A control method and system for holding torque of a stepper motor

Abstract

The application provides a kind of control method and system of holding torque of step motor, comprising: at least one current limiting unit is selected to access in the power supply circuit and current limiting circuit of step motor drive IC, step motor controller controls the current limiting function of shielding current limiting unit, so that step motor drive IC drives step motor to start and normally operates with rated current after inputting motor start signal, step motor drive IC drives step motor to stop operating after inputting motor stop signal, step motor controller controls partial or all current limiting function of current limiting unit to open, at this time, step motor has a self-sustaining current to generate holding torque.The application provides smaller self-sustaining current for motor under the premise of meeting motor holding torque by designing current limiting unit with simple circuit structure, so as to achieve the effect of reducing heat and power consumption of motor, improving service life of motor, low cost and high economic benefit.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, specifically to a method and system for controlling the holding torque of a stepper motor. Background Technology

[0002] In scenarios requiring high control precision and handling large torque loads, such as those used in medical devices, stepper motors need to be powered on when stopped to maintain a certain torque and prevent them from being driven to rotate by external forces, thus maintaining their current mechanical position. Without self-sustaining current, the motor cannot maintain its self-sustaining force and is easily driven to rotate passively under external forces, thus deviating from the controlled position. Therefore, motor control with high precision requirements and heavy loads typically requires maintaining current to preserve self-sustaining force when the motor is stopped.

[0003] See Figure 1 Vcc provides the logic power for the driver IC, and VCM provides the power for the motor. Typically, the current-limiting circuit of the driver IC requires external current-limiting resistors R1 and R2 to limit the motor's operating current. Currently, stepper motor driver chips only have two H-bridges and lack self-holding current control. When the motor stops, to maintain its position from external deflection, the holding current must be maintained at the rated operating current. However, due to torque differences in the motor shaft threads or gears, only a small amount of current is usually needed to maintain the torque and position when the motor stops. Using the rated current as the holding current leads to high heat generation and power loss when the motor stops, reducing its lifespan.

[0004] Furthermore, using a dedicated driver chip with a stop current control would significantly increase the cost of the stepper motor control scheme, resulting in lower economic efficiency. This leads most users to prefer to tolerate the high power consumption and heat generation issues caused by a scheme without a self-sustaining current control.

[0005] Therefore, there is an urgent need for a low-cost control method and circuit for the holding torque of a stepper motor that can reduce the self-sustaining current when the motor stops, thereby reducing the motor's heat generation and power consumption. Summary of the Invention

[0006] This invention provides a stepper motor holding torque control method and circuit, which is mainly used to solve the problems of excessive self-holding current when the stepper motor stops, resulting in high heat generation and power loss, reduced motor life and high cost. The invention achieves the effects of reducing the self-holding current when the motor stops, reducing motor heat generation and power consumption, improving motor life, and achieving low cost and high economic benefits.

[0007] The present invention achieves the above objectives through the following technical solutions:

[0008] A method for controlling the holding torque of a stepper motor includes: a stepper motor driver IC connected to a first power supply, the first power supply providing a rated voltage to the motor; at least one of the power supply circuit and current limiting circuit of the stepper motor driver IC being connected to a current limiting unit; a stepper motor controller disabling the current limiting function of the current limiting unit, enabling the stepper motor driver IC to drive the stepper motor to start and operate normally with a rated current after receiving a motor start signal; and the stepper motor driver IC driving the stepper motor to stop operation after receiving a motor stop signal. Based on a set current limiting value and the rated voltage of the stepper motor, the stepper motor controller controls the current limiting unit to activate some or all of its current limiting functions. At this time, the stepper motor has a self-sustaining current that generates holding torque, the self-sustaining current being less than the rated current of the stepper motor.

[0009] The current limiting unit is at least one current limiting circuit, a power switching circuit, or a combination of the current limiting circuit and the power switching circuit. The current limiting circuit includes at least one current limiting element and a switching element. The switching element receives a control signal and controls the connection or disconnection of the current limiting element. The power switching circuit includes a power selection circuit and a switch control circuit. The power selection circuit includes at least one second power supply with a voltage lower than the first power supply voltage. The switch control circuit receives the control signal and switches the first power supply and the second power supply to the stepper motor driver IC. When the power selection circuit is switched to connect, the second power supply provides a self-sustaining current to the stepper motor.

[0010] A further embodiment is that the switching element is a transistor or a relay, with the input and output terminals of the transistor or the normally open contact of the relay connected in parallel with the current limiting element. When the stepper motor controller outputs the shielding control signal to the control terminal of the transistor or the coil of the relay, causing the transistor to conduct or the normally open contact of the relay to close, the two ends of the current limiting element are short-circuited, and the current flowing through it remains unchanged. When the stepper motor controller outputs the turn-on control signal to the control terminal of the transistor or the coil of the relay, causing the transistor to turn off or the normally open contact of the relay to open, the current flowing through the current limiting element decreases.

[0011] A further embodiment is that the switch control circuit includes a first diode, a second diode, a first switch, and a second switch, where the first switch and the second switch are both switching elements. The stepper motor driver IC is connected to the negative terminal of the first diode through the first switch, and the positive terminal of the first diode is connected to the first power supply. The stepper motor driver IC is connected to the negative terminal of the second diode through the second switch, and the positive terminal of the second diode is connected to the second power supply. The unidirectional conductivity of the diode is used to prevent the first power supply from flowing back into the second power supply.

[0012] Specifically, when the stepper motor controller outputs the shielding control signal to the first switch and the second switch, the first switch is turned on and the second switch is turned off, at which time the first power supply is connected and the second power supply is disconnected; when the stepper motor controller outputs the turn-on control signal to the first switch and the second switch, the first switch is turned off and the second switch is turned on, at which time the first power supply is disconnected and the second power supply is switched on.

[0013] A further embodiment is that the switch control circuit includes a first relay and a second relay. The stepper motor driver IC is connected to the first power supply through the normally open contact of the first relay, and the normally closed contact of the second relay is connected to the coil circuit of the first relay. The stepper motor driver IC is connected to the second power supply through the normally open contact of the second relay, and the normally closed contact of the first relay is connected to the coil circuit of the second relay. The relays form an interlock control circuit to prevent the first power supply and the second power supply from being connected at the same time.

[0014] Specifically, when the stepper motor controller outputs the shielding control signal to the first relay coil, the first relay coil is energized and the second relay coil is de-energized. The normally open contact of the first relay closes and the normally closed contact opens, while the normally closed contact of the second relay closes and the normally open contact opens. At this time, the first power supply is connected and the second power supply is disconnected. When the stepper motor controller outputs the start control signal to the second relay coil, the second relay coil is energized and the first relay coil is de-energized. The normally open contact of the second relay closes and the normally closed contact opens, while the normally closed contact of the first relay closes and the normally open contact opens. At this time, the first power supply is disconnected and the second power supply is connected.

[0015] A further embodiment is that the stepper motor driver IC is connected to the first power supply through the current limiting circuit, and the current limiting element is connected in series with the first power supply. When the stepper motor controller outputs the shielding control signal to the switching element, the current limiting element is short-circuited, and the first power supply directly supplies power. When the stepper motor controller outputs the turn-on control signal to the switching element, the current limiting element is connected to the first power supply, and the first current provides a self-sustaining current for the stepper motor after being limited by the current limiting element.

[0016] A further embodiment is that the stepper motor driver IC is directly connected to the first power supply, and its current limiting circuit is connected to the current limiting circuit. The current limiting element is connected in series to the current limiting circuit of the stepper motor driver IC. The current limiting circuit is a constant voltage circuit. When the stepper motor controller outputs the shielding control signal to the switching element, the current limiting element is short-circuited, and the current through the current limiting circuit remains unchanged. When the stepper motor controller outputs the turn-on control signal to the switching element, the current limiting element is connected to the current limiting circuit. The current in the current limiting circuit is further limited by the current limiting element to provide a self-sustaining current for the stepper motor.

[0017] A further solution is that the stepper motor driver IC is connected to a power switching circuit, and the second power supply voltage is higher than the low-voltage protection voltage of the stepper motor driver IC. The stepper motor driver IC is connected to the first power supply and the second power supply respectively through the switching element. When the stepper motor controller outputs the shielding control signal to the switching element, the first power supply is connected and the second power supply is disconnected; when the stepper motor controller outputs the turn-on control signal to the switching element, the first power supply is disconnected and switched to the second power supply, so that the current through the stepper motor is lower than the rated current, thereby achieving the purpose of current limiting.

[0018] A further embodiment is that the combined current limiting circuit of the current limiting circuit and the power switching circuit includes: the stepper motor driver IC is connected to the first power supply through the current limiting circuit and the power switching circuit; or the stepper motor driver IC is connected to the first power supply through the power switching circuit and its current limiting loop is connected to the current limiting circuit; or the stepper motor driver IC is connected to the first power supply through the current limiting circuit and the power switching circuit and its current limiting loop is connected to the current limiting circuit.

[0019] A stepper motor holding torque control system includes a stepper motor, a stepper motor driver IC, and a stepper motor controller. The stepper motor controller is connected to the control signal interface of the stepper motor driver IC and outputs electrical pulse signals to the stepper motor driver IC. The stepper motor driver IC drives the stepper motor to convert the electrical pulse signals into corresponding angular or linear displacements. This system is applied to the stepper motor holding torque control method. The system also includes a current limiting unit. The stepper motor driver IC is connected to a first power supply, which provides the stepper motor with a rated voltage. At least one of the power supply circuit and the current limiting circuit of the stepper motor driver IC is connected to the current limiting unit. The stepper motor controller controls the current limiting function of the current limiting unit to achieve a self-sustaining current less than the rated current when the stepper motor stops. This self-sustaining current is used to generate holding torque.

[0020] Therefore, the present invention has the following beneficial effects:

[0021] 1. This invention designs a current limiting unit with a simple circuit structure. When the motor stops, the current limiting unit is connected to the motor drive IC. Under the premise of meeting the motor holding torque, it provides a smaller self-sustaining current to the motor. This greatly reduces the heat generation and power consumption generated by the traditional motor holding torque control scheme based on rated voltage. Therefore, compared with the traditional motor holding torque control scheme, the motor loss can be greatly reduced and the service life can be extended.

[0022] 2. The current limiting unit circuit of the present invention has a simple structure and the components used can be flexibly selected according to actual needs. Compared with the traditional dedicated drive chip for controlling the stop current, its cost is very low, thus greatly improving economic efficiency.

[0023] 3. The current limiting unit provided by the present invention can be flexibly combined and applied according to actual needs through a variety of combined current limiting methods, and has wide applicability.

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the prior art motor driver IC driving the motor.

[0026] Figure 2 This is the flowchart of the stepper motor holding torque control method of the present invention. Figure 1 .

[0027] Figure 3 This is the flowchart of the stepper motor holding torque control method of the present invention. Figure 2 .

[0028] Figure 4 This is a circuit diagram of the current limiting circuit of the present invention connected to the power supply circuit of the driver IC.

[0029] Figure 5 This is a circuit diagram of the current limiting circuit of the present invention connected to the current limiting loop of the driver IC.

[0030] Figure 6 This is a circuit diagram of the power switching circuit of the present invention connected to the power circuit of the driver IC.

[0031] Figure 7 This is a schematic diagram of the combined current limiting circuit of the present invention connected to the power supply circuit of the driver IC. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] An embodiment of a stepper motor holding torque control method

[0034] See Figure 2 The present invention relates to a method for controlling the holding torque of a stepper motor, comprising:

[0035] S1: The stepper motor driver IC is connected to the first power supply, which provides the rated voltage to the motor. At least one of the power supply circuit and the current limiting circuit of the stepper motor driver IC is connected to the current limiting unit.

[0036] S2: The stepper motor controller controls the current limiting function of the current limiting unit to enable the stepper motor driver IC to start and operate normally with the rated current after the input motor start signal.

[0037] S3: After the input motor stop signal, the stepper motor driver IC drives the stepper motor to stop running. According to the set current limit value and the rated voltage of the stepper motor, the stepper motor controller controls the current limiting unit to enable part or all of the current limiting function. At this time, the stepper motor has a self-sustaining current that generates holding torque. The self-sustaining current is less than the rated current of the stepper motor.

[0038] See Figure 3 The current limiting unit is at least one current limiting circuit, a power switching circuit, or a combination of the current limiting circuit and the power switching circuit. The current limiting circuit includes at least one current limiting element and a switching element. The switching element receives a control signal and controls the connection or disconnection of the current limiting element. The power switching circuit includes a power selection circuit and a switch control circuit. The power selection circuit includes at least one second power supply with a voltage lower than the first power supply voltage. The switch control circuit receives the control signal and switches the first power supply and the second power supply to the stepper motor driver IC. When the power selection circuit is switched to connect, the second power supply provides a self-sustaining current to the stepper motor.

[0039] Specifically, in this embodiment, the first power supply is higher than the low voltage protection voltage of the stepper motor driver IC, and equal to or higher than the rated voltage of the stepper motor. When the first power supply is higher than the rated voltage of the stepper motor, the input current to the motor is made to be the rated current by connecting a current-limiting resistor in series in the power supply circuit.

[0040] As can be seen, by designing a current limiting unit with a simple circuit structure, this invention controls the current limiting unit to connect to the motor drive IC when the motor stops, providing a smaller self-sustaining current to the motor while meeting the motor holding torque requirements. This greatly reduces the heat generation and power consumption generated by the traditional method of using rated voltage as the motor holding torque. Therefore, compared with the traditional motor holding torque control scheme, it can greatly reduce motor losses and extend the service life.

[0041] In this embodiment, the switching element is a transistor or a relay. The input and output terminals of the transistor or the normally open contact of the relay are connected in parallel with the current limiting element. When the stepper motor controller outputs the shielding control signal to the control terminal of the transistor or the coil of the relay, causing the transistor to conduct or the normally open contact of the relay to close, the two ends of the current limiting element are short-circuited, and the current passing through it remains unchanged. When the stepper motor controller outputs the turn-on control signal to the control terminal of the transistor or the coil of the relay, causing the transistor to turn off or the normally open contact of the relay to open, the current passing through the current limiting element decreases.

[0042] Specifically, the description of the switching element as a transistor or relay in this embodiment is exemplary. Transistors or relays are commonly used control switches, but they do not cover all switching control devices or circuit structures. For example, the switching element can also be a small contactor, or a logic control element with switching control function, etc.

[0043] In this embodiment, the switch control circuit includes a first diode, a second diode, a first switch, and a second switch. The first switch and the second switch are both switching elements. The stepper motor driver IC is connected to the negative terminal of the first diode through the first switch, and the positive terminal of the first diode is connected to the first power supply. The stepper motor driver IC is connected to the negative terminal of the second diode through the second switch, and the positive terminal of the second diode is connected to the second power supply. The unidirectional conductivity of the diode is used to prevent the first power supply from flowing back into the second power supply.

[0044] Specifically, when the stepper motor controller outputs the shielding control signal to the first switch and the second switch, the first switch is turned on and the second switch is turned off, at which time the first power supply is connected and the second power supply is disconnected; when the stepper motor controller outputs the turn-on control signal to the first switch and the second switch, the first switch is turned off and the second switch is turned on, at which time the first power supply is disconnected and the second power supply is switched on.

[0045] Specifically, in this embodiment, the first switch and the second switch can be transistor-controlled switches. The two control output terminals of the stepper motor controller are respectively connected to the control terminals of the first switch and the second switch, and the controller controls the first switch or the second switch to conduct by outputting a high level / low level.

[0046] Specifically, if a relay is used as the switching element in this embodiment, the first switch and the second switch can be a set of normally open contacts and normally closed contacts of the relay. The relay output terminal of the stepper motor controller outputs a signal to the coil of the relay, and the first switch or the second switch is closed / opened by the coil being energized or de-energized.

[0047] In this embodiment, the switch control circuit includes a first relay and a second relay. The stepper motor driver IC is connected to the first power supply through the normally open contact of the first relay, and the normally closed contact of the second relay is connected to the coil circuit of the first relay. The stepper motor driver IC is connected to the second power supply through the normally open contact of the second relay, and the normally closed contact of the first relay is connected to the coil circuit of the second relay. The relays form an interlock control circuit to prevent the first power supply and the second power supply from being connected at the same time.

[0048] Specifically, when the stepper motor controller outputs the shielding control signal to the first relay coil, the first relay coil is energized and the second relay coil is de-energized. The normally open contact of the first relay closes and the normally closed contact opens, while the normally closed contact of the second relay closes and the normally open contact opens. At this time, the first power supply is connected and the second power supply is disconnected. When the stepper motor controller outputs the start control signal to the second relay coil, the second relay coil is energized and the first relay coil is de-energized. The normally open contact of the second relay closes and the normally closed contact opens, while the normally closed contact of the first relay closes and the normally open contact opens. At this time, the first power supply is disconnected and the second power supply is connected.

[0049] Specifically, this embodiment can be further extended based on the interlock control circuit described above, such as by adding switching elements to form a dual interlock control circuit.

[0050] See Figure 4In this embodiment, the stepper motor driver IC is connected to the first power supply VCM through the current limiting circuit. The current limiting element is connected in series with the first power supply VCM. When the stepper motor controller outputs the shielding control signal to the switching element, the current limiting element is short-circuited, and the first power supply VCM is directly powered. When the stepper motor controller outputs the turn-on control signal to the switching element, the current limiting element is connected to the first power supply VCM, and the first current provides a self-sustaining current for the stepper motor after being limited by the current limiting element.

[0051] Specifically, before the stepper motor is about to start, the control signal MT1VM_EN is set to a high level. At this time, the MOSFET is turned on, and the motor is powered by the first power supply VCM. After the motor stops, the control signal MT1VM_EN is immediately set to a low level. At this time, the MOSFET is turned off, and the first power supply VCM is connected to a current-limiting resistor to limit the current, thereby reducing the self-sustaining current of the motor.

[0052] See Figure 5 In this embodiment, the stepper motor driver IC is directly connected to the first power supply VCM, and its current limiting circuit is connected to the current limiting circuit. The current limiting element is connected in series to the current limiting circuit of the stepper motor driver IC. The current limiting circuit is a constant voltage. When the stepper motor controller outputs the shielding control signal to the switching element, the current limiting element is short-circuited, and the current through the current limiting circuit remains unchanged. When the stepper motor controller outputs the turn-on control signal to the switching element, the current limiting element is connected to the current limiting circuit. The current in the current limiting circuit is further limited by the current limiting element to provide a self-sustaining current for the stepper motor.

[0053] Specifically, in this embodiment, before the stepper motor is about to start, MT1VM_EN is set to a high level, and the two MOSFETs are turned on. At this time, only the rated current-limiting resistor is connected. (When calculating the current, it is necessary to consider whether to include the MOSFET on-resistance based on the size of the current-limiting resistor). After the motor stops, MT1VM_EM is immediately set to a low level, the MOSFETs are turned off, the current-limiting resistor increases, and the current through the motor decreases, thus achieving the purpose of current limiting.

[0054] See Figure 6In this embodiment, the stepper motor driver IC is connected to a power switching circuit. The voltage of the second power supply VCM1 is higher than the low-voltage protection voltage of the stepper motor driver IC. The stepper motor driver IC is connected to the first power supply VCM and the second power supply respectively through the switching element. When the stepper motor controller outputs the shielding control signal to the switching element, the first power supply VCM is connected and the second power supply is disconnected. When the stepper motor controller outputs the turn-on control signal to the switching element, the first power supply VCM is disconnected and the second power supply VCM1 is connected, so that the current through the stepper motor is lower than the rated current, thereby achieving the purpose of current limiting.

[0055] Specifically, in this embodiment, before the stepper motor is about to start, MT1VM_EN is set to a high level, the MOSFET is turned on, and the first power supply VCM supplies power to the driver IC. The motor runs at its rated current. Immediately after the motor stops, MT1VM_EN is set to a low level, the MOSFET is turned off, and the second power supply VCM1 becomes the motor drive power supply. Since the voltage does not reach the rated voltage, the motor current decreases, thereby achieving the purpose of reducing the motor current.

[0056] See Figure 3 In this embodiment, the combined current limiting circuit of the current limiting circuit and the power switching circuit includes: the stepper motor driver IC is connected to the first power supply through the current limiting circuit and the power switching circuit; or the stepper motor driver IC is connected to the first power supply through the power switching circuit and its current limiting loop is connected to the current limiting circuit; or the stepper motor driver IC is connected to the first power supply through the current limiting circuit and the power switching circuit and its current limiting loop is connected to the current limiting circuit.

[0057] As can be seen, the current limiting unit provided by the present invention can be flexibly combined and applied according to actual needs through a variety of combined current limiting methods, and has wide applicability.

[0058] See Figure 7 Specifically, in this embodiment, the stepper motor driver IC is connected to the first power supply VCM through the current limiting circuit and the power switching circuit, and its current limiting loop is connected to the current limiting circuit. The current limiting circuit of the power loop includes current limiting resistors R5 and R6, and switching elements S3 and S4. The power switching circuit includes the connected second power supply VCM1, anti-reverse current diodes connected in series with the first power supply and the second power supply, and switching elements S5 and S6. The current limiting circuit of the current limiting loop includes current limiting resistors R3 and R4, and switching elements S1 and S2. The stepper motor controller controls the shielding or connection of the current limiting circuit and the power switching circuit through multiple control signals. When only one control signal is used, the current limiting circuit and the power switching circuit are simultaneously shielded or connected.

[0059] An embodiment of a stepper motor holding torque control system

[0060] This invention relates to a stepper motor holding torque control system, comprising a stepper motor, a stepper motor driver IC, and a stepper motor controller. The stepper motor controller is connected to the control signal interface of the stepper motor driver IC and outputs electrical pulse signals to the stepper motor driver IC. The stepper motor driver IC drives the stepper motor to convert the electrical pulse signals into corresponding angular or linear displacements. Applied to the stepper motor holding torque control method, the system also includes a current limiting unit. The stepper motor driver IC is connected to a first power supply, which provides the stepper motor with a rated voltage. At least one of the power supply circuit and the current limiting circuit of the stepper motor driver IC is connected to the current limiting unit. The stepper motor controller controls the current limiting function of the current limiting unit to achieve a self-sustaining current less than the rated current when the stepper motor stops. This self-sustaining current is used to generate holding torque.

[0061] Specifically, the circuit structure of the current limiting unit described in this embodiment can be expanded according to actual current limiting needs. The control system connects multiple current limiting units to the motor drive IC according to the actual maximum current limiting needs to form a standardized control system. According to actual current limiting needs, the switching elements are controlled to connect to the required current limiting circuit.

[0062] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for controlling the holding torque of a stepper motor, characterized in that, include: A stepper motor driver IC is connected to a first power supply, which provides the motor with a rated voltage. At least one of the power supply circuit and the current limiting circuit of the stepper motor driver IC is connected to a current limiting unit. The stepper motor controller controls the current limiting function of the current limiting unit to be disabled, so that the stepper motor driver IC drives the stepper motor to start and run normally with the rated current after inputting a motor start signal. After inputting a motor stop signal, the stepper motor driver IC drives the stepper motor to stop running. According to the set current limiting value and the rated voltage of the stepper motor, the stepper motor controller controls the current limiting unit to enable part or all of the current limiting function. At this time, the stepper motor has a self-sustaining current that generates holding torque. The self-sustaining current is less than the rated current of the stepper motor. The current limiting unit is at least one current limiting circuit, a power switching circuit, or a combination of the current limiting circuit and the power switching circuit. The current limiting circuit includes at least one current limiting element and a switching element. The switching element receives a control signal and controls the connection or disconnection of the current limiting element. The power switching circuit includes a power selection circuit and a switch control circuit. The power selection circuit includes at least one second power supply with a voltage lower than the first power supply voltage. The switch control circuit receives the control signal and switches the first power supply and the second power supply to the stepper motor driver IC. When the power selection circuit is switched to connect, the second power supply provides a self-sustaining current to the stepper motor.

2. The stepper motor holding torque control method according to claim 1, characterized in that: The switching element is a transistor or a relay. The input or output terminal of the transistor or the normally open contact of the relay is connected in parallel with the current limiting element. When the stepper motor controller outputs a shielded control signal to the control terminal of the transistor or the coil of the relay, causing the transistor to conduct or the normally open contact of the relay to close, the two ends of the current limiting element are short-circuited, and the current passing through it remains unchanged. When the stepper motor controller outputs an on control signal to the control terminal of the transistor or the coil of the relay, causing the transistor to turn off or the normally open contact of the relay to open, the current passing through the current limiting element decreases.

3. The stepper motor holding torque control method according to claim 2, characterized in that: The switch control circuit includes a first diode, a second diode, a first switch, and a second switch. The first switch and the second switch are both switching elements. The stepper motor driver IC is connected to the negative terminal of the first diode through the first switch, and the positive terminal of the first diode is connected to the first power supply. The stepper motor driver IC is connected to the negative terminal of the second diode through the second switch, and the positive terminal of the second diode is connected to the second power supply. The unidirectional conductivity of the diode is used to prevent the first power supply from flowing back to the second power supply. Specifically, when the stepper motor controller outputs the shielding control signal to the first switch and the second switch, the first switch is turned on and the second switch is turned off, at which time the first power supply is connected and the second power supply is disconnected; when the stepper motor controller outputs the turn-on control signal to the first switch and the second switch, the first switch is turned off and the second switch is turned on, at which time the first power supply is disconnected and the second power supply is switched on.

4. The stepper motor holding torque control method according to claim 2, characterized in that: The switch control circuit includes a first relay and a second relay. The stepper motor driver IC is connected to the first power supply through the normally open contact of the first relay, and the normally closed contact of the second relay is connected to the coil circuit of the first relay. The stepper motor driver IC is connected to the second power supply through the normally open contact of the second relay, and the normally closed contact of the first relay is connected to the coil circuit of the second relay. The relays form an interlock control circuit to prevent the first power supply and the second power supply from being connected at the same time. Specifically, when the stepper motor controller outputs the shielding control signal to the first relay coil, the first relay coil is energized and the second relay coil is de-energized. The normally open contact of the first relay closes and the normally closed contact opens, while the normally closed contact of the second relay closes and the normally open contact opens. At this time, the first power supply is connected and the second power supply is disconnected. When the stepper motor controller outputs the start control signal to the second relay coil, the second relay coil is energized and the first relay coil is de-energized. The normally open contact of the second relay closes and the normally closed contact opens, while the normally closed contact of the first relay closes and the normally open contact opens. At this time, the first power supply is disconnected and the second power supply is connected.

5. The stepper motor holding torque control method according to claim 2, characterized in that: The stepper motor driver IC is connected to the first power supply through the current limiting circuit. The current limiting element is connected in series with the first power supply. When the stepper motor controller outputs the shielding control signal to the switching element, the current limiting element is short-circuited, and the first power supply directly supplies power. When the stepper motor controller outputs the turn-on control signal to the switching element, the current limiting element is connected to the first power supply, and the first power supply provides a self-sustaining current to the stepper motor after being current-limited by the current limiting element.

6. The stepper motor holding torque control method according to claim 2, characterized in that: The stepper motor driver IC is directly connected to the first power supply, and its current limiting circuit is connected to the current limiting circuit. The current limiting element is connected in series to the current limiting circuit of the stepper motor driver IC. The current limiting circuit is a constant voltage circuit. When the stepper motor controller outputs the shielding control signal to the switching element, the current limiting element is short-circuited, and the current through the current limiting circuit remains unchanged. When the stepper motor controller outputs the turn-on control signal to the switching element, the current limiting element is connected to the current limiting circuit. The current in the current limiting circuit is further limited by the current limiting element to provide a self-sustaining current for the stepper motor.

7. The stepper motor holding torque control method according to any one of claims 3 to 4, characterized in that: The stepper motor driver IC is connected to a power switching circuit. The second power supply voltage is higher than the low-voltage protection voltage of the stepper motor driver IC. The stepper motor driver IC is connected to the first power supply and the second power supply respectively through the switching element. When the stepper motor controller outputs the shielding control signal to the switching element, the first power supply is connected and the second power supply is disconnected. When the stepper motor controller outputs the turn-on control signal to the switching element, the first power supply is disconnected and the second power supply is connected, so that the current through the stepper motor is lower than the rated current, thereby achieving the purpose of current limiting.

8. The stepper motor holding torque control method according to any one of claims 5 to 7, characterized in that: The combined current limiting circuit of the current limiting circuit and the power switching circuit includes: the stepper motor driver IC is connected to the first power supply through the current limiting circuit and the power switching circuit; or the stepper motor driver IC is connected to the first power supply through the power switching circuit and its current limiting loop is connected to the current limiting circuit; or the stepper motor driver IC is connected to the first power supply through the current limiting circuit and the power switching circuit and its current limiting loop is connected to the current limiting circuit.

9. A control system for maintaining torque of a stepper motor, comprising a stepper motor, a stepper motor driver IC, and a stepper motor controller, wherein the stepper motor controller is connected to the control signal interface of the stepper motor driver IC and outputs electrical pulse signals to the stepper motor driver IC, and the stepper motor driver IC is used to drive the stepper motor to convert the electrical pulse signals into corresponding angular displacement or linear displacement, characterized in that, The method for controlling the holding torque of a stepper motor as described in any one of claims 1 to 8 further includes: The current limiting unit is provided. The stepper motor driver IC is connected to a first power supply, which provides the rated voltage to the stepper motor. At least one of the power supply circuit and the current limiting circuit of the stepper motor driver IC is connected to the current limiting unit. The stepper motor controller controls the current limiting function of the current limiting unit to achieve a self-sustaining current less than the rated current when the stepper motor stops. The self-sustaining current is used to generate holding torque.

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