation unit, 36...display unit, 40...light projection unit, 41...voltage amplification unit, 42...charge accumulation unit, 42a...capacitor element, 43...switching control unit, 44...pulse light generation unit, 45...laser diode, 45A...anode, 45K...cathode, 46...transistor, 50...light receiving unit, 51...reverse voltage control unit, 52...light receiving unit, 53...avalanche photodiode, 54...current-voltage conversion unit, 55...signal amplification unit, 56...dark current measurement unit, 101...optical distance measuring sensor, 140...light emitting unit, 144...pulse light generating unit, 201...equipment, 244...pulse light generating unit, 220...control unit, 223...pulse control unit, 240...light emitting unit, 241...constant voltage supply unit, 243...switching control unit, 243a...AC signal source, 301...correction system, 340...light emitting unit, 343...switching control unit, 343a...transistor, 343b...constant current source, 344...pulse light generating unit, 346...transistor

Claims

1. An optical distance measuring sensor that estimates a distance to an object by measuring the time from when light is irradiated onto the object to when reflected light is received, a charge storage unit that stores charges for generating a pulse current to be supplied to the light-emitting element; a setting unit that sets a target sensitivity of the optical distance measuring sensor; a pulse current control unit that generates the pulse current in synchronization with a repetitive signal and pulse-drives the light-emitting element, the pulse current control unit adjusting the pulse current based on the target sensitivity; a light receiving element that receives the reflected light; a first temperature sensor; a nonvolatile memory that stores characteristic data of the individual light receiving elements; a light receiving element control unit that adjusts the multiplication factor of the light receiving element based on the temperature measured by the first temperature sensor, the characteristic data, and the target sensitivity; a calculation unit that calculates the time based on an output signal repeatedly obtained from the light receiving element with the multiplication factor adjusted, Optical distance sensor.

2. the pulse current control unit adjusts the amount of charge accumulated by the charge accumulation unit based on the target sensitivity, thereby adjusting the pulse current. The optical distance measuring sensor according to claim 1 .

3. the pulse current control unit adjusts the amount of charge by controlling a voltage applied to the charge storage unit. The optical distance measuring sensor according to claim 2 .

4. The optical distance measuring sensor includes: A second temperature sensor; a heater for maintaining an operable temperature of the light-emitting element based on the temperature measured by the second temperature sensor, The optical distance measuring sensor according to claim 1 .

5. the heater, the first temperature sensor, the light-emitting element, and the light-receiving element are mounted on the same substrate; The optical distance measuring sensor according to claim 4 .

6. the first temperature sensor and the second temperature sensor are shared; The optical distance measuring sensor according to claim 4 .

7. the characteristic data includes a breakdown voltage of the light receiving element, a temperature coefficient of the breakdown voltage, and a temperature at which the breakdown voltage was obtained; The optical distance measuring sensor according to claim 1 .

8. The light emitting element is a laser diode. The optical distance measuring sensor according to claim 1 .

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