Sensor control circuit

Abstract

To solve a problem that the detection signal reaching a receiving element is very small and the measurement of a detection object cannot be correctly performed in a conventional sensor control circuit.SOLUTION: A sensor control circuit 10 according to the present invention includes a transmission element control circuit 11 and an intermittent control circuit 14. The transmission element control circuit detects the magnitude of the change in a transmission factor βsen of the detection signal from a transmission element 101 to the reception element 102 acquired by a monitor signal Vrec by the difference between the signal level of a reference signal V+ and the signal level of the monitor signal Vrec, and changes the transmission element control signal for canceling the change in the transmission factor βsen according to the magnitude of the change. The intermittent control circuit periodically switches the transmission element control signal between a detection mode in which the transmission intensity of the detection signal is transmitted to the output terminal To in accordance with the signal level of the transmission element control signal, and a non-detection mode in which the transmission intensity of the detection signal is fixed to substantially zero.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a sensor control circuit, for example, a sensor control circuit having a transmitting element that transmits a detection signal and a receiving element that receives the detection signal. [Background technology]

[0002] There is a sensor system that transmits and receives a detection signal between a transmitting element and a receiving element, and detects that an object to be detected has entered a detection range set by the detection signal. In such a sensor system, the output intensity of the transmitting element may be controlled. Thus, an example of a control circuit for the output intensity of the transmitting element in the sensor system is disclosed in Patent Document 1.

[0003] The sensor control circuit described in Patent Document 1 has an output terminal that outputs a transmitting element control signal to a transmitting element that transmits a detection signal to be irradiated to an object to be detected, which controls the transmission intensity of the detection signal, an input terminal to which a monitor signal that causes a receiving element that receives the detection signal to vary its signal level depending on the magnitude of the receiving intensity of the detection signal is input, and a transmitting element control circuit that generates the transmitting element control signal based on the amount of change in the transmission rate of the detection signal from the transmitting element to the receiving element obtained by the monitor signal, and the transmitting element control circuit changes the transmitting element control signal in a direction that cancels out the change in the transmission rate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-117200 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the sensor control circuit described in Patent Document 1 has a problem that in a situation where the ambient light is strong, the closer the ambient light is to the detection light, the more the ambient light causes a detection error, making it impossible to perform correct detection. Also, the sensor control circuit described in Patent Document 1 has a problem that in an environment where the transmissibility between the transmitting element and the receiving element is extremely low, the transmissibility measurement cannot be performed correctly unless the detection signal reaching the receiving element is made extremely small. In this case, even if the ambient light is not that strong, a detection error will occur. In other words, the sensor control circuit described in Patent Document 1 has a problem that it cannot perform correct measurement of the detection target when the detection signal reaching the receiving element must be made very small. [Means for solving the problem]

[0006] One aspect of the sensor control circuit according to the present invention has an output terminal that outputs a transmitting element control signal to a transmitting element that transmits a detection signal to be irradiated to an object to be detected, the transmitting element control signal controlling the transmission intensity of the detection signal; an input terminal to which a monitor signal is input, which causes a receiving element that receives the detection signal to vary its signal level in accordance with the magnitude of the reception intensity of the detection signal; a transmitting element control circuit that detects the magnitude of a change in a transmission rate of the detection signal from the transmitting element to the receiving element obtained by the monitor signal based on the difference between the signal level of a reference signal and the signal level of the monitor signal, and changes the transmitting element control signal in a direction that cancels out the change in the transmission rate in accordance with the magnitude of the change; and an intermittent control circuit that periodically switches between a detection mode in which the transmitting element control signal is transmitted to the output terminal such that the transmission intensity of the detection signal is an intensity in accordance with the signal level of the transmitting element control signal, and a non-detection mode in which the transmission intensity of the detection signal is fixed to substantially zero. Effect of the Invention

[0007] According to the sensor control circuit of the present invention, by generating a transmitting element drive control signal that intermittently drives the transmitting element, the maximum drive current of the transmitting element is increased, thereby increasing the maximum signal level of the detection signal that reaches the receiving element, and thereby improving the measurement accuracy of the object to be detected. [Brief description of the drawings]

[0008] [Figure 1] 4 is a graph illustrating the driving characteristics of an infrared light emitting diode. [Diagram 2] 1 is a block diagram of a sensor system to which a sensor control circuit according to a first embodiment is applied; [Diagram 3] FIG. 2 is a diagram illustrating an example of a driver circuit and an intermittent control circuit according to the first embodiment. [Figure 4] 4 is a timing chart illustrating an operation of the sensor control circuit according to the first embodiment. [Diagram 5] FIG. 11 is a block diagram of a sensor system according to a first modified example of the first embodiment. [Figure 6] FIG. 13 is a block diagram of a sensor system according to a second modified example of the first embodiment. [Figure 7] FIG. 11 is a block diagram of a sensor system to which a sensor control circuit according to a second embodiment is applied. [Figure 8] FIG. 11 is a block diagram of a sensor system to which a sensor control circuit according to a third embodiment is applied. [Figure 9] FIG. 11 is a block diagram of a sensor system using a plurality of sensor control circuits according to a third embodiment. [Figure 10] 13 is a timing chart for explaining the operation of the linked measurement system using a plurality of sensor control circuits according to the third embodiment. [Figure 11] FIG. 13 is a block diagram of a sensor system to which a sensor control circuit according to a fourth embodiment is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] First embodiment For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. In addition, each element shown in the drawings as a functional block performing various processes can be configured in hardware with a CPU (Central Processing Unit), memory, and other circuits, and can be realized in software with a program loaded into memory. Therefore, it is understood by those skilled in the art that these functional blocks can be realized in various forms by hardware alone, software alone, or a combination thereof, and are not limited to any one of them. In addition, the same elements are given the same symbols in each drawing, and duplicated explanations are omitted as necessary.

[0010] The above-mentioned program can be stored and provided to a computer using various types of non-transitory computer readable media. The non-transitory computer readable medium includes various types of tangible storage media. Examples of the non-transitory computer readable medium include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R / W, and semiconductor memory (e.g., mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory)). The program may be provided to a computer by various types of transitory computer readable media. Examples of the transitory computer readable medium include electric signals, optical signals, and electromagnetic waves. The transitory computer readable medium can provide the program to a computer via a wired communication path such as an electric wire and an optical fiber, or via a wireless communication path.

[0011] In the following description, a sensor control circuit, a sensor system including a transmitting element and a receiving element that are sensor elements controlled by the sensor control circuit, and a sensor embedded device that performs various controls using the output signal of the sensor system will be described. The transmitting element and receiving element that constitute the sensor element used in the sensor control circuit are elements that transmit and receive a medium that propagates through space as a detection signal. Possible media that propagate through space include visible light, invisible light, sound, ultrasonic waves, heat, water pressure, and radio waves. In the following, an example of a sensor system using a light emitting unit and a light receiving unit that transmit and receive invisible light signals as the transmitting element and receiving element will be described.

[0012] The sensor control circuit 10 according to the first embodiment drives the transmitting element intermittently to make the maximum signal level of the detection signal output by the transmitting element higher than when the transmitting element is continuously driven (hereinafter referred to as steady drive). In order to explain the drive characteristics of an infrared emitting diode used when infrared rays are used as a detection signal, a graph explaining the drive characteristics of an infrared emitting diode is shown in FIG.

[0013] The graph in Figure 1 shows how the maximum allowable forward current IF changes depending on the length of the on and off times when an infrared light emitting diode, which has a maximum forward current IF of 100mA in steady-state operation, is driven intermittently. In the example shown in Figure 1, when the pulse duration tp, which is the light emission period, is set to 5msec and the pulse period T is set to 50msec (tp / T=0.1), the maximum forward current IF can be increased to 240mA, which is 2.4 times that in steady-state operation. Also, when the pulse duration tp, which is the light emission period, is set to 100μsec and the pulse period T is set to 5msec (tp / T=0.02), the maximum forward current IF can be increased to 1A, which is 10 times that in steady-state operation.

[0014] In the sensor driving circuit of embodiment 1, by intermittently driving the light-emitting unit, it is possible to increase the intensity of the detection light and thereby improve the detection accuracy of the detection light even in a situation where the detection light, which becomes the detection signal, is easily buried in ambient light, or where the transmittance (the transmission rate of the detection signal, hereinafter simply referred to as the transmission rate βsen) between the light-emitting unit and the light-receiving unit is low and the detection signal does not sufficiently reach the light-receiving unit.

[0015] The configuration for performing the intermittent drive operation will be described in detail below. Fig. 2 shows a block diagram of a sensor system 1 to which the sensor control circuit according to the first embodiment is applied. The sensor system 1 has a sensor control circuit 10, a sampling circuit 80, a light emitting unit 101, and a light receiving unit 102. The sampling circuit 80 can be provided as a device separate from the sensor control circuit 10, or can be configured integrally with the sensor control circuit 10.

[0016] The sensor control circuit 10 has an output terminal To, an input terminal Ti, a transmitting element control circuit 11, a driver circuit 13, and an intermittent control circuit 14. The transmitting element control circuit 11 outputs a transmitting element control signal Vo that controls the transmission intensity of a detection signal to a transmitting element (e.g., a light-emitting unit 101) that transmits a detection signal to be irradiated to an object to be detected OBJ. In the sensor control circuit 10 according to the first embodiment, the driver circuit 13 provides a drive current, the current value of which changes according to the voltage level of the transmitting element control signal Vo output from the transmitting element control circuit 11, to the light-emitting unit 101 via the output terminal To.

[0017] A monitor signal Vrec, whose signal level is varied according to the magnitude of the reception intensity of the detection signal by a receiving element (eg, the light receiving unit 102) that receives the detection signal, is input to the input terminal Ti.

[0018] The transmitting element control circuit 11 detects the magnitude of change in the transmission rate βsen of the detection signal from the light-emitting unit 101 to the light-receiving unit 102, obtained by the monitor signal Vrec, from the difference between the signal level of the reference signal V+ and the signal level of the monitor signal Vrec, and changes the transmitting element control signal Vo in a direction that cancels out the change in the transmission rate βsen according to the magnitude of the change.

[0019] 2 shows an inverting amplifier including an amplifier 12, a first impedance element Zs, and a second impedance element Zf as an example of the transmitting element control circuit 11. Specifically, the first impedance element Zs is provided between the input terminal Ti and the inverting input terminal of the amplifier 12. The second impedance element Zf is provided between the output terminal and the inverting input terminal of the amplifier 12. A reference signal V+ is input to the non-inverting input terminal of the amplifier 12. Note that, although the example shown in FIG. 2 shows that a DC voltage is used as the reference signal V+, a pulse signal synchronized with the light-on and light-off cycle of the light-emitting unit 101 can also be used as the reference signal V+.

[0020] The driver circuit 13 outputs a drive current having a current value corresponding to the voltage level of the transmitting element control signal Vo to the light emitting unit 101. In the example shown in Fig. 2, the driver circuit 13 outputs a transfer ratio detection voltage Vk indicating the magnitude of the transfer ratio βsen detected by the sensor control circuit 10. Although the transmitting element control signal Vo can be used as this transfer ratio detection voltage Vk, by using a transfer ratio detection voltage Vk having a voltage value proportional to the magnitude of the driving current output by the driver circuit 13, it becomes easier to match the transfer ratio detection voltage Vk to the operating range of the sampling circuit 80.

[0021] The intermittent control circuit 14 periodically switches between a detection mode in which the transmitting element control signal Vo is transmitted to the output terminal To such that the transmission intensity of the detection signal corresponds to the signal level of the transmitting element control signal Vo, and a non-detection mode in which the transmission intensity of the detection signal is substantially fixed to zero. More specifically, the intermittent control circuit 14 switches between a detection mode in which the driver circuit 13 sets the magnitude of the drive current to a magnitude corresponding to the signal level of the transmitting element control signal Vo, and a non-detection mode (in other words, a mute mode) in which the driver circuit 13 stops outputting the drive current.

[0022] The sampling circuit 80 outputs a digital value corresponding to the magnitude of the transmission ratio detection voltage Vk. To convert the magnitude of the transmission ratio detection voltage Vk in the detection mode into a transmission ratio detection value Dk, which is a digital value, the sampling circuit 80 obtains a detection timing control signal TX_on that instructs switching between the detection mode and the non-detection mode from the intermittent control circuit 14, and converts the transmission ratio detection voltage Vk into the transmission ratio detection value Dk during the period when the detection timing control signal TX_on indicates the detection mode.

[0023] Here, the driver circuit 13 and the intermittent control circuit 14 can be configured in various forms such as a digital circuit, an analog circuit, etc., but can also be configured by combining an analog circuit and a digital circuit. Therefore, an example of a specific configuration of the driver circuit 13 and the intermittent control circuit 14 will be described. Figure 3 shows a diagram for explaining an example of the driver circuit 13 and the intermittent control circuit 14 according to the first embodiment.

[0024] In the example shown in FIG. 3, the driver circuit 13 is configured with a single-transistor amplifier, and the intermittent control circuit 14 generates the detection timing control signal TX_on using, for example, an MCU (Micro Controller Unit) including a calculation unit capable of executing a program.

[0025] In the example shown in FIG. 3, the driver circuit 13 has a gate resistor Rg, a source resistor Rk, and an output transistor PT. For example, an N-type MOSFET (Metal Oxide Silicon Field Effect Transistor) can be used as the output transistor PT. A transmission element control signal Vo is input to the gate of the output transistor PT via the gate resistor Rg. The source of the output transistor PT is connected to a ground terminal via the source resistor Rk. The drain of the output transistor PT is connected to an output terminal To. The driver circuit 13 outputs a transmission ratio detection voltage Vk from between the source of the output transistor PT and the source resistor Rk. In the example shown in FIG. 3, a voltage value derived from the product of the drive current output by the output transistor PT and the source resistor Rk becomes the transmission ratio detection voltage Vk.

[0026] The intermittent control circuit 14 has a timing control circuit 15 and a transistor Q. The timing control circuit 15 is, for example, an MCU including a calculation unit capable of executing a program. The timing control circuit 15 outputs a detection timing control signal TX_on that switches between high and low levels at a period set according to the specifications of the sensor control circuit 10. This detection timing control signal TX_on is a signal that sets the sensor control circuit 10 in detection mode during a low level period and in non-detection mode during a high level period. The transistor Q is, for example, a bipolar transistor. The detection timing control signal TX_on is applied to the base of the transistor Q. The emitter of the transistor is connected to a ground terminal, and the collector of the transistor Q is connected to the gate of the output transistor PT.

[0027] 3, during the period when the timing control circuit 15 keeps the detection timing control signal TX_on at a high level, the transistor Q is in an on state, and the gate of the output transistor PT is set to a low level (lower than the threshold voltage of the output transistor PT) regardless of the magnitude of the transmission element control signal Vo, thereby causing the driver circuit 13 to stop outputting the drive current. On the other hand, during the period when the timing control circuit 15 keeps the detection timing control signal TX_on at a low level, the transistor Q is in an off state, and the transmission element control signal Vo is transmitted to the gate of the output transistor PT, so that the driver circuit 13 outputs a drive current whose magnitude corresponds to the voltage level of the transmission element control signal Vo. In the sensor system 1 according to the first embodiment, by intermittently driving the light-emitting unit 101 using the driver circuit 13 and the intermittent control circuit 14, a larger drive current can be passed than when the light-emitting unit 101 is steadily driven, and the light-emitting unit 101 can emit light more brightly, so that the light-receiving unit 102 can detect the detection light as a sufficiently large reception signal even if the ambient light is strong or the transmission rate βsen is low.

[0028] Here, when the light-emitting unit 101 is driven intermittently, timing becomes important for sampling the transmission rate detection voltage Vk corresponding to the magnitude of the detected light with high accuracy by the sampling circuit 80. Therefore, the operation of the sensor control circuit and the sampling timing in the first embodiment will be described.

[0029] FIG. 4 shows a timing chart for explaining the operation of the sensor control circuit according to the first embodiment. In the example shown in FIG. 4, the sensor control circuit 10 is controlled to the non-detection mode before the timing T1 and after the timing T2, and the sensor control circuit 10 is controlled to the detection mode from the timing T1 to the timing T2. In the non-detection mode, the detection timing control signal TX_on is maintained at a high level. Therefore, the transistor Q of the intermittent control circuit 14 is turned on, and the gate voltage Vg of the output transistor PT of the driver circuit 13 is maintained at a low level, so that the output transistor PT is turned off. Therefore, in the non-detection mode, the supply of the drive current to the light-emitting unit 101 is stopped, and the transfer ratio detection voltage Vk is maintained at a low level. Also, in the non-detection mode, the light-emitting unit 101 is in a non-emitting state, so that the value of the monitor signal Vrec is reduced, and the transmitting element control circuit 11 maintains the transmitting element control signal Vo at a high voltage level.

[0030] On the other hand, in the detection mode, the detection timing control signal TX_on is maintained at a low level. Therefore, the transistor Q of the intermittent control circuit 14 is turned off, the transmitting element control signal Vo is transmitted as the gate voltage Vg of the output transistor PT of the driver circuit 13, and the output transistor PT is turned on. Therefore, in the detection mode, a drive current is supplied to the light-emitting unit 101, and the transmission ratio detection voltage Vk changes from a low level to a value corresponding to the transmission ratio βsen.

[0031] In the sensor control circuit 10 according to the first embodiment, at timing T1 when the non-detection mode is switched to the detection mode, a high-voltage level transmitting element control signal Vo is applied to the gate of the output transistor PT, so that the gate voltage Vg and the transmissibility detection voltage Vk jump up once immediately after timing T1. After that, in the sensor control circuit 10, the transmitting element control signal Vo and the transmissibility detection voltage Vk converge to values ​​corresponding to the magnitude of the transmissibility βsen. In the sensor control circuit 10 according to the first embodiment, the gate voltage of the output transistor PT is 0V during the non-detection mode, so that the sensor control circuit 10 operates in a saturation region where no output current flows, and at the start of the detection mode, the mute of the gate voltage of the output transistor PT is released, the transmitting control signal Vo is applied to the gate voltage of the output transistor PT, and the magnitude of the output current changes following the voltage level. In the sensor control circuit 10 according to the first embodiment, at the timing of switching from the non-detection mode to the detection mode, the transmitting element control signal Vo first switches to a saturation region close to the power supply voltage, and then the transmitting element control circuit 11 gradually transitions to the active region, so it takes some time for the feedback loop formed by the sensor control circuit 10, the light-emitting unit 101, and the light-receiving unit 102 to stabilize and for the output transistor PT to switch from the saturation region to the active region and become stable. In the example shown in Fig. 4, this period is the period during which overshoot appears to occur in the waveforms of the gate voltage Vg and the transfer ratio detection voltage Vk.

[0032] In the sensor control circuit 10, the sampling circuit 80 samples the transmission ratio detection voltage Vk at a timing when the voltage fluctuation of the transmission ratio detection voltage Vk becomes stable within a predetermined range. This sampling timing can be determined by verifying a timing at which the voltage becomes sufficiently stable in a prior verification. The time required for the voltage fluctuation of the transmission ratio detection voltage Vk to converge varies depending on the pulse width tp, the pulse period T, and the voltage level of the reference signal V+. Therefore, it is preferable to determine a range of time at which the transmission ratio detection voltage Vk becomes sufficiently stable in a prior verification according to these parameters, and set the sampling time within the determined range of time. As an example, it is considered to adjust the parameters so that the voltage fluctuation of the transmission ratio detection voltage Vk becomes stable within a predetermined range in the latter half of the detection mode closer to the non-detection mode.

[0033] As described above, the sensor control circuit 10 according to the first embodiment can intermittently drive the light-emitting unit 101 to emit light at a higher maximum light emission amount than when the light-emitting unit 101 is steadily driven. Increasing the maximum light emission amount in this way can increase the detection signal received by the light-receiving unit 102, and prevent a decrease in the detection accuracy of the transmissibility βsen in the sensor control circuit 10 caused by the detection light being drowned out by ambient light or becoming extremely small due to a low transmissibility βsen.

[0034] Moreover, the sensor control circuit 10 has a feedback loop that causes the light emitting unit 101 to emit light so that the monitor signal Vrec output by the light receiving unit 102 is at a constant voltage level. In such a sensor control circuit 10, if an intermittent drive is performed by applying a pulse signal to the reference signal V+ without using the intermittent control circuit 14, the difference between the voltage level of the reference signal V+ provided to the non-inverting input terminal of the amplifier 12 in the non-detection mode and the voltage level of the inverting input voltage V- at the inverting input terminal of the amplifier 12 falls within the range of the dead zone generated between the input terminals of the amplifier 12, causing a problem that the feedback loop becomes unstable. However, in the sensor control circuit 10 according to the first embodiment, the intermittent control circuit 14 puts the driver circuit 13 into a mute state, and a stable operation can be achieved by a stable feedback loop without causing instability in the feedback loop due to the dead zone of the amplifier 12.

[0035] In the above embodiment, even if an unstable period occurs on the input side of the transmitting element control circuit 11, the sensor system 1 is controlled to reliably enter the non-detection mode by providing the intermittent control circuit 14 on the output side, but as a method of placing the sensor system 1 in the non-detection mode, there is also a method of intermittently controlling the signal transmitted from the monitor signal to the inverting input terminal of the amplifier 12 so that an unstable period does not occur on the input side of the transmitting element control circuit 11. Therefore, one modified example using this method will be described. Figure 5 shows a block diagram of a sensor system 1a according to a first modified example of the first embodiment.

[0036] As shown in FIG. 5, the sensor system 1a according to the modification has an intermittent control circuit 14a instead of the intermittent control circuit 14 of the sensor system 1. The intermittent control circuit 14a switches the path from the input terminal Ti to the first impedance element Zs. In the detection mode, the voltage of the monitor signal Vrec is supplied to the first impedance element Zs, and in the non-detection mode, the voltage Vup is supplied to the first impedance element Zs, thereby switching between the detection mode and the non-detection mode of the sensor system 1a. That is, in the sensor system 1a according to the modification, the intermittent control circuit 14a periodically switches between a detection mode in which the transmission strength of the detection signal is transmitted to the output terminal so as to correspond to the signal level of the transmission element control signal Vo, and a non-detection mode in which the transmission strength of the detection signal is fixed to substantially zero.

[0037] The intermittent control circuit 14a includes a timing control circuit 15a and a switch SW. The switch SW switches whether to provide the amplifier 12 with the voltage Vup or the monitor signal Vrec based on the detection timing control signal TX_on output by the timing control circuit 15a. Specifically, when the detection timing control signal TX_on is at a low level (a level indicating a detection mode), the intermittent control circuit 14a connects the switch SW to the input terminal Ti, and the amplifier 12 is provided with the monitor signal Vrec. On the other hand, when the detection timing control signal TX_on is at a high level (a level indicating a non-detection mode), the intermittent control circuit 14a connects the switch SW to the terminal to which the voltage Vup is applied, and the amplifier 12 is provided with the voltage Vup. Here, the voltage Vup is preferably equal to or higher than the voltage level of the monitor signal Vrec assumed when the light receiving unit 102 receives the maximum amount of light, such as the power supply voltage supplied to the amplifier 12 or the maximum voltage assumed for the monitor signal Vrec. In addition, the voltage Vup preferably has a voltage value greater than the signal level of the reference signal V+.

[0038] In the sensor system 1a according to the modified example, by maintaining the inverting input of the amplifier 12 at a high voltage, the transmitting element control signal Vo output by the amplifier 12 is maintained at a low level regardless of the amount of light received by the light receiving unit 102, so that a non-detection mode in which the light emitting unit 101 is turned off can be achieved. In addition, in the sensor system 1a according to the modified example, by providing the monitor signal Vrec as is to the amplifier 12, the transmitting element control signal Vo output by the amplifier 12 changes according to the amount of light received by the light receiving unit 102, so that a detection mode in which the amount of light emitted by the light emitting unit 101 changes according to the magnitude of the transmissibility βsen can be achieved. In other words, the sensor system 1a according to the modified example can also achieve the same functions as the sensor system 1 according to the first embodiment.

[0039] A sensor system 1b that discloses another method of setting the sensor system 1 to the non-detection mode will be described. In the sensor system 1b, a voltage Vup is applied from the monitor signal Vrec to the inverting input terminal of the amplifier 12 via a third impedance element Zu so that an unstable period does not occur on the input side of the transmission element control circuit 11, thereby offsetting the inverting input voltage V-, and then the non-inverting input terminal of the amplifier 12 is intermittently controlled. Here, a modified example that realizes this method will be described. FIG. 6 shows a block diagram of the sensor system 1b according to a second modified example of the first embodiment.

[0040] As shown in FIG. 6, the sensor system 1b according to the second modification has an intermittent control circuit 14b instead of the intermittent control circuit 14 of the sensor system 1. The intermittent control circuit 14b has a switch SW that switches the path of the input signal to the non-inverting input terminal of the amplifier 12. The switch SW and the timing control circuit 15a switch between the detection mode and the non-detection mode of the sensor system 1b by supplying a reference voltage Vref as a reference for the detection operation in the detection mode and supplying 0V in the non-detection mode. Even when the non-inverting input terminal of the amplifier 12 becomes 0V in the non-detection mode, the voltage Vup is supplied as a DC bias voltage to the inverting input terminal of the amplifier 12 via the third impedance element Zu, so that the output of the amplifier 12 is fixed to a low level. In this case, it is necessary to note that the voltage Vup supplied via the third impedance element Zu needs to be set to a voltage value that allows the output of the amplifier 12 to be fixed to a low level even if the individual variations in the offset voltage, etc. of the amplifier 12 are at a maximum value.

[0041] Embodiment 2 In the second embodiment, a modified example of the sensor control circuit 10 according to the first embodiment will be described. In the description of the second embodiment, the same components as those described in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

[0042] Fig. 7 shows a block diagram of a sensor system 2 to which a sensor control circuit 20 according to the second embodiment is applied. As shown in Fig. 7, in the sensor system 2, a sampling circuit 81 is added to the sensor system 1 according to the first embodiment. Also, in the sensor control circuit 20, the intermittent control circuit 14 is replaced with an intermittent control circuit 24. In the intermittent control circuit 24, the timing control circuit 15 is replaced with a timing control circuit 25 to which a function of outputting a measurement timing control signal RX_on is added.

[0043] The sampling circuit 81 functions as an ambient light measurement unit that samples the signal level of the monitor signal Vrec in the non-detection mode and outputs the ambient light measurement value Denv. In the second embodiment, the monitor signal Vrec that enters the light receiving unit 102 during the period when the light emitting unit 101 is turned off based on the measurement timing control signal RX_on output by the timing control circuit 25 contains only the ambient light component, so the monitor signal Vrec during this period is converted into the ambient light measurement value Denv by the sampling circuit 81.

[0044] It is not always necessary to use both the detection timing control signal TX_on and the measurement timing control signal RX_on to control the operation timing of the sampling circuit 81 and the sampling circuit 80. For example, when the timing control circuit 25, the sampling circuit 80, and the sampling circuit 81 are included in one processor, it is also possible to organize an operation sequence by a program executed in the processor and operate the sampling circuit 80 and the sampling circuit 81 sequentially according to this operation sequence. In the example shown in FIG. 7, the detection timing control signal TX_on and the measurement timing control signal RX_on are shown merely to explain the operation timing of the sampling circuit 80 and the sampling circuit 81, and it should be noted that there are various methods for controlling the operation timing of the sampling circuit 80 and the sampling circuit 81.

[0045] For example, in the environment in which the sensor system 2 is installed, the level of sunlight entering the light receiving unit 102 from the direction of the window changes depending on the season, time, and weather. Therefore, when the ambient light measurement value Denv measured using the sampling circuit 81 exceeds a preset value, it is possible to, for example, sound an alarm or present the ambient light measurement value Denv to workers in the vicinity. By providing such a notification, the workers can take measures to reduce the ambient light level, such as closing the curtains in the building or installing a light-shielding wall on the inside of the window.

[0046] In this way, by visualizing the ambient light measurement value Denv and issuing an alarm, the ambient light level can be controlled so that it does not exceed a certain range. This solves the problem in the sensor system of embodiment 2 that the detected light is submerged in the ambient light, making it impossible to perform accurate measurements.

[0047] Third embodiment In the third embodiment, a further modification of the sensor control circuit 20 according to the second embodiment will be described. In the description of the third embodiment, the same components as those described in the second embodiment will be denoted by the same reference numerals as those in the second embodiment, and the description thereof will be omitted.

[0048] FIG. 8 shows a block diagram of a sensor system 3 to which a sensor control circuit 30 according to the third embodiment is applied. As shown in FIG. 8, in the sensor system 3 according to the third embodiment, the sensor control circuit 20 of the sensor system 2 according to the second embodiment is replaced with the sensor control circuit 30. In the sensor control circuit 30, the intermittent control circuit 24 of the sensor control circuit 20 is replaced with an intermittent control circuit 34. In addition, in the intermittent control circuit 34, the timing control circuit 25 of the intermittent control circuit 24 is replaced with a timing control circuit 35. In the timing control circuit 35, a trigger terminal TRG is added to the timing control circuit 25, and a function of starting an operation in response to a start pulse provided from another circuit is added. In addition, when the timing control circuit 35 starts an operation, it sequentially outputs a measurement timing control signal RX_on and a detection timing control signal TX_on. In addition, in the sensor control circuit 30, a trigger output terminal TX_out that outputs the detection timing control signal TX_on to another circuit is added. By using such an intermittent control circuit 34, it is possible to link a plurality of sensor systems 3 according to the third embodiment by a daisy chain or the like to perform linked operations.

[0049] FIG. 9 shows a block diagram of an interlocking measurement system using a plurality of sensor control circuits 30 according to the third embodiment. The interlocking measurement system shown in FIG. 9 has n sensor systems 3. A start pulse ST is input from another circuit to the trigger terminal TRG of the sensor system 3 arranged in the first stage. A detection timing control signal TX_on of the sensor system 3 arranged in the previous stage is input to the trigger terminal TRG of the sensor system 3 arranged in the second stage or later. In the example shown in FIG. 9, the sensor system 3 arranged in the last stage is configured not to output the detection timing control signal TX_on, but the detection timing control signal TX_on of the sensor system 3 arranged in the last stage may be returned to the sensor system 3 in the first stage.

[0050] How the start pulse ST is generated can be set appropriately based on the requirements of the system in which the sensor system 3 is used. For example, the start pulse ST may be generated by the timing control circuit 35 of the sensor system 3 arranged in the first stage, or may be provided by a system that integrates the entire interlocking measurement system. In addition, it is also possible to return the detection timing control signal TX_on of the sensor system 3 arranged in the last stage to the sensor system 3 in the first stage so that the interlocking operation is repeated, and to adjust the timing of acquiring the transmission ratio detection value Dk by the system that integrates the entire interlocking measurement system.

[0051] Here, the operation of the linked measurement system will be described by taking as an example the operation of the linked measurement system using the sensor system 3 that links a plurality of sensor systems. Fig. 10 shows a timing chart for explaining the operation when a daisy chain system is configured using a plurality of (e.g., three) sensor systems 3 according to the third embodiment. In the example shown in Fig. 10, in order to wait for the completion of the previous operation before starting the next operation, each operation is started with the falling edge of the pulse signal (Tx_on in the example of Fig. 10) output after two pulse signals of each stage as a trigger.

[0052] In the example of an interlocking measurement system using multiple sensor systems 3 shown in FIG. 10, a start pulse ST is first input from outside. Then, the first-stage sensor system 3 is triggered by the input of the falling edge of the start pulse ST, and sequentially outputs the measurement timing control signal RX_on and the detection timing control signal TX_on. Next, the second-stage sensor system 3 is triggered by the input of the falling edge of the first-stage detection timing control signal TX_on, and sequentially outputs the measurement timing control signal RX_on and the detection timing control signal TX_on. Next, the third-stage sensor system 3 is triggered by the input of the falling edge of the second-stage detection timing control signal TX_on, and sequentially outputs the measurement timing control signal RX_on and the detection timing control signal TX_on.

[0053] In this way, by sequentially operating a plurality of sensor systems 3 in a daisy chain connection, it becomes possible to detect the transmissibility βsen for a detection range that is too wide for one sensor system to handle. Furthermore, when a plurality of sensor systems 3 are sequentially operated in a daisy chain connection, even if the light receiving unit 102 of another sensor system 3 is disposed within a range where the detection light emitted by the light emitting unit 101 of the plurality of sensor systems 3 reaches, interference between the sensor systems 3 can be prevented, and deterioration of the measurement accuracy of the transmissibility βsen can be prevented.

[0054] As a sensor system to be daisy-chained, a sensor system 1 that does not have a sampling circuit 81 may be used. In this case, a function of starting an operation in response to a start pulse ST may be added to the timing control circuit 15.

[0055] Fourth embodiment In the fourth embodiment, a modified example of the sensor system 1 according to the first embodiment will be described. In the description of the fourth embodiment, the same components as those described in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

[0056] FIG. 11 shows a block diagram of a sensor system 4 to which a sensor control circuit according to the fourth embodiment is applied. As shown in FIG. 11, the sensor system 4 according to the fourth embodiment is obtained by adding an attenuation filter (e.g., a neutral density filter 82) to the sensor system 1 according to the first embodiment. The neutral density filter 82 is disposed in front of a receiving surface where a receiving element (e.g., a light receiving unit 102) receives a detection signal (e.g., detection light), and transmits the detection light to the light receiving unit 102 in an attenuated state. As the neutral density filter 82 for attenuating the detection light, a light-shielding object having a passing area that narrows the range through which light passes, such as a round hole or a square hole, or a light-transmitting object made of a material that attenuates light can be used. The type of attenuation filter is changed depending on the type of the detection signal, such as light, sound, or vibration.

[0057] In this way, by providing the neutral density filter 82 in front of the receiving surface of the light-receiving unit 102, it is possible to reduce only the signal level of the ambient light contained in the monitor signal, and to substantially expand the input dynamic range of the light-receiving unit 102. This is because, in the sensor system 4, a feedback loop is configured to adjust the output of the light-emitting unit 101 so that the amount of light received by the light-receiving unit 102 is kept constant even with the neutral density filter 82, but ambient light is attenuated by the neutral density filter 82. In addition, in the sensor system 4, the input dynamic range of the light-receiving unit 102 can be utilized to the maximum by setting the light-attenuation degree of the neutral density filter 82 so that the amount of light received by the light-receiving unit 102 is the maximum value of the input dynamic range of the light-receiving unit 102 at the maximum light emission when the light-emitting unit 101 is driven intermittently.

[0058] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0059] 1~4 Sensor system 10, 20, 30 Sensor control circuit 11 Transmitting element control circuit 12 Amplifier 13 Driver circuit 14, 24, 34 Intermittent control circuit 15, 25, 35 Timing control circuit 80, 81 Sampling circuit 82 Neutral Density Filter 101 Light emitting part 102 Light receiving part Zs First impedance element Zf Second impedance element Zu Third impedance element SW Switch OBJ Undetected object Vk Transmission ratio detection voltage V+ reference signal Vref Reference voltage V- Inverting input voltage Vrec monitor signal Vo Transmitting element control signal Rg Gate resistance Ti input terminal To output terminal TX_on detection timing control signal RX_on Measurement timing control signal TRG Trigger input terminal TX_out Trigger output terminal Dk transmission rate detection value Denv Ambient Light Measurements

Claims

1. an output terminal for outputting a transmission element control signal for controlling a transmission intensity of a detection signal to be irradiated to the object to be detected, to the transmission element; an input terminal to which a monitor signal is input, the monitor signal being varied in signal level in response to the magnitude of the reception strength of the detection signal by a receiving element that receives the detection signal; a transmitting element control circuit that detects the magnitude of a change in a transfer rate of the detection signal from the transmitting element to the receiving element, the change being obtained by the monitor signal, from a difference between a signal level of a reference signal and a signal level of the monitor signal, and changes the transmitting element control signal in a direction that cancels the change in the transfer rate according to the magnitude of the change; an intermittent control circuit that periodically switches between a detection mode in which the transmitting element control signal is transmitted to the output terminal such that the transmission intensity of the detection signal corresponds to a signal level of the transmitting element control signal, and a non-detection mode in which the transmission intensity of the detection signal is fixed to substantially zero; A sensor control circuit having a

2. 2. The sensor control circuit according to claim 1, further comprising a transmissibility calculation unit that samples a transmissibility detection voltage corresponding to a signal level of the transmitting element control signal during a latter half period of the detection mode closer to the non-detection mode, and outputs a transmissibility detection value.

3. 2. The sensor control circuit according to claim 1, further comprising an ambient light level calculation section that samples the signal level of the monitor signal during the non-detection mode and outputs an ambient light level measurement value.

4. The intermittent control circuit includes: a timing control circuit for controlling a timing of switching between the detection mode and the non-detection mode; the timing control circuit starts its operation in response to a start pulse provided from another first circuit; 2. The sensor control circuit according to claim 1, further comprising: a signal notifying a timing of switching from the detection mode to the non-detection mode, the signal being output as the start pulse to another second circuit.

5. The intermittent control circuit includes: a gate resistor to one end of which the transmission element control signal is input; an output transistor having a gate connected to the other end of the gate resistor and a drain connected to the output terminal; an intermittent control unit that switches the gate of the output transistor so that the transmission element control signal is applied to the gate of the output transistor in the detection mode and is fixed to a low level in the non-detection mode; The sensor control circuit of claim 1 , further comprising:

6. 2. The sensor control circuit according to claim 1, further comprising an attenuation filter disposed in front of a receiving surface where the receiving element receives the detection signal, the attenuating filter transmitting the detection signal to the receiving element in an attenuated state.

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