Four-wheel robot motor starting control method based on low-resolution Hall sensor

Abstract

The invention discloses a four-wheel robot motor starting control method based on a low-resolution Hall sensor, and belongs to the technical field of motor driving and motion control. The invention particularly relates to a zero-speed starting method and device of a surface-mounted BLDC motor based on a low-resolution Hall sensor (120-degree electrical angle interval). The zero-speed starting method and device are suitable for four-wheel drive equipment such as an agricultural robot. According to the method, through Hall signal redundancy processing, back electromotive force modeling prediction and model adaptive compensation at zero speed, accurate estimation of the initial position of the motor is realized, so that stable starting is realized in heavy-load, low-speed and non-pavement environment such as agricultural robots. An expensive high-precision position sensor is not needed, and the method has the advantages of being low in cost, high in reliability and high in environment adaptability.

Description

Technical Field

[0001] This invention belongs to the field of motor drive and motion control technology, and particularly relates to a method for starting control of a four-wheeled robot motor based on a low-resolution Hall sensor. Background Technology

[0002] When agricultural robots operate on unpaved roads (such as dirt roads in greenhouses), they typically employ a four-wheel independent drive structure, with each wheel powered by a brushless DC motor driven by a sensorless or low-precision position sensor (such as a three-phase Hall effect sensor).

[0003] However, the 120° interval three-phase Hall sensors typically equipped with surface-mount BLDC motors only provide a 60° electrical angle resolution. This results in inaccurate angles during zero-speed or low-speed load starts, causing the motor to fail to output stable torque and easily lead to vibration, slippage, or even stalling. Existing methods, such as installing high-precision encoders or high-frequency injection, suffer from high costs, hardware complexity, or inapplicability. Therefore, a low-cost and reliable motor starting control scheme based on low-resolution Hall sensors is needed. Summary of the Invention

[0004] Purpose of the Invention: The purpose of this invention is to provide a motor start-up control method for a four-wheeled robot based on a low-resolution Hall sensor. Through staged control, angle interpolation, and progressive fusion, reliable zero-speed load start-up and low-speed operation of a heavy-duty four-wheeled robot on unpaved roads can be achieved.

[0005] Technical solution: The present invention provides a method for motor start-up control of a four-wheeled robot based on a low-resolution Hall sensor, comprising the following steps:

[0006] Step 1: Set up four surface-mount brushless DC motors on the robot to drive four drive wheels respectively, and collect position information through low-resolution Hall sensors. When the robot starts, select one drive wheel at a time to enter the start-up process, while the other three wheels remain in a short-circuit braking state.

[0007] Step 2: Select the drive wheel number, and apply the above current vector to each of the four drive wheels to achieve static alignment between the rotor flux direction and the stator flux direction, and establish a reference electrical angle;

[0008] Step 3: Under the current closed loop, advance along the electrical angle direction with a preset step size. By gradually increasing the q-axis current in the coordinate system, the motor can achieve smooth acceleration under load until the Hall edge signal is detected.

[0009] Step 4: In two adjacent Hall edge signals, time interpolation is performed using the edge period to predict the continuous electrical angle;

[0010] Step 5: When the motor speed reaches the set threshold, the back EMF observer is activated to obtain the angle estimate, and the estimated angle is weighted and fused with the Hall interpolation angle to obtain the fused speed.

[0011] Step 6: During normal operation, FOC control is performed using the observer angle;

[0012] Step 7: Set up three protections: slippage detection, stall, and overcurrent protection. When an abnormality is detected, reduce the output current or stop the start-up.

[0013] Furthermore, step 2 specifically involves: selecting drive wheel numbers as follows: By applying a fixed current vector in the stator coordinate system:

[0014]

[0015] in For alpha-axis current, For beta-axis current, Set to 0.4-0.6 times the rated phase current of the motor controller;

[0016] By applying the above current vectors to the four drive wheels respectively, the rotor flux linkage direction is statically aligned with the stator flux linkage, and a reference electrical angle is established. Specifically, a constant amplitude alignment current is applied along the stator alpha axis to cause the motor rotor to rotate to the flux linkage equilibrium position while stationary. At this point, the system reads the combined signal from the three-phase Hall sensors and records the corresponding electrical angle as the reference electrical angle zero point, which is used as the starting reference for subsequent open-loop propulsion and angle interpolation.

[0017] Furthermore, step 3 specifically involves: under current closed-loop control, adjusting the current along the electrical angle direction in preset step sizes. The propulsion, electrical angle command is:

[0018] ,

[0019] in, For the control cycle of the motor, and at the same time In a coordinate system, the injected command current is:

[0020] ,

[0021] in and They are respectively shaft and shaft current, The gradually increasing first-order inertial rising function is expressed as:

[0022]

[0023] Representing the time constant, by gradually increasing the q-axis current, the motor achieves smooth acceleration under load until the first Hall edge signal is detected. .

[0024] Furthermore, step 4 specifically involves: using the edge period to perform time interpolation between two adjacent Hall edge signals to predict the continuous electrical angle.

[0025]

[0026] The motor moves at a constant speed between two consecutive Hall effect edges. This indicates the time between the previous two consecutive Hall effect edges. Indicates the current time. This indicates the time of the last Hall edge triggering, and the estimated electrical angular velocity is:

[0027] .

[0028] Furthermore, step 5 specifically involves: when the motor speed reaches a set threshold... At that time, the back potential observer is activated to obtain the angle estimate. and interpolation with Hall The fusion speed is obtained by weighting the angles together.

[0029] i f u s e d = ( 1 − α ) i ^ H a l l + α i o b s , α ∈ [ 0 , 1 ] ,

[0030] in Weighting coefficients:

[0031] ,

[0032] in The fusion bandwidth constant, The current electrical angular velocity of the motor. The electric angular velocity gradually increases with the current velocity, causing the fusion velocity to gradually transition to the observer angle. .

[0033] Furthermore, step 6 specifically involves: during the normal operation phase, using the observer angle... Perform FOC control:

[0034] ,

[0035] ,

[0036] in, and They are respectively shaft and The proportional unit coefficient in the PI controller of the shaft. and They are respectively shaft and Integral unit coefficients in the PI controller. and They are respectively shaft and Sampled value of shaft current. and They are respectively shaft and Commanded value of shaft current. Set it to 0, and It is controlled by a speed loop PI regulator.

[0037] Furthermore, step 7 specifically involves setting up three protection mechanisms: slippage detection, stall detection, and overcurrent protection. When an abnormality is detected, the output current is reduced or the start-up is aborted. The specific judgment is as follows:

[0038] Stall protection: if the electric angular velocity ,and And the duration is greater than the threshold. If the system is stalled, the starting procedure will be terminated and the system will enter a recoverable fault mode.

[0039] Slip detection: If This reduces the output command current. ;

[0040] Overcurrent protection: If If the startup procedure is terminated immediately, the system will enter a recoverable fault mode.

[0041] The present invention also discloses a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method of the present invention.

[0042] The present invention also discloses a computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implements the steps of the method of the present invention.

[0043] The present invention also discloses a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the method of the present invention.

[0044] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0045] 1. This invention achieves accurate estimation of the initial position of the motor through Hall signal redundancy processing at zero speed, back EMF modeling and prediction, and adaptive model compensation, thereby enabling smooth starting in heavy-load, low-speed, unpaved road environments such as agricultural robots. This invention eliminates the need for expensive high-precision position sensors, offering advantages such as low cost, high reliability, and strong environmental adaptability.

[0046] 2. This invention eliminates the need for expensive precision encoders, achieving reliable zero-speed load start-up solely through three-phase Hall effect sensors. The "sequential wheel start + high-rigidity holding of other wheels" strategy prevents the entire vehicle from lifting or veering off course.

[0047] 3. This invention employs a "Hall interpolation + progressive fusion" method to achieve a smooth transition from low to medium-high speeds, avoiding torque jumps. This can improve the start-up success rate and operational stability of agricultural robots on complex unpaved roads. Attached Figure Description

[0048] Figure 1 This is the control flowchart of the present invention. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0050] The following description uses a four-wheeled agricultural robot as an example, along with accompanying drawings, to further illustrate the specific implementation of the invention. The robot has a total mass of 160 kg and operates on unpaved roads (dirt roads inside greenhouses). The robot employs four independently driven hub motors, each a surface-mount brushless DC motor (SBLDC, Ld≈Lq), with a pole pair number of... Rated current Rated speed Rated torque It is equipped with a planetary gear carrier reducer with a reduction ratio of 1:5. The position sensor is a three-phase 120° spaced Hall element, corresponding to a resolution of 60° electrical angle.

[0051] First execute Figure 1 In the static alignment phase (S0), when the robot is stationary and a start command is issued, the front left wheel motor is selected first to enter the start-up process, while the other three wheels maintain short-circuit braking (equivalent to high-rigidity holding) to prevent the vehicle from veering off course or drifting during start-up. First, a constant alignment current is applied to the left front wheel on the stator alpha shaft. The size is set to 0.4 times the rated current: Alignment duration At this point, the rotor flux linkage and the stator flux linkage establish a reference direction. This serves as the initial angle for subsequent open-loop acceleration. After applying a specified current command to the front left wheel, the system switches to short-circuit braking, and then sequentially aligns the initial angles of all four wheels. This sequential starting strategy ensures balanced force distribution across the vehicle, preventing starting failures caused by simultaneous wheel vibration or stalling.

[0052] After all wheels are aligned at rest, the system enters the open-loop micro-step acceleration phase (S0→S1). Motor acceleration is achieved using an open-loop angular propulsion method. The electric angle advance step size is specified for each step. Set as motor current loop control frequency of This is a multiple, meaning an increase of 5 degrees of electrical angle per second. Simultaneously, it gradually increases... The shaft current is used to generate accelerating torque, and the current reference value adopts a first-order inertial rising function:

[0053] .

[0054] During this stage, the motor can smoothly overcome static friction and rolling resistance under load, achieving low-speed acceleration until the first Hall edge signal is detected.

[0055] When a Hall edge is detected, the Hall time interpolation angle estimation stage (S1) begins. This utilizes the time interval between two adjacent Hall edges. Perform linear interpolation to calculate the angle:

[0056] i ^ ( t ) = i k + t − t k T h ⋅ 6 0 ° , t ∈ [ t k , t k + 1 ] ,

[0057] At this stage, the following measures are adopted: As the angle input for FOC control, as the motor speed gradually increases, the edge interval time shortens, the angle estimation error decreases, and the system smoothly enters medium-low speed operation.

[0058] When the motor speed reaches 100 rpm, it enters the gradual fusion switching phase (S2). At this time, the sliding mode back EMF observer is activated to obtain the estimated angle. Interpolation angle with Hall Perform weighted fusion:

[0059] ,

[0060] in, This refers to the motor speed. This is the fusion cutoff frequency. As the speed increases, the observer weight gradually increases, eventually switching completely to the observer angle.

[0061] During normal operation, FOC control is performed using the observer angle, and the electromagnetic torque is:

[0062] ,

[0063] in , .exist At that time, the motor output torque is approximately This is sufficient to drive the robot to start smoothly. During this stage, the speed loop operates in closed loops, ensuring that the entire vehicle follows the speed command.

[0064] Experiments have verified that this method can stably drive the robot to start at zero speed with load, avoiding the jitter and step loss problems caused by traditional 120° Hall direct commutation. The starting success rate exceeds 98%, and it shows good robustness on unpaved dirt roads and gravel mixed roads.

Claims

1. A method for motor starting control of a four-wheeled robot based on a low-resolution Hall sensor, characterized in that, Includes the following steps: Step 1: Set up four surface-mount brushless DC motors on the robot to drive four drive wheels respectively, and collect position information through low-resolution Hall sensors. When the robot starts, select one drive wheel at a time to enter the start-up process, while the other three wheels remain in a short-circuit braking state. Step 2: Select the drive wheel number, and apply the above current vector to each of the four drive wheels to achieve static alignment between the rotor flux direction and the stator flux direction, and establish a reference electrical angle; Step 3: Under the current closed loop, advance along the electrical angle direction with a preset step size. By gradually increasing the q-axis current in the coordinate system, the motor can achieve smooth acceleration under load until the Hall edge signal is detected. Step 4: In two adjacent Hall edge signals, time interpolation is performed using the edge period to predict the continuous electrical angle; Step 5: When the motor speed reaches the set threshold, the back EMF observer is activated to obtain the angle estimate, and the estimated angle is weighted and fused with the Hall interpolation angle to obtain the fused speed. Step 6: During normal operation, FOC control is performed using the observer angle; Step 7: Set up three protections: slippage detection, stall, and overcurrent protection. When an abnormality is detected, reduce the output current or stop the start-up.

2. The method for motor starting control of a four-wheeled robot based on a low-resolution Hall sensor according to claim 1, characterized in that, Step 2 specifically involves selecting the drive wheel number as follows: By applying a fixed current vector in the stator coordinate system: in For alpha-axis current, For beta-axis current, Set to 0.4-0.6 times the rated phase current of the motor controller; By applying the above current vectors to the four drive wheels respectively, the rotor flux linkage direction is statically aligned with the stator flux linkage, and a reference electrical angle is established. Specifically, by applying a constant current in the alpha axis direction of the stator, the rotor flux tends to stabilize, and the electrical angle corresponding to the Hall state at this time is read as the reference electrical angle zero point for subsequent control.

3. The method for motor starting control of a four-wheeled robot based on a low-resolution Hall sensor according to claim 1, characterized in that, Step 3 specifically involves: under current closed-loop control, adjusting the current along the electrical angle direction with a preset step size. The propulsion, electrical angle command is: ； in, For the control cycle of the motor, and at the same time In a coordinate system, the injected command current is: ； in and They are respectively shaft and shaft current, The gradually increasing first-order inertial rising function is expressed as: ； Representing the time constant, by gradually increasing the q-axis current, the motor achieves smooth acceleration under load until the first Hall edge signal is detected. .

4. The method for motor starting control of a four-wheeled robot based on a low-resolution Hall sensor according to claim 1, characterized in that, Step 4 specifically involves: using the edge period to perform time interpolation between two adjacent Hall edge signals to predict the continuous electrical angle. ； In this context, it is assumed that the motor's motion is uniform between two consecutive Hall effect edges. This indicates the time between the previous two consecutive Hall edges. Indicates the current time. This indicates the time of the last Hall edge triggering, and the estimated electrical angular velocity is: 。 5. The method for motor starting control of a four-wheeled robot based on a low-resolution Hall sensor according to claim 1, characterized in that, Step 5 specifically involves: when the motor speed reaches the set threshold... At that time, the back potential observer is activated to obtain the angle estimate. and interpolation with Hall The fusion speed is obtained by weighting the angles together. ； in Weighting coefficients: ； in The fusion bandwidth constant, The current electrical angular velocity of the motor. It increases with the current electric angular velocity, causing the fusion velocity to transition to the observer angle. .

6. The method for motor starting control of a four-wheeled robot based on a low-resolution Hall sensor according to claim 1, characterized in that, Step 6 specifically involves: during normal operation, using the observer angle... Perform FOC control: ； ； in, and They are respectively shaft and The proportional unit coefficient in the PI controller of the shaft. and They are respectively shaft and Integral unit coefficients in the PI controller. and They are respectively shaft and Sampled value of shaft current. and They are respectively shaft and Commanded value of shaft current. Set it to 0, and It is controlled by a speed loop PI regulator.

7. The method for motor starting control of a four-wheeled robot based on a low-resolution Hall sensor according to claim 1, characterized in that, Step 7 specifically involves setting up three protection mechanisms: slippage detection, stall detection, and overcurrent protection. When an abnormality is detected, the output current is reduced or the start-up is aborted. The specific judgment is as follows: Stall protection: if the electric angular velocity ,and And the duration is greater than the threshold. If the system is stalled, the starting procedure will be terminated and the system will enter a recoverable fault mode. Slip detection: If This reduces the output command current. ; Overcurrent protection: If If the startup procedure is terminated immediately, the system will enter a recoverable fault mode.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method of claim 1.

9. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method of claim 1.

10. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method of claim 1.

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