An E-bike wheel speed detection device based on photoelectric sensing

Abstract

The invention discloses an E-bike wheel speed detection device based on photoelectric induction, comprising a photoelectric sensor and a reflective strip; the reflective strip is arranged on a wheel hub, and the photoelectric sensor is fixed to a frame; the photoelectric sensor comprises a transmitting component and a receiving component; the reflective strip can rotate with the wheel hub to correspond to the infrared transmitting component, when the reflective strip corresponds to the transmitting component, the transmitting component emits infrared light, and after being reflected by the reflective strip, the receiving component receives the reflected infrared light reflected by the reflective strip; the wheel speed is calculated by the time interval between two detected reflective strips, and the sensing distance between the photoelectric sensor and the reflective strip can be adjusted; the shape of the wheel hub does not need to be changed, and the device is suitable for most wheel hubs, and is also suitable for various types of E-bikes with external speed measurement.

Description

Technical Field

[0001] The invention relates to the field of speed measurement, and in particular to wheel speed detection by photoelectric induction. Background Art

[0002] The speed measurement of E-bike is generally to install a sensor device with a Hall chip on the rear fork, and fix one or more magnets on the spokes. When the wheel rotates and the magnet passes through the sensor, the TTL level signal output by the sensor will flip, and the controller calculates the speed through the time interval of several adjacent inversion levels. This sensor using the Hall induction principle has strict requirements for the installation distance. The general installation distance is about 5 to 20 mm, and it needs to be installed directly in front of the sensor. Therefore, this sensor not only has a short sensing distance but also is inconvenient to install. Summary of the invention

[0003] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides an E-bike wheel speed detection device based on photoelectric sensing, which emits infrared rays through a photoelectric sensor, which are reflected by a reflective strip and then received by the photoelectric sensor, and the wheel speed is calculated by the time interval between two detected reflective strips.

[0004] Technical solution: To achieve the above-mentioned purpose, an E-bike wheel speed detection device based on photoelectric sensing of the present invention includes a photoelectric sensor and a reflective strip; the reflective strip is arranged on the wheel hub, and the photoelectric sensor is installed on the frame; the photoelectric sensor includes a transmitting component and a receiving component; the reflective strip can rotate with the wheel hub to correspond to the transmitting component, and when the reflective strip corresponds to the infrared transmitting component, the transmitting component emits infrared light, and after being reflected by the reflective strip, the receiving component receives the reflected infrared light reflected by the reflective strip.

[0005] Furthermore, the photoelectric sensor also includes an MCU micro control unit; the receiving component outputs a Vout output voltage after receiving the reflected infrared light, and the MCU micro control unit detects fluctuations in the Vout output voltage.

[0006] Furthermore, the transmitting component includes an IR infrared diode and an Rlimit adjustable resistor; the Rlimit adjustable resistor changes its resistance value to change the If current of the infrared diode, and the radiation intensity of the infrared diode is positively correlated with the magnitude of the If current.

[0007] Furthermore, the receiving component includes a PT phototransistor and an RL adjustable resistor; the Ic current of the PT phototransistor is positively correlated with the intensity of the reflected light, and the Vout output voltage output by the receiving component changes with the change of the Ic current.

[0008] Furthermore, the Vout output voltage is affected by the resistance values ​​of the Rlimit adjustable resistor and the RL adjustable resistor; when the reflective strip is too far away from the sensor, the resistance values ​​of the Rlimit adjustable resistor and the RL adjustable resistor need to be adjusted to increase the sensing distance of the reflective strip.

[0009] Furthermore, the infrared emitting component and receiving component form a photosensitive circuit with the Q1 transistor, the R1 resistor, the C1 capacitor and the C2 capacitor. The input signal at the R1 resistor end of the photosensitive circuit is a periodic PWM pulse. The level output of the PWM port of the photosensitive circuit controls the conduction and cutoff of the Q1 transistor. The photosensitive circuit outputs an AD signal, namely, the Vout output voltage.

[0010] Furthermore, the MCU micro control unit receives an AD signal from the PA2 port, and the PA3 port outputs a high level when the reflective strip passes by, and the PA3 port does not output when the reflective strip does not pass by.

[0011] Furthermore, the high level output of the PA3 port of the MCU microcontroller unit is input to the base of the Q2 transistor in the speed measurement signal output circuit through the R5 resistor. The speed measurement signal output circuit outputs a low level when receiving the high level output of the PA3 port, and outputs a high level when not receiving the high level output of the PA3 port. The output end signal of the speed measurement signal output circuit is transmitted to the controller, and the controller calculates the rotation speed of the wheel according to the average time interval of several adjacent low level pulses.

[0012] Furthermore, the infrared photodiode and the phototransistor are separated by a light blocking plate, and the infrared photodiode cannot pass through the light blocking plate.

[0013] Furthermore, the photosensitive circuit, MCU microcontroller unit and speed measurement signal output circuit form a circuit board, the circuit board is arranged in a hollow sensor housing, a light-transmitting plate is arranged at the hollow part of the sensor housing, and the circuit board, the light-transmitting plate and the sensor housing are combined into a photoelectric sensor; the photoelectric sensor is arranged on the vehicle frame, and one side of the light-transmitting plate faces the side of the wheel hub.

[0014] Beneficial effect: The present invention transmits infrared rays through a photoelectric sensor, which is reflected by a reflective strip and then received by the photoelectric sensor. The wheel speed is calculated by the time interval between the two detected reflective strips. At the same time, the input signal through the light-transmitting plate and the R1 resistor end of the photosensitive circuit is a periodic PWM pulse, which reduces the influence of ambient light on the measurement of the photoelectric sensor. The sensing distance between the photoelectric sensor and the reflective strip is adjusted; there is no need to change the shape of the wheel hub, and the invention is suitable for most wheel hubs, and is also suitable for various types of E-bikes with external speed measurements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Attached Figure 1Schematic diagram of photoelectric sensor;

[0016] Attached Figure 2 Photosensitive circuit diagram;

[0017] Attached Figure 3 MCU micro control unit circuit diagram;

[0018] Attached Figure 4 Speed ​​measurement signal output circuit;

[0019] Attached Figure 5 MCU microcontroller unit judgment logic flow chart;

[0020] Attached Figure 6 Schematic diagram of photoelectric sensor;

[0021] Attached Figure 7 Distribution diagram of reflective strips on wheels;

[0022] Attached Figure 8 Schematic diagram of photoelectric sensor installation. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] As attached Figure 1-8 As shown, an E-bike wheel speed detection device based on photoelectric sensing includes a photoelectric sensor 42 and a reflective strip 1; the reflective strip 1 is arranged on a wheel hub 41, and the photoelectric sensor 42 is installed on a frame 43; the photoelectric sensor 42 includes a transmitting component and a receiving component; the reflective strip 1 can rotate with the wheel hub 41 to correspond to the infrared transmitting component, and when the reflective strip 1 corresponds to the transmitting component, the transmitting component emits infrared light, and after being reflected by the reflective strip 1, the receiving component receives the reflected infrared light reflected by the reflective strip 1.

[0025] The photoelectric sensor further includes an MCU micro control unit 21 ; the receiving component outputs a Vout output voltage 8 after receiving the reflected infrared light, and the MCU micro control unit 21 detects fluctuations in the Vout output voltage 8 .

[0026] As attached Figure 1 As shown, the infrared emission component includes an IR diode 4 and an Rlimit adjustable resistor 2; the Rlimit adjustable resistor 2 changes its resistance value to change the If current 6 of the infrared diode 4, and the radiation intensity of the infrared diode 4 is positively correlated with the magnitude of the If current 6; the larger the Rlimit adjustable resistor 2, the smaller the If current 6, and the radiation intensity of the infrared diode 4 will also decrease as the If current 6 decreases. The infrared diode can radiate infrared light when there is a forward current passing through it, and the greater the current passing through, the stronger the radiation intensity, and the infrared light is invisible to the human eye, which can avoid affecting the line of sight.

[0027] As attached Figure 1 As shown, the receiving component includes a PT phototransistor 5 and an RL adjustable resistor 3; the Ic current 7 of the PT phototransistor 5 is positively correlated with the reflected light intensity, and the Vout output voltage 8 output by the receiving component changes with the change of the Ic current 7; the stronger the reflected light intensity, the greater the Ic current 7, and since Vout = Vcc-Ic*RL, the Vout output voltage 8 will decrease as the Ic current 7 increases; the characteristic of the PT phototransistor 5 is that it will be turned on when there is light irradiation, and will be turned off when there is no irradiation.

[0028] As attached Figure 1 As shown, the Vout output voltage 8 is affected by the resistance of the Rlimit adjustable resistor 2 and the RL adjustable resistor 3; when the reflective strip 1 is too far from the sensor, the resistance of the Rlimit adjustable resistor 2 and the RL adjustable resistor 3 need to be adjusted to increase the sensing distance of the reflective strip 1. Adjusting the Rlimit resistor value will change the If current 6, and adjusting the RL resistor value will change the Ic current 7; therefore, when the If current 6 and the Ic current 7 change, the Vout output voltage will be affected, so the resistance values ​​of these two resistors will affect the distance of the phototransistor 4 sensing the shading strip; the selected resistance value can reach a sensing distance of 50mm.

[0029] As attached Figure 2 As shown, the infrared emitting component and receiving component form a photosensitive circuit with the Q1 transistor 12, the R1 resistor 11, the C1 capacitor 13 and the C2 capacitor 14, the input end of the IR infrared diode 4 and the collector of the PT phototransistor 5 input a stable voltage, and at the same time, the input end of the IR infrared diode 4 and the collector of the PT phototransistor 5 are grounded through a circuit in which the C1 capacitor 13 and the C2 capacitor 14 are connected in parallel; the output end of the R infrared diode 4 is connected to the collector of the Q1 transistor 12, and the periodic PWM pulse is input to the base of the Q1 transistor 12 through the R1 resistor 11, the emitter of the Q1 transistor 12 is grounded through the R3 resistor 2, and the PT phototransistor 5 is grounded through the R2 resistor 3; the voltage at the end of the R2 resistor 3 is the AD signal output by the photosensitive circuit, that is, the Vout output voltage 8;

[0030] As attached Figure 2 As shown, the level output of the PWM port of the photosensitive circuit controls the conduction and cutoff of the Q1 transistor 12. When the PWM is at a high level, the Q1 transistor 12 is turned on, and the IR infrared diode 4 emits infrared rays; when the PWM is at a low level, the Q1 transistor 12 is turned off, and the IR infrared diode 4 does not emit infrared rays; in one cycle of PWM, the high level time is set to 350us, and the low level time is 50ms. This setting can ensure that the reflective strip 1 is detected when the wheel rotates quickly;

[0031] Compared with DC output, periodic pulse waves can reduce ambient light interference because when DC output is used, the MCU microcontroller unit 21 cannot determine whether the voltage change at the end of the resistor R2 3 is caused by the reflective strip reflecting the irradiation of the infrared diode 4 or by ambient light.

[0032] As attached Figure 3 As shown, the MCU micro-control unit 21 receives the AD signal from the PA2 port, and the PA3 port outputs a high level when the reflective strip 1 passes by, and the PA3 port does not output when the reflective strip 1 does not pass by; the AD signal 8 is connected to the PA2 port of the MCU micro-control unit 21 through the R4 resistor 22, and is connected to the ground through the R4 resistor 22 in series with the C8 capacitor 23; the VDD port of the MCU micro-control unit 21 is connected to the VSS port through the C9 capacitor 24, and the VSS port is grounded; the PB0INRST port of the MCU micro-control unit 21 is grounded through the C7 capacitor 25.

[0033] As attached Figure 5 As shown, the high and low levels of the periodic PWM pulse wave will cause the voltage fluctuation of the R2 resistor 3 terminal. The voltage difference of the R2 resistor 3 terminal is used to detect whether there is a reflective strip passing by. The logic flow is judged. When the PWM outputs a high level pulse, the MCU micro-control unit 21 obtains the voltage V1 of the sampling terminal. When the PWM outputs a low level pulse, the MCU micro-control unit 21 obtains the voltage V2 of the sampling terminal. Δoffset=V1-V2 is set as its own offset voltage. At the same time, when the reflective strip 1 is set to be close, the MCU micro-control unit 21 obtains the maximum voltage V3 of the sampling terminal, and Δmax=V3-V1 is set. When Δoffset is greater than or equal to one third of Δmax, it is determined that the reflective strip 1 has passed by, and the MCU micro-control unit 21 outputs a high level. When Δoffset is less than one third of Δmax, no output is made.

[0034] The farther the reflective strip 1 is from the photoelectric sensor, the weaker the intensity of the light reflected by the reflective strip 1 is, and the voltage V1 output by the photoelectric transistor 5 will also decrease, that is, Δoffset will decrease.

[0035] As attached Figure 4As shown, the PA3 port of the MCU microcontroller unit 21 outputs a high level, which is input to the base of the Q2 transistor 32 in the speed measurement signal output circuit through the R5 resistor 31. The emitter of the Q2 transistor 32 is grounded, and the 5V voltage is input to the speed measurement signal output circuit through the R6 resistor 33 and connected to the collector of the Q2 transistor 32. The collector of the Q2 transistor 32 outputs a signal through the R7 resistor 34. When the speed measurement signal output circuit receives a high level output from the PA3 port, the Q2 transistor 32 is turned on, and the speed measurement signal output circuit outputs a low level through the R7 resistor 34. When the PA3 port does not receive a high level output, the Q2 transistor 32 is turned off, and the speed measurement signal output circuit outputs a high level through the R7 resistor 34. The signal at the output end of the speed measurement signal output circuit is transmitted to the controller, and the controller calculates the rotation speed of the wheel according to the average time interval of several adjacent low level pulses.

[0036] As attached Figure 1 As shown, the infrared photodiode 4 and the phototransistor 5 are separated by a light blocking plate 9 to prevent the infrared light emitted by the infrared diode 4 from being directly received by the phototransistor 5 without being reflected by the reflective strip 1; and to prevent the MCU microcontroller unit 21 from misjudging the reflective strip 1 from passing.

[0037] As attached Figure 6-8 As shown, the photosensitive circuit, the MCU microcontroller unit (21) and the speed measurement signal output circuit form a circuit board (44); the circuit board (44) is arranged in a hollow sensor housing; a light-transmitting plate (45) is arranged at the hollow portion of the sensor housing; the circuit board (44), the light-transmitting plate (45) and the sensor housing are combined into a photoelectric sensor (42); the photoelectric sensor (42) is arranged on a vehicle frame (43), and one side of the light-transmitting plate (45) faces the side of the wheel hub (41).

[0038] The light-transmitting plate is made of infrared-transmitting PC, which can transmit infrared light and has a very high visible light shielding rate. It can also effectively reduce the interference of ambient light on the photosensitive elements of the internal circuit.

[0039] Example

[0040] When detecting the speed, the periodic PWM pulse is input to the base of the Q1 transistor 12 through the R1 resistor 11. When the PWM is at a high level, the Q1 transistor 12 is turned on, and the IR infrared diode 4 emits infrared rays; when the PWM is at a low level, the Q1 transistor 12 is turned off, and the IR infrared diode 4 does not emit infrared rays;

[0041] When PWM outputs a high-level pulse, the MCU microcontroller unit 21 obtains the voltage V1 at the sampling end, and when PWM outputs a low-level pulse, the MCU microcontroller unit 21 obtains the voltage V2 at the sampling end; Δoffset=V1-V2 is set as its own offset voltage, and when the reflective strip 1 is set to be close, the MCU microcontroller unit 21 obtains the maximum voltage V3 at the sampling end, and sets Δmax=V3-V1; when Δoffset is greater than or equal to one third of Δmax, it is determined that the reflective strip 1 passes by, and the MCU microcontroller unit 21 outputs a high level; when Δoffset is less than one third of Δmax, no output is made;

[0042] The PA3 port of the MCU microcontroller unit 21 outputs a high level which is input to the base of the Q2 transistor 32 in the speed measurement signal output circuit through the R5 resistor 31. When the speed measurement signal output circuit receives the high level output from the PA3 port, the Q2 transistor 32 is turned on, and the speed measurement signal output circuit outputs a low level through the R7 resistor 34. When the PA3 port does not output a high level, the Q2 transistor 32 is turned off, and the speed measurement signal output circuit outputs a high level through the R7 resistor 34. The signal at the output end of the speed measurement signal output circuit is transmitted to the controller, and the controller calculates the wheel speed based on the average time interval of several adjacent low level pulses.

[0043] The above are preferred embodiments of the present invention. It should be pointed out that a person skilled in the art may make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the protection scope of the present invention.

Claims

1. An E-bike wheel speed detection device based on photoelectric sensing, characterized in that: The vehicle comprises a photoelectric sensor (42) and a reflective strip (1); the reflective strip (1) is arranged on a wheel hub (41), and the photoelectric sensor (42) is installed on a vehicle frame (43); the photoelectric sensor (42) comprises a transmitting component and a receiving component; the reflective strip (1) can rotate with the wheel hub (41) to correspond to the transmitting component, and when the reflective strip (1) corresponds to the transmitting component, the transmitting component emits infrared light, and after being reflected by the reflective strip (1), the receiving component receives the reflected infrared light reflected by the reflective strip (1); The photoelectric sensor further comprises an MCU microcontroller unit (21); the receiving component outputs a Vout output voltage (8) after receiving the reflected infrared light, and the MCU microcontroller unit (21) detects fluctuations in the Vout output voltage (8); The transmitting component and the receiving component, together with the Q1 transistor (12), the R1 resistor (11), the C1 capacitor (13) and the C2 capacitor (14), form a photosensitive circuit; the input signal at the R1 resistor (11) end of the photosensitive circuit is a periodic PWM pulse; the level output of the PWM port of the photosensitive circuit controls the conduction and cutoff of the Q1 transistor (12); and the photosensitive circuit outputs an AD signal, namely a Vout output voltage (8); When PWM is at a high level, the Q1 transistor (12) is turned on, and the infrared photodiode (4) emits infrared rays; when PWM is at a low level, the Q1 transistor (12) is turned off, and the infrared photodiode (4) does not emit infrared rays.

2. The E-bike wheel speed detection device based on photoelectric sensing according to claim 1, characterized in that: The transmitting component comprises an infrared photodiode (4) and an Rlimit adjustable resistor (2); the Rlimit adjustable resistor (2) changes its resistance value to change the If current (6) of the infrared photodiode (4); the radiation intensity of the infrared photodiode (4) is positively correlated with the magnitude of the If current (6).

3. The E-bike wheel speed detection device based on photoelectric sensing according to claim 2, characterized in that: The receiving component comprises a PT phototransistor (5) and an RL adjustable resistor (3); the Ic current (7) of the PT phototransistor (5) is positively correlated with the intensity of the reflected light, and the Vout output voltage (8) output by the receiving component changes with the change of the Ic current (7).

4. The E-bike wheel speed detection device based on photoelectric sensing according to claim 3, characterized in that: The Vout output voltage (8) is affected by the resistance value of the Rlimit adjustable resistor (2) and the resistance value of the RL adjustable resistor (3); when the reflective strip (1) is too far away from the sensor, the resistance value of the Rlimit adjustable resistor (2) and the resistance value of the RL adjustable resistor (3) need to be adjusted to increase the sensing distance of the reflective strip (1).

5. The E-bike wheel speed detection device based on photoelectric sensing according to claim 1, characterized in that: The MCU micro control unit (21) receives an AD signal from the PA2 port, and the PA3 port outputs a high level when the reflective strip (1) passes by, and does not output when the reflective strip (1) does not pass by.

6. The E-bike wheel speed detection device based on photoelectric sensing according to claim 5, characterized in that: The high level output of the PA3 port of the MCU microcontroller unit (21) is input to the base of the Q2 transistor (32) in the speed measurement signal output circuit through the R5 resistor (31). The speed measurement signal output circuit outputs a low level when receiving the high level output of the PA3 port, and outputs a high level when not receiving the high level output of the PA3 port. The output end signal of the speed measurement signal output circuit is transmitted to the controller, and the controller calculates the rotation speed of the wheel according to the average time interval of several adjacent low level pulses.

7. The E-bike wheel speed detection device based on photoelectric sensing according to claim 6, characterized in that: The infrared photodiode (4) and the phototransistor (5) are separated by a light blocking plate (9), and the infrared photodiode (4) cannot pass through the light blocking plate (9).

8. The E-bike wheel speed detection device based on photoelectric sensing according to claim 7, characterized in that: The photosensitive circuit, the MCU microcontroller unit (21) and the speed measurement signal output circuit form a circuit board (44); the circuit board (44) is arranged in a hollow sensor housing; a light-transmitting plate (45) is arranged at the hollow portion of the sensor housing; the circuit board (44), the light-transmitting plate (45) and the sensor housing are combined to form a photoelectric sensor (42); the photoelectric sensor (42) is arranged on a vehicle frame (43), and one side of the light-transmitting plate (45) faces the side of the wheel hub (41).

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