Noise reduction circuit for paper shredder

Abstract

A noise reduction circuit for a paper shredder comprises a rectifier bridge DB1; a current sampling resistor R21; a control chip; the current sampling resistor R21 is connected in series in an alternating current path of the rectifier bridge DB1, so that current passing through a motor of the paper shredder flows back to a power supply through the current sampling resistor R21; voltage drops at the two ends of the current sampling resistor R21 are increased along with the increase of the current of the motor, and after rectification and filtering, a voltage value, namely a current parameter of real-time operation of the motor, is provided for a pin 12 of the control chip through a resistor R16; and the control chip controls the output power of the motor according to the current parameters. According to the noise reduction circuit for the paper shredder provided by the utility model, the current transmitted to the motor can be detected by improving the circuit structure on the main control board of the paper shredder, so that the rotating speed of the motor is controlled, and the aim of reducing noise is fulfilled.

Description

Technical Field

[0001] The utility model belongs to the technical field of electronic control circuits for paper shredders, and particularly relates to a noise reduction circuit for paper shredders. Background Art

[0002] Paper shredders are commonly used equipment in the office field. Among the conventional paper shredder products currently on the market, their circuits are DC or series-excited induction motors according to the motor type. The AC power supply is rectified into pulsating DC power and then supplied to the motor. No power control is performed on the motor's current and voltage. During operation, the voltage on the motor is always equal to the power supply voltage, causing the motor to have high speed and high noise when it is unloaded, and slow speed when it is heavily loaded. The paper feeding speed and noise are inconsistent when counting a small number of sheets and a large number of sheets. The paper shredder is noisy and the user experience is poor.

[0003] Some paper shredders currently on the market install a magnet or a porous grating at the tail of the motor rotor shaft, and a Hall detector or infrared receiving tube next to it. When the motor rotates, the Hall or infrared receiving tube outputs pulse signals of different lengths and timings depending on the speed. The control circuit corresponds the length of the pulse signal timing to the speed of the motor and adjusts the power to the motor to control the motor speed. However, this type of motor requires special processing and customization, the product structure is complex and the cost is high, and there are disadvantages such as troublesome production and assembly.

[0004] To address the above shortcomings, the present application proposes an improved noise reduction circuit by improving the circuit structure. Utility Model Content

[0005] In response to the above deficiencies in the existing technology, the present invention provides a noise reduction circuit for a paper shredder. By improving the circuit structure on the main control board of the paper shredder, the current delivered to the motor can be detected, thereby controlling the motor speed and achieving the purpose of noise reduction.

[0006] The utility model solves the problem through the following technical solutions.

[0007] A noise reduction circuit for a paper shredder includes: a rectifier bridge DB1; a current sampling resistor R21; and a control chip. The current sampling resistor R21 is connected in series in the AC path of the rectifier bridge DB1, so that all current passing through the shredder's motor flows back to the power supply through the current sampling resistor R21. The voltage drop across the current sampling resistor R21 increases as the motor current increases. After rectification and filtering, the voltage value, i.e., the real-time current parameter of the motor, is provided to pin 12 of the control chip through resistor R16. The control chip controls the output power of the motor based on the current parameter.

[0008] The motor output adjustment principle of the noise reduction circuit is as follows: when the 19-pin AC power zero-crossing detection pin of the control chip has a rising edge signal in the positive half cycle and a falling edge signal in the negative half cycle, it is judged as a zero-crossing signal. After the delay setting time, the 25-pin control chip outputs a low level, causing U2 to turn on and trigger the thyristor TR1. Only then will voltage and current be added to the motor, and the motor will have power output. Because the thyristor is not turned on at the beginning of the positive or negative half cycle of the power supply, the voltage and current of the thyristor are not added to the motor during the delay period, so the motor output power becomes smaller during this cycle, achieving the purpose of adjusting the motor output power. The longer the delay time between the start of zero crossing and the chip output turning on the thyristor, the larger the thyristor phase shift trigger angle, the shorter the thyristor conduction time in the half cycle of the AC power, the lower the motor operating voltage, the less current passes through, and the smaller the motor power will be.

[0009] The specific work of this noise reduction circuit is to set a full-power output threshold value in the range of 0 current and overload current value. When it is detected that the actual operating current of the motor is above the threshold value, the optocoupler U4 is always turned on, the thyristor is always in the on state, and the AC power is output at full power. When the current is below the threshold current value when the motor is actually running, as mentioned above, there are many gears for setting the current. The actual current is compared with the set current gear value. The corresponding gear outputs the interrupt 0 point that has been set for this gear and the fixed delay time parameters for opening the thyristor (that is, different parameters for the motor output power percentage) are adjusted. That is, by adjusting the conduction angle of the thyristor (dual thyristor) to control the current passing time of the motor, thereby controlling the input power of the motor, so that the motor power output outputs different powers synchronously according to the set gear current. The larger the current, the higher the gear, and the greater the power output to the motor by the circuit. Because there are more papers, the greater the current, the greater the gear power provided to the motor to maintain the balance of the motor speed.

[0010] Compared with the prior art, the present invention has the following beneficial effects: it provides a noise reduction circuit for a paper shredder, and by improving the circuit structure on the main control board of the paper shredder, it can detect the current delivered to the motor, thereby realizing the control of the motor speed and achieving the purpose of noise reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a circuit diagram of the analysis and processing module (main control MCU) in the present invention.

[0012] Figure 2 This is a circuit diagram of the power module and the trash can extraction detection module in the present invention.

[0013] Figure 3 This is a schematic diagram of the circuit related to the motor in the present utility model. DETAILED DESCRIPTION

[0014] The present invention is described in further detail below with reference to the accompanying drawings and specific implementation methods.

[0015] In the following embodiments, the same or similar numbers throughout represent the same or similar components or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0016] In the description of the present invention, it should be understood that the terms: center, longitudinal, transverse, length, width, thickness, up, down, front, back, left, right, vertical, horizontal, top, bottom, inside, outside, clockwise, counterclockwise, etc. indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and therefore cannot be understood as limiting the present invention. In addition, the terms: first, second, etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features shown. In the description of the present invention, unless otherwise clearly specified and limited, the terms: install, connect, connect, etc. should be understood in a broad sense, and ordinary technicians in this field can understand the specific meanings of the above terms in this application according to the specific circumstances.

[0017] See also Figures 1 to 3 , Figure 2 J1 and Figure 3 Connect to J1 in the circuit. Power supply L is divided into three paths after passing through fuse F1, varistor VR1, EMC_C1, and common-mode inductor T1 to form an electromagnetic compatibility circuit. The first path is rectified by resistor R1 and diodes D1_1 and D1_2, filtered by EC1 and EC2 to a high voltage. After passing through the power supply circuit including the U1 switching power chip, it is converted into 24V DC and directly supplies the relay. The 24V is then stabilized to 5V by U2 and filtered by capacitors EC4 and C4 to supply the control chip and other circuits.

[0018] After the second route comes out of R1, it enters the control chip 19th pin (interrupt pin) as the chip zero-crossing voltage detection circuit after voltage reduction and current limiting by R35, R36, and R37. It detects both the rising and falling edge signals of the power supply voltage and can provide the chip with a zero-crossing pulse signal of the power supply voltage regardless of the positive or negative cycle of the power supply.

[0019] The third voltage passes through the trash can detection safety switch SW1 and is connected to the AC input terminal 2 of the rectifier bridge DB1. Pin 2 of DB1's AC input is connected to the thyristor TR1 (bidirectional thyristor) power regulation circuit (the control chip adjusts the thyristor's power through the optocoupler U2). The resistor C_TR and the capacitor C_TR are connected in series, and then connected in parallel with the surge absorption varistor TR_VDR to the thyristor T1 and T2 pins to protect the thyristor. The circuit passes through the motor temperature control, then to the PTC fuse, and the current sampling resistor R21 to ground, that is, the input power supply N, to form a complete AC path. The rectifier bridge DB1 outputs regulated DC power between DC output pins 1 and 4, with pin 4 being positive and pin 1 being negative. The double-pole switching relay RELAY_REV (controlled on and off by the chip Q2) then controls the direction of the DC current, achieving the forward and reverse rotation functions of the motor, allowing the machine to shred and reverse paper normally.

[0020] The current sampling resistor R21 is connected in series in the AC path of DB1. The current passing through the motor flows back to the power supply through R21. The voltage drop across R21 increases with the increase of the motor current. After rectification and filtering by R13, D8, and C6 (the maximum input voltage is adjusted by the voltage divider R14 and R15), the voltage value, which is the real-time current parameter of the motor, is provided to the control chip 12 through R16.

[0021] The principle of motor output regulation of different powers is as follows: when the mains zero-crossing detection pin at pin 19 of the chip has a rising edge signal in the positive half cycle and a falling edge signal in the negative half cycle, it is judged as a zero-crossing signal. After the delay setting time, the control chip pin 25 outputs a low level, causing U2 to turn on and trigger the thyristor TR1. Only then will voltage and current be added to the motor, and the motor will have power output. Because the thyristor is not turned on at the beginning of the positive or negative half cycle of the power supply, the voltage and current of the thyristor are not added to the motor during the delay period, so the motor output power becomes smaller during this cycle, achieving the purpose of regulating the motor output power. The longer the delay time between the start of zero crossing and the turn-on of the thyristor by the chip output, the larger the thyristor phase shift trigger angle, the shorter the thyristor turn-on time in half a cycle of the mains, the lower the operating voltage of the motor, the less current passes through, and the smaller the motor power will be.

[0022] Different countries have different mains frequencies, 50Hz and 60Hz. At 60Hz, the positive to negative half-cycle time of the power supply is 8.3ms, which is shorter than the 10ms at 50Hz. For example, when outputting 50% power, the delay time to open the thyristor after interrupting the zero crossing is half of 8.3ms at 60Hz and half of 10ms at 50Hz. Therefore, the machine needs to detect the mains power frequency. By measuring the different positive and negative pulse times of the zero-crossing detection pin and the length of the timing, the AC frequency of the mains power is detected, corresponding to different frequencies. Outputting different delay times for opening the thyristor after interruption ensures the same output power at different frequencies.

[0023] The specific work of this noise reduction circuit is to set a full-power output threshold value in the range of 0 current and overload current value. When it is detected that the actual operating current of the motor is above the threshold value, the optocoupler U4 is always turned on, the thyristor is always in the on state, and the AC power is output at full power. When the current is below the threshold current value when the motor is actually running, as mentioned above, there are many gears for setting the current. The actual current is compared with the set current gear value. The corresponding gear outputs the interrupt 0 point that has been set for this gear and the fixed delay time parameters for opening the thyristor (that is, different parameters for the motor output power percentage) are adjusted. That is, by adjusting the conduction angle of the thyristor (dual thyristor) to control the current passing time of the motor, thereby controlling the input power of the motor, so that the motor power output outputs different powers synchronously according to the set gear current. The larger the current, the higher the gear, and the greater the power output to the motor by the circuit. Because there are more papers, the greater the current, the greater the gear power provided to the motor to maintain the balance of the motor speed.

[0024] Therefore, although the load of the motor changes, the real-time current detection will detect the changing voltage. The chip will select different current gears based on different voltages to output a power to the motor that can balance the motor speed, thereby increasing or decreasing the motor input power and reaching a stable speed.

[0025] When the motor current exceeds the threshold value, the motor must run at full power to balance the speed. If it continues to increase and exceeds the maximum gear of the movement blade protection current, the output pin of the control chip will turn off the thyristor to stop the motor from working, protecting the paper shredding blade and structure from damage. The panel overload LED indicator will light up to remind the user to pay attention.

[0026] Other auxiliary functions of the shredder are as follows.

[0027] The trash can pull-out detection circuit is connected to the safety switch SW1. During normal operation, the mains power is stepped down and limited by R22, R23, and R24, and rectified by D10. The maximum clamping input voltage of ZD3 is within the normal operating range of the chip. The voltage after filtering by C11 is passed through R25 to provide a high level to the chip's trash can detection pin 15. When the trash can is pulled out, the safety switch SW1 is disconnected, there is no mains power before R22, and the chip detection pin 15 has a voltage of 0. The voltage can be used to determine whether the trash can is pulled out.

[0028] The overheat protection function of the machine is that the thermostat is tied to the motor housing. When the motor operating temperature rises and reaches or exceeds the thermostat protection temperature, the thermostat is disconnected, and the mains voltage is reduced and current-limited by R17, R18, and R19, rectified by D7 and filtered by C8, and clamped by ZD2 to the highest chip operating voltage. A high-level motor overheat signal is provided to the chip 17 pin through R20, and the chip turns off the thyristor and relay to stop the motor.

[0029] As can be seen from the above description, the utility model provides a noise reduction circuit for a paper shredder. By improving the circuit structure on the main control board of the paper shredder, the current delivered to the motor can be detected, thereby realizing the control of the motor speed and achieving the purpose of noise reduction.

[0030] The protection scope of the present invention includes but is not limited to the above embodiments. The protection scope of the present invention is based on the claims. Any replacement, deformation, and improvement of the technology that can be easily thought of by technicians in this field fall within the protection scope of the present invention.

Claims

1. A noise reduction circuit for a paper shredder, characterized in that: include: Rectifier bridge DB1; Current sampling resistor R21; Control chip; The current sampling resistor R21 is connected in series in the AC path of the rectifier bridge DB1, so that the current passing through the shredder's motor flows back to the power supply through the current sampling resistor R21; The voltage drop across the current sampling resistor R21 increases as the motor current increases. After rectification and filtering, the voltage value, i.e., the current parameter of the motor's real-time operation, is provided to pin 12 of the control chip through the resistor R16. The control chip controls the output power of the motor according to the current parameter.

Images