Fault-tolerant control method for unmanned aerial vehicle electric brake system pressure sensor failure

Abstract

The application discloses a fault-tolerant control method for an unmanned aerial vehicle electric brake system pressure sensor failure, comprising: performing a self-check, recording the brake pressure value, brake motor rotor position angle and brake motor rotor corresponding steering during the self-checking process; when the brake control system receives a pressure sensor fault signal, the rotor of the brake motor is quickly retreated to the idle stroke gap during the self-checking to ensure the release pressure; the brake motor is controlled to rotate forward, and the motor control current during the self-checking is used to stably increase the motor rotor position to the corresponding pressure value according to the brake pressure given value and the motor rotor position angle during the self-checking; the current is maintained to keep the rotor position from falling. When the pressure drop process needs to be followed, the rotor of the brake motor must be retreated to the position with zero idle stroke pressure during the self-checking, then the value of the motor rotor position angle corresponding to the new pressure given value is found again, and the brake motor is controlled to rotate forward to the new given value.

Description

Technical Field

[0001] This invention belongs to the field of unmanned aerial vehicle (UAV) electric braking technology, specifically relating to a fault-tolerant control method for a UAV electric braking system when the pressure sensor fails. Background Technology

[0002] The pressure sensor is the sole basis for responding to braking system commands. If the pressure sensor fails, the braking output will become uncontrollable, posing a significant safety hazard to the aircraft.

[0003] The main difficulties in fault-tolerant control when pressure sensors fail are: (1) Although the braking pressure and the current of the brake motor are generally proportional, this proportional relationship becomes unusable in the control process due to the severe hysteresis nonlinearity of the brake caliper and brake disc. (2) In the electric braking system, there is a motor rotor position sensor, and there is also a corresponding proportional relationship between the rotor position and the pressure. However, due to the severe hysteresis nonlinearity of the brake caliper and brake disc, coupled with the deformation caused by the small stiffness coefficients of the motor shaft and the reducer shaft system, this proportional relationship cannot represent the braking force, and therefore cannot be used as the basis for pressure control. Summary of the Invention

[0004] To address the challenges of fault-tolerant control when pressure sensors fail, this invention employs a pre-braking self-test method to obtain the curve of actual brake pressure rise versus brake motor rotor angle, thereby achieving fault tolerance for the pressure sensor. Furthermore, the fault-tolerant control strategy is divided into two different strategies: one for rising pressure and the other for falling pressure.

[0005] To achieve the above objectives, the present invention specifically adopts the following technical solution.

[0006] A fault-tolerant control method is provided for the failure of a pressure sensor in an unmanned aerial vehicle (UAV) electric braking system, including: When the electric braking system is powered on, the electric braking system performs an automatic self-test. The method requires increasing the brake pressure from zero value during the no-travel period to the maximum value required for braking, and records the brake pressure value, the corresponding brake motor rotor position angle value, and the corresponding direction of rotation of the brake motor rotor during the self-test process. When the brake control system receives a pressure sensor fault signal, it controls the rotor of the brake motor to quickly retract to the empty stroke gap during self-test to ensure pressure release. The brake motor is controlled to rotate in the forward direction with pressure. Based on the given brake pressure value and the corresponding rotor position angle during self-test, the motor current is reduced to a small current value that keeps the motor stable and does not rotate after it reaches the position. The small control current that keeps the motor stable during self-test is used to steadily increase the rotor position of the motor to the corresponding pressure value. Maintain the motor control current to prevent the motor rotor position from dropping.

[0007] As a further explanation of the present invention, the automatic self-test process specifically includes: When the self-test begins, the brake motor receives a control command and rotates forward to push the brake pads on the brake caliper against the brake disc. If the brake pads have not yet pressed against the brake disc and are in the free stroke position, the rotor of the brake motor rotates through a certain angle. During the free stroke phase, if the pressure sensor output is not zero, the pressure value is considered as zero-point drift. If the brake motor continues to apply pressure and the pressure value begins to increase, it indicates that the brake pads have pressed against the brake disc. The position angle of the motor rotor where the brake pads and the brake disc just touch is defined as the zero position. The brake motor continues to apply pressure to the maximum pressure value required for braking, so that fault-tolerant control of any required pressure can be achieved in case of failure. The brake pressure value and the curve value corresponding to the rotor position angle of the brake motor are recorded. After recording, the brake motor is retracted to a suitable free travel clearance, and the self-test is completed.

[0008] As a further explanation of the present invention, the statement that the pressure value is identified as zero-point drift means that the pressure value is forcibly identified as zero.

[0009] As a further explanation of the present invention, the definition of the position angle of the motor rotor where the brake pad and the brake disc just touch is the zero position, specifically: The rotor position angle of the motor is determined by a Hall sensor. The brake control system records the Hall sensor count value corresponding to the zero position and identifies the Hall sensor count value as a relative zero value. That is, a value greater than the relative zero value is a positive angle value, and a value less than the relative zero value is a negative angle value.

[0010] As a further explanation of the present invention, the step of controlling the brake motor to rotate in the forward direction under pressure, and reducing the motor current to a small current value that maintains the motor's stability and prevents it from rotating after reaching the set brake pressure value and the corresponding motor rotor position angle during self-test, using the small control current that keeps the motor from rotating during self-test to stably increase the motor rotor position to the corresponding pressure value, specifically includes: Control the brake motor to rotate forward and increase it to the zero position; then, based on the curve corresponding to the brake pressure value and the rotor position angle of the brake motor recorded by the self-test, find the value of the rotor position angle of the motor corresponding to the pressure setpoint, and stably increase the rotor position of the motor at the pressure value corresponding to the pressure rise.

[0011] As a further explanation of the present invention, when the fault-tolerant control method needs to follow the pressure drop process, the rotor of the brake motor must be retracted to the motor position where the empty stroke pressure is zero during self-test. Then, the value of the motor rotor position angle corresponding to the new pressure setpoint is found again, and the brake motor is controlled to rotate forward to the new setpoint. This achieves tracking when the pressure value is less than the original setpoint, and the current closed loop maintains the motor rotor position unchanged.

[0012] As a further explanation of the present invention, the pressure sensor acquires the pressure on the brake wheel through a pressure feedback signal acquisition circuit, and outputs a fault signal of the pressure sensor through a fault detection circuit.

[0013] Compared with the prior art, the present invention has the following advantages: (1) The present invention obtains the curve of actual braking pressure rise and motor rotor angle by means of self-testing method before braking, thereby realizing the fault tolerance of pressure sensor.

[0014] (2) The fault-tolerant control strategy of the present invention is divided into two different strategies: the increase and the decrease of the pressure given.

[0015] (3) The present invention uses a method to achieve pressure accuracy tracking by stabilizing the rotor position and minimizing overshoot. Attached Figure Description

[0016] Figure 1 This is a curve showing the pressure and motor position angle generated during the self-test process before braking in one embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the pressure control process maintained by a self-test curve when the pressure sensor fails, according to one embodiment of the present invention. Implementation

[0018] 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 embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a fault-tolerant control method for a UAV electric braking system when the pressure sensor fails, comprising the following steps: Step 1: Pre-braking self-check. Record the pressure value, motor rotor position angle, and corresponding direction of rotation of the motor rotor during the self-check process. Specifically: When the electric braking system is powered on, it performs an automatic self-test (this method must increase the pressure from zero during the no-travel phase to the maximum pressure required for braking, ensuring fault-tolerant control throughout the braking pressure process, i.e., fault-tolerant control of any required pressure in case of a fault). At the start of the self-test, the motor receives a control command and rotates forward, pushing the brake pads on the brake caliper against the brake disc. If the brake pads have not yet pressed against the brake disc, i.e., in the no-travel position, the motor rotor rotates a certain angle during this phase. During the no-travel phase, the pressure sensor value should be "zero." If the pressure sensor output is not zero, this pressure value is considered zero-point drift, i.e., it is forcibly considered "zero." The motor continues to apply pressure. Once the pressure sensor value begins to increase, it indicates that the brake pads have pressed against the brake disc, and the position where the brake pads and brake disc just touch is defined as the "zero" position on the motor rotor. (For example, the motor rotor position angle is measured using a Hall sensor. The Hall sensor count value is recorded, and this value is considered a relative "zero" value; values ​​greater than this relative "zero" value are considered positive angles, and values ​​less than this relative "zero" value are considered negative angles.) The motor is then pressurized to the maximum pressure required for braking, allowing for fault-tolerant control at any required pressure in case of a fault. The pressure value and the curve value corresponding to the motor position angle are recorded. After recording, the motor is retracted, the brake pressure is released, and the motor returns to the appropriate "free travel clearance." The self-test is then complete. Figure 1 As shown. It should be noted that the pressure rise and pressure fall are represented by different curves; normal braking uses pressure control via a closed-loop braking pressure system.

[0020] Step 2: When the brake control system receives a pressure sensor fault signal, it controls the motor pressure to decrease, causing the motor rotor to quickly retract to the self-test travel clearance, ensuring pressure release. Then, it starts rotating the motor forward, increasing to the "zero" motor position. Based on the pressure curve recorded during the self-test process in Step 1, it finds the corresponding motor rotor position angle value based on the pressure setpoint, such as... Figure 2 As shown, a small control current is used to keep the motor stationary during self-testing, and the position of the brake motor rotor is stably increased and controlled at the corresponding pressure value when the pressure rises, ensuring that there is no overshoot and maintaining the accuracy of pressure control.

[0021] Step 3: Maintain the motor control current to prevent the motor rotor position from dropping.

[0022] It is also important to note that: The above-described fault-tolerant control method ensures that even if the pressure sensor fails, the brake pressure will continue to rise to the given value and will follow the command to continue rising, but it cannot follow the command to decrease the pressure. When it is necessary to follow the pressure increase, the Hall value of the motor rotor position corresponding to the pressure value is found during self-test, the current is increased to make the rotor rotate to that value, and the current closed loop is entered to maintain the rotor position.

[0023] If we want to follow the pressure drop process at this time, we must make the motor return to the position where the free stroke pressure is "zero" during the self-test, then find the motor rotor position value corresponding to the new pressure setpoint, and then rotate it forward to the new setpoint. This will enable the tracking of the pressure when the applied pressure is less than the original setpoint, and the current closed loop will maintain the position unchanged.

[0024] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0025] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fault-tolerant control method for a UAV electric braking system when the pressure sensor fails, characterized in that, include: When the electric braking system is powered on, the electric braking system performs an automatic self-test. The method requires increasing the brake pressure from zero value during the no-travel period to the maximum value required for braking, and records the brake pressure value, the corresponding brake motor rotor position angle value, and the corresponding direction of rotation of the brake motor rotor during the self-test process. The automatic self-test process specifically includes: at the start of the self-test, the brake motor receives a control command and rotates forward to push the brake pads on the brake caliper against the brake disc. If the brake pads have not yet pressed against the brake disc and are in the idle stroke position, the rotor of the brake motor rotates through a certain angle. During the idle stroke phase, if the pressure sensor output is not zero, the pressure value is considered as zero-point drift. The brake motor continues to apply pressure. If the pressure value begins to increase, it indicates that the brake pads have pressed against the brake disc, and the rotor position angle at which the brake pads and brake disc just touch is defined as the zero position. The brake motor continues to apply pressure to the maximum pressure value required for braking, and records the curve value corresponding to the brake pressure value and the rotor position angle of the brake motor. After recording, the brake motor is retracted to a suitable idle stroke clearance, and the self-test is completed. When the brake control system receives a pressure sensor fault signal, it controls the rotor of the brake motor to quickly retract to the empty stroke gap during self-test to ensure pressure release. The brake motor is controlled to rotate in the forward direction with pressure. Based on the brake pressure setpoint and the motor rotor position angle corresponding to the self-test, the brake motor is controlled to rotate forward and increase to the zero position. Then, based on the curve corresponding to the brake pressure value and the brake motor rotor position angle recorded in the self-test, the value of the motor rotor position angle corresponding to the pressure setpoint is found. The motor rotor position is stably increased and controlled to the corresponding pressure value when the pressure rises. After reaching the position, the motor current is reduced to a small current value that keeps the motor stable and does not rotate. Maintain the motor control current to prevent the motor rotor position from dropping; When the fault-tolerant control method needs to follow the pressure drop process, the rotor of the brake motor is retracted to the motor position where the empty stroke pressure is zero during self-test. Then, the value of the motor rotor position angle corresponding to the new pressure setpoint is found again, and the brake motor is controlled to rotate forward to the new setpoint. This achieves tracking when the pressure value is less than the original setpoint, and the current closed loop maintains the motor rotor position unchanged.

2. The fault-tolerant control method for the failure of the pressure sensor in the UAV electric braking system according to claim 1, characterized in that, The statement that the pressure value is considered to be zero-point drift means that the pressure value is forcibly considered to be zero.

3. The fault-tolerant control method for the failure of the pressure sensor in the UAV electric braking system according to claim 1, characterized in that, The zero position is defined as the angle at which the motor rotor just touches the brake pad and the brake disc. Specifically: The rotor position angle of the motor is determined by a Hall sensor. The brake control system records the Hall sensor count value corresponding to the zero position and identifies the Hall sensor count value as a relative zero value. That is, a value greater than the relative zero value is a positive angle value, and a value less than the relative zero value is a negative angle value.

4. The fault-tolerant control method for the failure of the pressure sensor in the UAV electric braking system according to claim 1, characterized in that, The pressure sensor acquires the pressure on the brake wheel through a pressure feedback signal acquisition circuit, and outputs a fault signal of the pressure sensor through a fault detection circuit.

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