Large-torque output stepping motor cascade control method

Abstract

The invention belongs to the technical field of stepping motor control, and particularly relates to a cascade control method for a large-torque output stepping motor. Comprising a stepping motor 1, a stepping motor 2, a precession mechanism, a controller and a torque sensor, rotating shafts extend out of the two sides of the stepping motor 1, transmission friction plates are installed on the rotating shafts at the tail of the stepping motor 1, an output shaft at one end of the stepping motor 1 is connected with a load, and the torque sensor is installed on the output shaft. A rotating shaft of the stepping motor 2 is provided with a transmission friction plate, the transmission friction plate of the stepping motor 2 is meshed with a transmission friction plate, away from the load, of the stepping motor 1, and the controller is connected with the precession mechanism, the stepping motor 1, the stepping motor 2 and the torque sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of stepper motor control, and more specifically, relates to a cascade control method for a large torque output stepper motor. Background Art

[0002] The stepper motor system can provide precise speed and angle control, and provide various levels of torque, and is widely used in many fields such as measurement and control, engineering machinery, CNC equipment, and robotics. High-torque stepper motors have a broad market in mining, machinery manufacturing, and other fields.

[0003] High-torque stepper motors have complex structures, large volume and mass, and high prices, which restrict their wide application. Low-power stepper motors have advantages such as simple structure, small volume and mass, and low price, but their small torque output capacity cannot be used in the field of high torque. It can be seen from the torque-speed curve of the stepper motor that to improve the torque output capacity of the stepper motor, it can be achieved by reducing the speed of the stepper motor, but the stepper motor has an extreme value (maximum value) of torque output, which cannot be increased indefinitely, and when the speed of the stepper motor is reduced, there is a risk of vibration or resonance caused by overlapping with the natural frequency of the stepper motor. There are few theories and practices for increasing the torque of the stepper motor system by cascading low-torque stepper motors, and it is still in its infancy. The limited solutions for stepper motor cascading generally adopt the solution of rigid connection of the stepper motor output shaft. The disadvantage is that it cannot provide the stepper motor system with real-time incorporation or disconnection of the stepper motor that needs to increase torque under load conditions. Only when the stepper motor is stopped can the rigid connection part be engaged, which cannot meet the real-time requirements of engineering applications. When multiple stepper motors are combined into a system, the drive current, PWM frequency and other parameters of each stepper motor need to be adjusted according to the number of stepper motors and the load size. When adjusting the PWM frequency, the natural frequency of the stepper motor system should also be considered to avoid co-frequency or overlap with it, so as to prevent system vibration and resonance. Signal transmission is generally only done by wired transmission. When the system is in a strong electromagnetic environment, the anti-interference and reliability of the signal, especially the control signal and sensor signal transmission, should be considered. Such problems should be solved through optoelectronic isolation, wireless communication and other methods. Summary of the invention

[0004] To solve the problem that low-torque stepper motors cannot provide high torque, multiple low-torque stepper motors can be integrated in a cascaded manner to increase the output torque of the stepper motor system. When adjusting the PWM frequency of the stepper motor system, it is necessary to avoid overlapping with the system's inherent frequency to prevent vibration and resonance. Signal transmission should use multiple modes such as photoelectric isolation, wireless communication, and wired communication as much as possible to improve reliability and accuracy.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A cascade control method for a large torque output stepper motor, comprising a stepper motor 1, a stepper motor 2, a precession mechanism, a controller and a torque sensor, wherein rotating shafts are extended from both sides of the stepper motor 1, and transmission friction plates are installed on the rotating shafts at the tail of the stepper motor 1, an output shaft at one end of the stepper motor 1 is connected to a load, and a torque sensor is installed on the output shaft, a transmission friction plate is installed on the rotating shaft of the stepper motor 2, and the transmission friction plate of the stepper motor 2 is meshed with the transmission friction plate of the stepper motor 1 away from the load, and the controller is connected to the precession mechanism, the stepper motor 1, the stepper motor 2 and the torque sensor;

[0007] When the load torque P measured by the torque sensor is greater than the maximum torque output P of a single stepper motor max When

[0008] P≥P max (1)

[0009] At this time, the stepper motor controller reads the value of the torque measurement sensor and determines that equation (1) is established. The controller will send a command to the precession mechanism under the stepper motor 2 to move a fixed step length, so as to achieve engagement with the transmission friction plate of the front stepper motor 1. At the same time, the controller starts to send the same PWM rotation control signal to the stepper motor 2 as that of the stepper motor 1, so as to achieve synchronous rotation of the two stepper motors, and then achieve synchronous output of torque.

[0010] The technical solution is further optimized in that the material of the friction plate is a paper-based friction material, a resin-based friction material, a carbon fiber friction material or a semi-metallic friction material.

[0011] The technical solution is further optimized in that the precession mechanism is fixedly connected to the stepper motor 2, and the precession mechanism is driven by a servo motor driving a planetary reducer, which in turn drives a rack and pinion pair.

[0012] Further optimization of this technical solution also includes assuming that the natural frequency of the stepper motor is f g , it is necessary to control the PWM frequency of the controller output to avoid f g , to ensure that the stepper motor system does not vibrate or resonate, set the PWM frequency to f PWM , then

[0013] f PWM =a·f g ,a≥2.5 (3).

[0014] The technical solution is further optimized in that the controller is connected to the torque sensor wirelessly.

[0015] In a further optimization of the technical solution, the wireless is Wifi, zigbee or Bluetooth.

[0016] Different from the prior art, the above technical solution has the following beneficial effects:

[0017] 1. The stepper motors are cascaded through controllable transmission friction plates to multiply the torque of the stepper motor system; the cascaded stepper motors are controlled by the same PWM to achieve rotation synchronization and torque output synchronization between the stepper motors; the driving current of each stepper motor is reduced, power consumption is reduced, and reliability is improved.

[0018] 2. By controlling the PWM frequency, the natural frequency of the stepper motor can be avoided to avoid system vibration and resonance.

[0019] 3. By using both wired and wireless methods to transmit torque sensor signals, the accuracy of signal transmission can be ensured by judging the differences or errors between the two. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of cascade stepper motor system. DETAILED DESCRIPTION

[0021] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0022] 1. Cascade stepper motors to build a high-torque stepper motor system.

[0023] The high torque stepper motor has complex structure, large size and mass, high price and other problems, which restrict its wide application. Through the transmission friction plate between two or more stepper motors, the stepper motor body precession control (friction plate meshing control), and the use of the same PWM for synchronous control of multiple stepper motors, the purpose of theoretically doubling the torque of the cascade stepper motor can be achieved. The system is as follows Figure 1 As shown, it includes a stepper motor 1, a stepper motor 2, a precession mechanism, a controller and a torque sensor. The stepper motor 1 has rotating shafts extending from both sides, and a transmission friction plate is installed on the rotating shaft at the tail of the stepper motor 1. The output shaft at one end of the stepper motor 1 is connected to the load, and a torque sensor is installed on it. The transmission friction plate is installed on the rotating shaft of the stepper motor 2, and the transmission friction plate of the stepper motor 2 is meshed with the transmission friction plate of the stepper motor 1 away from the load. The controller is connected to the precession mechanism, the stepper motor 1, the stepper motor 2 and the torque sensor. Specifically, there are the following three aspects.

[0024] a) There are rotating shafts extending from both sides of the stepper motor, and a transmission friction plate is installed on the shaft at the tail of the stepper motor 1. The material of the friction plate can be paper-based friction material, resin-based friction material, carbon fiber friction material, semi-metallic friction material, etc. Through the meshing of two transmission friction plates, the torque of multiple stepper motors can be coaxially output, thereby improving the torque output capacity of the stepper motor system. If the energy loss of the friction plate is ignored, the torque output value of the cascade stepper motor system should be equal to the sum of the output torques of each stepper motor.

[0025] b) The engagement of the transmission friction plates between the stepper motors relies on the precession mechanism that is fixed to the stepper motor 2 body. The precession mechanism is driven by a servo motor driving a planetary reducer, which in turn drives a gear rack pair; or it is moved by a servo motor through a planetary reducer, a ball screw, etc. The action of the precession mechanism is given by the stepper motor controller. The specific process is: a torque measurement sensor is installed on the output shaft of the cascade stepper motor system. When the measured load torque P is greater than the maximum torque output P of a single stepper motor, the precession mechanism is driven by a planetary reducer, a ball screw, etc. max When

[0026] P≥P max (1)

[0027] At this time, the stepper motor controller reads the value of the torque measurement sensor and determines that equation (1) is true. The controller will send a command to the precession mechanism under stepper motor 2 to move a fixed step length, so as to achieve engagement with the transmission friction plate of stepper motor 1. At the same time, the stepper motor controller starts to send the same PWM rotation control signal to stepper motor 2 as stepper motor 1, so as to achieve synchronous rotation of the two stepper motors and thus synchronous output of torque.

[0028] c) For the case of two stepper motors in cascade, the system's torque output capacity is doubled. In order to reduce the power consumption, heat generation and electromagnetic environment interference of a single stepper motor, the drive current of a single stepper motor should be reduced. At this time, stepper motor 1 and stepper motor 2 have equal drive currents:

[0029]

[0030] Where I1 is the driving current of stepper motor 1, I2 is the driving current of stepper motor 2, P is the actual load torque of the system, K t is the motor constant (or the torque constant of the motor).

[0031] 2. In order to increase the torque output capacity of the stepper motor, the stepper motor will increase the torque by reducing the speed. When the speed of the stepper motor is reduced, it may approach or overlap with the natural frequency of the stepper motor, which will cause vibration or resonance of the stepper motor. Assume that the natural frequency of the stepper motor is f g, it is necessary to control the PWM frequency of the controller output to avoid f g , to ensure that the stepper motor system does not vibrate or resonate, set the PWM frequency to f PWM , then

[0032] f PWM =a·f g ,a≥2.5 (3)

[0033] 3. The working areas of stepper motor cascade systems and high-torque stepper motor systems often have strong electromagnetic field interference. The transmission of sensitive and high-precision signals needs to consider the reliability of signal transmission. Wireless signal transmission can overcome electromagnetic interference very well, but its real-time performance and reliability are not as good as those of wired transmission. Wired signal transmission has better real-time performance, but is susceptible to electromagnetic interference. The present invention uses both wireless and wired methods to transmit torque sensor signals, wherein the wireless method uses Wifi, zigbee, Bluetooth and other technologies. Assume that the torque value obtained by the stepper motor controller wirelessly is P wireless , the torque value obtained by wired method is P wire , theoretically the two should be equal, that is:

[0034] P wireless =P wire (4)

[0035] If the wired or wireless transmission is an analog signal, an error threshold ε is set. When the error between the two is less than ε, the stepper motor controller adopts the transmission value, that is:

[0036] |P wireless -P wire |≤ε (5)

[0037] The torque combination between the stepper motors of the present invention is achieved by the meshing of the transmission friction plate; the cascaded stepper motors are controlled by the same PWM to achieve the rotation synchronization and torque output synchronization between the stepper motors. The torque sensor signal is transmitted by wired and wireless methods at the same time, and the difference or error between the two is judged to ensure the accuracy of signal transmission.

[0038] The problem that a single small-torque stepper motor cannot provide large torque is solved, and the torque output capacity of the stepper motor system is improved through cascading.

[0039] By controlling the PWM frequency, the vibration and resonance problems of the stepper motor system can be eliminated or suppressed; by using simultaneous wired and wireless transmission, the reliability and accuracy of signal transmission in complex electromagnetic environments can be ensured.

[0040] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or terminal device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of further restrictions, the elements defined by the sentence "include..." or "comprise..." do not exclude the existence of other elements in the process, method, article or terminal device including the elements. In addition, in this article, "greater than", "less than", "exceed" and the like are understood to exclude the number itself; "above", "below", "within" and the like are understood to include the number itself.

[0041] Although the above embodiments have been described, once those skilled in the art know the basic creative concepts, they can make additional changes and modifications to these embodiments. Therefore, the above description is only an embodiment of the present invention and does not limit the patent protection scope of the present invention. All equivalent structures or equivalent process changes made using the contents of the present invention specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A cascade control method for a high torque output stepper motor, characterized in that: It includes a stepper motor 1, a stepper motor 2, a precession mechanism, a controller and a torque sensor. Rotating shafts are extended from both sides of the stepper motor 1. Transmission friction plates are installed on the rotating shafts at the tail of the stepper motor 1. An output shaft at one end of the stepper motor 1 is connected to a load, on which a torque sensor is installed. A transmission friction plate is installed on the rotating shaft of the stepper motor 2. The transmission friction plate of the stepper motor 2 is meshed with the transmission friction plate of the stepper motor 1 away from the load. The controller is connected to the precession mechanism, the stepper motor 1, the stepper motor 2 and the torque sensor. When the load torque P measured by the torque sensor is greater than the maximum torque output P of a single stepper motor max When P≥P max (1) At this time, the stepper motor controller reads the value of the torque measurement sensor and determines that equation (1) is established. The controller will send a command to the precession mechanism under the stepper motor 2 to move a fixed step length, so as to achieve engagement with the transmission friction plate of the front stepper motor 1. At the same time, the controller starts to send the same PWM rotation control signal to the stepper motor 2 as that of the stepper motor 1, so as to achieve synchronous rotation of the two stepper motors, and then achieve synchronous output of torque.

2. The high torque output stepper motor cascade control method according to claim 1, characterized in that: The friction plate is made of paper-based friction material, resin-based friction material, carbon fiber friction material or semi-metal friction material.

3. The high torque output stepper motor cascade control method according to claim 1, characterized in that: The precession mechanism is fixedly connected to the stepper motor 2, and the precession mechanism is driven by a servo motor driving a planetary reducer, which in turn drives a rack and pinion pair.

4. The high torque output stepper motor cascade control method according to claim 1, characterized in that: It also includes the assumption that the natural frequency of the stepper motor is f g , it is necessary to control the PWM frequency of the controller output to avoid f g , to ensure that the stepper motor system does not vibrate or resonate, set the PWM frequency to f PWM , then f PWM =a•f g ,a≥2.5 (3)。 5. The high torque output stepper motor cascade control method according to claim 1, characterized in that: The controller is connected to the torque sensor in a wireless manner.

6. The high torque output stepper motor cascade control method according to claim 5, characterized in that: The wireless is Wifi, zigbee or Bluetooth.

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