Closed-loop control motor-driven ball screw reciprocating pump and control method

Abstract

The invention relates to the technical field of reciprocation pump control, in particular to a closed-loop control motor-driven ball screw reciprocation pump and a control method, and the closed-loop control motor-driven ball screw reciprocation pump is mainly characterized in that an outlet of a fluid end module is connected with a pressure sensor; the pressure sensor, the motor controller, the rotary transformer and the position sensor are electrically connected with the central controller, the central controller is used for outputting a control signal enabling the driving motor to rotate to the motor controller, and the motor controller is used for controlling the driving motor to operate. According to the scheme, a brake is removed, the defects caused by the brake are avoided, in the prior art, no matter whether a brake pad is abraded or the inertia problem of the brake exists, a brake system cannot be achieved in the industry of the reciprocating pump at all, and in the reciprocating pump, the brake pad is not abraded. The speed, the position and the thrust of the reciprocating pump device are accurately controlled in a full-digital manner through the central controller, so that the ball screw reciprocating pump with the structure achieves the purpose of industrial use in the industry.

Description

Technical Field

[0001] The present invention relates to the technical field of equipment control, and in particular to a closed-loop controlled motor-driven ball screw reciprocating pump and a control method thereof. Background Art

[0002] Traditional reciprocating pumps use a crank-connecting rod structure to drive a piston or plunger, achieving reciprocating motion through several strokes. The existing technology has improved this by using the rotational motion of a motor to achieve the reciprocating motion of a screw. Specifically, referring to CN112503153A, there is disclosed a device and method for achieving reciprocating motion of a fracturing pump by rotating a screw nut. The device includes a brake B, a gear B, a gear C, a screw nut B, a motor, and a screw B. The gear C is connected to the power output end of the motor, the gear C is meshed with the gear B, the screw nut B is sleeved on the screw B, the gear B is sleeved on the screw nut B, and the brake B cooperates with the screw nut B. The device achieves reciprocating motion of the fracturing pump by rotating the screw nut. The above scheme reduces the moment of inertia during reversing, and when the drive is at a constant speed, the reversing shock is small.

[0003] In practice, the above solution uses brakes to slow down the vehicle and then reverse the rotation. However, this method is difficult to implement in actual use because under the conditions of large inertia and high speed, it is difficult for the analog-controlled brake to accurately control the movement position. In addition, the brake will inevitably wear and heat up under the action of friction, resulting in an increased failure rate and the need for regular maintenance. On the other hand, the brake structure is too bulky and occupies a large space. There is a certain response time when working, that is, there is a delay. Since the reciprocating pump requires the brake to be repeatedly started and stopped, it puts a heavy burden on the mechanical device and the accumulated position deviation is large. Summary of the Invention

[0004] The object of the present invention is to provide a closed-loop controlled motor driven ball screw reciprocating pump and a control method thereof to solve the above-mentioned problems in the prior art.

[0005] The present invention is achieved through the following technical solutions: In a first aspect, a closed-loop controlled motor-driven ball screw reciprocating pump includes several drive modules connected to a hydraulic end module, the drive modules including a position sensor, a central controller, a power unit, and a transmission unit. The power unit is connected to the hydraulic end module via the transmission unit and is used to drive the transmission unit to perform reciprocating motion. The outlet of the hydraulic end module is connected to a pressure sensor, and the position sensor is used to collect position data of the transmission unit. The power unit includes a motor controller, a gear set, a drive motor, a ball screw, and a rotary transformer. The pressure sensor, motor controller, rotary transformer and position sensor are electrically connected to the central controller. The central controller is used to output a control signal to the motor controller to rotate the drive motor. The motor controller is used to control the operation of the drive motor. The drive motor is connected to the ball screw through a gear set, and one end of the ball screw is connected to the transmission unit.

[0006] Preferably, the gear set includes a first gear, a second gear and two third gears, the first gear is connected to the output end of the drive motor and is meshed with the second gear, the second gear is rotatably connected to the bearing seat via a rotating shaft and is meshed with only one of the third gears, and the two third gears are meshed; The ball screw includes a screw rod, a screw nut and a ball. The third gear is fixedly connected to the screw nut. The screw rod is located in the screw nut. A threaded raceway is provided in the screw nut. Balls are provided in the threaded raceway. The screw nut drives the screw rod to perform linear reciprocating motion through the ball, thereby converting the rotational motion of the motor into linear reciprocating motion of the screw rod.

[0007] Preferably, the transmission unit includes a plunger sleeve and a plunger, one end of the plunger is connected to the screw rod, and the other end is located in the plunger sleeve and moves.

[0008] In a second aspect, the present invention further provides a closed-loop control method for controlling a motor-driven ball screw reciprocating pump, comprising a closed-loop control method for controlling a motor-driven ball screw reciprocating pump as described above, wherein the central controller is configured to output a control signal for rotating the drive motor to the motor controller, comprising: After receiving the power-on signal of the device, the screws on the same side of each group of drive modules are set as target screws, the position data of the target screws are obtained, and the position difference threshold and error threshold between adjacent target screws are set; Based on the position data, the position difference threshold and the error threshold, it is determined whether the position difference condition is met between the two target screw rods. If the position difference condition is met, the target displacement is obtained to calculate the motor speed, and the calculated motor speed value is sent to the motor controller of each drive motor; If the position difference condition is not met, the adjustment value is obtained, the target screw of one of the drive modules is selected as the reference screw, and the motor controller outputs a control signal to adjust the position of the other screw based on the adjustment value.

[0009] Preferably, the calculating of the motor speed includes:

[0010] Where, is the displacement of a single pump group, is the total displacement of the system, is the plunger radius, is the lead of the screw, is the motor speed, m is the number of screw rods, is the transmission ratio of the gear set.

[0011] Where, is the target displacement of the pump, is the plunger radius, is the lead of the screw, is the number of strokes per minute, is the motor speed, is the transmission ratio of the gear set.

[0012] Preferably, it also includes: The current real-time speed of the motor is obtained through the rotary transformer, and the current displacement of the hydraulic end module is obtained at the same time, and the difference between the current displacement and the target displacement is calculated; The motor speed for the next cycle is calculated based on the difference.

[0013] Preferably, the driving motors are provided in groups i, and calculating the rotational speeds of the motors in groups i includes: When i=1:

[0014] When i is greater than 1: When the motors in group i are in the acceleration section or the constant speed section:

[0015] When the motors in group i are in the deceleration stage:

[0016] in, ; Where, 、 、…、 is the speed of the next cycle of the 1st to i-th drive motor, 、 、…、 For each reciprocating motion, the predicted speed value of the current position in the position-speed control mode, is the benchmark parameter for speed adjustment, is the position difference threshold between the target screw rod and the reference screw rod in the i-th group, is the position difference between the first target screw and the i-th target screw, 、 、…、 is the PID control proportional gain of the 1st to i-th drive motors, is the difference between the speed of the kth cycle and the target speed, For the first drive motor PID control integral gain, is the sampling period, the time interval between two controller calculations and outputs, is the position data of the i-th screw rod, is the position data of the reference screw, is the current operating cycle number of the reference screw, is the current operating cycle number of the i-th screw, is the total stroke of the screw at one end.

[0017] Preferably, it also includes: The first pump pressure of the current hydraulic end module is obtained through the pressure sensor, the torque value of the current motor is obtained through the motor controller, and the current theoretical second pump pressure is calculated based on the torque value; Setting a safety pump pressure threshold, obtaining a first difference between the first pump pressure and the safety pump pressure threshold, and obtaining a second difference between the second pump pressure and the safety pump pressure threshold; And set several judgment thresholds, and output the current diagnosis result through the first difference, the second difference and the several judgment thresholds.

[0018] Preferably, the outputting of the current diagnosis result by using the first difference, the second difference and a plurality of judgment thresholds includes: Setting a first pump pressure threshold, a second pump pressure threshold, and a third pump pressure threshold; Determine whether the first difference is greater than or equal to the third pump pressure threshold, or whether the second difference is greater than or equal to the third pump pressure threshold, and if so, send a control signal for emergency shutdown of the system; If not, determine whether the first difference is greater than or equal to the second pump pressure threshold, or whether the second difference is greater than or equal to the second pump pressure threshold. If so, provide a control signal for deceleration and constant pressure; If not, determine whether the first difference is greater than or equal to the second pump pressure threshold, or whether the second difference is greater than or equal to the second pump pressure threshold. If so, send an alarm signal. If not, the system operates normally.

[0019] Preferably, the control signal output by the motor controller to adjust the position of other screw rods based on the adjustment value includes: After the position adjustment of the remaining screw rods is completed, the position data of the target screw rod on the same side is obtained again to obtain the position difference data. If the position difference conditions are met, the target displacement is obtained to calculate the motor speed. If the position difference conditions are not met within the operating cycle or the preset time period, a fault signal is sent to the central controller.

[0020] The technical solution of the present invention has at least the following advantages and beneficial effects: The above structure provided by the present invention mainly includes a pressure sensor connected to the outlet of the hydraulic end module; the pressure sensor, motor controller, rotary transformer and position sensor are electrically connected to the central controller, and the central controller is used to output a control signal to rotate the drive motor to the motor controller, and the motor controller is used to control the operation of the drive motor. The above solution eliminates the brake and avoids the disadvantages brought by the brake. In the prior art, whether it is the wear of the brake pads or the problem of brake inertia, the brake system will not be able to be implemented in the industry of reciprocating pumps at all. In the present invention, the speed, position and thrust of the reciprocating pump device are precisely controlled by the central controller in full digitalization, so that the ball screw reciprocating pump of this structure can achieve the purpose of industrial use in industry. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 Schematic diagram of the system structure of the present invention; Figure 2 This is a schematic diagram of the control flow of the central controller of the present invention; Figure 3 Schematic diagram of the structure of the power unit of the present invention; Figure 4 It is a structural schematic diagram of the plunger sleeve of the present invention; Figure 5 It is a schematic diagram of the overall structure of the present invention.

[0022] Icon: 1-drive motor, 2-rotating transformer, 3-screw, 4-ball, 5-screw nut, 6-third gear, 7-second gear, 8-first gear, 9-plunger, 10-plunger sleeve, 11-hydraulic end module, 12-power unit. DETAILED DESCRIPTION

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0024] The division of modules in this application is a logical division. In actual application, there may be other division methods. For example, multiple modules can be combined or integrated into another system, or some features can be ignored or not executed.

[0025] In addition, the connection, coupling or communication in this application may be a direct connection, coupling or communication between related objects, or an indirect connection, coupling or communication through other devices. In addition, the connection, coupling or communication between objects may be electrical or other similar forms, which are not limited in this application.

[0026] Please refer to Figure 1-Figure 5 The present invention provides a closed-loop control motor-driven ball screw reciprocating pump, comprising a plurality of drive modules connected to a hydraulic end module 11, wherein the drive modules include a position sensor, a central controller, a power unit 12, and a transmission unit. The power unit 12 is connected to the hydraulic end module 11 via the transmission unit. The power unit 12 is used to drive the transmission unit to perform reciprocating motion. The outlet of the hydraulic end module 11 is connected to a pressure sensor. The position sensor is used to collect position data of the transmission unit. The position sensor is provided on the transmission unit and can be mounted on a plunger to measure the travel distance of the plunger. The hydraulic end module includes conventional structures such as a cylinder body and a cylinder sleeve, a suction valve and a discharge valve, and a sealing device, which will not be described in detail in this embodiment.

[0027] The power unit 12 includes a motor controller, a gear set, a drive motor 1, a ball screw, and a rotary transformer 2. The pressure sensor, motor controller, rotary transformer 2 and position sensor are electrically connected to the central controller. The central controller is used to output a control signal to the motor controller to rotate the drive motor 1. The motor controller is used to control the operation of the drive motor 1. The drive motor 1 is connected to the screw rod 3 through a gear set, and one end of the screw rod 3 is connected to the transmission unit.

[0028] Specifically, the central controller: reads the data from each sensor, reads the drive motor 1 and motor controller parameters fed back by the three drive motors 1, sends control commands to the three motor controllers, calculates the speed and position related to the screw and motor, and performs other related logic processing and data processing.

[0029] Resolver 2: Coaxially mounted on the motor shaft, used for reading the motor position and calculating the motor speed. Motor controller: The motor controller is mainly used to control the position, torque, speed, and acceleration of the drive motor 1, receive control commands from the central controller, and at the same time feedback relevant parameters of the motor controller body (such as temperature, fault, etc.) and the speed, position, and torque of the drive motor 1.

[0030] Position sensor: used for screw position correction and safety stroke protection, and provides feedback to the central controller. One sensor is configured for each screw group.

[0031] Pressure sensor: used to detect the liquid pressure at the output terminal of the reciprocating pump.

[0032] The above structure provided by the present invention mainly includes the outlet of the hydraulic end module 11 being connected to a pressure sensor; the pressure sensor, the motor controller, the rotary transformer 2, and the position sensor being electrically connected to the central controller, the central controller being used to output a control signal to the motor controller for rotating the drive motor 1, and the motor controller being used to control the operation of the drive motor 1. The above solution eliminates the brake, thus avoiding the disadvantages of the brake. In the prior art, both the wear of the brake pads and the inertia of the brake would make the brake system impossible to implement in the industrial application of reciprocating pumps. In the present invention, the speed, position, and thrust of the reciprocating pump device are precisely controlled by the central controller in a fully digital manner, so that the ball screw reciprocating pump of this structure can achieve the purpose of industrial application.

[0033] In an exemplary embodiment of the present invention, the gear set includes a first gear 8, a second gear 7, and two third gears 6. The first gear 8 is connected to the output end of the drive motor 1 and is meshed with the second gear 7. The second gear 7 is rotatably connected to the bearing seat via a rotating shaft and is meshed with only one of the third gears 6. The two third gears 6 are meshed. The ball screw includes a screw rod 3, a screw nut 5 and a ball 4. The third gear 6 is fixedly connected to the screw nut 5. The screw rod 3 is located in the screw nut 5. A threaded raceway is provided in the screw nut 5. The screw nut 5 drives the screw rod 3 to perform linear reciprocating motion through the ball 4, converting the rotational motion of the drive motor 1 into linear reciprocating motion of the screw rod 3.

[0034] In an exemplary embodiment of the present invention, the transmission unit includes a plunger sleeve 10 and a plunger 9 . One end of the plunger 9 is connected to the screw rod 3 , and the other end is located in the plunger sleeve 10 and moves.

[0035] When in use, the two third gears 6 form a pair of forward and reverse rotations, thereby pushing the plunger 9 to perform reciprocating pumping. The operation of the reciprocating pump is realized by converting the rotary motion of the driving motor 1 into the linear reciprocating motion of the screw rod 3 through this device.

[0036] In a second aspect, the present invention further provides a closed-loop control method for controlling a motor-driven ball screw reciprocating pump, comprising a closed-loop control method for controlling a motor-driven ball screw reciprocating pump as described above, wherein the central controller is configured to output a control signal for rotating the drive motor to the motor controller, comprising: S101: After receiving a power-on signal from the device, the lead screws on the same side of each group of drive modules are set as target lead screws, position data of the target lead screws is obtained, and a position difference threshold and an error threshold between adjacent target lead screws are set; It is understandable that in the same drive module, there are two sets of screw rods. When comparing and calculating the position difference, the screw rods on the same side are used, for example, the position data of the screw rods on the left side of the same drive module are used for subsequent calculations.

[0037] S102: Determine whether the current position difference condition between the two target screws is met based on the position data, the position difference threshold, and the error threshold. If the position difference condition is met, obtain the target displacement and calculate the motor speed, and send the calculated motor speed value to the motor controller of each drive motor; Specifically, the screw in the first drive module is set as the reference screw to determine whether the other screws meet the position difference conditions; Next, consider current position conversion: Because the screw reciprocates, the same position exists in both the forward and reverse directions. For ease of understanding and calculation, assume the motor rotates clockwise, with the screw position being 0->L; if the motor rotates counterclockwise, the screw position is L->2L. L is the total travel of the screw at one end.

[0038]

[0039] Where, is the position difference between the i-th target screw and the reference screw, is the position data of the i-th screw rod, is the position data of the reference screw, is the position difference threshold between the target screw rod and the reference screw rod in the i-th group, is the current operating cycle number of the reference screw, is the current operating cycle number of the i-th screw, is the total stroke of the screw at one end.

[0040] when If the error is less than or equal to the error threshold, the output meets the position difference condition; otherwise, it does not meet the position difference condition.

[0041] S103: If the position difference condition is not met, an adjustment value is obtained, a target screw of one of the drive modules is selected as a reference screw, and a control signal is output to the motor controller to adjust the position of the other screws based on the adjustment value.

[0042] Specifically, the central controller sends the calculated positions of the 2# screw group and the 3# screw group to be adjusted and the preset motor speed (for example, 20 rpm) to the 2# drive motor controller and the 3# drive motor controller respectively.

[0043] After receiving the control instruction, the 2# drive motor controller and the 3# drive motor controller control the drive motors to run to their respective target positions at a preset motor speed.

[0044] The 2# and 3# drive motor controllers each cycle detect whether their respective motors are in position. If so, they send feedback instructions to the central controller, which then checks the lead screw position again to see if it is correct. If the lead screw position is correct, the next level of logic control is added.

[0045] If the 2# drive motor controller and the 3# drive motor controller do not run to the target position within the preset limit time (for example: 30000ms), a super fault is sent and the fault is also transmitted to the central controller.

[0046] In an exemplary embodiment of the present invention, the calculating of the motor speed includes:

[0047] Where, is the displacement of a single pump group, is the total displacement of the system, is the plunger radius, is the lead of the screw, is the motor speed, m is the number of screw rods, is the transmission ratio of the gear set.

[0048] Preferably, it also includes: The current real-time speed of the motor is obtained through the rotary transformer, and the current displacement of the hydraulic end module is obtained at the same time, and the difference between the current displacement and the target displacement is calculated. Among them, the current displacement of the hydraulic end module can be calculated by the current speed of the motor or obtained through a sensor.

[0049] The motor speed for the next cycle is calculated based on the difference.

[0050] In an exemplary embodiment of the present invention, the drive motors are provided in groups i, and calculating the rotational speed of the motors in the groups i includes: When i=1:

[0051] When i is greater than 1: When the motors in group i are in the acceleration section or the constant speed section:

[0052] When the motors in group i are in the deceleration stage:

[0053] in, ; It should be noted that the calculation of absolute values is removed here. The purpose is that the positive and negative values represent whether the vehicle is ahead or behind, which is related to the above speed PID adjustment.

[0054] Where, 、 、…、 is the speed of the next cycle of the 1st to i-th drive motor, 、 、…、 The predicted speed value of the current position in the position-speed control mode for each reciprocating motion, where the position-speed control mode is the corresponding data collected from the historical data. is the benchmark parameter for speed adjustment, is the position difference threshold between the target screw rod and the reference screw rod in the i-th group, is the position difference between the i-th target screw and the reference screw, 、 、…、 is the PID control proportional gain of the 1st to i-th drive motors, is the difference between the speed of the kth cycle and the target speed, For the first drive motor PID control integral gain, is the sampling period, the time interval between two controller calculations and outputs, is the position data of the i-th screw rod, is the position data of the reference screw, is the current operating cycle number of the reference screw, is the current operating cycle number of the i-th screw, is the total stroke of the screw at one end.

[0055] An exemplary embodiment of the present invention further includes: The first pump pressure of the current hydraulic end module is obtained through the pressure sensor, the torque value of the current motor is obtained through the motor controller, and the current theoretical second pump pressure is calculated based on the torque value; Setting a safety pump pressure threshold, obtaining a first difference between the first pump pressure and the safety pump pressure threshold, and obtaining a second difference between the second pump pressure and the safety pump pressure threshold; And set several judgment thresholds, and output the current diagnosis result through the first difference, the second difference and the several judgment thresholds.

[0056] Specifically, outputting the current diagnosis result through the first difference, the second difference, and a plurality of judgment thresholds includes: Setting a first pump pressure threshold, a second pump pressure threshold, and a third pump pressure threshold; Determine whether the first difference is greater than or equal to the third pump pressure threshold, or whether the second difference is greater than or equal to the third pump pressure threshold, and if so, send a control signal for emergency shutdown of the system; If not, determine whether the first difference is greater than or equal to the second pump pressure threshold, or whether the second difference is greater than or equal to the second pump pressure threshold. If so, provide a control signal for deceleration and constant pressure; If not, determine whether the first difference is greater than or equal to the second pump pressure threshold, or whether the second difference is greater than or equal to the second pump pressure threshold. If so, send an alarm signal. If not, the system operates normally.

[0057] In addition, the control signals output by the motor controller to adjust the positions of other lead screws based on the adjustment value include: After the position adjustment of the remaining screw rods is completed, the position data of the target screw rod on the same side is obtained again to obtain the position difference data. If the position difference conditions are met, the target displacement is obtained to calculate the motor speed. If the position difference conditions are not met within the operating cycle or the preset time period, a fault signal is sent to the central controller.

[0058] The closed-loop control system provided by the present invention is primarily composed of a central controller, a motor controller, a drive motor, a rotary transformer, a position sensor, and a pressure sensor. The pressure sensor acquires the current first pump pressure of the hydraulic end module, while the central controller issues speed, acceleration, torque, and position commands, as well as real-time calculation and correction instructions. The motor controller executes the central controller's commands, controls the drive motor, and provides feedback on the execution results. The drive motor executes the motor controller's commands and operates. The rotary transformer is coaxial with the drive motor, providing real-time feedback on the drive motor's speed, acceleration, and rotational position. The position sensor accurately detects and provides feedback on the starting point of the screw rod's movement. Based on the feedback from the rotary transformer and position sensor, the central controller and motor controller perform real-time calculations and correction instructions to form a closed-loop control system, ensuring stable overall operation, balanced pressure, and smooth commutation of the reciprocating pump.

[0059] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0060] If the integrated unit is implemented as a software functional unit and sold or used as a standalone product, it can be stored on a computer-readable storage medium. This computer software product, stored on a storage medium, includes instructions for causing a computer device (which may be a personal computer, server, or network device, etc.) to perform all or part of the steps of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0061] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A closed-loop controlled motor driven ball screw reciprocating pump, comprising a plurality of drive modules connected to a hydraulic end module, characterized in that: The drive module includes a position sensor, a central controller, a power unit and a transmission unit. The power unit is connected to the hydraulic end module through the transmission unit. The power unit is used to drive the transmission unit to reciprocate. The outlet of the hydraulic end module is connected to a pressure sensor. The position sensor is used to collect position data of the transmission unit. The power unit includes a motor controller, a gear set, a drive motor, a ball screw, and a rotary transformer. The pressure sensor, motor controller, rotary transformer and position sensor are electrically connected to the central controller. The central controller is used to output a control signal to the motor controller to rotate the drive motor. The motor controller is used to control the operation of the drive motor. The drive motor is connected to the ball screw through a gear set, and one end of the ball screw is connected to the transmission unit.

2. A closed-loop controlled motor driven ball screw reciprocating pump according to claim 1, characterized in that: The gear set includes a first gear, a second gear and two third gears, the first gear is connected to the output end of the drive motor and is meshed with the second gear, the second gear is rotatably connected to the bearing seat via a rotating shaft and is meshed with only one of the third gears, and the two third gears are meshed; The ball screw includes a screw rod, a screw nut and a ball. The third gear is fixedly connected to the screw nut. The screw rod is located in the screw nut. A threaded raceway is provided in the screw nut. Balls are provided in the threaded raceway. The screw nut drives the screw rod to perform linear reciprocating motion through the ball, thereby converting the rotational motion of the drive motor into linear reciprocating motion of the screw rod.

3. A closed-loop controlled motor driven ball screw reciprocating pump according to claim 1, characterized in that: The transmission unit includes a plunger sleeve and a plunger, one end of the plunger is connected to the screw rod, and the other end is located in the plunger sleeve and moves.

4. A closed-loop control method for a motor-driven ball screw reciprocating pump, characterized in that: The closed-loop controlled motor-driven ball screw reciprocating pump according to any one of claims 1 to 3, wherein the central controller is configured to output a control signal causing the drive motor to rotate to the motor controller, comprising: After receiving the power-on signal of the device, the screws on the same side of each group of drive modules are set as target screws, the position data of the target screws are obtained, and the position difference threshold and error threshold between adjacent target screws are set; Based on the position data, the position difference threshold and the error threshold, it is determined whether the position difference condition is met between the two target screw rods. If the position difference condition is met, the target displacement is obtained to calculate the motor speed, and the calculated motor speed value is sent to the motor controller of each drive motor; If the position difference condition is not met, the adjustment value is obtained, the target screw of one of the drive modules is selected as the reference screw, and the motor controller outputs a control signal to adjust the position of the other screw based on the adjustment value.

5. A closed-loop control method for a motor-driven ball screw reciprocating pump according to any one of claim 4, characterized in that: The motor speed calculation comprises: Where, is the displacement of a single pump group, is the total displacement of the system, is the plunger radius, is the lead of the screw, is the motor speed, m is the number of screw rods, is the transmission ratio of the gear set.

6. A closed-loop control method for a motor-driven ball screw reciprocating pump according to any one of claim 5, characterized in that: Also includes: The current real-time speed of the motor is obtained through the rotary transformer, and the current displacement of the hydraulic end module is obtained at the same time, and the difference between the current displacement and the target displacement is calculated; The motor speed for the next cycle is calculated based on the difference.

7. A closed-loop control method for a motor-driven ball screw reciprocating pump according to any one of claim 6, characterized in that: The drive motors are provided in groups i, and calculating the rotational speed of the motors in group i includes: When i=1: When i is greater than 1: When the motors in group i are in the acceleration section or the constant speed section: When the i-th group of motors is in the deceleration stage: in, ; Where, 、 、…、 is the speed of the next cycle of the 1st to i-th drive motor, 、 、…、 For each reciprocating motion, the predicted speed value of the current position in the historical data, is the benchmark parameter for speed adjustment, is the position difference threshold between the target screw rod and the reference screw rod in the i-th group, is the position difference between the i-th target screw and the reference screw, 、 、…、 is the PID control proportional gain of the 1st to i-th drive motors, is the difference between the speed of the kth cycle and the target speed, For the first drive motor PID control integral gain, is the sampling period, the time interval between two controller calculations and outputs, is the position data of the i-th screw rod, is the position data of the reference screw, is the current operating cycle number of the reference screw, is the current operating cycle number of the i-th screw, is the total stroke of the screw at one end.

8. A closed-loop control method for a motor-driven ball screw reciprocating pump according to any one of claim 7, characterized in that: Also includes: The first pump pressure of the current hydraulic end module is obtained through the pressure sensor, the torque value of all the current motors is obtained through the motor controller, and the current theoretical second pump pressure is calculated based on the torque value; Setting a safety pump pressure threshold, obtaining a first difference between the first pump pressure and the safety pump pressure threshold, and obtaining a second difference between the second pump pressure and the safety pump pressure threshold; And set several judgment thresholds, and output the current diagnosis result through the first difference, the second difference and the several judgment thresholds.

9. A closed-loop control method for a motor-driven ball screw reciprocating pump according to any one of claim 7, characterized in that: Outputting the current diagnosis result by using the first difference, the second difference and a plurality of judgment thresholds includes: Setting a first pump pressure threshold, a second pump pressure threshold, and a third pump pressure threshold; Determine whether the first difference is greater than or equal to the third pump pressure threshold, or whether the second difference is greater than or equal to the third pump pressure threshold, and if so, send a control signal for emergency shutdown of the system; If not, determine whether the first difference is greater than or equal to the second pump pressure threshold, or whether the second difference is greater than or equal to the second pump pressure threshold. If so, provide a control signal for deceleration and constant pressure; If not, determine whether the first difference is greater than or equal to the second pump pressure threshold, or whether the second difference is greater than or equal to the second pump pressure threshold. If so, send an alarm signal. If not, the system operates normally.

10. A closed-loop control method for a motor-driven ball screw reciprocating pump according to claim 4, characterized in that: The control signal output by the motor controller to adjust the position of other screw rods based on the adjustment value includes: After the position adjustment of the remaining screw rods is completed, the position data of the target screw rod on the same side is obtained again to obtain the position difference data. If the position difference conditions are met, the target displacement is obtained to calculate the motor speed. If the position difference conditions are not met within the operating cycle or the preset time period, a fault signal is sent to the central controller.

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