Stepping motor silent drive method with decreasing turn-off time and its drive circuit

Abstract

The present invention discloses a silent driving method for a stepping motor with a decreasing turn-off time and its driving circuit. The silent driving method for a stepping motor with a decreasing turn-off time includes step S1: an input current command is transmitted to a comparator and serves as the negative input signal of the comparator, and a current detection circuit real-time detects the actual current flowing through the coil of the stepping motor. Step S2: a current chopping control circuit controls the turn-off time of an H-bridge power circuit according to the turn-off time parameter provided by a decreasing turn-off time control circuit and the state output by the comparator. The silent driving method for a stepping motor with a decreasing turn-off time and its driving circuit disclosed by the present invention replace the fixed attenuation time Toff control mode, improve the problem of excessive step current fluctuation of the traditional chopper constant current driving scheme at low motor speeds, and enable the stepping motor to operate more silently at low speeds.

Description

Technical Field

[0001] The present invention belongs to the technical field of stepper motor drive, and particularly relates to a stepper motor silent drive method with decreasing turn-off time and a stepper motor silent drive circuit with decreasing turn-off time. Background Art

[0002] Chopper constant current drive is the most commonly used drive method for stepper motors at present, and its drive structure is as Figure 4 shown. The circuit consists of a current detection (current sensing) circuit, a comparator, a current chopper control circuit, and an H-bridge power circuit. The current sensing circuit detects the actual current flowing through the stepper motor coil and inputs it to the comparator for comparison with the target current set by the current command. The comparison result is input to the chopper constant current control circuit; the current chopper control circuit controls the opening or closing of the power transistors in the H-bridge power circuit according to the set turn-off time and the comparator result, so as to increase or decrease the current flowing through the motor coil. As Figure 5 shown, the chopper constant current regulation process consists of multiple current hysteresis processes. In the charging stage, the power transistor is turned on in the forward direction. The current in the motor coil gradually increases. When the set current value is reached, the charging ends and the circuit enters the decay stage; in the decay stage, the power transistor is turned on in the reverse direction, so that the current flowing through the motor coil gradually decreases; after continuously decaying for the Toff time, the circuit re-enters the charging stage. Such repeated adjustment makes the current flowing through the motor coil gradually stable near the set current value.

[0003] Chopper constant current drive adopts closed-loop feedback control, with fast current response, and can quickly stabilize the current in the motor coil at the set value. However, its inherent current regulation method determines that there will be a ripple after the current is stabilized. The size of the ripple depends on the Ton and Toff times. After the current enters the steady state, the current rise during the Ton time and the current fall during the Toff time are balanced. Therefore, by reducing the Toff time and increasing the chopping frequency, the step current jitter after stabilization can be effectively reduced. However, on the one hand, too high a chopping frequency will increase the switching loss of the power circuit; on the other hand, there will be mechanical oscillations during the step switching of the stepper motor, and too small a current hysteresis regulation amplitude will also affect the position stabilization speed of the stepper motor.

[0004] Therefore, in view of the above problems, further improvements are made. Summary of the Invention

[0005] The main object of the present invention is to provide a stepper motor silent drive method with decreasing turn-off time and its drive circuit, which replaces the fixed decay time Toff control method, improves the problem of excessive step current fluctuation of the traditional chopper constant current drive scheme at low motor speeds, and enables the stepper motor to operate more silently at low speeds.

[0006] Another object of the present invention is to provide a silent driving method for a stepping motor with a decreasing turn-off time and its driving circuit. A decreasing turn-off time control circuit is added to the traditional current chopping driving scheme with a fixed turn-off time (Toff) to control the turn-off time of current chopping, that is, the circuit adjusts the driving current in the current chopping mode with the normal fixed turn-off time (Toff), but the turn-off time (Toff) of current chopping decreases every once in a while. In this way, under the current chopping mode of gradually decreasing turn-off time (Toff), the set current value is achieved. Compared with the traditional current chopping driving scheme with a fixed turn-off time (Toff), the current chopping driving scheme with a decreasing turn-off time (Toff) proposed by the present invention has a faster response of the driving current, a smaller current ripple after stabilization, and effectively improves the problem of excessive stepped current ripple of the fixed turn-off time current chopping driving scheme at low speeds.

[0007] To achieve the above object, the present invention provides a silent driving method for a stepping motor with a decreasing turn-off time, which is used to improve the problem of excessive stepped current fluctuation of the motor at low speeds, and includes the following steps:

[0008] Step S1: One path of the input current command is transmitted to a comparator and serves as the negative input signal of the comparator. The current detection circuit continuously detects the actual current flowing through the coil of the stepping motor and uses the detected current value as the positive input signal of the comparator, so that the comparator makes a comparison and outputs a corresponding state to the current chopping control circuit;

[0009] Step S2: The current chopping control circuit controls the turn-on time and turn-off time of the H-bridge power circuit according to the turn-off time parameter provided by the decreasing turn-off time control circuit and the state output by the comparator, so that the current flowing through the coil of the stepping motor increases or decreases, and after controlling the turn-off time multiple times, the current chopping hysteresis amplitude is gradually reduced, thereby realizing a driving current with sequentially reduced ripples, and further reducing the fluctuation of the stepped current of the stepping motor at low speeds.

[0010] As a further preferred technical solution of the above technical solution, step S2 is specifically implemented as the following steps:

[0011] Step S2.1: Another path of the input current command is transmitted to the command switching circuit of the decreasing turn-off time control circuit to determine whether the input current command has changed. When it is detected that the input current command is inconsistent with the previous current command temporarily stored in its register, an indication signal indicating the start of a new current command is output to the turn-off time setting circuit of the decreasing turn-off time control circuit; when it is detected that the input current command is consistent with the previous current command temporarily stored in its register, an indication signal indicating that the current command remains unchanged is output to the turn-off time setting circuit;

[0012] Step S2.2: The comparator also outputs the corresponding status to the current steady-state detection circuit of the decreasing turn-off time control circuit to determine whether the drive current hysteresis regulation enters the steady-state balance. When the current steady-state detection circuit determines that the current drive current reaches the steady-state index (including the number of current chopping hysteresis regulation times reaching the set number (through the steady-state counter, it can be detecting the rising edge or the falling edge of the comparator output signal, and it is a preferred solution to judge whether the current reaches the steady-state index), the duration of the current chopping hysteresis regulation reaches the set time, and the time period of the current chopping hysteresis regulation remains unchanged, etc.), an indication signal that the output current enters the steady-state balance is transmitted to the turn-off time setting circuit;

[0013] Step S2.3: The turn-off time setting circuit combines the input initial turn-off time parameter Tin, the output of the instruction switching detection circuit (whether there is a new current instruction input), and the output of the current steady-state detection circuit (whether the current enters the steady-state balance), thereby generating a new turn-off time parameter Tout.

[0014] As a further preferred technical solution of the above technical solution, step S2.3 is specifically implemented as the following steps:

[0015] Step S2.3.1: The turn-off time parameter Tout initially set by the turn-off time setting circuit is equal to the initial turn-off time parameter Tin;

[0016] Step S2.3.2: Each time the turn-off time setting circuit receives the indication signal that the current enters the steady-state balance transmitted by the current steady-state detection circuit, the output turn-off time parameter Tout is reduced to a predetermined ratio (preferably halved) of the previous turn-off time parameter, thereby sequentially reducing the ripple of the drive current until the output turn-off time parameter Tout reaches the predetermined value (preferably Tout = Tin / 16) and then remains unchanged. And each time the output turn-off time parameter Tout changes, the current steady-state detection circuit clears the indication signal that the current enters the steady-state balance, and the steady-state counter restarts counting;

[0017] Step S2.3.3: Each time the turn-off time setting circuit receives the indication signal at the start of a new current instruction transmitted by the instruction switching detection circuit, the turn-off time parameter Tout is restored to the initial turn-off time parameter Tin for output.

[0018] As a further preferred technical solution of the above technical solution, in step S2, the decreasing turn-off time control circuit automatically adjusts the number of times the turn-off time parameter decreases within an instruction period of an input current, where:

[0019] When the stepping motor rotates faster, each instruction execution period is shorter (the faster it makes the turn-off time parameter reach the predetermined value), and the number of times the turn-off time decreases is less;

[0020] When the speed of the stepper motor is slower, each instruction execution cycle is longer (the slower the off-time parameter reaches the predetermined value), and the more times the off-time reduction is executed.

[0021] To achieve the above objectives, the present invention further provides a stepper motor silent driving circuit with decreasing off-time, comprising a decreasing off-time control circuit and a current chopping driving circuit, wherein:

[0022] The current chopping drive circuit includes a current detection circuit, a comparator, a current chopping control circuit, and an H-bridge power circuit. The input current instruction is transmitted all the way to the comparator and serves as the negative input signal of the comparator. The current detection circuit detects the actual current flowing through the coil of the stepper motor in real time and uses the current value obtained by the detection as the positive input signal of the comparator, so that the comparator makes a comparison, thereby outputting the corresponding state to the current chopping control circuit. The current chopping control circuit controls the (opening time and) closing time of the H-bridge power circuit according to the closing time parameter provided by the decreasing closing time control circuit and the state output by the comparator, so that the current flowing through the coil of the stepper motor increases or decreases, and after controlling the closing time multiple times, the current chopping hysteresis amplitude is gradually reduced, thereby realizing a driving current with a sequential reduction in ripples, thereby reducing the fluctuation of the step current of the stepper motor at a low speed;

[0023] The decreasing off-time control circuit includes a current steady-state detection circuit, an instruction switching circuit and an off-time setting circuit. The instruction switching circuit is used to detect whether the input current instruction has changed and transmit the result to the off-time setting circuit. The current steady-state detection circuit is used to determine whether the driving current hysteresis adjustment enters a steady-state balance and transmit the result to the off-time setting circuit. The time setting circuit provides the corresponding off-time parameters to the current chopping control circuit according to the output results of the instruction switching circuit and the current steady-state detection circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The invention discloses a stepping motor silent driving method with decreasing off-time and a structural schematic diagram of a driving circuit thereof.

[0025] Figure 2 The present invention is a stepper motor silent driving method with decreasing off-time and a current regulation schematic diagram of a driving circuit thereof.

[0026] Figure 3 The invention discloses a stepping motor silent driving method with decreasing off-time and a decreasing off-time control circuit diagram of a driving circuit thereof.

[0027] Figure 4 This is a diagram of an existing current chopping drive circuit.

[0028] Figure 5It is a schematic diagram of the existing chopper constant current drive current regulation. Specific implementation mode

[0029] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments in the following description are only examples, and those skilled in the art can think of other obvious variations. The basic principles defined in the following description of the present invention can be applied to other implementation schemes, deformation schemes, improvement schemes, equivalent schemes, and other technical schemes without departing from the spirit and scope of the present invention.

[0030] In the preferred embodiment of the present invention, those skilled in the art should note that the stepping motor, current command, etc. involved in the present invention can be regarded as the prior art.

[0031] Preferred embodiment.

[0032] The present invention provides a method for driving a stepping motor silently with a decreasing turn-off time, which is used to improve the problem of excessive step current fluctuation of the motor at low speeds, and includes the following steps:

[0033] Step S1: One path of the input current command is transmitted (through the DAC module) to the comparator and used as the negative input signal of the comparator. The current detection circuit continuously detects the actual current flowing through the coil of the stepping motor and uses the detected current value as the positive input signal of the comparator, so that the comparator makes a comparison, and then outputs the corresponding state to the current chopping control circuit;

[0034] Step S2: The current chopping control circuit controls the turn-on time and turn-off time of the H-bridge power circuit according to the turn-off time parameter provided by the decreasing turn-off time control circuit and the state output by the comparator, so that the current flowing through the coil of the stepping motor increases or decreases, and after controlling the turn-off time multiple times, the current chopping hysteresis amplitude is gradually reduced (the hysteresis interval of the current flowing through the coil of the stepping motor becomes smaller and smaller), so as to realize the driving current with sequentially reduced ripples, and further reduce the fluctuation of the step current of the stepping motor at low speeds.

[0035] Specifically, step S2 is specifically implemented as the following steps:

[0036] Step S2.1: Another path of the input current command is transmitted to the command switching circuit of the decreasing turn-off time control circuit to determine whether the input current command changes. When it is detected that the input current command is inconsistent with the current command stored in its register at the previous moment, an indication signal indicating the start of a new current command is output to the turn-off time setting circuit of the decreasing turn-off time control circuit; when it is detected that the input current command is consistent with the current command stored in its register at the previous moment, an indication signal indicating that the current command remains unchanged is output to the turn-off time setting circuit;

[0037] Step S2.2: The comparator also outputs the corresponding status to the current steady-state detection circuit of the decreasing turn-off time control circuit to determine whether the drive current hysteresis regulation enters the steady-state balance. When the current steady-state detection circuit determines that the current drive current reaches the steady-state index (including the number of current chopping hysteresis regulation times reaching the set number (through the steady-state counter, it can be the rising edge or the falling edge of the output signal of the detection comparator, and it is the preferred solution to determine whether the current reaches the steady-state index), the duration of the current chopping hysteresis regulation reaches the set time, and the time period of the current chopping hysteresis regulation remains unchanged, etc.), the indication signal that the output current enters the steady-state balance is transmitted to the turn-off time setting circuit;

[0038] Step S2.3: The turn-off time setting circuit combines the input initial turn-off time parameter Tin, the output of the command switching detection circuit (whether there is a new current command input), and the output of the current steady-state detection circuit (whether the current enters the steady-state balance), so as to generate a new turn-off time parameter Tout.

[0039] More specifically, step S2.3 is specifically implemented as the following steps:

[0040] Step S2.3.1: The turn-off time parameter Tout initially set by the turn-off time setting circuit is equal to the initial turn-off time parameter Tin;

[0041] Step S2.3.2: Each time the turn-off time setting circuit receives the indication signal that the current enters the steady-state balance transmitted by the current steady-state detection circuit, it reduces the output turn-off time parameter Tout to a predetermined ratio (preferably halved) of the previous turn-off time parameter, so as to gradually reduce the ripple of the drive current until the output turn-off time parameter Tout reaches the predetermined value (preferably Tout = Tin / 16) and then remains unchanged. And each time the output turn-off time parameter Tout changes, the current steady-state detection circuit clears the indication signal that the current enters the steady-state balance, and the steady-state counter restarts counting;

[0042] Step S2.3.3: Each time the turn-off time setting circuit receives the indication signal at the start of a new current command transmitted by the command switching detection circuit, it restores the turn-off time parameter Tout to the initial turn-off time parameter Tin for output.

[0043] Furthermore, in step S2, the decreasing turn-off time control circuit automatically adjusts the number of times the turn-off time parameter decreases within one instruction cycle of an input current, where:

[0044] When the stepping motor rotates faster, each instruction execution cycle is shorter (the faster it makes the turn-off time parameter reach the predetermined value), and the number of times the turn-off time decreases is less;

[0045] When the rotational speed of the stepper motor is slower, the execution period of each instruction is longer (the slower speed causes the turn-off time parameter to reach the predetermined value), and the number of times the execution turn-off time decreases is more.

[0046] The present invention also discloses a stepper motor silent drive circuit with a decreasing turn-off time, which is applied to the above-mentioned stepper motor silent drive method with a decreasing turn-off time, and includes a decreasing turn-off time control circuit and a current chopping drive circuit, wherein:

[0047] The current chopping drive circuit includes a current detection circuit, a comparator, a current chopping control circuit, and an H-bridge power circuit. One path of the input current instruction is transmitted to the comparator and serves as the negative input signal of the comparator. The current detection circuit real-time detects the actual current flowing through the coil of the stepper motor and takes the detected current value as the positive input signal of the comparator, so that the comparator makes a comparison, and then outputs the corresponding state to the current chopping control circuit. The current chopping control circuit controls the (on-time and) turn-off time of the H-bridge power circuit according to the turn-off time parameter provided by the decreasing turn-off time control circuit and the state output by the comparator, so that the current flowing through the coil of the stepper motor increases or decreases, and after controlling the turn-off time multiple times, the current chopping hysteresis amplitude is gradually decreased, thereby realizing the driving current with sequentially reduced ripple, and further reducing the fluctuation of the step current at low rotational speeds of the stepper motor;

[0048] The decreasing turn-off time control circuit includes a current steady-state detection circuit, an instruction switching circuit, and a turn-off time setting circuit. The instruction switching circuit is used to detect whether the input current instruction changes and transmit the result to the turn-off time setting circuit. The current steady-state detection circuit is used to judge whether the driving current hysteresis regulation enters the steady-state balance and transmit the result to the turn-off time setting circuit. The time setting circuit provides the corresponding turn-off time parameter to the current chopping control circuit according to the results output by the instruction switching circuit and the current steady-state detection circuit.

[0049] The principle of the present invention is:

[0050] The chopping constant-current silent drive scheme with a decreasing turn-off time proposed by the present invention has a current regulation process similar to that of the chopping constant-current drive scheme with a fixed turn-off time. Its current regulation process is as Figure 2 shown, and can be regarded as a combination of the chopping constant-current regulation processes with multiple fixed turn-off times. Since the turn-off time parameter input to the chopping constant-current control loop is halved successively, the current chopping hysteresis amplitude also decreases accordingly, thereby realizing a driving current with smaller ripple. The example process of halving the turn-off time is as follows:

[0051] 1) When a new current instruction starts, the circuit chops and regulates the driving current under the initial set turn-off time control.

[0052] 2) Detect whether the driving current enters the steady-state balance;

[0053] 3) The current enters a steady-state balance, and the Toff time is reduced to 1 / 2. Under the control of the new turn-off time, the driving current continues to be stably driven.

[0054] 4) Re-detect whether the driving current enters a steady-state balance;

[0055] 5) Repeat step 3;

[0056] 6) The above process is repeated 4 times, and the Toff time is reduced to 1 / 16; it remains unchanged and no longer halves;

[0057] 7) At any time, if the current command is updated, immediately return to step 1 for control.

[0058] The driving method with decreasing turn-off time proposed by the present invention is implemented by a decreasing turn-off time control circuit, and its structure is as Figure 3 shown, which consists of an instruction switching detection circuit, a current steady-state detection circuit, and a turn-off time setting circuit. The instruction switching detection circuit is used to detect changes in the input current command. The circuit is implemented by a group of registers and an exclusive-OR circuit. When it detects that the input current command is inconsistent with the current command stored in the register at the previous moment, it gives a new instruction start indication signal. The current steady-state detection circuit is used to detect whether the hysteresis regulation of the driving current enters a dynamic balance. The circuit is implemented by a counter and a judgment circuit. The counter receives the output result of the comparator, and the counter increments by 1 each time a rising edge is detected. When the count value reaches the set number of current hysteresis times, an indication signal that the output current enters a steady state is output. After the start of a new current command or the turn-off time is halved, the current steady-state indication signal is cleared, the counter is cleared, and counting starts again. The turn-off time setting circuit generates a new turn-off time Tout according to the input turn-off time parameter Tin and the detection results of the instruction switching detection circuit and the current steady-state detection circuit. First, the circuit outputs the initially set turn-off time parameter: Tout = Tin. After that, each time the circuit detects the current steady-state indication signal, the output turn-off time parameter is halved once: Tout = Tout / 2. Until the output turn-off time parameter Tout = Tout / 16, it remains unchanged. During the adjustment process, once a new instruction start indication signal is received, the output turn-off time returns to the initial set value Tout = Tin.

[0059] The current chopping drive scheme for decreasing the turn-off time (Toff) proposed by the present invention only adds an attenuation time control circuit on the turn-off time parameter setting path, without changing the original chopping constant current control loop, and the implementation is simple. During the operation of the circuit, no additional parameter modification control is required, and the circuit automatically performs the operation of halving the turn-off time. In addition, the circuit can automatically adjust the number of times the turn-off time is halved within one instruction cycle. The faster the motor speed, the shorter each instruction execution cycle, and the fewer times the circuit performs the operation of halving the turn-off time, or even none; the slower the motor speed, the longer each instruction execution cycle, and the more times the circuit performs the operation of halving the turn-off time, until the turn-off time reaches the set number of halving times and then remains unchanged. This design fully takes into account the requirements of the stepper motor for the response speed and ripple of the drive current. On the premise of ensuring the response speed, it reduces the current ripple of the chopping constant current drive scheme, makes the drive current more accurately stable near the instruction set value, and the stepper motor rotates more smoothly and quietly.

[0060] The turn-off time setting circuit includes a shifter, and the decreasing operation of the turn-off time Tout input to the current chopping drive loop is realized by the shifter. Every time the load signal is detected, the turn-off time Tin is updated to the shifter, and the output turn-off time Tout = Tin. Every time the shift signal is detected, the shifter shifts down, and the output turn-off time is halved Tout = Tout / 2. The register and the exclusive-OR unit (circuit) constitute an instruction switching detection circuit. When it is detected that the input current instruction is inconsistent with the current instruction stored in the register at the previous moment, a new instruction start indication signal load is given. The current steady-state detection circuit is realized by a steady-state counter. The steady-state counter receives the result of the comparator in the current chopping drive loop, and the counter is incremented by 1 every time a rising edge is detected. When the count value reaches the set number of current hysteresis times m, it means that the current chopping regulation has entered dynamic balance, and then the shift signal shift is output.

[0061] It is worth mentioning that the technical features such as the stepper motor and the current instruction involved in this patent application for invention should be regarded as the prior art. The specific structures, working principles, and possible control methods and spatial arrangement methods of these technical features can be selected conventionally in the art, and should not be regarded as the invention points of this patent for invention. This patent for invention will not be further specifically elaborated.

[0062] For those skilled in the art, it is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A silent driving method for a stepping motor with a decreasing turn-off time, which is used to improve the problem of excessive step current fluctuation of the motor at low speeds, and is characterized in that, It includes the following steps: Step S1: One path of the input current command is transmitted to a comparator and serves as the negative input signal of the comparator. The current detection circuit real-time detects the actual current flowing through the coil of the stepper motor and uses the detected current value as the positive input signal of the comparator, so that the comparator makes a comparison and outputs the corresponding state to the current chopping control circuit; Step S2: The current chopping control circuit controls the off-time of the H-bridge power circuit according to the off-time parameter provided by the decreasing off-time control circuit and the state output by the comparator, so that the current flowing through the coil of the stepper motor increases or decreases, and after controlling the off-time multiple times, the current chopping hysteresis amplitude is gradually decreased, thereby realizing the driving current with gradually reduced ripple, and further reducing the fluctuation of the step current at low speed of the stepper motor; Step S2 is specifically implemented as the following steps: Step S2.1: The other path of the input current command is transmitted to the command switching circuit of the decreasing off-time control circuit to judge whether the input current command changes. When it is detected that the input current command is inconsistent with the previous moment current command temporarily stored in its register, an indication signal of the start of a new current command is output to the off-time setting circuit of the decreasing off-time control circuit; when it is detected that the input current command is consistent with the previous moment current command temporarily stored in its register, an indication signal that the current command remains unchanged is output to the off-time setting circuit; Step S2.2: The comparator also outputs the corresponding state to the current steady-state detection circuit of the decreasing off-time control circuit to judge whether the driving current hysteresis regulation enters a steady-state balance. When the current steady-state detection circuit judges that the current driving current reaches the steady-state index, an indication signal that the output current enters the steady-state balance is transmitted to the off-time setting circuit; Step S2.3: The off-time setting circuit combines the input initial off-time parameter Tin, the output of the command switching detection circuit, and the output of the current steady-state detection circuit to generate a new off-time parameter Tout.

2. The silent driving method for a stepping motor with a decreasing turn-off time according to claim 1, and is characterized in that, Step S2.3 is specifically implemented as the following steps: Step S2.3.1: The off-time parameter Tout initially set by the off-time setting circuit is equal to the initial off-time parameter Tin; Step S2.3.2: Each time the off-time setting circuit receives the indication signal that the output current enters the steady-state balance transmitted by the current steady-state detection circuit, the output off-time parameter Tout is reduced to a predetermined ratio of the previous off-time parameter, thereby gradually reducing the ripple of the driving current until the output off-time parameter Tout reaches the predetermined value and then remains unchanged. And each time the output off-time parameter Tout changes, the current steady-state detection circuit clears the indication signal that the output current enters the steady-state balance, and the steady-state counter restarts counting; Step S2.3.3: Each time the off-time setting circuit receives the indication signal of the start of a new current command transmitted by the command switching detection circuit, the off-time parameter Tout is restored to the initial off-time parameter Tin for output.

3. The silent driving method for a stepping motor with a decreasing turn-off time according to claim 2, and is characterized in that, In step S2, the number of times the off-time parameter is reduced within an instruction cycle of the input current is automatically adjusted by the off-time control circuit, wherein: When the speed of the stepper motor is faster, the execution cycle of each instruction is shorter, and the number of times the shutdown time is reduced is less; When the speed of the stepper motor is slower, each instruction execution cycle is longer, and the number of times the execution shutdown time is reduced is greater.

4. A silent driving circuit for a stepping motor with a decreasing turn-off time, which is applied to the silent driving method for a stepping motor with a decreasing turn-off time according to any one of claims 1-3, and is characterized in that, It includes a decreasing off-time control circuit and a current chopping drive circuit, wherein: The current chopping drive circuit includes a current detection circuit, a comparator, a current chopping control circuit, and an H-bridge power circuit. The input current instruction is transmitted all the way to the comparator and serves as the negative input signal of the comparator. The current detection circuit detects the actual current flowing through the coil of the stepper motor in real time and uses the current value obtained by the detection as the positive input signal of the comparator, so that the comparator makes a comparison, thereby outputting the corresponding state to the current chopping control circuit. The current chopping control circuit controls the off time of the H-bridge power circuit according to the off time parameter provided by the decreasing off time control circuit and the state output by the comparator, so that the current flowing through the coil of the stepper motor increases or decreases, and after controlling the off time multiple times, the current chopping hysteresis amplitude is gradually reduced, thereby realizing a driving current with a sequentially reduced ripple, thereby reducing the fluctuation of the step current of the stepper motor at a low speed; The decreasing off-time control circuit includes a current steady-state detection circuit, an instruction switching circuit and an off-time setting circuit. The instruction switching circuit is used to detect whether the input current instruction has changed and transmit the result to the off-time setting circuit. The current steady-state detection circuit is used to determine whether the driving current hysteresis adjustment enters a steady-state balance and transmit the result to the off-time setting circuit. The time setting circuit provides the corresponding off-time parameters to the current chopping control circuit according to the output results of the instruction switching circuit and the current steady-state detection circuit.

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