A signal processing circuit and photoelectric sensor that shields against external light

Abstract

This invention discloses a signal processing circuit and a photoelectric sensor that shield against external light, relating to the field of photoelectric sensing technology, and aims to solve the problem of high cost of existing photoelectric sensors in resisting light interference. The signal processing circuit that shields against external light includes an operational amplifier U1, whose output is connected to the AD port of an MCU, its positive input is connected to the power supply, and its negative input is connected to the output of the preceding circuit through a resistor R3 and a capacitor C2. One end of both resistor R1 and capacitor C1 is connected to the output of operational amplifier U1, and the other end is connected to the negative input of operational amplifier U1. The anode of diode D1 is connected to the output of operational amplifier U1, and its cathode is connected to one end of resistor R2. The other end of resistor R2 is connected to the negative input of operational amplifier U1.

Description

Technical Field

[0001] This invention relates to the field of photoelectric sensing technology, and in particular to a signal processing circuit and photoelectric sensor that shield against external light, applicable to background suppression type photoelectric sensors. Background Technology

[0002] Early photoelectric sensors were typically incompatible with fluorescent lighting, as traditional lighting was prevalent at the time. Even when interference was a concern, it was mitigated by adjusting the sensor's installation angle. However, with technological advancements and the widespread adoption of energy-efficient LED lights, more complex and precise devices are emerging, placing higher demands on the installation location of photoelectric sensors (which inevitably faces the light source). Light interference resistance is one such requirement. Simultaneously, environmental factors limit the cost of product design. Due to the small size of the sensors and the need for light interference resistance, the complexity of the circuitry and algorithms becomes crucial. Leading domestic and international brands address this by integrating chips (custom chips) and increasing structural complexity (by stacking two circuit boards), thus increasing costs. Summary of the Invention

[0003] The purpose of this invention is to provide a signal processing circuit and photoelectric sensor that shield against external light, enabling anti-background light interference at a lower cost.

[0004] The technical solution to achieve the purpose of this invention is as follows: A signal processing circuit that shields against external light includes an operational amplifier U1, whose output is connected to the AD port of an MCU, its positive input is connected to a power supply, and its negative input is connected to the output of a preceding circuit through a resistor R3 and a capacitor C2. One end of both resistor R1 and capacitor C1 is connected to the output of operational amplifier U1, and the other end is connected to the negative input of operational amplifier U1. The anode of diode D1 is connected to the output of operational amplifier U1, and the cathode is connected to one end of resistor R2. The other end of resistor R2 is connected to the negative input of operational amplifier U1.

[0005] The amplification factor of the inverting amplifier circuit composed of U1, R1, C1, R3, and C2 is 15 times that of the inverting amplifier circuit composed of U1, D1, R2, R3, and C2.

[0006] A background suppression type photoelectric sensor includes the signal processing circuit described above, and also includes dual photosensitive receivers PD1 and PD2 for receiving pulsed light from an LED. The positive terminals of both are connected to a power supply. The negative terminal of photosensitive receiver PD1 and the connection point of resistor R6 are connected to the positive input terminal of differential amplifier U2 via capacitor C4. The positive input terminal of differential amplifier U2 is also connected to a power supply via resistor R5. The negative terminal of photosensitive receiver PD2 and the connection point of resistor R7 are connected to the negative input terminal of differential amplifier U2 via capacitor C5. The output terminal of differential amplifier U2 is connected to the negative input terminal of operational amplifier U1 via capacitor C2 and resistor R3. Capacitor C3 and resistor R4 are connected in parallel between the negative input terminal and the output terminal of differential amplifier U2.

[0007] The pulsed light emission frequency is 3kHz and the pulse width is 2μs.

[0008] The photoelectric sensor operates using a triangulation method. The LED driving circuit emits pulsed light, which is focused onto the surface of the object being detected through a lens. The object then reflects the light back to the receiving lens, which focuses it onto photosensitive receivers PD1 and PD2. After receiving the signal, the dual photosensitive receivers PD1 and PD2 convert the photocurrent signal into a voltage signal through a resistor sampling circuit composed of resistors R6 and R7. This voltage signal is then sent to a differential amplifier U2, where the differential signal is amplified and sent to the signal processing circuit for processing before being sent to the MCU's AD port. The MCU uses a software algorithm to output high or low levels to control the output circuit, enabling normally closed or normally open outputs.

[0009] Compared with the prior art, this invention achieves external light shielding through signal processing circuitry and sets the light emission frequency in the photoelectric sensor to about 3kHz with a pulse width of 2μs, thus realizing the anti-light interference of the photoelectric sensor at a lower cost.

[0010] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0011] Figure 1 This is a circuit structure diagram of the background suppression photoelectric sensor of the present invention.

[0012] Figure 2 This is an interference-free waveform diagram when the object being detected is far away.

[0013] Figure 3 This is an interference-free waveform diagram when the object being detected is close to the object.

[0014] Figure 4 This is a waveform diagram when the interference of this invention is strong.

[0015] Figure 5 This is a waveform diagram when the interference of the present invention is weak. Detailed Implementation

[0016] See Figure 1 A background suppression photoelectric sensor employs a triangulation method. Its specific functions are as follows: First, a pulsed light is emitted through an LED driving circuit. This light is then focused onto the surface of the object being detected through a lens. The object reflects the light back to the receiving lens and focuses it onto a photosensitive receiving tube. To suppress background interference, dual photosensitive receiving tubes PD1 and PD2 are used. After receiving the signal, PD1 and PD2 convert the photocurrent signal into a voltage signal through a sampling circuit composed of resistors R6 and R7. This voltage signal is then sent to a differential amplifier U2, which amplifies the difference signal and sends it to the frame. Figure 1 After processing by the subsequent circuitry, the signal is sent to the MCU's AD port for sampling. After software algorithm processing, the MCU outputs a high or low level to control the output circuit, thereby achieving normally closed or normally open output.

[0017] The normal switching frequency range of an LED light driver power supply is 30kHz-100kHz. We choose a signal frequency that avoids this band. If we choose a frequency greater than 100kHz, the power consumption and MCU selection requirements of the product will be higher, which will result in higher costs. Therefore, we choose a frequency lower than the lower limit of 30kHz. In order to leave enough room, the final light projection frequency is set at about 3kHz with a pulse width of 2μs.

[0018] Figure 1 box Figure 1 The circuit shown is the signal processing circuit for shielding external light according to the present invention. The specific circuit diagram is as follows: It includes an operational amplifier U1, whose output terminal is connected to the AD port of the MCU, the positive input terminal is connected to a 1V power supply, and the negative input terminal is connected to the output terminal of the previous stage circuit through resistor R3 and capacitor C2. One end of resistor R1 and capacitor C1 are both connected to the output terminal of operational amplifier U1, and the other end is both connected to the negative input terminal of operational amplifier U1. The positive terminal of diode D1 is connected to the output terminal of operational amplifier U1, and the negative terminal is connected to one end of resistor R2. The other end of resistor R2 is connected to the negative input terminal of operational amplifier U1.

[0019] Figure 2-3 The diagram shows the projection timing and the waveforms at points a and b corresponding to interference-free conditions. From time t1 to t2, the active components in the circuit are U1, D1, R2, R3, and C2, which form an inverting amplifier circuit. From time t2 to t3, the active components in the circuit are U1, R1, C1, R3, and C2, which also form an inverting amplifier circuit. The amplification factor from t2 to t3 is approximately 15 times that from t1 to t2. The waveform starting at time t2 is significantly amplified in reverse. Since the op-amp is powered by a single +5V supply, the output is forced to be amplified in reverse to 0V, and the output waveform is narrowed to about 3μs, thus providing anti-interference.

[0020] like Figure 4 As shown, when the interference is strong, a waveform similar to that of the detected object is received. However, due to the high frequency of the interference, the MCU's AD sampling can determine that there is interference at this time. The software will add an algorithm to process it so that it will not make false actions.

[0021] like Figure 5 As shown, when a waveform similar to that of a distant object is received, the value obtained by the MCU's AD sampling is processed by the software to perform corresponding actions.

[0022] The technical solutions of the present invention are not limited to the above embodiments. All technical solutions obtained by equivalent substitution fall within the scope of protection claimed by the present invention.

Claims

1. A signal processing circuit that shields against external light, characterized in that... The circuit includes operational amplifier U1, whose output is connected to the MCU's AD port, positive input is connected to the power supply, and negative input is connected to the output of the preceding circuit through resistor R3 and capacitor C2. One end of resistor R1 and capacitor C1 are both connected to the output of operational amplifier U1, and the other end is connected to the negative input of operational amplifier U1. The anode of diode D1 is connected to the output of operational amplifier U1, and the cathode is connected to one end of resistor R2. The other end of resistor R2 is connected to the negative input of operational amplifier U1. The amplification factor of the inverting amplifier circuit composed of U1, R1, C1, R3, and C2 is 15 times that of the inverting amplifier circuit composed of U1, D1, R2, R3, and C2.

2. A background suppression type photoelectric sensor, comprising the signal processing circuit as described in claim 1, further comprising dual photosensitive receivers PD1 and PD2 for receiving pulsed light from an LED, the positive terminals of which are both connected to a power supply; the negative terminal of photosensitive receiver PD1 and the connection point of resistor R6 are connected to the positive input terminal of differential amplifier U2 through capacitor C4; the positive input terminal of differential amplifier U2 is also connected to a power supply through resistor R5; the negative terminal of photosensitive receiver PD2 and the connection point of resistor R7 are connected to the negative input terminal of differential amplifier U2 through capacitor C5; the output terminal of differential amplifier U2 is connected to the negative input terminal of operational amplifier U1 through capacitor C2 and resistor R3; and capacitor C3 and resistor R4 are connected in parallel between the negative input terminal and the output terminal of differential amplifier U2.

3. The photoelectric sensor according to claim 2, characterized in that: The pulsed light emission frequency is 3kHz and the pulse width is 2μs.

4. The operating method of the photoelectric sensor according to claim 2 or 3, characterized in that, Using the triangulation method, the LED driver circuit emits pulsed light, which is focused onto the surface of the object being detected through a lens. The object then reflects the light back to the receiving lens, which focuses it onto photosensitive receivers PD1 and PD2. After receiving the signal, the dual photosensitive receivers PD1 and PD2 convert the photocurrent signal into a voltage signal through a resistor sampling circuit composed of resistors R6 and R7. This voltage signal is then sent to the differential amplifier U2, where the difference signal is amplified and sent to the signal processing circuit for processing before being sent to the MCU's AD port. The MCU uses a software algorithm to output high or low levels to control the output circuit, enabling normally closed or normally open outputs.

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